128 research outputs found

    Integrated Circuit Design for High Data Rate Polymer Microwave Fiber Communication

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    The rapid development of semiconductor processes with a maximum frequency of oscillation well above 300 GHz enables new applications at frequencies above 100 GHz to be researched and developed. Such applications include wireless backhaul, wireless access, radar and radiometer sensors, wireless energy distribution and harvesting, etc.\ua0For several of these applications, a throughput in data rate well above 10 Gbps, even up to 100 Gbps, is required. Optical fiber communication is the leading option for high data rate and long-range wired communication. However, for shorter ranges like chip-to-chip or module-to-module (up to ten meters), millimeter-wave communication over a polymer microwave fiber (PMF) is an interesting alternative due to its potential low cost. Other advantages include flexibility, less sensitivity to temperature variations, and a more relaxed mechanical tolerance requirement. Similar to optical fiber, dispersion occurs on PMFs and will cause symbol interference. Different ways to deal with this effect are investigated, for example, pulse shaping and equalization of the signal.\ua0This work proposes and presents various circuit solutions enabling high data rate communication. Two technologies are used, 250 nm InP DHBT and 130 nm SiGe BiCMOS. An energy-efficient solution using an RF-DAC and power detector for pulse amplitude modulated links are evaluated, as well as an I/Q modulated solution. I/Q (de-)modulators require more complexity, but the increased spectral efficiency can also increase the data rate further.\ua0\ua0In summary, I explore the opportunities and challenges of short-range, ultra-high data rate, PMF bound communication, which is found to support 56 Gbps error-free (BER<10-12) data and 102 Gbps with a BER=2.1*10-3

    Ionosphere Monitoring with Remote Sensing

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    This book focuses on the characterization of the physical properties of the Earth’s ionosphere, contributing to unveiling the nature of several processes responsible for a plethora of space weather-related phenomena taking place in a wide range of spatial and temporal scales. This is made possible by the exploitation of a huge amount of high-quality data derived from both remote sensing and in situ facilities such as ionosondes, radars, satellites and Global Navigation Satellite Systems receivers

    Materials Analysis Using a THz Imaging System Based on Atomic Vapour

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    This thesis studies the response of the interaction between Rydberg atomic vapour and a THz frequency field. When Caesium atoms at room temperature are excited to a Rydberg state using three infrared lasers and a 0.55 THz field resonant with the 14P3/2 → 13D5/2 transition is applied, the atoms respond by emitting a green optical fluorescence corresponding to the 13D5/2 → 6P3/2 decay. This response is exploited to investigate the absorption coefficient for different polymer materials that transmit well in the THz frequency range using the Beer–Lambert law. We calibrate the system to obtain a measure of THz intensity. As the THz imaging system is highly sensitive to environmental changes, and to show that our results are consistent, we provide a comparison of results between our atomic detection method and a commercial thermal power meter. Additionally, we measure the absorption coefficient of the same materials at a frequency of 1.1 THz, and the results are compared with those measured at 0.55 THz. The THz imaging system is also used to perform some experiments in order to demonstrate its effectiveness in real-world applications. The system provides an interesting image contrast in the case of a sample containing two different polymer materials measured at two THz frequencies. The result is a proof-of-concept that multispectral THz imaging can provide additional information and is motivation to improve our THz imaging system by introducing a dual-species THz imager. We also investigate the polarisation spectroscopy of an excited-state transition of rubidium vapour at room temperature as a step towards a rubidium THz imaging system. The narrow dispersive signal produced by this spectroscopy technique is ideal for laser frequency stabilisation of excited-state transitions

    X-band RF Transmitter Design For Multi-Purpose Small Satellite Communication Operations

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    This thesis provides a description of the analysis, design, and tests of an X-band RF Transmitter communication system for small satellites. X-band transmitter systems are becoming popular in the upcoming deep space missions. Most of the deep-space ground stations have been using X-band frequencies to receive or transmit signals. The X-band (\u3c10 GHz) can offer lower atmospheric losses and up to a couple of Mbps data rates for multiple satellite operations. Nowadays, many small satellites have been using frequency bands such as VHF, UHF, L, and S-band frequencies for communication. From deep space to the ground station, the low-frequency ranges are inadequate in providing Mbps level data rates and enough bandwidth for deep space missions. The main focus of this thesis was the development of the subsystems such as gain block amplifier, Mixer, Bandpass Filter, and RF power amplifier. The subsystems were designed separately, then they were connected together to perform an end-to-end system test. One of the thesis aims is to design a manageable, power-efficient, and especially cost-effective X-band RF transmitter system. We presented a transmitter system demonstration in this thesis that can also be used in other orbits such as LEO, MEO, or GEO. Additionally, we presented a whole transceiver architecture. However, we focused on specifically designing transmitter subsystems. Initially, the top-level transmitter system objectives were determined. Then, the link budget was calculated. In the next stage, the RF front-end components were determined. Moreover, we simulated a transmitter system to foresee the output power, EVM, LO and IF frequency requirements, harmonics and spurious signals, cascaded gain and noise figure, and phase noise. From the calculated link budget, we were able to close the link by obtaining a 3 dB link margin. At the end of this calculation, we successfully obtained 1.45 Mbps for uplink data rate and 3.05 Kbps downlink rate. We used modulated signal to evaluate EVM. From the simulated transmitter chain, the output EVM was obtained as 1.456% RMS. From the filter board, we obtained an 8.5 dB insertion loss at 8.45 GHz. From the Mixer board, we’ve got 10 dB conversion loss and greater than 20 dB isolation between LO-RF ports. From the gain block amplifier board, we obtained a +9 dB gain at 8.45 GHz. The bandpass filter, mixer, and gain block amplifier boards were designed by using FR-4 dielectric material. We also designed a 5 W RF power amplifier board. From this board, we successfully obtained +37 dBm output at bias current at 200 mA. We reached almost 30% Power-added efficiency (PAE). In the end, we connected all the subsystems together using male-to-male SMA connectors to observe output by using a spectrum analyzer. We obtained transmitter output as +10.67 dBm at 8.45 GHz with a -10.7 dBm input power level. One benefit of this thesis is that its content has inspired other students in the department to develop similar subsystems. The other benefit of this work might be to inspire the way for next-generation X-band communication systems for use in small satellites, such as for deep space missions. This thesis might also be a reference source for institutions with a limited budget to develop a cost-effective satellite communication subsystem and contribute to space exploration for their educational and research objectives

    Cooperative Radio Communications for Green Smart Environments

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    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

    Design of the Synthetic Aperture Microwave Imager-2 for measurement of the edge current density on MAST-U

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    The Synthetic Aperture Microwave Imager-2 (SAMI-2) is a 2D Doppler backscattering (DBS) diagnostic designed for multiple high quality simultaneous measurements of the edge pitch angle on the Mega-Ampere Spherical Tokamak Upgrade (MAST-U). The specification, design and testing of the SAMI-2 microwave front end, predominantly antennas and mixer circuitry, are described in this thesis. Dual-polarisation sinuous antennas are designed and shown to fulfil their performance criteria over the 20-40 GHz range. A four-channel microwave in-phase and quadrature (IQ) downconverter is designed to mix the radio frequency (RF) signals from each antenna in the SAMI-2 phased array to a lower frequency, for digitisation. The down-converter is tested and found to achieve its performance specifications over the entire frequency range of the antennas. The 2D DBS technique was demonstrated by Synthetic Aperture Microwave Imager (SAMI) on the Mega-Ampere Spherical Tokamak (MAST) to measure the edge magnetic pitch angle. A radial profile of the edge pitch angle enables calculation of the edge current density, a difficult quantity to measure, which is valuable for the validation of models and understanding of pedestal dynamics and edge plasma instabilities, e.g. ELMs. In active probing mode, the SAMI-2 diagnostic is designed to make the first measurements of the edge current density by a DBS diagnostic. In passive mode, SAMI-2 will measure Bernstein wave mode conversion, to inform spherical tokamak microwave heating systems

    Advancements in Multinuclear Multichannel NMR and MRI

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    The introduction of receive arrays revolutionized ^1H MRI and in vivo NMR by increasing SNR and enabling accelerated imaging. All MRI scanners manufactured today are equipped to receive signals from ^1H array coils, but few support multi-channel reception for other nuclei. The extension of receive arrays to non^1H nuclei has proven difficult because of the lack of broadband array receivers. These nuclei often have low sensitivity and stand to benefit greatly from the increase in SNR arrays provide. This dissertation presents a variety of technologies that have been developed to enable the development and use of X-nuclear and multi-nuclear arrays. Frequency conversion receiver front-ends provide a straightforward and cost-effective approach for adapting standard ^1H multi-channel array receivers for use with other nuclei. Two generations of frequency translation receiver front-ends have been developed that use active mixers to convert the received signal from a non^1H array to the ^1H frequency for reception by the host system receiver. This first-generation system has been demonstrated on 4.7T and 7T systems without any decrease in SNR as compared to the stock systems, and has been shown to be capable of accommodating ^1H decoupling. The second-generation receiver was developed to add the capability to simultaneously convert signals received from multiple nuclei as well as to streamline the setup and use of the translation system. Frequency translation has been shown to be able to convert ^1H-only multi-channel receivers for use with other nuclei with minimal degradation of SNR. In addition, a standalone broadband system capable of simultaneous multi-nuclear imaging and spectroscopy at 1T and 4.7T has been developed. This system can either operate completely independently or interface with existing systems. The broadband system has been demonstrated with simultaneous imaging and spectroscopy of three nuclei. This work allows existing multi-channel MRI receivers to be adapted to receive signals from nuclei other than hydrogen, allowing for the use of receive arrays for in vivo multi-nuclear NMR

    A fast engineering approach to high efficiency power amplifier linearization for avionics applications

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    This PhD thesis provides a fast engineering approach to the design of digital predistortion (DPD) linearizers from several perspectives: i) enhancing the off-line training performance of open-loop DPD, ii) providing robustness and reducing the computational complexity of the parameters identification subsystem and, iii) importing machine learning techniques to favor the automatic tuning of power amplifiers (PAs) and DPD linearizers with several free-parameters to maximize power efficiency while meeting the linearity specifications. One of the essential parts of unmanned aerial vehicles (UAV) is the avionics, being the radio control one of the earliest avionics present in the UAV. Unlike the control signal, for transferring user data (such as images, video, etc.) real-time from the drone to the ground station, large transmission rates are required. The PA is a key element in the transmitter chain to guarantee the data transmission (video, photo, etc.) over a long range from the ground station. The more linear output power, the better the coverage or alternatively, with the same coverage, better SNR allows the use of high-order modulation schemes and thus higher transmission rates are achieved. In the context of UAV wireless communications, the power consumption, size and weight of the payload is of significant importance. Therefore, the PA design has to take into account the compromise among bandwidth, output power, linearity and power efficiency (very critical in battery-supplied devices). The PA can be designed to maximize its power efficiency or its linearity, but not both. Therefore, a way to deal with this inherent trade-off is to design high efficient amplification topologies and let the PA linearizers take care of the linearity requirements. Among the linearizers, DPD linearization is the preferred solution to both academia and industry, for its high flexibility and linearization performance. In order to save as many computational and power resources as possible, the implementation of an open-loop DPD results a very attractive solution for UAV applications. This thesis contributes to the PA linearization, especially on off-line training for open-loop DPD, by presenting two different methods for reducing the design and operating costs of an open-loop DPD, based on the analysis of the DPD function. The first method focuses on the input domain analysis, proposing mesh-selecting (MeS) methods to accurately select the proper samples for a computationally efficient DPD parameter estimation. Focusing in the MeS method with better performance, the memory I-Q MeS method is combined with feature extraction dimensionality reduction technique to allow a computational complexity reduction in the identification subsystem by a factor of 65, in comparison to using the classical QR-LS solver and consecutive samples selection. In addition, the memory I-Q MeS method has been proved to be of crucial interest when training artificial neural networks (ANN) for DPD purposes, by significantly reducing the ANN training time. The second method involves the use of machine learning techniques in the DPD design procedure to enlarge the capacity of the DPD algorithm when considering a high number of free parameters to tune. On the one hand, the adaLIPO global optimization algorithm is used to find the best parameter configuration of a generalized memory polynomial behavioral model for DPD. On the other hand, a methodology to conduct a global optimization search is proposed to find the optimum values of a set of key circuit and system level parameters, that properly combined with DPD linearization and crest factor reduction techniques, can exploit at best dual-input PAs in terms of maximizing power efficiency along wide bandwidths while being compliant with the linearity specifications. The advantages of these proposed techniques have been validated through experimental tests and the obtained results are analyzed and discussed along this thesis.Aquesta tesi doctoral proporciona unes pautes per al disseny de linealitzadors basats en predistorsió digital (DPD) des de diverses perspectives: i) millorar el rendiment del DPD en llaç obert, ii) proporcionar robustesa i reduir la complexitat computacional del subsistema d'identificació de paràmetres i, iii) incorporació de tècniques d'aprenentatge automàtic per afavorir l'auto-ajustament d'amplificadors de potència (PAs) i linealitzadors DPD amb diversos graus de llibertat per poder maximitzar l’eficiència energètica i al mateix temps acomplir amb les especificacions de linealitat. Una de les parts essencials dels vehicles aeris no tripulats (UAV) _es l’aviònica, sent el radiocontrol un dels primers sistemes presents als UAV. Per transferir dades d'usuari (com ara imatges, vídeo, etc.) en temps real des del dron a l’estació terrestre, es requereixen taxes de transmissió grans. El PA _es un element clau de la cadena del transmissor per poder garantir la transmissió de dades a grans distàncies de l’estació terrestre. A major potència de sortida, més cobertura o, alternativament, amb la mateixa cobertura, millor relació senyal-soroll (SNR) la qual cosa permet l’ús d'esquemes de modulació d'ordres superiors i, per tant, aconseguir velocitats de transmissió més altes. En el context de les comunicacions sense fils en UAVs, el consum de potència, la mida i el pes de la càrrega útil són de vital importància. Per tant, el disseny del PA ha de tenir en compte el compromís entre ample de banda, potència de sortida, linealitat i eficiència energètica (molt crític en dispositius alimentats amb bateries). El PA es pot dissenyar per maximitzar la seva eficiència energètica o la seva linealitat, però no totes dues. Per tant, per afrontar aquest compromís s'utilitzen topologies amplificadores d'alta eficiència i es deixa que el linealitzador s'encarregui de garantir els nivells necessaris de linealitat. Entre els linealitzadors, la linealització DPD és la solució preferida tant per al món acadèmic com per a la indústria, per la seva alta flexibilitat i rendiment. Per tal d'estalviar tant recursos computacionals com consum de potència, la implementació d'un DPD en lla_c obert resulta una solució molt atractiva per a les aplicacions UAV. Aquesta tesi contribueix a la linealització del PA, especialment a l'entrenament fora de línia de linealitzadors DPD en llaç obert, presentant dos mètodes diferents per reduir el cost computacional i augmentar la fiabilitat dels DPDs en llaç obert. El primer mètode se centra en l’anàlisi de l’estadística del senyal d'entrada, proposant mètodes de selecció de malla (MeS) per seleccionar les mostres més significatives per a una estimació computacionalment eficient dels paràmetres del DPD. El mètode proposat IQ MeS amb memòria es pot combinar amb tècniques de reducció del model del DPD i d'aquesta manera poder aconseguir una reducció de la complexitat computacional en el subsistema d’identificació per un factor de 65, en comparació amb l’ús de l'algoritme clàssic QR-LS i selecció de mostres d'entrenament consecutives. El segon mètode consisteix en l’ús de tècniques d'aprenentatge automàtic pel disseny del DPD quan es considera un gran nombre de graus de llibertat (paràmetres) per sintonitzar. D'una banda, l'algorisme d’optimització global adaLIPO s'utilitza per trobar la millor configuració de paràmetres d'un model polinomial amb memòria generalitzat per a DPD. D'altra banda, es proposa una estratègia per l’optimització global d'un conjunt de paràmetres clau per al disseny a nivell de circuit i sistema, que combinats amb linealització DPD i les tècniques de reducció del factor de cresta, poden maximitzar l’eficiència de PAs d'entrada dual de gran ample de banda, alhora que compleixen les especificacions de linealitat. Els avantatges d'aquestes tècniques proposades s'han validat mitjançant proves experimentals i els resultats obtinguts s'analitzen i es discuteixen al llarg d'aquesta tesi

    Programmable DSP-enabled multi-adaptive optical transceivers based on OFDM technology for software defined networks

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    The dynamic behavior of the traffic demand, due to the advent of technologies such as cloud services or Internet of Things (IoT), is increasing. In fact, heterogeneous connections with different characteristics (bandwidth or bit rate) are expected that coexist in the optical networks. In this respect, an evolution towards Elastic Optical Networks (EONs) has emerged as a cost-effective, flexible and dynamic solution, to face the new claims. The main idea is the efficient utilization of the optical spectrum by combining flexible transceivers, flexi-grid and flexible optical switching. Including the principles of Software Defined Network (SDN) paradigm further flexibility and adaptability can be achieved. The Sliceable Bandwidth Variable Transceiver (S-BVT), as a key element in EONs, provides flexibility and adaptability to the optical networks. It is able to dynamically tune the optical bandwidth or bit rate changing parameters such as the modulation format, bandwidth, among others, to find a trade-off between transmission reach and spectral efficiency, serving multiples destinations. The combination of programmable Digital Signal Processing (DSP) modules with advanced transmission techniques based on Orthogonal Frequency Division Multiplexing (OFDM) technology using Direct Detection (DD) or COherent (CO) detection are proposed to be implemented at the S-BVT making it suitable for elastic optical metro/regional networks. Furthermore, the envisioned migration from fixed-grid to flexi-grid, can benefit from the use of S-BVTs since they are able to generate or receive multiple channels and slicing the aggregated flow into multiples flows with different capacities and destinations. We propose the use of S-BVTs based on multi-band OFDM systems. In particular, we focus on the theoretical model of an advanced transmission technique based on OFDM technology with DD. Then we evaluate the system for a realistic optical metro network. In the context of flexi-grid optical metro/regional networks, as well as the sliceability of the channels, the reduction of channel width for low bit rate connections can be envisioned. It involves that the signal traverses several nodes with the corresponding filtering elements, causing a substantially decrease and distortion of the signal bandwidth. This phenomenon known as filter narrowing effect has been also studied in this thesis, by simulations and experimentally for an adaptive cost-effective OFDM system using DD and for a standard OOK system. Apart from adaptive, flexible and programmable transceivers, metro optical networks have to be equipped with flexible optical switching systems at the node level. In this respect, we propose the adoption of adaptive S-BVTs based on advanced transmission techniques using DD with Discrete MultiTone (DMT) modulation and adaptive capabilities in combination with Semiconductor Optical Amplier (SOA)-based switching nodes. SOAs can be conveniently used for optical switching in metro networks because of their low cost or low power consumption, among others relevant characteristics. The system has been experimentally analyzed with and without considering filtering elements. Thanks to the combination of adaptive DMT modulation and SOA-based switching nodes, impairments due to the fiber links and the filtering elements can be compensated. Finally, to enhance the tranmission distance and data rate, we propose the combination of multidimensional constellations implemented at the DSP modules of the S-BVT with CO detection and OFDM technology. Thus, the deployed infrastructure is more efficiently exploited since the quadrature and the polarization dimensions are used to transmit the signal. In particular, we focus on CO-OFDM systems using Dual Polarization Quadrature Phase Shift Keying (DPQPSK) constellation transmitting the signal over the time and the polarization dimensions in the optical domain.El comportamiento dinámico de la demanda de tráfico, debido a la llegada de tecnologías como los servicios en la nube o el Internet of Things (IoT), está aumentando. De hecho, se espera que coexistan en las redes ópticas conexiones heterogéneas con características diferentes, tales como ancho de banda o tasa de bits. Para hacer frente a estas demandas es crucial una evolución de las redes ópticas. En este sentido, las Elastic Optical Networks (EONs) emergen como una solución rentable, flexible y dinámica. La idea principal se basa en la utilización eficiente del espectro óptico mediante la combinación de transceptores flexibles, redes flexibles y conmutación óptica flexible. Una mayor flexibilidad y adaptabilidad se puede conseguir incluyendo los principios del paradigma conocido como Software Defined Network (SDN). La adopción de la arquitectura SDN implica la separación del plano de control y de datos, permitiendo la programabilidad dinámica de la red. Un elemento clave en las EONs es el Sliceable Bandwidth Variable Transceiver (SBVT), ya que provee de flexibilidad y adaptabilidad a las redes ópticas. El S-BVT es capaz de cambiar el ancho de banda o la tasa de bits medicando parámetros como el formato de modulación, el ancho de banda o la codificación de Forward Error Correction (FEC), entre otros, para encontrar un equilibrio entre el alcance de la transmisión y la eficiencia espectral, sirviendo múltiples destinos. La combinación de módulos programables de Digital Signal Processing (DSP) con técnicas de transmisión avanzadas, basadas en la tecnología Orthogonal Frequency Division Multiplexing (OFDM) con detección directa o detección coherente, se han propuesto para ser implementadas en el S-BVT, haciéndolo adecuado para su uso en redes ópticas elásticas metropolitanas y regionales. Además, la migración prevista de las redes fijas a las redes flexibles, con el fin de explotar la granularidad de 12:5 GHz, puede beneficiarse del uso de S-BVTs ya que son capaces de generar y recibir múltiples canales y dividir el flujo agregado en múltiples flujos con diferentes capacidades y destinos. A este respecto, proponemos el uso de S-BVTs basados en señales OFDM multi banda combinadas en el dominio eléctrico con el fin de limitar los recursos optoelectrónicas y relajar los requerimientos de los convertidores digitales analógicos y analógicos digitales. En particular, nos centramos en el modelo teórico de una técnica de transmisión avanzada basada en la tecnología OFDM con detección directa. A continuación, evaluamos el sistema para una red metropolitana óptica realista. En el contexto de redes metropolitanas y regionales flexibles, además de la capacidad de división de los canales, se puede prever una posible reducción del ancho de canal para las conexiones de baja tasa de bits. Esto implica que la señal atraviese varios nodos con los correspondientes elementos filtrantes causando un substancial decremento y distorsión del ancho de banda de la señal. Este fenómeno conocido como el efecto de estrechamiento de filtrado ha sido también estudiado en esta tesis, mediante simulaciones y de manera experimental para un sistema OFDM rentable y adaptativo usando detección directa y un sistema estándar On-Off Keying (OOK). El sistema OFDM de detección directa ha resultado ser un buen candidato para aumentar la flexibilidad y la robustez frente a las deficiencias de transmisión sin necesidad de compensar la dispersión. Aparte de los transceptores adaptables, flexibles y programables, las redes ópticas metropolitanas deben estar equipadas con sistemas de conmutación óptica flexible a nivel de nodo. En este sentido, proponemos la adopción de S-BVTs adaptativos basados en técnicas de transmisión avanzadas usando detección directa con modulación Discrete MultiTone (DMT) y capacidades adaptativas, adoptando nodos de conmutación basados en Semiconductor Optical Amplifier (SOA). Los SOAs pueden ser utilizados para la conmutación óptica en redes metropolitanas debido a su bajo coste o bajo consumo de energía, entre otras características relevantes. El sistema ha sido analizado experimentalmente considerando y sin considerar la presencia de elementos filtrantes. Gracias a la combinación de la modulación DMT adaptativa y los nodos de conmutación basados en SOA, las degradaciones debidas a los enlaces de fibra y a los elementos filtrantes se pueden compensar. Finalmente, para mejorar la distancia de transmisión y la tasa de datos, proponemos la combinación de constelaciones multidimensionales implementadas en los módulos DSP del S-BVT utilizando detectaron coherente y la tecnología OFDM. De hecho, los sistemas OFDM coherentes tienen un espacio de señal 4D (dos cuadraturas y dos polarizaciones), que puede ser utilizado con constelaciones multidimensionales, pudiendo éstas ser más eficientes que las convencionales Binary Phase-Shift Keying (BPSK) o Quadrature Phase-Shift Keying (QPSK). De este modo, la infraestructura desplegada se explota de manera más eficiente, ya que tanto la dimensión de cuadratura como de polarización se utilizan para transmitir la señal. Además, los sistemas OFDM coherentes pueden recuperar la amplitud y la fase de la señal en el receptor, mitigando los efectos de la fibra aumentando, de esta forma, la distancia de transmisión. El sistema OFDM coherente que utiliza el formato de constelación Dual Polarization Quadrature Phase Shift Keying (DPQPSK) y que transmite la señal a lo largo del tiempo ha demostrado ser una solución prometedora.El comportament dinàmic de la demanda de transit, a causa de l'arribada de tecnologies, com poden ser els serveis al núvol o l'Internet of Things (IoT), està creixent. De fet, s'espera que coexisteixin a les xarxes òptiques connexions heterogènies amb característiques diferents, tal com l'ample de banda o la taxa de bits. Per a fer front a aquestes demandes és crucial una revolució de les xarxes òptiques. En aquest sentit, les Elastic Optical Networks (EONs) emergeixen com una solució rendible, flexible i dinàmica. La idea principal es basa en la utilització eficient de l'espectre òptic mitjançant la combinació de transceptors flexibles, xarxes flexibles i commutació òptica flexible. Una major flexibilitat i adaptabilitat es pot aconseguir incloent els principis del paradigma conegut com a Software Defined Networks (SDN). L’adopció de l'arquitectura SDN implica la separació del plànol de control i de dades permetent la programabilitat de la xarxa d'una forma dinàmica. Un element clau en les EONs és l'Sliceable Bandwith Variable Transceiver (S-BVT), ja que aporta flexibilitat i adaptabilitat a les xarxes òptiques. L' S-BVT és capaç de canviar l'ample de banda o la taxa de bits modificant paràmetres com el format de modulació, l'ample de banda o la codificació del Forward Error Correction (FEC), entre altres, per a trobar un equilibri entre l’assistència assolida i l’eficiència espectral, servint múltiples destinacions. La combinació de mòduls de Digital Signal Processing (DSP) amb tècniques de transmissió avançades basades en la tecnologia Orthogonal Frequency Division Multiplexing (OFDM) i detecció directa o detecció coherent s'han proposat per a ser implementades en l'S-BVT, fent-lo adient per a les xarxes òptiques elàstiques metropolitanes i regionals. A més, la migració prevista des de les xarxes fixes a les xarxes flexibles, amb el fi d'explotar la granuralitat de 12:5GHz, pot beneficiar-se de l’ús d'S-BVTs ja que són capaços de generar i rebre múltiples canals i dividir el flux agregat en múltiples fluxos amb diferents capacitats i destinacions. Per aquest motiu, proposem l’ús d'S-BVTs basats en senyals OFDM multi banda combinats en el domini elèctric amb el fi de limitar els recursos optoelectrònics i relaxar els requeriments dels convertidors digitals analògics i analògics digitals. Particularment, ens centrem en el model teòric d'una tècnica de transmissió avançada basada en la tecnologia OFDM amb detecció directa. A continuació, avaluem el sistema per a una xarxa metropolitana òptica realista. En el context de xarxes metropolitanes i regionals flexibles, a més de la propietat de divisió dels canals, es pot preveure una possible reducció de l'ample de canal per a les connexions de baixa taxa de bits. Això implica que el senyal travessi diversos nodes amb els corresponents elements filtrants causant un substancial decrement i distorsió de l'ample de banda del senyal. Aquest fenomen conegut com l'efecte d'estretament de filtrat ha sigut també estudiat en aquesta tesi, mitjançant simulacions i de manera experimental en el cas d'un sistema OFDM rendible i adaptatiu utilitzant detecció directa i un sistema estàndard On-Off Keying (OOK). El sistema OFDM de detecció directa ha resultat ser un bon candidat per augmentar la flexibilitat i la robustesa front a les deficiències de transmissió sense necessitat de compensar la dispersió. A part dels transceptors adaptables, flexibles i programables, les xarxes òptiques metropolitanes han d'estar equipades amb sistemes de commutació òptica flexible a nivell de node. En aquest sentit, proposem l’adopció d'un S-BVT adaptatiu basat en tècniques de transmissió avançades i utilitzant detecció directa amb modulació Discrete MultiTone (DMT) i capacitats adaptatives, adoptant nodes de comunicació basats en Semi-conductor Optical Amplifier (SOA). Els SOAs poden ser utilitzats per la commutació _òptica en xarxes metropolitanes degut al seu baix cost o baix consum d'energia, entre altres característiques rellevants. El sistema ha sigut analitzat experimentalment considerant i sense considerar la presència d'elements filtrants. Gràcies a la combinació de la modulació DMT adaptativa i dels nodes de commutació basats en SOA, les degradacions degudes als enllaços de fibra i als elements filtrants es poden compensar. Finalment, per a millorar la distància de transmissió i la taxa de dades, proposem la combinació de constel·lacions multidimensionals implementades als mòduls DSP de l'SBVT utilitzant detecció coherent i la tecnologia OFDM. De fet, els sistemes coherents OFDM tenen un espai de senyal 4D (dues quadratures i dues polaritzacions), que pot ser utilitzat amb constel·lacions multidimensionals, arribant a ser més eficients que les modulacions convencionals Binary Phase-Shift Keying (BPSK) o Quadrature Phase-Shift Keying (QPSK). D'aquesta manera, la infraestructura desplegada s'explota de forma més eficient, ja que tant la dimensió de quadratura com de polarització s'utilitzen per transmetre el senyal. A més, els sistemes coherents basats en OFDM poden recuperar l'amplitud i la fase del senyal en el receptor, mitigant els efectes de la fibra i d'aquesta forma augmentant la distància de transmissió. El sistema OFDM coherent que utilitza el format de constel·lació Dual Polarization Quadrature Phase Shift Keying (DPQPSK) i que transmet el senyal al llarg del temps ha demostrat ser una solució prometedora.Postprint (published version
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