## 3 Results
### Velocity Domain Results  
In this section, the main outcomes of this study are reported; in particular, the estimated velocities are analyzed for each considered device and for single GNSS cases. In Figures 7 and 8, the behaviors of the horizontal and vertical velocity errors are shown; in all panels, the solution obtained using Doppler shift measurements is represented by the red line, while the blue line represents the solution obtained with the TDCP technique. In this case, the figures are composed as described in the previous section. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Novatel**} & \multicolumn{3}{c}{**uBlox**} & \multicolumn{3}{c}{**Xiaomi**} \\ \hline  & & **Min** & **Mean** & **Max** & **Min** & **Mean** & **Max** & **Min** & **Mean** & **Max** \\ \hline \multirow{2}{*}{**GAL**} & Doppler & - & - & - & 5 & 7.21 & 8 & 0 & 2.99 & 5 \\  & TDCP & - & - & - & 5 & 7.20 & 8 & 0 & 2.00 & 3 \\ \hline \multirow{2}{*}{**BDS**} & Doppler & - & - & - & 5 & 5.77 & 6 & 3 & 5.00 & 6 \\  & TDCP & - & - & - & 5 & 5.77 & 6 & 2 & 4.97 & 5 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._  
Figure 7: Horizontal Doppler-based and TDCP-based velocity error. 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 BeiDou. 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. For the performance in the velocity domain using GPS measurements, the panels (a) (b), and (c) of Figures 7 and 8 are considered. From the figures, it is evident that Doppler-based and TDCP-based velocities are accurately estimated when GPS measurements from Novatel are used, while when using GPS measurements provided by uBBox, the TDCP velocity error is mostly about one order of magnitude less than Doppler one, as emphasized by the mean errors. Nevertheless, frequent spikes in the TDCP solution can be noted and are caused by anomalous measurements, supposedly due to cycle slips. For GPS measurements collected by Xiaomi, panel (c), sudden climbs in horizontal and vertical errors are evident in both the Doppler and TDCP cases (more pronounced in the latter), due to poor geometry; indeed, such error increases correspond to the DOP increase shown in Figure 6.  
For Glonass measurements with uBBox, the first part of the session is characterized by frequent spikes in the TDCP solution, panel (d), while in the second part, a degradation in both the Doppler and TDCP solutions is present, due to a reduction in the available measurements and to a consequent geometry worsening; maximum errors are higher, being about a few m/s. When using Glonass measurements from the Xiaomi device, panel (e), the number of available Doppler measurements is mainly four in the first part of the session and below four in the second part, making the solution computation impossible. In the first part,  
Figure 8: Vertical Doppler-based and TDCP-based velocity error. 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 BeiDou. The panel in the first column, **(a**), refers to the Novatel device; panels in the second column, (**b,d,f,h**), to uBBox; and panels in the third column, (**c,e,g,i**), to Xiaomi. sudden jumps in error values indicate the presence of blunders among the measurements. TDCP measurement availability is worse with longer solution unavailability; blunders are also present, leading to a maximum error exceeding 30 m/s.