文档介绍：中文摘要
中文摘要
北斗卫星导航定位系统是我国自主研发的卫星导航定位系统。该系统提供快速定位、
实时导航、简短通信和精确授时等功能,对于促进我国的国防与民用导航定位事业的发展
具有重要的意义。该系统采用直接序列扩频技术。而在直接序列扩频技术中,只有扩频码
同步才有可能正确解算出传输的信息。因此,扩频码同步是影响导航系统系统性能的关键
技术,码同步不仅是正确接收信息的前提,同时也关系到系统能否在高动态条件下进行精
确定位。码捕获是码同步的重要组成部分之一。因此,研究和实现北斗卫星导航系统中的
扩频码捕获技术有着重要的意义。
本文首先介绍了扩频通信理论,然后描述了可编程逻辑器件开发流程及其配置。在此
基础上,对常用的几种伪码捕获方法进行了分析,并重点研究了采用数字匹配滤波法捕获
北斗卫星信号的技术,匹配滤波器的设计采用加法树结构实现,避免了在计算相关值时过
多地耗用乘法器。并对匹配滤波器进行了改进,采用分段匹配的捕获方法。在捕获验证阶
段采用N中取M的峰值检测捕获搜索方法,有效降低了虚警概率。
文章在将整个系统进行了Matlab仿真的基础上重点研究了该捕获法的FPGA实现。文
章采用VHDL硬件描述语言,完成了数字下变频器(包括DDS、混频器和FIR低通滤波器)、
匹配滤波器、判决验证模块等关键模块设计、及其仿真。最后在Altera公司的CycloneⅡ
EP2C70F672I8专用开发板上进行系统的初步调试与测试,验证了系统的可行性。

关键词:伪码捕获、匹配滤波、FPGA、VHDL
I
ABSTRACT
ABSTRACT
Compass Positioning System is researched and developed by our country .The system
provides swift location, real-time navigation, munication as well as precise time
service, and takes a great important role in the field of development of national defense and
civil navigation and orientation. This system is a system based on direct sequence spread
spectrum (DSSS) technique. In DSSS system, if the synchronization of Pseudo Noise Code is
very bad, exact information do not received. So, it affects the performance of the whole system,
because this technology is not only the precondition of working well, but also the key of precise
positioning. Acquisition is one of the most important parts of code synchronization. Therefore,
research and implement acquisition of the Pseudo Noise Code pass is of great
significance to improve the positioning precision and the user terminal’s performance index.
First of all, this article introduces the spread spectrum, especially DSSS. Then the
programmed logic device FPGA is investigated in depth, including the design flow and
configurative mode of FPGA. On this basis, the article analyzes mon methods of
pseudo-code acquisition and focuses on the technology of using digital matched filtering
method to captur