Accuracy Evaluation of Broadcast Ephemeris for BDS-2 and BDS-3

Abstract

The BDS-3 system was completed in July 2020 and began to provide services to users around the world. The inspection of its operation, especially the detailed evaluation of the orbit, clock error, TGD and other indicators, plays an important role in the subsequent positioning. This study conducts an investigation of the satellite broadcast ephemeris of the BDS-2 and BDS-3. The difference between the satellite orbit position calculated by the broadcast ephemeris and the position calculated by the precise ephemeris is used for analysis. First, the ephemeris form January 2020 to February 2020 are investigated. The results show that the broadcast ephemeris accuracy of the BDS-2 MEO satellite is the highest, while the GEO satellite broadcast ephemeris accuracy is the lowest. And their three-dimensional orbit difference is 3m and 7.5m, respectively. Second, the BDS-3 MEO satellite broadcast ephemeris accuracy is higher than the BDS-2, its three-dimensional orbit accuracy is about 0.39m, while its clock error is slightly smaller than the BDS-2. The result of ephemeris calculation is basically equivalent to the clock error of satellite-to-earth observation, which is related to the addition of the clock error of the inter-satellite link in the BDS-3. Finally, the clock error of the BDS-3 MEO satellite with the H clock is basically the same as that of the MEO satellite with the Rb clock.