SIST EN 300 961 V8.1.1:2003

• 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)

SIST EN 300 961 V8.1.1:2003 is the Slovenian adoption of the ETSI European Standard for Digital cellular telecommunications system (Phase 2+) (GSM) full rate speech transcoding, based on GSM 06.10 version 8.1.1 Release 1999. It specifies the Regular Pulse Excitation-Long Term Prediction (RPE-LTP) speech coder and decoder for the full-rate Traffic Channel, including the PCM interfaces, bit-exact fixed-point processing, code homing, and digital test sequences for implementers and test labs.

What does SIST EN 300 961 V8.1.1:2003 specify?

SIST EN 300 961 V8.1.1:2003 applies to the full-rate Traffic Channel (TCH) in the digital cellular telecommunications system. The standard focuses on the speech transcoder itself and says that use for other applications was not considered.

It defines the mapping between 160 speech samples in 13-bit uniform PCM and 260-bit encoded frames, and the reverse mapping back to 160 reconstructed samples. It also specifies conversion between 8-bit A-law or µ-law (PCS1900) PCM and 13-bit uniform PCM.

Annex	What it covers
Annex A	Codec performance, speech and non-speech behaviour, delay, and subjective relevance of bits
Annex B	Test sequence disks
Annex C	Change request history

The document is organized into clauses on scope, transmission characteristics, functional description of the codec, code homing, computational detail, and digital test sequences.

What are the key requirements of SIST EN 300 961 V8.1.1:2003?

SIST EN 300 961 V8.1.1:2003 is a frame-based, bit-exact specification. For an implementation, the most important points are the frame structure, the PCM conversion rules, the delay target, the fixed-point arithmetic rules, and the test sequences.

• Clause 1 fixes the speech frame structure at 160 samples per 20 ms frame, with 8 kHz sampling and an average coded rate of 13 kbit/s. In practice, this sets the timing and packet size every implementation must handle.
• Clause 1.4 defines the conversion between 8-bit A-law or µ-law (PCS1900) PCM and 13-bit uniform PCM by reference to ITU-T G.721 procedures. This matters when the codec is connected to telephony equipment that uses companded PCM instead of linear samples.
• Clause 1.7 gives the output bit order and the subjective importance of the encoded parameters. Channel coding in GSM 05.03 uses that order, so implementers must keep the parameter sequence exactly as defined.
• Clause 2 sets the relevant transmission characteristics for the audio interfaces and states a transcoder delay below 30 ms, with 20 ms as the theoretical minimum. This is the practical integration target for handset, network, and TRAU designs.
• Clause 3 describes the RPE-LTP processing chain: offset compensation, pre-emphasis, LPC analysis, long-term prediction on 40-sample subframes, RPE grid selection, APCM quantization, and the reverse synthesis path. This is the core algorithm the software or hardware must reproduce.
• Clause 4 defines code homing frames and the homing state for both encoder and decoder. This supports in-band resetting for bit-exact testing and loopback verification.
• Clause 5 defines the fixed-point implementation, including 16-bit and 32-bit arithmetic, saturation, scaling, rounding, and the required tables. This is what makes two independent implementations produce the same bits.
• Clause 6 provides encoder-only and decoder-only digital test sequences, plus additional homing and 8-bit A-law and µ-law sequence sets. These are the practical verification vectors for compliance and regression testing.

What terms does SIST EN 300 961 V8.1.1:2003 define?

• GSM - Global System for Mobile Communication, the digital cellular system addressed by the standard.
• RPE-LTP - Regular Pulse Excitation-Long Term Prediction, the speech coding method used in this transcoder.
• LPC - Linear Predictive Coding, the short-term analysis method that derives reflection coefficients from speech frames.
• LTP - Long Term Prediction, the subframe predictor that uses past reconstructed speech to model periodicity.
• PCM - Pulse Code Modulation, the uniform speech sample format used as input and output in linear form.
• A-law - An 8-bit telephony companding law used for PCM conversion on the network side.
• µ-law (PCS1900) - The 8-bit companding law used alongside A-law in the specified PCM conversion path.
• TCH - Traffic Channel, specifically the full-rate channel where this transcoder applies.

Who uses SIST EN 300 961 V8.1.1:2003?

GSM speech codec developers, mobile-station and network-side implementers, TRAU equipment suppliers, and test laboratories use this standard. Quality and conformity teams use it to check bit-exact operation, PCM conversion, code homing, delay, and the digital test sequence results.

It is also relevant to engineers preparing type-approval or interoperability tests, because the document gives both the algorithm and the verification vectors needed to compare an implementation against the reference behaviour.

Which standards are used with SIST EN 300 961 V8.1.1:2003?

Reference	Contribution
GSM01.04	Abbreviations and acronyms used in the GSM series
GSM05.03	Channel coding and bit rearrangement after transcoding
GSM06.01	Full-rate speech processing functions and reference speech chain
GSM06.32	Voice Activity Detector (VAD), used in code homing state notes
GSM11.10	Mobile Station conformity specification and detailed performance context
ETS 300 085	Handset terminal attachment requirements context
ITU-T G.711	PCM and companding context for A-law and µ-law conversion
ITU-T G.712	Transmission performance characteristics of PCM equipment
ITU-T G.726	ADPCM reference for the PCM conversion procedures
ITU-T Q.35	Tone characteristics relevant to non-speech performance
ITU-T V.21	300 bit/s modem context in annex performance notes
ITU-T V.23	600/1200 baud modem context in annex performance notes

What does the SIST EN 300 961 V8.1.1:2003 document contain?

The document contains simplified block diagrams of the encoder and decoder, detailed clause-by-clause algorithms, and tables for parameter allocation, quantization, scaling, and fixed-point arithmetic. It also gives the homing-frame definitions and the state values used to reset the codec in a bit-exact way.

Clause 6 and Annex A.3 describe the digital test files, their roles, and their file formats for encoder input, coded parameters, and decoder output. Annex A adds performance notes for speech, tones, voice-band data, and delay, while Annex C records the change request history.

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.:[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 300 961 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) ...