# BDS-3 Triple-Frequency Timing Group Delay/Differential Code Bias and Its Effect on Positioning
## 5 Conclusions  
The new signals, B1C and B2a of BDS-3, have better signal quality and higher code accuracy, leading to significant development of multifrequency positioning. DCB is the primary error in precise positioning and ionospheric modeling. The DCB correction models of BDS-3 for IF123, IF1213 and UC123, based on broadcast ephemeris clocks and precise clock products, are derived in this paper. The experiments of the DCB influences on the SPP and PPP are demonstrated. The following conclusions can be drawn:  
1. The 1-month average STD of the DCB product released by CAS for most of the satellites of the BDS-3 is smaller than 0.5 ns, and the difference between TGD and DCB for most satellites is less than 2 ns.
2. The TGD significantly impacts the SPP positioning accuracy. The improvement rate of IF123 and IF1213 is in the range of 73-90%, and that of UC is in the range of 27-30% after the TGD is corrected. The average positioning accuracies of IF123 and IF1213 with TGD correction in the E, N and U components are 0.91, 0.91, 2.84 m and 0.96, 0.94, 2.79 m, respectively, while those of UC123 are 1.00, 1.32 and 2.84 m. In addition, the correction effect of the DCB is slightly better than TGD.
3. IF123, IF1213 and UC123 PPP improved their positioning accuracy by 31-66% after DCB correction, but the accuracy improvement was shown mostly at the early stage of the epoch. After a period of convergence, the effect on the positioning accuracy of the 3 models was less than 3 mm with or without DCB corrections. The convergence time was 26.1, 26.9 and 38.3 min for IF123, IF1213 and UC123, respectively, which is 6.79%, 2.54% and 8.59% shorter than before the correction.
4. The distribution of the pseudorange residuals approaches zero-mean random noise after the DCB is corrected. Usually, the uncorrected DCB is absorbed by IFB, ionospheric delay and floating ambiguity, but the tropospheric delay is less affected by DCB.  
Conceptualization, Y.D.; methodology, Y.D. and X.J.; software, Y.D. and J.L.; formal analysis, Y.D. and Q.L.; investigation, Y.D. and W.Y.; writing--original draft, Y.D.; writing--review and editing, Y.Y. and X.J.; visualization, Y.D., J.L. and Q.L.; resources, J.L. and W.Y.; validation, W.Y.; supervision, Y.Y.; funding acquisition, Y.Y. and X.J. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (41874041 and 41931076).  
Data Availability StatementThe GNSS observation data from the IGS MGEX networks can be obtained at [[ftp://igs.gnsswhu.cn/pub/gps/data](ftp://igs.gnsswhu.cn/pub/gps/data)]([ftp://igs.gnsswhu.cn/pub/gps/data](ftp://igs.gnsswhu.cn/pub/gps/data)) (accessed on 10 April 2023). The precise products from GFZ are available at [[ftp://igs.gnsswhu.cn/pub/gps/products/mgex](ftp://igs.gnsswhu.cn/pub/gps/products/mgex)]([ftp://igs.gnsswhu.cn/pub/gps/products/mgex](ftp://igs.gnsswhu.cn/pub/gps/products/mgex)) (accessed on 10 April 2023). The DCB products provided by CAS can be obtained at [[ftp://igs.gnsswhu.cn/pub/gps/products/mgex/dcb](ftp://igs.gnsswhu.cn/pub/gps/products/mgex/dcb)]([ftp://igs.gnsswhu.cn/pub/gps/products/mgex/dcb](ftp://igs.gnsswhu.cn/pub/gps/products/mgex/dcb)) (accessed on 10 April 2023).  
The authors are grateful to iGMAS and MGEX for providing data and products for analysis.  
The authors declare no conflict of interest.