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1、南京航空航天大学 硕士学位论文 LDPC码在数字混沌通信中的应用 姓名：杨波 申请学位级别：硕士 专业：通信与信息系统 指导教师：叶明 20090101 南京航空航天大学硕士学位论文 i 摘 要 混沌通信技术作为一种新型的无线通信技术，由于其具有低截获概率、传输速率高、功耗 低以及设备成本相对低廉等诸多优点，已经成为当今无线通信领域研究的一个热点。然而混沌 通信频谱宽、功率低且传输速率很高，使其更容易受到各种干扰而影响传输质量，所以研究信 道编解码技术在混沌通信系统中的应用有着较好的实用价值。 低密度奇偶校验(LDPC)码是基于稀疏校验矩阵的线性分组码，当使用 BP 迭代译码算法时， 它具有非
2、常逼近 Shannon 限的性能。LDPC 码的数学定义简单，灵活性较大，在一定条件下译码 复杂度可低于 Turbo 码。在混沌通信中加入 LDPC 编码能有效的改变系统的性能和抗干扰能力， 并由于 LDPC 码译码复杂度的降低，从而能保持及时通信。 本文首先讨论了混沌序列的基本特性及其产生方法，对一些常见的混沌序列的统计特性及 其功率谱进行了分析；然后简述了 LDPC 码的定义、构造方式和基本编译码算法，并在高斯白 噪声信道下对 BP 译码算法的性能进行了仿真；在理论分析和仿真了数字混沌调制方法混沌 键控（CSK）和差分混沌键控（DCSK）误比特率性能的基础上，探讨了将 LDPC 码与上述混
3、沌 通信系统相结合改善系统性能的途径； 论文还研究了混沌通信系统与现有窄带通信系统共存时， 两系统之间的相互影响，并从理论上分析了上述混沌系统的抗干扰能力；理论分析和计算机仿 真结果表明，在 LDPC 码得到应用后，混沌通信系统的抗窄带系统干扰能力有了明显的提高， 因此 LDPC 码可能成为未来混沌通信系统的主要信道编码方案。 关键词：混沌通信，低密度奇偶校验（LDPC） ，BP 译码算法，混沌键控（CSK） ，差分混沌 键控（DCSK） ，信道编码 LDPC 码在数字混沌通信中的应用 ii ABSTRACT As a new type of wireless communication te
4、chnology, Chaos communication technology has become a hot topic in the wireless communication research and development area, due to its inherent advantages such as low probability of intercept, high transmission rate, low power consumption and low equipment cost, etc. However, because of the feature
5、s of wide spectrum, high transmission rate and low power consumption, chaotic communications become more vulnerable to all kinds of interference and the quality of transmission is influenced inevitably. Consequently, it is necessary and valuable to study the channel coding and decoding technology in
6、 the chaos communication system. Low-density parity check (LDPC) code is a kind of linear block codes, based on the sparse parity-check matrix. It possesses the performance of closing to the Shannon limit when the BP iterative decoding algorithm is adopted. LDPC code has a simple mathematical defini
7、tion, better flexibility, and its decoding complexity is lower than the Turbo code in some circumstances. By adding LDPC code to the chaos communication, the performance of the system and anti-jamming ability can be effectively enhanced. On the other hand, due to the decrease of complexity of LDPC d
8、ecoder, the system can implement the communication in time. This paper first discusses the basic characteristics of chaotic sequence and its generating methods and analyses statistical properties and power spectrum of some common chaos sequences. Then outlines the definition of LDPC code, mode of co
9、nstruction , basic encoding and decoding algorithms, and a simulation of the BP decoding algorithm has been carried out under Gaussian white noise channel. On the basis of the theoretical analysis of error performance and simulation of the digital chaos modulation methodsCSK and DCSK, ways to enhanc
10、e the system performance have been discussed which combine LDPC code with the above-mentioned chaotic communication system. Finally, in this paper, the interaction between the chaotic communication system and the existing narrow-band communication system have been examined when these two systems coe
11、xist, and the anti-jamming capability of above-mentioned chaotic system have been analyzed theoretically. The result of theoretical analysis and simulation show the anti-interference ability of chaotic communication system toward the narrow-band system has been greatly enhanced when the LDPC code is
12、 applied. Accordingly, the LDPC code may become the main channel coding scheme for the future chaotic communication systems. 南京航空航天大学硕士学位论文 iii Key Words: chaotic communications, Low-density parity check (LDPC), BP decoding algorithm, CSK , DCSK, channel coding LDPC 码在数字混沌通信中的应用 vi 图、表清单 表 2.1 各混沌序列的统计特性.8 图 2.1 不同分歧数对)( n xg的影响.9 图 2.2 不同分歧数对 4( ) n gx的影响 .10 图 2.3 初始值为 0.07 的不同长度的 Logistic 映射.10 图 2.4 初值为 0.07 和 0.07001 的 Logistic 映射.11 图 2.5 混沌序列的相关特性图.12 图 2.6 混沌序列的功率谱密度.13 图 2.7 常见混沌序列的直方图.13 图 2.8 Logistic 映射的概率密度函数.14 图 3.1 A(9,2,3) LDPC 码 Tanner 图.19 图 3.2 A(9,2,3)LDPC 码的(3,2)子码.
