Precise point positioning (PPP) is a very important function of satellite navigation system. In this contribution, the combination of BDS-2 and BDS-3 PPP is researched. To begin with, the frequency and application of BDS-2 and BDS-3 are introduced. Then, the prin-ciple of BDS-2 and BDS-3 combined PPP, the generation and estimation method of inter-system bias (ISB) are elaborated. Finally, the global satellite visibility of BDS-2 and BDS-3, the global Position Dilution of Precision (PDOP) value and the results of BDS-2/BDS-3 PPP are analyzed based on the 51-day data of 30 stations from multi-GNSS experiment (MGEX) network in 2020. The experimental results show that: (1) The number of visible satellites of BDS-2 in Asia Pacific region is 8-15, while the number of visible satellites in most parts of the western hemisphere is less than 4; the number of visible satellites of BDS-3 in the eastern hemisphere is 8-14, while the number of visible satellites in the western hemisphere is 7-11; BDS-3 is more evenly distributed in the world than BDS-2, but the number of satellites in the eastern hemisphere is also slightly more than that in the western hemisphere. (2) The root mean square (RMS) of BDS-2/BDS-3 static PPP in the East (E), North (N) and Up (U) directions are 1.0 cm, 0.6 cm and 1.7 cm respectively; the positioning accuracy of BDS-2/BDS-3 PPP in the E, N and U directions are improved by 16.7%, 14.3% and 10.5% respectively compared with BDS-3 PPP. The RMS of BDS-2/BDS-3 kinematic PPP in the E, N and U directions are 2.0 cm, 1.3 cm and 4.1 cm respectively; the positioning accuracy of BDS-2/BDS-3 PPP in the E, N and U directions are improved by 33.3%, 38.1% and 29.3% respectively compared with BDS-3 PPP. (3) Compared with BDS-3 static PPP, the convergence time of BDS-2/BDS-3 are shortened by 6.1%, 11.5%, 10.1% and 10.3% in the E, N, U and three dimensional (3D) directions respectively. Compared with BDS-2, the convergence time of BDS-3 is shortened by more than 50%. The convergence time of BDS-2/BDS-3 kinematic PPP in the E, N, U and 3D directions is shorter than BDS-3 by 31.1%, 43.8%, 38.1% and 34.6% respectively; the convergence time of BDS-3 is shorter than BDS-2 by 61.1%, 59.7%, 60.9% and 57.1% respectively. In brief, the success of BDS-3 global networking has greatly promoted the positioning performance of the entire BDS system. (C) 2021 COSPAR. Published by Elsevier B.V. All rights reserved.
