# Atmospheric Effects on OFDM Wireless Links Operating in the Millimeter Wave Regime
## 9 Conclusions  
The transmission quality of the 5 th generation (5G) millimeter wave (MMW) wireless communication was studied for various atmospheric weather conditions. The current work is focused on the investigation of the attenuation and phase shift introduced by weather effects, especially the influence of different rainy scenarios. The link reliability was examined via constellation diagram and BER in the presence of AWGN for different rainfall rates. Simulation results indicate that OFDM channel performance is strongly affected by rainy conditions. It is shown that absorptive and dispersive behavior of the medium transfer function results in distorted magnitude and phase QAM signaling, leading to an increased error rate. The OFDM MMW channel performance can be significantly improved by considering the effects emerging due to local atmospheric conditions in the receiver demodulator scheme. Online weather reports from local meteorological stations can provide side information on the propagation characteristics that will enable compensation of waveform magnitude and phase distortions at the receiver. This will significantly reduce the error rate leading to an improvement of the link availability and reliability. Furthermore, the on-line meteorological data could also be useful for selecting the optimal parameters for the QAM constellation and the appropriate OFDM modulation numerology to increase network efficiency. It is demonstrated that by employing an adaptive, pre-demodulation phase correction scheme that the atmospheric dispersion phenomena on the millimeter wave can be compensated, resulting in an improvement of the link reliability, as summarized in Table 5.  
It is important to note that by using Phase Dispersion Compensator in the pre-demodulation stage of the receiver, the reliability of the channel during rainy conditions is improved. It is shown that for all examined scenarios, even for extremely bad weather conditions, the compensation revealed a reduction in the error probability, almost to the level expected in clear weather (no rain) scenarios (see Figure 5). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Frequency**} & \multirow{2}{*}{**Rainfall**} & \multicolumn{2}{c}{**Without Compensator**} & \multicolumn{2}{c}{**With Compensator**} & \multirow{2}{*}{**Improvement**} \\ \cline{3-4} \cline{6-7}  & & \multirow{2}{*}{**Average EVM**} & & \multirow{2}{*}{**BER**} & & **Average EVM** & \multirow{2}{*}{**BER**} & **Factor [\%]** \\ \cline{3-4} \cline{6-7}  & & & & & & \(EVM_{w-comp}\) & & \\ \hline \multirow{3}{*}{28} & 5 & 0.170 & \(2.817\times 10^{-5}\) & 0.165 & \(1.210\times 10^{-5}\) & 2.99 \\ \cline{2-7}  & 10 & 0.364 & \(7.044\times 10^{-5}\) & 0.335 & \(1.548\times 10^{-5}\) & 7.85 \\ \cline{2-7}  & 15 & 0.567 & \(2.137\times 10^{-4}\) & 0.507 & \(1.667\times 10^{-5}\) & 10.61 \\ \hline \multirow{3}{*}{39} & 5 & 0.346 & \(2.183\times 10^{-5}\) & 0.301 & \(1.151\times 10^{-5}\) & 12.79 \\ \cline{2-7}  & 10 & 0.687 & \(1.756\times 10^{-4}\) & 0.573 & \(1.290\times 10^{-5}\) & 16.58 \\ \cline{2-7}  & 15 & 1.028 & \(1.996\times 10^{-3}\) & 0.839 & \(1.369\times 10^{-5}\) & 18.39 \\ \hline \multirow{3}{*}{60} & 5 & 0.514 & \(5.335\times 10^{-4}\) & 0.397 & \(1.349\times 10^{-5}\) & 22.69 \\ \cline{2-7}  & 10 & 0.953 & \(2.994\times 10^{-2}\) & 0.694 & \(1.528\times 10^{-5}\) & 27.19 \\ \cline{1-1} \cline{2-7}  & 15 & 1.376 & \(1.183\times 10^{-1}\) & 0.961 & \(1.587\times 10^{-5}\) & 30.11 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Average EVM and BER improvements due to Phase Dispersion Compensation for 200 m wireless link operating with 64 QAM and Signal-to-noise ratio (SNR) = 25 dB. The necessity of phase compensation depends on the link operational frequency, the signal to noise ratio, as well as on the rain intensity. Major improvements are demonstrated in high rain rates, when the weather conditions cause severe phase distortions.