# Effects of Atmospheric Turbulence on Optical Wireless Communication in NEOM Smart City
## 7 Results and Discussion  
All attenuation sources were neglected to focus on the effect of the atmospheric turbulence on the FSO link for NEOM city. The simulations are maintained with computer capabilities: processor Intel(R) Core(TM) i7-7500U CPU @ 2.90 GHz and 8.00 GB RAM, with sample number used in simulations--\(10^{7}\). Using Equations (1)-(5), the refractive index structure parameter was calculated for every month. The monthly average meteorological data, \(T\), \(H\), and \(v\), plotted in Figure 3, were used for this calculation. Figure 4 shows the monthly variation in the refractive index for the study years. The results indicate that the strength of the atmospheric turbulence is moderate and high in winter and summer, respectively, as indicated in Table 2.  
Figure 3: (**a**) Monthly Average Temperature, (**b**) Monthly Average Humidity, and (**c**) Monthly Average Wind Speed. The effects of NEOM meteorological parameters, including the temperature, wind speed, and humidity, on the turbulence strength in both seasons can be summarized as follows:  
* In 2019, as shown in Figure 4, the \(C_{n}^{2}\) peak occurred in the summer season (May), in which the temperature was high (\(T=30.42\)\({}^{\circ}\)C) and relative humidity was low (\(H=33.14\%\)). The minimum \(C_{n}^{2}\) value occurred in the winter season (February), in which the temperature was low (\(T=18.24\)\({}^{\circ}\)C) and humidity was high (\(H=46.4\%\)). The results indicated that the increase in the temperature can affect the atmospheric turbulence strength more than the increase in humidity. This agrees with the experimental result of the author [61]. * As mentioned previously, in the summer season, the wind speed did not vary significantly. In the winter season, the maximum \(C_{n}^{2}\) occurred in December for both years in which the wind speed was high (up to \(\sim\eta=5\) m/s). Moreover, December was the hottest month among the winter months. This finding indicates that the turbulence strength increases with the increasing wind speed and temperature in the winter season, as shown in Figure 5.  
The above-mentioned findings highlight that the higher temperatures lead to strong turbulence in the summer season, and the high wind speed leads to moderate turbulence in the winter season. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Season**} & \multirow{2}{*}{**Year**} & \multicolumn{2}{c}{\(C_{n}^{2}\)} & \\ \cline{2-4}  & & **Min \(\times 10^{-14}\)** & **Max \(\times 10^{-14}\)** & **Turbulence Strength** \\ \hline \multirow{2}{*}{Winter} & 2019 & 1.21 & 2.89 & Moderate \\ \cline{2-4}  & 2020 & 1.26 & 3.42 & \\ \hline \multirow{2}{*}{Summer} & 2019 & 3.82 & 5.1 & \\ \cline{2-4}  & 2020 & 4.96 & 5.9 & High \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Result Calculation of Refractive Index Structure Parameter. Figure 4: Month-wise Variation in \(C_{n}^{2}\) Under the Influence of Weather Conditions. Figure 6 shows the scintillation index values calculated using Equation (7). In the calculation, we considered the transmission distance as (1 km). The month-wise variation in the scintillation index under wavelengths ranging from 532 to 1550 nm was examined. The scintillation index and wavelength are inversely proportional. For example, in June, the scintillation index \(\sigma_{I}^{2}\) decreased from 4.087 to 1.75 as the wavelength increased from 532 to 1550 nm. The intensity fluctuation depends on the wavelength. Moreover, the results highlight that at a wavelength of 1550 nm, the effect of atmospheric turbulence on the FSO system in NEOM city can be reduced. This result is inconsistent with the works in [30; 62]. Furthermore, the scintillation is higher in summer than that in winter. For example, for \(\lambda=\)1550 nm, the scintillation values in June and December are \(\sigma_{I}^{2}=1.174\) and \(\sigma_{I}^{2}=0.65\), respectively.