Essentials of Radio Wave Propagation

This page intentionally left blank Essentials of Radio Wave Propagation If you need to maximise efficiency in wireless network planning an understanding of radio propagation issues is vital, and this quick reference guide is for you. Using real-world case studies, practical problems and minimum mathematics, the author explains simply and clearly how to predict signal strengths in a variety of situations. Fundamentals are explained in the context of their practical significance. Applications, including point-to-point radio links, broadcasting and earth–space communications, are thoroughly treated, and more sophisticated methods, which form the basis of software tools both for network planning and for spectrum management, are also described. For a rapid understanding of and insight into radio propagation, sufficient to enable you to undertake real-world engineering tasks, this concise book is an invaluable resource for network planners, hardware designers, spectrum managers, senior technical managers and policy makers who are either new to radio propagation or need a quick reference guide. christopher haslett is the Principal Propagation Adviser at Ofcom, the UK Communication Industries Regulator. As well as experience conducting and directing research projects, he has many years’ industrial radio-planning experience with Cable and Wireless plc., and as Director of Planning and Optimisation at Aircom International Ltd., where he directed the optimisation of UMTS networks. He was also a Senior Lecturer at the University of Glamorgan. The Cambridge Wireless Essentials Series Series Editors william webb, Ofcom, UK sudhir dixit, Nokia, US A series of concise, practical guides for wireless industry professionals. Martin Cave, Chris Doyle and William Webb, Essentials of Modern Spectrum Management Christopher Haslett, Essentials of Radio Wave Propagation Forthcoming Andy Wilton and Tim Charity Essentials of Wireless Network Deployment Steve Methley Essentials of Wireless Mesh Networking Malcolm Macleod and Ian Proudler Essentials of Smart Antennas and MIMO Stephen Wood and Roberto Aiello Essentials of Ultra-Wideband David Crawford Essentials of Mobile Television Chris Cox Essentials of UMTS For further information on any of these titles, the series itself and ordering information see www.cambridge.org/wirelessessentials. Essentials of Radio Wave Propagation Christopher Haslett Ofcom, UK CAMBRIDGE UNIVERSITY PRESS Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo Cambridge University Press The Edinburgh Building, Cambridge CB2 8RU, UK Published in the United States of America by Cambridge University Press, New York www.cambridge.org Information on this title: www.cambridge.org/9780521875653 © Cambridge University Press 2008 This publication is in copyright. Subject to statutory exception and to the provision of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published in print format 2007 ISBN-13 978-0-511-37112-7 eBook (NetLibrary) ISBN-10 0-511-37112-8 eBook (NetLibrary) ISBN-13 978-0-521-87565-3 hardback ISBN-10 0-521-87565-X hardback Cambridge University Press has no responsibility for the persistence or accuracy of urls for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate. Contents Preface page ix Acknowledgements xi 1 Propagation in free space and the aperture antenna 1 1.1 Propagation in free space: simplified explanation 1 1.2 The aperture antenna: simplified explanation 2 1.3 Further details and calculations 3 1.4 Point-to-point transmission 10 1.4.1 Transmitting, directing and capturing power 10 1.4.2 Transmission loss between practical antennas 12 1.4.3 Determining the power required 14 1.4.4 Example calculations 16 1.4.5 Equivalent isotropic radiated power (EIRP) 18 1.5 Near-field effects: simplified explanation 18 1.5.1 Further detail on the near-field issue 19 1.6 Polarisation 24 1.7 Summary 25 2 Point-to-area transmission 26 2.1 Overview 26 2.2 Power density and electric field strength 28 2.3 Converting from field strength to received signal power 30 2.4 Predicting the field strength at a distance 31 2.5 The effect of frequency 33 v vi contents 2.6 Prediction methods for digital mobile communication 35 2.6.1 The Okumura–Hata model 35 2.6.2 Comparison between propagation at 900 MHz and propagation at 1800 MHz 37 2.7 Base-station antennas 38 2.7.1 Sectored antennas 43 2.8 Mobile-station antennas 46 2.9 Interference and the noise floor 47 2.10 Summary 48 3 The effect of obstacles 50 3.1 Knife-edge diffraction 50 3.1.1 Huygens’ principle and the Cornu spiral 53 3.2 Clearance requirements 61 3.3 A resume of the assumptions and approximations 62 3.4 Diffraction through an aperture 62 3.5 Reflection from a finite surface 64 3.6 Antenna radiation patterns 67 3.6.1 The radiation pattern of an aperture antenna 67 3.7 Multiple diffracting edges 70 3.7.1 Comparison of methods 71 3.8 Diffraction by practical obstacles 78 3.9 The GTD/UTD 78 3.10 Clearance requirements and Fresnel zones 79 3.11 Summary 81 4 Reflection, scatter and penetration 83 4.1 Introduction 83 4.2 Standing wave patterns 85 4.3 Determining reflection coefficients 90 4.4 Propagation over a flat plane 92 contents vii 4.5 Propagation over water 95 4.6 Rayleigh and Rician multipath environments 98 4.7 Reflections from rough surfaces 101 4.8 Penetration of materials 106 4.9 Summary 108 5 Estimating the received signal strength in complex environments 110 5.1 Aggregating multiple contributions 110 6 Atmospheric effects 116 6.1 Multipath propagation in the atmosphere 116 6.2 Ducting 117 6.3 The k-factor and the standard atmosphere 118 6.4 Anomalous propagation and multipath fading 120 6.5 Diversity techniques 125 6.5.1 Space diversity 126 6.5.2 Frequency diversity 127 6.5.3 Angle diversity 129 6.5.4 Polarisation diversity 129 6.5.5 Summary of diversity on fixed links 129 6.5.6 Diversity in mobile communications 130 6.6 Diffraction fading 130 6.7 Selective fading in long-distance, high-capacity microwave links 132 6.8 Ducting and interference in point-to-area systems 135 6.9 Rain attenuation 138 6.10 Atmospheric absorption 141 6.11 Atmospheric effects and Earth–space links 142 6.12 Noise and temperature effects 145 6.12.1 Noise calculations on Earth–space systems 146 6.13 Summary 148 viii contents 7 System design and interference management 150 7.1 Determining the most appropriate frequencies for specific services 150 7.2 System design 152 7.2.1 Terrestrial point-to-point system design 153 7.2.2 Broadcast systems 163 7.2.3 Earth–space systems 166 7.2.4 In-building systems 170 7.3 Summary 171 8 Software-based tools 172 8.1 Software tools for management of fixed-links networks 172 8.2 Planning tools for public mobile networks 174 8.3 Mitigating against uncertainties 176 8.3.1 Statistical methods 176 8.4 Summary 181 9 Summary 182 Appendix 1 The decibel scale 185 Appendix 2 Phasor arithmetic and phasor diagrams 188 Appendix 3 Formula sheet 191 Appendix 4 Explanation of the link budget 195 Further reading 196 References 197 Recommendations of the Radiocommunication Bureau of the International Telecommunications Union (ITU), Geneva 198 Author’s biography 199 Index 200 Preface The objective of this book is to allow the reader to predict the received signal power produced by a particular radio transmitter. The first two chapters examine propagation in free space for point-to-point and point-to-area transmission, respectively. This is combined with a discussion regarding the characteristics of antennas for various purposes. In chapter 3, the effect of obstacles, whether buildings or mountains, is discussed and analytical methods, whereby the strength of a signal is the shadow of an obstacle can be predicted, are presented. The following chapter investigates the nature of reflections and the effect that reflections have on the nature of a received signal. Chapter 5 shows how the level of a received signal can be predicted considering all propagation mechanisms. The many effects on a radio wave that are caused by precipitation and the structure of the atmosphere are explained in chapter 6. Chapter 7 demonstrates how knowledge gained can be used to design point-to-point radio links, broadcast systems, Earth–space systems and in-building systems. In chapter 8, the value of software tools in the planning of various radio networks is explained. ix Acknowledgements I believe that understanding of a topic such as radio wave propagation seeps in over the years rather than being something that can be accumulated rapidly. This is always facilitated by discussion and debate with others in the field. For such discussion and debate I am particularly indebted to David Bacon, Les Barclay, Ken Craig, Martin Hall, Malcolm Hamer, Tim Hewitt, Mireille Levy, John Pahl, James Richardson, Richard Rudd, Mike Willis and Charles Wrench. xi 1 Propagation in free space and the aperture antenna This chapter introduces the basic concepts of radio signals travelling from one antenna to another. The aperture antenna is used initially to illustrate this, being the easiest concept to understand. The vital equations that underpin the day-to-day lives of propagation engineers are introduced. Although this chapter is introductory in nature, practical examples are covered. The approach adopted is to deliver the material, together with the most significant equations, in a simplified manner in the first two subsections before providing more detail. Following this, the focus is on developing methods of predicting the received signal power on point-to-point links given vital information such as path length, frequency, antenna sizes and transmit power.

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