05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
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Item Open Access Analytic free-energy expression for the 2D-Ising model and perspectives for battery modeling(2023) Markthaler, Daniel; Birke, Kai PeterAlthough originally developed to describe the magnetic behavior of matter, the Ising model represents one of the most widely used physical models, with applications in almost all scientific areas. Even after 100 years, the model still poses challenges and is the subject of active research. In this work, we address the question of whether it is possible to describe the free energy A of a finite-size 2D-Ising model of arbitrary size, based on a couple of analytically solvable 1D-Ising chains. The presented novel approach is based on rigorous statistical-thermodynamic principles and involves modeling the free energy contribution of an added inter-chain bond DAbond(b, N) as function of inverse temperature b and lattice size N. The identified simple analytic expression for DAbond is fitted to exact results of a series of finite-size quadratic N N-systems and enables straightforward and instantaneous calculation of thermodynamic quantities of interest, such as free energy and heat capacity for systems of an arbitrary size. This approach is not only interesting from a fundamental perspective with respect to the possible transfer to a 3D-Ising model, but also from an application-driven viewpoint in the context of (Li-ion) batteries where it could be applied to describe intercalation mechanisms.Item Open Access Efficient modeling and computation methods for robust AMS system design(2018) Gil, Leandro; Radetzki, Martin (Prof. Dr.-Ing.)This dissertation copes with the challenge regarding the development of model based design tools that better support the mixed analog and digital parts design of embedded systems. It focuses on the conception of efficient modeling and simulation methods that adequately support emerging system level design methodologies. Starting with a deep analysis of the design activities, many weak points of today’s system level design tools were captured. After considering the modeling and simulation of power electronic circuits for designing low energy embedded systems, a novel signal model that efficiently captures the dynamic behavior of analog and digital circuits is proposed and utilized for the development of computation methods that enable the fast and accurate system level simulation of AMS systems. In order to support a stepwise system design refinement which is based on the essential system properties, behavior computation methods for linear and nonlinear analog circuits based on the novel signal model are presented and compared regarding the performance, accuracy and stability with existing numerical and analytical methods for circuit simulation. The novel signal model in combination with the method proposed to efficiently cope with the interaction of analog and digital circuits as well as the new method for digital circuit simulation are the key contributions of this dissertation because they allow the concurrent state and event based simulation of analog and digital circuits. Using a synchronous data flow model of computation for scheduling the execution of the analog and digital model parts, very fast AMS system simulations are carried out. As the best behavior abstraction for analog and digital circuits may be selected without the need of changing component interfaces, the implementation, validation and verification of AMS systems take advantage of the novel mixed signal representation. Changes on the modeling abstraction level do not affect the experiment setup. The second part of this work deals with the robust design of AMS systems and its verification. After defining a mixed sensitivity based robustness evaluation index for AMS control systems, a general robust design method leading to optimal controller tuning is presented. To avoid over-conservative AMS system designs, the proposed robust design optimization method considers parametric uncertainty and nonlinear model characteristics. The system properties in the frequency domain needed to evaluate the system robustness during parameter optimization are obtained from the proposed signal model. Further advantages of the presented signal model for the computation of control system performance evaluation indexes in the time domain are also investigated in combination with range arithmetic. A novel approach for capturing parameter correlations in range arithmetic based circuit behavior computation is proposed as a step towards a holistic modeling method for the robust design of AMS systems. The several modeling and computation methods proposed to improve the support of design methodologies and tools for AMS system are validated and evaluated in the course of this dissertation considering many aspects of the modeling, simulation, design and verification of a low power embedded system implementing Adaptive Voltage and Frequency Scaling (AVFS) for energy saving.Item Open Access Optimization of disassembly strategies for electric vehicle batteries(2021) Baazouzi, Sabri; Rist, Felix Paul; Weeber, Max; Birke, Kai PeterVarious studies show that electrification, integrated into a circular economy, is crucial to reach sustainable mobility solutions. In this context, the circular use of electric vehicle batteries (EVBs) is particularly relevant because of the resource intensity during manufacturing. After reaching the end-of-life phase, EVBs can be subjected to various circular economy strategies, all of which require the previous disassembly. Today, disassembly is carried out manually and represents a bottleneck process. At the same time, extremely high return volumes have been forecast for the next few years, and manual disassembly is associated with safety risks. That is why automated disassembly is identified as being a key enabler of highly efficient circularity. However, several challenges need to be addressed to ensure secure, economic, and ecological disassembly processes. One of these is ensuring that optimal disassembly strategies are determined, considering the uncertainties during disassembly. This paper introduces our design for an adaptive disassembly planner with an integrated disassembly strategy optimizer. Furthermore, we present our optimization method for obtaining optimal disassembly strategies as a combination of three decisions: (1) the optimal disassembly sequence, (2) the optimal disassembly depth, and (3) the optimal circular economy strategy at the component level. Finally, we apply the proposed method to derive optimal disassembly strategies for one selected battery system for two condition scenarios. The results show that the optimization of disassembly strategies must also be used as a tool in the design phase of battery systems to boost the disassembly automation and thus contribute to achieving profitable circular economy solutions for EVBs.Item Open Access Anwendungsfälle und Methoden der künstlichen Intelligenz in der anwendungsorientierten Forschung im Kontext von Industrie 4.0(2020) Maschler, Benjamin; White, Dustin; Weyrich, MichaelEs wird erwartet, dass datengetriebene Methoden künstlicher Intelligenz im Kontext Industrie 4.0 die Zukunft industrieller Fertigung prägen werden. Obwohl das Thema in der Forschung sehr präsent ist, bleibt der Umfang der tatsächlichen Nutzung dieser Methoden unklar. Dieser Beitrag analysiert daher von 2013 bis 2018 veröffentlichte wissenschaftliche Artikel, um statistische Daten über den Einsatz von Methoden künstlicher Intelligenz in der Industrie zu gewinnen. Besonderes Augenmerk wird dabei auf die Trainings- und Evaluations-Datentypen, die Verbreitung in verschiedenen Industriezweigen, die betrachteten Anwendungsfälle sowie die geographische Herkunft dieser Artikel gelegt. Die resultierenden Erkenntnisse werden in praxisnahe Hinweise für Entscheider destilliert.Item Open Access Decentralized interference coordination for the downlink of fully loaded heterogeneous wireless networks(2019) Bleicher, Zarah M. L.; Speidel, Joachim (Prof. Dr.-Ing.)The relentless evolution towards an overwhelming increase of mobile data traffic, where mobile phone subscribers demand the highest data rates and comprehensive coverage presents current and future mobile communication networks with demanding requirements. Previous homogeneous networks were mostly designed to optimize the sum capacity and peak data rates rather than take the individual user experience into account, and therefore failed to meet these requirements. Multi-layer networks, also known as heterogeneous networks, can improve the coverage and capacity of the cellular network and bring the network closer to the user. Moreover, the introduction of the smaller cells into the macro cellular network can improve the performance, especially in hotspots and indoors, which results in a better user experience. Frequency spectrum is rare and valuable, thus solely adding further bandwidth does not meet the demand. However, when reusing the bandwidth, inter-cell interference from neighboring cells leads to performance degradations, in particular for users located at the cell edges. Within a multi-layer network, additional and even more dynamic interference is present, caused by different kinds of cells, like macro-, pico-, femtocells, and relays. Therefore, addressing the interference issue is essential. This thesis examines suitable interference coordination algorithms and introduces an advanced interference coordination technique for heterogeneous networks. Whereas current techniques require significant communication between base stations, reduce the available bandwidth notably or do not consider interference between the small cells, the advanced technique is located in the small cells with only marginal information exchange. Its performance is investigated by means of computer simulations for fully loaded heterogeneous networks on the system layer. As a result, the proposed technique reduces the impact on the surrounding cells significantly, making in-home communication services attractive, leading to a tremendous advantage for service providers as well as the end-user.Item Open Access Modulationsdotierte Germanium-MOSFETs für den Spin-Transport in zweidimensionalen Lochgasen(2023) Weißhaupt, David; Schulze, Jörg (Prof. Dr. habil.)Die Halbleiter-Spintronik beschäftigt sich mit der Entwicklung neuer Bauelementkonzepte, die den intrinsischen Spin-Freiheitsgrad des Elektrons ausnutzen. Dabei werden spin-basierte Logik-Bauelemente aufgrund des geringen Energiebedarfs zum Umschalten der Spin-Orientierung als aussichtsreiche Kandidaten für zukünftige Transistor-Anwendungen diskutiert. Anzuführen sind hierfür beispielsweise der Spin-Feldeffekttransistor (FET) nach Datta und Das sowie der Spin-Metall-Oxid-Halbleiter-FET von Sugahara und Tanaka. Für diese Bauteilkonzepte müssen jedoch vier grundlegende Komponenten beherrscht werden: Die Spin-Information muss in den Halbleiter eingebracht (Spin-Injektion), transportiert sowie evtl. manipuliert (Spin-Transport & Spin-Manipulation) und final wiederum detektiert (Spin-Detektion) werden. Für die Integration dieser Bauelemente in die bestehende komplementäre Metall-Oxid-Halbleiter-Technologie ist eine elektrische Spin-Injektion bzw. Spin-Detektion notwendig. Die Realisierung von halbleiterbasierten spintronischen Bauelementen erfordert allerdings ein Materialsystem, das gute Spin-Transporteigenschaften sowie eine starke Spin-Bahn-Wechselwirkung für eine potenzielle Spin-Manipulation aufweist. Als vielversprechendes System hat sich hier das zwei-dimensionale Lochgas (engl. „two-dimensional hole gas“, 2DHG), welches in einer Si1-xGex/Ge/Si1-xGex Heterostruktur gebildet wird, erwiesen. Trotz der guten Eignung dieses Systems konnte bisher noch keine elektrische Spin-Injektion demonstriert werden, hauptsächlich wegen der Schwierigkeit, zuverlässige ferromagnetische Kontakte mit dem vergrabenen 2DHG herzustellen. Diese Arbeit befasst sich nun mit der elektrischen Spin-Injektion und Spin-Detektion in ein hochbewegliches (µ = (3,02 ± 0,01) ⋅ 10^4 cm^2/Vs) Ge 2DHG. Die für das Ge 2DHG zugehörige Si1-xGex/Ge/Si1-xGex Heterostruktur wurde dabei mittels Molekularstrahlepitaxie epitaktisch auf einem Si-Substrat gezüchtet. Um dieses Ziel zu erreichen, werden verschiedene Untersuchungsschwerpunkte adressiert. Zunächst werden zur Optimierung der Spin-Transporteigenschaften unterschiedliche Designs der Si1-xGex/Ge/Si1-xGex Heterostruktur auf der (100) Kristallorientierung untersucht. Dazu wurden anhand von Hall-Strukturen Tieftemperaturmagnetwiderstandsmessungen durchgeführt. Hierbei werden Shubnikov-de Haas Oszillationen beobachtet, aus denen die Ladungsträgerdichte, effektive Masse und Quantenstreuzeit des Ge 2DHGs extrahiert werden. Das daraus resultierende optimierte Design mit einer Modulationsdotierung von N_A = 5 ⋅ 10^17 cm^-3 und einer Ge-Quantentopf (engl. „quantum well“, QW) Dicke von d = 15 nm wird dann auf die (111) Kristallorientierung übertragen. Für die elektrische Spin-Injektion und Spin-Detektion werden als ferromagnetischen Kontakt dünne Mn5Ge3-Schichten, die mittels Interdiffusion direkt in den Ge-QW wachsen, benutzt. Dazu wird vor der Bildung der Kontakte die gesamte Si1-xGex-Deckschicht oberhalb des Ge-QWs mithilfe eines Trocken-Ätzprozesses entfernt. Zur Untersuchung der magnetischen Eigenschaften werden die so hergestellten Mn5Ge3-Mikromagnete mit einem supraleitenden Quanteninterferenzmagnetometer analysiert. Dabei konnte nur für die (111) Kristallorientierung die ferromagnetische Natur der gewachsenen Mn5Ge3-Schicht nachgewiesen werden. Durch die Variation der Formanisotropie ergeben sich unterschiedliche Koerzitivfeldstärken. Der Nachweis der elektrischen Spin-Injektion erfolgt schließlich anhand von Magnetwiderstandsmessungen an lateralen Mn5Ge3/Ge 2DHG/Mn5Ge3 Spin-Ventil Bauelementen. Dazu werden die zuvor untersuchten ferromagnetischen Mn5Ge3-Kontakte in einem Abstand von ca. l ≈ 135 nm im vergrabenen Ge-QW platziert. Die Experimente zeigen einen Riesenmagnetowiderstand (engl. „giant magneto resistance“, GMR) als Nachweis einer erfolgreichen elektrischen Spin-Injektion. Neben der elektrischen Spin-Injektion beinhaltet das auch den Spin-Transport im Ge 2DHG sowie die finale Spin-Detektion am zweiten ferromagnetischen Mn5Ge3-Kontakt. In Übereinstimmung zu den Spin-Transportuntersuchungen zeigt das GMR-Signal eine starke Abhängigkeit von der Temperatur und konnte bis zu einer maximalen Temperatur von T = 13 K beobachtet werden. Neben der elektrischen Spin-Injektion und Spin-Detektion wird für die Realisierung von Spin-Transistoren eine funktionierende Gate-Technologie vorausgesetzt. Um diese zu demonstrieren, werden zunächst auf Basis des Ge 2DHGs klassische modulationsdotierte Feldeffekttransistoren (MODFET) hergestellt und elektrisch charakterisiert. Mit einem An-Aus-Verhältnis von I_ON/I_OFF = 3,2⋅10^6 bei einer Steilheit von SS = 64 mV⁄dec könnte der Ge 2DHG MODFET unabhängig von der Halbleiter-Spintronik auch für zukünftige Tieftemperaturanwendungen interessant sein. Der Spin-FET nach Datta und Das würde dann durch das Tauschen der Source-Drain-Kontakte in ferromagnetische Mn5Ge3-Kontakte entstehen. Technologisch bedingt sind im Rahmen dieser Arbeit allerdings nur Transistoren mit einer minimalen Gate-Länge von L = 1 µm herstellbar. Da der Spin im Ge 2DHG über diese Länge nicht transportiert werden kann, ist die Realisierung eines Spin-Transistors technologiebedingt nicht möglich.Item Open Access Un-coordinated multi-user and inter-cell interference alignment based on partial and outdated information for large cellular networks(2016) Aziz, Danish; Speidel, Joachim (Prof. Dr.-Ing.)The cellular networks have gone through rapid evolution during the past decade. However, their performance is still limited due to the problem of interference. Therefore, interference management in current and future cellular networks is still an ongoing research topic. Interference Alignment is one of the techniques to manage the interference efficiently by using "align" and "suppression" strategy. In the first part of this thesis we focus on Coordinated inter cell interference alignment in a large cellular network. We assess the performance of interference alignment based transmit precoding under specific receiver strategies and coordination scenarios by comparing with different state of the art precoding schemes. We continue our assessment by considering imperfect channel state information at the transmitter. The results show that the gains of coordinated alignment based transmission are very sensitive to the receiver strategies and imperfections as compared to the other precoding schemes. However, in case of the availability of good channel conditions with very slow moving users, coordinated interference alignment outperforms the other baselines even with imperfect channel state information. In addition to that, we propose efficient user selection methods to enhance the performance of coordinated alignment. The results of our assessment draws important conclusions about the application of coordinated interference alignment in practical systems. In the second part of the thesis we consider a cellular system where each cell is serving multiple users simultaneously using the same radio resource. In this scenario, we have to manage not only the inter cell interference but also the multi user interference. For this purpose, we propose a novel Uncoordinated transmit precoding scheme for multi user cellular networks which is based on the alignment of multi user interference with partial and outdated inter cell interference. We show analytically that our scheme approaches the performance optimal transmission scheme. With the help of simulations we show that our proposal outperforms the state of the art non-alignment based multi user transmit precoding schemes We further propose user selection methods which exploit the diversity gains and improve the system spectral efficiency. In order to assess the feasibility of our proposal in a real system, we evaluate our scheme with practical constraints like imperfect information at the transmitter and limited feedback in uplink channel. For the proof of concept we also evaluate the performance of our scheme with measured channels using a software defined measurement platform. Finally, we also assess the application of our proposal in future heterogeneous networks. The outcome of our efforts states that as an interference alignment based transmission scheme, our scheme is a good candidate to manage the two dimensional interference in multi user cellular networks. It outperforms the non-alignment baselines in many scenarios even with practical constraints.Item Open Access Rehearsal-based continual learning with deep neural networks for image classification(2024) Wiewel, Felix; Yang, Bin (Prof. Dr.-Ing.)Item Open Access Dependable reconfigurable scan networks(2022) Lylina, Natalia; Wunderlich, Hans-Joachim (Prof.)The dependability of modern devices is enhanced by integrating an extensive number of extra-functional instruments. These are needed to facilitate cost-efficient bring-up, debug, test, diagnosis, and adaptivity in the field and might include, e.g., sensors, aging monitors, Logic, and Memory Built-In Self-Test (BIST) registers. Reconfigurable Scan Networks (RSNs) provide a flexible way to access such instruments as well the device's registers throughout the lifetime, starting from post-silicon validation (PSV) through manufacturing test and finally during in-field operation. At the same time, the dependability properties of the system can be affected through an improper RSN integration. This doctoral project overcomes these problems and establishes a methodology to integrate dependable RSNs for a given system considering the most relevant dependability aspects, such as robustness, testability, and security compliance of RSNs.Item Open Access Digital pre-distortion of broadband communication links using open-loop architecture(2021) Wiewel, FlorianThe ever-increasing demand for higher data rates and lower latency in wireless communications ultimately forces the developers of the underlying systems to use broadband links with higher order modulation formats to meet this demand. The use of these modulation formats results in strict linearity requirements on the system. On top of that power, efficiency is also an important aspect, since it has an impact on the operational costs and ecological compatibility. In a typical macrocell for modern wireless communication systems, the power amplifier (PA) of the base station consumes about 60% of the overall power and it is also the PA, which typically exhibits the strongest nonlinear transfer characteristic in the system. Unfortunately, power efficiency and linearity represent conflicting requirements in PA design. As a result, a compromise between these two requirements has to be made. Usually, the PA is designed for high power efficiency and with moderate nonlinear transfer characteristics. To compensate for the nonlinearity in the PA a technique called digital pre-distortion (DPD) is applied, which estimates the nonlinearity in the PAs transfer characteristic and applies the corresponding inverse transfer function to the complex baseband input signal of the PA in the digital domain. In contrast to many of the DPD experiments found in literature, which are applied to signals with bandwidths in the range of tens of megahertz, the targeted linearization bandwidth in this work is 5 GHz. For this purpose an open-loop DPD architecture based on the Volterra theory of nonlinear systems specifically the p-th order inverse has been implemented in software and applied to different amplifiers including a waveguide E-band transmitter operating around 73 GHz. Up to a signal bandwidth of around 1 GHz significant improvements in terms of signal quality could be observed in the conducted experiments. For signals with higher bandwidths problems with signal integrity caused the DPD to fail. Finally, the various problems are analyzed and potential improvements for increasing the DPD performance for wideband signals are suggested.
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