摘要
多目标遥测(Multi-target Telemetry)系统目前已经成为遥测领域的研究热点。一般情况下,多目标遥测系统通常采用直接序列扩频码分多址(Direct Sequence Code Division Multiple Access, DS-CDMA)系统。这是因为扩频系统具有抗干扰能力强、隐蔽性能好、可以实现码分多址等许多独特的性能。而码分多址技术具有系统容量大,能抵抗信道的频率选择性衰落以及提供方便的多用户接入等优势。因此,DS-CDMA特别适合多目标遥测系统。
对于扩频通信系统,扩频码的同步问题一直是一个重点研究的问题。在有多个用户地址的直扩系统(Direct Sequence Spread Spectrum communication system, DS-SS)中,不同地址的扩频信号之间会产生多址干扰,这是多用户扩频系统中扩频同步的难点之一。本文正是对于这一问题进行研究,提出了扩频同步系统的设计方案。
本文首先阐述了扩频通信系统的理路基础,介绍了两种常用的扩频码,并选择以平衡Gold码作为扩频系统的扩频码。对于扩频同步系统的捕获和跟踪两个组成部分进行了分别的研究。针对同步系统的捕获部分,对目前两种常用的直扩系统的扩频码捕获方法滑动相关捕获法和匹配滤波器捕获法进行了分析和比较,并提出一个改进的捕获算法,即基于FFT的匹配滤波器捕获法作为同步系统的方案。针对同步系统的跟踪部分,本文提出以延时锁定环路( delay locked loop, DLL)作为同步系统跟踪的方案。
然后本文应用MATLAB软件对同步系统的捕获和跟踪算法进行了软件仿真和验证。最后,本文以VHDL语言基于Altera公司的FPGA芯片对同步系统的设计方案予以硬件实现,并在Quartus II软件下完成同步系统的硬件时序仿真,仿真结果验证了方案的可行性,可以满足多目标遥测系统的实际要求,为其工程实现奠定了基础。本系统采用模块化的设计,以备将来的扩展和改进,体现了良好的灵活性。
Multi-target Telemetry has become a hot spot in the telemetry field. Generally speaking, it chooses Direct Sequence Code Division Multiple Access (DS-CDMA) system for the Multi-target Telemetry system. Because Direct Sequence Spread Spectrum communication system (DS-SS) has series advantage such as strong anti-jamming, well covered and which can implement CDMA. And the CDMA can offer more system capacity, restrain frequency selection decline in channel and offer Multi-access conveniently. So these make it very fit for Multi-target Telemetry system.
Spread spectrum code synchronization is a stress research to Spread Spectrum Communication system all the time. In the Direct Sequence Spectrum system with multiple users, Multiple Access Interference (MAI) will arise in spread spectrum signals of different access. This is one of the difficulties for Multi-user spread spectrum system. This dissertation takes a research for the problem, and proposes a design of direct sequence spectrum synchronization system.
At fist, in this dissertation, it expatiates on the theory of spread spectrum communication and introduces two common spread spectrum code, which are m sequence and Gold sequence. The spread spectrum code synchronization system contains two important parts, including spread spectrum code acquisition and spread spectrum code tracing, they are both introduced in the dissertation. This dissertation analyzes and compares two conventional acquisition ways of sliding correlator and matched filter . Then selects a new structure of the acquisition, it named matched filter fast acquisition based on FFT. And this dissertation selects the delay locked loop (DLL) as the design of the tracing.
And then, the dissertation takes a soft simulation and verifies about the design of the acquisition and tracing using MATLAB. At the end, the dissertation gives an implementation to the direct sequence spectrum synchronization system by applying the High-speed hardware description language (VHDL), basing on FPGA of Altera, and performs hardware simulation in Quartus II. The results of simulation show that the direct sequence spectrum synchronization system is feasible and meet to the requirements of Multi-target telemetry system, which lays a foundation for the engineering realization. The system uses the method of blocking designing, which makes it flexible. So it is easy to extend and improve the system in the future.
引文
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