Marko Matulin

Impact of packet loss on the perceived quality of UDP-based multimedia streaming: a study of user quality of experience in real-life environments

Multimedia content delivery has become one of the pillar services of modern day mobile and fixed networks. The variety of devices, platforms, and content providers together with increasing network capacity has impacted the popularity of this type of service. Considering this context, it is crucial to ensure end-to-end service quality that can fulfill users’ expectations. The user quality of experience (QoE) for multimedia streaming is tempered by numerous objective and subjective parameters; therefore, it is important to understand the relationships among them. In this paper, we thoroughly examine the impact of packet loss on user QoE in cases when multimedia streaming service is based on underlying User Datagram Protocol. The dependencies between the chosen objective and subjective parameters and the user QoE were examined in a real-life environment by conducting a survey with 602 test subjects who rated the quality of a 1-h documentary film (72 different test sequences were prepared for the rating process). Based on the obtained results, we ranked the objective parameters by their order of importance in relation to their impact on user QoE as follows: (1) total duration of packet loss occurrences (PLOs), i.e., quality distortions in a video; (2) number of PLOs; (3) packet loss rate; and (4) duration of a single PLO. We also demonstrated how the overall user experience can be redeemed, despite the perceived quality distortions, if the content is entertaining to the viewer. The user experience was also found to be influenced by the existence/non-existence of video subtitles.

Modelling user quality of experience from objective and subjective data sets using fuzzy logic

One of the paramount research questions in the scientific community today is how to remotely assess user quality of experience (QoE) for a specific service. To this end, various user QoE assessment models have been developed; however, they are mostly based on the data gathered from controlled environment experimentation. The aim of this research was to model user QoE for the User Datagram Protocol-based video streaming service from the results of uncontrolled subjective tests. Specifically, using fuzzy logic, we have correlated the values of three objective network parameters (the packet loss rate and the number and duration of packet loss occurrences in one streaming session) with test subjects’ subjective perception about perceived quality distortions. The dependencies between different values of the parameters and the subjects’ perception of video quality were used to develop a no reference objective video quality assessment model for assessing user QoE. The key distinguishing feature of the developed model lays in the process of subjective evaluation, which was conducted with a panel of 602 test subjects who evaluated the quality of 1-h video in home environments. For this purpose, 72 different test sequences were prepared for rating. We showed that a strong positive linear relationship exists between the assessed QoE of the model and the Mean Opinion Scores of the subjects (a Pearson correlation coefficient equal to 0.8841).

Development of Fuzzy Relationships between Different Quality of Experience Parameters

User psycho-acoustic and visual perception of telecommunication service quality depends on a wide palette of objective and subjective parameters. This is especially relevant in the process of evaluation, assessment or prediction of user Quality of Experience (QoE) for specific service, because these processes require the revelation of the correlations between different parameters. Using the User Datagram Protocol (UDP) based video streaming service as an example, in this paper we investigate the impact of three objective parameters (the packet loss rate, the number and the duration of packet loss occurrences) on user perception by conducting subjective quality tests. We then use Fuzzy C- Means (FCM) clustering approach to cluster test subjects’ ratings as well as to define degrees of membership of each rating to specific fuzzy cluster. Based on the obtained degrees of membership, the fuzzy relationships between different objective and subjective parameters are approximated using the normal distributions.