## 2 Related Work
### VR Conferencing  
The purpose of video conference is to facilitate the possibility of instant communication between participants who are not physically together, through using network and multimedia technology, for participants to appear to be physically together. The traditional approach is to transmit the video and audio data [18; 19] of each participant in their different spaces to all other participants through a multipoint control unit (MCU). At present, the technology for video conference has become increasingly flawless and has been widely used in the current COVID-19 pandemic. However, as video conference cannot provide a sense of presence, an immersive experience cannot be generated, opening the way for the introduction of virtual reality conference [20]. So far, the research and application of VR conference rooms is still in the start-up stage of development and exploration, with no widely accepted systematic theory. In [21], a virtual reality conference room based on the traditional MCU architecture was proposed, in which participants could be placed in a virtual space for communication. A three-dimensional image in a virtual environment was rendered by processing the two-dimensional video information of the participants. This method could display the real image of people in a virtual space, as well as the body information in real time. However, the participants in the images still wore a head display, which may reduce the effectiveness of communication.A novel network video conference system based on MR display devices and AI segmentation technology was proposed in [22]. This was a robust, real-time video conference software application that made up for the simple interaction and lack of immersion and realism of traditional video conference, allowing users to interact in a conference in a new way. However, similar to [21] mentioned above, the participants in the images wore a head display. The presentation of real-time images of human subjects lacked realism if the observer's position was much different from the camera. In [23], a more complex virtual reality conference system was proposed, which involved the generation of avatars and animation, especially facial expression animation. The authors provided three feasible means of multiperson cooperation: VR painting, slide display, and model import. There was also the general design of the network module. To finish, the experience of wearing the head display device was evaluated, and the conclusion was that the experience of wearing the head display device was better. A novel video transmission scheme of a virtual space conference was proposed in [24], which was based on perceptual control. In the system, the perception of each participant was calculated, with the construction of a perceptual space matrix based on this, wherein the matrix parameters were used to control the codec, effectively encoding the video object and thereby reducing the total bandwidth. The same approach was applied to audio objects. In [25], the methods for evaluating the authenticity of immersive virtual reality, augmented reality (AR), and hybrid reality were summarized. The conclusion was drawn following the analysis of a large number of relevant articles. Most methods consisted of a combination of objective and subjective measures. The most commonly used assessment tools were questionnaires, many of which were customized and unverified. The existence questionnaire was the most commonly used one, which was usually used to evaluate the authenticity and participation of one's existence and perception. The research on VR conferencing is still in its early stages. Ref. [26] discussed the features and obstacles found within virtual conference solutions (both 2D and 3D) through a systematic literature review investigation. As a result, 67 key features and 74 obstacles users experience when interacting with virtual conferencing technologies were identified.