Research On The Technologies Of Satellite-Ground Clock Synchronization In Spread Spectrum TT&C System

Accurate clock synchronization between satellite and ground tracking, telemetry and control (TT&C) station is of great significant for space missions such as the formation and networking of satellites, since it is the major means to synchronize satellites in a constellation. Based on the spread spectrum telemetry and control network being constructed in our country, the thesis studies the high precision satellite-ground clock synchronization technology. Main research results are showed as follow.1. According to the synchronization theory between satellite and TT&C station, a formula for measuring the time deviation between satellite and TT&C station is deduced. Then, a scheme for measuring the time deviation using the range acquisition channel is introduced, which is compatible to the spread spectrum TT&C system.2. The key technologies in the scheme, including tacking the pseudo code phase accurately and precise sampling of satellite clock, are studied. A fast pseudo code acquisition technique using FFT is introduced to capture the spread spectrum signal. A carrier aided delay locked loop (DLL) is used to estimate the pseudo code phase under severe Doppler modulation and generate the snapshot pulse for sampling satellite clock. 4-phase clock with phase offset 0°, 90°, 180°, 270°respectively, which are generated by the DCM (Digital Clock Manager) module of FPGA, are employed to measure the intervals between the satellite 1PPS clock signal and the snapshot pulse thus record the satellite clock.3. The proposed key technologies are implemented on the FPGA and DSP platform for a TT&C transponder with clock synchronization function, the design techniques are introduced as well.4. The synchronization error of the system is analyzed and validated by experiments based on the designed TT&C transponder for synchronization. The result shows that the satellite-ground clock synchronization scheme can measure the time deviation precisely, and the 1σerror is 6.6ns.Considering the technology discussed in this thesis has been realized in the TT&C transponder for synchronization and has gotten good performance, it has good utility value.