# Guard Band Protection Scheme to Facilitate Coexistence of 5G Base Stations and Radar Altimeters
## 3 Numerical Results  
We use the aforementioned interference analysis model to evaluate the interference received by radar altimeters from 5G base stations, leveraging the guard band protection method based on Monte Carlo simulation. The received interference is determined by the random placement of 5G base stations within the radar altimeter coverage, random antenna pointing and beamforming directions of the 5G base station, and random channel conditions. The simulation results are obtained by repeating 1000 snapshots with randomness, maintaining the same environment and the same antenna pattern at the same radar altimeter height. Introducing new random variables in each simulation snapshot allows us to derive the variation in interference signal power from 5G base stations on the radar altimeter. Subsequently, the simulation results are analysed and expressed as a cumulative distribution function (CDF), which is compared with the threshold of the radar altimeter at \(-6\) dB to explore the possibility of coexistence between 5G base stations and the radar altimeter after using the guard band protection method. As various factors influence the airplane approach speed, a uniform descent speed is assumed. The simulation uses data for the Boeing 737-800. 5G downlinks are assigned to the 3.7-4.0 GHz band with a 100 MHz bandwidth, while the radar altimeter operates in the 4.2-4.4 GHz band with a 196 MHz channel bandwidth. While most airports are situated on the outskirts of a city, some are located in urban areas, such as helicports. Hence, we assume 5G base stations are distributed in the rural, suburban, and urban environments. The 5G base station is modelled using parameters from Table 2, and the simulation involves parameters from Table 3 for the radar altimeter. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Unit** & **Value** \\ \hline Carrier frequency & GHz & 3.7–4.0 \\ BS channel bandwidth & MHz & 100 \\ UE channel bandwidth & MHz & 20 \\  & & Rural: 35 \\ BS antenna height & m & Suburban: 25 \\  & & Urban: 20 \\ Antenna array & & \(4\times 4,8\times 8\), and \(16\times 16\) \\ Vertical 3-dB beamwidth & \(\circ\) & 65 \\ Horizontal 3-dB beamwidth & \(\circ\) & 90 \\ Vertical element spacing & & 0.5\(\Delta\) \\ Horizontal subarray spacing & & \(2.1\lambda\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: 5G base station parameters [20]. Figure 7: Adjacent channel interference ratio vs. guard band. According to our previous work [9], the interference received by the radar altimeter from 5G base stations increases as the airplane altitude decreases. The received interference peaks at altitudes of 116 ft, 87 ft, and 75 ft in rural, suburban and urban environments, respectively, as outlined in Table 4. We perform a detailed analysis by simulating the airplane at these altitudes in the rural, suburban, and urban environments with 50 MHz and 150 MHz guard bands, as well as without a guard band. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Environment** & **Antenna Array** & **Received Interference (dB)** \\ \hline \multirow{3}{*}{Rural} & 4 \(\times\) 4 & 34.3446 \\  & 8 \(\times\) 8 & 40.3652 \\  & 16 \(\times\) 16 & 46.3858 \\ \hline \multirow{3}{*}{Suburban} & 4 \(\times\) 4 & 22.3548 \\  & 8 \(\times\) 8 & 28.3754 \\  & 16 \(\times\) 16 & 34.396 \\ \hline \multirow{3}{*}{Urban} & 4 \(\times\) 4 & 12.0633 \\  & 8 \(\times\) 8 & 18.0839 \\ \cline{1-1}  & 16 \(\times\) 16 & 23.6751 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Peak received interference without any protective measure [9].