LLD: Lightweight Latency Decrease Scheme of LDPC Hard Decision Decoding for 3-D TLC NAND Flash Memory

Abstract

The low-density parity-check code (LDPC) has been widely used to significantly enhance the reliability of 3-D NAND flash memory. However, in cases where the raw bit error rate (RBER) of the data is high, it not only demands more sense levels but also requires a large number of iterations, leading to a notable read latency issue. To mitigate this challenge, this paper introduces an innovative lightweight latency decrease (LLD) scheme. Initially, by examining the correlation between the number of iterations and the hard decision level (HDL), a functional model that encapsulates the relationship between iteration and offset is established. Building upon this model, the all-wordlines latency decrease (AWLD) scheme is proposed. In an effort to further decrease latency, an in-depth analysis of the similarities among different wordlines within a flash memory block is conducted, leading to the development of an optimized one-wordline lightweight latency decrease (OWLLD) scheme. For scenarios involving random reading of small data volumes, the interplay between function models of various overlapping regions is delved into, which ultimately results in the proposal of a further optimized one-page lightweight latency decrease (OPLLD) scheme. Experimental findings reveal that the OPLLD scheme can enhance the iterative performance of LDPC by up to 94.63% and reduce latency by up to 66.89% compared to traditional algorithms, while incurring minimal storage and computational overhead. This clearly indicates that the proposed scheme substantially enhances the read latency performance of LDPC in flash memory.