arXiv subjects

Orestis Georgiou

Publications and source records attributed to Orestis Georgiou.

At least 19 recordsLinked to original sources

arXiv2025

AcoustoBots: A swarm of robots for acoustophoretic multimodal interactions

Acoustophoresis has enabled novel interaction capabilities, such as levitation, volumetric displays, mid-air haptic feedback, and directional sound generation, to open new forms of multimodal interactions. However, its traditional implementation as a singular static unit limits its dynamic range and application versatility. This paper introduces AcoustoBots - a novel convergence of acoustophoresis with a movable and reconfigurable phased array of transducers for enhanced application versatility. We mount a phased array of transducers on a swarm of robots to harness the benefits of multiple mobile acoustophoretic units. This offers a more flexible and interactive platform that enables a swarm of acoustophoretic multimodal interactions. Our novel AcoustoBots design includes a hinge actuation system that controls the orientation of the mounted phased array of transducers to achieve high flexibility in a swarm of acoustophoretic multimodal interactions. In addition, we designed a BeadDispenserBot that can deliver particles to trapping locations, which automates the acoustic levitation interaction. These attributes allow AcoustoBots to independently work for a common cause and interchange between modalities, allowing for novel augmentations (e.g., a swarm of haptics, audio, and levitation) and bilateral interactions with users in an expanded interaction area. We detail our design considerations, challenges, and methodological approach to extend acoustophoretic central control in distributed settings. This work demonstrates a scalable acoustic control framework with two mobile robots, laying the groundwork for future deployment in larger robotic swarms. Finally, we characterize the performance of our AcoustoBots and explore the potential interactive scenarios they can enable.

cs.RO↗

arXiv2021

Smart Radio Environments

This Roadmap takes the reader on a journey through the research in electromagnetic wave propagation control via reconfigurable intelligent surfaces. Meta-surface modelling and design methods are reviewed along with physical realisation techniques. Several wireless applications are discussed, including beam-forming, focusing, imaging, localisation, and sensing, some rooted in novel architectures for future mobile communications networks towards 6G.

physics.class-ph↗

arXiv2021

LoRa Network Performance Under Ambient Energy Harvesting and Random Transmission Schemes

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.

cs.NI↗

arXiv2021

Optimal Non-Uniform Deployments of LoRa Networks

LoRa wireless technology is an increasingly prominent solution for massive connectivity and the Internet of Things. Stochastic geometry and numerical analysis of LoRa networks usually consider uniform end-device deployments. Real deployments however will often be non-uniform, for example due to mobility. This letter mathematically investigates how non-uniform deployments affect network coverage and suggest optimal deployment strategies and uplink random access transmission schemes. We find that concave deployments of LoRa end-devices with a sub-linear spread of random access inter-transmission times provide optimal network coverage performance.

cs.NI↗

arXiv2020

Reconfigurable Intelligent Surfaces and Machine Learning for Wireless Fingerprinting Localization

Reconfigurable Intelligent Surfaces (RISs) promise improved, secure and more efficient wireless communications. We propose and demonstrate how to exploit the diversity offered by RISs to generate and select easily differentiable radio maps for use in wireless fingerprinting localization applications. Further, we apply machine learning feature selection methods to prune the large state space of the RIS, thus reducing complexity and enhancing localization accuracy and position acquisition time. We evaluate our proposed approach by generation of radio maps with a novel radio propagation modelling and simulations.

eess.SP↗

arXiv2020

Designing Mid-Air Haptic Gesture Controlled User Interfaces for Cars

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.

cs.HC↗

arXiv2020

Mid-Air Haptic Bio-Holograms in Mixed Reality

We present a prototype demonstrator that integrates three technologies, mixed reality head-mounted displays, wearable bio-sensors, and mid-air haptic projectors to deliver an interactive tactile experience with a bio-hologram. Users of this prototype are able to see, touch and feel a hologram of a heart that is beating at the same rhythm as their own. The demo uses an Ultrahaptics device, a Magic Leap One Mixed Reality headset, and an Apple Watch that measures the wearer's heart rate, all synchronized and networked together such that updates from the wristband dynamically change the haptic feedback and the animation speed of the beating heart thus creating a more personalised experience.

cs.HC↗

arXiv2020

Mid-Air Haptics in Aviation -- creating the sensation of touch where there is nothing but thin air

The exciting new technology known as mid-air haptics has been adopted by several industries including Automotive and Entertainment, however it has yet to emerge in simulated pilot training or in real-life flight decks. Full-flight simulators are expensive to manufacture, maintain and operate. Not only that, each simulator is limited to one aircraft type, which is inefficient for the majority of airlines that have several in service. With the growing trend in touchscreen instrumentation, cockpit displays require the pilot's attention to be drawn away from their view out of the window. But by using gesture recognition interfaces combined with mid-air haptic feedback, we can mitigate this shortcoming while also adding another dimension to the existing technology for pilots already familiar with using legacy cockpits, complete with traditional instrumentation. Meanwhile, simulation environments using augmented and virtual reality technology offers quality immersive training to the extent that pilots can go from hundreds of hours of simulated training to being responsible for hundreds of lives on their very first flight. The software re-programmability and dynamic richness afforded by mid-air haptic technologies combined with a basic full-motion platform could allow for an interchange of instrumentation layouts thus enhancing simulation immersiveness and environments. Finally, by borrowing and exploring concepts within the automotive sector, this concept paper presents how flight deck design could evolve by adopting this technology. If pilot testimony suggests that they can adapt to virtual objects, can this replace physical controls?

cs.HC↗

arXiv2019

Wireless localization with diffusion maps

In the Wireless Localization Matching Problem (WLMP) the challenge is to match pieces of equipment with a set of candidate locations based on wireless signal measurements taken by the pieces of equipment. This challenge is complicated by the noise that is inherent in wireless signal measurements. Here we propose the use of diffusion maps, a manifold learning technique, to obtain an embedding of positions and equipment coordinates in a space that enables coordinate comparison and reliable evaluation of assignment quality at very low computational cost. We show that the mapping is robust to noise and using diffusion maps allows for accurate matching in a realistic setting. This suggests that the diffusion-map-based approach could significantly increase the accuracy of wireless localization in applications.

eess.SP↗

arXiv2019

Comment on "The hard sphere quantum propagator: exact results via partial wave analysis''

There is no known exact expression for the propagator of a non-relativistic particle colliding with a hard sphere. De Prunelé (2008 {\it J.~Phys.~A:~Math.~Theor.} {\bf 41} 255305) derived a partial wave expansion of the propagator and compared it against some known approximations, including the semiclassical Van Vleck-Gutzwiller (VG) propagator; the VG propagator was evaluated entirely numerically. Here we point out that the VG propagator for the particle-sphere problem admits an analytic expression in terms of elementary functions.

quant-ph↗

arXiv2018

Spatial networks with wireless applications

Many networks have nodes located in physical space, with links more common between closely spaced pairs of nodes. For example, the nodes could be wireless devices and links communication channels in a wireless mesh network. We describe recent work involving such networks, considering effects due to the geometry (convex,non-convex, and fractal), node distribution, distance-dependent link probability, mobility, directivity and interference.

cs.NI↗

arXiv2018

Pulsed Schlieren Imaging of Ultrasonic Haptics and Levitation using Phased Arrays

Ultrasonic acoustic fields have recently been used to generate haptic effects on the human skin as well as to levitate small sub-wavelength size particles. Schlieren imaging and background-oriented schlieren techniques can be used for acoustic wave pattern and beam shape visualization. These techniques exploit variations in the refractive index of a propagation medium by applying refractive optics or cross-correlation algorithms of photographs of illuminated background patterns. Here both background-oriented and traditional schlieren systems are used to visualize the regions of the acoustic power involved in creating dynamic haptic sensations and dynamic levitation traps. We demonstrate for the first time the application of back-ground-oriented schlieren for imaging ultrasonic fields in air. We detail our imaging apparatus and present improved algorithms used to visualize these phenomena that we have produced using multiple phased arrays. Moreover, to improve imaging, we leverage an electronically controlled, high-output LED which is pulsed in synchrony with the ultrasonic carrier frequency.

physics.med-ph↗

arXiv2018

Connectivity of Underlay Cognitive Radio Networks with Directional Antennas

In cognitive radio networks (CRNs), the connectivity of secondary users (SUs) is difficult to be guaranteed due to the existence of primary users (PUs). Most prior studies only consider cognitive radio networks equipped with omni-directional antennas causing high interference at SUs. We name such CRNs with omni-directional antennas as Omn-CRNs. Compared with an omni-directional antenna, a directional antenna can concentrate the transmitting/receiving capability at a certain direction, consequently resulting in less interference. In this paper, we investigate the connectivity of SUs in CRNs with directional antennas (named as Dir-CRNs). In particular, we derive closed-form expressions of the connectivity of SUs of both Dir-CRNs and Omn-CRNs, thus enabling tractability. We show that the connectivity of SUs is mainly affected by two constraints: the spectrum availability of SUs and the topological connectivity of SUs. Extensive simulations validate the accuracy of our proposed models. Meanwhile, we also show that Dir-CRNs can have higher connectivity than Omn-CRNs mainly due to the lower interference, the higher spectrum availability and the higher topological connectivity brought by directional antennas.

cs.NI↗

arXiv2018

Entropy of Spatial Network Ensembles

We analyze complexity in spatial network ensembles through the lens of graph entropy. Mathematically, we model a spatial network as a soft random geometric graph, i.e., a graph with two sources of randomness, namely nodes located randomly in space and links formed independently between pairs of nodes with probability given by a specified function (the "pair connection function") of their mutual distance. We consider the general case where randomness arises in node positions as well as pairwise connections (i.e., for a given pair distance, the corresponding edge state is a random variable). Classical random geometric graph and exponential graph models can be recovered in certain limits. We derive a simple bound for the entropy of a spatial network ensemble and calculate the conditional entropy of an ensemble given the node location distribution for hard and soft (probabilistic) pair connection functions. Under this formalism, we derive the connection function that yields maximum entropy under general constraints. Finally, we apply our analytical framework to study two practical examples: ad hoc wireless networks and the US flight network. Through the study of these examples, we illustrate that both exhibit properties that are indicative of nearly maximally entropic ensembles.

physics.soc-ph↗

arXiv2017

Low Power Wide Area Network Analysis: Can LoRa Scale?

Low Power Wide Area (LPWA) networks are making spectacular progress from design, standardisation, to commercialisation. At this time of fast-paced adoption, it is of utmost importance to analyse how well these technologies will scale as the number of devices connected to the Internet of Things (IoT) inevitably grows. In this letter, we provide a stochastic geometry framework for modelling the performance of a single gateway LoRa network, a leading LPWA technology. Our analysis formulates unique peculiarities of LoRa, including its chirp spread-spectrum modulation technique, regulatory limitations on radio duty cycle, and use of ALOHA protocol on top, all of which are not as common in today's commercial cellular networks. We show that the coverage probability drops exponentially as the number of end-devices grows due to interfering signals using the same spreading sequence. We conclude that this fundamental limiting factor is perhaps more significant towards LoRa scalability than for instance spectrum restrictions. Our derivations for co-spreading factor interference found in LoRa networks enables rigorous scalability analysis of such networks.

cs.NI↗

arXiv2017

Spectral statistics of random geometric graphs

We use random matrix theory to study the spectrum of random geometric graphs, a fundamental model of spatial networks. Considering ensembles of random geometric graphs we look at short range correlations in the level spacings of the spectrum via the nearest neighbour and next nearest neighbour spacing distribution and long range correlations via the spectral rigidity Delta_3 statistic. These correlations in the level spacings give information about localisation of eigenvectors, level of community structure and the level of randomness within the networks. We find a parameter dependent transition between Poisson and Gaussian orthogonal ensemble statistics. That is the spectral statistics of spatial random geometric graphs fits the universality of random matrix theory found in other models such as Erdos-Renyi, Barabasi-Albert and Watts-Strogatz random graph.

physics.soc-ph↗

arXiv2017

Optimal Non-uniform Deployments in Ultra-Dense Finite-Area Cellular Networks

Network densification and heterogenisation through the deployment of small cellular access points (picocells and femtocells) are seen as key mechanisms in handling the exponential increase in cellular data traffic. Modelling such networks by leveraging tools from Stochastic Geometry has proven particularly useful in understanding the fundamental limits imposed on network coverage and capacity by co-channel interference. Most of these works however assume infinite sized and uniformly distributed networks on the Euclidean plane. In contrast, we study finite sized non-uniformly distributed networks, and find the optimal non-uniform distribution of access points which maximises network coverage for a given non-uniform distribution of mobile users, and vice versa.

cs.NI↗

arXiv2017

How does mobility affect the connectivity of interference-limited ad-hoc networks?

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 use the 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 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. Our novel results can be used to analyse this trade-off and optimize network performance.

cs.NI↗