Gps Signal Baseband Algorithm Design And Simulation Software Implementation

Since the beginning of the21st century, GPS (Global Positioning System)applications have been deep into all aspects of our daily lives, so GPS receiver productsare becoming more and more. Because the GPS signal simulator is able to supply thesimulation environment in researching and testing phases of the GPS receivers, it hasoccupied its own place in today’s GPS market.In this project, GPS signal simulator can be divided into the baseband part whichcontains DSP, FPGA and DAC module and RF part which contains the local oscillatormodule, the modulation module and the fading channel. This article will only introducethe algorithm and modeling process of DSP and FPGA part in detail.Firstly, this paper introduces the structure and modulation mode of the GPSsatellite navigation signal; then describes the modeling process of the DSP part, themajor contents include: introduce the differences between various time systems, thenconvert the UTC time to the GPS time which needed for the GPS system; calculate thesatellites’ position and determine their visibility by using of the GPS time and user’slocation information; in this paper, the source will simulate up to eight satellitenavigation signals for consideration of the system cost, so it will introduce an optimizedstar selection algorithm and test its performance; introduce GPS satellite navigationmessage’s format and framing process briefly; describe the delay correction process, andchoose one algorithmic method to calculate the Doppler frequency offset, which canreduce the amount of computation of system.Secondly, use MATLAB to build a software verification platform which not onlycan verifies the correctness of the carrier phase and code phase of the digital IF signalwhich generated by FPGA, but also can generates digital IF signal to verify theperformance of GPS software receiver.Finally, the paper summarizes all of work, and provides testing pattern, then pointsout a prospect of the future work.