Download - Tommi Koistinen Nokia Networks
Voice Coding in 3G NetworksS-38.130 Postgraduate Course in Telecommunications
Spring 2001
Tommi KoistinenNokia Networks
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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
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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
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3GPP R4� separates MSC to MSC Server and to Media Gateway
UTRANUTRAN
SGSNSGSN GGSNGGSN
MTMT
MSC ServerMSC Server
HSS/CSCFHSS/CSCF
Multimedia IP networksMultimedia IP networks
PSTN/legacy networksPSTN/legacy networks
MGWMGW
Iu-PS
Iu-CScontrol
MGWMGWIu-CS
user data
MSC ServerMSC Server
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3GPP R4�R5� IP Multimedia Subsystem (IMS)
UTRANUTRAN
SGSNSGSN GGSNGGSN
MTMT
HSS/CSCFHSS/CSCF
Multimedia IP networksMultimedia IP networks
PSTN/legacy networksPSTN/legacy networks
MRFMRF
Iu-PS
MGWMGW
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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)
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Media Resource Functions Unit� audio/video conferencing services� speech enhancements ?
UTRANUTRAN
SGSNSGSN GGSNGGSN
MTMT
Multimedia IP networksMultimedia IP networks
MRFMRFUTRANUTRANMTMT IP terminalIP terminal
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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)
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PSTN48(16) kbps
PSTN48(16) kbps MSCMSCMSCMSC
Transcoder16 ↔ 16
Transcoder16 ↔ 16
BSSBSS
MSMS
BSSBSS
MSMS
Transcoder16 ↔ 16
Transcoder16 ↔ 16
Tandem Avoidance in 2G
Better speech quality with Tandem Free Operation (TFO)
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Tandem Avoidance in 3G
Transcoder Free Operation (TrFO)AMR modes are negotiated by inband procedure.
UTRANUTRANMTMT
MSC ServerMSC Server
PSTN/legacy networksPSTN/legacy networks
MGWMGW MGWMGW
MSC ServerMSC Server
AMR
AMR ?
GSM BSSGSM BSS
EFR!
AMR ?
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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)
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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
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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�
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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
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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
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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
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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
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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
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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
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Wideband speech coding� Narrowband 300 � 3400 Hz� Wideband 50 � 7000 Hz
� Wideband AMR speech codec (3GPP R5)
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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
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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
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Demostration II: AMR-NB vs. AMR-WB
Clean speech (highest modes):
1. sample: AMR-NB 12.2 kbps2. sample: AMR-WB 23.85 kbps
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Demostration III: GSM EFR vs. AMR-WB
Erroneous channel:
1. sample: GSM EFR 12.2 kbps2. sample: AMR-WB 6.6-14.25 kbps
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Demostration IV: AMR-NB vs. AMR-WB
Music (highest modes):
1. sample: AMR-NB 12.2 kbps2. sample: AMR-WB 23.85 kbps