ASTSMAC: Application Suitable Time-Slot Sharing MAC Protocol for Vehicular Ad Hoc Networks

Vehicles and roadside units can be connected by a vehicular ad hoc network (VANET), which is an important component of future intelligent transport systems that can support various safety and non-safety related services. The network topology changes rapidly in VANET due to the high mobility of vehicles, making it difficult to design a reliable and efficient medium access control (MAC) protocol. Many MAC protocols based on time-division multiple access (TDMA) have been proposed for VANET to optimize network performance, but few of them consider the different requirements of nodes. Nodes may have diverse requirements for spectrum access, and one node may have a diversified strategy for transmitting messages over time, as its motion and network topology change rapidly. The application layer should dynamically adjust the package generation frequency as needed to reduce unnecessary spectrum access. In this paper, we propose a novel application suitable time slot sharing MAC protocol (ASTSMAC) for the broadcasting of the basic safety messages (BSMs) that can adapt to different transmission cycle requirements in the application layer program. In our scheme, one slot can be shared by more than one node, even if they are in each other's communication range. Simulation results show that ASTSMAC can provide significantly higher packet delivery ratio and lower collision rate. Further, the network can accommodate more nodes when the traffic-density is high.