Math @ Duke

Publications [#319383] of Henry Pfister
Papers Published
 Zhang, F; Pfister, HD, Modulation codes for flash memory based on loadbalancing theory,
2009 47th Annual Allerton Conference on Communication, Control, and Computing, Allerton 2009
(December, 2009),
pp. 10391046, IEEE, ISBN 9781424458714 [doi]
(last updated on 2019/07/18)
Abstract: In this paper, we consider modulation codes for practical multilevel flash memory storage systems with q cell levels. Instead of maximizing the lifetime of the device [7], [1], [2], [4], we maximize the average amount of information stored per celllevel, which is defined as storage efficiency. Using this framework, we show that the worstcase criterion [7], [1], [2] and the averagecase criterion [4] are two extreme cases of our objective function. A selfrandomized modulation code is proposed which is asymptotically optimal, as q → ∞, for an arbitrary input alphabet and i.i.d. input distribution. In practical flash memory systems, the number of celllevels q is only moderately large. So the asymptotic performance as q → ∞ may not tell the whole story. Using the tools from loadbalancing theory, we analyze the storage efficiency of the selfrandomized modulation code. The result shows that only a fraction of the cells are utilized when the number of celllevels q is only moderately large. We also propose a loadbalancing modulation code, based on a phenomenon known as "the power of two random choices" [10], to improve the storage efficiency of practical systems. Theoretical analysis and simulation results show that our loadbalancing modulation codes can provide significant gain to practical flash memory storage systems. Though pseudorandom, our approach achieves the same loadbalancing performance, for i.i.d. inputs, as a purely random approach based on the power of two random choices. ©2009 IEEE.


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