SIST EN 300 912 V8.2.1:2003

• Abstract:

  R99 @ SMG#30, CR SMG#30bis, 31

• Status: Published
• Publication Date: 30-Nov-2003
• ICS: 33.070.50 - Global System for Mobile Communication (GSM)
• Technical Committee: SS EIT - Technical Board for the electrotechnical, information technology and telecommunications fields
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Dec-2003
• Due Date: 01-Dec-2003
• Completion Date: 01-Dec-2003
• Ref Project: ETSI EN 300 912 V8.2.1 (2000-09) - Digital cellular telecommunications system (Phase 2+) (GSM); Radio subsystem synchronization (GSM 05.10 version 8.2.1 Release 1999)

Overview

SIST EN 300 912 V8.2.1:2003 defines the essential requirements for synchronization in the radio subsystem of the digital cellular telecommunications system (GSM Phase 2+), specifically Release 1999. Developed by the Slovenian Institute for Standardization (SIST), this standard aligns with EN 300 912 and ETSI GSM 05.10 V8.2.1. Synchronization is critical to ensuring seamless, interference-free communication across the GSM network, maintaining accurate timing between the Base Transceiver Station (BTS), Mobile Stations (MS), and Cordless Telephony System Fixed Parts (CTS-FP).

The document covers synchronization procedures for frequency and timing alignment throughout the GSM radio network, ensuring that various network elements transmit and receive signals harmoniously to prevent interference and data errors.

Key Topics

• Radio Subsystem Synchronization
  Defines how BTS, MS, and CTS-FP achieve precise alignment of time and frequency to support efficient GSM communications.

• Timebase Counters
  Specifies the counters used to manage frames, timeslots, and symbol periods for accurate synchronization.

• Timing Advance Mechanism
  Explains the process by which the BTS instructs the MS to adjust its transmit timing to compensate for propagation delay, ensuring correct signal arrival.

• Frequency Source Requirements
  Details the specifications for frequency sources (oscillators) at various network elements for both carrier generation and timebase clocking.

• Delay Tracking and Assessment
  Describes ongoing delay measurement processes for both circuit-switched and packet-switched channels, supporting dynamic adjustment to maintain synchronization quality.

• Pseudo-Synchronization and Handover Procedures
  Includes options for pseudo-synchronization and special procedures for handovers between cells or systems, optimizing continuity of service.

• Cordless Telephony System (CTS)
  Outlines specific synchronization needs for GSM Cordless Telephony (CTS), ensuring the CTS-MS attains and maintains accurate timing with the CTS-FP.

Applications

GSM Network Deployment and Operation
This standard is fundamental for mobile network designers, engineers, and operators who are deploying and maintaining GSM infrastructure. Key practical applications include:

• Mobile Base Station Configuration
  Ensuring base stations implement synchronization algorithms, comply with timing advance procedures, and meet strict frequency accuracy.

• Handover Optimization
  Supporting seamless handoffs between cells or BTSs by maintaining precise synchronization, facilitating uninterrupted service for end users.

• Interference Reduction
  Synchronizing transmissions across the network to minimize overlap and interference, which is crucial for network efficiency and voice/data quality.

• GPRS and Packet Services
  Maintaining synchronization for channels supporting GPRS and packet-switched services for accurate timing in data sessions.

• Cordless Telephony Integration
  Enabling effective operation and synchronization of GSM Cordless Telephony Systems (CTS), a critical feature for environments needing local wireless extensions.

• Compliance Testing
  Supporting network audits and equipment conformance assessments against international GSM synchronization requirements.

Related Standards

This standard references several key international GSM and telecommunications standards, including:

• GSM 05.02: Multiplexing and multiple access on the radio path
• GSM 05.05: Radio transmission and reception
• GSM 05.08: Radio subsystem link control
• GSM 03.60/03.64: GPRS service descriptions and radio interface stages
• GSM 04.08/04.60: Mobile radio interface protocols and GPRS radio link control
• GSM 01.04: Abbreviations and acronyms used in digital cellular systems
• GSM 03.30/03.52/05.56: Radio network planning, CTS lower layers, and CTS radio subsystem specifications

By harmonizing with these documents, SIST EN 300 912 V8.2.1:2003 helps ensure consistent GSM network performance and interoperability across Europe and globally.

Keywords: GSM, radio subsystem synchronization, timing advance, frequency correction, mobile telecommunications, base station, mobile station, core network, GPRS, CTS, handover, delay tracking, synchronization standard, digital cellular standards.

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Digital cellular telecommunications system (Phase 2+) (GSM); Radio subsystem synchronization (GSM 05.10 version 8.2.1 Release 1999)33.070.50Globalni sistem za mobilno telekomunikacijo (GSM)Global System for Mobile Communication (GSM)ICS:Ta slovenski standard je istoveten z:EN 300 912 Version 8.2.1SIST EN 300 912 V8.2.1:2003en01-december-2003SIST EN 300 912 V8.2.1:2003SLOVENSKI
STANDARD
ETSIEN300912V8.2.1(2000-09)EuropeanStandard(Telecommunicationsseries)Digitalcellulartelecommunicationssystem(Phase2+);Radiosubsystemsynchronization(GSM05.10version8.2.1Release1999)GLOBALSYSTEMFORMOBILECOMMUNICATIONSRSIST EN 300 912 V8.2.1:2003

ETSIETSIEN300912V8.2.1(2000-09)2(GSM05.10version8.2.1Release1999)ReferenceREN/SMG-020510Q8KeywordsDigitalcellulartelecommunicationssystem,GlobalSystemforMobilecommunications(GSM)ETSI650RoutedesLuciolesF-06921SophiaAntipolisCedex-FRANCETel.:[phone]Fax:[phone]SiretN°34862356200017-NAF742CAssociationàbutnonlucratifenregistréeàlaSous-PréfecturedeGrasse(06)N°7803/88ImportantnoticeIndividualcopiesofthepresentdocumentcanbedownloadedfrom:http://www.etsi.orgThepresentdocumentmaybemadeavailableinmorethanoneelectronicversionorinprint.Inanycaseofexistingorperceiveddifferenceincontentsbetweensuchversions,thereferenceversionisthePortableDocumentFormat(PDF).Incaseofdispute,thereferenceshallbetheprintingonETSIprintersofthePDFversionkeptonaspecificnetworkdrivewithinETSISecretariat.Usersofthepresentdocumentshouldbeawarethatthedocumentmaybesubjecttorevisionorchangeofstatus.InformationonthecurrentstatusofthisandotherETSIdocumentsisavailableathttp://www.etsi.org/tb/status/Ifyoufinderrorsinthepresentdocument,sendyourcommentto:[e-mail]opartmaybereproducedexceptasauthorizedbywrittenpermission.Thecopyrightandtheforegoingrestrictionextendtoreproductioninallmedia.©EuropeanTelecommunicationsStandardsInstitute2000.Allrightsreserved.SIST EN 300 912 V8.2.1:2003

ETSIETSIEN300912V8.2.1(2000-09)3(GSM05.10version8.2.1Release1999)ContentsIntellectualPropertyRights.5Foreword.51Scope.61.1References.61.2Definitionsandabbreviations.72Generaldescriptionofsynchronizationsystem.73Timebasecounters.83.1Timingstateofthesignals.83.2Relationshipbetweencounters.84Timingoftransmittedsignals.95BTSRequirementsforSynchronization.95.1Frequencysource.95.2Timebasecounters.95.3InternalBTScarriertiming.105.4InitialTimingadvanceestimation.105.5Maximumtimingadvancevalue.105.6Delaytracking.105.6.1Forcircuitswitchedchannels.105.6.2Forpacketswitchedchannels.105.6.3Delayassessmenterror.115.6.4Pico-BTSdelaytracking.115.7Timeslotlength.115.8RangeofTimingadvance.116MSRequirementsforSynchronization.116.1MScarrierfrequency.126.2Internaltimebase.126.3AssessmentofBTStiming.126.4Timingoftransmission.126.5ApplicationofTimingAdvance.126.5.1Forcircuitswitchedchannels.126.5.2Forpacketswitchedchannels.126.6AccesstoanewBTS.136.7Temporarylossofsignal.146.8Timingofintracellchannelchange.146.9ApplicationofnewTimingAdvancevalue.146.10Definitionof"readytotransmitwithinxms".146.11DefinitionofadditionalreactiontimesforGPRSmobilestations.146.11.1Uplinkanddownlinkassignmentreactiontimes.146.11.2Changeinchannelcodingschemecommandedbynetwork.146.11.3Contentionresolutionreactiontime.156.11.4Reactiontimeinresponsetoothercommandingmessages.156.12ObservedFrequencyOffset(OFO)reportedbytheCTS-MS.157CTS-FPRequirementsforSynchronization.157.1Frequencysourcedefaultrequirements.157.2FrequencysourceforaCTS-FPassistedbyaCTS-MS.157.3InternalCTS-FPcarriertiming.157.4Timeslotlength.157.5AssessmentofCTS-MSdelay.16SIST EN 300 912 V8.2.1:2003

ETSIETSIEN300912V8.2.1(2000-09)4(GSM05.10version8.2.1Release1999)AnnexA(normative):Additionalrequirementsforpseudo-synchronization,synchronizedhandoversandpseudo-synchronizedhandovers.17A.1Generaldescriptionsanddefinitions.17A.1.1Conventions.17A.1.2Definitions.17A.1.3Detailsofoperations.17A.2BTSrequirements.18A.2.1Thepseudo-synchronizationscheme.18A.2.1.1BTSatimedifferenceestimate.18A.2.1.2Thereceptionepochcriterion.18A.2.1.3Pseudo-synchronizedhandover.18A.2.2Thesynchronizationrequirement.18A.3MSrequirements.19A.3.1Provisionoftimedifferenceinformation.19A.3.2Aftereachsuccessfulhandover.19A.3.3Synchronizedorapseudosynchronizedhandover.19AnnexB(informative):CTSBCHtimeslotshiftingpropertiesforCTS-MSsynchronization.20B.1DeterminationofTNbytheCTS-MSwhenCTSBCHshiftingisnotactive.20B.2DeterminationofTNbytheCTS-MSwhenCTSBCHshiftingisactive.20AnnexC(informative):Changecontrolhistory.21History.22SIST EN 300 912 V8.2.1:2003

ETSIETSIEN300912V8.2.1(2000-09)5(GSM05.10version8.2.1Release1999)IntellectualPropertyRightsIPRsessentialorpotentiallyessentialtothepresentdocumentmayhavebeendeclaredtoETSI.TheinformationpertainingtotheseessentialIPRs,ifany,ispubliclyavailableforETSImembersandnon-members,andcanbefoundinETSISR000314:"IntellectualPropertyRights(IPRs);Essential,orpotentiallyEssential,IPRsnotifiedtoETSIinrespectofETSIstandards",whichisavailablefromtheETSISecretariat.LatestupdatesareavailableontheETSIWebserver(http://www.etsi.org/ipr).PursuanttotheETSIIPRPolicy,noinvestigation,includingIPRsearches,hasbeencarriedoutbyETSI.NoguaranteecanbegivenastotheexistenceofotherIPRsnotreferencedinETSISR000314(ortheupdatesontheETSIWebserver)whichare,ormaybe,ormaybecome,essentialtothepresentdocument.ForewordThisEuropeanStandard(Telecommunicationsseries)hasbeenproducedbyETSITechnicalCommitteeSpecialMobileGroup(SMG).ThepresentdocumentdefinestherequirementsforsynchronizationontheGSMradiosub-systemofthedigitalmobilecellularandpersonalcommunicationsystemsoperatinginthe900MHzand1800MHzband(GSM900andDCS1800).ThecontentsofthepresentdocumentaresubjecttocontinuingworkwithinSMGandmaychangefollowingformalSMGapproval.ShouldSMGmodifythecontentsofthepresentdocumentitwillthenberepublishedbyETSIwithanidentifyingchangeofreleasedateandanincreaseinversionnumberasfollows:Version8.x.ywhere:8indicatesrelease1999ofGSMPhase2+.xtheseconddigitisincrementedforallchangesofsubstance,i.e.technicalenhancements,corrections,updates,etc.ythethirddigitisincrementedwheneditorialonlychangeshavebeenincorporatedinthespecification.NationaltranspositiondatesDateofadoptionofthepresentdocument:25August2000Dateoflatestannouncementofthepresentdocument(doa):30November2000DateoflatestpublicationofnewNationalStandardorendorsementofthepresentdocument(dop/e):31May2001DateofwithdrawalofanyconflictingNationalStandard(dow):31May2001SIST EN 300 912 V8.2.1:2003

ETSIETSIEN300912V8.2.1(2000-09)6(GSM05.10version8.2.1Release1999)1ScopeThepresentdocumentdefinestherequirementsforsynchronizationontheradiosub-systemofthedigitalcellulartelecommunicationssystemsGSM.However,itdoesnotdefinethesynchronizationalgorithmstobeusedintheBaseTransceiverStation(BTS),CTSFixedPart(CTS-FP)andMobileStation(MS).Theseareuptothemanufacturertospecify.1.1ReferencesThefollowingdocumentscontainprovisionswhich,throughreferenceinthistext,constituteprovisionsofthepresentdocument.• Referencesareeitherspecific(identifiedbydateofpublication,editionnumber,versionnumber,etc.)ornon-specific.• Foraspecificreference,subsequentrevisionsdonotapply.• Foranon-specificreference,thelatestversionapplies.• Anon-specificreferencetoanETSshallalsobetakentorefertolaterversionspublishedasanENwiththesamenumber.• ForthisRelease1999document,referencestoGSMdocumentsareforRelease1999versions(version8.x.y).[1]GSM01.04:"Digitalcellulartelecommunicationssystem(Phase2+);Abbreviationsandacronyms".[2]GSM03.60:"Digitalcellulartelecommunicationssystem(Phase2+);GeneralPacketRadioService(GPRS);ServiceDescriptionStage2".[3]GSM03.64:"Digitalcellulartelecommunicationssystem(Phase2+);GeneralPacketRadioService(GPRS);GPRSRadioInterfaceStage2".[4]GSM04.08:"Digitalcellulartelecommunicationssystem(Phase2+);Mobileradiointerfacelayer3specification".[5]GSM04.60:"Digitalcellulartelecommunicationssystem(Phase2+);GeneralPacketRadioService(GPRS);MobileStation(MS)-BaseStationSystem(BSSinterface;RadioLinkControl(RLC)andMediumAccessControl(MAC)LayerSpecification".[6]GSM05.02:"Digitalcellulartelecommunicationssystem(Phase2+);Multiplexingandmultipleaccessontheradiopath".[7]GSM05.05:"Digitalcellulartelecommunicationssystem(Phase2+);Radiotransmissionandreception".[8]GSM05.08:"Digitalcellulartelecommunicationssystem(Phase2+);Radiosubsystemlinkcontrol".[9]GSM03.30:"Digitalcellulartelecommunicationssystem(Phase2+);Radionetworkplanningaspects".[10]GSM03.52:"Digitalcellulartelecommunicationssystem(Phase2+);GSMCordlessTelephonySystem(CTS),Phase1;LowerlayersoftheCTSRadioInterface;Stage2".[11]GSM05.56:"Digitalcellulartelecommunicationssystem(Phase2+);GSMCordlessTelephonySystem(CTS),Phase1;CTS-FPRadiosubsystem".SIST EN 300 912 V8.2.1:2003

ETSIETSIEN300912V8.2.1(2000-09)7(GSM05.10version8.2.1Release1999)1.2DefinitionsandabbreviationsInadditiontothosebelow,abbreviationsusedinthepresentdocumentarelistedinGSM01.04.BTS:BaseTransceiverStationCTS-FP:CTSFixedPartCTS-MS:MSoperatinginCTSmodeTimingAdvance:signalsentbytheBTStotheMSwhichtheMSusestoadvanceitstimingsoftransmissionstotheBTSsoastocompensateforpropagationdelayQuartersymbolnumber:timingofquartersymbolperiods(12/13µs)withinatimeslot.Symbolperiodcanbe1or3bitperiodsdependinguponmodulationTimeslotnumber:timingoftimeslotswithinaTDMAframeTDMAframenumber:countofTDMAframesrelativetoanarbitrarystartpointCurrentServingBTS:BTSononeofwhosechannels(TCH,DCCH,CCCHorPDCH)theMSiscurrentlyoperatingCurrentServingCTS-FP:CTS-FPononeofwhosechannels(TCHorCTScontrolchannels)theCTS-MSiscurrentlyoperatingTimebasecounters:setofcounterswhichdeterminethetimingstateofsignalstransmittedbyaBTSorMSMStimingoffset:delayofthereceivedsignalrelativetotheexpectedsignalfromanMSatzerodistanceunderstaticchannelconditionswithzerotimingadvance.Thisisaccurateto±1symbol,andreportedonceperSACCHorafteraRACHas.required(i.e.atthesamerateastimingadvance).Forexample,foranMSwitharoundtrippropagationdelayofPsymbols,butwithatimingadvanceofTsymbols,thereportedtimingoffsetwillbeP-Tquantizedtothenearestsymbol.ForGPRStheMStimingoffsetisnotreportedTimingAdvanceIndex:TimingAdvanceIndexTAIusedforGPRS,whichdeterminesthepositionofthesubchannelonPTCCH(seeGSM05.02)usedbytheMStosendanaccessburst,fromwhichthenetworkcanderivethetimingadvanceObservedFrequencyOffset(OFO):differenceoffrequencyofsignalsreceivedbyaCTS-MSfromaCTS-FPandaBTS.TheObservedFrequencyOffsetismeasuredandreportedbytheCTS-MSonCTS-FPrequirement.TheObservedFrequencyOffsetisexpressedinppmwithanaccuracyof1/64ppm(i.e.about0.016ppm)Timegroup(TG):UsedforCompact,timegroupsshallbenumberedfrom0to3andaparticulartimegroupshallbereferredtobyitstimegroupnumber(TG)(seeGSM05.02)2GeneraldescriptionofsynchronizationsystemThisclausegivesageneraldescriptionofthesynchronizationsystem.Detailedrequirementsaregiveninclauses3to7.TheBTSsendssignalsontheBCCHor,forCOMPACTontheCPBCCH,toenabletheMStosynchronizeitselftotheBTSandifnecessarycorrectitsfrequencystandardtobeinlinewiththatoftheBTS.ThesignalssentbytheBTSforthesepurposesare:a)Frequencycorrectionbursts.b)Synchronizationbursts.Thetimingsoftimeslots,TDMAframes,TCHframes,controlchannelframes,and(forCOMPACT)therotationoftimegroupsareallrelatedtoacommonsetofcounterswhichruncontinuouslywhethertheMSandBTSaretransmittingornot.Thus,oncetheMShasdeterminedthecorrectsettingofthesecounters,allitsprocessesaresynchronizedtothecurrentservingBTS.SIST EN 300 912 V8.2.1:2003

ETSIETSIEN300912V8.2.1(2000-09)8(GSM05.10version8.2.1Release1999)TheMStimesitstransmissionstotheBTSinlinewiththosereceivedfromtheBTS.TheBTSsendstoeachMSa"timingadvance"parameter(TA)accordingtotheperceivedroundtrippropagationdelayBTS-MS-BTS.TheMSadvancesitstimingbythisamount,withtheresultthatsignalsfromdifferentMS'sarrivingattheBTSandcompensatedforpropagationdelay.Thisprocessiscalled"adaptiveframealignment".Additionally,synchronizationfunctionsmaybeimplementedinboththeMSandtheBTStosupporttheso-calledpseudosynchronizationscheme.ThesupportofthisschemeisoptionalexceptthatMSshallmeasureandreporttheObservedTimingDifference(OTD),whichisamandatoryrequirement.Thedetailedspecificationsofthepseudo-synchronizationschemeareincludedinannexA.InCTS,theCTS-FPsendssignalsontheCTSBCHtoenabletheMStosynchronizeitselftotheCTS-FPandifnecessarycorrectitsfrequencystandardtobeinlinewiththatoftheCTS-FP.ThesignalssentbytheCTS-FPforthesepurposesare:a)Frequencycorrectionbursts.b)Synchronizationbursts.Thetimingsoftimeslots,TDMAframes,CTSBCH,CTSARCH,CTSAGCHandCTSPCHframesareallrelatedtoafirstcommonsetofcounterswhichruncontinuouslywhethertheCTS-MSandCTS-FParetransmittingornot.Thus,oncetheCTS-MShasdeterminedthecorrectsettingofthesefirstcounters,theCTS-MSisabletoattachtothecurrentservingCTS-FP.Inaddition,duringCTS-MSattachment,theCTS-FPsendstotheCTS-MStheremainingcountersforSACCHandTCHframes.Then,allprocessesoftheCTS-MSaresynchronizedtothecurrentservingCTS-FP.TheCTS-MStimesitstransmissionstotheCTS-FPinlinewiththosereceivedfromtheCTS-FP.ThetimingadvanceparameterissettozeroforCTS.Additionally,theCTS-FPmaybeassistedbyaCTS-MStoadjustitsfrequencysource.WhenrequiredbytheCTS-FP,theCTS-MSestimatesifpossibleandreportstheObservedFrequencyOffsetoftheCTS-FPwithaspecifiedBTS.TheCTS-FPmaythenadjustitsfrequencysourceaccordingtothisvalue.3Timebasecounters3.1TimingstateofthesignalsThetimingstateofthesignalstransmittedbyaBTS,aMS,aCTS-FP,oranCompactBTSandMSisdefinedbythefollowingcounters:-QuartersymbolnumberQN(0-624)-SymbolnumberBN(0-156);-TimeslotnumberTN(0-7);-TDMAframenumberFN(0to(26x51x2048)-1=2715647);orforanonattachedCTS-MS,TDMAframenumbermodulo52T4(0-51);orforCompact,TDMAframenumberFN(0to(52x51x1024)-1=2715647).InCTS,theCTS-MSshallmanagedifferentsetsofcountersforCTSoperationandGSMoperation.3.2RelationshipbetweencountersTherelationshipbetweenthesecountersisasfollows:-QNincrementsevery12/13µs;-BN=IntegerpartofQN/4;-TNincrementswheneverQNchangesfromcount624to0;-FNincrementswheneverTNchangesfromcount7to0;orSIST EN 300 912 V8.2.1:2003

ETSIETSIEN300912V8.2.1(2000-09)9(GSM05.10version8.2.1Release1999)-foraCTS-MS,T4incrementswheneverTNchangesfromcount7to0.4TimingoftransmittedsignalsThetimingofsignalstransmittedbytheMS,BTSandCTS-FParedefinedinGSM05.02.TheMScanusethetimingofreceiptofthesynchronizationbursttosetupitstimebasecountersasfollows:QNissetbythetimingofthetrainingsequence;TN=0whenthesynchburstisreceived;FN=51((T3-T2)mod(26))+T3+51x26xT1whenthesynchburstisreceived,(whereT3=(10xT3')+1,T1,T2andT3'beingcontainedininformationfieldsinsynchronizationburst).ForCompact,theMScanusethetimingofreceiptofthesynchronizationbursttosetupitstimebasecountersasfollows:QNissetbythetimingofthetrainingsequence;FN=(R1x51+R2)x52+51whenthesynchburstisreceived(whereR1andR2arecontainedininformationfieldsinsynchronizationburst);TNisdeterminedfromTGasdescribedinGSM05.02,whereTGiscontainedininformationfieldsinsynchronizationburst.ForCTS,thetimebasecountersaresetasfollows:QNissetbythetimingofthetrainingsequence;TNissetaccordingtotheCTSBCH-SBposition(seeAnnexC);T4=51whentheCTSBCH-SBisreceived(priortoattachment);FN=(51((T3-T2)mod(26))+T3+51x26xT1)mod(2715648)whentheCTS-MSreceivesthelastCTSAGCHburstofthenon-hoppingaccessprocedure,whereT2=T4mod(26),andT1andT3beingcontainedinthisCTSimmediateassignmentmessage.Thereafter,thetimebasecountersareincrementedasinsubclause3.2.(WhenadjacentBTS'sarebeingmonitoredforhandoverpurposes,orforcellreselectionpurposesingroupreceivemode,theMSmaychoosetostorethevaluesofQN,TNandFNforalltheBTS'swhosesynchronizationburstshavebeendetectedrelativetoQN,TNandFNforitscurrentservingBTS).5BTSRequirementsforSynchronizationTheconditionsunderwhichtherequirementsofsubclauses5.4and5.6mustbemetshallbe3dBbelowthereferencesensitivitylevelorinputlevelforreferenceperformance,whicheverapplicable,inGSM05.05and3dBlesscarriertointerferenceratiothanthereferenceinterferenceratiosinGSM05.05.5.1FrequencysourceTheBTSshalluseasinglefrequencysourceofabsoluteaccuracybetterthan0,05ppmforbothRFfrequencygenerationandclockingthetimebase.ThesamesourceshallbeusedforallcarriersoftheBTS.ForthepicoBTSclasstheabsoluteaccuracyrequirementisrelaxedto0,1ppm.5.2TimebasecountersItisoptionalwhetherthetimebasecountersofdifferentBTS'saresynchronizedtogether.SIST EN 300 912 V8.2.1:2003

ETSIETSIEN300912V8.2.1(2000-09)10(GSM05.10version8.2.1Release1999)ForCOMPACTinterbasestationtimesynchronizationisrequiredsuchthattimeslotnumber(TN)=i(i=0to7)andframenumber(FN)withFNmod208=0shalloccuratthesametimeinallcells.ThetimebasecountersofdifferentBTSsshallbesynchronizedtogethersuchthatthetimingdifferencebetweendifferentBTSsshallbelessthan1symbolperiod,48/13µs(whichcanbe1or3bitsdependinguponmodulation)measuredattheBTSantenna.5.3InternalBTScarriertimingThechannelsofdifferentcarrierstransmittedbyaBTSshallbesynchronizedtogether,i.e.controlledbythesamesetofcounters.Thetimingdifferencebetweenthedifferentcarriersshallbelessthan1/4symbolperiods,measuredattheBTSantenna.Forpico-BTS,thetimingdifferencebetweendifferentcarriersshallbelessthan2symbolperiods,measuredattheBTSantenna.5.4InitialTimingadvanceestimationWhentheBTSdetectsanaccessbursttransmissiononRACHorPRACH,itshallmeasurethedelayofthissignalrelativetotheexpectedsignalfromanMSatzerodistanceunderstaticchannelconditions.Thisdelay,calledthetimingadvance,shallberoundedtothenearestsymbolperiodandincludedinaresponsefromtheBTSwhenapplicable.Forthepico-BTSthereisnorequirementtomeasurethistimingadvance.However,eitherthismeasuredvalueoraprogrammablevalueoftimingadvanceshallbeincludedintheresponsefromtheBTSwhenatimingadvancevalueneedstobesent.5.5MaximumtimingadvancevalueThemaximumtimingadvanc
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