Simulation Of GPS Satellite Navigation Signal Abnormalities In The Baseband Section

Along with the booming development of satellite navigation cause and large advances in technology of navigation application field, the demand of improving satellite navigation service quality monitoring system of our country is becoming stronger and stronger. At present, our country's satellite navigation service quality monitoring system is not perfect, the navigation service quality monitoring ability is weak, either with no ability of interference detection and alarm. So the study of abnormal condition in navigation signal is necessarily in pressing demand of our country's navigation industry. In this paper, the research results can provide technical support for the research of abnormal navigation signal, and also play a great role in promoting the development of the satellite navigation system.The accuracy of the navigation system positioning largely depends on the quality of navigation satellite signal, when the navigation signal's transmission in space is disturbed or the satellite's hardware equipment is in abnormal work mode,the satellite signal waveform distortion will happen. These anomalies can drop the positioning precision of the user receiver,worsely this may make users lose the ability of positioning. Through investigation and analysis, the cables, star clock, carrier, pseudo code, I/Q branch orthogonality, out-of-band rejection, in-band stray, equivalent isotropically radiated power will appear abnormal situation in the process of the satellite navigation signal from producing to receiving. This paper focus on the study and discussion of baseband pseudo-code anomaly (TMA?TMB?TMC) in mode of GPS code,and the instructions and analysis of exception principle and hardware implementation.Firstly, this paper introduces the development status of navigation signal simulator and the research status of abnormal navigation signal, makes the significance of navigation signal's abnormal situation research clear. Secondly, the paper expounds the working principle of normal navigation signal simulation and the main process of hardware implementation.It introduces the working principle of abnormal navigation signal simulation system, working process and working mode later. Thirdly, this paper analyzes the mechanism of abnormal navigation baseband signal, and it has carried various abnormal situations on the Matlab simulation analysis, also it tells the method of how to achieve abnormal simulations on the FPGA. Finally, in this paper, the results of simulation implementation have been showed and discussed.This topic's research task comes from the national 863 project in the subject 1 "Overall multi-mode navigation service quality monitoring and simulation test system development and demonstration",the purpose is to build simulation environment for multi-mode navigation abnormal signals, and provides necessary test conditions for multiple mode navigation signal service quality monitoring. This paper's main work is to proceed abnormal simulation on the basis of the existing normal navigation signals.Firstly, It completes the algorithm's study and simulation combining with the working characteristics of the FPGA and the Verilog language programming features on Matlab;then, it realizes abnormal signal simulation algorithm and functional simulation using Verilog language programming in the Quartus ? software platform;next, it downloads the program to the FPGA chip for debugging.In the end, this paper realizes the simulation of navigation signal pseudo-code abnormality(TMA, TMB, TMC) and I/Q branch's orthogonality abnormality under the mode of GPS.