# Multi-IRS-Assisted mmWave UAV-BS Network for Coverage Extension
## 5 Simulation Results and Discussion
\begin{table}
\begin{tabular}{l c} \hline \hline
**Parameters** & **Value** \\ \hline Carrier Frequency \(f\) & 28 GHz \\ \hline Bandwidth & 100 MHz [43] \\ \hline Environment & Dense Urban, 139.6864\({}^{\circ}\) E \(\sim\)139.7004\({}^{\circ}\) E, \\ \hline \hline \multirow{4}{*}{UAV, UE area \(\Omega\)} & \multirow{2}{*}{139.688\({}^{\circ}\) E-139.7\({}^{\circ}\) E,} \\  & \\ \hline \hline \multirow{4}{*}{UAV, 1.1 km \(\times\) 0.9 km} & \multirow{2}{*}{1.2 km \(\times\) 1.2 km} \\  & \\ \hline \hline \end{tabular}
\begin{tabular}{l c} \hline \hline
**Parameters** & **Value** \\ \hline Carrier Frequency \(f\) & 28 GHz \\ \hline Bandwidth & 100 MHz [43] \\ \hline Environment & Dense Urban, 139.6864\({}^{\circ}\) E \(\sim\)139.7004\({}^{\circ}\) E, \\ \hline \hline \multirow{4}{*}{UAV, 1.2 km \(\times\) 1.2 km} \\  & \\ \hline UAV, UE area \(\Omega\) & 139.688\({}^{\circ}\) E-139.7\({}^{\circ}\) E, \\ \hline \hline \multirow{4}{*}{UAV, 1.1 km \(\times\) 0.9 km} \\  & \\ \hline UE height & 1.2 m \\ \hline IRS height \(\kappa\) & 30 m \\ \hline Range of incident and reflection angle at IRS \(\zeta\) & 15–75\({}^{\circ}\) (vertically, horizontally) \\ \hline Neiboring BS position & (139.68676\({}^{\circ}\) E, 35.69350\({}^{\circ}\) N, 209 m) \\ \hline Minimum UAV height & 50 m \\ \hline Maximum UAV height & 70 m \\ \hline The number of UAVs & 1 \\ \hline The number of IRSs \(M\) & 1000 (4 \(\times\) 250) \\ \hline The number of UEs \(N\) & 13,349 \\ \hline The number of hotspots & 0–3 \\ \hline The ratio of UEs inside hotspots & 30–70\% \\ \hline Hotspots radius & 10–20\% of area length \\ \hline EIRP (Trans. power + Antenna gain) & 68 dBm [44] \\ \hline Transmit output power \(P_{\rm t}\) & 45 dBm [44] \\ \hline Tx antenna gain \(G_{\rm t}\) & 23 dBi \\ \hline UE Rx antenna gain \(G_{\rm r}\) & 0 dBi \\ \hline Noise density \(\sigma_{\rm n}^{2}\) & \(-\)174 dBm/Hz \\ \hline Additional loss by LoS \(\eta_{\rm LoS}\) & 3.5 dB [38] \\ \hline Additional loss by NLoS \(\eta_{\rm NLoS}\) & 47 dB [38] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation parameters. Figure 6 shows a two-dimensional plane illustrating the UAV placement and the IRSs used for path improvement for certain UE distributions. The horizontal axis represents the east-west distance in meters, while the vertical axis similarly indicates the north-south distance. Filled rectangles represent buildings, with those taller than \(\kappa\) and with an IRS-installed color-coded green, while all others were colored black. UEs depicted as blue circles are positioned so as not to overlap with buildings, and the red star indicates the optimal horizontal position of the UAV that maximizes the minimum reception SNR among all these UEs. IRSs that were used at least once to improve reception SNR are indicated with pink diamonds. Figure 7 shows the pairs of IRSs and UEs used for route improvement connected by red lines for the distribution of UEs at 6:00, 12:00, 18:00, and 0:00 on a weekday in July 2024. The shown number of UEs is reduced to 1 % of the true number of UEs in this figure just for the sake of visibility. Because the target area is a business area where the Tokyo Metropolitan Government and many companies set up their offices, the result indicates that the population is small in the early morning and late at night and increases during the daytime. It can also be confirmed that the number of IRSs utilized increases or decreases according to the population and distribution. Figure 8 shows the received SNR of each UE without the use of an IRS, with the same UE distribution as in Figure 6. The horizontal and vertical axes are the same as in Figure 6. The color map on the right represents the normalized SNR, which has been normalized to a maximum value of 1 and a minimum value of 0 throughout all scenarios, regardless of the use of an IRS or adjacent BSs, with higher SNRs in red and lower SNRs in blue.