Analysis and improvement of medium access control protocols in wireless networks. Performance modelling and Quality-of-Service enhancement of IEEE 802.11e MAC in wireless local area networks under heterogeneous multimedia traffic.

摘要

In order to efficiently utilize the scarce wireless resource as well as keep upudwith the ever-increasing demand for Quality-of-Service (QoS) of multimediaudapplications, wireless networks are undergoing rapid development and dramaticudchanges in the underlying technologies and protocols. The Medium Access Controlud(MAC) protocol, which coordinates the channel access and data transmission ofudwireless stations, plays a pivotal role in wireless networks.udPerformance modelling and analysis has been and continues to be of greatudtheoretical and practical importance in the design and development of wirelessudnetworks. This research is devoted to developing efficient and cost-effectiveudanalytical tools for the performance analysis and enhancement of MAC protocols inudWireless Local Area Networks (WLANs) under heterogeneous multimedia traffic.udTo support the MAC-layer QoS in WLANs, the IEEE 802.11e Enhanced DistributedudChannel Access (EDCA) protocol has proposed three QoS differentiation schemesudin terms of Arbitrary Inter-Frame Space (AIFS), Contention Window (CW), andudTransmission Opportunity (TXOP). This research starts with the development ofudnew analytical models for the TXOP scheme specified in the EDCA protocol underudPoisson traffic. A dynamic TXOP scheme is then proposed to adjust the TXOPudlimits according to the status of the transmission queue. Theoretical analysis andudsimulation experiments show that the proposed dynamic scheme largely improvesudthe performance of TXOP. To evaluate the TXOP scheme in the presence ofudiiudheterogeneous traffic, a versatile analytical model is developed to capture the trafficudheterogeneity and model the features of burst transmission. The performance resultsudhighlight the importance of taking into account the heterogeneous traffic for theudaccurate evaluation of the TXOP scheme in wireless multimedia networks.udTo obtain a thorough and deep understanding of the performance attributes ofudthe EDCA protocol, a comprehensive analytical model is then proposed toudaccommodate the integration of the three QoS schemes of EDCA in terms of AIFS,udCW, and TXOP under Poisson traffic. The performance results show that the TXOPudscheme can not only support service differentiation but also improve the networkudperformance, whereas the AIFS and CW schemes provide QoS differentiation only.udMoreover, the results demonstrate that the MAC buffer size has considerable impactudon the QoS performance of EDCA under Poisson traffic. To investigate theudperformance of EDCA in wireless multimedia networks, an analytical model isudfurther developed for EDCA under heterogeneous traffic. The performance resultsuddemonstrate the significant effects of heterogeneous traffic on the total delay andudframe losses of EDCA with different buffer sizes. Finally, an efficient admissionudcontrol scheme is presented for the IEEE 802.11e WLANs based on analyticaludmodelling and a game-theoretical approach. The admission control scheme canudmaintain the system operation at an optimal point where the utility of the AccessudPoint (AP) is maximized with the QoS constraints of various users.