## 5 Discussion and Conclusions  
In the future, it is expected that LEO constellations will collaborate with GNSS satellite constellations to provide LEO-augmented PNT services for GNSS-challenging environments and autonomous driving. High-dynamic, high-precision, and real-time PNT services require the support of high-precision real-time LEO satellite products, such as high-precision real-time LEO satellite clocks. Currently, the determination of LEO clocks is mainly based on GNSS observations onboard LEO satellites. Therefore, GNSS real-time products are crucial for the precision of the real-time LEO satellite clock estimates, not only with regard to their accuracy but also to their latency and continuity. To address this issue, this study analyzes the impact of the latency and continuity of the GNSS real-time products on LEO satellite clocks, employing two methods of real-time LEO satellite clock determination. For the \"arc-estimation\" and \"epoch-estimation\" methods of determining LEO clocks, the loss of the GNSS real-time products was classified into the \"end-loss\" and \"mid-gap\" scenarios. Tests were conducted for these two scenarios using Sentinel-3B's GPS L1/L2 onboard observation data and the CNES real-time products. Results showed that as the loss duration increases, both the \"mid-gap\" or \"end-loss\" situations would lead to unignorable  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Near-Real-Time Clocks**} & \multicolumn{2}{c}{**Real-Time Clocks**} \\ \hline
**Gap Length** & **VS. K (ns)** & **VS. R (ns)** & **VS. K (ns)** & **VS. R (ns)** \\ \hline
0 min & 0.0230 & 0.2345 & 0.0871 & 0.2609 \\ \hline
5 min & 0.0249 & 0.2435 & 0.0881 & 0.2610 \\ \hline
10 min & 0.0262 & 0.2598 & 0.0901 & 0.2630 \\ \hline
15 min & 0.0265 & 0.2610  
degradations in the precision of LEO satellite real-time clocks. For the \"epoch-estimation\" method, when the \"end-loss\" duration of both GNSS clocks and orbits increases to 120 s in different scenarios, the precision of LEO clocks decreases from 0.2 ns to around 1 ns when not extrapolating the GNSS satellite clocks, and to 0.93 ns when extrapolating the GNSS clocks. If ultra-rapid GNSS orbits are used instead of considering the orbits as delayed, with the GNSS clocks extrapolated over the latency period, the real-time LEO satellite clock precision amounts to around 0.5 ns for a latency of 120 s. When directly predicting LEO satellite clocks for 120 s, the prediction precision decreases from 0.21 to 0.23 ns. For the \"arc-estimation\" method, when the \"mid-gap\" duration increases from 5 to 60 min, the real-time clock precision achieved by the user decreases from 0.26 to 0.32 ns. In summary, the latency and continuity of GNSS products significantly impact the filter-based real-time LEO satellite clock determination. Using appropriate methods to improve the GNSS orbit and clock prediction or interpolation methods in real-time, or shorten the latency and gaps, would be essential to guarantee high precision of the real-time LEO satellite clocks. **Author Contributions:** Formal analysis, M.W. ; Funding acquisition, M.W. and K.W. ; Methodology, M.W. and K.W. ; Software, M.W., J.W., W.X., J.L., B.C., Y.G. and X.Y. ; Writing--original draft, M.W. ; Writing--review and editing, M.W., K.W. and A.E.-M. All authors have read and agreed to the published version of the manuscript. **Funding:** This work is supported by the International Partnership Program of the Chinese Academy of Sciences. Grant No. 021 GJHE2020301 PN. The work is also funded by the Special Research Assistant Funding Project, Chinese Academy of Sciences (CAS) (No. 110400T0 XW), the National Time Service Center, CAS (No. E167 SC14), the National Natural Science Foundation of China (No. 12473078, No. 4240403), and the Australian Research Council--Discovery Project (No. DP 240101710).