# Vortex: Network-Driven Opportunistic Routing for Ad Hoc Networks
## 4 Performance Evaluation
### Simulation Results
Moreover, every protocol slightly degrades the reliability as the source terminal ratio increases because the concentration can occur at multiple points simultaneously, increasing the number of degradation points throughout the networks. In addition to that, the reliability improvement of VORTEX over other protocols can be explained by its forwarding flexibility while the conventional protocols suffer from the over-concentration of routes and traffic in the area of source terminals and the neighboring area of guide routes for forwarding. Figure 4(b),c show a similar order of performance order as the former simulations. Figure 4(b) shows the delay gradually decreases as the number of source terminals increases. This is mainly due to the dispersion of traffic and a decrease in queuing delay, which is caused by the increase in forwarding routes. The improvement in VORTEX can be explained by the same reason described in the last paragraph that more flexible route selection in VORTEX adaptively distributes concentrated traffic around source terminals better than the others. Figure 4(c) shows that the hop count of AODV and VORTEX is almost constant, whereas the others increase their hop count as the traffic concentrates. The increase in the number of hop counts is mainly due to the fact that congested links  
Figure 4: Results of Simulation 2.  
generally have lower reliability and efficiency, that is, the protocols have a tendency to forward packets detouring such links. Figure 5d shows characteristic trends compared with the other simulation results that some protocols greatly degrade the energetic efficiency, especially in congested environments. The degradation was mainly due to the decrease in reliability and the increase in hop count. On the other hand, VORTEX could achieve the best efficiency among the protocols because it achieved the best reliability and reasonable hop count increment. In addition to that, the flexible and efficient forwarding strategy of VORTEX contributes to suppressing the number of forwarding, namely the energy consumption, as is the case with the other simulations. **Discussions:**  
Through the above simulations, we have confirmed that the proposed routing protocol, VORTEX, can achieve better performance than any other conventional comparable protocols from the following viewpoints. **(1)** VORTEX could achieve the best reliability among the protocols owing to its diverse route usage suppressing unnecessary forwarding. **(2)** VORTEX could restrain the increase in end-to-end delay owing to its prompt forwarding process and appropriate forwarding route selection with OR even though a certain degree of hop count increase could be observed. **(3)** VORTEX could achieve the lowest energy consumption to deliver a single packet to the destination terminals since it has high reliability and reasonable hop count that requires less packet forwarding compared with the other conventional protocols. In other words, the related results showed that VORTEX achieved (a) 3.92-10.20% improvement in average packet delivery ratio, (b) 7.42-14.89% reduction in average end-to-end delay, (c) 1.79-2.68% reduction in average hop count, and (d) 5.56-9.48% reduction average energy consumption per packet delivery on average. Moreover, CHOR, our previous work, requires a route discovery procedure in a similar way as the conventional routing protocols do to find terminals that would be assigned as rendezvous points through which packets should travel. VORTEX, on the other hand, uses tiered structures as a comprehensive guide for packets to travel and the tier gradient spontaneously directs packets to designated destination terminals suppressing forwarding that go off the appropriate directions. Thus, VORTEX achieved higher adaptability to network state changes and this improves both reliability and efficiency compared with CHOR  
Figure 5: Results of Simulation 3.  
since the routing performance of CHOR strongly depends on the initial route discovery and CHOR is difficult to change routing tables adaptively during a session.