# The Effect of BDS-3 Time Group Delay and Differential Code Bias Corrections on Positioning
## 4 Result and Discussion  
### Performance of SPP  
#### 4.1.1 Single-Frequency  
In Figures 5-11, the positioning errors of B1I, B3I, B1C and B2a single-frequency SPP in the east (E), north (N) and up (U) components of the six stations on 1 April 2020 are respectively given. We chose 1 April 2020 for one particular day, and the results show similar features on other days. It should be illustrated that the data are discontinuous because the residuals with absolute values greater than 30 m are detected and the observations will be deleted. Simultaneously combined with the below figures, three important conclusions can be drawn here. Firstly, combined with Figures 5-10, it can be seen that after the modification of TGD and DCB parameters, the positioning accuracy of single-frequency (B1I, B1C and B2a) SPP has been significantly improved. For SPP based on the B3I signal, positioning results based on the B3I signal are not affected by TGD parameters. In addition, the positioning error of B3I is shown in Figure 11. Second, with the TGD or DCB parameters corrected, the performance of SPP for single-frequency BDS-3 can achieve the positioning accuracy of the metre-level. Third, we can explicitly see that the positioning results of the \"tgd-corr\" and \"dcb-corr\" schemes are significantly improved compared to the \"non-corr\" schemes. After correcting the TGD or DCB parameters, the positioning error ranges from \(-5\) to \(5\) m, while positioning error of uncorrected TGD or DCB is more discrete and larger. Figure 12 describes boxplot for the three-dimensional (3D) positioning errors with different schemes of six selected stations within 30 days. In Figure 12, it is intuitive to indicate that the outliers for the 3D positioning errors of single-frequency at each station are very small. Due to the BDS-3 pseudorange influenced by TGD or DCB parameters, thence, \"tgd-corr\" or \"dcb-corr\" scheme showed better positioning accuracy, compared with the scheme of \"non-corr\". We further compare the positioning error distribution based on \"tgd-corr\" and \"dcb-corr\" schemes, and we can conclude that with median and 75 percentile values being below 10 m, as shown in Figure 12. In addition, median and 75 th percentile positioning errors with the TGD or DCB uncorrected are much larger than the results for other schemes, indicating that the correction of TGD or DCB parameters  
Figure 4: The distribution of six selected iGMAS station. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Station** & **Receiver** & **Antenna** \\ \hline BJF1 & CETC-54-GMR & LEIAR25.R4 \\ BRCH & CETC-54-GMR & NOV750.R4 \\ GUA1 & GNSS-GGR & RINT-8 CH \\ WUH1 & CETC-54-GMR & LEIAR25.R4c \\ HMNS & GNSS-GGR & RINT-8 CH \\ KUN1 & UB480-13478 & NOV750.R4 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summaries the basic information of iGMAS stations. need to be considered during the BDS-3 solution process. Besides, the positioning error distribution of all stations is basically similar, which will not be repeated here. Figure 5: Horizontal positioning error scatters with and without TGD or DCB correction of BII SPP at six stations. Figure 6: Vertical positioning error scatters with and without TGD or DCB correction of BII SPP at six stations. Figure 8: Vertical positioning error scatters with and without TGD or DCB correction of B1C SPP at six stations. Figure 7: Horizontal positioning error scatters with and without TGD or DCB correction of B1C SPP at six stations. Figure 10: Vertical positioning error scatters with and without TGD or DCB correction of B2a SPP at six stations. Figure 9: Horizontal positioning error scatters with and without TGD or DCB correction of B2a SPP at six stations. For further research of the accuracy of positioning, we summarized the RMS and mean of the six stations for 30 days in Table 4. Analysis of the obtained results can be summarized in that the positioning accuracy of BDS-3 single-frequency SPP can achieve meter-level worldwide.