| How to enhance multimedia quality of service (QoS) is a critical step for IEEE 802.11wireless local area network (WLAN) applications. This requires that, 1) the system has themechanism to support multiple classes of services, and 2) the mechanism should be ableto adjust its policies and parameters to adapt to dynamic network conditions. This paperaddresses the problem of how to optimize system performance and support multimedia QoSfrom (medium access control) MAC level.MAC layer has fundamental impact on overall performance of WLANs. It is veryimportant to know the impact of MAC parameters (contention window size, inter-framespaces and etc.) on system performance and to support multimedia applications based onsuch information in a dynamic network. This paper proposes a theoretical model and anadaptive algorithm to solve the problem.First, the paper proposes a mathematical model to describe the behavior of MAC ona system with service di?erentiation. This model is based on Markov property and takesinto account the important parameters (contention window, inter-frame spaces and etc.)to show their impacts on system performance. On the other hand, based on the resultsof the theoretical model, the paper proposes a distributed adaptive algorithm, which canintelligently adjust its parameters to optimize the system performance and support QoS.Meanwhile, the algorithm ensures user fairness and system stability. It is also very simpleand is compatible with the current standard.Simulation results demonstrate the correctness of the proposed model. It can accuratelymodel the impact of important MAC parameters on system performance and guide thesystem design. Furthermore, the results show that the distributed algorithm outperformsthe current 802.11 scheme and the fixed di?erentiation scheme in terms of throughput,delay and jitter. This shows that the proposed algorithm can improve the performance andprovide QoS support for multimedia services in dynamic network conditions. |
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