The intrusion pathways and physical mechanisms associated with intrusions of cold, nutrient-rich South Atlantic Central Water (SACW) onto the continental shelf of the Espírito Santo Basin (ESB), off southeast Brazil (18°S-22°S), are investigated. The approach consists of analyses of a set of simplified, process-oriented, primitive-equation numerical models supported by the analyses of an independent, more realistic numerical model and available observations. The cross-isobath circulation is found to be strongly dominated by wind-driving, consistent with previous findings. In the model experiments, SACW enters the ESB shelf through two preferential pathways along the Tubarão Bight area (TB, 19.5°S-22°S). These pathways are found to be locations where an equatorward along-isobath pressure gradient force (PGFy∗) of ∼2 x 10-6 m s-2 develops in response to steady wind forcing. This equatorward PGFy∗ is essentially in geostrophic balance, and therefore induces onshore flow across the shelf edge and most of the shelf proper. The Brazil Current (BC) imparts an additional equatorward PGFy∗ on the shelf. The momentum budget reveals that the ageostrophic residue of the PGFy∗ is compensated mostly by momentum advection and bottom friction. Buoyancy arrest might be important under more intense SACW intrusion events, as suggested by the maximum observed values of the slope Burger number (0.32-0.92). Among the deep ocean forcing mechanisms considered, the intrinsic pycnocline uplifting effect of the BC seems to be responsible for ∼1.4°C colder upwelled water under steady, upwelling-favorable wind forcing, relative to a flat stratification scenario. The BC also seems to induce local intrusions by inertially overshooting the shelf edge, consistent with Rossby numbers of ∼0.3-0.5, as estimated for the area along the TB shelf edge. Finally, the planetary β-effect is also related to a background equatorward PGFy∗. In addition, the steady response of the continental shelf to a periodic (in the along-shelf direction) pressure forcing at the shelf edge is compared with the BC-forced primitive-equation numerical solutions. A simple Arrested Topographic Wave (ATW) analytical model is found to be successful in representing the general features of the numerical solutions. The cross-shelf e-folding scales of the cross-shelf velocity estimated from the numerical solutions agree in order of magnitude with the cross-shelf penetration scale q-1 = [-2r/(lfs)]½ = 10 km predicted by the ATW, where r is a linear bottom resistance parameter, l is the along-shelf wavenumber of the forcing at the shelf edge, f is the Coriolis parameter and s is the bottom slope. Furthermore, the use of quadratic bottom stress accounts for some of the relative increase in the numerical onshore penetration scales, which are predicted to be qquadratic-1 = [-2CD/(lfs)]½ [Ubot]½, where CD is a quadratic bottom friction parameter and Ubot is the near-bottom velocity magnitude. The kind of steady response to periodic deep ocean forcing examined here may provide insight into other continental shelves under the influence of western boundary currents. / Os caminhos e os mecanismos físicos associados ao fenômeno de intrusão da Água Central do Atlântico Sul (ACAS) na plataforma continental da Bacia do Espírito Santo (BES) ao largo da costa sudeste (18°S-22°S) são investigados nesta dissertação. A abordagem consiste da análise de experimentos numéricos de equações primitivas simplificados, combinados com a análise de um modelo numérico mais completo, e com análise de observações disponíveis. Conclui-se que a circulação na direção perpendicular às isóbatas é fortemente dominada pelo vento, de acordo com resultados pretéritos. Nos experimentos numéricos, a ACAS ingressa na plataforma da BES através de dois caminhos preferenciais de intrusão no Embaiamento de Tubarão (ET, 19,5°S-22°S). Estes caminhos de intrusão coincidem com áreas em que uma Força do Gradiente de Pressão na direção paralela às isóbatas (PGFy∗), com magnitude de ∼2 x 10-6 m s-2, se forma em resposta ao vento. A PGFy∗ se encontra essencialmente em balanço geostrófico, e impulsiona um escoamento na direção da costa. A Corrente do Brasil (CB) induz uma PGFy∗ adicional favorável à intrusão. O balanço de momentum revela que o resíduo ageostrófico da PGFy∗ é balanceado principalmente pela advecção de momentum e pelo atrito de fundo. O mecanismo de desligamento da camada de Ekman de fundo por empuxo (tradução livre de buoyancy arrest) pode ser importante em eventos mais intensos de intrusão de ACAS, em razão das estimativas do número de Burger de inclinação (tradução livre de slope Burger number) observado (0,32-0,92). O efeito de soerguimento da termoclina ligado à CB aparenta diminuir em ∼1,4 °C a temperatura da água que aflora em eventos de ressurgência costeira. A CB também parece produzir intrusões locais na borda da plataforma por efeitos inerciais, de acordo com as estimativas de ∼0,3-0,5 para o número de Rossby ao longo da borda da plataforma. Por fim, o efeito β planetário também é associado a uma PGFy∗ básica na direção do equador. Adicionalmente, a resposta estacionária da plataforma continental a um campo de pressão periódico ao longo da borda da plataforma é comparada com as soluções numéricas. Um simples modelo analítico do tipo Onda Topográfica Aprisionada (OTA, tradução livre de Arrested Topographic Wave) representa as características gerais das soluções numéricas. As escalas de decaimento Neperiano (e) na direção perpendicular à plataforma estimadas a partir das soluções numéricas são comparáveis à escala de penetração q-1 = [-2r/(lfs)]½ = 10 km prevista pela OTA, onde r é um coeficiente linear de atrito de fundo, l é o número de onda da forçante, f é o parâmetro de Coriolis e s é a inclinação do fundo. O uso de uma parametrização quadrática para o atrito de fundo prevê parte da diminuição da e. A escala de penetração quadrática é qquadratic-1 = [-2CD/(lfs)]½[Ubot]½, onde CD é um coeficiente quadrático de atrito de fundo e Ubot é a magnitude da velocidade próxima ao fundo. Este tipo de resposta estacionária da plataforma a uma forçante periódica ligada ao oceano profundo pode ajudar a elucidar processos físicos em outras plataformas continentais que se encontram sob a influência de correntes de limite oeste.

L’étude présentée dans cette thèse relève de la mécanique des fluides expérimentale et numérique appliquée aux écoulements pariétaux de refroidissement de chambres de combustion aéronautiques. En présence de phénomènes thermo-acoustiques, comme les instabilités de combustion, il est important d’évaluer si les capacités de l’écoulement pariétal à protéger les parois de chambre restent suffisantes. C’est ainsi que nous nous sommes intéressés aux écoulements de paroi multiperforée soumis à une excitation acoustique. Dans ce but, le banc d’essais MAVERIC a été amélioré grâce à l’installation d’un système qui permet de forcer acoustiquement l’écoulement transverse dans lequel les jets pariétaux débouchent. Nous avons pu alors mettre en évidence la forte sensibilité de ce type d’écoulements à l’excitation acoustique. Le bon accord entre les résultats expérimentaux et les simulations numériques aux grandes échelles (LES) effectuées est très encourageant dans le cas d’un forçage par onde stationnaire. Le forçage par onde progressive, étudié uniquement par simulations numériques, s’est révélé être capable de modifier significativement la topologie de l’écoulement. Enfin, à partir de l’outil numérique AVBP-AVTP qui permet le couplage de calculs fluide-solide, nous avons réalisé une étude de l’influence de la présence d’une excitation acoustique sur le comportement thermique de l’écoulement autour d’une paroi multiperforée de chambre de combustion. / This experimental and numerical study in the field of fluid mechanics deals with jets-in cross flow configurations that are relevant for the cooling of aero engine combustion chambers. Indeed, in presence of instabilities it is important to determine to which extent the film cooling is able to do its job of preserving the combustion chamber walls from the thermal load. The test facility MAVERIC has been upgraded in order to acoustically force the crossflow in which the jets are discharging. The strong sensitivity of the overall flow unsteady properties to the presence of the acoustic forcing has been clearly evidenced. The agreement between the experimental results and large-eddy simulations proved to be quite encouraging for a stationary acoustic wave whereas the case of a propagating acoustic wave investigated only numerically reveals also quite a significant change of the flow topology. In this context, the effect of the acoustic forcing on the wall thermal behavior has been analyzed thanks to the use of the fluid-solid coupled AVBP-AVTP solver.

Dans le contexte du réchauffement et du changement climatique, il est important d’étudier les distributions, les cycles saisonniers et les tendances des gaz à l’état de trace dans l’atmosphère tels que la vapeur d’eau. L'Observatoire de Physique du Globe de Clermont-Ferrand a en charge plusieurs dispositifs d’observation dont le site instrumenté Cézeaux, Opme et Puy de Dôme (CO-PDD) situés dans le centre de la France (45◦ N, 3◦ E). Le site des Cézeaux dispose d’un LIDAR Rayleigh – Mie - Raman fournissant en routine des profils verticaux de vapeur d’eau et de paramètres optiques caractérisant les cirrus. Le site du puy de Dôme est équipé d’un spectroscope à cavité optique (CRDS-Picarro). Des mesures de colonnes totales de vapeur d’eau sont disponibles sur tous ces sites par GPS. Le site d’Opme est équipé d’un pluviomètre. Enfin Météo-France effectue le travail de contrôle qualité des données météorologiques sur les stations de mesure en France et ces données ont été utilisées dans cette thèse. La validation des données sur le site du puy de Dôme a été la première la première exploitation dans cette thèse. Des comparaisons des données sur le puy de Dôme ont montré un très bon accord entre les données de vapeur d’eau extraites de la station météorologique du puy de Dôme, de Météo France et les donnes CRDS du puy de Dôme, avec une corrélation de 0.94 et 0.98 respectivement. Les profils verticaux obtenus par LIDAR ont permis de sélectionner une anomalie de vapeur d’eau et d’identifier une intrusion stratosphère-troposphère en analysant les processus dynamique associés à cette anomalie. Les données OLR ont montré que cette intrusion est accompagnée de convection profonde et enfin LACYTRAJ confirme l'origine stratosphérique d’une partie de la masse d'air présente au-dessus de Clermont-Ferrand au cours de l’anomalie. Les longues séries d’observations (ex : Puy de Dôme 1995-2015) et des ré-analyse ECMWF ERA-Interim (1979-2017) et la diversité des sources de données (ex : satellites AIRS et COSMIC), nous permettent de documenter, analyser et comparer la variabilité, les cycles et la tendance de la vapeur d'eau à la surface et dans la troposphère, à différentes échelles de temps et déterminer les processus géophysiques responsables des distributions de vapeur d'eau sur le site CO-PDD. Le cycle annuel de la vapeur d'eau est clairement établi pour les deux sites de différentes altitudes et pour tous les types de mesure. Les sites de Cézeaux et du puy de Dôme ne présentent presque aucun cycle diurne, suggérant que la variabilité de la vapeur d'eau à la surface sur ces deux sites est plus influencée par les systèmes météorologique sporadiques que par les variations diurnes régulières. Les données LIDAR montrent une plus grande variabilité mensuelle de la distribution verticale que les produits satellites COSMIC et AIRS. La colonne totale de vapeur d'eau GPS sur le site des Cézeaux présente une tendance positive (0,42 ± 0,45 g/kg*décade entre 2006-2017). L'analyse par régressions multi-linéaires montre que les forçages continentaux (East Atlantic, East Atlantic-West Russia) ont une plus grande influence que le forçage océanique (Nord Atlantic Oscillation) sur les variations de vapeur d'eau. / In the context of global warming and climate change, it is important to study the distributions, seasonal cycles and trends of trace gases in the atmosphere such as water vapor. of the Observatoire de Physique du Globe de Clermont-Ferrand is in charge of several observation devices including the instrumented site Cézeaux, Opme and Puy de Dôme (CO-PDD) located near the center of France (45◦ N, 3◦ E). The site of Cézeaux is instrumented by a Rayleigh - Mie–LIDAR Raman providing routine vertical profiles of water vapor mixing ratio and optical parameters characterizing cirrus clouds. The puy de Dôme site is equipped with an optical cavity spectroscope (CRDS-Picarro). Measurements of total water vapor columns are available on all these sites by GPS. The Opme site is equipped with rain gauges. Finally, Météo-France performs the quality control work and of data on meteorological stations in France and these data were used in this thesis. The validation of the puy de Dôme data was the first the first task in this thesis. Comparisons between the puy de Dôme data sets showed a very good agreement between the water vapor datafrom the OPGC meteorological station of Puy de Dôme, Météo France and CRDS data with a correlation of 0.94 and 0.98 respectively. The vertical profiles deduced from the LIDAR allowed to identify a water vapor anomaly and a stratosphere-troposphere intrusion associated with this anomaly. OLR data showed that this intrusion could be linked with deep convection and LACYTRAJ confirms the stratospheric origin of a part of the air mass present above Clermont-Ferrand. Long series of observations (eg Puy de Dôme 1995-2015) and ECMWF ERA-Interim re-analysis (1979-2017) and the diversity of data sources (eg AIRS and COSMIC satellites), allowed us to document, analyze and compare the variability, cycles and trend of surface and tropospheric water vapor at different time scales and determine the geophysical processes responsible for water vapor distributions at the site of CO-PDD. The annual cycle of water vapor is clearly established for the two sites of different altitudes and for all types of measurement. Cézeaux and puy de Dôme present almost no diurnal cycle, suggesting that the variability of surface water vapor at this site is more influenced by a sporadic meteorological system than by regular diurnal variations. The LIDAR dataset shows a greater monthly variability of the vertical distribution than the COSMIC and AIRS satellite products. The Cézeaux site presents a positive trend for the GPS water vapor total column (0.42 ± 0.45 g/kg*decade during 2006–2017) and a significant negative trend for the surface water vapor mixing ratio (−0.16 ± 0.09 mm/decade during 2002–2017). The multi-linear regression analysis shows that continental forcings (East Atlantic Pattern and East Atlantic-West Russia Pattern) have a larger influence than oceanic forcing (North Atlantic Oscillation) on the water vapor variations.

此篇論文，主要是討論遞迴式神經網路。在文中，我們將架構一個單層的神經網路結構。並利用三種不同的學習法則來套用此架構。我們也做了圓軌跡和圖形８的模擬，以及討論了此架構的收斂性。 / Our task in this paper is to discuss the Recurrent Neural Network. We construct a singal layer neural network and apply three different learning rules to simulate circular trajectory and figure eight. Also, we present the proof of convergence.

<p><p>Varken förr eller senare har köksträdgårdsodlingen stått på en sådan hög nivå som under den victorianska tiden – vare sig i Sverige eller i Storbritannien! Examensarbetet syftar till att plocka fram numera kanske bortglömda arbetsmetoder för köksväxt- och fruktodling från tiden kring förra sekelskiftet samt vissa växter som fortfarande kan vara av intresse idag. En viktig fråga är om dessa metoder och växter kan tillföra något när vi nu försöker skapa ett ekologiskt hållbart samhälle.</p><p>   På det lilla Årups slott i nordöstra Skåne fanns en gång en numera försvunnen köksträdgård. Författaren till detta examensarbete försökte först utan framgång hitta historien bak denna specifika trädgård. Istället har fältstudier, samtal och litteraturjämförelser mellan svenska och engelska trädgårdshandböcker fått ge en allmän bild av dåtida arbetsmetoder i köksträdgården. Den viktigaste boken har varit ”The Victorian Kitchen garden” som baserades på ett TV-program med samma namn från 1990-talet. Litteraturstudierna visar att även om det är mycket som skiljer svenskt och engelskt sätt att arbeta i trädgården, finns ändå en överskuggande gemensam tanke: att bruka och inte förbruka jorden! En tanke som är i högsta grad aktuell ännu idag.                     </p><p>   När så småningom en ”victoriansk” köksträdgård hittades på Trolle-Ljungby slott i Skåne, gavs det en fantastisk möjlighet till jämförelser mellan litteraturens arbetssätt med verkligheten. I examensarbetet ingår bl a en beskrivning av Trolle-Ljungbys odlingar av blommor, grönsaker liksom mer eller mindre exotiska frukter både på friland och i växthus – allt odlat enligt gamla traditionella metoder. Som ett komplement till denna beskrivning, följer författarens kommentarer och jämförelser utifrån de iakttagelser som gjorts under litteraturstudierna. Rekommendation ställs mot funktion.</p><p>   Detta examensarbete visar att det finns både specifika metoder liksom rena förhållningssätt till natur och miljö från den victorianska tiden som fortfarande är i allra högsta grad användbara och viktiga. Låt oss därför vara lite lata och inte uppfinna hjulet igen. Det räcker med att ta ett kliv tillbaka till framtiden – till den victorianska köksträdgården.</p></p>

Multiple-input, multiple-output (MIMO) techniques have been proposed to meet the needs for higher data rates and lower delays in future wireless communication systems. The downlink capacity of multiuser MIMO systems is achieved when the system transmits to several users simultaneously. Frequently, many more users request service than the transmitter can simultaneously support. Thus, the transmitter requires a scheduling algorithm for the users, which must balance the goals of increasing throughput, reducing multiuser interference, lowering delays, ensuring fairness and quality of service (QoS), etc. In this thesis, we investigate the application of genetic algorithms (GAs) to perform scheduling in multiuser MIMO systems. GAs are a fast, suboptimal, low-complexity method of solving optimization problems, such as the maximization of a scheduling metric, and can handle arbitrary functions and QoS constraints. We first examine a system that transmits using capacity-achieving dirty paper coding (DPC). Our proposed GA structure both selects users and determines their encoding order for DPC, which affects the rates they receive. Our GA can also schedule users independently on different carriers of a multi-carrier system. We demonstrate that the GA performance is close to that of an optimal exhaustive search, but at a greatly reduced complexity. We further show that the GA convergence time can be significantly reduced by tuning the values of its parameters. While DPC is capacity-achieving, it is also very complex. Thus, we also investigate GA scheduling with two linear precoding schemes, block diagonalization and successive zero-forcing. We compare the complexity and performance of the GA with "greedy" scheduling algorithms, and find the GA is more complex, but performs better at higher signal-to-noise ratios (SNRs) and smaller user pool sizes. Both algorithms are near-optimal, yet much less complex than an exhaustive search. We also propose hybrid greedy-genetic algorithms to gain benefits from both types of algorithms. Lastly, we propose an improved method of optimizing the transmit covariance matrices for successive zero-forcing. Our algorithm significantly improves upon the performance of the existing method at medium to high SNRs, and, unlike the existing method, can maximize a weighted sum rate, which is important for fairness and QoS considerations. / Communications

An important goal of ecological studies is to identify and explain patterns or variation in species assemblages. Ecologists have discovered that global variation in the number of species in an assemblage relates strongly to climate, area, and topographic variability in terrestrial environments. Is the same true for other characteristics of species assemblages? The focus of this thesis is to determine whether species assemblage structure, defined primarily as the body mass frequency distributions and species abundance distributions relate in convergent ways to a set of a few environmental variables across broad spatial scales. First, I found that for mammals and trees most of their geographic variation across North and South America in assemblage structure is statistically related to temperature, precipitation, and habitat heterogeneity (e.g. different vegetation types) in convergent ways. I then examined bird assemblages across islands and continents. Despite the evolutionary and ecological differences between island and continental assemblages, I found that much of the variation in bird assemblage structure depends on temperature, precipitation, land area, and island isolation in congruent patterns in continent and island bird assemblages. Frank Preston modeled species richness based on the total number of individuals and the number of individuals of the rarest species. Building on Preston’s model, Chapter 2 hypothesized that gradients of diversity correlate with gradients in the number of individuals of the rarest species, which in turn are driven by gradients in temperature and precipitation. This hypothesis assumes that species abundance distributions relate to temperature and precipitation in similar ways anywhere in the world. I found that both the number of individuals of the rarest species (m) and the proportion of species represented by a single individual in samples of species assemblages (Φ) were strongly related to climate. Moreover, global variation in species richness was more strongly related to these measures of rarity than to climate. I propose that variation in the shape of the log-normal species abundance distribution is responsible for global gradients of species richness: rare species (reflected in m and Φ) persist better in benign climates. Even though body mass frequency distributions of assemblages show convergent patterns in relation to a set of a few environmental variables, the question remains as to what processes are responsible for creating the geographical variation in the body-size distribution of species. Several mechanisms (e.g. heat conservation and resource availability hypotheses) have been proposed to explain this variation. Chapter 5 tested and found no empirical support for the predictions derived from each of these mechanisms; I showed that species of all sizes occur across the entire temperature gradient. In conclusion, assemblage structure among various taxonomic groups across broad spatial scales relate in similar ways to a set of a few environmental variables, primarily mean annual temperature and mean annual precipitation. While the exact mechanisms are still unknown, I hypothesize several to explain the patterns of convergent assembly. Résumé Un but important de l'écologie est d'identifier et d'expliquer la variation de premier ordre dans les caractéristiques des assemblages d'espèces. Un des patrons ayant déjà été identifié par les écologistes, c'est que la variation mondiale de la richesse en espèces est liée à la variation du climat, de l'aire et de la topographie. Est-ce que d'autres caractéristiques des assemblages d'espèces peuvent être reliées à ces mêmes variables? Le but de cette thèse est de déterminer si la structure des assemblages d'espèces, ici définie comme la distribution des fréquences de masse corporelle ainsi que la distribution d'abondances des espèces, est reliée de manière convergente à un petit ensemble de variables environnementales, et ce, partout dans le monde. D'abord, j'ai déterminé que, pour les mammifères et les arbres, la majorité de la variation géographique dans la structure des assemblages d'espèces est reliée statistiquement à température, précipitation, et l’hétérogénéité du couvert végétal , et ce, de manière convergente pour l'Amérique du Nord et du Sud. Je me suis ensuite penché sur l'assemblage des oiseaux sur les îles et les continents. Malgré les larges différences évolutives et écologiques qui distinguent les îles des continents, je démontre que la majorité de la variation dans la structure des assemblages d'oiseaux dépend de la température, la précipitation, la superficie et l’isolation de façon congruente sur les îles et les continents. Frank Preston a modélisé la richesse en espèces d'une localité, basée sur le nombre total d'individus ainsi que le nombre d'individus de l’espèce la plus rare. En s'appuyant sur les modèles de Preston, Chapître 3 propose une nouvelle hypothèse voulant que les gradients de diversité dépendent des gradients du nombre d'individus de l’espèce la plus rare. Celle-ci dépend des gradients de température et de précipitation. Cette hypothèse repose sur le postulat que la distribution d’abondances des espèces dépend de la température et la précipitation, et ce, de la même manière n’importe où au monde. J’ai mis en évidence que le nombre d’individus de l’espèce la plus rare (m), ainsi que la proportion d’espèces représentées par un individu unique () dans des échantillons locaux étaient fortement reliés au climat. D’ailleurs, la variation globale de la richesse en espèces était plus fortement reliée à ces indices de rareté qu’au climat. Je propose que la variation dans la forme de la distribution log-normale d’abondances d’individus soit responsable des gradients mondiaux de richesse en espèces. En d’autres mots, les espèces rares (indiquées par m et ) persistent mieux dans des climats bénins. Malgré que la distribution des fréquences de masse corporelle des assemblages d'espèces soit liée de manière convergente à seulement quelques variables environnementales, la question demeure à savoir quels processus sont responsables des gradients géographiques de variation en masse corporelle des espèces. Plusieurs mécanismes ont été proposés pour expliquer cette variation. Dans Chapitre 5, j'ai testé les prédictions dérivées de chacun de ces mécanismes sans trouver de support empirique pour aucun. Je démontre aussi que des espèces de toutes tailles se retrouvent sur le gradient de température en entier. En conclusion, la structure des assemblages d'espèces, pour différents groupes taxonomiques et à travers le monde, est liée de façon similaire à un petit nombre de variables environnementales. Bien que les mécanismes soient encore inconnus, j'en propose plusieurs pouvant expliquer ces patrons d'assemblages convergents.

Varken förr eller senare har köksträdgårdsodlingen stått på en sådan hög nivå som under den victorianska tiden – vare sig i Sverige eller i Storbritannien! Examensarbetet syftar till att plocka fram numera kanske bortglömda arbetsmetoder för köksväxt- och fruktodling från tiden kring förra sekelskiftet samt vissa växter som fortfarande kan vara av intresse idag. En viktig fråga är om dessa metoder och växter kan tillföra något när vi nu försöker skapa ett ekologiskt hållbart samhälle.    På det lilla Årups slott i nordöstra Skåne fanns en gång en numera försvunnen köksträdgård. Författaren till detta examensarbete försökte först utan framgång hitta historien bak denna specifika trädgård. Istället har fältstudier, samtal och litteraturjämförelser mellan svenska och engelska trädgårdshandböcker fått ge en allmän bild av dåtida arbetsmetoder i köksträdgården. Den viktigaste boken har varit ”The Victorian Kitchen garden” som baserades på ett TV-program med samma namn från 1990-talet. Litteraturstudierna visar att även om det är mycket som skiljer svenskt och engelskt sätt att arbeta i trädgården, finns ändå en överskuggande gemensam tanke: att bruka och inte förbruka jorden! En tanke som är i högsta grad aktuell ännu idag.                         När så småningom en ”victoriansk” köksträdgård hittades på Trolle-Ljungby slott i Skåne, gavs det en fantastisk möjlighet till jämförelser mellan litteraturens arbetssätt med verkligheten. I examensarbetet ingår bl a en beskrivning av Trolle-Ljungbys odlingar av blommor, grönsaker liksom mer eller mindre exotiska frukter både på friland och i växthus – allt odlat enligt gamla traditionella metoder. Som ett komplement till denna beskrivning, följer författarens kommentarer och jämförelser utifrån de iakttagelser som gjorts under litteraturstudierna. Rekommendation ställs mot funktion.    Detta examensarbete visar att det finns både specifika metoder liksom rena förhållningssätt till natur och miljö från den victorianska tiden som fortfarande är i allra högsta grad användbara och viktiga. Låt oss därför vara lite lata och inte uppfinna hjulet igen. Det räcker med att ta ett kliv tillbaka till framtiden – till den victorianska köksträdgården.

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The search for the closest lattice point arises in many communication problems, and is known to be NP-hard. The Maximum Likelihood (ML) Detector is the optimal detector which yields an optimal solution to this problem, but at the expense of high computational complexity. Existing near-optimal methods used to solve the problem are based on the Sphere Decoder (SD), which searches for lattice points confined in a hyper-sphere around the received point. The SD has emerged as a powerful means of finding the solution to the ML detection problem for MIMO systems. However the bottleneck lies in the determination of the initial radius. This thesis is concerned with the detection of transmitted wireless signals in Multiple-Input Multiple-Output (MIMO) digital communication systems as efficiently and effectively as possible. The main objective of this thesis is to design efficient ML detection algorithms for MIMO systems based on the depth-first search (DFS) algorithms whilst taking into account complexity and bit error rate performance requirements for advanced digital communication systems. The increased capacity and improved link reliability of MIMO systems without sacrificing bandwidth efficiency and transmit power will serve as the key motivation behind the study of MIMO detection schemes. The fundamental principles behind MIMO systems are explored in Chapter 2. A generic framework for linear and non-linear tree search based detection schemes is then presented Chapter 3. This paves way for different methods of improving the achievable performance-complexity trade-off for all SD-based detection algorithms. The suboptimal detection schemes, in particular the Minimum Mean Squared Error-Successive Interference Cancellation (MMSE-SIC), will also serve as pre-processing as well as comparison techniques whilst channel capacity approaching Low Density Parity Check (LDPC) codes will be employed to evaluate the performance of the proposed SD. Numerical and simulation results show that non-linear detection schemes yield better performance compared to linear detection schemes, however, at the expense of a slight increase in complexity. The first contribution in this thesis is the design of a near ML-achieving SD algorithm for MIMO digital communication systems that reduces the number of search operations within the sphere-constrained search space at reduced detection complexity in Chapter 4. In this design, the distance between the ML estimate and the received signal is used to control the lower and upper bound radii of the proposed SD to prevent NP-complete problems. The detection method is based on the DFS algorithm and the Successive Interference Cancellation (SIC). The SIC ensures that the effects of dominant signals are effectively removed. Simulation results presented in this thesis show that by employing pre-processing detection schemes, the complexity of the proposed SD can be significantly reduced, though at marginal performance penalty. The second contribution is the determination of the initial sphere radius in Chapter 5. The new initial radius proposed in this thesis is based on the variable parameter α which is commonly based on experience and is chosen to ensure that at least a lattice point exists inside the sphere with high probability. Using the variable parameter α, a new noise covariance matrix which incorporates the number of transmit antennas, the energy of the transmitted symbols and the channel matrix is defined. The new covariance matrix is then incorporated into the EMMSE model to generate an improved EMMSE estimate. The EMMSE radius is finally found by computing the distance between the sphere centre and the improved EMMSE estimate. This distance can be fine-tuned by varying the variable parameter α. The beauty of the proposed method is that it reduces the complexity of the preprocessing step of the EMMSE to that of the Zero-Forcing (ZF) detector without significant performance degradation of the SD, particularly at low Signal-to-Noise Ratios (SNR). More specifically, it will be shown through simulation results that using the EMMSE preprocessing step will substantially improve performance whenever the complexity of the tree search is fixed or upper bounded. The final contribution is the design of the LRAD-MMSE-SIC based SD detection scheme which introduces a trade-off between performance and increased computational complexity in Chapter 6. The Lenstra-Lenstra-Lovasz (LLL) algorithm will be utilised to orthogonalise the channel matrix H to a new near orthogonal channel matrix H ̅.The increased computational complexity introduced by the LLL algorithm will be significantly decreased by employing sorted QR decomposition of the transformed channel H ̅ into a unitary matrix and an upper triangular matrix which retains the property of the channel matrix. The SIC algorithm will ensure that the interference due to dominant signals will be minimised while the LDPC will effectively stop the propagation of errors within the entire system. Through simulations, it will be demonstrated that the proposed detector still approaches the ML performance while requiring much lower complexity compared to the conventional SD.