Research And Realization Of The Real-time Regeneration Simulation And High-precision Time-interval Measurement

The satellite navigation industry is developing rapidly with the development of science and technology,and the demand for GPS receivers is increasing as a very important positioning and timing terminal in the satellite navigation industry.GPS simulator can effectively help to verify the performance of GPS receivers and is an important tool for analyzing the performance of GPS receivers,so the research and implementation of GPS simulator is of great engineering significance.In this thesis,the real-time regeneration simulator of GPS L1 signals is designed using FPGA+ARM platform,and the two main functions of regeneration and time synchronization of GPS L1 signals are accomplished,and the main research contents are as follows:(1)According to the GPS ICD file,this thesis investigates the signal regime of GPS L1 in depth.The capture and tracking of GPS satellite signals are completed,and the current positioning results are calculated.And based on the GPS receiver,it continues to design the regenerative simulator of GPS L1 signal.This thesis uses DDS technology to generate Carrier Signal and C/A code in real time,and modulates the signal together with the Navigation Message extracted by ARM to complete the regeneration of GPS L1 signal.The test results show that the GPS receiver designed in this thesis can successfully capture and track the GPS signal,and the calculated positioning result is better than 3 m.The simulated regenerated signal generated by the regenerative simulator has a positioning result better than 5 m.(2)For the measurement requirements of the time interval between local 1PPS and standard 1PPS,first use the carry structure inside the FPGA to complete the delay unit interpolation,and measure the time interval less than the system clock.At the same time,it is combined with pulse counting method to solve the problem of small measurement range of delay cell interpolation method.Finally,the code density test with nonlinear calibration is used to solve the problem of uneven delay cell size in the delay interpolation method.The actual test shows that the method can achieve high precision measurement of the time interval between local 1PPS and standard 1PPS,providing the stable and high-precision time interval measurement values required for time synchronization.(3)This thesis uses a combination of high-precision time interval measurement technology and crystal taming technology to complete the time synchronization between the local clock and the GPS satellite clock.The time interval is converted to voltage control value by FPGA,and then the voltage control value is converted to voltage control voltage by DAC7512 to control the local crystal.The test results show that the accuracy of the synchronized 1PPS obtained by this method is better than 700 ps compared with the standard1 PPS,and the local crystal can maintain a stable state for a long time.