Multichannel Cognitive Medium Access Control Protocol for Vehicular Ad-Hoc Networks

Intelligent transportation system (ITS) has enjoyed a tremendous growth in the last decade and the advancement in communication technologies has played a major role behind the success of ITS. Due to the nature of communication in vehicular environments, wireless access is considered as an integral part of any ITS system. The IEEE 1609.4 has evolved as a standard for wireless access for vehicular environment (WAVE), which describes multichannel access operations over the 5.9GHz dedicated short range communications (DSRC) spectrum. Communication Channels in the 1609.4 are grouped into service and control channels. Control channels (CCHs) are used for transmission of safety and management messages (e.g., traffic congestion data, data for emergency services) whereas service channels (SCHs) are used for the nodes to transmit service data (e.g., voice,video). In existing channel access mechanism, a node stays in the control channel to receive safety and management messages and then switches to service channel for data transmission. The key problem with this channel access mechanism is that half of the service channel intervals remain idle and unused as all nodes have to listen to control channel during that interval, which makes the WAVE system underutilized and inefficient. In this paper, we propose a medium access control (MAC) protocol for WAVE system to improve the channel utilization and reliability of safety messages. The proposed protocol has been developed based on the concept of cognitive radio and it outperforms the existing channel access mechanism by a significant margin in terms of channel utilization. Simulation results confirm that the proposed cognitive MAC protocol increases the channel utilization up to 70% compared to the IEEE 1609.4 standard, and maintains reliability for the safety related data transmission.