一种基于区分服务的IEEE 802.11 QoS信道访问控制机制

A QoS-aware 802.11 media access control mechanism based on differentiated services

研究表明,无线移动自组织网络具有带宽有限,信道质量不稳定,节点移动造成网络拓扑结构变化等诸多特性,这些特性严重损害了网络性能,以致在传统无线移动网络中支持具有严格QoS要求的多媒体应用面临严峻的挑战.本文提出了一种基于区分服务的信道接入控制机制,以更好地支持实时通信流.该机制对传统的IEEE 802.11DCF机制进行了部分改进,在目的节点引入了拒绝服务分组NTS,使目的节点可以根据网络的状态以一定的概率p拒绝低优先级数据分组.概率p被设计为关于分组重传次数的单调递增函数,被重传次数越多,说明信道竞争越激烈,也越有必要提高低优先级数据的拒绝概率以保护高优先级的实时数据分组.本文随后以马尔科夫链对该机制进行了建模分析,并通过相关模型的计算得出了数据流的饱和吞吐量,分组丢弃概率,饱和时延.分析结果表明该机制能够使高优先级数据流占用更多的带宽,并且降低了高优先级数据流的端到端平均时延以及分组丢弃概率.

Research shows that the main characteristics of wireless mobile ad hoc networks include finite bandwidth,unstable channel quality,and the change of network topology caused by node mobility.These characteristics degrade the network performance significantly and especially identify challenges for providing QoS guarantees for real-time multimedia applications over wireless mobile ad hoc networks（MANETs）.This paper proposes a QoS-aware MAC mechanism based on Differentiated Services for MANETs,which mainly supports real-time data flow transfer.This mechanism makes an improvement based on traditional IEEE 802.11 DCF mechanism.The main idea is introducing new types of service-denied frames named NTS,which makes destination nodes refuse low-priority data with probability p,according to dynamic channel conditions.Probability p is designed for a monotonic function increasing with number of frame retransmission attempt.As the number of retransmission attempt increases,it indicates that the competition in channel is getting more fierce,which makes it more necessary for protecting high-priority frames,by means of refusing low-priority data with higher probability.We study the behavior of several nodes with a Markov model.Using the model,we evaluate the saturation throughput,packet drop probability,as well as time delay performance.Our mathematical analyses demonstrate that the proposed mechanism improves the performance of real-time data flow with a high-priority significantly,in terms of achieved bandwidth,end-to-end delay and frame dropping probability.