## 5 Summary  
The Galileo HAS delivers high-precision Positioning, Navigation, and Timing (PNT) capabilities on a global scale. As the advent of intelligent and autonomous devices gains momentum, the study of PPP time transfer has become a focal point of interest in the kinematic model. This article delves into the characteristics of Galileo/GPS PPP time transfer facilitated by the Galileo HAS service in the kinematic model and presents several key findings. Initially, employing the single GPS PPP approach, which relies on the Galileo HAS service, is advised against for one-way timekeeping. Under static conditions, the PPP time transfer for GPS, Galileo, and the combined Galileo/GPS systems all achieve sub-nanosecond precision. The Galileo-only PPP time transfer outperforms the GPS-only PPP, with the Galileo/GPS PPP time transfer demonstrating the most superior performance. Regarding frequency stability, GPS, Galileo, and the Galileo/GPS PPP systems can attain levels of approximately (5.80 \(\times\) 10\({}^{-14}\), 4.82 \(\times\) 10\({}^{-14}\), 4.07 \(\times\) 10\({}^{-14}\)) at 960 s, respectively, and \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline \multirow{2}{*}{**Time-Links**} & \multicolumn{3}{c}{960 s} & \multicolumn{3}{c}{15,360 s} \\ \cline{2-7}  & \multicolumn{1}{c}{**G**} & \multicolumn{1}{c}{**E**} & \multicolumn{1}{c}{**E/G**} & \multicolumn{1}{c}{**G**} & \multicolumn{1}{c}{**E**} & \multicolumn{1}{c}{**EG**} \\ \hline BRUX-TPBB & 1.62 \(\times\) 10\({}^{-13}\) & 1.34 \(\times\) 10\({}^{-13}\) & 7.22 \(\times\) 10\({}^{-14}\) & 3.06 \(\times\) 10\({}^{-14}\) & 2.80 \(\times\) 10\({}^{-14}\) & 1.16 \(\times\) 10\({}^{-14}\) \\ NIST-PTBB & 7.89 \(\times\) 10\({}^{-13}\) & 2.84 \(\times\) 10\({}^{-13}\) & 1.72 \(\times\) 10\({}^{-13}\) & 1.70 \(\times\) 10\({}^{-13}\) & 8.05 \(\times\) 10\({}^{-14}\) & 4.45 \(\times\) 10\({}^{-14}\) \\ OP71-PTBB & 2.37 \(\times\) 10\({}^{-13}\) & 1.82 \(\times\) 10\({}^{-13}\) & 7.49 \(\times\) 10\({}^{-14}\) & 5.41 \(\times\) 10\({}^{-14}\) & 5.04 \(\times\) 10\({}^{-14}\) & 1.30 \(\times\) 10\({}^{-14}\) \\ TWIT-PTBB & 7.26 \(\times\) 10\({}^{-13}\) & 7.83 \(\times\) 10\({}^{-13}\) & 2.82 \(\times\) 10\({}^{-13}\) & 2.07 \(\times\) 10\({}^{-13}\) & 2.18 \(\times\) 10\({}^{-13}\) & 7.84 \(\times\) 10\({}^{-14}\) \\ USW-PTBB & 6.55 \(\times\) 10\({}^{-13}\) & 3.21 \(\times\) 10\({}^{-13}\) & 1.83 \(\times\) 10\({}^{-13}\) & 2.15 \(\times\) 10\({}^{-13}\) & 1.22 \(\times\) 10\({}^{-13}\) & 4.78 \(\times\) 10\({}^{-14}\) \\ USN-PTBB & 6.09 \(\times\) 10\({}^{-13}\) & 3.04 \(\times\) 10\({}^{-13}\) & 1.79 \(\times\) 10\({}^{-13}\) & 2.18 \(\times\) 10\({}^{-13}\) & 1.16 \(\times\) 10\({}^{-13}\) & 4.83 \(\times\) 10\({}^{-14}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The MDEV of GPS (G), Galileo (E), and Galileo/GPS (E/G) PPP in the static model at 960 s and 15,360 s for six time links. Figure 16: The MDEV of GPS, Galileo, or Galileo/GPS PPP time transfer in the kinematic model. approximately (1.19 \(\times\) 10\({}^{-14}\), 1.13 \(\times\) 10\({}^{-14}\), 8.69 \(\times\) 10\({}^{-15}\)) at the extended stability duration of 15,360 s.  
In the realm of PPP time transfer facilitated by the Galileo HAS service in the kinematic model, the GPS-only and Galileo-only PPP time transfer methods often encounter convergence issues due to a limited number of satellites, which can significantly impair the accuracy of time transfer in the kinematic model, exceeding the threshold of 1 nanosecond. Nonetheless, when instances of re-convergence are rare, these single-system PPP methods can still achieve sub-nanosecond synchronization. Happily, the Galileo/GPS combined PPP time transfer maintains a commendable level of precision, approximately at 0.48 nanoseconds, in the kinematic. Consequently, it is advisable to employ a multi-system fusion approach for PPP time transfer endeavors in the kinematic model. Regarding frequency stability, PPP time transfer exhibits a markedly lower accuracy compared to static PPP time transfer in the kinematic model.