Ivanil S. Bonatti

Improving the MODEX algorithm for direction estimation

We propose a modification in the MODEX method for direction finding using array of sensors. This proposal alters the MODEX candidates for the estimation and, as a consequence, reduces the computational effort, improves the performance and preserves the optimum asymptotic efficiency for both uncorrelated and correlated (coherent) sources.

Analysis of piecewise-linear oscillators with hysteresis

This brief proposed applying the point transformation method of Andronov to analyze the different kinds of oscillation that may occur in piecewise-linear systems, of the first, second, and third order, when a relay with hysteresis is used in the feedback loop.

Driving AC motors through a long cable: the inverter switching strategy

Since the possibility of unacceptable overvoltages on the components of a power system must be anticipated, the voltage and current profiles along the line must be obtained when analyzing AC motors driven through long cables. Precise models are used in this paper to investigate the system response to voltage and current excitations in order to identify frequency-critical situations. The appropriate driving strategy is eventually obtained.

Transmission Line Modeling: A Circuit Theory Approach

As shown in this paper, the classical transmission line equations for the distributed parameters model can be obtained from standard two-port network matrices avoiding the explicit use of partial differential equations. This is performed through a lemma derived directly from the Cayley--Hamilton theorem. The main advantage of this approach is that the modeling arises naturally in the frequency domain, allowing the consideration of frequency-dependent parameters (as, for instance, the resistance and inductance variations caused by the skin effect), normally not taken into account in time domain models.

An Adaptive Run Length Encoding method for the compression of electrocardiograms

A compression method, based on the choice of a wavelet that minimizes the distortion of compression for each electrocardiogram considered, is proposed in this paper. The scaling filter used on the determination of the wavelet function is obtained from the resolution of an optimization problem, which is unconstrained since the scaling filter is parametrized in a way that the constraints applied to the scaling filter are embedded on the parameters. The coefficients of projection of the signal over the wavelet subspaces are calculated and only the most significant ones are retained, being the significant coefficients determined in order to satisfy a pre-specified distortion measure. The bitmap that informs the positions of the retained coefficients is encoded along with the values of the coefficients by using an improved version of the Run Length Encoding technique. Experiments that compare the proposed approach with other techniques illustrate the efficiency of the method.

ABCD Matrix: A Unique Tool for Linear Two-Wire Transmission Line Modelling

The aim of this note is to show that all the behaviour of a two-wire transmission line can be directly derived from the application of ABCD matrix mathematical concepts, avoiding the explicit use of differential equations. An important advantage of this approach is that the transmission line modelling arises naturally in the frequency domain. Therefore the consideration of frequency-dependent parameters can be carried out in a simple way compared with the time-domain. Some standard examples of transmission lines are analysed through the use of ABCD matrices and a case study of a balun network is presented.

A genetic algorithm to compress electrocardiograms using parameterized wavelets

A compression method, based on the choice of a wavelet that matches the electrocardiogram signal to be compressed, is proposed in this paper. The coefficients of the scaling filter that minimize the distortion of the compressed signal are used to determine the wavelet. The choice of the scaling filter is done by the parametrization of the scaling coefficients in a way that all the constraints are satisfied for any set of parameters. A genetic algorithm is used to determine the parameters that minimize the distortion of the compressed signal. The performance of the proposed algorithm is analyzed and compared with the compression using the classical wavelet Db3.

An Exponential Energy Saving Strategy to Wireless Sensor Network

Energy saving strategies for wireless sensor networks, that change the sleeping time of sensor nodes as function of activity level of the sensing field, in order to improve the trade-off between the average network energy consumption and the average data delivery delay is presented in this paper. The exponential increase or decrease of sleeping time considers the event detection frequency in the sensing field as well as the level of activity of sensor forwarding sensing data of the others sensor nodes. These strategies have been simulated and the average data delivery delay was compared with the one produced by another strategy recently reported. The simulation results show that the proposed strategy reduces the energy consumption of the sensor nodes with small degradation of the data delivery delay.

A fuzzy algorithm to solve the problem of QoS unicast routing in IP networks

In this paper, a QoS unicast routing problem is solved by means of a generalized fuzzy-constrained model. Both imprecision of the IP network state information and the fuzziness of QoS constraints are taken into account invoking fuzzy set theory. We have developed an algorithm, which is based on the classic Ford-Moore-Bellman algorithm, whose outcome is a fuzzy set of non-dominated paths. Its effectiveness is verified by comparison with results of a known crisp model.

Wireless link dimensioning: priority versus sharing

The introduction of the multiple access service GPRS (general packet radio service) on GSM networks (global system for mobile communications) increases the use efficiency of radio resource through the sharing of data and voice users on the available channels in GSM networks. A comparison of two techniques for wireless link dimensioning of telecommunications networks is presented in this paper. The synthesis models are developed considering that the resources are shared between voice and data users. Schemes considering Markovian model and priority model are presented. Traffic overload simulations were made in order to analyze the behavior of the resulting quality of service parameters.