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Dissertations / Theses on the topic 'Electrical Networks'
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1
SILVA, DENIS LAGE FERREIRA DA. "NONLINEAR ELECTRICAL NETWORKS SIMULATION." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2009. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=14447@1.
Full textAbstract:
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
As simulações de redes elétricas são atualmente fundamentais para o setor elétrico. Uma de suas principais utilidades é permitir a análise de falhas e ocorrências, que eventualmente passariam despercebidas. Existe atualmente, uma grande variedade de algoritmos para realizar simulações de redes lineares, que correspondem à grande maioria dos testes realizados em uma rede elétrica típica, quando submetidos a situações usuais. Contudo, existem consumidores de grande porte que possuem cargas não-lineares com uma grande influência na rede que a alimenta. Sendo assim, torna-se necessário modelar esta carga não-linear para que possa ser inserida no simulador da rede elétrica. Este trabalho propõe um método para a formulação das equações de estado de redes não-lineares de forma sistemática. A formulação do problema é, neste caso, parte fundamental da sua solução, já que atualmente existem, comercialmente, algoritmos capazes de resolver equações diferenciais não-lineares, como as que serão abordadas. Este trabalho apresenta a simulação de uma rede elétrica contendo sub-redes lineares e sub-redes não-lineares, utilizando um modelo de linhas de transmissão a parâmetros distribuídos através de filtros digitais, permitindo a simulação da subrede linear em taxas mais baixas.
Electrical network simulations are currently very important to the electricity sector. A major benefit from simulations is to permit a deeper insight into faulty network situations, that otherwise could eventually pass unnoticed. Currently, there are many algorithms that simulate linear networks, which comprise the majority of the tests done in a typical network, when subject to normal situations. However, there are large consumers, whose loads are nonlinear. These loads represent large influences to their power feeding network. Thus, it becomes necessary to model this nonlinear sub network so it can be inserted into the electrical network simulator. The purpose of this work is to develop a formulation approach for the nonlinear state equations that represents a nonlinear electrical network. The formulation of the network is, in this case, an essential part of the solution, since there are currently algorithms capable of solving nonlinear differential equations, like the ones that will be studied in this work.
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Jannotti, John 1974. "Network layer support for overlay networks." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/29274.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.Includes bibliographical references (p. 98-103).
Overlay networks are virtual networks formed by cooperating nodes that share an underlying physical network. They represent a flexible and deployable approach for applications to obtain new network semantics without modification of the underlying network, but they suffer from efficiency concerns. This thesis presents two new primitives for implementation in the network layer (i.e., the routers of the physical network). These primitives support the efficient operation and construction of overlay networks. Packet Reflection allows end hosts to request that routers perform specialized routing and duplication for certain packets. Path Painting allows multiple end hosts to determine where their disparate paths to a rendezvous point meet, in order to facilitate overlay topology building that reflects the topology of the underlying network. Both primitives can be incrementally deployed for incremental benefit. This thesis describes a variety applications of these primitives: application level multicast systems with various semantics, an extended Internet Indirect Infrastructure with latency benefits over the original proposal, and an extension to Chord which would allows faster lookups. Experimental results on simulated topologies indicate that when all routers support the proposed primitives, less that 5% overhead (in terms of link usage and latency) remains in two common overlay network usage scenarios. In addition, the benefits gained from deployment are significant even at low deployment levels. At approximately 25% deployment, the primitives have reduced overhead by over 50%. When intelligent deployment strategies are used, link usage overhead is less than 30% at less than 10% deployment. Finally, the results indicate that these benefits affect the area local to the deployed routers, providing a deployment incentive to independent networks.
by John Jannotti.
Ph.D.
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Kim, MinJi Ph D. Massachusetts Institute of Technology. "Network coding for robust wireless networks." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/71276.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 157-167).
Wireless networks and communications promise to allow improved access to services and information, ubiquitous connectivity, and mobility. However, current wireless networks are not well-equipped to meet the high bandwidth and strict delay requirements of future applications. Wireless networks suffer from frequent losses and low throughput. We aim to provide designs for robust wireless networks. This dissertation presents protocols and algorithms that significantly improve wireless network performance and effectively overcome interference, erasures, and attacks. The key idea behind this dissertation is in understanding that wireless networks are fundamentally different from wired networks, and recognizing that directly applying techniques from wired networks to wireless networks limits performance. The key ingredient underlying our algorithms and protocols is network coding. By recognizing the algebraic nature of information, network coding breaks the convention of routing networks, and allows mixing of information in the intermediate nodes and routers. This mixing has been shown to have numerous performance benefits, e.g. increase in throughput and robustness against losses and failures. We present three protocols and algorithms, each using network coding to harness a different characteristic of the wireless medium. We address the problem of interference, erasures, and attacks in wireless networks with the following network coded designs. -- Algebraic NC exploits strategic interference to provide a distributed, randomized code construction for multi-user wireless networks. Network coding framework simplifies the multi-user wireless network model, and allows us to describe the multi-user wireless networks in an algebraic framework. This algebraic framework provides a randomized, distributed code construction, which we show achieves capacity for multicast connections as well as a certain set of non-multicast connections. -- TCP/NC efficiently and reliably delivers data over unreliable lossy wireless networks. TCP, which was designed for reliable transmission over wired networks, often experiences severe performance degradation in wireless networks. TCP/NC combines network coding's erasure correction capabilities with TCP's congestion control mechanism and reliability. We show that TCP/NC achieves significantly higher throughput than TCP in lossy networks; therefore, TCP/NC is well suited for reliable communication in lossy wireless networks. -- Algebraic Watchdog takes advantage of the broadcast nature of wireless networks to provide a secure global self-checking network. Algebraic Watchdog allows nodes to detect malicious behaviors probabilistically, and police their neighbors locally using overheard messages. Unlike traditional detection protocols which are receiver-based, this protocol gives the senders an active role in checking the nodes downstream. We provide a trellis-based inference algorithm and protocol for detection, and analyze its performance. The main contribution of this dissertation is in providing algorithms and designs for robust wireless networks using network coding. We present how network coding can be applied to overcome the challenges of operating in wireless networks. We present both analytical and simulation results to support that network coded designs, if designed with care, can bring forth significant gains, not only in terms of throughput but also in terms of reliability, security, and robustness.
by MinJi Kim.
Ph.D.
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Taiwo, Olugbenga Adekunle. "Network access selection in heterogeneous wireless networks." Master's thesis, University of Cape Town, 2013. http://hdl.handle.net/11427/16832.
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In heterogeneous wireless networks (HWNs), both single-homed and multi-homed terminals are supported to provide connectivity to users. A multiservice single-homed multi-mode terminal can support multiple types of services, such as voice call, file download and video streaming simultaneously on any one of the available radio access technologies (RATs) such as Wireless Local Area Network (WLAN), and Long Term Evolution (LTE). Consequently, a single-homed multi-mode terminal having multiple on-going calls may need to perform a vertical handover from one RAT to another. One of the major issues in HWNs is how to select the most suitable RAT for multiple handoff calls, and the selection of a suitable RAT for multiple-calls from a single-homed multi-mode terminal in HWNs is a group decision problem. This is because a single-homed multi-mode terminal can connect to only one RAT at a time, and therefore multiple handoff calls from the terminal have to be handed over to the same RAT. In making group decision for multiple-calls, the quality of service (QoS) requirements for individual calls needs to be considered. Thus, the RAT that most satisfies the QoS requirements of individual calls is selected as the most suitable RAT for the multiple-calls. Whereas most research efforts in HWNs have concentrated on developing vertical handoff decision schemes for a single call from a multi-mode terminal, not much has been reported in the literature on RAT-selection for multiple-calls from a single-homed multi-mode terminal in next generation wireless networks (NGWNs). In addition, not much has been done to investigate the sensitivity of RAT-selection criteria for multiple-calls in NGWNs. Therefore, this dissertation addresses these issues by focusing on following two main aspects: (1) comparative analysis of four candidate multi-criteria group decision-making (MCGDM) schemes that could be adapted for making RAT-selection decisions for multiple-calls, and (2) development of a new RAT-selection scheme named the consensus RAT-selection model. In comparative analysis of the candidate RAT-selection schemes, four MCGDM schemes namely: distance to the ideal alternative-group decision making (DIA-GDM), multiplicative exponent weighting-group decision making (MEW-GDM), simply additive weighting-group decision making (SAW-GDM), technique for order preference by similarity to Ideal solution-group decision making (TOPSIS-GDM) are considered. The performance of the multiple-calls RAT-selection schemes is evaluated using the MATLAB simulation tool. The results show that DIA-GDM and TOPSIS-GDM schemes are more suitable for multiple handoff calls than SAW-GDM and MEW-GDM schemes. This is because they are consistent and less-sensitive in making RAT-selection decision than the other two schemes, with regards to RAT-selection criteria (service price, data rate, security, battery power consumption and network delay) in HWNs. In addition, the newly developed RAT-selection scheme incorporates RAT-consensus level for improving RAT-selection decisions for multiple-calls. Numerical results conducted in MATLAB validate the effectiveness and performance of the newly proposed RAT-selection scheme for multiple-calls in HWNs.
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Lee, Anna H. "Simplified random network codes for multicast networks." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33306.
Full textAbstract:
Thesis (M. Eng. and S.B.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 43).
Network coding is a method of data transmission across a network which involves coding at intermediate nodes. Network coding is particularly attractive for multicast. Building on the work done on random linear network codes, we develop a constrained, simplified code construction suitable for multicast in wireless networks. We analyze bounds on sufficient code size and code success probability via an algebraic framework for network coding. We also present simulation results that compare generalized random network codes with our code construction. Issues unique to the simplified code are explored and a relaxation of the code to improve code performance is discussed.
by Anna H. Lee.
M.Eng.and S.B.
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Shi, Xiaomeng Ph D. Massachusetts Institute of Technology. "Energy aware network coding in wireless networks." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78533.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 97-104).
Energy is one of the most important considerations in designing reliable low-power wireless communication networks. We focus on the problem of energy aware network coding. In particular, we investigate practical energy efficient network code design for wireless body area networks (WBAN). We first consider converge-cast in a star-shaped topology, in which a central base station (BS), or hub, manages and communicates directly with a set of nodes. We then consider a wireless-relay channel, in which a relay node assists in the transmission of data from a source to a destination. This wireless relay channel can be seen as a simplified extended star network, where nodes have relay capabilities. The objective is to investigate the use of network coding in these scenarios, with the goal of achieving reliability under low-energy and lower-power constraints. More specifically, in a star network, we propose a simple network layer protocol, study the mean energy to complete uploads of given packets from the nodes to the BS using a Markov chain model, and show through numerical examples that when reception energy is taken into account, the incorporation of network coding offers reductions in energy use. The amount of achievable gains depends on the number of nodes in the network, the degree of asymmetry in channel conditions experienced by different nodes, and the relative difference between transmitting and receiving power at the nodes. We also demonstrate the compatibility of the proposed scheme with the IEEE 802.15.6 WBAN standard by describing ways of incorporating network coding into systems compliant to the standard. For a wireless relay channel, we explore the strategic use of network coding according to both throughput and energy metrics. In the relay channel, a single source communicates to a single sink through the aid of a half-duplex relay. The fluid flow model is used to describe the case where both the source and the relay are coding, and Markov chain models are proposed to describe packet evolution if only the source or only the relay is coding. Although we do not attempt to explicitly categorize the optimal network coding strategies in the relay channel under different system parameters, we provide a framework for deciding whether and where to code, taking into account of throughput maximization and energy depletion constraints.
by Xiaomeng Shi.
Ph.D.
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Kim, Anthony Eli. "On network coding capacity : matroidal networks and network capacity regions." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62657.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 68-70).
One fundamental problem in the field of network coding is to determine the network coding capacity of networks under various network coding schemes. In this thesis, we address the problem with two approaches: matroidal networks and capacity regions. In our matroidal approach, we prove the converse of the theorem which states that, if a network is scalar-linearly solvable then it is a matroidal network associated with a representable matroid over a finite field. As a consequence, we obtain a correspondence between scalar-linearly solvable networks and representable matroids over finite fields in the framework of matroidal networks. We prove a theorem about the scalar-linear solvability of networks and field characteristics. We provide a method for generating scalar-linearly solvable networks that are potentially different from the networks that we already know are scalar-linearly solvable. In our capacity region approach, we define a multi-dimensional object, called the network capacity region, associated with networks that is analogous to the rate regions in information theory. For the network routing capacity region, we show that the region is a computable rational polytope and provide exact algorithms and approximation heuristics for computing the region. For the network linear coding capacity region, we construct a computable rational polytope, with respect to a given finite field, that inner bounds the linear coding capacity region and provide exact algorithms and approximation heuristics for computing the polytope. The exact algorithms and approximation heuristics we present are not polynomial time schemes and may depend on the output size.
by Anthony Eli Kim.
M.Eng.
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Ahmed, Ebad. "Delay gains from network coding in wireless networks." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/41253.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 73-77).
We consider a single-hop cellular wireless system with a single source (base station) broadcasting a stream of incoming files to multiple receivers over stochastic time-varying channels with non-zero erasure probabilities. The base station charges a price per receiver per file with the aim of maximizing its profit. Customers who wish to transmit files to the receivers decide to enter the system based on the price, the queuing delay, and the utility derived from the transaction. We look at network coding and scheduling as possible strategies for file transmission, and obtain approximate characterizations of the optimal customer admission rate, optimal price and the optimal base-station profit as functions of the first and second moments of the service time processes under mild assumptions. We show that network coding leads to significant gains in the base station profits as compared to scheduling, and also demonstrate that the optimal network coding window size is highly insensitive to the number of receivers, which suggests that pricing and coding decisions can be decoupled. We also investigate the behavior of network coding in the case where the number of receivers is sufficiently large, and derive scaling laws for the asymptotic gains from network coding. We subsequently propose a way to extend our analysis of single-source, multiple-receiver systems to multiple-source, multiple-receiver systems in general network topologies and obtain explicit characterizations of the file download completion time under network coding and scheduling, also taking into account the effects of collisions and interference among concurrent packet transmissions by two or more sources.
(cont.) Our formulation allows us to model multi-hop networks as a series of single-hop multiple-source, multiple-receiver systems, which provides a great deal of insight into the workings of larger and denser multi-hop networks such as overlay networks and peer-to-peer systems, and appears to be a promising application of network coding in such networks in the future.
by Ebad Ahmed.
M.Eng.
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Mak, Wai Y. "Ad Hoc Network Architecture for Multi-Media Networks." Thesis, Monterey California. Naval Postgraduate School, 2007. http://hdl.handle.net/10945/2988.
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The desire for more intelligence in the battlefield has given rise to the idea of routing video images over wireless sensor networks. This would apprise combat decision makers with actual images of battlefield developments and allow them to make sound decisions. To achieve this objective, the characteristics of video traffic must be studied and understood. This thesis focuses on evaluating the possibility of routing video images over a wireless sensor network. Video traffic is modeled and simulations are performed via the use of the Sun Small Programmable Object Technology (Sun SPOT) Java development kits configured in three different network topologies: the star topology, binary tree topology and chain topology. It is known that video traffic is self similar and can be obtained by aggregating a large number of On-Off message sources. Hence, an On-Off model using Pareto distribution function is used to model video traffic over the network. In this thesis four self-similar shaping parameters, i.e., alpha(On) = 1.2, 1.4, 1.7 and 1.9 are used in the simulations. The performance of each topology is evaluated based on parameters like mean throughput, mean interarrival time, mean packet drop, and mean delay.Singapore Armed Forces author.
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Masood, Syed Haani. "Distribution of files using network-coding in opportunistic networks." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106560.
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The immense growth in mobile data usage has placed mobile operators in a challenging position. User experience is threatened to degrade due to network capacity issues. The route towards network upgrades is an expensive one especially due to the high licensing fees attached to spectrum acquisition. We propose a scheme based on community identification for distributing large files to subscribers using opportunistic communication. The scheme is able to offload large files from the cellular network and without having to invest in any infrastructure. The cellular network initially seeds the file to the most central subscriber in each community which is then spread to all subscribers via opportunistic contacts. Network coding is utilized for the opportunistic exchange of file packets between subscribers. We show that seeding the file in each community is important to ensure better file delivery times and also reduces the overhead of the number of packet exchanges required during file dissemination. Our scheme also provides incentives for influential subscribers in the network which contribute more towards the opportunistic dissemination of file.L'immense croissance de l'utilisation des données mobiles a placé les opérateurs mobiles dans une position difficile. L'expérience utilisateur est menacée de se dégrader en raison de problèmes de capacité du réseau. La route vers la mise à niveau du réseau est coûteuse en particulier en raison des frais de licence élevés attachés à l'acquisition du spectre. Nous proposons un schéma basé sur l'identification communautaire pour la distribution de gros fichiers à des abonnés en utilisant la communication opportuniste. Le système est capable de se décharger de gros fichiers sur le réseau cellulaire et sans avoir à investir dans n'importe quelle infrastructure. Le réseau cellulaire d'abord les graines du fichier à l'abonné la plus centrale dans chaque communauté, qui est ensuite étendue à tous les abonnés via des contacts opportunistes. Réseau de codage est utilisé pour l'échange de paquets de fichiers opportunistes entre les abonnés. Nous montrons que l'ensemencement du fichier dans chaque communauté est important pour assurer une meilleure délais de livraison du fichier et réduit également la surcharge du nombre d'échanges de paquets nécessaires pendant la diffusion de fichiers. Notre programme prévoit également des incitations pour les abonnés influents dans le réseau qui contribuent davantage vers la diffusion opportuniste de fichier.
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Masuabi, Francis Mphakiseng. "A hybrid network/host mobility management scheme for next generation networks." Master's thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/12627.
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Includes bibliographical references.The author proposes a hybrid network/host interworking scheme to allow the MN to transition smoothly between different access networks supporting two distinct mobility approaches.
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Farry, Michael P. (Michael Patrick). "Sensor networks for social networks." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36764.
Full textAbstract:
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 51-55).
This thesis outlines the development of software that makes use of Bayesian belief networks and signal processing techniques to make meaningful inferences about real-world phenomena using data obtained from sensor networks. The effectiveness of the software is validated by applying it to the problem of detecting face-to-face social interactions between groups of people, given data readings from sensors that record light, temperature, acceleration, sound, and proximity. This application represents a novel method for social network construction which is potentially more accurate and less intrusive than traditional methods, but also more meaningful than newer methods that analyze digitally mediated communication.
by Michael P. Farry.
M.Eng.
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Bazrafshan, Mohammadhafez. "Modeling and Optimization of Electrical Power Networks." Thesis, The University of Texas at San Antonio, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10929124.
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The electrical power network is moving towards sustainability and cost-efficiency. The former is achieved by incorporating distributed renewable generation and the latter requires employing intelligent control and optimization techniques. As the main interface between the electricity grid and its consumers, the distribution network will play a pivotal role in the near future. In practice, distribution networks operate under unbalanced conditions and far from single-phase simplifications. Thus, the majority of this dissertation aims to provide comprehensive computational tools for multi-phase distribution networks. A final part of this work touches upon transmission networks to explore benefits of combining control and optimization algorithms in various time-scales.
In Chapter 2, models of the most practical distribution elements, including wye and delta ZIP loads, transmission lines with missing phases, step-voltage regulators (SVRs), and three-phase transformers are assembled. Specifically for SVRs, novel nodal admittance models are derived from first principles. Concatenation of these models yields the bus admittance matrix (Y-Bus). Using linear algebra, it is then shown that Y-Bus invertibility is compromised only when the network includes ungrounded or delta-connected transformers. For such devices, we mathematically show why a previously proposed modification in their nodal admittance restores Y-Bus invertibility. Mathematical guarantees for Y-Bus invertibility is important since, for instance, it allows one to run the Z-Bus method to compute voltage solutions of power flow equations.
In Chapter 3, theoretical convergence of the Z-Bus method in multi-phase distribution networks with wye and delta ZIP loads is studied. By viewing the Z-Bus method as a fixed-point iteration, sufficient conditions for its contraction are derived. These conditions define a region, expressed in terms of Y-Bus and ZIP loads, in which unique voltage solutions to power flow equations exist.
Chapter 4 considers a planning problem for inverter-based renewable systems in multi-phase distribution networks. The objective is to minimize the installation costs of distributed generators (DG) during the planning stage and the costs of power import plus DG curtailment during operations. Three- and single-phase inverter models that preserve the underlying mapping between renewable uncertainty to power injection are presented. Scenario-based characterization of distributed generation and loads as well as power flow linearizations are leveraged to render a stochastic formulation for optimal DG placement and sizing. The proposed problem is a mixed-integer second-order cone program that is solved efficiently. Simulations on several medium-to-large-sized distribution test feeders promise that optimal stochastic planning of DGs reduces costs during validation, compared to a scheme where uncertainty is only represented by its average value.
Chapter 5 presents an optimal power flow (OPF) problem that allows for tap selection of various types of SVRs. The goal is to minimize power import while satisfying operational constraints. A set of power flow equations are derived that explicitly account for the tap ratios based on the nodal admittance model of SVRs (Chapter 2). Chordal semidefinite relaxations of the power flow equations are pursued for non-SVR edges. For each SVR type, novel relaxations are proposed to handle the non-convex primary-to-secondary voltage relationship. The formulation is a semidefinite program (SDP). Numerical tests on the IEEE 37-bus distribution feeder indicate the success of the proposed SDP in selecting taps of wye, closed-delta, and open-delta SVRs.
Chapter 6 augments the transmission OPF problem with a load-following controller whose costs are expressed through the linear quadratic regulator (LQR). The power network is described by a set of nonlinear differential algebraic equations (DAEs). By linearizing the DAEs around a known equilibrium, a linearized OPF with operational constraints is formulated first. This OPF is then augmented by a set of linear matrix inequalities equivalent to the implementation of an LQR controller. The resulting formulation, termed LQR-OPF, is an SDP which furnishes optimal steady-state setpoints and an optimal feedback law to steer the system to the new steady state with minimum load-following control costs. Experiments on test cases demonstrate that the setpoints computed by LQR-OPF result in lower overall costs and frequency deviations compared to those of a scheme where OPF and load-following control are considered separately.
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Downes, David. "Interactive models of electrical machines." Thesis, Nottingham Trent University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273777.
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Magagula, Linoh A. "A network-based coordination design for seamless handover between heterogeneous wireless networks." Doctoral thesis, University of Cape Town, 2010. http://hdl.handle.net/11427/10801.
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Includes bibliographical references (leaves 136-144).The rapid growth of mobile and wireless communication over the last few years has spawned many different wireless networks. These heterogeneous wireless networks are envisioned to interwork over an IP-based infrastructure to realize ubiquitous network service provisioning for mobile users. Moreover, the availability of multiple-interface mobile nodes (MNs) will make it possible to communicate through any of these wireless access networks. This wireless network heterogeneity combined with the availability of multiple-interface MNs creates an environment where handovers between the different wireless access technologies become topical during mobility events. Therefore, operators with multiple interworking heterogeneous wireless networks will need to facilitate seamless vertical handovers among their multiple systems. Seamless vertical handovers ensure ubiquitous continuity to active connections hence satisfy the quality of experience of the mobile users.
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Orimolade, Joseph Folorunsho. "Access network selection schemes for multiple calls in next generation wireless networks." Doctoral thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/25380.
Full textAbstract:
There is an increasing demand for internet services by mobile subscribers over the wireless access networks, with limited radio resources and capacity constraints. A viable solution to this capacity crunch is the deployment of heterogeneous networks. However, in this wireless environment, the choice of the most appropriate Radio Access Technology (RAT) that can Tsustain or meet the quality of service (QoS) requirements of users' applications require careful planning and cost efficient radio resource management methods. Previous research works on access network selection have focused on selecting a suitable RAT for a user's single call request. With the present request for multiple calls over wireless access networks, where each call has different QoS requirements and the available networks exhibit dynamic channel conditions, the choice of a suitable RAT capable of providing the "Always Best Connected" (ABC) experience for the user becomes a challenge. In this thesis, the problem of selecting the suitable RAT that is capable of meeting the QoS requirements for multiple call requests by mobile users in access networks is investigated. In addressing this problem, we proposed the use of Complex PRoprtional ASsesment (COPRAS) and Consensus-based Multi-Attribute Group Decision Making (MAGDM) techniques as novel and viable RAT selection methods for a grouped-multiple call. The performance of the proposed COPRAS multi-attribute decision making approach to RAT selection for a grouped-call has been evaluated through simulations in different network scenarios. The results show that the COPRAS method, which is simple and flexible, is more efficient in the selection of appropriate RAT for group multiple calls. The COPRAS method reduces handoff frequency and is computationally inexpensive when compared with other methods such as the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS), Simple Additive Weighting (SAW) and Multiplicative Exponent Weighting (MEW). The application of the proposed consensus-based algorithm in the selection of a suitable RAT for group-multiple calls, comprising of voice, video-streaming, and file-downloading has been intensively investigated. This algorithm aggregates the QoS requirement of the individual application into a collective QoS for the group calls. This new and novel approach to RAT selection for a grouped-call measures and compares the consensus degree of the collective solution and individual solution against a predefined threshold value. Using the methods of coincidence among preferences and coincidence among solutions with a predefined consensus threshold of 0.9, we evaluated the performance of the consensus-based RAT selection scheme through simulations under different network scenarios. The obtained results show that both methods of coincidences have the capability to select the most suitable RAT for a group of multiple calls. However, the method of coincidence among solutions achieves better results in terms of accuracy, it is less complex and the number of iteration before achieving the predefined consensus threshold is reduced. A utility-based RAT selection method for parallel traffic-streaming in an overlapped heterogeneous wireless network has also been developed. The RAT selection method was modeled with constraints on terminal battery power, service cost and network congestion to select a specified number of RATs that optimizes the terminal interface utility. The results obtained show an optimum RAT selection strategy that maximizes the terminal utility and selects the best RAT combinations for user's parallel-streaming for voice, video and file-download.
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Qureshi, Asfandyar. "Flexible application driven network striping over Wireless Wide Area Networks." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33338.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 157-161).
Inverse multiplexing, or network striping, allows the construction of a high-bandwidth virtual channel from a collection of multiple low-bandwidth network channels. Striping systems usually employ a packet scheduling policy that allows applications to be oblivious of the way in which packets are routed to specific network channels. Though this is appropriate for many applications, many other applications can benefit from an approach that explicitly involves the application in the determination of the striping policy. Horde is middleware that facilitates flexible striping over Wireless Wide Area Network (WWAN) channels. Horde is unusual in that it separates the striping policy from the striping mechanism. It allows applications to describe network Quality-of-Service (QoS) objectives that the striping mechanism attempts to satisfy. Horde can be used by a set of data streams, each with its own QoS policy, to stripe data over a set of WWAN channels. The WWAN QoS variations observed across different channels and in time, provide opportunities to modulate stream QoS through scheduling. The key technical challenge in Horde is giving applications control over certain aspects of the data striping operation while at the same time shielding the application from low-level details. Horde exports a set of flexible abstractions replacing the application's network stack. Horde allows applications to express their policy goals as succinct network-QoS objectives. Each objective says something, relatively simple, about the sort of network QoS an application would like for some data stream(s). We present the Horde architecture, describe an early implementation, and examine how different policies can be used to modulate the quality-of-service observed across different independent data streams. Through experiments conducted on real and simulated network channels, we confirm our belief that the kind of QoS modulation Horde aims to achieve is realistic for actual applications.
by Asfandyar Qureshi.
M.Eng.
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Sibanda, Clifford Clifton Leonard. "Media independent handovers : network selection for mobile IP nodes in heterogeneous wireless networks." Master's thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/5104.
Full textAbstract:
Includes abstract.Includes bibliographical references (p. 79-82).
In Next Generation Networks (NGN), also known as 4G, Beyond 3G, Converged, Integrated and Interworked Network, user node mobility in wireless and wired environments will seamlessly cross disparate network boundaries. The effort to offer ubiquitous computing, providing access to services anywhere and anytime, strongly encourages the ability to roam across the different existing and future networks. Literature shows investigation of concepts such as Always Best Connected (ABC) when heterogeneous networks co-exist , which will work or compete with other schemes like Home Network Default (HND), Compatibility and Network Operator Agreements (CNOA) to guide network selection or access . With the variety of available networks, the mobile node may be faced with having to decide which network to connect to. We concentrate on the network selection aspects of these envisaged mobile, overlay and integrated environment in heterogeneous networks. The standard developments by the IEEE802.21 Working group and the IETF Networking group form the base of our approach that seeks to see mobility across heterogeneous networks a reality. We propose an IEEE802.21 Media Independent Handover Function (MIHF) based network discovery and network selection, leading to a handover. The selection may be further assisted by an MIHF capable Broker Node that is Third party to the Network Providers to provide a central yet distributed database of the available networks as encountered by the Mobile Node, to cater for Nodes with no prior knowledge of networks and software repository. A Mobile Node (MN) in our solution uses 802.21 communication messages to obtain information about foreign networks encountered before selecting the networks to connect to. Our evaluation through simulations, shows that network selection in heterogeneous wireless networks environment for the appropriately equipped devices is greatly enhanced by the use of the Media Independent Handover Protocol. In scenarios where the mobile node has no prior knowledge of the encountered different network architectures, the use of a Broker node can, for an optimal number of available networks also greatly enhance the mobile node’s network selection by reducing the delay associated and the packet losses incurred.
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Tang, Yaojing. "Deployment of Smart Energy to Undeveloped Electrical Networks." Thesis, KTH, Industriella informations- och styrsystem, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-81411.
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This thesis presents an approach to design and implementation of a Renewable Power Complex (RPC) containing several intermittent sources. The purpose of RPC is to improve the poor rural distribution network voltage portfolio which can be traced back to the typical long distance radial lines. With the purpose of improve system overall voltage, iterative studies are conducted to calculate the requirements of RPC in terms of capacity. Afterwards, the proposed approach is verified at a test system. From implementation perspective, the capacity of the inverter interfacing the generation unit is a bottleneck that limits the possible dimension of the RPC. Consequently, the RPC is actually composed by several atomic units with a much smaller scale. The software where the potentials of intermittent generation sources can be estimated given the geographic information is used to optimize the size of RPC atomic units. Finally, the thesis tackles a high level design of automations system under which the RPC is operated. The functionality described are all compliant with commonly accepted IEC 61850 standards with the intention to ease the future implementation.
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Jonah, Emmanuel Ohieku. "The topology and electrical properties of nanoparticle networks." Doctoral thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/8806.
Full textAbstract:
Includes bibliographical references.The bulk and surface network topologies of milled silicon nanoparticle aggregates in layers deposited on porous and non-porous substrates have been quantitatively characterised using laboratory and synchrotron based small angle X-ray scattering and ultra-small angle X-ray scattering, as well as with a new surface scattering technique developed for this research, which can be described as wide angle low q scattering. A new scaling model applied to the small angle and ultra-small angle X-ray scattering data which was originally developed to describe branched polymers was shown to be applicable to the description of the networks of silicon particles. The milled particles which have a highly polydisperse size distribution, form agglomerates, which in turn cluster to form larger structures with a very high degree of aggregation. Results from the new scattering technique showed the rough surface of the printed layers to have a fractal structure with step heights of 10% to 20% between adjacent particles. This value is consistent with the topology of the particle aggregates in the layer inferred from ultra-small angle X-ray scattering. Flow properties of the inks on different substrates lead to quantitative differences in the mean aggregate separation, with slowly curing systems on materials which allow good capillary flow resulting in denser networks with smaller aggregates and better contact between particles. The electrical conductance of the layers was shown to be linearly related to parallel connections of the minimum paths of particles through the aggregates as determined from the analysis of ultra-small angle X-ray scattering data. The capacitance of the layers was shown to have a linear dependence on both the separation between primary particles and series connection of the minimum paths.
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Labra, Muñoz Jacqueline Andrea. "Electrical characterization of protein networks and inorganic nanoparticles." Tesis, Universidad de Chile, 2018. http://repositorio.uchile.cl/handle/2250/168282.
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Magíster en Ciencias de la Ingeniería, Mención Eléctrica.
Ingeniera Civil EléctricaEsta última década, el uso de móleculas como bloques funcionales en circuitos electrónicos ha cobrado gran relevancia. Con este objetivo en mente, es crucial entender cómo ocurre el transporte de carga a través de dichas moléculas. Siendo entonces necesario encontrar una forma que permita medir objetos cuyos tamaños abarcan unos pocos nanómetros (moléculas, nanopartículas, etc.). Esta tesis presenta el diseño y la fabricación de dos tipos de dispositivos, donde cada dispositivo consiste en un par de nanoelectrodos (fuente y drenaje), y es el espacio entre ambos electrodos (llamado "gap") el lugar en donde se atraparán las moléculas para posteriormente poder ser caracterizadas eléctricamente. La caracterización eléctrica consiste en comparar las curvas de corriente y voltage (I-V) a través de un "gap" cuando está abierto, es decir, un gap que no contiene moléculas y está bien definido; y el mismo gap después de que las moléculas han sido depositadas (y atrapadas) en él. El primer tipo de dispositivo se denomina "direct-electron-beam nanogap", en el cual la separación entre el par de electrodos es de aproximadamente 75-95 nm. Estos dispositivos son requeridos para medir redes de ferritinas (un tipo de proteína esférica). Las muestras de ferritina incluyen ferritina con distinto contenido de hierro (20-800 átomos de hierro por molécula de ferritina) y también ferritina con nanopartículas de oro dentro de su cavidad. Se observó que las redes de ferritina conmutan al aplicar un rango de voltaje de +/- 8V, donde la dirección de conmutación cambia con el tiempo. Además, a partir de las mediciones realizadas en un microscopio electrónico de efecto túnel (STM, por sus sigles in inglés), se estableció que las moléculas individuales de ferritina (con 20 y 800 átomos de hierro) prácticamente no conducen; el mismo comportamiento se encontró en el caso de la ferritina con contenido de oro. Las mediciones se realizaron en aire, a temperatura ambiente. Se propone que el mecanismo de conducción de las ferritinas está determinado principalmente por la presencia de múltiples ferritinas (una red) y no está relacionado con el contenido (de hierro u oro) dentro de la cavidad de la misma. El segundo tipo de dispositivo se denomina "self-aligned nanogap", en el cual la distancia entre los electrodos es de entre 9 y 20 nm. Estos dispositivos son necesarios para medir nanopartículas (NPs) de hierro y de hierro-níquel, cubiertas con una capa de óxido del metal respectivo. Se registraron las curvas I-V a temperatura ambiente, en vacío. Se encontró que, en promedio, las NPs más grandes son más conductivas que las NPs más pequeñas, y que si la densidad de NPs es mayor, la probabilidad de tener varias conectadas en paralelo aumenta, aumentando así la corriente. También se midieron ciclos de I-Vmientras se aumentaba la temperatura (desde 20 K hasta 300 K), en vacío. Al estudiar la dependencia de la resistencia a la temperatura, se obtuvo que sólo en grandes NPs de hierro la resistencia era altamente dependiente. En el caso de las NPs de hierro-níquel, la dependencia fue más débil de lo esperado. Además, se usó un modelo modificado del bloqueo de Coulomb (incluyendo las cargas de compensación), en donde la forma de las curvas I-V para cada tipo de NP fue consistente con dicho modelo. Sin embargo, la dependencia de la resistencia a la temperatura indica que este modelo sólo es consistente con el resultado obtenido para las grandes NPs de hierro (único caso con alta dependencia).
Esta investigación fue financiada por la Unión Europea mediante un proyecto RISE (DAFNEOX) SEP-210165479 y por los proyectos FONDECYT REGULAR, números 1140770 y 116175
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Remmelzwaal, Leendert Amani. "Salience-affected neural networks." Master's thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/12111.
Full textAbstract:
Includes abstract.Includes bibliographical references (leaves 46-49).
In this research, the salience of an entity refers to its state or quality of standing out, or receiving increased attention, relative to neighboring entities. By neighbouring entities we refer to both spatial (i.e. similar visual objects) and temporal (i.e. related concepts). In this research we model the effect of non-local connections using an ANN, creating a salience-affected neural network (SANN). We adapt an ANN to embody the capacity to respond to an input salience signal and to produce a reverse salience signal during testing. The input salience signal applied during training to each node has the effect of varying the node’s thresholds, depending on the activation level of the node. Each node produces a nodal reverse salience signal during testing (a measure of the threshold bias for the individual node). The reverse salience signal is defined as the summation of the nodal reverse salience signals observed at each node.
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Jennings, Michael (Michael Vincent). "The application of network coding to multicast routing in wireless networks." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40532.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 58-62).
This thesis considers the application of network coding and opportunistic routing to improve the performance of multicast flows in wireless networks. Network coding allows routers to randomly mix packets before forwarding them. This randomness ensures that routers that hear the same transmission are unlikely to forward the same packets, which permits routers to exploit wireless opportunism with minimal coordination. By mixing packets, network coding is able to reduce the number of transmissions necessary to convey packets to multiple receivers, which can lead to a large increase in throughput for multicast traffic. We discuss the design of a multicast enabled variant of MORE, a network coding based protocol for file transfer in wireless mesh networks, and evaluate this extension, which we call MORE-M, in a 20-node indoor wireless testbed. We compare MORE-M to a wireless multicast protocol that takes an approach similar to that of wired multicast by using the ETX metric to build unicast routing trees. We also compare MORE-M to a multicast enabled variant of the ExOR routing protocol. Experiments show that MORE-M's gains increase with the number of destinations, and are 35-200% greater than that of ExOR. We then consider the problem of video streaming in a wireless local area network for applications such as video conferencing. A network coding based protocol that uses opportunistic receptions at clients is proposed. We evaluate the design in our testbed and demonstrate that the use of network coding and, in particular, the use of wireless opportunism increase the quality of the video stream.
by Michael Jennings.
S.M.
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Banerji, Pratip K. "An analysis of network management traffic and requirements in wireless networks." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/42744.
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Niu, Weihe. "Exact Modeling of Time-Interval-Modulated Switched Networks." PDXScholar, 1993. https://pdxscholar.library.pdx.edu/open_access_etds/4622.
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The frequency response analysis of switched networks plays a very important part in designing various kinds of power converter circuits. In this thesis two frequency response techniques for analyzing switching power converters are discussed. One method provides a mathematical description which treats the converter as a periodic time varying system. A linearized small signal model is subsequently derived. The major part of the thesis concentrates on this accurate exact small-signal technique. The derivation involves state space representation and the use of the time varying transfer function. A Fourier analysis is performed to show the relationship between the frequency response of the network and the time varying transfer function. The obtained expressions are in closed form. The method has proven to be exact. The complexity of this technique is overcome by automating its derivation in conjunction with a circuit simulator. An alternative method, relying only on a sampled-data representation, is also derived, which provides a less complicated algorithm. However the accuracy of this method suffers, particularly at high frequencies. The accuracy of the exact small-signal technique is verified by experimentation.
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Savov, Emil I. "Multichannel photonic networks." Thesis, University of Ottawa (Canada), 1991. http://hdl.handle.net/10393/7835.
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This thesis presents several alternatives for fibre-optic local and metropolitan area networks. The issues considered are mainly related to the physical layer of the networks, i.e., the topology and the optical communications problems. The following approaches were considered in more detail: photonic switching using spatial light modulators; subcarrier-multiplexing techniques using direct optical detection, and in particular the transmission of 64-QAM signals by optical fibre; and subcarrier-multiplexing techniques combined with coherent optical detection. The spatial light modulator appears to be one of the most promising means for building a large-size (e.g., 1000 $\times$ 1000) optical space switch. The main constraints are the attenuation of the optical signal and the crosstalk between the channels. Other problems such as fan-in and fan-out are also addressed. Theoretical and experimental results are presented on the fibre-optic transmission of microwave 64-QAM signals at 90 Mb/s rate. Two important methods of improving the system performance are discussed and demonstrated: laser reflection-induced intensity noise minimization, and error-correction coding using a self-orthogonal convolutional code. The applicability of this transmission technique to the distribution of digital video services is assessed. The concept of photonic networks which use subcarrier-multiplexing techniques together with coherent optical detection is presented. The different radio and optical modulation formats that can be used are investigated and compared for several system modes of operation. The effects of laser phase noise on the system performance are also addressed. An 8-port homodyne phase-diversity receiver is analyzed theoretically.
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Wei, Dali. "Clustering algorithms for sensor networks and mobile ad hoc networks to improve energy efficiency." Doctoral thesis, University of Cape Town, 2007. http://hdl.handle.net/11427/5084.
Full textAbstract:
Includes bibliographical references (leaves 161-172).Many clustering algorithms have been proposed to improve energy efficiency of ad hoc networks as this is one primary challenge in ad hoc networks. The design of these clustering algorithms in sensor networks is different from that in mobile ad hoc networks in accordance with their specific characteristics and application purposes. A typical sensor network, which consists of stationary sensor nodes, usually has a data sink because of the limitation on processing capability of sensor nodes. The data traffic of the entire network is directional towards the sink. This directional traffic burdens the nodes/clusters differently according to their distance to the sink. Most clustering algorithms assign a similar number of nodes to each cluster to balance the burden of the clusters without considering the directional data traffic. They thus fail to maximize network lifetime. This dissertation proposes two clustering algorithms. These consider the directional data traffic in order to improve energy efficiency of homogeneous sensor networks with identical sensor nodes and uniform node distribution. One algorithm is for sensor networks with low to medium node density. The other is for sensor networks with high node density. Both algorithms organize the clusters in such a way that the cluster load is proportional to the cluster energy stored, thereby equalizing cluster lifetimes and preventing premature node/cluster death. Furthermore, in a homogeneous sensor network with low to medium node density, the clusterhead is maintained in the central area of the cluster through re-clustering without ripple effect to save more energy. The simulation results show that the proposed algorithms improve both the lifetime of the networks and performance of data being delivered to the sink. A typical mobile ad hoc network, which usually consists of moveable nodes, does not have a data sink. Existing energy-efficient clustering algorithms maintain clusters by periodically broadcasting control messages. In a typical mobile ad hoc network, a greater speed of node usually needs more frequent broadcasting. To efficiently maintain the clusters, the frequency of this periodic broadcasting needs to meet the requirement of the potentially maximum speed of node. When the node speed is low, the unnecessary broadcasting may waste significant energy. Furthermore, some clustering algorithms limit the maximum cluster size to moderate the difference in cluster sizes. Unfortunately, the cluster sizes in these algorithms still experience significant difference. The larger clusters will have higher burdens. Some clustering algorithms restrict the cluster sizes between the maximum and minimum limits. The energy required to maintain these clusters within the maximum and minimum sizes is quite extensive, especially when the nodes are moving quickly. Thus, energy efficiency is not optimized.
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Pagonis, Meletios. "Electrical power aspects of distributed propulsion systems in turbo-electric powered aircraft." Thesis, Cranfield University, 2015. http://dspace.lib.cranfield.ac.uk/handle/1826/9873.
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The aerospace industry is currently looking at options for fulfilling the technological development targets set for the next aircraft generations. Conventional engines and aircraft architectures are now at a maturity level which makes the realisation of these targets extremely problematic. Radical solutions seem to be necessary and Electric Distributed Propulsion is the most promising concept for future aviation. Several studies showed that the viability of this novel concept depends on the implementation of a superconducting power network. The particularities of a superconducting power network are described in this study where novel components and new design conditions of these networks are highlighted. Simulink models to estimate the weight of fully superconducting machines have been developed in this research work producing a relatively conservative prediction model compared to the NASA figures which are the only reference available in the literature. A conceptual aircraft design architecture implementing a superconducting secondary electrical power system is also proposed. Depending on the size of the aircraft, and hence the electric load demand, the proposed superconducting architecture proved to be up to three times lighter than the current more electric configurations. The selection of such a configuration will also align with the general tendency towards a superconducting network for the proposed electric distributed propulsion concept. In addition, the hybrid nature of these configurations has also been explored and the potential enhanced role of energy storage mechanisms has been further investigated leading to almost weight neutral but far more flexible aircraft solutions. For the forecast timeframe battery technology seems the only viable choice in terms of energy storage options. The anticipated weight of the Lithium sulphur technology is the most promising for the proposed architectures and for the timeframe under investigation. The whole study is based on products and technologies which are expected to be available on the 2035 timeframe. However, future radical changes in energy storage technologies may be possible but the approach used in this study can be readily adapted to meet such changes.
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Lee, Etty J. (Etty Joanne). "Free-space optical networks : fade and interference mitigation and network congestion control." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/60154.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 337-341).
Optical communication through the atmospheric channel is commonly known as free-space optical (FSO) communication. When communicating through a clear FSO channel, not only is there atmospheric turbulence which results in fading of the received signal, but there may also be interference that scatters into the receiver and deteriorates performance. In this thesis, we consider mitigating the fading and interference with diversity coherent and diversity incoherent detection. We derive the performance of diversity coherent and diversity incoherent receivers in the presence of fading and various worst case interference types. Diversity coherent detection provides significant power gain over diversity direct detection, and most of the benefit can be achieved with a moderate amount of diversity. Moreover, diversity always improves the performance of coherent detection, whereas diversity improves the performance of direct detection only until an optimal diversity value, beyond which it degrades the performance. We also derive the improvement in expected outage length with diversity, and quantify the amount of interference that the system can handle while still achieving a given outage probability. Although signal fades or 'outages' in an FSO link can be mitigated on the Physical Layer, they cannot be completely eliminated. In a free-space optical network, these outages affect the performance and design of the Transport Layer. The effect of outages on the TCP sender is to diminish its throughput significantly due to drastic reduction of its rate when its packets do not get received through the outage. We consider a class of TCP-based protocols that is better suited for free-space optical networks. In particular, the protocols in this class have the sender distinguish whether a packet loss is due to an outage or congestion and not reduce its rate if the loss was due to an outage. We analyze, using an approximate channel model for FSO links, the maximum performance that can be achieved by a sender in this class, and compare the performance against a TCP sender's performance. The protocols in this class can gain back the performance loss in TCP due to link outages and they are particularly beneficial when the path has FSO links with strong turbulence and large bandwidth-delay product. We discuss a possible way to implement the distinguishing of packet loss due to congestion from packet loss due to link outage.
by Etty J. Lee.
Ph.D.
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Gudapati, Supriya. "Securing mobile ad hoc networks." Thesis, California State University, Long Beach, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1604882.
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Wireless sensor networks has been growing rapidly over the past few decades. Due to their flexibility, wireless sensor networks have been in practice in many areas. Unlike other network architectures, Mobile Ad hoc networks (MANETs) have no central architecture; every node is free to work both as a transmitter and receiver and it depends on neighboring nodes to send relay messages. Due to their advantages, MANETs are used in many different applications like health care and military. However the wide distribution of MANETs makes it vulnerable to malicious attacks. Hence it is necessary to design a secure system for MANETs. In this report, we implement a secure system named Enhanced Adaptive Acknowledgement especially for MANETs. To ensure higher security and reduce the network overhead and delay, we use a different approach called hybrid cryptography in our proposed scheme. Enhanced Adaptive Acknowledgment detects higher malicious attackers without greatly disturbing the network performances. In the simulation we compare the differences within the Enhanced Adaptive Acknowledgment (EAACK) before and after introducing the Hybrid cryptography approach.
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Mismar, Thabet. "Cooperative Localization in Cellular Networks." University of Toledo / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1430155461.
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Nejatali, Abdolhossein. "Electrical impedance tomography with neural networks and fuzzy sets." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq23645.pdf.
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Jombert, Alice Stécy. "Electrical properties of various single-wall carbon nanotube networks." Thesis, Durham University, 2010. http://etheses.dur.ac.uk/7/.
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This thesis investigates conduction mechanisms of covalently and non covalently functionalised single wall carbon nanotube (SWCNT) networks. Unlike previous strategies where diamines were used, a novel route to covalently bridge SWCNTs by organic molecular linkers is proposed. The bridging relies on using modified Sonogashira and Ullmann couplings, which have the advantage of using spectroscopic evidence to ascertain the success of the bridging. Platinum-enriched SWCNTs were produced by coordinating Pt to pyridine ligands grafted on SWCNTs. Networks of covalently bridged SWCNTs, Pt-enriched SWCNTs and their SWCNT precursors were fabricated by vacuum filtration. In addition to these networks, networks of non covalent ly functionalised SWCNTs were built up using layer-bylayer (LbL) deposition. This second approach required the wrapping up of SWCNTs by ionic surfactants to exploit their electrostatic interactions. Electrical properties, such as current- voltage and the current dependence on temperature and electrode separation are discussed for both filtered SWCNT and SWCNT LbL networks. Combined analyses of these characteristics were carried out to identify dominant conduction mechanisms. In this study, a modified quantum tunnelling model was proposed to best describe the in-plane electrical behaviour of the filtered SWCNT networks. As for SWCNT LbL networks, the in-plane conduction was shown to be governed by the Poole-Frenkel mechanisms while direct tunnelling dominates the out-of-plane conduction. Furthermore, the charge storage capacity of cut-SWCNT LbL networks integrated into metal- insulator-semiconductor devices are discussed in view of organic memory device applications.
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Marguet, Raphaël. "Improved fault localization method for electrical power distribution networks." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GRENT015/document.
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Ces travaux proposent des améliorations de méthodes de localisation desdéfauts électriques sur les réseaux électriques de distribution. Les réseaux de transportont rapidement été instrumenté en élément de protection. En effet, un incident survenantsur le réseau de transport peut entrainer de graves conséquences s’il n’est pas traité rapidement.Les réseaux de distribution quand à eux possèdent un schéma de protectionminimal. Cependant le développement des smart grids (ou réseaux intelligents) amène denouvelles possibilités avec l’ajout d’équipements de mesures sur le réseau de distribution.Les travaux présentés dans cette thèse développent deux méthodes de localisation de défaut.La première permet de mieux utiliser l’équipement déjà en place (indicateurs depassage de défaut) afin d’isoler de manière rapide et fiable la zone concernée par le défaut.La deuxième permet une localisation précise (en distance) des différents lieux de défautspossibles à partir de mesures électriquesThis thesis proposes to improve fault localization methods for electricalpower distribution networks. Transmission networks were quickly equipped with protectionand fault localization equipments. Indeed, faults on the transmission network need tobe dealt with quickly in order to avoid serious consequences. Unlike transmission networks,distribution networks have a minimal protection scheme. The smart grid developmentsbring new possibilities with the installation of new equipments giving access to many newvariables. The work presented in this thesis develop two fault localization method. Thefirst aims in using the equipment already installed (fault indicators) in order to isolatequickly and efficiently the zone concerned by the fault. The second method performs aprecise localization (in distance) of the different possible fault locations from the electricalmeasurements made on the network
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Bidin, Abdul Rahman. "Electrodynamic sensors and neural networks for electrical charge tomography." Thesis, Sheffield Hallam University, 1993. http://shura.shu.ac.uk/19355/.
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This research into the feasibility of imaging particulate processes using electrical charge tomography investigates four techniques: the multi-sensing of electrical charge in a cross-section, a neural network based classifier for flow regime identification, cross correlation based velocity determination and spectral analysis of electrodynamic signals. A single charged-particle model is developed to simulate the induction effect on a sensor by a charge. The spatial representation of the voltage induced onto sixteen sensors, placed on the boundary of a circular pipe, gives a flow distribution profile over the cross-section. A two charged-particle model is developed to simulate the electrodynamic effect of two particles on a tomographic sensor configuration. As in the single particle model, a spatial representation of the voltages induced onto the sensors is presented. This voltage profile is due to the combined effects of position and charge of the two particles. A multi-particle model is developed to predict the voltage profile of several flow regimes: full, annular, core, half and stratified. The model is extended to provide the loading and concentration of a given flow. A measurement system is constructed consisting of sixteen sensors equally spaced around the boundary of a circular 100mm pipe. Measurements on a bead drop system are designed to verify the single particle model. A sand flow system, consisting mainly of 300 micron sized particles, is used for measurements of the induced voltages due to different flow regimes. The latter are created artificially by using baffles of different shapes that obstruct the sand flow. The voltage profile from the sixteen sensors gives spatial information about the flow regime. These voltage profiles are normalised into patterns that are presented to a Kohonen neural network for classification. Two regime classification between well differentiated regimes gives an accuracy of identification of 95%. This is expanded to provide classification of three regimes with more variability in the input patterns giving success rates between 50% to 70%. A power spectral density analysis of the measured electrodynamic signals gives observable features for particle characterisation during flow. In full flow, with no baffles obstructing the sand flow, a consistently high frequency spectra of 550Hz is observed. At flow rates above 0.540 kgs-1, the frequency spectra shifts to a lower range of 200Hz. In obstructed flow, such as in stratified regime, an inhomogeneous phase is inferred from the drop in frequency of the power spectra at relatively low flowrates (0.36kgs-1). These results suggest a relationship between the observed spectra and the phenomenon of clustering of particles at higher concentrations. The potential of electrodynamic spectroscopy for particle characterisation in terms of size distribution is discussed. Knowledge of flow regime voltage profile, regime identification and concentration provided a basis for an empirically based image reconstruction algorithm. Finally the achievements of the thesis are discussed and suggestions made for further work.
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Van, den Berg Claire Barbara. "Structural and electrical characteristics of printed metal nanoparticle networks." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/22914.
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The structural and electrical properties of metal nanoparticle (NP) networks and their dependence on the constituent phases have been investigated. Percolation and effective media theories have been used to describe the physical properties of disordered systems, as well as providing a link between their structural features and the corresponding electrical transport properties. Silver and palladium nanoparticulate layers in ethyl cellulose polymer binder (ETHOCELTM), were fabricated onto paper using the method of screen printing. The metal-binder ratios were varied in order to observe changes in the microstructure when a percolating network consisting of the metal NPs is formed through the layer.
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Rogers, Daniel J. "Hybrid and thin power electronics for electrical power networks." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/6836.
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A new hybrid diverter design for an On-Load Tap Changer (OLTC) is presented and experimentally validated. The design differs from existing semiconductor-assisted OLTC systems in that the part of the system containing semiconductor devices is connected in a purely shunt con guration to the main current path, resulting in a system that is electrically robust and very low loss. The new design provides zero-current, zero-voltage operation of both diverter switches at all times, eff ectively eliminating arc-induced contact wear. Contact lifetime of over twenty-five million operations is demonstrated. Contact wear rates under the new design are compared experimentally with those under alternative contact protection schemes and are shown to be dramatically reduced. A fast electromechanical switch intended for use under the new hybrid diverter is presented. The low-wear conditions created by the new diverter allows a dramatic reduction in the switch moving mass when compared to that of the standard OLTC, allowing sub-half-cycle actuation times to be achieved. A study of switch topology is made in order to guide the design process. An analysis of a magnetic actuator providing both high actuation and static contact forces is also presented. In a second strand of this thesis, a general method of formulating optimal modulation problems for thin power electronic systems incorporating a buck converter is presented. The method is employs a frequency domain representation of the buck converter where the describing equations are formed into a square matrix relating a set of input harmonics to sets of output harmonics. This allows the interaction between the buck converter and a set of linear filters to be modelled in a systematic way. Two example circuits, the Inverter-Less Active Filter and the Controllable Network Transformer, are used as example problems. The use of general-purpose optimisation software for finding optimal modulation waveforms for these circuits is demonstrated.
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Guldbrand, Anna. "Earth faults in extensive cable networks : electrical distribution systems /." Lund : Department of measurement technology and industrial electrical engineering, Lund University, 2009. http://www.iea.lth.se.
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Zhang, Chenghua. "Peer-to-peer energy trading in electrical distribution networks." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/109074/.
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In response to the challenges posed by the increasing penetration of distributed generation from renewable energy sources and the increasing electricity retail prices with decreasing Feed-In Tariff rates, a new energy trading arrangement, “peer-to-peer (P2P) energy trading” has been proposed. It refers to the direct energy trading among consumers and prosumers in distribution networks, which is developed based on the “P2P economy” concept (also known as sharing economy). A hierarchical system architecture model has been proposed in order to identify and categorise the key elements and technologies involved in P2P energy trading. A P2P energy trading platform called “Elecbay” is designed. The P2P bidding is simulated using game theory. Test results in a grid-connected LV Microgrid with distributed generators and flexible demands show that P2P energy trading is able to improve the local balance of energy generation and consumption, and the enhanced variety of peers is able to further facilitate the balance. Two necessary control systems are proposed for the Microgrid with “Elecbay”. A voltage control system which combines droop control and on-load-tap-changer (OLTC) control is designed and simulated. Simulation results show that the proposed voltage control system is sufficient for supporting the P2P energy trading in the Microgrid. The total number of operation times of the OLTC is reduced with P2P energy trading compared to the reference scenario. The information and communication technology (ICT) infrastructures for the P2P bidding platform and the voltage control system are investigated. The information exchange among peers and other parties (Elecbay, distribution system operators, etc.) is designed based on TCP/IP protocol. Existing and private communication networks with different communication medium, bandwidths, etc., are modelled. Simulation results show that the existing ICT infrastructures are sufficient for supporting both the P2P energy trading platform and the voltage control system. Therefore, no large amount of additional investments are required.
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Andersen, David G. (David Godbe) 1975. "Resilient overlay networks." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/86657.
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Sloan, Cooper Stokes. "Neural bus networks." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/119711.
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Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 65-68).
Bus schedules are unreliable, leaving passengers waiting and increasing commute times. This problem can be solved by modeling the traffic network, and delivering predicted arrival times to passengers. Research attempts to model traffic networks use historical, statistical and learning based models, with learning based models achieving the best results. This research compares several neural network architectures trained on historical data from Boston buses. Three models are trained: multilayer perceptron, convolutional neural network and recurrent neural network. Recurrent neural networks show the best performance when compared to feed forward models. This indicates that neural time series models are effective at modeling bus networks. The large amount of data available for training bus network models and the effectiveness of large neural networks at modeling this data show that great progress can be made in improving commutes for passengers.
by Cooper Stokes Sloan.
M. Eng.
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Albrecht, Frederick Mark. "Using fuzzy logic for congestion control at the user-network interface of asynchronous transfer mode networks." Master's thesis, University of Cape Town, 1997. http://hdl.handle.net/11427/22459.
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The aim of this thesis was to design a fuzzy logic controller that could be used to prevent congestion in Asynchronous Transfer Mode networks. The controller would be located at the User-Network Interface of the network and would be used to monitor the incoming traffic. The control action would be to allow conforming traffic through to the network unmodified, while tagging or dropping non-conforming traffic. Three fuzzy logic controllers are presented, the latter two being improvements on design(s) that preceded it. All three controllers are designed to police the sustainable cell rate of Variable Bit Rate (VBR) traffic sources, and take the Sustainable Cell Rate and Peak Cell Rate as input Parameters. The first two controllers require an additional parameter called the Burst Threshold, while the third controller takes the Initial Burst Size as its third traffic parameter. The controllers then continuously analyse the state of the traffic by applying a set of rules that it was given and decides whether the source is conforming or non-conforming, taking corrective action if required. The first controller included two buffers that were used to determine the state of the connection. It was however found that it would be too difficult to determine what sizes to make those buffers, and therefore that design was abandoned in favour of the second controller. The second controller eliminated the need for buffers in the design, while still being able to tag or drop non-conforming cells and allowing conforming cells through unmodified. This was done by including a token leaky bucket in the design and modifying the fuzzy sets and rule base of the fuzzy logic engine accordingly. A
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Zacot, Chimi I. "Shipboard wireless sensor networks utilizing Zigbee technology." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Sep%5FZacot.pdf.
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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, September 2006.Thesis Advisor(s): Xiaoping Yang. "September 2006." Includes bibliographical references (p. 59). Also available in print.
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Thouin, Frédéric. "Bayesian inference in networks." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104476.
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Bayesian inference is a method that can be used to estimate an unknown and/or unobservable parameter based on evidence that is accumulated over time.In this thesis, we apply Bayesian inference techniques in the context of two network-based problems.First, we consider multi-target tracking in networks with superpositional sensors, i.e., sensors that generate measurements equal to the sum of individual contributions of each target.We derive a tractable form for a novel moment-based multi-target filter called the Additive Likelihood Moment (ALM) filter. We show, through simulations, that our particle approximation of the ALM filter is more accurate and computationally efficient than Markov chain Monte Carlo-based particle methods to perform radio-frequency (RF) tomographic tracking of multiple targets.The second problem we study is multi-path available bandwidth estimation in computer networks.We propose a probabilistic-rate-based definition for the available bandwidth, probabilistic available bandwidth (PAB), that addresses flaws of the classical utilization-based definition and existing estimation tools. We design a network-wide estimation tool that uses factor graphs, belief propagation and adaptive sampling to minimize the overhead. We deploy our tool on the Planet Lab network and show that it can produce accurate estimates of the PAB and achieve significant gains (over 70%) in terms of measurement overhead and latency over a popular estimation tool (Pathload). We extend our tool to i) track PAB in time and ii) use chirps to further reduce the number of required measurements by over 80%. Our simulations and online experiments demonstrate that our tracking algorithm is more accurate than block-based approaches without any significant additional complexity.L'inférence bayésienne est une méthode qui peut être utilisée pour estimer des paramètres inconnus et/ou inobservables à partir de preuves accumulées au fil du temps. Dans cette thèse, nous appliquons les techniques d'inférence bayésienne à deux problèmes de réseautique.Premièrement, nous considérons la poursuite de plusieurs cibles dans des réseaux de capteurs où les mesures générées sont égales à la somme des contributions individuelles de chaque cible. Nous obtenons une forme traitable pour un filtre multi-cibles appelé filtre Additive Likelihood Moment (ALM). Nous montrons, au moyen de simulations, que notre approximation particulaire du filtre ALM est plus précise et efficace que les méthodes particulaires de Monte-Carlo par chaînes de Markov pour effectuer une poursuite tomographique de plusieurs cibles à l'aide de radiofréquences.Le deuxième problème que nous étudions est l'estimation simultanée pour plusieurs chemins de bande passante disponible dans les réseaux informatiques. Nous proposons une définition probabiliste de la bande passante disponible, probabilistic available bandwidth (PAB), qui vise a corriger les failles de i) la définition classique fondée sur l'utilisation et ii) des outils d'estimation existants. Nous concevons un outil d'estimation pour l'ensemble du réseau qui utilise les réseaux bayésiens, la propagation de croyance et d'échantillonnage adapté pour minimiser le surdébit. Nous validons notre outil sur le réseau Planet Lab et montrons qu'il peut produire des estimations précises de la PAB et procure des gains significatifs (plus de 70%) en termes de surdébit et de latence en comparaison avec un outil d'estimation populaire (Pathload). Nous proposons ensuite une extension à notre outil pour i) suivre la PAB dans le temps et ii) utiliser les ``chirps'' pour réduire davantage le nombre de mesures requises par plus de 80%. Nos simulations et expériences en ligne montrent que notre algorithme de suivi est plus précis, sans complexité supplémentaire notable, que les approches qui traitent l'information en bloc sans modèle dynamique.
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Sharma, Divya Alok. "Routing in opportunistic networks." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=121530.
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Opportunistic networking is employed in scenarios where end-to-end communication paths between nodes cannot be assumed due to continuously changing network topology. In these networks, data is routed in a "store-carry-forward" fashion by exploiting the transient communication opportunities that arise when mobile nodes equipped with short-range wireless interfaces come within each other's transmission range. Designing efficient routing schemes for opportunistic networks is challenging as they face a trade-off between delivery performance and resource consumption. In this thesis, we propose a novel opportunistic routing algorithm that addresses this trade-off by incorporating information about the node contact pattern in the network. Aggregating contact events into a weighted graph enables us to detect communities and learn about the neighbourhoods of nodes. This information is utilized by our algorithm to assess the usefulness of every forwarding opportunity that arises. Performance evaluation of the proposed algorithm shows that it is capable of achieving good delivery performance while consuming significantly fewer resources in comparison to the existing opportunistic routing algorithms.Le réseautage opportuniste est utilisé dans les scénarios où l'existence de routes de communication entre agents ne peut pas être présumé dû à l'altération constante de la topologie du réseau. Dans ces réseaux, l'information est acheminée grâce à une procédure de "sauvegarde-report" qui exploite les opportunités de communication transitoires qui ont lieu lorsque des agents équippés d'interface sans-fil à petite portée entrent dans leurs périmètres de portée respectifs. Établir des plans de communication efficaces dans le contexte de réseaux opportunistes est un défi puisque ceux-ci font face à un compromis entre performance de livraison et consommation de ressources. Dans cette thèse, nous proposons un algorithme de routage opportuniste original qui addresse ce compromis en incorporant l'information liée aux contacts entre noeuds du réseau. Assembler les évènements de contacts dans un graphe pondéré nous permet de détecter les communautés et d'apprendre le voisinage de chaque noeud. Cette information est utilisée par notre algorithme afin d'évaluer l'utilité de chaque opportunité de communication qui se présente. Une analyse de la performance de l'algorithme proposé montre qu'il est capable d'atteindre une bonne performance de livraison tout en consommant significativement moins de ressources lorsque comparé aux algorithmes de routage opportuniste actuels.
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Dai, Lillian Lei 1978. "Proactive mobile wireless networks : an infrastructureless wireless network architecture for delay-sensitive applications." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44409.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 197-213).
Infrastructureless wireless networks are an important class of wireless networks that is best suited for scenarios where there is temporary and localized telecommunication demand. Such networks consist of wireless devices that can form a network autonomously without the need for pre-deployed telecommunication infrastructures such as base-stations and access points. Over the past several decades, significant research and development efforts have been devoted to a particular type of infrastructureless wireless networks called mobile ad hoc wireless networks (MANETs). In addition to autonomous network formation, wireless devices in MANETs have routing capabilities and help one another to forward information in a multihop fashion. The applications envisioned for MANETs include communication during disaster relief, search and rescue, and small tactical unit operations where the existing telecommunication infrastructures may be destroyed or are unavailable. While significant strides have been made in all aspects of MANET networking, adoption of such technology has been limited to date despite its potential. We believe that this lack of adoption is due to a fundamental mismatch between application demands and the MANET network architecture. While the flexibility of anytime and anywhere communication offered by MANETs is appealing, these networks are not designed to provide assured service for delay-sensitive applications such as communication during a search and rescue mission or in a battlefield. In fact, MANETs may be frequently disconnected due to mobility and/or device failure. Such disconnections may persist for an unacceptable length of time, during which, there may be loss of critical time-sensitive information and degraded network performance due to mismatches to routing and transport layer protocols.
(cont.) To provide service assurance in these scenarios, it is insufficient to limit technical improvements to the traditional networking layers (such as power control, coding, or routing) since network disconnections may still occur. We argue that a Proactive Wireless Network Architecture is needed - one that proactively maintains network connectivity in order to provide assured message delivery for applications with high quality of service (QoS) demands. The two key features of a proactive wireless network are: (1) Network disconnection prediction via localization, trajectory prediction, and large-scale channel estimation and (2) Network topology control via the adaptive deployment of additional wireless devices, called helper nodes, and by proactively controlling their movements toward regions of predicted disconnections prior to the occurrence of such disconnections. Hence, unlike MANETs, proactive wireless networks are designed to anticipate and respond to network disconnection events via active connectivity maintenance with helper nodes, thereby preventing network disruptions and message loss. In this dissertation, we present the proposed proactive wireless network architecture, quantify operating scenarios where the proposed network architecture is a sensible choice, and present system-level performance analyses under various helper node deployment schemes.
by Lillian Lei Dai.
Ph.D.
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Lin, Katherine Xiaoyan. "Green optical network design : power optimization of wide area and metropolitan area networks." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/66434.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 133-134).
Advancements in technology are fueling huge growth in network traffic capacity. Demand for low cost, reliable, and high bitrate transmissions grows 40-110% internationally every year. To date, most research has focused on cost minimization of wide area and metropolitan area networks. In this thesis, we concentrate instead on finding scalable WAN designs with respect to power constraints and optimal MAN topologies with minimal capital and operating expenditures. We find optical bypass networks to be most scalable with respect to power consumption, especially when quality of service and network flexibility, reliability, and protection are considered. The power consumption of the standard bypass network can be lowered further through a hybrid design in which whole wavelengths of core, stable traffic between node pairs are routed via direct, fixed lightpaths using patch panelling and unexpected, bursty traffic is switched on a standard optical bypass network. We analyze power distribution among components and find the OXC switch most scalable at each node and O/E/O switches and routers wasteful. Finally, we prove that shortest path and minimum hop routing is power optimal and traffic balanced routing should be avoided. We approximate MAN topologies with regular graphs for tractable analysis. We augment a previous cost-based joint optimization formulation [13] with power expenditure modelling and obtain closed form solutions for optimal node degree and normalized network costs. We find that the optimal node connectivity increases 20-25% due to the added operating expenditures. Normalized network cost and normalized network cost per unit traffic also rise by approximately 25%. Our results show that the Generalized Moore graph with node degree between 0.05N and 0.08N is both power and cost minimal for a purely optical network.
by Katherine Xiaoyan Lin.
M.Eng.
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Rezaee, Arman. "Network coding, multi-packet reception, and feedback : design tools for wireless broadcast networks." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/68508.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 89-92).
In this thesis, we address the combination of three technologies in wireless broadcast networks: network coding, multi-packet reception (MPR) and feedback. We will primarily discuss the performance of a single-hop network, both with and without these technologies. A single-hop network can be used as a building block for larger and more topologically diverse networks and provides a basis for analyzing the interaction of these mechanisms. Because many applications are interested in speedy transmission of data, we have focused our attention on answering the question of how to optimally use these technologies in order to reduce the overall transmission time. Initially, we consider a fully connected network and show that MPR capability of m can reduce the total time for a file transfer by as much as a factor of m/2 without network coding. We emphasize that a two-fold MPR capability will not reduce the total dissemination time without network coding and is thus ineffective. We also show that no gain can be obtained, if network coding is used without MPR. However the combination of network coding and MPR can reduce the total transfer time by as much as a factor of m. We then consider transmission of a file over a broadcast erasure channel with a potentially large number of receivers. Noting that traditional reliable multicast protocols suffer from the inevitable feedback implosion associated with servicing a large number of receivers, we present a novel feedback protocol dubbed SMART, Speeding Multicast by Acknowledgment Reduction Technique. The protocol involves an asymptotically optimal predictive model which determines a suitable feedback time that assures most receivers have completed the download. We also introduce a new single slot feedback mechanism, which enables any number of receivers to give their feedback simultaneously. We show that scheduling the feedback according to this predictive model and enhancing the protocol by the single slot mechanism reduces the feedback traffic as well as transmission of extraneous coded packets, and will provide a good completion time characteristic for all users. We show that counter to conventional wisdom, Quality of Experience (QoE) of multicast sessions is not sensitive to the number of users, however it is very sensitive to imbalanced effective rate and heterogeneity among users. Furthermore, we show that SMART performs nearly as well as an omniscient transmitter that requires no feedback.
by Arman Rezaee.
S.M.
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Ganti, Sudhakar N. M. "Access protocols and network architectures for very high-speed optical fiber local area networks." Thesis, University of Ottawa (Canada), 1993. http://hdl.handle.net/10393/6917.
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The single mode optical fiber possesses an enormous bandwidth of more than 30 THz in the low-loss optical region of 1.3 $\mu$m and 1.5 $\mu$m. Through Wavelength Division Multiplexing (WDM), the optical fiber bandwidth can be divided into a set of high-speed channels, where each channnel is assigned its own unique wavelength. An M x M passive optical star coupler is a simple broadcast medium, in which light energy incident at any input is uniformly coupled (or distributed) to all the outputs. Thus, a passive star along with the WDM channels can be used to configure a Local Area Network (LAN). In this LAN, users require tunable devices to access a complete or a partial set of the WDM channels. Due to these multiple channels, many concurrent packet transmissions corresponding to different user pairs are possible and thus the total system throughput can be much higher than the data rates of each individual channel. To fairly arbitrate the data channels among the users, media access protocols are needed. Depending upon the number of data channels and the number of users, two possible situations arise. In the first case, the number of users is much larger than the number of data channels and in the second, the number of users equals to the the number of channels. In both cases, data channel contention may arise if multiple users access the same given channel and must be resolved. This thesis proposes media access protocols for passive optical star networks. All the proposed protocols are slotted in nature, i.e., the time axis on each channel is divided into slots. The well known Slotted-ALOHA and Reservation ALOHA protocols are extended to the multi channel network environment. The thesis also proposes switching protocols (equal number of channels and users), contention-based reservation protocols for this network architecture. To interconnect these star networks, a multi-control channel protocol is also proposed along with two interconnecting techniques. Since there are multiple data channels, the data packets on different channels may be destined to the same user. However, if the user is equipped with only one receiver, the user can receive only one packet and ignores others. This is called a 'receiver collision' and the thesis also studies the effect of these receiver collisions on the data channels. Two network architectures, one for a packet circulating ring network and the other for a circuit switched application are described. Finally, the thesis studies some implementation considerations for these protocols.
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Nagarajan, Ramprasad. "MPLS Rerouting for Next Generation Networks." The Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1419350248.
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