## 4 Discussion  
The positioning performance of three single systems (GPS-only, BDS-3-only, and Galileo-only) and three dual systems (GC, GE, and CE) in static and kinematic PPP solutions has been thoroughly investigated and assessed based on one-month observations (September 2022) of 143 MGEX stations that are capable of tracking GPS, BDS-3, and Galileo signals. The positioning accuracy and convergence time of single-system kinematic PPP with different precise products are also studied.  
For the single systems, in terms of RMS and convergence time distributions, the static PPP of GPS-only has slightly better RMS than Galileo-only in both the horizontal and vertical components, while it is much better than BDS-3-only; for the kinematic PPP, the RMS of GPS-only is significantly smaller than the other two systems. The convergence time shows different patterns in the two components. For all the PPP solutions, whether in the horizontal component or the vertical component, there is no doubt that the convergence time performance of GPS-only ranks first. Galileo-only outperforms BDS-3-only in the horizontal, while BDS-3-only outperforms Galileo-only in the vertical. Meanwhile, the relationship among RMS, convergence time, and latitude is being investigated. The GPS-only solution shows a trend of progressively worse performance from high to low latitudes. Galileo-only has the same pattern as GPS-only. For BDS-3-only, it performs significantly better in the low and high latitude zones than in the middle latitude zone.  
For the dual-system combinations, the RMS and convergence times of the three system combinations have nearly the same distribution pattern, with the GE combination having the highest positioning accuracy and the shortest convergence time, followed by the GC combination, and finally the CE combination. For GPS-based dual-system combinations, using Galileo and BDS-3 combined has not improved the positioning accuracy of GPS, nor has it shortened the convergence time. For the dual-system combination based on  
Figure 18: Distribution of the RMS of the BDS-3 kinematic PPP solutions with five types of precise products for the 143 MGEX tracking stations in September 2022. (**a**) Horizontal component, (**b**) Vertical component.  
Galileo, combined with GPS and BDS-3, the RMS value will be reduced by more than 0.10 cm for static PPP and more than 2.00 cm for kinematic PPP, and the convergence time will be reduced by more than 4.0 min and more than 10.0 min, respectively. For the dual-system combination based on BDS-3 combined with GPS and Galileo, the RMS value will be reduced by more than 0.30 cm for static PPP and more than 2.00 cm for kinematic PPP, and the convergence time will be reduced by more than 4.5 and 15.0 min, respectively.  
For single-system kinematic PPP solutions with different types of precise products, the positioning performance of different products under different systems is also different. For GPS, the median RMS difference between the best performing product and the worst performing product can reach more than 0.50 cm. However, the difference in convergence time is smaller, less than two minutes. For Galileo, the difference in RMS between products can reach a maximum of about 2.00 cm. The maximum difference in convergence time is only 2.5 min. Finally, for BDS-3, the maximum difference of the RMS can reach 1.90 cm, and the maximum difference of the convergence time can reach 30.0 min.