Orientador: Renato da Rocha Lopes / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-18T15:38:37Z (GMT). No. of bitstreams: 1 Simoes_GlaucoCesarCrystalPereira_M.pdf: 1336036 bytes, checksum: 7f787abec0f0f88f41c09ef5dc04d775 (MD5) Previous issue date: 2011 / Resumo: Sistemas de comunicação sem fio com múltiplas antenas atingem altas taxas de transmissão de dados e boa robustez ao desvanecimento do canal de comunicação quando os sinais que trafegam pelo sistema são processados conjuntamente em sua transmissão e/ou em sua recepção. Em geral, as técnicas de detecção de sinais assumem o conhecimento perfeito do canal de comunicações, tanto no transmissor, quanto no receptor do sistema, uma hipótese que nem sempre é válida. Neste sentido, é importante analisar o desempenho do sistema frente a erros de estimação do canal de comunicações. Neste trabalho, esta análise é feita através da comparação do cálculo da probabilidade de erro de símbolos com as taxas de erro de símbolos obtidas através de simulação computacional para o detector zero-forcing, assumindo a utilização dos critérios de detecção linear e através da aplicação da técnica de cancelamento sucessivo de interferências / Abstract: Multiple antenna wireless communication systems achieve high data transmission rates and good robustness to channel fading when signals traveling through the system are jointly processed in their transmitters and/ or receivers. In general, signal detection techniques assume perfect knowledge of the channel state information, in both transmitter and receiver, a hypothesis which is not always valid. In this sense, it is important to analyze is done by the comparison between the calculus of the probability of symbol error and the symbol error rate obtained by computer simulation for the zero-forcing detector, assuming the use of linear criteria detection and by applying the technique of successive interference cancellation / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

Opportunistic selection algorithms have grown in importance as next generation wireless systems strive towards higher data rates and spectral efficiencies. For example, in orthogonal frequency division multiple access(OFDMA), the system bandwidth is divided into many sub channels. For each sub channel, the user with the highest channel gain is opportunistically assigned to it. .Likewise, in a multi-source, multi-destination (MSD) cooperative relay system, a relay node must be assigned for every source-destination (SD) pair. The assignment decisions are based on local channel knowledge and must be fast so as to maximize the time available for data transmission. We develop novel multiple access based splitting-based selection algorithms for OFDMA and MSD systems. These systems are unique in that the same user and relay can be the most suitable one for multiple sub channels and multiple SD pairs, respectively. For OFDMA systems, we propose an algorithm called Split Select that assigns for every sub channel the user with the highest channel gain over it. For MSD systems, we propose a contention-based en masse assignment (CBEA) algorithm that assigns to each SD pair a relay that is capable of aiding it. Both Split Select and CBEA are fast and scale well with the number of nodes. For example, Split Select requires just 2.2 slots, on average, to assign a sub channel to its best user even when there are an asymptotically large number of contending users. Likewise, CBEA often takes far less than one slot, on average, to assign a relay to each SD pair.

Wireless resources are scarce, shared and time-varying making resource allocation mechanisms, e.g., scheduling, a key and challenging element of wireless system design. In designing good schedulers, we consider three types of performance metrics: system capacity, quality of service (QoS) seen by users, and the energy expenditures (battery lifetimes) incurred by mobile terminals. In this dissertation we investigate the impact of scheduling policies on these performance metrics, their interactions, and/or tradeoffs, and we specifically focus on flow-level performance under stochastic traffic loads. In the first part of the dissertation we evaluate interactions among flow-level performance metrics when integrating QoS and best effort flows in a wireless system using opportunistic scheduling. We introduce a simple flow-level model capturing the salient features of bandwidth sharing for an opportunistic scheduler which ensures a mean throughput to each QoS stream on every time slot. We show that the integration of QoS and best effort flows results in a loss of opportunism, which in turn results in a reduction of the stability region, degradation in system capacity, and increased file transfer delay. In the second part of the dissertation we study several ways in which mobile terminals can backoff on their uplink transmit power (thus slow down their transmissions) in order to extend battery lifetimes. This is particularly effective when a wireless system is underloaded, so the degradation in the users' perceived performance can be negligible. The challenge, however, is developing a mechanism that achieves a good tradeoff among transmit power, idling/circuit power, and the performance customers will see. We consider systems with flow-level dynamics supporting either real-time or best effort (e.g., file transfers) sessions. We show that significant energy savings can be achieved by leveraging dynamic spare capacity. We then extend our study to the case where mobile terminals have multiple transmit antennas. In the third part of the dissertation we develop a framework for user association in infrastructure-based wireless networks, specifically focused on adaptively balancing flow loads given spatially inhomogeneous traffic distributions. Our work encompasses several possible user association objective functions resulting in rate-optimal, throughput-optimal, delay-optimal, and load-equalizing policy, which we collectively denote [alpha]-optimal user association. We prove that the optimal load vector that minimizes this function is the fixed point of a certain mapping. Based on this mapping we propose an iterative distributed user association policy and prove that it converges to the globally optimal decision in steady state. In addition we address admission control policies for the case where the system cannot be stabilized. / text

With the growth of wireless technologies in sectors like the military, aviation, etc, there is a need to determine the authenticity of a genuine user. Today's conventional authentication mechanisms are based on three factors: knowledge, possession and biometrics. These factors are prone to theft, hardware failure, expensive, etc. Consequently, there is a need of a stronger solution. One such solution is Location Based Authentication that considers the location information of a user. The location information is time based and thus hard to steal. However, accuracy of the GPS, signal strength inside the building, etc, affects its potential. Consequently, there is a need to address alternatives. One such alternative is to implement a puzzle-based authentication scheme based on the location information. In the proposed scheme, the server asks dynamic location-based questions and the client answers them based on the proposed route of travel. This scheme strengthens the current authentication mechanisms.

The main objective of this research is to improve the energy efficiency of low throughput wireless biomedical systems by employing digital design techniques. The power consumed in conventional wireless EEG (biomedical) systems is dominated by digital microcontroller and the radio frequency (RF) transceiver. To reduce the power associated with the digital processor, data compression can reduce the volume of data transmitted. An adaptive data compression algorithm has been proposed to ensure accurate representations of critical epileptic signals, while also preserving the overall power. Further advances in power reduction are also presented by designing a custom baseband processor for data compression. A functional system has been hardware verified and ASIC optimized to reduce the power by over 9X compared to existing methods. The optimized processor can operate at 32MHz with a near threshold supply of 0.5V in a conventional 45nm technology. While attempting to reach high frequencies in the near threshold regime, the probability of timing violations can reduce the robustness of the system. To further optimize the implementation, a low voltage clock tree design has been investigated to improve the reliability of the digital processor. By implementing the proposed clock tree design methodology, the digital processor can improve its robustness (by reducing the probability of timing violations) while reducing the overall power by more than 5 percent. Future work suggests examining new architectures for low-throughput processing and investigating the proposed systems' potential for a multi-channel EEG implementation.

Orientador: Michel Daoud Yacoub / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-15T14:34:24Z (GMT). No. of bitstreams: 1 Dias_UgoSilva_D.pdf: 7207559 bytes, checksum: 799e62195e2d2cf1cf1a42599b611bf6 (MD5) Previous issue date: 2010 / Resumo: Esta tese propõe, investiga e valida estatísticas de primeira e segunda ordens para canais com desvanecimento em ambientes sem fio. A caracterização estatística contempla tanto a obtenção de modelos teóricos quanto investigações práticas através de campanhas de medições de campo. Os modelos probabilísticos analisados aqui, chamados ?-µ e a-µ, foram recentemente propostos com o intuito de prover uma análise mais realista do canal rádio-móvel. Por apresentarem um grau de liberdade a mais do que as distribuições tradicionais, uma maior flexibilidade é alcançada. Mais especificamente, as contribuições desta tese são: a obtenção da distribuição conjunta da envoltória e da fase para canais em desvanecimento ?-µ e a validação do seu modelo de fase. Além disso, e sem menos importância, a distribuição a-µ é validada amplamente. Suas funções de distribuição cumulativa, correlação cruzada, autocorrelação e espectro de potência da envoltória, estas últimas encontradas em formulações fechadas, bem como a taxa de cruzamento de nível, são investigadas na prática através do uso de um sistema de medição de campo construído especialmente para este fim. Comparações entre o modelo de canal a-µ e os modelos tradicionais da literatura são realizadas e um excelente ajuste entre os dados teóricos e experimentais é encontrado / Abstract: This thesis proposes, investigates and validates first and second order statistics of fading channels in wireless environments. The statistical characterization includes both theoretical models and practical investigations through field measurements. The investigated channel models, namely ?-µ and a-µ, have recently been proposed in order to provide a more realistic analysis of the propagated signal. Because these fading models have one more degree of freedom than the traditional distributions, a greater flexibility is achieved. More specifically, the contributions of this thesis are: the ?-µ phase-envelope joint distribution derivation and its phase model validation. Furthermore, the distribution a-µ is fully validated. Its cumulative distribution, cross-correlation, autocorrelation and power spectrum functions of the envelope, these latter obtained in closed-form expressions, and the level crossing rate, are investigated in practice by using a field measurement system, specifically built for this purpose. Comparisons between the a-µ channel model and the traditional distributions are performed and excellent fits between the theoretical and experimental data are found / Doutorado / Telecomunicações e Telemática / Doutor em Engenharia Elétrica

Abstract The contemporary information age is equipped with rich and affordable telecommunication services. In the future, people have even more flexibility when true wireless Internet and real-time multimedia are provided seamlessly over heterogeneous wireless networks. Optimally combining the capacity and services of the current and emerging networks requires a holistic view of mobility, resource and service management. This thesis contributes to the research and development of these hybrid systems with three main contributions. Firstly, a system architecture for vertical handoff in location-aware heterogeneous wireless networks is proposed. The proposed architecture enables the mobile node to prepare for approaching vertical handoffs and wake-up a hotspot interface. The needed communication procedures are discussed, and inter-related issues of mobility and geolocation information are considered in proportion to usability, advantages and limitations. Secondly, a framework for the analysis of vertical handoff algorithm sensitivity to various mobility parameters including velocity, handoff delay and dwell time is introduced. Handoff smoothing with a dwell-timer is analyzed as one potential scheme for optimizing vertical handoff locally. It is compared to a power based algorithm to find out its sensitivity to the changes in effective data rates, velocity of the terminal and the amount of handoff delay. The analysis focuses on the transition region, having case studies on both moving-in and moving-out scenarios. An optimal value for dwell-timer is found through simulations, showing a performance gain over power based algorithm as a function of mean throughput. The analysis is extended also to a multiple network scenario. Thirdly, experimental results on the behaviour of protocols used in wireless IP networks are presented. Prototype systems demonstrate results of using Mobile IP with a fuzzy logic algorithm for vertical handoff in a heterogeneous network environment and the role of IPv6 when using a voice application in a wireless LAN environment. Latest contributions include developing plug-and-play middleware functionalities for Symbian mobile devices, extending the use of the earlier results to state-of-the-art mobile devices.

Diplomová práca sa zaoberá štúdiom koexistencie, ktorá môže nastať medzi bezdrôtovými komunikačnými systémami LoRa a Wi-Fi v bezlicenčnom ISM pásme 2,4 GHz. V teoretickej časti práce sú stručne popísané fyzické vrstvy obidvoch systémov. Následne sú definované spoločné frekvenčné pásma a koexistenčné scenáre, ktoré môžu vzniknúť medzi uvažovanými systémami v spoločnom rádiofrekvenčnom (RF) pásme. V experimentálnej časti práce je prezentované laboratórne meracie pracovisko, ktoré bolo navrhnuté na meranie rôznych koexistenčných scenárov medzi technológiou LoRa a Wi-Fi. Funkčnosť navrhnutej koncepcie je overená experimentálnym meraním. Výsledky meraní sú detailne komentované a prezentované. Je navrhnutá laboratórna úloha a vzorový protokol pre vzdelávacie účely v Laboratóriu Mobilných a Bezdrôtových komunikácií.

Motivated by the increasing demand for higher data rates, coverage, and spectral efficiency, current and next generation wireless systems adapt transmission parameters and even who is being transmitted to, based on the instantaneous channel states. For example, frequency-domain scheduling(FDS) is an instance of adaptation in orthogonal frequency division multiple access(OFDMA) systems in which the base station opportunistically assigns different subcarriers to their most appropriate user. Likewise ,transmit antenna selection(AS) is another form of adaptation in which the transmitter adapts which subset of antennas it transmits with. Cognitive radio(CR), which is a next generation technology, itself is a form of adaptation in which secondary users(SUs) adapt their transmissions to avoid interfering with the licensed primary users(PUs), who own the spectrum. However, adaptation requires channel state information(CSI), which might not be available apriori at the node or nodes that are adapting. Further, the CSI might not be perfect due to noise or feedback delays. This can result in suboptimal adaptation in OFDMA systems or excessive interference at the PUs due to transmissions by the SUs in CR. In this thesis, we focus on adaptation techniques in current and next generation wireless systems and evaluate the impact of CSI –both perfect and imperfect –on it. We first develop a novel model and analysis for characterizing the performance of AS in frequency-selective OFDMA systems. Our model is unique and comprehensive in that it incorporates key LTE features such as imperfect channel estimation based on dense, narrow band demodulation reference signal and coarse, broad band sounding reference signal. It incorporates the frequency-domain scheduler, the hardware constraint that the same antenna must be used to transmit over all the subcarriers that are allocated to a user, and the scheduling constraint that the allocated subcarriers must all be contiguous. Our results show the effectiveness of combined AS and FDS in frequency-selective OFDMA systems even at lower sounding reference signal powers. We then investigate power adaptation in underlay CR, in which the SU can transmit even when the primary is on but under stringent interference constraints. The nature of the interference constraint fundamentally decides how the SU adapts its transmit power. To this end, assuming perfect CSI, we propose optimal transmit power adaptation policies that minimize the symbol error probability of an SU when they are subject to different interference and transmit power constraints. We then study the robustness of these optimal policies to imperfections in CSI. An interesting observation that comes out of our study is that imperfect CSI can not only increase the interference at the PU but can also decrease it, and this depends on the choice of the system parameters, interference, and transmit power constraints. The regimes in which these occur are characterized.

Este trabalho apresenta o desenvolvimento de um método para garantir a proteção dos dados contra falhas de comunicação, em redes de sensores inteligentes sem fios. A rede sem fios foi empregada nos ensaios de modelos físicos reduzidos em centrífuga para estudar o comportamento das âncoras \"tartaruga\", utilizadas nas linhas de ancoragem de sistemas oceânicos para produção de óleo e gás em águas profundas. O emprego da tecnologia de redes de sensores sem fios tem aumentado em muitas áreas da sociedade, principalmente na engenharia. Dessa forma, muitos problemas estão sendo enfrentados e estudados pelos pesquisadores. Sobretudo no que diz respeito à interferência ambiental, relação de potência e alcance, integridade da informação, miniaturização dos dispositivos, autonomia de energia, limitação de algoritmos e vida útil. A inserção da tecnologia de redes de sensores inteligentes sem fios nos ensaios de modelos físicos reduzidos em centrífuga, além de ser inédita no Brasil, permitirá avanços significativos na determinação de parâmetros que, atualmente, são de difícil obtenção com tecnologias convencionais como os sistemas de aquisição de dados e controle que utilizam cabos e fios. Muitas vezes depara-se com a inconveniência do peso dos cabos e dificuldades de instalação dos dispositivos nos modelos, pela sua pouca portabilidade. / This work present a method development to guarantee of the integrity data in the wireless smart sensor networks, employed in centrifuge physical modeling tests of anchors used as fixing devices of deep water production oil and gas systems. The use of wireless smart sensor networks technology has been increasing in many engineering areas. In spite of this evidence, lots of problems are being faced and studied by the researchers, environmental interference, power and reach relations, integrity of the information, miniaturization of the devices, energy autonomy, algorithms and useful life. The use of the wireless smart sensor networks technology in the reduced physical models test in centrifuge, by first time in Brazil, will allow significant advances in the parameters determination. The conventional instrumentation presents inconvenience of the weight cables and difficulties of the devices in the models by limited portability.