Rewritable coset coding for flash memories

Abstract

Flash memory is a nonvolatile memory technology that suffers from errors due to charge leakage, can tolerate limited erasures, and where erasures have to be performed in large blocks. We show that using cosets of a linear code can provide correction against uniform charge leakage, and can enhance the rewritability of flash memory which leads to fewer erasures. We introduce two coset coding schemes that are generalizations of the scheme in Jacobvitz et al. (2013). For the same worst case rewrite cost, we show that coset codes can encode more information than rank modulation codes. The average case performance of coset codes is demonstrated via numerical simulations. 1. INTRODUCTION Flash memory is a nonvolatile memory technology that has become a dominant medium of storage over the past decade in both consumer and enterprise applications. In this memory technology charge is injected iteratively into a cell to bring the charge to a desired level, and the level of the charge encodes the bits that are to be recorded. Multilevel flash memory is used to increase the density of information stored, and also to improve the speed of reading and writing data to the memory. Despite being a fast medium, multilevel flash memory technology suffers from a couple of deficiencies that we describe below