The implementation of safety applications in vehicular ad hoc network (VANET) depends on the dissemination of safety related messages. A self-sorting MAC protocol is proposed for high-density scenarios. The protocol allows vehicles to sort with others in a collision-tolerance manner before data transmission. The vehicles establish a logic queue by the self-sorting process, and the queue is able to access the channel once the length reaches the set threshold. Vehicles in the queue will access

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... channel by time-division multiple access (TDMA) when the queue occupies the channel. A queue will compete for accessing the channel on behalf of all the nodes in the queue, which greatly alleviates the contention for access from all nodes. In contrast with completely random access, the slot a queue select to access the channel depends on the completion time of the self-sorting process. In this case, the queue accomplishing the self-sorting process first can avoid collisions with other queues since they are still in the self-sorting process. The performance of the proposed protocol is evaluated compared with other typical MAC protocols in VANET. The analysis and simulation results in highway and city scenarios show that the proposed protocol can significantly reduce packets loss and delay especially in dense scenarios.