## 3 Results  
### Solar Irradiation Simulation Results  
This section presents the results of the simulations that evaluate the impact of sunlight interference on the communication performance by examining the transmission power and FoV, based on the definitions provided in Section 2.1. In the first simulation, the SNR is assessed at various transmission powers of 0.1 W, 1 W, and 10 W, with FoVs ranging from 0.1\({}^{\circ}\) to 10\({}^{\circ}\). The results, depicted in Figure 8a, overall, suggest that a higher transmission power allows for a wider FoV operation with minimal performance degradation and vice versa. As the transmission power decreases, the SNR gap between the ideal case and the case affected by solar interference becomes wider. This gap becomes wider as the FoV widens, reaching up to 10 dB at 0.1 W for the widest FoV. For the highest transmission power of 10 W, the SNR remains close to the ideal value, regardless of the solar irradiance and FoV, demonstrating strong resistance to interference. At significantly narrow FoVs of between 0.1\({}^{\circ}\) and 0.2\({}^{\circ}\), the gap becomes trivial across all the power levels, meaning that the effects of the solar interference are negligible in these cases. Notably, the required FoV for maintaining a suitable SNR becomes narrower as the transmission power decreases, implying that weaker signals need a narrower FoV to mitigate interference and maintain performance. This is because a reduction in the optical signal power increases susceptibility to ambient noise, such as solar irradiance. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Notation** & **Definition** & **Value(s)** \\ \hline \(r_{s}\) & Altitude of the satellite & 540 km, 550 km, \\ \(r_{E}\) & Radius of the Earth & 6371 km \\ \(d_{sun}\) & Distance between Earth & 1 AU \\  & and the sun & (149,597,870 km) \\ \(A_{d}\) & APD’s area & 707 \(\upmu\)m\({}^{2}\) \\ \(\theta_{FoV}\) & Angle of the field of view & 1\({}^{\circ}\), 3\({}^{\circ}\), and 6\({}^{\circ}\) \\ \(P_{Max}^{L}\) & The maximum transmission power & 0.1 W, 1 W, and 10 W \\ \(M\) & Beam divergence used for m & 65 mrad \\ \(F\) & Excess noise factor & 5.5 \\ \(B\) & APD’s bandwidth & 3 GHz \\ \(R_{L}\) & Load’s resistance & 50 \(\Omega\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation parameters. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Number of Planes** &
\begin{tabular}{c} **Number of Satellites** \\ **Per Plane** \\ \end{tabular} & **Altitude (km)** & **Inclination** \\ \hline
72 & 22 & 540 & 53.2\({}^{\circ}\) \\
72 & 22 & 550 & 53\({}^{\circ}\) \\
6 & 58 & 560 & 97.6\({}^{\circ}\) \\
4 & 43 & 560 & 97.6\({}^{\circ}\) \\
36 & 20 & 570 & 70\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Orbital components in the inter-shell. The second simulation, as shown in Figure 8b, focuses on the influence of the FoV on the communication performance under varying transmission power conditions. The analysis is conducted at FoVs of 1\({}^{\circ}\) and 3\({}^{\circ}\), with the addition of a 6\({}^{\circ}\) FoV, corresponding to the practical application of a fast-steering mirror (FSM) module in positioning acquisition and tracking (PAT) systems [18]. The results demonstrate that the transmission power is directly proportional to the SNR and that a higher power level is required to maintain performance as the FoV widens. For instance, at a 1\({}^{\circ}\) FoV, the required transmission powers to achieve an SNR of \(\sim\)10 dB are 0.78 W without sunlight interference and 1.14 W with sunlight interference. At a 3\({}^{\circ}\) FoV, these values increase to 7.03 W and 7.47 W, respectively. When using a 6\({}^{\circ}\) FoV, the FSM configuration fails to reach the SNR threshold, even at a high transmission power of 10 W.  
As a result, the transmission power should be increased as the FoV widens. For example, at the same power level (1 W) with sunlight interference, the SNR significantly decreases by 15.6 dB when increasing the FoV from 1\({}^{\circ}\) to a 6\({}^{\circ}\) FoV.