# Impact of Weather Factors on Unmanned Aerial Vehicles' Wireless Communications
## 3 Results and Discussion  
### Atmospheric Weather Variations  
Using the previously defined parameters, we simulated different atmospheric conditions while assuming a range of frequencies and propagation distances to evaluate the effect of weather factors on wireless signal propagation and its resultant effect on the BER at the receiver. While the simulation for attenuation under different atmospheric conditions covered the range of 1 to 100 GHz, BER and bandwidth suboptimization related \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Values/Range of Values** & **Units** \\ \hline Maximum permissible BER (\(p_{b}\)) & 0.01 & \\ QAM modulation order (\(M\)) & 4, 16, 32, 64, 256 & \\ Reference SNR & 20 & dB \\ Carrier frequency (\(f_{c}\)) & 2.4 & GHz \\ Number of sub-carriers (\(N\)) & 4, 16, 32, 64, 256 & \\ Symbol rate (\(R_{s}\)) & 15, 30, 60, 120 & Kbd/s \\ Relative speed & 0 to 200 & km/h \\ Phase noise linewidth (\(\beta\)) & 10 \(\times\) 10\({}^{-6}\) & Hz \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Doppler shift and SNR degradation simulation parameters. Figure 7: Simulation parameter processing and result analysis flow. simulations used the frequency range of 1 to 10 GHz, as currently available UAVs operate in this frequency range. Figures 8-10 illustrate the attenuation due to atmospheric gases, clouds/fog, and rain. Figure 11 shows the BER results for atmospheric weather conditions using different modulation schemes (BPSK, QPSK, 16-QAM, 64-QAM, and 256-QAM), and introduces two important metrics associated with the modulation schemes, maximum operating frequency (\(f_{max}\)) and reduction in maximum operating bandwidth (\(B_{nd}\)). Figure 12 illustrates the effect of bandwidth suboptimization in terms of \(f_{max}\) and \(B_{nd}\) due to atmospheric weather variations for two different power transmissions: 25 and 75 mW. Figure 8a-d illustrate the influence of atmospheric gases on the signal attenuation across varying frequencies ranging from 1 GHz to 100 GHz, encompassing a broad range of operational frequencies allocated for the 5G mobile cellular networks [35]. The simulations were conducted with specific values for the associated parameters, including propagation distance, height, water vapor density, temperature, and pressure. Each figure focuses on the impact of varying one parameter at a time, while keeping the others constant. Figure 8a exhibits the attenuation as a function of the carrier frequency and for different propagation distances (500, 1000, 1500, and 2000 m). The water vapor density, height, temperature, and pressure were maintained at 23.01 g/m\({}^{3}\), 400 m, 25 \({}^{\circ}\)C, and 1013.25 hPa, respectively. As expected, a noticeable increase in attenuation was observed across all frequencies as the propagation distance increased. This phenomenon is attributed to the increased absorption of the energy of the signal along a longer path. As expected, two specific attenuation peaks are observed for each distance, one at 22 GHz and the other at 60 GHz corresponding to water and oxygen resonant absorption, respectively. Figure 8b shows the effect of the height (100 to 400 m). The water vapor density, propagation distance, temperature, and pressure were held constant at 23.01 g/m\({}^{3}\), 2000 m, 25 \({}^{\circ}\)C, and 1013.25 hPa, respectively. Interestingly, no significant increase in attenuation was observed as the height increased, presumably because of the minimal changes in atmospheric parameters (temperature, water vapor density, and pressure) across the assumed heights. Figure 8c depicts the impact of water vapor density variation for densities ranging between 0.23 and 23.01 g/m\({}^{3}\). The other parameters (propagation distance, height, temperature, and pressure) were maintained constant. As expected, the attenuation increased as the water vapor density increased for a local maximum of 23.01 g/m\({}^{3}\), which corresponds to the water vapor absorption resonance frequency at 22 GHz.