Research On High Dynamic GPS Software Receiver Method

The 21st century has witnessed extensive applications of the global positioning system (GPS):for civilian products, almost all smart phones are equipped with GPS modules and all high-end vehicles provide real-time satellite navigation; for military purposes, GPS devices can also be found on fighter aircrafts, space shuttles, missiles and other advanced equipment. With the increasing development of technology, the application areas of GPS has been constantly expanding, including GPS receivers in high dynamic environments to satisfy ever-increasing demands. In the high dynamic environment, high-speed movement of GPS receivers results in large Doppler shift on their signal carrier frequency, which leads to the required quality of service hardly be met. To address this problem, this paper investigates GPS receivers in the high dynamic environment, analyzing their signal characteristics and processing progress.First of all, we review current research results of the GPS receiver, introduce the three major components of GPS systems and describe the composition and characteristics of GPS signals, based on which the principles of signal acquisition, tracking and positioning solution are elaborated.Next, in order to better study the processing methods of high dynamic GPS signals, we design a software to simulate the features of high dynamic GSP signal source, which is able to generate GPS IF signals given the predefined carrier movement model. In the third chapter, we provide details about the software’s principles and simulation process. Besides, we also analyze the differences between GPS signals in high dynamic and common scenarios as well as various factors that influence these distinctions. Then, by analyzing visible stars and their ephemeris data using satellite ephemeris, we obtain the desired analog signal source.After acquiring the above simulated high dynamic GPS signals, the acquisition and tracking algorithms for high dynamic environments are investigated. Simulation results indicate that the XFAST-based adaptive filter acquisition algorithm is able to capture signals quickly and accurately.Finally, using the rough estimations of the carrier frequency and the phase of pseudo-code gained in the capturing phase as the input of the tracking loop, we further study signal tracking algorithms. On the basis of GPS signals’tracking principle, influence and performance, we design second-order and third-order PLLs and add a nonlinear Kalman filter to enhance estimate accuracy for the tracking loop in high dynamic cases. Simulations show that the third-order PLL aided by a Kalman filter can achieve higher level of sensitivity.In this paper, we analyze high dynamic GPS signals through simulations and investigate the corresponding tracking process, which lays an initial foundation for the further optimization of GPS receivers in high dynamic environment.