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© 2024 Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0, Traditional dynamic energy management methods optimize the energy usage in wireless sensor nodes adjusting their behavior to the operating conditions. However, this comes at the cost of losing the predictability in the operation of the sensor nodes. This loss of predictability is particularly problematic for the battery life, as it determines when the nodes need to be serviced. In this paper, we propose an energy and relevance-aware monitoring method, which leverages the principles of self-awareness to address this challenge. On one hand, the relevance-aware behavior optimizes how the monitoring efforts are allocated to maximize the monitoring accuracy; while on the other hand, the power-aware behavior adjusts the overall energy consumption of the node to achieve the target battery life. The proposed method is able to balance both behaviors so as to achieve the target battery life, at the same time is able to exploit variations in the collected data to maximize the monitoring accuracy. Furthermore, the proposed method coordinates two different adaptive schemes, a dynamic sampling period scheme, and a dual prediction scheme, to adjust the behavior of the sensor node. The evaluation results show that the proposed method consistently meets its battery lifetime goal, even when the operating conditions are artificially changed, and is able to improve the mean square error of the collected signal by up to 20% with respect to the same method with the relevance-aware behavior disabled, and of up to 16% with respect the same algorithm with just the adaptive sampling period or the dual prediction scheme enabled. Consequently showing the ability of the proposed method of making appropriate decisions to balance the competing interest of its two behaviors and coordinate the two adaptive schemes to improve their performance., This study was supported by the Agència de Gestió d’Ajuts Universitaris i de Recerca (AGAUR 2019 DI 075 to David Arnaiz). The founder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript., Peer Reviewed, Postprint (published version)

Modular quantum computing architectures are a promising alternative to monolithic QPU (Quantum Processing Unit) designs for scaling up quantum devices. They refer to a set of interconnected QPUs or cores consisting of tightly coupled quantum bits that can communicate via quantum-coherent and classical links. In multi-core architectures, it is crucial to minimize the amount of communication between cores when executing an algorithm. Therefore, mapping a quantum circuit onto a modular architecture involves finding an optimal assignment of logical qubits (qubits in the quantum circuit) to different cores with the aim to minimize the number of expensive inter-core operations while adhering to given hardware constraints. In this paper, we propose for the first time a Quadratic Unconstrained Binary Optimization (QUBO) technique to encode the problem and the solution for both qubit allocation and inter-core communication costs in binary decision variables. To this end, the quantum circuit is split into slices, and qubit assignment is formulated as a graph partitioning problem for each circuit slice. The costly inter-core communication is reduced by penalizing inter-core qubit communications. The final solution is obtained by minimizing the overall cost across all circuit slices. To evaluate the effectiveness of our approach, we conduct a detailed analysis using a representative set of benchmarks having a high number of qubits on two different multi-core architectures. Our method showed promising results and performed exceptionally well with very dense and highly-parallelized circuits that require on average 0.78 inter-core communications per two-qubit gate., MB and SF would like to acknowledge funding from Intel Corporation. EA and CGA acknowledge support from the EU, grant HORIZON-EIC-2022-PATHFINDEROPEN-01-101099697 (QUADRATURE). SA acknowledges support from the EU, grant HORIZON-ERC-2021-101042080 (WINC) and GV acknoledges support from NWO QSC grant BGR2 17.269, Peer Reviewed, Postprint (author's final draft)

Quantum computing has revolutionized the field of computer science with its extraordinary ability to handle classically intractable problems. To realize its potential, however, quantum computers need to scale to millions of qubits, a feat that will require addressing fascinating yet extremely challenging interconnection problems. In this paper, we provide a context analysis of the nascent quantum computing field from the perspective of communications, with the aim of encouraging the on-chip networks community to contribute and pave the way for truly scalable quantum computers in the decades to come., Authors acknowledge support from the European Research Council (ERC) under GA 101042080 (WINC) and the European Innovation Council (EIC) Pathfinder scheme, GA 101099697 (QUADRATURE)., Peer Reviewed, Postprint (author's final draft)

© 2023 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., Hyperdimensional computing (HDC) is an emerging computing paradigm that represents, manipulates, and communicates data using long random vectors known as hypervectors. Among different hardware platforms capable of executing HDC algorithms, in-memory computing (IMC) has shown promise as it is very efficient in performing matrix-vector multiplications, which are common in the HDC algebra. Although HDC architectures based on IMC already exist, how to scale them remains a key challenge due to collective communication patterns that these architectures required and that traditional chip-scale networks were not designed for. To cope with this difficulty, we propose a scale-out HDC architecture called WHYPE, which uses wireless in-package communication technology to interconnect a large number of physically distributed IMC cores that either encode hypervectors or perform multiple similarity searches in parallel. In this context, the key enabler of WHYPE is the opportunistic use of the wireless network as a medium for over-the-air computation. WHYPE implements an optimized source coding that allows receivers to calculate the bit-wise majority of multiple hypervectors (a useful operation in HDC) being transmitted concurrently over the wireless channel. By doing so, we achieve a joint broadcast distribution and computation with a performance and efficiency unattainable with wired interconnects, which in turn enables massive parallelization of the architecture. Through evaluations at the on-chip network and complete architecture levels, we demonstrate that WHYPE can bundle and distribute hypervectors faster and more efficiently than a hypothetical wired implementation, and that it scales well to tens of receivers. We show that the average error rate of the majority computation is low, such that it has negligible impact on the accuracy of HDC classification tasks., Postprint (author's final draft)

The purpose of this project is to study the impact of shared micro-mobility on the environment and the development of advanced solutions to reduce the environmental impacts of shared micro-mobility. This project consists of the design and development of a solar energy harvesting system for powering an e-scooter used in a shared micro-mobility MaaS., El propósito de este proyecto es estudiar el impacto de la micromovilidad compartida en el medio ambiente y el desarrollo de soluciones avanzadas para reducir los impactos ambientales de la micromovilidad compartida. Este proyecto consiste en el diseño y desarrollo de un sistema de captación de energía solar para alimentar un e-scooter utilizado en un MaaS de micromovilidad compartida., L'objectiu d'aquest projecte és estudiar l'impacte de la micro-mobilitat compartida en el medi ambient i el desenvolupament de solucions avançades per reduir els impactes ambientals de la micro-mobilitat compartida. Aquest projecte consisteix en el disseny i desenvolupament d'un sistema de captació d'energia solar per alimentar un scooter elèctric utilitzat en un MaaS de micro-mobilitat compartit.

The grand challenge of scaling up quantum computers requires a full-stack architectural standpoint. In this position paper, we will present the vision of a new generation of scalable quantum computing architectures featuring distributed quantum cores (Qcores) interconnected via quantum-coherent qubit state transfer links and orchestrated via an integrated wireless interconnect., All authors acknowledge support from the EU, grant HORIZON-ERC-101042080 and grant HORIZON-EIC-2022-PATHFINDEROPEN-01-101099697, QUADRATURE., Peer Reviewed, Postprint (author's final draft)

Modular quantum computing architectures offer a promising alternative to monolithic designs for overcoming the scaling limitations of current quantum computers. To achieve scalability beyond small prototypes, quantum architectures are expected to adopt a modular approach, featuring clusters of tightly connected quantum bits with sparser connections between these clusters. Efficiently distributing qubits across multiple processing cores is critical for improving quantum computing systems’ performance and scalability. To address this challenge, we propose the Hungarian Qubit Assignment (HQA) algorithm, which leverages the Hungarian algorithm to improve qubit-to-core assignment. The HQA algorithm considers the interactions between qubits over the entire circuit, enabling fine-grained partitioning and enhanced qubit utilization. We compare the HQA algorithm with state-of-the-art alternatives through comprehensive experiments using both real-world quantum algorithms and random quantum circuits. The results demonstrate the superiority of our proposed approach, outperforming existing methods, with an average improvement of 1.28×., This work was supported in part by the European Research Council (ERC) under Grant 101042080 (WINC) and in part by the European Innovation Council (EIC) Pathfinder scheme under Grant 101099697 (QUADRATURE)., Peer Reviewed, Postprint (author's final draft)

Wireless communications at the chip scale emerge as a interesting complement to traditional wire-based approaches thanks to their low latency, inherent broadcast nature, and capacity to bypass pin constraints. However, as current trends push towards massive and bandwidth-hungry processor architectures, there is a need for wireless chip-scale networks that exploit and share as many channels as possible. In this context, this work addresses the issue of channel sharing by exploring the design space of multi-channel Medium Access Control (MAC) protocols for chip-scale networks. Distinct channel assignment strategies for both random access and token passing are presented and evaluated under realistic traffic patterns. It is shown that, even with the improvements enabled by the multiple channels, both protocols maintain their intrinsic advantages and disadvantages., This work is supported by the European Commission under H2020 grant WiPLASH (GA 863337) and HE grant WINC (GA 101042080)., Peer Reviewed, Postprint (author's final draft)

Quantum reinforcement learning (QRL), a cutting-edge field at the intersection of quantum computing and artificial intelligence, has the potential to revolutionize domains like chemistry and autonomous systems with its computational advantages. The free energy-based reinforcement learning algorithm (FERL) is a QRL algorithm inspired by the classical deep Q-learning algorithm (DQN) which uses a quantum Boltzmann machine (QBM) as the Q-function with quantum annealing (QA) as the solver. It has demonstrated considerable advantage compared to its classical counterpart DQN. The aim of this project is exploring the replacement of QA with the quantum approximate optimization algorithm (QAOA) and its recursive variant (RQAOA). We focus on the one-dimensional beam target steering control task based on the beam optics of the TT24-T4 transfer line at CERN. We perform and compare simulations of QA and QAOA, obtaining successful results for both QAOA and RQAOA, noticing that the performance of FERL using RQAOA for p=1 as a solver is very similar to the obtained through simulated QA for this scenario. The success of this experiment might lead the application of the QAOA solver to the hybrid actor-critic algorithm in development at CERN which allows to tackle control tasks using a continuous action space., L'aprenentatge per reforçament quàntic (QRL), un camp de vanguardia a la intersecció de la computació quàntica i la intel·ligència artificial, té el potencial de revolucionar àmbits com la química i els sistemes autònoms gràcies als seus avantatges computacionals. L'algorisme d'aprenentatge per reforçament basat en l'energia lliure (FERL) és un algorisme de QRL inspirat en l'algorisme clàssic d'aprenentatge profund deep Q-learning (DQN), que utilitza una màquina quàntica de Boltzmann (QBM) com a funció Q amb alineament quàntic (QA) com a solucionador. Ha demostrat una notable avantatge en comparació amb el seu homòleg clàssic DQN. L'objectiu d'aquest projecte és explorar la substitució del QA per l'algorisme quàntic d'optimització aproximada (QAOA) i la seva variant recursiva (RQAOA). Ens centrem en la tasca de control de la direcció d'objectiu de feix unidimensional basada en l'òptica de feix de la línia de transferència TT24-T4 a CERN. Realitzem i comparem simulacions de QA i QAOA, obtenint resultats satisfactoris per a QAOA i RQAOA, observant que el rendiment de FERL utilitzant RQAOA per a p=1 com a solucionador és molt similar al que s'obté a través de QA simulat per a aquest escenari. L'èxit d'aquest experiment podria conduir a l'aplicació del solucionador QAOA a l'algorisme d'actor-crític híbrid en desenvolupament a CERN, el qual permet abordar tasques de control utilitzant un espai d'acció continu.

© 2023 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., Self-awareness has been successfully utilized to create adaptive behaviors in wireless sensor nodes. However, its adoption can be daunting in scenarios, such as structural health monitoring, where the monitored environment is too complex for it to be accurately modeled by a sensor node. This article addresses this challenge by proposing a novel and lightweight anomaly-aware monitoring method for structural health monitoring that can be directly executed by a sensor node. Instead of modeling the complete structure, the proposed anomaly-aware monitoring method uses the vibration measurements of the sensor node to identify local deviations in the dynamic response of the monitored structure. The self-awareness module can then use this information to guide the dynamic behavior of the sensor node, replacing more resource-intensive structural models. We use data from multiple public benchmark structures to evaluate different features and propose an unsupervised feature selection method. Additionally, we evaluate different anomaly detection algorithms comparing their ability to detect local structural damages, also taking into account their memory and energy cost. The proposed method has been implemented in a commercial sensor node, and deployed in a scaled structure where various damage scenarios were simulated to validate the proposed method, where it was able to successfully detect the presence of damages in over 88% of the cases. Finally, we showcase how the proposed method can enhance self-awareness through the use of a simulation, where the proposed monitoring method was able to extend the battery life of the sensor node by over 59%, without impacting the node’s ability to swiftly detect damages in the structure., This work was supported in part by the Industrial Doctorate Plan of the Department of Research and Universities of the Generalitat de Catalunya. The work of David Arnaiz was supported by Agència de Gestió d’Ajuts Universitaris de Recerca under Grant AGAUR 2019 DI 075., Peer Reviewed, Postprint (published version)

Multi-Chiplet architectures are being increasingly adopted to support the design of very large systems in a single package, facilitating the integration of heterogeneous components and improving manufacturing yield. However, chiplet-based solutions have to cope with limited inter-chiplet routing resources, which complicate the design of the data interconnect and the power delivery network. Emerging in-package wireless technology is a promising strategy to address these challenges, as it allows to implement flexible chiplet interconnects while freeing package resources for power supply connections. To assess the capabilities of such an approach and its impact from a full-system perspective, herein we present an exploration of the performance of in-package wireless communication, based on dedicated extensions to the gem5-X simulator. We consider different Medium Access Control (MAC) protocols, as well as applications with different runtime profiles, showcasing that current in-package wireless solutions are competitive with wired chiplet interconnects. Our results show how in-package wireless solutions can outperform wired alternatives when running artificial intelligence workloads, achieving up to a 2.64× speed-up when running deep neural networks (DNNs) on a chiplet-based system with 16 cores distributed in four clusters., This work has been partially supported by the EC H2020 WiPLASH project (GA No. 863337) and the EC H2020 FVLLMONTI project (GA No. 101016776), Peer Reviewed, Postprint (author's final draft)

Quantum computing is envisioned as a potential revolution that could solve particular problems that classical computers can't solve. While there's a lot of research in algorithms for quantum computing, the current limitations in the development of this technology lies in the hardware and the physical implementation. The basic unit of information, the qubit, is extremely sensitive to crosstalk, electromagnetic radiations and thermal excitation. Nowadays, only a few hundred useful qubits have been built on a chip, yet thousands or even millions are required to beat classical computers. Apart from qubits, quantum computers require extra circuitry such as control and readout electronics. Resonators that show a high quality factor are known as excellent candidates to perform qubit measurements. Moreover, their nature indicates they could act as quantum buses and quantum memories. However, they take a large area and are built with expensive technologies and show a very limited configurability. In this work, a 22-nm FDSOI CMOS tunnable resonator is proposed, to operate at cryogenic temperatures. The physical principles that are presented and derived show how this resonator can be configured to read an array of qubits in a multiplexed fashion. The design maximizes quality factor and tunable frequency range. As future works, the fact that the resonance frequency is modifiable means this design could be used to coherently move information between distant qubits.

In the current contribution, we examine the feasibility of fully-energy-autonomous operation of reconfigurable intelligent surfaces (RIS) through wireless energy harvesting (EH) from incident information signals. Towards this, we first identify the main RIS energy-consuming components and present a suitable and accurate energy-consumption model that is based on the recently proposed integrated controller architecture and includes the energy consumption needed for channel estimation. Building on this model, we introduce a novel RIS architecture that enables EH through RIS unit-cell (UC) splitting. Subsequently, we introduce an EH policy, where a subset of the UCs is used for beamsteering, while the remaining UCs absorb energy. In particular, we formulate a subset allocation optimization problem that aims at maximizing the signal-to-noise ratio (SNR) at the receiver without violating the RIS’s energy consumption demands. As a problem solution, we present low-complexity heuristic algorithms. The presented numerical results reveal the feasibility of the proposed architecture and the efficiency of the presented algorithms with respect to both the optimal and very high-complexity brute-force approach and the one corresponding to random subset selection. Furthermore, the results reveal how important the placement of the RIS as close to the transmitter as possible is, for increasing the harvesting effectiveness., This work was supported by the Luxembourg National Research Fund (FNR) under the CORE project RISOTTI (ref. 14773976), the European Commission’s Horizon 2020 research and innovation programme (ARIADNE) under grant agreement No. 871464, and the Digital Futures center., Peer Reviewed, Postprint (published version)

Wireless communications in the terahertz band have been recently proposed as complement to conventional wired interconnects within computing packages. Such environments are typically highly reverberant, hence showing long channel impulse responses and severely limiting the achievable rates. Fortunately, this communications scenario is static and can be pre-characterized, which opens the door to techniques such as time reversal. Time reversal acts a spatial matched filter and has a spatiotemporal focusing effect, which allows not only to increase the achievable symbol rates, but also to create multiple spatial channels. In this paper, the multi-user capability of time reversal is explored in the context of wireless communications in the terahertz band within a computing package. Full-wave simulations are carried out to validate the approach, whereas modulation streams are simulated to evaluate the error rate as a function of the transmitted power, symbol rate, and number of simultaneous transmissions., Authors acknowledge support from the European Union’s Horizon 2020 research and innovation program, grant agreement 863337 (WiPLASH), the European Research Council (ERC) under grant agreement 101042080 (WINC) as well as the European Innovation Council (EIC) PATHFINDER scheme, grant agreement No 101099697 (QUADRATURE)., Peer Reviewed, Postprint (author's final draft)

(English) Despite its tremendous potential, it is still unclear how quantum computing will scale to satisfy the requirements of its most powerful applications. Continued progress in the fabrication and control of qubits is certainly required. However, there are hard limits to the number of qubits that can be integrated into a single chip. Multi-core quantum computing has been identified as a solution to the scalability problem of quantum computing, and included in the development roadmaps of the leading industry. Nevertheless, interconnecting quantum chips is not trivial, as quantum communications have their share of quantum weirdness. Quantum data cannot be copied, and decoherence is an unforgiving noise source for every qubit transfer, where every extra nanosecond counts and retransmission is physically impossible. Despite all these challenges, a comprehensive approach to quantum computer design based on multi-core architectures that leverages all the potential of quantum communications is crucial to unlocking the scalability issues. In this context, the present thesis aims to lay the foundations of such a communications-enabled multi-core quantum computing architecture, as a proposed vision for the ultimate success of quantum computing. Our goal is to design a multi-core architecture that entangles computing and communication with a complete understanding of their intertwining requirements. In this way, while putting together dozens of quantum cores (i.e. thousands or millions of qubits collaborating), we alleviate the requirements for control circuits and improve qubit isolation. In order to achieve this goal, we tackle three main tasks. First, we propose a layered approach for a double full-stack comms-enabled many-core quantum computer architecture (chapter 2), aligned with our vision. We aim to provide the basis for an architecture that may be technology-agnostic and intertwine quantum computing and communications. Secondly, using design space exploration, we, (Español) pesar de su gran potencial, es difícil de prever cómo escalará la computación cuántica para satisfacer los requisitos de sus aplicaciones más poderosas. Sin duda es necesaria la mejora en la fabricación y el control de qubits. Sin embargo, existen límites estrictos para la cantidad de qubits que se pueden integrar en un solo chip. Como solució, se ha propuesta la computación cuántica multinúcleo, que ya protagoniza las hojas de ruta de la industria puntera. Sin embargo, interconectar chips cuánticos no es trivial, al tener las comunicaciones cuánticas sus particularidades. Los datos cuánticos no se pueden copiar y la decoherencia es una fuente de ruido implacable: cada nanosegundo cuenta y la retransmisión es físicamente imposible. A pesar de todos estos desafíos, un enfoque integral para el diseño de computadoras cuánticas basado en arquitecturas multinúcleo que aproveche todo el potencial de las comunicaciones cuánticas es crucial para desbloquear los problemas de escalabilidad. En este contexto, la presente tesis tiene como objetivo sentar las bases de tal arquitectura, en la que las comunicaciones juegan un papel fundamental. Nuestro objetivo es diseñar una arquitectura multinúcleo que combine la informática y la comunicación con una comprensión completa de sus requisitos entrelazados. De esta manera, uniendo decenas de núcleos cuánticos (es decir, miles o millones de qubits colaborando), aliviamos a su vez los requisitos de los circuitos de control y mejoramos el aislamiento de los qubits. Para lograr este objetivo, abordamos tres tareas principales. En primer lugar, proponemos un enfoque en capas para una arquitectura de computadora cuántica multinúcleo que entrelaza computación y comunicación (capítulo 2), alineada con nuestra visión. Nuestro objetivo es proporcionar la base para una arquitectura que pueda ser independiente de la tecnología y entrelace la computación cuántica y las comunicaciones. En segundo lugar, utilizando la técnica de exploraci, Postprint (published version)

Graph Neural Networks (GNNs) have garnered a lot of recent interest because of their success in learning representations from graph-structured data across several critical applications in cloud and HPC. Owing to their unique compute and memory characteristics that come from an interplay between dense and sparse phases of computations, the emergence of recon-figurable dataflow (aka spatial) accelerators offers promise for acceleration by mapping optimized dataflows (i.e., computation order and parallelism) for both phases. The goal of this work is to characterize and understand the design-space of dataflow choices for running GNNs on spatial accelerators in order for mappers or design-space exploration tools to optimize the dataflow based on the workload. Specifically, we propose a taxonomy to describe all possible choices for mapping the dense and sparse phases of GNN inference, spatially and temporally over a spatial accelerator, capturing both the intra-phase dataflow and the inter-phase (pipelined) dataflow. Using this taxonomy, we do deep-dives into the cost and benefits of several dataflows and perform case studies on implications of hardware parameters for dataflows and value of flexibility to support pipelined execution., Parts of this work were supported through a fellowship by NEC Laboratories Europe, Project grant PID2020-112827GB-I00 funded by MCIN/AEI/ 10.13039/501100011033, RTI2018-098156-B-C53 (MCIU/AEI/FEDER,UE) and grant 20749/FPI/18 from Fundación Séneca., Peer Reviewed, Postprint (author's final draft)

Analog In-Memory Computing (AIMC) is emerging as a disruptive paradigm for heterogeneous computing, potentially delivering orders of magnitude better peak performance and efficiency over traditional digital signal processing architectures on Matrix-Vector multiplication. However, to sustain this throughput in real-world applications, AIMC tiles must be supplied with data at very high bandwidth and low latency; this poses an unprecedented pressure on the on-chip communication infrastructure, which becomes the system's performance and efficiency bottleneck. In this context, the performance and plasticity of emerging on-chip wireless communication paradigms provide the required breakthrough to up-scale on-chip communication in large AIMC devices. This work presents a many-tile AIMC architecture with inter-tile wireless communication that integrates multiple heterogeneous computing clusters, embedding a mix of parallel RISC-V cores and AIMC tiles. We perform an extensive design space exploration of the proposed architecture and discuss the benefits of exploiting emerging on-chip communication technologies such as wireless transceivers in the millimeter-wave and terahertz bands., This work was supported by the WiPLASH project (g.a. 863337), founded from the European Union’s Horizon 2020 research and innovation program., Peer Reviewed, Postprint (author's final draft)

Wireless Networks-on-Chip (WNoCs) are regarded as a disruptive alternative to conventional interconnection networks at the chip scale, yet limited by the relatively low aggregate bandwidth of such wireless networks. Hence, any method to increase the amount of concurrent channels in this scenario is of high value. In this direction, and since WNoC implies close integration of multiple antennas on a chip anyway, in this paper we present a feasibility study of compact monopole antenna arrays in a flip-chip environment at millimeter-wave and sub-terahertz frequencies. By means of a full-wave solver, we evaluate the feasibility to create, at will, concentrations of field in different spots of the chip. This way, we set the steps towards spatial multiplexing that enables concurrent multicast communications and also increases the aggregate bandwidth of the wireless network. Our results at 60 GHz show two clearly separable parallel channels that radiate simultaneously from two opposite corners of the chip, achieving a Signal-to-Interference Ratio (SIR) of around 40 dB, which proves that the channels are independent of each other even in such an enclosed environment. Further, we see potential to expand our approach to three or more concurrent channels, and to frequencies beyond 100 GHz., Authors acknowledge support from the European Union’s Horizon 2020 research and innovation program, grant agreement 863337., Peer Reviewed, Postprint (author's final draft)

The 4I4U project, which runs through 2022, aims to engage the community of citizens made up of students between the ages of 15 to 23 in the urban mobility of the future while empowering them to become actors of change who can participate in the development and evolution of their city. Led by a European Consortium composed of two cities, Barcelona in Spain and Toulouse in France, as well as education entities from high school to universities and clusters of companies in the field of urban mobility, and co-funded by the EIT Urban Mobility, the main objectives of 4I4U focus on raising awareness among young citizens in the context of urban mobility, developing their capabilities to become actors, highlighting their needs and finally creating a methodology and an environment that help students from ideation to action for the mobility of the future. The objectives of 4I4U are achieved by planning a set of seminars, round tables and brainstorming sessions to raise awareness or understanding of different aspects of urban mobility. To move from ideation to action, small groups of students design and produce a first ideation to understand and be able to project themselves into the proposed solution. This activity will be carried out under the mentoring of cities and industrialists, using the means of training institutions.

Quantum many-core processors are envisioned as the ultimate solution for the scalability of quantum computers. Based upon Noisy Intermediate-Scale Quantum (NISQ) chips interconnected in a sort of quantum intranet, they enable large algorithms to be executed on current and close future technology. In order to optimize such architectures, it is crucial to develop tools that allow specific design space explorations. To this aim, in this paper we present a technique to perform a spatio-temporal characterization of quantum circuits running in multi-chip quantum computers. Specifically, we focus on the analysis of the qubit traffic resulting from operations that involve qubits residing in different cores, and hence quantum communication across chips, while also giving importance to the amount of intra-core operations that occur in between those communications. Using specific multi-core performance metrics and a complete set of benchmarks, our analysis showcases the opportunities that the proposed approach may provide to guide the design of multi-core quantum computers and their interconnects., Peer Reviewed, Postprint (author's final draft)

The next generation of wireless communications within the framework of 6G will be operational at the low THz frequency band. Although THz systems will dramatically enhance several performance indicators such as the data rate, spectral efficiency, and latency, exploiting such technology is challenging. Electromagnetic waves confront severe propagation losses including atmospheric attenuation and diffraction. Thus, such communications are limited to line-of-sight scenarios. In 5G networks, Reconfigurable Intelligent Surfaces (RISs) are intro-duced to solve this issue by redirecting the incident wave toward the receiver and implement virtual-line-of-sight communications. In this paper, we aim to employ this paradigm for 6G networks and design a graphene-based RIS optimized to perform at multiple low atmospheric attenuation channels. We investigate the performance of this multi-wideband design through numerical and analytical analysis., Peer Reviewed, Postprint (author's final draft)

Nanoscale wireless networks are expected to revolutionize a variety of domains, with significant advances conceivable in in-body healthcare. These nanonetworks will consist of energy-harvesting nanodevices passively flowing through the bloodstream, taking actions at certain locations, and communicating results to a more powerful Body Area Network (BAN). Assuming such a setup and electro-magnetic nanocommunication in the Terahertz (THz) frequencies, we propose a network architecture that can support fine-grained localization of the energy-harvesting in-body nanonodes, as well as their two-way communication with the outside world. The main novelties of our proposal lie in the utilization of location-aware and Wake-up Radio (WuR)-based wireless nanocommunication paradigms, as well as Software-Defined Metamaterials (SDMs), for supporting the envisioned functionalities in THz-operating energy-harvesting in-body nanonetworks. We argue that, on a high level, the proposed architecture can handle a large number of nanonodes, while simultaneously dealing with a short range of THz in-body propagation and highly constrained nanonodes., The author Filip Lemic was supported by the EU Marie Curie Actions Individual Fellowship project Scalable Localization-enabled In-body Terahertz Nanonetwork (SCaLeITN), grant nr. 893760., Peer Reviewed, Postprint (author's final draft)

The next generation of wireless networks is expected to tap into the terahertz (THz) band (0.1–10 THz) to satisfy the extreme latency and bandwidth density requirements of future applications. However, the development of systems in this band is challenging as THz waves confront severe spreading and penetration losses, as well as molecular absorption, which leads to strong line-of-sight requirements through highly directive antennas. Recently, reconfigurable intelligent surfaces (RISs) have been proposed to address issues derived from non-line-of-sight (non-LoS) propagation, among other impairments, by redirecting the incident wave toward the receiver and implementing virtual-line-of-sight communications. However, the benefits provided by a RIS may be lost if the network operates at multiple bands. In this article, the suitability of the RIS paradigm in indoor THz scenarios for 6G is assessed grounded on the analysis of a tunable graphene-based RIS that can operate in multiple wideband transparency windows. A possible implementation of such a RIS is provided and numerically evaluated at 0.65/0.85/1.05 THz separately, demonstrating that beam steering and other relevant functionalities are realizable with excellent performance. Finally, the challenges associated with the design and fabrication of multiwideband graphene-based RISs are discussed, paving the way to the concurrent control of multiple THz bands in the context of 6G networks., Peer Reviewed, Postprint (author's final draft)

The reconfigurable intelligent surface is a promising technology for the manipulation and control of wireless electromagnetic signals. In particular, it has the potential to provide significant performance improvements for wireless networks. However, to do so, a proper reconfiguration of the reflection coefficients of unit cells is required, which often leads to complex and expensive devices. To amortize the cost, one may share the system resources among multiple transmitters and receivers. In this paper, we propose an efficient reconfiguration technique providing control over multiple beams independently. Compared to time-consuming optimization techniques, the proposed strategy utilizes an analytical method to configure the surface for multi-beam radiation. This method is easy to implement, effective and efficient since it only requires phase reconfiguration. We analyze the performance for indoor and outdoor scenarios, given the broadcast mode of operation. The aforesaid scenarios encompass some of the most challenging scenarios that wireless networks encounter. We show that our proposed technique provisions sufficient improvements in the observed channel capacity when the receivers are close to the surface in the indoor office environment scenario. Further, we report a considerable increase in the system throughput given the outdoor environment., The work of Gabriele Gradoni was supported by the Royal Society under Grant INF\R2\192066. This work was supported in part by the European Commission through the H2020 RISE-6G Project under Grant 101017011 and in part by the EPSRC under Grant EP/V048937/1., Peer Reviewed, Postprint (author's final draft)

Graph Neural Networks (GNNs) have exploded onto the machine learning scene in recent years owing to their capability to model and learn from graph-structured data. Such an ability has strong implications in a wide variety of fields whose data are inherently relational, for which conventional neural networks do not perform well. Indeed, as recent reviews can attest, research in the area of GNNs has grown rapidly and has lead to the development of a variety of GNN algorithm variants as well as to the exploration of ground-breaking applications in chemistry, neurology, electronics, or communication networks, among others. At the current stage research, however, the efficient processing of GNNs is still an open challenge for several reasons. Besides of their novelty, GNNs are hard to compute due to their dependence on the input graph, their combination of dense and very sparse operations, or the need to scale to huge graphs in some applications. In this context, this article aims to make two main contributions. On the one hand, a review of the field of GNNs is presented from the perspective of computing. This includes a brief tutorial on the GNN fundamentals, an overview of the evolution of the field in the last decade, and a summary of operations carried out in the multiple phases of different GNN algorithm variants. On the other hand, an in-depth analysis of current software and hardware acceleration schemes is provided, from which a hardware-software, graph-aware, and communication-centric vision for GNN accelerators is distilled., This work is possible thanks to funding from the European Union’s Horizon 2020 research and innovation programme under Grant No. 863337 (WiPLASH project) and the Spanish Ministry of Economy and Competitiveness under contract TEC2017-90034-C2-1-R (ALLIANCE project) that receives funding from FEDER., Peer Reviewed, Postprint (published version)

© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., Significant effort has been devoted to the development of dynamic monitoring techniques to exploit the temporal correlation among observations with the intention of improving the energy efficiency in wireless sensor nodes. However, the unpredictable nature of these approaches can also be a drawback for their adoption in safety-critical applications. For battery-powered sensor nodes, the predictability of the battery lifetime of the node is paramount for their correct maintenance and operation. Nevertheless, little effort has been made to provide some level of predictability in the available dynamic sampling techniques. The work presented in this article aims to solve this problem by proposing a dynamic monitoring method, capable of exploiting temporal correlation, to improve its energy usage, while at the same time being able to comply with the battery lifetime constraints. The initial evaluation tests show that the proposed sampling method is able to outperform traditional non-adaptive sampling approaches in terms of energy usage, while being able to achieve its battery lifetime goals, even in the presence of disturbances in the energy consumption of the sensor node., Award-winning, Postprint (published version)

Multi-core quantum computing has been identified as a solution to the scalability problem of quantum computing. However, interconnecting quantum chips is not trivial, as quantum communications have their share of quantum weirdness: quantum decoherence and the no-cloning theorem makes transferring qubits a harsh challenge, where every extra nanosecond counts and retransmission is simply impossible. In this paper, we present our first steps towards thorough modeling of quantum communications for multi-core quantum computers, which may be considered as a middle point between the well-known paradigms of Quantum Internet and Network-on-Chip. In particular, we stress the deep entanglement that exists between latency and error rates in quantum computing, and how this affects the quantum network design for this scenario. Moreover, we show the concomitant trade-off between computation and communication resources for a set of parameters out of state-of-the-art experimental research. The observed behavior lets us foresee the potential of multi-core quantum architectures., Peer Reviewed, Postprint (author's final draft)

L'estat de l'art dels aparells d'imatge per ressonància magnètica (IRM) es compon majoritàriament d'aparells basats en imants superconductors, que fan que aquests sistemes siguin especialment cars. En conseqüència, part de la recerca sobre IRM dels darrers anys s'ha centrat a buscar alternatives, com els aparells d'IRM basats en imants permanents. L'objectiu d'aquest projecte és dissenyar un aparell d'IRM basat en un imant permanent, tenint en compte especialment el disseny de bobines de gradient. Mitjançant el càlcul de tres paràmetres a partir de dades provinents de simulacions electromagnètiques, les geometries de les bobines que generaven els gradients més lineals han estat seleccionades i posteriorment bobinades al voltant de peces obtingudes amb impressió 3D. Diverses imatges es presenten com a resultats per avaluar la tria d'aquestes geometries. Més enllà de l'IRM, aquestes bobines de gradient també s'utilitzen per millorar l'homogeneïtat del camp magnètic generat per l'imant permanent, la qual cosa millora la resolució d'altres aplicacions de la ressonància magnètica nuclear, com l'espectroscòpia., El estado del arte de los equipos de imagen por resonancia magnética (IRM) consiste mayoritariamente en equipos basados en imanes superconductores, que hacen que estos sistemas sean especialmente caros. Consecuentemente, parte de la investigación sobre IRM de los últimos años ha estado centrada en buscar alternativas como los equipos de IRM basados en imanes permanentes. El objetivo de este proyecto es diseñar un equipo de IRM basado en un imán permanente, prestando especial atención al diseño de bobinas de gradiente. Mediante el cálculo de tres parámetros a partir de datos procedentes de simulaciones electromagnéticas, las geometrías de las bobinas que generaban los gradientes más lineales han sido seleccionadas y posteriormente bobinadas alrededor de piezas obtenidas mediante impresión 3D. Varias imágenes se presentan como resultados para evaluar la elección de estas geometrías. Además de IRM, estas bobinas de gradiente también se usan para mejorar la homogeneidad del campo magnético generado por el imán permanente, lo que mejora la resolución de otras aplicaciones de la resonancia magnética nuclear, como la espectroscopia., Most of the state-of-the-art magnetic resonance imaging (MRI) scanners are based on superconducting magnets, which makes these systems especially expensive. Consequently, part of the research on MRI of the last years has been focused on moving towards cheaper systems based on permanent magnets. This project aims to design an MRI solution based on a permanent magnet, paying particular attention to gradient coils. With the computation of three parameters from electromagnetic simulation results, the coil geometries that generated the most linear gradients were selected and subsequently wound around 3D-printed pieces. MRI data is presented to assess the chosen geometries. Furthermore, these gradient coils are used to improve the homogeneity of the magnetic field generated by the permanent magnet, which enhances the resolution in other applications of nuclear magnetic resonance, like spectroscopy., Outgoing

Relational data present in real world graph representations demands for tools capable to study it accurately. In this regard Graph Neural Network (GNN) is a powerful tool, wherein various models for it have also been developed over the past decade. Recently, there has been a significant push towards creating accelerators that speed up the inference and training process of GNNs. These accelerators, however, do not delve into the impact of their dataflows on the overall data movement and, hence, on the communication requirements. In this paper, we formulate analytical models that capture the amount of data movement in the most recent GNN accelerator frameworks. Specifically, the proposed models capture the dataflows and hardware setup of these accelerator designs and expose their scalability characteristics for a set of hardware, GNN model and input graph parameters. Additionally, the proposed approach provides means for the comparative analysis of the vastly different GNN accelerators., The authors gratefully acknowledge support from the Spanish Ministry of Science and Innovation (MICINN) under grant EIN2019-103461 and from the European Comission under grant H2020-863337-WIPLASH., Peer Reviewed, Postprint (author's final draft)

Communications within a chip or even groups of chips are typically carried out using physical connections to transmit signals between them. Nowadays, the use of wireless communications using antennas inside chip packages is being explored to eliminate the physical barrier and be able to build more efficient architectures. The main objective of this thesis is to model and simulate different types of commercial chip packages (Flip-chip, Interposer and Wirebond) and characterize the behaviour of the wireless channel within a chip. This is a crucial first step to understand the potential performance and efficiency of wireless communications in this scenario. To do this, multiple simulations have been carried out in an electromagnetic field simulation software (CST Studio Suite) using different materials, sizes and frequencies. As a result of the simulations, we have managed to characterize the communications channel for each type of chip proposed in terms of path loss and delay spread, allowing us to determine which conditions are the most suitable for in-package transmission between its antennas.

Recent developments in nanotechnology herald nanometer-sized devices expected to bring light to a number of groundbreaking applications. Communication with and among nanodevices will be needed for unlocking the full potential of such applications. As the traditional communication approaches cannot be directly applied in nanocommunication, several alternative paradigms have emerged. Among them, electromagnetic nanocommunication in the terahertz (THz) frequency band is particularly promising, mainly due to the breakthrough of novel materials such as graphene. For this reason, numerous research efforts are nowadays targeting THz band nanocommunication and consequently nanonetworking. As it is expected that these trends will continue in the future, we see it beneficial to summarize the current status in these research domains. In this survey, we therefore aim to provide an overview of the current THz nanocommunication and nanonetworking research. Specifically, we discuss the applications envisioned to be supported by nanonetworks operating in the THz band, together with the requirements such applications pose on the underlying nanonetworks. Subsequently, we provide an overview of the current contributions on the different layers of the protocol stack, as well as the available channel models and experimentation tools. Finally, we identify a number of open research challenges and outline several future research directions., The author Filip Lemic was supported by the EU Marie Skłodowska-Curie Actions Individual Fellowships (MSCAIF) project Scalable Localization-enabled In-body Terahertz Nanonetwork (SCaLeITN, grant nr. 893760). The author Pieter Stroobant was supported by a PhD grant of Ghent University’s Special Research Fund (BOF). This work was partly funded by the Ghent University’s BOF/GOA project “Autonomic Networked Multimedia Systems”. This work was also supported by the Spanish Ministry of Economy and Competitiveness under contract TEC2017-90034-C2-1-R (ALLIANCE project) that receives funding from FEDER, and by the European Commission under grants No. 736876 and No. 863337., Peer Reviewed, Postprint (author's final draft)

Generative Adversarial Networks (GANs) has become a new big topic as they are able to produce diverse high-resolution and photo-realistic images, often indistinguishable from real images and this ability has powered many real-world applications. However, these networks are limited on generating from random samples (latent vectors) with the image domain trained for. The interest of this thesis is to be able to adapt this type of models and increase the functionality of them by transforming real images through attribute conditions.

Software-Defined Metamaterials (SDMs) show a strong potential for advancing the engineered control of electromagnetic waves. As such, they are envisioned to enable a variety of exciting applications, among others in the domains of smart textiles, high-resolution structural monitoring, and sensing in challenging environments. Many of the applications envisage deformations of the SDM structures, such as their bending, stretching or rolling, which implies that the locations of metamaterial elements will be changing relative to one another. In this paper, we argue that if the metamaterial elements would be accurately localizable, this location information could potentially be utilized for enabling novel SDM applications, as well as for optimizing the control of the elements themselves. To enable their localization, we assume that these elements are controlled wirelessly through a Terahertz (THz)-operating nanonetwork. We consider the elements to be power-constrained, with their sole powering option being to harvest energy from different environmental sources. By means of simulation, we demonstrate sub-millimeter accuracy of the two-way Time of Flight (ToF)-based localization, as well as high availability of the service (i.e., consistently more than 80% of the time), which is a result of the low energy consumed in the localization process. Finally, we qualitatively characterize the latency of the proposed localization service, as well as outline several challenges and future research directions., This work was supported by the EU Marie Curie Actions Individual Fellowship, Belgium (MSCA IF) project Scalable Localization-enabled In-body Terahertz Nanonetwork (SCaLeITN), grant nr. 893760. Filip Lemic’s research stay at the Terahertz Wireless Communications Lab at Shanghai Jiao Tong University, China was supported by the Research Foundation - Flanders (FWO), Belgium in the form of a grant for a long stay abroad (grant nr. V406320N). This work also received support from the European Union via the Horizon 2020 Future Emerging Topics call (FETOPEN, grant no. 736876)., Peer Reviewed, Postprint (author's final draft)

Esta tesis presenta el diseño e implementación de la Visual Configuration Tool, y una sección de testing que describe la validación y el proceso de verificación deeste módulo de extensión del DSS-Sim.

Despite its tremendous potential, it is still unclear how quantum computing will scale to satisfy the requirements of its most powerful applications. Among other issues, there are hard limits to the number of qubits that can be integrated into a single chip. Multi-core architectures are a firm candidate for unlocking the scalability of quantum processors. Nonetheless, the vulnerability and complexity of quantum communications make this a challenging approach. A comprehensive design should imply consolidating the communications stack in the quantum computer architecture. In this paper, we explain how this vision, by entangling communications and computation in the core of the design, may help to solve the open challenges. We also summarize the first results of our application of structured design methodologies backing this vision. With our work, we hope to contribute with design guidelines that may help unleash the potential of quantum computing., Peer Reviewed, Postprint (author's final draft)

Deep neural network (DNN) models continue to grow in size and complexity, demanding higher computational power to enable real-time inference. To efficiently deliver such computational demands, hardware accelerators are being developed and deployed across scales. This naturally requires an efficient scale-out mechanism for increasing compute density as required by the application. 2.5D integration over interposer has emerged as a promising solution, but as we show in this work, the limited interposer bandwidth and multiple hops in the Network-on-Package (NoP) can diminish the benefits of the approach. To cope with this challenge, we propose WIENNA, a wireless NoP-based 2.5D DNN accelerator. In WIENNA, the wireless NoP connects an array of DNN accelerator chiplets to the global buffer chiplet, providing high-bandwidth multicasting capabilities. Here, we also identify the dataflow style that most efficienty exploits the wireless NoP's high-bandwidth multicasting capability on each layer. With modest area and power overheads, WIENNA achieves 2.2X-5.1X higher throughput and 38.2% lower energy than an interposer-based NoP design., This work was supported by the European Commission under grant 863337 and NSF under Award OAC-1909900., Peer Reviewed, Postprint (author's final draft)

As the current standardization for the 5G networks nears completion, work towards understanding the potential technologies for the 6G wireless networks is already underway. One of these potential technologies for the 6G networks is reconfigurable intelligent surfaces. They offer unprecedented degrees of freedom towards engineering the wireless channel, i.e., the ability to modify the characteristics of the channel whenever and however required. Nevertheless, such properties demand that the response of the associated metasurface is well understood under all possible operational conditions. While an understanding of the radiation pattern characteristics can be obtained through either analytical models or full-wave simulations, they suffer from inaccuracy and extremely high computational complexity, respectively. Hence, in this paper, we propose a neural network-based approach that enables a fast and accurate characterization of the metasurface response. We analyze multiple scenarios and demonstrate the capabilities and utility of the proposed methodology. Concretely, we show that this method can learn and predict the parameters governing the reflected wave radiation pattern with an accuracy of a full-wave simulation (98.8–99.8%) and the time and computational complexity of an analytical model. The aforementioned result and methodology will be of specific importance for the design, fault tolerance, and maintenance of the thousands of reconfigurable intelligent surfaces that will be deployed in the 6G network environment., This research was funded by the European Commission grant number H2020-FETOPEN736876 (VISORSURF) and by ICREA under the ICREA Academia program., Peer Reviewed, Postprint (published version)

El projecte tractarà de la concepció, disseny i implementació d'un mapa de contaminació ambiental a Terrassa en temps real

In the quest of large-scale quantum computers, multi-core distributed architectures are considered a compelling alternative to be explored. A crucial aspect in such approach is the stringent demand on communication among cores when qubits need to interact, which conditions the scalability potential of these architectures. In this work, we address the question of how the cost of the communication among cores impacts on the viability of the quantum multi-core approach. Methodologically, we consider a design space in which architectural variables (number of cores, number of qubits per core), application variables for several quantum benchmarks (number of qubits, number of gates, percentage of two-qubit gates) and inter-core communication latency are swept along with the definition of a figure of merit. This approach yields both a qualitative understanding of trends in the design space and companion dimensioning guidelines for the architecture, including optimal points, as well as quantitative answers to the question of beyond which communication performance levels the multi-core architecture pays off. Our results allow to determine the thresholds for inter-core communication latency in order for multi-core architectures to outperform single-core quantum processors., Peer Reviewed, Postprint (author's final draft)

Metasurfaces, the ultrathin, 2D version of metamaterials, have recently attracted a surge of attention for their capability to manipulate electromagnetic waves. Recent advances in reconfigurable and programmable metasurfaces have greatly extended their scope and reach into practical applications. Such functional sheet materials can have enormous impact on imaging, communication, and sensing applications, serving as artificial skins that shape electromagnetic fields. Motivated by these opportunities, this progress report provides a review of the recent advances in tunable and reconfigurable metasurfaces, highlighting the current challenges and outlining directions for future research. To better trace the historical evolution of tunable metasurfaces, a classification into globally and locally tunable metasurfaces is first provided along with the different physical addressing mechanisms utilized. Subsequently, coding metasurfaces, a particular class of locally tunable metasurfaces in which each unit cell can acquire discrete response states, is surveyed, since it is naturally suited to programmatic control. Finally, a new research direction of software-defined metasurfaces is described, which attempts to push metasurfaces toward unprecedented levels of functionality by harnessing the opportunities offered by their software interface as well as their inter- and intranetwork connectivity and establish them in real-world applications., This work was supported by the European Union’s Horizon 2020 research and innovation programme-Future Emerging Topics (FETOPEN) under grant agreement No 736876 (VISORSURF). Financial support by the National Priorities Research Program grant No. NPRP9-383-1-083 from the Qatar National Research Fund is also acknowledged. O.T. acknowledges the financial support of the Stavros Niarchos Foundation within the framework of the project ARCHERS (“Advancing Young Researchers’ Human Capital in Cutting Edge Technologies in the Preservation of Cultural Heritage and the Tackling of Societal Challenges”)., Peer Reviewed, Postprint (published version)

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., Traditional industry is experiencing a worldwide evolution with Industry 4.0. Wireless sensor networks (WSNs) have a main role in this evolution as an essential part of data acquisition. The way in which WSNs are powered is one of the main challenges to face if industry wants to achieve the digital transformation. Energy harvesting technologies are one of the possible solutions to this challenge. The main purpose of this paper is to present a novel method to taxonomize knowledge in the field of mechanical energy harvesting to enhance the use of energy harvesting technologies in industrial applications. The methodology is based on the analysis of key parameters and performance metrics for existing technologies. The taxonomy is applied to rail axles in order to select the energy harvesting technology that is more appropriate for this specific location, demonstrating the potential of mechanical energy harvesting technologies (MEHTs) for the railway industry, as a use case of industrial environment. In addition, the taxonomy allows to identify the upcoming challenges for research purposes while analyzing the compatibility among mechanical energy harvesting technologies in order to create hybrid harvesters., Peer Reviewed, Postprint (author's final draft)

Programmable metasurfaces have garnered significant attention as they confer unprecedented control over the electromagnetic (EM) response of any surface. Such feature has given rise to novel design paradigms such as Software-Defined Metamaterials (SDM) and Reconfigurable Intelligent Surfaces (RIS) with multiple groundbreaking applications. However, the development of programmable metasurfaces tailored to the particularities of a potentially large application pool becomes a daunting task because the design space becomes remarkably large. This paper aims to ease the design process by proposing a methodology that employs a semi-analytical formulation to model the response of a metasurface and, then, derives performance scaling trends as functions of a representative set of design and application-specific variables. Although the methodology is amenable to any EM functionality, this paper explores its use for the case of beam steering at 26 GHz for 5G applications. Conventional beam steering metrics are evaluated as functions of the unit cell size, number of unit cell states, and metasurface size for different incidence and reflection angles. It is shown that metasurfaces 5¿×5¿ or larger with unit cells of ¿/3 and four unit cell states ensure good performance overall. Further, it is demonstrated that performance degrades significantly for angles larger than ¿>60o and that, to combat this, extra effort is needed in the development of the unit cell. These performance trends, when combined with power and cost models, will pave the way to optimal metasurface dimensioning., This work was supported in part by the European Commission (VISORSURF) under Grant H2020-FETOPEN-736876, and in part by Catalan Institution for Research and Advanced Studies (ICREA) through the ICREA Academia Programme. Odysseas Tsilipakos acknowledges support by the Stavros Niarchos Foundation within the framework of the project Advancing Young Researchers Human Capital in Cutting Edge Technologies in the Preservation of Cultural Heritage and the Tackling of Societal Challenges (ARCHERS)., Peer Reviewed, Postprint (published version)

© <2020>. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0, Nowadays, constellations and distributed networks of satellites are emerging as clear development trends in the space system market to enable augmentation, enhancement, and possibilities of new applications for future Earth Observation (EO) missions. While the adoption of these satellite architectures is gaining momentum for the attaining of ever more stringent application requirements and stakeholder needs, the efforts to analyze their benefits and suitability, and to assess their impact for future programmes remains as an open challenge to the EO community. In this context, this paper presents the mission and system architecture conceived during the Horizon 2020 ONION project, a European Union research activity that proposes a systematic approach to the optimization of EO space infrastructures. In particular, ONION addressed the design of complementary assets that progressively supplement current programs and took part in the exploration of needs and implementation of architectures for the Copernicus Space Component for EO. Among several use cases considered, the ONION project focused on proposing system architectures to provide improved revisit time, data latency and image resolution for a demanding application scenario of interest: Marine Weather Forecast (MWF). A set of promising system architectures has been subject of a comprehensive assessment, based on mission analysis expertise and detailed simulation for evaluating several key parameters such as revisit time and data latency of each measurement of interest, on-board memory evolution and power budget of each satellite of the constellation, ground station contacts and inter-satellite links. The architectures are built with several heterogeneous satellite nodes distributed in different orbital planes. Each platform can embark different instrument sets, which provide the required measurements for each use case. A detailed mission analysis has then been performed to the selected architecture for the MWF use ca, This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 687490., Peer Reviewed, Postprint (author's final draft)

Being a very promising technology, with impressive advances in the recent years, it is still unclear how quantum computing will scale to satisfy the requirements of its most powerful applications. Although continued progress in the fabrication and control of qubits is required, quantum computing scalability will depend as well on a comprehensive architectural design considering a distributed multi-core approach as an alternative to the traditional monolithic version, hence including a communications perspective. However, this goes beyond introducing mere interconnects. Rather, it implies consolidating the full communications stack in the quantum computer structure. In this paper, we propose a double full-stack architecture encompassing quantum computation and quantum communications, which we use to address the monolithic versus distributed question with a structured design methodology. For that, we revisit the different quantum computing layers to capture and model their essence by highlighting the open design variables and performance metrics. Using behavioral models and actual measurements from existing quantum computers, the results of simulations suggest that multicore architectures may effectively unleash the full quantum computer potential., Peer Reviewed, Postprint (author's final draft)

State-of-the-art, flat structures called metasurfaces can filter and steer light and sound, render an object completely invisible to electromagnetic waves, and much more. They can deliver automation, remote operation, and advanced performance to a wide variety of existing systems, with applications in communications, medical imaging, sensing, and security. However, for non-specialists, individual metasurfaces are currently restricted to limited reusability and accessibility. This book brings together various scientific disciplines with the aim of outlining a programmable 'plug-and-play' metasurface. The book focuses on a recently proposed platform - known as the HyperSurface - that provides many electromagnetic functions of metasurfaces in a single structure, which can be controlled and reconfigured by software. This revolutionary approach paves the way for new opportunities in wireless communications and programmable wireless environments: HyperSurfaces could link networks with objects and physical environments and create smarter systems that are far more responsive to user demands. Walls that absorb radiation or block digital eavesdropping, and wireless, long-distance charging of devices are among the many possibilities. The book aspires to provide the foundational knowledge for creating an Internet of Materials, enabling smart environments at any scale - from indoor wireless communications to medical imaging equipment. Although the set of disciplines involved covers a considerable span, we hope that the material will benefit experts and students alike., Peer Reviewed, Postprint (published version)

Quantum computers have emerged as an alternative computer paradigm that will allow to solve some complex problems of large numbers that are not tractable for classical computers, e.g. factorization. Quantum computers also have the ability to simulate quantum mechanics in a real and direct way. The development of quantum computers faces many unique obstacles. In recent years, various quantum computer prototypes have been created by com- panies such as Google and IBM, on which we can run some quantum algorithms. But these prototypes are far from the quantum computers we envision and can function like today?s classical computers. It is said that we are in the time of Noisy Intermediate-Scale Quantum (NISQ) computers. This means that current quantum computers are very noisy and their size is very small compared to classical comput- ers. The challenge with small, noisy quantum devices running quantum algorithms is that due to the hardware limitations they face which must be respected, quantum algorithm needs to be modified before their execution on quantum devices. To solve this problem in quantum computers, a mapping process is needed, which is part of the compilation step that modifies the quantum algorithms to take into account all the limitations of the targeted quantum device. After mapping process, the resulting quantum circuit usually has a higher number of gates and (execution time) latency, decreasing the algorithm?s reliability. Different mapping solutions have been already proposed. Most of them are meant for a specific quan- tum processor and different in methodology, approach and features. In addition, they are usually only compared in terms of added gates (gate overhead) or added circuit execution time (latency overhead). No thorough comparative analysis of the different mapping solutions performance and features has been performed so far. In this thesis, we apply structured Design Space Exploration to the mapping of quantum circuits. By doing so, we will b

Terahertz (THz) band communications are emerging as a key technology for the next generation of wireless communications, with the potential to realize ultra-broadband Terabit-per-second (Tbps) links. However, the unique characteristics of this band pose several challenges that prevent the realization of practical communication systems as of today. At link level, the use of directional antennas (DAs) in both ends is needed to overcome a high path loss, which means that traditional medium access control (MAC) protocols cannot be reused. In this thesis, an Adaptive Directional Antenna Protocol for THz networks (ADAPT) is proposed. This is a novel MAC protocol for ultra-broadband directional wireless networks with a centralized architecture. It is based on a receiver-initiated 3-way handshake for link-level synchronization and collision avoidance. Due to the use of DAs, space is discretized in virtual sectors and a turning antenna in the access point periodically sweeping the area to provide coverage to all nodes. Adaptive sector time and adaptive modulation mechanisms are designed to improve the protocol capabilities. Apart from the 3-way handshake protocol (ADAPT-3), a 1-way version is also presented (ADAPT-1). Their performance is investigated in terms of throughput and packet discard rate through extensive simulations in TeraSim, an ns-3-based THz networks simulator. In parallel, an analytical model of the protocol is developed and validated. Results demonstrate that the proposed protocol improves the state of the art and enables small cells with throughput rates in excess of 100 Gigabit-per-second., Las telecomunicaciones en la banda de Terahercios (THz) están emergiendo como una tecnología clave para la siguiente generación de comunicaciones móviles, con potencial para llevar a la práctica enlaces de Terabit-por-segundo (Tbps). Sin embargo, las características únicas de esta banda introducen nuevos retos aún por resolver. En la capa de enlace, el uso de antenas direccionales para contrarrestar el efecto de las altas pérdidas de propagación no permite reutilizar protocolos tradicionales de control de acceso al medio (MAC). En este trabajo se presenta ADAPT (Adaptive Directional Antenna Protocol for THz networks), un protocolo MAC para redes direccionales de gran ancho de banda. El protocolo se basa en un 3-way handshake iniciado por el receptor para garantizar sincronismo a nivel de enlace y evitar colisiones. Debido al uso de antenas direccionales, el espacio se discretiza en sectores virtuales y una antena giratoria en el punto de acceso cubre periódicamente toda el área. El protocolo incluye un tiempo de sector adaptativo, así como un mecanismo de adaptación de la modulación. Además de la versión 3-way (ADAPT-3), también se presenta una versión 1-way (ADAPT-1). El rendimiento del protocolo se ha evaluado en términos de throughput y probabilidad de descarte con simulaciones en TeraSim, un simulador de redes en THz basado en ns-3. Paralelamente, se ha desarrollado y validado un modelo analítico del protocolo. Los resultados muestran que el protocolo mejora el estado del arte y permite velocidades superiores a los 100 Gigabit-por-segundo., Les telecomunicacions a la banda de Terahertzs (THz) estan emergint com una tecnologia clau per a la pròxima generació de comunicacions mòbils, amb potencial per portar a la pràctica enllaços de Terabit-per-segon (Tbps). No obstant, les característiques úniques d'aquesta banda introdueixen nous reptes encara per resoldre. A la capa d'enllaç, l'ús d'antenes direccionals per contrarestar l'efecte de les altes pèrdues de propagació no permet reutilitzar protocols tradicionals de control d'accés al medi (MAC). En aquest treball es presenta ADAPT (Adaptive Directional Atenna Protocol for THz networks), un nou protocol MAC per a xarxes direccionals i de gran ample de banda. El protocol es basa en un 3-way handshake iniciat pel receptor per garantir sincronisme a nivell d'enllaç i evitar col·lisions. Degut a l'ús d'antenes direccionals, l'espai es discretitza en sectors virtuals i una antena giratòria al punt d'accés cobreix periòdicament tota l'àrea. El protocol inclou un temps de sector adaptatiu, així com un mecanisme d'adaptació de la modulació. A banda de la versió 3-way (ADAPT-3), també es presenta una versió 1-way (ADAPT-1). El rendiment del protocol s'ha avaluat en termes de throughput i probabilitat de descartar el paquet amb extenses simulacions a TeraSim, un simulador de xarxes en THz basat en ns-3. Paral·lelament, s'ha desenvolupat i validat un model analític del protocol. Els resultats mostren que el protocol millora l'estat de l'art i permet velocitats superiors als 100 Gigabit-per-segon.