Analysis of earth rotation parameters from GNSS navigation messages and its correlation with broadcast ephemeris rotation error

Due to error of earth rotation parameters (ERPs) adopted when generating the broadcast ephemeris, GNSS ephemeris is subject to orientation deficiencies shown as constellational orbit rotation. Moreover, significant rotation inconsistencies are indicated among different GNSS ephemerides as they utilize different ERPs. Based on the ERP datasets from modernized GNSS broadcast navigation messages, we investigate the correlation between ephemeris rotation error and broadcast ERPs for GPS and BDS-3 systems, and then explore ephemeris rotation correction using broadcast ERPs. Compared to the rotation parameters derived from orbit comparison, we demonstrate that the GPS and BDS-3 broadcast ephemeris rotation errors exhibit a prominent correlation with broadcast ERPs. The correlation coefficients between polar motion errors and X/Y-axis rotation parameters exceed 0.88 for GPS and 0.77 for BDS, whereas no significant correlation is found between the UT1-UTC error and the Z-axis rotation parameter. Thus, we propose a method to correct the orbital orientation inconsistencies between BDS-3 and GPS by aligning their broadcast ERPs, explicitly the polar motion. The GPS broadcast ERPs are utilized as a reference due to their higher precision and real-time availability. After rotation correction, BDS-3 broadcast ephemeris reveals an orbit precision improvement of approximately 3.0 and 1.0 cm in the along-track and cross-track components, respectively. Using this method, we also evaluate the impact of rotation errors on GPS and BDS-3 combined precise point positioning based on broadcast ephemerides. A remarkable positioning improvement is indicated from 8.9 cm to 6.9 cm in the north direction after BDS-3 ephemeris is corrected.
The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)