【作者】 丁继成；

【导师】 赵琳；

【作者基本信息】 哈尔滨工程大学 ， 导航、制导与控制， 2009， 博士

【摘要】 近年来,随着基于位置服务(Location Based Service, LBS)应用需求的增加,弱信号环境下的定位技术引起了全世界的关注。高灵敏度GPS和辅助GPS (Assisted GPS, A-GPS)定位技术已成为许多国家科研机构及相关单位的重点研究对象。本课题正是在这样一种背景下对没有外部辅助源的接收机核心功能——基带信号处理展开深入研究。(1)接收机研究平台设计。采用软件方式直接模拟数字中频GPS信号,深入研究了GPS中频信号功率控制技术、误差源仿真技术和信号传播延迟等相关技术,利用实测星历和输入参数将正常导航解算时各种信号传播误差的修正方法应用于由真距至伪距的反向推算；开发了常规GPS接收机信号捕获和跟踪模块,为新技术的研究测试提供了开发平台。实现了基于FPGA/ARM硬件平台的GPS接收机,利用信号处理模块对实测信号和模拟信号的处理验证了研究平台的有效性。(2)系统地研究了微弱信号捕获中相干积分操作在多种非理想环境下的性能。分析推导了由任意位数A/D转换导致的功率损失通用公式及最优增益设置方法；从等效噪声功率的角度研究了互相关干扰的影响；由相干积分检测量的幅度变化对残余多普勒频率误差、导航电文数据调制的影响进行了深入分析,为弱信号捕获方案的设计提供了理论依据。(3)对微弱GPS信号捕获技术进行深入研究。从理论上证明并经试验验证了当积分时间增加时,差分相干检测的输出序列服从高斯分布。为提高接收机对微弱信号的检测能力和参数估计精度,设计了频率误差自主实时修正的差分相干弱信号捕获方案,理论分析和测试表明该方法能够提高信号检测概率、减小频率估计误差的不确定性,满足弱信号跟踪需求。(4)深入研究接收机处于弱信号环境,环路未锁定时无法实现信号跟踪的问题。针对传统PLL载波环估计误差较大和EKF (Extented Kalman Filtering)算法需要对非线性方程进行近似处理的缺点,利用SRUKF (Square Root Unscented Kalman Filtering)实现载波环参数估计,将最优路径动态规划技术应用于GPS位同步,取得了比目前广泛应用的直方图法更为理想的效果,在此基础上,将SRUKF估计技术与位同步技术结合,研究设计了环路未锁定时串行和并行两种载波跟踪方案,并通过实验验证了方案的合理性。更多还原

【Abstract】 Along with the increasing application requirements of LBS (Location Based Service), the positioning technology in weak signal environment has caused worldwide concern. HSGPS (High sensitive GPS) and A-GPS (assisted GPS) have been taken as the most important research object by scientific research institutions and relevant departments in many countries. It is in such a background that the thesis makes an in-depth research on the core function of GPS receiver without external assisted source, i.e., the baseband signal processing.Firstly, a GPS research platform is designed. The thesis adopt software simulator to generate IF GPS signals. The error sources simulation techniques, various range delay simulation and signal power control techniques according to real almanac are researched. The thesis develops the capturing and tracking module of the regular GPS receiver, provide a research platform for new methods application. A software receiver on the basis of FPGA/ARM hardware platform is realized. In the end, software platform is applied to process analog signal and true signal, and the results verify the validity the complete research platform.Secondly, the thesis makes an intensive study of the performance of coherent integral in the non-ideal environment. The A/D conversion with arbitrary quantization bit rate and optimal AGC (Automation Gain Control) gain control setting methods are studied. Besides, the paper analysis cross-correlation interference, capturing frequency error and the influence of data bit inversion through different methods. These tasks provided theory basis for design a weak signal acquisition scheme.Third, research weak GPS signal acquisition technique. The part verify the differential coherent outputs have character of Gaussian Distribution. To improve the detection probility and parameter estimation, the thesis proposes a modified differential coherent weak signal capturing scheme using frequency error automatically real-time correction. Theoretical analysis and test proved that the method is superior to the traditional method in the performance of signal detection and frequency estimation accuracy can meet the demand for weak signal tracking.Finally, if the receiver is just in weak signal environment when it starts, the loop will keep in the state of loss lock, and can not find the data edge to implement weak signal tracking through lms update. In order to solve this problem, a carrier loop parameter estimation model based on SRUKF (Square Root Unscented Kalman Filtering) has been designed. On the premise of steady tracking, this scheme improved the traditional PLL’s error, and avoided the complexity of traditional EKF (Extended Kalman Filtering) algorithm in computing nonlinear equation. The optimal dynamic path planning algorithm has been applied to GPS-bit synchronization, and better results have been obtained than the current histogram method which is widely used. In the end, through combining SRUKF estimation technology with new bit synchronization method, the thesis designed serial and parallel schemes in the state of loop’s lost lock, and one of the two schemes can be chosen according to practical situation. The result of experiment and analysis confirmed the reasonableness of the two schemes.更多还原