Research On QC LDPC Code Check Matrix Structure And Decoding Algorithm

Low-Density Parity Check(LDPC)Codes are one kind of linear block codes with sparse check matrix.Because of their excellent error correcting performance approaching the Shannon limit,and the potential of achieving high-speed encoding and decoding,LDPC codes have become one of the most attractive hotspot in channel coding community.Although fruitful results of the theoretical and applied researching of the LDPC codes have been achieved,but in the practical process of LDPC codes,the contradiction between the performance of the construction and decoding algorithm of LDPC codes and their implementational complexity is still an unsolved problem.This Thesis through analysis the factors affect the performance of LDPC decoder,combining theory and simulation analysis for the structural characteristics of QC LDPC(Quasi-Cyclic)code and the IRA(Irregular Repeat Accumulate)code,constructed a quasi-cyclic LDPC check matrix with low encoding complexity,improved Shuffled BP decoding algorithm to obtain fast convergence,low complexity decoding algorithm.The main contents are as follows:First of all,this Thesis detailed analysis LDPC code conventional coding algorithm,found the complexity of LDPC coding algorithm need to be reduced and Simulation analysis of the factors affecting the performance of LDPC decoder.Secondly,using the double diagonal structure in IRA code,constructing the base matrix in QC LDPC code with eIRA structure to reduce coding complexity.In order to avoid eIRA code structure introducing low weight code words cause error floor and increasing the probability of undetected error,using a modified PEG algorithm construction the information node portion in the base matrix of QC LDPC code can increase girth and minimizing the probability of occurrence of low weight code words.The simulation results show that the class code performance is better than the randomization code and the encoding complexity is lower,realization is strong.The performance similar with the same structure only can be used in a fixed rate of IEEE802.16e and DVB-S2 standard,the rate selection of the algorithm proposed is more flexible.Finally,in the LLR BP decoding algorithm,introducing a relaxation factor in variable node message processing,by introducing the relaxation factor make the confidence from the value variable nodes of the l-1 iterations associated with the l iterations,although the introduction of relaxation factor increases the complexity in the partial,reducing the number of iterations in general.Simulation results show that the algorithm performance is better than the LLR BP decoding algorithm while reducing iterations and decoding performance is better than the min-sum decoding algorithms and the associated improved algorithm.