Cooperative Radio Communications for Green Smart Environments

The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin

Cooperative Radio Communications for Green Smart Environments

The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin

Wireless indoor localisation within the 5G internet of radio light

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonNumerous applications can be enhanced by accurate and efficient indoor localisation using wireless sensor networks, however trade-offs often exist between these two parameters. In this thesis, realworld and simulation data is used to examine the hybrid millimeter wave and Visible Light Communications (VLC) architecture of the 5G Internet of Radio Light (IoRL) Horizon 2020 project. Consequently, relevant localisation challenges within Visible Light Positioning (VLP) and asynchronous sampling networks are identified, and more accurate and efficient solutions are developed. Currently, VLP relies strongly on the assumed Lambertian properties of light sources. However, in practice, not all lights are Lambertian. To support the widespread deployment of VLC technology in numerous environments, measurements from non-Lambertian sources are analysed to provide new insights into the limitations of existing VLP techniques. Subsequently, a novel VLP calibration technique is proposed, and results indicate a 59% accuracy improvement against existing methods. This solution enables high accuracy centimetre level VLP to be achieved with non- Lambertian sources. Asynchronous sampling of range-based measurements is known to impact localisation performance negatively. Various Asynchronous Sampling Localisation Techniques (ASLT) exist to mitigate these effects. While effective at improving positioning performance, the exact suitability of such solutions is not evident due to their additional processes, subsequent complexity, and increased costs. As such, extensive simulations are conducted to study the effectiveness of ASLT under variable sampling latencies, sensor measurement noise, and target trajectories. Findings highlight the computational demand of existing ASLT and motivate the development of a novel solution. The proposed Kalman Extrapolated Least Squares (KELS) method achieves optimal localisation performance with a significant energy reduction of over 50% when compared to current leading ASLT. The work in this thesis demonstrates both the capability for high performance VLP from non- Lambertian sources as well as the potential for energy efficient localisation for sequentially sampled range measurements.Horizon 202

Digital Processing for an Analogue Subcarrier Multiplexed Mobile Fronthaul

In order to meet the demands of the fifth generation of mobile communication networks (5G), such as very high bit-rates, very low latency and massive machine connectivity, there is a need for a flexible, dynamic, scalable and versatile mobile fronthaul. Current industry fronthaul standards employing sampled radio waveforms for digital transport suffer from spectral inefficiency, making this type of transport impractical for the wide channel bandwidths and multi-antenna systems required by 5G. On the other hand, analogue transport does not suffer from these limitations. It is, however, prone to noise, non-linearity and poor dynamic range. When combined with analogue domain signal aggregation/multiplexing, it also lacks flexibility and scalability, especially at millimetre wave frequencies. Measurements (matched in simulation) of analogue transport at millimetre wave frequencies demonstrate some of these issues. High data rates are demonstrated employing wide bandwidth channels combined using traditional subcarrier multiplexing techniques. However, only a limited number of channels can be multiplexed in this manner, with poor spectral efficiency, as analogue filter limitations do not allow narrow gaps between channels. To this end, over the last few years, there has been significant investigation of analogue transport schemes combined with digital channel aggregation/ de-aggregation (combining/ separating multiple radio waveforms in the digital domain). This work explores such a technique. Digital processing is used at the transmitter to flexibly multiplex a large number of channels in a subcarrier multiplex, without the use of combiners, mixers/ up-converters or Hilbert transforms. Orthogonal Frequency Division Multiplexing (OFDM) - derived Discrete Multi-Tone (DMT) and Single Sideband (SSB) modulated channels are integrated within a single Inverse Fast Fourier Transform (IFFT) operation. Channels or channel groups are mapped systematically into Nyquist zones by using, for example, a single IFFT (for a single 5G mobile numerology) or multiple IFFTs (for multiple 5G mobile numerologies). The analogue transport signal generated in this manner is digitally filtered and band-pass sampled at the receiver such that each corresponding channel (e.g. channels destined to the same radio frequency (RF)/ millimetre wave (mmW) frequency) in the multiplex is presented at the same intermediate frequency, due to the mapping employed at the transmitter. Analogue or digital domain mixers/ down-converters are not required with this technique. Furthermore, each corresponding channel can be readily up-converted to their respective RF/mmW channels with minimal per-signal processing. Measurement results, matched in simulation, for large signal multiplexes with both generic and 5G mobile numerologies show error-vector magnitude performance well within specifications, validating the proposed system. For even larger multiplexes and/or multiplexes residing on a higher IF exceeding the analogue bandwidth and sampling rate specifications of the ADCs at the receiver, the use of a bandwidth-extension device is proposed to extend the mapping to a mapping hierarchy and relax the analogue bandwidth and sampling rate requirements of the ADCs. This allows the receiver to still use digital processing, with only minimal analogue processing, to band-pass sample smaller blocks of channels from the larger multiplex, down to the same intermediate frequency. This ensures that each block of channels is within the analogue bandwidth specification of the ADCs. Performance predictions via simulation (based on a system model matched to the measurements) show promising results for very large multiplexes and large channel bandwidths. The multiplexing technique presented in this work thus allows reductions in per-channel processing for heterogeneous networking (or multi-radio access technologies) and multi-antenna configurations. It also creates a re-configurable and adaptable system based on available processing resources, irrespective of changes to the number of channels and channel groups, channel bandwidths and modulation formats

Oberflächenemittierende Laser mit vertikaler Kavität (VCSELs) und VCSEL-Arrays für Kommunikation und Sensorik

Future generations of optical wireless communication and sensing systems require compact, low-cost, reliable, and highly efficient light sources capable of transmitting modulated beams across free space at gigabit per second (Gbps) data rates and pulsed beams with sub-nanosecond rise and fall times. The infrared vertical cavity surface emitting laser (VCSEL) is exactly one such light source. Fifth generation (5G) systems promise to connect billions of people and trillions of Internet of Things gadgets and sensors at 1 to beyond 20 Gbps via newly auctioned millimeter wave (30 GHz to 300 GHz) spectral bands. By circa 2030 sixth generation (6G) systems envision vast broadband capacity with zero latency – enabling real-time virtual and mixed realities, human-machine interfaces, autonomous vehicles, and much more. The 6G technology adds terahertz wave emitters including infrared VCSELs and VCSEL arrays to vastly increase data rates, boost energy and spectral efficiency, and take advantage of available and unregulated spectral bands. I design, fabricate, and test new experimental VCSEL diodes and novel two-dimensional (2D) VCSEL diode arrays. I study the physics and performance trade-offs of VCSEL light emitters aimed at 5G and 6G optical wireless communication and sensing applications. Via in-house computer modeling and simulation programs, I design VCSEL epitaxial structures – composed of nanometer-thick aluminum-gallium-arsenide, indium-gallium arsenide, and gallium-arsenide-phosphide layers – with peak target emission wavelengths of 940 and 980 nanometers. A commercial foundry grows my experimental VCSEL epitaxial wafers by metal-organic vapor phase epitaxy on 3-inch diameter gallium-arsenide substrates. In my university cleanroom, I fabricate my VCSELs as quarter wafer test pieces using a new VCSEL Array 2018 mask set which contains single VCSELs, and several variations of novel 2D electrically parallel triple (3-element), septuple (7-element), and novemdecuple (19-element) geometric device designs. My fabricated devices feature high frequency, coplanar ground-signal-ground metal contact pads, and top-epitaxial-surface emission. I perform all device tests in my university laser diode laboratory via direct, on-wafer electrical probing under computer control, starting with continuous wave light output power-current-voltage sweeps via a calibrated photodiode-integrating sphere and variable current source. For emission spectra and small-signal frequency response measurements, I collect the emitted VCSEL light with a standard OM1 multiple mode optical fiber (MMF) – connected to either an optical spectrum analyzer or a photoreceiver. For on-wafer data transmission tests across OM1 MMF patch cords, I modulate my VCSELs with nonreturn to zero, pseudorandom bit patterns in the form of 2-level pulse amplitude modulation. I achieve record combinations of optical output power, bandwidth, and efficiency for my large oxide aperture diameter (larger than 20 micrometers) VCSELs and for my VCSEL arrays. For example, I demonstrate 200 milliwatts of optical output power, a bandwidth of 18 GHz, and a wall plug efficiency of 35 percent with a 19-element VCSEL array. I set several records for error free data transmission, for example, 40 Gbps for my triple and septuple VCSEL arrays and 25 Gbps for my novemdecuple VCSEL arrays, well beyond the previous record of 10 Gbps. My work is the first to investigate trade-offs in the highly nontrivial physics of VCSEL arrays aimed at high power and high bandwidth arrays for free space data transmission – producing new guiding principles for further device optimization and product development.Zukünftige Generationen optischer drahtloser Kommunikations- und Sensorsysteme erfordern kompakte, kostengünstige, zuverlässige und hocheffiziente Lichtquellen, die modulierte Strahlen mit Datenraten von Gigabit pro Sekunde (Gbps) und gepulste Strahlen mit Anstieg- und Abfallzeiten im Sub-Nanosekundenbereich über den freien Raum übertragen können. Infrarote, oberflächenemittierende Laser mit vertikaler Kavität (VCSEL) sind genau eine solche Lichtquelle. Systeme der fünften Generation (5G) versprechen, Milliarden von Menschen und Billionen von Geräten und Sensoren für das Internet der Dinge mit 1 bis über 20 Gbps über neu versteigerte Millimeterwellen-Spektralbänder (30 GHz bis 300 GHz) zu verbinden. Bis etwa 2030 sehen Systeme der sechsten Generation (6G) eine enorme Breitbandkapazität ohne Latenzzeit vor – sie ermöglichen virtuelle und gemischte Realitäten in Echtzeit, Mensch-Maschine-Schnittstellen, autonome Fahrzeuge und vieles mehr. Die 6G-Technologie fügt Terahertz-Wellensender hinzu, einschließlich Infrarot-VCSELs und VCSEL-Arrays, um die Datenraten signifikant zu erhöhen, die Energie- und Spektraleffizienz zu steigern und die verfügbaren und noch unregulierten Spektralbänder zu nutzen. In der vorliegenden Arbeit werden neue experimentelle VCSEL-Dioden und neuartige zweidimensionale (2D) VCSEL-Diodenarrays entworfen, hergestellt und getestet. Die Physik der VCSEL-Lichtemittern, welche auf 5G- und 6G-optische drahtlose Kommunikations- und Sensoranwendungen ausgerichtet sind, wird untersucht und Performance-Tradeoffs für die angedachten Anwendungen werden identifiziert und analysiert. Über hauseigene Computermodellierungs- und Simulationsprogramme wurden epitaktische VCSEL-Strukturen – bestehend aus nanometerdicken Aluminium-Gallium-Arsenid-, Indium-Gallium-Arsenid- und Gallium-Arsenid-Phosphid-Schichten – mit Peak-Zielemissionswellenlängen von 940 und 980 Nanometern entworfen. Ein kommerzieller Hersteller hat die experimentellen VCSEL-Epitaxiewafer durch metallorganische Gasphasenepitaxie auf Gallium-Arsenid-Substraten mit einem Durchmesser von 3 Zoll gewachsen. In einem Reinraum an der Universität wurden die VCSELs als Viertelwafer-Teststücke mit einem neuen VCSEL Array 2018-Maskensatz gefertigt, der einzelne VCSELs und mehrere Variationen von neuartigen elektrisch parallelen 2D-Tripel- (3-Element), Septuple- (7-Element) und Novemdecuple- (19-Elemente) Strukturdesigns enthält. Bei den prozessierten Strukturen handelt es sich um Top-Emitter mit hochfrequenzkompatiblen koplanare Masse-Signal-Masse-Metallkontaktpads. Alle Device-Tests wurden computergesteuert in einem universitären Laserdiodenlabor durch direktes elektrisches On-Wafer Probing durchgeführt, beginnend mit Dauerstrich-Lichtausgangsleistung-Strom-Spannungs-Sweeps über eine kalibrierte Photodioden-Integrationskugel und eine variable Stromquelle. Für Emissionsspektren und Kleinsignal-Frequenzgangmessungen wurde das emittierte VCSEL-Licht mit einer standardmäßigen OM1-Multimode-Glasfaser (MMF) eingesammelt – verbunden mit einem optischen Spektrumanalysator oder einem Fotoempfänger. Für On-Wafer-Datenübertragungstests über OM1-MMF-Patchkabel wurden die VCSELs mit pseudozufälligen Bitmustern im Non-Return-To-Zero Format mit 2-Level-Pulsamplitudenmodulation moduliert. In dieser Arbeit werden bisher unerreichte Kombinationen von optischer Ausgangsleistung, Bandbreite und Effizienz für VCSEL und VCSEL-Arrays mit großer Oxid-Apertur (größer als 20 Mikrometer) demonstriert. Beispielsweise werden 200 Milliwatt optische Ausgangsleistung, eine Bandbreite von 18 GHz und eine Konversionseffizienz elektrischer zu optischer Leistung von 35 Prozent mit einem 19-Element-VCSEL-Array erreicht. Zudem werden mehrere Rekorde für fehlerfreie Datenübertragung aufgestellt, zum Beispiel 40 Gbps für Triple- und Septuple-VCSEL-Arrays und 25 Gbps für Novemdecuple-VCSEL-Arrays, weit über den bisherigen Stand der Technik von 10 Gbps hinaus. Diese Arbeit ist die erste, die Trade-Offs in der hochgradig nichttrivialen Physik von VCSEL-Arrays untersucht, die auf Arrays mit hoher Leistung und hoher Bandbreite für die Datenübertragung im freien Raum abzielen – und damit neue Leitprinzipien für die weitere Bauelementoptimierung und Produktentwicklung schafft.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

High Bit Rate Wireless and Fiber-Based Terahertz Communication

RÉSUMÉ Dans le spectre électromagnétique, la bande des térahertz s’étend de 100 GHz à 10 THz (longueurs d’onde de 3 mm à 30 μm). Des décennies auparavant, le spectre des THz était connu sous le nom de « gap térahertz » en raison de l’indisponibilité de sources et détecteurs efficaces à ces fréquences. Depuis quelques années, la science a évolué pour faire migrer la technologie THz des laboratoires aux produits commerciaux. Il existe plusieurs applications des ondes THz en imagerie, spectroscopie et communications. Dans cette thèse, nous nous intéressons aux communications THz à travers deux objectifs. Le premier objectif est de développer une source THz de haute performance dédiée aux communications et basée sur les technologies optiques avec des produits commerciaux uniquement. Le second objectif est de démontrer l’utilisation de fibres optiques afin de renforcer la robustesse des communications THz sans fil. Nous débutons cette thèse avec une revue de la littérature scientifique sur le sujet de la communications THz sans fil et filaire. D’abord, nous discutons des deux méthodes communément utilisées (électronique et optique) pour démontrer des liens de communications THz avec leurs avantages et inconvénients. Nous présentons par la suite la possibilité d’utiliser un système de spectroscopie THz pour des applications en communications avec des modifications mineures au montage. Nous présentons ensuite plusieurs applications gourmandes en bande passante qui pourraient bénéficier du spectre THz, incluant la diffusion en continu (streaming) de flux vidéo aux résolutions HD et 4K non compressés. Ensuite, nous discutons de la motivation d’utiliser de longues fibres THz et notamment du fait qu’elles ne sont pas destinées à remplacer les fibres optiques conventionnelles de l’infrarouge, mais plutôt à augmenter la robustesse des liens THz sans fil. En particulier, les fibres THz peuvent être utilisées pour garantir le lien de communication dans des environnements géométriques complexes ou difficile à atteindre, ainsi que pour immuniser le lien THz aux attaques de sécurité. Plusieurs designs de fibres et guides d’onde précédemment démontrées dans la littérature sont discutés avec, entre autres, leurs méthodes de fabrication respectives. Nous discutons ensuite de la possibilité d’utiliser un simple guide d’onde diélectrique et sous-longueur d’onde pour transmettre l’information à un débit de l’ordre de plusieurs Gbps sur une distance de quelques mètres.----------ABSTRACT The Terahertz (THz) spectral range spans from 100 GHz to 10 THz (wavelength: 3 mm to 30 μm) in the electromagnetic spectrum. Decades ago, the THz spectral range is often named as ‘THz gap’ due to the non-availability of efficient THz sources and detectors. In the recent years, the science has evolved in bringing the THz technology from lab scale to commercial products. There are several potential applications of THz frequency band such as imaging, spectroscopy and communication. In this thesis, we focus on THz communications by addressing two objectives. The first objective is to develop a high-performance photonics-based THz communication system using all commercially available components. The second objective is to demonstrate the THz-fiber based communications, which can be used to increase the reliability of THz wireless links. We begin this thesis with a scientific literature review on the subject of THz wireless and fiber-based communications. First, the two different methodologies (all electronics based and photonics-based THz system) that is commonly used in the demonstration of THz communications is discussed along with their advantages and challenges. We then present the flexibility of photonics-based THz system where it is possible to switch it with minor modifications for THz spectroscopic studies and THz communication applications. Several bandwidth hungry applications that demands the use of THz spectrum for next generation communications is detailed. This includes the streaming of uncompressed HD/4K and beyond high-resolution videos, where the THz spectrum can be beneficial. Next, the motivation of using long THz fibers is discussed and we convince the readers that the THz fibers are not meant to replace the fibers in the optical-infrared region but to increase the reliability of THz wireless links. Particularly, the THz fibers can be used to provide connectivity in complex geometrical environments, secure communications and signal delivery to hard-to-reach areas. Several novel fiber/waveguide designs along with their fabrication technologies from the literature are presented. We then show that a simple solid core dielectric subwavelength fiber can be used to transmit the information in the order of several Gbps to a distance of a few meters

Cellular and Wi-Fi technologies evolution: from complementarity to competition

This PhD thesis has the characteristic to span over a long time because while working on it, I was working as a research engineer at CTTC with highly demanding development duties. This has delayed the deposit more than I would have liked. On the other hand, this has given me the privilege of witnessing and studying how wireless technologies have been evolving over a decade from 4G to 5G and beyond. When I started my PhD thesis, IEEE and 3GPP were defining the two main wireless technologies at the time, Wi-Fi and LTE, for covering two substantially complementary market targets. Wi-Fi was designed to operate mostly indoor, in unlicensed spectrum, and was aimed to be a simple and cheap technology. Its primary technology for coexistence was based on the assumption that the spectrum on which it was operating was for free, and so it was designed with interference avoidance through the famous CSMA/CA protocol. On the other hand, 3GPP was designing technologies for licensed spectrum, a costly kind of spectrum. As a result, LTE was designed to take the best advantage of it while providing the best QoE in mainly outdoor scenarios. The PhD thesis starts in this context and evolves with these two technologies. In the first chapters, the thesis studies radio resource management solutions for standalone operation of Wi-Fi in unlicensed and LTE in licensed spectrum. We anticipated the now fundamental machine learning trend by working on machine learning-based radio resource management solutions to improve LTE and Wi-Fi operation in their respective spectrum. We pay particular attention to small cell deployments aimed at improving the spectrum efficiency in licensed spectrum, reproducing small range scenarios typical of Wi-Fi settings. IEEE and 3GPP followed evolving the technologies over the years: Wi-Fi has grown into a much more complex and sophisticated technology, incorporating the key features of cellular technologies, like HARQ, OFDMA, MU-MIMO, MAC scheduling and spatial reuse. On the other hand, since Release 13, cellular networks have also been designed for unlicensed spectrum. As a result, the two last chapters of this thesis focus on coexistence scenarios, in which LTE needs to be designed to coexist with Wi-Fi fairly, and NR, the radio access for 5G, with Wi-Fi in 5 GHz and WiGig in 60 GHz. Unlike LTE, which was adapted to operate in unlicensed spectrum, NR-U is natively designed with this feature, including its capability to operate in unlicensed in a complete standalone fashion, a fundamental new milestone for cellular. In this context, our focus of analysis changes. We consider that these two technological families are no longer targeting complementarity but are now competing, and we claim that this will be the trend for the years to come. To enable the research in these multi-RAT scenarios, another fundamental result of this PhD thesis, besides the scientific contributions, is the release of high fidelity models for LTE and NR and their coexistence with Wi-Fi and WiGig to the ns-3 open-source community. ns-3 is a popular open-source network simulator, with the characteristic to be multi-RAT and so naturally allows the evaluation of coexistence scenarios between different technologies. These models, for which I led the development, are by academic citations, the most used open-source simulation models for LTE and NR and havereceived fundings from industry (Ubiquisys, WFA, SpiderCloud, Interdigital, Facebook) and federal agencies (NIST, LLNL) over the years.Aquesta tesi doctoral té la característica d’allargar-se durant un llarg període de temps ja que mentre treballava en ella, treballava com a enginyera investigadora a CTTC amb tasques de desenvolupament molt exigents. Això ha endarrerit el dipositar-la més del que m’hagués agradat. D’altra banda, això m’ha donat el privilegi de ser testimoni i estudiar com han evolucionat les tecnologies sense fils durant més d’una dècada des del 4G fins al 5G i més enllà. Quan vaig començar la tesi doctoral, IEEE i 3GPP estaven definint les dues tecnologies sense fils principals en aquell moment, Wi-Fi i LTE, que cobreixen dos objectius de mercat substancialment complementaris. Wi-Fi va ser dissenyat per funcionar principalment en interiors, en espectre sense llicència, i pretenia ser una tecnologia senzilla i barata. La seva tecnologia primària per a la convivència es basava en el supòsit que l’espectre en el que estava operant era de franc, i, per tant, es va dissenyar simplement evitant interferències a través del famós protocol CSMA/CA. D’altra banda, 3GPP estava dissenyant tecnologies per a espectres amb llicència, un tipus d’espectre costós. Com a resultat, LTE està dissenyat per treure’n el màxim profit alhora que proporciona el millor QoE en escenaris principalment a l’aire lliure. La tesi doctoral comença amb aquest context i evoluciona amb aquestes dues tecnologies. En els primers capítols, estudiem solucions de gestió de recursos de radio per a operacions en espectre de Wi-Fi sense llicència i LTE amb llicència. Hem anticipat l’actual tendència fonamental d’aprenentatge automàtic treballant solucions de gestió de recursos de radio basades en l’aprenentatge automàtic per millorar l’LTE i Wi-Fi en el seu espectre respectiu. Prestem especial atenció als desplegaments de cèl·lules petites destinades a millorar la eficiència d’espectre llicenciat, reproduint escenaris de petit abast típics de la configuració Wi-Fi. IEEE i 3GPP van seguir evolucionant les tecnologies al llarg dels anys: El Wi-Fi s’ha convertit en una tecnologia molt més complexa i sofisticada, incorporant les característiques clau de les tecnologies cel·lulars, com ara HARQ i la reutilització espacial. D’altra banda, des de la versió 13, també s’han dissenyat xarxes cel·lulars per a espectre sense llicència. Com a resultat, els dos darrers capítols d’aquesta tesi es centren en aquests escenaris de convivència, on s’ha de dissenyar LTE per conviure amb la Wi-Fi de manera justa, i NR, l’accés a la radio per a 5G amb Wi-Fi a 5 GHz i WiGig a 60 GHz. A diferència de LTE, que es va adaptar per funcionar en espectre sense llicència, NR-U està dissenyat de forma nativa amb aquesta característica, inclosa la seva capacitat per operar sense llicència de forma autònoma completa, una nova fita fonamental per al mòbil. En aquest context, el nostre focus d’anàlisi canvia. Considerem que aquestes dues famílies de tecnologia ja no estan orientades cap a la complementarietat, sinó que ara competeixen, i afirmem que aquesta serà el tendència per als propers anys. Per permetre la investigació en aquests escenaris multi-RAT, un altre resultat fonamental d’aquesta tesi doctoral, a més de les aportacions científiques, és l’alliberament de models d’alta fidelitat per a LTE i NR i la seva coexistència amb Wi-Fi a la comunitat de codi obert ns-3. ns-3 és un popular simulador de xarxa de codi obert, amb la característica de ser multi-RAT i, per tant, permet l’avaluació de manera natural d’escenaris de convivència entre diferents tecnologies. Aquests models, pels quals he liderat el desenvolupament, són per cites acadèmiques, els models de simulació de codi obert més utilitzats per a LTE i NR i que han rebut finançament de la indústria (Ubiquisys, WFA, SpiderCloud, Interdigital, Facebook) i agències federals (NIST, LLNL) al llarg dels anys.Esta tesis doctoral tiene la característica de extenderse durante mucho tiempo porque mientras trabajaba en ella, trabajaba como ingeniera de investigación en CTTC con tareas de desarrollo muy exigentes. Esto ha retrasado el depósito más de lo que me hubiera gustado. Por otro lado, gracias a ello, he tenido el privilegio de presenciar y estudiar como las tecnologías inalámbricas han evolucionado durante una década, de 4G a 5G y más allá. Cuando comencé mi tesis doctoral, IEEE y 3GPP estaban definiendo las dos principales tecnologías inalámbricas en ese momento, Wi-Fi y LTE, cumpliendo dos objetivos de mercado sustancialmente complementarios. Wi-Fi fue diseñado para funcionar principalmente en interiores, en un espectro sin licencia, y estaba destinado a ser una tecnología simple y barata. Su tecnología primaria para la convivencia se basaba en el supuesto en que el espectro en el que estaba operando era gratis, y así fue diseñado simplemente evitando interferencias a través del famoso protocolo CSMA/CA. Por otro lado, 3GPP estaba diseñando tecnologías para espectro con licencia, un tipo de espectro costoso. Como resultado, LTE está diseñado para aprovechar el espectro al máximo proporcionando al mismo tiempo el mejor QoE en escenarios principalmente al aire libre. La tesis doctoral parte de este contexto y evoluciona con estas dos tecnologías. En los primeros capítulos, estudiamos las soluciones de gestión de recursos de radio para operación en espectro Wi-Fi sin licencia y LTE con licencia. Anticipamos la tendencia ahora fundamental de aprendizaje automático trabajando en soluciones de gestión de recursos de radio para mejorar LTE y funcionamiento deWi-Fi en su respectivo espectro. Prestamos especial atención a las implementaciones de células pequeñas destinadas a mejorar la eficiencia de espectro licenciado, reproduciendo los típicos escenarios de rango pequeño de la configuración Wi-Fi. IEEE y 3GPP siguieron evolucionando las tecnologías a lo largo de los años: Wi-Fi se ha convertido en una tecnología mucho más compleja y sofisticada, incorporando las características clave de las tecnologías celulares, como HARQ, OFDMA, MU-MIMO, MAC scheduling y la reutilización espacial. Por otro lado, desde la Release 13, también se han diseñado redes celulares para espectro sin licencia. Como resultado, los dos últimos capítulos de esta tesis se centran en estos escenarios de convivencia, donde LTE debe diseñarse para coexistir con Wi-Fi de manera justa, y NR, el acceso por radio para 5G con Wi-Fi en 5 GHz y WiGig en 60 GHz. A diferencia de LTE, que se adaptó para operar en espectro sin licencia, NR-U está diseñado de forma nativa con esta función, incluyendo su capacidad para operar sin licencia de forma completamente independiente, un nuevo hito fundamental para los celulares. En este contexto, cambia nuestro enfoque de análisis. Consideramos que estas dos familias tecnológicas ya no tienen como objetivo la complementariedad, sino que ahora están compitiendo, y afirmamos que esta será la tendencia para los próximos años. Para permitir la investigación en estos escenarios de múltiples RAT, otro resultado fundamental de esta tesis doctoral, además de los aportes científicos, es el lanzamiento de modelos de alta fidelidad para LTE y NR y su coexistencia con Wi-Fi y WiGig a la comunidad de código abierto de ns-3. ns-3 es un simulador popular de red de código abierto, con la característica de ser multi-RAT y así, naturalmente, permite la evaluación de escenarios de convivencia entre diferentes tecnologías. Estos modelos, para los cuales lideré el desarrollo, son por citas académicas, los modelos de simulación de código abierto más utilizados para LTE y NR y han recibido fondos de la industria (Ubiquisys, WFA, SpiderCloud, Interdigital, Facebook) y agencias federales (NIST, LLNL) a lo largo de los años.Postprint (published version

A Study on Transmission Efficiency Improvement through Theoretical Analysis in Multi-user MIMO

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