【作者】 郭赵强；

【导师】 慕建君；

【作者基本信息】 西安电子科技大学 ， 计算机系统结构， 2009， 硕士

【摘要】 低密度校验(LDPC)码由于其低译码复杂度和可任意逼近香农限的良好性能而成为目前最佳的编码技术之一,越来越多的编码研究学者开始关注如何构造性能好的LDPC码。Tanner图的构造是基于图模型构造LDPC码中一个非常重要的问题。通过构造良好的LDPC码的Tanner图,可以改善LDPC码的译码性能。本文在对LDPC码现有理论研究基础上,基于启发性的搜索方法和EMD算法的特点,提出了一种新的二部图展开算法。本文的主要工作概括为：1.简要阐述了LDPC码基于图模型的编译码思想,系统分析了影响LDPC码译码性能的主要因素——二部图的度分布序列、环和连通性,重点研究了二部图的连通性对LDPC码译码性能的影响。2.详细分析了LDPC码中构造二部图的几种构造算法：消环算法和改善图的连通性的算法。并通过仿真表明这些算法都能有效降低LDPC码的误码率和错误平层。同时,对所构LDPC码译码性能进行了简单的分析。3.在深入研究以上几种构图算法的基础上,给出了IPEG算法中ACE值的计算方法,提出了基于EMD算法的一种二部图展开算法,新的展开算法更适合在EMD算法中使用。同时给出了EMD算法的仿真及其性能分析。更多还原

【Abstract】 Low-density parity-check codes (LDPC) in graphical models come to be one of the best coding technologies because of their low-complicity iterative decoding algorithm and capacity approaching performance, and it is how to construct LDPC code with good performance that attract more and more researchers’eyes in recent years. The construction of bipartite graph plays an important role in the LDPC code-construction which is based on graphical models. The performance of low-density parity-check codes can be improved by constructing a good Tanner graph.In this dissertation, the basic principles of the coding and decoding of LDPC codes are studied systematically. A new algorithm of bipartite-graph-expanding is proposed for construction of Tanner graph. The main results and contents are summarized as follows.1. The principles of coding and decoding for low-density parity-check codes are briefly summarized, the main factors which can impact the performance of LDPC codes such as degree sequence, cycles and connectivity of Tanner graph are systematically analyzed, emphasis on the graph connectivity.2. Several algorithms for constructing Tanner graph of LDPC codes such as cycle-eliminating algorithms and connectivity-improving algorithms are analyzed in detail. The simulation results show that the codes constructed with these algorithms has lower bit error rate and error floor. The graph of simulation performance is presented. Besides, the performance of the codes constructed with these algorithms is analyzed.3. Based on the study of construction algorithm mentioned before, a mothed of computing ACE value is given, a new bipartite-graph-expanding algorithm based on EMD algorithm is proposed, and the new algorithm is fit for EMD algorithm. Moreover, the software simulation was given, and the performance of EMD algorithm was analyzed.更多还原