Research On Encoding And Decoding Technologies Of LDPC Codes

Channel Coding theory and technology are the indispensable key technologies of modern communications system, and they have experienced rapid development and obtained a huge amount of research results under the guidance of the Shannon channel coding theorem in recent decades. At present, Low-density parity-check codes, which is concerned by more and more researchers who devote their mind to coding, has become one of the best coding technology because of its low complexity iterative decoding algorithm and its approximate to the limited channel capacity.In this paper, on the basis of the existing theory of low-density parity-check codes, its coding and decoding ideas based on the figure model are expatiated systemically. The detailed derivation of the belief propagation (BP) algorithm information updated rules based both on the white Gaussian noise channels and on log-likelihood ratio probability measurements are made. And based on the algorithm mentioned above, an optimized approximate algorithm is given. A ladder code which can achieve linear encoding with specific H-matrix is introduced. RU algorithm which can achieve rapid encoding is given. A practical greedy algorithm is presented to find the key weighted factor g in view of Gaussian white noise channel.The major factors which impact LDPC's performance are summarized.Analyzing the impact of degree distribution on the long-length LDPC and introducing the optimized degree distribution algorithm under the AWGN channel based on density evolution or Gaussian approximation and differential evolution. Constructing method of the LDPC codes based on cyclic shift matrix is reviewed. Combined with density evolution theory, the design of the degree distribution pairs and searching results of the irregular LDPC codes based on block matrix structure is given. The performance curves of LDPC codes with different code length at the rate of 1/2 are also showed.