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.

Is Wi-Fi 6 ready for virtual reality (VR) mayhem? The common use case for untethered VR is running a video game on a powerful desktop and streaming the generated content to a head-mounted display (HMD) over Wi-Fi. In this work, we investigated a challenging use case using one Wi-Fi 6 access point (AP) and three HMDs. Specifically, we evaluated experimentally the performance of VR streaming in terms of latency using: i) the distributed coordination function (DCF), ii) orthogonal frequency-division multiple access (OFDMA) in the downlink (DL) and the uplink (UL) and iii) multi-user multiple input multiple output (MU-MIMO). We showed that VR streaming to three users, up to 100 Mbps each, works flawlessly using either DCF or DL OFDMA, with latency in the order of 50 ms. In addition, our study unveiled the disruption of tracking data transmissions in the uplink using UL OFDMA, which had a negative impact on latency by delaying game rendering.

Affective virtual reality (VR) gaming systems rely on timely physiological data collection, in order to generate personalized responses that enhance the emotional impact of a video game on its user. In this context, we propose a simple policy for timely data collection from wireless sensor nodes placed on the human body. Our policy is applied at each sensor node. Upon each packet arrival we check whether the buffer is full or not. If the buffer is full, then we empty it before adding the packet. In this very simple way, we avoid buffer congestion and impose timeliness. We simulated this aggressive buffer reset policy using a body area network (BAN) model in OMNeT++. By varying the packet generation rate of each node, we showed that our policy outperforms first come first served (FCFS) and last come first served (LCFS) queueing policies in terms of peak age, while packet reception is barely affected. Buffer resets can be easily integrated into existing random access protocols to support timely data collection.

The Industrial Internet of Things (IoT) has gained a lot of momentum thanks to the introduction of Time Slotted Channel Hopping (TSCH) in IEEE 802.15.4. At last, we can enjoy collision-free, low-latency wireless communication in challenging environments. Nevertheless, the fixed size of time slots in TSCH provides an opportunity for further enhancements. In this paper, we propose an enhanced centralized TSCH scheduling (ECTS) algorithm with simple packet aggregation while collecting data over a tree topology. Having in mind that the payload of a sensor node is rather short, we attempt to put more than one payload in one packet. Thus, we occupy just one cell to forward them. We investigated the schedule compactness of ECTS in Matlab, and we evaluated its operation, after implementing it in Contiki-NG, using Cooja. Our results show that ECTS with packet aggregation outperforms TASA in terms of slotframe duration and imposes fairness among the nodes in terms of latency. A validation exercise using real motes confirms its successful operation in real deployments.

A large number of wireless sensor nodes in a certain area results in high contention. Inevitably, the transmissions of any possible critical data packets may fail due to collisions. In this article, we introduce an aspect of human intelligence in wireless sensor networks, influenced by cooperative networking, which enhances the timely delivery of critical data. Mutual aid among sensors (MAAS), is an emergency out-of-the-box medium access control (MAC) function for IEEE 802.15.4-2020. Specifically, the network coordinator detects critical data packets and sets an emergency flag to its next beacon, to inform the nodes that they may overhear data packets. When a node overhears a critical data packet from a neighboring node it switches to sleep mode and stays idle until the end of the superframe. Thus, interference is mitigated locally and temporarily. Simulation results, using the CC2650 radio parameters in OMNeT++, show that interference is reduced significantly, in favor of the timely delivery of critical data packets.

In body area networks (BANs), a node placed near the hub has a significant signal strength advantage. This issue, known as near-far problem, indicates that a near node may serve as a relay for a far node. Currently, the established orthogonal multiple access (OMA) requires the allocation of a specific resource block to a single node. In contrast, the emerging non-orthogonal multiple access (NOMA) allows simultaneous transmissions and uses successive interference cancellation (SIC) to recover the signals. For the first time in the literature, we introduce NOMA in BANs, to allow simultaneous transmissions from two nodes at a time, with distinguishable power levels. The crucial part of this technique is the dynamic pairing of the nodes by the hub. First, we review the fundamentals of uplink NOMA and we propose an access protocol in compliance with IEEE 802.15.6-2012, which combines random OMA with scheduled NOMA. Next, we propose three node pairing strategies, namely a random, a correlative and a conditional one, to meet the requirements of several applications. These strategies are evaluated with packet level simulations in OMNeT++. Our results show that the proposed scheme outperforms the basic OMA scheme at high packet rates and provides a feasible direction for novel relay-based applications.

Communication in Body Area Networks (BANs) involves weak signals, due to safety regulations, huge pathloss from the absorption and usually high mobility. In this work, we introduce an improved mobility aware relaying scheme for BANs, as an alternative to the two-hop star topology extension of IEEE 802.15.6-2012, in order to enhance packet delivery. Specifically, an emergency phase (EP) is added after the regular random access phase (RAP1) of the superframe and the connected nodes transmit rescue beacons to reach disconnected nodes. When a disconnected node receives a rescue beacon, it participates in the current EP. The packets are buffered and relayed to the hub by the connected nodes. Simulation results show that it is feasible to receive more packets compared to the standard with a justified increase of energy consumption due to random access which is compensated with increased packet delivery.

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 in 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.

The discussion concerning programmable MAC in Body Area Networks (BANs) is due to the demand for simple and low-power sensor nodes. Additionally, the diverse applications in BANs require low-level modifications to support adaptive services or custom functions. In this work, we propose a novel scheme for programmable MAC, which requires a minor modification to the beacon frame of IEEE 802.15.6-2012. Specifically, our main contribution is the attachment of a command to the beacon, which is broadcasted at the beginning of each superframe by the hub. The hub requests an action, typically a modification of a MAC capability field, by the nodes with a metric which satisfies a constraint. Thus, one command at a time, the proposed scheme is applied with a negligible overhead. Two adaptive use cases, based on signal strength, are implemented to demonstrate this scheme. Firstly, the hub requests the nodes with high signal strength to enable relay support and secondly, the hub requests the nodes with low signal strength to set a sleeping pattern. In the first case packet delivery increases significantly, while in the second case each node saves an amount of energy.