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Advances in Multimedia
Volume 2014, Article ID 372693, 22 pages
Research Article

A IEEE 802.11e HCCA Scheduler with a Reclaiming Mechanism for Multimedia Applications

TeCIP Institute, Scuola Superiore Sant’Anna, 56124 Pisa, Italy

Received 31 August 2013; Revised 9 January 2014; Accepted 6 February 2014; Published 20 March 2014

Academic Editor: Mei-Ling Shyu

Copyright © 2014 Anna Lina Ruscelli and Gabriele Cecchetti. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The QoS offered by the IEEE 802.11e reference scheduler is satisfactory in the case of Constant Bit Rate traffic streams, but not yet in the case of Variable Bit Rate traffic streams, whose variations stress its scheduling behavior. Despite the numerous proposed alternative schedulers with QoS, multimedia applications are looking for refined methods suitable to ensure service differentiation and dynamic update of protocol parameters. In this paper a scheduling algorithm, Unused Time Shifting Scheduler (UTSS), is deeply analyzed. It is designed to cooperate with a HCCA centralized real-time scheduler through the integration of a bandwidth reclaiming scheme, suitable to recover nonexhausted transmission time and assign that to the next polled stations. UTSS dynamically computes with an complexity transmission time providing an instantaneous resource overprovisioning. The theoretical analysis and the simulation results highlight that this injection of resources does not affect the admission control nor the centralized scheduler but is suitable to improve the performance of the centralized scheduler in terms of mean access delay, transmission queues length, bursts of traffic management, and packets drop rate. These positive effects are more relevant for highly variable bit rate traffic.