VoIP Quality Study Using E-Model Extension

Wireless Access Research
Adil Raja August 2007
A Methodology for Deriving VoIP
Equipment Impairment Factors for a
Mixed NB/WB Context
Adil Raja
13th August, 2007
Wednesday 14 November 2012

VoIP- The Shift to WB Paradigm
• The NB and WB would have to coexist for
some time.
 i.e. operate either in cascade or in parallel.
• This work proposes an extension to E-Model
for the parallel case.

The E-Model
• An Instrumental Model initially designed for
NB handset telephony.
• R= R0-Is-Id-Ie,eff+A
• R0=93.2 – the basic SNR.
• Is - simultaneous impairments e.g. OLR, non-
optimum sidetone.
• Id - e.g e2e delay and echo.
• Ie,eff Impairments due to low-bitrate codecs and
packet loss.
• A – Advantage factor.

The E-Model…
• R <-> MOS

Moller’s WB extension to E-Model
• Consider Two experiments
• Each experiment is composed of two sets of speech
samples.
• MOS evaluation is done based on ACR paradigm.
• One set is evaluated in the NB/WB context.
• The other set is evaluated in the NB context, by
downsampling the WB coded speech samples.

Example

Example
STUDY GROUP 12 – DELAYED
CONTRIBUTION 46
Discussion on unified objective
methodologies for the comparison
of voice quality of narrowband and
wideband scenarios

The Extension
• Rnb=a+(eRnb/wb/b-1)
• a=169.38
• b=176.32
• The R-scale is stretched by 29%
• A linear extension with somewhat similar
results exists.

R-scale extension with PESQ
• Two sets of speech samples are created.
• Both contain stimuli coded by NB and WB
codecs. (124 samples each).
• The first (NB/WB) set is evaluated using
PESQ-WB.
• The NB coded stimuli were upsampled to
16 kHz.

R-scale extension with PESQ
• How to evaluate the 2nd part of the test?
• For the 2nd (NB) part of test three options
were considered for evaluating the
samples.
• In Option 1 All the files (ref|deg of NB|
WB) were downsampled to 8 kHz.
• This qualifies as a NB test.

R-scale extension … Option 1
RNB=a+b*RNB/WB
Max RNB=100.48
Suggests no extension.

The outcome

All Evaluation is done by
PESQ-WB.
Contracts the scale
instead.

• Same as Option 2 but the Ref samples for
NB stimuli are downsampled/upsampled.
• This would clearly tantamount to repeating
option 1 but with PESQ-WB

An Alternative
Using Supp 23 Exp 1&3.
Mapping between PESQ-
WB & -NB evaluted NB
coded samples.
Max RNB=107.1786

The Codecs
• G.729
• AMR-NB – 7.4 & 12.2 kbps
• G.723.1 – 6.3 kbps
• G.722.1 24/32 kbps
• G.722.2 – all 9 modes

Other metrics
• MLR - [0,2.5,. . . , 15, 20, . . . , 40]%
• CLP - 10, 50, 60, 70 and 80%.
• PI – 10-60 ms.
• A total of 2,820 conditions were simulated
• A given condition was applied to a file for 30 times; to
negate the effect of loss location.
• Thus a total of 3,38,400 speech files were created.
• Evaluation was done on beowulf using PESQ-WB

Ie,wb,eff vs various codecs

Scatter plot –training data

Scatter plot-Testing data

Surface plots of the derived
functions

Parameter Significance

Ie,wb,eff vs mlr and mbl

Ie,wb,eff vs mlr and PI

VoIP Quality Study Using E-Model Extension

Recommended

Recommended

More Related Content

Viewers also liked

Viewers also liked (12)

Similar to VoIP Quality Study Using E-Model Extension

Similar to VoIP Quality Study Using E-Model Extension (20)

More from adil raja

More from adil raja (20)

Recently uploaded

Recently uploaded (20)

VoIP Quality Study Using E-Model Extension