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Sistema autônomo de comunicação sem fio em malha alimentado por energia solar fotovoltaica.; An autonomous wireless mesh communication system powered by solar energy.

Alonso, Rafael Herrero
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 29/05/2009 Português
Relevância na Pesquisa
45.78%
A tecnologia de comunicação em redes sem fio em malha, com base no padrão IEEE 802.11, tem sido uma solução tecnológica relevante no cenário atual das redes sem fio. Entretanto, com a eliminação dos cabos para comunicação de dados, as redes sem fio em malha dependem de fonte de energia para energizar os pontos de acesso da rede, que nem sempre está disponível na forma cabeada no local da instalação. Neste cenário, sendo o Brasil um país situado em uma zona tropical com alta incidência anual de radiação solar, a possibilidade da utilização da conversão da energia solar em elétrica é uma alternativa para eliminar a dependência de fonte de energia cabeada dos pontos de acesso da rede sem fio em malha. Este trabalho apresenta considerações sobre o desenvolvimento de sistemas autônomos de comunicação sem fio em malha, alimentados por energia solar fotovoltaica, compactos e de fácil instalação em área urbana e rural. Apresenta também, informações sobre o protótipo implementado denominado SAM Solar e respectiva avaliação quanto a autonomia, área de cobertura, número de usuários, altura mínima de instalação e taxa de transferência.; The wireless mesh network communication technology, based on the IEEE802.11 standard...

Protocolo ISO 11783: procedimentos para comunicação serial de dados do controlador de tarefa; ISO 11783 protocol: procedures for serial data communication with the task controller

Pereira, Robson Rogério Dutra
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 29/01/2009 Português
Relevância na Pesquisa
45.79%
O recente crescimento da utilização de tecnologias de automação e eletrônica embarcada em máquinas e implementos agrícolas tem estabelecido uma nova prática na área agrícola. Estas novas práticas relacionadas com a agricultura de precisão (AP) têm demandado a utilização de sensores e redes de comunicação embarcadas para aquisição de dados e controle dos dispositivos em campo. A incompatibilidade entre equipamentos e formatos de dados tornou-se um grande obstáculo. A tendência global é de uso de sistemas padronizados de acordo com a norma ISO 11783 (também conhecida como ISOBUS) nos dispositivos, ou Electronic Control Unit (ECU), utilizados na produção agrícola. No Brasil, essas ferramentas ainda não são largamente aplicadas. O objetivo deste trabalho é sistematizar as informações necessárias dos procedimentos para comunicação de uma ECU do implemento com a ECU de trator de gerenciamento. Focou-se no desenvolvimento dos arquivos padrões necessários e no programa da ECU do implemento, e testes de validação da comunicação dos dispositivos via rede ISO 11873. Estabeleceu-se a relação entre as informações sistematizadas e os dispositivos embarcados em máquinas agrícolas. Os dispositivos embarcados consistem em cinco ECUs interconectadas pela rede ISO 11783. Quatro ECUS estão localizados no tractor: ECU do GPS...

Semantically reliable group communication

Pereira, José, 1973-
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Tese de Doutorado
Publicado em //2002 Português
Relevância na Pesquisa
45.73%
A utilização de computadores e redes de transmissão de dados em diversas aplicações do quotidiano, torna desejável a adopção de técnicas de tolerância a faltas em sistemas baseados em hardware e software não especializados. A comunicação em grupo é, neste contexto, uma tecnologia particularmente atraente, pois oferece ao programador garantias de fiabilidade que simplificam significativamente a aplicação de técnicas de tolerância a faltas. No entanto, a experiência tem mostrado que a concretização deste modelo em sistemas heterogéneos e de grande escala levanta problemas de desempenho. Embora as limitações de desempenho possam ser evitadas através de um relaxamento das garantias de fiabilidade, os protocolos resultantes são normalmente menos úteis, nomeadamente, na replicação com coerência forte. O desafio reside pois no relaxamento das garantias de fiabilidade sem deixar de oferecer um modelo adequado à programação de aplicações tolerantes a faltas. Esta dissertação estuda modelos e mecanismos que permitem conciliar as vantagens da comunicação em grupo com o elevado desempenho, recorrendo para isso ao enfraquecimento selectivo das garantias oferecidas pelos protocolos. A nossa proposta consiste no uso pelo protocolo de informação sobre a semântica das mensagens...

Throughput limits of two 802.15.4 wireless networks applications for signal acquisition

Alves, Joel; Catarino, André P.; Carvalho, Helder; Monteiro, João L.; Rocha, A. M.
Fonte: IEEE Publicador: IEEE
Tipo: Conferência ou Objeto de Conferência
Publicado em /06/2011 Português
Relevância na Pesquisa
45.74%
This work describes the development and test of a wireless sensor network used by a biomedical signal monitoring system. Data communication is based on a body area network (BAN) materialized as a wireless network in two versions, one based on the 802.15.4 specification and another on a higher-level Zigbee protocol. The system was developed using the Jennic JN5148 microcontroller, Jennics ZBPro stack and the JenOs RT kernell. The final system was tested with the devices at different distances, and with a varying number of sensor nodes communicating simultaneously. For each of these combinations the signal quality and frequency of communication errors were recorded. The version implemented using Zigbee protocol was able to acquire and send sensor signals at a sample rate of 7 kSamples/s (12-bit samples, final net rate of 84 kbps) with a percentage of lost frames below 4%. It was also shown that the system supports simultaneous communication of three sensor nodes at 3 kS/s (36 kbps) each, with a percentage of losses of less than 4%. These results are important since they support the possibility of having several sensors acquiring fast biomedical signals and sending them to a central unit in real time.; Fundação para a Ciência e a Tecnologia (FCT) - Projeto Bioswim

World Congress on Communication for Development : Lessons, Challenges, and the Way Forward

The Communication Initiative; Food and Agriculture Organization of the United Nations; World Bank
Fonte: Washington, DC: World Bank Publicador: Washington, DC: World Bank
Português
Relevância na Pesquisa
45.76%
The first World Congress on Communication for Development (WCCD) took place in Rome, Italy, on October 25-27, 2006. The main goal of the WCCD was to position and promote the field of Communication for Development in the overall agenda of development and international cooperation. Toward this end, three types of stakeholders, who rarely interact, gathered in Rome: academics, practitioners, and policy and decision makers. The interaction and exchange of perspectives among these three groups served to enhance the overall understanding of the field of Communication for Development by a broader audience.

Um paradigma orientado a análise de performance de redes de pacotes; A paradigm oriented to performance analysis of packet switched networks

Spohn, Marcelo
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
Português
Relevância na Pesquisa
45.72%
A crescente complexidade das redes de comunicação de dados tem como conseqüência direta tornar cada vez mais complexas as tarefas de projetar seu dimensionamento e evolução. Um passo preliminar vitalmente importante no projeto de uma rede é a coleta de dados relacionados ao uso esperado da rede. Os padrões de tráfego estimados são usados nos cálculos de dimensionamento dos recursos. Fortemente relacionada a estas atividades está a previsão da performance em termos de throughput da rede, tempos de resposta, probabilidade de congestionamento, entre outras. Uma análise de performance efetiva depende de se representar precisamente a configuração da rede e da carga de tráfego a ela submetida. Técnicas de modelagem analítica ou de simulação podem ser usadas para determinar a performance esperada do sistema. Neste trabalho a usada a técnica de simulação para modelar o tráfego da rede usando dados coletados em uma rede real por monitoração. Trabalhando-se com o modelo validado e possível ajustar a carga de tráfego para representar mudanças esperadas nos volumes de tráfego, e testar o efeito na performance de diferentes configurações de rede. Isso possibilita que os processos de planejamento e projeto sejam executados com confiança...

Combined rate and power allocation with link scheduling in wireless data packet relay networks with fading channels

Huang , Minyi; Dey, Subhrakanti
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
45.73%
We consider a joint rate and power control problem in a wireless data traffic relay network with fading channels. The optimization problem is formulated in terms of power and rate selection, and link transmission scheduling. The objective is to seek high

Predicting Client Satisfaction through (E-Mail) Network Analysis: The Communication Score Card

Brunberg, Dirk; Gloor, Peter A.; Giacomelli, Gianni
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/08/2013 Português
Relevância na Pesquisa
45.74%
This study seeks to better understand the network characteristics of client support teams by analyzing the teams' e-mail communication networks and comparing it to client organization's satisfaction. In collaboration with a large service provider we studied the impact of network properties on the satisfaction of client organizations. In particular, we found that social network metrics correlate with client satisfaction as measured by Net Promoter Score (NPS). A Communication Score Card is suggested as a dashboard to continuously measure client satisfaction, illustrating that data-driven analysis might help improving service providers' service quality management.; Comment: Presented at COINs13 Conference, Chile, 2013 (arxiv:1308.1028)

Impact of network structure on the capacity of wireless multihop ad hoc communication

Krause, Wolfram; Glauche, Ingmar; Sollacher, Rudolf; Greiner, Martin
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/03/2004 Português
Relevância na Pesquisa
45.74%
As a representative of a complex technological system, so-called wireless multihop ad hoc communication networks are discussed. They represent an infrastructure-less generalization of todays wireless cellular phone networks. Lacking a central control authority, the ad hoc nodes have to coordinate themselves such that the overall network performs in an optimal way. A performance indicator is the end-to-end throughput capacity. Various models, generating differing ad hoc network structure via differing transmission power assignments, are constructed and characterized. They serve as input for a generic data traffic simulation as well as some semi-analytic estimations. The latter reveal that due to the most-critical-node effect the end-to-end throughput capacity sensitively depends on the underlying network structure, resulting in differing scaling laws with respect to network size.; Comment: 30 pages, to be published in Physica A

Long-term evolution of techno-social networks: Statistical regularities, predictability and stability of social behaviors

Godoy-Lorite, Antonia; Guimera, Roger; Sales-Pardo, Marta
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/06/2015 Português
Relevância na Pesquisa
45.79%
In social networks, individuals constantly drop ties and replace them by new ones in a highly unpredictable fashion. This highly dynamical nature of social ties has important implications for processes such as the spread of information or of epidemics. Several studies have demonstrated the influence of a number of factors on the intricate microscopic process of tie replacement, but the macroscopic long-term effects of such changes remain largely unexplored. Here we investigate whether, despite the inherent randomness at the microscopic level, there are macroscopic statistical regularities in the long-term evolution of social networks. In particular, we analyze the email network of a large organization with over 1,000 individuals throughout four consecutive years. We find that, although the evolution of individual ties is highly unpredictable, the macro-evolution of social communication networks follows well-defined statistical laws, characterized by exponentially decaying log-variations of the weight of social ties and of individuals' social strength. At the same time, we find that individuals have social signatures and communication strategies that are remarkably stable over the scale of several years.

Placement Optimization of Energy and Information Access Points in Wireless Powered Communication Networks

Bi, Suzhi; Zhang, Rui
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
45.76%
The applications of wireless power transfer technology to wireless communications can help build a wireless powered communication network (WPCN) with more reliable and sustainable power supply compared to the conventional battery-powered network. However, due to the fundamental differences in wireless information and power transmissions, many important aspects of conventional battery-powered wireless communication networks need to be redesigned for efficient operations of WPCNs. In this paper, we study the placement optimization of energy and information access points in WPCNs, where the wireless devices (WDs) harvest the radio frequency energy transferred by dedicated energy nodes (ENs) in the downlink, and use the harvested energy to transmit data to information access points (APs) in the uplink. In particular, we are interested in minimizing the network deployment cost with minimum number of ENs and APs by optimizing their locations, while satisfying the energy harvesting and communication performance requirements of the WDs. Specifically, we first study the minimum-cost placement problem when the ENs and APs are separately located, where an alternating optimization method is proposed to jointly optimize the locations of ENs and APs. Then...

Communication models with distributed transmission rates and buffer sizes

Arrowsmith, David; di Bernardo, Mario; Sorrentino, Francesco
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
45.74%
The paper is concerned with the interplay between network structure and traffic dynamics in a communications network, from the viewpoint of end-to-end performance of packet transfer. We use a model of network generation that allows the transition from random to scale-free networks. Specifically, we are able to consider three different topologycal types of networks: (a) random; (b) scale-free with \gamma=3; (c) scale free with \gamma=2. We also use an LRD traffic generator in order to reproduce the fractal behavior that is observed in real world data communication. The issue is addressed of how the traffic behavior on the network is influenced by the variable factors of the transmission rates and queue length restrictions at the network vertices. We show that these factors can induce drastic changes in the throughput and delivery time of network performance and are able to counter-balance some undesirable effects due to the topology.; Comment: 4 pages, 5 figures, IEEE Symposium on Circuits and Systems, Island of Kos, Greece, 2006

Deterministic Online Call Control in Cellular Networks and Triangle-Free Cellular Networks

Chan, Joseph Wun-Tat; Chin, Francis Y. L.; Han, Xin; Lam, Ka-Cheong; Ting, Hing-Fung; Zhang, Yong
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/09/2010 Português
Relevância na Pesquisa
45.76%
Wireless Communication Networks based on Frequency Division Multiplexing (FDM in short) plays an important role in the field of communications, in which each request can be satisfied by assigning a frequency. To avoid interference, each assigned frequency must be different to the neighboring assigned frequencies. Since frequency is a scarce resource, the main problem in wireless networks is how to fully utilize the given bandwidth of frequencies. In this paper, we consider the online call control problem. Given a fixed bandwidth of frequencies and a sequence of communication requests arrive over time, each request must be either satisfied immediately after its arrival by assigning an available frequency, or rejected. The objective of call control problem is to maximize the number of accepted requests. We study the asymptotic performance of this problem, i.e., the number of requests in the sequence and the bandwidth of frequencies are very large. In this paper, we give a 7/3-competitive algorithm for call control problem in cellular network, improving the previous 2.5-competitive result. Moreover, we investigate the triangle-free cellular network, propose a 9/4-competitive algorithm and prove that the lower bound of competitive ratio is at least 5/3.; Comment: 12 pages...

Network Coded Multi-Hop Wireless Communication Networks: Channel Estimation and Training Design

Peng, Mugen; Hu, Qiang; Xie, Xinqian; Zhao, Zhongyuan; Poor, H. Vincent
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 20/12/2014 Português
Relevância na Pesquisa
45.78%
User cooperation based multi-hop wireless communication networks (MH-WCNs) as the key communication technological component of mobile social networks (MSNs) should be exploited to enhance the capability of accumulating data rates and extending coverage flexibly. As one of the most promising and efficient user cooperation techniques, network coding can increase the potential cooperation performance gains among selfishly driven users in MSNs. To take full advantages of network coding in MH-WCNs, a network coding transmission strategy and its corresponding channel estimation technique are studied in this paper. Particularly, a $4-$hop network coding transmission strategy is presented first, followed by an extension strategy for the arbitrary $2N-$hop scenario ($N\geq 2$). The linear minimum mean square error (LMMSE) and maximum-likelihood (ML) channel estimation methods are designed to improve the transmission quality in MH-WCNs. Closed form expressions in terms of the mean squared error (MSE) for the LMMSE channel estimation method are derived, which allows the design of the optimal training sequence. Unlike the LMMSE method, it is difficult to obtain closed-form MSE expressions for the nonlinear ML channel estimation method. In order to accomplish optimal training sequence design for the ML method...

Attention on Weak Ties in Social and Communication Networks

Weng, Lilian; Karsai, Márton; Perra, Nicola; Menczer, Filippo; Flammini, Alessandro
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/05/2015 Português
Relevância na Pesquisa
45.74%
Granovetter's weak tie theory of social networks is built around two central hypotheses. The first states that strong social ties carry the large majority of interaction events; the second maintains that weak social ties, although less active, are often relevant for the exchange of especially important information (e.g., about potential new jobs in Granovetter's work). While several empirical studies have provided support for the first hypothesis, the second has been the object of far less scrutiny. A possible reason is that it involves notions relative to the nature and importance of the information that are hard to quantify and measure, especially in large scale studies. Here, we search for empirical validation of both Granovetter's hypotheses. We find clear empirical support for the first. We also provide empirical evidence and a quantitative interpretation for the second. We show that attention, measured as the fraction of interactions devoted to a particular social connection, is high on weak ties --- possibly reflecting the postulated informational purposes of such ties --- but also on very strong ties. Data from online social media and mobile communication reveal network-dependent mixtures of these two effects on the basis of a platform's typical usage. Our results establish a clear relationships between attention...

Near-Optimal Random Walk Sampling in Distributed Networks

Sarma, Atish Das; Molla, Anisur Rahaman; Pandurangan, Gopal
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
45.74%
Performing random walks in networks is a fundamental primitive that has found numerous applications in communication networks such as token management, load balancing, network topology discovery and construction, search, and peer-to-peer membership management. While several such algorithms are ubiquitous, and use numerous random walk samples, the walks themselves have always been performed naively. In this paper, we focus on the problem of performing random walk sampling efficiently in a distributed network. Given bandwidth constraints, the goal is to minimize the number of rounds and messages required to obtain several random walk samples in a continuous online fashion. We present the first round and message optimal distributed algorithms that present a significant improvement on all previous approaches. The theoretical analysis and comprehensive experimental evaluation of our algorithms show that they perform very well in different types of networks of differing topologies. In particular, our results show how several random walks can be performed continuously (when source nodes are provided only at runtime, i.e., online), such that each walk of length $\ell$ can be performed exactly in just $\tilde{O}(\sqrt{\ell D})$ rounds, (where $D$ is the diameter of the network)...

Truthy: Enabling the Study of Online Social Networks

McKelvey, Karissa; Menczer, Fil
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
45.76%
The broad adoption of online social networking platforms has made it possible to study communication networks at an unprecedented scale. Digital trace data can be compiled into large data sets of online discourse. However, it is a challenge to collect, store, filter, and analyze large amounts of data, even by experts in the computational sciences. Here we describe our recent extensions to Truthy, a system that collects Twitter data to analyze discourse in near real-time. We introduce several interactive visualizations and analytical tools with the goal of enabling citizens, journalists, and researchers to understand and study online social networks at multiple scales.; Comment: ACM Computer Supported Cooperative Work '13, Demonstration

LabelRank: A Stabilized Label Propagation Algorithm for Community Detection in Networks

Xie, Jierui; Szymanski, Boleslaw K.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
45.76%
An important challenge in big data analysis nowadays is detection of cohesive groups in large-scale networks, including social networks, genetic networks, communication networks and so. In this paper, we propose LabelRank, an efficient algorithm detecting communities through label propagation. A set of operators is introduced to control and stabilize the propagation dynamics. These operations resolve the randomness issue in traditional label propagation algorithms (LPA), stabilizing the discovered communities in all runs of the same network. Tests on real-world networks demonstrate that LabelRank significantly improves the quality of detected communities compared to LPA, as well as other popular algorithms.; Comment: Proc. IEEE Network Science Workshop, 2013

Path lengths, correlations, and centrality in temporal networks

Pan, Raj Kumar; Saramäki, Jari
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
45.8%
In temporal networks, where nodes interact via sequences of temporary events, information or resources can only flow through paths that follow the time-ordering of events. Such temporal paths play a crucial role in dynamic processes. However, since networks have so far been usually considered static or quasi-static, the properties of temporal paths are not yet well understood. Building on a definition and algorithmic implementation of the average temporal distance between nodes, we study temporal paths in empirical networks of human communication and air transport. Although temporal distances correlate with static graph distances, there is a large spread, and nodes that appear close from the static network view may be connected via slow paths or not at all. Differences between static and temporal properties are further highlighted in studies of the temporal closeness centrality. In addition, correlations and heterogeneities in the underlying event sequences affect temporal path lengths, increasing temporal distances in communication networks and decreasing them in the air transport network.; Comment: 10 pages, 8 figures, Published version

Communication framework for distributed computer vision on stationary and mobile platforms

Armenio, Christopher
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
45.8%
Recent advances in the complexity and manufacturability of digital video cameras coupled with the ubiquity of high speed computers and communication networks have led to burgeoning research in the fields of computer vision and image understanding. As the generated vision algorithms become increasingly complex, a need arises for robust communication between remote cameras on mobile units and their associated distributed vision algorithms. A communication framework would provide a basis for modularization and abstraction of a collection of computer vision algorithms; the resulting system would allow for straightforward image capture, simplified communication between algorithms, and easy replacement or upgrade of existing component algorithms. The objective of this thesis is to create such a communication framework and demonstrate its viability and applicability by implementing a relatively complex system of distributed computer vision algorithms. These multi-camera algorithms include body tracking, pose estimation and face recognition. Although a plethora of research exists documenting individual algorithms which may utilize multiple networked cameras, this thesis aims to develop a novel way of sharing information between cameras and algorithms in a distributed computation system. In addition...