EMDOR: Emergency message dissemination with ACK-overhearing based retransmission

In vehicular ad hoc networks (VANETs), providing drivers with safety service such as the reliable delivery of an emergency message is a challenge. To propagate the emergency message quickly to all vehicles, the broadcasting technique can be utilized, however, the broadcasting is vulnerable to unreliability. In this paper, we therefore propose a scheme to improve the broadcast reliability by allowing nodes to overhear an ACK message. A selected node transmits an ACK message on behalf of other receiving nodes. If a node overhears an ACK message, but has not received the corresponding message, the node considers that the emergency message is lost and requests the selected node to rebroadcast the emergency message. Using ns-2 simulator, we verify that our proposed scheme provides more reliable service than other existing solutions.