Abstract-High-capacity NAND flash memory can achieve high density storage by using multi-level cells (MLC) to store more than one bit per cell. Although this larger storage capacity is certainly beneficial, the increased density also increases the raw bit error rate (BER), making powerful error correction coding necessary. Traditional flash memories employ simple algebraic codes, such as BCH codes, that can correct a fixed, specified number of errors. This paper investigates the application of lowdensity parity-check (LDPC) codes which are well known for their ability to approach capacity in the AWGN channel. We obtain soft information for the LDPC decoder by performing multiple cell reads with distinct word-line voltages. The values of the word-line voltages (also called reference voltages) are optimized by maximizing the mutual information between the input and output of the multiple-read channel. Our results show that using this soft information in the LDPC decoder provides a significant benefit and enables the LDPC code to outperform a BCH code with comparable rate and block length over a range of block error rates.
As in the precursor conference paper REF this paper uses mutual information maximization as the objective function that drives the optimization of the word-line voltages (thresholds) used for the multiple reads that provide enhanced precision.
Soft Information for LDPC Decoding in Flash: Mutual-Information Optimized Quantization
2011 IEEE Global Telecommunications Conference - GLOBECOM 2011
2011 IEEE Global Telecommunications Conference - GLOBECOM 2011
Computer Science