【作者】 李亚汉；

【导师】 王新梅；

【作者基本信息】 西安电子科技大学 ， 通信与信息系统， 2005， 硕士

【摘要】 低密度校验码是一种能逼近香农容量限的渐进好码，长码时其性能甚至超过了Turbo码，其译码采用了具有线性复杂度的置信传播算法，复杂度低于Turbo码，并且几乎所有错误可检。由于低密度校验码的诸多优点，它在信息可靠传输中的良好应用前景已经引起世界各国学术界和IT业界的高度重视，成为当今信道编码领域最受瞩目的研究热点之一，低密度校验码的应用也已经被提到日程上来，被列为4G关键技术。 作者认真学习了LDPC码的基本原理，参与了重庆金美公司方案讨论，基于LDPC码的特征，提出一种改进型的LDPC码与卷积码级联方案。此外，对于扩展密度校验码作了一点探讨。 本论文主要完成的工作包括以下几个方面： 1．基于Tanner图模型详细介绍了LDPC码的表示和构造以及LDPC码的硬判决译码(比特翻转算法)和软判决迭代译码(和积算法)。 2．介绍了对LDPC码性能影响的几个因素，特别关注了构造大围长的几种方法。 3．研究了LDPC码的级联方式，提出一种改进型的LDPC码与卷积码级联方案，该方案具有：编译码复杂度低，可并行译码，时延小、易于硬件实现，纠错性能突出的特点。 4．对于GLD码，介绍了构造方法和编译码的基本原理，性能仿真表明了其良好的纠错性能。 许多优秀的LDPC码级联方案已被提出，在具体方案中，应选择适当构造的LDPC码。LDPC码的实用化还要有相当长的一段路，虽然长码时LDPC码的性能可以超越Turbo码，但是短码却比Turbo码差得很多，GLD码在短码时的性能介于LDPC码和Turbo码之间，且GLD码可并行译码，有利于集成电路的设计。更多还原

【Abstract】 Low-Density Parity-Check (LDPC) codes are a class of capacity approaching error-correcting codes. By using low complexity belief propagation algorithm, LDPC codes are able to get near Shannon limit decoding performance with almost all errors detectable. For long code lengths, LDPC codes can even outperform Turbo codes. Due to the advantages of LDPC codes, their applications in reliable communications have received great interests and have become one of the most attractive fields in channel coding community. Now, the application of LDPC codes has been put on the agenda. LDPC codes are regarded as a key technique in the 4G.This thesis investigates some aspects of LDPC codes with emphasis on message passing algorithms and girths of LDPC codes. Another part of the paper touches on GLD codes. The main contents and results are as follows.1. Based on Tanner graph, the representation and construction of LDPC codes are introduced and two decoding algorithms for LDPC codes, i.e., bit-flipping algorithm and sum-product algorithm are discussed.2. Several factors influencing LDPC codes are talked about, emphasis on methods for large girth construction.3. The efficient encoding problem of LDPC codes is mentioned and an improved scheme about concatenated LDPC and convolutional codes is proposed. Several codes can be encoded and decoded at the same time in the scheme. The realization of this scheme has low complexity and short delay. The scheme also has excellent performance.4. The theory about GLD codes is introduced. The results of simulations show the performance of these codes is outstanding.Several good Concatenated schemes about LDPC codes have been put forward, but in realization, selecting proper LDPC codes must be seriously considered. Although LDPC codes are superior to Turbo codes, it is not the case for short LDPC codes. Performance of GLD codes is between them in short code lengths. GLD decoder has a regular and parallel structure which makes it very suitable for practical integrated circuit (IC) implementations.更多还原