Browsing by resource type "conference paper"
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- 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.
- 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.
- Accessibility Not on Demand - An Impaired SituationPublication . Silva, João de Sousa e; Gonçalves, Ramiro; Pereira, AntónioDigital accessibility is recognized as a fundamental tool for an egalitarian society. Nevertheless, software accessibility is an under addressed topic in the discipline of software engineering and the academy in general. As a result, its development and implementation is compromised. This problem is depicted here with the help of some experiments that shows the poor attention which is dedicated to this topic. Some hypotheses that try to explain this problem are formulated, and some possible solutions are debated. As a conclusion, some insights are given and a new possible researched avenue is presented.
- Accuracy versus complexity of MARG-based filters for remote control pointing devicesPublication . Rasteiro, Miguel ; Costelha, Hugo; Conde Bento, Luis; Assunção, PedroAlthough most current pointing devices rely on relative rotation increments, absolute orientation allows for a more intuitive interaction. However, this is difficult to implement in low-energy consumption devices since accurate fusion filters are computationally intensive. This work presents a comparative study of low-complexity filters and state-of-the-art orientation tracking systems, enabling to access complexity versus portability. A relevant set of different MARG units currently available on the market were studied under systematic tests and human subjective user analysis. Experimental results show that it is possible to obtain similar accuracy using low-complexity filters to the ones observed with state-of-the-art orientation tracking systems. © 2015 IEEE.
- Acessibilidade no Ciclo de Vida do Software: Um exercício de maiêutica na engenharia de softwarePublication . Silva, João de Sousa e; Goncalves, Ramiro; Pereira, AntónioA acessibilidade é bastante desqualificada na engenharia de software, o que compromete a sua vulgarização. Neste artigo, este problema é explicado e são evidenciadas algumas das suas consequências. São apresentados alguns conceitos chave da acessibilidade digital, que vão além da acessibilidade Web. A principal contribuição deste artigo é a apresentação de um esquisso de proposta de modelo de desenvolvimento, onde a acessibilidade está presente em todo o ciclo de vida de software, de uma forma explícita e justificada, tendo como base as quatro principais fases presentes na maioria dos modelos de desenvolvimento de software.
- Active stereo tracking of multiple free-moving targetsPublication . Perdigoto, Luis; Barreto, João P.; Caseiro, Rui; Araujo, Helder; Perdigoto, Luis;This article presents a general approach for the active stereo tracking of multiple moving targets. The problem is formulated on the plane, where cameras are modeled as ”line scan cameras” and targets are described as points with unconstrained motion. We propose to control the active system parameters in such a manner that the images of the targets in the two views are related by an homography. This homography is specified during the design stage and implicitly encodes the tracking behavior. It is shown that this formulation leads to an elegant geometric framework that enables to decide about the feasibility of a particular active tracking task. We apply it to prove that two cameras with rotation and zoom control, can track up to three moving targets, while assuring that the image location of each target is the same for both views. In addition, the framework is also useful for devising tracking strategies and deriving the required control equations. This feature is illustrated through a real experiment on tracking two independent targets using a binocular stereo head.
- Ad-hoc changes in IoT-aware business processesPublication . Domingos, Dulce; Martins, Francisco; Martinho, Ricardo; Silva, MárioThe Internet of Things makes it possible to adapt the behaviour of business processes in response to real-time context updates. In addition, physical items can run and validate parts of the business processes and optimise their execution, while reducing message transmissions. State-of-the-art event-driven, service-oriented architecture approaches contribute to enabling inter-organisational collaboration and interoperability of heterogeneous hardware, but their applicability is limited to preplanned, well-structured processes. We take a step forward by supporting ad-hoc changes within business processes, considering changes in the state of the Things; likewise, whenever needed, the software controlling the behaviour of sensors may be dynamically reconfigured as a result of changes in the functional specifications of business processes.
- Adaptive least squares prediction for stereo image codingPublication . Lucas, Luis F. R.; M. M. Rodrigues, Nuno; Silva, Eduardo A. B. da; Faria, SergioState-of-the art approaches towards stereo image coding exploit inter-view redundancy by employing block-matching methods for disparity estimation and compensation. However, the efficiency of these methods is affected by mismatched areas, due to occlusions, brightness variations, or perspective distortion between objects of the two views. In this paper we present a new prediction scheme for stereo image coding, that combines an implicit disparity estimation method, with an adaptive least squares (LS)-based filtering. The Multidimensional Multiscale Parser image coding algorithm was used to evaluate the efficiency of the proposed scheme. Experimental results demonstrate the advantage of LS prediction in stereo image coding. Furthermore, the rate-distortion performance of the MMP based stereo encoder is well above that of the state-of-the-art H.264/AVC Stereo Profile, especially at medium and high bit rates.