# An Analysis of Satellite Multichannel Differential Code Bias for BeiDou SPP and PPP
## 5 Impact of BDS Satellite DCB on Positioning  
### Performance of SPP  
Six global GNSS tracking stations that could simultaneously observe BDS B1I, B2a, B3I, and B1C signals on DOY 158 of 2021 were selected in this SPP experiment, including JFNG, POTS, SGOC, ULAB, URUM, and WUH2. Multi-system DCB products provided by the CAS were selected to correct the code bias. The broadcast ephemeris and the reference coordinates were provided by the IGS. The experimental single-frequency SPP adopted B1I, B2a, B3I, and B1C signals, and the dual-frequency SPP adopted B1I+B2a, B1I+B3I, B1I+B1C, B2a+B3I, B2a+B1C, and B3I+B1C signal combinations. Three strategies were adopted in the experiment: (1) strategy I (no-corr): SPP without any time delay correction; (2) strategy II (tgd-corr): SPP for time  
Figure 14: Mean values and STDs of the differences between DCBs and the combined OSB values of BDS satellites. Figure 13: The differences between DCBs and the combined OSB values. delay correction using the IGS broadcast ephemeris or complementary use of TGD from the broadcast ephemeris (D1 and D2 broadcast ephemerides from B1I and B3I signals and B-CNVA1 and B-CNVA2 broadcast ephemerides from B1C and B2a signals of BDS-3) provided by the Test and Assessment Research Center (TARC) of the China Satellite Navigation Office; (3) strategy III (dcb-corr): SPP using DCB for delay correction. The impact of DCB on the positioning accuracy of the BDS was analyzed by comparing the correction effect of the TGD provided in the broadcast ephemeris. SPP selects least squares for parameter estimation. The tropospheric delay is corrected using the Saastamoinen model. The ionospheric delay is corrected by the Klobuchar model. Shown in Figure 15 are the single-frequency SPP errors in the east (E), north (N), and up (U) directions with the signals of B1I, B2a, B3I, and B1C for the WHU2 station with different strategies. The positioning errors in the E, N, and U directions are displayed in the top, middle, and bottom rows of the panels. Each column of panels corresponds to results with one of the four signals, i.e., B1I, B2a, B3I, and B1C from left to right. In each panel, the positioning errors with no correction, TGD correction, and DCB correction are displayed as green, blue, and red points, and the corresponding mean values and root mean square (RMS) values are also marked. The positioning accuracy of single-frequency SPP was obviously improved after TGD or DCB correction, as shown in Figure 15. The mean values of positioning errors in the E, N, and U directions are 1.06, 0.33, and 0.39 m with TGD correction and 1.06, 0.32, and 0.38 m with DCB correction, which are improved by an average of 23.21% and 23.54% compared with no correction. The mean values of positioning errors of B1I, B2a, and B1I SPP in the three directions are improved by an average of 34.40%, 21.37%, and 37.09% with TGD correction and by an average of 34.99%, 21.33%, and 37.84% with DCB correction, respectively. The TGD and DCB correction effects for B1I, B1C, and B2a are basically the same. As the satellite clock of the broadcast ephemeris refers to the B3I signal, there is no difference in the B3I results under the three strategies, as shown in Figure 15.  
The horizontal (2D) and three-dimensional (3D) mean values and RMS values of positioning errors with the three strategies were calculated and are shown in Figure 16. After TGD and DCB correction of single-frequency SPP, horizontal and 3D positioning accuracies were significantly improved compared with no correction, and the improvement effect of TGD and DCB correction was basically identical. Considering the results of the  
Figure 15: Positioning errors of single-frequency SPP for the WHU2 station with the three strategies. six stations, the horizontal positioning and 3D positioning accuracies were improved by 41.94% and 41.93% with TGD correction and by 44.09% and 44.07% with DCB correction, respectively.