TMED: A Spider-Web-Like Transmission Mechanism for Emergency Data in Vehicular Ad Hoc Networks

The vehicular ad hoc network (VANET) is an emerging mobile ad hoc network, which is an important component of the Internet of Things and has been widely applied in intelligent transportation systems in recent years. For large-scale VANETs, it is important to design efficient transmission schemes for time critical emergency data. Greedy perimeter stateless routing protocol is a typical geographic-based routing protocol and greedy perimeter coordinator routing protocol is typical for map-based but they do not consider the QoS of the transmission link and hence are not suitable for emergency data transmissions. Some bioinspired protocols and situation-aware protocols are more suitable for emergency situations. However, they have some limitations in terms of the computational complexity and convergence rate which can cause large time delays. In this paper, we propose a novel spider-web-like transmission mechanism for emergency data (TMED) in vehicular ad hoc networks, in which a spider-web-like transmission model combining geographic information system and electronic maps is established. In this mechanism, the request-spiders and confirmed-spiders are sent out to obtain the transmission path from a source vehicle to a destination vehicle to improve the packet delivery ratio and average transmission delay of emergency data. TMED combines a dynamic multipriority message queue management method with a restricted greedy forwarding strategy based on position prediction to significantly reduce the end-to-end delay of packets. We use SUMO and NS2 to simulate TMED in a city scenario and compare its performance with GPSR, GPCR, and ACAR based on the packet delivery ratio, average transmission delay, and routing overhead. The simulation results show that TMED outperforms these previously proposed protocols.