Sunghyun Choi

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Today’s IEEE 802.11 WLANs (Wireless LANs) provide multiple transmission rates so that different rates can be exploited in an adaptive manner depending on the underlying channel condition in order to maximize the system performance. Many rate adaptation schemes have been proposed so far while most (if not all) of the commercial devices implement a simple(More)
Link adaptation to dynamically select the data transmission rate at a given time has been recognized as an effective way to improve the goodput performance of the IEEE 802.11 wireless local-area networks (WLANs). Recently, with the introduction of the new high-speed 802.11a physical layer (PHY), it is even more important to have a well-designed link(More)
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(More)
IEEE 802.11 Wireless Local Area Network (WLAN) physical layers (PHYs) support multiple transmission rates. The PHY rate to be used for a particular frame transmission is solely determined by the transmitting station. The transmission rate should be chosen in an adaptive manner since the wireless channel condition varies over time due to such factors as(More)
and Introduction Legacy 802.11 • Distributed Coordination Function • Point Coordination Function QoS Support Mechanisms Of 802.11e • Basic Improvements of the Legacy 802.11 Mac • HCF Contention-based Medium Access • Hybrid Coordination Function, Controlled Medium Access • Improved Efficiency Evaluation Summary and Conclusions
Reducing the energy consumption by wireless communication devices is perhaps the most important issue in the widely-deployed and exponentially-growing IEEE 802.11 Wireless LANs (WLANs). TPC (Transmit Power Control) and PHY (physical layer) rate adaptation have been recognized as two most effective ways to achieve this goal. The emerging 802.11h standard,(More)
IEEE 802.11e Medium Access Control (MAC) is an emerging supplement to the IEEE 802.11 Wireless Local Area Network (WLAN) standard to support Quality-of-Service (QoS). The 802.11e MAC is based on both centrally-controlled and contention-based channel accesses. In this paper, we evaluate the contention-based channel access mechanism, called enhanced(More)
How to control hand-off drops is a very important Quality-of-Service (QoS) issue in cellular networks. In order to keep the hand-off dropping probability below a pre-specified target value (thus providing a <i>probabilistic</i> QoS guarantee), we design and evaluate <i>predictive</i> and <i>adaptive</i> schemes for the bandwidth reservation for the existing(More)
Robust streaming of video over 802.11 wireless local area networks poses many challenges, including coping with bandwidth variations, data losses, and heterogeneity of the receivers. Currently, each network layer (including physical layer, media access control (MAC), transport, and application layers) provides a separate solution to these challenges by(More)