# Evaluation of Network RTK Positioning Performance Based on BDS-3 New Signal System
## 6 Conclusions  
This paper first describes the current research status of the BDS-3 system and then gives the algorithm processing model of network RTK. Finally, the experimental verification is carried out based on five actual reference stations and one test station of a provincial CORS network in central China. The service effects of BDS-3 new signal combination (B1C+B2a) and transition signal combination (B1I+B3I) were compared from the aspects of atmospheric correction accuracy and regional modeling accuracy. Finally, taking the GPS system as reference, five schemes were designed to evaluate the positioning performance of network RTK in the BDS-3 system. The following conclusions are drawn:  
* When the combination of B1C+B2a and B1I+B3I of a single BDS-3 constellation provides VRS service, the fixed rate of terminal RTK is above 95%, and the horizontal and elevation accuracy are within 1 cm and 2 cm, respectively. The single BDS-3 system is sufficient to meet the needs of providing network RTK high-precision positioning service in surveying and mapping operations. In addition, the terminal positioning effect statistics show that the positioning accuracy of BDS-2 is relatively poor, GPS is superior to BDS-2, the positioning accuracy of BDS-3 is better than that of GPS and BDS-2, BDS-2/3 combined processing of B1I+B3I transition signal has the best effect, and its accuracy in the E and N directions is better than 0.5 cm, and that in the U direction is better than 1.5 cm.
* Based on the analysis of atmospheric correction, regional atmospheric modeling, and network RTK terminal positioning accuracy, it can be seen that the new signal combination (B1C+B2a) of the BDS-3 system is slightly better than the transition signal combination (B1I+B3I). In addition, the double-difference atmospheric correction of the reference station and the accuracy of regional atmospheric modeling both show a positive correlation with elevation angle, so it is necessary to carry out reasonable weighting processing for the satellite according to elevation angle in regional atmospheric modeling.
* According to the above analysis, when a single BDS-3 constellation provides network RTK service, the combination of B1C+B2a is suggested to be adopted as the main frequency signals for calculation. When the BDS-2/3 combined solution provides network RTK service, it is recommended to adopt the B1I+B3I combination as the main frequency signals for the solution.  
It should be noted that the above analysis of BDS-3 is based on two conventional BDS-3 signal combinations, namely the new signal combination (B1C+B2a) and the transition signal combination (B1I+B3I). It is also a signal combination recommended in the literature [15], and the effects of other signal combinations need to be further studied. The slight superiority of the new BDS-3 signal combination (B1C+B2a) over the transition signal combination (B1I+B3I) may be attributed to the advanced signal structure and modulation technology. In the next step, more relevant experiments and analyses will be designed to find deeper reasons.  
Conceptualization, P.W. and H.L.; software, P.W. and Z.Y.; formal analysis, B.S.; data curation, X.X.; writing--original draft preparation, P.W.; writing--review and editing, G.N., B.S. and X.X. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the project \"Key Research and Development Project of Hubei Province\" (No. 2020 BAB095), the project \"Pre-funded Project of Hubei Industrial Innovation Consortium\" (No. 2020 DEB018), the project \"The National Key Research and Development Scheme Strategic International Cooperation in Science and Technology Innovation Program\" (No.2018 YFE0206500).  
Not Applicable.  
The authors declare no conflict of interest.