The growing demand for ubiquitous broadband network connectivity and continuously falling prices in hardware operating on the unlicensed bands have put Wi-Fi technology in a position to lead the way in rapid innovation towards high performance wireless for the future. The success story of Wi-Fi contributed to the development of widespread variety of options for unlicensed access (e.g., Bluetooth, Zigbee) and has even sparked regulatory bodies in several countries to permit access to unlicensed devices in portions of the spectrum initially licensed to TV services. In this thesis we present novel spectrum management algorithms for networks employing 802.11 and TV white spaces broadly aimed at efficient use of spectrum under consideration, lower contention (interference) and high performance. One of the target scenarios of this thesis is neighbourhood or citywide wireless access. For this, we propose the use of IEEE 802.11-based multi-radio wireless mesh network using omnidirectional antennae. We develop a novel scalable protocol termed LCAP for efficient and adaptive distributed multi-radio channel allocation. In LCAP, nodes autonomously learn their channel allocation based on neighbourhood and channel usage information. This information is obtained via a novel neighbour discovery protocol, which is effective even when nodes do not share a common channel. Extensive simulation-based evaluation of LCAP relative to the state-of-the-art Asynchronous Distributed Colouring (ADC) protocol demonstrates that LCAP is able to achieve its stated objectives. These objectives include efficient channel utilisation across diverse traffic patterns, protocol scalability and adaptivity to factors such as external interference. Motivated by the non-stationary nature of the network scenario and the resulting difficulty of establishing convergence of LCAP, we consider a deterministic alternative. This approach employs a novel distributed priority-based mechanism where nodes decide on their channel allocations based on only local information. Key enabler of this approach is our neighbour discovery mechanism. We show via simulations that this mechanism exhibits similar performance to LCAP. Another application scenario considered in this thesis is broadband access to rural areas. For such scenarios, we consider the use of long-distance 802.11 mesh networks and present a novel mechanism to address the channel allocation problem in a traffic-aware manner. The proposed approach employs a multi-radio architecture using directional antennae. Under this architecture, we exploit the capability of the 802.11 hardware to use different channel widths and assign widths to links based on their relative traffic volume such that side-lobe interference is mitigated. We show that this problem is NP-complete and propose a polynomial time, greedy channel allocation algorithm that guarantees valid channel allocations for each node. Evaluation of the proposed algorithm via simulations of real network topologies shows that it consistently outperforms fixed width allocation due to its ability to adapt to spatio-temporal variations in traffic demands. Finally, we consider the use of TV-white-spaces to increase throughput for in-home wireless networking and relieve the already congested unlicensed bands. To the best of our knowledge, our work is the first to develop a scalable micro auctioning mechanism for sharing of TV white space spectrum through a geolocation database. The goal of our approach is to minimise contention among secondary users, while not interfering with primary users of TV white space spectrum (TV receivers and microphone users). It enables interference-free and dynamic sharing of TVWS among home networks with heterogeneous spectrum demands, while resulting in revenue generation for database and broadband providers. Using white space availability maps from the UK, we validate our approach in real rural, urban and dense-urban residential scenarios. Our results show that our mechanism is able to achieve its stated objectives of attractiveness to both the database provider and spectrum requesters, scalability and efficiency for dynamic spectrum distribution in an interference-free manner.

Il est attendu que les radios flexibles constituent un tournant technologique majeur dans le domaine des communications sans fil. Le point de vue adopté en radios flexibles est de considérer les canaux de communication comme un ensemble de ressources qui peuvent être accédées sur demande par un réseau primaire sous licence ou de manière opportuniste par un réseau secondaire à plus faible priorité. Pour la couche physique, le réseau primaire n'a idéalement aucune information sur l'existence d'un ou plusieurs réseaux secondaires, de sorte que ces derniers doivent explorer l'environnement aérien de manière autonome à la recherche d'opportunités d'accès au canal et exploiter ces ressources de manière optimale au sein du réseau secondaire. Les phases d'exploration et d'exploitation, qui impliquent la gestion de nombreux agents, doivent être très fiables, rapides et efficaces. L'objectif du présent rapport est de modéliser, d'analyser et de proposer des solutions efficaces et quasi optimales pour ces dernières opérations. En particulier, en ce qui concerne la phase d'exploration, nous nous appuierons sur le principe d'entropie maximale pour modéliser des canaux de communication, pour lesquels nous calculerons le test optimal de Neyman-Pearson de détection de plusieurs sources via un réseau de capteurs. Cette procédure permet à un réseau secondaire d'établir la présence de ressources spectrales disponibles. La complexité calculatoire de l'approche optimale appelle cependant la mise en place de méthodes moins onéreuses, que nous rappellerons et discuterons. Nous étendrons alors le test de détection en l'estimation aveugle de la position de sources multiples, qui permet l'acquisition d'informations détaillées sur les ressources spectrales disponibles. Le dernier chapitre d'importance sera consacré à la phase d'exploitation optimale des ressources au niveau du réseau secondaire. Pour ce faire, nous obtiendrons une approximation fine du débit ergodique d'un canal multi-antennes à accès multiples et proposerons des solutions peu coûteuses en termes de feedback afin que les réseaux secondaires s'adaptent rapidement aux évolutions rapides du réseau primaire. Les outils mathématiques et algorithmes proposés dans ce rapport proviennent essentiellement de récents progrès en théorie des matrices aléatoires, et plus spécifiquement de l'étude de matrices aléatoires à grandes dimensions et à entrées statistiquement indépendantes. Une introduction précise des concepts principaux ainsi que des résultats récents requis à la compréhension complète du présent document sont également proposés.

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 / For a better understanding and diagnosis of the pathologies affecting the spatialorganization of our skeleton it is necessary to address them in 3D. CT-Scan and MRI areimaging modalities commonly used to study the musculoskeletal system in 3D. Moreover,patients are recorded in reclining position thus gravity effect can’t be taken into account.Furthermore, CT-Scan exposes patient to high radiation doses and MRI is used mostly tocharacterize soft tissues. With the EOS system, from a pair of low dose biplanar radiographs wecan reconstruct bones in 3D, and the radiographs are recorded in standing position thus gravityeffects are considered. This thesis contributes to the improvement of the 3D reconstructionmethods of lower limbs from biplanar radiographs. In this thesis we have proposed andevaluated: 1) A 3D reconstruction method of the lower limbs based on parametric models andstatistical inferences. 2) A method for the auto-improvement of the 3D reconstruction of thelower limbs. This method combines image processing and the recalculation of the statisticalinferences. 3) Finally, methods based on similarity measures and shape criteria were used todetect automatically the medial and lateral side of the femur and tibia. The aim of thesemethods is to avoid the inversion of the femoral and tibial condyles in biplanar radiographs.These inversions have an impact in the calculation of clinical measurements, particularly thetorsional ones. The reconstruction method proposed in this thesis is already integrated withinthe sterEOS® software, available in 60 hospitals around the world. The methods developed inthis thesis have led us to a semi-automatic, accurate and robust reconstruction of lower limbs.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This research, of qualitative character, studies RadioComFM , of the city Pelotas ( RS ) in order to investigate how communicational strategies for social mobilization of community radio contribute to the democratization of communication . To answer this problem, it is defined as a general goal, to investigate the communicational strategies of RadioCom FM and its interfaces with social mobilization and democratization of communication. The specific objectives are to identify the profile of RadioCom; to check social mobilization strategies present in the radio programming schedule; and to understand the relationship between community media, social mobilization strategies and democratization of communication. It is used as research strategy, the case study, with the following sources of evidence: documentary research; observation of programming and daily of the radio; and semi structured interviews. The interviews were conducted with managers and people that participate of the radio programming schedule. The collected data were systematized and interpreted with the use of the method of thematic content analysis. Thus, it is identifies, in RadioCom, a multidimensional media, that comprises , in the complex of a structure of community communication, the collective, legal-normative, political and socio-communicational dimensions. In relation to communicational strategies for social mobilization checked in the programming schedule, it is inferred that the RadioCom is qualified by the plurality of contents of public interest and the differential bias of the commercial media. The interlacement of the concepts of community media, social mobilization strategies and democratization of communication are established by the meanings given to each concept. So, by the investigation of communicational strategies for social mobilization, it is concluded that the RadioCom contributes to the processes of democratization of communication, configuring itself as a strategy to do so. / Esta pesquisa, de caráter qualitativo, estuda a RádioCom FM, da cidade de Pelotas (RS), com o intuito de investigar como as estratégias comunicacionais de mobilização social das rádios comunitárias contribuem para a democratização da comunicação. Para responder a essa problemática, define-se, como objetivo geral, investigar as estratégias comunicacionais da RádioCom FM e suas interfaces com a mobilização social e a democratização da comunicação. Os objetivos específicos são identificar o perfil da RádioCom; verificar as estratégias de mobilização social presentes na programação da rádio; e perceber as relações existentes entre mídia comunitária, estratégias de mobilização social e democratização da comunicação. Utiliza-se como estratégia de pesquisa, o estudo de caso, com as seguintes fontes de evidência: pesquisa documental; observação da programação e do cotidiano da rádio; e entrevistas semiestruturadas. As entrevistas foram realizadas com gestores e com pessoas que participam da programação da rádio. As informações coletadas foram sistematizadas e interpretadas com o emprego do método de análise de conteúdo temática. Desta forma, identifica-se, na RádioCom, uma mídia multidimensional, que compreende, no complexo de uma estrutura de comunicação comunitária, as dimensões coletiva, jurídico-normativa, política e sócio-comunicacional. Em relação às estratégias comunicacionais de mobilização social verificadas na programação, infere-se que a RádioCom é qualificada pela pluralidade de conteúdos de interesse público e pelo viés diferenciado dos meios de comunicação comerciais. O entrelaçamento dos conceitos de mídia comunitária, estratégias de mobilização social e democratização da comunicação estabelecem-se pelas significações dadas a cada conceituação. Assim, pela investigação das estratégias comunicacionais para a mobilização social, conclui-se que a RádioCom contribui para os processos de democratização da comunicação, configurando-se como estratégia para tal.

Cognitive radios have been proposed as a new technology to counteract the spectrum scarcity issue and increase the spectral efficiency. In cognitive radios, the sparse assigned frequency bands are opened to secondary users, provided that interference induced on the primary licensees is negligible. Cognitive radios are established in two steps: the radios firstly sense the available frequency bands by detecting the presence of primary users and secondly communicate using the bands that have been identified as not in use by the primary users.<p><p>In this thesis we investigate how to improve the efficiency of cognitive radio networks when multiple cognitive radios cooperate to sense the spectrum or control their interferences. A major challenge in the design of cooperating devices lays in the need for exchange of information between these devices. Therefore, in this thesis we identify three specific types of control information exchange whose efficiency can be improved. Specifically, we first study how cognitive radios can efficiently exchange sensing information with a coordinator node when the reporting channels are noisy. Then, we propose distributed learning algorithms allowing to allocate the primary network sensing times and the secondary transmission powers within the secondary network. Both distributed allocation algorithms minimize the need for information exchange compared to centralized allocation algorithms. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Cognitive radio (CR) networks and heterogeneous cellular networks are promising approaches to satisfy the demand for higher data rates and better connectivity. A CR network increases the utilization of the radio spectrum by opportunistically using it. Heterogeneous networks provide high data rates and improved connectivity by spatially reusing the spectrum and by bringing the network closer to the user. Interference presents a critical challenge for reliable communication in these networks. Accurately modeling it is essential in ensuring a successful design and deployment of these networks. We first propose modeling the aggregate interference power at a primary receiver (PU-Rx) caused from transmissions by randomly located cognitive users (CUs) in a CR network as a shifted lognormal random process. Its parameters are determined using a moment matching method. Extensive benchmarking shows that the proposed model is more accurate than the lognormal and Gaussian process models considered in the literature, even for a relatively dense deployment of CUs. It also compares favorably with the asymptotically exact stable and symmetric truncated stable distribution models, except at high CU densities. Our model accounts for the effect of imperfect spectrum sensing, interweave and underlay modes of CR operation, and path-loss, time-correlated shad-owing and fading of the various links in the network. It leads to new expressions for the probability distribution function, level crossing rate (LCR), and average exceedance duration (AED). The impact of cooperative spectrum sensing is also characterized. We also apply and validate the proposed model by using it to redesign the primary exclusive zone to account for the time-varying nature of interference. Next we model the uplink inter-cell aggregate interference power in homogeneous and heterogeneous cellular systems as a simpler lognormal random variable. We develop a new moment generating function (MGF) matching method to determine the lognormal’s parameters. Our model accounts for the transmit power control, peak transmit power constraint, small scale fading and large scale shadowing, and randomness in the number of interfering mobile stations and their locations. In heterogeneous net-works, the random nature of the number and locations of low power base stations is also accounted for. The accuracy of the proposed model is verified for both small and large values of interference. While not perfect, it is more accurate than the conventional Gaussian and moment-matching-based lognormal and Gamma distribution models. It is also performs better than the symmetric-truncated stable and stable distribution models, except at higher user density.

One statement that we can make with absolute certainty in our current time is that wireless communication is now the standard and the de-facto type of communication. Cognitive radios are able to interpret the frequency spectrum and adapt. The aim of this work is to be able to predict whether a frequency channel is going to be busy or free in a specific time located in the future. To do this, the problem is modeled as a time series problem where each usage of a channel is treated as a sequence of busy and free slots in a fixed time frame. For this time series problem, the method being implemented is one of the latest, state-of-the-art, technique in machine learning for time series and sequence prediction: long short-term memory neural networks, or LSTMs.

Spin torque oscillator (STO) technology has a unique blend of features, including but not limited to octave tunability, GHz operating frequency, and nanoscaled size, which makes it highly suitable for microwave and radar applications. This thesis studies the fundamentals of STOs, utilizes the state-of-art STO's advantages, and proposes two STO-based microwave systems targeting its microwave applications and measurement setup, respectively. First, based on an investigation of possible STO applications, the magnetic tunnel junction (MTJ) STO shows a great suitability for microwave oscillator in multi-standard multi-band radios. Yet, it also imposes a large challenge due to its low output power, which limits it from being used as a microwave oscillator. In this regard, different power enhancement approaches are investigated to achieve an MTJ STO-based microwave oscillator. The only possible approach is to use a dedicated CMOS wideband amplifier to boost the output power of the MTJ STO. The dedicated wideband amplifier, containing a novel Balun-LNA, an amplification stage and an output buffer, is proposed, analyzed, implemented, measured and used to achieve the MTJ STO-based microwave oscillator. The proposed amplifier core consumes 25.44 mW from a 1.2 V power supply and occupies an area of 0.16 mm2 in a 65 nm CMOS process. The measurement results show a S21 of 35 dB, maximum NF of 5 dB, bandwidth of 2 GHz - 7 GHz. This performance, as well as the measurement results of the proposed MTJ STO-based microwave oscillator, show that this microwave oscillator has a highly-tunable range and is able to drive a PLL. The second aspect of this thesis, firstly identifies the major difficulties in measuring the giant magnetoresistance (GMR) STO, and hence studying its dynamic properties. Thereafter, the system architecture of a reliable GMR STO measurement setup, which integrates the GMR STO with a dedicated CMOS high frequency IC to overcome these difficulties in precise characterization of GMR STOs, is proposed. An analysis of integration methods is given and the integration method based on wire bonding is evaluated and employed, as a first integration attempt of STO and CMOS technologies. Moreover, a dedicated high frequency CMOS IC, which is composed of a dedicated on-chip bias-tee, ESD diodes, input and output networks, and an amplification stage for amplifying the weak signal generated by the GMR STO, is proposed, analyzed, developed, implemented and measured. The proposed dedicated high frequency circuits for GMR STO consumes 14.3 mW from a 1.2 V power supply and takes a total area of 0.329 mm2 in a 65 nm CMOS process. The proposed on-chip bias-tee presents a maximum measured S12 of -20 dB and a current handling of about 25 mA. Additionally, the proposed dedicated IC gives a measured gain of 13 dB with a bandwidth of 12.5 GHz - 14.5 GHz. The first attempt to measure the (GMR STO+IC) pair presents no RF signal at the output. The possible cause and other identified issues are given. / <p>QC 20140114</p>

The onset of quantum computing threatens commonly used schemes for information secrecy across wireless communication channels, particularly key-based data-level encryption. This calls for secrecy schemes that can provide everlasting secrecy resistant to increased computational power of an adversary. One novel physical layer scheme proposes that an intended receiver capable of performing analog cancellation of a known key-based interference would hold a significant advantage in recovering small underlying messages versus an eavesdropper performing cancellation after analog-to-digital conversion. This advantage holds even in the event that an eavesdropper can recover and use the original key in their digital cancellation. Inspired by this scheme, a flexible software-defined radio receiver design capable of maintaining analog cancellation ratios consistently over 40 dB, reaching up to and over 50 dB, is implemented in this thesis. Maintaining this analog cancellation requires very precise time-frequency synchronization along with accurate modeling and simulation of the channel effects on the interference. The key sources of synchronization error preventing this test bed from achieving and maintaining perfect interference cancellation, sub-sample period timing errors and limited radio frequency stability, are explored for possible improvements. To further prove robustness of the implemented secrecy scheme, the testbed is shown to operate with both phase-shift keying and frequency-modulated waveforms. Differences in the synchronization algorithm used for the two waveforms are highlighted. Interference cancellation performance is measured for increasing interference bandwidth and shown to decrease with such. The implications this testbed has on security approaches based on intentional interference employed to confuse eavesdroppers is approached from the framework proposed in the motivating everlasting secrecy scheme. Using analog cancellation levels from the hardware testbed, it is calculated that secrecy rates up to 2.3 bits/symbol are gained by receivers (intended or not) performing interference cancellation in analog rather than on a digital signal processor. Inspired by the positive gains in secrecy over systems not performing analog cancellation prior to signal reception, a novel secrecy scheme that focuses on the advantage an analog canceller holds in receiver amplifier compression is proposed here. The adversary amplifier is assumed to perform linear cancellation after the interference has passed through their nonlinear amplifier. This is accomplished by deriving the distribution of the interference residual after undergoing an inverse tangent transfer function and perfect linear cancellation. Parameters of this scheme are fit for the radios and cancellation ratios observed in the testbed, resulting in a secrecy gain of 0.95 bits/symbol. The model shows that larger message powers can still be kept secure for the achieved levels of cancellation, thus providing an even greater secrecy gain with increased message transmission power.

In radio frequency (RF), filtering is an essential part of RF transceivers. They are employed for different purposes of band selection, channel selection, interference cancellation, image rejection, etc. These are all translated in selecting the wanted signal while mitigating the rest. This can be performed by either selecting the desired frequency range by a band pass filter or rejecting the unwanted part by a band stop filter. Although there has been tremendous effort to design RF tunable filters, there is still lack of designs with frequency and bandwidth software-tuning capability at frequencies above 4 GHz. This prevents the implementation of Software Defined Radios (SDR) where software tuning is a critical part in supporting multiple standards and frequency bands. Designing a tunable integrated filter will not only assist in realization of SDR, but it also causes an enormous shrinkage in the size of the circuit by replacing the current bulky off-chip filters. The main purpose of this research is to design integrated band pass and band stop filters aimed to perform interference cancellation. In order to do so, two systems are proposed for this thesis. The first system is a band pass filter capable of frequency and band with tuning for C band frequency range (4-8 GHz) and is implemented in 0.13 µm BiCMOS technology. Frequency tunability is accomplished by using a variable capacitor (varactor) and bandwidth tuning is carried out by employing a negative transconductance cell to compensate for the loss of the elements. Additional circuitry is added to the band pass filter to enhance the selectivity of the filter. The second system is a band stop filter (notch) with the same capability as the band pass filter in terms of tuning. This system is implemented in C band, similar to its band stop counterpart and is capable of tuning its depth by using a negative transconductance in an LC tank. A negative feedback is added to the circuit to improve the bandwidth. While implemented in the same process as the band pass filter, it only employs CMOS transistors since it is generally more attractive due to its lower cost and scalability. Both of the systems mentioned use a varactor for changing the center frequency which is a nonlinear element. Therefore, the nonlinearity of it is modelled using two different methods of nonlinear feedback and Volterra series in order to gain further understanding of the nonlinear process taking place in the LC tank. After the validation of the models proposed using Cadence Virtuoso simulator, two methods of design and tuning are suggested to improve the linearity of the system. After post layout-extraction, the band pass filter is capable of Q tuning in the range of 3 to 270 and higher. With the noise figure of 10 to 14 dB and input 1-dB compression point as high as 2 dBm, the system shows a reasonably good performance along its operating frequency of 4 to 8 GHz. The band stop filter which is designed in the same frequency band can achieve better than 55 dB of rejection with the noise figure of 6.7 to 8.8 dB and 1-dB compression point of -4 dBm. With the power consumption of 39 to 70 mW, the band stop filter can be used in a low power receiver to suppress unwanted signals. The technique used in the band stop filter can be applied to higher frequency ranges if the circuit is implemented in a more advanced silicon technology. Implementing the mentioned filters in a receiver along with other elements of low noise amplifiers, mixers, etc. would be a major step toward full implementation of SDR systems. Studying the linearity theory of varactors would help future designers identify the sources of nonlinearity and suggest more efficient tuning techniques to improve the linearity of RF electronic systems. / Master of Science