On the Impact of Combinations of Terminal and Network Degradations on the Conversational Quality of Wideband Telephony
* Presenting author
In the field of perceptual quality assessment of telephony systems, one recent trend is to gain more knowledge about the impact of terminal equipment, especially in combination with network degradations. While such combinations are quite well understood by experts, the quality impact of such combinations on the naive end user, especially in conversational situations, has hardly been studied yet. Therefore this conference contribution reports on a comprehensive conversation test investigating combinations of terminal and network degradations. Concerning the experimental method, one challenge of conversation tests is a good balance between a large number of test conditions and a feasible number of participant groups. Another challenge is that the experimental context can influence results, which can for instance become an issue when different types of test conditions are distributed across individual tests. To address both challenges, we chose a balanced incomplete block design (BIBD) which allows to test 34 test conditions with the same number of participant groups while limiting the number of calls per group to twelve.Since BIBDs are known in the literature but rarely used in telephony quality tests, this conference contribution will not only discuss the test results but also the lessons learned when applying this methodology.