Frequency-domain receiver design for doubly-selective channels

This work is devoted to the broadband wireless transmission techniques, which are serious candidates to be implemented in future broadband wireless and cellular systems, aiming at providing high and reliable data transmission and concomitantly high mobility. In order to cope with doubly-selective channels, receiver structures based on OFDM and SC-FDE block transmission techniques, are proposed, which allow cost-effective implementations, using FFT-based signal processing. The first subject to be addressed is the impact of the number of multipath components, and the diversity order, on the asymptotic performance of OFDM and SC-FDE, in uncoded and for different channel coding schemes. The obtained results show that the number of relevant separable multipath components is a key element that influences the performance of OFDM and SC-FDE schemes. Then, the improved estimation and detection performance of OFDM-based broadcasting systems, is introduced employing SFN (Single Frequency Network) operation. An initial coarse channel is obtained with resort to low-power training sequences estimation, and an iterative receiver with joint detection and channel estimation is presented. The achieved results have shown very good performance, close to that with perfect channel estimation. The next topic is related to SFN systems, devoting special attention to time-distortion effects inherent to these networks. Typically, the SFN broadcast wireless systems employ OFDM schemes to cope with severely time-dispersive channels. However, frequency errors, due to CFO, compromises the orthogonality between subcarriers. As an alternative approach, the possibility of using SC-FDE schemes (characterized by reduced envelope fluctuations and higher robustness to carrier frequency errors) is evaluated, and a technique, employing joint CFO estimation and compensation over the severe time-distortion effects, is proposed. Finally, broadband mobile wireless systems, in which the relative motion between the transmitter and receiver induces Doppler shift which is different or each propagation path, is considered, depending on the angle of incidence of that path in relation to the direction of travel. This represents a severe impairment in wireless digital communications systems, since that multipath propagation combined with the Doppler effects, lead to drastic and unpredictable fluctuations of the envelope of the received signal, severely affecting the detection performance. The channel variations due this effect are very difficult to estimate and compensate. In this work we propose a set of SC-FDE iterative receivers implementing efficient estimation and tracking techniques. The performance results show that the proposed receivers have very good performance, even in the presence of significant Doppler spread between the different groups of multipath components

3D scanning of Porto Alegre Museum Artifacts : the crockery of the Rocco Bakery

3D Scanning of Porto Alegre Museum Artifacts: The Crockery of the Rocco Bakery Antiques usually require careful handling, so these objects cannot be made available to the general public and are handled only by restoration specialists. This article focuses on the preservation of antiquities in terms of cultural heritage and the availability of these objects for access by visitors, it describes and evaluates the development of a method to support the digitisation of objects considered solids of revolution. The artifacts were provided by the Museu Joaquim José Felizardo in the city of Porto Alegre, Brazil, and were used to set the table in the former Confeitaria Rocco (bakery). The 3D process consisted of the following steps: laser scanning, data processing of the coordinates obtained from the surface of the object into point clouds, creation of the virtual model, creation of a physical model using additive manufacturing, and evaluation of the physical model in comparison with the original artifact. The obtained results show that highly accurate models can be created using the proposed method. Therefore, virtual data can be obtained for the conservation, restoration and creation of replicas for studies and accessibility

Effect of acetone vapor smoothing process on surface finish and geometric accuracy of fused deposition modeling ABS parts.

FDM is a widely used additive manufacturing process, however, it has some limitations, such as surface finish, due to the staircase effect caused by the layer-by-layer deposition. Studies have been conducted on surface finish of ABS parts with the use of acetone, but the process parameters and the resulting effects have not been fully investigated in the literature. Therefore, the aim of this study was to investigate the effects of acetone vapor smoothing process on surface finish and geometric accuracy of fused deposition modeling ABS parts. Specimens with different geometries were created and printed using two directions in different scales. The parts were exposed to acetone vapor for 20, 30 and 40 minutes. 3D deviation maps, roughness and microscopic analyses were conducted. The staircase effect was reduced at the expense of some geometric deviations, which varied according to the exposure time and part orientation. The smoothing process applied to the flat surfaces proved to be quite effective in reducing roughness by 90%, however, this reduction led to an undesirable rounding of the sharp edges. The results obtained in this study are consistent with those found in the literature and may help improve the quality of the ABS printed parts

Instrumento e sistema musical eletrônico

Universidade Federal do Rio Grande do SulArquiteturaDepositad

Potencialidades do uso de scanner 3d a laser e frezadora CNC para o desenvolvimento de novos produtos

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Prótese eletrônica para membros superiores e método de controle em prótese eletrônica

Universidade Federal do Rio Grande do SulArquiteturaDepositad

MuseuVR : a cultural heritage application in virtual reality with three-dimensional scanning

Novas abordagens de comunicação e de aprendizagem estão surgindo a partir das tecnologias digitais emergentes. Neste contexto, a digitalização 3D, utilizada em conjunto com a realidade virtual, possibilita novas formas de produção e de interação com acervos digitais. Utilizando tais tecnologias, desenvolveu-se um programa em realidade virtual, intitulado de MuseuVR, no qual as obras foram obtidas a partir de técnicas de digitalização tridimensional. Para o manuseio das peças presentes no ambiente digital, criou-se um sistema de interação baseado em gestos corporais (interface natural). Com auxílio do design, tal iniciativa busca gerar inovação, unindo diferentes tecnologias e campos do conhecimento, estimulando, por exemplo, a educação patrimonial com foco no usuário.New approaches into communication and learning fields are emerging from digital technologies. In this context, 3D digitization, used in conjunction with virtual reality, enables new forms of production and interaction with digital collections. Using such technologies, a virtual reality program, entitled MuseuVR, was developed, with three-dimensional scanning techniques. For the handling of the pieces obtained thought 3D scanning, an interaction system based on body gestures (natural interface) was created. With the help of design, this initiative seeks to generate innovation, uniting different technologies and fields of knowledge, stimulating cultural heritage education with a focus on the user experience

Avaliação dos modelos obtidos por diferentes sistemas de digitalização 3D para produtos personalizados

O objetivo é avaliar modelos obtidos por diferentes sistemas de digitalização tridimensional e verificar se as variações geométricas podem gerar implicações nas medidas antropométricas para o projeto de produtos personalizados. Para as comparações e análises, a perna direita de um sujeito foi digitalizada, pelo scanner 3D de luz branca (Artec Eva) e pelo scanner por infravermelho (kinect da Microsoft). Os modelos 3D obtidos foram comparados através do software Geomagic Qualify. Também, através da usinagem CNC foram realizadas comparações de análises visuais, por mapeamento de pressão e por termografia. Os resultados obtidos foram satisfatórios tanto para o uso do scanner Kinect quanto para o Artec Eva. Porém, houve uma diferença dimensional de aproximadamente 7 mm entre os modelos 3D, o que demonstra uma maior precisão de medidas nos modelos obtidos pelo scanner Artec Eva. No entanto, não invalida o uso do Kinect para o desenvolvimento de projetos de produto personalizados. O que irá determinar qual o scanner 3D mais adequado para cada tipo de produto é a necessidade do grau de precisão para que o produto desempenhe sua função com maior conforto e eficiência

Effects of different coating materials on three-dimensional optical scanning accuracy

The processes of three-dimensional optical scanning depend on the reflection of the surface to be digitized. To scanspecular or translucent surfaces, it is necessary to apply a coating material which interferes with the accuracy of thethree-dimensional measurements. This study proposes the use of gold, silver, platinum, and carbon by sputtering to coatthe surfaces to be scanned. The effects of these materials on the accuracy of the three-dimensional scanning were evalu-ated and compared with those of two frequently used materials, namely, talc and non-aqueous wet developer for pene-trant testing. To verify the resulting geometric variations, specimens were scanned before and after the application ofeach coating material. The results showed that the intrinsic errors of the three-dimensional scanning process, such asthe registration of several point clouds, can have more significant effects than the coating material used. Measurementstaken from a single point cloud showed dimensional tolerances of approximately 0.01mm for gold, platinum, and carboncoating. These coatings offer significantly higher accuracy than the traditionally used developer and are suggested foraccurate three-dimensional scanning of specular and translucent surfaces

Startups de empresas de base tecnológica e a computação na nuvem: a viabilização de um modelo mais dinâmico

In the present entrepreneurship scenario, the technological based companies startups have been distinguished examples of innovation and competitiviness. Nevertheless those initiatives face uncertainty scenarios and big risks. Add to that a fierce competition and resource raising dificulties. Startups companies increasingly demand more and more flexible and scalable structures â at reasonable costs â in order to rise up more quickly and efficiently. Validating their concepts and ideas quickly as a way to reduce risks have been the strategy tendencies, and the cloud computing is a way to make feasible.No presente cenário de empreendedorismo, as startups de empresas de base tecnológica tem se destacado como exemplos de inovação e competitividade. Contudo, estas iniciativas enfrentam cenários de incertezas e de grandes riscos. Soma-se a isto a competição acirrada e a dificuldade de captação de recursos. Cada vez mais as startups demandam uma estrutura mais flexível e escalável – a custos competitivos – para que possam se erguer de forma rápida e eficiente. Validar seus conceitos e ideias rapidamente de forma a mitigar riscos tem sido o tom das estratégias atualmente e a computação em nuvem contribui muito para sua viabilização