1 research outputs found
Polar-Coded Forward Error Correction for MLC NAND Flash Memory Polar FEC for NAND Flash Memory
With the ever-growing storage density, high-speed, and low-cost data access,
flash memory has inevitably become popular. Multi-level cell (MLC) NAND flash
memory, which can well balance the data density and memory stability, has
occupied the largest market share of flash memory. With the aggressive memory
scaling, however, the reliability decays sharply owing to multiple
interferences. Therefore, the control system should be embedded with a suitable
error correction code (ECC) to guarantee the data integrity and accuracy. We
proposed the pre-check scheme which is a multi-strategy polar code scheme to
strike a balance between reasonable frame error rate (FER) and decoding
latency. Three decoders namely binary-input, quantized-soft, and pure-soft
decoders are embedded in this scheme. Since the calculation of soft
log-likelihood ratio (LLR) inputs needs multiple sensing operations and
optional quantization boundaries, a 2-bit quantized hard-decision decoder is
proposed to outperform the hard-decoded LDPC bit-flipping decoder with fewer
sensing operations. We notice that polar codes have much lower computational
complexity compared to LDPC codes. The stepwise maximum mutual information
(SMMI) scheme is also proposed to obtain overlapped boundaries without
exhausting search. The mapping scheme using Gray code is employed and proved to
achieve better raw error performance compared to other alternatives. Hardware
architectures are also given in this paper.Comment: submitted to SCIENCE CHINA: Information Science