Conselho Nacional de Desenvolvimento Científico e Tecnológico / É conhecido que derivações microscópicas obtidas através de métodos de teoria quântica de campos (TQC) podem conduzir a complicadas equações de movimento (EdM) que possuem um termo dissipativo com memória e um termo de ruído colorido. Um caso particularmente interessante é o modelo que escreve a interação entre um sistema e um banho térmico a temperatura T. Motivado por isso, usamos uma prescrição que nos permite reescrever EdMs não-markovianas semelhantes as obtidas em TQC em termos de um sistema de equações locais, para então confrontarmos a solução desse sistema com a solução aproximada usada correntemente na literatura, a chamada aproximação markoviana. A pergunta chave a qual se pretende responder aqui é: dado um conjunto de parâmetros que descrevem o modelo, a aproximação markoviana é suficientemente boa para descrever a dinâmica do sistema se comparada a dinâmica obtida atravéS da EdM não-markoviana? Além disso, consideramos uma versão linear da ELG de forma que pudéssemos determinar o nível de confiança da nossa metodologia numérica, procedimento este realizado comparando-se a solução analítica com a solução numérica. Como exemplo de aplicação prática do tema discutido aqui, comparamos a evolução não-markoviana do inflaton com a evolução markoviana do mesmo num modelo de universo primordial denominado inflação não-isentrópica (warm inflation). / It is known that microscopic derivations based on quantum field theory (QFT)methods can lead to quite complicated equations of motion (EoM) with a dissipation term with memory and a colored noise term. A very interesting particular case is the model that describes the interaction between a system and a thermal bath at some temperature T. Motivated by this, we use a prescription that allow us to rewrite similar non-Markovian EoMs to that obtained in QFT in terms of a set of local equations, so that we can contrast the solution of this system of equations with the approximated solution currently used in the literatury, the so-called Markovian approximation. The key question we want to address here is: given a set of parameters that characterizes the system and the bath, is the Markovian approximation good enough to represent the system's dynamics? We also have considered a linear version of the non-Markovian equation in order to check the confiability of our numerical approach. For that, we have compared the analytical solution with the numerical one. As an example of practical application of the theme discussed here, we contrast the non-Markovian and the Markovian evolution of the inflaton field in an early universe model called warm in inflation.

Esta tese apresenta uma nova aproximação variacional baseada no Método da Coordenada Geradora e na Teoria do Funcional da Densidade. Nesta nova aproximação, a função de onda de muitos corpos é representada como uma superposição de determinantes de Slater Kohn-Sham não-ortogonais calculados a partir de Hamiltonianos diferentes que carregam uma coordenada geradora atuando como parâmetro de deformação. A discretização integral sobre o conjunto de coordenadas geradoras fornece a energia total variacional do sistema e a contribuição de cada determinante na combinação da respectiva função de onda de muitos corpos. A flexibilidade desta nova metodologia permitiu aplicá-la no estudo das energias totais do estado fundamental e excitado dos átomos da série isoeletrônica do Hélio, utilizando diferentes conjuntos de coordenadas geradoras, diferentes aproximações para o potencial de troca e correlação e diferentes maneiras de implementar a coordenada geradora dentro do Hamiltoniano Kohn-Sham. Em seguida, as bases desta nova metodologia foram estendidas para o caso dependente do tempo, permitindo estudar, por exemplo, processos não-lineares como excitações duplas, conhecidas por sua forte dependência dos efeitos de memória. A nova metodologia foi aplicada no estudo das oscilações paramétricas de um sistema de dois elétron sob um potencial harmônico, o átomo de Hooke. Os resultados demonstram que a escolha adequada das coordenadas geradoras reproduz com precisão os efeitos lineares e não-lineares dos elétrons do sistema que não podem ser descritos pela Teoria do Funcional da Densidade Dependente do Tempo utilizando a aproximação adiabática. Assim, a nova metodologia mostra-se: flexível, pois permite calcular propriedades do estado fundamental e excitado, estáticas e dinâmicas dos sistemas eletrônicos fornecendo ainda uma aproximação variacional para as respectivas funções de onda de muitos corpos em todos os casos; e também viável, pois fornece resultados promissores no caso independente do tempo constituindo uma ferramenta simples e computacionalmente barata de incluir os efeitos de memória em qualquer aproximação adiabática no caso dependente do tempo. / A new variational approach based on the Generator Coordinate Method and Density- Functional Theory is presented. It represents the interacting many-body wave function as a superposition of non-orthogonal Kohn-Sham Slater determinants arising from different Hamiltonians featuring a generator coordinate acting as a deformation parameter. An integral discretization procedure over the set of generator coordinates provides the variational total energy of the system and the weight of each determinant in the approximation of the respective interacting many-body wave functions. The method was used to calculate the ground and excited state total energies of the Helium isoelectronic serie of atoms using different sets of generator coordinates, different approximations to the exchange-correlation potential and different implementations of the generator coordinate whithin the Kohn-Sham Hamiltonian. Next, the time dependent extension of the method is presented allowing its application, for example, on the study of nonlinear processess as double excitations which are known to be strongly dependent of the memory effects. As an illustration, the method is sucessfully applied to driven parametric oscillations of a two interacting electrons in a harmonic potential, the Hooke\'s atom. It is demonstrated that a proper choice of time-dependent generator coordinates in conjunction with the adiabatic local-density approximation reproduces the exact linear and nonlinear twoelectron dynamics quite accurately, including features associated with double excitations that cannot be captured by Time-Dependent Density-Functional Theory in the adiabatic approximation. Therefore, the method is considered, flexible since it allows to calculate ground and excited-states, static and dynamic properties of the electronic systems yeilding a variational approach to the interacting many-body wave functions for all cases, and feasible, since it improves the results for ground and excited-states total energies in the time-independente case, besides to be a conceptually and computationally simple tool to build memory effects into any existing adiabatic exchange-correlation potential in the time-dependent case.

Les techniques multiporteuses de type OFDM sont aujourd'hui largement déployées dans tous les systèmes de communication sans fils notamment dans les réseaux cellulaires (L TE), les réseaux de diffusion (DVB) ou encore les réseaux WiFi. Cependant, les modulations multiporteuses se caractérisent par une très grande dynamique mesurée par le Peak to Average Power Ratio (PAPR), ce qui empêche d'alimenter l'amplificateur de puissance non linéaire (utilisé avant l'émission des signaux) à son point optimal et ainsi conduit à diminuer son efficacité énergétique. Des techniques de réduction du PAPR peuvent alors être mises en oeuvre pour réduire le PAPR du signal et des techniques de prédistorsion peuvent alors être utilisées pour compenser les non-linéarités de l'amplificateur de puissance. L'approche développée dans le cadre de cette thèse a pour objectif d'étudier une solution intelligente pour les implémentations futures pour contrôler la réduction du PAPR et les étapes de linéa risation de manière flexible en fonction de certains paramètres prédéfinis afin qu'ils deviennent adaptatifs et auto-configurables. Plus précisément, notre travail a principalement porté sur l'analyse des différentes distorsions dans la bande (in-band distortions)mesurées par I'EVM ou Error Vector Magnitude et en dehors de la bande de transmission (out-of-band distortions) mesurées par I'ACPR ou Adjacent Channel Power Ratio de signaux à porteuses multiples. En particulier de nombreux résultats analytiques complétés par des résultats de simulation permettant d'évaluer I'EVM et I'ACPR en fonction des caractéristiques de l'amplification nonlinéaire en prenant en compte ou pas l'effet mémoire de l'amplificateur et la mise en oeuvre de techniques d'écrêtage et de pré-distorsion ont été obtenus. Ces résultats constituent une étape importante dans l'optimisation globale de la complexité, de la linéarité et de l'efficacité énergétique des émetteurs aussi bien pour la diffusion de la télévision numérique que pour les réseaux cellulaires de 4 ème génération (L TE) ou de 5""' génération. / OFDM multicarrier techniques are now widely deployed in most wireless communication systems, in particular in cellularnetworks (L TE), broadcast networks (DVB) and WiFi networks. However, multi-carrier modulations are characterized by avery large dynamic amplitude measured by the Peak to Average Power Ratio (PAPR). which prevents radio frequencydesigners to feed the signal at the optimal point of the Power Amplifier (PA) which reduces the PA energy efficiency. Inliterature, the PAPR reduction and linearization techniques are the main approaches to solve the PAPR problem, the PAnonlinearities problem. as well as the low PA efficiency problem.The approach developed in this thesis was to study an intelligent solution for future implementations to control thereduction of PAPR and the linearization steps in a flexible way according to some predefined parameters so that theybecome adaptive and self-configurable. More specifically, our work focused on the analytical analysis of in-band measureby the Error Vector Magnitude (EVM) and out-of-band distortions measured by the Adjacent Chanel Power Ratio (ACPR)for clipped multicarrier signals taking into account the impact of non-linear amplification, memory effects and predistortion.In particular. many analytical results complemented by simulation results to evaluate the EVM and ACPR are proposed.These analytical expressions depend on the PA characteristics taking into account or not the PA memory effects and theuse of clipping and pre-distortion techniques. lt is worthwhile to note that our proposed theoretical analyses could be veryuseful for optimizing future transmitter efficiency and linearity in the field of broadcasting applications for the deployment oDVB-T2 transmitters as well as for L TE cellular networks.

L'amplificateur de puissance est le module le plus critique dans les équipements de communication radio. Il détermine la qualité de la liaison par sa linéarité et a une contribution conséquente dans la consommation de l'émetteur ; environ 60% de l'énergie consommée est consacré à l'amplification. Il est donc crucial de le faire fonctionner avec un rendement énergétique élevé. Cependant, ces deux spécifications principales de l'amplificateur que sont la linéarité et le rendement énergétique sont antagoniques. Par conséquent, la conception d'un module d'amplification de puissance suppose de trouver un compromis entre la linéarité et le rendement. L'optimisation de ce compromis est la raison d'être des techniques de linéarisation d'amplificateurs et d'amélioration du rendement, parmi lesquelles la prédistorsion numérique (DPD) et les techniques de réduction du PAPR du signal (CFR).Le cœur de cette thèse est la linéarisation d'amplificateurs RF haute-puissance et large-bande par prédistorsion numérique (DPD). Dans ces travaux, nous abordons trois problématiques liées à la prédistorsion et qui constituent des verrous technologiques importants. Le premier aspect concerne l'implémentation de la prédistorsion numérique dans un contexte multi-bande où le signal à linéariser comporte plusieurs formes d'ondes, situées à des fréquences différentes. La seconde problématique est l'utilisation conjointe de la prédistorsion avec une technique de CFR. Dans la majorité des applications haute-puissance, les techniques de DPD et de CFR sont présentes de manière complémentaire, cependant elles sont utilisées de façon autonome et disjointe. Celles-ci gagneraient en performances de linéarisation en étant implémentées de manière plus concertée. . Le dernier thème abordé par cette thèse est l'effet des désadaptations d'impédance de l'antenne sur le mode de fonctionnement de l'amplificateur. La variation de l'impédance d'antenne entraine des réflexions de signal vers l'amplificateur qui modifient ses spécifications de linéarité et de rendement. Nous améliorons la linéarité du système DPD + AP, lorsque l'amplificateur est soumis à des variations de l'impédance à sa charge, grâce à une correction adaptative de gain / Power amplifier is one of the most critical element within radiocommunications systems. The PA is their main source of nonlinearities and it has a great contribution on the emitter's power consumption. Running the PA with highest power efficiency is thus as crucial as having it linear for a good communication quality. However these two specifications of the PA are antagonistic and PA manifacturers need to find a compromise between linearity and power efficiency. Digital Predistortion (DPD) and Crest factor Reduction techniques are intended to improve power efficiency while preserving linearity or inversely. Linearization of wideband RF power amplifiers using Digital Predistortion is the focus of this thesis. Three DPD issues are investigated in these works. The first issue deals with multiband linearization where signals with various waveforms located at different frequency bands are amplified. The second objective of this thesis is to study a concurrent DPD/CFR systems based on an automatic estimation of the necessary CFR gain. The last part of this dissertation deals with PA linearization under antenna load variations. Indeed, the impedance of antenna may vary because of electromagnetic objects that are present in its vicinity. Those impedance variations may instigate signal reflections toward the PA, that modify some of its main specifications (linearity, delivered power and efficiency). Our goal in this field is to preserve DPD linearization performances under antenna load mismatch

No description available.

Many communications signal formats are not power efficient because of their large peak-to-average power ratios (PARs). Moreover, in the presence of nonlinear devices such as power amplifiers (PAs) or mixers, the non-constant-modulus signals may generate both in-band distortion and out-of-band interference. Backing off the signal to the linear region of the device further reduces the system power efficiency. To improve the power efficiency of the communication system, one can pursue two approaches: i) linearize the PA; ii) reduce the high PAR of the input signal. In this dissertation, we first explore the optimal nonlinearity under the peak power constraint. We show that the optimal nonlinearity is a soft limiter with a specific gain calculated based on the peak power limit, noise variance, and the probability density function of the input amplitude. The result is also extended to the fading channel case. Next, we focus on digital baseband predistortion linearization for power amplifiers with memory effects. We build a high-speed wireless test-bed and carry out digital baseband predistortion linearization experiments. To implement adaptive PA linearization in wireless handsets, we propose an adaptive digital predistortion linearization architecture that utilizes existing components of the wireless transceiver to fulfill the adaptive predistorter training functionality. We then investigate the topic of PAR reduction for OFDM signals and forward link CDMA signals. To reduce the PAR of the OFDM signal, we propose a dynamic selected mapping (DSLM) algorithm with a two-buffer structure to reduce the computational requirement of the SLM method without sacrificing the PAR reduction capability. To reduce the PAR of the forward link CDMA signal, we propose a new PAR reduction algorithm by introducing a relative offset between the in-phase branch and the quadrature branch of the transmission system.

Ce travail de thèse s'intéresse à l'optimisation des performances de transmissions multimédias par une approche originale combinant des circuits radiofréquences, tel que l'am-plificateur de puissance et les distorsions du canal de transmission. Les signaux OFDM sont très sensibles aux non-linéarités de l'amplificateur à cause des fortes fluctuations du niveau du signal, caractérisées par le PAPR. Afin de réduire le PAPR, on propose tout d'abord d'améliorer la méthode TR en termes de rapidité de convergence et de réduction du PAPR, en comparant plusieurs algorithmes d'optimisation. On montre que l'algorithme du gradient con-jugué offre les meilleures performances tout en respectant les spécifications fréquentielles du standard IEEE 802.11a. Par la suite, la méthode TR est évaluée expérimentalement en pré-sence d'un amplificateur de puissance (SZP-2026Z) en utilisant un banc de mesures. On montre ainsi que la méthode TR permet une amélioration de la qualité de transmission. Cette amélioration peut être utilisée pour modifier le point de fonctionnement de l'amplificateur et per-mettre ainsi une réduction de 18 % de la puissance consommée. Les résultats expérimentaux ont conduit au choix d'un modèle réaliste d'amplificateur en considérant les effets mémoires. Ce dernier a été intégré dans une chaîne de simulation SISO comprenant également un modèle réaliste de canal de transmission. La chaîne décrite a permis d'évaluer les performances de la méthode TR dans des conditions de transmission réalistes. Enfin, on propose d'appliquer la méthode TR dans une chaîne MIMO-OFDM en boucle fermée dédiée à la transmission de contenus multimédias scalables dans un environnement réaliste, en utilisant le standard IEEE 802.11n. Cette étude présente une évaluation originale de l'impact de la méthode TR sur la qualité visuelle des images transmises, en prenant en compte le contenu multimédia, la non-linéarité de l'amplificateur et les distorsions apportées par le canal. / In this thesis, we are interested on the performances optimization of multimedia transmissions systems with an original contribution combining RF circuits' imperfections presented by the power amplifier (PA) nonlinearities and the transmission channel distortions. The studied system uses the OFDM technique which is the most widespread multicarrier modulation in recent radio communications systems. However, its major drawback is the high PAPR value, which degrades the transmission quality due to the PA nonlinearities. To reduce the PAPR, we first propose to improve the TR method in terms of convergence speed and PAPR reduction, by studying several optimization algorithms. We show that the conjugate gradient algorithm provides the best performance while respecting the frequency specifica-tions of the IEEE 802.11a standard. Thereafter, TR method has been evaluated experimentally in the presence of a commercial PA (SZP-2026Z) and using a measurement bench. It is shown that the TR method improves the quality of service (QoS), with 18% reduction in PA power consumption. The experimental study has resulted to choosing a realistic PA model consider-ing memory effects. This PA model has been integrated into a SISO simulation chain includ-ing also a realistic channel model. This chain is used to evaluate the TR method performances under realistic transmission conditions. Finally, we propose to apply the TR method in a closed-loop MIMO-OFDM chain dedicated to the transmission of scalable multimedia con-tent in a realistic context with the IEEE 802.1n standard. This study presents a new contribu-tion of the TR method evaluation to improve the visual quality of the JPWL transmitted imag-es, considering in the same time the multimedia content, the PA nonlinearity and the channel transmission distortions.

This diploma thesis deals with optimization of transmitter amplifier parameters for LoRaWAN network. The issue of optimization is first based on the conditions of ETSI EN 300 220, which takes into account the eventuality of interference the adjacent channels in the band. The optimizations are designed specifically for the Qorvo RF5110g integrated circuit, so that the amplifier meets the requirements of the above standard at the limit of the maximum allowed output power and also with respect to radio ecology.

High electron mobility transistors (HEMTs) realized using AlxGa1-xN/GaN are relatively new technology which is prominent for high-speed and high-power applications. Some of the main problems with this technology were identified as dynamic RDSon, current collapse and threshold voltage instabilities due to the off-state stress. What was less investigated is the effect of the off-state stress on the leakage current at lower voltages. In this work, multiple devices with various initial leakage currents are stressed at different stress conditions (drain voltage, temperature, duration) and the development of drain-source on-state resistance (RDSon), threshold voltage (Vth) and drain-source leakage current (IDSS) after stress are tracked. It was found out that devices with initially higher leakage exhibit higher RDSon and Vth before stress, which simulations attributed to the higher Al mole fraction in the back-barrier or less unintentional doping in the channel layer. During the off-state stress (VDS = 900 V), the leakage current shortly rises and then sharply drops, presumably because of the charge redistribution in the back-barrier. After the stress, no larger changes were observed for RDSon and Vth , but they were for the leakage current i.e., initially low leakage devices had post-stress leakage increase, while initially high leakage devices had post-stress leakage decrease. This is assumed to be caused by the charge redistribution. Parasitic capacitance measurements showed the rise of the pre-stress input, output and reverse transfer capacitances with the pre-stress leakage, which could presumably be explained by higher Al mole fraction inducing more charges in the channel layer, deeming higher Al mole fraction in the back-barrier as a main assumed cause for all the observed effects. After the stress, capacitance changes were tentatively explained by the charge redistribution in the back-barrier. Finally, high temperature was shown to significantly reduce the observed long time to recovery. However, more measurements are needed to further observe this influence. Additionally, more experiments (e.g., on wafer, G-ω measurement, etc.) are needed in general to further investigate the mechanisms behind these memory effects. / Transistorer med extra hög elektronmobilitet, sk HEMT-ar (high electron mobility transistor) kan fabriceras med hjälp av materialen galliumnitrid (GaN) och aluminium-galliumnitrid (AlxGa1-xN). GaN HEMT-ar lämpar sig mycket väl för kraftkomponenter för höga frekvenser. Några av problemen med denna nya teknologi är hög resistans mellan ”drain” och ”source”, RDSon, reduktion av mättnadsströmmen (”current collapse”) och instabiliteter hos styrets tröskelspänning (Vth) när komponenterna stressas i avslaget tillstånd. Mindre känt är effekterna av stress för en avslagen komponent på läckströmmen (IDSS) vid låga påkänningar. I detta arbete har komponenter med varierande läckströmmar utsatts för olika typer av stress, t ex drain-spänning och höjd temperatur under olika långa tider samtidigt som parametrarna RDSon, Vth och IDSS har uppmätts. Det kunde noteras att komponenter med initialt högre läckströmmar hade högre RDSon och Vth innan de utsattes för stress, vilket med hjälp av simuleringar kunde visas bero på högre Al-molfraktion i skiktet under AlxGa1-xN-lagret, alternativt lägre dopning i kanal-lagret. Vid stress (VDS = 900 V) med komponenterna i avslaget tillstånd ökade läckströmmen kortvarigt för att sedan minska, troligtvis beroende på att laddningar omfördelas i lagret under kanal-skiktet. Efter stress sågs inte några större förändringar hos RDSon och Vth , men förändringar syntes på läckströmmen: komponenter med initialt låga läckströmmar visade ökning av läckströmmen efter stress, medan komponenter med initialt höga läckströmmar visade en post-stress minskning av läckström. Detta antas bero på den nämnda omfördelningen av laddningar djupare ner i komponenterna. Mätningar av parasitisk kapacitans visade på en ökning av pre-stress in- och ut-kapacitanserna (Ciss, Coss) samt ”gate-drain”-kapacitansen som funktion av pre-stress läckströmmar. Detta kan möjligtvis förklaras av att en högre andel Al inducerar mer laddningar i kanalen, vilket indikerar att högre Al-molfraktion i skiktet under kanal-lagret är orsaken till många av de effekter som setts. Kapacitansförändringar efter stress förklaras troligen av att laddningarna i detta lager återgår. Till sist noteras också att hög temperatur tydligt reducerade den långa tiden som komponenterna behövde för att återhämta sig. Det var också tydligt att mer mätningar är nödvändiga för att ytterligare säkerställa de uppmätta förändringarna, t ex mätningar av G-ω på icke kapslade chips, skulle kunna öka förståelsen för dessa minneseffekter.

Cette thèse porte sur l'étude de différents aspects de la physique nucléaire depuis les basses énergies jusqu'aux énergies intermédiaires. Pour les basses énergies, où la matière nucléaire est essentiellement constituée de nucléons en interaction, la partie I traite de la fusion-fission des noyaux super-lourds, et la partie II des règles de somme associées aux interactions de type Skyrme. Pour les énergies intermédiaires, la matière nucléaire étant alors considérée comme une phase hadronique principalement constituée de pions, la partie III se focalise sur l'hydrodynamique relativiste de la matière nucléaire avec brisure spontanée de symétrie chirale. Dans la partie I, on s'intéresse à la formation puis à la désexcitation des noyaux super-lourds. On étudie donc la formation du noyau composé avec effets de mémoire. Pour la désexcitation d'un noyau super-lourd, l'existence d'un puits isomérique dans la barrière de potentiel change la dynamique de désexcitation et augmente les temps de fission. Cette dernière étude pourrait être utile à l'étude de la dynamique de la fission des actinides. Dans la partie II, les règles de somme M1 et M3 associées aux potentiels phénoménologiques de type Skyrme sont calculées à partir de leurs définitions intrinsèques. On détermine alors M1 jusqu'au niveau tensoriel et M3 avec potentiel central. Dans la partie III, pour le traitement hydrodynamique de la matière hadronique appliqué aux collisions d'ions lourds on peut, en première approximation, écarter les modifications induites par la brisure spontanée de symétrie chirale mais pas celles dues à l'aspect dissipatif. / This study focuses on different aspects of nuclear physics from low energies to intermediate ones. For the low energies, the nuclear matter is essentially constituted from interacting nucleons. Part I is on the fusion-fission of super-heavy elements, while Part II is on the Skyrme interactions-associated sum rules. In the case of the intermediate energies, where the nuclear matter is considered as being an hadronic phase mainly constituted from pions, Part III is focused on nuclear matter relativistic hydrodynamics with spontaneous chiral symmetry breaking. In Part I, the formation and the desexcitation of super-heavy nuclei are being studied. We analyzed the formation of compound nuclei including the memory effects. For super-heavy nuclei desexcitation, the existence of isomeric state within the potential barrier modifies the desexcitation dynamics and increases the fission time. This latter study could be useful for the study of the actinides fission. In Part II, the phenomenological Skyrme effective interactions- associated M1 and M3 sum rules are being calculated based on their intrinsic definitions. We identify then M1 up to the tensorial level and M3 with central potential. In Part III, as for the hadronic matter hydrodynamics being applied to heavy ions collisions, and as a first approach only, we can neglect spontaneous chiral symmetry but certainly not the dissipative impact.