Το αντικείμενο της παρούσης διατριβής είναι η μοντελοποίηση με χρήση στοχαστικών διαδικασιών, ασυρμάτων μη επιλεκτικών στη συχνότητα καναλιών με διαλείψεις (frequency non-selective fading channels). Η γνώση και μοντελοποίηση των χρονικών μεταβολών των ασυρμάτων καναλιών είναι αναγκαία για ένα πλήθος σύγχρονων εφαρμογών όπως μεταξύ άλλων η εκτίμηση της ταχύτητας κίνησης της φορητής συσκευής, μεταγωγή (handoff), δυναμική καταχώρηση συχνοτήτων και ο δυναμικός έλεγχος της ισχύος εκπομπής της φορητής μονάδας. Επίσης, βασιζόμενοι σε στοχαστικά μοντέλα, μπορούν να εκτιμηθούν διάφορα μεγέθη των καναλιών, όπως η μέση χρονική διάρκεια των ριπών σφαλμάτων (error bursts) και η απόδοση των χρησιμοποιουμένων πρωτοκόλλων επικοινωνίας. Στην παρούσα διατριβή μελετώνται μη επιλεκτικά στη συχνότητα κανάλια με διαλείψεις για κινητές συσκευές λήψης (mobile fading channels) και στατικά κανάλια με διαλείψεις (fixed wireless fading channels). Στην πρώτη περίπτωση διερευνάται το πρόβλημα του στατικού πομπού με κινούμενο δέκτη, ενώ στη δεύτερη περίπτωση διερευνάται το πρόβλημα όπου η κατάσταση τόσο του πομπού όσο και του δέκτη είναι στατική. Στα μη επιλεκτικά στη συχνότητα κανάλια των κινητών συσκευών, οι χρονικές μεταβολές συμβαίνουν λόγω της ταυτόχρονης άφιξης πολυοδευουσών συνιστωσών (multipath components) στον κινητό δέκτη. Οι συνιστώσες αυτές έχουν τυχαία φάση, συνεπώς προκαλούν στο λαμβανόμενο σήμα ταχείες αυξομειώσεις, λόγω του ότι μπορούν να υπερτίθενται με τυχαίο τρόπο. Με τη σειρά τους, οι πολυοδεύουσες συνιστώσες μπορούν να καταφθάνουν στον κινητό δέκτη διαδιδόμενες σε δυο ή τρεις διαστάσεις. Το τελευταίο εξαρτάται από το αν καταφθάνουν υπό κάποια γωνία ανύψωσης σε σχέση με το επίπεδο κίνησης του δέκτη . Οι χρονικές μεταβολές του λαμβανόμενου σήματος επηρεάζονται επίσης από το φαινόμενο της σκίασης (shadowing ή shadow fading), το οποίο έχει ως αποτέλεσμα η μέση τιμή αυτού να παίρνει τυχαίες τιμές σε κάθε τοπική περιοχή (local area). Η σκίαση είναι το αποτέλεσμα της αλληλεπίδρασης των πολυοδευουσών συνιστωσών με υψηλά κτήρια και εμπόδια, ώστε μέρος της ισχύος να μη φθάνει στον κινητό δέκτη. Στα στατικά μη επιλεκτικά στη συχνότητα κανάλια, οι τυχαίες φάσεις των πολυοδευουσών συνιστωσών και κατά συνέπεια οι χρονικές μεταβολές του λαμβανομένου σήματος είναι αποτέλεσμα της αλληλεπίδρασης αυτών των συνιστωσών με τα κινούμενα αντικείμενα / σκεδαστές του καναλιού. Η γνώση των βασικών στοχαστικών διαδικασιών που χρησιμοποιούνται για την μοντελοποίηση του λαμβανόμενου σήματος σε ασύρματα κανάλια κρίνεται απαραίτητη. Κατάλληλες τροποποιήσεις και επεξεργασία αυτών των διαδικασιών οδήγησαν στα περισσότερα εκ των αποτελεσμάτων της παρούσης διατριβής. Αυτές οι διαδικασίες είναι το εκτεταμένο μοντέλο Suzuki (extended Suzuki model) και το μοντέλο του Loo (Loo model). Η πρώτη διαδικασία προκύπτει από το πολλαπλασιασμό μιας διαδικασίας Rice και μιας κανονικής λογαριθμικής (lognormal) διαδικασίας (μοντέλο Rice-lognormal). Η δεύτερη διαδικασία προκύπτει ως το μέτρο της πρόσθεσης δυο διανυσμάτων, όπου το πλάτος του ενός ακολουθεί την κατανομή Rayleigh, ενώ το πλάτος του άλλου ακολουθεί την κατανομή lognormal. Οι διαδικασίες αυτές ανήκουν στην κατηγορία των σύνθετων στοχαστικών (composite stochastic), αφού μοντελοποιούν ταυτόχρονα την επίδραση της σκίασης και της πολυόδευσης σε μη επιλεκτικά στη συχνότητα κανάλια κινητών συσκευών λήψης. Όσο αφορά τα στατικά ασύρματα κανάλια, οι χρονικές μεταβολές τους καθορίζονται κάνοντας χρήση μιας κατάλληλης διαδικασίας Rice. Η δημιουργία ενός καινούργιου στοχαστικού μοντέλου για κανάλια κινητών συσκευών με διαλείψεις ήταν το ένα από τα αποτελέσματα της παρούσης διατριβής. Συγκεκριμένα, προέκυψε μια νέα σύνθετη στοχαστική διαδικασία, η οποία ανήκει στην κατηγορία των μοντέλων τύπου Suzuki και προκύπτει από τον πολλαπλασιασμό μιας διαδικασίας Weibull και μια κανονικής λογαριθμικής (lognormal) διαδικασίας (μοντέλο Weibull-lognormal). Το σύνθετο μοντέλο Weibull-lognormal παρουσιάζεται στην απλή του μορφή με δυσδιάστατη ισοτροπική σκέδαση (two dimensional-2D isotropic scattering) και σε μια τροποποιημένη εκδοχή με δυσδιάστατη ανισοτροπική σκέδαση (anisotropic scattering). Στη συνέχεια, η εισαγωγή τρισδιάστατης (three dimensional-3D) ανισοτροπικής σκέδασης στο εκτεταμένο μοντέλο Suzuki και στο μοντέλο του Loo επέτρεψε να καθοριστεί με ακρίβεια η επίδραση αυτής στις χρονικές μεταβολές μη επιλεκτικών στη συχνότητα καναλιών για κινητές συσκευές λήψης. Η τρισδιάστατη σκέδαση μοντελοποιήθηκε θεωρώντας κατάλληλες κατανομές των γωνιών άφιξης (angle of arrival-AOA) των πολυοδευουσών συνιστωσών, τόσο στο αζιμούθιο επίπεδο (azimuth plane) κίνησης του δέκτη, όσο και στο κάθετο επίπεδο ανύψωσης (elevation plane). Τέλος, μελετήθηκε το στατικό μη επιλεκτικό στη συχνότητα ασύρματο κανάλι. Πιο συγκεκριμένα, η κινητικότητα των σκεδαστών σε αυτά τα κανάλια μοντελοποιήθηκε κατάλληλα μέσω τριών κατανομών πιθανότητας για τις ταχύτητες των σκεδαστών. Στη συνέχεια, η κινητικότητα των σκεδαστών συνδέθηκε με αναλυτικό τρόπο με τις χρονικές μεταβολές αυτών των καναλιών. / The topic of this thesis is to study frequency non-selective wireless fading channels using stochastic processes. Knowledge and modeling of wireless channel time variations is essential for a variety of modern applications such as estimation of the mobile receiver velocity, handoff, dynamic frequency allocation, power control of the mobile unit emitted power and so on. Moreover, based on stochastic models, we are able to estimate several channel metrics such as average time duration of error bursts and the performance of the utilized communication protocols. This thesis studies frequency non-selective mobile fading channels and fixed wireless channels. The former have static transmitter and mobile receiver, while the latter have both static transmitter and receiver. In mobile channels, time variations (fades) occur due to the simultaneous arrival of multipath components at the mobile receiver. Those components have random phases, thus they cause in the received signal rapid fluctuations as they are added randomly. In turn, the multipath components can arrive at the mobile receiver via a two or a three dimensional propagation scenario. Time variations are also affected by the shadowing effect, which causes variations to the received signal local mean. Shadowing results from the interaction of multipath components with tall buildings and obstacles such that a part of the power does not arrive at the mobile receiver. In frequency non-selective fixed wireless channels, the random phases of the multipath components and consequently the time variations arise from the interaction of those components with the channel mobile objects/scatterers. Τhe knowledge of the main stochastic processes used to model the received signal in wireless channels is necessary. Most of the results in this thesis were derived by appropriate modifications and further development of those processes, which are the extended Suzuki model and the Loo model. The former arises by multiplying a Rice and a lognormal process. The latter arises as the amplitude of the sum of a Rayleigh and a lognormal phasor vector. Both processes belong to the category of composite stochastic as they simultaneously model the influence of shadowing and multipath propagation in frequency non-selective mobile channels. As for the fixed wireless channels, the time variations of them are determined through a suitable Rice process. The creation of a novel stochastic model for mobile fading channels was one achievement of this thesis. Α new stochastic process pertaining to the Suzuki class of models was derived, which arises by multiplying a Weibull and a lognormal process (Weibull-lognormal model). The composite Weibull-lognormal model is presented in its simple form with two dimensional (2D) isotropic scattering and in a modified version with two dimensional anisotropic scattering. Afterwards, the utilization of three dimensional (3D) anisotropic scattering in the extended Suzuki and Loo models allowed us to accurately determine the impact of three dimensional scattering on the time variations of frequency non-selective mobile channels. Three dimensional scattering was modeled by considering suitable distributions for the multipath angle of arrival (AOA) at both the azimuth receiver’s plane and the vertical elevation plane. Finally, the narrowband fixed wireless channel was studied. More specifically, the scatterers’ mobility at fixed wireless channels was appropriately modeled via three probability distributions for the scatterers’ velocities. Afterwards, the scatterers’ mobility was analytically connected with the time variations of those channels.

<p>Distributed optimization methods allow us to decompose an optimization problem</p><p>into smaller, more manageable subproblems that are solved in parallel. For this</p><p>reason, they are widely used to solve large-scale problems arising in areas as diverse</p><p>as wireless communications, optimal control, machine learning, artificial intelligence,</p><p>computational biology, finance and statistics, to name a few. Moreover, distributed</p><p>algorithms avoid the cost and fragility associated with centralized coordination, and</p><p>provide better privacy for the autonomous decision makers. These are desirable</p><p>properties, especially in applications involving networked robotics, communication</p><p>or sensor networks, and power distribution systems.</p><p>In this thesis we propose the Accelerated Distributed Augmented Lagrangians</p><p>(ADAL) algorithm, a novel decomposition method for convex optimization prob-</p><p>lems with certain separability structure. The method is based on the augmented</p><p>Lagrangian framework and addresses problems that involve multiple agents optimiz-</p><p>ing a separable convex objective function subject to convex local constraints and</p><p>linear coupling constraints. We establish the convergence of ADAL and also show</p><p>that it has a worst-case O(1/k) convergence rate, where k denotes the number of</p><p>iterations.</p><p>Moreover, we show that ADAL converges to a local minimum of the problem</p><p>for cases with non-convex objective functions. This is the first published work that</p><p>formally establishes the convergence of a distributed augmented Lagrangian method</p><p>ivfor non-convex optimization problems. An alternative way to select the stepsizes</p><p>used in the algorithm is also discussed. These two contributions are independent</p><p>from each other, meaning that convergence of the non-convex ADAL method can</p><p>still be shown using the stepsizes from the convex case, and, similarly, convergence</p><p>of the convex ADAL method can be shown using the stepsizes proposed in the non-</p><p>convex proof.</p><p>Furthermore, we consider cases where the distributed algorithm needs to operate</p><p>in the presence of uncertainty and noise and show that the generated sequences of</p><p>primal and dual variables converge to their respective optimal sets almost surely. In</p><p>particular, we are concerned with scenarios where: i) the local computation steps</p><p>are inexact or are performed in the presence of uncertainty, and ii) the message</p><p>exchanges between agents are corrupted by noise. In this case, the proposed scheme</p><p>can be classified as a distributed stochastic approximation method. Compared to</p><p>existing literature in this area, our work is the first that utilizes the augmented</p><p>Lagrangian framework. Moreover, the method allows us to solve a richer class of</p><p>problems as compared to existing methods on distributed stochastic approximation</p><p>that consider only consensus constraints.</p><p>Extensive numerical experiments have been carried out in an effort to validate</p><p>the novelty and effectiveness of the proposed method in all the areas of the afore-</p><p>mentioned theoretical contributions. We examine problems in convex, non-convex,</p><p>and stochastic settings where uncertainties and noise affect the execution of the al-</p><p>gorithm. For the convex cases, we present applications of ADAL to certain popular</p><p>network optimization problems, as well as to a two-stage stochastic optimization</p><p>problem. The simulation results suggest that the proposed method outperforms</p><p>the state-of-the-art distributed augmented Lagrangian methods that are known in</p><p>the literature. For the non-convex cases, we perform simulations on certain simple</p><p>non-convex problems to establish that ADAL indeed converges to non-trivial local</p><p>vsolutions of the problems; in comparison, the straightforward implementation of the</p><p>other distributed augmented Lagrangian methods on the same problems does not</p><p>lead to convergence. For the stochastic setting, we present simulation results of</p><p>ADAL applied on network optimization problems and examine the effect that noise</p><p>and uncertainties have in the convergence behavior of the method.</p><p>As an extended and more involved application, we also consider the problem</p><p>of relay cooperative beamforming in wireless communications systems. Specifically,</p><p>we study the scenario of a multi-cluster network, in which each cluster contains</p><p>multiple single-antenna source destination pairs that communicate simultaneously</p><p>over the same channel. The communications are supported by cooperating amplify-</p><p>and-forward relays, which perform beamforming. Since the emerging problem is non-</p><p>convex, we propose an approximate convex reformulation. Based on ADAL, we also</p><p>discuss two different ways to obtain a distributed solution that allows for autonomous</p><p>computation of the optimal beamforming decisions by each cluster, while taking into</p><p>account intra- and inter-cluster interference effects.</p><p>Our goal in this thesis is to advance the state-of-the-art in distributed optimization by proposing methods that combine fast convergence, wide applicability, ease</p><p>of implementation, low computational complexity, and are robust with respect to</p><p>delays, uncertainty in the problem parameters, noise corruption in the message ex-</p><p>changes, and inexact computations.</p> / Dissertation

Les médias et de nombreuses études scientifiques évoquent fréquemment la notion de vie privée en lien avec des exemples de cyber attaques. Le vol par des hackers de 12 millions d’identifiants d’utilisateurs Apple en 2012 illustre que les objets communicants sont des maillons vulnérables exploités par les hackers pour accéder aux données personnelles des usagers. Dans cette thèse, nous allons étendre la notion de vie privée aux objets eux-mêmes, au-delà des utilisateurs, en montrant que dans des réseaux de capteurs sans fil où les communications ont lieu de machine à machine, la connaissance des adresses fixes des différents appareils constituant le réseau représente une source d’information permettant de déduire beaucoup d’éléments de contexte et d’environnement.Actuellement, tous les standards de communication sans fil intègrent la capacité de sécuriser les données transportées, y compris les protocoles de communication dédiés aux réseaux de capteurs, conçus pour fonctionner en milieu contraint et à basse consommation. Cependant, l’en-tête des trames envoyées sur l’air comportant les informations nécessaires au routage et au bon fonctionnement du réseau, figure toujours en texte clair. La collecte de ces métadonnées par écoute passive représente un danger pour les environnements et les applications qui font usage de ces réseaux.Le travail mené dans cette thèse a pour objectif d’explorer comment de simples attaques passives sur des réseaux meshés basés sur le standard IEEE 802.15.4, visant à collecter et exploiter les métadonnées de ces trames échangées sur l’air, permettent d’inférer des informations critiques sur le réseau lui-même, l’environnement dans lequel il est déployé et les comportements des personnes qui en font usage. Plusieurs solutions visant à dissimuler les adresses des nœuds du réseau sont ensuite étudiées. Ces solutions sont de deux types : soit elles rendent anonymes les dispositifs empêchant de remonter à la source des messages, soit elles reposent sur l’utilisation de pseudonymes permettant de conserver la possibilité d’auditer le trafic.Afin d’évaluer les caractéristiques et les performances de ces solutions, un simulateur a été mis en œuvre afin de reproduire le comportement d’un réseau de capteurs meshés embarquant l’OS Contiki. Ce simulateur a permis d’évaluer la solution la plus prometteuse issue de l’état de l’art, nommée MT6D, en comparant ses performances avec un réseau de référence ne dissimulant pas les métadonnées. Cette analyse a fait ressortir certains inconvénients, en particulier l’augmentation importante des trames de contrôle nécessaires au routage, et a permis d’élaborer les spécifications d’une solution plus optimale pour l’embarqué.Nous avons ainsi introduit Ephemeral, qui présente la capacité de dissimuler les adresses des dispositifs dans les messages envoyés sur l’air, par l’usage de pseudonymes, sans augmenter la quantité de trames de contrôle indispensables au routage. Une fois mis en œuvre avec le simulateur afin de valider les performances théoriques attendues, Ephemeral est déployé en environnement réel sur un réseau de capteurs IEEE 802.15.4 équipant un bâtiment. Ce retour d’expérimentation permet de confirmer qu’Ephemeral constitue une solution économe du point de vue de la consommation d’énergie et de la bande passante du réseau, pour masquer les identifiants des dispositifs impliqués dans les communications. / Privacy notion is frequently linked with cyber attack examples by media and scientific researches. In 2012, the hacking of 12 millions Apple user identifiers demonstrates that connected objects represent leaks exploited by hackers to access to user personal data. In this thesis, we will extend the privacy notion to the objects. To do this, we will show that in wireless sensor networks where communications are carried out from machine-to-machine, the knowledge of the static addresses of the devices within the network discloses information allowing deduction about elements of context and environment.Nowadays, the wireless communication standards provide security mechanisms whatever the communication protocols used including the low power ones designed to run on constrained environment. However, the frame header that comprises necessary information for routing and for the proper functioning of the network is always sent in clear text. Collecting and gathering these metadata by eavesdropping is dangerous for the environments and applications based on these networks.The work carried out in this thesis aims to explore how simple passive attacks on meshed networks based on IEEE 802.15.4 used to collect and exploit metadata allow to infer critical information about the network, the environment where the network is deployed and the behavior of users. Two kinds of solutions to hide the node addresses are studied. The first one provides anonymity for the devices. In the second kind of solutions, pseudonyms are used by nodes enabling the capability to audit the traffic within the network.To evaluate the characteristics and the performances of the solutions, a simulator has been used to reproduce the behavior of a meshed wireless sensor network embedding Contiki OS. This simulator allows to compare the performances of MT6D the most promising solution of our state of the art with that of a reference network do not mask the metadata. With this analyze, we can highlight some drawbacks and more especially the control frames overhead needed for the routing. We give the necessary specifications to deploy the most optimal solution for the embedded devices.Thus we propose Ephemeral that allows hiding device addresses provided in the sent frames by using pseudonyms without overhead on the control frames. After deployment in the simulation environment to evaluate expected theoretical performances, Ephemeral has been tested in real environment. The network is made up of twenty IEEE 802.15.4 sensor nodes deployed on a building. The results show that Ephemeral is an efficient low power and bandwidth-saving solution to hide device identifiers used in wireless communications.

Adaptive and smart systems are growing in popularity as we shift toward personalization as a culture. With progressive demands on energy efficiency, it is increasingly important to focus on the utilization of energy in a novel way. This thesis investigates a microelectromechanical system (MEMS) mirror with the express intent to provide flexibility in solid state lighting (SSL). By coupling the micromirror to an optical source, the reflected light may be reshaped and directed so as to optimize the overall illumination profile. In addition, the light may be redirected in order to provide improved signal strength in visible light communications (VLC) with negligible impact on energy demands. With flexibility and full analog control in mind, the design of a fully integrated tip-tilt-piston micromirror with an additional variable focus degree of freedom is outlined. Electrothermal actuators are used to both steer the light and tune the focal length. A detailed discussion of the underlying physics behind composite beams and thermal actuators is addressed. This leads directly into an overview of the two main mirror components, namely the segmented mirror and the deflection actuators. An in-depth characterization of the dynamics of the mirror is discussed including the linearity of the thermal response. Frequency domain analysis of such a system provides insight into tunable mechanical properties such as the resonant frequency and quality factor. The degenerate resonant modes can be separated significantly. It is shown that the frequency response may be tuned by straining specific actuators and that it follows a predictable pattern. As a result, the system can be scanned at increasingly large angles. In other words, coupled mechanical modes allow variable damping and amplification. A means to determine the level of coupling is examined and the mode shape variations are tracked as a function of the tuning parameters. Finally, the applications of such a device are explored and tested. Such applications include reliable signal-to-noise ratio (SNR) enhancements in VLC of 30 dB and color tunable steerable lights using laser diodes. A brief discussion of the implications of dynamic illumination and tunable systems is juxtaposed with an explanation behind the integration of an electrothermal micromirror and an all digital driver.

With the traditional static spectrum management, a significant portion of the licensed spectrum is underutilized in most of time while the unlicensed spectrum is over-crowded due to the growing demand for wireless radio spectrum from exponential growth of various wireless devices. Dynamic Spectrum Access utilizes the wireless spectrum in a more intelligent and flexible way. Cognitive radios are a promising enabler for Dynamic Spectrum Access because they can sense and access the idle channels. With cognitive radios, the unlicensed users (SUs) can opportunistically identify and access the vacant portions of the spectrum of the licensed users (PUs). In cognitive radio networks (CRNs), multiple idle channels may be available to SUs. If two or more SUs want to communicate with each other, they must select a channel which is available to all of them. The process of two or more SUs to meet and establish a link on a commonly-available channel is known as rendezvous. 1) Multiple Radios for Fast Rendezvous in CRNs: The existing works on rendezvous implicitly assume that each cognitive user is equipped with one radio (i.e., one wireless transceiver). As the cost of wireless transceivers is dropping, this feature can be exploited to significantly improve the rendezvous performance at low cost. We investigate the rendezvous problem in CRNs where cognitive users are equipped with multiple radios and different users may have different numbers of radios. We first study how the existing rendezvous algorithms can be generalized to use multiple radios for faster rendezvous. We then propose a new rendezvous algorithm, called role-based parallel sequence (RPS), which specifically exploits multiple radios for more efficient rendezvous. Our basic idea is to let the cognitive users stay in a specific channel in one dedicated radio and hop on the available channels with parallel sequences in the remaining general radios. We prove that RPS provides guaranteed rendezvous (i.e., rendezvous can be completed within a finite time) and derive the upper bounds on the maximum time-to-rendezvous (TTR) and the expected TTR. The simulation results show that i) multiple radios can cost-effectively improve the rendezvous performance, and ii) the proposed RPS algorithm performs better than the ones generalized from the existing algorithms. 2) Efficient Channel-Hopping Rendezvous Algorithm Based on Available Channel Set: All the existing rendezvous algorithms that provide guaranteed rendezvous (i.e., rendezvous can be achieved within finite time) generate channel-hopping (CH) sequences based on the whole channel set. However, some channels may be unavailable (e.g., being used by the licensed users) and these existing algorithms would randomly replace the unavailable channels by the available ones in the CH sequence. This random replacement is not effective, especially when the number of unavailable channels is large. We design a new rendezvous algorithm, called Interleaved Sequences based on Available Channel set (ISAC), that attempts rendezvous on the available channels only for faster rendezvous. ISAC constructs an odd subsequence and an even subsequence and interleaves these two subsequences to compose a CH sequence. We prove that ISAC provides guaranteed rendezvous. We derive the upper bounds on the maximum time-to-rendezvous to be O(

Orientadores: Jose Marcos Travassos Romano, Cristiano Magalhães Panazio / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-09T08:52:54Z (GMT). No. of bitstreams: 1 Menezes_AlamSilva_M.pdf: 3586178 bytes, checksum: 0b475a352c1a0c8fc6c72a6a3c846f45 (MD5) Previous issue date: 2007 / Resumo: A presente dissertação apresenta um estudo da tecnologia dos rádios cognitivos bem como uma avaliação dos possíveis ganhos desta promissora técnica em relação aos atuais meios de acesso ao espectro eletromagnético. Numa segunda frente de trabalho, tratamos do problema de equalização cega no contexto de canais SIMO, com uma única entrada e múltiplas saídas. Propomos a predição linear multicanal como estrutura de equalização em sistemas OFDM e avaliamos por meio de simulações a viabilidade da técnica proposta / Abstract: In this work, we provide a study of the cognitive radio technology and the potential gains that this technique may provide with regard to current electromagnetic spectrum access techniques. In a second workphase, we deal with the problem of blind equalization in the context of single input multiple output channels (SIMO). We propose the use of a multichannel linear prediction structure to equalize OFDM systems and we assess its performance through numerical simulations / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

One of the major driving elements behind the explosive boom in wireless revolution is the advances in the field of modulation which plays a fundamental role in any communication system, and especially in cellular radio systems. Hence, the elaborate choice of an efficient modulation scheme is of paramount importance in the design and employment of any communications system. Work presented in this thesis is an investigation (study) of the feasibility of whether multilevel FSK modulation scheme would provide a viable alternative modem that can be employed in TDMA cordless communications systems. In the thesis the design and performance analysis of a non-coherent multi-level modem that offers a great deal of bandwidth efficiency and hardware simplicity is studied in detail. Simulation results demonstrate that 2RC pre-modulation filter pulse shaping with a modulation index of 0.3, and pre-detection filter normalized equivalent noise bandwidth of 1.5 are optimum system parameter values. Results reported in chapter 5 signify that an adjacent channel rejection factor of around 40 dB has been achieved at channel spacing of 1.5 times the symbol rate while the DECT system standards stipulated a much lower rejection limit criterion (25-30dB), implying that CP-QFSK modulation out-performs the conventional GMSK as it causes significantly less ACI, thus it is more spectrally efficient in a multi-channel system. However, measured system performance in terms of BER indicates that this system does not coexist well with other interferers as at delay spreads between 100ns to 200ns, which are commonly encountered in such indoor environment, a severe degradation in system performance apparently caused by multi-path fading has been noticed, and there exists a noise floor of about 40 dB, i.e. high irreducible error rate of less than 5.10-3. Implementing MRC diversity combiner and BCH codec has brought in a good gain.

The current and future demand for wireless technology is increasing rapidlyin the era of Internet-of-things, information-shower, auto-drive vehicles andthe fifth generation of mobile communications. The flourishing in wirelesstechnologies comes from their advantages such as mobility, flexibility, easy toextend, easy to install and easy to do the maintenance. However, the wirelesstechnology is suffering from many problems such as; lack of security andthe shortage of spectrum bands. The security remains a major challenge forthe wireless communications because of the broadcasting nature of wirelesssignals and massive researches have been conducted to deal with it. Beamformingis one of the physical layer security solutions that is proposed toimprove the security by focusing the majority of the transmitted power towardthe legitimate destination. The main concern about the beamformingtechnique is the relatively small amount of power that escapes from the sidelobes where any illegal user equipped with a sufficiently sensitive receivercan detect its information. The literature has been received many differentsolutions to secure the side lobes emissions. These solutions suffer from fourcommon limitations; 1) the need to modulate the signal at the antenna level,2) the data rates are restricted by the switching speed, 3) they can not easily beintegrated with the current infrastructure, and 4) they work only with phasemodulation. In this thesis, a new, simple, economic, easy to get integratedwith current phased array systems and effective solution has been proposedand analytically analysed under different circumstances, including noiseless,noisy and Rician fading channels and the effect of phase shift errors. The secondproblem addressed in this thesis is the poor spectral efficiency of spaceshift keying modulation. This thesis proposes a new physical layer directcode to improve the spectral efficiency of space shift keying modulation byexploiting the indices of both active and inactive transmitting antennas.

To meet the urgent demand of high-speed data rate and to support large number of users, the massive multiple-input multiple-output (MIMO) technology is becoming one of the most promising candidates for the next generation wireless communications, namely the 5G. To realize the full potential of massive MIMO, it is necessary to have the channel state information (CSI) (partially) available at the transmitter. Hence, an efficient channel estimation is one of the key enablers and also critical challenges for 5G communications. Dealing with such problems, this dissertation investigates the design of efficient pilot-data transmission pattern and channel estimation in massive MIMO for both multipair relaying and peer-to-peer systems. Firstly, this dissertation proposes a pilot-data transmission overlay scheme for multipair MIMO relaying systems employing either half- or full-duplex (HD or FD) communications at the relay station (RS). In the proposed scheme, pilots are transmitted in partial overlap with data to decrease the channel estimation overhead. The RS can detect the source data by exploiting the asymptotic orthogonality of massive MIMO channels. Due to the transmission overlay, the effective data period is extended, hence improving system throughput. Both theoretical and simulation results verify that the proposed pilot-data overlay scheme outperforms the conventional separate pilot-data design in the limited coherence interval scenario. Moreover, a power allocation problem is formulated to properly adjust the transmission power of source data transmission and relay data forwarding which further improves the system performance. Additionally, this dissertation proposes and analyzes an efficient HD decode-and-forward (DF) scheme, named sum decode-and-forward (SDF), with the physical layer network coding (PNC) in the multipair massive MIMO two-way relaying system. As comparison, a joint decode-and-forward (JDF) scheme applied to the multipair massive MIMO relaying is also proposed and investigated. In the SDF scheme, a half number of pilots are saved compared to the JDF scheme which in turn increases the spectral efficiency of the system. Both the theoretical analyses and numerical results verifies such superiority of the SDF scheme. Further, the power efficiency of the proposed schemes is also investigated. Simulation results show that the signal transmission power can be rapidly reduced if the massive antenna arrays are equipped on the RS and the required data transmission power can further decrease if the training power is fixed. Finally, this dissertation investigates the general channel estimation problem in the massive MIMO system which employs the hybrid analog/digital precoding structure with limited radio-frequency (RF) chains. By properly designing RF combiners and performing multiple trainings, the performance of the proposed channel estimation can approach that of full-chain estimations depending on the degree of channel spatial correlation and the number of RF chains which is verified by simulation results in terms of both mean square error (MSE) and spectral efficiency. Moreover, a covariance matching method is proposed to obtain channel correlation in practice and the simulation verifies its effectiveness by evaluating the spectral efficiency performance in parametric channel models. / Graduate / 0537 / 0544 / leyuanpan@gmail.com

京都大学 / 0048 / 新制・課程博士 / 博士(情報学) / 甲第22589号 / 情博第726号 / 新制||情||124(附属図書館) / 京都大学大学院情報学研究科通信情報システム専攻 / (主査)教授 守倉 正博, 教授 原田 博司, 教授 大木 英司 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM