Ericsson Technology Review: Evolving LTE to fit the 5G future

5G AND THE EVOLUTION OF LTE ✱
JANUARY 31, 2017 ✱ ERICSSON TECHNOLOGY REVIEW 1
ERICSSON
TECHNOLOGY
5G wireless access
Gradual migration
Tight interworking
LTE Evolution
Existing spectrum
1GHz 3GHz 10GHz 30GHz 100GHz
New spectrum
NR
No compatibility constraints
C H A R T I N G T H E F U T U R E O F I N N O V A T I O N | # 1 ∙ 2 0 1 7
EVOLVINGLTE
TOFITTHE5GFUTURE

✱ 5G AND THE EVOLUTION OF LTE
2 ERICSSON TECHNOLOGY REVIEW ✱ JANUARY 31, 2017
OUMER TEYEB,
GUSTAV WIKSTRÖM,
MAGNUS STATTIN,
THOMAS CHENG,
SEBASTIAN FAXÉR,
HIEU DO
With 5G research progressing at a rapid pace, the standardization
process has started in 3GPP. As the most prevalent mobile broadband
communication technology worldwide, LTE constitutes an essential piece
of the 5G puzzle. As such, its upcoming releases (Rel-14 and Rel-15) are
intended to meet as many 5G requirements as possible and address the
relevant use cases expected in the 5G era.
Since its first commercial deployment by
TeliaSonera in December 2009 [1], LTE has
become one of the most successful mobile
communication technologies worldwide.
Currently, there are 537 commercial LTE
networks deployed in 170 countries with
1.7 billion subscribers – a number that is
expected to rise to a staggering 4.6 billion
by 2022 [2].
■Inthesevenyearsthathavepassedsincethe
launchofLTE,majoradvanceshavebeenmade
intermsofbothperformanceandversatility.
Forexample,LTERel-8introduceda20MHz
bandwidthwithpeakdownlink(DL)dataratesof
300Mbpsanduplink(UL)dataratesof75Mbps
[3].MinorexpansionsweremadeforRel-9,such
asmulticast/broadcastservices,location-based
servicesandduallayerbeamforming.LTERel-
10,alsoknownasLTE-Advanced,introduced
severalnewfeaturessuchascarrieraggregation
(CA)toprovideupto100MHzbandwidthas
EvolvingLTE
TO FIT THE
5Gfuture

wellasenhancedsupportformulti-antennas,
heterogeneousdeploymentsandrelaying[4].
Thesefeaturesenabledpeakdataratesinexcessof
1GbpsinDLand500MbpsinUL.
Rel-11andRel-12includedenhancementssuch
asthesupportofmachinetypecommunications
(MTC),dualconnectivity(DC),LTE-WLANradio
interworking,andnationalsecurityandpublic
safety(NSPS)servicesincludingdirectdevice-to-
device(D2D)communication[5].Furtheradvances
weremadeinRel-13,includingspectralefficiency
enhancementsviaFullDimensionmultiple-input,
multiple-output(FD-MIMO),supportforutilizing
unlicensedspectrumviaLicensedAssistedAccess
(LAA)andLTE-WLANaggregation,extended
supportforMTCthroughNarrowbandInternet
ofThings(NB-IoT)andenhancedMTC(eMTC),
enhancedCA(upto32carriers),indoorpositioning
enhancements,andsingle-cell-point-to-multipoint
(SC-PTM)forbroadcast/multicastservices[6].
SinceOctober2015,3GPPhasusedtheterm
LTE-AdvancedProforRel-13andonwards,
signifyingthatLTEhasreachedamaturitylevel
thatnotonlyaddressesenhancedfunctionality/
efficiencybutalsothesupportofnewusecases.
Why5G?
Globalmobiledatatrafficisexpectedtogrowata
compoundannualrateof45percentinthecoming
years,whichrepresentsatenfoldincreasebetween
2016and2022[2].Thisincreaseisdrivenlargelyby
themassiveadoptionofmobilevideostreaming.
Ontopofthat,theIoTisshiftingfromvisionto
reality,andofthe29billionconnecteddevicesitis
expectedtoincludeby2022,18billionwillbeIoT
(ormachine-to-machine)devices[2].Future5G
networkswillneedtosupportthesechallenging
newusecasesinacostandenergyefficientmanner.
LTE HAS REACHED
A MATURITY LEVEL
THAT NOT ONLY
ADDRESSES ENHANCED
FUNCTIONALITY/EFFICIENCY
BUT ALSO THE SUPPORT OF
NEW USE CASES
Abbreviations
AS – access stratum | BS – base station | CA – carrier aggregation | CN – core network | CP – control plane |
CSI – channel state information | CSI-RS – CSI reference signal | D2D – device-to-device | DC – dual connectivity |
DL – downlink | DoNAS – data over non-access stratum | DSRC – dedicated short range communications |
eMBB – enhanced mobile broadband | eMTC – enhanced MTC | eNB – evolved node B | FD-MIMO – Full Dimension
MIMO | HARQ – hybrid automatic repeat request | IoT – Internet of Things | ITS – intelligent transportation system
| ITU – International Telecommunication Union | LAA – Licensed Assisted Access | MBMS – Multimedia Broadcast/
Multicast Service | MCL – maximum coupling loss | MIMO – multiple-input, multiple-output | mMTC – massive
machine type communications | mm-wave – millimeter wave | MTC – machine type communications |
MU-MIMO – multi-user MIMO | NAS – non-access stratum | NB-IoT – Narrowband Internet of Things |
NR – New Radio | PCell – primary cell | RRC – Radio Resource Control | RS – reference signal | RTT – round-trip
time | SCell – secondary cell | SL – sidelink | SR – scheduling request | TTI – transmission time interval |
UL – uplink | UP – user plane | URLLC – ultra-reliable low latency communications | V2I – vehicle-to-infrastructure |
V2N – vehicle-to-network | V2P – vehicle-to-pedestrian | V2V – vehicle-to-vehicle | V2X – vehicle-to-everything |
3GPP – 3rd generation partnership project

Althoughtherequirementsfor5Gcapabilitiesare
stillbeingfinalizedbothintheITU[7]and3GPP
[8],thereisapreliminaryagreementregardingthe
threemainusecasesthetechnologymustsupport.
AsillustratedinFigure1,theyare:enhanced
mobilebroadband(eMBB),ultra-reliablelow
latencycommunications(URLLC)andmassive
machinetypecommunications(mMTC).eMBB
referstotheextendedsupportofconventional
MBBthroughimprovedpeak/average/cell-edge
datarates,capacityandcoverage.URLLCisa
requirementforemergingcriticalapplicationssuch
asindustrialinternet,smartgrids,infrastructure
protection,remotesurgeryandintelligent
transportationsystems(ITSs).Lastbutcertainly
notleast,mMTCisnecessarytosupportthe
envisioned5GIoTscenariowithtensofbillionsof
connecteddevicesandsensors.
Therearetwotracksthatmakeupthe5Gradio
accessroadmapin3GPP,asillustratedinFigure 2.
OneisbasedontheevolutionofLTEandtheother
onNewRadio(NR)access.IntheLTE-5Gtrack,
enhancementswillcontinuetoenableittosupport
asmany5Grequirementsandusecasesaspossible.
UnliketheLTE-5Gtrack,theNR-5Gtrackis
freefrombackwardcompatibilityrequirements
andtherebyabletointroducemorefundamental
changes,suchastargetingspectrumathigh
(mm-wave)frequencies.However,NRisbeing
designedinascalablemannersoitcouldeventually
bemigratedtofrequenciesthatarecurrently
servedbyLTE.
WhiletheprospectsfortheNR-5Gtrackare
exciting,theoperatorsthathavealreadymade
significantinvestmentsinLTEdonotneedtobe
concerned–atransitionfromLTEto5Gthrough
5Gplug-insisthemostlogicalcourseofaction.
BoththeexpectationsforLTERel-14[9]–whichis
scheduledforcompletioninMarch2017–andthe
strongambitionsforLTERel-15indicatethatthe
developmentplansfortheLTE-5Gtrackaresolid.
TheprocessofmakingLTE5G-readyinvolves
avarietyofenhancementsandnewfeaturesin
Rel-14andRel-15.Themostsignificantonesare
enhancementstouserdataratesandsystem
capacitywithFD-MIMO,improvedsupportfor
unlicensedoperations,andlatencyreduction
inbothcontrolanduserplanes(UPs).The
enhancementsinRel-14andRel-15alsoaim
toprovidebettersupportforusecasessuchas
massiveMTC,criticalcommunicationsandITS.
Userdatarateandsystemcapacity
enhancements
FD-MIMOandunlicensedoperationsarethetwo
mainfeaturesintheupcomingreleasesofLTEthat
areintendedtobringaboutimproveduserdata
ratesandsystemcapacitythatmeet5Gstandards.
FD-MIMO
TheMIMOenhancementin3GPPmakesit
possibletodynamicallyadapttransmissionboth
verticallyandhorizontallybyutilizingasteerable
two-dimensionalantennaarray.Theconcept
ofFD-MIMOinfutureLTEreleasesbuildson
thechannelstateinformation(CSI)feedback
mechanismsintroducedinLTERel-13,inwhich
precodingmatrixcodebookssupporttwo-
dimensionalportlayoutswithupto16antenna
ports.Non-precodedCSIreferencesignals(CSI-
RSs)aretransmittedfromeachantennaand
broadcastinthecell,andtheprecoderisderived
bytheterminal.LTERel-13alsointroduced
anotherCSIfeedbacktypewithterminal-specific,
beamformedCSI-RS,inthesamefashionas
physicaldownlinksharedchannel(PDSCH).In
THE PROCESS OF
MAKING LTE 5G-READY
INVOLVES A VARIETY OF
ENHANCEMENTS AND
NEW FEATURES IN REL-14
AND REL-15

Figure 2
5G radio access
roadmap
Figure 1
The three main 5G use
cases and examples of
associated applications
Video
Smart office
ITS
Connected
city/home
Smart
logistics
Smart
grid
Factory
automation
URLLC mMTC
eMBB
Smart
sensors
Remote
operation
5G wireless access
Gradual migration
Tight interworking
LTE Evolution
Existing spectrum
New spectrum
NR
No compatibility constraints

thiscase,thebeamformingdirectionforeach
terminalisdecidedbythebasestationratherthan
beingderivedfromterminalfeedback.
Toenhancebothnon-precodedand
beamformedCSI-RSoperation,Rel-14will
introduceseveralnewfeatures,includinghybrid
non-precoded/beamformedCSImodewith
optimizedfeedback;aperiodictriggeringofCSI-
RSmeasurements;supportforupto32antenna
ports;spatiallyrich,advancedCSIfeedback;anda
semi-open-looptransmissionscheme.
Hybridnon-precodedandbeamformedCSI
modewithoptimizedfeedbackwillmakeit
possibletointermittentlytransmitaninitial,
non-precodedCSI-RS.Theterminalscanthen
respondwithadesireddirectionforasecond,more
frequent,beamformedCSI-RS.
AperiodictriggeringofCSI-RSmeasurements
facilitatesCSI-RSresourcepooling,enabling
theefficientuseofmeasurementresourcesand
thereductionofCSI-RSoverhead.Asaresult,
moreterminalsinthecellwillhaveaccessto
beamformedCSI-RSoperation.
Supportfor32antennaportsmakesitpossible
tousefeedback-basedoperationwithmassive
antennasetups,whichincreasesthegainsfrom
multi-userMIMO(MU-MIMO).
Spatiallyrich,advancedCSIfeedbackwill
includeinformationaboutmultiplechannel
propagationpaths,sothatinterferencebetween
co-scheduledterminalscanbeavoidedor
suppressed.Performanceisthencomparableto
reciprocity-basedmassiveMU-MIMOsystems.
Thesemiopen-looptransmissionscheme
combinesfull-dimensionbeamformingand
transmitdiversity,targetinghigh-speedterminals
whereabeamdirectionisknownbutshort-term
CSIchangestooquickly.
Theanticipatedimprovementinsystemcapacity
anduserthroughputwithRel-14FD-MIMOis
illustratedinFigure3–a3GPP3Durbanmicro
scenariofeaturing8x4dualpolarizedarrayand
non-full-buffertraffic.Performanceonthecelledge
increasesroughly2.5timeswithadvancedCSI
feedbackandsupportfor32antennaports.
LTEoperationsinunlicensedspectrum
Toaddresseverincreasingtrafficdemands,many
networkoperatorsareconsideringcomplementary
useofunlicensedspectrum.LAAwasintroduced
inLTERel-13forDLoperation,anditisbeing
enhancedinRel-14tosupportUL.LAAusesCA
tocombinealicensedbandprimarycell(PCell)
withunlicensedbandsecondarycells(SCells).The
SCellsusuallyhaverestrictedtransmissionpower,
however,whichresultsincoverageareasthatare
smallerthanthosethatPCellsareabletoprovide.
Inthisarrangement,aPCellprovidesreliable
coverageforcontrolmessagesandhigh-priority
traffic,whiletheSCellsprovidealargeamount
ofspectrumandhighdatarateswhenavailable.
Figure4showshowLAAoffersacombinationof
themainbenefitsprovidedbybothlicensedand
unlicensedspectrum.
Severalsolutionshavebeenincorporated
into3GPPtoachievecoexistencewithother
technologies–suchasWLAN–thatoperatein
thesamebandasLAA.Theseincludedynamic
carriermeasurement/selection,Listen-Before-
Talkprotocol,anddiscontinuoustransmission
withlimitedmaximumduration.Smartand
adaptivetrafficmanagementbetweenlicensed
andunlicensedcarriers–andbetweenunlicensed
carriers–couldalsofurtherenhancecoexistence.
Figure5showsthenetworkcapacityinanLAA
outdoorcoexistencescenariowhereeachof
SEVERAL SOLUTIONS
HAVE BEEN INCORPORATED
INTO 3GPP TO ACHIEVE
COEXISTENCE WITH OTHER
TECHNOLOGIES – SUCH AS
WLAN – THAT OPERATE IN
THE SAME BAND AS LAA

Capacity
Data rate
QoS
Reliability
Mobility support
LAA unlicensed
LTE macro
performance
LTE small cells
Improved performance
Licensed spectrum Unlicensed spectrum
Relativegain[%]
Rel-14 32 ports Rel-14 32 ports + advanced CSIRel-14 16 ports + advanced CSI
Cell edge throughput gain [%]
Capacity gain [%]
Mean user throughput gain [%]
160
140
120
100
80
60
40
16
56
28
36
119
47
42
135
52
20
0
Figure 4
Illustration of LAA
Figure 3
Performance of Rel-14
FD-MIMO over a 16 port
Rel-13 baseline (without
advanced CSI) at high
system load

twooperatorsdeployfourLAAorfourWLAN
nodesperhotspot[10].TheLAAcellssupport
substantiallyhigheroffloadingcapacityonthe
same20MHzchannelcomparedwiththeWLAN
nodes.ThisisbecausetherobustLAAphysical
layerdesignallowsreliableandefficientfrequency
reuse.Infact,themoreefficientLAAnetwork
leavesmorecapacityfortheco-channelWLAN.
FurtherLAAenhancementsareexpectedin
LTERel-15,mostnotablyULcontrolinformation
transmissionandrandomaccesschannelsupport
ontheunlicensedbandSCells.Thiswouldmake
itpossibletooffloadmoretrafficfromthelicensed
bandPCellsandallowforfurtherdeploymentas
wellasenablingusecasessuchasfiberconnected
remoteradioheads.
AnotherpotentialenhancementinLTERel-15
isdualconnectivitybetweenlicensedbandmain
evolvednodeB(eNB)andunlicensedbandsecondary
eNB.Thiswouldfurtherbroadendeployment
possibilitiesbyallowingaggregationbetween
networknodesthatarenotconnectedvialow-latency
backhaul.Finally,Rel-15mayenablemoredeployment
optionsandscenarios,suchasstandaloneandmMTC
operationsinunlicensedspectrum.
Latencyreduction
AnotherimportantaspectofLTEenhancement
istheimplementationoflatencyreduction
techniquesfortheuserandcontrolplanes(UPs
andCPs).Latencyreductionnotonlycontributes
todatarateenhancementsbutalsoenablesnewuse
casessuchascriticalcommunicationandITS.
Userplanelatencyreduction
ImplementingfastULaccessisthefirststep
towardreducingUPlatency.AsspecifiedinRel-
14,fastULaccessmakesitpossibletoconfigure
aterminalwithanuplinkgrantavailableineach
millisecond,tobeusedonlywhenthereisuplink
datatotransmit.Usingthecurrentscheduling
request(SR)basedaccess,theterminalmust
transmitarequest,waitforagrant,andthenwait
tousethegrant.AcomparisonoffastULaccess
withSRaccessisillustratedintheaandbtracks
ofFigure6.Thepre-configuredgrantinfastUL
accessminimizesthewaitingtime,whichreduces
theaverageradioaccessdelayforuplinkdataby
morethanhalf.
Theotherlatencyreductionstepconsists
oftwoenhancementsthatarebothtargeted
forspecificationinRel-15.Thefirstisreduced
processingtime:makingtheterminalrespond
todownlinkdataanduplinkgrantsinthree
millisecondsinsteadoffour.Thesecondisthe
introductionofshortertransmissiontimeintervals
(TTIs):speedingupthewholechainofwaitingfor
atransmitopportunity,schedulingandpreparing
foratransmission,transmittingthedata,and
ultimatelyprocessingthereceiveddataand
sendingfeedback.
WithashortTTI,asillustratedinthectrack
ofFigure6,transmissionscanbemadewitha
shorterduration(aslittleasone-seventhofthe
lengthofanormalLTETTI).Eachoftheseshort
transmissionscanbescheduledseparatelywitha
newDLin-bandcontrolchannel,withfeedback
sentinanewULcontrolchannel.Thescheduling
andfeedbackaresentinadjacentsubframesforthe
shortesttransmissiontime,resultinginatotalradio
accessone-waytransmissiondelayofabout0.5ms,
includingdataprocessingtime.
Figure7illustratesthegainsinround-triptime
(RTT)madebyemployingshortTTIandfastUL
access.Fromsimulations,improvementshavealso
beenobservedinthethroughputforFileTransfer
LATENCY REDUCTION
NOT ONLY CONTRIBUTES TO
DATA RATE ENHANCEMENTS
BUT ALSO ENABLES NEW
USE CASES SUCH AS
CRITICAL COMMUNICATION
AND ITS

Fast UL grant
Fast UL grant
UL grant
inactiveinactiveinactive
active
active active
Data
Data
Data
Data
Data
Delay
Delay
Delay
UL data UL data UL data
SR
a) SR based access b) Fast UL access c) Short TTI + Fast UL access
Figure 5
LAA-WLAN outdoor
coexistence (40MHz
shared carriers, both
networks operating at
5GHz)
Figure 6
SR access (a), fast UL
access (b), and short TTI
in conjunction with fast
UL access (c)
Networkcapacity[%]
Two Wi-Fi networks LAA and Wi-Fi networks
Wi-Fi
network 1
Wi-Fi
network 2
Wi-Fi
network 2
LAA
network 2
160
180
140
120
100
80
60
40
20
0

Protocol(FTP)downloadbyupto70percent:
aneffectcausedbyafasterTCPbitrateramp-up
thankstotheshorterRTTofdataandresponse.
Signalingreduction
LTEstatetransitionsinvolvesignificantsignaling:
goingfromRRC_IDLEtoRRC_CONNECTED
comprises9transmissionsovertheairinterface.
Twooptionsforsignalingreductionwere
introducedinRel-13:RRCconnectionsuspend/
resumeforusewithUPbaseddatatransferover
dataradiobearers(DRBs)anddataovernon-
accessstratum(DoNAS)forCP-baseddata
transferoverthesignalingradiobearer(SRB).
Thesuspend/resumefeatureallowsthedata
connectiontobesuspendedtemporarilyandthe
contexttobestoredintheRANandcorenetwork
(CN)duringRRC_IDLE.Atthenexttransitionto
RRC_CONNECTED,theconnectionisresumed
withthestoredcontext,significantlyreducing
thesignalingtofourorfivetransmissions.The
DoNASfeatureachievesasimilarreductionof
signalingbyomittingaccessstratum(AS)security
andbytransferringdataovertheCPinsteadof
establishingtraditionalUPradiobearers.
Toaccommodatetheeverincreasingnumber
ofdevices,smalland/orinfrequentdatavolumes
andstricterdelayrequirements,Rel-14andRel-
15aimforfurtherreductionofsignalingbetween
terminalsandnetworknodes(RANandCN).
InRel-14,thesuspend/resumefeatureisbeing
improvedbyreducingthesignalingbetween
thebasestation(BS)andtheCN.InRel-13,the
BS-CNconnectionwasreleasedtogetherwith
theairinterfaceconnection.InRel-14,theBS-CN
connectioncanbekeptwhentheBS-terminal
connectionissuspended.TheRANtakesover
theresponsibilityofpagingtheterminaluponthe
arrivalofDLdata,forexample.
Twoadditionalcontrolplanelatencyreduction
Ping round-trip latency (ms)
120%
100%
80%
60%
40%
20%
0%
<4 5 10 15 20 25 30
LTE Rel-14/15 LTE Rel-13
ShortTTI+FastUL
ShortTTI
FastUL
SRperiodicity1ms
SRperiodicity5msSR
periodicity10m
s
Figure 7 Impact of short TTI and fast UL access on RTT

LTE MTC
(Cat-M1)
NB-IoT
Bandwidth
1.4MHz
200kHz
164dB 300/375kbps1)
0.8/1Mbps2)
Connected and
idle mode
mobility
Idle mode
mobility
21/63kbps
1) Half duplex, 2) Full duplex
10+ years
10+ years164dB+
Coverage
(MCL)
Battery life Throughput
(DL/UL)
Mobility
Figure 8 NB-IoT and LTE MTC key performance indicators (Rel-13)
improvementsareexpectedinRel-14orRel-15.
Thefirstisanenhancementthatwouldenable
earlierdatatransmissionbymakingitpossibleto
multiplexUPradiobearerdatawithconnection
resumesignaling.Thesecondisknownasrelease
assistanceindication,whichwouldallowthe
terminaltoindicatethatithasnomoreULdata
andthatitdoesnotanticipateDLdata,thereby
enablingearlytransitiontoRRC_IDLE.
Newusecasesfor5G
AnumberofimprovementsinLTERel-14and
Rel-15aredesignedtoprovideimprovedsupport
forusecasessuchasmassiveMTC,critical
communicationsandITS.
Massivemachinetypecommunications
LTEMTCandNB-IoTweredevelopedto
addressmMTCusecases[11].Theyoffer
similarimprovementswithregardtocoverage
enhancement,batterylife,signalingefficiencyand
scalability,butaddressslightlydifferentdemands
intermsofflexibilityandperformance.Asshownin
Figure8,LTEMTCismorecapableofsupporting
higherdataratesandbothintra-RATandinter-
RATconnectedmodemobility.Withthenew
LTEMTCCategoryM1(Cat-M1)andNB-IoT,
whichwerespecifiedin3GPPRel-13,itis
anticipatedthatmodemcostcanbedrastically
reducedcomparedwithRel-8Cat-1devices.
Costwillvarydependingonfeatures,options
andimplementation.Modemcostreductionsare
expectedtobeintheorderof75-80percentfor
Cat-M1[12]andevenmoreforNB-IoTwithits
furtherreducedfeatureset.
LTERel-14aimstofurtherenhanceLTE
MTCandNB-IoTbyimprovingperformance
andaddressingmoreusecases.Higherdata
ratesandefficiencywillbeachievedinRel-14by
allowinglargerchunksofdatatobecarriedineach

transmissionandincreasingthenumberofhybrid
automaticrepeatrequest(HARQ)processesto
enableparalleloutstandingtransmissionswhile
waitingforfeedback.Largerchannelbandwidth
forLTEMTC(upto5MHz)enhancessupport
forvoiceandaudiostreamingaswellasother
applicationsandscenarios.NB-IoTenhancements
forrandomaccessandpagingincreasethe
versatilityofnon-anchorcarriers.
Rel-14willfurtherenablepositioning
applications(inwhichknowledgeofdevice
locationiscritical)bysupportingenhanced
referencesignalsthattakeintoaccountthesmaller
NB-IoT/LTEMTCbandwidth.Enhancements
toconnectedmodemobilitywillimproveservice
continuity.Multicasttransmissionwillmakethe
deliveryofthesamecontenttomultipledevices
moreefficient,optimizingusecasessuchas
firmwareupgradesandsynchronouscontrolof
thingslikestreetlights,forexample.Supportforthe
lowerNB-IoTpowerclassof14dBmwillenablethe
useofsmallerbatteriesandsupportdeviceswitha
smallformfactor.
VoicecoverageforLTEMTCwillbeimproved
inRel-14byincreasingVoLTEcoverageforhalf-
duplexFDD/TDDthroughtechniquesthat
reduceDLrepetitions,newrepetitionfactors,and
adjustedschedulingdelays.MTCdevicesanduse
caseswillalsobenefitfromthesignalingreduction
enhancementsinLTERel-14.
mMTCusecaseswillalsobenefitfromafew
otherenhancementsinLTERel-15,including:
〉〉 latencyimprovementsresultingfromthemultiplexingof
userdatawithconnectionresumesignaling
〉〉 efficiencyimprovementsresultingfromenhancedaccess/
loadcontrolinidleandconnectedmodes
〉〉 batterylifeimprovementsresultingfromrelaxedDL
monitoringrequirementsinidlemode
〉〉 improvedsupportforadditionalusecasessuchas
wearables.
Criticalcommunication
Usecasessuchaspowergridsurveillance,safety-
criticalremotecontrol,andcriticalmanufacturing
operationsrequirebothlowlatencyandhigh
reliabilityabovethecurrentHARQlevel(see
Figure9).InorderforLTEtomeetthese5G
requirements,thereisanaimfortwoimprovements
tobemadeforRel-15:reliableshortTTIoperation
andreliable1msoperation.
BybuildingontheshortTTIandfastUL
features,thepacketerrorratecanbereduced
toa10-5levelthroughacombinationofrobust
codingofcontrolanddatamessages,diversity,and
automaticrepetitionswithoutfeedback.Sincethe
processingiskeptonashorttimescale,theentire
chainoftransmissionscanbedeliveredwithin1ms
withthecombinedreliabilityofmultipletrials.(The
targetissmallcells,suchasfactoriesandoffices.)
Inaddition,wide-areacoveragewithrelaxed
latencybutextremereliabilitycanalsobetargeted
byautomaticrepetitionsofrobustlycoded1ms
transmissionswithenhancedfeedback.
Intelligenttransportationsystems
TheuseofICTtoenablesaferandmore
efficient transportation systems is known as ITS.
3GPP has been developing a solution for vehicle-
to-everything (V2X) communications for Rel-14,
addressing the connection between vehicles
(vehicle-to-vehicle or V2V), vehicle-to-network
(V2N), vehicle-to-infrastructure (V2I), and
vehicle-to-pedestrian (V2P), as illustrated
in Figure 10.
LTE-basedITSbenefitsfromthecoverageof
theexistingnetworksandthecentralizedsecurity.
However,newITSusecasesaredemandingin
termsoflatencyandsystemcapacity.Therefore,the
directD2Dinterface,knownassidelink(SL),and
theLTEcellularairinterfacearebeingenhancedin
Rel-14tosupporttheserequirements.
Forexample,increasedpilotsymboldensity
willmakeitpossibletooptimizetheSLfor
quicklychangingpropagationconditionsand
severefrequencyshiftsatthereceiverduetohigh
relativespeed(upto500km/h)andhighercarrier
frequency(upto6GHz).
Improvedradioresourcemanagementis
anotherimportantenhancementtosupportITS

V2P over optimized LTE
cellular interfaceV2N over LTE cellular with
enhanced multicast
V2V/V2P/V2I over enhanced LTE sidelink interface
1s
1 2 3 4 5 6 7 8 9
100ms
10ms
1ms
Reliability (error rate 10–x
)
5G URLLC requirements
LTE Rel-13
Latency
Figure 10
Illustration of different
ITS scenarios and
interfaces
Figure 9
Critical communication
use cases and
requirements

applications.Thisisbasedonasensing-based
resourceselectionprotocol,whereeachdevice
autonomouslylearnshowotherdevicesusethe
radioresourcesandpredictstheirfuturebehavior,
takingadvantageofthequasi-periodicnatureof
theITSmessages.
Rel-14supportstheusageofgeographical
locationinformationtoenablecentralizedresource
allocationintheeNBortoautonomouslyselecta
resourcewithinaconfiguredradioresourcepool.
ItalsosupportsMultimediaBroadcast/Multicast
Service(MBMS)protocolsthatareoptimizedfor
lowlatencyandcoverage,andefficientdeliveryof
V2Xmessages.Finally,theexpectedenhancements
willprovidefairandefficientcoexistencewith
non-3GPPITStechnologiessuchasdedicated
shortrangecommunications(DSRC).
Figure11showsanumericalcomparisonofthe
capabilityofdifferenttechnologiesforbroadcasting
V2Vmessages.Intypicalscenarios(urbanand
highway),thesolutionsbasedonLTE(SLwith
centralizedresourceallocationandcellular
multicast)performsignificantlybetterthantheone
basedonDSRC.
Conclusion
LTEiswellpositionedtodeliveronallthemost
important5Grequirements,includinguserdata
rateandsystemcapacityenhancementswith
FD-MIMO,improvedsupportforunlicensed
Figure 11 Comparison of different
technologies for broadcasting ITS messages
Reliability(packetreceptionratio)
Highway scenario, distance = 300m
10 messages per second
Reliability of broadcasting ITS packets
Urban scenario, distance = 80m
2 messages per second
0.8
0.9
1
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
LTE sidelink
DSRC
LTE cellular multicast

1. Network Computing, First Commercial LTE Network Goes Live,
available at: http://www.networkcomputing.com/networking/
first-commercial-lte-network-goes-live/752107374
2. Ericsson, Ericsson Mobility Report 2016, November 2016, available at:
https://www.ericsson.com/assets/local/mobility-report/documents/2016/
ericsson-mobility-report-november-2016.pdf
3. David Astély et al., LTE: The Evolution of Mobile Broadband, IEEE
Communications Magazine, April 2009, available at:
http://ieeexplore.ieee.org/document/4907406/
4. Stefan Parkvall et al., Evolution of LTE toward IMT-Advanced, IEEE
Communications Magazine, February 2011, available at:
5. David Astély et al., LTE Rel-12 and Beyond, IEEE Communications
Magazine, July 2013, available at: http://ieeexplore.ieee.org/
document/6553692/
6. Juho Lee et al., LTE-advanced in 3GPP Rel-13/14: an evolution toward
5G, IEEE Communications Magazine, March 2016, available at:
7. ITU-R, IMT Vision – Framework and overall objectives of the future
development of IMT for 2020 and beyond, Recommendation ITU-R
M.2083-0, September 2015, available at: http://www.itu.int/
dms_pubrec/itu-r/rec/m/R-REC-M.2083-0-201509-I!!PDF-E.pdf
8. 3GPP Technical Report 38.913, Study on Scenarios and Requirements
for Next Generation Access Technologies, October 2016, available at:
http://www.3gpp.org/ftp/Specs/archive/38_series/38.913/38913-e00.zip
9. C. Hoymann et al., LTE Rel-14 Outlook, IEEE Communications
Magazine, June 2016, available at:
10. 3GPP Technical Report 36.899, Study on Licensed-Assisted Access
to Unlicensed Spectrum (Rel-13), June 2015, available at:
http://www.3gpp.org/ftp/Specs/archive/36_series/36.889/36889-d00.zip
11. Alberto Rico-Alvarino et al., An Overview of 3GPP Enhancements
on Machine to Machine Communications, IEEE Communications
Magazine, June 2016, available at:
12. 3GPP Technical Report 36.888, Study on provision of low-cost
Machine-Type Communications (MTC) User Equipment (UEs) based
on LTE (Rel-12), June 2013, available at:
http://www.3gpp.org/ftp/Specs/archive/36_series/36.888/36888-c00.zip
References:
operations,andlatencyreductioninbothuserplane
andsignaling.TheimprovementsplannedinRel-
14andRel-15willnotonlyensurethatLTEwill
providebettersupportformassiveMTCandITS;
theywillalsoenableLTEtoaddressnewusecases
suchascriticalcommunications.

Oumer Teyeb
◆ is a senior researcher.
He earned a Ph.D. in
mobile communications
from Aalborg University,
Denmark, in 2007 and has
been working at Ericsson
Research in Stockholm,
Sweden, since 2011. His
main areas of research
are protocol and the
architectural aspects of
cellular networks, and the
interworking of cellular
networks with local area
wireless networks such as
WLAN.
Gustav Wikström
◆ is a senior researcher. He
received his Ph.D. in particle
physics from Stockholm
University, Sweden, in
2009. After a postdoctoral
position at the University
of Geneva, Switzerland, he
joined Ericsson Research in
2011, where he is currently
leading the work to reduce
user plane latency and
enable high reliability for
future use cases in LTE
and NR.
Magnus Stattin
◆ joined Ericsson
Research in 2005 after
completing a Ph.D. in
radio communication
systems at the KTH Royal
Institute of Technology in
Stockholm, Sweden. He is
now a principal researcher
whose work focuses on
the areas of radio resource
management and radio
protocols of various
wireless technologies.
He is active in concept
development and 3GPP
standardization of LTE,
LTE-Advanced and future
wireless technologies.
In 2015, he received the
Ericsson Inventor of the
Year Award.
Thomas Cheng
◆ is a senior specialist in
wireless communication
technologies. He holds an
M.Sc. from National Taiwan
University and a Ph.D. from
the California Institute of
Technology. Since joining
Ericsson in 1999, he has
been driving a wide range
of R&D projects evolving
cellular wireless PHY and
MAC layer designs from
2.5G EDGE, 3G HSPA, 4G
LTE and 5G technologies.
He received the Ericsson
Inventor of the Year Award
in 2012.
Sebastian Faxér
◆ is a researcher at
Ericsson Research. He
received an M.Sc. in applied
physics and electrical
engineering from Linköping
University, Sweden, in
2014 and joined Ericsson
the same year. Since
then, he has worked on
concept development and
standardization of multi-
antenna technologies for
LTE and 5G.
Hieu Do
◆ is a researcher at
Ericsson Research.
He received a Ph.D. in
electrical engineering from
the KTH Royal Institute of
Technology in Stockholm,
Sweden in 2013. Since
joining Ericsson in 2014 he
has been active in concept
development and 3GPP
standardization of V2X
communications.
theauthors

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