Jens Berger

T-V-model: Parameter-based prediction of IPTV quality

The paper presents a parameter-based model for predicting the perceived quality of transmitted video for IPTV applications. The core model we derived can be applied both to service monitoring and network or service planning. In its current form, the model covers H.264 and MPEG-2 coded video (standard and high definition) transmitted over IP-links. The model includes factors like the coding bit-rate, the packet loss percentage and the type of packet loss handling used by the codec. The paper provides an overview of the model, of its integration into a multimedia model predicting audio-visual quality, and of its application to service monitoring. A performance analysis is presented showing a high correlation with the results of different subjective video quality perception tests. An outlook highlights future model extensions.

Modeling Call Quality for Time-Varying Transmission Characteristics Using Simulated Conversational Structures

This study investigates the perception of speech quality over telephone channels with time-varying transmission characteristics for simulated conversational structures. The aim is to establish a relationship between subjective quality associated with short speech samples (5―6 seconds) and quality associated with overall conversations (1― 2 minutes). Two two-part experiments were conducted. In the first part of each experiment, dialog-final ratings within the temporal structure of a telephone conversation were assessed. Varying transmission characteristics were realized with ten different degradation profiles of preprocessed speech samples obtained mainly from real mobile channels to ensure authentic types of degradation. The second part was carried out to obtain separate short-term ratings of the speech samples used in the first part. Experiments 1 and 2 tested different conversation durations (1 and 2 minutes). The results demonstrate that dialog-final ratings vary with respect to the degradation profile, revealing a recency effect and a strong impact of individual bad samples. Two related models which implement these findings are presented. With these models, dialog-final quality ratings can be estimated significantly better than by plain averaging of short sample ratings (about 10% absolute improvement). They also perform better than two algorithms taken from literature. Both models can be applied to the instrumental method described in ITU-T Rec. P.862 [1], resulting in about 13% absolute improvement. They were evaluated with the results of two different experiments, which were performed independently but on the basis of our test procedure. In these experiments similar profiles but a different type of quality degradation, different sample durations, and different speech material were used. The models proved to be valid and reliable for the time span investigated (1―2 minutes) and for the profiles used. One of them is now being recommended by the ETSI STQ mobile group.

A new dimension-based framework model for the quality of speech communication services

In this paper, we identify quality dimensions which are relevant for speech communication services, such as mobile telephony or Voice-over-IP. These include dimensions perceived when listening to degraded speech, talking against echoes, double-talk capabilities, interacting with delay, conversing over channels with time-varying characteristics, and service-related dimensions experienced during speech connection set-up and maintenance. For each dimension, we review subjective evaluation metrics and instrumental quality prediction models. We group these dimensions in a framework model which is able to diagnostically assess speech communication services, and may be used for monitoring and maintenance.

Towards a universal value scale for quantifying the quality of speech communication across services

This paper reports on ongoing work in ITU-T Study Group 12 on developing a universal scale quantifying quality across different types of speech communication services. In contrast to a quality rating scale, this scale should be deliberated from the judgment context as far as possible. As a consequence, it should be possible to compare different types of services on such a scale, in order to justify investments made in comparison to QoE gains to be expected. The paper explains the underlying rationale of such a scale, defines the requirements it has to fulfill, and outlines the way to its derivation. It invites further discussion to this work item of ITU-T Study Group 12, and could serve as an example for other types of services.