# Seamless Handover Scheme for MEC/SDN-Based Vehicular Networks
## 5 Performance Evaluation
### Simulation Results  
Figures 6 and 7 present the recorded PDR for the developed MEC-based handover scheme and the traditional handover scheme without the MEC involvement. Figure 6 provides the PDR for both systems at different traffic densities, with the distance to the RSU. These results were for a VNET with 400 vehicles, i.e., N = 400, and the vehicles' speed was 50 Km/h. Up to 300 m away from the RSU, both handover schemes achieved almost the same PDR; however, after 300 m, the value of the PDR for both systems changed. This change increased after 400 m, since at this distance the handover process had started or was close to starting in the traditional handover scheme. Moreover, with the increase in the traffic density, the PDR decreased due to the higher probability of collisions. Figure 7 provides the PDR for both systems, the proposed and the traditional handover scheme, at different vehicle velocities. These results were for a VNET with 400 vehicles, i.e., N = 400, and a traffic density of 0.1 veh/m. Five vehicle velocities were considered, i.e., those given in Table 1. With the increase in the vehicle velocity, the PDR decreased. Up to 50 Km/h the change in the PDR for both systems due to different velocities was small; however, it increased for the 60 and 70 km/h velocities. The developed MEC/SDN-based handover scheme achieved an improvement in the PDR compared to the traditional handover scheme by an average of 47%. Furthermore, the developed scheme achieved a greater improvement in the PDR for a high traffic density and high vehicle velocity  
Figure 6: PDR at different traffic densities, with the distance to RSU. Figure 7: PDR at different vehicle velocities, with the distance to RSU. compared to the traditional scheme. The percentage improvement in the PDR in the case of high vehicle velocity was 64%. The second performance metric considered was the percentage of blocked tasks. Three systems were considered for the performance evaluation: the first system represented the traditional VANET with the traditional handover scheme; the second system represented the MEC-based VANET with a traditional handover scheme; and the third system represented the developed MEC/SDN-based VANET with the developed handover scheme. For the three systems, our previously developed offloading scheme, introduced in [41], was used. Figures 8-10 provide the three systems' percentage of blocked tasks in different scenarios. The statistical analysis of the results for each of the three systems is presented in Table 2. This includes the mean and the standard deviation (Std) of the results for each system. Figure 8: Percentage of blocked tasks for the three systems with different numbers of vehicles. Figure 9: Percentage of blocked tasks for the three systems at different vehicle velocities. Figure 8 provides the average percentage of blocked tasks for each system in three scenarios with different numbers of deployed vehicles. The developed MEC/SDN-based system achieved a better performance in terms of blocked tasks compared with the other two system. This performance improvement increased with the increase in the number of vehicles in the network. This was due to the introduction of the MEC units managed by SDN, which provided a path for data offloading. Moreover, the developed handover scheme reduced the probability of task blocking because of the consideration of the migration time of the computing tasks. Figure 9 provides the percentage of blocked tasks for the three systems at different vehicle velocities. These results were for a VANET with 400 vehicles, i.e., N = 400, and a traffic density of 0.1 veh/m. The percentage of blocked tasks increased in all three systems with the increase in the vehicle's velocity. However, the percentage increase in the number of blocked tasks for the developed scheme was the lowest. Figure 10 shows the percentage of blocked tasks for the three systems at different values of traffic density. The three systems were simulated for 400 vehicles, i.e., N = 400, and a vehicle velocity of 50 Km/h.