GNSS/RNSS Integrated PPP Time Transfer: Performance with Almost Fully Deployed Multiple Constellations and a Priori ISB Constraints Considering Satellite Clock Datums

Currently, the space segment of all five satellite systems capable providing precise time transfer services, namely BDS (including BDS-3 and BDS-2), GPS, GLONASS, Galileo, Quasi-Zenith Satellite System (QZSS), has almost been fully deployed, which will definitely benefit with satellite-based point positioning (PPP) technology. This study focuses on latest performance BDS/GPS/GLONASS/Galileo/QZSS five-system combined PPP transfer. The accuracy integrated was 0.061 ns, frequency stability 1.24 × 10−13, 2.28 10−14, 8.74 10−15 at an average 102, 103, 104 s, respectively, significantly outperforms single-system cases. We also verified outstanding locations limited sky view. In addition, a method is proposed to mitigate day-boundary jumps inter-system bias (ISB) estimates by considering difference in clock datums between two adjacent days. After applying priori ISB constraints, can be improved 37.9–51.6%, 14.8–21.6%, 5.3–7.6% 20.0–29.6% three times, respectively.