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
2
Juan
J. R
amos
-Muñ
oz, Á
ngel
M. G
ómez
, Jua
n M
. Lop
ez-S
oler
Uni
vers
ity o
f Gra
nada
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
3
Juan
J. R
amos
-Muñ
oz, Á
ngel
M. G
ómez
, Jua
n M
. Lop
ez-S
oler
Uni
vers
ity o
f Gra
nada
Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005.
Introduction
Background
Bursts degrade the perceived quality in Voice over IP
VoIP services are extremely delay concerned
Enhanced VoIP services must be subjectively
evaluated
4
Juan
J. R
amos
-Muñ
oz, Á
ngel
M. G
ómez
, Jua
n M
. Lop
ez-S
oler
Uni
vers
ity o
f Gra
nada
Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005.
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
5
Juan
J. R
amos
-Muñ
oz, Á
ngel
M. G
ómez
, Jua
n M
. Lop
ez-S
oler
Uni
vers
ity o
f Gra
nada
Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005.
Basic and Multi-flow Block Interleavers Algorithms
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
6
Juan
J. R
amos
-Muñ
oz, Á
ngel
M. G
ómez
, Jua
n M
. Lop
ez-S
oler
Uni
vers
ity o
f Gra
nada
Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005.
Basic and Multi-flow Block Interleavers Algorithms
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
7
Juan
J. R
amos
-Muñ
oz, Á
ngel
M. G
ómez
, Jua
n M
. Lop
ez-S
oler
Uni
vers
ity o
f Gra
nada
Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005.
Basic and Multi-flow Block Interleavers Algorithms
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.
8
Juan
J. R
amos
-Muñ
oz, Á
ngel
M. G
ómez
, Jua
n M
. Lop
ez-S
oler
Uni
vers
ity o
f Gra
nada
Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005.
Basic and Multi-flow Block Interleavers Algorithms
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.
9
Juan
J. R
amos
-Muñ
oz, Á
ngel
M. G
ómez
, Jua
n M
. Lop
ez-S
oler
Uni
vers
ity o
f Gra
nada
Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005.
Basic and Multi-flow Block Interleavers Algorithms
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
10
Juan
J. R
amos
-Muñ
oz, Á
ngel
M. G
ómez
, Jua
n M
. Lop
ez-S
oler
Uni
vers
ity o
f Gra
nada
Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005.
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
11
Juan
J. R
amos
-Muñ
oz, Á
ngel
M. G
ómez
, Jua
n M
. Lop
ez-S
oler
Uni
vers
ity o
f Gra
nada
Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005.
Experimental Results
Experimental results were obtained by simulation. We adopt a single error model based on a Markov chain (Yajnik et al [9]).
12
Juan
J. R
amos
-Muñ
oz, Á
ngel
M. G
ómez
, Jua
n M
. Lop
ez-S
oler
Uni
vers
ity o
f Gra
nada
Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005.
Experimental Results
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
13
Juan
J. R
amos
-Muñ
oz, Á
ngel
M. G
ómez
, Jua
n M
. Lop
ez-S
oler
Uni
vers
ity o
f Gra
nada
Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005.
Experimental Results
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
14
Juan
J. R
amos
-Muñ
oz, Á
ngel
M. G
ómez
, Jua
n M
. Lop
ez-S
oler
Uni
vers
ity o
f Gra
nada
Intelligibility Evaluation of a VoIP Multi-flow Block Interleaver. IWAN 2005.
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