## 4 Simulation and Performance Analysis
### Performance Analysis  
The simulation results for analyzing the impact of GPS outage on EGR, effect of vehicle speed on the functionality of EGR, and the investigation of how vehicle density affects performance is presented in this section. (a) Performance Analysis Under GPS Outage  
In this section, we determine whether or not EGR is a viable and effective approach for information dissemination under GPS outage problems and how geometrical localization assists EGR to improve the its performance in terms of throughput, end-to-end delay, and one-hop link disconnection. For this simulation, the velocity of the vehicles are 30 km/h. GPS outage time is the length of time in which vehicles lost GPS signal. Figure 8 shows the end-to-end delay of EGR versus the state-of-the-art geocast routing approaches. It is clear from the result that, as GPS outage time increases, the end-to-end delay for all the geocast routing approaches increases. The end-to-end delay for the EGR is stable and does not increase much with the increase in GPS outage time. However, it is increasing rapidly for J-GEDIR, P-GEDIR, and SLD-GEDIR. For example, GPS outage time is 50 ms; the end-to-end delay for EGR is 15 ms, and for J-GEDIR, P-GEDIR, and SLD-GEDIR, the delays are 50 ms, 65 ms, and 71 ms respectively. This is due to the fact  
that, with P-GEDIR boundary vehicles as forwarder, J-GEDIR chooses the vehicles from the furthest junctions. The boundary and farthest crossing vehicles are sometimes sensitive to link failure because of the frequent occurrence of GPS outage. All three, J-GEDIR, P-GEDIR, and SLD-GEDIR, do not employ any localization technique for GPS outage problems, whereas the EGR uses geometrical localization for the same problem. The proposed EGR gives an average of 70% lower end-to-end delay as compare to SLD-GEDIR, wherein the end-to-end delay for EGR is about 75% to 80% lower than that of J-GEDIR and P-GEDIR, respectively. Thus, when compared to state-of-the-art routing approaches, the proposed EGR performs better. Figure 9 shows the throughput of EGR versus state-of-the-art geocast routing approaches. It is clear from the result that, as GPS outage time increases, the throughput for all the geocast routing approaches decreases. For the EGR, it is stable and is not decreasing much with the increase in GPS outage time. However, it is decreasing rapidly for J-GEDIR, P-GEDIR, and SLD-GEDIR. For example, GPS outage time is 50 ms; the throughput for EGR is 240 Kbps, and, for J-GEDIR, P-GEDIR, and SLD-GEDIR, the throughput is 170 Kbps, 30 Kbps, and 31 Kbps, respectively. When GPS outage time is 150 ms, the throughput for EGR is 230 Kbps, and for J-GEDIR, P-GEDIR, and SLD-GEDIR, the throughput is 100 Kbps, 20 Kbps, and 17 Kbps, respectively. This is due to the fact that link failure occurs more frequently due to occurrence of GPS outage for all three, J-GEDIR, P-GEDIR, and SLD-GEDIR, and they do not employ any localization technique for the GPS outage problem, whereas the EGR uses geometrical localization to cope with the same problem. The proposed EGR gives an average of 72% better throughput compared to SLD-GEDIR, wherein the throughput for EGR is about 80% to 90% greater than that of J-GEDIR and P-GEDIR, respectively. The proposed EGR performs better compared to state-of-the-art routing approaches. Figure 10 compares the results of one-hop link disconnection between EGR and contemporary routing approaches for different values of GPS outage time. It is evident that one-hop link disconnection for EGR is minimal and stable compared to other contemporary routing approaches for GPS outage times of 0 ms and 100 ms. It is because the forwarding vehicle selection process is completed within the residual link lifetime time However, as GPS outage increases to more than 100 ms, the one-hop link disconnections abruptly increase, since the forwarding vehicle selection process could not be finished in the residual link lifetime time in both EGR and SLD-GEDIR. In comparison to J-GEDIR, P-GEDIR,  
Figure 8: Effect of GPS outage on end-to-end delay.