Introduction

Tremendous consumer interest in multimedia applications is driving the need for successively higher data rates in wireless networks. The IEEE 802.11n standard for high throughput Wireless Local Area Networks (WLANs) improves significantly upon the data rates experienced by end users of current WLAN systems, e.g., 802.11a, b, and g.

The soon-to-be ratified 802.11n standard specifies a high data rate multiple-input, multiple-output (MIMO) based physical layer which employs orthogonal frequency division multiplexing (OFDM) and up to four spatial streams [1]. Both high data rate and long-range coverage are achieved by employing spatial signal processing techniques such as spatial spreading and transmit beamforming [2], among others. 802.11n introduces a range of MAC-layer enhancements also, but these are beyond the scope of this chapter.

In this chapter, we give an overview of two spatial processing alternatives available to implementers of 802.11n. We examine spatial spreading and transmit beamforming schemes, as well as possible receiver structures. Comparisons in terms of performance and complexity are also given.

The chapter is organized as follows. Section 9.2 gives a brief overview of MIMO OFDM, as well as the relevant system aspects of the 802.11n physical layer (PHY). Section 9.3 describes spatial spreading. Section 9.4 describes eigenvector-based transmit beamforming and schemes for channel sounding and calibration. Section 9.5 describes receiver structure alternatives for use with the above mentioned techniques.

The story of free and open software is a scientific adventure, packed with extraordinary, larger-than-life characters and epic achievements. From infrastructure for the Internet to operating systems like Linux, this movement involves some of the great accomplishments in computing over the past quarter century. The story encompasses technological advances, global software collaboration on an unprecedented scale, and remarkable software tools for facilitating distributed development. It involves innovative business models, voluntary and corporate participation, and intriguing legal questions. Its achievements have had widespread impact in education and government, as well as historic cultural and commercial consequences. Some of its attainments occurred before the Internet's rise, but it was the Internet's emergence that knitted together the scientific bards of the open source community. It let them exchange their innovations and interact almost without regard to constraints of space, time, or national boundary. Our story recounts the tales of major open community projects: Web browsers that fueled and popularized the Internet, the long dominant Apache Web server, the multifarious development of Unix, the near-mythical rise of Linux, desktop environments like GNOME, fundamental systems like those provided by the Free Software Foundation's GNU project, infrastructure like the X Window System, and more. We will encounter creative, driven scientists who are often bold, colorful entrepreneurs or eloquent scientific spokesmen. The story is not without its conflicts, both internal and external to the movement.

This chapter attempts to present a balanced view of what the future seems likely to hold for the open source movement based on past and present trends and the underlying structural, social, political, scientific, and economic forces at work. We will first sketch what we believe are the likely dominant modes for software development and then we will elaborate on the rationales for our projections.

First of all, we believe the open source paradigm is moving inexorably toward worldwide domination of computer software infrastructure. Its areas of dominance seem likely to include not only the network and its associated utilities, but also operating systems, desktop environments, and the standard office utilities. Significantly, it seems that precisely the most familiar and routine applications will become commoditized and satisfied by open source implementations, facilitating pervasive public recognition of the movement. The software products whose current dominance seems likely to decline because of this transformation include significant components of the Microsoft environment from operating systems to office software.

However, despite a likely widespread increase in the recognition, acceptance, and use of open source, this does not imply that open software will dominate the entire universe of software applications. The magnitude of financial resources available to proprietary developers is enormous and increasing, giving such corporations a huge advantage in product development. One might note, for example, that expenditures on research and development by publicly traded software companies increased tenfold between 1986 and 2000, from 1 to 10% of industrial research expenditures (Evans, 2002).

As the popularity of IEEE 802.11 wireless LANs (WLANs) grows rapidly, many new 802.11 wireless standards are emerging. New 802.11 standards are being developed in two major categories: specifications that make use of advanced wireless technologies in Radio Frequency (RF) and Physical layer (PHY), such as 802.11n, and specifications that address the needs in wireless network management, performance measurements, inter-networking, fast roaming, and the needs in other various specific applications and use scenarios. These include 802.11k, 802.11p, 802.11r, 802.11s, 802.11T, 802.11u, 802.11v, 802.11w and 802.11y. In this chapter, we discuss briefly the goals and scopes of these emerging standards. Emphasis will be given on 802.11n standard because of the significance in the technology advances it brings in.

IEEE 802.11n: Enhancements for Higher Throughput

802.11n is a long anticipated upgrade to the IEEE 802.11a/b/g wireless local-area network standards. It is expected to bring significant increase in MAC throughput of over 100 megabits per second (Mbps) and an enhanced communication range in the 2.4 and 5 GHz bands. 802.11n is also required to make efficient use of the unlicensed spectral resources by achieving at least 3 bits per second per Hz at the highest 802.11n rate.

The first draft of 802.11n supports PHY rates as high as 270 Mbps or five times that of a 802.11a/g network, which runs at 54 Mbps. The PHY rates can increase even more, up to 600 Mbps with four spatial streams and 40 MHz bandwidth, in the longer term when more receiver and transmitter antennas are employed.

The free software movement emerged in the early 1980s at a time when the ARPANET network with its several hundred hosts was well-established and moving toward becoming the Internet. The ARPANET already allowed exchanges like e-mail and FTP, technologies that significantly facilitated distributed collaboration, though the Internet was to amplify this ability immensely. The TCP/IP protocols that enabled the Internet became the ARPANET standard on January 1, 1983. As a point of reference, recall that the flagship open source GNU project was announced by Richard Stallman in early 1983. By the late 1980s the NSFNet backbone network merged with the ARPANET to form the emerging worldwide Internet. The exponential spread of the Internet catalyzed further proliferation of open source development. This chapter will describe some of the underlying enabling technologies of the open source paradigm, other than the Internet itself, with an emphasis on the centralized Concurrent Versions System (CVS) versioning system as well as the newer decentralized BitKeeper and Git systems that are used to manage the complexities of distributed open development. We also briefly discuss some of the well-known Web sites used to host and publicize open projects and some of the services they provide.

The specific communications technologies used in open source projects have historically tended to be relatively lean: e-mail, mailing lists, newsgroups, and later on Web sites, Internet Relay Chat, and forums. Most current activity takes place on e-mail mailing lists and Web sites (Feller and Fitzgerald, 2002).

Systems coupling embedded computing and sensing have vast potential, particularly when wirelessly networked. However, the focus of much of the literature for wireless sensor network is on idealized systems with potentially millions of members (see for example), with minimal power, weight, and size. This focus on idealized systems can lead to discounting the use of current WLAN technologies such as 802.11, or WiFi, in sensor network applications. In this chapter we discuss the applicability of WiFi, as the preeminent WLAN technology, to wireless sensor network applications. We begin this discussion with an introduction to wireless sensor networks. Then we describe how the adhoc capabilities and communication efficiency of 802.11 radios are suited to certain sensor network applications. Finally, to illustrate a type of sensor network for which 802.11 radio properties are appropriate we provide an overview of a prototype wireless network for sonobuoys developed by Sensoria Corporation and Exponent Corporation, which was demonstrated using 802.11b radios.

Introduction

One application of ubiquitous computing is to create autonomous or semi-autonomous systems that monitor and report changes in the physical environment. When communicating wirelessly, this large range of systems is called wireless sensor networks. These networks are envisioned as large numbers of individual sensing “nodes”, each connected to its neighbors wirelessly, and networked together to enable communication, coordination, and collaboration. This interaction is envisioned between groups of nodes locally as well as across the network to entities potentially on external networks.

The market for 802.11 wireless local area networks (WLANs) continues to grow at a rapid pace. Business organizations value the simplicity and scalability of WLANs as well as the relative ease of integrating wireless access with existing network resources. WLANs support user demand for seamless connectivity, flexibility and mobility. This chapter provides an overview of wireless networks and the 802.11 WLAN standards, followed by a presentation of troubleshooting wireless network problems with the types of analysis required to resolve them.

Introduction

802.11 is no longer a “nice-to-have.” It is a critical element in all enterprise networks, whether by design, by extension or by default. Office workers expect to have a wireless option as part of the overall network design. Mobile users extend their reach by using wireless networks wherever they are available, including in public places, in a prospect's conference room, or at home. Even when the policy states “No Wireless,” wireless networking is alive and well as a built-in default on most laptops today. 802.11 enables tremendous mobility, and is becoming the foundation for other technologies, like campuswide wireless voice.

Maintaining the security, reliability and overall performance of a wireless LAN requires the same kind of ability to look “under the hood” as the maintenance of a wired network - and more. Wireless networking presents some unique challenges for the network administrator and requires some new approaches to familiar problems.

The IEEE 802.11n standard is the first wireless LAN standard based on MIMO-OFDM, a technique that significant range and rate relative to conventional wireless LAN. This chapter describes the main features of the 802.11n standard including packet structures, preamble formats, and coding aspects. Performance results show that net user throughputs over 100 Mbps are achievable, which is about four times larger than the maximum achievable throughput using IEEE 802.11a/g. For the same throughput, MIMO-OFDM achieves a range that is about 3 times larger than non-MIMO systems.

Introduction

The appetite for higher data rate continues as consumer demand for bandwidth hungry applications like gaming, streaming audio and video grows. Advancement in handset processors and further integration of technologies like higher mega-pixel cameras into handsets, create a never ending need for more bandwidth consuming applications at longer ranges and more efficient utilization of the limited spectrum available to Network Operators. 3G technology falls short in meeting this demand, while coverage is often worse than what customers are used to from 2.5G networks.

On the other hand, wireless LAN, the technology initially expected to provide only limited range and bandwidth has come a long way. Since the introduction of proprietary WLAN products in 1990 and the adoption of the first IEEE 802.11 standard in 1997, maximum data rates have made an impressive growth that is depicted in Figure 8.1.

Foreword: A World Without Wires

Contributed by Steve Andrews, BT Group's Chief of Mobility and Convergence

Wireless working is mainstream. Whether on the go, at home at work or in the local coffee shop, it is increasingly possible to get the information we require, whenever we want it on the device we want it on. It is clear then that this is no longer a technology of the future. Wireless technology is radically changing the way local authorities, individuals and businesses work, talk and play. And it is doing so right now.

Simply put, there is a huge benefit for councils who understand the evolution to a wireless world, helping them to fulfil their vision of creating an e-enabled town or city. We have already seen it start happening in the U.S. and other parts of the world and the UK is now well underway. From Philadelphia to Westminster, municipal wireless networks are springing up in cities across the globe; ambitious but realistic projects which help council workers, communities and local businesses alike to mobilise and reap the benefits that wireless broadband networks can bring.

According to Gartner, Wi-Fi is accessible on 80% of professional PCs, as well as being in homes across the country, where people are increasingly getting comfortable with the wireless world. Wireless communications have taken a foothold throughout Europe and IDC research shows that two thirds of the European working population is equipped with mobile devices and predicts that during 2007 there will be 99.3 million mobile-enabled workers in Europe.

This chapter focuses on wireless mesh infrastructure systems used for creating large scale Wi-Fi based infrastructure networks, and examines three different approaches currently available for implementing them. It examines the strengths and weaknesses of each approach with particular focus on an analysis of the capacity that is available to users.

Introduction

Mesh is a type of network architecture. Other common network architectures have included Ethernet, originally a shared bus topology for local area networks (LANs) in which every node taps into a common cable that carries all transmissions from all nodes to an egress point. In bus networks, any node on the network senses all transmissions from every other node in the network. Today, most LANs use a star architecture in which every node is connected using a dedicated link to a central switch connected to an egress point (switches can be interconnected to form larger networks).

Mesh networks are different – physical layer connectivity from every node to the egress is not required. As long as a node is connected to at least one other node in the mesh network, it will have full connectivity to the entire network because each mesh node forwards packets to other nodes in the network as required. Mesh protocols automatically determine the best route through the network and can dynamically reconfigure the network if a link becomes unusable.

There are many different types of mesh networks.

The wireline systems have moved to supporting richer voice over packet switched services with the introduction of Skype and Vonage type services. This has completely displaced the traditional circuit-switched services. This trend to move away from circuit-switched services is catching on in the cellular networks are moving towards supporting fundamental services like voice over the packet domain using the IMS over packet networks. In addition, there is widespread adoption of the wireless LAN systems at home, office and commercial environments. Cellular operators are seeing WLAN not as competing technology, but as something that complements it by allowing the offloading of MSs to the WLAN systems to increase the cellular system capacity and potentially extending coverage. Integrated WiFi and 2G/3G cellular is seen as having the best of two worlds, capitalizing on the strengths offered by each technology. Operators are equipping cellphones with WLAN capability and it was only natural to ask the question if the same applications supported over the packet domain in the wireline and cellular networks can also be supported over the WLAN systems.

This chapter discusses the topics of making WLAN systems interwork with the 2G/3G systems, service continuity between the two systems addressing domain registration and call continuity with emphasis on voice. This chapter is written covering the solutions as it applies to 3GPP2. Most of these solutions also apply to 3GPP and exceptions will be highlighted. This chapter is also written from a mobile device perspective since the device plays a central role in handling mobility between the different WLAN and 2G/3G technologies.

The development of the IEEE 802.11n standard amendment enables MIMO-OFDM waveform transmission in the 2.4 GHz band. Additional PHY modifications relative to 802.11a/g include 40 MHz channels, additional data tones in 20MHz channels, and rate 5/6 coding. MAC enhancements include two types of frame aggregation. In this paper we model and simulate the sensitivity of an 802.11n device in the presence Bluetooth interference. Spatial and temporal properties of both systems are considered. Results are provided in terms of packet error rate, throughput, and required separation between devices.

Introduction

The most current draft of IEEE 802.11n (11n) enables MIMO-OFDM waveform transmission in the 2.4 GHz band [11]. Therefore, analysis of IEEE 802.11b/g coexistence with Bluetooth (BT) devices [1], [2], [3], and [5] must be extended to cover 11n. Not only will 11n extend the physical layer (PHY) for spatial division multiplexing with one to four spatial streams, but will also increase the data rate with additional data tones in 20MHz as compared to 802.11g, and rate 5/6 coding. In addition, 11n will create a new 40 MHz channel width, for more than double the data rate, relative to 20 MHz transmissions.

The scope of 11n is to increase the throughput of IEEE 802.11, not just the PHY data rate. In order to do so, the efficiency of the medium access control (MAC) layer must also be improved. Two types of frame aggregation have been developed: aggregate MAC protocol data unit (A-MPDU) and aggregate MAC service data unit (A-MSDU).

The first wave of publicly owned information networks was in communities that already owned electric utilities. Today, cities of all kinds are being offered seemingly attractive deals from private companies that want to build new information networks. They would do well to also evaluate publicly owned alternatives. Public ownership means ownership by citizens, customers or the community. It provides communities with an ongoing voice in the design and operation of their information and communication infrastructure, and can ensure values that are not being enforced by federal regulators, including universal access and competition.

Introduction

Ten years after the 1996 Telecommunications Act, which was supposed to accelerate the introduction of high-speed communications systems, the U.S. has dropped from first to 15th in the world for the percentage of residents with high-speed Internet access.

Increasingly, local governments are stepping in where the private sector and federal government have failed. Hundreds of cities are currently debating strategies to develop citywide broadband networks. They share common goals – universal coverage, equitable access, increased competition, and more effective use of the new communications systems for municipal services, especially those related to public safety.

Their discussions often ignore or give short shrift to a crucial issue: who will own the information network?

Ownership matters. Public ownership of the physical infrastructure may be the only way to guarantee future competition. It is clearly the only way that communities can influence the design of their future information systems on an ongoing basis.