Polarization effects in fiber-optic communication systems

In this thesis we perform a detailed analysis of the state of polarization (SOP) of light scattering process using a concatenation of ber-coil based polarization controllers (PCs). We propose a polarization-mode dispersion (PMD) emulator, built through the concatenation of bercoil based PCs and polarization-maintaining bers (PMFs), capable of generate accurate rst- and second-order PMD statistics. We analyze the co-propagation of two optical waves inside a highbirefringence ber. The evolution along the ber of the relative SOP between the two signals is modeled by the de nition of the degree of co-polarization parameter. We validate the model for the degree of co-polarization experimentally, exploring the polarization dependence of the four-wave mixing e ect into a ber with high birefringence. We also study the interaction between signal and noise mediated by Kerr e ect in optical bers. A model accurately describing ampli ed spontaneous emission noise in systems with distributed Raman gain is derived. We show that the noise statistics depends on the propagation distance and on the signal power, and that for distances longer than 120 km and signal powers higher than 6 mW it deviates signi catively from the Gaussian distribution. We explore the all-optical polarization control process based on the stimulated Raman scattering e ect. Mapping parameters like the degree of polarization (DOP), we show that the preferred ampli cation of one particular polarization component of the signal allows a polarization pulling over a wavelength range of 60 nm. The e ciency of the process is higher close to the maximum Raman gain wavelength, where the DOP is roughly constant for a wavelength range of 15 nm. Finally, we study the polarization control in quantum key distribution (QKD) systems with polarization encoding. A model for the quantum bit error rate estimation in QKD systems with time-division multiplexing and wavelength-division multiplexing based polarization control schemes is derived.

Methodologies for traffic profiling in communication networks

Internet Tra c, Internet Applications, Internet Attacks, Tra c Pro ling, Multi-Scale Analysis abstract Nowadays, the Internet can be seen as an ever-changing platform where new and di erent types of services and applications are constantly emerging. In fact, many of the existing dominant applications, such as social networks, have appeared recently, being rapidly adopted by the user community. All these new applications required the implementation of novel communication protocols that present di erent network requirements, according to the service they deploy. All this diversity and novelty has lead to an increasing need of accurately pro ling Internet users, by mapping their tra c to the originating application, in order to improve many network management tasks such as resources optimization, network performance, service personalization and security. However, accurately mapping tra c to its originating application is a di cult task due to the inherent complexity of existing network protocols and to several restrictions that prevent the analysis of the contents of the generated tra c. In fact, many technologies, such as tra c encryption, are widely deployed to assure and protect the con dentiality and integrity of communications over the Internet. On the other hand, many legal constraints also forbid the analysis of the clients' tra c in order to protect their con dentiality and privacy. Consequently, novel tra c discrimination methodologies are necessary for an accurate tra c classi cation and user pro ling. This thesis proposes several identi cation methodologies for an accurate Internet tra c pro ling while coping with the di erent mentioned restrictions and with the existing encryption techniques. By analyzing the several frequency components present in the captured tra c and inferring the presence of the di erent network and user related events, the proposed approaches are able to create a pro le for each one of the analyzed Internet applications. The use of several probabilistic models will allow the accurate association of the analyzed tra c to the corresponding application. Several enhancements will also be proposed in order to allow the identi cation of hidden illicit patterns and the real-time classi cation of captured tra c. In addition, a new network management paradigm for wired and wireless networks will be proposed. The analysis of the layer 2 tra c metrics and the di erent frequency components that are present in the captured tra c allows an e cient user pro ling in terms of the used web-application. Finally, some usage scenarios for these methodologies will be presented and discussed.

Visible light communication systems for road safety applications

Esta tese apresenta um estudo explorat��rio sobre sistemas de comunica����o por luz vis��vel e as suas aplica����es em sistemas de transporte inteligentes como forma a melhorar a seguran��a nas estradas. Foram desenvolvidos neste trabalho, modelos conceptuais e anal��ticos adequados �� caracteriza����o deste tipo de sistemas. Foi desenvolvido um prot��tipo de baixo custo, capaz de suportar a dissemina����o de informa����o utilizando sem��foros. A sua realiza����o carece de um estudo detalhado, nomeadamente: i) foi necess��rio obter modelos capazes de descrever os padr��es de radia����o numa ��rea de servi��o pr��-definida; ii) foi necess��rio caracterizar o meio de comunica����es; iii) foi necess��rio estudar o comportamento de v��rios esquemas de modula����o de forma a optar pelo mais robusto; finalmente, iv) obter a implementa����o do sistema baseado em FPGA e componentes discretos. O prot��tipo implementado foi testado em condi����es reais. Os resultados alcan��ados mostram os m��ritos desta solu����o, chegando mesmo a encorajar a utiliza����o desta tecnologia em outros cen��rios de aplica����o.

Communication middleware for the future mobile internet

A evolu����o constante em novas tecnologias que providenciam suporte �� forma como os nossos dispositivos se ligam, bem como a forma como utilizamos diferentes capacidades e servi��os on-line, criou um conjunto sem precedentes de novos desafios que motivam o desenvolvimento de uma recente ��rea de investiga����o, denominada de Internet Futura. Nesta nova ��rea de investiga����o, novos aspectos arquiteturais est��o ser desenvolvidos, os quais, atrav��s da re-estrutura����o de componentes nucleares subjacentesa que comp��em a Internet, progride-a de uma forma capaz de n��o s��o fazer face a estes novos desafios, mas tamb��m de a preparar para os desafios de amanh��. Aspectos chave pertencendo a este conjunto de desafios s��o os ambientes de rede heterog��neos compostos por diferentes tipos de redes de acesso, a cada vez maior mudan��a do tr��fego peer-to-peer (P2P) como o tipo de tr��fego mais utilizado na Internet, a orquestra����o de cen��rios da Internet das Coisas (IoT) que exploram mecanismos de intera����o Maquinaa-Maquina (M2M), e a utiliza����o de mechanismos centrados na informa����o (ICN). Esta tese apresenta uma nova arquitetura capaz de simultaneamente fazer face a estes desafios, evoluindo os procedimentos de conectividade e entidades envolvidas, atrav��s da adi����o de uma camada de middleware, que age como um mecanismo de gest��o de controlo avan��ado. Este mecanismo de gest��o de controlo aproxima as entidades de alto n��vel (tais como servi��os, aplica����es, entidades de gest��o de mobilidade, opera����es de encaminhamento, etc.) com as componentes das camadas de baixo n��vel (por exemplo, camadas de liga����o, sensores e atuadores), permitindo uma otimiza����o conjunta dos procedimentos de liga����o subjacentes. Os resultados obtidos n��o s�� sublinham a flexibilidade dos mecanismos que compoem a arquitetura, mas tamb��m a sua capacidade de providenciar aumentos de performance quando comparados com outras solu����es de funcionamento espec��fico, enquanto permite um maior leque de cen��ios e aplica����es.

Communication between nodes for autonomic and distributed management

Over the last decade, the most widespread approaches for traditional management were based on the Simple Network Management Protocol (SNMP) or Common Management Information Protocol (CMIP). However, they both have several problems in terms of scalability, due to their centralization characteristics. Although the distributed management approaches exhibit better performance in terms of scalability, they still underperform regarding communication costs, autonomy, extensibility, exibility, robustness, and cooperation between network nodes. The cooperation between network nodes normally requires excessive overheads for synchronization and dissemination of management information in the network. For emerging dynamic and large-scale networking environments, as envisioned in Next Generation Networks (NGNs), exponential growth in the number of network devices and mobile communications and application demands is expected. Thus, a high degree of management automation is an important requirement, along with new mechanisms that promote it optimally and e ciently, taking into account the need for high cooperation between the nodes. Current approaches for self and autonomic management allow the network administrator to manage large areas, performing fast reaction and e ciently facing unexpected problems. The management functionalities should be delegated to a self-organized plane operating within the network, that decrease the network complexity and the control information ow, as opposed to centralized or external servers. This Thesis aims to propose and develop a communication framework for distributed network management which integrates a set of mechanisms for initial communication, exchange of management information, network (re) organization and data dissemination, attempting to meet the autonomic and distributed management requirements posed by NGNs. The mechanisms are lightweight and portable, and they can operate in di erent hardware architectures and include all the requirements to maintain the basis for an e cient communication between nodes in order to ensure autonomic network management. Moreover, those mechanisms were explored in diverse network conditions and events, such as device and link errors, di erent tra c/network loads and requirements. The results obtained through simulation and real experimentation show that the proposed mechanisms provide a lower convergence time, smaller overhead impact in the network, faster dissemination of management information, increase stability and quality of the nodes associations, and enable the support for e cient data information delivery in comparison to the base mechanisms analyzed. Finally, all mechanisms for communication between nodes proposed in this Thesis, that support and distribute the management information and network control functionalities, were devised and developed to operate in completely decentralized scenarios.

U-TRACER�� - the use of communication technology in higher education - an information visualization tool for the context of Portuguese public higher education

Information Visualization is gradually emerging to assist the representation and comprehension of large datasets about Higher Education Institutions, making the data more easily understood. The importance of gaining insights and knowledge regarding higher education institutions is little disputed. Within this knowledge, the emerging and urging area in need of a systematic understanding is the use of communication technologies, area that is having a transformative impact on educational practices worldwide. This study focused on the need to visually represent a dataset about how Portuguese Public Higher Education Institutions are using Communication Technologies as a support to teaching and learning processes. Project TRACER identified this need, regarding the Portuguese public higher education context, and carried out a national data collection. This study was developed within project TRACER, and worked with the dataset collected in order to conceptualize an information visualization tool U-TRACER��. The main goals of this study related to: conceptualization of the information visualization tool U-TRACER��, to represent the data collected by project TRACER; understand higher education decision makers perception of usefulness regarding the tool. The goals allowed us to contextualize the phenomenon of information visualization tools regarding higher education data, realizing the existing trends. The research undertaken was of qualitative nature, and followed the method of case study with four moments of data collection.The first moment regarded the conceptualization of the U-TRACER��, with two focus group sessions with Higher Education professionals, with the aim of defining the interaction features the U-TRACER�� should offer. The second data collection moment involved the proposal of the graphical displays that would represent the dataset, which reading effectiveness was tested by end-users. The third moment involved the development of a usability test to the UTRACER �� performed by higher education professionals and which resulted in the proposal of improvements to the final prototype of the tool. The fourth moment of data collection involved conducting exploratory, semi-structured interviews, to the institutional decision makers regarding their perceived usefulness of the U-TRACER��. We consider that the results of this study contribute towards two moments of reflection. The challenges of involving end-users in the conceptualization of an information visualization tool; the relevance of effective visual displays for an effective communication of the data and information. The second relates to the reflection about how the higher education decision makers, stakeholders of the U-TRACER�� tool, perceive usefulness of the tool, both for communicating their institutions data and for benchmarking exercises, as well as a support for decision processes. Also to reflect on the main concerns about opening up data about higher education institutions in a global market.

The impact of communication disability on quality of life of people with aphasia and their caregivers

Aphasia is a chronic acquired communication disorder that may change people with aphasia (PWA) and their caregivers��� lives for ever. Social and emotional changes are frequently reported by both, although the impact of these changes in quality of life (QOL) needs further research. This study identifies predictors and variables that influence PWA���s and their caregivers��� QOL and social relationships (SR). A cross-sectional descriptive, correlational and comparative study was undertaken with 255 individuals from Portuguese general population (mean age 43 years, range 25-84 years; 148 females, 107 males), 25 PWA (mean age 54 years, range 20-71; 12 females and 13 males), and 25 caregivers (mean age 51 years, range 26-73; 17 females and 8 males). All the participants completed the World Health Quality of Life Bref instrument, the SR domain of the World Health Organization Quality of Life ��� 100 scale, and the Center for Epidemiologic Studies Depression Scale. Participants with aphasia completed the Lisbon Aphasia Assessment Battery, Barthel Index, Frenchay Activities Index, Communication Disability Profile and the Modified Mini-Mental State which evaluated language disability, aphasia coefficient, activities, participation and cognition. In addition, caregivers completed the Carers��� Assessment of Managing Index to assess coping strategies. PWA and their caregivers are less satisfied with their QOL and SR than Portuguese general population; whereas PWA have the worse QOL and SR. Thus, aphasia seems to impact negatively in their QOL and SR. Emotional status has great importance for QOL and SR among the three groups. PWA���s activities and participation have great impact in both PWA���s and caregivers��� QOL and SR. Additionally, emotional status and participation are the best predictors of PWA���s QOL. Along with these two variables, activities of the PWA are the best predictors of caregivers��� QOL. Participation is the best predictor of PWA���s SR; emotional status and number of cohabitants are best predictors for caregivers��� SR. Aphasia assessment and intervention should take into account all the factors that influence PWA���s and caregivers��� QOL and SR so the central goal of enhancing it can be achieved. These results are important for identifying and planning support needs and are useful in the orientation of the activities carried out by the service providers allowing the adjustment of health programs and policies based on people���s real life needs.