Precise real-time navigation of the LEO satellite enhanced by BDS-3 PPP-B2b service

For the real-time navigation of LEO satellites based on GNSS, the achievable real-time orbit accuracy is generally limited by the quality of GNSS broadcast ephemeris. In this paper, the correction data released by the BDS-3 PPP-B2b service are introduced to correct the broadcast ephemeris of GPS and BDS-3 satellites, aiming to enhance the real-time orbit accuracy of LEO satellites. Experimental analysis reveals that the errors in the orbits and clock offsets of GPS and BDS-3 satellites are significantly reduced after applying PPP-B2b corrections. Considering that PPP-B2b corrections are only available within the Asia-Pacific region, centered around China, for those epochs where some of the tracked GPS/BDS-3 satellites have access to PPP-B2b corrections while others must rely solely on broadcast ephemerides, an improved measurement update strategy (IMUS) is proposed. This strategy excludes the observations of those GPS/BDS-3 satellites relying on broadcast ephemeris from the measurement update of real-time navigation filtering when the number of satellites available for PPP-B2b reaches a certain threshold. Real-time navigation experiments are conducted on the LT-1A satellite separately using single GPS L1/L2 and single BDS-3 B1C/B2a observations. The results demonstrate that, regardless of whether it is based on GPS or BDS-3, the improvement in real-time orbit accuracy achieved by IMUS after applying PPP-B2b corrections is slightly greater than that achieved by the conventional measure update strategy (CMUS), which treats all tracked satellites equally without differentiation. This indicates that the proposed IMUS could further enlarge the enhancement effect of PPP-B2b corrections on LEO real-time navigation. With the application of PPP-B2b corrections and IMUS, the real-time orbit accuracy of the LT-1A satellite, based on GPS and BDS-3, improves by more than 10% and 8%, respectively, over the entire orbital arc compared to using broadcast ephemeris alone. If only considering the arcs within the Asia-Pacific region, the improvement percentages rise to over 24% and 11% with GPS and BDS-3, respectively. This has fully demonstrated that the secure and free PPP-B2b corrections present an excellent option for achieving more accurate real-time navigation for these LEO satellites equipped with GPS/BDS-3 receivers.