Abstract-In a vehicular network, every vehicle broadcasts update messages that contain location and speed information periodically to its one hop neighbors. The broadcast efficiency measures the average rate at which a vehicle receives these packets from any of its neighbors. As the node density increases, heightened interference lowers broadcast efficiency if congestion control mechanism is not used. In this paper, we analyze the broadcast efficiency under Rayleigh fading channel, and provide congestion control and power control strategies that maximize the efficiency. A worst-case guaranteed strategy achieving at least 95% of the optimal is also provided for cases when the network nodes have high mobility. Ns-2 simulations show that our analytical results accurately predict the system dynamic.

Reliable and timely multi-hop propagation of messages among vehicles is essential for a safer and greener transportation system. Various broadcast-based forwarding strategies are envisioned for infrastructure-less vehicle-to-vehicle (v2v) communications. This paper proposes a prioritized broadcast contention control (PBCC) module/layer that provides reliable and low latency multi-hop connection. The PBCC forwarding algorithm optimizes the back-off distribution to improve the probability of successful broadcast and prioritizes forwarders based on location information. This module can be implemented in WAVE devices with minimum system modification. We integrate simple vehicular mobility models into ns-2 and implement a WAVE/802.11p communication protocol stack. Extensive simulations demonstrate PBCC's superiority in multi-hop delay. Geographical routing Unicast based geographical forward Broadcast based geographical forward Broadcast based forward with implicit ACK Contention based forward Topology based routing Mobile ad hoc routing Proactive routing Reactive routing