463 research outputs found

    Next generation >200 Gb/s multicore fiber short-reach networks employing machine learning

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    This work proposes and evaluates the use of machine learning (ML) techniques on >200 Gb/s short-reach systems employing weakly coupled multicore fiber (MCF) and Kramers-Kronig (KK) receivers. The short-reach systems commonly found in intra data centers (DC) connections demand low cost-efficient direct detection receivers (DD). The KK receivers allow the combination of higher modulation order, such as 16-QAM used in coherent systems, with the low complexity and low cost of DD. Thus, the use of KK receivers allows to increase the bit rate and spectral efficiency while maintaining the cost of DD systems as this is an important requirement in DC. The use of MCF allows to increase the system capacity as well as the system cable density, although the use of MCF induces additional distortion, known as inter-core crosstalk (ICXT), to the system. Thus, low complexity ML techniques such as k-means clustering, k nearest neighbor (KNN) and artificial neural network (ANN) (estimation feedforward neural network (FNN) and classification feedforward neural network) are proposed to mitigate the effects of random ICXT. The performance improvement provided by the k-means clustering, KNN and the two types of FNN techniques is assessed and compared with the system performance obtained without the use of ML. The use of estimation and classification FNN prove to significantly improve the system performance by mitigating the impact of the ICXT on the received signal. This is achieved by employing only 10 neurons in the hidden layer and four input features. It has been shown that k-means or KNN techniques do not provide performance improvement compared to the system without using ML. These conclusions are valid for direct detection MCF-based short-reach systems with the product between the skew (relative time delay between cores) and the symbol rate much lower than one (skew x symbol rate « 1). By employing the proposed ANNs, the system shows an improvement of approximately 12 dB on the ICXT level, for the same outage probability when comparing with the system without the use of ML. For the BER threshold of 10−1.8 and compared with the standard system operating without employing ML techniques, the system operating with the proposed ANNs show a received optical power improvement of almost 3 dB and a ICXT level improvement of approximately 9 dB when the mean BER is analized.Este trabalho propõe e avalia o uso de técnicas de machine learning (ML) em sistemas de curto alcance com ritmo binário superior a 200 Gb/s utilizando receptores Kramers-Kronig (KK) e fibras multinúcleo (MCF). Os sistemas de curto alcance usualmente encontrados em conexões intra-data centers (DC) exigem receptores de deteção direta (DD) de baixo custo. Os receptores KK permitem a combinação de sistemas de modulação de maior ordem, tais como o 16-QAM, usado em sistemas coerentes, com o baixo custo dos receptores DD. Portanto, o uso de receptores KK permite melhorar o ritmo binário e eficiência espectral e manter a eficiência de custo dos sistemas DD, o que é importante em DC. O uso de fibras multinúcleo permite o aumento da capacidade do sistema, bem como a densidade de cabos. No entanto, o uso de MCF introduz uma distorção adicional no sistema conhecida como inter-core crosstalk (ICXT). Para mitigar os efeitos do ICXT aleatório, são propostas e avaliadas técnicas de ML de baixa complexidade como k-means clustering, k nearest neighbor (KNN) e rede neuronais artificiais (ANN). O desempenho associado à utilização de algoritmos de ML (k-means, KNN e duas redes neuronais do tipo feedforward (FNN): uma para estimação e outra para classificação), é avaliado e comparado com o desempenho do sistema obtido sem o uso de ML. A utilização de FNN para estimação e classificação conduziram a uma melhoria significativa no desempenho do sistema, mitigando o impacto do ICXT no sinal recebido. Isso é alcançado com o uso de uma rede neuronal com uma arquitetura muito simples contendo quatro entradas e 10 neurónios na camada escondida. Foi demonstrado que os algoritmos k-means e KNN não proporcionam melhoria de desempenho em comparação com o sistema sem o uso de ML. Essas conclusões são válidas para sistemas DD de curto alcance baseados em MCF com o produto entre o skew (atraso relativo entre os núcleos) e o ritmo de símbolos muito menor que um (skew x symbol rate « 1). Com o uso das ANNs, o sistema apresenta uma melhoria de aproximadamente 12 dB na probabilidade de indisponibilidade quando comparado com o sistema sem o uso de ML. Para o limite de BER de 10−1.8 , e comparado com o sistema padrão sem o uso de técnicas de ML, o sistema com o uso de ANN mostra uma melhoria na potência óptica recebida de quase 3 dB e uma melhoria no nível de ICXT de aproximadamente 9 dB em relação ao BER médio

    Speckle pattern interferometry : vibration measurement based on a novel CMOS camera

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    A digital speckle pattern interferometer based on a novel custom complementary metaloxide- semiconductor (CMOS) array detector is described. The temporal evolution of the dynamic deformation of a test object is measured using inter-frame phase stepping. The flexibility of the CMOS detector is used to identify regions of interest with full-field time averaged measurements and then to interrogate those regions with time-resolved measurements sampled at up to 7 kHz. The maximum surface velocity that can be measured and the number of measurement points are limited by the frame rate and the data transfer rate of the detector. The custom sensor used in this work is a modulated light camera (MLC), whose pixel design is still based on the standard four transistor active pixel sensor (APS), but each pixel has four large independently shuttered capacitors that drastically boost the well capacity from that of the diode alone. Each capacitor represents a channel which has its own shutter switch and can either be operated independently or in tandem with others. The particular APS of this camera enables a novel approach in how the data are acquired and then processed. In this Thesis we demonstrate how, at a given frame rate and at a given number of measurement points, the data transfer rate of our system is increased if compared to the data transfer rate of a system using a standard approach. Moreover, under some assumptions, the gain in system bandwidth doesn’t entail any reduction in the maximum surface velocity that can be reliably measured with inter-frame phase stepping

    A Survey on Reservoir Computing and its Interdisciplinary Applications Beyond Traditional Machine Learning

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    Reservoir computing (RC), first applied to temporal signal processing, is a recurrent neural network in which neurons are randomly connected. Once initialized, the connection strengths remain unchanged. Such a simple structure turns RC into a non-linear dynamical system that maps low-dimensional inputs into a high-dimensional space. The model's rich dynamics, linear separability, and memory capacity then enable a simple linear readout to generate adequate responses for various applications. RC spans areas far beyond machine learning, since it has been shown that the complex dynamics can be realized in various physical hardware implementations and biological devices. This yields greater flexibility and shorter computation time. Moreover, the neuronal responses triggered by the model's dynamics shed light on understanding brain mechanisms that also exploit similar dynamical processes. While the literature on RC is vast and fragmented, here we conduct a unified review of RC's recent developments from machine learning to physics, biology, and neuroscience. We first review the early RC models, and then survey the state-of-the-art models and their applications. We further introduce studies on modeling the brain's mechanisms by RC. Finally, we offer new perspectives on RC development, including reservoir design, coding frameworks unification, physical RC implementations, and interaction between RC, cognitive neuroscience and evolution.Comment: 51 pages, 19 figures, IEEE Acces

    Electronic scan weather radar: scan strategy and signal processing for volume targets

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    2013 Fall.Includes bibliographical references.Following the success of the WSR-88D network, considerable effort has been directed toward searching for options for the next generation of weather radar technology. With its superior capability for rapidly scanning the atmosphere, electronically scanned phased array radar (PAR) is a potential candidate. A network of such radars has been recommended for consideration by the National Academies Committee on Weather Radar Technology beyond NEXRAD. While conventional weather radar uses a rotating parabolic antenna to form and direct the beam, a phased array radar superimposes outputs from an array of many similar radiating elements to yield a beam that is scanned electronically. An adaptive scan strategy and advanced signal designs and processing concepts are developed in this work to use PAR effectively for weather observation. An adaptive scan strategy for weather targets is developed based on the space-time variability of the storm under observation. Quickly evolving regions are scanned more often and spatial sampling resolution is matched to spatial scale. A model that includes the interaction between space and time is used to extract spatial and temporal scales of the medium and to define scanning regions. The temporal scale constrains the radar revisit time while the measurement accuracy controls the dwell time. These conditions are employed in a task scheduler that works on a ray-by-ray basis and is designed to balance task priority and radar resources. The scheduler algorithm also includes an optimization procedure for minimizing radar scan time. In this research, a signal model for polarimetric phased array weather radar (PAWR) is presented and analyzed. The electronic scan mechanism creates a complex coupling of horizontal and vertical polarizations that produce the bias in the polarimetric variables retrieval. Methods for bias correction for simultaneous and alternating transmission modes are proposed. It is shown that the bias can be effectively removed; however, data quality degradation occurs at far off boresight directions. The effective range for the bias correction methods is suggested by using radar simulation. The pulsing scheme used in PAWR requires a new ground clutter filtering method. The filter is designed to work with a signal covariance matrix in the time domain. The matrix size is set to match the data block size. The filter's design helps overcome limitations of spectral filtering methods and make efficient use of reducing ground clutter width in PAWR. Therefore, it works on modes with few samples. Additionally, the filter can be directly extended for staggered PRT waveforms. Filter implementation for polarimetric retrieval is also successfully developed and tested for simultaneous and alternating staggered PRT. The performance of these methods is discussed in detail. It is important to achieve high sensitivity for PAWR. The use of low-power solid state transmitters to keep costs down requires pulse compression technique. Wide-band pulse compression filters will partly reduce the system sensitivity performance. A system for sensitivity enhancement (SES) for pulse compression weather radar is developed to mitigate this issue. SES uses a dual-waveform transmission scheme and an adaptive pulse compression filter that is based on the self-consistency between signals of the two waveforms. Using SES, the system sensitivity can be improved by 8 to 10 dB

    Multifrequency Aperture-Synthesizing Microwave Radiometer System (MFASMR). Volume 1

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    Background material and a systems analysis of a multifrequency aperture - synthesizing microwave radiometer system is presented. It was found that the system does not exhibit high performance because much of the available thermal power is not used in the construction of the image and because the image that can be formed has a resolution of only ten lines. An analysis of image reconstruction is given. The system is compared with conventional aperture synthesis systems

    Study and control of turbulent transport in the Boundary Plasma region of the TJ-II stellarator and the JET tokamak

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    Mención Internacional en el título de doctorThermonuclear fusion has been proposed as a sustainable, clean and safe energy source to meet the energy demands of the future. There are, however, still several challenges that need to be overcome in order to realize a viable fusion power plant. One of the great challenges is the integration of physics and technology optimization. Performance of magnetic fusion reactors is limited by heat and particle losses. The heat and particle losses are understood to be governed by the non-linear interplay of turbulence and plasma flows but uncertainty remains on e.g. physics of the sudden transitions between confinement regimes, isotopic scaling of confinement, non-linear saturation mechanisms of plasma turbulence, power exhausts and plasma-wall interaction. This thesis investigates the interplay of flows and turbulence in the TJ-II stellarator and the influence of magnetic configuration on plasma-wall interaction in the JET tokamak. A deep understanding of the mechanisms leading to turbulence self-regulation via Zonal Flows (ZFs) is of paramount importance. In this sense, the assessment of Long Range Correlations (LRC) in the plasma edge, by the use of Langmuir probe systems, have been proven to be a powerful strategy to study the interaction between ZFs and turbulence. Improvements in the experimental strategy to characterize LRC have been applied to study the interplay between neoclassical radial electric fields and ZFs and the transition to improved confinement regimes in the TJ-II stellarator. Experimental studies reveal the role of neoclassical radial electric fields to control the amplitude of Zonal Flows resulting in the development of both long (neoclassical) and short (due to Zonal Flows) radial electric field scales with important implication in the physics understanding of transport self-regulation mechanisms. A comprehensive description of the influence of plasma scenarios on the radial width of ZFs is given here, with a special focus on its dependence with heating and isotope scaling. For the first time, the characterization of low frequency fluctuating ZFs and mean radial electric fields has been experimentally studied during the L-H transition in Hydrogen and Deuterium plasmas in the stellarator TJ-II. No evidence of isotope effect on the L-H transition dynamics was observed. These observations emphasize the critical role of both zero frequency (equilibrium) and low frequency varying large-scale flows for stabilizing turbulence during the triggering of the L-H transition in magnetically confined toroidal plasmas and show that there are different paths to reach the L-H transition with impact on the conditions to access the H-mode regime. In addition to the relevance of studies carried out in stellarators, experimental validation of relevant plasma scenarios in large tokamaks constitute the fundamental test bench for future burning fusion reactors such as ITER. For example in the last years it has been shown that, in the JET tokamak, with the new ITER-like wall, global plasma confinement is strongly linked to the divertor magnetic topology, which influences the Boundary Plasma and the Plasma Wall Interaction. In this Thesis we show a study on how the neutral fluxes are affected by the divertor magnetic configuration and, as a consequence, how the SOL plasma changes. We also present a detailed preliminary analysis of the dynamic behavior of Ion and Neutral fluxes during the ELM-cycle. The results point to the Recycling coefficient, which varies significantly within this short time-scale, something that could have important implications in the understanding of the H-mode performance.El aprovechamiento de la energía de la fusión termonuclear se ha propuesto como un método limpio y sostenible para hacer frente a las demandas energéticas futuras. Sin embargo, actualmente todavía se deben superar retos científicos y técnicos para hacer viable la operación de un reactor nuclear de fusión. Uno de los mayores retos es el entendimiento de la física del plasma que tiene lugar en los reactores de fusión así como la optimización tecnológica de los propios reactores. El rendimiento de los futuros reactores de fusión está limitado por las pérdidas de partículas y de calor. Ambos fenómenos están gobernados por la interacción no lineal entre la turbulencia del plasma y los flujos a gran escala, conocidos como Flujos Zonales. Por otra parte, la física de las transiciones espontáneas entre regímenes de diferente nivel de confinamiento, el efecto isotópico y sus implicaciones, los mecanismos de saturación no lineal de la turbulencia así como la evacuación de los flujos de calor y la física de la interacción entre el plasma y la pared necesita todavía ser entendida. Esta tesis describe la investigación empírica de la interacción entre las diferentes escalas de turbulencia de plasma en el stellarator TJ-II y la influencia de la configuración magnética en la física de la interacción plasma-pared en el tokamak JET. A este efecto, se han utilizado dos diagnósticos: las sondas electrostáticas (conocidas como sondas de Langmuir) y espectroscopía rápida en el espectro visible. Es de suma importancia la comprensión profunda de los mecanismos que conducen a la autorregulación de la turbulencia por la acción de los Flujos Zonales (ZF). En este sentido, se ha demostrado que la evaluación de las correlaciones de largo alcance (LRC) en el borde del plasma, mediante el uso de los sistemas de sondas de Langmuir, es una estrategia poderosa para estudiar la interacción entre ZF y la turbulencia. Las mejoras en la estrategia experimental para caracterizar LRC se han aplicado para estudiar la interacción entre los campos eléctricos radiales neoclásicos ZF durante la transición a regímenes de confinamiento mejorados en el stellarator TJ-II. Los estudios experimentales llevados a cabo revelan el papel de los campos eléctricos radiales neoclásicos en el control de la amplitud de los flujos zonales que resultan en el desarrollo de escalas de campos eléctricos radiales largos (neoclásicos) y cortos (debidos a los flujos zonales), con una importante implicación en la comprensión física de los mecanismos de auto-regulación transporte radial. Aquí se proporciona una descripción completa de la influencia de los escenarios de plasma en el ancho radial de las ZF, con un enfoque especial en su dependencia con el calentamiento y la masa isotópica. Por primera vez, la caracterización de estas fluctuaciones globales de baja frecuencia y campos eléctricos radiales se ha estudiado experimentalmente durante la transición L-H en plasmas de hidrógeno y deuterio en el stellarador TJ-II. No se observó evidencia de efecto isótopo en la dinámica de transición L-H. Estas observaciones enfatizan el papel crítico del campo eléctrico neoclásico (o de equilibrio) y los flujos a gran escala de baja frecuencia para estabilizar la turbulencia durante el inicio de la transición L-H en plasmas toroidales confinados magnéticamente. Esto muestra que existen diferentes caminos para alcanzar la transición de LH con impacto sobre las condiciones de acceso al régimen de confinamiento mejorado. Además de la relevancia de los estudios realizados en stellarators, la validación experimental de escenarios relevantes de plasma en grandes tokamaks constituye el banco de pruebas fundamental para futuros reactores de fusión como ITER. Por ejemplo, en los últimos años se ha demostrado que, en el tokamak JET, con la nueva pared, que es idéntica a la que estará instalada en ITER, el confinamiento global del plasma está fuertemente vinculado a la topología del divertor, lo que influye en la física y en las características del borde del plasma y de la interacción plasma-pared. En esta tesis, mostramos un estudio sobre cómo los flujos de partículas neutras se ven afectados por la configuración magnética del divertor y, en consecuencia, cómo cambia la parte más externa del plasma, en la que las líneas de campo no están cerradas sobre sí mismas, sino que se cierran a través de los elementos metálicos del dispositivo, conocida como “Scrape-Off Layer”. También presentamos un análisis preliminar detallado del comportamiento dinámico de los flujos de iones y neutros durante las inestabilidades de tipo ELM. Los resultados apuntan al coeficiente de reciclado, que varía significativamente dentro de esta breve escala de tiempo, algo que podría tener implicaciones importantes en la comprensión del rendimiento en modo de alto confinamiento.Este trabajo se ha realizado en el marco del proyecto ENE2012-38620-C02-01 (referencia BES-2013-065215), del Ministerio de Ciencia, Innovación y Universidades (MICINN).Programa Oficial de Doctorado en Plasmas y Fusión Nuclear por la Universidad Carlos III de MadridPresidente: Luis Conde López.- Secretario: Isabel García Cortés.- Vocal: Alexander Vladimirovich Melniko

    High-multiplicity space-division multiplexed transmission systems

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