Study On The Technology Of Online PPP Time Transfer

Time transfer is an important part for the time laboratory to establish and maintain time scale and provide time service. The establishment of International Atomic Time(TAI) scale requires to compare the atomic clocks distributed in laboratories around the world by using high-precision time transfer technology, then TAI can be obtained by combining the Lab clock data all over the word and appropriate corrections.In the high-precision time and frequency transfer, the lag time is required more and more short, and the real-time time transfer is important for the time keeping and time measurement. Based on the actual application requirements of Key Lab of Timefrequency Standard of the Chinese Academy of Sciences, first, the principles and processing methods of GPS Precise Point Positioning(PPP) high-precision time transfer technology are studied. And then online PPP time transfer technology and its algorithms are researched in detail, and the real-time high-precision time transfer system is realized based on online GPS PPP. The system consists of a client and a server. The user selects the observation data and sets the necessary parameters through the client, then starts the calculation, and the server can automatically match the IGS ephemeris and clock products and download available ephemeris and start to calculate time difference. At last, the GPS PPP time transfer results and other information(precise coordinates and tropospheric delay, etc) are returned to the client by the online PPP server. Then the user can quickly obtain high-precision time transfer result between two stations.The main contents are shown as follows:1) The mainly methods of time transfer are analyzed.2) The GPS PPP time transfer method and the effect of link error on time transfer is studied. Based on improving the precision of PPP time transfer, the research of realtime online GPS PPP time transfer method is carried out. A two-way Kalman estimation algorithm for PPP time transfer is proposed, which solves the one-way Kalman estimation has a greate influence on PPP time transfer error at convergence period. The impact of the IGS ultra rapid, rapid and final ephemeris and clock products on online PPP time transfer is analysed, which provides a reference for the user to select the ephemeris and clock products for PPP time transfer.3) The online GPS PPP system is desiged by using Client/Server(C/S) mode, which can automatically match the IGS ephemeris and clock products and provide online real-time GPS PPP high-precision time transfer service. The online PPP software can also be used to monitor the time scale automatically and provide a reference for time keeping.4) The system is tested with a real operating environment, then the function of each module and the run state of the system are validated. It is indicated that the function of the online PPP software is perfect, simple operation, stable running. The final results of the system are analyzed. Based on the comparison to the results of other similar softwares, the actual performance of online GPS PPP is validated. The result shows that the long-distance time transfer can be made quickly and easily by using online GPS PPP time transfer technology and its precision attains subnanosecond.