The Impact of TDMA Frame Size on Latency in a Neighbor-Aware VANET MAC

Despite various proposed Medium Access Control (MAC) approaches, efficient medium access in VANET remains a significant challenge for the broadcast of safety messages. A key contributing factor, especially with the high node mobility apparent in VANET, is the hidden terminal problem. Since the hidden terminal problem is fundamentally a problem of lack of awareness, increased neighbor awareness at the MAC layer has been suggested as a possible solution. An increased awareness of neighboring nodes´ slot allocation requires an increased number of TDMA slots. In this paper we evaluate the impact of TDMA frame size in a neighbor-aware MAC. An analytical model is developed to support the simulation results, based on a Markovian multi-server queue. The results show that the end-to-end latency is mostly affected by the TDMA frame cycle time when supply of slots outstrips demand. However, when slots become scarce, latency is adversely affected by times spent waiting for access to available slots.