ADAPTIVE POWER ALLOCATION FOR COOPERATIVE NOMA SYSTEM WITH IMPERFECT SIC

InternationalJournalofElectronicsand CommunicationEngineering(IJECE)

ISSN(P):2278–9901;ISSN(E):2278–991X

Vol.11,Issue2,Jul–Dec2022;1

8

ADAPTIVEPOWERALLOCATIONFORCOOPERATIVENOMASYSTEMWITH IMPERFECTSIC

VarunikaDixit1&Dr.A.K.Shankhwar2

1ReserachScholar,HBTU,Kanpur,India

2AssociateProfessor,DepartmentofElectronicsEngineering,HBTU,Kanpur,India

ABSTRACT

Nowadays,thewirelessnetworksdemandhighspectralefficiency,reliabilityandenergyefficiencyforfutureneeds.Inthe recentdecade,non-orthogonalmultipleaccess(NOMA)withtwo-usercooperativeschemeshasreceivedconsiderable attentionfor5Gsystems.Thisworkdemonstratesbetweenthesourceandfaruserthatnotasinglelinkisdirectly establishedandwecommunicateviathenearuser.Weintroduceanadaptivepowerallocationschemewiththe combinationofcooperativeNOMAnetworks.Thepreferredschemeselectsthebestuserrelayonthebasisofperformance whilethedistributionofpowerallocationcoefficientsiscalculatedinordertoavoidthewastageofpower.Thisapproach alsogivesabriefdiscussionontheissueofimperfectsuccessiveinterferencecancellation(SIC)problemswiththe combinationofadaptivescheme.Acomprehensiveanalysisontheachievabledatarate,sumrateandsumcapacity performanceofthepreferredschemeisdoneontheMATLABmfileuserinterfaceandclosedformexpressionisobtained. Throughanumericalapproach,wecomparetheperformancesoffixedandfairadaptivepowerallocationnetworks.These simulationsresultwithvariousprocessparameterssuchastransmitpowerforthesameerrorperformanceofafixedand fairpowerallocationscheme.Thatshowstheimprovementintheadaptiveschemeintermsofachievablecapacityusing differentpowerallocationschemes.

KEYWORDS:AdaptivePowerAllocationScheme,CooperativeNOMANetwork,FifthGeneration,Non-Orthogonal MultipleAccess(NOMA),SuccessiveInterferenceCancellation

ArticleHistory

Received:13Jul2022|Revised:19Jul2022|Accepted:25Jul2022

I.INTRODUCTION

Whenthenumberofdevicescanincreasetoenhanceconnectivity,non-orthogonalmultipleaccess(NOMA)techniques makeadifferencefromotherfundamentalorthogonalmultipleaccess(OMA)schemes[1].TheNOMAtechnique encouragesmultipleuserstotransmittheinformationwithdifferentpowerdomains,butatthesametime,codeand frequency[2].NOMAallowsthesuperpositioncodingatthetransmitterendandachievestheactualinformationusing successiveinterferencecancellation(SIC)techniquesatthereceiverend.ThemainworkofNOMAisdistributingthe properpowertousersaccordingtotheirchannelstatus.Atthereceivers,thesuccessivedetectionstrategyisperformedand theuserhavingbetterchannelstatusconveysthemessagesignalsremainingtoallotherusers.Inthesimplemanner,the user-relayneedstobeusedfortheenhancementofresponsebetweenthepoorconnection’suserandthesource[3].

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Consequently,CooperativeNOMAisaneffectualtechniquethatopposedifferentchannellossessuchasfading, shadowingandpathloss.Thismustbebroadeningthecoverageareaofcommunicationsystems[4].Underthistechnique, theclosestusersfrombasestation(BS),i.e.,knownasnearusers,shouldbeusedasrelayforotherfarusersfromBS,i.e., knownasfarusers.Dependingonthecurrentscenario,cooperativeworkscanbecategorisedintotwotypes.Thededicated relaysarethefirstcategoryofcooperationrelayscheme.Theserelayssetupthelinkbetweenthebasestation/sourceand NOMAusers.However,usercooperationschemeactsasasecondcategory,wheretheweakuserscanbereceiveddata fromthestrongusers.Stronglyconnectedusersactasrelaysforweakconnectedusersfromthebasestation/source[5],[6]. Thesimplestformofcooperativerelayingnetworkcontainsthreeprimarynodes,namedasthesource,relayand destination.Inparticular,AmplifyandForward(AF)relayfirstlycollectthesignalfromsourcenodethenaheadthe measuredsignaltothedestinationnode[7].In[8]authordetectsthatDecodeandForward(DF)relayfirstlyendeavoursto accessthereceivedsignalandretransmitstheretainedinformationtothedestinationnode.Thecombinationisnatural becausetheinformationforthefarusersisknowntothenearusersowingtoSIC.Theselectionofrelayperformsavitalrole formulti-relaynetworksthatistheonlypathtodesirelow-complexityandhighdiversitygain.However,theseworksarefully focusedonthededicatedrelaycooperationschemetofindoutbestwayforthefixedrelayselectioncriteria[9],[10].

Inthispaper,anAdaptivecooperativetransmissionschemeisfullyexploitedonthepreviouslyavailable informationinNOMAsystems[11].Thesystemperformanceofadaptiveusercooperative-NOMAismajorroleforthe investigationoftheimpactofuserrelayselection(URS).IntheSICreceiver,Thesubtractedsignalisimperfectwith respecttotheNOMAconceptanditsimpactisalsopresentedonoverallcapacityperformance[12],[13].Thebasickey featuresofthethesisaresummarizedasbelow:

 Weobtainthesumcapacity(SC)ofpreferredNOMAunderbothperfectandimperfectSICframework.Inorder to,previousresultofresearchersisconfirmedbyoursimulationresults.

 ForafixedpowerallocationofAdaptiveNOMA,wecreateanadaptivenetworkutilizestandardcooperative NOMAasacriterion.WeadditionallyperformedtheAdaptiveNOMA-RSschemeunderperfectSIC,whereas performancegainsunderimperfectSICsignificantlyconcentrateonthelevelofresidualinterference.

 ForafairpowerallocationofAdaptiveNOMA,wecreateanadaptivenetworkutilizestandardcooperative NOMAasacriterion.WeadditionallyperformedtheAdaptiveNOMAschemeunderperfectSIC,whereas performancegainsunderimperfectSICsignificantlyconcentrateonthelevelofresidualinterference.

II.SYSTEMMODEL

Consideradownlinkscenariowithhalf-duplexuserrelayassistedNOMAschemeasillusioninFigure1.Accordingtothat onebasestation(BS)orsource,twousers,andamplify-and-forward(AF)-basedtransmissionprotocol.Itisalsoinvolving theusercooperationrelay.Weassumethateachnodecanaccuratelydetectitschannelstateinformation(CSI)usingby equippingahalf-duplexmodeantenna.Thereisnodirectcommunicationbetweenthesourceandthefaruserscauseof physicalobstaclesandshadowingeffect.Thesourcetorelayandrelaytouserchannelsarefacinganindependentand identicallyRayleighflatfading.Theuser1worksasapotentialrelayfortheuser2.Ourassumptionsshouldonlybe applicableforurbanareaswheremultiplenodesmaybepositioned.Theselinesareinterestingtopicfortheprevious researches.

IncooperativeNOMA,thecommunicationisestablishedusingsuitablelinkandit’salsoinfluencedthedatarate ofauser.Thedesignofsystemmodelisexaminedsuchamannerafterthataperfectcancellationshouldbeappliedinthe users.ThemodelcontainsthebenefitsofboththeNOMAandcooperativediversityschemes.Originofeverytimeframe, theBStransmitsthesuperimposedsignalofaj user.Thatsignalmaybeexpressedasfollows:

Where, isthemessagesignalof userofsourcesignal.Thefixedpowerallocationcoefficientsfactoris with0< <1and + =1.Thedenotesthetransmitpowerconstraintforthemessage .Atthe user relay,user1decodeshigherpowersymbol byowinglowerpowersymboluser2actasanoise,andrevokesitto performcancellationtechnique.Consequently,thereceivedmessagesignalatthe userrelayingisrepresentedas:

Where,expresspowerthattransmitstowardstheBSand iszeromeanandunitvariancecomplexadditive Gaussiannoise,i.e.,representedas

ThelowerandhigherdataratecanbedistributedaccordingtothepairofSU1andU1-U2continuously.The channelcoefficientsare ~ = , = forthelinkssourcetotheuser1(S–U1),anduser1totheuser2(U1U2),respectively.Thedistancebetweenvehicleiandjrepresentsas inmeters,and denotesthepathlossexponentialparameter.Withoutlossofgenerality,User’schannelhasbeenanticipatedas

| becauseitisassumedthat<

Infairpowerallocationsection,theschemeisbasedondistributionofprioritytoone’suser.Wecansaythatthe calculationofpowerallocationcoefficientsisbasedonthetargetrateoffaruser.Oncethetargetrateoffaruseris assignedbygivenformula,alltheremainingpowerisallocatedtothenearuser.Thisschemeisalsoknownasthedynamic powerallocationoftheusers.Therefore,thepowerallocationcoefficientsofthefairPAschemearegivenas:

whereφdenotesthetargetSINRwhichderivedfromtargetrateoffaruserandisequalto2 ofthethreshold targetrate.ThepowercoefficientofotheruserisassignedastheoneminusofthepowerallocationcoefficientsofthefairPA.

Figure1:SystemModelofAdaptiveCooperativeNOMA.

Conversely,NOMAtransmitsthedatabetweenbasestationanddestinationamongdifferenttransmissionphases. Weusetodenotethesignaltonoiseratio(SNR)foruserjtodetectuseri’ssignalinthispaper.Incellularnetworks,SIC shouldbesuccessfullyappliedandthedatarateofuserisincreasinginlinearmannerthatalsomakeenhancementonthe transmittedSNRTherefore,thesignaltonoiseratio(SNR)attheuser2canberepresentedasbelowinNOMAsystem:

Moreover,wefirstlydecodedataoftheuser2thantheuser1.Itcancelsfromthereceivedsignalanddetectsits owndata.isdefinedasthepowerspectraldensityofwhiteGaussiannoise.Therefore,thereceivedSNRatuser1related tosource’sdata canbeexpressedas:

WeconsiderthedownlinkandrecallthatSICreceiverdecodestheuserinformationonebyoneiterativelyunless wefindthedesiredsignalofthatuser.AccordingtoSICscheme,regenerationoftheoriginalindividualwaveformshould performtoapproachonthedesiredsignal.So,one’ssubtractedallthehighlypoweredsignalfromthereceivedsignal. Theoretically,itiseasytocompletesuchadifficulttaskwithoutanyerror,inpractical,itisexperiencingsomecancellation error.Onthatbasis,weexplorethatsomehigh-powersignalispresentaftertheSIC.Indownlink,theSNRforthefaruser withcancellationerroriswrittenas:

Where,istermedassuccessiveerrorcancellationthatrepresentstheundesiredportionofthemessagesignal. Theself-interferencecancellationrepresentsperfectlyas=0inbeforeinstances.Inthesection,thedenominatorofSNR termisincludedimperfectcancellationterm.

III.PROPOSEDPOWERALLOCATIONSCHEMES

Thesystemmodelshouldbediscussedonbelowlines:

 Infirststep,thesourcenodeisconsideredastheCSIbetweenuserrelayingnodeandfaruser/orthedestination nodebeforetransmission.Assumethatthesourcenodehaspreviousknowledgeofchannelstatebetweenitself andtheothernodes(relaynodeanddestinationnode).Ouraimistooptimizethesystemperformanceandthe powerallocationshouldbeconsideredaccordingtoknowninformation.

 Thesourcenodeitselfconveysandinformspowerallottedinformationtotheuser1,whichareactasrelays.They selecttheseuserscooperaterelayaccordingtothepowerandhigherrate.

 Theseselectedrelaysareamplifyingandforwardingoffaruser’sinformation.

 Thefaruserrecoverstheinformationfromthesourceviauserrelaysnodethatpassesandforwardsit,then combinethem.

Consequently,theachievableratesforU1andU2arerepresentedbelow,respectively:

Allthe stageconsistsonselectingtheappropriateuserrelayinganddestinationlinkonthebasisofone’s availabledistance,whichmaximizesthedatarateof atfaruser,i.e.,

Inthissubsection,wefocustheeffectofuserpairingonthesumrateandalltheuser’sdatarateusingFixed NOMAisexplored.ThisAdaptiveNOMAachievessumratecanberepresentedas:

IV.NUMERICALSTUDIES

InFigure2,wesetthesumrateachievedofboththeweakandstronguserbythetwoPowerallocationschemes,isshown asafunctionoftransmitpowerindBm,withfixedpowerallocationfactorof0.75and0.25.Asperformancestandard,we contrastbetweenthefairandfixedPApoliciesassuminguserpairingandperfectSIC.Obviously,theperformanceofthe proposedadaptivePAschemeisbetterfor4userrelaysystemwith3userrelaysystem.Foreachuserrelay,theyare selectedaccordingtotheplacementofuserfromtheBS.Thedistanceisvaryingwithrespecttouser.InthefairPA strategy,powerallocationfactorvaluesarecalculatedonthebasisofformula3,whichcanbetheuserwithbetterchannel condition.ButthefixedPAstrategycannotbesogoodresultasshowninfairPAstrategy.Additionally,theadaptivePA schemeisfavourableatmosttothestronguser.Afterthat,Noismainlyadoptedintermsofthermalerrorsandetc.The valueofpathlossisassignedtothe4.

ConsiderFigure3,theimpactofimperfectSICofintheachievablecapacitygainareresiduallyinvestigatedin termsofSICfactorandISfactor.Ascanbeseen,thecapacityincreasesasincrementoftransmitpower.Thecapacitygain obviouslydependsintermsofinterferencecoefficientatthemediumtohightransmitpower.ByusingfairPA,the capacityofgraphisimprovedasthepowerallocationcoefficientincreaseswithothernon-adaptivetechnologies.

Figure2:ImpactofUserPairingAchievedby AdaptiveCooperativeNOMAonSumRate.

Furthermore,weareverifyingimpressiveimpactofimperfectSIConthecapacity.Thevalueofpathlossis assignedtothe4.ButtheresultofimperfectSICwithrespecttothefixedPA,asshowninthefigure4,givesthe tremendouseffectofthisresearchareas.

Figure5presentsthedatarateandsumrateversusdistanceforstrongusers.Inaddition,wenoticethevariation thedistancewithrespecttothedatarateofthefaruser.Figuredemonstrateshowvariationofdistancegainfordifferent powerallocationschemesthatcanbeobtainedbypairingitwithdifferentusers.

Figure3:ImpactofImperfectSICAchievedbyFairPowerAllocation Scheme.

Figure4:ImpactofImperfectSICAchievedbyFixedPower AllocationScheme.

Intheotherhand,theperformanceofthefairPAisshowingbetterresultaccordingtothefixedPAschemeforall distancevalues.Thatisalsojustifiablethateveryrelayallocatestheadaptivepowerselectiontowardsandalsoprovide controllabilitytofadingeffects.

V.CONCLUSIONS

BycomparingOMAbasedapproaches,NOMAschemedefinitelyimprovestheusageoftransmissioninthepresenceof limitedsources.Inthispaper,wecanaddanadaptiveapproachwithoriginalcooperativeNOMAscheme.Theuser cooperationshouldbeadoptedintheparticularresearchwork.Wherealltheusersarecharacterizedonthebasisofchannel conditionsregardingtheothers’messagesinNOMAsystems.Theseresultshavebeendrawnintermsoftransmitpower anddistance.FixedandfairoptionsofadaptivePAcoefficienthavebeenappliedinthispaper,thusthemainimportantis studyingtherelayselectionstrategyforcooperativeNOMA[13].Afterthatfuturetechnologywilltryonthesimultaneous wirelessinformationandpowertransfertoNOMAaspracticallyavailable.Optimalrelayselectionstrategyisbeneficialto theavailabilityofCSIandlimitedfeedback.AnalyticalresultshavebeendevelopedthosetheadaptivePAstrategiesis selectedtherelaysonthebasisofitsmaximumvalue.Inaddition,thesimulationresultshaveauthenticatedtheadvantage ofthispowerallocationscheme.

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Figure5:AdaptiveCooperativeNOMAonSumRatewiththe DistanceofFarUserPairing.

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AUTHORDETAILS

VarunikaDixitcompletedtheB.TechdegreefromDrAITHKanpurin2019.SheiscurrentlypursuingtheM.Techwith theDepartmentofElectronicandCommunicationEngineering,HarcourtButlerTechnicalUniversity.Herresearch interestsbuildinnon-orthogonalmultipleaccessandvehicularnetworks.

Dr.A.K.Shankhwar,ProfessorandHead,ElectronicsEngineeringDept.,SchoolofEngineering,HBTUKanpur.He successfullycompletedthePhdinDesignandPerformanceEvaluationofGeneralizedRakeReceiverforHighDataRate forMobileRadioM.N.N.I.T.Allahabad.Before,hecompletedtheM.TechinDigitalTechniquesinInstrumentationfrom SGSITSIndore/RGPVBhopalandB.TechinElectronicsEngineeringfromKNITSultanpur/AvadhUniversity,Faizabad.