UE-friendly6GTechnologies

1

TableofContents

1.Introduction 2

2.UE-friendlyScenariosandRequirements 2

3.KeyUE-friendlyTechnologies 4

3.1Satellite-terrestrialintegrationandmulti-bandconvergencetosupportwide-area

ubiquitousconnectivityforUEs

4

3.1.1Satellite-terrestrialintegrationtosupportwide-areaconnectivityforUEs 4

3.1.2Multi-bandconvergencetosupportubiquitousconnectivityforUEs 11

3.2UEnativenetworkingtosupportflexibleconnectivityforUEs 20

3.3Integratedcommunication,sensingandcomputingtoextendUEservicesand

capabilities

2

1

3.3.1Capabilityofsensingservicesandusers 23

3.3.2CapabilityofsensingnetworkandUEs 24

3.3.3Capabilityofsensingcomputingpower 27

3.4Cellfreetechnologytosupport'0'perceivedmobilityexperienceofUEs 31

3.4.1Cellfreetechniques 32

3.4.2Uplinkassistedmobilityenhancement 35

3.5Backscatterandalmost-zeropowerreceivertosupport'0'powercommunicationof

UEs

3

6

3.5.1Backscattercommunicationtechnology 37

3.5.2Almost-zeropowerreceiver 45

3.5.3PA-lesstechniques 49

3.6Novelmultipleaccesstosupportgrant-freetransmissionanduplinkasynchronous

transmissionofUEs

5

1

3.6.1NOMA 52

3.6.2Uncoordinatedmultipleaccesstechnology 53

3.7CombinationofAIandcommunicationtoimproveuserexperience 56

3.7.1UE-friendlyAI-basedcommunicationtechnology 57

3.7.2UE-friendlyAItechnology 60

3.7.3ProspectsforwirelessAI-basedUEs 63

4.Summary 65

5.References 66

6.Abbreviations 68

7.Contributors 71

2

UE-friendly6GTechnologies

1.Introduction

Thefirst6GconferenceheldbytheUniversityofOuluin2019kickedofftheglobalresearchon6G.Fromthe6Gwhitepapersreleasedbyvariousorganizationssofar,thevastmajorityconsiderthatthe6Gvisionistoenabledigitaltwin[1]ordeepintegrationofthedigitalandphysicalworlds.TheEU'sHexa-Xprojectproposesavisiontoconnecthuman,physical,anddigitalworldswith6Gkeyenablersandrevolvearoundinteractionsbetweenthesethreeworlds[2].IMT-2030(6G)PromotionGrouppublishedWhitePaperon6GVisionandCandidateTechnologiesin2021,

proposes“intelligentconnectionofeverything,digitaltwin”society[3]as6Gvision.

Inthe6G-orientedphysical-digitalintegratedworld,UEswillplayanimportantrolebecausetheyarethenerveendingsthatbuildthedigitalworld,themediumthroughwhichthephysicalworldinteractswiththedigitalworld,andtheonesprovidingservicesofthephysicalanddigitalintegratedworld[4].ThecapabilityandperformanceofUEsaffectthedepthandbreadthoftheirreachinthephysicalworld,directlydeterminingthelevelandoperationalefficiencyofthedigitalworldand

affectingtheuserexperience.

ThiswhitepaperwillintroduceUE-friendly6Gkeytechnologiesfromthe

aspectsof6G-orientedUEapplicationscenariosandrequirements.

2.UE-friendlyScenariosandRequirements

Towardsyear2030andbeyond,itisexpectedthathundredsofbillionsofdeviceswillbeconnectedtomeetthediversifiedneedsofdifferentscenarios.Thesedevicesincludesensors(forenvironmentalmonitoring,industrialmanufacturing,bodyareanetwork,etc.),waterandpowermeters,smarthomedevices,wearabledevices(watches,XRglasses,etc.),mobilephones,etc.Facingnewscenariosand

enhancedcapabilitiesof6G,UEchallengessuchaspowerconsumption,complexity,

coverage,cost,andsizewillfurtheraggravate,andmayhavetofacenewchallengesneverseenbefore,becomingbottleneckstothedevelopmentof6G.Thesechallenges

are:

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Contradictionbetweenthefuturedemandforwide-areaaccessandthe

limitedcoverageandperformanceofcurrentUEs

Challengesincludingcost,size,andpowerconsumptionofUEsfor

full-bandmulti-standardubiquitousaccess

Lackofflexibilityanduniversalityofcurrentnetworkingandaccess

LimitedsensingandcomputingcapabilitiesofcurrentUEs

UEservicediscontinuityandexperiencedegradationcausedbycell

reselectionorhandoverfailure

Contradictionbetweenrestrictionsofbatteryandpowersupplytechnologies

andthe'0'-powerconsumptionrequirementsofUEs

Contradictionbetweenmassivesmallpackettransmissionandhigh

schedulingoverhead

LimitedAIcapabilityofminiaturizedUEsandpossibilityoffurther

improvingtheUEperformancewithAItechnology

Theabove-mentionedchallengesleadtoUEsnotbeing“friendly”enoughtofunctioninthefutureworldofphysical-digitalconvergence;therefore,studiesonUE-friendly6GtechnologiesareurgentlyneededtoalleviateburdensonUEs,“l(fā)eavingcomplextaskstonetworksandmakingoperationseasyforusers”.IntermsofUEs,the“UE-friendly”conceptistoimprovetheuserexperiencebyreducingthepowerconsumption,costs,andcomplexityofUEs,supportingtheUEdiversity,expandingaccessscenarios,increasingtheuplinkefficiency(e.g.,energyefficiencyandspectrumefficiency),andimprovingtheuserexperience,ortosacrificetheexperienceatonepointforabetterexperienceatmostpoints.Intermsofnetworks,the“UE-friendly”conceptistosimplifyrelevantprocessesandtechnicalcomplexity

ofUEsbyimprovingnetworkcapabilities.

ThespecificareasofUE-friendlytechnologiescoveredinthiswhitepaper

include:

Satellite-terrestrialintegrationandmulti-bandconvergencetosupport

wide-areaubiquitousconnectivityforUEs

UEnativenetworkingtosupportflexibleconnectivityforUEs

Integratedcommunication,sensingandcomputingtoextendUEservices

andcapabilities

Cellfreetechnologytosupport'0'perceivedmobilityexperienceofUEs

4

Backscatterandalmost-zeropowerreceivertosupport'0'power

communicationofUEs

Novelmultipleaccesstosupportgrant-freetransmissionanduplink

asynchronoustransmissionofUEs

CombinationofAIandcommunicationtoimproveuserexperience.

3.KeyUE-friendlyTechnologies

3.1Satellite-terrestrialintegrationandmulti-bandconvergenceto

supportwide-areaubiquitousconnectivityforUEs

3.1.1Satellite-terrestrialintegrationtosupportwide-areaconnectivityforUEs

Awide-areaaccesstechnologycanprovidewirelessaccessforUEsandusersinawideareaanytimeanywhere.Currently,theterrestrialcellularmobilecommunicationsystemcoversmorethan70%oftheglobalpopulation,butduetotechnicalandeconomicconstraints,itonlycovers20%ofthelandareaand6%oftheearth'ssurfacearea,whichisnotnearlyenoughforseamlesswide-areaaccess.Satellitecommunication,withaseriesofoutstandingadvantages,suchaswidecoverageandlowrelianceoninfrastructure,offersalow-costsolutionforterrestrialcellularsystemstosolvethenetworkcoverageovertheremaining94%oftheearth.Theintegrateddevelopmentoftheterrestrialcellularandhigh,medium,andlowearthorbitsatellitecommunicationsystemscreatingaspace-groundintegratedcommunicationsystemwillgreatlyexpandtheaccessareaofUEsandrealizeseamlessaccessandubiquitousconnectionwithanyoneoranythinganywhereanytimeallovertheworld.In6Gspace-groundintegratedsystems,theorganicintegrationofsatellitecommunicationUEsandterrestrialcellularcommunicationUEsisthekeytoachieveseamlesswide-areaaccessandubiquitousconnectionof

UEs.

ComparedwithterrestrialcellularcommunicationUEs,currentsatellitecommunicationUEsarenotfriendlyintermsofformfactor,powerconsumption,communicationrate,integration,networkconnectivity,andsoon.Thisisbecause,ontheonehand,thelongtransmissiondistanceofsatellitecommunicationleadsto

seriouslarge-scalefading:acommunicationsatellitewillsufferextremelargepath

5

lossifitisaGEOsynchronoussatelliteusingmmWaveandevenhigherfrequencybands;andontheotherhand,thelowdegreeofstandardizationinthefieldofsatellite

communicationresultsinalackofstandardizedinterfacesbetweensystems.

Table1comparestypicalterrestrialcellularcommunicationUEsandsatellitecommunicationUEs,including5GmobilephoneUEs,Tiantong-1satelliteUEsandAPStar-6DsatelliteUEs.Amongthem,Tiantong-1satelliteisthefirstmobilecommunicationsatelliteinChina,andAPStar-6DsatelliteisthemostadvancedKu

bandhigh-throughputsatelliteinChina.

Table1.DifferenceBetweenSatelliteUEsandTerrestrialMobileUEs

Item

SatelliteCommunicationUE

TerrestrialMobileUE

Tiantong

satelliteUEs

(GEO,Sband)

APStarsatelliteUEs(GEO,Ku/Kaband)

Sub6G

UEs

mmWave

UEs

Form

Handheld

VSATstations

(Antenna

diameter

0.6m~1.2m)

Portable

UE

(Antennadiameter:0.1m)

Handheld

CPE

Max

transmitting

power

33dBm

8W~16W

(39dBm~42dBm)

1W

(30dBm)

23dBm

23dBm

Datarate

1.2Kbps~

9.6Kbps

Downlink:

80Mbps

@50MHz

Uplink:

10Mbps@8MHz

Downlink:

37.5Kbps

@500KHz

Uplink:

7Kbps@

200KHz

Downlink:

Assuming4MIMO

layers,

256QAM,100MHz

bandwidth,and

sub-carrierspacingof30kHz,

thepeak

downlinkdatarateis1.745Gbpsfor5ms

single

cycle

frame

structures

Downlink:>4Gbps；

Uplink:

>340Mbps

6

Uplink:

Assuming1layer,

100MHz

bandwidth,and30kHzsub-carrierspacing,

theuplinkpeakdatarateis

95Mbps

(64QAM)

or

127Mbps(256QAM)for5ms

single

cycle

frame

structures

Standardization

Tiantong-1

standard

Downlink:DVB-S2

Uplink:DVB-RCS

3GPP5GNR(FR1)

3GPP5G

NR(FR2)

Lithography

process

40nmbasebandchip

28nmor40nmbasebandchip

5nm

baseband

chip

5nm

baseband

chip

Communicationmode

Dualmode

(LTE+Tiantong)/Singlemode

Singlemode

Multi-mode

Multi-mode

Numberof

users

Hundredsof

thousands

Tensofthousands

Ericssonestimates5Gmobilesubscriptionswillexceed580millionbytheendof2021

Note:5GmobilephoneUEindicatorsaresourcedfromtheCCSA5GUEindustrystandard“2018-2364T-YDT3627-2019_5Gdigitalcellularmobiletelecommunicationnetwork-technicalrequirementsofeMBBuserequipment(Phase1)”.The5GmmWaveCPEUEdataissourcedfromthemillimeterwavetestconductedintheMTNetlaboratoryorganizedbytheChinaAcademyofInformationandCommunicationsTechnology.

InTable1,Tiantong-1handheldphonessupportboththesatellitecommunicationsystemand4GLTEstandard,howeverbysimplyintegratingtwochips,withoutanyoptimizationinsystemhandoverandresourceconservation.Atpresent,themainreasonwhyitisdifficulttodeeplyintegratesatellitecommunicationUEsand

terrestrialcellularcommunicationUEsisthevastdifferencebetweenthesetwo

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communicationsystems,andthelackofunifiedmanagementoversatellite

communicationnetworksandterrestrialcellularnetworks.

Ontheonehand,thechoiceofairinterfacetransmissiontechnologydirectlydeterminestheimplementationplanofcommunicationUEchipset.Therefore,tointegratetwoairinterfacesinharmonyandsharingresourcesbetweenthem,thefirstthingistodesignanintegratedairinterfacetransmissiontechnologyaccordingtodifferentcommunicationchannelcharacteristics,differentcommunicationscenarios,andresourceconstraints.Ontheotherhand,theorganicintegrationofsatellitecommunicationUEsandgroundcommunicationUEsmeanstheUEs’freeaccesstonetworksthroughsatellitenodesorgroundbasestationsanytimeanywherewithseamlesshandover.Tothisend,itisnecessarytodesignasatellite-terrestrialintegratednetworkarchitecturethatcoverssatelliteaccessnetworksandgroundaccessnetworks,subjecttoaunifiedaccessmanagementmechanism.Besides,efficientandreal-timemobilitymanagementtechnologiesarealsoneededtoenablebetteruserexperience.Comparedwithterrestrialcellularcommunicationsystems,satellitecommunicationhaslongertransmissiondistanceandthusseriouslarge-scalefading.ThepathlossisespeciallylargewhentheuserlinksareinKu/KAandotherHFbands.Withagivenloadcapacityofsatellitecommunication,increasingthesizeofUEantennaandtheG/TvalueofUEsiseffectiveforhigh-speeddatatransmission.Loweringthecostoflarge-scalephasedarrayofUEsisanessentialapproachtothe

large-scaleapplicationofsatellite-groundintegratedHFUEs.

However,thegreatdifferencesbetweensatellitecommunicationandterrestrialcellularcommunication,includingdifferentchannelmodelsanddifferenttransmissionenvironments,aswellasthecharacteristicsofsatellitecommunication,suchaslimitedon-boardresources,longtransmissiondistance,andhigh-speedmovementofLEOsatellitenodes,bringchallengestotheintegrationofairinterfacetransmissiontechnologies,integrationofnetworkarchitectures,andintegrationofmobilitymanagement.The3GPP’snon-terrestrialnetworks(NTN)projectiscommittedtointegratingsatellitecommunicationwith5GandsolvingtheproblemoftheNewRadio(NR)supportingNTN.3GPPNTNstandardizationwilllayafoundationfor6Gsatellite-terrestrialintegrationresearch.FromtheperspectiveofUEfriendliness,the

keytechnologiesof6Gsatellite-terrestrialintegrationincludethespace-ground

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integratedflexiblenetworkarchitecture,6Gsatellite-terrestrialintegratedtransmission

technology,low-costUEphasedarrayantennatechnology,etc.

1.Space-groundintegratedflexiblenetworkarchitecture

Atpresent,thearchitectureofsatellitenetworksdifferslargelyfromthatofterrestrialcellularnetworks.Facingthefuturespace-groundintegrationscenario,integratinghigh,medium,andlowearthorbitsatellitenetworksandterrestrialcellularnetworks,adoptingaunifiedflexiblenetworkarchitecture,andbuildinganend-to-endservicenetwork,toenabletheglobalunifiedaccessserviceandmobilitymanagementservice,willbeconducivetosimplifyingtheUEprocessesandreducingthehandover

latency.

Thespace-groundintegratedaccessnetworkbasedonmicro-serviceisthekeylinkofbuildingaflexiblenetwork.Throughcloudnativetechnologiessuchascontainer,thewirelessprotocolfunctionisreconstructedusingtheconceptofmicro-service,andsimilarfunctionsbetweendifferentlayersarere-encapsulatedasmicro-servicestoremoveredundancyandrealizetheservice-orienteddesignof

wirelessaccessnetworks.Eachmicro-serviceoftheaccessnetworkcanevolve

independentlyandexpandflexibly.Micro-service-basedaccessnetworksincludesservicessuchasresourceallocation,retransmissioncontrol,encryption&decryption,mobilitymanagement,signalprocessing,networkaccess,etc.Inaspace-groundintegratedaccessnetwork,theunifiedaccessserviceimplementedthroughsatellite-groundcollaborationallowsUEstointelligentlyselectthesatelliteaccessnodeorgroundaccessnodeforaccess,soastoensuretheoptimalaccess.ForUEs,usingaunifiednetworkaccessmechanismmeansthattheaccessnetworkis

transparentandinvisibletoUEs,whichgreatlysimplifiestheUEimplementation.

2.6Gsatellite-terrestrialintegratedtransmissiontechnology

Theunifiedairinterfacetransmissiontechnologyofsatellite-terrestrialintegrationcaneffectivelysimplifytheproductdesignofUEsandexpandtheindustrialecologicalchain.Onthebasisofmaintainingaconsistenttechnicalsystem,differentapplicationrequirementscanbefulfilledbychangingthesoftwareconfigurableandadaptivenatureofairinterfaceparametersandprotocol

mechanisms.

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Comparedwithtraditionalterrestrialcellularcommunicationsystemsandsatellitecommunicationsystems,transmissionchannelenvironmentsaremorecomplexinspace-groundintegratedsystems,andlargelyvaryingcharacteristicssuchastransmissionlatency,large-scalefading,Dopplerfrequencyoffset,andscattering.Theurgentproblemstobesolvedby6Gtechnologyistomakeefficientuseofmulti-dimensionalresourcessuchastime,space,frequency,codeandpowerandtodesignaunifiedairinterfacetransmissiontechnologyforsatellite-terrestrial

integration.

Thelargepropagationlossofsatellite-terrestrialtransmissionpath,limitedon-boardresources,extendedlinktime,andhigh-speedmotionofLEOsatellitesposegreatchallengestothesynchronizationandaccesstechnologydesign.Toeffectivelyreduceprocessinglatencyandimproveuserexperience,robusttimingsynchronizationandextremelysimplerandomaccessschemesneedtobestudied.EspeciallyforUEswithoutGNSSpositioningandtime-frequencypre-compensationcapabilities,morerobustuplinkphysicalrandomaccesschannelhavetobedesignedtocorrecttiming

offsetsandfrequencydeviations.

Carriermodulationisavitaltransmissiontechnology,whichessentiallydeterminesthemodeofdatatransmission,spectrumutilization,andtime-frequencysynchronizationscheme.Featuringitsflexibilityandexcellentperformance,multi-carriermodulationisthemaindirectionofcommunicationdevelopmentinthefuture.6Gmulti-carriermodulationtechnologyneedstofullyconsiderthedifferencesbetweensatellitecommunicationandterrestrialcellularcommunicationintransmissionchannelmodel,linkmargin,Dopplerfrequencyoffset,noderesources,

andothercharacteristics,whilebringingsatellite-terrestrialtransmission,broadband,

narrowband,highandlowfrequenciesintoaunifiedframework,andbalancingspectrumefficiency,carrierwaveflexibility,peak-to-averageratio(PAR),andother

indicators.

The6Gerawillwitnessagradualshiftfromtheterrestrialnetworkpeople-centeredurbancoveragenetworkingmodetotheobject-basedglobalcoveragenetworkingmode.TheInternetofThings(IoTs),especiallythesatelliteIoT,willbeanimportantapplicationscenarioof6G.Asspectrumresourcesgetincreasinglyscarce,

withtherapidgrowthofconnectiondensity,thefirststepfortheIoTistoprovide

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moreaccessresources.Inaddition,thesatelliteIoTalsoneedstofocusonsolvingthesignalingstormandenergyconsumptioncausedbytherapidmovementofLEOsatellites.Non-orthogonalmultipleaccess(NOMA)hasgreatadvantagesinprovidingmoreconnectionsandunauthorizedtransmission.However,insatellitecommunication,thereareproblemsofinsignificantchannelgaindifferenceamongmultipleusersunderthesamebeamandinsufficienton-boardprocessingcapacity.Tosolvetheseproblems,newNOMAtechnologiesneedtobestudiedtooptimize

codebookdesignandreducereceiveralgorithms.

3.Low-costUEphasedarrayantennatechnology

ThecostofaUEphasedarrayantennaiscloselyrelatedtochipsettechnology.Atpresent,themainstreamRFchipsetsusedbyphasedarraytechnologyinmillimeterwavebandarebasedonGaAsandGaN.Withthesilicon-basedchipsetsgraduallyenteringmillimeterwaveband,phasedarrayRFchipsetsbasedonCMOS,SiGe,and

SOIhavebeenputintoapplicationsoneafteranother.

AlthoughGaAsandGaNRFchipsetshavebetteremissionefficiencyandlowernoisefigure,forsatellitecommunicationUEsincivilmarkets,siliconbasedchipsetwithgeneralelectricalperformanceindicatorshavemoreadvantagesbecauseoftheirlowcostandhighintegration.Amongthecurrentthreetechnologiesforsilicon-basedRFchipsets,CMOSchipsetisthecheapestwithpoorperformanceindex,whileCMOS-SOIchipsetischeaperwithbestemissionefficiency,andpoornoisecoefficient,andSiGechipsetiscostlierwithbetternoisecoefficient,andmoderateemissionefficiency.Withalargeaperture,antennasinsatellitecommunicationapplicationsmayhavetointegratethousandsofchannelswithphasedarraytechnology.Therefore,theCMOSbasedRFchipsetisgenerallyusedin

implementation.

Inaddition,withevolutionoftechnologies,silicon-basedCMOSchipsetcanbeproducedwithcurrent65nm,45nm,and28nmprocesslines,indicatingahighyieldandahugecapacity.Atthesametime,bymakingfulluseofmaturedigitalcircuittechnologies,inadditiontointegratingthereception,transmission,phase-shiftattenuationcontrolofmultiplechannelsandthepowerdivisionnetworkbetweenmultiplechannelsintoonechipset,theCMOStechnologycanalsointegratethe

digitalcontrolpartssuchasserial-to-parallelconversioncircuit,temperaturecontrol

11

circuit,powerdetectioncurrent,andself-testcircuittogether,realizinghighintegrationofphasedarrayantennasunderthehelpofRFSOCpackaging.Therefore,inordertolowerthecostforlarge-scalecommercialapplications,thesilicon-basedCMOStechnologyisthemainstreaminthefieldofphasedarrayantennasfor

internationalsatelliteUEs.

Forfuturemassiveproduction,thelow-costCMOS-basedUEphasedarrayantennatechnologystillhassomeproblemstoovercomesuchaslowefficiency,lowpower,andhighnoisefigure.ThelowelectronmobilityofsiliconmaterialsunderminestheproductionefficiencyofCMOSchipsets,withonly20%forproductionofsingle-diechipsetsinmillimeterwavebandwhichisintheinternationallyleadinglevel,farfromthatofGaAschips(usually40%).Asforoutputpower,atpresent,50mWssingle-diechipsetscanbeproduced,whichisfarbehindtheusual5WsoutputpowerofGaAschipsets.Fornoisefigure,thecurrently

achievable3dBatthisstageisstillfarfrom1.5dBofGaAs.

3.1.2Multi-bandconvergencetosupportubiquitousconnectivityforUEs

Inordertomeetdiversedevelopmentscenarios,thewirelesscommunicationtechnologyevolvescontinually,newtransmissionandaccesstechnologiesareemergingconstantly,andthecommunicationfrequencybandscontinuetoexpandintohigherfrequencybands.Thewirelesscommunicationsystemshowingtheubiquitousandcollaborativefeatureswillevolveintoaheterogeneous,interconnected,andintegratednetworkwherevarioussystemsandfrequencybandscoexist,formingmulti-dimensionalstereoscopiccoverage,formutualcomplementationand

collaboration.

AsfortheUEs,thismeansthattherewillbemultipleaccessnetworksatthesametime,providingdiversifiedaccessmeansofcommunication.However,inordertoavoidinterference,differentaccessnetworksareoftenconfiguredwithdifferentcommunicationfrequencybands.Inaddition,duetothehistoricalreasonsofspectrumresourcemanagement,oneaccessnetworkmaybeallocatedwithseveralfragmentedfrequencybands.Therefore,theUEshavetosupportavarietyofcommunicationsystemsandmultipleRFfrequencybandstoaccessdifferentnetworks.Inthefuture6Gera,servicedemandtypeswillbedividedintomanysubdivisions,andtheUEs

needmorediversifiedaccesscapabilities.Selectingtheoptimalaccesscapability,

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effectivelyintegratingmultiplemodesandmultiplefrequencybands,andimproving

thespectrumefficiencyofUEswillbecomemorechallenging.

1.RFfront-endmoduletechnology

WhethertheUEssupportmulti-modeandmultiband(MMMB)mainlyliesonbasebandchipset,RFchipset,andRFfront-end.ComparedwithdigitalbasebandchipsetandRFchipsettechnologies,MMMBbringsgreaterchallengestoRFfront-end.TheRFfront-enddeterminesthecommunicationmode,receivedsignalstrength,connectionstability,transmissionpower,andotherimportantperformance

indicatorstheUEssupport,directlyaffectingtheuserexperience.

RFfront-endconsistsofaseriesofanalogdevices,includingswitches,poweramplifiers(PAs),lownoiseamplifiers(LNAs),filters,duplexers,etc.Eachcommunicationsystemandeachfrequencybandneedtobeequippedwithaspecialfilterorduplexer,whichisdifficulttoshare.Ontheonehand,withtheincreasingnumberoffrequencybandssupportedbyUEs,moreandmorecomponentsareinstalledinthedevice.Ontheotherhand,sizeoftheUEsisanimportantaspect,especiallythemostimportantconsumerdevicesintheworld,whichmustbelightandthin.Duetotherequirementsofstructuraldesign,itisimpossibletoincreasethePCBareafortheRFfrontend.Inaddition,astheRFsystemintheUEsbecomesmoreandmorecomplex,thetestefficiencyofdiscreteschemesdecreasesrapidly.Withbothdevicespaceandtesttimeconstraints,theRFfront-enddevicemodularizationhasbecomeamajortrend,whichnotonlyreducesthedevicesize,butalsoimproves

theperformance,increasesthedebuggingefficiency,andreducesthecost.

RFfront-endmodularizationistointegrateseveralhigh-performancedeviceswithdifferenttechnologiesintheformofSysteminPackage(SIP),includingRFswitches,low-noiseamplifiers,filters,duplexers,poweramplifiers,andotherdiscretedevices.OneofthechallengesofRFfront-endmodularizationmainlycomesfromhigh-performancefilters.1.5GHz~3.0GHzspectrum,knownasthegoldenbandofmobilecommunication,themostdistinctivefeaturesofthisfrequencybandrangeare"congestion"and"interference".FDDLTEBand1/2/3/4,TDDLTEB34/39/40/41,andallcommercialfrequencybandsofTDS-CDMAareinthisbandrange,andevenimportantnon-cellularcommunicationssuchasGPS,Wi-Fi2.4G,andBluetooth

operateinthisrange.Withtheadventof5G,theUERFfront-endmaybe

13

configuredwithmoreandmorefrequencybands,forexample,dozensorevenhundredsoffiltersmaybeimplemented,makingtheRFfront-enddesignextremely

complex.

Ontheotherhand,5GNRhastoextendtothemmWavespectrumtomeettheexplodingvolumeofdatatraffi