In this thesis we formulate joint cell, channel and power allocation problems within wireless communication networks. The objectives are to maximize the user with mini- mum data throughput (Shannon capacity) or to maximize the total system throughput, referred to as the max-min and max-sum problem respectively. The complexity is stud- ied together with proposed optimization- and heuristic-based approaches. In the first paper an overall joint cell, channel and power allocation max-min prob- lem is formulated. We show that the decision problem is NP-hard and that the op- timization problem is not approximable unless P is equal to NP, for instances with a sufficiently large number of channels. Further, it follows that for a feasible binary cell and channel allocation, the remaining continuous power allocation optimization problem is still not approximable unless P is equal to NP. In addition, it is shown that first-order optimality conditions give global optimum of the single channel power al- location optimization problem, although the problem is in general not convex. In the following two papers heuristics for solving the overall problem are proposed. In the second paper we consider the single channel problem with convex combinations of the max-min and the max-sum objective functions. This variable utility provides the ability of tuning the amount of fairness and total throughput. The third paper investi- gates the multiple channel setting. On a system with three cells, eight mobile users and three channels, we perform an exhaustive search over feasible cell and channel alloca- tions. The exhaustive search is then compared to the less computationally expensive heuristic approaches, presenting potential earnings to strive for. A conclusion is that several of the proposed heuristics perform very well. The final paper incorporates fixed relay stations into the overall joint cell, channel and power allocation max-min problem. The complexity is inherited from the formula- tion without relay stations. Further, we propose a heuristic channel allocation approach that shows good performance, compared to an optimization based approach, in numer- ical simulations on the relay setting. / Financial support by the Swedish Foundation for Strategic Research (SSF) QC 20110915

Face aux enjeux énergétiques actuels, l’électronique de puissance est un domaine de recherche de premier plan. La relative fragilité des composants présents dans les chaînes de conversion implique néanmoins de devoir prendre en compte la gestion des défaillances dès la phase de conception. La défaillance d'un composant est une situation hautement critique tant sur le plan de la sécurité environnante que sur le plan de l'indisponibilité du système qui en découle. Cette problématique de sûreté de fonctionnement constitue la ligne directive de ce travail de thèse, visant à imaginer, et concevoir des solutions permettant de sécuriser ces structures en présence de défauts. Dans cette thèse, nous étudions de nouveaux composants magnétiques offrant un excellent compromis entre la densité de puissance traitée et rendement de conversion, mais très sensibles à toutes perturbations électriques. Une méthode de pré-dimensionnement des composants magnétiques a été développée et des solutions ont été apportés pour sécuriser et maintenir le fonctionnement de la chaîne de conversion suite à l’apparition de plusieurs défauts. / In the research field, power electronics is an important issue in the actual energy challenges. Nowadays, new converters, called « multilevel or multicell converters », are used in many applications requiring high-current with high-power density. This is due to their high frequency performances and good waveforms signals. The main advantages of such converters concern the high efficiency and good system integration. Most embedded systems are required to maintain operation even if failures or faults occur. New magnetic devices called InterCell Transformers (ICTs) in multicell converters help to improve the efficiency and compactness. Nevertheless, such magnetic components are inherently sensitive to any impecfection coming from the converter. The goal of this PhD thesis is to bring solutions to make ICTs more fault tolerant. Therefore, a pre-design methodology for a robust ICT is presented in order to maintain the operation after the occurrence of one or several faults. Several solutions are presented and detailled

In recent years, the interest for parallel multicell converters has grown, which is partially due to the possibility of coupling the inductors used to connect the different commutation cells together. Coupling the inductors to form an InterCell Transformer (ICT) does not usually modify the output current, but it reduces the current ripple in the windings and the flux swing in some regions of the core. It can be shown that this brings a reduction of copper and core losses in the magnetic component. The reduction of the phase current ripple also reduces the difference between turn on and turn off current in the switches, which brings a reduction of switching losses for devices generating more losses at turn off than at turn on. The design of an ICT is not that different from any other magnetic component but it is very specific and inherent features must be taken into account. Taking full benefit of the potential advantages of ICTs requires the development of special tools and methods which are the focus of the study. We show how to design ICTs considering several topologies and different methods, from the most precise and time-consuming to the less accurate but more quickly calculated. The explanation of the ICT design is divided in four main parts: Copper Losses, Core Losses, Flux Density Saturation and Thermal Aspects. Further attention is given to high frequency copper losses since complex phenomena such as skin and proximity effects highly influence the ICT design. Based on Finite Element Method simulations, smart practices are suggested to reduce high and low frequency copper losses, not only in ICTs but also in inductors and transformers. Simple tables are developed to help transformer designers to identify the best configuration of conductors inside a given core window, depending on the current waveform and frequency, number of turns and geometrical parameters. Optimization routines to reduce the ICT total mass, volume, losses or cost are developed and multidimensional interpolation of pre-simulated values of AC resistance and leakage inductance is used to speed up the optimization routine. Comparison of ICT designs with regard to core and conductor material, number of cells and switching frequency is performed. Comparison with regular inductors is also made in order to verify the benefits of this kind of magnetic component. Multilevel converter control aspects applied to three- hase systems is also investigated in terms of the ICT flux. Zero sequence signals, specific for a PWM strategy and converter/load topology, are created in order to minimize the flux in ICTs and consequently reduce even further the mass and size of these components. Comparison between several PWM methods are performed and experimentally verified.

Enabling multiple base stations to utilize the spatial dimension in a coordinated manner has been shown to be a fruitful technique for improving the spectral efficiency in wireless interference networks. This thesis considers multicell systems where base stations and mobile stations are equipped with multiple antennas. The base stations coordinate their spatial precoding, but individually serve their mobile stations with data. For such coordinated precoding systems, interference alignment (IA) is a useful theoretical tool, due to its ability to serve the maximum number of interference-free data streams. Three topics related to interference alignment and coordinated precoding are studied. First, the feasibility of IA over a joint space-frequency signal space is studied. A necessary condition for space-frequency IA feasibility is derived, and the possible gain over space-only IA is analyzed. An upper bound on the degree of freedom gain is shown to increase in the number of subcarriers, but decrease in the number of antennas. Numerical studies, using synthetically generated channels and real-world channels obtained from indoors and outdoors channel measurements, are used for sum rate performance evaluation. The results show that although a degree of freedom gain is noticeable due to the space-frequency precoding, the sum rate of the system is mainly improved due to a power gain. Second, distributed channel state information (CSI) acquisition techniques are proposed, which provide estimates of the information necessary to perform distributed coordinated precoding. The methods are based on pilot-assisted channel estimation in the uplink and downlink, and correspond to different tradeoffs between feedback and signaling, backhaul use, and computational complexity. Naively applying the existing WMMSE algorithm for distributed coordinated precoding together with the estimated CSI however results in poor performance. A robustification of the algorithm is therefore proposed, relying on the well known diagonal loading technique. An inherent property of the WMMSE solutions is derived and, when enforced onto solutions with imperfect CSI, results in diagonally loaded receive filters. Numerical simulations show the effectiveness of the proposed robustification. Further, the proposed robustified and distributed WMMSE algorithm performs well compared to existing state-of-the-art robust WMMSE algorithms. In contrast to our approach, the existing methods however rely on centralized CSI acquisition. Third, coordinated precoding systems with hardware impairments are studied. Assuming that impairment compensation techniques have been applied, a model is used to describe the aggregate effect of the residual hardware impairments. An iterative resource allocation method accounting for the residual hardware impairments is derived, based on an existing resource allocation framework. Numerical simulations show that the proposed method outperforms all benchmarks. In particular, the gain over impairments-aware time-division multiple access is substantial. / Genom att låta flera radiobasstationer samarbeta är det möjligt att förbättra spektraleffektiviteten i trådlösa interferensnätverk. Fokus i denna licentiatavhandling ligger på multicellnätverk där både radiobasstationer och mobilenheter har flera antenner. Radiobasstationerna väljer sina spatiella förkodare gemensamt, men skickar data individuellt till sina respektive mobilenheter. För sådana system med koordinerad förkodning ('coordinated precoding') är interferensupprätning ('interference alignment') ett användbart teoretiskt verktyg, eftersom det möjliggör överföring av maximalt antal dataströmmar i nätverket. I avhandlingen studeras tre aspekter av interferensupprätning och koordinerad förkodning. Först undersöks interferensupprätning när signalrummet består av en kombination av rymd- och frekvensdimensioner. Ett nödvändigt villkor härleds för existensen av rymd/frekvens-interferensupprätning, och prestandavinsten analyseras i jämförelse med system där enbart rymddimensionerna används för interferensupprätning. Det föreslagna systemet utvärderas med hjälp av numeriska simuleringar och uppmätta inomhus- och utomhuskanaler. Resultaten visar att rymd/frekvens-interferensupprätning ger upphov till ett ökat antal frihetsgrader, men att summadatatakten främst förbättras tack vare en upplevd effektförstärkning. Därefter undersöks tekniker för skattning av den nödvändiga kanalkännedom som krävs för att genomföra koordinerad förkodning. Det finns flera sätt att erhålla den nödvändiga informationen, t.ex. genom olika kombinationer av kanalskattning, feedback, signalering och användning av backhaulnätverk. Speciellt söks distribuerade metoder, eftersom dessa är fördelaktiga vid praktisk implementering. Tre metoder för skattning av kanalkännedom föreslås. Dessa motsvarar olika avvägningar mellan kanalskattning och signalering, och en av metoderna är helt distribuerad. När den skattade informationen används med en existerande algoritm för koordinerad förkodning blir prestandan undermålig. Därför föreslås två förändringar av algoritmen, vilka leder till mer robusta prestanda. Förändringarna bygger på den välkända diagonal loading-tekniken. Utvärdering av det föreslagna systemet, som består av distribuerad erhållning av kanalkännedom samt den förbättrade algoritmen för koordinerad förkodning, genomförs med numerisk simulering. Resulterande prestanda är i nivå med ett tidigare föreslaget system, som dock kräver centraliserad tillgång till kanalskattningarna, till skillnad från vår nya lösning. Slutligen studeras ett system med koordinerad förkodning och icke-perfekt radiohårdvara. En modell för distortionsbruset orsakad av bristerna i radiohårdvaran används, och en iterativ resurstilldelningsteknik föreslås baserad på ett existerande ramverk. Den föreslagna algoritmen kan implementeras distribuerat över mobilenheterna, men kan i allmänhet inte implementeras distribuerat över radiobasstationerna. Den föreslagna algoritmen utvärderas med numeriska simuleringar, och resultaten visar att prestanda är bättre än alla referensmetoder. Detta visar betydelsen av att hantera bristerna i radiohårdvaran i resurstilldelningen. Sammantaget visar avhandlingen på möjligheterna att öka spektraleffektiviteten i framtida multicellnätverk med hjälp av koordinerad förkodning. / <p>QC 20140512</p>

Three dimensional multicell tumor spheroids (MCTS) provide an experimental model where the influence of microenvironmental conditions on protein expression can be determined. Sequential trypsin digestion of HT29 colon carcinoma MCTS enabled segregation into four populations comprising proliferating cells from the surface (SL), an intermediate region (IR), nonproliferating hypoxic cells from the perinecrotic region (PN), and a necrotic core (NC). Total protein was extracted from each population and subjected to iTRAQ-based quantitative proteomics analysis. From a total of 887 proteins identified, 209 were observed to be up-regulated and 114 were down-regulated in the PN and NC regions relative to the SL. Among the up-regulated proteins, components of glycolysis, TCA cycle, lipid metabolism, and steroid biosynthesis increased progressively toward the PN and NC regions. Western blotting, immunohistochemistry, and enzyme assays confirmed that significant changes in the expression of proteins involved in cellular metabolism occur in the nonproliferating fraction of cells within the viable rim. The presence of full length, functional proteins within the NC was unexpected, and further analysis demonstrated that this region contains cells that are undergoing autophagy. This study has identified possible targets that may be suitable for therapeutic intervention, and further studies to validate these are required.

Future cellular networks are expected to support extremely high data rates and user capacities. This thesis investigates the downlink of a wireless cellular system that takes advantage of multiple antennas at base stations and mobile stations, frequency reuse across all cells, and cooperation among base stations. We identify asynchronous interference resulting from multi-cell communication as a key challenge, prove the existence of a downlink/uplink duality in that case, and present a linear precoding scheme that exploits this duality. Since this result is not directly extendable to orthogonal frequency division multiplexing (OFDM), we propose a `hybrid' algorithm for two cooperating base stations, which combines linear and nonlinear precoding. This algorithm minimizes the sum mean squared error of the system and is extendable to OFDM. Finally, we consider the problem of user selection for multiuser precoding in OFDM-based systems. We extend an available single-cell user selection scheme to multiple cooperating cells.

Future cellular networks are expected to support extremely high data rates and user capacities. This thesis investigates the downlink of a wireless cellular system that takes advantage of multiple antennas at base stations and mobile stations, frequency reuse across all cells, and cooperation among base stations. We identify asynchronous interference resulting from multi-cell communication as a key challenge, prove the existence of a downlink/uplink duality in that case, and present a linear precoding scheme that exploits this duality. Since this result is not directly extendable to orthogonal frequency division multiplexing (OFDM), we propose a `hybrid' algorithm for two cooperating base stations, which combines linear and nonlinear precoding. This algorithm minimizes the sum mean squared error of the system and is extendable to OFDM. Finally, we consider the problem of user selection for multiuser precoding in OFDM-based systems. We extend an available single-cell user selection scheme to multiple cooperating cells.

Managing interference is the main technical challenge in wireless networks. Multiple input multiple output (MIMO) methods are key components to overcome the interference bottleneck and deliver higher data rates. The most efficient MIMO techniques require channel state information (CSI). In practice, this information is inaccurate due to errors in CSI acquisition, as well as mobility and delay. CSI inaccuracy reduces the performance gains provided by MIMO. When compounded with uncoordinated intercell interference, the degradation in MIMO performance is accentuated. This dissertation investigates the impact of CSI inaccuracy on the performance of increasingly complex interference limited networks, starting with a single interferer scenario, continuing to a heterogeneous network with a femtocell overlay, and finishing with a clustered multicell coordination model for randomly deployed transmitting nodes. First, this dissertation analyzes limited feedback beamforming and precoded spatial multiplexing over temporally correlated channels. Assuming uncoordinated interference from one dominant interferer, using Markov chain convergence theory, the gain in the average successful throughput at the mobile user is shown to decrease exponentially with the feedback delay. The decay rate is amplified when the user is interference limited. Interference cancellation methods at the receiver are shown to mitigate the effect of interference. This work motivates the need for practical MIMO designs to overcome the adverse effects of interference. Second, limited feedback beamforming is analyzed on the downlink of a more realistic heterogeneous cellular network. Future generation cellular networks are expected to be heterogeneous, consisting of a mixture of macro base stations and low power nodes, to support the increasing user traffic capacity and reliability demand. Interference in heterogeneous environments cannot be coordinated using traditional interference mitigation techniques due to the on demand and random deployment of low power nodes such as femtocells. Using tools from stochastic geometry, the outage and average achievable rate of limited feedback MIMO is computed with same-tier and cross-tier interference, and feedback delay. A hybrid fixed and random network deployment model is used to analyze the performance in a fixed cell of interest. The maximum density of transmitting femtocells is derived as a function of the feedback rate and delay. The detrimental effect of same-tier interference is quantified, as the mobile user moves from the cell-center to the cell-edge. The third part of this dissertation considers limited coordination between randomly deployed transmitters. Building on the established degrading effect of uncoordinated interference on practical MIMO methods, and the analytical tractability of random deployment models, interference coordination is analyzed. Using multiple antennas at the transmitter for interference nulling in ad hoc networks is first shown to achieve MIMO gains using single antenna receivers. Clustered coordination is then investigated for cellular systems with randomly deployed base stations. As full coordination in the network is not feasible, a random clustering model is proposed where base stations located in the same cluster coordinate. The average achievable rate can be optimized as a function of the number of antennas to maximize the coordination gains. For multicell limited feedback, adaptive partitioning of feedback bits as a function of the signal and interference strength is proposed to minimize the loss in rate due to finite rate feedback. / text

No description available.

Abstract Uplink resource allocation strategies in modern cellular networks are studied in this thesis. With the presence of multiple antenna transmission, multiple base station (BS) coordination and multicarrier techniques, the resource allocation problem is reformulated and jointly optimized over a large set of variables. The focus is on the sum power minimization with per user rate constraints. A centralized multicarrier coordinated cellular network with multiple antennas implemented at the BS side is considered, where BSs can be adaptively clustered to detect signals from one mobile station (MS). The power, subcarrier, beamforming vector and BS cluster (BSC) are the design variables to be jointly optimized to satisfy the rate constraint per user. The first considered scenario is a simple single carrier multicell system. The power control problem with per user rate constraint can be optimally solved by the proposed algorithm, where power vector, BSC and beamforming vectors are separately updated until the sum power converges. The scenario is extended to more complicated multicarrier systems. The resource allocation problem is non-deterministic polynomial-time hard (NP-hard). Suboptimal algorithms are proposed to tackle the problem. To get more insights to the performance gap between the proposed algorithms and the capacity achieving bound, the scenario is specified to a single cell system with nonlinear receiver so that the calculation of the lower bound is possible. Efficient geometric aided fast converging power minimization algorithms are proposed to calculate the power bound of the multiple access channel (MAC) with per user rate constraint. By comparing the capacity achieving lower bound with the proposed algorithm, the BSW that starts from full rate allocation looks promising to have a good tradeoff between the convergence speed and the sum power consumption. Besides the resource allocation algorithms in the cellular network, the physical modeling and corresponding design of the network itself are also considered. The radio propagation in the elevation domain is modeled and considered. The diversity gain from the elevation domain is achieved by extra degree of freedom of beamforming in elevation domain. The antenna array can be either a uniform linear array or a uniform planar array with elements placed horizontally. The proposed power control algorithms are simulated in the 3D network scenarios. The effects of antenna array design in different propagation scenarios are compared. / Tiivistelmä Työssä tutkitaan ylälinkin resurssien kohdentamisstrategioita matkapuhelinverkoissa. Olettaen koordinointi useiden monikantoaaltotekniikoita käyttävien moniantennitukiasemien (BS) välillä, resurssien kohdentamisongelma muotoillaan uudelleen ja optimoidaan yli suuren joukon optimointimuuttujia. Erityisesti keskitytään yhteenlasketun tehon minimointiongelmaan käyttäjäkohtaisien siirtonopeusrajoitteiden kanssa. Työssä oletetaan keskitetty koordinointi useiden monikantoaaltotekniikoita käyttävien moniantennitukiasemien välillä, joten tukiasemat voidaan adaptiivisesti ryhmitellä yhden matkaviestimen signaalin havannointia varten. Lähetysteho, kantoaaltoallokaatio, keilanmuodostus ja tukiasemaklusterointi ovat ongelman muuttujia, jotka optimoidaan yhdessä siten, että käyttäjäkohtaiset siirtonopeusrajoitteet täyttyvät. Ensimmäinen käsitelty tapaus on yksinkertainen yhden operaattorin monisolujärjestelmä. Tehonsäätöongelma käyttäjäkohtaisten siirtonopeusrajoitusten kanssa voidaan optimaalisesti ratkaista ehdotetulla algoritmilla, jossa lähetysteho, keilanmuodostusvektorit ja tukiasemaklusterointi päivitetään erikseen, kunnes yhteenlaskettu teho suppenee. Tarkastelu laajennetaan monimutkaisempaan monikantoaaltojärjestelmään. Kun käyttäjäkohtainen siirtonopeustavoite kiinnitetään, ongelma voidaan vastaavasti hajottaa osittaisiksi alikantoaaltokohtaisiksi osaongelmiksi, jossa kukin osaongelma voidaan optimaalisesti ratkaista. Jos alikantoaaltokohtaista siirtonopeustavoitetta ei ole kiinnitetty, tehonsäätöongelmasta tulee ei-polynomisesti monimutkainen. Optimaalisia algoritmeja ehdotetaan ongelman ratkaisemiseksi. Jotta voitaisiin saada tietoa todellisesta suorituskykyerosta ehdotettujen algoritmien ja kapasiteettioptimaalisen rajan välillä, vertailu tehdään yhden solun simulointimallissa epälineaarisen vastaanottimen kanssa siten, että kapasiteettioptimaalisen alarajan laskeminen on mahdollista. Tätä varten kehitetään tehokas geometria-avusteinen ja nopeasti konvergoituva algoritmi tehon minimointia varten käyttäjäkohtaisten siirtonopeusrajoitusten kanssa. Vertaamalla kapasiteettioptimaalista alarajaa ehdotettujen algoritmien suorituskykyyn huomataan, että ehdotettu BSW algoritmi on hyvä kompromissi konvergoitumisnopeuden ja tehonkulutuksen välillä. Matkapuhelinverkkojen resurssienkohdentamisalgoritmien lisäksi työssä huomioidaan myös verkon fyysinen mallintaminen ja vastaava suunnittelu. Työssä mallinnetaan radiokanavan ominaisuudet myös korkeustasossa, joka mahdollistaa diversiteetin hyödyntämisen korkeustason keilanmuodostuksessa. Antenniryhmä voi olla joko yhtenäinen lineaarinen ryhmä tai yhtenäinen tasoryhmä, jossa antennielementit on sijoitettu tasoon. Ehdotettuja tehonsäätöalgoritmeja simuloidaan kolmiulotteisessa verkkoskenaarioissa, jossa verrataan antenniryhmäsuunnittelun vaikutuksia eri radiokanavaskenaarioissa.