Real-time estimation of multi-GNSS integer recovery clock with undifferenced ambiguity resolution

Precise satellite clock product is an important prerequisite to support the real-time precise positioning service. In this contribution, the multi-GNSS integer recovery clock (MIRC) model is developed to improve both the accuracy and efficiency of real-time clock estimates. In the proposed method, the undifferenced ambiguities of GPS, BDS, Galileo and GLONASS are fixed to integers, and thus the integer properties of the ambiguities are recovered and the accuracy of the clock estimates is also improved. In addition, benefiting from the removal of large quantities of ambiguity parameters, the computation time is greatly reduced which can guarantee the high processing efficiency of real-time clock estimates. Multi-GNSS observations from 151 globally distributed Multi-GNSS Experiment tracking stations are processed with the proposed MIRC model over a one-month period (DOY 240–270, 2018). Compared to the float satellite clocks, the precision (standard deviation, STD) of the real-time MIRC with respect to CODE 30 s final multi-GNSS satellite clock products was improved by 53.0% from 0.046 to 0.022 ns for GPS, 42.7% from 0.096 to 0.055 ns for BDS, 63.7% from 0.097 to 0.035 ns for Galileo and 33.9% from 0.153 to 0.101 ns for GLONASS, respectively. With the proposed method, the average computation time per epoch with multi-GNSS observations for 50-, 100- and 150-station networks was improved by 7.3%, 82.7% and 97.1% compared to that of standard float clock estimation. Multi-GNSS kinematic precise point positioning (PPP) ambiguity resolution was also performed with the derived real-time MIRC products. Compared to the float PPP solutions, the position accuracy of the multi-GNSS MIRC-based fixed solutions was improved by 77.2%, 49.7% and 52.7% from 24.2, 13.3 and 30.7 mm to 5.5, 6.7 and 14.5 mm for the east, north and up components, respectively.