Página 13 dos resultados de 2591 itens digitais encontrados em 0.033 segundos

## Control schemes for real-time communication in high-speed networks; Control schemes in high speed real-time communication networks

Shen, Li-Tao
Tipo: Artigo de Revista Científica Formato: vi, 118 leaves : ill. ; 29 cm.
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(Thesis) Thesis (Ph. D.)--University of Florida, 1992.; (Bibliography) Includes bibliographical references (leaves 111-117).; Typescript.; Vita.; (Statement of Responsibility) by Li-Tao Shen.

## Using Predictable Observer Mobility for Power Efficient Design of Sensor Networks

Chakrabarti, Arnab; Sabharwal, Ashutosh; Aazhang, Behnaam; Chakrabarti, Arnab; Sabharwal, Ashutosh; Aazhang, Behnaam
Tipo: Conference paper
Português
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Conference Paper; In this paper, we explore a novel avenue of saving power in sensor networks based on predictable mobility of the observer (or data sink). Predictable mobility is a good model for public transportation ve- hicles (buses, shuttles and trains), which can act as mobile observers in wide area sensor networks. To understand the gains due to predictable mobility, we model the data collection process as a queuing system, where random arrivals model randomness in the spatial distribution of sensors. Using the queuing model, we analyze the success in data collection, and quantify the power consumption of the network. Even though the mod- eling is performed for a network which uses only single hop communi- cation, we show that the power savings over a static sensor network are significant. Finally, we present a simple observer-driven communication protocol, which follows naturally from the problem formulation and can be used to achieve the predicted power savings.

## Cognitive Blind Interference Alignment for Macro-Femto Cellular Networks

Morales Céspedes, Máximo; Plata, J.; Toumpakaris, D.; García-Armada, Ana
Fonte: IEEE - The Institute of Electrical and Electronics Engineers, Inc Publicador: IEEE - The Institute of Electrical and Electronics Engineers, Inc
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/bookPart; info:eu-repo/semantics/conferenceObject
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A cognitive Blind Interference Alignment scheme is devised for use in macro-femto cellular networks. The proposed scheme does not require any channel state information at the transmitter or data sharing among the Macro Base Station and the Femto Access Points. It achieves transmission to femto cell users without affecting the rates of the Macro users. This is achieved by appropriately combining the supersymbols of the Macro Base Stations and the Femto Access Points. It is shown that in some scenarios the use of this scheme results to considerable rates for Femto users.; This work has been partially funded by research projects COMONSENS (CSD2008-00010) and GRE3N (TEC2011-29006-C03-02). † This research work was partly carried out at the ESAT Laboratory of KU Leuven in the frame of the Belgian Programme on Interuniversity Attractive Poles Programme initiated by the Belgian Science Policy Office: IUAP P7/23 ‘Belgian network on stochastic modeling analysis design and optimization of communication systems’ (BESTCOM) 2012-2017.; The proceeding at: 2014 IEEE Global Communications Conference took place 8-12 December 2014 in Austin, TX, USA.

## Energy conservation in wireless sensor networks

Vincent, Patrick J.
Formato: xviii, 182 p.: ill. ; 28 cm.
Português
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This dissertation presents a system-level approach for minimizing the power expended in achieving communication between a ground-based sensor network and an overhead Unmanned Aerial Vehicle (UAV). A subset of sensor nodes, termed a transmit cluster, aggregates data gathered by the network and forms a distributed antenna array, concentrating the radiated transmission into a beam aimed towards the UAV. We present a method for more uniformly distributing the energy burden across the sensor network, specifying the time that should elapse between reassignments of the transmit cluster and the number of hops that should be placed between successive transmit clusters. We analyze the performance of two strategies for reconfiguring the communication burden between the sensor network and the UAV in order to bring the UAV and the sensor network's beam into alignment quickly, while minimizing the energy expenditure. We analyze the optimal number of nodes that should participate in a beamforming process in order to minimize the energy expended by the network, and we provide a framework to analyze the minimum energy expended in a simple beamforming algorithm. Finally, we analyze the probability that an arbitrarily selected sensor node is connected to a specified number of other nodes and we present an algorithm for the formation of near-linear arrays given random placement of nodes.

## Exploiting Feedback in Cooperative Relay Networks

Ahmed, Nasir; Ahmed, Nasir
Tipo: Thesis; Text; Text
Português
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PhD Thesis; Recent results on multiple antenna transmission techniques have shown great po- tential in their ability to improve the overall performance in fading channels. Despite the promise shown by employing multiple antenna's, practical implementations may not be feasible due to size and hardware limitations of mobile nodes. Cooperative Cod- ing is a new transmission paradigm which pools together the resources of neighboring nodes in a network to improve performance without requiring multiple antennas at any of the mobile devices. The power of node collaboration can be seen by considering the relay channel, the simplest cooperative network. Recently, protocols have been developed for the wireless relay channel that allow the network to behave as a virtual multiple antenna system. In this thesis we show that in addition to eÂ±cient network protocols, exploit- ing channel state information can yield even more performance in the relay setting by allowing for temporal power and rate control. When power control is used for a given transmission rate, minimizing the outage probability is the appropriate method to maximize performance in the block fading channel. In a relay setting, we derive the optimal power control strategy when the transmitters in the network have perfect knowledge of the network channel state. In practice having perfect channel state knowledge at the transmitters is not possible. In this direction...

## Trajectory Privacy Preservation in Mobile Wireless Sensor Networks

Jin, Xinyu
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Português
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In recent years, there has been an enormous growth of location-aware devices, such as GPS embedded cell phones, mobile sensors and radio-frequency identification tags. The age of combining sensing, processing and communication in one device, gives rise to a vast number of applications leading to endless possibilities and a realization of mobile Wireless Sensor Network (mWSN) applications. As computing, sensing and communication become more ubiquitous, trajectory privacy becomes a critical piece of information and an important factor for commercial success. While on the move, sensor nodes continuously transmit data streams of sensed values and spatiotemporal information, known as trajectory information". If adversaries can intercept this information, they can monitor the trajectory path and capture the location of the source node. This research stems from the recognition that the wide applicability of mWSNs will remain elusive unless a trajectory privacy preservation mechanism is developed. The outcome seeks to lay a firm foundation in the field of trajectory privacy preservation in mWSNs against external and internal trajectory privacy attacks. First, to prevent external attacks, we particularly investigated a context-based trajectory privacy-aware routing protocol to prevent the eavesdropping attack. Traditional shortest-path oriented routing algorithms give adversaries the possibility to locate the target node in a certain area. We designed the novel privacy-aware routing phase and utilized the trajectory dissimilarity between mobile nodes to mislead adversaries about the location where the message started its journey. Second...

## Doing Business 2014 Economy Profile : Azerbaijan

World Bank; International Finance Corporation
Fonte: World Bank Group, Washington, DC Publicador: World Bank Group, Washington, DC
Tipo: Publications & Research :: Working Paper; Publications & Research
Português
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This economy profile presents the Doing Business indicators for Azerbaijan. In a series of annual reports, Doing Business assesses regulations affecting domestic firms in 189 economies and ranks the economies in 10 areas of business regulation, such as starting a business, resolving insolvency and trading across borders. This year's report data cover regulations measured from June 2012 through May 2013. The report is the 11th edition of the Doing Business series.

## Cognitive Diversity Routing in Wireless Sensor Networks

EL-JABI, ZOUHEIR,
Fonte: Quens University Publicador: Quens University
Português
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Energy efficiency and network lifetime are key factors in characterizing wireless sensor networks due to the nodes having a finite and exhaustible source of energy. Due to the nodes limited energy, it is vital to have the node functioning for as long as possible otherwise it will render the technology futile. Transmission is the most energy consuming activity a node undertakes, therefore by decreasing the number of unnecessary transmissions, the energy consumption in the nodes decreases significantly. In order to reduce unnecessary transmissions, energy-efficient data dissemination techniques have been developed to deliver the data using the minimum number of necessary transmissions. The topic of this thesis is to develop a routing protocol that will extend the network lifetime by introducing cognition to routing. Cognitive routing is an approach to make nodes more intelligent by utilizing information from the lower layers and network in order to make more informant decisions. Data from the physical layer can relay important information about the state of the node, its neighbors, and the surrounding environment hence enabling the node to make energy-efficient and aware decisions. The routing protocol formulates an energy profile, a channel profile and a traffic profile in order to make adapted and intelligent decisions. Diversity routing is used to increase the reliability of transmissions in the network to reduce unnecessary transmissions as communication is the primary reason for energy consumption in wireless sensor networks. Combining these two approaches in one protocol allows for cognitive routing to operate based on energy constraints obtained from the lower levels hence optimizing the process yielding a longer network lifetime.; Thesis (Master...

## Neural networks for transmission over nonlinear MIMO channels

Al-Hinai, Al Mukhtar
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 1618796 bytes; application/pdf
Português
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Multiple-Input Multiple-Output (MIMO) systems have gained an enormous amount of attention as one of the most promising research areas in wireless communications. However, while MIMO systems have been extensively explored over the past decade, few schemes acknowledge the nonlinearity caused by the use of high power amplifiers (HPAs) in the communication chain. When HPAs operate near their saturation points, nonlinear distortions are introduced in the transmitted signals, and the resulting MIMO channel will be nonlinear. The nonlinear distortion is further exacerbated by the fading caused by the propagation channel. The goal of this thesis is: 1) to use neural networks (NNs) to model and identify nonlinear MIMO channels; and 2) to employ the proposed NN model in designing efficient detection techniques for these types of MIMO channels. In the first part of the thesis, we follow a previous work on modeling and identification of nonlinear MIMO channels, where it has been shown that a proposed block-oriented NN scheme allows not only good identification of the overall MIMO input-output transfer function but also good characterization of each component of the system. The proposed scheme employs an ordinary gradient descent based algorithm to update the NN weights during the learning process and it assumes only real-valued inputs. In this thesis...

## Performance Evaluation and Comparative Analysis of SubCarrier Modulation Wake-up Radio Systems for Energy-Efficient Wireless Sensor Networks

Oller, Joaquim; Demirkol, Ilker; Casademont, Jordi; Paradells, Josep; Gamm, Gerd Ulrich; Reindl, Leonhard
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
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Energy-efficient communication is one of the main concerns of wireless sensor networks nowadays. A commonly employed approach for achieving energy efficiency has been the use of duty-cycled operation of the radio, where the node's transceiver is turned off and on regularly, listening to the radio channel for possible incoming communication during its on-state. Nonetheless, such a paradigm performs poorly for scenarios of low or bursty traffic because of unnecessary activations of the radio transceiver. As an alternative technology, Wake-up Radio (WuR) systems present a promising energy-efficient network operation, where target devices are only activated in an on-demand fashion by means of a special radio signal and a WuR receiver. In this paper, we analyze a novel wake-up radio approach that integrates both data communication and wake-up functionalities into one platform, providing a reconfigurable radio operation. Through physical experiments, we characterize the delay, current consumption and overall operational range performance of this approach under different transmit power levels. We also present an actual single-hop WuR application scenario, as well as demonstrate the first true multi-hop capabilities of a WuR platform and simulate its performance in a multi-hop scenario. Finally...

## Dense Subgraphs on Dynamic Networks

Sarma, Atish Das; Lall, Ashwin; Nanongkai, Danupon; Trehan, Amitabh
Tipo: Artigo de Revista Científica
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In distributed networks, it is often useful for the nodes to be aware of dense subgraphs, e.g., such a dense subgraph could reveal dense subtructures in otherwise sparse graphs (e.g. the World Wide Web or social networks); these might reveal community clusters or dense regions for possibly maintaining good communication infrastructure. In this work, we address the problem of self-awareness of nodes in a dynamic network with regards to graph density, i.e., we give distributed algorithms for maintaining dense subgraphs that the member nodes are aware of. The only knowledge that the nodes need is that of the dynamic diameter $D$, i.e., the maximum number of rounds it takes for a message to traverse the dynamic network. For our work, we consider a model where the number of nodes are fixed, but a powerful adversary can add or remove a limited number of edges from the network at each time step. The communication is by broadcast only and follows the CONGEST model. Our algorithms are continuously executed on the network, and at any time (after some initialization) each node will be aware if it is part (or not) of a particular dense subgraph. We give algorithms that ($2 + \epsilon$)-approximate the densest subgraph and ($3 + \epsilon$)-approximate the at-least-$k$-densest subgraph (for a given parameter $k$). Our algorithms work for a wide range of parameter values and run in $O(D\log_{1+\epsilon} n)$ time. Further...

## Multi-Gigabits Millimetre Wave Wireless Communications for 5G: From Fixed Access to Cellular Networks

Wang, Peng; Li, Yonghui; Song, Lingyang; Vucetic, Branka
Tipo: Artigo de Revista Científica
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With the formidable growth of various booming wireless communication services that require ever-increasing data throughputs, the conventional microwave band below 10 GHz, which is currently used by almost all mobile communication systems, is going to reach its saturation point within just a few years. Therefore, the attention of radio system designers has been pushed towards ever-higher segments of the frequency spectrum in a quest for capacity increase. In this article, we investigate the feasibility, advantages and challenges of future wireless communications over the E-band frequencies. We start from a brief review of the history of E-band spectrum and its light licensing policy as well as benefits/challenges. Then we introduce the propagation characteristics of E-band signals, based on which some potential fixed and mobile applications at the E-band are investigated. In particular, we analyze the achievability of non-trivial multiplexing gain in fixed point-to-point E-band links and propose an E-band mobile broadband (EMB) system as a candidate for the next generation mobile communication networks. The channelization and frame structure of the EMB system are discussed in details.; Comment: 25 pages, 4 figures, 2 tables, to appear in IEEE Communications Magazine

## Topological data analysis of contagion maps for examining spreading processes on networks

Taylor, Dane; Klimm, Florian; Harrington, Heather A.; Kramar, Miroslav; Mischaikow, Konstantin; Porter, Mason A.; Mucha, Peter J.
Tipo: Artigo de Revista Científica
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Social and biological contagions are influenced by the spatial embeddedness of networks. Historically, many epidemics spread as a wave across part of the Earth's surface; however, in modern contagions long-range edges -- for example, due to airline transportation or communication media -- allow clusters of a contagion to appear in distant locations. Here we study the spread of contagions on networks through a methodology grounded in topological data analysis and nonlinear dimension reduction. We construct "contagion maps" that use multiple contagions on a network to map the nodes as a point cloud. By analyzing the topology, geometry, and dimensionality of manifold structure in such point clouds, we reveal insights to aid in the modeling, forecast, and control of spreading processes. Our approach highlights contagion maps also as a viable tool for inferring low-dimensional structure in networks.; Comment: Main Text and Supplementary Information

## Multi-Hop Bandwidth Management Protocol for Mobile Ad Hoc Networks

Pattanayak, Binod Kumar; Mishra, Manoj Kumar; Jagadev, Alok Kumar; Nayak, Manojranjan
Tipo: Artigo de Revista Científica
Português
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An admission control scheme should play the role of a coordinator for flows in a data communication network, to provide the guarantees as the medium is shared. The nodes of a wired network can monitor the medium to know the available bandwidth at any point of time. But, in wireless ad hoc networks, a node must consume the bandwidth of neighboring nodes, during a communication. Hence, the consumption of bandwidth by a flow and the availability of resources to any wireless node strictly depend upon the neighboring nodes within its transmission range. We present a scalable and efficient admission control scheme, Multi-hop Bandwidth Management Protocol (MBMP), to support the QoS requirements in multi-hop ad hoc networks. We simulate several options to design MBMP and compare the performances of these options through mathematical analysis and simulation results, and compare its effectiveness with the existing admission control schemes through extensive simulations.; Comment: 20 pages,30 figures

## Underwater Efficient Energy Communication in Wireless Sensor Networks

Reddy, S. Pavan Kumar; Reddy, Y. Ganesh Kumar; Mouli, K. Chandra; Seshadri, U.
Tipo: Artigo de Revista Científica
Português
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This paper will focus on the energy efficiency issue in Underwater Wireless Sensor Networks. In underwater environment, the two main issues are namely: reliability and energy efficiency. These two issues are twisted pair. Reliability requires error correction, and error-correction requires energy. More reliability tends to imply higher energy consumption, causing difficulty in applications that require nodes to be operated underwater for long periods of time without batteries recharging, and in aquatic environments that render hard the task of recharging or replacing batteries. Appropriate strategy must therefore be in-place to ensure reliable data transmission, while conserving energy. We propose a mathematical function of the efficiency of acoustic data communication in real underwater environment. We did the analysis of existing error-correction techniques, and then propose a new technique that is the hybrid error correction technique that improves the efficiency among the existing techniques.; Comment: This paper is withdrawn because of its originality

## Opportunistic Information Dissemination in Mobile Ad-hoc Networks: adaptiveness vs. obliviousness and randomization vs. determinism

Farach-Colton, Martin; Anta, Antonio Fernandez; Milani, Alessia; Mosteiro, Miguel A.; Zaks, Shmuel
Tipo: Artigo de Revista Científica
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In this paper the problem of information dissemination in Mobile Ad-hoc Networks (MANET) is studied. The problem is to disseminate a piece of information, initially held by a distinguished source node, to all nodes in a set defined by some predicate. We use a model of MANETs that is well suited for dynamic networks and opportunistic communication. In this model nodes are placed in a plane, in which they can move with bounded speed, and communication between nodes occurs over a collision-prone single channel. In this setup informed and uninformed nodes can be disconnected for some time (bounded by a parameter alpha), but eventually some uninformed node must become neighbor of an informed node and remain so for some time (bounded by a parameter beta). In addition, nodes can start at different times, and they can crash and recover. Under the above framework, we show negative and positive results for different types of randomized protocols, and we put those results in perspective with respect to previous deterministic results.

## Secure Multidimensional Queries in Tiered Sensor Networks

Yu, Chia-Mu; Lu, Chun-Shien; Kuo, Sy-Yen
Tipo: Artigo de Revista Científica
Português
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In this paper, aiming at securing range query, top-k query, and skyline query in tiered sensor networks, we propose the Secure Range Query (SRQ), Secure Top-$k$ Query (STQ), and Secure Skyline Query (SSQ) schemes, respectively. In particular, SRQ, by using our proposed \emph{prime aggregation} technique, has the lowest communication overhead among prior works, while STQ and SSQ, to our knowledge, are the first proposals in tiered sensor networks for securing top-$k$ and skyline queries, respectively. Moreover, the relatively unexplored issue of the security impact of sensor node compromises on multidimensional queries is studied; two attacks incurred from the sensor node compromises, \emph{collusion attack} and \emph{false-incrimination attack}, are investigated in this paper. After developing a novel technique called \emph{subtree sampling}, we also explore methods of efficiently mitigating the threat of sensor node compromises. Performance analyses regarding the probability for detecting incomplete query-results and communication cost of the proposed schemes are also studied.

## Modeling the evolution of continuously-observed networks: Communication in a Facebook-like community

Opsahl, Tore; Hogan, Bernie
Tipo: Artigo de Revista Científica
Português
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Building on existing stochastic actor-oriented models for panel data, we employ a conditional logistic framework to explore growth mechanisms for tie creation in continuously-observed networks. This framework models the likelihood of tie formation distinguishing it from hazard models that consider time to tie formation. It enables multiple growth mechanisms for network evolution (homophily, focus constraints, reinforcement, reciprocity, triadic closure, and popularity) to be modeled simultaneously. We apply this framework to communication within a Facebook-like community. The findings exemplify the inadequacy of descriptive measures that test single mechanisms independently. They also indicate how system design shapes behavior and network evolution.

## Simulated evolution of protein-protein interaction networks with realistic topology

Peterson, Jack; Presse, Steve; Peterson, Kristin S.; Dill, Ken A.
Tipo: Artigo de Revista Científica