Design And Implementation Of Beidou Global Multi-Frequency Satellite Signal Simulation System

With the completion of the global network of Beidou-3 satellites,the application of Beidou navigation has become more and more extensive,and the market has put forward the demand of multi-frequency points for the Beidou navigation satellite receiver.Beidou global multi-frequency satellite signal simulation system is a device that can simulate Beidou multi-frequency satellite navigation signals.Users can configure simulation scenarios on the host computer to test the performance of Beidou multi-frequency navigation receivers in complex environments indoors.Therefore,the Beidou global multi-frequency satellite signal simulation system is of great significance for the research of high-performance Beidou multi-frequency navigation receivers.Based on the research of satellite signal simulator at home and abroad,this paper designs and implements the Beidou global multi-frequency satellite signal simulation system.The main tasks are as follows:(1)Based on the basic principle of Bei Dou satellite navigation signals,three pseudo-random sequences of m,Gold and Weil are studied in depth and the correlation characteristics are simulated,and the signal systems of Bei Dou B1 I,B1C and B2 a are analyzed;(2)In view of the large difference between the real satellite signal and the simulated satellite signal,the satellite signal delay technology,real-time calculation technology,and high-precision digital signal synthesis technology are deeply studied,and mathematical models such as space propagation delay and earth rotation delay are constructed.A Doppler frequency shift simulation method based on DDS technology is designed,which improved the authenticity of the simulated satellite signal and realizes the high-precision simulation of the satellite signal;(3)Aiming at the problem of large output frequency error and low stability of the oven controlled crystal oscillator,a crystal oscillator taming method based on FPGA is designed.The method uses the clock signal output by the oven controlled crystal oscillator as the source clock of the FPGA,measures the time interval between the standard second pulse signal of the Beidou timing receiver and the second pulse signal generated inside the FPGA,and performs voltage control according to the measurement difference.After several times of voltage control,the oven controlled crystal oscillator is tamed,and the stability and accuracy of the oven controlled crystal oscillator are greatly improved;(4)This paper designs the overall scheme of the Beidou global multi-frequency satellite signal simulation system,designs the circuit of each module in the system,and realizes the function of each module.The functions of visible star calculation,phase calculation,frequency control word calculation,navigation message writing and data interaction are realized by DSP,and the functions of pseudocode generation,carrier generation and signal modulation are realized by FPGA,and digital intermediate frequency signal is generated.The system finally realizes the simulation of Beidou B1 I,B1C and B2 a satellite navigation signals;(5)The test platform of Beidou global multi frequency point satellite simulation system is designed,and the IF signal,signal acquisition,static positioning,dynamic positioning,signal power control and operation power consumption of the signal simulation system are tested and analyzed.The test results show that the signal simulated by the system is correct,the accuracy of static simulation and dynamic simulation is better than 3m,the system power control is accurate,has good signal power control ability,and the operation power consumption is low,only 5.2W.All the performances of the Beidou global multi frequency satellite simulation system designed in this paper meet the design requirements.