Teses em Engenharia Elétrica (Doutorado) - PPGEE/ITEC

URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/2317

O Doutorado Acadêmico inicio-se em 1998 e pertence ao Programa de Pós-Graduação em Engenharia Elétrica (PPGEE) do Instituto de Tecnologia (ITEC) da Universidade Federal do Pará (UFPA).

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Agora exibindo 1 - 5 de 5

Acesso aberto (Open Access)
Avaliação de técnica semi-supervisionada de análise de vetor comprimido (C2VA) em imagens de satélites para detecção de mudanças de uso e cobertura da terra
(Universidade Federal do Pará, 2017-12-15) SIRAVENHA, Ana Carolina Quintão; PELAES, Evaldo Gonçalves; http://lattes.cnpq.br/0255430734381362
Remote sensing image databases and Geographical Information System have the potential to act as accurate tools for environmental monitoring. Carajas Mountains are an important mineral deposit in Brazil and as environmental laws protect a great portion of this region, they have been at the core of conflicts involving human and nature interests. The biggest mining project in Brazil is active in this region (Carajas project) and this analysis aims at identifying the environmental impact caused directly or indirectly by this activity using state of the art methods. This study collects information of land-use and land-coverage from an area larger than 111, 000 km2 including five municipalities, aiming at observing the landscape intervention from a big scale perspective. Therefore, employing the resultant products of the multi-spectral approach called compressed change vector analysis, this work analyses both the environmental changes in five municipalities of the Carajas Mountains: Parauapebas, Canaa dos Carajas, Ourilandia do Norte, Sao Felix do Xingu and Tucuma. From the point of view of the applicability of the proposed tools, it was noticed that the combination of the compressed change vector analysis with the fuzzy clustering is sufficiently efficient for the detection and analysis of changes in land use and land coverage. The quantitative and qualitative evaluation metrics show good accuracy compared to the manually obtained reference images. The results show that in general the vegetative coverage was replaced by pasture lands, which in turn were replaced by urban occupations. The comparison with official statistics and by visual inspection indicate good accuracy of the present study in the estimation of vegetative cover. The presence of environmentally protected areas has prevented the increase of deforestation in the mountains, in which the observed change rates were at least 15% lower than non-protected regions.
Acesso aberto (Open Access)
Mapeamento de bits para adaptação rápida a variações de canal de sistemas QAM codificados com LDPC
(Universidade Federal do Pará, 2017-09-29) CORRÊA, Fernanda Regina Smith Neves; UCHÔA-FILHO, Bartolomeu Ferreira; http://lattes.cnpq.br/7752341440632617; PELAES, Evaldo Gonçalves; http://lattes.cnpq.br/0255430734381362
Low-Density parity-check (LDPC) codes are being adopted as the error correction strategy in di erent system standards, such as the G.hn (home networking standard) and the IEEE 802.11n (wireless local standard). In these LDPC-coded quadrature amplitude modulation (QAM) systems, mapping the LDPC coded bits properly to the di erent sub-channels considering the fact that sub-channels have di erent qualities ensures an improved overall system performance. Accordingly, this thesis presents a new bit mapping technique based on the assumption that bits transmitted in \good" sub-channels, help bits transmitted in \bad" sub-channels. This can be made possible through some restrictions to be imposed on the associated Tanner graph, akin to Root-LDPC codes. An optimization of the root-like bit mapping through extrinsic information transfer (EXIT) charts analysis is also presented. We show that this mapping has the advantage of a reduced optimization search space when applied to single-carrier based systems. Moreover, in situations where the search space is not só reduced, such as in orthogonal frequency division multiplexing (OFDM)-based applications, we arrive at a rule of thumb associated with the bit mapping constraints that practically eliminates the need for an optimization. Finally, a study of the impact of the level of reliability imbalance across the sub-channels on the performance of the root-like bit mapping is presented. Simulation results show that the new bit mapping strategy improves performance, and that in the presence of channel variations, the system can, adaptively, apply a new bit mapping without the need of a complex optimization, which can be very useful in practical systems.
Acesso aberto (Open Access)
Uma metodologia temporal para avaliação do desempenho de códigos concatenados em sistemas OFDM para transmissão de vídeo 4K-UHD
(Universidade Federal do Pará, 2024-08-16) COSTA, Thiago de Araújo; CASTRO, Bruno Souza Lyra; http://lattes.cnpq.br/1897829604434609; BARROS, Fabrício José Brito; http://lattes.cnpq.br/9758585938727609
The communication channel is a critical part of the process of information degradation. In the 4K ultra-resolution video transmission domain, the communication channel is a crucial part where information degradation occurs, inevitably leading to errors during reception. To enhance the transmission process in terms of fidelity, advanced technologies such as digital video broadcasting terrestrial (DVB-T) and its evolutionary successor, digital video broadcasting terrestrial second generation (DVB-T2), are utilized to mitigate the effects of data transmission errors. In the transition, a notable change is the replacement of the concatenated channel coding pairs. Within this scenario, this research presents an innovative methodology for the temporal analysis of 4K ultraresolution video quality under the influence of additive white Gaussian noise (AWGN) and Rayleigh channels. This analytical endeavor is facilitated through the application of concatenated coding schemes, specifically, the Bose-Chaudhuri-Hocquenghem concatenated low-density parity check (BCH-LDPC) and Reed-Solomon concatenated convolutional (RS-CONV) coders. A more comprehensive understanding of video quality can be attained by considering its temporal variations, a crucial aspect of the ongoing evolution of technological paradigms. In this study, the Structural Similarity Index (SSIM) serves as the main metric for quality assessment during simulations. Furthermore, the simulated Peak Signal-to-Noise Ratio (PSNR) values validate these findings, exhibiting consistent alignment with the SSIM-based evaluations. Additionally, the performance of the BCH-LDPC significantly outperforms that of RSCONV under the 64-QAM modulation scheme, yielding superior video quality levels that approximate or surpass those achieved by RS-CONV under QPSK (Quadrature Phase Shift Keying) modulation, leading to an increase in spectral efficiency. This enhancement is evidenced by SSIM gains exceeding 78% on average. The computation of average gains between distinct technologies in video quality analysis furnishes a robust and comprehensive evaluation framework, empowering stakeholders to make informed decisions within this domain.
Acesso aberto (Open Access)
Metodologias de discretização espacial sem malha baseadas nos potenciais de Coulomb e Lennard-Jones para o método radial de interpolação por pontos (RPIM) aplicadas para solução numérica das equações de Maxwell
(Universidade Federal do Pará, 2017-12-04) SOUSA, Washington César Braga de; RABELO, Wilson Ricardo Matos; http://lattes.cnpq.br/7978676206209168; OLIVEIRA, Rodrigo Melo e Silva de; http://lattes.cnpq.br/4768904697900863
In this thesis, three new particle interaction methods based on the Coulomb's and Lennard- Jones' potentials have been developed (and computationally implemented), aiming to generate meshless spatial discretization which can be used to the Radial Point Interpolation Method (RPIM) for solving partial di erential equations. These new methods, called Coulomb Law Discretization Method (CLDM), Electric Charge Gaussian Gradation Method (ECGGM) e Lennard-Jones Discretization Method (LJDM),employ adapted versions of Coulomb's and Lennard-Jones' vector forces equations for obtaining a balanced distribution of nodes in space (equilibrium state), in order to achieve high discretization quality of space and complex structures. For this aim, a new quality metrics is introduced. This doctoral thesis is presented as an aggregation of three scienti c papers, which present respectively the methods: CLDM, ECGGM and LJDM. The RPIM and the uniaxial perfectly matched layers (UPML) are used for solving Maxwell's equations in time domain for 2D (TMz mode) and 3D problems. The CLDM, ECGGM and LJDM methods (each in conjunction with the RPIM method) are applied to electromagnetic scattering problems, based on circular, elliptic and triangular metal cylinders (2D case). The LJDM / RPIM method is applied to the 3D case. The obtained results are in accordance with analytical solutions.
Acesso aberto (Open Access)
Modelling and mitigation of alien crosstalk for DSL systems
(Universidade Federal do Pará, 2017-12-11) GOMES, Diego de Azevedo; KLAUTAU JÚNIOR, Aldebaro Barreto da Rocha; http://lattes.cnpq.br/1596629769697284; PELAES, Evaldo Gonçalves; http://lattes.cnpq.br/0255430734381362
G.fast is the most recent ITU-T standard for DSL transmission, which targets copper topologies with short distances and adopts a bandwidth of 106 MHz extensible to 212 MHz. In several situations, G.fast systems will be composed by or coexist with uncoordinated (or alien) lines, which are sources of strong crosstalk, because these lines are not part of the vectored group. This document presents a formulation to explain the performance of the alien crosstalk mitigation methods according to the number of alien lines in a certain environment, the mechanism that de nes the interference correlation of it and an alien crosstalk mitigation method for downstream DSL transmission impaired by multiple interferers called AMMIS. Simulation results show that alien crosstalk mitigation methods found in the literature can indeed improve the performance of G.fast systems, but only under speci c conditions. We have contrasted these situations and we provide guidelines about the feasibility of the crosstalk mitigation techniques in scenarios with distinct number of alien lines. Additionally, the AMMIS shows promising results in relation to the bit rate when compared with literature methods in scenarios with a large number of interferers, with the additional advantage of allows power savings. As support for the simulations, we also present a set of alien crosstalk measurements.

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