The scope of this work is to map both conventional and less conventional methods of signal detection in the radio channel, computer simulation of selected methods and subsequent implementation selected method (algorithm) to FPGA chip.

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, que o cenário das telecomunicações atualmente apresenta, a mesma foi escolhida para alguns exemplos deste estudo. / In 1997, the concept of cognitive radio was proposed for the first time and evolved significantly to the present days, as a solution to the problem of electromagnetic spectrum scarcity. In the proposed approach, opportunistic users utilize frequency bands originally assigned to licensed users through dynamic spectrum access when the licensed users are not using them. To make this possible, without interfering or degrading the signals from the licensed users, it is necessary to fulfill four essential requirements of cognitive radios: spectrum sensing, spectrum decision, spectrum sharing, and spectrum mobility. In this work, spectrum sensing based on energy detection was investigated. An algorithm was developed for the determination of channel occupation and the number of samples needed for the detection process to achieve pre-established probabilities of detection and false-alarm. Simulations results are presented showing that noise uncertainty degrade the performance of the system when the signal-to-noise ratio is low. The developed algorithm allows determining a lower threshold for the signal-to-noise ratio, when noise uncertainty exists. The detection probability behavior as a function of the false alarm probability having the number of samples and the signal-to noise ratio as parameters is presented. The resulting curves are often denominated ROC - Receiver Operation Characteristics in the literature. Due to the high social and political interest in the TV broadcasting band, that telecommunications scenario currently presents, this band was chosen for same examples in this study.

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, que o cenário das telecomunicações atualmente apresenta, a mesma foi escolhida para alguns exemplos deste estudo. / In 1997, the concept of cognitive radio was proposed for the first time and evolved significantly to the present days, as a solution to the problem of electromagnetic spectrum scarcity. In the proposed approach, opportunistic users utilize frequency bands originally assigned to licensed users through dynamic spectrum access when the licensed users are not using them. To make this possible, without interfering or degrading the signals from the licensed users, it is necessary to fulfill four essential requirements of cognitive radios: spectrum sensing, spectrum decision, spectrum sharing, and spectrum mobility. In this work, spectrum sensing based on energy detection was investigated. An algorithm was developed for the determination of channel occupation and the number of samples needed for the detection process to achieve pre-established probabilities of detection and false-alarm. Simulations results are presented showing that noise uncertainty degrade the performance of the system when the signal-to-noise ratio is low. The developed algorithm allows determining a lower threshold for the signal-to-noise ratio, when noise uncertainty exists. The detection probability behavior as a function of the false alarm probability having the number of samples and the signal-to noise ratio as parameters is presented. The resulting curves are often denominated ROC - Receiver Operation Characteristics in the literature. Due to the high social and political interest in the TV broadcasting band, that telecommunications scenario currently presents, this band was chosen for same examples in this study.

Spectrum sensing is an important aspect of cognitive radio systems. In order to efficiently utilize the spectrum, the role of spectrum sensing is essential in cognitive radio networks. The transmitter detection based techniques: energy detection, cyclostationary feature detection, and matched filter detection, is most commonly used for the spectrum sensing. The Energy detection technique is implemented in the 2-hop cooperative cognitive radio network in which Orthogonal Space Time Block Coding (OSTBC) is applied with the Decode and Forward (DF) protocol at the cognitive relays. The Energy detection technique is simplest and gives good results at the higher Signal to Noise Ratio (SNR) values. However, at the low SNR values its performance degrades. Moreover, each transmitter detection technique has a SNR threshold, below which it fails to work robustly. This thesis aims to find the most reliable and accurate spectrum sensing technique in the 2-hop cooperative cognitive radio network. Using Matlab simulations, a comparative analysis of three transmitter detection techniques has been made in terms of higher probability of detection. In order to remove the shortcomings faced by all the three techniques, the Fuzzy-combined logic sensing approach is also implemented and compared with transmitter detection techniques. / Atti Ur Rehman (atti.rehmman@gmail.com) ph: +358-440458080

The growing interest for high data rate wireless communications over the last few decades gave rise to the emergence of a number of wideband wireless systems. The resulting scarcity of frequency spectrum has been forcing wireless system designers to develop methods that will push the spectral elciency to its limit. One such method is to have multiple systems utilize the same spectrum by allowing some unavoidable interference to occur between them. The idea of co-channel systems is tested in the industrial, scientific and medical (ISM) bands and it is found to be a very beneficial approach. Therefore, it can be foreseen that co-channel systems might be a potential solution to the growing spectral crowding problem. Besides the systems that are designed to be co-channel, it is sometimes also possible to encounter that multiple systems occupy the same band undesirably. This kind of unintentional co-channel system scenarios might occur especially due to the dense re-use of available frequency bands. Another reason for unwanted co-channel usage might be the coexistence of third generation (3G) and fourth generation (4G) systems. Since 4G systems will probably be targeting to use the same frequency bands as their 3G counterparts, and since the transition from 3G to 4G will take some time, unintentional co-channel scenarios might be observed between the 3G and 4G systems. This dissertation consists of baseband receiver algorithms for OFDMA-based systems that target at handling the potential co-channel interference (CCI) in various co-channel system scenarios. Three CCI avoidance and two CCI cancellation algorithms are proposed that can be applied to intentional and unintentional co-channel systems. Femtocells, which have recently been introduced as a new class of personal-use base stations that can coexist with macrocell networks in a shared spectrum manner, might constitute an appropriate example for both types of co-channel systems. Therefore, they are considered to be one of the co-existing systems in most of the algorithms presented.

There has been a recent explosive growth in mobile data consumption. This, in turn, imposes many challenges for mobile services providers and regulators in many aspects. One of these primary challenges is maintaining the radio spectrum to handle the current and upcoming expansion in mobile data traffic. In this regard, a radio spectrum regulatory framework based on secondary spectrum access is proposed as one of the solutions for the next generation wireless networks. In secondary spectrum access framework, secondary (unlicensed) systems coexist with primary (licensed) systems and access the spectrum on an opportunistic base. In this thesis, aspects related to finding the free of use spectrum portions - called spectrum opportunities - are treated. One way to find these opportunities is spectrum sensing which is considered as an enabler of opportunistic spectrum access. In particular, this thesis investigates some topics in blind spectrum sensing where no priori knowledge about the possible co-existing systems is available. As a standalone contribution in blind spectrum sensing arena, a new blind sensing technique is developed in this thesis. The technique is based on discriminant analysis statistical framework and called spectrum discriminator (SD). A comparative study between the SD and some existing blind sensing techniques was carried out and showed a reliable performance of the SD. The thesis also contributes by exploring sensing parameters optimization for two existing techniques, namely, energy detector (ED) and maximum-minimum eigenvalue detector (MME). For ED, the sensing time and periodic sensing interval are optimized to achieve as high detection accuracy as possible. Moreover, a study of sensing parameters optimization in a real-life coexisting scenario, that is, LTE cognitive femto-cells, is carried out with an objective of maximizing cognitive femto-cells throughput. In association with this work, an empirical statistical model for LTE channel occupancy is accomplished. The empirical model fits the channels' active and idle periods distributions to a linear combination of multiple exponential distributions. For the MME, a novel solution for the filtering problem is introduced. This solution is based on frequency domain rectangular filtering. Furthermore, an optimization of the observation bandwidth for MME with respect to the signal bandwidth is analytically performed and verified by simulations. After optimizing the parameters for both ED and MME, a two-stage fully-blind self-adapted sensing algorithm composed of ED and MME is introduced. The combined detector is found to outperform both detectors individually in terms of detection accuracy with an average complexity lies in between the complexities of the two detectors. The combined detector is tested with measured TV and wireless microphone signals. The performance evaluation in the different parts of the thesis is done through measurements and/or simulations. Active measurements were performed for sensing performance evaluation. Passive measurements on the other hand were used for LTE downlink channels occupancy modeling and to capture TV and wireless microphone signals. / <p>QC 20150209</p>

The owned spectrum allocation policy, in use since the early days of modern radio communications, has been proven to effectively control interference among radio communication systems. However, the overwhelming proliferation of new operators, innovative services and wireless technologies during the last years has resulted, under this static regulatory regime, in the depletion of spectrum bands with commercially attractive radio propagation characteristics. An important number of spectrum measurements, however, have shown that spectrum is mostly underutilized, thus indicating that the virtual spectrum scarcity problem actually results from static and inflexible spectrum management policies rather than the physical scarcity of radio resources. This situation has motivated the emergence of Dynamic Spectrum Access (DSA) methods based on the Cognitive Radio (CR) paradigm, which has gained popularity as a promising solution to conciliate the existing conflicts between spectrum demand growth and spectrum underutilization. The basic underlying idea of DSA/CR is to allow unlicensed (secondary) users to access in an opportunistic and non-interfering manner some licensed bands temporarily unoccupied by the licensed (primary) users. Due to the opportunistic nature of this principle, the behavior and performance of a DSA/CR network depends on the spectrum occupancy patterns of the primary system. A realistic and accurate modeling of such patterns becomes therefore essential and extremely useful in the domain of DSA/CR research. The potential applicability of spectrum usage models ranges from analytical studies to the design and dimensioning of secondary networks as well as the development of innovative simulation tools and more efficient DSA/CR techniques. Spectrum occupancy modeling in the context of DSA/CR constitutes a rather unexplored research area. This dissertation addresses the problem of modeling spectrum usage in the context of DSA/CR by contributing a comprehensive and holistic set of realistic models capable to accurately capture and reproduce the statistical properties of spectrum usage in real radio communication systems in the time, frequency and space dimensions. The first part of this dissertation addresses the development of a unified methodological framework for spectrum measurements in the context of DSA/CR and presents the results of an extensive spectrum measurement campaign performed over a wide variety of locations and scenarios in the metropolitan area of Barcelona, Spain, to identify potential bands of interest for future DSA/CR deployments. To the best of the author's knowledge, this is the first study of these characteristics performed under the scope of the Spanish spectrum regulation and one of the earliest studies in Europe. The second part deals with various specific aspects related to the processing of measurements to extract spectrum occupancy patterns, which is largely similar to the problem of spectrum sensing in DSA/CR. The performance of energy detection, the most widely employed spectrum sensing technique in DSA/CR, is first assessed empirically. The outcome of this study motivates the development of a more accurate theoretical-empirical performance model as well as an improved energy detection scheme capable to outperform the conventional method while preserving a similar level of complexity, computational cost and application. The findings of these studies are finally applied in the third part of the dissertation to the development of innovative spectrum usage models for the time (in discrete- and continuous-time versions), frequency and space domains. The proposed models can been combined and integrated into a unified modeling approach where the time, frequency and space dimensions of spectrum usage can simultaneously be reproduced, thus providing a complete and holistic characterization of spectrum usage in real systems for the analysis, design and simulation of the future DSA/CR networks.

Die extrem große Bandbreite, die UWB-Systeme zur Übertragung von Daten nutzen können, ermöglicht theoretisch eine sehr hohe Datenrate. Eine mögliche Umsetzung der UWB-Technologie ist die sogenannte Multiband-Impuls-Radio-Architektur (MIRA). Dieses UWB-System basiert auf der Übertragung von Daten mittels kurzer Impulse parallel in mehreren Frequenzbändern. Als Empfänger kommen einfache Energiedetektoren zum Einsatz. Diese Komponenten haben entscheidenden Einfluss auf die Leistungsfähigkeit des gesamten Systems. Deshalb liegt der Schwerpunkt dieser Arbeit auf der Untersuchung der Leistungsfähigkeit und im speziellen der Herleitung der Bitfehlerwahrscheinlichkeiten für Energiedetektoren in unterschiedlichen UWB-Kanälen. Aufgrund des sehr einfachen Aufbaus eines Energiedetektors wird dieser auch in vielen anderen Bereichen eingesetzt. So werden Energiedetektoren zur Detektion von freien Bereichen im Übertragungsspektrum bei Cognitive Radio und für weitere unterschiedliche Übertragungssysteme wie z.B. Sensorsysteme mit geringer Datenrate und Übertragungssysteme die zusätzlich Ortung ermöglichen, genutzt.

This dissertation investigates Ultra-Wideband (UWB) techniques for the next generation Radio Frequency Identification (RFID) towards the Internet-of-Things (IoT). In particular, an ultra-high frequency (UHF) wireless-powered UWB radio (UHF/UWB hybrid) with asymmetric links is explored from system architecture to circuit implementation. Context-aware, location-aware, and energy-aware computing for the IoT demands future micro-devices (e.g., RFID tags) with capabilities of sensing, processing, communication, and positioning, which can be integrated into everyday objects including paper documents, as well as food and pharmaceutical packages. To this end, reliable-operating and maintenance-free wireless networks with low-power and low-cost radio transceivers are essential. In this context, state-of-the-art passive RFID technologies provide limited data rate and positioning accuracy, whereas active radios suffer from high complexity and power-hungry transceivers. Impulse Radio UWB (IR-UWB) exhibits significant advantages that are expected to overcome these limitations. Wideband signals offer robust communications and high-precision positioning; duty-cycled operations allow link scalability; and baseband-like architecture facilitates extremely simple and low-power transmitters. However, the implementation of the IR-UWB receiver is still power-hungry and complex, and thus is unacceptable for self-powered or passive tags. To cope with μW level power budget in wireless-powered systems, this dissertation proposes an UHF/UWB hybrid radio architecture with asymmetric links. It combines the passive UHF RFID and the IR-UWB transmitter. In the downlink (reader-tag), the tag is powered and controlled by UHF signals as conventional passive UHF tags, whereas it uses an IR-UWB transmitter to send data for a short time at a high rate in the uplink (tag-reader). Such an innovative architecture takes advantage of UWB transmissions, while the tag avoids the complex UWB receiver by shifting the burden to the reader. A wireless-powered tag providing -18.5 dBm sensitivity UHF downlink and 10 Mb/s UWB uplink is implemented in 180 nm CMOS. At the reader side, a non-coherent energy detection IR-UWB receiver is designed to pair the tag. The receiver is featured by high energy-efficiency and flexibility that supports multi-mode operations. A novel synchronization scheme based on the energy offset is suggested. It allows fast synchronization between the reader and tags, without increasing the hardware complexity. Time-of-Arrival (TOA) estimation schemes are analyzed and developed for the reader, which enables tag localization. The receiver prototype is fabricated in 90 nm CMOS with 16.3 mW power consumption and -79 dBm sensitivity at 10 Mb/s data rate. The system concept is verified by the link measurement between the tag and the reader. Compared with current passive UHF RFID systems, the UHF/UWB hybrid solution provides an order of magnitude improvement in terms of the data rate and positioning accuracy brought by the IR-UWB uplink. / QC 20120110

The rapid increasing interest in wireless communication has led to the continuous development of wireless devices and technologies. The modern convergence and interoperability of wireless technologies has further increased the amount of services that can be provided, leading to the substantial demand for access to the radio frequency spectrum in an efficient manner. Cognitive radio (CR) an innovative concept of reusing licensed spectrum in an opportunistic manner promises to overcome the evident spectrum underutilization caused by the inflexible spectrum allocation. Spectrum sensing in an unswerving and proficient manner is essential to CR. Cooperation amongst spectrum sensing devices are vital when CR systems are experiencing deep shadowing and in a fading environment. In this thesis, cooperative spectrum sensing (CSS) schemes have been designed to optimize detection performance in an efficient and implementable manner taking into consideration: diversity performance, detection accuracy, low complexity, and reporting channel bandwidth reduction. The thesis first investigates state of the art spectrums sensing algorithms in CR. Comparative analysis and simulation results highlights the different pros, cons and performance criteria of a practical CSS scheme leading to the problem formulation of the thesis. Motivated by the problem of diversity performance in a CR network, the thesis then focuses on designing a novel relay based CSS architecture for CR. A major cooperative transmission protocol with low complexity and overhead - Amplify and Forward (AF) cooperative protocol and an improved double energy detection scheme in a single relay and multiple cognitive relay networks are designed. Simulation results demonstrated that the developed algorithm is capable of reducing the error of missed detection and improving detection probability of a primary user (PU). To improve spectrum sensing reliability while increasing agility, a CSS scheme based on evidence theory is next considered in this thesis. This focuses on a data fusion combination rule. The combination of conflicting evidences from secondary users (SUs) with the classical Dempster Shafter (DS) theory rule may produce counter-intuitive results when combining SUs sensing data leading to poor CSS performance. In order to overcome and minimise the effect of the counter-intuitive results, and to enhance performance of the CSS system, a novel state of the art evidence based decision fusion scheme is developed. The proposed approach is based on the credibility of evidence and a dissociability degree measure of the SUs sensing data evidence. Simulation results illustrate the proposed scheme improves detection performance and reduces error probability when compared to other related evidence based schemes under robust practcial scenarios. Finally, motivated by the need for a low complexity and minmum bandwidth reporting channels which can be significant in high data rate applications, novel CSS quantization schemes are proposed. Quantization methods are considered for a maximum likelihood estimation (MLE) and an evidence based CSS scheme. For the MLE based CSS, a novel uniform and optimal output entropy quantization scheme is proposed to provide fewer overhead complexities and improved throughput. While for the Evidence based CSS scheme, a scheme that quantizes the basic probability Assignment (BPA) data at each SU before being sent to the FC is designed. The proposed scheme takes into consideration the characteristics of the hypothesis distribution under diverse signal-to-noise ratio (SNR) of the PU signal based on the optimal output entropy. Simulation results demonstrate that the proposed quantization CSS scheme improves sensing performance with minimum number of quantized bits when compared to other related approaches.