SIST EN 300 961 V8.0.2:2003

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 8.0.2 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 8.0.2SIST EN 300 961 V8.0.2:2003en01-december-2003SIST EN 300 961 V8.0.2:2003SLOVENSKI
STANDARD
ETSIEN300961V8.0.2(2000-11)EuropeanStandard(Telecommunicationsseries)Digitalcellulartelecommunicationssystem(Phase2+);Fullratespeech;Transcoding(GSM06.10version8.0.2Release1999)GLOBALSYSTEMFORMOBILECOMMUNICATIONSRSIST EN 300 961 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)2(GSM06.10version8.0.2Release1999)ReferenceREN/SMG-110610Q8KeywordsDigitalcellulartelecommunicationssystem,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 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)3(GSM06.10version8.0.2Release1999)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.223.2.1RPEdecodingsection.223.2.2LongTermPredictionsection.223.2.3Shorttermsynthesisfilteringsection.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 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)4(GSM06.10version8.0.2Release1999)5.2.0Scalingoftheinputvariable.315.2.1Downscalingoftheinputsignal.315.2.2Offsetcompensation.315.2.3Pre-emphasis.315.2.4Autocorrelation.315.2.5Computationofthereflectioncoefficients.325.2.6TransformationofreflectioncoefficientstoLog.-AreaRatios.335.2.7QuantizationandcodingoftheLog.-AreaRatios.335.2.8DecodingofthecodedLog.-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.355.2.12Longtermanalysisfiltering.375.2.13Weightingfilter.375.2.14RPEgridselection.385.2.15APCMquantizationoftheselectedRPEsequence.385.2.16APCMinversequantization.395.2.17RPEgridpositioning.395.2.18Updateofthereconstructedshorttermresidualsignaldp[-120.-1].405.3FixedpointimplementationoftheRPE-LTPdecoder.405.3.1RPEdecodingsection.405.3.2Longtermsynthesisfiltering.405.3.3Computationofthedecodedreflectioncoefficients.415.3.4Shorttermsynthesisfilteringsection.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 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)5(GSM06.10version8.0.2Release1999)A.2Subjectiverelevanceofthespeechcoderoutputbits.57A.3Formatfortestsequencedistribution.59A.3.1Typeoffilesprovided.59A.3.2Fileformatdescription.60AnnexB(informative):Testsequencedisks.62AnnexC(informative):ChangeRequestHistory.63History.64SIST EN 300 961 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)6(GSM06.10version8.0.2Release1999)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_300961v080002p0.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 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)7(GSM06.10version8.0.2Release1999)ThecontentsofthepresentdocumentissubjecttocontinuingworkwithinSMGandmaychangefollowingformalSMGapproval.ShouldSMGmodifythecontentsofthepresentdocumentitwillbere-releasedwithanidentifyingchangeofreleasedateandanincreaseinversionnumberasfollows:Version8.x.ywhere:8indicatesRelease1999ofGSMPhase2+xtheseconddigitisincrementedforallchangesofsubstance,i.e.technicalenhancements,corrections,updates,etc.ythethirddigitisincrementedwheneditorialonlychangeshavebeenincorporatedinthespecification.NationaltranspositiondatesDateofadoptionofthisEN:3November2000DateoflatestannouncementofthisEN(doa):28February2001DateoflatestpublicationofnewNationalStandardorendorsementofthisEN(dop/e):31August2001DateofwithdrawalofanyconflictingNationalStandard(dow):31August2001SIST EN 300 961 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)8(GSM06.10version8.0.2Release1999)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_300961v080002p0.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 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)9(GSM06.10version8.0.2Release1999)[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.Insubclause1.7,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 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)10(GSM06.10version8.0.2Release1999)-earphoneorloudspeaker.Intheterminalequipment,theA/Dfunctionmaybeachievedeither:-bydirectconversionto13bituniformPCMformat;-orbyconversionto8bit/A-orµ-law(PCS1900)compandedformat,basedonastandardA-orµ-law(PCS1900)codec/filteraccordingtoITU-TRecommendationG.711/714,followedbythe8-bitto13-bitconversionaccordingtotheprocedurespecifiedinsubclause1.4.FortheD/Aoperation,theinverseoperationstakeplace.InthelattercaseitshouldbenotedthatthespecificationsinITU-TrecommendationG.714(supersededbyG.712)areconcernedwithPCMequipmentlocatedinthecentralpartsofthenetwork.Whenusedintheterminalequipment,thisspecificationdoesnotonitsownensuresufficientout-of-bandattenuation.Thespecificationofout-of-bandsignalsisdefinedinsection2betweentheacousticsignalandthedigitalinterfacetotakeintoaccountthatthefilteringintheterminalcanbeachievedbothbyelectronicandacousticaldesign.1.4PCMFormatconversionTheconversionbetween8bitA-orµ-law(PCS1900)compandedformatandthe13-bituniformformatshallbeasdefinedinITU-TRecommendationG.721(supersededbyG.726),subclause4.2.1,sub-blockEXPANDandsubclause4.2.7,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 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)11(GSM06.10version8.0.2Release1999)1.6PrinciplesoftheRPE-LTPdecoderThesimplifiedblockdiagramoftheRPE-LTPdecoderisshowninfigure1.2.Thedecoderincludesthesamestructureasthefeed-backloopoftheencoder.Inerror-freetransmission,theoutputofthisstagewillbethereconstructedshorttermresidualsamples.Thesesamplesarethenappliedtotheshorttermsynthesisfilterfollowedbythede-emphasisfilterresultinginthereconstructedspeechsignalsamples.1.7SequenceandsubjectiveimportanceofencodedparametersAsindicatedinfigure1.1thethreedifferentgroupsofdataareproducedbytheencoderare:-theshorttermfilterparameters;-theLongTermPrediction(LTP)parameters;-theRPEparameters.Theencoderwillproducethisinformationinauniquesequenceandformat,andthedecodershallreceivethesameinformationinthesameway.Intable1.1,thesequenceofoutputbitsb1tob260andthebitallocationforeachparameterisshown.Thedifferentparametersoftheencodedspeechandtheirindividualbitshaveunequalimportancewithrespecttosubjectivequality.BeforebeingsubmittedtothechannelencodingfunctionthebitshavetoberearrangedinthesequenceofimportanceasgiveninGSM05.03.TherankinghasbeendeterminedbysubjectivetestingandtheprocedureusedisdescribedinannexA,subclauseA.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 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)12(GSM06.10version8.0.2Release1999)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==================================================================Sub-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 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)13(GSM06.10version8.0.2Release1999)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 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)14(GSM06.10version8.0.2Release1999)2TransmissioncharacteristicsThisclausespecifiesthenecessaryperformancecharacteristicsoftheaudiopartsforproperfunctioningofthespeechtranscoder.SometransmissionperformancecharacteristicsoftheRPE-LTPtranscoderarealsogiventoassistthedesignerofthespeechtranscoderfunction.TheinformationgivenhereisredundantandthedetailedspecificationsarecontainedinrecommendationGSM11.10.Theperformancecharacteristicsarereferredtothe13bituniformPCMinterface.NOTE:Tosimplifytheverificationofthespecifications,theperformancelimitsmaybereferredtoanA-orµ-law(PCS1900)measurementinterfaceaccordingtoITU-TRecommendationG.711.Inthisway,standardmeasuringequipmentsforPCMsystemscanbeutilizedformeasurements.Therelationshipbetweenthe13bitformatandtheA-orµ-law(PCS1900)compandedshallfollowtheproceduresdefinedinsubclause1.4.2.1Performancecharacteristicsoftheanalogue/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.Theindividualblocksaredescribedinthefollowingsubclauses.3.1FunctionaldescriptionoftheRPE-LTPencoderThePre-processingsectionoftheRPE-LTPencodercomprisesthefollowingtwosub-blocks:-offsetcompensation(3.1.1);-pre-emphasis(3.1.2).TheLPCanalysissectionoftheRPE-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 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)15(GSM06.10version8.0.2Release1999)TheShorttermanalysisfilteringsectionoftheRPE-LTPcomprisesthefollowingfoursub-blocks:-decodingofthequantizedLog.-AreaRatios(LARs)(3.1.8);-interpolationofLog.-AreaRatios(3.1.9);-transformationofLog.-AreaRatiosintoreflectioncoefficients(3.1.10);-shorttermanalysisfiltering(3.1.11).TheLongTermPredictor(LTP)sectioncomprises4sub-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).TheRPEencodingsectioncomprisesfivedifferentsub-blocks:-weightingfilter(3.1.18);-adaptivesampleratedecimationbyRPEgridselection(3.1.19);-APCMquantizationoftheselectedRPEsequence(3.1.20);-APCMinversequantization(3.1.21);-RPEgridpositioning(3.1.22).Pre-processingsection3.1.1OffsetcompensationPriortothespeechencoderanoffsetcompensation,byanotchfilterisappliedinordertoremovetheoffsetoftheinputsignalsotoproducetheoffset-freesignalsof.sof(k)=so(k)-so(k-1)+alpha*sof(k-1)(3.1.1)alpha=32735*2-153.1.2Pre-emphasisThesignalsofisappliedtoafirstorderFIRpre-emphasisfilterleadingtotheinputsignalsoftheanalysissection.s(k)=sof(k)-beta*sof(k-1)(3.1.2)beta=28180*2-15LPCanalysissection3.1.3SegmentationThespeechsignals(k)isdividedintonon-overlappingframeshavingalengthofT0=20ms(160samples).AnewLPC-analysisoforderp=8isperformedforeachframe.SIST EN 300 961 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)16(GSM06.10version8.0.2Release1999)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),whereavocaltractrepresentationconsistingofseriesofuniformcylindricalsectionsisassumed.Sucharepresentationcanbedescribedbythereflectioncoefficientsorthearearatiosofconnectedsections.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 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)17(GSM06.10version8.0.2Release1999)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-termanalysisfilteringsectionThecurrentframeofthespeechsignalsisretainedinmemoryuntilcalculationoftheLPCparametersLAR(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)sectionSIST EN 300 961 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)18(GSM06.10version8.0.2Release1999)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 V8.0.2:2003

ETSIETSIEN300961V8.0.2(2000-11)19(GSM06.10version8.0.2Release1999)3.1.15Coding/DecodingoftheLTPgainsThelongtermpredictiongainsbj,(j=0,.,3)areencodedwith2bitseach,accordingtothefollowingalgorithm:ifbj<=DLB(i)thenbcj=0;i=0ifDLB(i-1) ...