QCH-MAC: A Qos-Aware Centralized Hybrid MAC Protocol for Vehicular Ad Hoc NETworks

The standard IEEE 802.11p was proposed to support the rapid exchange of data between the vehicles themselves and between the vehicles and the RSU (Road Side Unit). Besides, the Medium Access Control (MAC) protocols in Vehicular Ad-hoc Network (VANET), presented in the literature, have many weaknesses in supporting real time traffic. Indeed, some of them combine the advantage of TDMA with CSMA/CA to organize the channel access, therefore collisions may occur when safety messages are transmitted. In the context of hard real time, meeting deadlines requires prior knowledge of the possible communications between vehicles. Thus, we introduce an extension of the Enhanced Distributed Channel Access (EDCA) defined in IEEE 802.11p combined with TDMA, called Qos-aware Centralized Hybrid MAC protocol (QCHMAC). To evaluate our proposed protocol, we implemented it in ns-3 and we used the simulator SUMO to generate vehicular mobility traces. The simulation results reveal that QCH-MAC significantly outperforms pure TDMA in terms of transmission delay, packet loss rate and network throughput.