228 research outputs found
Characterization and modelling of software defined radio front-ends
Doutoramento em Engenharia ElectrotécnicaO presente trabalho tem por objectivo estudar a caracterização e modelação
de arquitecturas de rádio frequência para aplicações em rádios definidos por
software e rádios cognitivos. O constante aparecimento no mercado de novos
padrões e tecnologias para comunicações sem fios têm levantado algumas
limitações à implementação de transceptores rádio de banda larga. Para além
disso, o uso de sistemas reconfiguráveis e adaptáveis baseados no conceito
de rádio definido por software e rádio cognitivo assegurará a evolução para a
próxima geração de comunicações sem fios. A ideia base desta tese passa por
resolver alguns problemas em aberto e propor avanços relevantes, tirando
para isso partido das capacidades providenciadas pelos processadores digitais
de sinal de forma a melhorar o desempenho global dos sistemas propostos.
Inicialmente, serão abordadas várias estratégias para a implementação e
projecto de transceptores rádio, concentrando-se sempre na aplicabilidade
específica a sistemas de rádio definido por software e rádio cognitivo. Serão
também discutidas soluções actuais de instrumentação capaz de caracterizar
um dispositivo que opere simultaneamente nos domínios analógico e digital,
bem como, os próximos passos nesta área de caracterização e modelação.
Além disso, iremos apresentar novos formatos de modelos comportamentais
construídos especificamente para a descrição e caracterização não-linear de
receptores de amostragem passa-banda, bem como, para sistemas nãolineares
que utilizem sinais multi-portadora.
Será apresentada uma nova arquitectura suportada na avaliação estatística
dos sinais rádio que permite aumentar a gama dinâmica do receptor em
situações de multi-portadora. Da mesma forma, será apresentada uma técnica
de maximização da largura de banda de recepção baseada na utilização do
receptor de amostragem passa-banda no formato complexo.
Finalmente, importa referir que todas as arquitecturas propostas serão
acompanhadas por uma introdução teórica e simulações, sempre que possível,
sendo após isto validadas experimentalmente por protótipos laboratoriais.This work investigates the characterization and modeling of radio frequency
front-ends for software defined radio and cognitive radio applications. The
emergence of new standards and technologies in the wireless communications
market are raising several issues to the implementation of wideband
transceiver systems. Also, reconfigurable and adaptable systems based on
software defined and cognitive radio models are paving the way for the next
generation of wireless systems. In this doctoral thesis the fundamental idea is
to address the particular open issues and propose appropriate advancements
by exploring and taking profit from new capabilities of digital signal processors
in a way to improve the overall performance of the novel schemes.
Receiver and transmitter strategies for radio communications are summarized
by concentrating on the usability for software defined radio and cognitive radio
systems. Available instrumentation and next steps for analog and digital radio
frequency hardware characterization is also discussed.
Wideband behavioral model formats are proposed for nonlinear description and
characterization of bandpass sampling receivers, as well as, for multi-carrier
nonlinear systems operation. The proposed models share a great flexibility and
have the freedom to be simply expanded to other fields.
A new design for receiver dynamic range improvement in multi-carrier
scenarios is proposed, which is supported on the useful wireless signals
statistical evaluation. Additionally, receiver-side bandwidth maximization based
on higher-order bandpass sampling approaches is evaluated.
All the proposed designs and modeling strategies are accompanied by
theoretical backgrounds and simulations whenever possible, being then
experimentally validated by laboratory prototypes
High-Power Microwave/ Radio-Frequency Components, Circuits, and Subsystems for Next-Generation Wireless Radio Front-Ends
As the wireless communication systems evolve toward the future generation, intelligence will be the main signature/trend, well known as the concepts of cognitive and software-defined radios which offer ultimate data transmission speed, spectrum access, and user capacity. During this evolution, the human society may experience another round of `information revolution\u27. However, one of the major bottlenecks of this promotion lies in hardware realization, since all the aforementioned intelligent systems are required to cover a broad frequency range to support multiple communication bands and dissimilar standards. As the essential part of the hardware, power amplifiers (PAs) capable of operating over a wide bandwidth have been identified as the key enabling technology. This dissertation focuses on novel methodologies for designing and realizing broadband high-power PAs, their integration with high-quality-factor (high-Q) tunable filters, and relevant investigations on the reliabilities of these tunable devices. It can be basically divided into three major parts:
1.Broadband High-Efficiency Power Amplifiers. Obtaining high PA efficiency over a wide bandwidth is very challenging, because of the difficulty of performing broadband multi-harmonic matching. However, high efficiency is the critical feature for high-performance PAs due to the ever-increasing demands for environmental friendliness, energy saving, and longer battery life. In this research, novel design methodologies of broad-band highly efficient PAs are proposed, including the first-ever mode-transferring PA theory, novel matching network topology, and wideband reconfigurable PA architecture. These techniques significantly advance the state-of-the-art in terms of bandwidth and efficiency.
2.Co-Design of PAs and High-Q Tunable Filters. When implementing the intelligent communication systems, the conventional approach based on independent RF design philosophy suffers from many inherent defects, since no global optimization is achieved leading to degraded overall performance. An attractive method to solve these difficulties is to co-design critical modules of the transceiver chain. This dissertation presents the first-ever co-design of PAs and tunable filters, in which the redundant inter-module matching is entirely eliminated, leading to minimized size & cost and maximized overall performance. The saved hardware resources can be further transferred to enhance system functionalities. Moreover, we also demonstrate that co-design of PAs and filters can lead to more functionalities/benefits for the wireless systems, e.g. efficient and linear amplification of dual-carrier (or multi-carrier) signals.
3.High-Power/Non-Linear Study on Tunable Devices. High-power limitation/power handling is an everlasting theme of tunable devices, as it determines the operational life and is the threshold for actual industrial applications. Under high-power operation, the high RF voltage can lead to failures like tuners\u27 mechanical deflections and gas discharge in the small air spacing of the cavity. These two mechanisms are studied independently with their instantaneous and long-term effects on the device performance. In addition, an anti-biased topology of electrostatic RF MEMS varactors and tunable filters is proposed and experimentally validated for reducing the non-linear effect induced by bias-noise. These investigations will enlighten the designers on how to avoid and/or minimize the non-ideal effects, eventually leading to longer life cycle and performance sustainability of the tunable devices
MISAT: Designing a Series of Powerful Small Satellites Based upon Micro Systems Technology
MISAT is a research and development cluster which will create a small satellite platform based on Micro Systems Technology (MST) aiming at innovative space as well as terrestrial applications. MISAT is part of the Dutch MicroNed program which has established a microsystems infrastructure to fully exploit the MST knowledge chain involving public and industrial partners alike.
The cluster covers MST-related developments for the spacecraft bus and payload, as well as the satellite architecture. Particular emphasis is given to distributed systems in space to fully exploit the potential of miniaturization for future mission concepts. Examples of current developments are wireless sensor and actuator networks with plug and play characteristics, autonomous digital Sun sensors, re-configurable radio front ends with minimum power consumption, or micro-machined electrostatic accelerometer and gradiometer system for scientific research in fundamental physics as well as geophysics.
As a result of MISAT, a first nano-satellite will be launched in 2007 to demonstrate the next generation of Sun sensors, power subsystems and satellite architecture technology. Rapid access to in-orbit technology demonstration and verification will be provided by a series of small satellites. This will include a formation flying mission, which will increasingly rely on MISAT technology to improve functionality and reduce size, mass and power for advanced technology demonstration and novel scientific applications.
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