GP140563NB M2MOverview of the Physical Layer Design v2.docx

GP140563NB M2MOverview of the Physical Layer Design v2.docx

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GP140563NBM2MOverviewofthePhysicalLayerDesignv2

NBM2M-OverviewofthePhysicalLayerDesign

1Introduction

AtGERAN#62anewSIwasagreedtostudyCellularSystemSupportforUltraLowComplexityandLowThroughputInternetofThings[1].Twooptionswereenvisagedin[1]:

“anon-legacybaseddesign,and/orabackwardcompatibleevolutionofGSM/EDGE”.Thiscontributiondescribesthephysicallayerdesignof“Narrow-bandM2M（NBM2M）”,anon-legacybasedsolutionproposedbythesourcingcompaniesforCellularIoT.

2Overview

TosupportmassivenumberoflowthroughputMTCdeviceswithalimitednumberof200KHzresourceblocks（termed"RB"）,eachRBisdividedintoalargenumberof“narrowband”physicalchannelswhichareindividuallymodulatedandpulse-shaped.ChannelizationisdoneinaFDMmanner,forboththeuplinkandthedownlink.

Withanarrow-bandchannelcoveragecanbesignificantlyimprovedthankstoamuchhigherpowerspectraldensity（PSD）,especiallyintheuplink.Othertechniqueslikespreadingandrepetitionareemployedinboththeuplinkandthedownlinktofurtherextendthecoverage.

Thechannelspacingintheuplinkisafraction（e.g.1/3）ofthatinthedownlink.Thiscreatesmanymorephysicalchannelsintheuplinkthaninthedownlink.Withasignificantlyhighernumberofparalleluplinkdatatransmissions,theaggregateuplinktransmitpowerincreasesproportionally,andsodoestheachievableuplinkcapacity.Anotherconsiderationisthatthelowcostobjectiveimpliesalowuplinktransmitpower,hencethechannelspacingshouldbesufficientlylowtonotlimittheuplinkPSD.

UnlikeinGSM,thedurationofaburstisvariable,andaphysicalchannelisonlydefinedinthefrequencydomain,notinthetimedomain.Therearethreetypesofphysicalchannels:

physicalbroadcastandsynchronizationchannle（PBSCH）,physicaldownlinksharedchannel（PDSCH）andphysicaluplinksharedchannel（PUSCH）.ThePBSCHcarriessynchronizationsignalandbroadcastinformation.ThePDSCHcarriesdata,controlinformation,paging,signalling,etc.ThePUSCHcarriesdata,signalling,randomaccessmessage,etc.AphysicalchannelcarriesoneormoretypesofburstinthewayofTDMA.Thevariouskindofburstwillbedefinedinthefollowingsections.

Thebasestationoperatesinfullduplexmodeinordertomaximizenetworkcapacity.MTCdevicesoperateinhalfduplexmodetoreducetheRFcost.

3Channelization

3.1Downlink

Afrequencyresourceblockissub-dividedinto12downlinkphysicalchannels,withachannelspacingof15kHz.ThedownlinkchannelizationisillustratedinFigure1.

Figure1Downlinkchannelization

Abasestationsectormaybeallocateddownlinkchannelsfromoneormoreresourceblocks.Theassignedchannelsforeachbasestationsectordependonthecellfrequencyplanningandre-useschemethatisusedforthedeployment.

AtleastonedownlinkphysicalchannelperbasestationsectorisreservedforPBSCH.TheremainingdownlinkphysicalchannelsareusedforPDSCH.

AMTCdeviceisnotrequiredtoreceivemultipledownlinkchannelssimultaneously.AMTCdeviceshallbecapableofre-tuningitsreceiverfromonedownlinkphysicalchanneltoadifferentdownlinkphysicalchannel.

3.2Uplink

Afrequencyresourceblockissub-dividedinto36uplinkphysicalchannels,withachannelspacingof5kHz.Agivenbasestationsectormaybeassignedanysubsetoftheuplinkchannels,dependingonthefrequencyplanningandre-useschemethatisusedforthedeployment.

TheuplinkchannelizationforasingleresourceblockisillustratedinFigure2.

Figure2Uplinkchannelization

Abasestationsectormaybeallocateduplinkchannelsfromoneormoreresourceblocks.Theassignedchannelsforeachbasestationsectordependonthecellfrequencyplanningandre-useschemethatisusedforthedeployment.

Ifabasestationsectorisallocatedmultiplecontiguousuplinkphysicalchannels,thenitmaychoosetoallocate2,4or8contiguousuplinkphysicalchannelstothesameMTCdeviceforchannelbonding.Thisenableshigheruplinkdatarates（andpotentiallylowerpowerconsumption）forMTCdevicesthathavesufficientlinkbudget.

AMTCdeviceshallbecapableofre-tuningitstransmitterfromoneuplinkphysicalchanneltoadifferentuplinkphysicalchannel.

4Multipleaccessandtimestructure

TheaccessschemeisTimeDivisionMultipleAccess（TDMA）withvariabletimedurationinphysicalchannels.Thechannelspacingis15kHzfordownlinkand5kHzforuplink（withoutchannelbonding）.Physicalchannel’scontentcontainsoneormultipletypesofbursts.

4.1Slot

SlotisthetimeunitbearingscheduledM2Mdatamappedfromhigher-layer.Oneslotlastsfor10ms.

4.2M-hyperframes,M-superframesandM-frames

AdiagrammaticrepresentationofallthetimeslotandframestructuresisinFigure3.

ThelongestrecurrenttimeperiodofthestructureiscalledM-hyperframeandhasadurationof20971520ms（or5h49mn31s520ms）.

OneM-hyperframeissubdividedin4 096M-superframeswhichhaveadurationof5120ms（or5,12seconds）.TheM-superframesarenumberedmodulothisM-hyperframe（M-superframenumber,orM-SFN,from0to4095）.M-superframeisusedforDRX/DTXanditsM-SFNfrom0to4095allowstheminimumDRX/DTXperiod5120mswhilemaximumDRX/DTXperiodupto20971520ms.

OneM-superframeissubdividedin64M-frameswhichhaveadurationof80ms.TheM-framesarenumberedmodulothisM-superframe（M-framenumber,orM-FN,from0to63）.M-frameisthetimeunitofbroadcastandsynchronizationinformationforPBSCH,alsoisthetimeintervalunitofperiodicdownlinkcontrolinformation（DCI）forPDSCH.

OneM-framecomprisingeightslotsandtheslotsarenumberedmodulothisM-frame（slotnumber,orSN,from0to7）.SlotistheminimumschedulinggranularityforPDSCHandPUSCH.

Figure3TimestructureforM-hyperframes,M-superframesandM-frames

4.3Burststructure

Aburstisdefinedasthecontentofphysicalchannelwithavariabledurationofoneorseveralslots.Therearethreebursttypes:

1.SynchronizationandbroadcastburstinPBSCH.EachsynchronizationandbroadcastbursthasafixedlengthofoneM-frameduration.

2.DCIburstinPDSCH.EachDCIburstcontainstwoparts,thefixed-lengthpartandthevariable-lengthpart.Thereasonforavariablelengthisthattheschedulinginformationisvariabledependingonthenumberofusersbeingscheduled.Thelengthofviariable-lengthpartisindicatedinthefixed-lengthpart.

3Non-DCIburstinPDSCHandPUSCH,eachnon-DCIbursthavevariablelength.ThisisusedforrandomaccessaswellasdatatransmissioninPUSCH.Withalongsymbolduration（e.g.266.7usinthecaseof3.75KHzsymbolrate）,theuplinksymboltimingisconsideredrobustenoughforrancomaccess.

Theburststructuresfornormalcoveragearesuggestedtobedefinedasfollows:

1.Abroadcastandsynchronizationburstlasts80ms,containingtwoparts:

broadcastinformationandsynchronizationsequence.AdiagrammaticrepresentationofonebroadcastandsynchronizationburststructureisinFigure4.

Figure4BroadcastandsynchronizationburststructureinPBSCH

2.Thefixed-lengthpartofaDCIburstlasts30ms（3slots）.AdiagrammaticrepresentationofthisisinFigure5,wherepreamblesymbolsareusedforre-synchronizationwhentheMTCdevicewakesupaftershortDRX/DTX,pilotsymbolsareusedfordemodulation.Bothcanbeusedformeasurement.

Figure5Fixed-lengthpartofDCIBurstinPDSCH

3.Non-DCIburstinPDSCHorthevariable-partofaDCIbursthasavariabledurationandcontainsmultipleslots.Eachslothasatotaldurationof120symbolsandcontainsmultipleunitstructureA’s,eachcontainingafixednumberofpilotsymbolsanddatasymbols.AdiagrammaticrepresentationisinFigure6.

Figure6Variable-lengthpartofDCIBurstandnon-DCIburstinPDSCHwithunitstructureA

4.Anon-DCIburstinPUSCHhasavariabledurationandcontainsmultipleN-slots.EachN-slotcontainsNslots,whereNisapositiveintegerdependingonchannelbondingfactorBfordifferentuplinkchannelbandwidth.

EachN-slotcontainsmultipleunitstructureA’s（forPSKmodulation）orunitstructureB’s（forGMSKmodulation）.Thedifferencebetweenthetwounitstructuresistheproportionofpilotsymbols.Adiagrammaticrepresentationofnon-DCIburstinPUSCHwithunitstructureAandBisinFigure7.

Figure7Non-DCIburstinuplinkwithunitstructureAandB

Thereasonfornotplacingallpilotsymbolsinthemiddleoftheburst（asinGSM）isthatnarrowbandtransmissionisverysensitivetodopplershiftandresidualfrequencyerror,andthescatteredpilotsymbolsfacilitatetrackingofchannelvariationinthereceiver.

ThepilotsymboloverheadforGMSKmodulationishigherthanthatforPSKmodulation.ItisbecauseGMSKneedsguardsymbolperiodforinherentsymbolISIcausedbyitsshapingfilter.

Eachburstforextendedcoverageisderivedfromburstfornormalcoveragebyspreading（atsymbollevel）andrepetition（atburstlevel）.Burstlengthforextendedcoveragecanbecalculatedby:

whereSFandRFarethespreadingfactorandrepetitionfactor,respectively.Bothfactorscantakevaluesfrom{1,2,4,8,…}.

Synchonizationandbroadcastburstaredesignedtocaterfortheworstcoverageareas.DCIburstisdesignedtooutperformnon-DCIburstbyatleast3dBintermsofcoverage（withavalueofSF*RFbeingatleast2timeshigherthannon-DCIburst）.

AdiagrammaticrepresentationofburstfornormalcoverageextendedbyspreadingandrepetitionoperationisinFigure8.

Figure8Burstspreadingandrepetitionforextendedcoverage

4.4DCIinterval

Downlinkcontrolinformation（DCI）occursperiodiclyintimewhi