# UAV Communication Recovery under Meteorological Conditions
## 3 Methods
### UAV Coverage Radius with Elevation Angle under Different Weather Conditions  
In this subsection, we analyze the impact of specific attenuation due to rain, fog, dry snow, and gas on the communications between the UAV and ground receivers. For simplicity, we only consider the case of \(\eta_{NLoS}=\eta_{NLoS1}\) in Equation (10); then, we can obtain the corresponding implicit function of the maximum coverage radius of the UAV with respect to the elevation angle. The rainfall rate (\(R_{\text{rain}}\)), liquid water density (\(R_{\text{fog}}\)), and snowfall rate (\(R_{\text{snow}}\)) are set as 12.5 mm/h, 0.5 g/m\({}^{3}\), and 5 mm/h, respectively. The relationships between the UAV coverage radius and the elevation angle under rain, fog, and dry snow in the four regions are shown in Figure 6. In addition, for convenience of comparison, we add the relationship curves between the coverage radius and elevation angle of the UAV when there are only atmospheric conditions. As shown in Figure 6, the coverage radius of the UAV at the frequency of 28 GHz is greater than that at the frequency of 71 GHz in all four regions. Furthermore, the relationship between the UAV coverage radius under different weather conditions is \(C_{r}{}^{\text{gas}}\,>\,C_{r}{}^{\text{snow}}\,>\,C_{r}{}^{\text{fog}}\,>\,C_{ r}^{\text{rain}}\), where \(C_{r}\) denotes the UAV coverage radius. It can be seen that under different weather conditions, rain has the greatest impact on the coverage radius of the UAV, which is due to the different degrees of attenuation of the propagation signal by the several weather models that we introduce. Based on our previous work [16], the attenuation of the propagated signal caused by different weather conditions at the two frequencies of 28 GHz and 71 GHz is compared, as shown in Figure 7. We can see that the degree of attenuation of the propagation signal by rain is the largest among the three types of weather from Figure 7. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Regions** & \multicolumn{2}{c}{**Region 1**} & \multicolumn{2}{c}{**Region 2**} & \multicolumn{2}{c}{**Region 3**} & \multicolumn{2}{c}{**Region 4**} \\ \hline NumRef & 2 & 3 & 2 & 3 & 2 & 3 & 2 & 3 \\ \hline
28 GHz & 15\% & 25\% & 26\% & 41\% & 38\% & 61\% & 51\% & 77\% \\ \hline
71 GHz & 15\% & 25\% & 26\% & 41\% & 38\% & 61\% & 51\% & 77\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Percentage reduction in maximum coverage radius for double and triple reflections relative to single reflection. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Regions** & **NumRef** & **28 GHz** & **71 GHz** \\ \hline \multirow{3}{*}{Region 1} & 1 & 333.1 & 130.9 \\ \cline{2-5}  & 2 & 284.0 & 111.6 \\ \cline{2-5}  & 3 & 251.0 & 98.7 \\ \hline \multirow{3}{*}{Region 2} & 1 & 288.7 & 113.5 \\ \cline{2-5}  & 2 & 214.6 & 84.4 \\ \cline{2-5}  & 3 & 171.1 & 67.3 \\ \hline \multirow{3}{*}{Region 3} & 1 & 253.8 & 99.8 \\ \cline{2-5}  & 2 & 156.8 & 61.7 \\ \cline{2-5}  & 3 & 99.3 & 39.1 \\ \hline \multirow{3}{*}{Region 4} & 1 & 218.0 & 85.7 \\ \cline{2-5}  & 2 & 107.6 & 42.4 \\ \cline{2-5}  & 3 & 50.1 & 19.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The maximum coverage radius (in m) of the UAV under different reflection numbers in the four regions only considering the atmosphere. Specifically, the maximum UAV coverage radius data under different weather conditions in the four regions are summarized in Table 5. Based on these maximum coverage radius data, the percentage reductions in the maximum coverage radius for different weather conditions relative to atmospheric conditions are summarized in Table 6. We found that the percentage reduction in the coverage radius under different weather conditions was generally greater at 71 GHz than at 28 GHz in the four regions.