软判决译码在信道编码中的应用
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工学硕士学位论文 软判决译码在信道编码中的应用
陶慧琪
哈尔滨工业大学 2007年7月 国内图书分类号：TN911.22 国际图书分类号: 654
工学硕士学位论文 软判决译码在信道编码中的应用
硕士研究生：陶慧琪 导师：关宇东 副教授 申请学位级别：工学硕士 学科、专业：信息与通信工程
所在单位：电子与信息技术研究院 答辩日期：2007年7月 授予学位单位：哈尔滨工业大学 Classified Index：TN911.22 U.D.C.: 654
Dissertation for the Master’s Degree in Engineering THE APPLICATION OF SOFT-DECODING IN CHANNEL CODEING
Candidate： Tao Huiqi Supervisor： Associate Prof. Guan Yudong Academic Degree Applied for： Master of Engineering Specialty： Information and Communication Engineering
Affiliation： School of Electronics and Information Technology
Date of Defence： July, 2007
Degree Conferring Institution： Harbin Institute of Technology 哈尔滨工业大学工学硕士学位论文
- I - 摘 要 软判决译码，又称软译码，它充分利用接收信号波形中的信息，使译码器能以更大的准确概率判决所接收的码字。使用相同的算法，软判决译码能比硬判决译码获得额外的2~3dB的编码增益，因此软判决译码在信道编码中有重要的应用。本文对软判决译码的基本原理和方法、具体实现及应用做了研究和探讨，给出了一些实验的结果和数据。 本文首先介绍了软判决译码的基本原理和方法，对其中比较重要的算法—广义最小距离(Generalized Minimum Distance，GMD)算法和Chase算法做了详细的讨论。 分组码的软判决译码是本文研究的重要内容。因为分组码的软判决是以硬判决译码为基础的，因此本文以BCH码（RS码）为重点，介绍了常用的分组码译码算法，包括捕错译码算法及其修正算法，BM迭代译码算法。实现了(15,7)BCH码、Golay码、(15,9)RS码等的译码，实验仿真表明，本文使用VHDL设计的BCH码、Golay码的译码器能以与编码相同的速度完成译码，相比其它方法，大大地缩短了译码延迟。在此基础上，使用Chase算法中的CHS2实现了(15,7)BCH码、Golay码的软判决译码，并对其做了改进，得到性能更好同时复杂度并没有增加太多的软译码方式，设计实验验证了它的性能。 卷积码的Viterbi算法及其软判决译码是本文研究的重点。在编程实现卷积码的Viterbi译码和软判决译码的基础上，本文讨论了级联码与乘积码，这是构造长码进而得到渐近好码的重要手段，也是信道编码研究的重要内容之一。在讨论级联码的时候，将卷积码的软判决应用到其中，得到更好的性能。随后，本文讨论了由Viterbi算法扩展得到的一个重要算法：软输出Viterbi算法(Soft-Output Viterbi Algorithm，SOVA)，编程实现了该算法，设计实验将其应用于软输出迭代译码，验证了软输出迭代译码的优异性能。
关键词 信道编码 ；软判决 ；广义最小距离算法 ；软输出Viterbi算法 哈尔滨工业大学工学硕士学位论文
- II - Abstract Soft Decision Decoding(SDD) makes full use of the information in the received signal wave form, it lets decoder has a more accurate probability to decide the codes received, so it has a important application in channel coding. Compared with Hard Decision Decoding(HDD), using the same algorithm, SDD can gain additional 2~3dB encoding benefit. This thesis researches and discusses about the principle and method of the SDD, then implements and applies SDD, and gives results and data of experiments. First, the principle and method of Soft Decision Decoding is introduced, aiming at some important algorithms —Generalized Minimum Distance (GMD) algorithm and Chase algorithm, this paper has detailed discussion. The Soft Decision Decoding of block codes is an important topic discussed in this paper. Because the SSD of block codes is based on Hard Decision Decoding ,we take BCH codes(RS codes) as an important point to introduce the normal block codes decoding algorithms ,including Error-Trapping Decoding algorithm and its modified algorithm, BM iterative algorithm. Decoding of the Golay code and (15,9)RS code are implemented, simulation experiments show that the decoders of BCH codes and Golay code designed by VHDL can execute the decoding as fast as encoding. Compared with other methods, the decoders reduce the delay time greatly. Based on them, this thesis uses the CHS2 of Chase algorithm to get the SDD of BCH codes, then modifies it to get a better performance and low complexity SDD method, tests it through experiments at last. Viterbi algorithm of convolutional codes and its Soft Decision Decode are important parts in this paper. Based on the implementing Viterbi algorithm of convolutional codes and Soft Decision Decoding, this thesis discusses concatenated code and product code. They are important methods to create long codes and then gain the approximate good codes, also the important research contents in channel coding field. Applying the Viterbi algorithm of convolutional code to the concatenate code, we get a more perfect performance. Then, SOVA, 哈尔滨工业大学工学硕士学位论文 - III - Soft-Output Viterbi Algorithm, an important soft-output algorithm extended from Viterbi algorithm, is discussed; it’s realized in this paper. The application of SOVA in iterative decoding of Turbo codes is also discussed. Through showing the process by experiments, we can see the excellent performance of SOVA.
Keywords channel coding ; soft-decision ; GMD ; SOVA
