【作者】 苗剑峰；

【导师】 陈武； 刘建业；

【作者基本信息】 南京航空航天大学 ， 导航、制导与控制， 2009， 博士

【摘要】 GPS软件接收机以其内部结构开放性以及可编程的优点,使得用户仅需通过开发高性能的内部核心程序模块即可实现接收机的更新换代,从而改善系统的整体性能。软件接收机技术已经成为卫星定位系统现代化进程的重要组成部分。一方面,通过对GPS软件接收机的研究,能够充分了解并掌握接收机核心技术,为推动北斗二代全球定位系统以及惯性/卫星深组合系统的自主研发奠定一定的基础。另一方面,在建筑密度较高,信号接收环境复杂的区域,GPS接收机的稳定性和连续性受到严重限制。因此,深入研究接收机内部结构,开发新型的核心算法,以改善其鲁棒性以及定位精度成为迫切需要解决的问题。本文主要对GPS软件接收机的核心算法进行研究,对实现GPS软件接收机在特定环境中的应用提出一些新的方案。全文将理论研究与工程应用紧密结合,取得了满意的成果,对推广GPS接收机在复杂信号接收环境下的工程应用具有重要的参考意义。本文首先分析研究了多观测量GPS软件接收机的实现过程,基于正常载噪比信号的并行码空间捕获算法以及二阶环路的载波、C/A码跟踪通用解决方案。研究设计了软件接收机的整体结构和实现研究方案。接着,论文针对GPS弱信号捕获,研究了相干/非相干积分相结合的改进型块数据捕获算法。该算法分析了不同时长相干积分的频率搜索栅格配置,并提出一种易于工程实现的平方损耗补偿方法。以GPS基站辅助信息为基础,本文还提出一种导航数据位同步弱信号捕获算法,该方法采用基站辅助信息缩小载波频率的搜索范围。通过位同步技术消除信号中的导航数据位,采用长时间序列的相干积分代替非相干积分实现对弱信号的有效捕获。在GPS信号跟踪方面,本文对经典二阶锁相环的噪声进行了系统性建模分析。仿真实验表明,由于有色噪声的存在,二阶锁相环很难通过减小噪声带宽实现对信号的精确跟踪,信号跟踪环路的窄带性能受到制约。针对传统二阶环路存在的问题,本文研究了基于Kalman滤波器的载波、C/A码新型跟踪环路结构。文中分析了载波观测方程的线性化方案。通过解耦系统噪声,设计了载波跟踪环路的Kalman滤波器。为了提高整个载波、C/A码的闭环跟踪精度,文章分析了基于状态反馈的载波数控振荡器改进模型和C/A码多通道并行相关状态反馈模型。本文采用实测信号对该新型跟踪环路的有效性进行了验证。最后,本文针对在香港楼宇集群环境中GPS应用存在的现实问题,提出了一种抗差自适应GPS软件接收机方案。通过引入等价权矩阵和自适应控制因子,实时调整观测量和系统状态量在Kalman最优估值中的权重比,本文实现了在特定环境下对GPS信号的精确跟踪。本文通过分别与传统二阶环路和基于Kalman滤波器的GPS软件接收机对比,验证了抗差自适应GPS软件接收机的有效性。本文的研究工作,对于卫星定位系统接收机核心技术的进一步深入研究,及其在复杂环境下的工程应用具有重要的推进作用。更多还原

【Abstract】 GPS Software Receiver (GSR) is a Software Radio Technology based new receiver architecture. Because of the abilities of accessible to the inside architectures and reprogramebale to the kernel algorithms, GSR provides a powerful tool for GPS research. The users only need to develop high performance algorithm module to upgrade the whole system. The GSR has become one of the most important directions in GPS modernization. On one hand, the research on GSR provides opportunities to learn and master the key technology of receivers in satellites passive navigation system. These experiences will intensively promote the development of COMPASS satellite positioning system in our country. On the other hand, GPS signals are attenuated by complicated electromagnetic environment in some developed high-density cities, such as Hong Kong. In this area, the stability and continuity of GPS applications are seriously restricted. Therefore, it is necessary to intensively study the inside architecture of GPS receiver, and develop high performance kernel algorithm to enhance the system’s robustness and precision.This dissertation studies the following techniques: multiple-measurements GSR research based on normal signals, weak signals acquisition algorithms, Kalman filter based carrier/CA code tracking algorithms and the robust and adaptively GPS signals tracking loop. These techniques have important value for the application of GSR in complicated electromagnetic environment.Firstly, the design and application of multiple-measurements GSR based on normal signals are analyzed. Through presenting the characteristic of GPS signals’construction and the mechanism of Software Radios, the parallel code phase acquisition algorithm and the classic second order based Phase Lock Loop (PLL) and Delay Lock Loop (DLL) are described and analyzed. Then this dissertation proposed the multiple-measurems algorithms. Moreover, experiments demonstrate its validity in acquisition and tracking GPS signals.For weak signals acquisition, two methods are proposed. Without external assistance, an improved coherent/non-coherent block acquisition algorithm is presented. It analyzes the Doppler search grids configuration at different coherent data length, also a practical compensation algorithm for the square loss is proposed. However, there still exist some conflict problems in coherent/non-coherent integration. Facing this challenge, under assisted GPS system, the navigation bit synchronization based long sequence coherent weak signal acquisition method is proposed. It narrows down the Doppler search region using base station’s information, and eliminates the bit transfer by synchronizing navigation data bit. This new method brings more Signal to Noise Ratio and less time consuming.Strictly analysis, there are many colored jitter noises exist in traditional second order PLL tracking procedure except the white noise. The simulation experiments show that the colored jitter noise can hardly be reduced by simply narrow down the bandwidth. The estimated precision of PLL is seriously restricted, so high performance GPS signal tracking algorithm need to be developed.Kalman filter based GPS signals PLL and DLL in GSR is studied. A linearisation method for Arctan carrier phase discriminator is presented. Through decorrelating the system noise, a Kalman filter based PLL/DLL is built up to optimal estimate the signal tracking parameters. In order to refine the precision of the closed loop system, an advanced PLL state feed back control law and a parallel correlation feed back loop constructure are proposed. Two sets of real sampled data are adopted to demonstrate this new GPS signal tracking loop, the result shows that Kalman filter based PLL+DLL provide higher precision in carrier phase estimation, Doppler frequency estimation and CA code phase estimation.Precisely and continuously tracking GPS signals under complicated electromagnetic environment is important for many applications. At the end of this dissertation, an adaptive and robust Kalman filter based PLL+DLL solution is studied. This filter is able to improve phase tracking precision through automatically adjusting the mis-modelling of the dynamic process and reducing the effects of larger measurement errors under low signal-to-ratio environments. Compared with the traditional second order and standard Kalman filter based tracking loops, the robustness and efficiency of this new filter is demonstrated by real data testing experiments.The research work in this dissertation lays a firm foundation in the further development of GSR,and will improve the application of GSR more effectively in engineering under various environment.更多还原