| DVB-S2 is the second-generation Digital Video Broadcasting specification for satellite applications developed by Digital Video Broadcasting (DVB) Project in 2003.Compare with DVB-S, it has been specified around three concepts: best transmission performance approaching the Shannon limit, total flexibility, and reasonable receiver complexity. Channel coding is based on more recent developments by the scientific community: low-density parity-check codes are adopted.Low-density parity-check codes were first introduced by Gallager in 1960. But due to the calculating effort in implementing, they were mostly ignored. The study of LDPC codes was resurrected in the mid-1990's with the work of MacKay, Luby, and others. LDPC codes are one of the hottest topics in coding theory today. Indeed, the performance is almost as close to the Shannon limit as that of Turbo codes.This dissertation is based on the application of LDPC codes in DVB-S2 standard. Firstly , the dissertation reviews the traditional channel-coding schemes and the research about LDPC codes. Secondly,it introduces the generation coding schemes of LDPC codes and the principle of Belief-Propagation algorithm. The encoding complexity of LDPC codes length n seems indeed to be of order n2, the dissertation study the coding scheme with linear time complexity. Afterward, it introduces the coding schemes used in DVB-S2 and gets the parity check matrix by simulation. It gives some solutions for designing the encoder. Various log-likelihood-ratio-based Belief-Propagation decoding algorithms and their reduced-complexity derivatives for LDPC codes used in DVB-S2 are presented, in order to avoid the"tanh"function in the check-node updates. Finally, the dissertation proposes a new method for get the correction factor using in the Normalized BP-Based decoding and Offset BP-Based decoding. Simulation results show that these reduced-complexity decoding algorithms for LDPC codes achieve a performance very close to that of the BP algorithm. |
PDF Full Text Request