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UBC Theses and Dissertations

Quality of service enhancements in IEEE 802.11 wireless LANs Wong, George Wai


One of the most important of the many developments in telecommunications is the convergence of voice, video, and data communications within the Internet Protocol (IP) suite. IP was originally designed to support best-effort data services. The development of IP-based multimedia networking applications has imposed Quality of Service (QoS) requirements on the IP network, especially with respect to real-time traffic. The Internet Engineering Task Force (IETF) is currently working on QoS differentiation at the LP layer; however the result is sub-optimal without lower layers' support. With the increasing use of wireless Internet services over 802.11 wireless LANs, it is essential to focus on QoS differentiation support at the 802.11 MAC layer. To improve the current 802.11 MAC protocol, the IEEE Task Group E was formed and is defining QoS enhancements for the 802.11 MAC layer by introducing an Enhanced Distributed Coordination Function (EDCF). The EDCF provides prioritization enhancement of the 802.11 Distributed Coordination Function (DCF). The objective of this thesis is to propose and evaluate a novel packet retransmission algorithm called Age-Dependent Backoff to improve the QoS performance of EDCF. The ADB algorithm dynamically varies the persistent factor associated with the contention window, based on real-time packet queue age and lifetime. ADB maintains the backward compatibility property of EDCF and involves relatively easy implementation at low cost. Extensive simulation results obtained using OPNET software show that EDCF with the ADB retransmission algorithm provides low values for delay, jitter, and drop rate for realtime traffic without sacrificing the throughput of best-effort data traffic. ADB is a viable, novel and low cost means to improve the QoS performance of EDCF.

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