## 3 Results
### Geographical Distribution of the Single Systems  
In order to study the geographical distribution pattern of the single system, we use the RMS and convergence time of each tracking station for one month and take its median to represent the convergence time and RMS of the station and present it in the global map. We display the convergence time statistics of static PPP across three single systems over one month (September 2022) for the horizontal and vertical components at the selected 143 stations using a color bar (but different scales) along a global map in Figure 7. To make the analysis more intuitive, the mean convergence time of the different latitude zones for static PPP is listed in Table 2, where H and V represent the horizontal and vertical components, respectively, and N and S represent the northern and southern hemispheres, respectively. Accordingly, the range from 60\({}^{\circ}\) to 90\({}^{\circ}\) is defined as the high-latitude zone (denoted by High_N in the northern hemisphere and High_S in the southern hemisphere), the range from 30\({}^{\circ}\) to 60\({}^{\circ}\) as the middle-latitude zone (Med_N and Med_S), and the range from 0\({}^{\circ}\) to 30\({}^{\circ}\) as the low-latitude zone (Low_N and Low_S). Further, the tracking station numbers in the different latitude zones are listed. For static PPP in the horizontal component, we can see that the convergence time of GPS-only tracking stations in the high latitudes is well below 10.00 min, which is shorter than that in the low and middle latitudes. In addition, the convergence time in other zones is less than 15.00 min, except for the low latitudes in the northern hemisphere. Galileo-only tracking stations have a convergence time of less 20.00 min in the middle latitudes of the southern hemisphere  
Figure 6: Distribution of the convergence time and RMS of kinematic PPP solutions in three single systems (G is short for GPS, E is short for Galileo, and C is short for BDS-3) in September 2022. (**a**) Horizontal component of convergence time, (**b**) Horizontal component of RMS, (**c**) Vertical component of convergence time, (**d**) Vertical component of RMS. and in the high latitudes all around the world. For BDS-3-only, stations in the middle latitudes have a convergence time of more than 23.00 min, while the time for stations in the high latitudes is shorter than 17.00 min. The three single systems all follow the law that in the northern hemisphere, the higher the latitude, the shorter the convergence time, whereas in the southern hemisphere, the convergence time is shortest in the low latitudes and slightly worse in the middle and high latitudes. In terms of the vertical component, the three single-system tracking stations have a similar distribution, that is, the convergence time from high latitude to low latitude changes in turn long. Figure 8 shows the convergence time statistics of kinematic PPP, the same as in Figure 7. Further, Table 3 depicts the mean RMS of the different latitude zones for kinematic PPP. For kinematic PPP in the horizontal component, it is evident that the distributions of the convergence times of Galileo-only tracking stations show striking similarity to the static PPP. GPS-only tracking stations have a convergence time of above 24.00 min in the middle latitudes, but it is below 22.00 min in the high latitudes. BDS-3-only tracking stations have a convergence time of about 30.00 min, which is shorter than the stations in the low and middle latitudes. GPS-only and Galileo-only tracking stations have a vertical component distribution that is equivalent to the static PPP. The convergence time for BDS-only tracking stations is shorter in the low and high latitude zones than in the middle latitude zone. In general, the higher the latitude, the shorter the convergence time for most tracking stations.