A Scalable and Cooperative MAC Protocol for Control Channel Access in VANETs

Abstract

In this paper, a scalable and cooperative medium access control (MAC) protocol (SCMAC) is proposed to support the periodic beaconing over the control channel in vehicular ad hoc networks. The main concerned aspects in SCMAC are communication reliability and protocol scalability. The communication reliability is guaranteed by cooperative beaconing. When broadcasting a beacon, the node embeds the slot state information into the beacon so that surrounding nodes can determine the availability of each slot. Together with the contention window, collisions can be alleviated. The protocol scalability is achieved by the slot access method and the proactive slot reservation. On one hand, the slot access method reduces the average delay by using the smaller beaconing period as the node density is decreasing. On the other hand, the proactive slot reservation always keeps enough idle slots so that more nodes can quickly join the network. Correspondingly, the beaconing period will increase and all nodes can gain chances to broadcast beacons. The simulation results show that SCMAC can achieve the reliable and scalable periodic beaconing in vehicular environments.

Keywords

• VANET
• MAC
• cooperative beaconing
• protocol scalability