Cognitive radio technology is a promising technology to solve the wireless spectrum scarcity problem by intelligently allowing secondary, or unlicensed, users access to the primary, licensed, users' frequency bands. Cognitive technology involves two main tasks: 1) sensing the wireless medium to assess the presence of the primary users and 2) designing secondary spectrum access techniques that maximize the secondary users' benefits while maintaining the primary users' privileged status. On the spectrum sensing side, we make two contributions. First, we maximize a utility function representing the secondary throughput while constraining the collision probability with the primary below a certain value. We optimize therein the channel sensing time, the sensing decision threshold, the channel probing time, together with the channel sensing order for wideband primary channels. Second, we design a cooperative spectrum sensing technique termed sensing with equal gain combining whereby cognitive radios simultaneously transmit their sensing results to the fusion center over multipath fading reporting channels. The proposed scheme is shown to outperform orthogonal reporting systems in terms of achievable secondary throughput and to be robust against phase and synchronization errors. On the spectrum access side, we make four contributions. First, we design a secondary scheduling scheme with the goal of minimizing the secondary queueing delay under constraints on the average secondary transmit power and the maximum tolerable primary outage probability. Second, we design another secondary scheduling scheme based on the spectrum sensing results and the primary automatic repeat request feedback. The optimal medium access probabilities are obtained via maximizing the secondary throughput subject to constraints that guarantee quality of service parameters for the primary. Third, we propose a three-message superposition coding scheme to maximize the secondary throughput without degrading the primary rate. Cognitive relaying is employed as an incentive for the primary network. The scheme is shown to outperform a number of reference schemes such as best relay selection. Finally, we consider a network of multiple primary and secondary users. We propose a three-stage distributed matching algorithm to pair the network users. The algorithm is shown to perform close to an optimal central controller, albeit at a reduced computational complexity.

Pour comprendre et diagnostiquer les pathologies qui affectent l'organisation spatialede notre squelette, il est essentiel d'aborder ces problématiques en 3D. Le CT-Scan et l'IRMsont des modalités d'imagerie couramment utilisées en milieu clinique pour étudier en 3D notresystème musculosquelettique. La plupart de ces systèmes d'imagerie proposent une acquisitioncouchée sur laquelle les effets gravitaires ne sont pas pris en compte. Le CT-Scan est unemodalité particulièrement irradiante et l'IRM est plus spécifiquement dédiée à l'étude des tissusmous. Le système EOS permet de reconstruire en 3D les os à partir d'une paire deradiographies biplanes à faible dose d'irradiation. En plus, le système EOS propose uneacquisition en position debout, prenant en compte les effets gravitaires. Cette thèse contribue àl'amélioration des méthodes de reconstruction 3D des membres inférieurs à partir des radiosbiplanes. Dans le cadre de thèse on a proposé et évalué : 1) Une méthode de reconstruction3D des membres inférieurs s'appuyant sur des modèles paramétrés et des inférencesstatistiques. 2) Une méthode d'auto-amélioration de la reconstruction 3D des membresinférieurs en utilisant du traitement d'images local et le recalcul d'inférences statistiques. 3)Enfin, des méthodes utilisant des critères de similarité d'images et des critères morphologiquespour détecter de manière automatique le côté médial et latéral du fémur et du tibia. Le but estd'éviter l'inversion par l'opérateur de condyles fémoraux et plateaux tibiaux, affectant la valeurdes paramètres cliniques, surtout les torsions. La méthode de reconstruction proposée dans lecadre de cette thèse est intégrée dans le logiciel sterEOS® et utilisée dans une soixantained'hôpitaux au monde. Les méthodes développées dans le cadre de cette thèse ont permis deprogresser vers la reconstruction semi-automatisée, précise et robuste du membre inférieur

Thesis (Ph. D.)--History, Technology and Society, Georgia Institute of Technology, 2006. / Dr. Susan Smulyan, Committee Member ; Dr. John Tone, Committee Member ; Dr. Larry Foster, Committee Member ; Dr. Steve Usselman, Committee Member ; Dr. John Krige, Committee Chair.

MATOS, Teresa Cristina Furtado. Rádios Comunitárias: sintonia dissonante e auto-imagem. 2006. 238f. – Tese (Doutorado) – Universidade Federal do Ceará, Programa de Pós-graduação em Sociologia, Fortaleza (CE), 2006. / Submitted by Márcia Araújo (marcia_m_bezerra@yahoo.com.br) on 2014-01-22T13:17:47Z No. of bitstreams: 1 2006-TESE-TCFMATOS.pdf: 2320094 bytes, checksum: 3781b9de13f01f1cfdb5c82ae007bb45 (MD5) / Approved for entry into archive by Márcia Araújo(marcia_m_bezerra@yahoo.com.br) on 2014-01-22T13:45:25Z (GMT) No. of bitstreams: 1 2006-TESE-TCFMATOS.pdf: 2320094 bytes, checksum: 3781b9de13f01f1cfdb5c82ae007bb45 (MD5) / Made available in DSpace on 2014-01-22T13:45:25Z (GMT). No. of bitstreams: 1 2006-TESE-TCFMATOS.pdf: 2320094 bytes, checksum: 3781b9de13f01f1cfdb5c82ae007bb45 (MD5) Previous issue date: 2006 / The present work evaluates the struggle found within the field of community radios in relation to the meaning of what a “community radio” is. Beginning with the category “self-image”, considered as a relational construct, the process of community radios’ image built-up is discussed considering its relationship to several segments and social concerns. The research is directed mainly towards the community radios’ universe in the city of Fortaleza, Ceara, and aims at understanding the struggle environment considering a long course approach extending from the founding movement of community radios that took place in 1980 in the city to present day bringing it closer to the development path of the mass media in Brazil. / O presente trabalho analisa o conflito existente no campo da radiofonia comunitária em torno dos sentidos do que seja uma “emissora comunitária”. A partir da categoria “auto-imagem”, entendida como uma construção relacional, se discute o processo de formulação da imagem das rádios comunitárias, considerando sua relação com diversos segmentos e interesses sociais. A pesquisa se centra, principalmente, no universo de emissoras comunitárias da cidade de Fortaleza-CE, e busca compreender o ambiente de disputas numa perspectiva de longo curso, desde a fundação do movimento de rádios comunitárias na cidade, que ocorre a partir dos anos 1980, até hoje, aproximando-o da trajetória de desenvolvimento dos meios de comunicação no Brasil.

abstract: In this dissertation, I propose potential techniques to improve the quality-of-service (QoS) of real-time applications in cognitive radio (CR) systems. Unlike best-effort applications, real-time applications, such as audio and video, have a QoS that need to be met. There are two different frameworks that are used to study the QoS in the literature, namely, the average-delay and the hard-deadline frameworks. In the former, the scheduling algorithm has to guarantee that the packet's average delay is below a prespecified threshold while the latter imposes a hard deadline on each packet in the system. In this dissertation, I present joint power allocation and scheduling algorithms for each framework and show their applications in CR systems which are known to have strict power limitations so as to protect the licensed users from interference. A common aspect of the two frameworks is the packet service time. Thus, the effect of multiple channels on the service time is studied first. The problem is formulated as an optimal stopping rule problem where it is required to decide at which channel the SU should stop sensing and begin transmission. I provide a closed-form expression for this optimal stopping rule and the optimal transmission power of secondary user (SU). The average-delay framework is then presented in a single CR channel system with a base station (BS) that schedules the SUs to minimize the average delay while protecting the primary users (PUs) from harmful interference. One of the contributions of the proposed algorithm is its suitability for heterogeneous-channels systems where users with statistically low channel quality suffer worse delay performances. The proposed algorithm guarantees the prespecified delay performance to each SU without violating the PU's interference constraint. Finally, in the hard-deadline framework, I propose three algorithms that maximize the system's throughput while guaranteeing the required percentage of packets to be transmitted by their deadlines. The proposed algorithms work in heterogeneous systems where the BS is serving different types of users having real-time (RT) data and non-real-time (NRT) data. I show that two of the proposed algorithms have the low complexity where the power policies of both the RT and NRT users are in closed-form expressions and a low-complexity scheduler. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2016

Made available in DSpace on 2015-05-14T13:26:57Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 2935206 bytes, checksum: d45685765ac0067ad1edb63c7457e494 (MD5) Previous issue date: 2011-05-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Este trabajo busca analizar el significado de la relación entre los jóvenes y el movimiento de radios comunitarias, así como su consecuencia en el área de los valores constitutivos de las identidades sociales juveniles. Tiene como objetivo principal analizar la participación de los jóvenes en la organización de una radio comunitaria de la ciudad de João Pessoa. Para ello, observa las relaciones establecidas entre el trabajo cotidiano de la radio y del barrio, para que, de esa manera, si puedan identificar elementos que se articulan y actúan en la construcción de las identidades de los jóvenes. / O presente trabalho busca analisar o significado da relação entre jovens e movimento de rádios comunitárias e seu reflexo na área dos valores constituintes das identidades sociais juvenis. Tem como foco a participação de jovens na organização de uma rádio comunitária da cidade de João Pessoa. Para tanto, observa as relações de socialidade estabelecidas no plano do cotidiano da rádio e do bairro em que esta se encontra, de forma que, assim, se possam identificar elementos que se articulam e agem na construção das identidades juvenis.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / O presente trabalho analisa o conflito existente no campo da radiofonia comunitÃria em torno dos sentidos do que seja uma âemissora comunitÃriaâ. A partir da categoria âauto-imagemâ, entendida como uma construÃÃo relacional, se discute o processo de formulaÃÃo da imagem das rÃdios comunitÃrias, considerando sua relaÃÃo com diversos segmentos e interesses sociais. A pesquisa se centra, principalmente, no universo de emissoras comunitÃrias da cidade de Fortaleza-CE, e busca compreender o ambiente de disputas numa perspectiva de longo curso, desde a fundaÃÃo do movimento de rÃdios comunitÃrias na cidade, que ocorre a partir dos anos 1980, atà hoje, aproximando-o da trajetÃria de desenvolvimento dos meios de comunicaÃÃo no Brasil. / The present work evaluates the struggle found within the field of community radios in relation to the meaning of what a âcommunity radioâ is. Beginning with the category âself-imageâ, considered as a relational construct, the process of community radiosâ image built-up is discussed considering its relationship to several segments and social concerns. The research is directed mainly towards the community radiosâ universe in the city of Fortaleza, Ceara, and aims at understanding the struggle environment considering a long course approach extending from the founding movement of community radios that took place in 1980 in the city to present day bringing it closer to the development path of the mass media in Brazil.

Many different types of promising spectrum sensing algorithms for Cognitive Radio (CR) have already been developed. However, many of these algorithms lack robustness with respect to signal statistical parameters uncertainties, such as the noise variance or the shape of its distribution (often assumed to be simply Gaussian). In conjunction with the low Signal-to-Noise Ratio (SNR) requirements, this lack of robustness can often render interesting sensing algorithms impractical for real-life applications. In this thesis, we primarily focus on the impact of heavy-tail noise distributions on different CR detectors and the use of signal limiters (mostly the spatial sign function) to improve their robustness to such noise distributions. Introducing a non-linear transformation of the received signal prior to its processing by the detector fundamentally changes the signal distribution which in turn modifies the distribution of the detector statistic. In order to parametrize the detector and study its performance, it is then necessary to know the shape of the modified distribution.Three types of detectors are investigated: a generic second-order cyclic-feature detectors, a Scaled-Largest Eigenvalue (SLE) detector studied in the context of stationary time-series and a new Sequential Likelihood Ratio Test (SLRT) detector. The analysis conducted for each detector revolves around the influence of its parameters, the distribution of the detector statistic and several comparisons with similar detectors for various detection scenarios. Our results indicate that at the cost of a moderate performance loss in a Gaussian noise environment, all the detectors fitted with a signal limiter become robust to impulsive noise and noise parameters uncertainties. We provide analytical approximations for the detectors statistical distribution that allow us to use the detectors in such configurations as well as to study their performance for different signal limiters and noise distributions. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Cognitive radios is one of the hot topics for emerging and future wireless commu- nication. It has been proposed as a suitable solution for the spectrum scarcity caused by the increase in frequency demand. The concept is based on allowing unlicensed users, called cognitive or secondary users, to share the unoccupied frequency bands with their owners, called the primary users, under constraints on the interference they cause to them. The objective of our work is to propose some enhancements to cognitive radio systems while taking into account practical constraints. Cogni- tive radios requires a capability to detect spectrum holes (spectrum sensing) and a scheduling flexibility to avoid the occupied spectrum and selectively use the empty spectrum (dynamic resource allocation). Thus, the work is composed of two main parts. The first part focuses on cooperative spectrum sensing. We compute in this part the analytical performance of cooperative spectrum sensing under non identical and imperfect channels. Different schemes are considered for the cooperation between users such as hard binary, censored information, quantized, and soft information. The second part focuses on the dynamic resource allocation. We first propose low-cost re- source allocation algorithms that use location information to estimate the interference to primary users to replace absence of instantaneous channel state information. We extend these algorithms to handle practical implementation constraints such as dis- 5 crete bit-loading and collocated subcarriers allocations. We then propose a reduced dimension approach based on the grouping of subcarriers into clusters and performing the resource allocation over clusters of subcarriers instead of single subcarriers. This approach is shown to reduce the computational complexity of the algorithm with lim- ited performance loss. In addition, it is valid for a generic set of resource allocation problems in presence of co-channel interference between users.

With the proliferation of mobile applications and the abundance of wireless devices, it is increasingly common for devices to support multiple radios. When two devices are communicating they should choose the best available radio based on user preference and application requirements. This type of “radio switching” should happen automatically, so that the system optimizes performance dynamically. To achieve this objective, we design an Autonomous and Intelligent Radio Switching (AIRS) system to leverage the radio heterogeneity common in today's wireless devices. The AIRS system consists of three key components. First, we design a radio preference evaluation module to dynamically select the best radio according to users' preference, application's QoS requirements, and the device battery usage. Second, we propose a link quality measurement and prediction module to predict the radio quality under a variety of mobility and interference conditions. Third, we present a radio switching decision making module to switch to the preferred available radio intelligently, based on the preference and link quality evaluations. The AIRS system maintains connectivity, as well as improves link quality, via dynamic and intelligent radio switching, regardless of interference or collisions from the interfaces of other devices. The radio preference evaluation module is able to generate and adjust a preference list dynamically. Multiple users' requirements are satisfied in a mutually beneficial manner and the selected radio is Pareto optimal. The link prediction module is able to achieve an accuracy above 90% under a variety of mobility and interference conditions. The module can dynamically increase the link measurement interval and significantly reduce its power consumption, without sacrificing accuracy. The decision algorithm uses several parameters to avoid switching radios too frequently, and is able to provide dynamic, but stable radio switching, while balancing the competing objectives of high throughput and low power consumption. Overall, the AIRS system is able to achieve high goodput (application level throughput) and long battery life as applied to handoff management in a frequently changing mobile environment.