## 2 System Model and Configuration
### Characteristic Analysis of Transmission Arc Segment  
The ground track of sun-synchronous circular orbit has repetition characteristics, and the repeat period is 31 days when the altitude is 500 km. Figure 1 illustrates the LEO EO satellite passing over the three G/Ss in 31 days, where the red, blue and yellow orbits correspond to pass over the Kashgar G/S, Beijing G/S and Sanya G/S, respectively. Considering the amount of simulation calculation and the attenuation characteristics of dynamic channel model, the sampling interval during transmission is set to 1 s. The quantitative analysis results are shown in Table 3.  
It can be seen from Table 3 that:  
1. The statistical transmission arc segment characteristics of the aforementioned three G/Ss (minimum duration, maximum duration and mean duration) are relatively close and have little relationship with G/S locations.
2. Kashgar G/S and Beijing G/S with similar latitude have similar transmission arc segment characteristics.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Orbit type & LEO sun-synchronous circular orbit \\ Satellite altitude & 500 km \\ G/S location & Kashgar, Beijing, Sanya \\ Downlink carrier frequency & 26.64 GHz \\ Polarization & Circular \\ Roll-off factor & 0.2 \\ Symbol rate & 600 Mbaud \\ Maximum EIRP & 47 dBW \\ G/S pointing error loss & 1 dB \\ Polarization mismatch loss & 0.5 dB \\ G/S G/T & 40 dB/K \\ Inserted system margin & 3 dB \\ \hline \hline \end{tabular}
\end{table}
Table 2: System parameters and link budget characteristics of the end-to-end simulation.  
Figure 1: Schematic diagram of transmission arc segment in 31 days.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**G/S**} & \multirow{2}{*}{**Number**} & \multicolumn{4}{c}{**Duration/min**} \\ \cline{3-5}  & & **Minimum** & **Maximum** & **Mean** & **Total** \\ \hline Kashgar & 123 & 0.99 & 9.12 & 7.19 & 883.86 \\ Beijing & 126 & 1.37 & 9.13 & 7.16 & 901.75 \\ Sanya & 98 & 1.13 & 9.05 & 7.14 & 700.19 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Statistic of satellite-to-ground data transmission arc segment in 31 days.  
3. Since Sanya G/S has lower latitude, there are relatively fewer opportunities for LEO satellites to establish data transmission link with it. The number and the total duration of transmission arc segments are less than Kashgar G/S and Beijing G/S, with a relative proportion of about 80%.  
By calculating the duration falling into the inter cell range within elevation angles from 5\({}^{\circ}\) to 90\({}^{\circ}\) at an interval of 1\({}^{\circ}\), the results are clearly shown in Figure 2. It can be seen that the distribution trend of three G/Ss is similar, which decrease rapidly with the increase of elevation angles, and a large number of transmission arc segments are located in the area with small elevation angles.  
Figure 3 shows the cumulative distribution of transmission arc segments from the minimum 5\({}^{\circ}\) elevation angle. It can be seen that the data laws of three G/Ss are basically the same, and the proportions below 10\({}^{\circ}\), 20\({}^{\circ}\) and 30\({}^{\circ}\) are about 36%, 72% and 86%, respectively. In order to improve the transmission efficiency, we should make full use of the long transmission arc segments with small elevation angle and increase the useful data rate.  
Figure 3: Cumulative distribution of transmission arc segments from the minimum 5\({}^{\circ}\) elevation angle.  
Figure 2: Transmission arc segment duration distributions of every 1\({}^{\circ}\) elevation angle.