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PublishedonJul03,2013

GoodoneforUMTS

GoodoneforUMTS

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1.General1.WhatistheexperienceandinvolvementinyourcurrentandpreviousUMTSdesignprojects?Talkaboutyourcurrentandpreviousprojects,yourresponsibilities,designobjectives,toolsused,activitiesinvolved,challenges,objectivesmet,etc.LinkBudget2.WhatisatypicalNodeBsensitivitylevel?TheserviceandloaddeterminestheNodeBsensitivityingeneral,inanoloadcondition,thesensitivityisbetween115dBmto125dBm.ForEricsson,theNodeBsensitivityleveliscalculatedataround:CS12.2:124dBmPS64:

119dBmPS128:115dBmPS384:115dBm3.WhatisatypicalUEsensitivitylevel?TheserviceandloaddeterminestheUEsensitivityingeneral,innoloadcondition,thesensitivityisbetween105dBmand120dBm.ForEricsson,theUEsensitivityleveliscalculatedataround:CS12.2:119dBmPS64:112dBmPS128:110dBmPS384:105dBmHSDPA:95dBm4.WhatisatypicalNodeBmaximumoutputpower?ThemaximumNodeBoutputpowerisusually20Wor40W,thatis,43dBmor46dBm.5.WhatisUEmaximumtransmitpowerinyourlinkbudget?21dBm=2w6.Whatisatypicalantennagain?Theantennagaindependsonantennamodelinlinkbudgetweusearound17dBi.7.Whatisatypicalmaximumpathloss?Themaximumpathlossisdependentontheserviceandvendorrecommendationstypicallyitisinbetween135to140dBforurbanareasandbetween150to160dBforruralareas.8.WhatisdifferencebetweendBianddBd?dBiisthegainindBfromisotropicsourcedBdisthegainfromadipolesource.dBd+2.15=dBi.9.WhatisthedifferencebetweendBanddBm?dBmisaunitofpowerlevel,measuredinmilliwattsinlogarithmscale,thatis,dBm=10*log(W*1000)whereWisthepowerinWattsdBisnotaunit,itisthedifferenceindBm.10.Whatis0dBm?0dBm=1milliwatt.11.HowdoesTMAwork?ATMAreducessystemnoise,improvesuplinksensitivityandleadstolongerUEbatterylife.Sensitivityistheminimuminputpowerneededtogetasuitablesignaltonoiseratio(SNR)attheoutputofthereceiver.Itisdeterminedbyreceivernoisefigure,thermonoisepowerandrequiredSNR.Thermonoisepowerisdeterminedbybandwidthandtemperature,SNRisdeterminedbymodulationtechnique,thereforetheonlyvariableisnoisefigure.2.ThecascadingnoisefigurecanbecalculatedbyFriisequation(HeraldFriis):NFt=NF1+(NF21)/G1+(NF31)/(G1*G2)+...+(NFi1)/(G1*G2*...*Gi)Astheequationshows,thefirstblockimposestheminimumandthemostprominentnoisefigureonthesystem,andthefollowingblocksimposeslessandlessimpacttothesystemprovidedthegainsarepositive.Linearpassivedeviceshavenoisefigureequaltotheirloss.ATMAtypicallyhasagainof12dB.Therearetypicallytopjumper,mainfeederandabottomjumperbetweenantennaandBTS.ATMAplacednearantennawithashortjumperfromantennaprovidesthebestnoisefigureimprovementthenoisefigurewillberestrictedtothetopjumperloss(NF1)andTMA((NF21)/G1),andtheremainingblocks(mainfeederandbottomjumper)havelittleeffect.Tosummarize,aTMAhasagainthatsclosetofeederloss.12.Whataretheprosandcons(advantagesanddisadvantages)ofTMA?Ontheupside,aTMAreducessystemnoise,improvesuplinksensitivityandleadstolongerUEbatterylife.Onthedownside,TMAimposesanadditionalinsertionloss(typically0.5dB)onthedownlinkandincreasessiteinstallationandmaintenancecomplexity.13.WhatistypicalTMAgain?TMAtypicallyhasa12dBgainhowever,theeffectivegaincomesfromnoisefigurereductionandthegainiscloseorequivalenttothefeederloss.14.WhyTMAareinstalledatthetopneartheantennaandnotthebottomneartheNodeB?BasedonFriisEquation,havingaTMAneartheBTSwillhavethetopjumperandmainfeederlosses(noisefigures)cascadedinandaTMAwillnotbeabletohelpsuppressthelosses.15.WhatisUMTSchiprate?3.84MHz.16.Whatisprocessinggain?Processinggainistheratioofchiprateoverdatabitrate,usuallyrepresentedindecibel(dB)scale.Forexample,with3.84MHzchiprateand12.2kdatarate,theprocessinggainis:PG12.2k=10*log(3,840,000/12,200)=25dB17.WhataretheprocessinggainsforCSandPSservices?CS12.2:25dBPS64:18dBPS128:15dBPS384:10dBHSDPA:2dB18.Howtocalculatemaximumnumberofusersonacell?Tocalculatethemaximumnumberofusers(M)onacell,weneedtoknow:W:chiprate(forUMTS3,840,000chipspersecond)EbNo:Eb/Norequirement(assuming3dBforCS12.2k)i:othercelltoincellinterferenceratio(assuming60%)R:userdatarate(assuming12,200kbpsforCS12.2k):loadingfactor(assuming50%)Take12.2kbpsasexample:M=W/(EnNo*(1+i)*R)*=3,840,000(3*(1+0.6)*12,200)*0.5=32.8ThenumberofuserscouldalsobehardlimitedbyOVSFcodespace.TakeCS12.2kforexample:ACS12.2kbearerneeds1SF128code.TotalavailablecodesforCS12.2k=1282(1SF64)2(4SF256)=124.Considersofthandoverfactorof1.8andloadingfactorof50%:124/1.8*.05=34uers/cell.19.WhatisEb/No?3.BydefinitionEb/Noisenergybitovernoisedensity,i.e.istheratiooftheenergyperinformationbittothepowerspectraldensity(ofinterferenceandnoise)afterdispreading.Eb/No=ProcessingGain+SIRForexample,ifEb/Nois5dBandprocessinggainis25dBthentheSIRshouldbe20dBorbetter.20.WhataretheEb/Notargetsinyourdesign?TheEb/Notargetsaredependentontheservice:Ontheuplink,typicallyCSis5to6dBandPSis3to4dBPSisabout2dBlower.Onthedownlink,typicallyCShas6to7dBandPSis5to6dBPSisabout1dBlower.21.WhyisEb/NorequirementlowerforPSthanforCS?PShasabettererrorcorrectioncapabilityandcanutilizeretransmission,thereforeitcanaffordtoalowerEb/No.CSisrealtimeandcannottoleratedelaysoitneedsahigherEb/NotomaintainastrongerRFlink.22.WhatisEc/Io?Ec/IoistheratiooftheenergyperchipinCPICHtothetotalreceivedpowerdensity(includingCPICHitself).23.SometimeswesayEc/IoandsometimeswesayEc/No,aretheydifferent?Io=owncellinterference+surroundingcellinterference+noisedensityNo=surroundingcellinterference+noisedensityThatis,IoisthetotalreceivedpowerdensityincludingCPICHofitsowncell,NoisthetotalreceivedpowerdensityexcludingCPICHofitsowncell.TechnicallyEc/Ioshouldbethecorrectmeasurementbut,duetoequipmentcapability,Ec/Noisactuallymeasured.InUMTS,Ec/NoandEc/Ioareoftenusedinterchangeably.24.WhatisRSCP?RSCPstandsforReceivedSignalCodePowertheenergyperchipinCPICHaveragedover512chips.25.WhatisSIR?SIRistheSignaltoInterferenceRatiotheratiooftheenergyindedicatedphysicalcontrolchannelbitstothepowerdensityofinterferenceandnoiseafterdispreading.26.Whatistheloadingfactorinyourdesign?Thedesignedloadingtypicallyis50%however,sometimesacarriermaywanttodesignupto75%load.27.Giveasimpledefinitionofpolecapacity?Theuplinknoiseincreaseswiththeloadingexponentially.Whentheuplinknoiseapproachesinfinitythennomoreuserscanbeaddedtoacellandthecellloadingiscloseto100%andhasreacheditspolecapacity.Mathematically,tocalculatetheuplinkpolecapacityweneedtoknow:W:chiprate(forUMTS3,840,000chipspersecond)R:userdatarate(assuming12,200kbpsforCS12.2k)f:othercelltoincellinterferenceratio(assuming65%)EbNo:Eb/Norequirement(assuming5dB)AF:Activityfactor(assuming50%)PoleCapacity=(W/R)/((1+f)*AF*10^(EbNo/10))=120.6Tocalculatethedownlinkpolecapacitywealsoneedtoknow::downlinkchannelsorthogonalityfactor(assuming55%)PoleCapacity=(W/R)/((1+f)*10^(EbNo/10))=64.0628.WhatistypicalpolecapacityforCS12.2,PS64,PS128andPS384?Withsameassumptionsasabove:CS12.2k:120.6(UL),64.1(DL).PS64k:34.8(UL),12.8(DL).PS128k:16.2(UL),8.4(DL).PS384k:16.2(UL),2.8(DL).PS384khasonly128kontheuplink,thereforetheuplinkcapacityisthesameforboth.4.29.HowmanytypesofhandoversarethereinUMTS?Softhandover,softerhandover,interfrequencyhandover,interRAThandover,interRATcellchange(UEmovingoutofUMTScoverageintoGSM/GPRS/EGDGEcoverage).30.Whatissofthandoverandsofterhandover?Softhandover:whenaUEisconnectedtocellsownedbydifferentNodeB.Softerhandover:whenaUEisconnectedtocellsownedbythesameNodeB.31.Howdoessoft/softerhandoverwork?Soft/softerhandoverdownlink:UErakereceiverperformsmaximumratiocombining,i.e.UEcombinesmultipathsignalsandformastrongersignal.Softhandoveruplink:RNCperformsselectioncombining,i.e.RNCselectsthebettersignalcomingfrommultipleNodeB.Softerhandoveruplink:NodeBperformsmaximumratiocombining,i.e.NodeBrakereceivercombinessignalsfromdifferentpathsandformsastrongersignal.32.Whyistheresofthandovergain?Softhandovergaincomesfromthefollowing:Macrodiversitygainoverslowfading.Microdiversitygainoverfastfading.DownlinkloadsharingovermultipleRFlinks.Bymaintainingmultiplelinkseachlinkcouldtransmitatalowerpower,resultinginlowerinterferencethereforeagain.33.Briefdescribetheadvantagesanddisadvantagesofsofthandover?Advantages:Overcomefadingthroughmacrodiversity.ReducedNodeBpowerwhichinturndecreasesinterferenceandincreasescapacity.ReducedUEpower(up4dB),decreasinginterferenceandincreasingbatterylife.Disadvantages:UEusingseveralradiolinksrequiresmorechannelizationcodes,andmoreresourcesontheIubandIurinterfaces.34.Whatarefastfadingandslowfading?Fastfadingisalsocalledmultipathfading,asaresultofmultipathpropagation.WhenmultipathsignalsarrivingataUE,theconstructiveanddestructivephasescreateavariationinsignalstrength.Slowfadingisalsocalledshadowing.WhenaUEmovesawayfromacellthesignalstrengthdropsdown

slowly.35.Whatarefastfadingmarginandslowfadingmargin?Tofactorinthefastfadingandslowfading,weneedtohaveamargininthelinkbudgetandtheyarecalledfastfadingmarginandslowfadingmargin.Inlinkbudget,thefastfadingmarginisusuallysetto23slowfadingmarginissetto710.36.Whatisatypicalsofthandovergaininyourlinkbudget?CS12.2k:3dB(UL),2dB(DL).PS64k:1dB(UL),0dB(DL).PS128k:1dB(UL),0dB(DL).PS384k:1dB(UL),0dB(DL).37.WhatisthepercentageintimeaUEisexpectedtobeinsoftorsofterhandover?TypicallyaUEshouldbeinsofthandovermodeatnomorethan35to40%ofthetimeinsofterhandovermodeatabout5%ofthetime.38.WhatisatypicalEiRP?TheEiRPdependsNodeBtransmitpower,cableandconnectorlossandantennagain.Withasamplesystemof43dBmtransmitpower,a3dBcableandconnectorlossanda17dBiantennagain,theEiRP=433+17=57dBm.5.39.HowmuchpowerusuallyaNodeBisallocatedtocontrolchannels?Thepowerallocatedtocontrolchannelsmaydependonequipmentvendorrecommendation.Typicallynomorethan20%ofthetotalNodeBpowerisallocatedtocontrolchannels,includingCPICH.However,ifHSDPAisdeployedonthesamecarrierthenthetotalpowerallocatedtocontrolchannelmaygoupto25to30%becauseoftheadditionalHSDPAcontrolchannelsrequired.40.WhatisatypicalCPICHpower?CPICHpowertypicallytakesabout10%ofthetotalNodeBpower.Fora20W(43dBm)NodeB,CPICHisaround2W(33dBm).Inurbanareaswhereinbuildingcoverageistakencareofbyinbuildinginstallations,theCPICHmaysometimesgoaslowas5%because:Thecoverageareaissmallsinceusersareclosetothesite,andMorepowercanbeallocatedtotrafficchannels.41.HowmuchisyourHSDPA(max)linkpower?HSDPAlinkpoweristypically4to5dBbelowthemaximumNodeBmaximumoutputpower.Forexample,for43dBmmaximumNodeBpowertheHSDPAlinkpoweris39dBm.42.Considerdownlinkonly,whatarethemajorcomponentsincalculatingmaximumpathloss,startingfromNodeB?NodeBCPICHtransmitpower.Jumperandfeederconnectorloss.Antennagain.Overtheairloss.Building/vehiclepenetrationloss.Bodyloss.Etc.43.Whatismaximumpathloss?Themaximumpathlossishowmuchsignalisallowedtodropfromatransmittertoareceiverandmaintainsasgoodsignal.44.Simplelinkbudget:witha30dBmCPICHanda100dBmUEsensitivity,ignoringanythinginbetween,whatisthemaximumpathloss?30(100)=30+100=130dB.45.SupposeIhaveamaximumpathlossof130dBm,whatisthenewpathlossifa5dBbodylossisadded?125dB.46.Whatischannelizationcode?Channelizationcodesareorthogonalcodesusedtospreadthesignalandhenceprovidechannelseparation,thatis,channelizationcodesareusedtoseparatechannelsfromacell.47.Howmanychannelizationcodesareavailable?Thenumberofchannelizationcodesavailableisdependentonthelengthofcode.Intheuplinkthelengthisdefinedasbetween4and256.Inthedownlinkthelengthisdefinedasbetween4and512.48.Arechannelizationcodesmutuallyorthogonal?Ifso,whyisOrthogonalityFactorrequiredinthelinkbudget?Yes,channelizationcodesaremutuallyorthogonal.Nonetheless,duetomultipathwithvariabletimedelay,channelsfromthesamecellarenolongerperfectlyorthogonalandmayinterferewitheachother.ADownlinkOrthogonalityFactor,typically5060%,isthereforeneededinthelinkbudgettoaccountfortheinterferenceandhencereducespolecapacity.49.Whatisscramblingcode?Howmanyscramblingcodesthereare?6.ScramblingcodesareusedtoseparatecellsandUEsfromeachother,thatis,eachcellorUEshouldhaveauniquescramblingcode.Thereare512scramblingcodesonthedownlinkandmillionsontheuplink.50.Whatisscramblingcodegroup?The512scramblingcodesaredividedinto64codegroupseachcodegrouphas8scramblingcodes.Codegroupi(i=0to63)hascodesfromi*8to(i+1)*81,i.e.(07)(815)(504511).51.Doyoudividescramblingcodegroupsintosubgroups?Pleasegiveanexample.Yes,wedividethe64codegroupsintosubgroups:Macrolayergroup:24codegroupsreservedformacro(outdoor)sites.Microlayergroup:16codegroupsreservedformicro(inbuilding)sites.Expansiongroup:24codegroupsreservedforfutureexpansionsites.52.Whichserviceusuallyneedshigherpower,CSorPS?ConsiderdownlinkandtakeCS12.2andPS384kforexample.Theprocessinggainis25forCS12.2and10forPS384.TheEb/Norequirementis7forCS12.2and5forPS384.ThereforethepowerrequirementishigherforCS12.2thanPS384.53.WhatisEb/NorequirementforHSDPA?TheEb/NorequirementforHSDPAvarieswithuserbitrate(datarate),typically2for768kbpsand5for2Mbps.54.Whatisnoiserise?Whatdoesahighernoiserisemeanintermsofnetworkloading?Foreverynewuseraddedtotheservice,additionalnoiseisaddedtothenetwork.Thatis,eachnewusercausesanoiserise.Intheory,thenoiseriseisdefinedastheratiooftotalreceivedwidebandpowertothenoisepower.Highernoiserisevalueimpliesmoreusersareallowedonthenetwork,andeachuserhastotransmithigherpowertoovercomethehighernoiselevel.Thismeanssmallerpathlosscanbetoleratedandthecellradiusisreduced.Tosummarize,ahighernoiserisemeanshighercapacityandsmallerfootprint,alowernoiserisemeanssmallercapacityandbiggerfootprint.55.Whatispilotpollution?Simplyspeaking,whenthenumberofstrongcellsexceedstheactivesetsize,thereispilotpollutioninthearea.Typicallytheactivesetsizeis3,soiftherearemorethan3strongcellsthenthereispilotpollution.Definitionofstrongcell:pilotswithinthehandoverwindowsizefromthestrongestcell.Typicalhandoverwindowsizeisbetween4to6dB.Forexample,iftherearemorethan2cells(besidesthestrongestcell)within4dBofthestrongestcellthenthereispilotpollution.56.Whatisatypicalhandoverwindowsizeinyournetwork?Ahandoverwindowsizeisusuallybetween4to6dB.57.Whatissofthandoverandsofterhandover?SofthandoveriswhenUEhasconnectiontomultiplecellsondifferentNodeB.SofterhandoveriswhenUEhasconnectiontomultiplecellsonsameNodeB.IndownlinkaUEcancombinesignalsfromdifferentcells,improvingthesignalquality.Foruplinkandsofthandover,RNCselectsthebestsignalfromdifferentNodeB.Foruplinkandsofterhandover,aNodeBcombinesthesignalfromdifferentsectors.58.Duringahandover,ifonecellsendsapowerdownrequestandtwocellssendapoweruprequest,shalltheUEpoweruporpowerdown?Powerdown.Aslongasagoodlinkcanbemaintaineditisnotnecessarytopowerupinordertomaintainmultiplelinks.Maintainingunnecessarymultiplelinksincreasesnoiseriseandshallbeavoided.59.SupposewearedesigningaCSnetworkandaPSnetwork,isthereamajordifferenceinthedesignconsideration?Serverdominanceisthekeydifference.InaCSnetworkweshalllimitthenumberofstrongserversinanygivenareatonomorethantheactivesetsizetoavoidpilotpollution(inthedownlink).InaPSnetwork,however,thereisntsoft7.handoverinthedownlinksotheserverdominanceisveryimportantmeaningideallythereshouldbeonlyonedominantserverinagivenarea.Whatistheactivesetsizeonyournetwork?3.60.HowmanyfingersdoesaUErakereceiverhave?4.61.Whatiscompressedmode?BeforeUEcanperforminterfrequencyorIRAThandover,itneedstohavesometimetolockontothecontrolchanneloftheotherfrequencyorsystemandlistentothebroadcastinformation.Certainidleperiodsarecreatedinradioframesforthispurposeandiscalledcompressedmode.62.DescribethepowercontrolschemesinUMTS?OpenloopforUEtoaccessthenetwork,i.e.usedatcallsetuporinitialaccesstosetUEtransmitpower.Closedouterloop:RNCcalculatestheSIRtargetandsendsthetargettoNodeB(every10msframe).Closedinnerloop:NodeBsendstheTPCbitstoUEtoincreaseordecreasethepowerat1,500timesasecond.63.Whatisthefrequencyofpowercontrol(howfastispowercontrol)?Openloop:dependsonparametersetting:T300timetowaitbetweenRRCretries(100msto8000ms,typical1500ms)Closedouterloop:100timesasecond.Closedinnerloop:1,500timesasecond.64.Brieflydescribewhyopenlooppowercontrolisneededandhowitworks?WhenaUEneedstoaccesstothenetworkitusesRACHtobegintheprocess.RACHisasharedchannelontheuplinkusedbyallUE,thereforemayencountercontention(collision)duringmultipleuseraccessattemptsandinterferewitheachother.EachUEmustestimatetheamountofpowertouseontheaccessattemptsincenofeedbackfromtheNodeBexistsasitdoesonthededicatedchannel.ThepurposeofopenlooppowercontrolistominimizethechanceofcollisionandminimizetheinitialUEtransmitpowertoreduceinterferencetootherUE.InitialUEtransmitpower=Primary_CPICH_PowerCPICH_RSCP+UL_Interferrnce+constant_Value_CprachInsteadofsendingthewholemessage,atest(preamble)issent.WaitforanswerfromNodeB.IfnoanswerfromNodeBincreasethepower.Tryandtryuntilsucceedortimeout.65.Whatispowercontrolheadroom?Powercontrolheadroomisalsocalledpowerrise.InanonfadingchanneltheUEneedsto

transmitacertainfixedpower.InafadingchennelaUEreactstopowercontrolcommandsandusuallyincreasesthetransmitpower.Thedifferencebetweentheaveragepowerlevelsoffadingandnonfadingchannelsiscalledpowerriseorheadroom.66.Whenin3waysofthandover,ifaUEreceivespowerdownrequestfromonecellandpoweruprequestfromtheother2cells,shouldtheUEpowerupordownandwhy?Powerdown.Maintainingonegoodlinkissufficienttosustainacallandhavingunnecessarystrongerlinkscreatesmoreinterference.67.SupposetwoUEareservedbythesamecell,theUEwithweakerlink(poorRFcondition)usesmorecapacity,whydoesthismean?TheUEwithweakerRFlinkwillrequireNodeBtotransmithighertrafficpowerinordertoreachtheUE,resultinginlesspowerforotherUEthereforeconsumesmorecapacity.8.68.UnderwhatcircumstancescanaNodeBreachitscapacity?Whatarethecapacitylimitations?NodeBreachesitsmaximumtransmitpower,runsoutofitschannelelements,uplinknoiserisereachesitsdesigntarget,etc.69.Whatiscellbreathingandwhy?Thecellcoverageshrinksastheloadingincreases,thisiscalledcellbreathing.Intheuplink,asmoreandmoreUEareservedbyacell,eachUEneedstotransmithigherpowertocompensatefortheuplinknoiserise.Asaconsequence,theUEwithweakerlink(UEatgreaterdistance)maynothaveenoughpowertoreachtheNodeBthereforeacoverageshrinkage.Inthedownlink,theNodeBalsoneedstotransmithigherpowerasmoreUEarebeingserved.AsaconsequenceUEwithweakerlink(greaterdistance)maynotbereachablebytheNodeB.70.IsUMTSanuplinklimitedordownlinklimitedsystem?AUMTSsystemcouldbeeitheruplinklimitedordownlinklimiteddependingontheloading.Inalightlyloadedsystem,theUEtransmitpowersetsacoveragelimitationthereforeitisuplinklimited.Inaheavilyloadedsystem,theNodeBtransmitpowerlimitsthenumberofUEsitcanservethereforeitisdownlinklimited.71.Whatistheimpactofhigherdatarateoncoverage?HigherdataratehaslowerprocessinggainandthereforeaNodeBneedstotransmitmorepowertomeettherequiredEb/Nothismeansthecoverageissmallerforhigherdatarate.72.WhatisOCNS?OCNSstandsforOrthogonalChannelNoiseSimulator.ItisasimulatednetworkloadusuallybyincreasingthenoiserisefigureintheNodeB.UTRAN73.WhataretheinterfacesbetweeneachUTRANcomponent?Uu:UEtoNodeBIub:NodeBtoRNCIur:RNCtoRNCIu:RNCtoMSC74.BrieflydescribetheUEtoUTRANprotocolstack(airinterfacelayers).Theradiointerfaceisdividedinto3layers:1.Physicallayer(Layer1,L1):usedtotransmitdataovertheair,responsibleforchannelcoding,interleaving,repetition,modulation,powercontrol,macrodiversitycombining.2.Linklayer(L2):issplitinto2sublayersMediumAccessControl(MAC)andRadioLinkControl(RLC).MAC:responsibleformultiplexingdatafrommultipleapplicationsontophysicalchannelsinpreparationforovertheairtransmition.RLC:segmentsthedatastreamsintoframesthataresmallenoughtobetransmittedovertheradiolink.3.Upperlayer(L3):verticallypartitionedinto2planes:controlplaneforsignalinganduserplanforbearertraffic.RRC(RadioResourceControl)isthecontrolplanprotocol:controlstheradioresourcesfortheaccessnetwork.Inimplementation:1.UEhasall3layers.2.NodeBhasPhysicalLayer.3.RNChadMAClayerandRRClayer.75.BrieflydescribeUMTSairinterfacechanneltypesandtheirfunctions.Thereare3typesofchannelsacrossairinterfacephysicalchannel,transportchannelandlogicalchannel:1.PhysicalChannel:carriesdatabetweenphysicallayersofUEandNodeB.2.TransportChannel:carriesdatabetweenphysicallayerandMAClayer.3.LogicalChannel:carriesdatabetweenMAClayerandRRClayer.9.76.GivesomeexamplesofPhysical,TransportandLogicalchannels.1.LogicalChannel:Controlchannel:BCCH,PCCH,CCCH,DCCH.Trafficchannel:DTCH,CTCH.2.TransportChannel:Commoncontrolchannel:BCH,FACH,PCH,RACH,CPCH.Dedicatedchannel:DCH,DSCH.3.PhysicalChannel:Commoncontrolchannel:PCCPCH,SCCPCH,PSCH,SSCH,CPICH,AICH,PICH,PDSCH,PRACH,PCPCH,CD/CAICH.Dedicatedchannel:DPDCH,DPCCH.77.WhataretheRRCoperationmodes?Idlemodeandconnectedmode.78.WhataretheRRCstates?Thereare4RRCStates:Cell_DCH,Cell_FACH,URA_PCHandCell_PCH.URA=UTRANRegistrationArea.79.Whataretransparentmode,acknowledgedmodeandunacknowledgedmode?TransparentmodecorrespondstothelowestserviceoftheRLClayer,nocontrolsandnodetectionofmissingdata.Unacknowledgedmodeoffersthepossibilityofsegmentandconcatenateofdatabutnoerrorcorrectionorretransmissionthereforenoguaranteeofdelivery.Acknowledgedmodeoffers,inadditiontoUMmodefunctions,acknowledgementoftransmission,flowcontrol,errorcorrectionandretransmission.80.Whichlayer(s)performcipheringfunction?RRCforacknowledgedmode(AM)andunacknowledgedmode(UM).MACfortransparentmode(TM).81.WhatisOVSF?OrthogonalVariableSpreadingFactor.82.HowmanyOVSFcodespacesareavailable?TotalOVSFcodes=256.Reserved:1SF64forSCCPCH,1SF256forCPICH,PCCPCH,PICHandAICHeach.Totalavailablecodespace=2564(1SF64)4(4SF256)=248.83.Cancodespacelimitthecellcapacity?10.Yes,cellcapacitycanbehardlimitedbycodespace.TakeCS12.2kforexample:ACS12.2kbearerneeds1SF128code.TotalavailablecodesforCS12.2k=1282(1SF64)2(4SF256)=124.Considersofthandoverfactorof1.8:124/1.8=68uers/cell.84.CanauserhaveOVSFcodeas1111?No,because1111(256times)isusedbyCPICH.85.Whatarethesymbolrates(bitspersymbol)forBPSK,QPSK,8PSKand16QAM?BPSK:1.QPSK:2.8PSK:3.16QAM:4.86.BrieflydescribeUMTSframestructure.UMTSframeduration=10ms.Eachframeisdividedinto15timeslots.Eachtimeslotisdividedinto2560chips.Therefore2560chips/TS*15TS/frame*(1000ms/10ms)frame/sec=3,840,000chip/sec.87.Whatiscellselectioncriterion?Cellselectionisbasedon:Qmean:theaverageSIRofthetargetcell.Qmin:minimumrequiredSIR.Pcompensation:acorrectionvaluefordifferenceUEclasses.S=QmeanQminPcompensationIfS>0thenthecellisavalidcandidate.AUEwillcamponthecellwiththehighestS.88.BrieflydescribeCapacityManagementanditsfunctions:CapacityManagementisresponsibleforthecontroloftheloadinthecell.Itconsistsof3mainfunctions:DedicatedMonitoredResourceHandling:tracksutilizationofcriticalresourcesofthesystem.AdmissionControl:accepts/refusesadmissionrequestsbasedonthecurrentloadonthededicatedmonitoredresourcesandthecharacteristicsoftherequestCongestionControl:detects/resolvesoverloadsituationsPlanning89.Whatarethemajor4KPIsinpropagationmodeltuningandtypicalacceptablevalues?The4KPIsarestandarddeviationerror,rootmeansquareerror,meanerrorandcorrelationcoefficient.Thetypicalacceptablevaluesare:Standarddeviationerror:thesmallerthebetter,usually7to9dB.Meanerror:thesmallerthebetter,usually2to3.Rootmeansquareerror:thesmallerthebetter,usuallyCorrelationcoefficient:thelargerthebetter,usually70%to90%.90.Whatistheminimumnumberofbinsrequiredforacertainpropagationmodel?Themorebinsthemorelikelytocomeupwithagoodmodel.Usuallyaminimumof2,000binesisconsideredacceptable,butsometimesaslowas500binsmaybeaccepted.91.Howmanyscramblingcodesarethere?Thereare512scramblingcodesinthedownlinkand16,777,216codesintheuplink.92.Howmanyscramblingcodegroupsaretherefordownlink?Thereare64codegroups,eachgrouphas8scramblingcodes.11.93.Canweassignsamescramblingcodestosistersectors(sectorsonsamesite)?No,becausescramblingcodeonthedownlinkisusedforcellidentity.Asarequirement,scramblingcodeshavetomaintainasafeseparationtoavoidinterference.94.Arescramblingcodesorthogonal?No,scramblingcodesarenotorthogonalsincetheyarenotsynchronizedateachreceiver.Theyarepseudorandomsequencesofcodes.95.Canweassignscramblingcodes1,2and3tosistersectors?Yes.96.InIS95wehaveaPNreusefactor(PNstepsize)andthereforecannotuseall512PNcodes,whyisntitnecessaryforUMTSscramblingcodes?BecauseIS95isasynchronizednetwork,differentPNcodeshavethesamecodesequencewithatimeshift,thereforeweneedtomaintainacertainPNstepsizetoavoidmultipathproblem.Forexample,iftwosectorsintheneighborhoodhaveasmallPNseparationthensignalarrivingfromcellAmayrunintothetimedomainofcellB,causinginterference.UMTS,ontheotherhand,isnotasynchronizednetworkandallscramblingcodesaremutuallyorthogonalsononeedtomaintainastepsize.97.WhatarecoveragethresholdsinyourUMTSdesignandwhy?ThecoveragethresholdsarebasedonUEsensitivity,fadingandpenetrationloss.AssumingUEsensitivityof110dBm,fademarginof5dB:Outdoor:110dBmsensitivity+5dBfademargin=105dBm.Invehicle:110dBm+5dB+8dBinvehiclepenetrationloss=97dBm.Inbuilding:

110dBm+5dB+15dBinbuildingpenetrationloss=90dBm.98.WhatistheEc/Iotargetinyourdesign?TheEc/Iotargettypicallyisbetween12to14dB.However,ifanetworkisdesignedfordatathentheEc/Iotargetcouldgohighertoaround10dBbecauseserverdominanceismorecriticalforadatanetworksincethereisntsoftwareinthedownlink.99.WhatisMonteCarlosimulation?SinceUMTScoverageisdependentontheloading,staticcoverageandqualityanalysis(RSCPandEc/Io)representsthenetworkperformanceinnoloadcondition.MonteCarlosimulationisthereforeusedtoillustratenetworkperformanceundersimulatedloadingconsition.100.WhatisthekeydifferencebetweenastaticanalysisandaMonteCarlosimulation?StaticanalysiscanonlyshowRSCPandEc/Ioinnoloadcondition.MonteCarlosimulationnotonlycanshowRSCPandEc/Ioinsimulatedloadingconditionbutalsocanshowmanymoreothers:meanserved,cellloading,uplinkanddownlinkcapacitylimitsreached,etc.101.Whatshouldberunfirst(whatinformationshouldbereadyandloaded)beforerunningaMonteCarlosimulation?BeforerunningMonteCarlosimulation,thefollowingshouldbecompletedorinplace.Runprediction.Spreadthetraffic.Defineterminaltypes.102.HowmanysnapshotsanditerationdoyouusuallyhavewhenrunningMonteCarlosimulation?(Dependonsoftwaretoolrecommendations).103.WhatarethedesignKPIs?(RSCP,Ec/Io,meanserved,softhandoverratio)104.WhatplotsdoyouusuallycheckafterrunningMonteCarlofortroublespots?12.(RSCP,Ec/Io,serviceprobability,reasonsforfailure)105.WhatarethetypicalreasonsoffailureinMonteCarlosimulation?DownlinkEb/Nofailure(Capacity).DownlinkEb/Nofailure(Range).UplinkEb/Nofailure.LowpilotSIR.Noiseriselimitreached.Etc.106.Whatdoestrafficspreadmean?Trafficspreadmeansspreadingtraffic(numberofterminals)inacellcoveragearea.107.Doyouuselivetrafficorevenloadtrafficinyourdesign?(Depends).Optimization108.Whataretheoptimizationtoolsyouuse?Drivetest,analysis,others?109.AreSystemInformationBlocks(SIB)transmittedallthetime?No,systeminformationblockismultiplexedwithsynchronizationchannel.Synchronizationchanneloccupiesthefirsttimeslot(TS)andSIBoccupiestheother9timeslots.110.HowdoesUEcamp(synchronize)toaNodeB?1.UEusestheprimarysynchronizationchannel(PSCH)forslotalignment(TSsynchronization).2.AfteraligningtoNodeBtimeslot,UEthenusessecondarysynchronizationchannel(SSCH)toobtainframesynchronizationandscramblingcodegroupidentification.3.UEthenusesscramblingcodeIDtoobtainCPICH,thuscampingtoaNodeB.111.Whatcouldbethecauseofsofthandoverfailure?UEissue.ResourceunavailableattargetNodeB.InadequateSHOthresholddefined.Etc.112.Whatarethethreesetsinhandover?The3setsinhandoverare:ActivesetthelistofcellswhichareinsofthandoverwithUE.MonitoredsetthelistofcellsnotinactivesetbutRNChastoldUEtomonitor.DetectedsetlistofcellsdetectedbytheUEbutnotconfiguredintheneighborlist.113.WhatarethemajordifferencesbetweenGSMandUMTShandoverdecision?GSM:TimebasedmobilemeasuresofRxLevandRxQualmobilesendsmeasurementreporteverySACHperiod(480ms).BSCinstructsmobiletohandoverbasedonthesereports.UMTS:EventtriggeredreportingUEsendsameasurementreportonlyoncertaineventtriggers.UEplaysmorepartinthehandoverdecision.114.Whataretheevents1a,1b,1c,etc.?e1aaPrimaryCPICHentersthereportingrange,i.e.addacelltoactiveset.e1baprimaryCPICHleavesthereportingrange,i.e.removedacellfromactiveset.e1canonactiveprimaryCPICHbecomesbetterthananactiveprimaryCPICH,i.e.replaceacell.13.e1d:changeofbestcell.e1e:aPrimaryCPICHbecomesbetterthananabsolutethreshold.e1f:aPrimaryCPICHbecomesworsethananabsolutethreshold.115.Whatareevent2a2dand3a3d?Events2a2dareforinterfrequencyhandovermeasurementsandevents3a3dareforIRAThandovermeasurements.e3a:theUMTScellqualityhasmovedbelowathresholdandaGSMcellqualityhadmovedaboveathreshold.e3b:theGSMcellqualityhasmovedbelowathreshold.e3c:theGSMcellqualityhasmovedaboveathreshold.e3d:therewasachangeintheorderofbestGSMcelllist.116.Whatmayhappenwhentheresamissingneighbororanincorrectneighbor?Accessfailureandhandoverfailure:mayattempttoaccesstoawrongscramblingcode.Droppedcall:UEnotawareofastrongscramblingcode,stronginterference.Poordatathroughput.Poorvoicequality.Etc.117.Whatcanwetrytoimprovewhenaccessfailureishigh?WhenaccessfailureishighwecantrythefollowingtoimproveRACHperformance:IncreasemaximumUEtransmitpowerallowed:Max_allowed_UL_TX_Power.Increasepowerquickly:power_Offset_P0.Increasenumberofpreamblessentinagivenpreamblecycle:preamble_Retrans_Max.Increasethenumberofpreamblecycles:max_Preamble_Cycle.IncreasenumberofRRCConnectionRequestretries:N300.118.WhataretheconditionsyoutypicallysettotriggerIRAThandover?RSCPandEc/IoareusedtotriggerIRAThandover:RSCP100dBm.Ec/Io16dBm.119.WhatarethetypicalKPIsyouusetomeasureanetworkandwhatcriteria?Accessfailurerate(2%).Callsetuptime(CS:over95%ofthetime

SpilloverPoorCellReselectionCoreNetworkIssuesNonavailabilityofresources.AdmissionControldeniesHardwareIssuesImproperRACHParametersExternalInterference135.(FORERICSSONEXPERIENCED)WhatisRTWP?Whatisthesignificanceofit?ReceivedTotalWidebandPowerItgivestheTotalUplinkPower(Interference)levelreceivedatNodeB136.(FORERICSSONEXPERIENCED)WhatistheSystemReferencePointatwhichallthePowerLevelsaremeasuredinEricssonNodeB?SystemRefPointforE///NodeBisattheoutputofTMA(BetweenTMAandAntenna)137.Whatarethetypicalvaluesforreportingrange1aandreportingrange1b?3dBand5dBrespectively.138.Whatwillbetheimpactwhenyouchangereportingrange1afrom3to4dBandtimetotrigger1a100to320ms,withoutchanginganyotherparameters?ReductioninnumberofEvent1aDelayedEvent1atriggerReductioninAverageActiveSetSizeDelayinEvent1acouldincreaseDLinterference,whichcouldleadtoadropcallorincreaseinAveragePowerPerUser(reductionincellcapacity)139.WhatisAdmissionControl?AdmissionControlisanalgorithmwhichcontrolstheResourceAllocationforanewcallandadditionalresourceallocationforanexistingcall.Incase,ifacellisheavilyaloadedandenoughresourcesintermsofpower,codesorCEsarenotavailable,admissioncontroldeniespermissionfortheadditionalresourcerequirement.140.WhatisCongestionControl?16.CongestionControlmonitorsthedynamicutilizationofspecificcellresourcesandinsuresthatoverloadconditionsdonotoccur.Ifoverloadconditionsdooccur,CongestionControlwillimmediatelyrestrictAdmissionControlfromgrantingadditionalresources.Inaddition,CongestionControlwillattempttoresolvethecongestionbyeitherdownswitching,orterminatingexistingusers.Oncethecongestioniscorrected,thecongestionresolutionactionswillcease,andAdmissionControlwillbeenabled.DLTransmittedCarrierPower100%pwrAdmbeMarginDlPwrpwrAdmpwrAdm+pwrAdmOffset85%75%65%Admit:(AllGuaranteed)&(AllNonGuaranteed)&(AllGuaranteedHS)Admit:(AllGuaranteed)&(NonGuaranteed/Handover)&(AllGuaranteedHS)Admit:(Guaranteed/Handover)&(AllGuaranteedHS)maximumTransmissionPowerPowerReservedforPowerControlCongestionTriggeredCongestionResolvedpwrAdm+pwrAdmOffset+pwrOffset90%DLTransmittedCarrierPower100%pwrAdmbeMarginDlPwrpwrAdmpwrAdm+pwrAdmOffset85%75%65%Admit:(AllGuaranteed)&(AllNonGuaranteed)&(AllGuaranteedHS)Admit:(AllGuaranteed)&(NonGuaranteed/Handover)&(AllGuaranteedHS)Admit:(Guaranteed/Handover)&(AllGuaranteedHS)maximumTransmissionPowerPowerReservedforPowerControlCongestionTriggeredCongestionResolvedpwrAdm+pwrAdmOffset+pwrOffset90%141.WhatisthemaximumnumberofChannelizationCodesthatcanbeallocatedforHS,asper3GPPstandard?15codesofSF16.142.WhatisCodeMultiplexinginHSDPA?SharingtheHSChannelizationCodesamongmorethanoneHSuserswithinthe2msTTIperiod.143.(FORERICSSONEXPERIENCED)InEricssonSystem,howisthePowerallocatedforHSDPA>PowerunutilizedbyR99PS,CSandCommanChannels,isusedforHS(PHS=PmaxhsPowerMarginPnonHS)144.WhatareEventsthatcantriggertheHSDPACellChange?Event1dHSChangeofBestCellintheActiveSetEvent1borEvent1cRemovaloftheBestCellfromtheActiveSet145.HowistypicallytheCallSetupTimeofaCSVcallcalculatedinUMTSusingL3messages?CSTiscalculatedasthetimedifferencebetweenAlertingandthefirstRRCConnectionRequest(CallInitiation)messages.146.FunctionsofRNC:Assignandreleaseradiochannels,monitorsconnectionquality,controlshandovers,faultandconfigurationmanagement.147.Macrodiversity:connectedtwoormorecell,reducedtransmitpower.

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