低密度奇偶校验码的研究及其在超宽带通信中的应用-通信与信息系统专业毕业论文.docx

摘要
低密度奇偶校验(LDPC)码是一种具有稀疏奇偶检验矩阵的线性分组码,它在与基于置信传播(BP)迭代译码算法相结合的条件下具有逼近 Shannon 限的性能。该码的译码复杂度与码长成线性关系,使长编码分组的应用成为可能。此外,编码方面也找到了与码长成线性关系的好码构造法。
本文首先介绍了 LDPC 码的编码原理,然后介绍它的几种译码算法,并仿真分析了几种的典型的译码算法。编、译码方法是研究 LDPC 码在各种信道应用中的实现前提和基础;还给出了 LDPC 码在 Rayleigh 信道下的计算机模拟结果;最后完成了 LDPC 码与 OFDM 系统相结合的性能分析,并利用π旋转 LDPC 码设计了一种多带正交频分复用(MB-OFDM)超宽带的实现方案。
本课题主要工作及创新点为:构造了一种准规则结构的 LDPC 码,分析了它在二进制对称信道下的短码性能,这种码的码率改变灵活、长码构造简单,但直接实现编码器的复杂度与码的长度平方成正比,还有待于进一步改进;将非规则 LDPC 码与 OFDM 系统相结合,并跟 Turbo 码进行比较,表明它具有较优异的误码率性能,并且这种优异的性能是在复杂度不太高的情况下实现的;利用π旋转 LDPC 码设计了一种 MB-OFDM 的实现方案,通过仿真计算分析了π旋转 LDPC 码与卷积码的性能差异。
关键词:检验矩阵;LDPC 码;置信传播;正交频分复用;超宽带。
Abstract
Low-density parity-check (LDPC) codes which is a class of linear block codes, specified by a sparse parity-check matrix. It may approach the Shannon limit when uses the belief propagation (BP) iterative decoding algorithm, which makes the plexity is linear to the codes length, so that the application of long block codes es true. Besides, good codes which plexity is linear to the length have searched. LDPC codes can improve the transmitted reliability in narrowband circumstance.
As the preconditions of study the performance of LDPC codes in various channels, firstly, decoding algorithms and encoding structures are introduced in this paper,and several typical decoding algorithms pared by simulating in this gives puter simulated results on Rayleigh channel. Finally, the performance bining LDPC codes to m OFDM system is analysed, a MB-OFDM scheme is also achieved by π rotation LDPC codes in this paper.
In this topic, a new constructed method of quasi-regular LDPC codes is proposed and the short codes performances are analyzed on BSC channel. The characteristics of the new method has flexible code rate and liable to construct long codes. But the plexity is in proportion to the square of the codes length. So, this method should be improved. Irregular LDPC codes and OFDM system bined, and the performances between it and turbo codes pared. The results