# UAV-Assisted Hybrid Scheme for Urban Road Safety Based on VANETs
## 4 Experiments  
In this section, we analyze the performance of our proposed UAV-assisted (UAVa) protocol to study the efficiency of UAVa and compare its overall performance with the traditional routing protocol AODV. We considered the realistic urban scenario in Dhaka, Bangladesh, as shown in Figure 4a-c. Figure 4a represents the SUMO software view of our simulated area, Figure 4b represents the OpenStreetMap view of our simulated area, and Figure 4c represents the actual geographical view of our simulated area. We used the simulation tool Network Simulator (NS-2.35) to evaluate UAVa [28]. Using two mobility generator tools, Simulation of Urban Mobility (SUMO) [29], and VanetMobiSim [30], to generate realistic movements for vehicles and UAVs, respectively, the tools know the flexibility and sustainability of nodes movement. The hybrid random walk mobility model for UAVs describes the UAV movement which may cover congested intersection areas. Geographic data were imported from OpenStreetMap (OSM) to integrate the road layout into our simulation [30]. Figure 4: Map of the simulated area in Dhaka, Bangladesh: (**a**) SUMO software view of our simulated area. (**b**) OpenStreetMap view of our simulated area. (**c**) actual geographical view of our simulated area. Simulation Setup:  
The vehicle simulation was conducted in the 9000 m \(\times\) 4000 m area shown in Figure 4c. The initial position of the node is distributed randomly. This urban map is stretched, encompassing nearly 20 intersections and 46 road segments. The vehicles moved with speed not more than 40 km/h, and UAVs moved with speed not more than 60 km/h. We assumed that the coverage area of all RSUs did not surpass 200 m, and UAVs did not surpass 300 m.  
To simulate this network, we used 106 vehicles, 15 RSUs, and 4 UAVs. The simulation parameters are given in Table 2. The communication range of the node is set to 200 m, and the channel's data transmission rate is set to 6 Mbps. We used the IEEE 802.11p specification for implementation of the MAC layer. For each node pair (source-destination), and packet size (512 bytes), we found the data from Constant Bit Rate (CBR). We also adopted User Datagram Protocol (UDP) and Transmission Control Protocol (TCP) as transportation layer protocols for our project, UDP for RSU to Vehicle, UAV to Vehicle, and RSU to UAV communications and TCP for internal communication between cellular networks. In our project, we are using UAVs as a relay on an emergency basis to make our simulations more accurate. Hello packets are broadcasted every 1 (s). It is worth mentioning that the transmission range of vehicles and RSUs are considered the same when communicating between them (\(\approx\)200 m), and the transmission ranges of nodes and UAVs in congested intersections will be considered the same when the same communication is established (\(\approx\)300 m). Based on multiple tests in the simulation environment, we can say that the chances of success in radio transmission between RSU and UAV are great. The probability of success is too high for hybrid radio transmission (between RSUs and cellular networks). In order to evaluate the simulation protocol more realistically, the initial geographic location of the node and RSU has been well allocated through the network. UAVs and nodes' mobility is regulated, as their movement is restricted only in the simulated area. Every simulation has a total time set to 180 s.  
The other simulation parameters are summarized in Table 2. Certain parameters were chosen based on previous research [8; 31; 32; 33]. In this way, based on multiple metrics, some evaluation indicators are estimated, such as the average throughput, the instant throughput, the packet delivery ratio, the residual energy, and the end-to-end delay.