Driven by road safety requirements and intelligent traffic control, Vehicular Ad-hoc Networks (VANETs) have been attracting significant interest in both academia and industry. One key goal of VANETs is to provide sufficient Quality-of-Service (QoS) for real-time safety applications. The MAC protocol for VANETs is crucial to provide for an efficient and reliable medium access. The challenge is to design it to be able to cope with rapid topology changes, high node mobility [1] and different QoS requirements. Safety applications require a high reliability and a bounded delay while non-critical applications are rather throughput sensitive [2]. These applications facilitate wireless broadcast warning messages between neighboring vehicles to inform drivers on time about dangerous situations like accidents. The IEEE 1609.4 standard defines a MAC layer implementation for multichannel operations in VANETs for such broadcasts. In this poster paper, we present a distributed hybrid MAC scheme for emergency systems. The proposed scheme improves the Control Channel (CCH) utilization and uniformly distributes the load on Service Channels (SCHs). In the proposed scheme, the network switches its mode from general to emergency in order to effectively utilize common service channels thus increase the probability for timely reception of messages. In addition, the proposed scheme reduces the rate of transmission collisions and latency, thus resulting in high probability of message delivery. The proposed MAC scheme is simulated and compared with the existing competitors. The obtained results depict that the proposed hybrid scheme outperforms its competitors and thus validates its performance.
['Saifullah Khan', 'Muhammad Alam', 'Nils Mullner', 'Martin Fränzle']
Poster: A hybrid MAC scheme for emergency systems in urban VANETs environment