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EEL-6936. Advanced Topics in Wireless Communications
A Technical Study of Long Term Evolut ion (LTE) and LTE-Advanced
By OlufemiAmao
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Contents
Introduction5
1.BriefHistoryofCellularSystems.6
2.BasicTransmissionSchemeinLTE.9
2.1DownlinkTransmission.9
2.1UplinkTransmission.11
3.PhysicalLayerOverviewofLTE 13
3.1DownlinkPhysical Layer.13
3.2UplinkPhysicalLayerOverview..16
4.Physical Channels andSignals..18
4.1DownlinkPhysicalChannels..18
4.2DownlinkPhysicalSignals20
4.3UplinkPhysicalChannels21
4.4UplinkPhysicalSignals21
5.MIMOTechnologiesinLTEandLTEAdvanced22
6.OtherLTEAdvancedTechnologies27
6.1Carrieraggregation27
6.2CoordinatedMultipointTransmission/Reception29
6.3Relaying31
Conclusion..33
Reference...34
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Figures
Figure1.1:Cellularhistory.........................................................................................7
Figure1.2:3Gevolution..............................................................................................8
Figure2.1: OFDMSignalBlockGenerator..................................................................9
Figure2.2: SchedulingconceptinOFDM..................................................................10
Figure2.3:OFDMSignalrepresentedinFrequencyTimedomain.............................11
Figure2.4:TransmitterstructureforSCFDMA.........................................................12
Figure2.5:Differencesbetween SCFDMAandOFDM...........................................12
Figure3.1:FDDFrameStructure.13
Figure3.2:TDDFrame (for5msswitchpointperiodicity)14
Figure3.3: OFDMresourceblockconcept15
Figure3.4:Overviewofdownlinkphysicalchannelprocessing..16
Figure3.5:Overviewofuplinkphysicalchannelprocessing.17
Figure4.1:Transportchannelsmappedtophysicalchannelsinthedownlink.19
Figure4.2:TransportchannelsmappedtophysicalchannelsintheUplink.21
Figure5.1:SimplifiedtransmissionmodelforaMIMOsystemwith3TXandRXantenna22
Figure5.2Closedloopspatialmultiplexingusing NantennaandMlayers.23
Figure5.3:OpenloopspatialmultiplexingwithNantennasandMlayers25
Figure5.4:SFBCwithtwotransmitantennasondownlink..26
Figure5.5:SFBC+FSTDwithfourtransmitantennasondownlink.26
Figure6.1:carrieraggregationtechniques.27
Figure6.2:ExampleofLTEcarrieraggregationscheme..28
Figure6.3:IntraandInterCoMPconcept..29
Figure6.4:demodulationbasedonUEspecificRS.30
Figure6.5:demodulationbasedoncellspecificRS.30
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Figure6.6:Onewayrelaymodel.31
Figure6.7:Twowayrelaymodel 31
Figure6.8:Shared relaymodel 32
Figure6.9:Powercomparisonanalysiswithdifferentrelaytechniques32
Tables
Table2.1Transmissionbandwidthconfiguration..............................................................10
Table5.1:CodebookfortransmissionforTwo antennaports...........................................24
Table5.2CodebookfortransmissionforFourantennaports.............................................24
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Introduction
InApril
2008,
astudy
termed
Requirement
for
Further
Advancement
for
EUTRA
also
called
LongTermEvolutionAdvanced(LTEAdvanced)wasinitiated.LTEAdvancedaimstoenhancethe
systemperformanceandcapabilitiesinexistingLTE.ThemaingoalofLTEAdvancedistoensure
thatalltherequirementofIMTAdvancedasdefinedbytheInternationalTelecommunication
Union(ITU)ismetandevenexceeded.Hence,agoodunderstandingofLTEisrequiredinorderto
understandandappreciatethekeytechnologicalcomponentsthatarebeingconsideredinLTE
Advanced.LTEAdvancedshouldbebackwardcompatiblewithLTE.Anoverviewofthephysical
layerinLTEisreviewedinthisreport;thisiscloselyfollowedwithareviewofsomeofthose
componentsspecifictoLTEAdvanced.
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Chapter1BriefHistoryofCellularsystems
Cellularsystemshaveconstantlyevolvedsincetheywere firstproposed in1947.Their
ubiquitousreachhasdrivenglobalorganizationssuchastheThirdGenerationPartnership
Project(3GPP)tothedevelopmentsofmobiletechnologies.The3GPPisacollaborationof
groupsoftelecommunicationsassociations,setuptomakeagloballyapplicablethirdgeneration
(3G)mobilephonesystemspecification,withinthescopeoftheInternationalMobile
Telecommunications2000(IMT2000)projectoftheInternationalTelecommunicationUnion
(ITU). 3GPPTSGRANisthetechnicalspecificationgroupthathasdevelopedWidebandCode
DivisionMultipleAccess(WCDMA),HighSpeedPacketAccess(HSPA),aswellasLTE.Thegroups
iscurrently intheforefrontoffuturetechnologies.
Thehistoryofthemobilecellularsystemsisoftendividedintogenerationstodistinguishthe
technologicaldevelopmentandimprovementovertheyears.Firstgenerationcellularsystems
(1G)suchasAMPS,werebasedonanalogcommunicationtechnologythatoftenprovidedsome
voiceandverylimitedcircuitswitcheddataservices.FirstgenerationsystemsuseFrequency
DivisionMultipleAccess(FDMA)andoperateinthe450and800MHzfrequencyband.
Secondgenerationcellularsystems(2G),arebasedondigitalcommunicationstechnology.
Comparedtotheirpredecessors,2Gsystemshadimprovedspectralefficiency(increased
numberofuserspercell).Thiswaspossiblebecausedigitalvoicecouldbecompressedand
multiplexedmoreeffectively,thusallowingforfargreatermobilephonepenetration.Basedon
thetypeofmultiplexingused,2GsystemsarecategorizedaseitherTimeDivisionMultiplexing
Access(TDMA) basedsuchasGSMorCodeDivisionMultipleAccess(CDMA)basedsuchasIS95.
TheinitialformofGSMoperatedinthe900,1800and1900MHzfrequencyandusedTDMAas
itsmultiaccessschemeforcircuitbasedtransmissionofdigitizedvoice.Aninitialdatarateofup
to9.6kb/swaspossible.Theprimarydataservicesin2Gweretextmessaging(SMS)andcircuit
switcheddataservicessuchasemail.Theneedtoimprovetheexisting2Gusheredinafew
upgradesthatresultedinsomepacketswitchedfunctionalityandwasknownas2.5Gbased
cellulartechnology.GPRS,EDGEand1XRTTT.
Thirdgenerationtechnologies3G,setthestagefortheinternationalizationofcellular
standards. Priortothis,CDMAbasedsystemsweremainlydeployedinNorthAmericawhile
GSMsystemswerecommoninEurope.Radioaccessdevelopmenton3Gishandledin3GPP,
althoughtheinitialdevelopmentstartedbefore3GPPwasformed.Unlike2Gor2.5G,3Gallows
simultaneoususeofvoiceanddataservicesandoperatedatahigherdatarates.Additional
workon3Ghasbeendrivenbytheneedforacellularsystemthatwouldprovidereducedcost
perbit,Increasedserviceprovisioning,flexibilityofuseonexistingandnewfrequencybands,
simplifiedarchitectureandareasonableterminalpowerconsumption. Therehavebeen
substantialresearchactivitiesdedicatedtowardsimproving3G.The3GPPdocumentsare
dividedintoreleases,whereeachreleasehasasetofadded features,comparedtothe
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previousreleases.3GinEuropewasnamedUniversalMobileTelecommunicationsServices
(UMTS).
WidebandCDMA(WCDMA)wasselectedasthetechnologyforUMTSinthepairedspectrum
(FDD)andTDCDMA(TimeDivisionCDMA)intheunpairedspectrum(TDD).Itoffereda
downlinkspeedofabout384Kbsandanuplinkofabout128Kbps.3GsystemsbasedonTDSCDMAwaslaterdevelopedinChinaandmergedasadditionaloptionforTDDmode.Thefirst
majoradditionofradioaccessfeaturestoWCDMAwasinRelease5(HSDPA)andRelease6
(EnhancedUplink).Together,theyarereferredtoas(HighSpeedPacketAccess)HSPA.HSPA
providesamaxdownlinkspeedofabout 14Mbit/sanduplinkofabout5.7Mbit/s. HSPA+
increasedHSPAsdataratesresultinginadownlinkof56Mbit/sandanuplinkofupto22Mbit/s
inrelease7,usingthesameaccesstechnologyasrelease6butwithimprovedantenna
technologyandhigherordermodulation.
Release8offeredasignificantimprovementinperformanceovertheexisting3Gstandards.A
feasibilitystudyontheLongTermEvolution(LTE)wasproposedin2004aspartofrel8.LTE
representsanefficientpacketbasedradioaccessnetworkthatprovidesfullIPbased
functionalitywithlowlatencyandlowcost.LTEisseenasanevolutionoftheUMTS/3GPP3G
standardswithincreasedspeedsandgeneralimprovedperformance,althoughtherearemajor
stepchangesbetweenLTEandits3GPPpredecessors. Anumberofnewtechnologiesthatmake
uptheLTEsuiteswouldbeintroducedanddiscussedinsubsequentchaptersofthisreport.
Figure
1.1:
Cellular
history
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Fourthgenerationsystems(4G)isexpectedtomeetIMTAdvancedrequirements foran allIP
packetswitchednetworks,mobileultrabroadbandgigabitspeedaccessandmulticarrier
transmission.LTErev8doesnotmeetthestandardsfor4Gsystems,hencetheneedforLTE
Advancedasdescribedinrel9andbeyond.LTEAdvancedmeetstherequirementfor4G.LTE
AdvancediscompatiblewiththefirstreleaseofLTE(LTErel8)equipmentandcansharethe
samefrequencyband.TheITUhascoinedthetermIMTAdvancedtoidentifymobilesystems
whosecapabilitiesgobeyondthoseofIMT2000
Figure2.2:3gevolution
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Chapter2 BasicTransmissionSchemeinLTE
2.1 DownlinkTransmission
LTE downlink transmission scheme is based on Orthogonal Frequency Division Multiplexing
(OFDM).OFDMmakesuseofalargenumberofcloselypackedorthogonalsubcarriersthatare
transmitted inparallel.Eachsubcarrier ismodulated independentlyat lowsymbolrate.When
severalhundredsofthesesubcarriersarecombinedusingan IFFTprocess,theresult isadata
rate similar to conventional singlecarriermodulation in the samebandwidth.As longas the
orthogonalnaturesof the subcarriers aremaintained, subcarriersdonot interferewitheach
other.Carrierspacing in LTE is fixedat15KHz. TheOFDMsignalgeneration isshown in the
figure2.1below.
Source(s) 1:NQAM
Modulator
QAM symbol rate =N/Tusymbols/sec
Nsymbolstreams
1/Tusymbol/sec
IFFT
OFDMsymbols
1/Tusymbols/s
N:1Useful OFDMsymbols
Figure2.1:OFDMSignalBlockGenerator
OFDMprovidesahighdegreeofrobustnessagainstchannelfrequencyselectivityduetoits
relativelongsymboltimeandcyclicprefix.Thecyclicprefixensuresintersymbolinterference
(ISI)doesnotspillintothenextFFTperiod,byensuringthatthedelayspreadiscontainedwithin
thecyclicprefix.LTEdefinestwoformsofCyclicprefix;normalandextended. Cyclicprefix
contributestotheoverall length of the OFDM symbol and are discarded before the FFT
operation at the receiver. Anormalcyclicprefixofabout5sisusedinsmallcellenvironment,
whileextendedcyclicprefixofsize17scanbeusedinenvironmentwithextremetime
dispersionorinthecaseofSingleFrequencynetwork.
InSinglecarrier,equalizationisoftenusedtocorrectsignaldistortionthatoccursdueto
frequencyselectivenatureofthechannel.Theadditionalcomplexityassociatedwithusing
equalizationathighbandwidthabove5MHz,makessinglecarrierunattractiveforLTE. OFDM
providesadditionalbenefitstoLTEsuchastheabilitytoscheduleresourceinboththetimeand
frequencydomainusingresourceblockconceptofOrthogonalFrequencyDivisionMultiple
Access(OFDMA)asshowninfigure2.2and2.3.OFDMAallowssubsetsofthesubcarrierstobe
allocateddynamicallyamongthedifferentusersonthechannelasshownbelow.
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Figure2.2:schedulingconceptinOFDM
Thecoreofthetransmissionaccessschemeistousesharedchanneltransmission.Ascheduler
canvaryresourcesforeachtimeinstantandbywhichusersthesharedresourcesshouldbe
assigned.Thepossibilityforchanneldependentschedulinginthefrequencydomainisuseful
whenchannelsarevarying.Schedulingdecisionscanbetakenasoftenasonceevery1msand
thegranularityinthefrequencydomainis180kHz.Inthefrequencydomainthedownlink
subcarriersaregroupedintoresourceblocks,witheachresourceblockconsistingof12
consecutivesubcarriers(12*15KHz=180KHz).
Inaddition,toaccommodatedifferentspectralregulationsandavailability,LTEisdesignedto
supportvariablechannelbandwidthbyvaryingthenumberofsubcarriersusedfortransmission.
Thesubcarrierspacingisconstantregardlessofthetransmissionbandwidth.Toallowfor
operationindifferentlysizedspectrumallocations,thetransmissionbandwidthisinsteadvaried
byvaryingthenumberofOFDMsubcarriers.Subcarriersaregroupedas12consecutivepairs
knownasresourceblock.TheconceptofResourceBlockisexplainedinchapter3.
Channel bandwidthBWChannel[MHz]
1.4 3 5 10 15 20
No of Resource Block(180KHz)
6 15 25 50 75 100
Table 2.1 Transmission bandwidth configuration
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LTEcanalso bedeployed indifferentfrequencybands fromaslowas450MHzbandupto,at
least,2.6GHzwithsupportforbothFrequecyDivisionDuplex(FDD)andTimedivisionDuplex
(TDD).Thereisnospecified FFTsizeandsamplingfrequencyfortheLTEdownlink.The
samplingratefs=_fNFFTisoftena multipleorsubmultipleof3.84MHzwhichcorrespondsto
the chiprateinWCDMA.
Figure2.3:OFDMSignalrepresentedinFrequencyTimedomain
2.2.UplinkTransmission
TheuplinkaccessinLTEusesSingleCarrierFrequencyDivisionMultipleAccess(SC
FDMA).Comparedtothedownlink,thereissignificantlowerpoweravailabilityintheuplink.SC
FDMAwaschosenbecauseitcombinesthelowpeaktoaverageratio(PAR)techniquesofsingle
carriersystemswiththemultipathresistanceandflexibleallocationthatOFDMAoffers.SC
FDMAcanbeseenasanOFDMmodulationthatisprecededbyaDiscreteFourierTransform
(DFT)operation,hencetheyaresometimesreferredtoasDFTSOFDM.InSCFDMA,data
symbolsinthetimedomainareconvertedtothefrequencydomainusingdiscreteFourier
transform(DFT),inthefrequencydomaintheyaremappedtothedesiredlocationintheoverall
channelbandwidthbeforebeingconvertedbacktotimedomainusinganinverseFFT(IFFT)
.Cyclicprefixisthenaddedtothetimedomainsignal.
UplinkLTEisbasedonorthogonalseparationofusers.Itisthetaskoftheuplinkschedulerto
assignresourcesinbothtimeandfrequencydomaintodifferentusers.Mobiledevicesare
allowedtotransmitwithinacellduringagiventimeintervalbythescheduler.Onlyacontiguous
frequencyregioncanbeassignedtotheterminalsintheuplinkasaconsequenceoftheuseof
singlecarriertransmissionin LTEuplink.ThisisoftenreferredtoaslocalizedDFTSOFDM
transmission.Ablockdiagramshowingthetransmitterstructureandthedifferencebetween
OFDMandSCFDMAisdepictedinfigure2.4andfigure2.5respectively.
Sub-carriersFFT
Time
Symbols
5 MHz Bandwidth
Guard Intervals
Frequency
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DFTSub-carrierMapping
CPinsertion
Size-NTX Size-NFFT
Coded symbol rate= R
NTXsymbols
IFFT
Figure2.4:TransmitterstructureforSCFDMA.
Figure2.5:Differencesbetween SCFDMAandOFDM
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Chapter3 PhysicalLayerOverviewofLTE
AlthoughLTEdownlinkanduplinkusesadifferentmultipleaccessschemes,OFDMAandSC
FDMArespectively,theyshareacommonframestructure.Theframestructurerepresentsa
timedomainrepresentationoftheslotandsymbol.
Thesizeofvariousfieldsinthetimedomainisexpressedasanumberoftimeunit,
FFTsizeKHzT 2048150001s seconds.Thisischosenforbackwardcompatibilitywith
UMTS.(UMTSchiprate is3.84MHz oneeighthoftheassumedLTEsamplingfrequency).
Downlinkanduplinktransmissionsareorganizedintoradioframesofsize10ms(
ms10307200 sf TT ).Atype1framestructureisdefinedforFDD,whiletype2isdefinedfor
TDD.ForFDD,10subframesareavailablefordownlinktransmissionand10subframesare
availableforuplinktransmissionsineach10msinterval.Uplinkanddownlinktransmissionsare
separatedinthefrequencydomain.Eachradioframeis ms10307200 sf TT longandconsists
of20slotsstartingfrom 0to19,with length ms5.0T15360 sslot T .
Figure3.1:FDDFrameStructure
ForTDD,Eachradioframeoflength ms10307200 sf TT consistsoftwohalfframesoflength
ms5153600 s T each.Eachhalfframeconsistsoffivesubframesoflength ms107203 s T .For
eachsubframeinaradioframe,Ddenotesthesubframeisreservedfordownlink
transmissions,UdenotesthesubframeisreservedforuplinktransmissionsandSdenotesa
specialsubframewiththethreefieldsDwPTS,GPandUpPTS..ThelengthofDwPTSandUpPTS
variesanditssubjecttothetotallengthofDwPTS,GPandUpPTSbeingequalto ms107203 s T .
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Figure3.2:TDDFrame (for5msswitchpointperiodicity).
10msradioframerepresentsthelargestunitoftime.Thisisfurtherdividedintoasubframeof1
mswhichcontainstwo0.5msslots.AslotcontainssevenOFDMsymbolswhennormalcyclic
prefixisusedandsixOFDMsymbolswhenextendedcyclicprefixisused.WhennormalCPis
used,theCPlengthforthefirstOFDMsymbolineachslotisslightlylongerthanthatofthe
othersixtoaccommodateanintegernumberofOFDM.Thisimpliesthatasubframe(1ms)
consistsof14OFDMsymbols(inthecaseofnormalCP)and12OFDMsymbolinthecaseof
extendedCP.
Inthefrequencydomain,resourcesaregroupedintoresourceblocksmadeupof12consecutive
subcarriersperslot,thiscorrespondstoabandwidthof180Khz.TheResourceElementdepicts
thesmallestunitofresource,madeupofonesubcarrierforadurationofoneOFDMsymbol.A
Resourceblockisthusmadeupof84resourceelementswhennormalCPisusedor72resource
elementinthecaseofextendedCP.(12x7ofdm/slotand12x6ofdm/slotrespectively).Thisis
showninfigure3.3
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Figure3.3: OFDMresourceblockconcept
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3.1DownlinkPhysicalLayeroverview
InLTE,theenhancedbasestationthatprovidesphysicallayerfunctionalityisreferredtoas
evolvedNodeB(eNodeB).Thephysicallayerisprimarilyresponsiblefortranslatingdataintoa
reliablesignalbetweentheeNodeBandtheUserEquipment(UE).Thephysicallayeralso
interfaceswiththehigherlayers,specificallywiththeMAClayerviatransportchannels.DataisdeliveredtothephysicallayerintheformofTransportBlocksthatareofcertainsize.
ScramblingModulation
mapper
Layermapper
Precoding
Resource
elementmapper
OFDMsignal
generation
Resource
elementmapper
OFDMsignal
generationScrambling
Modulation
mapper
layersantenna
portscodewords
Figure
3.4:
Overview
of
downlink
physical
channel
processing.
Toreducetransmissionerrors,a24bitCyclicRedundancyCheck(CRC)andchannelcodingare
appendedtoeachblockofdata.TheCRCisusedatthereceivertodetecterrorsinthedecoded
transportblock.Inaddition,scramblingisappliedtoalldownlinkphysicalchannelstoreduce
interferencerejection.Thescramblingsequenceusesanorder31Goldcode,whichcanresultin
231sequencesthat arenotcyclicshiftsofeachother.QuadraticPermutationPolynomial(QPP)
basedTurbocodingisusedinLTEwithanoverallcoderate(R)of1/3.AQPPbasedreducesthe
complexityoftheTurboencoder/decoderbecausetheyaremaximumcontentionfree,which
impliesthattheyprovidemaximumflexibilityinsupportedparallelism.ForexampleifK=512,
supportedparallelismfactorswill include{1,2,4,8,16,32,64,128,256,512}.Trellis
terminationisusedfortheturbocoding.
LTEemploysabitlevelscramblingonalltransportchannels.Theblockofbitsundergoesan
exclusiveoroperationwithabitlevelscramblingsequence.Scramblinghelpsthereceiverto
fullyutilizetheprocessinggainbyreducinginterferenceatthereceiver.Differentscrambling
sequencesareusedindifferentneighboringcellthusrandomizinginterferingsignalsatthe
receiverafterdescrambling. MBSFNbasedtransmissionusescellcommonscrambling,the
samesequenceisusedinallparticipatingcells.
Themodulationmappertakesblockofscrambled binarydigits,0or1,asinputandoutputsa
complexvaluedmodulationsymbols,x=I+jQ.LTEsupportsthefollowingmodulationschemes;
QPSK,16QAMand64QAM.InthecaseofQPSK,twobitsarerepresentedby1symbol,whilein
16QAMand64QAMfourandsixbitsarerepresentedpersymbolrespectively.Notallchannels
supportsthethreemodulationscheme.Forexample,whiletheDownlinkSharedChannel(DL
SCH)supportsallthreemodulationschemes,BroadcastChannel(BCH)onlysupportsQPSK.
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Layermappingandprecoding arepartofantennamappingprocessandtheyrelatetoMultiple
InputMultipleOutput(MIMO)application.TheconceptofMIMOisusedinLTEandLTE
Advancedandisdiscussedinchapter5.Splittingantennamappingintotwosteps makesit
easiertodescribethedifferentMIMOschemesthatareusedinLTE.Thelayermappingprovides
demultiplexingofthemodulationsymbolsofeachcodewordintooneormultiplelayers.The
numberoflayersisalwaysasleastasmanyasthenumberoftransportblockstobetransmitted.
Precodingtakessymbolsfromeachlayerthatwasproducedfromlayermapping,andprocesses
themtogether.Theresultisthenmappedtodifferentsubcarriers(frequencydomain)and
antennaport(spatialdomain).
MIMOsystemsaredefinedintermsofthenumberoftransmitterandthenumberofreceivers.
Forexample,a4x2MIMOimpliesthereare4transmittersand2receivers.A2x2MIMOsystem
hasequalnumberoftransmitterandreceiver(2Transmitterand2Receivers)resultingina1:1
relationshipwithrespecttolayersandthetransmittingantennaport.However,a4X2hasa2:1
relationshipresultinginredundancyinoneorbothdatastreams.Layermappingspecifieshow
theextratransmitterantennasareused.Themappingconfigurationemployeddependsonthe
multiantennaschemethatisbeingused.
3.2UplinkPhysicalLayer overview
Asmentionedinsection2.2,uplinktransmissionisbasedonSCFDMA.CRCinsertion,Channel
codingandbitlevelscramblingaresimilartothedownlinkphysicallayerdescribedinsection
3.1.Uplinkscramblingishowevermobileterminalspecific,thusdifferentterminalsusedifferent
scramblingsequence.LTEUplinkalsosupports QPSK,16QAMand64QAMmodulationscheme.
Figure3.5:Overviewofuplinkphysicalchannelprocessing.
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Chapter4 PhysicalChannelsandSignals
Thephysicalchannelsintheuplinkanddownlinkoperatedifferentlyduetothedifferent
requirementsandconstraints.Thedownlinkphysicalchannelcorrespondstoasetofresource
elementscarryinginformationoriginatingfromhigherlayerssuchastheMAClayer.Dataona
transportchannelisorganizedintotransportblockswithinaTransmissionTimeInterval(TTI).EachtransportblockhasaTransportFormat(TF)thatspecifieshowthetransportblockistobe
transmittedovertheradiointerface.Suchspecificationincludes,themodulationscheme,block
size,ratecontrolandantennaemapping.
4.1DownlinkPhysicalChannels
Thefollowingdownlinkphysicalchannelsaredefined;
PhysicalBroadcastChannel,PBCH
PhysicalDownlinkSharedChannel,PDSCH
PhysicalMulticastChannel,PMCH
PhysicalDownlinkControlChannel,PDCCH
PhysicalControlFormatIndicatorChannel,PCFICH
PhysicalHybridARQIndicatorChannel,PHICH
ThefollowingphysicalsignalsareusedinLTEdownlink;
Primarysynchronizationsignal
Secondarysynchronizationsignal
Referencesignals
PhysicalBroadcastChannel(PBCH)
Thephysicalbroadcastchannelcarriescellspecificsysteminformationthatareusedto
configureandallowaccesstootherchannelsneededinthecell.Itistransmittedinthecenterof
thechannelandoccupies72subcarriers(equivalentto6RB).Inthetimedomain,thePBCHis
locatedinslot1ofthefirstfourOFDMsymbols.Theonlymodulationschemesupportedis
QPSK.
PhysicalDownlinkSharedChannel(PDSCH)
DownlinkdataistransmittedviathePDSCHchannel.ThechannelissharedamongmultipleUEs
inthetimedomain.LTEfeaturessuchasspatialmultiplexing,rateadaptationandchannel
dependentschedulingaresupportedinthischannel.UnlikePBCH,themodulationscheme
supportedareQPSK,16QAMand64QAM.
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PhysicalMulticastChannel(PMCH)
ThischannelisresponsiblefortransportingMulticastChannel(MCH).Italsosupports
QPSK,16QAMand64QAM.
PhysicalDownlinkControlChannel(PDCCH)
PDCCH carries the channelallocationand control information. It ismadeupofoneormore
consecutiveControlChannelElements (CCEs),whereacontrolchannelelement ismadeupof
nine resourceelementgroups.OnlyQPSKmodulation is supported in this channel.AControl
FormatIndicator(CFI)thatiscarriedbythePhysicalControlFormatIndicatorchannel(PCFICH)
indicatesthenumberofOFDMsymbolthatisallocatedforthePDCCH.
PhysicalControlFormatIndicatorChannel(PCFICH)
ThePhysicalControlFormatIndicatorchannel(PCFICH)isthephysicalchannelthatcarriesthe
CFIwhichdictatesthenumberofOFDMsymbolsusedfortransmissionofPDCCHina
subframe.ItislocatedatOFDMsymbol0ofeverysubframe.Inthefrequencydomain,thesub
carriersallocatedforPCFICHisdeterminedbyCellIDinformation.
PhysicalHybridARQIndicatorChannel,PHICH
AcknowledgementandNegative Acknowledgement(ACKandNAK) aresenttotheUEviathe
PHICH.
Figure4.1Transportchannelsmappedtophysicalchannelsinthedownlink
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4.2DownlinkPhysicalSignals
Onthedownlink,LTEdefinesthreephysicalsignals;
PrimarySynchronization
SecondarySynchronization
ReferenceSignals
Theprimaryandsecondarysynchronizationsignalsarespecificsequencesinsertedintothelast
twoOFDMsymbolsinthefirstslotofsubframeszeroandfive.Theyaremainlyusedforcell
searchprocedure.Inadditiontotheprimaryandsecondarysynchronizationsignals,thecell
searchprocedurealsoexploitsthereferencesignalsaspartofitsoperation.Inthetimedomain,
boththeprimaryandsecondarysignalsaretransmittedtwiceper10msradioframe.Inthe
frequencydomain,thesignalsalwaysoccupythecentral62subcarriersofthechannel.This
ensuresthecellsearchprocedureisthesameregardlessofthechannelbandwidth.TheUE
determinesthetimingandcenterfrequencyfromthePrimarysynchronizationsignal.
Theprimarysynchronizationsignalsinthesubcarriersaremodulatedusingafrequencydomain
ZadoffChusequence.AZadoffChusequenceisaConstantAmplitudeZeroAutocorrelation
(CAZAC)sequencewaveformwithexcellentautocorrelationpropertiesandlowcrosscorrelation
withothersequences.Whenappliedtoradiosignals,itresultsinanelectromagneticsignalof
constantamplitude.Thephaseofeachsubcarrierisdeterminedbytherootindexnumberina
sequencegeneratorwiththerootindexnumbercorrespondingtothecellidentity.Thereare
504uniquecellidentitiesandthepowerlevelineachsubcarriersarethesame.
Thesecondarysynchronizationsignalisusedtoidentifythecellidentitysubgroups.Its
frequencyrepresentationissimilartotheprimarysynchronizationdescribedabove.The
sequencegenerationfunctionutilizesaninterleavedconcatenationoftwolength31binary
sequence.The504uniqueidentitiesmentionedintheparagraphaboveisgroupedinto168
uniquecellidentitygroups(from0to167),witheachgroupcontainingthreeuniqueidentities.
Thelaterisachievedbycyclicshiftingeachsequence.Theprimarysynchronizationgivesthe
identityinformation.
Referencesignalsareusedtoreducethepossibilityofamplitude,phaseandtimingerrorsinthe
receivedsignals.Sucherrorsmighthavebeenintroducedbytheradiochannelandimpairments
fromthetransmitter.Thereferencesignalsdonotcarryanyuniqueinformationbutprovides
knownphaseandamplitudereferencethatcanbeusedtoreliabledecodesignalsthatwould
havebeenerroneouslydecodedinitsabsence. Inthetimedomain,thereferencesignalsare
generatedeverytwosymbolsperslotwhileinthefrequencydomain,theyareallocatedinevery
sixthsubcarriers.Inadditiontocellspecificreferencesignals,LTEdefinesMBSFNreference
signalsandUEspecificreferencesignals.
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4.3UplinkPhysicalChannel
Thefollowingphysicalchannelsareusedintheuplink;PhysicalUplinkSharedChannel(PUSCH),
PhysicalUplinkControlChannel(PUCCH)andthePhysicalRandomChannel(PRACH).
PUSCHisthechannelthatcarriesusertraffic.SimilartothePDSCH,themodulationscheme
supportedareQPSK,16QAMand64QAM.UplinkSharedChannel(ULSCH)andUplinkControl
information (UCI)arealsotransportedviathischannel.PUCCHcarriesuplinkcontrol
Informationsuchasschedulingrequests,periodicChannelQualityIndicator(CQI),and
acknowledgements.RandomaccesspreamblessenttoeNodeB isinitiatedvia thePRACH.It
shouldbenotedthataUEcannottransmitonbothPUCCHandPUSCHsimultaneously.This
impliesthatiftheUEneedstosenddatainthesamesubframeasthescheduledperiodicCQI
report,PUSCHwouldbeusedinsteadof PUCCH.
Figure4.2TransportchannelsmappedtophysicalchannelsintheUplink
UplinkPhysicalSignals
4.4UplinkPhysicalSignals
LTEdefinestwophysicalsignalsintheuplink,namelyDemodulationReferencesignal(DMRS)
andtheSoundingReferenceSignal(SRS).DMRSisusedforuplinkchannelestimationand
synchronization.ItfacilitatescoherentdemodulationbasedontheZadhoffChusequence,
whichprovidesitwithgoodtimedomainautocorrelationpropertiesandconstantamplitude.In
thefrequencydomain,itisthesamesizeastheassignedresource,whileinthetimedomain;it
istransmittedinthefourthSCFDMAsymbolofthePUSCHslot.SRSisalsobasedonthe
ZadhoffChusequenceanditsusedtofacilitatefrequencydependentscheduling.Subcarrier
allocationisdictatedbythebandwidthallocationconfiguredintheSRS.
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Chap
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Figure5.2Closedloopspatialmultiplexingusing NantennaandMlayers
TheclosedloopspatialmultiplexingrequirestheUEtofeedbacktherankindicator(RI),thePMI
andthechannelqualityindicatorCQIintheuplink.TheRIindicatesthenumberofspatiallayers
thattheUEscurrentchannelconditioncansupport.TheeNodeBmaydecidethetransmission
rank(M)basedontheRIreportedbytheUEorbasedonotherfactorssuchasavailablepower
transmission.The eNodeBsendsthescheduledUEtheintendedprecodingmatrix,thatwould
beusedaspartofthedownlinkcontrolinformationusingathreebitTransmitPrecodingMatrix
Indicator(TPMI)fieldfortwotransmitantennasandasixbitTPMIfieldforfourtransmit
antennas.Withoutcyclicdelaydiversity(CDD),precodingforspatialmultiplexingisdefinedby
)(
)(
)(
)(
)(
)1(
)0(
)1(
)0(
ix
ix
iW
iy
iy
P
Ydenotesthecomplexsymboltransmittedonthenthantenna,xdenotesthemodulation
symboltransmittedonthemthlayerandWdenotestheNXMprecodingmatrix.For
transmissionontwoantennaports, 1,0p ,theprecodingmatrix )(iW oftable5.1isused
whilefor transmissiononfourantennaports, 3,2,1,0p ,theprecodingmatrixtable5.2is
employed.
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Codebookindex
Number of layers
1 2
0
1
1
2
1
10
01
2
1
1
1
1
2
1
11
11
2
1
2
j
1
2
1
jj
11
2
1
3
j
1
2
1 -
Table 5.1: Codebook for transmission for Two antenna ports 1,0 .
Codebookindex
nu Number of layers
1 2 3 4
0 Tu 11110 }1{
0W 2}14{
0W 3}124{
0W 2}1234{
0W
1 Tjju 111 }1{
1W 2}12{
1W 3}123{
1W 2}1234{
1W
2 Tu 11112 }1{
2W 2}12{
2W 3}123{
2W 2}3214{
2W
3 Tjju 113 }1{
3W 2}12{
3W 3}123{
3W 2}3214{
3W
4 Tjjju 2)1(2)1(14 }1{4W 2}14{4W 3}124{4W 2}1234{4W 5 Tjjju 2)1(2)1(15
}1{5W 2
}14{5W 3
}124{5W 2
}1234{5W
6 Tjjju 2)1(2)1(16 }1{
6W 2}13{
6W 3}134{
6W 2}1324{
6W
7 Tjjju 2)1(2)1(17 }1{7W 2}13{7W 3}134{7W 2}1324{7W 8 Tu 11118
}1{8W 2
}12{8W 3
}124{8W 2
}1234{8W
9 Tjju 119 }1{
9W 2}14{
9W 3}134{
9W 2}1234{
9W
10 Tu 111110 }1{
10W 2}13{
10W 3}123{
10W 2}1324{
10W
11 Tjju 1111 }1{
11W 2}13{
11W 3}134{
11W 2}1324{
11W
12 Tu 111112 }1{
12W 2}12{
12W 3}123{
12W 2}1234{
12W
13 Tu 111113 }1{
13W 2}13{
13W 3}123{
13W 2}1324{
13W
14 Tu 111114 }1{
14W 2}13{
14W 3}123{
14W 2}3214{
14W
15 Tu 111115 }1{
15W 2}12{
15W 3}123{
15W 2}1234{
15W
Table 5.2 Codebook for transmission for Four antenna ports 3,2,1,0 .
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Theprecodingcodebooksshownabovearedesignedtohaveconstantmodulus,thusallphysical
transmitantennakeepthesametransmitpowerlevelregardlessoftheprecodingmatrix.This
ensurestheefficiencyofthepoweramplifier.Theprecodingmatrixesarenested,thatis,each
precodingmatrixinahigherranksubcodebookcanfindatleastoneprecodingmatrixinalower
rankprecodingmatrix.ThispropertyensuresproperperformanceincaseswhentheeNodeB
decidestousetransmissionrankthanwhatisindicatedintheRI.
Openloopspatialmultiplexingareused insituationwhenthefeedbackreceivedfromtheUEis
unreliable,forexamplewhentheUEismovingatafastspeedcausingchannelconditiontovary
fasterthanthefeedbackcanreport.Theopenloopisillustratedinthefigurebelowconsistingof
NantennasandMlayerswithNgreaterorequaltoM.
Figure 5.3: Open-loop spatial multiplexing with Nantennas and Mlayers.
UnlikeSUMIMO,MUMIMOschemeissupportedinboththedownlinkanduplinkLTE.Inthe
uplink,TwoormoreUEscanbescheduledtotransmitusingthesametimefrequency.Tomake
eachsignalunique,theeNodeBassignsorthogonalreferencesignalstotheschedulesUEs.A
ZadoffChusequenceisdefinedasthebasesequencefortheuplinkreferencesignals.
OrthogonalreferencesignalscanbecreatedfromthecyclicallyshiftedZadofffChusequence.
ThuseachUEcanbeassignedadifferentcyclicallyshiftedZadofffChusequence,resultingin
uniquereferencesignalforeachUE.Fordatatransmissionontheuplink,acyclicshiftvalueis
alwaysincludedinthecontrolsignalandneedstobereceivedbeforeaUEcanstarttransmitting
data.ThisistrueevenincaseswhereMUMIMOschemeisnotused.
Rank1transmissionistheonlymodesupported inthedownlinkwhenMUMIMOschemeis
used.Differentrank1precodingmatricesareusedwhenmultipleUEsareconfiguredtousethe
sametimefrequencyresource.PerUEpreconfiguredPowerlevelmightbehardtomaintainin
MUMIMO,hencetheneedtointroduceda1bitsignalingtoindicateiftheUEneedstoreduce
itspowerby half(3dB).
TransmitdiversityisanotherMIMOschemeusedinLTEandLTEAdvanced.Inthedownlink,the
diversityschemecanbeappliedtoallthephysicalchannels,notjustthePDSCH.TheUE
recognizesthenumberoftransmitantennabyblindlydecodingthePBCH.Spacefrequency
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blockcode(SFBC)isusedinthecaseoftwotransmitantenna.ForeasierUEimplementationand
toproviderobustnessagainstcorrelationbetweenchannelsfromdifferenttransmitantennas,a
combinationofSFBCandfrequencyswitchedtransmitdiversity(FSTD)isusedinthecaseoffour
transmitantenna.Thisisshowninfigure5.4and5.5below.
Figure5.4:SFBCwithtwotransmitantennasondownlink.
Figure5.5:SFBC+FSTDwithfourtransmitantennasondownlink
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Chapter6:Other LTEAdvancedTechnologies
6.1carrieraggregation
CarrieraggregationtechnologyisintroducedinLTEAdvanced tosupportveryhighdatarate
transmissionsovera wider frequencybandwidthsthanexistingLTEsupports.LTErel8as
showninTable2.1,supportsabandwidthrangingfrom1.4Mhzto20Mhz,whileLTEAdvanced
should supportabandwidthextensionupto around100MHz.Inorder tosupportawider
transmissionbandwidth whilepreservingbackwardcompatibilitywithLTERel8,Carrier
aggregationtechniquehasbeenintroduced.Itinvolvestheaggregationofmultiplebasic
frequencyblockscalledcomponentcarriers(CC)witheachCChavingamaximumof110
resourceblocks(RBs)(whichissupportedintheLTERel8).Otherradioparameterssuchasthe
subcarrierspacing,subframelengthandphysicalchannelparameters thatwasdiscussedin
previouschapters,remainsthesameacrossCCs.ThisistoensureallLTEandLTEAdvancedUEs
canworkinthesamenetwork.
Figure6.1carrieraggregationtechniques
TwotypesofCarrieraggregationtechniquesarebeingproposedforLTEAdvanced;Continuous
andNoncontinuous.Continuouscarrieraggregationinvolvesusingmultipleavailable
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componentcarrierthatareadjacenttoeachotherwhiletheNoncontinuousaggregation
techniquesinvolvesusingcomponentcarriersthatareseparatedalongthefrequencyband.
WhileContinuouscarrieraggregationwouldseemeasiertoaccomplished,mostservice
providersmightfindithard(ifnotimpossible)toobtaincontinuous100MHzfrequencyband
duetothescarcityinspectrumallocation.WithNoncontinuousCarrierAggregationtechnique,
dataistransmittedovermultipleseparatedcarriersacrossalargefrequencyrangewith
differentchannelcharacteristics.Noncontinuouscarrieraggregationschemecanbe
implementedeitheratthemediumaccesscontrol(MAC)orthePhysicallayer.Ifimplementedin
theMAClayer,transmissionparametersareconfiguredindependentlyforeachcomponent
carrier.Thisimpliesthateachcomponentcarriermaintainsitsowntransmissionconfiguration
parameters(suchasthemodulationscheme,codingrateandMIMOconfiguration)inthe
physicallayeraswellasintheMAClayer.Inthephysicallayeraggregationscheme,asingleMAC
entityisusedbyalltheaggregatedcomponentcarriers.BackwardcompatibilityforLTERel8 is
ensuredbyusingthesameconfigurationparametersandschemes.
Figure6.2 ExampleofLTEcarrieraggregationscheme
Tosupportasymmetricdatatrafficintheuplinkanddownlink,anumberofschemeshavebeen
proposedtoaidtheeNodeBinidentifyingtheexactcomponentcarriersthataUEhasselected
forthedownlink.Thefirstschemeproposestheconfigurationofaphysicalrandomaccess
channel(PRACH)oneachcomponentcarrierwithdifferentparameters.TheeNodeBcanextract
thenumberofcomponentcarriersthattheUEisusingfromRACHpreambleviaanuplink
componentcarrier.Thesecondschemeinvolvestheconfigurationon allthedownlink
componentcarrierswiththesamePRACHparameters.Allassociateddownlinkcomponent
receivesabroadcastviaaninitialrandomaccessresponsewithspecifictransmission
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configuration.TheeNodeBcanthenextractthecomponentcarriersthatarebeingusedbythe
UE.A thirdschemeissimplebutlessflexible.Itusesonlyonedownlinkcomponentcarrierto
bearthecontrolchannelsrelevanttotherandomaccessprocess.Withthisschemeinuse,the
eNodeBdoesnot havetodetectthedownlinkcomponentcarriersthatareinusebythe UE.
6.2 CoordinatedMultipointTransmission/Reception
CoordinatedMultipointTransmissionandReception(CoMP) isanothercandidatetechnology
being consideredforLTEAdvanced.CoMPinvolvestheuseofantennasfrommultiplecellsites
inacoordinatedfashion.Bycoordinatingtransmissionbetweenmultipleantennas,higher
systemcapacityandimprovedcelledgedataratecanbeachieved.Beamformingorprecoding
gainscanbeachieved by takingintoaccounttheinstantaneouschannelconditions.Thereare
twocategoriesforcoordinatingmultipleantennas;Dynamicschedulingcoordinationand Jointtransmission/reception.CoMPcanbeusedwithinacelloracrossmultiplecells.
Figure6.3:IntraandInterCoMPconcept
InIntrasiteCoMP,thecoordinationiswithinthecellandlesscomplex,whileinIntersiteCoMP
thecoordinationcanspanacross2ormorecells,thusitisconsideredmorecomplexwith
respecttotheformer.
ChannelestimationonthedownlinkcanbeobtainedusingUEspecificreferencesignalsorcell
specificreferencesignal.InthecaseofUEspecific,referencesignalissubjecttothesame
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transmittersideprecodingasthedata,beforetransmittingfrommultipleantenna.TheUEdoes
notneedtobeawareofthetransmissionpointsinvolved,hencethismethodcanbeusedin
existingLTErel8.Inaddition,standardizedcodebookordifferentdeploymentscenariosarenot
needed.
Figure6.4:demodulationbasedonUEspecificRS
Withcellspecificreferencesignals,theUEneedstotakeintoaccounttheweightsappliedatthe
differenttransmissionpoints.Thisimpliestheuseofstandardizedtransmissionweightsand
codebooks.Maximumratiocombinationandinterferencerejectioncombiningcanbeusedto
coherentlycombinesignalsintheuplink.Onthetransmitterside,theknowledgeofthechannel
isalsousedtodeterminetheCoMPprocessing.The UEcanreportthequalityofthenetwork
usingtheCQIwiththeaidofreferencesignals.
Figure6.5:demodulationbasedoncellspecificRS
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6.3 Relaying
Arelayutilizesmultihopcommunication toenhancethetargeteddatarateinLTEAdvanced.
Fromalinkbudgetperspective,reducingthedistancebetweenthetransmitterandreceivercan
increasethepowerrate.Severalrelaytechniqueshavebeendevelopedoverthepastdecades
suchastheanalogrepeater,thatusesacombinationofdirectionalantennasandpower
amplifierstorepeatthetransmitsignal.Thefirstcommercialwirelessnetworktoincorporate
multihopcommunicationwasIEEE802.16j.InLTEAdvanced,threerelaytechniquesarebeing
considered;onewayrelay,twowayrelay,andsharedrelay.
Onewayrelaymodelismadeupofonesingleantennarelaypersectorsservingonlyusersinits
sector.Communicationtakesplaceintwoorthogonalphases,thefirstphasebeingtheeNodeBs
transmissiontotherelay,whilethesecondphaseinvolvestherelaystransmissiontotheUE.A
decodeandforwardoperationisthenperformed.Onewayrelaycanenhancecapacitynearthe
celledgebutmightbelimitedbyinterference.
Figure6.6:Onewayrelaymodel
Twowayrelaymodelalsocalledbidirectionalrelayingismadeupofasingleamplifyand
forwardrelaypersectorandallowsimultaneousuplink/downlinkcommunication.Twoway
relaymodelavoidsthehalfduplexlossofonewayrelaybecausebothUEandeNodeBtransmit
totherelayatthesametimeinthefirsttimeslot.Therelaythenrebroadcastduringthe
secondslot,hencecommunicationstilltakesplaceintwoorthogonalphase.DownlinkanduplinkratecanbemaximizedwithTwowayrelaymodelduetothefullduplexadvantage.With
theaidofchannelstateinformationandknowledgeoftheirownmessages,theUEandeNodeB
areabletodecodeinformationfromanotherparty.Duetoamplifyandforwardnatureoftwo
wayrelaying,ithasapotentialtoamplifyinterference.
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Figure6.7:Twowayrelaymodel
SharedrelayusesapointtomultipointtechniquewhereseveraleNodeBcansharetherelay.
SimilartoOnewayrelay,itusesadecodeandforwardmechanism,howevermultipleantenna
relayareplacedattheintersectionofmultiplecells.Therelaythendecodesthesignalsfromthe
intersectingbasestations.Interferencecanbecanceledbyusingmultiplereceiveantennaswith
MIMOtechnologies.ExploitingtheMIMOMAC(multipleaccess)channeltodecodethree
signalscochannelandthenusingMIMObroadcastchanneltodeliverthreeinterferencefree
signals.Thiswouldresultinthe removalof muchofthedominantinterference.Byspatially
removinglocalinterference,sharedrelayensuresthehighestratewhencomparedtotheother
relaymethodsthatwaspreviouslydiscussed.
Figure6.8:Shared relaymodel
Figure6.9:Powercomparisonanalysiswithdifferentrelaytechniques
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Conclusion
ThereportlookedatthephysicallayerinLTEandsomecandidatetechnologyproposedinLTE
Advanced.BackwardcompatibilitywithLTErel8isanimportantpriorityindevelopingLTE
Advanced.Withregardstocarrieraggregation,thisimpliesthatUEsincapableofsupporting
LTEAdvancedmustbeabletodemodulateanddecodethedownlinkdatachannelfromoneof
thecomponentcarrierswithoutperformanceloss.Asdiscussedinsection6.1,therearetwo
methodsproposedforcarrieraggregation;continuousandnoncontinuous.Forcontinuous
spectrumallocation,theUEmightbeaffectedbyinterferencefromadjacentcomponent
carriers.Toavoidsuchcondition,Guardbandsmaybenecessarybetweenadjacentcomponent
carriers.Consequently,theneedforanintercarrierguardbandmayresultinlossin
transmissionbandwidth.Toaccountforthelossduetoguardbandandensurethe20MHz
transmissionbandwidthispreserved,theentiretransmissionbandwidthmightneedtobewider
than20MHz.
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References
1. 3GPP, TR 36.814, "Further Advancements for E-UTRA; Physical LayerAspects".
2. 3GPP, TR 36.913, "Requirements for Further Advancements for E-UTRA
(LTE-Advanced) (Release 8)".
3. LTE-Advanced Evolving LTE towards IMT-Advanced, Stefan Parkvall, Erik
Dahlman, Anders Furuskr, Ylva Jading, Magnus Olsson, Stefan Wnstedt,
Kambiz Zangi
4. HSPA to LTE-Advanced, Rysavy Research
5. Investigation on Optimum Radio Parameter Design in Layered OFDM for LTE-
Advanced, Kazuaki Takeda, Satoshi Nagata, Yoshihisa Kishiyama, Motohiro
Tanno, Kenichi Higuchi, and Mamoru Sawahashi
6. Device-to-Device Communication as an Underlay to LTE-Advanced Networks,
Klaus Doppler, Mika Rinne, Carl Wijting, Cssio B. Ribeiro, and Klaus Hugl, Nokia
Research Center
7. Long Term Evolution: Towards 4th Generation of Mobile Telephony and Beyond
Sao Tomai1, Grega Jaku2
8. Progress on LTE Advanced-the new 4G standard, Eiko Seidel
9. LTE The UMTS Long Term Evolution from Theory to Practice, Stefania
Sesia,Issam Toufik,Mathew Baker.
10. Overview of the 3GPP Long Term Evolution Physical Layer, Jim Zyren
11. 3G Evolution HSPA and LTE for Mobile Broadband, Erik Dahlman,StefanParkvall,Johan Skold and Per Beming.
12. UMTS Long Term Evolution (LTE) Technology Introduction: Application Note
1MA111, RHODE & SCHWARZ.
13. Technical Solutions for the 3G Long-Term Evolution Hannes Ekstrm et al.
-
8/13/2019 A Technical Study of Long Term Evolution (LTE) and LTE-Advanced by Olufemi Amao
35/35
14. Carrier Aggregation for LTE-Advanced Mobile Communication Systems
Guangxiang Yuan et al
15. LTE-Advanced The solution for IMT-Advanced, Hideshi Murai, Maria
Edvardsson, Erik Dahlman
16. Illustration of MIMO channel matrix in a wireless communication system using
multiple transmitters (Tx) and receivers (Rx) , Benjamin Baumgrtner
17. LTE and the Evolution to 4G Wireless, Moray Rumney