1. Scalable Speech Coding for IP Networks
Koji Seto
Signal Processing Research Lab. (SPRL),
Department of Electrical Engineering,
Santa Clara University, CA 95053, USA
IEEE Signal Processing Society Santa Clara Valley Chapter
Ph.D. Elevator Pitch to Professionals
Wednesday Dec. 9, 2015

2. However, the iLBC lacks some of the key features:
Motivation
Transition from the PSTN to an all IP Network (Voice over IP)
Challenge of VoIP:
Lack of guarantee for reasonable speech quality because of the possibility of packet loss.
Requires High Robustness to Packet Loss
Most current speech codecs [CELP]:
Frame dependency causes error propagation in the case of packet loss!!
Solution:
CELP + Side Information
Frame-independent Coding [iLBC (internet Low Bit-rate Codec)]
However, the iLBC lacks some of the key features:
Rate Flexibility
Scalability
Wideband Support

3. Proposed codec Block diagram of the encoder+ –
Multi-Rate iLBC Enc.
Layer 1
Lower-band signal
HPF
50Hz
QMF Analysis Filter Bank
LPF
3kHz
(-1)n
Multi-Rate iLBC Dec.
TDBWE Enc.
TDBWE Dec.
Wideband input signal
Higher-band signal
Layer 5
Layer 2
WPT/MDCT
(0–4 kHz)
AVQ Dec.
Perceptual Weighting
(4–8 kHz)
AVQ
(0–1or2 kHz)
Layer 3
Layer 4
(1or2–8 kHz)
(0–8 kHz)
Rate Flexibility: by encoding in the frequency domain
Scalability: by encoding the coding error from a lower layer
Wideband Support: by employing bandwidth scalability

4. Note: PLC algorithm is not optimized for our proposed codec
Proposed codec was developed by adding the following three functionalities to the iLBC
Rate Flexibility: by encoding in the frequency domain
Scalability: by encoding the coding error from a lower layer
Wideband Support: by employing bandwidth scalability
Proposed Codec using the WPT (Wavelet Transform) and the MDCT vs. G.729.1
Clean channel condition
Lossy channel condition
(16 kbps)
Note: PLC algorithm is not optimized for our proposed codec

5. Key Contributions
A Scalable Wideband Speech Codec for IP Networks using the iLBC was developed by adding Rate Flexibility, Scalability, and Wideband Support to the original iLBC.
This work shows that there is a convincing alternative option to the current industry trend for codec design, which is to consider a frame-independent codec such as the iLBC-based codec as a choice of the core-layer codec.
This work also shows that using the wavelet transform (WT) instead of the MDCT to encode the coding error from a core codec is an effective technique to use possibly for any codec.