Essentials of Radio Wave Propagation

Transcription

1 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.

2 The Cambridge Wireless Essentials Series Series Editors william webb, Ofcom, UK sudhir dixit, Nokia, US Aseries of concise, practical guides for wireless industry professionals. Martin Cave, Chris Doyle and William Webb, Essentials of Modern Spectrum Management, 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

3 Essentials of Radio Wave Propagation Ofcom, UK

4 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 Information on this title: ª Cambridge University Press 2008 This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 2008 Printed in the United Kingdom at the University Press, Cambridge A catalogue record for this publication is available from the British Library ISBN 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.

5 Contents Preface Acknowledgements page ix xi 1 Propagation in free space and the aperture antenna Propagation in free space: simplified explanation The aperture antenna: simplified explanation Further details and calculations Point-to-point transmission Transmitting, directing and capturing power Transmission loss between practical antennas Determining the power required Example calculations Equivalent isotropic radiated power (EIRP) Near-field effects: simplified explanation Further detail on the near-field issue Polarisation Summary 25 2 Point-to-area transmission Overview Power density and electric field strength Converting from field strength to received signal power Predicting the field strength at a distance The effect of frequency 33 v

6 vi contents 2.6 Prediction methods for digital mobile communication The Okumura Hata model Comparison between propagation at 900 MHz and propagation at 1800 MHz Base-station antennas Sectored antennas Mobile-station antennas Interference and the noise floor Summary 48 3 The effect of obstacles Knife-edge diffraction Huygens principle and the Cornu spiral Clearance requirements Aresume of the assumptions and approximations Diffraction through an aperture Reflection from a finite surface Antenna radiation patterns The radiation pattern of an aperture antenna Multiple diffracting edges Comparison of methods Diffraction by practical obstacles The GTD/UTD Clearance requirements and Fresnel zones Summary 81 4 Reflection, scatter and penetration Introduction Standing wave patterns Determining reflection coefficients Propagation over a flat plane 92

7 contents vii 4.5 Propagation over water Rayleigh and Rician multipath environments Reflections from rough surfaces Penetration of materials Summary Estimating the received signal strength in complex environments Aggregating multiple contributions Atmospheric effects Multipath propagation in the atmosphere Ducting The k-factor and the standard atmosphere Anomalous propagation and multipath fading Diversity techniques Space diversity Frequency diversity Angle diversity Polarisation diversity Summary of diversity on fixed links Diversity in mobile communications Diffraction fading Selective fading in long-distance, high-capacity microwave links Ducting and interference in point-to-area systems Rain attenuation Atmospheric absorption Atmospheric effects and Earth space links Noise and temperature effects Noise calculations on Earth space systems Summary 148

8 viii contents 7 System design and interference management Determining the most appropriate frequencies for specific services System design Terrestrial point-to-point system design Broadcast systems Earth space systems In-building systems Summary Software-based tools Software tools for management of fixed-links networks Planning tools for public mobile networks Mitigating against uncertainties Statistical methods Summary 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

9 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

10 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