Research On Synchronization System Of Police Micro Scale Base Station

With the rapid development of electronic communications,the police network system requires higher clock accuracy and stability for its micro base station.The local clock frequency source,Oven Controlled Crystal Oscillator,can steady output clock in the short term,however,the frequence will drift due to the changes of time,temperature or other factors.It is impossible to guarantee the accuracy of the output clock.While the1 PPS signal of the GPS receiver has a good frequency accuracy,its stability is poor in the short term.For the above reasons,a clock synchronization system based on taming and holding technique is designed in this thesis.In order to tame and calibrate the local clock frequency source with the 1PPS signal of the GPS tracked by digital phase-locked loop,its frequency drift characteristic is trained by the Automatic Oscillation Model.When the system in the case of the loss of GPS signal due to unexpected conditions in the short time,the frequency drift trend will be predicted by the model according to the training of the Automatic Oscillation Model in the early stage,and use the predictive value to continue adjusting the output of the local clock source until the GPS signal is restored.And then use this program to build a hardware platform and debug it,so that the synchronization system output accuracy can reach910-order of magnitude,and its stability can reach1110-order of magnitude.The advantages and the practical value of the program compared with other clock synchronization system is firstly described in this thesis.Then,the overall design of the clock synchronization system is introduced,including the design specifications,system design program,the principle and background of the corresponding technology as well as the algorithm.And then describes the specific implementation process based on the FPGA hardware platform of the system: In the tame mode,through the phase comparation,loop regulation,frequency synthesis and feedback frequency division of the digital phase locked loop to form a closed-loop system to output of the accurate clock.When the GPS signal is lost,the digital phase locked loop loses the reference input signal that causes its loop can not work,and the drift characteristics of the Oven Controlled Crystal Oscillator will be presented by the output.At this point the system switches its working condition to the hold mode,the Automatic Oscillation Model predicts the frequency control word by the mode for training the drift characteristicswith the Kalman filter algorithm in the early stage and continue to provide the correct frequency control word to the system so that the system can continue to output accurate and stable clock signal after the GPS signal loss.Finally,the test shows that when the GPS signal exists the system can output favourable clock signal by the tame mode,and can be maintained after its loss.The unique of this design is that when the GPS signal fails,the system can adjust the working state adaptively and keep the micro base station still work efficiently.This will be an important reference for the future research of the microcomputer base synchronization system.