# BDS-3 Time Group Delay and Its Effect on Standard Point Positioning
## 3 Experimental Data and Processing Strategies
### Bds-3
First, the signal- and dual-frequency SPP solutions without the TGD correction present the systematic error. Compared with the \"non-corr\" scheme, the accuracy in B1I SPP is improved with the TGD correction by approximately 68.0%, 69.2% and 49.2% in the N, E and U components, respectively. The positioning errors of B1C SPP with the \"tgd-corr\" scheme are reduced by 64.8% from 1.18 m to 3.35 m and by 64.4% from 1.48 m to 4.16 m and by 51.2% from 2.91 m to 5.96 m in the E, N and U components, respectively. In the \"tgd-corr\" scheme, the RMS values of B2a SPP are significantly reduced by 60.2% from 2.84 m to 1.13 m, by 55.4% from 3.59 m to 1.60 m and by 19.8% from 5.09 m to 4.18 m in the E, N and U components, respectively. Likewise, compared with the \"non-corr\" scheme, the RMS of B1I/B3I SPP is reduced by 75% and 71% in the horizontal components, and the positioning accuracy can reach 1 m-2 m after TGD correction, and the vertical component is reduced by 45.4%, from 5.42 m to 2.96 m. The accuracy of BIC/B2a SPP with the \"tgd-corr\" scheme is improved by 66.1% and 62.1% on the horizontal components, the N and E can reach 1.66 m and 1.85 m by correcting the TGD parameters, respectively, and the vertical component is improved by 43.3%, from 6.31 m to 3.58 m. Second, we focus on the new signals from BDS-3. We observe that the positioning accuracy of the new signals is analogous to that of the old signals of BDS-3. Both the new and old signals can achieve a positioning accuracy similar to that of BDS-2. However, BDS-2 provides regional location services, while BDS-3 provides global location services. Third, we note that  
Figure 13:1 Box-whisker diagrams of the distributions of the 3D positioning errors in the tgd-corr (red) and non-corr (blue) schemes at the BRCH, GUA1, LHA1, WUH1, XIA1 and XIA5 stations for the 41-day period (tgd: tgd-corr, non: non-corr) using the BDS-3 satellites. The box heights and the bars inside the boxes denote the IQRs and medians of the distributions, respectively. The whiskers’ lengths represent the maximum and minimum values of the distributions (unit: m). Outliers are identified with plus signs (see text). the positioning accuracy of the dual-frequency SPP is even worse than that of single-frequency: This result is affected by the fact that the dual-frequency observation noise is significantly enlarged due to different factors, including the TGD parameter error. Figure 13:2 Daily RMSs of old signals from BDS-3 with and without TGD correction for the BRCH station. Figure 13:3 Daily RMSs of the new signals from BDS-3 with and without TGD correction for the BRCH station. We now turn to Figure 26, which depicts the code residual scatters at the BRCH station with different schemes, with each colour representing different satellites. We see that there is a clear system bias in the code residual of each satellite with the \"non-corr\" scheme. It is noteworthy that there is no significant system bias with the \"tgd-corr\" scheme; thus, this finding further verifies that the TGD of the old and new signals from BDS-3 need to be modified. Comparing the two schemes, it can be found that the data from the \"non-corr\" scheme are less than the data from the \"tgd-corr\" scheme, possibly because the code residuals are too large during the calculation process. We focus on Figure 27, which shows the average global PDOP on DOY 10 2019, with an elevation cut-off angle of 5\({}^{\circ}\). Compared with the other methods, the \"non-corr\" scheme is more robust than the other methods.