Juraci Ferreira Galdino
Instituto Militar de Engenharia
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Publication
Featured researches published by Juraci Ferreira Galdino.
Iet Communications | 2009
A. M. A. Filho; Ernesto Leite Pinto; Juraci Ferreira Galdino
A new variable step-size least mean squares (VSS-LMS) algorithm for the estimation of frequency-selective communications channels is herein presented. In contrast to previous works, in which the step-size adaptation is based on the instantaneous samples of the error signal, this algorithm is derived on the basis of analytical minimisation of the ensemble-averaged mean-square weight error. A very simple rule for step-size adaptation is obtained, using a small number of communication system parameters. This is another significant difference from other proposals, in which a large number of control parameters should be tuned for proper use. The algorithm here proposed is shown to be applicable to both time-varying and time-invariant scenarios. While the lack of a termination rule for step-size adaptation is a common characteristic of other schemes, the algorithm here presented adopts a criterion for stopping the step-size adaptation that assures optimal steady-state performance and leads to large computational savings. A simulation-based performance comparison with other VSS-LMS schemes is provided, including their application to maximum likelihood sequence estimation receivers using per survivor processing (MLSE/PSP). The results show that the algorithm proposed in this work has good performance characteristics and a very low computational cost, specially in the application to MLSE/PSP receivers. Besides, this algorithm is shown to be robust to changes in the signal-to-noise ratio (SNR).
IEEE Transactions on Communications | 2004
Juraci Ferreira Galdino; Ernesto Leite Pinto; M.S. de Alencar
The performance of the least mean square (LMS) algorithm on the estimation of time-varying channels is analytically evaluated, using the estimation error correlation matrix, the mean-square weight error (MSWE) and the mean-square estimation error (MSE) as parameters. Expressions for those parameters are obtained from a set of hypotheses usually adopted in the communication systems context. The channel is modeled as a wide sense stationary (WSS) discrete time stochastic field with known autocorrelation. The expressions for the steady-state MSWE and MSE are particularized for the class of WSS channel models, and an original analysis of the optimum LMS step-size parameter for usual channel models is addressed. For the sake of comparison with other works, the analytical step-size optimization for random-walk models is also considered. Several estimates of MSWE curves obtained by computer simulation are compared with analytical results for validation purposes. A very good agreement between simulated and analytical results for both the MSWE expressions and the optimum value of the LMS step-size parameter is shown.
vehicular technology conference | 2006
Waslon Terllizzie A. Lopes; Francisco Madeiro; Juraci Ferreira Galdino; Marcelo Sampaio de Alencar
The performance of wireless communications systems can be significantly improved using the modulation diversity technique, which is basically based on the combination of a suitable choice of the reference angle of an MPSK constellation with independent interleaving of the symbol components. This technique presents good performance assuming the absence of estimation errors for channels characterized by flat fading. In this paper, the performance of this technique is analyzed taking into account the effects of channel estimation errors. It is shown, by simulation, that the efficiency of this technique is maintained even under this assumption. Additionally, the impact of the Doppler effect on the system performance is treated and a tradeoff between the interleaving depth and the error probability is achieved.
IEEE Transactions on Communications | 2003
Juraci Ferreira Galdino; Ernesto Leite Pinto; Marcelo Sampaio de Alencar
This article proposes the use of denoising techniques at the receiver front-end in order to combat the effects of additive noise in digital transmission over frequency-selective channels. The proposed technique does not require knowledge of the channel impulse response, and is, therefore, potentially suitable for application in several receiver structures, including those with blind equalizers and adaptive receivers for mobile communications.
military communications conference | 2012
Marcelo Camilo; David Fernandes Cruz Moura; Juraci Ferreira Galdino; Ronaldo M. Salles
Cognitive Radio is a technology that enables the spectrum sharing in an opportunistic fashion. However, as the development of cognitive radio technology occurs, its security problems like jamming arise. In this paper, we studied the jamming attack in cognitive radio networks. We sketched a scenario comprised by a primary user, a secondary user, and a spectrum jammer (namely attacker). Since the legitimate secondary user needs to transmit control messages and data in the available channels, we derived the best combinations of the number of control and data channels to the legitimate secondary user in face of different data applications considering the quality of service requirements reliability and throughput. We also considered the device with and without power constraints.
military communications conference | 1998
Juraci Ferreira Galdino; Ernesto Leite Pinto
We address adaptive maximum-likelihood sequence estimation using per survivor processing (MLSE-PSP) over frequency selective fast fading channels. Special care is dedicated to the choice of the adaptive filtering algorithm (AFA) used in these schemes and its influence on the receiver bit error rate (BER) performance. We present an in-depth investigation of LMS and KF performance in the MLSE-PSP context. Regarding the KF algorithm, we focus attention on statistical channel models and propose the use of a second-order autoregressive (AR(2)) modeling as an alternative to the first-order autoregressive (AR(1)) modeling, which has been adopted in other works. The performance of the MLSE-PSP schemes is extensively evaluated by Monte Carlo simulation. Several experiments under conditions of varying signal-to-noise ratio (SNR), maximum Doppler shift (f/sub D/) and data block length (BL) are reported. The results presented indicate that the use of AR(2) produces remarkable performance improvement.
international conference on communications | 2002
Juraci Ferreira Galdino; Ernesto Leite Pinto; M.S. de Alencar
The performance of the least-mean-square (LMS) algorithm on the estimation of time-varying channels is analytically evaluated, using the estimation error correlation matrix and the mean square error (MSE) as parameters. Expressions for those parameters are obtained from a set of hypotheses usually adopted in the communication systems context. The channel is modeled as a wide sense stationary discrete time stochastic field with known autocorrelation. The expression for the steady state MSE is particularized assuming wide sense stationary-uncorrelated scattering (WSS-US) channel model. Several estimates of MSE curves obtained by computer simulation are compared with analytical results for validation purposes. A very good agreement between simulated and analytical results is shown.
Digital Signal Processing | 2013
C. C. dos Santos; Juraci Ferreira Galdino; Ernesto Leite Pinto
An analysis of the optimization of the LMS (Least Mean Square) algorithm for the estimation of time-varying and frequency-selective communication channels is here presented. In contrast to previous works on this subject, in which the step-size optimization is rooted on the assumption of specific channel models, this analysis is much more generic in respect to the modelling of both the Doppler and delay spreadings. Besides, it addresses not only the steady-state performance of channel estimators, but also their transient behaviors. Several useful approximate expressions for designing LMS-based channel estimators are herein derived and validated by comparisons with simulation and with a previous work on this kind of analysis. These expressions are remarkably suitable for practical application, since they depend on a few parameters of the communication system. With regard to the channel variability, the knowledge of the Doppler spread parameter is shown to be enough to optimize the performance of a LMS channel estimator using the analysis here presented.
Journal of Computer Networks and Communications | 2012
David Fernandes Cruz Moura; Fabrício Alves Barbosa da Silva; Juraci Ferreira Galdino
This paper presents case studies of attacks aimed at tactical software defined radios based on a classification with the most common sources of vulnerabilities, classes of attacks, and types of intrusions that military radio sets may suffer. Besides that, we also describe how attack mitigation strategies can impact the development of SDR infrastructures. By using such approach, we identify several possible sources of vulnerabilities, attacks, intrusions, and mitigation strategies, illustrating them onto typical tactical radio network deployment scenarios, as an initial and necessary step for the definition of realistic and relevant security requirements for military software defined radio applications.
IEEE Communications Letters | 2009
David Fernandes Cruz Moura; Ronaldo M. Salles; Juraci Ferreira Galdino
In this paper, we introduce the MM ¿k=1 K PP/DY/1/B queue, which encompasses typical features held in modern wireless combat networks, like time-correlated interarrival times, deterministic-time batch services and finite-buffer capacity. Steady-state solutions, performance measures of interest and an application case study are presented and verified through simulations.