Assessment of BDS-3 terrestrial reference frame realized by broadcast ephemeris: comparison with GPS/Galileo

The consistency of terrestrial reference frames (TRFs) realized by global navigation satellite system (GNSS) broadcast ephemerides is of great importance for multi-GNSS combined positioning. Based on BDS-3 broadcast ephemeris over 2020, we assess the coincidence level of BeiDou Coordinate System (BDCS) accessible via broadcast orbits with the newest international TRF (i.e., ITRF2014), which is also compared with the respective results of GPS and Galileo. The orbital realization of BDCS coincides with ITRF2014 at the level of 10 cm, although the broadcast orbits are constrained to BDCS only on the positions of regional stations in China. Obvious systematic errors in z-origin and orientation are found in BDS-3 broadcast orbital realized TRF, resulting in positioning errors up to 10 and 25 cm, respectively. By contrast, random errors are dominating the orbital realization of TRFs for Galileo and GPS, with an uncertainty of approximately 5 cm. The annual instability of z-origin for BDS-3 shows manufacturer- and orbit-plane-dependent characteristics, probably triggered by imperfect orbit models. A posterior model is proposed to calibrate the periodic errors in z-origin. Limited by the Monday update of earth orientation parameters prediction, the orientation stability of BDS-3 broadcast orbits degrade from Tuesday within one week, which may be amplified as no global geodetic constraints are applied. If these rotation errors are removed, the root-mean-square error of BDS-3 broadcast orbits can be reduced by 30–50% in the along and cross direction. In addition, we prove that the uncertainty of GNSS broadcast TRFs can be assessed by orbit comparison or comparisons between sets of station coordinates. Although the latter approach generally obtains larger uncertainty, results from these two approaches are at the same level.