Repositório RCAAP

A flexible real-time communication system must support modifications to the message set which it conveys. These changes can be requested by a human operator, during system set-up or maintenance, or autonomously bythe control system while responding to variations in theenvironment. In the former case, a response time up to a few seconds can be acceptable. However, in the latter, thephysical properties of the environment can require thatchanges to the message set are carried out in a short term. In this case, a response time in the order of a few milliseconds can be demanded. In this paper we analyse the responsiveness of the FTTCANprotocol, in particular of its synchronous messaging system. Then, a method is proposed to improve such responsiveness with regard to urgent requests for changes in the message set.

In this contribution it is demonstrated the efficiency of apodized Bragg gratings, with negative variation of the refractive index, as optical filters in wavelength division multiplexing (WDM) systems, acting simultaneously as demultiplexers and dispersion compensators. Using a negative apodized Bragg grating, with a Gaussian profile, it is possible to demultiplex a 160 Gbit/s (8×20 Gbit/s) WDM signal packed in approximately 1.5 nm (≈0.85 bit/s/Hz spectral efficiency).

This paper presents a brief description of the TRIPE III robot which won the 2000 edition of the Micro-Rato Contest. It is a reactive robot that combines several interesting features. In particular, it has a high level of H/W integration resulting in a low chip count (μC, motor drives and voltage regulator), it is capable of achieving a speed 70% higher than most similar robots and it efficiently combines beacon-following, obstacle avoidance and wall-following behaviours allowing it to profit from its speed.

The increasing demand for bandwidth in industrial automation requires the usage of high-speed networks in this field. Besides high data rates, the network must also guarantee deterministic timing behaviour in order to support real-time applications.IEEE1394, also known as FireWire™, is a relatively new high performance serial bus system, which was originally designed to connect multimedia devices. The objective of this paper is to evaluate the real-time behaviour of IEEE1394 in respect of industrial automation by analysing data transfer times and global clock support. It will be shown that IEEE1394 provides guaranteed timing constraints, and the influence of the most essential network parameters will be examined.

One of the actual problems identified in industrial systems is the representation of data related to heterogeneous devices with different proprietary characteristics. A data model designed to provide a common view of information associated to various types of devices is strongly required. An immediate advantage of such an issue would be a common view of data for activities that regard installation, configuration, maintenance, and management of the devices in a system. This paper describes the Distributed Data Repository (DDR) model that aims to provide a uniform perspective for the distributed components of an industrial system, independent of any implementation detail. To achieve this goal, STEP standard has been used. The specification of the conceptual model is based on STEP AP 212 that defines the elements necessary to describe an industrial system. The paper presents an object-oriented implementation approach that makes use of STEP Part 21 file format and STEP Standard Data Access Interface.

Ethernet’s worldwide acceptance in commercial environments has created an eagerness to expand its responsibilities on the plant floor. The network’s performance capabilities make it ideal for tasks such as data monitoring, trending, and program maintenance. However, many predict that recent technological advancements in Ethernet, including Fast Ethernet, Gigabit Ethernet and switch technology, will also enable it to handle mission critical control responsibilities currently being managed by existing industrial automation networks. Meanwhile, others contend that Ethernet has a long way to go before it can assume an expanded role in the manufacturing environment. This article provides an overview of Ethernet, describes how Ethernet networks are implemented in manufacturing today, and discusses a number of practical and important considerations regarding their implementation in the future.

The need to find solutions that would support the increasing number of users, has been stimulating many research groups to explore new techniques to increase the capacity of the mobile radio systems. This technique is nominated as SDMA. After a short introduction about GSM, this article presents a resume of some essential concepts to understand the study that was made. Then, some techniques to increase the system capacity, including the SDMA, are presented for FTDMA- and CDMA-based type systems.

ConCise is a Philips research project on Configurable Architecture Processors, which is expected to make this kind of systems cost-effective for large scale production in the near future. This article starts by presenting the ConCISe architecture. Then it describes the development of a simulator for a ConCISe processor and discusses some of the simulation results. The analysis of these results is done from a cost/performance perspective.

This Work aims to discuss, under the general frame of a static and functional model for a Neurophysiology virtual machine, a sub-set of particular problems that have been under teh author's line of work within the Neurophyssiological environment. (...)

The evolution of the telecommunication networks, in particular of the Internet, provided the growth of the new technologies and the emerging of the concept of distributed objects. This concept puts many new challenges to migration of existing applications to a distributed environment. (...)

As actividades relacionadas com o ensino e investigação que decorrem no Departamento de Electrónica e Telecomunicações da Universidade de Aveiro continuam naturalmente a encontrar nesta revista um primeiro espaço de divulgação. (...)

The requirement of automatic antenna tracking on Earth-Satellite links and approaches used to cope with the problem are discussed. The hardware and mainly the software of a cheap and reliable implemented solution for a 3,5 meter parabolic antenna are described.

This paper presents the Portuguese Experience within the IBCoBN project of the European ACTS program aiming to use CaTV networks as a communication infrastructure for interactive services. In particular, high quality videotelephony has been evaluated in a set of remote care services to support the continuance of independent living of people with special needs and to allow the development of new community support structures.

The paper reflects the Portuguese participation in CANS (Citizen Access Network and Services) Project of the European Telematics Programme which main goal was to demonstrate the usage of new technologies for improvement of contacts between the citizens and their service providers. In the paper we present the remote service developed for the Portuguese Experiment, the equipment that has been designed and implemented, and the results of the evaluation that has been performed.

An application to visualize voxel based volumes using a ray-caster is presented. This application is meant to allow studing the quality of obtained visualizations and thus the values of a set of parameters relevant to the final quality may be selected.

This is the first of two papers discussing practical issues and results on the implementation of low-cost transceivers for several wireless optical LANs, covering most physical layer elements. Target optical LANs under consideration have bit-rates varying between 4Mbps and 25Mbps, and input photodiode capacitance may vary between 10pF and 50pF. PPM modulation, either in a 4-PPM or 16-PPM format, istypically used in the physical layer. Several differential front-end topologies are presented bothin discrete and integrated (CMOS) implementations, targeting different LANs. Strategies for bandwidth improvement, interference reduction and dynamic range improvement have been used in some of these topologies. These strategies lead to a switched-gain transceiver with a transimpedance gain*bandwidth of 25THzΩ , achieved witha 10pF capacitance photodiode.

This is the second of two papers discussing practical issues and results on the implementation of low-cost transceivers for several wireless optical LANs, covering most physical layer elements. Target optical LANs under consideration have bit-rates varying between 4Mbps and 25Mbps, and input photodiode capacitance may vary between 10pF and 50pF. PPM modulation, either in a 4-PPM or 16-PPM format, is typically used in the physical layer. This paper presents circuits related with sectored receivers, clock recovery and symbol detection.  A final section presents some of the problems related with the evolution of these lowcost systems.

This paper describes a circuit able to measure Signal to Noise ratios developed for Infrared applications. The Signal to Noise ratio is of major importance in IR Sectored Receivers because it provides the basis of selection or combining of signals coming from different optical sectors. This circuit estimates the ratio of the average optical signal sensed in the photo-detector and the average noise power present in the same photo-detector, with a 50dB output dynamic range.

The Micro-Rato Contest of the University of Aveiro is a competition among small autonomous and mobile robots. Organised by the Electronics and Telecommunications Department of the University of Aveiro (DETUA), the contest aims at promoting, in a festival-like enviroment, the practical and integrated use of several subjects tipically taught in electronics courses. Along its past 4 editions, the Micro-Rato Contest has had a growing participation, either in number of teams as well as in audience. It is, today, a relatively well-known initiative in the country, particularly in universities and institutes offering degrees in robotics or in electronics.Hence, due to the popularity achieved, the present issue of Revista do DETUA devotes a section to the contest, including a description of the rules and technical specifications as well as seven short papers briefly describing some of the robots which performed best in the last edition.

Um dos grandes problemas no controlo de robôs é a detecção e desvio de obstáculos em tempo real. A criação de algoritmos para solucionar este problema depende da variedade de sensores utilizados no robô. A navegação autónoma de um robô prende-se com o desvio de obstáculo em tempo real e com o alcance de um objectivo. Esse objectivo pode ser, por exemplo, um farol a emitir um feixe de luz infravermelha ou uma determinada localização no espaço. (...)