Percorrer por autor "Soares, S."
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- ArQoS®: System to monitor QoS/QoE in VoIPPublication . S. Cardeal; Neves, Filipe; Soares, S.; Tavares, F.; Assunção, PedroThe evolution of telecommunications technology from circuit to packet switching, in which the Internet is the great paradigm, offers nowadays more flexibility in services and higher efficiency in the transport infrastructure that was not experienced before. As consequence, several new services have emerged. Among them, Voice over IP (VoIP) is, indubitably, one of the most popular, mainly because it allows anyone to make low cost voice calls, making it a very attractive service. This is perhaps one of the main factors responsible for the fast development of VoIP technology. However, IP networks were not designed for services with real time requirements and factors like delay, jitter, codec distortions and packet loss lead to degradations that directly influence de VoIP user experience. The quality experienced by these users is highly dependent on network conditions and also on the subjective experience perceived by them. Thus, new challenges have brought with this evolution of telecommunications networks. In order to meet the assigned Service Level Agreement (SLA's), service providers around the world need to monitor and guarantee the agreed Quality of Service (QoS) to its customers. Consequently, an emergent way to measure QoS arises in the field of the telecommunications sector: the Quality of Experience (QoE) assessment and monitor that takes into account that subjective experience. Thus, a new challenging need arises: the development of systems and methods for assessing quality of experience, such that, network operators and service providers can actually know how users evaluate the quality of the service provided to them. In this paper, a system for assessing QoS/QoE is described: the ArQoS®. This is an integrated system provided by Portugal Telecom Inovação (PTIn) which implements QoE assessment methods to assess the networks performance and their telecommunications services. Beyond the existing methods already supported by the system, a novel QoE monitor for VoIP services was recently integrated as a result of fundamental research carried out at PTIn Labs. The ArQoS® is a probing system based on different types of probes, actually comprising two systems operating in two different modes: the active system (intrusive mode) and the passive system (non-intrusive mode).
- Depth map concealment using interview warping vectors from geometric transformsPublication . Marcelino, S.; Assunção, P.; Faria, S.M.M.; Soares, S.This paper deals with reconstruction of corrupted depth maps received by multivew video-plus-depth (MVD) decoders from error prone channels. An interview-based method is proposed using warping vectors obtained through a block matching approach with geometric transforms (BMGT) between two colour views. It is shown that BMGT is able to find efficient warping vectors for reconstruction of lost regions in the depth maps associated with the colour views. The proposed concealment method uses an additional contour reconstruction technique, applied to arbitrary shapes within the lost regions, which is used for weighted interpolation. In comparison to a reference method based on simple weighted interpolation, the proposed method is able to achieve PSNR gains in synthesised views up to 5.61dB, at data loss ratios up to 40%.
- Efficient depth error concealment for 3D video over error-prone channelsPublication . Marcelino, S.; Assunção, P.; Faria, Sérgio M. M. de; Soares, S.This paper addresses the problem of multivew videoplus-depth (MVD) decoding with corrupted depth maps due to transmission errors. A method for spatial error concealment of depth maps in MVD is proposed to efficiently recover lost blocks. The proposed method relies on the colour image and geometric curve fitting for accurate reconstruction of the lost contour segments in the corresponding depth map areas. Such reconstructed depth map contours are then used as boundaries at different depth planes to recover the missing depth values through weighted interpolation. The method performance is evaluated by the objective quality (PSNR) of the synthesised views. Images decoded with the reconstructed depth maps are compared with those of a reference method based on bidirectional interpolation. The proposed method exhibits PSNR gains up to 1.66dB higher than the reference one and better performance is consistently achieved for different visual content.
- Error recovery of image-based depth maps using Bézier curve fittingPublication . Marcelino, S.; Assunção, Pedro; Faria, Sergio; Soares, S.This paper proposes a method to recover lost regions in image-based depth maps used in video plus depth 3D format. This method performs depth maps reconstruction taking into account depth contours within the lost regions. This is achieved by extracting the contours and recovering their lost segments based on Bézier curve fitting, followed by spatial interpolation. The proposed method maintains contour smoothness and uses them as the boundary limits of homogeneous depth regions, which are then filled through weighted pixel interpolation. The experimental results show that the proposed method yields better synthesized images than classic spatial concealment methods, uniquely based on pixel interpolation techniques. The method presented in this paper is able to outperform the reference method, in terms of PSNR by up to 1.91dB. The subjective quality is also shown as being significantly better.
- Quality evaluation of depth map error concealment using a perceptually-aware objective metricPublication . Marcelino, S.; Faria, S.; Pepion, R.; Le Callet, P.; Soares, S.; Assunção, P.This paper presents a quality evaluation study on the performance of error concealment methods for depth maps used in multiview video-plus-depth (MVD). The research deals with the problem of decoding corrupted depth maps received from error-prone networks, where the quality of the reconstructed depth data is not always directly related to the quality of the virtual views synthesised by those maps. Even after error concealment such distortions are not particularly perceived as other known types, such as coding distortion. Thus, traditional quality metrics are not adequate to capture all the relevant features. In this work, the performance of two error concealment methods for depth maps is evaluated using a perceptually-aware objective metric. This metric is validated through subjective assessment of virtual views synthesised with concealed depth maps. Each subjective test is performed by comparing the relative quality between between two synthesised images using different error concealment methods. The perceptual impact of reconstruction in corrupted depth of MVD is evaluated under various loss rates, using several colour images and depth maps encoded at multiple quantisation steps. The achieved results reveal that the proposed objective quality metric is mostly inline with user preferences, in respect to the relative performance of each error concealment method.
- Quantification of Maximal Force Produced in Standard and Contra-Standard Sculling in Synchronized Swimming. A Pilot StudyPublication . Diogo, V.; Soares, S.; Tourino, C.; Carmo, C.; Aleixo, I.; Morouço, P.; Figueiredo, P.; Vilas-Boas, J. P.; Fernandes, R. J.Studies carried out in synchronized swimming are very scarce, namely those which include biomechanical analysis of the sculling technique. The purpose of this study was to measure the maximal force produced in standard and contra-standard sculling, using a 30s maximal tethered synchronized swimming test. One former female synchronized swimmer and one former female swimmer performed a 2x30s maximum intensity tethered synchronized swimming test, in standard and contra-standard sculling conditions, respectively. Parameters studied were maximal, mean and minimum force, the time when maximal and minimum force occurred, and fatigue index. Results showed that the higher values of maximal and mean force were found in standard sculling, both for the synchronized swimmer and the swimmer. The swimmer attained higher values of absolute and relative maximal force in the standard sculling, but lower values in the contra-standard technique, when compared to the synchronized swimmer. Fatigue Index results evidence that the maximal force declined during the 30s in both participants and in both sculling conditions. This parameter was higher for the contra-standard sculling performed by the swimmer, and for the standard sculling for the synchronized swimmer. In conclusion, there were differences in force production in standard and contra-standard sculling between a swimmer and a synchronized swimming. Those differences could probably be explained by differences in skill competence.
- Robust decoding of MDC depth maps for enhanced 3D video over hybrid broadcasting networksPublication . Marcelino, S.; Correia, P.; Faria, Sergio; Soares, S.; Assunção, PedroThis paper addresses the problem of robust decoding of 3D video over hybrid broadcast networks, using Multiple Description Coding (MDC). Despite the fact that MDC allowsdecoding of any description even when the others are lost in the multipath network, the resulting coarsely decoded depth maps produce unacceptable distortion in synthesised views. This is particularly harmful in the case of intra-coded depth slices because of subsequent error propagation. To achieve improved quality in the virtual views synthesised from MDC depth maps received with lost descriptions, a method is proposed based on the depth geometric information extracted from the received descriptions and also from texture motion. Accurate recovery of either lost or coarsely decoded depth slices from one single description, is achieved by jointly using motion information, depth map edges and spatially neighbouring depth values. Comparing with MDC decoding without enhanced reconstruction of lost descriptions, the proposed method reaches quality gains up to 2.29dB for loss rates of 10%.