In this article, we explore communication problems in virtual reality (VR) systems from the perspective of wireless networking. Our starting point is that the dynamics of real-time interaction between the physical and virtual worlds cannot be fully captured by the frame rate. Particularly, the frame rate can be very high, but the actual user experience can be disappointing. We argue that the key idea is to think of VR as the mediator of the senses, especially vision, rather than a conventional video streaming application. This is indeed a remarkable opportunity to recall Weaver's classification and define three fundamental problems in VR systems: i) responsiveness, ii) timeliness, and iii) effectiveness. Responsiveness refers to the delay between an action in the physical world and its display in the virtual world. Timeliness is related to the frequency of updates imposed by the frame rate. Effectiveness considers the visual content of a video frame and its likelihood of extrapolation. Our framework offers a concise and objective description of VR systems, that allows us to evaluate performance, identify potential issues, and design impactful solutions.

We study the peeker's advantage in first-person shooters, a classic problem in multiplayer games. A player, the peeker, who first observes another player, the defender, has a strategic advantage. The peeker has the opportunity to aim and shoot first, as the defender is not aware of the peeker's presence for a short amount of time. Formally, the peeker's advantage is the length of time that the peeker sees the defender without being seen. This is an inherent problem of multiplayer games, where each player runs their own instance of the game and relies on updates from an authoritative game server to get informed about the global game state. In this article, we explore the peeker's advantage with extensive simulations, by varying the system delays, the network delays, and the reaction times of the players. First, we present our multiplayer abstraction that captures the essence of first-person shooters, including client and server logic as well as the exchanged messages. Next, we show that the game frame rate is the most influential factor, while the game server tick rate and network delays have minimal impact. Specifically, we show that by using 120 fps in the game and 60 ticks/s on the game server, the peeker's advantage can be dropped below 100 ms. Finally, using realistic, standards-compliant simulations, we show that this advantage is consistent across multiple configurations, both in local area networks and over the Internet.

Large-scale virtual reality (VR) enables novel art forms in large physical environments. A key technical solution in such cases is to split the rendering process between a client and a streamer. In this article, we focused on the peculiarities of VR split rendering and particularly on the performance of Wi-Fi. First, we calculated the network delay budget and then conducted a set of experiments to evaluate the single-user and multi-user performance of VR split rendering systems over Wi-Fi in terms of latency. Our findings were summarized as recommendations on: i) the frame rate, ii) the encoding bitrate, iii) the signal strength, iv) the channel bandwidth, and v) the multiple access techniques. In particular, our multi-user tests highlighted cases where using the highest settings or latest features of Wi-Fi can compromise performance. Finally, we applied our recommendations to a large-scale multi-user case study that took place physically in the multi-purpose hall of our university campus and virtually in the Turret Singers environment of SteamVR Home. This article serves as a reference to the critical aspects of VR split rendering systems over Wi-Fi.

Hitting a high frame rate is the holy grail of virtual reality (VR). Indeed, a high frame rate offers an amazing experience, but also pushes current technology to its limits. This is particularly true for networked VR gaming systems which rely on split rendering between a client and a server. In this paper, we investigate the impact of frame rate on such systems in terms of responsiveness and timeliness, using both experiments and simulations. Responsiveness refers to how quickly the information is exchanged, while timeliness refers to the frequency of updates. In terms of responsiveness, we show that 90 fps and 120 fps may tolerate up to 6 ms network delay. In terms of timeliness, we show that the best choices are 120 fps when network delay is low and 60 fps when network delay is high.

Virtual Reality (VR) streaming enables end-users to seamlessly immerse themselves in interactive virtual environments using even low-end devices. However, the quality of the VR experience heavily relies on Wireless Fidelity (Wi-Fi) performance, since it serves as the last hop in the network chain. Our study delves into the intricate interplay between Wi-Fi and VR traffic, drawing upon empirical data and leveraging a Wi-Fi simulator. In this work, we further evaluate Wi-Fi’s suitability for VR streaming in terms of the Quality of Service (QoS) it provides. In particular, we employ Unity Render Streaming to remotely stream real-time VR gaming content over Wi-Fi 6 using Web Real-Time Communication (WebRTC), considering a server physically located at the network’s edge, near the end user. Our findings demonstrate the system’s sustained network performance, showcasing minimal round-trip time (RTT) and jitter at 60 and 90 frames per second (fps). In addition, we uncover the characteristics and patterns of the generated traffic streams, unveiling a distinctive video transmission approach inherent to WebRTC-based services: the systematic packetization of video frames (VFs) and their transmission in discrete batches at regular intervals, regardless of the targeted frame rate. This interval-based transmission strategy maintains consistent video packet delays across video frame rates but leads to increased Wi-Fi airtime consumption. Our results demonstrate that shortening the interval between batches is advantageous, as it enhances Wi-Fi efficiency and reduces delays in delivering complete frames.

Communication in Body Area Networks (BANs) involves extremely weak signals because of safety regulations. Human mobility adds one more layer of complexity as it has an effect on path loss depending on the activity. In this paper, we improve the quality of service (QoS) by searching for the lost nodes. Specifically, an Emergency Phase (EP) is added after RAP1 of IEEE 802.15.6-2012 superframe. The connected nodes transmit rescue beacons to reach distressed nodes, i.e. nodes that are disconnected. If a distressed node receives a rescue beacon, it participates to the current EP. The packets are buffered and relayed to the hub by the connected nodes. Our results show that when EP is enabled it is feasible to reach more nodes.