# Relative Positioning in Remote Areas Using a GNSS Dual Frequency Smartphone
## 3 Satellite Visibility and Observed Signals
### Satellite Visibility  
Figure 4 below, shows the skyplots and geometry during each test, as seen by each GNSS receiver used.  
Figure 4: \(Cont\).  
Figure 4: _Cont._  
From the skyplots in Figure 4a,b, we see that the satellites tracked by the two smartphones are slightly different. When we look at the comparison with geodetic grade receivers, the differences are more noticeable, with the mobile device tracking fewer satellites, as seen in Figure 4c-f. This is most notorious in the case of the Galileo constellation, as we can see in Figure 5 and Table 2.  
In Table 2, we see, for Galileo and GPS constellations, the minima, and maxima number of satellites in view, obtained for observations with a \(0^{\circ}\) elevation mask, by the smartphones and by the geodetic receivers used in the experiments.  
The constellations geometry, defined by the PDOP average, is also shown in the table. Figure 5 shows the satellite number along the observation interval, seen on each test by the different devices, for Galileo and GPS.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & & **Galileo** & & & **GPS** & & & **Galileo + GPS** & \\ \hline
**Test** & **\# SV** & **\# SV** & **PDOP** & **\# SV** & **\# SV** & **PODP** & **\# SV** & **\# SV** & **Max.** & **PDOP** & **Device** \\ \hline
1 & 3 & 7 & 3.7 & 7 & 12 & 1.7 & 11 & 17 & 1.4 & Smartphone A \\  & 4 & 7 & 2.6 & 7 & 11 & 1.8 & 13 & 17 & 1.3 & Smartphone B \\ \hline
2 & 5 & 7 & 2.7 & 6 & 12 & 1.6 & 12 & 17 & 1.3 & Smartphone \\  & 6 & 8 & 2.3 & 7 & 12 & 1.5 & 13 & 19 & 1.1 & Alloy \\ \hline
3 & 3 & 6 & 6.1 & 8 & 12 & 1.7 & 13 & 17 & 1.3 & Smartphone \\  & 7 & 8 & 2.0 & 10 & 12 & 1.4 & 17 & 19 & 1.1 & PolaRx5 \\ \hline
4 & 3 & 6 & 7.3 & 6 & 11 & 1.7 & 10 & 16 & 1.4 & Smartphone \\  & 6 & 9 & 2.3 & 8 & 11 & 1.6 & 15 & 18 & 1.2 & Alloy \\ \hline
5 & 4 & 7 & 4.1 & 6 & 10 & 1.9 & 11 & 16 & 1.5 & Smartphone \\  & 8 & 11 & 1.8 & 8 & 11 & 1.6 & 16 & 20 & 1.1 & Alloy \\ \hline
6 & 1 & 5 & 4.1 & 7 & 12 & 1.6 & 9 & 16 & 1.4 & Smartphone \\  & 5 & 9 & 2.3 & 9 & 12 & 1.6 & 15 & 20 & 1.1 & Alloy \\ \hline \hline \end{tabular}
\end{table}
Table 2: Satellites in view and PDOP for Galileo, GPS, and Galileo + GPS constellations.  
Figure 4: Skyplot: Test 1 smartphone A (**a**) and smartphone B (**b**); Test 2 smartphone (**c**) and Alloy receiver (**d**); Test 3 smartphone (**e**) and PolaRx5 receiver (**f**); Test 4 smartphone (**g**), Test 5 smartphone (**h**); Test 6 smartphone (**i**).  
Looking at Table 2, Figure 4a,b and Figure 5a, we see a slight difference in the tracked satellites, and geometry, for the smartphones used during Test 1. For smartphone B we have a better PDOP when we only consider the Galileo satellites, while for smartphone A we see a slightly better PDOP when we consider only the GPS satellites. This can be explained by the differences in the number of satellites shown in Figure 5a, as device B observed more Galileo satellites than device A, whereas in the case of GPS the opposite occurred.  
In tests 2 to 6, we see that the smartphone tracked a smaller number of satellites, either Galileo or GPS, when compared to the two geodetic receivers, the Trimble Alloy and the Septentrio PolaRx5. This can be explained by the much lower quality of the antenna but also by the smaller number of channels available on non-geodetic devices.  
Figure 5: Number satellites for Galileo and GPS: Test 1 (**a**); Test 2 (**b**); Test 3 (**c**); Test 4 (**d**); Test 5 (**e**); Test 6 (**f**).