1、I 本科毕业设计（论文）本科毕业设计（论文） 题 目 LDPC 码性能研究 II 摘 要 信道编码是数字通信系统的重要组成部分。LDPC 信道编码技术是编码界的重要 成果之一。 1/2 码率的二元 LDPC 码在 AWGN 信道下的性能距信息理论中的 Shannon 极限仅差 0.0045dB，它是目前距 Shannon 极限最近的纠错码。Gallagar 在 1962 年提 出 LDPC 码，1996 年经过 Mackey、Spielman和 Wiberg等人的再发现后，LDPC 码以 其性能优越、全并行迭代译码结构、便于硬件实现等优点，在无线通信、存储工业等 领域得到了广泛应用。 校验矩阵
2、的构造是编码的前提，本文采用了随机构造法构造，并对矩阵的多种变 换方法进行分析，比较了优缺点。译码算法是 LDPC 码的关键，译码复杂度的大小直 接影响系统的实现。主要分硬判决译码、软判决和复合译码。设计中采用的译码方式 是软判决译码。 在性能分析方面， 利用 matlab 仿真码长、 列重和迭代次数对 LDPC 码性能的影响。 仿真结果表明，在一定范围内，LDPC 码长码的误码性能优于短码；码长较小时，列 重的增加会使性能变差， 而对于长码， 列重在一定范围内的增大会改善 LDPC 的误码 性能；增加迭代次数会使误码率降低，但当迭代次数大到一定值时，误码率将不会再 随着迭代次数的增加而降低。
3、 关键词 LDPC 码 信道编码 矩阵变换 性能分析 III Abstract Channel coding is an important component for digital communication systems. LDPC channel coding technology is one important achievement of the encoding results. The performance of half of the binary bit-rate LDPC codes in AWGN channel only has a tap of 0.0045d
4、B to the Shannon Limit that makes it be the latest error-correcting codes from the Shannon Limit. Gallager proposed LDPC codes in 1962, after Mackey and others re-discovered it in 1996, with best performance, completely decoding algorithm in parallel scheme and easily realized for hardware design, L
5、DPC codes has already been widely used in many practical systems such as wireless communication system and storage system. The construction of the Check matrix is a precondition for coding; the randomized method was used in this paper. Several ways to transform the matrix was discussed and being com
6、pared about the merits of each method. The decoding algorithm is the key to LDPC code and the complexity of decoding direct impact realization of the system. There are three kinds of decoding algorithms: hard-decision method, soft-decision methods and hybrid decoding. The hard-decision method was used in this design. Based on studying the basic theory of LDPC codes, the impact of codes length, column weight and iteration times on BER performance of LDPC codes are demonstrated by computer simulat
