# Impact of Weather Factors on Unmanned Aerial Vehicles' Wireless Communications
## 3 Results and Discussion
### Atmospheric Weather Variations
Algorithm 1 depicts the procedure to determine \(f_{max}\) using an exemplary set of parameters, and path loss model. ```
1:Maximum Operating Frequency Calculation for BER = 0.01
2:Input:
3:\(P_{l}=0.025\) W \(\triangleright\) Transmit power
4:\(d=2000\) m \(\triangleright\) Distance between transmitter and receiver
5:\(f_{\text{min}}\)= 1 GHz, \(f_{\text{max}}\) = 100 GHz \(\triangleright\) Frequency range
6:\(B=1\) MHz \(\triangleright\) Bandwidth
7:\(T=290\) K \(\triangleright\) Temperature
8:\(\text{BER}_{\text{target}}=0.01\)\(\triangleright\) Target BER
9:Constants:
10:\(c=3\times 10^{8}\) m/s \(\triangleright\) Speed of light
11:\(k=1.38\times 10^{-23}\) J/K \(\triangleright\) Boltzmann's constant
12:Initialize:
13:\(N_{0}=k\times T\)\(\triangleright\) Noise spectral density
14:\(f_{\text{operating}}\) = 0 GHz \(\triangleright\) Variable to store the maximum operating frequency
15:Step 1:Compute noise power
16:\(P_{\text{noise}}=N_{0}\times B\)
17:Step 2:Frequency loop from



purple, and green correspond to sub-carrier quantities of 4, 16, 32, 64, and 256, respectively. While the dotted horizontal lines in blue, orange, yellow, and green correspond to the minimum SNR threshold to maintain a BER of 0.01 for QAM modulation orders of 4, 16, 32, 64, and 256, respectively. Due to fixed carrier frequency of 2.4 GHz, with respect to the relative motion, the same Doppler shift variation applies to all four cases. Figure 13a depicts the degradation for the fixed symbol rate (\(R\)s) of 15 Kbd/s. In this case, the fastest degradation of SNR is observed. This is due to the higher ICI noise power applied to a narrower bandwidth for a given number of sub-carrier \(N\). The reason for a narrower bandwidth per sub-carrier is a relatively smaller symbol rate, that makes the symbol duration longer in the time domain but narrower in the frequency domain. In this case, for a sub-carrier count of \(N=4\), the SNR threshold for the maximum BER is not reached for any combination of speed and modulation order and, hence, reliable operation is possible under all conditions. For \(N=16\), the SNR threshold for 4, 16, 32, 64, and 256-QAM is reached at 110, 108, 105, 102, and 82 km/h, respectively. As the number of sub-carriers increases with \(N=32\), the maximum permissible relative speed reduces to 55, 54, 53, 51, and 40 km/h for 4, 16, 32, 64, and 256-QAM, respectively. This trend continues and, as the number of sub-carriers increases, the range of maximum permissible relative speed decreases. Specifically, with \(N=64\), the maximum operating speed drops to 27 km/h, while for N = 256 operation is not possible beyond a speed of 5 km/h. Figure 13: Illustration of SNR degradation caused by Doppler shift at carrier frequency of 2.4 GHz, and for four distinct symbol rates (\(R_{s}\)): (**a**) illustrates SNR degradation for \(R_{s}\) of 15 Kbd/s; (**b**) depicts SNR degradation for \(R_{s}\) of 30 Kbd/s; (**c**) elucidates SNR degradation for \(R_{s}\) of 60 Kbd/s; and (**d**) elucidates SNR degradation for \(R_{s}\) of 120 Kbd/sIn each figure, SNR degradations for the number of sub-carriers (\(N\)) corresponding to 4, 16, 32, 64, and 256 are represented by blue, red, orange, purple, and green solid lines, respectively. Dotted horizontal lines in blue, red, orange, yellow, purple, and green correspond to the minimum required SNR threshold (in dB) to yield a BER of 0.01 for QAM modulation order (\(M\)) of 4, 16, 32, 64, and 256, respectively. The reference static channel-based SNR against which degradation is computed is fixed at 20 dB. Figure 13b shows the degradation corresponding to symbol rate of 30 Kbd/s. In this case, due to doubling of the sub-carrier spacing, twice as much bandwidth is occupied in comparison to the symbol rate of 15 Kbd/s. The net effect is a reduction in SNR degradation and a corresponding increase in operating speed ranges for all cases of sub-carrier count \(N\) and modulation schemes. With doubling of the sub-carrier spacing, the corresponding Doppler speed range also doubled.