# Vortex: Network-Driven Opportunistic Routing for Ad Hoc Networks
## 4 Performance Evaluation
### Simulation Results  
Figures 3-5 show the results of **Simulation 1**, **Simulation 2**, and **Simulation 3**, respectively. Note that the results of energy consumption per packet delivery are normalized to AODV. **Simulation 1:**  
As shown in Figure 2(a), VORTEX could achieve a higher probability of packet delivery compared with conventional unicast routing and ORs. Moreover, the ORs that use the shortest route as a guide, SOAR, and OxDSR, could not improve their reliability, whereas the other ORs can achieve higher reliability. This is because the shortest route does not always result in the best route and may be less reliable than detour routes. Moreover, the shortest route as a guide enforces a certain degree of restriction on opportunistic forwarding and that may degrade the route diversity of OR. On the other hand, ExOR, HRAN, LCAR, CHOR, and VORTEX can achieve higher delivery ratios even in sparse environments. This is due to the fact that their routing procedure can improve route diversity compared to the other routing protocols in this simulation. Moreover, these routing protocols have a better probability when the number of neighboring terminals is larger because they can reap the benefit of route diversity increment to forward packets. However, the result shows that the delivery ratio of ExOR decreases slightly when the number of terminals is greater than 600. This can be explained by its complex routing procedure, that is, the complexity of the ETX calculation and scalability limitations due to the fact that ExOR has to obtain the information from all the terminals in a network. Although some ORs and VORTEX have almost the same characteristics in this result, VORTEX has a slightly higher delivery ratio because VORTEX can achieve more route diversity than other ORs, especially in the destination unknown state. Moreover, the forwarding of VORTEX especially in the state has more routing flexibility than CHOR since packets in CHOR are designed to travel through terminals that are treated as rendezvous points in the degenerated routing table. In other words, packets in VORTEX travel through higher-tier terminals, and more terminals are involved in forwarding. This allows VORTEX to increase route diversity, and this increase contributes to improving reliability. Figure 3: Results of Simulation 1. Figure 3b shows the end-to-end delay which represents the time gap between the initiation time of packet forwarding at a source terminal and the time when the destination terminal receives the packet. The result shows that there is not a large difference between the protocols. Packets forwarded by the shortest route generally have a shorter delay on wired networks. However, in ad hoc networks, the route with the smallest hop count does not always have the shortest delay because communication environment issues such as link quality affect the delay and may result in degradation. Thus, the delay becomes almost the same because ORs can forward packets using appropriate and multiple routes that have a better environment even though the hop count of ORs shown in Figure 3c is larger than the shortest route-based protocols. Moreover, VORTEX can achieve greater route diversity than CHOR because cluster-free hierarchization improves the route selection applicability and this increases the possibility of using the shortest route in terms of delay. This can also be seen from the result of the hop count that VORTEX has a slightly smaller count than ExOR, LCAR, and CHOR. Figure 3d shows that the ORs could achieve lower energy consumption compared with AODV. This is because that AODV has lower end-to-end reliability as well as lower link reliability than the protocols and requires more retransmission to forward packets to the next hop terminal. Moreover, broadcast-based forwarding also contributes to suppressing the energy consumption per packet forwarding since it can simultaneously forward the same packet to multiple receivers with a single transmission.