Journal of Communication and Information 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. 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A. de Souza and José Cândido S. Santos Filho) (Rausley A. A. de Souza and José Cândido S. Santos Filho) Thu, 02 Jan 2020 16:55:10 -0200 OJS 60 Optimized Energy Consumption for Slotted Aloha and CSMA/CA Multihop Ad Hoc Networks <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> Bruna Alves da Silva, Renato Mariz de Moraes ##submission.copyrightStatement## Thu, 09 Jul 2020 18:23:36 -0300 Low-Complexity Tree-Based Iterative Decoding for Coded SCMA <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> Ana Luiza Scharf, Bartolomeu Uchˆoa-Filho, Bruno Fontana da Silva, Didier Ruyet ##submission.copyrightStatement## Tue, 07 Jul 2020 15:28:31 -0300 Asymptotic System Performance over Generalized Fading Channels with Application to Maximal-Ratio Combining <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> Francisco Raimundo Albuquerque Parente, Flavio du Pin Calmon, José Cândido Silveira Santos Filho ##submission.copyrightStatement## Thu, 02 Jul 2020 16:45:49 -0300 Brillouin Effect Impact in RoF Systems with Photonic-Assisted RF Amplification <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> Eduardo Saia Lima, Luiz Augusto Melo Pereira, Ramon Maia Borges, Matheus Sêda Borsato Cunha, Arismar Cerqueira Sodré Junior ##submission.copyrightStatement## Wed, 24 Jun 2020 09:12:08 -0300 Channel Equalization Based on Decision Trees <p>This paper analyzes the application of decision trees&nbsp;to the problem of communication channel equalization. Decision&nbsp;trees are interesting structures because they are nonlinear and&nbsp;relatively simple from a computational standpoint. They are&nbsp;tested for channel models that give rise to classification tasks of&nbsp;different complexity and compared to the Bayesian equalizer and&nbsp;the Wiener linear equalizer. The results are quite encouraging, as&nbsp;they show that the tree-based equalizer reaches, in many cases,&nbsp;a performance similar to that of the Bayesian filter at a lower&nbsp;computational cost.</p> David Felice Falivene Baptista, Rafael Ferrari, Romis Attux ##submission.copyrightStatement## Mon, 22 Jun 2020 20:10:07 -0300 Performance Evaluation of Low-Complexity Algorithms for Orthogonal Time-Frequency Space Modulation <p>Data transmission in wireless systems brings numerous challenges, especially when it involves propagating in a multipath scenario over rapidly time-varying channels. In this context, Orthogonal Time-Frequency Space (OTFS) modulation has been recently proposed to work with time-frequency selective channels with high Doppler. In this modulation, the symbols are first multiplexed in a delay-Doppler domain rather than in the time-frequency domain used by Orthogonal Frequency Division Multiplexing (OFDM). The studies point out advantages of OTFS performance over OFDM in many aspects, such as data rate increase in high mobility. Another advantage is the sparsity of the channel produced by OTFS that allows using low-complexity algorithms for the detection of the data. In this paper, the performance of OTFS modulation in a doubly dispersive channel is evaluated with several low-complexity variants of the message passing algorithm (MPA) in terms of complexity and Bit Error Rate (BER) performance. The results show that MPA and Approximate Message Passing simplified by Expectation Propagation (AMP-EP) algorithms achieve higher performance. However, when taking into account both complexity and BER performance, AMP simplified by First-Order (AMP-FO) achieves the best performance complexity tradeoff.</p> Dayse Gonçalves Correia Bandeira, Didier Le Ruyet, Mylene Pischella, João Cesar Moura Mota ##submission.copyrightStatement## Wed, 10 Jun 2020 14:20:52 -0300 Receivers for the uplink of multiuser generalized spatial modulation MIMO systems <p><span class="fontstyle0">Generalized spatial modulation is envisioned as a promising communication paradigm for the next communication systems, in which high data rates and reliability are important features, but also energy and infrastructure-saving solutions are seeked. This work presents a variety of efficient suboptimal signal detection strategies for the uplink of multiuser GSM MIMO systems. They are comprised of user decoupling strategies followed by GSM signal detection schemes, and offer different balances of detection performance and computational complexity. Simulation results exhibit the performance of these strategies under different system scenarios and channel propagation effects.</span> </p> José Calpa, João Alfredo Cal-Braz, Rodrigo David, Raimundo Sampaio-Neto ##submission.copyrightStatement## Sun, 31 May 2020 09:47:53 -0300 SDMA Grouping Based on Unsupervised Learning for Multi-User MIMO Systems <p>In this study, we investigate a spatial division multiple access (SDMA) grouping scheme to maximize the total data rate of a multi-user multiple input multiple output (MU-MIMO) system. Initially, we partition the set of mobile stations (MSs) into subsets according to their spatial compatibility. We explore different clustering algorithms, comparing them in terms of computational complexity and capability to partition MSs properly. Since we consider a scenario with a massive arrange of antenna elements and that operates on the mmWave scenario, we employ a hybrid beamforming scheme and analyze its behavior in terms of the total data rate. The analog and digital precoders exploit the channel information obtained from clustering and scheduling, respectively.&nbsp; The simulation results indicate that a proper partition of MSs into clusters can take advantage of the spatial compatibility effectively and reduce the multi-user (MU) interference. The hierarchical clustering (HC) enhances the total data rate 25% compared with the baseline approach, while the density-based spatial clustering of applications with noise (DBSCAN) increases the total data rate 20%.</p> Francisco Hugo Costa Neto, Tarcisio Ferreira Maciel ##submission.copyrightStatement## Fri, 29 May 2020 18:34:40 -0300 A Cepstral Method to Estimate the Stable Optimal Solution for Feedforward Occlusion Cancellation in Hearing Aids <p>The occlusion effect is a common complaint from&nbsp;users of hearing aids with narrow or unvented earmolds. This&nbsp;phenomenon makes the user hear his own voice muffled. In the&nbsp;scientific literature, fixed and adaptive controllers have been&nbsp;proposed for occlusion effect reduction. This work proposes&nbsp;a cepstral method to estimate the stable optimal solution for&nbsp;feedforward occlusion cancellation and a fixed controller that&nbsp;utilizes this estimate to reduce the occlusion effect in hearing&nbsp;aids. The cepstral method operates on a feedback structure at a&nbsp;calibration process. Simulations have shown that the performance&nbsp;of the cepstral method improves as the length of the signal uttered&nbsp;by the hearing aid user increases, resulting in estimates with&nbsp;average normalized misalignment less than -19 and -34 dB for&nbsp;signals lasting 1.5 and 5 s. The estimates are significantly more&nbsp;accurate below 500 Hz, which is the frequency range common to&nbsp;the occlusion effect. In addition, results have pointed out that the&nbsp;controller attenuated the occlusion effect, averagely decreasing by&nbsp;0.17 dB the distortion power and increasing by 0.13 the objective&nbsp;perceptual quality MOS-LQO score.</p> Bruno Catarino Bispo, Renata Coelho Borges ##submission.copyrightStatement## Sat, 23 May 2020 15:07:24 -0300 Multichannel Source Separation Using Time-Deconvolutive CNMF <p><span style="left: 110.981px; top: 219.639px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.843704);">This paper addresses the separation of audio sources</span><span style="left: 60.4849px; top: 231.946px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.885248);">from convolutive mixtures captured by a microphone array. We</span><span style="left: 60.4849px; top: 244.252px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.851621);">approach the problem using complex-valued non-negative matrix</span><span class="" style="left: 60.4849px; top: 256.56px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.858616);">factorization (CNMF), and extend previous works by tailoring</span><span style="left: 60.4849px; top: 268.867px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.836988);">advanced (single-channel) NMF models, such as the deconvolutive</span><span class="" style="left: 60.4849px; top: 281.173px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.863316);">NMF, to the multichannel factorization setup. Further, a sparsity-</span><span style="left: 60.4849px; top: 293.48px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.804771);">promoting scheme is proposed so that the underlying estimated</span><span style="left: 60.4849px; top: 305.787px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.819299);">parameters better fit the time-frequency properties inherent</span><span style="left: 60.4849px; top: 318.093px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.815457);">in some audio sources. The proposed parameter estimation</span><span style="left: 60.4849px; top: 330.401px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.854986);">framework is compatible with previous related works, and can be</span><span class="" style="left: 60.4849px; top: 342.708px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.85244);">thought of as a step toward a more general method. We evaluate</span><span style="left: 60.4849px; top: 355.014px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.856324);">the resulting separation accuracy using a simulated acoustic</span><span style="left: 60.4849px; top: 367.321px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.860362);">scenario, and the tests confirm that the proposed algorithm</span><span class="" style="left: 60.4849px; top: 379.627px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.812608);">provides superior separation quality when compared to a state-</span><span style="left: 60.4849px; top: 391.934px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.822849);">of-the-art benchmark. Finally, an analysis on the effects of the</span><span style="left: 60.4849px; top: 404.242px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.878436);">introduced regularization term shows that the solution is in fact</span><span class="" style="left: 60.4849px; top: 416.548px; font-size: 11.0761px; font-family: sans-serif; transform: scaleX(0.811751);">steered toward a sparser representation.</span></p> Thadeu Luiz Barbosa Dias, Wallace Alves Martins, Luiz Wagner Pereira Biscainho ##submission.copyrightStatement## Thu, 14 May 2020 19:18:59 -0300