ETSF15CommunicationSystemsandNetworksStefanHöst
4GmobilecommunicationsystemLTE
Planoflecture
• Somehistoryofmobilenetworks—Pastandfuture• EPS:Ideaofnetworkstructure• EPC:Packetnetworks• LTE:Radiochannel• Whatcomesnext?
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1st generation
• Analogtransmissionwithnosecurity• Smallregions(countries)• FirstNTT(‘79),secondNMT(’81)• NMT(Nordic),NTT(Jap),
AMPS(NA+Aus),TACS(UK),Radiocom 2000(Fr),RTMI(It)
• NMTshutdown2007
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2nd generation• Digitalvoicechannel(10kb/s),Circuitswitched• News:
• SIMcard(SubscriberIdentificationModule)• SMS:First3December1992:“MerryChristmas”
• Largerregions(continents)• GSM(Eur),IS-136(N+SAm+Aus),
IS-95(NA+Asia),PDC(Jap)• GSM1991
2.5generation=>Datachannels• HSCSD,GPRS,EDGE(E-GPRS),IS-95B
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3rd generation
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• Packetswitchedforvoiceanddata• 144kb/s– 3Mb/s• Global• CDMA2000(2000)• UMTS(2001)
• News:• UTRAN
UniversalTerrestrialRadioAccessNetwork
4th generation
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• Packetswitcheddatatraffic(VoiceoverIPor3G)
• 100Mb/s-1Gb/s• Global:• LTE(LongTermEvolution)• Feb2007Firstdemo(Ericsson)• Dec2009firstcommercial
(StockholmandOslo)
• News:Smartphonesandapps• iPhone2007
5th generation
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• Packetswitcheddatatraffic• 1-100Gb/s• 1Gb/s/user
• ≈2020• News:Smallcells,homecell,IoT (M2M),Car2Car,MassiveMIMO,etc
https://www.youtube.com/watch?v=Fq2A6bi_sDE
Mobiletraffic(CISCOVNI2016-2021)
• Globalmobiledatatrafficgrew63%in2016• 4.4EBinDec’15to7.2EBinDec’16• 18foldgrowthoverlast5years
• Globalmobiledevicesandconnectionsin2016grewto8.0billion(estimated11.6billionin2021– 1.5/capita)• 45%smartdevicesgenerate81%oftrafficin2016
• 86%in2021
• 26%4Gconnectionsgenerate69%datain2016• 53%4Gin2021willgenerate79%traffic• 0.2%5G(25million)
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TotalIPtraffic
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194.4
160.6132.1
108.588.772.5
Totalmobiledev.71.9EB/M(≈ totalof2015)
TotalMobiletraffic
10
7
49
35
2417
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Growthofdevices
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Growthoftechnology
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Mobiledatatrafficgrowthin2016
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4G– LTELongTermEvolution
Standardizedby3GPP(3rd GenerationPartnershipProject)• RadioAccessNetworks(RAN)• Service&SystemsAspects(SA)• CoreNetwork&Terminals(CT)• GSMEDGERadioAccessNetworks
(GERAN).
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EPS(EvolvedPacketSystem)
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SGW
MME HSS
PGW
eNodeB
Internet
E-UTRAN (LTE) EPC
UE
EPSchallenges• Highspeedradiolink• Bandwidthisextremelyexpensive.Squeezeoutallbitsyoucan
• AccesstoInternet• HowtosendIPpackets
• Authentication,securityandaccounting• Usermobility• HandoverbetweeneNBs• Howtotransferdatainthenetwork
• Costefficientinfrastructure
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EPSinterfacesEPC<->eNB• S1interface• SplitinS1-MMEandS1-U• Nocentralised nodeeNB <->eNB• X2interface• Coordinationandpositioning• SynchronisationeNB <->UE• LTE-Uu orEUTRAN-Uu
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EPC
LTE-Uu
E-UTRANEvolvedUniversalTerrestrialRadioAccessNetwork
RANresponsiblefor• Resourcemanagement• Schedulinganddynamic
resourceallocation
• Compression• IPheadcompression
reducesoverhead
• Security• Encryptionofdata
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• Positioning• UEphysicalposition
• ConnectiontoEPC• Userandcontrolplane
Protocolstack
• S1oftentunneledthroughthefixnetworkarchitecture• Atunnelisawaytosendpacketsoverothertypesof
network,e.g.• IPv6overIPv4andviceversa• IPoverIPsec
• GTP:GPRSTunnelingProtocol
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ExampleoftunnelingIPv4overIPv6usingGRE(GenericRoutingEncapsulation)
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IPpacketsinEPC(Userplane)
SGW• Collectingcharginginfo• LocalanchortowardseNB• Canchangeduetomobility
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SGW
MME HSS
PGWeNB
PGW• IPedgeforuser• IPaddressallocationtoUE• QoS filtering• Mobilityanchor• Doesnotchangeduring
session.PreservestheIPaddr
S5/S8S1LTE-UuUE
IPpacketsinEPC(Usermobility)
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SGW PGW
eNB
eNB
UE
SGW PGWeNB
UE
UE
Protocolstacks(Dataplane)
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GTP:GPRSTunnelingProtocolPDCP:PacketDataConvergenceProtocol
(IP<->Radio,Headercompression,security)RLC:RadioLinkControl
(Segmentation,reordering)
ControlplaneinEPC
HSS(HomeSubscriberServer)• Subscriberdatabase• SIMcardkeyexchange• AAA• Authentication,Authorization
andAccounting24
SGW
MME HSS
PGWeNB
MME(MobilityManagementEntity)• CommunicateswitheNB
andSGW• Managetunnelsand
encryption
S5/S8S1LTE-UuUE
USIMcardUMTSSubscriberIdentityModuleTheUSIMcardisanapplicationonasmartcardandcontains:• IMSI(Internationalmobilesubscriberidentity)15digits• AuthenticationkeyK andsequencenumberSQNAuthenticationprocess:
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KASME isusedforencryptionofmessages
K,SQN->AUTNK,RAND->XRESK,SQN,RAND->KASME
Theradiochannel
• Licensedfrequencybands(slotsof20MHz)• In0.5-4GHz
• CostinorderofBillions$• Alternative:FDDandTDD• MostcommonFDD
• Efficienttransmission• UElowpower=>long(er)batterylife
=>signalverylowpoweratreceiver26
Frequencyallocation(3kHz-300GHz)
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2.4/5.8GHzFree(WiFi)LTE
eNodeBstructure(physicallayer)
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OFDMError
controlFraming
interleaveDACAFE RF
shift
OFDMOrthogonalFrequencyDivisionMultiplexing
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P2S
S2P
(a1,...,aN )
ai ∈Z16
16-QAM mapping:
(x1,..., xN ) (y1,..., yN ) = IFFT (
!x)
(yN−L+1,..., yN ,y1,..., yN )
QAM
QAM
QAM
IFFT
cos2π f0t
sin2π f0ts(t)
Re DAC
CP
Im DAC
Can be used with M=4, 16, 64 or 256
AFE
Time-frequecymultipleaccess
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TDMA:
Time
Freq
uenc
y
…
User 1User 2User 3User 4
FDMA:
Time
Freq
uenc
y
…
Time-frequecymultipleaccess
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OFDMA:
Time
Freq
uenc
y
…
User 1User 2User 3User 4
InLTE• AResourceElement(RE)isonecarrieroveroneOFDM
symbolThisistheleasttime-frequencyresolution• 15kHzX71.4us
Resourceblock(RB)
ApairofRB(sub-frame)istheleastassignedresource
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Framestructureintime
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Resourceallocationinfrequency
BW [MHz] 1.4 3 5 10 15 20
N 128 256 512 1024 1536 2048
#alloc RB (in Freq) 6 12 25 50 75 100
#used carrier 72 144 300 600 900 1200
Oversampling 1.78 1.78 1.71 1.71 1.71 1.71
Max Rate [Mb/s] 6 12 25 50 75 100
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Max Rate is for 64-QAM, i.e. 6 bit/carrierThen [b/s]Impact of control signals and error control is not included
R = # carrier ⋅6 ⋅7 ⋅2 ⋅10 ⋅100
ExampleOneOFDMsymbolforBW=10MHzand64-QAM
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ExampleOneOFDMsymbolforBW=10MHzand64-QAM
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Plotof(all) frequencydomainsamplesasI-Q
4Gmobilenetworks
• PacketNetwork:EPC• Dataplane:PGW&SGW• Controlplane:MME&HSS• Incorenetwork
• AccessNetwork:LTE(E-UTRAN)• Upto20MHzbandwidth(=>100Mbps)• OFDMsignaling
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Whatcomesnext1C-RAN
Basebandunit(BBU)• BinarydatatoBBsamples
• QAMmapping• IFFT• Coding
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BBU EPCRU
eNodeB (SoA)
Radiounit(RU)• BBsamplestoRFsignal
• Digital/analogconversion• MixingtoRF• AFE
CPRI
BBU hotel@ Data center
BBU
Whatcomesnext1C-RANToutilizerecoursesbettersplitBBUandRRUinnetwork• UseCPRItotransmitBBsamplesbetweenBBUandRRU
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BBU EPCRRU
RRU
RRU=RemoteRadioUnit
Problem:Datarateexpansionintransmissionofradiosamplesofapproximatelyafactor10Needcompression
backhaulfronthaul
Whatcomesnext2Smallcells
• Smallcellsworkin• Shortdistance(lowpower)• Highdatarate(fewusers)
• Inpublicplaces,offices,shoppingmalls,etc
• Evenplansforsmallcellsinhomes• Insteadof,orcombinedwith,WiFi?
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EPC
Internet
Problems• Howtobackhaul/fronthaul• Cantheybepartof
coordination?• Picocell:withcoordination• Femto cell:nocoordination
Whatcomesnext3Convergednetwork• Usersbecomesmoremobile
• Whenpriceandratedifferencesdiminishmostusersdon’tcareaboutchoiceofconnection
• Convergence:• Onenetwork,manyaccesses• Flexiblenetwork• OneAuthentication(andpricing)• Seamlesshandoverbetweennetworks,e.g.LTE-WiFi• Dualconnectionsandtrafficoff-loading• Allunitseverywhere
• Problem:• Partlynewnetworkstructure(e.g.whereisIPedge)
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Whatcomesnext3Convergednetwork
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Fixedormobilenetwork(separated,SoA)
Fixedandmobilenetwork(convergednetwork)
MassiveMIMO
• Highcapacity• Pinpointusersor
equipment• Efficientsignalling
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Tx
Rx
X
Y1
Rx Y2
Rx Yn
MIMO:Multiple-inMultiple-outantennas
Problems:• Synchronisation• Backhaul/fronthaul
Whatcomesnext45G• Roughlyafactorof10inperformance
• 10timesfaster,bandwidth,Datarate,etc• 10batterylife(forlowpowerdevices)• 1000timestrafficvolume• 10timesharder(atleast)
• Smallcellseverywhere• Everythingisconnected
• Car2Car,M2M/IoT,Cloudcomputing,Skynet,…
• Expectedtolaunchtestslatest2020• Problems:
• Backhaul/fronthaul,RANsync,Energyefficiency,etc
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