# Study on Drone Handover Methods Suitable for Multipath Interference Due to Obstacles
## 3 How to Evaluate Flying Drones
### Overview of 3D Cross Layer Simulator  
In this study, a three-dimensional cross-layer simulator was developed for the virtual evaluation of drone flight. The simulator configuration is shown in Figure 8. The simulator uses a physical propagation simulator (EEM: ray tracing method) and numerical analysis software (MATLAB R2020a: OFDM signal processing) [37] for the physical layer, and a network simulator (OPNET: including network protocol, and the upper layer uses a network simulator (OPNET: including network protocols and applications) [38]. A control tool that optimally transfers information data between these commercially available analysis simulators was constructed, which passes the received power analyzed at the physical layer to a network simulator at a higher layer for continuous and integrated evaluation from the physical layer to the application layer. In addition, topography and building data are imported from the map data, thereby enabling analysis in a virtual network environment with a 3D configuration. Furthermore, the system can handle the performance evaluation of the entire system as well as the evaluation indices and extracted analysis specified for each layer. The ray tracing method converts radio waves into optical waves. The ray tracing method approximates radio waves as light using direct waves and reflection and diffraction paths and enables analysis, including real-space conditions, for performance evaluation between transmitting and receiving stations using drones and other devices with height differences. Figure 9 shows the structure of the linkage of each simulator, which exchanges propagation information and signal processing analysis information between the EEM and MATLAB. The results of these analyses were passed to OPNET, which uses network protocols to evaluate the throughput and delay. As the drone (STA) flies and moves, the results of each propagation and signal analysis are output as a CSV file and fed back into the OPNET evaluation model. However, the number of output CSV files increases as time is divided based on the moving speed and the desired analysis accuracy. Therefore, it is necessary to divide the time into an appropriate number of analyses. The simulation flow divides the drone flight path into arbitrary time segments, as shown in Figure 10, and performs a propagation analysis for each point at each segmented time. The transmission rate is determined by selecting the modulation and coding scheme index (MCS index) that can be transmitted based on the received power obtained from the propagation analysis. The result of the determined transmission rate is passed to the upper layer to calculate the throughput. The throughput is calculated at the Layer 2 level, including the media access control (MAC) header and control frame transmission and reception procedures, as well as the throughput available to the application, including the frame header and control frame transmission and reception procedures above the IP layer. Moreover, it supports traffic such as video, voice, hypertext transfer protocol (HTTP), and evaluation metrics for each layer, facilitating the performance evaluation of applications.  
Figure 8: Three-dimensional cross layer simulator configuration.  
Figure 10: Simulation flow.  
Figure 9: Simulator linkage.