TY - THES A1 - Heck, Klaus T1 - Wireless LAN performance studies in the context of 4G networks N2 - Wireless communication is nothing new. The first data transmissions based on electromagnetic waves have been successfully performed at the end of the 19th century. However, it took almost another century until the technology was ripe for mass market. The first mobile communication systems based on the transmission of digital data were introduced in the late 1980s. Within just a couple of years they have caused a revolution in the way people communicate. The number of cellular phones started to outnumber the fixed telephone lines in many countries and is still rising. New technologies in 3G systems, such as UMTS, allow higher data rates and support various kinds of multimedia services. Nevertheless, the end of the road in wireless communication is far from being reached. In the near future, the Internet and cellular phone systems are expected to be integrated to a new form of wireless system. Bandwidth requirements for a rich set of wireless services, e.g.\ video telephony, video streaming, online gaming, will be easily met. The transmission of voice data will just be another IP based service. On the other hand, building such a system is by far not an easy task. The problems in the development of the UMTS system showed the high complexity of wireless systems with support for bandwidth-hungry, IP-based services. But the technological challenges are just one difficulty. Telecommunication systems are planned on a world-wide basis, such that standard bodies, governments, institutions, hardware vendors, and service providers have to find agreements and compromises on a number of different topics. In this work, we provide the reader with a discussion of many of the topics involved in the planning of a Wireless LAN system that is capable of being integrated into the 4th generation mobile networks (4G) that is being discussed nowadays. Therefore, it has to be able to cope with interactive voice and video traffic while still offering high data rates for best effort traffic. Let us assume a scenario where a huge office complex is completely covered with Wireless LAN access points. Different antenna systems are applied in order to reduce the number of access points that are needed on the one hand, while optimizing the coverage on the other. No additional infrastructure is implemented. Our goal is to evaluate whether the Wireless LAN technology is capable of dealing with the various demands of such a scenario. First, each single access point has to be capable of supporting best-effort and Quality of Service (QoS) demanding applications simultaneously. The IT infrastructure in our scenario consists solely of Wireless LAN, such that it has to allow users surfing the Web, while others are involved in voice calls or video conferences. Then, there is the problem of overlapping cells. Users attached to one access point produce interference for others. However, the QoS support has to be maintained, which is not an easy task. Finally, there are nomadic users, which roam from one Wireless LAN cell to another even during a voice call. There are mechanisms in the standard that allow for mobility, but their capabilities for QoS support are yet to be studied. This shows the large number of unresolved issues when it comes to Wireless LAN in the context of 4G networks. In this work we want to tackle some of the problems. KW - Drahtloses lokales Netz KW - Wireless LAN KW - Voice-over-IP (VoIP) KW - Quality-of-Service (QoS) KW - IEEE 802.11e KW - 4G Networks KW - Wireless LAN KW - Voice-over-IP (VoIP) KW - Quality-of-Service (QoS) KW - IEEE 802.11e KW - 4G Networks Y1 - 2005 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-14896 ER - TY - JOUR A1 - Hein, Rebecca M. A1 - Latoschik, Marc Erich A1 - Wienrich, Carolin T1 - Inter- and transcultural learning in cocial virtual reality: a proposal for an inter- and transcultural virtual object database to be used in the implementation, reflection, and evaluation of virtual encounters JF - Multimodal Technologies and Interaction N2 - Visual stimuli are frequently used to improve memory, language learning or perception, and understanding of metacognitive processes. However, in virtual reality (VR), there are few systematically and empirically derived databases. This paper proposes the first collection of virtual objects based on empirical evaluation for inter-and transcultural encounters between English- and German-speaking learners. We used explicit and implicit measurement methods to identify cultural associations and the degree of stereotypical perception for each virtual stimuli (n = 293) through two online studies, including native German and English-speaking participants. The analysis resulted in a final well-describable database of 128 objects (called InteractionSuitcase). In future applications, the objects can be used as a great interaction or conversation asset and behavioral measurement tool in social VR applications, especially in the field of foreign language education. For example, encounters can use the objects to describe their culture, or teachers can intuitively assess stereotyped attitudes of the encounters. KW - virtual stimuli KW - implicit association test KW - virtual reality KW - social VR KW - InteractionSuitcase Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-278974 SN - 2414-4088 VL - 6 IS - 7 ER - TY - JOUR A1 - Hein, Rebecca M. A1 - Wienrich, Carolin A1 - Latoschik, Marc E. T1 - A systematic review of foreign language learning with immersive technologies (2001-2020) JF - AIMS Electronics and Electrical Engineering N2 - This study provides a systematic literature review of research (2001–2020) in the field of teaching and learning a foreign language and intercultural learning using immersive technologies. Based on 2507 sources, 54 articles were selected according to a predefined selection criteria. The review is aimed at providing information about which immersive interventions are being used for foreign language learning and teaching and where potential research gaps exist. The papers were analyzed and coded according to the following categories: (1) investigation form and education level, (2) degree of immersion, and technology used, (3) predictors, and (4) criterions. The review identified key research findings relating the use of immersive technologies for learning and teaching a foreign language and intercultural learning at cognitive, affective, and conative levels. The findings revealed research gaps in the area of teachers as a target group, and virtual reality (VR) as a fully immersive intervention form. Furthermore, the studies reviewed rarely examined behavior, and implicit measurements related to inter- and trans-cultural learning and teaching. Inter- and transcultural learning and teaching especially is an underrepresented investigation subject. Finally, concrete suggestions for future research are given. The systematic review contributes to the challenge of interdisciplinary cooperation between pedagogy, foreign language didactics, and Human-Computer Interaction to achieve innovative teaching-learning formats and a successful digital transformation. KW - foreign language learning and teaching KW - intercultural learning and teaching KW - immersive technologies KW - education KW - human-computer interaction KW - systematic literature review Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-268811 VL - 5 IS - 2 ER - TY - THES A1 - Henjes, Robert T1 - Performance Evaluation of Publish/Subscribe Middleware Architectures T1 - Leistungsuntersuchung von Publish/Subscribe Middleware Architekturen N2 - While developing modern applications, it is necessary to ensure an efficient and performant communication between different applications. In current environments, a middleware software is used, which supports the publish/subscribe communication pattern. Using this communication pattern, a publisher sends information encapsulated in messages to the middleware. A subscriber registers its interests at the middleware. The monograph describes three different steps to determine the performance of such a system. In a first step, the message throughput performance of a publish/subscribe in different scenarios is measured using a Java Message Service (JMS) based implementation. In the second step the maximum achievable message throughput is described by adapted models depending on the filter complexity and the replication grade. Using the model, the performance characteristics of a specific system in a given scenario can be determined. These numbers are used for the queuing model described in the third part of the thesis, which supports the dimensioning of a system in realistic scenarios. Additionally, we introduce a method to approximate an M/G/1 system numerically in an efficient way, which can be used for real time analysis to predict the expected performance in a certain scenario. Finally, the analytical model is used to investigate different possibilities to ensure the scalability of the maximum achievable message throughput of the overall system. N2 - Bei der Entwicklung moderner Applikationen ist es notwendig eine effiziente und performante Kommunikation zwischen den einzelnen Anwendungen sicherzustellen. In der Praxis kommt dabei eine Middleware Software zum Einsatz, die das Publish/Subscribe Kommunikationsmuster unterstützt. Dabei senden Publisher Informationen in Form von Nachrichten an die Middleware. Die Subscriber hingegen zeigen durch die Nutzung von Filtern der Middleware an, welche Informationen zugestellt werden sollen. Die Arbeit beschreibt ein dreistufiges Verfahren zur Leistungsbestimmung eines solchen Systems. Zunächst wird durch Messung die Leistung von Publish/Subscribe Systemen in verschiedenen Szenarien untersucht am Beispiel von Java Message Service (JMS) basierten Implementierungen. Danach wird der maximale Nachrichtendurchsatz in Abhängigkeit der Filterkomplexität und des Nachrichtenreplikationsgrades durch einfache Modelle beschrieben. Damit können die Leistungskennwerte für ein System und vorgegebenen Randbedingungen beschrieben werden. Im dritten Teil wird mittels Leistungsbewertung und durch Anwendung eines Warteschlangenmodells die Leistung in praxisnahen Umfeld beschrieben, so dass eine Dimensionierung möglich wird. Zusätzlich wird ein mathematisch, approximatives Verfahren vorgestellt, um ein M/G/1 System numerisch effizient berechnen zu können, was bei der Echtzeitbewertung eines Systems zur Leistungsvorhersage benutzt werden kann. Des Weiteren werden mittels des Modells Möglichkeiten untersucht die Skalierbarkeit des Gesamtsystems in Bezug auf den Nachrichtendurchsatz sicherzustellen. T3 - Würzburger Beiträge zur Leistungsbewertung Verteilter Systeme - 04/10 KW - Middleware KW - Publish-Subscribe-System KW - Java Message Service KW - Leistungsbewertung KW - Middleware KW - Publish-Subscribe-System KW - Java Message Service KW - Performance Evaluation Y1 - 2010 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-53388 ER - TY - JOUR A1 - Hentschel, Simon A1 - Kobs, Konstantin A1 - Hotho, Andreas T1 - CLIP knows image aesthetics JF - Frontiers in Artificial Intelligence N2 - Most Image Aesthetic Assessment (IAA) methods use a pretrained ImageNet classification model as a base to fine-tune. We hypothesize that content classification is not an optimal pretraining task for IAA, since the task discourages the extraction of features that are useful for IAA, e.g., composition, lighting, or style. On the other hand, we argue that the Contrastive Language-Image Pretraining (CLIP) model is a better base for IAA models, since it has been trained using natural language supervision. Due to the rich nature of language, CLIP needs to learn a broad range of image features that correlate with sentences describing the image content, composition, environments, and even subjective feelings about the image. While it has been shown that CLIP extracts features useful for content classification tasks, its suitability for tasks that require the extraction of style-based features like IAA has not yet been shown. We test our hypothesis by conducting a three-step study, investigating the usefulness of features extracted by CLIP compared to features obtained from the last layer of a comparable ImageNet classification model. In each step, we get more computationally expensive. First, we engineer natural language prompts that let CLIP assess an image's aesthetic without adjusting any weights in the model. To overcome the challenge that CLIP's prompting only is applicable to classification tasks, we propose a simple but effective strategy to convert multiple prompts to a continuous scalar as required when predicting an image's mean aesthetic score. Second, we train a linear regression on the AVA dataset using image features obtained by CLIP's image encoder. The resulting model outperforms a linear regression trained on features from an ImageNet classification model. It also shows competitive performance with fully fine-tuned networks based on ImageNet, while only training a single layer. Finally, by fine-tuning CLIP's image encoder on the AVA dataset, we show that CLIP only needs a fraction of training epochs to converge, while also performing better than a fine-tuned ImageNet model. Overall, our experiments suggest that CLIP is better suited as a base model for IAA methods than ImageNet pretrained networks. KW - Image Aesthetic Assessment KW - CLIP KW - language-image pre-training KW - text supervision KW - prompt engineering KW - AVA Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-297150 SN - 2624-8212 VL - 5 ER - TY - THES A1 - Herrler, Rainer T1 - Agentenbasierte Simulation zur Ablaufoptimierung in Krankenhäusern und anderen verteilten, dynamischen Umgebungen T1 - Agent based simulation of processes in hospitals and other distributed, dynamic environments. N2 - Verteilte dynamische Systeme unter lokalen und globalen Gesichtspunkten zu optimieren ist eine schwierige Aufgabe. Zwar sind grundsätzliche Auswirkungen einzelner Maßnahmen häufig bekannt, durch widerstrebende Ziele, Wechselwirkungen zwischen Prozessen und Nebenwirkungen von Maßnahmen ist ein analytisches Vorgehen bei der Optimierung nicht möglich. Besonders schwierig wird es, wenn lokale Einheiten einerseits ihre Ziele und Autonomie behalten sollen, aber durch zentrale Vorgaben bzw. Anreize so gesteuert werden sollen, dass ein übergeordnetes Ziel erreicht wird. Ein praktisches Beispiel dieses allgemeinen Optimierungsproblems findet sich im Gesundheitswesen. Das Management von modernen Kliniken ist stets mit dem Problem konfrontiert, die Qualität der Pflege zu gewährleisten und gleichzeitig kosteneffizient zu arbeiten. Hier gilt es unter gegeben Rahmenbedingungen und bei Respektierung der Autonomie der Funktionseinheiten, Optimierungsmaßnahmen zu finden und durchzuführen. Vorhandene Werkzeuge zur Simulation und Modellierung bieten für diese Aufgabe keine ausreichend guten Vorgehensmodelle und Modellierungsmechanismen. Die agentenbasierte Simulation ermöglicht die Abbildung solcher Systeme und die Durchführung von Simulationsexperimenten zur Bewertung einzelner Maßnahmen. Es werden Lösungswege und Werkzeuge vorgestellt und evaluiert, die den Benutzer bei der Formalisierung des Wissens und der Modellierung solch komplexer Szenarien unterstützen und ein systematisches Vorgehen zur Optimierung ermöglichen. N2 - To optimize distributed dynamic systems or organizations under local and global constraints is a difficult task. Although basic effects of single improvement steps are often known, it is difficult to examine a complex system with conflicting goals, interdependent processes and sideeffects. A special situation occurs, when local entities are supposed to keep autonomy but should be directed by a central instance, to reach a global goal. A concrete example of this optimization problem can be found in health care. The management of modern hospitals has to ensure the quality of service and at the same time work cost efficient. They want to find improvement steps, which on the one hand respect the typical local autonomy of functional units and on the other hand reduce cost factors like the avarage stay duration of patients. Existing tools for modelling and simulation don't provide adequate methodologies and techniques for this problem. Agent based simulation allowes to realize suitable models and finding improvement steps in simulation studies. New approaches and tools are presented and evaluated, that support users in knowledge formalization and model building. KW - Simulation KW - Prozessoptimierung KW - Modellierung KW - Mehragentensystem KW - Krankenhaus KW - Simulation KW - Process Optimization KW - Agentbased System KW - Hospital Y1 - 2007 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-24483 ER - TY - THES A1 - Herrmann, Christian T1 - Robotic Motion Compensation for Applications in Radiation Oncology T1 - Robotergestützte Bewegungskompensation für Anwendungen in der Radioonkologie N2 - Aufgrund vieler Verbesserungen der Behandlungsmethoden im Laufe der letzten 60 Jahre, erlaubt die Strahlentherapie heutzutage präzise Behandlungen von statischen Tumoren. Jedoch birgt die Bestrahlung von sich bewegenden Tumoren noch große Herausforderungen in sich, da bewegliche Tumore oft den Behandlungsstrahl verlassen. Dabei reduziert sich die Strahlendosis im Tumor während sich diese im umliegenden gesunden Gewebe erhöht. Diese Forschungsarbeit zielt darauf ab, die Grenzen der Strahlentherapie zu erweitern, um präzise Behandlungen von beweglichen Tumoren zu ermöglichen. Der Fokus der Arbeit liegt auf der Erstellung eines Echtzeitsystems zur aktiven Kompensation von Tumorbewegungen durch robotergestützte Methoden. Während Behandlungen befinden sich Patienten auf einer Patientenliege, mit der statische Lagerungsfehler vor Beginn einer Behandlung korrigiert werden. Die in dieser Arbeit verwendete Patientenliege "HexaPOD" ist ein paralleler Manipulator mit sechs Freiheitsgraden, der große Lasten innerhalb eines eingeschränkten Arbeitsbereichs präzise positionieren kann. Obwohl der HexaPOD ursprünglich nicht für dynamische Anwendungen konzipiert wurde, wird dieser für eine dauerhafte Bewegungskompensation eingesetzt, in dem Patienten so bewegt werden, dass Tumore präzise im Zentralstrahl während der Dauer einer gesamten Behandlung verbleiben. Um ein echtzeitfähiges Kompensationssystem auf Basis des HexaPODs zu realisieren, muss eine Reihe an Herausforderungen bewältigt werden. Echtzeitaspekte werden einerseits durch die Verwendung eines harten Echtzeitbetriebssystems abgedeckt, andererseits durch die Messung und Schätzung von Latenzzeiten aller physikalischen Größen im System, z.B. Messungen der Tumor- und Atemposition. Neben der konsistenten und durchgängigen Berücksichtigung von akkuraten Zeitinformation, werden alle software-induzierten Latenzen adaptiv ausgeglichen. Dies erfordert Vorhersagen der Tumorposition in die nahe Zukunft. Zahlreiche Prädiktoren zur Atem- und Tumorpositionsvorhersage werden vorgeschlagen und anhand verschiedenster Metriken evaluiert. Erweiterungen der Prädiktionsalgorithmen werden eingeführt, die sowohl Atem- als auch Tumorpositionsinformationen fusionieren, um Vorhersagen ohne explizites Korrelationsmodell zu ermöglichen. Die Vorhersagen bestimmen den zukünftigen Bewegungspfad des HexaPODs, um Tumorbewegungen zu kompensieren. Dazu werden verschiedene Regler entwickelt, die eine Trajektorienverfolgung mit dem HexaPOD ermöglichen. Auf der Basis von linearer und nicht-linearer dynamischer Modellierung des HexaPODs mit Methoden der Systemidentifikation, wird zunächst ein modellprädiktiver Regler entwickelt. Ein zweiter Regler wird auf Basis einer Annahme über das Arbeitsprinzip des internen Reglers im HexaPOD entworfen. Schließlich wird ein dritter Regler vorgeschlagen, der beide vorhergehenden Regler miteinander kombiniert. Für jeden dieser Regler werden vergleichende Ergebnisse aus Experimenten mit realer Hardware und menschlichen Versuchspersonen präsentiert und diskutiert. Darüber hinaus wird die geeignete Wahl von freien Parametern in den Reglern vorgestellt. Neben einer präzisen Verfolgung der Referenztrajektorie spielt der Patientenkomfort eine entscheidende Rolle für die Akzeptanz des Systems. Es wird gezeigt, dass die Regler glatte Trajektorien realisieren können, um zu garantieren, dass sich Patienten wohl fühlen während ihre Tumorbewegung mit Genauigkeiten im Submillimeterbereich ausgeglichen wird. Gesamtfehler werden im Kompensationssystem analysiert, in dem diese zu Trajektorienverfolgungsfehlern und Prädiktionsfehlern in Beziehung gesetzt werden. Durch Ausnutzung von Eigenschaften verschiedener Prädiktoren wird gezeigt, dass die Startzeit des Systems bis die Verfolgung der Referenztrajektorie erreicht ist, wenige Sekunden beträgt. Dies gilt insbesondere für den Fall eines initial ruhenden HexaPODs und ohne Vorwissen über Tumorbewegungen. Dies zeigt die Eignung des Systems für die sehr kurz fraktionierten Behandlungen von Lungentumoren. Das Tumorkompensationssystem wurde ausschließlich auf Basis von klinischer Standard-Hardware entwickelt, die in vielen Behandlungsräumen zu finden ist. Durch ein einfaches und flexibles Design können Behandlungsräume in kosteneffizienter Weise um Möglichkeiten der Bewegungskompensation ergänzt werden. Darüber hinaus werden aktuelle Behandlungsmethoden wie intensitätsmodulierte Strahlentherapie oder Volumetric Modulated Arc Therapy in keiner Weise eingeschränkt. Aufgrund der Unterstützung verschiedener Kompensationsmodi kann das System auf alle beweglichen Tumore angewendet werden, unabhängig davon ob die Bewegungen vorhersagbar (Lungentumore) oder nicht vorhersagbar (Prostatatumore) sind. Durch Integration von geeigneten Methoden zur Tumorpositionsbestimmung kann das System auf einfache Weise zur Kompensation von anderen Tumoren erweitert werden. N2 - Radiation therapy today, on account of improvements in treatment procedures over the last 60 years, allows precise treatment of static tumors inside the human body. However, irradiation of moving tumors is still a challenging task as moving tumors often leave the treatment beam and the radiation dose delivered to the tumor reduces simultaneously increasing that on healthy tissue. This research work aims to push the frontiers of radiation therapy in order to enable precise treatment of moving tumors with focus on research and development of a unique real-time system enabling active motion compensation through robotic means to compensate tumor motion. During treatment, patients lie on a treatment couch which is normally used for static position corrections of patient set-up errors prior to radiation treatment. The treatment couch used, called HexaPOD, is a parallel manipulator with six degrees of freedom which can precisely position heavy loads inside a small region. Despite the HexaPOD not initially built with dynamics in mind, it is used in this work for sustained motion compensation by moving patients such that tumors stay precisely located at the center of the treatment beam during the complete course of treatment. In order to realize real-time tumor motion compensation by means of the HexaPOD, several challanges need to be addressed. Real-time aspects are covered by the adoption of a hard real-time operation system in combination with measurement and estimation of latencies of all physical quantities in the compensation system such as tumor or breathing position measurements. Accurate timing information is respected consistently in the whole system and all software-induced latencies are adaptively compensated for. This requires knowledge of future tumor positions from predictors. Several predictors for breathing and tumor motion predictions are proposed and evaluated in terms of a variety of different performance metrics. Extensions to prediction algorithms are introduced fusing both breathing and tumor position information to allow for predictions without the need of an explicit correlation model. Predictions determine the future motion path of the HexaPOD in order to compensate for tumor motion. Several control schemes are developed to enable reference tracking for the HexaPOD. Based on linear and non-linear dynamic modelling of the HexaPOD with system identification methods, a first controller is derived in the form of a model predictive controller. A second controller is proposed based on an assumption of the working principle of the HexaPOD's internal controller. Finally, a third controller is derived as combination of the first and second one. For each of these controllers, comparative results with real hardware experiments and humans in the loop as well as choices of free parameters are presented and discussed. Apart from precise tracking, emphasis is placed on patient comfort which is of crucial importance for acceptance of the system. It is demonstrated that smooth trajectories can be realized by the controllers to guarantee that patients feel comfortable while their tumor motion is compensated at sub-millimeter accuracies. Overall errors of the system are analyzed by relating them to tracking and prediction errors. By exploiting the properties of different predictors, it is shown that the startup time until tracking is reached can be reduced to only a few seconds, even in the case of an initially at-rest HexaPOD and with no initial knowledge of tumor motion. This makes the system especially suitable for the relatively short-fractionated treatment sessions for lung tumors. The tumor motion compensation system has been developed solely based on standard clinical hardware, found in most treatment rooms. With a simple and flexible design, existing treatment can be updated in a cost-efficient way to introduce motion compensation capabilities. Simultaneously, the system does not impose any constraints on state-of-the-art treatment types such as intensity modulated radiotherapy or volumetric modulated arc therapy. Supporting different compensation modes, the system can be applied to any moving tumor whether its motion is predictable (lung tumors) or unpredictable (prostate tumors). By integration of adequate tumor position determination methods, the system can be easily extended to other tumors as well. T3 - Forschungsberichte in der Robotik = Research Notes in Robotics - 7 KW - Robotik KW - Bewegungskompensation KW - Regelung KW - Strahlentherapie KW - Vorhersage KW - Tumorbewegung KW - Echzeit KW - Prediction KW - Tumor motion KW - Real-time Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-79045 SN - 978-3-923959-88-4 ER - TY - RPRT A1 - Herrmann, Martin A1 - Rizk, Amr T1 - On Data Plane Multipath Scheduling for Connected Mobility Applications T2 - KuVS Fachgespräch - Würzburg Workshop on Modeling, Analysis and Simulation of Next-Generation Communication Networks 2023 (WueWoWAS’23) N2 - Cooperative, connected and automated mobility (CCAM) systems depend on a reliable communication to provide their service and more crucially to ensure the safety of users. One way to ensure the reliability of a data transmission is to use multiple transmission technologies in combination with redundant flows. In this paper, we describe a system requiring multipath communication in the context of CCAM. To this end, we introduce a data plane-based scheduler that uses replication and integration modules to provide redundant and transparent multipath communication. We provide an analytical model for the full replication module of the system and give an overview of how and where the data-plane scheduler components can be realized. KW - multipath scheduling KW - connected mobility applications Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-322033 N1 - Aktualisierte Version unter https://doi.org/10.25972/OPUS-35344 ER - TY - RPRT A1 - Herrmann, Martin A1 - Rizk, Amr T1 - On Data Plane Multipath Scheduling for Connected Mobility Applications T2 - KuVS Fachgespräch - Würzburg Workshop on Modeling, Analysis and Simulation of Next-Generation Communication Networks 2023 (WueWoWAS’23) N2 - Cooperative, connected and automated mobility (CCAM) systems depend on a reliable communication to provide their service and more crucially to ensure the safety of users. One way to ensure the reliability of a data transmission is to use multiple transmission technologies in combination with redundant flows. In this paper, we describe a system requiring multipath communication in the context of CCAM. To this end, we introduce a data plane-based scheduler that uses replication and integration modules to provide redundant and transparent multipath communication. We provide an analytical model for the full replication module of the system and give an overview of how and where the data-plane scheduler components can be realized. KW - multipath scheduling KW - connected mobility applications Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-353444 N1 - Ursprüngliche Version unter https://doi.org/10.25972/OPUS-32203 ET - aktualisierte Version ER - TY - THES A1 - Hess, Martin T1 - Motion coordination and control in systems of nonholonomic autonomous vehicles T1 - Bewegungskoordination und Regelung in Gruppen nichtholonomer autonomer Fahrzeuge N2 - This work focuses on coordination methods and the control of motion in groups of nonholonomic wheeled mobile robots, in particular of the car-like type. These kind of vehicles are particularly restricted in their mobility. In the main part of this work the two problems of formation motion coordination and of rendezvous in distributed multi-vehicle systems are considered. We introduce several enhancements to an existing motion planning approach for formations of nonholonomic mobile robots. Compared to the original method, the extended approach is able to handle time-varying reference speeds as well as adjustments of the formation's shape during reference trajectory segments with continuously differentiable curvature. Additionally, undesired discontinuities in the speed and steering profiles of the vehicles are avoided. Further, the scenario of snow shoveling on an airfield by utilizing multiple formations of autonomous snowplows is discussed. We propose solutions to the subproblems of motion planning for the formations and tracking control for the individual vehicles. While all situations that might occur have been tested in a simulation environment, we also verified the developed tracking controller in real robot hardware experiments. The task of the rendezvous problem in groups of car-like robots is to drive all vehicles to a common position by means of decentralized control laws. Typically there exists no direct interaction link between all of the vehicles. In this work we present decentralized rendezvous control laws for vehicles with free and with bounded steering. The convergence properties of the approaches are analyzed by utilizing Lyapunov based techniques. Furthermore, they are evaluated within various simulation experiments, while the bounded steering case is also verified within laboratory hardware experiments. Finally we introduce a modification to the bounded steering system that increases the convergence speed at the expense of a higher traveled distance of the vehicles. N2 - Diese Arbeit befasst sich mit Methoden zur Bewegungskoordination und Regelung in Gruppen autonomer, nichtholomer Fahrzeuge, wobei vornehmlich autoähnliche mobile Roboter betrachtet werden. Diese Fahrzeuge sind besonders eingeschränkt in ihrer Bewegungsfreiheit. Im Hauptteil der Arbeit werden die Probleme der Formationsbewegung und des Rendezvous in Gruppen verteilter Fahrzeuge betrachtet. Für ein bestehendes Verfahren zur Bewegungsplanung für Formationen nichtholonomer, mobiler Fahrzeuge werden eine Reihe von Verbesserungen vorgestellt. Diese ermöglichen dem erweiterten Verfahren den Umgang mit Referenztrajektorien mit nicht-konstanter Geschwindigkeit und stetig differenzierbarer Krümmung. Außerdem werden im Gegensatz zum ursprünglichen Ansatz unerwünschte Sprungstellen in den Geschwindigkeits- und Krümmungsprofilen der Fahrzeuge vermieden. Desweiteren wird in dieser Arbeit das Schneeräumen auf Flughafenrollfeldern mittels Formationen autonomer Schneepflugfahrzeuge diskutiert. Dabei werden Lösungen für die Teilprobleme Bewegungsplanung der Formationen und Spurführungsregelung der einzelnen Fahrzeuge vorgestellt. Zusätzlich zu den durchgeführten Simulationen werden außerdem die Ergebnisse von Hardwareexperimenten mit der entwickelten Spurführungsregelung präsentiert. Das Rendezvous-Problem in Gruppen autoähnlicher Roboter besteht darin, die Fahrzeuge durch dezentrale Regelgesetze zu einer gemeinsamen Position in der Ebene zu bewegen. Dabei besteht typischerweise keine direkte Interaktionsverbindung zwischen allen Fahrzeugen der Gruppe. In dieser Arbeit werden verteilte Rendezvous-Regelgesetze für Fahrzeuge mit unbeschränktem und mit beschränktem Lenkwinkel eingeführt und deren Konvergenzeigenschaften mit Methoden zur Stabilitätsanalyse nicht-linearer Systeme untersucht. Die vorgestellten Regelsysteme werden weiterhin anhand von Simulationen und Hardwareexperimenten verifiziert. Schließlich wird noch eine Erweiterung des Systems für Fahrzeuge mit beschränktem Lenkwinkel vorgestellt, welches die Konvergenzgeschwindigkeit auf Kosten der zurückgelegten Distanz der Fahrzeuge erhöht. T3 - Forschungsberichte in der Robotik = Research Notes in Robotics - 2 KW - Robotik KW - Autonomer Roboter KW - Mobiler Roboter KW - Bewegungskoordination KW - Dezentrale Regelung KW - Nichtlineare Regelung KW - Rendezvous KW - Kooperierende mobile Roboter KW - Formationsbewegung KW - Nichtholonome Fahrzeuge KW - Mehrfahrzeugsysteme KW - Unstetige Regelung KW - Autonomous multi-vehicle systems KW - multi-vehicle formations KW - multi-vehicle rendezvous KW - car-like robots KW - nonholonomic vehicles Y1 - 2009 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-46442 SN - 978-3-923959-55-6 ER -