## 4 Simulation Experiments  
This section presents experiments conducted to verify the proposed DoA estimation algorithm and beamforming scheme. For this purpose, we present a performance comparison with a baseline beamforming scheme using the widely studied MUSIC algorithm. Here, a recently proposed improved variant of the MUSIC algorithm [17] is used, which offers higher accuracy and lower computational complexity than the conventional MUSIC algorithm. In all experiments, the UAVs and the BS are assumed to be in the defined local NDE frame. On the BS side, there is an antenna array with 16 elements lying on the z axis. The BS height is 15 m above the ground. The spacing between the array elements is half of the wavelength, which is 0.165 m in this case. Two UAV models in addition to the target UAV are include, which fly in circles and produce uplink signals that act as interference with the receiver. The speed values of the UAVs are selected in accordance with those applied in 3 GPP Release 15. The maximum speed is 160 km/h, and a moderate value of 60 km/h is chosen. The target UAV's transmission power is 23 dBm, and the transmitted signal-to-interference ratios (SIRs) are 1 dB and 2 dB. The noise power is \(-95\) dBm. The carrier frequency is 0.9 GHz, and the speed of light is assumed to be \(3.0\times 10^{8}\) m/s. The wireless air-ground channel model is built in accordance with the specifications of 3 GPP Release 15 [3]. The small-scale fading parameters of the channel are determined in accordance with the third alternative model for fast fading in that document. The number of clusters contained in a signal is 15 [35]. The sampling interval of the improved MUSIC algorithm is \(0.03255\times 10^{-9}\) s, and the number of snapshots is 3000. The symbol length is \(66.7\times 10^{-9}\) s.  
The receiving power \(Pr\) (in mW) of each UAV is expressed as follows:  
\[Pr=10^{(Pt-PL)/10}, \tag{16}\]  
where \(P_{t}\) and \(PL\) denote the transmission power (in dBm) and the path loss (in dB), respectively. The path loss is a function of the 3-dimensional (3-D) distance between the UAV and the BS and the UAV's altitude [3]:  
\[PL=max(23.9-1.8\text{log}_{10}(h),20)\text{log}_{10}(d_{3D})+20\text{log}_{10} (\frac{40\pi f_{c}}{3}), \tag{17}\]  
where \(d_{3D}\) and \(h\) are the 3-D distance and the UAV's height, respectively, and \(f_{c}\) is the carrier frequency. The settings of the interfering UAVs are identical in all experiments. Throughout the rest of this section, 'UAV' refers to the target UAV unless otherwise stated. The simulation parameters are summarized in Table 2.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Number of array elements & 16 \\ BS height & 15 m \\ Spacing between array elements & 0.165 m (half of wavelength) \\ UAV speed & 60 km/h, 160 km/h \\ Transmission power (target UAV) & 23 dBm \\ Transmission SIR & 1 dB, 2 dB \\ Noise power & \(-95\) dBm \\ Carrier frequency & 0.9 GHz \\ Light speed & \(3.0\times 10^{8}\) m/s \\ Path loss model & The Rural Macro cell model in [3] \\ Fast fading model & The third alternative in [3] \\ Number of clusters & 15 \\ Sampling interval & \(0.03255\times 10^{-9}\) s \\ Number of snapshots & 3000 \\ Symbol length & \(66.7\times 10^{-9}\) s \\ \hline \hline \end{tabular}
\end{table}
Table 2: Simulation Parameters.