Traditional cryptographic encryption techniques at higher layers require a certain form of information sharing between the transmitter and the legitimate user to achieve security. Besides, it also assumes that the eavesdropper has an insufficient computational capability to decrypt the ciphertext without the shared information. However, traditional cryptographic encryption techniques may be insufficient or even not suit- able in wireless communication systems. Physical layer security (PLS) can enhance the security of wireless communications by leveraging the physical nature of wireless transmission. Thus, in this thesis, we study the PLS performance in emerging wireless transmission systems. The thesis consists of two main parts. We first consider the PLS design and analysis for ground-based networks em- ploying random unitary beamforming (RUB) scheme at the transmitter. With RUB technique, the transmitter serves multiple users with pre-designed beamforming vectors, selected using limited channel state information (CSI). We study multiple-input single-output single-eavesdropper (MISOSE) transmission system, multi-user multiple-input multiple-output single-eavesdropper (MU-MIMOSE) transmission system, and massive multiple-input multiple-output multiple-eavesdropper (massive MI- MOME) transmission system. The closed-form expressions of ergodic secrecy rate and the secrecy outage probability (SOP) for these transmission scenarios are derived. Besides, the effect of artificial noise (AN) on secrecy performance of RUB-based transmission is also investigated. Numerical results are presented to illustrate the trade-off between performance and complexity of the resulting PLS design. We then investigate the PLS design and analysis for unmanned aerial vehicle (UAV)-based networks. We first study the secrecy performance of UAV-assisted relaying transmission systems in the presence of a single ground eavesdropper. We derive the closed-form expressions of ergodic secrecy rate and intercept probability. When multiple aerial and ground eavesdroppers are located in the UAV-assisted relaying transmission system, directional beamforming technique is applied to enhance the secrecy performance. Assuming the most general κ-μ shadowed fading channel, the SOP performance is obtained in the closed-form expression. Exploiting the derived expressions, we investigate the impact of different parameters on secrecy performance. Besides, we utilize a deep learning approach in UAV-based network analysis. Numerical results show that our proposed deep learning approach can predict secrecy performance with high accuracy and short running time. / Graduate

Analytical modelling and characterization of Weighted Fair Queueing (WFQ) have recently received considerable attention by several researches since WFQ offers the minimum delay and optimal fairness guarantee. However, all previous work on WFQ has focused on developing approximations of the scheduler with an infinite buffer because of supposed scalability problems in the WFQ computation. The main aims of this thesis are to study WFQ system, by providing an analytical WFQ model which is a theoretical construct based on a form of processor sharing for finite capacity. Furthermore, the solutions for classes with Poisson arrivals and exponential service are derived and verified against global balance solution. This thesis shows that the analytical models proposed can give very good results under particular conditions which are very close to WFQ algorithms, where accuracy of the models is verified by simulations of WFQ model. Simulations were performed with QNAP-2 simulator. In addition, the thesis presents several performance studies signifying the power of the proposed analytical model in providing an accurate delay bounds to a large number of classes. These results are not able to cover all unsolved issues in the WFQ system. They represent a starting point for the research activities that the Author will conduct in the future. The author believes that the most promising research activities exist in the scheduler method to provide statistical guarantees to multi-class services. The author is convinced that alternative software, for example, on the three class model buffer case, is able to satisfy the large number of buffer because of the software limitation in this thesis. While they can be a good topic for long-term research, the short-medium term will show an increasing interest in the modification of the WFQ models to provide differentiated services.

Made available in DSpace on 2014-12-17T14:09:19Z (GMT). No. of bitstreams: 1 JonatasALJ_TESE.pdf: 9049452 bytes, checksum: dd9b668c8bc7791108be8a6bbc44e152 (MD5) Previous issue date: 2014-04-28 / A self-flotator vibrational prototype electromechanical drive for treatment of oil and water emulsion or like emulsion is presented and evaluated. Oil production and refining to obtain derivatives is carried out under arrangements technically referred to as on-shore and off-shore, ie, on the continent and in the sea. In Brazil 80 % of the petroleum production is taken at sea and area of deployment and it cost scale are worrisome. It is associated, oily water production on a large scale, carrier 95% of the potential pollutant of activity whose final destination is the environment medium, terrestrial or maritime. Although diversified set of techniques and water treatment systems are in use or research, we propose an innovative system that operates in a sustainable way without chemical additives, for the good of the ecosystem. Labyrinth adsor-bent is used in metal spirals, and laboratory scale flow. Equipment and process patents are claimed. Treatments were performed at different flow rates and bands often monitored with control systems, some built, other bought for this purpose. Measurements of the levels of oil and grease (OGC) of efluents treaty remained within the range of legal framework under test conditions. Adsorbents were weighed before and after treatment for obtaining oil impregna-tion, the performance goal of vibratory action and treatment as a whole. Treatment technolo-gies in course are referenced, to compare performance, qualitatively and quantitatively. The vibration energy consumption is faced with and without conventional flotation and self-flotation. There are good prospects for the proposed, especially in reducing the residence time, by capillary action system. The impregnation dimensionless parameter was created and confronted with consecrated dimensionless parameters, on the vibrational version, such as Weber number and Froude number in quadratic form, referred to as vibrational criticality. Re-sults suggest limits to the vibration intensity / Um prot?tipo vibr?til autoflotador de acionamento eletromec?nico para tratamento de ?gua de produ??o de petr?leo e emuls?o cong?nere ? apresentado e avaliado. A produ??o de petr?leo para refinamento e obten??o de derivados ? realizada sob modalidades tecnicamente referidas como on-shore e off-shore, isto ?, no continente e no mar. No Brasil 80% da produ??o petrol?-fera ? feita no mar e ?rea de implanta??o e escala de custo s?o preocupantes. Associa-se ?gua oleosa de produ??o, efluente abundante em larga escala, carreadora de 95% do potencial polu-idor da atividade cujo destino final ? o meio ambiente mar?timo ou terrestre. Embora diversi-ficado conjunto de t?cnicas e sistemas de tratamento d ?gua encontram-se em uso ou pesqui-sa, prop?e-se um sistema inovador que opera de forma sustent?vel sem aditivos qu?micos, pa-ra o bem do ecossistema. Utilizou-se labirinto adsorvente, em espirais met?licos, e escala la-boratorial de fluxo. Patentes de equipamento e processo s?o reivindicadas. Realizaram-se tra-tamentos em vaz?es e faixas de frequ?ncia distintas, monitoradas com sistemas de controle, uns constru?dos, outros aquistados para tal. Medi??es do teor de ?leo e graxa (TOG) do eflu-ente tratado mantiveram-se dentro do intervalo de enquadramento legal nas condi??es de en-saio. Pesaram-se os adsorventes antes e ap?s o tratamento para obten??o da impregna??o de ?leo, meta de desempenho da a??o vibrat?ria e tratamento como um todo. Tecnologias atuais de tratamento s?o referenciadas para compara??o de desempenho, qualitativa e quantitativa-mente. Confrontou-se consumo energ?tico operando-se em vibra??o, com e sem flota??o con-vencional, e com autoflota??o. Vislumbram-se boas perspectivas de rendimento do sistema proposto, sobretudo, na redu??o do tempo de resid?ncia por a??o de capilaridade. Criou-se o par?metro adimensional de impregna??o e se lhe confrontou com consagrados par?metros a-dimensionais, na vers?o vibracional, como n?mero de Weber e n?mero de Froud quadr?tico, referido como criticalidade vibr?til. Resultados sugerem limites ? intensidade vibrat?ria

Dans la modélisation et l'évaluation des performances de la communication cellulaire sans fil, la géométrie stochastique est largement appliquée afin de fournir des solutions plus efficaces et plus précises. Le processus ponctuel de Poisson homogène (H-PPP), est le processus ponctuel le plus largement utilisé pour modéliser les emplacements spatiaux des stations de base (BS) en raison de sa facilité de traitement mathématique et de sa simplicité. Pour les fortes corrélations spatiales entre les emplacements des stations de base, seuls les processus ponctuels (PP) avec inhibitions et attractions spatiales peuvent être utiles. Cependant, le temps de simulation long et la faible aptitude mathématique rendent les PP non-Poisson non adaptés à l'évaluation des performances au niveau du système. Par conséquent, pour surmonter les problèmes mentionnés, nous avons les contributions suivantes dans cette thèse: Premièrement, nous introduisons une nouvelle méthodologie de modélisation et d’analyse de réseaux cellulaires de liaison descendante, dans laquelle les stations de base constituent un processus ponctuel invariant par le mouvement qui présente un certain degré d’interaction entre les points. L'approche proposée est basée sur la théorie des PP inhomogènes de Poisson (I-PPP) et est appelée approche à double amincissement non homogène (IDT). L’approche proposée consiste à approximer le PP initial invariant par le mouvement avec un PP équivalent constitué de la superposition de deux I-PPP conditionnellement indépendants. Les inhomogénéités des deux PP sont créées du point de vue de l'utilisateur type ``centré sur l'utilisateur''. Des conditions suffisantes sur les paramètres des fonctions d'amincissement qui garantissent une couverture meilleure ou pire par rapport au modèle de PPP homogène de base sont identifiées. La précision de l'approche IDT est justifiée à l'aide de données empiriques sur la distribution spatiale des stations de base. Ensuite, sur la base de l’approche IDT, une nouvelle expression analytique traitable du rapport de brouillage moyen sur signal (MISR) des réseaux cellulaires où les stations de base présentent des corrélations spatiales est introduite. Pour les PP non-Poisson, nous appliquons l'approche IDT proposée pour estimer les performances des PP non-Poisson. En prenant comme exemple le processus de points β-Ginibre ( β -GPP), nous proposons de nouvelles fonctions d’approximation pour les paramètres clés dans l’approche IDT afin de modéliser différents degrés d’inhibition spatiale et de prouver que MISR est constant en densification de réseau. Nous prouvons que la performance MISR dans le cas β-GPP ne dépend que du degré de répulsion spatiale, c'est-à-dire β , quelles que soient les densités de BS. Les nouvelles fonctions d'approximation et les tendances sont validées par des simulations numériques.Troisièmement nous étudions plus avant la méta-distribution du SIR à l’aide de l’approche IDT. La méta-distribution est la distribution de la probabilité de réussite conditionnelle compte tenu du processus de points. Nous dérivons et comparons l'expression sous forme fermée pour le b-ème moment dans les cas PP H-PPP et non-Poisson. Le calcul direct de la fonction de distribution cumulative complémentaire (CCDF) pour la méta-distribution n'étant pas disponible, nous proposons une méthode numérique simple et précise basée sur l'inversion numérique des transformées de Laplace. L'approche proposée est plus efficace et stable que l'approche conventionnelle utilisant le théorème de Gil-Pelaez. La valeur asymptotique de la CCDF de la méta distribution est calculée dans la nouvelle définition de la probabilité de réussite. En outre, la méthode proposée est comparée à certaines autres approximations et limites, par exemple l’approximation bêta, les bornes de Markov et les liaisons de Paley-Zygmund. Cependant, les autres modèles et limites d'approximation sont comparés pour être moins précis que notre méthode proposée. / In the modeling and performance evaluation of wireless cellular communication, stochastic geometry is widely applied, in order to provide more efficient and accurate solutions. Homogeneous Poisson point process (H-PPP) with identically independently distributed variables, is the most widely used point process to model the spatial locations of base stations (BSs) due to its mathematical tractability and simplicity. For strong spatial correlations between locations of BSs, only point processes (PPs) with spatial inhibitions and attractions can help. However, the long simulation time and weak mathematical tractability make non-Poisson PPs not suitable for system level performance evaluation. Therefore, to overcome mentioned problems, we have the following contributions in this thesis: First, we introduce a new methodology for modeling and analyzing downlink cellular networks, where the base stations constitute a motion-invariant point process that exhibits some degree of interactions among the points. The proposed approach is based on the theory of inhomogeneous Poisson PPs (I-PPPs) and is referred to as inhomogeneous double thinning (IDT) approach. The proposed approach consists of approximating the original motion-invariant PP with an equivalent PP that is made of the superposition of two conditionally independent I-PPPs. The inhomogeneities of both PPs are created from the point of view of the typical user. The inhomogeneities are mathematically modeled through two distance-dependent thinning functions and a tractable expression of the coverage probability is obtained. Sufficient conditions on the parameters of the thinning functions that guarantee better or worse coverage compared with the baseline homogeneous PPP model are identified. The accuracy of the IDT approach is substantiated with the aid of empirical data for the spatial distribution of the BSs. Then, based on the IDT approach, a new tractable analytical expression of mean interference to signal ratio (MISR) of cellular networks where BSs exhibits spatial correlations is introduced.For non-Poisson PPs, we apply proposed IDT approach to approximate the performance of non-Poisson PPs. Taking β-Ginibre point process (β -GPP) as an example, we propose new approximation functions for key parameters in IDT approach to model different degree of spatial inhibition and we successfully prove that MISR for β -GPP is constant under network densification with our proposed approximation functions. We prove that of MISR performance under β-GPP case only depends on the degree of spatial repulsion, i.e., β , regardless of different BS densities. We also prove that with the increase of β or (given fixed γ or β respectively), the corresponding MISR for β-GPP decreases. The new approximation functions and the trends are validated by numerical simulations. Third, we further study meta distribution of the SIR with the help of the IDT approach. Meta distribution is the distribution of the conditional success probability given the point process. We derive and compare the closed-form expression for the b-th moment under H-PPP and non-Poisson PP case. Since the direct computation of the complementary cumulative distribution function (CCDF) for meta distribution is not available, we propose a simple and accurate numerical method based on numerical inversion of Laplace transforms. The proposed approach is more efficient and stable than the conventional approach using Gil-Pelaez theorem. The asymptotic value of CCDF of meta distribution is computed under new definition of success probability. Furthermore, the proposed method is compared with some other approximations and bounds, e.g., beta approximation, Markov bounds and Paley-Zygmund bound. However, the other approximation models and bounds are compared to be less accurate than our proposed method.