扩频通信系统中chirp干扰的识别与抑制

研究

摘要：扩频通信作为目前正在不断发展的先进通信技术，它的最大特点就是传输带宽比传统的通信方式要大几百倍以上。由此具有抗干扰能力强，频谱功率低，保密性好，易实现码分多址等优点。特别是其中的直接序列扩频通信方式，发展的最为成熟，应用最为广泛。扩频通信系统对于平稳噪声有很好的抵抗力，但是对于非平稳的chirp噪声的干扰表现却不佳，而现在国内外也正在研究这方面的课题。论文实现了一种基于在chirp基上展开的分数阶傅立叶变换来处理扩频通信系统中遇到的chirp干扰问题，利用分数阶傅立叶变换对于chirp信号良好的聚焦性，当chirp干扰噪声的旋转角度在与其调频斜率一致时，分数阶傅立叶变换域便会呈现冲激，在适当的阈值下搜索并去除冲激后再进行反变换，从而来去除chirp干扰，并在此基础上做了计算机仿真实验。仿真实验结果表明，该算法是有效可行的。 关键词：扩频通信；分数阶傅立叶变换；chirp信号；干扰识别；干扰抑制

Research on the identification and suppression of chirp

interference in spread spectrum communication

systems

Abstract：Spread Spectrum communication is a continuous developing advanced communication technology, whose biggest character is that its transmission bandwidth is wider over hundreds times than the traditional means of communication. Spread Spectrum communication has many advantages such as good anti-interference, low spectrum power, good confidentiality, and easy to realize the CDMA. In particular, the direct sequence spread spectrum communication, is the most mature and the most widely used communication ways. The spread spectrum communication system has good resistance performance for the stationary noise, but for the non-stationary chirp noise, the performance is poor. Now the domestic and abroad are also looking into the issue. In this paper, the solution which is based on the chirp-launched on fractional Fourier transform to deal with the spread spectrum communication system encountered the chirp interference, using the good focus of the chirp signal in fractional Fourier transform, when rotate the chirp noise a appropriate angle corresponding with the chirp rate, fractional Fourier Transform representation will show a strong pulse .than search the pulse in the appropriate threshold and after the removal of the noise, transform the signal back. And all of those had been done in the form of computer simulation. The simulation results show that the method is feasible and effective.

Keywords: Spread Spectrum communication; fractional Fourier transform; chirp signal; Interference identification; Interference suppression

目录

第一章 绪论 ........................................................... 1

1.1 引言 ............................................................ 1 1.2 本课题目前的研究现状和研究意义 .................................. 1 1.3 论文研究的主要内容和组织结构 .................................... 2 第二章 扩频通信 ....................................................... 4

2.1 扩频通信概述 .................................................... 4 2.1.1 扩频通信的定义 .............................................. 5 2.1.2 扩频通信的理论基础 .......................................... 6 2.2 直接序列扩频工作方式 ............................................ 8 2.3 其他工作方式 ................................................... 15 第三章 分数阶傅里叶变换 .............................................. 18 3.1 分数阶傅里叶变换的研究与发展 ................................... 18 3.2 分数阶傅里叶变换定义及其性质 ................................... 19 3.2.1 分数阶傅里叶变换的定义 ..................................... 20 3.2.2 分数阶傅里叶变换的性质 ..................................... 22 第四章 扩频通信系统中chirp干扰的识别与抑制的实现 ..................... 24

4.1 扩频通信中调制信号的仿真 ....................................... 24 4.2 chirp干扰噪声的仿真 ........................................... 26 4.3 分数阶傅里叶变换处理chirp噪声的基本原理 ........................ 28 4.3.1 chirp噪声的聚集性在分数阶傅里叶域的解释 .................... 28 4.3.2 chirp噪声分数阶傅里叶域滤波的基本原理 ...................... 29 4.3.3 chirp噪声分数阶傅里叶域滤波模型 ............................ 30 4.4 chirp干扰识别与抑制的实验 ...................................... 31

4.4.1 chirp干扰识别与抑制算法 .................................... 31 4.4.2 三种调制方式的chirp识别与抑制实验 .......................... 36 第五章 总结 .......................................................... 45 致谢 .................................................................. 47 参考文献 .............................................................. 48 附录 .................................................................. 49