16 research outputs found
A Modulo-Based Architecture for Analog-to-Digital Conversion
Systems that capture and process analog signals must first acquire them
through an analog-to-digital converter. While subsequent digital processing can
remove statistical correlations present in the acquired data, the dynamic range
of the converter is typically scaled to match that of the input analog signal.
The present paper develops an approach for analog-to-digital conversion that
aims at minimizing the number of bits per sample at the output of the
converter. This is attained by reducing the dynamic range of the analog signal
by performing a modulo operation on its amplitude, and then quantizing the
result. While the converter itself is universal and agnostic of the statistics
of the signal, the decoder operation on the output of the quantizer can exploit
the statistical structure in order to unwrap the modulo folding. The
performance of this method is shown to approach information theoretical limits,
as captured by the rate-distortion function, in various settings. An
architecture for modulo analog-to-digital conversion via ring oscillators is
suggested, and its merits are numerically demonstrated
Lecture Notes on Network Information Theory
These lecture notes have been converted to a book titled Network Information
Theory published recently by Cambridge University Press. This book provides a
significantly expanded exposition of the material in the lecture notes as well
as problems and bibliographic notes at the end of each chapter. The authors are
currently preparing a set of slides based on the book that will be posted in
the second half of 2012. More information about the book can be found at
http://www.cambridge.org/9781107008731/. The previous (and obsolete) version of
the lecture notes can be found at http://arxiv.org/abs/1001.3404v4/
Joint Empirical Coordination of Source and Channel
In a decentralized and self-configuring network, the communication devices
are considered as autonomous decision-makers that sense their environment and
that implement optimal transmission schemes. It is essential that these
autonomous devices cooperate and coordinate their actions, to ensure the
reliability of the transmissions and the stability of the network. We study a
point-to-point scenario in which the encoder and the decoder implement
decentralized policies that are coordinated. The coordination is measured in
terms of empirical frequency of symbols of source and channel. The encoder and
the decoder perform a coding scheme such that the empirical distribution of the
symbols is close to a target joint probability distribution. We characterize
the set of achievable target probability distributions for a point-to-point
source-channel model, in which the encoder is non-causal and the decoder is
strictly causal i.e., it returns an action based on the observation of the past
channel outputs. The objectives of the encoder and of the decoder, are captured
by some utility function, evaluated with respect to the set of achievable
target probability distributions. In this article, we investigate the
maximization problem of a utility function that is common to both encoder and
decoder. We show that the compression and the transmission of information are
particular cases of the empirical coordination.Comment: accepted to IEEE Trans. on I
Capacity Results for Wireless Cooperative Communications with Relay Conferencing
In this dissertation we consider cooperative communication systems with relay conferencing, where the relays own the capabilities to talk to their counterparts via either wired or wireless out-of-band links. In particular, we focus on the design of conferencing protocols incorporating the half-duplex relaying operations, and study the corresponding capacity upper and lower bounds for some typical channels and networks models, including the diamond relay channels (one source-destination pairs and two relays), large relay networks (one source-destination pairs and N relays), and interference relay channels (two source-destination pairs and two relays).
First, for the diamond relay channels, we consider two different relaying schemes, i.e., simultaneous relaying (for which the two relays transmit and receive in the same time slot) and alternative relaying (for which the two relays exchange their transmit and receive modes alternatively over time), for which we obtain the respective achievable rates by using the decode-and-forward (DF), compress-and-forward (CF), and amplify-and-forward (AF) relaying schemes with DF and AF adopted the conferencing schemes. Moreover, we prove some capacity results under some special conditions.
Second, we consider the large relay networks, and propose a "p-portion" conferencing scheme, where each relay can talk to the other "p-portion" of the relays. We obtain the DF and AF achievable rates by using the AF conferencing scheme. It is proved that relay conferencing increases the throughput scaling order of the DF relaying scheme from O(log(log(N ))) for the case without conferencing to O(log(N )); for the AF relaying scheme, it achieves the capacity upper bound under some conditions.
Finally, we consider the two-hop interference relay channels, and obtain the AF achievable rates by adopting the AF conferencing scheme and two different decoding schemes at the destination, i.e., single-user decoding and joint decoding. For the derived joint source power allocation and relay combining problem, we develop some efficient iterative algorithms to compute the AF achievable rate regions. Moreover, we compare the achievable degree-of-freedom (DoF) performance of these two decoding schemes, and show that single-user decoding with interference cancellation at the relays is optimal
Control of modular multilevel converters in high voltage direct current power systems
This thesis focuses on a comprehensive analysis of Modular Multilevel Converters (MMC) in High
Voltage Direct Current (HVDC) applications from the viewpoint of presenting new mathematical
dynamic models and designing novel control strategies. In the first step, two new mathematical
dynamic models using differential flatness theory (DFT) and circulating currents components
are introduced. Moreover, detailed step-by-step analysis-based relationships are achieved for
accurate control of MMCs in both inverter and rectifier operating modes. After presenting these
new mathematical equations-based descriptions of MMCs, suitable control techniques are
designed in the next step. Because of the nonlinearity features of MMCs, two nonlinear control
strategies based on direct Lyapunov method (DLM) and passivity theory-based controller
combined with sliding mode surface are designed by the use of circulating currents componentsbased
dynamic model to provide a stable operation of MMCs in HVDC applications under various
operating conditions. The negative effects of the input disturbance, model errors and system
uncertainties are suppressed by defining a Lyapunov control function to reach the integralproportional
terms of the flat output errors that should be finally added to the initial inputs.
Simulation results in MATLAB/SIMULINK environment verify the positive effects of the proposed
dynamic models and control strategies in all operating conditions of the MMCs in inverter mode,
rectifier mode and HVDC applications.Esta tese visa proceder a uma análise abrangente de conversores multinÃvel modulares (MMC)
para transmissão a alta tensão em corrente contÃnua (HVDC), almejando apresentar novos
modelos matemáticos em sistemas dinâmicos e projetar novas estratégias de controlo. Na
primeira etapa são introduzidos dois novos modelos matemáticos dinâmicos que usam
differential flatness theory e as componentes de correntes circulantes. Ainda, é estabelecida
uma modelação matemática para o controlo preciso dos MMCs, operando em modo inversor ou
modo retificador. Depois de apresentar as novas equações matemáticas, as técnicas de controlo
mais adequadas são delineadas. Devido à s caracterÃsticas não lineares dos MMCs, são projetadas
duas estratégias de controlo não-lineares baseadas no método direto de Lyapunov e no controlo
do tipo passivity theory-based combinado com controlo por modo de deslizamento através do
uso de modelos dinâmicos baseados em correntes circulantes para fornecer uma operação
estável aos MMCs em aplicações de HVDC sob várias condições de operação. Os efeitos negativos
das perturbações de entrada, erros de modelação e incertezas do sistema são suprimidos
através da definição da função de controlo de Lyapunov para alcançar os termos de integraçãoproporcionalidade
dos erros de saÃda para que possam finalmente ser adicionados à s entradas
iniciais. Os resultados da simulação computacional realizados em ambiente MATLAB/SIMULINK
verificam os efeitos positivos dos modelos dinâmicos propostos e das novas estratégias de
controlo em todas as condições de operação dos MMCs no modo inversor, retificador e em
aplicações HVDC
When all information is not created equal
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 191-196).Following Shannon's landmark paper, the classical theoretical framework for communication is based on a simplifying assumption that all information is equally important, thus aiming to provide a uniform protection to all information. However, this homogeneous view of information is not suitable for a variety of modern-day communication scenarios such as wireless and sensor networks, video transmission, interactive systems, and control applications. For example, an emergency alarm from a sensor network needs more protection than other transmitted information. Similarly, the coarse resolution of an image needs better protection than its finer details. For such heterogeneous information, if providing a uniformly high protection level to all parts of the information is infeasible, it is desirable to provide different protection levels based on the importance of those parts. The main objective of this thesis is to extend classical information theory to address this heterogeneous nature of information. Many theoretical tools needed for this are fundamentally different from the conventional homogeneous setting. One key issue is that bits are no more a sufficient measure of information. We develop a general framework for understanding the fundamental limits of transmitting such information, calculate such fundamental limits, and provide optimal architectures for achieving these limits. Our analysis shows that even without sacrificing the data-rate from channel capacity, some crucial parts of information can be protected with exponential reliability. This research would challenge the notion that a set of homogenous bits should necessarily be viewed as a universal interface to the physical layer; this potentially impacts the design of network architectures. This thesis also develops two novel approaches for simplifying such difficult problems in information theory. Our formulations are based on ideas from graphical models and Euclidean geometry and provide canonical examples for network information theory. They provide fresh insights into previously intractable problems as well as generalize previous related results.by Shashibhushan Prataprao Borade.Ph.D