车辆网络MAC层的Markov链综合分析模型

应用于车载自组网的IEEE 802.11p媒体接入控制（MAC）层采用增强型分布信道接入机制，为验证该机制能否满足不同类型消息的服务质量（QoS），在考虑不同竞争窗口值、消息内部碰撞和信道忙时的退避挂起机制的基础上，构建了基于二维Markov链的分析模型，该模型综合了饱和情况和非饱和情况. 通过该模型，分析了不同类型队列消息的归一化吞吐量和丢包率性能指标. 结果表明，归一化吞吐量随车辆数的增加而减小，随不同类型数据包产生量的增加而增加；丢包率随车辆数的增加而增加；高优先级队列始终有较大归一化吞吐量值. 验证了IEEE 802.11p能保证不同类型消息的QoS.

Comprehensive Analysis Model for MAC Layer in Vehicular Networks Based on Markov Chain

The enhanced distributed channel access mechanism is adopted by IEEE 802.11p medium access control (MAC) layer,which is used for communication in vehicular ad hoc networks. An analysis model based on two-dimensional Markov chain, colligated the saturated and unsaturated condition, was proposed to study the quality of service (QoS) requirements of different applications, taking different contention windows, internal collision and frozen mechanism into account. On this basis, the performance metrics, such as normalized throughput and drop rate, were studied. The results show that the value of normalized throughput decreases with the increasing number of vehicles, but increases with the packet generation increasing. The drop rate increases with the increasing number of vehicles as well. However, the higher priority categories have larger value of normalized throughput, which verifies that the IEEE 802.11p can provide QoS for different messages.