An improved BDS-3 PPP-B2b positioning approach by estimating signal in space range errors

In 2020, BeiDou global navigation satellite system (BDS-3) officially launched a real-time precise point positioning (PPP) service via the B2b signal broadcast by 3 BDS-3 Geostationary Earth Orbit (GEO) satellites. This featured service of BDS-3, named PPP-B2b service, has captured increasing attention in recent years. It is well-known that satellite orbit and clock products play an important role in PPP processing. Limited by the distribution and number of permanent monitoring stations, the quality of PPP-B2b orbit and clock correction products is not as good as the products from the real-time service (RTS) of the international GNSS service (IGS). It is expected that the performance of the BDS-3 PPP-B2b service can be improved when the signal in space range errors, which account for the combined effects of remaining satellite orbit errors and clock errors, are compensated in PPP-B2b positioning. This study presents an improved approach for BDS-3 PPP-B2b positioning. In the proposed approach, ionosphere-free code measurements and ionosphere-free phase measurements are adopted. Apart from receiver position, receiver clock offset, zenith tropospheric wet delay and ambiguities, which are estimated in typical PPP-B2b positioning, the signal in space range error after applying PPP-B2b correction is also estimated and modeled as a random-walk noise for each satellite. Several experiments are conducted in different environments to assess the proposed approach. In the simulated kinematic experiment with GNSS observations from 6 stationary IGS stations, positioning accuracy with the proposed approach shows an average improvement of 21.1% in the horizontal and 25.4% in the vertical compared with the typical PPP-B2b positioning. In the land vehicle-borne experiment, an improvement of 36.0% in the horizontal and 19.0% in the vertical is achieved by using the proposed approach. In the offshore boat-borne experiment, the proposed approach outperforms the typical PPP-B2b positioning by an improvement of 15.8% horizontal and 55.7% vertical.