2009/10/12 by Fan Zhang, Henry D. Pfister, Zhang, Fan +1
Computer Science · Mathematics · #Advanced Data Storage Technologies #Cellular Automata and Applications #FOS: Computer and information sciences #Information Theory (cs.IT) #Interconnection Networks and Systems #cs.IT #math.IT
paper · pdf · doi:10.48550/arxiv.0910.2005
This work was presented in the 47-th Allerton conference
arxiv created 2009/10/12 · openalex publication_date 2009/10/12 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
In this paper, we consider modulation codes for practical multilevel flash memory storage systems with cell levels. Instead of maximizing the lifetime of the device [Ajiang-isit07-01, Ajiang-isit07-02, Yaakobiverdysiegelwolfallerton08, FinucaneLiuMitzenmacheraller08], we maximize the average amount of information stored per cell-level, which is defined as storage efficiency. Using this framework, we show that the worst-case criterion [Ajiang-isit07-01, Ajiang-isit07-02, Yaakobiverdysiegelwolfallerton08] and the average-case criterion [FinucaneLiuMitzenmacheraller08] are two extreme cases of our objective function. A self-randomized modulation code is proposed which is asymptotically optimal, as, for an arbitrary input alphabet and i.i.d. input distribution. In practical flash memory systems, the number of cell-levels is only moderately large. So the asymptotic performance as may not tell the whole story. Using the tools from load-balancing theory, we analyze the storage efficiency of the self-randomized modulation code. The result shows that only a fraction of the cells are utilized when the number of cell-levels is only moderately large. We also propose a load-balancing modulation code, based on a phenomenon known as "the power of two random choices" [Mitzenmacher96thepower], to improve the storage efficiency of practical systems. Theoretical analysis and simulation results show that our load-balancing modulation codes can provide significant gain to practical flash memory storage systems. Though pseudo-random, our approach achieves the same load-balancing performance, for i.i.d. inputs, as a purely random approach based on the power of two random choices.