# BDS-3 Triple-Frequency Timing Group Delay/Differential Code Bias and Its Effect on Positioning
## 3 Results and Analysis
### Analysis of PPP Positioning Accuracy
#### 3.2.2 UC123  
The time series of positioning errors for UC123-0 PPP at AREG station are presented in Figure 10, and the inset in each figure is the time series during the first 1 h. The UC in the figure shows the same situation as the IF combination filtering. Additionally, dcb-corr has better accuracy than the non-corr in the initial epoch. UC also provides stable cm-level positioning after convergence.  
The average convergence times for different UC combinations are plotted in Figure 11. UC123 corrected by DCB shows significant accuracy improvement in the E, N and U components, but the accuracy improvement occurs mainly during the initial epochs. For the convergence time, the dcb-corr of UC123-0-UC123-3 all show an improvement compared with the non-corr, and the difference between the combinations after correction is insignificant.  
The average positioning accuracies of the UC123 model in all-day solutions and after convergence are shown in Tables 7 and 8, respectively.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Model**} & \multicolumn{4}{c}{**non-corr/cm**} & \multicolumn{4}{c}{**dcb-corr/cm**} \\ \cline{2-7}  & E & **N** & **U** & **E** & **N** & **U** \\ \hline IF123 & 1.58 & 0.87 & 2.09 & 1.58 & 0.87 & 2.09 \\ IF1213 & 1.58 & 0.86 & 2.06 & 1.58 & 0.85 & 2.06 \\ \hline \end{tabular}
\end{table}
Table 6: Average positioning accuracy of PPP after convergence for IF123 and IF1213 models.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Model**} & \multirow{2}{*}{**Scheme**} & \multicolumn{4}{c}{**Positioning Accuracy/cm**} & \multirow{2}{*}{**Convergence**} \\ \cline{3-4} \cline{6-6}  & & E & N & U & Time/min \\ \hline \multirow{3}{*}{UC123} & non-corr & 9.56 & 6.45 & 13.07 & 41.9 \\  & dcb-corr & 5.69 & 4.39 & 8.46 & 38.3 \\ \cline{1-1}  & Improvement/\% & 40.48\% & 31.94\% & 35.27\% & 8.59\% \\ \hline \end{tabular}
\end{table}
Table 7: Average positioning accuracy of PPP for UC123 model.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Model**} & \multirow{2}{*}{**Scheme**} & \multicolumn{4}{c}{**Positioning Accuracy/cm**} & \multirow{2}{*}{**Convergence**} \\ \cline{3-4} \cline{6-6}  & & E & N & U & Time/min \\ \hline \multirow{3}{*}{IF123} & non-corr & 9.44 & 6.48 & 12.39 & 28.0 \\  & dcb-corr & 3.61 & 2.18 & 4.96 & 26.1 \\ \cline{1-1}  & Improvement/\% & 61.76\% & 66.36\% & 59.97\% & 6.79\% \\ \cline{1-1}  & non-corr & 6.96 & 4.76 & 9.68 & 27.6 \\ \cline{1-1}  & dcb-corr & 3.79 & 2.33 & 5.23 & 26.9 \\ \cline{1-1}  & Improvement/\% & 44.55\% & 51.05\% & 45.97\% & 2.54\% \\ \hline \end{tabular}
\end{table}
Table 5: Average positioning accuracy of PPP for IF123 and IF1213 models.  
Tables 7 and 8 show that the positioning accuracy of UC123 dcb-corr reached 5.69 cm, 4.39 cm and 8.46 cm in the E, N and U components, respectively, with improvement of approximately 31-41% compared with the non-corr positioning mode. The positioning accuracy of UC123 after convergence is comparable to that of IF123 and IF1213; all are better than 1 cm in the N component, 2 cm in the E component and 2.5 cm in the U component. The convergence time of the UC123 with dcb-corr is 38.3 min, which is approximately 8.59% shorter than that of non-corr. The slower convergence of UC than IF may be explained by the fact that UC requires estimating more parameters and a longer convergence time is needed. The IF and UC DCB corrections only have an accuracy improvement in the initial epoch. This is because the high-accuracy carrier makes a better contribution over time. Thus, the positioning accuracy after convergence of the non-corr and dcb-corr is essentially the same.