arXiv subjects

José Cândido Silveira Santos Filho

Publications and source records attributed to José Cândido Silveira Santos Filho.

7 recordsLinked to original sources

arXiv2026

A Unified Framework for Mixed Fading Sums

This paper introduces a unified analytical framework that yields exact, compact, and tractable solutions for the probability density function (PDF) and cumulative distribution function (CDF) of the sum of a broad class of mixed independent positive random variables. To demonstrate its breadth and practical value, the proposed framework is applied to the longstanding problem of deriving the exact statistics of mixed sums of fading variates. Specifically, we derive novel expressions for the PDF and CDF of sums of Gaussian-class and non-Gaussian-class fading distributions, thereby covering a plethora of conventional, generalized, and recently introduced fading models. The framework accommodates independent and identically distributed (i.i.d.) sums, independent but not necessarily identically distributed (i.n.i.d.) sums, and mixed-type sums. Furthermore, we conduct an exact performance analysis of equal-gain combining and maximal-ratio combining diversity receivers operating under mixed fading conditions. The proposed framework provides an exact and versatile analytical foundation for channel modeling and performance evaluation across a wide range of wireless fading scenarios. Finally, we introduce the novel $α$-$μ$ \textit{Mixture distribution} that unifies all Gaussian-class fading models.

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arXiv2025

Impact of Fading Correlation on the High-SNR Regime of Reconfigurable Intelligent Surfaces

This paper addresses three critical limitations in previous analyses of RIS-aided wireless systems: propagation environments with fixed diversity gain, restricted spatial correlation profiles, and approximation methods that fail to capture the system behavior in the high signal-to-noise ratio (SNR) regime. To overcome these challenges, we conduct an exact asymptotic analysis focused on the left tail of the SNR distribution, which plays a critical role in high-SNR system performance. Additionally, to account for general correlation profiles and fading environments with variable diversity and coding gains, we consider arbitrarily correlated Nakagami-m fading channels. The analytical results show that fading correlation induces a horizontal shift in the asymptotic behavior -- represented as a straight line in the log-dB scale -- of the PDF and CDF, displacing these curves to the left. The asymptotic linear coefficient quantifies this shift, while the angular coefficient remains unaffected. Moreover, the results reveal that the high sensitivity of the linear coefficient to correlation arises from the aggregated contribution of all marginal asymptotic terms, effectively capturing each channel's correlation characteristics.

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arXiv2022

Performance analysis of downlink MIMO-NOMA systems over Weibull fading channels

This work analyzes the performance of a downlink multi-user multiple-input multiple-output (MU-MIMO) non-orthogonal multiple access (NOMA) communications system. To reduce hardware complexity and exploit antenna diversity, we consider a transmit antenna selection (TAS) scheme and equal-gain combining (EGC) receivers. Further, we consider Weibull-distributed fading channels to account for non-linearities of the propagation medium and to cover, as special cases, important fading scenarios such as Rayleigh and exponential models. Performance metrics such as the outage probability (OP) and the average bit error rate (ABER) are derived in an exact manner. An asymptotic analysis for the OP and for the ABER is also carried out. Moreover, we obtain exact expressions for the probability density function (PDF) and the cumulative distribution function (CDF) of the end-to-end signal-to-noise ratio (SNR). Interestingly, our results indicate that, except for the first user (nearest user), in a high-SNR regime the ABER achieves a performance floor that depends solely on the user's power allocation coefficient and on the type of modulation, and not on the channel statistics or the amount of transmit and receive antennas. To the best of the authors' knowledge, no performance analyses have been reported in the literature for the considered scenario. The validity of all our expressions is confirmed via Monte-Carlo simulations.

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arXiv2021

New Findings on GLRT Radar Detection of Nonfluctuating Targets via Phased Arrays

This paper addresses the standard generalized likelihood ratio test (GLRT) detection problem of weak signals in background noise. In so doing, we consider a nonfluctuating target embedded in complex white Gaussian noise (CWGN), in which the amplitude of the target echo and the noise power are assumed to be unknown. Important works have analyzed the performance for the referred scenario and proposed GLRT-based detectors. Such detectors are projected at an early stage (i.e., prior to the formation of a post-beamforming scalar waveform), thereby imposing high demands on hardware, processing, and data storage. From a hardware perspective, most radar systems fail to meet these strong requirements. In fact, due to hardware and computational constraints, most radars use a combination of analog and digital beamformers (sums) before any estimation or further pre-processing. The rationale behind this study is to derive a GLRT detector that meets the hardware and system requirements. In this work, we design and analyze a more practical and easy-to-implement GLRT detector, which is projected after the analog beamforming. The performance of the proposed detector is analyzed and the probabilities of detection (PD) and false alarm (PFA) are derived in closed form. Moreover, we show that in the low signal-to-noise ratio (SNR) regime, the post-beamforming GLRT detector performs better than both the classic pre-beamforming GLRT detector and the square-law detector. This finding suggests that if the signals are weak, instead of processing the signals separately, we first must to reinforce the overall signal and then assembling the system's detection statistic. At last, the SNR losses are quantified, in which the superiority of the post-beamforming GLRT detector was evidenced as the number of antennas and samples increase.

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arXiv2019

On the Binary Lossless Many-Help-One Problem with Independently Degraded Helpers

Although the rate region for the lossless many-help-one problem with independently degraded helpers is already "solved", its solution is given in terms of a convex closure over a set of auxiliary random variables. Thus, for any such a problem in particular, an optimization over the set of auxiliary random variables is required to truly solve the rate region. Providing the solution is surprisingly difficult even for an example as basic as binary sources. In this work, we derive a simple and tight inner bound on the rate region's lower boundary for the lossless many-help-one problem with independently degraded helpers when specialized to sources that are binary, uniformly distributed, and interrelated through symmetric channels. This scenario finds important applications in emerging cooperative communication schemes in which the direct-link transmission is assisted via multiple lossy relaying links. Numerical results indicate that the derived inner bound proves increasingly tight as the helpers become more degraded.

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arXiv2018

Correspondence Analysis of Government Expenditure Patterns

We analyze expenditure patterns of discretionary funds by Brazilian congress members. This analysis is based on a large dataset containing over $7$ million expenses made publicly available by the Brazilian government. This dataset has, up to now, remained widely untouched by machine learning methods. Our main contributions are two-fold: (i) we provide a novel dataset benchmark for machine learning-based efforts for government transparency to the broader research community, and (ii) introduce a neural network-based approach for analyzing and visualizing outlying expense patterns. Our hope is that the approach presented here can inspire new machine learning methodologies for government transparency applicable to other developing nations.

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arXiv2018

How Reliable and Capable is Multi-Connectivity?

Multi-connectivity (MCo) is considered to be a key strategy for enabling reliable transmissions and enhanced data rates in fifth-generation mobile networks, as it provides multiple links from source to destination. In this work, we quantify the communication performance of MCo in terms of outage probability and throughput. For doing so, we establish a simple, yet accurate analytical framework at high signal-to-noise ratio (SNR), in which the number of links, the spectral efficiency, the path loss, and the SNR are incorporated, giving new insights into the potentials of MCo as compared with single-connectivity (SCo). These are our main contributions: (1) finding the exact coding gain of the outage probability for parallel block-fading channels; (2) quantifying the performance improvement of MCo over SCo in terms of SNR gain; and (3) comparing optimal and suboptimal combining algorithms for MCo at the receiver side, namely joint decoding, selection combining, and maximal-ratio combining, also in terms of SNR gain. Additionally, we apply our analytical framework to real field channel measurements and thereby illustrate the potential of MCo to achieve high reliability and high data rates in real cellular networks.

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