# UAV Communication Recovery under Meteorological Conditions
## 4 UAV Communication Recovery Strategy with Results
### Results of UAV Coverage Recovery  
By adding the corresponding compensated path loss (\(PL_{cps}\)) to the initial \(PL_{\text{max}}\), which can be achieved by increasing the UAV's transmit power, the maximum coverage radius during UAV-ground communications in rainy conditions can be restored to the coverage radius experienced under atmospheric conditions without rain, as shown in Figure 18.  
Figure 18: The coverage radius versus height after compensating for the \(PL_{\text{max}}\) under different weather conditions (Region 1, Freq = 28 GHz).  
In addition, Figure 18 demonstrates that, under various weather conditions, compensating for the maximum path loss fully restores the UAV's coverage radius to the radius without these weather conditions (indicated by the dashed line in Figure 18). Furthermore, when compensating for the maximum path loss to restore communications, the drone's height must also be adjusted accordingly. Further, the coverage area and the corresponding coverage radius of the UAV in the four regions with a frequency of 28 GHz before the rain, during the rain, and after the restoration of communications are shown in Figure 19. It can be seen from this figure that the rainfall causes the coverage radius of the UAV to decrease by 28.9 m, 21.7 m, 16.0 m, and 11.9 m in the four areas, respectively. The corresponding reduced coverage areas of the four regions are 2623.9, 1479.3, 804.2, and 444.9 m\({}^{2}\), respectively. Therefore, the reduction in the coverage in the four regions is decreasing in order, i.e., the reduction in coverage is most obvious in the suburban environment and least obvious in high-rise urban environments. By adding the compensated path loss, the coverage radius of the UAV in the four regions is restored to slightly larger values than before the rain.  
The UAV's acceleration (deceleration) is assumed to be 10 m per square second. We present the required recovery time for communications under different rainfall rates (\(R_{\text{rain}}\)), liquid water densities (\(R_{\text{fog}}\)), and snowfall rates (\(R_{\text{snow}}\)) in Figure 20. The figure illustrates that higher frequencies result in shorter recovery times under identical weather conditions. When the frequency is 28 GHz, the relationship between the recovery time and weather conditions is \(T_{max}^{\text{rain}}>T_{max}^{\text{fog}}>T_{max}^{\text{snow}}\). At 71 GHz, the relationship between the recovery time and weather conditions in the same area becomes \(T_{max}^{\text{rain}}>T_{max}^{\text{snow}}>T_{max}^{\text{fog}}\), where \(T_{max}\) represents the maximum recovery time. Specifically, the maximum recovery times for rain, fog, and snow in the four regions are over 2.0 s, 0.5 s, and 0.2 s when the frequency is 28 GHz. When the frequency is 71 GHz, the maximum recovery times for rain, fog, and snow in the four regions are over 1.0 s, 0.3 s, and 0.5 s, respectively.  
Figure 19: UAV coverage area and corresponding radius (**a**) before the rain, (**b**) during the rain, and (**c**) after the communication is restored in four regions.