Ingeniero Civil Eléctrico / Los constantes y cada vez más acelerados avances tecnológicos, han generado que los sistemas de comunicación se optimicen considerablemente con el transcurso de los años. Dentro de los cambios más importantes que se han visto en el último tiempo, destaca la disminución del uso de los clásicos sistemas de telecomunicaciones basados en portadoras únicas, dándose paso a sistemas más complejos en donde la información se transmite utilizando múltiples portadoras. Dentro de este último grupo de técnicas, uno de los que más sobresale es orthogonal frequency division multiplexing (OFDM), el cual ha sido y es, ampliamente utilizado en múltiples aplicaciones o estándares de comunicación. El uso extensivo de OFDM se debe a varias ventajas que esta técnica posee, tales como: alcanzar altas tasas de transmisión de datos, generar señales robustas ante canales inalámbricos, tener una alta eficiencia espectral, entre otros. Pero, aun cuando éstos exhiben múltiples ventajas, también presentan ciertos inconvenientes que deben ser tratados como lo son: los altos niveles de peak-to-average power ratio (PAPR) que caracterizan a las señales OFDM y la sensibilidad a errores originados por la desincronización entre el transmisor y receptor. Esto último, facilita la generación de interferencia entre portadoras (inter-carrier interference, ICI) y, por ende, un aumento en la probabilidad de error. En este trabajo se examina el funcionamiento de los sistemas basados en OFDM, partiendo desde la generación de la señal, hasta su comportamiento espectral. Pero por otro lado, también se analiza como la implementación de pulsos que cumplen con el primer criterio de Nyquist (Nyquist-I), favorece al rendimiento de esta clase de sistemas. El uso de pulsos Nyquist-I para combatir los inconvenientes típicos mostrados por los sistemas basados en OFDM ha sido propuesto por múltiples investigadores. En este trabajo se estudia en detalle una nueva familia de pulsos Nyquist-I llamada improved parametric linear combination pulses (IPLCP), la cual se propone para combatir un completo listado de aspectos perjudiciales mostrados por sistemas OFDM reales, a diferencia de otros pulsos que solamente buscan solucionar uno de ellos. Para analizar el rendimiento de la nueva familia de pulsos, se le compara con otras ya conocidas en términos del ICI, la razón señal a interferencia (signal-to-interference ratio, SIR), el PAPR y la tasa de probabilidad de error de bit (bit error rate, BER). Finalmente, el análisis demuestra que la nueva familia es la que mejor se desempeña en promedio en términos de los parámetros de estudio recién mencionados, dejando en claro que la implementación del IPLCP favorece al rendimiento de los sistemas de comunicación basados en la tecnología OFDM.

With the ongoing push for wireless systems to accommodate more users and support higher data rates more efficient modulation schemes have been created that are more advanced than simple FM and AM modulation used for radio broadcasting. These modulation schemes, such as orthogonal frequency division multiplexing (OFDM), suffer from high peak to average power ratios. Standard Class A and Class AB amplifiers cannot simultaneously achieve good linearity and efficiency, and therefore there has been an increase in the development of new topologies to combat this issue. Common features to these circuits is power combining of two or more separate transistors. In this work, we consider various ways of two-source power combining and identify four topologies of interest. We notice that linear power-efficient amplifiers reported to date are based upon two of the identified combining strategies. We believe that no amplifiers have been reported that leverage the other two alternatives. This work produces a fully-functional amplifier based on one of these alternatives. The prototypes are intended to serve as concept verification of the architecture and hence are implemented at lower (1 MHz) frequencies.

No description available.

<p> The anaerobic-to-aerobic power ratio is a useful tool to evaluate the strengths and weaknesses of both the aerobic and anaerobic energy systems. The traditional method of calculation has shown this ratio to increase with age in children and to plateau by late adolescence or early adulthood. However, by using the traditional approach, the aerobic component of the ratio is likely highly influenced by anaerobic sources and therefore, may not demonstrate the true proportional changes observed in the respective physiological capacities comprising this ratio with age through childhood and adolescence. The purpose of this study was to examine the age-related development of the power ratio using two new approaches. The lactate threshold (LT) and ventilatory anaerobic threshold (VAT) were identified in 31 competitive male hockey players ranging from 10 to 21 years of age and compared across three discrete age groups. Peak mechanical anaerobic power was obtained from a Wingate test (WAnT) and incorporated into the numerator of the power ratio, while peak mechanical aerobic power was obtained from a modified McMaster all-out progressive test and included into the denominator of the ratio. Mechanical power at the LT and VAT were also identified and integrated into the denominator of the power ratio and results compared to the traditional approach to identify similarities or differences in developmental trends with age. Furthermore, the reliability of the traditional, LT and VAT approaches was examined with retests of six subjects using intra-class correlation analysis and Method Error analysis. When power ratio approaches were compared among discrete age groups, significant differences (P≤0.05) were found between the youngest and oldest age groups for each of the three approaches. Notwithstanding the trend for progressive increases with advancing age group for all approaches, significant correlations with age were only found for the traditional approach (r=0.36). Finally, the VAT approach was the most reliable (r=0.95; ME=0.13) while the LT and traditional approaches demonstrated strong but non-significant test-retest correlations. Results of this study suggest that the LT and VAT approaches may theoretically be more accurate methods of measuring the power ratio than the traditional approach, as there is likely less anaerobic contribution to the denominator of the ratio. Each of the new approaches demonstrates expected age-related trends, and notwithstanding methodological and sample limitations, the VAT in particular, appears to be a more reliable and accurate means of assessing the power ratio compared to the traditional or LT approach.</p> / Thesis / Master of Science (MSc)

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

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.

<p>DVB (Digital Video Broadcasting) is the television digital system. It's however much more than a simple replacement for existing analogue television transmission, this system has many advantages such as picture quality and allows you a range of new features and services including subtitling, multiple audio tracks, interactive content, multimedia content. </p><p>The system is based in the OFDM technology, which allows DVB system to exploit the spectrum frequencies in a better way, saving spectrum, but OFDM has an important drawback that is the peak to average power ratio problem. OFDM is based on the FFT algorithms generating orthogonal subcarriers. </p><p>This thesis talks about the improvement of the PAPR problem using the soft compression method. </p><p>The simulation has been developed in Simulink® and Matlab®. With all the information presented in this thesis, any user can simulate the system. Thus, this thesis can be improved using other techniques to solve the PAPR problem.</p>

DVB (Digital Video Broadcasting) is the television digital system. It's however much more than a simple replacement for existing analogue television transmission, this system has many advantages such as picture quality and allows you a range of new features and services including subtitling, multiple audio tracks, interactive content, multimedia content. The system is based in the OFDM technology, which allows DVB system to exploit the spectrum frequencies in a better way, saving spectrum, but OFDM has an important drawback that is the peak to average power ratio problem. OFDM is based on the FFT algorithms generating orthogonal subcarriers. This thesis talks about the improvement of the PAPR problem using the soft compression method. The simulation has been developed in Simulink® and Matlab®. With all the information presented in this thesis, any user can simulate the system. Thus, this thesis can be improved using other techniques to solve the PAPR problem.

In order to improve the drawback of the high peak-to-average power ratio (PAPR) on the multi-carrier systems, in this paper we derive a statistical characterization approach of the time domain signal power variance metric by means of every user¡¦s spreading code combination and subcarrier scrambling. We obviously reduce the PAPR on the multi-carrier code division multiple access (MC-CDMA) systems by resorting the combination of spreading codes and scrambling the polarities of subcarriers. Due to the large calculative number of exhaustive search, we use a low complexity Replacement Search Method (RSM) to reduce the calculation times of searching, and obtain a good result. Moreover, we can get a better PAPR reduction performance by increasing the number of iteration.

This thesis considers the use of the tone reservation (TR) technique in orthogonal frequency division multiplexing (OFDM) systems. The nonlinear distortion is usually introduces by the high power amplifiers (HPA) used in wireless communications systems. It orders to reduce the inter-modulation distortion (IMD) in OFDM systems. In addition to the original peak-to-average power ratio (PAPR)-reduction criterion, we propose signal-to-distortion plus noise power ratio (SDNR) criterion and distortion power plus inverse of signal power (DIS) criterion. Based on these criteria, the cross-entropy (CE) algorithm is introduced to determine desired values of the peak reduction carriers (PRCs) to improve the bit error rate (BER) of nonlinearly distorted. Computational complexity is always the major concern of PAPR technique. Therefore, the real-valued PRCs and the modified transform decomposition (MTD) method are introduced here to dramatically decrease complexity of inverse fast Fourier transform (IFFT) operation with slightly performance loss. The simulation results show that the proposed criteria provide a better BER performance and a lower computational complexity.