ECMAC: Edge-Assisted Cluster-Based MAC Protocol in Software-Defined Vehicular Networks

Vehicular networks have emerged as a promising means to mitigate safety hazards in modern transportation systems. On highways, emergency situations associated with vehicles necessitate a reliable media access control (MAC) protocol that can provide timely warnings of possible vehicle collisions. In this paper, we present an edge-assisted cluster-based MAC protocol (ECMAC) for packet dissemination in software-defined vehicular networks. To reduce the control messaging overhead for clustering, ECMAC separates the cluster control plane (i.e., managing cluster formation) from the data plane (i.e., actual data transmission and forwarding) by using a software-defined network controller in a cellular network edge server. For transmitting packets, we design a time-division multiple access (TDMA) schedule algorithm to guarantee a high reliability and a low latency. The TDMA schedule in ECMAC is determined by a joint optimization process in the cellular edge, which is formulated as a binary integer linear programming problem and solved by a heuristic approach based on the divide-and-conquer paradigm. This joint optimization process minimizes the signal interference by jointly considering channel assignment and time slot allocation, thereby ensuring reliable communication. Through extensive simulations, our performance results show that ECMAC improves the successful delivery ratio of emergency packets by at least 25 %, compared with state-of-the-art approaches.