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ContentsContents 11.Introduction 32.Scenarios 42.1.CoverageEnhancementScenarios 42.1.1.BlindSpotsCoverageEnhancement 42.1.2.WideAreaCoveragewithLowCostSolution 52.2.PersonalizedCommunicationServicesScenarios 62.2.1.NearFieldSecurityCommunicationScenarios 62.2.2.AcousticalControlScenarios 73.ProgressinKeyTechnology 83.1.RIS-BasedNear-fieldCommunications 83.1.1.RISConstructingNear-fieldWirelessPropagationEnvironment 83.1.2.TypicalNear-fieldModesbasedonRIS 103.1.3.RISNear-FieldBeamFocusingCodebookDesign 123.2.SensingandPositioning 163.2.1.RIS-AssistedSensingStrategy 163.2.2.ImpactofRISSidelobeonSensing 183.2.3.RISCollaborativeSensingandLocalization 193.2.4.RIS-AidedJointCommunicationandPositioningScheme 213.3.PhysicalLayerSecurity 273.3.1.RIS-AssistedPhysicalLayersecurityTransmissionTechniques 293.3.2.PhysicalLayerKeyGenerationTechniquesAssistedbyRIS 323.4.Low-CostNetworkingDesign 353.4.1.CostCategoriesandPerformanceAnalysis 353.4.2.ReducedOverheadTransmissionScheme 363.5.ResearchonRISDeployment 413.5.1.DynamicCoverageEnabledbyZeroPowerStaticRIS 413.5.2.DistributedandCentralizedRISDeploymentinMultiAntennaNetworks 424.ProgressinVerificationTest 434.1.SystemLevelSimulationVerification 434.1.1.MethodologyofSystemLevelSimulation 434.1.2.EvaluationIndicatorsandFactors 444.2.TrailTestVerification 464.2.1.RISReflectorEnablestheEnhancementofIndoormmWaveCoverage 464.2.2.TransmissiveMetasurfaceEnablestheEnhancementofmmWaveCoverageattheBottomofBuildings 484.2.3.Shenzhen5GCurrentNetworkRISTestingSystem 494.2.4.HangzhouAsianGames5G-ARISApplicationPilot 535.ProgressinEngineeringPracticeandStandardization 555.1.OverviewonEngineeringPractice 555.2.OverviewonStandardEvolution 565.2.1.IMT-2030(6G) 565.2.2.CCSA 575.2.3.ETSI 575.2.4.3GPP 575.3.PotentialEnhancementAspectsforStandardization 586.NetworkDeploymentChallenges 616.1.ContinuousCoverageinHigh-FrequencyMillimeter-WaveBands 616.2.ChallengesofRISubiquitousdeployment 626.3.ChallengesofControlMode 626.4.ChallengesofIntegratedCommunication-Sensing-EnergizingNetworks 637.Conclusion 64References 65Abbreviations 71Listofcontributors 731.IntroductionThefifthgenerationmobilecommunication(5G)networkhasbeencommerciallyimplementedforfouryears,withanincreasinglycompletenetworkfoundationandenhancedinnovationcapabilities.Theempowermenteffectcontinuestobeprominent,andtheassignmenteffectbecomesmoresignificant.By2023,approximately4815Gbasestationshavebeenbuiltglobally,withatotalof1.42billion5Gmobilephoneusers.Theapplicationof5Gindustryhasalsobeenintegratedinto60majorcategoriesofthenationaleconomy,becominganacceleratorforpromotingthedigitaltransformationandupgradingoftherealeconomy.NewkeytechnologicalinnovationssuchasMulti-InputMulti-Output(MIMO)andMillimeterWave(mmWave)haveinjectedacontinuousstreamofvitalityintotheintergenerationalevolutionofmobilecommunicationsystems,increasingnetworkcapacitybythousandsoftimesandprovidingubiquitousconnectivityforbillionsofdevices.However,thehighcomplexity,highcost,andhighenergyconsumptionbroughtaboutby5Gkeytechnologieshavenotbeenresolved.Forexample,expandingtheapplicationoflarge-scaleMIMOfromthefrequencybandbelow6GHztothemmWavefrequencybandtypicallyrequiresmorecomplexsignalprocessingandmoreexpensiveandenergyconsumingRFhardware.Therefore,thefuturesixthgenerationmobilecommunication(6G)willcontinuetoexplorehigherspectrumefficiency,higherenergyutilizationefficiency,andhighercost-effectivenesstoachievethebeautifulvisionoflargercapacity,lowerlatency,higherreliability,highersecurity,andmorecomprehensivecoverage.ReconfigurableIntelligentSurface(RIS)isanewtechnologythatcontrolsthepropagationcharacteristicsofelectromagneticwavesthroughadjustableelectromagneticcomponents.Itiscomposedoftightlyarrangedlow-costpassiveelectromagneticmetamaterials.Byintroducingadjustabledevicearraysandcontrolmodules,theworkingstateofeachcomponentisindependentlyadjustable,causingamplitudeand/orphasechangesintheincidentsignal,therebyachievingfine-grainedthree-dimensionalbeamforming.RIScanactasarelaynodetoempowercommunicationnetworks,potentiallybreakingtheuncontrollablefactorsbroughtbytherandomnessanduncertaintyoftraditionalwirelessenvironmentstomobilecommunicationnetworks,reshapingthewirelesspropagationenvironment,providingnewdegreesoffreedom,andpavingthewayfortheimplementationofintelligentandprogrammablewirelessenvironments.RIShastheadvantagesoflowpowerconsumption,lowcost,lowthermalnoise,fullduplex,andeasydeployment,andhasthepotentialfordeploymentinfuturenetworks.RIS,asanemerginginterdisciplinarytechnology,requiresthecollaborativecooperationofdisciplinessuchaswirelesscommunication,radiofrequencyengineering,electromagnetics,andmetamaterials.Relevantresearchandexperimentalworkhasbeencarriedoutbytheglobalacademicandindustrialcommunities.Afterseveralyearsofvigorousresearch,breakthroughshavebeenmadeintheresearchofRIS,aimedatcommercialimplementation.Theindustryisworkingtogethertoactivelyovercomeengineeringchallengesandgraduallymovetowardsthetechnologicalgoalsoflowcost,lowpowerconsumption,andeasydeployment,layingasolidfoundationforthewidespreaddeploymentofRISinthefuture.Thiswhitepapersummarizesthelatestdevelopmentsintheindustryfromseveralaspects,includingapplicationscenarios,keytechnologies,verificationtesting,engineeringpractice,andstandardization,inordertoconsolidatetheindustry'sconsensusonthevalueofthistechnology.Atthesametime,itproposesthechallengesthatRISmayfaceinfuturenetworkdeployment,advocatesfortheindustrytoovercomedeploymentdifficultiestogether,andopensupthewayforearlycommercialimplementation.2.Scenarios2.1.CoverageEnhancementScenarios2.1.1.BlindSpotsCoverageThemosttypicalapplicationscenarioofReconfigurableintelligentsurface(RIS)isservingaslow-cost,low-powerchannelenvironmentcontrolnodesonthesideofwirelesscommunicationchannels.AsshowninFigure2.1,RISisdeployedtoenhancedeepcoveragerequirementssuchasfillingcoveragegapsinmobilenetworksandincreasingmulti-streamthroughput.RISisdeployedbetweenBSandcoverageblindspotstodynamicallyconstructnon-line-of-sightreflectionpathsoralterelectromagneticwavetransmissioncharacteristics.Thereexistcoverageholesinthecellularnetworkwheresignalisblockedbyobstacles,includingtheshadowareaofbuilding,thestreetcornerindenseurbanarea,theedgebetweenindoorandoutdoor(orbetweenin-vehicleandout-vehicle).Intheabovescenarios,RIScanbedeployedbetweenthebasestationandthecoverageholestoimprovethecoverageperformancethrougheffectivelyreflecting/transmittingthetransmissionsignaltoreachtheblindareaofcoverage.(a)(b)(c)Figure2.1CoverageEnhancementScenarioswithRISassistedinmobilenetwork:(a)Blindspotscoverageenhancement;(b)O2Icoverageenhancement;(c)Indoorcoverageenhancement.2.1.2.WideAreaCoveragewitAdditionally,RIScanbeutilizedtooptimizethedesignofActiveAntennaUnits(AAUs),enablingtherealizationoflow-cost,low-power,andcompactwide-angle,high-gainAAUs.ByintegratingpassivereflectiveRISwithAAUs,itbecomespossibletoachieveintegrateddynamicintelligentcontrol,expandingthecoverageangleofbasestationswhileeffectivelyincreasingtheaperturegainoftheantennaarrayandenhancingbasestationcoveragegain,asillustratedinFigure2.2.Furthermore,byintegratingrefractiveRISwithAAUs,itisfeasibletofurtherextendthecoverageangleofbasestations,effectivelyexpandingthecoveragerangeofbasestations,therebyaddressinglow-capacityscenariosinremoteandsuburbanareasandmitigatingcoverageblindspotsatlowcostandpowerconsumption,asdepictedinFigure2.3.Figure2.2AAUsintegratedwithpassivereflectiveRIS.Figure2.3AAUsintegratedwithpassiverefractiveRIS.2.2.PersonalizedCommunicationServicesScenarios2.2.1.NearFieldSecurityCommunicaThetransmissioncharacteristicsofelectromagneticwavesaredistance-dependent.TheregionwherethetransmissiondistanceexceedstheRayleighdistanceiscalledthefar-fieldregion,whiletheregionwhereitislessistermedthenear-fieldregion.Inthenear-fieldregion,theuniquesphericalwave-basednear-fieldpropagationnotonlycarryangleinformationbutalsodistanceinformation.Therefore,electromagneticbeamsconvergesimultaneouslyintheangularanddistancedomains,formingnear-fieldbeamfocusing[1].InwirelessnetworksassistedbyRIS,thenear-fieldrangeisdeterminedbytheharmonicmeanofthedistancesbetweenthebasestation(BS)andtheRIS,andbetweentheRISandtheuserequipment(UE).Hence,aslongaseitherofthesedistancesislessthantheRayleighdistance,RIS-assistedcommunicationoperatesinthenear-fieldregion[1].Whenusersarelocatedinthenear-fieldradiationzoneofRIS,near-fieldcodebookstailoredtospecificuserscanbeconfiguredfortheRIS.Thisfocusesthenear-fieldbeamsontheauthorizeduser'sspecificangleanddistance,asdepictedinFigure2.4.Otherusers,eveniflocatedinthesameangularareaastheauthorizeduser,cannotinterceptwirelesssignalstoachieveeavesdropping,ensuringhigh-securitylevelcommunicationservicesforspecificusers.Figure2.4NearFieldSecurityCommunicationScenariosofRIS.2.2.2.AcousticalContInadditiontoitsapplicationinelectromagneticwavecontrol,RIScanalsobeutilizedforacousticalwavecontrol.Arelevanttechnicalteam[2]hasdevelopedacousticalRISwithprogrammablecontrolcapabilities.BymanipulatingtheresonancemodesofeachacousticalRISunit,thephasedifferenceofacousticalwavescanbedynamicallycontrolledwithouttheneedformanualadjustmentstothesoundsourceorsurroundingscatters.Thisdynamiccontrolcaninfluencethedistributionofthesoundfieldthroughouttheentirespace,enablingthesuppressionorenhancementofthesoundfieldintensityataspecificlocationwithinthespace.Thiscapabilityprovidesservicessuchassilencingorvolumeenhancementforspecificusers,asillustratedinFigure2.5.Figure2.5AcousticalControlScenariosofRIS.3.ProgressinKeyTechnology3.1.RIS-BasedNear-fieldCommunications3.1.1.RISConstructingTraditionalwirelesscommunicationnetworks(1G~5G)mainlyusefrequenciesbelow6GHz,andevenbelow3GHz.Limitedbywavelength,thesenetworksgenerallyuseasmallnumberofantennaarrays.Duetothelow-dimensionalantennaarrayandlowfrequency,thewirelessnear-fieldrangeisusuallylimitedtoafewmetersorevenafewcentimeters.Therefore,thefar-fieldassumptioncanbeusedtodesigntraditionalwirelesscommunicationsystemseffectively.However,consideringthelargeapertureandextremelyhighfrequencyofELAA,the6Gnetworkpresentsasuperlargenear-fieldareaofhundredsofmeters,andthetraditionalfar-fieldplanewaveassumptionisnolongerapplicable[3].Therefore,inthe6Gnetwork,thenear-fieldareaisnotnegligible,whichstimulatestheresearchofnewnear-fieldcommunication(Near-fieldCommunications,NFC)paradigms.Fromtheperspectiveofspatialresourceutilization,thetypicaldeploymentoftraditionalcellularnetworksisastandardnetworkarchitecturecenteredonthecell.Underthisnetworkarchitecture,especiallyinitsmainstreamsub-6GHzfrequencyband,thefar-fieldapproximationissufficientasacharacterizationmeans.Traditionalwirelesscommunicationsystemshavefullyexploitedandutilizedfar-fieldspatialresources.Furtherexplorationandutilizationofnear-fieldspatialresourcesareexpectedtoprovidenewphysicalspatialdimensionsforwirelesscommunicationsystems.Future6Gnetworkswillbeequippedwithlargerantennaapertures,andwillusehigherfrequencybandssuchasmillimeterwavesandterahertz.Thiswillmakethenear-fieldcharacteristicsmoresignificant.Atthesametime,theintroductionofnewtechnologiessuchasRIS[4,5],ultra-large-scaleMIMO,andcell-free(Cell-free)[6]willmakenear-fieldscenariosubiquitousinfuturewirelessnetworks.Near-fieldcommunicationtechnologyisalsooneoftheenablingtechnologiestoachievehigherdataraterequirements,high-precisionsensingdemands,andwirelesspowertransmissionneedsoftheIoTinthefuture6Gnetwork,andhastheopportunitytobecomeoneofthekeytechnologiesofthefuture6Gwirelessairinterface.Amongthem,RIS,withitsmanycharacteristicssuchaslargesize,passiveabnormaladjustment,lowcost,lowpowerconsumption,andeasydeployment,hastheopportunitytobuildaubiquitousnear-fieldwirelesspropagationenvironmentinthefuture6Gnetwork,andbringanewnetworkparadigm[7].Thenear-fieldpropagationcharacteristicsbringmorepossibilitiesforthefuture6Gnetwork,buttheconstructionofthenear-fieldpropagationenvironmentbasedonthetraditionalactivephasedarrayantennaalsofacesmanychallenges:(1)theultralargesizeactivephasedarrayantenna(APAA)hasgreatlyimprovedintermsofhardwarecost,complexity,powerconsumption,weightandvolume,whichisdifficulttoachieveintensivedeployment,andtheavailablenear-fieldcoverageareaislimited;(2)Thenear-fielddistancereachesthemaximumnearthenear-axisoftheAPAAarrayandgraduallydecreaseswiththeincreaseoftheoff-axisangle,whichfurtherlimitsthecoverageofthenear-field;(3)UnlikecommunicationservicesbenefitingfromtheNonLine-of-Sight(NLOS)multipathenvironment,theidealpropagationenvironmentforperceptualpositioningandwirelessenergytransmissionservicesisthenear-fieldLine-of-Sight(LOS)channel.OnlythetraditionalAPAAwithcentralizeddeploymentisadopted,andtheprobabilitybetweenitandthetargetisNLOSmultipathchannel.AlthoughmanyliteratureshavestudiedtheCell-free/CoordinatedMulti-Point(CoMP)technologiesbasedonthetraditionalactivephasedarrayantenna[6,8],althoughthiskindofdistributedantennatechnologycanalleviatetheAPAAproblemofcentralizeddeploymenttoacertainextent,itisstilllimitedbytheinherenttechnicalcharacteristicsoftheactivephasedarrayantenna,anditisdifficulttoachieveintensiveubiquitousdeployment.TheuniquetechnicalfeaturesofRIScanbeusedasaneffectivemeanstosolvethechallengesfacedbytraditionalactivephasedarrayantennas.First,RIS,asaprogrammabletwo-dimensionalelectromagneticmetasurface,canabnormallycontrolelectromagneticwavesinapassivemanner,withtheadvantagesoflowcostandlowpowerconsumption,andcanbeeasilymadeintoalargeantennaaperture,thusrealizingdensedeploymentatalowcost.Second,RIStypesarediverseandcanflexiblyadapttocomplexanddiversedeploymentenvironments.Fromafunctionalperspective,RIStypescanincludechannelcontroltype(e.g.,reflectiveRIS,transmissiveRIS,andsemi-transparentsemi-reflectiveRIS),informationmodulationtypeRIS(e.g.,RIS-basednewbasestation,RIS-basedbackscattertransmitter,andRIS-basedcompanioncommunication),andRIS-basednewphasedarrayantennas,etc.RIScanbeeasilymadeintodifferentsizes,shapes,andsurfaceformstomeetdifferentdeploymentrequirements.Finally,thesimpleandeasy-to-deployfeaturesofRIScanalsoeasilybuildanear-fieldLOSenvironment,therebybettersupportingtheneedsofperceptionpositioningandwirelesspowertransmission.Inaddition,sinceRISispassivecontrol,itnaturallyhasalowlevelofelectromagneticradiation,whichcanstillmeetthehumanelectromagneticradiationsafetyindexspecificabsorptionrate(SpecificAbsorptionRate,SAR)intheubiquitousnear-fieldenvironment.Insummary,comparedwithtraditionalactivephasedarrayantennas,RIShasthecharacteristicsofpassivecontrol,lowcost,andeasydeployment,andcanbedenselyandwidelydeployed,thushavingtheopportunitytobuildaubiquitousnear-fieldchannelenvironmentforfuture6Gnetworks.TheintroductionofRIShasconstructedacascadedchannel,andthewirelesspropagationenvironmentoffuture6Gnetworkswillbemorecomplexanddiversecomparedwithtraditionalnetworks.Fromtheperspectiveofnear-fieldpropagationenvironment,thetypicalnear-fieldmodesconstructedbyRIScanbeclassifiedasTable3.1-Table3.4.Thesesceneclassificationscanbereferredtowhenanalyzingthenear-fieldpropagationcharacteristicsofRIS.Table3.1Near-fieldfromtheperspectiveofRISfunction.FunctiontypeNear-fieldCharacteristics1Extendnear-fieldcoverageareaRISTypeforChannelRegulation2Overcomenear-fieldcoveragegaps3ConstructnewLOSnear-fieldRIS-basedNewPAAAchievelargeaperturephased-arrayantennaswithlowcostandcomplexity,enhancingnear-fieldcoveragedistance.RISTypeforInformationModulationForlow-rateIoTdevicecommunication,buildanear-fieldtransmittingenvironmentTable3.2Near-fieldfromtheperspectiveoftransmissionandreflectiontypes.Near-fieldCharacteristicsReflectiveRISConstructinganear-fieldpropagationenvironmentwithinthepositiveanglerange(0,π)oftheRISincidentonsignalelectromagneticwavesTransmissionRISConstructinganear-fieldpropagationenvironmentwithintherangeofthereverseangle(π,2π)oftheRISincidentonthesignalelectromagneticwaveSimultaneousTransmittingandReflectingReconfigurableIntelligentSurfaces(STAR-RIS)Constructanear-fieldpropagationenvironmentwithintheanglerange[0,2π)Table3.3Passive/ActiveRISnear-field.Near-fieldCharacteristicsPassiveRISFocustheincidentelectromagneticwavesignalinthenear-field,butthesignalstrengthislimitedActiveRISFocustheincidentelectromagneticwavesignalinthenear-fieldandamplifythesignal.ItcanovercometheproblemoflimitedsignalstrengthinpassiveRIS,butthecomplexityisslightlyhigherTable3.4Near-fieldandfar-fieldcombinationsinRISnetworks.Near-fieldCharacteristicsSingleRIScascadedchannel(NB-RIS-UE)NB-RISchannel:near-field/far-fieldRIS-UEchannel:near-field/far-fieldMultipleRISscascadedchannels(NB-RIS-RIS-UE)RIS-RISchannel:near-field/far-fieldNB-RISchannel:near-field/far-fieldRIS-UEchannel:near-field/far-field(RIScascadedchannel)+(NBandUEdirectchannel)NB-UEdirectchannel:near-field/far-fieldRIS-RISchannel:near-field/far-fieldNB-RISchannel:near-field/far-fieldRIS-UEchannel:near-field/far-field3.1.3.RISNear-FieldBeamFocusiToachievesignificantspectralefficiencygain,reconfigurableintelligentsurface(RIS)needstoensureasufficientlylargeradiationarraysize.Astheradiationarraysizeexpandsandthecarrierfrequencyincreasesfurther,theprobabilityofuserequipment(UE)beinginthenear-fieldregionoftheRISgreatlyincreases.Traditionalchannelmodelbasedontheplane-waveassumptionarenotsuitablefordescribingthenear-fieldchannel.Therefore,itisnecessarytofurtherconsideradoptingachannelmodelbasedonthespherical-waveassumption[9].Thechannelmodelbasedontheplane-waveassumption,groundedinFouriertheory,treatsthepropagationofradiowavesasalinearsystem[10].Basedonthis,5GNewRadio(NR)designscodebookusingdiscreteFouriertransform(DFT)vectors.WhiletheDFT-basedcodebookissuitableforfar-fieldbeamforming,whendirectlyappliedtonear-fieldbeamfocusing,severesignal-to-noiseratio(SNR)lossesoccurduetomismatcheswiththenear-fieldchannel.Incontrast,thebeamfocusingschemebasedonthespherical-waveassumptioncancompensateformismatcheswiththenear-fieldchannel,formingtheoptimalcoherentbeamformerforthenear-fieldchannel[11].Takinga1m×1mRISwith1-bitphasequantizationinthemillimeter-wave(mmWave)frequencyband(30GHz)asanexample,suchanRIScanintegrateapproximately40,000radiationelements.Figure3.1illustratesthecomparisonofbeamforminggainsachievedbytheRISusingtheDFT-basedcodebookforbeamformingandemployingthebeamfocusingscheme.Itcanbeobservedthatwithina100mRayleighdistancedR,thebeamforminggainoftheDFT-basedcodebookexhibitsadampingoscillationtrend,whichislowerthanthatofthebeamfocusingscheme.Here,theRayleighdistanceisdefinedasdR=,whereDrepresentstheapertureoftheradiationarray,λdenotesthecarrierwavelength,anditistypicallyone-quarteroftheFraunhoferdistance,acommonlyusedboundarybetweennearandfarfields[12].FromtheresultsshowninFigure3.1,thefollowingobservationscanbemade:1)Thenear-fieldrangeofalarge-sizeRIScanextendtooverahundredmeters,indicatingthatthemajorityofUEwillbewithinthenear-fieldregionoftheRIS.2)WhendirectlyapplyingthetraditionalDFT-basedcodebooktoalarge-sizeRIS,significantbeamforminggainlosscomparedtothebeamfocusingschemeoccurs.Therefore,itisnecessarytoconsiderdesigninganewcodebookforlarge-sizeRIStoadapttonear-fieldcommunication.Figure3.1ComparisonofbeamforminggainsbetweenDFT-basedcodebookandbeamfocusingscheme.ToovercometheSNRlossgeneratedbydirectlyapplyingtheDFT-basedcodebooktothenear-fieldregionoftheRIS,thering-typecodebook(RTC)whichismoresuitablefornear-fieldbeamformingbasedontheFresnelprincipleisproposed[13].TheRTCconsistsoftwolayers:thefirstlayeristhering-typevectorfocusinglayer,andthesecondlayeristheDFTvectorsteeringlayer,whichiscompatiblewiththeDFT-basedcodebook.(ab)Figure3.2SchematicDiagramoftheRTC.(a)Firstlayer(b)Secondlayer.TheprincipleofachievingbeamfocusingusingtheRTCisillustratedinFigure3.2.BasedonthepositioninformationoftheUErelativetothecenteroftheradiationarrayoftheRIS,thefirstlayeroftheRTCisusedtoindicatetheformationofanormalfocusedbeam.ThisbeamfocusesthefocalpointonthefocalplanewheretheUEislocated,asshowninFigure3.2(a).Subsequently,theDFTvectorinthesecondlayerofthecodebookisusedtosteerthefocusedbeamformedbythefirstlayeralongthefocalplanetopointtowardstheUEatacertainangle,asdepictedinFigure3.2(b).(a)(b)(c)(d)Figure3.3PhasedistributionoftheRISelementsindicatedbytheRTC.(a)Phasedistributionofthefirstlayerfocusingvector;(b)PhasedistributionofthesecondlayerDFTvector;(c)Phasedistributionofsteeredfocusedbeam(d)Quantizedphasedistribution.Figure3.3presentsanexampleofthephasedistributionoftheRIStoachievebeamfocusingthroughtheRTC.Firstly,thering-typephasedistributionofthefirstlayeriscomputedbasedontheFresnelprinciple,asshownin(1)-(5).Then,thering-typephasedistributionissuperimposedwiththeDFTsteeringvectorphasedistributionofthesecondlayertoobtainthephasedistributionofthesteeredfocusedbeam.Finally,thequantizedphasedistributionisoutputted.Therangeofthem-thfullbandcanbecalculatedasfollowsRm=mλ)2+2mdλ,(1)whereλrepresentsthefree-spacewavelength,andddenotesthespacingbetweenRISelements.LetLrepresenthalfofthediagonallengthoftheRISarray.WhenLisgreaterthanRN?1andlessthanorequaltoRN,thenumberofsubbands,denotedasPN,canbeobtained.Here,Prepresentsthenumberofsubbandsineachfullband,whichcanbecalculatedasfollowsP=2BIT,(2)whereBITrepresentsthenumberofphasequantizationbitsfortheRIS.Therangeofeachsub-bandcanbecalculatedasfollows0<x+y<?,<x+y<?n,n=2,3,?,PN,whereTn=2+,n=1,2,?,PN,(3)(4)(5)xi,yirepresentsthecoordinatesoftheRISelements.ToverifytheperformanceenhancementoftheproposedRTCwithinthecoverageareaoftheRIS,numericalsimulationresultsareprovided.ThesimulationscenarioisillustratedinFigure3.4,withacarrierfrequencysetat30GHzinthemmWave.Itisassumedthatthedirectlinkbetweenthebasestation(BS)andtheUEisobstructedbyobstacles,andthesignalistransmittedtotheUEthroughtheBS-RISandRIS-UElinks.A0.64m×0.64m1-bitphasequantizationrectangularRISisdeployedapproximately80mawayfromtheBS.OthermajornumericalsimulationparametersarelistedinTable3.5.Figure3.4SimulationscenarioofRIS-aidedcommunication.Table3.5Numericalsimulationparameters.ParameterCarrierfrequency30GHzBandwidth400MHzBStransmitpower30dBmBSantennagain5dBiBSantennanumberDistancebetweenBSandRIS80mBStoRISpathlossUMi-LOSRISelementgain3.5dBiRISelementnumberRIStoUEpathlossUMi-LOSUEantennagain5dBiUEantennanumber1UEnoisefigureShadowingσ=4OtherlossFigure3.5andFigure3.6depicttheSNRandthroughputcomparison,respectively,whentheRISemploystheproposedRTCandtraditionalDFT-basedcodebookforbeamforming.ItisevidentthattheproposedRTCoutperformstheDFT-basedc
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