Institute Telecomunicaes

Coimbra, Portugal

Institute Telecomunicaes

Coimbra, Portugal

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Lourenco A.,Polytechnic Institute of Lisbon | Lourenco A.,Institute Telecomunicaes | Lourenco A.,University of Lisbon | Silva H.,Institute Telecomunicaes | And 3 more authors.
Computational Intelligence and Neuroscience | Year: 2011

The ECG signal has been shown to contain relevant information for human identification. Even though results validate the potential of these signals, data acquisition methods and apparatus explored so far compromise user acceptability, requiring the acquisition of ECG at the chest. In this paper, we propose a finger-based ECG biometric system, that uses signals collected at the fingers, through a minimally intrusive 1-lead ECG setup recurring to Ag/AgCl electrodes without gel as interface with the skin. The collected signal is significantly more noisy than the ECG acquired at the chest, motivating the application of feature extraction and signal processing techniques to the problem. Time domain ECG signal processing is performed, which comprises the usual steps of filtering, peak detection, heartbeat waveform segmentation, and amplitude normalization, plus an additional step of time normalization. Through a simple minimum distance criterion between the test patterns and the enrollment database, results have revealed this to be a promising technique for biometric applications. © 2011 André Loureno et al.

Soares J.M.,University of Lisbon | Franceschinis M.,Instituto Superiore Mario Boella | Rocha R.M.,University of Lisbon | Rocha R.M.,Institute Telecomunicaes | And 2 more authors.
Eurasip Journal on Wireless Communications and Networking | Year: 2011

Opportunistic wireless sensor networks (WSNs) have recently been proposed as solutions for many remote monitoring problems. Many such problems, including environmental monitoring, involve large deployment scenarios with lower-than-average node density, as well as a long time scale and limited budgets. Traditional approaches designed for conventional situations, and thus not optimized for these scenarios, entail unnecessary complexity and larger costs. This paper discusses the issues related with the design and test of opportunistic architectures, and presents one possible solution - CHARON (Convergent Hybrid-replication Approach to Routing in Opportunistic Networks). Both algorithm-specific and comparative simulation results are presented, as well as real-world tests using a reference implementation. A comprehensive experimental setup was also used to seek a full characterization of the devised opportunistic approach including the derivation of a simple analytical model that is able to accurately predict the opportunistic message delivery performance in the used test bed. Copyright © 2011 Jorge M. Soares et al.

Boavida J.B.M.,Institute Telecomunicaes | Morgado J.A.P.,Institute Telecomunicaes | Morgado J.A.P.,Portuguese Air Force Academy | Fernandes C.A.F.,Institute Telecomunicaes
Optics and Laser Technology | Year: 2011

Optimized HR-AR-DFB laser structures are proposed foreseeing their use in directly modulated optical communication systems. They present, simultaneously, high single-longitudinal-mode yield, stable single-longitudinal-mode operation, high power efficiency and stable emitted wavelength. Lasers harder to manufacture were previously proposed elsewhere and did not succeed in achieving such high performances. A detailed assessment of the proposed lasers is presented and discussed. © 2010 Elsevier Ltd. All rights reserved.

Basin D.,ETH Zurich | Caleiro C.,Institute Telecomunicaes | Ramos J.,Institute Telecomunicaes | Vigano L.,University of Verona
Theoretical Computer Science | Year: 2011

The distributed temporal logic DTL is an expressive logic, well suited for formalizing properties of concurrent, communicating agents. We show how DTL can be used as a metalogic to reason about and relate different security protocol models. This includes reasoning about model simplifications, where models are transformed to have fewer agents or behaviors, and verifying model reductions, where to establish the validity of a property it suffices to consider its satisfaction on only a subset of models. We illustrate how DTL can be used to formalize security models, protocols, and properties, and then present three concrete examples of metareasoning. First, we prove a general theorem about sufficient conditions for data to remain secret during communication. Second, we prove the equivalence of two models for guaranteeing message-origin authentication. Finally, we relate channel-based and intruder-centric models, showing that it is sufficient to consider models in which the intruder completely controls the network. While some of these results belong to the folklore or have been shown, mutatis mutandis, using other formalisms, DTL provides a uniform means to prove them within the same formalism. It also allows us to clarify subtle aspects of these model transformations that are often neglected or cannot be specified in the first place. © 2011 Elsevier B.V. All rights reserved.

Freire N.M.A.,University of Coimbra | Freire N.M.A.,Institute Telecomunicaes | Cardoso A.J.M.,Institute Telecomunicaes | Cardoso A.J.M.,University of Beira Interior
IEEE Transactions on Industrial Electronics | Year: 2014

Reliability and availability levels are crucial aspects for assessing the economic viability of wind energy conversion systems. Therefore, fault-tolerant systems can make a valuable contribution. This paper presents a fault-tolerant permanent-magnet synchronous generator (PMSG) drive employing new direct control techniques. For postfault operation, a direct power control (DPC) of a four-switch three-phase converter and a direct torque control of a three-switch three-phase rectifier are proposed. Switching tables are theoretically formulated for both control techniques. Two alternative tables are obtained for the DPC of the grid-side converter, permitting the choice between implementation simplicity and enhanced performance. All necessary reconfigurations to handle open-circuit faults are triggered by a reliable fault diagnostic method, which has a low computational demand, without requiring additional measurements. Experimental results are presented, demonstrating the feasibility of the proposed fault-tolerant PMSG drive. © 1982-2012 IEEE.

Rodrigues J.J.P.C.,Institute Telecomunicaes | Rodrigues J.J.P.C.,University of Beira Interior | Pereira O.R.E.,University of Beira Interior | Neves P.A.C.S.,Institute Telecomunicaes | And 2 more authors.
Journal of Network and Computer Applications | Year: 2011

A body sensor network is a network of small sensor devices (biosensors) that sense health parameters of an individual, allowing 24/7 monitoring, providing biofeedback services. These networks have typically two layers: the sensor array and a sink node. The sink node manages the network, gathering sensor data continuously. However, raw sensor data is not enough to achieve biofeedback. One of the challenges body sensor networks present is the processing of raw biosensor data, in order to achieve a proper medical visualization of monitored parameters. This paper surveys some of the current approaches, proposes an interface classification based on features, and presents a solution based on a mobile device. The mobile application can run on a Java and Bluetooth enabled phone, allowing data retrieval, storage, and analysis in a single solution. The mobile application proposes a three-layer approach to BSN operation, adding the mobile device to the solution. The final system provides the user with a completely functional health-monitoring platform, which is easy to use and setup, validated through a complete series of tests on different mobile devices. © 2010 Elsevier Ltd. All rights reserved.

Rodrigues J.J.P.C.,Institute Telecomunicaes | Rodrigues J.J.P.C.,University of Beira Interior | Oliveira M.,University of Beira Interior | Vaidya B.,Institute Telecomunicaes
Eurasip Journal on Wireless Communications and Networking | Year: 2010

Mobile devices present the opportunity to enhance our fast-growing and globally connected society, improving user-experience through novel approaches for information dissemination through mobile communication. The research community is developing new technologies, services, and applications to enable ubiquitous environments based on mobile technology. This paper tackles several important challenges such as communication cost and device limitations for development of ubiquitous multimedia applications. And we propose a system for news delivery using a set of wireless multimedia applications. For this purpose, we have performed a case study with Apple iPhone's platform, featuring two multimedia application contexts, namely, Web and native applications. The multimedia mobile applications draw on iPhone's assets, enabling context-awareness to distribute news, improving communication efficiency and setting-up viewing optimizations, thus enhancing user-experience. The proposed system is evaluated and validated through a series of real-life experiments on real devices, with online full availability. Moreover, due to the Web application availability, the system is not restrained to Apple's iPhone platform, but can also benefit users with other devices. Copyright © 2010 Joel J. P. C. Rodrigues et al.

Correa G.,Federal University of Pelotas | Assuncao P.A.,Polytechnic Institute of Leiria | Assuncao P.A.,Institute Telecomunicaes | Agostini L.V.,Federal University of Pelotas | Da Silva Cruz L.A.,University of Coimbra
IEEE Transactions on Circuits and Systems for Video Technology | Year: 2016

Several different methods have been investigated in recent years, aiming at computational complexity reduction and scaling of High Efficiency Video Coding (HEVC) software implementations. However, maintaining the encoding time per frame or group of pictures (GOPs) below an adjustable upper bound is still an open research issue. A solution for this problem is devised in this paper based on a set of Pareto-efficient encoding configurations, identified through rate-distortion-complexity analysis. The proposed method combines a medium-granularity encoding time control with a fine-granularity encoding time control to accurately limit the HEVC encoding time below a predefined target for each GOP. It is shown that the encoding time can be kept below a desired target for a wide range of encoding time reductions, e.g., up to 90% in comparison with the original encoder. The results also show that compression efficiency loss (Bjontegaard delta-rate) varies from negligible (0.16%) to moderate (9.83%) in the extreme case of 90% computational complexity reduction. © 1991-2012 IEEE.

Oliveira R.A.,Federal University of Technology of Parana | Marques C.A.F.,Institute Telecomunicaes | Cook K.,University of Sydney | Canning J.,University of Sydney | And 2 more authors.
Applied Physics Letters | Year: 2011

A flexural wave is applied to an optical fiber during the process of Bragg grating inscription using the direct writing method through a phase mask. Using this approach, we can dither the writing process to allow complex grating writing. Examples we demonstrate are tunable sampled gratings and phase-shifted gratings. © 2011 American Institute of Physics.

Alonso J.M.,University of Oviedo | Perdigao M.S.,Institute Telecomunicaes | Perdigao M.S.,Polytechnic Institute of Coimbra | Perdigao M.S.,University of Coimbra | And 4 more authors.
IEEE Transactions on Industrial Electronics | Year: 2011

In this paper, a digitally controlled electronic ballast is presented. The ballast corresponds to the so-called universal or multiwatt ballasts, which are intended to operate different lamps with different power ratings without performing any change in the hardware. Thus, the ballast must incorporate some kind of circuitry so that the rated power of the connected lamp can be identified. The ballast must also adjust some of its parameters in order to supply the lamp adequately, which usually means the following: 1) as close as possible to the nominal power and 2) with the best efficiency. In the proposed ballast, the parameters selected to adapt the power circuit to each lamp are the switching frequency and the resonant tank inductance. The resonant tank inductance is varied by means of a magnetic regulator whose inductance can be adjusted through a dc bias current. Due to the relatively high complexity of the proposed converter, a digital control circuit is developed to control both the resonant inverter used to drive the lamp and the dcdc converter employed to supply the control winding of the magnetic regulator. Experimental results from a laboratory prototype for lamp powers ranging from 15 to 58 W are provided. © 2006 IEEE.

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