Über die Autorin bzw. den Autor

Yang Xiao, PhD, is a Professor in the Department of Computer Science at The University of Alabama. He is a Senior Member of the IEEE and currently serves as Editor in Chief of International Journal of Security and Networks (IJSN), International Journal of Sensor Networks (IJSNet), and International Journal of Telemedicine and Applications (IJTA). His areas of research include security, telemedicine, sensor networks, and wireless networks. He has published more than 300 papers in major journals, refereed conference proceedings, and books related to the aforementioned areas.

Yi Pan, PhD, is a Yamacraw Professor in the Department of Computer Science at Georgia State University. His research interests include parallel and distributed computing, optical networks, wireless networks, and bioinformatics. His work on computing using reconfigurable optical buses has inspired extensive subsequent work by many researchers, and his research results have been cited by more than 100 researchers worldwide. He is a co-holder of three U.S. patents (pending) and five provisional patents; has coedited eleven books or conference proceedings; and has published more than 130 research papers.

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Emerging Wireless Lans, Wireless Pans, And Wireless Mans

IEEE 802.11, IEEE 802.15, 802.16 Wireless Standard Family

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Emerging Wireless Lans, Wireless Pans, And Wireless Mans

IEEE 802.11, IEEE 802.15, 802.16 Wireless Standard Family

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Emerging Wireless LANs, Wireless PANs, and Wireless MANs

John Wiley & Sons

Chapter One

KAVEH GHABOOSI, MATTI LATVA-AHO, and YANG XIAO

1.1 INTRODUCTION

A wireless local area network (WLAN) is an information system intended to offer diverse location-independent network service access to portable wireless devices using radio waves instead of wired infrastructure. In corporate enterprises, WLANs are typically deployed as the ultimate connection between an existing cable infrastructure network and a cluster of mobile clients, giving them wireless access to the shared resources of the corporate network across a building or campus setting. Fundamentally, WLANs liberate customers from reliance on hard-wired access to the network backbone, giving them anywhere, anytime network services access. The pervasive approval of WLANs depends upon industry standardization to ensure product compatibility and reliability among various brands and manufacturers. Among existing system architectures, the IEEE 802.11 family is the most popular and accepted standard concerning medium access control (MAC) and physical (PHY) layers in WLANs; therefore, in this chapter, we briefly overview its basic features in both aforementioned layers. We start our investigation with the MAC layer and its fundamental components. Supported network types, different network services, and media access schemes are covered, accordingly. Subsequently, the physical layer and its basic characteristics are discussed. Different technologies, including frequency hopping (FH), direct-sequence spread spectrum (DSSS) and its high rate (HR) counterpart (i.e., HR/DSSS), and orthogonal frequency division multiplexing (OFDM), recommended for the IEEE 802.11 physical layer are then explored. As a result, this chapter can be assumed as a comprehensive overview of the IEEE 802.11 standard.

1.2 IEEE 802.11 MAC PROTOCOL

In 1997, the IEEE 802.11 working group (WG) proposed the IEEE 802.11 WLAN standard and, subsequently, a revised version was released in 1999. The primary medium access scheme in IEEE 802.11 MAC is the distributed coordination function (DCF), a contention-based protocol which is based on the carrier sense multiple-access/collision avoidance (CSMA/CA) protocol. In the DCF, mobile terminals should contend for the shared wireless channel, and as a result, the medium access delay for each station (STA) cannot be bounded in heavy-traffic-load circumstances. Thus, the DCF is capable of offering only asynchronous data transmission on a best effort (BE) basis. In order to support real-time traffic such as voice and video, the point coordination function (PCF) scheme has been advised as a noncompulsory option. Basically, the PCF is based on a centralized polling scheme for which a point coordinator (PC) residing in an access point (AP) provides contention-free services to the associated stations in a polling list. In addition to the IEEE 802.11 standard, there is a well-known book by Gast which is considered as a complete scientific review of 802.11 families. Due to the popularity of the aforementioned book, we will use it frequently throughout the section to refer the reader to more technical issues and discussions.

Recently, considerable interest in wireless networks supporting quality of service (QoS) has grown noticeably. The PCF is already available in IEEE 802.11 to offer QoS but has not yet been implemented in reality due to its numerous technical limitations and performance drawbacks. For that reason, the 802.11 WG initiated IEEE 802.11e activity to develop the existing 802.11 MAC to facilitate support of QoS. Regarding the 802.11e amendment, not only the IEEE 802.11e standard but also recognized introductory and survey papers will be used repeatedly as key references. We cite many technical issues from these works and the references therein to more appropriately explain 802.11/802.11e-based system features.

1.2.1 Categories of 802.11 Networks

The key constructing component of an 802.11 network is the basic service set (BSS), a group of wireless terminals that communicate with each other over a common radio channel. Data transmission is accomplished within a basic service area, defined by radio propagation characteristics of wireless channel. BSSs come in two categories, as illustrated in Fig. 1.1.

The infrastructure BSS networks are primary for mobile stations to access the Internet via an AP so that, in most of cases, communications between two stations within the same service set do not happen. In communications between mobile stations in the same service set, the AP deployment acts as an intermediate node for all information exchanges comprising communications. In other words, any data communication between two wireless clients should take two successive hops, i.e., source STA to AP and AP to destination STA. Obviously, the exploitation of APs in infrastructure networks brings two major advantages. On the one hand, no restriction is placed on the physical distance between mobile stations. On the other hand, allowing straight communication between wireless terminals would apparently preserve system capacity but at the cost of increased physical and MAC layer complexity. The most important functions of an AP are to assist stations in accessing the Internet and help save battery power in associated wireless stations. If a mobile terminal is in the power-saving (PS) mode, the AP buffers those frames destined to reach the station during the period it will be in PS status. When the terminal exits the PS mode, the AP forwards the cached data frames to the station one by one. Hence, APs evidently play a key role in infrastructure networks to make implementation of PS mechanisms possible.

In the independent BSS (IBSS), mobile stations are allowed to communicate directly. Characteristically, IBSSs are composed of a few stations configured for a particular goal and for a short period of time. IBSSs are sometimes referred to as ad hoc BSSs or simply ad hoc networks.

IEEE 802.11 allows wireless networks of arbitrary size to be installed and utilized by introducing the extended service set (ESS) concept. Basically, the ESS is constructed by chaining neighboring BSSs and requires a backbone system that provides a particular set of services. Figure 1.2 illustrates an ESS as a combination of three neighboring BSSs. Switching between adjacent BSSs while being connected to the system is called a handoff. Stations with the same ESS are able to communicate with each other even if they are not in the same BSS or are moving from one point to another. For associated stations within an ESS, a wireless network should behave as if it were a single layer 2 local area network (LAN). In such an architecture, APs are similar to layer 2 bridges; consequently, the backbone network should be a layer 2 network as well (e.g., Ethernet). Several APs in a single area may be connected to a single switch or can even use virtual LANs (VLANs) if the link layer connection spans a larger area. 802.11 supplies link layer mobility within an ESS, but only if the backbone network is a single link layer domain, such as a shared Ethernet or a VLAN.

Theoretically, extended service areas are the highestlevel abstraction supported by 802.11 wireless networks. In order to let non-802.11 network devices use the same MAC address to exchange data traffic with an associated station...