Distributed Multi-Priority Congestion Control Approach for IEEE 802.11p Vehicular Networks

There are various applications with different Quality of Service (QoS) requirements and transmission priorities in the IEEE 802.11p vehicular network. It is more important to ensure the successful transmission for the high priority traffic compared with the low priority traffic, especially in congested networks. Based on such consideration, this paper proposes a novel distributed multi-priority congestion control approach for the IEEE 802.11p vehicular network, where four traffic categories with different transmission priorities are configured. In the proposed congestion control approach, each access category queue in a vehicle periodically measures the congestion condition with the local transmission information, including the queue length and the amount of failure transmissions. When the measured congestion condition is over the congestion threshold, the minimum contention window size is increased to reduce the channel load. For the lower priority traffic, a smaller congestion threshold is set to guarantee the performance of the higher priority traffic. Compared with the IEEE 802.11p, the proposed approach can ensure the successful transmission for the highest priority traffic flow and make the collision probability remain at a low level in the dense network.