The QoS offered by the IEEE 802.11e reference scheduler is satisfactory in the case of Constant Bit Rate traffic streams, but\nnot yet in the case of Variable Bit Rate traffic streams, whose variations stress its scheduling behavior. Despite the numerous\nproposed alternative schedulers with QoS, multimedia applications are looking for refined methods suitable to ensure service\ndifferentiation and dynamic update of protocol parameters. In this paper a scheduling algorithm, Unused Time Shifting Scheduler\n(UTSS), is deeply analyzed. It is designed to cooperate with a HCCA centralized real-time scheduler through the integration of\na bandwidth reclaiming scheme, suitable to recover nonexhausted transmission time and assign that to the next polled stations.\nUTSS dynamically computes with an O(1) complexity transmission time providing an instantaneous resource overprovisioning.\nThe theoretical analysis and the simulation results highlight that this injection of resources does not affect the admission control\nnor the centralized scheduler but is suitable to improve the performance of the centralized scheduler in terms of mean access delay,\ntransmission queues length, bursts of traffic management, and packets drop rate. These positive effects are more relevant for highly\nvariable bit rate traffic.
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