Cluster-based Medium Access Scheme for VANETs

In recent years research on active safety systems with the main focus on environment sensing has been done. Therefore vehicles are equipped with sensors which record information about the nearby traffic situation and possible hazards. For anticipatory driving additional information outside of the range of the sensors' area needs to be collected. This can be done by introducing data transfer between vehicles, which allows to gather data of a larger area and therefore improves the anticipatory capabilities of the system. One main aspect in the data exchange between vehicles is the organization of the access to the medium. It has to be able to cope with all the problems of mobile ad-hoc networks. Especially the hidden station problem is an important factor in vehicular ad-hoc networks (VANETs). But also the high density of nodes, high dynamics and a limited data rate require a fair and efficient access to the medium. In this paper we present a medium access scheme for vehicular ad-hoc networks which is based on clustering of the vehicles. Thus the effect of hidden stations can be minimized, which leads to a more reliable data transfer than IEEE 802.11 based systems can provide.