Percorrer por tipo de recurso "conference paper"
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- A 1.2V 900nW conductance converterPublication . Miranda, Nuno; Morais, RaulThis article describes a new electrical conductance converter method suitable for very low power applications, where energy constraints prevails over speed and measurement accuracy. Method idea gather voltage time integration and shopper stabilization techniques to process noisy low amplitude signals and to overcome severe limitations of weak inversion channel CMOS circuitry. Main features and tradeoffs are exploited. A 1.2V ASIC implementation on standard 0.35μm CMOS schematics is also presented. Post-layout simulations shows a total power consumption lower than 900nW including current source excitation inherent to the conductance measurement. Such low power consumption allows the measurement of several physical parameters on self-powered wireless networks.
- A 130 nm CMOS LNA for 30 GHz applicationsPublication . Ribeiro, R.; Moreira Mendes, Luís Miguel; Vaz, J. C.; Rosario, M. J.; Freire, J. C.This paper presents the design of a 30 GHz low noise amplifier in a 130 nm CMOS technology. The amplifier is based on a cascode topology. The circuit uses autotransformers in the input and output matching networks. This design approach eliminates the necessity of the use of source degeneration and allows obtaining an ultra compact LNA. The amplifier presents a forward gain (S21) of 7.4 dB at 30 GHz with a bandwidth of 10 GHz, input and output VSWRs better than 1.22:1 and a noise figure of 3.7 dB. The LNA is unconditionally stable and consumes only 7 mW when supplied with 1.2 V. The amplifier fits an area of 0.08 mm2, which is one of the smallest areas reported.
- 360° Video Coding using Adaptive Tile PartitioningPublication . Carreira, J.; Faria, Sergio M. M. de; Tavora, Luis M. N.; Navarro, Antonio; Assuncao, Pedro A.Encoding 360° video with ultra high definition requires high bit rate to guarantee either immersive experiences and acceptable QoE in video delivery services, or high performance in machine vision applications. However, since in general the full Field-of-View (FoV), i.e., 360°, is not required at once, a great deal of bandwidth can be saved by allowing partial decoding of limited size FoVs. The conventional approach to accomplish such goal has been to encode several fixed-size independent tiles of each video frame. In this work a novel tile-based video coding scheme is proposed to achieve further reduction on the average maximum bit rate required for partial delivery of 360° video. The proposed method dynamically adapts the tile sizes to the omnidirectional video content in order to obtain uniform bit rate in each one. Therefore, more complex image regions, i.e., those requiring higher bit rates are partitioned in smaller tiles, allowing finer bit rate granularity when FoVs with higher spatiotemporal complexity are selected for transmission and decoding. The simulation results show that the proposed adaptive tile-based coding mechanism outperforms the conventional fixed-size tilling methods, achieving an average of 4.78% and 16.88% bit rate reduction for FoVs of 90° × 90° and 45° × 45°, respectively.
- 3D Indoor Radio Coverage for 5G Planning: a Framework of Combining BIM with Ray-tracingPublication . Louro, João; Fernandes, Telmo Rui; Rodrigues, Hugo; Caldeirinha, Rafael F. S.This paper presents a framework to predict indoor radio wave coverage in buildings. Such method includes the capability to import BIM (Building Information Modelling) files that contain structured physical geometry and dimension data, including the material types that are of uttermost importance in evaluating their dielectric properties. Appropriated extraction of physical and dielectric attributes of the building elements was used as input to a 3D radio wave propagation ray-tracing developed in MatLab that allows the prediction of the received radio signal level at any location within the computational volume. Results are presented for line-of-sight contributions and first and second order reflections. Despite the generic nature of the proposed framework, prediction results are presented at 3.6 GHz, envisaging emerging 5G indoor radio coverage.
- 3D key-frame extraction method based on visual saliencyPublication . Ferreira, Lino; Assunção, Pedro; Cruz, Luis A. da SilvaThis paper presents a method for key-frame extraction from 3D video using visual saliency to weight the 3D content according to a user attention model. Key-frames are found in temporal segments of arbitrary length (i.e., 3D scenes) using a dynamic programming algorithm which minimises the dissimilarity between the reconstructed and the original temporal segment. The dissimilarity measure is based on a combination of frame difference and visual relevance estimated through visual saliency maps. These maps result from attention modeling, taking into account spatial, temporal and depth features of the 3D video content. The results, evaluated using the Shot Reconstruction Degree and the Fidelity measure, show that the proposed method outperforms those obtained from uniform sampling and attention curve methods. This method may be useful for fast browsing of 3D video repositories.
- 3D PARTICLE SYSTEMS FOR AUDIO APPLICATIONSPublication . Fonseca, NunoAlthough particle systems are well know for their use in computer graphics, their application in sound is very rare or almost non-existent. This paper presents a conceptual model for the use of particle systems in audio applications, using a full rendering system with virtual microphones: several virtual particles are spread over a virtual 3D space, where each particle reproduces one of the available audio streams (or a modified version), and the overall sound is captured by virtual microphones. Such system can be used on several audio-related areas like sound design, 3D mixing, reverb/impulse response design, granular synthesis, audio up-mixing, and impulse response up-mixing.
- 3D printed models-based lab activities to enhance learning-teaching processes in Structural Engineering coursesPublication . Celorrio-Barragué, Luis; Calvo-Simón, Sergio; Gaspar, Marcelo; Vidal-Cortés, Mariano; Martín-Ramos, PabloThree-dimensional (3D) printing is a promising tool in Engineering education, as it can facilitate learning, contribute to the development of key skills and competences, increase the engagement and interest of students, and promote their creativity. In this work, a set of laboratory activities aimed at enhancing the learning-teaching experience of sophomore and junior students of engineering degrees related to structures is presented. To improve their understanding and their ability to calculate the stability, strength and rigidity of built structures, the use of 3D printed models is put forward. These printed models can be used as specimens in lab tests and also as visualization objects to improve students' comprehension in lectures. Moreover, they offer interesting advantages in terms of their lower cost, easy manipulation, low weight and short time of production. Five lessons, designed for Strength of Materials and Theory of Structures courses, which cover tensile testing, the analysis of truss and plane frames, bolted and welded joints, and constructive details in reinforced concrete structures are discussed.
- 3D video shot boundary detection based on clustering of depth-temporal featuresPublication . Ferreira, Lino; Assunção, Pedro; Cruz, Luis A. da SilvaThis paper proposes an algorithm for automatic detection of 3D video shots with different perceptual features. The proposed algorithm is able to identify distinct three-dimensional visual scenes by detecting 3D video shot boundaries based on clustering of depth-temporal features. A combination of texture variation along the temporal dimension and depth variance is used by K-means clustering to find the stereo frames which comprised the 3D scene boundaries. An important characteristic of the proposed algorithm in comparison with others published in the literature for temporal segmentation of classic 2D video is that no thresholds are used in the decision processes neither training data sets. The experimental results show that the proposed method is capable of achieving high recall (e.g., 0.95) and precision rate (e.g., 1.0) in video sequences with both sharp and smooth 3D scene transitions.
- 4D Light Field Disparity Map estimation using Krawtchouk PolynomialsPublication . Lourenco, Rui; Rivero-Castillo, Daniel; Thomaz, Lucas A.; Assuncao, Pedro A. A.; Tavora, Luis M. N.; Faria, Sergio M. M. deThis work presents an improved method to estimate disparity maps obtained from light field cameras using a novel edge detection algorithm based on Krawtchouk polynomials. The proposed method takes advantage of these polynomials to determine gradient information and find the edges based on automatically estimated weak and strong thresholds. The calculated edges in the gray scale epipolar plane image representation of a light field are then used to improve the accuracy of object boundaries in the the disparity map. The proposed method achieves better results when compared to other edge detection algorithms, both in terms of objective and subjective quality, specifically by reducing the mean squared error and the artifacts in the object boundaries. Furthermore, on average, the proposed method outperforms the state-of-the-art depth estimation algorithms, in terms of the objective quality of the final disparity map, namely for the commonly used HCI dataset.
- 802.21-MPA-IMS ArchitecturePublication . Rodrigues, Carlos Miguel de Jesus; Rabadão, Carlos; Pereira, AntónioMobility has become a keyword nowadays with the evolution of mobile devices market and proliferation of realtime services. IP Multimedia Subsystem (IMS) is a single, standardized service framework that supports voice, video, data and messaging services, but does not provide seamless mobility for packet based sessions. This paper purposes an IMS architecture with IEEE 802.21 and media-independent pre-authentication (MPA) integrated. IEEE 802.21 can enable this seamless mobility in IMS and, additionally, MPA provides a secure handover optimization scheme, reducing, as a consequence, handover latency. The main goal of this architecture is to provide seamless and secure handovers between different access technologies in an IMS-based environment.