Adaptive Broadcasting for VANETs With Dynamic and Diverse Emergency Requirements.

The multi-hop broadcast is of crucial significance to emergency message dissemination in vehicular ad hoc networks (VANETs). However, current solutions focus on a single and fixed goal, which cannot satisfy the dynamic and diverse emergency message requirements. In this article, we propose an adaptive broadcast-relay selection scheme to fill up this gap. An adaptive control message is designed to reflect the dynamic and diverse emergency message requirements. An adaptive relay pattern switching mechanism is designed to accommodate such requirements based on the adaptive control message. Delay-sensitive messages are broadcasted by an adaptive sender-based relay pattern, in which the link quality is used to address the inherent transmission reliability problem. Delay-insensitive messages are broadcasted by an adaptive receiver-based relay pattern, in which the time interval of adjacent potential relays is set to address the inherent packet collision problem. The unique features of our solution are twofold. One is the stronger adaptivity due to the implementation of the dynamic relay patterns, and the other is the wider applications due to the satisfaction of multiple types of emergency messages. Extensive simulations demonstrate the advantages of our solution in terms of transmission delay, dissemination speed, and adaptability in different scenarios.