GPS数字中频信号仿真

发布时间：2018-04-03 18:02

本文选题：GPS　切入点：中频信号　出处：《杭州电子科技大学》2013年硕士论文

【摘要】：GPS信号源可以为接收机的开发与测试提供仿真环境，从而检验接收机是否达到了预期的设计目标。由于卫星发射时使用高频率载波，这些高频率不容易过滤和解调。于是，接收机在处理接收数据前都是先对接收到的射频信号（RF signal）经天线前端下变频转化为中频信号(IF signal)，由A/D采样并量化成数字中频信号后，接下来再进行信号处理。所以，GPS接收机的所有研究都是从数字中频信号这一基础开始的，只有提供合适的中频数字信号才能被GPS接收机接收处理。因此， GPS数字中频信号的模拟对GPS软件接收机的研制开发有着重要意义。本文中以GPS中频信号的生成仿真为研究目标。在整个研究过程中，主要的研究内容如下：首先深入理解GPS信号体制和扩频通信的有关知识，详细介绍了伪随机码和导航电文的结构内容。GPS信号有两种伪随机码——粗捕获码(C/A码)和精捕获码(P码)。由于，P码专供接收机作为军用伪码，一般用户不能使用。本文研究内容是以L1载波上C/A码作为对象，仿真实现GPS数字中频信号。为了实现后续信号的仿真，详细论述了GPS信号从发射到接收转换为中频信号的数学模型，给出了信号传播过程中的误差源——电离层延迟、对流层延迟、噪声以及多径效应的模拟模型，通过迭代算法求出信号发射时刻，同时对卫星和接收机之间的多普勒频移进行研究，这些为信号的仿真提供了理论和算法基础。本文通过MATLAB编程实现了GPS卫星C/A码，导航电文以及数字中频信号的生成。同时，搭建了GPS数字中频信号的Simulink模型，实现了数字中频信号生成的系统级仿真，并给出了仿真结果。通过软件仿真的中频信号为接收机许多算法的研究，比如卫星信号的捕获、跟踪算法等提供了基础；而且参数可控的GPS中频信号发生器具有良好的灵活性，通过设置不同的参数就可以提供不同的仿真环境，方便且易操作。本文研究的成果也可以为卫星模拟器的研究提供借鉴。最后在MATLAB/Simulink仿真基础上，，利用DSP Builder工具对GPS信号源硬件实现的关键部分——载波数控振荡器(NCO)和码数控振荡器(NCO)的生成进行研究，提出了相关参数的设置方法，最后完成信号调制生成部分，并在Modelsim仿真工具下进行验证。这为以后在FPGA平台对中频信号源的硬件研究与实现提供了良好的过渡。
[Abstract]:The GPS signal source can provide a simulation environment for the development and testing of the receiver, so as to verify whether the receiver has achieved the desired design objectives.These high frequencies are not easy to filter and demodulate due to the use of high-frequency carriers when satellites are launched.Therefore, before the receiver processes the received data, the received RF signal is converted into if signal by down-conversion of the front end of the antenna. The if signal is sampled and quantized into digital intermediate frequency signal by A / D, and then the signal is processed.So all the research of GPS receiver is based on the digital intermediate frequency signal. Only by providing the appropriate if digital signal can it be received and processed by the GPS receiver.Therefore, the simulation of GPS digital if signal is of great significance to the research and development of GPS software receiver.The aim of this paper is to simulate the generation of GPS if signal.In the whole research process, the main research contents are as follows:Firstly, we deeply understand the knowledge of GPS signal system and spread spectrum communication, and introduce in detail the structure of pseudorandom code and navigation message. There are two kinds of pseudorandom code, coarse acquisition code and C / A code.As the receiver is designed to be used as a military pseudo code, general users can not use it.In this paper, the C / A code on L1 carrier is taken as the object, and the GPS digital if signal is realized by simulation.In order to realize the simulation of subsequent signal, the mathematical model of GPS signal from transmitting to receiving to if signal is discussed in detail. The error source-ionospheric delay and tropospheric delay in the process of signal propagation are given.The simulation model of noise and multipath effect is used to calculate the time of signal transmission by iterative algorithm, and the Doppler frequency shift between satellite and receiver is studied, which provides a theoretical and algorithmic basis for signal simulation.In this paper, GPS satellite C / A code, navigation message and digital if signal are generated by MATLAB programming.At the same time, the Simulink model of GPS digital if signal is built, the system level simulation of digital if signal generation is realized, and the simulation results are given.The if signal simulated by software provides the basis for the research of many algorithms of the receiver, such as the acquisition of satellite signal, tracking algorithm and so on, and the GPS if signal generator with controllable parameters has good flexibility.Different simulation environment can be provided by setting different parameters, which is convenient and easy to operate.The results of this paper can also be used for reference in the research of satellite simulator.Finally, on the basis of MATLAB/Simulink simulation, the generation of carrier numerical control oscillator and code numerical control oscillator is studied by using DSP Builder tool, and the method of setting related parameters is put forward.Finally, the signal modulation generation part is completed and verified under the Modelsim simulation tool.This provides a good transition for the hardware research and implementation of if signal source in FPGA platform.
【学位授予单位】：杭州电子科技大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：P228.4

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