## 5 Quality of Experience (QoE) Assessment  
According to the International Telecommunication Union (ITU), Quality of Experience (QoE) could be defined as the overall acceptability of an application or service perceived subjectively by the end-user [80]. QoE assessment is the practice of measuring or estimating  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Network Approach** & **Scope** \\ \hline
5G network & Edge computing and Edge caching brings content and resources nearer to the client. \\ \hline
6G network & AI-powered 6G service applications (AR, VR, XR, MR) reduce device battery consumption, computation capacity, and end-to-end latency. \\ \hline Network caching & Cache the VR content to optimize the bandwidth and latency. \\ \hline Information Centric Networking (ICN) & Content-centric, location-independent models enable retrieval of content over any network interfaces available. \\ \hline Mobile Edge Computing (MEC) & Reduce the intensive computing burden on VR devices. The MEC server assists the mobile VR device by processing some computational and rendering tasks and then delivering the task to the mobile device. \\ \hline \hline \end{tabular}
\end{table}
Table 6: Comparison of network approaches.  
the QoE for a group of users of an application or a service using a defined approach and taking into account the affecting variables [80].  
The nature of 360-degree videos which can cause different distortions provides distinct challenges for modeling QoE measurement. To begin, 360-degree videos are captured using many dioptric cameras from different angles, which are then stitched together using a mosaicking algorithm [3]. [PERSON], [PERSON] [81] found that distortions such as blurring, apparent seams, ghosting, broken edges, missing information, and geometrical distortions might arise during the stitching process or capturing process because of the camera inconsistency. For example, the lighting may alter depending on the camera angle which causes the stitched 360-degree video with different illumination affected the user's viewing experience.  
Next, 360-degree video streaming required high bandwidth requirements as mentioned in Section 2 of this article. As a result, the video content must be compressed to lower quality, resulting in distortions such as blurring, blocking, ringing, and the staircase effect, all of which can impact the user experience heavily [81]. Due to network restrictions, delays, rebuffering, and quality variations can produce disorientation and cybersickness by disturbing the flow of movement, which also has a detrimental impact on the watching experience.  
Using an HMD to view VR 360-degree videos provides an immersive experience. A realistic environment with a higher immersion level and user presence could influence the QoE [82; 83]. Thus, more factors than just video quality need to be considered, such as visual realism, acoustic realism and proprioceptive matching between the video content and user's movements influence the sense of presence strongly [84]. Furthermore, Ref. [85] discovered that more diegetic VR interfaces, or situations in which all of the things perceived by a user belong to the virtual world, lead to better user experiences. In comparison to traditional 2D displays, the HMD is significantly closer to the eye, which may cause distortions to be perceived clearly and cause more eye strain and tiredness [86]. Space between pixels may also be noticeable due to the proximity of the screen to the eyes. These effects may raise perceptual and cognitive load (PCL), resulting in stress [87]. Compared to 2D video, it provides more interactivity with the viewing angle but may also cause cybersickness easily.  
Currently, there are two main approaches in the QoE assessment of 360-degree video, which are Objective QoE assessment and Subjective QoE assessment.