A novel cooperative MAC protocol for safety applications in cognitive radio enabled vehicular ad-hoc networks

Abstract Recent developments in intelligent transportation system (ITS) require a reliable medium access control (MAC) protocol to support the high-priority safety message broadcast. The rapid increase in spectrum demand is addressed by implementing cooperation in cognitive radio-based vehicular ad-hoc networks (CR-VANETs). In this paper, a novel cooperative MAC for CR-VANET (CCRV- MAC) is proposed for safety applications. CCRV facilitates collaboration among vehicles to exchange channel status reports for pro-active channel switching in the case of primary user (PU) appearance. Additional control signals are introduced to enable transmission mode selection. The helper nodes rebroadcast failed transmission by employing the proposed cooperative makeup strategy. The protocol is modelled using a Markov chain and is analyzed for various performance parameters using NS-2. It is also compared with two existing MAC protocols. In the results, CCRV shows enhanced throughput and packet delivery ratio. The average delay in CCRV MAC is reduced by approximately 37% compared to existing cognitive radio network (CRN) and vehicular ad-hoc network (VANET) based MAC approaches. Analysis of overhead and delay illustrates the reliability of CCRV as it suffers a maximum average delay of 69 ms under adverse conditions which is well below the permissible limit of 100 ms.