Wireless Infrared Communications

185 Pages·1994·5.128 MB·English

by  John R. Barry (auth.)

Wireless Infrared
Communications
THE KLUWER INTERNATIONAL SERIES
IN ENGINEERING AND COMPUTER SCIENCE
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Wireless Infrared
Communications
John R. Barry
Georgia Institute ofTechnology
Atlanta, Georgia, USA
...
"
SPRINGER SCIENCE+BUSINESS MEDIA. LLC
Library of Congress Cataloging-in-Publication Data
Barry, John R., 1963-
Wireless infrared communications / John R. Barry.
p. cm. -- (The Kluwer international series in engineering and
computer science ; 280. Communications and information theory)
lncludes bibliographical references and index.
ISBN 978-1-4613-6162-6 ISBN 978-1-4615-2700-8 (eBook)
DOI 10.1007/978-1-4615-2700-8
1. Wireless communication systems. 1. Title. II. Series: Kluwer
international series in engineering and computer science ; SECS
280. III. Series: Kluwer international series in engineering and
computer science. Communications and information theory.
TK5103.2.B37 1994
621.382'7--dc20 94-19272
CIP
Copyright C!l) 1994 by Springer Science+Business Media New York
OriginalIy published by Kluwer Academic PubIishers in 1994
Softcover reprint of the hardcover 1s t edition 1994
AlI rights reserved. No part of this publication may be reproduced, stored in
a retrieval system or transmitted in any form or by any means, mechanical,
photo-copying, recording, or otherwise, without the prior written permission of
the publisher, Springer Science+Business Media, LLC.
Printed on acid-free pap er.
Contents
Foreword vii
Preface ix
1. Introduction 1
1.1 Comparison of Infrared and Radio Communications 2
1.2 The Wireless Infrared Channel 3
1.3 History of Wireless Infrared Communications 6
1.4 A High-Speed Wireless LAN 10
1.5 Optoelectronic Components 11
1.6 Outline 12
2. Link Analysis and Optics Design 15
2.1 Introduction 15
2.2 Thin-Film Optical Filters 17
2.3 Truncated Spherical Concentrators 24
2.4 Joint Optimization of Transmitter and Filter 37
2.5 Summary and Conclusions 46
3. Receiver Design 49
3.1 Introduction 49
3.2 Limitations on Photodetector Bandwidth 51
3.3 Analysis of Current-Feedback Pair 52
3.4 Optimal Filtering for Quadratic Noise Spectrum 57
3.5 Choosing the Right Transistor 59
3.6 Design Procedures 60
3.7 Optional Design Embellishments 68
3.8 Summary and Conclusions 77
vi
4. Modeling Multipath Dispersion 79
4.1 Introduction 79
4.2 Models for Diffuse Reflectors and Transmitters 81
4.3 Multiple-Bounce Impulse Response 84
4.4 Simulation and Experimental Results 87
4.5 Multipath-Induced Power Penalty 102
4.6 Summary 107
5. Modulation and Equalization 109
5.1 Intensity Modulation and Direct Detection 109
5.2 Binary Modulation 112
5.3 Multi-Level Modulation 120
5.4 Discussion 133
5.5 ML Sequence Detection and Equalization for PPM 135
5.6 Coherent Optical Communication 146
5.7 Summary 147
6. System-Level Issues 149
6.1 Introduction 149
6.2 Single-Cell Architectures 150
6.3 Overlapping Cells 153
6.4 Summary 158
7. Conclusions and Future Work 161
7.1 Conclusions 161
7.2 Future Work 162
References 167
A. Power Efficiency on the Linear Gaussian-Noise Channel 175
Index 179
Foreword
The demand for wireless access to network services is growing in virtually all
communications and computing applications. Once accustomed to unteathered opera
tion, users resent being tied to a desk or a fixed location, but will endure it when there
is some substantial benefit, such as higher resolution or bandwidth. Recent technolog
ical advances, however, such as the scaling of VLSI, the development of low-power
circuit design techniques and architectures, increasing battery energy capacity, and
advanced displays, are rapidly improving the capabilities of wireless devices.
Many of the technological advances contributing to this revolution pertain to the
wireless medium itself. There are two viable media: radio and optical. In radio,
spread-spectrum techniques allow different users and services to coexist in the same
bandwidth, and new microwave frequencies with plentiful bandwidth become viable
as the speed of the supporting low-cost electronics increases. Radio has the advantage
of being available ubiquitously indoors and outdoors, with the possibility of a seam
less system infrastructure that allows users to move between the two. There are unan
swered (but likely to be benign) biological effects of microwave radiation at higher
power densities. Optical communications is enhanced by advances in photonic
devices, such as semiconductor lasers and detectors. Optical is primarily an indoor
technology - where it need not compete with sunlight - and offers advantages such
as the immediate availability of a broad bandwidth without the need for regulatory
approval. There are well-characterized dangers to the human eye from optical radia
tion at higher power densities.
While optical wireless communication is attractive for certain high-speed applica
tions, there are a number of challenging design problems that must be faced. One is to
obtain sufficient signal-to-noise ratio in the presence of strong interference, such as
natural and man-made light, while staying within the margins of eye safety. Another
is to obtain full coverage of a room by diffusing the light, allowing the user to go any
where, which further compromises the signal power density at the receiver. Yet
another is to design detectors with sufficient area and simultaneously enough band
width to allow a high data rate. In addition, as with radio systems, there is the chal
lenge of dealing with intersymbol interference created by multipath.
viii
This book provides a comprehensive description of the technical challenges
inherent in diffuse infrared wireless networking. It is an outgrowth of a research
project at the University of California at Berkeley which led to John Barry's doctoral
dissertation, supplemented by his subsequent work at the Georgia Institute of Tech
nology. The original goal of this research was a 100 Mb / s diffuse optical transmis
sion to a single wireless terminal. We are indebted to the IBM T. J. Watson Research
Center, and to Scott Kirkpatrick and Colin Harrison in particular, for first presenting
us with the challenges and encouraging our research on wireless infrared. Prototyping
efforts have continued at Berkeley under the direction of Professor Joseph Kahn and
his students, with the support of mM and Hewlett Packard.
I believe that the prospects for commercial applications of optical-based wireless
communications are very bright, particularly for high-performance indoor local-area
networks. I hope that John Barry's book will playa significant role in convincing the
technical community of the viability of this technology. A wealth of exciting new
applications await.
David G. Messerschmitt
Professor and Chair
Department of Electrical Engineering
and Computer Science
University of California, Berkeley
Preface
The capabilities of infrared technology extend far beyond the mere remote control
of home appliances. A natural application is wireless networking for portable com
puters, a concept that was first proposed over 15 years ago by IBM researchers,! and
has recently become a commercial reality; several companies now offer wireless
infrared modems, with data rates of 1 to 4 Mb/s and ranges of 10 to 15 m. Despite a
growing interest in wireless infrared communications, surprisingly little has been
published by the research community. Fundamental questions have gone unanswered.
For example, can infrared support broadband data rates of 100 Mb/ s and higher?
What are the inherent obstacles to achieving high transmission speeds, and how can
they best be mitigated? These are the questions that my colleagues and I were asking
in 1989, when we teamed up with IBM-Hawthorne and began our work on wireless
infrared communication. The ensuing research led to my doctoral dissertation at the
University of California at Berkeley, which in tum formed the basis for this book.
The original goal of this project was to investigate the communication-theoretic
aspects of the physical layer of a wireless infrared network, with emphasis on deter
mining which modulation techniques can best exploit the unique characteristics of the
medium. We soon realized, however, that a prerequisite for such a study is a thorough
understanding of the underlying channel itself, including the effects of background
light, optical components, multipath optical propagation, and receiver electronics.
Therefore, a bulk of our effort was directed at these issues, as reflected in the structure
of this book: chapter 2 addresses optics design, chapter 3 addresses electronic
receiver design, and chapter 4 address multipath optical propagation. Modulation is
not addressed until chapter 5.
This book differs from my doctoral dissertation in several substantial ways. For
example, chapter 2 has been completely rewritten, and a more accurate method for
accommodating reflection losses has been included. In addition, new material
1. F. R. Gfeller, H. R. Muller, and P. Vettiger, "Infrared Communication for In-House Ap
plications," IEEE COMPCON, Washington D. C., pp. 132-138, September 5-8, 1978.
x
addressing non-hemispherical concentrators and isotropic radiation has been added.
The new numerical results of chapter 2 propagate into chapter 3 as well. Chapter 5
has also been improved with the addition of a detailed discussion on equalization for
pulse-position modulation in the presence of intersymbol interference. Finally, where
possible, the pace has been relaxed and the tone made more conversational. I hope the
resulting book provides a useful introduction for both design engineers and communi
cation theorists to the principles of wireless infrared communications.
Acknowledgments
Funding for this project was provided by the T. 1. Watson Research Center of
IBM, the National Science Foundation under grant number MIP-86-57523, Sony Cor
poration, Dolby Laboratories, and the California State MICRO Program. Subsequent
research at Georgia Tech was funded by an IBM Faculty Development Award and by
the National Science Foundation under grant number NCR-9308968.
Many colleagues and friends deserve thanks for their influence on this project. I
am especially grateful to Professors Edward Lee and David Messerschmitt for their
constant encouragement and inspiration. I am also greatly indebted to Professor
Joseph Kahn, whose guidance has strongly influenced much of this book. I am
grateful to Peter Hortensius of IBM for providing early guidance during the summer
of 1990, and also for sharing his ideas on multipath dispersion that led to the theory of
chapter 4. Professor David Brillinger, Malik Audeh, and Gene Marsh provided useful
comments on an early draft of this manuscript. Bill Krause deserves credit for the
experimental multi path measurements of chapter 4. Conversations with the following
colleagues were also helpful: Andy Burstein, Jeff Carruthers, Shih-Fu Chang, Andrea
Goldsmith, Paul Haskell, Jim Hollenhorst, Chris Hull, Phil Lapsley, Chung-Sheng Li,
Horng-Dar Lin, Vijay Madisetti, Kris Pister, Annis Porter, Rajiv Ramaswami, Gil Sih,
Ravi Subramanian, and Greg Uehara.
John R. Barry