## 3 Results
### Preliminary Data Analysis: Measurement Availability, Signal Strength, and Geometry
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Mean (dB-Hz)**} & \multicolumn{3}{c}{**Max (dB-Hz)**} & \multicolumn{3}{c}{**Min (dB-Hz)**} \\ \hline  & **Novatel** & **uBlox** & **Xiaomi** & **Novatel** & **uBlox** & **Xiaomi** & **Novatel** & **uBlox** & **Xiaomi** \\ \hline
**GPS** & 44.7 & 41.3 & 37.7 & 49.6 & 50.0 & 44.9 & 31.0 & 10.0 & 13.3 \\ \hline
**GLO** & - & 39.8 & 31.5 & - & 49.0 & 43.4 & - & 10.0 & 11.2 \\ \hline
**GAL** & - & 40.2 & 36.2 & - & 51.0 & 44.0 & - & 13.0 & 16.9 \\ \hline
**BDS** & - & 36.9 & 30.2 & - & 51.0 & 43.1 & - & 10.0 & 9.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mean, maximum, and minimum \(C/N_{0}\) values in dB-Hz for single GNSS and device (mask angle and \(C/N_{0}\) limit not applied). Figure 5: \(C/N_{0}\) behavior over time (mask angle and \(C/N_{0}\) limit not applied) for satellite G02, panel (a), and for satellite G06, panel (b). actually used Doppler and CP measurements are reduced in comparison to the ones shown in Figures 2 and 4. In Figure 6, the numbers of used Doppler shift and TDCP measurements are shown for each GNSS and for each considered device, following the scheme described in the previous figures. TDCP measurements are obtained by differencing two consecutive CPs, so it is sufficient that at least one of the two CPs is missing for inhibiting TDCP measurement; for this reason, it is expected that the number of TDCP measurements is less than the number of Doppler measurements. In the same figure, the corresponding 3D DOP is shown too. The numbers of used Doppler and TDCP measurements are drawn in cyan and blue, respectively; the corresponding 3D DOP values are drawn in magenta and red, respectively. The number of measurements and the corresponding 3D DOP are strictly related; indeed, DOP increases when the number of measurements decreases and vice versa. An analysis of the GPS-only case reveals that for the Novatel device (panel (a)), the numbers of Doppler and TDCP measurements are the same (except for the first epoch, when the TDCP measurements cannot be obtained). For uBlox, panel (b), some punctual reductions in measurements, can be noted but the numbers of Doppler and TDCP measurements are always larger than four, allowing the estimation of velocity. For Xiaomi, panel (c), a larger difference between TDCP and Doppler shifts can be app  
Figure 6: Numbers of Doppler and TDCP measurements (mask angle and \(C/N_{0}\) limit applied). Each panel refers to a single device and to a single GNSS. Panels in the first row, (**a–c**), refer to GPS; panels in the second row, (**d**,**e**), to Glonass; panels in the third row, (**f**,**g**), to Galileo; and panels in the fourth row, (**h**,**i**), to BeilDou. The panel in the first column, (**a**), refers to the Novatel device; panels in the second column, (**b**,**d**,**f**,**h**), to uBlox; and panels in the third column, (**c**,**e**,**g**,**i**), to Xiaomi. going down to four. Regarding geometry, for the Novatel device, the 3D DOP behavior, in panel (a), is regular, with values below 2.5 and with two small jumps in correspondence with changes in measurement availability; the red and magenta lines are coincident. For uBlox, only a few additional jumps are visible in panel (b), related to the sudden variations in measurements. The frequent variations in GPS measurements in Xiaomi lead to irregularities in the red and magenta lines; when four TDCP measurements are available, the corresponding DOP value exceeds 15 (panel (c)). For Glonass, panels (d) and (e), the number of measurements used varies between four and seven for uBlox, and few differences between the Doppler and TDCP cases can be noted. For the Xiaomi case, the number of used Doppler shift measurements is between one and five; the situation is even worse for TDCP measurements, which exhibit significant drops in comparison to the Doppler shift.