Abstract
The Japanese Quasi-Zenith Satellite System (QZSS) has recently (October 2017) reached its first 4-satellite constellation. In this contribution, the standalone performance of this 4-satellite QZSS constellation is assessed by means of its triple-frequency (L1 + L2 + L5) real-time kinematic (RTK) integer ambiguity resolution and precise positioning capabilities. Our analyses are carried out for data collected in Perth, Australia, and include a study of the noise characteristics of the QZSS code and phase data, particularly concerning their precision, time correlation and multipath. Our results show that while the phase observations on different frequencies are of similar precision, the code observations on different frequencies show considerably different precisions and can be ordered, from high to low, as L5, L2 and L1. As to positioning and ambiguity resolution, we demonstrate that the Position Dilution Of Precision (PDOP) and the Ambiguity Dilution Of Precision (ADOP) exhibit complementary characteristics, both of which are important for predicting precise positioning capabilities. We show that despite the large PDOPs, the ADOPs are sufficiently small to indicate (almost) instantaneous successful ambiguity resolution. This is confirmed by our empirical data analyses, demonstrating that instantaneous ambiguity resolution is feasible, despite the relatively poor 4-satellite receiver-to-satellite positioning geometry over Australia, thus showing that already now centimeter-level stand-alone QZSS positioning is possible with the current 4-satellite constellation (February–March 2018).
Highlights
The Quasi-Zenith Satellite System (QZSS) is a Japanese satellite positioning system operated by Japan Aerospace Exploration Agency (JAXA)
Our evaluations showed that while the impact of atmospheric residuals on the noisy code observations can still be neglected, the differential tropospheric delays impact on the precise phase observations can reach significant levels compared to the phase precision
For the four-satellite QZSS constellation as a stand-alone system, we provided an initial assessment of L1 + L2 + L5 real-time kinematic (RTK) performance in the form of integer ambiguity resolution success rate and positioning accuracy
Summary
The Quasi-Zenith Satellite System (QZSS) is a Japanese satellite positioning system operated by Japan Aerospace Exploration Agency (JAXA). Nadarajah et al (2016) assessed multi-GNSS single-frequency real-time kinematic (RTK) positioning and attitude determination performance through combining QZSS L1/L5 signals with their counterparts from GPS, Galileo and IRNSS. With four operational QZSS satellites available in orbit, it is possible to carry out positioning based on standalone QZSS. In this contribution, using the signals from all the four. QZSS satellites on the three frequencies L1, L2 and L5, a first assessment of standalone QZSS ambiguity resolution performance and positioning accuracy is presented. Considering a short-baseline RTK model, the single-epoch ambiguity resolution performance is investigated based on the QZSS triple-frequency observations, through ambiguity dilution of precision (ADOP) and integer bootstrapped success rate.
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