北斗导航信号捕获算法研究及北斗授时服务系统设计

发布时间：2018-10-21 14:03

【摘要】：随着北斗导航系统的不断完善,北斗导航服务已经覆盖亚洲大部分地区,北斗终端用户不断增加,使用环境越来越复杂,用户对接收机的性能要求不断提高。因此,提高接收机弱信号接收能力,直接关系到导航系统的连续性、精确性、可用性和完好性。对于GPS接收机以及北斗二代民用型接收机,国内的众多研制单位在弱信号接收技术方面已经积累了大量经验并取得了重大突破,但和国际水平相比仍存在很大差距。因此,北斗二代接收机应将弱信号接收能力作为导航系统的一个重要考核指标,而灵敏度性能作为体现接收机对弱信号接收能力好坏的重要指标,应该受到高度重视。捕获过程是基带信号处理的第一步,捕获算法的性能直接关系到接收机的灵敏度,因此不断提高捕获算法的性能是永恒追求的目标。在对捕获算法研究之前,需要有中频信号来验证捕获算法的性能,因此,本文先分析了北斗卫星的B1I信号结构,进而分析了北斗卫星B1I信号的中频信号模型,然后介绍了产生中频信号的方法和过程。最后通过仿真比较了不同信噪比下产生信号的结果。导航接收机对信号的处理流程分为射频部分和基带部分,基带部分中信号捕获是首先要进行的环节。本文在捕获研究之前介绍了信号捕获的原理,基于捕获原理分析了串行捕获算法和并行码相位捕获算法,对两者的性能进行了比较分析,结果表明两种捕获算法的性能相同,但是并行码相位捕获算法在捕获时间上优于串行捕获算法。之后分析了弱信号情况下的高灵敏度捕获算法,提高捕获灵敏度的方法为:相干积分、非相干积分和差分相干积分。但是由于D1数据经过了二次NH编码,相干积分和差分相干积分无法直接使用,只有非相干积分可以使用。因此本文提出一种改进型全比特算法,通过仿真将改进型的全比特捕获算法和非相干积分捕获算法进行了比较,结果表明改进型的全比特算法使用较少的信号数据就可以获得和非相干积分捕获算法相同的性能,但是全比特算法较为耗时,需要进一步优化。针对北斗授时服务在民用中并不普及的问题,本文设计了一款基于北斗导航的授时系统,利用北斗授时服务对局域网终端进行精确授时。授时系统使用FPGA+MCU+导航模块+Wi-Fi模块的架构,FPGA并行处理数据能力强,可以实时接收导航模块的时间信息,通过控制LED点阵显示屏实时显示时间信息。在网络授时方面使用了NTP协议,通过MCU与Wi-Fi模块实现该协议。然后具体介绍了各个部分的原理和实现方法,介绍了硬件开发的详细过程。最后,对系统的运行效果进行了展示。
[Abstract]:With the continuous improvement of Beidou navigation system, Beidou navigation service has been covering most of Asia, Beidou end users are increasing, the use environment is becoming more and more complex, and users' performance requirements for the receiver are constantly improving. Therefore, improving the receiver's weak signal reception capability is directly related to the continuity, accuracy, availability and completeness of the navigation system. For the GPS receiver and Beidou second generation civil receiver, many domestic research and development units have accumulated a lot of experience and made a great breakthrough in weak signal receiving technology, but there is still a big gap compared with the international level. Therefore, the second generation Beidou receiver should take the weak signal receiving ability as an important evaluation index of the navigation system, and the sensitivity performance as an important index to reflect the receiver's ability to receive the weak signal, which should be attached great importance to. The acquisition process is the first step in baseband signal processing. The performance of the acquisition algorithm is directly related to the sensitivity of the receiver, so it is an eternal goal to continuously improve the performance of the acquisition algorithm. Before studying the acquisition algorithm, it is necessary to have intermediate frequency signal to verify the performance of the acquisition algorithm. Therefore, this paper first analyzes the B1I signal structure of Beidou satellite, and then analyzes the intermediate frequency signal model of Beidou satellite B1I signal. Then the method and process of producing if signal are introduced. Finally, the results of signal generation under different signal-to-noise ratio (SNR) are compared by simulation. The signal processing flow of the navigation receiver is divided into radio frequency part and baseband part. Signal capture is the first step in the baseband part. In this paper, the principle of signal acquisition is introduced before the research of acquisition. Based on the principle of acquisition, the serial acquisition algorithm and the parallel code phase acquisition algorithm are analyzed, and the performance of the two acquisition algorithms is compared and analyzed. The results show that the performance of the two acquisition algorithms is the same. But the parallel code phase acquisition algorithm is superior to the serial acquisition algorithm in acquisition time. Then the high sensitivity acquisition algorithm for weak signal is analyzed. The methods to improve the acquisition sensitivity are: coherent integral, incoherent integral and differential coherent integral. However, since D1 data is encoded by quadratic NH, coherent integrals and differential coherent integrals cannot be directly used, only incoherent integrals can be used. Therefore, an improved full-bit algorithm is proposed in this paper. The improved full-bit acquisition algorithm and the incoherent integral acquisition algorithm are compared by simulation. The results show that the improved full-bit algorithm can obtain the same performance as the incoherent integral acquisition algorithm with less signal data, but the full-bit algorithm is time-consuming and needs further optimization. In order to solve the problem that Beidou time service is not popularized in civil use, this paper designs a time service system based on Beidou navigation, which uses Beidou time service to accurately serve the local area network terminal. The system uses the structure of Wi-Fi module of FPGA MCU navigation module. FPGA has strong ability to process data in parallel. It can receive the time information of navigation module in real time and display time information in real time by controlling LED dot matrix display screen. In the aspect of network timing, NTP protocol is used, which is realized by MCU and Wi-Fi module. Then the principle and implementation of each part are introduced in detail, and the detailed process of hardware development is introduced. Finally, the running effect of the system is demonstrated.
【学位授予单位】：西安电子科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN967.1

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