Application of Improved GPS Satellite Clock Error Prediction Model in Real-Time Precise Point Positioning

High-precision real-time GNSS precision point positioning (PPP) is based on precision satellite clock error and orbit estimation and its service. The prediction accuracy of IGS ultra-rapid orbit products has reached the requirements of real-time PPP. Thus, the estimation of high-precision satellite clock error and real-time service (RTS) are important factors restricting the application of PPP. The current IGS RTS relies on good network communication, and the clock corrections is broadcast frequently. Once communication is interrupted, the satellite clock corrections cannot be obtained, and PPP users will not be able to perform high-precision positioning. Under this concern, the manuscript considers the stable and significant periodic characteristics of satellite atomic clock, a satellite clock error prediction model combined polynomial with multi-periodic harmonic-based function is proposed, analyzing the accuracy of different order polynomial plus multi-periodic harmonic-based function to model the clock error of different arc length, and uses the model coefficients to extrapolate the satellite clock corrections, therefore, high-precision real-time satellite clock error would be recovered with broadcast ephemeris satellite clock error. The experimental results indicate that the higher the polynomial order is, the higher the modeling accuracy of clock error is. Combining with harmonic-based function can further improve the accuracy of modeling performance, and the 8-th harmonic function is better than 4-th harmonic-based function. When the communication is interrupted for several minutes, the higher-order polynomial would be limited on the clock error extrapolation accuracy. The clock error extrapolation model using low-order polynomial plus harmonic function, and 0.5 h arc length saved satellite clock corrections, the extrapolated clock corrections can meet the millimeter level static positioning accuracy and centimeter level kinematic positioning accuracy, which providing a feasible reference scheme for the user to maintain stable and high-precision positioning when communication is suddenly interrupted for several minutes, and also be meaningful for the modeling of BDS satellite clock error and its real-time clock error service.