Research On An Improved Decoding Algorithm Combined BP Alogrithm And WBF Algorithm For Low-Density Parity-Check Codes

Due to the long distance and great signal loss between signals of deep space communication channel, it is necessary to increase the channel gain and receiver sensitivity of the system. As an important technology of deep space communication, channel coding can improve the performance of the system greatly. LDPC codes will be used in the fields of deep space communication broadly, because of its excellent performance approaching to Shannon limit.Firstly, this graduate thesis introduces LDPC codes including the history, the developing situation, the definition, the structure, the construction of parity check matrix for LDPC codes, the encoding algorithms and the decoding algorithms, specially BF algorithm, WBF algorithm, BP algorithm, LLRBP algorithm, Min-Sum algorithm and its improved algorithms. And the computation complexity and decoding performance have been analyzed and compared.Secondly, to reduce the high computation complexity and long running time, an improved decoding algorithm is proposed which combines the BP algorithm and WBF algorithm. First BP iteration is used to decode received codes, and decide if the decoding results meet the calibration equations. If they meet the equations, the above results are outputted as decoding results. If they don't meet the equations, the flipping criterions which are passed from check nodes to information nodes are weighted by the reliable information of received sequence based on WBF algorithm. The bit whose flipping criterion is biggest is flipped. Then check sum is computed again in order to decide if the BP iterative decoding process should be stopped.Finally, a simulation system is built based in AWGN channel, and the decoding performances of existing algorithm have been simulated using MATLAB software. Meanwhile, the improved decoding algorithm which combines BP algorithm and WBF algorithm have been simulated under different conditions such as maximum iteration numbers, code lengths and code rates, etc. And the performance of the improved decoding algorithm which are influenced by the above factors have been analyzed. This thesis gives a comparison between improved decoding and existing decoding algorithm.The improved decoding algorithm can decrease the running time effectively and it can maintain the excellent decoding performance as BP algorithm.