General Information

Abstract

CRs from SMG#32

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 300 961 V8.1.1 (2000-11) - Digital cellular telecommunications system (Phase 2+) (GSM); Full rate speech; Transcoding (GSM 06.10 version 8.1.1 Release 1999)

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SIST EN 300 961 V8.1.1:2003

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Overview

SIST EN 300 961 V8.1.1:2003 establishes the standard for full rate speech transcoding in digital cellular telecommunications systems (GSM Phase 2+). Developed by the Slovenian Institute for Standardization (SIST), this document aligns with European Standard EN 300 961 and corresponds to GSM 06.10 version 8.1.1 (Release 1999), supporting the audio processing needs of GSM networks.

The standard specifies how speech is encoded and decoded for GSM full-rate traffic channels using the Regular Pulse Excitation - Long Term Prediction - Linear Predictive Coding (RPE-LTP) algorithm. It details the transcoding process, covering the full path from analogue or digital audio input through encoding, channel transmission, and decoding for output. Compliance with this standard ensures high interoperability, voice quality, and efficient speech compression in GSM telecommunications.

Key Topics

  • Transcoding Process
    The document describes converting uncompressed 13-bit uniform PCM audio samples into a compressed bitstream and vice versa, using the RPE-LTP algorithm. Encoding involves breaking down speech into blocks, extracting and coding prediction parameters, and compressing residual signals.

  • GSM Full Rate Speech Coding
    Focuses on the GSM full-rate codec, ensuring compatibility and optimization for the core mobile networks using a data rate of 13 kbit/s per channel.

  • Performance Requirements
    Defines delay, quality, and conversion characteristics for analogue/digital interfaces essential for reliable network and device integration.

  • Test and Verification
    Provides methods and test sequences for validation of correct transcoder implementation, supporting interoperability and consistent speech quality.

  • Audio Format Conversion
    Supports conversion between A-law/μ-law companded PCM and 13-bit uniform PCM to facilitate international and multi-network compatibility.

  • Codec Homing & Synchronization
    Describes procedures for returning encoder and decoder states to a known reference, essential for error recovery and maintaining robust operation in real-world networks.

Applications

SIST EN 300 961 V8.1.1:2003 delivers practical benefits in a variety of GSM telecommunication scenarios, including:

  • Mobile Networks:
    Standardizes speech compression, enabling efficient usage of bandwidth in GSM cellular networks and supporting large-scale deployment of reliable voice services.

  • Terminal Equipment:
    Ensures consistent voice quality and predictable device performance when implemented in mobile phones, base stations, and network infrastructure handling speech traffic.

  • Cross-Network Compatibility:
    Facilitates interconnection with public switched telephone networks (PSTN) and international networks, thanks to standardized PCM conversion and compliance with ITU recommendations.

  • Conformance Testing:
    Provides a clear reference for manufacturers, test labs, and operators to verify that equipment meets GSM speech transcoding requirements through standardized digital test sequences.

  • Quality of Service (QoS):
    Supports delivering clear and intelligible voice communications over GSM by tightly specifying functional and performance benchmarks.

Related Standards

For full benefit and interoperability, SIST EN 300 961 V8.1.1:2003 references and complements other standards in telecommunications, including:

  • GSM 06.01: Full rate speech processing functions
  • GSM 05.03: Channel coding
  • GSM 11.10: Mobile station conformity specifications
  • ITU-T G.711: Pulse code modulation (PCM) of voice frequencies
  • ITU-T G.726: Adaptive differential pulse code modulation (ADPCM)
  • ITU-T G.712: Transmission performance characteristics of PCM
  • ITU-T Q.35, V.21, V.23: Telephony tones and modem standards

These standards together create a comprehensive framework for ensuring high-quality digital voice services across GSM and inter-network environments.

Keywords: GSM, full rate speech, transcoding, RPE-LTP, digital cellular telecommunications, mobile communication, audio compression, codec, PCM conversion, voice quality, telecommunications standard, SIST EN 300 961

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SIST EN 300 961 V8.1.1:2003

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Frequently Asked Questions

SIST EN 300 961 V8.1.1:2003 is a standard published by the Slovenian Institute for Standardization (SIST). Its full title is "Digital cellular telecommunications system (Phase 2+) (GSM); Full rate speech; Transcoding (GSM 06.10 version 8.1.1 Release 1999)". This standard covers: CRs from SMG#32

CRs from SMG#32

SIST EN 300 961 V8.1.1:2003 is classified under the following ICS (International Classification for Standards) categories: 33.070.50 - Global System for Mobile Communication (GSM). The ICS classification helps identify the subject area and facilitates finding related standards.

SIST EN 300 961 V8.1.1:2003 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.

Standards Content (Sample)


2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Digital cellular telecommunications system (Phase 2+) (GSM); Full rate speech; Transcoding (GSM 06.10 version 8.1.1 Release 1999)33.070.50Globalni sistem za mobilno telekomunikacijo (GSM)Global System for Mobile Communication (GSM)ICS:Ta slovenski standard je istoveten z:EN 300 961 Version 8.1.1SIST EN 300 961 V8.1.1:2003en01-december-2003SIST EN 300 961 V8.1.1:2003SLOVENSKI
STANDARD
ETSIEN300961V8.1.1(2000-11)EuropeanStandard(Telecommunicationsseries)Digitalcellulartelecommunicationssystem(Phase2+);Fullratespeech;Transcoding(GSM06.10version8.1.1Release1999)GLOBALSYSTEMFORMOBILECOMMUNICATIONSRSIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)2(GSM06.10version8.1.1Release1999)ReferenceREN/SMG-110610Q8R1KeywordsDigitalcellulartelecommunicationssystem,GlobalSystemforMobilecommunications(GSM)ETSI650RoutedesLuciolesF-06921SophiaAntipolisCedex-FRANCETel.:+33492944200Fax:+33493654716SiretN°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:editor@etsi.frCopyrightNotificationNopartmaybereproducedexceptasauthorizedbywrittenpermission.Thecopyrightandtheforegoingrestrictionextendtoreproductioninallmedia.©EuropeanTelecommunicationsStandardsInstitute2000.Allrightsreserved.SIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)3(GSM06.10version8.1.1Release1999)ContentsIntellectualPropertyRights.6Foreword.61Scope.81.1References.81.1.1Abbreviations.91.2Outlinedescription.91.3Functionaldescriptionofaudioparts.91.4PCMFormatconversion.101.5PrinciplesoftheRPE-LTPencoder.101.6PrinciplesoftheRPE-LTPdecoder.111.7Sequenceandsubjectiveimportanceofencodedparameters.112Transmissioncharacteristics.142.1Performancecharacteristicsoftheanalogue/digitalinterfaces.142.2Transcoderdelay.143FunctionaldescriptionoftheRPE-LTPcodec.143.1FunctionaldescriptionoftheRPE-LTPencoder.143.1.1Offsetcompensation.153.1.2Pre-emphasis.153.1.3Segmentation.153.1.4Autocorrelation.163.1.5SchurRecursion.163.1.6TransformationofreflectioncoefficientstoLog.-AreaRatios.163.1.7QuantizationandcodingofLog.-AreaRatios.163.1.8DecodingofthequantizedLog.-AreaRatios.173.1.9InterpolationofLog.-AreaRatios.173.1.10TransformationofLog.-AreaRatiosintoreflectioncoefficients.173.1.11Shorttermanalysisfiltering.173.1.12Sub-segmentation.183.1.13CalculationoftheLTPparameters.183.1.14Coding/DecodingoftheLTPlags.183.1.15Coding/DecodingoftheLTPgains.193.1.16Longtermanalysisfiltering.193.1.17Longtermsynthesisfiltering.193.1.18WeightingFilter.203.1.19AdaptivesampleratedecimationbyRPEgridselection.203.1.20APCMquantizationoftheselectedRPEsequence.203.1.21APCMinversequantization.213.1.22RPEgridpositioning.223.2Decoder.223.2.1RPEdecodingclause.223.2.2LongTermPredictionclause.223.2.3Shorttermsynthesisfilteringclause.223.2.4Post-processing.224Codechoming.264.1Functionaldescription.264.2Definitions.264.3Encoderhoming.274.4Decoderhoming.274.5Encoderhomestate.284.6Decoderhomestate.285ComputationaldetailsoftheRPE-LTPcodec.285.1Datarepresentationandarithmeticoperations.285.2FixedpointimplementationoftheRPE-LTPcoder.30SIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)4(GSM06.10version8.1.1Release1999)5.2.0Scalingoftheinputvariable.315.2.1Downscalingoftheinputsignal.315.2.2Offsetcompensation.315.2.3Pre-emphasis.315.2.4Autocorrelation.325.2.5Computationofthereflectioncoefficients.325.2.6TransformationofreflectioncoefficientstoLog.-AreaRatios.335.2.7QuantizationandcodingoftheLog.-AreaRatios.345.2.8DecodingofthecodedLog.-AreaRatios.345.2.9Computationofthequantizedreflectioncoefficients.345.2.9.1InterpolationoftheLARpp[1.8]togettheLARp[1.8].345.2.9.2Computationoftherp[1.8]fromtheinterpolatedLARp[1.8].355.2.10Shorttermanalysisfiltering.355.2.11CalculationoftheLTPparameters.365.2.12Longtermanalysisfiltering.375.2.13Weightingfilter.375.2.14RPEgridselection.385.2.15APCMquantizationoftheselectedRPEsequence.385.2.16APCMinversequantization.395.2.17RPEgridpositioning.395.2.18Updateofthereconstructedshorttermresidualsignaldp[-120.-1].405.3FixedpointimplementationoftheRPE-LTPdecoder.405.3.1RPEdecodingclause.405.3.2Longtermsynthesisfiltering.405.3.3Computationofthedecodedreflectioncoefficients.415.3.4Shorttermsynthesisfilteringclause.415.3.5De-emphasisfiltering.425.3.6Upscalingoftheoutputsignal.425.3.7Truncationoftheoutputvariable.425.4TablesusedinthefixedpointimplementationoftheRPE-LTPcoderanddecoder.436Digitaltestsequences.446.1Inputandoutputsignals.446.2Configurationfortheapplicationofthetestsequences.446.2.1Configuration1(encoderonly).456.2.2Configuration2(decoderonly).456.3Testsequences.466.3.1Testsequencesforconfiguration1.466.3.2Testsequencesforconfiguration2.466.3.3AdditionalTestsequencesforCodecHoming.506.3.3.1Codechomingframes.506.3.3.2Sequenceforanextensivetestofthedecoderhoming.506.3.3.3Sequencesforfindingthe20msframingoftheGSMfullratespeechencoder.506.3.3.4Formatsandsizesofthesynchronizationsequences.51AnnexA(informative):Codecperformance.53A.1PerformanceoftheRPE-LTP.53A.1.1Introduction.53A.1.2Speechperformance.53A.1.2.1Singleencoding.53A.1.2.2Speechperformancewheninterconnectedwithcodingsystemsonananaloguebasis.54A.1.2.2.1Performancewith32kbit/sADPCM(G.721,supersededbyG.726).54A.1.2.2.2PerformancewithanotherRPE-LTPcodec.54A.1.2.2.3PerformancewithencodingotherthanRPE-LTPand32kbit/sADPCM(G.721,supersededbyG.726).54A.1.3Non-speechperformance.55A.1.3.1Performancewithsinglesinewaves.55A.1.3.2PerformancewithDTMFtones.55A.1.3.3Performancewithinformationtones.55A.1.3.4Performancewithvoice-banddata.55A.1.4Delay.55A.1.5Bibliography.57SIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)5(GSM06.10version8.1.1Release1999)A.2Subjectiverelevanceofthespeechcoderoutputbits.57A.3Formatfortestsequencedistribution.59A.3.1Typeoffilesprovided.59A.3.2Fileformatdescription.60AnnexB(informative):Testsequencedisks.62AnnexC(informative):ChangeRequestHistory.63History.64SIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)6(GSM06.10version8.1.1Release1999)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).Thepresentdocumentspecifiesthefullratespeechtranscodingwithinthedigitalcellulartelecommunicationssystem.NOTE:ThepresentdocumentisareproductionofrecommendationT/L/03/11"13kbit/sRegularPulseExcitation-LongTermPrediction-LinearPredictiveCoderforuseinthedigitalcellulartelecommunicationssystem".Archiveen_300961v080101p0.ZIPwhichaccompaniesthepresentdocument,containstestsequences,asdescribedinclause6andannexA.3.Thearchivecontainsthefollowing:Disk1.zipAnnexB:TestsequencesfortheGSMFullRatespeechcodec;TestsequencesSEQ01.xxxtoSEQ05.xxx.(Disk1.zipcontainsLHAcompressedfiles.)Disk2.zipAnnexB:TestsequencesfortheGSMFullRatespeechcodecwithhomingframes;TestsequencesSEQ01H.*toSEQ02H.*.Disk3.zipAnnexB:TestsequencesfortheGSMFullRatespeechcodecwithhomingframes;TestsequencesSEQ03H.*toSYNC159.COD.Disk4.zipAnnexB:8bitA-lawtestsequencesfortheGSMFullRatespeechcodecwithandwithouthomingframes(Disk4.zipcontainsself-extractingfiles).Disk5.zipAnnexB:8bitµ-lawtestsequencesfortheGSMFullRatespeechcodecwithandwithouthomingframes(Disk5.zipcontainsself-extractingfiles).SIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)7(GSM06.10version8.1.1Release1999)ThecontentsofthepresentdocumentissubjecttocontinuingworkwithinSMGandmaychangefollowingformalSMGapproval.ShouldSMGmodifythecontentsofthepresentdocumentitwillbere-releasedwithanidentifyingchangeofreleasedateandanincreaseinversionnumberasfollows:Version8.x.ywhere:8indicatesRelease1999ofGSMPhase2+.xtheseconddigitisincrementedforallchangesofsubstance,i.e.technicalenhancements,corrections,updates,etc.ythethirddigitisincrementedwheneditorialonlychangeshavebeenincorporatedinthespecification.NationaltranspositiondatesDateofadoptionofthisEN:24November2000DateoflatestannouncementofthisEN(doa):28February2001DateoflatestpublicationofnewNationalStandardorendorsementofthisEN(dop/e):31August2001DateofwithdrawalofanyconflictingNationalStandard(dow):31August2001SIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)8(GSM06.10version8.1.1Release1999)1ScopeThetranscodingprocedurespecifiedinthepresentdocumentisapplicableforthefull-rateTrafficChannel(TCH)inthedigitalcellulartelecommunicationssystem.Theuseofthistranscodingschemeforotherapplicationshasnotbeenconsidered.InGSM06.01,areferenceconfigurationforthespeechtransmissionchainofthedigitalcellulartelecommunicationssystemisshown.Accordingtothisreferenceconfiguration,thespeechencodertakesitsinputasa13bituniformPCMsignaleitherfromtheaudiopartofthemobilestationoronthenetworkside,fromthePSTNviaan8bit/A-orµ-law(PCS1900)to13bituniformPCMconversion.TheencodedspeechattheoutputofthespeechencoderisdeliveredtoachannelencoderunitwhichisspecifiedinGSM05.03.Inthereceivedirection,theinverseoperationstakeplace.Thepresentdocumentdescribesthedetailedmappingbetweeninputblocksof160speechsamplesin13bituniformPCMformattoencodedblocksof260bitsandfromencodedblocksof260bitstooutputblocksof160reconstructedspeechsamples.Thesamplingrateis8000sample/sleadingtoanaveragebitratefortheencodedbitstreamof13kbit/s.Thecodingschemeistheso-calledRegularPulseExcitation-LongTermprediction-LinearPredictiveCoder,here-afterreferredtoasRPE-LTP.ThepresentdocumentalsospecifiestheconversionbetweenA-andµ-law(PCS1900)PCMand13bituniformPCM.Performancerequirementsfortheaudioinputandoutputpartsareincludedonlytotheextentthattheyaffectthetranscoderperformance.Thepresentdocumentalsodescribesthecodecdowntothebitlevel,thusenablingtheverificationofcompliancetothepresentdocumenttoahighdegreeofconfidencebyuseofasetofdigitaltestsequences.Thesetestsequencesaredescribedandarecontainedinarchiveen_300961v080101p0.ZIPwhichaccompaniesthepresentdocument.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]GSM05.03:"Digitalcellulartelecommunicationssystem(Phase2+);Channelcoding".[3]GSM06.01:"Digitalcellulartelecommunicationssystem(Phase2+);Fullratespeech;Processingfunctions".[4]GSM11.10:"Digitalcellulartelecommunicationssystem(Phase2+);MobileStation(MS)conformityspecification".[5]ETS300085:"IntegratedServicesDigitalNetwork(ISDN);3,1kHztelephonyteleservice;Attachmentrequirementsforhandsetterminals(CandidateNET33)".[6]ITU-TRecommendationG.711:"Pulsecodemodulation(PCM)ofvoicefrequencies".[7]ITU-TRecommendationG.712:"Transmissionperformancecharacteristicsofpulsecodemodulation".SIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)9(GSM06.10version8.1.1Release1999)[8]ITU-TRecommendationG.726:"40,32,24,16kbit/sadaptivedifferentialpulsecodemodulation(ADPCM)".[9]ITU-TRecommendationQ.35:"Technicalcharacteristicsoftonesforthetelephoneservice".[10]ITU-TRecommendationV.21:"300bitspersecondduplexmodemstandardizedforuseinthegeneralswitchedtelephonenetwork".[11]ITU-TRecommendationV.23:"600/1200-bandmodemstandardizedforuseinthegeneralswitchedtelephonenetwork".[12]GSM06.32:"Digitalcellulartelecommunicationssystem(Phase2+);VoiceActivityDetector(VAD)".1.1.1AbbreviationsAbbreviationsusedinthepresentdocumentarelistedinGSM01.04.1.2OutlinedescriptionThepresentdocumentisstructuredasfollows:Subclause1.3containsafunctionaldescriptionoftheaudiopartsincludingtheA/DandD/Afunctions.Subclause1.4describestheconversionbetween13bituniformand8bitA-lawsamples.Subclauses1.5and1.6presentasimplifieddescriptionoftheprinciplesoftheRPE-LTPencodinganddecodingprocessrespectively.Inclause1.7,thesequenceandsubjectiveimportanceofencodedparametersaregiven.Clause2dealswiththetransmissioncharacteristicsoftheaudiopartsthatarerelevantfortheperformanceoftheRPE-LTPcodec.SometransmissioncharacteristicsoftheRPE-LTPcodecarealsospecifiedinclause2.Clause3presentsthefunctionaldescriptionoftheRPE-LTPcodinganddecodingprocedures,whereasclause4describesthecomputationaldetailsofthealgorithm.ProceduresfortheverificationofthecorrectfunctioningoftheRPE-LTParedescribedinclause5.PerformanceandnetworkaspectsoftheRPE-LTPcodecarecontainedinannexA.1.3FunctionaldescriptionofaudiopartsTheanalogue-to-digitalanddigital-to-analogueconversionwillinprinciplecomprisethefollowingelements:1)Analoguetouniformdigital:-microphone;-inputleveladjustmentdevice;-inputanti-aliasingfilter;-sample-holddevicesamplingat8kHz;-analogue-to-uniformdigitalconversionto13bitsrepresentation.Theuniformformatshallberepresentedintwo'scomplement.2)Uniformdigitaltoanalogue:-conversionfrom13bit/8kHzuniformPCMtoanalogue;-aholddevice;-reconstructionfilterincludingx/sinxcorrection;-outputleveladjustmentdevice;SIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)10(GSM06.10version8.1.1Release1999)-earphoneorloudspeaker.Intheterminalequipment,theA/Dfunctionmaybeachievedeither:-bydirectconversionto13bituniformPCMformat;-orbyconversionto8bit/A-orµ-law(PCS1900)compandedformat,basedonastandardA-orµ-law(PCS1900)codec/filteraccordingtoITU-TRecommendationG.711/714,followedbythe8-bitto13-bitconversionaccordingtotheprocedurespecifiedinclause1.4.FortheD/Aoperation,theinverseoperationstakeplace.InthelattercaseitshouldbenotedthatthespecificationsinITU-TrecommendationG.714(supersededbyG.712)areconcernedwithPCMequipmentlocatedinthecentralpartsofthenetwork.Whenusedintheterminalequipment,thepresentdocumentdoesnotonitsownensuresufficientout-of-bandattenuation.Thespecificationofout-of-bandsignalsisdefinedinclause2betweentheacousticsignalandthedigitalinterfacetotakeintoaccountthatthefilteringintheterminalcanbeachievedbothbyelectronicandacousticaldesign.1.4PCMFormatconversionTheconversionbetween8bitA-orµ-law(PCS1900)compandedformatandthe13-bituniformformatshallbeasdefinedinITU-TRecommendationG.721(supersededbyG.726),clause4.2.1,sub-blockEXPANDandclause4.2.7,sub-blockCOMPRESS.TheparameterLAW=1shouldbeusedforA-lawandLAW=0shouldbeusedforµ-law(PCS1900).1.5PrinciplesoftheRPE-LTPencoderAsimplifiedblockdiagramoftheRPE-LTPencoderisshowninfigure1.1.Inthisdiagramthecodingandquantizationfunctionsarenotshownexplicitly.Theinputspeechframe,consistingof160signalsamples(uniform13bitPCMsamples),isfirstpre-processedtoproduceanoffset-freesignal,whichisthensubjectedtoafirstorderpre-emphasisfilter.The160samplesobtainedarethenanalysedtodeterminethecoefficientsfortheshorttermanalysisfilter(LPCanalysis).Theseparametersarethenusedforthefilteringofthesame160samples.Theresultis160samplesoftheshorttermresidualsignal.Thefilterparameters,termedreflectioncoefficients,aretransformedtolog.arearatios,LARs,beforetransmission.Forthefollowingoperations,thespeechframeisdividedinto4sub-frameswith40samplesoftheshorttermresidualsignalineach.Eachsub-frameisprocessedblockwisebythesubsequentfunctionalelements.Beforetheprocessingofeachsub-blockof40shorttermresidualsamples,theparametersofthelongtermanalysisfilter,theLTPlagandtheLTPgain,areestimatedandupdatedintheLTPanalysisblock,onthebasisofthecurrentsub-blockofthepresentandastoredsequenceofthe120previousreconstructedshorttermresidualsamples.Ablockof40longtermresidualsignalsamplesisobtainedbysubtracting40estimatesoftheshorttermresidualsignalfromtheshorttermresidualsignalitself.Theresultingblockof40longtermresidualsamplesisfedtotheRegularPulseExcitationanalysiswhichperformsthebasiccompressionfunctionofthealgorithm.AsaresultoftheRPE-analysis,theblockof40inputlongtermresidualsamplesarerepresentedbyoneof4candidatesub-sequencesof13pulseseach.ThesubsequenceselectedisidentifiedbytheRPEgridposition(M).The13RPEpulsesareencodedusingAdaptivePulseCodeModulation(APCM)withestimationofthesub-blockamplitudewhichistransmittedtothedecoderassideinformation.TheRPEparametersarealsofedtoalocalRPEdecodingandreconstructionmodulewhichproducesablockof40samplesofthequantizedversionofthelongtermresidualsignal.Byaddingthese40quantizedsamplesofthelongtermresidualtothepreviousblockofshorttermresidualsignalestimates,areconstructedversionofthecurrentshorttermresidualsignalisobtained.Theblockofreconstructedshorttermresidualsignalsamplesisthenfedtothelongtermanalysisfilterwhichproducesthenewblockof40shorttermresidualsignalestimatestobeusedforthenextsub-blocktherebycompletingthefeedbackloop.SIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)11(GSM06.10version8.1.1Release1999)1.6PrinciplesoftheRPE-LTPdecoderThesimplifiedblockdiagramoftheRPE-LTPdecoderisshowninfig1.2.Thedecoderincludesthesamestructureasthefeed-backloopoftheencoder.Inerror-freetransmission,theoutputofthisstagewillbethereconstructedshorttermresidualsamples.Thesesamplesarethenappliedtotheshorttermsynthesisfilterfollowedbythede-emphasisfilterresultinginthereconstructedspeechsignalsamples.1.7SequenceandsubjectiveimportanceofencodedparametersAsindicatedinfig1.1thethreedifferentgroupsofdataareproducedbytheencoderare:-theshorttermfilterparameters;-theLongTermPrediction(LTP)parameters;-theRPEparameters.Theencoderwillproducethisinformationinauniquesequenceandformat,andthedecodershallreceivethesameinformationinthesameway.Intable1.1,thesequenceofoutputbitsb1tob260andthebitallocationforeachparameterisshown.Thedifferentparametersoftheencodedspeechandtheirindividualbitshaveunequalimportancewithrespecttosubjectivequality.BeforebeingsubmittedtothechannelencodingfunctionthebitshavetoberearrangedinthesequenceofimportanceasgiveninGSM05.03.TherankinghasbeendeterminedbysubjectivetestingandtheprocedureusedisdescribedinannexA,clauseA.2.Table1.1:Encoderoutputparametersinorderofoccurrenceandbitallocationwithinthespeechframeof260bits/20ms==================================================================ParameterParameterParameterVar.NumberBitno.numbernamenameofbits(LSB-MSB)====================================================================================================================================1LAR16b1-b62LAR26b7-b12FILTER3Log.AreaLAR35b13-b174ratiosLAR45b18-b22PARAMETERS51-8LAR54b23-b266LAR64b27-b307LAR73b31-b338LAR83b34-b36==================================================================Sub-frameno.1==================================================================LTP9LTPlagN17b37-b43PARAMETERS10LTPgainb12b44-b45------------------------------------------------------------------11RPEgridpositionM12b46-b47RPE12BlockamplitudeXmax16b48-b53PARAMETERS13RPE-pulseno.1x1(0)3b54-b5614RPE-pulseno.2x1(1)3b57-b59.25RPE-pulseno.13x1(12)3b90-b92==================================================================SIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)12(GSM06.10version8.1.1Release1999)Sub-frameno.2==================================================================LTP26LTPlagN27b93-b99PARAMETERS27LTPgainb22b100-b101------------------------------------------------------------------28RPEgridpositionM22b102-b103RPE29BlockamplitudeXmax26b104-b109PARAMETERS30RPE-pulseno.1x2(0)3b110-b11231RPE-pulseno.2x2(1)3b113-b115.42RPE-pulseno.13x2(12)3b146-b148==================================================================Table1.1:Encoderoutputparametersinorderofoccurrenceandbitallocationwithinthespeechframeof260bits/20msSub-frameno.3==================================================================LTP43LTPlagN37b149-b155PARAMETERS44LTPgainb32b156-b157------------------------------------------------------------------45RPEgridpositionM32b158-b159RPE46BlockamplitudeXmax36b160-b165PARAMETERS47RPE-pulseno.1x3(0)3b166-b16848RPE-pulseno.2x3(1)3b169-b171.59RPE-pulseno.13x3(12)3b202-b204==================================================================Sub-frameno.4==================================================================LTP60LTPlagN47b205-b211PARAMETERS61LTPgainb42b212-b213------------------------------------------------------------------62RPEgridpositionM42b214-b215RPE63BlockamplitudeXmax46b216-b221PARAMETERS64RPE-pulseno.1x4(0)3b222-b22465RPE-pulseno.2x4(1)3b225-b227.76RPE-pulseno.13x4(12)3b258-b260==================================================================SIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)13(GSM06.10version8.1.1Release1999)InputPre-processingsignalShorttermanalysisfilterShorttermLPCanalysis+RPEgridselectionandcoding(1)(2)LTPanalysisLongtermanalysisfilter+RPEgriddecodingandpositioning(4)(5)(3)-LTPparameters(9bits/5ms)ReflectioncoefficientscodedasLog.-AreaRatios(36bits/20ms)RPEparameters(47bits/5ms)Toradiosubsystem(1)Shorttermresidual(2)Longtermresidual(40samples)(3)Shorttermresidualestimate(40samples)(4)Reconstructedshorttermresidual(40samples)(5)Quantizedlongtermresidual(40samples)Figure1.1:SimplifiedblockdiagramoftheRPE-LTPencoderRPEgriddecodingandpositioningReflectioncoefficientscodedasLog.-AreaRatios(36bits/20ms)RPEparameters(47bits/5ms)FromradiosubsystemLTPparameters(9bits/5ms)+ShorttermsynthesisfilterLongtermsynthesisfilterPost-processingOutputsignalFigure1.2:SimplifiedblockdiagramoftheRPE-LTPdecoderSIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)14(GSM06.10version8.1.1Release1999)2TransmissioncharacteristicsThisclausespecifiesthenecessaryperformancecharacteristicsoftheaudiopartsforproperfunctioningofthespeechtranscoder.SometransmissionperformancecharacteristicsoftheRPE-LTPtranscoderarealsogiventoassistthedesignerofthespeechtranscoderfunction.TheinformationgivenhereisredundantandthedetailedspecificationsarecontainedinrecommendationGSM11.10.Theperformancecharacteristicsarereferredtothe13bituniformPCMinterface.NOTE:Tosimplifytheverificationofthespecifications,theperformancelimitsmaybereferredtoanA-orµ-law(PCS1900)measurementinterfaceaccordingtoITU-TRecommendationG.711.Inthisway,standardmeasuringequipmentsforPCMsystemscanbeutilizedformeasurements.Therelationshipbetweenthe13bitformatandtheA-orµ-law(PCS1900)compandedshallfollowtheproceduresdefinedinclause1.4.2.1Performancecharacteristicsoftheanalogue/digitalinterfacesConcerning1)discriminationagainstout-of-bandsignals(sending)and2)spuriousout-of-bandsignals(receiving),thesamerequirementsasdefinedinETSIstandardTE04-15(digitaltelephone,candidateNET33)apply.2.2TranscoderdelayConsiderabacktobackconfigurationwheretheparametersgeneratedbytheencoderaredeliveredtothespeechdecoderassoonastheyareavailable.Thetranscoderdelayisdefinedasthetimeintervalbetweentheinstantaspeechframeof160sampleshasbeenreceivedattheencoderinputandtheinstantthecorresponding160reconstructedspeechsampleshavebeenout-putbythespeechdecoderatan8kHzsamplerate.Thetheoreticalminimumdelaywhichcanbeachievedis20ms.Therequirementisthatthetranscoderdelayshouldbelessthan30ms.3FunctionaldescriptionoftheRPE-LTPcodecTheblockdiagramoftheRPE-LTP-coderisshowninfigure3.1.Theindividualblocksaredescribedinthefollowingclauses.3.1FunctionaldescriptionoftheRPE-LTPencoderThePre-processingclauseoftheRPE-LTPencodercomprisesthefollowingtwosub-blocks:-Offsetcompensation(3.1.1);-Pre-emphasis(3.1.2).TheLPCanalysisclauseoftheRPE-LTPencodercomprisesthefollowingfivesub-blocks:-Segmentation(3.1.3);-Auto-Correlation(3.1.4);-SchurRecursion(3.1.5);-TransformationofreflectioncoefficientstoLog.-AreaRatios(3.1.6);-QuantizationandcodingofLog.-AreaRatios(3.1.7).SIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)15(GSM06.10version8.1.1Release1999)TheShorttermanalysisfilteringclauseoftheRPE-LTPcomprisesthefollowingfoursub-blocks:-DecodingofthequantizedLog.-AreaRatios(LARs)(3.1.8);-InterpolationofLog.-AreaRatios(3.1.9);-TransformationofLog.-AreaRatiosintoreflectioncoefficients(3.1.10);-Shorttermanalysisfiltering(3.1.11).TheLongTermPredictor(LTP)clausecomprises4sub-blocksworkingonsubsegments(3.1.12)oftheshorttermresidualsamples:-CalculationofLTPparameters(3.1.13);-CodingoftheLTPlags(3.1.14)andtheLTPgains(3.1.15);-DecodingoftheLTPlags(3.1.14)andtheLTPgains(3.1.15);-Longtermanalysisfiltering(3.1.16),andLongtermsynthesisfiltering(3.1.17).TheRPEencodingclausecomprisesfivedifferentsub-blocks:-Weightingfilter(3.1.18);-AdaptivesampleratedecimationbyRPEgridselection(3.1.19);-APCMquantizationoftheselectedRPEsequence(3.1.20);-APCMinversequantization(3.1.21);-RPEgridpositioning(3.1.22).Pre-processingclause3.1.1OffsetcompensationPriortothespeechencoderanoffsetcompensation,byanotchfilterisappliedinordertoremovetheoffsetoftheinputsignalsotoproducetheoffset-freesignalsof.sof(k)=so(k)-so(k-1)+alpha*sof(k-1)(3.1.1)alpha=32735*2-153.1.2Pre-emphasisThesignalsofisappliedtoafirstorderFIRpre-emphasisfilterleadingtotheinputsignalsoftheanalysisclause.s(k)=sof(k)-beta*sof(k-1)(3.1.2)beta=28180*2-15LPCanalysisclause3.1.3SegmentationThespeechsignals(k)isdividedintonon-overlappingframeshavingalengthofT0=20ms(160samples).AnewLPC-analysisoforderp=8isperformedforeachframe.SIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)16(GSM06.10version8.1.1Release1999)3.1.4AutocorrelationThefirstp+1=9valuesoftheAuto-Correlationfunctionarecalculatedby:159ACF(k)=s(i)s(i-k),k=0,1.,8(3.2)i=k3.1.5SchurRecursionThereflectioncoefficientsarecalculatedasshowninfigure3.2usingtheSchurRecursionalgorithm.Theterm"reflectioncoefficient"comesfromthetheoryoflinearpredictionofspeech(LPC),whereavocaltractrepresentationconsistingofseriesofuniformcylindricalclausesisassumed.Sucharepresentationcanbedescribedbythereflectioncoefficientsorthearearatiosofconnectedclauses.3.1.6TransformationofreflectioncoefficientstoLog.-AreaRatiosThereflectioncoefficientsr(i),(i=1.8),calculatedbytheSchuralgorithm,areintherange:-1<=r(i)<=+1Duetothefavourablequantizationcharacteristics,thereflectioncoefficientsareconvertedintoLog.-AreaRatioswhicharestrictlydefinedasfollows:1+r(i)Logarea(i)=log10(----------)(3.3)1-r(i)Sinceitisthecompandingcharacteristicofthistransformationthatisofimportance,thefollowingsegmentedapproximationisused.r(i);|r(i)|<0.675LAR(i)=sign[r(i)]*[2|r(i)|-0.675];0.675<=|r(i)|<0.950sign[r(i)]*[8|r(i)|-6.375];0.950<=|r(i)|<=1.000(3.4)withtheresultthatinsteadofhavingtodivideandobtainthelogarithmofparticularvalues,itismerelynecessarytomultiply,addandcomparethesevalues.Thefollowingequation(3.5)givestheinversetransformation.LAR'(i);|LAR'(i)|<0.675r'(i)=sign[LAR'(i)]*[0.500*|LAR'(i)|+0.337500];0.675<=|LAR'(i)|<1.225sign[LAR'(i)]*[0.125*|LAR'(i)|+0.796875];1.225<=|LAR'(i)|<=1.625(3.5)3.1.7QuantizationandcodingofLog.-AreaRatiosTheLog.-AreaRatiosLAR(i)havedifferentdynamicrangesanddifferentasymmetricdistributiondensities.Forthisreason,thetransformedcoefficientsLAR(i)arelimitedandquantizeddifferentlyaccordingtothefollowingequation(3.6),withLARc(i)denotingthequantizedandintegercodedversionofLAR(i).LARc(i)=Nint{A(i)*LAR(i)+B(i)}(3.6)withNint{z}=int{z+sign{z}*0.5}(3.6a)FunctionNintdefinestheroundingtothenearestintegervalue,withthecoefficientsA(i),B(i),anddifferentextremevaluesofLARc(i)foreachcoefficientLAR(i)givenintable3.1.SIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)17(GSM06.10version8.1.1Release1999)Table3.1:QuantizationoftheLog.-AreaRatiosLAR(i)LARNoiA(i)B(i)MinimumLARc(i)MaximumLARc(i)120.0000.000-32+31220.0000.000-32+31320.0004.000-16+15420.000-5.000-16+15513.6370.184-8+7615.000-3.500-8+778.334-0.666-4+388.824-2.235-4+3Short-termanalysisfilteringclauseThecurrentframeofthespeechsignalsisretainedinmemoryuntilcalculationoftheLPCparametersLAR(i)iscompleted.Theframeisthenreadoutandfedtotheshorttermanalysisfilteroforderp=8.However,priortotheanalysisfilteringoperation,thefiltercoefficientsaredecodedandpre-processedbyinterpolation.3.1.8DecodingofthequantizedLog.-AreaRatiosInthisblockthequantizedandcodedLog.-AreaRatios(LARc(i))aredecodedaccordingtoequation(3.7).LAR''(i)=(LARc(i)-B(i))/A(i)(3.7)3.1.9InterpolationofLog.-AreaRatiosToavoidspurioustransientswhichmayoccurifthefiltercoefficientsarechangedabruptly,twosubsequentsetsofLog.-AreaRatiosareinterpolatedlinearly.Withineachframeof160analysedspeechsamplestheshorttermanalysisfilterandtheshorttermsynthesisfilteroperatewithfourdifferentsetsofcoefficientsderivedaccordingtotable3.2.Table3.2:InterpolationofLARparameters(J=actualsegment)kLAR'J(i)=0.120.75*LAR''J-1(i)+0.25*LAR''J(i)13.260.50*LAR''J-1(i)+0.50*LAR''J(i)27.390.25*LAR''J-1(i)+0.75*LAR''J(i)40.159LAR''J(i)3.1.10TransformationofLog.-AreaRatiosintoreflectioncoefficientsThereflectioncoefficientsarefinallydeterminedusingtheinversetransformationaccordingtoequation(3.5).3.1.11ShorttermanalysisfilteringTheShorttermanalysisfilterisimplementedaccordingtothelatticestructuredepictedinfigure3.3.d0(k)=s(k)(3.8a)u0(k)=s(k)(3.8b)di(k)=di-1(k)+r'i*ui-1(k-1)withi=1,.8(3.8c)ui(k)=ui-1(k-1)+r'i*di-1(k)withi=1,.8(3.8d)d(k)=d8(k)(3.8e)Long-TermPredictor(LTP)clauseSIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)18(GSM06.10version8.1.1Release1999)3.1.12Sub-segmentationEachinputframeoftheshorttermresidualsignalcontains160samples,correspondingto20ms.Thelongtermcorrelationisevaluatedfourtimesperframe,foreach5mssubsegment.Forconvenienceinthefollowing,wenotej=0,.,3thesub-segmentnumber,sothatthesamplespertainingtothej-thsub-segmentoftheresidualsignalarenowdenotedbyd(kj+k)withj=0,.,3;kj=k0+j*40andk=0,.,39wherek0correspondstothefirstvalueofthecurrentframe.3.1.13CalculationoftheLTPparametersForeachofthefoursub-segmentsalongtermcorrelationlagNj,(j=0,.,3),andanassociatedgainfactorbj,(j=0,.,3)aredetermined.Foreachsub-segment,thedeterminationoftheseparametersisimplementedinthreesteps.1)Thefirststepistheevaluationofthecross-correlationRj(lambda)ofthecurrentsub-segmentofshorttermresidualsignald(kj+i),(i=0,.,39)andtheprevioussamplesofthereconstructedshorttermresidualsignald'(kj+i),(i=-120,.,-1):39j=0,.3Rj(lambda)=d(kj+i)*d'(kj+i-lambda);kj=k0+j*40i=0lambda=40,.,120(3.9)Thecross-correlationisevaluatedforlagslambdagreaterthanorequalto40andlessthanorequalto120,i.e.correspondingtosamplesoutsidethecurrentsub-segmentandnotdelayedbymorethantwosub-segments.2)ThesecondstepistofindthepositionNjofthepeakofthecross-correlationfunctionwithinthisinterval:Rj(Nj)=max{Rj(lambda);lambda=40.120};j=0,.,3(3.10)3)Thethirdstepistheevaluationofthegainfactorbjaccordingto:bj=Rj(Nj)/Sj(Nj);j=0,.,3(3.11)with39Sj(Nj)=d'2(kj+i-Nj);j=0,.,3(3.12)i=0Itisclearthatthelast120samplesofthereconstructedshorttermresidualsignald'(kj+i),(i=-120,.,-1)shallberetaineduntilthenextsub-segmentsoastoallowtheevaluationoftherelations(3.9),.,(3.12).3.1.14Coding/DecodingoftheLTPlagsThelongtermcorrelationlagsNj,(j=0,.,3)canhavevaluesintherange(40,.,120),andsoshallbecodedusing7bitswith:Ncj=Nj;j=0,.,3(3.13)Atthereceivingend,assuminganerrorfreetransmission,thedecodingofthesevalueswillrestoretheactuallags:Nj'=Ncj;j=0,.,3(3.14)SIST EN 300 961 V8.1.1:2003

ETSIETSIEN300961V8.1.1(2000-11)19(GSM06.10version8.1.1Release1999)3.1.15Coding/DecodingoftheLTPgainsThelongtermpredictiongainsbj,(j=0,.,3)areencodedwith2bitseach,accordingtothefollowingalgorithm:ifbj<=DLB(i)thenbcj=0;i=0ifDLB(i-1) ...