Cross-layer transmit power and beacon rate adaptation for VANETs

The key benefit of VANETs comes in the form of safety applications. Broadcast is the predominant form of communication for safety messages. However, due to the fast changes occurring in the network topology (sparse, dense, congested), vehicles within a VANET may face many disturbances such as collisions which can cause performance degradations. Thus it becomes hard to maintain an efficient channel utilization and so maximize the network capacity. In this paper, the idea is to take into account the dynamically changing topology of a VANET (local traffic density) and have each vehicle able to dynamically adapt its PHY QoS-parameter (Transmit Power) according to its fast changing channel conditions, network load, and link quantities of upper-layers. The proposed mechanism, called Transmit Power Adaptation (TPA) relies on channel estimate at PHY layer and uses feedback from an adaptive beaconing system (also presented) which builds the local view of a vehicle at the network layer. We have evaluated the performance of TPA through simulation with ns-3 simulator. Results show that TPA clearly outperforms the default 802.11 broadcasting mechanism in terms of network capacity. TPA also outperforms a similar adaptive technique not based on channel estimate in terms of network capacity for three scenarios.