# Study of Fast and Reliable Time Transfer Methods Using Low Earth Orbit Enhancement
## 5 Conclusions  
This study introduces a novel method for enhancing GNSS time transfer through the use of LEO satellites. The LEO satellite constellation was designed following a Walker constellation. The observational data from the LEO satellites were simulated based on data from all stations in the MGEX observation network. The GNSS observation data incorporated GPS data and precision products offered by the IGS. Utilizing these data, an enhanced PPP with LEO was developed. The receiver clock offset and time transfer link clock offset were additionally calculated. This study investigated the convergence performance and reliability of LEO-augmented GPS time transfer through experimental examples. Four scenarios were designed to assess the impact of LEO enhancement on time transfer reliability. Based on the comprehensive analysis and discussion presented above, the following conclusions were formulated: \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Number of LEO** & **harb-sydn** & **ohi2-syog** & **piel-ons1** \\ \hline
1 & 0.085 & 0.101 & 0.169 \\
2 & 0.056 & 0.099 & 0.140 \\
3 & 0.032 & 0.058 & 0.036 \\
4 & 0.031 & 0.056 & 0.031 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Standard deviations of convergence interval clock offsets of the three links across the four enhancement scenarios (ns). Figure 17: Convergence time histograms of the three links across the four enhancement scenarios. 1. The receiver clock offset calculated using the LEO-augmented PPP model demonstrated accelerated convergence. The receiver clock offsets for three representative stations--areg, harb, and ons1--were examined. The convergence velocity of the receiver clock offsets was contrasted with those derived solely from GPS data. The convergence speed post-LEO augmentation was enhanced, with varying degrees of enhancement observed across different links. A convergence confidence interval was established to determine convergence time. The results showed that harb's cesium clock had the greatest increase in convergence speed at 65.0%. ons1's hydrogen clock had an increase of 50.0%, while areg's rubidium clock had the slowest increase at 18.8%. Therefore, LEO-augmented PPP affected clock offset convergence speeds differently on stations with different atomic clock frequency sources, reflecting the performance of the atomic clocks. The performance of atomic clocks directly determines the accuracy of time measurement, which in turn affects the measurement results of satellite signals and is indirectly reflected in the later data processing. 2. The analysis focused on the convergence performance of the clock offsets of the ten time transfer links. The convergence speed of all the time transfer link clock offsets exhibited uniform performance. The convergence speed achieved with the LEO-augmented PPP was superior to that of the GPS-only model. PPP model based on LEO satellites fusion has different improvements in the convergence speed of time transfer links of different atomic clock types, and the improvement in the convergence speed of time transfer links of different baseline lengths is also different. There were no obvious differences in time transfer links at different latitudes. The enhanced convergence speed has been demonstrated to be more advantageous for securing the speed and real-time performance of GNSS time transfer. 3. The standard deviation of the clock offsets for the time transfer link, as derived from both satellite constellation schemes during the convergence time range, was calculated. The PPP model based on LEO satellites fusion did significantly improve stability in the convergence interval. Additionally, the Allan deviation was employed to assess the frequency stability of the time transfer link clock offset in the convergence interval. The findings demonstrate that the frequency stability obtained by the PPP model based on LEO satellite fusion in the convergence interval was significantly better than that of the sole GPS.