A Threshold-Based Dynamic TXOP Scheme for Intra-AC QoS Differentiation in IEEE 802.11e Networks

The IEEE 802.11e Enhanced Distributed Channel Access (EDCA) protocol has been proposed for provisioning of differentiated Quality-of-Service (QoS) between various Access Categories (ACs), i.e., inter-AC QoS, in Wireless Local Area Networks (WLANs). However, the EDCA lacks the support of the intra-AC QoS provisioning, which is indispensable in the practical WLANs since the network loads are always asymmetric between traffic flows of ACs with the same priority. To address the intra-AC QoS issue, this paper proposes a Threshold-Based Dynamic Transmission Opportunity (TBD-TXOP) scheme which sets the TXOP limits adaptive to the current status of the transmission queue based on the pre-setting threshold. We further develop an analytical model to evaluate the performance of this scheme. QoS performance metrics in terms of throughput, end-to-end delay, and frame loss probability are derived. The performance results demonstrate the efficacy of TBD-TXOP for the intra-AC QoS differentiation.