# Vortex: Network-Driven Opportunistic Routing for Ad Hoc Networks
## 4 Performance Evaluation
### Simulation Results
Figure 3d also shows that there are similar results in energy consumption, which can be explained by the results of packet delivery ratio and hop count. In other words, the protocols with higher delivery ratios have slightly longer hop counts and the protocols with lower ratios have shorter hop counts. Therefore, the comprehensive energy consumption becomes almost the same value since they require an equivalent number of transmissions. **Simulation 2:**  
Figure 4a shows that LCAR, CHOR, and VORTEX can achieve better performance than the other protocols, whereas the others degrade their performance as the moving speed increases. The reason for the degradation in the conventional protocol is mainly due to the difficulty in the route establishment in the high mobility environment. Therefore, the route-based protocols including the tunnel-based protocol, AODV, SOAR, HRAN, and OxDSR, may not be able to establish appropriate routes or guides for forwarding. In addition, ExOR faces the difficulty of collecting valid information in highly mobile environments, which degrades the accuracy of the information and can make it difficult to forward packets with appropriate routes. On the other hand, forwarding in LCAR, CHOR, and VORTEX can dynamically adapt to the topology changes due to terminal mobility with their flexible forwarding strategy. Moreover, the hierarchical forwarding of VORTEX, namely the forwarding that packets climb up and descend the tier gradients, contributes to improving reliability by using multiple routes simultaneously since VORTEX does not require a route-like forwarding guide. The end-to-end delay and hop count shown in Figure 4b,c represent a similar characteristic in **Simulation 1**. The results show an increasing trend with increasing moving speed due to the difficulty of optimal route selection. However, the opportunistic forwarding strategy in ORs can effectively suppress the delay even though the hop counts increase slightly for the same reason previously explained in the result of **Simulation 1**. In addition to that, we can see that ExOR has a larger hop count than the other protocols. This is because the forwarder list selection in highly mobile environments becomes difficult as explained, and the list becomes obsolete in a short time. This could result in an inappropriate forwarder list with a larger hop count being used in the environment. Figure 4d shows the same characteristics as with the result of **Simulation 1** that ORs can achieve better energy efficiency than AODV. This fact is derived from the same reason as explained in **Simulation 1** part, that is, ORs could achieve a higher delivery ratio and require fewer retransmissions to recover reliability. In addition to that, the reliability degradation of ExOR, HRAN, SOAR, and OxDSR in high mobility environments also  
degrades their efficiency, whereas LCAR, CHOR, and VORTEX could achieve almost the same efficiency as in the former simulation. This is because their reliability is relatively higher than the others, especially with CHOR and VORTEX. Moreover, VORTEX achieves higher reliability and a smaller hop count than CHOR, resulting in the highest efficiency. The efficiency improvement of VORTEX is also derived from its forwarding strategy, that is, its hierarchical forwarding strategy both in the destination unknown and fixed states can effectively suppress unnecessary forwarding according to the assigned structure. This is because forwarded packets are routed in logically appropriate directions in the unknown state, and in both logically and physically appropriate directions in the fixed state. Simulation 3:  
Figure 4(a) shows that ORs could achieve better reliability than AODV. This is mainly due to the flexibility of forwarding in ORs, that is, improved route diversity of ORs effectively distributes the concentrated traffic around source terminals, which generally causes reliability degradation.