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 transmitting safety and management messages (e. g., traffic congestion data, data for emergency services) whereas service channels (SCHs) are used by the nodes for transmitting service data (e. g., text, voice, video). In the existing channel access mechanism, nodes are not allowed to use service channels (i.e., remain idle) during control channel interval and vice verse. This causes half of the service channel intervals to remain idle, which makes the WAVE system heavily underutilized and inefficient. In this paper, we propose a medium access control (MAC) protocol for WAVE system to improve the channel utilization (CU) 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, jitter and robust delivery of safety data. Simulation results confirm that the proposed cognitive MAC protocol increases the CU up to 70% compared to the IEEE 1609.4 standard, and improves reliability for the safety related data transmission.