Ultra-Wideband Wireless Communications and Networks - Hardcover

Hardcover

ISBN 10: 0470011440 ISBN 13: 9780470011447

Publisher: Wiley, 2006

Synopsis

Learn about Ultra-wideband (UWB) transmission - the most talked about application in wireless communications.

UWB wireless communication is a revolutionary technology for transmitting large amounts of digital data over a wide spectrum of frequency bands with very low power for a short distance. This exciting new text covers the fundamental aspects of UWB wireless communications systems for short-range communications. It also focuses on more advanced information about networks and applications. Chapters include: Radio Propagation and Large Scale Variations, Pulse Propagation and Channel Modelling, MIMO (Multiple Input, Multiple Output) RF Subsystems and Ad Hoc Networks.

• Focuses on UWB wireless communications rather than UWB radar, which has been covered before.
• Provides long and short-term academic and technological value.
• Teaches readers the fundamentals, challenges and up-to-date technical processes in this field.

About this title

About the Author

Professor Xuemin Shen works in the Department of Electrical and Computer Engineering at the University of Waterloo, Canada. His research interests are Wireless/Internet interworking, Resource and mobility management, Voice over mobile IP, WiFi, WAP, Bluetooth, UWB wireless applications, ad hoc wireless networks.

Dr. Mohsen Guizani is Professor and Chair of the Department of Computer Science at Western Michigan university. Dr. Guizani's research interests include Computer Networks, Wireless Communications and Computing, Design and Analysis of Computer Systems, and Optical Networking. He is the founder and Editor-In-Chief of Wireless Communications and Mobile Computing Journal, published by John Wiley.

Professor Robert Caiming works in the Center for Manufacturing Research/Electrical and Computer Engineering Department at Tennessee Technological University, USA. His research interests include Wireless communications and systems (3G, 4G, UWB), Radar/communications signal processing and Time-domain Electromagnetics.

Professor Tho Le-Ngoc works in the Department of Electrical and Computer Engineering at McGill University. His research interests include Broadband Communications: Advanced Transmission, Multiple-Access and Dynamic Capacity Allocation Techniques.

From the Back Cover

Ultra-wideband (UWB) technology has great potential for applications in wireless communications, radar and location. It has many benefits due to its ultra-wideband nature, which include high data rate, less path loss and better immunity to multipath propagation, availability of low-cost transceivers, low transmit power and low interference. Despite R&D results so far demonstrating that UWB radio is a promising solution for high-rate short-range wireless communications, further extensive investigation is necessary towards developing effective and efficient UWB communication systems and UWB technology.

Ultra-wideband Wireless Communications and Networks explores both the fundamental aspects and the more advanced topics of networks and applications. Challenges and up-to-date technical progress in the field are presented, with timely reporting of results from cutting-edge research and state-of-the-art technology in UWB wireless communications.

• Unique focus on UWB wireless communications rather than previously covered UWB radar aspects.
• Topics include: radio propagation and large scale variations, pulse propagation and channel modelling, MIMO (Multiple Input – Multiple Output) RF subsystems and ad hoc networks.
• Features a wealth of tables, illustrations and photographs.

This book is aimed at professionals wishing to enhance their knowledge of UWB wireless communications systems for short range communications. It will also appeal to senior undergraduate and graduate students who require information on the key topics in this area.

Ultra-wideband Wireless Communications and Networks explores both the fundamental aspects and the more advanced topics of networks and applications. Challenges and up-to-date technical progress in the field are presented, with timely reporting of results from cutting-edge research and state-of-the-art technology in UWB wireless communications.

• Unique focus on UWB wireless communications rather than previously covered UWB radar aspects.
• Topics include: radio propagation and large scale variations, pulse propagation and channel modelling, MIMO (Multiple Input – Multiple Output) RF subsystems and ad hoc networks.
• Features a wealth of tables, illustrations and photographs.

This book is aimed at professionals wishing to enhance their knowledge of UWB wireless communications systems for short range communications. It will also appeal to senior undergraduate and graduate students who require information on the key topics in this area.

Excerpt. © Reprinted by permission. All rights reserved.

Ultra-Wideband Wireless Communications and Networks

John Wiley & Sons

Copyright © 2006 John Wiley & Sons, Ltd
All right reserved.
ISBN: 978-0-470-01144-7

Chapter One

Introduction

Robert Caiming Qiu, Xuemin (Sherman) Shen, Mohsen Guizani and Tho Le-Ngoc

1.1 Fundamentals

1.1.1 Overview of UWB

Ultra-wideband (UWB) transmission has recently received significant attention in both academia and industry for applications in wireless communications. UWB has many benefits, including high data rate, availability of low-cost transceivers, low transmit power, and low interference. It operates with emission levels that are commensurate with common digital devices such as laptops, palm pilots, and pocket calculators. The approval of UWB technology made by the Federal Communications Commission (FCC) of the United States in 2002 reserves the unlicensed frequency band between 3.1 and 10.6 GHz (7.5 GHz) for indoor UWB wireless communication systems. Industrial standards such as IEEE 802.15.3a (high data rate) and IEEE 802.15.4a (very low data rate with ranging) based on UWB technology have been introduced. On the other hand, the Department of Defense (DoD) UWB systems are different from commercial systems in that jamming is a significant concern. Although R&D efforts in recent years have demonstrated that UWB radio is a promising solution for high-rate short-range and moderate-range wireless communications and ranging, further extensive investigation, experimentation, and development are necessary to produce effective and efficient UWB communication systems. In particular, UWB has found a new application for lower-data-rate moderate-range wireless communications, illustrated by IEEE 802.15.4a and DoD systems with joint communication and ranging capabilities unique to UWB. Unlike the indoor environment in 802.15.3a (WPAN), the new environments for sensors, IEEE 802.15.4a, and DoD systems will be very different, ranging from dense foliage to dense urban obstructions. The application of UWB to low-cost, low-power sensors has a promise. The centimeter accuracy in ranging and communications provides unique solutions to applications, including logistics, security applications, medical applications, control of home appliances, search-and-rescue, family communications and supervision of children, and military applications.

1.1.2 History

Although, often considered as a recent breakthrough in wireless communications, UWB has actually experienced well over 40 years of technological developments. The physical cornerstone for understanding UWB pulse propagation was established by Sommerfeld a century ago (1901) when he attacked the diffraction of a time-domain pulse by a perfectly conducting wedge. In fact, one may reasonably argue that UWB actually had its origins in the spark-gap transmission design of Marconi and Hertz in the late 1890s. In other words, the first wireless communication system was based on UWB. Owing to the technical limitations, narrowband communication was preferred to UWB. Much like the spread spectrum or the code division multiple access (CDMA), UWB followed a similar path with early systems designed for military covert radar and communication. After the accelerating development since 1994 when some of the research activities were declassified, UWB picked up momentum after the FCC notice of inquiry in 1998. The interest in UWB was 'sparked' since the FCC issued a Report and Order allowing its commercial deployment with a given spectral-mask requirement for both indoor and outdoor applications.

1.1.3 Regulatory

UWB technology is defined by the FCC as any wireless scheme that occupies a fractional bandwidth W/[f.sub.c] [greater than or equal to] 20 %, where W is the transmission bandwidth and [f.sub.c] is the band center, or more than 500 MHz of absolute bandwidth. The FCC approved [3] the deployment of UWB on an unlicensed basis in the 3.1-10.6 GHz band subject to a modified version of Part 15.209 rules. The essence of the rulings is that power spectral density (PSD) of the modulated UWB signal must satisfy the spectral masks specified by spectrum-regulating agencies. The spectral mask for indoor applications specified by the FCC in the United States is shown in Figure 1.1.

1.1.4 Applications

High data rate (IEEE 802.15.3a): One typical scenario is promising wireless data connectivity between a host (e.g., a desk PC) and associated peripherals such as keyboards, mouse, printer, and so on. A UWB link functions as a 'cable replacement' with transfer data rate requirements that range from 100 Kbps for a wireless mouse to 100 Mbps for rapid file sharing or download of images/graphic files. Additional driver applications relate to streaming of digital media content between consumer electronics appliances (digital TV sets, VCRs, audio CD/DVD, and MP3 players, and so on). In summary, UWB is seen as having potential for applications that to date have not been fulfilled by other wireless short-range technologies currently available, for example, 802.11 LANs and Bluetooth PANs.

Low data rate (IEEE 802.15.4a): Emerging applications of UWB are foreseen for sensor networks that are critical to mobile computing. Such networks combine low- to medium-rate communications (50 kbps to 1 Mbps) with ranges of 100 m with positioning capabilities. UWB allows centimeter accuracy in ranging as well as in low-power and low-cost implementation of communications systems. In fact, the IEEE 802.15.4a, a standard for low-power, low-date-rate wireless communications, is primarily focused on position location applications. The price point will be in the sub-$1 range for asset tracking and tagging, up to $3 to $4 per node for industrial-control applications. These features allow a new range of applications, including military applications, medical applications (monitoring of patients), family communications/supervision of children, search-and-rescue (communications with fire fighters, or avalanche/earthquake victims), control of home applications, logistics (package tracking), and security applications (localizing authorized persons in high-security areas).

1.1.5 Pulse- or Multicarrier-Based UWB

The main stream papers in the literature deal with pulse-based UWB systems. One reason may be due to the fact that the pulse-based UWB was not sufficiently understood compared to orthogonal frequency-division multiplexing (OFDM) based UWB.

The major reasons for the standard body (IEEE 802.15.3a) to adopt multiband scheme are: (1) it has spectrum flexibility/agility. Regulatory regimes may lack large contiguous spectrum allocation. Spectrum agility may ease coexistence with existing services. (2) Energy collected per RAKE finger scales with longer pulse widths used, which prefers fewer RAKE fingers. (3) Reduced bandwidth after down-conversion mixer reduces power consumption and linearity requirements of receiver. (4) A fully digital solution for signal processing is more feasible than single band solution for the same occupied bandwidth. (5) Transmitter pulse shaping is made easier; longer pulses are easier to synthesize and less distorted by integrated circuits (IC) package and antenna systems. (6) It is capable of utilizing a frequency-division multiple-access (FDMA) mode for severe near-far scenarios.

Multiband pulsed scheme: The main disadvantage of narrow time-domain pulses is that building RF and analog circuits as well as high-speed analog-to-digital converters (ADCs) to process the signal of extremely wide bandwidth is challenging, and usually results in high power consumption. Collection of sufficient energy in dense multipath environments requires a large number of RAKE fingers. The pulsed multiband approach can eliminate the disadvantages associated with a large front-end processing bandwidth, by dividing the spectrum into several subbands. The advantage of this approach is that the information can be processed over a much smaller bandwidth, thereby reducing the complexity of the design and the power consumption, lowering the cost, and improving spectrum flexibility and worldwide compliance. However, it is difficult to collect significant multipath energy using a single RF chain. In addition, very stringent frequency-switching time requirements (<100 ps) are placed at both the transmitter and the receiver.

Multiband OFDM scheme: Multipath energy collection is an important issue as it is a major factor that determines the range of a communication system. The multiband OFDM system transmits information on each of the subbands. This technique has nice properties including the ability to efficiently capture multipath energy with a single RF chain. The drawback is that the transmitter is slightly more complex because it requires an inverse fast Fourier transform (IFFT) and the peak-to-average ratio may be higher than that of the pulse-based multiband approaches. It seems to be very challenging for both the pulse-based and the OFDM-based multiband solutions to meet the target costs imposed by the market.

1.2 Issues Unique to UWB

1.2.1 Antennas

UWB antennas can be modeled as the front-end pulse shaping filters that affect the baseband detection. A narrowband system does not have this problem. In narrowband systems front-end filters are typically designed as matched filters; and since the fractional bandwidth is so small, the antenna frequency response can be designed to lie in the frequency domain. That is not true for a UWB system in which the pulse-waveform distortion is often present. The impulse response of the antenna can change with angle in both elevation and azimuth. Specifically, the transmitted pulse at different elevation angles will be distorted as compared with the pulse observed at bore site.

1.2.2 Propagation and Channel Model

UWB itself represents an unprecedented conceptual revolution. The huge chunk of spectrum (as high as 7.5 GHz) can be legally used for commercial wireless communications to carry information bits up to 480 Mbps or higher that will be propagated via a medium. This medium will attenuate and distort the incident pulse-based signals. The major paradigm shift required for this new concept is to 'think' in the time domain and envision UWB time-domain pulses as basic UWB signals since it is prohibitively inconvenient to envision UWB signals in the frequency domain. The basic building blocks for UWB signals are short 'pulses' rather than the harmonic sine waves. These short-pulse UWB signals of huge transmission bandwidth provide the superresolution of the received signals at the receiver. This fundamental property changes the structure of many basic problems: for example, fading, and time-resolvable multipaths.

Fading is due to the overlapping superposition of unresolved multipaths. Compared with time-resolvable multipaths the major narrowband nuisance of fading is no longer important for UWB: it is only 3-4 dB for UWB in contrast to 30-60 dB for narrowband. Basically, a UWB channel is quasi-static in that the collected total energy is almost constant at each instant. Thus, time-resolvable multipaths will become the dominant mechanism for energy transmission and capture, since a huge number (hundreds) of paths are resolved in contrast to several paths (in a 5 MHz system). The transmitted energy is carried through these time-resolvable multipaths. The UWB pulse signals associated with those individual paths are the basic building blocks of a UWB system and require a careful treatment. Another conceptual difference is in the necessity to consider the per-path pulse distortion that is neglected in Turin's multipath channel model (Turin 1958) widely used in wireless communications. Turin's model is based on empirical experimental data obtained using a typical narrowband measurement system. The generalized multipath model is based on the transient physical mechanisms obtained directly from Maxwell's equations.

1.2.3 Modulations

In choosing modulation schemes for UWB systems [2], one must consider a number of aspects such as data rate, transceiver complexity, spectral characteristics, robustness against narrowband interference, intersymbol interference, error performance, and so on. For pulsed UWB systems, the widely used forms of modulation schemes include pulse amplitude modulation (PAM), on-off keying (OOK), and pulse position modulation (PPM). To satisfy the FCC spectral mask, passband pulses are used to transmit information in pulsed UWB systems. Although these passband pulses could be obtained by modulating a baseband pulse using a sinusoidal carrier signal, the term binary phase-shift keying (BPSK) is still somewhat imprecise in the context of pulsed UWB signaling as the carrier-modulated baseband pulse is usually treated as a single entity - the UWB pulse shape.

The three modulation schemes mentioned above are illustrated in Figure 1.2. For a single-user system with binary PPM signaling, bit '1' is represented by a pulse without any delay and bit '0' is represented by a pulse with a delay [tau] relative to the time reference. A major factor governing the performance of this system, like any other PPM-based system, is the set of time shifts used to represent different symbols. The most commonly used PPM scheme is the orthogonal signaling scheme for which the UWB pulse shape is orthogonal to its time-shifted version. There also exists an optimal time shift for an M-ary PPM scheme. The time shifts for both the orthogonal and the optimal schemes depend on the choice of the UWB pulse p(t). For binary PAM signaling, information bits modulate the pulse polarity. For OOK signaling, information bit '1' is represented by the presence of a pulse and no pulse is sent for bit '0'.

Binary PAM and PPM schemes have similar performances. The OOK scheme is less attractive than the PAM or PPM scheme because of its inferior error performance in the same environment. However, if receiver complexity is the main design concern, a simple energy-detection scheme can be applied to OOK signals, resulting in a receiver of lowest achievable complexity. PSD of the modulated UWB signal must satisfy the spectral masks specified by spectrum-regulating agencies. In the United States, the spectral mask for indoor applications specified by the FCC is from 3.1 GHz to 10.6 GHz. OOK and PPM signals have discrete spectral lines. These spectral lines could cause severe interference to existing narrowband radios, and various techniques such as random dithering could be applied in PPM to lower these discrete spectral lines and smoothen the spectrum. Because of the random polarities of the information symbols, the PAM scheme inherently offers a smooth PSD when averaged over a number of symbol intervals. In this sense, PAM signaling is attractive.

1.2.4 A/D Sampling

Most of the existing detection schemes require an ADC that operates at a minimum of the Nyquist rate. For high-performance design, the sampling rate is in the multi-GHz range for UWB signaling (minimum bandwidth is 500 MHz). In addition to the extremely high-sampling frequency, the ADC must support a relatively high resolution (e.g., greater than 4-6 bits) to resolve signals from the narrowband interferences. Such a speed mandates the use of an interleaved flash ADC, which tends to be power hungry with the power scaling exponentially increasing with bit precision. Although achievable with today's CMOS technology, such an ADC must be avoided in low-power operations. One technique to avoid using such a high-speed ADC is to implement the correlator in the analog domain. One technical challenge associated with the analog implementation method is the difficulty in obtaining the receiver template waveform and deriving the precise timing of symbols and received paths. In the digital implementation, a bank of correlators that are delayed relative to one another by a fraction of the pulse duration can be applied to correlate with the received digitized signal, and the local peaks corresponding to the possible received pulses are located. With analog implementation, this is difficult to achieve because some sort of analog delay units, and novel multipath tracking methods are needed. Another approach is to represent the samples using fewer bits. One bit (mono-bit) representation of samples, a traditional approach, finds a new application in UWB in reducing ADC speed.

(Continues...)

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Edition details

• Publisher: Wiley
• Publication date: 2006
• Language: English
• ISBN 10: 0470011440
• ISBN 13: 9780470011447
• Binding: Hardcover
• Edition number: 1
• Number of pages: 320
• Editor: Shen Xuemin, Guizani Mohsen, Qiu Robert Caiming, Le-Ngoc Tho