Low-Power Wireless Infrared Communications

158 Pages·1999·4.219 MB·English

by  Rob Otte, Leo P. de Jong, Arthur H. M. van Roermund (auth.)

Low-Power Wireless Infrared Communications
Low-Power Wireless
Infrared Communications
by
Rob Otte
Philips Research
Leo P. de Jong
Delft University of Technology
and
Arthur H.M. van Roermund
Eindhoven University of Technology
SPRINGER SCIENCE+BUSINESS MEDIA, LLC
A c.I.P. Catalogue record for this book is available from the Library of Congress.
ISBN 978-1-4419-5106-9 ISBN 978-1-4757-3015-9 (eBook)
DOI 10.1007/978-1-4757-3015-9
Printed on acid-free paper
AII Rights Reserved
©1999 Springer Science+Business Media New York
Originally published by Kluwer Academic Publishers, Boston in 1999
Softcover reprint of the hardcover 1 st edition 1999
No part of the material protected by this copyright notice may be reproduced or
utiJized in any form or by any means, electronic or mechanical,
includ ing photocopying, recording or by any information storage and
retrieval system, without written permission from the copyright owner.
Contents
Preface ix
1 Introduction 1
2 Overview 5
2.1 Historical overview 5
2.2 Relevance . . . . . 7
2.3 Global system requirements 8
3 Link design - optical considerations 13
3.1 Intensity modulation and direct detection 13
3.2 Signal and noise level at the receiver .. 18
3.3 Optical concentration and diversity . . . 22
3.3.1 Maximum possible concentration 22
3.3.2 Angular diversity . . . . . . . 23
3.3.3 Concentrator implementation . 26
3.4 Reflections ............... . 29
3.4.1 Modelling of reflective surfaces 30
3.4.2 Reflection of ambient radiation 31
3.4.3 LOS transmission versus non-LOS transmission 32
3.5 Electro-optical components and optical filters 34
3.5.1 Emitters ... 34
3.5.2 Detectors ...... . 35
3.5.3 Optical filters . . . . . 37
3.6 Sources of ambient radiation 38
3.6.1 Optical spectra and normalization 38
3.6.2 Lighting flicker 45
3.7 Conclusions . . . . . . . . . 48
v
4 Link design - electronic considerations 51
4.1 Front-end noise . . . . . . . . . . . . . . . . . . . . . . . . . . .. 52
4.1.1 Optimization of an FET input stage . . . . . . . . . . .. 52
4.1.2 Noise optimization with current constraint and chip area
constraint . . . . . . . . . . . . . . . . . . . . . 56
4.1.3 Comparison of front-end noise to ambient noise 57
4.1.4 Noise in APDs . . . 59
4.2 Front-end feedback network 59
4.3 Front-end bandwidth . 62
4.4 Front-end biasing . 63
4.5 Conclusions.... 65
5 Modulation schemes 67
5.1 Optical intensity modulation systems versus radio systems. 69
5.2 Baseband modulation schemes ...... 70
5.2.1 On-off keying (OOK) ....... 70
5.2.2 Pulse position modulation (PPM) 74
5.3 Bandpass modulation schemes. . . . . . . 78
5.3.1 Phase reversal keying (PRK) . . . 79
5.3.2 Quadrature phase shift keying (QPSK) 81
5.3.3 Frequency shift keying (FSK) . . 82
5.4 Comparison of schemes; choice of PPM. 84
5.5 Conclusions................ 85
6 PPM reception 87
6.1 BER deterioration due to optical interference 87
6.1.1 Low-frequency BER deterioration model. 88
6.1.2 High-frequency BER deterioration model 91
6.2 PPM modulator and demodulator implementation 93
6.3 Conclusions...................... 97
7 Synchronization in PPM receivers 99
7.1 Slot synchronization . . . . . . . . . . . . . . 100
7.1.1 Methods of preprocessing . . . . . . . 100
7.1.2 Slot-clock recovery in x-pulse systems 103
7.2 Frame synchronization . . . . . . . . . . . . . 109
7.2.1 Frames with pauses: x-frame PPM. . 109
7.2.2 Synchronizable patterns and frame errors 113
7.2.3 Performance of the synchronizer 120
7.3 Conclusions................ 128
8 Conclusions 131
Vi
A Radiometric and photometric quantities 135
B The area under the Gaussian tail Q(k) 139
C Calculation of the x-frame PPM power density spectrum 141
D Distribution of frame errors 145
Bibliography 149
Summary 157
The authors 159
vii
Preface
Today, wireless infrared transmission has entered our homes, offices, industry
and health care, with applications in the field of remote control, telemetry, and
local communication.
This book is about the underlying technology.
As it is an outgrowth of my Ph.D. thesis, the emphasis is on fundamental
aspects rather than industrial aspects, like the standardization effort by the
IrDA [7]. I guess that this is not a drawback, as, eventually, the laws of physics
apply to all of us! As the applied radiation is not necessarily in the infrared,
throughout the book we usually prefer the term optical transmission.
As most equipment is battery-powered, the emphasis is on power optimiza
tion of the optical transmission system. System parameters as well as environ
mental parameters that determine the eventual transmission quality are iden
tified, to facilitate well-reasoned system design. Many design rules, based on
calculations, measurements and simulations are presented to help the designer
push the performance close to the limits set by nature and the available tech
nology.
The first chapters introduce the subject and the present the scope of the
book. Then, the basic transmission link is introduced in chapter 3, and strate
gies to optimize its signal-to-noise ratio are discussed. Lighting flicker is identi
fied as a possible source of interference. Then, receiver noise and bandwidth are
discussed in chapter 4, mainly based on the material presented in [66], [67], [69].
It is argued that noise optimization and bandwidth optimization do not neces
sarily conflict. Chapter 5 provides the reader with an overview of modulation
techniques [24]. Pulse position modulation (PPM) is recognized as an attrac
tive technique for low-power purposes. Chapter 6 further concentrates on PPM
reception. The influence of lighting flicker is estimated and a prototype for syn
chronizer evaluation is presented. As receiver synchronization in PPM systems
is a subject hardly covered by literature, chapter 7 is entirely devoted to an in
depth discussion of possible synchronization subsystems, containing previously
unpublished material about PPM frame synchronization.
As mentioned earlier, this book is the result of my Ph.D. work in the Elec-
IX
tronics department at the Delft University of Technology. Personally, I would
like to thank Prof. dr. ir. J. Davidse, who stimulated my enthusiasm for elec
tronics design in general, and my enthusiasm for starting as a Ph.D. student at
the Electronics department in particular. Further, Arthur, Leo and I would like
to thank all people who contributed one way or another. Rob Janse has drawn
many transparencies and posters that we used for presentations. Loek van Schie
has solved many computer hardware problems and advised us many times. My
roommates Jan Westra and Michiel Kouwenhoven, for always making time for
stimulating discussions and for discussions on a various range of subjects during
lunches. The students who did their M.Sc. in the project: Ellie Cijvat, Marc
Joosen, Tibor Kuitenbrouwer and Tri Sampurno. Many thanks also go to Prof.
dr. ir. C.A. Grimbergen and Dr. A.C. Metting van Rijn at the University of
Amsterdam for the many discussions we have had about the medical applica
tion of wireless optical telemetry systems. Further, we would like to thank Dr.
C.A. Schrama and Mr. H. Rijn of the Nederlands Meetinstituut (NMi), the
Dutch 'institute of measurements', for calibrating the double-monochromator,
and Mr. Schrama for his support when measuring the spectra of many lamps.
Mr. Simon North and Mrs. Zaat-Jones corrected many linguistic errors in parts
ofthis book. I would like to thank Jan Westra, for his stimulating opinion about
writing this book. Last but not least, all the friends and family who supported
me in hard times.
Rob Otte,
Veldhoven, July 1999.
x
Chapter 1
Introduction
Due to the rapid developments in electronic integrated circuit technology and
sensor technology, the amount of information that is processed in modern elec
tronic equipment is increasing rapidly. In many cases the information-carrying
signal has to be processed at a location other than where it was generated, so
that some system is required to transport the information from one location to
another. Examples are the multi-channel telemetry systems currently used in
process control, in cars and in surveillance, and other transmission systems such
as remote controls, systems for audio and video transmission, local computer
networks and inter-satellite communication. Other examples are the systems
used in medical health care for measuring and monitoring physiological quanti
ties such as the heart rate, blood pressure, muscular activity and brain activity.
These systems are evolving and developing very quickly, since there is a demand
for faster diagnosis and more accurate monitoring. This demand is caused by
the fact that the number of patients in medical health care is increasing, while
on the other hand the financial resources are not.
Sometimes the information is transported by, cable. However, particularly
when mobile systems are involved, wireless transmission is preferred. Also in
stationary applications, cables might be unattractive for practical reasons, such
as in dangerous or inaccessible environments. In medical situations wireless
transmission offers the advantage of not affecting the patients physiology. Fur
ther, wireless transmission allows for easier nursing and better patient com
fort, whill:) inherently offering electrical isolation of the patient. Particularly in
the operating theatre and at the intensive care, these advantages are impor
tant. When working with unpredictably behaving patients, such as children,
the mentally disabled and epileptic patients, or in sport physiology, wireless
transmission facilitates a high mobility. For these reasons, this book is about
wireless transmission.
Traditionally, wireless transmission is considered as almost synonymous with
1
R. Otte et al., Low-Power Wireless Infrared Communications
© Springer Science+Business Media New York 1999
2 Chapter 1. Introduction
radio transmission, although wireless transmission by means of carriers other
than electromagnetic waves in the RF-range, such as acoustic or optical waves,
might perform as well or even better.
In this book, the focus is on the design of optical transmission systems for
a wide range of applications and data rates. The choice of optical transmission
was prompted by the fact that radio transmission suffers from EMC problems as
the radio spectrum gets increasingly crowded. Now that personal communica
tion systems and wireless computer networks are evolving rapidly, the available
spectrum is considered to be a scarce resource. Simultaneously, there is an
increase in the interference level caused by switched power supplies and other
high-frequency equipment. Particularly in medical centres and industrial envi
ronments, the applicability of radio systems is already seriously limited by these
problems. Extensive frequency allocation regulations can only partly solve them.
Although eventually EMC aspects will become an integral part of every system
design, future applications require the exploration of new wavelength ranges.
For indoor applications, the optical wavelength range is an attractive one.
First, because the frequencies involved are very high, essentially a large total
transmission bandwidth is possible, facilitating fast transmission systems. Sec
ond, because of the short wavelength, optical radiation is confined within a
room since the radiation is either reflected or absorbed by the walls. Therefore
cell planning in networks is simple. At the moment the optical spectrum is a
universally available resource, without frequency and wavelength regulations.
Although this situation might change in the' future, this will hardly limit the
potential of optical communications.
Many systems and standards currently in use are ad hoc designs to attain
some specific object. The purpose of this book is to give an overview of the
techniques used in wireless optical systems, and to identify the effects that
limit their performance. These effects are modelled to provide rules that help
the designer to create a system in a systematic way. This results in an optimal
system, in the sense that the theoretical possible system performance, as derived
from limitations that are investigated in the following chapters, is approached
closely.
In most mobile applications, the transmitter has to be lightweight and bat
tery powered. In those cases, low power consumption is of paramount impor
tance. Therefore, transmitter power minimization is a basic issue at all levels
of system design.
Throughout all chapters, the aim is to arrive at a systematic approach focus
ing on fundamental, rather than on technological limitations and constraints.
The latter, such as the optical wavelength and the maximum transmitter and
receiver speed, are considered more briefly, since they strongly depend on the
available technologies, which evolve rapidly, and on the actual application. Of
course, this approach does not mean that technological aspects can be disre-