# GNSS Positioning Using Mobile Devices with the Android Operating System
## 4 Results and Discussion
### Real-Time Kinematic Positioning  
The main concept behind the real-time kinematic (RTK) positioning is that you need to obtain real-time differential corrections broadcasted by one or more permanent stations. In this work, the \"Servizio di Posizionamento Interregionalue\" GNSS (SPIN GNSS) Network ([[https://www.spingnss.it/spiderweb/frmIndex.aspx](https://www.spingnss.it/spiderweb/frmIndex.aspx)]([https://www.spingnss.it/spiderweb/frmIndex.aspx](https://www.spingnss.it/spiderweb/frmIndex.aspx))) was considered, selecting the Virtual Reference Station (VRS) as differential correction, and the Radio Technical Commission for Maritime (RTCM) 3.0 message for the broadcasted throw. To use both u-blox and smartphone contemporarily, it is necessary to have the GNSS Internet Radio software ([[https://igs.bkg.bund.de/ntrip/download](https://igs.bkg.bund.de/ntrip/download)]([https://igs.bkg.bund.de/ntrip/download](https://igs.bkg.bund.de/ntrip/download))) that allows obtaining the differential corrections for a location near to the test site. This last software also allows us to save the corrections in a text file, to provide the same input data for both the u-blox and smartphone. Then, the RTKNAVI tool that is part of the RTKLIB software, was used to perform the network real-time kinematic (NRTK) positioning. Even in this case, the authors performed two different measurement campaigns with a session length of 5 and 10 minutes, respectively. This choice was due to the time interval that a generic user can wait for obtaining a positioning accuracy of about 5 cm, as described in [12]. As in the previous case, the test site that is in the open-sky area (site B) was chosen. Nevertheless, using the Huawei P10+ smartphone, no signal observation with phase ambiguities fixed as an integer value [24] were obtained, as it is possible to see from Table 11. Completely different results were obtained considering the u-blox receiver (Table 12). In this case, in 83% of solutions, the phase ambiguities were fixed as integer values, and the accuracies were about 3-4 cm both for 2D and up component. The second part of this analysis regards the positioning quality for observation epochs, where the phase ambiguities are not fixed (float solutions). Analyzing these results, it should be emphasized that the u-blox receiver provided precisions comparable to the fixed solutions, while accuracies were around 40 cm for both 2D and up components. Considering Tables 11 and 13, it is evident how these two different smartphones provided completely different results, not only in terms of percentage of fix solutions but also in terms of \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Fix** & \multicolumn{3}{c}{**0\%**} \\ \hline  & East & North & Up \\ Precision & N/A & N/A & N/A \\ Accuracy & N/A & N/A & N/A \\ \hline
**Float** & \multicolumn{3}{c}{**100\%**} \\ \hline  & East & North & Up \\ Precision & 3.089 & 2.677 & 4.888 \\ Accuracy & 4.822 & 3.184 & 5.516 \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Real-time positioning results using Huawei receiver and a session length equal to 5 min. Values in meters. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Fix** & \multicolumn{3}{c}{**83\%**} \\ \hline  & East & North & Up \\ Precision & 0.004 & 0.005 & 0.013 \\ Accuracy & 0.034 & 0.012 & 0.041 \\ \hline
**Float** & \multicolumn{3}{c}{**17\%**} \\ \hline  & East & North & Up \\ Precision & 0.014 & 0.007 & 0.042 \\ Accuracy & 0.293 & 0.359 & 0.391 \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Real-time positioning results using the u-blox receiver and a session length equal to 5 min. Values in meters. precision and accuracy. The Samsung S8+ provided good results in terms of accuracy, even if the precision values were not so elevated, reaching a low percentage of fix epochs (14%). The behavior of Huawei P10+ results was completely different. The accuracies were in the interval between 3.18 m and 5.52 m, while the precisions were within 2.67 m and 4.88 m. Moreover, no fix solutions were available with this kind of device.