Tommi Koistinen Nokia Networks

Voice Coding in 3G NetworksS-38.130 Postgraduate Course in Telecommunications

Spring 2001

Tommi KoistinenNokia Networks

2 © NOKIA Backgrounds_c.PPT/ 27.01.2000 / ao

ContentsPART I� Short introduction to 3GPP reference architecture models

� Media Gateway (MG)� Multimedia Resource Functions (MRF)

PART II� Speech compression � why ?� Tandem avoidance� Adaptive Multirate (AMR) speech codec� Wideband speech coding (AMR-WB)� Demonstrations


3GPP Release 99� R99; first phase of 3G� entities involved with speech processing are circled with red

UTRANUTRAN

SGSNSGSN GGSNGGSN

MTMT

3G MSC3G MSC

HLRHLR

Multimedia IP networksMultimedia IP networks

PSTN/legacy networksPSTN/legacy networksTranscoderTranscoder

Iu-PS

Iu-CS


3GPP R4� separates MSC to MSC Server and to Media Gateway

UTRANUTRAN

SGSNSGSN GGSNGGSN

MTMT

MSC ServerMSC Server

HSS/CSCFHSS/CSCF


PSTN/legacy networksPSTN/legacy networks

MGWMGW

Iu-PS

Iu-CScontrol

MGWMGWIu-CS

user data



3GPP R4�R5� IP Multimedia Subsystem (IMS)

UTRANUTRAN

SGSNSGSN GGSNGGSN

MTMT

HSS/CSCFHSS/CSCF



MRFMRF

Iu-PS

MGWMGW


Media Gateway� support for several interfaces (A-interface for 2G and Iu-interface for 3G)

and for several transmission protocols (ATM, IP, TDM)� support for several codecs including the Adaptive Multirate (AMR) codec

and future coming wideband codecs� electric and acoustic echo cancellation� announcement services� DTMF and call progress tone generation and detection� support for fax/modem/data protocols� support for Tandem Free Operation (TFO) and Transcoder Free Operation

(TrFO)� bad frame handling� IP protocol handling (RTP/RTCP, encryption, QoS support)


Media Resource Functions Unit� audio/video conferencing services� speech enhancements ?

UTRANUTRAN

SGSNSGSN GGSNGGSN

MTMT


MRFMRFUTRANUTRANMTMT IP terminalIP terminal


Tandem Avoidance in 2G

PSTN64 kbpsPSTN

64 kbps MSCMSCMSCMSC

Transcoder64 ↔ 16

Transcoder64 ↔ 16

BSSBSS

MSMS

BSSBSS

MSMS

Transcoder64 ↔ 16

Transcoder64 ↔ 16

Current status: no Tandem Free Operation (TFO)


PSTN48(16) kbps

PSTN48(16) kbps MSCMSCMSCMSC

Transcoder16 ↔ 16

Transcoder16 ↔ 16

BSSBSS

MSMS

BSSBSS

MSMS

Transcoder16 ↔ 16

Transcoder16 ↔ 16


Better speech quality with Tandem Free Operation (TFO)



Transcoder Free Operation (TrFO)AMR modes are negotiated by inband procedure.

UTRANUTRANMTMT



MGWMGW MGWMGW


AMR

AMR ?

GSM BSSGSM BSS

EFR!

AMR ?


Speech Compression � Why ?

� to save transmission capacity� to save radio resources� to save storage capacity

� more compression (40%) with voice activity detection (VAD)and discontinuous transmission (DTX)

� error robustness with bad frame handling (BFH)


Speech coding techniques� Waveform coders

� correlation between adjacent samples� G.711, G.726 ADPCM etc.

� Analysis-by-synthesis types of coders� Code Excited Linear Prediction (CELP)� G.723, G.729, GSM EFR, GSM AMR


The CELP model

A(z)1 s(n)^

+

v(n)

c(n)

u(n)

gc

fixedcodebook

adaptive codebook gp

LP synthesis

post-filtering s'(n)^

�vocal tract��glottis�


Adaptive Multirate (AMR) speech codec� only mandatory codec for 3G� improved speech quality in both half-rate and full-rate modes

by means of codec mode adaptation i.e. varying the balancebetween speech and channel coding for the same gross bit-rate

� ability to trade speech quality and capacity smoothly andflexibly by a combination of channel and codec modeadaptation; this can be controlled by the network operator on acell by cell basis

C/I

MOS

Mode 1Mode 2Mode 3


AMR source rates

Codec mode Source codec bit-rate AMR_12.20 12.20 kbit/s FR AMR_10.20 10.20 kbit/s FR AMR_7.95 7.95 kbit/s FR / HR AMR_7.40 7.40 kbit/s FR / HR AMR_6.70 6.70 kbit/s FR / HR AMR_5.90 5.90 kbit/s FR / HR AMR_5.15 5.15 kbit/s FR / HR AMR_4.75 4.75 kbit/s FR / HR AMR_SID 1.80 kbit/s FR / HR


Structure of AMR encoder

windowingand

autocorrelationR[ ]

Levinson-Durbin

R[ ] A(z)

A(z)

LSPquantization

compute targetfor

innovation

update filtermemories fornext subframe

Open-loop pitch search Adaptive codebooksearch

Innovative codebooksearch

Filter memoryupdate

interpolation

subframesLSP A(z)

LSP

computeweightedspeech

(4 subframes)

findopen-loop pitch

find best innovation

fixed codebook

gain quantization

A(z)^

x(n)

pitchindex

codeindex

frame subframe

s(n)compute targetfor adaptivecodebook

Tofind best delay

and gain

x(n)

computeimpulseresponse

A(z)^

A(z)h(n)

h(n)

A(z)

LPC analysis(twice per frame)

A(z)

(twice per frame)

x (n)2

quantizeLTP-gain

computeadaptive

codebookcontribution

LSPindices

LTPgain

index

gain indexfixed codebook

interpolationfor the 4

subframesLSP A(z)^

for the 4

Pre-processing

Pre-processing

computeexcitation


Encoder output

Parameter 1st 2nd 3rd 4th Total2 LSP sets 38 Pitch delay 9 6 9 6 30 Pitch gain 4 4 4 4 16 Fixed code 35 35 35 35 140 Fixed gain 5 5 5 5 20 Total 244


Structure of AMR decoder

LSPindices

decode LSP

interpolation of LSP for the4 subframes

LSP

decodeadaptivecodebook

decodeinnovativecodebook

pitchindex

codeindex

decodegains

A(z)^

constructexcitation

frame subframe post-processing

s'(n)^s(n)^post filter

gainsindices

synthesisfilter


Demostration I: Full Rate vs. AMR-NB

Erroneous channel (C/I= 26�4 dB) :

1. sample: FR 13 kbps2. sample: AMR-NB 5.9-12.2 kbps


Wideband speech coding� Narrowband 300 � 3400 Hz� Wideband 50 � 7000 Hz

� Wideband AMR speech codec (3GPP R5)


AMR-WB source rates

Codec mode Source codec bit-rateAMR-WB_23.85 23.80 kbit/s AMR-WB_23.05 23.05 kbit/s AMR-WB_19.85 19.85 kbit/s AMR-WB_18.25 18.25 kbit/s AMR-WB_15.85 15.85 kbit/s AMR-WB_14.25 14.25kbit/s AMR-WB_12.65 12.65 kbit/s AMR-WB_8.85 8.85 kbit/s AMR-WB_6.6 6.6 kbit/s AMR-WB_SID 1.75 kbit/s


EFR vs. AMR-NB vs. AMR-WB(in 16 kbps full rate traffic channel)

Excellent

Very good

Unacceptable

Poor

Good

Error-free

Carrier-to-interface ratio (dB)

13 10 7 4

Subje

ctiv

e sp

eech

qual

ity

AMR-WB

AMR-NB

EFR


Demostration II: AMR-NB vs. AMR-WB

Clean speech (highest modes):

1. sample: AMR-NB 12.2 kbps2. sample: AMR-WB 23.85 kbps


Demostration III: GSM EFR vs. AMR-WB

Erroneous channel:

1. sample: GSM EFR 12.2 kbps2. sample: AMR-WB 6.6-14.25 kbps


Demostration IV: AMR-NB vs. AMR-WB

Music (highest modes):

1. sample: AMR-NB 12.2 kbps2. sample: AMR-WB 23.85 kbps

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Tommi Koistinen Nokia Networks