Percorrer por autor "Cruz, Luis"
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- A flexible monitor for assessing 3D video QoE in real-timePublication . João, Ricardo; Marinheiro, Rui; Assunção, Pedro; Cruz, LuisWith the evolution of 3D technology, 3D IPTV services may prove to be a common service widely distributed by operators. So it is important that they have the necessary means to easily and inexpensively monitor the Quality of Experience (QoE) of this new service. Deployment of 3D video QoE monitors anywhere in the network will enable operators to adapt their service and network infrastructure in order to guarantee a desired QoE level, e.g., in scenarios where 3D IPTV streaming is offered to users with multi-homed equipment and simultaneous access to the network by means of heterogeneous smartcells in the customer premises. This paper presents a prototype developed for monitoring 3D video QoE in multiple use-case scenarios. A novel aspect is that this monitor may inspect video using several inputs, allowing different coding standards and encapsulation schemes. It can either analyze offline captures or perform real-time monitoring, and operate either using a graphical user interface or in command line mode. The latter allows its integration in network embedded devices like smartcells. The prototype puts in practice a flexible architecture that allows easy integration of modules new QoE evaluation models.. To demonstrate the monitor applicability and validate its performance in a real use-case scenario, a video-plus-depth QoE assessment model was implemented and extensive tests were performed with real traffic data, using the ITU-T G.1050 recommendation to simulate network impairments. It has been demonstrated that inferred quality results have a very high correlation with the measured quality values
- Optimal priority MDC video streaming for networks with path diversityPublication . Correia, Pedro; Ferreira, Lino; Assunção, Pedro; Cruz, Luis; Silva, VitorThis paper proposes a robust video streaming scheme for priority networks with path diversity, based on a combined approach of multiple description coding (MDC) with optimal picture classification into two priorities. A binary classification algorithm is proposed to define high (HP) and low (LP) priority network abstraction layer units (NALU), which in turn define the packet priorities. An optimisation algorithm is used to find HP pictures, based on dynamic programming and relying on minimisation of the packet loss concealment distortion. The paper shows that the proposed algorithm is able to effectively improve the decoded video without increasing the MDC stream redundancy. The overall performance evaluation, carried out by simulating MDC video streaming over lossy networks with path diversity, demonstrates that the proposed algorithm yields higher video quality for a wide range of packet loss rates (PLR). Comparing with no-priority MDC video streaming schemes, the simulation results show that the proposed algorithm can improve the average PSNR results in 0.7-3.2dB for packet loss rates between 3% and 15%.
- Using Count Data and Ordered Models in National Forest Recreation Demand AnalysisPublication . Simões, Paula; Barata, Eduardo; Cruz, LuisThis research addresses the need to improve our knowledge on the demand for national forests for recreation and offers an in-depth data analysis supported by the complementary use of count data and ordered models. From a policy-making perspective, while count data models enable the estimation of monetary welfare measures, ordered models allow for the wider use of the database and provide a more flexible analysis of data. The main purpose of this article is to analyse the individual forest recreation demand and to derive a measure of its current use value. To allow a more complete analysis of the forest recreation demand structure the econometric approach supplements the use of count data models with ordered category models using data obtained by means of an on-site survey in the Bussaco National Forest (Portugal). Overall, both models reveal that travel cost and substitute prices are important explanatory variables, visits are a normal good and demographic variables seem to have no influence on demand. In particular, estimated price and income elasticities of demand are quite low. Accordingly, it is possible to argue that travel cost (price) in isolation may be expected to have a low impact on visitation levels.