An optimized MAC Protocol for Safety Messages9 Broadcasting in VANETs

In Vehicular ad hoc networks (VANETs), the MAC protocol is mainly used for ensuring the fair, reliable and efficient access of wireless channels for communication vehicles above the PHY layer. Aiming at the safety messages' broadcasting problems such as high packet loss rate and serious delay caused by complex communication environment in VANETs, this paper proposes an optimized MAC broadcasting method, considering channel access back-off mechanism and message generation rate of the MAC protocol: using one-dimensional(1-D) saturated Markov chain model to describe back-off mechanism of safety message broadcasting, and using a generating rate self-adaptive control method for beacon messages to solve the channel congestion problem happened with the high traffic density. The communication performance of VANETs using the proposed optimization scheme is analyzed by two parameters: message delivery rate and transmission delay. Simulation results show that this optimized model not only guarantees the transmission time slot of emergency messages, but also effectively reduces the impact of load increase caused by vehicle density increase, and ensures the delivery rate of beacon message.