Design And Implementation Of The Two-way Time Synchronization Baseband Based On TDD System

Time synchronization between satellite and ground refers to the satellite and the ground station to establish a link for time-frequency transmission to eliminate the clock difference between the satellite and the ground station,so that the time reference between satellite and ground to be consistent.Time synchronization between satellite and ground is one of the key technologies in satellite navigation system and the four major systems in the world have their own solutions.Compared to the UHF band used by GPS Block-IIR series satellites,the Ka-band used by Beidou system can provide higher ranging accuracy and information transmission rate.At present,Beidou system is carrying out inter-satellite time synchronization and time synchronization between satellite and ground based on Ka-band.This thesis topic from Western Light of The Chinese Academy of Sciences Project named “research on the methods of time synchronization between satellite and ground based on Ka link”.Aiming to the work pattern of the Ka-band inter-satellite link,the working system and the movement characteristics of the three different satellites of GEO,IGSO and MEO in the Beidou navigation system,the thesis studies the two-way time synchronous baseband based on TDD system.In this thesis,we design and implement a two-way time synchronization between satellite and ground hardware platform based on FPGA+DSP architecture.Then focus on the design and implementation work of two-way time synchronous baseband based on TDD system.The method of bidirectional ranging and clock difference calculation based on analog dynamic signals is studied.The main contents of the thesis are as follow:1.The bidirectional time synchronization method based on TDD system is studied.To design hardware simulation platform for bidirectional time synchronization.The system of the ranging signal is defined,in particular the frame format of the data and the TDD-based operating sequence.2.Based on the FPGA+DSP architecture,to achieve the TDD signal generation,acquisition,tracking,synchronization,pseudorange extraction and clock error calculation.3.Aiming at the motion characteristics of GEO,IGSO and MEO satellites of Beidou navigation system,the dynamic simulation of Doppler frequency anddistance between satellite and ground is designed and completed.4.Aiming at the characteristics of satellite dynamics,the acquisition and tracking algorithms are optimized to improve the acquisition speed and dynamic tracking ability.In order to solve the problem of inconsistency in the measurement time of TDD mode,the method of calculating the clock difference based on Pseudorange Epoch Imputation are achieved.This thesis uses Altera Stratix?series FPGA and TI C6000 series DSP to build the hardware platform and to achieve Bidirectional time synchronization based on TDD structure.The test results show that the system achieves the ranging accuracy of 0.6544 ns and the ranging stability of 0.2262 ns on the static mode,and the statistical mean of the clock error is-1.0133 ns,and the measurement stability of the clock difference is 0.1854 ns.On the dynamic mode,the statistical mean of the clock error is-2.6935 ns,and the measurement stability of the clock difference is 0.4421 ns.