Papers by Bartolomeu Uchôa
IEEE Access
In this paper, a comprehensive analysis of the signal-to-noise ratio wall (SNRw) of cognitive rad... more In this paper, a comprehensive analysis of the signal-to-noise ratio wall (SNRw) of cognitive radio (CR)based non-cooperative spectrum sensing (nCSS) and cooperative spectrum sensing (CSS) using energy detection (ED) is presented. The analysis considers a novel realistic noise uncertainty (NU) model in which it is assumed that the estimated noise variance used to determine the decision threshold is unbiased and follows a truncated-Gaussian random distribution with configurable limits. Expressions are derived for the individual detection performances at CRs and global detection performances at the fusion center in terms of probability of false alarm and probability of detection and the SNRw of ED in nCSS and CSS in hard-decision fusion under the k-out-of-M rule, and soft-decision fusion, considering the proposed NU model, respectively. Empirical SNRw algorithms are also proposed, allowing for the SNRw computation of any detector, including the ED, in nCSS and CSS. All theoretical findings are verified through computer simulations or empirical results. INDEX TERMS Congitive radio; energy detection; noise uncertainty; signal-to-noise ratio wall; spectrum sensing.
Abstract—This paper deals with the multiplicative finite-field matrix channel, a discrete memoryl... more Abstract—This paper deals with the multiplicative finite-field matrix channel, a discrete memoryless channel whose input and output are matrices (over a finite field) related by a multiplicative transfer matrix. The model considered here assumes that all transfer matrices with the same rank are equiprobable, so that the channel is completely characterized by the rank distribution of the transfer matrix. This model is seen to be more flexible than previously proposed ones in describing random linear network coding systems subject to link erasures, while still being suffi-ciently simple to allow tractability. The model is also conservative in the sense that its capacity provides a lower bound on the capacity of any channel with the same rank distribution. A main contribution is to express the channel capacity as the solution of a convex optimization problem which can be easily solved by numerical computation. For the special case of constant-rank input, a closed-form expression for th...
IEEE Access
5G and beyond 5G (B5G) wireless systems promise to support services with different requirements i... more 5G and beyond 5G (B5G) wireless systems promise to support services with different requirements in the same network, as enhanced mobile broadband (eMBB), ultra-reliable low-latency communications (URLLC), and massive machine type communication (mMTC). One alternative is to consider the network slicing paradigm, where the wireless network resources are shared (or sliced) among active services with different requirements. In addition, another emerging technology, that is considered as a key enabler for B5G wireless systems, is the intelligent reflecting surfaces (IRS). From the deployment of an IRS, it is possible to improve the received signal quality and consequently increase the overall network capacity. Therefore, in this paper, we investigate the use of IRS to support simultaneous eMBB and URLLC services. We evaluate the achievable rate of an IRS-aided radio access network, where the uplink resources are shared between eMBB and URLLC users either under heterogeneous orthogonal multiple access (H-OMA) or heterogeneous non-orthogonal multiple access (H-NOMA) techniques. Results show that exploiting an IRS can considerably increase the eMBB rate and the URLLC reliability simultaneously, regardless of whether operating under H-OMA or H-NOMA. Moreover, we also provide some insights on the best user pairing strategy, showing that higher rates are achieved by matching many eMBB users near to the IRS with a URLLC user close to the base station. INDEX TERMS Enhanced Mobile Broadband (eMBB), Intelligent Reflecting Surfaces (IRS), Network Slicing, Ultra-Reliable Low-Latency Communications (URLLC).
Frontiers in Communications and Networks
ArXiv, 2014
We evaluate the secrecy performance of a multiple access cooperative network where the destinatio... more We evaluate the secrecy performance of a multiple access cooperative network where the destination node is wiretapped by a malicious and passive eavesdropper. We propose the application of the network coding technique as an alternative to increase the secrecy at the destination node, on the top of improving the error performance of the legitimate communication, already demonstrated in the literature. Network coding is leveraged by assuming that the legitime cooperative nodes are able to perform non-binary linear combinations of different frames before the transmission. Different scenarios with and without channel state information (CSI) at the transmitter side are evaluated. The effectiveness of the proposed schemes is evaluated in terms of secrecy outage probability through theoretic and numerical analyses. It is shown that, even when the legitimate transmitters do not have any CSI, the secrecy can be increased through the use of network coding when compared to the direct transmiss...
Anais de XXXVIII Simpósio Brasileiro de Telecomunicações e Processamento de Sinais
Resumo-Este artigo investiga o desempenho do Acesso Múltiplo Não-Ortogonal em uma rede de ondas m... more Resumo-Este artigo investiga o desempenho do Acesso Múltiplo Não-Ortogonal em uma rede de ondas milimétricas com 2 usuários. Em particular, consideramos um cenário no qual tanto a estação base quanto os usuários estão equipados com um arranjo linear de antenas. Portanto, consideramos beamforming na BS e no UE sem nenhum conhecimento do estado do canal. Dado que a alocação de potência e o problema de Acesso Inicial entrelaçam-se, neste artigo, um problema conjunto de IA e alocação de potência é considerado visando otimizar a taxa de soma alcançável considerando um restrição de taxa mínima para cada usuário. Uma vez que tal problema é dito não-convexo, para resolvê-lo dividimos o mesmo em dois subproblemas de otimização (IA e alocação de potêncis), os quais são resolvidos utilizando a técnica de Otimização por Enxame de Partículas. Simulações são realizadas com o objetivo de comparar as taxas de soma alcançáveis dos sistemas NOMA e OMA. Os resultados mostram que a solução proposta supera o sistema OMA.
Anais de XXXVIII Simpósio Brasileiro de Telecomunicações e Processamento de Sinais
Resumo-Uma abordagem combinatorial foi recentemente proposta para o projeto de constelações de si... more Resumo-Uma abordagem combinatorial foi recentemente proposta para o projeto de constelações de sinais multidimensionais para canais com desvanecimento. Mesmo sendo flexível e garantindo diversidade de espaço de sinais completa, a técnica adota a detecção ótima exponencialmente complexa de máxima verossimilhança (ML). Neste trabalho, propomos dois algoritmos de detecção de baixa complexidade, um sub-ótimo, baseado em listas, e o outro ótimo, baseado numa simplificação do ML. Ambos os algoritmos apresentam um bom compromisso entre desempenho e complexidade. Resultados de simulação mostram que o desempenho ótimo ou próximo do ótimo pode ser alcançado com redução de até 98% da complexidade de detecção. Palavras-Chave-Detecção em lista, diversidade de espaço de sinais, diversidade completa.
Anais de XXXVIII Simpósio Brasileiro de Telecomunicações e Processamento de Sinais
This paper presents new case studies for the statistical analysis for wavelength resolution SAR i... more This paper presents new case studies for the statistical analysis for wavelength resolution SAR image stacks. The statistical analysis considers the Anderson-Darling goodnessof-fit test in a set of pixel samples from the same position obtained from a SAR image stack. The test is applied in wavelengthresolution SAR image stacks. The present work consists of two case studies based on the use of multiple-pass stacks and Type I error using the False Discovery Rate controlling procedures. In addition, an application scenario is presented for the studied scenarios.
Journal of Communication and Information Systems, 2018
A multiway relay network (mRN), which is widely employed in the literature, is extended to repres... more A multiway relay network (mRN), which is widely employed in the literature, is extended to represent a larger number of practical scenarios, such as a vehicular ad hoc network (VANET). For the proposed system, generalized multiway relay network (g-mRN), three transmission strategies are presented and analyzed in terms of effective rate, for different numbers of users. Assuming that the average signal-to-noise ratio (SNR) is known to the transmitters, the maximum effective rate is obtained through the optimal choice of the message rates. We also derive the effective rate for fixed message rates. Numerical results show that the best strategy under the optimal message rates is the one in which all users transmit simultaneously in the multiple access phase. But when considering fixed message rates, the best transmission strategy depends upon the SNR. These results are important in that they can be used as guidelines for selecting the right strategy and message rates depending on the situation.
Anais de XXXV Simpósio Brasileiro de Telecomunicações e Processamento de Sinais
IEEE Transactions on Signal Processing, 2014
IEEE Transactions on Signal Processing, 2015
In this paper, we consider a wireless-powered cooperative communication network consisting of one... more In this paper, we consider a wireless-powered cooperative communication network consisting of one hybrid accesspoint (AP), one source, and one relay. In contrast to conventional cooperative networks, the source and relay in the considered network have no embedded energy supply. They need to rely on the energy harvested from the signals broadcasted by the AP for their cooperative information transmission. Based on this three-node reference model, we propose a harvest-then-cooperate (HTC) protocol, in which the source and relay harvest energy from the AP in the downlink and work cooperatively in the uplink for the source's information transmission. Considering a delay-limited transmission mode, the approximate closed-form expression for the average throughput of the proposed protocol is derived over Rayleigh fading channels. Subsequently, this analysis is extended to the multi-relay scenario, where the approximate throughput of the HTC protocol with two popular relay selection schemes is derived. The asymptotic analyses for the throughput performance of the considered schemes at high signal-to-noise radio are also provided. All theoretical results are validated by numerical simulations. The impacts of the system parameters, such as time allocation, relay number, and relay position, on the throughput performance are extensively investigated. Index Terms-Energy harvesting, wireless-powered cooperative communication network, cooperative communications, harvest-then-cooperate, average throughput, relay selection. I. INTRODUCTION As a sustainable solution to prolonging the lifetime of energy constrained wireless networks, the energy harvesting technique has recently drawn significant attention, e.g. see [2] and references therein. It enables wireless nodes to collect energy from the surrounding environment. Apart from the conventional renewable energy sources such as solar and wind, radio frequency (RF) signals radiated by ambient transmitters
2014 International Telecommunications Symposium (ITS), 2014
This paper describes a new coded cooperation scheme based on single parity-check turbo-product co... more This paper describes a new coded cooperation scheme based on single parity-check turbo-product codes. The channel soft-information from the source and the relays are also combined in a novel way at the destination. The scheme has simple encoding and decoding, and unveils potential for large cooperation gains in fast fading channels.
2014 11th International Symposium on Wireless Communications Systems (ISWCS), 2014
We propose a dynamic hybrid antenna/relay selection scheme for multiple-access relay systems. The... more We propose a dynamic hybrid antenna/relay selection scheme for multiple-access relay systems. The proposed scheme aims to boost the system throughput while keeping a good error performance. By using the channel state information, the destination node performs a dynamic selection between the signals provided by the multi-antenna relay, located in the intercell region, and the relay nodes geographically distributed over the cells. The multi-antenna relay and the single-antenna relay nodes employ the decode-remodulate-and-forward and amplifyand-forward protocols, respectively. Results reveal that the proposed scheme offers a good tradeoff between spectral efficiency and diversity gain, which is one of the main requirements for the next generation of wireless communications systems.
Motivated by physical-layer network coding, this paper considers communication in multiplicative ... more Motivated by physical-layer network coding, this paper considers communication in multiplicative matrix channels over finite chain rings. Such channels are defined by the law $Y =A X$, where $X$ and $Y$ are the input and output matrices, respectively, and $A$ is called the transfer matrix. It is assumed a coherent scenario in which the instances of the transfer matrix are unknown to the transmitter, but available to the receiver. It is also assumed that $A$ and $X$ are independent. Besides that, no restrictions on the statistics of $A$ are imposed. As contributions, a closed-form expression for the channel capacity is obtained, and a coding scheme for the channel is proposed. It is then shown that the scheme can achieve the capacity with polynomial time complexity and can provide correcting guarantees under a worst-case channel model. The results in the paper extend the corresponding ones for finite fields.
We propose a cooperative diversity scheme for a communication system consisting of NT cooperating... more We propose a cooperative diversity scheme for a communication system consisting of NT cooperating nodes that receive ⌈log 2 (NT)⌉ feedback bits from the destination node on the channel state information. This information is used appropriately to obtain cooperative diversity and signal-to-noise ratio (SNR) gains. A simple linear detector and an interference cancelation detector are proposed. It is shown that their error rates are quite close to that of the maximum likelihood detector. An upper bound for the average bit error probability for binary phase-shift keying (BPSK) modulation over a Rayleigh fading channel is derived. In addition, through computer simulations, it is verified that the proposed scheme offers a good error performance when the inter-user channel SNR is high or when the inter-user channel has a well-defined line-of-sight component. In other words, the new scheme becomes interesting when the cooperating nodes are close to each other.
This letter introduces the class of generalized punctured convolutional codes (GPCCs), which is b... more This letter introduces the class of generalized punctured convolutional codes (GPCCs), which is broader than and encompasses the class of the standard punctured convolutional codes (PCCs). A code in this class can be represented by a trellis module, the GPCC trellis module, whose topology resembles that of the minimal trellis module. The GPCC trellis module for a PCC is isomorphic to the minimal trellis module. A list containing GPCCs with better distance spectrum than the best known PCCs with same code rate and trellis complexity is presented.
IEEE Transactions on Information Theory, 1999
The multilevel coding approach of Imai and Hirakawa is used to construct trellis-matched codes fo... more The multilevel coding approach of Imai and Hirakawa is used to construct trellis-matched codes for binary-input partial-response channels. For the codes to be trellis-matched, the signal constellations are selected according to certain constraints, but no conditions are imposed on the component codes. New codes for the channel compare favorably to existing codes.
IEEE Transactions on Communications, 2002
2009 IEEE International Workshop on Multimedia Signal Processing, 2009
The process of adding high-density information onto printed material enables and improves interes... more The process of adding high-density information onto printed material enables and improves interesting hardcopy document applications, such as: security, authentication, physical-electronic round tripping, item-level tagging as well as consumer/product interaction. This investigation on robust and high capacity print codes aims to maximize information payload in a given printed page area, subject to robustness to distortions originated by printing and scanning
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Papers by Bartolomeu Uchôa