# An Analysis of Satellite Multichannel Differential Code Bias for BeiDou SPP and PPP
## 5 Impact of BDS Satellite DCB on Positioning
### Performance of PPP  
To further analyze the static PPP performance of DCB corrections, a dual-frequency PPP experiment based on DCB was carried out on observation data from the six stations using the strategy shown in Table 7. Figure 20 indicates the positioning errors of dual-frequency PPP with the two strategies for the E, N, and U directions of the ULAB, URUM, and WUH2 stations. Strategy I (no-corr) and strategy II (dcb-corr) are indicated by solid and dotted lines. The red, yellow, blue, green, and purple lines indicate B1I+B2a, B1I+B3I, B2a+B3I, B2a+B3I, B3I+B1C, and B3I+B1C PPP, respectively. The convergence criteria are that deviation in the E and N directions is less than 0.05 m and that subsequent epochs are stable within 0.05 m, with the convergence time of the PPP being the time taken from the beginning of the solution to the epoch. As can be seen from Figure 20, DCB can effectively improve PPP accuracy and the results are more stable, though the improvement in convergence time is not obvious. The positioning results of B2a+B3I are significantly different from those of other signal combinations at the following three stations. Compared with the positioning results with no correction, positioning accuracy in the E, N, and U directions was improved by 6.23%, 20.97%, and 17.07% with DCB correction. The convergence time of B2a+B3I PPP with DCB correction was shorter than that with no correction, as shown in Figure 20. The convergence time of the B1I+B2a, B1I+B3I, B2a+B1C, and B3I+B1C signal combinations of PPP decreased. Only the convergence of the B2a+B3I signal combination was accelerated by 27.96%. Mean \begin{table}
\begin{tabular}{c c} \hline \hline
**Content** & **Strategy** \\ \hline Positioning model & Ionosphere-free combination \\ Elevation mask & 10\({}^{\circ}\) \\ Sampling rate & 30 s \\ Observation weighting & Elevation angle weighting \\ Satellite orbit and clock & Products from GFZ analysis center \\ Satellite and receiver antennas & isgi14.4x \\ Station coordinates & IGS coordinates of the weekly solution \\ Satellite DCB corrections & DCB products provided by the CAS \\ Troposphere delayed & Dry component: Saasanomion model \\ Ionosphere delay & Wet component: random wandering process estimation \\ Relativistic effects & White noise process estimation \\ Phase wrap & Model correction \\ Solid tide & Model correction \\ Earth rotation & Model correction \\ Receiver clock error & White noise process estimation \\ Station coordinates & Time constant estimation \\ Ambiguity & Float solution, constant estimation \\ Deal with signal combination & B1I+B2a, B1I+B3I, B2a+B3I, \\  & B2a+B1C, B3I+B1C \\ Processing strategies & Strategy I (no-corr): no correction \\ Strategy II (dcb-corr): DCB correction \\ Filtering & Extended Kalman filtering \\ \hline \hline \end{tabular}
\end{table} 
Table 7: BDS PPP processing strategy. Figure 19: Horizontal and 3D positioning errors of dual-frequency SPP with the three strategies. deviation in the E, N, and U directions under the five signal combinations after correcting DCB reached the centimeter level. The mean values of the positioning errors in the E, N, and U directions with DCB correction were 1.79, 1.13, and 3.77 cm, respectively, which were reduced by 39.40%, 9.42%, and 8.36% compared with the positioning results with no correction. The PPP of B2a+B1C signal combinations with DCB correction had the largest improvement, and the positioning errors of the three directions were reduced by 25.84% on average after DCB correction. The mean RMS values of the positioning errors in the E, N, and U directions changed from 1.29, 0.57, and 1.60 cm with no correction to 1.21, 0.58, and 1.59 cm after DCB correction. Considering that the DCB of the new signal of BDS-3 may affect the estimation of the receiver clock and the combined ionosphere-free ambiguity parameters of the parameters to be estimated, this may lead to longer convergence time for PPP. Overall, the correction of DCBs has a negative impact on the convergence time of PPP.