The improvement of BDS Observation Geometry with LEO constellations in Orbit Determination

Abstract

The ability of low earth orbit (LEO) satellites with space-borne global navigation satellite system (GNSS) to improve the accuracy of GNSS satellite orbit determinations has been demonstrated. In this paper, the ability of LEO satellites to improve the observation geometry in the process of the determination of BeiDou Navigation Satellite System (BDS) satellite orbits is the focus. First, the visible BDS satellite model with ground stations and LEO satellites is derived, and the definition of the position dilution of precision (PDOP) is proposed for assessing the observation geometries of BDS satellite orbit determination. Then, the observation geometry of BDS geosynchronous earth orbit (GEO), inclined geosynchronous satellite orbit (IGSO) and medium earth orbit (MEO) satellites are individually analysed by regional ground stations. By designing LEO satellites with different inclinations, altitudes and right ascensions of ascending nodes (RAANs), the PDOP improvements achieved through combinations with different orbital LEO satellites are calculated. Finally, the PDOP improvements caused by incorporating different numbers of LEO constellations are compared. The results show that LEO satellites can improve the observation geometries of BDS satellites, especially when the monitoring of observation configurations by only ground stations is very poor. The PDOP improvements of BDS GEO satellites caused by LEO satellites are more significant than those of IGSO or MEO satellites; i.e., the improvement percentage of C04 is better than 60%. Generally, LEO satellites with high altitudes are more suitable for PDOP improvements to BDS satellites than are LEO satellites with low altitudes; moreover, LEO satellites with high inclinations are more suitable for PDOP improvements to BDS GEO satellites than LEO satellites with low inclinations are. The influence of the RAAN on the PDOP improvements of IGSO and MEO satellites is relatively larger than its influence on the PDOP improvement of GEO satellites. The PDOP improvement percentage and stability of BDS satellites, especially GEO satellites, increase with the number of incorporated LEO satellites. When incorporating the LEO constellation 16/4/1:1000 km, 70°, the maximum improvements of the GEO and IGSO satellites are above 84% and 77%. The improvements of the GEO, IGSO and MEO satellites are above 81%, 42% and 58% respectively.