Figure 1: The research involved: (i) a design futuring workshop on acoustophoresis, (ii) the development and feasibility assessment of two SONARIOS (i.e., scenarios), and (iii) the synthesis of three strong concepts, along with key tensions and responsibilities in shaping the future of acoustophoresis applications.

Gesture-based interactions for automotive infotainment systems pose advantages over touchscreens such as alleviating the visual field. While the focus of these advantages is on improving the driving task, it is also important that a user feels in control and perceives influence over the in-vehicle system. This is known as the user's sense of agency in psychology, and sensory feedback is a key aspect. The current study involved a dual-task driving (simulator) and gesture-controlled infotainment interaction, accompanied by mid-air haptic or audio feedback. With 30 participants, we utilized an experimental approach with implicit and explicit measures of agency, as well as trust and usability. Results illustrated no difference in explicit judgements of agency, however mid-air haptic feedback improved the implicit feeling. More trust was also reported in the system with mid-air haptics. Our findings provide empirical evidence for mid-air haptics fostering user agency and trust in gesture-based automotive UI.

The rapid development of touchless systems has introduced many innovations in social interaction scenarios in recent years. People now can interact with touchless systems in social applications that are aimed to be used in everyday situations in the future. This accelerated development makes us ask, what will the next generation of touchless systems be like? How can we responsibly develop new touchless technologies in the future? To answer the first question, we brought together 20 experts to ideate, speculate, and evaluate possible touchless applications for social interactions. A total of 48 ideas were generated from two consecutive workshops. Then, to answer the second question, we critically analyzed those ideas through a thematic analysis using a responsible innovation (RI) framework, and identified key ethical considerations to guide developers, practitioners when designing future touchless systems. We argue that the social scenarios described, and the RI framework proposed in this paper are a useful starting point for responsibly designing the next generation of touchless systems.

This paper describes an interactive multimodal and multisensory fortune-telling experience for digital signage applications that combines digital human agents along with touchless haptic technology and gesture recognition. For the first time, human-to-digital human interaction is mediated through hand gesture input and mid-air haptic feedback, motivating further research into multimodal and multisensory location-based experiences using these and related technologies. We take a phenomenological approach and present our design process, the system architecture, and discuss our gained insights, along with some of the challenges and opportunities we have encountered during this exercise. Finally, we use our singular implementation as a paradigm as a proxy for discussing complex aspects such as privacy, consent, gender neutrality, and the use of digital non-fungible tokens at the phygital border of the metaverse.

The widespread of audio-visual online communication highlights the importance of enhancing their ability to transmit emotional color and personal experience. Non-verbal biometric cues and signals were recently recognized to convey such missing emotional context when added to virtual interactions. Motivated by that, we present a haptic system allowing for a biometric signal transfer in a fully touchless and seamless way. We utilize camera-based heart-rate signal readings and ultrasonic mid-air haptic technology to affect the audience with a temporal tactile pattern representing the speaker’s heart rate. We assess the usability and engagement enhancement of such a system in two user-studies involving one-way communication, i.e., watching a short emotional video. Our analysis of biometric data and subjective responses hints toward changed values of arousal and valence as well as physiological responses when the haptic feedback was applied in a group of participants. Finally, we outline a further research agenda to confirm our observations with different emotions and communication scenarios.

LoRa networks have been deployed all over the world and are a major enabling wireless technology for the Internet of Things (IoT). Massive connectivity applications such as smart metering, agriculture, and supply chain & logistics are most suitable for LoRa deployments due to their long range, low cost, and low power features. Meanwhile, energy harvesting technologies that extract energy from ambient sources have enabled the battery-less operation of many small wireless sensors. This paper studies the merger of these two technologies and mathematically models device and network performance using tools from stochastic geometry and Markov analysis. To that end, we derive the steady-state distribution of the capacitor voltage, the outage probability due to co-spreading factor interference at the LoRa gateway, and propose adaptive charging time schemes in order to mitigate energy outage events.

Wireless power transfer creates new opportunities for interaction with tangible and wearable devices, by freeing designers from the constraints of an integrated power source. We explore the use of focused ultrasound as a means of transferring power to a distal device, transforming passive props into dynamic active objects. We analyse the ability to transfer power from an ultrasound array commonly used for mid-air haptic feedback and investigate the practical challenges of ultrasonic power transfer (e.g., receiving and rectifying energy from sound waves). We also explore the ability to power electronic components and multimodal actuators such as lights, speakers and motors. Finally, we describe exemplar wearable and tangible device prototypes that are activated by UltraPower, illustrating the potential applications of this novel technology.

Ultrasonic mid-air haptic feedback enables the tactile exploration of virtual objects in digital environments. However, an object’s shape and texture is perceived multimodally, commencing before tactile contact is made. Visual cues, such as the spatial distribution of surface elements, play a critical first step in forming an expectation of how a texture should feel. When rendering surface texture virtually, its verisimilitude is dependent on whether these visually inferred prior expectations are experienced during tactile exploration. To that end, our work proposes a method where the visual perception of roughness is integrated into the rendering algorithm of mid-air haptic texture feedback. We develop a machine learning model trained on crowd-sourced visual roughness ratings of texture images from the Penn Haptic Texture Toolkit (HaTT). We establish tactile roughness ratings for different mid-air haptic stimuli and match these ratings to our model’s output, creating an end-to-end automated visuo-haptic rendering algorithm. We validate our approach by conducting a user study to examine the utility of the mid-air haptic feedback. This work can be used to automatically create tactile virtual surfaces where the visual perception of texture roughness guides the design of mid-air haptic feedback.

On the brink of the internet of things (IoT) revolution, different low power wide area network (LPWAN) technologies are competing for market share and scalability. In this paper we leverage stochastic geometry tools to better understand how one should model the uplink wireless coverage in a multi-cell LoRa network while taking under consideration both the effects of co-spreading factor interference and the spatial diversity afforded by the LoRa network server. To that end, we propose a tractable model that captures these two system peculiarities and mathematically show that gateway densification has an overall positive effect on network coverage thus supporting the scalability of LoRa networks.

We present advancements in the design and development of in-vehicle infotainment systems that utilize gesture input and ultrasonic mid-air haptic feedback. Such systems employ state-of-the-art hand tracking technology and novel haptic feedback technology and promise to reduce driver distraction while performing a secondary task therefore cutting the risk of road accidents. In this paper, we document design process considerations during the development of a mid-air haptic gesture-enabled user interface for human-vehicle-interactions. This includes an online survey, business development insights, background research, and an agile framework component with three prototype iterations and user-testing on a simplified driving simulator. We report on the reasoning that led to the convergence of the chosen gesture-input and haptic-feedback sets used in the final prototype, discuss the lessons learned, and give hints and tips that act as design guidelines for future research and development of this technology in cars.

Ultrasound is beyond the range of human hearing and tactile perception. In the past few years, several modulation techniques have been invented to overcome this and evoke perceptible tactile sensations of shapes and textures that can be felt, but not seen. Therefore, mid-air haptic technology has found use in several human computer interaction applications and is the focus of multiple research efforts. Visualising the induced acoustic pressure field can help understand and optimise how different modulation techniques translate into tactile sensations. Here, rather than using acoustic simulation tools to do that, we exploit the micro-displacement of a thin layer of oil to visualize the impinging acoustic pressure field outputted from an ultrasonic phased array device. Our demo uses a light source to illuminate the oil displacement and project it onto a screen to produce an interactive lightbox display. Interaction is facilitated via optical hand-tracking technology thus enabling an instantaneous and aesthetically pleasing visualisation of mid-air haptics.

Employing a 2x2 within-subjects design, forty-eight experienced drivers (28 male, 20 female) undertook repeated button selection and 'slider-bar' manipulation tasks, to compare a traditional touchscreen with a virtual mid-air gesture interface in a driving simulator. Both interfaces were tested with and without haptic feedback generated using ultrasound. Results show that combining gestures with mid-air haptic feedback was particularly promising, reducing the number of long glances and mean off-road glance time associated with the in-vehicle tasks. For slider-bar tasks in particular, gestures-with-haptics was also associated with the shortest interaction times, highest number of correct responses and least 'overshoots', and was favoured by participants. In contrast, for button-selection tasks, the touchscreen was most popular, enabling the highest accuracy and quickest responses, particularly when combined with haptic feedback to guide interactions, although this also increased visual demand. The study shows clear potential for gestures with mid-air ultrasonic haptic feedback in the automotive domain.

Haptics is an important part of the VR space as seen by the plethora of haptic controllers available today. Recent advancements have enabled touchless haptic feedback through the use of focused ultrasound thereby removing the need for a controller. Here, we present the world's first mid-air haptic rhythm game in VR and describe the reasoning behind its interface and gameplay, and in particular, how these were enabled by the effective use of state-of-the-art ultrasonic haptic technology.

Haptics is an important part of the VR space as seen by the plethora of haptic controllers available today. By using a novel ultrasonic haptic device, we developed and integrated mid-air haptic sensations without the need to wear or hold any equipment in a VR game experience. The compelling experience combines visual, audio and haptic stimulation in a supernatural narrative in which the user takes on the role of a wizard apprentice. By using different haptified patterns we could generate a wide range of sensations which mimic supernatural interactions (wizard spells). We detail our methodology and briefly discuss our findings and future work.

The performance of distributed wireless communication systems is dictated by the system boundaries and the interference regimes. In this paper, we present a novel coverage and connectivity analysis of a wireless system within confined domains. Specifically, a system where the receiver connects to the nearest transmitter is analyzed. Using tools from stochastic geometry, we derive general expressions quantifying the dependence of the system performance on the location of the receiver for general geometries, inclusive of circles and rectangles. The developed theory and expressions provide new insights on where additional nodes must be deployed in an existing network in order to maximize a desired quality of service. We further extend the analysis to networks with multiple collaborating transmitters which use maximum ratio transmission (MRT) or joint transmission such as in CoMP and other distributed antenna systems. Our results indicate that while having more collaborating transmitters can improve the performance of the system, artefacts due to the domain geometries cannot be eliminated. We corroborate our analysis through simulations.

We propose a new approach towards wireless localisation related to scenarios where the device positions are known a priori, however the device IDs are not, and therefore need to be matched using RF methods. We propose a maximum-likelihood based matching algorithm called MLMatch for resolving this problem based on measured RSSI values. Since the search space of node-to-positions permutations grows factorially with the number of target devices, an Integer Linear Programming formulation is therefore utilised to reduce computation time. In addition, we analyse the stability of the algorithm with respect to different fading models and other wireless propagation parameters such as pathloss. Finally, we report on experiments performed indoors and outdoors using up to 33 wireless devices in order to validate our results.

We experimentally validate that the spectral flatness of a received RF signal is significantly correlated with ranging errors based on signal strength inversion techniques. Therefore, we propose the use of spectral flatness as a heuristic weight for wireless localisation methods employing weighted multilateration, and demonstrate significant localisation accuracy improvements.

We propose new approaches toward wireless localization of devices belonging to the Internet of Things (IoT), specifically related to scenarios where the device positions are known a priori, however, the device IDs are not. These positions and device IDs therefore need to be matched using radio frequency positioning methods, which are more time and cost efficient as compared to manual installation. Immediate examples of real world applications include but are not limited to smart lighting and heating. We propose maximum-likelihood matching algorithms called MLMatch and MLMatch3D for resolving this problem based on measured received signal strength indicator values. Since the search space of node-to-position permutations grows factorially with the number of target devices, we propose several searching methods including mixed integer programming, linear programming relaxation to reduce computation time. The MLMatch3D algorithm further addresses the problem whereby nodes are located at multiple rooms and/or floors of a building. This algorithm first utilizes a graph partitioning method to determine in which room a node is located, followed by MLMatch for finding room specific positions corresponding to each node. In addition, this paper analyzes the stability of these algorithms with respect to different wireless fading models as well as compares the performance of these algorithms in various environments via numerical simulations. Finally, we report on experiments performed indoors and outdoors using up to 33 wireless devices in order to demonstrate the problem and validate our results.

The connectivity properties of ad hoc networks have been extensively studied over the past few years, from local observables, to global network properties. In this paper we introduce a novel layer of network dynamics which lives and evolves on top of the ad hoc network. Nodes are assumed selfish and a snow-drift type game is defined dictating the way nodes decide to allocate their cooperative resource efforts towards other nodes in the network. The dynamics are strongly coupled with the physical network causing the cooperation network topology to converge towards a stable equilibrium state, a global maximum of the total pay-off. We study this convergence from a connectivity perspective and analyse the inherent parameter dependence. Moreover, we show that direct reciprocity can be an efficient incentive to promote cooperation within the network and discuss the analogies between our simple yet tractable framework with D2D proximity based services such as LTE-Direct. We argue that cooperative network dynamics have many application in ICT, not just ad hoc networks, and similar models as the one described herein can be devised and studied in their own right.

One limiting factor to the performance of mobile ad hoc networks is the amount of interference that is experienced by each node. In this paper we will use the well established Random Waypoint Mobility Model (RWPM) to represent such a network of mobile devices, and show that the connectivity of a receiver at different parts of the network domain varies significantly. This is a result of a large portion of the nodes in the RWPM being located near the centre of the domain resulting in increased levels of interference between neighbouring devices. A non-trivial trade-off therefore exists between the spatial intensity of interfering signals and non-interfering (useful) ones. Using tools from stochastic geometry, we derive novel closed form expressions for the spatial distribution of nodes in a rectangle and the connection probability for an interference limited network indicating the impact an inhomogeneous distribution of nodes has on a network's performance. Results can therefore be used to analyse this trade-off and optimize network performance, for example through dynamic transmission schemes and adaptive routing protocols.

In this paper, we present a framework for distributively optimizing the transmission strategies of secondary users in an ad hoc cognitive radio network. In particular, the proposed approach allows secondary users to set their transmit powers and channel access probabilities such that, on average, the quality of service of both the primary and secondary networks are satisfied. The system under consideration assumes several primary and secondary transceiver pairs and assumes no cooperation or information exchange between neither primary and secondary users nor among secondary users. The outage probability, and consequently the connection probability, is derived for the system and is used in defining a new performance metric in the optimization problem using tools from stochastic geometry. We refer to this metric as the spatial density of successful transmission. We corroborate our derivations through numerical evaluations. We further demonstrate that even in the absence of any form of cooperation, an acceptable quality of service can be attained in the cognitive radio environment.

Random geometric networks are mathematical structures consisting of a set of nodes placed randomly within a bounded set V ⊆ ℝdmutually coupled with a probability dependent on their Euclidean separation, and are the classic model used within the expanding field of ad hoc wireless networks. In order to rank the importance of the network's communicating nodes, we consider the well established `betweenness' centrality measure (quantifying how often a node is on a shortest path of links between any pair of nodes), providing an analytic treatment of betweenness within a random graph model by deriving a closed form expression for the expected betweenness of a node placed within a dense random geometric network formed inside a disk of radius R. We confirm this with numerical simulations, and discuss the importance of the formula for mitigating the `boundary effect' connectivity phenomenon, for cluster head node election protocol design and for detecting the location of a network's `vulnerability backbone'.

For data sets retrieved from wireless sensors to be insightful, it is often of paramount importance that the data be accurate and also location stamped. This paper describes a maximum-likelihood based multihop localization algorithm called kHopLoc for use in wireless sensor networks that is strong in both isotropic and anisotropic network deployment regions. During an initial training phase, a Monte Carlo simulation is utilized to produce multihop connection density functions. Then, sensor node locations are estimated by maximizing local likelihood functions of the hop counts to anchor nodes. Compared to other multihop localization algorithms, the proposed kHopLoc algorithm achieves higher accuracy in varying network configurations and connection link-models.

We study wireless ad hoc networks in the absence of any channel contention or transmit power control and ask how antenna directivity affects network connectivity in the interference limited regime. We answer this question by deriving closed-form expressions for the outage probability, capacity and mean node degree of the network using tools from stochastic geometry. These novel results provide valuable insights for the design of future ad hoc networks. Significantly, our results suggest that the more directional the interfering transmitters are, the less detrimental are the effects of interference to individual links. We validate our analytical results through computer simulations.

Wireless networks are fundamentally limited by the intensity of the received signals and by their inherent interference. It is shown here that in finite ad hoc networks where node placement is modelled according to a Poisson point process and no carrier sensing is employed for medium access, the SINR received by nodes located at the border of the network deployment/operation region is on average greater than the rest. This is primarily due to the uneven interference landscape of such networks which is particularly kind to border nodes giving rise to all sorts of performance inhomogeneities and access unfairness. Using tools from stochastic geometry we quantify these spatial variations and provide closed form communication-theoretic results showing why the receiver's location is so important.

We study the effect of stochastic wireless channel models on the connectivity of ad hoc networks. Unlike in the deterministic geometric disk model where nodes connect if they are within a certain distance from each other, stochastic models attempt to capture small-scale fading effects due to shadowing and multipath received signals. Through analysis of local and global network observables, we present conclusive evidence suggesting that network behaviour is highly dependent upon whether a stochastic or deterministic connection model is employed. Specifically we show that the network mean degree is lower (higher) for stochastic wireless channels than for deterministic ones, if the path loss exponent is greater (lesser) than the spatial dimension. Similarly, the probability of forming isolated pairs of nodes in an otherwise dense random network is much less for stochastic wireless channels than for deterministic ones. The latter realisation explains why the upper bound of k-connectivity is tighter for stochastic wireless channels. We obtain closed form analytic results and compare to extensive numerical simulations.

We consider the probability that a dense wireless network confined within a given convex geometry is fully connected. We exploit a recently reported theory to develop a systematic methodology for analytically characterizing the connectivity probability when the network resides within a convex right prism, a polyhedron that accurately models many geometries that can be found in practice. To maximize practicality and applicability, we adopt a general point-to-point link model based on outage probability, and present example analytical and numerical results for a network employing 2 × 2 multiple-input multiple-output (MIMO) maximum ratio combining (MRC) link level transmission confined within particular bounding geometries. Furthermore, we provide suggestions for extending the approach detailed herein to more general convex geometries.

Nodes in ad hoc networks with randomly oriented directional antenna patterns typically have fewer short links and more long links which can bridge together otherwise isolated subnetworks. This network feature is known to improve overall connectivity in 2D random networks operating at low channel path loss. To this end, we advance recently established theoretical results to obtain analytic expressions for the mean degree of 3D networks for simple but practical anisotropic gain profiles, including those of patch, dipole and end-fire array antennas. Our analysis reveals that for homogeneous systems (i.e, neglecting boundary effects) directional radiation patterns are superior to the isotropic case only when the path loss exponent is less than the spatial dimension. Moreover, we establish that ad hoc networks utilizing directional transmit and isotropic receive antennas (or vice versa) are always sub-optimally connected regardless of the environment path loss. We extend our analysis to investigate inhomogeneous systems, and study the geometrical reasons why boundary effects cause directional radiating nodes to be at a disadvantage to isotropic ones. Finally, we discuss multi-directional gain patterns consisting of many equally spaced lobes which could be used to mitigate boundary effects and improve overall network connectivity.