Variable-Node-Based Belief-Propagation Decoding With Message Pre-Processing for NAND Flash Memory

With the fast development of non-volatile storage technology, NAND flash memory faces more and more challenges such as data reliability and lifetime. To overcome the issue of the reliability, low-density parity-check (LDPC) codes are considered as a main candidate of error-correction-codes (ECCs) for NAND flash storages. However, conventional soft decoding algorithms for LDPC codes suffer from the drawback of slow convergence speed, which increases the decoding latency. For achieving fast convergence speed, a variable-node-based belief-propagation with message pre-processing (VNBP-MP) decoding algorithm for binary LDPC codes and a non-binary VNBP-MP (NVNBP-MP) decoding algorithm for non-binary LDPC codes are proposed. Both of the algorithms utilize the characteristics of the NAND flash channel to perform the message pre-processing operations. In theory, the propagation of unreliable messages can be effectively prevented and the propagation of reliable messages can be speeded up. To further improve the decoding convergence, the treatment for oscillating variable nodes is considered after the message pre-processing operations. The simulation results also show that the proposed algorithms both have a noticeable improvement in convergence speed and latency, without compromising error-correction performance, compared with the existing soft decoding algorithms.