Papers by Marcelo De Alencar
2014 22nd European Signal Processing Conference (EUSIPCO), 2014
Cognitive radio is one of the most promising techniques of wireless communications, due to its ma... more Cognitive radio is one of the most promising techniques of wireless communications, due to its many applications. Cognitive networks have the capability to congregate different cognitive users via cooperative spectrum sensing. Examples of cognitive networks can be found in important and different applications, such as digital television and wireless sensor networks. The objective of this paper is to analyze how signal processing techniques are used to provide reliable performance in such networks. Applications of signal processing in cognitive networks are presented and detailed.
Anais do XXVI Simpósio Brasileiro de Telecomunicações, 2008
Resumo-Neste trabalho são apresentados os resultados da investigação de transmissão do serviço de... more Resumo-Neste trabalho são apresentados os resultados da investigação de transmissão do serviço de televisão móvel em redes UMTS/WCDMA FDD. Para tanto, foram realizadas simulações e obtidos alguns indicadores de desempenho, como a razão entre a interferência de outras e da própria célula, fator de carga, número de usuários atendidos simultaneamente, razão portadora-interferência e potência média de transmissão das estações radiobase.
Anais do XXII Simpósio Brasileiro de Telecomunicações
This paper presents the allocation of cells of a mobile cellular network as a dynamic ordered ord... more This paper presents the allocation of cells of a mobile cellular network as a dynamic ordered orderk multiplicatively weighted Voronoi diagram. The farthest neighbor search is applied to the channel allocation scheme of a temporary base station. Whenever a temporary base station is deployed, its power, antenna height, group of channels and other features are to be configured. The nearest and the farthest point search are applied to the problem of finding the nearest and the farthest base station surrounding the temporary station, in order to identify the group of channels to be allocated. Proximity relations are acquired from the Voronoi diagram and used in solving the problem of allocating channels with a minimum cochannel interference.
Revista Principia - Divulgação Científica e Tecnológica do IFPB
Devido à crescente demanda pelos sistemas de comunicação móveis sem fio, as operadoras de comunic... more Devido à crescente demanda pelos sistemas de comunicação móveis sem fio, as operadoras de comunicações móveis estão procurando reduzir o tamanho de suas células, ao máximo, visando ao aumento de suas respectivas capacidades [...].
Journal of Microwaves, Optoelectronics and Electromagnetic Applications
This paper presents a model that uses bio-inspired optimization algorithms to control of the mutu... more This paper presents a model that uses bio-inspired optimization algorithms to control of the mutual coupling (MC) in Multiple-Input Multiple-Output (MIMO) systems. The method promotes an increase in the channel throughput and a reduction in the distance among the array elements, searching values less than a half wavelength. A microstrip antenna design, at the frequency of 26 GHz, is used as a prototype for MIMO system testing and performance analysis. Genetic Algorithm (GA) is used to optimize, to determine the antenna physical parameters and to improve its performance. The mutual impedance concept is used to model the MC. The particle swarm optimization (PSO) algorithm is used to optimize the channel throughput and to reduce the distance between the elements. Simulation results show that it is possible to obtain a MIMO system performance improvement of 11.1% in channel throughput, the microstrip width is reduced by 14.5% and the distance among the elements can be reduced by 23.7%, considering the MC. Index Terms− Bio-inspired algorithms, channel throughput, MIMO systems, mutual coupling. I. INTRODUCTION In recent years, the number of mobile data network users has grown at a steady pace worldwide, and this has largely increased the number of connections and equipments. According to the Group Speciale Mobile Association (GSMA), there were 5.3 billion mobile users around the world by the end of 2021. The Fourth Generation (4G) network has 58% of connections (excluding licensed cellular technology and Internet of things) and Fifth Generation (5G) network technology is already in use in 70 countries around the world [1]. The MIMO technique, which uses antenna arrays in transmission and reception, increases the transmission rate and is poised to achieve the radio channel transmission limits required in modern wireless networks [2]. The concept of MIMO systems brings new challenges for fifth generation (5G) networks, with the massive increase in the number of antennas and the corresponding research associated with its performance [3]-[5]. Some researchers use GA to optimize antennas, in microstrip design, by changing their physical dimensions and the format of the patches array [6], or by the minimization and evaluation of a single rectangular patch [7], [8]. In [9], the authors also use GA for linear optimization of an antenna array.
Anais do XIX Simpósio Brasileiro de Telecomunicações
Anais do XIX Simpósio Brasileiro de Telecomunicações
Admitindo a ausência de erros de estimação de canal, pode-se melhorar significativamente o desemp... more Admitindo a ausência de erros de estimação de canal, pode-se melhorar significativamente o desempenho de sistemas de comunicação digital, em canais com desvanecimento, combinando-se rotação de constelações e entrelaçamento das componentes dos símbolos transmitidos. Este artigo apresenta uma análise de desempenho desta recente técnica considerando a utilização de esquemas de estimação de canal no receptor. Em particular, a avaliação de desempenho do sistemaé feita utilizando o algoritmo LMS (Least Mean Square) e de um PLL (Phase-Lock Loop) para estimar o módulo e da fase do canal, respectivamente. Mostra-se por meio de simulações, que a técnicaé eficaz mesmo considerando a presença de erros de estimação. Adicionalmente, o impacto do efeito Doppler sobre o sistemaé investigado estabelecendo-se um compromisso entre atraso e desempenho para o esquema proposto.
Anais do XVIII Simpósio Brasileiro de Telecomunicações
A serious problem related to the transmission of vectorquantized images through noisy channels is... more A serious problem related to the transmission of vectorquantized images through noisy channels is that whenever errors occur, the nearest neighbor rule is broken. As a consequence, very annoying blocking e ects may appear in the reconstructed images. In the present work, a simple and fast method for organizing the vector quantization (VQ) codebooks is presented. The key idea behind the proposed method is to ensure that similar (dissimilar) binary representations of the indexes of the codevectors correspond to similar (dissimilar) codevectors themselves. It is shown that the organized codebooks improve the performance of the transmission system in the sense that they lead to reconstructed images with better quality when compared to the ones obtained by using non-organized codebooks.
Anais do XVIII Simpósio Brasileiro de Telecomunicações
This paper presents a modi cation on the original spacetime code scheme with the objective of imp... more This paper presents a modi cation on the original spacetime code scheme with the objective of improving its performance. Interleaving and rotation of the signal constellation, which do not a ect the performance of the system for the additive white Gaussian noise channel, are introduced. The spectrum e ciency of the scheme is not altered and the modi cation of the modulator is very simple. Simulations are carried out to show that the error probability is improved, for the proposed scheme, in a fading environment.
Anais do XIX Simpósio Brasileiro de Telecomunicações
Anais do XX Simpósio Brasileiro de Telecomunicações, 2003
Resumo-Neste trabalho são apresentadas expressões exatas para a probabilidade de erro de bit (BEP... more Resumo-Neste trabalho são apresentadas expressões exatas para a probabilidade de erro de bit (BEP) dos esquemas de modulação 64-QAM e-PAM para um canal com desvanecimento Rayleigh. Diferentemente das abordagens apresentadas na literatura, o canal de comunicaçõesé visto como um canal sujeito ao ruído aditivo, queé modelado como a razão entre uma variável aleatória (v.a.) gaussiana e uma v.a. Rayleigh. A partir da função cumulativa de probabilidade (FCP) do processo que modela esse ruído aditivo são obtidas expressões exatas para a BEP desses esquemas de modulação. Palavras-Chave-Comunicações móveis, canal com desvanecimento Rayleigh, probabilidade de erro de bit, QAM, PAM.
Tsinghua Science and Technology
This paper presents a unified theoretical analysis of the energy detection of Gaussian and M-PSK ... more This paper presents a unified theoretical analysis of the energy detection of Gaussian and M-PSK signals in Ä ,˛ , and Á fading channels at the output of an energy detector subject to impulsive noise (Bernoulli-Gaussian model). As a result, novel, simple, and accurately approximated expressions for the probability of detection are derived. More precisely, the generalized Gauss-Laguerre quadrature is applied to approximate the probability of detection as a simple finite sum. Monte Carlo simulations corroborate the accuracy and precision of the derived approximations. The results are further extended to cooperative energy detection with hard decision combining information.
Anais do 2002 International Telecommunications Symposium
This paper presents a performance analysis of two QPSK detection schemes for flat Rayleigh fading... more This paper presents a performance analysis of two QPSK detection schemes for flat Rayleigh fading channels. Closed-form expressions for the bit error probability of both schemes are obtained. It is shown that they present the same error probability and a complexity analysis is carried out to determine the best scheme in terms of the number of operations (multiplications, divisions, subtractions and comparisons) executed by each detector.
Anais do XX Simpósio Brasileiro de Telecomunicações
Resumo-Neste artigoé apresentada uma nova expressão, fechada e exata, para a probabilidade de err... more Resumo-Neste artigoé apresentada uma nova expressão, fechada e exata, para a probabilidade de erro de bit (BEP, bit error probability) do esquema-QAM (-ary quadrature amplitude modulation) para um canal com desvanecimento Rayleigh. Tambémé obtida uma nova expressão, fechada e exata, para a BEP do esquema R-QAM (rectangular QAM) arbitrário sujeito ao desvanecimento Rayleigh.
Proceedings of the 17th ACM Symposium on Performance Evaluation of Wireless Ad Hoc, Sensor, & Ubiquitous Networks
This article presents a mathematical modelling, using stochastic analysis, of the effect of an in... more This article presents a mathematical modelling, using stochastic analysis, of the effect of an interference buildup caused by a sudden increase in the number of users that access a digital cellular communication system. For such an increase in power, a heavy tail probability distribution is generated, producing an expected increase in the error probability during the adaptation process.
Anais do XXVII Simpósio Brasileiro de Telecomunicações
Resumo-Os arranjos de antenas fornecem uma diretividade elevada e controlável,útil para sistemas ... more Resumo-Os arranjos de antenas fornecem uma diretividade elevada e controlável,útil para sistemas de comunicações. Projetos desse tipo não são triviais, devidoà característica não-linear dos arranjos nos diversos campos de aplicações, requerendo o uso de técnicas de otimização, como os algoritmos supervisionados LMS (least mean square) e RLS (recursive least square). Com o propósito de otimizar o controle eletrônico da resposta espacial de arranjos de antenas por algoritmos supervisionados foi desenvolvida uma ferramenta computacional capaz de posicionar o lóbulo principal e rejeitar interferências com direções de chegada conhecida, considerando os efeitos do acoplamento mútuo entre os elementos do arranjo. Palavras-Chave-Arranjo de antenas, Acoplamento mútuo, Antenas adaptativas, Resposta espacial.
IEEE Access
Ultra densification of the number of antennas combined with the use of large bandwidths in the mi... more Ultra densification of the number of antennas combined with the use of large bandwidths in the millimeter wave (mmWave) spectrum is considered one of the main methodologies to achieve the quality of service requirements for future generations of wireless communications. Massive multiple-input multiple-output (mMIMO) cell-free (CF) systems have a large number of access points (APs) distributed in the coverage area, serving simultaneously a smaller number of users consuming the same time-frequency resources. In order to support realistic CF networks designs, this work proposes a performance analysis based on ray tracing simulations. The propagation modeling considers reflection, diffraction, diffuse scattering, atmospheric molecular absorption and foliage and rainfall losses. CF networks with APs equipped with multiple antennas operating in the 26 GHz, 38 GHz and 73 GHz bands are evaluated. From the simulation results, the communication channel is characterized and parameterized. Different performance analysis of CF networks are performed, based on downlink spectral efficiency. In addition, the performance of CF networks in rainy environments is evaluated, and it has been observed that this architecture promotes resistance to the effect of rain attenuation. INDEX TERMS Cell-free, massive MIMO, millimeter wave, ray tracing, spectral efficiency.
arXiv (Cornell University), Jan 27, 2022
The paper considers a queueing system with limited processor sharing. No more than n jobs may be ... more The paper considers a queueing system with limited processor sharing. No more than n jobs may be served simultaneously. This system may be used for modeling bandwidth sharing in wireless communication systems and processes of service in computer networks. If there are n jobs in the considered queueing system and a new job arrives, then the arriving job is lost or the service of a job is interrupted and this job is lost. We study two rules to choose the job to be lost. In accordance with one of these rules, the job with the shortest remaining length is lost. Relations are obtained between the state probabilities of considered system and the state probabilities of the corresponding unlimited processor sharing system. These relations allows to compute the state probabilities for considered system if the state probabilities for the unlimited processor sharing system are known.
AEU - International Journal of Electronics and Communications, 2021
Abstract The rapidly increasing data demand from current Internet services, such as cloud computi... more Abstract The rapidly increasing data demand from current Internet services, such as cloud computing and high-quality video streaming, is raising the pressure on network operators to provide reliable high-speed connections while keeping costs low. Without having to rely on the bandwidth expansion of optical waveguides or modulation level efficiency, one of the ways to increase spectral efficiency of a network is by the optimal utilization of already existing resources. For elastic optical networks (EON) this can be solved by the Routing, Modulation and Spectrum Assignment (RMSA). However, another problem arises, due to the nature of computer network traffic, that makes it difficult to assess the longevity of physical components and to plan a network to serve a maximum amount of bandwidth demand for predetermined time span. To help alleviating these problems, this paper presents an investigation of a novel technique for resource planning and consume estimation based on simulations. First, traffic matrix prediction is made using recurrent neural networks (RNN), and then simulations are ran to estimate the consumed bandwidth for a point in time. For the traffic forecasting, real traffic data has been used to train the RNN, obtained from an anonymous dataset containing the traffic history of the ABILENE and GEANT networks from the years 2004–2005, which is a relatively recent available dataset. Furthermore, heuristic algorithms are proposed to apply the RMSA to the predicted traffic, in a quasi-optimal manner, in order to minimize the use of network resources for future traffic, by releasing available capacity in the existing optical fiber links in an incremental traffic approach. The results show that the proposed RNN models are indeed capable of predicting the traffic matrices a month ahead, with low mean squared error. RMSA simulations were also performed using heuristics in order to estimate the consumed bandwidth in the context of EON networks, revealing that, for the proposed heuristics, the results favor the shortest path routing heuristic over the load balancing heuristic for a long-term bandwidth open capacity maximization and better resource savings.
ITS'98 Proceedings. SBT/IEEE International Telecommunications Symposium (Cat. No.98EX202)
The Renyi entropy of order α can provide information on the minimum and maximum values of a proba... more The Renyi entropy of order α can provide information on the minimum and maximum values of a probability distribution p=min{p1 ,p2,...,pN} and p=max(p1,p2 ,...,pN). The absolute minimum valve of a given probability distribution is shown to be related to the limit of the Renyi entropy, as α→-∞, or p=2-limα→-∞Hα(P). The absolute maximum valve is given by p=2-limα→∞Hα(P)
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Papers by Marcelo De Alencar