Improving QZSS Precise Orbit Determination using Space-based and Ground-based Observations

The Quasi-Zenith Satellite System (QZSS) is a Japanese navigation satellite system that provides position, navigation and timing service, as well as augmentation services, to users in the Asia-Pacific region. Since the QZSS consists of satellites in inclined geosynchronous orbit and geostationary orbit, the changes in the observation geometry are smaller than those of other global navigation satellite systems (GNSSs) in medium Earth orbit such as global positioning satellites (GPSs). This feature is suitable for providing navigation signals to users in a specific region with a limited number of satellites. However, it is known that the QZSS orbit accuracy, especially in the along-track and cross-track directions, tends to have a large uncertainty with a limited number of ground-based observations alone as compared to other GNSSs. Therefore, the use of observation data with different sensitivity from ground-based L-band observations for QZSS precise orbit determination (POD) is beneficial to improve the accuracy of the QZSS orbit and clock estimates. This paper proposes an extended QZS system with low-Earth-orbit (LEO) satellites for observing QZSS L-band signals for future precise positioning services and reports the contribution of various types of LEO constellations to QZSS orbit and clock accuracy.