# Comparison Analysis on the Accuracy of Galileo PPP Using Different Frequency Combinations in Europe
## 4 Conclusions  
The Galileo constellation has been demonstrated to have good signal quality and high precision satellite orbits/clocks products. However, the dual-frequency E1/E5a observations are generally used for the satellite clock estimation and PPP. The contribution of different frequency combinations to the static and kinematic PPP is unclear. Therefore, stations located in the European region, which is distributed with dense reference networks and promising augmented PPP service, were selected for the demonstration.  
First, we compared the accuracy of dual-frequency Galileo E1/E5a PPP and BDS B1/B3 PPP with that of GPS L1/L2. Though the number of observed Galileo satellites was less than GPS, the accuracy could be improved by 59% and 12% in the north and up direction. Moreover, BDS could achieve better accuracy in the north direction than GPS, whereas the accuracy on the east and up components are worse. Overall, dual-frequency GPS, Galileo, and BDS PPP can achieve better than 5 mm accuracy in the horizontal direction and better than 10 mm in the up direction.  
Then, the accuracy improvement of static PPP using additional Galileo frequencies on PPP was analyzed, including the different dual-frequency and multi-frequency combinations. Results indicated that the Galileo performs better than the GPS and BDS PPP; however, the E1/E5b combinations degrade the accuracy due to the additional frequency-induced biases. Overall, the triple- and four-frequency raw PPP can improve the accuracy in the top direction by 11%, reaching 4.8 mm. Moreover, analysis indicates that the multi-GNSS combinations can improve the accuracy of hourly static PPP, reaching 5.6 mm/9.2 mm/12.6 mm for the raw PPP model.  
Finally, the convergence time and accuracy of kinematic PPP were analyzed using the PCR indicator. The single GPS and BDS PPP takes more than 30 min to achieve 80% PCR, and the performance can be greatly improved after combining the Galileo observations. Besides, the PCR are correlated with the receiver-related biases. An average 80% PCR can be achieved after 20 min and 97% can be achieved after 30 min. The Galileo kinematic PPP are also degraded by the E1/E5b observation combinations.  
[PERSON] completed the theoretical research and design of the manuscript and completed the writing of the manuscript. [PERSON] developed the software for the PPP processing and guided the experimental process. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Anhui Educational Commission Key Project (KJ2020A00706), the National Natural Science Foundation of China (42104018) and Natural Science Foundation of Jiangsu Province (20 KJB170008).  
Not applicable.  
The raw GPS data are available from [[https://igs.bkg.bund.de/](https://igs.bkg.bund.de/)]([https://igs.bkg.bund.de/](https://igs.bkg.bund.de/)), (accessed on 19 October 2021). All processed GPS data during the study are available from the corresponding author by request.  
Figure 12: PCR for different Galileo frequency combinations.  
**Acknowledgments:** The authors would like to thank the IGS network and EUREF network for providing the multi-GNSS data; MGEX for providing the precise orbits and biases correction files. The authors would also like to thank all anonymous reviewers for their valuable comments, which refined the present work.  
**Conflicts of Interest:** The authors declare no conflict of interest.