2015
Autores
Rodrigues, P; Oliveira, A; Sinogas, P; Taing, S; Eisner, J; Watts, S; Boissinot, V; Salgado, HM; Ferreira, JC; Pessoa, L; Da Silva, JM;
Publicação
Proceedings of the International Astronautical Congress, IAC
Abstract
Spectrum allocation for current wireless communication systems is performed by the regulatory and licensing bodies, who allocate spectrum bands for given applications. This strict allocation severely limits the effectiveness and flexibility of the spectrum use. Cognitive radio (CR) has been demonstrated as a key emerging technology to provide flexible and efficient use of the available spectrum by allocating frequency bands dynamically, and to improve the performance of radio systems in congested or jammed environments. Frequencies that are reserved or usually occupied can be exploited if the cognitive radio system identifies them as being free. Such a system is also able to monitor and deal with degrading communication performance or regulatory constraints. It automatically adjusts radio settings to use the best wireless channels in its environment, ensuring appropriate quality of service, efficiency and versatility. The SCREEN project proposes to extend the concept of cognitive radio to space and particularly to SatCom applications. This is an on-going project funded by the Horizon 2020 European Union programme. CR has never been used or tested in space, since previous research has been focused in terrestrial technologies. By addressing this topic and demonstrating its capabilities and benefits for space applications, SCREEN will contribute to a better management of this scarce resource that is bandwidth. While it has already been demonstrated that CR technology radically improves the performance for terrestrial applications at many different levels, the same benefits also apply in Space and especially in the SatCom segment, where the services provided need to ensure quality to the clients, for market competitiveness. CR has the potential to enable different approaches for managing the growing satellite communication demands and provides flexibility to explore new types of hybrid networks. SatCom operators will benefit from having the flexibility to allocate frequency slots dynamically, according to the instantaneous traffic patterns, instead of reserving fixed bands within regulatory constraints. Additionally, by optimising the spectrum management, SatCom operators can accommodate more users at the same time, without sacrificing the network performance. In this paper we will describe the overall concept behind the SCREEN project and present the results of a complete framework analysis, consisting of technical conclusions, market and impact analyses, regulatory considerations/constraints and requirements. Based on this analysis we further present functional, performance and test requirements for the project, which will show the project direction and outcome, together with the expected benefits that this technology will bring to Space applications. Copyright
2015
Autores
Salgado, HM; Neto, RE; Pessoa, LM; Batista, PJ;
Publicação
Optoelectronics - Materials and Devices
Abstract
2015
Autores
Tavares, JS; Pessoa, LM; Salgado, HM;
Publicação
2015 17th International Conference on Transparent Optical Networks (ICTON)
Abstract
Spatial division multiplexing (SDM) is seen as an effective technique to overcome the present limits of fiber capacity and satisfy future bandwidth requirements, by substantially increasing optical transport capacities [1-5]. Similarly to single-mode fiber based modern telecommunication systems, the nonlinear penalties will eventually become the ultimate limiting factor in SDM systems, arising from crosstalk effects in multimode core or few mode fibers, which generate intramodal and intermodal nonlinearities. Here we explore the concept of conjugated twin waves in few mode fibers based SDM optical systems, as a means to overcome these nonlinear impairments and assess the performance of SDM systems for different PCTW configurations and coupling regimes. Our numerical simulation results show that this technique is an effective means to overcome the nonlinear impairments arising in mode division multiplexed systems, improving performance by up to 10 dB, in the strong coupling regime.
2015
Autores
Castro, H; Andrade, MT; Almeida, F; Tropea, G; Melazzi, NB; Mousas, AS; Kaklamani, DI; Chiariglione, L; Difino, A;
Publicação
MULTIMEDIA TOOLS AND APPLICATIONS
Abstract
The Web is rapidly becoming the prime medium for human socialization. The resources that enable that process (social web sites, blogs, media objects, etc.) present growing complexity and, collectively, weave an ever more intricate web of relationships. Current technology for declaring those relationships is predominantly implicit, ambiguous and semantically poor. As a consequence, their automatic assessment is complex and error prone, preventing the satisfaction of users' needs such as effective semantic searches. To address these limitations, whilst enabling the explicit declaration of semantically unambiguous relationships between digital resources, a solution employing structured semantic descriptors and ontologies was conceived, based on MPEG-21. This paper explains the functioning of the devised mechanism, and goes beyond that, into the definition of two novel employment venues for it, at the service of two real-world usage scenarios. These demonstrate the mechanism's added value as a powerful alternative for the semantically aware interconnection of web resources, and highlight the increased QoE that said mechanism enables.
2015
Autores
Andrade, MT; Costa, TSd;
Publicação
JMMC - Journal of Media & Mass Communication
Abstract
2015
Autores
Otebolaku, AM; Andrade, MT;
Publicação
JOURNAL OF AMBIENT INTELLIGENCE AND HUMANIZED COMPUTING
Abstract
The emergence of pervasive computing, the rapid advancements in broadband and mobile networks and the incredible appeals of smart devices are driving unprecedented universal access and delivery of online-based media resources. As more and more media services continue to flood the Web, mobile users will continue to waste invaluable time, seeking content of their interest. To deliver relevant media items offering richer experiences to mobile users, media services must be equipped with contextual knowledge of the consumption environment as well as contextual preferences of the users. This article investigates context-aware recommendation techniques for implicit delivery of contextually relevant online media items. The proposed recommendation services work with a contextual user profile and a context recognition framework, using case base reasoning as a methodology to determine user's current contextual preferences, relying on a context recognition service, which identifies user's dynamic contextual situation from device's built-in sensors. To evaluate the proposed solution, we developed a case-study context-aware application that provides personalized recommendations adapted to user's current context, namely the activity he/she performs and consumption environment constraints. Experimental evaluations, via the case study application, real-world user data, and online-based movie metadata, demonstrate that context-aware recommendation techniques can provide better efficacy than the traditional approaches. Additionally, evaluations of the underlying context recognition process show that its power consumption is within an acceptable range. The recommendations provided by the case study application were assessed as effective via a user study, which demonstrates that users are pleased with the contextual media recommendations.
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