Improving min-sum LDPC decoding throughput by exploiting intra-cell bit error characteristic in MLC NAND flash memory

Abstract

Multi-level per cell (MLC) technique significant- ly improves storage density, but also poses new challenge to data integrity in NAND flash memory. Therefore, low-density parity-check (LDPC) code and soft-decision memory sensing have become indispensable in future NAND flash-based solid state drive design. However, these more powerful technologies inevitably increase the memory read latency and hence degrade the decoding throughput. Motivated by intra-cell unbalanced bit error probability and data dependency in MLC NAND flash memory, this paper proposes two techniques, i.e. intra-cell data placement interleaving and intra-cell data dependency aware min-sum decoding, to effectively improve the throughput of LDPC decoding. Experimental results show that, the proposed techniques used in an integrated way can improve the LDPC decoding throughput by up to 85% when the MLC NAND flash chip is heavily cycled, compared with conventional design practice.