• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 82
  • 61
  • 18
  • 8
  • 5
  • 4
  • 3
  • 2
  • Tagged with
  • 198
  • 198
  • 88
  • 51
  • 48
  • 43
  • 42
  • 37
  • 35
  • 32
  • 32
  • 29
  • 24
  • 22
  • 22
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

High resolution optical coherent-channel analyzer using balanced-coherent detection and temperature-tuned DFB laser as local oscillator

Isaac, Rejoy 17 May 2011 (has links)
The rapid increase in demand for bandwidth in optical networks over the last two decades has led to the development of wavelength division multiplexing where multiple channels are transmitted simultaneously at different wavelengths over a single optical-fiber to maximize the usage of the bandwidth available in fiber. Increasing demand for bandwidth has led to narrower channel spacing and the use of advanced modulation schemes that are more spectrally efficient than traditional on-off keying techniques [1]. Nonlinearities and dispersion effects in fiber accumulate over a long distance and can adversely affect the quality of a channel. Hence the ability to measure detailed features of the optical spectrum is crucial to study the performance of a communication link. A conventional optical spectrum analyzer (OSA) based on a diffraction grating has a wide wavelength or frequency scanning range, but suffers from poor frequency resolution. The narrowest resolution bandwidth reported for a grating based OSA is - 0.06nm or 7.5GHz at 1550nm [1]. Various spectral features of interest, such as the transmission spectrum of a laser and modulation spectrum of a channel require sub-picometer resolution, which cannot be achieved by conventional methods using a diffraction grating. High resolution spectrum analyzers (HRSAs) have been built based on heterodyne detection where a portion of the optical spectrum is converted to radio-frequency (RF) with DC corresponding to the local-oscillator (LO) central frequency [3-6]. This is a common technique used in RF-spectrum analyzers. The resolution bandwidth is determined by the electrical bandwidth of the optical receiver. The lowest resolution bandwidth reported is of the order of tens of MHz [6]. Widespread implementation of these instruments however, has been limited owing to their cost and size, one of the major factors being the external cavity (ECT) lasers used as the local-oscillator source in such instruments. We have built a coherent-channel analyzer (CCA) based on balanced coherent detection using a commercial distributed-feedback (DFB) laser as the LO. The use of a DFB laser for the CCA has the potential of reducing the cost of the instrument by at least one-tenth of the price of an HRSA. In this thesis we describe the working of the CCA. We provide an end-to-end system model, analyze the resolution and sensitivity performance of the system, and demonstrate a frequency resolution of 100MHz over the DFB tuning range of 200GHz with a sensitivity of -95dBm. The CCA provides a practical, cost and size effective alternative to the HRSA at the cost of tunability. / Graduate
2

Algorithms and Protocols for Constrained Path Selection and Fault Monitoring in Packet Networks

Ahuja, Satyajeet Singh January 2008 (has links)
Efficient resource utilization and fast failure recovery are essential design goals of next-generation backbone networks. The need for efficient resource utilization has motivated the development of various protocols and techniques that offer data services over legacy backbone networks such as Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH). Enabling improved utilization with enhanced network reliability requires various network optimizations, both at the protocol and system levels. In this dissertation, we present a set of network optimization techniques that improve the performance of an end-user connected to classical packet networks such as Internet. First, we introduce an efficient path selection algorithm that enables seamless bandwidth upgrade for an existing Ethernet connection over SONET/SDH backbone using virtual concatenation technique. We also provide a heterogenous concatenation technique that improves the bandwidth utilization and that is easy to maintain. Second, we present a novel failure localization technique, that can detect single-link or simultaneous multiple-link failures. This technique is based on constructing a set of monitoring paths and cycles from one or more monitoring locations in the network. Third, we present an efficient routing and wavelength assignment scheme for backbone networks with stale network-state information. Finally, we present an e±cient server placement scheme for supporting multiple-description-coding (MDC) based media streaming over content delivery networks. We show that by using MDC-encoded media, intelligent server placement, and efficient path selection, the performance of an end-user can be greatly improved.
3

Coarse WDM wavelength-routed passive optical networks

Shachaf, Y. January 2008 (has links)
The emergence of new bandwidth-intensive applications articulated by distance learning, online gaming, Web 2.0 and movie delivery by means of high-definition video, has ultimately justified the necessity of upgrading the access network infrastructure to provide fat-bandwidth pipelines at subscriber close proximity. Passive optical networks (PONs) are an emerging technology to deliver these services. This thesis presents innovative work performed towards the application of coarse wavelength division multiplexing (CWDM) to route communications to and from reflective optical network units (ONUs) incorporated in time and wavelength division multiplexed PONs. The concept of coarse and dense WDM grid integration and its adaptation in access networks to map, for the first time, selective closely-spaced wavelengths into coarse passband windows of Gaussian and flat-top arrayed waveguide gratings (AWGs), exhibiting coarse-fine grooming, is initially developed. This is followed by the identification of a new network architecture combining multiple PONs, using a coarse AWG to form a next-generation access network. A significant feature of this approach allows for time division multiplexing (TDM) and WDM PON technologies to be integrated through the 7 nm coarse passband windows of a single AWG, providing for interoperability and high scalability. The network performance through simulation, in the presence of polarisation-dependent wavelength shift and associated polarisation-dependent loss, shows the capability of a single optical line terminal (OLT) to access various physical PONs in 25 km proximity with multiple wavelengths through a single AWG router. This approach enables centralised bandwidth allocation and a smooth migration path between time-shared and densely-penetrated access networks. Furthermore, to demonstrate full-duplex operation, allowing for increased bandwidth utilisation of the reflective access network architecture, full-duplex functionality is achieved by using polarisation division multiplexing. This is implemented in the OLT by assigning each ONU downstream data and continues waves on orthogonal states of polarisation. Hence, by assuming the use of symmetrical broadband services, the novel multi-PON access network verifies its potential to double the bandwidth utilisation for each subscriber, allowing for increased bidirectional network throughput. In addition, an experimental test-bed is performed which demonstrates the core operation of the network being, by means of a readily-available 2.7 nm-wide AWG router. Hence, the practical feasibility of the new access network concept is demonstrated.
4

Design and dimensioning of multi-wavelength transport networks

Wuttisittikulkij, Lunchakorn January 1998 (has links)
No description available.
5

A Game Theoretical Approach to Constrained OSNR Optimization Problems in Optical Networks

Pan, Yan 17 July 2009 (has links)
Optical signal-to-noise ratio (OSNR) is considered as the dominant performance parameter at the physical layer in optical networks. This thesis is interested in control and optimization of channel OSNR by using optimization and game-theoretic approaches, incorporating two physical constraints: the link capacity constraint and the channel OSNR target. To start, we study OSNR optimization problems with link capacity constraints in single point-to-point fiber links via two approaches. We first present a framework of a Nash game between channels towards optimizing individual channel OSNR. The link capacity constraint is imposed as a penalty term to each cost function. The selfish behavior in a Nash game degrades the system performance and leads to the inefficiency of Nash equilibria. From the system point of view, we formulate a system optimization problem with the objectives of achieving an OSNR target for each channel while satisfying the link capacity constraint. As an alternative to study the efficiency of Nash equilibria, we use the system framework to investigate the effects of parameters in cost functions in the game-theoretic framework. Then extensions to multi-link and mesh topologies are carried out. We propose a partition approach by using the flexibility of channel power adjustment at optical switches. The multi-link structure is partitioned into stages with each stage being a single sink. By fully using the flexibility, a more natural partition approach is applied to mesh topologies where each stage is a single link. The closed loop in mesh topologies can be unfolded by selecting a starting link. Thus instead of maximization of channel OSNR from end to end, we consider minimization of channel OSNR degradation between stages. We formulate a partitioned Nash game which is composed of ladder-nested stage Nash games. Distributed algorithms towards the computation of a Nash equilibrium solution are developed for all different game frameworks. Simulations and experimental implementations provide results to validate the applicability of theoretical results.
6

A Game Theoretical Approach to Constrained OSNR Optimization Problems in Optical Networks

Pan, Yan 17 July 2009 (has links)
Optical signal-to-noise ratio (OSNR) is considered as the dominant performance parameter at the physical layer in optical networks. This thesis is interested in control and optimization of channel OSNR by using optimization and game-theoretic approaches, incorporating two physical constraints: the link capacity constraint and the channel OSNR target. To start, we study OSNR optimization problems with link capacity constraints in single point-to-point fiber links via two approaches. We first present a framework of a Nash game between channels towards optimizing individual channel OSNR. The link capacity constraint is imposed as a penalty term to each cost function. The selfish behavior in a Nash game degrades the system performance and leads to the inefficiency of Nash equilibria. From the system point of view, we formulate a system optimization problem with the objectives of achieving an OSNR target for each channel while satisfying the link capacity constraint. As an alternative to study the efficiency of Nash equilibria, we use the system framework to investigate the effects of parameters in cost functions in the game-theoretic framework. Then extensions to multi-link and mesh topologies are carried out. We propose a partition approach by using the flexibility of channel power adjustment at optical switches. The multi-link structure is partitioned into stages with each stage being a single sink. By fully using the flexibility, a more natural partition approach is applied to mesh topologies where each stage is a single link. The closed loop in mesh topologies can be unfolded by selecting a starting link. Thus instead of maximization of channel OSNR from end to end, we consider minimization of channel OSNR degradation between stages. We formulate a partitioned Nash game which is composed of ladder-nested stage Nash games. Distributed algorithms towards the computation of a Nash equilibrium solution are developed for all different game frameworks. Simulations and experimental implementations provide results to validate the applicability of theoretical results.
7

Proposta, simulação e testes de arquitetura para redes ópticas passivas GPON e XG-PON / Proposal, simulation and tests of architecture for passive optical networks GPON and XG-PON

Cardoso, Rodrigo Alves, 1986- 06 September 2015 (has links)
Orientador: Edson Moschim / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-27T23:28:40Z (GMT). No. of bitstreams: 1 Cardoso_RodrigoAlves_M.pdf: 10022519 bytes, checksum: 6cc7c615004e4ecdf7f5acc095cd2d2f (MD5) Previous issue date: 2015 / Resumo: O objetivo deste trabalho foi propor uma arquitetura de rede óptica passiva (PON) capaz de suportar um sistema GPON e permitir a evolução para redes PON de nova geração, ou XG-PON, de maneira que ambas as tecnologias possam coexistir na mesma infraestrutura de rede óptica. Na arquitetura foram considerados um mecanismo de proteção parcial e equipamentos que possibilitam sua efetiva construção. Foi apresentado um modelo matemático que permitiu a validação da arquitetura em função do cálculo do power budget de acordo com as premissas estabelecidas pelas normas das tecnologias PON. Um modelo de cálculo de disponibilidade de redes com proteção parcial foi apresentado. De posse destes modelos foram obtidos resultados do alcance máximo da rede, número máximo de clientes suportados, as classes requeridas de equipamentos GPON e XG-PON e a relação entre o comprimento do enlace protegido e a disponibilidade, sendo obtido um alcance máximo de 13 km e disponibilidade próxima a 5-9s para uma rede com proteção parcial. O desempenho do sistema foi validado utilizando o simulador Optisystem e testes realizados em equipamentos reais / Abstract: The aim of this work was to propose a Passive Optical Network architecture (PON) capable of supporting a GPON system and enable the evolution to next-generation PON network, or XG-PON, where both technologies can coexist in the same optical network infrastructure. In the architecture were considered a partial protection mechanism and devices that allow their deployment in real situations. It was presented a mathematical model to validation of the architecture based in the power budget calculation and in the premises established by the PON technologies recommendations. A mathematical model to calc availability in networks with partial protection was presented. Using these models were obtained the maximum reach of the network, maximum supported clients, which GPON and XG-PON equipment classes were required and the relationship between the length of the protected link and availability. It was obtained a maximum reach of 13 km and network availability next to 5-9s using partial protection. The system¿s performance was validated using the Optisystem simulator and tests performed in real equipment / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica
8

Internetworking architectures for optical network units in a wavelength division multiplexed passive optical network.

January 2007 (has links)
Zhao, Qiguang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (leaves 72-76). / Abstracts in English and Chinese. / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Telecommunications network hierarchy --- p.2 / Chapter 1.2 --- PON architectures for access networks --- p.4 / Chapter 1.2.1 --- TDM-PON --- p.5 / Chapter 1.2.2 --- WDM-PON --- p.7 / Chapter 1.3 --- Motivation of this thesis --- p.8 / Chapter 1.4 --- Outline of this thesis --- p.11 / Chapter Chapter 2 --- Previous Internetworking Architectures for Optical Network Units in Passive Optical Networks --- p.12 / Chapter 2.1 --- Introduction --- p.13 / Chapter 2.2 --- Previous internetworking architectures with ONU-broadcast capability / Chapter 2.2.1 --- Virtual ring network construction --- p.14 / Chapter 2.2.2 --- Reflection mechanism employing a FBG --- p.15 / Chapter 2.2.3 --- Loop-back mechanism in TDM-PON --- p.16 / Chapter 2.3 --- Previous internetworking architectures with ONU-VPGs formation capability --- p.17 / Chapter 2.3.1 --- E-CDMA application --- p.17 / Chapter 2.3.2 --- SCM technique --- p.18 / Chapter 2.3.3 --- Reflective waveband grouping mechanism --- p.20 / Chapter 2.4 --- Previous protection scheme for internetworking architectures --- p.21 / Chapter 2.4.1 --- Local ring protection in TDM-PON --- p.21 / Chapter 2.5 --- Summary --- p.22 / Chapter Chapter 3 --- Novel Internetworking Architecture with ONU-Broadcast Capability in a WDM-PON --- p.24 / Chapter 3.1 --- Introduction --- p.25 / Chapter 3.2 --- Network topology and wavelength assignment --- p.26 / Chapter 3.3 --- Operation principle --- p.27 / Chapter 3.4 --- Experimental demonstration --- p.31 / Chapter 3.5 --- Power budget and scalability --- p.34 / Chapter 3.6 --- Summary --- p.36 / Chapter Chapter 4 --- Novel Internetworking Architectures with ONU- VPGs Formation Capability in a WDM-PON --- p.37 / Chapter 4.1 --- Introduction --- p.38 / Chapter 4.2 --- Novel architecture with ONU-VPGs formation based on RF tone technique --- p.39 / Chapter 4.2.1 --- Introduction --- p.39 / Chapter 4.2.2 --- Network topology and wavelength assignment --- p.40 / Chapter 4.2.3 --- Media access control protocol: CSMA/CA protocol --- p.42 / Chapter 4.2.4 --- Experimental demonstration --- p.43 / Chapter 4.2.5 --- Discussion --- p.47 / Chapter 4.2.6 --- Summary --- p.49 / Chapter 4.3 --- Novel architecture with ONU-VPGs formation in optical layer --- p.51 / Chapter 4.3.1 --- Introduction --- p.51 / Chapter 4.3.2 --- Network topology and wavelength assignment --- p.51 / Chapter 4.3.3 --- Operation principle --- p.54 / Chapter 4.3.4 --- Experimental demonstration --- p.56 / Chapter 4.3.5 --- Discussion --- p.58 / Chapter 4.3.6 --- Summary --- p.65 / Chapter 4.4 --- Comparisons --- p.66 / Chapter 4.5 --- Summary --- p.67 / Chapter Chapter 5 --- Summary and Future Works --- p.68 / Chapter 5.1 --- Summary of the thesis --- p.69 / Chapter 5.2 --- Future works --- p.70 / LIST OF PUBLICATIONS --- p.71 / BIBLIOGRAPHY --- p.72
9

Limitations and Improvement of Subcarrier Multiplexed Systems over Optical Fiber

Tebben, Daniel James 24 April 2006 (has links)
Optical coherent techniques are used to eliminate the power fading found in optical subcarrier multiplexed systems. In a double-side band optical subcarrier system the signal experiences a periodic power fading that is dependent on the fiber dispersion and subcarrier frequency. This power fading is manifested during the direct detection of the subcarrier system using a square-law photodetector. Using a modified optical local oscillator to coherently detect the subcarrier channel this power fading can be eliminated. An optical local oscillator is centered at the optical carrier in order to perform homodyne detection. However, the local oscillator is modulated by a term equal the subcarrier frequency of interest. This is then a dual-frequency optical local oscillator. By controlling the phases of the local oscillator and the local subcarrier oscillator independently in the homodyne detection scheme, both the phase error and power fading of the detected subcarrier channel can be eliminated. This technique also allows the subcarrier to be selected optically, before the optical-to-electrical conversion. Analytical and simulation results are given to show the benefits of optical coherent detection in double-sideband subcarrier systems. By eliminating the periodic power loss found in the double-sideband subcarrier system the signal becomes dispersion limited and not power limited. A comparison of double-sideband and single-sideband subcarrier systems is presented. Multiple subcarriers and subcarrier spacing are also investigated for both double sideband and single sideband subcarrier systems. Optical phase and modulator noise are also considered in the analysis and simulation of coherent detection using a dual frequency optical local oscillator. Since the implementation used to eliminate the power fading is a phase correction based process, the phase noise of both the source and local oscillator lasers must be considered and the technique compared to typical direct and coherent detection techniques. Also, the effects of modulator nonlinearity are simulated for multichannel subcarrier multiplexed systems and comparisons made between the performance of using the dual-frequency local oscillator and typical detection techniques. It is shown that the advantages of the dual-frequency LO are retained in the presence of both phase noise and modulator nonlinearity. / Ph. D.
10

Efficient embeddings of meshes and hypercubes on a group of future network architectures.

Chen, Yawen January 2008 (has links)
Meshes and hypercubes are two most important communication and computation structures used in parallel computing. Network embedding problems for meshes and hypercubes on traditional network architectures have been intensively studied during the past years. With the emergence of new network architectures, the traditional network embedding results are not enough to solve the new requirements. The main objective of this thesis is to design efficient network embedding schemes for realizing meshes and hypercubes on a group of future network architectures. This thesis is organized into two parts. The first part focuses on embedding meshes/tori on a group of double-loop networks by evaluating the traditional embedding metrics, since double-loop networks have been intensively studied and proven to have many desirable properties for future network architecture. We propose a novel tessellation approach to partition the geometric plane of double-loop networks into a set of parallelogram tiles, called P-shape. Based on the characteristics of P-shape, we design a simple embedding scheme, namely P-shape embedding, that embeds arbitrary-shape meshes and tori on double-loop networks in a systematic way. A main merit of P-shape embedding is that a large fraction of embedded mesh/torus edges have edge dilation 1, resulting in a low average dilation. These are the first results, to our knowledge, on embedding meshes and tori on general doubleloop networks which is of great significance due to the popularity of these architectures. Our P-shape construction bridges between regular graphs and double-loop networks, and provides a powerful tool for studying the topological properties of double-loop networks. In the second part, we study efficient embedding schemes for realizing hypercubes on a group of array-basedWDMoptical networks by analyzing the new embedding metric of wavelength requirement, as WDM optical networking is becoming a promising technology for deployment in many applications in advanced telecommunication and parallel computing. We first design routing and wavelength assignments of both bidirectional and unidirectional hypercubes on WDM optical linear arrays, rings, meshes and tori with the consideration of communication directions. For each case, we identify a lower bound on the number of wavelengths required, and design the embedding scheme and wavelength assignment algorithm that uses a provably near-optimal number of wavelengths. To further reduce the wavelength requirement, we extend the results to WDM ring networks with additional links, namely WDM chordal rings. Based on our proposed embedding schemes, we provide the analysis of chord length with optimal number of wavelengths to realize hypercubes on 3-degree and 4-degree WDM chordal rings. Furthermore, we propose an embedding scheme for realizing dimensional hypercubes on WDM optical arrays by considering the hypercubes dimension by dimension, called lattice embedding, instead of embedding hypercubes with all dimensions. Based on lattice embedding, the number of wavelengths required to realize dimensional hypercube on WDM arrays can been significantly reduced compared to the previous results. By our embedding schemes, many communications and computations, originally designed based on hypercubes, can be directly implemented in WDM optical networks, and the wavelength requirements can be easily derived using our obtained results. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1345349 / Thesis (Ph.D.) - University of Adelaide, School of Computer Science, 2008

Page generated in 0.0931 seconds