高灵敏度异步扩频解调技术研究

发布时间：2018-01-23 07:29

本文关键词： 异步扩频低信噪比高动态捕获跟踪符号同步　出处：《南京理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：异步扩频测控体制在我国的卫星导航测距领域应用广泛,该体制的研究重点就是如何实现对异步扩频信号的解扩解调。异步扩频信号的解扩解调过程中,又大致分为以下几个部分:伪码相位与多普勒频偏的粗捕、伪码相位的跟踪、载波频率的捕获与同步、符号同步等。在星地通信中,对扩频信号捕获和跟踪的难度远大于地面通信,其原因主要有两个方面:首先是信道环境较为复杂,接收到的信号信噪比难以保障;另一方面,通信设备所在载体往往具有较高的移动速度和加速度,这就带来了较高的多普勒频移和频移变化率,大大增加了的难度。本文针对课题要求,在对现有常用捕获、跟踪方法进行研究的基础上,设计了针对低信噪比、高动态的异步直接扩频信号进行捕获和跟踪的算法,并对其进行了仿真和FPGA实现。主要内容包括:阐述了扩频通信领域目前常用的几种伪码捕获方法,分析了它们各自的实现原理与性能情况,指出其优缺点,并使用Matlab加以仿真;提出了改进的"基于频域并行捕获技术"方案,不但可以适应较大的输入信噪比范围和多普勒范围,而且大大缩小了运算量,将捕获时间缩短至1.4秒以内,仿真表明,它可以在载噪比55dBHz下实现捕获概率100%,误捕概率为0;设计了跟踪精度较高的载波辅助的DLL码跟踪环路架构;设计了能在较大的动态下完成相位的精确跟踪的双环路载波跟踪环;设计了基于早迟门的符号同步方案。最后,针对某航天工程应用,本文对异步直接扩频信号的捕获和载波同步算法进行了硬件实现。
[Abstract]:Asynchronous spread spectrum measurement and control system is widely used in the field of satellite navigation and ranging in China. The research focus of this system is how to realize despreading demodulation of asynchronous spread spectrum signal and despreading demodulation process of asynchronous spread spectrum signal. It can be divided into the following parts: coarse capture of pseudo-code phase and Doppler frequency offset, tracking of pseudo-code phase, acquisition and synchronization of carrier frequency, symbol synchronization and so on. The difficulty of acquisition and tracking of spread spectrum signal is much more difficult than that of ground communication. There are two main reasons: firstly, the channel environment is more complex and the signal to noise ratio is difficult to guarantee; On the other hand, the carrier of communication equipment often has higher moving speed and acceleration, which brings higher Doppler frequency shift and frequency shift change rate, which greatly increases the difficulty. Based on the research of the existing acquisition and tracking methods, an algorithm for acquisition and tracking of asynchronous direct spread spectrum signals with low signal-to-noise ratio and high dynamic performance is designed. The main contents are as follows: the common methods of PN code acquisition in the field of spread spectrum communication are described, and their implementation principle and performance are analyzed. Its advantages and disadvantages are pointed out and simulated by Matlab. An improved "parallel acquisition technique based on frequency domain" is proposed, which can not only adapt to the larger range of input SNR and Doppler, but also greatly reduce the computational cost and shorten the acquisition time to less than 1.4 seconds. The simulation results show that the acquisition probability is 100 and the false capture probability is 0 under the carrier noise ratio of 55 dBHz. A carrier assisted DLL code tracking loop architecture with high tracking accuracy is designed. A double loop carrier tracking loop is designed, which can accurately track the phase in a large dynamic state. The symbol synchronization scheme based on the early and late gate is designed. Finally, the acquisition of asynchronous direct spread spectrum signals and the carrier synchronization algorithm are implemented in hardware for a space engineering application.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN914.42

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