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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
61

Analysis of Bandwidth and Latency Constraints on a Packetized Cloud Radio Access Network Fronthaul

Chaudhary, Jay Kant 20 May 2020 (has links)
Cloud radio access network (C-RAN) is a promising architecture for the next-generation RAN to meet the diverse and stringent requirements envisioned by fifth generation mobile communication systems (5G) and future generation mobile networks. C-RAN offers several advantages, such as reduced capital expenditure (CAPEX) and operational expenditure (OPEX), increased spectral efficiency (SE), higher capacity and improved cell-edge performance, and efficient hardware utilization through resource sharing and network function virtualization (NFV). However, these centralization gains come with the need for a fronthaul, which is the transport link connecting remote radio units (RRUs) to the base band unit (BBU) pool. In conventional C-RAN, legacy common public radio interface (CPRI) protocol is used on the fronthaul network to transport the raw, unprocessed baseband in-phase/quadrature-phase (I/Q) samples between the BBU and the RRUs, and it demands a huge fronthaul bandwidth, a strict low-latency, in the order of a few hundred microseconds, and a very high reliability. Hence, in order to relax the excessive fronthaul bandwidth and stringent low-latency requirements, as well as to enhance the flexibility of the fronthaul, it is utmost important to redesign the fronthaul, while still profiting from the acclaimed centralization benefits. Therefore, a flexibly centralized C-RAN with different functional splits has been introduced. In addition, 5G mobile fronthaul (often also termed as an evolved fronthaul ) is envisioned to be packet-based, utilizing the Ethernet as a transport technology. In this thesis, to circumvent the fronthaul bandwidth constraint, a packetized fronthaul considering an appropriate functional split such that the fronthaul data rate is coupled with actual user data rate, unlike the classical C-RAN where fronthaul data rate is always static and independent of the traffic load, is justifiably chosen. We adapt queuing and spatial traffic models to derive the mathematical expressions for statistical multiplexing gains that can be obtained from the randomness in the user traffic. Through this, we show that the required fronthaul bandwidth can be reduced significantly, depending on the overall traffic demand, correlation distance and outage probability. Furthermore, an iterative optimization algorithm is developed, showing the impacts of number of pilots on a bandwidth-constrained fronthaul. This algorithm achieves additional reduction in the required fronthaul bandwidth. Next, knowing the multiplexing gains and possible fronthaul bandwidth reduction, it is beneficial for the mobile network operators (MNOs) to deploy the optical transceiver (TRX) modules in C-RAN cost efficiently. For this, using the same framework, a cost model for fronthaul TRX cost optimization is presented. This is essential in C-RAN, because in a wavelength division multiplexing-passive optical network (WDM-PON) system, TRXs are generally deployed to serve at a peak load. But, because of variations in the traffic demands, owing to tidal effect, the fronthaul can be dimensioned requiring a lower capacity allowing a reasonable outage, thus giving rise to cost saving by deploying fewer TRXs, and energy saving by putting the unused TRXs in sleep mode. The second focus of the thesis is the fronthaul latency analysis, which is a critical performance metric, especially for ultra-reliable and low latency communication (URLLC). An analytical framework to calculate the latency in the uplink (UL) of C-RAN massive multiple-input multiple-output (MIMO) system is presented. For this, a continuous-time queuing model for the Ethernet switch in the fronthaul network, which aggregates the UL traffic from several massive MIMO-aided RRUs, is considered. The closed-form solutions for the moment generating function (MGF) of sojourn time, waiting time and queue length distributions are derived using Pollaczek–Khinchine formula for our M/HE/1 queuing model, and evaluated via numerical solutions. In addition, the packet loss rate – due to the inability of the packets to reach the destination in a certain time – is derived. Due to the slotted nature of the UL transmissions, the model is extended to a discrete-time queuing model. The impact of the packet arrival rate, average packet size, SE of users, and fronthaul capacity on the sojourn time, waiting time and queue length distributions are analyzed. While offloading more signal processing functionalities to the RRU reduces the required fronthaul bandwidth considerably, this increases the complexity at the RRU. Hence, considering the 5G New Radio (NR) flexible numerology and XRAN functional split with a detailed radio frequency (RF) chain at the RRU, the total RRU complexity is computed first, and later, a tradeoff between the required fronthaul bandwidth and RRU complexity is analyzed. We conclude that despite the numerous C-RAN benefits, the stringent fronthaul bandwidth and latency constraints must be carefully evaluated, and an optimal functional split is essential to meet diverse set of requirements imposed by new radio access technologies (RATs). / Ein cloud-basiertes Mobilfunkzugangsnetz (cloud radio access network, C-RAN) stellt eine vielversprechende Architektur für das RAN der nächsten Generation dar, um die vielfältigen und strengen Anforderungen der fünften (5G) und zukünftigen Generationen von Mobilfunknetzen zu erfüllen. C-RAN bietet mehrere Vorteile, wie z.B. reduzierte Investitions- (CAPEX) und Betriebskosten (OPEX), erhöhte spektrale Effizienz (SE), höhere Kapazität und verbesserte Leistung am Zellrand sowie effiziente Hardwareauslastung durch Ressourcenteilung und Virtualisierung von Netzwerkfunktionen (network function virtualization, NFV). Diese Zentralisierungsvorteile erfordern jedoch eine Transportverbindung (Fronthaul), die die Antenneneinheiten (remote radio units, RRUs) mit dem Pool an Basisbandeinheiten (basisband unit, BBU) verbindet. Im konventionellen C-RAN wird das bestehende CPRI-Protokoll (common public radio interface) für das Fronthaul-Netzwerk verwendet, um die rohen, unverarbeitet n Abtastwerte der In-Phaseund Quadraturkomponente (I/Q) des Basisbands zwischen der BBU und den RRUs zu transportieren. Dies erfordert eine enorme Fronthaul-Bandbreite, eine strenge niedrige Latenz in der Größenordnung von einigen hundert Mikrosekunden und eine sehr hohe Zuverlässigkeit. Um die extrem große Fronthaul-Bandbreite und die strengen Anforderungen an die geringe Latenz zu lockern und die Flexibilität des Fronthauls zu erhöhen, ist es daher äußerst wichtig, das Fronthaul neu zu gestalten und dabei trotzdem von den erwarteten Vorteilen der Zentralisierung zu profitieren. Daher wurde ein flexibel zentralisiertes CRAN mit unterschiedlichen Funktionsaufteilungen eingeführt. Außerdem ist das mobile 5G-Fronthaul (oft auch als evolved Fronthaul bezeichnet) als paketbasiert konzipiert und nutzt Ethernet als Transporttechnologie. Um die Bandbreitenbeschränkung zu erfüllen, wird in dieser Arbeit ein paketbasiertes Fronthaul unter Berücksichtigung einer geeigneten funktionalen Aufteilung so gewählt, dass die Fronthaul-Datenrate mit der tatsächlichen Nutzdatenrate gekoppelt wird, im Gegensatz zum klassischen C-RAN, bei dem die Fronthaul-Datenrate immer statisch und unabhängig von der Verkehrsbelastung ist. Wir passen Warteschlangen- und räumliche Verkehrsmodelle an, um mathematische Ausdrücke für statistische Multiplexing- Gewinne herzuleiten, die aus der Zufälligkeit im Benutzerverkehr gewonnen werden können. Hierdurch zeigen wir, dass die erforderliche Fronthaul-Bandbreite abhängig von der Gesamtverkehrsnachfrage, der Korrelationsdistanz und der Ausfallwahrscheinlichkeit deutlich reduziert werden kann. Darüber hinaus wird ein iterativer Optimierungsalgorithmus entwickelt, der die Auswirkungen der Anzahl der Piloten auf das bandbreitenbeschränkte Fronthaul zeigt. Dieser Algorithmus erreicht eine zusätzliche Reduktion der benötigte Fronthaul-Bandbreite. Mit dem Wissen über die Multiplexing-Gewinne und die mögliche Reduktion der Fronthaul-Bandbreite ist es für die Mobilfunkbetreiber (mobile network operators, MNOs) von Vorteil, die Module des optischen Sendeempfängers (transceiver, TRX) kostengünstig im C-RAN einzusetzen. Dazu wird unter Verwendung des gleichen Rahmenwerks ein Kostenmodell zur Fronthaul-TRX-Kostenoptimierung vorgestellt. Dies ist im C-RAN unerlässlich, da in einem WDM-PON-System (wavelength division multiplexing-passive optical network) die TRX im Allgemeinen bei Spitzenlast eingesetzt werden. Aufgrund der Schwankungen in den Verkehrsanforderungen (Gezeiteneffekt) kann das Fronthaul jedoch mit einer geringeren Kapazität dimensioniert werden, die einen vertretbaren Ausfall in Kauf nimmt, was zu Kosteneinsparungen durch den Einsatz von weniger TRXn und Energieeinsparungen durch den Einsatz der ungenutzten TRX im Schlafmodus führt. Der zweite Schwerpunkt der Arbeit ist die Fronthaul-Latenzanalyse, die eine kritische Leistungskennzahl liefert, insbesondere für die hochzuverlässige und niedriglatente Kommunikation (ultra-reliable low latency communications, URLLC). Ein analytisches Modell zur Berechnung der Latenz im Uplink (UL) des C-RAN mit massivem MIMO (multiple input multiple output) wird vorgestellt. Dazu wird ein Warteschlangen-Modell mit kontinuierlicher Zeit für den Ethernet-Switch im Fronthaul-Netzwerk betrachtet, das den UL-Verkehr von mehreren RRUs mit massivem MIMO aggregiert. Die geschlossenen Lösungen für die momenterzeugende Funktion (moment generating function, MGF) von Verweildauer-, Wartezeit- und Warteschlangenlängenverteilungen werden mit Hilfe der Pollaczek-Khinchin-Formel für unser M/HE/1-Warteschlangenmodell hergeleitet und mittels numerischer Verfahren ausgewertet. Darüber hinaus wird die Paketverlustrate derjenigen Pakete, die das Ziel nicht in einer bestimmten Zeit erreichen, hergeleitet. Aufgrund der Organisation der UL-Übertragungen in Zeitschlitzen wird das Modell zu einem Warteschlangenmodell mit diskreter Zeit erweitert. Der Einfluss der Paketankunftsrate, der durchschnittlichen Paketgröße, der SE der Benutzer und der Fronthaul-Kapazität auf die Verweildauer-, dieWartezeit- und dieWarteschlangenlängenverteilung wird analysiert. Während das Verlagern weiterer Signalverarbeitungsfunktionalitäten an die RRU die erforderliche Fronthaul-Bandbreite erheblich reduziert, erhöht sich dadurch im Gegenzug die Komplexität der RRU. Daher wird unter Berücksichtigung der flexiblen Numerologie von 5G New Radio (NR) und der XRAN-Funktionenaufteilung mit einer detaillierten RF-Kette (radio frequency) am RRU zunächst die gesamte RRU-Komplexität berechnet und später ein Kompromiss zwischen der erforderlichen Fronthaul-Bandbreite und der RRU-Komplexität untersucht. Wir kommen zu dem Schluss, dass trotz der zahlreichen Vorteile von C-RAN die strengen Bandbreiten- und Latenzbedingungen an das Fronthaul sorgfältig geprüft werden müssen und eine optimale funktionale Aufteilung unerlässlich ist, um die vielfältigen Anforderungen der neuen Funkzugangstechnologien (radio access technologies, RATs) zu erfüllen.
62

Analysis of the Impact of Reactive Power Control on Voltage Stability in Transmission Power Grids

Cabadag, Rengin Idil 16 June 2020 (has links)
Voltage stability is the ability of a power system to maintain acceptable voltages at all buses under normal and abnormal operating conditions. The scarcity of reactive power or reactive power imbalance is the main reason of voltage instabilities. The energy supply of Germany will be dominated by renewable energy sources (RES) within energy transition actions leading to a decrease in conventional power plants especially in the transmission grid. Since the conventional power plants are still main reactive power sources, key challenge in the future will be the provision of system services such as control of reactive power to maintain voltage stability in the transmission networks. A wide range of technology that is able to provide the required dynamic reactive power compensation is already available. However, in order to find the most effective implementation, it is necessary to investigate and compare these different technologies for a voltage stable grid operation. The main challenge regarding comparative studies that incorporate reactive power compensation devices is the development and the implementation of reliable comparison strategies. This thesis analyses the impact of reactive power on the voltage stability phenomena both in long-term and short-term time frames under various grid situations. Voltage stability margins in the long-term time frame are quantified by gradually increasing the reactive power injection into certain buses until the voltage collapses. Voltage stability in the short-term time frame is assessed by applying grid faults and simulating the time-domain grid response. A transient voltage severity ratio (TVSR) is developed in this thesis as the main comparison metric to evaluate and compare the performance of investigated compensation devices. Additionally, TVSR and other developed comparison metrics in this thesis are used to determine the optimal settings of the controller parameters of compensation devices. As a result, the submitted thesis shows a practical and reliable approach to analyze the performance of different compensation devices under different grid situations.
63

Resource Allocation for Multiple Access and Broadcast Channels under Quality of Service Requirements Based on Strategy Proof Pricing

Shen, Fei 14 November 2014 (has links)
The efficient allocation of power is a major concern in today’s wireless communications systems. Due to the high demand in data rate and the scarcity of wireless resources such as power, the multi-user communication systems like the multiple access channel (MAC) and broadcast channel (BC) have become highly competitive environments for the users as well as the system itself. Theory of microeconomics and game theory provide the good analytical manner for the selfish and social welfare conflict problems. Instead of maximizing the system sum rate, our proposed system deals with fulfilling the utility (rate) requirement of all the users with efficient power allocation. The users formulate the signal to interference-plus-noise ratio (SINR) based quality-of-service (QoS) requirements. We propose the framework to allocate the power to each user with universal pricing mechanisms. The prices act as the control signal and are assumed to be some virtual currency in the wireless system. They can influence the physical layer operating points to meet the desired utility requirements. Centralized and distributed power allocation frameworks are discussed separately in the thesis with different pricing schemes. In wireless systems we have users that are rational in the game theoretic sense of making decisions consistently in pursuit of their own individual objectives. Each user’s objective is to maximize the expected value of its own payoff measured on a certain utility scale. Selfishness or self-interest is an important implication of rationality. Therefore, the mobiles which share the same spectrum have incentives to misinterpret their private information in order to obtain more utility. They might behave selfishly and show also malicious behavior by creating increased interference for other mobiles. Therefore, it is important to supervise and influence the operation of the system by pricing and priority (weights) optimization. In the centralized resource allocation, we study the general MAC and BC (with linear and nonlinear receiver) with three types of agents: the regulator, the system optimizer and the mobile users. The regulator ensures the QoS requirements of all users by clever pricing and prevents cheating. The simple system optimizer solves a certain system utility maximization problem to allocate the power with the given prices and weights (priorities). The linear and nonlinear pricing mechanisms are analyzed, respectively. It is shown that linear pricing is a universal pricing only if successive interference cancellation (SIC) for uplink transmission or dirty paper coding (DPC) for downlink transmission is applied at the base station (BS). For MAC without SIC, nonlinear pricing which is logarithmic in power and linear in prices is a universal pricing scheme. The prices, the resulting cost terms, the optimal power allocation to achieve the QoS requirement of each user in the feasible rate region are derived in closed form solutions for MAC with and without SIC using linear and nonlinear pricing frameworks, respectively. The users are willing to maximize their achievable rate and minimize their cost on power by falsely reporting their channel state information (CSI). By predicting the best cheating strategy of the malicious users, the regulator is able to detect the misbehavior and punish the cheaters. The infinite repeated game (RG) is proposed as a counter mechanism with the trigger strategy using the trigger price. We show that by anticipating the total payoff of the proposed RG, the users have no incentive to cheat and therefore our framework is strategy-proof. In the distributed resource allocation, each user allocates its own power by optimizing the individual utility function. The noncooperative game among the users is formulated. The individual prices are introduced to the utility function of each user to shift the Nash equilibrium (NE) power allocation to the desired point. We show that by implicit control of the proposed prices, the best response (BR) power allocation of each user converges rapidly. The Shannon rate-based QoS requirement of each user is achieved with minimum power at the unique NE point. We analyse different behavior types of the users, especially the malicious behavior of misrepresenting the user utility function. The resulting NE power allocation and achievable rates of all users are derived when malicious behavior exists. The strategy-proof mechanism is designed using the punishment prices when the types of the malicious users are detected. The algorithm of the strategy-proof noncooperative game is proposed. We illustrate the convergence of the BR dynamic and the Price of Malice (PoM) by numerical simulations. The uplink transmission within the single cell of heterogeneous networks is exactly the same model as MAC. Therefore, the results of the pricing-based power allocation for MAC can be implemented into heterogeneous networks. Femtocells deployed in the Macrocell network provide better indoor coverage to the user equipments (UEs) with low power consumption and maintenance cost. The industrial vendors show great interest in the access mode, called the hybrid access, in which the macrocell UEs (MUEs) can be served by the nearby Femtocell Access Point (FAP). By adopting hybrid access in the femtocell, the system energy efficiency is improved due to the short distance between the FAP and MUEs while at the same time, the QoS requirements are better guaranteed. However, both the Macrocell base station (MBS) and the FAP are rational and selfish, who maximize their own utilities. The framework to successively apply the hybrid access in femtocell and fulfill the QoS requirement of each UE is important. We propose two novel compensation frameworks to motivate the hybrid access of femtocells. To save the energy consumption, the MBS is willing to motivate the FAP for hybrid access with compensation. The Stackelberg game is formulated where the MBS serves as the leader and the FAP serves as the follower. The MBS maximizes its utility by choosing the compensation prices. The FAP optimizes its utility by selecting the number of MUEs in hybrid access. By choosing the proper compensation price, the optimal number of MUEs served by the FAP to maximize the utility of the MBS coincides with that to maximize the utility of the FAP. Numerous simulation results are conducted, showing that the proposed compensation frameworks result in a win-win solution. In this thesis, based on game theory, mechanism design and pricing framework, efficient power allocation are proposed to guarantee the QoS requirements of all users in the wireless networks. The results are applicable in the multi-user systems such as heterogeneous networks. Both centralized and distributed allocation schemes are analyzed which are suitable for different communication scenarios. / Aufgrund der hohen Nachfrage nach Datenrate und wegen der Knappheit an Ressourcen in Funknetzen ist die effiziente Allokation von Leistung ein wichtiges Thema in den heutigen Mehrnutzer-Kommunikationssystemen. Die Spieltheorie bietet Methoden, um egoistische und soziale Konfliktsituationen zu analysieren. Das vorgeschlagene System befasst sich mit der Erfüllung der auf Signal-zu-Rausch-und-Interferenz-Verhältnis (SINR) basierenden Quality-of-Service (QoS)-Anforderungen aller Nutzer mittels effizienter Leistungsallokation, anstatt die Übertragungsrate zu maximieren. Es wird ein Framework entworfen, um die Leistungsallokation mittels universellen Pricing-Mechanismen umzusetzen. In der Dissertation werden zentralisierte und verteilte Leistungsallokationsalgorithmen unter Verwendung verschiedener Pricing-Ansätze diskutiert. Die Nutzer in Funksystemen handeln rational im spieltheoretischen Sinne, indem sie ihre eigenen Nutzenfunktionen maximieren. Die mobilen Endgeräte, die dasselbe Spektrum nutzen, haben den Anreiz durch bewusste Fehlinterpretation ihrer privaten Informationen das eigene Ergebnis zu verbessern. Daher ist es wichtig, die Funktionalität des Systems zu überwachen und durch Optimierung des Pricings und Priorisierungsgewichte zu beeinflussen. Für den zentralisierten Ressourcenallokationsansatz werden der allgemeine Mehrfachzugriffskanal (Multiple Access Channel, MAC) und der Broadcastkanal (BC) mit linearen bzw. nichtlinearen Empfängern untersucht. Die Preise, die resultierenden Kostenterme und die optimale Leistungsallokation, mit der die QoS-Anforderungen in der zulässigen Ratenregion erfüllt werden, werden in geschlossener Form hergeleitet. Lineare und nichtlineare Pricing-Ansätze werden separat diskutiert. Das unendlich oft wiederholte Spiel wird vorgeschlagen, um Spieler vom Betrügen durch Übermittlung falscher Kanalinformationen abzuhalten. Für die verteilten Ressourcenvergabe wird das nichtkooperative Spiel in Normalform verwendet und formuliert. Die Nutzer wählen ihre Sendeleistung zur Maximierung ihrer eigenen Nutzenfunktion. Individuelle Preise werden eingeführt und so angepasst, dass die QoS-Anforderungen mit der Leistungsallokation im eindeutigen Nash-Gleichgewicht erfüllt werden. Verschiedene Arten des Nutzerverhaltens werden bezüglich der Täuschung ihrer Nutzenfunktion analysiert, und ein Strategy-Proof-Mechanismus mit Strafen wird entwickelt. Die Ergebnisse für den MAC sind anwendbar auf heterogene Netzwerke, wobei zwei neuartige Ansätze zur Kompensation bereitgestellt werden, die den hybriden Zugang zu Femtozell-Netzwerken motivieren. Mithilfe des Stackelberg-Spiels wird gezeigt, dass die vorgeschlagenen Ansätze in einer Win-Win-Situation resultieren.
64

Charakterisierung der Modenverwirbelungskammer der TU Dresden und Untersuchung von Verfahren zur Bestimmung der unabhängigen Rührerstellungen

Pfennig, Stephan 18 December 2014 (has links)
Die Elektromagnetische Verträglichkeit (EMV) betrachtet die Fähigkeit eines elektrischen Gerätes, in seiner elektromagnetischen Umgebung störungsfrei zu funktionieren, ohne diese dabei unzulässig zu stören. Zur Prüfung der Elektromagnetischen Verträglichkeit werden verschiedene Messumgebungen verwendet. Die Messung der strahlungsgebundenen Störfestigkeit und Störaussendung kann zum Beispiel in einer Modenverwirbelungskammer (MVK) erfolgen. Bei der Störfestigkeitsmessung wird der Prüfling einem externen Prüffeld ausgesetzt und untersucht, ob dieser die definierten Kriterien für einen störungsfreien Betrieb erfüllt. Für das Prüffeld muss vor der Messung nachgewiesen werden, dass die Anforderungen an dessen Homogenität eingehalten werden. Einen entscheidenden Einfluss auf die Homogenität des Prüffeldes hat der sogenannte Rührer. Bei einer MVK handelt es sich prinzipiell um einen Hohlraumresonator, in den ein mechanischer Rührer, d.h. ein elektrisch großer, drehbarer Streukörper integriert wird. Durch die Drehung des Rührers verändert sich die Feldverteilung in der MVK, was auch als Verwirbelung bezeichnet wird. Prinzipiell ergibt sich für jede Stellung des Rührers ein inhomogenes Feld mit lokalen Minima und Maxima. Ein Ziel bei der Verwendung von Modenverwirbelungskammern ist es, mit Hilfe geeigneter Verfahren Rührerstellungen zu finden, deren Feldverteilungen in Überlagerung ein möglichst homogenes Prüffeld erzeugen. Zum Lehrstuhl für Theoretische Elektrotechnik und Elektromagnetische Verträglichkeit der Technischen Universität Dresden gehört seit 2010 eine Modenverwirbelungskammer. Die Charakterisierung dieser MVK sowie eine weiterführende Untersuchung zur Wahl der Rührerstellungen bilden die Schwerpunkte der vorliegenden Arbeit. / In 2010 the Chair of Electromagnetic Theory and Compatibility of Technical University Dresden could extend its laboratories by a reverberation chamber with the dimensions 5.3 m, 3.7m and 3.0 m. Since then, a detailed characterisation of the chamber as well as further investigations have been the main emphasis of the authors research. The submitted doctoral thesis presents the obtained results. With the design, the fundamentals of operation and further characterisation of the reverberation chamber, given in Chapter 1 and 2, it aims to give an introduction and better understanding of reverberation chambers. On this basis, the authors research focused on methods for determining the independent stirrer positions in reverberations chambers. The results of the investigations are presented and summarised in chapter 3. One scope of Electromagnetic Compatibility are radiated immunity measurements. Besides the GTEM cell and the anechoic chamber the reverberation chamber gains in importance as an alternative measurement environment. A reverberation chamber is a shielded room with reflecting walls and one or more integrated mechanical stirrers. By rotating the stirrer the spatial boundary conditions for the electromagnetic field quantities are altered. The resulting change of the spatial field distribution depends on the location within the chamber and the geometry of the stirrer. Each stirrer position yields an inhomogeneous field distribution created by interfering waves. A general aim is to find a set of stirrer positions, whose superimposed field distributions create a more uniform test field. In practice, the given requirements for the homogeneity of the test field shall, with regards to an optimisation of measurement time, be realized with a minimum number of stirrer positions. In this context the term ’independent stirrer positions’ was established and describes stirrer positions, whose field distributions are linearly uncorrelated and therefore assumed to be practical for creating a more homogeneous test field using only a minimal number of stirrer positions. A general method for determining the number of independent stirrer positions in reverberation chambers is presented. The method uses a certain number of measurement positions in a defined test volume in order to characterize the spatial field distribution inside the chamber. Using the Pearson correlation coefficient the field distributions of the stirrer positions are tested for linear correlation and pairs of independent stirrer positions are determined. On this basis, cliques of pairwise independent stirrer positions are identified using appropriate algorithms. It is shown that the general method yields detailed information about the number and distribution of the independent stirrer positions and is therefore particularly suitable to evaluate other methods. Finally, the standard method according to IEC 61000-4-21 as well as selected alternative methods, that have been proposed in the past, are evaluated and compared based on the results of the general method.
65

Modellierung und Entwurf von resonanten Mikroaktoren mit elektrostatischem Antrieb

Klose, Thomas 23 February 2016 (has links)
Resonante Mikrobauelemente mit elektrostatischem Antrieb finden seit einigen Jahren vermehrt Anwendung in vielen Bereichen der Technik. So beruhen beispielsweise Drehraten- oder Beschleunigungssensoren, die im Automobilbau eingesetzt werden auf diesem Prinzip. Neue Anwendungsfelder ergeben sich vor allem für Aktoren, beispielsweise für die am Fraunhofer IPMS entwickelten Mikroscannerspiegel mit Out-of-plane-comb-Antrieb. Sie dienen zur geometrischen Ablenkung von Licht und können zur Realisierung von hochintegrierten Systemen zur Ausgabe (Laser-Projektor) oder Aufnahme (Laser-Imager) von Daten genutzt werden. Zum Entwurf von Mikroaktoren gibt es eine Reihe von Arbeiten, die sich meist auf ein konkretes Antriebsprinzip beziehen oder den Entwurf im Allgemeinen behandeln. Die vorliegende Arbeit verfolgt daher das Ziel, speziell die Randbedingungen beim Entwurf resonanter Mikroaktoren mit Out-of-plane-comb-Antrieb zu identifizieren bzw. zu systematisieren sowie die gewonnenen Erkenntnisse in einem effizienten Entwurfsprozess umzusetzen. Dabei sollen möglichst auch relevante nichtlineare Effekte berücksichtigt werden, sodass sich neue Möglichkeiten zur Optimierung der Bauelemente und damit zur Erweiterung des Entwurfsraums ergeben.:1 Einordnung und Ziele der Arbeit 2 Grundlagen und Stand der Technik 2.1 Herstellungstechnologien 2.2 MEMS-Aktoren 2.2.1 Antriebsprinzipien 2.2.2 Elektrostatische Antriebe 2.3 Der Fraunhofer IPMS Mikroscannerspiegel 2.3.1 Synchronisierte Anregung 2.3.2 Parametrische Anregung 2.3.3 Anwendungsmöglichkeiten und Grenzen 2.4 Motivationen der Arbeit 3 Randbedingungen beim Entwurf 3.1 Vereinbarungen und Definitionen 3.1.1 Material- und Strukturvereinfachungen 3.1.2 Koordinatensysteme 3.1.3 Mathematische Vereinfachungen und Definitionen 3.2 Strukturmechanische Randbedingungen 3.2.1 Richtungsabhängige Materialeigenschaften 3.2.2 Geometrische Nichtlinearitäten 3.2.3 Strukturmechanische Spannungen 3.2.4 Eigenschwingungen 3.2.5 Fertigungstoleranzen 3.2.6 Dynamische Deformation 3.2.7 Strukturdämpfung 3.3 Fluidmechanische Randbedingungen 3.3.1 Näherungen zur Slip-Korrektur 3.3.2 Gültigkeit der quasistatischen Näherung 3.3.3 Dämpfungsmechanismen innerhalb der Kammstruktur 3.3.4 Dämpfungsmechanismen der bewegten Spiegelplatte 3.4 Randbedingungen der Elektrik bzw. Elektrostatik 3.4.1 Antriebskapazitäten und Randfelder 3.4.2 Spannungsfestigkeit 3.4.3 Leistungsaufnahme 3.4.4 Elektromechanische Stabilität 3.5 Optische Randbedingungen 4 Nichtlineare Dynamik 4.1 Stabilitätsanalyse 4.1.1 Fixpunkte und Grenzzyklen 4.1.2 Stabilität 4.1.3 Bifurkationen 4.1.4 Diskussion 4.2 Geometrische Nichtlinearitäten 4.2.1 Einfluss auf die Dynamik 4.2.2 Diskussion 4.2.3 Möglichkeiten zur Beeinflussung 5 Werkzeuge für den Entwurf 5.1 Anforderungen an Entwurfswerkzeuge 5.1.1 Kopplung physikalischer Domänen 5.1.2 Spezielle Anforderungen an FEM-Werkzeuge 5.1.3 Ordnungsreduktion 5.1.4 Spezielle Anforderungen an Optimierungswerkzeuge 5.2 Relevante Entwurfswerkzeuge 5.2.1 MOSCITO Optimierungsumgebung 5.2.2 MATLAB-Toolbox SUGAR 5.3 Klassenbibliothek IMtk 5.3.1 Programmierparadigmen 5.3.2 Vererbungsstrategie 5.3.3 Ordnungsreduktion 5.3.4 Verifikation der Modelle 5.3.5 Gültigkeitsbedingungen 6 Entwurfsprozess 6.1 Strategie des Bauelemententwurfs 6.2 Entwurfsbeispiel 6.2.1 Anforderungen und Randbedingungen 6.2.2 Vorauslegung 6.2.3 Eigenwertanalyse 6.2.4 Statische nichtlineare Analysen 6.2.5 Deformationsanalyse 6.2.6 Statische nichtlineare gekoppelte Analysen 6.2.7 Dynamische nichtlineare gekoppelte Analysen 6.3 Diskussion 7 Zusammenfassung und Ausblick Literaturverzeichnis Abbildungsverzeichnis Tabellenverzeichnis Listings Anlagenverzeichnis A Materialeigenschaften A.1 Einkristallines Silizium A.2 Umgebungsluft B MEMS-Prozess des Fraunhofer IPMS B.1 Prozessablaufplan AME1 B.2 Prozessabh ̈angige Materialeigenschaften C Strukturmechanische FE-Analysen C.1 FEM-Werkzeuge am Fraunhofer IPMS C.1.1 ANSYS C.1.2 COMSOL Multiphysics TM C.2 Nichtlinearitäten prismatischer Torsionsstäbe C.3 Typische Eigenformen von Mikroscannerspiegeln C.4 Mechanische Spannungen in Torsionsfedern C.5 Dynamische Deformation der Spiegelplatte C.6 Konvergenzeigenschaften von FE-Netzen D Dämpfungsmechanismen D.1 Slide-film-Dämpfung D.2 Squeeze-film-Dämpfung E Bewegungs-Dgl. des IPMS Mikroscannerspiegels E.1 Fixpunkte E.2 Stabilität E.3 Bifurkationen E.4 Phasenportraits F IMtk-Klassenbibliothek F.1 Klassenübersicht F.2 Funktionen F.3 Datenstruktur IMTK F.4 Eigenschaften und Methoden der Basisklasse imtk element F.5 Implementation F.6 Beispiele G Experimentelle Ergebnisse (Entwurfsbeispiel) G.1 Charakterisierung G.1.1 Synchronisierte Anregung G.1.2 Parametrische Anregung G.2 Dynamische Deformation / Electrostatically driven microsystems are utilized in technical systems for several years. For instance, they are used in automotive applications as acceleration sensors or angular rate sensors. New fields of applications appear especially for actuators. The scanning micromirror of the Fraunhofer Institute for Photonic Microsystems is such an actuator. It is a micro-­optical-­electrical microsystem (MOEMS) which is driven resonantly by an electrostatic comb drive and can be used in scanning laser imaging systems or laser projectors. Several technical and scientific publications occupy with the design and the simulation of microactuators, which refer usually to a concrete drive principle or to the issues of design in general. The intention of this thesis is to identify and systematize particularly the boundary conditions of design regarding to resonant micro actuators with out-­of-­plane­comb drive. The findings are implemented in efficient design tools and design processes. One emphasis thereby is the investigation of nonlinear properties and effects. This includes geometrically non-­linearities of suspensions as well as non-linearities caused by fluid damping and the electrostatic comb drive. The findings are utilized in an analytical, nonlinear stability analysis of the device's equation of motion as well as in an object oriented software library for the MATLAB environment, which can be used to create nonlinear reduced order models of scanning micromirrors. With the developed techniques for design and optimization the available parameter range of scanning micromirrors can be extended. By that means, it is possible to improve the properties of existing devices as well as create new devices with outreaching performance.:1 Einordnung und Ziele der Arbeit 2 Grundlagen und Stand der Technik 2.1 Herstellungstechnologien 2.2 MEMS-Aktoren 2.2.1 Antriebsprinzipien 2.2.2 Elektrostatische Antriebe 2.3 Der Fraunhofer IPMS Mikroscannerspiegel 2.3.1 Synchronisierte Anregung 2.3.2 Parametrische Anregung 2.3.3 Anwendungsmöglichkeiten und Grenzen 2.4 Motivationen der Arbeit 3 Randbedingungen beim Entwurf 3.1 Vereinbarungen und Definitionen 3.1.1 Material- und Strukturvereinfachungen 3.1.2 Koordinatensysteme 3.1.3 Mathematische Vereinfachungen und Definitionen 3.2 Strukturmechanische Randbedingungen 3.2.1 Richtungsabhängige Materialeigenschaften 3.2.2 Geometrische Nichtlinearitäten 3.2.3 Strukturmechanische Spannungen 3.2.4 Eigenschwingungen 3.2.5 Fertigungstoleranzen 3.2.6 Dynamische Deformation 3.2.7 Strukturdämpfung 3.3 Fluidmechanische Randbedingungen 3.3.1 Näherungen zur Slip-Korrektur 3.3.2 Gültigkeit der quasistatischen Näherung 3.3.3 Dämpfungsmechanismen innerhalb der Kammstruktur 3.3.4 Dämpfungsmechanismen der bewegten Spiegelplatte 3.4 Randbedingungen der Elektrik bzw. Elektrostatik 3.4.1 Antriebskapazitäten und Randfelder 3.4.2 Spannungsfestigkeit 3.4.3 Leistungsaufnahme 3.4.4 Elektromechanische Stabilität 3.5 Optische Randbedingungen 4 Nichtlineare Dynamik 4.1 Stabilitätsanalyse 4.1.1 Fixpunkte und Grenzzyklen 4.1.2 Stabilität 4.1.3 Bifurkationen 4.1.4 Diskussion 4.2 Geometrische Nichtlinearitäten 4.2.1 Einfluss auf die Dynamik 4.2.2 Diskussion 4.2.3 Möglichkeiten zur Beeinflussung 5 Werkzeuge für den Entwurf 5.1 Anforderungen an Entwurfswerkzeuge 5.1.1 Kopplung physikalischer Domänen 5.1.2 Spezielle Anforderungen an FEM-Werkzeuge 5.1.3 Ordnungsreduktion 5.1.4 Spezielle Anforderungen an Optimierungswerkzeuge 5.2 Relevante Entwurfswerkzeuge 5.2.1 MOSCITO Optimierungsumgebung 5.2.2 MATLAB-Toolbox SUGAR 5.3 Klassenbibliothek IMtk 5.3.1 Programmierparadigmen 5.3.2 Vererbungsstrategie 5.3.3 Ordnungsreduktion 5.3.4 Verifikation der Modelle 5.3.5 Gültigkeitsbedingungen 6 Entwurfsprozess 6.1 Strategie des Bauelemententwurfs 6.2 Entwurfsbeispiel 6.2.1 Anforderungen und Randbedingungen 6.2.2 Vorauslegung 6.2.3 Eigenwertanalyse 6.2.4 Statische nichtlineare Analysen 6.2.5 Deformationsanalyse 6.2.6 Statische nichtlineare gekoppelte Analysen 6.2.7 Dynamische nichtlineare gekoppelte Analysen 6.3 Diskussion 7 Zusammenfassung und Ausblick Literaturverzeichnis Abbildungsverzeichnis Tabellenverzeichnis Listings Anlagenverzeichnis A Materialeigenschaften A.1 Einkristallines Silizium A.2 Umgebungsluft B MEMS-Prozess des Fraunhofer IPMS B.1 Prozessablaufplan AME1 B.2 Prozessabh ̈angige Materialeigenschaften C Strukturmechanische FE-Analysen C.1 FEM-Werkzeuge am Fraunhofer IPMS C.1.1 ANSYS C.1.2 COMSOL Multiphysics TM C.2 Nichtlinearitäten prismatischer Torsionsstäbe C.3 Typische Eigenformen von Mikroscannerspiegeln C.4 Mechanische Spannungen in Torsionsfedern C.5 Dynamische Deformation der Spiegelplatte C.6 Konvergenzeigenschaften von FE-Netzen D Dämpfungsmechanismen D.1 Slide-film-Dämpfung D.2 Squeeze-film-Dämpfung E Bewegungs-Dgl. des IPMS Mikroscannerspiegels E.1 Fixpunkte E.2 Stabilität E.3 Bifurkationen E.4 Phasenportraits F IMtk-Klassenbibliothek F.1 Klassenübersicht F.2 Funktionen F.3 Datenstruktur IMTK F.4 Eigenschaften und Methoden der Basisklasse imtk element F.5 Implementation F.6 Beispiele G Experimentelle Ergebnisse (Entwurfsbeispiel) G.1 Charakterisierung G.1.1 Synchronisierte Anregung G.1.2 Parametrische Anregung G.2 Dynamische Deformation
66

Opportunistic Routing with Network Coding in Powerline Communications

Tsokalo, Ievgenii 30 November 2018 (has links)
Opportunistic Routing (OR) can be used as an alternative to the legacy routing (LR) protocols in networks with a broadcast lossy channel and possibility of overhearing the signal. The power line medium creates such an environment. OR can better exploit the channel than LR because it allows the cooperation of all nodes that receive any data. With LR, only a chain of nodes is selected for communication. Other nodes drop the received information. We investigate OR for the one-source one-destination scenario with one traffic flow. First, we evaluate the upper bound on the achievable data rate and advocate the decentralized algorithm for its calculation. This knowledge is used in the design of Basic Routing Rules (BRR). They use the link quality metric that equals the upper bound on the achievable data rate between the given node and the destination. We call it the node priority. It considers the possibility of multi-path communication and the packet loss correlation. BRR allows achieving the optimal data rate pertaining certain theoretical assumptions. The Extended BRR (BRR-E) are free of them. The major difference between BRR and BRR-E lies in the usage of Network Coding (NC) for prognosis of the feedback. In this way, the protocol overhead can be severely reduced. We also study Automatic Repeat-reQuest (ARQ) mechanism that is applicable with OR. It differs to ARQ with LR in that each sender has several sinks and none of the sinks except destination require the full recovery of the original message. Using BRR-E, ARQ and other services like network initialization and link state control, we design the Advanced Network Coding based Opportunistic Routing protocol (ANChOR). With the analytic and simulation results we demonstrate the near optimum performance of ANChOR. For the triangular topology, the achievable data rate is just 2% away from the theoretical maximum and it is up to 90% higher than it is possible to achieve with LR. Using the G.hn standard, we also show the full protocol stack simulation results (including IP/UDP and realistic channel model). In this simulation we revealed that the gain of OR to LR can be even more increased by reducing the head-of-the-line problem in ARQ. Even considering the ANChOR overhead through additional headers and feedbacks, it outperforms the original G.hn setup in data rate up to 40% and in latency up to 60%.:1 Introduction 2 1.1 Intra-flow Network Coding 6 1.2 Random Linear Network Coding (RLNC) 7 2 Performance Limits of Routing Protocols in PowerLine Communications (PLC) 13 2.1 System model 14 2.2 Channel model 14 2.3 Upper bound on the achievable data rate 16 2.4 Achieving the upper bound data rate 17 2.5 Potential gain of Opportunistic Routing Protocol (ORP) over Common Single-path Routing Protocol (CSPR) 19 2.6 Evaluation of ORP potential 19 3 Opportunistic Routing: Realizations and Challenges 24 3.1 Vertex priority and cooperation group 26 3.2 Transmission policy in idealized network 34 3.2.1 Basic Routing Rules (BRR) 36 3.3 Transmission policy in real network 40 3.3.1 Purpose of Network Coding (NC) in ORP 41 3.3.2 Extended Basic Routing Rules (BRR) (BRR-E) 43 3.4 Automatic ReQuest reply (ARQ) 50 3.4.1 Retransmission request message contents 51 3.4.2 Retransmission Request (RR) origination and forwarding 66 3.4.3 Retransmission response 67 3.5 Congestion control 68 3.5.1 Congestion control in our work 70 3.6 Network initialization 74 3.7 Formation of the cooperation groups (coalitions) 76 3.8 Advanced Network Coding based Opportunistic Routing protocol (ANChOR) header 77 3.9 Communication of protocol information 77 3.10 ANChOR simulation . .79 3.10.1 ANChOR information in real time .80 3.10.2 Selection of the coding rate 87 3.10.3 Routing Protocol Information (RPI) broadcasting frequency 89 3.10.4 RR contents 91 3.10.5 Selection of RR forwarder 92 3.10.6 ANChOR stability 92 3.11 Summary 95 4 ANChOR in the Gigabit Home Network (G.hn) Protocol 97 4.1 Compatibility with the PLC protocol stack 99 4.2 Channel and noise model 101 4.2.1 In-home scenario 102 4.2.2 Access network scenario 102 4.3 Physical layer (PHY) layer implementation 102 4.3.1 Bit Allocation Algorithm (BAA) 103 4.4 Multiple Access Control layer (MAC) layer 109 4.5 Logical Link Control layer (LLC) layer 111 4.5.1 Reference Automatic Repeat reQuest (ARQ) 111 4.5.2 Hybrid Automatic Repeat reQuest (HARQ) in ANChOR 114 4.5.3 Modeling Protocol Data Unit (PDU) erasures on LLC 116 4.6 Summary 117 5 Study of G.hn with ANChOR 119 5.1 ARQ analysis 119 5.2 Medium and PHY requirements for “good” cooperation 125 5.3 Access network scenario 128 5.4 In-home scenario 135 5.4.1 Modeling packet erasures 136 5.4.2 Linear Dependence Ratio (LDR) 139 5.4.3 Worst case scenario 143 5.4.4 Analysis of in-home topologies 145 6 Conclusions . . . . . . . . . . . . . . . 154 A Proof of the neccessity of the exclusion rule 160 B Gain of ORPs to CSRPs 163 C Broadcasting rule 165 D Proof of optimality of BRR for triangular topology 167 E Reducing the retransmission probability 168 F Calculation of Expected Average number of transmissions (EAX) for topologies with bi-directional links 170 G Feedback overhead of full coding matrices 174 H Block diagram of G.hn physical layer in ns-3 model 175 I PER to BER mapping 177
67

Multiple-Input Multiple-Output Detection Algorithms for Generalized Frequency Division Multiplexing

Matthé, Maximilian 14 September 2018 (has links)
Since its invention, cellular communication has dramatically transformed personal lifes and the evolution of mobile networks is still ongoing. Evergrowing demand for higher data rates has driven development of 3G and 4G systems, but foreseen 5G requirements also address diverse characteristics such as low latency or massive connectivity. It is speculated that the 4G plain cyclic prefix (CP)-orthogonal frequency division multiplexing (OFDM) cannot sufficiently fulfill all requirements and hence alternative waveforms have been in-vestigated, where generalized frequency division multiplexing (GFDM) is one popular option. An important aspect for any modern wireless communication system is the application of multi-antenna, i.e. MIMO techiques, as MIMO can deliver gains in terms of capacity, reliability and connectivity. Due to its channel-independent orthogonality, CP-OFDM straightforwardly supports broadband MIMO techniques, as the resulting inter-antenna interference (IAI) can readily be resolved. In this regard, CP-OFDM is unique among multicarrier waveforms. Other waveforms suffer from additional inter-carrier interference (ICI), inter-symbol interference (ISI) or both. This possibly 3-dimensional interference renders an optimal MIMO detection much more complex. In this thesis, weinvestigate how GFDM can support an efficient multiple-input multiple-output (MIMO) operation given its 3-dimensional interference structure. To this end, we first connect the mathematical theory of time-frequency analysis (TFA) with multicarrier waveforms in general, leading to theoretical insights into GFDM. Second, we show that the detection problem can be seen as a detection problem on a large, banded linear model under Gaussian noise. Basing on this observation, we propose methods for applying both space-time code (STC) and spatial multiplexing techniques to GFDM. Subsequently, we propose methods to decode the transmitted signals and numerically and theoretically analyze their performance in terms of complexiy and achieved frame error rate (FER). After showing that GFDM modulation and linear demodulation is a direct application of Gabor expansion and transform, we apply results from TFA to explain singularities of the modulation matrix and derive low-complexity expressions for receiver filters. We derive two linear detection algorithms for STC encoded GFDM signals and we show that their performance is equal to OFDM. In the case of spatial multiplexing, we derive both non-iterative and iterative detection algorithms which base on successive interference cancellation (SIC) and minimum mean squared error (MMSE)-parallel interference cancellation (PIC) detection, respectively. By analyzing the error propagation of the SIC algorithm, we explain its significantly inferior performance compared to OFDM. Using feedback information from the channel decoder, we can eventually show that near-optimal GFDM detection can outperform an optimal OFDM detector by up to 3dB for high SNR regions. We conclude that GFDM, given the obtained results, is not a general-purpose replacement for CP-OFDM, due to higher complexity and varying performance. Instead, we can propose GFDM for scenarios with strong frequency-selectivity and stringent spectral and FER requirements.
68

Spin Toqure Oscillator Based BFSK Modulation

Ma, Rui, Kreißig, Martin, Protze, Florian, Ellinger, Frank, Purbawati, Ruiz-Calaforra, Hem, Ebels, Ursula 20 August 2019 (has links)
This work presents a spin torque nano-oscillator (STNO) based binary frequency shift keying (BFSK) modulation schema implemented on a printed circuit board (PCB). Maximal input data rate reaches 20 Mbit/s. Depending on the STNO used, carrier frequency can range from 1 to 10 GHz. Both DC and AC currents flowing through the STNO can be tuned between 0 to 4 mA. Using one magnetic tunnel junction (MTJ) STNO, a 380 MHz frequency shift around the center frequency 9 GHz was observed, when the modulated current was toggled between 0.8 mA and 1.2 mA at a rate of 20 Mbit/s. This is the first work demonstrating that the STNOs are applicable for BFSK modulation on the wireless application level.
69

Entwicklung eines rauscharmen Lagemesssystems für sensorlose magnetisch gelagerte Antriebe mit Fluss-Bypass-Kompensation für hohe Sättigungstoleranz

Schleicher, André 25 April 2018 (has links)
Das neuartige Fluss-Bypass-Verfahren ist ein sensorloses Messsystem für magnetisch gelagerte Antriebe. Durch Integration eines zusätzlichen nichtlinearen Flusspfad gelingt eine teilweise Kompensation des Sättigungseinflusses, der sonst bei hohen Flüssen zu verschwindender Messempfindlichkeit führen kann. Durch die transformatorische Signalübertragung mittels Hilfswicklungen werden ein hoher Signal-Rauschabstand bei hoher Messbandbreite erreicht.
70

Rolled-up magnetic nanomembranes

Müller, Christian 27 June 2018 (has links)
The combination of strain engineering, lithography, thin film deposition and etching techniques is an elegant approach to create single microtubes and well-defined arrays of magnetic microtubes. In this work we have successfully shown that strain engineering techniques developed for rolled-up nanomembranes can be applied to magnetic materials and material combinations. To obtain sufficiently strained nanomembranes, different substrates and sacrificial layers in combination with the magnetic layers were used. Careful tuning of the etching parameters ensured a controlled roll-up process without damage or oxidation of the magnetic layer. Additionally, rolled-up nanomembranes were further integrated in a highly parallel fashion on chip, by development and application of multi-step fabrication procedures. Based on the prepared rolled-up magnetic structures and their planar counterparts we have performed a comprehensive study of their magnetic properties, mainly under the influence of magnetic field, strain and temperature. The role of the special cylindrical or curved geometry and their impact on the magnetic properties was outlined and explained based on our understanding. Moreover, the magnetic properties were also discussed in relationship to other influencing material parameters, e.g. composition, crystallographic structure, and surface effects. The first experimental magnetization study on rolled-up InGaAs/Fe3Si heterostructures was presented. It was demonstrated for tube arrays that the change in the geometry from a planar film to the cylindrical shape has a significant effect on the magnetization behavior. A deeper study provided insight into the magnetic switching behavior of single tubes and arrays. Rolled-up Au/Co/Au tubes and showed that in addition to shape anisotropy, magnetostrictive anisotropy due to the anisotropic stress release can inverse the magnetization direction. Exchange coupling at ferromagnetic/antiferromagnetic interfaces due to partial oxidation of Co was observed at low temperatures. The results suggest possibilities to tune magnetic properties by controlling the tube dimensions and careful control of thin film growth parameters. The cylindrical shape, the layer thickness the number of rotations and the type of magnetic material are proven to have a strong influence on the magnetic domain patterns and magnetization behavior. Therefore, Ni/Fe tubes have been studied by means of magneto optical Kerr effect. It was found that the magnetization reversal in rolled-up tubes with 1.2 and 2.5 windings occurs via nucleation and propagation of magnetic domain walls. On the other hand, we have demonstrated for rolled-up Au/Co tubes that a certain magnetic layer thickness is required to observe magnetic stripe domains. In another experiment performed with magnetic force microscopy, rolled-up Co/Pt nanomembranes with magnetic domains radially aligned due to perpendicular anisotropy, which behaves as radially polarized cylindrical magnets, were achieved. Moreover, we have demonstrated an elegant approach to create compact MR devices based on rolled-up Co/Cu-ML nanomembranes. We have shown the magnetization behavior and the MR magnitude in comparison to the corresponding planar structures. The influence of number of Co/Cu bilayers, non-magnetic spacer layer, interface roughness and multiple windings on MR was discussed. Our fabrication method can be applied to the most common magnetic materials. Certainly, further optimization of MR towards application as magnetic sensor or magneto-fluidic sensors can be achieved by change of Co/Cu-layer thickness, increase of rolling length and reduced spacer layer thickness. Finally, we have shown a fabrication route to realize freestanding tubes based on Ni-Mn-Ga alloys grown by molecular beam epitaxy on GaAs substrates. The evolution of structural and magnetic properties induced by roll-up was investigated in detail and showed a pronounced influence of crystallographic orientation and strain state of the Ni-Mn-Ga alloys. These insights are fundamental in order to realize thin nanomembranes and freestanding three-dimensional FSMA structures with defined composition for smart applications as compact actuators and microsensors. Consequently, rolled-up magnetic nanomembranes offer a great chance in reducing the size of electronic components and can bring several functionalities to the device. These facts make rolled-up tubes highly attractive for the detection, stimulation and manipulation of small objects, such as ions, molecules, cells and particles. It is expected in the future, that magnetic lab-in-a-tube systems will further account in analysis of microfluidic systems. On the other hand, rolled-up structures significantly contribute to the field of shapeable magnetoelectronics.

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