Ultrawideband (UWB) is one of the promising technologies for future short-range high data rate communications (e.g. for wireless personal area networks) and longer range low data rate communications (e.g. wireless sensor networks).Despite its various advantages and potentials (e.g. low-cost circuitry, unlicensed reuse of licensed spectrum, precision ranging capability etc.), UWB also has its own challenges. The goal of this dissertation is to identify and address some of those challenges, and provide a framework for practical UWB transceiver design.In this dissertation, various modulation options for UWB systems are reviewed in terms of their bit error rate (BER) performances, spectral characteristics, modem and hardware complexities, and data rates. Time hopping (TH) code designs for both synchronous (introduced an adaptive code assignment technique) and asynchronous UWB impulse radio (IR) systems are studied. An adaptive assignment of two different multiple access parame ters (number of pulses per symbol and number of pulse positions per frame)is investigated again considering both synchronous and asynchronous scenarios, and a mathematical framework is developed using Gaussian approximations of interference statistics for different scenarios. Channel estimation algorithms for multiuser UWB communication systems using symbol-spaced (proposed a technique that decreases the training size), frame-spaced (proposed a pulse-discarding algorithm for enhanced estimationperformance), and chip-spaced (using least squares (LS) estimation) sampling are analyzed.A comprehensive review on multiple accessing andinterference avoidance/cancellation for IR-UWB systems is presented.BER performances of different UWB modulation schemes in the presence of timing jitter are evaluated and compared in static and multipath fading channels, and finger estimation error, effects of jitter distribution, and effects of pulse shape are investigated. A unified performance analysis app roach for different IR-UWB transceiver types (stored-reference, transmitted-reference, and energy detector) employing various modulation options and operating at sub-Nyquist sampling rates is presented. The time-of-arrival (TOA) estimation performance of different searchback schemesunder optimal and suboptimal threshold settings are analyzed both for additive white Gaussian noise (AWGN) and multipath channels.

The idea that the radio spectrum is growing ever more scarce has become commonplace, and is being reinforced by the recent bidding wars among telecom operators. New wireless applications tend to be deployed in the relatively narrow unlicensed frequency bands, worsening the problem of interference for all users.  However, not all frequency bands are in use in every location all the time, creating temporal and spatial gaps (also known as white spaces) that cognitive radio systems aim to take advantage of. In order to achieve that, such systems need to be able to constantly scan large chunks of the radio spectrum to keep track of which frequency bands are locally available any given moment, thus allowing users to switch to one of these unoccupied frequency bands once the current band becomes unusable (or less useful). This requirement of wideband sensing capabilities often translates into the need to install specialized radio components, raising the costs of such systems, and is often at odds with the focus on monitoring the current band as is done by traditional wireless devices. The goal of this master’s thesis project is to simplify cognitive radio systems by shifting the wideband sensing functionality to a specialized and inexpensive embedded platforms that will act as a white space sensor, thus freeing cognitive radio users from this task and making it easier to integrate dynamic spectrum management techniques into existing systems. To do that a wireless sensor gateway platform developed by a previous master’s thesis has been repurposed as a prototype white space detector and tested against several wireless transmitters.  The aim is to develop a standalone platform that can be deployed all around an area to collect data that can be used to create a geographical map of the use of the spectrum. Such a system should require as little maintenance as possible, thus auto-update and self-configuring features have been implemented in the detector, as well as a simple scanning protocol that allows for remote configuration of the wideband sensing parameters. Furthermore, a basic server has been developed to aggregate and display the data provided by the different sensors. / Tanken att radiospektrum blir allt knappare har blivit vardagsmat, och förstärks av de senaste budgivning krig mellan teleoperatörer. Nya trådlösa applikationer tenderar att sättas i de relativt smala olicensierade frekvensband, förvärrade problemet med störningar för alla användare. Men inte alla frekvensband som används i varje plats hela tiden, skapar tidsmässiga och rumsliga luckor (även känd som vita fläckar) som kognitiva radiosystem syftar till att dra nytta av.  För att uppnå detta, sådana system måste hela tiden kunna scanna stora delar av radiospektrum för att hålla reda på vilka frekvensband är lokalt tillgängliga varje givet ögonblick, vilket gör omkopplaren när den nuvarande bandet blir obrukbar.  Det här kravet på bredbands avkänning kapaciteter översätter ofta in behovet av att installera specialiserade radiokomponenter, höja kostnaderna för sådana system, och är ofta i strid med fokus på övervakning av strömmen band med traditionella trådlösa enheter. Målet med detta examensarbete är att förenkla kognitiva radiosystem med wideband avkänning funktionalitet till en specialiserad och billig inbäddad plattform som kommer att fungera som ett vitt utrymme sensor, vilket frigör kognitiva radio användare från denna uppgift och gör det enklare att integrera dynamiskt spektrum förvaltning tekniker i befintliga system. För att göra det en trådlös sensor gateway plattform som utvecklats av ett tidigare examensarbete har apterat som en prototyp blanktecken detektor och testas mot flera trådlösa sändare. Målet är att utveckla en fristående plattform som kan sättas runt för att skapa en geografisk karta av användningen av spektrum och kräva så lite underhåll som möjligt, har automatisk uppdatering och självkonfigurerande funktioner implementerats i detektorn, samt som en enkel scanning protokoll som möjliggör fjärrkonfiguration av den bredbandiga avkänningsparametrarna. Dessutom har en grundläggande server utvecklats för att aggregera och visa uppgifterna från de olika sensorerna.

[pt] O rádio cognitivo é uma tecnologia que visa o compartilhamento do espectro radioelétrico entre usuários primários licenciados e os demais usuários secundários de maneira harmoniosa, sem provocar interferências que prejudiquem a prestação dos serviços e visando uma melhoria na eficiência do uso do espectro radioelétrico, que é um recurso cada vez mais escasso. No âmbito da pesquisa referente a esta dissertação, é construído e implementado no GNU Radio um esquema de avaliação de desempenho de detectores para rádio cognitivo, é construído o detector de energia, e são implementadas simulações computacionais e ensaios por meio de duas USRP para avaliar o desempenho do detector criado, visando os requisitos do padrão IEEE 802.22. / [en] Cognitive radio is a technology that aims to share the radio spectrum between licensed primary users and other secondary users in a harmonious way without causing interference that prevent the services provision and aiming at an improvement in the efficiency in the use of the radioelectric spectrum, which is a resource increasingly scarce. In the scope of the research related to this dissertation, a performance evaluation scheme of cognitive radio detectors is constructed and implemented in GNU Radio, the energy detector is constructed, and computational simulations and tests are implemented through two USRPs to evaluate the performance of the detector created, targeting the requirements of the IEEE 802.22 standard.

[pt] A tecnologia de rádios cognitivos está surgindo como uma eficaz alternativa para aumentar o número de usuários de serviços de dados em banda larga em diversas faixas de frequências. O conceito pretende resolver a escassez do espectro a partir de duas características básicas: a capacidade cognitiva e a capacidade de reconfiguração. A capacidade cognitiva refere-se à habilidade do rádio de conhecer o meio no qual pretende operar, identificar de forma oportunista os espaços espectrais não utilizados na sua totalidade ou em alguns intervalos de tempo e, a partir da sua reconfiguração transmitir informação sem provocar interferência no usuário principal da porção do espectro utilizado. Esta dissertação de mestrado apresenta os resultados obtidos da análise do desempenho de regras de fusão para sensoriamento remoto cooperativo. Na primeira parte são abordados os fundamentos teóricos de Rádio cognitivo e os aspectos mais importantes do gerenciamento do espectro radioelétrico, além dos fundamentos do detector de energia, detector mais simples de implementar e utilizar para o sensoriamento em redes cognitivas. A seguir são abordadas diferentes técnicas para sensoriamento em redes cognitivas, apresentando os esquemas de decisão e a detecção convencional do espectro cooperativo, os métodos Hard decision e Soft decision. Finalmente uma avaliação das regras de sensoriamento cooperativo em cenários reais é realizada para obter as conclusões do trabalho. / [en] Cognitive radio technology is emerging as an effective alternative to increase the number of users in several frequency bands. The concept aims to solve the scarcity of the spectrum from two basic characteristics: the cognitive capacity and the capacity of reconfiguration. Cognitive ability refers to the ability of the radio to know the medium in which it is operating, to identify in an opportunistic way the unused spectral spaces in their totality or in some intervals of time and, from its reconfiguration transmit information without causing interference in the user of the portion of the spectrum used. This dissertation presents the results obtained from the analysis of the performance of fusion rules for cooperative remote sensing. The first part deals with the theoretical foundations of cognitive radio and the most important aspects of radioelectric spectrum management, as well as the fundamentals of the energy detector, the most important detector used in cognitive networks. Next, different techniques for sensing in cognitive networks are presented, presenting decision schemes and conventional detection of the cooperative spectrum, the Hard decision and Soft decision methods. Finally, an evaluation of the rules of cooperative sensing in real scenarios is carried out to obtain the conclusions of the work.

Les systèmes de communications sans fil ne cessent de se multiplier pour devenir incontournables de nos jours. Cette croissance cause une augmentation de la demande des ressources spectrales, qui sont devenues de plus en plus rares. Afin de résoudre ce problème de pénurie de fréquences, Joseph Mitola III, en 2000, a introduit l'idée de l'allocation dynamique du spectre. Il définit ainsi le terme " Cognitive Radio " (Radio Intelligente), qui est largement pressenti pour être le prochain Big Bang dans les futures communications sans fil [1]. Dans le cadre de ce travail on s'intéresse à la problématique du spectrum sensing qui est la détection de présence des Utilisateurs Primaires dans un spectre sous licence, dans le contexte de la radio intelligente. L'objectif de ce travail est de proposer des méthodes de détection efficaces à faible complexité et/ou à faible temps d'observation et ceci en utilisant le minimum d'information a priori sur le signal à détecter. Dans la première partie on traite le problème de détection d'un signal aléatoire dans le bruit. Deux grandes méthodes de détection sont utilisées : la détection d'énergie ou radiomètre et la détection cyclostationnaire. Dans notre contexte, ces méthodes sont plus complémentaires que concurrentes. Nous proposons une architecture hybride de détection des bandes libres, qui combine la simplicité du radiomètre et la robustesse des détecteurs cyclostationnaires. Deux méthodes de détection sont proposées qui se basent sur cette même architecture. Grâce au caractère adaptatif de l'architecture, la détection évolue au cours du temps pour tendre vers la complexité du détecteur d'énergie avec des performances proches du détecteur cyclostationnaire ou du radiomètre selon la méthode utilisée et l'environnement de travail. Dans un second temps on exploite la propriété parcimonieuse de la Fonction d'Autocorrelation Cyclique (FAC) pour proposer un nouvel estimateur aveugle qui se base sur le compressed sensing afin d'estimer le Vecteur d'Autocorrelation Cyclique (VAC), qui est un vecteur particulier de la Fonction d'Autocorrelation Cyclique pour un délai fixe. On montre par simulation que ce nouvel estimateur donne de meilleures performances que celles obtenues avec l'estimateur classique, qui est non aveugle et ceci dans les mêmes conditions et en utilisant le même nombre d'échantillons. On utilise l'estimateur proposé, pour proposer deux détecteurs aveugles utilisant moins d'échantillons que nécessite le détecteur temporel de second ordre de [2] qui se base sur l'estimateur classique de la FAC. Le premier détecteur exploite uniquement la propriété de parcimonie du VAC tandis que le second détecteur exploite en plus de la parcimonie la propriété de symétrie du VAC, lui permettant ainsi d'obtenir de meilleures performances. Ces deux détecteurs outre qu'ils sont aveugles sont plus performants que le détecteur non aveugle de [2] dans le cas d'un faible nombre d'échantillons.

The doctoral thesis deals with spectrum sensing in cognitive radio networks (CRN). A number of international organizations are currently actively engaged in standardization of CRN and it points out to the fact that this technology will be widely used in the near future. One of the key features of this technology is a dynamic access to the spectrum, which can be affected by many different harmful factors occurring in the communication chain. The thesis investigates the influence of selected factors on the spectrum sensing process. Another contribution of the work is the optimization of the Kolmogorov - Smirnov statistical test that can be applied for the primary user signal detection. The work also incorporates the analysis of the influence of the harmful effects caused by the commonly used transmitters and receivers on various spectrum sensing methods. The investigations are verified by the results of the simulations and also by the measurements with experimental platforms based on the software-defined radio (SDR).

Les systèmes de communications sans fil ne cessent de se multiplier pour devenir incontournables de nos jours. Cette croissance cause une augmentation de la demande des ressources spectrales, qui sont devenues de plus en plus rares. Afin de résoudre ce problème de pénurie de fréquences, Joseph Mitola III, en 2000, a introduit l'idée de l'allocation dynamique du spectre. Il définit ainsi le terme « Cognitive Radio » (Radio Intelligente), qui est largement pressenti pour être le prochain Big Bang dans les futures communications sans fil [1]. Dans le cadre de ce travail on s'intéresse à la problématique du spectrum sensing qui est la détection de présence des Utilisateurs Primaires dans un spectre sous licence, dans le contexte de la radio intelligente. L'objectif de ce travail est de proposer des méthodes de détection efficaces à faible complexité et/ou à faible temps d'observation et ceci en utilisant le minimum d'information a priori sur le signal à détecter. Dans la première partie on traite le problème de détection d'un signal aléatoire dans le bruit. Deux grandes méthodes de détection sont utilisées : la détection d'énergie ou radiomètre et la détection cyclostationnaire. Dans notre contexte, ces méthodes sont plus complémentaires que concurrentes. Nous proposons une architecture hybride de détection des bandes libres, qui combine la simplicité du radiomètre et la robustesse des détecteurs cyclostationnaires. Deux méthodes de détection sont proposées qui se basent sur cette même architecture. Grâce au caractère adaptatif de l'architecture, la détection évolue au cours du temps pour tendre vers la complexité du détecteur d'énergie avec des performances proches du détecteur cyclostationnaire ou du radiomètre selon la méthode utilisée et l'environnement de travail. Dans un second temps on exploite la propriété parcimonieuse de la Fonction d'Autocorrelation Cyclique (FAC) pour proposer un nouvel estimateur aveugle qui se base sur le compressed sensing afin d'estimer le Vecteur d'Autocorrelation Cyclique (VAC), qui est un vecteur particulier de la Fonction d'Autocorrelation Cyclique pour un délai fixe. On montre par simulation que ce nouvel estimateur donne de meilleures performances que celles obtenues avec l'estimateur classique, qui est non aveugle et ceci dans les mêmes conditions et en utilisant le même nombre d'échantillons. On utilise l'estimateur proposé, pour proposer deux détecteurs aveugles utilisant moins d'échantillons que nécessite le détecteur temporel de second ordre de [2] qui se base sur l'estimateur classique de la FAC. Le premier détecteur exploite uniquement la propriété de parcimonie du VAC tandis que le second détecteur exploite en plus de la parcimonie la propriété de symétrie du VAC, lui permettant ainsi d'obtenir de meilleures performances. Ces deux détecteurs outre qu'ils sont aveugles sont plus performants que le détecteur non aveugle de [2] dans le cas d'un faible nombre d'échantillons. / The wireless communications systems continue to grow and has become very essential nowadays. This growth causes an increase in the demand of spectrum resources, which have become more and more scarce. To solve this problem of spectrum scarcity, Joseph Mitola III, in the year 2000, introduced the idea of dynamic spectrum allocation. Mitola defines the term “Cognitive Radio”, which is widely expected to be the next Big Bang in wireless communications [1]. In this work we focus on the problem of spectrum sensing which is the detection of the presence of primary users in licensed spectrum, in the context of cognitive radio. The objective of this work is to propose effective detection methods at low-complexity and/or using short observation time, using minimal a priori information about the signal to be detected. In the first part of this work we deal with the problem of detecting a random signal in noise. Two main methods of detection are used: energy detection or radiometer and cyclostationary detection. In our context, these methods are more complementary than competitive. We propose a hybrid architecture for detecting free bands, which combines the simplicity of the radiometer and the robustness of the cyclostationary detection. Two detection methods are proposed that are based on this same hybrid architecture. Thanks to the adaptive nature of the architecture, the complexity of the detector decreases over time to tend to the one of an energy detector with close performance to the cyclostationary detector or to the performance of a radiometer, depending on the used method and on the working environment. In the second part of this work we exploit the sparse property of the Cyclic Autocorrelation Function (CAF) to propose a new blind estimator based on compressed sensing that estimates the Cyclic Autocorrelation Vector (CAV) which is a particular vector of the CAF for a given lag. It is shown by simulation that this new estimator gives better performances than those obtained with the classical estimator, which is non-blind, under the same conditions and using the same number of samples. Using the new estimator, we propose two blind detectors that require fewer samples than the second order time domain detector of [2] which is based on the classical estimator of the CAF. The first detector uses only the sparse property of the CAV while the second detector exploits the symmetry property of the CAV in addition to its sparse property, resulting in better performances. Both detectors, although they are blind, are more efficient than the non-blind detector of [2] in the case of a small number of samples.