1. Voice Coding in 3G Networks
S Postgraduate Course in Telecommunications
Spring 2001
Tommi Koistinen
Nokia Networks

2. Contents
PART 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

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

4. 3GPP R4
separates MSC to MSC Server and to Media Gateway

5. 3GPP R4…R5
IP Multimedia Subsystem (IMS)

6. 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)

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

8. Tandem Avoidance in 2G
Current status: no Tandem Free Operation (TFO)

9. Tandem Avoidance in 2G
Better speech quality with Tandem Free Operation (TFO)

10. Tandem Avoidance in 3G Transcoder Free Operation (TrFO)
AMR modes are negotiated by inband procedure.

11. 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)

12. 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

13. The CELP model
”vocal tract”
”glottis”

14. 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

15. AMR source rates

16. Structure of AMR encoder

17. Encoder output

18. Structure of AMR decoder

19. Demostration I: Full Rate vs. AMR-NB
Erroneous channel (C/I= 26…4 dB) :
1. sample: FR 13 kbps
2. sample: AMR-NB kbps

20. Wideband speech coding
Narrowband 300 – 3400 Hz
Wideband 50 – 7000 Hz
Wideband AMR speech codec (3GPP R5)

21. AMR-WB source rates

22. EFR vs. AMR-NB vs. AMR-WB (in 16 kbps full rate traffic channel)
Excellent
AMR-NB
Very good
Subjective speech quality
EFR
Good
Poor
Unacceptable
Error-free 13 10 7 4
Carrier-to-interface ratio (dB)

23. Demostration II: AMR-NB vs. AMR-WB
Clean speech (highest modes):
1. sample: AMR-NB 12.2 kbps
2. sample: AMR-WB kbps

24. Demostration III: GSM EFR vs. AMR-WB
Erroneous channel:
1. sample: GSM EFR 12.2 kbps
2. sample: AMR-WB kbps

25. Demostration IV: AMR-NB vs. AMR-WB
Music (highest modes):
1. sample: AMR-NB 12.2 kbps
2. sample: AMR-WB kbps