Acquisition And Tracking Algorithm For GPS Receiver And Its FPGA Design

Global Positioning System (GPS) is a new-generation satellite-based positioning system , which has a global, round-the-clock, continuous, high-precision navigating and positioning functions and can also provide precise location, speed and time for its users. Therefore, it is widely used in every walk of life. As we know, client parts of GPS system mainly consist of types of GPS receivers. Acquisition and tracking algorithms is not only a key technology but also technical difficulties in the GPS receiver . In this paper, the Matlab simulation and realization in Field Programmable Gates Array (FPGA) have been introduced in detail dealing with GPS signal acquisition and tracking system.At first, this paper introduces the structure of GPS signal and the principle of GPS receiver. The modulation mechanisms of GPS signal are explained in detail, especially the generation and the character of C/A code.Secondly, The basic theory of GPS signal acquisition is described. Serial Search Acquisition algorithm is advanced and researched deeply. A model of immediate frequency (IF) GPS Signal Simulator with Simulink software is established to explain the acquisition technology. In this platform, the feature of the algorithm is simulated and analyzed.Thirdly, The GPS signal tracking technology is presented in this paper. The structure of code tracking loop and carrier tracking loop has been researched. In the field of code tracking loop, the non- coherent early-late code delay loop which can separate carrier is used and studied. In the filed of carrier tracking, a costas loop which is insensitive for 180 phase shifts is adopted, meanwhile, a math model shows that how the GPS signal demodulates. At last, the code loop parameter is analyzed by Matlab and the result is matched.Finally, the GPS signal acquisition and tracking system is realized on FPGA by Quartus II. Based on the structure of the digital correlator, the modules of the system have been designed and implemented with hardware describe language of FPGA, from top document to important modules such as C/A module, NCO module.