# Impact of Weather Factors on Unmanned Aerial Vehicles' Wireless Communications
## 3 Results and Discussion
### Atmospheric Weather Variations
This occurs due to the reduced error vector margins between symbols when employing higher-order modulation schemes. Because of the reduced error vector margin, the symbol decision boundary is crossed even under reduced interference, reduced SNR, and Doppler shift. Since [PERSON]  
Figure 11: BER as a function of frequency for gas, cloud/fog, and rain-based attenuation. Top row (**a1–c1**) represents BER resulting from attenuations due to gas, cloud/fog, and rain, respectively, with atmospheric parameter values causing relatively lesser attenuation. Bottom row (**a2–c2**) represents BER resulting from attenuation due to gas, cloud/fog, and rain, respectively, with atmospheric parameter values causing higher attenuation, resulting in reduction of operating bandwidth. connected with UAV operations due to their mobility, the connection between the bit error rate and the modulation scheme is very significant. As the simplest measure, bit error rate could be mitigated by switching to a lower order modulation, which leads to increased separation between the symbols in the constellation space. In summary, as the atmospheric weather conditions deteriorate, the SNR degrades due to the increase in resultant attenuation. This degradation is mitigated by a corresponding reduction in operating frequency. At lower operating frequencies, the free space path loss decreases, and, with this reduction, the received signal energy improves at the receiver, thereby enhancing the SNR. The value of \(f_{max}\) decreases as well, resulting in operating bandwidth reduction, or bandwidth suboptimization. Our analysis on the impact of incoherent weather conditions on UAV operations is command and control communication centered. While it provides a detailed insight into the bandwidth suboptimization, it does not consider other aspects of UAV operations under incoherent weather conditions. For example, under dense clouds/fog, due to impairment of visibility, UAVs needing constant visibility by the operator may not be operable. Similarly, under rainy conditions, the operations of UAVs are subject to required protection from water for fail-proof operation of the onboard electronics. As rain is the most severe factor affecting UAV operations, suitable mitigation techniques could be used to permit UAV operation under severe rain conditions. A water-resistant mechanical design would protect the on-board circuitry against precipitation. Signal attenuation under severe rainfall and the consequent communication reliability could be addressed through the implementation of diversity schemes, such as a multiple input, multiple output (MIMO) radio front-end. Furthermore, communication reliability could be enhanced by improving the signal-to-noise ratio through increased power transmission and/or reduced operating frequency and modulation order. Table 4 presents the results of \(f_{max}\) and \(B_{red}\) for the specified modulation schemes and weather conditions under two distinct power transmissions, 25 mW and 75 mW. For each power transmission, the corresponding \(f_{max}\) and \(B_{red}\) values are provided for both mild and inclement weather conditions. The light orange color fonts are used for convenient differentiation of the three attenuation factors: gases, clouds/fog, and rain. This same color scheme applies to the associated atmospheric variable that primarily affects the attenuation. The right pointing arrow implies the associated values assumed by the corresponding atmospheric variables for the light and inclement weather conditions. With two distinct power transmissions and two separate weather conditions, a total of four combinations of power and weather conditions are created. These combinations are marked as--(a) low power and mild weather (LPMW), (b) low power and inclement weather (LPIW), (c) high power and mild weather (HPMW), and (d) high power and inclement weather (HPIW). The \(f_{max}\) for various modulation schemes are shown in the \(f_{max\_LPMW}\), \(f_{max\_LPHW}\), \(f_{max\_HPMW}\), and \(f_{max\_HPWN}\) columns.