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Federico M. Ang EE 296 (Preliminary Work Plan)

2003-16896

Thesis Topic: Joint source-channel coding for low bit rate wideband speech transmission over packet-

switched networks

Objectives:

1.  Familiarization with the involved wideband speech coder algorithms.

2.  Verify the MELP bitstream residual redundancies computation results presented in the paper by

Fazel and Fuja.

3.  To apply the concept of taking advantage of the residual redundancies to other parametric

wideband speech coders.

Background:

From information theory, residual redundancy is taken as an average measure of excess from a

given number of bits used to represent information in a bit stream. Based on the paper by Fazel and

Fuja, it is possible to achieve substantial gain from a MELP speech coder by exploiting the inherent

redundancy that can be observed from its bitstream. This redundancy, in turn, can be quantified by

modelling every change in the parameters involved within the coder as one-step Markov chains. From

this probabilistic model, transition probabilities between each possible value of a parameter can be

computed. The probabilistic values then determine the residual redundancy based on the frequency of 

changes that is observed. These a priori information can be used to tune any source or channel decoder

(i.e. Source-Optimized Channel Coding (SOCC), Source-Controlled Channel Decoding (SCCD)) to improve

the coding gain.

Two (2) low bit rate wideband speech codecs are being developed at the DSP laboratory,

namely: The (1) Wideband Linear Predictive (WLP) and the (2) Wideband Sinusoidal (WS). The WLP

makes use of the MELP speech codec within its split-band coding scheme and is a good candidate for

gain improvement. As for the WS coder, residual redundancy computation could also be applied

because of its parametric nature. Once we have proven that both coders have significant residual

redundancies within their bitstreams, then the development of a joint source-channel coding scheme

would be an effective solution to improve the usual error control schemes inherent in channel codes.

Methodology: 1.  Understand how each codec runs in MATLAB.

2.  Prepare speech training set from the TIMIT database (standard database used).

3.  Extract the parameters within the bitstream.

4.  Decide on the parameters to be analyzed.

a.  For the WLP, the parameters of interest are based on the paper

b.  For the WS, the parameters are the amplitudes and the frequencies

5.  Compute for the transition matrices, the entropies, and the residual redundancies for both

codecs.

6.  Compare with the results from the paper and evaluate.