GPS软件接收机捕获算法研究

发布时间：2018-12-28 17:13

【摘要】：近年来,伴随着导航定位技术的不断发展,全球卫星导航系统(Global Navigation Satellite System, GNSS)无论在军事领域还是民用方面都得到了迅速而广泛的应用,如交通运输、气象预报、社会治安、自然灾害救助、个人移动电话定位等目前,世界上已有的卫星导航系统有美国的GPS、俄罗斯的GLONASS、中国的北斗系统以及欧洲的伽利略导航系统(Galileo)。随着技术的不断革新,传统的硬件接收机已经无法满足人们的需求,兼容性、灵活性更强的软件接收机在微处理器制造工艺和技术的支持下成为未来的趋势。本文重点研究GPS软件接收机捕获阶段的问题。软件接收机要求能够对接收到的信号进行模拟下变频、A/D采样、伪码同步等实时处理。其中伪码同步又包括捕获和跟踪两部分,而实现同步首先必须实现同步捕获(粗同步)。捕获阶段通常要求接收到的伪码与本地伪码对齐在某一范围内,一旦实现同步捕获,就可以通过锁相环(PLL)来实现伪码的跟踪过程。若捕获阶段能将本地伪码与接收端伪码相位误差确定在半个码片之内,跟踪阶段将很快锁定伪码相位；反之,将耗费大量的时间来实现同步跟踪。同理,载波频率的捕获也直接影响到载波频率跟踪阶段时间长短。因此,捕获算法的设计是软件接收机设计中的关键问题。本课题重点研究GPS软件接收机的直接序列扩频伪码捕获问题,并从数字化处理、捕获算法研究、捕获电路的优化几个方面进行了研究设计。首先,论文介绍了GNSS的基本发展情况及GPS系统所采用的直接序列扩频通信原理,研究了GPS信号构成、信号的产生及特性,阐述了软件接收机各组成部分,从结构、功能等方面对比硬件接收机与软件接收机。其次,分析捕获原理,重点阐述了常用的三种捕获算法,即滑动相关捕获、并行频率捕获及匹配滤波器捕获,并从算法的运算量、复杂程度、硬件实现上进行对比,分析利弊,总结影响捕获的三个重要因素,即卫星运动产生的多普勒效应、搜索信号时采用的所搜步长以及捕获数据的长度。并提出适合本文捕获研究的信号检测、判决方法、数字下变频模块等。最后,根据上文对常用捕获方法的分析,提出改进FFT快速捕获方法。本文对C/A码的码相位并行搜索,对多普勒频移实施串行搜索,大大缩减搜索空间。采用FFT算法并行完成接收信号与本地伪码的相关运算,并在使用FFT运算过程中,利用圆周相关运算,减少FFT运算次数,从而减少计算量提高捕获速度。然后利用仿真分析,与传统算法进行对比。
[Abstract]:In recent years, with the continuous development of navigation and positioning technology, the global satellite navigation system (Global Navigation Satellite System, GNSS) has been rapidly and widely used in both military and civil fields, such as transportation, weather forecasting, social security. Natural disaster relief, personal mobile phone positioning and so on. At present, the existing satellite navigation systems in the world include the GPS, of the United States, the GLONASS, of Russia, the Beidou system of China, and the Galileo navigation system (Galileo). Of Europe. With the continuous innovation of technology, the traditional hardware receiver has been unable to meet the needs of people. The software receiver with more compatibility and flexibility has become a trend in the future with the support of microprocessor manufacturing process and technology. This paper focuses on the acquisition phase of GPS software receiver. The software receiver is required to process the received signals in real time, such as analog downconversion, A / D sampling, pseudo code synchronization and so on. The pseudo-code synchronization includes capture and tracking, and synchronization must be realized first (coarse synchronization). The acquisition phase usually requires that the received pseudo-code is aligned with the local pseudo-code in a certain range. Once synchronous acquisition is realized, the pseudo-code tracking process can be realized by phase-locked loop (PLL). If the acquisition phase can determine the phase error between the local pseudo code and the receiver pseudo code within half a chip, the tracking phase will quickly lock the pseudo code phase; conversely, it will take a lot of time to realize synchronous tracking. In the same way, the acquisition of carrier frequency also directly affects the duration of carrier frequency tracking phase. Therefore, the design of acquisition algorithm is a key problem in software receiver design. This paper focuses on the acquisition of direct sequence spread spectrum pseudo-code for GPS software receiver, and designs and researches from several aspects, such as digital processing, acquisition algorithm and the optimization of acquisition circuit. Firstly, the paper introduces the basic development of GNSS and the principle of direct sequence spread spectrum communication used in GPS system, studies the structure of GPS signal, the generation and characteristics of GPS signal, and expounds the components of software receiver. The function compares the hardware receiver with the software receiver. Secondly, the principle of acquisition is analyzed, and three common acquisition algorithms, namely sliding correlation acquisition, parallel frequency acquisition and matched filter acquisition, are described. The advantages and disadvantages are compared from the calculation, complexity and hardware implementation of the algorithm. Three important factors affecting capture are summarized, which are Doppler effect caused by satellite motion, search step size used in searching signal and length of captured data. The signal detection, decision method, digital downconversion module and so on are proposed. Finally, according to the analysis of common acquisition methods above, an improved FFT fast capture method is proposed. In this paper, the code phase parallel search of C / A code and the serial search of Doppler frequency shift are carried out, which greatly reduces the search space. The FFT algorithm is used to perform the correlation operation between the received signal and the local pseudo code in parallel. In the process of using FFT, the circular correlation operation is used to reduce the number of FFT operations, thus reducing the amount of computation to improve the acquisition speed. Then the simulation analysis is used to compare with the traditional algorithm.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P228.4

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