Assessing GPS/Galileo real-time precise point positioning with ambiguity resolution based on phase biases from CNES

摘要

The real-time precise point positioning (RT PPP) with ambiguity resolution (AR) technique has attracted increasing attention due to its high accuracy and low cost. With the availability of RT precise orbits, clocks, and multi-frequency phase bias products for multi-GNSS constellations, which are provided freely by the Centre National d'Etudes Spatiales (CNES), it is possible now to investigate RT PPP AR based on undifferenced and uncombined PPP model. However, only a few studies described these phase bias model tersely, especially in the multi-frequency and multi-system PPP AR. Moreover, the impact on inter-frequency clock bias (IFCB) for triple-frequency GPS/Galileo RT PPP by using the phase bias products have not been investigated. In this paper, the transformation between multi-frequency phase bias model and integer recovery clock (IRC) model was formulated where IFCBs are well considered. Meanwhile, the convergence time, positioning accuracy, narrow-lane ambiguity N1 fixing rate of GPS/Galileo PPP AR were analyzed by using a modified version of the Precise Point Positioning with Integer and Zero-difference Ambiguity Resolution Demonstrator (PPP-WIZARD). Experiments with GPS/Galileo observation from 50 stations over 32 days were performed in static and kinematic modes. Data were processed with four strategies: dual-frequency float and fixed PPP, triple-frequency float and fixed PPP. Results showed that the effect of the IFCB of GPS Block IIF could be mitigated by using the phase bias products from CNES. Among four solutions, the triple-frequency PPP AR achieved the fastest convergence time of 10.43 and 12.55 min in static and kinematic modes, respectively. The average RMS values are 1.2, 1.5, 3.1 cm in static mode while 2.0, 2.5, 3.8 cm in kinematic mode with the 3 h observation session by triple-frequency PPP AR in the east, north and up directions, respectively. Compared with dual-frequency PPP AR, triple-frequency PPP AR could contribute to improving the performance of convergence time and positioning accuracy, especially when few satellites can be observed.