Application and accuracy analysis of raw one way inter-satellite link observations of BDS-3 full operational constellation

The Ka-band Inter-Satellite Links (ISL) has been introduced as an innovative measurement technique for orbit determination (OD) and time synchronization (TS) of the global BeiDou Navigation Satellite System (BDS-3), complementing traditional L-band ground-satellite tracking. For the first time, OD and TS have been conducted for the entire full-operational constellation of BDS-3 using raw one-way ISL data. The normal equation (NEQ) accumulation technique is employed to estimate critical parameters, such as the ISL hardware delays (Ka-biases), to derive long-term average solutions. With the support of ISL, an orbital accuracy of 8.0 cm for Medium Earth Orbits (MEOs), 11.6 cm for Inclined Geosynchronous Orbits (IGSOs), and 24.0 cm for Geostationary Orbits (GEO) can be achieved using a ground network consisting of 20 stations. An extended observation model was developed for ISL heterogeneous data at both ends due to the presence of a specialized GEO satellite C61 which exclusively provides ISL data without broadcasting civil L-band signals. Subsequently, the OD and TS capabilities were validated using one-way ISL for GEO C61, resulting in an OD accuracy of approximately 3.7 cm in the radial direction, 7.9 cm in the normal direction, 27.7 cm in the tangential direction, and 29.0 cm in 3-D position; with a TS accuracy of around 0.1 ns. In most cases, one-way ISL transmission and reception Ka-biases remain stable over considerable periods, achieving an accuracy of 0.2 ns. However, apparent abnormal jumps in Ka-bias were observed, which were determined to be sudden changes in L-band hardware delay from navigation signals rather than jumps in ISL hardware delay itself. This finding marks the distinction between L-band hardware delay jumps and atomic clock jumps for navigation satellites. Additionally, the residuals of one-way ISLs exhibit periodic terms. Investigations indicate that these residuals vary with the antenna azimuth and elevation angles of each link and are specific to individual satellites. This variation may be attributed to small deviations in the on-board ISL receivers or antennas. This discovery is valuable for modeling ISL observations.