## 3 Results
### Preliminary Data Analysis: Measurement Availability, Signal Strength, and Geometry
An analysis of the corresponding geometry reveals that for the uBlox device, the 3D DOP values are about 2.5 for the first part of the session, while they jump to values greater than 15 in the second part, characterized by fewer available measurements (panel (d)). For Xiaomi, the number of Glonass measurements is not sufficient in the second part of the session, making the velocity estimation and DOP computation impossible (panel (e)). For Galileo, panels (f) and (g), the behavior of the available measurements seems very regular for uBlox, with between six and eight measurements available for Doppler and between five and eight measurements available for TDCP. For Xiaomi, the number of Doppler measurements is often below four, making the estimation of velocity impossible, while TDCP measurements are always insufficient for the velocity estimation. In an analysis of the corresponding geometry, uBlox shows a good DOP behavior, comparable to the GPS-only case (panel (f)). Xiaomi has sufficient Doppler measurements for estimating velocity only in the last part of the session, while the TDCP measurements are insufficient for the entire session, as shown in panel (g). For BeiDou, the numbers of Doppler and TDCP measurements regularly span between five and six for uBlox (panel (h)), and the number of measurements is most of the time equal to five, with drops to three for Doppler and to two for TDCP, for Xiaomi (panel (i)). For uBlox, the geometry with five measurements is poor, leading to DOP values greater than 15, while with six measurements, DOP values become below 5 (panel (h)). For Xiaomi, when five measurements are available, 3D DOP values are between 2 and 3, and during the sudden measurement drops, DOP values become large, exceeding 15, as shown in panel (i). The availability of Doppler and TDCP measurements during the session is summarized in Table 3, where the minimum, maximum, and average numbers of measurements are shown for each considered GNSS and device. It is evident that Novatel and uBlox are able to track approximately the same GPS satellites while Xiaomi shows a lower minimum value, just sufficient for velocity estimation. The Xiaomi device demonstrates a deficiency in available Glonass and Galileo measurements in comparison to uBlox, which leads to frequent solution unavailability. Regarding BeiDou, uBlox and Xiaomi devices have comparable measurement availability, which is reduced for Xiaomi mainly because of IGSO C08 satellite unavailability. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & & & **Novatel** & & & **uBlox** & & & **Xiaomi** & \\ \hline \multirow{3}{*}{**GPS**} & & **Min** & **Mean** & **Max** & **Min** & **Mean** & **Max** & **Min** & **Mean** & **Max** \\ \cline{2-10}  & Doppler & 8 & 8.71 & 9 & 7 & 8.70 & 9 & 4 & 8.51 & 9 \\  & TDCP & 8 & 8.71 & 9 & 6 & 8.69 & 9 & 4 & 8.39 & 9 \\ \hline \multirow{3}{*}{**GLO**} & Doppler & - & - & - & 4 & 4.97 & 7 & 1 & 3.10 & 5 \\  & TDCP & - & - & - & 4 & 4.93 & 7 & 1 & 2.96 & 5 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Minimum, mean, and maximum numbers of Doppler and TDCP measurements (mask angle and \(C/N_{0}\) limit applied).