本文選題：GPS　切入點(diǎn)：中頻信號　出處：《杭州電子科技大學(xué)》2013年碩士論文

【摘要】：GPS信號源可以為接收機(jī)的開發(fā)與測試提供仿真環(huán)境，從而檢驗(yàn)接收機(jī)是否達(dá)到了預(yù)期的設(shè)計(jì)目標(biāo)。由于衛(wèi)星發(fā)射時(shí)使用高頻率載波，這些高頻率不容易過濾和解調(diào)。于是，接收機(jī)在處理接收數(shù)據(jù)前都是先對接收到的射頻信號（RF signal）經(jīng)天線前端下變頻轉(zhuǎn)化為中頻信號(IF signal)，由A/D采樣并量化成數(shù)字中頻信號后，接下來再進(jìn)行信號處理。所以，GPS接收機(jī)的所有研究都是從數(shù)字中頻信號這一基礎(chǔ)開始的，只有提供合適的中頻數(shù)字信號才能被GPS接收機(jī)接收處理。因此， GPS數(shù)字中頻信號的模擬對GPS軟件接收機(jī)的研制開發(fā)有著重要意義。 本文中以GPS中頻信號的生成仿真為研究目標(biāo)。在整個(gè)研究過程中，主要的研究內(nèi)容如下： 首先深入理解GPS信號體制和擴(kuò)頻通信的有關(guān)知識(shí)，詳細(xì)介紹了偽隨機(jī)碼和導(dǎo)航電文的結(jié)構(gòu)內(nèi)容。GPS信號有兩種偽隨機(jī)碼——粗捕獲碼(C/A碼)和精捕獲碼(P碼)。由于，P碼專供接收機(jī)作為軍用偽碼，一般用戶不能使用。本文研究內(nèi)容是以L1載波上C/A碼作為對象，仿真實(shí)現(xiàn)GPS數(shù)字中頻信號。 為了實(shí)現(xiàn)后續(xù)信號的仿真，詳細(xì)論述了GPS信號從發(fā)射到接收轉(zhuǎn)換為中頻信號的數(shù)學(xué)模型，給出了信號傳播過程中的誤差源——電離層延遲、對流層延遲、噪聲以及多徑效應(yīng)的模擬模型，通過迭代算法求出信號發(fā)射時(shí)刻，同時(shí)對衛(wèi)星和接收機(jī)之間的多普勒頻移進(jìn)行研究，這些為信號的仿真提供了理論和算法基礎(chǔ)。 本文通過MATLAB編程實(shí)現(xiàn)了GPS衛(wèi)星C/A碼，導(dǎo)航電文以及數(shù)字中頻信號的生成。同時(shí)，搭建了GPS數(shù)字中頻信號的Simulink模型，實(shí)現(xiàn)了數(shù)字中頻信號生成的系統(tǒng)級仿真，并給出了仿真結(jié)果。通過軟件仿真的中頻信號為接收機(jī)許多算法的研究，比如衛(wèi)星信號的捕獲、跟蹤算法等提供了基礎(chǔ)；而且參數(shù)可控的GPS中頻信號發(fā)生器具有良好的靈活性，通過設(shè)置不同的參數(shù)就可以提供不同的仿真環(huán)境，方便且易操作。本文研究的成果也可以為衛(wèi)星模擬器的研究提供借鑒。 最后在MATLAB/Simulink仿真基礎(chǔ)上，，利用DSP Builder工具對GPS信號源硬件實(shí)現(xiàn)的關(guān)鍵部分——載波數(shù)控振蕩器(NCO)和碼數(shù)控振蕩器(NCO)的生成進(jìn)行研究，提出了相關(guān)參數(shù)的設(shè)置方法，最后完成信號調(diào)制生成部分，并在Modelsim仿真工具下進(jìn)行驗(yàn)證。這為以后在FPGA平臺(tái)對中頻信號源的硬件研究與實(shí)現(xiàn)提供了良好的過渡。
[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.
【學(xué)位授予單位】：杭州電子科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2013
【分類號】：P228.4

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