瞬时GPS信号仿真及导航算法研究

【作者】 宋华；

【导师】 顾逸东； 袁洪；

【作者基本信息】 中国科学院研究生院（空间科学与应用研究中心） ， 计算机应用技术， 2008， 博士

【摘要】 目前,对GPS的研究和应用多集中在利用连续接收到的信号,通过捕获、连续跟踪的方法解调出导航电文,对接收机进行定位、测速等。但在某些特定的情况下,接收机接收到的信号是非连续的或者是间断的,有时甚至是瞬时的。例如,在遮挡严重的城市街道及室内等弱信号环境下接收到的信号、接收机在受压制性干扰时接收到的片段“干净”信号、单天线自旋弹载GPS接收机接收的信号以及人为的为降低功耗而瞬时开机接收到的信号等,在这些情况下信号都是间断的。如何在上述情况下合理有效地利用间断的瞬时GPS信号将是个很有意义的课题。本文研究了瞬时GPS中频数字信号仿真方法,建立了仿真系统,以此为基础研究了瞬时GPS信号定位、测速导航算法问题,得到的具有创新意义的结果如下:(1)GPS中频数字信号模拟仿真。对GPS卫星信号经过无线传播信道、GPS接收机天线、射频下变频、滤波和采样量化之后形成数字化中频信号的整个过程进行建模和仿真。建立了各种仿真误差模型,以便模拟产生的信号能较真实的反映各种误差源的影响;针对高动态自旋载体,研究了姿态变化情况下的GPS卫星信号多普勒频移的计算模型,并结合天线的增益方向图,给出了可见卫星判断和信号幅度调制模拟的方法;详细给出中频信号状态的计算方法、计算过程,建立了计算机仿真系统。相对于传统的硬件RF GPS卫星信号模拟器而言,该仿真系统具有可重新编程的能力,可以针对GPS系统中影响伪距精度和跟踪性能的各种误差源进行高精度的建模,所以可以做为算法研究和测试的有力工具;(2)瞬时信号定位的关键技术。对瞬时信号定位的关键技术,如导航电文的获取、码相位的提取和信号发射时间的恢复等进行研究。提出了优化的缩小搜索步长和曲线拟合细化码相位的方法,并采用Monte Carlo模拟的方法估计了在不同信噪比下,瞬时信号的长度与码相位细化精度的关系。全面地梳理了瞬时信号定位的各个关键技术,详细给出了基于改进的迭代最小二乘法进行瞬时信号定位解算的方法;(3)瞬时信号测速方法。将经典和现代谱估计理论应用于瞬时GPS信号测速,经过分析比较,提出了基于周期图理论的瞬时信号测速方法,经仿真验证,利用该方法能达到测速的目的,并取得较好的精度,满足一般用户测速需求;(4)基于瞬时信号定位原理,提出了单天线自旋弹载GPS接收机实现方案。将卡尔曼滤波理论应用于单天线自旋弹载GPS接收机的定位信息平滑处理,并利用其预测功能对弹道测量异常值识别和处理,进一步保证了导航精度和鲁棒性。本文的研究结果,对于利用瞬时GPS信号进行导航的研究具有理论意义,对单天线自旋弹载GPS软件接收机的研制有现实的应用价值。更多还原

【Abstract】 In normal situations where continuous Global Position System (GPS) signals can be received, the position and velocity measurement of the GPS receiver are accomplished by continuous tracking of GPS signals with PLL/FLL and DLL to get the navigation data. However, GPS receivers can receive only incontinuous or partial GPS signals in some circumstances, such as indoors, urban areas with lots of buildings, signals reflected by objects in ocean, signals received by the single antenna of rotating projectile, or partial signals by turning off GPS receivers regularly to save limited power, and so on. It’s still an open issue how to measure velocity and calculate location of GPS receivers with partial GPS signals.To address above issues, this dissertation presents researches on the simulation method of GPS partial intermediate frequency (IF) signal and the development of a software-based IF GPS signal simulation system. Based on signals outputted from the simulation system, methods of positioning and velocity measurement with partial GPS signal are further researched. The innovative results from this dissertation are as follows:(1) The simulation of GPS IF signal. A mathematical signal model is built to express the digitized IF GPS signal as a function of various errors during propagation, such as satellite clock error, ephemeris error, ionosphere error, and troposphere error etc, which make the simulated signals are more approximate to GPS signals in real environments. It can simulate the process of frequency down-conversion, sampling and quantization. For high dynamic rotating projectile with attitude changing with time, the algorithm of calculating the Doppler frequency shift of the GPS signal is given. In addition, With the GPS receiver’s antenna radiation pattern, a simulation method for visible GPS satellites forecast and signal magnitude modulation is also proposed. Based on above model and algorithms, the mechanism of estimating GPS satellite signal status is given in detail and a simulation system is developed. Compared to the conventional RF GPS simulator, this simulation system avoids the uncertainty brought by the method of RF GPS signal generation. Moreover, it can model error sources that affect the pseudo-range precision and tracking performance, and therefore is more suitable for theoretic algorithm research.(2) Key technologies of positioning with partial GPS signals. Key technologies of positioning with partial GPS signals are researched in depth, including the method of getting navigation data, extracting code phase, as well as signal transmitting time recovery, etc. A method that refines the code phase with the optimized shortening the search step length and curve fitting methods is proposed, and a graph that expresses the relation between the precision of the code phase and the length of the partial signal in different SNR are obtained with the Monte Carlo simulation method. The feasibility of the positioning method with partial GPS signals is verified with the modified iterative Least Square method.(3) Velocity measurement with partial GPS signals. The classical and modern spectral estimation theories are applied to GPS velocity measurement. After comparative study, a Periodogram-based velocity measurement method is proposed, and simulation is performed to verify that the velocity can be measured with this method and the precision of the velocity is adequate to meet user’s demands in certain scenarios.(4) Based on the positioning technologies with partial GPS signal as researched above, the design of a spinning projectile GPS receiver solution with single antenna is proposed. Kalman filter theory is applied to smooth the positioning results that are calculated with periodic and partial GPS signals, and the forecast function of Kalman filer is used to estimate and process the exceptional measurements, which highly improves the navigation precision.The research results as represented in this dissertation have not only theoretical value for the research of navigation methods with partial GPS signals, but also practical significance in development and application of spinning projectile GPS receiver with single antenna. Further research and work will be continued along these directions.更多还原