ISSN : 1796-2048
Volume : 4    Issue : 2    Date : April 2009

The Design of VoIP Systems With High Perceptual Conversational Quality
Benjamin W. Wah and Batu Sat
Page(s): 49-62
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This paper describes our work on real-time two-party and multi-party VoIP (voice-over-IP) systems
that can achieve high perceptual conversational quality. It focuses on the fundamental
understanding of conversational quality and its trade-offs among the design of speech codecs and
strategies for network control, playout scheduling, and loss concealments. We have studied three
key aspects that address the limitations of existing work and improve the perceptual quality of VoIP
systems. Firstly, we have developed a statistical approach based on just-noticeable difference
(JND) to significantly reduce the large number of subjective tests, as well as a classification method
to automatically learn and generalize the results to unseen conditions. Using network and
conversational conditions measured at run time, the classifier learned helps adjust the control
algorithms in achieving high perceptual conversational quality. Secondly, we have designed a
cross-layer speech codec to interface with the loss-concealment and playout scheduling algorithms
in the packet-stream layer in order to be more robust and effective against packet losses. Thirdly,
we have developed a distributed algorithm for equalizing mutual silences and an overlay network for
multi-party VoIP systems. The approach leads to multi-party conversations with high listening only
speech quality and balanced mutual silences.

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