This thesis examines the high peak-to-average-power ratio (PAPR) problem of OFDM and other spectrally-efficient multicarrier modulation schemes, specifically their stringent requirements for highly linear, power-inefficient amplification. The thesis then presents a most intriguing answer to the PAPR-problem in the form of a constant-envelope OFDM (CE-OFDM) waveform, a waveform which employs phase modulation to transform the high-PAPR OFDM signal into a constant envelope signal, like FSK or GMSK, which can be amplified with non-linear power amplifiers at near saturation levels of efficiency. A brief analytical description of CE-OFDM and its suboptimal receiver architecture is provided in order to define and analyze the key parameters of the waveform and their performance impacts. The primary contribution of this thesis is a highly tunable software-defined radio (SDR) implementation of the waveform which enables rapid-prototyping and testing of CE-OFDM systems. The digital baseband processing of the waveform is executed on a general purpose processor (GPP) in the Linux Ubuntu 14.04 operating system, and programmed using the GNU Radio SDR software framework with a mixture of Python and C++ routines. A detailed description of the software implementation is provided, and baseband simulations of the SDR CE-OFDM receiver in additive white Gaussian noise (AWGN) validate the performance of the implemented signal processing. A fully-functional CE-OFDM radio system is proposed in which GPPs executing the software defined transmitter and receiver routines are interfaced with Ettus Universal Software Radio Peripheral (USRP) transceiver front ends. A software testbench is created to enable rapid configuration and testing of the CE-OFDM waveform over all permutations of its parameters, over both simulated and physical RF channels, to draw deeper insights into the characteristics of the waveform and the necessary design considerations and improvements for further development and deployment of CE-OFDM systems. / Master of Science

Analyses and designs of a peak-power tracking system using microprocessor control are performed. Large-signal stability of the system for various modes of operation is analyzed to predict system dynamics. The stability analysis is supported mainly by qualitative graphical representations of different component blocks of the system. Small-signal stability analysis around the equilibrium points is done to assure proper performance and operation of this particular peak-power tracking system. Specific design details and procedures are discussed, and predictions from the analyses are verified through hardware. / Master of Science

Yes / There is no single, universally accepted method of measuring isometric neck strength to inform exercise prescription and injury risk prediction. This study aimed to establish the inter- and intra-rater reliability of a commercially available fixed frame dynamometer in measuring peak isometric neck strength. A convenience sample of male (n = 16) and female (n = 20) university students performed maximal isometric contractions for flexion (Flex), extension (Ext), left- (LSF) and right-side flexion (RSF) in a quadruped position over three sessions. The intra-rater reliability results were good-to-excellent for both males (ICC = 0.83–0.90) and females (ICC = 0.86–0.94) and acceptable (CV < 15%) across all directions for both males and females. The inter-rater reliability results were excellent (ICC = 0.96–0.97) and acceptable (CV < 11.1%) across all directions. Findings demonstrated a significant effect for sex (p ≤ 0.05): males were stronger in all four directions, and a significant effect for direction (p ≤ 0.05): Ext tested stronger (193 N) than Flex (176 N), LSF (130 N) and RSF (125 N). The findings show that the VALD fixed frame dynamometer can reliably assess isometric neck strength and can provides reference values for healthy males and females.

The critical conduction mode (CRM) power factor correction converters (PFC) are widely used in industry for low power offline switching mode power supplies. For the CRM PFC, the main advantage is to reduce turn-on loss of the main switch. However, the large inductor current ripple in CRM PFC creates huge DM EMI noise, which requires a big EMI filter. The switching frequency of the CRM PFC is variable in half line cycle which makes the EMI characteristics of the CRM PFC are not clear and have not been carefully investigated. The worst case of the EMI noise, which is the baseline to design the EMI filter, is difficult to be identified. In this paper, an approximate mathematical EMI noise model based on the investigation of the principle of the quasi-peak detection is proposed to predict the DM EMI noise of the CRM PFC. The developed prediction method is verified by measurement results and the predicted DM EMI noise is good to evaluate the EMI performance. Based on the noise prediction, the worst case analysis of the DM EMI noise in the CRM PFC is applied and the worst case can be found at some line and load condition, which will be a great help to the EMI filter design and meanwhile leave an opportunity for the optimization of the whole converter design. What is more, the worst case analysis can be extended to 2-channel interleaved CRM PFC and some interesting characteristics can be observed. For example, the great EMI performance improvement through ripple current cancellation in traditional constant frequency PFC by using interleaving techniques will not directly apply to the CRM PFC due to its variable switching frequency. More research needs to be done to abstract some design criteria for the boost inductor and EMI filter in the interleaved CRM PFC. / Master of Science

In this dissertation, three major contributions are presented in a photovoltaic (PV) energy system. Firstly, a three-port grid-forming (GFM) microinverter and a lithium-ion battery pack are integrated at the back of PV panel. As a result, they form an AC-PV energy system module that produces an AC output voltage. The technoeconomic analysis, battery capacity optimization, PV panel size optimization, electrical and thermal model of batteries, battery heat generation model, battery management system and thermal management system are discussed in the AC-PV module by using stochastic analysis and battery test results. Secondly, a three-phase 540 KVA bidirectional inverter and a 1.86 MWh lithium-ion battery energy storage system (BESS) were integrated at the Florida Solar Energy Center (FSEC). A case study is performed for this system by acquiring the energy consumption of the building, the reduced energy consumption, the battery testing, the load shifting, and the peak shaving. The total harmonic distortion (THD) values are also provided. Among eight power management scenarios, the scenarios that include PV panels are satisfied via simulation. However, the scenarios that do not include PV panels are analyzed and presented based on the real-world setting measurements. Thirdly, a modified droop control method is designed for grid-tied and off-grid scenarios. The simulation results are obtained based on three scenarios. The first one is that the voltage and frequency regulation control algorithm is discussed when GFM inverters have the equal power ratings. Then, the load sharing control algorithm is determined based on different GFM inverters' power ratings. The last scenario includes Grid connection. Loads are added and removed from the system to ensure that the frequency and voltage stability is the range of continuous operation. The coupling reactance effect on power sharing is investigated.

The 2008 Climate Change Act set legally-binding carbon reduction targets. Demand side management (DSM) includes energy use reduction and peak shaving and offers significant potential to reduce the amount of carbon used by the electricity grid. The demand side management (DSM) schemes that have tried to meet this challenge have been dominated by engineering-based approaches and so favour tools like automation (which aims to make shifting invisible) and pricing (which requires customer response) to shift demand. These approaches tend to focus on the tools for change and take little account of people and energy-use practices. This thesis argues that these approaches are limited and therefore unlikely to produce the level of response that will be needed in future. The thesis therefore investigates the potential for time-shifting domestic energy demand but takes a different angle by trying to understand how people use energy in their daily lives, whether this use can be shifted and some of the implications of shifting it. The centrepiece of the work is an empirical study of eleven households energy-use practices. The interdisciplinary methodology involved in-house observations, interviews, photographs, metered energy data and disruptive interventions. The data was collected in two phases. Initially, a twenty-four hour observation was carried out in each household to find out how energy was implicated in everyday practices. Next, a series of three challenges were carried out, aimed at assessing the implications of disrupting practices by time-shifting food preparation, laundry and work/ leisure. A practice theory approach is used to shift the focus of attention from appliances, tools for change, behaviour or even people, to practices. The central finding of this work is that practices were flexible. This finding is nuanced, in the light of the empirical research, by an extended discussion on the nature of practices; in particular, the relationship between practices and agency and the temporal-spatial locatedness of practices. The findings demonstrate that, in this study at least, expanding the range of demand response options was possible. The research suggests numerous possibilities for extending the potential of practices to shift in time and space, shift the energy used in practices or substitute practices for other non-energy-using practices, though there are no simple technological or behavioural fixes . More profoundly, however, the thesis concludes that infrastructures of provision , such as the electricity grid and the companies that run it, underpin and facilitate energy-use practices irrespective of the time of day and year. In this context technology-led demand response schemes may ultimately contribute to the problem they purport to solve. A more fundamental interrogation of demand and the infrastructures that serve it is therefore necessary and is almost entirely absent from the demand response debate.

Ce travail comprend des études concernant lendommagement, la rupture et leurs influences sur la perméabilité du béton. Des analyses théoriques et expérimentales ont été présentées pour mettre en évidence le mécanisme dinitiation et de propagation des fissures dans le béton, ainsi que lévolution de la perméabilité de ce matériau sous laction dune charge et de la température. Une étude bibliographique est dabord réalisée. Elle constituera une base de connaissance bien utile pour les problèmes étudiés dans ce travail. Les comportements mécaniques, les modèles constitutifs du béton, notamment les modèles dendommagement et de rupture, ont été analysés en détail. Le modèle Mazars a été choisi comme le modèle de référence pour le développement de nos recherches. Lévolution de la perméabilité du béton en fonction des charges mécaniques appliquées ou de la température est également abordée dans cette étude bibliographique. Un programme dessai a été réalisé pour déterminer les paramètres de ruptures de bétons ordinaires couramment utilisés au Vietnam. Lénergie de rupture, le facteur dintensité de contrainte et la longueur caractéristique des zones de rupture ont été définis comme des fonctions de la résistance en compression et de la taille des éprouvettes dessai. Une loi deffet déchelle est aussi établie pour les différents types bétons analysés. Lapproche non-locale dans lintégration de la loi de comportement a été introduite dans le code aux éléments finis Lagamine, afin de tenir compte de la localisation de la déformation dans les zones endommagées du béton. Des exemples de simulations ont montré lavantage du modèle dendommagement non-local. Une analyse de sensibilité des résultats numériques avec les paramètres dendommagement est réalisée et permet de déterminer ces paramètres par calage pour les bétons testés. Les jeux de paramètres ainsi obtenus ont été validés par comparaison entre les réponses numériques et expérimentales sur des poutres simples en béton armé. Un deuxième programme dessai a également été effectué dans ce travail pour étudier lévolution de la perméabilité du béton sous laction de la charge mécanique et de la température. Les valeurs de la perméabilité à leau et au gaz sont mesurées simultanément et permettent dobtenir une comparaison relative. Ces résultats expérimentaux accompagnés dautres résultats expérimentaux de la littérature ont été pris comme base pour la proposition des modèles mécaniques, thermiques et thermo-mécaniques dévolution de la perméabilité du béton. Lévolution de la perméabilité est considérée non seulement comme une fonction de lendommagement diffus, mais aussi de lendommagement localisé. Afin de calculer les valeurs de la perméabilité du béton fissuré, la loi de Poiseuille a été utilisée. Une technique est alors proposée afin de pouvoir utiliser cette loi dans une approche continue. Cette loi pourrait alors être utilisée pour déterminer la perméabilité à travers un milieu fissuré. Les lois dévolution de la perméabilité proposées ont été implémentées dans le code Lagamine. Des exemples de simulation ont été réalisés pour calculer la perméabilité structurelle à travers des structures en béton dune part sous chargement et dautre part sous chargement et température simultanément / This work concerns the study of the damage, the fracture and their effects on the permeability values of concrete. Theoretical and experimental analysis have been represented to clarify the mechanism of crack initiation and crack propagation in concrete as well as the evolution of permeability values of this material under the action of mechanical load and temperature. A literature preview was carried out first to have a good background of considered problems in this work. Mechanical behaviors, constitutive models, especially damage and fracture models have been analyzed in detail. The Mazars damage model has been chosen as the base to develop further researches. The permeability of concrete was also mentioned in this study based on the published results in literature. An experimental program has been carried out to determine fracture parameters of ordinary concretes commonly used in Vietnam. Fracture energy, stress intensity factor and characteristic length of fracture process zones were represented as functions of compressive resistance and structural dimensions. The size effect law was also established for considered concretes. Nonlocal approach of integral formula was added in finite elements code Lagamine to take into account the strain localization in damaged zones of concrete. Some examples of simulation were realized to prove the advantages of nonlocal damage model. The dependence of numerical results on damage parameters was taken as a basis to carry out a calibrating process of these parameters for considered ordinary concretes. The obtained sets of damage parameters have been validated by a comparison of numerical responses beside experimental ones of simple reinforced concrete beams. A second experimental program was also realized in this work to study the evolution of permeability of concrete under the action of mechanical loading and temperature. The values of water and gas permeability are measured in the same time to have a relative comparison of these ones. These experimental results together with experimental results in literature were taken as a basis of the proposition of some mechanical, thermo-mechanical models of fluid permeability of concrete. The evolution of permeability was considered not only as a function of diffuse damage but also localized damage. In order to calculate permeability values of cracked concrete, the Poiseuille law has been used, a technique was then proposed to be able to use this law in a continuous approach that could have a good prediction of permeability through cracked media. The proposed laws of permeability were implanted in Lagaminde code. Some examples of simulation have been carried out to calculate the structural permeability through concrete structures under mechanical action and under thermo-mechanical action

Multi-carrier systems based on orthogonal frequency division multiplexing (OFDM) are efficient technologies for the implementation of broadband wireless communication systems. OFDM is widely used and has been adopted for current mobile broadband wireless communication systems such as IEEE 802.a/g wireless LANs, WiMAX, 3GPP LTE, and DVB-T/H digital video broadcasting systems. Despite their many advantages, however, OFDM-based systems suffer from potentially high peak-to-average power ratio (PAR). Since communication systems typically include nonlinear devices such as RF power amplifiers (PA) and digital-to-analog converters (DAC), high PAR results in increased symbol error rates and spectral radiation. To mitigate these nonlinear effects and to avoid nonlinear saturation effects of the PA, the operating point of a signal with high peak power must be backed off into the linear region of the PA. This so-called output backoff (OBO) results in a reduced power conversion efficiency which limits the battery life for mobile applications, reduces the coverage range, and increases both the cost of the PA and power consumption in the cellular base station. With the increasing demand for high energy efficiency, low power consumption, and greenhouse gas emission reduction, PAR reduction is a key technique in the design of practical OFDM systems. Motivated by the PAR reduction problem associated with multi-carrier systems, such as OFDM, this research explores the state of the art of PAR reduction techniques and develops new signal processing techniques that can achieve a minimum PAR for given system parameters and that are compatible with the appropriate standards. The following are the three principal contributions of this dissertation research. First, we present and derive the semi-analytical results for the output of asymptotic iterative clipping and filtering. This work provides expressions and analytical techniques for estimating the attenuation factor, error vector magnitude, and bit-error-rate (BER), using a noise enhancement factor that is obtained by simulation. With these semi-analytical results, we obtain a relationship between the BER and the target clipping level for asymptotic iterative clipping and filtering. These results serve as a performance benchmark for designing PAR reduction techniques using iterative clipping and filtering in OFDM systems. Second, we analyze the impact of the selected mapping (SLM) technique on BER performance of OFDM systems in an additive white Gaussian noise channel in the presence of nonlinearity. We first derive a closed-form expression for the envelope power distribution in an OFDM system with SLM. Then, using this derived envelope power distribution, we investigate the BER performance and the total degradation (TD) of OFDM systems with SLM under the existence of nonlinearity. As a result, we obtain the TD-minimizing peak backoff (PBO) and clipping ratio as functions of the number of candidate signals in SLM. Third, we propose an adaptive clipping control algorithm and pilotaided algorithm to address a fundamental issue associated with two lowcomplexity PAR reduction techniques, namely, tone reservation (TR) and active constellation extension (ACE). Specifically, we discovered that the existing low-complexity algorithms have a low clipping ratio problem in that they can not achieve the minimum PAR when the target clipping level is set below the initially unknown optimum value. Using our proposed algorithms, we overcome this problem and demonstrate that additional PAR reduction is obtained for any low value of the initial target clipping ratio. / text

L’évolution des systèmes de télécommunications, liée à une demande sans cesse croissante en termes de débit et de volume de données, se concrétise par le développement de systèmes proposant des bandes passantes très larges, des modulations à très hautes efficacités spectrales, de la flexibilité en puissance et en fréquence d’émission. Par ailleurs, la mise en œuvre de ces dispositifs doit se faire avec un souci permanent d’économie d’énergie d’où la problématique récurrente de l’amplification de puissance RF qui consiste à allier au mieux rendement, linéarité et bande passante. L’architecture conventionnelle d’une chaine d’émission RF consiste dans une première étape à réaliser l’opération de modulation-conversion de fréquence (Modulateur IQ) puis dans une deuxième étape l’opération de conversion d’énergie DC-RF (Amplificateur de Puissance), ces deux étapes étant traditionnellement traitées de manière indépendante. L’objectif de ces travaux de thèse est de proposer une approche alternative qui consiste à combiner ces deux opérations dans une seule et même fonction : le modulateur vectoriel de puissance à haute efficacité énergétique. Le cœur du dispositif, conçu en technologie GaN, repose sur un circuit à deux étages de transistors HEMT permettant d’obtenir un gain en puissance variable en régime de saturation. Il est associé à un modulateur de polarisation multi-niveaux spécifique également en technologie GaN. Le dispositif réalisé a permis de générer directement, à une fréquence de 2.5 GHz, une modulation vectorielle 16QAM (100Msymb/s) de puissance moyenne 13 W, de puissance crête 25W avec un rendement global de 40% et une linéarité mesurée par un EVM à 5%. / The evolution of telecommunications systems, linked to a constantly increasing demand in terms of data rate and volume, leads to the development of systems offering very wide bandwidths, modulations with very high spectral efficiencies, increased power and frequency flexibilities in transmitters. Moreover, the implementation of such systems must be done with a permanent concern for energy saving, hence the recurring goal of the RF power amplification which is to combine the best efficiency, linearity and bandwidth. Conventional architectures of RF emitter front-ends consist in a first step in performing the frequency modulation-conversion operation (IQ Modulator) and then in a second step the DC-RF energy conversion operation (Power Amplifier), these two steps being usually managed independently. The aim of this thesis is to propose an alternative approach that consists in combining these two operations in only one function: a high efficiency vector power modulator. The core of the proposed system is based on a two-stage GaN HEMT circuit to obtain a variable power gain operating at saturation. It is associated with a specific multi-level bias modulator also design using GaN technology. The fabricated device generates, at a frequency of 2.5 GHz, a 16QAM modulation (100Msymb/s) with 13W average power, 25W peak power, with an overall efficiency of 40% and 5% EVM.

Made available in DSpace on 2016-03-15T19:37:41Z (GMT). No. of bitstreams: 1 Jair Fiuza - EE2006.pdf: 870543 bytes, checksum: 939198dd0585c5cbae3d86adf6c858cc (MD5) Previous issue date: 2006-08-29 / The performance of a distributed Raman amplifier at S - Band using the TrueWave® Reach Low Water Peak fiber in a 100km span is analyzed through numerical simulations. The manufacturer, the OFS Fitel Denmark Ap, has experimentally characterized the physical parameters of the fiber, such as, attenuation, dispersion and Raman gain efficiency at Band - S. The low fiber attenuation around pump wavelength region, around 0,34dB/km at 1370nm, allow the achievement of approximately 10dB over 70nm in the S - Band &#8722; using 4 (four) pump lasers with pump power on the order of tenth of mWatts . / O desempenho de um amplificador Raman distribuído na Banda - S utilizando a fibra óptica TrueWave® Reach Low Water Peak em um enlace de 100km é analisado através de simulações numéricas. O fabricante, a OFS Fitel Denmark Ap, caracterizou experimentalmente os parâmetros físicos da fibra óptica, tais como atenuação, dispersão, e eficiência de ganho Raman na Banda - S. A baixa absorção dessa fibra óptica na região espectral onde se localizam os lasers de bombeamento, em torno de 0,34dB/km, para 1370nm, permite a utilização de 4 lasers de bombeamento com potências da ordem de dezenas de mWatts, para garantir um ganho on-off da ordem de 10dB em 70nm (1460 a 1530nm) na Banda - S.