## 4 Analysis of LEO Satellite Downlink  
To analyze the LEO downlink in interference situations, we set the scenario considering antenna patterns, the path loss in the space environment, and the interference source. The radiation patterns were obtained from the data transmitting antenna of the LEO satellite and the receiving ground station antenna in Section 2. We considered the bore-sight error  
Figure 5: Bore-sight error and atmospheric attenuation when transmitting signals from the LEO satellite to the Earth ground station: (**a**) bore-sight error; (**b**) atmospheric attenuation. Figure 6: Normalized received power at \(\theta_{gs}=10^{\circ}\): (**a**) in free space; (**b**) in the space environment. loss by assuming that the transmitting and receiving antennas are slightly misaligned in the off-axis situation. The path loss calculated in Section 3 was then applied in the downlink analysis. In the given scenario, the LEO satellite transmits the data to the ground station, and the ground station antenna tracks the LEO satellite. The LEO satellite is located at the elevation angle of \(\theta_{gs}\). At the same time, it is assumed that the elevation angle \(\theta_{j}\) of the interference source moves from 0\({}^{\circ}\) to 90\({}^{\circ}\) at an altitude of 10 km. The input power of the interference source can be adaptively controlled from 100 dBm to 150 dBm and is connected to a 10 dBi gain antenna. The interference power range was derived to maintain the target J/S such as 0 dB, 5 dB, 10 dB, and 15 dB when the interference source is located at various elevation angles. The detailed link budget parameters are listed in Table 1.  
Figure 7 shows the J/S result according to the elevation angle \(\theta_{j}\) and the interference power. \"\(\Circuit\)\" markers indicate the points at which the J/S is 0 dB. As can be seen, the result exhibits a large variance due to fluctuation in the antenna radiation pattern, which makes it difficult to observe the J/S tendency. To overcome this issue, we applied the regression model to \"\(\Circuit\)\" markers in our J/S result. This regression model (\(f_{1}\)) is based on a quadratic function often used to fit raw data to a curved distribution [35; 36]. The quadratic regression model can be expressed as (4)  
\[f_{1}(\theta_{j})=a_{1}\theta_{j}^{2}+a_{2}\theta_{j}+a_{3} \tag{4}\]  
where \(a_{1}\), \(a_{2}\), and \(a_{3}\) are coefficients that best fit the points (\"\(\Circuit\)\" makers) with J/S = 0 dB, which is illustrated as the solid line. We then easily examined the tendency of the results by observing the single curved line. \begin{table}
\begin{tabular}{c c} \hline
**Downlink Parameters** & **Values** \\ \hline Receiving antenna gain & 59 dBi \\ Satellite altitude & 550–2200 km \\ Frequency range & 8025–8400 MHz \\ Transmitting power & 30 dBm \\ Transmitting antenna bore-sight gain (dBi) & 4.4 dBi \\ Effective isotopic radiation power (EIRP), \(G_{t}+P_{t}\) & 34.4 dBm \\ Free-space path loss & \(L_{f}\) dB \\ Bore-sight error loss & \(L_{b}\) dB \\ Atmospheric attenuation & \(L_{at}\) dB \\ Interference source power & 100–150 dBm \\ Interference source antenna gain & 10 dBi \\ Interference source altitude & 10 km \\ \hline \end{tabular}
\end{table} 
Table 1: Downlink parameters for the link budget in the scenario. Figure 7: J/S according to the elevation angle \(\theta_{j}\) and the interference power. “\(\Circuit\)” is when J/S = 0 dB, and the solid line is the regression model. Figure 8 illustrates J/S according to the elevation angle \(\theta_{j}\) and the interference power at \(\theta_{gs}\) = 10\({}^{\circ}\). To obtain the J/S in the space environment, we applied the bore-sight error loss and atmospheric attenuation in Section 3 to the link budget calculation. In Figure 8a, the solid line indicates the regression model for the points with J/S = 0 dB in the space environment. To observe the effect of the space environment, we also examined the regression model (dashed line) without the space environment.