Voice Coding in 3G 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 BSSEFR!

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)

g c

fixedcodebook

adaptive codebook g p

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 balance between speech and channel coding for the same gross bit-rate

• ability to trade speech quality and capacity smoothly and flexibly by a combination of channel and codec mode adaptation; this can be controlled by the network operator on a cell 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

w in d o w in ga n d

a u to co rre la tio nR [ ]

L e v in so n -D u rb in

R [ ] A (z)

A (z)

L S Pqu a n tiza t io n

co m p u te ta rg e tfo r

in nov a tio n

u p d a te filte rm e m o ries fo rn e x t su b fram e

O p en - lo o p p itc h se a rc h Adaptive codebooksearch

Innova tive codebooksearch

F ilter m em oryupdate

in te rp o la tio n

su b fra m esL SP A(z)

L S P

c o m p u tew e ig h te d

sp e e c h(4 su b fra m e s )

findo p en -lo o p p itc h

fin d b e s t in n o v a tio n

f ix e d c o d e bo o k

g a in q u a n t iz a tio n

A(z)^

x(n)

pitchind ex

c o d ein d ex

fram e subfram e

s(n)c om p u te targ e t

fo r ad aptiv eco d eb oo k

T ofin d b e s t d e la y

a nd g a in

x(n)

c om p uteim p u lse

re sp o n s eA(z)^

A(z)h(n)

h(n)

A (z)

LP C analysis(tw ice per fram e)

A (z)

(tw ice per fram e)

x (n)2

q u a n tizeL T P -g a in

com puteadaptive

codebookcontribu tio n

L S Pind ic e s

L T Pg a in

in d e x

g a in in d e xfix e d co d eb o o k

in te rp o la t io nfor th e 4

su b fra m e sL SP A(z)^

fo r th e 4

P re - p ro c e ss in g

Pre-pro cessing

c om p u tee xc ita tio n


Encoder output

Parameter 1st 2nd 3rd 4th Total 2 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

L S Pin dices

d eco de L S P

inte rp o la tio n o f L S P fo r th e4 su b fram e s

L S P

dec o dea d aptiv e

c od ebo ok

d eco deinn ov ativeco de bo ok

pitchindex

cod eindex

de codegains

A (z)^

con struc tex c ita tio n

fram e sub fram e post-p rocess ing

s'(n )^s(n)^p o st f il te r

gainsind ices

synthe sisfilter


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-rate AMR-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-freeCarrier-to-interface ratio (dB)

13 10 7 4

Subj

ecti

ve s

peec

h qu

alit

yAMR-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

Voice Coding in 3G Networks

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