Research On The LDPC Code Encoding And Decoding Algorithms With Low Error Floor

Low-Density Parity-Check(LDPC)codes is a class of channel coding scheme with good error correction capability,which can achieve or approach the Shannon limit in a variety of channels.At present,LDPC codes have been adopted by many modern communication system standards,and in particular,5G communication systems currently under have also determined to adopt LDPC codes as channel coding schemes for data channels in embb scenes.Error floor is an important aspect in the theory of LDPC codes and the research of iterative decoding algorithms.It is mainly manifested that in a certain high signal-to-noise ratio region,the bit error rate decrease very slowly with the increase of signal-to-noise ratio.In view of this phenomenon,this paper starts with the investigation of error-prone substructrues such as stopping sets and trapping sets of LDPC codes,and do some research on how to reduce the error floor of LDPC codes.I.The basic principle of LDPC codes is briefly summarized,the coding principle of LDPC codes and the message passing decoding algorithm of LDPC code in different channels are introduced,and the main factors affecting the performance of LDPC code error floor are analyzed.II.The search algorithms for error-prone substructures that affect the LDPC codes error floor performance under BEC and AWGN channel are summarized.Taking 5G short code as an example,the algorithms of searching for the dominant trapping sets based on the error impulse in the AWGN channel and the exhaustive algorithm for searching LDPC trapping sets by solving linear programming problems are emphatically analyzed,and the two algorithms are compared.Finally,an algorithm for estimating the performance of LDPC codes error floor by trapping sets is introduced in detail,and the corresponding simulation is carried out.III.Based on the analysis of existing different schemes which can improve the performance of LDPC codes error floor,a joint coding and decoding algorithm is proposed to lower the error floor of LDPC short code.Firstly,in order to solve the problem of destroying the validity of original LDPC coder after adding new checking nodes,and a new connection mode of the new check node is presented.The new mode eliminates the low weight codewords determined by the minimum distance without destroying the original coding,thereby increasing the minimum distance of the code.Combined with the backtracking iterative decoding algorithm,trapping sets are further eliminated.The simulation results take LDPC short codes as examples,which show that in the high SNR region,the frame error rate performance of the proposed joint algorithm can be improved by an order of magnitude compared with the traditional SPA iterative decoding algorithm.