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1、Understanding Cellular Radio Understanding Cellular Radio William Webb Artech House Boston London Library of Congress Cataloging-in-Publication Data Webb, William, Dr. Understanding cellular radio / William Webb. p.cm. (Artech House mobile communications library) Includes bibliographical references
2、and index. ISBN 0-89006-994-8 (alk. paper) 1. Cellular radio.I. Title.II. Series. TK6570.M6W431998 621.38456dc2198-2921 CIP British Library Cataloguing in Publication Data Webb, William Understanding cellular radio(Artech House mobile communications library) 1. Cellular radio I. Title 621.38456 ISBN
3、 0-89006-994-8 Cover illustration by Eli Cedrone 1998 ARTECH HOUSE, INC. 685 Canton Street Norwood, MA 02062 All rights reserved. Printed and bound in the United States of America. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, in- cluding p
4、hotocopying, recording, or by any information storage and retrieval system, with- out permission in writing from the publisher. All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. Artech House cannot attest to the accuracy of this in
5、forma- tion. Use of a term in this book should not be regarded as affecting the validity of any trade- mark or service mark. International Standard Book Number: 0-89006-994-8 Library of Congress Catalog Card Number: 98-2921 10 9 8 7 6 5 4 3 2 1 Contents Prefacexi Objectivesxi Acknowledgmentsxii Part
6、 IWireless Communications Systems1 1Introduction3 1.1Why a book simply explaining technical aspects?3 1.2Scope of material covered4 1.3Acronyms, abbreviations, and other ways to make it 1.3complicated4 1.4How to read this book5 1.5Further reading6 v 2Overview of a Cellular System7 2.1Introduction7 2
7、.2Why it is called cellular?7 2.3System overview9 3Basic Cellular System Design21 3.1Introduction21 3.2The scarcity of radio spectrum22 3.3The use of cells as a means to conserve spectrum27 3.4Why one channel can serve many users31 3.5Basic network design principles35 3.6Connecting up the network41
8、3.6.1Leased link42 3.6.2Microwave links43 3.6.3Satellite links46 Part IIGetting Calls to Moving Subscribers49 4Keeping Track of Where the Users Are51 4.1Introduction51 4.2The concept of location areas51 4.3Attach and detach53 4.4Periodic location updating54 4.5The mobile in a call55 5How Calls are M
9、ade Between Two Users57 5.1Introduction57 5.2Paging57 5.3Responding to a paging message59 6Hand-off69 6.1The mobile in a call69 6.2Handing the mobile to another cell69 viUnderstanding Cellular Radio 6.3Cell selection in idle mode71 7Network Management, Roaming, and Authentication73 7.1Network manage
10、ment73 7.1.1Monitoring the correct working of the network74 7.1.2Delivering network statistics74 7.1.3Changing network configuration75 7.1.4Adding and deleting subscribers75 7.1.5Generating bills76 7.1.6Monitoring fraud77 7.1.7Providing customer care77 7.2International roaming78 7.3Authentication an
11、d ciphering79 7.4Call routing82 Part IIITransmitting the Signal85 8Radio Propagation87 8.1Introduction87 8.1.1Distance-related attenuation89 8.1.2Slow fading91 8.1.3Fast fading91 8.2Wideband channels94 8.3Predicting cellular coverage95 8.4Sectorization96 8.5Microcells and underlay/overlay networks98
12、 9Radio Systems101 9.1From speech to radio waves101 9.2Speech coding102 9.3Error correction coding and interleaving106 9.4Interleaving110 9.5Modulation111 Contentsvii 9.6Frequency hopping112 9.6.1Overcoming fading112 9.6.2Reducing interference114 9.7Equalization116 9.8Multiple access118 9.8.1FDMA120
13、 9.8.2TDMA121 9.8.3CDMA123 9.8.4CDMA power control132 9.9Packet and circuit switching133 10TDMA or CDMA137 10.1Introduction to the debate137 10.2A more general look at CDMA versus TDMA138 10.2.1Division of the frequencies140 10.2.2Distributing the interference140 10.2.3Making TDMA interference more
14、even141 10.3Comparison of advantages and disadvantages142 10.3.1Capacity142 10.3.2Greater range143 10.3.3Sectorization143 10.3.4No frequency planning145 10.3.5Macrocell/microcell145 10.3.6Risk147 10.3.7Cost147 10.3.8Bandwidth flexibility147 10.3.9Frequency hopping versus direct sequence147 10.4Summa
15、ry148 Part IVSpecific Radio Systems151 11Cellular Systems153 11.1The difference between analog and digital cellular153 viiiUnderstanding Cellular Radio 11.2Cellular systems in overview155 11.3GSM160 11.3.1Framing format160 11.3.2How mobiles measure adjacent cells174 11.3.3Numbering scheme175 11.3.4S
16、pectrum efficiency176 11.4CDMAone177 11.4.1Soft hand-off181 12Cordless Systems183 12.1Overview of cordless183 12.2DECT185 12.3PHS187 13Overview of Wireless Local Loop Systems191 13.1Introduction191 13.2Access technologies194 13.3The attraction of WLL systems197 13.4Current status of WLL200 13.5The d
17、ifferences between WLL and cellular201 13.6WLL propagation201 13.6.1Fast fading203 13.6.2New obstructions204 13.6.3Rainfall204 14WLL Technologies207 14.1Introduction207 14.2The Lucent AirLoop WLL system208 14.2.1Local exchange (termed a switch in GSM)211 14.2.2CATU (termed a base station controller
18、in GSM)211 14.2.3CTRU (termed a base station in GSM)212 14.2.4The subscriber unit (mobile in GSM)212 14.3DECT as a WLL technology212 Contentsix 15The Future of WLL217 15.1Introduction217 15.2Technical advances in WLL218 15.3Technical advances in other access techniques219 15.4Changing user demand220
19、 15.5Predictions for WLL222 16Satellite Systems225 16.1Why use satellites?225 16.2How satellite systems work226 16.3Will satellite systems be successful?227 17The Future of Cellular231 17.1What could be better than current systems?231 17.2The third-generation ideal232 17.2.1GSM evolution235 17.3Mobi
20、le/fixed convergence237 17.4The longer term future238 Bibliography241 Model Answers247 Glossary257 About The Author271 Index273 xUnderstanding Cellular Radio Preface Objectives As I have increasingly moved away from the world of research and into thatofmanagementandbusiness,ithasbecomeapparenttometh
21、atthere are many people from a nontechnical background who need to under- standcellularsystemsinmoredetailinordertobeabletoperformtheir job,beitanalyzingfinancialinvestments,runningcallcenters,ormarket- ing cellular services. The problem is that cellular and wireless local loop systems have become i
22、ncreasingly complex over the years and under- standingthesesystemsisbecomingdifficultevenforengineers.Indeed,I doubt whether there is anyone in the world who can really claim to understandfullyallthepartsoftheGlobalSystemforMobileCommunications (GSM)indetailsomewillbeexpertsinspeechcoders,othersiner
23、ror correctors, security algorithms, or network protocols. The complexity of these systems, coupled with the dramatic growth of cellular and the resultant influx of people into the industry, has resulted in increasingly xi frustratedindividualsseekingtobetterunderstandthesesystemsandhas spawned a pl
24、ethora of training courses. Unfortunately, these courses often do little to help. Those performing the training are themselves sometimes ill-informed about cellular radio design and simply pass on inaccuracies to their class. Givingtrainingcoursesmyselfandinteractingwiththenontechnical staffdaily,th
25、isstateofaffairsbecamecleartome.Inansweringtheques- tions raised during these exchanges, it became apparent that I could do much to inform these nontechnical individuals about wireless and, par- ticularly,cellulartechnology.Theresultofthesetrainingcoursesanddis- cussions is this book. I hope that it
26、 helps you understand cellular radio. Acknowledgments I would not have been in a position to write this had it not been for ProfessorRaymondSteele,whotaughtmemostofwhatIknowaboutthe world of cellular radio and ensured, with his annotations of “NCE” (meaning“notclearly explained”) across my early tex
27、ts, that my writing style developed into one suitable for such a book. This book has also becomeamuchmorereadableoneasaresultofthosenontechnicalindi- viduals who acted as reviewers to ensure that I had not left any concepts insufficiently explained. Key amongst these were my wife, Alison, and my bro
28、ther, Matthew, who ensured that the book was approachable. I suspect that there are not many technical books where close family have played such an interactive role! xiiUnderstanding Cellular Radio Part I Wireless Communications Systems 1 Introduction 1.1Why a book simply explaining technical aspect
29、s? Therearemanyexcellentbookscoveringcellularradioandtelecommu- nications systems, ranging from introductory texts through to detailed descriptions of esoteric parts of cellular radio networks. However, all these books are written primarily for engineers or for students studying mathematicallyrelate
30、ddisciplines.Thereseemstobeanabsenceoftexts explaining the technical aspects of the system without any mathematics andinamannerthatcanbeunderstoodbythosewithnopreviousexpo- suretoengineeringconcepts.However,thereisanincreasingnumberof peoplewhoworkalongsideengineerswithincellularnetworkswhoneed toun
31、derstandthebasicsofthesystemoperationbutdonotcomefroman engineeringdiscipline.Examplesofsuchpeopleincludemanagers,busi- ness planners, customer service staff, billing and network management experts, and investment analysts. 3 This book has been written for these nonengineers. It assumes that theread
32、erdoesnothaveaknowledgeofengineeringtermssuchasdeci- bels and megabytes per second and explains such terms carefully before usingthem.Ituseseachchapterasabuildingblockonwhichthematerial covered in subsequent chapters can be based, taking the reader from a low-levelunderstandingtothepointwheretheyare
33、familiarwithallthe key building blocks in the system. 1.2Scope of material covered This book covers cellular radio and related systems such as Wireless Local Loop (WLL), satellite, and cordless. Most readers will be interested mainlyinthecellularaspectsandmayseetheothersystemsasanunneces- saryadditi
34、on.However,anunderstandingoftheserelatedsystemshelps toexplainsomeofthekeyaspectsofthedesignofcellularandthechanges likely in cellular systems in the future. Inevitably,inatextexplainingconceptssimplytononengineers,the depth of the content will not be as great as would be the case in some of the oth
35、er books available on cellular radio. However, surprisingly little has been lost in the “simplification” process and, with the exception of someofthehighlydetailedengineeringaspectsofthesystem,thereader whomakesittotheendshouldhaveasgoodanunderstandingofcellular as many of the cellular engineers pra
36、cticing today. Inordertoenlightenthediscussion,exampleshavebeenusedwher- ever possible. In most cases these examples have been taken from the GSMcellularsystemoneofthemostsuccessfulcellularsystemsatthe moment. 1.3Acronyms, abbreviations, and other ways to make it complicated Alltechnicalareasaboundw
37、ithacronyms.Theyarenecessarytoshorten thespaceittakestowritecomplicateddescriptionsandtomakeconver- sation easier. However, they also have the effect of making the area impenetrable to those not well versed in the technology. Wherever an acronym is introduced, the unabbreviated text will always be p
38、rovided 4Understanding Cellular Radio before the acronym. Thereafter, the acronym will be used consistently. Ofcourse,thereisadetailedglossaryatthebackofthebookthatprovides anexplanationofwhateachofthetermsmeans,shouldyoufeellikeyou are getting lost at any point. 1.4How to read this book Thisbookhas
39、beendividedintofourpartsinordertostructuretheinfor- mation more clearly. The contents of each of the different parts is as follows. Part One. Wireless communications systemsThis part provides an over- view of what complete cellular systems look like and provides details of whytheyarestructuredinthis
40、manner.Itfinisheswithanexplanationof thebasicdesignofacompletecellularsystem.Bytheendofthispart,the reader should understand the key building blocks of the cellular system, their function, and the basic reasons for their design. Part Two. Getting calls to moving subscribersThispartlooksatthewayin wh
41、ichthemobileradiosystemknowswherethesubscribersare,isableto get calls sent to them, and is able to maintain the communications even when the subscriber moves around. Much of the design of a cellular sys- tem is based around coping with subscriber mobility; hence, an under- standing of this part help
42、s the reader understand much of the cellular architecture. Part Three. Transmitting the signalThis part moves into the techniques usedtoensurethattheradiosignaltravelssuccessfullyfromthetransmit- ter to the receiver. In this part reside all the detailed areas of processing the transmitted and receiv
43、ed signal that are necessary in modern radio systems. Part Four. Specific radio systemsThis part looks at a few key radio sys- tems currently in use, explaining their design, their differences, and whichradiosystemsareusedinwhichsituations.Thispartcoversthecel- lulartechnologies,thecordlesstechnolog
44、ies,WLLsystemsindetail,and Introduction5 the emerging satellite personal communications systems. It concludes with a look at next-generation cellular systems. Thisbookisdesignedtobereadfromstarttofinish.Asnewconcepts andtechniquesareencountered,theyareexplainedcarefully,butthere- after,usedinthesame
45、mannerasanengineerwouldusetheterms.Ifthe readerhasnotreadtheearlychapters,thensomeofthetermsinthelater chaptersmaynotbeclear.Noteveryonewantstoreadabookfromendto end, so to assist those who want to read particular parts, key concepts havebeenintroducedinboxedsections,sittingasidefromthemaintext. The
46、seboxesarereferencedintheglossary.Hence,readerswhoonlylook at particular parts should look in the index or glossary if there are any unfamiliar terms in order to find an explanation. Becausethebookhasbeendesignedtobereadfromstarttofinish,it has deliberately been kept relatively short and approachabl
47、e. Once you haveunderstoodthisbook,youwillbewellplacedtotacklethemyriadof more detailed engineering texts on cellular that are available. Questions have been provided at the end of each section, and model answers are available at the rear of the book. The questions cover the materialofthechapteranda
48、redesignedtohelpreadersassurethemselves of their grasp of the important points in the chapter. 1.5Further reading This book is only the starting point in gaining an understanding of the complex and multifaceted world of mobile radio systems. There are hundredsofotherbooksavailablethatdescribeparticu
49、laraspectsinmore detail.Tocataloguethemallwouldbealongtaskthatwouldbesoonout- dated.Instead,attheendofthebook,alistofsomeofthebestreference workswithdetailsoftheirlevelofcomplexityandrelevanceisprovided. 6Understanding Cellular Radio 2 Overview of a Cellular System 2.1Introduction This chapter gives you a first look at a cellular radio telephone system. From now on, these systems will be known simply as cellular. It focuses on a complete cellular system while subsequent chapters of the book examinethecontentsofeachoftheboxesinincreasingdetail,helpingyou understandwhythesystemisputt