# Atmospheric Effects on OFDM Wireless Links Operating in the Millimeter Wave Regime
## 6 Channel Simulation Model  
The channel model was simulated by integrating the OFDM signaling with the medium frequency dependent transfer function resulted from the millimeter propagation model (MPM) for different weather condition scenarios. The received signal is decoded in the presence of AWGN by the OFDM demodulator.  
The flow chart shown in Figure 3 summarizes the procedure employed in the numerical simulation calculating the resulted atmospheric absorptive and dispersive effects on the waveform constellation. Information related to the signaling designated for the next generation cellular network was taken from technical specifications presented above.  
The model was implemented in MATLAB environment using 5G modeling Toolbox [12]. The model consists of the following steps:  
1. Transmitted data signal settings: generation of transmission vector containing a given number (\(N_{b}\) = 24,000 or 50,400) of random bits in time domain.
2. Channel properties: the channel characteristics were calculated from the MPM by setting the carrier frequency (28, 39 or 60 GHz) and bandwidths (200 or 400 MHz).
3. Signaling: the modulation method for the current analysis is considered to be OFDM with the parameters presented in Table 3: Symbol Rate, Cyclic Prefix Length, Guard Band Length, and Modulation Order. The modulation was built by creating complex QAM envelopes for each of the OFDM subcarriers. The modulator transmits a complex envelop waveform in accordance with Equation (12).
4. The medium: the atmospheric medium was modeled by the MPM to generate the transfer function (9) in the frequency domain for a given distance (200 m) and different weather condition scenarios. The meteorological parameters were set to: temperature (25 \({}^{\circ}\)C), pressure (1 atm), relative humidity (\(RH\) = 0, 10, 50, 100%) suspended liquid water content (\(W\) = 0, 0.1, 1, 5 g/m\({}^{3}\)), or rain rate (\(R\) = 0, 5, 10, 15 mm/h). Note that for the case of suspended liquid water droplets and rain the relative humidity is set to be 100%.  
Figure 3: Flow chart of a baseband OFDM complex envelope evolution along the channel.  
\begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Subcarrier Spacing (SCS)**} & \multirow{2}{*}{**SCS \(\lambda\)/=2\({}^{h}\)\(\cdot\)15 [kHz]**} & \multicolumn{2}{c}{**Number**} & \multirow{2}{*}{**Number of Slots**} & \multirow{2}{*}{**Number of OFDM**} \\  & & & **Splot** & & **Per Frame** \\ \hline
0 & 15 & 14 & 10 & 1 \\ \hline
1 & 30 & 14 & 20 & 2 \\ \hline
2 & 60 & 14 & 40 & 4 \\ \hline
3 & 120 & 14 & 80 & 8 \\ \hline
4 & 240 & 14 & 160 & 16 \\ \hline \end{tabular}
\end{table}
Table 2: Orthogonal frequency division multiplexing (OFDM) symbols configuration in 5G NR [26].  
The channel performance was studied to find the constellation diagram at the receiver and the resulted Bit Error Rate (BER). The BER is calculated by comparing the received bit sequence with the transmitted one.  
The quality of the reception is also measured via the constellation diagram in the signal vector I/Q space. Each point in the constellation diagram represents a given QAM symbol as a vector. The constellation diagram demonstrates amplitude and phase distortions emerging due to the dispersive propagation as well as the additive noise associating with the demodulation.