Dual-Stage Planning for Elastic Optical Networks Integrating Machine-Learning-Assisted QoT Estimation

Following the emergence of Elastic Optical Networks (EONs), Machine Learning (ML) has been intensively investigated as a promising methodology to address complex network management tasks, including, e.g., Quality of Transmission (QoT) estimation, fault management, and automatic adjustment of transmission parameters. Though several ML-based solutions for specific tasks have been proposed, how to integrate the outcome of such ML approaches inside Routing and Spectrum Assignment (RSA) models (which address the fundamental planning problem in EONs) is still an open research problem. In this study, we propose a dual-stage iterative RSA optimization framework that incorporates the QoT estimations provided by a ML regressor, used to define lightpaths' reach constraints, into a Mixed Integer Linear Programming (MILP) formulation. The first stage minimizes the overall spectrum occupation, whereas the second stage maximizes the minimum inter-channel spacing between neighbor channels, without increasing the overall spectrum occupation obtained in the previous stage. During the second stage, additional interference constraints are generated, and these constraints are then added to the MILP at the next iteration round to exclude those lightpaths combinations that would exhibit unacceptable QoT. Our illustrative numerical results on realistic EON instances show that the proposed ML-assisted framework achieves spectrum occupation savings up to 52.4% (around 33% on average) in comparison to a traditional MILP-based RSA framework that uses conservative reach constraints based on margined analytical models

CDC ROADM design tradeoffs due to physical layer impairments in optical networks

In this work, we assess the impact of several physical layer impairments (PLIs) on the performance of optical networks based on colorless, directionless and contentionless reconfigurable optical add/drop multiplexers (ROADMs), through Monte-Carlo simulation, and considering polarization division multiplexing 4 and 16 quadrature amplitude modulation (QAM) signals, at 28 GBaud, for 37.5 GHz optical channels. The PLIs taken into account are the amplified spontaneous emission noise, optical filtering, in-band crosstalk and nonlinear interference noise caused by Kerr effect. A detailed model of the ROADM node is built considering two typical ROADM architectures, broadcast and select (B&S) and route and select (R&S), and two different add/drop structures, multicast switches (MCSs) and wavelength selective switches (WSSs), resulting in four different ROADM node scenarios. Our results have shown that for 16QAM signals, the B&S ROADMs with WSSs-based add/drop structures is the scenario that has the best relation cost/performance, foreseeing its use in metro networks, while for 4QAM signals, the R&S ROADM with WSSs-based add/drop structure scenario allows a larger ROADM cascade at an expectable lower cost anticipating its implementation in long-haul networks

Minimization of Interchannel Interference E ects in Nyquist-WDM Systems

ABSTRACT: The need of increasing the capacity of current deployed optical networks to perform terabits transmissions has been driven to the development of superchannel systems, (principally based on Nyquist-WDM) to be carried out in flexible grid or gridless scenarios. Nevertheless, one of the main issues to be mitigated in these systems is the interchannel interference (ICI), whose effect is intensified when the spectral channel spacing is reduced (for further spectral efficiency increment). In this thesis, we present a study of the ICI effects in Nyquist-WDM systems by means of BER calculation as a function of several system parameters such as: frequency channel spacing, roll-off factor of the digital pulse-shaping filter, laser's linewidth, transmission distance, mark probability of the pseudo-random bit sequence, optical-to-signal noise ratio, among others. Besides, two methods enabling ICI mitigation are proposed: on one hand, a method based on FEC-coded sequence distribution among optical carriers for applications of multiple carriers (superchannels) as a single entity, and on the other hand, a method to perform nonsymmetrical demodulation (NSD) based on the k-means algorithm enabling time-varying distortions mitigation. In contradiction of techniques for ICI mitigation in recent art, these proposals avoid the use of multiple-input multiple-output equalizers or training sequences. Specifically, for NSD approach, information of adjacent channels is not required

Impact of physical layer impairments on SDM networks based on ROADM nodes

Current transport optical networks are approaching its capacity limits, mainly due to new applications and services that require a huge amount of resources. To increase the network capacity, multiband solutions, that exploit the unused capacity of actual fibers, in particular the L-band, are being currently commercially explored. However, this strategy is assumed as a short to medium term solution. A long-term solution is to use spatial-division multiplexing (SDM) in the optical domain, which leads to the concept of SDM-based optical networks. In this work, different SDM switching architectures (spatial, spatial-wavelength, wavelength, fractional space-full wavelength) are studied and compared in terms of cost per bit, power consumption and flexibility. For the switching architectures with spatial and spatial-wavelength granularities (the architectures that have superior performance), the most relevant physical impairments (PLIs) (amplifiers noise, non-linear interference, narrowing penalty due to filtering and in-band crosstalk) are analytically studied, for a SDM reconfigurable optical add-drop multiplexer (ROADM) cascade. Furthermore, a Monte Carlo simulation is used to assess more rigorously the PLIs effects on the performance of SDM ROADMs, with spatial-wavelength switching architecture, in cascade. The main difference, regarding PLIs, between the single spatial channel ROADM architecture and the SDM ROADM architectures is the enhanced effect of in-band crosstalk. For cascaded ROADMs with 16 directions, 19 spatial channels and filtering isolation of -25 dB, the in-band crosstalk can lead to a 2 dB optical signal-to-noise ratio penalty. Due to this penalty, the signal crosses less 9 ROADMs than in a single spatial channel ROADM architecture.As redes óticas de transporte atuais estão a aproximar-se do seu limite de capacidade devido às novas aplicações e serviços que requerem uma maior quantidade de recursos de rede. Uma possível solução de curto a médio prazo para a falta de recursos é o uso de múltiplas bandas da fibra, para além da banda C. Uma solução a longo prazo será o uso de multiplexagem com divisão no espaço (SDM) no domínio óptico. Neste trabalho são estudados, o custo por bit, consumo de energia e flexibilidade, das diferentes arquiteturas SDM (no espaço, no espaço e comprimento de onda, no comprimento de onda, fracionada no espaço e completa no comprimento de onda). Para as arquiteturas com granularidades no espaço e no espaço e comprimento de onda estuda-se analiticamente os efeitos das principais limitações do nível físico (PLIs) (ruído dos amplificadores, interferência não-linear, penalidade de filtragem e diafonia homódina), para cascatas de multiplexadores óticos de inserção/extração reconfiguráveis (ROADMs). Usa-se uma simulação Monte Carlo para calcular mais rigorosamente os efeitos das PLIs na arquitetura com granularidade no espaço e comprimento de onda. A principal diferença, em termos de PLIs, entre uma rede SDM e uma rede com um único canal espacial é o efeito da diafonia homódina. Para uma rede com 16 direções, 19 canais espaciais e isolamento dos filtros de -25 dB, a diafonia homódina causa uma penalidade na relação sinal-ruído óptica de 2 dB e o sinal atravessa menos 9 ROADMs que numa rede com apenas um canal espacial

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

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

Resource Allocation in Flexible-Grid Optical Networks with Nonlinear Interference

As the backbone of modern communications, the optical networks are anticipated to provide higher data rate and flexibility to support the exponentially growing volume and heterogeneity of traffic requirements. Flexible-grid optical networks have been proposed to improve the utilization of spectrum resources. However, the physical layer conditions are more complex and variable in flexible-grid networks than fixed-grid wavelength division multiplexing networks. Therefore, the consideration of physical layer impairment (PLI) is necessary in the planning stage of flexible-grid optical networks. In this thesis, we mainly study the allocation of physical layer resources such as modulation formats, power spectral densities (PSDs), and carrier frequencies for all the channels in flexible-grid networks. To accurately estimate the quality of transmission, both linear and nonlinear PLIs are considered. Novel resource allocation problems are formulated and solved to include a nonlinear channel model and additional degrees of freedom in flexible-grid optical networks. The network performance and efficiency improvements over previous works are demonstrated via numerical calculations.Paper A proposes a resource allocation algorithm for a single flexible-grid fiber link based on a nonlinear signal distortion model, i.e., the Gaussian noise (GN) model, as a first step towards a whole-network design.Based on the accurate estimation of channel PLIs provided by the GN model, the proposed algorithm can allocate resources more efficiently in terms of spectrum usage. Its performance is demonstrated through comparisons with the benchmark algorithm utilizing the transmission reach method.Paper B and Paper C extend the proposed formulation to the network level and study the impact of nonlinear interference on transmission reaches and resource usage. Specifically, with precalculated routes and spectrum orderings for all the channels, Paper B allocates resources in a three-node network with optimized PSD. In Paper C, the algorithm is further extended to more complex networks to demonstrate its scalability and performance. In Paper D, we jointly allocate route, spectrum, modulation format, and PSD for each connection request in the flexible-grid network. A mixed integer linear programming problem is formulated to search for the optimal resource allocation. A heuristic algorithm based on problem decomposition is also developed to reduce computational complexities.The joint resource allocation approach can improve the spectrum efficiency even further compared with previous separate planning strategies

Design, monitoring and performance evaluation of high capacity optical networks

Premi Extraordinari de Doctorat, promoció 2018-2019. Àmbit de les TICInternet traffic is expected to keep increasing exponentially due to the emergence of a vast number of innovative online services and applications. Optical networks, which are the cornerstone of the underlying Internet infrastructure, have been continuously evolving to carry the ever-increasing traffic in a more flexible, cost-effective, and intelligent way. Having these three targets in mind, this PhD thesis focuses on two general areas for the performance improvement and the evolution of optical networks: i) introducing further cognition to the optical layer, and ii) introducing new networking solutions revolutionizing the optical transport infrastructure. In the first part, we present novel failure detection and identification solutions in the optical layer utilizing the optical spectrum traces captured by cost-effective coarse-granular Optical Spectrum Analyzers (OSA). We demonstrate the effectiveness of the developed solutions for detecting and identifying filter-related failures in the context of Spectrum-Switched Optical Networks (SSON), as well as transmitter-related laser failures in Filter-less Optical Networks (FON). In addition, at the subsystem level we propose an Autonomic Transmission Agent (ATA), which triggers local or remote transceiver reconfiguration by predicting Bit-Error-Rate (BER) degradation by monitoring State-of-Polarization (SOP) data obtained by coherent receivers. I have developed solutions to push further the performance of the currently deployed optical networks through reducing the margins and introducing intelligence to better manage their resources. However, it is expected that the spectral efficiency of the current standard Single-Mode Fiber (SMF) based optical network approaches the Shannon capacity limits in the near future, and therefore, a new paradigm is required to keep with the pace of the current huge traffic increase. In this regard, Space Division Multiplexing (SDM) is proposed as the ultimate solution to address the looming capacity crunch with a reduced cost-per-bit delivered to the end-users. I devote the second part of this thesis to investigate different flavors of SDM based optical networks with the aim of finding the best compromise for the realization of a spectrally and spatially flexible optical network. SDM-based optical networks can be deployed over various types of transmission media. Additionally, due to the extra dimension (i.e., space) introduced in SDM networks, optical switching nodes can support wavelength granularity, space granularity, or a combination of both. In this thesis, we evaluate the impact of various spectral and spatial switching granularities on the performance of SDM-based optical networks serving different profiles of traffic with the aim of understanding the impact of switching constraints on the overall network performance. In this regard, we consider two different generations of wavelength selective switches (WSS) to reflect the technology limitations on the performance of SDM networks. In addition, we present different designs of colorless direction-less, and Colorless Directionless Contention-less (CDC) Reconfigurable Optical Add/Drop Multiplexers (ROADM) realizing SDM switching schemes and compare their performance in terms of complexity and implementation cost. Furthermore, with the aim of revealing the benefits and drawbacks of SDM networks over different types of transmission media, we preset a QoT-aware network planning toolbox and perform comparative performance analysis among SDM network based on various types of transmission media. We also analyze the power consumption of Multiple-Input Multiple-Output (MIMO) Digital Signal Processing (DSP) units of transceivers operating over three different types of transmission media. The results obtained in the second part of the thesis provide a comprehensive outlook to different realizations of SDM-based optical networks and showcases the benefits and drawbacks of different SDM realizations.Se espera que el tráfico de Internet siga aumentando exponencialmente debido a la continua aparición de gran cantidad de aplicaciones innovadoras. Las redes ópticas, que son la piedra angular de la infraestructura de Internet, han evolucionado continuamente para transportar el tráfico cada vez mayor de una manera más flexible, rentable e inteligente. Teniendo en cuenta estos tres objetivos, esta tesis doctoral se centra en dos áreas cruciales para la mejora del rendimiento y la evolución de las redes ópticas: i) introducción de funcionalidades cognitivas en la capa óptica, y ii) introducción de nuevas estructuras de red que revolucionarán el transporte óptico. En la primera parte, se presentan soluciones novedosas de detección e identificación de fallos en la capa óptica que utilizan trazas de espectro óptico obtenidas mediante analizadores de espectros ópticos (OSA) de baja resolución (y por tanto de coste reducido). Se demuestra la efectividad de las soluciones desarrolladas para detectar e identificar fallos derivados del filtrado imperfecto en las redes ópticas de conmutación de espectro (SSON), así como fallos relacionados con el láser transmisor en redes ópticas sin filtro (FON). Además, a nivel de subsistema, se propone un Agente de Transmisión Autónomo (ATA), que activa la reconfiguración del transceptor local o remoto al predecir la degradación de la Tasa de Error por Bits (BER), monitorizando el Estado de Polarización (SOP) de la señal recibida en un receptor coherente. Se han desarrollado soluciones para incrementar el rendimiento de las redes ópticas mediante la reducción de los márgenes y la introducción de inteligencia en la administración de los recursos de la red. Sin embargo, se espera que la eficiencia espectral de las redes ópticas basadas en fibras monomodo (SMF) se acerque al límite de capacidad de Shannon en un futuro próximo, y por tanto, se requiere un nuevo paradigma que permita mantener el crecimiento necesario para soportar el futuro aumento del tráfico. En este sentido, se propone el Multiplexado por División Espacial (SDM) como la solución que permita la continua reducción del coste por bit transmitido ante ése esperado crecimiento del tráfico. En la segunda parte de esta tesis se investigan diferentes tipos de redes ópticas basadas en SDM con el objetivo de encontrar soluciones para la realización de redes ópticas espectral y espacialmente flexibles. Las redes ópticas basadas en SDM se pueden implementar utilizando diversos tipos de medios de transmisión. Además, debido a la dimensión adicional (el espacio) introducida en las redes SDM, los nodos de conmutación óptica pueden conmutar longitudes de onda, fibras o una combinación de ambas. Se evalúa el impacto de la conmutación espectral y espacial en el rendimiento de las redes SDM bajo diferentes perfiles de tráfico ofrecido, con el objetivo de comprender el impacto de las restricciones de conmutación en el rendimiento de la red. En este sentido, se consideran dos generaciones diferentes de conmutadores selectivos de longitud de onda (WSS) para reflejar las limitaciones de la tecnología en el rendimiento de las redes SDM. Además, se presentan diferentes diseños de ROADM, independientes de la longitud de onda, de la dirección, y sin contención (CDC) utilizados para la conmutación SDM, y se compara su rendimiento en términos de complejidad y coste. Además, con el objetivo de cuantificar los beneficios e inconvenientes de las redes SDM, se ha generado una herramienta de planificación de red que prevé la QoT usando diferentes tipos de fibras. También se analiza el consumo de energía de las unidades DSP de los transceptores MIMO operando en redes SDM con tres tipos diferentes de medios de transmisión. Los resultados obtenidos en esta segunda parte de la tesis proporcionan una perspectiva integral de las redes SDM y muestran los beneficios e inconvenientes de sus diferentes implementacionesAward-winningPostprint (published version

Optimization, Design, and Analysis of Flexible-Grid Optical Networks with Physical-Layer Constraints

The theme of this thesis is the optimization, design, and analysis of flexible-grid optical networks that are constrained by physical-layer impairments (PLIs). We consider three flexible-grid network scenarios. The networks in the first class are static nonlinear transparent backbone networks where physical-layer resources are allocated to each traffic demand. The networks in the second class are traffic-variable nonlinear translucent backbone networks where regenerator sites are necessary to recover optical signals from the accumulated noise in long-distance transmission. The third class is data-center networks based on optical spatial division multiplexing. Within each class, our focus is primarily on an efficient and balanced allocation of network resources. Both optimization formulations and heuristic algorithms are proposed for each class. The contributions of this thesis can thus be categorized into three topics, as outlined below.First, we consider the optimization of network resources in the presence of PLI. The PLI between optical connections is characterized by the Gaussian noise (GN) model and incorporated into resource allocation algorithms. As an example, for a link-level optical communication system, the spectrum usage can be reduced by roughly up to 22% by accurately modelling the PLIs and assigning proper modulation formats and spectrum to optical connections. For resource allocation in the network level, the power spectral density of each optical connection is optimized in addition to the previously mentioned resources.As a second topic, the design of flexible-grid optical networks is studied. Specifically, we consider the regenerator location problem in traffic-variable translucent backbone networks. Due to the constantly changing traffic, the PLIs suffered by optical connections are also stochastic and, thus, have to be handled from a probabilistic perspective. A statistical network assessment process is used to characterize the noise distributions suffered by optical connections on each link, based on which a heuristic algorithm is proposed to select a set of regenerator sites with the minimum blocking probability.Finally, we study the trade-off between the blocking probability and total throughput in the modular data center networks (DCNs) based on different optical spatial division multiplexing switching schemes. This performance trade-off is caused by the coexistence of traffic demands with extremely different data rates and number of requests in DCNs. A heuristic resource allocation algorithm is proposed to enable flexible tuning of the objective function and achieve a balanced network performance