Inter-Vehicle Communication Systems rely on multi-hop broadcast to disseminate information to locations beyond the transmission range of individual nodes. Message dissemination is especially difficult in urban areas crowded with tall buildings because of the line-of-sight problem. In this paper, we propose a new efficient IEEE 802.11 based multi-hop broadcast protocol (UMB) which is designed to address the broadcast storm, hidden node, and reliability problems of multi-hop broadcast in urban areas. This protocol assigns the duty of forwarding and acknowledging the broadcast packet to only one vehicle by dividing the road portion inside the transmission range into segments and choosing the vehicle in the furthest non-empty segment without apriori topology information. When there is an intersection in the path of the message dissemination, new directional broadcasts are initiated by the repeaters located at the intersections. We have shown through simulations that our protocol has a very high success rate and efficient channel utilization when compared with other flooding based protocols.

In this paper, two IEEE 802.11-based multihop broadcast protocols, namely urban multihop broadcast and ad hoc multihop broadcast, are proposed to address the broadcast storm, hidden node, and reliability problems of multihop broadcast in vehicular networks. In the proposed protocols, the functions of forwarding and acknowledging the broadcast packet are assigned to only one vehicle by dividing the road portion inside the transmission range into segments and choosing the vehicle in the furthest nonempty segment without a priori topology information. The simulation results confirm that our protocols have very high success rate and efficient channel utilization when compared with other flooding-based protocols. It is also concluded that there is no need for infrastructure support unless the line of sight among different road segments incident to an intersection is blocked with obstacles.

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