Дисертації з теми "Intensity Modulated -Direct Detection"

Une approche pour augmenter le débit par longueur d'onde, est d'utiliser la modulation DMT (Discrete Multitone) à haute efficacité spectrale. Le travail présenté dans cette thèse se focalise principalement sur l'optimisation de la consommation en puissance et le coût de la DMT, qui présentent des obstacles majeurs à son industrialisation. Dans ce cadre, nous avons tout d'abord développé des nouvelles techniques permettant d'exclure la symétrie Hermitienne des modulations DMT, réduisant ainsi considérablement la consommation en puissance et le coût du système. Nous avons ensuite proposé un algorithme de compression linéaire asymétrique permettant de réduire la puissance optique de la modulation DMT avec une complexité modérée. Un nouveau modèle comportemental du VCSEL basé sur la caractéristique quasi-statique a été également développé. Nous avons enfin validé expérimentalement les techniques que nous avons proposées. Plusieurs résultats de simulations et de mesures sont ainsi présentés
A possible approach to maximize the data rate per wavelength, is to employ the high spectral efficiency discrete multitone (DMT) modulation. The work presented in this thesis mainly focuses on optimizing the power consumption and cost of DMT, that are the major obstacles to its market development. Within this context, we have first developed novel techniques permitting to discard the use of Hermitian symmetry in DMT modulations, thus significantly reducing the power consumption and the system cost. We have next proposed an asymmetric linear companding algorithm permitting to reduce the optical power of conventional DCO-OFDM modulation with a moderate complexity. A new VCSEL behavioural model based on the use of the VCSEL quasi-static characteristic was also developed to accurately evaluate the VCSEL impact on DMT modulations. Finally, we have built an experimental system to experimentally validate our proposed techniques. Several simulations and measurement results are then provided

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.
Includes bibliographical references (p. 85-88).
by Jeffrey Matthew Roth.
M.Eng.

Radiation therapy accounts for treatment of over one million cancer patients each year in the United States alone, and its use will continue to grow rapidly in the coming years. Recently, many important advancements have been developed that greatly improve the outcomes and effectiveness of this treatment technique, the most notable being Intensity Modulated Radiation Therapy (IMRT). IMRT is a sophisticated treatment technique where the radiation dose is conformed to the tumor volume, thereby sparing nearby healthy tissue from excessive radiation dose. While IMRT is a valuable tool in the planning of radiation treatments, it is not without its difficulties. This research has created, developed, and tested an innovative approach to IMRT treatment planning, coined Direct Compensator Profile Optimization (DCPO), which is shown to eliminate many of the difficulties typically associated with IMRT planning and delivery using solid compensator based treatment. The major innovation of this technique is that it is a direct delivery parameter optimization approach which has adopted a parameterized surface representation using Non-Uniform Rational B-Splines (NURBs) to replace the conventional beamlet weight optimization approach. This new approach brings with it three key advantages: 1) a reduced number of parameters to optimize, reducing the difficulty of numerical optimization; 2) the ability to ensure complete equivalence of planned and actual manufactured compensators; and 3) direct inclusion of delivery device effects during planning with no performance penalties, eliminating the degrading fluence-to-delivery parameter conversion process. Detailed research into the affects of the DCPO approach on IMRT planning has been completed and a thorough analysis of the developments is provided herein. This research includes a complete description of the DCPO surface representation scheme, inverse planning process, as well as quantification of the manufacturing constraint control procedure. Results are presented which demonstrate the performance and innovation offered by this new approach and show that the resulting compensator shapes can be manufactured to nearly 100 percent of the designed shape.
Ph.D.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering PhD

The primary goal of this thesis is to improve the precision and efficiency of radiation therapy treatment. This goal is achieved by developing and implementing a direct aperture optimization (DAO) platform where the multileaf collimator (MLC) is rotated between each aperture. The approach is referred to as rotating aperture optimization (RAO). A series of tests is performed to evaluate how a final optimized plan depends on MLC parameters. Imposing constraints on the leaf sequence results in increased efficiency and a simplification of the treatment plan without compromising the quality of the dose distribution. It is also shown that an arrangement of equispaced collimator angles takes full advantage of the flexibility associated with collimator rotation. A study including ten recurring nasopharynx cancer patients is used to evaluate the capabilities of RAO compared to other optimization techniques. It is shown that RAO plans require significantly less linac radiation output (monitor units or MU) while maintaining equivalent dose distribution quality compared to plans generated with the conventional fluence based approach. Furthermore with an improved collimator rotation speed, the RAO plans should be executable in the same or less time than plans generated with the fluence-based approach. For the second part of the study it is shown that plans generated with RAO are as good as or better than plans generated with standard fixed collimator DAO. Film and ion chamber measurements indicate that RAO plans can be delivered more accurately than DAO plans. Additional applications of DAO were investigated through collaboration with two PhD students. First, Monte Carlo was used to generate pencil beam dose distributions for DAO inverse treatment planning (MC-DAO). The MC-DAO technique correctly models traditionally difficult treatment geometries such as small fields and tissue inhomogeneities. The MC-DAO also takes advantage of the improved MU efficiency associated with the DAO technique. Secondly DAO is proposed for adaptive radiation therapy. The results show that plan re-adaptation can be performed more quickly than complete plan regeneration thereby minimizing the time the patient has to spend in the treatment room and reducing the potential for geometric errors in treatment delivery.

In optimization of intensity-modulated radiation therapy treatment plans, dose-volumehistogram (DVH) functions are often used as objective functions to minimize the violationof dose-volume criteria. Neither DVH functions nor dose-volume criteria, however,are ideal for gradient-based optimization as the former are not continuously differentiableand the latter are discontinuous functions of dose, apart from both beingnonconvex. In particular, DVH functions often work poorly when used in constraintsdue to their being identically zero when feasible and having vanishing gradients on theboundary of feasibility.In this work, we present a general mathematical framework allowing for direct optimizationon all DVH-based metrics. By regarding voxel doses as sample realizations ofan auxiliary random variable and using kernel density estimation to obtain explicit formulas,one arrives at formulations of volume-at-dose and dose-at-volume which are infinitelydifferentiable functions of dose. This is extended to DVH functions and so calledvolume-based DVH functions, as well as to min/max-dose functions and mean-tail-dosefunctions. Explicit expressions for evaluation of function values and corresponding gradientsare presented. The proposed framework has the advantages of depending on onlyone smoothness parameter, of approximation errors to conventional counterparts beingnegligible for practical purposes, and of a general consistency between derived functions.Numerical tests, which were performed for illustrative purposes, show that smoothdose-at-volume works better than quadratic penalties when used in constraints and thatsmooth DVH functions in certain cases have significant advantage over conventionalsuch. The results of this work have been successfully applied to lexicographic optimizationin a fluence map optimization setting.
Vid optimering av behandlingsplaner i intensitetsmodulerad strålterapi används dosvolym- histogram-funktioner (DVH-funktioner) ofta som målfunktioner för att minimera avståndet till dos-volymkriterier. Varken DVH-funktioner eller dos-volymkriterier är emellertid idealiska för gradientbaserad optimering då de förstnämnda inte är kontinuerligt deriverbara och de sistnämnda är diskontinuerliga funktioner av dos, samtidigt som båda också är ickekonvexa. Speciellt fungerar DVH-funktioner ofta dåligt i bivillkor då de är identiskt noll i tillåtna områden och har försvinnande gradienter på randen till tillåtenhet. I detta arbete presenteras ett generellt matematiskt ramverk som möjliggör direkt optimering på samtliga DVH-baserade mått. Genom att betrakta voxeldoser som stickprovsutfall från en stokastisk hjälpvariabel och använda ickeparametrisk densitetsskattning för att få explicita formler, kan måtten volume-at-dose och dose-at-volume formuleras som oändligt deriverbara funktioner av dos. Detta utökas till DVH-funktioner och så kallade volymbaserade DVH-funktioner, såväl som till mindos- och maxdosfunktioner och medelsvansdos-funktioner. Explicita uttryck för evaluering av funktionsvärden och tillhörande gradienter presenteras. Det föreslagna ramverket har fördelarna av att bero på endast en mjukhetsparameter, av att approximationsfelen till konventionella motsvarigheter är försumbara i praktiska sammanhang, och av en allmän konsistens mellan härledda funktioner. Numeriska tester genomförda i illustrativt syfte visar att slät dose-at-volume fungerar bättre än kvadratiska straff i bivillkor och att släta DVH-funktioner i vissa fall har betydlig fördel över konventionella sådana. Resultaten av detta arbete har med framgång applicerats på lexikografisk optimering inom fluensoptimering.

This thesis investigates methods of reducing radiation dose calculation errors as applied to a specialized x-ray therapy called intensity modulated radiation therapy (IMRT). There are three major areas of investigation. First, limits of the popular 2D pencil beam kernel (PBK) dose calculation algorithm are explored. The ability to resolve high dose gradients is partly related to the shape of the PBK. Improvements to the spatial resolution can be achieved by modifying the dose kernel shapes already present in the clinical treatment planning system. Optimization of the PBK shape based on measured-to-calculated test pattern dose comparisons reduces the impact of some limitations of this algorithm. However, other limitations remain (e.g. assuming spatial invariance, no modeling of extra-focal radiation, and no modeling of lateral electron transport). These limitations directed this thesis towards the second major investigation - Monte Carlo (MC) simulation for IMRT. MC is considered to be the "gold standard" for radiation dose calculation accuracy. This investigation incorporates MC calculated beamlets of dose deposition into a direct aperture optimization (DAO) algorithm for IMRT inverse planning (MC-DAO) . The goal is to show that accurate tissue inhomogeneity information and lateral electronic transport information, combined with DAO, will improve the quality/accuracy of the patient treatment plan. MC simulation generates accurate beamlet dose distributions in traditionally difficultto- calculate regions (e.g. air-tissue interfaces or small (≤ 5 cm² ) x-ray fields). Combining DAO with MC beamlets reduces the required number of radiation units delivered by the linear accelerator by ~30-50%. The MC method is criticized for having long simulation times (hours). This can be addressed with distributed computing methods and data filtering ('denoising'). The third major investigation describes a practical implementation of the 3D Savitzky-Golay digital filter for MC dose 'denoising'. This thesis concludes that MC-based DAO for IMRT inverse planning is clinically feasible and offers accurate modeling of particle transport and dose deposition in difficult environments where lateral electronic dis-equilibrium exists.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

With the rapid growth of wireless data demands and saturation of radio frequency (RF) capacity, visible light communication (VLC) has become a promising candidate to complement conventional RF communication, especially for indoor short range applications. However the performance of the system depends on the propagation and type of system used. An optical Orthogonal Frequency Division Multiplexing (O-OFDM) together with multiple input multiple output (MIMO) in different scenario and modulation techniques are studied in the thesis. A novel optical wireless communication (OWC) multi-cell system with narrow field of view (FOV) is studied. In this system the intensity modulated beam from four light sources are used for communication. The system allows beams to be concentrated in specific areas of the room to serve multiple mobile devices with low interference and hence increase system capacity. The performance of asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM), direct current biased optical OFDM (DCO-OFDM) and single carrier (SC) modulation are then compared in this system considering single user and multiusers scenarios. The performance of the multi-cell is compared with single cell with wide FOV. It is shown that the capacity for multi-cell system increases with the number of users to 4 times the single user capacity. Also the findings show that multi-cell system with narrow beams can outperform a single wide beam system in terms of coverage area and hence average throughput of about 2.7 times the single wide beam system capacity. One of the impairments in line of sight (LOS) OWC systems is coverage which degrades the performance. A mobile receiver with angular diversity detectors in MIMO channels is studied. The objective is to improve the rank of the channel matrix and hence system throughput. Repetition coding (RC), spatial multiplexing (SMP) and spatial modulation (SM) concepts are used to evaluate throughput across multiple locations in a small room scenario. A novel adaptive spatial modulation (ASM) which is capable of combating channel rank deficiency is devised. Since the receiver is mobile, the channel gains are low in some locations of the room due to the lack of LOS paths between transmitters and receivers. To combat the situation adaptive modulation and per antenna rate control (PARC) is employed to maximise spectral efficiency. The throughputs for fixed transmitters and receivers are compared with the oriented/inclined detectors for different cases. Angular diversity detectors offer a better throughput improvement than the state of the art vertical detectors, for example in ASM angular diversity receiver gives throughput of about 1.6 times that of vertical detectors. Also in SMP the angular detectors offer throughput about 1.4 times that of vertical detectors. SMP gives the best performance compared to RC, SM and ASM, for example SMP gives throughput about 2.5 times that of RC in both vertical detectors and angular diversity receivers. Again SMP gives throughput about 6 times that of SM in both vertical detectors and angular diversity receivers. Also SMP provides throughput about 2 times that of ASM in both vertical detectors and angular diversity receivers. ASM exhibit improvement in throughput about average factor of 3.5 times SM performance in both vertical detectors and angular diversity detectors. As the performance of the system may be jeopardized by obstructions, specular and diffuse reflection models for indoor OWC systems using a mobile receiver with angular diversity detectors in MIMO channels are considered. The target is to improve the MIMO throughput compared to vertically oriented detectors by exploiting reflections from different reflecting surfaces in the room. The throughput across multiple locations in the small room by using RC, SMP and SM approaches is again evaluated. The results for LOS only channels against LOS with specular or diffuse reflection conditions, for both vertical and angular oriented receivers are then compared. The results show that exploiting specular and diffuse reflections provide significant improvements in link performance. For example the reflection coefficient (α) of 0.9 and the antenna separation of 0.6 m, RC diffuse model shows throughput improvement of about 1.8 times that of LOS for both vertical detectors and angular diversity receivers. SM diffuse model shows throughput improvement of about 3 times that of LOS for both vertical detectors and angular diversity receivers. ASM diffuse model shows throughput improvement of about 2 times that of LOS for both vertical detectors and angular diversity receivers. SMP diffuse model shows throughput improvement of about 1.5 times that of LOS for both vertical detectors and angular diversity receiver.

The evolution of the Home Area Network (HAN) is lead by the proliferation of connected devices inside the home and the deployment of high broadband access network which now allows the delivery of services that can exceed 1Gbit/s. To ensure efficient in-house exchanges, the HAN has to move rapidly toward multi-Gigabit/s connections, in particular the wireless connectivity generally preferred by the customers. Current wireless systems have limited capacities, but new radio standards delivering data-rates up to 7Gbit/s are emerging. Nevertheless, as they address the unlicensed millimeter-wave band, from 57 to 66 GHz, their radio coverage is limited to a single room. Indeed, at such frequencies, the free-space losses are high and the waves do not cross the walls. This thesis proposes to solve this problem by means of the Radio over Fiber (RoF) technology. This consists in capturing the 60GHz radio signals emitted in one room, converting them into optical signals for transmission through optical fibers, and reemitting them in another room. Thus, several RoF transducers will be installed in the home and interconnected by a suitable optical infrastructure to create systems acting at the same time as repeaters and as distribution systems. From the viewpoint of the HAN market, such systems will be competitive only if they are low cost. As a consequence, this work focuses on direct modulation with direct detection (IM-DD) at Intermediate Frequency (IF). In other words, the 60GHz signal is down-converted at a lower frequency around 5GHz before the laser modulation and up-converted to 60GHz after the photodetection. Concerning the optical fiber, silica multimode fiber (MMF) is privileged as it allows the use of low cost and largely available optoelectronic devices working at 850nm.The thesis proposes different RoF architectures, from point-to-point interconnecting two rooms to multipoint-to-multipoint acting as logical buses. After an analog characterization of the optoelectronic components, the RoF link and the domestic cable, these architectures are designed, built and characterized step by step using OFDM modulation according to existing wireless 60GHz standards. Real-time transmissions between commercial devices have also been performed to validate these architectures. Moreover, advanced RoF infrastructures are proposed. First, the RoF systems can be easily improved if the access to their optical media is managed by the radio MAC layer. This approach is therefore studied showing its feasibility. Secondly, an optical system, seen by users as a premium product, has to support the legacy home services commonly used as well as the new ones that could emerge in the future. Thus, innovative multiservice and multiformat infrastructures conveying on a unique optical cable wired IP data, broadcast terrestrial or satellite television, the 60GHz wireless connectivity, and specific formats as HDMI signals are proposed and tested

Neste trabalho a técnica de multiportadoras OFDM (Orthogonal Frequency Division Multiplexing), aplicada a sistemas ópticos, é estudada, com foco principal na geração e transmissão dos chamados supercanais ópticos modulados em altíssimas taxas (até Terabits/s). O OFDM prevê um melhor aproveitamento da largura de banda e, quando comparada à técnica FDM (Frequency Division Multiplexing), permite uma redução de aproximadamente 50% do espectro ocupado. Esta economia proporcionada pela técnica torna-a forte candidata para uso em redes ópticas reconfiguráveis, pois provê melhor eficiência espectral aos sinais com reconfiguração de tráfego remoto. Dois cenários serão abordados: o primeiro, em que o sinal com multiportadoras moduladas de forma híbrida (QAM - quadradure amplitude modulation) é gerado no domínio elétrico para, em seguida, modular uma portadora óptica; e o segundo, no qual as multiportadoras são geradas no domínio óptico e, posteriormente, moduladas individualmente também no domínio óptico - e neste caso o formato de modulação pode variar. Para o segundo caso, três técnicas de geração de supercanais serão estudadas e avaliadas a fim de se realizar uma comparação entre elas. Neste trabalho também serão comparadas as técnicas de recepção óptica direta e coerente, aplicadas a sistemas OFDM. Os resultados para o estudo da geração de multiportadoras ópticas, obtidos através de simulações no software Optisystem v. 9.0, são validados por resultados experimentais obtidos no Laboratório de Comunicações Ópticas da Fundação CPqD.
This manuscript presents a study on the multicarrier modulation technique OFDM (Orthogonal frequency division multiplexing) applied to optical systems. The OFDM technique provides a better use of bandwidth and, compared with FDM (Frequency Division Multiplexing), provides a nearly 50% reduction of the occupied bandwidth. This feature makes the OFDM technique an ideal candidate for reconfigurable optical networks because it allows better spectral efficiency to the signals with remote traffic reconfiguration. The study focuses, mainly, on the theoretical investigation of OFDM applied to the transmission of the so-called optical superchannels, modulated at very high bit rates (above Terabits/s). Two scenarios are discussed: in the first, the multicarrier signal, modulated in a hybrid format (QAM - quadrature amplitude modulation), is generated in the electrical domain before modulating the optical carrier, and in the second the multicarrier beam is generated in the optical domain and subsequently each subcarrier is digitally modulated. In this second approach, three superchannel generation techniques are studied and evaluated for being compared. This work will also compare the direct and coherent detection techniques applied to OFDM systems. The results for the optical multicarrier generation study, obtained by numerical simulation (platform Optisystem v. 9.0), are validated by experimental results obtained at the Laboratory of Optical Communication CPqD Foundation.

Le travail de thèse porte sur une étude d'impact de différentes structures SOA sur la transmission optique de signaux OFDM modulés en intensité et reçus en détection directe (IMDD-OOFDM), dans le cadre des réseaux d'accès de nouvelle génération (σGPτσ). Dans la première partie du travail, nous avons d’abord validé expérimentalement la modélisation d’un RSτA sur une large plage d’utilisation. Ce modèle a ensuite été implémenté dans le cadre d'une plate-forme de co-simulation pour les systèmes de transmission IMDD-OOFDM et pour la conversion en longueur d'onde de signaux OOFDM avec une validation expérimentale. Une analyse approfondie des performances de transmission a été ensuite menée en termes de puissance optique et de longueur d’onde injectées, de longueur de fibre, de l’émission spontanée amplifiée (ASE), de la bande passante électrique et des non-linéarités du RSτA. Nous avons notamment montré théoriquement qu’une capacité minimale de transmission de 8,9 Gb/s sur 100 km pouvait être atteinte sur une plage de 100 nm avec le RSOA utilisé et avec l’aide d’une modulation adaptative (AMττFDM). Nous avons également démontré expérimentalement, pour la première fois à notre connaissance, la conversion de longueur d'onde de signaux optiques OOFDM-16QAM sur une plage de 70 nm en utilisant l'effet XGM du RSOA. Dans la seconde partie, nous avons développé la modélisation de plusieurs structures de SOA : un SOA à îlots quantiques (QD SOA), un SOA bi-électrodes et deux SOA cascadés en configuration contra-propagative. Nous avons étudiés leurs performances en transmission à l’aide de la modulation AMττFDM. Nous avons montré que ces structures présentent une capacité de transmission allant jusqu’à 30 Gb/s avec des distances de transmission jusqu'à 60 km. Nous avons montré également que le QD-SOA présente de meilleures performances en termes de capacité de transmission pour des distances allant jusqu'à 140 km en comparaison avec les deux autres configurations
The thesis work deals with study of different SOA structures impact on the transmission of intensity modulation and direct detection OFDM signals in the context of the next generation access networks. In the first part of the work, we have experimentally validated a comprehensive wideband RSOA field model. It was the nused as part of a co-simulation platform for IMDD-OOFDM and OOFDM wavelength conversion transmission systems. Thanks to this co-simulation platform that presents good agreement with the measurement, and our experimental setup, we analyze the transmission performance in terms of optical input power, fiber length, ASEnoise, electrical bandwidth and RSOA nonlinearities. We showed by simulation that an AMOOFDM signal transmission over a 100 nm wavelength range with a minimum transmission capacity of 8.9 Gb/s for fiber lengths up to 100 km can be reached. Finally, we experimentally demonstrated, for the first time to the best of our knowledge, the feasibility of performing wave length conversion over 70 nm of OOFDM-16QAM optical signals using the XGM effect in an RSOA. In the second part of this work we develop a simplified quantum dot –SOA and two electrode SOAintensity modulator models and study their effect on a numerical OFDM IMDD transmission system, we also study a two cascaded SOA in a counter propagating configuration as an intensity modulator. We find that for the three configurations we can achieve a high transmission capacity of around 30 Gb/s for transmission distances up to 60 Km, we also find that the QD-SOA will have the best performance in terms of transmission capacity for distances up to 140 Km in comparison with the two other SOA configurations

L'évolution des Réseaux Locaux Domestiques (RLD) est influencée par l'augmentation irréfrénée du nombre de terminaux connectés dans nos domiciles et par le déploiement de réseaux d'accès optiques haut débit qui délivrent désormais des services dépassant le Gigabit/s. Pour continuer à échanger efficacement les données, les RLD doivent évoluer vers le multi-Gigabit/s, et plus particulièrement la très appréciée connectivité sans fil. Les systèmes radio actuels ont des capacités limitées, néanmoins de nouveaux standards dont le débit excède 7Gbit/s voient le jour. Mais comme ces derniers exploitent la bande millimétrique, entre 57 et 66 GHz, leur couverture radio est limitée à la taille d'une pièce. En effet, à de telles fréquences, les pertes en espace libre sont très élevées et les ondes ne traversent pas les murs. Cette thèse propose de résoudre cette limitation au moyen de solutions Radio sur Fibre (RoF pour Radio over Fiber). Cette technique consiste à capturer les signaux radio émis dans une première pièce, puis à les convertir en signaux optiques pour les transmettre par fibre optique jusqu'à une seconde pièce où ils seront réémis. Plusieurs transducteurs RoF seront donc installés dans le domicile et interconnectés entre eux au moyen d'une infrastructure optique adaptée, créant ainsi des systèmes se comportant à la fois comme répéteurs and comme système de distribution. Pour le marché du RLD, de telles solutions sont compétitives que si elles sont bas coût. Par conséquent, ce travail se focalise sur la modulation directe avec détection directe (IM-DD) en Fréquence Intermédiaire (FI). En d'autres termes, le signal radio à 60GHz est translaté à une plus faible fréquence, autour de 5GHz, pour moduler directement un laser, puis il est restitué à 60GHz après la détection directe. Concernant la fibre optique, la multimode silice (MMF) est privilégiée puisqu'elle permet l'utilisation de composants optoélectroniques bas coût et largement disponible. Cette thèse propose différentes architectures RoF, de la point-à-point reliant deux pièces à la multipoint-à-multipoint agissant comme un bus logique. Après une caractérisation analogique des composants optoélectroniques, du lien RoF et du câble domestique, ces architectures sont construites et caractérisées étape par étape sur la base d'une modulation OFDM conforme aux standards radio 60GHz. Des transmissions temps réel entre terminaux commerciaux sont également réalisées afin de valider ces architectures. Pour finir, des infrastructures RoF avancées sont proposées. Premièrement, les systèmes RoF peuvent être améliorés si l'accès à leur couche optique est contrôlé par la couche MAC radio. Cette approche est donc étudiée, démontrant ainsi sa faisabilité. Deuxièmement, les systèmes optiques, perçus par les utilisateurs comme des produits premium, doivent supporter aussi bien les services de base du RLD que ceux qui vont émerger dans les années à venir. Ainsi, des infrastructures multiservice and multiformat innovantes transportant sur un unique câble optique des données IP, la télévision hertzienne et satellite, les signaux radio 60GHz et d'autres formats spécifiques tels que l'HDMI sont proposées puis testées
The evolution of the Home Area Network (HAN) is lead by the proliferation of connected devices inside the home and the deployment of high broadband access network which now allows the delivery of services that can exceed 1Gbit/s. To ensure efficient in-house exchanges, the HAN has to move rapidly toward multi-Gigabit/s connections, in particular the wireless connectivity generally preferred by the customers. Current wireless systems have limited capacities, but new radio standards delivering data-rates up to 7Gbit/s are emerging. Nevertheless, as they address the unlicensed millimeter-wave band, from 57 to 66 GHz, their radio coverage is limited to a single room. Indeed, at such frequencies, the free-space losses are high and the waves do not cross the walls. This thesis proposes to solve this problem by means of the Radio over Fiber (RoF) technology. This consists in capturing the 60GHz radio signals emitted in one room, converting them into optical signals for transmission through optical fibers, and reemitting them in another room. Thus, several RoF transducers will be installed in the home and interconnected by a suitable optical infrastructure to create systems acting at the same time as repeaters and as distribution systems. From the viewpoint of the HAN market, such systems will be competitive only if they are low cost. As a consequence, this work focuses on direct modulation with direct detection (IM-DD) at Intermediate Frequency (IF). In other words, the 60GHz signal is down-converted at a lower frequency around 5GHz before the laser modulation and up-converted to 60GHz after the photodetection. Concerning the optical fiber, silica multimode fiber (MMF) is privileged as it allows the use of low cost and largely available optoelectronic devices working at 850nm.The thesis proposes different RoF architectures, from point-to-point interconnecting two rooms to multipoint-to-multipoint acting as logical buses. After an analog characterization of the optoelectronic components, the RoF link and the domestic cable, these architectures are designed, built and characterized step by step using OFDM modulation according to existing wireless 60GHz standards. Real-time transmissions between commercial devices have also been performed to validate these architectures. Moreover, advanced RoF infrastructures are proposed. First, the RoF systems can be easily improved if the access to their optical media is managed by the radio MAC layer. This approach is therefore studied showing its feasibility. Secondly, an optical system, seen by users as a premium product, has to support the legacy home services commonly used as well as the new ones that could emerge in the future. Thus, innovative multiservice and multiformat infrastructures conveying on a unique optical cable wired IP data, broadcast terrestrial or satellite television, the 60GHz wireless connectivity, and specific formats as HDMI signals are proposed and tested

Les centres de données deviennent de plus en plus importants, allant de petites fermes de serveurs distribuées à des grandes fermes dédiées à des tâches spécifiques. La diffusion de services "dans le nuage" conduit à une augmentation incessante de la demande de trafic dans les centres de données. Dans cette thèse, nous étudions l'évolution des réseaux dans les centres de données et proposons des solutions à court et à long terme pour leur intra-connexion physique. Aujourd'hui, la croissance de la demande de trafic met en lumière la nécessité urgente d’interfaces à grande vitesse capables de faire face à la bande passante exigeant de nouvelles applications. Ainsi, à court terme, nous proposons de nouveaux transpondeurs optiques à haut débit, mais à faible coût, permettant la transmission de 200 Gb /s utilisant des schémas de modulation en intensité et à détection directe. Plusieurs types de modulations d’impulsions en amplitude avancées sont explorés, tout en augmentant la vitesse à des débits symboles allant jusqu’à 100 GBd. La génération électrique à haute vitesse est réalisé grâce à un nouveau convertisseur analogique-numérique intégré, capable de doubler les vitesses des entrées et de générer des signaux à plusieurs niveaux d’amplitude. Cependant, le trafic continuera sa croissance. Les centres de données actuels reposent sur plusieurs niveaux de commutateurs électroniques pour construire un réseau d'interconnexion capable de supporter une telle grande quantité de trafic. Dans une telle architecture, la croissance du trafic est directement liée à une augmentation du nombre des composants du réseau, y-compris les commutateurs avec plus de ports, les interfaces et les câbles. Le coût et la consommation d'énergie qui peut être attendus à l'avenir est intenable, ce qui appelle à une réévaluation du réseau. Par conséquent, nous présentons ensuite un nouveau concept fondé sur la commutation de "slots" optiques (Burst Optical Slot Switching, i.e. BOSS) dans lequel les serveurs sont connectés via des nœuds BOSS à travers des anneaux de fibres multiplexé en longueur d'onde et en temps, et organisés dans une topologie en tore. Au cours de cette thèse, nous étudions la mise en œuvre des nœuds BOSS; en particulier, la matrice de commutation et les transpondeurs optiques. L'élément principal au sein de la matrice de commutation est le bloqueur de slots, qui est capable d'effacer n’importe quel paquet (slot) sur n’importe quelle longueur d'onde en quelques nanosecondes seulement. D'une part, nous explorons l'utilisation d'amplificateurs optiques à semi-conducteurs comme portes optiques à utiliser dans le bloqueur des slots, et étudier leur cascade. D'autre part, nous développons un bloqueur de slots intégré monolithiquement capable de gérer jusqu'à seize longueurs d'onde avec la diversité de polarisation. Ensuite, nous présentons plusieurs architectures de transpondeur et nous étudions leur performance. La signalisation des transpondeurs doit répondre à deux exigences principales: le fonctionnement en mode paquet et la résistance au filtrage serré. D'abord, nous utilisons des transpondeurs élastiques qui utilisent des modulations Nyquist N-QAM, et qui adaptent le format de modulation en fonction du nombre de nœuds à traverser. Ensuite, nous proposons l'utilisation du multiplexage par répartition orthogonale de la fréquence en cohérence optique (CO-OFDM). Avec une structure de paquet inhérente et leur grande adaptabilité fréquentielle, nous démontrons que les transpondeurs CO-OFDM offrent une capacité plus élevée et une meilleure portée que leurs homologues Nyquist. Finalement, nous comparons notre solution BOSS avec la topologie Clos replié utilisée aujourd'hui. Nous montrons que notre architecture BOSS nécessite 400 fois moins de transpondeurs et de câbles que les réseaux de commutation électronique d'aujourd'hui, ce qui ouvre la voie à des centres de données hautement évolutifs et durables
Data centers are becoming increasingly important and ubiquitous, ranging from large server farms dedicated to various tasks such as data processing, computing, data storage or the combination thereof, to small distributed server farms. The spread of cloud services is driving a relentless increase of traffic demand in datacenters, which is doubling every 12 to 15 months. Along this thesis we study the evolution of data center networks and present short- and long-term solutions for their physical intra-connection. Today, rapidly-growing traffic in data centers spotlights the urgent need for high-speed low-cost interfaces capable to cope with hungry-bandwidth demanding new applications. Thereby, in the short-term we propose novel high-datarate low-cost optical transceivers enabling up to 200 Gb/s transmission using intensity-modulation and direct-detection schemes. Several advanced pulse amplitude modulation schemes are explored while increasing speeds towards record symbol-rates, as high as 100 GBd. High-speed electrical signaling is enabled by an integrated selector-power digital-to- analog converter, capable of doubling input baud-rates while outputting advance multi-level pulse amplitude modulations. Notwithstanding, data centers’ global traffic will continue increasing incessantly. Current datacenters rely on high-radix all-electronic Ethernet switches to build an interconnecting network capable to pave with such vast amount of traffic. In such architecture, traffic growth directly relates to an increase of networking components, including switches with higher port-count, interfaces and cables. Unsustainable cost and energy consumption that can be expected in the future calls for a network reassessment. Therefore, we subsequently present a novel concept for intra-datacenter networks called burst optical slot switching (BOSS); in which servers are connected via BOSS nodes through wavelength- and time-division multiplexed fiber rings organized in a Torus topology. Along this thesis we investigate on the implementation of BOSS nodes; in particular, the switching fabric and the optical transceivers. The main element within the switching fabric is the slot blocker, which is capable of erasing any packet of any wavelength in a nanosecond time-scale. On the one hand, we explore the use of semiconductor optical amplifiers as means of gating element to be used within the slot blocker and study their cascadability. On the other hand we develop a monolithically integrated slot blocker capable of handling up to sixteen wavelength channels with dual-polarization diversity. Then we present several transceiver architectures and study their performances. Transceivers’ signaling needs to fulfill two main requirements: packet-mode operation, i.e. being capable of recovering few microsecond –long bursts; and resiliency to tight filtering, which occurs when cascading many nodes (e.g. up to 100). First we build packet-mode Nyquist-pulse-shaped N-QAM transceivers, which adapt the modulation format as a function of the number of nodes to traverse. Later we propose the use of coherent-optical orthogonal frequency division multiplexing (CO-OFDM). With inherent packet structure and high spectral tailoring capabilities, we demonstrate that CO-OFDM-based transceivers offer higher capacity and enhanced reach than its Nyquist counterpart. Finally, we compare our BOSS solution to today’s Folded Clos topology, and show that our BOSS architecture requires x400 fewer transponders and cables than today’s electronic switching networks, which paves the way to highly scalable and sustainable datacenters

碩士
國立臺灣大學
電信工程學研究所
94
In this thesis, we examine single carrier modulation with frequency domain equalization (SC-FDE) for optical communication systems using intensity modulation with direct detection (IM/DD) in the presence of additive white Gaussian noise. SC-FDE is a technique whose processing is quite similar to that of OFDM. Unlike OFDM, however, SC-FDE is compatible with IM/DD channels because it does not require the transmission of a strong dc. For an IM/DD channel, at high data rate regime, the effect of intersymbol interference (ISI) starts to dominate system performance. Inthis paper, we examine the use of SC-FDE and pulse position modulation (PPM) to combat ISI for IM/DD channels. Such a system enjoys the average power efficiency of PPM and the low complexity equalization of SC-FDE. We analyze the bit error performance of SC-FDE and compare it with a few known techniques.

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Simple two channel receivers for 32-PSK and 64-PSK modulated signals have been proposed which allow digital data (namely bits), to be recovered directly instead of the traditional approach of symbol detection followed by symbol to bit mappings. This allows for binary rather than M-ary receiver decisions, reduces the amount of signal processing operations and permits parallel recovery of the bits. The noise performance of these receivers quantified by the Bit Error Rate (BER) assuming an Additive White Gaussion Noise interference model is evaluated as a function of E^/N^, the signal to noise ratio, and transmitted phase angles of the signals. The performance results of the direct bit detection receivers (DBDR) when compared to that of conventional phase measurement receivers demonstrate that DBDR's are optimum in BER sense. The simplicity of the receiver implementations and the BER of the delivered data make DBDR's attractive for high speed, spectrally efficient digital communication systems.

碩士
國立清華大學
通訊工程研究所
104
Orthogonal frequency division multiplexing (OFDM) passive optical network (PONs) implementing with double-side band intensity modulation and direct detection (IMDD) is considered as a cost-effective design. However, radio frequency (RF) power fading induced by chromatic dispersion causes non-uniform receiving performance among users. Generally speaking, user who suffered from the most serious fading cannot reach the specific forward error correction (FEC) threshold. To solve above dilemma, most of researchers adaptively design signal level in optical line terminal (OLT) depending on different transmission distance. However, such adaptive approach hugely enhances the system complexity and hardware costs. Therefore, we employ multicarrier code division multiple access (MC-CDMA) technique to equalize users’ received performance via spreading subcarriers’ data with orthogonal code. After frequency spreading, all users would suffer from the same RF power fading response and thus have the same performance. In this thesis, we simulatively and experimentally proof that the proposed MC-CDMA PON could achieve a universal transmitter design for users ranging from back-to-back to 100 km. Meanwhile, we apply minimum mean square error (MMSE) equalizer, combining with multi-code interference (MCI) cancellation digital signal process (DSP) to further enhanced system performance in a long reach PON. Our experimental results reveal that even under about 20 dB RF power fading, the proposed scheme can still provide 21.7 dB power budget and only about 2 dB sensitivity deviation is observed.

The atmospheric lightwave propagation is considerably influenced by the random variations in the refractive index of air pockets due to turbulence. This undesired effect significantly degrades the performance of free-space optical (FSO) communication systems. Interestingly, the severity of such random degradations is highly related to the range of atmospheric propagation. In this thesis, we introduce relay-assisted FSO communications as a very promising technique to combat the degradation effects of atmospheric turbulence. Considering different configurations of the relays, we quantify the outage behavior of the relay-assisted system and identify the optimum relaying scheme. We further optimize the performance of the relay-assisted FSO system subject to some power constraints and provide optimal power control strategies for different scenarios under consideration. Moreover, an application of FSO relaying technique in quantum communications is investigated. The results demonstrate impressive performance improvements for the proposed relay-assisted FSO systems with respect to the conventional direct transmission whether applied in a classical or a quantum communication channel.