低密度校验码的理论分析及在图像传输中的应用研究

【作者】 张国栋；

【导师】 张有志；

【作者基本信息】 山东大学 ， 通信与信息系统， 2005， 硕士

【摘要】 1962年,Gallager提出了一种具有非常稀疏校验矩阵的线形分组码,人们称为Gallager码。由于当时计算机水平发展有限和人们普遍认为级联码更易于实现,导致人们逐渐忽视了Gallager码的存在。直到1995年,Mackay、Neal和Wiberg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。通过进一步研究,人们在Gallager码的基础上提出了更具有广泛意义的低密度奇偶校验码——LDPC码。近年来,性能卓越的LDPC码成为信道编码领域的研究热点,它必将在实际系统中得到广泛的应用。 本文对LDPC码的基本理论和应用进行了研究,并通过计算机仿真获得了该码的性能。论文的主要工作包括:首先介绍了LDPC码的定义和分类方法,并归纳了几种常用的LDPC码构造方法和步骤:然后介绍了LDPC码的编码算法,详细介绍了消息传递和置信传播译码算法原理;之后用计算机仿真LDPC码获得了不同条件下的性能曲线,并在实际系统中应用LDPC码,包括对LDPC码在图像传输中的应用做了系统仿真,获得了良好的性能。最后针对LDPC码在图像传输中的应用提出了两种改进方案,包括对图像的重点部位使用不同码率进行重点保护和对图像的重点比特位采用不同码长的重点保护。在获得相同系统性能条件下,两种方案减少了传输时延,提高了系统的频带利用率。更多还原

【Abstract】 In 1962,Gallager proposed a special linear grouping codes with a very sparse parity check matrix. The codes are intituled Gallager coder. Because the computing condition is limited and most people consider that concatenated coder is easy to implement, people ignore Gallager codes little by little. Up to 1995 years, Mackay, Neal and Wiberg rediscovered the merit of Gallager codes and proved its performance can approach Shannon limit. By further research, people bring forward low density parity codes(LDPC codes) with a more widely meaning. In a few years recently, This LDPC codes with more excellent performance will become a new research hotspot in channel error-correcting encoder field. This codes will gain broad application in actual system.This paper gives a research for the basic theory of LDPC codes and its application. The performance of LDPC codes is acquired by computer simulation. This paper mainly include: First, the definition and classify method are introduced. Some useful construction methods are summarized. Then, the encoding algorithms to LDPC codes are provided. The theories of message passing algorithm and belief propagation algorithm are detailed introduced. Whereafter, the performance curves of LDPC codes are received by computer simulation and LDPC codes are applied to the actual system. These include systematic simulation of LDPC codes in image transmission. By simulating, I attain good performance. At last, I propose two ameliorating projects aiming at the application of LDPC codes in image transmission. These two projects include important protection of important image parts using different code ratio and important protection of important image bits using different code length. In the condition of the same systematic performance, these two projects reduce transmission time relay and improve systematic using ratio of frequency band. The finality of paper summarizes my research problem and points out farther research orientation.更多还原