Abstract
Rapid ambiguity resolution in precise point positioning (PPP-AR) has constantly been a difficulty preventing efficient initializations of user solutions. A successful initialization normally requires a few tens of minutes if only GPS data are processed, but can be accelerated significantly by integrating a second GNSS to both enhance the satellite geometry for faster ambiguity convergence and double the ambiguity quantity for higher partial-AR success rates. However, each GNSS asks for its own reference satellite to form resolvable ambiguities, namely intra-system PPP-AR. We propose to estimate station-specific inter-system phase biases (ISPBs) and then form resolvable ambiguities between, instead of within, GNSS (i.e., inter-system PPP-AR) aiming at providing one more ambiguity candidate for more efficient partial AR. We use 24 days of 5-s GPS/BeiDou data from 47 stations in China spanning an area of roughly 2000\(\times \)2000 km to carry out both intra- and inter-GPS/BeiDou PPP-AR. We find that about 85% of ISPBs vary minimally within 0.05 cycles from day to day, favoring precise predictions for real-time PPP-AR, despite the rare subdaily ISPB anomalies of up to 0.1 cycles and abrupt jumps of up to 0.3 cycles at a few stations. From hourly kinematic solutions, we find that 42.3% of them can be initialized successfully within 5 min in case of inter-GPS/BeiDou PPP-AR in contrast to only 29.7% in case of intra-GPS/BeiDou. The mean initialization time is therefore reduced appreciably from 649 to 586 s. This 10% improvement, though minor, is reasonable and still encouraging on account of the fact that only one extra resolvable ambiguity is contributed during the transition from intra- to inter-GPS/BeiDou PPP-AR, while both actually have the same model strength. Moreover, we provide a preliminary theoretical framework to implement inter-GNSS or tightly coupled GNSS models which can be extended to other multi-GNSS analysis.
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Acknowledgements
This work is funded by National Science Foundation of China (41674033), China Earthquake Instrument Development Project (Y201707) and State Key Research and Development Programme (2016YFB0501802). We are grateful to IGS, NBASS (National BDS Augmentation Service System), CMONOC (Crustal Movement Observation Network of China) and Curtin University (saegnss2.curtin.edu.au/ldc) for the GPS/BeiDou data and the high-quality orbit, clock and ERP products. We thank the high-performance computing facility at Wuhan University where all computational works of this study were accomplished.
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Geng, J., Li, X., Zhao, Q. et al. Inter-system PPP ambiguity resolution between GPS and BeiDou for rapid initialization. J Geod 93, 383–398 (2019). https://doi.org/10.1007/s00190-018-1167-6
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DOI: https://doi.org/10.1007/s00190-018-1167-6