【作者】 赵健；

【导师】 吴芝路；

【作者基本信息】 哈尔滨工业大学 ， 信息与通信工程， 2006， 硕士

【摘要】 DVB-S2是第二代卫星数字视频广播标准,由DVB(Digital Video Broadcasting)项目组于2003年发布。与DVB-S标准相比,能够在合理的接收机复杂度下得到更好的性能和更大的灵活性。其性能如此优异的一个重要原因是采用了当今纠错编码技术发展的最新成果——低密度校验(LDPC,Low-Density Parity-Check)码。LDPC码由Gallager于1960年首次提出,只是限于当时的技术发展水平难于实现而未能引起足够重视,直到上世纪九十年代中期,Mackay, Luby等人重新发现LDPC码与Turbo码一样也是一种能够逼近香农限的非常好码,从而使LDPC码成为新的研究热点。本文以DVB-S2标准中LDPC码的应用为研究背景,首先介绍了信道编码技术的发展及LDPC码的研究现状,然后详细阐述了LDPC码通用编码方法和置信传播译码算法基本原理。针对LDPC码通用编码算法的复杂度与码长的平方成正比的问题,重点研究了LDPC码的快速编码方法,总结出了使LDPC码能够达到线性编码的途径。接着,本文介绍了DVB-S2标准中LDPC码的特点及编码方法,给出了通过仿真得到的非规则校验矩阵,针对编码器设计中遇到的一些问题提出了改进方法。阐述了对数域置信传播算法的几种表达形式,针对其校验节点更新运算中包含双曲正切运算,难于实际应用的问题,将几种减小复杂度的译码算法应用于译码中。最后,给出了一种确定简化译码算法中修正因子的新方法,仿真证明简化译码算法在运算复杂度大幅下降的情况下性能与标准译码算法相近。目前LDPC码的研究重点已经从理论转向实用,因而本文的研究对LDPC码的应用和DVB-S2标准的推广具有一定的实际意义。更多还原

【Abstract】 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.更多还原