In this paper, we propose a novel model-based resource allocation framework to provide quality-of-service (QoS) support in the downlink (DL) of an IEEE 802.16e mobile WiMAX system. First, we develop a queueing model that links important performance measures of DL service flows to a set of tunable parameters. Based on the queueing model, we show how these parameters could be set to appropriate values to meet the QoS performances sought by admitted service flows. We then introduce a resource allocation scheme that uses these parameter values in packet scheduling decisions. In this queue- and channel-aware scheme, the queue-length-based packet scheduler is complemented by a cross-layer orthogonal frequency-division multiple access (OFDMA) slot allocation mechanism that adapts to channel conditions at the destination mobile stations (MSs). Compared with existing schemes, the proposed scheme is compatible with the updated definition of some key resource allocation concepts in IEEE 802.16e and offers a simple yet more effective way to provide QoS to a heterogeneous mix of applications. Its cross-layer aspect ensures efficient resource utilization in the presence of link adaptations due to mobility and channel fading. It also offers greater flexibility to service providers by allowing probabilistic delay guarantees to delay-sensitive multimedia applications. Simulation results show the performance benefits of the proposed scheme in providing QoS support for both real-time and non-real-time applications in mobile WiMAX systems.
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