# Single-Baseline RTK Positioning Using Dual-Frequency GNSS Receivers Inside Smartphones
## 6 Conclusions  
The precise positioning using mobile devices is still currently a challenge. The goal of cm-level accuracy in real-time has not yet been reached, mainly due to the quality of GNSS raw measurements obtained from smartphones. As discussed in previous studies, this is not the final purpose of the employment of these devices, especially because there are some unclear aspects, such as the difficulty of determining the exact position of the smartphone GNSS antenna. Even if the position of the GNSS chipset is known in most of the manufacturer schemas, the antenna position is usually not highlighted. So, the idea is to focus the attention on the precision of the solution, in order to guarantee high reliability of the obtained results.  
From this study, it is confirmed that it is possible to reach a cm-level of precision if an RTK single-baseline positioning approach is considered, even if the master device is a smartphone too. Firstly, a typical RTK positioning using a geodetic receiver as master and a smartphone as rover is considered: this has represented the \"best\" possible scenario where a smartphone device can work in real-time, under the assumption that a CORS network is not available. In this case, this work has demonstrated once again that it is not useful to reach a fixed solution using smartphone devices, because both the quality of GNSS signals and the software available today for real-time positioning are not able to fix the phase ambiguities in the right way. Considering the FLOAT-only solutions, it is possible to reach a precision of about few mm both in the case of single- or multi-frequency solutions.  
The exploitation of multi-constellation GNSS chipsets allows us to obtain better precision with respect to the GPS-only results, especially in when considering the smartphone-smartphone baseline: the best results can be obtained when considering the GPS+Galileo constellations, with a precision of about 2 cm both for 2D and Up components in the case of L1+L5 frequencies, or 3 cm for 2D components and 2 cm for the Up component in the case of an L1 frequency. When the GLONASS constellation is also added, the results are worse. In case of the employment of the only L1 frequency, the precision is about 13 cm for 2D components and 80 cm for the Up, while when adding the L5 frequency there is an improvement only for this last component, reaching a precision of about 50 cm. The accuracies are not bad too, allowing the achievement of a sub-meter solution for 2D components in all cases and a level of accuracy of about 1 m for the Up component.  
In conclusion, it is possible to affirm that these results are very promising for cooperative positioning using smartphone devices in outdoor environments.  
Figure 11: Comparison between L1 and L1+L5 solutions considering GPS+Galileo constellations and ratio = 30.  
**Author Contributions:** Conceptualization: P.D.; Methodology: P.D. and V.D.P.; Software: P.D.; Validation: V.D.P.; Formal Analysis: V.D.P.; Writing-Original Draft Preparation: V.D.P.; Writing-Review & Editing: P.D.; Supervision: P.D.  
**Funding:** This research received no external funding but it is part of the research activities made at the PIC4 SeR Interdepartmental Centre of Politecnico di Torino (Italy).  
**Acknowledgments:** The authors would like to thank reviewers for their helpful comments and suggestions.  
**Conflicts of Interest:** The authors declare no conflict of interest.