# BDS-3 Time Group Delay and Its Effect on Standard Point Positioning
## 3 Experimental Data and Processing Strategies
### Bds-3  
Figures 11-17 present the horizontal and vertical positioning error scatters plots of the BDS-3 single-frequency SPP, with and without TGD correction, from 21 January 2019 for the six stations. It should be explained that the data are discontinuous because of the lack of observational data in the figures. In addition, we mentioned before that the pre-test and post-test residuals will be checked in our program, and the observations will be deleted when the absolute value of the residual is greater than 30 m. Considering all seven figures, there are three findings highlighted here. First, simultaneously considering Figures 13-16, it can be seen that the positioning accuracy values of the B1C and B2a signals have improved significantly with the \"tgd-corr\" scheme. We can conclude that the TGD parameters need to be modified in the BIC-and B2a-based positioning. As mentioned in the ICD file, the TGD of B1C is the group delay differential between the B1C pilot component and the B3I signal, and the TGD of B2a is the group delay differential between the B2a pilot component and the B3I signal. Second, both the old signals and the new signals, in the case of correcting the TGD parameters, can achieve the metre-level positioning accuracy. Third, we can clearly see that the \"tgd-corr\" scheme results in a significant improvement compared to the \"non-corr\" scheme positioning results in the E, N and U components. Taking the B1C signal of the LHA1 station as an example, in Figures 13 and 14, the horizontal and vertical positioning errors are within the range of \(-5\) m to \(5\) m after the correction of the TGD parameters, and those from the uncorrected TGD parameters range from \(-10\) m to \(10\) m.  
Figure 12: Vertical positioning error scatter plots of B1I SPP with and without 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 13: Horizontal positioning error scatter plots of B1C SPP with and without 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 14: Vertical positioning error scatter plots of BIC SPP with and without 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 15: Horizontal positioning error scatter plots of B2a SPP with and without 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 16: Vertical positioning error scatter plots of B2a SPP with and without 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 17: Vertical positioning error scatter plots of B3I SPP without TGD correction for the BRCH station. In each plot, the horizontal axis is the universal time (h) and the vertical axes indicate the errors of the E, N and U components (unit: m). We now turn to Figures 18-21, in which the four panels separately show the horizontal and vertical positioning error scatter plots of BDS-3 B1I/B3I- and B1C/B2a-based SPP from 21 January 2019. As we can see from the four figures, both the old and new signals of BDS-3 dual-frequency SPP can reach metre-level positioning accuracy. We focus on the B1C/B2a-based positioning errors shown in Figures 20 and 21. The positioning error from the \"tgd-corr\" scheme is within \(\pm\)5 m, and the positioning error from the \"non-corr\" scheme is within \(\pm\)10 m in the E, N and U components. Combined with Figures 17 and 18, we can still conclude that the TGD correction effect of the new signal is obviously similar to that of the old signal.