Wireless Local Area Networks (WLANs) have become increasingly popular due to the recent availability of affordable devices providing multiple and high rate capabilities. Optimizing the performance of WLANs for emerging new Internet applications that demand High Throughput (HT) is an important and a highly challenging issue. In this book, we present a new practical Rate Adaptation (RA) algorithm, termed L3S, which extends legacy schemes with new MIMO features suitable for the forthcoming 802.11n high-speed MIMO-based WLAN products. We implement our rate adaptation algorithm in real hardware devices and evaluate its performance and compare it to the existing rate control mechanisms. Our experiments demonstrate that our scheme allows the current 802.11n devices to have a greater adaptability to a variety of wireless channel conditions and performs better than state-of-the-art rate adaptation algorithms.

"IEEE 802.11 wireless local area networks (WLANs) become more and more popular and widely deployed in public hotspots, enterprise environments, and residential areas to provide seamless coverage and improve user connectivity. However, the high density of Access Points (APs) and the stations (STAs) associated to each AP results in increased intra-cell and inter-cell interference, which can cause high collision rates, long backoff intervals, and degraded received signal-to-interference-plus-noise ratio (SINR). To manage such interference, it is required to explore medium access control (MAC) enhancement, efficient channel assignment, and load balancing techniques, which can improve the performance experienced by users. In this work, we develop and evaluate interference-aware enhanced MAC and radio resource allocation algorithms in 802.11 WLANs, aiming to increase the network throughput. To improve the achievable throughput in a single-cell WLAN, a channel-aware adaptive carrier sensing multiple access with collision avoidance (CSMA/CA) scheme is developed to take advantage of multi-user diversity, while supporting distributed and asynchronous operation. By dynamically adjusting the contention window of each STA according to its channel state, this approach prioritizes STAs who gain most from using a channel and enhances channel utilization. A three-dimensional Markov chain is developed to model and evaluate the proposed adaptive CSMA/CA, which significantly improves throughput, especially in a large network.To manage the inter-cell interference in a multi-cell WLAN, the channel assignment and AP-STA association are investigated. Applying difference-of-convex-functions (DC) programming, two different optimization problems are solved aiming to minimize interference sum utility and maximize STA throughput. Distributed schemes are also developed in which APs and STAs can self-configure channel selection and association to mitigate the interference and thereby improve the network throughput. It is shown that the proposed approaches are highly efficient and robust with fast convergence and low complexity.To balance the load and provide service customization in a multi-cell WLAN, AP-STA association and airtime control are studied in a virtualized network, where physical APs are shared by multiple Internet service providers (ISPs). More specifically, an optimization problem is formulated on the STAs' transmission probabilities to maximize the overall network throughput, while providing airtime usage guarantees for the ISPs. The algorithm to reach the optimal transmission probability and detailed implementation are also discussed. Illustrative results confirm the superior and robust performance of the developed association and airtime control scheme." --

The current generation of IEEE 802.11 Wireless Local Area Networks (WLANs) pro- vide multiple data rates from which the different physical (PHY) layers may choose. The rate adaptation algorithm (RAA) is an essential component of 802.11 WLANs which completely determines the data rate a device may use. Some of the key chal- lenges facing data rate selection are the constantly varying wireless channel, selecting the data rate that will result in the maximum throughput, assessing the conditions based on limited feedback and estimating the link conditions at the receiver. Current RAAs lack the ability to sense their environment and adapt accordingly. 802.11 WLANs are deployed in many locations and use the same technique to choose the data rate in all locations and situations. Therefore, these RAAs suffer from the inability to adapt the method they use to choose the data transmission rate. In this thesis, a new RAA for 802.11 WLANs is proposed which provides an answer to the many challenges faced by RAAs. The proposed RAA is termed SARA which stands for Situation-Aware Rate Adaptation, and combines the use of the received signal strength and packet error rate to enable situational awareness. SARA adapts to the current environmental situation experienced at the moment to rapidly take advantage of changing channel conditions. In addition to SARA, a method to optimize the transmission power for, but not limited to, IEEE 802.11 WLANs is proposed which can determine the minimum transmission power required by a station (STA) or base station (BS) for successful transmission of a data packet. The technique reduces the transmission power to the minimum level based on the current situation while maintaining QoS constraints. The method employs a Binary Search to quickly determine the minimum transmission power with low complexity and delay. Such a technique is useful to conserve battery life in mobile devices for 802.11 WLANs. Both algorithms are implemented on an Atheros device driver for the FreeBSD operating system. SARA is compared to the benchmark algorithm SampleRate while an estimate of the energy consumed as well as the energy saved is provided for the minimum transmission power determination.

A new edition of the most comprehensive and up-to-date overview of the features of the 802.11n and 802.11ac WLAN standards.

The tremendous growth of Information and Communication Technology (ICT) has unknowingly influenced our lifestyle. We are making more phone calls, exchanging more emails and spending more time on the World Wide Web than we did a decade ago. The nature of information content is also evolving. High definition video streaming, online shopping, online banking and content sharing libraries are some of the new paradigms that have replaced the simple web applications of early days. In such circumstances, the objectives for future networks are more challenging. This book focuses on the IEEE 802.11 MAC and identifies several challenges that require further research. The IEEE 802.11 standard for local area networks, specifically the IEEE 802.11e, is discussed in a tutorial style. The primary focus is on rate-adaptation schemes for multi-rate WLANs stations and design of QoS enabled routing protocol by incorporating information from the IEEE 802.11e compliant MAC. The book serves as a valuable reference for researchers, professionals and students who would like to gain a more formal understanding of Cross-layer optimization techniques and specifically the IEEE 802.11 standard.