EUser Description, Speech Quality FactorsUser Description, Speech QualityFactors Ericsson Radio Systems AB24/1553-HSC 103 12 Uen Rev B1999-02-101 (29) Ericsson Radio Systems ABUser Description, Speech Quality Factors2 (29) 24/1553-HSC 103 12 Uen Rev B1999-02-10 Ericsson Radio Systems ABUser Description, Speech Quality FactorsContents1 Introduction................................................................................................... 52 Background................................................................................................... 73 What can be achieved?................................................................................ 94 Technical description, Speech Levels........................................................114.1 General .................................................................................................... 114.2 Algorithm..................................................................................................114.3 Main differences from CME 20 R6.1.......................................................134.4 Main controlling parameters.................................................................... 134.5 Value ranges and defaults values........................................................... 135 Technical description, Echo control...........................................................155.1 General .................................................................................................... 155.2 Algorithm..................................................................................................165.3 Main differences from CME 20 R6.1.......................................................175.4 Main controlling parameters, ECP101.....................................................175.5 Value ranges and defaults values, ECP101........................................... 185.6 Main controlling parameters, ECP303/ECP404...................................... 195.7 Value ranges and defaults values, ECP303/ECP404.............................195.8 Main controlling parameters, ECP323/ECP424...................................... 205.9 Value ranges and defaults values, ECP323/ECP424.............................205.10 Main controlling parameters, EC256c................................................... 205.11 Value ranges and defaults values, EC256c..........................................216 Technical description, Radio Network and Radio Network features......236.1 General .................................................................................................... 236.2 Main differences from CME 20 R6.1, Handover.....................................246.3 Main controlling parameters, Handover .................................................. 246.4 Value ranges and defaults values, handover..........................................247 Technical description, Transmission Network.......................................... 257.1 General .................................................................................................... 258 Abbreviations................................................................................................ 279 References.....................................................................................................2924/1553-HSC 103 12 Uen Rev B1999-02-103 (29) Ericsson Radio Systems ABUser Description, Speech Quality FactorsThis page is intentionally left blank4 (29) 24/1553-HSC 103 12 Uen Rev B1999-02-10 Ericsson Radio Systems ABIntroduction1 IntroductionThis document is intended as an engineering guideline for speechquality factors in the CME 20 system. It should be noted that eventhough this is a BSS document it also contains information about theEricsson MSC. Since the R6.1 release of the CME 20 system there arethree different speech codecs that can be used, two full rate codecs (FullRate and Enhanced Full Rate) and one half rate codec (Half Rate). Thisis of course dependent on transcoder hardware, TRA R4 or higher isrequired to be able to use EFR or HR. The upper limit of the speechquality is set by these three codecs. The speech codec (see ref. 1, ref. 2and ref. 3) quality is xed and the focus is thus on the speechdegradation factors. The following areas have been identied. Speech Levels:The speech levels affect speaker level, distortion and echocanceller performance. Echo control:Poor network echo cancelling results in disturbing echo for callsto the PSTN and PLMN with full duplex hands-free mobiles.Echo effect can also be caused by acoustic coupling in mobiles. Radio Network and Radio Network features:High bit error rate as a result of a low carrier/noise (C/N) and/orcarrier/interference (C/I) ratio causes interruptions or degradationof the speech. The speech degradation because of radioenvironment factors can be minimised by using the radio networkfeatures Discontinuous transmission (DTX), Power control andFrequency hopping. The use of the radio network feature DTXaffect the speech quality by removing the true background. Thehandover procedure creates a short speech interruption. Transmission Network:High bit error rate (BER) causes degradation of the speech. Thespeech quality is sensitive to BER on the A-bis and A-ter interface. Mobile stations:The implementation of audio functions in the mobile stationsaffects the speech quality, i.e. speaker, microphone and speechprocessing. The mobile stations is not further discussed in thisdocument.24/1553-HSC 103 12 Uen Rev B1999-02-105 (29) Ericsson Radio Systems ABIntroductionThis page is intentionally left blank6 (29) 24/1553-HSC 103 12 Uen Rev B1999-02-10 Ericsson Radio Systems ABBackground2 BackgroundOver the past years, more and more focus have been put on the speechquality in the CME 20 system. However it is not obvious to see whichfactors that affects the speech quality.24/1553-HSC 103 12 Uen Rev B1999-02-107 (29) Ericsson Radio Systems ABBackgroundThis page is intentionally left blank8 (29) 24/1553-HSC 103 12 Uen Rev B1999-02-10 Ericsson Radio Systems ABWhat can be achieved?3 What can be achieved?With this document the operator should be able to understand whichfactors that can affect the speech quality in the CME 20 system. Theoperator should also get a knowledge of how the different factors canbe controlled.24/1553-HSC 103 12 Uen Rev B1999-02-109 (29) Ericsson Radio Systems ABWhat can be achieved?This page is intentionally left blank10 (29) 24/1553-HSC 103 12 Uen Rev B1999-02-10 Ericsson Radio Systems ABTechnical description, Speech Levels4 Technical description, Speech Levels4.1 GeneralThe speech levels are important for the user perception of the speechbut also for the handling of the speech within the system.Low speech levels results in a low audio volume and that the transcodercan not utilise the full dynamic of the PCM coded speech.Too high speech levels result in distorted speech. The level ofdistortion is dependant on the top and average speech level of theindividual speaker.Clipping can occur both if the PCM coded speech level on the A-interface is too high and as a result of a too high amplication using theLevel Control in the transcoder.Unbalanced levels increase the risk for echo problems. Theperformance of the echo canceller is sensitive to a too large unbalancebetween the up- and downlink. The worst situation is when the uplinklevel is higher than the downlink level.High speech levels in the down link increase the risk for acoustic echoin the mobile.4.2 AlgorithmThe intention shall be to have the same line levels for the entiretelephone network. This is dependant on the transmission, andadjustments of the line level might be needed. In CME 20 the levelscan be adjusted with the Level Control function in the transcoder (TRA)and attenuated in the ETC (located in the MSC). The ETC can onlyattenuate down link levels.PSTNPLMNMSCMSCETCETCETCABTS TRCA-bisBSCA-terABTSA-bisBSC/TRCFigure 1 The level control in the transcoders (located in the TRC) can adjust the A -interface line levels. The ETC, in the MSC, can attenuate downlink line levelsfrom PSTN, PLMN and other MSCs. (The TRC can be co-located with the BSC orremote as shown in the picture).Normal line levels have an average of -16 to -22 dBm0 with a topfactor of about 16 dB. The individual differences can be very largethough. For the normal speaker the result is peak levels of -6 to 0dBm0. The clipping level is 3,14 dBm0 for PCM A-law coded speech24/1553-HSC 103 12 Uen Rev B1999-02-1011 (29) Ericsson Radio Systems ABTechnical description, Speech Levelsand 3,17 dBm0 for PCM -law coded speech (see ref. 4) and theclipping margin is then 3 dB, for the worst normal case.PCM Clipping LevelClipping marginTop factorNormal Level3.14 dBm00 dBm0-16 dBm0-22 dBm0Figure 2 Line level concepts (for A-law)Measurements of the line levels should be performed before makingline level adjustments. Adjustments shall only be performed if the leveldiffer from what can be considered as normal.Transcoder line level adjustmentThe line levels can be adjusted with the level control function in thetranscoder. The levels can be adjusted independently for both uplinkand downlink. The level control function has a value range of -12 to 12dB in steps of 1 dB. The level control is set for all TRAs in the TRC.The following general guidelines apply: The Level Control values shall be treated as an installationparameter. Changes shall only be related to an updatedtransmission plan. The function shall not be used as an additionalvolume control. The intention shall be to have the same Level Control settingswithin the whole PLMN. Within an MSC the values shall be thesame. The risk for increased echo problems when using Level Control,creating unbalanced levels, shall be considered. MS acoustic echo problems can occur when using high downlinkline levels. These echo problems vary between different mobileterminal types. The performance of the network echo canceller is degraded forunbalanced levels, especially if uplink is higher.12 (29) 24/1553-HSC 103 12 Uen Rev B1999-02-10 Ericsson Radio Systems ABTechnical description, Speech LevelsLine level adjustments, ETC AttenuatorsETC can attenuate the downlink line level from PSTN, MSCs and otherPLMNs. The attenuation, not possible for all types of ETCs, is set as anapplication system parameter. The attenuation should only be applied ifa permanent difference in the transmission plan exists, where allpossible connections, for this ETC, have the same line level.4.3 Main differences from CME 20 R6.1There is no main difference from CME 20 R6.1. The introduction ofremote TRC, split between BSC and TRC, which is introduced in R7 isshown in Figure 1 on page 11. The remote TRC will however notaffect the speech quality or line levels.4.4 Main controlling parametersThe Level Control function are controlled by the TRC command, RadioControl X-Ceiver Administration Line Level Change, RXLLC.ULP is the uplink positive line level adjustments in dB.ULM is the uplink negative line level adjustments in dB.DLP is the downlink positive line level adjustments in dB.DLN is the downlink negative line level adjustments in dB.4.5 Value ranges and defaults valuesParameternameDefaultvalueRecommendedvalueValue range UnitULP 0 0 0 to 12 dBULM 0 0 0 to 12 dBDLP 0 0 0 to 12 dBDLN 0 0 0 to 12 dB24/1553-HSC 103 12 Uen Rev B1999-02-1013 (29) Ericsson Radio Systems ABTechnical description, Speech LevelsThis page is intentionally left blank14 (29) 24/1553-HSC 103 12 Uen Rev B1999-02-10 Ericsson Radio Systems ABTechnical description, Echo control5 Technical description, Echo control5.1 GeneralEcho effects are present in all types of networks. The echo is notnoticed in the PSTN because of the short round trip delay. This isthough a problem in digital mobile systems because of the interleavingand processing delay. The round trip delay in CME 20 is about 180-200 ms. This means that the echo returns to the mobile with a 180-200ms delay (if satellite transmission are used the delay will be evenlonger). The echoes can be of two different types, hybrid and acoustic,see Figure 3 on page 15.The echoes generated outside the own PLMN are handled by the echocancellers in the CME 20 system. This is because the echo is generatedoutside the own PLMN, but can be heard in the GSM mobile.SpeakerMic180 ms round tripdelayEcho CancellerHybrid2-wires 4-wiresHands-free (duplex)Acoustic (nonlinear) echoes:Acoustic coupling between themobile speaker and the microphone,hands-free (duplex) mobile is theworst case.Hybrid (linear) echoes:4-wire to 2-wire connectionsPLMNPSTNPLMNFigure 3 The echoes generated in PSTN and other PLMN networks.Hybrid echo:The hybrid echoes are created in the PSTN network, by the hybrid usedwhen changing from four to two wire circuits. The hybrid normally24/1553-HSC 103 12 Uen Rev B1999-02-1015 (29) Ericsson Radio Systems ABTechnical description, Echo controlprovides an Echo Return Loss (ERL) of > 15 dB, the echo is 15 dBlower than the unreected signal.Acoustic echo:The acoustic echoes are created by acoustic coupling between speakerand microphone. The level of the acoustic echo is dependent on the EL(Echo Loss). Duplex hands-free mobiles has low EL, which createsacoustic echo of high level.In the own PLMN network the mobiles should handle the echo control.The mobiles should provide an EL of 46 dB (see ref. 5) to eliminatethe need for internal PLMN echo cancellers. This is hard to achievewith hands-free mobiles. The hands-free mobiles normally uses voiceswitching or echo suppressors to achieve the 46 dB EL requirement.The characteristics of the echo originated in the MS are very differentfrom those of the PSTN echo. The acoustics echo from the MS is muchmore non-linear (due to speech coding and decoding in the echo path)and the end path delay is very long (of the order of 200 ms). These arethe reasons why we cannot remove the MS echo with the same type ofecho canceller that is developed for the PSTN echo. The MCC (MobileCross-talk Control) function is specially designed to deal with theacoustic echo from the MS.5.2 AlgorithmEcho Canceller DescriptionThe basic function, see Figure 4 on page 16, of an echo canceller is tosubtract the echo from the near end, PSTN, speech. This is performedby creating a model of the speech, sent from the mobile side. Themodel is stored in a FIR lter. The FIR model is then used to subtractthe generated echo. The remaining echo is suppressed by the non-linearprocessor (NLP). The double talk detector (DTD) stops the FIR modeladaptation when double talk is detected the tone detector (TD) disablesthe echo canceller for data and fax communication).TDHybridNLPDTDTDFIRMobileFarendPSTN,PLMNNearendEcho CancellerFigure 4 Basic structure of an echo canceller.Basic functionality16 (29) 24/1553-HSC 103 12 Uen Rev B1999-02-10 Ericsson Radio Systems ABTechnical description, Echo controlThe CME 20 system can have pool and/or trunk echo cancellers. Echocancellers in pool means that the cancellers are treated as a commonresource where a canceller device is selected if needed. The echocanceller in pool, is connected directly to the group switch. The trunkecho canceller is installed on trunk bases. The trunk echo canceller isdisabled/enabled with control from the AXE, or from time slot 16signalling.MCC FunctionMCC is an optional function specially designed for the MS echoproblem. The ECP323 product, obtained by loading the ECP 323 DSPDSU on the ECP 303 HWP and with the ECP Software (SW) in AXE,is a network echo canceller that removes the echo originated in thePSTN network and in the same time features the MCC function, tocancel the acoustical echo originated in the mobile terminal.Different echo cancellersThe different echo cancellers provided by Ericsson is: ECP101The rst generation of Ericssons echo cancellers in pool. ECP303The second generation of Ericssons echo cancellers in pool. ECP404The same as ECP303 but built on the new hardware platformBYB501. ECP323/ECP424The same as ECP303/ECP404 but with the MCC function. EC256cThe echo canceller for trunk solutions. Manufactured by Tellabs.5.3 Main differences from CME 20 R6.1The main difference from CME 20 R6.1 is that the new echo cancellerECP404 has been added and also the new MCC functionality (ECP323and ECP424).5.4 Main controlling parameters, ECP101The echo canceller parameters are changed with the MSC commandNetwork Terminal Initial Data Change, NTIDC.The following control parameters exist: DTL (Double Talk Level)The DTL parameter species the minimum Echo Return Loss(ERL).The ERL species the loss (attenuation) between the original andthe reected signal.24/1553-HSC 103 12 Uen Rev B1999-02-1017 (29) Ericsson Radio Systems ABTechnical description, Echo control EPD (End Path Delay)The EPD parameter species the maximum, near end, delay. NLP (Non Linear processor)The NLP Parameter controls the level of suppression and ifcomfort noise shall be injected instead of the suppressed echo. TDM (Tone Disable Mode)The TDM parameter sets the disabling mode for fax and data.Disabling according to CCITT recommendations G.164 and G.165. LAW (PCM coding)The LAW parameter sets the PCM coding standard. Codingaccording to A-law or -law is supported.5.5 Value ranges and defaults values, ECP101Table 1ParameternameValuerangeInterpretation DefaultvalueCommentDTL 0, 0 dB 21, 3 dB2 6 dBThe performance of ECPOOL issensitive to the DTL setting.Lowering the DTL value effects theoverall echo cancellingperformance. i.e the recommendedsetting, 6 dB, shall not be changedunless connections with lower than6 dB ERL exist.EPD 8 to 64(steps of 8)ms 64 No change in performance can benoticed for lower EPD settings andthe parameter shall thus not bechanged.NLP 0, No NLP 21, NLP type 12, NLP type 1,noise injection3, NLP type 24 NLP type 2,noise injectionThe high clipping level, type1, andnoise injection are recommended.The type 2 have a 3 dB lowerclipping level.TDM 0, OFF 21, G.1642 G.165The TDM used is marketdependant. The TDM according toG.165 is recommended for betterfax and low speed dataperformance.LAW MULAW -law -ALAW A-lawThe PCM coding standard used ismarket dependent.18 (29) 24/1553-HSC 103 12 Uen Rev B1999-02-10 Ericsson Radio Systems ABTechnical description, Echo control5.6 Main controlling parameters, ECP303/ECP404The echo canceller parameters are changed with the MSC commandNetwork Terminal Initial Data Change, NTIDC.Note DTL is handled by the ECP303/ECP404 algorithm and theparameter only exists for ECP101.The following control parameters exist: EPD (End Path Delay)The EPD parameter species the maximum, near end, delay.Only settings with 16, 32 or 64ms are used. NLP (Non Linear processor)The NLP Parameter controls the level of suppression and ifcomfort noise shall be injected instead of the suppressed echo. TDM (Tone Disable Mode)The TDM parameter sets the disabling mode for fax and data.Disabling according to CCITT recommendations G.164 and G.165(see ref. 7 and ref. 8) is supported. LAW (PCM coding)The LAW parameter sets the PCM coding standard. Codingaccording to A-law or -law is supported.5.7 Value ranges and defaults values, ECP303/ECP404Table 2ParameternameValuerangeInterpretation DefaultvalueCommentEPD 16, 32,64ms 64 No change in performance canbe noticed for lower EPDsettings and the parameter shallthus not be changed.NLP 0, NLP disabled 21, NLP enabled2, NLP enabled, noiseinjectionThe NLP enabled with comfortnoise injection, 2 isrecommended.TDM 0, OFF 21, G.1642 G.165The TDM used is marketdependant. The TDM accordingto G.165 is recommended forbetter fax and low speed dataperformance.LAW MULAW -law -ALAW A-lawThe PCM coding standard usedis market dependent.24/1553-HSC 103 12 Uen Rev B1999-02-1019 (29) Ericsson Radio Systems ABTechnical description, Echo control5.8 Main controlling parameters, ECP323/ECP424The ECP323/ECP424 product has the same performance as ECP303/ECP404 except for NLP and TDM. NLP (Non Linear processor)The NLP parameter species the working mode of the NLP: off,on with or without comfort noise injection. TDM (Tone Disable Mode)The TDM parameter species at which tone the EC devicedisables during periods of voice-band data trafc.5.9 Value ranges and defaults values, ECP323/ECP424Table 3ParameternameValuerangeInterpretation DefaultvalueCommentNLP 0, NLP and MCCdisabled21, NLP and MCCenabled2, NLP and MCCenabled, noiseinjectionThe MCC is always enabledwhen the NLP is enabled. TheNLP enabled with comfort noiseinjection, 2 is recommended.TDM 0, OFF 11, G.1645.10 Main controlling parameters, EC256cThe echo canceller parameters are changed with the MSC commandNetwork Terminal Initial Data Change, NTIDC.The echo canceller EC256c is controlled with AXE commands, someadditional parameters can be changed from the echo cancellers frontpanel.AXE command operated parameters: EPD (End Path Delay)The EPD parameter species the maximum, near end, delay. HLC (High Level compensation)The HLC parameter controls the high level compensation of farend speech. NLP (Non Linear processor)The NLP Parameter controls the level of suppression and ifcomfort noise shall be injected instead of the suppressed echo. Parameters selectable by front panel control(Other parameters exist but with no effect on speech quality)20 (29) 24/1553-HSC 103 12 Uen Rev B1999-02-10 Ericsson Radio Systems ABTechnical description, Echo control ERL (Echo Return Loss)The ERL parameter species the minimum ERL which ispossible to handle. ERL species the loss (attenuation) betweenthe original and the reected signal. DTD (Data Tone Disabler)The DTD parameter sets the disabling mode for fax and data.Disabling according to CCITT recommendations G.164 and G.165(see ref. 6 and ref. 7) is supported.5.11 Value ranges and defaults values, EC256cTable 4ParameternameValuerangeInterpretation DefaultvalueCommentEPD 1 32 ms 33 64 msNo change in performance canbe noticed for lower EPDsettings and the parameter shallthus not be changed.HLC 0 deactivated 01 activatedNLP 000 to111111xx0 Off, canceller onlyx01 Off during doubletalk, CCITTx11 On, Continuously0x1 DST OFF, HardNLP1x1 DST ON,background noisetransparency"x" means that either 0 or 1 canbe used.ERL 0 0 dB 63 3 dB6 6 dBFront panel controlDTD Off G165G164 2100 Hz ToneFront panel controlG165 2100 Hz Tone +phase reversal24/1553-HSC 103 12 Uen Rev B1999-02-1021 (29) Ericsson Radio Systems ABTechnical description, Echo controlThis page is intentionally left blank22 (29) 24/1553-HSC 103 12 Uen Rev B1999-02-10 Ericsson Radio Systems ABTechnical description, Radio Network and Radio Network features6 Technical description, Radio Network andRadio Network features6.1 GeneralThe speech quality is degraded by high BER for the air interface. TheBER and frame erasure ratio (FER) are dependent on a number offactors such as fading and interference. Therefore a good cell planningis needed to avoid co-channel interference, adjacent-channelinterference, time dispersion and other types of radio interference. TheBER and FER caused by the radio network is the most importantspeech quality degradation factor. The degradation can be minimised byusing the radio network features DTX, Power control and Frequencyhopping. The handovers while moving from cell to cell will alsointroduce a speech quality disturbance.DTXThe radio network feature DTX (see ref. 8) reduces the totalinterference in the network, it only transmits when speech is detected.In normal conversation this will lead to a decreased transmitting time ofabout 50%. The general speech quality for the network can therefore beincreased. The use of DTX affects the speech quality, both positivelyand negatively. Positively by reducing the total interference level in thenetwork. Negatively by injecting comfort noise instead of the truebackground. This could be disturbing for connections with highbackground noise levels where the background is very different fromthat of the comfort noise generated, i.e. murmur backgrounds. It shouldbe noted that the DTX and comfort noise generation is part of thespeech codec and can therefore differ from one codec to another.Frequency hoppingFrequency hopping (see ref. 9) can reduce the effect on the speechquality caused by multipath fading and interference. The signal strengthvariations, or the interference, is broken up into pieces of duration shortenough for the interleaving and speech coding process to correct theerrors. The average speech quality is thus increased compared to a nonfrequency hopping network.Power controlDynamic power control (see ref. 10 and ref. 11) used together withfrequency hopping and DTX results in a further increase in theprotection against fading dips and interference. This is achieved by thefact that the output power is controlled with respect to received signalstrength as well as with respect to speech quality (BER). Theimprovement in interference protection can be utilised directly as animprovement in general speech quality. It can also be utilised inreplanning the radio network for high capacity, while leaving thegeneral speech quality constant.Quality based power control contributes to better speech quality.Dynamic MS & BTS power control introduced in CME 20 R6 BSSgives the following enhancements:24/1553-HSC 103 12 Uen Rev B1999-02-1023 (29) Ericsson Radio Systems ABTechnical description, Radio Network and Radio Network features enhanced signal strength based part that gives increased C/I gainsin the radio network compared with the existing power control, a quality based part that raises the power in the presence ofinterference, which gives generally better speech quality.HandoverAt handover there will be a short speech interruption in both downlinkand uplink. There will also be signalling going on in conjuction withthe handover. This signalling will steal speech frames and can by thatintroduce some degradation. This degradation can be minimized byoptimising the timer TIMER3105 and avoid unneccesary repetativesignalling.6.2 Main differences from CME 20 R6.1, HandoverThe default value for TIMER3105 has been changed from 4 to 6. Note!The recommended values for parameters TIMER3105 and Ny1 are 8and 18 respectively.6.3 Main controlling parameters, HandoverDuring a handover the system will send physical information messageson the new channel and repeat this messages until the mobile stationhas established layer 2. The system will however not send more thanNy1 number of messages. The following two parameters is set by theBSC command RAEPC. TIMER3105The TIMER3105 timer denes the time between repetition ofphysical information messages during the handover procedure. NOOFPHYSINFOMSG (Ny1)The NOOFPHYSINFOMSG parameter indicates the maximumnumber of repetitions of physical information messages during thehandover procedure. The parameter is sometimes referred to asNy1.6.4 Value ranges and defaults values, handoverParameter name DefaultvalueRecommendedvalueValuerangeUnitTIMER3105 6 8 0 to 255 centisecondsNOOFPHYSINFOMSG 35 18 0 to 255 times24 (29) 24/1553-HSC 103 12 Uen Rev B1999-02-10 Ericsson Radio Systems ABTechnical description, Transmission Network7 Technical description, TransmissionNetwork7.1 GeneralThe speech quality is dependent on a good transmission network. Highbit error rate (BER) on the A-bis and A-ter interface contributes todegraded speech. The PCM coded speech used between TRC and MSCis less sensitive to the effects of high BERs than the GSM coded speechtransmitted between the BTS and the TRC.The audible effects on speech quality due to increasing or decreasingBER, on the A-bis and A-ter interface, are unnoticeable providing thatthe transmission fulls the performance objectives stated in ref. 12.Requirements considering BER (steady state) on digital transmissionlinks are treated in the CCITT recommendations G821 ref. 12.24/1553-HSC 103 12 Uen Rev B1999-02-1025 (29) Ericsson Radio Systems ABTechnical description, Transmission NetworkThis page is intentionally left blank26 (29) 24/1553-HSC 103 12 Uen Rev B1999-02-10 Ericsson Radio Systems ABAbbreviations8 AbbreviationsBER Bit Error RateBSC Base Station ControllerBTS Base Transceiver StationDTX Discontinuous TransmissionEFR Enhanced Full RateEL Echo LossERL Echo Return LossETC Exchange Terminal CircuitFER Frame Erasure RateFIR Finite Impulse Response lterHR Half RateMCC Mobile Cross-talk ControlMSC Mobile service Switching CenterPCM Pulse Code ModulationPLMN Public Land Mobile NetworkPSTN Public Switched Telephone NetworkTRA Transcoding and Rate AdaptionTRC Transcoder Controller24/1553-HSC 103 12 Uen Rev B1999-02-1027 (29) Ericsson Radio Systems ABAbbreviationsThis page is intentionally left blank28 (29) 24/1553-HSC 103 12 Uen Rev B1999-02-10 Ericsson Radio Systems ABReferences9 References1 GSM TS 06.10, Full rate speech transcoding2 GSM TS 06.20, Half rate speech transcoding3 GSM TS 06.60, Enhanced full rate speech transcoding4 CCITT G.711, Pulse Code Modulation (PCM) of voice frequencies5 GSM TS 03.50, Transmission Planning Aspects of the SpeechService in the GSM Public Land Mobile Network (PLMN)System.6 CCITT G.164, Echo suppressors7 CCITT G.165, Echo cancellers8 User Description, DTX, 7/1553-HSC 103 12Uen9 User Description, Frequency hopping, 8/1553-HSC 103 12Uen10 User Description, Dynamic BTS power control, 6/1553-HSC 10312Uen11 User Description, Dynamic MS power control, 5/1553-HSC 10312Uen12 CCITT G.821, Error performance of an international digitalconnection operating at a bit rate below the primary rate andforming part of an integrated services digital network.24/1553-HSC 103 12 Uen Rev B1999-02-1029 (29) Ericsson Radio Systems AB