Research On One LDPC Codes And The Applications In Optical Communication System

Low-Density Parity-Check (LDPC) Codes, a type of progressive code approaching Shannon capacity limit, can achieve a better performance than Turbo code at long code length. Because of the advantages of LDPC code, for example, lower decoding complexity and lower error floor, applications of LDPC codes in reliable communications has received significant academic attention and has become one of today's most popular research focus in the field of channel coding.In this paper, encoding and decoding algorithm of LDPC is studied and given specific improvement on the basis of basic decoding principle of LDPC code. According to the special requirements of optical communication system, the encoding method and decoding performance regarding one type of specially structured LDPC code is studied, as well as its application in optical communication system.Main content as followsFirstly, a brief introduction to the composition of communication system as well as the basic theory and history of channel coding technology is presented. Then, following a brief introduction to basic concept of linear block code, a systematic, yet general discussion of the proposition, history and research progress of LDPC code are given with focus on bipartite graph, regularity and irregularity, minimum distance and relative important concepts.Regarding the encoding method of LDPC code, the paper introduces LDPC code from random construction. Besides, the paper introduces two types of widely applied decoding algorithm—the BF algorithm and the BP algorithm. On that basis, a type of quasi-cyclic LDPC code named QC-LDPC code is introduced. Then, a detailed research on the encoding algorithm and encoding performance of QC-LDPC is described—followed by the specified research over the tectonic encoding method of QC-LDPC based on computerized search. The special structure of QC-LDPC code favors high-speed decoder plait, and it satisfies the high speed and efficiency required by optical fiber communication system.Finally, for high speed optical fiber communication applications, the paper studies some issues about the practical application of QC-LDPC code—the use of cyclic shift register to encode QC-LDPC code, the method on the selection of maximum iteration number and its performance verification, the affection of channel estimation error on the soft decoding performance of LDPC.