# Performance Analysis of BDS-5G Combined Precise Point Positioning
## 3 Results and Discussion
### Static PPP  
#### 3.2.1 Quantity  
The 24 h of BDS satellite observations were initialized every 4 h to obtain the convergence effect plots of static PPP in XYZ directions and tropospheric zenith wet delay under Scenes 1 and 2.  
The static PPP convergence effect for Scene 1 is shown in Figure 4, with different numbers of 5G base stations involved in localization. In the case of no base station participation, represented in red, the convergence speed of its XYZ directions and tropospheric zenith wet delay is significantly slower than that of the case with 5G base stations participating in positioning. As the quantity of participating 5G base stations increases, the static PPP converges faster. The results of Scene 2 are shown in Figure 5; the same conclusions can be drawn and the beneficial effect of the 5G base station  
To more clearly illustrate the effect of base station number on the effectiveness of PPP in different occlusion scenes, the mean convergence time and STD variation of the error for six initializations in a day were counted. In the static solution process, we considered an error of less than 0.1 m for 30 consecutive epochs as convergence.  
From the mean results after six initializations in different scenes (Figure 6), in the static PPP mode, the convergence time showed a decreasing trend in all three XYZ directions as the number of base stations increased. In Scene 1, the convergence speed accelerated by 23 min, 51 min, and 19 min in the XYZ directions for the three base stations involved in localization compared to no base station. When the quantity of 5G base stations was increased to three and then to four and five, the trend of decreasing convergence time diminished and then plateaued. As the quantity of base stations involved in the positioning solution increased, the STD of the post-convergence error decreased slightly, and the STD of five-base station positioning was 1.187 m, 0.7873 m, and 1.551 m in the XYZ directions.  
Figure 5: Convergence for different numbers of base stations in Scene 2, (a) X direction, (b) Y direction, (c) Z direction, (d) Zenith wet delay.  
Figure 6: Convergence speed (a) and standard deviation (STD) (b) of the errors for different numbers of base stations under Scene 1 and Scene 2.  
The convergence speed in Scene 2 improved more rapidly than in Scene 1 as the quantity of base stations increased, and the convergence speed accelerated by 76 min, 69 min, and 33 min in the XYZ directions for the three-base station case compared with the no base station case, which is a greater reduction than that in Scene 1. At the same time, compared with Scene 1 where the convergence advantage became less pronounced for more than three base stations, when the quantity of base stations increased to four and five, the convergence speed in Scene 2 still had some advantages. With four to five base stations involved in the solution, the convergence times for Scene 1 and Scene 2 converged to within 15 min. The change in the STD of the error after convergence was less pronounced, but there was also a general tendency to decrease, from over 2.0 m to under 1.5 m in both the XY directions.  
Therefore, we conclude that 5G base stations participating in static PPP can effectively reduce the convergence time and increase the positioning accuracy to a certain extent. The more 5G base stations, the better the positioning effect. This advantage is more obvious in an environment where satellites are blocked.