An adaptive and reliable MAC mechanism for IEEE 1609.4 and 802.11p VANETs

The Carrier Sense Multiple Access (CSMA) based MAC protocol adopted in IEEE 802.11p has some inherent disadvantages because it cannot avoid collisions effectively. The channel switching scheme defined in IEEE 1609.4 might result in inefficient use of wireless resources. In this paper, we propose an adaptive and reliable Medium Access Control (MAC) mechanism combining the CSMA with the Time Division Multiple Access (TDMA) to solve the problems mentioned above. In our mechanism, the length of the Control Channel (CCH) interval and the Service Channel (SCH) interval can be adjusted adaptively according to the traffic density of vehicles, which then could improve the utilization of wireless resources. Meanwhile, the utilization of TDMA enhances the reliability of packet delivery. Simulation results show that our mechanism outperforms the existing one defined in IEEE 802.11p/1609.4 in reliability and resource utilization. To the best of our knowledge, this is the first attempt to improve the performance of VANET considering both the channel switching scheme and the MAC protocol in a joint way.