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Admission control and scheduling for guarantee the packet loss rate and delay in IEEE 802.11e WLANs

Authors Fan, Wing Fai
Issue Date 2004
Summary IEEE 802.11 is the most famous Wireless LANs technology being used because of its low cost and easy deployment. However, IEEE 802.11 MAC protocol was developed without any significant Quality of Service (QoS) guarantees to real-time multimedia applications. In order to satisfy the QoS requirements such as bandwidth, delay and packet loss rate, IEEE 802.11e standard is developing to enhance QoS support in the current IEEE 802.11 Medium Access Control (MAC) protocol. Hybrid Coordination Function (HCF) introduced in the new standard consists of Enhanced Distributed Channel Access (EDCA) and HCF Controlled Channel Access (HCCA), which extend the DCF and PCF respectively. In the TGe Consensus Proposal, a simple reference design of scheduling and admission control algorithm is proposed for HCCA. It considers mean data rate and mean packet size of traffic flows to allocate Transmission Opportunity (TXOP) duration using fixed Service Interval (SI). Thus, the packet delay bound of all stations are guaranteed and not exceed the SI. However, the scheme does not take the data rate and packet size variation of Variable Bit Rate (VBR) traffic into account. Thus, the packet loss rate of VBR traffic can be very high. In this thesis, the packet loss rate of VBR traffic in the reference scheme is analyzed and quantified. Another method to determine the TXOP duration is proposed for the reference admission control so that the packet loss rate of VBR flows can be guaranteed. The numerical results show that the packet loss rate of the reference scheme is about 20%. Given the packet loss requirement 0.01, the effective TXOP found by above method can guarantee the packet loss rate of VBR flows better than that of the reference scheme by 20 times. Although the packet loss rate of VBR flows can be guaranteed by above work, the efficiency of the admission control is sacrificed. Also, the reference admission control uses the most stringent SI to guarantee the packet delay for all stations and the over provisioning of network resources to some stations with larger delay bound occurs. A novel admission control and scheduling algorithm using variable SI are proposed to solve the above problems. Simulation results show that, the efficiency of the admission control using variable SI is better than that using fixed SI about 20%-30%. In addition to the data rate variation, the admission control algorithm is inefficient because it is implemented based on the minimum physical rate. However, at most of the time, the physical rate of the mobile stations is higher than the minimum physical rate. Based on the reference scheme, a more efficient admission control algorithm named Physical Rate Based Admission Control scheme (PRBAC) to support CBR traffic, which considers the rate variation due to the station mobility and wireless channel characteristics. The numerical and simulation results illustrate that the proposed scheme can improve the admission control efficiency with acceptable packet loss rate.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2004
Language English
Format Thesis
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