Chapter 8 Accuracy Analyses of Precise Orbit Determination and Timing for COMPASS/Beidou-2 4GEO/5IGSO/4MEO Constellation

摘要

Up to the end of October 2012, 14 COMPASS/Beidou-2 regional satellite navigation satellites are fully operational. Different with Global Positioning System (GPS), the space segment of COMPASS consists of Geostationary Earth Orbit (GEO) satellites, Inclined Geosynchronous Satellite Orbit (IGSO) satellites and Medium Earth Orbit (MEO) satellites, and navigation information is provided by monitoring stations limited in regional area. Besides, attitude control mode is different for each type of satellites. The predictability of satellite attitude will make broadcast ephemeris precisely predicted. In this study, satellite telemetry data are compared with nominal attitude to assess the accuracy of satellite attitude prediction. Experiments show that the accuracy is different for each type satellites, and overall prediction accuracy is better than 1°. The analyses of pseudo-range multipath noise for receivers from different manufacturers show that the random noise characteristics is significantly for the US and European manufacturers' receivers, and the magnitude is larger than domestic manufacturers', but strong daily repeatability of multipath noise characteristics is displayed for domestic receivers. The accuracy of precision orbit determination (OD) for COMPASS using regional and global monitoring stations data are compared to evaluate the impact of monitoring stations' distribution on the accuracy of satellite OD. Satellite Leaser Range (SLR) residuals are adopted to assess the satellite orbit accuracy in station line-of-sight direction. The results show that the accuracy of satellite orbit overlap is about 0.2, 1.2 and 0.6 m in R/T/N direction for regional monitor network, the accuracy for MEO overlap is slightly worse than two other type satellites, and the SLR residual is better than 1 m. The two-way satellite time frequency transfer (TWSTFT) observations are adopted to evaluate the accuracy of satellite clock error estimations. Experiments show that the standard deviation of satellite clock estimations solved by OD is about 1.4 ns. Global monitoring stations can increase the depth of coverage for MEO satellites, and the accuracy of clock estimations may be improved by about 0.6 ns. The observations from multi-constellation GNSS receiver are adopted to realize the system timing service. The results show that the stability of time system for COMPASS is consistent with GPS, the standard deviation of comparison for COMPASS and GPS precise timing is about 1.5 ns, the real time timing is about 3 ns.