【作者】 王朋；

【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， 2007， 硕士

【摘要】 低密度奇偶校验码(LDPC)码是由Gallager在1962年首先提出的一种纠错码,LDPC码是一种具有稀疏校验矩阵的线性分组码。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,1993年性能可逼近香农限的Turbo码的出现,带来了纠错编码理论上的突破。Mackey和Luby等人对Gallager码重新进行了研究,发现Gallager码具有逼近香农限的性能,从而使LDPC码成为新的研究热点。DVB-S2是新一代数字卫星广播标准,采用更高效的信道编码技术和自适应编码调制技术,其中信道编码采用LDPC码作为内码,BCH码作为外码。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,传输效率要高出30%。本文首先介绍了LDPC码的基础知识、构造方法,介绍了规则码、不规则码的概念并比较了他们的性能;探讨了LDPC码基于近似下三角矩阵的线性编码算法;接下来讨论了LDPC码的传统编译码原理,重点研究了DVB-S2标准LDPC码的编译码方法。接着,本文介绍了DVB-S2标准中LDPC码的特点及编码方法,针对DVB-S2系统中LDPC码的编码原理,详细阐述了LDPC码的传统编码算法、下三角形式校验矩阵的LDPC码编码和编码复杂度等问题,以及达到线性编码的方法。阐述了对数域置信传播(BP)算法及其改进算法,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,在译码算法中应用了最小和算法、简化的最小和算法和归一化最小和算法,减小译码复杂度。最后,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。更多还原

【Abstract】 Low Density Parity-Check (LDPC) Codes were first discovered by Gallager in the early 1962, This class of codes decoded with soft-in soft-out (SISO) iterative decoding performs amazingly well. But due to the calculating effort in implementing, they were mostly ignored. Turbo codes was discovered by C.berrou et al.in 1993,which was a break in error-correcting coding theory for its performance can approach to the Shannon limit. Since then Mackey and Luby rediscoverd Gallager codes by finding that its performance can also approach Shannon limit in 1995. LDPC codes are one of the hottest topics in coding theory today.DVB-S2 is the next generation standard of the digital satellite broadcasting,which adopts the more effective technique of channel coding and self-adapting code modulation,Among them, channel coding adopts LDPC as its inner code and BCH as its outer code. Compare with DVB-S, it has been specified around three concepts: best transmission performance approaching the Shannon limit, total flexibility, and reasonable receiver complexity, 30% higher transmission eficiency than DVB-S.First the thesis introduce basic knowledge of LDPC codes. Then the thesis discuss the problem of linear encoding of LDPC codes and introduce the encoding algorithm based on approximate lower triangulations. Next the thesis discusses the basic principle of LDPC encoding and decoding and then explains the LDPC encoding and decoding in the standing of DVB-S2. Afterward, it introduces the coding schemes used in DVB-S2 and gets the parity check matrix by simulation.In the light of the principle of LDPC encoding in the standing of DVB-S2, the thesis expound general encoding of LDPC,parity-check matrix in lower triangular of LDPC encoding and the complexity of encoding , and the coding scheme with linear time complexity. the dissertation study log-likelihood-ratio-based Belief-Propagation decoding algorithms and it’s improve. In order to avoid the“tanh”function in the check-node updates,the min-sum algorithm、simplified min-sum algorithm is used in the decoding. Si mulation 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