# Impact of Weather Factors on Unmanned Aerial Vehicles' Wireless Communications
## 3 Results and Discussion
### Atmospheric Weather Variations
The top row with Figure 11(a1)-11(c1) represents the BER associated with gas, clouds/fog, and rain, respectively, under mild conditions; whereas the bottom row with Figure 11(a2)-(c2) represents the respective BER under inclement conditions. For all the simulations, the BER threshold for performance evaluation is set to 1%. The values of distance \(d\), height \(h\), ambient temperature \(T_{a}\), ambient pressure \(p_{u}\), power transmission \(P_{tx}\), and channel bandwidth \(B_{ch}\) are 2000 m, 400 m, 25 \({}^{\circ}\)C, 1013.25 hPa, 75 mW, and 20 MHz, respectively, for all six cases. The mild and inclement weather conditions for each category of gas, clouds/fog, and rain are differentiated by the values used for water vapor density (_vwd_), liquid water density (_lwd_), and rain rate \(R_{r}\), respectively. For each of the six cases, five modulation schemes, viz., BPSK, QPSK, 16-QAM, 64-QAM, and 256-QAM, are evaluated for their BER performance. The point of intersection between the 1% reference BER line and the BER curve associated with a particular modulation scheme indicates the respective maximum operating frequency \(f_{max}\). In other words, \(f_{max}\) for a given modulation scheme is the maximum permissible operating frequency for which the BER does not exceed the threshold. Figure 11(a1) illustrates the BER performance as a function of the frequency in the presence of gas attenuation under mild conditions, represented by a water vapor density of 0.23 g/m\({}^{3}\), which in turn corresponds to 1% relative humidity. This condition represents extremely dry air conditions and, as such, the attenuation due to atmospheric gases is minimum. The \(f_{max}\) for each modulation scheme is at its absolute maximum value in this case. For reference, \(f_{max}\) for BPSK/QPSK is marked by a green crosshair in this plot. Figure 11(a2) shows the BER performance for the assumed modulation schemes under inclement weather conditions for atmospheric gases. In this case, 100% relative humidity is assumed, which translates to 23.01 g/m\({}^{3}\) of water vapor density. Compared to the  
Figure 10: Rain based attenuation as a function of frequency: (**a**) illustrates the variation in attenuation for four distinct values of distances; (**b**) demonstrates the variation in attenuation for different heights; (**c**) depicts the effect on attenuation due to rain rate variation. mild weather conditions, operating bandwidth reduction, \(B_{\textit{rad}}\), of 1 MHz resulted for BPSK/QPSK. Figure 11(b1) depicts the BER performance for the assumed modulation schemes under mild cloud/fog conditions, represented by a liquid water density (_lwd_) of 0.05 g/m\({}^{3}\), yielding a visibility of 300 m.  
Figure 11(b2) illustrates the BER performance under corresponding inclement cloud/fog conditions. In this case, _lwd_ of 10 g/m\({}^{3}\), corresponding to a visibility of 5 m, is assumed. This represents extremely thick cloud/fog conditions. In comparison to the mild cloud/fog conditions, a \(B_{\textit{rad}}\) of 295 MHz resulted in this case. The substantial increase in \(B_{\textit{rad}}\) is attributable to the increased attenuation caused by inclement cloud/fog conditions. Figure 11(c1) presents the BER performance under mild rain conditions, utilizing a rain rate \(R_{r}\) of 1 mm/h under the specified condition. In comparison to the operating bandwidth observed under mild gases and cloud/fog conditions, mild rain results in a reduction of the operating bandwidth by 8 MHz and 2 MHz for BPSK and QPSK based operations, respectively. Figure 11(c2) illustrates the case of extremely heavy rain using \(R_{r}\) of 120 mm/h. As expected, due to a significant increase in attenuation, \(f_{\textit{max}}\) for BPSK/QPSK is significantly reduced, yielding a \(B_{\textit{rad}}\) of 2075 MHz. Sensitivity of the bit error rate to the modulation scheme is shown by the results. The BER increases as more and more symbols are accommodated in the symbol constellation using a higher order modulation scheme.