【作者】 董吉虹；

【导师】 白明；

【作者基本信息】 天津理工大学 ， 信号与信息处理， 2007， 硕士

【摘要】 GPS全球定位系统是美国国防部为军事目的而建立的卫星导航系统,其主要目的是解决海上、陆地和空中运载工具的导航定位问题。GPS作为新一代卫星导航系统,不仅具有全球、全天候、连续、高精度导航与定位能力,而且具有优良的抗干扰性和保密性。因此,发展全球定位系统是当今导航技术现代化的一个重要标志。在GPS接收机中,为了得到导航电文并对其进行解算,要完成复杂的信号处理过程。其中,怎样捕获到卫星信号,并对C/A码进行跟踪是研制GPS接收机的重要问题之一。本文在对GPS信号的结构进行深入的分析后,结合FPGA的特点,对算法进行设计及优化后,给出了相应的仿真。本文的内容主要包括以下几个方面:1.对GPS信号结构的产生原理进行了深入地分析,并对GPS信号的调制机理进行详细地阐述。2.在GPS信号的捕获方面,采用了基于FFT频域的快速捕获的方法,即将接收到的GPS信号先利用快速傅立叶变换(FFT)变换到频域,在频域完成相应的运算后,再利用傅立叶反变换(IFFT)变换到时域。从而大大减少了计算量,加快了信号捕获的速度,提高了捕获性能。3.在C/A码跟踪部分,本文采用了非相干延迟锁定环对C/A码进行跟踪。来自载波跟踪环路的本地载波将输入的信号变成基带信号,然后分别和本地码的三个不同相位序列进行相乘,将相乘结果进行累加,经过处理将得到码相位和当前的载波频率送到载波跟踪环路。4.载波跟踪环,本文采用的是科斯塔斯环。载波跟踪环和码跟踪环在结构上相似,故本文只对关键的载波NCO进行了仿真。本文的创新点主要是使用FPGA对整个GPS信号的捕获及C/A码的跟踪进行设计。此外,根据FPGA的特点,在不改变外部硬件设计的前提下,改变相应的IP核或相关的VHDL程序就可对系统进行各种优化设计,以适应不同类型的GPS接收机的不同功能。更多还原

【Abstract】 Global positioning system (GPS) is a satellite navigation system established to solve the navigating and positioning problems on land or sea and in the air. As a new generation of satellite navigation system, it not only has global, round-the-clock, continuous, high-precision navigating and positioning functions, but also possesses excellent interference immunity and confidentiality. Therefore, the development of GPS navigation technology has become ever more important in the advancement of navigation industry.In order to receive navigation messages and calculate their values, it is necessary to complete complex signal processing in the GPS receiver, while how to capture the satellite signals and track the C/A code is one of the most important issues. In this paper, the corresponding simulation results of GPS signals were provided based on the detailed GPS signal’s structure analyses, FPGA features, and optimized algorithm.The contents of this paper include the following aspects:1. An in-depth study on the structure and theory of GPS signal is conducted, and the modulation mechanisms of GPS signal are explained in detail.2. To capture the GPS signal, a rapid acquisition method based on the FFT parallel code is employed. The incoming signals are firstly translated into frequency domain and correlated, and then the results are translated back to the time domain by using IFFT. Accordingly, a much more complex computation is avoided and the searching speed for GPS signals is much faster than sequential detecting technique.3. A non-coherent DLL is used to track the C/A code. The local carriers from carrier tracking loop turn the input signals into the baseband signal, and the baseband signals multiply the three different phase sequence of the local yards, then deal with cumulative results, at last, put the code phase and current carrier frequency into carrier tracking loop.4. Costas loop is used as the carrier tracking loop. It is similar to the C/A tracking loop in structure. Thus, only the simulation of carrier NCO has been given in this paper.In this paper, a novel approach by using FPGA to capture the GPS signals and track the C/A codes is employed. According to the characteristics of FPGA, various system optimizations could be realized by just changing the corresponding IP core or related VHDL program without changing any hardware. The advantages and flexibility of the novel approach are easily adapted to the different functions of the different GPS receivers.更多还原