User experience based network management is important for operators so that they can provide best quality services. In case of a VR service, which is much more complex than traditional video streaming in terms of content creation, network transmission and device requirements, the provision of a satisfying immersive experience is more challenging. The first step of this effort would be to find out what factors have an impact on user experience, and define reference metrics and parameters that would help operators make assessment of user experience, do trouble shooting and design target solutions. The analysis of impact on user experience involves the whole E2E VR service chain:

• Creation of content. VR content creation would involve multiple steps such as capture, stitching, projection, and encoding, each step would have an impact on the content itself. It is necessary to look into each step and find out what factors are relevant to the VR experience;
• Network transmission. The amount of video data of VR content entails a high streaming bitrate, and may lead to a risk of network and/or access link congestion and re-buffering, and thus an impediment to limiting latency. Latency is one of the key elements to create the feeling of immersiveness, and thus has considerable impact on user experience.
• Device requirement. Compared with a traditional device, be it a mobile phone or a tablet, a VR device exhibits many more attributes, designed to help create immersive experience. The degree of freedom it provides to users, the sensitivity of sensors that enable quick catching of head movement, and many other attributes, all need to be studied and evaluated about their relevance to user experience.

The present document investigates the QoE metrics relevant with VR experience from the aforementioned three aspects, and also the way of reporting these QoE metrics to the network for further analysis.

The present document provides a study on the QoE metrics relevant to VR service. The study focuses on:

• Defining a device reference model for VR QoE measurement points.
• Studying key performance indicators that may impact the experience of VR service.
• Identifying the existing QoE parameters and metrics defined in SA4 standards such as TS 26.247, TS 26.114 which are relevant to Virtual Reality user experience;
• Identifying and defining new QoE parameters and metrics relevant to Virtual Reality user experience, taking into consideration the use cases listed in TR 26.918, and any sources that show the relevance of new metrics, e.g. scientific literature, specifications/solutions from other standard organizations.
• Analysing potential improvements to the existing QoE reporting so as to better accommodate VR services.
• Providing recommendations to future standards work in SA4 on the QoE parameters and metrics and, as necessary, coordinate with other 3GPP groups and external SDOs, e.g. MPEG, ITU-T.