Contention-based adaptive position update for intermittently connected VANETs

Position information of nodes in vehicular ad hoc networks (VANETs) plays a key role in geographic routing. A sender or intermediate node employs position information of its neighbors and destination node to make routing decision. Under a greedy forwarding algorithm, the neighboring node closest to the destination node is selected as the next hop. Hence, it is critical in geographic routing to ensure that the selected next hop has a better position than other neighboring nodes. Position information is usually propagated to local nodes through periodical beaconing. In most geographic routing protocols, each node broadcasts beacons in a fixed interval, but this method can not always achieve both position accuracy and low overhead. In this paper, we propose a contention-based adaptive position update (CAPU) scheme for intermittently connected VANETs. CAPU concentrates on the position accuracy of the next hop when data transmission happens. If the position deviation of the next hop is greater than the permitted deviation range, the next hop updates its position. A special next hop timeout approach is proposed to find and delete the unreachable next hop as soon as possible. CAPU can find key nodes in local topology for greedy forwarding and intermittent connectivity. In addition, contention beacons broadcasted by key nodes maintain the local topology. Experimental results show that the proposed approach provides key position information for routing decision and exhibits better routing performance with acceptable overhead.