Design And Implementation Of Beidou Navigation Timing Terminal Module

The accuracy of time reference is required to be higher and higher in modern electronic systems.In view of this demand,combined with Beidou navigation system and time synchronization technology,a high-precision timing terminal module is designed in this thesis.The Beidou navigation timing terminal module has high practical value for its high precision and reliable function.Beidou one-way time service(RNSS)technology is adopted in the time service terminal module.This module calibrates the local time to synchronize with the satellite navigation system time.In addition to satellite time service,the function of synchronous calibration with external 10 MHz frequency standard and IRIG-B code signal included in the timing module.The time service module outputs various types of time and frequency,which can meet the needs of different systems.According to the functional requirements of the modules,the overall design divides the functional units reasonably.Modular design is adopted in specific implementation scheme.The main work completed is as follows:1.The satellite signal receiving unit uses lea-m8 t chip as the satellite signal receiver.Low noise amplifier and SAW filter enhance the receiving antenna gain larger than double of comparable modules and resolve the problem of poor signal receiving ability in bad environment.2.The function of time code unit circuit is complex,and multiple sequential circuits run synchronously.The FPGA is adopted to solve these problems.The area of unit circuit is greatly reduced,which is 75% smaller than that of discrete circuit,with all functions working well.3.In the synchronous calibration process of time keeping module,the tiny phase difference cannot be measured accurately,which affects the time accuracy.In this design,the time amplitude expansion method was used to measure the small time interval,and the measurement accuracy was improved.The error caused by the calibration process is effectively eliminated,and the calibration accuracy of the module was one or two order of magnitude higher.4.For the calibration error generated from the noise in Beidou signal,the Kalman filtering algorithm was used to smooth the calibration data and adjust the synchronous calibration voltage to the needs.This method effectively reduced time error of the module less than 50 ps reaching the domestic leading level.The signal stability and synchronization accuracy of the designed time service terminal module are significantly improved compared with similar modules The results show that the frequency stability of 10 MHz signal is better than 1 × 10-9,the short-term stability is less than 4 × 10-13 / s,the synchronization accuracy of B code is less than 25 ns,the synchronization accuracy of 1PPS is less than 3 ns,and the time synchronization accuracy of NTP is better than 0.1ms.According to the test results,the stability of 10 MHz signal was 2 times higher,the synchronization accuracy of B code is 4 times higher,and the synchronization accuracy of 1PPS and NTP is 10 times higher than that of similar modules.The design goal is achieved.