# A New DGNSS Positioning Infrastructure for Android Smartphones
## 5 Conclusions  
This paper described the DGNSS positioning infrastructure that delivers improved accuracy to a huge number of users. The infrastructure enables most of calculations to be performed in the server side, bringing benefits to all of relevant smartphones. When implementing the DGNSS infrastructure, all smartphone types were considered. Because different satellite systems are supported by different smartphones, the infrastructure developed in this paper considers all the combinations of satellite systems used in smartphones.  
A comparison of the proposed infrastructure against the ground truth, for all tests performed in open areas, demonstrated that the RMS horizontal positioning error was reduced to less than 2 m. The test in the open area showed that average horizontal positioning errors were reduced from 2.3 m to 0.8 m, and the RMS horizontal error was reduced from 2.6 m to 1.5 m. The strength of DGNSS is particularly apparent in low-latitude or high-latitude regions, where it removes most of the errors caused by the ionosphere. Another test in Macau (low-latitude regions) showed that the positioning error of the standalone smartphone in the afternoon was much larger than that in the morning. Although the test was performed in 2017 when the solar activity reached almost the minimum, the average horizontal positioning error reached 4.0 m, and the RMS error was as large as 4.4 m. With the infrastructure, the average horizontal positioning error was reduced to 0.4 m, and the RMS error was reduced to 1.8 m.  
It is well known that the DGNSS operation does not reduce the receiver related error (e.g., multipath errors). The receiver related error must be considered by DGNSS in urban areas especially for safety-critical applications, for example, the lane-level positioning system and the collision warning system. In this study, the performance of DGNSS in urban areas was studied, and the test demonstrated that the DGNSS still adds value in the urban environments.  
We also compared the DGNSS based on NMEA messages with the range-domain DGNSS; the comparison showed that the accuracy of a smartphone with infrastructure is still worse than that of range-domain DGNSS on surveying grade devices. Based on the results, the RMS error of  
Figure 8: Trajectory of the pedestrian in the urban area.  
range-domain DGNSS was less than 1 m, and the accuracy of the smartphone positioning with the infrastructure was approximately 1.5 m. The performance of the infrastructure depends on a number of factors, such as the model applied in the chipsets, the position determination algorithms and the weighing methods, as well as the performance of the antenna. In the current infrastructure, we assumed that the most conventional models and algorithms are used in the GNSS chipsets. To obtain the higher accuracy in the future, the direct cooperation with chipset manufactures is required to understand the models and algorithms used in the chipsets.  
The article main idea was proposed by [PERSON] and [PERSON]. [PERSON] and [PERSON] performed the experiments and analyzed the results. [PERSON] and [PERSON] wrote the manuscript and all the authors participated in amending the manuscript. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Shenzhen Science and Technology Innovation Commission (grant number: JCYJ20170818104822282), National Key Research and Development Program of China (grant number: 2016 YFB0502100, 2016 YFB0502101) and Hong Kong Research Grants Council (RGC) (grant number: 152223/18E).  
The authors declare no conflict of interest.