An efficient undifferenced method for estimating multi-GNSS high-rate clock corrections with data streams in real time
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Precise satellite clock corrections are the key elements for the implementation of Real-Time Precise Point Positioning (RTPPP). To fully promote the capability of multi-GNSS RTPPP, an efficient method is proposed for the precise estimation of multi-GNSS high-rate satellite clock corrections in real time. Different from the epoch-differenced methods in the current literature, the proposed method is based on undifferenced observations and the function models are established to achieve high processing efficiency and full-parameter accessibility at the same time. In the proposed method, main data processing is performed based on two function models: the full-parameter (FP) model and the high-rate (HR) model. In the FP model, both code and phase observations are used, mainly for the estimation of the large number of phase ambiguities, which is actually the most time-consuming part in clock estimation. In the HR model, high-rate clock corrections are estimated with only phase observations, in which the latest ambiguity estimates and corresponding variance information obtained from the FP model are introduced as phase corrections to reduce the size of the normal equations and guarantee high processing efficiency for the HR processing. With the proposed method, real-time estimation of high-rate (1 Hz) clock corrections for a quad-system (GPS/GLONASS/Galileo/BeiDou) solution with real-time streams has been realized and validated. Satellite clock corrections are encoded to state-space representative corrections and broadcasted to the user side to support multi-GNSS RTPPP. Results show that the proposed method is highly efficient and can provide 1 Hz or even higher-rate clock corrections for multi-GNSS in real time. Quad-system real-time satellite clocks are compared with the post-processed products from GFZ. Positioning performances of RTPPP, including positioning accuracy and convergence speed, have also been validated and analyzed. All the results show that the proposed method is effective, efficient, accurate and promising in multi-GNSS real-time high-rate clock estimation.
KeywordsMulti-GNSS Real time High-rate clock estimation Undifferenced observations Real-Time Precise Point Positioning (RTPPP)
The authors would like to acknowledge the MGEX, GA, CNES, GFZ and CODE for providing access to the real-time multi-GNSS data streams, real-time SSR satellite orbit corrections for multi-GNSS (CLK93), post-processed satellite orbit, clock and intra-frequency DCB products. Many kind helps from Dr. Denis Laurichesse are highly appreciated. Funding supports from China Natural Science Funds (Nos. 41804037 and 41674022) and National key Research Program of China “Collaborative Precision Positioning Project” (No. 2016YFB0501900) are also gratefully acknowledged. The second author is supported by the CAS Pioneer Hundred Talents Program. The third author acknowledges LU JIAXI International team program supported by the K.C. Wong Education Foundation and CAS.
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