Exploiting Intracell Bit-Error Characteristics to Improve Min-Sum LDPC Decoding for MLC NAND Flash-Based Storage in Mobile Device

Abstract

A multilevel per cell (MLC) technique significantly improves the storage density, but also poses serious data integrity challenge for NAND flash memory. This consequently makes the low-density parity-check (LDPC) code and the soft-decision memory sensing become indispensable in the next-generation flash-based solid-state storage devices. However, the use of LDPC codes inevitably increases memory read latency and, hence, degrades speed performance. Motivated by the observation of intracell unbalanced bit error probability and data dependence in the MLC NAND flash memory, this paper proposes two techniques, i.e., intracell data placement interleaving and intracell data dependence aware LDPC decoding, to efficiently improve the LDPC decoding throughput and energy efficiency for the MLC NAND flash-based storage in a mobile device. Experimental results show that, by exploiting the intracell bit-error characteristics, the proposed techniques together can improve the LDPC decoding throughput by up to 84.6% and reduce the energy consumption by up to 33.2% while only incurring less than 0.2% silicon area overhead.