# An Analysis of Satellite Multichannel Differential Code Bias for BeiDou SPP and PPP
## 5 Impact of BDS Satellite DCB on Positioning
### Performance of SPP
The mean values of horizontal positioning errors for B1I, B2a, and B1C were reduced by an average of 35.94%, 30.70%, and 34.87% with TGD correction and by an average of 34.20%, 29.82%, and 35.33% with DCB correction, respectively (all compared with the positioning results with no correction). The 3D positioning errors of B1I, B2a, and B1C were reduced by 43.80%, 29.76%, and 41.33% with TGD correction and by 42.53%, 29.22%, and 41.76% with DCB correction, respectively. The DCB correction effect of B1I was better than that of B1C and B2a. DCB products provided by the CAS and TGD from the TARC and IGS had the same effect on positioning. Figures 17 and 18 describe the positioning errors of the BDS dual-frequency ionosphere-free combination SPP under the above three strategies (taking the WUH2 station as an example). The red and blue sequences are more concentrated and continuous than the green ones in Figures 17 and 18, especially the solution result of B3I+B1C, which indicates that the positioning results are improved after TGD and DCB correction. Comprehensively considering the calculation results of the six stations, the positioning accuracies were improved by 49.12% with TGD correction and by 51.95% with DCB correction compared with the positioning results with no correction. The mean values of positioning errors in the E, N, and U directions were 0.47, 0.33, and 0.60 m with TGD correction and 0.39, 0.26, and 0.62 m with DCB correction. The effect of DCB and TGD correction on the E and N directions was better than that on the U direction. The mean RMS values of positioning errors in the E, N, and U directions were on average 1.30 m with no correction, 1.13 m with TGD correction, and 0.97 m with DCB correction. Figure 19 shows the mean values and RMS values of horizontal and 3D positioning errors under different strategies. Compared with the performance of single-frequency SPP in Figure 15, the corrective effect of dual-frequency combination is more obvious. As can be seen from Figure 19, the horizontal and 3D positioning accuracies were improved by 8.21% and 6.44% with TGD correction and improved by 18.99% and 12.85% with DCB correction, respectively. The mean values of horizontal positioning errors with no correction, TGD correction, and DCB correction are 2.23, 2.05, and 1.81 m, respectively, and the corresponding mean 3D positioning errors are 2.86, 2.68, and 2.44 m, respectively. The RMS values for horizontal positioning errors are 1.73, 1.62, and 1.39 m, respectively, and the RMS values of 3D positioning errors are 2.10, 1.99, and 1.85 m in the three strategies. For the positioning results with different signal combinations, the correction effect of DCB was obviously better than that of TGD, and B1I+B1C and B3I+B1C had the best and worst correction effect in terms of DCB. Using the positioning results with no correction as a reference, the positioning accuracies of B1I+B2a, B1I+B1C, B2a+B3I, B2a+B1C, and B3I+B1C with TGD correction are respectively increased by 16.66%, 34.69%, 11.49%, 4.19%, and 1.11%. Meanwhile, the positioning accuracies of B1I+B2a, B1I+B3I, B1I+B1C, B2a+B3I, and  
Figure 16: Horizontal and 3D positioning errors of single-frequency SPP with the three strategies. B2a+B1C with DCB correction are increased by 17.61%, 24.75%, 40.48%, 30.50%, and 12.87%, respectively. Figure 17: Positioning errors of BDS dual-frequency SPP (combination of B1I+B2a, B1I+B3I, and B1I+B1C) for the WUH2 station with the three strategies. Figure 18: Positioning error of BDS dual-frequency SPP (combination of B2a+B3I, B2a+B1C, and B3I, +B1C) for the WUH2 station with the three strategies.