Design and Performance Analysis of the Real-Time HCCA Scheduler for IEEE 802.11e WLANs

This paper presents a new scheduling algorithm, called Real-Time HCCA (RTH), devised to support Quality of Service (QoS) at the flow level in an IEEE 802.11e network using the Hybrid Coordinator Function (HCF) Controlled Channel Access (HCCA) function. RTH separates online activities which take place at the frame transmission timescale, from offline activities which take place at the flow lifetime timescale. Complex computations are relegated to offline activities, while online tasks are kept as simple as possible. More specifically, at admission control time, RTH computes a periodic schedule based on the well-known Earliest Deadline First algorithm for 802.11e Traffic Streams (TSs). In doing so, the Stack Resource Policy is applied to account for non-pre-emptability of frame transmissions. Furthermore, the parameters are configured so as to reduce the MAC overhead due to polling uplink TSs. On the other hand, online scheduling is enforced simply by reading the pre-computed schedule, at little or no computational cost. RTH performance is assessed in terms of the admission control limit and of the amount of channel capacity that is left for contention-based access. Under both criteria, RTH is shown to outperform the sample scheduler proposed in IEEE 802.11e.