## 3 Results and Analysis  
### Performance Metric Definition  
In order to support a 1000-Hz sensing rate, we set the basic UL sensing frame rate to 1000 Hz. This means that VR devices generate their sensing frame every 1 ms. In this paper, we applied a separate WLAN structure that we proposed. In addition to the structure proposal, we compared the delay and packet loss rate properties of our proposed algorithm in various situations with conventional EDCA cases. The main focus of this analysis is \(T_{transfer\_UL}\) of Equation (1), because \(T_{transfer\_UL}\) is relatively large despite its small UL frame size. \(T_{transfer\_UL}\) can be further decomposed as follows:  
\[T_{transfer\_UL}=T_{preamble}+T_{data}+T_{contention}+T_{IFSs}+T_{sync} \tag{2}\]  
where \(T_{contention}\) includes the back-off time, as well as channel-busy duration during a back-off procedure, when the delays are caused by channel access of initial transmission and retransmissions. Because \(T_{IFSs}\) is a fixed-time duration defined in the IEEE 802.11 standard, it cannot be changed. \(T_{preamble}\) is also determined by the IEEE 802.11 standard. However, by using UL OFDMA transmission, only one \(T_{preamble}\) is required for multiple stations, because UL stations transmit their preamble  
Figure 6: Proposed algorithm to adjust uplink (UL) VR sensing information report rate, and examine its feasibility of VR capacity for a given user profile. simultaneously at the beginning of the UL transmission. \(T_{data}\) is the time duration required for over-the-air data transmission. In the EDCA case, the cumulative \(T_{\textit{preamble}}\) would require a much longer duration, even though it does not include any information for VR applications. Therefore, the proposed scheme utilizes the multi-user physical frame structure to reduce the effective \(T_{\textit{preamble}}\) although it requires a longer \(T_{\textit{data}}\), owing to the small size of the resource unit (RU) for a single device. The RU is a unit of the frequency resource for OFDMA transmission, and the size and location of the RU for UL OFDMA transmission can be indicated by the trigger frame. The proposed wireless multi-user VR system can reduce not only the effective \(T_{\textit{preamble}}\), but also \(T_{\textit{outention}}\). Because not all VR devices in the VR AP BSS are allowed to transmit their UL control data without receiving the trigger frame, there would be no contention. On the other hand, because VR devices cannot transmit their UL data without a trigger frame from the VR AP, we added a new delay factor \(T_{\textit{sync}}\). \(T_{\textit{sync}}\) is a delay parameter caused by the time gap between the trigger frame reception and VR traffic generation. In this paper, we assumed the existence of nine wireless VR devices, including VR controllers and VR headsets. Additional specific simulation parameters are shown in Table 1. Because of the effect of preamble overhead reduction, a duration that is nine times that of \(T_{\textit{SU-UL}}\) could be replaced by a single \(T_{\textit{MU-UL}}\) duration in the proposed multi-user VR mode case. \(T_{\textit{AIFS}}\) is the required time duration for channel sensing before trying to perform the channel access procedure. \(M_{\textit{Queue}}\) is the size of the queue parameter for each device. If the \(M_{\textit{Queue}}\) is filled, and an additional frame comes to the queue, the IEEE 802.11 system would discard the last frame, which is calculated as a packet loss that increases the packet loss rate. \(\lambda_{\textit{Trigger}}\) is the trigger frame delivery rate controlled by VRCL, as mentioned above. VRCL could configure this value to provide seamless VR UX. Even though \(\lambda_{\textit{Motion}}\), which is the motion sensing rate, is fixed to 1000 Hz by hardware, the VRCL controls its delivery rate, and undelivered information is used to generate interpolation frames in a VR headset. \(N_{\textit{retx}}\) is a parameter for the maximum number of retransmissions (retx).