## 3 Experimental Evaluation
### Convergency  
Compared with RTK, PPP requires a longer convergence time to achieve centimeter-level positioning accuracy. In this section, factors of kinematic and static PPP convergence time are discussed from the previous hourly convergence performance and receiver antenna type. From the positioning results of the first hour of static and kinematic BDS-3 (B1 cB2a), BDS-2+3 (B1 IB3I), GPS, GPS + BDS-3 (B1 cB2a), and GPS + BDS-2+3 (B1 IB3I) PPP, the average 3D positioning errors of all stations on all days were calculated, which are shown in Figure 11, where S means static, K means kinematic, B means BDS, G means GPS, 12 means B1 cB2a, and 13 means B1 IB3I. Figure 10: Kinematic PPP positioning accuracy histogram. Figure 11 shows that the convergence efficiency of the static PPP of a single system is significantly higher than that of a kinematic one. In addition, the differences between different systems are also obvious. Among them, whether it is static or kinematic PPP, the convergence effect of BDS (B1 IB3I) is worse those that of GPS and BDS (B1 CB2a), mainly due to the number of satellites observed by individual stations is small, which leads to poor overall convergence, as shown in Figures 2 and 12. When the number of observation satellites is the same, because the observation noise of BDS (B1 IB3I) is relatively large, the error of BDS (B1 IB3I) PPP is greater than that of BDS (B1 CB2a) PPP. Compared with the single system, the dual system has significantly improved the convergence efficiency. Static PPP of BDS (B1 CB2a) and GPS can converge to 0.1 m within 40 min, and the combined static PPP of BDS-3 (B1 CB2a) and GPS can converge to 0.1 m within 20 min. For kinematic PPP, the single-constellation PPP did not converge to 0.1 m within 60 min. The kinematic PPP of BDS-3 (B1 CB2a) + GPS and BDS-2+3 (B1 IB3I) + GPS can converge to 0.1 m within 30 min and 35 min, respectively. Similar to the positioning accuracy, the number of satellites is an important factor in the convergence time of PPP. Under the condition of a large number of satellites (more than four satellites), GPS has the best convergence efficiency. For the positioning accuracy and convergence time, the performances of GPS + BDS (B1 CB2a) or GPS + BDS (B1 IB3I) PPP are superior to the single-constellation PPP. Figure 11: Positioning convergence in the first hour of static (**a**) and kinematic (**b**) PPP. Figure 12: Positioning convergence in the first hour of LPGS and MAYG stations perform PPP. To further analyze the convergence of BDS-3 (B1 cB2a), the receiver types were classified and counted, and the positioning errors of each station at different epochs were observed. Table 4 shows the receiver model and antenna model at each station. The 20-day data are used for static PPP, and the positioning error of each station during the first hour is analyzed according to the receiver type, as shown in Figure 13.  
Figure 13 shows that there is no obvious difference between the receiver type and the convergence time. The main reason is the technological advancement of various manufacturers, and the antenna of the high-end receiver has little effect on BDS (B1 CB2a) PPP. The PPP convergence speed is closely related to the number of satellites. Figure 14 shows the percentage with less than five satellites participating in static PPP at the PIE1 station in a day (20 day in total). Compared with other stations, the static PPP of PIE1 station has a poorer convergence performance, as shown in Figure 13. The percentage of PIE1 stations with less than five satellites participating in the 20-day PPP solutions is more than 40%, and the static PPP does not converge to less than 0.1 m within 60 min.