The Design Of Local Synchronous Clock Based On GPS Timing

With the wide application of sensor network, the operation of the system requires ahighly accurate and stable clock. Meanwhile, the communication and the control amongthe distributed systems and the main system must meet with the requirement of clocksynchronization. This article aims at designing the local precise clock and clocksynchronization based on the GPS clock.In order to accomplish the development of local precise clock system and clocksynchronization, the main work is around the following aspects:First of all, this thesis begins with the research on the GPS timing and basebandalgorithm. This part of the thesis begins with the GPS signal acquisition and tracking.The phase of C/A code is gotten after tracking, which is used to generate the GPS time.Then, a deep research was done on the generation of GPS clock, analyzing the model ofionosphere delay error which is carried out after the acquisition and tracking. Theresearch of GPS laid the foundation for the research of local clock system.Secondly, the GPS clock is used to design the local precise clock on FPGA. TheGPS PPS is measured by pulse of OCXO with the time measurement module, gettingthe phase error between the GPS PPS and counted1s. The time measurement accuracycan reach200ps. The jitter of the phase error is eliminated after the execution ofKalman filter algorithm. The phase error is converted into analog voltage by the DAC.The analog voltage is used to control the output frequency of DCO. The feedback loopis used to lock the GPS PPS as a DPLL. When the loop is steadily locked, the real-timeclock module is able to output the local precise time.Finally, the local precision clock is applied in a distributed network-usersystem.The server machine uses the local precise clock as the standard clock. The clientmachine uses the NTP protocol to communicate with the server to obtain clocksynchronization. The filtering algorithm of clock skew is added on the NTP protocol toimprove clock synchronization accuracy and stability.