Multi-GNSS broadcast ephemeris errors assessment and weight determination of different constellations for SPP

Broadcast ephemeris plays an important role in positioning, navigation, and timing (PNT) services. With the rise of new constellations of Galileo and BDS3, satellite services are moving towards multi-GNSS fusion. Therefore, systematic evaluation of the multi-GNSS broadcast ephemeris and determination of the impact of ranging errors of different constellations in the multi-GNSS standard single point positioning (SPP) are necessary. In the contribution, the 120-day broadcast ephemeris from 1 January 2022 to 30 April 2022 and precise ephemeris provided by three analysis centers (German Research Center for Geosciences (GFZ), European Centre for Orbital Determination (CODE), and Wuhan University (WHU)) are used to analyze the orbits, clock offsets, and signal-in-space ranging error (SISRE) for GPS, GLONASS, Galileo, BDS2, BDS3, and QZSS (G, R, E, C2, C3, and J). The ephemeris analysis shows that the assessments using the precise ephemeris from the three analysis centers are consistent. The average daily SISREs for different constellations evaluated by GFZ products are 0.16 ± 0.07 m (E), 0.38 ± 0.19 m (J), 0.46 ± 0.19 m (C3), 0.50 ± 0.17 m (G), 1.30 ± 0.27 m (C2), and 2.40 ± 0.73 m (R), respectively. In addition, we propose a weight determination method using joint weighting of SISREs and satellite elevation angle (Ele + SIS) based on the analysis. One consecutive week of observations tracked by 23 permanent reference stations is selected, and a comparison experiment is conducted using the classical elevation angle weighting scheme (Ele) and the Ele + SIS scheme in dynamic SPP to verify the feasibility. Compared to the classic Ele scheme, the positioning accuracy of GREC2C3J combined SPP using the Ele + SIS scheme is improved by 34.2 % in the 3D direction, and the 95th percentile of the positioning errors is reduced by 31.5 %. The same dynamic SPP test using data after one year of modeling the Ele + SIS weighting scheme shows that the enhancement of the positioning accuracy of the Ele + SIS scheme decreases by only 3.7 %, which demonstrates that the Ele + SIS scheme can be used in real-time application.