1998

[DCA98-01]  Componentes para Construção de Interfaces Gráficas em 3D

Wu Shin Ting, Marcelo de Gomensoro Malheiros, Flávio Fernandes Navarro

Abstract:Advances in computer technology have made interactive graphics systems a practical tool in a variety of areas such as engineering, science, art, medicine, entertainment, advertising, and education. Several 2D graphics toolkits, which integrate rendering and interaction, are successfully used for the development of 2D graphics applications. Despite of the availability of 3D graphics toolkits, such as GKS, PHIGS+, and OpenGL, writing interactive 3D graphics applications is still a tedious, time-consuming, and difficult task. According to Strauss and Carey, the main problem of those 3D toolkits is that they ``are commited to display-oriented application development and provide little help for direct, 3D interaction support'' and, as a solution, they propose the toolkit OpenInventor - an ``abstract 3D object''-oriented approach - in which the 3D objects are not merely display list; the 3D objects are abstract representations that can render themselves and make geometric computations when necessary. A drawback of this ``abstract 3D object''-oriented approach is that it solely reduces the application development efforts when the 3D object information can be easily represented by the structure available in the toolkit. Otherwise, the developers must add new object representations with all the necessary geometric, visualization, and interaction operations. It again may be a non-trivial task, demanding expertise from the programmers. Furthermore, since there are no conventions for the new object code design, the reusability of these codes is arguable. As an intermediary solution of the two abovementioned approaches, this report presents an architecture on the basis of a ``smart display list''-oriented approach. The key idea of our approach is to establish a precise frontier between application data models and application-independent visualization and interaction techniques, without affecting the flexibility of 3D direct manipulations achieved by the abstract 3D object-oriented approach. Thus, it is possible to design a 3D graphics toolkit which is really responsible for the application-indenpendent functionalities. Consequently, the reusability of the toolkit is increased. An implementation of the designed 3D graphics toolkit, together with some experimental results, are also presented.

Keywords: 3D Direct Manipulation, Graphics Interface Toolkit, Computer Graphics, Human-Computer Interface

[DCA98-02]  Uma Introdução a JOIN: Um Sistema de Processamento Massivamente Paralelo na Internet

Eduardo J. Huerta Yero, Marco A. Amaral Henriques

Abstract: The processing power of computers and the network bandwidth have rapidly increased in the last years. The computers connected by Internet can offer an aggregate computing power much larger than the most advanced parallel machine. These facts open the possibility of exploiting this enormous processing power as a massively parallel computer. This technical report introduces Join, a system that aims at implementing a Massively Parallel Virtual Computer (MPVC). An MPVC can be seen as a large set of independent heterogeneous computers connected by an irregular network like Internet. Different from other approaches, Join is based on the wide availability of the Java language and easy to use interfaces that give access to Internet, and provides a way to compensate the owners of the computers participating in the system for their services.These characteristics make the proposed system capable of grouping a large number of computers and thus exploiting a large portion of the potential computing power available in the Internet.

Keywords: Parallel Processing, Distributed Processing, WWW, Java, Hypercubes

[DCA98-03]  Otimised Training Techning for Feedforward Neural Networks

Fernando José Von Zuben, Leandro Nunes de Castro

Abstract: In this technical report we describe, analyse and present the source codes for several non-linear unconstrained optimization techniques applied to supervised training of feedfoward neural networks. The functions and algorithms contained in this report were used in the simulation results presented in the masters' thesis entitled: Analyses and Synthesis of Artificial Neural Network Training Strategies. All the codes presented were developed using Matlab(r) version 4.0 and some of them were update for version 5.0. We start with a tutorial about the learning techniques and after each method is presented, its source code is given. It is not our goal to indicate directly the relative efficiency of these algorithms in a given application, instead we analyse its main characteristics and present the source codes. We illustrate the default values especification for each algorithm presenting a simple example.

Keywords: non-linear optimization, error backpropagation, Matlab(r), artificial neural networks.

[DCA98-04]  An Approach for Estimating the Number of Clusters in Multivariate Data by Self-Organizing Maps

José Alfredo F. Costa, Márcio Luiz de Andrade Netto

[DCA98-05]  Calculation of Distances Among Macro and Microcells in Cellular Systems with Doubly Reused Frequencies

Kosta Karpuzovski, Marco Aurélio Amaral Henriques

Abstract:This work describes the concept of frequency channel doubly-reuse in cellular systems, specifically the calculation of signal to interference ratio in such systems. The basic concept is to use the same frequency channel of urban cellular mobile phones by cellular phones for indoor environments using a weak transmition power. This fact creates the need to determine how interference affects the signal quality on the borders of the cells. To calculate the signal to interference ratio in a simple and precise way, it is proposed to create a huge matrix whose elements represent macro and microcells. The matrix is scanned and when a cell using the same frequency of a reference cell is found, the distance between then is calculated based on their coordinates. Because this method can find easily which cells use and which cells do not use a given frequency, it can estimate more precisely the cochannel interferences. A program for this model was developed and its results were used to verify the calculations made by other methods being developed presently.

Keywords: Double Reuse of Frequencies, Cellular Communications, Microcells

[DCA98-06]  Aumentando a Precisão e a Flexibilidade de Modelos para Sistemas Celulares com Duplo Reuso de Freqüências em Estágio Final de Instalação

Milton H. Kataoka, Marco Aurélio Amaral Henriques

Abstract:Cellular systems based on double reuse (DR) of frequencies allow the use of the same frequency band by macrocells and microcells. As a result, they achieve an enhancement in spectrum utilization efficiency when compared with systems that allocate different bands for different type of cells. Another advantage of these systems is the capability of having a single handset for use with both macrocells and microcells. In this work it is presented a new and more precise model for calculation of cochannel interference in systems employing DR, where macro and microcells are installed all over the region being considered (final stage of installation). The improvement in precision is based on two new techniques to determine (1) distances between cochannel base stations and mobile terminal and (2) regions where microcells of certain frequencies should not be installed. To obtain acceptable levels of signal-to-interference ratio with greater flexibility, this work presents also a new concept called guard ring. This ring allows a more flexible adjustment of the size of the regions mentioned in (2) above, without the requirement that the region area has to be a multiple of macrocell area, as done in previous works on this subject. Based on the new calculation model, a Java program was developed, giving more precise data about system behavior than those available previously.

Keywords: Double reuse of frequencies, Cellular communications, Microcells

[DCA98-07]  Um Modelo para Análise de Instalação Progressiva de Sistemas Celulares Baseados em Duplo Reuso de Freqüências

Cristina Enomoto, Marco Aurélio Amaral Henriques

Abstract:With the explosion in the number of cellular telephone users many problems have arised. Among them, the overload on the installed systems and the need for new frequency bands in the spectrum are noteworthy. To improve system capacity, it is a common approach to install new and small (micro) cells at the areas with great demand and not served satisfactorily by the (large) cells of a conventional system. Several commercial systems based on the microcell concept have been proposed and installed in hospitals, factories, subways and so on. The scheme of Double Reuse of Frequencies allows the conventional (macrocells) and new (microcells) systems to share the same group of channels and type of modulation. This eliminates the need of licensing new frequency bands and makes the user free from the burden of carring different handsets for different systems. Although the Double Reuse (DR) can improve the traffic capacity of cellular systems, it changes their behavior due to an increase in cochannel interference. Because of that, systems based on the DR concept have to be carefully designed. In previous works related to DR systems, there are many approximations in the system- calculation model. Such approximations aim at simplifying the calculation, but at the cost of producing errors that can be significant, depending on system parameters. In this work it is proposed a new model for the calculation of cochannel interference. The model considers a gradual increase in the number of microcells and eliminates most of the approximations that were common in previous works on this subject. A program based on this more precise model was written in C to analyse the behavior of DR systems from the initial stages (few microcells installed) to the final stage (all microcells installed and operational) of deployment. The program makes possible a more reliable analysis and shows more precisely the situation that can be found in practice.

Keywords: Double Reuse of Frequency, Cellular Telephone, Interference

[DCA98-08]  EDGE - An Extensible and Distributed Graphic Environment

Carlos Neves Lenz César, Uwe von Lukas, Wu Shin - Ting, and Bernd Kehr

Keywords: Extensible Environment, Distributed System, Collaborative Environment, 3D Graphics Interactive System