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Sensoriamento espectral baseado na detecção de energia para rádios cognitivos.; Spectrum sensing based on energy detection for cognitive radios.

Apaza Medina, Euler Edson
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 19/09/2014 PT
Relevância na Pesquisa
46.29%
Em 1997, o conceito de rádio cognitivo foi proposto pela primeira vez e evoluiu significativamente até os dias de hoje, como solução para o problema da escassez de espectro eletromagnético. Nessa proposta, usuários oportunistas, através de acesso dinâmico ao espectro, fazem uso das faixas de frequências atribuídas a usuários licenciados, quando eles não as estão utilizando. Para que isso seja possível, sem interferir ou degradar os sinais dos usuários licenciados, é necessário atender a quatro requisitos essenciais de rádios cognitivos: Sensoriamento espectral, Decisão do espectro, Compartilhamento do espectro e Mobilidade espectral. Neste trabalho, o sensoriamento espectral é investigado com base na detecção de energia. Um algoritmo é desenvolvido para se determinar o número de canais ocupados e o número de amostras necessárias na detecção para se atingir probabilidades de detecção e falso alarme pré-estabelecidas. Resultados de simulações são apresentadas mostrando que a incerteza do ruído degrada o desempenho do sistema quando a relação sinal-ruído é baixa. O algoritmo desenvolvido permite também determinar o limite inferior para a relação sinal-ruído, quando há incerteza do ruído. O comportamento da probabilidade de detecção em função da probabilidade de falso alarme parametrizado para número de amostras e relação sinal-ruído é apresentado. As curvas resultantes são muitas vezes referidas como curvas ROC - Receiver Operation Characteristics na literatura. Em função do grande interesse sócio-político pela banda de TV...

Hardware implementation of a spectrum analyzer based in SDR; Implementação em hardware de um analisador de espectros baseado em SDR

Carreira, João Carlos da Silva
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Dissertação de Mestrado
ENG
Relevância na Pesquisa
46.29%
A metrologia de rádio-frequência surgiu com as primeiras experiências de sistemas de rádio, pois era importante avaliar as condçiões em que eram feitas essas experiências assim como avaliar o desempenho dos próprios sistemas. Um dos instrumentos fundamentais na metrologia de rádiofrequência é o analisador de espectros, que tem como principal função apresentar porções do espectro de rádio-frequência, normalmente potência em função da frequência, para posterior análise efectuada pelo utilizador. Nos últimos tempos temos vindo a assistir a uma revolução ao nível dos sistemas de telecomunicações com o desenvolvimento do conceito de Software Defined Radio (SDR). Com a implementação deste novo conceito pretendese criar sistemas de rádio reconfiguráveis por software, permitindo-lhes assim uma maior flexibilidade e adaptação áss diversas normas de comunicação via rádio-frequência. Com este documento pretende-se mostrar uma implementação de um analisador de espectros de baixo custo baseado num sistema SDR. Para tal, foi efectuada uma procura por componentes disponíveis no mercado e com base nesta procura decidiu-se implementar este sistema para uma gama de frequências de entrada entre 2.1 GHz e 2.6 GHz e uma frequência intermédia de 100 MHz. Sendo este um sistema de rádio com alguma complexidade...

Arquiteturas eficientes para sensoriamento espectral e classificação automática de modulações usando características cicloestacionárias

Lima, Arthur Diego de Lira
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Elétrica; Automação e Sistemas; Engenharia de Computação; Telecomunicações Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Elétrica; Automação e Sistemas; Engenharia de Computação; Telecomunicações
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
46.27%
The increasing demand for high performance wireless communication systems has shown the inefficiency of the current model of fixed allocation of the radio spectrum. In this context, cognitive radio appears as a more efficient alternative, by providing opportunistic spectrum access, with the maximum bandwidth possible. To ensure these requirements, it is necessary that the transmitter identify opportunities for transmission and the receiver recognizes the parameters defined for the communication signal. The techniques that use cyclostationary analysis can be applied to problems in either spectrum sensing and modulation classification, even in low signal-to-noise ratio (SNR) environments. However, despite the robustness, one of the main disadvantages of cyclostationarity is the high computational cost for calculating its functions. This work proposes efficient architectures for obtaining cyclostationary features to be employed in either spectrum sensing and automatic modulation classification (AMC). In the context of spectrum sensing, a parallelized algorithm for extracting cyclostationary features of communication signals is presented. The performance of this features extractor parallelization is evaluated by speedup and parallel eficiency metrics. The architecture for spectrum sensing is analyzed for several configuration of false alarm probability...

Cognitive ultra wideband radio spectrum sensing window length optimization algorithm

Zeng, Liaoyuan; McGrath, Sean; Liu, Guanghui
Fonte: SpringerOpen Publicador: SpringerOpen
Tipo: info:eu-repo/semantics/article; all_ul_research; ul_published_reviewed
ENG
Relevância na Pesquisa
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peer-reviewed; A critical objective of cognitive radio (CR) system is to enhance the spectrum efficiency, and one of the key factors that can determine the spectrum efficiency is the system spectrum sensing performance with respect to sensing window length. For non-coherent detection-based sensing technique, the length of the sensing window required to meet the detection criteria is inversely proportional to the detected signal-to-noise ratio (SNR) of the primary users (PUs). This fact may result in an inadequate use of the white or gray space for the conventional CR system whose transmission and sensing window length are both fixed because a high detected PUs SNR can lead to an excessive long fixed sensing window which occupies the potential CR transmission opportunities while a low received PUs SNR can result in an insufficient sensing window length which degrades the CR detection criteria. In this paper, to improve the spectrum efficiency compared with the fixed sensing/transmission window length-based CR system, we propose an adaptive spectrum sensing window length optimization algorithm. We design the algorithm based on the ultra wideband (UWB) system which is an ideal candidate for the implementation of the CR technology. Based on the analysis of the CR-UWB’s spectrum sensing technique in terms of the factors such as spectrum efficiency...

Managing the Radio Spectrum : Framework for Reform in Developing Countries

Wellenius, Björn; Neto, Isabel
Fonte: Washington, DC: World Bank Publicador: Washington, DC: World Bank
Relevância na Pesquisa
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Bringing management of the radio spectrum closer to markets is long overdue. The radio spectrum is a major component of the infrastructure that underpins the information society. Spectrum management, however, has not kept up with major changes in technology, business practice, and economic policy that have taken place worldwide during the last two decades. For many years traditional government administration of the spectrum worked reasonably well, but more recently it has led to growing technical and economic inefficiencies as well as obstacles to technological innovation. Two alternative approaches to spectrum management are being tried in several countries, one driven by the market (tradable spectrum rights) and another driven by technology innovation (spectrum commons). This paper discusses the basic features, advantages and limitations, scope of application, and requirements for implementation of these three approaches. The paper then discusses how these approaches can be made to work under conditions that typically prevail in developing countries...

Radio Spectrum Management Development in India : A Framework for Strengthening Radio Spectrum Management and Policies

World Bank
Fonte: Washington, DC Publicador: Washington, DC
EN_US
Relevância na Pesquisa
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This report provides a detailed review of the current spectrum management regime in India; provides a perspective on best practice as may be applied in India and in addition provides a consideration of measures which could be taken to enhance spectrum management activities in India. The radio spectrum in India is a national resource, owned and managed by the Government. The authority for day-to-day spectrum management activities is vested Wireless Planning and Coordination (WPC) in New Delhi. Formal interfaces have been established with key spectrum user organizations, whose spectrum management staff may be found in other parts of India, remote from the capital city. The spectrum management regime has to date been strongly biased towards fulfilling the needs of the State and serving radio communications requirements funded by public sources. However, during the last 5 to 8 years a demanding private sector has made significant investments in the roll-out of new services and systems. The private sector (and indeed several segments of the public sector) is not entirely satisfied with the level of service provided by the spectrum management organization. This report performs the following functions: 1) it provides a detailed review of the current spectrum management regime in India; 2) it provides a commentary on best practice as may be applied in India in connection with each of the above areas; and 3) it provides a consideration of measures which could be taken to enhance spectrum management activities in India.

The Radio Spectrum : Opportunities and Challenges for the Developing World

Wellenius, Björn; Neto, Isabel
Fonte: World Bank, Washington, DC; World Bank, Washington, DC Publicador: World Bank, Washington, DC; World Bank, Washington, DC
Relevância na Pesquisa
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The radio spectrum is a major component of the telecommunications infrastructure that underpins the information society. Spectrum management, however, has not kept up with major changes in technology, business practice, and economic policy during the past two decades. Traditional spectrum management practice is predicated on the spectrum being a limited resource that must be apportioned among uses and users by government administration. For many years this model worked well, but more recently the spectrum has come under pressure from rapid demand growth for wireless services and changing patterns of use. This has led to growing technical and economic inefficiencies, as well as obstacles to technological innovation. Two alternative approaches are being tried, one driven by the market (spectrum property rights) and another driven by technology innovation (commons). Practical solutions are evolving that combine some features of both. Wholesale replacement of current practice is unlikely, but the balance between administration, property rights, and commons is clearly shifting. Although the debate on spectrum management reform is mainly taking place in high-income countries, it is deeply relevant to developing countries as well.

The Clock Proxy Auction for Allocating Radio Spectrum Licenses

Mochón, Asunción; Sáez, Yago; Gómez-Barroso, J.L.; Isasi, Pedro
Fonte: Springer Publicador: Springer
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/article Formato: application/pdf; text/plain
Publicado em /04/2011 ENG
Relevância na Pesquisa
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The combinatorial clock-proxy auction is analyzed as a selling mechanism of a portion of the “digital dividend” in an European country. We assumed bidders with bounded rationality making their bidding decisions based on a system of recommendation that learns from the environment. The auction outcome when all bidders follow the proposed strategies was compared with the efficient outcome of the auction. Although significant differences were found in the seller’s income, no significant variations were found in the distribution of spectrum licenses among bidders.; This article has been financed by the Spanish research MCyT project MSTAR, Ref: TIN2008-06491-C04-03/TIN.

Detección e identificación de señales para radio cognitiva

Cruz Barquero, María Ángeles de la
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: info:eu-repo/semantics/bachelorThesis; info:eu-repo/semantics/masterThesis
SPA
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El espectro radioeléctrico es un recurso muy escaso y necesario para las transmisiones radio. Actualmente, se encuentra muy saturado y la asignación de recursos existente hoy en día da lugar a la infrautilización de las frecuencias para la transmisión radio. Se están desarrollando distintas tecnologías cuyo objetivo es la eficiencia en la transmisión y la asignación de recursos radio, como es el caso de la radio cognitiva. Una de las necesidades de la radio cognitiva, consiste en la detección del tipo de señal que transmiten dispositivos desconocidos. Para ello, se ha realizado un análisis de distintas técnicas que permiten identificar el tipo de señal que utiliza un dispositivo desconocido para transmitir vía radio. Se han analizado teóricamente una serie de técnicas que permitirán en primer lugar detectar la existencia de una señal en el espectro, para a continuación, determinar el tipo de modulación de la señal detectada. Finalmente se ha llevado a cabo una implementación y simulación de estos métodos, analizando su rendimiento con distintas señales y situaciones.; The radio spectrum is a scarce resource that is necessary for radio transmissions. Currently, it is very saturated and the way that resources are allocated leads to the underutilization of frequencies for radio transmission. Several technologies are being developed with the aim of transmission efficiency and radio resource allocation...

Sound As a Dollar? The Propertization of Spectrum Resources and Implications for Non-Profit Community Radio in Guatemala

Henderson, Victoria L.
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 2204610 bytes; application/pdf
EN; EN
Relevância na Pesquisa
56.3%
This research analyzes Guatemala’s 1996 telecommunications reform, with an emphasis on how the introduction of private property rights in the electromagnetic spectrum has affected provision of, and access to, non-profit community radio, a critical media for the country’s indigenous Maya. The Guatemalan ‘experiment’ is the first applied test of Ronald Coase’s 1959 call for property rights in radio spectrum. To date, spectrum liberalization in most countries, including Canada, has upheld a model of resource stewardship in which the state retains ownership of the spectrum and a measure of control over frequency allocations. In Guatemala, by contrast, the state has ceded spectrum control to the private sector by auctioning off legal title to electromagnetic frequencies and allowing secondary markets in spectrum trading to develop. Formerly free under license to Guatemalan nationals only, FM frequencies sold with title under Guatemala’s revamped telecommunications law fetch as much as US$750,000 at auction. Broadcasting rights have disproportionately accrued to foreign nationals and commercial operators, while community broadcasters operating without title are accused of ‘stealing’ spectrum resources (causing interference on titled bandwidth)...

Management and Sensing of Spectrum in Cognitive Radio

Akhavan Astaneh, Saeed
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
56.29%
Under the contemporary spectrum usage regulations, radio frequency bands are allocated statically to licensed users in a large geographical area and over a long period of time. Recent investigations have revealed that such static spectrum allocation has led to very poor usage of the overall spectrum. Cognitive radio has emerged as a new communication paradigm to improve the utilization of the radio spectrum. It is defined as an intelligent wireless communication system that allows coexistence of unlicensed users with the licensed ones as long as the perceived interference at the licensed user is capped below some acceptable level. In addition, the users in this system adopt efficient communication protocols to enhance spectral efficiency. We employ cooperative mechanisms wherein multiple users cooperate in order to accomplish the following tasks: 1) Cooperative spectrum sensing: In this task, the licensed users do not actively engage. Instead, the unlicensed users passively monitor the activity of the licensed users and transmit only during their absence. 2) Cooperative spectrum management: The licensed and unlicensed users can benefit from cooperation with each other, e.g., they can assist each other in transmission via relaying. In this fashion...

Separação cega de fontes aplicada no sensoriamento do espectro em rádio cognitivo; Blind source separation applied in spectrum sensing in cognitive radio

Rocha, Gustavo Nozella
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Dissertação
POR
Relevância na Pesquisa
46.34%
A tecnologia de rádio cognitivo tem sido uma importante área de pesquisa em telecomunicações para a solução do problema da escassez espectral. Isto porque, além de permitirem a alocação dinâmica do espectro eletromagnético, os rádios cognitivos devem ser capazes de identificar as transmissões de usuários não cognitivos no canal. Esta operação só é possível por meio do sensoriamento contínuo do espectro eletromagnético. Neste contexto, este trabalho apresenta um estudo detalhado sobre o sensoriamento de espectro, uma importante etapa da tecnologia de rádios cognitivos. Para a apresentação deste trabalho foi realizado um estudo detalhado a respeito de rádio definido por software (SDR), sem o qual não seria possível o trabalho com rádios cognitivos, uma vez que este é implementado por meio da tecnologia de SDR. Também foram apresentadas as ferramentas GNU Radio e USRP, que, juntas, formam uma solução de SDR, por meio de implementações de receptores AM. Os fundamentos teóricos de sensoriamento de espectro e separação cega de fontes (BSS) são apresentados e, em seguida, é realizado um estudo aprofundado do uso de BSS para o sensoriamento espectral. A partir do estudo de BSS, é possível utilizar novas métricas de decisão a respeito da presença ou não de um usuário primário no canal. Durante todo este trabalho foram realizadas implementações e simulações no MATLAB com a finalidade de executar diversas situações e...

Radio cognitiva – Estado del arte; Cognitive radio – State of the Art

Aguilar Rentería, Julio Héctor; Navarro Cadavid, Andrés
Fonte: Universidad Icesi; Facultad de Ingeniería Publicador: Universidad Icesi; Facultad de Ingeniería
Tipo: article; Artículo Formato: PDF; p.31-53; Electrónico
SPA
Relevância na Pesquisa
46.31%
El crecimiento de la tecnología radio en los últimos años ha sido muy grande y presenta retos importantes para el uso adecuado del espectro. Es bien conocido que el uso actual del espectro radio no es el más eficiente, por lo que se han planteado tecnologías que permitan usar de manera más eficiente este espectro. Los desarrollos en tecnologías de Radio Software en los años noventa y en la primera década del 2000, han permitido que la tecnología de Radio Cognitivo empiece a tomar fuerza en diversos ámbitos de los sistemas de radio. En este artículo se hace una revisión detallada de esta tecnología y los avances recientes, así como algunos de los retos por superar; The wireless technology is growing very quickly, in the actuality the new technologies applied to the radius link appear with a multiplicity of names that change as the application and the use that do of them: Bluetooth, GSM, Microwaves, Links Satellites, Wi-Fi, WiMax, ZigBee, etc. Each system uses a hardware and devoted software and exclusive chord to his functionalities to send and receive the waves of radio. Some of these bands of the spectrum can justify by the fact that some applications work better in determinate spaces inside the spectrum electric radio. This exponential growth of wireless applications creates an every time main demand of spectrum electric radio what has motivated the research of technologies of radio that can scalar to satisfy the future demands...

An Analysis of the Broadband (22-3900 MHz) Radio Spectrum of HB3 (G132.7+1.3): The Detection of Thermal Radio Emission from an Evolved Supernova Remnant?

Urosevic, D.; Pannuti, T.; Leahy, D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.28%
We present an analysis of the broadband radio spectrum (from 22 to 3900 MHz) of the Galactic supernova remnant (SNR) HB3 (G132.7+1.3). Published observations have revealed that a curvature is present in the radio spectrum of this SNR, indicating that a single synchrotron component appears is insufficient to adequately fit the spectrum. We present here a fit to this spectrum using a combination of a synchrotron component and a thermal bremsstrahlung component. We discuss properties of this latter component and estimate the ambient density implied by the presence of this component to be n \~ 10 cm^-3. We have also analyzed extracted X-ray spectra from archived {\it ASCA} GIS observations of different regions of HB3 to obtain independent estimates of the density of the surrounding interstellar medium (ISM). From this analysis, we have derived electron densities of 0.1-0.4 f^-1/2 cm^-3 for the ISM for the three different regions of the SNR, where f is the volume filling factor. By comparing these density estimates with the estimate derived from the thermal bremsstrahlung component, we argue that the radio thermal bremsstrahlung emission is emitted from a thin shell enclosing HB3. The presence of this thermal bremsstrahlung component in the radio spectrum of HB3 suggests that this SNR is in fact interacting with an adjacent molecular cloud associated with the HII region W3. By extension...

On the Limits of Predictability in Real-World Radio Spectrum State Dynamics: From Entropy Theory to 5G Spectrum Sharing

Ding, Guoru; Wang, Jinlong; Wu, Qihui; Yao, Yu-Dong; Li, Rongpeng; Zhang, Honggang; Zou, Yulong
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/05/2015
Relevância na Pesquisa
46.25%
A range of applications in cognitive radio networks, from adaptive spectrum sensing to predictive spectrum mobility and dynamic spectrum access, depend on our ability to foresee the state evolution of radio spectrum, raising a fundamental question: To what degree is radio spectrum state (RSS) predictable? In this paper, we explore the fundamental limits of predictability in RSS dynamics by studying the RSS evolution patterns in spectrum bands of several popular services, including TV bands, ISM bands, and Cellular bands, etc. From an information theory perspective, we introduce a methodology of using statistical entropy measures and Fano inequality to quantify the degree of predictability underlying real-world spectrum measurements. Despite the apparent randomness, we find a remarkable predictability, as large as 90%, in the real-world RSS dynamics over a number of spectrum bands for all popular services. Furthermore, we discuss the potential applications of prediction-based spectrum sharing in 5G wireless communications.; Comment: To appear, IEEE Communications Magazine (Accepted from open call), 2015

Discovery of $\gamma$-ray emission from a steep radio spectrum NLS1 B3 1441+476

Liao, Neng-Hui; Liang, Yun-Feng; Weng, Shan-Shan; Gu, Min-Feng; Fan, Yi-Zhong
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/10/2015
Relevância na Pesquisa
46.23%
Narrow line Seyfert 1 galaxies (NLS1s) usually do not host relativistic jet and the $\gamma$-ray NLS1s are expected to be rare. All $\gamma$-ray NLS1s reported to date have flat radio spectra and the jets are found to be closely aligned. No $\gamma$-ray mis-aligned NLS1 has been predicted before. In this work we analyze the first seven-year $Fermi$/Large Area Telescope (LAT) data of a steep radio spectrum NLS1 B3 1441+476 and report the {\it first} detection of $\gamma$-rays in such a kind of objects. No rapid variability is observed from radio to $\gamma$ rays and additionally low core dominance ($\lesssim$ 0.7) and Compton dominance ($\lesssim$ 1) are found. B3 1441+476 has a compact radio morphology and a radio spectrum turnover at $\sim$ 100MHz. A radiation model successfully reproducing some steep-spectrum radio quasars can reasonably fit the spectral energy distribution of B3 1441+476. All these facts strongly suggest that B3 1441+476 hosts a mis-aligned and plausibly underdeveloped relativistic jet, which provides a valuable target to reveal the formation and evolution of relativistic jets in NLS1s.; Comment: Welcome comments

Synchrotron aging and the radio spectrum of SN 1993J

Chandra, Poonam; Ray, Alak; Bhatnagar, Sanjay
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 16/02/2004
Relevância na Pesquisa
46.2%
We combine the GMRT low frequency radio observations of SN 1993J with the VLA high frequency radio data to get a near simultaneous spectrum around day 3200 since explosion. The low frequency measurements of the supernova determine the turnover frequency and flux scale of the composite spectrum and help reveal a steepening in the spectral index, $\Delta \alpha \sim 0.6$, in the optically thin part of the spectrum. This is the first observational evidence of a break in the radio spectrum of a young supernova. We associate this break with the phenomenon of synchrotron aging of radiating electrons. From the break in the spectrum we calculate the magnetic field in the shocked region independent of the equipartition assumption between energy density of relativistic particles and magnetic energy density. We determine the ratio of these two energy densities and find that this ratio is in the range: $8\times 10^{-6}-5\times 10^{-4}$. We also predict the nature of the evolution of the synchrotron break frequency with time, with competing effects due to diffusive Fermi acceleration and adiabatic expansion of the radiative electron plasma.; Comment: 12 pages, 2 figures. Accepted for publication in ApJL

The Late-Time Radio Spectrum of SN1993J

Perez-Torres, M. A.; Alberdi, A.; Marcaide, J. M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.23%
We present VLA radio continuum measurements of SN1993J in M81 at the frequencies of 0.32 (P-band), 1.3 and 1.7 (L-band), 4.9 (C-band), 8.5 (X-band), and 14.9 (U-band) GHz carried out on December 17 and 21, 2000, about 2820 days after the supernova explosion. We find that a power-law spectrum, free-free absorbed by an homogeneous, or clumpy, distribution of ionized gas yields the best fit to the radio data. A combined homogeneous-clumpy model is not favored, but neither totally excluded. This result contrasts with the modeling of the early ($t \lessim $230 days) radio emission from SN1993J, where a mixture of homogeneous and clumpy absorbers appeared to be necessary to adequately describe the behavior of the light curves. The radio spectrum of supernova SN1993J between 0.32 and 14.9 GHz is well characterized by $\alpha = -0.67 \pm 0.02 $ ($S_\nu \propto \nu^\alpha$), typical of an optically thin radio supernova. A fit to the radio spectra of SN1993J from $\sim$ 70 up to 2820 days shows that the observed spectral index of SN1993J has been slowly evolving since $t\sim$1000 days on, with the observed spectral index changing from $\alpha \approx -1$ to $\alpha=-0.67$. This spectral evolution seems to suggest that, in addition to the radiative (synchrotron) losses...

Estudi del desenvolupament i situació reglamentària de la ràdio cognitiva

Martínez Domingo, Esther; Rifà Pous, Helena
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: Trabalho de Conclusão de Curso Formato: application/pdf
Publicado em //2011 CAT
Relevância na Pesquisa
46.21%
Este proyecto estudia la tecnología Radio Cognitiva. El concepto clave de esta tecnología es que permite a usuarios sin licencia compartir el espectro radioeléctrico de forma oportunista con los usuarios con licencia. Para empezar, se analizarán las características principales, su funcionamiento y como coexisten con los usuarios principales. Más adelante, se explicaran los métodos que se usan para la gestión del espectro radioeléctrico y las actividades de estandarización para la implementación de las redes de radio cognitiva. Por último, se analizara la posibilidad de la implementación de esta tecnología en España, analizando las ventajas e inconvenientes de inicializar un mercado secundario del espectro radioeléctrico.; This thesis studies the Cognitive Radio technology. The key concept of this technology is allowing unlicensed users to share the radio spectrum opportunistically with the licensed users. To begin, main features are going to be studied, as well as its performance and how it coexists with primary users. Later, methods used for spectrum management and the standardization activities for the implementation of cognitive radio networks will be presented. Finally, the possibility of implementing this technology in Spain is presented analyzing the advantages and disadvantages of setting up a secondary market for spectrum.; Aquest projecte estudia la tecnologia Ràdio Cognitiva. El concepte clau d’aquesta tecnologia és que permet a usuaris sense llicència compartir l’espectre radioelèctric de forma oportunista amb els usuaris amb llicència. Per començar...

ISO observations of a sample of Compact Steep Spectrum and GHz Peaked Spectrum radio galaxies

Fanti, Carla; Pozzi, Francesca; Fanti, Roberto; Baum, Stefi; O'Dea, Christopher; Bremer, Martin; Dallacasa, Daniele; Falcke, Heino; de Graauw, Thijs; Marecki, Andrzej; Miley, George; Rottgering, Huub; Schilizzi, Richard; Snellen, Ignas; Spencer, Ralph; St
Fonte: Astronomy and Astrophysics Publicador: Astronomy and Astrophysics
Tipo: Artigo de Revista Científica Formato: 300678 bytes; application/pdf
EN_US
Relevância na Pesquisa
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We present results from observations obtained with ISOPHOT, on board the ISO satellite1, of a representative sample of seventeen CSS/GPS radio galaxies and of a control sample of sixteen extended radio galaxies spanning similar ranges in redshift (0.2≤z≤0.8) and radio luminosity (P2.7GHz≥1026 W/Hz). The observations have been performed at =60, 90, 174 and 200 µm. The original purpose of these observations was to check whether CSS/GPS sources are associated with very gas rich galaxies, as required by the scenario in which the growth of the radio source is inhibited by the dense medium of the host galaxy. Unfortunately the resulting performance of ISOPHOT was worse than expected. As a consequence, the detection limit at 60µm is similar to that obtained previously with IRAS but better than that at 90µm. Seven of the CSS/GPS sources have detections ≥3 at one or more wavelengths, one of which is detected at ≥5 . For the comparison sample five objects have detections ≥3 one of which is at ≥5 . By co–adding the data we have obtained average flux densities at the four wavelengths. We found no evidence that the FIR luminosities of the CSS/GPS sources are significantly different from those of the extended objects and therefore there is not any support for CSS/GPS sources being objects “frustrated” by an abnormally dense ambient medium. The two samples were then combined...