An improved GNSS orbit extrapolation method for real-time PPP users

Precise orbits are required for real-time precise point positioning (PPP). Nowadays, real-time orbit corrections with respect to broadcast ephemerides are normally transmitted to the users with an update interval between 5 and 60 s. Due to time latency, users extrapolate to calculate the satellite positions at the needed epochs. However, since the original satellite orbits change rapidly, users have to extrapolate the orbit corrections. Nevertheless, the correction accuracy of GLONASS decreases faster over time than GPS, Galileo, and Beidou, in addition, the calculation efficiency of the satellite position seems not perfect. In this study, an improved polynomial fitting method was proposed to improve the orbit extrapolation ability of polynomial by introducing the satellite velocities and accelerations into the fitting model. Experimental results of GPS, GLONASS, Galileo, and Beidou show that the accuracy of extrapolated orbits could be within a few centimeters when the time latency is approximate 10 min and 40 min for eclipsing and non-eclipsing satellites, respectively. And these results also have been confirmed through the PPP experiments from eight global distribution stations with multi-GNSS observation data on 2019-1-1. Thus, by utilizing the new method, it is possible to directly extrapolate the original satellite orbits, which suggests that the application of real-time precise orbits can be independent of broadcast ephemeris. (C) 2022 Published by Elsevier B.V. on behalf of COSPAR.