# Cooperative UAV Scheme for Enhancing Video Transmission and Global Network Energy Efficiency
## 4 Evaluation
### Simulation Results
Figure 5 summarizes the average number of live UAVs and remaining energy during the entire simulation time for UAVs flying with different speed limits for both SD-UAVNet and VOEI. Figure 4: Remaining energy over time for UAVs flying with different speed limits. (**a**) UAV flying with speed ranging from 1 to 5 m/s; (**b**) UAV flying with speed ranging from 5 to 10 m/s; (**c**) UAV flying with speed ranging from 10 to 15 m/s; (**d**) UAV flying with speed ranging from 15 to 20 m/s. By analyzing the results of Figure 5a, we can conclude that VOEI provides FANET operations without reducing the number of UAVs, regardless of the flying speed. On the other hand, we can see that the number of live UAVS reduces as soon as the speed limits increases for SD-UAVNet scenario. This is explained by the results of Figure 4.  
By analyzing the results of Figure 5b, we can see that the remaining energy of UAVs considering VOEI remains higher than 60% in all flying speeds. This is because CN considers global FANET context information to establish reliable and energy-efficiency routes, which prevent UAV loss caused by energy issues such as explained before. On the other hand, SD-UAVNet tends to spend more energy as soon as the speed limits increases, leading to the premature death of all UAVs as shown in Figure 5a. This is because the energy consumption is higher in high speed limits, and SD-UAVNet does not consider UAV replacement or energy-efficiency operations. Figure 6 shows the video quality level measured by the SSIM metric during the simulation time for videos delivered by SD-UAVNet and VOEI, while UAVs flying with different speed limits. By analyzing the results of Figure 6, we can conclude that videos delivered by SD-UAVNet and VOEI have a similar quality level. This is because both establish a route between the source and destination in a similar way. However, it is important to highlight that, in some cases, videos delivered by SD-UAVNet have higher variation in the video quality compared to videos delivered by VOEI. This is because SD-UAVNet does not consider battery replacement of UAVs with lower energy level and also relays replacement, which leads to the UAV loss caused by energy issues. Such UAV can be responsible for relaying packets for a given video, and thus it might cause route failure and packet loss. In this sense, such video will not be delivered with a good quality level due to route failure, increasing the video quality variation. Videos delivered by VOEI have similar quality during the entire simulation, regardless of the flying speed. This is because VOEI provides the cooperation of UAVs for enhancing video transmission and global energy efficiency by introducing a battery replacement of UAVs with lower energy level and also relay replacement. It is important to highlight that VOEI is able to deliver videos with QoE support during the entire simulation, regardless of the flying speed, which is not achieved by SD-UAVNet. This is due to the controller node in VOEI being responsible for avoiding network disconnections, route failures, and void areas caused by the death of UAVs. Figure 5: Remaining energy and number of live UAVs during the entire simulation for UAVs flying with different speed limits. (**a**) Nodes of live UAV; (**b**) Remaining Energy. From our performance evaluation analysis, we conclude that VOEI improves energy-efficiency operations to deliver videos with QoE support over FANET compared to SD-UAVNet. In this sense, it can effectively mitigate the energy challenges of FANET, since it provides energy-efficiency operations, avoiding network death, route failure, and void area, as well as network partitioning  
Figure 6: SSIM over time for UAVs flying with different speed limits. (**a**) UAV flying with speed raging from 1 to 5 m/s; (**b**) UAV flying with speed raging from 5 to 10 m/s; (**c**) UAV flying with speed raging from 10 to 15 m/s; (**d**) UAV flying with speed raging from 15 to 20 m/s. compared to SD-UAVNet.