Abstract
Carrier-phase integer ambiguity resolution (AR) is the key to improving the positioning accuracy of precise point positioning (PPP). However, in theory, the integer property of ambiguities in PPP are destroyed due to the absorption of phase biases. In this study, we analyzed a set of clock products consisting of a code clock, phase clock and wide-lane (WL) bias based on the decoupled clock (DCK) model, to facilitate PPP AR. The determination of the datum of the receiver clock as well as ambiguity were analyzed in detail to arrive at ways to eliminate rank deficiency. To fix ambiguity at the server end, we propose an approach by rounding directly with “fixing solution” (FS) and “partial ambiguity hold” (PAH) strategies, to increase the fixing rate and avoid the biased solution resulting from ambiguity datum loss. With respect to the International GNSS Service (IGS) legacy clocks, the mean standard deviations (STDs) of the phase clock and code clock were about 0.02 and 1.05 ns respectively, while the WL bias was about 0.12 cycles. Additionally, the convergence speed and stability of the decoupled phase clock are significantly improved compared with the conventional PPP model. Experiments on PPP positioning performance were conducted using 1 week of GPS data from more than 100 stations, considering the IGS weekly solutions as a benchmark. The ambiguity-fixed PPP with decoupled clocks had almost the same accuracy as the integer-recovered clock model, but the average accuracy improvements compared with the conventional PPP model in the east, north, and up components were 59.2, 32.4, and 20.3%, respectively, in the static mode, and approximately 38.0, 26.2, and 19.2% in the kinematic mode. These results demonstrate that users can achieve ambiguity-fixed solutions and obtain high-precision positioning coordinates with our decoupled clock products.
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Data availability
The datasets that support the findings of this research are available from the corresponding author upon reasonable request. The GPS observations and IGS products can be accessed at https://cddis.nasa.gov/archive/, the integer-recovered clock can be assessed at ftp://igs.ensg.ign.fr/pub/igs/products/, and decoupled clock products can be found at https://github.com/liush18/DCK.
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Acknowledgements
This work was supported by the Collaborative Precision Positioning Project funded by the Ministry of Science and Technology of China (No. 2016YFB0501900) and China Natural Science Funds (No. 41674022). The authors acknowledge LU JIAXI International team program supported by the K.C. Wong Education Foundation and CAS. The authors are grateful to IGS for providing the GPS data and satellite products.
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SL and YY proposed the initial idea and designed the experiments for this study; SL analyzed the data and wrote the manuscript; Y.Y. revised the manuscript.
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Liu, S., Yuan, Y. Generating GPS decoupled clock products for precise point positioning with ambiguity resolution. J Geod 96, 6 (2022). https://doi.org/10.1007/s00190-021-01593-7
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DOI: https://doi.org/10.1007/s00190-021-01593-7