49 research outputs found

    Architectures and protocols for sub-wavelength optical networks: contributions to connectionless and connection-oriented data transport

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    La r脿pida evoluci贸 d鈥橧nternet i l鈥櫭爉plia gamma de noves aplicacions (per exemple, multim猫dia, videoconfer猫ncia, jocs en l铆nia, etc.) ha fomentat canvis revolucionaris en la manera com ens comuniquem. A m茅s, algunes d鈥檃questes aplicacions demanden grans quantitats de recursos d鈥檃mple de banda amb diversos requeriments de qualitat de servei (QoS). El desenvolupament de la multiplexaci贸 per divisi贸 de longitud d鈥檕na (WDM) en els anys noranta va fer molt rendible la disponibilitat d鈥檃mple de banda. Avui dia, les tecnologies de commutaci贸 貌ptica de circuits s贸n predominants en el nucli de la xarxa, les quals permeten la configuraci贸 de canals (lightpaths) a trav茅s de la xarxa. No obstant aix貌, la granularitat d鈥檃quests canals ocupa tota la longitud d鈥檕na, el que fa que siguin ineficients per a proveir canals de menor ample de banda (sub-longitud d鈥檕na). Segons la comunitat cient铆fica, 茅s necessari augmentar la transpar猫ncia dels protocols, aix铆 com millorar l鈥檃provisionament d鈥檃mple de banda de forma din脿mica. Per tal de fer aix貌 realitat, 茅s necessari desenvolupar noves arquitectures. La commutaci贸 貌ptica de r脿fegues i de paquets (OBS/OPS), s贸n dues de les tecnologies proposades. Aquesta tesi contribueix amb tres arquitectures de xarxa destinades a millorar el transport de dades sub-longitud d鈥檕na. En primer lloc, aprofundim en la naturalesa sense connexi贸 en OBS. En aquest cas, la xarxa incrementa el seu dinamisme a causa de les transmissions a r脿fega. A m茅s, les col路lisions entre r脿fegues degraden el rendiment de la xarxa fins i tot a c脿rregues molt baixes. Per fer front a aquestes col路lisions, es proposa un esquema de resoluci贸 de col路lisions pro actiu basat en un algorisme d鈥檈ncaminament i assignaci贸 de longitud d鈥檕na (RWA) que balanceja de forma autom脿tica i distribu茂da la c脿rrega en la xarxa. En aquest protocol, el RWA i la transmissi贸 de r脿fegues es basen en l鈥檈xplotaci贸 i exploraci贸 de regles de commutaci贸 que incorporen informaci贸 sobre contencions i encaminament. Per donar suport a aquesta arquitectura, s鈥檜tilitzen dos tipus de paquets de control per a l鈥檈ncaminament de les r脿fegues i l鈥檃ctualitzaci贸 de les regles de commutaci贸, respectivament. Per analitzar els beneficis del nou algorisme, s鈥檜tilitzen quatre topologies de xarxa diferents. Els resultats indiquen que el m猫tode proposat millora en diferents marges la resta d鈥檃lgorismes RWA en funci贸 de la topologia i sense penalitzar altres par脿metres com el retard extrem a extrem. La segona contribuci贸 proposa una arquitectura h铆brida sense i orientada a connexi贸 sobre la base d鈥檜n protocol de control d鈥檃cc茅s al medi (MAC) per a xarxes OBS (DAOBS). El MAC ofereix dos m猫todes d鈥檃cc茅s: arbitratge de cua (QA) per a la transmissi贸 de r脿fegues sense connexi贸, i pre-arbitratge (PA) per serveis TDM orientats a connexi贸. Aquesta arquitectura permet una 脿mplia gamma d鈥檃plicacions sensibles al retard i al bloqueig. Els resultats avaluats a trav茅s de simulacions mostren que en l鈥檃cc茅s QA, les r脿fegues de m茅s alta prioritat tenen garantides zero p猫rdues i lat猫ncies d鈥檃cc茅s molt baixes. Pel que fa a l鈥檃cc茅s PA, es reporta que la duplicaci贸 de la c脿rrega TDM augmenta en m茅s d鈥檜n ordre la probabilitat de bloqueig, per貌 sense afectar en la mateixa mesura les r脿fegues sense connexi贸. En aquest cap铆tol tamb茅 es tracten dos dels problemes relacionats amb l鈥檃rquitectura DAOBS i el seu funcionament. En primer lloc, es proposa un model matem脿tic per aproximar el retard d鈥檃cc茅s inferior i superior com a conseq眉猫ncia de l鈥檃cc茅s QA. En segon lloc, es formula matem脿ticament la generaci贸 i optimitzaci贸 de les topologies virtuals que suporten el protocol per a l鈥檈scenari amb tr脿fic est脿tic. Finalment, l鈥櫭簂tima contribuci贸 explora els beneficis d鈥檜na arquitectura de xarxa 貌ptica per temps compartit (TSON) basada en elements de c脿lcul de camins (PCE) centralitzats per tal d鈥檈vitar col路lisions en la xarxa. Aquesta arquitectura permet garantir l鈥檃provisionament orientat a connexi贸 de canals sub-longitud d鈥檕na. En aquest cap铆tol proposem i simulem tres arquitectures GMPLS/PCE/TSON. A causa del enfocament centralitzat, el rendiment de la xarxa dep猫n en gran mesura de l鈥檃ssignaci贸 i aprovisionament de les connexions. Amb aquesta finalitat, es proposen diferents algorismes d鈥檃ssignaci贸 de ranures temporals i es comparen amb les corresponents formulacions de programaci贸 lineal (ILP) per al cas est脿tic. Per al cas de tr脿fic din脿mic, proposem i avaluem mitjan莽ant simulaci贸 diferents heur铆stiques. Els resultats mostren els beneficis de proporcionar flexibilitat en els dominis temporal i freq眉encial a l鈥檋ora d鈥檃ssignar les ranures temporals.The rapid evolving Internet and the broad range of new data applications (e.g., multimedia, video-conference, online gaming, etc.) is fostering revolutionary changes in the way we communicate. In addition, some of these applications demand for unprecedented amounts of bandwidth resources with diverse quality of service (QoS). The development of wavelength division multiplexing (WDM) in the 90's made very cost-effective the availability of bandwidth. Nowadays, optical circuit switching technologies are predominant in the core enabling the set up of lightpaths across the network. However, full-wavelength lightpath granularity is too coarse, which results to be inefficient for provisioning sub-wavelength channels. As remarked by the research community, an open issue in optical networking is increasing the protocol transparency as well as provisioning true dynamic bandwidth allocation at the network level. To this end, new architectures are required. Optical burst/packet switching (OBS/OPS) are two such proposed technologies under investigation. This thesis contributes with three network architectures which aim at improving the sub-wavelength data transport from different perspectives. First, we gain insight into the connectionless nature of OBS. Here, the network dynamics are increased due to the short-lived burst transmissions. Moreover, burst contentions degrade the performance even at very low loads. To cope with them, we propose a proactive resolution scheme by means of a distributed auto load-balancing routing and wavelength assignment (RWA) algorithm for wavelength-continuity constraint networks. In this protocol, the RWA and burst forwarding is based on the exploitation and exploration of switching rule concentration values that incorporate contention and forwarding desirability information. To support such architecture, forward and backward control packets are used in the burst forwarding and updating rules, respectively. In order to analyze the benefits of the new algorithm, four different network topologies are used. Results indicate that the proposed method outperforms the rest of tested RWA algorithms at various margins depending on the topology without penalizing other parameters such as end-to-end delay. The second contribution proposes a hybrid connectionless and connection-oriented architecture based on a medium access control (MAC) protocol for OBS networks (DAOBS). The MAC provides two main access mechanisms: queue arbitrated (QA) for connectionless bursts and pre-arbitrated (PA) for TDM connection-oriented services. Such an architecture allows for a broad range of delay-sensitive applications or guaranteed services. Results evaluated through simulations show that in the QA access mode highest priority bursts are guaranteed zero losses and very low access latencies. Regarding the PA mode, we report that doubling the offered TDM traffic load increases in more than one order their connection blocking, slightly affecting the blocking of other connectionless bursts. In this chapter, we also tackle two of the issues related with the DAOBS architecture and its operation. Firstly, we model mathematically the lower and upper approximations of the access delay as a consequence of the connectionless queue arbitrated access. Secondly, we formulate the generation of the virtual light-tree overlay topology for the static traffic case.Postprint (published version

    Remote Sensing Data Compression

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    A huge amount of data is acquired nowadays by different remote sensing systems installed on satellites, aircrafts, and UAV. The acquired data then have to be transferred to image processing centres, stored and/or delivered to customers. In restricted scenarios, data compression is strongly desired or necessary. A wide diversity of coding methods can be used, depending on the requirements and their priority. In addition, the types and properties of images differ a lot, thus, practical implementation aspects have to be taken into account. The Special Issue paper collection taken as basis of this book touches on all of the aforementioned items to some degree, giving the reader an opportunity to learn about recent developments and research directions in the field of image compression. In particular, lossless and near-lossless compression of multi- and hyperspectral images still remains current, since such images constitute data arrays that are of extremely large size with rich information that can be retrieved from them for various applications. Another important aspect is the impact of lossless compression on image classification and segmentation, where a reasonable compromise between the characteristics of compression and the final tasks of data processing has to be achieved. The problems of data transition from UAV-based acquisition platforms, as well as the use of FPGA and neural networks, have become very important. Finally, attempts to apply compressive sensing approaches in remote sensing image processing with positive outcomes are observed. We hope that readers will find our book useful and interestin

    Mapping and Monitoring Forest Cover

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    This book is a compilation of six papers that provide some valuable information about mapping and monitoring forest cover using remotely sensed imagery. Examples include mapping large areas of forest, evaluating forest change over time, combining remotely sensed imagery with ground inventory information, and mapping forest characteristics from very high spatial resolution data. Together, these results demonstrate effective techniques for effectively learning more about our very important forest resources

    Quality of service in optical burst switching networks

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    Tese dout., Engenharia Electr贸nica e Computa莽茫o, Universidade do Algarve, 2009Funda莽茫o para e Ci锚ncia e a Tecnologi

    Offset time-emulated architecture for optical burst switching-modelling and performance evaluation

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    L'evoluci贸 de les xarxes publiques de transport de dades destaca per el continu augment de la demanda de tr脿fic a la que estan sotmeses. La causa 茅s la imparable popularitzaci贸 d'Internet i del seu 煤s per a tot tipus d'aplicacions. Les xarxes de commutaci贸 de r脿fegues 貌ptiques (OBS: Optical Bursts Switching) s贸n una soluci贸 extraordin脿riament prometedora per la pr貌xima generaci贸 de xarxes, tant per la flexibilitat que ofereixen com per el seu alt rendiment fruit de l'explotaci贸 de la multiplexaci贸 estad铆stica en el domini 貌ptic.Aquesta tesi presenta l'an脿lisi, modelitzaci贸 i avaluaci贸 de les xarxes de commutaci贸 de r脿fegues 貌ptiques basades en l'emulaci贸 del temps de compensaci贸 (emulated offset time: E-OBS). El concepte d'E-OBS defineix una arquitectura de xarxa OBS per al transportar i commutar r脿fegues 貌ptiques en una xarxa troncal en la que, al contrari de l'arquitectura convencional (C-OBS) en la que el temps de compensaci贸 s'introdueix des dels nodes d'acc茅s, el temps de compensaci贸 s'introdueix en cadascun dels nodes de la xarxa per mitj脿 d'un retardador de fibra addicional. L'arquitectura E-OBS permet superar algunes de les desavantatges inherents a arquitectures C-OBS, per貌 la seva gran virtut 茅s la compatibilitat amb les xarxes de commutaci贸 de circuits 貌ptics (OCS: Optical Circuit Switching) actuals i les futures xarxes de commutaci贸 de paquets 貌ptics (OPS: Optical Packet Switching), de manera que les xarxes OBS basades en una arquitectura E-OBS) poden facilitat enormement la transici贸 de unes a les altres.A ala vista dels principals requeriments de disseny de les xarxes OBS, que s贸n la resoluci贸 de contencions en el domini 貌ptic, la provisi贸 de qualitat de servei (QoS) i l'貌ptim encaminament de les r脿fegues per tal de minimitzar la congesti贸 de la xarxa, . en aquesta tesi es proposa un disseny de l'arquitectura E-OBS basada en (i) un m猫tode viable per a la provisi贸 del temps de compensaci贸, (ii) una qualitat alta global de servei, i (iii) un mecanisme d'encaminament que minimitzi congesti贸 de xarxa.- La primera part d'aquesta tesi proporciona la informaci贸 documental necess脿ria per al disseny d'E-OBS.- La segona part se centra en l'estudi de la funcionalitat i viabilitat de l'arquitectura E-OBS. S'introdueixen els principis d'operaci贸 d'E-OBS i s'identifiquen els principals esculls que presenten les arquitectures C-OBS i que deixen de ser-ho en una arquitectura E-OBS. Alguns d'aquests esculls s贸n la dificultat d'utilitzar un algorisme d'encaminament amb rutes alternatives, la complexitat dels algoritmes de reserva de recursos i la seva falta d'equitat, la complexitat en la provisi贸 de la QoS, etc. En aquesta segona part es constata que l'arquitectura E-OBS redueix la complexitat dels de reserva de recursos i es verifica la viabilitat d'operaci贸 i de funcionament de la provisi贸 del tremps de compensaci贸 en aquesta arquitectura a partir de figures de comportament obtingudes amb retardadors de fibra comercialment disponibles.- La tercera part encara el problema de la provisi贸 de la QoS. Primer s'hi revisen els conceptes b脿sics de QoS aix铆 com els mecanismes de tractament de la QoS per a xarxes OBS fent-ne una comparaci贸 qualitativa i de rendiment de tots ells. Com a resultat s'obt茅 que el mecanisme que presenta un millor comportament 茅s el d'avortament de la transmissi贸 de les r脿fegues de m茅s baixa prioritat quan aquestes col路lisionen amb una de prioritat m茅s alta (es l'anomenat Burst Preemption mechanism), el qual en alguns casos presenta un problema de senyalitzaci贸 innecess脿ria. Aquesta tercera part es conclou amb la proposta d'un mecanisme de finestra a afegir al esquema de Burst Preemption que nom茅s funciona sobre una arquitectura E-OBS i que soluciona aquest problema.- En la quarta part s'afronta el problema de l'encaminament en xarxes OBS. S'estudia el comportament dels algoritmes d'encaminament adaptatius, els a茂llats amb rutes alternatives i els multicam铆 distribu茂ts, sobre xarxes E-OBS. A la vista dels resultats no massa satisfactoris que s'obtenen, es planteja una soluci贸 alternativa que es basa en model d'optimitzaci贸 no lineal. Es formulen i resolen dos models d'optimitzaci贸 per als algoritmes encaminament de font multicam铆 que redueixen notablement la congesti贸 en les xarxes OBS.Finalment, aquesta tesi conclou que l'arquitectura E-OBS 茅s factible, que 茅s m茅s eficient que la C-OBS, que proveeix efica莽ment QoS, i que 茅s capa莽 d'operar amb diverses estrat猫gies d'encaminament i de reduir efica莽ment la congesti贸 de xarxa.The fact that the Internet is a packet-based connection-less network is the main driver to develop a data-centric transport network. In this context, the optical burst switching (OBS) technology is considered as a promising solution for reducing the gap between transmission and switching speeds in future networks.This thesis presents the analysis, modelling, and evaluation of the OBS network with Emulated offset-time provisioning (E-OBS). E-OBS defines an OBS network architecture to transport and switch optical data bursts in a core network. On the contrary to a conventional offset-time provisioning OBS (C-OBS) architecture, where a transmission offset time is introduced in the edge node, in an E-OBS network the offset time is provided in the core node by means of an additional fibre delay element. The architecture is motivated by several drawbacks inherent to C-OBS architectures. It should be pointed out that the E-OBS has not been studied intensively in the literature and this concept has been considered rather occasionally.Due to the limitations in optical processing and queuing, OBS networks need a special treatment so that they could solve problems typical of data-centric networks. Contention resolution in optical domain together with quality of service (QoS) provisioning for quality demanding services are, among other things, the main designing issues when developing OBS networks. Another important aspect is routing problem, which concerns effective balancing of traffic load so that to reduce burst congestion at overloaded links. Accounting for these requirements, the design objectives for the E-OBS architecture are (i) feasibility of offset-time provisioning, (ii) an overall high quality of service, and (iii) reduction of network congestion. These objectives are achieved by combining selected concepts and strategies, together with appropriate system design as well as network traffic engineering.The contributions in this thesis can be summarized as follows.- At the beginning, we introduce the principles of E-OBS operation and we demonstrate that C-OBS possesses many drawbacks that can be easily avoided in E-OBS. Some of the discussed issues are the problem of unfairness in resources reservation, difficulty with alternative routing, complexity of resources reservation algorithms, efficiency of burst scheduling, and complexity in QoS provisioning. The feasibility of E-OBS operation is investigated as well; in this context, the impact of congestion in control plane on OBS operation is studied. As a result, we confirm the feasibility of E-OBS operation with commercially available fibre delay elements.- Then, we provide both qualitative and quantitative comparison of the selected, most addressed in the literature, QoS mechanisms. As an outcome a burst preemption mechanism, which is characterized by the highest overall performance, is qualified for operating in E-OBS. Since the preemptive mechanism may produce the overbooking of resources in an OBS network we address this issue as well. We propose the preemption window mechanism to solve the problem. An analytical model of the mechanism legitimates correctness of our solution.- Finally, we concern with a routing problem - our routing objective is to help the contention resolution algorithms in the reduction of burst losses. We propose and evaluate two isolated alternative routing algorithms designed for labelled E-OBS networks. Then we study multi-path source routing and we use network optimization theory to improve it. The presented formulae for partial derivatives, to be used in a non-linear optimization problem, are straightforward and very fast to compute. It makes the proposed non-linear optimization method a viable alternative for linear programming formulations based on piecewise linear approximations.Concluding, E-OBS is shown to be a feasible OBS network architecture of profitable functionality, to support efficiently the QoS provisioning, and to be able to operate with different routing strategies and effectively reduce the network congestion

    Modeling And Control For Robotic Assistants: Single And Multi-Robot Manipulation

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    As advances are made in robotic hardware, the complexity of tasks they are capable of performing also increases. One goal of modern robotics is to introduce robotic platforms that require very little augmentation of their environments to be effective and robust. Therefore the challenge for a roboticist is to develop algorithms and control strategies that leverage knowledge of the task while retaining the ability to be adaptive, adjusting to perturbations in the environment and task assumptions. This work considers approaches to these challenges in the context of a wet-lab robotic assistant. The tasks considered are cooperative transport with limited communication between team members, and robot-assisted rapid experiment preparation requiring pouring reagents from open containers useful for research and development scientists. For cooperative transport, robots must be able to plan collision-free trajectories and agree on a final destination to minimize internal forces on the carried load. Robot teammates are considered, where robots must reach consensus to minimize internal forces. The case of a human leader, and robot follower is then considered, where robots must use non-verbal information to estimate the human leader\u27s intended pose for the carried load. For experiment preparation, the robot must pour precisely from open containers with known fluid in a single attempt. Two scenarios examined are when the geometries of the pouring and receiving containers and behaviors are known, and when the pourer must be approximated. An analytical solution is presented for a given geometry in the first instance. In the second instance, a combination of online system identification and leveraging of model priors is used to achieve the precision-pour in a single attempt with considerations for long-term robot deployment. The main contributions of this work are considerations and implementations for making robots capable of performing complex tasks with an emphasis on combining model-based and data-driven approaches for best performance

    Enabling Technologies for Cognitive Optical Networks

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    Estimation of field-scale soil moisture content and its uncertainties using Sentinel-1 satellite imagery

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    Flight Mechanics/Estimation Theory Symposium, 1994

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    This conference publication includes 41 papers and abstracts presented at the Flight Mechanics/Estimation Theory Symposium on May 17-19, 1994. Sponsored by the Flight Dynamics Division of Goddard Space Flight Center, this symposium featured technical papers on a wide range of issues related to orbit-attitude prediction, determination and control; attitude sensor calibration; attitude determination error analysis; attitude dynamics; and orbit decay and maneuver strategy. Government, industry, and the academic community participated in the preparation and presentation of these papers

    Journal of Telecommunications and Information Technology, 2009, nr 1

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