Rewriting Flash Memories by Message Passing

TL;DR

This paper introduces a new WOM coding scheme for flash memory that combines message passing, error correction, and capacity achievement, with practical hardware implementation potential and superior rewriting performance.

Contribution

It presents a novel WOM code construction based on LDGM codes and message passing, achieving capacity and enhanced rewriting success, along with a framework for error correction using BCH codes.

Findings

Achieves rewriting capacity with LDGM-based WOM codes.

Outperforms polar WOM codes in high success probability regions.

Provides a general framework for error-correcting WOM codes using conjugate code pairs.

Abstract

This paper constructs WOM codes that combine rewriting and error correction for mitigating the reliability and the endurance problems in flash memory. We consider a rewriting model that is of practical interest to flash applications where only the second write uses WOM codes. Our WOM code construction is based on binary erasure quantization with LDGM codes, where the rewriting uses message passing and has potential to share the efficient hardware implementations with LDPC codes in practice. We show that the coding scheme achieves the capacity of the rewriting model. Extensive simulations show that the rewriting performance of our scheme compares favorably with that of polar WOM code in the rate region where high rewriting success probability is desired. We further augment our coding schemes with error correction capability. By drawing a connection to the conjugate code pairs studied in the context of quantum error correction, we develop a general framework for constructing error-correction WOM codes. Under this framework, we give an explicit construction of WOM codes whose codewords are contained in BCH codes.