# An Analysis of Satellite Multichannel Differential Code Bias for BeiDou SPP and PPP
## 7 Conclusions  
In this paper, we systematically introduced the BDS DCB and OSB products and derived correction formulas for the positioning of BDS DCB under broadcast ephemerides and precise ephemerides. Subsequently, we analyzed the stability and correlation of the  
Figure 21: The mean values and RMS values of positioning errors with and without DCB correction for dual-frequency PPP. short- and long-term DCB and OSB products provided by the CAS. Finally, the results of BDS positioning based on DCB and TGD were analyzed. BDS DCBs and OSBs have long-term stability and high correlation between the two products. For the original data provided by DCB and OSB products, the stability of each signal pair of DCB from high to low is as follows: C2I-C7I (BDS-2), C1X-C5X, C1X-C6I, C1X-C7Z, C2I-C6I, C1X-C8X, C2I-C6I (BDS-2), C1P-C5P, and C1P-C6I. The STD of OSBs fluctuates between 1.14 ns and 3.84 ns. The best and worst stability was found for the C2I OSBs of the BDS-3 and the C6I OSBs of the BDS-2, respectively. The mean difference between the DCBs and combined OSBs for each channel fluctuates between \(-2.53\) ps and 2.69 ps, and the STD fluctuates between 1.06 ps and 79.97 ps, which shows that the two parameters have high consistency. The changes in BDS-2 DCBs of the IGSO satellites were opposite to those of the MEO and GEO satellites in the fluctuating period. The DCBs of the BDS-3 for the IGSO satellites were more stable than those of the MEO satellites. Through monthly stability analysis of the DCBs and OSBs, it can be seen that IGSO satellites C07, C08, C09, C10, C13, and C16 of BDS-2 and satellites C32, C35, and C41 of BDS-3 fluctuated greatly in individual months. For BDS SPP, TGD and DCB are both beneficial to the performance of BDS positioning. The impact of DCB correction on SPP is similar to that of TGD correction on single-frequency positioning and superior to that of TGD correction on dual-frequency positioning. The DCB correction of dual-frequency SPP is better than that of single-frequency SPP. In single-frequency SPP, compared with the positioning results with no correction, the positioning accuracies with TGD and DCB correction were improved by 41.94% and 44.09% in the horizontal direction and 41.93% and 44.07% in 3D, respectively. The improvements from DCB correction for B1I, BIC, and B2a became less obvious in turn. In dual-frequency SPP, 3D positioning accuracy with TGD and DCB correction was improved by 6.44% and 12.85%. The improvement effect with DCB correction in terms of positioning ordered from highest to lowest is as follows: B1I+B1C, B2a+B3I, B1I+B3I, B2a+B1C, B1I+B2a, and B3I+B1C. The impact of DCB correction on PPP reaches the centimeter level, and DCB correction effectively improves positioning accuracy; however, correction does delay convergence time to a certain extent. Compared with the positioning results with no correction, horizontal and 3D positioning accuracy was improved on average by 13.53% and 13.84%, respectively. PPP with the combination of B1I+B3I had the largest improvement after DCB correction. The DCB correction effect is more obvious in PPP of B1I+B3I, B2a+B1C, and B3I+B1C signal combinations. Conceptualization, G.W. and Y.Z. ; methodology, Y.Z. and Q.A. ; software and analysis, H.W. and X.S. ; writing, Y.Z. and G.W. All authors have read and agreed to the published version of the manuscript. This work was sponsored by the National Science Foundation of China (Grant No. 42204036, No. 41971416 and No. 42074074). The CDDIS website ([[https://cddis.nasa.gov/archive/gnss](https://cddis.nasa.gov/archive/gnss)]([https://cddis.nasa.gov/archive/gnss](https://cddis.nasa.gov/archive/gnss)) (accessed on 7 June 2021)) was used to obtain the MGEX stations data. The TARC website ([[http://csno-tarc.cn/datacenter/ephemeris](http://csno-tarc.cn/datacenter/ephemeris)]([http://csno-tarc.cn/datacenter/ephemeris](http://csno-tarc.cn/datacenter/ephemeris)) (accessed on 7 June 2021)) was used to obtain the different types of BDS broadcast ephemerides.