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摘 要
从人类开始进入信息社会至今，通信技术的发展取得了令人瞩目的成绩。随着通信的普及，信道中的各种干扰也愈加增多。如何在恶劣的环境条件下保证信息能够有效可靠的传输已俨然成为当今通信研究人员所面临的重大难题。
扩频通信是指用于传输信号的信道带宽远远大于信号自身带宽的一种通信方式。与传统无线通信方式相比，其在抗噪声、抗干扰、抗多径衰落、码分多址、信号的隐蔽性及保密性等方面有着无与伦比的优势，从而与光纤通信、卫星通信一起被誉为信息时代的三大主流通信传输方式。本文主要阐述用simulink软件对CDMA直扩收发系统进行仿真，研究其优越的抗噪声、抗干扰、抗多径、多址等性能。
本文的主要内容有：
1. 对扩频通信中各种主要技术进行一定的理论分析；
2. 对当前一些流行的模型实现方法进行描述，包括数字匹配滤波捕获技术、迟早环跟踪技术等；
3. 介绍如何使用simulink软件进行扩频通信系统的仿真；
4. 结合仿真结果对扩频通信系统进行性能分析。
关键词：扩频通信；simulink；CDMA直扩收发系统；
Abstract
From the information society humans enter, the development of communication technology has making miraculous progress. As the popularization of communication, a variety of Interference in transport channel increases dramatically. That how to transport information efficiently and correctly under the adverse circumstances has become a rough problem the researcher of communication has to face with
Spread spectrum communication is a kind of communication patterns in which the band bandwidth used to transport information is far larger than the original signal. Compared with the traditional wireless communication, it has many unparalleled advantages on the performance of anti-noise, anti-jamming, fighting against multi-path fading, code division multiple access and the elusive and confidentiality of the signal. It has become the three major communication patterns with the fiber communication and satellite communications. This text mainly expound that how to simulate the DS-CDMA system use the SIMNLINK software and study it’s superior capacity of anti-noise, anti-jamming, fighting against multi-path fading and code division multiple access.
The main body of this article as follows:
1. Studying the main technology theoretically in Spread spectrum communication;
2. Depicting some current mode, including digital matched filter for capture, L L-DPLL for coder tacking and so on;
3. Illuminating how to use the SIMULINK software to simulate the DS-CDMA system;
4. Analyzing the performance of the DS-CDMA system combined with the consequence of simulation.
Keyword: spread spectrum communication; simulink; DS-CDMA
本文首先具体分析了扩频通信的理论基础，并对直接序列扩频通信系统作了全面的介绍，尤其是扩频同步系统中的捕获及跟踪两部分，谈到了常用的几种方案，重点讨论了本次仿真中采用的数字匹配滤波器捕获法及双 值延迟锁定环跟踪法。随后，文章详细介绍了如何使用simulink对直接序列扩频系统进行仿真。并对各模块的设计及参数设置进行了说明。同时给出了各点的时域波形及频域波形，并做了相应的分析。
通过这次仿真及分析工作，我们可以明显的看到直接序列扩频系统优越的抗干扰和抗噪声的能力，尤其是在信道信噪比达到负值如此恶劣的情况下依然能够从中提取出信源信息。同时，扩频系统的抗多径衰落及其多址性能也相当出色，这不但有效解决了无线通信中的多径干扰这一大难题，而且其码分多址特性使得在紧张的频谱资源条件下，尽可能的提升使用用户的数量。
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发表于 22:33