## 1 Introduction
\(T_{procL\_in\_device}\) is a processing delay for a processor unit in VR devices, which handles sensing data and generates data packets. The generated data packets are transmitted to the associated VR computing device over a WLAN link in the proposed system. One-hop wireless packet delivery over a WLAN link causes a delay, \(T_{transfer\_UL}\), which could be a relatively large value depending on the  
Figure 1: Wireless multiuser virtual reality (VR) system, based on IEEE 802.11 system. wireless channel condition, including channel congestion caused by channel contention. \(T_{transfer\_UL}\) is the most dominant delay component in the proposed multi-user VR system. The VR computing device, which is generally a PC, requires a processing delay, \(T_{proc\_in\_PC}\). In order to provide seamless VR UX by minimizing a processing delay, high-processing performance is preferred. The VR computing device generates VR feedback packets, including VR video data, and transmits them to its associated VR devices over a WLAN link. The delay caused by this WLAN transmission is considered as \(T_{transfer\_DL}\). Since the transmission causing the delay of \(T_{transfer\_DL}\) is from one node (VR computing device) to multiple nodes (wearable VR devices), and the transmission causing the delay of \(T_{transfer\_UL}\) is from multiple nodes (wearable VR devices) to one node (VR computing device). \(T_{transfer\_DL}\) can be more easily controlled than \(T_{transfer\_UL}\). The downlink delay, \(T_{transfer\_DL}\), is the second most important delay component in the proposed system. The VR devices decode the packet and operate to generate sensory feedback, which causes a processing delay, \(T_{proc\_in\_device}\). For instance, a VR headset decodes VR video image and perform video enhancement procedure, for a seamless and immersive UX. \(T_{proc2\_in\_device}\) is a delay component for this kind of hardware processing, to provide sensory feedback. IEEE 802.11 systems are designed as contention-based, channel access, wireless communication systems [9]. Because of the properties of contention-based channel access, the performance of IEEE 802.11 ad/ay systems degrades dramatically as the number of wireless stations (STAs) increases [10]. In other words, even though most advanced WLAN protocols and VIDEO codecs are utilized, supporting multi-user VR with low latency is almost impossible, owing to the multiple access inefficiency of WLAN. VR devices need to upload their sensing information to trace user position and pose frequently, and each VR device usually keeps track of its position with a 1000-Hz sensing rate. This means that in multi-user VR, small uplink frames are generated very frequently, by multiple VR devices. Severe WLAN channel contention is caused by an overwhelming number of small VR control frames, leading to a very long channel access delay, which makes the operation of multi-user VR over WLAN impossible. Such problems cannot be solved by conventional IEEE 802.11 distributed coordination function (DCF) and enhanced distributed channel access (EDCA), which do not guarantee frame delivery delay [9]. In order to provide multi-user VR services over WLANs, the channel access delay needs to be minimized, and the frame rate of VR video and the arrival rate of uplink (UL) frames should be adaptively adjusted, depending on the wireless environment. Since both the technical progress of frame-interpolation schemes [11; 12; 13; 14; 15; 16] and the frame-interpolation module are expected to be commonly employed in next-generation VR headsets [17], users could have stable high-refresh-rate vision with a lower downlink (DL) VR video frame rate. Sensing data, which is not fed back to computing machines, including VR-ready PCs, can be utilized by the frame-interpolation module to generate interpolation frames, with accurate moving data from the user. These interpolation frames are not based on future frames [11], because these are real-time video frames. The interpolation frames are generated from past frames and motion track data.