## 4 Conclusions  
In this paper, the performance of TDCP and Doppler shift velocity estimation is analyzed. The performance of the two methods is assessed in terms of horizontal and vertical velocity errors, exploiting mean, rms, and maximum error indicators. The two techniques were evaluated using real data collected by three different devices: a professional receiver, a low-cost receiver, and a smartphone. A preliminary analysis of the data provided by the three devices was performed and revealed the following:  
* The professional receiver provides continuous CP measurements, while discontinuities have been noted for the low-cost receiver and, even more, for the smartphone chip. * For all the considered devices, Doppler shift measurements are more continuous than CP measurements. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & **Novatel** & **uBlox** & **Xiaomi** \\ \hline \multirow{3}{*}{**GPS**} & & **(\%)** & **(\%)** & **(\%)** \\ \cline{2-5}  & Doppler & 100.00 & 100.00 & 99.94 \\  & TDCP & 99.97 & 99.85 & 99.67 \\ \hline \multirow{2}{*}{**GLO**} & Doppler & - & 65.89 & 2.42 \\  & TDCP & - & 63.74 & 2.12 \\ \hline \multirow{2}{*}{**GAL**} & Doppler & - & 99.52 & 0.00 \\  & TDCP & - & 99.91 & 0.00 \\ \hline \multirow{2}{*}{**BDS**} & Doppler & - & 100.00 & 99.27 \\  & TDCP & - & 99.97 & 97.85 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Reliable availability for single devices and single GNSSs. * The signal strength for the professional receiver is in general higher and more stable than that for the low-cost device, and the difference with respect to the smartphone is even more evident. * For the smartphone, during the test, it was observed that a very limited number of Galileo and Glonass measurements was available, leading to a reduced solution availability and a large error in the velocity solution. * RAIM-FDE has no impact on both Doppler shift and TDCP velocities when a high-grade device is used, while evident benefits are appreciated considering the measurements of low-cost devices. * The effects of RAIM-FDE are evident in the uBlox and Xiaomi cases, leading to a reduction in almost all the errors, for both the horizontal and vertical components. In the velocity domain, TDCP measurements from a professional receiver led to a more accurate solution for both the horizontal and vertical components. The smallest difference between the TDCP and Doppler shift solutions has been observed for the smartphone case. In particular, remarkable performance was obtained using Doppler shift measurements; in this case, the performance of the smartphone is similar to that of the professional receiver. When TDCP measurements from a low-cost device and from a smartphone are used, spikes are evident and lead to a degraded final solution. The spikes were due to erroneous CP observables and cycle slips. In order to mitigate these effects, a RAIM-FDE algorithm was included in the velocity estimation. The algorithm is able to identify and exclude multiple simultaneous outliers, leading to a sensible reduction in the velocity error. For all the configurations using professional and high-sensitivity receivers, the reliable availability is close to 100%, with a reduction in all the statistical parameters in the velocity domain. The performance of the RAIM-FDE block is strongly affected by the measurement redundancy. This effect is particularly evident for the Glonass and Galileo cases using the Xiaomi device, where the reliable availability is more than halved. This work has studied the potentiality of an advanced technique for GNSS velocity, namely TDCP. From the results, it emerges that such a technique could find interesting applications according to the used device: in a geodetic-grade receiver, it could be used for precise applications like mobile mapping; in low-cost devices, it could be used on UAV platforms, increasing the performance of velocity estimation for navigational purposes.