5. Estimation Strategy and Accuracy Analysis of GNSS Real-Time Precise Satellite Clock Error

The rapid development of the Beidou navigation satellite system (BDS) accelerates the user demands for high-precision position and navigation. International GNSS Monitoring and Assessment System (iGMAS) built by China independently provides a good platform for GNSS high-precise real-time products. In this paper, the precise satellite clock error resolving model and strategy are studied, the feasibility of real-time precise clock error estimation on the premise of guarantee accuracy is researched, and the precision of real-time precise clock error using iGMAS site resources (built and planning) is verified. The results show: There is convergence process in the Un-difference mode to realize real-time clock estimation and the convergence RMS accuracy comparing to IGS is about 0.2 ns; Epoch single-difference model eliminates the continuous ambiguity, so there is no convergence process, the precision is better than 0.2 ns; On the whole, the precision of Un-difference mode and epoch single-difference model is quite; From the calculation efficiency and high-precision clock error application, the epoch single-difference model is adapt to GNSS real-time precise clock estimation because of less resolved parameters; Using iGMAS site resources (built and planning) recently, the precision of clock estimated by epoch single-difference model is about 0.2 ns.