Assessment and Analysis of the Four-Satellite QZSS Precise Point Positioning and the Integrated Data Processing With GPS

The Quasi-Zenith Satellite System (QZSS), which serves Japan and its surrounding areas, is a regional navigation satellite system developed by Japan Aerospace Exploration Agency. The system is now in a four-satellite constellation with preliminary standalone navigation and positioning capabilities. In this paper, the performance of QZSS-only precise point positioning (PPP) in both static and kinematic modes is initially evaluated using the datasets spanning 11 days from 11 tracking stations in Asia-Pacific regions and the final precise orbit and clock products from the analysis centers GFZ and WUM. For completeness, the GPS/QZSS integrated data processing with GFZ and WUM final products as well as the L6E real-time orbit and clock corrections is also analyzed. The results indicate that the static positioning accuracy of QZSS-only PPP is approximately 4, 2 and 15 cm in the east, north and up directions, respectively, and the static convergence time of QZSS-only PPP with WUM and GFZ products can be 75.2, 44.3 and 45.6 min, and 153.5, 201.6 and 162.8 min in the three directions, respectively. As for the QZSS-only kinematic PPP solutions, the re-convergence repeatedly occurs due to limited available satellites. To achieve more reliable solutions, the inter-system bias parameter in GPS/QZSS PPP processing is recommended to be estimated as random walk process or white noise process. The improvement of post-processed GPS/QZSS PPP over GPS-only case is marginal on position accuracies, but can be several minutes on convergence time. Compared with post-processed GPS/QZSS PPP, the real-time one achieves worse position accuracies but comparable convergence time.