Research On Joint Source And Channel Coding Scheme Based On QC-LDPC Code

With the rapid development of communication technology,the traditional architecture of digital communication system is facing great challenges,in the actual application,the traditional source channel coding separation design of the communication system is difficult to achieve optimal system performance,in order to solve this problem,the researchers designed a joint source channel coding(JSCC)communication system,this system can make full use of the redundant information of the source and the statistical characteristics of the channel to achieve the best system performance.At present,the JSCC system is mainly divided into two categories: one is that there is a certain source compression format,and the other is no source compression format.This thesis mainly studies on the source channel coding and decoding algorithms of JSCC system without source compression format,and the main research work and innovation are as follows:(1)Source channel code type of the traditional JSCC system is random low density parity check(LDPC)code,which decoding structure is complex,and only when the code length is longer will show good decoding performance.In this paper,a quasi-cyclic LDPC(QC-LDPC)code with simple coding performance and excellent decoding performance is constructed as the source channel code of the JSCC system to improve the performance of this system.And the decoding performance and decoding complexity of the system are analyzed by simulation.The simulation results show that the performance of the JSCC system based on QC-LDPC code is better than the JSCC system based on random LDPC code.(2)In order to solve the trapping sets problem of QC-LDPC codes in JSCC system,in this paper,a ACG-ALP decoding algorithm which is not affected by the structure of the QC-LDPC code is used to decode the channel code,which improve the reliability of channel transmission,and then improve the performance of the JSCC system.The simulation results show that the proposed scheme can lower the decoding error floor of the JSCC system under high SNR.(3)In order to further improve the performance of the JSCC system in the waterfall and error floor,the two stage SPA channel decoding method is proposed.The two stage SPA decoding algorithm is applied to solve trap set problem of the QC_LDPC code,and low the error floor of channel decoding.And then to improve the reliability of the information transmission between the source decoder and channel decoder.So the performance of the JSCC system will improve.The simulation results show that this scheme can effectively improve the performance of the JSCC system.