Quality of Experience - Engineering Processes and QoE

Engineering Processes and QoE

As an important measure of the end-to-end performance at the services level from the user's perspective the QoE is an important metric for the design of systems and engineering processes. This is particularly relevant for video services because bad network performance may highly affect the user's experience, mainly because these services are compressed and have low entropy. So, when designing systems the expected output, i.e. the expected QoE, is often taken into account also as a system output metric.

This QoE metric is often measured at the end devices and can conceptually be seen as the remaining quality after the distortion introduced during the preparation of the content and the delivery through the network until it reaches the decoder at the end device. There are several elements in the video preparation and delivery chain and some of them may introduce distortion. This causes the degradation of the content and several elements in this chain can be considered as "QoE relevant" for video services. These are the encoding system, transport network, access network, home network and end device.

The concept of QoE in engineering is also known as Perceived Quality of Service (PQoS), in the sense of the QoS as it is finally perceived by the end-user. The evaluation of the PQoS for audiovisual content will provide a user with a range of potential choices, covering the possibilities of low, medium or high quality levels. Moreover the PQoS evaluation gives the service provider and network operator the capability to minimize the storage and network resources by allocating only the resources that are sufficient to maintain a specific level of user satisfaction.

Another approach for measuring QoE in Video content is using a referenceless analysis. In this case, the QoE is not measure comparing an original video to delivered one, but by trying to detect artifacts such as blockiness, blur or jerkiness directly in the video. This approach is based on the idea that customers don't know the original content.

The evaluation of the PQoS is a matter of objective and subjective evaluation procedures, each time taking place after the encoding process (post-encoding evaluation). Subjective quality evaluation processes (PQoS evaluation) require large amount of human resources, establishing it as a time-consuming process. Objective evaluation methods, on the other hand, can provide PQoS evaluation results faster, but require large amount of machine resources and sophisticated apparatus configurations. Towards this, objective evaluation methods are based and make use of multiple metrics.

Example : PQoS for a web site.