Systematic Error Estimation and Accuracy Evaluation for Two-Way Satellite Time and Frequency Transfer Observing Data

The time delay could hardly be calibrated accurately for the two-way satellite time and frequency transfer equipment. Therefore the time delay error and its secular drift would not only restrict the time synchronization accuracy, but also restrict the broadcast parameters accuracy for the satellite navigation system. In order to solve this problem in the self-sending-self-receiving observation, we bring forward two systematic error estimation methods, named SLR co-location comparison method and combined precise orbit determination (POD) method. We also introduce a across sending and receiving systematic error estimation method based on the restriction from the station clock offsets estimated by multiple precise orbit determination (MPOD). And the three-station circle error and clock offset consistency are introduced to evaluate the systematic error estimation accuracy. Tests are carried out with the Beidou satellite navigation system (BDS) real data. Results show that the accuracy of the SLR co-location comparison method is better than 0.3 ns, while the combined POD method better than 0.5 ns for the self-sending-self-receiving observation. And for the across sending and receiving systematic error, the estimation accuracy is better than 0.4 ns, with circle errors among three stations better than 0.1 ns. The station clock offset consistency from two different C-band antennas is better than 0.3 ns. The high accuracy time synchronization can be achieved among different stations in the satellite navigation system, and two different C-band equipment could backup with each other.