Seminar Webcast
IT - Coimbra

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Raul Campos

September, 30th 2005
Multiple Description Image and Video Coding for Noisy Channels ( PDF)

Presentation by: Manuela Pereira
Length: 59 min

Multiple Description Image and Video Coding for Noisy Channels
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Nowadays, the high performance of image/video coding techniques makes possible several new applications that were impossible before due to the high bit rates involved. Moreover, today's networks achieve high transmission speeds and support data rates sufficient for video applications even in mobile communications. These two facts together promise a whole new world of communications. In fact, in the last decade the use of mobile communication and multimedia communication has seen an enormous increase, with the wireless channels considered as a transport medium for various types of multimedia information. Due to the high bit rates involved with multimedia, the scarcity of wireless bandwidth, the time-varying characteristics of the channel, and the power limitations of wireless devices, multimedia communications, specially the wireless ones, are a tremendous challenge. A particular joint source and channel coding method, known as Multiple Description Coding (MDC), has proven to be an effective way to provide error resilience with a relatively small reduction in compression ratio. The idea in MDC is to generate multiple independent descriptions of the source such that each description independently describes the source with a certain desired fidelity. When more than one description is available, they can be combined to enhance the quality. MDC is robust due to the redundancy of the MD of the same source and it may be scalable as each correctly received description improves the decoder performance. Also, MDC does not require prioritized transmission, as each description is independently decodable. We propose a robust joint source channel MDC method that is adapted to the transmission of images and videos on non stationary channels. The main advantage of this method is that it is well adapted for applications implying transmissions using unreliable and variable channels. Moreover, for its compression and synchronization capabilities it is appropriate for real time transmissions. We show that the proposed method present the best results, in terms of signal to noise ratio and of visual quality, when compared with other multiple description methods existing in the state of the art. Moreover, it is well adapted for applications where the standard methods of error control cannot easily adapt to the characteristics of the channel.

About the Speaker:
Prof. Auxiliar do Dep. de Informática da Universidade da Beira Interior
Investigadora do Pólo de Coimbra do Instituto de Telecomunicações

July, 21st 2005
Smart Antennas for Mobile Communications, The Importance of the Propagation Channel and Scenarios ( PDF)

Presentation by: João Gil
Length: 55 min

Smart Antennas for Mobile Communications,
The Importance of the Propagation Channel and Scenarios
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This seminar will deal with issues involved in the deployment of the so-called Smart Antennas (SAs), focusing on the importance of the propagation channel for their implementation in a mobile communications cellular network. Answers will be given on, e.g., How critical is the spatial separation of several grouped mobile users? How and why does it depend on the type of cellular environment? There will be a summarised introduction on the main types of SA structures and involved algorithms, following with a short description of some known Spatial Channel Models (standard and literature examples). Then, research will be presented on beamforming in multiuser propagation scenarios, dealing with its dependence on the spatial distribution of mobile users, e.g., grouped near a bus stop, or spread in a city plaza. Some related physical metrics will be provided, showing their relationships to beamforming performance and propagation channel richness. A natural link to Multiple-Input-Multiple-Output (MIMO) models, structures and techniques arises, since these are very much dependent on such channel richness and channel separation.

About the Speaker:
João M. Gil was born in Coimbra, Portugal, in 1971. He received the Ph.D. degree in Electrical and Computer Engineering from IST (Technical University of Lisbon) in 2004. He is currently a researcher of Instituto de Telecomunicações, at Lisbon, focusing work on channel characterisation and adaptive antennas, for Wireless/Mobile Communications. He received the Licenciatura and Master of Science degrees in Electrical Engineering from the University of Coimbra, Portugal, in 1994 and 1997, respectively. Since 1997, he has been an Assistant Lecturer at ESTG, Leiria Polytechnic Institute.

May, 11th 2005
Ethernet Passive Optical Networks (EPONs) - current developments ( PDF)

Presentation by: Marek Hajduczenia
Length: 62 min

Optical Access Networks - Current Developments Webcast
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Ethernet Passive Optical Networks (EPONs) are one of the major emerging access network technologies, providing means for low-cost deployment of optical connection line between the carrier s central office (CO) and the customer s site (curb FTTC, premises FTTP, home FFTH depending on the deployment scenario). EPON networks build on and extend the International Telecommunications Union (ITU) standard G.983 (defining other type of access networks APONs) while attempting to realize the Full Service Access Network (FSAN) dream by delivering converged data, video and voice services (so-called tri-play) over the same optical access network structure. During the seminar the current state of the art for EPONs will be presented, with detailed discussion on application of WDMA/TDMA/CDMA multiple access techniques and particular limitations imposed by each of them. Particular attention will be paid to recent developments in CWDMA (Coarse Wavelength Division Multiple Access), where novel VCSELs and low-cost tunable lasers promise a cost-effective solution for local access loop. Moreover, recent breakthrough in wavelength conversion and silicon laser technology promises rapid developments in CDMA (Coded Division Multiple Access), allowing for implementation of efficient coded access techniques and thus increased number of potential subscribers connected to a given distribution network. The seminar will be concluded with economical aspects of EPON developments and future prospects for 10 Gbit/s extension of EPON networks and current research results.

About the Speaker:
Marek Hajduczenia was born in Bialystok, Poland in 1979. He received his Msc and Engineer diplomas in electronics and telecommunication, specialization in optical transmission systems,, from Technical University in Bialystok, in 2003. In 2004 he was accepted for PhD studies at University of Coimbra, Portugal, and is currently working at Siemens S.A. on projects connected with EPONs (Dynamic Bandwidth Allocation schemes, network architectures). His main research interests include self-similar stochastic processes, access networks control management layer, IPv4/IPv6 transition problems, optical burst switching.

April, 13th 2005

Electromagnetic Scattering from Foliage and Vegetation:
Modelling and applications in Modern Wireless Communication Systems
( PDF)

Presentation by Rafael Caldeirinha
Length: 68 min
Electromagnetic Scattering from Foliage and Vegetation:
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Electromagnetic scattering and propagation in foliage and vegetation is a complex problem because of the multiple scattering between a mixture of randomly distributed components of the medium, including the ground surface. The task of modelling a complete vegetation medium must include all the interactions between the separate components of the vegetation, including the soil. Various volume and scattering theories have been developed for modelling the scattering and propagation in such random media. Basically, there are three main approaches: the field approach, the energy/intensity approach and the statistical approach. In the past few years, some research work has been done within the Instituto de Telecomunicações in Collaboration with several british research Institutions to develop models based on such formulation. This presentation aims to give an overview of those models developed, together with some results and comparisons with experimental data.

March, 9th 2005

Optical Access Networks ( PDF)
Presentation by Henrique J. A. da Silva
Length: 67 min
Optical Access Networks Webcast
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