Journal of Communication and Information Systems 2020-09-24T10:05:32-03:00 Rausley A. A. de Souza and José Cândido S. Santos Filho Open Journal Systems <p>The Journal of Communication and Information Systems (JCIS) features high-quality, peer-reviewed technical papers in several areas of communications and information systems. The JCIS is jointly sponsored by the Brazilian Telecommunications Society (SBrT) and the IEEE Communications Society (ComSoc). As from June 2020, Prof. Rausley Adriano Amaral de Souza from National Institute of Telecommunications (Inatel) and Prof. José Cândido Silveira Santos Filho from University of Campinas (UNICAMP) are the Editors-in-Chief of the JCIS.&nbsp;</p> <p>There are no article publication or submission charges. Previous editions of the JCIS can be accessed <a href="/index.php/JCIS/issue/archive" target="_blank" rel="noopener">here</a>.</p> <p>This is an open access journal which means that all content is freely available without charge to the user or his/her institution, permanently accessible online immediately upon assignment of the DOI. Users are allowed to read, download, copy, distribute, print, search, or link to the full texts of the articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This is in accordance with the BOAI definition of open access.</p> <p>ISSN: 1980-6604</p> A Hybrid Firefly-Genetic Algorithm for Planning of Optical Transport Networks 2020-09-24T10:05:32-03:00 Bruno Quirino de Oliveira Marcos Antônio de Sousa Flávio Henrique Teles Vieira <p class="Abstract"><span lang="EN-US">The network design is a well-known combinatorial optimization problem that is classified as NP-Hard. The main purpose of design is often the same, to allocate and size available resources in the most possible efficient way in terms of budget, considering optimization models oriented towards minimizing costs. In this paper, it is proposed to use a hybrid optimization method called Hybrid Firefly-Genetic Algorithm to solve the Integer Linear Programming (ILP) problem, for Optical Transport Network (OTN) planning, considering cost minimization. The method combines the discrete firefly algorithm with the standard genetic algorithm. To apply this method, first it is proposed a mathematical formulation for the optical network planning problem. The other novelty of the proposed model is that it accomplishes the optical network design with the possibility of multiple destinations of the demand traffic matrix and with dynamic allocation of transmission systems modularity. Computational experiments are carried out to evaluate the performance of the hybrid Firefly-Genetic algorithm. The results show that the proposed algorithm outperforms other metaheuristics described in the literature.</span></p> <p>&nbsp;</p> 2020-09-24T10:05:32-03:00 ##submission.copyrightStatement## An open-source end-to-end ASR system for Brazilian Portuguese using DNNs built from newly assembled corpora 2020-09-01T16:46:22-03:00 Igor Macedo Quintanilha Sergio Lima Netto Luiz Wagner Pereira Biscainho <p>In this work, we present a baseline end-to-end&nbsp;system based on deep learning for automatic speech recognition&nbsp;in Brazilian Portuguese. To build such a model, we employ&nbsp;a speech corpus containing 158 hours of annotated speech&nbsp;by assembling four individual datasets, three of them publicly&nbsp;available, and a text corpus containing 10.2 millions of sentences.&nbsp;We train an acoustic model based on the DeepSpeech 2 network,&nbsp;with two convolutional and five bidirectional recurrent layers. By&nbsp;adding a newly trained 15-gram language model at the character&nbsp;level, we achieve a character error rate of only 10.49% and a&nbsp;word error rate of 25.45%, which are on a par with other works&nbsp;in different languages using a similar amount of training data.</p> 2020-09-01T16:46:22-03:00 ##submission.copyrightStatement## Analysis of Acoustic Feedback Cancellation Systems based on Direct Closed-Loop Identification 2020-08-25T21:02:57-03:00 Bruno Catarino Bispo Cézar F. Yamamura Wellington M. S. Nogueira Edson A. R. Theodoro Pedro Miguel Rodrigues <div class="page" title="Page 1"> <div class="layoutArea"> <div class="column"> <p>This work presents, using the least squares estimation theory, a theoretical and experimental analysis on the performance of the standard adaptive filtering algorithms when applied to acoustic feedback cancellation. Expressions for the bias and covariance matrix of the acoustic feedback path estimate provided by these algorithms are derived as a function of the signals statistics as well as derivatives of the cost function. It is demonstrated that, in general, the estimate is biased and presents a large covariance because the closed-loop nature of the system makes the cross-correlation between the loudspeaker and system input signals non-zero. Simulations are carried out to exemplify the results using speech signals, a long acoustic feedback path and the recursive least squares algorithm. The results illustrate that these algorithms converge very slowly to a solution that is not the true acoustic feedback path. The relationship between the performance of the adaptive filtering algorithms and the aforementioned cross-correlation is proven by varying the signal-to-noise ratio and the delay introduced by the forward path.</p> </div> </div> </div> 2020-08-25T21:02:57-03:00 ##submission.copyrightStatement## Frequency Selective Surface Microwave Absorber for WLAN Applications 2020-07-17T09:11:00-03:00 Thais Carvalho Areias Roberta N. G. Carvalho Mauricio Weber Benjó da Silva Leni J. Matos José Jaime G. Peixoto Neto Antônio Luiz P. S. Campos Alfredo Gomes Neto <p>Many researchers are studying electromagnetic wave absorbers. This is mainly due to the large number of existing wireless systems. The absorbers find numerous applications, from commercial to military systems. Allied to this, also the interest in Frequency Selective Surfaces (FSS), which are, basically, spatial filters, grows. Thus, this work proposes the use of FSS to design electromagnetic absorbers. In this study, Altair FEKO software was used. A prototype is built to validate the analysis performed. A good agreement between the numerical and experimental results is observed. Furthermore, measured results show that the absorber panel suppresses reflection (below – 10 dB) from 1.98 GHz to 3.08 GHz, covering the entire ISM band.</p> 2020-07-17T09:11:00-03:00 ##submission.copyrightStatement## Unified Scheduling Framework for Dual Connectivity in Multi-RAT NSA 5G Networks 2020-07-13T18:06:56-03:00 Roberto Pinto Antonioli Diego Aguiar Sousa Emanuel Bezerra Rodrigues Igor Moaco Guerreiro Carlos Filipe Moreira e Silva Tarcisio Ferreira Maciel Francisco Rodrigo Porto Cavalcanti <p>Supporting the dual connectivity technology in non-stand-alone 5G scenarios involves three main functionalities: a user device (UD)-base station (BS) association (UBA) mechanism, a flow control algorithm (FCA) to determine the data split transmitted by each BS and radio resource management (RRM) algorithms. However, previous works only focused on the design of at most two of these functionalities. In this<br>letter, we go beyond and design a unified scheduling framework including the three aforementioned functionalities. The proposed framework targets the user satisfaction maximization and runs in a completely decentralized fashion, where the UBA algorithm runs independently at each UD, the FCA is executed at the master LTE BS and the RRM is performed individually by each BS. Simulations show the incremental gains of each proposed functionality as well as the total gain of the unified framework.</p> 2020-07-13T18:06:56-03:00 ##submission.copyrightStatement## Coexistence Analysis Between 5G NR and TVRO in C-Band 2020-07-13T11:03:27-03:00 Luciano Camilo Alexandre Lucas de Oliveira Veiga Agostinho Linhares José Reis Pinto Moreira Marcelo Abreu Arismar Cerqueira Sodré Junior <p class="Abstract"><span lang="EN-US">This work reports a coexistence analysis between 5G New Radio (5G NR) and Satellite Television Receive Only (TVRO) in C-Band. The coexistence experiments were based on the two following systems: broadcast of analog and digital TV channels, received by a 1.7 meters parabolic antenna pointed to the Star One C2 geostationary satellite from Embratel; 100 MHz-bandwidth 5G NR link at 3.55 GHz with two printed logperiodic antennas. The performance analysis has been carried out as a function of the TV channel quality signal, by means of varying the 5G power level at vertical polarization. Measured spectra of either RF and IF signals are presented for demonstrating a probable interference problem due to the installation of 5G base stations close to TVRO user homes. For instance, there are still 22 million TVRO users in Brazil and 120 million homes attended by C-Band satellites in United States for radio and TV services.</span></p> <p>&nbsp;</p> 2020-07-13T10:59:46-03:00 ##submission.copyrightStatement## Optimized Energy Consumption for Slotted Aloha and CSMA/CA Multihop Ad Hoc Networks 2020-07-09T18:23:36-03:00 Bruna Alves da Silva Renato Mariz de Moraes <p>Ad hoc and wireless sensor networks are characterized by their ability to monitor phenomena in the most adverse scenarios. However, to perform well, these networks need to be self-adjusting and save energy. In general, these networks operate without human interference and require strategies to provide longer operating life. This paper investigates the energy consumption in a random multihop ad hoc network, comparing the slotted Aloha with the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) implemented in the IEEE 802.11 Distributed Coordination Function (DCF) as medium access control (MAC) protocols. We obtain the optimal transmission power as a function of physical and link layers parameters which results the optimized energy consumption per successfully transmitted bit. In this paper, we find that there are values of these parameters that can be used to extend the battery life of wireless communication devices comparing the Aloha and CSMA/CA performance.</p> 2020-07-09T18:23:36-03:00 ##submission.copyrightStatement## Low-Complexity Tree-Based Iterative Decoding for Coded SCMA 2020-07-07T15:28:31-03:00 Ana Luiza Scharf Bartolomeu Uchˆoa-Filho Bruno Fontana da Silva Didier Ruyet <p>Sparse Code Multiple Access (SCMA) is a powerful multiple access technique for future generations of wireless communication where users are allowed to transmit through pre-defined channel resources with a controlled degree of collision. The base-station then recovers all the users' data through some iterative method. The well-known Message-Passing Algorithm (MPA) has excellent performance but has exponential decoding complexity. Alternative decoding algorithms, such as MPA in the log-domain (Log-MPA), have been proposed in the literature aiming to reduce the decoding complexity while not significantly decreasing performance. In recent work, the authors proposed a modification in the conventional Log-MPA by exploring a tree structure associated with the decoding equations. By properly avoiding symbols with low reliability, a pruned tree is obtained, yielding an arbitrary trade-off between performance and complexity in the joint detection. In the present work, we extend this contribution by showing that the advantages of the tree-based decoding algorithm are magnified when SCMA is coupled to an error-correcting code, in particular, a Low-Density-Parity-Check (LDPC) code. Through computer simulations, we show that an improved performance-decoding complexity trade-off is obtained.</p> 2020-07-07T15:28:31-03:00 ##submission.copyrightStatement## Asymptotic System Performance over Generalized Fading Channels with Application to Maximal-Ratio Combining 2020-07-02T16:48:47-03:00 Francisco Raimundo Albuquerque Parente Flavio du Pin Calmon José Cândido Silveira Santos Filho <p>The performance of wireless communications systems is affected by many aspects of the fading phenomenon, such as clustering,&nbsp;nonlinearity, scattered waves, and line of sight. Even though several&nbsp;fading models exist which address a multitude of propagation conditions, in many cases the fading statistics or&nbsp;the associated system performance cannot be obtained in a closed&nbsp;form. In such cases, it is difficult to decipher how each physical aspect of fading impacts the system performance. In this work, we propose a unified asymptotic characterization at high signal-to-noise ratio&nbsp;to obtain simple, general closed-form expressions for the diversity and&nbsp;coding gains of essential performance metrics, namely, symbol error rate and outage probability. We cover generalized propagation conditions and all the referred fading aspects. The analysis is further extended to investigate the performance of multibranch maximal-ratio combining. Capitalizing on the fact that the asymptotic channel distribution around the origin fully determines the diversity and coding gains, our results provide new insights into how each physical aspect of fading ultimately affects the wireless system performance.</p> 2020-07-02T16:45:49-03:00 ##submission.copyrightStatement## Brillouin Effect Impact in RoF Systems with Photonic-Assisted RF Amplification 2020-06-24T09:12:08-03:00 Eduardo Saia Lima Luiz Augusto Melo Pereira Ramon Maia Borges Matheus Sêda Borsato Cunha Arismar Cerqueira Sodré Junior <p>This work reports the impact of the stimulated Brillouin scattering (SBS) in a radio-over-fiber (RoF) system with photonic-assisted radiofrequency (RF) amplification. Such photonically amplified RoF systems employs long pieces of highly nonlinear fibers (HNLFs) for stimulating the four-wave mixing (FWM) nonlinear effect, in conjunction with appropriate management of the optical modulation index, aiming to provide RF gain. Numerical and experimental results demonstrate SBS might reduce the FWM nonlinear efficiency and limit the overall system power efficiency. We propose using only 35 m of HNLF for ensuring high photonic-assisted RF gain and increasing the SBS threshold in 14 dB. The digital performance of the photonically amplified RoF system is investigated in terms of root mean square error vector magnitude (EVMRMS), before and after mitigating SBS. The 35-m HNLF piece implies in enhancing the system digital performance and reducing in 6 dB the required optical power for attaining 19 dB of photonic-assisted RF gain.</p> 2020-06-24T09:12:08-03:00 ##submission.copyrightStatement##