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Multiuser and cooperative orthogonal frequency division multiplexing(OFDM) systems are being actively researched and adopted in wireless standards, owing to their advantages of robustness to multipath fading, modularity, and ability to achieve high data rates. In OFDM based systems, perfect frequency and timing synchronization is essential to maintain orthogonality among the subcarriers at the receiver. In multiuser OFDM on the uplink, timing offsets (TOs) and/or carrier frequency offsets (CFOs) of different users, caused due to path delay differences between different users, Doppler and/or poor oscillator alignment, can destroy orthogonality among subcarriers at the receiver. This results in multiuser interference (MUI)and consequent performance degradation. In this thesis, we are concerned with the analysis and mitigation of the effect of large CFOs and TOs in multiuser OFDM systems, including uplink orthogonal frequency division multiple access (OFDMA),uplink single-carrier frequency division multiple access(SC-FDMA), and cooperative OFDM. Uplink OFDMA: In the first part of this thesis, we analytically quantify the effect of large CFOs and TOs on the signal-to-interference plus noise ratio(SINR) and uncoded bit error rate(BER) performance of uplink OFDMA on Rayleigh and Rician fading channels, and show analytical results to closely match with simulation results. Such an SINR/BER analysis for uplink OFDMA in the presence of both large CFOs as well as TOs has not been reported before. We also propose interference cancelling(IC) receivers to mitigate the performance degradation caused due to large CFOs and TOs of different users. SC-FDMA versus OFDMA: An issue with uplink OFDMA is its high peak-to-average power ratio(PAPR).Uplink SC-FDMA is proposed in the standards as a good low-PAPR alternative to uplink OFDMA; e.g., SC-FDMA has been adopted in the uplink of 3GPP LTE. A comparative investigation of uplink SC-FDMA and OFDMA from a sensitivity to large CFOs and TOs view point has not been reported in the literature. Consequently, in the second part of the thesis, we carry out a comparative study of the sensitivity of SC-FDMA and OFDMA schemes to large CFOs and TOs of different users on the uplink. Our results show that while SC-FDMA achieves better performance due to its inherent frequency diversity advantage compared to OFDMA in the case of perfect synchronization, its performance can get worse than that of OFDMA in the presence of large CFOs and TOs. We further show that use of low-complexity multistage IC techniques, with the knowledge of CFOs and TOs of different users at the receiver, can restore the performance advantage of SC-FDMA over OFDMA. Cooperative OFDM: Cooperative OFDM is becoming popular because of its ability to provide spatial diversity in systems where each node has only one antenna. In most studies on cooperative communications, perfect time synchronization among cooperating nodes is assumed. This implies that the transmissions from different cooperating nodes reach the destination receiver in orthogonal time slots. In practice, however, due to imperfect time synchronization, orthogonality among different nodes’ signals at the destination receiver can be lost, causing inter-symbol interference(ISI).In the third part of the thesis, we investigate cooperative OFDM communications using amplify-and-forward(AF) protocol at the relay, in the presence of imperfect timing synchronization. We derive analytical expressions for the ISI as function of timing offset for cooperative OFDM with AF protocol, and propose an IC receiver to mitigate the effects of timing offset induced ISI.

Un système temps réel critique nécessite une validation temporelle utilisant un test d'ordonnançabilité avant sa mise en œuvre. Cette thèse traite le problème d'ordonnancement des taches à offset (transactions) sur une architecture monoprocesseur, en priorités fixes et en priorités dynamiques. Les méthodes existantes pour un test exact ont une complexité exponentielle et seules existent des méthodes approchées, donc pessimistes, qui sont pseudo-polynomiales. En priorités fixes nous proposons des méthodes pseudo-polynomiales, basées sur l'analyse de temps de réponse qui sont moins pessimistes que les méthodes existantes. Nous présentons quelques propriétés (accumulativité monotonique, dominance de tâches) rendant exacte les méthodes d'analyse approchées pour certains cas de systèmes, et optimisant le temps de calcul. En priorités dynamiques, nous proposons un test d'ordonnançabilité exact avec une complexité pseudo-polynomiale. Ce test est basé sur l'analyse de la demande processeur. Les qualités des résultats de nos méthodes sont confirmées par des évaluations expérimentales.

Bakterien Legionella pneumophila orsakar sjukdomen Legionella vilket har ökat i världen de senaste 20 åren och har troligtvis ett ännu större mörkertal. Den frodas i vattenrör mellan temperaturen 25–50 grader och vid installation av varmvattenrör i byggnader måste det tas hänsyn i riskzoner. Ett speciellt riskområde är varmvattenavstick som skapas för att kunna dra vidare vattenrör i framtiden. Där utsätts vattnet för större risk för stillastående och sjunkande temperaturprofil beroende på längd. Med hjälp av COMSOL Multiphysics® Modelling Software har ett teoretiskt ramverk för dimensionering av varmvattenavstick i byggnader skapats. Resultatet visar på hur stor strömningshastighet i vattenflödet, isoleringstjocklek och luftrörslängd har påverkan på hur långt avsticket kan vara utan att understiga kritisk temperatur. Resultatet kan användas som beslutsstöd givet att liknande avstickmodell och flödesprofil används samt om strömningshastighet i röret inte är längre än det i rapporten. / The bacterium Legionella pneumophila causes the disease Legionella which has seen an increase in the world over the last 20 years and likely has an even greater number of unrecorded cases. It thrives in water pipes between the temperature of 25-50 degrees and when installing hot water pipes in buildings certain factors must be taken into account. A special risk area is hot water branches that are created to be able to extend water pipes in the future. There, the water is at greater risk of stagnant and decreasing temperature profile depending on its length. With the help of COMSOL Multiphysics® Modelling Software, a theoretical framework for the dimensioning of hot water distances in buildings has been created. The result shows how the velocity in the water flow, the insulation thickness and the length of the air pipe have a great influence on how long the branch can be without falling below the critical temperature. The results can be used as decision support if one has a similar branch model and flow profile and also given a that a lower flow rate is not used.

L’installation des énergies marines renouvelables s’effectue dans le respect des législations environnementales françaises. La séquence Eviter-Réduire-Compenser (ERC) est ainsi appliquée pour aboutir à une non-perte nette de biodiversité. L’objectif de la thèse est de questionner l’efficacité de cette séquence, et plus particulièrement celle de la compensation écologique, en tant qu’instrument d’internalisation et de lutte contre l’érosion de la biodiversité marine. Une approche empirique qualitative a ainsi été mise en oeuvre pour (i) identifier les facteurs écologiques et sociétaux ainsi que leurs caractéristiques théoriques qui doivent permettre à la compensation d’atteindre l’objectif de non-perte nette de biodiversité ; et (ii) contrôler si ces conditions sont vérifiées en pratique dans le cas de l’éolien en mer en Europe et en France. L’analyse met en avant les enjeux juridiques, institutionnels, méthodologiques et sociétaux à relever pour permettre à la compensation écologique d’atteindre son objectif. Sur la base de ce constat, une évaluation multicritères est proposée afin de renforcer les étapes d’évitement et de réduction pour finalement mieux définir les besoins de compensation écologique en mer. L’analyse met par ailleurs en évidence un glissement d’une compensation basée sur une équivalence écologique stricte à une compensation fondée sur une équivalence écologique relâchée. Les actions de compensation tendent à être plus généralistes et/ou davantage dirigées vers les services écosystémiques que sur les composantes des écosystèmes. Associées aux mesures d’accompagnement, elles peuvent contribuer à faciliter l’acceptabilité sociale d’un projet d’aménagement. / The installation of marine renewable energies is carried out in compliance with French environmental legislation. The mitigation hierarchy is thus applied to achieve an objective of no net loss of biodiversity. This thesis aims at questioning the effectiveness of the mitigation hierarchy and more specifically biodiversity offsetting as an internalization instrument to halt the erosion of marine biodiversity. We use a qualitative empirical approach to (i) identify the ecological and societal factors as well as their theoretical characteristics that are supposed to enable the offsets achieving the objective of no net loss of biodiversity; and (ii) control whether these conditions are verified in practice for the case of offshore wind farms in Europe and France. The analysis highlights the legal, institutional, methodological and societal issues to be addressed in order to enable biodiversity offsetting to achieve the no net loss priority. On the basis of this observation, a multi-criteria assessment is carried out to reinforce the avoidance and reduction steps of the mitigation hierarchy in order to better define offsetting needs. Ultimately, the analysis shows a shift in biodiversity offsetting based on a strict ecological equivalence to a biodiversity offsetting based on a released ecological equivalence. Offsetting actions tend to be more generalist and / or more directed to ecosystem services than to ecosystem components. Associated with accompanying measures, offsetting actions can help to increase the social acceptability of a development project.

Text in English / In recent years, there have been tremendous advances in information technology, robotics, communication technology, nanotechnology, and artificial intelligence, resulting in the merging of physical, digital, and biological worlds that have come to be known as the "fourth industrial revolution”. In this context, the present study engages such technology in the green economy and to tackle the techno-economic environmental impact assessments challenges associated with floating solar system applications in the agricultural sector of South Africa. In response, this exploratory study aimed to examine the development of a Geographical Information System (GIS)-based support platform for Environmental Impact Assessment (EIA) and due-diligence analyses for future planned agricultural floating solar systems, especially with the goal to address the vast differences between the environmental impacts for land-based and water-based photovoltaic energy systems. A research gap was identified in the planning processes for implementing floating solar systems in South Africa’s agricultural sector. This inspired the development of a novel GIS-based modelling tool to assist with floating solar system type energy infrastructure planning in the renewable energy discourse. In this context, there are significant challenges and future research avenues for technical and environmental performance modelling in the new sustainable energy transformation. The present dissertation and geographical research ventured into the conceptualisation, designing and development of a software GIS-based decision support tool to assist environmental impact practitioners, project owners and landscape architects to perform environmental scoping and environmental due-diligence analysis for planned floating solar systems in the local agricultural sector. In terms of the aims and objectives of the research, this project aims at the design and development of a dedicated GIS toolset to determine the environmental feasibility around the use of floating solar systems in agricultural applications in South Africa. In this context, the research objectives of this study included the use of computational modelling and simulation techniques to theoretically determine the energy yield predictions and computing environmental impacts/offsets for future planned agricultural floating solar systems in South Africa. The toolset succeeded in determining these aspects in applications where floating solar systems would substitute Eskom grid power. The study succeeded in developing a digital GIS-based computer simulation model for floating solar systems capable of (a) predicting the anticipated energy yield, (b) calculating the environmental offsets achieved by substituting coal-fired generation by floating solar panels, (c) determining the environmental impact and land-use preservation benefits of any floating solar system, and (d) relating these metrics to water-energy-land-food (WELF) nexus parameters suitable for user project viability analysis and decision support. The research project has demonstrated how the proposed GIS toolset supports the body of geographical knowledge in the fields of Energy and Environmental Geography. The new toolset, called EIAcloudGIS, was developed to assist in solving challenges around energy and environmental sustainability analysis when planning new floating solar installations on farms in South Africa. Experiments conducted during the research showed how the geographical study in general, and the toolset in particular, succeeded in solving a real-world problem. Through the formulation and development of GIS-based computer simulation models embedded into GIS layers, this new tool practically supports the National Environmental Management Act (NEMA Act No. 107 of 1998), and in particular, associated EIA processes. The tool also simplifies and semi-automates certain aspects of environmental impact analysis processes for newly envisioned and planned floating solar installations in South Africa. / Geography / M.Sc. (Geography)