An Efficient Broadcast MAC Scheme for Traffic Safety Applications in Automotive Networks

Paper in proceedings, 2006

We consider intelligent transport systems which aim at providing more safety to vehicles by forming a wireless ad-hoc network among the vehicles. To provide safety, each vehicle informs its neighbors about its status by periodically broadcasting data packets. For such a network to provide safety, having an efficient broadcast MAC layer that can provide a low end-to-end delay, regular packet receptions, and fast adaptation to topology changes is essential. We consider CSMA-based broadcast MAC protocols and argue that schemes based on RTS-CTS handshake are not suitable for this type of networks as they suffer from high overhead, long end-to-end delay, and poor adaptation to topology changes. The IEEE 802.11 approach of ignoring RTS-CTS handshake for broadcast packets solves the overhead, delay, and topology adaptation problems. However, it suffers from the hidden terminal problem resulting in low delivery ratio. To address this problem, we propose the Long Range Busy Tone (LRBT) protocol. In this protocol, similar to IEEE 802.11, we ignore the RTS-CTS handshake completely. To provide protection against the hidden terminals, the transmitter sends a packet along with a longer range busy tone to block the hidden terminals. The simulation results confirm that this method offers higher delivery ratio and less inter-packet delay compared to the simple broadcast scheme.