# BDS-3 Time Group Delay and Its Effect on Standard Point Positioning
## 3 Experimental Data and Processing Strategies
### BDS2 + BDS-3  
With the previous validation, we can conclude that the TGD parameters of the B1I, B1C and B2a signals need to be corrected. Therefore, for the BDS-2 + BDS-3 combination, we give only the positioning results with the TGD correction in this subsection. Figures 28-31 display the horizontal and vertical positioning error scatter plots for B1I and B3I SPP on 21 January 2019. The positioning errors in the B1I/B3I signal from a single day are described in Figures 32 and 33. From the positioning  
Figure 27: Average global PDOP of BDS-3 on DOY 10 2019, with an elevation cut-off angle of 5\({}^{\circ}\).  
Figure 26: Code residual scatter plots for the BRCH station with/without TGD correction. In each plot, the horizontal and vertical axes indicate the universal time (h) and the code residual, respectively (unit: m).  
results, it can be concluded that the positioning accuracy of the BDS-2 + BDS-3 combined system is higher than that of BDS-2 or BDS-3 because the increase in the number of BDS-3 satellites has made up for the regional limitations of BDS-2.  
Figure 28: Horizontal positioning error scatter plots of BII SPP with TGD correction for the six selected stations. In each plot, the horizontal and vertical axes indicate the E component error and the N component error, respectively (unit: m).  
Figure 29: Vertical positioning error scatter plots of BII SPP with TGD correction for the six selected stations. In each plot, the horizontal and vertical axes indicate the universal time (h) and the U component error, respectively (unit: m).  
Figure 31: Vertical positioning error scatter plots of B3I SPP with TGD correction for the six selected stations. In each plot, the horizontal and vertical axes indicate the universal time (h) and the U component error, respectively (unit: m).  
Figure 30: Horizontal positioning error scatter plots of B3I SPP with TGD correction for the six selected stations. In each plot, the horizontal and vertical axes indicate the E component error and the N component error, respectively (unit: m).  
To further evaluate the impact of the TGD parameters on the positioning accuracy of BDS-2 + BDS-3, the daily RMS values for each station are calculated (Figure 34), and the mean values for all stations are calculated (Figure 35).  
Figure 33: Vertical positioning error scatter plots of B1I/B3I SPP with TGD correction for the six selected stations. In each plot, the horizontal and vertical axes indicate the universal time (h) and the U component error, respectively (unit: m).  
Figure 32: Horizontal positioning error scatter plots of B1I/B3I SPP with TGD correction for the six selected stations. In each plot, the horizontal and vertical axes indicate the E component error and the N component error, respectively (unit: m).  
stations are shown in Table 7. Compared with BDS-2 and BDS-3, we can conclude that the positioning accuracy of the BDS-2 + BDS-3 combination system performs better than BDS-2 or BDS-3. Moreover, the single- and dual-frequency positioning errors of BDS-2+BDS-3 can reach 1 m-2 m. We expect that BDS-2 + BDS-3 can achieve a better performance when the global system will be completed in 2020.