%% Books
@book{fds336754,
Author = {Tarokh, V},
Title = {Preface},
Publisher = {Springer US},
Year = {2009},
Month = {December},
ISBN = {9781441906724},
url = {http://dx.doi.org/10.1007/978-1-4419-0673-1},
Doi = {10.1007/978-1-4419-0673-1},
Key = {fds336754}
}
%% Papers Published
@article{fds370318,
Author = {Soloveychik, I and Tarokh, V},
Title = {Region selection in Markov random fields: Gaussian
case},
Journal = {Journal of Multivariate Analysis},
Volume = {196},
Year = {2023},
Month = {July},
url = {http://dx.doi.org/10.1016/j.jmva.2023.105178},
Abstract = {We consider the problem of model selection in Gaussian
Markov fields in the sample deficient scenario. The
benchmark information-theoretic results in the case of
d-regular graphs require the number of samples to be at
least proportional to the logarithm of the number of
vertices to allow consistent graph recovery. When the number
of samples is less than this amount, reliable recovery of
all edges is impossible. In many applications, it is more
important to learn the distribution of the edge (coupling)
parameters over the network than the specific locations of
the edges. Assuming that the entire graph can be partitioned
into a number of spatial regions with similar edge
parameters and reasonably regular boundaries, we develop new
information-theoretic sample complexity bounds and show that
a bounded number of samples can be sufficient to
consistently recover these regions. Finally, we introduce
and analyze an efficient region growing algorithm capable of
recovering the regions with high accuracy. We show that it
is consistent and demonstrate its performance benefits in
synthetic simulations.},
Doi = {10.1016/j.jmva.2023.105178},
Key = {fds370318}
}
@article{fds351055,
Author = {Hasan, A and Pereira, JM and Farsiu, S and Tarokh,
V},
Title = {Identifying Latent Stochastic Differential
Equations},
Journal = {Ieee Transactions on Signal Processing},
Volume = {70},
Pages = {89-104},
Year = {2022},
Month = {January},
url = {http://dx.doi.org/10.1109/TSP.2021.3131723},
Abstract = {We present a method for learning latent stochastic
differential equations (SDEs) from high dimensional time
series data. Given a high-dimensional time series generated
from a lower dimensional latent unknown Itô process, the
proposed method learns the mapping from ambient to latent
space, and the underlying SDE coefficients, through a
self-supervised learning approach. Using the framework of
variational autoencoders, we consider a conditional
generative model for the data based on the Euler-Maruyama
approximation of SDE solutions. Furthermore, we use recent
results on identifiability of latent variable models to show
that the proposed model can recover not only the underlying
SDE coefficients, but also the original latent variables, up
to an isometry, in the limit of infinite data. We validate
the method through several simulated video processing tasks,
where the underlying SDE is known, and through real world
datasets.},
Doi = {10.1109/TSP.2021.3131723},
Key = {fds351055}
}
@article{fds362106,
Author = {Huo, Q and Shi, Y and Liu, C and Tarokh, V and Ferrari,
S},
Title = {Online Action Change Detection for Automatic Vision-based
Ground Control of Aircraft},
Journal = {Aiaa Science and Technology Forum and Exposition, Aiaa
Scitech Forum 2022},
Year = {2022},
Month = {January},
ISBN = {9781624106316},
url = {http://dx.doi.org/10.2514/6.2022-2031},
Abstract = {Classical action recognition algorithms require the user to
pre-select the time window for the action by clipping the
video or choosing the initial and final time frames.
Recently, new deep learning algorithms have been developed
to detect a key action from an untrimmed video. However,
they are unsuitable for temporally segmenting continuous
action sequences and are too computationally expensive for
implementation on autonomous systems. This paper presents a
fast and accurate online action change detection framework.
Given a streaming RGB video, the algorithm is used to detect
any changes in the sequence. If a new action is discovered,
the action recognition module will be applied to classify
the action. Compared to existing methods, this two-stage
approach reduces computational cost by not applying the
recognition algorithm on every time window and improves
classification accuracy by locating the starting time step
of each action. In a simulated airport environment created
using Unreal Engine ™, the framework is demonstrated and
validated by detecting and recognizing sequential gestures
from a ground crew, who sends gesture commands to control
the movement of an autonomous aircraft. A hybrid optimal
controller is developed to combine the visual information
obtained from the framework and prior information, such as
airport map and reference lines, to control the aircraft to
safely navigate to a terminal gate.},
Doi = {10.2514/6.2022-2031},
Key = {fds362106}
}
@article{fds363206,
Author = {Momenifar, M and Diao, E and Tarokh, V and Bragg,
AD},
Title = {Dimension reduced turbulent flow data from deep vector
quantisers},
Journal = {Journal of Turbulence},
Volume = {23},
Number = {4-5},
Pages = {232-264},
Year = {2022},
Month = {January},
url = {http://dx.doi.org/10.1080/14685248.2022.2060508},
Abstract = {Analysing large-scale data from simulations of turbulent
flows is memory intensive, requiring significant resources.
This major challenge highlights the need for data
compression techniques. In this study, we apply a
physics-informed Deep Learning technique based on vector
quantisation to generate a discrete, low-dimensional
representation of data from simulations of three-dimensional
turbulent flows. The deep learning framework is composed of
convolutional layers and incorporates physical constraints
on the flow, such as preserving incompressibility and global
statistical characteristics of the velocity gradients. The
accuracy of the model is assessed using statistical,
comparison-based similarity and physics-based metrics. The
training data set is produced from Direct Numerical
Simulation of an incompressible, statistically stationary,
isotropic turbulent flow. The performance of this lossy data
compression scheme is evaluated not only with unseen data
from the stationary, isotropic turbulent flow, but also with
data from decaying isotropic turbulence, a Taylor–Green
vortex flow, and a turbulent channel flow. Defining the
compression ratio (CR) as the ratio of original data size to
the compressed one, the results show that our model based on
vector quantisation can offer CR (Formula presented.) with a
mean square error (MSE) of (Formula presented.), and
predictions that faithfully reproduce the statistics of the
flow, except at the very smallest scales where there is some
loss. Compared to the recent study of Glaws. et al. [Deep
learning for in situ data compression of large turbulent
flow simulations. Phys Rev Fluids. 2020;5(11):114602], which
was based on a conventional autoencoder (where compression
is performed in a continuous space), our model improves the
CR by more than 30%, and reduces the MSE by an order of
magnitude. Our compression model is an attractive solution
for situations where fast, high quality and low-overhead
encoding and decoding of large data are required.},
Doi = {10.1080/14685248.2022.2060508},
Key = {fds363206}
}
@article{fds363388,
Author = {Le, CP and Soltani, M and Dong, J and Tarokh, V},
Title = {Fisher Task Distance and its Application in Neural
Architecture Search},
Journal = {Ieee Access},
Volume = {10},
Pages = {47235-47249},
Year = {2022},
Month = {January},
url = {http://dx.doi.org/10.1109/ACCESS.2022.3171741},
Abstract = {We formulate an asymmetric (or non-commutative) distance
between tasks based on Fisher Information Matrices, called
Fisher task distance. This distance represents the
complexity of transferring the knowledge from one task to
another. We provide a proof of consistency for our distance
through theorems and experiments on various classification
tasks from MNIST, CIFAR-10, CIFAR-100, ImageNet, and
Taskonomy datasets. Next, we construct an online neural
architecture search framework using the Fisher task
distance, in which we have access to the past learned tasks.
By using the Fisher task distance, we can identify the
closest learned tasks to the target task, and utilize the
knowledge learned from these related tasks for the target
task. Here, we show how the proposed distance between a
target task and a set of learned tasks can be used to reduce
the neural architecture search space for the target task.
The complexity reduction in search space for task-specific
architectures is achieved by building on the optimized
architectures for similar tasks instead of doing a full
search and without using this side information. Experimental
results for tasks in MNIST, CIFAR-10, CIFAR-100, ImageNet
datasets demonstrate the efficacy of the proposed approach
and its improvements, in terms of the performance and the
number of parameters, over other gradient-based search
methods, such as ENAS, DARTS, PC-DARTS.},
Doi = {10.1109/ACCESS.2022.3171741},
Key = {fds363388}
}
@article{fds364294,
Author = {Momenifar, M and Diao, E and Tarokh, V and Bragg,
AD},
Title = {A Physics-Informed Vector Quantized Autoencoder for Data
Compression of Turbulent Flow},
Journal = {Data Compression Conference Proceedings},
Volume = {2022-March},
Pages = {312-321},
Year = {2022},
Month = {January},
ISBN = {9781665478939},
url = {http://dx.doi.org/10.1109/DCC52660.2022.00039},
Abstract = {Analyzing large-scale data from simulations of turbulent
flows is memory intensive, requiring significant resources.
This major challenge highlights the need for data
compression techniques. In this study, we apply a
physics-informed Deep Learning technique based on vector
quantization to generate a discrete, low-dimensional
representation of data from simulations of three-dimensional
turbulent flows. The deep learning framework is composed of
convolutional layers and incorporates physical constraints
on the flow, such as preserving incompressibility and global
statistical characteristics of the velocity gradients. The
accuracy of the model is assessed using statistical,
comparison-based similarity and physics-based metrics. The
training data set is produced from Direct Numerical
Simulation of an incompressible, statistically stationary,
isotropic turbulent flow. The performance of this lossy data
compression scheme is evaluated not only with unseen data
from the stationary, isotropic turbulent flow, but also with
data from decaying isotropic turbulence, and a Taylor-Green
vortex flow. Defining the compression ratio (CR) as the
ratio of original data size to the compressed one, the
results show that our model based on vector quantization can
offer CR = 85 with a mean square error (MSE) of O(10-3), and
predictions that faithfully reproduce the statistics of the
flow, except at the very smallest scales where there is some
loss. Compared to the recent study based on a conventional
autoencoder where compression is performed in a continuous
space, our model improves the CR by more than 30 percent,
and reduces the MSE by an order of magnitude. Our
compression model is an attractive solution for situations
where fast, high quality and low-overhead encoding and
decoding of large data are required.},
Doi = {10.1109/DCC52660.2022.00039},
Key = {fds364294}
}
@article{fds364343,
Author = {Soltani, M and Wu, S and Li, Y and Ding, J and Tarokh,
V},
Title = {On The Energy Statistics of Feature Maps in Pruning of
Neural Networks with Skip-Connections},
Journal = {Data Compression Conference Proceedings},
Volume = {2022-March},
Pages = {482},
Year = {2022},
Month = {January},
ISBN = {9781665478939},
url = {http://dx.doi.org/10.1109/DCC52660.2022.00093},
Abstract = {We propose a new structured pruning framework for
compressing Deep Neural Networks (DNNs) with
skip-connections, based on measuring the statistical
dependency of hidden layers and predicted outputs. The
dependence measure defined by the energy statistics of
hidden layers serves as a model-free measure of information
between the feature maps and the output of the network. The
estimated dependence measure is subsequently used to prune a
collection of redundant and uninformative layers. Extensive
numerical experiments on various architectures show the
efficacy of the proposed pruning approach with competitive
performance to state-of-the-art methods.},
Doi = {10.1109/DCC52660.2022.00093},
Key = {fds364343}
}
@article{fds364344,
Author = {Dong, J and Wu, S and Soltani, M and Tarokh, V},
Title = {Multi-Agent Adversarial Attacks for Multi-Channel
Communications},
Journal = {Proceedings of the International Joint Conference on
Autonomous Agents and Multiagent Systems,
Aamas},
Volume = {3},
Pages = {1580-1582},
Year = {2022},
Month = {January},
ISBN = {9781713854333},
Abstract = {Recently Reinforcement Learning (RL) has been applied as an
anti-adversarial remedy in wireless communication networks.
However studying the RL-based approaches from the
adversary's perspective has received little attention.
Additionally, RL-based approaches in an anti-adversary or
adversarial paradigm mostly consider single-channel
communication (either channel selection or single channel
power control), while multi-channel communication is more
common in practice. In this paper, we propose a multi-agent
adversary system (MAAS) for modeling and analyzing
adversaries in a wireless communication scenario by careful
design of the reward function under realistic communication
scenarios. In particular, by modeling the adversaries as
learning agents, we show that the proposed MAAS is able to
successfully choose the transmitted channel(s) and their
respective allocated power(s) without any prior knowledge of
the sender strategy. Compared to the single-agent adversary
(SAA), multi-agents in MAAS can achieve significant
reduction in signal-to-noise ratio (SINR) under the same
power constraints and partial observability, while providing
improved stability and a more efficient learning process.
Moreover, through empirical studies we show that the results
in simulation are close to the ones in communication in
reality, a conclusion that is pivotal to the validity of
performance of agents evaluated in simulations.},
Key = {fds364344}
}
@article{fds364345,
Author = {Wu, S and Diao, E and Elkhalil, K and Ding, J and Tarokh,
V},
Title = {Score-Based Hypothesis Testing for Unnormalized
Models},
Journal = {Ieee Access},
Volume = {10},
Pages = {71936-71950},
Year = {2022},
Month = {January},
url = {http://dx.doi.org/10.1109/ACCESS.2022.3187991},
Abstract = {Unnormalized statistical models play an important role in
machine learning, statistics, and signal processing. In this
paper, we derive a new hypothesis testing procedure for
unnormalized models. Our approach is motivated by the
success of score matching techniques that avoid the
intensive computational costs of normalization constants in
many high-dimensional settings. Our proposed test statistic
is the difference between Hyvärinen scores corresponding to
the null and alternative hypotheses. Under some reasonable
conditions, we prove that the asymptotic distribution of
this statistic is Chi-squared. We outline a bootstrap
approach to learn the test critical values, particularly
when the distribution under the null hypothesis cannot be
expressed in a closed form, and provide consistency
guarantees. Finally, we conduct extensive numerical
experiments and demonstrate that our proposed approach
outperforms goodness-of-fit benchmarks in various
settings.},
Doi = {10.1109/ACCESS.2022.3187991},
Key = {fds364345}
}
@article{fds365734,
Author = {Venkatasubramanian, S and Wongkamthong, C and Soltani, M and Kang, B and Gogineni, S and Pezeshki, A and Rangaswamy, M and Tarokh,
V},
Title = {Toward Data-Driven STAP Radar},
Journal = {Proceedings of the Ieee Radar Conference},
Publisher = {IEEE},
Year = {2022},
Month = {January},
url = {http://dx.doi.org/10.1109/RadarConf2248738.2022.9764354},
Abstract = {Using an amalgamation of techniques from classical radar,
computer vision, and deep learning, we characterize our
ongoing data-driven approach to space-time adaptive
processing (STAP) radar. We generate a rich example dataset
of received radar signals by randomly placing targets of
variable strengths in a predetermined region using RFView, a
site-specific radio frequency modeling and simulation tool
developed by ISL Inc. For each data sample within this
region, we generate heatmap tensors in range, azimuth, and
elevation of the output power of a minimum variance
distortionless response (MVDR) beamformer, which can be
replaced with a desired test statistic. These heatmap
tensors can be thought of as stacked images, and in an
airborne scenario, the moving radar creates a sequence of
these time-indexed image stacks, resembling a video. Our
goal is to use these images and videos to detect targets and
estimate their locations, a procedure reminiscent of
computer vision algorithms for object detection-namely, the
Faster Region Based Convolutional Neural Network (Faster
R-CNN). The Faster R-CNN consists of a proposal generating
network for determining regions of interest (ROI), a
regression network for positioning anchor boxes around
targets, and an object classification algorithm; it is
developed and optimized for natural images. Our ongoing
research will develop analogous tools for heatmap images of
radar data. In this regard, we will generate a large,
representative adaptive radar signal processing database for
training and testing, analogous in spirit to the COCO
dataset for natural images. Subsequently, we will build
upon, adapt, and optimize the existing Faster R-CNN
framework, and develop tools to detect and localize targets
in the heatmap tensors discussed previously. As a
preliminary example, we present a regression network in this
paper for estimating target locations to demonstrate the
feasibility of and significant improvements provided by our
data-driven approach.},
Doi = {10.1109/RadarConf2248738.2022.9764354},
Key = {fds365734}
}
@article{fds365907,
Author = {Soloveychik, I and Tarokh, V},
Title = {Large deviations of convex polyominoes*},
Journal = {Electronic Journal of Probability},
Volume = {27},
Year = {2022},
Month = {January},
url = {http://dx.doi.org/10.1214/22-EJP835},
Abstract = {Many open problems in machine learning, pattern recognition,
and geometric analysis require enumeration of different
types of lattice polygons, and in particular convex
polyominoes. In this work, we develop a large deviation
principle for convex polyominoes under different
restrictions, such as fixed area and/or perimeter.},
Doi = {10.1214/22-EJP835},
Key = {fds365907}
}
@article{fds366703,
Author = {Kojima, S and Feng, Y and Maruta, K and Ootsu, K and Yokota, T and Ahn, CJ and Tarokh, V},
Title = {Towards Deep Learning-Guided Multiuser SNR and Doppler Shift
Detection for Next-Generation Wireless Systems},
Journal = {Ieee Vehicular Technology Conference},
Volume = {2022-June},
Year = {2022},
Month = {January},
ISBN = {9781665482431},
url = {http://dx.doi.org/10.1109/VTC2022-Spring54318.2022.9860990},
Abstract = {In order to meet the ever-growing demand for data traffic,
highly efficient multiple access schemes, such as OFDMA, are
widely used in modern communication standards. In such
multiple access schemes, adaptive modulation and coding
(AMC) are used to optimize the transmission rate of each
user. However, feedback information, such as SNR and Doppler
shift, characterizing the communication environment of each
user is indispensable of key importance for AMC. In the
past, these information and parameters were often estimated
using reference signals. However, the reference signal
becomes overhead, resulting in throughput degradation and
processing delay. Furthermore, the computation burden can be
large as it is necessary to perform channel parameter
estimation individually for each user. Previously, over the
single-user channel, we have proposed a joint SNR and
Doppler shift detection method via a spectrogram-based
data-driven method, without the reference signal. This paper
extends this framework to multiuser OFDM multiple access
channels. In the newly proposed method, SNR and Doppler
shift for all users can be detected simultaneously via deep
learning-guided object detection algorithms from each
spectrogram image. Simulation results are provided to
validate the effectiveness of the proposed
method.},
Doi = {10.1109/VTC2022-Spring54318.2022.9860990},
Key = {fds366703}
}
@article{fds368346,
Author = {Cannella, C and Tarokh, V},
Title = {Semi-Empirical Objective Functions for MCMC Proposal
Optimization},
Journal = {Proceedings International Conference on Pattern
Recognition},
Volume = {2022-August},
Pages = {4758-4764},
Year = {2022},
Month = {January},
ISBN = {9781665490627},
url = {http://dx.doi.org/10.1109/ICPR56361.2022.9956603},
Abstract = {Current objective functions used for training neural MCMC
proposal distributions implicitly rely on architectural
restrictions to yield sensible optimization results, which
hampers the development of highly expressive neural MCMC
proposal architectures. In this work, we introduce and
demonstrate a semi-empirical procedure for determining
approximate objective functions suitable for optimizing
arbitrarily parameterized proposal distributions in MCMC
methods. Our proposed Ab Initio objective functions consist
of the weighted combination of functions following
constraints on their global optima and transformation
invariances that we argue should be upheld by general
measures of MCMC efficiency for use in proposal
optimization. Our experimental results demonstrate that Ab
Initio objective functions maintain favorable performance
and preferable optimization behavior compared to existing
objective functions for neural MCMC optimization. We find
that Ab Initio objective functions are sufficiently robust
to enable the confident optimization of neural proposal
distributions parameterized by deep generative networks
extending beyond the regimes of traditional MCMC
schemes.},
Doi = {10.1109/ICPR56361.2022.9956603},
Key = {fds368346}
}
@article{fds369086,
Author = {Hasan, A and Elkhalil, K and Ng, Y and Pereira, JM and Farsiu, S and Blanchet, J and Tarokh, V},
Title = {Modeling Extremes with d-max-decreasing Neural
Networks},
Journal = {Proceedings of the 38th Conference on Uncertainty in
Artificial Intelligence, Uai 2022},
Pages = {759-768},
Year = {2022},
Month = {January},
ISBN = {9781713863298},
Abstract = {We propose a neural network architecture that enables
non-parametric calibration and generation of multivariate
extreme value distributions (MEVs). MEVs arise from Extreme
Value Theory (EVT) as the necessary class of models when
extrapolating a distributional fit over large spatial and
temporal scales based on data observed in intermediate
scales. In turn, EVT dictates that d-max-decreasing, a
stronger form of convexity, is an essential shape constraint
in the characterization of MEVs. As far as we know, our
proposed architecture provides the first class of
non-parametric estimators for MEVs that preserve these
essential shape constraints. We show that the architecture
approximates the dependence structure encoded by MEVs at
parametric rate. Moreover, we present a new method for
sampling high-dimensional MEVs using a generative model. We
demonstrate our methodology on a wide range of experimental
settings, ranging from environmental sciences to financial
mathematics and verify that the structural properties of
MEVs are retained compared to existing methods.},
Key = {fds369086}
}
@article{fds370106,
Author = {Le, CP and Dong, J and Soltani, M and Tarokh, V},
Title = {TASK AFFINITY WITH MAXIMUM BIPARTITE MATCHING IN FEW-SHOT
LEARNING},
Journal = {Iclr 2022 10th International Conference on Learning
Representations},
Year = {2022},
Month = {January},
Abstract = {We propose an asymmetric affinity score for representing the
complexity of utilizing the knowledge of one task for
learning another one. Our method is based on the maximum
bipartite matching algorithm and utilizes the Fisher
Information matrix. We provide theoretical analyses
demonstrating that the proposed score is mathematically
well-defined, and subsequently use the affinity score to
propose a novel algorithm for the few-shot learning problem.
In particular, using this score, we find relevant training
data labels to the test data and leverage the discovered
relevant data for episodically fine-tuning a few-shot model.
Results on various few-shot benchmark datasets demonstrate
the efficacy of the proposed approach by improving the
classification accuracy over the state-of-the-art methods
even when using smaller models.},
Key = {fds370106}
}
@article{fds369995,
Author = {Le, Q and Diao, E and Wang, X and Anwar, A and Tarokh, V and Ding,
J},
Title = {Personalized Federated Recommender Systems with Private and
Partially Federated AutoEncoders},
Journal = {Conference Record Asilomar Conference on Signals, Systems
and Computers},
Volume = {2022-October},
Pages = {1157-1163},
Year = {2022},
Month = {January},
ISBN = {9781665459068},
url = {http://dx.doi.org/10.1109/IEEECONF56349.2022.10051918},
Abstract = {Recommender Systems (RSs) have become increasingly important
in many application domains, such as digital marketing.
Conventional RSs often need to collect users' data,
centralize them on the server-side, and form a global model
to generate reliable recommendations. However, they suffer
from two critical limitations: the personalization problem
that the RSs trained traditionally may not be customized for
individual users, and the privacy problem that directly
sharing user data is not encouraged. We propose Personalized
Federated Recommender Systems (PersonalFR), which introduces
a personalized autoencoder-based recommendation model with
Federated Learning (FL) to address these challenges.
PersonalFR guarantees that each user can learn a personal
model from the local dataset and other participating users'
data without sharing local data, data embeddings, or models.
PersonalFR consists of three main components, including
AutoEncoder-based RSs (ARSs) that learn the user-item
interactions, Partially Federated Learning (PFL) that
updates the encoder locally and aggregates the decoder on
the server-side, and Partial Compression (PC) that only
computes and transmits active model parameters. Extensive
experiments on two real-world datasets demonstrate that
PersonalFR can achieve private and personalized performance
comparable to that trained by centralizing all users' data.
Moreover, PersonalFR requires significantly less computation
and communication overhead than standard FL
baselines.},
Doi = {10.1109/IEEECONF56349.2022.10051918},
Key = {fds369995}
}
@article{fds370060,
Author = {Dong, J and Ren, S and Deng, Y and Khatib, O and Malof, J and Soltani, M and Padilla, W and Tarokh, V},
Title = {BLASCHKE PRODUCT NEURAL NETWORK (BPNN): A PHYSICS-INFUSED
NEURAL NETWORK FOR PHASE RETRIEVAL OF MEROMORPHIC
FUNCTIONS},
Journal = {Iclr 2022 10th International Conference on Learning
Representations},
Year = {2022},
Month = {January},
Abstract = {Numerous physical systems are described by ordinary or
partial differential equations whose solutions are given by
holomorphic or meromorphic functions in the complex domain.
In many cases, only the magnitude of these functions are
observed on various points on the purely imaginary jω-axis
since coherent measurement of their phases is often
expensive. However, it is desirable to retrieve the lost
phases from the magnitudes when possible. To this end, we
propose a physics-infused deep neural network based on the
Blaschke products for phase retrieval. Inspired by the
Helson and Sarason Theorem, we recover coefficients of a
rational function of Blaschke products using a Blaschke
Product Neural Network (BPNN), based upon the magnitude
observations as input. The resulting rational function is
then used for phase retrieval. We compare the BPNN to
conventional deep neural networks (NNs) on several phase
retrieval problems, comprising both synthetic and
contemporary real-world problems (e.g., metamaterials for
which data collection requires substantial expertise and is
time consuming). On each phase retrieval problem, we compare
against a population of conventional NNs of varying size and
hyperparameter settings. Even without any hyper-parameter
search, we find that BPNNs consistently outperform the
population of optimized NNs in scarce data scenarios, and do
so despite being much smaller models. The results can in
turn be applied to calculate the refractive index of
metamaterials, which is an important problem in emerging
areas of material science.},
Key = {fds370060}
}
@article{fds361494,
Author = {Xu, X and Hasan, A and Elkhalil, K and Ding, J and Tarokh,
V},
Title = {Characteristic Neural Ordinary Differential
Equations},
Year = {2021},
Month = {November},
Abstract = {We propose Characteristic-Neural Ordinary Differential
Equations (C-NODEs), a framework for extending Neural
Ordinary Differential Equations (NODEs) beyond ODEs. While
NODEs model the evolution of a latent variables as the
solution to an ODE, C-NODE models the evolution of the
latent variables as the solution of a family of first-order
quasi-linear partial differential equations (PDEs) along
curves on which the PDEs reduce to ODEs, referred to as
characteristic curves. This in turn allows the application
of the standard frameworks for solving ODEs, namely the
adjoint method. Learning optimal characteristic curves for
given tasks improves the performance and computational
efficiency, compared to state of the art NODE models. We
prove that the C-NODE framework extends the classical NODE
on classification tasks by demonstrating explicit C-NODE
representable functions not expressible by NODEs.
Additionally, we present C-NODE-based continuous normalizing
flows, which describe the density evolution of latent
variables along multiple dimensions. Empirical results
demonstrate the improvements provided by the proposed method
for classification and density estimation on CIFAR-10, SVHN,
and MNIST datasets under a similar computational budget as
the existing NODE methods. The results also provide
empirical evidence that the learned curves improve the
efficiency of the system through a lower number of
parameters and function evaluations compared with
baselines.},
Key = {fds361494}
}
@article{fds361495,
Author = {Dong, J and Ren, S and Deng, Y and Khatib, O and Malof, J and Soltani, M and Padilla, W and Tarokh, V},
Title = {Blaschke Product Neural Networks (BPNN): A Physics-Infused
Neural Network for Phase Retrieval of Meromorphic
Functions},
Year = {2021},
Month = {November},
Abstract = {Numerous physical systems are described by ordinary or
partial differential equations whose solutions are given by
holomorphic or meromorphic functions in the complex domain.
In many cases, only the magnitude of these functions are
observed on various points on the purely imaginary jw-axis
since coherent measurement of their phases is often
expensive. However, it is desirable to retrieve the lost
phases from the magnitudes when possible. To this end, we
propose a physics-infused deep neural network based on the
Blaschke products for phase retrieval. Inspired by the
Helson and Sarason Theorem, we recover coefficients of a
rational function of Blaschke products using a Blaschke
Product Neural Network (BPNN), based upon the magnitude
observations as input. The resulting rational function is
then used for phase retrieval. We compare the BPNN to
conventional deep neural networks (NNs) on several phase
retrieval problems, comprising both synthetic and
contemporary real-world problems (e.g., metamaterials for
which data collection requires substantial expertise and is
time consuming). On each phase retrieval problem, we compare
against a population of conventional NNs of varying size and
hyperparameter settings. Even without any hyper-parameter
search, we find that BPNNs consistently outperform the
population of optimized NNs in scarce data scenarios, and do
so despite being much smaller models. The results can in
turn be applied to calculate the refractive index of
metamaterials, which is an important problem in emerging
areas of material science.},
Key = {fds361495}
}
@article{fds361525,
Author = {Diao, E and Tarokh, V and Ding, J},
Title = {Decentralized Multi-Target Cross-Domain Recommendation for
Multi-Organization Collaborations},
Year = {2021},
Month = {October},
Abstract = {Recommender Systems (RSs) are operated locally by different
organizations in many realistic scenarios. If various
organizations can fully share their data and perform
computation in a centralized manner, they may significantly
improve the accuracy of recommendations. However,
collaborations among multiple organizations in enhancing the
performance of recommendations are primarily limited due to
the difficulty of sharing data and models. To address this
challenge, we propose Decentralized Multi-Target
Cross-Domain Recommendation (DMTCDR) with Multi-Target
Assisted Learning (MTAL) and Assisted AutoEncoder (AAE). Our
method can help multiple organizations collaboratively
improve their recommendation performance in a decentralized
manner without sharing sensitive assets. Consequently, it
allows decentralized organizations to collaborate and form a
community of shared interest. We conduct extensive
experiments to demonstrate that the new method can
significantly outperform locally trained RSs and mitigate
the cold start problem.},
Key = {fds361525}
}
@article{fds361526,
Author = {Le, CP and Dong, J and Soltani, M and Tarokh, V},
Title = {Task Affinity with Maximum Bipartite Matching in Few-Shot
Learning},
Year = {2021},
Month = {October},
Abstract = {We propose an asymmetric affinity score for representing the
complexity of utilizing the knowledge of one task for
learning another one. Our method is based on the maximum
bipartite matching algorithm and utilizes the Fisher
Information matrix. We provide theoretical analyses
demonstrating that the proposed score is mathematically
well-defined, and subsequently use the affinity score to
propose a novel algorithm for the few-shot learning problem.
In particular, using this score, we find relevant training
data labels to the test data and leverage the discovered
relevant data for episodically fine-tuning a few-shot model.
Results on various few-shot benchmark datasets demonstrate
the efficacy of the proposed approach by improving the
classification accuracy over the state-of-the-art methods
even when using smaller models.},
Key = {fds361526}
}
@article{fds356488,
Author = {Kojima, S and Maruta, K and Feng, Y and Ahn, CJ and Tarokh,
V},
Title = {CNN-Based Joint SNR and Doppler Shift Classification Using
Spectrogram Images for Adaptive Modulation and
Coding},
Journal = {Ieee Transactions on Communications},
Volume = {69},
Number = {8},
Pages = {5152-5167},
Year = {2021},
Month = {August},
url = {http://dx.doi.org/10.1109/TCOMM.2021.3077565},
Abstract = {This paper proposes a novel convolutional neural network
(CNN) based joint classification method to characterize the
signal-to-noise power ratio (SNR) and Doppler shift using
spectrogram images, in order to enable efficient adaptive
modulation and coding (AMC) designs. It is necessary to
maintain high communication performances even in stringent
environments where transceivers move at high speed due to
the diversification of wireless applications. To optimize
the transmission rate in such dynamic environments, AMC
scheme is known to be effective. AMC is generally designed
based on feedback information (FBI) such as the SNR and
Doppler shift acquired on the receiving side. Here, the
challenge is an increase in calculation burden, processing
delay and estimation accuracy of the FBI. We focused on the
spectrogram which is composed of power values in the time
and frequency domains. Its two-dimensional fluctuation
represents the Doppler shift as well as noise values. In the
proposed method, such key information for AMC can be
simultaneously extracted from a single spectrogram via a
trained CNN. Therefore it is expected to contribute to
reducing the computational burden and speeding up the signal
processing. Simulation results are presented to demonstrate
that the proposed method achieves better performance than
traditional methods.},
Doi = {10.1109/TCOMM.2021.3077565},
Key = {fds356488}
}
@article{fds357266,
Author = {Cannella, C and Tarokh, V},
Title = {Semi-Empirical Objective Functions for MCMC Proposal
Optimization},
Volume = {abs/2106.02104},
Year = {2021},
Month = {June},
Abstract = {Current objective functions used for training neural MCMC
proposal distributions implicitly rely on architectural
restrictions to yield sensible optimization results, which
hampers the development of highly expressive neural MCMC
proposal architectures. In this work, we introduce and
demonstrate a semi-empirical procedure for determining
approximate objective functions suitable for optimizing
arbitrarily parameterized proposal distributions in MCMC
methods. Our proposed Ab Initio objective functions consist
of the weighted combination of functions following
constraints on their global optima and transformation
invariances that we argue should be upheld by general
measures of MCMC efficiency for use in proposal
optimization. Our experimental results demonstrate that Ab
Initio objective functions maintain favorable performance
and preferable optimization behavior compared to existing
objective functions for neural MCMC optimization. We find
that Ab Initio objective functions are sufficiently robust
to enable the confident optimization of neural proposal
distributions parameterized by deep generative networks
extending beyond the regimes of traditional MCMC
schemes},
Key = {fds357266}
}
@article{fds357267,
Author = {Diao, E and Ding, J and Tarokh, V},
Title = {GAL: Gradient Assisted Learning for Decentralized
Multi-Organization Collaborations},
Volume = {abs/2106.01425},
Year = {2021},
Month = {June},
Abstract = {Collaborations among multiple organizations, such as
financial institutions, medical centers, and retail markets
in decentralized settings are crucial to providing improved
service and performance. However, the underlying
organizations may have little interest in sharing their
local data, models, and objective functions. These
requirements have created new challenges for
multi-organization collaboration. In this work, we propose
Gradient Assisted Learning (GAL), a new method for multiple
organizations to assist each other in supervised learning
tasks without sharing local data, models, and objective
functions. In this framework, all participants
collaboratively optimize the aggregate of local loss
functions, and each participant autonomously builds its own
model by iteratively fitting the gradients of the
overarching objective function. We also provide asymptotic
convergence analysis and practical case studies of GAL.
Experimental studies demonstrate that GAL can achieve
performance close to centralized learning when all data,
models, and objective functions are fully
disclosed.},
Key = {fds357267}
}
@article{fds357268,
Author = {Diao, E and Ding, J and Tarokh, V},
Title = {SemiFL: Semi-Supervised Federated Learning for Unlabeled
Clients with Alternate Training},
Volume = {abs/2106.01432},
Year = {2021},
Month = {June},
Abstract = {Federated Learning allows the training of machine learning
models by using the computation and private data resources
of many distributed clients. Most existing results on
Federated Learning (FL) assume the clients have ground-truth
labels. However, in many practical scenarios, clients may be
unable to label task-specific data due to a lack of
expertise or resource. We propose SemiFL to address the
problem of combining communication-efficient FL such as
FedAvg with Semi-Supervised Learning (SSL). In SemiFL,
clients have completely unlabeled data and can train
multiple local epochs to reduce communication costs, while
the server has a small amount of labeled data. We provide a
theoretical understanding of the success of data
augmentation-based SSL methods to illustrate the bottleneck
of a vanilla combination of communication-efficient FL with
SSL. To address this issue, we propose alternate training to
`fine-tune global model with labeled data' and `generate
pseudo-labels with the global model.' We conduct extensive
experiments and demonstrate that our approach significantly
improves the performance of a labeled server with unlabeled
clients training with multiple local epochs. Moreover, our
method outperforms many existing SSFL baselines and performs
competitively with the state-of-the-art FL and SSL
results.},
Key = {fds357268}
}
@article{fds357269,
Author = {Yanchenko, AK and Soltani, M and Ravier, RJ and Mukherjee, S and Tarokh,
V},
Title = {A Methodology for Exploring Deep Convolutional Features in
Relation to Hand-Crafted Features with an Application to
Music Audio Modeling},
Volume = {abs/2106.00110},
Year = {2021},
Month = {May},
Abstract = {Understanding the features learned by deep models is
important from a model trust perspective, especially as deep
systems are deployed in the real world. Most recent
approaches for deep feature understanding or model
explanation focus on highlighting input data features that
are relevant for classification decisions. In this work, we
instead take the perspective of relating deep features to
well-studied, hand-crafted features that are meaningful for
the application of interest. We propose a methodology and
set of systematic experiments for exploring deep features in
this setting, where input feature importance approaches for
deep feature understanding do not apply. Our experiments
focus on understanding which hand-crafted and deep features
are useful for the classification task of interest, how
robust these features are for related tasks and how similar
the deep features are to the meaningful hand-crafted
features. Our proposed method is general to many application
areas and we demonstrate its utility on orchestral music
audio data.},
Key = {fds357269}
}
@article{fds358777,
Author = {Feng, Y and Wongkamthong, C and Soltani, M and Ng, Y and Gogineni, S and Kang, B and Pezeshki, A and Calderbank, R and Rangaswamy, M and Tarokh,
V},
Title = {Knowledge-Aided Data-Driven Radar Clutter
Representation},
Journal = {Ieee National Radar Conference Proceedings},
Volume = {2021-May},
Year = {2021},
Month = {May},
ISBN = {9781728176093},
url = {http://dx.doi.org/10.1109/RadarConf2147009.2021.9455318},
Abstract = {We use a knowledge-aided, data-driven, location-aware
approach based on the RFView simulation software to model
and estimate the effect of ground clutter in airborne
radars. Using the RFView simulator, we produce many samples
of potential clutter effects and, by employing the K-means
clustering algorithm on the corresponding geographical power
map given by RFView, represent them by a small number of
virtual scatterers. These virtual scatterers are used for
clutter estimation. We show comparable accuracy for
significantly less computational time complexity to those of
state-of-the-art methods using RFView realistic clutter-like
data.},
Doi = {10.1109/RadarConf2147009.2021.9455318},
Key = {fds358777}
}
@article{fds355092,
Author = {Ding, J and Diao, E and Zhou, J and Tarokh, V},
Title = {On Statistical Efficiency in Learning},
Journal = {Ieee Transactions on Information Theory},
Volume = {67},
Number = {4},
Pages = {2488-2506},
Year = {2021},
Month = {April},
url = {http://dx.doi.org/10.1109/TIT.2020.3047620},
Abstract = {A central issue of many statistical learning problems is to
select an appropriate model from a set of candidate models.
Large models tend to inflate the variance (or overfitting),
while small models tend to cause biases (or underfitting)
for a given fixed dataset. In this work, we address the
critical challenge of model selection to strike a balance
between model fitting and model complexity, thus gaining
reliable predictive power. We consider the task of
approaching the theoretical limit of statistical learning,
meaning that the selected model has the predictive
performance that is as good as the best possible model given
a class of potentially misspecified candidate models. We
propose a generalized notion of Takeuchi's information
criterion and prove that the proposed method can
asymptotically achieve the optimal out-sample prediction
loss under reasonable assumptions. It is the first proof of
the asymptotic property of Takeuchi's information criterion
to our best knowledge. Our proof applies to a wide variety
of nonlinear models, loss functions, and high dimensionality
(in the sense that the models' complexity can grow with
sample size). The proposed method can be used as a
computationally efficient surrogate for leave-one-out
cross-validation. Moreover, for modeling streaming data, we
propose an online algorithm that sequentially expands the
model complexity to enhance selection stability and reduce
computation cost. Experimental studies show that the
proposed method has desirable predictive power and
significantly less computational cost than some popular
methods.},
Doi = {10.1109/TIT.2020.3047620},
Key = {fds355092}
}
@article{fds356190,
Author = {Le, CP and Soltani, M and Dong, J and Tarokh, V},
Title = {Fisher Task Distance and Its Application in Neural
Architecture Search},
Volume = {abs/2103.12827},
Year = {2021},
Month = {March},
Abstract = {We formulate an asymmetric (or non-commutative) distance
between tasks based on Fisher Information Matrices, called
Fisher task distance. This distance represents the
complexity of transferring the knowledge from one task to
another. We provide a proof of consistency for our distance
through theorems and experiments on various classification
tasks from MNIST, CIFAR-10, CIFAR-100, ImageNet, and
Taskonomy datasets. Next, we construct an online neural
architecture search framework using the Fisher task
distance, in which we have access to the past learned tasks.
By using the Fisher task distance, we can identify the
closest learned tasks to the target task, and utilize the
knowledge learned from these related tasks for the target
task. Here, we show how the proposed distance between a
target task and a set of learned tasks can be used to reduce
the neural architecture search space for the target task.
The complexity reduction in search space for task-specific
architectures is achieved by building on the optimized
architectures for similar tasks instead of doing a full
search and without using this side information. Experimental
results for tasks in MNIST, CIFAR-10, CIFAR-100, ImageNet
datasets demonstrate the efficacy of the proposed approach
and its improvements, in terms of the performance and the
number of parameters, over other gradient-based search
methods, such as ENAS, DARTS, PC-DARTS.},
Key = {fds356190}
}
@article{fds356189,
Author = {Xing, J and Fischer, D and Labh, N and Piersma, R and Lee, BC and Xia, YA and Sahai, T and Tarokh, V},
Title = {Talaria: A Framework for Simulation of Permissioned
Blockchains for Logistics and Beyond},
Volume = {abs/2103.02260},
Year = {2021},
Month = {March},
Abstract = {In this paper, we present Talaria, a novel permissioned
blockchain simulator that supports numerous protocols and
use cases, most notably in supply chain management. Talaria
extends the capability of BlockSim, an existing blockchain
simulator, to include permissioned blockchains and serves as
a foundation for further private blockchain assessment.
Talaria is designed with both practical Byzantine Fault
Tolerance (pBFT) and simplified version of
Proof-of-Authority consensus protocols, but can be revised
to include other permissioned protocols within its modular
framework. Moreover, Talaria is able to simulate different
types of malicious authorities and a variable daily
transaction load at each node. In using Talaria, business
practitioners and policy planners have an opportunity to
measure, evaluate, and adapt a range of blockchain solutions
for commercial operations.},
Key = {fds356189}
}
@article{fds356487,
Author = {Soltani, M and Wu, S and Li, Y and Ravier, R and Ding, J and Tarokh,
V},
Title = {Compressing Deep Networks Using Fisher Score of Feature
Maps},
Journal = {Data Compression Conference Proceedings},
Volume = {2021-March},
Pages = {371},
Year = {2021},
Month = {March},
ISBN = {9780738112275},
url = {http://dx.doi.org/10.1109/DCC50243.2021.00083},
Abstract = {In this paper, we propose a new structural technique for
pruning deep neural networks with skip-connections. Our
approach is based on measuring the importance of feature
maps in predicting the output of the model using their
Fisher scores. These scores subsequently used for removing
the less informative layers from the graph of the network.
Extensive experiments on the classification of CIFAR-10,
CIFAR-100, and SVHN data sets demonstrate the efficacy of
our compressing method both in the number of parameters and
operations.},
Doi = {10.1109/DCC50243.2021.00083},
Key = {fds356487}
}
@article{fds361403,
Author = {Momenifar, M and Diao, E and Tarokh, V and Bragg,
AD},
Title = {Dimension Reduced Turbulent Flow Data From Deep Vector
Quantizers},
Journal = {Journal of Turbulence 2022},
Year = {2021},
Month = {March},
Abstract = {Analyzing large-scale data from simulations of turbulent
flows is memory intensive, requiring significant resources.
This major challenge highlights the need for data
compression techniques. In this study, we apply a
physics-informed Deep Learning technique based on vector
quantization to generate a discrete, low-dimensional
representation of data from simulations of three-dimensional
turbulent flows. The deep learning framework is composed of
convolutional layers and incorporates physical constraints
on the flow, such as preserving incompressibility and global
statistical characteristics of the velocity gradients. The
accuracy of the model is assessed using statistical,
comparison-based similarity and physics-based metrics. The
training data set is produced from Direct Numerical
Simulation of an incompressible, statistically stationary,
isotropic turbulent flow. The performance of this lossy data
compression scheme is evaluated not only with unseen data
from the stationary, isotropic turbulent flow, but also with
data from decaying isotropic turbulence, a Taylor-Green
vortex flow, and a turbulent channel flow. Defining the
compression ratio (CR) as the ratio of original data size to
the compressed one, the results show that our model based on
vector quantization can offer CR$=85$ with a mean square
error (MSE) of $O(10^{-3})$, and predictions that faithfully
reproduce the statistics of the flow, except at the very
smallest scales where there is some loss. Compared to the
recent study of Glaws. et. al. (Physical Review Fluids,
5(11):114602, 2020), which was based on a conventional
autoencoder (where compression is performed in a continuous
space), our model improves the CR by more than $30$
percent...},
Key = {fds361403}
}
@article{fds356188,
Author = {Le, CP and Soltani, M and Ravier, R and Tarokh, V},
Title = {Improved Automated Machine Learning from Transfer
Learning},
Volume = {abs/2103.00241},
Year = {2021},
Month = {February},
Abstract = {In this paper, we propose a neural architecture search
framework based on a similarity measure between some
baseline tasks and a target task. We first define the notion
of the task similarity based on the log-determinant of the
Fisher Information matrix. Next, we compute the task
similarity from each of the baseline tasks to the target
task. By utilizing the relation between a target and a set
of learned baseline tasks, the search space of architectures
for the target task can be significantly reduced, making the
discovery of the best candidates in the set of possible
architectures tractable and efficient, in terms of GPU days.
This method eliminates the requirement for training the
networks from scratch for a given target task as well as
introducing the bias in the initialization of the search
space from the human domain.},
Key = {fds356188}
}
@article{fds356186,
Author = {Ng, Y and Hasan, A and Elkhalil, K and Tarokh, V},
Title = {Generative Archimedean Copulas},
Volume = {abs/2102.11351},
Pages = {643-653},
Year = {2021},
Month = {February},
Abstract = {We propose a new generative modeling technique for learning
multidimensional cumulative distribution functions (CDFs) in
the form of copulas. Specifically, we consider certain
classes of copulas known as Archimedean and hierarchical
Archimedean copulas, popular for their parsimonious
representation and ability to model different tail
dependencies. We consider their representation as mixture
models with Laplace transforms of latent random variables
from generative neural networks. This alternative
representation allows for computational efficiencies and
easy sampling, especially in high dimensions. We describe
multiple methods for optimizing the network parameters.
Finally, we present empirical results that demonstrate the
efficacy of our proposed method in learning multidimensional
CDFs and its computational efficiency compared to existing
methods.},
Key = {fds356186}
}
@article{fds356187,
Author = {Hasan, A and Elkhalil, K and Ng, Y and Pereira, JM and Farsiu, S and Blanchet, JH and Tarokh, V},
Title = {Modeling Extremes with d-max-decreasing Neural
Networks},
Volume = {abs/2102.09042},
Year = {2021},
Month = {February},
Abstract = {We propose a novel neural network architecture that enables
non-parametric calibration and generation of multivariate
extreme value distributions (MEVs). MEVs arise from Extreme
Value Theory (EVT) as the necessary class of models when
extrapolating a distributional fit over large spatial and
temporal scales based on data observed in intermediate
scales. In turn, EVT dictates that $d$-max-decreasing, a
stronger form of convexity, is an essential shape constraint
in the characterization of MEVs. As far as we know, our
proposed architecture provides the first class of
non-parametric estimators for MEVs that preserve these
essential shape constraints. We show that our architecture
approximates the dependence structure encoded by MEVs at
parametric rate. Moreover, we present a new method for
sampling high-dimensional MEVs using a generative model. We
demonstrate our methodology on a wide range of experimental
settings, ranging from environmental sciences to financial
mathematics and verify that the structural properties of
MEVs are retained compared to existing methods.},
Key = {fds356187}
}
@article{fds356185,
Author = {Chan, CH and Tarokh, V and Xiong, M},
Title = {Convergence Rate of Empirical Spectral Distribution of
Random Matrices from Linear Codes},
Journal = {Ieee Transactions on Information Theory},
Volume = {67},
Number = {2},
Pages = {1080-1087},
Year = {2021},
Month = {February},
url = {http://dx.doi.org/10.1109/TIT.2020.3039175},
Abstract = {It is known that the empirical spectral distribution of
random matrices obtained from linear codes of increasing
length converges to the well-known Marchenko-Pastur law, if
the Hamming distance of the dual codes is at least 5. In
this paper, we prove that the convergence rate in
probability is at least of the order n{-1/4} where n is the
length of the code.},
Doi = {10.1109/TIT.2020.3039175},
Key = {fds356185}
}
@article{fds360666,
Author = {Zhou, J and Ding, J and Tan, KM and Tarokh, V},
Title = {Model linkage selection for cooperative learning},
Journal = {Journal of Machine Learning Research},
Volume = {22},
Year = {2021},
Month = {January},
Abstract = {We consider the distributed learning setting where each
agent or learner holds a specific parametric model and a
data source. The goal is to integrate information across a
set of learners and data sources to enhance the prediction
accuracy of a given learner. A natural way to integrate
information is to build a joint model across a group of
learners that shares common parameters of interest. However,
the underlying parameter sharing patterns across a set of
learners may not be known a priori. Misspecifying the
parameter sharing patterns or the parametric model for each
learner often yields a biased estimator that degrades the
prediction accuracy. We propose a general method to
integrate information across a set of learners that is
robust against misspecification of both models and parameter
sharing patterns. The main crux of our proposed method is to
sequentially incorporate additional learners that can
enhance the prediction accuracy of an existing joint model
based on user-specified parameter sharing patterns across a
set of learners. Theoretically, we show that the proposed
method can data-adaptively select a parameter sharing
pattern that enhances the predictive performance of a given
learner. Extensive numerical studies are conducted to assess
the performance of the proposed method.},
Key = {fds360666}
}
@article{fds355221,
Author = {Yang, H and Jing, D and Tarokh, V and Bewley, G and Ferrari,
S},
Title = {Flow parameter estimation based on on-board measurements of
air vehicle traversing turbulent flows},
Journal = {Aiaa Scitech 2021 Forum},
Pages = {1-10},
Year = {2021},
Month = {January},
ISBN = {9781624106095},
Abstract = {Inspired by principles from particle transport theory in
fluid dynamics, we recently developed a new energy-efficient
control approach via implicit model following (IMF) for air
vehicles traversing turbulent flows. However, the control
design requires prior knowledge of the vortex timescale of
the turbulent flow. In this paper, we propose an approach to
estimate the turbulent flow parameters based on noisy
on-board measurements without prior knowledge of the exact
flow conditions, and validate it on a two-dimensional
cellular flow model. By sparse identification of nonlinear
dynamics (SINDy), the nonlinear vehicle dynamics with wind
effects introduced are approximated as a sparsely weighted
combination of user-defined candidate functions.
Accordingly, separate optimization problems are set up to
determine the weights representing the active level of
candidate functions in the unknown nonlinear dynamics. We
then identify the flow parameters by analyzing the weights
statistically. Finally, the ability of the proposed method
to estimate the flow parameters, including the mean
velocity, the vortex length scale and the vortex timescale,
is demonstrated by testing the algorithms on different
measurement data sets with various initial conditions and
flow parameters. We show that this method can accurately
estimate the flow parameters within a permissible range of
error.},
Key = {fds355221}
}
@article{fds356193,
Author = {Le, CP and Soltani, M and Ravier, R and Tarokh, V},
Title = {Task-aware neural architecture search},
Journal = {2015 Ieee International Conference on Acoustics, Speech, and
Signal Processing (Icassp)},
Volume = {2021-June},
Pages = {4090-4094},
Year = {2021},
Month = {January},
url = {http://dx.doi.org/10.1109/ICASSP39728.2021.9414412},
Abstract = {The design of handcrafted neural networks requires a lot of
time and resources. Recent techniques in Neural Architecture
Search (NAS) have proven to be competitive or better than
traditional handcrafted design, although they require domain
knowledge and have generally used limited search spaces. In
this paper, we propose a novel framework for neural
architecture search, utilizing a dictionary of models of
base tasks and the similarity between the target task and
the atoms of the dictionary; hence, generating an adaptive
search space based on the base models of the dictionary. By
introducing a gradient-based search algorithm, we can
evaluate and discover the best architecture in the search
space without fully training the networks. The experimental
results show the efficacy of our proposed task-aware
approach.},
Doi = {10.1109/ICASSP39728.2021.9414412},
Key = {fds356193}
}
@article{fds357013,
Author = {Angjelichinoski, M and Soltani, M and Choi, J and Pesaran, B and Tarokh,
V},
Title = {Deep Pinsker and James-Stein Neural Networks for Decoding
Motor Intentions From Limited Data.},
Journal = {Ieee Transactions on Neural Systems and Rehabilitation
Engineering : a Publication of the Ieee Engineering in
Medicine and Biology Society},
Volume = {29},
Pages = {1058-1067},
Year = {2021},
Month = {January},
url = {http://dx.doi.org/10.1109/tnsre.2021.3083755},
Abstract = {Non-parametric regression has been shown to be useful in
extracting relevant features from Local Field Potential
(LFP) signals for decoding motor intentions. Yet, in many
instances, brain-computer interfaces (BCIs) rely on simple
classification methods, circumventing deep neural networks
(DNNs) due to limited training data. This paper leverages
the robustness of several important results in
non-parametric regression to harness the potentials of deep
learning in limited data setups. We consider a solution that
combines Pinsker's theorem as well as its adaptively optimal
counterpart due to James-Stein for feature extraction from
LFPs, followed by a DNN for classifying motor intentions. We
apply our approach to the problem of decoding eye movement
intentions from LFPs collected in macaque cortex while the
animals perform memory-guided visual saccades to one of
eight target locations. The results demonstrate that a DNN
classifier trained over the Pinsker features outperforms the
benchmark method based on linear discriminant analysis (LDA)
trained over the same features.},
Doi = {10.1109/tnsre.2021.3083755},
Key = {fds357013}
}
@article{fds361828,
Author = {Kojima, S and Feng, Y and Maruta, K and Ootsu, K and Yokota, T and Ahn, CJ and Tarokh, V},
Title = {Investigation of Input Signal Representation to CNN for
Improving SNR Classification Accuracy},
Journal = {Ieee Vehicular Technology Conference},
Volume = {2021-September},
Year = {2021},
Month = {January},
ISBN = {9781665413688},
url = {http://dx.doi.org/10.1109/VTC2021-Fall52928.2021.9625566},
Abstract = {With the increase in demand for wireless data traffic,
high-speed communication systems are required in many
environment. Adaptive modulation and coding is an important
technique to realize this, but it requires feedback of
communication environment information represented by SNR.
Conventional SNR estimation methods have a problem of
degrading estimation accuracy in fast-moving environments
and the presence of carrier frequency offset (CFO).
Convolutional neural network (CNN) is capable of estimating
the SNR from the trained received signal dataset accurately.
This paper investigates an input signal representation to
further improve the SNR classification accuracy by CNN. We
then propose to combine respective spectrogram data of IQ
domains. It can extract the features related to SNR from the
received signal to the maximum extent possible and thus
achieve highly accurate SNR estimation. Simulation results
show that the proposed approach outperforms the other
existing candidates.},
Doi = {10.1109/VTC2021-Fall52928.2021.9625566},
Key = {fds361828}
}
@article{fds362635,
Author = {Ng, Y and Hasan, A and Elkhalil, K and Tarokh, V},
Title = {Generative Archimedean Copulas},
Journal = {37th Conference on Uncertainty in Artificial Intelligence,
Uai 2021},
Pages = {643-653},
Year = {2021},
Month = {January},
Abstract = {We propose a new generative modeling technique for learning
multidimensional cumulative distribution functions (CDFs) in
the form of copulas. Specifically, we consider certain
classes of copulas known as Archimedean and hierarchical
Archimedean copulas, popular for their parsimonious
representation and ability to model different tail
dependencies. We consider their representation as mixture
models with Laplace transforms of latent random variables
from generative neural networks. This alternative
representation allows for computational efficiencies and
easy sampling, especially in high dimensions. We describe
multiple methods for optimizing the network parameters.
Finally, we present empirical results that demonstrate the
efficacy of our proposed method in learning multidimensional
CDFs and its computational efficiency compared to existing
methods.},
Key = {fds362635}
}
@article{fds370107,
Author = {Diao, E and Ding, J and Tarokh, V},
Title = {HETEROFL: COMPUTATION AND COMMUNICATION EFFICIENT FEDERATED
LEARNING FOR HETEROGENEOUS CLIENTS},
Journal = {Iclr 2021 9th International Conference on Learning
Representations},
Year = {2021},
Month = {January},
Abstract = {Federated Learning (FL) is a method of training machine
learning models on private data distributed over a large
number of possibly heterogeneous clients such as mobile
phones and IoT devices. In this work, we propose a new
federated learning framework named HeteroFL to address
heterogeneous clients equipped with very different
computation and communication capabilities. Our solution can
enable the training of heterogeneous local models with
varying computation complexities and still produce a single
global inference model. For the first time, our method
challenges the underlying assumption of existing work that
local models have to share the same architecture as the
global model. We demonstrate several strategies to enhance
FL training and conduct extensive empirical evaluations,
including five computation complexity levels of three model
architecture on three datasets. We show that adaptively
distributing subnetworks according to clients' capabilities
is both computation and communication efficient.},
Key = {fds370107}
}
@article{fds359640,
Author = {Le, CP and Soltani, M and Ravier, RJ and Tarokh, V},
Title = {Task-Aware Neural Architecture Search.},
Journal = {Icassp},
Pages = {4090-4094},
Publisher = {IEEE},
Year = {2021},
ISBN = {978-1-7281-7606-2},
Key = {fds359640}
}
@article{fds351064,
Author = {Elkhalil, K and Hasan, A and Ding, J and Farsiu, S and Tarokh,
V},
Title = {Fisher Auto-Encoders},
Journal = {24th International Conference on Artificial Intelligence and
Statistics (Aistats)},
Volume = {130},
Pages = {352-360},
Publisher = {PMLR},
Editor = {Banerjee, A and Fukumizu, K},
Year = {2021},
Key = {fds351064}
}
@article{fds356191,
Author = {Ding, J and Diao, E and Zhou, J and Tarokh, V},
Title = {On Statistical Efficiency in Learning.},
Journal = {Ieee Trans. Inf. Theory},
Volume = {67},
Pages = {2488-2506},
Year = {2021},
url = {http://dx.doi.org/10.1109/TIT.2020.3047620},
Doi = {10.1109/TIT.2020.3047620},
Key = {fds356191}
}
@article{fds357586,
Author = {Cannella, C and Soltani, M and Tarokh, V},
Title = {Projected Latent Markov Chain Monte Carlo: Conditional
Sampling of Normalizing Flows},
Publisher = {OpenReview.net},
Year = {2021},
Abstract = {We introduce Projected Latent Markov Chain Monte Carlo
(PL-MCMC), a technique for sampling from the exact
conditional distributions learned by normalizing flows. As a
conditional sampling method, PL-MCMC enables Monte Carlo
Expectation Maximization (MC-EM) training of normalizing
flows from incomplete data. Through experimental tests
applying normalizing flows to missing data tasks for a
variety of data sets, we demonstrate the efficacy of PL-MCMC
for conditional sampling from normalizing
flows.},
Key = {fds357586}
}
@article{fds362636,
Author = {Elkhalil, K and Hasan, A and Ding, J and Farsiu, S and Tarokh,
V},
Title = {Fisher Auto-Encoders.},
Journal = {Aistats},
Volume = {130},
Pages = {352-360},
Publisher = {PMLR},
Editor = {Banerjee, A and Fukumizu, K},
Year = {2021},
Key = {fds362636}
}
@article{fds356192,
Author = {Diao, E and Ding, J and Tarokh, V},
Title = {HeteroFL: Computation and Communication Efficient Federated
Learning for Heterogeneous Clients},
Volume = {abs/2010.01264},
Publisher = {OpenReview.net},
Year = {2020},
Month = {October},
Abstract = {Federated Learning (FL) is a method of training machine
learning models on private data distributed over a large
number of possibly heterogeneous clients such as mobile
phones and IoT devices. In this work, we propose a new
federated learning framework named HeteroFL to address
heterogeneous clients equipped with very different
computation and communication capabilities. Our solution can
enable the training of heterogeneous local models with
varying computation complexities and still produce a single
global inference model. For the first time, our method
challenges the underlying assumption of existing work that
local models have to share the same architecture as the
global model. We demonstrate several strategies to enhance
FL training and conduct extensive empirical evaluations,
including five computation complexity levels of three model
architecture on three datasets. We show that adaptively
distributing subnetworks according to clients' capabilities
is both computation and communication efficient.},
Key = {fds356192}
}
@article{fds351056,
Author = {Angjelichinoski, M and Pesaran, B and Tarokh, V},
Title = {Deep Cross-Subject Mapping of Neural Activity},
Volume = {abs/2007.06407},
Year = {2020},
Month = {July},
Abstract = {Objective. In this paper, we consider the problem of
cross-subject decoding, where neural activity data collected
from the prefrontal cortex of a given subject (destination)
is used to decode motor intentions from the neural activity
of a different subject (source). Approach. We cast the
problem of neural activity mapping in a probabilistic
framework where we adopt deep generative modelling. Our
proposed algorithm uses deep conditional variational
autoencoder to infer the representation of the neural
activity of the source subject into an adequate feature
space of the destination subject where neural decoding takes
place. Results. We verify our approach on an experimental
data set in which two macaque monkeys perform memory-guided
visual saccades to one of eight target locations. The
results show a peak cross-subject decoding improvement of
$8\%$ over subject-specific decoding. Conclusion. We
demonstrate that a neural decoder trained on neural activity
signals of one subject can be used to robustly decode the
motor intentions of a different subject with high
reliability. This is achieved in spite of the non-stationary
nature of neural activity signals and the subject-specific
variations of the recording conditions. Significance. The
findings reported in this paper are an important step
towards the development of cross-subject brain-computer that
generalize well across a population.},
Key = {fds351056}
}
@article{fds351060,
Author = {Ravier, RJ and Soltani, M and Simões, M and Garagic, D and Tarokh,
V},
Title = {GeoStat Representations of Time Series for Fast
Classification},
Volume = {abs/2007.06682},
Year = {2020},
Month = {July},
Abstract = {Recent advances in time series classification have largely
focused on methods that either employ deep learning or
utilize other machine learning models for feature
extraction. Though successful, their power often comes at
the requirement of computational complexity. In this paper,
we introduce GeoStat representations for time series.
GeoStat representations are based off of a generalization of
recent methods for trajectory classification, and summarize
the information of a time series in terms of comprehensive
statistics of (possibly windowed) distributions of easy to
compute differential geometric quantities, requiring no
dynamic time warping. The features used are intuitive and
require minimal parameter tuning. We perform an exhaustive
evaluation of GeoStat on a number of real datasets, showing
that simple KNN and SVM classifiers trained on these
representations exhibit surprising performance relative to
modern single model methods requiring significant
computational power, achieving state of the art results in
many cases. In particular, we show that this methodology
achieves good performance on a challenging dataset involving
the classification of fishing vessels, where our methods
achieve good performance relative to the state of the art
despite only having access to approximately two percent of
the dataset used in training and evaluating this state of
the art.},
Key = {fds351060}
}
@article{fds351059,
Author = {Cannella, C and Soltani, M and Tarokh, V},
Title = {Projected Latent Markov Chain Monte Carlo: Conditional
Sampling of Normalizing Flows},
Volume = {abs/2007.06140},
Year = {2020},
Month = {July},
Abstract = {We introduce Projected Latent Markov Chain Monte Carlo
(PL-MCMC), a technique for sampling from the
high-dimensional conditional distributions learned by a
normalizing flow. We prove that a Metropolis-Hastings
implementation of PL-MCMC asymptotically samples from the
exact conditional distributions associated with a
normalizing flow. As a conditional sampling method, PL-MCMC
enables Monte Carlo Expectation Maximization (MC-EM)
training of normalizing flows from incomplete data. Through
experimental tests applying normalizing flows to missing
data tasks for a variety of data sets, we demonstrate the
efficacy of PL-MCMC for conditional sampling from
normalizing flows.},
Key = {fds351059}
}
@article{fds351061,
Author = {Angjelichinoski, M and Soltani, M and Choi, J and Pesaran, B and Tarokh,
V},
Title = {Deep James-Stein Neural Networks for Brain-Computer
Interfaces},
Journal = {2015 Ieee International Conference on Acoustics, Speech, and
Signal Processing (Icassp)},
Volume = {2020-May},
Pages = {1339-1343},
Publisher = {IEEE},
Year = {2020},
Month = {May},
ISBN = {9781509066315},
url = {http://dx.doi.org/10.1109/ICASSP40776.2020.9053694},
Abstract = {Nonparametric regression has proven to be successful in
extracting features from limited data in neurological
applications. However, due to data scarcity, most
brain-computer interfaces still rely on linear classifiers.
This work leverages the robustness of the James-Stein
theorem in nonparametric regression to harness the
potentials of deep learning and foster its successful
application in neural engineering with small data sets. We
propose a novel method that combines James-Stein regression
for feature extraction, and deep neural network for
decoding; we refer to the architecture as deep James-Stein
neural network (DJSNN). We apply the DJSNN to decode eye
movement goals in a memory-guided visual saccades to one of
eight target locations. The results demonstrate that the
DJSNN outperforms existing methods by a substantial margin,
especially at deep cortical sites.},
Doi = {10.1109/ICASSP40776.2020.9053694},
Key = {fds351061}
}
@article{fds348335,
Author = {Diao, E and Ding, J and Tarokh, V},
Title = {DRASIC: Distributed recurrent autoencoder for scalable image
compression},
Journal = {Data Compression Conference Proceedings},
Volume = {2020-March},
Pages = {3-12},
Publisher = {IEEE},
Year = {2020},
Month = {March},
url = {http://dx.doi.org/10.1109/DCC47342.2020.00008},
Abstract = {We propose a new architecture for distributed image
compression from a group of distributed data sources. The
work is motivated by practical needs of data-driven codec
design, low power consumption, robustness, and data privacy.
The proposed architecture, which we refer to as Distributed
Recurrent Autoencoder for Scalable Image Compression
(DRASIC), is able to train distributed encoders and one
joint decoder on correlated data sources. Its compression
capability is much better than the method of training codecs
separately. Meanwhile, the performance of our distributed
system with 10 distributed sources is only within 2 dB peak
signal-to-noise ratio (PSNR) of the performance of a single
codec trained with all data sources. We experiment
distributed sources with different correlations and show how
our data-driven methodology well matches the Slepian-Wolf
Theorem in Distributed Source Coding (DSC). To the best of
our knowledge, this is the first data-driven DSC framework
for general distributed code design with deep
learning.},
Doi = {10.1109/DCC47342.2020.00008},
Key = {fds348335}
}
@article{fds366448,
Author = {Diao, E and Ding, J and Tarokh, V},
Title = {Multimodal Controller for Generative Models},
Year = {2020},
Month = {February},
Abstract = {Class-conditional generative models are crucial tools for
data generation from user-specified class labels. Existing
approaches for class-conditional generative models require
nontrivial modifications of backbone generative
architectures to model conditional information fed into the
model. This paper introduces a plug-and-play module named
`multimodal controller' to generate multimodal data without
introducing additional learning parameters. In the absence
of the controllers, our model reduces to non-conditional
generative models. We test the efficacy of multimodal
controllers on CIFAR10, COIL100, and Omniglot benchmark
datasets. We demonstrate that multimodal controlled
generative models (including VAE, PixelCNN, Glow, and GAN)
can generate class-conditional images of significantly
better quality when compared with conditional generative
models. Moreover, we show that multimodal controlled models
can also create novel modalities of images.},
Key = {fds366448}
}
@article{fds348337,
Author = {Angjelichinoski, M and Choi, J and Banerjee, T and Pesaran, B and Tarokh, V},
Title = {Cross-subject decoding of eye movement goals from local
field potentials.},
Journal = {Journal of Neural Engineering},
Volume = {17},
Number = {1},
Pages = {016067},
Year = {2020},
Month = {February},
url = {http://dx.doi.org/10.1088/1741-2552/ab6df3},
Abstract = {<h4>Objective</h4>We consider the cross-subject decoding
problem from local field potential (LFP) signals, where
training data collected from the prefrontal cortex (PFC) of
a source subject is used to decode intended motor actions in
a destination subject.<h4>Approach</h4>We propose a novel
supervised transfer learning technique, referred to as data
centering, which is used to adapt the feature space of the
source to the feature space of the destination. The key
ingredients of data centering are the transfer functions
used to model the deterministic component of the
relationship between the source and destination feature
spaces. We propose an efficient data-driven estimation
approach for linear transfer functions that uses the first
and second order moments of the class-conditional
distributions.<h4>Main results</h4>We apply our data
centering technique with linear transfer functions for
cross-subject decoding of eye movement intentions in an
experiment where two macaque monkeys perform memory-guided
visual saccades to one of eight target locations. The
results show peak cross-subject decoding performance of
[Formula: see text], which marks a substantial improvement
over random choice decoder. In addition to this, data
centering also outperforms standard sampling-based methods
in setups with imbalanced training data.<h4>Significance</h4>The
analyses presented herein demonstrate that the proposed data
centering is a viable novel technique for reliable LFP-based
cross-subject brain-computer interfacing and neural
prostheses.},
Doi = {10.1088/1741-2552/ab6df3},
Key = {fds348337}
}
@article{fds348861,
Author = {Zhou, Y and Wang, Z and Ji, K and Liang, Y and Tarokh,
V},
Title = {Proximal gradient algorithm with momentum and flexible
parameter restart for nonconvex optimization},
Journal = {Ijcai International Joint Conference on Artificial
Intelligence},
Volume = {2021-January},
Pages = {1445-1451},
Year = {2020},
Month = {January},
Abstract = {Various types of parameter restart schemes have been
proposed for proximal gradient algorithm with momentum to
facilitate their convergence in convex optimization.
However, under parameter restart, the convergence of
proximal gradient algorithm with momentum remains obscure in
nonconvex optimization. In this paper, we propose a novel
proximal gradient algorithm with momentum and parameter
restart for solving nonconvex and nonsmooth problems. Our
algorithm is designed to 1) allow for adopting flexible
parameter restart schemes that cover many existing ones; 2)
have a global sub-linear convergence rate in nonconvex and
nonsmooth optimization; and 3) have guaranteed convergence
to a critical point and have various types of asymptotic
convergence rates depending on the parameterization of local
geometry in nonconvex and nonsmooth optimization. Numerical
experiments demonstrate the convergence and effectiveness of
our proposed algorithm.},
Key = {fds348861}
}
@article{fds348802,
Author = {Jeong, S and Li, X and Yang, J and Li, Q and Tarokh,
V},
Title = {Sparse Representation-Based Denoising for High-Resolution
Brain Activation and Functional Connectivity Modeling: A
Task fMRI Study.},
Journal = {Ieee Access},
Volume = {8},
Pages = {36728-36740},
Year = {2020},
Month = {January},
url = {http://dx.doi.org/10.1109/access.2020.2971261},
Abstract = {In the field of neuroimaging and cognitive neuroscience,
functional Magnetic Resonance Imaging (fMRI) has been widely
used to study the functional localization and connectivity
of the brain. However, the inherently low signal-to-noise
ratio (SNR) of the fMRI signals greatly limits the accuracy
and resolution of current studies. In addressing this
fundamental challenge in fMRI analytics, in this work we
develop and implement a denoising method for task fMRI
(tfMRI) data in order to delineate the high-resolution
spatial pattern of the brain activation and functional
connectivity via dictionary learning and sparse coding
(DLSC). In addition to the traditional unsupervised
dictionary learning model which has shown success in image
denoising, we further utilize the prior knowledge of task
paradigm to learn a dictionary consisting of both
data-driven and model-driven terms for a more stable sparse
representation of the data. The proposed method is applied
to preprocess the motor tfMRI dataset from Human Connectome
Project (HCP) for the purpose of brain activation detection
and functional connectivity estimation. Comparison between
the results from original and denoised fMRI data shows that
the disruptive brain activation and functional connectivity
patterns can be recovered, and the prominence of such
patterns is improved through denoising. The proposed method
is then compared with the temporal non-local means
(tNLM)-based denoising method and shows consistently
superior performance in various experimental settings. The
promising results show that the proposed DLSC-based fMRI
denoising method can effectively reduce the noise level of
the fMRI signals and increase the interpretability of the
inferred results, therefore constituting a crucial part of
the preprocessing pipeline and provide the foundation for
further high-resolution functional analysis.},
Doi = {10.1109/access.2020.2971261},
Key = {fds348802}
}
@article{fds366449,
Author = {Soltani, M and Wu, S and Ding, J and Ravier, R and Tarokh,
V},
Title = {On the information of feature maps and pruning of deep
neural networks},
Journal = {Proceedings International Conference on Pattern
Recognition},
Pages = {6988-6995},
Year = {2020},
Month = {January},
ISBN = {9781728188089},
url = {http://dx.doi.org/10.1109/ICPR48806.2021.9412579},
Abstract = {A technique for compressing deep neural models achieving
competitive performance to state-of-the-art methods is
proposed. The approach utilizes the mutual information
between the feature maps and the output of the model in
order to prune the redundant layers of the network.
Extensive numerical experiments on both CIFAR-10, CIFAR-100,
and Tiny ImageNet data sets demonstrate that the proposed
method can be effective in compressing deep models, both in
terms of the numbers of parameters and operations. For
instance, by applying the proposed approach to DenseNet
model with 0.77 million parameters and 293 million
operations for classification of CIFAR-10 data set, a
reduction of 62.66% and 41.00% in the number of parameters
and the number of operations are respectively achieved,
while increasing the test error only by less than
1%.},
Doi = {10.1109/ICPR48806.2021.9412579},
Key = {fds366449}
}
@article{fds350557,
Author = {Wu, S and Diao, E and Ding, J and Tarokh, V},
Title = {Deep Clustering of Compressed Variational
Embeddings.},
Journal = {Dcc},
Volume = {2020-March},
Pages = {399-399},
Publisher = {IEEE},
Editor = {Bilgin, A and Marcellin, MW and Serra-Sagristà, J and Storer,
JA},
Year = {2020},
ISBN = {978-1-7281-6457-1},
url = {http://dx.doi.org/10.1109/DCC47342.2020.00051},
Abstract = {Motivated by the ever-increasing demands for limited
communication bandwidth and low-power consumption, we
propose a new methodology, named joint Variational
Autoencoders with Bernoulli mixture models (VAB), for
performing clustering in the compressed data domain. The
idea is to reduce the data dimension by Variational
Autoencoders (VAEs) and group data representations by
Bernoulli mixture models (BMMs). Once jointly trained for
compression and clustering, the model can be decomposed into
two parts: a data vendor that encodes the raw data into
compressed data, and a data consumer that classifies the
received (compressed) data. In this way, the data vendor
benefits from data security and communication bandwidth,
while the data consumer benefits from low computational
complexity. To enable training using the gradient descent
algorithm, we propose to use the Gumbel-Softmax distribution
to resolve the infeasibility of the back-propagation
algorithm when assessing categorical samples.},
Doi = {10.1109/DCC47342.2020.00051},
Key = {fds350557}
}
@article{fds350558,
Author = {Diao, E and Ding, J and Tarokh, V},
Title = {DRASIC: Distributed Recurrent Autoencoder for Scalable Image
Compression.},
Journal = {Dcc},
Pages = {3-12},
Publisher = {IEEE},
Editor = {Bilgin, A and Marcellin, MW and Serra-Sagristà, J and Storer,
JA},
Year = {2020},
ISBN = {978-1-7281-6457-1},
Key = {fds350558}
}
@article{fds350559,
Author = {Zhou, Y and Wang, Z and Ji, K and Liang, Y and Tarokh,
V},
Title = {Proximal Gradient Algorithm with Momentum and Flexible
Parameter Restart for Nonconvex Optimization},
Journal = {Proceedings of the Twenty Ninth International Joint
Conference on Artificial Intelligence},
Pages = {1445-1451},
Publisher = {ijcai.org},
Editor = {Bessiere, C},
Year = {2020},
Key = {fds350559}
}
@article{fds351057,
Author = {Le, CP and Zhou, Y and Ding, J and Tarokh, V},
Title = {Supervised Encoding for Discrete Representation
Learning.},
Journal = {Icassp},
Volume = {2020-May},
Pages = {3447-3451},
Publisher = {IEEE},
Year = {2020},
ISBN = {978-1-5090-6631-5},
url = {http://dx.doi.org/10.1109/ICASSP40776.2020.9054118},
Abstract = {Classical supervised classification tasks search for a
nonlinear mapping that maps each encoded feature directly to
a probability mass over the labels. Such a learning
framework typically lacks the intuition that encoded
features from the same class tend to be similar and thus has
little interpretability for the learned features. In this
paper, we propose a novel supervised learning model named
Supervised-Encoding Quantizer (SEQ). The SEQ applies a
quantizer to cluster and classify the encoded features. We
found that the quantizer provides an interpretable graph
where each cluster in the graph represents a class of data
samples that have a particular style. We also trained a
decoder that can decode convex combinations of the encoded
features from similar and different clusters and provide
guidance on style transfer between sub-classes.},
Doi = {10.1109/ICASSP40776.2020.9054118},
Key = {fds351057}
}
@article{fds351058,
Author = {Ng, Y and Pereira, JM and Garagic, D and Tarokh, V},
Title = {Robust Marine Buoy Placement for Ship Detection Using
Dropout K-Means.},
Journal = {Icassp},
Volume = {2020-May},
Pages = {3757-3761},
Publisher = {IEEE},
Year = {2020},
ISBN = {978-1-5090-6631-5},
url = {http://dx.doi.org/10.1109/ICASSP40776.2020.9053064},
Abstract = {Marine buoys aid in the battle against Illegal, Unreported
and Unregulated (IUU) fishing by detecting fishing vessels
in their vicinity. Marine buoys, however, may be disrupted
by natural causes and buoy vandalism. In this paper, we
formulate marine buoy placement as a clustering problem, and
propose dropout k-means and dropout k-median to improve
placement robustness to buoy disruption.We simulated the
passage of ships in the Gabonese waters near West Africa
using historical Automatic Identification System (AIS) data,
then compared the ship detection probability of dropout
k-means to classic k-means and dropout k-median to classic
k-median. With 5 buoys, the buoy arrangement computed by
classic k-means, dropout k-means, classic k-median and
dropout k-median have ship detection probabilities of 38%,
45%, 48% and 52%.},
Doi = {10.1109/ICASSP40776.2020.9053064},
Key = {fds351058}
}
@article{fds351062,
Author = {Cannella, C and Ding, J and Soltani, M and Zhou, Y and Tarokh,
V},
Title = {Perception-Distortion Trade-Off with Restricted Boltzmann
Machines.},
Journal = {Icassp},
Volume = {2020-May},
Pages = {4022-4026},
Publisher = {IEEE},
Year = {2020},
ISBN = {978-1-5090-6631-5},
url = {http://dx.doi.org/10.1109/ICASSP40776.2020.9052991},
Abstract = {In this work, we introduce a new procedure for applying
Restricted Boltzmann Machines (RBMs) to missing data
inference tasks, based on linearization of the effective
energy function governing the distribution of observations.
We compare the performance of our proposed procedure with
those obtained using existing reconstruction procedures
trained on incomplete data. We place these performance
comparisons within the context of the perception-distortion
trade-off observed in other data reconstruction tasks, which
has, until now, remained unexplored in tasks relying on
incomplete training data.},
Doi = {10.1109/ICASSP40776.2020.9052991},
Key = {fds351062}
}
@article{fds351063,
Author = {Hasan, A and Pereira, JM and Ravier, RJ and Farsiu, S and Tarokh,
V},
Title = {Learning Partial Differential Equations From Data Using
Neural Networks.},
Journal = {Icassp},
Volume = {2020-May},
Pages = {3962-3966},
Publisher = {IEEE},
Year = {2020},
ISBN = {978-1-5090-6631-5},
url = {http://dx.doi.org/10.1109/ICASSP40776.2020.9053750},
Abstract = {We develop a framework for estimating unknown partial
differential equations (PDEs) from noisy data, using a deep
learning approach. Given noisy samples of a solution to an
unknown PDE, our method interpolates the samples using a
neural network, and extracts the PDE by equating derivatives
of the neural network approximation. Our method applies to
PDEs which are linear combinations of user-defined
dictionary functions, and generalizes previous methods that
only consider parabolic PDEs. We introduce a regularization
scheme that prevents the function approximation from
overfitting the data and forces it to be a solution of the
underlying PDE. We validate the model on simulated data
generated by the known PDEs and added Gaussian noise, and we
study our method under different levels of noise. We also
compare the error of our method with a Cramer-Rao lower
bound for an ordinary differential equation (ODE). Our
results indicate that our method outperforms other methods
in estimating PDEs, especially in the low signal-to-noise
(SNR) regime.},
Doi = {10.1109/ICASSP40776.2020.9053750},
Key = {fds351063}
}
@article{fds351065,
Author = {Wang, J and Xue, M and Culhane, R and Diao, E and Ding, J and Tarokh,
V},
Title = {Speech Emotion Recognition with Dual-Sequence LSTM
Architecture.},
Journal = {Icassp},
Volume = {2020-May},
Pages = {6474-6478},
Publisher = {IEEE},
Year = {2020},
ISBN = {978-1-5090-6631-5},
url = {http://dx.doi.org/10.1109/ICASSP40776.2020.9054629},
Abstract = {Speech Emotion Recognition (SER) has emerged as a critical
component of the next generation of human-machine
interfacing technologies. In this work, we propose a new
duallevel model that predicts emotions based on both MFCC
features and mel-spectrograms produced from raw audio
signals. Each utterance is preprocessed into MFCC features
and two mel-spectrograms at different time-frequency
resolutions. A standard LSTM processes the MFCC features,
while a novel LSTM architecture, denoted as Dual-Sequence
LSTM (DSLSTM), processes the two mel-spectrograms
simultaneously. The outputs are later averaged to produce a
final classification of the utterance. Our proposed model
achieves, on average, a weighted accuracy of 72.7% and an
unweighted accuracy of 73.3%-a 6% improvement over current
state-of-the-art unimodal models-and is comparable with
multimodal models that leverage textual information as well
as audio signals.},
Doi = {10.1109/ICASSP40776.2020.9054629},
Key = {fds351065}
}
@article{fds348338,
Author = {Zhang, Y and Ravier, RJ and Zavlanos, MM and Tarokh,
V},
Title = {A Distributed Online Convex Optimization Algorithm with
Improved Dynamic Regret},
Journal = {Proceedings of the Ieee Conference on Decision and
Control},
Volume = {2019-December},
Pages = {2449-2454},
Year = {2019},
Month = {December},
url = {http://dx.doi.org/10.1109/CDC40024.2019.9029474},
Abstract = {In this paper, we consider the problem of distributed online
convex optimization, where a network of local agents aim to
jointly optimize a convex function over a period of multiple
time steps. The agents do not have any information about the
future. Existing algorithms have established dynamic regret
bounds that have explicit dependence on the number of time
steps. In this work, we show that we can remove this
dependence assuming that the local objective functions are
strongly convex. More precisely, we propose a gradient
tracking algorithm where agents jointly communicate and
descend based on corrected gradient steps. We verify our
theoretical results through numerical experiments.},
Doi = {10.1109/CDC40024.2019.9029474},
Key = {fds348338}
}
@article{fds348336,
Author = {DIao, E and DIng, J and Tarokh, V},
Title = {Restricted Recurrent Neural Networks},
Journal = {Proceedings 2019 Ieee International Conference on Big Data,
Big Data 2019},
Volume = {abs/1908.07724},
Pages = {56-63},
Year = {2019},
Month = {December},
url = {http://dx.doi.org/10.1109/BigData47090.2019.9006257},
Abstract = {Recurrent Neural Network (RNN) and its variations such as
Long Short-Term Memory (LSTM) and Gated Recurrent Unit
(GRU), have become standard building blocks for learning
online data of sequential nature in many research areas,
including natural language processing and speech data
analysis. In this paper, we present a new methodology to
significantly reduce the number of parameters in RNNs while
maintaining performance that is comparable or even better
than classical RNNs. The new proposal, referred to as
Restricted Recurrent Neural Network (RRNN), restricts the
weight matrices corresponding to the input data and hidden
states at each time step to share a large proportion of
parameters. The new architecture can be regarded as a
compression of its classical counterpart, but it does not
require pre-training or sophisticated parameter fine-tuning,
both of which are major issues in most existing compression
techniques. Experiments on natural language modeling show
that compared with its classical counterpart, the restricted
recurrent architecture generally produces comparable results
at about 50% compression rate. In particular, the Restricted
LSTM can outperform classical RNN with even less number of
parameters.},
Doi = {10.1109/BigData47090.2019.9006257},
Key = {fds348336}
}
@article{fds348803,
Author = {Feng, Y and Zhou, Y and Tarokh, V},
Title = {Recurrent Neural Network-Assisted Adaptive Sampling for
Approximate Computing},
Journal = {Proceedings 2019 Ieee International Conference on Big Data,
Big Data 2019},
Pages = {2240-2246},
Year = {2019},
Month = {December},
ISBN = {9781728108582},
url = {http://dx.doi.org/10.1109/BigData47090.2019.9006504},
Abstract = {We propose an adaptive signal sampling approach that
dynamically adjusts the sampling rate to approximate the
local Nyquist rate of the signal. The proposed adaptive
sampling approach consists of a recurrent neural
network-based change detector that detects the point of
frequency change and a local Nyquist rate estimator based on
a multi-rate signal processing scheme. We empirically
demonstrate that our adaptive sampling approach
significantly reduces the overall sampling rate for various
types of signals and therefore improves the computational
efficiency of subsequent signal processing.},
Doi = {10.1109/BigData47090.2019.9006504},
Key = {fds348803}
}
@article{fds349201,
Author = {Ravier, RJ and Calderbank, AR and Tarokh, V},
Title = {Prediction in Online Convex Optimization for Parametrizable
Objective Functions},
Journal = {Proceedings of the Ieee Conference on Decision and
Control},
Volume = {2019-December},
Pages = {2455-2460},
Year = {2019},
Month = {December},
url = {http://dx.doi.org/10.1109/CDC40024.2019.9030013},
Abstract = {Many techniques for online optimization problems involve
making decisions based solely on presently available
information: fewer works take advantage of potential
predictions. In this paper, we discuss the problem of online
convex optimization for parametrizable objectives, i.e.
optimization problems that depend solely on the value of a
parameter at a given time. We introduce a new regularity for
dynamic regret based on the accuracy of predicted values of
the parameters and show that, under mild assumptions,
accurate prediction can yield tighter bounds on dynamic
regret. Inspired by recent advances on learning how to
optimize, we also propose a novel algorithm to
simultaneously predict and optimize for parametrizable
objectives and study its performance using numerical
experiments.},
Doi = {10.1109/CDC40024.2019.9030013},
Key = {fds349201}
}
@article{fds349562,
Author = {Zhang, Y and Ravier, RJ and Tarokh, V and Zavlanos,
MM},
Title = {Distributed Online Convex Optimization with Improved Dynamic
Regret},
Pages = {2449-2454},
Publisher = {IEEE},
Year = {2019},
Month = {November},
Abstract = {In this paper, we consider the problem of distributed online
convex optimization, where a group of agents collaborate to
track the global minimizers of a sum of time-varying
objective functions in an online manner. Specifically, we
propose a novel distributed online gradient descent
algorithm that relies on an online adaptation of the
gradient tracking technique used in static optimization. We
show that the dynamic regret bound of this algorithm has no
explicit dependence on the time horizon and, therefore, can
be tighter than existing bounds especially for problems with
long horizons. Our bound depends on a new regularity measure
that quantifies the total change in the gradients at the
optimal points at each time instant. Furthermore, when the
optimizer is approximatly subject to linear dynamics, we
show that the dynamic regret bound can be further tightened
by replacing the regularity measure that captures the path
length of the optimizer with the accumulated prediction
errors, which can be much lower in this special case. We
present numerical experiments to corroborate our theoretical
results.},
Key = {fds349562}
}
@article{fds342380,
Author = {Shao, S and Jacob, PE and Ding, J and Tarokh, V},
Title = {Bayesian Model Comparison with the Hyvärinen Score:
Computation and Consistency},
Journal = {Journal of the American Statistical Association},
Volume = {114},
Number = {528},
Pages = {1826-1837},
Year = {2019},
Month = {October},
url = {http://dx.doi.org/10.1080/01621459.2018.1518237},
Abstract = {The Bayes factor is a widely used criterion in model
comparison and its logarithm is a difference of
out-of-sample predictive scores under the logarithmic
scoring rule. However, when some of the candidate models
involve vague priors on their parameters, the log-Bayes
factor features an arbitrary additive constant that hinders
its interpretation. As an alternative, we consider model
comparison using the Hyvärinen score. We propose a method
to consistently estimate this score for parametric models,
using sequential Monte Carlo methods. We show that this
score can be estimated for models with tractable likelihoods
as well as nonlinear non-Gaussian state-space models with
intractable likelihoods. We prove the asymptotic consistency
of this new model selection criterion under strong
regularity assumptions in the case of nonnested models, and
we provide qualitative insights for the nested case. We also
use existing characterizations of proper scoring rules on
discrete spaces to extend the Hyvärinen score to discrete
observations. Our numerical illustrations include
Lévy-driven stochastic volatility models and diffusion
models for population dynamics. Supplementary materials for
this article are available online.},
Doi = {10.1080/01621459.2018.1518237},
Key = {fds342380}
}
@article{fds348339,
Author = {Zhou, Y and Feng, Y and Tarokh, V and Gintautas, V and McClelland, J and Garagic, D},
Title = {Multi-Level Mean-Shift Clustering for Single-Channel Radio
Frequency Signal Separation},
Journal = {Ieee International Workshop on Machine Learning for Signal
Processing, Mlsp},
Volume = {2019-October},
Pages = {1-6},
Publisher = {IEEE},
Year = {2019},
Month = {October},
ISBN = {9781728108247},
url = {http://dx.doi.org/10.1109/MLSP.2019.8918879},
Abstract = {Emerging wireless communication applications have led to a
crowded radio frequency (RF) spectrum. Therefore, it is
desired to develop signal separation techniques that can
extract different RF signals from their mixtures. Existing
signal separation approaches typically require multiple
observations of the signal mixtures and depend on
statistical independence among the signals. In this paper,
we consider separating multiple RF wireless signals from
their single-channel superposition. These RF signals are
transmitted in their corresponding high-frequency pass bands
with diverse power spectrum densities, bandwidths, and time
durations. We propose a signal separation approach that
exploits the mean-shift clustering algorithm with multiple
levels of cluster sizes to identify RF signals with
different bandwidths in the spectrogram of the superposed
signal. We demonstrate the effectiveness of our approach by
separating RF signals using real datasets.},
Doi = {10.1109/MLSP.2019.8918879},
Key = {fds348339}
}
@article{fds342500,
Author = {Angjelichinoski, M and Banerjee, T and Choi, J and Pesaran, B and Tarokh, V},
Title = {Minimax-optimal decoding of movement goals from local field
potentials using complex spectral features.},
Journal = {Journal of Neural Engineering},
Volume = {16},
Number = {4},
Pages = {046001},
Year = {2019},
Month = {August},
url = {http://dx.doi.org/10.1088/1741-2552/ab1a1f},
Abstract = {<h4>Objective</h4>We consider the problem of predicting eye
movement goals from local field potentials (LFP) recorded
through a multielectrode array in the macaque prefrontal
cortex. The monkey is tasked with performing memory-guided
saccades to one of eight targets during which LFP activity
is recorded and used to train a decoder.<h4>Approach</h4>Previous
reports have mainly relied on the spectral amplitude of the
LFPs as decoding feature, while neglecting the phase without
proper theoretical justification. This paper formulates the
problem of decoding eye movement intentions in a
statistically optimal framework and uses Gaussian sequence
modeling and Pinsker's theorem to generate minimax-optimal
estimates of the LFP signals which are used as decoding
features. The approach is shown to act as a low-pass filter
and each LFP in the feature space is represented via its
complex Fourier coefficients after appropriate shrinking
such that higher frequency components are attenuated; this
way, the phase information inherently present in the LFP
signal is naturally embedded into the feature space.<h4>Main
results</h4>We show that the proposed complex spectrum-based
decoder achieves prediction accuracy of up to [Formula: see
text] at superficial cortical depths near the surface of the
prefrontal cortex; this marks a significant performance
improvement over conventional power spectrum-based
decoders.<h4>Significance</h4>The presented analyses
showcase the promising potential of low-pass filtered LFP
signals for highly reliable neural decoding of intended
motor actions.},
Doi = {10.1088/1741-2552/ab1a1f},
Key = {fds342500}
}
@article{fds345908,
Author = {Krishnamurthy, S and Bliss, DW and Richmond, CD and Tarokh,
V},
Title = {Peak sidelobe level gumbel distribution of antenna arrays
with random phase centers},
Journal = {Ieee Transactions on Antennas and Propagation},
Volume = {67},
Number = {8},
Pages = {5399-5410},
Year = {2019},
Month = {August},
url = {http://dx.doi.org/10.1109/TAP.2019.2917469},
Abstract = {The maximum value of an antenna array's sidelobe
beampattern, or radiation pattern in the power domain, is an
important parameter determining its performance. In this
paper, when array antenna elements have random phase
centers, we approximate the maximum sidelobe value, or peak
sidelobe level, as a Gumbel distribution using the extreme
value theory (EVT). Before the EVT result, an expression for
the beampattern distribution at each angle in the array
field of view is found. From this expression, the pointwise
convergence of the difference between the beampattern and
exponential distributions in the limit of a large number of
antennas is obtained. Using the exponential distribution
approximation, EVT is applied with samples of the
beampattern. A bound is given for the difference between the
beampattern sample maximum and its true maximum in the
sidelobe region.},
Doi = {10.1109/TAP.2019.2917469},
Key = {fds345908}
}
@article{fds343754,
Author = {Banerjee, T and Allsop, S and Tye, KM and Ba, D and Tarokh,
V},
Title = {Sequential Detection of Regime Changes in Neural
Data},
Journal = {International Ieee/Embs Conference on Neural Engineering,
Ner},
Volume = {2019-March},
Pages = {139-142},
Year = {2019},
Month = {May},
url = {http://dx.doi.org/10.1109/NER.2019.8716926},
Abstract = {The problem of detecting changes in firing patterns in
neural data is studied. The problem is formulated as a
quickest change detection (QCD) problem. Important
algorithms from the literature are reviewed. A new
algorithmic technique is discussed to detect deviations from
learned baseline behavior. The algorithms studied can be
applied to both spike and local field potential data. The
algorithms are applied to mice spike data to verify the
presence of behavioral learning.},
Doi = {10.1109/NER.2019.8716926},
Key = {fds343754}
}
@article{fds339923,
Author = {Ding, J and Zhou, J and Tarokh, V},
Title = {Asymptotically Optimal Prediction for Time-Varying Data
Generating Processes},
Journal = {Ieee Transactions on Information Theory},
Volume = {65},
Number = {5},
Pages = {3034-3067},
Year = {2019},
Month = {May},
url = {http://dx.doi.org/10.1109/TIT.2018.2882819},
Abstract = {We develop a methodology (referred to as kinetic prediction)
for predicting time series undergoing unknown changes in
their data generating distributions. Based on
Kolmogorov-Tikhomirov's {\varepsilon } -entropy, we propose
a concept called {\varepsilon } -predictability that
quantifies the size of a model class (which can be
parametric or nonparametric) and the maximal number of
abrupt structural changes that guarantee the achievability
of asymptotically optimal prediction. Moreover, for
parametric distribution families, we extend the
aforementioned kinetic prediction with discretized function
spaces to its counterpart with continuous function spaces,
and propose a sequential Monte Carlo-based implementation.
We also extend our methodology for predicting smoothly
varying data generating distributions. Under reasonable
assumptions, we prove that the average predictive
performance converges almost surely to the oracle bound,
which corresponds to the case that the data generating
distributions are known in advance. The results also shed
some light on the so called 'prediction-inference dilemma.'
Various examples and numerical results are provided to
demonstrate the wide applicability of our
methodology.},
Doi = {10.1109/TIT.2018.2882819},
Key = {fds339923}
}
@article{fds341252,
Author = {Xiang, Y and Ding, J and Tarokh, V},
Title = {Estimation of the evolutionary spectra with application to
stationarity test},
Journal = {Ieee Transactions on Signal Processing},
Volume = {67},
Number = {5},
Pages = {1353-1365},
Publisher = {IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS
INC},
Year = {2019},
Month = {March},
url = {http://dx.doi.org/10.1109/TSP.2018.2890369},
Abstract = {In this paper, we propose a new inference procedure for
understanding non-stationary processes, under the framework
of evolutionary spectra developed by Priestley. Among
various frameworks of modeling non-stationary processes, the
distinguishing feature of the evolutionary spectra is its
focus on the physical meaning of frequency. The classical
estimate of the evolutionary spectral density is based on a
double-window technique consisting of a short-time Fourier
transform and a smoothing. However, smoothing is known to
suffer from the so-called bias leakage problem. By
incorporating Thomson's multitaper method that was
originally designed for stationary processes, we propose an
improved estimate of the evolutionary spectral density, and
analyze its bias/variance/resolution tradeoff. As an
application of the new estimate, we further propose a
non-parametric rank-based stationarity test, and provide
various experimental studies.},
Doi = {10.1109/TSP.2018.2890369},
Key = {fds341252}
}
@article{fds339989,
Author = {Banerjee, T and Whipps, G and Gurram, P and Tarokh,
V},
Title = {Cyclostationary statistical models and algorithms for
anomaly detection using multi-modal data},
Journal = {2018 Ieee Global Conference on Signal and Information
Processing, Globalsip 2018 Proceedings},
Volume = {abs/1807.06945},
Pages = {126-130},
Year = {2019},
Month = {February},
url = {http://dx.doi.org/10.1109/GlobalSIP.2018.8646417},
Abstract = {A framework is proposed to detect anomalies in multi-modal
data. A deep neural network-based object detector is
employed to extract counts of objects and sub-events from
the data. A cyclostationary model is proposed to model
regular patterns of behavior in the count sequences. The
anomaly detection problem is formulated as a problem of
detecting deviations from learned cyclostationary behavior.
Sequential algorithms are proposed to detect anomalies using
the proposed model. The proposed algorithms are shown to be
asymptotically efficient in a well-defined sense. The
developed algorithms are applied to a multi-modal data
consisting of CCTV imagery and social media posts to detect
a 5K run in New York City.},
Doi = {10.1109/GlobalSIP.2018.8646417},
Key = {fds339989}
}
@article{fds361404,
Author = {Zhou, Y and Wang, Z and Ji, K and Liang, Y and Tarokh,
V},
Title = {Momentum Schemes with Stochastic Variance Reduction for
Nonconvex Composite Optimization},
Year = {2019},
Month = {February},
Abstract = {Two new stochastic variance-reduced algorithms named SARAH
and SPIDER have been recently proposed, and SPIDER has been
shown to achieve a near-optimal gradient oracle complexity
for nonconvex optimization. However, the theoretical
advantage of SPIDER does not lead to substantial improvement
of practical performance over SVRG. To address this issue,
momentum technique can be a good candidate to improve the
performance of SPIDER. However, existing momentum schemes
used in variance-reduced algorithms are designed
specifically for convex optimization, and are not applicable
to nonconvex scenarios. In this paper, we develop novel
momentum schemes with flexible coefficient settings to
accelerate SPIDER for nonconvex and nonsmooth composite
optimization, and show that the resulting algorithms achieve
the near-optimal gradient oracle complexity for achieving a
generalized first-order stationary condition. Furthermore,
we generalize our algorithm to online nonconvex and
nonsmooth optimization, and establish an oracle complexity
result that matches the state-of-the-art. Our extensive
experiments demonstrate the superior performance of our
proposed algorithm over other stochastic variance-reduced
algorithms.},
Key = {fds361404}
}
@article{fds349561,
Author = {Zhou, Y and Yang, J and Zhang, H and Liang, Y and Tarokh,
V},
Title = {SGD converges to global minimum in deep learning via
star-convex path},
Journal = {7th International Conference on Learning Representations,
Iclr 2019},
Year = {2019},
Month = {January},
Abstract = {Stochastic gradient descent (SGD) has been found to be
surprisingly effective in training a variety of deep neural
networks. However, there is still a lack of understanding on
how and why SGD can train these complex networks towards a
global minimum. In this study, we establish the convergence
of SGD to a global minimum for nonconvex optimization
problems that are commonly encountered in neural network
training. Our argument exploits the following two important
properties: 1) the training loss can achieve zero value
(approximately), which has been widely observed in deep
learning; 2) SGD follows a star-convex path, which is
verified by various experiments in this paper. In such a
context, our analysis shows that SGD, although has long been
considered as a randomized algorithm, converges in an
intrinsically deterministic manner to a global
minimum.},
Key = {fds349561}
}
@article{fds345909,
Author = {Zhou, Y and Yang, J and Zhang, H and Liang, Y and Tarokh,
V},
Title = {SGD converges to global minimum in deep learning via
star-convex path},
Journal = {7th International Conference on Learning Representations,
Iclr 2019},
Year = {2019},
Month = {January},
Abstract = {© 7th International Conference on Learning Representations,
ICLR 2019. All Rights Reserved. Stochastic gradient descent
(SGD) has been found to be surprisingly effective in
training a variety of deep neural networks. However, there
is still a lack of understanding on how and why SGD can
train these complex networks towards a global minimum. In
this study, we establish the convergence of SGD to a global
minimum for nonconvex optimization problems that are
commonly encountered in neural network training. Our
argument exploits the following two important properties: 1)
the training loss can achieve zero value (approximately),
which has been widely observed in deep learning; 2) SGD
follows a star-convex path, which is verified by various
experiments in this paper. In such a context, our analysis
shows that SGD, although has long been considered as a
randomized algorithm, converges in an intrinsically
deterministic manner to a global minimum.},
Key = {fds345909}
}
@article{fds347667,
Author = {Wang, Z and Ji, K and Zhou, Y and Liang, Y and Tarokh,
V},
Title = {Spiderboost and momentum: Faster stochastic variance
reduction algorithms},
Journal = {Advances in Neural Information Processing
Systems},
Volume = {32},
Year = {2019},
Month = {January},
Abstract = {SARAH and SPIDER are two recently developed stochastic
variance-reduced algorithms, and SPIDER has been shown to
achieve a near-optimal first-order oracle complexity in
smooth nonconvex optimization. However, SPIDER uses an
accuracy-dependent stepsize that slows down the convergence
in practice, and cannot handle objective functions that
involve nonsmooth regularizers. In this paper, we propose
SpiderBoost as an improved scheme, which allows to use a
much larger constant-level stepsize while maintaining the
same near-optimal oracle complexity, and can be extended
with proximal mapping to handle composite optimization
(which is nonsmooth and nonconvex) with provable convergence
guarantee. In particular, we show that proximal SpiderBoost
achieves an oracle complexity of O(Equation Presented) in
composite nonconvex optimization, improving the
state-of-the-art result by a factor of O(Equation
Presented). We further develop a novel momentum scheme to
accelerate SpiderBoost for composite optimization, which
achieves the near-optimal oracle complexity in theory and
substantial improvement in experiments.},
Key = {fds347667}
}
@article{fds366450,
Author = {Ding, J and Calderbank, R and Tarokh, V},
Title = {Gradient information for representation and
modeling},
Journal = {Advances in Neural Information Processing
Systems},
Volume = {32},
Year = {2019},
Month = {January},
Abstract = {Motivated by Fisher divergence, in this paper we present a
new set of information quantities which we refer to as
gradient information. These measures serve as surrogates for
classical information measures such as those based on
logarithmic loss, Kullback-Leibler divergence, directed
Shannon information, etc. in many data-processing scenarios
of interest, and often provide significant computational
advantage, improved stability, and robustness. As an
example, we apply these measures to the Chow-Liu tree
algorithm, and demonstrate remarkable performance and
significant computational reduction using both synthetic and
real data.},
Key = {fds366450}
}
@article{fds348862,
Author = {Diao, E and Ding, J and Tarokh, V},
Title = {Restricted Recurrent Neural Networks.},
Journal = {Ieee Bigdata},
Pages = {56-63},
Publisher = {IEEE},
Editor = {Baru, C and Huan, J and Khan, L and Hu, X and Ak, R and Tian, Y and Barga, RS and Zaniolo, C and Lee, K and Ye, YF},
Year = {2019},
ISBN = {978-1-7281-0858-2},
Key = {fds348862}
}
@article{fds366451,
Author = {Wang, Z and Ji, K and Zhou, Y and Liang, Y and Tarokh,
V},
Title = {SpiderBoost and Momentum: Faster Variance Reduction
Algorithms.},
Journal = {Neurips},
Pages = {2403-2413},
Editor = {Wallach, HM and Larochelle, H and Beygelzimer, A and d'Alché-Buc, F and Fox, EB and Garnett, R},
Year = {2019},
Key = {fds366451}
}
@article{fds339856,
Author = {Ding, J and Tarokh, V and Yang, Y},
Title = {Model Selection Techniques: An Overview},
Journal = {Ieee Signal Processing Magazine},
Volume = {35},
Number = {6},
Pages = {16-34},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2018},
Month = {November},
url = {http://dx.doi.org/10.1109/MSP.2018.2867638},
Abstract = {In the era of big data, analysts usually explore various
statistical models or machine-learning methods for observed
data to facilitate scientific discoveries or gain predictive
power. Whatever data and fitting procedures are employed, a
crucial step is to select the most appropriate model or
method from a set of candidates. Model selection is a key
ingredient in data analysis for reliable and reproducible
statistical inference or prediction, and thus it is central
to scientific studies in such fields as ecology, economics,
engineering, finance, political science, biology, and
epidemiology. There has been a long history of model
selection techniques that arise from researches in
statistics, information theory, and signal processing. A
considerable number of methods has been proposed, following
different philosophies and exhibiting varying performances.
The purpose of this article is to provide a comprehensive
overview of them, in terms of their motivation, large sample
performance, and applicability. We provide integrated and
practically relevant discussions on theoretical properties
of state-of-the-art model selection approaches. We also
share our thoughts on some controversial views on the
practice of model selection.},
Doi = {10.1109/MSP.2018.2867638},
Key = {fds339856}
}
@article{fds338599,
Author = {Ding, J and Diao, E and Zhou, J and Tarokh, V},
Title = {A Penalized Method for the Predictive Limit of
Learning},
Journal = {2015 Ieee International Conference on Acoustics, Speech, and
Signal Processing (Icassp)},
Volume = {2018-April},
Pages = {4414-4418},
Publisher = {IEEE},
Year = {2018},
Month = {September},
ISBN = {9781538646588},
url = {http://dx.doi.org/10.1109/ICASSP.2018.8461832},
Abstract = {Machine learning systems learn from and make predictions by
building models from observed data. Because large models
tend to overfit while small models tend to underfit for a
given fixed dataset, a critical challenge is to select an
appropriate model (e.g. set of variables/features). Model
selection aims to strike a balance between the goodness of
fit and model complexity, and thus to gain reliable
predictive power. In this paper, we study a penalized model
selection technique that asymptotically achieves the optimal
expected prediction loss (referred to as the limit of
learning) offered by a set of candidate models. We prove
that the proposed procedure is both statistically efficient
in the sense that it asymptotically approaches the limit of
learning, and computationally efficient in the sense that it
can be much faster than cross validation methods. Our theory
applies for a wide variety of model classes, loss functions,
and high dimensions (in the sense that the models'
complexity can grow with data size). We released a python
package with our proposed method for general usage like
logistic regression and neural networks.},
Doi = {10.1109/ICASSP.2018.8461832},
Key = {fds338599}
}
@article{fds339263,
Author = {Banerjee, T and Choi, J and Pesaran, B and Ba, D and Tarokh,
V},
Title = {Wavelet Shrinkage and Thresholding Based Robust
Classification for Brain-Computer Interface},
Journal = {2015 Ieee International Conference on Acoustics, Speech, and
Signal Processing (Icassp)},
Volume = {2018-April},
Pages = {836-840},
Publisher = {IEEE},
Year = {2018},
Month = {September},
url = {http://dx.doi.org/10.1109/ICASSP.2018.8462321},
Abstract = {A macaque monkey is trained to perform two different kinds
of tasks, memory aided and visually aided. In each task, the
monkey saccades to eight possible target locations. A
classifier is proposed for direction decoding and task
decoding based on local field potentials (LFP) collected
from the prefrontal cortex. The LFP time-series data is
modeled in a nonparametric regression framework, as a
function corrupted by Gaussian noise. It is shown that if
the function belongs to Besov bodies, then the proposed
wavelet shrinkage and thresholding based classifier is
robust and consistent. The classifier is then applied to the
LFP data to achieve high decoding performance. The proposed
classifier is also quite general and can be applied for the
classification of other types of time-series data as well,
not necessarily brain data.},
Doi = {10.1109/ICASSP.2018.8462321},
Key = {fds339263}
}
@article{fds339264,
Author = {Xiang, Y and Ding, J and Tarokh, V},
Title = {Evolutionary Spectra Based on the Multitaper Method with
Application to Stationarity Test},
Journal = {2015 Ieee International Conference on Acoustics, Speech, and
Signal Processing (Icassp)},
Volume = {2018-April},
Pages = {3994-3998},
Publisher = {IEEE},
Year = {2018},
Month = {September},
url = {http://dx.doi.org/10.1109/ICASSP.2018.8461443},
Abstract = {In this work, we propose a new inference procedure for
understanding non-stationary processes, under the framework
of evolutionary spectra developed by Priestley. Among
various frameworks of modeling non-stationary processes, the
distinguishing feature of the evolutionary spectra is its
focus on the physical meaning of frequency. The classical
estimate of the evolutionary spectral density is based on a
double-window technique consisting of a short-Fourier
transform and a smoothing. However, smoothing is known to
suffer from the so-called bias leakage problem. By
incorporating Thomson's multitaper method that was
originally designed for stationary processes, we propose an
improved estimate of the evolutionary spectral density, and
analyze its bias/variance/resolution tradeoff. As an
application of the new estimate, we further propose a
non-parametric rank-based stationarity test, and provide
various experimental studies.},
Doi = {10.1109/ICASSP.2018.8461443},
Key = {fds339264}
}
@article{fds338434,
Author = {Banerjee, T and Whipps, G and Gurram, P and Tarokh,
V},
Title = {Sequential Event Detection Using Multimodal Data in
Nonstationary Environments},
Journal = {2018 21st International Conference on Information Fusion,
Fusion 2018},
Pages = {1940-1947},
Publisher = {IEEE},
Year = {2018},
Month = {September},
url = {http://dx.doi.org/10.23919/ICIF.2018.8455835},
Abstract = {The problem of sequential detection of anomalies in
multimodal data is considered. The objective is to observe
physical sensor data from CCTV cameras, and social media
data from Twitter and Instagram to detect anomalous
behaviors or events. Data from each modality is transformed
to discrete time count data by using an artificial neural
network to obtain counts of objects in CCTV images and by
counting the number of tweets or Instagram posts in a
geographical area. The anomaly detection problem is then
formulated as a problem of quickest detection of changes in
count statistics. The quickest detection problem is then
solved using the framework of partially observable Markov
decision processes (POMDP), and structural results on the
optimal policy are obtained. The resulting optimal policy is
then applied to real multimodal data collected from New York
City around a 5K race to detect the race. The count data
both before and after the change is found to be
nonstationary in nature. The proposed mathematical approach
to this problem provides a framework for event detection in
such nonstationary environments and across multiple data
modalities.},
Doi = {10.23919/ICIF.2018.8455835},
Key = {fds338434}
}
@article{fds361726,
Author = {Soloveychik, I and Tarokh, V},
Title = {Asymptotically Pseudo-Independent Matrices},
Year = {2018},
Month = {September},
Abstract = {We show that the family of pseudo-random matrices recently
discovered by Soloveychik, Xiang, and Tarokh in their work
`Symmetric Pseudo-Random Matrices' exhibits asymptotic
independence. More specifically, any two sequences of
matrices of matching sizes from that construction generated
using sequences of different non-reciprocal primitive
polynomials are asymptotically independent.},
Key = {fds361726}
}
@article{fds336659,
Author = {Shahrampour, S and Noshad, M and Ding, J and Tarokh,
V},
Title = {Online Learning for Multimodal Data Fusion with Application
to Object Recognition},
Journal = {Ieee Transactions on Circuits and Systems Ii: Express
Briefs},
Volume = {65},
Number = {9},
Pages = {1259-1263},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2018},
Month = {September},
url = {http://dx.doi.org/10.1109/TCSII.2017.2754141},
Abstract = {We consider online multimodal data fusion, where the goal is
to combine information from multiple modes to identify an
element in a large dictionary. We address this problem in
the context of object recognition by focusing on tactile
sensing as one of the modes. Using a tactile glove with
seven sensors, various individuals grasp different objects
to obtain 7-D time series, where each component represents
the pressure sequence applied to one sensor. The pressure
data of all objects is stored in a dictionary as a
reference. The objective is to match a streaming vector time
series from grasping an unknown object to a dictionary
object. We propose an algorithm that may start with prior
knowledge provided by other modes. Receiving pressure data
sequentially, the algorithm uses a dissimilarity metric to
modify the prior and form a probability distribution over
the dictionary. When the dictionary objects are dissimilar
in shape, we empirically show that our algorithm recognize
the unknown object even with a uniform prior. If there
exists a similar object to the unknown object in the
dictionary, our algorithm needs the prior from other modes
to detect the unknown object. Notably, our algorithm
maintains a similar performance to standard offline
classification techniques, such as support vector machine,
with a significantly lower computational
time.},
Doi = {10.1109/TCSII.2017.2754141},
Key = {fds336659}
}
@article{fds338435,
Author = {Banerjee, T and Choi, J and Pesaran, B and Ba, D and Tarokh,
V},
Title = {Classification of Local Field Potentials using Gaussian
Sequence Model},
Journal = {2018 Ieee Statistical Signal Processing Workshop, Ssp
2018},
Pages = {218-222},
Publisher = {IEEE},
Year = {2018},
Month = {August},
url = {http://dx.doi.org/10.1109/SSP.2018.8450778},
Abstract = {A problem of classification of local field potentials
(LFPs), recorded from the prefrontal cortex of a macaque
monkey, is considered. An adult macaque monkey is trained to
perform a memory based saccade. The objective is to decode
the eye movement goals from the LFP collected during a
memory period. The LFP classification problem is modeled as
that of classification of smooth functions embedded in
Gaussian noise. It is then argued that using minimax
function estimators as features would lead to consistent LFP
classifiers. The theory of Gaussian sequence models allows
us to represent minimax estimators as finite dimensional
objects. The LFP classifier resulting from this mathematical
endeavor is a spectrum based technique, where Fourier series
coefficients of the LFP data, followed by appropriate
shrinkage and thresholding, are used as features in a linear
discriminant classifier. The classifier is then applied to
the LFP data to achieve high decoding accuracy. The function
classification approach taken in the paper also provides a
systematic justification for using Fourier series, with
shrinkage and thresholding, as features for the problem, as
opposed to using the power spectrum. It also suggests that
phase information is crucial to the decision
making.},
Doi = {10.1109/SSP.2018.8450778},
Key = {fds338435}
}
@article{fds336646,
Author = {Magnusson, S and Enyioha, C and Li, N and Fischione, C and Tarokh,
V},
Title = {Communication Complexity of Dual Decomposition Methods for
Distributed Resource Allocation Optimization},
Journal = {Ieee Journal of Selected Topics in Signal
Processing},
Volume = {12},
Number = {4},
Pages = {717-732},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2018},
Month = {August},
url = {http://dx.doi.org/10.1109/JSTSP.2018.2848718},
Abstract = {Dual decomposition methods are among the most prominent
approaches for finding primal/dual saddle point solutions of
resource allocation optimization problems. To deploy these
methods in the emerging Internet of things networks, which
will often have limited data rates, it is important to
understand the communication overhead they require.
Motivated by this, we introduce and explore two measures of
communication complexity of dual decomposition methods to
identify the most efficient communication among these
algorithms. The first measure is ϵ-complexity, which
quantifies the minimal number of bits needed to find an
ϵ-accurate solution. The second measure is b-complexity,
which quantifies the best possible solution accuracy that
can be achieved from communicating b bits. We find the exact
ϵ-and b-complexity of a class of resource allocation
problems where a single supplier allocates resources to
multiple users. For both the primal and dual problems, the
ϵ-complexity grows proportionally to 2(1ϵ) and the
b-complexity proportionally to 1/2b. We also introduce a
variant of the ϵ-and b-complexity measures where only
algorithms that ensure primal feasibility of the iterates
are allowed. Such algorithms are often desirable because
overuse of the resources can overload the respective
systems, e.g., by causing blackouts in power systems. We
provide upper and lower bounds on the convergence rate of
these primal feasible complexity measures. In particular, we
show that the b-complexity cannot converge at a faster rate
than O(1/b). Therefore, the results demonstrate a tradeoff
between fast convergence and primal feasibility. We
illustrate the result by numerical studies.},
Doi = {10.1109/JSTSP.2018.2848718},
Key = {fds336646}
}
@article{fds341924,
Author = {Shahrampour, S and Beirami, A and Tarokh, V},
Title = {Supervised Learning Using Data-dependent Random Features
with Application to Seizure Detection},
Journal = {Proceedings of the Ieee Conference on Decision and
Control},
Volume = {2018-December},
Pages = {1168-1173},
Year = {2018},
Month = {July},
ISBN = {9781538613955},
url = {http://dx.doi.org/10.1109/CDC.2018.8619558},
Abstract = {The randomized-feature technique has been successfully
applied to large-scale supervised learning. Despite being
significantly more efficient compared to kernel methods in
terms of computational cost, random features can be improved
from generalization (prediction accuracy) viewpoint.
Recently, it has been shown that such improvement can be
achieved using data-dependent randomization. We recently
proposed an algorithm based on a data-dependent score
function that explores the set of possible random features
and exploits the promising regions. The method has shown
promising empirical success (on various datasets) in terms
of generalization error compared to the state-of-the-art in
random features. Restricting our attention to cosine feature
maps, in this work, we provide exact theoretical constraints
under which the score function converges to the spectrum of
the best model in the learning class. We further present
another application of the method in Epileptic Seizure
Recognition.},
Doi = {10.1109/CDC.2018.8619558},
Key = {fds341924}
}
@article{fds339987,
Author = {Soloveychik, I and Tarokh, V},
Title = {Stationary Geometric Graphical Model Selection},
Volume = {abs/1806.03571},
Year = {2018},
Month = {June},
Abstract = {We consider the problem of model selection in Gaussian
Markov fields in the sample deficient scenario. In many
practically important cases, the underlying networks are
embedded into Euclidean spaces. Using the natural geometric
structure, we introduce the notion of spatially stationary
distributions over geometric graphs. This directly
generalizes the notion of stationary time series to the
multidimensional setting lacking time axis. We show that the
idea of spatial stationarity leads to a dramatic decrease in
the sample complexity of the model selection compared to
abstract graphs with the same level of sparsity. For
geometric graphs on randomly spread vertices and edges of
bounded length, we develop tight information-theoretic
bounds on sample complexity and show that a finite number of
independent samples is sufficient for a consistent recovery.
Finally, we develop an efficient technique capable of
reliably and consistently reconstructing graphs with a
bounded number of measurements.},
Key = {fds339987}
}
@article{fds336637,
Author = {Ding, J and Shahrampour, S and Heal, K and Tarokh,
V},
Title = {Analysis of Multistate Autoregressive Models},
Journal = {Ieee Transactions on Signal Processing},
Volume = {66},
Number = {9},
Pages = {2429-2440},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2018},
Month = {May},
url = {http://dx.doi.org/10.1109/TSP.2018.2811757},
Abstract = {In this paper, we consider the inference problem for a wide
class of time-series models, referred to as multistate
autoregressive models. The time series that we consider are
composed of multiple epochs, each modeled by an
autoregressive process. The number of epochs is unknown, and
the transitions of states follow a Markov process of an
unknown order. We propose an inference strategy that enables
reliable and efficient offline analysis of this class of
time series. The inference is carried out through a
three-step approach: detecting the structural changes of the
time series using a recently proposed multiwindow algorithm,
identifying each segment as a state and selecting the most
appropriate number of states, and estimating the Markov
source based upon the symbolic sequence obtained from
previous steps. We provide theoretical results and
algorithms in order to facilitate the inference procedure
described above. We demonstrate the accuracy, efficiency,
and wide applicability of the proposed algorithms via an
array of experiments using synthetic and real-world
data.},
Doi = {10.1109/TSP.2018.2811757},
Key = {fds336637}
}
@article{fds336660,
Author = {Magnusson, S and Enyioha, C and Li, N and Fischione, C and Tarokh,
V},
Title = {Convergence of Limited Communication Gradient
Methods},
Journal = {Ieee Transactions on Automatic Control},
Volume = {63},
Number = {5},
Pages = {1356-1371},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2018},
Month = {May},
url = {http://dx.doi.org/10.1109/TAC.2017.2743678},
Abstract = {Distributed optimization increasingly plays a central role
in economical and sustainable operation of cyber-physical
systems. Nevertheless, the complete potential of the
technology has not yet been fully exploited in practice due
to communication limitations posed by the real-world
infrastructures. This work investigates fundamental
properties of distributed optimization based on gradient
methods, where gradient information is communicated using a
limited number of bits. In particular, a general class of
quantized gradient methods are studied, where the gradient
direction is approximated by a finite quantization set.
Sufficient and necessary conditions are provided on such a
quantization set to guarantee that the methods minimize any
convex objective function with Lipschitz continuous gradient
and a nonempty and bounded set of optimizers. A lower bound
on the cardinality of the quantization set is provided,
along with specific examples of minimal quantizations.
Convergence rate results are established that connect the
fineness of the quantization and the number of iterations
needed to reach a predefined solution accuracy.
Generalizations of the results to a relevant class of
constrained problems using projections are considered.
Finally, the results are illustrated by simulations of
practical systems.},
Doi = {10.1109/TAC.2017.2743678},
Key = {fds336660}
}
@article{fds336638,
Author = {Soloveychik, I and Xiang, Y and Tarokh, V},
Title = {Pseudo-Wigner Matrices},
Journal = {Ieee Transactions on Information Theory},
Volume = {64},
Number = {4},
Pages = {3170-3178},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2018},
Month = {April},
url = {http://dx.doi.org/10.1109/TIT.2017.2777464},
Abstract = {We consider the problem of generating pseudo-random matrices
based on the similarity of their spectra to Wigner's
semicircular law. We introduce the notion of an r
-independent pseudo-Wigner matrix ensemble and prove the
closeness of the spectra of its matrices to the semicircular
density in the Kolmogorov distance. We give an explicit
construction of a family of N × N pseudo-Wigner ensembles
using dual BCH codes and show that the Kolmogorov complexity
of the obtained matrices is of the order of log(N) bits for
a fixed designed Kolmogorov distance precision. We compare
our construction with the quasi-random graphs introduced by
Chung et al. and demonstrate that the pseudo-Wigner matrices
pass stronger randomness tests than the adjacency matrices
of these graphs (lifted by the mapping 0 → 1 and 1 → -1
) do. Finally, we provide numerical simulations verifying
our theoretical results.},
Doi = {10.1109/TIT.2017.2777464},
Key = {fds336638}
}
@article{fds336639,
Author = {Soloveychik, I and Xiang, Y and Tarokh, V},
Title = {Symmetric Pseudo-Random Matrices},
Journal = {Ieee Transactions on Information Theory},
Volume = {64},
Number = {4},
Pages = {3179-3196},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2018},
Month = {April},
url = {http://dx.doi.org/10.1109/TIT.2018.2800004},
Abstract = {We consider the problem of generating symmetric
pseudo-random sign (±1) matrices based on the similarity of
their spectra to Wigner's semicircular law. Using binary
m-sequences (Golomb sequences) of lengths n=2m-1 , we give a
simple explicit construction of circulant n × n sign
matrices and show that their spectra converge to the
semicircular law when n grows. The Kolmogorov complexity of
the proposed matrices equals to that of Golomb sequences and
is at most 2log2(n) bits.},
Doi = {10.1109/TIT.2018.2800004},
Key = {fds336639}
}
@article{fds336640,
Author = {Ding, J and Zhou, J and Tarokh, V},
Title = {Optimal prediction of data with unknown abrupt change
points},
Journal = {2017 Ieee Global Conference on Signal and Information
Processing, Globalsip 2017 Proceedings},
Volume = {2018-January},
Pages = {928-932},
Publisher = {IEEE},
Year = {2018},
Month = {March},
ISBN = {9781509059904},
url = {http://dx.doi.org/10.1109/GlobalSIP.2017.8309096},
Abstract = {We develop a novel methodology for predicting time series
under unknown abrupt changes in data generating
distributions. Based on Kolmogorov and Tikhomirov's e
entropy, we propose a concept called e-predictability that
quantifies the size of a model class and the maximal number
of structural changes that allows the achievability of
asymptotic optimal prediction. To predict under abrupt
changes, our basic idea is to apply ϵ-net to discretize a
nonparametric or parametric model class with an
appropriately chosen e, and then apply a kinetic model
averaging over the quantizers. Under reasonable assumptions,
we prove that the average predictive performance is
asymptotically as good as the oracle, i.e. when all the data
generating distributions are known in advance. We show that
the assumptions hold for a rather wide class of time
variations. The results also address some puzzles related to
the 'prediction-inference dilemma' in the context of change
point analysis.},
Doi = {10.1109/GlobalSIP.2017.8309096},
Key = {fds336640}
}
@article{fds336641,
Author = {DIng, J and Xiang, Y and Shen, L and Tarokh, V},
Title = {Detecting structural changes in dependent
data},
Journal = {2017 Ieee Global Conference on Signal and Information
Processing, Globalsip 2017 Proceedings},
Volume = {2018-January},
Pages = {750-754},
Publisher = {IEEE},
Year = {2018},
Month = {March},
ISBN = {9781509059904},
url = {http://dx.doi.org/10.1109/GlobalSIP.2017.8309060},
Abstract = {In the era of big data, a frequently encountered task is to
model and identify structural changes in the data generating
process. It is quite challenging especially when data are
dependent and massive, requiring computationally efficient
analysis. To address the challenge, we model the data
generating process as a segment-wise autoregression, and
propose a multi-window method that is both effective and
efficient for discovering the structural changes. The
proposed approach was motivated by transforming a
segment-wise autoregression into a multivariate time series
that is asymptotically segment-wise independent and
identically distributed. We then derive theoretical
guarantees for (almost surely) selecting the true number of
change points of segment-wise independent multivariate time
series. In particular, we prove that a wide variety of
penalized selection procedure produces a strongly consistent
selection of the optimal number of change points, under mild
assumptions. We demonstrate the theory and strength of the
proposed algorithms by experiments on both synthetic and
real-world data.},
Doi = {10.1109/GlobalSIP.2017.8309060},
Key = {fds336641}
}
@article{fds336642,
Author = {Han, Q and Ding, J and Airoldi, E and Tarokh, V},
Title = {Modeling nonlinearity in multi-dimensional dependent
data},
Journal = {2017 Ieee Global Conference on Signal and Information
Processing, Globalsip 2017 Proceedings},
Volume = {2018-January},
Pages = {206-210},
Publisher = {IEEE},
Year = {2018},
Month = {March},
ISBN = {9781509059904},
url = {http://dx.doi.org/10.1109/GlobalSIP.2017.8308633},
Abstract = {Given massive data that may be time dependent and
multi-dimensional, how to efficiently explore the underlying
functional relationships across different dimensions and
time lags? In this work, we propose a methodology to
sequentially and adaptively model nonlinear multivariate
time series data. Data at each time step and dimension is
modeled as a nonlinear function of past values corrupted by
noise, and the underlying nonlinear function is assumed to
be approximately expandable in a spline basis. We cast the
modeling of data as finding a good fit representation in the
linear span of multi-dimensional spline basis, and use a
variant of h-penalty regularization in order to reduce the
dimensionality of representation. Using adaptive filtering
techniques, we design our online algorithm to automatically
tune the underlying parameters based on the minimization of
the regularized sequential prediction error. We demonstrate
the generality and flexibility of the proposed approach on
both synthetic and real-world datasets. Moreover, we
analytically investigate the performance of our algorithm by
obtaining bounds of the prediction errors.},
Doi = {10.1109/GlobalSIP.2017.8308633},
Key = {fds336642}
}
@article{fds361405,
Author = {Soloveychik, I and Tarokh, V},
Title = {Region Detection in Markov Random Fields: Gaussian
Case},
Year = {2018},
Month = {February},
Abstract = {We consider the problem of model selection in Gaussian
Markov fields in the sample deficient scenario. The
benchmark information-theoretic results in the case of
d-regular graphs require the number of samples to be at
least proportional to the logarithm of the number of
vertices to allow consistent graph recovery. When the number
of samples is less than this amount, reliable detection of
all edges is impossible. In many applications, it is more
important to learn the distribution of the edge (coupling)
parameters over the network than the specific locations of
the edges. Assuming that the entire graph can be partitioned
into a number of spatial regions with similar edge
parameters and reasonably regular boundaries, we develop new
information-theoretic sample complexity bounds and show that
a bounded number of samples can be sufficient to
consistently recover these regions. Finally, we introduce
and analyze an efficient region growing algorithm capable of
recovering the regions with high accuracy. We show that it
is consistent and demonstrate its performance benefits in
synthetic simulations.},
Key = {fds361405}
}
@article{fds361406,
Author = {Soloveychik, I and Tarokh, V},
Title = {Large Deviations of Convex Polyominoes},
Year = {2018},
Month = {February},
Abstract = {Enumeration of various types of lattice polygons and in
particular polyominoes is of primary importance in many
machine learning, pattern recognition, and geometric
analysis problems. In this work, we develop a large
deviation principle for convex polyominoes under different
restrictions, such as fixed area and/or perimeter.},
Key = {fds361406}
}
@article{fds336643,
Author = {Soloveychik, I and Xiang, Y and Tarokh, V},
Title = {Explicit symmetric pseudo-random matrices},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Volume = {2018-January},
Pages = {424-428},
Publisher = {IEEE},
Year = {2018},
Month = {January},
ISBN = {9781509030972},
url = {http://dx.doi.org/10.1109/ITW.2017.8277999},
Abstract = {We consider the problem of generating symmetric
pseudo-random sign (±1) matrices based on the similarity of
their spectra to Wigner's semicircular law. Using binary
m-sequences (Golomb sequences) of lengths n = 2m - 1, we
give a simple explicit construction of circulant n × n sign
matrices and show that their spectra converge to the
semicircular law when n grows. The Kolmogorov complexity of
the proposed matrices equals to that of Golomb sequences and
is at most 2log2(n) bits.},
Doi = {10.1109/ITW.2017.8277999},
Key = {fds336643}
}
@article{fds342381,
Author = {Shahrampour, S and Tarokh, V},
Title = {Learning bounds for greedy approximation with explicit
feature maps from multiple kernels},
Journal = {Advances in Neural Information Processing
Systems},
Volume = {2018-December},
Pages = {4690-4701},
Publisher = {NEURAL INFORMATION PROCESSING SYSTEMS (NIPS)},
Editor = {Bengio, S and Wallach, H and Larochelle, H and Grauman, K and CesaBianchi, N and Garnett, R},
Year = {2018},
Month = {January},
Abstract = {Nonlinear kernels can be approximated using
finite-dimensional feature maps for efficient risk
minimization. Due to the inherent trade-off between the
dimension of the (mapped) feature space and the
approximation accuracy, the key problem is to identify
promising (explicit) features leading to a satisfactory
out-of-sample performance. In this work, we tackle this
problem by efficiently choosing such features from multiple
kernels in a greedy fashion. Our method sequentially selects
these explicit features from a set of candidate features
using a correlation metric. We establish an out-of-sample
error bound capturing the trade-off between the error in
terms of explicit features (approximation error) and the
error due to spectral properties of the best model in the
Hilbert space associated to the combined kernel (spectral
error). The result verifies that when the (best) underlying
data model is sparse enough, i.e., the spectral error is
negligible, one can control the test error with a small
number of explicit features, that can scale
poly-logarithmically with data. Our empirical results show
that given a fixed number of explicit features, the method
can achieve a lower test error with a smaller time cost,
compared to the state-of-the-art in data-dependent random
features.},
Key = {fds342381}
}
@article{fds336662,
Author = {Enyioha, C and Magnússon, S and Heal, K and Li, N and Fischione, C and Tarokh, V},
Title = {On variability of renewable energy and online power
allocation},
Journal = {Ieee Transactions on Power Systems},
Volume = {33},
Number = {1},
Pages = {451-462},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2018},
Month = {January},
url = {http://dx.doi.org/10.1109/TPWRS.2017.2709544},
Abstract = {As electric power system operators shift from conventional
energy to renewable energy sources, power distribution
systems will experience increasing fluctuations in supply.
These fluctuations present the need to not only design
online decentralized power allocation algorithms, but also
characterize how effective they are given fast-changing
consumer demand and generation. In this paper, we present an
online decentralized dual descent (OD3) power allocation
algorithm and determine (in the worst case) how much of
observed social welfare can be explained by fluctuations in
generation capacity and consumer demand. Convergence
properties and performance guarantees of the OD3 algorithm
are analyzed by characterizing the difference between the
online decision and the optimal decision. We demonstrate
validity and accuracy of the theoretical results in the
paper through numerical experiments using real power
generation data.},
Doi = {10.1109/TPWRS.2017.2709544},
Key = {fds336662}
}
@article{fds339996,
Author = {Shahrampour, S and Beirami, A and Tarokh, V},
Title = {On data-dependent random features for improved
generalization in supervised learning},
Journal = {32nd Aaai Conference on Artificial Intelligence, Aaai
2018},
Volume = {abs/1712.07102},
Pages = {4026-4033},
Year = {2018},
Month = {January},
Abstract = {The randomized-feature approach has been successfully
employed in large-scale kernel approximation and supervised
learning. The distribution from which the random features
are drawn impacts the number of features required to
efficiently perform a learning task. Recently, it has been
shown that employing data-dependent randomization improves
the performance in terms of the required number of random
features. In this paper, we are concerned with the
randomized-feature approach in supervised learning for good
generalizability. We propose the Energy-based Exploration of
Random Features (EERF) algorithm based on a data-dependent
score function that explores the set of possible features
and exploits the promising regions. We prove that the
proposed score function with high probability recovers the
spectrum of the best fit within the model class. Our
empirical results on several benchmark datasets further
verify that our method requires smaller number of random
features to achieve a certain generalization error compared
to the state-of-the-art while introducing negligible
pre-processing overhead. EERF can be implemented in a few
lines of code and requires no additional tuning
parameters.},
Key = {fds339996}
}
@article{fds339991,
Author = {Banerjee, T and Choi, J and Pesaran, B and Ba, D and Tarokh,
V},
Title = {CLASSIFICATION OF LOCAL FIELD POTENTIALS USING GAUSSIAN
SEQUENCE MODEL},
Journal = {2018 Ieee Statistical Signal Processing Workshop
(Ssp)},
Pages = {683-687},
Publisher = {IEEE},
Year = {2018},
ISBN = {978-1-5386-1571-3},
Key = {fds339991}
}
@article{fds339992,
Author = {Banerjee, T and Whipps, GT and Gurram, P and Tarokh,
V},
Title = {Sequential Event Detection Using Multimodal Data in
Nonstationary Environments.},
Journal = {Fusion},
Pages = {1940-1947},
Publisher = {IEEE},
Year = {2018},
ISBN = {978-0-9964527-6-2},
Key = {fds339992}
}
@article{fds339986,
Author = {Shahrampour, S and Beirami, A and Tarokh, V},
Title = {On Data-Dependent Random Features for Improved
Generalization in Supervised Learning.},
Journal = {Aaai},
Pages = {4026-4033},
Publisher = {AAAI Press},
Editor = {McIlraith, SA and Weinberger, KQ},
Year = {2018},
Key = {fds339986}
}
@article{fds348340,
Author = {Shahrampour, S and Tarokh, V},
Title = {Learning Bounds for Greedy Approximation with Explicit
Feature Maps from Multiple Kernels.},
Journal = {Neurips},
Pages = {4695-4706},
Editor = {Bengio, S and Wallach, HM and Larochelle, H and Grauman, K and Cesa-Bianchi, N and Garnett, R},
Year = {2018},
Key = {fds348340}
}
@article{fds348341,
Author = {Banerjee, T and Whipps, GT and Gurram, P and Tarokh,
V},
Title = {Cyclostationary Statistical Models and Algorithms for
Anomaly Detection Using Multi-Modal Data.},
Journal = {Globalsip},
Pages = {126-130},
Publisher = {IEEE},
Year = {2018},
ISBN = {978-1-7281-1295-4},
Key = {fds348341}
}
@article{fds348342,
Author = {Ding, J and Tarokh, V and Yang, Y},
Title = {Model Selection Techniques - An Overview.},
Journal = {Corr},
Volume = {abs/1810.09583},
Year = {2018},
Key = {fds348342}
}
@article{fds336647,
Author = {Han, Q and Ding, J and Airoldi, EM and Tarokh, V},
Title = {SLANTS: Sequential Adaptive Nonlinear Modeling of Time
Series},
Journal = {Ieee Transactions on Signal Processing},
Volume = {65},
Number = {19},
Pages = {4994-5005},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2017},
Month = {October},
url = {http://dx.doi.org/10.1109/TSP.2017.2716898},
Abstract = {We propose a method for adaptive nonlinear sequential
modeling of time series data. Data are modeled as a
nonlinear function of past values corrupted by noise, and
the underlying nonlinear function is assumed to be
approximately expandable in a spline basis. We cast the
modeling of data as finding a good fit representation in the
linear span of multidimensional spline basis, and use a
variant of $l-1$-penalty regularization in order to reduce
the dimensionality of representation. Using adaptive
filtering techniques, we design our online algorithm to
automatically tune the underlying parameters based on the
minimization of the regularized sequential prediction error.
We demonstrate the generality and flexibility of the
proposed approach on both synthetic and real-world datasets.
Moreover, we analytically investigate the performance of our
algorithm by obtaining both bounds on prediction errors and
consistency in variable selection.},
Doi = {10.1109/TSP.2017.2716898},
Key = {fds336647}
}
@article{fds339993,
Author = {Boyer, R and Babadi, B and Kalouptsidis, N and Tarokh,
V},
Title = {Corrections to “Asymptotic Achievability of the
Cramér–Rao Bound for Noisy Compressive Sampling” [Mar
09 1233-1236]},
Journal = {Ieee Transactions on Signal Processing},
Volume = {65},
Number = {18},
Pages = {4973-4974},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2017},
Month = {September},
url = {http://dx.doi.org/10.1109/tsp.2017.2723352},
Doi = {10.1109/tsp.2017.2723352},
Key = {fds339993}
}
@article{fds336648,
Author = {Ding, J and Xiang, Y and Shen, L and Tarokh, V},
Title = {Multiple Change Point Analysis: Fast Implementation and
Strong Consistency},
Journal = {Ieee Transactions on Signal Processing},
Volume = {65},
Number = {17},
Pages = {4495-4510},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2017},
Month = {September},
url = {http://dx.doi.org/10.1109/TSP.2017.2711558},
Abstract = {One of the main challenges in identifying structural changes
in stochastic processes is to carry out analysis for time
series with dependency structure in a computationally
tractable way. Another challenge is that the number of true
change points is usually unknown, requiring a suitable model
selection criterion to arrive at informative conclusions. To
address the first challenge, we model the data generating
process as a segment-wise autoregression, which is composed
of several segments (time epochs), each of which modeled by
an autoregressive model. We propose a multiwindow method
that is both effective and efficient for discovering the
structural changes. The proposed approach was motivated by
transforming a segment-wise autoregression into a
multivariate time series that is asymptotically segment-wise
independent and identically distributed. To address the
second challenge, we derive theoretical guarantees for
(almost surely) selecting the true number of change points
of segment-wise independent multivariate time series.
Specifically, under mild assumptions, we show that a
Bayesian information criterion like criterion gives a
strongly consistent selection of the optimal number of
change points, while an Akaike information criterion like
criterion cannot. Finally, we demonstrate the theory and
strength of the proposed algorithms by experiments on both
synthetic- and real-world data, including the Eastern U.S.
temperature data and the El Nino data. The experiment leads
to some interesting discoveries about temporal variability
of the summer-time temperature over the Eastern U.S., and
about the most dominant factor of ocean influence on
climate, which were also discovered by environmental
scientists.},
Doi = {10.1109/TSP.2017.2711558},
Key = {fds336648}
}
@article{fds336649,
Author = {Shahrampour, S and Noshad, M and Tarokh, V},
Title = {On Sequential Elimination Algorithms for Best-Arm
Identification in Multi-Armed Bandits},
Journal = {Ieee Transactions on Signal Processing},
Volume = {65},
Number = {16},
Pages = {4281-4292},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2017},
Month = {August},
url = {http://dx.doi.org/10.1109/TSP.2017.2706192},
Abstract = {We consider the best-arm identification problem in
multi-armed bandits, which focuses purely on exploration. A
player is given a fixed budget to explore a finite set of
arms, and the rewards of each arm are drawn independently
from a fixed, unknown distribution. The player aims to
identify the arm with the largest expected reward. We
propose a general framework to unify sequential elimination
algorithms, where the arms are dismissed iteratively until a
unique arm is left. Our analysis reveals a novel performance
measure expressed in terms of the sampling mechanism and
number of eliminated arms at each round. Based on this
result, we develop an algorithm that divides the budget
according to a nonlinear function of remaining arms at each
round. We provide theoretical guarantees for the algorithm,
characterizing the suitable nonlinearity for different
problem environments described by the number of competitive
arms. Matching the theoretical results, our experiments show
that the nonlinear algorithm outperforms the
state-of-the-art. We finally study the side-observation
model, where pulling an arm reveals the rewards of its
related arms, and we establish improved theoretical
guarantees in the pure-exploration setting.},
Doi = {10.1109/TSP.2017.2706192},
Key = {fds336649}
}
@article{fds336650,
Author = {Deng, Z and Ding, J and Heal, K and Tarokh, V},
Title = {The number of independent sets in hexagonal
graphs},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {2910-2914},
Publisher = {IEEE},
Year = {2017},
Month = {August},
ISBN = {9781509040964},
url = {http://dx.doi.org/10.1109/ISIT.2017.8007062},
Abstract = {We derive the tightest known bounds on η = 2ν, where ν is
the growth rate of the logarithm of the number of
independent sets on a hexagonal lattice. To obtain these
bounds, we generalize a method proposed by Calkin and Wilf.
Their original strategy cannot immediately be used to derive
bounds for η, due to the difference in symmetry between
square and hexagonal lattices, so we propose a modified
method and an algorithm to derive rigorous bounds on η. In
particular, we prove that 1.546440708536001 ≤ η ≤
1.5513, which improves upon the best known bounds of 1.5463
≤ η ≤ 1.5527 given by Nagy and Zeger. Our lower bound
matches the numerical estimate of Baxter up to 9 digits
after the decimal point, and our upper bound can be further
improved by following our method.},
Doi = {10.1109/ISIT.2017.8007062},
Key = {fds336650}
}
@article{fds336651,
Author = {Soloveychik, I and Xiang, Y and Tarokh, V},
Title = {Pseudo-wigner matrices from dual BCH codes},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {1381-1385},
Publisher = {IEEE},
Year = {2017},
Month = {August},
ISBN = {9781509040964},
url = {http://dx.doi.org/10.1109/ISIT.2017.8006755},
Abstract = {We consider the problem of generating symmetric
pseudo-random sign (±1) matrices based on the similarity of
their spectra to Wigner's semicircular law. We introduce
r-independent pseudo-Wigner ensembles and prove closeness of
their spectra to the semicircular density in Kolmogorov
distance. We give an explicit construction of a family of N
× N pseudo-Wigner ensembles using dual BCH codes and show
that the Kolmogorov complexity of the obtained matrices is
of the order of log (N) bits for a fixed Kolmogorov distance
precision. Finally, we provide numerical simulations
verifying our theoretical results.},
Doi = {10.1109/ISIT.2017.8006755},
Key = {fds336651}
}
@article{fds336644,
Author = {Shahrampour, S and Tarokh, V},
Title = {Nonlinear sequential accepts and rejects for identification
of top arms in stochastic bandits},
Journal = {55th Annual Allerton Conference on Communication, Control,
and Computing, Allerton 2017},
Volume = {2018-January},
Pages = {228-235},
Publisher = {IEEE},
Year = {2017},
Month = {July},
url = {http://dx.doi.org/10.1109/ALLERTON.2017.8262742},
Abstract = {We address the M-best-Arm identification problem in
multi-Armed bandits. A player has a limited budget to
explore K arms (M < K), and once pulled, each arm yields a
reward drawn (independently) from a fixed, unknown
distribution. The goal is to find the top M arms in the
sense of expected reward. We develop an algorithm which
proceeds in rounds to deactivate arms iteratively. At each
round, the budget is divided by a nonlinear function of
remaining arms, and the arms are pulled correspondingly.
Based on a decision rule, the deactivated arm at each round
may be accepted or rejected. The algorithm outputs the
accepted arms that should ideally be the top M arms. We
characterize the decay rate of the misidentification
probability and establish that the nonlinear budget
allocation proves to be useful for different problem
environments (described by the number of competitive arms).
We provide comprehensive numerical experiments showing that
our algorithm outperforms the state-of-The-Art using
suitable nonlinearity.},
Doi = {10.1109/ALLERTON.2017.8262742},
Key = {fds336644}
}
@article{fds336645,
Author = {Soloveychik, I and Tarokh, V and Paulson, JA},
Title = {On the spectral norms of pseudo-wigner and related
matrices},
Journal = {55th Annual Allerton Conference on Communication, Control,
and Computing, Allerton 2017},
Volume = {2018-January},
Pages = {61-66},
Publisher = {IEEE},
Year = {2017},
Month = {July},
url = {http://dx.doi.org/10.1109/ALLERTON.2017.8262719},
Abstract = {We investigate the spectral norms of symmetric N × N
matrices from two pseudo-random ensembles. The first is the
pseudo-Wigner ensemble introduced in 'Pseudo-Wigner
Matrices' by Soloveychik, Xiang and Tarokh and the second is
its sample covariance-Type analog defined in this work. Both
ensembles are defined through the concept of r-independence
by controlling the amount of randomness in the underlying
matrices, and can be constructed from dual BCH codes. We
show that when the measure of randomness r grows as Np,
where p (0,1] and ϵ > 0, the norm of the matrices is almost
surely within o(log1 + ϵN/Nmin[ρ, 2/3]) distance from 1.
Numerical simulations verifying the obtained results are
provided.},
Doi = {10.1109/ALLERTON.2017.8262719},
Key = {fds336645}
}
@article{fds336652,
Author = {Jeong, S and Kang, J and Pahlavan, K and Tarokh, V},
Title = {Fundamental Limits of TOA/DOA and Inertial Measurement
Unit-Based Wireless Capsule Endoscopy Hybrid
Localization},
Journal = {International Journal of Wireless Information
Networks},
Volume = {24},
Number = {2},
Pages = {169-179},
Publisher = {Springer Nature},
Year = {2017},
Month = {June},
url = {http://dx.doi.org/10.1007/s10776-017-0342-7},
Abstract = {In this paper, performance analysis of hybrid localization
based on radio-frequency (RF) and inertial measurement unit
(IMU) measurements for a single wireless capsule endoscopy
(WCE) traveling the gastrointestinal tract is studied.
Specifically, the multiple body-mounted sensors are
considered which are located on the front and back of a
patient’s medical jacket and form the uniform rectangular
arrays (URAs). With the aim of locating the WCE, two types
of RF measurements, namely time-of-arrival (TOA) and
direction-of-arrival (DOA), are estimated from the received
signals at the URAs transmitted by the WCE, which are
integrated with the IMU acceleration measurements via the
standard extended Kalman filter. Here, a posterior
Cramér–Rao Bound (PCRB) of the proposed TOA/DOA and
IMU-based hybrid localization is derived as fundamental
limits on squared position error, where the accuracies of
TOA and DOA measurements are entailed by means of CRB to
account for their dependency on the environmental
parameters, while the accuracies of the IMU measurements are
addressed with the acceleration measurement error standard
deviation. Numerical results are provided, sustained by
simulations which verify the millimeter accuracy of the
TOA/DOA and IMU-based hybrid localization within the
regulation of medical implant communication services and the
exactness of the PCRB.},
Doi = {10.1007/s10776-017-0342-7},
Key = {fds336652}
}
@article{fds339994,
Author = {Farhadi, H and Xiang, Y and Jeong, S and Li, X and Guo, N and Sepulcre, J and Tarokh, V and Li, Q},
Title = {Inferring the causality network of Abeta and Tau
accumulation in the aging brain: a statistical inference
approach},
Journal = {Journal of Nuclear Medicine : Official Publication, Society
of Nuclear Medicine},
Volume = {58},
Pages = {2 pages},
Publisher = {SOC NUCLEAR MEDICINE INC},
Year = {2017},
Month = {May},
Key = {fds339994}
}
@article{fds336653,
Author = {Wei, L and Sarwate, AD and Corander, J and Hero, A and Tarokh,
V},
Title = {Analysis of a privacy-preserving PCA algorithm using random
matrix theory},
Journal = {2016 Ieee Global Conference on Signal and Information
Processing, Globalsip 2016 Proceedings},
Pages = {1335-1339},
Publisher = {IEEE},
Year = {2017},
Month = {April},
ISBN = {9781509045457},
url = {http://dx.doi.org/10.1109/GlobalSIP.2016.7906058},
Abstract = {To generate useful summarization of data while maintaining
privacy of sensitive information is a challenging task,
especially in the big data era. The privacy-preserving
principal component algorithm proposed in [1] is a promising
approach when a low rank data summarization is desired.
However, the analysis in [1] is limited to the case of a
single principal component, which makes use of bounds on the
vector-valued Bingham distribution in the unit sphere. By
exploring the non-commutative structure of data matrices in
the full Stiefel manifold, we extend the analysis to an
arbitrary number of principal components. Our results are
obtained by analyzing the asymptotic behavior of the
matrix-variate Bingham distribution using tools from random
matrix theory.},
Doi = {10.1109/GlobalSIP.2016.7906058},
Key = {fds336653}
}
@article{fds336654,
Author = {Enyioha, C and Magnússon, S and Heal, K and Li, N and Fischione, C and Tarokh, V},
Title = {Robustness analysis for an online decentralized descent
power allocation algorithm},
Journal = {2016 Information Theory and Applications Workshop, Ita
2016},
Publisher = {IEEE},
Year = {2017},
Month = {March},
ISBN = {9781509025299},
url = {http://dx.doi.org/10.1109/ITA.2016.7888135},
Abstract = {As independent service providers shift from conventional
energy to renewable energy sources, the power distribution
system will likely experience increasingly significant
fluctuation in supply, given the uncertain and intermittent
nature of renewable sources like wind and solar energy.
These fluctuations in power generation, coupled with
time-varying consumer demands of electricity and the massive
scale of power distribution networks present the need to not
only design real-time decentralized power allocation
algorithms, but also characterize how effective they are
given fast-changing consumer demands and power generation
capacities. In this paper, we present an Online
Decentralized Dual Descent (OD3) power allocation algorithm
and determine (in the worst case) how much of observed
social welfare and price volatility can be explained by
fluctuations in generation capacity and consumer demand.
Convergence properties and performance guarantees of the OD3
algorithm are analyzed by characterizing the difference
between the online decision and the optimal decision. The
theoretical results in the paper are validated and
illustrated by numerical experiments using real
data.},
Doi = {10.1109/ITA.2016.7888135},
Key = {fds336654}
}
@article{fds336656,
Author = {Kurien, BG and Ashcom, JB and Shah, VN and Rachlin, Y and Tarokh,
V},
Title = {Robust interferometric imaging via prior-less phase
recovery: Redundant spacing calibration with
generalized-closure phases},
Journal = {Monthly Notices of the Royal Astronomical
Society},
Volume = {464},
Number = {2},
Pages = {2356-2376},
Publisher = {Oxford University Press (OUP)},
Year = {2017},
Month = {January},
url = {http://dx.doi.org/10.1093/mnras/stw2323},
Abstract = {Atmospheric turbulence presents a fundamental challenge to
Fourier phase recovery in optical interferometry. Typical
reconstruction algorithms employ Bayesian inference
techniques which rely on prior knowledge of the scene under
observation. In contrast, redundant spacing calibration
(RSC) algorithms employ redundancy in the baselines of the
interferometric array to directly expose the contribution of
turbulence, thereby enabling phase recovery for targets of
arbitrary and unknown complexity. Traditionally RSC
algorithms have been applied directly to single-exposure
measurements, which are reliable only at high photon flux in
general. In scenarios of low photon flux, such as those
arising in the observation of dim objects in space, one must
instead rely on time-averaged, atmosphere-invariant
quantities such as the bispectrum. In this paper, we develop
a novel RSC-based algorithm for prior-less phase recovery in
which we generalize the bispectrum to higher order
atmosphere-invariants (nspectra) for improved sensitivity.We
provide a strategy for selection of a high-signal-to-noise
ratio set of n-spectra using the graph-theoretic notion of
the minimum cycle basis. We also discuss a key property of
this set (wrap-invariance), which then enables reliable
application of standard linear estimation techniques to
recover the Fourier phases from the 2π-wrapped n-spectra
phases. For validation, we analyse the expected
shot-noise-limited performance of our algorithm for both
pairwise and Fizeau interferometric architectures, and
corroborate this analysis with simulation results showing
performance near an atmosphere-oracle Cramer-Rao bound.
Lastly, we apply techniques from the field of compressed
sensing to perform image reconstruction from the estimated
complex visibilities.},
Doi = {10.1093/mnras/stw2323},
Key = {fds336656}
}
@article{fds336657,
Author = {Jeong, S and Li, X and Yang, J and Li, Q and Tarokh,
V},
Title = {Dictionary learning and sparse coding-based denoising for
high-resolution task functional connectivity MRI
analysis},
Journal = {Lecture Notes in Computer Science (Including Subseries
Lecture Notes in Artificial Intelligence and Lecture Notes
in Bioinformatics)},
Volume = {10541 LNCS},
Pages = {45-52},
Publisher = {Springer International Publishing},
Year = {2017},
Month = {January},
ISBN = {9783319673882},
url = {http://dx.doi.org/10.1007/978-3-319-67389-9_6},
Abstract = {We propose a novel denoising framework for task functional
Magnetic Resonance Imaging (tfMRI) data to delineate the
high-resolution spatial pattern of the brain functional
connectivity via dictionary learning and sparse coding
(DLSC). In order to address the limitations of the
unsupervised DLSC-based fMRI studies, we utilize the prior
knowledge of task paradigm in the learning step to train a
data-driven dictionary and to model the sparse
representation. We apply the proposed DLSC-based method to
Human Connectome Project (HCP) motor tfMRI dataset. Studies
on the functional connectivity of cerebrocerebellar circuits
in somatomotor networks show that the DLSC-based denoising
framework can significantly improve the prominent
connectivity patterns, in comparison to the temporal
non-local means (tNLM)-based denoising method as well as the
case without denoising, which is consistent and
neuroscientifically meaningful within motor area. The
promising results show that the proposed method can provide
an important foundation for the high-resolution functional
connectivity analysis, and provide a better approach for
fMRI preprocessing.},
Doi = {10.1007/978-3-319-67389-9_6},
Key = {fds336657}
}
@article{fds336658,
Author = {Beirami, A and Razaviyayn, M and Shahrampour, S and Tarokh,
V},
Title = {On optimal generalizability in parametric
learning},
Journal = {Advances in Neural Information Processing
Systems},
Volume = {2017-December},
Pages = {3456-3466},
Year = {2017},
Month = {January},
Abstract = {We consider the parametric learning problem, where the
objective of the learner is determined by a parametric loss
function. Employing empirical risk minimization with
possibly regularization, the inferred parameter vector will
be biased toward the training samples. Such bias is measured
by the cross validation procedure in practice where the data
set is partitioned into a training set used for training and
a validation set, which is not used in training and is left
to measure the outof-sample performance. A classical cross
validation strategy is the leave-one-out cross validation
(LOOCV) where one sample is left out for validation and
training is done on the rest of the samples that are
presented to the learner, and this process is repeated on
all of the samples. LOOCV is rarely used in practice due to
the high computational complexity. In this paper, we first
develop a computationally efficient approximate LOOCV
(ALOOCV) and provide theoretical guarantees for its
performance. Then we use ALOOCV to provide an optimization
algorithm for finding the regularizer in the empirical risk
minimization framework. In our numerical experiments, we
illustrate the accuracy and efficiency of ALOOCV as well as
our proposed framework for the optimization of the
regularizer.},
Key = {fds336658}
}
@article{fds339995,
Author = {Beirami, A and Razaviyayn, M and Shahrampour, S and Tarokh,
V},
Title = {On Optimal Generalizability in Parametric
Learning},
Journal = {Advances in Neural Information Processing
Systems},
Volume = {30},
Pages = {11 pages},
Publisher = {NEURAL INFORMATION PROCESSING SYSTEMS (NIPS)},
Editor = {Guyon, I and Luxburg, UV and Bengio, S and Wallach, H and Fergus, R and Vishwanathan, S and Garnett, R},
Year = {2017},
Month = {January},
Key = {fds339995}
}
@article{fds339997,
Author = {Soloveychik, I and Xiang, Y and Tarokh, V},
Title = {Pseudo-Wigner Matrices from Dual BCH Codes.},
Journal = {Corr},
Volume = {abs/1701.05544},
Year = {2017},
Key = {fds339997}
}
@article{fds339998,
Author = {Deng, Z and Ding, J and Heal, K and Tarokh, V},
Title = {The number of independent sets in hexagonal
graphs.},
Journal = {Isit},
Pages = {2910-2914},
Publisher = {IEEE},
Year = {2017},
ISBN = {978-1-5090-4096-4},
Key = {fds339998}
}
@article{fds339999,
Author = {Jeong, S and Li, X and Yang, J and Li, Q and Tarokh,
V},
Title = {Dictionary Learning and Sparse Coding-Based Denoising for
High-Resolution Task Functional Connectivity MRI
Analysis.},
Journal = {Mlmi@Miccai},
Volume = {10541},
Pages = {45-52},
Publisher = {SPRINGER},
Editor = {Wang, Q and Shi, Y and Suk, H-I and Suzuki, K},
Year = {2017},
ISBN = {978-3-319-67388-2},
Key = {fds339999}
}
@article{fds340001,
Author = {Shahrampour, S and Tarokh, V},
Title = {Nonlinear Sequential Accepts and Rejects for Identification
of Top Arms in Stochastic Bandits.},
Journal = {Corr},
Volume = {abs/1707.02649},
Year = {2017},
Key = {fds340001}
}
@article{fds336663,
Author = {Wei, L and Zheng, Z and Hero, A and Tarokh, V},
Title = {Scaling laws and phase transitions for target detection in
MIMO radar},
Journal = {2016 Ieee Information Theory Workshop, Itw
2016},
Pages = {345-348},
Publisher = {IEEE},
Year = {2016},
Month = {October},
ISBN = {9781509010905},
url = {http://dx.doi.org/10.1109/ITW.2016.7606853},
Abstract = {The performance of MIMO radar has been a subject of intense
study in the past decades. For such a system, however, the
important phenomenon of phase transition has received little
attention in the literature. In this paper, we study the
phase transition on the target detection probability of a
SNR maximizing detector. Such a detector declares a target
to be present when the largest eigenvalue of the observed
data matrix exceeds a threshold. In particular, we identify
a critical value below and above which the limiting
detection performance is described by the Tracy-Widom law
and the Gaussian law, respectively. Under both laws, the
scaling limits and asymptotic expansions of misdetection
probability at the vanishing regime are derived using tools
from random matrix theory.},
Doi = {10.1109/ITW.2016.7606853},
Key = {fds336663}
}
@article{fds336664,
Author = {Kurien, BG and Tarokh, V and Rachlin, Y and Shah, VN and Ashcom,
JB},
Title = {Resolving phase ambiguities in the calibration of redundant
interferometric arrays: Implications for array
design},
Journal = {Monthly Notices of the Royal Astronomical
Society},
Volume = {461},
Number = {4},
Pages = {3585-3597},
Publisher = {Oxford University Press (OUP)},
Year = {2016},
Month = {October},
url = {http://dx.doi.org/10.1093/mnras/stw1507},
Abstract = {We provide new results enabling robust interferometric image
reconstruction in the presence of unknown aperture piston
variation via the technique of redundant spacing calibration
(RSC). The RSC technique uses redundant measurements of the
same interferometric baseline with different pairs of
apertures to reveal the piston variation among these pairs.
In both optical and radio interferometry, the presence of
phase-wrapping ambiguities in the measurements is a
fundamental issue that needs to be addressed for reliable
image reconstruction. In this paper, we show that these
ambiguities affect recently developed RSC phasor-based
reconstruction approaches operating on the complex
visibilities, as well as traditional phase-based approaches
operating on their logarithm. We also derive new sufficient
conditions for an interferometric array to be immune to
these ambiguities in the sense that their effect can be
rendered benign in image reconstruction. This property,
which we call wrap-invariance, has implications for the
reliability of imaging via classical three-baseline phase
closures as well as generalized closures.We show that
wrap-invariance is conferred upon arrays whose
interferometric graph satisfies a certain cycle-free
condition. For cases in which this condition is not
satisfied, a simple algorithm is provided for identifying
those graph cycles which prevent its satisfaction. We apply
this algorithm to diagnose and correct a member of a pattern
family popular in the literature.},
Doi = {10.1093/mnras/stw1507},
Key = {fds336664}
}
@article{fds336665,
Author = {Magnússon, S and Heal, K and Enyioha, C and Li, N and Fischione, C and Tarokh, V},
Title = {Convergence of limited communications gradient
methods},
Journal = {Proceedings of the American Control Conference},
Volume = {2016-July},
Pages = {1421-1426},
Publisher = {IEEE},
Year = {2016},
Month = {July},
ISBN = {9781467386821},
url = {http://dx.doi.org/10.1109/ACC.2016.7525116},
Abstract = {Distributed control and decision making increasingly play a
central role in economical and sustainable operation of
cyber-physical systems. Nevertheless, the full potential of
the technology has not yet been fully exploited in practice
due to communication limitations of real-world
infrastructures. This work investigates the fundamental
properties of gradient methods for distributed optimization,
where gradient information is communicated at every
iteration, when using limited number of communicated bits.
In particular, a general class of quantized gradient methods
are studied where the gradient direction is approximated by
a finite quantization set. Conditions on the quantization
set are provided that are necessary and sufficient to
guarantee the ability of these methods to minimize any
convex objective function with Lipschitz continuous gradient
and a nonempty, bounded set of optimizers. Moreover, a lower
bound on the cardinality of the quantization set is
provided, along with specific examples of minimal
quantizations. Furthermore, convergence rate results are
established that connect the fineness of the quantization
and number of iterations needed to reach a predefined
solution accuracy. The results provide a bound on the number
of bits needed to achieve the desired accuracy. Finally, an
application of the theory to resource allocation in power
networks is demonstrated, and the theoretical results are
substantiated by numerical simulations.},
Doi = {10.1109/ACC.2016.7525116},
Key = {fds336665}
}
@article{fds336666,
Author = {Zheng, Z and Wei, L and Haas, ZJ and Tarokh, V},
Title = {Transmit beamforming in Rayleigh product MIMO channels:
Ergodic mutual information and symbol error
rate},
Journal = {2016 Ieee International Conference on Communications, Icc
2016},
Publisher = {IEEE},
Year = {2016},
Month = {July},
ISBN = {9781479966646},
url = {http://dx.doi.org/10.1109/ICC.2016.7511213},
Abstract = {In this paper, we consider MIMO beamforming in the presence
of Rayleigh product channels. Based on a derived largest
eigenvalue distribution, the key performance metrics of the
beamforming system are obtained, assuming perfect channel
knowledge at the transmitter and receiver. Using the
closed-form expressions, we gain insights into the behavior
of MIMO beamforming systems in scenarios of practical
interest.},
Doi = {10.1109/ICC.2016.7511213},
Key = {fds336666}
}
@article{fds336655,
Author = {Kuiper, PK and Kolitz, SE and Tarokh, V},
Title = {Base camp quality of life standardization and
improvement},
Journal = {Proceedings International Carnahan Conference on Security
Technology},
Publisher = {IEEE},
Year = {2016},
Month = {July},
ISBN = {9781509010707},
url = {http://dx.doi.org/10.1109/CCST.2016.7815688},
Abstract = {The United States (US) Army has over 66,000 soldiers engaged
in contingency operations across the world. Current
budgetary constraints and an uncertain global security
environment require these operations to be executed as
efficiently as possible. Base camps are the secured areas
where soldiers live when deployed to contingency operations.
Base camps impose a significant financial and tactical
burden during contingency operations and sub-optimal soldier
quality of life decisions have significantly contributed to
costs. Quality of life (QOL) refers to the non-security and
non-mission related services that directly sustain the
mission effectiveness of soldiers. Current US Army base camp
tactics, techniques, and procedures (TTPs) do not
sufficiently specify QOL services, and more detailed
doctrine should be developed to support combat units
executing contingency operations. In this investigation we
employ quantitative methods to select decisions that improve
QOL and inform doctrine. We leverage a QOL function and
resource consumption data developed by US Army Natick
Soldier Research, Development and Engineering Center's
(Natick Labs) to build a model that improves QOL under the
constraints of four fundamental resources: fuel, water,
waste water, and solid waste. We employ a mixed integer
linear program modeling approach and execute sensitivity
analysis to evaluate the strength of our results. Our final
model is formulated as a chance constraint optimization to
address the uncertainty associated with resource
availability in contingency operations. Our results provide
QOL decisions that reduce resource consumption while
maintaining an equivalent QOL level when compared to current
TTPs. The model provides quantitative rigor, informing
decision makers of specific base camp design principles for
the development of doctrine.},
Doi = {10.1109/CCST.2016.7815688},
Key = {fds336655}
}
@article{fds336667,
Author = {Farhadi, H and Atai, J and Skoglund, M and Nadimi, ES and Pahlavan, K and Tarokh, V},
Title = {An adaptive localization technique for wireless capsule
endoscopy},
Journal = {International Symposium on Medical Information and
Communication Technology, Ismict},
Volume = {2016-June},
Publisher = {IEEE},
Year = {2016},
Month = {June},
ISBN = {9781509028498},
url = {http://dx.doi.org/10.1109/ISMICT.2016.7498884},
Abstract = {Wireless capsule endoscopy (WCE) is an emerging technique to
enhance Gastroenterologists information about the patient's
gastrointestinal (G.I.) tract. Localization of capsule
inside human body in this case is an active area of
research. This can be thought of as a sub-domain of micro
and bio-robotics fields. If capsule and micro-robot
localization problem in human body is solved, then it may
potentially lead to less invasive treatments for G.I.
diseases and other micro-robot assisted medical procedures.
Several approaches have been investigated by the researchers
to estimate capsule location. The proposed solutions are
mainly static and thus prone to the changes in the
propagation medium. We propose an adaptive algorithm based
on expectation maximization technique for capsule
localization. The proposed algorithm adaptively updates the
estimated location based on the received radio frequency
(RF) signal measurements.},
Doi = {10.1109/ISMICT.2016.7498884},
Key = {fds336667}
}
@article{fds336668,
Author = {Ding, J and Noshad, M and Tarokh, V},
Title = {Complementary lattice arrays for coded aperture
imaging.},
Journal = {Journal of the Optical Society of America
A},
Volume = {33},
Number = {5},
Pages = {863-881},
Year = {2016},
Month = {May},
url = {http://dx.doi.org/10.1364/josaa.33.000863},
Abstract = {In this work, we propose the concept of complementary
lattice arrays in order to enable a broader range of designs
for coded aperture imaging systems. We provide a general
framework and methods that generate richer and more flexible
designs compared to the existing techniques. Besides this,
we review and interpret the state-of-the-art uniformly
redundant array designs, broaden the related concepts, and
propose new design methods.},
Doi = {10.1364/josaa.33.000863},
Key = {fds336668}
}
@article{fds336669,
Author = {Magnusson, S and Enyioha, C and Heal, K and Li, N and Fischione, C and Tarokh, V},
Title = {Distributed resource allocation using one-way communication
with applications to power networks},
Journal = {2016 50th Annual Conference on Information Systems and
Sciences, Ciss 2016},
Pages = {631-636},
Publisher = {IEEE},
Year = {2016},
Month = {April},
ISBN = {9781467394574},
url = {http://dx.doi.org/10.1109/CISS.2016.7460576},
Abstract = {Typical coordination schemes for future power grids require
two-way communications. Since the number of end
power-consuming devices is large, the bandwidth requirements
for such two-way communication schemes may be prohibitive.
Motivated by this observation, we study distributed
coordination schemes that require only one-way limited
communications. In particular, we investigate how dual
descent distributed optimization algorithm can be employed
in power networks using one-way communication. In this
iterative algorithm, system coordinators broadcast
coordinating (or pricing) signals to the users/devices who
update power consumption based on the received signal. Then
system coordinators update the coordinating signals based on
the physical measurement of the aggregate power usage. We
provide conditions to guarantee the feasibility of the
aggregated power usage at each iteration so as to avoid
blackout. Furthermore, we prove the convergence of
algorithms under these conditions, and establish its rate of
convergence. We illustrate the performance of our algorithms
using numerical simulations. These results show that one-way
limited communication may be viable for coordinating/operating
the future smart grids.},
Doi = {10.1109/CISS.2016.7460576},
Key = {fds336669}
}
@article{fds336670,
Author = {Ding, J and Noshad, M and Tarokh, V},
Title = {Data-driven learning of the number of states in multi-state
autoregressive models},
Journal = {2015 53rd Annual Allerton Conference on Communication,
Control, and Computing, Allerton 2015},
Pages = {418-425},
Year = {2016},
Month = {April},
ISBN = {9781509018239},
url = {http://dx.doi.org/10.1109/ALLERTON.2015.7447034},
Abstract = {In this work, we consider the class of multi-state
autoregressive processes that can be used to model
non-stationary time series of interest. In order to capture
different autoregressive (AR) states underlying an observed
time series, it is crucial to select the appropriate number
of states. We propose a new and intuitive model selection
technique based on the Gap statistics, which uses a null
reference distribution on the stable AR filters to identify
whether adding a new AR state significantly improves the
performance of the model. To that end, we define a new
distance measure between two AR filters based on the mean
squared prediction error, and propose an efficient method to
generate stable filters that are uniformly distributed in
the coefficient space. Numerical results are provided to
evaluate the performance of the proposed
approach.},
Doi = {10.1109/ALLERTON.2015.7447034},
Key = {fds336670}
}
@article{fds336671,
Author = {Ding, J and Bouabdallah, A and Tarokh, V},
Title = {Key Pre-Distributions From Graph-Based Block
Designs},
Journal = {Ieee Sensors Journal},
Volume = {16},
Number = {6},
Pages = {1842-1850},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2016},
Month = {March},
url = {http://dx.doi.org/10.1109/JSEN.2015.2501429},
Abstract = {With the development of wireless communication technologies
which considerably contributed to the development of
wireless sensor networks (WSNs), we have witnessed
ever-increasing WSN-based applications which induced a host
of research activities in both academia and industry. Since
most of the target WSN applications are very sensitive,
security issue is one of the major challenges in the
deployment of WSN. One of the important building blocks in
securing WSN is key management. Traditional key management
solutions developed for other networks are not suitable for
WSN, since WSN networks are resource (e.g., memory,
computation, and energy) limited. Key pre-distribution
algorithms have recently evolved as efficient alternatives
of key management in these networks. Secure communication is
achieved between a pair of nodes either by the existence of
a key allowing for direct communication or by a chain of
keys forming a key path between the pair. In this paper, we
consider prior knowledge of network characteristics and
application constraints in terms of communication needs
between sensor nodes, and we propose methods to design key
pre-distribution schemes, in order to provide better
security and connectivity while requiring less resources.
Our methods are based on casting the prior information as a
graph. Motivated by this idea, we also propose a class of
quasi-symmetric designs referred here to as g-designs. Our
proposed key pre-distribution schemes significantly improve
upon the existing constructions based on the unital designs.
We give some examples and point out open problems for future
research.},
Doi = {10.1109/JSEN.2015.2501429},
Key = {fds336671}
}
@article{fds336672,
Author = {Ding, J and Noshad, M and Tarokh, V},
Title = {Order Selection of Autoregressive Processes Using Bridge
Criterion},
Journal = {Proceedings 15th Ieee International Conference on Data
Mining Workshop, Icdmw 2015},
Pages = {615-622},
Publisher = {IEEE},
Year = {2016},
Month = {January},
ISBN = {9781467384926},
url = {http://dx.doi.org/10.1109/ICDMW.2015.216},
Abstract = {A new criterion is introduced for determining the order of
an autoregressive model fit to time series data. The
proposed technique is shown to give a consistent and
asymptotically efficient order estimation. It has the
benefits of the two well-known model selection techniques,
the Akaike information criterion and the Bayesian
information criterion. When the true order of the
autoregression is relatively large compared with the sample
size, the Akaike information criterion is known to be
efficient, and the new criterion behaves in a similar
manner. When the true order is finite and small compared
with the sample size, the Bayesian information criterion is
known to be consistent, and so is the new criterion. Thus
the new criterion builds a bridge between the two classical
criteria automatically. In practice, where the observed time
series is given without any prior information about the
autoregression, the proposed order selection criterion is
more flexible and robust compared with classical approaches.
Numerical results are presented demonstrating the robustness
of the proposed technique when applied to various
datasets.},
Doi = {10.1109/ICDMW.2015.216},
Key = {fds336672}
}
@article{fds336673,
Author = {Ding, J and Noshad, M and Tarokh, V},
Title = {Learning the Number of Autoregressive Mixtures in Time
Series Using the Gap Statistics},
Journal = {Proceedings 15th Ieee International Conference on Data
Mining Workshop, Icdmw 2015},
Pages = {1441-1446},
Publisher = {IEEE},
Year = {2016},
Month = {January},
ISBN = {9781467384926},
url = {http://dx.doi.org/10.1109/ICDMW.2015.209},
Abstract = {Using a proper model to characterize a time series is
crucial in making accurate predictions. In this work we use
time-varying autoregressive process (TVAR) to describe
non-stationary time series and model it as a mixture of
multiple stable autoregressive (AR) processes. We introduce
a new model selection technique based on Gap statistics to
learn the appropriate number of AR filters needed to model a
time series. We define a new distance measure between stable
AR filters and draw a reference curve that is used to
measure how much adding a new AR filter improves the
performance of the model, and then choose the number of AR
filters that has the maximum gap with the reference curve.
To that end, we propose a new method in order to generate
uniform random stable AR filters in root domain. Numerical
results are provided demonstrating the performance of the
proposed approach.},
Doi = {10.1109/ICDMW.2015.209},
Key = {fds336673}
}
@article{fds340003,
Author = {Enyioha, C and Magnússon, S and Heal, K and Li, N and Fischione, C and Tarokh, V},
Title = {Robustness analysis for an online decentralized descent
power allocation algorithm.},
Journal = {Ita},
Pages = {1-8},
Publisher = {IEEE},
Year = {2016},
ISBN = {978-1-5090-2529-9},
Key = {fds340003}
}
@article{fds340002,
Author = {Magnússon, S and Enyioha, C and Heal, K and Li, N and Fischione, C and Tarokh, V},
Title = {Distributed resource allocation using one-way communication
with applications to power networks.},
Journal = {Ciss},
Pages = {631-636},
Publisher = {IEEE},
Year = {2016},
ISBN = {978-1-4673-9457-4},
Key = {fds340002}
}
@article{fds340004,
Author = {Shahrampour, S and Noshad, M and Tarokh, V},
Title = {On Sequential Elimination Algorithms for Best-Arm
Identification in Multi-Armed Bandits.},
Journal = {Corr},
Volume = {abs/1609.02606},
Year = {2016},
Key = {fds340004}
}
@article{fds340005,
Author = {Kuiper, PK and Kolitz, SE and Tarokh, V},
Title = {Base camp quality of life standardization and
improvement.},
Journal = {Iccst},
Pages = {1-8},
Publisher = {IEEE},
Year = {2016},
ISBN = {978-1-5090-1072-1},
Key = {fds340005}
}
@article{fds336678,
Author = {Pahlavan, K and Geng, Y and Cave, DR and Bao, G and Ml, L and Agu, E and Karellas, A and Sayrafian, K and Tarokh, V},
Title = {A novel cyber physical system for 3-D imaging of the small
intestine in vivo},
Journal = {Ieee Access},
Volume = {3},
Pages = {2730-2742},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2015},
Month = {December},
url = {http://dx.doi.org/10.1109/ACCESS.2015.2508003},
Abstract = {Small intestine is the longest organ in the gastrointestinal
tract where much of the digestion and the food absorption
take place. Wireless video capsule endoscope (VCE) is the
first device taking 2-D pictures from the lesions and the
abnormalities in the entire length of the small intestine.
Since precise localization and mapping inside the small
intestine is a very challenging problem, we cannot measure
the distance traveled by the VCE to associate lesions and
abnormalities to locations inside the small intestine, and
we cannot use the 2-D pictures to reconstruct the 3-D image
of interior of the entire small intestine in vivo. This
paper presents the architectural concept of a novel cyber
physical system (CPS), which can utilize the 2-D pictures of
the small intestine taken by the VCE to reconstruct the 3-D
image of the small intestine in vivo. Hybrid localization
and mapping techniques with millimetric accuracy for inside
the small intestine is presented as an enabling technology
to facilitate the reconstruction of 3-D images from the 2-D
pictures. The proposed CPS architecture provides for
large-scale virtual experimentations inside the human body
without intruding the body with a sizable equipment using
reasonable clinical experiments for validation. The 3-D
imaging of the small intestine in vivo allows a lesion to be
pinpointed for follow-up diagnosis and/or treatment and the
abnormalities may be observed from different angles in 3-D
images for more thorough examination.},
Doi = {10.1109/ACCESS.2015.2508003},
Key = {fds336678}
}
@article{fds336674,
Author = {Nadimi, ES and Blanes-Vidal, V and Harslund, JLF and Ramezani, MH and Kjeldsen, J and Johansen, PM and Thiel, D and Tarokh,
V},
Title = {In vivo and in situ measurement and modelling of intra-body
effective complex permittivity.},
Journal = {Healthcare Technology Letters},
Volume = {2},
Number = {6},
Pages = {135-140},
Year = {2015},
Month = {December},
url = {http://dx.doi.org/10.1049/htl.2015.0024},
Abstract = {Radio frequency tracking of medical micro-robots in
minimally invasive medicine is usually investigated upon the
assumption that the human body is a homogeneous propagation
medium. In this Letter, the authors conducted various trial
programs to measure and model the effective complex
permittivity ε in terms of refraction ε', absorption ε″
and their variations in gastrointestinal (GI) tract organs
(i.e. oesophagus, stomach, small intestine and large
intestine) and the porcine abdominal wall under in vivo and
in situ conditions. They further investigated the effects of
irregular and unsynchronised contractions and simulated
peristaltic movements of the GI tract organs inside the
abdominal cavity and in the presence of the abdominal wall
on the measurements and variations of ε' and ε''. They
advanced the previous models of effective complex
permittivity of a multilayer inhomogeneous medium, by
estimating an analytical model that accounts for reflections
between the layers and calculates the attenuation that the
wave encounters as it traverses the GI tract and the
abdominal wall. They observed that deviation from the
specified nominal layer thicknesses due to non-geometric
boundaries of GI tract morphometric variables has an impact
on the performance of the authors' model. Therefore, they
derived statistical-based models for ε' and ε'' using
their experimental measurements.},
Doi = {10.1049/htl.2015.0024},
Key = {fds336674}
}
@article{fds336675,
Author = {Noshad, M and Ding, J and Tarokh, V},
Title = {Sequential learning of Multi-state autoregressive time
series},
Journal = {Proceeding of the 2015 Research in Adaptive and Convergent
Systems, Racs 2015},
Pages = {44-51},
Publisher = {ACM Press},
Year = {2015},
Month = {October},
ISBN = {9781450337380},
url = {http://dx.doi.org/10.1145/2811411.2813523},
Abstract = {Modeling and forecasting streaming data has fundamental
importance in many real world applications. In this paper,
we present an online model selection technique that can be
used to model non-stationary time series in a sequential
manner. Multi-state autoregressive (AR) model is used to
describe non-stationary time series, and a dynamic algorithm
is applied to learn the states at each time step. The
proposed technique estimates a candidate AR filter from the
most recent data points at every time step, and checks
whether starting a new state significantly decreases
prediction error or not. To that end, a time-varying
threshold is compared with the reduction in the prediction
error caused by postulating a new AR filter. The threshold
is calculated by sampling and clustering uniformly
distributed stable AR filters. Numerical simulations show
that the proposed algorithm accurately estimates the state
transitions with a small delay.},
Doi = {10.1145/2811411.2813523},
Key = {fds336675}
}
@article{fds340007,
Author = {Babadi, B and Kalouptsidis, N and Tarokh, V},
Title = {Comment on "Asymptotic Achievability of the Cramér-Rao
Bound for Noisy Compressive Sampling"},
Volume = {abs/1509.04375},
Year = {2015},
Month = {September},
Abstract = {In [1], we proved the asymptotic achievability of the
Cram\'{e}r-Rao bound in the compressive sensing setting in
the linear sparsity regime. In the proof, we used an
erroneous closed-form expression of $\alpha \sigma^2$ for
the genie-aided Cram\'{e}r-Rao bound $\sigma^2 \textrm{Tr}
(\mathbf{A}^*_\mathcal{I} \mathbf{A}_\mathcal{I})^{-1}$ from
Lemma 3.5, which appears in Eqs. (20) and (29). The proof,
however, holds if one avoids replacing $\sigma^2 \textrm{Tr}
(\mathbf{A}^*_\mathcal{I} \mathbf{A}_\mathcal{I})^{-1}$ by
the expression of Lemma 3.5, and hence the claim of the Main
Theorem stands true. In Chapter 2 of the Ph. D. dissertation
by Behtash Babadi [2], this error was fixed and a more
detailed proof in the non-asymptotic regime was presented. A
draft of Chapter 2 of [2] is included in this note,
verbatim. We would like to refer the interested reader to
the full dissertation, which is electronically archived in
the ProQuest database [2], and a draft of which can be
accessed through the author's homepage under:
http://ece.umd.edu/~behtash/babadi_thesis_2011.pdf.},
Key = {fds340007}
}
@article{fds336676,
Author = {Akçakaya, M and Tarokh, V},
Title = {Sparse Signal Recovery from a Mixture of Linear and
Magnitude-Only Measurements.},
Journal = {Ieee Signal Processing Letters},
Volume = {22},
Number = {9},
Pages = {1220-1223},
Year = {2015},
Month = {September},
url = {http://dx.doi.org/10.1109/lsp.2015.2393295},
Abstract = {We consider the problem of exact sparse signal recovery from
a combination of linear and magnitude-only (phaseless)
measurements. A k-sparse signal x ∈ ℂ n is measured as r
= Bx and y = |Cx|, where B ∈ ℂ m1×n and C ∈ ℂ m2×n
are measurement matrices and | · | is the element-wise
absolute value. We show that if max(2m1, 1) + m2 ≥ 4k - 1,
then a set of generic measurements are sufficient to recover
every k-sparse x exactly, establishing the trade-off between
the number of linear and magnitude-only measurements.},
Doi = {10.1109/lsp.2015.2393295},
Key = {fds336676}
}
@article{fds336677,
Author = {Krishnamurthy, S and Bliss, D and Richmond, C and Tarokh,
V},
Title = {Peak sidelobe level gumbel distribution for arrays of
randomly placed antennas},
Journal = {Ieee National Radar Conference Proceedings},
Volume = {2015-June},
Number = {June},
Pages = {1671-1676},
Publisher = {IEEE},
Year = {2015},
Month = {June},
ISBN = {9781479982325},
url = {http://dx.doi.org/10.1109/RADAR.2015.7131267},
Abstract = {Extreme Value Theory (EVT) is used to analyze the peak
sidelobe level distribution for array element positions with
arbitrary probability distributions. Computations are
discussed in the context of linear antenna arrays using
electromagnetic energy. The results also apply to planar
arrays of random elements that can be transformed into
linear arrays. For sparse arrays with small number of
elements, Gaussian approximations to the beampattern
distribution at a particular angle introduce inaccuracies to
the probability calculations. EVT is applied without making
these Gaussian approximations. It is shown that the peak
sidelobe level distribution converges weakly to a Gumbel
distribution in the limit of a large number of beampattern
samples. This result is for both sparse and dense arrays of
randomly placed antennas over a large aperture. The
definition of a large aperture in this context is ambiguous,
but a possible rule-of-thumb is that it is at least a
wavelength.},
Doi = {10.1109/RADAR.2015.7131267},
Key = {fds336677}
}
@article{fds356194,
Author = {Deng, Z and Ding, J and Noshad, M and Tarokh, V},
Title = {Capacity of Hexagonal Checkerboard Codes},
Volume = {abs/1506.02163},
Year = {2015},
Month = {June},
Abstract = {In this paper, we propose a new method to bound the capacity
of checkerboard codes on the hexagonal lattice. This
produces rigorous bounds that are tighter than those
commonly known.},
Key = {fds356194}
}
@article{fds340006,
Author = {Ding, J and Noshad, M and Tarokh, V},
Title = {Data-Driven Learning of the Number of States in Multi-State
Autoregressive Models.},
Journal = {Corr},
Volume = {abs/1506.02107},
Year = {2015},
Key = {fds340006}
}
@article{fds340009,
Author = {Yi, H and Shin, WY and Tarokh, V},
Title = {An environmentally friendly approach to the relay-aided
cellular network architecture},
Journal = {2014 Ieee 11th Consumer Communications and Networking
Conference, Ccnc 2014},
Pages = {541-542},
Publisher = {IEEE},
Year = {2014},
Month = {January},
ISBN = {9781479923557},
url = {http://dx.doi.org/10.1109/ccnc.2014.6994432},
Abstract = {We solve the problem of environmentally friendly (i.e.,
energy-efficient) base station and relay-station planning
for a simplified cooperative cellular network. We assume a
two-hop transmission model based on the time-division
multiplexing operation. We propose a twostep iterative
algorithm where each iteration consists of an assignment
step and a positioning step. We use the energy-normalized
throughput as a greenness measure, defined as the ratio of
the sum-rate to the total energy consumptions. Numerical
evaluation is performed to find 1) the optimal positions of
base-stations and relay-stations and 2) the optimal numbers
of base-stations and relay-stations in terms of maximizing
the energy-normalized throughput in a one-dimensional
network.},
Doi = {10.1109/ccnc.2014.6994432},
Key = {fds340009}
}
@article{fds336679,
Author = {Kurien, BG and Rachlin, Y and Shah, VN and Ashcom, JB and Tarokh,
V},
Title = {Compressed sensing techniques for image reconstruction in
optical interferometry},
Journal = {Optics Infobase Conference Papers},
Year = {2014},
Month = {January},
ISBN = {9781557523082},
Abstract = {We develop a novel method of image reconstruction from
bispectrum and magnitude observables of an optical
interferometer using Compressed-Sensing techniques.We
validate our method in simulation and with actual
measurements from a Fizeau interferometer. © 2014
OSA.},
Key = {fds336679}
}
@article{fds336680,
Author = {Nadimi, ES and Blanes-Vidal, V and Tarokh, V and Johansen,
PM},
Title = {Bayesian-based localization of wireless capsule endoscope
using received signal strength.},
Journal = {Annual International Conference of the Ieee Engineering in
Medicine and Biology Society. Ieee Engineering in Medicine
and Biology Society. Annual International
Conference},
Volume = {2014},
Pages = {5988-5991},
Year = {2014},
Month = {January},
url = {http://dx.doi.org/10.1109/embc.2014.6944993},
Abstract = {In wireless body area sensor networking (WBASN) applications
such as gastrointestinal (GI) tract monitoring using
wireless video capsule endoscopy (WCE), the performance of
out-of-body wireless link propagating through different body
media (i.e. blood, fat, muscle and bone) is still under
investigation. Most of the localization algorithms are
vulnerable to the variations of path-loss coefficient
resulting in unreliable location estimation. In this paper,
we propose a novel robust probabilistic Bayesian-based
approach using received-signal-strength (RSS) measurements
that accounts for Rayleigh fading, variable path-loss
exponent and uncertainty in location information received
from the neighboring nodes and anchors. The results of this
study showed that the localization root mean square error of
our Bayesian-based method was 1.6 mm which was very close to
the optimum Cramer-Rao lower bound (CRLB) and significantly
smaller than that of other existing localization approaches
(i.e. classical MDS (64.2mm), dwMDS (32.2mm), MLE (36.3mm)
and POCS (2.3mm)).},
Doi = {10.1109/embc.2014.6944993},
Key = {fds336680}
}
@article{fds336681,
Author = {Akçakaya, M and Nam, S and Basha, TA and Kawaji, K and Tarokh, V and Nezafat, R},
Title = {An augmented Lagrangian based compressed sensing
reconstruction for non-Cartesian magnetic resonance imaging
without gridding and regridding at every
iteration.},
Journal = {Plos One},
Volume = {9},
Number = {9},
Pages = {e107107},
Year = {2014},
Month = {January},
url = {http://dx.doi.org/10.1371/journal.pone.0107107},
Abstract = {<h4>Background</h4>Non-Cartesian trajectories are used in a
variety of fast imaging applications, due to the incoherent
image domain artifacts they create when undersampled. While
the gridding technique is commonly utilized for
reconstruction, the incoherent artifacts may be further
removed using compressed sensing (CS). CS reconstruction is
typically done using conjugate-gradient (CG) type
algorithms, which require gridding and regridding to be
performed at every iteration. This leads to a large
computational overhead that hinders its applicability.<h4>Methods</h4>We
sought to develop an alternative method for CS
reconstruction that only requires two gridding and one
regridding operation in total, irrespective of the number of
iterations. This proposed technique is evaluated on phantom
images and whole-heart coronary MRI acquired using 3D radial
trajectories, and compared to conventional CS reconstruction
using CG algorithms in terms of quantitative vessel
sharpness, vessel length, computation time, and convergence
rate.<h4>Results</h4>Both CS reconstructions result in
similar vessel length (P = 0.30) and vessel sharpness
(P = 0.62). The per-iteration complexity of the proposed
technique is approximately 3-fold lower than the
conventional CS reconstruction (17.55 vs. 52.48 seconds in
C++). Furthermore, for in-vivo datasets, the convergence
rate of the proposed technique is faster (60±13 vs.
455±320 iterations) leading to a ∼23-fold reduction in
reconstruction time.<h4>Conclusions</h4>The proposed
reconstruction provides images of similar quality to the
conventional CS technique in terms of removing artifacts,
but at a much lower computational complexity.},
Doi = {10.1371/journal.pone.0107107},
Key = {fds336681}
}
@article{fds336682,
Author = {Nam, S and Hong, SN and Akçakaya, M and Kwak, Y and Goddu, B and Kissinger, KV and Manning, WJ and Tarokh, V and Nezafat,
R},
Title = {Compressed sensing reconstruction for undersampled
breath-hold radial cine imaging with auxiliary
free-breathing data.},
Journal = {Journal of Magnetic Resonance Imaging : Jmri},
Volume = {39},
Number = {1},
Pages = {179-188},
Year = {2014},
Month = {January},
url = {http://dx.doi.org/10.1002/jmri.24098},
Abstract = {<h4>Purpose</h4>To improve compressed sensing (CS)
reconstruction of accelerated breath-hold (BH) radial cine
magnetic resonance imaging (MRI) by exploiting auxiliary
data acquired between different BHs.<h4>Materials and
methods</h4>Cardiac function is usually assessed using
segmented cine acquisitions over multiple BHs to cover the
entire left ventricle (LV). Subjects are given a resting
period between adjacent BHs, when conventionally no data are
acquired and subjects rest in the scanner. In this study the
resting periods between BHs were used to acquire additional
free-breathing (FB) data, which are subsequently used to
generate a sparsity constraint for each cardiac phase.
Images reconstructed using the proposed sparsity constraint
were compared with conventional CS using a composite image
generated by averaging different cardiac phases. The
efficacy of the proposed reconstruction was compared using
indices of LV function and blood-myocardium
sharpness.<h4>Results</h4>The proposed method provided
accurate LV ejection fraction measurements for 33% and 20%
sampled datasets compared with fully sampled reference
images, and showed 14% and 11% higher blood-myocardium
border sharpness scores compared to the conventional
CS.<h4>Conclusion</h4>The FB data acquired during resting
periods can be efficiently used to improve the image quality
of the undersampled BH data without increasing the total
scan time.},
Doi = {10.1002/jmri.24098},
Key = {fds336682}
}
@article{fds350812,
Author = {Kurien, BG and Rachlin, Y and Shah, VN and Ashcom, JB and Tarokh,
V},
Title = {Compressed sensing techniques for image reconstruction in
optical interferometry},
Journal = {Optics Infobase Conference Papers},
Year = {2014},
Month = {January},
ISBN = {9781557523082},
url = {http://dx.doi.org/10.1364/srs.2014.sm2f.3},
Abstract = {We develop a novel method of image reconstruction from
bispectrum and magnitude observables of an optical
interferometer using Compressed-Sensing techniques.We
validate our method in simulation and with actual
measurements from a Fizeau interferometer. © 2014
OSA.},
Doi = {10.1364/srs.2014.sm2f.3},
Key = {fds350812}
}
@article{fds340008,
Author = {Yi, H and Shin, WY and Tarokh, V},
Title = {The design of environmentally friendly networks using
coordinated multi-point (CoMP) transmission},
Journal = {2014 Ieee 11th Consumer Communications and Networking
Conference, Ccnc 2014},
Pages = {517-518},
Publisher = {IEEE},
Year = {2014},
Month = {January},
ISBN = {9781479923557},
url = {http://dx.doi.org/10.1109/ccnc.2014.6994388},
Doi = {10.1109/ccnc.2014.6994388},
Key = {fds340008}
}
@article{fds336683,
Author = {Akcakaya, M and Tarokh, V},
Title = {Distortion-based achievability conditions for joint
estimation of sparse signals and measurement parameters from
undersampled acquisitions},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {291-295},
Publisher = {IEEE},
Year = {2013},
Month = {December},
ISBN = {9781479904464},
url = {http://dx.doi.org/10.1109/ISIT.2013.6620234},
Abstract = {In this paper, we consider an undersampling system model of
the form y = A(T(x, θ)) + n, where x is a k-sparse signal,
T(·, · is a (possibly non-linear) function specified by a
parameter vector θ and acting on x, A is a sensing matrix,
and n is additive measurement noise. We consider an
information theoretic decoder that aims to recover the
sparse signal and the transformation parameter vector
jointly, and study the achievability conditions for
estimating the underlying signal within a specified ℓ2
distortion for Gaussian sensing matrices. We compare the
achievable distortion of the joint estimation process to
that of the standard noisy compressed sensing model, where
the sparse signal is directly measured with a sensing matrix
with the same number of measurements. We also provide a
numerical example to illustrate potential applications. ©
2013 IEEE.},
Doi = {10.1109/ISIT.2013.6620234},
Key = {fds336683}
}
@article{fds336684,
Author = {Sabbaghian, M and Sulyman, AI and Tarokh, V},
Title = {Analysis of the impact of nonlinearity on the capacity of
communication channels},
Journal = {Ieee Transactions on Information Theory},
Volume = {59},
Number = {11},
Pages = {7671-7683},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2013},
Month = {November},
url = {http://dx.doi.org/10.1109/TIT.2013.2274268},
Abstract = {We study the impact of nonlinearities on the transmission
rate of a communication system by establishing lower and
upper bounds on the channel capacity. Our analysis is based
on a general transmission model that includes transmitter
and receiver nonlinearities, environmental thermal noise,
and receiver chain noise. Using this model, we derive lower
and upper bounds for the channel capacity of additive white
Gaussian noise channels, fading channels, and multiple input
multiple output channels in various thermal noise and
receiver noise regimes. © 1963-2012 IEEE.},
Doi = {10.1109/TIT.2013.2274268},
Key = {fds336684}
}
@article{fds340010,
Author = {Akçakaya, M and Tarokh, V},
Title = {New Conditions for Sparse Phase Retrieval},
Volume = {abs/1310.1351},
Year = {2013},
Month = {October},
Abstract = {We consider the problem of sparse phase retrieval, where a
$k$-sparse signal ${\bf x} \in {\mathbb R}^n \textrm{ (or }
{\mathbb C}^n\textrm{)}$ is measured as ${\bf y} = |{\bf
Ax}|,$ where ${\bf A} \in {\mathbb R}^{m \times n} \textrm{
(or } {\mathbb C}^{m \times n}\textrm{ respectively)}$ is a
measurement matrix and $|\cdot|$ is the element-wise
absolute value. For a real signal and a real measurement
matrix ${\bf A}$, we show that $m = 2k$ measurements are
necessary and sufficient to recover ${\bf x}$ uniquely. For
complex signal ${\bf x} \in {\mathbb C}^n$ and ${\bf A} \in
{\mathbb C}^{m \times n}$, we show that $m = 4k-2$ phaseless
measurements are sufficient to recover ${\bf x}$. It is
known that the multiplying constant $4$ in $m = 4k-2$ cannot
be improved.},
Key = {fds340010}
}
@article{fds336685,
Author = {Kwak, Y and Nam, S and Akçakaya, M and Basha, TA and Goddu, B and Manning,
WJ and Tarokh, V and Nezafat, R},
Title = {Accelerated aortic flow assessment with compressed sensing
with and without use of the sparsity of the complex
difference image.},
Journal = {Magnetic Resonance in Medicine},
Volume = {70},
Number = {3},
Pages = {851-858},
Year = {2013},
Month = {September},
url = {http://dx.doi.org/10.1002/mrm.24514},
Abstract = {Phase contrast (PC) cardiac MR is widely used for the
clinical assessment of blood flow in cardiovascular disease.
One of the challenges of PC cardiac MR is the long scan time
which limits both spatial and temporal resolution.
Compressed sensing reconstruction with accelerated PC
acquisitions is a promising technique to increase the scan
efficiency. In this study, we sought to use the sparsity of
the complex difference of the two flow-encoded images as an
additional constraint term to improve the compressed sensing
reconstruction of the corresponding accelerated PC data
acquisition. Using retrospectively under-sampled data, the
proposed reconstruction technique was optimized and
validated in vivo on 15 healthy subjects. Then,
prospectively under-sampled data was acquired on 11 healthy
subjects and reconstructed with the proposed technique. The
results show that there is good agreement between the
cardiac output measurements from the fully sampled data and
the proposed compressed sensing reconstruction method using
complex difference sparsity up to acceleration rate 5. In
conclusion, we have developed and evaluated an improved
reconstruction technique for accelerated PC cardiac MR that
uses the sparsity of the complex difference of the two
flow-encoded images.},
Doi = {10.1002/mrm.24514},
Key = {fds336685}
}
@article{fds336686,
Author = {Shin, WY and Lucani, DE and Médard, M and Stojanovic, M and Tarokh,
V},
Title = {On the effects of frequency scaling over capacity scaling in
underwater networks - Part I: Extended network
model},
Journal = {Wireless Personal Communications},
Volume = {71},
Number = {3},
Pages = {1683-1700},
Publisher = {Springer Nature},
Year = {2013},
Month = {August},
url = {http://dx.doi.org/10.1007/s11277-012-0904-z},
Abstract = {In this two-part paper, information-theoretic capacity
scaling laws are analyzed in an underwater acoustic network
with n regularly located nodes on a square, in which both
bandwidth and received signal power can be limited
significantly. Parts I and II deal with an extended network
of unit node density and a dense network of unit area,
respectively. In both cases, a narrow-band model is assumed
where the carrier frequency is allowed to scale as a
function of n, which is shown to be crucial for achieving
the order optimality in multi-hop (MH) mechanisms. We first
characterize an attenuation parameter that depends on the
frequency scaling as well as the transmission distance.
Upper and lower bounds on the capacity scaling are then
derived. In Part I, we show that the upper bound on capacity
for extended networks is inversely proportional to the
attenuation parameter, thus resulting in a highly
power-limited network. Interestingly, it is shown that the
upper bound is intrinsically related to the attenuation
parameter but not the spreading factor. Furthermore, we
propose an achievable communication scheme based on the
nearest-neighbor MH transmission, which is suitable due to
the low propagation speed of acoustic channel, and show that
it is order-optimal for all operating regimes of extended
networks. Finally, these scaling results are extended to the
case of random node deployments providing fundamental limits
to more complex scenarios of extended underwater networks.
© 2012 Springer Science+Business Media New
York.},
Doi = {10.1007/s11277-012-0904-z},
Key = {fds336686}
}
@article{fds336687,
Author = {Shin, WY and Lucani, DE and Médard, M and Stojanovic, M and Tarokh,
V},
Title = {On the effects of frequency scaling over capacity scaling in
underwater networks - Part II: Dense network
model},
Journal = {Wireless Personal Communications},
Volume = {71},
Number = {3},
Pages = {1701-1719},
Publisher = {Springer Nature},
Year = {2013},
Month = {August},
url = {http://dx.doi.org/10.1007/s11277-012-0982-y},
Abstract = {This is the second in a two-part series of papers on
information-theoretic capacity scaling laws for an
underwater acoustic network. Part II focuses on a dense
network scenario, where nodes are deployed in a unit area.
By deriving a cut-set upper bound on the capacity scaling,
we first show that there exists either a bandwidth or power
limitation, or both, according to the operating regimes
(i.e.; path-loss attenuation regimes), thus yielding the
upper bound that follows three fundamentally different
information transfer arguments. In addition, an
achievability result based on the multi-hop (MH)
transmission is presented for dense networks. MH is shown to
guarantee the order optimality under certain operating
regimes. More specifically, it turns out that scaling the
carrier frequency faster than or as n{1/4} is instrumental
towards achieving the order optimality of the MH protocol.
© 2013 Springer Science+Business Media New
York.},
Doi = {10.1007/s11277-012-0982-y},
Key = {fds336687}
}
@article{fds336690,
Author = {Shin, WY and Yi, H and Tarokh, V},
Title = {Energy-efficient base-station topologies for green cellular
networks},
Journal = {2013 Ieee 10th Consumer Communications and Networking
Conference, Ccnc 2013},
Pages = {91-96},
Publisher = {IEEE},
Year = {2013},
Month = {April},
ISBN = {9781467331333},
url = {http://dx.doi.org/10.1109/CCNC.2013.6488431},
Abstract = {We consider the problem of energy-efficient base-station
(BS) planning for green cellular network design. There exist
a number of criteria for greenness in the literature, but we
focus only on the energy-normalized throughput. We first
model energy consumption for a heterogeneous network,
consisting of macro and micro base-stations, and a network
topology. Then, we propose an iterative algorithm for the
green BS planning problem in the one-dimensional case: 1) We
find the positions of base-stations that maximize the
energy-normalized throughput for a fixed number of
base-stations, and 2) find the optimal number of
base-stations which maximizes the energy-normalized
throughput. In this work, we evaluate the energy-normalized
throughput accounting for adaptive modulation rates with
power control, which is a common feature of modern
communications systems. The convergence to a local maximum
for the proposed algorithm is shown using computer
simulations, and the corresponding energy-normalized
throughputs are evaluated for a number of system model
parameters. © 2013 IEEE.},
Doi = {10.1109/CCNC.2013.6488431},
Key = {fds336690}
}
@article{fds336689,
Author = {Ishibashi, K and Shin, WY and Ochiai, H and Tarokh,
V},
Title = {A peak power efficient cooperative diversity using star-QAM
with coherent/noncoherent detection},
Journal = {Ieee Transactions on Wireless Communications},
Volume = {12},
Number = {5},
Pages = {2137-2147},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2013},
Month = {April},
url = {http://dx.doi.org/10.1109/TWC.2013.032013.120507},
Abstract = {In this paper, we propose a new simple relaying strategy
based on bit-interleaved convolutionally coded
star-quadrature amplitude modulation (QAM) along with
coherent/noncoherent detection. Star-QAM is composed of
multiple concentric circles of phase-shift keying (PSK).
Exploiting this property, a hard limiter is used to enhance
power amplifier (PA) efficiency at the relay. Moreover, we
show that the proposed approach retains differential
detectability, which results in a significant reduction of
receiver complexity with robustness against phase ambiguity.
By analyzing our proposed cooperation with
coherent/noncoherent detection in terms of asymptotic
pairwise error probability (PEP), we show that the full
diversity order can be achieved on the condition that the
minimum free distance of the convolutional codes is larger
than the predetermined value specified by the number of
available relays. Furthermore, the effectiveness of the
proposed scheme in terms of PA efficiency is confirmed by
comparing the statistical distributions of the corresponding
instantaneous signal powers. All the theoretical results
agree with those obtained by computer simulations. ©
2002-2012 IEEE.},
Doi = {10.1109/TWC.2013.032013.120507},
Key = {fds336689}
}
@article{fds336691,
Author = {Cvetkovic, Z and Tarokh, V and Yoon, S},
Title = {On frequency offset estimation for OFDM},
Journal = {Ieee Transactions on Wireless Communications},
Volume = {12},
Number = {3},
Pages = {1062-1072},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2013},
Month = {February},
url = {http://dx.doi.org/10.1109/TWC.2013.012413.120087},
Abstract = {This paper presents a comparative study of Schmidl-Cox (SC)
and Morelli-Mengali (MM) algorithms for frequency offset
estimation in OFDM, along with a new least squares (LS) and
a new modified SC algorithm. All algorithms have comparable
accuracy approaching asymptotically the Cramer-Rao bound.
The complexity of the LS algorithm is between O(N) and O(N
log N) operations, where N is the length of the training
sequence, while the complexity of the SC algorithm is
between O(N log N) and O(N2) operations, and the complexity
of the MM algorithm is O(N2) operations. The modified
version of the SC algorithm requires only one training
sequence as opposed to two required by the original SC
algorithm, and significantly reduced O(N log N) complexity.
The sensitivity of the three algorithms to quantization of
the arg function (the argument of a complex number) is
analyzed and quantified. The analysis and simulation results
demonstrate that while all considered algorithms can be used
with coarse quantization of the \arg function, the LS
algorithm is least affected and the SC algorithm is most
affected by this quantization error. © 2002-2012
IEEE.},
Doi = {10.1109/TWC.2013.012413.120087},
Key = {fds336691}
}
@article{fds336693,
Author = {Babadi, B and Tarokh, V},
Title = {Spectral distribution of product of pseudorandom matrices
formed from binary block codes},
Journal = {Ieee Transactions on Information Theory},
Volume = {59},
Number = {2},
Pages = {970-978},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2013},
Month = {January},
url = {http://dx.doi.org/10.1109/TIT.2012.2223812},
Abstract = {Let {\bf A} \in \{-1,1\}^{N-{a} \times n} and {\bf B} \in
\{-1,1\}^{N-{b} \times n} be two matrices whose rows are
drawn i.i.d. from the codewords of the binary codes {\cal
C}a and {\cal C}b of length n and dual distances
{d^{\prime}}a and {d^{\prime}}b, respectively, under the
mapping 0 \mapsto 1 and 1 \mapsto -1. It is proven that as n
\rightarrow \infty with y-{a}:=n/N-{a} \in (0,\infty) and
y-{b}:=n/N-{b} \in (0, \infty) fixed, the empirical spectral
distribution of the matrix {\bf A} {\bf B}^{\ast }/\sqrt
{N-{a} N-{b}} resembles a universal distribution (closely
related to the distribution function of the free
multiplicative convolution of two members of the
Marchenko-Pastur family of densities) in the sense of the
Lévy distance, if the asymptotic dual distances of the
underlying binary codes are large enough. Moreover, an
explicit upper bound on the Lévy distance of the two
distributions in terms of ya, yb, {d^{\prime}}a , and
{d^{\prime}}b is given. Under mild conditions, the upper
bound is strengthened to the Kolmogorov distance of the
underlying distributions. Numerical studies on the empirical
spectral distribution of the product of random matrices from
BCH and Gold codes are provided, which verify the validity
of this result. © 1963-2012 IEEE.},
Doi = {10.1109/TIT.2012.2223812},
Key = {fds336693}
}
@article{fds336695,
Author = {Bechkit, W and Challal, Y and Bouabdallah, A and Tarokh,
V},
Title = {A highly scalable key pre-distribution scheme for wireless
sensor networks},
Journal = {Ieee Transactions on Wireless Communications},
Volume = {12},
Number = {2},
Pages = {948-959},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2013},
Month = {January},
url = {http://dx.doi.org/10.1109/TWC.2012.010413.120732},
Abstract = {Given the sensitivity of the potential WSN applications and
because of resource limitations, key management emerges as a
challenging issue for WSNs. One of the main concerns when
designing a key management scheme is the network
scalability. Indeed, the protocol should support a large
number of nodes to enable a large scale deployment of the
network. In this paper, we propose a new scalable key
management scheme for WSNs which provides a good secure
connectivity coverage. For this purpose, we make use of the
unital design theory. We show that the basic mapping from
unitals to key pre-distribution allows us to achieve high
network scalability. Nonetheless, this naive mapping does
not guarantee a high key sharing probability. Therefore, we
propose an enhanced unital-based key pre-distribution scheme
providing high network scalability and good key sharing
probability approximately lower bounded by 1-e{-1} ≈
0.632. We conduct approximate analysis and simulations and
compare our solution to those of existing methods for
different criteria such as storage overhead, network
scalability, network connectivity, average secure path
length and network resiliency. Our results show that the
proposed approach enhances the network scalability while
providing high secure connectivity coverage and overall
improved performance. Moreover, for an equal network size,
our solution reduces significantly the storage overhead
compared to those of existing solutions. © 2012
IEEE.},
Doi = {10.1109/TWC.2012.010413.120732},
Key = {fds336695}
}
@article{fds336694,
Author = {Larsson, P and Smida, B and Koike-Akino, T and Tarokh,
V},
Title = {Analysis of network coded HARQ for multiple unicast
flows},
Journal = {Ieee Transactions on Communications},
Volume = {61},
Number = {2},
Pages = {722-732},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2013},
Month = {January},
url = {http://dx.doi.org/10.1109/TCOMM.2012.121112.110202},
Abstract = {In this paper, we consider network coded (NCed) Hybrid-ARQ
(HARQ) for multiple unicast flows. The main contribution of
the paper is the derivation of throughput expressions for
NCed HARQ with arbitrary number of users in identical i.i.d.
channels amid packets for all users. We apply the result to
Rayleigh fading channels and two packet combining schemes:
incremental redundancy (IR) and chase combining (CC). We
verify the analytical results with simulations and observe
substantial SNR improvements over NCed ARQ and HARQ. The SNR
gains in the moderate/high and low throughput regimes are
mainly due to network coding and packet combining,
respectively. For low/moderate SNRs, NCed HARQ with IR
surpasses the CC performance. In addition, we introduce a
novel re-transmission strategy that makes the network coding
more efficient at low SNR. © 1972-2012 IEEE.},
Doi = {10.1109/TCOMM.2012.121112.110202},
Key = {fds336694}
}
@article{fds336688,
Author = {Kim, SJ and Kwon, UK and Yoon, SK and Tarokh, V},
Title = {Near field resonator isolation system: Theory to
implementation},
Journal = {Ieee Transactions on Circuits and Systems I: Regular
Papers},
Volume = {60},
Number = {5},
Pages = {1175-1187},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2013},
Month = {January},
url = {http://dx.doi.org/10.1109/TCSI.2013.2246252},
Abstract = {The absence of electromagnetic wave motivates various
studies of new communication channels in near field regime.
An approach studied here is based on resonant inductive
coupling and the use of Resonator Isolation (RI) system. The
main concept of the RI system is to physically isolate two
inductively coupled resonators from the signal input/output
components. The resonators are charged with initial energy,
and communicate by exchanging this energy according to the
fundamental phenomenon of electromagnetic theory. Analyzing
the energy exchange phenomenon, this paper presents two
corresponding communication channel models for the RI
system. Based on these channel models, the system
architecture of the RI system is implemented at a chip level
which consists of three components: resonator, analog
switch, and digital process. © 2004-2012
IEEE.},
Doi = {10.1109/TCSI.2013.2246252},
Key = {fds336688}
}
@article{fds336692,
Author = {Jalaleddini, K and Moezzi, K and Aghdam, AG and Alasti, M and Tarokh,
V},
Title = {Rate assignment in wireless networks: Stability analysis and
controller design},
Journal = {Ieee Transactions on Control Systems Technology},
Volume = {21},
Number = {2},
Pages = {521-529},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2013},
Month = {January},
url = {http://dx.doi.org/10.1109/TCST.2011.2181975},
Abstract = {In this brief, data-rate assignment in IS-856 uplink
(reverse link) is studied. The problem is first formulated
using an interference model, and then a dynamic control
strategy is developed for efficient rate assignment. In the
first step, the controller is designed for the special case
when the number of users in the network is fixed. Then, the
designed controller is further developed for a dynamic
network (where the number of users is subject to change) to
achieve the desired performance. To this end, the network is
formulated in the framework of switched systems, where any
new activation or deactivation of users is considered as
switching from one system to another. The controllers
obtained are then modified properly to retain network
stability and performance in the presence of time-delay.
Simulation results are presented to elucidate the
effectiveness of the proposed approach. © 2012
IEEE.},
Doi = {10.1109/TCST.2011.2181975},
Key = {fds336692}
}
@article{fds336696,
Author = {Sabbaghian, M and Sulyman, AI and Tarokh, V},
Title = {Capacity analysis for Gaussian channels with memoryless
nonlinear hardware},
Journal = {Ieee International Conference on Communications},
Pages = {3403-3407},
Publisher = {IEEE},
Year = {2013},
Month = {January},
ISBN = {9781467331227},
url = {http://dx.doi.org/10.1109/ICC.2013.6655074},
Abstract = {This paper presents the analysis of the impact of circuit
nonlinearities on the transmission rate of a communication
system. We consider a general transmission model that
includes transmitter- and receiver-side nonlinearities,
environmental thermal noise and receiver chain noise. Using
this model we establish lower and upper bounds for the
capacity of nonlinear additive white Gaussian noise channels
in various thermal noise and receiver noise regimes. © 2013
IEEE.},
Doi = {10.1109/ICC.2013.6655074},
Key = {fds336696}
}
@article{fds336697,
Author = {Nam, S and Akçakaya, M and Basha, T and Stehning, C and Manning, WJ and Tarokh, V and Nezafat, R},
Title = {Compressed sensing reconstruction for whole-heart imaging
with 3D radial trajectories: a graphics processing unit
implementation.},
Journal = {Magnetic Resonance in Medicine},
Volume = {69},
Number = {1},
Pages = {91-102},
Year = {2013},
Month = {January},
url = {http://dx.doi.org/10.1002/mrm.24234},
Abstract = {A disadvantage of three-dimensional (3D) isotropic
acquisition in whole-heart coronary MRI is the prolonged
data acquisition time. Isotropic 3D radial trajectories
allow undersampling of k-space data in all three spatial
dimensions, enabling accelerated acquisition of the
volumetric data. Compressed sensing (CS) reconstruction can
provide further acceleration in the acquisition by removing
the incoherent artifacts due to undersampling and improving
the image quality. However, the heavy computational overhead
of the CS reconstruction has been a limiting factor for its
application. In this article, a parallelized implementation
of an iterative CS reconstruction method for 3D radial
acquisitions using a commercial graphics processing unit is
presented. The execution time of the graphics processing
unit-implemented CS reconstruction was compared with that of
the C++ implementation, and the efficacy of the undersampled
3D radial acquisition with CS reconstruction was
investigated in both phantom and whole-heart coronary data
sets. Subsequently, the efficacy of CS in suppressing
streaking artifacts in 3D whole-heart coronary MRI with 3D
radial imaging and its convergence properties were studied.
The CS reconstruction provides improved image quality (in
terms of vessel sharpness and suppression of noise-like
artifacts) compared with the conventional 3D gridding
algorithm, and the graphics processing unit implementation
greatly reduces the execution time of CS reconstruction
yielding 34-54 times speed-up compared with C++
implementation.},
Doi = {10.1002/mrm.24234},
Key = {fds336697}
}
@article{fds340011,
Author = {Sulyman, AI and Al-Zahrani, Y and Al-Dosari, S and Tarokh, V and Al-Shebeili, S and Al-Sanie, A},
Title = {Two-stage constellation partition algorithm for
reduced-complexity multiple-input multiple-output–maximum-likelihood
detection systems},
Journal = {Iet Communications},
Volume = {6},
Number = {18},
Pages = {3350-3357},
Publisher = {Institution of Engineering and Technology
(IET)},
Year = {2012},
Month = {December},
url = {http://dx.doi.org/10.1049/iet-com.2012.0173},
Doi = {10.1049/iet-com.2012.0173},
Key = {fds340011}
}
@article{fds336698,
Author = {Nadimi, ES and Blanes-Vidal, V and Tarokh, V},
Title = {Semidefinite programming-based localization algorithm in
networks with inhomogeneous media},
Journal = {Proceeding of the 2012 Acm Research in Applied Computation
Symposium, Racs 2012},
Pages = {191-196},
Publisher = {ACM Press},
Year = {2012},
Month = {December},
ISBN = {9781450314923},
url = {http://dx.doi.org/10.1145/2401603.2401647},
Abstract = {In this paper, we study the asymptotic properties of a
semidefinite programming (SDP) based localization algorithm
in a network with inhomogeneous RF transmission medium given
incomplete and inaccurate pairwise distance measurements
between sensorssensors and sensors-anchors. We proposed a
novel relaxed SDP approach based on a graph realization
problem with noisy timeof- arrival (TOA) measurements with
additive Gaussian noise and inaccurate transmission
permittivity and permeability coefficients both with
additive standard Gaussian noise (varying dielectric
constant). Modeling the inhomogeneous RF transmission medium
as a series of homogeneous transmission mediums between any
two given points and given the true distances between a pair
of sensors and the set of known pair-wise distances between
sensorssensors and sensors-anchors, an upper bound for the
expected value of the optimal objective relaxed SDP problem
is obtained, showing that its asymptotic properties
potentially grows as fast as the summation of true distances
between the pair of sensorssensors and sensor-anchors and
the TOA noisy measurements mean and standard deviation.
Copyright 2012 ACM.},
Doi = {10.1145/2401603.2401647},
Key = {fds336698}
}
@article{fds336699,
Author = {Ishibashi, K and Ochiai, H and Tarokh, V},
Title = {Energy harvesting cooperative communications},
Journal = {Ieee International Symposium on Personal, Indoor and Mobile
Radio Communications, Pimrc},
Pages = {1819-1823},
Publisher = {IEEE},
Year = {2012},
Month = {December},
ISBN = {9781467325691},
url = {http://dx.doi.org/10.1109/PIMRC.2012.6362646},
Abstract = {In this paper, we propose a new cooperative wireless
transmission in a scenario where the source salvages the
energy during the relay's transmission considering the fact
that the source does not need to retrieve the transmitted
message. We also evaluate a direct wireless transmission
with wireless energy transfer as a reference. We analyze the
performance of these transmission techniques in terms of
outage probability. Our analytical results reveal the
advantage of energy salvage in combination with spatial
diversity over the direct transmission even if the energy
transfer efficiency is considerably low. © 2012
IEEE.},
Doi = {10.1109/PIMRC.2012.6362646},
Key = {fds336699}
}
@article{fds336700,
Author = {Fan, P and Panayirci, E and Li, P and Wang, C and Tarokh,
V},
Title = {Guest editorial: Special issue on high mobility wireless
communications},
Journal = {Journal of Modern Transportation},
Volume = {20},
Number = {4},
Pages = {197-198},
Year = {2012},
Month = {December},
url = {http://dx.doi.org/10.3969/j.issn.2095-087X.2012.04.001},
Doi = {10.3969/j.issn.2095-087X.2012.04.001},
Key = {fds336700}
}
@article{fds336702,
Author = {Nadimi, ES and Tarokh, V},
Title = {Bayesian source localization in networks with heterogeneous
transmission medium},
Journal = {Navigation},
Volume = {59},
Number = {3},
Pages = {163-175},
Publisher = {WILEY},
Year = {2012},
Month = {September},
url = {http://dx.doi.org/10.1002/navi.13},
Abstract = {Precise positioning and tracking information in networks
with a heterogeneous transmission medium presents a novel
networking paradigm. Most of the localization algorithms are
vulnerable to the variations of signal propagation speed,
dielectric constant, and path-loss coefficient resulting in
unreliable location estimation. In this paper, we propose a
novel robust probabilistic Bayesian-based approach using
received-signal-strength (RSS) measurements with varying
path-loss exponent in wireless networks with heterogeneous
medium. An application of such a localization method is
relative positioning of nodes in a wireless network with a
heterogeneous medium such as gastrointestinal tract
monitoring using wireless video capsule endoscopy. The
results of this study showed that the localization root mean
square error (RMSE) of our Bayesian-based method when a
sensor node was covered by four anchors was 1.0 mm which is
smaller than that of other existing localization approaches
under the same conditions such as classical MDS (43.1 mm),
dwMDS (24.7 mm), MLE (21.8 mm) and POCS (1.7 mm). Copyright
© 2012 Institute of Navigation.},
Doi = {10.1002/navi.13},
Key = {fds336702}
}
@article{fds336701,
Author = {Chae, CB and Hwang, I and Heath, RW and Tarokh, V},
Title = {Interference aware-coordinated beamforming in a multi-cell
system},
Journal = {Ieee Transactions on Wireless Communications},
Volume = {11},
Number = {10},
Pages = {3692-3703},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2012},
Month = {August},
url = {http://dx.doi.org/10.1109/TWC.2012.081312.112119},
Abstract = {In this paper, we propose jointly optimized linear
transceiver algorithms called interference aware-coordinated
beamforming (IA-CBF) for a two-cell system where each base
station is equipped with multiple transmit antennas. To
generalize IA-CBF to more than two-cell scenarios, a new
beam-switching mechanism combined with IA-CBF is proposed.
For a two-cell system, we derive a minimum-mean-square-error-type
IA-CBF algorithm based on a lower bound on the achievable
sum rate. We propose optimal (under an assumption of zero
other-cell interference) and suboptimal transmit/receive
beamforming vectors through zero-forcing IA-CBF algorithms.
We also investigate the optimality of the proposed IA-CBF
algorithms with respect to the number of receive antennas.
Numerical results confirm that the proposed system with two
transmit/receive antennas achieves the full degrees of
freedom (a.k.a. multiplexing gain) of the two-cell
multiple-input multiple-output channel while showing a
better sum rate performance than competitive solutions such
as non-cooperative eigen-beamforming and interference
nulling. A three-dimensional ray tracing tool is also used
to evaluate the proposed multi-cell IA-CBF algorithm. ©
2002-2012 IEEE.},
Doi = {10.1109/TWC.2012.081312.112119},
Key = {fds336701}
}
@article{fds336703,
Author = {Cho, S and Hwang, I and Tarokh, V and You, C},
Title = {A practical transmit beamforming strategy for closed-loop
MIMO communication},
Journal = {International Journal of Communication Systems},
Volume = {25},
Number = {8},
Pages = {1091-1099},
Publisher = {WILEY},
Year = {2012},
Month = {August},
url = {http://dx.doi.org/10.1002/dac.1310},
Abstract = {A new beamforming strategy is proposed for multiuser systems
with N transmit antennas at the transmitter and M ≤ N
single antenna receivers. The proposed scheme remarkably
improves on the classical spatial division multiple access,
and achieves the same data rates as spatial multiplexing for
all users but with significantly superior
performance/diversity gain. When compared with the Bell labs
layered space-time system, the symbol rate is the same and
the performance is much superior because of the presence of
diversity gain. In addition, unlike the Bell labs layered
space-time system, the receivers do not need to know each
other's vector channels. Finally, the proposed algorithm is
based on dirty-paper coding, but does not require much
complexity and is implementable. Copyright © 2011 John
Wiley & Sons, Ltd.},
Doi = {10.1002/dac.1310},
Key = {fds336703}
}
@article{fds336704,
Author = {Mercier, H and Tarokh, V and Labeau, F},
Title = {Bounds on the capacity of discrete memoryless channels
corrupted by synchronization and substitution
errors},
Journal = {Ieee Transactions on Information Theory},
Volume = {58},
Number = {7},
Pages = {4306-4330},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2012},
Month = {June},
url = {http://dx.doi.org/10.1109/TIT.2012.2191682},
Abstract = {We study the capacity of discrete memoryless channels with
synchronization errors and additive noise. We first show
that with very large alphabets, their capacity can be
achieved by independent and identically distributed input
sources, and establish proven tight lower and upper capacity
bounds. We also derive tight numerical capacity bounds for
channels where the synchronization between the input and
output is partly preserved, for instance using incorruptible
synchronization markers. Such channels include channels with
duplication errors, channels that only insert or delete
zeros, and channels with bitshift errors studied in magnetic
recording. Channels with small alphabets and corrupted by
synchronization errors have an infinite memory. Revisiting
the theoretical work of Dobrushin and adapting techniques
used to compute capacity bounds for finite-state
source/channel models, we compute improved numerical
capacity lower bounds for discrete memoryless channels with
small alphabets, synchronization errors, and memoryless
noise. An interesting and somewhat surprising result is that
as long as the input sequences are not completely deleted,
the capacity of channels corrupted by discrete timing errors
is always nonzero even if all the symbols are corrupted. ©
2012 IEEE.},
Doi = {10.1109/TIT.2012.2191682},
Key = {fds336704}
}
@article{fds336705,
Author = {Babadi, B and Tarokh, V},
Title = {Vertical spectrum sharing via distributed asynchronous
interference avoidance in cognitive radio
networks},
Journal = {2012 Ieee Consumer Communications and Networking Conference,
Ccnc'2012},
Pages = {869-873},
Publisher = {IEEE},
Year = {2012},
Month = {May},
ISBN = {9781457720710},
url = {http://dx.doi.org/10.1109/CCNC.2012.6181181},
Abstract = {In this paper, we study the problem of distributed spectrum
allocation under a vertical spectrum sharing scenario in a
cognitive radio network. The secondary users share the
spectrum licensed to the primary user by observing the
activity statistics of the primary users, and regulate their
transmission strategy in order to abide by the spectrum
sharing etiquette. When the primary user is inactive in a
subset of the available frequency bands, the secondary users
share the spectrum using the recently proposed GADIA
algorithm [1]. In this paper, we present analytical and
numerical results on the performance of the GADIA algorithm
in conjunction with the above-mentioned vertical spectrum
sharing scenario. These results reveal near-optimal
performance guarantees for the overall vertical spectrum
sharing scenario. © 2012 IEEE.},
Doi = {10.1109/CCNC.2012.6181181},
Key = {fds336705}
}
@article{fds336706,
Author = {Babadi, B and McKinney, SM and Tarokh, V and Ellenbogen,
JM},
Title = {DiBa: a data-driven Bayesian algorithm for sleep spindle
detection.},
Journal = {Ieee Transactions on Bio Medical Engineering},
Volume = {59},
Number = {2},
Pages = {483-493},
Year = {2012},
Month = {February},
url = {http://dx.doi.org/10.1109/tbme.2011.2175225},
Abstract = {Although the spontaneous brain rhythms of sleep have
commanded much recent interest, their detection and analysis
remains suboptimal. In this paper, we develop a data-driven
Bayesian algorithm for sleep spindle detection on the
electroencephalography (EEG). The algorithm exploits the
Karhunen-Loève transform and Bayesian hypothesis testing to
produce the instantaneous probability of a spindle's
presence with maximal resolution. In addition to possessing
flexibility, transparency, and scalability, this algorithm
could perform at levels superior to standard methods for EEG
event detection.},
Doi = {10.1109/tbme.2011.2175225},
Key = {fds336706}
}
@article{fds340012,
Author = {Babadi, B and McKinney, S and Tarokh, V and Ellenbogen,
JM},
Title = {A DATA-DRIVEN BAYESIAN ALGORITHM FOR SLEEP SPINDLE
DETECTION},
Journal = {Sleep},
Volume = {35},
Pages = {A134-A134},
Publisher = {OXFORD UNIV PRESS INC},
Year = {2012},
Month = {January},
Key = {fds340012}
}
@article{fds336707,
Author = {Babadi, B and Tarokh, V},
Title = {Distributed dynamic spectrum allocation for secondary users
in a vertical spectrum sharing scenario},
Journal = {Ieice Transactions on Communications},
Volume = {E95-B},
Number = {4},
Pages = {1044-1055},
Publisher = {Institute of Electronics, Information and Communications
Engineers (IEICE)},
Year = {2012},
Month = {January},
url = {http://dx.doi.org/10.1587/transcom.E95.B.1044},
Abstract = {In this paper, we study the problem of distributed spectrum
allocation under a vertical spectrum sharing scenario in a
cognitive radio network. The secondary users share the
spectrum licensed to the primary user by observing the
activity statistics of the primary users, and regulate their
transmission strategy in order to abide by the spectrum
sharing etiquette. When the primary user is inactive in a
subset of the available frequency bands, from the
perspective of the secondary users the problem reduces to a
distributed horizontal spectrum sharing. For a specific
class of networks, the latter problem is addressed by the
recently proposed GADIA algorithm [1]. In this paper, we
present analytical and numerical results on the performance
of the GADIA algorithm in conjunction with the
abovementioned vertical spectrum sharing scenario. These
results reveal nearoptimal performance guarantees for the
overall vertical spectrum sharing scenario. © 2012 The
Institute of Electronics, Information and Communication
Engineers.},
Doi = {10.1587/transcom.E95.B.1044},
Key = {fds336707}
}
@article{fds340013,
Author = {Sharma, A and Dey, S},
Title = {A comparative study of feature selection and machine
learning techniques for sentiment analysis.},
Journal = {Racs},
Pages = {1-7},
Publisher = {ACM},
Editor = {Cho, Y and Gantenbein, RE and Kuo, T-W and Tarokh,
V},
Year = {2012},
ISBN = {978-1-4503-1492-3},
Key = {fds340013}
}
@article{fds336713,
Author = {Nadimi, ES and Blanes-Vidal, V and Tarokh, V},
Title = {Localization of mobile nodes based on inaccurate
round-trip-time measurements using Bayesian
inference},
Journal = {Proceedings of the 2011 Acm Research in Applied Computation
Symposium, Racs 2011},
Pages = {152-157},
Publisher = {ACM Press},
Year = {2011},
Month = {December},
ISBN = {9781450310871},
url = {http://dx.doi.org/10.1145/2103380.2103412},
Abstract = {In this paper, we present a Bayesian-based localization
method to estimate the unknown location of a mobile station
(MS) in a network given the known location of a set of base
stations. In this study, the MS was covered by a base
station if the signal to interference and noise ratio (SINR)
was larger than a threshold. By assuming a priori knowledge
of the location of the MS and a Gaussian distribution for
the round-trip time (RTT) measurements, a posteriori
estimation of the unknown location of the MS using Bayesian
inference method was obtained. The impact of variation of
various variables on the localization accuracy such as
number of base stations covering the MS, number of base
stations interfering with the communication between the MS
and the covering base stations, fading factor between base
stations and the MS, SINR threshold and the path-loss
coefficient have been studied. In addition, the performance
of the developed Bayesian-based method in terms of
localization accuracy was evaluated when the MS was inside
and outside the convex hull of the base stations. The
results of this study showed an improvement in the mean
localization error and the localization root mean square
error (RMSE) compared to other similar studies. © 2011
ACM.},
Doi = {10.1145/2103380.2103412},
Key = {fds336713}
}
@article{fds336714,
Author = {Shin, WY and Lucani, DE and Médard, M and Stojanovic, M and Tarokh,
V},
Title = {Information-theoretic limits of dense underwater
networks},
Journal = {Conference Record Asilomar Conference on Signals, Systems
and Computers},
Pages = {1835-1839},
Publisher = {IEEE},
Year = {2011},
Month = {December},
ISBN = {9781467303231},
url = {http://dx.doi.org/10.1109/ACSSC.2011.6190340},
Abstract = {Information-theoretic throughput scaling laws are analyzed
in an underwater acoustic network with n regularly located
nodes on a unit square, in which both bandwidth and received
signal power can be severely limited. A narrow-band model is
assumed where the carrier frequency is allowed to scale as a
function of n. We first characterize an attenuation
parameter that depends on the frequency scaling as well as
the transmission distance. In the dense network having unit
area, a cut-set upper bound on the capacity scaling is then
derived. We show that there exists either a bandwidth or a
power limitation, or both, according to the path-loss
attenuation regimes, thus yielding the upper bound that has
three fundamentally different operating regimes. In the
dense network, we also describe an achievable scheme based
on the simple nearest-neighbor multi-hop transmission. The
operating regimes that guarantee the order optimality are
identified, where frequency scaling is instrumental towards
achieving the order optimality in the regimes. © 2011
IEEE.},
Doi = {10.1109/ACSSC.2011.6190340},
Key = {fds336714}
}
@article{fds336715,
Author = {Sabbaghian, M and Kwak, Y and Tarokh, V},
Title = {New codes from dual BCH codes with applications in Low PAPR
OFDM},
Journal = {Ieee Transactions on Wireless Communications},
Volume = {10},
Number = {12},
Pages = {3990-3994},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2011},
Month = {December},
url = {http://dx.doi.org/10.1109/TWC.2011.100611.101388},
Abstract = {Dual Bose-Ray-Chaudhuri (BCH) codes, despite their favorable
peak to average power ratio (PAPR) properties, have not been
used in coded orthogonal frequency division multiplexing
(OFDM) systems. This is due to unavailability of a practical
decoder and large performance gap to the Shannon limit. In
this paper, we propose an advanced approach to solve the
aforementioned problems. We construct a new code with
favorable PAPR properties based on dual BCH codes and
develop the associated maximum a posteriori (MAP) decoding
algorithm. By exploiting this code as the frequency domain
constituent code in a time-frequency turbo structure, we
reduce the gap between the performance and Shannon limit
while the bounded PAPR of OFDM symbols is guaranteed. By
comparative performance evaluation we illustrate that the
performance of this system is comparable with that of
capacity approaching codes while it has 7 dB lower PAPR. ©
2011 IEEE.},
Doi = {10.1109/TWC.2011.100611.101388},
Key = {fds336715}
}
@article{fds336716,
Author = {Moghari, MH and Akçakaya, M and O'Connor, A and Basha, TA and Casanova,
M and Stanton, D and Goepfert, L and Kissinger, KV and Goddu, B and Chuang,
ML and Tarokh, V and Manning, WJ and Nezafat, R},
Title = {Compressed-sensing motion compensation (CosMo): a joint
prospective-retrospective respiratory navigator for coronary
MRI.},
Journal = {Magnetic Resonance in Medicine},
Volume = {66},
Number = {6},
Pages = {1674-1681},
Year = {2011},
Month = {December},
url = {http://dx.doi.org/10.1002/mrm.22950},
Abstract = {Prospective right hemidiaphragm navigator (NAV) is commonly
used in free-breathing coronary MRI. The NAV results in an
increase in acquisition time to allow for resampling of the
motion-corrupted k-space data. In this study, we are
presenting a joint prospective-retrospective NAV motion
compensation algorithm called compressed-sensing motion
compensation (CosMo). The inner k-space region is acquired
using a prospective NAV; for the outer k-space, a NAV is
only used to reject the motion-corrupted data without
reacquiring them. Subsequently, those unfilled k-space lines
are retrospectively estimated using compressed sensing
reconstruction. We imaged right coronary artery in nine
healthy adult subjects. An undersampling probability map and
sidelobe-to-peak ratio were calculated to study the pattern
of undersampling, generated by NAV. Right coronary artery
images were then retrospectively reconstructed using
compressed-sensing motion compensation for gating windows
between 3 and 10 mm and compared with the ones fully
acquired within the gating windows. Qualitative imaging
score and quantitative vessel sharpness were calculated for
each reconstruction. The probability map and
sidelobe-to-peak ratio show that the NAV generates a random
undersampling k-space pattern. There were no statistically
significant differences between the vessel sharpness and
subjective score of the two reconstructions.
Compressed-sensing motion compensation could be an
alternative motion compensation technique for free-breathing
coronary MRI that can be used to reduce scan
time.},
Doi = {10.1002/mrm.22950},
Key = {fds336716}
}
@article{fds336708,
Author = {Babadi, B and Tarokh, V},
Title = {Spectral distribution of the product of two random matrices
based on binary block codes},
Journal = {2011 49th Annual Allerton Conference on Communication,
Control, and Computing, Allerton 2011},
Pages = {917-919},
Publisher = {IEEE},
Year = {2011},
Month = {December},
ISBN = {9781457718168},
url = {http://dx.doi.org/10.1109/Allerton.2011.6120264},
Abstract = {In this paper, we study the spectral distribution of the
product of two random matrices based on binary block codes,
and prove that if the dual distances of the underlying codes
are large enough, the asymptotic spectral distribution will
be close to a deterministic limit in the sense of Lévy
distance. These results extend our previous work on this
topic, and strengthen its applications to joint randomness
testing. © 2011 IEEE.},
Doi = {10.1109/Allerton.2011.6120264},
Key = {fds336708}
}
@article{fds336709,
Author = {Chae, CB and Hwang, I and Heath, RW and Tarokh, V},
Title = {Jointly optimized two-cell MIMO systems},
Journal = {2011 Ieee Globecom Workshops, Gc Wkshps 2011},
Pages = {421-425},
Publisher = {IEEE},
Year = {2011},
Month = {December},
ISBN = {9781467300407},
url = {http://dx.doi.org/10.1109/GLOCOMW.2011.6162484},
Abstract = {Jointly optimized interference aware coordinated beamforming
(IA-CBF) algorithms for a two-cell system are investigated,
where each base/mobile station is equipped with multiple
transmit antennas. We first derive a minimum-mean-square-error
IA-CBF algorithm based on a lower bound on the achievable
sum rate. We next propose optimal (under an assumption of
zero other-cell interference) and suboptimal
transmit/receive beamforming vectors through zero-forcing
IA-CBF algorithms. Numerical results confirm that the
proposed system shows better sum rate performance than
competitive solutions such as non-cooperative
eigen-beamforming and interference nulling. © 2011
IEEE.},
Doi = {10.1109/GLOCOMW.2011.6162484},
Key = {fds336709}
}
@article{fds336710,
Author = {Babadi, B and Tarokh, V},
Title = {Regularized recursive least squares for anomaly detection in
sparse channel tracking applications},
Journal = {Proceedings of the 2011 Acm Research in Applied Computation
Symposium, Racs 2011},
Pages = {277-281},
Publisher = {ACM Press},
Year = {2011},
Month = {December},
ISBN = {9781450310871},
url = {http://dx.doi.org/10.1145/2103380.2103437},
Abstract = {In this paper, we study the problem of anomaly detection in
sparse channel tracking applications via the l 1-regularized
least squares adaptive filter (SPARLS). Anomalies arise due
to unexpected adversarial changes in the channel and quick
detection of these anomalies is desired. We first prove
analytically that the prediction error of the SPARLS
algorithm can be substantially lower than that of the
widely-used Recursive Least Squares (RLS) algorithm.
Furthermore, we present Receiver Operating Characteristic
(ROC) curves for the detection/false alarm trade-off of
anomaly detection in a sparse multi-path fading channel
tracking scenario. These curves reveal the considerable
advantage of the SPARLS algorithm over the RLS algorithm. ©
2011 ACM.},
Doi = {10.1145/2103380.2103437},
Key = {fds336710}
}
@article{fds336711,
Author = {Krishnamurthy, S and Bliss, DW and Tarokh, V},
Title = {Sidelobe level distribution computation for antenna arrays
with arbitrary element distributions},
Journal = {Conference Record Asilomar Conference on Signals, Systems
and Computers},
Pages = {2045-2050},
Year = {2011},
Month = {December},
ISBN = {9781467303231},
url = {http://dx.doi.org/10.1109/ACSSC.2011.6190386},
Abstract = {This paper discusses the conditions in which the sidelobe
level distribution can be calculated in closed form for
arrays with randomly located antenna elements with arbitrary
element probability distributions. By using the number of
times a beampattern crosses a certain level in an upward
direction, sidelobe level distributions are found for
beampatterns with angle-dependent and angle-independent
statistics. The evaluation of the probability of exceeding a
given peak sidelobe is investigated as a function of the
antenna array spatial position variance in the asymptotic
limit of a large number of antennas. Examples are presented
including a multi-input multi-output (MIMO) radar
illustration. © 2011 IEEE.},
Doi = {10.1109/ACSSC.2011.6190386},
Key = {fds336711}
}
@article{fds336712,
Author = {Kim, KT and Noh, W and Tarokh, V},
Title = {Robust scalable physical layer network coding},
Journal = {2011 49th Annual Allerton Conference on Communication,
Control, and Computing, Allerton 2011},
Pages = {1446-1453},
Publisher = {IEEE},
Year = {2011},
Month = {December},
ISBN = {9781457718168},
url = {http://dx.doi.org/10.1109/Allerton.2011.6120338},
Abstract = {We present a new method of physical layer network coding
that transforms the received signal at a relay node before
re-transmission by eliminating the unreliable components of
the signal. This approach improves the physical layer
network coding performance, since only reliable components
of the signal are amplified and retransmitted. It also lends
itself to a robust and scalable implementation. Simulation
results show that the proposed robust scalable physical
layer network coding can provide 1 - 2[dB] and 4 - 14 [dB]
more coding gain than analog network coding and algebraic
network coding schemes in a multilayer wireless network,
respectively, and performs more reliably in a network where
there is more noise to remove. © 2011 IEEE.},
Doi = {10.1109/Allerton.2011.6120338},
Key = {fds336712}
}
@article{fds336718,
Author = {Akçakaya, M and Park, J and Tarokh, V},
Title = {A coding theory approach to noisy compressive sensing using
low density frames},
Journal = {Ieee Transactions on Signal Processing},
Volume = {59},
Number = {11},
Pages = {5369-5379},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2011},
Month = {November},
url = {http://dx.doi.org/10.1109/TSP.2011.2163402},
Abstract = {We consider the compressive sensing of a sparse or
compressible signal x ∈ R M. We explicitly construct a
class of measurement matrices inspired by coding theory,
referred to as low density frames, and develop decoding
algorithms that produce an accurate estimate x̂ even in the
presence of additive noise. Low density frames are sparse
matrices and have small storage requirements. Our decoding
algorithms can be implemented in O(Md2u) complexity, where
dv is the left degree of the underlying bipartite graph.
Simulation results are provided, demonstrating that our
approach outperforms state-of-the-art recovery algorithms
for numerous cases of interest. In particular, for Gaussian
sparse signals and Gaussian noise, we are within 2-dB range
of the theoretical lower bound in most cases. © 2011
IEEE.},
Doi = {10.1109/TSP.2011.2163402},
Key = {fds336718}
}
@article{fds336719,
Author = {Bai, D and Ghassemzadeh, SS and Miller, RR and Tarokh,
V},
Title = {Beam selection gain versus antenna selection
gain},
Journal = {Ieee Transactions on Information Theory},
Volume = {57},
Number = {10},
Pages = {6603-6618},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2011},
Month = {October},
url = {http://dx.doi.org/10.1109/TIT.2011.2165814},
Abstract = {We consider beam selection using a fixed beamforming network
(FBN) at a base station with M array antennas. In our
setting, a Butler matrix is deployed at the RF stage to form
M beams, and then the best beam is selected for
transmission. We introduce some properties of the noncentral
chi-square distribution and prove the resulting properties
of the beam selection gain verifying that beam selection is
superior to antenna selection in Rician channels with any
K-factors. Furthermore, we find asymptotically tight
stochastic bounds of the beam selection gain, which yield
approximate closed form expressions of the expected
selection gain and the ergodic capacity. Beam selection has
the order of growth of the ergodic capacity Θ (log (log M))
regardless of user location in contrast to Θ (log (log M))
for antenna selection. © 2011 IEEE.},
Doi = {10.1109/TIT.2011.2165814},
Key = {fds336719}
}
@article{fds336720,
Author = {Kim, SJ and Devroye, N and Mitran, P and Tarokh, V},
Title = {Achievable rate regions and performance comparison of half
duplex bi-directional relaying protocols},
Journal = {Ieee Transactions on Information Theory},
Volume = {57},
Number = {10},
Pages = {6405-6418},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2011},
Month = {October},
url = {http://dx.doi.org/10.1109/TIT.2011.2165132},
Abstract = {In a bi-directional relay channel, two nodes wish to
exchange independent messages over a shared wireless
half-duplex channel with the help of a relay. In this paper,
we derive achievable rate regions for four new half-duplex
protocols and compare these to four existing half-duplex
protocols and outer bounds. In time, our protocols consist
of either two or three phases. In the two phase protocols,
both users simultaneously transmit during the first phase
and the relay alone transmits during the second phase, while
in the three phase protocol the two users sequentially
transmit followed by a transmission from the relay. The
relay may forward information in one of four manners; we
outline existing amplify and forward (AF), decode and
forward (DF), lattice based, and compress and forward (CF)
relaying schemes and introduce the novel mixed forward
scheme. The latter is a combination of CF in one direction
and DF in the other. We derive achievable rate regions for
the CF and Mixed relaying schemes for the two and three
phase protocols. We provide a comprehensive treatment of
eight possible half-duplex bi-directional relaying protocols
in Gaussian noise, obtaining their relative performance
under different SNR and relay geometries. © 2011
IEEE.},
Doi = {10.1109/TIT.2011.2165132},
Key = {fds336720}
}
@article{fds336721,
Author = {Mileounis, G and Kalouptsidis, N and Babadi, B and Tarokh,
V},
Title = {Blind identification of sparse channels and symbol detection
via the em algorithm},
Journal = {17th Dsp 2011 International Conference on Digital Signal
Processing, Proceedings},
Publisher = {IEEE},
Year = {2011},
Month = {September},
ISBN = {9781457702747},
url = {http://dx.doi.org/10.1109/ICDSP.2011.6004920},
Abstract = {In this paper, we address the problem of blind
identification of sparse channels. For this purpose, the
Expectation-Maximization is modified to accommodate channel
sparsity. The resulting algorithm is applicable for linear
and nonlinear channels. Computer simulations on various
channel set ups illustrate that the proposed algorithm
achieves performance close to the genie-aided estimator. ©
2011 IEEE.},
Doi = {10.1109/ICDSP.2011.6004920},
Key = {fds336721}
}
@article{fds336722,
Author = {Akçakaya, M and Basha, TA and Goddu, B and Goepfert, LA and Kissinger,
KV and Tarokh, V and Manning, WJ and Nezafat, R},
Title = {Low-dimensional-structure self-learning and thresholding:
regularization beyond compressed sensing for MRI
reconstruction.},
Journal = {Magnetic Resonance in Medicine},
Volume = {66},
Number = {3},
Pages = {756-767},
Year = {2011},
Month = {September},
url = {http://dx.doi.org/10.1002/mrm.22841},
Abstract = {An improved image reconstruction method from undersampled
k-space data, low-dimensional-structure self-learning and
thresholding (LOST), which utilizes the structure from the
underlying image is presented. A low-resolution image from
the fully sampled k-space center is reconstructed to learn
image patches of similar anatomical characteristics. These
patches are arranged into "similarity clusters," which are
subsequently processed for dealiasing and artifact removal,
using underlying low-dimensional properties. The efficacy of
the proposed method in scan time reduction was assessed in a
pilot coronary MRI study. Initially, in a retrospective
study on 10 healthy adult subjects, we evaluated
retrospective undersampling and reconstruction using LOST,
wavelet-based l(1)-norm minimization, and total variation
compressed sensing. Quantitative measures of vessel
sharpness and mean square error, and qualitative image
scores were used to compare reconstruction for rates of 2,
3, and 4. Subsequently, in a prospective study, coronary MRI
data were acquired using these rates, and LOST-reconstructed
images were compared with an accelerated data acquisition
using uniform undersampling and sensitivity encoding
reconstruction. Subjective image quality and sharpness data
indicate that LOST outperforms the alternative techniques
for all rates. The prospective LOST yields images with
superior quality compared with sensitivity encoding or
l(1)-minimization compressed sensing. The proposed LOST
technique greatly improves image reconstruction for
accelerated coronary MRI acquisitions.},
Doi = {10.1002/mrm.22841},
Key = {fds336722}
}
@article{fds336723,
Author = {Kalouptsidis, N and Mileounis, G and Babadi, B and Tarokh,
V},
Title = {Adaptive algorithms for sparse system identification},
Journal = {Signal Processing},
Volume = {91},
Number = {8},
Pages = {1910-1919},
Publisher = {Elsevier BV},
Year = {2011},
Month = {August},
url = {http://dx.doi.org/10.1016/j.sigpro.2011.02.013},
Abstract = {In this paper, identification of sparse linear and nonlinear
systems is considered via compressive sensing methods.
Efficient algorithms are developed based on Kalman filtering
and Expectation-Maximization. The proposed algorithms are
applied to linear and nonlinear channels which are
represented by sparse Volterra models and incorporate the
effect of power amplifiers. Simulation studies confirm
significant performance gains in comparison to conventional
non-sparse methods. © 2011 Elsevier B.V. All rights
reserved.},
Doi = {10.1016/j.sigpro.2011.02.013},
Key = {fds336723}
}
@article{fds336724,
Author = {Sabbaghian, M and Kwak, Y and Smida, B and Tarokh,
V},
Title = {Near shannon limit and low peak to average power ratio turbo
block coded OFDM},
Journal = {Ieee Transactions on Communications},
Volume = {59},
Number = {8},
Pages = {2042-2045},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2011},
Month = {August},
url = {http://dx.doi.org/10.1109/TCOMM.2011.080111.090356},
Abstract = {In this paper, we present an advanced solution for the long
standing problem of large peak to average power ratio (PAPR)
in orthogonal frequency division multiplexing (OFDM)
systems. Although the design of low PAPR codewords has been
extensively studied and the existence of asymptotically good
codes with low PAPR is also proven, still no code has been
constructed to satisfy all requirements. The main goal of
the paper is to develop a coding scheme that not only
generates low PAPR codewords, but it also performs
relatively close to the Shannon limit. We achieve this goal
by implementing a time-frequency turbo block coded OFDM. In
this scheme, we design the frequency domain component to
have a tightly bounded PAPR. The time domain component code
is designed to obtain good performance while the decoding
algorithm has reasonable complexity. Through comparative
performance evaluation we show that utilizing the proposed
method, we achieve considerable improvement in terms of PAPR
while we slightly loose the performance compared to capacity
achieving codes with similar overall block length. © 2011
IEEE.},
Doi = {10.1109/TCOMM.2011.080111.090356},
Key = {fds336724}
}
@article{fds336725,
Author = {Jeon, SW and Devroye, N and Vu, M and Chung, SY and Tarokh,
V},
Title = {Cognitive networks achieve throughput scaling of a
homogeneous network},
Journal = {Ieee Transactions on Information Theory},
Volume = {57},
Number = {8},
Pages = {5103-5115},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2011},
Month = {August},
url = {http://dx.doi.org/10.1109/TIT.2011.2158874},
Abstract = {Two distinct, but overlapping, networks that operate at the
same time, space, and frequency is considered. The first
network consists of n randomly distributed primary users,
which form an ad hoc network. The second network again
consists of m randomly distributed ad hoc secondary users or
cognitive users. The primary users have priority access to
the spectrum and do not need to change their communication
protocol in the presence of the secondary users. The
secondary users, however, need to adjust their protocol
based on knowledge about the locations of the primary users
to bring little loss to the primary network's throughput. By
introducing preservation regions around primary receivers, a
modified multihop routing protocol is proposed for the
cognitive users. Assuming m=nβ with β>1, it is shown that
the secondary network achieves almost the same throughput
scaling law as a stand-alone network while the primary
network throughput is subject to only a vanishingly small
fractional loss. Specifically, the primary network achieves
the sum throughput of order n1/2 and, for any δ>0, the
secondary network achieves the sum throughput of order
m1/2-δ with an arbitrarily small fraction of outage. Thus,
almost all secondary source-destination pairs can
communicate at a rate of order m -1/2-δ. © 2011
IEEE.},
Doi = {10.1109/TIT.2011.2158874},
Key = {fds336725}
}
@article{fds336726,
Author = {Shin, WY and Jeon, SW and Devroye, N and Vu, MH and Chung, SY and Lee, YH and Tarokh, V},
Title = {Improved capacity scaling in wireless networks with
infrastructure},
Journal = {Ieee Transactions on Information Theory},
Volume = {57},
Number = {8},
Pages = {5088-5102},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2011},
Month = {August},
url = {http://dx.doi.org/10.1109/TIT.2011.2158881},
Abstract = {This paper analyzes the impact and benefits of
infrastructure support in improving the throughput scaling
in networks of n randomly located wireless nodes. The
infrastructure uses multiantenna base stations (BSs), in
which the number of BSs and the number of antennas at each
BS can scale at arbitrary rates relative to n. Under the
model, capacity scaling laws are analyzed for both dense and
extended networks. Two BS-based routing schemes are first
introduced in this study: an infrastructure-supported
single-hop (ISH) routing protocol with multiple-access
uplink and broadcast downlink and an infrastructure-
supported multihop (IMH) routing protocol. Then, their
achievable throughput scalings are analyzed. These schemes
are compared against two conventional schemes without BSs:
the multihop (MH) transmission and hierarchical cooperation
(HC) schemes. It is shown that a linear throughput scaling
is achieved in dense networks, as in the case without help
of BSs. In contrast, the proposed BS-based routing schemes
can, under realistic network conditions, improve the
throughput scaling significantly in extended networks. The
gain comes from the following advantages of these BS-based
protocols. First, more nodes can transmit simultaneously in
the proposed scheme than in the MH scheme if the number of
BSs and the number of antennas are large enough. Second, by
improving the long-distance signal-to-noise ratio (SNR), the
received signal power can be larger than that of the HC,
enabling a better throughput scaling under extended
networks. Furthermore, by deriving the corresponding
information-theoretic cut-set upper bounds, it is shown
under extended networks that a combination of four schemes
IMH, ISH, MH, and HC is order-optimal in all operating
regimes. © 2011 IEEE.},
Doi = {10.1109/TIT.2011.2158881},
Key = {fds336726}
}
@article{fds336727,
Author = {Babadi, B and Ghassemzadeh, SS and Tarokh, V},
Title = {Group randomness properties of pseudo-noise and gold
sequences},
Journal = {12th Canadian Workshop on Information Theory, Cwit
2011},
Pages = {42-46},
Year = {2011},
Month = {July},
ISBN = {9781457707438},
url = {http://dx.doi.org/10.1109/CWIT.2011.5872120},
Abstract = {In this paper, we study the group randomness of
pseudo-random sequences based on shortened first-order
Reed-Muller codes and the Gold sequences. In particular, we
characterize the empirical spectral distribution of random
matrices from shortened first-order Reed-Muller codes. We
show that although these sequences have very appealing
randomness properties across individual codewords, they do
not possess certain group randomness properties of i.i.d.
sequences. In other words, the spectral distribution of
random matrices from these sequences dramatically differs
from that of the random i.i.d. generated matrices. In
contrast, Gold sequences manifest the group randomness
properties of random i.i.d. sequences. Upper bounds on the
Kolmogorov complexity of these sequences are established,
and it has been shown that these bounds are much lower than
those of the random i.i.d. sequences, when the sequence
length is large enough. We discuss the implications of these
observations and motivate the need to develop novel
randomness tests encompassing both individual and group
randomness of sequences. © 2011 IEEE.},
Doi = {10.1109/CWIT.2011.5872120},
Key = {fds336727}
}
@article{fds336728,
Author = {Kim, SJ and Ghassemzadeh, SS and Miller, RR and Tarokh,
V},
Title = {Optimum cognitive radio transmission scheme for reducing
average interference power},
Journal = {12th Canadian Workshop on Information Theory, Cwit
2011},
Pages = {24-25},
Publisher = {IEEE},
Year = {2011},
Month = {July},
ISBN = {9781457707438},
url = {http://dx.doi.org/10.1109/CWIT.2011.5872115},
Abstract = {Reducing interference induced by secondary users is one of
the most challenging problems in spectrum sharing. In this
paper, we derive the optimum transmission strategy that
minimizes the average interference power created by
cognitive radios at a given point of space i.e. the location
of a primary receiver. Surprisingly, this is not given by
the water-filling solution. © 2011 IEEE.},
Doi = {10.1109/CWIT.2011.5872115},
Key = {fds336728}
}
@article{fds336729,
Author = {Ku, ML and Chen, Q and Ghassemzadeh, SS and Tarokh, V and Wang,
LC},
Title = {Service coverage for cognitive radio networks with
cooperative relays in shadowed hotspot areas},
Journal = {2011 Ieee Wireless Communications and Networking Conference,
Wcnc 2011},
Pages = {1759-1764},
Publisher = {IEEE},
Year = {2011},
Month = {June},
ISBN = {9781612842547},
url = {http://dx.doi.org/10.1109/WCNC.2011.5779428},
Abstract = {In this paper, we investigate the service coverage for
interweaving cognitive radio networks with cooperative
relays in shadowed areas within the metropolitan region. We
highlight the influence of relays on the primary and
secondary systems in severe shadow fading channels. The
outage probability is utilized as a comprehensive
performance metric to characterize the coverage quality for
the cognitive radio system with relays. We show that
cooperative spectrum sensing among the secondary transmitter
and relays can improve the vacant spectrum detection
probability and the false alarm probability, thereby making
the additionally introduced interference by relays to be
constrained within a tolerable limit. Overall, our analysis
unveils that both the spectrum utilization rate and the
spatial coverage can be significantly improved through the
use of the relays, and there exists the spatial selectivity
phenomena for both the primary and secondary systems. ©
2011 IEEE.},
Doi = {10.1109/WCNC.2011.5779428},
Key = {fds336729}
}
@article{fds336730,
Author = {Kwak, Y and Sabbaghian, M and Smida, B and Tarokh,
V},
Title = {Low peak to average power ratio Turbo Block QPSK coded
OFDM},
Journal = {2011 Ieee Consumer Communications and Networking Conference,
Ccnc'2011},
Pages = {637-641},
Publisher = {IEEE},
Year = {2011},
Month = {June},
ISBN = {9781424487905},
url = {http://dx.doi.org/10.1109/CCNC.2011.5766559},
Abstract = {In this work, we propose a QPSK OFDM code that has both low
peak to average power ratio and good bit error rate
performance. We consider a Time-frequency Turbo Block code.
This code is composed of the cosets of the first-order
binary Reed-Muller (RM) code in the frequency domain, and
Bose-Chaudhuri-Hocquenghem (BCH) code in the time domain.
Our contributions are two-fold: 1) we introduce two encoding
schemes that guarantee a PAPR of 3 dB for QPSK
constellation, 2) we propose moderate complexity decoding
procedures for these schemes. We evaluate the performance of
the proposed schemes for the additive white Gaussian noise
channel. Our code performs only slightly worse than the best
known Turbo codes but has significantly lower PAPR. This
gives a significant total power gain over the best known
Turbo codes. © 2011 IEEE.},
Doi = {10.1109/CCNC.2011.5766559},
Key = {fds336730}
}
@article{fds336731,
Author = {Babadi, B and Tarokh, V},
Title = {Spectral distribution of random matrices from binary linear
block codes},
Journal = {Ieee Transactions on Information Theory},
Volume = {57},
Number = {6},
Pages = {3955-3962},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2011},
Month = {June},
url = {http://dx.doi.org/10.1109/TIT.2011.2137330},
Abstract = {Let C be a binary linear block code of length n, dimension k
and minimum Hamming distance d over GF(2)n. Let d⊥ denote
the minimum Hamming distance of the dual code of C over
GF(2)n. Let εGF(2)n {-1,1}n be the component-wise mapping
ε(vi):=(-1)vi, for v=(v1,v 2,vn)∈GF(2)n. Finally, for
p<n, let ΦC be a p × n random matrix whose rows are
obtained by mapping a uniformly drawn set of size p of the
codewords of C under ε. It is shown that for d⊥ large
enough and y:=p/n ∈ (0,1) fixed, as n → ∞ the
empirical spectral distribution of the Gram matrix of 1/√n
ΦC resembles that of a random i.i.d. Rademacher matrix
(i.e., the MarchenkoPastur distribution). Moreover, an
explicit asymptotic uniform bound on the distance of the
empirical spectral distribution of the Gram matrix of 1/√n
ΦC to the MarchenkoPastur distribution as a function of y
and d⊥ is presented. © 2011 IEEE.},
Doi = {10.1109/TIT.2011.2137330},
Key = {fds336731}
}
@article{fds336732,
Author = {Kim, KT and Hwang, CS and Tarokh, V},
Title = {Network error correction from matrix network
coding},
Journal = {2011 Information Theory and Applications Workshop, Ita 2011
Conference Proceedings},
Pages = {394-402},
Publisher = {IEEE},
Year = {2011},
Month = {May},
ISBN = {9781457703614},
url = {http://dx.doi.org/10.1109/ITA.2011.5743611},
Abstract = {We present matrix network coding methods that are naturally
amenable to a distributed implementation method, i.e., do
not require the knowledge of network topology, and that are
suitable for network error correction. First, the Singleton
bound can be K-fold increased by employing a KK matrix
coefficient. Moreover, we prove that matrix network coding
outperforms linear network coding, since it corrects more
errors than linear network coding, while the amount of
header overhead per packet can be kept the same by reducing
the finite field size. This comes from the fact that the
finite field size of matrix network coding required to
guarantee the sufficient decoding probability is much
smaller than linear network coding. Secondly, matrix network
coding is refinable in the sense that, by receiving a larger
number of network coded packets, larger error correction
capabilities are achieved. Simulation results show that
matrix network coding can provide 0.7-2[dB] more coding gain
than the linear network coding schemes. © 2011
IEEE.},
Doi = {10.1109/ITA.2011.5743611},
Key = {fds336732}
}
@article{fds336733,
Author = {Smida, B and Efthymoglou, GP and Ghassemzadeh, SS and Tarokh,
V},
Title = {On effects of antenna pointing accuracy for on-the-move
satellite networks},
Journal = {Ieee Transactions on Vehicular Technology},
Volume = {60},
Number = {4},
Pages = {1677-1686},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2011},
Month = {May},
url = {http://dx.doi.org/10.1109/TVT.2011.2128356},
Abstract = {In this paper, we study the adjacent geostationary satellite
interference to/from on-the-move platforms with
motion-induced antenna pointing errors. First, using
satellite geometry, we derive tight upper and lower bounds
for the average uplink and downlink interferences. Then, we
derive the exact distribution of the adjacent satellite
interference, and using a Gaussian approximation, we compute
bounds for the outage probability for both links. Finally,
the outage performance is investigated by simulations and by
evaluation of the derived expressions. The performance
results show the accuracy of the analytical expressions and
quantify the link degradation due to random antenna pointing
errors in on-the-move satellite communication systems. ©
2011 IEEE.},
Doi = {10.1109/TVT.2011.2128356},
Key = {fds336733}
}
@article{fds336734,
Author = {Akçakaya, M and Nam, S and Hu, P and Moghari, MH and Ngo, LH and Tarokh,
V and Manning, WJ and Nezafat, R},
Title = {Compressed sensing with wavelet domain dependencies for
coronary MRI: a retrospective study.},
Journal = {Ieee Transactions on Medical Imaging},
Volume = {30},
Number = {5},
Pages = {1090-1099},
Year = {2011},
Month = {May},
url = {http://dx.doi.org/10.1109/tmi.2010.2089519},
Abstract = {Coronary magnetic resonance imaging (MRI) is a noninvasive
imaging modality for diagnosis of coronary artery disease.
One of the limitations of coronary MRI is its long
acquisition time due to the need of imaging with high
spatial resolution and constraints on respiratory and
cardiac motions. Compressed sensing (CS) has been recently
utilized to accelerate image acquisition in MRI. In this
paper, we develop an improved CS reconstruction method,
Bayesian least squares-Gaussian scale mixture (BLS-GSM),
that uses dependencies of wavelet domain coefficients to
reduce the observed blurring and reconstruction artifacts in
coronary MRI using traditional l(1) regularization. Images
of left and right coronary MRI was acquired in 7 healthy
subjects with fully-sampled k-space data. The data was
retrospectively undersampled using acceleration rates of 2,
4, 6, and 8 and reconstructed using l(1) thresholding, l(1)
minimization and BLS-GSM thresholding. Reconstructed right
and left coronary images were compared with fully-sampled
reconstructions in vessel sharpness and subjective image
quality (1-4 for poor-excellent). Mean square error (MSE)
was also calculated for each reconstruction. There were no
significant differences between the fully sampled image
score versus rate 2, 4, or 6 for BLS-GSM for both right and
left coronaries (=N.S.). However, for l(1) thresholding
significant differences were observed for rates higher than
2 and 4 for right and left coronaries respectively. l(1)
minimization also yields images with lower scores compared
to the reference for rates higher than 4 for both
coronaries. These results were consistent with the
quantitative vessel sharpness readings. BLS-GSM allows
acceleration of coronary MRI with acceleration rates beyond
what can be achieved with l(1) regularization.},
Doi = {10.1109/tmi.2010.2089519},
Key = {fds336734}
}
@article{fds336735,
Author = {Akçakaya, M and Hu, P and Chuang, ML and Hauser, TH and Ngo, LH and Manning, WJ and Tarokh, V and Nezafat, R},
Title = {Accelerated noncontrast-enhanced pulmonary vein MRA with
distributed compressed sensing.},
Journal = {Journal of Magnetic Resonance Imaging : Jmri},
Volume = {33},
Number = {5},
Pages = {1248-1255},
Year = {2011},
Month = {May},
url = {http://dx.doi.org/10.1002/jmri.22559},
Abstract = {<h4>Purpose</h4>To investigate the efficacy of distributed
compressed sensing (CS) to accelerate free-breathing,
electrocardiogram (ECG)-triggered noncontrast pulmonary vein
(PV) magnetic resonance angiography (MRA).<h4>Materials and
methods</h4>Fully sampled ECG-triggered noncontrast PV MRA,
using a spatially selective slab inversion preparation
sequence, was acquired on seven healthy adult subjects (27
± 17 years, range: 19-65 years, 4 women). The k-space data
were retrospectively randomly undersampled by factors of 2,
4, 6, 8, and 10 and then reconstructed using distributed CS
and coil-by-coil CS methods. The reconstructed images were
evaluated by two blinded readers in consensus for assessment
of major PV branches as well as the presence of artifacts in
left atrium (LA) and elsewhere. Diameters of right inferior
and right superior PV branches were measured. Additionally,
mean square errors (MSE) of the reconstructions were
calculated.<h4>Results</h4>Both CS methods resulted in image
quality scores similar to the fully sampled reference images
at undersampling factors up to 6-fold for distributed CS and
4-fold for coil-by-coil CS reconstructions. There was no
difference in the presence of artifacts in LA and freedom
from important artifacts elsewhere between the two
techniques up to undersampling factors of 10 compared to the
fully sampled reconstruction. For the PV diameters, no
systematic variation between the reference and the
reconstructions were observed for either technique. There
were no significant differences in MSE between the two
methods when compared at a given rate, but the difference
was significant when compared across all
rates.<h4>Conclusion</h4>The sparsity of noncontrast PV MRA
and the joint sparsity of different coil images allow
imaging at high undersampling factors (up to 6-fold) when
distributed CS is used.},
Doi = {10.1002/jmri.22559},
Key = {fds336735}
}
@article{fds340014,
Author = {Shin, W-Y and Lucani, DE and Medard, M and Stojanovic, M and Tarokh,
V},
Title = {On the Order Optimality of Large-scale Underwater
Networks},
Volume = {abs/1103.0266},
Year = {2011},
Month = {March},
Abstract = {Capacity scaling laws are analyzed in an underwater acoustic
network with $n$ regularly located nodes on a square, in
which both bandwidth and received signal power can be
limited significantly. A narrow-band model is assumed where
the carrier frequency is allowed to scale as a function of
$n$. In the network, we characterize an attenuation
parameter that depends on the frequency scaling as well as
the transmission distance. Cut-set upper bounds on the
throughput scaling are then derived in both extended and
dense networks having unit node density and unit area,
respectively. It is first analyzed that under extended
networks, the upper bound is inversely proportional to the
attenuation parameter, thus resulting in a highly
power-limited network. Interestingly, it is seen that the
upper bound for extended networks is intrinsically related
to the attenuation parameter but not the spreading factor.
On the other hand, in dense networks, we show that there
exists either a bandwidth or power limitation, or both,
according to the path-loss attenuation regimes, thus
yielding the upper bound that has three fundamentally
different operating regimes. Furthermore, we describe an
achievable scheme based on the simple nearest-neighbor
multi-hop (MH) transmission. We show that under extended
networks, the MH scheme is order-optimal for all the
operating regimes. An achievability result is also presented
in dense networks, where the operating regimes that
guarantee the order optimality are identified. It thus turns
out that frequency scaling is instrumental towards achieving
the order optimality in the regimes. Finally, these scaling
results are extended to a random network realization. As a
result, vital information for fundamental limits of a
variety of underwater network scenarios is provided by
showing capacity scaling laws.},
Key = {fds340014}
}
@article{fds336736,
Author = {Jia, P and Vu, M and Le-Ngoc, T and Hong, SC and Tarokh,
V},
Title = {Capacity- and Bayesian-based cognitive sensing with location
side information},
Journal = {Ieee Journal on Selected Areas in Communications},
Volume = {29},
Number = {2},
Pages = {276-289},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2011},
Month = {February},
url = {http://dx.doi.org/10.1109/JSAC.2011.110202},
Abstract = {We investigate spectrum sensing by energy detection based on
two different objective functions: a Bayesian sensing cost
or the network weighted sum capacity. The Bayesian cost is a
traditional detection measure which aims at minimizing a
combination of the miss-detection and false-alarm
probabilities, while the capacity objective is a
communication measure which aims at maximizing the network
throughput. Fading-dependent optimal sensing thresholds for
each objective are derived in closed-form for different
cases of location side information. To make sensing more
robust to channel fading, we also propose fading-independent
sub-optimal thresholds. Results show that location side
information helps improve performance when using the
threshold designed for that performance measure. However,
the Bayesian-based threshold does not utilize the side
information well in improving the network sum capacity. On
the other hand, the capacity-based threshold captures the
benefit of side information in both the capacity and
Bayesian cost measures. Furthermore, it helps to
significantly improve the network throughput. The proposed
sensing schemes with location side information can also be
generalized to a network with multiple cognitive users in a
simple and distributed manner. © 2006 IEEE.},
Doi = {10.1109/JSAC.2011.110202},
Key = {fds336736}
}
@article{fds336737,
Author = {Smida, B and Tarokh, V},
Title = {Analysis of interference in air-to-ground CDMA cellular
systems under idealized assumptions},
Journal = {Ieee Transactions on Communications},
Volume = {59},
Number = {1},
Pages = {258-267},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2011},
Month = {January},
url = {http://dx.doi.org/10.1109/TCOMM.2010.110310.080484},
Abstract = {In this paper, we study the air-to-ground cellular systems
with no frequency reuse. We provide an analysis of the
inter-cell interference under idealized assumptions: 3D
hexagonal cell planning, a line of sight channel model with
no shadowing and idealized antenna patterns. Based on this
model, we derive approximate bounds for the inter to
intra-cell interference ratio for the air-to-ground link. In
addition, we provide upper bounds on the interference and
the outage probability for the ground-to-air link.
Simulation results are provided to validate the accuracy of
the analytical results. © 2011 IEEE.},
Doi = {10.1109/TCOMM.2010.110310.080484},
Key = {fds336737}
}
@article{fds336738,
Author = {Chen, Q and Li, J and Fan, P and Tarokh, V},
Title = {An exponential model for evaluating error performance of
turbo codes},
Journal = {Globecom Ieee Global Telecommunications Conference},
Year = {2010},
Month = {December},
ISBN = {9781424456383},
url = {http://dx.doi.org/10.1109/GLOCOM.2010.5683671},
Abstract = {In this paper, an exponential model is proposed to
approximate the error performance of Turbo codes within low
and intermediate SNR region. Our analysis unveils that, the
proposed exponential model offers a simple but effective
method to approximate the waterfall region performance of
Turbo codes, which is generally intricate for analytical
bounding techniques. By combining the proposed exponential
model with the well known union bound estimate, the paper
derives a combined performance model to extend the
performance estimate within moderate to high SNR region.
Moreover, it is shown that, only the free distance term of
the weight spectrum is not always enough for a reasonable
estimate of the error floor region performance, especially
when the free distance multiplicity is small. Numerical
results are presented to validate the applicability of the
proposed performance model. ©2010 IEEE.},
Doi = {10.1109/GLOCOM.2010.5683671},
Key = {fds336738}
}
@article{fds336739,
Author = {Chen, Q and Li, J and Fan, P and Tarokh, V},
Title = {On the performance estimate for Turbo codes},
Journal = {2010 International Conference on Wireless Communications and
Signal Processing, Wcsp 2010},
Publisher = {IEEE},
Year = {2010},
Month = {December},
ISBN = {9781424475551},
url = {http://dx.doi.org/10.1109/WCSP.2010.5633812},
Abstract = {Recently, the scaling law has been extended to approximate
the waterfall performance for Turbo codes over the binary
erasure channel. However, the waterfall approximation over
other channels, such as the AWGN and Rayleigh fading
channels, is still unknown for Turbo codes. In this paper,
an exponential model was proposed to approximate the
waterfall performance for Turbo codes. The relationship
between the proposed exponential model and the scaling law
will be highlighted at first. Our analysis unveils that the
proposed exponential model could be regarded as a
generalized scaling law model, which makes it possible to
achieve better performance estimate. The results in this
paper explicitly shows that, the exponential model offers
reasonable waterfall approximation for both word error
probability and bit error probability for all packet sizes
over a diverse channel, such as the binary erasure channel,
the additive white Gaussian noise channel as well as the
Rayleigh fading channel. The complete performance model
could be derived by combining the exponential model and the
known union bound model. Finally, some further discussions
are presented to highlight the performance estimate problem
for Turbo codes. ©2010 IEEE.},
Doi = {10.1109/WCSP.2010.5633812},
Key = {fds336739}
}
@article{fds336740,
Author = {Babadi, B and Tarokh, V},
Title = {GADIA: A greedy asynchronous distributed interference
avoidance algorithm},
Journal = {Ieee Transactions on Information Theory},
Volume = {56},
Number = {12},
Pages = {6228-6252},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2010},
Month = {December},
url = {http://dx.doi.org/10.1109/TIT.2010.2081090},
Abstract = {In this paper, the problem of distributed dynamic frequency
allocation is considered for a canonical communication
network, which spans several networks such as cognitive
radio networks and digital subscriber lines (DSLs). A greedy
asynchronous distributed interference avoidance (GADIA)
algorithm for horizontal spectrum sharing has been proposed
that achieves performance close to that of a centralized
optimal algorithm. The convergence of the GADIA algorithm to
a near-optimal frequency allocation strategy is proved and
several asymptotic performance bounds have been established
for various spatial configurations of the network nodes.
Furthermore, the near-equilibrium dynamics of the GADIA
algorithm has been studied using the Glauber dynamics, by
identifying the problem with the antiferromagnetic
inhomogeneous long-range Potts model. Using the
near-equilibrium dynamics and methods from stochastic
analysis, the robustness of the algorithm with respect to
time variations in the activity of network nodes is studied.
These analytic results along with simulation studies reveal
that the performance is close to that of an optimum
centralized frequency allocation algorithm. Further
simulation studies confirm that our proposed algorithm
outperforms the iterative water-filling algorithm in the low
signal-to-interference-plus-noise ratio (SINR) regime, in
terms of achieved sum rate, complexity, convergence rate,
and robustness to time-varying node activities. © 2006
IEEE.},
Doi = {10.1109/TIT.2010.2081090},
Key = {fds336740}
}
@article{fds336742,
Author = {Shin, WY and Lucani, DE and Médard, M and Stojanovic, M and Tarokh,
V},
Title = {Multi-hop routing is order-optimal in underwater extended
networks},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {510-514},
Year = {2010},
Month = {August},
ISBN = {9781424469604},
url = {http://dx.doi.org/10.1109/ISIT.2010.5513480},
Abstract = {Capacity scaling laws are analyzed in an underwater acoustic
network with n regularly located nodes. A narrowband model
is assumed where the carrier frequency is allowed to scale
as a function of n. In the network, we characterize an
attenuation parameter that depends on the frequency scaling
as well as the transmission distance. A cut-set upper bound
on the throughput scaling is then derived in extended
networks. Our result indicates that the upper bound is
inversely proportional to the attenuation parameter, thus
resulting in a highly power-limited network. Furthermore, we
describe an achievable scheme based on the simple
nearest-neighbor multi-hop (MH) transmission. It is shown
under extended networks that the MH scheme is order-optimal
as the attenuation parameter scales exponentially with √n
(or faster). Finally, these scaling results are extended to
a random network realization. © 2010 IEEE.},
Doi = {10.1109/ISIT.2010.5513480},
Key = {fds336742}
}
@article{fds336743,
Author = {Larsson, P and Smida, B and Koike-Akino, T and Tarokh,
V},
Title = {Analysis of network coded HARQ for multiple unicast
flows},
Journal = {Ieee International Conference on Communications},
Publisher = {IEEE},
Year = {2010},
Month = {August},
ISBN = {9781424464043},
url = {http://dx.doi.org/10.1109/ICC.2010.5502226},
Abstract = {In this paper, we consider network coded (NCed) Hybrid-ARQ
(HARQ) for multiple unicast flows. The main contribution of
the paper is the derivation of throughput expression for
NCed HARQ with arbitrary number of users in i.i.d. channels.
We apply the result to Rayleigh fading channels for
incremental redundancy (IR) and chase combining (CC) based
NCed HARQ. We verify the analytical approach with
simulations. We observe substantial SNR improvements over
regular ARQ with network coding as well as classical (H)ARQ.
The SNR gains in the high and low throughput regimes are
mainly due to the network coding and HARQ aspects,
respectively. For low SNRs, NCed HARQ with IR surpasses the
CC performance. ©2010 IEEE.},
Doi = {10.1109/ICC.2010.5502226},
Key = {fds336743}
}
@article{fds336744,
Author = {Babadi, B and Kalouptsidis, N and Tarokh, V},
Title = {SPARLS: The sparse RLS algorithm},
Journal = {Ieee Transactions on Signal Processing},
Volume = {58},
Number = {8},
Pages = {4013-4025},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2010},
Month = {August},
url = {http://dx.doi.org/10.1109/TSP.2010.2048103},
Abstract = {We develop a recursive L1-regularized least squares (SPARLS)
algorithm for the estimation of a sparse tap-weight vector
in the adaptive filtering setting. The SPARLS algorithm
exploits noisy observations of the tap-weight vector output
stream and produces its estimate using an
expectation-maximization type algorithm. We prove the
convergence of the SPARLS algorithm to a near-optimal
estimate in a stationary environment and present analytical
results for the steady state error. Simulation studies in
the context of channel estimation, employing multipath
wireless channels, show that the SPARLS algorithm has
significant improvement over the conventional widely used
recursive least squares (RLS) algorithm in terms of mean
squared error (MSE). Moreover, these simulation studies
suggest that the SPARLS algorithm (with slight
modifications) can operate with lower computational
requirements than the RLS algorithm, when applied to
tap-weight vectors with fixed support. © 2010
IEEE.},
Doi = {10.1109/TSP.2010.2048103},
Key = {fds336744}
}
@article{fds340017,
Author = {Babadi, B and Kalouptsidis, N and Tarokh, V},
Title = {SPARLS: The Sparse RLS Algorithm},
Journal = {Ieee Transactions on Signal Processing},
Volume = {58},
Number = {8},
Pages = {4013-4025},
Publisher = {IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS
INC},
Year = {2010},
Month = {August},
url = {http://dx.doi.org/10.1109/TSP.2010.2048103},
Doi = {10.1109/TSP.2010.2048103},
Key = {fds340017}
}
@article{fds336745,
Author = {Babadi, B and Tarokh, V},
Title = {Random frames from binary linear block codes},
Journal = {2010 44th Annual Conference on Information Sciences and
Systems, Ciss 2010},
Publisher = {IEEE},
Year = {2010},
Month = {June},
ISBN = {9781424474172},
url = {http://dx.doi.org/10.1109/CISS.2010.5464847},
Abstract = {Let C be an [n, k, d] binary linear block code of length n,
dimension k and minimum Hamming distance d over GF(2n). Let
d⊥ denote the minimum Hamming distance of the dual code of
Cover GF(2n). Let ε : GF(2n) → {-1, 1}n be the
component-wise mapping ε(vi) := (-1)vi , for v = (vI, v2,
v2, ⋯, vn) ∈ GF(2n). Finally, for p < n, let ΦC be a p
x n random matrix whose rows are obtained by mapping a
uniformly drawn set of size p of the codewords of C under
ε. Recently, the authors have established that [3] for d
⊥ large enough and y := p/n ∈ (0,1) fixed, as n → ∞
the empirical eigen-distribution of the Gram matrix of
1/√n ΦC resembles that of a random i.i.d, Rademacher
matrix (i.e., the Marchenko-Pastur distribution). In this
paper, we overview this result and discuss its implications
on the design of frames for compressed sensing applications.
©2010 IEEE.},
Doi = {10.1109/CISS.2010.5464847},
Key = {fds336745}
}
@article{fds336746,
Author = {Mileounis, G and Babadi, B and Kalouptsidis, N and Tarokh,
V},
Title = {An adaptive greedy algorithm with application to nonlinear
communications},
Journal = {Ieee Transactions on Signal Processing},
Volume = {58},
Number = {6},
Pages = {2998-3007},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2010},
Month = {June},
url = {http://dx.doi.org/10.1109/TSP.2010.2044841},
Abstract = {Greedy algorithms form an essential tool for compressed
sensing. However, their inherent batch mode discourages
their use in time-varying environments due to significant
complexity and storage requirements. In this paper two
existing powerful greedy schemes developed in the literature
are converted into an adaptive algorithm which is applied to
estimation of a class of nonlinear communication systems.
Performance is assessed via computer simulations on a
variety of linear and nonlinear channels; all confirm
significant improvements over conventional methods. © 2010
IEEE.},
Doi = {10.1109/TSP.2010.2044841},
Key = {fds336746}
}
@article{fds340019,
Author = {Shin, W-Y and Lucani, DE and Medard, M and Stojanovic, M and Tarokh,
V},
Title = {On Capacity Scaling of Underwater Networks: An
Information-Theoretic Perspective},
Volume = {abs/1005.0855},
Year = {2010},
Month = {May},
Abstract = {Capacity scaling laws are analyzed in an underwater acoustic
network with $n$ regularly located nodes on a square. A
narrow-band model is assumed where the carrier frequency is
allowed to scale as a function of $n$. In the network, we
characterize an attenuation parameter that depends on the
frequency scaling as well as the transmission distance. A
cut-set upper bound on the throughput scaling is then
derived in extended networks. Our result indicates that the
upper bound is inversely proportional to the attenuation
parameter, thus resulting in a highly power-limited network.
Interestingly, it is seen that unlike the case of wireless
radio networks, our upper bound is intrinsically related to
the attenuation parameter but not the spreading factor.
Furthermore, we describe an achievable scheme based on the
simple nearest neighbor multi-hop (MH) transmission. It is
shown under extended networks that the MH scheme is
order-optimal as the attenuation parameter scales
exponentially with $\sqrt{n}$ (or faster). Finally, these
scaling results are extended to a random network
realization.},
Key = {fds340019}
}
@article{fds336747,
Author = {Zhao, H and Fan, P and Tarokh, V},
Title = {On the equivalence of interleavers for turbo codes using
quadratic permutation polynomials over integer
rings},
Journal = {Ieee Communications Letters},
Volume = {14},
Number = {3},
Pages = {236-238},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2010},
Month = {March},
url = {http://dx.doi.org/10.1109/LCOMM.2010.03.091695},
Abstract = {It is known that the equivalence of interleavers for turbo
codes using quadratic permutation polynomials (QPPs) over
integer rings can be exactly determined by the so-called
quadratic null polynomials (QNPs) over integer rings. For
generating QNPs or higher order null polynomials (NPs), some
theoretical results have been obtained in previous
literature. In this letter, it is proved that the
coefficients of previously obtained QNPs are not only
sufficient but also necessary for generating any QNPs. Based
on the necessary and sufficient conditions for generating
QNPs and QPPs, the enumeration of QPPs excluding their
equivalence is presented. The obtained results are helpful
to investigate the algebraic structure of QPP interleavers
as well as to avoid the equivalence in the design of QPP
interleavers. © 2010 IEEE.},
Doi = {10.1109/LCOMM.2010.03.091695},
Key = {fds336747}
}
@article{fds336749,
Author = {Mercier, H and Bhargava, VK and Tarokh, V},
Title = {A survey of error-correcting codes for channels with symbol
synchronization errors},
Journal = {Ieee Communications Surveys & Tutorials},
Volume = {12},
Number = {1},
Pages = {87-96},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2010},
Month = {March},
url = {http://dx.doi.org/10.1109/SURV.2010.020110.00079},
Abstract = {We present a comprehensive survey of errorcorrecting codes
for channels corrupted by synchronization errors. We discuss
potential applications as well as the obstacles that need to
be overcome before such codes can be used in practical
systems. © 2010 IEEE.},
Doi = {10.1109/SURV.2010.020110.00079},
Key = {fds336749}
}
@article{fds336741,
Author = {Akçakaya, M and Park, J and Tarokh, V},
Title = {Low density frames for compressive sensing},
Journal = {2015 Ieee International Conference on Acoustics, Speech, and
Signal Processing (Icassp)},
Pages = {3642-3645},
Publisher = {IEEE},
Year = {2010},
Month = {January},
ISBN = {9781424442966},
url = {http://dx.doi.org/10.1109/ICASSP.2010.5495898},
Abstract = {We consider the compressive sensing of a sparse or
compressible signal x ∈ ℝM. We explicitly construct a
class of measurement matrices, referred to as the low
density frames, and develop decoding algorithms that produce
an accurate estimate x̂ even in the presence of additive
noise. Low density frames are sparse matrices and have small
storage requirements. Our decoding algorithms for these
frames can be implemented in O(Mdvdc) complexity, where dc
and dv are the row and column weight of the frame
respectively. Simulation results are provided, demonstrating
that our approach significantly outperforms state-of-the-art
recovery algorithms for numerous cases of interest. ©2010
IEEE.},
Doi = {10.1109/ICASSP.2010.5495898},
Key = {fds336741}
}
@article{fds336748,
Author = {Akçakaya, M and Tarokh, V},
Title = {Shannon-theoretic limits on noisy compressive
sampling},
Journal = {Ieee Transactions on Information Theory},
Volume = {56},
Number = {1},
Pages = {492-504},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2010},
Month = {January},
url = {http://dx.doi.org/10.1109/TIT.2009.2034796},
Abstract = {In this paper, we study the number of measurements required
to recover a sparse signal in ℤM with L nonzero
coefficients from compressed samples in the presence of
noise. We consider a number of different recovery criteria,
including the exact recovery of the support of the signal,
which was previously considered in the literature, as well
as new criteria for the recovery of a large fraction of the
support of the signal, and the recovery of a large fraction
of the energy of the signal. For these recovery criteria, we
prove that O(L) (an asymptotically linear multiple of L)
measurements are necessary and sufficient for signal
recovery, whenever L grows linearly as a function of M. This
improves on the existing literature that is mostly focused
on variants of a specific recovery algorithm based on convex
programming, for which O(L log(M - L)) measurements are
required. In contrast, the implementation of our proof
method would have a higher complexity. We also show that O(L
log(M - L)) measurements are required in the sublinear
regime (L = o(M)). For our sufficiency proofs, we introduce
a Shannon-theoretic decoder based on joint typicality, which
allows error events to be defined in terms of a single
random variable in contrast to previous information-theoretic
work, where comparison of random variables are required. We
also prove concentration results for our error bounds
implying that a randomly selected Gaussian matrix will
suffice with high probability. For our necessity proofs, we
rely on results from channel coding and rate-distortion
theory. © 2009 IEEE.},
Doi = {10.1109/TIT.2009.2034796},
Key = {fds336748}
}
@article{fds340018,
Author = {Mileounis, G and Babadi, B and Kalouptsidis, N and Tarokh,
V},
Title = {An Adaptive Greedy Algorithm with Application to Sparse
Narma Identification.},
Journal = {Icassp},
Pages = {3810-3813},
Publisher = {IEEE},
Year = {2010},
ISBN = {978-1-4244-4296-6},
Key = {fds340018}
}
@article{fds336750,
Author = {Kalouptsidis, N and Mileounis, G and Babadi, B and Tarokh,
V},
Title = {Adaptive algorithms for sparse nonlinear channel
estimation},
Journal = {Ieee Workshop on Statistical Signal Processing
Proceedings},
Pages = {221-224},
Publisher = {IEEE},
Year = {2009},
Month = {December},
ISBN = {9781424427109},
url = {http://dx.doi.org/10.1109/SSP.2009.5278600},
Abstract = {In this paper, we consider the estimation of sparse
nonlinear communication channels. Transmission over the
channels is represented by sparse Volterra models that
incorporate the effect of Power Amplifiers. Channel
estimation is performed by compressive sensing methods.
Efficient algorithms are proposed based on Kalman filtering
and Expectation Maximization. Simulation studies confirm
that the proposed algorithms achieve significant performance
gains in comparison to the conventional non-sparse methods.
© 2009 IEEE.},
Doi = {10.1109/SSP.2009.5278600},
Key = {fds336750}
}
@article{fds336752,
Author = {Koike-Akino, T and Popovski, P and Tarokh, V},
Title = {Adaptive modulation and network coding with optimized
precoding in two-way relaying},
Journal = {Globecom Ieee Global Telecommunications Conference},
Publisher = {IEEE},
Year = {2009},
Month = {December},
ISBN = {9781424441488},
url = {http://dx.doi.org/10.1109/GLOCOM.2009.5425565},
Abstract = {We propose a precoding strategy which controls amplitude and
phase of receiving signals to improve throughput for
two-stage bidirectional relaying. We consider the case when
the nodes know channel state information (CSI) and can adopt
adaptive modulation techniques. We introduce a novel scheme
termed adaptive modulation and network coding (AMNC), which
jointly optimizes modulations and network coding based on
the CSI. For dynamic bit loading and power allocation, we
propose a practical time-sharing method called the segmented
precoding, in which a packet is split into several
sub-packets, and a set of modulation and network coding is
optimized in conjunction with amplitude and phase controls
for each sub-packet. It is demonstrated that our proposed
scheme can offer a significant improvement of achievable
throughput for two-way relaying.},
Doi = {10.1109/GLOCOM.2009.5425565},
Key = {fds336752}
}
@article{fds336753,
Author = {Moezzi, K and Jalaleddini, K and Aghdam, AG and Alasti, M and Tarokh,
V},
Title = {An adaptive rate assignment strategy for CDMA2000 IS-856
subject to RAB delay},
Journal = {Globecom Ieee Global Telecommunications Conference},
Publisher = {IEEE},
Year = {2009},
Month = {December},
ISBN = {9781424441488},
url = {http://dx.doi.org/10.1109/GLOCOM.2009.5426040},
Abstract = {In this paper, the problem of resource allocation in IS-856
uplink in the presence of time-delay is studied. A set of
nonlinear adaptive controllers are designed to stabilize the
wireless network and use the system resources efficiently.
The controllers obtained are then modified properly to
retain network stability and performance in the presence of
time-delay. Simulation results are presented to show the
effectiveness of the proposed approach.},
Doi = {10.1109/GLOCOM.2009.5426040},
Key = {fds336753}
}
@article{fds336755,
Author = {Koike-Akino, T and Larsson, P and Popovski, P and Tarokh,
V},
Title = {Non-linear network coding in two-way relaying discrete
channels},
Journal = {2009 International Conference on Wireless Communications and
Signal Processing, Wcsp 2009},
Publisher = {IEEE},
Year = {2009},
Month = {December},
ISBN = {9781424456680},
url = {http://dx.doi.org/10.1109/WCSP.2009.5371759},
Abstract = {In this paper, we present optimal network coding which can
maximize achievable rate region in two-way relaying discrete
channels, where there are two communicating nodes and one
relaying node. We focus on a low-complexity relaying
protocol termed the detect-and-forward (DtF) scheme, in
which the relaying node does not require channel decoding
but detection. We first analyze the achievable rate region
of any digital network coding function including non-linear
types. We then search for the optimal network code in favor
of maximizing two kinds of performance measures: the sum
rate and the product rate. For high SNR regimes, linear
network codes like the exclusive-or (XOR) function can offer
the maximum-achievable rate region. Whereas, for low SNR
regimes, it is verified that non-linear network codes like
the negate-or (NOR) function can outperform linear codes due
to the effect of error occurrence at the intermediate
relaying node. © 2009 IEEE.},
Doi = {10.1109/WCSP.2009.5371759},
Key = {fds336755}
}
@article{fds336756,
Author = {Jeon, SW and Devroye, N and Vu, M and Chung, SY and Tarokh,
V},
Title = {Cognitive networks achieve throughput scaling of a
homogeneous network},
Journal = {Final Proceedings of the 2009 7th International Symposium on
Modeling and Optimization in Mobile, Ad Hoc and Wireless
Networks, Wiopt 2009},
Year = {2009},
Month = {December},
ISBN = {9781424449200},
url = {http://dx.doi.org/10.4108/ICST.WIOPT2009.6358},
Abstract = {We study two distinct, but overlapping, networks which
operate at the same time, space and frequency. The first
network consists of n randomly distributed primary users,
which form either an ad hoc network, or an infrastructure-
supported ad hoc network in which l additional base stations
support the primary users. The second network consists of m
randomly distributed secondary or cognitive users. The
primary users have priority access to the spectrum and do
not change their communication protocol in the presence of
secondary users. The secondary users, however, need to
adjust their protocol based on knowledge about the locations
of the primary users so as not to harm the primary network's
scaling law. Base on percolation theory, we show that
surprisingly, when the secondary network is denser than the
primary network, both networks can simultaneously achieve
the same throughput scaling as a standalone ad hoc
network.},
Doi = {10.4108/ICST.WIOPT2009.6358},
Key = {fds336756}
}
@article{fds336751,
Author = {Kim, SJ and Ghassemzadeh, SS and Miller, RR and Tarokh,
V},
Title = {TAS protocols of a PASD system with limited feedback
information},
Journal = {Globecom Ieee Global Telecommunications Conference},
Publisher = {IEEE},
Year = {2009},
Month = {December},
ISBN = {9781424441488},
url = {http://dx.doi.org/10.1109/GLOCOM.2009.5426257},
Abstract = {In a Protocol Assisted Switched Diversity (PASD) system, the
time separated repetition blocks are accumulated in order to
increase decoding reliability. In this paper, we consider
transmit antenna selection (TAS) protocols in a PASD system.
To minimize system complexity we assume the feedback
information is limited to the SNR of the current pair of
antennas. We propose three TAS protocols : the random TAS
(R-TAS) protocol which selects antennas randomly, the
threshold TAS (T-TAS) protocol which keeps the current
selection if the predetermined SNR threshold level
requirement is met and the minimum number of transmission
TAS (MNT-TAS) protocol which determines the selection of a
new antenna set or keeping the current set based on the
evaluation of expectation of the number of necessary
remaining transmissions. We analyze the average number of
transmissions of three proposed protocols in a Rayleigh
fading channel and compare numerical evaluations to
simulation results under different system
conditions.},
Doi = {10.1109/GLOCOM.2009.5426257},
Key = {fds336751}
}
@article{fds336757,
Author = {Koike-Akino, T and Tarokh, V},
Title = {Sphere packing optimization and EXIT chart analysis for
multi-dimensional QAM signaling},
Journal = {Ieee International Conference on Communications},
Publisher = {IEEE},
Year = {2009},
Month = {November},
ISBN = {9781424434350},
url = {http://dx.doi.org/10.1109/ICC.2009.5199484},
Abstract = {We investigate on multi-dimensional QAM constellations
optimized by sphere packing with the known densest lattices.
We propose a greedy design method assisted by the sphere
detection. It is demonstrated that the optimized
constellations can significantly increase the squared
minimum distance in comparison to the conventional QAM
constellations. In addition, we analyze the optimized QAMs
through the use of an extrinsic information transfer (EXIT)
chart for iterative decoding. ©2009 IEEE.},
Doi = {10.1109/ICC.2009.5199484},
Key = {fds336757}
}
@article{fds336758,
Author = {Koike-Akino, T and Popovski, P and Tarokh, V},
Title = {Denoising strategy for convolutionally-coded bidirectional
relaying},
Journal = {Ieee International Conference on Communications},
Publisher = {IEEE},
Year = {2009},
Month = {November},
ISBN = {9781424434350},
url = {http://dx.doi.org/10.1109/ICC.2009.5198893},
Abstract = {In this paper, we present a forwarding strategy for
two-stage bidirectional relaying in which trellis-coded
modulation (TCM) is employed. We reveal that adaptive
network coding cannot resolve distance shortening occurred
at specific channel conditions when a certain TCM is used.
To overcome this issue, we introduce an improved
amplify-and-forward (AF) scheme termed pseudo AF (PAF). The
proposed strategy adaptively switches network coding and PAF
according to the channel information. Computer simulations
demonstrate that the proposed approach can improve
throughput performance. ©2009 IEEE.},
Doi = {10.1109/ICC.2009.5198893},
Key = {fds336758}
}
@article{fds336759,
Author = {Jalaleddini, K and Moezzi, K and Aghdam, AG and Alasti, M and Tarokh,
V},
Title = {Controller design for rate assignment in wireless
networks},
Journal = {Ieee International Conference on Communications},
Publisher = {IEEE},
Year = {2009},
Month = {November},
ISBN = {9781424434350},
url = {http://dx.doi.org/10.1109/ICC.2009.5198854},
Abstract = {In this paper, data-rate assignment in IS-856 uplink
(reverse link) is studied. The problem is first formulated
in an interference model framework, and then a dynamic
control strategy is developed for efficient rate assignment.
In the first step, the controller is designed for the
special case when the number of users in the network is
fixed. Then, the minimum time required for a dynamic network
(where the number of users is subject to change) to achieve
a desired performance is obtained. The simulation results
are presented to elucidate the effectiveness of the proposed
approach. ©2009 IEEE.},
Doi = {10.1109/ICC.2009.5198854},
Key = {fds336759}
}
@article{fds336760,
Author = {Kim, SJ and Devroye, N and Tarokh, V},
Title = {A class of Bi-directional multi-relay protocols},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {349-353},
Publisher = {IEEE},
Year = {2009},
Month = {November},
ISBN = {9781424443130},
url = {http://dx.doi.org/10.1109/ISIT.2009.5205684},
Abstract = {In a bi-directional relay channel, two nodes wish to
exchange independent messages over a shared wireless
halfduplex channel with the help of relays. Recent work has
considered information theoretic limits of the
bi-directional relay channel with a single relay. In this
work we consider bidirectional relaying with multiple
relays. We derive achievable rate regions and outer bounds
for half-duplex protocols with multiple decode and forward
relays and compare these to the same protocols with amplify
and forward relays in an additive white Gaussian noise
channel. We consider three novel classes of half-duplex
protocols: the (m, 2) 2 phase protocol with m relays, the
(m, 3) 3 phase protocol with m relays, and general (m, t)
Multiple Hops and Multiple Relays (MHMR) protocols, where m
is the total number of relays and 3 < t ≤ m + 2 is the
number of temporal phases in the protocol. Finally, we
provide a comprehensive treatment of the MHMR protocols with
decode and forward relaying and amplify and forward relaying
in Gaussian noise, obtaining their respective achievable
rate regions, outer bounds and relative performance at
different SNRs. The (m, m + 2) DF MHMR protocol achieves the
largest rate region under simulated channel conditions. ©
2009 IEEE.},
Doi = {10.1109/ISIT.2009.5205684},
Key = {fds336760}
}
@article{fds336762,
Author = {Yiu, S and Vu, M and Tarokh, V},
Title = {Interference and noise reduction by beamforming in cognitive
networks},
Journal = {Ieee Transactions on Communications},
Volume = {57},
Number = {10},
Pages = {3144-3153},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2009},
Month = {November},
url = {http://dx.doi.org/10.1109/TCOMM.2009.10.080501},
Abstract = {We consider beamforming in a cognitive network with multiple
primary users and a secondary user sharing the same
spectrum. Each primary and secondary user consists of a
transmitter and a receiver. In particular, we assume that
the secondary transmitter has Nt antennas and transmits data
to its single-antenna receiver using beamforming. The
beamformer is designed to maximize the cognitive
signal-to-interference ratio (CSIR). Using mathematical
tools from random matrix theory, we derive both lower and
upper bounds on the average interference created by the
cognitive transmitter at the primary receivers and the
average CSIR of the cognitive user. We further analyze and
prove the convergence of these two performance measures
asymptotically as the number of antennas Nt or primary users
Np increases. Specifically, we show that the average
interference per primary receiver converges to E[d-α], the
expected value of the path loss in the network, whereas the
average CSIR decays as 1/c when c = Np/Nt → ∞. In the
special case of Nt ≥ Np, the lower bound of the average
total interference approaches 0 and the upper bound of the
average CSIR approaches NtE[d-α] /σC2c where σC2c is the
noise variance at the cognitive receiver. © 2009
IEEE.},
Doi = {10.1109/TCOMM.2009.10.080501},
Key = {fds336762}
}
@article{fds336761,
Author = {Smida, B and Efthymoglou, GP and Ghassemzadeh, SS and Tarokh,
V},
Title = {Interference analysis between on-the-move users and GEO
satellites},
Journal = {Ieee Vehicular Technology Conference},
Publisher = {IEEE},
Year = {2009},
Month = {October},
ISBN = {9781424425174},
url = {http://dx.doi.org/10.1109/VETECS.2009.5073607},
Abstract = {We consider on the move satellite systems with geostationary
satellites. Using the antenna pointing distribution of
Weerackody and Gonzalez, we derive tight upper and lower
bounds of the interference between adjacent satellites
from/to the on-the-move platforms. We then compute the
distribution of the interference and the outage probability
of the system. Simulation results are provided demonstrating
that the analytical estimates are accurate. © 2009
IEEE.},
Doi = {10.1109/VETECS.2009.5073607},
Key = {fds336761}
}
@article{fds336764,
Author = {Bai, D and Mitran, P and Ghassemzadeh, SS and Miller, RR and Tarokh,
V},
Title = {Rate of channel hardening of antenna selection diversity
schemes and its implication on scheduling},
Journal = {Ieee Transactions on Information Theory},
Volume = {55},
Number = {10},
Pages = {4353-4365},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2009},
Month = {October},
url = {http://dx.doi.org/10.1109/TIT.2009.2027529},
Abstract = {For a multiple-antenna system, we find a simple and accurate
expression for the asymptotic distribution of the antenna
selection gain when the transmitter selects the transmit
antenna with the strongest channel. We use this to estimate
the underlying channel capacity distributions and obtain the
approximate ergodic capacity. This estimate is compared with
upper and lower bounds. This analysis demonstrates that
unlike multiple-input/multiple-output (MIMO) systems, the
channel for antenna selection systems hardens at a slower
rate, and thus a significant multiuser scheduling gain can
exist - Θ(1/log m) for channel selection as opposed to
Θ(1/√ m) for MIMO, where m is the number of transmit
antennas. © 2009 IEEE.},
Doi = {10.1109/TIT.2009.2027529},
Key = {fds336764}
}
@article{fds336763,
Author = {Koike-Akino, T and Devroye, N and Tarokh, V},
Title = {Frequency-domain bit-flipping equalizer for wideband MIMO
channels},
Journal = {Ieee Transactions on Wireless Communications},
Volume = {8},
Number = {10},
Pages = {4969-4973},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2009},
Month = {October},
url = {http://dx.doi.org/10.1109/TWC.2009.081644},
Abstract = {We propose a low-complexity equalizer whose performance
approaches that of the optimal maximum-likelihood estimators
in wideband multiple-input multiple-output (MIMO) channels.
The proposed algorithm makes use of a bit-flipping
refinement procedure preceded by a frequency-domain
equalizer and is based on local-optima searching algorithms.
Through performance evaluations, it is demonstrated that the
proposed equalizer can perform well when a large number of
diversity branches are available in severely dispersive
fading channels. © 2009 IEEE.},
Doi = {10.1109/TWC.2009.081644},
Key = {fds336763}
}
@article{fds336766,
Author = {Feng, L and Fan, P and Hao, L and Loo, KK and Tarokh,
V},
Title = {A new construction of signature waveforms for multi-rate
multi-cell QS-CDMA systems},
Journal = {Wireless Personal Communications},
Volume = {50},
Number = {4},
Pages = {493-507},
Publisher = {Springer Nature},
Year = {2009},
Month = {September},
url = {http://dx.doi.org/10.1007/s11277-008-9620-0},
Abstract = {In this paper, we propose a new construction of signature
waveform sets based on Generalized Loosely Synchronization
(GLS) sets and different chip waveforms. The new signature
sets are applied into the multi-rate multi-cell
quasi-synchronous CDMA (QS-CDMA) system where each cell is
assigned with a GLS set; different users in the same cell
are assigned with different GLS sequences in the same GLS
set; user's different streams are assigned with the same GLS
sequence but different chip waveforms. According to the
properties of GLS sets, the inter-cell interference (ICI)
and the multi-user interference (MUI) in the same cell can
be reduced significantly. The interferences among different
streams of the same user are handled by an optimal (or
suboptimal) multi-stream detector(s), notice that the
multi-stream detector mentioned here is also named as
multi-user detector in other references. We compare the
performance of the multi-rate multi-cell QS-CDMA system
employing the proposed sets with that of multi-rate system
employing well-known concatenated orthogonal/PN sets and
that of single-rate system employing GLS sets. The results
show that the multi-rate system employing the proposed sets
can achieve significant interference reduction. Meanwhile
the performance of multi-rate system is similar to that of
single-rate system due to the inclusion of multi-user
detection. © 2008 Springer Science+Business Media,
LLC.},
Doi = {10.1007/s11277-008-9620-0},
Key = {fds336766}
}
@article{fds336774,
Author = {You, C and Hwang, I and Kim, Y and Tarokh, V},
Title = {Dual antenna selection algorithms and feedback strategies
with reduced complexity for multiple-input multiple-output
systems},
Journal = {Iet Microwaves, Antennas & Propagation},
Volume = {3},
Number = {6},
Pages = {906-916},
Publisher = {Institution of Engineering and Technology
(IET)},
Year = {2009},
Month = {August},
url = {http://dx.doi.org/10.1049/iet-map.2008.0144},
Abstract = {A simple antenna selection strategy for multiple-input
multiple-output wireless systems with partial feedback is
presented. In the proposed scheme, both transmit and receive
antenna selection are done at the receiver, significantly
reducing feedback information. In addition, this scheme uses
row/column probability density function for antenna
selection to reduce computational complexity without
performance degradation. Unlike other schemes, two different
antenna selection algorithms are used in high and low
signal-to-noise ratio regimes, respectively, achieving
additional performance gain in comparison to the single
antenna selection algorithm. Simulation results show that
the proposed scheme nearly approaches the optimal
closed-loop capacity (known as water-filling capacity) as
random selection round for antenna selection increases. ©
2009 The Institution of Engineering and Technology.},
Doi = {10.1049/iet-map.2008.0144},
Key = {fds336774}
}
@article{fds336770,
Author = {Sharif, M and Tarokh, V and Hassibi, B},
Title = {Peak power reduction of OFDM signals with sign
adjustment},
Journal = {Ieee Transactions on Communications},
Volume = {57},
Number = {7},
Pages = {2160-2166},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2009},
Month = {August},
url = {http://dx.doi.org/10.1109/TCOMM.2009.07.080012},
Abstract = {It has recently been shown that significant reduction in the
peak to mean envelope power (PMEPR) can be obtained by
altering the sign of each subcarrier in a multicarrier
system with n subcarriers. However, finding the best sign
not only requires a search over 2n possible signs but also
may lead to a substantial rate loss for small size
constellations. In this paper, we first propose a greedy
algorithm to choose the signs based on p-norm minimization
and prove that the resulting PMEPR is guaranteed to be less
than c log n where c is a constant independent of n for any
n. This approach has lower complexity in each iteration
compared to the derandomization approach of [1] while
achieving similar PMEPR reduction. We further improve the
performance of the proposed algorithm by enlarging the
search space using pruning. Simulation results show that
PMEPR of a multicarrier signal with 128 subcarriers can be
reduced to within 1.6 dB of the PMEPR of a single carrier
system. In the second part of the paper, we address the rate
loss by proposing a block coding scheme in which only one
sign vector is chosen for K different modulating vectors.
The sign vector can be computed using the greedy algorithm
in n iterations. We show that the multi-symbol encoding
approach can reduce the rate loss by a factor of K while
achieving the PMEPR of c logKn, i.e., only logarithmic
growth in K. Simulation results show that the rate loss can
be made smaller than %10 at the cost of only 1db increase in
the resulting PMEPR for a system with 128 subcarriers. ©
2009 IEEE.},
Doi = {10.1109/TCOMM.2009.07.080012},
Key = {fds336770}
}
@article{fds336767,
Author = {Vu, M and Tarokh, V},
Title = {Scaling laws of single-hop cognitive networks},
Journal = {Ieee Transactions on Wireless Communications},
Volume = {8},
Number = {8},
Pages = {4089-4097},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2009},
Month = {August},
url = {http://dx.doi.org/10.1109/TWC.2009.080453},
Abstract = {We consider a cognitive network consisting of n cognitive
users uniformly distributed with constant density among
primary users. Each user has a single transmitter and a
single receiver, and the primary and cognitive users
transmit concurrently. The cognitive users use single-hop
transmission in two scenarios: (i) with constant transmit
power, and (ii) with transmit power scaled according to the
distance to a designated primary transmitter. We show that,
in both cases, the cognitive users can achieve a throughput
scaled linearly with the number of users n. The first
scenario requires the cognitive users to have the
transmitter-receiver (Tx-Rx) distance bounded, but it can be
arbitrarily large. Then with high probability, any network
realization has the throughput scaling linearly with n. The
second scenario allows the cognitive Tx-Rx distance to grow
with the network at a feasible exponent as a function of the
path loss and the power scaling factors. In this case, the
average network throughput grows at least linearly with n
and at most as n log(n). These results suggest that
single-hop transmission may be a suitable choice for
cognitive transmission. © 2006 IEEE.},
Doi = {10.1109/TWC.2009.080453},
Key = {fds336767}
}
@article{fds336768,
Author = {Babadi, B and Kalouptsidis, N and Tarokh, V},
Title = {Comparison of SPARLS and RLS algorithms for adaptive
filtering},
Journal = {2009 Ieee Sarnoff Symposium, Sarnoff 2009 Conference
Proceedings},
Publisher = {IEEE},
Year = {2009},
Month = {July},
ISBN = {9781424433827},
url = {http://dx.doi.org/10.1109/SARNOF.2009.4850336},
Abstract = {In this paper, we overview the Low Complexity Recursive
ℒ1-Regularized Least Squares (SPARLS) algorithm proposed
in [2], for the estimation of sparse signals in an adaptive
filtering setting. The SPARLS algorithm is based on an
Expectation-Maximization type algorithm adapted for online
estimation. Simulation results for the estimation of
multi-path wireless channels show that the SPARLS algorithm
has significant improvement over the conventional
widely-used Recursive Least Squares (RLS) algorithm, in
terms of both mean squared error (MSE) and computational
complexity.},
Doi = {10.1109/SARNOF.2009.4850336},
Key = {fds336768}
}
@article{fds336769,
Author = {Vu, M and Devroye, N and Tarokh, V},
Title = {On the primary exclusive region of cognitive
networks},
Journal = {Ieee Transactions on Wireless Communications},
Volume = {8},
Number = {7},
Pages = {3380-3385},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2009},
Month = {July},
url = {http://dx.doi.org/10.1109/TWC.2009.080454},
Abstract = {We study a cognitive network consisting of a single primary
transmitter and multiple secondary, or cognitive, users. The
primary transmitter, located at the center of the network,
communicates with primary receivers within a disc called the
primary exclusive region (PER). Inside the PER, no cognitive
users may transmit, in order to guarantee an outage
probability for the primary receivers within. Outside the
PER, uniformly distributed cognitive users may transmit,
provided they are at a certain protected radius from a
primary receiver. We analyze the aggregated interference
from the cognitive transmitters to a primary receiver within
the PER. Based on this interference and the outage
guarantee, we derive bounds on the radius of the PER,
showing its interdependence on the receiver protected
distance and other system parameters. We also extend the
analysis to allowing the cognitive users to scale their
power according to the distance from the primary
transmitter. These studies provide a closed-form,
theoretical analysis of such a network geometry with PER,
which may be relevant in the upcoming spectrum sharing
actions. © 2009 IEEE.},
Doi = {10.1109/TWC.2009.080454},
Key = {fds336769}
}
@article{fds336771,
Author = {Koike-Akino, T and Popovski, P and Tarokh, V},
Title = {Optimized constellations for two-way wireless relaying with
physical network coding},
Journal = {Ieee Journal on Selected Areas in Communications},
Volume = {27},
Number = {5},
Pages = {773-787},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2009},
Month = {June},
url = {http://dx.doi.org/10.1109/JSAC.2009.090617},
Abstract = {We investigate modulation schemes optimized for two-way
wireless relaying systems, for which network coding is
employed at the physical layer. We consider network coding
based on denoise-and-forward (DNF) protocol, which consists
of two stages: multiple access (MA) stage, where two
terminals transmit simultaneously towards a relay, and
broadcast (BC) stage, where the relay transmits towards the
both terminals. We introduce a design principle of
modulation and network coding, considering the superposed
constellations during the MA stage. For the case of QPSK
modulations at the MA stage, we show that QPSK
constellations with an exclusive-or (XOR) network coding do
not always offer the best transmission for the BC stage, and
that there are several channel conditions in which
unconventional 5-ary constellations lead to a better
throughput performance. Through the use of sphere packing,
we optimize the constellation for such an irregular network
coding. We further discuss the design issue of the
modulation in the case when the relay exploits diversity
receptions such as multiple-antenna diversity and path
diversity in frequency-selective fading. In addition, we
apply our design strategy to a relaying system using
higher-level modulations of 16QAM in the MA stage.
Performance evaluations confirm that the proposed scheme can
significantly improve end-to-end throughput for two-way
relaying systems. © 2006 IEEE.},
Doi = {10.1109/JSAC.2009.090617},
Key = {fds336771}
}
@article{fds336773,
Author = {Hwang, I and You, C and Kim, Y and Tarokh, V},
Title = {Downlink transmission rate-control strategies for
closed-loop multiple-input multiple-output
systems},
Journal = {Iet Communications},
Volume = {3},
Number = {4},
Pages = {620-629},
Publisher = {Institution of Engineering and Technology
(IET)},
Year = {2009},
Month = {April},
url = {http://dx.doi.org/10.1049/iet-com.2008.0456},
Abstract = {A novel downlink transmission rate-control and feedback
reduction strategy for closed-loop multiple-input
multiple-output (MIMO) multiple-input multiple-output
wireless systems is presented. Unlike conventional systems
that use signal to interference plus noise ratio at the
receiver as an indicator of channel quality, we propose
using instantaneous MIMO capacity as an indicator for the
downlink transmission rate-control. A set of instantaneous
capacity thresholds is first chosen such that the expected
weighted capacity loss because of thresholding effects are
minimised. While computing the thresholds, we also consider
the quality of service and weight function to meet different
traffics and user needs. Then a set of codebooks can be
constructed minimising the overall capacity loss with given
quality of service constraint. Simulation results show that,
with only four data rate-control bits, our algorithm gives
only 12 capacity loss in 4×4 MIMO systems and almost twice
better than the current IS-856 standard in single-input
single-output systems. In case of 5-bit feedback scenario,
the proposed algorithm outperforms conventional systems by
minimising instantaneous capacity loss. © 2009 The
Institution of Engineering and Technology.},
Doi = {10.1049/iet-com.2008.0456},
Key = {fds336773}
}
@article{fds340028,
Author = {Akçakaya, M and Park, J and Tarokh, V},
Title = {Compressive Sensing Using Low Density Frames},
Volume = {abs/0903.0650},
Year = {2009},
Month = {March},
Abstract = {We consider the compressive sensing of a sparse or
compressible signal ${\bf x} \in {\mathbb R}^M$. We
explicitly construct a class of measurement matrices,
referred to as the low density frames, and develop decoding
algorithms that produce an accurate estimate $\hat{\bf x}$
even in the presence of additive noise. Low density frames
are sparse matrices and have small storage requirements. Our
decoding algorithms for these frames have $O(M)$ complexity.
Simulation results are provided, demonstrating that our
approach significantly outperforms state-of-the-art recovery
algorithms for numerous cases of interest. In particular,
for Gaussian sparse signals and Gaussian noise, we are
within 2 dB range of the theoretical lower bound in most
cases.},
Key = {fds340028}
}
@article{fds340027,
Author = {Babadi, B and Kalouptsidis, N and Tarokh, V},
Title = {SPARLS: A Low Complexity Recursive $\mathcal{L}_1$-Regularized
Least Squares Algorithm},
Volume = {abs/0901.0734},
Year = {2009},
Month = {January},
Abstract = {We develop a Recursive $\mathcal{L}_1$-Regularized Least
Squares (SPARLS) algorithm for the estimation of a sparse
tap-weight vector in the adaptive filtering setting. The
SPARLS algorithm exploits noisy observations of the
tap-weight vector output stream and produces its estimate
using an Expectation-Maximization type algorithm. Simulation
studies in the context of channel estimation, employing
multi-path wireless channels, show that the SPARLS algorithm
has significant improvement over the conventional
widely-used Recursive Least Squares (RLS) algorithm, in
terms of both mean squared error (MSE) and computational
complexity.},
Key = {fds340027}
}
@article{fds340020,
Author = {Koike-Akino, T and Popovski, P and Tarokh, V},
Title = {Denoising Strategy for Convolutionally-Coded Bidirectional
Relaying},
Journal = {Ieee International Conference on Communications},
Pages = {3306-+},
Publisher = {IEEE},
Year = {2009},
Month = {January},
ISBN = {978-1-4244-3434-3},
Key = {fds340020}
}
@article{fds340021,
Author = {Kim, SJ and Ghassemzadeh, SS and Miller, RR and Tarokh,
V},
Title = {TAS Protocols of a PASD system with limited feedback
information},
Journal = {Globecom 2009 2009 Ieee Global Telecommunications
Conference, Vols 1 8},
Pages = {6173-+},
Publisher = {IEEE},
Editor = {Ulema, M},
Year = {2009},
Month = {January},
ISBN = {978-1-4244-4147-1},
Key = {fds340021}
}
@article{fds336765,
Author = {Kim, SJ and Devroye, N and Tarokh, V},
Title = {Bi-directional half-duplex relaying protocols},
Journal = {Journal of Communications and Networks},
Volume = {11},
Number = {5},
Pages = {433-444},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2009},
Month = {January},
url = {http://dx.doi.org/10.1109/JCN.2009.6388387},
Abstract = {The bi-directional relay channel is the natural extension of
a three-terminal relay channel where node a transmits to
node b with the help of a relay r to allow for two-way
communication between nodes a and b. That is, in a
bi-directional relay channel, a and b wish to exchange
independent messages over a shared channel with the help of
a relay r. The rates at which this communication may
reliably take place depend on the assumptions made on the
relay processing abilities. We overview information
theoretic limits of the bi-directional relay channel under a
variety of conditions, before focusing on half-duplex nodes
in which communication takes place in a number of temporal
phases (resulting in protocols), and nodes may forward
messages in four manners. The relay-forwarding considered
are: Amplify and forward (AF), decode and forward (DF),
compress and forward (CF), and mixed forward. The last
scheme is a combination of CF in one direction and DF in the
other. We derive inner and outer bounds to the capacity
region of the bi-directional relay channel for three
temporal protocols under these four relaying schemes. The
first protocol is a two phase protocol where a and b
simultaneously transmit during the first phase and the relay
r alone transmits during the second. The second protocol
considers sequential transmissions from a and b followed by
a transmission from the relay while the third protocol is a
hybrid of the first two protocols and has four phases. We
provide a comprehensive treatment of protocols in Gaussian
noise, obtaining their respective achievable rate regions,
outer bounds, and their relative performance under different
SNR and relay geometries. © 2009 KICS.},
Doi = {10.1109/JCN.2009.6388387},
Key = {fds336765}
}
@article{fds336772,
Author = {Babadi, B and Kalouptsidis, N and Tarokh, V},
Title = {Asymptotic achievability of the Cramér-Rao bound for noisy
compressive sampling},
Journal = {Ieee Transactions on Signal Processing},
Volume = {57},
Number = {3},
Pages = {1233-1236},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2009},
Month = {January},
url = {http://dx.doi.org/10.1109/TSP.2008.2010379},
Abstract = {We consider a model of the form =Ax + n, where x ε CM is
sparse with at most L nonzero coefficients in unknown
locations, y ε CN is the observation vector, A CN×M is the
measurement matrix and n ε CN is the Gaussian noise. We
develop a Cramér-Rao bound on the mean squared estimation
error of the nonzero elements of x, corresponding to the
genie-aided estimator (GAE) which is provided with the
locations of the nonzero elements of x. Intuitively, the
mean squared estimation error of any estimator without the
knowledge of the locations of the nonzero elements of x is
no less than that of the GAE. Assuming that L/N is fixed, we
establish the existence of an estimator that asymptotically
achieves the Cramér-Rao bound without any knowledge of the
locations of the nonzero elements of x as N → infinite;,
for Aa random Gaussian matrix whose elements are drawn
i.i.d. according to N (0,1). © 2009 IEEE.},
Doi = {10.1109/TSP.2008.2010379},
Key = {fds336772}
}
@article{fds340025,
Author = {Moezzi, K and Jalaleddini, K and Aghdam, AG and Alasti, M and Tarokh,
V},
Title = {An Adaptive Rate Assignment Strategy for CDMA2000 IS-856
Subject to RAB Delay},
Journal = {Globecom 2009 2009 Ieee Global Telecommunications
Conference, Vols 1 8},
Pages = {5989-+},
Publisher = {IEEE},
Editor = {Ulema, M},
Year = {2009},
Month = {January},
ISBN = {978-1-4244-4147-1},
Key = {fds340025}
}
@article{fds340022,
Author = {Jalaleddini, K and Moezzi, K and Aghdam, AG and Alasti, M and Tarokh,
V},
Title = {Controller Design for Rate Assignment in Wireless
Networks},
Journal = {Ieee International Conference on Communications},
Pages = {4025-+},
Publisher = {IEEE},
Year = {2009},
Month = {January},
ISBN = {978-1-4244-3434-3},
Key = {fds340022}
}
@article{fds340023,
Author = {Koike-Akino, T and Popovski, P and Tarokh, V},
Title = {Adaptive Modulation and Network Coding with Optimized
Precoding in Two-Way Relaying},
Journal = {Globecom 2009 2009 Ieee Global Telecommunications
Conference, Vols 1 8},
Pages = {5400-+},
Publisher = {IEEE},
Editor = {Ulema, M},
Year = {2009},
Month = {January},
ISBN = {978-1-4244-4147-1},
Key = {fds340023}
}
@article{fds340024,
Author = {Koike-Akino, T and Tarokh, V},
Title = {Sphere Packing Optimization and EXIT Chart Analysis for
Multi-Dimensional QAM Signaling},
Journal = {Ieee International Conference on Communications},
Pages = {3888-3892},
Publisher = {IEEE},
Year = {2009},
Month = {January},
ISBN = {978-1-4244-3434-3},
Key = {fds340024}
}
@article{fds340026,
Author = {Bai, D and Ghassemzadeh, SS and Miller, RR and Tarokh,
V},
Title = {Beam Selection Gain Versus Antenna Selection
Gain},
Journal = {Corr},
Volume = {abs/0902.0966},
Year = {2009},
Key = {fds340026}
}
@article{fds340029,
Author = {Jeon, S-W and Devroye, N and Vu, M and Chung, S-Y and Tarokh,
V},
Title = {Cognitive networks achieve throughput scaling of a
homogeneous network.},
Journal = {Wiopt},
Pages = {1-5},
Publisher = {IEEE},
Editor = {Chong, S and Choi, W},
Year = {2009},
ISBN = {978-1-4244-4919-4},
Key = {fds340029}
}
@article{fds336775,
Author = {Babadi, B and Tarokh, V},
Title = {The impact of spectrum sensing time on the performance of
the GADIA algorithm},
Journal = {2008 Ieee Symposium on New Frontiers in Dynamic Spectrum
Access Networks, Dyspan 2008},
Pages = {472-478},
Publisher = {IEEE},
Year = {2008},
Month = {December},
ISBN = {9781424420179},
url = {http://dx.doi.org/10.1109/DYSPAN.2008.56},
Abstract = {In this paper, we analyze the performance of the GADIA
(Greedy Asynchronous Distributed Interference Avoidance)
algorithm ([1], [2]) given the spectral sensing time of the
various active agents. Under the assumption that the sensing
time is small compared to the update intervals, it is shown
that the algorithm converges to an equilibrium point. We
also derive the steady state variance of the error due to
spectrum sensing collisions by different clusters. Moreover,
we propose a heuristic adaptive rate scheme that reduces the
number of frequency band switchings required to reach the
equilibrium. Simulation studies show that the algorithm
achieves more than 96% of the aggregate Shannon capacity
corresponding to optimal/near-optimal strategies. Additional
simulations are provided, verify our analytic results on the
performance of the algorithm. ©2008 IEEE.},
Doi = {10.1109/DYSPAN.2008.56},
Key = {fds336775}
}
@article{fds336776,
Author = {Bai, D and Ghassemzadeh, SS and Miller, RR and Tarokh,
V},
Title = {Beam selection gain from butler matrices},
Journal = {Ieee Vehicular Technology Conference},
Publisher = {IEEE},
Year = {2008},
Month = {December},
ISBN = {9781424417223},
url = {http://dx.doi.org/10.1109/VETECF.2008.107},
Abstract = {We consider a wireless transmission scenario, when a base
station is endowed with a fixed beamforming network, where M
antennas are employed at the base station to point beams to
predetermined azimuthal angles. In our setting, a Butler
matrix is deployed at the RF stage to form M beams, and then
the best beam is selected for transmission. We derive the
distribution of the beam selection gain for this scenario
under a Rician channel assumption as a function of both the
azimuthal location of the remote unit and the Rician
K-factor. Using some key properties of the noncentral
chi-square distribution, we prove that beam selection
outperforms antenna selection. ©2008 IEEE.},
Doi = {10.1109/VETECF.2008.107},
Key = {fds336776}
}
@article{fds336777,
Author = {Yiu, S and Vu, M and Tarokh, V},
Title = {Interference reduction by beamforming in cognitive
networks},
Journal = {Globecom Ieee Global Telecommunications Conference},
Pages = {4406-4411},
Publisher = {IEEE},
Year = {2008},
Month = {December},
ISBN = {9781424423248},
url = {http://dx.doi.org/10.1109/GLOCOM.2008.ECP.845},
Abstract = {We consider beamforming in a cognitive network with multiple
primary users and secondary users sharing the same spectrum.
In particular, we assume that each secondary transmitter has
Nt antennas and transmits data to its single- antenna
receiver using beamforming. The beamformer is designed to
maximize the cognitive user's signal-to-interference ratio
(SIR), defined as the ratio of the received signal power at
the desired cognitive receiver to the total interference
created at all the primary receivers. Using mathematical
tools from random matrix theory, we derive both lower and
upper bounds on the average interference at the primary
receivers and the average SIR of the cognitive user. We
further analyze and prove the convergence of these two
performance measures asymptotically as the number of
antennas Nt or primary users Np increases. Specifically, the
average interference per primary receiver converges to the
expected value of the path loss in the network whereas the
average SIR of the secondary user decays as 1/c when c =
Np/Nt - ∞. In the special case of Nt = Np,the average
total interference approaches 0 and the average SIR
approaches ∞. © 2008 IEEE.},
Doi = {10.1109/GLOCOM.2008.ECP.845},
Key = {fds336777}
}
@article{fds336778,
Author = {Koike-Akino, T and Popovski, P and Tarokh, V},
Title = {Denoising maps and constellations for wireless network
coding in two-way relaying systems},
Journal = {Globecom Ieee Global Telecommunications Conference},
Pages = {3790-3794},
Year = {2008},
Month = {December},
ISBN = {9781424423248},
url = {http://dx.doi.org/10.1109/GLOCOM.2008.ECP.727},
Abstract = {We investigate on the design of modulation schemes suited
for two-way wireless relaying systems that apply network
coding at the physical layer. We consider network coding
based on denoise-and-forward (DNF), which consists of two
stages: multiple access (MA) stage and broadcast (BC) stage.
For the case of QPSK constellation in the MA stage, we
introduce the modulation-related problems in DNF. We propose
two approaches to solve those issues. One uses only QPSK
constellations at the BC stage. The other allows the use of
unconventional 5-ary modulations, optimized according to the
channel condition. The performance evaluation shows that a
significant improvement in end-to-end throughput can be
achieved, in particular for Nakagami-Rice fading channels.
© 2008 IEEE.},
Doi = {10.1109/GLOCOM.2008.ECP.727},
Key = {fds336778}
}
@article{fds336779,
Author = {Entekhabi, AH and Sharif, M and Tarokh, V},
Title = {On the peak to average power reduction of OFDM signals using
reserved subcarriers},
Journal = {Ieee International Symposium on Personal, Indoor and Mobile
Radio Communications, Pimrc},
Publisher = {IEEE},
Year = {2008},
Month = {December},
ISBN = {9781424426447},
url = {http://dx.doi.org/10.1109/PIMRC.2008.4699707},
Abstract = {Orthogonal Frequency Division Multiplexing (OFDM) is an
attractive technique for high data rate transmissions in
wireless and wireline systems. However OFDM signals suffer
from high peak-to-mean envelope power (PMEPR). In this paper
we consider the problem of reducing this high PMEPR using
reserved peak reduction subcarriers as considered by Tellado
and Cioffi [9]. We analyze the fundamental tradeoff between
PMEPR reduction and the rate loss due to reserved
subcarriers. We first provide a lower bound on the
complementary cumulative distribution of PMEPR using
infinitely many reserved subcarriers. We then show that the
problem of minimizing the maximum of the absolute value of
the signal using reserved subcarriers can be stated as a
convex linear matrix inequality problem. While the problem
is proved to be convex, its complexity is cubic in the
number of OFDM subcarriers n which can be prohibitive when n
is large. We then propose a suboptimal Greedy algorithm
based on p-norm minimization that chooses only bipolar
values for each subcarrier that has less complexity and more
PMEPR reduction than the previously proposed algorithm in
[8]. Our results provide the best tradeoff possible between
PMEPR reduction and the associated rate loss and also leads
to a practical algorithm to approach those limits1. © 2008
IEEE.},
Doi = {10.1109/PIMRC.2008.4699707},
Key = {fds336779}
}
@article{fds336781,
Author = {Koike-Akino, T and Popovski, P and Tarokh, V},
Title = {Two-way relaying with network coding for frequency-selective
fading channels},
Journal = {Conference Record Asilomar Conference on Signals, Systems
and Computers},
Pages = {2221-2225},
Publisher = {IEEE},
Year = {2008},
Month = {December},
ISBN = {9781424429417},
url = {http://dx.doi.org/10.1109/ACSSC.2008.5074830},
Abstract = {In this paper, we present a design method of physical layer
network coding for reliable two-way relaying in frequency-
selective fading channels. We consider a two-stage protocol:
At the first stage, two terminals simultaneously transmit
data packets towards a relaying node. The relay maps the
received signal into a discrete constellation using
appropriate network coding, after which it is broadcasted to
the terminals at the second stage. In our previous work, it
has been revealed that network coding should be adaptively
changed according to the channel state information, and
unconventional signalling such as 5QAM can improve
throughput for some channel conditions. In this paper, our
design method of network coding is improved for the case of
frequency-selective fading channels. © 2008
IEEE.},
Doi = {10.1109/ACSSC.2008.5074830},
Key = {fds336781}
}
@article{fds336782,
Author = {Kim, SJ and Mitran, P and Tarokh, V},
Title = {Performance bounds for bidirectional coded cooperation
protocols},
Journal = {Ieee Transactions on Information Theory},
Volume = {54},
Number = {11},
Pages = {5235-5241},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2008},
Month = {November},
url = {http://dx.doi.org/10.1109/TIT.2008.929913},
Abstract = {In coded bidirectional cooperation, two nodes wish to
exchange messages over a shared half-duplex channel with the
help of a relay. In this correspondence, we derive
performance bounds for this problem for each of three
decode-and-forward protocols. The first protocol is a two
phase protocol where both users simultaneously transmit
during the first phase and the relay alone transmits during
the second. In this protocol, our bounds are tight. The
second protocol considers sequential transmissions from the
two users followed by a transmission from the relay while
the third protocol is a hybrid of the first two protocols
and has four phases. In the latter two protocols the bounds
are not identical. Numerical evaluation shows that in some
cases of interest our bounds do not differ significantly.
Finally, in the Gaussian case with path loss, we derive
achievable rates and compare the relative merits of each
protocol. This case is of interest in cellular systems.
Surprisingly, we find that in some cases, the achievable
rate region of the four phase protocol contains points that
are outside the outer bounds of the other two protocols. ©
2008 IEEE.},
Doi = {10.1109/TIT.2008.929913},
Key = {fds336782}
}
@article{fds340033,
Author = {Kim, SJ and Devroye, N and Tarokh, V},
Title = {Bi-directional half-duplex protocols with multiple
relays},
Volume = {abs/0810.1268},
Year = {2008},
Month = {October},
Abstract = {In a bi-directional relay channel, two nodes wish to
exchange independent messages over a shared wireless
half-duplex channel with the help of relays. Recent work has
considered information theoretic limits of the
bi-directional relay channel with a single relay. In this
work we consider bi-directional relaying with multiple
relays. We derive achievable rate regions and outer bounds
for half-duplex protocols with multiple decode and forward
relays and compare these to the same protocols with amplify
and forward relays in an additive white Gaussian noise
channel. We consider three novel classes of half-duplex
protocols: the (m,2) 2 phase protocol with m relays, the
(m,3) 3 phase protocol with m relays, and general (m, t)
Multiple Hops and Multiple Relays (MHMR) protocols, where m
is the total number of relays and 3<t< m+3 is the number of
temporal phases in the protocol. The (m,2) and (m,3)
protocols extend previous bi-directional relaying protocols
for a single m=1 relay, while the new (m,t) protocol
efficiently combines multi-hop routing with message-level
network coding. Finally, we provide a comprehensive
treatment of the MHMR protocols with decode and forward
relaying and amplify and forward relaying in the Gaussian
noise, obtaining their respective achievable rate regions,
outer bounds and relative performance under different SNRs
and relay geometries, including an analytical comparison on
the protocols at low and high SNR.},
Key = {fds340033}
}
@article{fds336783,
Author = {Shin, WY and Jeon, SW and Devroye, N and Vu, MH and Chung, SY and Lee, YH and Tarokh, V},
Title = {Improved throughput scaling in wireless ad hoc networks with
infrastructure},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {1118-1122},
Publisher = {IEEE},
Year = {2008},
Month = {September},
ISBN = {9781424422579},
url = {http://dx.doi.org/10.1109/ISIT.2008.4595161},
Abstract = {We analyze the benefits of infrastructure support in
improving the throughput scaling in networks of n randomly
located wireless nodes. The infrastructure uses
multi-antenna base stations (BSs), in which the number of
BSs and the number of antennas at each BS can scale at
arbtrary rates relative to n. We introduce two multi-antenna
BS-based routing protocols and analyze their throughput
scaling laws. Two conventional schemes not using BSs are
also shown for comparison. In dense networks, we show that
the BS-based routing schemes do not improve the throughput
scaling. In contrast, in extended networks, we show what our
BS-based routing schemes can, under certain network
conditions, improve the throughput scaling significantly. ©
2008 IEEE.},
Doi = {10.1109/ISIT.2008.4595161},
Key = {fds336783}
}
@article{fds336784,
Author = {Vu, M and Devroye, N and Tarokh, V},
Title = {The primary exclusive region in cognitive
networks},
Journal = {2008 5th Ieee Consumer Communications and Networking
Conference, Ccnc 2008},
Pages = {1014-1019},
Publisher = {IEEE},
Year = {2008},
Month = {September},
ISBN = {1424414571},
url = {http://dx.doi.org/10.1109/ccnc08.2007.232},
Abstract = {In this paper, we consider a cognitive network in which a
single primary transmitter communicates with primary
receivers within an area of radius R 0, called the primary
exclusive region (PER). Inside this region, no cognitive
users may transmit. Outside the PER, provided that the
cognitive transmitters are at a minimal distance εp from a
primary receiver, they may transmit concurrently with the
primary user. We determine bounds on the primary exclusive
radius R0 and the guard band εp to guarantee an outage
performance for the primary user. Specifically, for a
desired rate C0 and an outage probability β, the
probability that the primary user's rate falls below C0 is
less than β. This performance guarantee holds even with an
arbitrarily large number of cognitive users uniformly
distributed with constant density outside the primary
exclusive region. © IEEE.},
Doi = {10.1109/ccnc08.2007.232},
Key = {fds336784}
}
@article{fds336785,
Author = {Smida, B and Tarokh, V},
Title = {Ground-to-air interference analysis in cellular ATG
systems},
Journal = {Ciss 2008, the 42nd Annual Conference on Information
Sciences and Systems},
Pages = {225-228},
Publisher = {IEEE},
Year = {2008},
Month = {September},
ISBN = {9781424422470},
url = {http://dx.doi.org/10.1109/CISS.2008.4558525},
Abstract = {For air-to-ground cellular systems with no frequency reuse,
we provide an analysis of the inter-cell interference under
3D hexagonal cell planning and a line of sight channel model
with no shadowing and no fading assumptions. Based on this
model, we provide upper bounds on the interference and the
outage probability for the ground-to-air link. Simulation
results demonstrate that our upper bounds are tight. © 2008
IEEE.},
Doi = {10.1109/CISS.2008.4558525},
Key = {fds336785}
}
@article{fds336786,
Author = {Akçakaya, M and Tarokh, V},
Title = {Noisy compressive sampling limits in linear and sublinear
regimes},
Journal = {Ciss 2008, the 42nd Annual Conference on Information
Sciences and Systems},
Pages = {1-4},
Publisher = {IEEE},
Year = {2008},
Month = {September},
ISBN = {9781424422470},
url = {http://dx.doi.org/10.1109/CISS.2008.4558484},
Abstract = {The authors have recently established a set of results that
characterize the number of measurements required to recover
a sparse signal in ℂM with L non-zero coefficients from
compressed samples in the presence of noise. These results
indicate that for a number of different recovery criteria,
O(L) (an asymptotically linear multiple of L) measurements
are necessary and sufficient for signal recovery, whenever L
grows linearly as a function of M. We review these results
that improve on the existing literature, which are mostly
derived for a specific recovery algorithm based on convex
programming, where O(L log(M-L)) measurements are required.
The results discussed here also show that O(L log(M-L))
measurements are required in the sublinear regime (L =
o(M)). © 2008 IEEE.},
Doi = {10.1109/CISS.2008.4558484},
Key = {fds336786}
}
@article{fds336787,
Author = {Babadi, B and Tarokh, V},
Title = {A distributed asynchronous algorithm for spectrum sharing in
wireless ad hoc networks},
Journal = {Ciss 2008, the 42nd Annual Conference on Information
Sciences and Systems},
Pages = {831-835},
Publisher = {IEEE},
Year = {2008},
Month = {September},
ISBN = {9781424422470},
url = {http://dx.doi.org/10.1109/CISS.2008.4558635},
Abstract = {We propose a distributed asynchronous spectrum allocation
algorithm that achieves performance close to that of a
centralized optimal algorithm. In our network model, nodes
are grouped into a number of clusters. Each cluster chooses
its transmission frequency band based on its knowledge of
the interference that it experiences. The convergence of the
proposed distributed algorithm to a sub-optimal spectrum
assignment strategy is proved. Moreover, asymptotic bounds
on the performance of the algorithm are derived for one
dimensional spatial distribution of the clusters in the
network. These analytic results and additional simulation
studies verify performance close to that of an optimum
centralized frequency allocation algorithm. It is
demonstrated that the algorithm achieves about 90% of the
Shannon capacities corresponding to the optimum centralized
frequency band assignments. © 2008 IEEE.},
Doi = {10.1109/CISS.2008.4558635},
Key = {fds336787}
}
@article{fds336788,
Author = {Parker, PA and Bliss, DW and Tarokh, V},
Title = {On the degrees-of-freedom of the MIMO interference
channel},
Journal = {Ciss 2008, the 42nd Annual Conference on Information
Sciences and Systems},
Pages = {62-67},
Publisher = {IEEE},
Year = {2008},
Month = {September},
ISBN = {9781424422470},
url = {http://dx.doi.org/10.1109/CISS.2008.4558496},
Abstract = {The high signal-to-noise ratio capacity of the symmetric
MIMO interference channel is characterized as a function of
the interference-to-noise ratio. This work is a multiple
antenna extension of the degrees of freedom expressions
derived by Etkin et al. for the single antenna case. This
characterization considers the case where the number of
receive antennas is greater than or equal to the number of
transmit antennas and shows the number of degrees of freedom
available for communication as a function of
log(INR)/log(SNR). © 2008 IEEE.},
Doi = {10.1109/CISS.2008.4558496},
Key = {fds336788}
}
@article{fds336789,
Author = {Nam, S and Vu, M and Tarokh, V},
Title = {Relay selection methods for wireless cooperative
communications},
Journal = {Ciss 2008, the 42nd Annual Conference on Information
Sciences and Systems},
Pages = {859-864},
Publisher = {IEEE},
Year = {2008},
Month = {September},
ISBN = {9781424422470},
url = {http://dx.doi.org/10.1109/CISS.2008.4558640},
Abstract = {We study the problem of relay selection in a wireless
cooperative network. Assuming a single source, a single
destination, and N uniformly distributed candidate relays,
we seek to select a set of cooperating relays to minimize
the total transmission time of a fixed amount of data. We
propose two selection methods: Best expectation, which
adaptively selects the relays, and Best-m, which selects an
optimally pre-determined number of relays. Each method is
implemented with a simple and optimal algorithm. We further
provide closed-form, analytical approximations of these
algorithms' performance, which help simplify the process of
finding the optimal number of cooperating relays.
Simulations illustrate the performance of the proposed relay
selection methods and show a close match between the
analytical approximations and the numerical values. Through
some initial studies, we also observe a simple and
intriguing connection between the Best-m selection method
and the network geometry. Provided that the relays are
uniformly distributed, the source can simply cooperate with
all the relays within a radius of a fixed proportion of the
source-destination distance. © 2008 IEEE.},
Doi = {10.1109/CISS.2008.4558640},
Key = {fds336789}
}
@article{fds336792,
Author = {Smida, B and Tarokh, V},
Title = {Interference in air-to-ground cellular systems},
Journal = {Ieee International Conference on Communications},
Pages = {1077-1081},
Publisher = {IEEE},
Year = {2008},
Month = {September},
ISBN = {9781424420742},
url = {http://dx.doi.org/10.1109/ICC.2008.210},
Abstract = {Interference in cellular terrestrial systems has been
extensively studied in the literature mainly through the use
of simulations. The interference for CDMA cellular
air-to-ground systems has been similarly evaluated through
extensive simulations. However, the air-to-ground systems
are simpler to analyze than terrestrial systems. In this
note, we provide analytic bounds for inter-cell interference
in air-to-ground cellular systems with no frequency reuse.
We consider the standard 3D hexagonal cell plan and a line
of sight channel model with no shadowing and no fading.
Simulation results demonstrate that our approximations are
extremely tight. ©2008 IEEE.},
Doi = {10.1109/ICC.2008.210},
Key = {fds336792}
}
@article{fds336793,
Author = {Hong, SC and Vu, MH and Tarokh, V},
Title = {Cognitive sensing based on side information},
Journal = {Proceedings of the 2008 Ieee Sarnoff Symposium,
Sarnoff},
Publisher = {IEEE},
Year = {2008},
Month = {August},
ISBN = {1424418437},
url = {http://dx.doi.org/10.1109/SARNOF.2008.4520040},
Abstract = {We study a sensing algorithm for cognitive radios based on
Bayesian energy detection while utilizing available side
information. The side information available to the cognitive
user can consist of: (i) spatial locations of the cognitive
and primary receivers, (ii) received power of the
primary-signal at the cognitive user, and (iii) a priori
transmission probability of the primary user. Considering
several scenarios with different combinations of side
information, we derive the respective, optimal detection
thresholds for the cognitive user. Numerical results using
these thresholds show significant performance improvement
based on the side information. Specifically, information on
spatial locations can help stabilize the performance for a
wide range of the primary activity factor. Highly skewed a
priori primarytransmission probability further helps improve
the performance dramatically.},
Doi = {10.1109/SARNOF.2008.4520040},
Key = {fds336793}
}
@article{fds336794,
Author = {Kim, SJ and Devroye, N and Mitran, P and Tarokh, V},
Title = {Comparison of bi-directional relaying protocols},
Journal = {Proceedings of the 2008 Ieee Sarnoff Symposium,
Sarnoff},
Publisher = {IEEE},
Year = {2008},
Month = {August},
ISBN = {1424418437},
url = {http://dx.doi.org/10.1109/SARNOF.2008.4520117},
Abstract = {In a bi-directional relay channel, two nodes wish to
exchange independent messages over a shared wireless channel
with the help of a relay. In this paper, we derive
achievable rate regions for four new half-duplex protocols
and compare these to four existing half-duplex protocols and
outer bounds. In time, our protocols consist of either two
or three phases. In the two phase protocols, both users
simultaneously transmit during the first phase and the relay
alone transmits during the second phase, while in the three
phase protocol the two users sequentially transmit followed
by a transmission from the relay. The relay may forward
information in one of four manners; we outline existing
Amplify and Forward (AF) and Decode and Forward (DF)
relaying schemes and introduce novel Compress and Forward
(CF), and Mixed Forward schemes. We derive achievable rate
regions for the CF and Mixed relaying schemes for the two
and three phase protocols. Finally, we provide a
comprehensive treatment of 8 possible half-duplex
bi-directional relaying protocols in Gaussian noise,
obtaining their respective achievable rate regions, outer
bounds, and their relative performance under different SNR
and relay geometries.},
Doi = {10.1109/SARNOF.2008.4520117},
Key = {fds336794}
}
@article{fds336795,
Author = {Babadi, B and Tarokh, V},
Title = {Distributed dynamic frequency allocation in wireless
networks under time-varying user activities},
Journal = {Proceedings of the 2008 Ieee Sarnoff Symposium,
Sarnoff},
Publisher = {IEEE},
Year = {2008},
Month = {August},
ISBN = {1424418437},
url = {http://dx.doi.org/10.1109/SARNOF.2008.4520043},
Abstract = {We propose a framework to analyze the performance of the
distributed dynamic frequency allocation algorithm
introduced in [1] in the presence of time-varying activity
of clusters. In our network model, nodes are grouped into a
number of clusters. Each cluster chooses its transmission
frequency band based on its knowledge of the interference
that it experiences. Furthermore, each cluster can be in
active or inactive mode according to a two-state Markov
model. We derive conditions on the convergence of the
algorithm in mean and variance using stochastic analysis.
Additional simulation studies verify the results of
stochastic modeling and the performance of the
algorithm.},
Doi = {10.1109/SARNOF.2008.4520043},
Key = {fds336795}
}
@article{fds336796,
Author = {Babadi, B and Tarokh, V},
Title = {Iterative approach to base station positioning in cellular
networks},
Journal = {Proceedings of the 2008 Ieee Sarnoff Symposium,
Sarnoff},
Publisher = {IEEE},
Year = {2008},
Month = {August},
ISBN = {1424418437},
url = {http://dx.doi.org/10.1109/SARNOF.2008.4520067},
Abstract = {We consider the problem of finding the optimal spatial
configuration of a number of base stations in a cellular
network. We propose a framework to approximately maximize
the average Signal to Interference plus Noise Ratio (SINR),
with respect to the positions of a fixed number of base
stations. An iterative algorithm is proposed in the
one-dimensional case and the convergence of the algorithm is
proved. The generalization to higher dimensions is
straightforward. Additional simulation studies verify the
convergence and satisfactory performance of the proposed
algorithm for a variety of scenarios.},
Doi = {10.1109/SARNOF.2008.4520067},
Key = {fds336796}
}
@article{fds340032,
Author = {Kim, SJ and Devroye, N and Mitran, P and Tarokh, V},
Title = {Achievable rate regions for bi-directional
relaying},
Volume = {abs/0808.0954},
Year = {2008},
Month = {August},
Abstract = {In a bi-directional relay channel, two nodes wish to
exchange independent messages over a shared wireless
half-duplex channel with the help of a relay. In this paper,
we derive achievable rate regions for four new half-duplex
protocols and compare these to four existing half-duplex
protocols and outer bounds. In time, our protocols consist
of either two or three phases. In the two phase protocols,
both users simultaneously transmit during the first phase
and the relay alone transmits during the second phase, while
in the three phase protocol the two users sequentially
transmit followed by a transmission from the relay. The
relay may forward information in one of four manners; we
outline existing Amplify and Forward (AF), Decode and
Forward (DF) and Compress and Forward (CF) relaying schemes
and introduce the novel Mixed Forward scheme. The latter is
a combination of CF in one direction and DF in the other. We
derive achievable rate regions for the CF and Mixed relaying
schemes for the two and three phase protocols. In the last
part of this work we provide a comprehensive treatment of 8
possible half-duplex bi-directional relaying protocols in
Gaussian noise, obtaining their respective achievable rate
regions, outer bounds, and their relative performance under
different SNR and relay geometries.},
Key = {fds340032}
}
@article{fds336797,
Author = {Parker, PA and Mitran, P and Bliss, DW and Tarokh,
V},
Title = {On bounds and algorithms for frequency synchronization for
collaborative communication systems},
Journal = {Ieee Transactions on Signal Processing},
Volume = {56},
Number = {8 I},
Pages = {3742-3752},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2008},
Month = {August},
url = {http://dx.doi.org/10.1109/TSP.2008.924799},
Abstract = {Cooperative diversity systems are wireless communication
systems designed to exploit cooperation among users to
mitigate the effects of multipath fading. In fairly general
conditions, it has been shown that these systems can achieve
the diversity order of an equivalent multiple-input
multiple-output (MIMO) channel and, if the node geometry
permits, virtually the same outage probability can be
achieved as that of the equivalent MIMO channel for a wide
range of applicable signal-to-noise ratio (SNR). However,
much of the prior analysis has been performed under the
assumption of perfect timing and frequency offset
synchronization. In this paper, we derive the estimation
bounds and associated maximum a posteriori estimators for
frequency offset estimation in a cooperative communication
system. We show the benefit of adaptively tuning the
frequency of the relay node in order to reduce estimation
error at the destination. We also derive an efficient
estimation algorithm, based on the correlation sequence of
the data, which has mean squared error close to the
Cramér-Rao Bound (CRB). © 2008 IEEE.},
Doi = {10.1109/TSP.2008.924799},
Key = {fds336797}
}
@article{fds336798,
Author = {Akçakaya, M and Tarokh, V},
Title = {A frame construction and a universal distortion bound for
sparse representations},
Journal = {Ieee Transactions on Signal Processing},
Volume = {56},
Number = {6},
Pages = {2443-2450},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2008},
Month = {June},
url = {http://dx.doi.org/10.1109/TSP.2007.914344},
Abstract = {We consider approximations of signals by the elements of a
frame in a complex vector space of dimension N and formulate
both the noiseless and the noisy sparse representation
problems. The noiseless representation problem is to find
sparse representations of a signal r given that such
representations exist. In this case, we explicitly construct
a frame, referred to as the Vandermonde frame, for which the
noiseless sparse representation problem can be solved
uniquely using O(N2 operations, as long as the number of
non-zero coefficients in the sparse representation of r is
∈N for some 0 ≤ ∈ 0.5. It is known that ∈ ≤ 0.5
cannot be relaxed without violating uniqueness. The noisy
sparse representation problem is to find sparse
representations of a signal r satisfying a distortion
criterion. In this case, we establish a lower bound on the
tradeoff between the sparsity of the representation, the
underlying distortion and the redundancy of any given frame.
© 2008 IEEE.},
Doi = {10.1109/TSP.2007.914344},
Key = {fds336798}
}
@article{fds336799,
Author = {Vu, M and Devroye, N and Tarokh, V},
Title = {An overview of scaling laws in ad hoc and cognitive radio
networks},
Journal = {Wireless Personal Communications},
Volume = {45},
Number = {3},
Pages = {343-354},
Publisher = {Springer Nature},
Year = {2008},
Month = {May},
url = {http://dx.doi.org/10.1007/s11277-008-9479-0},
Abstract = {Currently, wireless communications are changing along the
lines of three main thrusts. The first is the introduction
of secondary spectrum licensing (SSL). Regulations on the
usage of licensed spectra are being loosened, encouraging
unused primary spectrum to be licensed, often in an
opportunistic manner, to secondary devices. The second is
the introduction of cognitive radios. These wireless devices
are able to sense and adapt in a "smart" manner to their
wireless environment, making them prime candidates to
becoming secondary users in SSL initiatives. Finally, as we
approach the communication limits of point-to-point
channels, and as wireless devices become cheap and
ubiquitous, the focus is shifting from single to multiple
communication links, or networks. In this paper, we provide
an overview of the recently established theoretical limits,
in the form of sum-rates, or throughput, of two main types
of networks: ad hoc networks, in which the devices are
homogeneous, and cognitive networks, in which a mixture of
primary and secondary (or cognitive) devices are present. We
summarize and provide intuition on how the throughput of a
network scales with its number of nodes n, as n → ∞,
under different network and node capability assumptions. ©
2008 Springer Science+Business Media, LLC.},
Doi = {10.1007/s11277-008-9479-0},
Key = {fds336799}
}
@article{fds336804,
Author = {Devroye, N and Vu, M and Tarokh, V},
Title = {Achievable rates and scaling laws for cognitive radio
channels},
Journal = {Eurasip Journal on Wireless Communications and
Networking},
Volume = {2008},
Pages = {1-12},
Publisher = {Springer Nature},
Year = {2008},
Month = {February},
url = {http://dx.doi.org/10.1155/2008/896246},
Abstract = {Cognitive radios have the potential to vastly improve
communication over wireless channels. We outline recent
information theoretic results on the limits of primary and
cognitive user communication in single and multiple
cognitive user scenarios. We first examine the achievable
rate and capacity regions of single user cognitive channels.
Results indicate that at medium SNR (0-20 dB), the use of
cognition improves rates significantly compared to the
currently suggested spectral gap-filling methods of
secondary spectrum access. We then study another information
theoretic measure, the multiplexing gain. This measure
captures the number of point-to-point Gaussian channels
contained in a cognitive channel as the SNR tends to
infinity. Next, we consider a cognitive network with a
single primary user and multiple cognitive users. We show
that with single-hop transmission, the sum capacity of the
cognitive users scales linearly with the number of users. We
further introduce and analyze the primary exclusive radius,
inside of which primary receivers are guaranteed a desired
outage performance. These results provide guidelines when
designing a network with secondary spectrum users. Copyright
© 2008 Natasha Devroye et al.},
Doi = {10.1155/2008/896246},
Key = {fds336804}
}
@article{fds336801,
Author = {Swami, A and Berry, RA and Sayeed, AM and Tarokh, V and Zhao,
Q},
Title = {Introduction to the issue on signal processing and
networking for dynamic spectrum access},
Journal = {Ieee Journal of Selected Topics in Signal
Processing},
Volume = {2},
Number = {1},
Pages = {1-3},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2008},
Month = {February},
url = {http://dx.doi.org/10.1109/JSTSP.2008.917511},
Doi = {10.1109/JSTSP.2008.917511},
Key = {fds336801}
}
@article{fds336790,
Author = {Bai, D and Ghassemzadeh, SS and Miller, RR and Tarokh,
V},
Title = {Performance analysis of a PASD antenna system in Rayleigh
fading channels},
Journal = {Ieee Wireless Communications and Networking Conference,
Wcnc},
Pages = {1014-1019},
Year = {2008},
Month = {January},
ISBN = {9781424419968},
url = {http://dx.doi.org/10.1109/wcnc.2008.184},
Abstract = {In this paper, we analyze the performance of a communication
system that employs Protocol Assisted Switched Diversity
(PASD) antennas under Rayleigh fading channel conditions.
The PASD system accumulates time-displaced blocks, each with
the same information but using different antennas, and then
combines their symbols using maximal ratio combining (MRC).
In the PASD system, quality of service (QoS) is ensured by
comparing the available signal-to-noise ratio (SNR) at the
output of the combiner against a preset threshold value. Our
analysis shows that this method reduces the number of
transmissions significantly as the channel deteriorates as
compared with ARQ without memory while it can satisfy the
symbol error rate (SER) requirement for most of blocks. It
is also shown that deploying more than one antenna is
important to stabilize the system when the channel becomes
static. © 2008 IEEE.},
Doi = {10.1109/wcnc.2008.184},
Key = {fds336790}
}
@article{fds336791,
Author = {Vu, M and Ghassemzadeh, SS and Tarokh, V},
Title = {Interference in a cognitive network with
beacon},
Journal = {Ieee Wireless Communications and Networking Conference,
Wcnc},
Pages = {876-881},
Year = {2008},
Month = {January},
ISBN = {9781424419968},
url = {http://dx.doi.org/10.1109/wcnc.2008.160},
Abstract = {We study a cognitive network consisting of multiple
cognitive users communicating in the presence of a single
primary user. The primary user is located at the center of
the network, and the cognitive users are uniformly
distributed within a circle around the primary user.
Assuming a constant cognitive user density, the radius of
this circle will increase with the number of users. We
consider a scheme in which the primary transmitter sends a
beacon signaling its own transmission. The cognitive users,
upon receiving this beacon, stay silent. Because of channel
fading, however, there is a non-zero probability that a
cognitive user misses the beacon and hence, with a certain
activity factor, transmits concurrently with the primary
user. Given the location of the primary receiver, we are
interested in the total interference caused by the cognitive
users to this receiver. In particular, we provide
closed-form bounds on the mean and variance of the
interference, and relate them to the outage probability on
the primary user. These analytical results can help in the
design of a cognitive network with beacon. © 2008
IEEE.},
Doi = {10.1109/wcnc.2008.160},
Key = {fds336791}
}
@article{fds336800,
Author = {Hwang, I and You, C and Kim, D and Kim, Y and Tarokh,
V},
Title = {A broadcast scheme for MIMO systems with channel state
information at the transmitter},
Journal = {Ieice Transactions on Communications},
Volume = {E91-B},
Number = {2},
Pages = {613-617},
Publisher = {Institute of Electronics, Information and Communications
Engineers (IEICE)},
Year = {2008},
Month = {January},
url = {http://dx.doi.org/10.1093/ietcom/e91-b.2.613},
Abstract = {We propose a new broadcast strategy for a multiple-input
multiple-output (MIMO) system with N transmit antennas at
the transmitter and M≤N single antenna receivers. The
proposed method, based on dirtypaper coding (DPC), spatially
separates the M users but does not suffer from the power
loss of classical spatial division multiple access (SDMA).
For the special case of M=N=2 and when the two single
antenna receivers are assumed to be co-located, the proposed
scheme produces a 2 transmit, 2 receiver antenna MIMO
transmission system that doubles the symbol rate of MIMO
space-time block code (STBC) systems from one to two symbol
per transmission time. It is proved theoretically and
experimentally that the proposed scheme provides the same
performance level as that of MIMO STBC systems (i.e., the
Alamouti scheme) for the first symbol, and the same
performance as the Bell labs layered space-time (BLAST)
system for the second symbol. When compared to the BLAST
system, the proposed scheme has the same symbol rate, but
achieves significantly better performance, since it provides
2 level diversity per symbol on the first symbol while the
BLAST system does not provide any diversity. Copyright ©
2008 The Institute of Electronics, Information and
Communication Engineers.},
Doi = {10.1093/ietcom/e91-b.2.613},
Key = {fds336800}
}
@article{fds336802,
Author = {Devroye, N and Vu, M and Tarokh, V},
Title = {Cognitive radio networks: Highlights of information
theoretic limits, models, and design},
Journal = {Ieee Signal Processing Magazine},
Volume = {25},
Number = {6},
Pages = {12-23},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2008},
Month = {January},
url = {http://dx.doi.org/10.1109/MSP.2008.929286},
Abstract = {In recent years, the development of intelligent, adaptive
wireless devices called cognitive radios, together with the
introduction of secondary spectrum licensing, has led to a
new paradigm in communications: cognitive networks.
Cognitive networks are wireless networks that consist of
several types of users: often a primary user (the primary
license-holder of a spectrum band) and secondary users
(cognitive radios). These cognitive users employ their
cognitive abilities to communicate without harming the
primary users. The study of cognitive networks is relatively
new and many questions are yet to be answered. In this
article we highlight some of the recent information
theoretic limits, models, and design of these promising
networks. © 2008 IEEE.},
Doi = {10.1109/MSP.2008.929286},
Key = {fds336802}
}
@article{fds336803,
Author = {Shin, OS and Kung, HT and Tarokh, V},
Title = {Construction of block orthogonal Golay sequences and
application to channel estimation of mimo-ofdm
systems},
Journal = {Ieee Transactions on Communications},
Volume = {56},
Number = {1},
Pages = {27-31},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2008},
Month = {January},
url = {http://dx.doi.org/10.1109/TCOMM.2008.050492},
Abstract = {In this paper, we construct a family of block orthogonal
Golay sequences that have low peak-to-mean envelope power
ratio (PMEPR) as well as blockwise orthogonal properties. We
then present an application of the sequences to channel
estimation of multiple-input multiple-output orthogonal
frequency division multiplexing (MIMO-OFDM) systems. We
compare the performance of the proposed algorithm with that
of a frequency division multiplexing (FDM) piloting
algorithm, and investigate the effect of co-channel
interference (CCI) on the channel estimation performance. ©
2008 IEEE.},
Doi = {10.1109/TCOMM.2008.050492},
Key = {fds336803}
}
@article{fds340030,
Author = {Entekhabi, AH and Sharif, M and Tarokh, V},
Title = {On the Peak to Average Power Reduction of OFDM Signals Using
Reserved Subcarriers},
Journal = {2008 Ieee 19th International Symposium on Personal, Indoor
and Mobile Radio Communications},
Pages = {1630-+},
Publisher = {IEEE},
Year = {2008},
Month = {January},
ISBN = {978-1-4244-2643-0},
Key = {fds340030}
}
@article{fds340031,
Author = {Bai, D and Ghassemzadeh, SS and Miller, RR and Tarokh,
V},
Title = {Beam Selection Gain from Butler Matrices},
Journal = {Ieee Vehicular Technology Conference},
Pages = {446-450},
Publisher = {IEEE},
Year = {2008},
Month = {January},
ISBN = {978-1-4244-1722-3},
Key = {fds340031}
}
@article{fds336805,
Author = {Akçakaya, M and Tarokh, V},
Title = {Performance study of various sparse representation methods
using redundant frames},
Journal = {Forty First Annual Conference on Information Sciences and
Systems, Ciss 2007 Proceedings},
Pages = {726-729},
Publisher = {IEEE},
Year = {2007},
Month = {December},
ISBN = {1424410371},
url = {http://dx.doi.org/10.1109/CISS.2007.4298400},
Abstract = {Sparse representations have recently received wide attention
because of their numerous potential applications. In this
paper, we consider sparse representations of signals with at
most L non-zero coefficients using a frame ℱ of size M in
CN. We bound the average distortion of such a representation
for any arbitrary frame ℱ by a numerical lower bound that
is only a function of the sparsity e = L/N of the
representation, and the redundancy (r - 1) = M/N - 1 of ℱ.
This numerical lower bound is shown to be much stronger than
the analytical and asymptotic bounds of [1] in low
dimensions (e.g. N = 6,8,10), but it is much less
straightforward to compute. We then study the performance of
randomly generated frames with respect to this numerical
lower bound, and to the analytical and asymptotic bounds of
[1]. When the optimal sparse representation algorithm is
used, it is observed that randomly generated frames perform
about 2 dB away from the theoretical lower bound in low
dimensions. We use the greedy orthogonal matching pursuit
(OMP) algorithm to study the performance of randomly
generated frames in higher dimensions. For small values of
ε, randomly generated frames using OMP perform close to the
lower bound and the results suggest that the loss of the
sub-optimal search using orthogonal matching pursuit
algorithm grows as a function of e. As N grows, a
concentration phenomenon for the performance of randomly
generated frames about their average is observed in all
cases, even when using the OMP algorithm. © 2007
IEEE.},
Doi = {10.1109/CISS.2007.4298400},
Key = {fds336805}
}
@article{fds336806,
Author = {Vu, M and Devroye, N and Sharif, M and Tarokh, V},
Title = {Scaling laws of cognitive networks},
Journal = {Proceedings of the 2nd International Conference on Cognitive
Radio Oriented Wireless Networks and Communications,
Crowncom},
Pages = {2-8},
Publisher = {IEEE},
Year = {2007},
Month = {December},
url = {http://dx.doi.org/10.1109/CROWNCOM.2007.4549764},
Abstract = {Opportunistic secondary spectrum usage has the potential to
dramatically increase spectral efficiency and rates of a
network of secondary cognitive users. In this work we
consider a cognitive network: n pairs of cognitive
transmitter and receiver wish to communicate simultaneously
in the presence of a single primary transmitter-receiver
link. We assume each cognitive transmitter-receiver pair
communicates in a realistic single-hop fashion, as cognitive
links are likely to be highly localized in space. We first
show that under an outage constraint on the primary link's
capacity, provided that the density of the cognitive users
is constant, the sum-rate of the n cognitive links scales
linearly with n as n → ∞. This scaling is in contrast to
the sum-rate scaling of √n seen in multi-hop ad-hoc
networks. We then explore the optimal radius of the primary
exclusive region: the region in which no secondary cognitive
users may transmit, such that the outage constraint on the
primary user is satisfied. We obtain bounds that help the
design of this primary exclusive region, outside of which
cognitive radios may freely transmit.},
Doi = {10.1109/CROWNCOM.2007.4549764},
Key = {fds336806}
}
@article{fds336807,
Author = {Hwang, I and You, C and Kim, Y and Tarokh, V},
Title = {Antenna selection strategies for MIMO systems},
Journal = {Ieee International Conference on Communications},
Pages = {4140-4143},
Publisher = {IEEE},
Year = {2007},
Month = {December},
ISBN = {1424403537},
url = {http://dx.doi.org/10.1109/ICC.2007.682},
Abstract = {Antenna selection strategies for multiple-input
multiple-output (MIMO) wireless systems is presented. In our
scheme, both transmit and receive antenna selection is done
at the receiver, significantly reducing feedback information
to the transmitter. Row/column probability density function
(pdf) is used for antenna selection to reduce computational
complexity without performance degradation. Unlike other
schemes, we used two different antenna selection algorithms
both for high SNR and low SNR regime, achieving additional
performance gain in comparison with the single antenna
selection algorithm. Simulation results show that our scheme
nearly approaches to the optimal closed-loop capacity (known
as water-filling capacity). © 2007 IEEE.},
Doi = {10.1109/ICC.2007.682},
Key = {fds336807}
}
@article{fds336810,
Author = {Hwang, I and Kim, D and You, C and Kim, Y and Tarokh,
V},
Title = {A new practical dirty-paper coding strategy in MIMO
system},
Journal = {Forty First Annual Conference on Information Sciences and
Systems, Ciss 2007 Proceedings},
Pages = {125-129},
Publisher = {IEEE},
Year = {2007},
Month = {December},
ISBN = {1424410371},
url = {http://dx.doi.org/10.1109/CISS.2007.4298285},
Abstract = {In this paper, we propose a new broadcast strategy for a
MIMO system with N transmit antennas at the transmitter and
M < N single antenna receivers. The proposed method
spatially separates the M users but does not suffer from the
power loss of classical SDMA. For the special case of M = N
= 2 and when the two single antenna receivers are assumed to
be colocated, the proposed scheme produces a 2 transmit, 2
receiver antenna MIMO scheme. This gives a MIMO transmission
scheme that doubles the symbol rate of MIMO STBC systems
(Alamouti scheme) from one to two symbol per transmission
time. It is proved that it provides the same performance
level as that of the Alamouti STBC for the first symbol, and
the same performance as the BLAST system for the second
symbol. When compared to the BLAST system, our scheme has
the same symbol rate, but enjoys significant performance
improvements, since it provides 2 level diversity per symbol
on the first symbol while the BLAST system does not provide
any diversity. © 2007 IEEE.},
Doi = {10.1109/CISS.2007.4298285},
Key = {fds336810}
}
@article{fds336811,
Author = {Parker, PA and Mitran, P and Bliss, DW and Tarokh,
V},
Title = {Training sequence design for wireless collaborative
communication systems in frequency-selective
fading},
Journal = {Conference Record Asilomar Conference on Signals, Systems
and Computers},
Pages = {2050-2057},
Publisher = {IEEE},
Year = {2007},
Month = {December},
ISBN = {9781424421107},
url = {http://dx.doi.org/10.1109/ACSSC.2007.4487598},
Abstract = {We consider a collaborative communication system consisting
of several nodes jointly communicating to a common
destination node. Once each node determines the message to
send, a space-time code across the sources is used to
transmit the signal to the destination. As there may be
frequency offsets and unknown frequency selective channels,
we assume a training sequence is sent in the preamble to
estimate these parameters. In this paper, we derive an
algorithm that designs training sequences that minimize the
Cramér-Rao Bound for frequency estimation in a
frequency-selective environment for a multiple node
collaborative communication system. © 2007
IEEE.},
Doi = {10.1109/ACSSC.2007.4487598},
Key = {fds336811}
}
@article{fds336812,
Author = {Akçakaya, M and Tarokh, V},
Title = {On sparsity, redundancy and quality of frame
representations},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {951-955},
Publisher = {IEEE},
Year = {2007},
Month = {December},
ISBN = {1424414296},
url = {http://dx.doi.org/10.1109/ISIT.2007.4557114},
Abstract = {We consider approximations of signals by the elements of a
frame in a complex vector space of dimension N and formulate
both the noiseless and the noisy sparse representation
problems. The noiseless representation problem is to find
sparse representations of a signal r given that such
representations exist. In this case, we explicitly construct
a frame, referred to as the Vandermonde frame, for which the
noiseless sparse representation problem can be solved
uniquely using O(N2) operations, as long as the number of
non-zero coefficients in the sparse representation of r is
∈N for some 0 ≤ ∈ ≤ 0.5, thus improving on a result
of Candès and Tao [3]. We also show that ∈ ≤ 0.5 cannot
be relaxed without violating uniqueness. The noisy sparse
representation problem is to find sparse representations of
a signal r satisfying a distortion criterion. In this case,
we establish a lower bound on the trade-off between the
sparsity of the representation, the underlying distortion
and the redundancy of any given frame. ©2007
IEEE.},
Doi = {10.1109/ISIT.2007.4557114},
Key = {fds336812}
}
@article{fds336813,
Author = {Kim, SJ and Mitran, P and John, C and Ghanadan, R and Tarokh,
V},
Title = {Coded bi-directional relaying in combat scenarios},
Journal = {Proceedings Ieee Military Communications Conference
Milcom},
Publisher = {IEEE},
Year = {2007},
Month = {December},
ISBN = {1424415136},
url = {http://dx.doi.org/10.1109/MILCOM.2007.4455154},
Abstract = {In this paper, we present three protocols for bidirectional
coded cooperation. In coded bi-directional cooperation, two
agents wish to communicate with each other in the presence
of a relay node that may help. The first protocol is a two
phase protocol where both users simultaneously transmit
during the first phase and the relay alone transmits during
the second. The second protocol considers sequential
transmissions from the two users followed by a transmission
from the relay while the third protocol is a hybrid of the
first two protocols and has four phases. In a shared
half-duplex channel, as each user is unable to receive a
signal while simultaneously transmitting, the first protocol
limits any received signal for the end users to arrive from
the relay only. In contrast, the second and third protocols
allow for each end-user to received signals from both the
relay and the other user. Thus, in the second and third
protocols, there is potential for additional
"side-information" at each receiving agent. In this paper,
we show that this side-information may be used to yield more
diversity and thereby greatly increase communication
reliability over fading channels. Finally, we consider
channel models based on the Joint Tactical Radio System
(JTRS), and compute outage probabilities and achievable
rates. Based on these results, the relative merits of each
protocol is discussed in various regimes. Furthermore,
experiments demonstrate the performance with the proposed
protocols dominates the traditional three phase coded
relaying protocol in which the side-information is not used.
These results may be explained by the additional diversity
provided by the proper utilization of the side-information.
These results have significant applications in the design of
net-centric systems for tactical environment, particularly
in the design of medium access control for mobile ad-hoc
networks and robust communication in tactical edge networks.
© 2007 IEEE.},
Doi = {10.1109/MILCOM.2007.4455154},
Key = {fds336813}
}
@article{fds336814,
Author = {Bai, D and Mitran, P and Ghassemzadeh, SS and Miller, RR and Tarokh,
V},
Title = {Channel hardening and the scheduling gain of antenna
selection diversity schemes},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {1066-1070},
Publisher = {IEEE},
Year = {2007},
Month = {December},
ISBN = {1424414296},
url = {http://dx.doi.org/10.1109/ISIT.2007.4557365},
Abstract = {For a multiple antenna system, we compute the asymptotic
distribution of antenna selection gain when the transmitter
selects the transmit antenna with the strongest channel. We
use this to asymptotically estimate the underlying channel
capacity distributions, and demonstrate that unlike
multiple-input/ multiple-output (MIMO) systems,the channel
for antenna selection systems hardens at a slower rate, and
thus a significant multiuser scheduling gain can exist.
Additionally, even without this scheduling gain, it is
demonstrated that transmit antenna selection systems
outperform open loop MIMO systems at low
signal-to-interference-plus-noise ratio (SINR) regimes,
particularly for small number of receive antennas. This may
have some implications on wireless system design, because
most of the users in modern wireless systems have low SINRs.
©2007 IEEE.},
Doi = {10.1109/ISIT.2007.4557365},
Key = {fds336814}
}
@article{fds361701,
Author = {Babadi, B and Tarokh, V},
Title = {A Distributed Dynamic Frequency Allocation
Algorithm},
Year = {2007},
Month = {November},
Abstract = {We consider a network model where the nodes are grouped into
a number of clusters and propose a distributed dynamic
frequency allocation algorithm that achieves performance
close to that of a centralized optimal algorithm. Each
cluster chooses its transmission frequency band based on its
knowledge of the interference that it experiences. The
convergence of the proposed distributed algorithm to a
sub-optimal frequency allocation pattern is proved. For some
specific cases of spatial distributions of the clusters in
the network, asymptotic bounds on the performance of the
algorithm are derived and comparisons to the performance of
optimal centralized solutions are made. These analytic
results and additional simulation studies verify performance
close to that of an optimum centralized frequency allocation
algorithm. It is demonstrated that the algorithm achieves
about 90% of the Shannon capacities corresponding to the
optimum/near-optimum centralized frequency band assignments.
Furthermore, we consider the scenario where each cluster can
be in active or inactive mode according to a two-state
Markov model. We derive conditions to guarantee finite
steady state variance for the output of the algorithm using
stochastic analysis. Further simulation studies confirm the
results of stochastic modeling and the performance of the
algorithm in the time-varying setup.},
Key = {fds361701}
}
@article{fds336816,
Author = {Sang, JK and Mitran, P and Tarokh, V},
Title = {Performance bounds for Bi-directional coded cooperation
protocols},
Journal = {Proceedings International Conference on Distributed
Computing Systems},
Publisher = {IEEE},
Year = {2007},
Month = {November},
url = {http://dx.doi.org/10.1109/ICDCSW.2007.109},
Abstract = {In coded bi-directional cooperation, two nodes wish to
exchange messages over a shared half-duplex channel with the
help of a relay. In this paper, we derive performance bounds
for this problem for each of three protocols. The first
protocol is a two phase protocol where both users
simultaneously transmit during the first phase and the relay
alone transmits during the second. In this protocol, our
bounds are tight. The second protocol considers sequential
transmissions from the two users followed by a transmission
from the relay while the third protocol is a hybrid of the
first two protocols and has four phases. In the latter two
protocols the inner and outer bounds are not identical, and
differ in a manner similar to the inner and outer bounds of
Cover's relay channel. Numerical evaluation shows that at
least in some cases of interest our bounds do not differ
significantly. Finally, in the Gaussian case with path loss,
we derive achievable rates and compare the relative merits
of each protocol in various regimes. Surprisingly, we find
that in some cases, the achievable rate region of the four
phase protocol sometimes contains points that are outside
the outer bounds of the other protocols. © 2007
IEEE.},
Doi = {10.1109/ICDCSW.2007.109},
Key = {fds336816}
}
@article{fds336818,
Author = {Akçakaya, M and Tarokh, V},
Title = {Performance of sparse representation algorithms using
randomly generated frames},
Journal = {Ieee Signal Processing Letters},
Volume = {14},
Number = {11},
Pages = {777-780},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2007},
Month = {November},
url = {http://dx.doi.org/10.1109/LSP.2007.901683},
Abstract = {We consider sparse representations of signals with at most L
nonzero coefficients using a frame F of size M in CN. For
any F, we establish a universal numerical lower bound on the
average distortion of the representation as a function of
the sparsity epsi; = L/N of the representation and
redundancy (r - 1) = M/N-1 of F. In low dimensions (e.g., N
= 6, 8, 10), this bound is much stronger than the analytical
and asymptotic bounds given in another of our papers. In
contrast, it is much less straightforward to compute. We
then compare the performance of randomly generated frames to
this numerical lower bound and to the analytical and
asymptotic bounds given in the aforementioned paper. In low
dimensions, it is shown that randomly generated frames
perform about 2 dB away from the theoretical lower bound,
when the optimal sparse representation algorithm is used. In
higher dimensions, we evaluate the performance of randomly
generated frames using the greedy orthogonal matching
pursuit (OMP) algorithm. The results indicate that for small
values of ε, OMP performs close to the lower bound and
suggest that the loss of the suboptimal search using
orthogonal matching pursuit algorithm grows as a function of
ε. In all cases, the performance of randomly generated
frames hardens about their average as N grows, even when
using the OMP algorithm. © 2007 IEEE.},
Doi = {10.1109/LSP.2007.901683},
Key = {fds336818}
}
@article{fds340034,
Author = {Devroye, N and Tarokh, V},
Title = {On the Degrees of Freedom in Cognitive Radio
Channels},
Volume = {abs/0707.1859},
Year = {2007},
Month = {July},
Abstract = {After receiving useful peer comments, we would like to
withdraw this paper.},
Key = {fds340034}
}
@article{fds336819,
Author = {Shin, OS and Chan, AM and Kung, HT and Tarokh, V},
Title = {Design of an OFDM cooperative space-time diversity
system},
Journal = {Ieee Transactions on Vehicular Technology},
Volume = {56},
Number = {4 II},
Pages = {2203-2215},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2007},
Month = {July},
url = {http://dx.doi.org/10.1109/TVT.2007.897642},
Abstract = {In this paper, we propose a wireless system that realizes
theoretical benefits of space-time cooperation.
Specifically, we design a space-time cooperative system
based on orthogonal frequency division multiplexing (OFDM),
which we refer to as a cooperative (CO)-OFDM system. Our
design includes a two-phase space-time cooperation protocol,
as well as a transmitter and receiver architecture that
facilitates cooperation. Furthermore, we devise a frame
structure, on which we build practical timing and frequency
synchronization algorithms and a channel estimation
algorithm. In particular, the proposed frequency
synchronization algorithm utilizes the underlying structure
of the cooperation protocol, and the proposed channel
estimation algorithm is based on a pairwise orthogonal
construction of two sequences. We validate the performance
of the proposed synchronization and channel estimation
algorithms through simulations. We then present simulation
results that demonstrate the overall performance advantage
of the CO-OFDM system over an OFDM system without
cooperation, not only under idealistic assumptions but also
under realistic situations where the proposed algorithms are
employed. © 2007 IEEE.},
Doi = {10.1109/TVT.2007.897642},
Key = {fds336819}
}
@article{fds336821,
Author = {Yim, R and Shin, OS and Tarokh, V},
Title = {Reverse-link rate control algorithms with fairness
guarantees for CDMA systems},
Journal = {Ieee Transactions on Wireless Communications},
Volume = {6},
Number = {4},
Pages = {1386-1397},
Publisher = {IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS
INC},
Year = {2007},
Month = {April},
url = {http://dx.doi.org/10.1109/TWC.2007.348335},
Abstract = {We propose a set of distributed rate control algorithms for
the reverse-link of CDMA systems using a pricing mechanism.
In the derivation, we assume that the base station
broadcasts a real-valued feedback in order to control the
reverse activity level. In addition, we assume that the
access terminals are able to transmit data at any rate
within a unite range, and that the transmission power is a
linear function of the transmission rate. For a specific
utility function, we show that the proposed algorithm
achieves social optimality, satisfies an interference power
constraint, and exhibits desirable short- and long-term
fairness behaviors. We then modify this algorithm so that it
can be applied to the case when the transmission power is a
convex function of the transmission rate. Next, we consider
the case that the feedback parameter is a single reverse
activity bit, and the underlying rates are elements of a
discrete set of admissible rates. This scenario is similar
to that of the IS-856 standard. We further modify our
algorithms so that they can be applied to this system setup,
and verify the performance using numerical simulations. It
is demonstrated that our algorithms exhibit short- and
long-term fairness behavior for this realistic scenario. ©
2007 IEEE.},
Doi = {10.1109/TWC.2007.348335},
Key = {fds336821}
}
@article{fds340036,
Author = {Akçakaya, M and Tarokh, V},
Title = {Performance Bounds on Sparse Representations Using Redundant
Frames},
Volume = {abs/cs/0703045},
Year = {2007},
Month = {March},
Abstract = {We consider approximations of signals by the elements of a
frame in a complex vector space of dimension $N$ and
formulate both the noiseless and the noisy sparse
representation problems. The noiseless representation
problem is to find sparse representations of a signal
$\mathbf{r}$ given that such representations exist. In this
case, we explicitly construct a frame, referred to as the
Vandermonde frame, for which the noiseless sparse
representation problem can be solved uniquely using $O(N^2)$
operations, as long as the number of non-zero coefficients
in the sparse representation of $\mathbf{r}$ is $\epsilon N$
for some $0 \le \epsilon \le 0.5$, thus improving on a
result of Candes and Tao \cite{Candes-Tao}. We also show
that $\epsilon \le 0.5$ cannot be relaxed without violating
uniqueness. The noisy sparse representation problem is to
find sparse representations of a signal $\mathbf{r}$
satisfying a distortion criterion. In this case, we
establish a lower bound on the trade-off between the
sparsity of the representation, the underlying distortion
and the redundancy of any given frame.},
Key = {fds340036}
}
@article{fds336817,
Author = {Parker, PA and Bliss, DW and Mitran, P and Tarokh,
V},
Title = {Adaptive frequency synchronization for collaborative
communication systems},
Journal = {Proceedings International Conference on Distributed
Computing Systems},
Pages = {82-87},
Publisher = {IEEE},
Year = {2007},
Month = {January},
ISBN = {0769528384},
url = {http://dx.doi.org/10.1109/ICDCSW.2007.96},
Abstract = {Cooperative diversity systems are wireless communication
systems designed to exploit cooperation among users to
mitigate the effects of multipath fading. In fairly general
conditions, it has been shown that these systems can achieve
the diversity order of an equivalent MISO channel and, if
the node geometry permits, virtually the same outage
probability is achieved as that of the equivalent MISO
channel for a wide range of applicable SNR. However, much of
the prior analysis has been performed under the assumption
of perfect timing and frequency offset synchronization. In
this paper, we derive the estimation bounds and associated
maximum likelihood estimators for frequency offset
estimation in a cooperative communication system. The
cooperative nature of the system is utilized to reduce the
estimation error with respect to standard (non-cooperative)
frequency estimation algorithms. For a worst case frequency
offset distribution among the nodes, we show that this
estimator is optimal in the sense of estimation error
variance. © 2007 IEEE.},
Doi = {10.1109/ICDCSW.2007.96},
Key = {fds336817}
}
@article{fds336820,
Author = {Tarokh, V and Alamouti, SM and Koivunen, V and Kim,
KH},
Title = {MIMO-OFDM and its application},
Journal = {Journal of Communications and Networks},
Volume = {9},
Number = {2},
Pages = {109},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2007},
Month = {January},
url = {http://dx.doi.org/10.1109/JCN.2007.6182828},
Doi = {10.1109/JCN.2007.6182828},
Key = {fds336820}
}
@article{fds336822,
Author = {Greenstein, LJ and Ghassemzadeh, SS and Hong, SC and Tarokh,
V},
Title = {Comparison study of UWB indoor channel models},
Journal = {Ieee Transactions on Wireless Communications},
Volume = {6},
Number = {1},
Pages = {128-135},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2007},
Month = {January},
url = {http://dx.doi.org/10.1109/TWC.2007.04691},
Abstract = {We compare three approaches for modeling the ultra-wideband
(UWB) indoor channel delay profile, including the one
adopted by the IEEE 802.15.3a Task Group. We do this using a
large database we collected (and have reported on
previously) spanning numerous indoor environments. Where
appropriate, we recalculate model parameters so as to be
compatible with the database. We test the models against the
database and against each other by computing certain
statistical 'attributes' of the ensemble of channel delay
profiles, e.g., the probability distribution, across the
ensemble, of the root-mean-square (rms) delay spread. We
show that each of the modeling approaches yields reasonable
agreement with the database for most or all of the
attributes tested, and we discuss the relative merits of the
three approaches. © 2007 IEEE.},
Doi = {10.1109/TWC.2007.04691},
Key = {fds336822}
}
@article{fds340035,
Author = {Babadi, B and Tarokh, V},
Title = {A Distributed Dynamic Frequency Allocation Algorithm For Ad
Hoc Networks},
Journal = {Corr},
Volume = {abs/0711.3247},
Year = {2007},
Key = {fds340035}
}
@article{fds340037,
Author = {Bai, D and Mitran, P and Ghassemzadeh, SS and Miller, RR and Tarokh,
V},
Title = {Rate of Channel Hardening of Antenna Selection Diversity
Schemes and Its Implication on Scheduling},
Journal = {Corr},
Volume = {abs/cs/0703022},
Year = {2007},
Key = {fds340037}
}
@article{fds340039,
Author = {Vu, M and Devroye, N and Sharif, M and Tarokh, V},
Title = {Scaling Laws of Cognitive Networks.},
Journal = {Crowncom},
Pages = {2-8},
Publisher = {IEEE},
Editor = {Chandramouli, R and Martin, F},
Year = {2007},
ISBN = {978-1-4244-0814-6},
Key = {fds340039}
}
@article{fds336826,
Author = {Rosenblum, M and Caramanis, C and Goemans, MX and Tarokh,
V},
Title = {Approximating fluid schedules in crossbar packet-switches
and Banyan networks},
Journal = {Ieee/Acm Transactions on Networking},
Volume = {14},
Number = {6},
Pages = {1374-1386},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2006},
Month = {December},
url = {http://dx.doi.org/10.1109/TNET.2006.886320},
Abstract = {We consider a problem motivated by the desire to provide
flexible, rate-based, quality of service guarantees for
packets sent over input queued switches and switch networks.
Our focus is solving a type of online traffic scheduling
problem, whose input at each time step is a set of desired
traffic rates through the switch network. These traffic
rates in general cannot be exactly achieved since they
assume arbitrarily small fractions of packets can be
transmitted at each time step. The goal of the traffic
scheduling problem is to closely approximate the given
sequence of traffic rates by a sequence of transmissions in
which only whole packets are sent. We prove worst-case
bounds on the additional buffer use, which we call backlog,
that results from using such an approximation. We first
consider the N × N, input queued, crossbar switch. Our main
result is an online packet-scheduling algorithm using no
speedup that guarantees backlog at most (N + 1)2/4 packets
at each input port and each output port. Upper bounds on
worst-case backlog have been proved for the case of constant
fluid schedules, such as the N2 - 2N + 2 bound of Chang,
Chen, and Huang (INFOCOM, 2000). Our main result for the
crossbar switch is the first, to our knowledge, to bound
backlog in terms of switch size N for arbitrary,
time-varying fluid schedules, without using speedup. Our
main result for Banyan networks is an exact characterization
of the speedup required to maintain bounded backlog, in
terms of polytopes derived from the network topology. ©
2006 IEEE.},
Doi = {10.1109/TNET.2006.886320},
Key = {fds336826}
}
@article{fds336827,
Author = {Ochiai, H and Mitran, P and Tarokh, V},
Title = {Variable-rate two-phase collaborative communication
protocols for wireless networks},
Journal = {Ieee Transactions on Information Theory},
Volume = {52},
Number = {9},
Pages = {4299-4313},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2006},
Month = {September},
url = {http://dx.doi.org/10.1109/TIT.2006.880055},
Abstract = {The performance of two-phase collaborative communication
protocols is studied for wireless networks. All the
communication nodes in the cluster are assumed to share the
same channel and transmit or receive collaboratively in a
quasi-static Rayleigh flat-fading environment. In addition
to small-scale fading, the effect of large-scale path loss
is also considered. Based on a decode-and-forward approach,
we consider various variable-rate two-phase protocols that
can achieve full diversity order and analyze the effect of
node geometry on their performance in terms of the outage
probability of mutual information. For the single-relay node
case, it is shown that if the collaborator node is close to
the source node, a protocol based on space-time coding (STC)
can achieve good diversity gain. Otherwise, a protocol based
on receiver diversity performs better. These protocols are
also compared with one based on fixed-rate repetition coding
and their performance tradeoffs with node geometry are
studied. The second part deals with multiple relays. It is
known that with N relays an asymptotic diversity order of
N+1 is achievable with STC-based protocols in the two-phase
framework. However, in the framework of collaborative STC,
those relay nodes which fail to decode remain silent (this
event is referred to as a node erasure). We show that this
node erasure has the potential to considerably reduce the
diversity order and point out the importance of designing
the STC to be robust against such node erasure. © 2006
IEEE.},
Doi = {10.1109/TIT.2006.880055},
Key = {fds336827}
}
@article{fds336828,
Author = {Devroye, N and Mitran, P and Tarokh, V},
Title = {Limits on communications in a cognitive radio
channel},
Journal = {Ieee Communications Magazine},
Volume = {44},
Number = {6},
Pages = {44-49},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2006},
Month = {June},
url = {http://dx.doi.org/10.1109/MCOM.2006.1668418},
Abstract = {In this article we review FCC secondary markets initiatives
and how smart wireless devices could be used to increase
spectral efficiency. We survey the current proposals for
cognitive radio deployment, and present a new, potentially
more spectrally efficient model for a wireless channel
employing cognitive radios; the cognitive radio channel.
This channel models the simplest scenario in which a
cognitive radio could be used and consists of a 2 Tx, 2 Rx
wireless channel in which one transmitter knows the message
of the other. We obtain fundamental limits on the
communication possible over such a channel, and discuss
future engineering and regulatory issues. © 2006
IEEE.},
Doi = {10.1109/MCOM.2006.1668418},
Key = {fds336828}
}
@article{fds336829,
Author = {Devroye, N and Mitran, P and Tarokh, V},
Title = {Achievable rates in cognitive radio channels},
Journal = {Ieee Transactions on Information Theory},
Volume = {52},
Number = {5},
Pages = {1813-1827},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2006},
Month = {May},
url = {http://dx.doi.org/10.1109/TIT.2006.872971},
Abstract = {Cognitive radio promises a low-cost, highly flexible
alternative to the classic single-frequency band,
single-protocol wireless device. By sensing and adapting to
its environment, such a device is able to fill voids in the
wireless spectrum and can dramatically increase spectral
efficiency. In this paper, the cognitive radio channel is
defined as a two-sender, two-receiver interference channel
in which sender 2 obtains the encoded message sender 1 plans
to transmit. We consider two cases: in the genie-aided
cognitive radio channel, sender 2 is noncausally presented
the data to be transmitted by sender 1 while in the causal
cognitive radio channel, the data is obtained causally. The
cognitive radio at sender 2 may then choose to transmit
simultaneously over the same channel, as opposed to waiting
for an idle channel as is traditional for a cognitive radio.
Our main result is the development of an achievable region
which combines Gel'fand-Pinkser coding with an achievable
region construction for the interference channel. In the
additive Gaussian noise case, this resembles dirty-paper
coding, a technique used in the computation of the capacity
of the Gaussian multiple-input multiple-output (MIMO)
broadcast channel. Numerical evaluation of the region in the
Gaussian noise case is performed, and compared to an inner
bound, the interference channel, and an outer bound, a
modified Gaussian MIMO broadcast channel. Results are also
extended to the case in which the message is causally
obtained. © 2006 IEEE.},
Doi = {10.1109/TIT.2006.872971},
Key = {fds336829}
}
@article{fds336830,
Author = {Mitran, P and Devroye, N and Tarokh, V},
Title = {On compound channels with side information at the
transmitter},
Journal = {Ieee Transactions on Information Theory},
Volume = {52},
Number = {4},
Pages = {1745-1755},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2006},
Month = {April},
url = {http://dx.doi.org/10.1109/TIT.2006.871044},
Abstract = {Costa has proved that for noncausally known Gaussian
interference at a power constrained transmitter
communicating over an additive white Gaussian noise channel
there is no capacity loss when compared to a scenario where
interference is not present. For the case of a transmitter
communicating over a quasistatic (i.e., nonergodic) fading
channel, his method does not apply. In this correspondence,
we derive upper and lower bounds on the capacity of compound
channels with side information at the transmitter, first for
finite alphabet channels and then, based on this result, for
channels on standard alphabets (this includes real
alphabets). For the special case of a degenerate compound
channel with only one possible realization, our bounds are
equivalent to the well-known capacity with side-information
formula of Gel'fand and Pinsker. For the quasistatic fading
channel, when fading is Ricean, we suggest a scheme based on
our lower bound for which the performance is found to be
relatively good even for moderate K -factor. As K → ∞,
the uncertainty on the channel vanishes and our scheme
obtains the performance of dirty paper coding, namely that
the interference is perfectly mitigated. As K → 0, the
proposed scheme treats the interferer as additional noise.
These results may be of importance for the emerging field of
cognitive radios where one user may be aware of another
user's intended message to a common receiver, but is unaware
of the channel path gains. © 2006 IEEE.},
Doi = {10.1109/TIT.2006.871044},
Key = {fds336830}
}
@article{fds336831,
Author = {Kim, IM and Ghassemzadeh, SS and Tarokh, V},
Title = {Optimized nonuniform PSK for multiclass traffic and its
application to space-time block codes},
Journal = {Ieee Transactions on Communications},
Volume = {54},
Number = {2},
Pages = {364-373},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2006},
Month = {February},
url = {http://dx.doi.org/10.1109/TCOMM.2005.863725},
Abstract = {We construct nonuniform phase-shift keying (PSK)
constellations that provide unequal error protection for
multiclass traffic such as compressed voice and video data.
Then closed-form expressions expression for the exact
bit-error rate (BER) of the nonuniform PSK constellations is
derived in multiple receive-antenna systems over Rayleigh
fading channels. Based on this BER analysis, we optimize the
nonuniform PSK constellations such that the BERs of all the
bits of each class are equalized or such that the total
transmission power is minimized subject to the average BER
constraints. In particular, we demonstrate that even for
transmitting single-class traffic, the optimized nonuniform
PSK constellations can be better than the conventional
uniform PSK. Finally, we extend the nonuniform PSK
constellations to space-time coded communications systems
with multiple transmit and multiple receive antennas. ©
2006 IEEE.},
Doi = {10.1109/TCOMM.2005.863725},
Key = {fds336831}
}
@article{fds336808,
Author = {Devroye, N and Mitran, P and Tarokh, V},
Title = {Cognitive decomposition of wireless networks},
Journal = {1st International Conference on Cognitive Radio Oriented
Wireless Networks and Communications 2006,
Crowncom},
Publisher = {IEEE},
Year = {2006},
Month = {January},
ISBN = {1424403812},
url = {http://dx.doi.org/10.1109/CROWNCOM.2006.363475},
Abstract = {In this paper, we provide a framework for a fundamental
study of the communication limits of networks of cognitive
devices. It is shown that all communication in a network of
cognitive and non-cognitive devices can be cast into
competitive, cognitive and cooperative behaviors. An
achievable rate region for the cognitive radio channnel
(which captures the most fundamental form of cognition -
vertical spectrum sharing), is presented. © 2006
IEEE.},
Doi = {10.1109/CROWNCOM.2006.363475},
Key = {fds336808}
}
@article{fds336823,
Author = {Yim, R and Shin, OS and Tarokh, V},
Title = {Distributed delay-aware rate control algorithm for the
reverse-link of CDMA systems},
Journal = {Ieee International Conference on Communications},
Volume = {10},
Pages = {4363-4368},
Publisher = {IEEE},
Year = {2006},
Month = {January},
ISBN = {1424403553},
url = {http://dx.doi.org/10.1109/ICC.2006.255324},
Abstract = {We propose a new distributed rate control algorithm for the
reverse link of CDMA systems. Specifically, when the
statistics of packet arrivals are known locally to each
access terminal (AT), this new algorithm aims to provide a
means to control the relative delay that each AT
experiences. For this algorithm, assuming that the arrival
process is Poisson and stationary, it is shown through
simulations that all ATs experience an equal amount of
average delay when the system is underloaded, and the same
packet drop probability when the system is overloaded.
Furthermore, we propose a modification to the algorithm that
gives priority to some desired ATs, and reduces their
relative average delay. Finally, simulation results indicate
that the algorithm achieves similar short-term average delay
even when the packet arrival process is not stationary. ©
2006 IEEE.},
Doi = {10.1109/ICC.2006.255324},
Key = {fds336823}
}
@article{fds336824,
Author = {Jung, YH and Nam, SH and Kim, Y and Chung, J and Tarokh,
V},
Title = {Differential spatial multiplexing for two and three transmit
antennas},
Journal = {Ieee International Conference on Communications},
Volume = {7},
Pages = {3317-3322},
Publisher = {IEEE},
Year = {2006},
Month = {January},
ISBN = {1424403553},
url = {http://dx.doi.org/10.1109/ICC.2006.255228},
Abstract = {In this paper, we construct a differential spatial
multiplexing method that can trade-off spatial diversity for
increased transmission rate in differential multi-input
multi-output (MIMO) systems. To achieve a desired
multiplexing gain while providing simple encoding and
decoding, GramSchmidt algorithm is used at the transmitter
to construct the unitary transmission matrix. In addition,
by applying optimum scaling factors to generate transmission
matrix, the symbol error rates can be minimized. Because the
transmission matrix itself is not the information we are
interested in, the equivalent channel parameters for each
transmitted information symbols are calculated and the
linear signal model for the information symbols is derived.
Since that model is exactly the same as that of the coherent
spatial multiplexing, all kinds of coherent detection
schemes can be directly applied. The advantage of the
proposed scheme over the differential space-time block codes
(STBC) and the effects of scaling factor are investigated by
computer simulation. In high transmission rate regimes, the
proposed differential spatial multiplexing method can
outperform the differential STBC having the same transmit
rate in the signal to noise ratios (SNRs) we are interested
in. © 2006 IEEE.},
Doi = {10.1109/ICC.2006.255228},
Key = {fds336824}
}
@article{fds336832,
Author = {Choi, YS and Alamouti, SM and Tarokh, V},
Title = {Complementary beamforming: New approaches},
Journal = {Ieee Transactions on Communications},
Volume = {54},
Number = {1},
Pages = {41-50},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2006},
Month = {January},
url = {http://dx.doi.org/10.1109/TCOMM.2005.861674},
Abstract = {Smart antenna technology can greatly improve the coverage
radius of wireless systems by focusing the transmitted
signal (beam) toward desired users. However, beamforming has
an important side effect as it creates a region, herein
referred to as the complementary region, where some users in
the network cannot sense the directional signals (beams). We
have referred to this as the hidden beam problem in Tarokh.
From a physical layer perspective, beamforming reduces
cochannel interference (CCI). However, in systems that use
medium access-control techniques such as the carrier-sense
multiple access (CSMA) protocol in wireless local area
networks, during a busy period of the channel, the users in
the complementary region may wrongly decide that the medium
is idle and transmit packets. This may cause CCI,
unnecessary retransmissions, subsequent backoff, and
increased network latency. We introduced the concept of
complementary beamforming (CBF) to address this issue in
Tarokh. In this paper, we propose two new methods, called
"subspace complementary beamforming" (SCBF) and
"complementary superposition beamforming" (CSBF). The SCBF
uses dummy data to ensure a controlled level of received
energy in all directions of eigenvectors unused by downlink
beamforming. The technique works in multipath fading
channels. The approach achieves similar results to those
reported in Tarokh. However, it enables the second technique
(CSBF) which can also send data content in the complementary
beam. This allows passive nodes in the network to receive
"broadcast" information, while the active nodes are engaged
in the exchange of user-specific data. It is shown that CBF
effects can be achieved simply by increasing the transmit
power of only one of antenna elements when space-division
multiple access is not applied. Simulations are provided in
order to quantify overall network performance improvements
when using CBF, confirming significant throughput and delay
performance enhancements. © 2006 IEEE.},
Doi = {10.1109/TCOMM.2005.861674},
Key = {fds336832}
}
@article{fds340040,
Author = {Devroye, N and Mitran, P and Tarokh, V},
Title = {Cognitive decomposition of wireless networks},
Journal = {2006 1st International Conference on Cognitive Radio
Oriented Wireless Networks and Communications},
Pages = {145-+},
Publisher = {IEEE},
Year = {2006},
Month = {January},
ISBN = {978-1-4244-0380-6},
Key = {fds340040}
}
@article{fds340041,
Author = {Rosenblum, M and Caramanis, C and Goemans, MX and Tarokh,
V},
Title = {Approximating fluid schedules in crossbar packet-switches
and Banyan networks.},
Journal = {Ieee/Acm Trans. Netw.},
Volume = {14},
Pages = {1374-1387},
Year = {2006},
url = {http://dx.doi.org/10.1145/1217706},
Doi = {10.1145/1217706},
Key = {fds340041}
}
@article{fds336833,
Author = {Devroye, N and Mitran, P and Tarokh, V},
Title = {Cognitive multiple access networks},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Volume = {2005},
Pages = {57-61},
Publisher = {IEEE},
Year = {2005},
Month = {December},
ISBN = {0780391519},
url = {http://dx.doi.org/10.1109/ISIT.2005.1523292},
Abstract = {A cognitive radio can sense the transmission of other users
in its environment and possibly extract the corresponding
messages. It can use this information to transmit over the
same channel while reducing interference from, and to other
users. In this paper, we define inter/intra-cluster
competitive, cooperative, and cognitive behavior in wireless
networks. We define inter-cluster cognitive behavior as
simultaneous transmissions by two or more clusters in which
some clusters know the messages to be transmitted by other
clusters, and so can act as relays or use a Gel'fand-Pinsker
coding-like technique to mitigate interference. We construct
an achievable region for the inter-cluster behavior of two
multiple access channels. In the Gaussian case, we compare
our achievable region to that of competitive behavior as
well as that of cooperative behavior.},
Doi = {10.1109/ISIT.2005.1523292},
Key = {fds336833}
}
@article{fds336834,
Author = {Shin, OS and Ghassemzadeh, SS and Greenstein, LJ and Tarokh,
V},
Title = {Performance evaluation of MB-OFDM and DS-UWB systems for
wireless personal area networks},
Journal = {Icu 2005: 2005 Ieee International Conference on Ultra
Wideband, Conference Proceedings},
Volume = {2005},
Pages = {214-219},
Year = {2005},
Month = {December},
ISBN = {078039397X},
Abstract = {Ultra-wideband (UWB) radio has been proposed for physical
layer standard of the future high-speed wireless personal
area networks (WFANs), One proposal is referred to as
multi-band orthogonal frequency division multiplexing
(MB-OFDM), and the other is direct-sequence ultra-wideband
(DS-UWB). In this paper, we evaluate the performance of
these physical layers as proposed to the IEEE 802.15 Task
Group 3a. Specifically, we evaluate and compare the 10%
outage frame error rate (FER) versus transmit-receive
distance for the two systems using standard UWB channel
models. In an AWGN channel, the two approaches yield
essentially the same performance. In fading channels, the
MB-OFDM system is shown to outperform the DS-UWB system for
the assumed receiver structures. However, the relative
performance ranking turns primarily on the signal processing
complexity of the receiver, especially at high rates.
Furthermore, the DS-UWB system is found to be more robust to
imperfect channel estimation than the MB-OFDM
system.},
Key = {fds336834}
}
@article{fds336836,
Author = {Kim, IM and Hong, SC and Ghassemzadeh, SS and Tarokh,
V},
Title = {Opportunistic beamforming based on multiple weighting
vectors},
Journal = {Ieee Transactions on Wireless Communications},
Volume = {4},
Number = {6},
Pages = {2683-2687},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2005},
Month = {November},
url = {http://dx.doi.org/10.1109/TWC.2005.857999},
Abstract = {In order to improve the throughput of the opportunistic
beamforming, the authors generalize the opportunistic
beamforming by using multiple random weighting vectors at
each time slot. The base station chooses the best weighting
vector and performs the opportunistic beamforming with this
optimum vector. For the case of equally strong independent
fast Rayleigh fading channels, the throughput of the
proposed scheme is analytically approximated and the optimum
number of random weighting vectors per time slot is
obtained. Numerical results demonstrate that the proposed
scheme considerably improves the throughput compared to the
conventional opportunistic beamforming for a low/realistic
number of users. © 2005 IEEE.},
Doi = {10.1109/TWC.2005.857999},
Key = {fds336836}
}
@article{fds336837,
Author = {Ochiai, H and Mitran, P and Poor, HV and Tarokh, V},
Title = {Collaborative beamforming for distributed wireless ad hoc
sensor networks},
Journal = {Ieee Transactions on Signal Processing},
Volume = {53},
Number = {11},
Pages = {4110-4124},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2005},
Month = {November},
url = {http://dx.doi.org/10.1109/TSP.2005.857028},
Abstract = {The performance of collaborative beamforming is analyzed
using the theory of random arrays. The statistical average
and distribution of the beampattern of randomly generated
phased arrays is derived in the framework of wireless ad hoc
sensor networks. Each sensor node is assumed to have a
single isotropic antenna and nodes in the cluster
collaboratively transmit the signal such that the signal in
the target direction is coherently added in the far-field
region. It is shown that with N sensor nodes uniformly
distributed over a disk, the directivity can approach N,
provided that the nodes are located sparsely enough. The
distribution of the maximum sidelobe peak is also studied.
With the application to ad hoc networks in mind, two
scenarios (closed-loop and open-loop) are considered.
Associated with these scenarios, the effects of phase jitter
and location estimation errors on the average beampattern
are also analyzed. © 2005 IEEE.},
Doi = {10.1109/TSP.2005.857028},
Key = {fds336837}
}
@article{fds336838,
Author = {Chung, J and Nam, SH and Jung, YH and Tarokh, V},
Title = {Trading-off transmission rate with transmit diversity in
differential detection},
Journal = {Ieee Vehicular Technology Conference},
Volume = {61},
Number = {3},
Pages = {1638-1641},
Year = {2005},
Month = {October},
Abstract = {In this paper we construct a method where rate can be
trade-off for diversity in differential detection transmit
diversity. Specifically, we show for the case 3 and 4
transmit and M receive anteanns, when using the PSK
constellation, it is possible to double the rate of
differential transmit diversity schemes (from 3/4 symbols
per channel use to 1.5 symbols per channel use) while
achieving 2(M-1) level diversity with extremely simple
encoding and decoding. © 2005 IEEE.},
Key = {fds336838}
}
@article{fds336839,
Author = {Yim, R and Rosenblum, M and Tarokh, V},
Title = {Delay bounds for packetizing time-varying fluid policies
with speedup and lookahead in single server
systems},
Journal = {Proceedings Ieee Infocom},
Volume = {4},
Pages = {2590-2601},
Publisher = {IEEE},
Year = {2005},
Month = {October},
ISBN = {0780389689},
url = {http://dx.doi.org/10.1109/INFCOM.2005.1498543},
Abstract = {We consider an online, processor sharing system with a
single server in a packet-switched network where the
processor multiplexes packets from multiple input ports onto
the same output link. Under a fluid model, in which incoming
data is treated as infinitely divisible, the multiplexer
allocates its output capacity to serve fractions of packets
from all input ports simultaneously (which we call a fluid
policy). However, due to the packet nature of the network
traffic, a multiplexer scheduler must approximate this fluid
policy by a schedule in which only whole packets are sent
(which we call a packetized policy). We assume that at each
time instant, the aggregate service rate demanded by a fluid
policy is no greater than the output link capacity. Then,
for a single server with N input ports, and a scheduler
using speedup s of at least 2 and a lookahead window of L
≥ 0 time steps, we prove bounds on worst-case maximum
additional delay D. In particular, we show that (⌈Ne-s⌉
- L - 2)+ ≤ D ≤ min {(⌈Ne1-s⌉ - L)+, ⌈Ne -s⌉}.
In the case when no lookahead is used (L = 0), a tighter
bound can be obtained: (⌈Ne-s⌉ - 2)+ ≤ D ≤
⌈Ne-s⌉. © 2005 IEEE.},
Doi = {10.1109/INFCOM.2005.1498543},
Key = {fds336839}
}
@article{fds336840,
Author = {Kim, IM and Hong, SC and Ghassemzadeh, SS and Tarokh,
V},
Title = {Optimum opportunistic beamforming based on multiple
weighting vectors},
Journal = {Ieee International Conference on Communications},
Volume = {4},
Pages = {2427-2430},
Year = {2005},
Month = {September},
Abstract = {In order to improve the throughput of the opportunistic
beamforming, we generalize the opportunistic beamforming by
using multiple random weighting vectors at each time slot.
The base station chooses the best weighting vector and
performs the opportunistic beamforming with this optimum
vector. For the case of equally strong independent fast
Rayleigh fading channels, we analytically approximate the
throughput of the proposed scheme and obtain the optimum
number of random weighting vectors per time slot. Numerical
results demonstrate that the proposed scheme considerably
improves the throughput compared to the conventional
opportunistic beamforming for a low/realistic number of
users. © 2005 IEEE.},
Key = {fds336840}
}
@article{fds336841,
Author = {Mitran, P and Ochiai, H and Tarokh, V},
Title = {Collaborative diversity enhancements for wireless
communications},
Journal = {Ieee International Conference on Communications},
Volume = {4},
Pages = {2437-2441},
Year = {2005},
Month = {September},
Abstract = {The use of the spatial dimension is known to greatly
increase the reliability of quasi-static (non-ergodic)
wireless channels. In this paper, we demonstrate that most
of this gain can also be achieved through collaborative
communications with single-antenna/multiple-antenna nodes
when there is one receiving agent. In particular, for the
single antenna case, we consider communication to take place
between clusters of nearby nodes. We show the existence of
collaborative codes for communications for which the
intra-cluster negotiation penalty is in principle small and
almost all the diversity gain of traditional space-time
codes may be realized. For example, for single
transmitter/receiver nodes with two collaborators that have
as little as 10 dB path loss advantage over the receiver,
the penalty for collaboration over traditional space-time
systems is negligible. © 2005 IEEE.},
Key = {fds336841}
}
@article{fds336842,
Author = {Ghassemzadeh, SS and Greenstein, LJ and Sveinsson, T and Kavčić, A and Tarokh, V},
Title = {UWB delay profile models for residential and commercial
indoor environments},
Journal = {Ieee Transactions on Vehicular Technology},
Volume = {54},
Number = {4},
Pages = {1235-1244},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2005},
Month = {July},
url = {http://dx.doi.org/10.1109/TVT.2005.851379},
Abstract = {We present models for the ultrawideband (UWB) channel delay
profile in indoor environments, based on the processing of
two large sets of measured data. Both measurement sets are
for a center frequency of 5 GHz, but the bandwidths are very
different - 1.25 GHz and 6 GHz. We model both line-of-sight
(LOS) and nonline-of-sight (NLOS) paths, and do so for both
single-family homes and commercial buildings. Also, we
consider both the profile at a receiver point, which we call
the multipath intensity profile (MIP), and the locally
spatially averaged profile, which we call the power delay
profile (PDP). For both cases, we find that the profile for
NLOS paths can be modeled as a decaying exponential times a
noise-like variation with lognormal statistics and that, for
LOS paths, the profile has the same form plus a strong
component at the minimum delay. The model consists of
statistical descriptions of the parameters of these
functions, including the effects of transmit-receive (T-R)
distance and of variations from building to building. We
show simulation results for a few cases to demonstrate that
the model accurately predicts key properties of the measured
channels, such as the distribution of rms delay spread. ©
2005 IEEE.},
Doi = {10.1109/TVT.2005.851379},
Key = {fds336842}
}
@article{fds336843,
Author = {Mitran, P and Ochiai, H and Tarokh, V},
Title = {Space-time diversity enhancements using collaborative
communications},
Journal = {Ieee Transactions on Information Theory},
Volume = {51},
Number = {6},
Pages = {2041-2057},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2005},
Month = {June},
url = {http://dx.doi.org/10.1109/TIT.2005.847731},
Abstract = {The use of the spatial dimension is known to greatly
increase the reliability of quasi-static (i.e., nonergodic)
wireless channels. In this paper, it is demonstrated that
most of this gain can also be achieved through collaborative
communications with single-antenna/ multiple-antenna nodes
when there is one receiving agent. In particular, for the
single-antenna case, communication is considered to take
place between clusters of nearby nodes. The existence of
collaborative codes for which the intra-cluster negotiation
penalty is, in principle, small (and almost all the
diversity gain of traditional space-time codes may be
realized) is shown. For example, for a single transmitter
node with two collaborators and one receiver node, if the
collaborators have as little as a 10-dB path loss advantage
over the receiver, the penalty for collaboration over
traditional space-time systems is negligible. © 2005
IEEE.},
Doi = {10.1109/TIT.2005.847731},
Key = {fds336843}
}
@article{fds336835,
Author = {Parker, P and Wolfe, PJ and Tarokh, V},
Title = {A signal processing application of randomized low-rank
approximations},
Journal = {Ieee Workshop on Statistical Signal Processing
Proceedings},
Volume = {2005},
Pages = {345-350},
Year = {2005},
Month = {January},
ISBN = {0780394046},
url = {http://dx.doi.org/10.1109/ssp.2005.1628618},
Abstract = {Low-rank approximations to linear operators find wide use in
signal processing. In the discrete case, assuming the
desired rank is known a priori, such approximations are
generally calculated using the singular value decomposition.
In this vein, randomized algorithms have recently been
developed in the context of theoretical computer science,
with the goal of achieving approximations arbitrarily close
to this optimal low-rank solution with very high
probability. Such algorithms function by finding
(deterministic) low-rank approximations to random
submatrices chosen probabilistically - thereby providing
significant reductions in computational complexity, and
leading to their applicability even in the case of very
large matrices. Here it is demonstrated that algorithms of
this type also show promise in signal processing
applications, in particular for the case of adaptive
beamforming in both the narrowband and wideband scenarios.
Quantitative simulation results are provided to indicate
that near-optimal nulling performance, as measured in terms
of signal-to-interference-plus-noise ratio, may be achieved
via straightforward modifications of the randomized
algorithms described above. Results indicate that a large
computational savings is possible, relative to standard
methods, with little corresponding loss in performance.
©2005 IEEE.},
Doi = {10.1109/ssp.2005.1628618},
Key = {fds336835}
}
@article{fds336844,
Author = {Ochiai, H and Mitran, P and Poor, HV and Tarokh, V},
Title = {On the effects of phase estimation errors on collaborative
beamforming in wireless ad hoc networks},
Journal = {2015 Ieee International Conference on Acoustics, Speech, and
Signal Processing (Icassp)},
Volume = {III},
Publisher = {IEEE},
Year = {2005},
Month = {January},
ISBN = {0780388747},
url = {http://dx.doi.org/10.1109/ICASSP.2005.1415795},
Abstract = {The performance of collaborative beamforming is studied
using the theory of random arrays in the framework of
wireless sensor networks. With the application to ad hoc
networks in mind, two scenarios, one denoted closed-loop and
the other open-loop, are considered. Associated with these
scenarios, the effects of phase jitter and location
estimation errors on the average beampattern are analyzed.
© 2005 IEEE.},
Doi = {10.1109/ICASSP.2005.1415795},
Key = {fds336844}
}
@article{fds340042,
Author = {Parker, P and Wolfe, PJ and Tarokh, V},
Title = {A signal processing application of randomized low-rank
approximations},
Journal = {2005 Ieee/Sp 13th Workshop on Statistical Signal Processing
(Ssp), Vols 1 and 2},
Pages = {311-316},
Publisher = {IEEE},
Year = {2005},
Month = {January},
ISBN = {0-7803-9403-8},
Key = {fds340042}
}
@article{fds336845,
Author = {Ochiai, H and Mitran, P and Tarokh, V},
Title = {Design and analysis of collaborative diversity protocols for
wireless sensor networks},
Journal = {Ieee Vehicular Technology Conference},
Volume = {60},
Number = {7},
Pages = {4645-4649},
Year = {2004},
Month = {December},
Abstract = {We consider wireless sensor networks where all the sensor
nodes share the same channel and transmit collaboratively in
a quasi-static Rayleigh fading environment. Intuition
suggests that collaborative communication can achieve a
higher diversity gain than traditional SISO systems. Based
on a decode-and-forward approach, we propose spectrally
efficient variable-rate two-phase protocols that can achieve
full diversity and analyze the effect of node geometry on
their performance in terms of the outage probability of
mutual information. Numerical results show that provided the
collaborator node is close to the source node, full
diversity gain can be readily achieved without loss of
bandwidth efficiency. © 2004 IEEE.},
Key = {fds336845}
}
@article{fds336846,
Author = {Bellorado, J and Ghassemzadeh, SS and Kavčić, A and Tarokh, B and Tarokh, V},
Title = {Time-hopping sequence design for narrowband interference
suppression},
Journal = {Ieee Vehicular Technology Conference},
Volume = {60},
Number = {6},
Pages = {3925-3929},
Year = {2004},
Month = {December},
Abstract = {In this paper, we present a simple interference mitigation
solution for coexistence of Ultra-Wideband (UWB) systems
with other wireless systems. Specifically, we consider the
design of time-hopping codes for UWB systems that deploy
impulse radio architecture. We give a methodology for the
construction of TH sequences that minimize the imposed UWB
interference on a given narrowband system. To illustrate the
effectiveness of our designed codes, we conduct physical
layer simulations of the interference induced by UWB signals
on close proximity wireless local area networks (WLANs) that
deploy IEEE 802. 11a standard. Our performance measure is
the IEEE 802.11a client rate degradation vs. distance from
its Access Point. Our results show that, when using
optimized TH codes, UWB systems can have no impact on the
achievable data-rates and range of IEEE 802.11a WLAN
devices; regardless of the position of the UWB system with
respect to these devices. © 2004 IEEE.},
Key = {fds336846}
}
@article{fds336847,
Author = {Ochiai, H and Mitran, P and Poor, HV and Tarokh, V},
Title = {Collaborative beamforming in ad hoc networks},
Journal = {2004 Ieee Information Theory Workshop Proceedings,
Itw},
Pages = {396-401},
Year = {2004},
Month = {December},
ISBN = {0780387201},
Abstract = {The performance of collaborative beamforming is analyzed
using the theory of random arrays. The statistical average
and distribution of the beampatterns of randomly generated
phased arrays are derived in the framework of wireless ad
hoc sensor networks. Each sensor node is assumed to have a
single isotropic antenna and nodes in the cluster
collaboratively transmit the signal such that the signal in
the target direction is coherently added in the far-field
region. The distribution of the maximum beampattern sidelobe
is also analyzed and a closed-form bound is derived based on
the Gaussian approximation method. ©2004
IEEE.},
Key = {fds336847}
}
@article{fds336848,
Author = {Rosenblum, M and Goemans, MX and Tarokh, V},
Title = {Universal bounds on buffer size for packetizing fluid
policies in input queued, crossbar switches},
Journal = {Proceedings Ieee Infocom},
Volume = {2},
Pages = {1126-1134},
Publisher = {IEEE},
Year = {2004},
Month = {November},
ISBN = {0780383559},
url = {http://dx.doi.org/10.1109/INFCOM.2004.1356999},
Abstract = {In this paper, we consider a type of on-line, traffic
scheduling problem in input queued, crossbar switches. The
input to a problem, at each time step, is a set of desired
traffic rates. These traffic rates in general cannot be
exactly achieved since they assume arbitrarily small
fractions of packets can be transmitted at each time step.
The goal of the traffic scheduling problem is to closely
approximate the given sequence of traffic rates by a
sequence of switch uses in which only whole packets are
sent. The focus of this paper is bounding the costs incurred
in using such an approximation, in terms of the additional
buffer size required. We establish universal bounds on the
additional buffer size due to sending only whole packets;
these bounds do not depend on the particular distribution of
the input traffic, require no speedup, and guarantee 100%
throughput. Specifically, for an N × N input queued,
crossbar switch, an on-line, packetizing algorithm is
presented that guarantees 100% throughput with a buffer
requirement of (N + 1) 2 /4 packets per input port with no
speedup. The algorithm can be improved to run in O(N log N)
time, using a fast algorithm for edge-coloring bipartite
multi-graphs. In the reverse direction, it is shown for an N
× N input queued, crossbar switch, that any on-line,
packetizing algorithm with no speedup requires a buffer size
of N/e - 2 packets per input port. We also extend the main
packetizing algorithm in this paper to a general class of
switch architectures.},
Doi = {10.1109/INFCOM.2004.1356999},
Key = {fds336848}
}
@article{fds336849,
Author = {Ghassemzadeh, SS and Jana, R and Rice, CW and Turin, W and Tarokh,
V},
Title = {Measurement and modeling of an ultra-wide bandwidth indoor
channel},
Journal = {Ieee Transactions on Communications},
Volume = {52},
Number = {10},
Pages = {1786-1796},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2004},
Month = {October},
url = {http://dx.doi.org/10.1109/TCOMM.2003.820755},
Abstract = {This paper describes the results of frequency-domain channel
sounding in residential environments. It consists of
detailed characterization of complex frequency responses of
ultra-wideband (UWB) signals having a nominal center
frequency of 5 GHz. A path loss model as well as a
second-order autoregressive model is proposed for frequency
response generation of the UWB indoor channel. Probability
distributions of the model parameters for different
locations are presented. Also, time-domain results such as
root mean square delay spread and percent of captured power
are presented. © 2004 IEEE.},
Doi = {10.1109/TCOMM.2003.820755},
Key = {fds336849}
}
@article{fds336850,
Author = {Cvetkovic, Z and Tarokh, V and Yoon, S},
Title = {Frequency synchronization in OFDM},
Journal = {2015 Ieee International Conference on Acoustics, Speech, and
Signal Processing (Icassp)},
Volume = {4},
Year = {2004},
Month = {September},
Abstract = {We present an OFDM frequency synchronization scheme. The
scheme uses periodic OFDM symbols, similarly to the
algorithms proposed previously by Morelli and Mengali and
Schmidl and Cox. The proposed scheme attains considerably
higher accuracy than the scheme by Schmidl and Cox requiring
a similar computational load. Compared to the scheme by
Morelli and Mengali, the proposed algorithm attains a
somewhat inferior accuracy but at a significantly reduced
computational complexity, i.e O(N) versus O(N 2) operations
for N-tone OFDM. In addition to that, the scheme proposed
here is considerably less sensitive to the accuracy of the
involved computations than the other two
schemes.},
Key = {fds336850}
}
@article{fds336851,
Author = {Hochwald, BM and Marzetta, TL and Tarokh, V},
Title = {Multiple-antenna channel hardening and its implications for
rate feedback and scheduling},
Journal = {Ieee Transactions on Information Theory},
Volume = {50},
Number = {9},
Pages = {1893-1909},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2004},
Month = {September},
url = {http://dx.doi.org/10.1109/TIT.2004.833345},
Abstract = {Wireless data traffic is expected to grow over the next few
years and the technologies that will provide data services
are still being debated. One possibility is to use multiple
antennas at base stations and terminals to get very high
spectral efficiencies in rich scattering environments. Such
multiple-input/multiple-output (MIMO) channels can then be
used in conjunction with scheduling and rate-feedback
algorithms to further increase channel throughput. This
paper provides an analysis of the expected gains due to
scheduling and bits needed for rate feedback. Our analysis
requires an accurate approximation of the distribution of
the MIMO channel mutual information. Because the exact
distribution of the mutual information in a Rayleigh-fading
environment is difficult to analyze, we prove a central
limit theorem for MIMO channels with a large number of
antennas. While the growth in average mutual information
(capacity) of a MIMO channel with the number of antennas is
well understood, it turns out that the variance of the
mutual information can grow very slowly or even shrink as
the number of antennas grows. We discuss implications of
this "channel-hardening" result for data and voice services,
scheduling, and rate feedback. We also briefly discuss the
implications when shadow fading effects are included. ©
2004 IEEE.},
Doi = {10.1109/TIT.2004.833345},
Key = {fds336851}
}
@article{fds336852,
Author = {Nam, SH and Hwang, CS and Chung, J and Tarokh, V},
Title = {Differential space time block codes using QAM for four
transmit antennas},
Journal = {Ieee International Conference on Communications},
Volume = {2},
Pages = {952-956},
Year = {2004},
Month = {August},
Abstract = {We develop differential space time block codes (STBC) using
non-constant modulus constellations for four transmit
antennas. The proposed method improves on the conventional
differential STBC techniques because of the larger minimum
distances of non-constant modulus constellations. The
transmitted signals are modulated using pulse amplitude
modulation (PAM). Encoding is similar to that of the
conventional differential STBC, while the receiver is
different. The signal at the receiver is divided by the
estimated channel power and then decoded using a
conventional QAM decoder which treats pairs of transmited
PAM symbols transmitted from two transmit antennas as one
QAM symbol. For transmission rates greater than 2
bits/channel use, the proposed method outperforms the
conventional differential STBC.},
Key = {fds336852}
}
@article{fds336853,
Author = {Chong, CV and Venkataramani, R and Tarokh, V},
Title = {Erratum: A new construction of 16-QAM Golay complementary
sequences (IEEE Trans. Informa. Theory (2003) 49,
(2953-2959))},
Journal = {Ieee Transactions on Information Theory},
Volume = {50},
Number = {6},
Pages = {1374},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2004},
Month = {June},
url = {http://dx.doi.org/10.1109/TIT.2004.828158},
Doi = {10.1109/TIT.2004.828158},
Key = {fds336853}
}
@article{fds336854,
Author = {Ghassemzadeh, SS and Greenstein, LJ and Sveinsson, T and Tarokh,
V},
Title = {An Impulse Response Model For Residential Wireless
Channels},
Journal = {Conference Record / Ieee Global Telecommunications
Conference},
Volume = {3},
Pages = {1211-1215},
Publisher = {IEEE},
Year = {2003},
Month = {December},
ISBN = {0780379748},
url = {http://dx.doi.org/10.1109/glocom.2003.1258431},
Abstract = {We present a statistical model for the Multipath Intensity
Profile (MIP) that can be used to construct an impulse
response of a residential wireless channel. The model
incorporates relevant parameters such as distance, global
rms delay spread and the correlation between received
multipaths. It describes the statistics of the MIP in
detail. This model, together with a suitable path loss
model, can be used to simulate residential wireless channels
for performance evaluation of various communication systems.
The MIP model is based on over 300,000 indoor frequency
responses measured in a 1.25GHz bandwidth centered on 5-GHz,
and simulation shows that it captures very well the main
statistical properties of the measured data.},
Doi = {10.1109/glocom.2003.1258431},
Key = {fds336854}
}
@article{fds336855,
Author = {Bellorado, J and Ghassemzadeh, SS and Greenstein, LJ and Sveinsson,
T and Tarokh, V},
Title = {Coexistence of Ultra-Wideband Systems with IEEE-802.1la
Wireless LANs},
Journal = {Conference Record / Ieee Global Telecommunications
Conference},
Volume = {1},
Pages = {410-414},
Year = {2003},
Month = {December},
Abstract = {In this study we provide a physical layer based analysis of
the coexistence issues of Ultra-Wideband (UWB) with other
devices in the same spectrum. Specifically, we have focused
on the UWB interference to and from devices using the
Wireless Local Area Network (WLAN) standard IEEE 802.11a.
Our results indicate that a UWB interferer operating at the
peak allowable power density induces minimal interference
into such WLAN devices in line-of sight (LOS) scenarios,
even at close range. However, in the non-LOS (NLOS) case, a
UWB interferer can severely affect the data-rate sustainable
by 802.1 la systems. Moreover, 802.11a interference into UWB
systems is shown to reduce the signal-to-interference ratio
(SIR) by as much as 36 dB when the interferer is within LOS
of the UWB receiver.},
Key = {fds336855}
}
@article{fds336856,
Author = {Hwang, CS and Nam, SH and Chung, J and Tarokh, V},
Title = {Differential space time block codes using QAM
constellations},
Journal = {Ieee International Symposium on Personal, Indoor and Mobile
Radio Communications, Pimrc},
Volume = {2},
Pages = {1693-1697},
Publisher = {IEEE},
Year = {2003},
Month = {December},
ISBN = {0780378229},
url = {http://dx.doi.org/10.1109/PIMRC.2003.1260403},
Abstract = {We propose differential space time block codes (STBC) using
quadrature amplitude modulation (QAM), which can not be
utilized in the conventional differential STBC. Since QAM
constellations have a larger minimum distance compared with
phase shift keying (PSK), the proposed method has the
advantage of SNR gain compared with conventional
differential STBC. The QAM signals are encoded in a manner
similar to that of conventional differential STBCs. To
decode QAM signals, the signals received are normalized by
the channel power estimated forgoing training symbols, and
then decoded with a conventional QAM decoder. When the
transmission rate is more than 3 bits/channel use in time
varying channels, the simulation results demonstrate that
the proposed method with the channel power estimation
outperforms the conventional differential STBC. © 2003
IEEE.},
Doi = {10.1109/PIMRC.2003.1260403},
Key = {fds336856}
}
@article{fds336858,
Author = {Tarokh, V and Choi, YS and Alamouti, S},
Title = {Complementary beamforming},
Journal = {Ieee Vehicular Technology Conference},
Volume = {58},
Number = {5},
Pages = {3136-3140},
Publisher = {IEEE},
Year = {2003},
Month = {December},
ISBN = {0780379543},
url = {http://dx.doi.org/10.1109/vetecf.2003.1286205},
Abstract = {We present complementary beamforming techniques which enable
the formation of multiple directional beams to some users
while guaranteeing a minimum power level to the rest of the
users in the network. These techniques can be used for many
different applications such as beamforming in wireless
networks that employ channel sensing for medium
access.},
Doi = {10.1109/vetecf.2003.1286205},
Key = {fds336858}
}
@article{fds336861,
Author = {Chong, CV and Venkataramani, R and Tarokh, V},
Title = {A New Construction of 16-QAM Golay Complementary
Sequences},
Journal = {Ieee Transactions on Information Theory},
Volume = {49},
Number = {11},
Pages = {2953-2959},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2003},
Month = {November},
url = {http://dx.doi.org/10.1109/TIT.2003.818418},
Abstract = {We present a new construction of 16-QAM Golay sequences of
length n = 2m, The number of constructed sequences is (14 +
12m) (m!/2)4 m+1. When employed as a code in an orthogonal
frequency-division multiplexing (OFDM) system; this set of
sequences has a peak-to-mean envelope power ratio (PMEPR) of
3.6. By considering two specific subsets of these sequences,
we obtain new codes with PMEPR bounds of 2.0 and 2.8 and
respective code sizes of (2 + 2m) (m!/2)4m+1 and (4 + 4m)
(m!/2)4 m+1. These are larger than previously known codes
for the same PMEPR bounds.},
Doi = {10.1109/TIT.2003.818418},
Key = {fds336861}
}
@article{fds336862,
Author = {Hwang, CS and Nam, SH and Chung, J and Tarokh, V},
Title = {Differential space time block codes using nonconstant
modulus constellations},
Journal = {Ieee Transactions on Signal Processing},
Volume = {51},
Number = {11},
Pages = {2955-2964},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2003},
Month = {November},
url = {http://dx.doi.org/10.1109/TSP.2003.818157},
Abstract = {We propose differential space time block codes (STBC) using
nonconstant modulus constellations, e.g., quadrature
amplitude modulation (QAM), which cannot be utilized in the
conventional differential STBC. Since QAM constellations
have a larger minimum distance compared with the phase shift
keying (PSK), the proposed method has the advantage of
signal-to-noise ratio (SNR) gain compared with conventional
differential STBC. The QAM signals are encoded in a manner
similar to that of the conventional differential STBC. To
decode nonconstant modulus signals, the received signals are
normalized by the channel power estimated forgoing training
symbols and then decoded with a conventional QAM decoder.
Assuming the knowledge of the channel power at the receiver,
the symbol error rate (SER) bound of the proposed method
under independent Rayleigh fading assumption is derived,
which shows better SER performance than the conventional
differential STBC. When the transmission rate is more than 3
bits/channel use in time-varying channels, the simulation
results demonstrate that the proposed method with the
channel power estimation outperforms the conventional
differential STBC. Specifically, the posed method using the
channel power estimation obtains a 7.3 dB SNR gain at a
transmission rate of 6 bits/channel use in slow fading
channels. Although the performance gap between the proposed
method and the conventional one decreases as the Doppler
frequency increases, the proposed method still exhibits
lower SER than the conventional one, provided the estimation
interval L is chosen carefully.},
Doi = {10.1109/TSP.2003.818157},
Key = {fds336862}
}
@article{fds336863,
Author = {Ghassemzadeh, SS and Tarokh, V},
Title = {UWB path loss characterization in residential
environments},
Journal = {Ieee Radio Frequency Integrated Circuits Symposium, Rfic,
Digest of Technical Papers},
Pages = {501-504},
Publisher = {IEEE},
Year = {2003},
Month = {August},
ISBN = {0780376943},
url = {http://dx.doi.org/10.1109/rfic.2003.1213994},
Abstract = {In this paper, we describe a simple method for measurement
of the Ultra-Wideband Band (UWB) frequency response for
evaluation of the path loss and impulse response of the UWB
indoor channel. We propose a simple statistical path loss
model for the residential channel that is based on over
300,000 frequency response measurements. The Probability
distributions of the model parameters for different
locations are presented.},
Doi = {10.1109/rfic.2003.1213994},
Key = {fds336863}
}
@article{fds336864,
Author = {Ghassemzadeh, SS and Tarokh, V},
Title = {UWB path loss characterization in residential
environments},
Journal = {2017 Ieee Mtt S International Microwave Symposium
(Ims)},
Volume = {1},
Pages = {365-368},
Year = {2003},
Month = {August},
Abstract = {In this paper, we describe a simple method for measurement
of the Ultra-Wideband Band (UWB) frequency response for
evaluation of the path loss and impulse response of the UWB
indoor channel We propose a simple statistical path loss
model for the residential channel that is based on over
300,000 frequency response measurements. The Probability
distributions of the model parameters for different
locations are presented.},
Key = {fds336864}
}
@article{fds340043,
Author = {Biglieri, E and Tarokh, V and Simon, MK},
Title = {Special issue on coding and signal processing for MIMO
system},
Journal = {Journal of Communications and Networks},
Volume = {5},
Number = {2},
Pages = {93-95},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2003},
Month = {June},
url = {http://dx.doi.org/10.1109/jcn.2003.6596571},
Doi = {10.1109/jcn.2003.6596571},
Key = {fds340043}
}
@article{fds336865,
Author = {Kim, IM and Tarokh, V},
Title = {Variable-rate space-time block codes in M-ary PSK
systems},
Journal = {Ieee Journal on Selected Areas in Communications},
Volume = {21},
Number = {3},
Pages = {362-373},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2003},
Month = {April},
url = {http://dx.doi.org/10.1109/JSAC.2003.809697},
Abstract = {We consider a multiple antenna system when combined array
processing with space-time coding is used. We present
variable rate space-time block codes for two, three, and
four transmit antennas and optimize the transmit power so
that the average bit-error rate (BER) is minimized.
Numerical results show that this optimum power allocation
scheme provides significant gain over the equal power
allocation scheme. We then classify all the variable rate
space-time block codes having the same code rates and
identify the unique code that achieves the lowest BER. We
explicitly compute the performance of the variable rate
codes over a Rayleigh-fading channel. The proposed variable
rate space-time block codes are useful for unequal error
protection in multiple transmit antenna systems.},
Doi = {10.1109/JSAC.2003.809697},
Key = {fds336865}
}
@article{fds336866,
Author = {Sotiriadis, PP and Tarokh, V and Chandrakasan,
AP},
Title = {Energy reduction in VLSI computation modules: An
information-theoretic approach},
Journal = {Ieee Transactions on Information Theory},
Volume = {49},
Number = {4},
Pages = {790-808},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2003},
Month = {April},
url = {http://dx.doi.org/10.1109/TIT.2003.809601},
Abstract = {We consider the problem of reduction of computation cost by
introducing redundancy in the number of ports as well as in
the input and output sequences of computation modules. Using
our formulation, the classical "communication scenario" is
the case when a computation module has to recompute the
input sequence at a different location or time with high
fidelity and low bit-error rates. We then consider
communication with different computational cost objective
than that given by bit-error rate. An example is
communication over deep submicrometer very-large scale
integration (VLSI) buses where the expected energy
consumption per communicated information bit is the cost of
computation. We treat this scenario using tools from
information theory and establish fundamental bounds on the
achievable expected energy consumption per bit in deep
submicrometer VLSI buses as a function of their utilization.
Some of our results also shed light on coding schemes that
achieve these bounds. We then prove that the best tradeoff
between the expected energy consumption per bit and bus
utilization can be achieved using codes constructed from
typical sequences of Markov stationary ergodic processes. We
use this observation to give a closed-form expression for
the best tradeoff between the expected energy consumption
per bit and the utilization of the bus. This expression, in
principle, can be computed using standard numerical methods.
The methodology developed here naturally extends to more
general computation scenarios.},
Doi = {10.1109/TIT.2003.809601},
Key = {fds336866}
}
@article{fds336857,
Author = {Ghassemzadeh, SS and Greenstein, LJ and Kavčić, A and Sveinsson, T and Tarokh, V},
Title = {UWB indoor path loss model for residential and commercial
buildings},
Journal = {Ieee Vehicular Technology Conference},
Volume = {58},
Number = {5},
Pages = {3115-3119},
Publisher = {IEEE},
Year = {2003},
Month = {January},
ISBN = {0780379543},
url = {http://dx.doi.org/10.1109/vetecf.2003.1286197},
Abstract = {We present a statistical model for the path loss of
ultra-wideband channels in indoor environments. In contrast
to previous measurements, the data reported here are for a
bandwidth of 6 GHz rather than 1.25 GHz; they encompass
commercial buildings in addition to single-family homes (20
of each); and local spatial averaging is included. As
before, the center frequency is 5.0 GHz. Separate models are
given for commercial and residential environments and-within
each category - for line-of-sight (LOS) and
non-line-of-sight (NLS) paths. All four models have the same
mathematical structure, differing only in their numerical
parameters. The two new models (LOS and NLS) for residences
closely match those derived from the previous measurements,
thus affirming the stability of our path loss modeling. For
greater accuracy, we therefore pool the two data sets in our
final models for residences. We find that the path loss
statistics for the two categories of buildings are quite
similar.},
Doi = {10.1109/vetecf.2003.1286197},
Key = {fds336857}
}
@article{fds336859,
Author = {Ghassemzadeh, SS and Greenstein, LJ and Kavčić, A and Sveinsson, T and Tarokh, V},
Title = {UWB indoor delay profile model for residential and
commercial environments},
Journal = {Ieee Vehicular Technology Conference},
Volume = {58},
Number = {5},
Pages = {3120-3125},
Publisher = {IEEE},
Year = {2003},
Month = {January},
ISBN = {0780379543},
url = {http://dx.doi.org/10.1109/vetecf.2003.1286198},
Abstract = {We present a statistical model for the delay profile of
ultra-wideband channels in indoor environments. Two kinds of
profiles are defined, namely the multipath intensity profile
(MIP) and the power delay profile (PDF). The MIP is he delay
profile at a point in space, while the PDF is a local
spatial average. The model is based on 60,000 complex
frequency response measurements from 20 commercial buildings
and 20 residential homes, with the transmitter and receiver
both in line-of-sight (LOS) and non-line-of-sight (NLS) of
each other. Simulations using the PDF model show excellent
statistical agreement with the measured data.},
Doi = {10.1109/vetecf.2003.1286198},
Key = {fds336859}
}
@article{fds336860,
Author = {Ghassemzadeh, SS and Greenstein, LJ and Kavčić, A and Sveinsson, T and Tarokh, V},
Title = {An empirical indoor path loss model for ultra-wideband
channels},
Journal = {Journal of Communications and Networks},
Volume = {5},
Number = {4},
Pages = {303-307},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2003},
Month = {January},
url = {http://dx.doi.org/10.1109/jcn.2003.6596612},
Abstract = {We present a statistical model for the path loss of
ultra-wideband (UWB) channels in indoor environments. In
contrast to our previously reported measurements, the data
reported here are for a bandwidth of 6GHz rather than
1.25GHz; they encompass commercial buildings in addition to
single-family homes (20 of each); and local spatial
averaging is included. As before, the center frequency is
5.0GHz. Separate models are given for commercial and
residential environments and, within each category, for
line-of-sight (LOS) and non-line-of-sight (NLS) paths. All
four models have the same mathematical structure, differing
only in their numerical parameters. The two new models (LOS
and NLS) for residences closely match those derived from the
previous measurements, thus affirming the stability of our
path loss modeling. We find, also, that the path loss
statistics for the two categories of buildings are quite
similar.},
Doi = {10.1109/jcn.2003.6596612},
Key = {fds336860}
}
@article{fds336867,
Author = {Ghassemzadeh, SS and Greenstein, LJ and Sveinsson, T and Tarokh,
V},
Title = {A multipath intensity profile model for residential
environments},
Journal = {Ieee Wireless Communications and Networking Conference,
Wcnc},
Volume = {1},
Pages = {150-155},
Publisher = {IEEE},
Year = {2003},
Month = {January},
ISBN = {0780377001},
url = {http://dx.doi.org/10.1109/WCNC.2003.1200336},
Abstract = {We describe a statistical model for the multipath intensity
profile (MIP) in residential environments. The work is based
on over 300,000 frequency response measurements at 712
locations in 23 homes. We show that, for non-line-of-sight
(NLS) path, the MIP is well-modeled as a decaying
exponential vs. delay, multiplied by a lognormal process
over delay; and that a similar model applies to
line-of-sight (LOS) paths. Moreover, we present simple
statistical descriptions for the parameters of these
functions.},
Doi = {10.1109/WCNC.2003.1200336},
Key = {fds336867}
}
@article{fds333011,
Author = {Tarokh, V and Naguib, A and Seshadri, N and Calderbank,
AR},
Title = {Erratum: Space-time codes for high data rate wireless
communications: Performance criteria in the presence of
channel estimation errors, mobility, and multiple paths
(IEEE Trans. Commun. (1999) 47, (199-207))},
Journal = {Ieee Transactions on Communications},
Volume = {51},
Number = {12},
Pages = {2141},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2003},
Month = {January},
url = {http://dx.doi.org/10.1109/TCOMM.2003.822179},
Doi = {10.1109/TCOMM.2003.822179},
Key = {fds333011}
}
@article{fds340044,
Author = {Ghassemzadeh, SS and Tarokh, V},
Title = {Invited - UWB path loss characterization in residential
environments},
Journal = {2017 Ieee Mtt S International Microwave Symposium
(Ims)},
Pages = {365-368},
Publisher = {IEEE},
Editor = {Thal, H},
Year = {2003},
Month = {January},
ISBN = {0-7803-7695-1},
Key = {fds340044}
}
@article{fds336868,
Author = {Tarokh, V and Kim, IM},
Title = {Existence and construction of noncoherent unitary space-time
codes},
Journal = {Ieee Transactions on Information Theory},
Volume = {48},
Number = {12},
Pages = {3112-3117},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2002},
Month = {December},
url = {http://dx.doi.org/10.1109/TIT.2002.805075},
Abstract = {We consider transmission using N transmit and reception
using M receive antennas in a wireless environment assuming
that neither the transmitter nor the receiver knows the
channel coefficients. For the scenario that the transmission
employs noncoherent T × N unitary space-time codes and for
a block-fading channel model where the channel is static
during T channel uses and varies from T channel uses to the
other, we establish the bound r ≤ min(T - N, N) on the
diversity advantage rM provided by the code. In order to
show that the requirement r ≤ min(T - N, N) cannot he
relaxed, for any given R, N, T, and r ≤ min(T - N, N), we
then construct unitary T × N space-time codes of rate R
that guarantee diversity advantage rM. Two constructions are
given that are also amenable to simple encoding and
noncoherent maximum-likelihood (ML) decoding
algorithms.},
Doi = {10.1109/TIT.2002.805075},
Key = {fds336868}
}
@article{fds341281,
Author = {Slock, D and Tarokh, V and Xia, X-G},
Title = {Editorial},
Journal = {Eurasip Journal on Advances in Signal Processing},
Volume = {2002},
Number = {3},
Publisher = {Springer Science and Business Media LLC},
Year = {2002},
Month = {December},
url = {http://dx.doi.org/10.1155/s1110865702001968},
Doi = {10.1155/s1110865702001968},
Key = {fds341281}
}
@article{fds336871,
Author = {Chong, CV and Tarokh, V},
Title = {Two constructions of 16-QAM Golay complementary
sequences},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {240},
Year = {2002},
Month = {September},
Abstract = {Two constructions of 16-quadrature amplitude modulation
(QAM) Golay complementary sequences from 4-QAM complementary
sequences were presented. These sequences can be applied as
pilot sequences in future orthogonal frequency division
miltiplexing (OFDM) systems. The symbols from the first
4-QAM sequence were denoted as major coordinates, and the
symbols from the other sequence was denoted as minor
coordinates.},
Key = {fds336871}
}
@article{fds336872,
Author = {Sotiriadis, PP and Tarokh, V and Chandrakasan,
A},
Title = {Energy reduction and fundamental energy limits in digital
VLSI circuits},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {393},
Publisher = {IEEE},
Year = {2002},
Month = {September},
ISBN = {0780375017},
url = {http://dx.doi.org/10.1109/isit.2002.1023665},
Abstract = {Energy reduction and fundamental energy limits in digital
VLSI circuits were discussed. Bus was used to calculate the
minimum cost of energy since its cost function is known.
Results can be extended to units modelled as finite state
machines and can also be used to calculate other energy
costs objectives such as time.},
Doi = {10.1109/isit.2002.1023665},
Key = {fds336872}
}
@article{fds336870,
Author = {Slock, D and Tarokh, V and Xia, XG},
Title = {Editorial},
Journal = {Eurasip Journal on Applied Signal Processing},
Volume = {2002},
Number = {5},
Pages = {445-446},
Publisher = {Springer Nature},
Year = {2002},
Month = {May},
url = {http://dx.doi.org/10.1155/S1110865702001920},
Doi = {10.1155/S1110865702001920},
Key = {fds336870}
}
@article{fds336873,
Author = {Slock, D and Tarokh, V and Xia, NG},
Title = {Applied Signal Processing: Editorial},
Journal = {Eurasip Journal on Applied Signal Processing},
Number = {3},
Pages = {209-210},
Year = {2002},
Month = {March},
Key = {fds336873}
}
@article{fds336869,
Author = {Haas, SM and Shapiro, JH and Tarokh, V},
Title = {Space-time codes for wireless optical communications},
Journal = {Eurasip Journal on Applied Signal Processing},
Volume = {2002},
Number = {3},
Pages = {211-220},
Publisher = {Springer Nature},
Year = {2002},
Month = {January},
url = {http://dx.doi.org/10.1155/s1110865702000604},
Abstract = {A space-time channel coding technique is presented for
overcoming turbulence-induced fading in an atmospheric
optical heterodyne communication system that uses multiple
transmit and receive apertures. In particular, a design
criterion for minimizing the pairwise probability of
codeword error in a space-time code (STC) is developed from
a central limit theorem approximation. This design criterion
maximizes the mean-to-standard-deviation ratio of the
received energy difference between codewords. It leads to
STCs that are a subset of the previously reported STCs for
Rayleigh channels, namely those created from orthogonal
designs. This approach also extends to other fading channels
with independent, zero-mean path gains. Consequently, for
large numbers of transmit and receive antennas, STCs created
from orthogonal designs minimize the pairwise codeword error
probability for this larger class of fading
channels.},
Doi = {10.1155/s1110865702000604},
Key = {fds336869}
}
@article{fds336874,
Author = {Tarokh, V and Hochwald, BM},
Title = {Existence and construction of block interleavers},
Journal = {Ieee International Conference on Communications},
Volume = {3},
Pages = {1855-1857},
Publisher = {IEEE},
Year = {2002},
Month = {January},
ISBN = {0780374002},
url = {http://dx.doi.org/10.1109/ICC.2002.997169},
Abstract = {The necessary and sufficient conditions on the existence of
(N1, N2) block interleavers of block size L, were
established. The interleaver was found to exist on the
condition that L ≥ N1N2. Explicit algebraic expressions
were also provided. It was proved that the rectangular
interleavers were not optimal.},
Doi = {10.1109/ICC.2002.997169},
Key = {fds336874}
}
@article{fds336875,
Author = {Sotiriadis, PP and Chandrakasan, A and Tarokh,
V},
Title = {Maximum achievable energy reduction using coding with
applications to deep sub-micron buses},
Journal = {Proceedings Ieee International Symposium on Circuits and
Systems},
Volume = {1},
Year = {2002},
Month = {January},
Abstract = {In this work we ask: How much can we reduce the power
consumption in deep-sub-micron buses using coding
techniques? We answer the question in two steps. First we
give the minimum energy per information bit required for
communicating through deep-sub-micron buses. Then, we show
that the minimum energy is asymptotically achievable using
coding. In addition, a simple differential coding scheme is
proposed that achieves most of the possible energy
reduction. The methodology used here also applies to more
general communication and computation models.},
Key = {fds336875}
}
@article{fds336876,
Author = {Turin, W and Jana, R and Ghassemzadeh, SS and Rice, CW and Tarokh,
V},
Title = {Autoregressive modeling of an indoor UWB
channel},
Journal = {2002 Ieee Conference on Ultra Wideband Systems and
Technologies, Uwbst 2002 Digest of Papers},
Pages = {71-74},
Publisher = {IEEE},
Year = {2002},
Month = {January},
ISBN = {0780374967},
url = {http://dx.doi.org/10.1109/UWBST.2002.1006321},
Abstract = {Based on frequency domain measurements in the 4.375-5.625
GHz band a channel model for the frequency response of the
indoor radio channel is introduced. In particular. a
second-order Autoregressive (AR) model is proposed for
frequency response generation of the ultra wide band indoor
channel. A complete characterization of the model parameters
is described along with probability distributions and
dependencies between parameters. © 2002
IEEE.},
Doi = {10.1109/UWBST.2002.1006321},
Key = {fds336876}
}
@article{fds336877,
Author = {Ghassemzadeh, SS and Jana, R and Rice, CW and Turin, W and Tarokh,
V},
Title = {A statistical path loss model for in-home UWB
channels},
Journal = {2002 Ieee Conference on Ultra Wideband Systems and
Technologies, Uwbst 2002 Digest of Papers},
Pages = {59-64},
Publisher = {IEEE},
Year = {2002},
Month = {January},
ISBN = {0780374967},
url = {http://dx.doi.org/10.1109/UWBST.2002.1006319},
Abstract = {This paper describes a simple statistical model for
evaluating the path loss in residential environments. It
consists of detailed characterization of path loss model
parameters of ultra-wideband band (UWB) signals having a
nominal center frequency of 5 GHz. The proposed statistical
path loss model is for the in-home channel and it is based
on over 300,000 frequency response measurements. Probability
distributions of the model parameters for different
locations are presented. Also, time domain results such as
RMS delay spread and percent of captured power are
presented. © 2002 IEEE.},
Doi = {10.1109/UWBST.2002.1006319},
Key = {fds336877}
}
@article{fds336878,
Author = {Kim, IM and Tarokh, V},
Title = {Variable rate sapce-time block codes in MPSK
systems},
Journal = {Conference Record Asilomar Conference on Signals, Systems
and Computers},
Volume = {2},
Pages = {1122-1126},
Year = {2002},
Month = {January},
Abstract = {We consider a multiple antenna system when combined array
processing with space-time coding is used [2]. We present
variable rate space-time block codes for two, three, and
four transmit antennas and optimize the transmit power so
that the average BER is minimized. Numerical results show
that this optimum power allocation scheme provides
significant gain over the equal power allocation scheme. We
then classify all the variable rate space-time block codes
having the same code rates and Identify the unique code that
achieves the lowest BER. We explicitly compute the
performance of the variable rate codes over a Rayleigh
fading channel. The proposed variable rate space-time block
codes are useful for unequal error protection in multiple
transmit antenna systems.},
Key = {fds336878}
}
@article{fds336884,
Author = {Chong, CV and Tarokh, V},
Title = {A simple encodable/decodable OFDM QPSK code with low
peak-to-mean envelope power ratio},
Journal = {Ieee Transactions on Information Theory},
Volume = {47},
Number = {7},
Pages = {3025-3029},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2001},
Month = {November},
url = {http://dx.doi.org/10.1109/18.959282},
Abstract = {We present a quadrature phase-shift keying (QPSK) coding
scheme for multicarrier communications. The scheme supports
simple encoding and extremely simple maximum-likelihood (ML)
decoding algorithms for orthogonal frequency-division
multiplexing (OFDM). Moreover, all the codewords have
peak-to-mean envelope power ratio (PMEPR) of at most 6
dB.},
Doi = {10.1109/18.959282},
Key = {fds336884}
}
@article{fds336879,
Author = {Chong, CV and Tarokh, V},
Title = {A simple encodable/decodable OFDM QPSK code with low
peak-to-mean envelope power ratio},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {315},
Year = {2001},
Month = {September},
Abstract = {We present a QPSK coding scheme for use in multicarrier
communications. The scheme supports simple encoding and
extremely simple maximum likelihood (ML) decoding algorithms
for orthogonal frequency division multiplexing (OFDM)
applications. Moreover, all the codewords have peak-to-mean
envelope power ratio (PMEPR) of at most 4.},
Key = {fds336879}
}
@article{fds336883,
Author = {Jafarkhani, H and Tarokh, V},
Title = {Multiple transmit antenna differential detection from
generalized orthogonal designs},
Journal = {Ieee Transactions on Information Theory},
Volume = {47},
Number = {6},
Pages = {2626-2631},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2001},
Month = {September},
url = {http://dx.doi.org/10.1109/18.945280},
Abstract = {We explicitly construct multiple transmit antenna
differential encoding/decoding schemes based on generalized
orthogonal designs. These constructions generalize the two
transmit antenna differential detection scheme that we
proposed before.},
Doi = {10.1109/18.945280},
Key = {fds336883}
}
@article{fds336880,
Author = {Rößing, C and Tarokh, V},
Title = {A construction of OFDM 16-QAM sequences having low peak
powers},
Journal = {Ieee Transactions on Information Theory},
Volume = {47},
Number = {5},
Pages = {2091-2094},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2001},
Month = {January},
url = {http://dx.doi.org/10.1109/18.930949},
Abstract = {Using a realization of 16-QAM as set addition of two scaled
versions of the 4-PSK constellation, we construct 16-QAM
sequences having low peak-to-mean envelope power ratios
(PMEPR) from 4-PSK Golay sequences. Various upper bounds on
the peak envelope powers of these sequences are established.
Transmission using these sequences provides twice as much
rate as transmission using complementary Golay sequences
with a maximum PMEPR of 3.6 (5.56dB).},
Doi = {10.1109/18.930949},
Key = {fds336880}
}
@article{fds336881,
Author = {Haas, SM and Shapiro, JH and Tarokh, V},
Title = {Space-time codes for wireless optical channels},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {244},
Publisher = {IEEE},
Year = {2001},
Month = {January},
url = {http://dx.doi.org/10.1109/ISIT.2001.936107},
Abstract = {A space-time channel coding technique is presented for
overcoming turbulence-induced fading in an atmospheric
optical communication system that uses multiple transmit and
receive apertures. In particular, a design criterion for
minimizing the pairwise probability of codeword error in a
space-time code (STC) is developed from a central limit
theorem approximation. This design criterion maximizes the
ratio of mean to standard deviation of the received energy
difference between codewords. It leads to STCs that are a
subset of the previously reported STCs for Rayleigh
channels, namely those created from orthogonal
designs.},
Doi = {10.1109/ISIT.2001.936107},
Key = {fds336881}
}
@article{fds336882,
Author = {Medvedev, I and Tarokh, V},
Title = {A channel-shortening multiuser detector for DS-CDMA
systems},
Journal = {Ieee Vehicular Technology Conference},
Volume = {3},
Number = {53ND},
Pages = {1834-1838},
Publisher = {IEEE},
Year = {2001},
Month = {January},
ISBN = {0780367286},
url = {http://dx.doi.org/10.1109/vetecs.2001.945011},
Abstract = {The multiple-access interference (MAI) encountered by
Direct-Sequence Code-Division Multiple Access (DS-CDMA)
users in a multipath environment is a key issue in the
detection of mobile communication users. The MAI is one of
the major reasons for the degradation in performance of
multiuser communication systems over single-user systems.
Although the optimum detection technique, Maximum-Likelihood
Sequence Estimation (MLSE), is well known, its complexity is
exponential with the number of users, which makes it
computationally unattractive. This paper presents a
multiuser detector that performs close to the optimum MLSE
while drastically reducing the decoding complexity. The
detection technique is based on a channel-shortening
algorithm and will allow for group detection of a subset of
the users via the MLSE.},
Doi = {10.1109/vetecs.2001.945011},
Key = {fds336882}
}
@article{fds336885,
Author = {Paterson, KG and Tarokh, V},
Title = {On the existence and construction of good codes with low
peak-to-average power ratios},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {217},
Publisher = {IEEE},
Year = {2000},
Month = {December},
ISBN = {0780358570},
url = {http://dx.doi.org/10.1109/isit.2000.866515},
Abstract = {The peak-to-average power ratio PAPR(C) of a code C is an
important characteristic of that code when it is used in
OFDM communications. We establish bounds on the region of
achievable triples (R, d, PAPR(C)) where R is the code rate
and d is the minimum Euclidean distance of the code. We
prove a lower bound on PAPR in terms of R and d and show
that there exist asymptotically good codes whose PAPR is at
most 8 log n. We give explicit constructions of
error-correcting codes with low PAPR by employing bounds for
hybrid exponential sums over Galois fields and
rings.},
Doi = {10.1109/isit.2000.866515},
Key = {fds336885}
}
@article{fds336888,
Author = {Paterson, KG and Tarokh, V},
Title = {On the existence and construction of good codes with low
peak-to-average power ratios},
Journal = {Ieee Transactions on Information Theory},
Volume = {46},
Number = {6},
Pages = {1974-1987},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2000},
Month = {September},
url = {http://dx.doi.org/10.1109/18.868473},
Abstract = {The first lower bound on the peak-to-average power ratio
(PAPR) of a constant energy code of a given length n,
minimum Euclidean distance and rate is established.
Conversely, using a nonconstructive Varshamov-Gilbert style
argument yields a lower bound on the achievable rate of a
code of a given length, minimum Euclidean distance and
maximum PAPR. The derivation of these bounds relies on a
geometrical analysis of the PAPR of such a code. Further
analysis shows that there exist asymptotically good codes
whose PAPR is at most 8 log n. These bounds motivate the
explicit construction of error-correcting codes with low
PAPR. Bounds for exponential sums over Galois fields and
rings are applied to obtain an upper bound of order (log n)2
on the PAPRs of a constructive class of codes, the trace
codes. This class includes the binary simplex code, duals of
binary, primitive Bose-Chaudhuri-Hocquenghem (BCH) codes and
a variety of their nonbinary analogs. Some open problems are
identified.},
Doi = {10.1109/18.868473},
Key = {fds336888}
}
@article{fds336886,
Author = {Tarokh, V and Jafarkhani, H},
Title = {Differential detection scheme for transmit
diversity},
Journal = {Ieee Journal on Selected Areas in Communications},
Volume = {18},
Number = {7},
Pages = {1169-1174},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2000},
Month = {July},
url = {http://dx.doi.org/10.1109/49.857917},
Abstract = {We present a transmission scheme for exploiting diversity
given by two transmit antennas when neither the transmitter
nor the receiver has access to channel state information.
The new detection scheme can use equal energy constellations
and encoding is simple. At the receiver, decoding is
achieved with low decoding complexity. The transmission
provides full spatial diversity and requires no channel
state side information at the receiver. The scheme can be
considered as the extension of differential detection
schemes to two transmit antennas.},
Doi = {10.1109/49.857917},
Key = {fds336886}
}
@article{fds336887,
Author = {Jafarkhani, H and Tarokh, V},
Title = {Image clustering using fuzzy graph theory},
Journal = {Smart Structures and Materials 2005: Active Materials:
Behavior and Mechanics},
Volume = {3972},
Pages = {245-252},
Year = {2000},
Month = {January},
Abstract = {We propose an image clustering algorithm which uses fuzzy
graph theory. First, we define a fuzzy graph and the concept
of connectivity for a fuzzy graph. Then, based on our
definition of connectivity we propose an algorithm which
finds connected subgraphs of the original fuzzy graph. Each
connected subgraph can be considered as a cluster. As an
application of our algorithm, we consider a database of
images. We calculate a similarity measure between any pairs
of images in the database and generate the corresponding
fuzzy graph. Then, we find the subgraphs of the resulting
fuzzy graph using our algorithm. Each subgraph corresponds
to a cluster. We apply our image clustering algorithm to the
key frames of news programs to find the anchorperson
clusters. Simulation results show that our algorithm is
successful to find most of anchorperson frames from the
database.},
Key = {fds336887}
}
@article{fds336889,
Author = {Tarokh, V and Jafarkhani, H},
Title = {On the computation and reduction of the peak-to-average
power ratio in multicarrier communications},
Journal = {Ieee Transactions on Communications},
Volume = {48},
Number = {1},
Pages = {37-44},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2000},
Month = {January},
url = {http://dx.doi.org/10.1109/26.818871},
Abstract = {For any code C defined over an equal energy constellation,
it is first shown that at any time instance, the problem of
determining codewords of C with high peak-to-average power
ratios (PAPR) in a multicarrier communication system is
intimately related to the problem of minimum-distance
decoding of C. Subsequently, a method is proposed for
computing the PAPR by minimum-distance decoding of C at many
points of time. Moreover, an upper bound on the error
between this computed value and the true one is derived.
Analogous results are established for codes defined over
arbitrary signal constellations. As an application of this
computational method, an approach for reducing the PAPR of C
proposed by Jones and Wilkinson is revisited. This approach
is based on introducing a specific phase shift to each
coordinate of all the codewords where phase shift are
independent of the codewords and known both to the
transmitter and the receiver. We optimize the phase shifts
offline by applying our method for computing the PAPR for
the coding scenario proposed by ETSI BRAN Standardization
Committee. Reductions of order 4.5 dB can be freely obtained
using the computed phase shifts. Examples are provided
showing that most of the grain is preserved when the
computed optimal phase shifts are rounded to quantenary
phase-shift keying (PSK), 8-PSK, and 16-PSK type phase
shifts.},
Doi = {10.1109/26.818871},
Key = {fds336889}
}
@article{fds340045,
Author = {Tarokh, V and Jafarkhani, H and Calderbank, AR},
Title = {Correction to "Space-time block codes from orthogonal
designs"},
Journal = {Ieee Transactions on Information Theory},
Volume = {46},
Number = {1},
Pages = {314-314},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {2000},
Month = {January},
url = {http://dx.doi.org/10.1109/tit.2000.1282193},
Doi = {10.1109/tit.2000.1282193},
Key = {fds340045}
}
@article{fds336894,
Author = {Tarokh, V and Vardy, A and Zeger, K},
Title = {Universal bound on the performance of lattice
codes},
Journal = {Ieee Transactions on Information Theory},
Volume = {45},
Number = {2},
Pages = {670-681},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {1999},
Month = {December},
url = {http://dx.doi.org/10.1109/18.749010},
Abstract = {We present a lower bound on the probability of symbol error
for maximum-likelihood decoding of lattices and lattice
codes on a Gaussian channel. The bound is tight for error
probabilities and signal-to-noise ratios of practical
interest, as opposed to most existing bounds that become
tight asymptotically for high signal-to-noise ratios. The
bound is also universal; it provides a limit on the highest
possible coding gain that may be achieved, at specific
symbol error probabilities, using any lattice or lattice
code in n dimensions. In particular, it is shown that the
effective coding gains of the densest known lattices are
much lower than their nominal coding gains. The asymptotic
(as n - behavior of the new bound is shown to coincide with
the Shannon limit for Gaussian channels. © 1999
IEEE.},
Doi = {10.1109/18.749010},
Key = {fds336894}
}
@article{fds336890,
Author = {Jafarkhani, H and Tarokh, V},
Title = {Design of successively refinable trellis-coded
quantizers},
Journal = {Ieee Transactions on Information Theory},
Volume = {45},
Number = {5},
Pages = {1490-1497},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {1999},
Month = {December},
url = {http://dx.doi.org/10.1109/18.771148},
Abstract = {We propose successively refinable trellis-coded quantizers
for progressive transmission. (Progressive transmission is
an essential component of image and multimedia browsing
systems.) A new trellis structure which is scalable is used
in the design of our trellis-coded quantizers. A
hierarchical set partitioning is developed to preserve
successive refinability. Two algorithms for designing
trellis-coded quantizers which provide embedded bit streams
are provided. The computational complexity of the proposed
schemes is compared with that of trellis-coded quantization.
Simulation results show excellent performances for
memoryless sources. © 1999 IEEE.},
Doi = {10.1109/18.771148},
Key = {fds336890}
}
@article{fds336891,
Author = {Jafarkhani, H and Tarokh, V},
Title = {Multiple description trellis-coded quantization},
Journal = {Ieee Transactions on Communications},
Volume = {47},
Number = {6},
Pages = {799-802},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {1999},
Month = {December},
url = {http://dx.doi.org/10.1109/26.771331},
Abstract = {We present a construction of multiple description
trellis-coded quantizers. We use the tensor product of
trellises to build a trellis which is applicable to multiple
description coding. The problems of index assignment and set
partitioning for the resulting trellis are considered. The
Viterbi algorithm provides the best path for encoding and
the design procedure utilizes a generalized Lloyd algorithm.
The encoding process simultaneously generates all the
transmitted sequences. Furthermore, the complexity of the
scheme is almost independent of the rate. The quantizer
provides remarkable performance with little encoding
complexity. © 1999 IEEE.},
Doi = {10.1109/26.771331},
Key = {fds336891}
}
@article{fds336893,
Author = {Paterson, KG and Tarokh, V},
Title = {On the existence and construction of good codes with low
peak-to-average power ratios},
Journal = {Hp Laboratories Technical Report},
Number = {51},
Year = {1999},
Month = {April},
Abstract = {The first lower bound on the peak-to-average power ratio
(PAPR) of a constant energy code of a given length n,
minimum Euclidean distance and rate is established.
Conversely, using a non-constructive Varshamov-Gilbert style
argument yields a lower bound on the achievable rate of a
code of a given length, minimum Euclidean distance and
maximum PAPR. The derivation of these bounds relies on a
geometrical analysis of the PAPR of such a code. Further
analysis shows that there exist asymptotically good codes
whose PAPR is at most 8 log n. These bounds motivate the
explicit construction of error-correcting codes with low
PAPR. Bounds for exponential sums over Galois fields and
rings are applied to obtain an upper bound of order (log n)2
on the PAPRs of a constructive class of codes, the trace
codes. This class includes the binary simplex code, duals of
binary, primitive BCH codes and a variety of their
non-binary analogues. Some open problems are
identified.},
Key = {fds336893}
}
@article{fds333012,
Author = {Tarokh, V and Jafarkhani, H and Calderbank, AR},
Title = {Space-time block coding for wireless communications:
Performance results},
Journal = {Ieee Journal on Selected Areas in Communications},
Volume = {17},
Number = {3},
Pages = {451-460},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {1999},
Month = {March},
url = {http://dx.doi.org/10.1109/49.753730},
Abstract = {We document the performance of space-time block codes [13],
[14], which provide a new paradigm for transmission over
Rayleigh fading channels using multiple transmit antennas.
Data is encoded using a space-time block code, and the
encoded data is split into n streams which are
simultaneously transmitted using n transmit antennas. The
received signal at each receive antenna is a linear
superposition of the n transmitted signals perturbed by
noise. Maximum likelihood decoding is achieved in a simple
way through decoupling of the signals transmitted from
different antennas rather than joint detection. This uses
the orthogonal structure of the space-time block code and
gives a maximum likelihood decoding algorithm which is based
only on linear processing at the receiver. We review the
encoding and decoding algorithms for various codes and
provide simulation results demonstrating their performance.
It is shown that using multiple transmit antennas and
space-time block coding provides remarkable performance at
the expense of almost no extra processing.},
Doi = {10.1109/49.753730},
Key = {fds333012}
}
@article{fds336895,
Author = {Tarokh, V and Jafarkhnni, H},
Title = {A differential detection scheme for transmit
diversity},
Journal = {Ieee Wireless Communications and Networking Conference,
Wcnc},
Volume = {3},
Pages = {1043-1047},
Publisher = {IEEE},
Year = {1999},
Month = {January},
ISBN = {0780356683},
url = {http://dx.doi.org/10.1109/WCNC.1999.796832},
Abstract = {We present a transmission scheme for exploiting diversity
given by two transmit antennas when neither the transmitter
nor the receiver has access to channel state information.
The new detection scheme can use PSK constellations and
encoding is simple. At the receiver, decoding is achieved
with low decoding complexity. The transmission provides full
spatial diversity and requires no channel state side
information at the receiver. The scheme can be thought as
the extension of differential detection schemes to two
transmit antennas.},
Doi = {10.1109/WCNC.1999.796832},
Key = {fds336895}
}
@article{fds336896,
Author = {Lo, T and Tarokh, V},
Title = {Space-time block coding-from a physical perspective},
Journal = {Ieee Wireless Communications and Networking Conference,
Wcnc},
Volume = {1},
Pages = {150-153},
Publisher = {IEEE},
Year = {1999},
Month = {January},
ISBN = {0780356683},
url = {http://dx.doi.org/10.1109/WCNC.1999.797804},
Abstract = {Space-time block coding (STBC) is an effective transmit
diversity scheme. It was presented previously by in terms of
coding and decoding by Alamouti (see IEEE J. Select. Areas
Commun., vol.16, no.8, p.1451-58, 1998) and by Tarokh,
Jafarkhani and Calderbank (see IEEE Trans. Inform. Theory,
1999). Here, STBC is examined from a different perspective;
namely the radiation patterns resulting from simultaneous
transmission from multiple transmit antennas.},
Doi = {10.1109/WCNC.1999.797804},
Key = {fds336896}
}
@article{fds336897,
Author = {Tarokh, V and Jafarkhani, H},
Title = {Algorithm for reducing the peak to average power ratio in a
multicarrier communications system},
Journal = {Ieee Vehicular Technology Conference},
Volume = {1},
Pages = {680-684},
Year = {1999},
Month = {January},
ISBN = {0780354354},
Abstract = {One of the main implementation disadvantages of a
multicarrier communication system is the possibly high peak
to average power ratio of the transmitted signals. One
proposed solution is given by Jones and Wilkinson. It is
based on applying a specific phase shift (not dependent on
the codeword) to each dimension of the transmitted
codewords. These phase shifts are known both to the
transmitter and the receiver. Thus the phase shifts can be
compensated for in the receiver without changing the
distance properties of the code. Therefore, neither the rate
nor the code performance is sacrificed. The phases need only
once be computed off-line and the complexity of the system
does not increase. Our combination is to provide an
algorithm to compute the phases that minimize the maximum
peak to average power ratio taken over all possible
transmitted signals. The new algorithm enables us to apply
the Jones-Wilkinson method to various medium length as well
as long codes of practical interest, a computational task
for which no solution was known before. We apply our
algorithm to some of the codes adapted for use in the
physical layer of future wireless local area networks by the
ETSI BRAN Hiperlan-II standardization committee. We report
the computed reductions in peak to average power
ratio.},
Key = {fds336897}
}
@article{fds336898,
Author = {Tarokh, V},
Title = {Space-time codes for high data rate wireless communication:
performance criteria in the presence of channel estimation
errors, mobility, and multiple paths},
Journal = {Ieee Transactions on Communications},
Volume = {47},
Number = {2},
Pages = {199-207},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {1999},
Month = {January},
url = {http://dx.doi.org/10.1109/26.752125},
Abstract = {Space-time coding is a bandwidth and power efficient method
of communication over fading channels that realizes the
benefits of multiple transmit antennas. Specific codes have
been constructed using design criteria derived for
quasi-static flat Rayleigh or Rician fading, where channel
state information is available at the receiver. It is
evident that the practicality of space-time codes will be
greatly enhanced if the derived design criteria remain valid
in the absence of perfect channel state information. It is
even more desirable that the design criteria not be unduly
sensitive to frequency selectivity and to the Doppler
spread. This paper presents a theoretical study of these
issues beginning with the effect of channel estimation
error. Here it is assumed that a channel estimator extracts
fade coefficients at the receiver and for constellations
with constant energy, it is proved that in the absence of
ideal channel state information the design criteria for
space-time codes is still valid. The analysis also
demonstrates that standard channel estimation techniques can
be used in conjunction with space-time codes provided that
the number of transmit antennas is small. We also derive the
maximum-likelihood detection metric in the presence of
channel estimation errors. Next, the effect of multiple
paths on the performance of space-time codes is studied for
a slowly changing Rayleigh channel. It is proved that the
presence of multiple paths does not decrease the diversity
order guaranteed by the design criteria used to construct
the space-time codes. Similar results hold for rapid fading
channels with or without multiple paths. The conclusion is
that the diversity order promised by space-time coding is
achieved under a variety of mobility conditions and
environmental effects.},
Doi = {10.1109/26.752125},
Key = {fds336898}
}
@article{fds336892,
Author = {Tarokh, V and Naguib, A},
Title = {Combined array processing and space-time
coding},
Journal = {Ieee Transactions on Information Theory},
Volume = {45},
Number = {4},
Pages = {1121-1128},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {1999},
Month = {January},
url = {http://dx.doi.org/10.1109/18.761255},
Abstract = {The information capacity of wireless communication systems
may be increased by employing multiple transmit and receiver
antennas. The goal of the system design is to exploit this
capacity in a practical way. To increase data rate over
wireless channels, space-time coding techniques appropriate
to multiple transmit antennas are employed. These space-time
codes introduce temporal and spatial correlation into
signals transmitted from different antennas to provide
diversity at the receiver, and coding gain over the uncoded
system. The encoding and decoding complexity are reduced by
partitioning the antennas at the transmitter into small
groups, and using individual space-time code, called
component codes, to transmit information from each group of
antennas.},
Doi = {10.1109/18.761255},
Key = {fds336892}
}
@article{fds333013,
Author = {Tarokh, V and Jafarkhani, H and Calderbank, AR},
Title = {Space-time block codes from orthogonal designs},
Journal = {Ieee Transactions on Information Theory},
Volume = {45},
Number = {5},
Pages = {1456-1467},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {1999},
Month = {January},
url = {http://dx.doi.org/10.1109/18.771146},
Abstract = {The theory of space-time block coding is presented as a
simple and elegant method for transmission using multiple
transmit antennas in a wireless Rayleigh/Rician environment.
These codes have a very simple maximum-likelihood decoding
algorithm which is only based on linear processing. Designs
that correspond to combined coding and linear processing at
the transmitter are also considered.},
Doi = {10.1109/18.771146},
Key = {fds333013}
}
@article{fds336899,
Author = {Jafarkhani, H and Tarokh, V},
Title = {Multiple description trellis coded quantization},
Journal = {Ieee International Conference on Image Processing},
Volume = {1},
Pages = {669-673},
Publisher = {IEEE Comput. Soc},
Year = {1998},
Month = {December},
ISBN = {0818688211},
url = {http://dx.doi.org/10.1109/icip.1998.723587},
Abstract = {We present a construction of multiple description trellis
coded quantizers. We use the tensor product of trellises to
build a trellis which is applicable to multiple description
coding. The problems of index assignment and set
partitioning for the resulting trellis are considered. The
Viterbi algorithm provides the best path for encoding and
the design procedure utilizes a generalized Lloyd algorithm.
The encoding process simultaneously generates all the
transmitted sequences. Furthermore, the complexity of the
scheme is almost independent of the rate. The quantizer
provides remarkable performance with little encoding
complexity.},
Doi = {10.1109/icip.1998.723587},
Key = {fds336899}
}
@article{fds336900,
Author = {Agrawal, D and Tarokh, V and Naguib, A and Seshadri,
N},
Title = {Space-time coded OFDM for high data-rate wireless
communication over wideband channels},
Journal = {Ieee Vehicular Technology Conference},
Volume = {3},
Pages = {2232-2236},
Year = {1998},
Month = {December},
Abstract = {The space-time coded orthogonal frequency division
multiplexing (OFDM) scheme is described to provide high
data-rate wireless communication over wideband channels.
Simulation results for a 4-PSK 16 state space-time coded
OFDM system are presented. The proposed scheme is capable of
reliable transmission at relatively lower signal to noise
ratio in variety of delay profiles, thus making it a robust
alternative.},
Key = {fds336900}
}
@article{fds333014,
Author = {Tarokh, V and Naguib, A and Seshadri, N and Calderbank,
AR},
Title = {Recent progress in space-time block and trellis
coding},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {314},
Publisher = {IEEE},
Year = {1998},
Month = {December},
url = {http://dx.doi.org/10.1109/ISIT.1998.708919},
Abstract = {Techniques for transmission and reception over wireless
channels using multiple transmit antennas are presented. ©
1998 IEEE.},
Doi = {10.1109/ISIT.1998.708919},
Key = {fds333014}
}
@article{fds333017,
Author = {Tarokh, V and Seshadri, N and Calderbank, AR},
Title = {Space-time codes for high data rate wireless communication:
Performance criterion and code construction},
Journal = {Ieee Transactions on Information Theory},
Volume = {44},
Number = {2},
Pages = {744-765},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {1998},
Month = {December},
url = {http://dx.doi.org/10.1109/18.661517},
Abstract = {We consider the design of channel codes for improving the
data rate and/or the reliability of communications over
fading channels using multiple transmit antennas. Data is
encoded by a channel code and the encoded data is split into
n streams that are simultaneously transmitted using n
transmit antennas. The received signal at each receive
antenna is a linear superposition of the n transmitted
signals perturbed by noise. We derive performance criteria
for designing such codes under the assumption that the
fading is slow and frequency nonselective. Performance is
shown to be determined by matrices constructed from pairs of
distinct code sequences. The minimum rank among these
matrices quantifies the diversity gain, while the minimum
determinant of these matrices quantifies the coding gain.
The results are then extended to fast fading channels. The
design criteria are used to design trellis codes for high
data rate wireless communication. The encoding/decoding
complexity of these codes is comparable to trellis codes
employed in practice over Gaussian channels. The codes
constructed here provide the best tradeoff between data
rate, diversity advantage, and trellis complexity.
Simulation results are provided for 4 and 8 PSK signal sets
with data rates of 2 and 3 bits/symbol, demonstrating
excellent performance that is within 2-3 dB of the outage
capacity for these channels using only 64 state encoders. ©
1998 IEEE.},
Doi = {10.1109/18.661517},
Key = {fds333017}
}
@article{fds333016,
Author = {Naguib, AF and Tarokh, V and Seshadri, N and Calderbank,
AR},
Title = {A space-time coding modem for high-data-rate wireless
communications},
Journal = {Ieee Journal on Selected Areas in Communications},
Volume = {16},
Number = {8},
Pages = {1459-1477},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {1998},
Month = {October},
url = {http://dx.doi.org/10.1109/49.730454},
Abstract = {This paper presents the theory and practice of a new
advanced modem technology suitable for high-data-rate
wireless communications and presents its performance over a
frequency-flat Rayleigh fading channel. The new technology
is based on space-time coded modulation (STCM) [1]-[5] with
multiple transmit and/or multiple receive antennas and
orthogonal pilot sequence insertion (O-PSI). In this
approach, data is encoded by a space-time (ST) channel
encoder and the output of the encoder is split into N
streams to be simultaneously transmitted using N transmit
antennas. The transmitter inserts periodic orthogonal pilot
sequences in each of the simultaneously transmitted bursts.
The receiver uses those pilot sequences to estimate the
fading channel. When combined with an appropriately designed
interpolation filter, accurate channel state information
(CSI) can be estimated for the decoding process. Simulation
results of the proposed modem, as applied to the IS-136
cellular standard, are presented. We present the frame error
rate (FER) performance results as a function of the
signal-to-noise ratio (SNR) and the maximum Doppler
frequency, in the presence of timing and frequency offset
errors. Simulation results show that for 10% FER, a 32-state
eight-phase-shift keyed (8-PSK) ST code with two transmit
and two receive antennas can support data rates up to 55.8
kb/s on a 30-kHz channel, at an SNR of 11.7 dB and a maximum
Doppler frequency of 180 Hz. Simulation results for other
codes and other channel conditions are also provided. We
also compare the performance of the proposed STCM scheme
with delay-diversity schemes and conclude that STCM can
provide significant SNR improvement over simple delay
diversity.},
Doi = {10.1109/49.730454},
Key = {fds333016}
}
@article{fds336901,
Author = {Tarokh, V and Lo, TKY},
Title = {Principal ratio combining for fixed wireles applications
when transmitter diversity is employed},
Journal = {Ieee Communications Letters},
Volume = {2},
Number = {8},
Pages = {223-225},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {1998},
Month = {August},
url = {http://dx.doi.org/10.1109/4234.709438},
Abstract = {We present a near-optimal detection method for decoding
codes appropriate to transmission using multiple transmit
antennas in a fixed wireless environment. The method is a
nontrivial generalization of maximum ratio combining. This
reduces the decoding complexity at the expense of some
sacrifice in performance.},
Doi = {10.1109/4234.709438},
Key = {fds336901}
}
@article{fds336902,
Author = {Jafarkhani, H and Tarokh, V},
Title = {Successively refinable trellis coded quantization},
Journal = {Data Compression Conference Proceedings},
Pages = {83-92},
Publisher = {IEEE Comput. Soc},
Year = {1998},
Month = {January},
ISBN = {0818684062},
url = {http://dx.doi.org/10.1109/dcc.1998.672134},
Abstract = {We propose successively refinable trellis coded quantizers
which are suitable for progressive transmission. A new
trellis structure which is scalable is used in the design of
our trellis coded quantizers. A hierarchical set
partitioning is used to preserve successive refinability.
Two algorithms for designing trellis coded quantizers which
provide embedded bit streams are provided. The computational
complexity of the proposed schemes is compared with that of
trellis coded quantization. Simulation results show good
performances for memoryless sources.},
Doi = {10.1109/dcc.1998.672134},
Key = {fds336902}
}
@article{fds336903,
Author = {Tarokh, V and Alamouti, SM and Poon, P},
Title = {New detection schemes for transmit diversity with no channel
estimation},
Journal = {Icupc 1998 Ieee 1998 International Conference on Universal
Personal Communications, Conference Proceedings},
Volume = {2},
Pages = {917-920},
Publisher = {IEEE},
Year = {1998},
Month = {January},
ISBN = {0780351061},
url = {http://dx.doi.org/10.1109/ICUPC.1998.733643},
Abstract = {We present two new detection methods for the simple transmit
diversity scheme proposed by Alamouti (see IEEE Journal on
Selected Areas of Communications, Special Issue on Signal
Processing for Wireless Communications, 1998). The new
detection schemes require no channel state information at
either the transmitter or the receiver. Using 2 transmit
antennas and 1 receive antenna, the scheme provides a
diversity order of two. Simulations have been included to
show that the scheme has almost a 3 dB penalty compared to
coherent detection.},
Doi = {10.1109/ICUPC.1998.733643},
Key = {fds336903}
}
@article{fds336904,
Author = {Alamouti, SM and Tarokh, V and Poon, P},
Title = {Trellis-coded modulation and transmit diversity: Design
criteria and performance evaluation},
Journal = {Icupc 1998 Ieee 1998 International Conference on Universal
Personal Communications, Conference Proceedings},
Volume = {1},
Pages = {703-707},
Publisher = {IEEE},
Year = {1998},
Month = {January},
ISBN = {0780351061},
url = {http://dx.doi.org/10.1109/ICUPC.1998.733058},
Abstract = {This paper presents the selection criteria for trellis codes
used with the simple transmit diversity scheme proposed in
Alamouti (1998) and reviewed in this paper. The optimum
metrics for soft decision Viterbi decoding are derived and
the asymptotic coding gains are calculated. The design
method achieves both coding gain and a diversity order of 2
using 2 transmit antennas and 1 receive antenna. It is also
demonstrated that trellis codes optimized for AWGN are also
optimal for use in conjunction with the transmit diversity
scheme in Rayleigh fading.},
Doi = {10.1109/ICUPC.1998.733058},
Key = {fds336904}
}
@article{fds336905,
Author = {Tarokh, V and Lo, TKY},
Title = {Principal ratio combining for fixed wireless applications
when transmitter diversity is employed},
Journal = {Icupc 1998 Ieee 1998 International Conference on Universal
Personal Communications, Conference Proceedings},
Volume = {2},
Pages = {907-909},
Publisher = {IEEE},
Year = {1998},
Month = {January},
ISBN = {0780351061},
url = {http://dx.doi.org/10.1109/ICUPC.1998.733641},
Abstract = {We present a near-optimal detection method for decoding
codes appropriate to transmission using multiple transmit
antennas in a fixed wireless environment. The method is a
non-trivial generalization of maximum ratio combining. This
reduces the decoding complexity at the expense of some
sacrifice in performance.},
Doi = {10.1109/ICUPC.1998.733641},
Key = {fds336905}
}
@article{fds333015,
Author = {Tarokh, V and Jafarkhani, H and Calderbank, AR},
Title = {The application of orthogonal designs to wireless
communication},
Journal = {1998 Information Theory Workshop, Itw 1998},
Pages = {46-47},
Publisher = {IEEE},
Year = {1998},
Month = {January},
ISBN = {0780344081},
url = {http://dx.doi.org/10.1109/ITW.1998.706408},
Abstract = {We introduce space-block codzng, a new paradigm for
transmission over Rayleigh fading channels using multiple
transmit antennas. Data is encoded using a space-block code
and the encoded data is split into n streams which are
simultaneously transmitted using n transmit antennas. The
received signal at each receive antenna is a linear
superposition of the n transmitted signal perturbed by
noise. Decoding is achieved in a simple way using the
orthogonal structure of tlie space-block code and maximum
likelihood decoding algorithm is totally based on linear
processing at the receiver. Space-black codes are designed
to achieve the maximum diversity gain of transmit and
receive antennas with the constraint of having a simple
decoding algorithm. It is shown that the classical
mathematical framework of orthogonal designs can be applied
to construct cliannel codes which have a simple decoding
algorithm, while providing tlie full spatial diversity
order. Space-block codes constructed in this way only exist
for few sporadic values of n and therefore there is a need
for a new mathematical theory. In this light, we introduce
the theory of Generalzzed Deszgns which provides codes for
both real and complex constellations for any number of
transmit antennas. Using this theory, we construct
space-block codes that achieve the maximum possible
transmission rate for any number of transmit antennas using
any arbitrary real constellation such as PAM. For any
arbitrary complex constellation such as PSK and QAM, we
construct space-block codes that achieve half of the maximum
possible transmission rate for any number of transmit
antennas. For tlie specific cases of two, three and four
transmit antennas, we provide space-block codes that achieve
respectively the whole, 3/4 and 3/4 of maximum possible
transmission rate using arbitrary complex constellations.
The best trade-off between tlie decoding delay and the
number of transmit antennas is also computed and it is shown
that the designed codes are optimal in this sense as well.
Various fundamental problems are posed which are both
inatliematically appealing and have immediate application to
the design of a physical layer for wireless communication
systems.},
Doi = {10.1109/ITW.1998.706408},
Key = {fds333015}
}
@article{fds336906,
Author = {Tarokh, V and Vardy, A},
Title = {Upper bounds on trellis complexity of lattices},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {385},
Publisher = {IEEE},
Year = {1997},
Month = {December},
ISBN = {0780339568},
url = {http://dx.doi.org/10.1109/ISIT.1997.613322},
Abstract = {Unlike block codes, n-dimensional lattices can have minimal
trellis diagrams with an arbitrarily large number of states,
branches, and paths. We show by a counter-example that there
is no f(n), a function of n, such that all rational lattices
of dimension n have a trellis with less than f(n) states.
Nevertheless, we prove that if Λ is a sublattice of Zn then
it has a trellis T, such that the maximum number of states
in T is upper bounded by the volume of Λ. Furthermore,
using a theorem due to Hermite, we show that every integral
lattice Λ has a trellis T, such that the total number of
paths in T can be bounded from above in terms of the volume
of Λ. The resulting bounds are exponential in the dimension
n and are seldom tight. Nonetheless, these are the first
known general upper bounds on trellis complexity of
lattices. © 1997 IEEE.},
Doi = {10.1109/ISIT.1997.613322},
Key = {fds336906}
}
@article{fds336907,
Author = {Tarokh, V and Vardy, A and Zeger, K},
Title = {Sequential decoding of lattice codes},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {497},
Publisher = {IEEE},
Year = {1997},
Month = {December},
ISBN = {0780339568},
url = {http://dx.doi.org/10.1109/ISIT.1997.613434},
Abstract = {We consider lattice tree-codes based on a lattice Λ having
a finite trellis diagram T. Such codes are easy to encode
and benefit from the structure of Λ . Sequential decoding
of lattice tree-codes is studied, and the corresponding Fano
(1963) metric is derived. An upper bound on the running time
of the sequential decoding algorithm is established, and
found to resemble the Pareto distribution. Our bound
indicates that the order of label groups in T plays an
important role in determining the complexity of sequential
decoding. Furthermore, it is proved that lattice tree-codes
of arbitrarily high rate, based on Λ and T, can be
sequentially decoded with the same complexity, and without
any possibility of buffer overflow. © 1997
IEEE.},
Doi = {10.1109/ISIT.1997.613434},
Key = {fds336907}
}
@article{fds336908,
Author = {Naguib, AF and Tarokh, V and Seshadri, N and Colderbank,
AR},
Title = {Space-time coded modulation for high data rate wireless
communications},
Journal = {Conference Record / Ieee Global Telecommunications
Conference},
Volume = {1},
Pages = {102-109},
Year = {1997},
Month = {December},
Abstract = {This paper presents the theory and practice of a new
advanced modem technology suitable for high data rate
wireless communications and presents its performance over a
frequency-flat Rayleigh fading channel. The new technology
is based on space-time coded modulation (STCM) with multiple
transmit and/or multiple receive antennas and orthogonal
pilot sequence insertion (O-PSI). In this approach data is
encoded by a space-time channel encoder and the output of
the encoder is split into N streams to be simultaneously
transmitted using N transmit antennas. The transmitter
inserts periodic orthogonal pilot sequences in each of the
simultaneously transmitted bursts. The receiver uses those
pilot sequences to estimate the fading channel. When
combined with an appropriately designed interpolation
filter, accurate channel state information (CSI) can be
estimated for the decoding process. Simulation results of
the proposed modem as applied to the IS-136 cellular
standard are presented. We present the frame error rate
(PER) performance as a function of the signal to noise ratio
(SNR) and Doppler spread in the presence of timing and
frequency offset errors. Simulation results show that, for
examples, for 10% PER, data rates up to 54 kbps per a 30 kHz
channel can be supported at a SNR of 11.7 dB and a Doppler
spread of 180 Hz using a 32-state 8-PSK space-time code with
2 transmit and 2 receive antennas. Simulation results for
other cases are also provided.},
Key = {fds336908}
}
@article{fds336909,
Author = {Tarokh, V and Vardy, A},
Title = {Upper bounds on trellis complexity of lattices},
Journal = {Ieee Transactions on Information Theory},
Volume = {43},
Number = {4},
Pages = {1294-1300},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {1997},
Month = {December},
url = {http://dx.doi.org/10.1109/18.605598},
Abstract = {Unlike block codes, n-dimensional lattices can have minimal
trellis diagrams with an arbitrarily large number of states,
branches, and paths. In particular, we show by a
counterexample that there is no f(n), a function of n, such
that all rational lattices of dimension n have a trellis
with less than f(n) states. Nevertheless, using a theorem
due to Hermite, we prove that every integral lattice A of
dimension n has a trellis T, such that the total number of
paths in T is upper-bounded by P(T) ≤ n!(2/√3) n2(n-1)/2
where V(ΛA) is the volume of Λ. Furthermore, the number of
states at time i in T is upper-bounded by |S i| ≤ (2/√3)
i2(n-1)/2V(Λ) 2i2/n. Although these bounds are seldom
tight, these are the first known general upper bounds on
trellis complexity of lattices. © 1997 IEEE.},
Doi = {10.1109/18.605598},
Key = {fds336909}
}
@article{fds336910,
Author = {Linder, T and Tarokh, V and Zeger, K},
Title = {Existence of optimal prefix codes for infinite source
alphabets},
Journal = {Ieee Transactions on Information Theory},
Volume = {43},
Number = {6},
Pages = {2026-2028},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {1997},
Month = {December},
url = {http://dx.doi.org/10.1109/18.641571},
Abstract = {It is proven that for every random variable with a countably
infinite set of outcomes and finite entropy there exists an
optimal prefix code which can be constructed from Huffman
codes for truncated versions of the random variable, and
that the average lengths of any sequence of Huffman codes
for the truncated versions converge to that of the optimal
code. Also, it is shown that every optimal infinite code
achieves Kraft's inequality with equality. © 1997
IEEE.},
Doi = {10.1109/18.641571},
Key = {fds336910}
}
@article{fds333018,
Author = {Tarokh, V and Naguib, A and Seshadri, N and Calderbank,
AR},
Title = {Low-rate multi-dimensional space-time codes for both slow
and rapid fading channels},
Journal = {Ieee International Symposium on Personal, Indoor and Mobile
Radio Communications, Pimrc},
Volume = {3},
Pages = {1206-1210},
Year = {1997},
Month = {December},
Abstract = {We consider the design of channel codes for improving the
data rate and/or the reliability of communications using
multiple transmit antennas over a fading channel. It is
assumed that the transmitter does not know the channel but
seeks to choose a codebook that guarantees a diversity gain
of r1 when there is no mobility and a diversity gain of
r2≥r1 when the channel is fast fading. A solution to this
problem is unveiled in this paper. Here, the encoded data is
split into n streams that are simultaneously transmitted
using n transmit antennas. The signal received at each
receive antenna is a superposition of the faded versions of
the n transmitted signals. We derive performance criteria
for designing codes having the aforementioned properties.
Performance is shown to be determined by diversity advantage
quantified by a rank/distance and coding advantage
quantified by a determinant/product criterion. The criteria
is used to design codes for both slow and rapid fading
channels. The constructed codes have remarkable performance
in low signal to noise ratios and are suitable for improving
the frequency reuse factor under a variety of mobility
conditions.},
Key = {fds333018}
}
@article{fds333020,
Author = {Calderbank, AR and Seshadri, N and Tarokh, V},
Title = {Space-time codes for wireless communication},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {146},
Publisher = {IEEE},
Year = {1997},
Month = {December},
url = {http://dx.doi.org/10.1109/ISIT.1997.613061},
Abstract = {The design of channel codes for improving the data rate
and/or the reliability of communications over fading
channels using multiple transmit antennas is considered. A
design criterion is provided and is then used to design
space-time codes for high data rate wireless communication.
These codes are trellis codes that are easy to encode and
decode and have remarkable performance. © 1997
IEEE.},
Doi = {10.1109/ISIT.1997.613061},
Key = {fds333020}
}
@article{fds333019,
Author = {Tarokh, V and Seshadri, N and Calderbank, AR},
Title = {Space-time codes for high data rate wireless communication:
Performance criteria},
Journal = {Ieee International Conference on Communications},
Volume = {1},
Pages = {299-303},
Year = {1997},
Month = {January},
Abstract = {We consider the design of channel codes for improving the
data rate and/or the reliability of communications over
fading channels using multiple transmit antennas. Here, data
is encoded by a channel code and the encoded data is split
into n streams that are simultaneously transmitted using n
transmit antennas. The received signal at each receive
antenna is a linear superposition of the n transmitted
signals. We derive performance criteria for designing
channel codes under the assumption that the fading is slow
and frequency non-selective. Performance is shown to be
determined by diversity gain quantified by ranks and coding
gain quantified by determinants of certain matrices that are
constructed from the code sequences.},
Key = {fds333019}
}
@article{fds333021,
Author = {Tarokh, V and Naguib, AF and Seshadri, N and Calderbank,
AR},
Title = {Space-time codes for high data rate wireless communication:
Mismatch analysis},
Journal = {Ieee International Conference on Communications},
Volume = {1},
Pages = {309-313},
Year = {1997},
Month = {January},
Abstract = {We revisit Space-Time Codes for a mobile communication
system that employs multiple antennas at the base and
optional antenna diversity at the mobile station. The
realistic case when the channel state is not completely
known is considered. It is assumed that the channel
estimator extracts the fade coefficients using orthogonal
pilot tones. Mismatch analysis is then carried out. It is
proved that in the absence of ideal channel state
information the design criteria for space-time codes
developed in [11] is still valid for equal energy
constellation case. Using our derivation, it is observed
that channel estimation techniques commonly used over
rapidly fading channels can be used in conjunction with
space-time codes provided that the number of transmit
antennas is small.},
Key = {fds333021}
}
@article{fds333022,
Author = {Seshadri, N and Tarokh, V and Calderbank, AR},
Title = {Space-time codes for wireless communication: Code
construction},
Journal = {Ieee Vehicular Technology Conference},
Volume = {2},
Pages = {637-641},
Year = {1997},
Month = {January},
Abstract = {We consider the design of channel codes for improving the
data rate and/or the reliability of communications over
fading channels using multiple transmit antennas. Here, data
is encoded by a channel code and the encoded data is split
into n streams that are simultaneously transmitted using n
transmit antennas. The received signal at each receive
antenna is a linear superposition of the n transmitted
signals. We review the performance criteria for designing
such codes under the assumption that the fading is slow and
frequency non-selective established in [3]. Performance is
determined by diversity gain quantified by ranks and coding
gain quantified by determinants of certain matrices that are
constructed from the code sequences. The performance
criterion is then used to design trellis codes for high data
rate wireless communication. These codes are easy to encode
and decode. They provide the best trade-off between data
rate, diversity gain, constellation size and trellis
complexity. Simulation results are provided for 4 and 8 PSK
signal sets with data rates of 2 and 3 bits/symbol,
demonstrating excellent performance that is within 2-3 dB of
the outage capacity for these channels.},
Key = {fds333022}
}
@article{fds336912,
Author = {Tarokh, V and Blake, LF},
Title = {Trellis complexity versus the coding gain of lattices
I},
Journal = {Ieee Transactions on Information Theory},
Volume = {42},
Number = {6 PART 1},
Pages = {1796-1807},
Publisher = {Institute of Electrical and Electronics Engineers
(IEEE)},
Year = {1996},
Month = {December},
url = {http://dx.doi.org/10.1109/18.556675},
Abstract = {The best possible tradeoff between the coding gain and
trellis complexity for lattices is studied. Three trellis
complexity functions are defined for lattices as a measure
of minimum trellis decoding complexity per dimension
required for achieving a coding gain γ. The properties of
these functions are studied from an analytic perspective. It
is also shown that the trellis decoding complexity per
dimension is lower-bounded by an explicit power of γ. ©
1996 IEEE.},
Doi = {10.1109/18.556675},
Key = {fds336912}
}
@article{fds336913,
Author = {Tarokh, V and Blake, IF},
Title = {Trellis complexity versus the coding gain of lattices
.2.},
Journal = {Ieee Transactions on Information Theory},
Volume = {42},
Number = {6},
Pages = {1808-1816},
Publisher = {IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS
INC},
Year = {1996},
Month = {November},
url = {http://dx.doi.org/10.1109/18.556676},
Abstract = {For an arbitrary rational lattice L with gain γ, the
average number of states (respectively, branches) in any
given trellis diagram of L is bounded below by a function of
γ. It is proved that this function grows exponentially in
γ. In the reverse direction, it is proved that given e > 0,
for arbitrarily large values of γ, there exist lattices of
gain γ with an average number of branches and states less
than exp (7 ). © 1996 IEEE.},
Doi = {10.1109/18.556676},
Key = {fds336913}
}
@article{fds336911,
Author = {Blake, IF and Tarokh, V},
Title = {On the trellis complexity of the densest lattice packings in
ℝn},
Journal = {Siam Journal on Discrete Mathematics},
Volume = {9},
Number = {4},
Pages = {597-601},
Publisher = {Society for Industrial & Applied Mathematics
(SIAM)},
Year = {1996},
Month = {January},
url = {http://dx.doi.org/10.1137/S0895480195283348},
Abstract = {An inequality relating the trellis complexity of lattices to
their dimension and Hermite parameter is established. Using
this inequality, a conjecture of Forney is proved indicating
that the trellis complexity of the densest lattice packings
in ℝn grows exponentially as a function of their coding
gain.},
Doi = {10.1137/S0895480195283348},
Key = {fds336911}
}
@article{fds340047,
Author = {Britten, D and Lemire, F and Tarokh, V},
Title = {A Constraint on the Existence of Simple Torsion-Free Lie
Modules},
Journal = {Proceedings of the American Mathematical
Society},
Volume = {123},
Number = {8},
Pages = {2315-2315},
Publisher = {JSTOR},
Year = {1995},
Month = {August},
url = {http://dx.doi.org/10.2307/2161254},
Doi = {10.2307/2161254},
Key = {fds340047}
}
@article{fds336914,
Author = {Tarokh, V and Blake, IF},
Title = {Trellis complexity versus the coding gain of
lattices},
Journal = {Ieee International Symposium on Information Theory
Proceedings},
Pages = {125},
Publisher = {IEEE},
Year = {1995},
Month = {January},
ISBN = {0780324536},
url = {http://dx.doi.org/10.1109/isit.1995.531329},
Abstract = {The growth of trellis diagrams of lattices versus their
coding gain is studied. It is established that this growth
exponentially in terms of the coding gain.},
Doi = {10.1109/isit.1995.531329},
Key = {fds336914}
}
@article{fds340046,
Author = {Britten, D and Lemire, F and Tarokh, V},
Title = {A constraint on the existence of simple torsion-free lie
modules},
Journal = {Proceedings of the American Mathematical
Society},
Volume = {123},
Number = {8},
Pages = {2315-2321},
Publisher = {American Mathematical Society (AMS)},
Year = {1995},
Month = {January},
url = {http://dx.doi.org/10.1090/S0002-9939-1995-1246518-1},
Abstract = {For any simple Lie algebra L with Cartan subalgebra H the
classification of all simple H-diagonalizable. H-modules
having a finite-dimensional weight space is known to depend
on determining the simple torsion-free Lmodules of finite
degree. It is further known that the only simple Lie
algebras which admit simple torsion-free modules of finite
degree are those of types An and Cn. For the case of An. we
show that there are no simple torsion-free An- modules of
degree k for n ≥ 4 and 2 ≤ k ≤ n - 2. We conclude with
some examples showing that there exist simple torsion-free
A. -modules of degrees 1, n - 1, and n. © 1995 American
Mathematical Society.},
Doi = {10.1090/S0002-9939-1995-1246518-1},
Key = {fds340046}
}
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Mathematics Department