La baisse de la fécondité permet aux couples d'investir davantage dans la scolarité de chacun de leurs enfants (évidence dans les pays occidentaux, d’Asie et d’Amérique latine). Ce postulat est l’un des arguments clés des politiques de planification familiale en Afrique subsaharienne. Pourtant, la plupart des études sur l'Afrique ont trouvé une corrélation nulle ou même une relation positive entre le nombre d'enfants dans un ménage et leur niveau de scolarité. Ces résultats mitigés sont généralement expliqués par des solidarités familiales et des transferts de ressources qui pourraient réduire la pression occasionnée par une descendance nombreuse sur les ressources du ménage, et des problèmes méthodologiques inhérents à plusieurs recherches sur la région. L’objectif principal de cette thèse était d’apporter une contribution à une meilleure compréhension des aspects méthodologiques et substantiels relatifs aux liens entre fécondité et scolarisation. Spécifiquement, la thèse visait à évaluer 1) le rôle des réseaux familiaux dans la scolarisation des enfants, 2) la simultanéité des décisions portant sur le nombre d’enfants et leur scolarisation, 3) l’impact causal du nombre d’enfants sur leur scolarisation, et 4) à comprendre les perceptions des parents sur l’école et les coûts et bénéfices de l’éducation des enfants, et dans quelle mesure ces perceptions sont prises en compte dans leurs stratégies reproductives. Quatre articles ont été rédigés en utilisant quatre sources de données complémentaires : l’Observatoire de population de Ouagadougou (OPO), l’enquête Demtrend, l’enquête santé de base et une enquête qualitative, toutes adossées à l’OPO. Dans le premier article, il est ressorti que les familles de grande taille bénéficient d’un appui plus fréquent des réseaux familiaux pour la scolarisation. De plus, les réseaux familiaux seraient en mesure de compenser l’effet négatif d’un nombre élevé d’enfants sur la scolarisation, mais seulement pour une partie de la population qui exclut les plus pauvres. Ainsi, les solidarités familiales de soutien à la scolarisation des enfants sont loin d’être généralisées. Le deuxième article a montré que les enfants dont les mères ont intentionnellement limité leur fécondité avaient de meilleures chances de scolarisation que ceux dont les mères ont connu des problèmes d’infécondité secondaire et n’ont pas atteint leur nombre d’enfants désiré. Par conséquent, les aspirations scolaires ne sont pas indépendantes des décisions de fécondité et l’hypothèse de fécondité naturelle n’est plus tenable dans ce contexte. Le troisième article a révélé, contrairement à la plupart des études antérieures sur l’Afrique subsaharienne, un effet négatif net de la taille de la fratrie sur le niveau d’éducation atteint des enfants, effet qui se renforce d’ailleurs au fur et à mesure que l’on avance dans le système éducatif. Dans le quatrième article, le discours des participants à l’enquête qualitative a indiqué que l’émergence de cette relation négative entre le nombre d’enfants et leur scolarisation dans les quartiers périphériques de Ouagadougou est intimement liée aux changements dans les coûts et bénéfices de l’éducation des enfants qui font reposer dorénavant de façon presque exclusive les dépenses scolaires sur les parents biologiques. / Lower fertility allows couples to invest more in each of their children’s schooling, a phenomenon that has been observed in Western rich countries, Asia and Latin America. This postulate is a key rationale of family planning policies in sub-Saharan Africa. Yet most studies on Africa have found no correlation or even a positive relationship between the number of children in a family and their educational attainment. These mixed results are usually explained by African family solidarity and resource transfers that might reduce pressures on household resources occasioned by many births, and methodological problems that have afflicted much research on the region. The main objective of this thesis was to contribute to a better understanding of the methodological and substantive aspects relating the links between fertility and schooling. Specifically, the thesis has assessed 1) the role of family networks in the schooling of children, 2) simultaneous decisions on the number of children and their education, 3) the causal impact of the number of children on their schooling and 4) parents' perceptions on the school and the costs and benefits of child schooling and how these perceptions are taken into account in their reproductive strategies. Four articles were written from four complementary sources of data: the Ouagadougou population Observatory (OPO), the Demtrend survey, the Baseline Health Survey and a qualitative survey; all of these surveys are based on the OPO study population. In the first article, the results show that large families receive more support of family networks for schooling than small families. In addition, family networks would be able to offset the negative effect of a high number of children on schooling, but only for a part of the population that excludes the poorest. Thus, the family solidarity for the schooling is far from universal. The results of the second article show that children whose mothers intentionally limited their fertility have better schooling than those with subfecund mothers who could not attain their desired family size. Therefore, fertility is not independent to schooling aspirations; the assumption of natural fertility is not tenable in this context. The third article show, in contrast to most prior studies on sub-Saharan Africa, a net negative effect of sibship size on the level of schooling achieved by children, one that grows stronger as they progress through the educational system. In the fourth article, the discourse of respondents collected by a qualitative survey indicate that the emergence of this negative relationship between the number of children and their schooling in the outskirts of Ouagadougou is closely linked to perceived changes in the costs and benefits of children's schooling. In present day Ouagadougou, school expenses appear to fall almost exclusively to biological parents.

Sistemas modernos de comunicação móvel sem fio, como os de quarta geração (4G), têm como principais metas prover elevada capacidade e alta qualidade de serviço (QoS) para os usuários. Para prover tal aumento de capacidade e QoS, sistemas 4G empregam diversas técnicas avançadas de transmissão e maior largura de banda, combinados com algoritmos de alocação de recursos que possam explorar de maneira eficiente tais técnicas, como por exemplo aproveitando as dimensões de diversidade do sistema. Em geral, porém, é necessário também aumentar a potência de transmissão para se atingir o ganho de capacidade desejado, o que implica maior custo para os provedores de serviço, menor tempo de vida para os dispositivos móveis e impacto ambiental cada vez mais pronunciado. Dado que a expectativa é que o número de usuários e a necessidade de dados continuem crescendo rapidamente, torna-se evidente a importância de analisar a relação entre capacidade e potência dispendida pelo sistema. Essa relação pode ser vista através da métrica de eficiência energética (EE), que é dada pela razão entre o número de bits efetivamente recebidos e a energia consumida no processo, revelando quão eficientemente o sistema transforma a energia consumida em informação efetivamente recuperada no receptor. Um sistema otimizado em relação à EE é capaz de transmitir mais informação por unidade de energia consumida, resultando em utilização mais racional e eficiente dos escassos recursos energéticos. Uma segunda questão acerca das metas é em relação à distribuição dos ganhos de capacidade/ QoS pela célula, i.e., quais usuários serão capazes de usufruir da maior capacidade e QoS. Em ambientes macrocelulares urbanos, a perda de percurso pode chegar a várias dezenas de decibéis em distâncias relativamente pequenas, além dos obstáculos naturais, como relevo, e artificiais, como prédios, o que limita ainda mais o desenvolvimento de sistemas energeticamente eficientes. Em abordagens tradicionais, tais problemas exigem a utilização de potências elevadas, em geral superiores à potência que os dispositivos podem utilizar, ou então requerem o aumento da densidade de estações rádio-base (BSs), o que geralmente resulta em custos inviáveis do ponto de vista dos operadores. Assim, busca-se em sistemas 4G emular o aumento da densidade de BSs através do conceito de redes heterogêneas, que são células com menor área de cobertura instaladas em pontos críticos de cobertura da célula original, como por exemplo a região de borda de célula, atendendo de maneira eficiente os usuários. No cenário de redes heterogêneas, um dos principais paradigmas é o conceito de redes cooperativas, no qual estações retransmissoras (RSs) reenviam o sinal recebido da estação fonte para estação destino, reduzindo a potência consumida com o canal móvel sem fio. Como utilizam conexão sem fio com a BS, as RSs podem ser instaladas em regiões com pouca infraestrutura sem a necessidade de grandes modificações, resultando em implantações bastante flexíveis. Assim, este trabalho de doutorado visa investigar estratégias de alocação de recursos baseadas no incremento da eficiência energética para sistemas celulares de quarta e quinta gerações utilizando o paradigma de redes cooperativas, determinando potencialidades e também itens que necessitam ser modificados, otimizados ou mesmo redefinidos, tendo em vista um aumento substancial da eficiência energética global da rede de comunicação sem fio. Busca-se durante o desenvolvimento do modelo de sistema capturar e quantificar as principais características de importantes sistemas celulares em uso atualmente, i.e., LTE-A e WiMAX, de modo que as decisões de design considerem os esforços de padronização, porém não se limitem a eles. Como a abordagem de alocação de recursos baseada em EE pode impactar nas métricas de desempenho do sistema, investiga-se também o compromisso entre as eficiências energética e espectral (SE), de modo que o aumento da EE não seja causado apenas pela degradação da SE e que seja possível obter maior EE para uma mesma SE e QoS. / Modern wireless communication systems, such as the fourth generation (4G) ones, have as main objectives to provide high capacity and quality of service (QoS) for the users. In order to provide such capacity and QoS gain, 4G systems use several advanced transmission techniques and higher bandwidth, combined with resource allocation algorithms that are able to efficiently exploit such techniques, as for example taking advantage of the diversity dimensions of the system. Generally, however, it is also necessary to increase the transmission power to achieve the desired capacity gain, which implies increased costs for service providers, shorter lifetime for the mobile devices and increasingly pronounced environmental impact. Since the expectation is that the number of users and data necessity will continue growing rapidly, it is evident the importance of analyzing the relation between capacity and power expended by the system. This relation can be seen through the energy efficiency (EE) metric, which is given by the ratio between the number of effectively received information bits and the energy consumed in the transmission process, revealing how efficiently the system transform consumed energy into effectively recovered information at the receiver. A system optimized regarding EE is able to transmit more information per unit of energy consumed, resulting in a more rational and efficient utilization of the scarce energetic resources. A second issue is relative to the distribution of the capacity/QoS gains over the whole cell, i.e, which users will be able to take advantage of the higher capacity and QoS. In urban macrocellular environments, the path-loss can reach several tens of decibels in relatively short distances, in addition to natural obstacles, such as land relief, or artificial, such as buildings, which further limits the development of energetically efficient systems. In traditional approaches, such problems require the use of high transmission power, generally greater than the power that the devices can use, or else require increased density of base-stations (BSs), which generally results in unviable costs from the operators point of view. Thus, in 4G systems it is sought to emulate the increase in the density of BSs through the concept of heterogeneous networks, which are cells with smaller coverage area installed in critical points of the original macrocell coverage, as for example the cell-edge area, serving efficiently the users. In the heterogeneous networks scenario, one of the main paradigms is the concept of cooperative networks, in which relay stations (RSs) retransmit the signal received from the source station to the destination station, reducing the power consumed with the mobile wireless channel. As the RSs use a wireless connection to the BS, they can be installed in places with poor infrastructure without requiring major modifications, resulting in very flexible deployments. Thus, this PhD work aims to investigate resource allocation strategies based on the improvement of the energy efficiency for fourth and fifty generation cellular systems using the cooperative networks paradigm, determining potentialities and also items that need to be modified, optimized or even redefined, aiming to a substantial increase in the overall energy efficiency of the wireless communication network. It is sought during the development of the system model to capture and quantify the main features of important cellular systems currently in use, i.e., LTE-A and WiMAX, so that the design decisions consider the standardization efforts, but do not be limited by them. Since the EE-based resource allocation approach can impact the performance metrics of the system, it will be investigated also the tradeoff between energy and spectral (SE) efficiencies, so that the increase in energy efficiency is not caused by degradation of the SE and also to be possible to obtain a higher EE for a same SE and QoS.

Sistemas modernos de comunicação móvel sem fio, como os de quarta geração (4G), têm como principais metas prover elevada capacidade e alta qualidade de serviço (QoS) para os usuários. Para prover tal aumento de capacidade e QoS, sistemas 4G empregam diversas técnicas avançadas de transmissão e maior largura de banda, combinados com algoritmos de alocação de recursos que possam explorar de maneira eficiente tais técnicas, como por exemplo aproveitando as dimensões de diversidade do sistema. Em geral, porém, é necessário também aumentar a potência de transmissão para se atingir o ganho de capacidade desejado, o que implica maior custo para os provedores de serviço, menor tempo de vida para os dispositivos móveis e impacto ambiental cada vez mais pronunciado. Dado que a expectativa é que o número de usuários e a necessidade de dados continuem crescendo rapidamente, torna-se evidente a importância de analisar a relação entre capacidade e potência dispendida pelo sistema. Essa relação pode ser vista através da métrica de eficiência energética (EE), que é dada pela razão entre o número de bits efetivamente recebidos e a energia consumida no processo, revelando quão eficientemente o sistema transforma a energia consumida em informação efetivamente recuperada no receptor. Um sistema otimizado em relação à EE é capaz de transmitir mais informação por unidade de energia consumida, resultando em utilização mais racional e eficiente dos escassos recursos energéticos. Uma segunda questão acerca das metas é em relação à distribuição dos ganhos de capacidade/ QoS pela célula, i.e., quais usuários serão capazes de usufruir da maior capacidade e QoS. Em ambientes macrocelulares urbanos, a perda de percurso pode chegar a várias dezenas de decibéis em distâncias relativamente pequenas, além dos obstáculos naturais, como relevo, e artificiais, como prédios, o que limita ainda mais o desenvolvimento de sistemas energeticamente eficientes. Em abordagens tradicionais, tais problemas exigem a utilização de potências elevadas, em geral superiores à potência que os dispositivos podem utilizar, ou então requerem o aumento da densidade de estações rádio-base (BSs), o que geralmente resulta em custos inviáveis do ponto de vista dos operadores. Assim, busca-se em sistemas 4G emular o aumento da densidade de BSs através do conceito de redes heterogêneas, que são células com menor área de cobertura instaladas em pontos críticos de cobertura da célula original, como por exemplo a região de borda de célula, atendendo de maneira eficiente os usuários. No cenário de redes heterogêneas, um dos principais paradigmas é o conceito de redes cooperativas, no qual estações retransmissoras (RSs) reenviam o sinal recebido da estação fonte para estação destino, reduzindo a potência consumida com o canal móvel sem fio. Como utilizam conexão sem fio com a BS, as RSs podem ser instaladas em regiões com pouca infraestrutura sem a necessidade de grandes modificações, resultando em implantações bastante flexíveis. Assim, este trabalho de doutorado visa investigar estratégias de alocação de recursos baseadas no incremento da eficiência energética para sistemas celulares de quarta e quinta gerações utilizando o paradigma de redes cooperativas, determinando potencialidades e também itens que necessitam ser modificados, otimizados ou mesmo redefinidos, tendo em vista um aumento substancial da eficiência energética global da rede de comunicação sem fio. Busca-se durante o desenvolvimento do modelo de sistema capturar e quantificar as principais características de importantes sistemas celulares em uso atualmente, i.e., LTE-A e WiMAX, de modo que as decisões de design considerem os esforços de padronização, porém não se limitem a eles. Como a abordagem de alocação de recursos baseada em EE pode impactar nas métricas de desempenho do sistema, investiga-se também o compromisso entre as eficiências energética e espectral (SE), de modo que o aumento da EE não seja causado apenas pela degradação da SE e que seja possível obter maior EE para uma mesma SE e QoS. / Modern wireless communication systems, such as the fourth generation (4G) ones, have as main objectives to provide high capacity and quality of service (QoS) for the users. In order to provide such capacity and QoS gain, 4G systems use several advanced transmission techniques and higher bandwidth, combined with resource allocation algorithms that are able to efficiently exploit such techniques, as for example taking advantage of the diversity dimensions of the system. Generally, however, it is also necessary to increase the transmission power to achieve the desired capacity gain, which implies increased costs for service providers, shorter lifetime for the mobile devices and increasingly pronounced environmental impact. Since the expectation is that the number of users and data necessity will continue growing rapidly, it is evident the importance of analyzing the relation between capacity and power expended by the system. This relation can be seen through the energy efficiency (EE) metric, which is given by the ratio between the number of effectively received information bits and the energy consumed in the transmission process, revealing how efficiently the system transform consumed energy into effectively recovered information at the receiver. A system optimized regarding EE is able to transmit more information per unit of energy consumed, resulting in a more rational and efficient utilization of the scarce energetic resources. A second issue is relative to the distribution of the capacity/QoS gains over the whole cell, i.e, which users will be able to take advantage of the higher capacity and QoS. In urban macrocellular environments, the path-loss can reach several tens of decibels in relatively short distances, in addition to natural obstacles, such as land relief, or artificial, such as buildings, which further limits the development of energetically efficient systems. In traditional approaches, such problems require the use of high transmission power, generally greater than the power that the devices can use, or else require increased density of base-stations (BSs), which generally results in unviable costs from the operators point of view. Thus, in 4G systems it is sought to emulate the increase in the density of BSs through the concept of heterogeneous networks, which are cells with smaller coverage area installed in critical points of the original macrocell coverage, as for example the cell-edge area, serving efficiently the users. In the heterogeneous networks scenario, one of the main paradigms is the concept of cooperative networks, in which relay stations (RSs) retransmit the signal received from the source station to the destination station, reducing the power consumed with the mobile wireless channel. As the RSs use a wireless connection to the BS, they can be installed in places with poor infrastructure without requiring major modifications, resulting in very flexible deployments. Thus, this PhD work aims to investigate resource allocation strategies based on the improvement of the energy efficiency for fourth and fifty generation cellular systems using the cooperative networks paradigm, determining potentialities and also items that need to be modified, optimized or even redefined, aiming to a substantial increase in the overall energy efficiency of the wireless communication network. It is sought during the development of the system model to capture and quantify the main features of important cellular systems currently in use, i.e., LTE-A and WiMAX, so that the design decisions consider the standardization efforts, but do not be limited by them. Since the EE-based resource allocation approach can impact the performance metrics of the system, it will be investigated also the tradeoff between energy and spectral (SE) efficiencies, so that the increase in energy efficiency is not caused by degradation of the SE and also to be possible to obtain a higher EE for a same SE and QoS.

It is well known that communication systems employing multiple transmit and multiple receive antennas provide high data rates along with increased reliability. It has been shown that coding across both spatial and temporal domains together, called Space-Time Coding (STC), achieves, a diversity order equal to the product of the number of transmit and receive antennas. Space-Time Block Codes (STBC) achieving the maximum diversity is called full-diversity STBCs. An STBC is called information-lossless, if the structure of it is such that the maximum mutual information of the resulting equivalent channel is equal to the capacity of the channel. This thesis deals with high-rate and information-lossless STBCs obtained from certain matrix algebras called Crossed-Product Algebras. First we give constructions of high-rate STBCs using both commutative and non-commutative matrix algebras obtained from appropriate representations of extensions of the field of rational numbers. In the case of commutative algebras, we restrict ourselves to fields and call the STBCs obtained from them as STBCs from field extensions. In the case of non-commutative algebras, we consider only the class of crossed-product algebras. For the case of field extensions, we first construct high-rate; full-diversity STBCs for arbitrary number of transmit antennas, over arbitrary apriori specified signal sets. Then we obtain a closed form expression for the coding gain of these STBCs and give a tight lower bound on the coding gain of some of these STBCs. This lower bound in certain cases indicates that some of the STBCs from field extensions are optimal m the sense of coding gain. We then show that the STBCs from field extensions are information-lossy. However, we also show that the finite-signal-set capacity of the STBCs from field extensions can be improved by increasing the symbol rate of the STBCs. The simulation results presented show that our high-rate STBCs perform better than the rate-1 STBCs in terms of the bit error rate performance. Then we proceed to present a construction of high-rate STBCs from crossed-product algebras. After giving a sufficient condition on the crossed-product algebras under which the resulting STBCs are information-lossless, we identify few classes of crossed-product algebras that satisfy this sufficient condition and also some classes of crossed-product algebras which are division algebras which lead to full-diversity STBCs. We present simulation results to show that the STBCs from crossed-product algebras perform better than the well-known codes m terms of the bit error rate. Finally, we introduce the notion of asymptotic-information-lossless (AILL) designs and give a necessary and sufficient condition under which a linear design is an AILL design. Analogous to the condition that a design has to be a full-rank design to achieve the point corresponding to the maximum diversity of the optimal diversity-multiplexing tradeoff, we show that a design has to be AILL to achieve the point corresponding to the maximum multiplexing gain of the optimal diversity-multiplexing tradeoff. Using the notion of AILL designs, we give a lower bound on the diversity-multiplexing tradeoff achieved by the STBCs from both field extensions and division algebras. The lower bound for STBCs obtained from division algebras indicates that they achieve the two extreme points, 1 e, zero multiplexing gain and zero diversity gain, of the optimal diversity-multiplexing tradeoff. Also, we show by simulation results that STBCs from division algebras achieves all the points on the optimal diversity-multiplexing tradeoff for n transmit and n receive antennas, where n = 2, 3, 4.

Cooperative relay communication is a promising means of wireless communication in which cooperation is used to create a virtual transmit array between the source and the destination, thereby providing spatial diversity for combating the fading channel. In this thesis we develop cooperative communication protocols namely the orthogonal amplify-and-forward (OAF), non-orthogonal and orthogonal selection decode-and-forward (NSDF and OSDF) protocols. The diversity-multiplexing gain tradeoff (DMT) of the three protocols is determined and DMT-optimal distributed space-time code constructions are provided. The code construction is based on Cyclic Division Algebras. The codes constructed are sphere decodable and in some instances incur minimum possible delay. Included in our results is the perhaps surprising finding that the OAF and NAF protocols have identical DMT when the time durations of the broadcast and cooperative phases are optimally chosen to suit the respective protocol. Two variants of the NSDF protocol are considered: fixed-NSDF and variable-NSDF protocol. In the variable-NSDF protocol, the fraction of time occupied by the broadcast phase is allowed to vary with multiplexing gain. In the two-relay case, the variable-NSDF protocol is shown to improve on the DMT of the best previously-known static protocol for higher values of multiplexing gain. Our results also establish that the fixed-NSDF protocol has a better DMT than the NAF protocol for any number of relays.

This thesis consists of two parts addressing two different problems in fading channels. The first part deals with asynchronous cooperative relay communication. The assumption of nodes in a cooperative communication relay network operating in synchronous fashion is often unrealistic. In this work we consider two different models of asynchronous operation in cooperative-diversity networks experiencing slow fading and examine the corresponding Diversity-Multiplexing Tradeoffs (DMT). For both models, we propose protocols and distributed space-time codes that asymptotically achieve the transmit diversity bound on DMT for all multiplexing gains and for number of relays N ≥ 2. The distributed space-time codes for all the protocols considered are based on Cyclic Division Algebras (CDA). The second part of the work addresses the DMT analysis of diversity embedded codes for MIMO channels. Diversity embedded codes are high rate codes that are designed so that they have a high diversity code embedded within them. This allows a form of opportunistic communication depending on the channel conditions. The high diversity code ensures that at least a part of the information is received reliably, whereas the embedded high rate code allows additional information to be transferred if the channel is good. This can be thought of coding the data into two streams: high priority and low priority streams so that the high priority stream gets a better reliability than the lower priority stream. We show that superposition based diversity embedded codes in conjunction with naive single stream decoding is sub-optimal in terms of the DM tradeoff. We then construct explicit diversity embedded codes by the superposition of approximately universal space-time codes from CDAs. The relationship between broadcast channels and the diversity embedded setting is then utilized to provide some achievable Diversity Gain Region (DGR) for MIMO broadcast Channels.

Recent breakthrough studies by Gali and Gertler (1999), Sbordone (2002) and Roberts (2001) argue that the New Keynesian Phillips curve (based on Calvo pricing model) is empirically valid concept and they conclude that the real marginal costs are preferred driving force to output gap in inflation dynamics for open economies. Neiss and Nelson (2002) and Gali, Gertler and Salido (2001), in turn, contradict that to date, there has been only little empirical evidence to support this statement. Neiss and Nelson (2002) add that "once output gap is defined consistently with economic theory, the gap-based New Keynesian Phillips curve has a fit with data which is at least as good as the real marginal costs-based one". For this purpose, my study investigates relationship between output gap and inflation described in the hybrid New Keynesian Phillips curve. Study estimates key coefficients of the hybrid gap-based New Keynesian Phillips curve, with both forward- and backward-looking inflation components, in the Czech Republic for periods 2000Q1 - 2012Q4 using Kalman filtration. My findings suggest that (i) output gap has a significant impact on Czech inflation dynamics (ii) share of forward-looking agents predominates to backward-looking agents in the Czech Republic and (iii) Czech inflation seems to be significantly driven by change in import prices.

Systems with multiple transmitting and receiving antennas in large-scale (LS-MIMO - large-scale multipleinput multiple-output) enable high spectral and energy efficiency gains, which results in an increase in the data transmission rate in the same band, without increasing the transmitted power per user. In addition, with the increase of the number of antennas in the base station (BS) it is possible to attend to a larger number of users per cell, in the same occupied band. Furthermore, it has been found in the literature that the reported advantages of LS-MIMO systems can be obtained with a large number of antennas on at least one side of the communication, usually in BS due to physical restriction in user equipments. However, such advantages have their cost: the use of a large number of antennas also difficult tasks involving signal processing, such as estimation of channel coefficients, precoding and signal detection. It is at this juncture that this Doctoral Thesis is developed, in which the computational complexity of performing efficient detection methods in LSMIMO communication systems is explored through the analysis of algorithms and optimization techniques in the solution of specific problems and still open. More precisely, this Thesis discusses and proposes promising detection techniques in LS-MIMO systems, aiming to improve performance metrics - in terms of error rate - and computational complexity - in terms of the number of mathematical operations. Initially, the problem is introduced through a conventional MIMO system model, where channels with imperfect estimates and correlation between transmitter (Tx) and receiver (Rx) antennas are considered. Preprocessing techniques based on lattice reduction (LR) are applied in linear detectors, in addition to the sphere decoder (SD), which proposes a lookup table procedure in order to provide a reduction in computational complexity. It is shown that the LR method in the pre-detection results in a significant performance gain in both the condition of uncorrelated and correlated channels, and in the latter scenario the improvement is even more remarkable due to the diversity gain provided. On the other hand, the complexity involved in the application of LR in high correlation scenarios becomes preponderant in linear detectors. In the LR-SD using the lookup table procedure, the optimum gain was reached in all scenarios, as expected, and resulted in a lower complexity than maximum likelihood (ML) detector, even with maximum correlation between antennas, which represents the most complex scenario for the LR technique. Next, the message passing (MP) detector is investigated, which makes use of Markov random fields (MRF) and factor graph (FG) graphical models. Moreover, it is shown in the literature that the message damping (MD) method applied to the MRF detector brings relevant performance gain without increasing computational complexity. On the other hand, the DF value is specified for only a restricted range of scenarios. Numerical results are extensively generated, in order to obtain a range of analysis of the MRF with MD, which resulted in the proposition of an optimal value for the DF, based on numerical curve fitting. Finally, in the face of the MGS detector, two approaches are proposed to reduce the negative impact caused by the random solution when high modulation orders are employed. The first is based on an average between multiple samples, called aMGS (averaged MGS). The second approach deploys a direct restriction on the range of the random solution, limiting in d the neighborhood of symbols that can be sorted, being called d-sMGS. Numerical simulation results show that both approaches result in gain of convergence in relation to MGS, especially: in regions of high system loading, d-sMGS detection demonstrated significant gain in both performance and complexity compared to aMGS and MGS; although in low-medium loading, the aMGS strategy showed less complexity, with performance marginally similar to the others. Furthermore, it is concluded that increasing the dimensions of the system favors a smaller restriction in the neighborhood. / Sistemas com múltiplas antenas transmissoras e múltiplas antenas receptoras em larga escala (LS-MIMO - large-scale multiple-input multiple-output) possibilitam altos ganhos em eficiência espectral e energética, o que resulta em aumento da taxa de transmissão de dados numa mesma banda ocupada, sem acréscimo da potência transmitida por usuário. Além disso, com o aumento do número de antenas na estação rádio-base (BS- base station) possibilita-se o atendimento de maior número de usuários por célula, em uma mesma banda ocupada. Ademais, comprovou-se na literatura que as vantagens relatadas dos sistemas LS-MIMO podem ser obtidas com um grande número de antenas em, pelo menos, um dos lados da comunicação, geralmente na BS devido à restrição física nos dispositivos móveis. Contudo, tais vantagens têm seu custo: a utilização de um grande número de antenas também dificulta tarefas que envolvem processamento de sinais, como estimação dos coeficientes de canal, precodificação e detecção de sinais. É nessa conjuntura em que se desenvolve esta Tese de Doutorado, na qual se explora o compromisso desempenho versus complexidade computacional de métodos eficientes de detecção em sistemas de comunicações LS-MIMO através da análise de algoritmos e técnicas de otimização na solução de problemas específicos e ainda em aberto. Mais precisamente, a presente Tese discute e propõe técnicas promissoras de detecção em sistemas LS-MIMO, visando a melhoria de métricas de desempenho - em termos de taxa de erro - e complexidade computacional - em termos de quantidade de operações matemáticas. Inicialmente, o problema é introduzido através de um modelo de sistema MIMO convencional, em que são considerados canais com estimativas imperfeitas e com correlação entre as antenas transmissoras (Tx) e entre as receptoras (Rx). Aplicam-se técnicas de pré-processamanto baseadas na redução treliça (LR - lattice reduction) em detectores lineares, além do detector esférico (SD - sphere decoder), o qual é proposto um procedimento de tabela de pesquisa a fim de prover redução na complexidade computacional. Mostra-se que o método LR na pré-detecção resulta em ganho de desempenho significante tanto na condição de canais descorrelacionados quanto fortemente correlacionados, sendo que, neste último cenário a melhoria é ainda mais notável, devido ao ganho de diversidade proporcionado. Por outro lado, a complexidade envolvida na aplicação da LR em alta correlação torna-se preponderante em detectores lineares. No LR-SD utilizando o procedimento de tabela de pesquisa, o ganho ótimo foi alcançado em todos os cenários, como esperado, e resultou em complexidade inferior ao detector de máxima verossimilhança (ML - maximum likelihood), mesmo com máxima correlação entre antenas, a qual representa o cenário de maior complexidade a técnica LR. Em seguida, o detector por troca de mensagens (MP - message passing) é investigado, o qual faz uso de modelos grafos do tipo MRF (Markov random fields) e FG (factor graph). Além disso, mostra-se na literatura que o método de amortecimento de mensagens (MD - message damping) aplicado ao detector MRF traz relevante ganho de desempenho sem aumento na complexidade computacional. Por outro lado, o valor do DF (damping factor) é especificado para somente uma variedade restrita de cenários. Resultados numéricos são extensivamente gerados, de forma a dispor de uma gama de análises de comportamento do MRF com MD, resultando na proposição de um valor ótimo para o DF, baseando-se em ajuste de curva numérico. Finalmente, em face ao detector MGS (mixed Gibbs sampling), são propostas duas abordagens visando a redução do impacto negativo causado pela solução aleatória quando altas ordens de modulação são empregadas. A primeira é baseada em uma média entre múltiplas amostras, chamada aMGS (averaged MGS). A segunda abordagem realiza uma restrição direta no alcance da solução aleatória, limitando em até d a vizinhança de símbolos que podem ser sorteados, sendo chamada de d-sMGS (d-simplificado MGS). Resultados de simulação numérica demonstram que ambas abordagens resultam em ganho de convergência em relação ao MGS, destacando-se: em regiões de alto carregamento, a detecção d-sMGS demonstrou ganho expressivo tanto em desempenho quanto em complexidade se comparada à aMGS e MGS; já em baixo-médio carregamentos, a estratégia aMGS demonstrou menor complexidade, com desempenho marginalmente semelhante às demais. Além disso, conclui-se que o aumento do número de dimensões do sistema favorece uma menor restrição na vizinhança.

Proportional, integral and derivative (PID) controller tuning guidelines in process industry have been in place for over six decades. Nevertheless despite their long design history PID tuning has remained an ‘art’ and no single comprehensive solution yet exists. In this study various considerations, with new and different perspectives, have been taken into account in PID tuning design. This study explores the issue of PID tuning from a practical point of view with particular focus on robust design in the presence of typical problems in process industry: process changes, valve stiction effects and unmeasured disturbances. The IMC tuning rule is recommended for setpoint tracking, while in the case of regulation, a newly proposed tuning rule, based on a combination of IMC and Ziegler-Nichols method, is demonstrated to give satisfactory results. The results were evaluated by simulation and were also validated on a computer-interfaced pilot scale continuous stirred tank heater (CSTH) process. / Chemical Engineering

Integrated systems with billions of transistors on a single chip are a now reality. These systems include multi-core microprocessors and are built today using deca-nanometer devices organized into synchronous digital circuits. The movement of data within such systems is regulated by a set of predictable timing signals, called clocks, which must be distributed to a large number of sequential elements. Collectively, these clocks have a significant impact on the frequency of operation and, consequently, on the performance of the systems. The clocks are also responsible for a large fraction of the power consumed by these systems. The objective of this dissertation is to better understand clock distribution in order to identify opportunities and strategies for improvement by analyzing the conditions under which the optimal tradeoff between power and performance can be achieved, by modeling the constraints associated with local and global clocking, by evaluating the impact of noise, and by investigating promising new design strategies for future integrated systems.