Decoding Algorithm Research And Its Implementation Of LDPC Codes Based On CMMB Standard

Low-density parity-check codes (LDPC) has become a hot issue of research in the channel coding field for its advantage in perfect decoding performance, close to Shannon limit, high decoding speed, strong error detecting ability and simple theoretical analysis. China Mobile Multimedia Broadcasting (CMMB) standard which is promulgated by SARFT and independently developed by China, takes RS code and LDPC as its channel coding. Code construction, decoding algorithm and hardware implementation of decoder were studied on LDPC by two different code rates in CMMB, respectively.In this thesis, a constructional method of LDPC on CMMB standard which is highly structured was discussed. According to this method, LDPC of CMMB was transformed into quasi-cyclic code to reduce the complexity of hardware implementation resulted from the random distribution of nonzero element in check sub-matrix.A modified alternate iteration of ASBP algorithm was proposed, due to the features that with the nodes of Shuffled BP algorithm (SBP) update late, the reliability increase. This proposed scheme can reduce 1/dc calculations without any performance degradation.Different from the random iterative updating sequence of Layered BP (LBP) algorithm, a dynamic decoding algorithm with a low reliability and a prior updating was optimized in detail. Compared with LBP, the convergence speed of dynamic decoding algorithm is greatly improved, and it can decrease the average iteration times about 50%.In view of the complexity of implementation and system throughput, layered normalized Min-Sum algorithm is adopted. Taking chip EP2S180 of Altera Stratix II series products as hardware platform, a LDPC decoder based on the selected rate-0.5 LDPC in CMMB was implemented and verified on FPGA. It was optimized from conserving memory resources and reducing the complexity of routing, the decoder architecture was proposed and also brief descriptions of various sub-modules were present. The results of simulation indicate that the performance of this decoder conforms to the requirement of CMMB standard, which used resources as much as 201Kbit.