It is nowadays common in all kinds of traffic-maritime, air, road-that vehicles use beaconing systems to broadcast their position and other navigational data to nearby vehicles to improve situational awareness. MAC protocols for the beaconing use case face special challenges: protocol overhead has a significant performance impact due to small packet size, fair and frequent access to the channel is required, and the broadcast nature limits the applicability of hand shakes. We propose LAMA, a MAC protocol for position awareness beaconing that is based on the locally shared position information. Our contention-free approach uses neither handshakes nor forwarding of state, thereby requiring only small constant protocol overhead per beacon and scaling well with large neighbor counts. Yet, it successfully suppresses interference, including hidden-terminal-type, while maximizing channel utilization through coordinated spatial reuse. In a quantitative evaluation using the ns-3 discrete event simulator we compare LAMA against SO-TDMA, the MAC protocol used in the maritime automatic identification system. We find that LAMA outperforms SO-TDMA with respect to several metrics in synthetic random topologies as well as in scenarios based on real vessel traffic traces.
