DEE_PhD http://hdl.handle.net/10362/1039 2013-05-22T21:10:11Z 2013-05-22T21:10:11Z Coutinho, Carlos Eduardo Dias http://hdl.handle.net/10362/9414 2013-04-30T09:33:51Z 2012-01-01T00:00:00Z

Title: NEGOSEIO: framework for the sustainability of model-oriented enterprise interoperability Authors: Coutinho, Carlos Eduardo Dias Abstract: This dissertation tackles the problematic of Enterprise Interoperability in the current globally connected world. The evolution of the Information and Communication Technologies has endorsed the establishment of fast, secure and robust data exchanges, promoting the development of networked solutions. This allowed the specialisation of enterprises (particularly SMEs) and favoured the development of complex and heterogeneous provider systems. Enterprises are abandoning their self-centrism and working together on the development of more complete solutions. Entire business solutions are built integrating several enterprises (e.g., in supply chains, enterprise nesting) towards a common objective. Additionally, technologies, platforms, trends, standards and regulations keep evolving and demanding enterprises compliance. This evolution needs to be continuous, and is naturally followed by a constant update of each networked enterprise’s interfaces, assets, methods and processes. This unstable environment of perpetual change is causing major concerns in both SMEs and customers as the current interoperability grounds are frail, easily leading to periods of downtime, where business is not possible. The pressure to restore interoperability rapidly often leads to patching and to the adoption of immature solutions, contributing to deteriorate even more the interoperable environment. This dissertation proposes the adoption of NEGOSEIO, a framework that tackles interoperability issues by developing strong model-based knowledge assets and promoting continuous improvement and adaptation for increasing the sustainability of interoperability on enterprise systems. It presents the research motivations and the developed framework’s main blocks, which include model-based knowledge management, collaboration service-oriented architectures implemented over a cloud-based solution, and focusing particularly on its negotiation core mechanism to handle inconsistencies and solutions for the detected interoperability problems. It concludes by validating the research and the proposed framework, presenting its application in a real business case of aerospace mission design on the European Space Agency (ESA). Description: Dissertation to obtain the degree of Doctor of Philosophy in Electrical and Computer Engineering(Industrial Information Systems)

2012-01-01T00:00:00Z Pereira, Miguel Ramos http://hdl.handle.net/10362/9368 2013-04-23T09:50:41Z 2012-01-01T00:00:00Z

Title: Time diversity solutions to cope with lost packets Authors: Pereira, Miguel Ramos Abstract: Modern broadband wireless systems require high throughputs and can also have very high Quality-of-Service (QoS) requirements, namely small error rates and short delays. A high spectral efficiency is needed to meet these requirements. Lost packets, either due to errors or collisions, are usually discarded and need to be retransmitted, leading to performance degradation. An alternative to simple retransmission that can improve both power and spectral efficiency is to combine the signals associated to different transmission attempts. This thesis analyses two time diversity approaches to cope with lost packets that are relatively similar at physical layer but handle different packet loss causes. The first is a lowcomplexity Diversity-Combining (DC) Automatic Repeat reQuest (ARQ) scheme employed in a Time Division Multiple Access (TDMA) architecture, adapted for channels dedicated to a single user. The second is a Network-assisted Diversity Multiple Access (NDMA) scheme, which is a multi-packet detection approach able to separate multiple mobile terminals transmitting simultaneously in one slot using temporal diversity. This thesis combines these techniques with Single Carrier with Frequency Division Equalizer (SC-FDE) systems, which are widely recognized as the best candidates for the uplink of future broadband wireless systems. It proposes a new NDMA scheme capable of handling more Mobile Terminals (MTs) than the user separation capacity of the receiver. This thesis also proposes a set of analytical tools that can be used to analyse and optimize the use of these two systems. These tools are then employed to compare both approaches in terms of error rate, throughput and delay performances, and taking the implementation complexity into consideration. Finally, it is shown that both approaches represent viable solutions for future broadband wireless communications complementing each other. Description: A dissertation submitted to Departamento de Engenharia Electrotécnica of Faculdade de Ciências e Tecnologia of Universidade Nova de Lisboa in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engenharia Electrotécnica e de Computadores

2012-01-01T00:00:00Z Amaral, Pedro Miguel Figueiredo http://hdl.handle.net/10362/8797 2013-02-15T11:02:37Z 2012-01-01T00:00:00Z

Title: Multipath inter-domain policy routing Authors: Amaral, Pedro Miguel Figueiredo Abstract: Routing can be abstracted to be a path nding problem in a graph that models the network. The problem can be modelled using an algebraic approach that describes the way routes are calculated and ranked. The shortest path problem is the most common form and consists in nding the path with the smallest cost. The inter-domain scenario introduces some new challenges to the routing problem: the routing is performed between independently con gured and managed networks; the ranking of the paths is not based on measurable metrics but on policies; and the forwarding is destination based hop-by-hop. In this thesis we departed from the Border gateway Protocol (BGP) identifying its main problems and elaborating on some ideal characteristics for a routing protocol suited for the inter-domain reality. The main areas and contributions of this work are the following: The current state of the art in algebraic modeling of routing problems is used to provide a list of possible alternative conditions for the correct operation of such protocols. For each condition the consequences in terms of optimality and network restrictions are presented. A routing architecture for the inter-domain scenario is presented. It is proven that it achieves a multipath routing solution in nite time without causing forwarding loops. We discuss its advantages and weaknesses. A tra c-engineering scheme is designed to take advantage of the proposed architecture. It works using only local information and cooperation of remote ASes to minimize congestion in the network with minimal signalling. Finally a general model of a routing protocol based on hierarchical policies is used to study how e cient is the protocol operation when the correctness conditions are met. This results in some conclusions on how the policies should be chosen and applied in order to achieve speci c goals. Description: Dissertação submetida para a obtenção do grau de Doutor em Engenharia Electrotécnica e de Computadores

2012-01-01T00:00:00Z Figueiredo, Michael http://hdl.handle.net/10362/8776 2013-02-11T11:45:04Z 2012-01-01T00:00:00Z

Title: Reference-free high-speed cmos pipeline analog-to-digital converters Authors: Figueiredo, Michael Abstract: More and more signal processing is being transferred to the digital domain to profit from the technological enhancement of digital circuits. Where technology scaling enhances the capabilities of digital circuits, it degrades the performance of analog circuits. However, it is important to note that the impact that technology scaling has on digital circuits is becoming smaller and smaller, which means that, in nanotechnologies, to enhance energy and area efficiency, we can not simply depend on the benefits of this scaling. Although, a share of the efficiency can be obtained from the technology, new circuit architectures and techniques have to be developed to really push the limits of efficiency. In data converters, more specifically analog-to-digital converters (ADCs), a decision can be made: research energy and area efficient analog circuit techniques and architectures that cope with technological scaling issues, or design algorithms that use digital circuitry to assist the poor analog technological performance. The former option is the premise for the work developed in this thesis. The work reported in this thesis explores various design techniques with the purpose of enhancing the power and area efficiency of building blocks mainly to be used in multiplying digital-to-analog converter based ADCs. Therefore, novel analog techniques are developed for the three main blocks of an MDAC-based stage, namely, the flash quantizer, the amplifier, and the switched capacitor network of the MDAC. These techniques include self-biasing and inverter-based design for the flash quantizer and amplifier. Regarding the MDAC, it combines three techniques: unity feedback factor, insensitivity to capacitor mismatch, and current-mode reference shifting. In the second part of this work, the designed amplifier is implemented and experimentally characterized demonstrating its practical feasibility and performance. The final part of this work explores the design and implementation of a medium-low resolution high speed pipeline ADC incorporating all the developed circuits. Experimental results validate the feasibility of the techniques and demonstrate the attractiveness in terms of power dissipation and reduced area. Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical and Computer Engineering of the Faculdade de Ciências e Tecnologia of Universidade Nova de Lisboa

2012-01-01T00:00:00Z