QoS Provisioning in Wi-Fi Networks: Capacity Modeling and Resource Control
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The ubiquitous Wireless Fidelity (Wi-Fi) networks, and their increasing quality of service (QoS) requirements for emerging applications, motivate extensive studies of QoS provisioning in such networks. Two tasks, namely, capacity modeling and resource control, are crucial in solving the problem: A performance model is first needed to predict the network QoS metrics from the network settings. We propose a new unified analytical model to study the saturation throughput and delay performance of 802.11e Enhanced Distributed Coordination Function (EDCA), which is easier to apply than the most current ones. In order to find usable mathematical models for most cases where analytical models are not feasible, we first advocate the application of metamodeling techniques to Wi-Fi performance studies and formulate a general metamodeling framework for such purpose. The results in three case studies support the validity of our methodology: our saturation capacity metamodel for 802.11 Distributed Coordination Function (DCF) displays an interesting log-linear relationship between capacity and number of users; our voice over Wi-Fi admission capacity metamodel gives a much tighter bound than bounds existing in the literature; and, finally, our throughput metamodel for a simple ad-hoc network, for the first time, characterizes the cross-layer effects between MAC and network layer. Our work, therefore, points out a new direction for future performance studies of Wi-Fi networks. Then, based on the performance models we derive, control schemes of input parameters can be designed to achieve certain level of QoS outputs in some cases. For example, we are able to design a Weighted Round Robin (WRR) scheduler at the MAC layer to control the share of the radio resources, by applying our analytical model to a special case of EDCA configuration. Furthermore, based on our fitted metamodel for the capacity of voice over Wi-Fi, a more practical admission control scheme is composed.
capacity, Wi-Fi, QoS, 802.11, WLAN, modeling, control, VoIP, call admission control, cross layer, DCF, EDCA