In this paper, a comprehensive overview of the new features of an upcoming new standard IEEE 802.11e to support Quality of Service (QoS) in Wireless Local Area Networks (WLANs) is presented. We address Medium Access Control (MAC) enhancements found in the current 802.11e draft specification by emphasizing the differences from the legacy 802.11 standard. New mechanisms for QoS support, namely Enhanced Distributed Coordination Function (EDCF) and Hybrid Coordination Function (HCF), defined in the 802.11e draft are evaluated. The performance of those new schemes is discussed via simulation results LIST OF ABBREVIATIONS ACK Acknowledgement AIFS Arbitration Inter Frame Space (802.11e) AP Access Point CA Collision Avoidance CDF Complementary Cumulative Distribution Function CFP Contention Free Period CF-Poll Contention Free – Poll CF-End Contention Free – End CP Contention Period CSMA Carrier Sense Multiple Access CW Contention Window CWmax Contention Window Maximum CWmin Contention Window Minimum DCF Distributed Coordination Function EDCF Enhanced DCF (802.11e) HC Hybrid Coordinator (802.11e) HCF Hybrid Coordination Function (802.11e) IEEE Institute of Electrical and Electronics Engineers ISM Industrial, Science, Medical LRE Limited Relative Error MAC Medium Access Control MSDU MAC Service Data Unit NAV Network Allocation Vector PC Point Coordinator PCF Point Coordination Function PF Persistence Factor (802.11e) PHY mode Physical Layer mode, coding and modulation scheme PIFS PCF Inter Frame Space (Q)BSS (QoS-supporting) Basic Service Set (802.11e) QoS Quality of Service RTS/CTS Request to Send/Clear to Send SIFS Short Inter Frame Space TBTT Target Beacon Transmission Time TC Traffic Category (802.11e) TXOP Transmission Opportunity (802.11e) WLAN Wireless Local Area Network
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