# BDS-3 Triple-Frequency Timing Group Delay/Differential Code Bias and Its Effect on Positioning
## 3 Results and Analysis  
### Analysis of SPP Positioning Accuracy  
#### 3.1.1 IF123 and IF1213  
The positioning errors in the horizontal and vertical components for IF123-0 and IF1213-0 SPP of the AREG station on DOY 182, 2022, are presented in Figure 4. It is worth noting that the AREG station on DOY 182 (1 July 2022) is our randomly selected representative station and the other days, combinations and stations have similar characteristics.  
Several conclusions can be drawn from Figure 4. Firstly, both IF123 and IF1213 models without TGD/DCB correction have a scattered error distribution in the E, N and U components with significant positioning errors. This is because the IF combinations amplify the observation noise that includes the UCDs. Secondly, the error distribution is concentrated after TGD/DCB is corrected, and the positioning error magnitudes are reduced. Finally, the positioning accuracies of IF123 and IF1213 are similar after TGD/DCB is corrected, and there is no significant difference.  
The box plots of the SPP positioning accuracy for different IF combinations are plotted in Figure 5.  
\begin{table}
\begin{tabular}{c c} \hline
**Item** & **Description** \\ \hline Satellite precise clock & GBM products from GFZ analysis center \\ Satellite PCO/PCV & Corrected with the igs14.atx \\ Phase window & Corrected [33] \\ Tidal displacement & Solid Earth tide, pole tide and ocean tide loading [34] \\ Relativistic effect & Corrected [34] \\ Station coordinates & Estimated as constant \\ Receiver clock offset & Estimated as white noise \\ IFB & IF1213 and UC123: Estimated as constant \\ Tropospheric delay & ZHD: Saastamoinen model [35] \\  & ZWD: estimated as random walk [34] \\  & IF123 and IF1213: eliminated by IF combination \\ Ionospheric delay & UC123: SPP corrected with BDGIM [36], PPP estimated as random walk \\ \hline \end{tabular}
\end{table}
Table 2: _Cont._  
Figure 4: SPP positioning error of IF123-0 and IF1213-0 at AREG.  
The positioning accuracy of all combinations without TGD/DCB correction is poor, with an accuracy of 5-8 m in the horizontal component and approximately 10 m in the vertical component. It is also clear that tgd-corr and dcb-corr positioning accuracy perform better and have a more concentrated error distribution compared with non-corr. The 75% quantile error is less than 1.5 m in the horizontal component and 3.5 m in the vertical component, and the positioning accuracies of the IF123 and IF1213 models are comparable.  
Furthermore, we found an interesting phenomenon: the accuracy of the 1 and 3 combinations was slightly better than that of the 0 and 2 combinations, especially in the E and N components. This phenomenon may be due to the use of old frequencies B1I and B3I in the 0 and 2 combinations, with an amplification factor of 3.527, which is greater than that of the new frequencies, B1C and B2a, used in the combination of 1 and 3.  
The average positioning accuracies of SPP for the IF123 and IF1213 models are shown in Table 3. We found that the average positioning accuracy of IF123 and IF1213 achieved better than 1 m in the E and N components and better than 3 m in the U component after TGD/DCB correction. The improvement rate of tgd-corr relative to non-corr was 73-90% for both IF models and the DCB correction effect was slightly better than TGD.