Aspects of Using the QZSS Satellite in the Trimble CenterPointTM RTXTM Service: QZSS Orbit and Clock Accuracy, RTX Positioning Performance Improvements

Mid of 2011 Trimble introduced the CenterPoint RTX real-time positioning service providing cm-accurate positions for real-time applications. This service targets applications in the precision markets like Precision Agriculture, Survey and Construction, and relies on the generation of precise orbit and clock information for GPS and GLONASS satellites in real-time. The CenterPoint RTX satellite corrections are generated with data from Trimble’s world-wide tracking network, consisting of approximately 100 globally distributed reference stations. A subset of currently 25 stations in the Asia-Pacific region is able to track the QZSS satellite. Unlike GPS and GLONASS, which were supported by CenterPoint RTX from the very beginning, the inclined geostationary orbit of the QZSS satellite causes some additional challenges on the orbit and clock estimation process. The most relevant aspects are the MEO satellite’s higher orbit, the geometry of the orbit track, and the tracking network available in the region of interest. To achieve the biggest benefit from QZSS in a high precision positioning solution, its orbit has to be in the same coordinate frame as the GPS or GLONASS orbits. In addition to that the satellite clocks have to be commonly corrected to the corresponding time system. As QZSS has a similar signal structure as GPS, it would be intuitive to treat QZSS like an additional GPS satellite. However this is unfortunately not possible without any further ado, since all satellites of the current GPS constellation transmit L1P, L1C and L2P signals, while QZSS does not provide either L1P or L2P. This paper describes the technical aspects of the inclusion of the QZSS satellite in the orbit and clock estimation process and GNSS receiver positioning engine, as well as the respective improvement in the overall system quality caused by the use of the additional QZSS satellite. Rover performance analyses will also be shown to demonstrate the effect of the QZSS satellite on the convergence of the RTX positioning solution and the final accuracy achieved on several locations in the Asia-Pacific region. The paper describes aspects of the methodology applied in the multi-system orbit and clock estimation and validation procedure. Achieved orbit and clock accuracies over a longer time span are demonstrated and discussed. The orbit accuracy is estimated to be better than 10 cm. The clock accuracy is estimated to be better than 2 cm.