# Study on Drone Handover Methods Suitable for Multipath Interference Due to Obstacles
## 3 How to Evaluate Flying Drones
### Power Calculation Method in 3D Cross Layer Simulator  
The calculation of the received power and SINR in the simulator follows the procedure shown in Figure 11 and Equation (1), which are explained below. The simulator incorporated a ray-tracing method that considers radio waves as rays. Map data containing terrain and buildings were prepared, and multiple rays from connected APs, other APs, and STAs were analyzed using the propagation analysis simulator. The received power \(P_{r}\) [dBW] was calculated from the analyzed ray and converted to the true unit of received power \(\overline{P}_{r}\) [mW] using Equation (1).  
\[\overline{P}_{r}=\sum_{i=1}^{N}10^{\frac{P_{r}^{(i)}}{10}}\times 10^{3}, \tag{1}\]  
where \(P_{r}^{(i)}\) denotes the received power of the \(i\)th ray and \(N\) denotes the maximum number of rays.  
Subsequently, SINR is calculated from Equation (2) using the maximum value of the converted received power, interference power, and interference power from other APs, and a table corresponding to SINR for the signals from each AP \(a\) is created.  
\[\text{SINR}=\frac{P_{r}}{\sigma+\max_{n\in\mathcal{A}\setminus\{a\}}P_{n}}, \tag{2}\]  
where \(\sigma\) denotes the interference power beyond the GI (guard interval) length plus the thermal noise, \(\mathcal{A}\) denotes the set of access points, and \(P_{n}\) denotes the interference power from access point \(n\in\mathcal{A}\setminus\{a\}\). GI is the signal interval used to avoid inter-symbol interference (ISI) of delayed waves in a multipath environment. In this study, the length of GI was set to 800 ns. To obtain the transmission rate from the obtained SINR, the minimum receiving sensitivity \(R_{\text{min}}\) [dB] was calculated using Equation (3), and the corresponding MCS was selected, as shown in Figure 11.  
\[R_{\text{min}}=\text{SINR}-85 \tag{3}\]  
Because the interference power was analyzed using the simulator, a guard interval function was added to improve the multipath interference, as specified in the IEEE802.11 ax standard [39]. As shown in Equation (4), if the multipath delay time \(t\) is shorter than the guard interval length GI, the signal is considered a valid signal.  
\[t\leqq\text{GI} \tag{4}\]  
Conversely, if the delay time is longer than the guard interval length, as shown in Equation (5), the signal is considered an interference.  
\[t\geqq\text{GI} \tag{5}\]  
Figure 11: Flow of SINR calculation.  
However, in this developed simulator, simple channel modeling was used, which only implements the geometry of buildings and other structures. Analysis in rigorous channel modeling for air-ground requires consideration of buildings and their materials and dielectric constants [31; 32]. In future work, modeling of the propagation environment will be implemented when more detailed analysis is required.  
Further discussing the simulator developed, the only uncertainty is the movement of the drone. In order to reproduce a dynamic propagation environment, other objects are assumed to move, and for evaluations that assume a vehicle, such as the V2X communication presented in reference [40], it is necessary to implement a Monte Carlo-like method for vehicle movement. The developed simulator is an event-driven method. This simulation method is that the analysis will be complex and require high computer specifications. In addition, because the system is event-driven, it is difficult to perform statistical evaluations such as numerical analysis. However, it can be extended to general cases, such as implementing propagation environment changes in a time series or setting parameters for arbitrary channel estimation errors. Therefore, although the method is not suitable for statistical evaluation, it is suitable for propagation model evaluation for social implementation and performance evaluation of new communication systems, which are the goals of this study, and we expect that it will contribute to similar research.