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Telecommunications Forum (TELFOR)

作者： Dragana Bajovic João Xavier Bruno Sinopoli Department of Electrical and Computer Engineering Carnegie Mellon University Pittsburgh PA USA Institute for Systems and Robotics (ISR) Instituto Superior Técnico Lisboa Portugal

We study the products W k ···W 1 of random stochastic, not necessarily symmetric matrices. It is known that, under certain conditions, the product W k · · · W 1 converges almost surely (a.s.) to a random rank-one matrix; the latter is equivalent to |λ 2 (W k · · · W 1 )| → 0 a.s., where λ 2 (·) is the second largest (in modulus) eigenvalue. In this paper, we show that the probability that |λ 2 (W k · · · W 1 )| stays above ε ∈ (0,1] in the long run decays to zero exponentially fast ~ e -kI . Furthermore, we explicitly characterize the rate of this convergence I and show that it depends only on the underlying graphs that support the matrices W k 's. Our results reveal that the rate I is essentially determined by the most likely way in which the union (over time) of the support graphs fails to form a directed tree.

关键词： Symmetric matrices Convergence Stochastic processes Computational modeling Eigenvalues and eigenfunctions Robot sensing systems

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Evaluation of Brain-computer Interfaces in Accessing Computer and other Devices by People with Severe Motor Impairments

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Procedia Computer Science 2012年 14卷 283-292页

作者： Gabriel Pires Urbano Nunes Miguel Castelo-Branco Institute for Systems and Robotics (ISR) University of Coimbra 3030-290 Coimbra Portugal Department of Electrical Engineering Polytechnic Institute of Tomar 2300-313 Tomar Portugal Biomedical Institute for Research in Light and Image (IBILI) University of Coimbra 3000-548 Coimbra Portugal

A brain-computer interface (BCI) translates brain signals into commands that can be used to control computer applications or external devices. BCI provides a non-muscular communication channel and therefore it assumes a crucial importance for individuals with motor functions severely affected. The evaluation of BCI by individuals with severe disabilities is of utmost importance to understand the BCI feasibility as an assistive technology. This paper summarizes some of the results achieved in our research lab, with different BCIs tested by individuals with severe motor disabilities, focusing on some practical aspects of BCI evaluation, and on the target population.

关键词： Brain-computer interface (BCI) P300 motor disabilities assistive technology

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Collaborative diffusive source localization in wireless sensor networks

Collaborative diffusive source localization in wireless sens...

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European Signal Processing Conference (EUSIPCO)

作者： Sabina Zejnilovic João Gomes Bruno Sinopoli Department of Electrical and Computer Engineering Carnegie Mellon University Pittsburgh PA USA Institute for Systems and Robotics-Instituto Superior Técnico (ISR/IST) Technical University of Lisbon Portugal

We propose a collaborative, energy efficient method for diffusive source localization in wireless sensor networks. The algorithm is based on distributed and iterative maximum-likelihood (ML) estimation, which is very sensitive to initialization. As a part of the proposed method we present an approach for obtaining a “good enough” initial value for the ML recursion based on infinite time approximation and semidefinite programming. We also present an approach for determining the sensor node that initiates the estimation process. To improve the convergence rate of the algorithm, we consider the case where selected nodes collaborate with their neighbors. Simulation results are used to characterize the performance and energy efficiency of the algorithm. We also illustrate estimation accuracy/energy consumption trade-off by varying the communication radius of sensor nodes.

关键词： Tin Maximum likelihood estimation Energy consumption Collaboration Wireless sensor networks Approximation methods

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Distributed Nesterov-like gradient algorithms

Distributed Nesterov-like gradient algorithms

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IEEE Conference on Decision and Control

作者： Dušsan Jakovetić José M. F. Moura João Xavier Department of Electrical and Computer Engineering Carnegie Mellon University Pittsburgh PA USA Institute for Systems and Robotics (ISR) Instituto Superior Técnico (IST) Technical University of Lisbon Lisbon Portugal

ISBN: (纸本)9781467320658

In classical, centralized optimization, the Nesterov gradient algorithm reduces the number of iterations to produce an ε-accurate solution (in terms of the cost function) with respect to ordinary gradient from O(1/ε) to equation. This improvement is achieved on a class of convex functions with Lipschitz continuous first derivative, and it comes at a very small additional computational cost per iteration. In this paper, we consider distributed optimization, where nodes in the network cooperatively minimize the sum of their private costs subject to a global constraint. To solve this problem, recent literature proposes distributed (sub)gradient algorithms, that are attractive due to computationally inexpensive iterations, but that converge slowly-the ε error is achieved in O(1/ε 2 ) iterations. Here, building from the Nesterov gradient algorithm, we present a distributed, constant step size, Nesterov-like gradient algorithm that converges much faster than existing distributed (sub)gradient methods, with zero additional communications and very small additional computations per iteration k. We show that our algorithm converges to a solution neighborhood, such that, for a convex compact constraint set and optimized stepsize, the convergence time is O(1/ε). We achieve this on a class of convex, coercive, continuously differentiable private costs with Lipschitz first derivative. We derive our algorithm through a useful penalty, network's Laplacian matrix-based reformulation of the original problem (referred to as the clone problem) - the proposed method is precisely the Nesterov-gradient applied on the clone problem. Finally, we illustrate the performance of our algorithm on distributed learning of a classifier via logistic loss.

关键词： Cloning Convergence Vectors Logistics Cost function Approximation algorithms

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Convergence rate analysis of distributed gradient methods for smooth optimization

Convergence rate analysis of distributed gradient methods fo...

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Telecommunications Forum (TELFOR)

作者： Dušan Jakovetić João Xavier José M. F. Moura Department of Electrical and Computer Engineering Carnegie Mellon University Pittsburgh PA USA Institute for Systems and Robotics (ISR) Instituto Superior Técnico (IST) Technical University of Lisbon Lisboa Portugal

We derive the convergence rate of a distributed gradient algorithm for smooth optimization in networked systems. We assume that each agent in the network has a convex cost function f i (x), known only to agent i, and the goal is to minimize the sum Σ N i=1 fi(x) of all agents' costs; such problem formulation arises in various networked applications, like, e.g., distributed inference or source localization in sensor networks. With the distributed gradient algorithm under study, each agent, at each iteration k, performs a weighted average of its own and its neighbors' solution estimates, and performs a step in the direction of the negative of its local function's gradient. We establish a novel result that the distributed gradient algorithm has the convergence rate O(1/k 2/3 ), in terms of the cost function optimality gap, under the assumption of convex f i 's with Lipschitz continuous and bounded gradients.

关键词： Convergence Gradient methods Algorithm design and analysis Upper bound Cost function Educational institutions

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Accurate Matlab/Simulink model of a Power Generation System Based on Fuel Cells

Accurate Matlab/Simulink model of a Power Generation System ...

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Annual Conference on IEEE Industrial Electronics Society

作者： A. S. Carvalho M. T. Outeiro Department of Electrical Engineering and Computers Engineering Faculty of Oporto University Institute of Systems and Robotics University of Porto

ISBN: (纸本)9781467324199

Modeling and simulation techniques are indispensable in every aspect of power system design. Power systems need to be simulated in a longer period of time and more frequently especially when they are being analyzed using complex computer algorithms. The MatLab/Simulink software is used in the simulation of a power generation system based on fuel cells. To provide a higher level of accuracy, a stiff algorithm is used. The accuracy of the simulation is verified by comparing the simulation results to these obtained experimentally in a prototype. Firstly the paper presents the electrical equivalent circuit of the PEM fuel cell, and its modelization in MatLab/Simulink. Secondly and once selected the topology and decided the control structure of the converter, its implementation in MatLab/Simulink software is presented. The model of the power generation system is performed in two parts, namely: the power circuit and the control circuit A special attention is given to the control strategy, providing detailed explanation to each control subsystem, particularly, the voltage control, the frequency control and PEM control. The simulation and experimental results that are focused on the stability of the system, and the resonant converter operation, are used to validate the accuracy of the model developed.

关键词： Mathematical model MATLAB Integrated circuit modeling Load modeling Topology Lead

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Products of Stochastic Matrices: Large Deviation Rate for Markov Chain Temporal Dependencies

Products of Stochastic Matrices: Large Deviation Rate for Ma...

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Annual Allerton Conference on Communication, Control, and Computing

作者： Dragana Bajovic Joao Xavier Bruno Sinopoli Institute for Systems and Robotics (ISR) Instituto Superior Tecnico (IST) Technical University of Lisbon Department of Electrical and Computer Engineering Carnegie Mellon University

ISBN: (纸本)9781467345378

We find the large deviation rate I for convergence in probability of the product W_k … W_1W_0 of temporally dependent random stochastic matrices. As the model for temporal dependencies, we adopt the Markov chain whose set of states is the set of all possible graphs that support the matrices W_k. Such model includes, for example, 1) token-based protocols, where a token is passed among nodes to determine the order of processing;and 2) temporally dependent link failures, where the temporal dependence is modeled by a Markov chain. We characterize the rate I as a function of the Markov chain transition probability matrix P. Examples further reveal how the temporal correlations (dependencies) affect the rate of convergence in probability I.

关键词： Markov processes Symmetric matrices Correlation Upper bound Protocols Convergence

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Consensus+Innovations Detection: Phase Transition Under Communication Noise

Consensus+Innovations Detection: Phase Transition Under Comm...

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Annual Allerton Conference on Communication, Control, and Computing

作者： Dusan Jakovetic Jose M. F. Moura Joao Xavier Department of Electrical and Computer Engineering Carnegie Mellon University Institute for Systems and Robotics (ISR) Instituto Superior Tecnico (IST) Technical University of Lisbon

ISBN: (纸本)9781467345378

We consider the tradeoffs between sensing and communication in a consensus+innovations distributed detection problem when the local communications among agents are noisy. Intuitively, we can expect that the error performance of the distributed detector is affected by both the sensing noise and the noise corrupting the communication among agents in the network. Too little communication (cooperation) and the distributed detector error performance will be dominated by the sensing noise. Too much communication and the detector error performance is dominated by the communication noise. We make this tradeoff precise through a large deviations analysis, i.e., by studying the exponential decay rate of the probability of error of the consensus+innovations distributed detector at each agent. Under a mild assumption of network connectedness, we show: 1) the weight sequences affecting the consensus and innovations potentials in the distributed detector need to be carefully designed for the error probability at every agent detector to decay exponentially fast;2) the network exhibits a phase transition with respect to the communication noise power. Below a threshold on the communication noise power, cooperation (communication) among agents improves the error detection performance;above threshold, inter-agent communication does not enhance the error detection performance.

关键词： noise(communication) error performance Phase transtormations Agents Communication Research detector NETWORKING AGENT Error probability Noise tradeoffs Error detection Distribute

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Proposal of a new real-time cooperative challenge in mobile robotics

Proposal of a new real-time cooperative challenge in mobile ...

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作者： Costa, P. Moreira, A. Gonçalves, J. Lima, J. Faculty of Engineering University of Porto Department of Electrical Engineering and Computers Porto Portugal Polytechnic Institute of Bragança Department of Electrical Engineering Bragança Portugal Robotics and Intelligent Systems Research Group INESC Porto Portugal

ISBN: (纸本)9783902661937

In this paper it is presented a new robot competition that is going to be included in Robotica 2011, the main robotics Portuguese Competition. The robot competition takes place in an emulated factory plant, where Automatic Guided Vehicles (AGVs) must cooperate to perform tasks. To accomplish their goals the AGVs must deal with localization, navigation, scheduling and cooperation problems, that must be solved autonomously. One option of prototyping the AGVs is the use of the Lego Mindstorms NXT technology. The presented example can play an important role in education due to the inherent multi-disciplinary concepts that are involved, motivating students to technological areas. It also plays an important role in research and development, because it is expected that the outcomes that will emerge here, will later be transfered to other application areas, such as service robots and manufacturing. © 2011 IFAC.

关键词： Automatic guided vehicles

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Electric vehicle simulator for energy consumption studies in electric mobility systems

Electric vehicle simulator for energy consumption studies in...

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2011 IEEE Forum on Integrated and Sustainable Transportation systems, FISTS 2011

作者： Maia, Ricardo Silva, Marco Araujo, Rui Nunes, Urbano ISR-Institute of Systems and Robotics University of Coimbra Portugal DEEC - Department of Electrical and Computer Engineering University of Coimbra Portugal IPC-ISEC - Polytechnic Institute of Coimbra Coimbra Portugal

ISBN: (纸本)9781457709906

One of the most important environmental problems in large cities is the vehicular emission. Electric Vehicles (EVs) are a growing alternative for internal combustion engine (ICE) vehicles. Since this kind of vehicle has low autonomy yet, it is important to optimize energy consumption, for instance by planning a suitable infrastructure of battery recharge and/or battery-switch stations. This paper presents an architecture for EV simulation, important to analyze traffic flow, its dynamics and the performance when there are obstructions or Intense traffic. There are several tools for traffic simulation, SUMO (Simulation of Urban MObility) is one of them. But none of the existing traffic simulators integrates models of EV that allow, for example, perform simulation studies regarding energy consumption. SUMO is a portable open source simulator with multi-modal traffic feature capabilities that permit the simulation of various types of vehicles. This work is an extension of the SUMO, two-dimensional (2D) vehicular simulation package. To allow the simulation of energy consumption of EV, two extensions were incorporated in SUMO: EV models and modeling of altitude, transforming SUMO into a three-dimensional (3D) simulator. The energy model effectiveness and correctness with 3D capabilities has been validated using two driving schedules (Urban Dynamometer Driving Schedule and Highway Fuel Economy Driving Schedule). This new tool will also support the study of better routes choice in 3D environment with EV aiming minimum energy consumption. © 2011 IEEE.

关键词： Energy utilization

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