Analysis of the Contributions of ISL to the Precise Orbit Determination of BDS-3 Satellites

The 3rd generation of the Chinese Beidou Navigation Satellite System (BDS-3) is the first GNSS deployed with Inter-Satellite Link (ISL) payloads within the whole constellation. A series of Precise Orbit Determination (POD) experiments have been conducted to investigate the contributions of ISL to the orbits of BDS-3 satellites in cases of different ground tracking coverage. Results show that the improvement in orbit precisions is most significant when only a regional ground network is available. When integrating with ISL observations, the single-day solution from a regional network is good enough to meet the performance requirement. For a globally distributed sparse tracking network, additional ISL measurements also better the orbit precision by 51% from the point of view of orbit Day Boundary Discontinuity (DBD) 1D RMS, the average of which decreases from 8.22 cm to 4.05 cm. Surprisingly, benefits of integrating ISL with ground tracking are still visible even with a denser global network. In this case, an average reduction of ~28% in orbit DBD 1D RMS can be observed after integrating ISL measurements, decreasing from 5.12 cm to 3.59 cm. In addition to range measurements, the profit of ISL clock measurements is also explored. It shows that combining ISL clock measurements with ground tracking reduces the orbit 1D RMS by 19%. And the orbit radial component exhibits the most benefits from additional ISL clock observations, with a DBD RMS reduction from 4.02 cm to 2.44 cm. Results from this research indicate the great potential of the ISL of BDS-3, which can not only guarantee the performance of standard services under unfavorable conditions but also improve the high-precision service capability of BDS-3.