Research On Decoding Algorithm Of Polar Code And Its Application In Flash Memory

As the first coding method that can be strictly proved by theory to achieve the Shannon capacity,the polar code has received extensive attention since its introduction.Furthermore,it was adopted as the control channel coding scheme for enhanced mobile bandwidth scenario of 5G in 2016.However,the channel polarization under the medium or short lengths is insufficient,leading to a serious degradation of the performance under the original SC decoding algorithm.By retaining more possible decoding results,the existing SCL and CRC-SCL decoding algorithms can effectively enhance the polar code decoding performance.Meanwhile,the decoding complexity and storage complexity of those algorithms are multiplied,which is not conducive to practical system applications.In view of the above shortcomings,this thesis focuses on the low complexity decoding algorithm of polar code and studies the application of polar code in real flash memory systems.The main research contents are as follows:Firstly,the simplified decoding algorithms based SC of polar code are introduced and analyzed,including SSC algorithm,SSCL algorithm and CRC-SSCL algorithm.According to represent SC decoding as message passing,a general framework for studying the improved algorithms is established.By removing the redundant calculation in the decoding process,theoretical analysis and simulation show that the simplified decoding algorithms can effectively reduce the computational complexity of the original algorithms without changing the decoding performance.Secondly,an improved decoding algorithm based on multiple CRC is proposed.Aimed at CRC-SSCL algorithm not to reduce the storage space of CRC-SCL algorithm,this thesis proposes Multi-CRC SSCL algorithm.In addition,the segmentation principle and performance analysis of algorithm are given.By segmenting the information sequence and multiplexing the storage space,theoretical analysis and simulation show that the proposed algorithm greatly reduces the storage complexity and computational complexity of the algorithm under the condition of almost no loss of decoding performance.Finally,the polar code application for NAND MLC flash memory systems is studied.In this thesis,the channel model of the system is determined based on the error characteristics in the actual flash memory system,and the simulation scheme of the polar code in the flash memory system is given.Since the polar code in the flash system simulation scheme generally adopts the SC or SCL decoding algorithm,the complexity of those algorithms is very high.In response to this phenomenon,the SSC algorithm and SSCL algorithms are applied to the flash memory system,which greatly reduce the computational complexity of the decoding algorithms.