Question 8/12 - Extension of the E-Model
(Continuation of Question 8/12)
Motivation
Study Group 12 has established a concept of impairment factors which aim at predicting the perceptive effects of different types of degradations on overall speech communication quality, for network planning purposes. The core algorithm related to this concept is the so-called E-model, a computational model for use in transmission planning, see Rec. G.107. This model is now frequently applied to plan traditional, narrow-band and handset-terminated networks, and to an increasing extent also for packet-based networks. Additionally, methodologies have been set up to derive impairment factors for codecs from subjective listening-only tests and from instrumental models (Recs P.833 and P.834).
With respect to the application of the E-model to the planning of modern networks, however, there are still several open questions, which strongly limit the model’s usability. They result from the terminal and transmission characteristics of modern networks, which could not have been taken into account at the time the model was established. In order to guarantee that the achieved concept keeps track with the technological progress in both the transmission system and the terminal equipment areas, it is highly desirable to maintain and update the model. The validity range of the E-model should be extended so that it cannot only be applied to traditional networks, but e.g. to packet-based transmission, wide-band systems, non-handset terminal equipment, and speech processing equipment implemented either in the network or in the user interface, too.
The following major Recommendations, in force at the time of approval of this Question, fall under its responsibility: G.107, P.833, P.834
Question
Study items to be considered include, but are not limited to:
- Which quality issues have to be taken into account when extending the E-model to terminal equipment other than standard handset telephones (e.g. HFTs, headsets)? Which parameters can be used to describe such terminal equipment?
- How can the perceptive effects introduced by speech-processing devices included in the network or in the terminal equipment (e.g. echo cancellers, level control devices, voice activity detectors, noise suppression devices) be covered by the E-model?
- How can strongly time-variant channel characteristics, e.g. due to bursty frame or packet loss, or in a cellular network, be taken into account in the E-model?
- How can the E-model be modified in order to better show the influences of pure delay on interactivity, in contrast to how delay influences overall user opinion? Are two instead of one output values needed for describing these influences?
- Can the E-model be used for conference call situations?
- How can perceptive quality dimensions other than “impairment” be covered, e.g.
- “speech sound quality”, e.g. due to terminal equipment other than handsets, due to transmission bandwidth other than the normal 3.1 kHz band, e.g. wide-band transmission, or due to frequency distortion or non-linear codecs,
conversational quality features not covered by the current E-model version, e.g. those resulting from the system’s double-talk performance (see Rec. G.108.1).
- Is it possible to extend the E-model to wideband transmission scenarios, or to develop a wideband transmission planning model?
- In how far is the additivity property of different types of impairments on a perceptual scale a valid underlying assumption of the E-model? Which deviations from this assumption are tolerable for network planning purposes? How can interdependencies be integrated into the E-model algorithm?
- What is the influence of user expectation on the overall quality, e.g. for terminal equipment other than handsets, or for computer-operated VoIP services?
- What are the psychological dimensions commonly handled by the term “expectation”?
How will user expectation develop with time (cf. Rec. G.113)?
- What are the experiences of the users of the E-model (e.g. the users of the planned ITU-T web interface to the E-model)?
Tasks
Tasks include, but are not limited to:
- Maintenance and enhancement of the E-model described in Rec. G.107 and input to depending Recommendations
- Maintenance of the Recommendations P.833 and P.834 for determining equipment impairment factors
It is anticipated that a new Recommendation on a wideband transmission planning model can be produced in the 2005–2008 Study Period.
Relationships
Recommendations: G.108, G.108.1, G.109, G.113, G.114, G.131, G.175, P.11, P.562
Questions: 7/12, 9/12, 14/12
Study Groups: ITU-T SG 15
Standardisation bodies: ETSI TC STQ, TIA TR-41, T1A1.
» List of Questions «
|
