# BDS-3 Triple-Frequency Timing Group Delay/Differential Code Bias and Its Effect on Positioning
## 3 Results and Analysis
### Effect of DCB on PPP Parameters  
In this section, the effects of pseudorange residuals, IFB, tropospheric delay, ionospheric delay and floating ambiguity with and without DCB correction are examined.  
Figure 12 provides the pseudorange residuals of IF123-0 at AREG on DOY 182, 2022; the different colors represent different satellites. The pseudorange residuals are significantly  
Figure 11: Average convergence time of UC123.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Model**} & \multicolumn{3}{c}{**non-corr/cm**} & \multicolumn{3}{c}{**dcb-corr/cm**} \\ \cline{2-7}  & **E** & **N** & **U** & **E** & **N** & **U** \\ \hline UC123 & 1.70 & 0.94 & 2.18 & 1.69 & 0.92 & 2.15 \\ \hline \end{tabular}
\end{table}
Table 8: Average positioning accuracy of PPP after convergence for UC123 model.  
Figure 10: Positioning errors of UC123-0 at AREG station; 24-h time series.  
larger when the DCB is not corrected, and there is a systematic bias. The pseudorange residuals after correcting the DCB are closer to zero-mean random noise.  
The IFB needs to be estimated for IF1213 and UC123 models due to the existing DCB. Figure 13 shows the IFB of the IF1213 and UC123 models at AREG. It is obvious from the figure that the non-corr is affected by satellite DCB, with significantly larger fluctuations, and gradually stabilizes with time. Moreover, dcb-corr positioning mode is only affected by the receiver DCB, and the fluctuation is less than 0.2 m over 24 h, indicating that the IFB parameters have short-term stability after correcting the satellite DCB.  
Figure 14 shows the slant total electronic content (STEC) at AREG. Different colors in the figure represent different satellites. When the DCB is not corrected, the part of the DCB will be absorbed by the ionospheric delay, resulting in an abnormal STEC. When the DCB is corrected, the STEC is more stable. A significant increase in STEC occurs at approximately 12 h, likely owing to the location of the AREG station being near the equatorial region of South America where ionospheric activity is active. There is a strong correlation between DCB and the ionosphere, and DCB has a strong influence on estimated ionospheric parameters.  
Figure 15 shows the tropospheric delay differences between dcb-corr and non-corr at AREG. There is almost no difference between the non-corr and dcb-corr tropospheric delays, and the difference remains less than 5 mm in the vast majority of epochs, indicating that the DCB correction has less impact on the estimated troposphere parameters.  
Figure 16 shows the floating ambiguity differences between dcb-corr and non-corr at AREG. As seen from the figure, the DCB effects on floating ambiguities are different for different satellites, especially at the beginning of the observation epochs. In contrast, the floating ambiguity difference converges to the same value for all satellites with the increase of the filtering time, and the fluctuation is gradually stabilized.  
Figure 12: Pseudorange residuals of IF123-0 model at AREG.  
Figure 13: IFB of IF1213 and UC123 models at AREG.