Manuel Esteve

Reference current computation methods for active power filters: accuracy assessment in the frequency domain

This paper focuses on the steady-state response of existing methods for computing the reference current of active power filters. For each class of methods, the main source of discrepancy between the load harmonic current and the computed reference current is identified and the frequency spectrum of the resulting error is analytically determined. Although this topic has been partially addressed in previous publications, the proposed frequency-domain approach provides valuable qualitative information about how the errors are produced and distributed, which is masked when the analysis is carried out in the time domain. First, the frequency-domain formulation is separately presented for each method. Then, a comparison of the resulting errors is performed on a case study. Finally, some experimental results are given to validate the proposed frequency-domain analysis.

CDN-Supported Collaborative Media Streaming Control

We propose a system called Comodin, based on a content distribution network (CDN), that provides collaborative media playback services. Specifically, the system enables an Internet-based interactive media service for e-learning and e-entertainment, allowing an explicitly formed group of clients to view and cooperatively control a shared remote media playback

A video streaming application for urban traffic management

Urban traffic control systems have based their technological infrastructure both on advanced analog close-circuit television systems (CCTV) and point-to-point links, providing difficult-to-scale and very expensive systems. The main goal of an urban traffic monitoring system is to capture, send, play and distribute video information from the streets of a certain city to a management centre where it is processed by different services. Current digitalization process of video networks, and the research carried out in the field of streaming media, has led vendors to present proprietary hardware and software solutions resulting in a strong dependency by their customers. This work presents an open urban traffic control system based in commercial off-the-shelf (COTS) philosophy for hardware and software components, as well as open source and standardized protocols. The existence of open standards for video encoding and protocols for streaming media transmission over IP networks has led to the proposal of such a system. The proposed system is a suitable solution in terms of scalability, cost, interoperability and performance for traffic control systems. Furthermore, its architecture can be easily adapted to other video applications and tools like command and control, surveillance or security systems for military and civilian applications.

Modeling content delivery networks and their performance

Content Distribution Networks (CDN) have recently appeared as a method for reducing response times experienced by Internet users through locating multiple servers close to clients. Many companies have deployed their own CDN-and so demonstrating the resulting effectiveness. However, many aspects of deployment and implementation remain proprietary, evidencing the lack of a general CDN model to help the research community analyze different working scenarios. In this paper, we propose a general expression for a content distribution environment and study the performance impact of design variables such as caching hit ratios, network latency, number of surrogates, and server capacity. Our conclusions are supported with simulations results.

Feedback Flow Control with Hysteresial Techniques for Multimedia Retrievals

The objective of this paper is to demonstrate the advantages of using hysteresial techniques in flow control mechanisms. The work scenario consists of a server transmitting video information to a group of clients. Each client stores the information in a buffer and then plays it back at a set consumption rate. To avoid “overflow” or “underflow” in the buffer, the client sends control messages (feedbacks) to the server which order adjustments in the transmission rate. Hysteresial techniques allow the minimization of this signaling traffic, even when there are rapid fluctuations in the buffer occupation. As a first step, an analytical model is developed using Markovian processes. This produces expressions of the most relevant parameters and allows the evaluation of the proposed flow control mechanism. The Markovian model has been compared with the performance of a multimedia application for video distribution, running in a real scenario. The results show that the model represents qualitatively the real scenario and consequently validates the model usefulness.

3D Wireless Sensor Network Modeling and Simulation

During the last years, an intensive research activity in WSN has supposed an important improvement in the technology of this networks. The design of wireless networks has always been focused on an specific point of view, networks in a bidimensional space. Nowadays this design is not enough and the study of the third dimension is needed. In this work we will see a study of three-dimensional networks and their behaviour in so important aspects like cover, connectivity and energy consumption. The development of some models of transmission for the study of energy consumption and the results obtained in simulations of three-dimensional networks are shown in the paper. We think that considering the desired efficiency of the network in all this different aspects we think there is a good beginning for the designers of 3D networks. There are also some conclusions obtained from the studies that can be useful for many different applications of this kind of networks.

I3WSN: Industrial Intelligent Wireless Sensor Networks for indoor environments

Sensor Web Enablement (SWE) technologies have been successfully applied to a great variety of outdoor scenarios but, in practical terms, little effort has been applied for indoor environments, and even less in the field of industrial applications. This article presents an intelligent SWE application for an indoor and industrial scenario, with the aim of improving and increasing the levels of human safety. The base low-level architecture is built on top of wireless sensor networks (WSN) connected to a Sensor Observation Service (SOS). Higher layers in the architecture include services that make real time decisions based on the collected data. Both simulation and experimental results are presented. The paper shows the viability of our approach in terms of performance, scalability, modularity and safety.

A social framework for content distribution in mobile transient networks

Transient networks are spontaneous networks that appear for a short period of time in order to provide basic services such as connectivity and content distribution among a small community. Nowadays mobile devices are becoming multimode by nature providing multiple connection paths. This paper investigates the efficiency and benefit of a mobile transient network where multiple nodes collaborate offering a multihomed network with community services by means of intelligent agents. The paper also proposes the required architecture and negotiation protocols for such scenario with two different services: file downloading and multimedia streaming.

Wireless CDN video streaming architecture for IPTV

Wireless IPTV (Internet Protocol TeleVision) aims to make the traditional IPTV and related services available to users anywhere, anytime, on any device, and through any network. Mobile streaming TV is one of the alternatives to deploy such a system; others are DVB-H or MediaFLO. In this paper we propose an alternative CDN-based architecture to distribute contents to different access networks, in order to create a triple screen platform. The core elements of the system are the video streamers, acting as surrogates of the mobile CDN-based architecture, installed in the access networks (including mobile), and the transcoding servers in the premises of the content providers. The paper focused on the wireless part of the system, analyzing the architecture and performance results related with the video coding and the efficiency obtained due to the placement of the streaming servers. The system has been deployed by a Spanish media company for its use with different Telcos, ISPs and media companies.

A negotiation framework for content distribution in mobile transient networks

Transient networks are spontaneous networks that appear for a short period of time in order to provide basic services such as connectivity and content distribution among a small community. Nowadays mobile devices are becoming multimode by nature providing multiple connection paths. This paper investigates the efficiency and benefit of a mobile transient network where multiple nodes collaborate, offering a multihomed network with community services by means of intelligent agents. The paper concretely proposes an architecture able to fully support a peer-to-peer transient community during both negotiation and service steps for two different modes: file download and multimedia streaming. The first mode, implemented on intelligent and cooperative agents, provides two negotiation models (fair and dynamic) in order to guarantee wider flexibility for different possible scenarios and community models; the second one implements a content delivery system into transient community, taking advantage of multihomed features of mobile devices.