radio txmission and network planning

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Radio Transmission Network and Frequency Planning

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1. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNINGLZB 1110162 Ericsson Radio Systems AB 1999 This book is a training document and containssimplifications. The contents are subject to revision without notice. Ericsson assumes nolegal responsibility for any error or damage resulting from the usage of this document.All rights reserved. Regardless of the purpose, no parts of this publication may bereproduced or utilized in any form or by any means, whether electronic or mechanical,including photocopying and microfilm,without the expressed written permission ofEricsson Radio Systems AB.LZB 111 0162

2. INTRODUCTION 1RUBRIKFRTECKNINGLIST OF HEADINGS RADIO-RELAY TRANSMISSION OVERVIEW 2Dokumentnr - Document no.001 51-LZB 1110162 RADIO COMMUNICATION SYSTEM 3Datum - Date Rev COMPONENTS1999-10-28 A RADIOWAVE PROPAGATION 4 THE INTERNATIONAL

TELECOMMUNICATION 5 UNION (ITU) QUALITY AND AVAILABILITYTARGETS 6 RADIO REGULATIONS 7 THE RADIO SPECTRUM AND CHANNEL 8ARRANGEMENT INTERFERENCE - BASIC CONCEPTS 9 NEAR INTERFERENCE10 FAR INTERFERENCE 11 PATH AND FREQUENCY PLANNING 12 RADIO-RELAY TRANSMISSION - DISCUSSION 13 RADIO TRANSMISSION NETWORKPLANNING - 14 APPLICATION RADIO-METEOROLOGICAL PARAMETERS FOR15 RL-DESIGN

3. INTRODUCTION This chapter provides a general presentation to this trainingdocument, its background and objective. TABLE OF CONTENTSBackground....................................................................................................................................................... 1Objective........................................................................................................................................................... 1Scope of thebook.............................................................................................................................................. 2Notes to the reader............................................................................................................................................4Acknowledgments............................................................................................................................................. 4i

4. INTRODUCTIONBackground Different applications of radio-relay transmission, inparticular, line-of- sight links, have grown considerably since radio-link techniques werecommercially introduced just prior to World War II. The vast number of applications andimplementations of radio-link systems since the 1950s have brought about severefrequency spectrum congestion, forcing the utilization of higher frequencies. In addition,sophisticated radio engineering solutions and the significant changes that have been maderequire a better understanding of radio engineering concepts and their applications. Thisbook is dedicated to improving the understanding of the radio network planning process.It includes a collection of the basic principles, methods, theory and guidelines for radiosystem planning and design that are often essential to the tasks performed by networkplanners and the designers of telecommunications operating organizations. We have


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carefully organized and presented what we believe to be indispensable basic concepts ofradiowave propagation, spectrum management and radio-system design in this RADIOTRANSMISSION NETWORK AND FREQUENCY PLANNING.Objective Thepurpose of this book is to provide essential design techniques for radio-relaytransmission, focusing on the general aspects of point-to- point services operating at

frequencies above 1 GHz. The book treats the basic principles of radiowave propagation,quality and availability targets, frequency aspects, interference and general informationrelated to the ITU organization and its administrative tasks. The book is intended in partor in its entirety, as training documentation for courses in radio transmission networkplanning and related subjects. It is therefore our intention to provide customers withsuggestions and advisory support as to how one starts a network-planning project basedon concrete input data. We aim to describe how radio-links operate, how to use ordimension terminals and their equipment, and how to select the necessary performanceparameters and equipment specifications to meet the needs of specific customers.Ericsson Radio Systems AB 11/038 02-LZU 102 152, Rev A, November 1999

5. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNINGScope ofthe book This book is subdivided and structured into 14 independent chapters. As aconsequence, each chapter functions as a specific guideline. Chapter 1 (this chapter),INTRODUCTION, provides a presentation of the book, its background and objectives.Chapter 2, RADIO-RELAY TRANSMISSION - AN OVERVIEW, presents somegeneral facts about the development of radio-relay transmission since its first commercialapplication in 1934. Chapter 3, RADIO COMMUNICATION SYSTEMCOMPONENTS, describes in some detail the components that make up radiocommunication systems, different traffic setups and possible interference sources andhow they can affect signal transmission. Chapter 4, RADIOWAVE PROPAGATION, apresentation of the basic principles and algorithms related to radiowave propagation usedin radio-relay transmission. Both loss and attenuation algorithms plus fade predictionmodels for different fading mechanisms are thoroughly discussed. The chapter alsoincludes a presentation of the basic concepts of main propagation mechanisms, Fresnelzone, equivalent and true Earth radii and the decibel scale. Chapter 5,INTERNATIONAL TELECOMMUNICATION UNION, describes in detail the ITUorganization and its administrative tasks. This chapter provides valuable information onhow to search and locate important ITU-R and ITU-T reports and recommendations onspecific subjects related to radio-relay transmission. Chapter 6, QUALITY ANDAVAILABILITY TARGETS, provides an extensive description of digital transmissionnetwork models used in error performance analysis and quality and availability targets inaccordance with ITU-T Recommendations G.821 and G.826. The chapter discussesquality and availability parameters, their calculation and their relationships to existingatmospheric fading mechanisms. Chapter 7, RADIO REGULATIONS, describes theITU-R publication Radio Regulations, its publisher, and the contents and the generalstructure of the publication. The primary objective of this chapter is to handle the subjectof Radio Regulations in connection with the use of frequencies for fixed terrestrial radio-links.2 Ericsson Radio Systems AB 1/038 02-LZU 102 152, Rev A, November 1999

6. INTRODUCTION Chapter 8, FREQUENCY SPECTRUM AND CHANNELALLOCATION, provides an introduction to the radio spectrum by pointing out some ofusual apprehensions concerning its limitations and crowding. In addition, the chapter also


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presents an introduction to radio- frequency channel arrangements, frequency economyand finally, it provides a complete list on channel arrangements for radio-relay systems inthe range 1.5 to 55 GHz. Chapter 9, INTERFERENCE - BASIC CONCEPTS, provides adetailed discussion of the different types of interference sources and their effects onradio-relay equipment. The location of several radio systems to the same site is also

discussed in some detail. In Chapter 10, NEAR INTERFERENCE, includes a discussionof the basic principles and definitions used in the calculation of near interference; somealgorithms are also provided. A presentation of intermodulation at the receiver andtransmitter includes some examples of intermodulation products. Chapter 11, FARINTERFERENCE, provides basic concepts and definitions used in the calculation of farinterference. A typical performance diagram and interference scenariois discussed. Thecalculation of the contributions of the individual interference signal levels, plus theresulting interference level at one receiver and threshold degradation. Chapter 12, PATHAND FREQUENCY PLANNING, covers some of the issues that may arise concerningpath profile, line-of-sight requirements, input signals and their variation, diversity,reflections and frequency planning. In addition, surveying possible radio-link paths and

site requirements are discussed. Chapter 13, RADIO-RELAY TRANSMISSION -DISCUSSION, the primary objective of this chapter is to encourage a discussion onspecific and general subjects of interest in transmission network planning, for instance,practices versus theory, current trends in today worlds market that affect radio-relaytransmission, personal experience and future prospects for radio-relay technology.Chapter 14, NETWORK PLANNING - APPLICATION, is to be customized andadjusted to specific applications. Instructions and guidelines are provided on how toselect the necessary performance parameters and equipment specifications to meet theneeds of specific customers. Ericsson Radio Systems AB 31/038 02-LZU 102 152, RevA, November 1999

7. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNINGNotes to thereader The contents treated in this book are subject to changes due to continueddevelopment in methodology and design. Furthermore, network planning is in someaspects strongly dependent on ITU recommendations, which are continuously the subjectof corrections, additions and improvements. Therefore, it is strongly recommended thatreaders are aware of ongoing ITU Study Group activities. References to some sources ofthe material used in each chapter are given in the last section of thatchapter.Acknowledgments Thanks to Malin Strm and Christer Lehman who patientlydrew most of the figures in this book. Thanks to Inger Meltzer for her kind assistancewith the layout of the front cover. The authors are very grateful to any comments andsuggestions that may improve the content of this book.4 Ericsson Radio Systems AB1/038 02-LZU 102 152, Rev A, November 1999

8. RADIO-RELAY TRANSMISSION OVERVIEW This chapter contains an overviewof radio-relay transmission with a brief review. In addition, it provides a summary onsuitable applications and describes the general aspects and advantages of networkplanning. The prediction cycle along its activity blocks employed in radio transmissionplanning is presented. TABLE OF CONTENTSTransmissionoptions......................................................................................................................................... 1Introduction............................................................................................................................


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............. 1 Radio links versus cable links

............................................................................................................. 1 Radio-relaytransmission - advantages ................................................................................................ 2Transmission - capacity and covereddistance..................................................................................... 2 Radio-relay transmission

- suitability .................................................................................................. 3The beginningof the radio-relay transmission era............................................................................................ 4The digitalizationera.........................................................................................................................................4Synchronous Digital Hierarchy(SDH).............................................................................................................. 4What isradio-network planning?...................................................................................................................... 5The trinityprinciple of networkplanning.......................................................................................................... 6Theprediction cycle

..........................................................................................................................................7References

................................................................................................................................................

......... 8 i 9. RADIO-RELAY TRANSMISSION - AN OVERVIEWTransmission

optionsIntroduction Transmission is generally made possible by employing the followingthree major media: optical-fiber cables copper coaxial cables radio-relay Anotheravailable transmission option is the use of satellite links, which are more appropriate,than the use of ordinary terrestrial radio-relay and cable, in such applications as long-haulroutes in international networks that do not require extremely high transmissioncapacity.Radio links versus cable links Radio-links exhibit many advantages incomparison to fiber-optic links, for example: cost-effective transmission links ininaccessible terrain and difficult environments the quick coverage of large areas by newoperators higher security due to the fact that equipment can be physically concentratedRadio-relay transmission is therefore a very attractive alternative for applications rangingfrom the coverage of the rural, sparsely populated areas, of developing countries havingineffective or minimal infrastructures to the well-developed industrial countries thatrequire expansion of their telecommunications networks. Ericsson Radio Systems AB12/038/ 02-LZU 102 158, Rev A, November 1999

10. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNINGRadio-relay transmission - advantages Considering the three transmission media mentionedabove, radio-relay transmission is the most suitable option for networks that are locatedin areas of difficult terrain topography or where other limitations are imposed on the useof optical fiber and/or copper coaxial cables. Generally speaking, radio-relaytransmission is most suitable in the following applications: long-haul routes for nationaland international networks covering areas of difficult terrain topography nationalnetworks containing radio-relay in parallel with optical fiber backbone routes urbanaccess routes connecting interurban optical-fiber cable routes and in-town terminalstations rapid geographical changes of station location as a consequence of catastrophicor emergency situations short-term projects access links from cellular to public


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networks cellular transmission networks radio in the local loop point-to-multipointoperation It is possible to combine the different applications presented above, thusmaking radio-relay transmission a very competitive optionboth technically andeconomically.Transmission - capacity and covered distance Figure 1 is a roughillustration of the possible transmission options as a function of the different ranges of

transmission capacity (Mbit/s) and distance (km). Except for some overlapping, thefigure clearly shows that the transmission options are complementary, while at the sametime, each option exhibits its own domain of optimal cost effectiveness.2 EricssonRadio Systems AB 02/038 02-LZU 102 152, Rev A, November 1999

11. RADIO-RELAY TRANSMISSION - AN OVERVIEW Capacity, Mbit/s thousandsOptical fiber hundreds Radio-relay point-to-point Satellites Fiber in the loop tens point-to-multipo int tens hundreds thousands Distance, km Figure 1: Transmission options fordifferent capacities and covered distances.Radio-relay transmission - suitability Table 1illustrates the different aspects of radio-relay transmission and the corresponding suitableconditions. Subject Suitable conditions for radio-relay transmission Transmissioncapacity Low, medium and high (not very high) Routes Short and medium (not very

long) Terrain topography Inaccessible terrain (not over water) Infrastructure None orhardly existing Project implementation Short time Initial operation High initialinvestment Coverage Continental rural and urban Special operation Emergency useDamaging intention Easy to protect important sites (nodes) Availability Very high (ifrequired) Table 1: Suitable conditions for radio-relay transmission. Ericsson RadioSystems AB 32/038/ 02-LZU 102 158, Rev A, November 1999

12. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNINGThebeginning of the radio-relay transmission era The worlds first commercial radio-relaylink was put into operation in 1934 after intensive preliminary attempts that were startedin 1931, in Paris, at the Laboratories Central des Tlcommunications, a subsidiary of theformer International Telephone and Telegraph Corporation, the former IT&T. It consistedof a 56 km radio-relay path across the English Channel between Calais (France) andDover (England), amplitude modulated (AM), using a klystron that generated 1 W RFoutput power and operating at 1.7 GHz. The hardware technology was provided by twomanufactures: the British company Standard Telephones and Cables (now a part ofNorthern Telecom) and the French company Le Matriel Tlphonique (now integratedinto Alcatel Telspace).The digitalization era Integrated semiconductor technology starteda new era in radio telecommunication. Optical fiber was not available for transmissionlate in 60s and early 70s. Digital transmission on coaxial cable was too expensive(repeaters at extremely short intervals) and slowly implemented for relatively longtelecommunication routes. Thus, low- cost semiconductor technology in the beginning ofthe 70s was therefore the start of a new telecommunications era. Digital transmission hasseveral advantages compared to analog transmission: Up to a certain threshold limit, thereceived signal can be restored to its original shape irrespective of the signal-to-noiseratio (SNR), thus enabling a large, almost unlimited number of repeaters. Radio-relaytransmission at high frequencies (10 GHz) The worlds first digital radio-relay link was a17 Mbit/s unit that was placed into operation in Japan, in 1969. It provided 240 telephonechannels in the 2 GHz frequency band.Synchronous Digital Hierarchy (SDH) SDH linkshave become the international standard for the expansion of telecommunication networkinfrastructures. Radio-relay transmission, and in particular microwave links have begun


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to be adapted to the SDH data format and a good number of ITU-T recommendations arenow available. These recommendations represent general directives aimed at ensuringthat radio systems are designed so that they conform to SDH interface specifications.4 Ericsson Radio Systems AB 02/038 02-LZU 102 152, Rev A, November 1999

13. RADIO-RELAY TRANSMISSION - AN OVERVIEW SDH provides some keybenefits in comparison with Plesiochronous Digital Hierarchy (PDH): Highertransmissions speeds are defined. Direct multiplexing is possible without intermediatemultiplexing stages. This is accomplished through the use of pointers in the multiplexingoverhead that directly identify the position of the payload. The SDH overhead supportsan effective network management, control over the traffic, network status etc. The SDHprotocol is able to handle both the European standard and American standard payloads.SDH technology will, for the next 20-30 years, offer a standardized method for theworldwide transmission of all types of data traffic for both existing and future datatransmission systems.What is radio-network planning? Network planning can be a quitecomplicated and time-consuming task. The degree of difficulty is a function of that whichis to be included in the task. For instance, the task may include initial planning plus an

overview of the entire network, frequency planning, site survey, path analysis,installation and tests. Network operational requirements may also constitute a crucialfactor in the planning process. Regardless the degree of difficulty, it will always be aniterative process! Generally speaking, the initial design of a radio-link is performed infour steps: Initial planning and site selection Topographical analysis Preliminarypath and frequency planning analysis Site survey Network planning as a multi-taskprocess is illustrated inFigure 2. Ericsson Radio Systems AB 52/038/ 02-LZU 102 158,Rev A, November 1999

14. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNINGNETWORK PLANNING Quality and Availability Network Management PredictionNetwork Traffic Radiowave Interference Status Demand Propagation Analysis Figure 2:Overview of network planning.The trinity principle of network planning The iterative,multi-task, process of network planning is controlled by three important factors: availability, currently expressed as a fraction of time quality, currently expressed in bi t-error ratio (BER) for digital links cost, expressed in the actual currency These threefactors constitute the basic body of network planning. The multi-task process, along withall of the possible items, is in some way related to these three factors, seeFigure 3. In fact,they are the parametersthat are usually supplied by the customer. The answer is alreadyknown before starting the network planning process!6 Ericsson Radio Systems AB02/038 02-LZU 102 152, Rev A, November 1999

15. RADIO-RELAY TRANSMISSION - AN OVERVIEW $ Costs 1 Coordination 9 Sitelayout 2 Flight-path obstacle 10 Near interference 3 Road requirements 11 Equipmentdata 4 Path length 12 Power supply requirements 5 Protective measures 13 Capacity 6Far interference 14 Obstacles 7 Interception risk 15 Terrain 8 Frequency aspects 16Interference risks 2 7 10 12 6 13 9 8 11 16 14 15 3 5 4 1 QUALITY AVAILABILITYBER % of time Figure 3: The trinity principle of network planning.The prediction cycleFigure 4 displays the four main actvity blocks which form the planning process:loss/attenuation, fading, frequency planning and quality and availability. A preliminaryfade margin is calculated in the loss/attenuation block which is used for preliminary fadepredictions in the fading block. If interference is present in the frequency planning block,


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then the threshold degradation is included in the fade margin. The updated fade marginwill become the effective fade margin and employed in the fading predictions. The resultsin the loss/attenuation and fading blocks will form the necessary input to the quality andavailability block. Ericsson Radio Systems AB 72/038/ 02-LZU 102 158, Rev A,November 1999

16. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNINGLoss/attenuation Fading Rain attenuation Diffraction-refraction loss Free-space andObstacle and Gas attenuation Reflections loss + Multipath propagation Always presentPredictable and predictable if present Not always present but statistically predictable Linkbudget Fading prediction Predictable Frequency if present Quality & AvailabilityPlanning Interference Figure 4: The prediction cycle.References Test av nyagenerationens SDH-radiont (in Swedish), Elektronik i Norden, 46, vol. 6,1997. Radio-Relay Systems, Huurdeman, A. A., Artech House,1995. Radio-System Design forTelecommunications (1-100 GHz), Freeman, R. L., 1987.8 Ericsson Radio SystemsAB 02/038 02-LZU 102 152, Rev A, November 1999

17. RADIO COMMUNICATION SYSTEM COMPONENTS This chapter deals with thecomponents that make up radio communication systems, different traffic setups andpossible interference sources and how they can affect signal transmission. TABLE OFCONTENTSIntroduction....................................................................................................................................................... 1Radio communication systems.......................................................................................................................... 1 Thetransmitter.................................................................................................................................... 3 Thereceiver......................................................................................................................................... 3 The antenna......................................................................................................................................... 4Feeder cabling..................................................................................................................................... 4Antenna coupling unit......................................................................................................................... 4 Frequencyand bandwidth....................................................................................................................4Traffic setup...................................................................................................................................................... 5 Simplex...............................................................................................................................................5 Two-frequencysimplex....................................................................................................................... 5Duplex................................................................................................................................................. 6Transmitter........................................................................................................................................................ 8Receiver............................................................................................................................................................ 12 Receiver characteristicdata................................................................................................................. 13Sensitivity..............................................................................................................................13 Sensitivity to co-channel Interference


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................................................................................... 15 Adjacent channelselection.................................................................................................... 16 Blocking level....................................................................................................................... 18Intermodulation level ............................................................................................................20Feeder cabling

................................................................................................................................................... 21 Coaxialcable.......................................................................................................................................21 Waveguides.........................................................................................................................................21Duplexfilters..................................................................................................................................................... 22Transmittercombiners....................................................................................................................................... 22Receivers multicouplers....................................................................................................................................

25Antennas............................................................................................................................................................ 26 Antenna gain for parabolic antennas................................................................................................... 27 Antenna diagram.................................................................................................................................28References......................................................................................................................................................... 30 i

18. RADIO COMMUNICATION SYSTEM COMPONENTSIntroduction The termsystem is nowadays generally used rather broadly. What are systems? One possibledefinition of a system is a set or arrangement of items, so related or connected, as to forman entire unit. Thus a radio system may range from encompassing a simple transceiver, alength of coaxial line and the antenna to which it is connected to, to encompassing acombination of many receivers, transmitters, control and coding apparatus, towers andantennas all assembled into a coordinated functioning complex. An ordinarycommunication system can therefore consist of many system components whose primarytask is the transmission of information-conveying signals to a user. The actualtransmission is transmitted via some sort of transmission medium. Common transmissionmediums are the atmosphere, coax cables or a fiber optical components. This implies thatthe signal carrying the information must assume a suitable form that is fitted to theparticular characteristics of the medium over which it is to be transmitted.Radiocommunication systems A radio communication system utilizes atmosphere aspropagation medium. The signal power of radio waves reduces as a function of distanceas they propagate through space. Radio links transmit directional information from atransmitter to a receiver using electromagnetic waves. Radio link systems are importantexamples of a radio communication system. Radio-link systems operate primarily in thefrequency range between 200 MHz and 60 GHz. Although Radio Regulations allocatesservices in the frequency range up to 275 GHz, it is unusual, for the present, to findcommercial radio-link systems that make use of frequencies higher than 60 GHz. Thefrequencies that are used for radio communications have successively moved upwardsfrom lower to higher frequencies (shorter wavelengths). Back in the early days of radio, it


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was easier to generate carrier frequencies of sufficient power at the lower frequencyspectrum. With the advent of new techniques, it became possible to successively developnew components that have made it possible to use higher and higher frequencies.Ericsson Radio Systems AB 13/038 02-LZU 102 152, Rev A, November 1999

19. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNING Anadditional motive for the use of ever-increasing frequencies for radio communication isthe increased frequency crowding that is taking place in the used and relatively lowfrequency ranges. Frequency crowding increases the risk of interference and presentslimitations in the possibility to transmit large amounts of bandwidth-demandinginformation. This presents a natural need for the utilization of frequency ranges that havenot been utilized earlier (i.e., high frequencies). At its outset, mobile communicationsutilized frequencies in the 30-40 MHz range which then successively increased andpassed 80, 160, 450 MHz, reaching frequencies of around 900 MHz (which is, forexample, used in mobile telephony applications). The range 1700-2500 MHz, used todayby a number of communications systems, will in the near future also be used to providemobile personal telephone services. An advantage of using higher frequencies for

communication is the increase in available bandwidth brought about by the utilization ofthese frequencies. For example, a speech channel depending on modulation scheme willtypically require a bandwidth of 12.5 to 25 kHz meaning that a 1 MHz interval cancontain 40-80 speech channels. It is obvious that there exists many more available 1 MHzintervals in, for example, the 900 or 1800 MHz ranges than in the 30 MHz range. On theother hand, the use of higher frequencies introduces certain difficulties resulting from thefact that a speech channel having a bandwidth of 25 kHz takes up a smaller relativebandwidth at 1800 MHz than it does at 30 MHz. This places much higher demands on theexactness of frequency generation and filtering, so that a channel maintains one and thesame bandwidth while at the same time maintaining sufficient isolation (filtering) to itsadjacent channels. Todays radio links employ frequencies ranging from approx. 200MHz up to 60 GHz. Relatively few speech channels are transmitted over the lower band(below 2 GHz) while the higher bands (above 2 GHz) are used for the simultaneoustransmission of up to 1920 speech channels. In these cases, the links are used for traffichaving high capacity requirements, the highways of the telephony network. The higherfrequencies make it easier to direct radiation between the transmitter and the receiverusing reasonably sized antennas, since the antennas directivity is a function of its size inrelation to the wavelength used. This also contributes to the effective increase in thepossibility to use available channels since they, for a geographical area, are easier toisolate from one another. Radio equipment that is included in radio-link systems may besubdivided into two main groups: mounted on the ground2 Ericsson Radio SystemsAB 3/038 02-LZU 102 152, Rev A, November 1999

20. RADIO COMMUNICATION SYSTEM COMPONENTS mounted on masts Mast-mounted radio equipment comprises, together with an antenna, a relatively compactsystem that has short feeder cabling. Ground- mounted radio equipment, on the otherhand, is generally connected to antennas via longer feeder cabling. Figure 1 provides aschematic illustration of a block diagram for a simplified radio communication system.At each end, the system consists of a transmitter, a receiver and an antenna. Feedercable(s) may also be required, depending on the application. Tx1 Tx2 Rx1 Rx2 Figure 1:Block diagram for a simplified radio communication system.The transmitter The purpose


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of the transmitter is to generate the carrier frequency that is to be used for thecommunication, to modulate this carrier frequency with the desired information andfinally, to amplify the signal so that it attains a sufficiently high power level so that itmay traverse the desired communication distance to the receiver.The receiver Thereceiver amplifies the received signal (which is at this point much weaker than when it

was transmitted), filters out any undesirable signals (interfering signals) that the receiverpicked up and finally, detects the existence of information in the carrier frequency.Ericsson Radio Systems AB 33/038 02-LZU 102 152, Rev A, November 1999

21. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNINGTheantenna The antenna adapts the generated signal to the surrounding environment (to thepropagation medium) and directs the radio waves that are to be transmitted towards thereceiving station. When receiving, the antenna receives the signal from the desireddirection and transfers it to the receiver. Antennas may be built having differentdirectivities, from more or less isotropic antennas (radiate equally in all directions) toantennas that exhibit extremely high directivities.Feeder cabling The purpose of thefeeder cable is to interconnect the antenna with the transmitter/receiver.Antenna coupling

unit The antenna-coupling unit makes it possible to utilize a common antenna for both thetransmitter and receiver. The transmitter and receiver can, for example, be connected toone and the same antenna either via a duplex filter or a transmitter/receiver switch. Theduplex filter prevents the transmitters frequency from blocking the receiver in a T/Rconfiguration. A transmitter/receiver switch disconnects the receiver in a T/Rconfiguration from the antenna when in transmitting mode and thereby prevents anyblockage of the receiver.Frequency and bandwidth A given radio connection isestablished at a specific frequency or radio channel. The available frequency range issubdivided into a number of such radio channels that are assigned bandwidths that reflectthe selected modulation scheme as well as the amount and type of information that is tobe transmitted. For example, a speech channel requires less bandwidth than a TVchannel. In many cases, it may be desirable to transmit many speech channelssimultaneously (multiplexed together) which increases bandwidth requirements. A datachannel can assume different bandwidths as a function of the transmission capacity.4 Ericsson Radio Systems AB 3/038 02-LZU 102 152, Rev A, November 1999

22. RADIO COMMUNICATION SYSTEM COMPONENTSTraffic setupSimplexEmploying the simplest form of radio connection setup, the transmitter and receiveroperate at the same frequency (transmit and receive over the same channel). In otherwords, simplex operation only permits the transmission of signals in either directionalternately. This traffic setup is referred to as simplex, see Figure 2. Simplex traffic wasthe most common setup back in the early days of radio. It is still often used, for example,when communicating via walkie-talkies. Simplex traffic requires good traffic disciplinein order to avoid both ends transmitting at the same time. f1 f1 Tx1 f1 Tx2 f1 T/R T/RRx1 Rx2 f1 f1 T/R = Transmitter/Receiver switch Figure 2: Block diagram of simplextraffic setup.Two-frequency simplex When employing two-frequency simplex, see Figure3, the transmitter and receiver operate over different channels. However, this setup doesnot allow simultaneous reception and transmission since sufficient filtering (usuallyperformed by the duplex filter) does not exist as a rule, and reception may be disturbedby the transmitter in a T/R configuration. Ericsson Radio Systems AB 53/038 02-LZU102 152, Rev A, November 1999


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23. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNING f1 f2 Tx1f2 Tx2 f1 T/R T/R Rx1 Rx2 f2 f1 T/R = Transmitter/Receiver switch Figure 3: Blockdiagram of two-frequency simplex setup. Note that two types of stations have beenintroduced in the case of two- frequency simplex traffic: one having the transmitterfrequency above the receiver frequency and one having the transmitter frequency beneath

the receiver frequency. Communication between such stations requires that the stationsbe of opposite types. In comparison with ordinary simplex, two-frequency simplex hasthe advantage that interference between two base stations is not present if the basestations transmitters are operating in the same duplex band. Frequency re-using is,however, strongly dependent on the mobiles geographical position.Duplex In the case ofduplex traffic, see Figure 4 and Figure 5, transmission and reception occursimultaneously and over separate frequencies (channels) which allows simultaneouscommunication in both directions, between the called and the calling parties, to takeplace. On occasion, so-called semi-duplex is used, in which case one of the stations(usually the fixed station, often referred to as the base station) operates in duplex and themobile station in simplex. Two channels are still used for this communication setup.6

Ericsson Radio Systems AB 3/038 02-LZU 102 152, Rev A, November 1999 24. RADIO COMMUNICATION SYSTEM COMPONENTS Tx1 f2 Tx2 f1 f1 f2Duplexer Duplexer f2 f1 Rx1 Rx2 Figure 4: Duplex traffic with simultaneoustransmission. Base station Mobile terminal Tx1 f2 Tx2 f1 f1 f2 Duplexer T/R f2 f1 Rx1Rx2 T/R = Transmitter/Receiver switch Figure 5: Semi-duplex traffic. The frequencyplan for duplex, see Figure 6, illustrates a duplex band separation between thetransmitting and receiving bands and the duplex spacing between the transmitted and thecorresponding received frequencies. Ericsson Radio Systems AB 73/038 02-LZU 102152, Rev A, November 1999

25. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNING Duplexspacing Tx-band Rx-band f Duplex band separation Figure 6: Frequency plan for duplex.In Figure 6, transmitter frequencies are shown as located in the lower duplex-half andreceiver frequencies in the upper duplex-half. This may be reversed, for example, in thecase of a radio link made up of several hops.Transmitter Figure 7 illustrates a simplifiedblock diagram of a transmitter. It has been assumed that the transmitter is capable oftransmitting digital information, which is usually the case nowadays. LP-filter BP-filter ~~ Modulator ~ ~ Digital ~ To antenna information Frequency generator Crystal Figure 7:Simplified block diagram of a transmitter. The simplified transmitter consists of afrequency generator, a modulator that modulates the digital information over thetransmitters carrier frequency and a power amplifier that amplifies the signal to attain asuitable power level before being sent to the antenna for radiation into the propagationmedium.8 Ericsson Radio Systems AB 3/038 02-LZU 102 152, Rev A, November1999

26. RADIO COMMUNICATION SYSTEM COMPONENTS The digital information ischaracterized by the fact that it only contains discrete levels, for example, binaryinformation (ones and zeroes). If speech is to be transmitted, the analog informationrepresented in the speech must first be digitized by a so-called speech coder. A frequentlyused form of speech coding is Pulse Code Modulation (PCM). A speech channel is thentransmitted as a bit stream having a transmission capacity of 64 kbit/s. The transmissionof speech, digitized to 64 kbit/s, requires a larger bandwidth than the equivalent analog


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speech channel would require. PCM is commonly used in connection with radio links andis used throughout the fixed telephone network (for digital networks). The special speechcoders that are used today for mobile communication provide high quality even at lowerbit speeds, for example, around 10 kbit/s. This facilitates increased frequency economy inthe propagation medium. The digital data stream then modulates the carrier frequency

that is picked up from the frequency generator. A modern frequency generator issynthesized, meaning that the desired frequency or channel is selected digitally, e.g.,from a keypad. A component that is vital to the operation of the frequency generator is astable frequency reference. This is achieved through the use of a crystal oscillator, wherethe crystal is the determining factor in frequency stability. Older equipment is often notfitted with frequency synthesizer functionality, which means that a particular crystal isrequired for each individual channel, i.e., for the particular frequency that is desired. As arule, crystals for such older equipment cannot be ordered until after the frequencyplanning phase has been completed, i.e., not until after the channel has been assigned tothe equipment in question. This must be performed individually for each unit ofequipment in the network, and therefore results in longer implementation lead times. The

transmitted signal is characterized by its center frequency and by a given bandwidtharound the center frequency. This bandwidth is a function of the transmitted information(the transmission capacity of the digital information) and the modulation, for example the3 dB bandwidth, B3 dB. The signal is characterized by its frequency spectrum, i.e., byenergy content as a function of frequency separation from the center frequency, seeFigure 8. Ericsson Radio Systems AB 93/038 02-LZU 102 152, Rev A, November1999

27. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNING It isimportant that the transmitter spectrum is not unnecessarily wide in order to achieveproper isolation to adjacent channels. In order to reduce overtone-like spectrum wideningresulting from modulation, it is common to precede the modulator by a low pass filterthat limits spectrum widening in the vicinity of the center frequency. In the same way, thepower or output stage is followed by a band-pass filter to limit the overtones and noisegenerated in the output power amplifier. The latter filter is often a part of the duplex filterthat facilitates simultaneous transmission and reception. dB 3 dB f0 f B3dB Figure 8:Transmitter spectrum of a modulated carrier. In addition to being a function of the filter,the appearance of the spectrum depends also on the method of modulation. A commonmodulation method is the Phase Shift Keying (PSK). It results in a spectrum that falls offrather slowly. Quadrature Phase Shift Keying (QPSK) is a more effective modulationmethod. This method results in a spectrum having half the width of that generated by thePSK method but otherwise having the same form (it is scaled to half the bandwidth).More modern modulation methods such as Gaussian Filtered Minimum Shift Keying(GMSK) have, in principle, the same effective bandwidth (the band in which the greaterportion of the power is concentrated) as that resulting from QPSK, but with the addedproperty that the spectrum outside of the effective bandwidth falls off significantly faster.This means that this modulation method allows one to pack channels closer togetherwhile still maintaining the same degree of isolation between channels. Modernmodulation methods are very involved in maintaining good frequency economy (efficientchannel packing).10 Ericsson Radio Systems AB 3/038 02-LZU 102 152, Rev A,November 1999


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28. RADIO COMMUNICATION SYSTEM COMPONENTS For larger separationsfrom the carrier frequency, the spectrum is characterized by sideband noise and spurioussignals (unwanted byproducts produced by the transmitter), see Figure 9. The noisespectrum is quantitatively expressed by the power density w (W/Hz), that is, the powerper unity of bandwidth, and normally decreases with larger frequency separation from the

unmodulated carrier. The bandwidth B (Hz) in Figure 9 contains a power which is w

B(W). Unmodulated carrier Sideband noise Frequency B Figure 9: Sideband noise. Thelevel of these spurious products is generally specified by European TelecommunicationsStandards Institute (ETSI) to max. -36 dBm for frequencies below 1 GHz and -30 dBmabove 1 GHz. For special applications there may be other specifications. The sidebandnoise produced by the transmitter, which is also a limiting factor for duplex operation aswell as the localization of different systems to one and the same site, is typically 140 dBbelow the carrier frequency per Hz of bandwidth (-140 dBc/Hz) within approximately 1%frequency separation from the carrier frequency and is -150 dBc/Hz for largerseparations, where the values apply without the use of a radio frequency (RF) filter.Ericsson Radio Systems AB 113/038 02-LZU 102 152, Rev A, November 1999

29. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNINGReceiver ~~ Mixer ~ ~ Detector Demodulator ~ ~ RF-filter Amplifier IF-filter Frequency generatorCrystal Figure 10: Simplified block diagram of a receiver. The weak signal coming fromthe antenna is amplified initially in a radio-frequency amplifier (RF amplifier). Theamplifier is normally preceded by a RF-filter which filters out unwanted signals, i.e.,those of other frequencies than the one desired. Since we are dealing with a high-frequency signal, it is very difficult to effectively filter out signals other than those thatlie at a relatively great separation from the midpoint of the carrier. A mixer follows theRF amplifier, which mixes the input signal with the signal from a local oscillator, andgives as output an intermediate frequency (IF). The local oscillator frequency is related tothe wanted receiver RF frequency in a way that always gives a fixed intermediatefrequency as a result. A common intermediate frequency is 70 MHz. It is at thisfrequency, which is significantly lower than the frequency of the input signal thatunwanted signals are filtered out. Generally a crystal filter is used for this purpose. TheIF filters bandwidth is generally equivalent to the wanted signals effective bandwidthand its attenuation often increases drastically with increasing separation from the centerfrequency. The IF filter is primarily responsible for the receivers adjacent channelselection. To enable the receiver to receive channels that cover a wider band, the localoscillator must be capable of being tuned in accordance with the incoming signalsfrequency in order to maintain a fixed IF frequency. The local oscillator is therefore, as inthe transmitter, often constructed as a digital frequency generator. Such tunable localoscillators allow receivers to be set to different receiver frequencies or channels. Adetector follows the IF amplifier and IF filter in which the wanted information isretrieved and a digital bit stream is generated. This may then be converted to intelligiblespeech via a speech decoder.12 Ericsson Radio Systems AB 3/038 02-LZU 102 152,Rev A, November 1999

30. RADIO COMMUNICATION SYSTEM COMPONENTSReceiver characteristic dataReceiver attributes are described in terms of its characteristic data: sensitivity sensitivity to co-channel interference adjacent channel selection blocking level resistance to intermodulation levelSensitivity The receivers sensitivity or threshold is


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generally defined in terms of the lowest input signal level that is required in order that thedetection of the received information attain a given level of minimum acceptable quality.The quality of a digital receiver is usually expressed in terms of the BER (Bit-ErrorRatio), e.g., 10-3 or 10-6. Receiver sensitivity is a function of: the receivers noisefactor the noise bandwidth the modulation method The greater the bandwidth of the

transmitted information the greater is the noise bandwidth. A broadband system istherefore less sensitive than is a narrowband system. Noise bandwidth is generallydetermined by the IF filter. Sensitivity is limited, as described above, by the noise level ofthe receiver input. It is estimated as N = F k T B......................................................................................... (1) where N = Receiver noiselevel F = Receiver noise factor k = Boltzmans constant, 1.3810-23, J/K T = Absolutetemperature at the receiver input, K Ericsson Radio Systems AB 133/038 02-LZU 102152, Rev A, November 1999

31. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNING B =Receiver effective bandwidth, normally the IF bandwidth, Hz or expressed in decibels N= F + k + T + B .................................................................................... (2) The receivers

noise factor is a measure of how much noise the receiver generates in relation to a noise-free amplifier. Typical values lie between 5 and10 dB. The value of the product kT,(K+T) in decibels, at room temperature is - 174 dBm/Hz. The effective bandwidth of thereceiver is expressed in dBHz. Example - calculating receiver sensitivity The followingpresents three example calculations of the theoretical sensitivity of a receiver. Example 1:To begin with, assume the receiver is being used for mobile communication in the UHFband (450 MHz). The method of modulation is FM (frequency modulation) with achannel separation of 25 kHz. The bandwidth of the receiver is then, typically, 12.5 kHz.Assume a receiver noise factor of 10 dB. Since the receivers effective bandwidth in thiscase is 41 dBHz (12.5 kHz = 12500 Hz converted to dBHz), equation (2) results in thefollowing value for receiver noise level N = 10 dB -174 dBm/Hz + 41 dBHz = -123 dBm

A given signal-to-noise ratio, S/N, is required to attain a given level of reception quality.In the case of FM, S/N= 10 dB is a typical value, which gives a receiver threshold of S= -123+10= -113 dBm. In the case of mobile radio, sensitivity is also often specified as avoltage (in micro-volts) which represents the EMK required to impart the necessarypower to a 50-ohm receiver or one that corresponds to the terminal voltage, i.e., half ofthe EMK. A sensitivity of -113 dBm corresponds to a terminal voltage of 0.5 microvoltsacross 50 ohms. Example 2: Assume a digital receiver, e.g., a radio link that demonstratesa transmission capacity of 2 Mbit/s. Assume that Phase Shift Keying (PSK) is themodulation method used. The bandwidth of the receiver is now typically 2 MHz. Assumea receiver noise factor of 10 dB.14 Ericsson Radio Systems AB 3/038 02-LZU 102152, Rev A, November 1999

32. RADIO COMMUNICATION SYSTEM COMPONENTS Since the effectivebandwidth of the receiver in this case is 63 dBHz (2 MHz = 2 000 000 Hz converted todBHz), equation (2) results in the following value for receiver noise level N = 10 dB -174dBm/Hz + 63 dBHz = -101 dBm A typical value for signal-to-noise ratio at a bit-errorratio of 10-3 and PSK modulation is S/N= 10 dB. The receiver threshold is therefore S= -101 dBm + 10 dB = -91 dBm. If the receivers measure of quality is instead set to a bit-error ratio of 10-6, then an S/N is required which is 3 dB higher, i.e., the receiverthreshold at BER=10-6 is now 3 dB higher than that at BER=10-3 which means at -88


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dBm. Example 3: Assume that the link is to transfer 8 Mbit/s using QPSK modulation,which requires a bandwidth equivalent to half of the transmission capacity, or in thiscase, 4 MHz. Assume a receiver noise factor of 10 dB. Since the receivers effectivebandwidth in this case is 66 dBHz (4 MHz = 4 000 000 Hz converted to dBHz), equation(2) results in the following value for receiver noise level N = 10 dB -174 dBm/Hz + 66

dBHz = -98 dBm QPSK requires an additional 3 dB higher S/N than does PSK, i.e., 13dB. Receiver threshold for an 8 Mbit/s link is therefore S/N= -98 dBm + 13 dB = -85dBm for BER=10-3 and S/N= -82 dBm for BER=10-6. Consequently, the receiverthreshold is 6 dB higher for 8 Mbit/s as compared to 2 Mbit/s which is equivalent to atransmission capacity that is 4 times higher (6dB).Sensitivity to co-channel InterferenceThis attribute is important when attempting to re-use a frequency or channel several timesover a geographical area. The amount of co- channel interference tolerated by a receiveris defined by its sensitivity to a given connection quality (expressed in BER) and it is afunction of the method of modulation used. As a rule, a receiver is exposed to both noiseand co-channel interference at the same time. Since the wanted signal lies close to thenoise threshold, less co-channel interference is tolerated, seen from a relative point of

view. When the level of the wanted signal is sufficiently high, the required relationshipbetween the wanted signal level and the level of the co-channel interferer is a constant(C/I, carrier to interference). Ericsson Radio Systems AB 153/038 02-LZU 102 152,Rev A, November 1999

33. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNING A C/I ofapproximately 8 dB is typically required for mobile communications FM receivers iflarger input signals are to be received. A digital radio link typically requires a C/I in thevicinity of 10-15 dB since input signals are well in excess of the threshold. Figure 11illustrates a typical curve of required C/I, at a given BER, as a function of input signallevel. The figure illustrates a receiver threshold degradation (3 dB) for a certain C/I ratio.C/I (dB) 30 20 17 3 dB 10 -90 -85 -80 -75 -70 C (dBm) Figure 11: Typical curve ofrequired C/I, at a given BER, as a function of input signal level.Adjacent channelselection Adjacent channel selection describes the receivers sensitivity to adjacentchannel interference. This attribute is also important when considering frequencyeconomy. The adjacent channel selection is determined, above all, by the modulationmethod, the frequency separation to the adjacent channel and the receivers IF filter. It isalso dependent on the wanted signal level in relation to the noise threshold. When thelevel of the wanted signal is sufficiently high, the required relationship between thewanted signal level and that of the interference level, is a constant (for a given frequencyseparation). Figure 12 illustrates a typical curve of allowable interference signals on alink as a function of frequency separation at an input signal of 1 dB above the threshold(1 dB threshold degradation) for 2, 8 and 34 Mbit/s. The curve principally illustrates theselection of the IF filter.16 Ericsson Radio Systems AB 3/038 02-LZU 102 152, RevA, November 1999

34. RADIO COMMUNICATION SYSTEM COMPONENTS 50 Maximum interferencelevel (dBm) 0 y34 i y8 j y2 50 k 100 0 50 100 150 200 250 x34 , x8 , x2 i j k Frequencyseparation (MHz) 34 Mbit/s 8 Mbit/s 2 Mbit/s Figure 12: Allowable interference signalfor 1 dB threshold degradation for 2, 8 and 34 Mbit/s. Adjacent channel selection is oftenspecified at 70 dB for mobile communications. This is a result of the desire to allowdifferent users to operate over adjacent channels without the necessity of having to


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coordinate their individual selection of site locations for their base stations. In moremodern mobile telephone systems, where an operator makes use of an entire band fortheir system, it is common place that adjacent channel selection requirements aresignificantly relaxed since the operator is able to perform frequency planning for theentire band in order to avoid interference between adjacent channels. This leads to the

fact that the channels are located closer to one another, i.e., a higher packing density,which results in better frequency economy. For the case that adjacent channels no longerfulfill the old requirement of 70 dB selection (or adjacent channel selection), one oftenrefers to the channels as being interleaved, i.e., interleaved with one another. In the caseof radio links, one usually uses an adjacent channel selection of 25-35 dB. The objectiveis that adjacent channels are to be usable in one and the same node, which is usuallyfacilitated by antenna isolation between neighboring paths. Ericsson Radio Systems AB173/038 02-LZU 102 152, Rev A, November 1999

35. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNING It iscommon place that the different connections in a network have different capacities.Interference characteristics between radio link systems, having different capacities, can

be described with the aid of a C/I matrix, see Table 1. This matrix allows one to find theC/I for a given threshold degradation that is required when the interfering link hasanother specific capacity. C/I [dB] and frequency separation for 3 dB degradation andBER=10-6 Capacity [Mbit/s] Frequency Separation [MHz] Carrier Interferer 0 7 14 21 282x2 2x2 21 -37


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threshold at -113 dBm, the blocking level will be -113+80= - 33 dBm. At a 10 MHzfrequency separation between a transmitter and a receiver, which is a typical duplexseparation in the 450 MHz band, the IF filter will exhibit a typical 20 dB attenuation andthe blocking level will be instead -33 dBm + 20 dB = -13 dBm. Ericsson RadioSystems AB 193/038 02-LZU 102 152, Rev A, November 1999

37. RADIO TRANSMISSION NETWORK AND FREQUENCYPLANNINGIntermodulation level Intermodulation results from the fact that receiversexhibit certainnonlinear behavior and are therefore sensitive to interference signalsoccurring at certain frequency combinations. These frequencies may combine, as a resultof this nonlinear behavior in the receiver, into one frequency that corresponds to thewanted received frequency. Intermodulation level is defined as the level assumed bythese interference signals, to bring about a given degradation in receiver sensitivity whenthe wanted signal is at the threshold level. Intermodulation level is a function of theordinal number for the intermodulation. The higher the ordinal number, the higher is thelevel of interference tolerated by the receiver. The only protection againstintermodulation is through filtering before applying the signal to the RF amplifier, i.e., in

the RF filter. Protection may also be achieved through frequency planning therebyavoiding the creation of dangerous intermodulation frequencies. Instead of specifying theintermodulation level, one may, on occasion, specify receiver intermodulation attenuation- which is the difference (in dB) between the level of the signals that cause theintermodulation product and the receivers threshold level. These levels are measured atthe receivers antenna connector. A typical value of intermodulation attenuation for 3rd-order intermodulation is 70 dB for mobile radio and in general somewhat worse for radiolinks. Then, the level of the interfering signals at the input of the receivers antennaconnector should be given by P Pth + 70 D = 3 dB............................................................ (3) where Pth is the threshold level of the receiverand D the threshold degradation. Typical values for intermodulation attenuation formobile and link are given in Table 2. Intermodulation attenuation (dB) Intermodulationorder Mobile Link 3 70 50 (?) 5 90 70 (?) Table 2: Typical values for intermodulationattenuation for mobile radio systems and radio link systems.20 Ericsson RadioSystems AB 3/038 02-LZU 102 152, Rev A, November 1999

38. RADIO COMMUNICATION SYSTEM COMPONENTS The intermodulation signalwill be suppressed when passing the receivers IF, to a degree corresponding to therelationship between the bandwidth of the intermodulation signal and that of the receiver.The suppression factor of intermodulation is expressed as follows, Bm R=...................................................................................................... (4) Bi where Bi is givenby Bi = n1 B1 + n2 B2 + n3 B3 + ... .......................................................... (5) and thedesired bandwidth of the receiver is Bm.Feeder cabling Feeder cabling between the radioequipment and the antenna may consist of coaxial cabling or a waveguide.Coaxial cableCoaxial cabling is normally used for frequencies around 2 GHz and lower - cableattenuation would otherwise be unreasonably high at higher frequencies. See the tablebelow showing coaxial cable attenuation at different frequencies: HF3/8 Cu2Y 6.1dB/100 m 400 MHz HF1 5/8 Cu2Y 6.35 dB/100 m 400 MHz HF3/8 Cu2Y 14 dB/100 m2000 MHz HF1 5/8 Cu2Y 3.1 dB/100 m 2000 MHzWaveguides Waveguides are used forfrequencies above 2 GHz. The most common waveguide forms are the rectangular, theelliptical and the circular. However, other forms also exist. Since the cross-section of a


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waveguide has a given relationship to wavelength, the selection of a waveguide isdependent on the frequency band to be used. The table below shows the attenuation forvarious waveguides at different frequencies: Ericsson Radio Systems AB 213/038 02-LZU 102 152, Rev A, November 1999

39. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNING E70 4.75dB/100 m 7300 MHz E130 11.2 dB/100 m 13000 MHz EW220 30 dB/100 m 20000MHzDuplex filters The purpose of duplex filtering is to protect the receiver from thedisturbing effects of the transmitter when transmission and reception are concurrent(duplex operation). The transmitter can interfere with the receiver in two ways: via thatportion of the transmitters sideband noisethat lies within the receivers passband, or viareceiver blocking caused by the transmitted power. Assume, for example, a mobilecommunication base station having a transmission power of 20 W (43 dBm). Typicalvalues for sideband noise lie approximately -140 dB/Hz below the carrier, which is in thiscase a level of -97 dBm/Hz (43 dBm -140 dB/Hz). For a bandwidth corresponding to12.5 kHz (41 dBHz), transmitter noise level would be within receiver bandwidth -56dBm (-97 dBm/Hz + 41 dBHz). The receivers own noise level was in the above example

-123 dBm. If one accepts an increase of the total noise level of 1 dB, i.e., an increase to -122 dBm, then the transmitters noise level to the receiver may not exceed -123-6=-129dBm. Transmitter noise must then be attenuated by at least 129-56=73 dB before arrivingat the receiver. This is accomplished via a bandpass filter at the output of the transmitterthat attenuates the signal by at least 73 dB within the receivers passband. We will nowconsider blocking requirements. A blocking level of -13 dBm and a transmitter power of43 dBm require a transmission signal attenuation of at least 56 dB. This can beaccomplished through the use of a bandpass filter located at the receiver input thatattenuates the transmitted frequency by at least 56 dB. A conclusion that may be drawnfrom the above example is that transmitter noise places greater demands on filtering thanit does on blocking.Transmitter combiners It is often desirable, for sites having more thanone transmitter, to be able to utilize one common antenna for all transmitters. To this end,so- called combiners are often used. The job of these combiners is as follows:22 Ericsson Radio Systems AB 3/038 02-LZU 102 152, Rev A, November 1999

40. RADIO COMMUNICATION SYSTEM COMPONENTS ensure that everytransmitter delivers its power to the antenna without any appreciable losses. to limit theoccurrence of intermodulation between the various transmitters A combiner may beeither passive or active. The simplest form of a passive combiner may be constructedusing hybrids as illustrated in Figure 14. In a hybrid, however, half (3 dB) of thetransmitted power is lost. The more transmitters combined to use one antenna, the greateris the number of hybrids required and the greater is the loss. Using 4 transmitters requiresthe use of 3 hybrids and the loss is 6 dB - using 8 transmitters requires a tree-connectionof 7 hybrids which results in a loss of 9 dB, and so on. LOAD TERMINATIONHYBRID COUPLER BANDPASS, LOW OR F F 2ND HARM, FILTERS ISOLATORIN EACH PATH Tx 1 Tx2 INPUT INPUT Figure 14: Example of a hybrid. An activecombiner combines a number of low-power transmitters via the use of hybrids or aresistive network into a common port where the collective signal is amplified via a linearamplifier to attain the desired output power. This technique is not very widely utilizeddue to the fact that it is difficult to achieve sufficient output power without introducingintermodulation. Figure 15 illustrates a schematic block diagram of another transmission


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combiner, a multiple connector. Each transmitter is connected via a so- called isolatorand a filter to a star network, in which the different transmitters are inputs to the networkand the antenna is the output. Ericsson Radio Systems AB 233/038 02-LZU 102 152,Rev A, November 1999

41. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNING Tx1 ~ ~ ~f1 -10dB at f Tx2 ~ ~ ~ Star net f2 etc Figure 15: Schematic block diagram of amultiple connector. The isolator, see Figure 16, normally a so-called circulator, is a non-reciprocal component that has negligible attenuation (at the most one or two dB) in itsforward direction and a significantly high attenuation (25- 30 dB) in its reverse direction.Its function being to prevent leakage from other transmitters into the transmitter that it isconnected to and thereby avoiding intermodulation. Figure 16: An isolator (circulator).The job of the filter is to create an mismatch as seen from the other transmitters so thattheir output power is primarily directed to the antenna and not inwards towards thenetwork and the other transmitters. Since the frequencies of the different transmittersgenerally lie relatively close to one another, the filters must be of the cavity type so thatsufficient signal attenuation is achieved across the frequency separations for the

particular transmitters in question.24 Ericsson Radio Systems AB 3/038 02-LZU 102152, Rev A, November 1999 42. RADIO COMMUNICATION SYSTEM COMPONENTS Typically, the lowest

frequency separation between neighboring transmitters is often around 500 kHz in boththe 450 and 900 MHz ranges, i.e., approximately an 0.1% frequency separation. Requiredattenuation for a neighboring transmitter for the achievement of sufficient mismatch canbe as low as 10 dB. This does not prevent transmitter power leakage through the filterinto the neighboring transmitter, which would cause damaging intermodulation. This iswhere the function of the isolator comes into play, providing additional attenuation toreduce transmitter leakage. Any intermodulation products are attenuated once again bythe cavity filter on their way out to the antenna. A typical combiner maintains anintermodulation level at the antenna output of 70 dB below each of the transmitterspower levels.Receivers multicouplers It is often desirable to use a single antenna even ifmore than one receiver is located at one and the same site. To this end, multicouplers areutilized. Figure 17 illustrates a schematic block diagram of a multicoupler. O 1 O 2 . ~ ~Power . . . ~ divider . . . . O 16 connected to each receiver Figure 17: Schematic blockdiagram of a multicoupler. The signal from the antenna is first filtered by a highlyselective bandpass filter, then amplified and then separated in a signal power divider(occasionally called splitter). Ericsson Radio Systems AB 253/038 02-LZU 102 152,Rev A, November 1999

43. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNING Aneffective filter located at the input to the multicoupler may often serve to reduce therequirement for a duplex filter. The following amplifier is intended to compensate for theattenuation and the noise resulting from the split and distribution of the signal to severalreceivers. The signal power divider is constructed to achieve a dual purpose. Firstly tomatch to the individual receivers to the antenna and secondly to isolate the receivers fromone another. Multicouplers present a problem in maintaining satisfactory performance inpreventing intermodulation and blocking at its input. A typical receiver multicoupler canconnect up to 16 receivers. All of the outputs of the multicouplers should be terminatedeven if they are not used for the connection of a receiver.Antennas The primary purpose


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of a radio system antenna is: when transmitting, to deliver to the surroundingenvironment the power generated by the transmitter without incurring any losses in thedesired direction when receiving, to deliver the available radiation power to the receiverAn antenna is characterized by the following attributes: impedance bandwidth directivity polarization Directivity in a given direction is defined as the ratio of the

intensity of radiation (the power per unit solid angle), in that direction, to the radiationintensity averaged over all directions. It may in turn be expressed by antenna gain andside lobe level. The antenna gain specifies the degree to which the power radiated in thedesired direction as compared to the level of the power radiated equally in all directions(i.e., an isotropic antenna). On occasion, antenna gain is specified as above but relative adipole antenna, which is 2.15 dB lower than the gain relative an isotropic antenna.26 Ericsson Radio Systems AB 3/038 02-LZU 102 152, Rev A, November 1999

44. RADIO COMMUNICATION SYSTEM COMPONENTS Antenna gain is specifiedin units of dBd or dBi to specify whether the gain information for a given antenna isrelative a dipole or an isotropic antenna. If the gain is specified in dB then the value givenis relative an isotropic antenna. To be effective, an antenna should be of the same

magnitude of size as the wavelength of the frequency in question. Vertical rod antennasare normally used for mobile communications. Such antennas radiate omnidirectionallyin the horizontal plane. Polarization is in this case vertical. The shortest antenna is oftenin such cases a quarter wavelength, i.e., just under 20 cm at 450 MHz. Base stationantennas are often directional in the vertical plane, which is achieved by using a numberof half-wave dipoles that are stacked one above the other. These antennas are referred toas being co-linear. The gain is then essentially proportional to the number ofelements.Antenna gain for parabolic antennas Parabolic antennas, which function asmirrors, are almost without exception used for radio links having frequencies fromapproximately 2 GHz and upwards. The following relationship apply to these antennas: 4 A 4 A f 2 2 d 2 f 2 G= = = ....................................................... (6) 2 0.3 20.32 where G = Antenna gain A = Effective antenna area, m2 d= Antenna diameter, m = Wavelength, m f= Frequency, GHz The antenna gain as calculated by equation (3) isspecified as a factor. The result of the equation (3) can be obtained in dB by applying thefollowing relationship: Ericsson Radio Systems AB 273/038 02-LZU 102 152, Rev A,November 1999

45. RADIO TRANSMISSION NETWORK AND FREQUENCY PLANNING G = 20.4+ 20 log(d ) + 20 log( f ) ......................................................... (7) The effective antennasurface is typically approximately 50-70% of the actual geometric surface, depending onthe manner in which the aperture is illuminated. It is clearly evident that the gain, for agiven antenna size, increases with decreasing wavelength, i.e., as frequency increases.Example: assume a parabolic antenna having a diameter of 2 m and operating at afrequency of 5 GHz. This corresponds to an area of 3.14 m2 and a wavelength of 0.06 m.Antenna gain can be calculated from equation (3) as being a factor of 10,965corresponding to 40.4 dB. But the measured gain of the antenna is only 37 dB, whichseems to imply that there is a 3-dB loss in effectivity, an efficiency of only 50%.Antennadiagram Side lobe level indicates how much lower the power is in a non-desired direction(side lobe) than that radiated in the desirable direction (main lobe), Figure 18. Side lobe Main lobe 0 Gbg bg = GS G (0) Figure 18: Main and side lobes. The front-to-backratio gives the relationship between the power radiated in the forward direction vs. the


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power radiated in the reverse direction. The lobe width that corresponds to a 3 dB lowergain in relation to the main lobe gain, see Figure 18, can be calculated as 0.3 =k............................................................................................... (8) df where = Lobewidth, degree k= Constant, 75-8528 Ericsson Radio Systems AB 3/038 02-LZU 102152, Rev A, November 1999

46. RADIO COMMUNICATION SYSTEM COMPONENTS d= Antenna diameter, m f=Frequency, GHz Figure 19 illustrates a schematic antenna diagram for a 18 GHz antennawith a 44.5 dBi gain. The antenna has a diameter of 1.2 m. The figure also shows thecorresponding diagram for the cross-polarization field. dB 0 10 20 30 copolar 40 50crosspolar 60 70 0 5 10 15 20 40 60 80 100 120 140 160 180 degree Figure 19: Antennadiagram for an 18 GHz antenna. Ericsson Radio Systems AB 293/038 02-LZU 102152, Rev A, November 1999

47. RADIO TRANSMISSION NETWORK AND FREQUENCYPLANNINGReferences Grundlggande Radioteknik (in Swedish), Billstrm, O.,Ericsson Radio Systems AB, 1993. Radio System Design for Telecommunications (1-100 GHz), Freeman, R. L., 1987.30 Ericsson Radio Systems AB 3/038 02-LZU 102

152, Rev A, November 1999 48. RADIOWAVE PROPAGATION This chapter provides a presentation of the basic

principles and algorithms related to radiowave propagation used in radio-relaytransmission. Both loss and attenuation algorithms plus fade prediction models fordifferent fading mechanisms are thoroughly discussed. The chapter also includes apresentation of the basic concepts of main propagation mechanisms, Fresnel zone,equivalent and true Earth radii and the decibel scale. TABLE OF CONTENTSThedecibel........................................................................................................................................................ 1 A relative comparison......................................................................................................................... 1 Somemotivations for using

decibels................................................................................................... 1 Absolutecomparisons .........................................................................................................................1 The comparison of fieldquantities...................................................................................................... 2 Anoverview........................................................................................................................................ 3The main propagation mechanisms................................................................................................................... 3 Propagationalong the earths surface .................................................................................................4Fading................................................................................................................................................................ 4 Definition............................................................................................................................................ 4Cause................................................................................................................................................... 4 General classification.......................................................................................................................... 4Classification based on source............................................................................................................ 5The Fresnel zone...............................................................................................................................................5 Definition............................................................................................................................................ 5


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The Fresnel ellipsoid........................................................................................................................... 6Equivalentand true earth radii.......................................................................................................................... 7 Earth-radius

factor............................................................................................................................... 7Equivalent and true Earth surface - acomparison............................................................................... 8Predictionmodels.............................................................................................................................................. 8Attenuation: free-space loss.............................................................................................................................. 9Definition............................................................................................................................................ 9Free-space loss between two isotropic antennas................................................................................. 9Diagram.................................................................................................................................

10Attenuation: gas................................................................................................................................................10 Definition............................................................................................................................................10 Thetroposphere................................................................................................................................... 11 Chemicalcomposition.........................................................................................................................11 Absorptionpeaks................................................................................................................................. 11Calculating total gas attenuation......................................................................................................... 12 Oxygen (dryair).................................................................................................................... 12 Watervapor........................................................................................................................... 13Total gas attenuation .............................................................................................................14Total specific gas attenuation -diagram............................................................................................................15Attenuation:reflection....................................................................................................................................... 15 Ground reflection interference............................................................................................................ 16 i

49. The problems of handling reflection................................................................................................... 16 Reflection coefficient.......................................................................................................................... 17 TheFresnel reflection coefficient ......................................................................................... 17Divergence factor..................................................................................................................18 Correction factor................................................................................................................... 18 Example:rough estimation of the total reflection coefficient .............................................................19 Calculation of the position of the reflection


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point............................................................................... 19Attenuation:precipitation.................................................................................................................................. 21 Types of precipitation......................................................................................................................... 21Snow......................................................................................................................................

.............. 21Hail.........................................................................................................................................

............. 22 Fog and haze

....................................................................................................................................... 22Rain..................................................................................................................................................... 22 Cumulative distribution of rain........................................................................................................... 23 Rain zones -diagram........................................................................................................................... 23The new ITU model for calculation of rain intensity.......................................................................... 24 The calculation of the specific rain

attenuation................................................................................... 26 Table containing thefrequency dependent coefficients ...................................................................... 27Calculating total rain attenuation........................................................................................................ 32 Calculating total rainattenuation for 0.01% .......................................................................................32Attenuation:obstruction.................................................................................................................................... 33 Knife-edge obstructions...................................................................................................................... 33 Knife-edgeloss curve.......................................................................................................................... 34Typical knife-edgelosses.................................................................................................................... 35 Single-peakmethod............................................................................................................................. 36Triple-peak method............................................................................................................................. 37Smoothly sphericalearth..................................................................................................................... 39 Typicallosses resulting from smoothly spherical earth...................................................................... 40 Clearance and path geometry.............................................................................................................. 41 The Earthbulge..................................................................................................................... 41 Pathgeometry ....................................................................................................................... 41The height of the line-of-sight...............................................................................................42Path losses......................................................................................................................................................... 42 Definition............................................................................................................................................42 Fademargin....................................................................................................................................


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..... 43 Power diagram

.................................................................................................................................... 43Effective fade margin.......................................................................................................................... 44Fading -prediction

models................................................................................................................................45 The concept of outage......................................................................................................................... 45 Rainfading.......................................................................................................................................... 45 Calculation of the fade margin based on a yearly basis........................................................ 45 Outage due to rain fading - annual basis............................................................................... 46 Transformation between yearly andworst month basis ........................................................ 46 From yearly to worstmonth.................................................................................... 46 From worst month toyearly.................................................................................... 47 Climatic parameters.............................................................................................................. 47 Presentation of

the rain fading models in diagram form ....................................................... 48 Multipathfading..................................................................................................................................49 The occurrence of multipath propagation............................................................................. 49 Flat and frequency selectivefading....................................................................................... 50 The effects of multipathpropagation .................................................................................... 51 Measures takenagainst multipath fading .............................................................................. 51 Outage dueto flat fading....................................................................................................... 52Introduction............................................................................................................. 52 Fadeoccurrence factor ............................................................................................ 52 Flatfading and error perform

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