Research Of Acquisition And Tracking Algorithm Based On GNSS Software Receiver

Applications of the satellite navigation technology are increasingly important and extensive in the aspects of military, economic and people's lives in various countries, such as missile guidance, engineering measurement and control, ship navigation and vehicle navigation, and so on. Countries are also paying more attention to the research and development of the satellite navigation technology. Now, there are four main global navigation satellite system(GNSS) in the world: GPS(U.S.A.), GLONASS(Russia), GALILEO(European Union) and BD(China). The compatible development trend with the coexistence of multiple GNSS systems requires additional performances of the GNSS receiver. The GNSS software receiver is more flexible, more compatible and adaptable to receiving of weak signal, will take the place of the hardware receiver using ASIC and become the direction of the GNSS receiver development. In this paper, acquisition and tracking process of the GNSS software receiver are mainly studied.This paper is based on the project of civil BD-2 compatible receiver, study acquisition and tracking process in a GPS/BD-2 dual-mode software receiver structure. Firstly, the paper introduces global navigation satellite system's background and GNSS developments at home and abroad, illustrates the general structure of the GNSS software receiver which is based on the soft-defined radio, analyzes the function of its hardware and software component. Then the local C/A code and local carrier for acquisition are generated in the matlab simulation environment, and this paper analyzes and calculates the parameters'values of acquisition process, selects three commonly used acquisition algorithms from numerous acquisition algorithms, analyzes their advantages and disadvantages, calculates their algorithm speed and cost of implementation, then finds the parallel code phase acquisition algorithm which is most suitable for the GNSS software receiver. In order to decrease algorithm's computation and improve acquisition algorithm's speed, an approach to improve the parallel code phase acquisition algorithm is proposed. In the matlab simulation environment, use the improved parallel code phase acquisition algorithm to simulate the acquisition of the collected satellite data, implement automatic acquisition threshold setting, acquire the initial phase and carrier frequency of C/A code successfully, and have faster acquisition speed. Finally, this paper discusses the carrier tracking loop and code tracking loop for satellite navigation signal, combines the two loops to design a tracking loop which use the costas loop, simulates the tracking of the satellite data in the matlab simulation environment, and demodulates out the navigation message.Satellite navigation signal's acquisition and tracking are key technologies in the design of the GNSS software receiver. Pros and cons of acquisition and tracking algorithm decide the performances of the GNSS software receiver. This paper use the improved acquisition algorithm to acquire the initial phase and carrier frequency of satellite navigation signal, tracking process accurate these parameters and demodulate out the navigation message, and implement the acquisition and tracking process in the matlab simulation environment. The simulation results prove the correctness and effectiveness of this acquisition algorithm and tracking design.