rach procedure

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Whatisthemosttrickypartindevicetroubleshooting?Myexperiencesays"Ifaproblemhappensinthemiddleofdoingsomething,itisrelativelyeasytofindtherootcauseandtroubleshootit(probablyImighthaveoversimplifiedthesituation:),butifsomethinghappenedbeforeanythingstarted,itwouldbeanightmare."Forexample,yousetthealltheparametersatthenetworkemulatorforaUEyouwanttotestandthenturnedontheUE.InaseveralsecondUEstartbootingandtheninacoupleofsecondyouseeacoupleofantennabarssomewhereatthetopofUEscreen..andtheninseveralsecondsyousee'SOS'or'ServiceNotAvailable'insteadofyournetworkoperatornamedisplayedonyourscreenandnormalAntennabars.ThisiswhatImeanby"probleminthemiddleofdoingsomething".Inthiscase,ifyoucollectUElogandequipmentlog,atleastyoucaneasilypinpointoutthelocationtheproblemhappensandstartfromthereforfurtherdetails.Butwhatifyouareinthissituation?yousetthealltheparametersatthenetworkemulatorsideandturnontheUE..UEstartbootingup..showingthemessagesaying"SearchingNetwork...."andgotstuckthere..withnoAntennabars..noteven'SOS'..justsaying"Noservice".AndIcollectedUEsidelogandNetworkEmulatorsidelog,butnosignallingmessage.Thisiswhereourheadachestarts.Asexamples,i)Whatifyoudon'tsee'RRCConnectionRequest'whenyourturnedontheWCDMAUE?ii)Whatifyoudon'tsee'ChannelRequest'whenyourturnedontheGSMUE?iii)Whatifyoudon'tsee'RACHPreamble'whenyourturnedontheLTEUE?Firstthingyouhavetodoistounderstandtheeverydetailsofthisprocedurenotonlyinthehighersignalinglayer,butalsoallthewaydowntothephysicallayersrelatedtothesefirststep.Andalsoyouhavetouseproperequipmentwhichcanshowthesedetailedprocess.Ifyouhaveanequipmentthatdoesnotprovidetheloggingoritprovideslogbutonlyhigherlayersingnalinglog,itwillbeextremlydifficulttotroubleshoot.Giventhatyouhavethepropertools,thenextthingyouhavetobereadyistounderstandthedetailedknowledgeoftheseprocess.Withouttheknowledge,howevergoodtoolsIhaveitdoesn'tmeananythingtome.So?IwanttoteachmyselfhereaboutthefirststepofLTEsignalingwhichisRACHprocess.(SomebodywouldsaytherearemanyofotherstepsevenbeforetheRACH,likefrequencySync,TimeSync,MIB/SIBdecoding..butitputtheseasidefornow..sinceitismorelikebasebandprocessing).

WhenRACHProcessoccurs?TwotypesofRACHprocess:ContentionbasedandContentionfreeExactlywhenandWhereaUEtransmitRACH?Whatispreambleformat?HowdoesNetworkknowsexactlywhenUEwilltransmittheRACH?PRACHPreambleSignalStructureHowtogenerateRACHSignal?ExactlywhenandwhereNetworktransmitRACHResponsePRACHParametersandit'sPhysicalMeaning

prachConfigIndexzeroCorrelationZoneConfigandHighspeedflagprachFreqOffsetrootSequenceIndex

RACHProcedureduringInitialRegistrationRACHProcedureSummaryHowcanwegetRARNTI?AnExampleofFullRACHProcessPRACHRetransmissionRACHProcessOverviewInDiagrams

RACHProcedureonInitialRegistrationRACHProcedureonHandoverContentionBasedRACHProcedureonHandoverNonContentionBasedRACHProcedureonDLDataArrivalwhenOutofSyncNonContentionBasedRACHProcedureonDLDataArrivalwhenOutofSyncContentionBasedRACHProcedureonULDataArrivalwhenOutofSyncRACHProcedureonRRCConnectionReestablishmentwhenOutofSync

PRACHRFSnapshot3GPPStandardforRACHProcess

WhenRACHProcessoccurs?



Itwouldbehelpfultounderstandifyouthinkaboutwhen'RRCConnection'happens(orwhenPRACHprocesshappensifyouareinterestedinlowerlayerstuffs)inWCDMA.Itwouldalsobehelpfulifyouthinkaboutwhen'ChannelRequest'happensinGSMUE.MyimpressionofLTERACHprocessislikethecombinationofPRACHprocess(WCDMA)andChannelRequest(GSM).Itmaynotbe100%correctanalogy..butanywayIgotthiskindofimpression.InLTE,RACHprocesshappensinfollowingsituation(3GPPspecification,10.1.5RandomAccessProcedureof36.300)

i)InitialaccessfromRRC_IDLEii)RRCConnectionReestablishmentprocedureiii)Handove(ContentionBasedorNonContetionBased)iv)DLdataarrivalduringRRC_CONNECTEDrequiringrandomaccessprocedureE.g.whenULsynchronisationstatusisnonsynchronisedv)ULdataarrivalduringRRC_CONNECTEDrequiringrandomaccessprocedureE.g.whenULsynchronisationstatusis"nonsynchronised"ortherearenoPUCCHresourcesforSRavailable.vi)ForpositioningpurposeduringRRC_CONNECTEDrequiringrandomaccessprocedureE.g.whentimingadvanceisneededforUEpositioning

TwotypesofRACHprocess:ContentionbasedandContentionfreeWhenaUEtransmitaPRACHPreamble,ittransmitswithaspecificpatternandthisspecificpatterniscalleda"Signature".IneachLTEcell,total64preamblesignaturesareavailableandUEselectrandomlyoneofthesesignatures.UEselect"Randomly"oneofthesesignatures?DoesthismeanthatthereissomepossibilitythatmultipleUEssendPRACHwithidenticalsignatures?Yes.Thereissuchapossibility.ItmeansthesamePRACHpreamblefrommultipeUEreachestheNWatthesametime..thiskindofPRACHcollisioniscalled"Contention"andtheRACHprocessthatallowsthistypeof"Contention"iscalled"Contentionbased"RACHProcess.InthiskindofcontentionbasedRACHprocess,Networkwouldgothroughadditionalprocessatlatersteptoresolvethesecontentionandthisprocessiscalled"ContentionResolution"step.Butthereissomecasesthatthesekindofcontentionisnotacceptableduetosomereason(e.g,timingrestriction)andthesecontentioncanbeprevented.Usuallyinthiscase,theNetworkinformseachoftheUEofexactlywhenandwhichpreamblesignatureithastouse.Ofcourse,inthiscaseNetworkwillallocatethesepreamblesignaturesothatitwouldnotcollide.ThiskindofRACHprocessiscalled"ContentionFree"RACHprocedure.Toinitiatethe"ContentionFree"RACHprocess,UEshouldbeinConnectedModebeforetheRACHprocessasinHandovercase.Typical'ContentionBased'RACHProcedureisasfollows:i)UE>NW:RACHPreamble(RARNTI,indicationforL2/L3messagesize)ii)UENW:L2/L3messageiv)MessageforearlycontentionresolutionNowlet'sassumethatacontentionhappenedatstepi).Forexample,twoUEssentPRACH.Inthiscase,bothoftheUEwillrecievethesameT_CRNTIandresourceallocationatstepii).Andasaresult,bothUEwouldsendL2/L3messagethroughthesameresourceallocation(meaningwiththesametime/frequencylocation)toNWatstepiii).WhatwouldhappenwhenbothUEtransmittheexactsameinformationontheexactsametime/frequencylocation?OnepossibilityisthatthesetwosignalactasinterferencetoeachotherandNWdecodeneitherofthem.Inthiscase,noneoftheUEwouldhaveanyresponse(HARQACK)fromNWandtheyallthinkthatRACHprocesshasfailedandgobacktostepi).TheotherpossibilitywouldbethatNWcouldsuccessfullydecodethemessagefromonlyoneUEandfailedtodecodeitfromtheotherUE.Inthiscase,theUEwiththesuccessfulL2/L3decodingonNWsidewillgettheHARQACKfromNetwork.ThisHARQACKprocessforstepiii)messageiscalled"contentionresolution"process.Typical'ContentionFree'RACHProcedureisasfollows:i)UENW:RACHPreamble(RARNTI,indicationforL2/L3messagesize)iii)UE



Toanswertothisquestion,youneedtoreferto3GPPspecificationTS36.211Table5.7.12.

Didyouopenthespecificationnow?ItshowsexactlywhenaUEissupposedtosendRACHdependingonaparametercalled"PRACHConfigurationIndex".Forexample,iftheUEisusing"PRACHConfigurationIdex0",itshouldtransmittheRACHonlyinEVENnumberSFN(SystemFrameNumber).Isthisgoodenoughanswer?DoesthismeanthatthisUEcantransmittheRACHinanytimewithinthespecifiedtheSFN?Theanswertothisquestionisin"SubFrameNumber"colulmnofthetable.Itsays"1"for"PRACHConfigurationIdex0".ItmeanstheUEisallowedtotransmitRACHonlyatsubframenumber1ofeveryevenSFN.Checkingyourunderstandingofthetable,Iwillgiveyouonequestion.Withwhich"PRACHConfigurationIdex",itwouldbetheeasiestfortheNetworktodetecttheRACHfromUE?andWhy?Theanswerwouldbe14,becauseUEcansendtheRACHinanySFNandanyslotswithintheframe.Inabigpicture,youshouldknowallthedimmensionsinthefollowingdiagram.(TheRedrectangleisPRACHsignal).



TheR_SlotisdeterminedbyPRACHConfigurationIndexandR_lengthisdeterminedbyPremableformat.F_offsetisderminedbythefollowingequationwhenthepreambleformatis0~3.n_RA_PRBoffsetinthisequationisspecifiedbyprachFreqOffsetinSIB2.(Referto36.2115.7Physicalrandomaccesschannelforthedetails)

Whatispreambleformat?Ifyouseethetable5.7.11showabove,youseethecolumntitledas"PreambleFormat".Whatisthepreambleformat?Itisdefinedasfollowingdiagram.YouwouldseethatthelengthofPRACHpreamblevariesdependingonthepreambleformat.Forexample,thelengthofPRACHwithpreambleformat0is(3186+24567)Samples.(Asyouknow,onesample(Ts)is1/30.72(=0.03255)us.Itisdefinedas1/(15000x2048)seconds(=0.03255us)in36.2114Framestructure).



Youmayask"Whyweneedthiskindofmultiplepreambleformat?",especially"WhyweneedvariousPRACHformatwithdifferentlengthintime?".Oneofthemainreasonwouldbethattheyusedifferentpreambleformatdependingoncellradius,butthisisoversimplifiedanswer.Iwanttorecommendabooktitled"LTE:TheUMTSFromTheorytoPractice"Section19.4.2ThePRACHStructure.ThisisthematerialthatdescribesthePRACHinthemostdetailedlevelIhaveeverread.Justasabriefconclusionforcellsize,wecanrewritethetableasfollows.

PreambleFormat

T_CP(inTs)

T_CP(inms)

T_SEQ(inTs)

T_SEQ(inms)

TotalLength(inms)

NumberofSubframes

GuardTime(inms) CellRadius

0 3168 0.103 24576 0.800 0.903 1 0.097 ~14km1 21024 0.684 24576 0.800 1.484 2 0.516 ~75km2 6240 0.203 2x24576 1.600 1.803 2 0.197 ~28km3 21024 0.684 2x24576 1.600 2.284 3 0.716 ~108km4 448 0.015 4096 0.133 0.148

Note1:T_CP(inms)=T_CP(inTs)x0.03255x1/1000,where0.03225isoneTsinus,1/1000isusedtoconverttheunitfrom'us'to'ms'Note2:T_SEQ(inms)=T_SEQ(inTs)x0.03255x1/1000,where0.03225isoneTsinus,1/1000isusedtoconverttheunitfrom'us'to'ms'Note3:GuardTime(inms)=NumberofSubframeTotalLengthNote4:CellRadiusisroughlythedistancethattheelectromaticwavecantravelduringtheguardtimeanddevidedby2.Incaseoffreespace(invacumm)itisroughlyis300(km/ms)xGuardTime(ms)/2.HowdoesNetworkknowsexactlywhenUEwilltransmittheRACH?Itissimple.NetworkknowswhenUEwillsendtheRACHevenbeforeUEsendsitbecauseNetworktellsUEwhentheUEissupposedtotransmittheRACH.(IfUEfailstodecodeproperlythenetworkinformationabouttheRACH,NetworkwillfailtodetectiteventhoughUEsendsRACH).FollowingsectionwilldescribenetworkinformatononRACH.WhichRRCMessagecontainsRACHConfiguration?ItisinSIB2andyoucanfindthedetailsin3GPP36.331.



numberOfRAPreambles:Therearetotal64RApreamblesthatUEcanrandomlychoosefrom.Butinsomecases,acellreserveseveralPreamblesfor'Noncontentionbased'PRACHprocedureandletUEusetherestofPreamblesrandomly(contentionbased).numberOfRAPreamblesindicateshowmanyRApreambles(RAsequences)isavailableforthecontentionbasedRACHprocess.PRACHSignalStructureFollowingfigureshowsthePRACHPremablesignalstructureincomparisonwithnormalUplinksubframe.Acoupleofpointstobespeciallymentionedare

PreambleLengthinFrequencyDomainisamountto6RBsofULSubframe,whichis1.08MhzPreambleLengthinTimeDomainincludingGuardTime(=CPLength+SEQUENCYLength+GTLength)canbe1or2or3dependingonPreambleFormatOnesubcarrierofPRACHPreambleis1.25Khzwhereas1subcarrierofULsubframeis15Khz.Itmeansthat12preamblesubcarrierisamountto1ULSubframesubcarrier.

HowtogenerateRACHSignal?Youdon'thavetoknowthedetailsofthisprocedureunlessyouaretheDSPorFPGAengineerimplementingLTEPHY.JustasacommonsenseaboutLTE,let'sknowthatPRACHisakindofZaddOffChuSequencegeneratedbythefollowingequation.

,whereu=physicalrootsequenceindexUEcanselectalogicalrootsequencebasedonRachRootSequenceIndex.OnceUEpickaspecificLogicalRootSequenceIndexvalue,itcanfigureoutthephysicalrootsequenceindex(u)basedonTable5.7.24.Thereare64preamblesavailableforeachcellandUEhastobeabletogeneratethe64preamblesforthecellitwant



tocampon.Youcaneasilygenerate64differentpreamblesjustbycyclicallyshiftinganexistingsequence,butthereisaconditionforthis.Allthepreamlesequencesshouldbeothogonaltoeachother.Otherwise,variouspreamblesfrommultipleUEswithinthesamecellcaninterfereeachother.SowehavetoshiftthegeneratedsequencebyaspecificallydesignedvalueandthisvalueiscalledCv(CyclicShiftValue)anditisdefinedasfollows.(IthinkdeterminingtheCvisoneofthemostcomplicatedprocessinPRACHpreamblegenerationbecauseitgetsinvolvedwithsomanydifferentparametersincascadingmanner).

First,youwouldnoticethatweusedifferentprocesstocalculateCvdependingonwhetherweuse'unrestrictedsets'or'restrictedsets'.Thisdecisionismadeby'Highspeedflag'informationelementsinSIB2.IfHighspeedflagissettobeTRUE,wehavetouse'restrictedsets'andifHighspeedflagisfalse,wehavetouse'unrestrictedsets'.N_csisspecifiedbyzeroCorrelationZoneConfiginformationelementsinSIB2.Asyouseeinthismapping,N_csvaluesalsogetsdifferentdependingonwhetherweuse'restrictedsets'or'unrestrictedsets'.

Nowlet'slookathowwegetNzc.Thisisprettystraightforward.Nzcisdeterminedbythefollowingtable.

IfthePreambleisusingtheunrestrictedsets,itisprettysimple.YouonlyhavetoknowNzc,NcstofigureoutCv.TheproblemiswhenthePreambleisusingthe'restrictedsets'.Asyouseetheequationabove,youneedtoknowthefollowing4valuestofigureoutCvin'restrictedsets'.

Theproblemisthatthecalculationofthesefourvariableisverycomplicatedasshownbelow.



Youwouldnoticedthatyouneedanothervaluetocalculatetodeterminewhichofthethreecasewehavetouse.Itisdu.Soweneedanotherprocesstodeterminedu.

Wewentthroughacomplicatedprocedurejusttodeterminonenumber(Cv).OncewegetCv,wecangeneratemultiplepreamblesusingthefollowingfunction.

Anyway,nowwegotaPRACHPreamblesequenceinhand,butthisisnotall.Inordertotransmitthisdata.Wehavetoconvertthisdataintoatimedomainsequenceandthisconversionisdonebythefollowingprocess.

ForthewholePRACHgenerationprocedure,pleasereferto5.7.2/5.7.3ofTS36.211.



ExactlywhenandwhereNetworktransmitRACHResponseWeallknowsthatNetworkshouldtransmitRACHResponseafteritrecievedRACHPreamblefromUE,butdoweknowexactlywhen,inexactlywhichsubframe,thenetworkshouldtransmittheRACHResponse?Thefollowingiswhat3GPP36.321(section5.1.4)describes.OncetheRandomAccessPreambleistransmittedandregardlessofthepossibleoccurrenceofameasurementgap,theUEshallmonitorthePDCCHforRandomAccessResponse(s)identifiedbytheRARNTIdefinedbelow,intheRAResponsewindowwhichstartsatthesubframethatcontainstheendofthepreambletransmission[7]plusthreesubframesandhaslengthraResponseWindowSizesubframes.ItmeanstheearliesttimewhenthenetworkcantransmittheRACHresponseis3subframelaterfromtheendofRACHPreamble.Thenwhatisthelatesttimewhenthenetworkcantransmitit?ItisdeterminedbyraResponseWindowSize.Thiswindowsizecanbethenumberbetween0and10intheunitofsubframes.ThismeansthatthemaximumtimedifferencebetweentheendofRACHpreambleandRACHResponseisonly12subframes(12ms)whichisprettytighttimingrequirement.PRACHParametersandPhysicalMeaning



RACHProcedureduringInitialRegistrationRACHProcedureSummaryFollwingisanexampleofRACHprocedurewhichhappensduringtheinitiailregistration.Ifyouwillbeanengineerwhoisworkingonprotocolstackdevelopmentortestcasedevelopment,youshouldbeveryfamiliarwithallthedetailsofthisprocess.

Again,wehavetoknoweverydetailsofeverystepwithoutmissinganythingtobeadeveloper,butofcourseitisnoteasytounderstandeverythingatasingleshot.So,let'sstartwithsomethingthemostimportantpart,whichIthinkisthedetailsofRACHresponse.FollowingdiagramshowsoneexampleofRACHResponsewith5Mhzbandwidth.Wedon't



havetomemorizethedetailedvalueitselfbutshouldbefamiliarwiththedataformatandunderstandwhichpartofthisbitstringmeanswhat.

IfyoudecodeULGrantpart,youwillgetthefollowingresult.YouwillnoticethattheinformationitcarrieswouldbeverysimilartoDCIformat0whichcarriesResourceAllocationforuplinkdata.ThisinformationinULGrantinRACHResponsemessageistheresourceallocationformsg3(e.g,RRCConnectionRequest).Note:ThisisexampleofRARforSystemBW5Mhz.IfthesytemBWgetsdifferent,youshouldhavedifferentRIVvalues(ifyouwanttohavethesameStart_RB,N_RBasinthisexample)oryouwillhavedifferentStart_RB,N_RB(ifyoukeepRIVasbelowandjustchangethesystemBW)

Letmedescribethisprocedureinverbalformagain.i)UEinitiateaRandomAccessProcedureonthe(uplink)RandomAccessChannel(RACH).(ThelocationofRACHinthefrequency/timeresourcegridtheRACHisknowntothemobileviathe(downlink)BroadcastChannel(BCH).Therandomaccessmessageitselfonlyconsistsof6bitsandthemaincontentisarandom5bitidentity)ii)NetworksendsaRandomAccessResponseMessage(RARM)atatimeandlocationonthePhysicalDownlinkSharedChannel(PDSCH)(ThetimeandlocationofRARMonPDSCHcanbecalculatedfromthetimeandlocationtherandomaccessmessagewassent.Thismessagecontainstherandomidentitysentbythedevice,aCellRadioNetworkTemporaryID(T_CRNTI)whichwillbeusedforallfurtherbandwidthassignments,andaninitialuplinkbandwidthassignment)iii)Themobiledevicethenusesthebandwidthassignmenttosendashort(around80bits)RRCConnectionRequestmessagewhichincludesit'sidentitywhichhaspreviouslybeenassignedtoitbythecorenetworkOnlythestepi)usesphysicallayerprocessingspecificallydesignedforrandomaccess.TheremainingstepsutilizesthesamephysicallayerprocessingasusedfornormaluplinkanddownlinkdatatransmissionHowcanwegetRARNTI?5.1.4RandomAccessResponsereception"in"TS36.321sayshowtocalculateRA_RNTIasfollows.



TheRARNTIassociatedwiththePRACHinwhichtheRandomAccessPreambleistransmitted,iscomputedas:RARNTI=1+t_id+10*f_idWheret_idistheindexofthefirstsubframeofthespecifiedPRACH(0



PRACHRetransmissionMostpartofprevioussectionwasabouttheidealRACHprocess,whichmeansthatUEsendPRACHandNetworksendRACHResponseatthefirsttrialandwentthroughallthewaytotheendofprocessatthefirsttrial.WhatifUEdoesnotreceiveRACHResponseatthefirsttrial?WhatisUEsupposedtodointhiscase?Theanswerissimple.Justretry(resend)PRACH.(Inthiscase,UEmightnothaveanyBackoffIndicatorvaluewhichnormallytransmittedinMACCEbeingsentwithRAR).ThereisanothercasewhereUEneedstoretryPRACH.ItisthecasewhereUEreceivedRARfromthenetwork,buttheRAPIDisnotforit(ItmeansthatRARisnotforsomeotherUE).Inthiscase,itishighlyprobablethataBackoffIndicatorvalueistransmittedwithRARtocontrolthePRACHretransmissiontiming.Thenyouwouldhavemorequestion.("I"inthefollowingdescriptionis"UE")

i)WhendoIhavetoretry?(Whatshouldbethetimedelaybetweentheprevioustransmissionandthenexttransmission?)ii)DoIhavetoretransmitthePRACHwiththesamepoweraspreviousone?Ortrywithalittlebithigherpower?IfIhavetotrywithalittlebithigherpower,howmuchpowerdoIhavetoincrease?iii)IfIkeepfailingtoreceiveRACHresponse,howmanytimeIhavetoretry?DoIhavetoretryuntilthebatteryrunsout?orretryonlyseveraltimesandgiveup?IfIhavetogiveupafteracertainamountofretry,exactlyhowmanytimesdoIhavetoretry?

Theanswerstoallofthesequestionsareprovidedbythenetwork.Theanswer(instruction)toquestioni)isprovidedbyNetworkviaaspecialRARMACPDUcalled"BackoffIndicator".Theanswertoquestionii)andiii)areprovidedbyNetworkviaSIB2asfollows.powerRampingStepistheanswertoquestionii)andpreambleTransMaxistheanswertoquestioniii).Inthefollowingexample,powerRampingStep=dB2.ItmeansUEhastoincreasePRACHpowerby2dBeverytimeitretries.preambleTransMax=n6.ItmeansUEretriesPRACHretransmitonly6timesandthengiveup.(Thisismyunderstandingatleastasofnow.Buttryingwithrealdevice,IseemanycasesUEdoesnotgiveupevenafteritreachespreambleTransMax.IwillgetthisupdatedasIfindmore)| +-radioResourceConfigCommon ::= SEQUENCE| | +-rach-Config ::= SEQUENCE| | | +-preambleInfo ::= SEQUENCE [0]| | | | +-numberOfRA-Preambles ::= ENUMERATED [n52]| | | | +-preamblesGroupAConfig ::= SEQUENCE OPTIONAL:Omit| | | +-powerRampingParameters ::= SEQUENCE| | | | +-powerRampingStep ::= ENUMERATED [dB2]| | | | +-preambleInitialReceivedTargetPower ::= ENUMERATED [dBm-104]| | | +-ra-SupervisionInfo ::= SEQUENCE| | | | +-preambleTransMax ::= ENUMERATED [n6]| | | | +-ra-ResponseWindowSize ::= ENUMERATED [sf10]| | | | +-mac-ContentionResolutionTimer ::= ENUMERATED [sf48]| | | +-maxHARQ-Msg3Tx ::= INTEGER (1..8) [4]

AdditionalFactors:PRACHConfigIndex(inSIB2)BackoffIndicator(inMACCE)T300(inSIB2)

FollowingisanexampleofPRACHRetrybeingobservedinarealdevice.ThisisthecasewhereUEsendPRACHandNWdoesnotsendRAR(YellowcellindicatesthetimingdeterminedbyPRACHConfigIndexwhenUEisallowedtosendPRACH.SeeExactlywhenandwhereNetworktransmitRACHResponse.GreencellindicatesthetimingwhenUEsendPRACHinthisspecificexample)



RACHProcessOverviewInDiagramsIhaveexplainedlongabouttheRACHprocess.Nowyoumayask"WhatisthetriggerthatletUEinitiatetheRACHprocess?".Youwillseevarioustriggersin3GTS36.300(10.1.5):OveralldescriptionofRACHProcess."TurningonUE"isoneofthetriggerforsure.Andfollowingisanothertriggerforthisprocess.

ThisisbasicallythesamesequencethatIexplainedinprevioussections,butIsimplifiedthediagraminprevioussectionstoletreaderfocusedmoreonmessagingpartofRACHprocedure.Inthisdiagram,youseesomeadditionalstepslikeHARQACK,DCI0(ULGrant).Thisflowismoresimilartoreallivenetworkprocedure.



FollowingisoneexampleforthissequencethatIgotfromlivenetworkandsummarizedwithimportantparameters.Ihopethiscanbeagoodpracticeforyou.(Note:ThisiswithFDD)SFN:402.4 RACHPreamble

RNTI=NoneTimingOffset=2LogicalRoot=219Preambleindex=33NCConfiguration=12SetType=UnrestrictedLogicalRoot=215PreambleFormat=0RbStart=2

SFN:402.8 MACRAResponse

MAC:6100B0C04C2C09

E=0(False)T=1RAPID=33TimingAdvanced=11HoppingFlag0=FalseFixedSizeResourceBlockAssignment=96(RBStart=46,RBLength=2)MCS=2,I_TBS=2,rv=0TPCCommandforPUCCH3=0ULDelay0=FalseCQIRequest=FalseT_CRNTI=11273

SFN:403.4 PUSCHRRCConnectionRequest

MAC:20061F5C2C04B2ACF6



SubHeader0R=OKE=1LCID=0(CCCH)F=0(False)L=6

SubHeader1R=OKE=0LCID=31(Padding)

CCCHRLC:5C2C04B2ACF6(RRCConnectionRequest)

SFN:403.8 PHICHACK SFN:404.7 PDCCH(DCIFormat1)+PDSCH(RRCConnectionSetup)

CCEStart=0CCELength=8DCIFormat1A(Hex:47D01E2)

Format=1DistributedVRBflag=0(Local)ResourceAllocation=500(RBStart=0,RBLength=11)MCS=0(I_TBS=0)HARQProcessNumber=7NDI(NewDataIndicator)=1(True)RV=0TPCCommandforPUCCH=1

MAC:3C201A1F5C2C04B2ACF660129808FD4E.....

SubHeader0R=OKE=1LCID=28(UEContentionResolutionIdentity)SubHeader1

R=OKE=1LCID=1(CCCH)F=0(False)L=26

SubHeader2

R=OKE=0LCID=31(Padding)

UEContentionResolutionIdentity

UEContentionResolutionIdentity=5C2C04B2ACF6

SFN:405.1 PUCCHUCIHARQACK

PUCCHFormat1AnPUCCH=16SFN:406.2 PUCCHUCISR NPUCCHRB=2SFN:406.6 PDCCHDCIFormat0

PDCCHDCIFormat0(Hex:0180540)



Format0HoppingFlag=0(False)RBAllocationof1stSlotinULsubframe=96MCS2,RV0NDI=1(True)TPC=1CyclicShiftforDMRS=0CQIRequested=0(False)

SFN:406.7 PDCCHDCIFormat0

DCIFormat0(Hex:0180540)











SFN:407.0 PUSCHRRCConnectionSetupComplete(FirstSegment)



MAC=3A3D01221088000020

SubHeader0R=OKE=1LCID=26(PowerHeadroomReport)SubHeader1R=OKE=1LCID=29(ShortBufferStatusReport)SubHeader2R=OKE=0LCID=1(identity)PowerHeadroomR=OKPowerHeadroom>11dB






SFN:407.1 PUSCHRRCConnectionSetupComplete(MidSegment)

MAC=0198023945E5340B07

SubHeader0R=OKE=0LCID=1(identity)

RLCAMD=98023945E5340B07

D/C=1(DataPDU)RF=0(AMDPDU)P=0(StatusReportNotRequested)Fl=3(FirstByteoftheDataFielddoesnotcorrespondstothefirstbyteofaRLCSDU.LastbyteofDatafielddoesnotcorrespondstothelastbyteofaRLCPDU)E=0(False)SN=2

PDCPCPSRB=3945E5340B07





MAC=01980241020BF60302


RLCAMD=980341020BF60302

D/C=1(DataPDU)RF=0(AMDPDU)P=0(StatusReportNotRequested)Fl=3(FirstByteoftheDataFielddoesnotcorrespondstothefirstbyteofaRLCSDU.LastbyteofDatafielddoesnotcorrespondstothelastbyteofaRLCPDU)E=0(False)



SN=3

PDCPCPSRB=41020BF60302




SFN:407.4 PHICHACK

....



Format0HoppingFlag=0(False)RBAllocationof1stSlotinULsubframe=96MCS2,RV0NDI=0(False)TPC=1CyclicShiftforDMRS=0CQIRequested=0(False)


MAC=01980427800100D0CC


RLCAMD=980427800100D0CC


PDCPCPSRB=27800100D0CC


MAC=3D010E9805715104E0

SubHeader0R=OKE=1LCID=29(ShortBufferStatusReport)

SubHeader1R=OK



E=0LCID=1(identity)

ShortBufferStatusReportLCGID=0BufferSize14>67



E=0LCID=1(Identity)

RLCAMD=980703D011D1271A


PDCPCPSRB=03D011D1271A

SFN:407.7 PHICHACK

.....SFN:407.8 PHICHACK

.....


MAC=019808808021100100

SubHeader0R=OKE=0LCID=1(Identity)

RLCAMD=9808808021100100


PDCPCPSRB=808021100100

SFN:407.9 PUSCHRRCConnectionSetupComplete(LastSegment)

MAC=3E21361F000000B0090010810600000000830600000000....

SubHeader0R=OKE=1LCID=30(LongBufferStatusReport)

SubHeader1R=OKE=1LCID=1(identity)F=0(False)L=54

SubHeader2



R=OKE=0LCID=31(Padding)

LongBufferStatusReportBufferSize#0=0(BS=0)BufferSize#1=0(BS=0)BufferSize#2=0(BS=0)BufferSize#3=0(BS=0)

RLCAMD=B0090010810600000000830600000000....

D/C=1(DataPDU)RF=0(AMDPDU)P=1(StatusReportRequested)Fl=2(FirstByteoftheDataFielddoesnotcorrespondstothefirstbyteofaRLCSDU.LastbyteofDatafieldcorrespondstothelastbyteofaRLCPDU)E=0(False)SN=9

PDCPCPSRB=0010810600000000830600000000....



PRACHRFSnapshot

3GPPStandardforRACHProcess3GTS36.300(10.1.5):OveralldescriptionofRACHProcess.Readthisfirst.3GTS36.211(5.7):RRCMessagesandIE(InformationElements)whichareinvolvedinRACHprocess.3GTS36.213(6):MACLayerProcedurerelatedtoRACHProcess.

rach procedure

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