## 6 Analysis and Results
### EMCR Evaluation
#### 6.2.2 EMCR over EHMR and CLWPR  
In order to compare the performance of EMCR with EMHR and CLWPR, we simulate all protocols for a range of vehicle densities, EMCR with no cache, and EMCR with three different cache times. Vehicles in the network have average speeds that range from 15 to 75 Mph. This section shows the performance comparison between EMCR with no cache, EMCR with different cache times, EMHR, and CLWPR. In Figure 12, the x-axis represents the number of vehicles, which varies from 15 to 100 vehicles, and the y-axis represents the packet delivery ratio (PDR). We observe that EMCR with no cache (0 s cache time) has better PDR than the EMHR and CLWPR. Increasing the cache time leads to an increased PDR. For example, EMCR with 5 s cache time has a higher PDR than EMCR with 2 s cache time but slightly less than EMCR with 10 s cache time. Overall, EMCR significantly increases the PDR compared to EMHR. Figure 13 shows that EMCR with 5 s and 10 s cache time has almost the same throughput performance and is slightly better than EMCR with 2 s cache time but better than EMCR with no cache with an increased number of vehicles. The throughput of EMCR with no cache has the same performance in terms of throughput as the EMHR and better throughput than CLWPR when the network is congested with the number of vehicles. However, the overall throughput performance obtained from EMCR is better than the throughput obtained from EMHR or CLWPR. Figure 14 shows the NRO of the network. Based on the definition of this metric, an increase in the PDR causes a decrease in the routing overhead. Therefore, the overhead of EMCR decreases by increasing the cache time. Figure 14 shows that the CLWPR protocol has the highest overhead, whereas the EMCR protocol has less overhead than EMHR even as the number of vehicles increases. Figure 12: Packet delivery ratio vs. Number of Vehicles. Figure 13: Throughput vs. Number of Vehicles. Figure 15 shows the average end-to-end delay. The average end-to-end delay in the EMCR protocol is reduced while increasing the number of vehicles, but the SCF mechanism causes some delay in the network. Increasing the cache time leads to a higher delay. As a result, the EMCR protocol has a higher delay than the EMHR protocol. However, increasing the cache time helps in decreasing the number of dropped packets, as depicted in Figure 16. Therefore, the EMCR protocol has better performance than EMHR in terms of the number of dropped packets. Moreover, the EMCR with 2 s cache time has a lower delay than the EMCR with 5 s and 10 s cache time. Furthermore, EMCR with 2 s has a lower delay than CLWPR because the CLWPR protocol cannot guarantee to deliver all packets in the hybrid network of VANET-WSN as it has the lowest PDR in Figure 12. Moreover, the number of dropped packets in CLWPR is high, and it is increasing as the number of vehicles increases in Figure 16.  
Figure 16: Number of dropped packets vs. Number of Vehicles. Figure 14: Normalized routing overhead vs. Number of Vehicles. Figure 15: Average end-to-end delay vs. Number of Vehicles. In terms of energy consumption, Figure 17 shows the energy consumption of the networks. Using EMCR with 2 s cache time has less energy consumption than 0 s, 5 s, and 10 s cache time. The reason is that when there is no cache, the SCF mechanism is not employed, and the packets cannot be stored in the presence of network disconnectivity, which increases the number of dropped packets. Moreover, increasing the cache time with 5 s and 10 s cache time means increasing the number of packets stored in the buffer until it overflows and starts to drop the packets, which consumes more energy. The EMCR protocol in all cache time cases consumes less energy than the EMHR and CLWPR protocols. Therefore, the EMCR has better performance than the EMHR and CLWPR protocols when the network is congested as the number of vehicles increases in terms of PDR, throughput, the number of dropped packets, energy consumption, and end-to-end delay.