# A Controlled-Environment Quality Assessment of Android GNSS Raw Measurements
## 4 Results and Discussion
### Positioning Solutions  
The positioning solutions were first obtained by directly postprocessing the raw measurements through the WLS algorithm in the GNSS Toolbox without implementing atmospheric corrections. Figure 11 displays the horizontal two-dimensional position solutions of the devices with the true position at the origin in the absence (panel **(a)**) and in the presence of carrier smoothing (panel **(b)**, while panel **(c)** is an enlargement of **(b)**). Looking at the left-sided unsmoothed scatter, there appears to be a bias. This is clearer on the smoothed solution on the right side. Precision improves the solution with smoothing, as expected, but with a slight decrease in accuracy, as seen from the figure and Table 2. There was also a deviation visible in the smoothed solution of the Huawei devices, which was not clear before. To explore further, Figure 12 was reported to see the solutions against time, and it is seen that there was an event around \(t^{*}\), after which the stability of the Huawei devices worsened. This coincided with the duty-cycle effect seen in the raw measurements, and the comparison of the raw measurements with the positions can be seen in Figure 13. From the figure, it can be established that this event was limited to the Huawei devices and not due to any instability of the signal coming in, as there was no seen effect on the \(C/N_{0}\) or the Nexus 9 device. Table 3 details the error and precision before and after the event in the devices, and it has to be noted that the North direction was affected the most, as seen  
Figure 11: Position comparison between devices in a controlled environment. (**a**) Smoothing OFF; (**b**) Smoothing ON with weight \(L=50\); (**c**) Smoothing ON with weight \(L=50\) (enlargement). Figure 10: Effect of cycle slips in a controlled environment (PRN 23). from the above figures as well. The big changes in mean and standard deviation of the Huawei devices were evident when compared to the Nexus 9. In Tables 2 and 3, the bias in height measurements was around 20 meters and, although it was affected by the event and smoothing, it remained high. Applying ionospheric and tropospheric corrections, this reduced to around 6 meters, as a result of nonperfect correction models and generic uncompensated errors. \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Smoothing OFF**} & \multicolumn{3}{c}{**Smoothing ON**} \\ \hline \multirow{2}{*}{**Device**} & **North (m)** & **East (m)** & **Height (m)** & **North (m)** & **East (m)** & **Height (m)** \\  & \(\mu\pm\sigma\) & \(\mu\pm\sigma\) & \(\mu\pm\sigma\) & \(\mu\pm\sigma\) & \(\mu\pm\sigma\) & \(\mu\pm\sigma\) \\ \hline Huawei P10 & \(-3.0\pm 2.1\) & \(-1.3\pm 1.0\) & \(-20.1\pm 3.4\) & \(-2.9\pm 0.5\) & \(-1.4\pm 0.5\) & \(-20.2\pm 0.6\) \\ Huawei P10 Plus & \(-2.9\pm 2.2\) & \(-1.2\pm 1.0\) & \(-20.1\pm 3.2\) & \(-2.9\pm 0.5\) & \(-1.3\pm 0.5\) & \(-19.9\pm 0.7\) \\ Nexus 9 & \(-2.8\pm 4.8\) & \(-1.4\pm 2.4\) & \(-20.2\pm 7.5\) & \(-2.8\pm 0.4\) & \(-1.4\pm 0.3\) & \(-20.2\pm 0.6\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Statistics of the positioning solutions obtained from smartphones inside the anechoic chamber. Figure 12: North (**a**) and East (**b**) position error comparison between devices in a controlled environment. Figure 13: PRN 23 (closest) measurements in the controlled environment, highlighting the change around \(t^{*}=210\) s.  
An important observation during position-measurement analysis was the effect of a low-elevation satellite on the position solution. There was significant deviation seen when including PRN 15, which was visible only partly during the test, and this was noticed in all three devices. Figure 14 shows the effects of such a satellite on the positioning results. When compared to Figure 11a, in which PRN 15 was excluded, it is clear that both accuracy and precision increased. In the presence of this satellite, there was a shift mainly in the North component, as seen Figure 15a.