Ericsson Technology Review: Microwave backhaul evolution – reaching beyond 100GHz
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No matter how efficiently we use it, existing spectrum will not be sufficient to meet future requirements on network performance. Both radio access and backhaul will need more spectrum in the mid to long term. In light of this, work has started on the use of frequencies beyond 100GHz, enabled largely by advances in high-frequency semiconductor technology. When the large-scale deployment of beyond 100GHz solutions occurs – in the period 2025 to 2030 – our research suggests that the W and D bands will be able to support capacities in the 5 to 100Gbps range, over distances up to a few kilometers.
![✱ THE NEW MICROWAVE BACKHAUL FRONTIER
2 ERICSSON TECHNOLOGY REVIEW ✱ FEBRUARY 21, 2017
JONAS EDSTAM,
JONAS HANSRYD,
SONA CARPENTER,
THOMAS
EMANUELSSON,
YINGGANG LI,
HERBERT ZIRATH
Microwave backhaul technology plays a significant role in providing
reliable mobile network performance and is well prepared to support
both the evolution of LTE and the introduction of 5G. Work has now
started on the longer-term use of frequencies beyond 100GHz, targeting
the support of 5G evolution toward 2030.
Constant pressure to improve performance
levels results in a need for more spectrum,
and the more efficient use of it – not just for
radio access, but for backhaul as well. By
continuously pushing technology limits, ever
higher frequencies have been brought into use
during the last few decades – a trend that will
continue in the future.
■ Asafinitenaturalresource,radiospectrumis
governedbynational,regionalandinternational
regulationstoensurethatsocialandeconomic
benefitsaremaximized.Spectrumisdividedinto
frequencybandsthatareallocatedtodifferent
typesofradioservices,suchascommunication,
broadcastingandradar,aswellasforscientificuse[1].
By2021,65percentoftheworld’scellsites
(excludingthoseinnortheastAsia)willbe
connectedusingmicrowavebackhaultechnology
[2].Therapidlygrowingcapacityrequirements
thatthisentailswillcreateaneedforsignificant
performanceimprovementsenabledbytechnology
evolutionandmoreefficientuseofexisting
spectrum[2,3,4].
Themicrowavebackhaulindustryhasstarted
preparingforthenextmajortechnologyand
performanceleaptoaccommodatethemarket’s
expectedvolumeneedsforthe2025to2030
backhaul
evolution– REACHING BEYOND 100GHZ
MICROWAVE](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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Ericsson Technology Review: Microwave backhaul evolution – reaching beyond 100GHz
- 1. THE NEW MICROWAVE BACKHAUL FRONTIER ✱ FEBRUARY 21, 2017 ✱ ERICSSON TECHNOLOGY REVIEW 1 ERICSSON TECHNOLOGY 0 50 100 150 200 250 300 350 400 450 0.1 1 10 100 Frequency (GHz) Attenuation(dB/km) N x 250MHz channels Frequency bands 100mm/h 50mm/h 20mm/h 5mm/h 0mm/h 90 22 29 87 15 29 49 30 100 110 120 130 140 68GHz Spectrum not yet allocated W band D band 150 160 170 180GHz C H A R T I N G T H E F U T U R E O F I N N O V A T I O N | # 2 ∙ 2 0 1 7 MICROWAVEBACKHAUL BEYOND100GHZ
- 2. ✱ THE NEW MICROWAVE BACKHAUL FRONTIER 2 ERICSSON TECHNOLOGY REVIEW ✱ FEBRUARY 21, 2017 JONAS EDSTAM, JONAS HANSRYD, SONA CARPENTER, THOMAS EMANUELSSON, YINGGANG LI, HERBERT ZIRATH Microwave backhaul technology plays a significant role in providing reliable mobile network performance and is well prepared to support both the evolution of LTE and the introduction of 5G. Work has now started on the longer-term use of frequencies beyond 100GHz, targeting the support of 5G evolution toward 2030. Constant pressure to improve performance levels results in a need for more spectrum, and the more efficient use of it – not just for radio access, but for backhaul as well. By continuously pushing technology limits, ever higher frequencies have been brought into use during the last few decades – a trend that will continue in the future. ■ Asafinitenaturalresource,radiospectrumis governedbynational,regionalandinternational regulationstoensurethatsocialandeconomic benefitsaremaximized.Spectrumisdividedinto frequencybandsthatareallocatedtodifferent typesofradioservices,suchascommunication, broadcastingandradar,aswellasforscientificuse[1]. By2021,65percentoftheworld’scellsites (excludingthoseinnortheastAsia)willbe connectedusingmicrowavebackhaultechnology [2].Therapidlygrowingcapacityrequirements thatthisentailswillcreateaneedforsignificant performanceimprovementsenabledbytechnology evolutionandmoreefficientuseofexisting spectrum[2,3,4]. Themicrowavebackhaulindustryhasstarted preparingforthenextmajortechnologyand performanceleaptoaccommodatethemarket’s expectedvolumeneedsforthe2025to2030 backhaul evolution– REACHING BEYOND 100GHZ MICROWAVE
- 3. THE NEW MICROWAVE BACKHAUL FRONTIER ✱ FEBRUARY 21, 2017 ✱ ERICSSON TECHNOLOGY REVIEW 3 period.Makingsuchleapsrequiresmanyyearsof researchanddevelopmentandagreatdealofwork onspectrumregulation,aswellastheexperience ofseveraltechnologyandproductgenerations tomatureperformanceforlarge-scaleuse.The aimistoopenupspectrumbeyond100GHz frequenciesforuptoward100Gbpscapacity tosupportdifferentapplicationsandusecases withhopdistancesofuptoafewkilometers.In thelongerterm,itisexpectedtoserveasahigh- capacitycomplementtotheuseofotherfrequency bands[2],especiallyinurbanandsuburbanareas, asshowninFigure1.Thesmallerphysicalantenna sizeatthesehigherfrequencieswillbeofparticular advantageintheselocations. Higherfrequenciesaremorelimitedinterms ofreachandcoverage,buttheycangenerally providewiderfrequencybands,andassuchhave higherdata-carryingcapacities.Drivenbygrowing communicationneeds,everhigherfrequencies havebeentakenintousesincethemiddleofthe lastcenturywhentheuseoffrequenciesofjusta fewGHzwasthenormformicrowavetransmission networks.Atpresent,the70/80GHzband – 71-76GHzpairedwith81-86GHz–israpidly gainingpopularity,asitenablescapacitiesinthe 1-20Gbpsrangeoverafewkilometers[2,3].It hastakenabout15yearsfromtheinitialeffortsin thisbandforlarge-scaleusagetostarttakingoff. Similareffortsarenowunderwaytoenabletheuse offrequenciesbeyond100GHz[5,6]forcapacities inthe5-100Gbpsrangeoverdistancescomparable to70/80GHztoday. Microwavebackhaulbeyond100GHz Microwavebackhaulorfixedservicesystems (astheyareknowninITU-Rterminology)are commonlyusedinamultitudeoffrequencybands rangingfrom6-86GHz.Therangeoffrequency bandsisneededtoprovidebackhaulfordiverse typesoflocations,fromsparseruralareasto ultra-denseurbanenvironments,withhop distancesrangingfromaslittleas100mto100km ormore.Theuseoffrequencybandsisgoverned byregulatoryrecommendationsonchannel arrangements[7].Beyond100GHz,spectrum hasbeenallocatedforfixedservicesystemsup to275GHz[1],butnochannelarrangements havebeenmade.However,regulatorystudies onchannelarrangementsareongoinginEurope [5],withthefocusonthe92-114.25GHzand130- 174.8GHzranges:commonlyreferredtoasthe WandDbandrespectively. THE AIM IS TO OPEN UP SPECTRUM BEYOND 100GHZ FREQUENCIES FOR UP TOWARD 100GBPS CAPACITY Terms and abbreviations BER – bit error rate | BPSK – binary phase shift keying | CMOS – complementary metal-oxide-semiconductor | DHBT – double heterojunction bipolar transistor | GaAs – gallium arsenide | GaN – gallium nitride | HBT – heterojunction bipolar transistor | HEMT – high electron mobility transistor | InP – indium phosphide | ITU-R – International Telecommunication Union Radiocommunication Sector | LOS – line-of-sight | mHEMT – metamorphic high electron mobility transistor | MIMO – multiple-input, multiple-output | MMIC – monolithic microwave integrated circuit | MOSFET – metal-oxide-semiconductor field-effect transistor | NFmin – minimum noise figure | pHEMT – pseudomorphic high electron mobility transistor | QAM – quadrature amplitude modulation | SOI – silicon on insulator | SiGe – silicon-germanium
- 4. ✱ THE NEW MICROWAVE BACKHAUL FRONTIER 4 ERICSSON TECHNOLOGY REVIEW ✱ FEBRUARY 21, 2017 Thespectrumabove100GHzconsistsofa multitudeofsub-bandsofdifferentsizeswith passiveserviceallocationsinbetween,asshown inFigure2.Thereasonevenwidercontinuous spectrumisnotmadeavailableistoprevent interferencewithpassiveradiocommunication servicessuchastheEarthExploration-Satellite ServiceandtheRadioAstronomyService. Thereissomeinterestintheuseoffrequencies beyondtheDbandforfixedservicesystemsin theevenlongerterm.Severalfrequencybandsin the275-1000GHzrangehavebeenidentifiedfor passiveservices,butthisdoesnotprecludetheiruse foractiveservices[1].ITU-Rwillcarryoutstudies untiltheWorldRadiocommunicationConference 2019ontheidentificationoffrequencybandsinthe 275-450GHzrangeforlandmobileradioandfixed servicesapplications[1].Itshouldbenotedthatthe 252-275GHzfrequencyrangeisalreadyallocated tofixedservices.If275-320GHzwasaddedto this,itwouldformacontinuous68GHzwideband withmoderateatmosphericabsorption,asshown inFigure2.Thiscouldbeusefulforfixedservice applicationsinthedistantfuture. Attenuationduetoatmosphericgasesandrain [8]increaseswithfrequencyandtherearealso severalabsorptionpeaks,asillustratedinFigure 2.However,betweenthepeaks,theattenuation increasesquiteslowlybeyond70GHz.Forexample, itincreasesabout2dB/kmfrom70GHztotheD bandandabout4dB/kmfrom70GHzto275GHz. Thefreespacepathloss[8]alsoincreaseswith frequency:byabout6dBfrom70GHztotheD bandandabout11dBfrom70GHzto275GHz,for Figure 1 Future use of spectrum for microwave backhaul, including solutions beyond 100GHz 70/80GHz and beyond 100GHz Multiband 70/80GHz, 15/18/23GHz and beyond 100GHz Multiband 15/18/23GHz and 6/7/8/11/13GHz 70/80, 60, 15/18/23GHz, 6/7/8/11/13GHz and beyond 100GHz Future 5G bands, 60GHz and beyond 100GHz Airport connectivity Port communication Broadcast network Network for authorites Business access Utility communication Fiber closure Events Macro cell backhaul Other uses for microwave transport Small cell backhaul
- 5. THE NEW MICROWAVE BACKHAUL FRONTIER ✱ FEBRUARY 21, 2017 ✱ ERICSSON TECHNOLOGY REVIEW 5 Figure 2 Frequency bands and atmospheric attenuation beyond 100 GHz 0 50 100 150 200 250 300 350 400 450 0.1 1 10 100 Frequency (GHz) Attenuation(dB/km) N x 250MHz channels Frequency bands 100mm/h 50mm/h 20mm/h 5mm/h 0mm/h 90 22 29 87 15 29 49 30 100 110 120 130 140 68GHz Spectrum not yet allocated W band D band 150 160 170 180GHz IT IS IMPORTANT FOR SPECTRUM REGULATIONS BEYOND 100GHZ TO ENABLE EMERGING AND FUTURE INNOVATIONS example.Thepropagationconditionsarethusonly slightlyworsebeyond100GHz. Itisimportantforspectrumregulations beyond100GHztoenableemergingandfuture innovationsthatcansupportcapacitiesontheroad toward100Gbps.Theyshouldcovertraditional linkconfigurations,suchasFDD,aswellas complementaryfutureinnovationsthatmight betterhandletheasymmetricandpartlyunpaired sub-bands,asillustratedinFigure3. Likefibertransportnetworks,microwave backhaulhashistoricallybeendesignedtobe symmetrical.Inmostcases,thefrequencybands aredividedsymmetricallyintohighandlowsub- bands,usedwithFDD.Usedtoboostcapacityand spectralefficiency,line-of-sight(LOS)multiple- input,multiple-output(MIMO)isaninnovation thatinitiallygainedinterest[4,9],buthaswaned latelyonaccountthemoreattractivemultiband solutions.However,thesmallspatialantenna separationrequiredforLOSMIMOintheDband makesitinterestingontheroadtoward100Gbps capacity.Multibandsolutions,whichenable enhanceddataratesbycombiningresourcesin multiplefrequencybands,constituteanessential partofmodernradioaccess.Assuch,theyhave recentlyalsobecomeatopicofgreatinterestin microwavebackhaul[3]bymakingitfeasibletouse higherfrequenciessuchas70/80GHzovermuch longerdistances.Multibandisalsoaveryattractive optionbeyond100GHz. Today,thelimitedspectrumwithunpairedor asymmetricsub-bandsisusedwithTDD.FDD withasymmetricchannelshasbeenstudied, butdeemedtoocomplexandoflimitedvalue inexistingsymmetricbands[10].Asymmetric multibandsolutionsmightbeofinterestin unpairedspectrum,ratherlikesupplemental downlinkforradioaccess.FlexibleFDD configurationsuseseparatetransmitandreceive
- 6. ✱ THE NEW MICROWAVE BACKHAUL FRONTIER 6 ERICSSON TECHNOLOGY REVIEW ✱ FEBRUARY 21, 2017 MIMO Multiband TDD Time Asymmetric FDD Frequency Asymmetric multiband Flexible FDD FrequencyMultiple antenna elements Lower frequency band for high availability High-capacity configurations Traditional configuration Unpaired and asymmetric spectrum configurations FDD Frequency Figure 3 Examples of potential configurations beyond 100GHz, to support high capacities and facilitate use of unpaired and asymmetric spectrum antennasinsteadofdiplexfiltersforisolation[5, 6].Thisdoesnotaddanyspectrumefficiency,but mightprovideforbetterperformancethanthat enabledbyTDDinunpairedspectrum. Theroadto100Gbpstransportsolutions Microwavebackhaultechnologyhasevolved tremendouslyinrecentdecades,repeatedly exceedingcapacitylimitsandreaching performancelevelsonlybelievedpossibleforfiber solutions.Thecommercial70/80GHzequipment thatiscurrentlybeingintroducedsupports 10Gbpsin2GHzchannels(8x250MHz)andit isreasonabletoexpect20Gbpssolutionsinthe future.Highercapacitiesarefacilitatedbywider channels,butnationalspectrumadministrations commonlylimitthemaximumallowedchannelsize tosecureafairdivisionamongdifferentusers.The maximumchannelsizeistypicallylimitedtoabout 10percentofthetotalband.Forhigherfrequency spectrum,withagreaterpossibilityoffrequency reuse,channelsofuptoabout20percentofthe totalbandmaybeallowed. Realisticsolutionsonthecontinuedroad towards100Gbpsindifferentfrequencybandsare showninFigure4.Evenwiderchannelsuptoabout 5GHz(20x250MHz)mightbeobtainableinthe Dband,enablingsolutionssupporting20Gbps, 40Gbpsandevenupto100Gbpsinthelonger term,asindicatedbythediamondsinFigure4. Buttherearemanytechnologychallengesonthis road,suchastransmitternoise,signaldistortion andotherimpairmentsthatmightlimitmaximum modulationorderforextremelywidechannels. Highercapacitiesandwiderchannelbandwidths alsoplacemorerequirementsondigitaldata converters.Moreadvancedsolutionsusingdual polarization–andevenLOSMIMO–would enhancecapacitybuttheyalsoaddcost. TheuseofLOSMIMOsolutionsbeyond
- 7. THE NEW MICROWAVE BACKHAUL FRONTIER ✱ FEBRUARY 21, 2017 ✱ ERICSSON TECHNOLOGY REVIEW 7 100MHz N x 250MHz 1 4 8 20 40 250MHz 1GHz 2GHz 5GHz 10GHz 100Gbps 40Gbps 20Gbps 10Gbps 1Gbps Aggregated channel width Capacity 20% of total spectrum per band 70/80GHz W D band Dual polarization Single polarization MIMO potential Figure 4 Realistic capacity versus channel bandwidth with single polarization, dual polarization and MIMO d_opt= cD fN 100GHzcarrierfrequenciesisattractivedueto thereductioninrequiredspacingbetweenthe antennaelementsasthefrequencyincreases.The optimalantennaseparationd_opt,inaverticaland horizontaldirection,maybewrittenas[11]: Wherefisthefrequency,cisthespeedoflight, Nisthenumberofantennaelementsinthevertical orhorizontaldirectionandDisthehoplength.A separationof70-80percentoftheoptimalvalue ispossible,withonlyalimiteddecreaseinsystem gain[9].Forexample,at155GHz,anantenna separationof0.4mwouldbeneededfora300m hopdistance,and0.8mfora1kmhop.Thereare technologicalchallenges(suchassignalprocessing) involvedindevelopingLOSMIMOintheDband, butinthelongertermitisexpectedtoenablethe finalstepto100Gbpscapacities,andevenbeyond, asillustratedinFigure4. Hoplengthsbeyond100GHz Whenassessingtheabilityofmicrowavebackhaul toprovidehigh-capacitytransportoverdistance, threeparametersshouldbeconsidered: 〉〉 thetotalsystemgain–thetransmittedpowerplusthe antennagainsminustherequiredreceivedsignalpower 〉〉 thetargetedavailability–theaccumulatedtimeaselected capacityshouldbesustainedoverthehop,whichisusually expressedinapercentageoftimeperyear,where 99.99-99.999percentarecommontelecomgradetargets 〉〉 thelocalclimate–thehopplanningisdonewith propagationpredictionmethodsusinglong-termrainand multipathstatisticaldataforthehoplocation Themaximumhoplengthversustotalsystemgain fordifferinglevelsofavailabilityandlocalclimate
- 8. ✱ THE NEW MICROWAVE BACKHAUL FRONTIER 8 ERICSSON TECHNOLOGY REVIEW ✱ FEBRUARY 21, 2017 SEMICONDUCTOR TECHNOLOGIES FOR BEYOND 100GHZ USE HAVE UNDERGONE A TREMENDOUS EVOLUTION IN THE PAST FEW DECADES conditionsat155GHzisshowninFigure 5.It illustratesthetotalsystemgainfortwoequipment examples:onewith50dBiantennas,whichisthe generalrecommendedmaximumantennagainin practicalmicrowavedeployments;andonewith 35dBi,whichistherecommendedmaximum antennagainforsiteswithmastsway,suchas smallcellbackhaulsitesmountedonlighting poles.Eachoftheexamplesisforconfigurations supportingthe10to100GbpsexamplesinFigure 4, whichallhavesimilarsystemgains.AsDband technologyismaturing,transmittedpowerand receiversensitivityofthesameorderasfortoday’s 70/80GHzequipmentareexpected,evenifearly implementationsmighthavemuchlowersystem gain,asillustratedinFigure5. The20,50and100mm/hrainrates,exceededfor 0.01percentoftimeperyear,arerepresentativefor mild,moderateandseverelocalclimateconditions. Theavailabilitiesof99.9percentand99.995 percentinFigure5correspondtoapropagation lossthatexceedsthetotalsystemgainforabout 9hours/yearandof26minutes/year.Using adaptivemodulation,alowermodulationlevel inheavyrainincreasesthesystemgaintoavoid transmissionerrors,butresultsinreducedcapacity. Forexample,reducingmodulationfrom64QAM toBPSKcorrespondto15dBincreaseofsystem gain,butareductionto17percentofcapacity.As Figure5illustrates,hoplengthsofafewhundred metersareachievableforlowergainantennas. Usinghighgainantennas,itispossibletoachieve hoplengthsofabout1-2kmandevenupto2-4km forloweravailabilitytargets,suchasmultiband configurations.Thehoplengthsinthe Dbandarethuswellsuitedforurbanand suburbandeployments. Semiconductortechnologiesaskeyenablers Semiconductordevicesareessentialinallmodern radiotechnology.Microwavebackhaulequipment hashistoricallyreliedongalliumarsenide(GaAs) circuits.Morerecently,galliumnitride(GaN) hasbeenintroducedincommercialproductsdue toitshighbreakdownvoltageenablinghigher transmitpower.Thereisalsoconsiderableinterest insiliconchipsets,basedonCMOSorSiGe-HBT, duetotheirlowerproductioncostperchipinhigh volumesandhighintegrationdensity.Theseare particularlyrelevantforshortrangedeployments wherehighoutputpowerislessimportant,suchas inthe60GHzfrequencyband. Drivenbythespace,defenseandimaging industries,semiconductortechnologiesforbeyond 100GHzusehaveundergoneatremendous evolutioninthepastfewdecades[12].Thereare todayafewcommercialtechnologiesavailablefor beyond100GHzapplicationsandseveralmoreare beingresearchedforevenhigherperformance, asshowninFigure6.Thethreemaintransistor technologyclassesareHBT,HEMT,andMOSFET [12],whereMOSFETistypicallyimplementedin SOICMOSforhighfrequencyoperation.Akey propertyisthefeaturesize,sinceatransistorwith smallerfeaturesizesupportshigherfrequencies. Asaruleofthumbcircuitsaredesignedtooperate atbelowhalffMAX,wherefMAXisthefrequency atwhichthetransistor’spowergainisequaltoone. Itispossibletobringtheoperationfrequencymuch closertofMAXbutdoingsoresultsinlowerenergy efficiencyandhigherdesigncosts.Otherimportant materialpropertiesaretheminimumnoisefigure (NFmin)andthebreakdownvoltage(Vbr),which determinereceiversensitivityandmaximum transmittedpower,respectively.Therightcolumn inFigure6indicatesthecommercialmaturityof thetechnology,whereadditionalaspectsarethe developmentandproductioncost.Flickernoise
- 9. THE NEW MICROWAVE BACKHAUL FRONTIER ✱ FEBRUARY 21, 2017 ✱ ERICSSON TECHNOLOGY REVIEW 9 *Ready to be commercialized in 1–2 years **NFmin is proportional to the frequency. Technology Feature size (nm) fMAX (GHz) Vbr (V) NFmin (dB) at 50GHz** Production or research? GaAs pHEMT 100 185 7 0.5 P GaAs mHEMT 70 450 3 0.5 R* GaAs mHEMT 35 900 2 1 R InP HEMT 130 380 1 <1 R InP HEMT 30 1200 1 <1 R GaN HEMT 60 250 20 1 1.2GaN HEMT 40 400 42 R SOI CMOS 45 280 1 2–3 P SiGe-HBT 130 400 1.4 2 P InP DHBT 250 650 4 3 R* R InP DHBT 130 1100 3 R Figure 5 Maximum hop length versus total system gain at 155GHz, for different rain intensities (exceeded 0.01 percent of the year) and for two different antenna configurations Figure 6 Overview of semiconductor technologies beyond 100GHz and their key parameters Total system gain [dB] Maxhoplength[km] 110 0 1 2 3 4 5 120 Maturing technology Adaptive modulation 130 140 150 160 170 180 35dBi antenna 50dBi antenna 0mm/h 20m m/h99.9% 5 0m m /h 99.9% 100mm/h 99.9% 50mm/h 99.995% 100mm/h 99.995% 20mm/h 99.995%
- 10. ✱ THE NEW MICROWAVE BACKHAUL FRONTIER 10 ERICSSON TECHNOLOGY REVIEW ✱ FEBRUARY 21, 2017 generation,memoryeffectsandtemperature behaviorarenotincludedinthetable,butshould alsobeconsidered. Themaximumtransmittedpowerlimitsthe systemgain.Researchhasbeenpublishedonpower amplifiersinGaAs,InPandSiGetechnologies deliveringmorethan10dBmofoutputpower beyond100GHz[13-15].GaNisinthefuture expectedtodemonstrateevenhigheroutputpower duetothematerialshighbreakdownvoltage.GaAs pHEMTprovideshighbreakdownvoltageand a lownoisefigureand,inafewyears,isalsoexpected tobeabletosupporttheDband.InPsupports veryhighfrequencies,albeitatahighmaterial cost.Becauseofitsgoodperformanceitcouldbe usefulforresearchandpredevelopmentactivities ofequipmentintheDband.Itmightalsobe applicableforlongertermcommercialapplications around275GHz. SilicontechnologiessuchasSOICMOSand SiGe-HBTaretodayfeasibleuptotheDband althoughthemaximumoutputpowerislimited duetothelowbreakdownvoltageofsiliconand thenoisefigureisworsecomparedtoGaNand GaAstechnologies.Duetotheexcellentproperties forhighintegration,silicontechnologiesare promisingforshort-range,low-costapplications beyond100GHz. Therearemanyadditionalobstaclestoovercome. Packagingandinterconnectabove100GHzare challengingduetotheshortwavelengths.Parasitic effectsaremorepronouncedandthetolerance requirementishighindesign,manufacturing andassembly,especiallywhenconsideringwide bandwidths.Crosstalkandunwantedresonances areadditionalissuessincethetypicalmonolithic microwaveintegratedcircuit(MMIC)sizeisofthe orderofthewavelength.Thismakestraditional interconnects,suchaswirebondingandflipchip, difficulttousewithhighyield. Researchonhigh-frequencytechnologiesis gainingglobalinterest.Oneexampleisthenon- galvanicchip-waveguideinterconnectscurrently beinginvestigatedbytheEuropeanUnion fundedHorizon2020projectM3TERA,where low-losssiliconwaveguidesaremadeusinga 3Dmicromachiningtechniquethatprovidesa siliconplatformwithembeddedcomponents forindustrializedassembly.Anotherexampleis theresearchprogramcommissionedbyJapan’s MinistryofInternalAffairsandCommunications, “R&DProgramonMulti-tensGigabitWireless CommunicationTechnologyatSubterahertz Frequencies,”whichinvestigatesradiosources beyond275GHz.AthirdexampleistheHorizon 2020fundedresearchprogramTWEETHER, whichfocusesonhigh-poweramplifiers beyond100GHz. Itisalongandwindingroadfromresearchtofull fledgecommercialequipmentthatmeetstheright performanceandcost.Ultimatelythiscanonlybe achievedwithacompetitiveindustryeco-system sharingacommonvision[6]. Puttingtheorytothetest WorkingwithresearchersatChalmersUniversity ofTechnologyinGothenburg,Sweden,Ericsson ResearchhasdevelopedaDbandtransceiver module,showninFigure7.Themodulecontains anInPDHBTMMICandaseparatecircuitboard forbiascontrolandconnectors.TheMMIC coverstheentireD-band.Theredsquareinthe photoshowsthelocationoftheMMIC,which measures1.3mmx0.9mm.Theclose-uponthe rightshowsthetransceiverMMICgluedtoa siliconcarrierandconnectedtothemodulewith wirebonds. BothtransmitterandreceiverMMICscontaina Gilbertcellmixerforupordownconversionanda frequencytriplerforlocaloscillatorgeneration.A low-noiseamplifierisimplementedinthereceiver RESEARCH ON HIGH- FREQUENCY TECHNOLOGIES IS GAINING GLOBAL INTEREST
- 11. THE NEW MICROWAVE BACKHAUL FRONTIER ✱ FEBRUARY 21, 2017 ✱ ERICSSON TECHNOLOGY REVIEW 11 Figure 7 D band transceiver module (left) with a red square indicating the position of the wire-bonded InP DHBT transceiver MMIC (shown in close-up on the right) MMIChavingapproximately15dBofgain,while amedium-poweramplifierisimplementedinthe transmitterMMICsupportingasaturatedoutput powerofmorethan10dBm[15].TheMMICs areassembledinaslotinsidea50µmthicksoft substratethatalsoextendsintoawaveguideasan E-planeprobe.Thewaveguideconnectstoadiplex filterthatinterfaceswithanantenna. Thetransmitterandreceivermoduleswere measuredback-to-backbeforebeingassembled intotheradioprototype.Figure8showsthe measuredbiterrorrate(BER)versusreceived signalpowerfora125MHzchannelat143GHz. Themodulessupportedupto5GHzchannelsand theinsetinFigure8showsthemeasurederror- freeconstellationforasymbolrateof4GBaud using16QAMforintotal16Gbps[15].Anoisefigure of9.5dBwasmeasuredforthereceiverMMIC, whichisagoodresultforreceiverchipsetsbased onbipolartechnologiesatthesefrequencies. The10-6 BERthresholdof-63dBmfor4QAM(in Figure8)indicatesthattheseearlytransmitterand receivermodulesaddapenaltyofmorethan8dB tothereceiversensitivity.Theseresultsemphasize theneedforcarefulcontrolofhowthemoduleis designedandbuilt. ThephotoontheleftinFigure9showsthe completeradioprototypemountedinanenclosure togetherwiththemodemandantennaforoutdoor over-the-airmeasurements.Theantennais only7.5cmindiameter,butstillprovides40dBi gain.Long-termtestsonfrequenciesbeyond 100GHzwillbeimportanttovalidatetheITU-R propagationandavailabilitymodels,similartowhat wasinitiallydoneinthe70/80GHzband[16].The smallantennafootprintsatthesehighfrequencies couldenablenewcompactradioconcepts,as illustratedtotherightinFigure9.
- 12. ✱ THE NEW MICROWAVE BACKHAUL FRONTIER 12 ERICSSON TECHNOLOGY REVIEW ✱ FEBRUARY 21, 2017 Figure 9 D band radio prototype (left) and visionary design idea (right) Received signal power, dBm Biterrorrate -70 10-12 10-10 10-8 10-6 10-4 0 0 -1 I (a.u.) Q(a.u.) -1 -2 -2 -3 -3 -4 -4 -5 -5 1 1 2 2 3 3 4 4 5 5 10-2 -65 4QAM 16QAM 32QAM 64QAM 128QAM 256QAM -60 -55 -50 -45 -40 -35 125MHz channel Figure 8 Measured bit error rate at 143GHz versus received signal power. Inset shows measured constellation diagram at 4GBaud and 16QAM modulation for in total 16Gbps
- 13. THE NEW MICROWAVE BACKHAUL FRONTIER ✱ FEBRUARY 21, 2017 ✱ ERICSSON TECHNOLOGY REVIEW 13 1. ITU,2016,RadioRegulations,part1chapterIIarticle5(Frequencyallocations)and part3resolution767(Studiestowardsanidentificationforusebyadministrations forland-mobileandfixedservicesapplicationsoperatinginthefrequencyrange 275-450GHz),availableat:https://www.itu.int/pub/R-REG-RR-2016 2. Ericsson, October 2016, Ericsson Microwave Outlook report 2016, available at: https://www.ericsson.com/assets/local/microwave-outlook/documents/ ericsson-microwave-outlook-report-2016.pdf 3. Ericsson Technology Review, January 2016, Microwave backhaul gets a boost with multiband, available at: https://www.ericsson.com/res/thecompany/docs/ publications/ericsson_review/2016/etr-multiband-booster-bachhaul.pdf 4. Ericsson Review, June 2011, Microwave capacity evolution, available at: http://www.ericsson.com/res/docs/review/Microwave-Capacity-Evolution.pdf 5. CEPT ECC WG SE19, Work items SE19_37 and SE19_38, more information can be found at: http://eccwp.cept.org/default.aspx?groupid=45 6. ETSI mWT ISG, Work item DGS/mWT-008, more information can be found at: https://portal.etsi.org/webapp/WorkProgram/Report_WorkItem.asp?WKI_ID=47907 7. ITU-R, 2012, Recommendation F.746, Radio-frequency arrangements for fixed service systems, available at: https://www.itu.int/rec/R-REC-F.746/en 8. ITU-R, 2015, Recommendation P.530, Propagation data and prediction methods required for the design of terrestrial line-of-sight systems, available at: https://www.itu.int/rec/R-REC-P.530/en 9. ECC Report 258, 2017, Guidelines on how to plan LOS MIMO for Point-to-Point Fixed Service Links, available at: http://www.erodocdb.dk/Docs/doc98/official/pdf/ECCREP258.PDF 10. ECC Report 211, 2014, Technical assessment of the possible use of asymmetrical point-to-point links, available at: http://www.erodocdb.dk/Docs/doc98/official/pdf/ECCREP211.PDF 11. 2005 IEEE 61st Vehicular Technology Conference, Vol. 1, 2005, Lattice array receiver and sender for spatially orthonormal MIMO communication, available at: http://ieeexplore.ieee.org/document/1543276/ 12. IEEE Transactions on Terahertz Science and Technology, vol. 1, no. 1, September 2011, An overview of solid-state integrated circuit amplifiers in the submillimeter-wave and THz regime, available at: http://ieeexplore.ieee.org/document/6005342/ 13. 2014 IEEE Radio Frequency Integrated Circuits Symposium, Tampa, FL, 2014, A 112-134GHz SiGe amplifier with peak output power of 120mW, available at: http://ieeexplore.ieee.org/document/6851686/ 14. 11th European Microwave Integrated Circuits Conference (EuMIC), London,2016, 150GHz GaAs amplifiers in a commercial 0.1-μm GaAs PHEMT process, available at: http://ieeexplore.ieee.org/document/7777493/ 15. IEEE Transactions on Microwave Theory and Techniques, vol. 64, no.4, April 2016, A D-Band 48Gbit/s 64QAM/QPSK Direct-Conversion I/Q Transceiver Chipset, available at: http://ieeexplore.ieee.org/document/7433461/ 16. Proceedings of the Fourth European Conference on Antennas and Propagation, Barcelona, 2010, Long term path attenuation measurement of the 71-76GHz band in a 70/80GHz microwave link, available at: http://ieeexplore.ieee.org/document/5505467/ References: Conclusion Theceaselessquesttoprovidehigherdata- carryingcapacitieshasledtotheuseofever higherfrequencieswheremorespectrumis generallyavailable.Thetremendousgrowth intheuseofthe70/80GHzbandthatwecan seetodaywasmadepossiblebyseveralyears ofresearchanddevelopmentandagreatdeal ofworkonspectrumregulation,aswellasthe experiencegainedfromseveraltechnologyand productgenerations.Similareffortsarenow underwayontheroadtomicrowavebackhaul beyond100GHz,supportedbytherapid evolutionofhighfrequencysemiconductor technologiesandpromisingnewdevices.In lightofthis,weexpecttoseethelarge-scale deploymentofbeyond100GHzsolutionsin2025 to2030.TheWandDbandswillundoubtedly beabletosupportcapacitiesinthe5to100Gbps range,overdistancesuptoafewkilometers.
- 14. ✱ THE NEW MICROWAVE BACKHAUL FRONTIER 14 ERICSSON TECHNOLOGY REVIEW ✱ FEBRUARY 21, 2017 Jonas Edstam ◆ is wireless strategy manager at Business Unit Network Products, Ericsson. He is an expert in microwave backhaul networks with more than 20 years of experience in the area. Since joining Ericsson in 1995, he has held various roles, working on a wide range of technology, system, network and strategy topics. His current focus is on the strategic network evolution to 5G and the convergence of access and backhaul. He holds a Ph.D. in physics from Chalmers University of Technology in Gothenburg, Sweden. Jonas Hansryd ◆ leads Ericsson’s research on microwave and millimeter-wave radios including antennas and high-capacity frontends to meet traffic demands on future microwave backhaul and 5G radio access. He has more than 20 years of R&D experience in advanced communication systems and joined Ericsson Research in 2008. He holds a Ph.D. in electrical engineering from Chalmers University of Technology in Gothenburg, Sweden, and served as a postdoctoral fellow at the applied engineering physics department at Cornell University between 2003 and 2004. Sona Carpenter ◆ received an M.E. (Hons.) in electronics and telecommunication from the Shri G. S. Institute of Technology and Science in Indore, India, in 2008. She is currently working toward a Ph.D. at Chalmers University of Technology in Gothenburg, Sweden. Her research interests include the design of millimeter- wave integrated circuits and systems with a focus on millimeter-wave high-speed wireless communication. In 2013, she was a recipient of the GaAs Association Ph.D. Student Fellowship Award. Thomas Emanuelsson ◆ is an expert in microwave technology at Ericsson whose work focuses on microwave point-to-point communication for the MINI-LINK system. This role includes coordination of future technology development, system and subsystem design as well as interaction with universities about research on upcoming technologies. He received his M.Sc. in electronic engineering from Chalmers University of Technology in Gothenburg, Sweden, where he currently holds the position of adjunct professor at the Microwave Electronics Laboratory in the Department of Microtechnology and Nanoscience. Yinggang Li ◆ is a senior specialist in microwave and millimeter- wave circuits, components and subsystems at Ericsson Research. He holds a Ph. D. in theoretical physics from Gothenburg University in Gothenburg, Sweden. Since joining Ericsson in 1996 he has worked on a number of product development projects and research programs. He is currently involved in Ericsson’s 5G hardware research program, focusing on the development of millimeter- wave technologies beyond 100GHz. Herbert Zirath ◆ is a research fellow leading the development of a D-band (110–170GHz) chipset for high-data-rate wireless communication at Ericsson. He holds a Ph.D. in electrical engineering from Chalmers University of Technology in Gothenburg, Sweden, where he has served as a professor in the Department of Microtechnology and Nanoscience since 1996. His research interests include MMIC designs for wireless communication and sensor applications based on III-V, III-N, graphene, and silicon devices. theauthors The authors would like to acknowledge the support and inspiration they received from their colleagues Mingquan Bao, Björn Bäckemo, Simon He, Johan Jonsson, Magnus Johnsson, Git Sellin, Martin Sjödin, Per-Arne Thorsén and Vessen Vassilev.
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