As one of the four global satellite navigation systems, Compass not only enhances satellite visibility and availability for positioning, navigation and timing (PNT) for users in China and the surrounding areas, but also improves PNT precision for global users. The improvements in satellite visibility and the dilution of precision are analyzed under GNSS compatibility and interoperation conditions. The contribution of the Compass satellite navigation system to global users, especially the benefits that users can acquire from the combination of Compass, GPS, GLONASS, and Galileo navigation systems, is analyzed using simulation data.

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BDS-3 currently has 28 operational satellites in orbit, of which 27 IGSO/MEO satellites provide open services on five frequencies simultaneously. In particular, the linear combinations of the BDS-3 B1C/B1I/B2a signals have significant benefits in reducing the influence of ionospheric delay error as well as improving ambiguity estimation and positioning accuracy. The presented optimal ionosphere-free combination (242, 218, − 345) and ionosphere-reduced combination (2, 2, − 3) can improve the measurement accuracy by about 20% compared to the BDS-3 B1C/B2a or GPS L1/L5 dual-frequency combination. The ionosphere-reduced combination (2, 2, − 3) with a wavelength of 10.9 cm is almost immune to the ionospheric delay error and has a smaller noise amplification factor compared to the existing dual-frequency combinations. Therefore, its combined ambiguities can be fixed directly even in the case of a long baseline, which can simplify the traditional precise positioning process based on the ionosphere-free combination. The numerical results of BDS-3 real data show that the triplefrequency ionosphere-free or ionosphere-reduced combinations can improve the single-point positioning accuracy by 16-20% and the phase differential positioning accuracy by 7-9%, respectively. The ambiguity resolution of the ionosphere-reduced combination (2, 2, − 3) is achieved with a fixing rate of 88.4% over long baseline up to 1600 km. The presented ionospherefree and ionosphere-reduced combinations are also very promising to be applied in current PPP applications to simplify the ambiguity fixing process as well as improve positioning accuracy and shorten convergence time.

Within the framework of differential augmentation, this paper introduces the basic technical framework and performance of the BeiDou Global Navigation Satellite System (BDS-3) Satellite-Based Augmentation System (BDSBAS), including orbit products, satellite clock offset products, ionosphere and its integrity performance. The basic principle of BDS-3 Precise Point Positioning (PPP-B2b) is expounded, the similarities and differences between the PPP service provided by BDS-3 and International Global Navigation Satellite System (GNSS) Service (IGS) are discussed, and the limitations of PPP-B2b are analyzed. Since both the BDSBAS and PPP-B2b utilize a ground monitoring station network to determine the satellite orbits and clock offset corrections, and broadcast differential corrections through the three Geostationary Orbit (GEO) satellites of BDS-3, the feasibility of the co-construction of BDSBAS and PPP-B2b is analyzed, strategies for the infrastructure sharing and correction broadcasting are presented, and the influences of BDSBAS correction broadcasting strategy adjustment are evaluated. In addition, it assesses the possibility of broadcasting differential corrections through the Inclined Geosynchronous Orbit (IGSO) satellites of BDS-3, and the feasibility of augmenting satellite navigation with Low Earth Orbit (LEO) satellites.