Decoding Research On Quasic Cyclic Low Density Parity Check Code

Low Density Parity-Check (LDPC) code was first discovered by Gallager in the early 1960s and was rediscovered and considered as a class of Shannon-limit-approaching code in the late 1990s. Quasi Cyclic (QC) LDPC code, which is a kind of constructed LDPC code, possess a similar decoding performance and an error floor character with random constructed LDPC code. Besides, its encoding algorithm can be easily realized. So QC LDPC code is also considered as a kind of practical LDPC code. Advanced researches on decoding algorithm and decoder structure of QC LDPC code are the focus of this thesis.Firstly, the fundamental principles of QC LDPC code including QC LDPC code's basic conception, construction and both the encoding and decoding algorithm are analyzed. Of encoding algorithm, a conventional algorithm and an efficient algorithm suitable for QC LDPC code are discussed. As far as the decoding algorithm concerned, Belief Propagation decoding algorithm,Min-Sum decoding algorithm, Normalized BP-Based decoding algorithm and Offset BP-Based decoding algorithm are analyzed respectively.Secondly, the simulation method of encoding algorithm for QC LDPC code is studied; the realizable scheme of BP algorithm and BP-Based algorithm are analyzed, presenting the simulation flow chart of iterative computation on check nodes and variable nodes; finally the implement complexity of hardware for BP algorithm,Min-Sum algorithm, Normalized BP-Based algorithm and Offset BP-Based algorithm are discussed.Besides, the simulation system and flow for QC LDPC code are designed; the channel model of AWGN channel, Rayleigh channel and power line communication pulse channel are proposed; the decoding performance under different code lengths, code structures and maximal iterative times in AWGN channel model are analyzed; the difference of decoding performance under BP algorithm and its improving algorithms are studied; at last the decoding performance in unrelated Rayleigh channel and PLC pulse channel are investigated.Finally, the BP decoding algorithm based on permutation matrix is studied and its decoding flow chart is provided; a decoding structure based on exchange unit is designed and the working process of the structure is offered; the circuit structure and routing way of the exchange unit are studied and a exchange unit based on Banyan configuration is designed to realize the exchange of iterative message.