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Publicações

Publicações por CTM

2016

Smartphone-based Transport Mode Detection for Elderly Care

Autores
Cardoso, N; Madureira, J; Pereira, N;

Publicação
2016 IEEE 18TH INTERNATIONAL CONFERENCE ON E-HEALTH NETWORKING, APPLICATIONS AND SERVICES (HEALTHCOM)

Abstract
Smartphones are everywhere, and they are a very attractive platform to perform unobtrusive monitoring of users. In this work, we use common features of modern smartphones to build a human activity recognition (HAR) system for elderly care. We have built a classifier that detects the transport mode of the user including whether an individual is inactive, walking, in bus, in car, in train or in metro. We evaluated our approach using over 24 hours of transportation data from a group of 15 individuals. Our tests show that our classifier can detect the transportation mode with over 90% accuracy.

2016

Cyber-physical systems clouds: A survey

Autores
Chaari, R; Ellouze, F; Koubaa, A; Qureshi, B; Pereira, N; Youssef, H; Tovar, E;

Publicação
COMPUTER NETWORKS

Abstract
Cyber-Physical Systems (CPSs) represent systems where computations are tightly coupled with the physical world, meaning that physical data is the core component that drives computation. Industrial automation systems, wireless sensor networks, mobile robots and vehicular networks are just a sample of cyber-physical systems. Typically, CPSs have limited computation and storage capabilities due to their tiny size and being embedded into larger systems. With the emergence of cloud computing and the Internet-of-Things (IoT), there are several new opportunities for these CPSs to extend their capabilities by taking advantage of the cloud resources in different ways. In this survey paper, we present an overview of research efforts on the integration of cyber-physical systems with cloud computing and categorize them into three areas: (1) remote brain, (2) big data manipulation, (3) and virtualization. In particular, we focus on three major CPSs namely mobile robots, wireless sensor networks and vehicular networks.

2016

User-friendly imaging algorithms for interferometry

Autores
Young, J; Thiebaut, E; Duvert, G; Vannier, M; Garcia, P; Mella, G;

Publicação
OPTICAL AND INFRARED INTERFEROMETRY AND IMAGING V

Abstract
OPTICON currently supports a Joint Research Activity (JRA) dedicated to providing easy to use image reconstruction algorithms for optical/IR interferometric data. This JRA aims to provide state-of-the-art image reconstruction methods with a common interface and comprehensive documentation to the community. These tools will provide the capability to compare the results of using different settings and algorithms in a consistent and unified way. The JRA is also providing tutorials and sample datasets to introduce the principles of image reconstruction and illustrate how to use the software products. We describe the design of the imaging tools, in particular the interface between the graphical user interface and the image reconstruction algorithms, and summarise the current status of their implementation.

2016

GRAVITY acquisition camera : characterization results

Autores
Anugu, N; Garcia, P; Amorim, A; Wiezorrek, E; Wieprecht, E; Eisenhauer, F; Ott, T; Pfuhl, O; Gordo, P; Perrin, G; Brandner, W; Straubmeier, C; Perraut, K;

Publicação
OPTICAL AND INFRARED INTERFEROMETRY AND IMAGING V

Abstract
GRAVITY acquisition camera implements four optical functions to track multiple beams of Very Large Telescope Interferometer (VLTI): a) pupil tracker: a 2 x 2 lenslet images four pupil reference lasers mounted on the spiders of telescope secondary mirror; b) field tracker: images science object; c) pupil imager: reimages telescope pupil; d) aberration tracker: images a Shack-Hartmann. The estimation of beam stabilization parameters from the acquisition camera detector image is carried out, for every 0.7 s, with a dedicated data reduction software. The measured parameters are used in: a) alignment of GRAVITY with the VLTI; b) active pupil and field stabilization; c) defocus correction and engineering purposes. The instrument is now successfully operational on-sky in closed loop. The relevant data reduction and on-sky characterization results are reported.

2016

Efficient Solar Scene Wavefront Estimation with Reduced Systematic and RMS Errors: Summary

Autores
Anugu, N; Garcia, P;

Publicação
GROUND-BASED SOLAR OBSERVATIONS IN THE SPACE INSTRUMENTATION ERA

Abstract
Wave front sensing for solar telescopes is commonly implemented with the Shack-Hartmann sensors. Correlation algorithms are usually used to estimate the extended scene Shack-Hartmann sub-aperture image shifts or slopes. The image shift is computed by correlating a reference sub-aperture image with the target distorted sub aperture image. The pixel position where the maximum correlation is located gives the image shift in integer pixel coordinates. Sub-pixel precision image shifts are computed by applying a peak-finding algorithm to the correlation peak Poyneer (2003); Ladahl (2010). However, the peak-finding algorithm results are usually biased towards the integer pixels, these errors are called as systematic bias errors Sjodahl (1994). These errors are caused due to the low pixel sampling of the images. The amplitude of these errors depends on the type of correlation algorithm and the type of peak-finding algorithm being used. To study the systematic errors in detail, solar sub-aperture synthetic images are constructed by using a Swedish Solar Telescope solar granulation image 1. The performance of cross-correlation algorithm in combination with different peak-finding algorithms is investigated. The studied peak-finding algorithms are: parabola Poyneer (2003); quadratic polynomial Difdahl (2010); threshold center of gravity Bailey (2003); Gaussian Nobach & Honkanen (2005) and Pyramid Bailey (2003). The systematic error study reveals that that the pyramid fit is the most robust to pixel locking effects. The RMS error analysis study reveals that the threshold centre of gravity behaves better in low SNR, although the systematic errors in the measurement are large. It is found that no algorithm is best for both the systematic and the RMS error reduction. To overcome the above problem, a new solution is proposed. In this solution, the image sampling is increased prior to the actual correlation matching. The method is realized in two steps to improve its computational efficiency. In the first step, the cross correlation is implemented at the original image spatial resolution grid (1 pixel). In the second step, the cross-correlation is performed using a sub-pixel level grid by limiting the field of search to 4 x 4 pixels centered at the first step delivered initial position. The generation of these sub-pixel grid based region of interest images is achieved with the bi-cubic interpolation. The correlation matching with sub-pixel grid technique was previously reported in electronic speckle photography Sjodahl (1994). This technique is applied here for the solar wavefront sensing. A large dynamic range and a better accuracy in the measurements are achieved with the combination of the original pixel grid based correlation matching in a large field of view and a sub-pixel interpolated image grid based correlation matching within a small field of view. The results revealed that the proposed method outperforms all the different peak finding algorithms studied in the first approach. It reduces both the systematic error and the RMS error by a factor of 5 (i.e., 75% systematic error reduction), when 5 times improved image sampling was used. This measurement is achieved at the expense of twice the computational cost. With the 5 times improved image sampling, the wave front accuracy is increased by a factor of 5. The proposed solution is strongly recommended for wave front sensing in the solar telescopes, particularly, for measuring large dynamic image shifts involved open loop adaptive optics. Also, by choosing an appropriate increment of image sampling in trade-off between the computational speed limitation and the aimed sub-pixel image shift accuracy, it can be employed in closed loop adaptive optics. The study is extended to three other class of sub-aperture images (a point source; a laser guide star; a Galactic Center extended scene). The results are planned to submit for the Optical Express journal.

2015

UNIT: Multicast using Unicast Trees

Autores
Teixeira, F; Coutinho, N; Figueira, D; Campos, R; Sargento, S; Ruela, J;

Publicação
2015 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATION WORKSHOP

Abstract
The proliferation of broadband wireless accesses has enabled the provisioning of multimedia communication services. Yet, the increasing demand for group-based multimedia services requires the development of new architectures capable of seamlessly delivering multi-party content and overcoming the prevailing heterogeneity and dynamics of current and next generation communication networks. In order to face these challenges we introduce UNIT, a solution that integrates multicast technologies for both core and access wireless mesh networks. UNIT is focused on the scalability and flexibility of the content delivery framework, adopting a hierarchical control strategy that enables seamless multi-party content transport over heterogeneous networks. Moreover, UNIT performs local reconfigurations of the content distribution tree in response to any context change, without impairing the remaining branches. The evaluation of UNIT in a real world demonstrator proves its feasibility and the efficiency of the proposed mechanisms regarding the control of the multi-party delivery trees.

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