Analytical Modelling of IEEE 802.11e Enhanced Distributed Channel Access Protocol in Wireless LANs

Abstract

The IEEE 802.11 Medium Access Control (MAC) protocols have gained widespread popularity and become ubiquitous in Wireless Local Area Networks (WLANs) owing to their attractive properties, such as easy deployment and low cost. The Distributed Coordination Function (DCF) is the fundamental MAC scheme of the IEEE 802.11 standard which can provide best-effort service but lacks support for differentiated Quality-of-Service (QoS). The Enhanced Distributed Channel Access (EDCA) protocol has been proposed in the IEEE 802.11e standard for provisioning of the MAC-level QoS differentiation. The EDCA specifies three important QoS differentiation schemes including Arbitrary Inter-frame Space (AIFS), Contention Window (CW), and Transmission Opportunity (TXOP). Analytical models of EDCA in the current literature have been primarily developed for the AIFS, CW, and TXOP schemes, separately. With the aim of obtaining a thorough and deep understanding of the performance of EDCA, in this chapter we first present a detailed survey of the existing work on modelling the DCF and EDCA protocols and then develop a comprehensive analytical model to accommodate the combination of the three QoS differentiation schemes in WLANs under unsaturated traffic conditions. We derive the QoS performance metrics in terms of throughput, end-to-end delay, and frame loss probability. The accuracy of the proposed model is verified by comparing the analytical results with those obtained from extensive NS-2 simulation experiments.