# Development Status and Service Performance Preliminary Analysis for BDSBAS
## 4 BDSBAS Service Performance Evaluation
### BDSBAS SF Service Accuracy  
According to the user algorithms of BDSBAS messages, the single point position (SPP) results of the BDSBAS SF service were achieved through 30 monitoring receivers' data. To reduce the observation errors such as multipath error, observation noise, carrier smoothed pseudoranges are used in the SPP estimation. In consideration of calculation efficiency and carrier-smoothed pseudoranges accuracy, the data with 20 s observation sampling interval were adopted. The coordinates of the monitoring receivers are regularly maintained with geodetic survey and GNSS network adjustment calculation, and the 3D coordinate accuracy of these receivers is usually better than 5 cm. As the precise coordinates of the monitoring receivers were already known, the position errors in horizontal and vertical directions were analyzed. The 95 th percentile values of absolute value of horizontal and vertical position errors of each day were evaluated, and the time series results during 10 days for 30 receivers were shown in Figure 3.  
In Figure 3, the lines in the top subgraph indicate the time series of horizontal position errors of 30 receivers and the lines in the bottom subgraph show the position errors in the vertical direction. Different colors indicate different monitoring receivers. The horizontal axis represents time in days, and the vertical axis represents position errors in meters. It shows that the variance of position errors for the same monitoring receiver is relatively stable in different days. The HPE of different receivers has little difference, varying from 1 m to 1.5 m, while the dispersion of VPE among different receivers is relatively large, varying from 1.5 m to 3 m. The VPE variation of different receivers is mainly caused by the accuracy of corresponding ionospheric grid corrections.  
The 24 h time series of position errors of one monitoring receiver are shown as an example, compared between the BDSBAS + GPS SF service and the GPS SF service. The position errors in the north-south, east-west and vertical directions are shown in the top, middle and bottom subgraphs of Figure 4, respectively. In the figure, the red lines indicate the positions errors of the BDSBAS + GPS SF service and the black lines represent the position errors of GPS SF service. The horizontal axis expresses time in hours. As shown in Figure 4, the 95% position errors of the BDSBAS + GPS SF service are 0.638 m, 0.506 m and 1.548 m in the north-south, east-west, and vertical directions, respectively, while the 95% position errors of the GPS SF service are 1.388 m, 0.851 m and 2.427 m in the north-south, east-west, and vertical directions, respectively. The position accuracy of the BDSBAS + GPS SF service is obviously improved compared with the GPS SF service.  
Figure 4: Comparison of position errors between the BDSBAS + GPS SF service (red lines) and the GPS SF service (black lines).  
Figure 3: Time series of 95 th percentile position errors for 30 monitoring receivers under BDSBAS SF service. One color represents one receiver.  
The average value of 95% absolute value of position errors over 10 days is used to evaluate the position accuracy of the monitoring receiver. The position accuracies of the BDSBAS + GPS SF service and the GPS SF service are compared analyzed and the statistics for 30 monitoring receivers are listed in Table 2.  
The results show that the horizontal and vertical position accuracies of the 30 monitoring receivers are less than 1.5 m and 3 m, respectively, achieved with BDSBAS + GPS SF service. The average accuracies of all 30 receivers in horizontal and vertical directions are about 1 m and 2 m and are improved by about 39% and 33%, respectively, compared with GPS SF service.