星间链路信道编码技术研究

摘要

星间链路的通信信道由于传输距离遥远加上存在来自各个方面的无线电干扰，使信号传输时延大，造成信号能量衰减严重。因此有必要在星间链路通信中采用信道编码。Turbo码与LDPC码以其各自逼近香农限的优越性能被引入到CCSDS标准并在卫星通信领域被广泛应用。

本文首先研究了Turbo码的编码原理及译码算法，在此基础上完成了Turbo码编译码系统的设计并对影响Turbo码性能的参数进行了分析和仿真。然后对LDPC码的编译码进行了系统的分析和研究，并结合星间链路信道的特点，选用QC-LDPC码字，设计了LDPC码编译码方案并对仿真结果进行了分析。

在此基础上，本文还根据Log-BP算法，结合PSO优化算法给出了改进的LDPC码译码算法并对该算法进行了仿真验证，仿真结果表明该算法性能与Log-BP算法相比在一定条件下可获得0.1dB的额外编码增益。

最后，论文根据对LDPC码的分析，运用Verilog语言在Quartus II环境下完成了LDPC码编译码器的FPGA设计，设计选用QC-LDPC码字和最小和算法，译码部分采用部分并行结构。论文对该设计进行了初步的编译码性能测试并对对译码器的码速率及占用资源进行了详细分析。综合结果表明在资源消耗上比以往设计有了很大改进。

关键词：星间链路，Turbo码，LDPC码，译码算法，部分并行译码结构

Abstract

The inter-satellite channel of ISL has large signal transmission time and serious signal attenuation because of long transmission distance and wireless interference from many aspects. Therefore it is necessary to using channel coding in inter-satellite channel. Turbo codes and LDPC codes have been introduced to CCSDS standard with their excellent performances of approaching to Shannon Limit and widely used in Satellite Communication.

This thesis firstly researches the basic theory of Turbo codes and the method of Turbo codes encoding and decoding, and then analyses the factors which impact the performance of Turbo codes. The analyses are proved by the simulation results. Then this thesis offers a comprehensive study on the performance of LDPC codes. The author then presents a scheme of LDPC codes encoding and decoding with QC-LDPC codes combined with characteristics of ISL channel whereafter the simulation results are given and analysed.

Ulteriorly, the author presents a new decoding algorithm based on Log-BP and PSO algorithm followed by simulation results, which shows that performance of proposed decoding algorithm is 0.1dB better than that of standard Log-BP decoding at certain conditions.

Finally, this thesis finishes the design FPGA program for LDPC codes encoding and decoding based on Quartus II system with Verilog language. The hardware decoding algorithm is SPA algorithm and is designed by partly parallel structure. Based on it, the author tests the system's primary encoding and decoding performance and analyses the decoder's decoding rate and expended resources, which shows a great improvement on hardware resources consumption compared to previous architectures.

Keywords:ISL, Turbo Codes, LDPC Codes, Decoding Algorithm, Partly Parallel Decoding Structure

目录

第一章绪论 (1)

1.1课题背景与研究意义 (1)

1.2星间链路通信与信道模型 (1)

1.3国内外研究现状 (4)

1.3.1Turbo码研究现状 (4)

1.3.2LDPC码研究现状 (6)

1.4本文主要研究工作和内容安排 (7)

第二章星间链路Turbo码技术研究 (8)

2.1Turbo码的编码原理 (8)

2.1.1分量编码器 (8)

2.1.2交织器 (9)

2.1.3删余矩阵 (9)

2.2Turbo码的译码算法 (10)

2.2.1基于后验概率的软输出译码算法 (11)

2.2.2SOV A算法 (13)

2.2.3译码算法比较 (15)

2.3星间链路Turbo码的编译码方案和性能分析 (16)

2.3.1仿真系统设计 (16)

2.3.2仿真性能分析 (20)

2.4本章小结 (23)

第三章星间链路LDPC码技术研究 (24)

3.1LDPC码的编码原理 (24)

3.1.1LDPC码的定义及二分图表示 (24)

3.1.2LDPC码校验矩阵的构造 (26)

3.1.3LDPC码的编码方法 (26)

3.2LDPC码的译码算法 (27)

3.2.1LDPC码的译码原理 (27)

3.2.2软判决译码算法 (28)