## 2 System Model
### System-Level Scenario  
The indoor hotspot deployment scenario focuses on small cells and high user density in buildings. This scenario, described in Table 2, represents InDs with a total area of 120 m \(\times\) 50 m. There are 12 small tri-sectored cells that are deployed with an inter-site distance (ISD) of 20 m. In this case, the AP antenna height is 3 m. The coverage radius of the APs is R = 6.7 m. The carrier frequency option is 100 GHz (THz waves). The bandwidth chosen is \(B_{t}\) = 400 MHz corresponding to numerology five of 5G NR. Up to 16 carriers can be aggregated up to 6.4 GHz of bandwidth. It is important to note that in case of the number of users and wireless devices increasing relative to the numbers considered here, the expected behavior of the overall system will remain the same as long as carrier aggregation is used, and they will not cause inter-interference as long as they operate in different bands. A total of 15 users per AP are distributed uniformly and all users are indoors with 3 km per hour velocity as can be seen in Figure 3. A full buffer model is assumed. Our 3D simulation channel model considers the 5G NR indoor office wireless propagation environment in terms of physical aspects of mmWave and THz waves.  
For this particular scenario in any considered operating frequency, the number of clusters, the number of subarrays (scatterers) per cluster and the positions of the clusters are determined by the detailed steps and procedures of [25].  
According to the 5G 3 GPP 3D channel models, the number of clusters and scatterers are determined using the Poisson and uniform distributions with specific parameters. Since we extend the operating frequency range up to 100 GHz, specific multi-antenna solutions and techniques need to be employed depending on the utilized spectrum. For higher frequency bands, the transmission is characterized by a considerable signal attenuation that limits the network coverage. To overcome this limitation, one of the key features is the adoption of a very large number of multi-antenna elements with a given aperture to increase the transmission/reception capability of MU-MIMO and beamforming. Since managing transmissions in higher frequency bands are complicated, beam management is necessary to establish the correspondence between the directions of the transmitter and the receiver-side beams by identifying the most suitable beam pair for both downlink and uplink.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{2}{c}{**Parameters**} & \multicolumn{2}{c}{**Indoor-Office**} \\ \hline \multirow{2}{*}{Layout} & Room size (WxLxH) & 120 m \(\times\) 50 m \(\times\) 3 m \\  & ISD & 20 m \\ \hline \multicolumn{2}{c}{AP antenna height \(h_{\text{AP}}\)} & 3 m (ceiling) \\ \hline \multirow{2}{*}{UE location} & LOS/NLOS & LOS and NLOS \\  & Height \(h_{\text{UE}}\) & 1.5 m \\ \hline \multicolumn{2}{c}{UE mobility (horizontal plane only)} & 3 km/h \\ \hline \multicolumn{2}{c}{Min. AP-UE distance (2D)} & 0 \\ \hline \multicolumn{2}{c}{UE distribution (horizontal)} & Uniform \\ \hline \hline \end{tabular}
\end{table}
Table 2: Evaluation parameters for indoor-office scenario.  
Figure 3: Indoor-office scenario layout.