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Publicações

Publicações por CTM

2010

Improving P2P video streaming in wireless mesh networks

Autores
Salta, N; Morla, R; Ricardo, M;

Publicação
The 9th IFIP Annual Mediterranean Ad Hoc Networking Workshop, Med-Hoc-Net 2010, Juan Les Pins, France, 23-25 June, 2010

Abstract
P2P Video Streaming has become a reliable and efficient solution for distributing video on the Internet. Similarly to regular P2P file-sharing, all the participating nodes exchange information. Wireless Mesh Networks, in turn, can be seen as a cost-effective solution to extend Internet access networks. In this paper we propose improvements to P2P Video Streaming. These improvements can provide gains in scenarios where the service is deployed over Wireless Mesh Networks and the nodes are simultaneously peers and packet forwarders. By using cross-layer interactions between application and network layers, we show that the proposed improvements reduce substantially the amount of traffic in the network. ©2010 IEEE.

2010

WiMetroNet A Scalable Wireless Network for Metropolitan Transports

Autores
Ricardo, M; Carneiro, G; Fortuna, P; Abrantes, F; Dias, J;

Publicação
Sixth Advanced International Conference on Telecommunications, AICT 2010, 9-15 May 2010, Barcelona, Spain

Abstract
This paper addresses Wireless Networks for Metropolitan Transports (WNMT), a class of moving or vehicle-to-infrastructure networks that may be used by public transportation systems to provide broadband access to their vehicles, stops, and passengers. We propose the WiMetroNet, a WNMT that is auto-configurable and scalable. It is based on a new Ad hoc routing protocol, the Wireless Metropolitan Routing Protocol (WMRP), which, coupled with data plane optimizations, was designed to be scalable to thousands of nodes. © 2010 IEEE.

2010

An efficient mechanism for establishing IP connectivity in next-generation networks

Autores
Campos, R; Ricardo, M;

Publicação
INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS

Abstract
The changes in the communication paradigm envisioned for next-generation networks (NGNs), with peer-to-peer/symmetric attachments gaining momentum and two Internet Protocol (IP) versions coexisting, will pose new challenges to mobile communication networks. Traditional IP auto-configuration mechanisms will not work properly, since they were designed mostly having in mind a client-server/asymmetric attachment model, they assume a single IP version paradigm, and they target the auto-configuration of devices only. The IST Ambient Networks (ANs) project has introduced a new concept the AN that enables handling every communication entity, either a single device or an entire network, as an AN. This paper describes a new efficient mechanism, named Basic Connectivity (BC) mechanism, for auto-configuring IP connectivity between attaching ANs. A proof-of-concept prototype, experimental results, and theoretical analysis show that BC suites the future networking paradigm and represents a solution more efficient than the current trial-and-error mechanism for auto-configuring IP connectivity. Copyright (C) 2009 John Wiley & Sons, Ltd.

2010

A semantic management model to enable the integrated management of media and devices

Autores
Viana, P; Alves, AP;

Publicação
MULTIMEDIA TOOLS AND APPLICATIONS

Abstract
The challenge of managing large scale media assets has led to the development of metadata schemas that are expected to enable efficient search and retrieval of multimedia content. Those approaches propose schemas that can range from simple keyword based descriptions to complex hierarchical organization of information. However, effective media asset management requires more than content searching and retrieval: underlying infrastructures are usually complex, require the use of a number of different equipment and management decisions have to be done based on information available from the multimedia metadata layer as well as on data describing system resources and capabilities. In this paper we propose a new ontology that aggregates information from different sources and enables a top level business oriented view of multimedia archives.

2010

A comparison between voltage and true power based embedded measurements for RF testing

Autores
Mota, P; Da Silva, JM;

Publicação
Proceedings of the 2010 IEEE 16th International Mixed-Signals, Sensors and Systems Test Workshop, IMS3TW 2010

Abstract
Peak voltage sensors, namely diode based detectors, have been used for in-circuit testing of RF circuits. These detectors are simple to implement but provide a limited accuracy. On the other hand, the power inferred from these measurements assumes that impedance is known. This work presents a comparison between measurements obtained with peak voltage and true power detectors. The trade-off between observing one and the other are discussed, namely as far as information concerning the output load is concerned. Simulation results, acquired with the model of a prototype demonstration chip, show that more accurate information is obtained with power rather than voltage measurements in case load impedance variations occur. Experimental results obtained with a prototype chip are currently being obtained. ©2010 IEEE.

2010

Evaluation of RF Pa nonlinearities based on cross-correlation between current and output voltage

Autores
Mota, P; Da Silva, JM; Veiga, R;

Publicação
5th Conference on Design and Technology of Integrated Systems in Nanoscale Era, DTIS 2010

Abstract
The estimation of 1 dB compression and third-order intercept points can be obtained after the cross-correlation between dynamic current and output voltage of radio frequency power amplifiers. Estimation is performed using power measures and not power inferred from voltage measures. The underlining theory and a correlator that allows implementing this measurement on-chip are presented. The trade-off between measuring voltage or the actual power is also discussed. It is also shown that different information concerning the output load is obtained when observing the PA's output voltage and power. Simulation results, obtained with the model of a prototype demonstration chip show that good accuracy can be obtained with relatively simple measurement conditions. These results include the analysis of optimum stimuli amplitudes and the effect of noise in estimation accuracy. © 2010 IEEE.

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