Humberto Abdalla

Modeling device manufacturing uncertainty in Electromagnetic Simulations

This work presents a technique for modeling of the effects of manufacturing uncertainty into Electromagnetic Simulations of microwave devices. The procedure combines the Unscented Transform (UT) with EM Simulations. The use of the UT allows efficient use of computational resources for the characterization of the random variables modeling the uncertainty. The technique is validated with the modeling of tolerance errors of an assembled microstrip pseudo-elliptic filter into the response of the electromagnetic simulation.

A traffic characterization procedure for multimedia applications in converged networks

This work presents a traffic characterization procedure for traffic engineering (TE) in converged networks. An analytical model, focused in a self-similar aggregated traffic characterization is proposed, which considers QoS restrictions for delay metrics. The model, together with evolutionary techniques, is used for the optimization of the link capacity assignment task in network planning with multi-service applications. The results show that the traffic characterization model is reliable as a part of the optimization of costs in converged networks.

Design of low-pass microstrip filters based on defected ground structure

An improved periodic defected ground structure (DGS) is investigated for low-pass filter (LPF) applications. The realization in microstrip configuration consists in making the equivalence between the geometry of a DGS structure and a parallel LC resonator circuit. Initially, one filter is designed using identical DGS, equally spaced. Varying empirically the dimensions of the DGS, we obtain an improvement of frequency responses. In order to verify the performances of the proposed changes in the filter, simulations were done between the uniform periodic DGS circuit and the improved non uniform periodic DGS. The results show that the latter exhibits better stopband performance, with suppressing ripples and enlarging the bandwidth. One modified DGS filter was designed and fabricated. The measurements show good consistency with the simulated results.

Enterprise Architecture to IT Governance: An Approach Based on Component Business Model and Performance Levels

The aim of this paper is to present an approach for a model that supports IT governance and management through the alignment of business with Information Technology – IT using Enterprise Architecture concepts, considering efficiency, effectiveness and security. Firstly, a theoretical review will be done emphasizing the assumptions that support IBM‘s Component Business Model, such as specialization, governance and strategy. Then, an approach is presented for the organization’s decomposition, considering IT and business alignment. Moreover, the performance levels concept is introduced to the CBM®. Finally, a governance and management model for components to be applied in case study is presented.

Fault tolerance in IEEE 802.11 WLANs

in this paper, we address the problem of enhancing the fault tolerance of IEEE 802.11 wireless local area networks focusing on tolerating access point - AP failures. We develop a fault detection approach, which promises to be more effective to identify AP failures. In particular, we focus on the problem of overcoming APs failures working with reconfiguration of the remaining APs by changing parameters such as power level and frequency channels. Our approach consists of two main phases: Design and Fault Response. In Design phase, we deal with quantifying, placement and setting up of APs according to both area coverage and performance criteria. In Fault Response phase we consider the reconfiguration of active APs in order to deal with AP fault in the service area. Finally, we describe one of the major characteristics of the proposed architecture, which is a simple implementation in concordance with established IEEE 802.11 standards and related management systems.

Analysis of the perturbation's size and the feeding topology on the dual-mode resonator in microstrip structure using FDTD

The dual-mode resonators have characteristics that make them highly attractive for use in wireless and mobile communications systems. In this work, the method of the finite differences time domain (FDTD) is used to analyze the behavior of the structure type according to the variation of the perturbations size and to the kind of the topology feeding.

Microwave multiplexers using complementary triplexer filters

This paper describes the design procedure of a multiplexer using the complementary triplexer filter. The described technique allows one to accomplish matched structures with a large range of frequencies. The required network conditions that can be realizable with complementary filters are shown. The design procedure is developed for the bandpass and bandstop complementary filters connected at a common junction for narrow band applications. A stripline structure was employed to realize one triplexer. There is good agreement between the experimental and theoretical results.

Experiences of Applying a Blended Learning Approach to Teaching Optical Communication Systems

Blended learning consists of the combination of e-learning and a traditional education approach, and is particularly suitable to the process of transitioning towards e-learning from traditional forms of learning and teaching. This paper describes the use of the blended learning model in a course entitled ‘Optical Communications’, given in the Electrical Engineering Department at the University of Brasilia, Brazil. Throughout the article, the authors will analyse technological solutions found for the different segments which make up the implemented teaching/learning environment and the main difficulties they came across in their bid to integrate new interactive technologies into the traditional educational process. Finally, the concrete experience of applying this methodology in the course will be discussed. A survey conducted at the end of the course showed that students were satisfied with the pedagogical approach. Concerning the main elements of the blend and its efficacy, the results indicate an overall positive assessment.

Modeling and characterization for microstrip filters in the manufacturing process through the unscented transform and use of electromagnetic simulators

This paper presents the unscented transform (UT) applied to uncertainty modeling of manufacturing tolerances at the design stage of microwave passive devices. The process combines the UT with electromagnetic simulations and assumes that the numerical sources of error are negligible in comparison to the imperfections due to the manufacturing process. The technique was validated with the simulation, construction, and test of several sets of identical microstrip filters with very good results. Although the combination of UT and electromagnetic simulators was presented for microstrip filters, it can also be used for different types of microwave devices.

Local digital radio in the 26 MHz band using DRM - Results of the Brasilia field trials

Following the proposal presented by the DRM consortium, some trials have been performed worldwide in an attempt to confirm the viability of the use of the 26 MHz for local broadcasting. This paper presents the results of the field trials performed in the city of Brasilia, Brazil, in 2006. The objective of these trials was to find in which conditions the DRM signal can be well received. Tests were performed in different reception environments, both stationary and mobile, in order to verify the influence of the surroundings in the signal reception. Furthermore, an attempt was made to find the thresholds above which the reception is successful.