P.H.P. de Carvalho

Experimental study of a Wavelet-based spectrum sensing technique

In this paper, the energy detection spectrum sensing technique, based on the wavelet transform, is investigated. In order to evaluate the accuracy of the methodology, spectrum measurements were made in bands allocated for FM broadcast (88-108 MHz) and mobile services (824-835 MHz). Modifications in an existing technique were proposed in order to improve the spectrum sensing when applied in real environments.

Neural model of electrical devices for circuit simulation

In this work, a neural model for nonlinear circuit devices is proposed. This is an alternative to the modeling of complex ill-defined input-output mapping in new, not well-known structures. The neural model has been used in simulation algorithms revealing good approximation and generalization performance. The model is also been used to estimate output derivatives, which are needed in some simulation and optimization algorithms.

Hybrid Traffic Model for Multimedia Network Performance Evaluation

This work proposes a hybrid traffic model for multimedia networks as a fundamental element in a network planning optimization procedure. The proposed model uses a combination of the fBm (fractional Brownian motion) and Markovian traffic characterization procedures combined with link parameters in order to produce more accurate values of QoS metrics. The hybrid traffic model was evaluated in a network scenario that aggregates different traffic types with different combinations of Hurst parameters and variance coefficients. The results show that the QoS metrics calculated with the hybrid traffic model appear to be more accurate than the ones obtained exclusively with the fBm or the Markovian models. With these results, the proposed model appears to be useful in network planning optimization methods. .

A 2.535 GHz fully integrated Doherty power amplifier in CMOS 65nm with constant PAE in backoff

A fully integrated Doherty power amplifier at 2.535 GHz is presented in 65 nm CMOS technology with constant PAE over a 8.75dB backoff. The amplifier has 23.4 dBm output power and both PAE peaks have the same level in 25%. Both sub-amplifiers have a single-ended cascode topology and optimized input and output networks to reduce losses and correctly balance their behavior.

A general and robust method for multi-criteria design of microwave oscillators using an evolutionary strategy

This paper describes a general and robust method applied to the optimization of microwave oscillators. This method is a combination of the harmonic balance method, the device-line measurement technique and a multi-objective evolutionary optimizer. The importance of using proper harmonic loads is considered. An example shows that the multi-objective evolutionary algorithm allows the robust exploitation of the trade-off curve of the figures of merit of the oscillator.

A New Efficient and General Design Method of Oscillators Based on Genetic Algorithm and on the Device-Line Measurement Technique

This paper introduces a new optimization method applied to negative-resistance microwave oscillators. The optimization is carried out using a Genetic Algorithm associated with the Device-line Measurement technique. The circuits are simulated using a Harmonic Balance simulator. The optimization results show that the proposed method can robustly find optimal or close-to-optimal solutions.

Performance Evaluation of Shortest Path Computation for IP and MPLS Multi-service Networks over Open Source Implementation

In this work is shown a performance evaluation of two open source platforms in the case of a link failure event, both of them based on the Shortest Path Computation routing paradigm. We present the results of measures using five different traffic flows in a multi-service network. The measures consider recovery time, latency and packet losses. We also illustrate the development of a simple routine for the establishment of new LSP (Label Switched Path) based in one of the open source platforms. Considering the results of our evaluation, some ideas and work in the area that may improve the results are suggested.

narrowband fading characterization in brasilia to aid in the design of public safety communication systems

This paper presents a set of software tools focused on the characterization of the propagation environment to aid in the design of public safety communication systems. Several measurement campaigns were made to extract the statistical behavior of the narrowband fading over a mobile environment on the UHF band in the city of Brasilia. A sampling method is defined making possible the analysis for long and short term fading components. A GIS-based software was developed and used to store and automatically process the collected data. The measured data and the software were further used to evaluate the coverage of APCO-25 public safety communication system.

Extended device-line method for determination of optimum operation point of microwave oscillators

In this paper, an efficient approach to the performance prediction of microwave oscillators derived from the device-line measurement technique is described. Analyses are carried out by harmonic balance simulations. The proposed method differs from the conventional device-line measurement by allowing the representation of harmonic frequency loads besides the fundamental frequency one. This feature can increase performance measurements, such as output power and DC to RF conversion efficiency.

Experimental test results of an asynchronous DS-CDMA satellite system

In this work a satellite communication system operating in an asynchronous DS-CDMA scheme is presented. The system is submitted to a set of tests in order to verify its behavior concerning the bit error rate and the loss of synchronism as a function of the process gain and the levels of interference. An investigation on the transmission of DS-CDMA signals over a shared frequency band with QPSK narrowband signals is also performed. An analytical method to determine the capacity of shared carriers in the frequency band in a DS-CDMA scheme is presented and experimentally tested.