juan j. ramos-muñoz, angel m. gómez, juan m. lopez-soler

Juan J. Ramos-Muñoz, Angel M. Gómez,Juan M. Lopez-Soler

Intelligibility Evaluation of a

VoIP Multi-flow Block Interleaver

Signal Theory, Telematics and

Communications Department

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Juan

J. R

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M. G

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, Jua

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Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005.

Outline

Introduction

Basic and Multi-flow Block Interleavers Algorithms

Intelligibility Estimation

Experimental Results

Conclusion

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Introduction

Background

Bursts degrade the perceived quality in Voice over IP

VoIP services are extremely delay concerned

Enhanced VoIP services must be subjectively

evaluated

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Introduction

In this work

We contribute to demonstrate some perceptual benefits that can be obtained by using active routers in VoIP

We propose a new delay-aware interleaver to mitigate the bursty-error-prone nature of IP

We evaluate the service performance by using Automatic Speech Recognition

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Given and an interleaver is defined by

Basic TypeI(s): to face bursts of length equal to s packets, with the minimum incurred delay, an (s x s) matrix is required Packets are written by rows, from left to right and from top to bottom. Packets are read by columns, from bottom to top and from left to right.

Type I(s) maximum interleaver delay is given by

Type I(s) is limited to such that

For typical VoIP values andTypeI(s) is restricted to bursts with length s < 5

ia ib ( ): / i ia b Z Z

max .( 1)D s s

max.( 1). fs s t d s

max 300d ms 20ft ms

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M. G

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We interleave packets from different flows to face consecutive losses by introducing a tolerable delay

We use the reference TypeII(nf) and propose TypeII(nf,s) where nf is the number of available flows and s is the maximum expected burst length

Round-robin interleaver (TypeII(nf)) is suited for nf ≥ s it requires one (nf x 1) interleaver matrix to write the matrix each row will be assigned to a single flow. the matrix will be read from bottom to top if no switching delay is assumed then Drawback: when nf < s, TypeII(nf) interleaver does not isolate all the

packet losses

max 0D

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M. G

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, Jua

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The proposed TypeII(nf,s) assures the isolation of losses for a given (nf ,s) pair of values, even when nf < s, with tolerable (bounded) delay

Memory requirements If s is a multiple of nf then one (s x s) matrix is

required. Otherwise, nf squared (s x s) matrices are needed.

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Let us defineRi

j as the number of consecutive rows that the flow i will be assigned for matrix j.rem(a,b) as the remainder of the integer division a/b.int(a) largest integral value not greater than a.

TypeII(nf,s) matrix writing procedure First matrix:

Ri1 = int(s/nf), for i = { 1, 2, …, nf - rem(s,nf)}.

Rj1 = int(s/nf) + 1 for j = { n f -rem(s,nf), nf -rem(s,nf)+1, …, nf}

Next j = 2, …, nf matrices and flows i = 2, …, nf

If Ri(j-1) = int(s/nf)+1 and R(i-1)

(j-1) = int(s/nf) then

Rij = int(s/nf) and R(i-1)

j = int(s/nf)+1

Type II(nf,s) matrix reading procedure Packets are read by columns, from bottom to top and from left to right.

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TypeII(nf ,s) maximum delay Dmax is given by

Dmax =º

where

r = rem(s,nf )

d = int((s-r) / nf )

For typical VoIP values andfor the best case TypeII(nf ,s) interleaver scatters bursts up to s < 15

favorably compared to TypeI(s) limited to s < 5

s·(r·(d +1)-1-(r - 1)·d) if r (nf - r) s·(r·(d +1)-1-((r - 1)·d+2·r - nf -1)) if r > (nf - r)

max 300d ms 20ft ms

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J. R

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-Muñ

oz, Á

ngel

M. G

ómez

, Jua

n M

. Lop

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nada


Intelligibility Estimation

For performance evaluation, we propose to use a high level end-user intelligibility estimation: ASR rate

Compared to MOS, ASR has lower cost and is more reproducible

For end-user intelligibility estimation ASR rate can be more suitable than other measures like PESQ (P.862) or the E-model

The Word Error Rate is defined by

100i s d

t

n n nWERn

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Experimental results were obtained by simulation. We adopt a single error model based on a Markov chain (Yajnik et al [9]).

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ngel

M. G

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, Jua

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For ASR evaluation we use the connected digit Project Aurora 2 database

The speech recognizer is based on eleven 16-state continuous Hidden Markov Models (HMM)

The HMM models are trained from a set of 8440 noise-free sentences, while the out-of-train-test set comprises 4004 noise-free sentences

More details are explained in the printed version of the paper

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J. R

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ngel

M. G

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, Jua

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II(nf ) II(nf ,s) I(s) nf WER s WER Dmax s WER Dmax

2 4.610 0.060 3 3.080 0.120 5 2.892 0.200 5 1.595 0.400

2

5.401

6 2.255 0.240 6 1.540 0.600 3 4.333 7 1.831 0.280 7 1.307 0.840 4 3.419 8 1.848 0.160 8 1.289 1.120 5 2.875 10 1.567 0.200 10 1.325 1.800 6 2.420 12 1.449 0.240 12 1.263 2.640 7 1.968 14 1.381 0.280 14 1.340 3.640 8 1.819 9 1.626 0.180 9 1.304 1.440 9 1.613 10 1.526 0.200 10 1.285 1.800 10 1.611 11 1.533 0.220 11 1.282 2.200 12 1.534 13 1.455 0.260 13 1.322 3.120

WER and Dmax (seconds) obtained values

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Juan

J. R

amos

-Muñ

oz, Á

ngel

M. G

ómez

, Jua

n M

. Lop

ez-S

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Uni

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f Gra

nada


Conclusion

Compared to a single-flow approach, our proposed interleaver reduces the packet delay and makes it applicable under conditions where the reference scheme is unfeasible.

Compared to the round-robin multi-flow interleaver, our proposed scheme increases the perceived end-user intelligibility (WER)

With a slight penalty on the introduced delay

We propose to consider ASR as a tool to measure VoIP services enhancements.

Future work: by setting up mapping functions for ASR rate to human intelligibility for ASR rate to MOS score

and using it together with AN technology, enhanced VoIP services can be envisaged.

Thank you for your attention

juan j. ramos-muñoz, angel m. gómez, juan m. lopez-soler

Documents

typeiinf interleaver

s x s matrix

s packets

length s

s wherenf

interleaver matrixto

maximum interleaver

nf squared s x s matrices