We consider wireless LANs such as IEEE 802.11 operating in the unlicensed radio spectrum. While their nominal bit rates have increased considerably, the MAC layer remains practically unchanged despite much research effort spent on improving its performance. We observe that most proposals for tuning the access method focus on a single aspect and disregard others. Our objective is to define an access method optimized for throughput and fairness, able to dynamically adapt to physical channel conditions, to operate near optimum for a wide range of error rates, and to provide equal time shares when hosts use different bit rates.We propose a novel access method derived from 802.11 DCF [2] (Distributed Coordination Function) in which all hosts use similar values of the contention window CW to benefit from good short-term access fairness. We call our method Idle Sense, because each host observes the mean number of idle slots between transmission attempts to dynamically control its contention window. Unlike other proposals, Idle Sense enables each host to estimate its frame error rate, which can be used for switching to the right bit rate. We present simulations showing how the method leads to high throughput, low collision overhead, and low delay. The method also features fast reactivity and time-fair channel allocation.

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Idle sense: an optimal access method for high throughput and fairness in rate diverse wireless LANs

The goal of this paper is to present exact formulae for the throughput of IEEE 802.11 networks in the absence of transmission errors and for various physical layers, data rates and packet sizes. Calculation of the throughput is more than a simple exercise. It is a mandatory part of provisioning any system based on 802.11 technology (whether in ad-hoc or infrastructure mode). We will discuss the practical importance of theoretical maximum throughput and present several applications.

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Theoretical maximum throughput of IEEE 802.11 and its applications

Wireless communication has become a ubiquitous part of modern life, from global cellular telephone systems to local and even personal-area networks. This 2004 book provides a tutorial introduction to digital mobile wireless networks, illustrating theoretical underpinnings with a wide range of real-world examples. The book begins with a review of propagation phenomena, and goes on to examine channel allocation, modulation techniques, multiple access schemes, and coding techniques. GSM and IS-95 systems are reviewed and 2.5G and 3G packet-switched systems are discussed in detail. Performance analysis and accessing and scheduling techniques are covered, and the book closes with a chapter on wireless LANs and personal-area networks. Many worked examples and homework exercises are provided and a solutions manual is available for instructors. The book is an ideal text for electrical engineering and computer science students taking courses in wireless communications. It will also be an invaluable reference for practising engineers.

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Mobile Wireless Communications

This article provides an overview of mechanisms used for power saving in the upcoming standards for wireless LANs: IEEE 80211 and ETSI RES 10 HIPERLAN Power saving on the MAC level is addressed by these standards in a quite different way We outline the main features of the mechanisms in both standards in terms of power saving In addition we present simulation studies of the power-saving mechanism in ad hoc configurations of IEEE 80211 networks, which demonstrate the optimization potential and some performance trade-offs quantitatively

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Power-saving mechanisms in emerging standards for wireless LANs: the MAC level perspective

The need for critical improvements to the North American surface transportation infrastructure vis-a-vis alleviation of congestion while enhancing public safety has led to new intelligent transportation system (ITS) infrastructure based on vehicle-to-vehicle (v2v) wireless communications. The allocation of 75 MHz in the 5.9 GHz band for dedicated short-range communications (DSRC) may also enable future delivery of rich media content to vehicles at short to medium ranges via vehicle-to-roadside (v2e) links. Recently, AASTM committee E17.51 endorsed a variant of the IEEE wireless LAN standard, denoted 802.11a roadside applications (R/A), as the platform for the DSRC link and data link layer. In this article, we provide a tutorial overview of DSRC applications and assess IEEE802.11 PHY and MAC layer characteristics in this context. It is anticipated that current 802.11 specifications need to be suitably altered to meet requirements for DSRC environments of multihop connectivity, high vehicle mobility, and heterogeneous services with a variety of QoS requirements for which the original design was not intended. This article captures the current state of the art of 802.11-based multiple access protocols and highlights open research issues.

F. Cail

Papers

IEEE 802.11 wireless LAN : Capacity analysis and protocol enhancement