@phdthesis{Geissler2022,
  author    = {Geißler, Stefan},
  title     = {Performance Evaluation of Next-Generation Data Plane Architectures and their Components},
  issn      = {1432-8801},
  doi       = {10.25972/OPUS-26015},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-260157},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {In this doctoral thesis we cover the performance evaluation of next generation data plane architectures, comprised of complex software as well as programmable hardware components that allow fine granular configuration. In the scope of the thesis we propose mechanisms to monitor the performance of singular components and model key performance indicators of software based packet processing solutions. We present novel approaches towards network abstraction that allow the integration of heterogeneous data plane technologies into a singular network while maintaining total transparency between control and data plane. Finally, we investigate a full, complex system consisting of multiple software-based solutions and perform a detailed performance analysis. We employ simulative approaches to investigate overload control mechanisms that allow efficient operation under adversary conditions. The contributions of this work build the foundation for future research in the areas of network softwarization and network function virtualization.},
  subject      = {Leistungsbewertung},
  language  = {en}
}
@phdthesis{Henjes2010,
  author    = {Henjes, Robert},
  title     = {Performance Evaluation of Publish/Subscribe Middleware Architectures},
  doi       = {10.25972/OPUS-4536},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-53388},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2010},
  abstract  = {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.},
  subject      = {Middleware},
  language  = {en}
}
@phdthesis{Klein2010,
  author    = {Klein, Alexander},
  title     = {Performance Issues of MAC and Routing Protocols in Wireless Sensor Networks},
  doi       = {10.25972/OPUS-4465},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-52870},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2010},
  abstract  = {The focus of this work lies on the communication issues of Medium Access Control (MAC) and routing protocols in the context of WSNs. The communication challenges in these networks mainly result from high node density, low bandwidth, low energy constraints and the hardware limitations in terms of memory, computational power and sensing capabilities of low-power transceivers. For this reason, the structure of WSNs is always kept as simple as possible to minimize the impact of communication issues. Thus, the majority of WSNs apply a simple one hop star topology since multi-hop communication has high demands on the routing protocol since it increases the bandwidth requirements of the network. Moreover, medium access becomes a challenging problem due to the fact that low-power transceivers are very limited in their sensing capabilities. The first contribution is represented by the Backoff Preamble-based MAC Protocol with Sequential Contention Resolution (BPS-MAC) which is designed to overcome the limitations of low-power transceivers. Two communication issues, namely the Clear Channel Assessment (CCA) delay and the turnaround time, are directly addressed by the protocol. The CCA delay represents the period of time which is required by the transceiver to detect a busy radio channel while the turnaround time specifies the period of time which is required to switch between receive and transmit mode. Standard Carrier Sense Multiple Access (CSMA) protocols do not achieve high performance in terms of packet loss if the traffic is highly correlated due to the fact that the transceiver is not able to sense the medium during the switching phase. Therefore, a node may start to transmit data while another node is already transmitting since it has sensed an idle medium right before it started to switch its transceiver from receive to transmit mode. The BPS-MAC protocol uses a new sequential preamble-based medium access strategy which can be adapted to the hardware capabilities of the transceivers. The protocol achieves a very low packet loss rate even in wireless networks with high node density and event-driven traffic without the need of synchronization. This makes the protocol attractive to applications such as structural health monitoring, where event suppression is not an option. Moreover, acknowledgments or complex retransmission strategies become almost unnecessary since the sequential preamble-based contention resolution mechanism minimizes the collision probability. However, packets can still be lost as a consequence of interference or other issues which affect signal propagation. The second contribution consists of a new routing protocol which is able to quickly detect topology changes without generating a large amount of overhead. The key characteristics of the Statistic-Based Routing (SBR) protocol are high end-to-end reliability (in fixed and mobile networks), load balancing capabilities, a smooth continuous routing metric, quick adaptation to changing network conditions, low processing and memory requirements, low overhead, support of unidirectional links and simplicity. The protocol can establish routes in a hybrid or a proactive mode and uses an adaptive continuous routing metric which makes it very flexible in terms of scalability while maintaining stable routes. The hybrid mode is optimized for low-power WSNs since routes are only established on demand. The difference of the hybrid mode to reactive routing strategies is that routing messages are periodically transmitted to maintain already established routes. However, the protocol stops the transmission of routing messages if no data packets are transmitted for a certain time period in order to minimize the routing overhead and the energy consumption. The proactive mode is designed for high data rate networks which have less energy constraints. In this mode, the protocol periodically transmits routing messages to establish routes in a proactive way even in the absence of data traffic. Thus, nodes in the network can immediately transmit data since the route to the destination is already established in advance. In addition, a new delay-based routing message forwarding strategy is introduced. The forwarding strategy is part of SBR but can also be applied to many routing protocols in order to modify the established topology. The strategy can be used, e.g. in mobile networks, to decrease the packet loss by deferring routing messages with respect to the neighbor change rate. Thus, nodes with a stable neighborhood forward messages faster than nodes within a fast changing neighborhood. As a result, routes are established through nodes with correlated movement which results in fewer topology changes due to higher link durations.},
  subject      = {Routing},
  language  = {en}
}
@phdthesis{Zinner2012,
  author    = {Zinner, Thomas},
  title     = {Performance Modeling of QoE-Aware Multipath Video Transmission in the Future Internet},
  doi       = {10.25972/OPUS-6106},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-72324},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2012},
  abstract  = {Internet applications are becoming more and more flexible to support diverge user demands and network conditions. This is reflected by technical concepts, which provide new adaptation mechanisms to allow fine grained adjustment of the application quality and the corresponding bandwidth requirements. For the case of video streaming, the scalable video codec H.264/SVC allows the flexible adaptation of frame rate, video resolution and image quality with respect to the available network resources. In order to guarantee a good user-perceived quality (Quality of Experience, QoE) it is necessary to adjust and optimize the video quality accurately. But not only have the applications of the current Internet changed. Within network and transport, new technologies evolved during the last years providing a more flexible and efficient usage of data transport and network resources. One of the most promising technologies is Network Virtualization (NV) which is seen as an enabler to overcome the ossification of the Internet stack. It provides means to simultaneously operate multiple logical networks which allow for example application-specific addressing, naming and routing, or their individual resource management. New transport mechanisms like multipath transmission on the network and transport layer aim at an efficient usage of available transport resources. However, the simultaneous transmission of data via heterogeneous transport paths and communication technologies inevitably introduces packet reordering. Additional mechanisms and buffers are required to restore the correct packet order and thus to prevent a disturbance of the data transport. A proper buffer dimensioning as well as the classification of the impact of varying path characteristics like bandwidth and delay require appropriate evaluation methods. Additionally, for a path selection mechanism real time evaluation mechanisms are needed. A better application-network interaction and the corresponding exchange of information enable an efficient adaptation of the application to the network conditions and vice versa. This PhD thesis analyzes a video streaming architecture utilizing multipath transmission and scalable video coding and develops the following optimization possibilities and results: Analysis and dimensioning methods for multipath transmission, quantification of the adaptation possibilities to the current network conditions with respect to the QoE for H.264/SVC, and evaluation and optimization of a future video streaming architecture, which allows a better interaction of application and network.},
  subject      = {Video{\"u}bertragung},
  language  = {en}
}
@phdthesis{Maeder2008,
  author    = {M{\"a}der, Andreas},
  title     = {Performance Models for UMTS 3.5G Mobile Wireless Systems},
  doi       = {10.25972/OPUS-2766},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-32525},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2008},
  abstract  = {Mobile telecommunication systems of the 3.5th generation (3.5G) constitute a first step towards the requirements of an all-IP world. As the denotation suggests, 3.5G systems are not completely new designed from scratch. Instead, they are evolved from existing 3G systems like UMTS or cdma2000. 3.5G systems are primarily designed and optimized for packet-switched best-effort traffic, but they are also intended to increase system capacity by exploiting available radio resources more efficiently. Systems based on cdma2000 are enhanced with 1xEV-DO (EV-DO: evolution, data-optimized). In the UMTS domain, the 3G partnership project (3GPP) specified the High Speed Packet Access (HSPA) family, consisting of High Speed Downlink Packet Access (HSDPA) and its counterpart High Speed Uplink Packet Access (HSUPA) or Enhanced Uplink. The focus of this monograph is on HSPA systems, although the operation principles of other 3.5G systems are similar. One of the main contributions of our work are performance models which allow a holistic view on the system. The models consider user traffic on flow-level, such that only on significant changes of the system state a recalculation of parameters like bandwidth is necessary. The impact of lower layers is captured by stochastic models. This approach combines accurate modeling and the ability to cope with computational complexity. Adopting this approach to HSDPA, we develop a new physical layer abstraction model that takes radio resources, scheduling discipline, radio propagation and mobile device capabilities into account. Together with models for the calculation of network-wide interference and transmit powers, a discrete-event simulation and an analytical model based on a queuing-theoretical approach are proposed. For the Enhanced Uplink, we develop analytical models considering independent and correlated other-cell interference.},
  subject      = {Mobilfunk},
  language  = {en}
}
@phdthesis{Pries2010,
  author    = {Pries, Jan Rastin},
  title     = {Performance Optimization of Wireless Infrastructure and Mesh Networks},
  doi       = {10.25972/OPUS-3723},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-46097},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2010},
  abstract  = {Future broadband wireless networks should be able to support not only best effort traffic but also real-time traffic with strict Quality of Service (QoS) constraints. In addition, their available resources are scare and limit the number of users. To facilitate QoS guarantees and increase the maximum number of concurrent users, wireless networks require careful planning and optimization. In this monograph, we studied three aspects of performance optimization in wireless networks: resource optimization in WLAN infrastructure networks, quality of experience control in wireless mesh networks, and planning and optimization of wireless mesh networks. An adaptive resource management system is required to effectively utilize the limited resources on the air interface and to guarantee QoS for real-time applications. Thereby, both WLAN infrastructure and WLAN mesh networks have to be considered. An a-priori setting of the access parameters is not meaningful due to the contention-based medium access and the high dynamics of the system. Thus, a management system is required which dynamically adjusts the channel access parameters based on the network load. While this is sufficient for wireless infrastructure networks, interferences on neighboring paths and self-interferences have to be considered for wireless mesh networks. In addition, a careful channel allocation and route assignment is needed. Due to the large parameter space, standard optimization techniques fail for optimizing large wireless mesh networks. In this monograph, we reveal that biology-inspired optimization techniques, namely genetic algorithms, are well-suitable for the planning and optimization of wireless mesh networks. Although genetic algorithms generally do not always find the optimal solution, we show that with a good parameter set for the genetic algorithm, the overall throughput of the wireless mesh network can be significantly improved while still sharing the resources fairly among the users.},
  subject      = {IEEE 802.11},
  language  = {en}
}
@phdthesis{Schlosser2011,
  author    = {Schlosser, Daniel},
  title     = {Quality of Experience Management in Virtual Future Networks},
  doi       = {10.25972/OPUS-5719},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-69986},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2011},
  abstract  = {Aktuell beobachten wir eine drastische Vervielf{\"a}ltigung der Dienste und Anwendungen, die das Internet f{\"u}r den Datentransport nutzen. Dabei unterscheiden sich die Anforderungen dieser Dienste an das Netzwerk deutlich. Das Netzwerkmanagement wird durch diese Diversit{\"a}t der nutzenden Dienste aber deutlich erschwert, da es einem Datentransportdienstleister kaum m{\"o}glich ist, die unterschiedlichen Verbindungen zu unterscheiden, ohne den Inhalt der transportierten Daten zu analysieren. Netzwerkvirtualisierung ist eine vielversprechende L{\"o}sung f{\"u}r dieses Problem, da sie es erm{\"o}glicht f{\"u}r verschiedene Dienste unterschiedliche virtuelle Netze auf dem gleichen physikalischen Substrat zu betreiben. Diese Diensttrennung erm{\"o}glicht es, jedes einzelne Netz anwendungsspezifisch zu steuern. Ziel einer solchen Netzsteuerung ist es, sowohl die vom Nutzer erfahrene Dienstg{\"u}te als auch die Kosteneffizienz des Datentransports zu optimieren. Dar{\"u}ber hinaus wird es mit Netzwerkvirtualisierung m{\"o}glich das physikalische Netz so weit zu abstrahieren, dass die aktuell fest verzahnten Rollen von Netzwerkbesitzer und Netzwerkbetreiber entkoppelt werden k{\"o}nnen. Dar{\"u}ber hinaus stellt Netzwerkvirtualisierung sicher, dass unterschiedliche Datennetze, die gleichzeitig auf dem gleichen physikalischen Netz betrieben werden, sich gegenseitig weder beeinflussen noch st{\"o}ren k{\"o}nnen. Diese Arbeit  besch{\"a}ftigt sich mit ausgew{\"a}hlten Aspekten dieses Themenkomplexes und fokussiert sich darauf, ein virtuelles Netzwerk mit bestm{\"o}glicher Dienstqualit{\"a}t f{\"u}r den Nutzer zu betreiben und zu steuern. Daf{\"u}r wird ein Top-down-Ansatz gew{\"a}hlt, der von den Anwendungsf{\"a}llen, einer m{\"o}glichen Netzwerkvirtualisierungs-Architektur und aktuellen M{\"o}glichkeiten der Hardwarevirtualisierung ausgeht. Im Weiteren fokussiert sich die Arbeit dann in Richtung Bestimmung und Optimierung der vom Nutzer erfahrenen Dienstqualit{\"a}t (QoE) auf Applikationsschicht und diskutiert M{\"o}glichkeiten zur Messung und {\"U}berwachung von wesentlichen Netzparametern in virtualisierten Netzen.},
  subject      = {Netzwerkmanagement},
  language  = {en}
}
@phdthesis{Martin2008,
  author    = {Martin, R{\"u}diger},
  title     = {Resilience, Provisioning, and Control for the Network of the Future},
  doi       = {10.25972/OPUS-2504},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-28497},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2008},
  abstract  = {The Internet sees an ongoing transformation process from a single best-effort service network into a multi-service network. In addition to traditional applications like e-mail,WWW-traffic, or file transfer, future generation networks (FGNs) will carry services with real-time constraints and stringent availability and reliability requirements like Voice over IP (VoIP), video conferencing, virtual private networks (VPNs) for finance, other real-time business applications, tele-medicine, or tele-robotics. Hence, quality of service (QoS) guarantees and resilience to failures are crucial characteristics of an FGN architecture. At the same time, network operations must be efficient. This necessitates sophisticated mechanisms for the provisioning and the control of future communication infrastructures. In this work we investigate such echanisms for resilient FGNs. There are many aspects of the provisioning and control of resilient FGNs such as traffic matrix estimation, traffic characterization, traffic forecasting, mechanisms for QoS enforcement also during failure cases, resilient routing, or calability concerns for future routing and addressing mechanisms. In this work we focus on three important aspects for which performance analysis can deliver substantial insights: load balancing for multipath Internet routing, fast resilience concepts, and advanced dimensioning techniques for resilient networks. Routing in modern communication networks is often based on multipath structures, e.g., equal-cost multipath routing (ECMP) in IP networks, to facilitate traffic engineering and resiliency. When multipath routing is applied, load balancing algorithms distribute the traffic over available paths towards the destination according to pre-configured distribution values. State-of-the-art load balancing algorithms operate either on the packet or the flow level. Packet level mechanisms achieve highly accurate traffic distributions, but are known to have negative effects on the performance of transport protocols and should not be applied. Flow level mechanisms avoid performance degradations, but at the expense of reduced accuracy. These inaccuracies may have unpredictable effects on link capacity requirements and complicate resource management. Thus, it is important to exactly understand the accuracy and dynamics of load balancing algorithms in order to be able to exercise better network control. Knowing about their weaknesses, it is also important to look for alternatives and to assess their applicability in different networking scenarios. This is the first aspect of this work. Component failures are inevitable during the operation of communication networks and lead to routing disruptions if no special precautions are taken. In case of a failure, the robust shortest-path routing of the Internet reconverges after some time to a state where all nodes are again reachable - provided physical connectivity still exists. But stringent availability and reliability criteria of new services make a fast reaction to failures obligatory for resilient FGNs. This led to the development of fast reroute (FRR) concepts for MPLS and IP routing. The operations of MPLS-FRR have already been standardized. Still, the standards leave some degrees of freedom for the resilient path layout and it is important to understand the tradeoffs between different options for the path layout to efficiently provision resilient FGNs. In contrast, the standardization for IP-FRR is an ongoing process. The applicability and possible combinations of different concepts still are open issues. IP-FRR also facilitates a comprehensive resilience framework for IP routing covering all steps of the failure recovery cycle. These points constitute another aspect of this work. Finally, communication networks are usually over-provisioned, i.e., they have much more capacity installed than actually required during normal operation. This is a precaution for various challenges such as network element failures. An alternative to this capacity overprovisioning (CO) approach is admission control (AC). AC blocks new flows in case of imminent overload due to unanticipated events to protect the QoS for already admitted flows. On the one hand, CO is generally viewed as a simple mechanism, AC as a more complex mechanism that complicates the network control plane and raises interoperability issues. On the other hand, AC appears more cost-efficient than CO. To obtain advanced provisioning methods for resilient FGNs, it is important to find suitable models for irregular events, such as failures and different sources of overload, and to incorporate them into capacity dimensioning methods. This allows for a fair comparison between CO and AC in various situations and yields a better understanding of the strengths and weaknesses of both concepts. Such an advanced capacity dimensioning method for resilient FGNs represents the third aspect of this work.},
  subject      = {Backbone-Netz},
  language  = {en}
}
@phdthesis{Herrmann2013,
  author    = {Herrmann, Christian},
  title     = {Robotic Motion Compensation for Applications in Radiation Oncology},
  isbn      = {978-3-923959-88-4},
  doi       = {10.25972/OPUS-6727},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-79045},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2013},
  abstract  = {Aufgrund vieler Verbesserungen der Behandlungsmethoden im Laufe der letzten 60 Jahre, erlaubt die Strahlentherapie heutzutage pr{\"a}zise 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 w{\"a}hrend sich diese im umliegenden gesunden Gewebe erh{\"o}ht. Diese Forschungsarbeit zielt darauf ab, die Grenzen der Strahlentherapie zu erweitern, um pr{\"a}zise Behandlungen von beweglichen Tumoren zu erm{\"o}glichen. Der Fokus der Arbeit liegt auf der Erstellung eines Echtzeitsystems zur aktiven Kompensation von Tumorbewegungen durch robotergest{\"u}tzte Methoden. W{\"a}hrend 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 eingeschr{\"a}nkten Arbeitsbereichs pr{\"a}zise positionieren kann. Obwohl der HexaPOD urspr{\"u}nglich nicht f{\"u}r dynamische Anwendungen konzipiert wurde, wird dieser f{\"u}r eine dauerhafte Bewegungskompensation eingesetzt, in dem Patienten so bewegt werden, dass Tumore pr{\"a}zise im Zentralstrahl w{\"a}hrend der Dauer einer gesamten Behandlung verbleiben. Um ein echtzeitf{\"a}higes Kompensationssystem auf Basis des HexaPODs zu realisieren, muss eine Reihe an Herausforderungen bew{\"a}ltigt werden. Echtzeitaspekte werden einerseits durch die Verwendung eines harten Echtzeitbetriebssystems abgedeckt, andererseits durch die Messung und Sch{\"a}tzung von Latenzzeiten aller physikalischen Gr{\"o}ßen im System, z.B. Messungen der Tumor- und Atemposition. Neben der konsistenten und durchg{\"a}ngigen Ber{\"u}cksichtigung von akkuraten Zeitinformation, werden alle software-induzierten Latenzen adaptiv ausgeglichen. Dies erfordert Vorhersagen der Tumorposition in die nahe Zukunft. Zahlreiche Pr{\"a}diktoren zur Atem- und Tumorpositionsvorhersage werden vorgeschlagen und anhand verschiedenster Metriken evaluiert. Erweiterungen der Pr{\"a}diktionsalgorithmen werden eingef{\"u}hrt, die sowohl Atem- als auch Tumorpositionsinformationen fusionieren, um Vorhersagen ohne explizites Korrelationsmodell zu erm{\"o}glichen. Die Vorhersagen bestimmen den zuk{\"u}nftigen Bewegungspfad des HexaPODs, um Tumorbewegungen zu kompensieren. Dazu werden verschiedene Regler entwickelt, die eine Trajektorienverfolgung mit dem HexaPOD erm{\"o}glichen. Auf der Basis von linearer und nicht-linearer dynamischer Modellierung des HexaPODs mit Methoden der Systemidentifikation, wird zun{\"a}chst ein modellpr{\"a}diktiver Regler entwickelt. Ein zweiter Regler wird auf Basis einer Annahme {\"u}ber das Arbeitsprinzip des internen Reglers im HexaPOD entworfen. Schließlich wird ein dritter Regler vorgeschlagen, der beide vorhergehenden Regler miteinander kombiniert. F{\"u}r jeden dieser Regler werden vergleichende Ergebnisse aus Experimenten mit realer Hardware und menschlichen Versuchspersonen pr{\"a}sentiert und diskutiert. Dar{\"u}ber hinaus wird die geeignete Wahl von freien Parametern in den Reglern vorgestellt. Neben einer pr{\"a}zisen Verfolgung der Referenztrajektorie spielt der Patientenkomfort eine entscheidende Rolle f{\"u}r die Akzeptanz des Systems. Es wird gezeigt, dass die Regler glatte Trajektorien realisieren k{\"o}nnen, um zu garantieren, dass sich Patienten wohl f{\"u}hlen w{\"a}hrend ihre Tumorbewegung mit Genauigkeiten im Submillimeterbereich ausgeglichen wird. Gesamtfehler werden im Kompensationssystem analysiert, in dem diese zu Trajektorienverfolgungsfehlern und Pr{\"a}diktionsfehlern in Beziehung gesetzt werden. Durch Ausnutzung von Eigenschaften verschiedener Pr{\"a}diktoren wird gezeigt, dass die Startzeit des Systems bis die Verfolgung der Referenztrajektorie erreicht ist, wenige Sekunden betr{\"a}gt. Dies gilt insbesondere f{\"u}r den Fall eines initial ruhenden HexaPODs und ohne Vorwissen {\"u}ber Tumorbewegungen. Dies zeigt die Eignung des Systems f{\"u}r die sehr kurz fraktionierten Behandlungen von Lungentumoren. Das Tumorkompensationssystem wurde ausschließlich auf Basis von klinischer Standard-Hardware entwickelt, die in vielen Behandlungsr{\"a}umen zu finden ist. Durch ein einfaches und flexibles Design k{\"o}nnen Behandlungsr{\"a}ume in kosteneffizienter Weise um M{\"o}glichkeiten der Bewegungskompensation erg{\"a}nzt werden. Dar{\"u}ber hinaus werden aktuelle Behandlungsmethoden wie intensit{\"a}tsmodulierte Strahlentherapie oder Volumetric Modulated Arc Therapy in keiner Weise eingeschr{\"a}nkt. Aufgrund der Unterst{\"u}tzung verschiedener Kompensationsmodi kann das System auf alle beweglichen Tumore angewendet werden, unabh{\"a}ngig 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.},
  subject      = {Robotik},
  language  = {en}
}
@phdthesis{Busch2016,
  author    = {Busch, Stephan},
  title     = {Robust, Flexible and Efficient Design for Miniature Satellite Systems},
  isbn      = {978-3-945459-10-2},
  doi       = {10.25972/OPUS-13652},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-136523},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2016},
  abstract  = {Small satellites contribute significantly in the rapidly evolving innovation in space engineering, in particular in distributed space systems for global Earth observation and communication services. Significant mass reduction by miniaturization, increased utilization of commercial high-tech components, and in particular standardization are the key drivers for modern miniature space technology. This thesis addresses key fields in research and development on miniature satellite technology regarding efficiency, flexibility, and robustness. Here, these challenges are addressed by the University of Wuerzburg's advanced pico-satellite bus, realizing a generic modular satellite architecture and standardized interfaces for all subsystems. The modular platform ensures reusability, scalability, and increased testability due to its flexible subsystem interface which allows efficient and compact integration of the entire satellite in a plug-and-play manner. Beside systematic design for testability, a high degree of operational robustness is achieved by the consequent implementation of redundancy of crucial subsystems. This is combined with efficient fault detection, isolation and recovery mechanisms. Thus, the UWE-3 platform, and in particular the on-board data handling system and the electrical power system, offers one of the most efficient pico-satellite architectures launched in recent years and provides a solid basis for future extensions. The in-orbit performance results of the pico-satellite UWE-3 are presented and summarize successful operations since its launch in 2013. Several software extensions and adaptations have been uploaded to UWE-3 increasing its capabilities. Thus, a very flexible platform for in-orbit software experiments and for evaluations of innovative concepts was provided and tested.},
  subject      = {Kleinsatellit},
  language  = {en}
}
@phdthesis{Betz2005,
  author    = {Betz, Christian},
  title     = {Scalable authoring of diagnostic case based training systems},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-17885},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2005},
  abstract  = {Diagnostic Case Based Training Systems (D-CBT) provide learners with a means to learn and exercise knowledge in a realistic context. In medical education, D-CBT Systems present virtual patients to the learners who are asked to examine, diagnose and state therapies for these patients. Due a number of conflicting and changing requirements, e.g. time for learning, authoring effort, several systems were developed so far. These systems range from simple, easy-to-use presentation systems to highly complex knowledge based systems supporting explorative learning. This thesis presents an approach and tools to create D-CBT systems from existing sources (documents, e.g. dismissal records) using existing tools (word processors): Authors annotate and extend the documents to model the knowledge. A scalable knowledge representation is able to capture the content on multiple levels, from simple to highly structured knowledge. Thus, authoring of D-CBT systems requires less prerequisites and pre-knowledge and is faster than approaches using specialized authoring environments. Also, authors can iteratively add and structure more knowledge to adapt training cases to their learners needs. The theses also discusses the application of the same approach to other domains, especially to knowledge acquisition for the Semantic Web.},
  subject      = {Computerunterst{\"u}tztes Lernen},
  language  = {en}
}
@phdthesis{Baier2018,
  author    = {Baier, Pablo A.},
  title     = {Simulator for Minimally Invasive Vascular Interventions: Hardware and Software},
  isbn      = {978-3-945459-22-5},
  doi       = {10.25972/OPUS-16119},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-161190},
  school      = {Universit{\"a}t W{\"u}rzburg},
  pages     = {118},
  year      = {2018},
  abstract  = {A complete simulation system is proposed that can be used as an educational tool by physicians in training basic skills of Minimally Invasive Vascular Interventions. In the first part, a surface model is developed to assemble arteries having a planar segmentation. It is based on Sweep Surfaces and can be extended to T- and Y-like bifurcations. A continuous force vector field is described, representing the interaction between the catheter and the surface. The computation time of the force field is almost unaffected when the resolution of the artery is increased. The mechanical properties of arteries play an essential role in the study of the circulatory system dynamics, which has been becoming increasingly important in the treatment of cardiovascular diseases. In Virtual Reality Simulators, it is crucial to have a tissue model that responds in real time. In this work, the arteries are discretized by a two dimensional mesh and the nodes are connected by three kinds of linear springs. Three tissue layers (Intima, Media, Adventitia) are considered and, starting from the stretch-energy density, some of the elasticity tensor components are calculated. The physical model linearizes and homogenizes the material response, but it still contemplates the geometric nonlinearity. In general, if the arterial stretch varies by 1\% or less, then the agreement between the linear and nonlinear models is trustworthy. In the last part, the physical model of the wire proposed by Konings is improved. As a result, a simpler and more stable method is obtained to calculate the equilibrium configuration of the wire. In addition, a geometrical method is developed to perform relaxations. It is particularly useful when the wire is hindered in the physical method because of the boundary conditions. The physical and the geometrical methods are merged, resulting in efficient relaxations. Tests show that the shape of the virtual wire agrees with the experiment. The proposed algorithm allows real-time executions and the hardware to assemble the simulator has a low cost.},
  subject      = {Computersimulation},
  language  = {en}
}
@phdthesis{Sun2014,
  author    = {Sun, Kaipeng},
  title     = {Six Degrees of Freedom Object Pose Estimation with Fusion Data from a Time-of-flight Camera and a Color Camera},
  isbn      = {978-3-923959-97-6},
  doi       = {10.25972/OPUS-10508},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-105089},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2014},
  abstract  = {Object six Degrees of Freedom (6DOF) pose estimation is a fundamental problem in many practical robotic applications, where the target or an obstacle with a simple or complex shape can move fast in cluttered environments. In this thesis, a 6DOF pose estimation algorithm is developed based on the fused data from a time-of-flight camera and a color camera. The algorithm is divided into two stages, an annealed particle filter based coarse pose estimation stage and a gradient decent based accurate pose optimization stage. In the first stage, each particle is evaluated with sparse representation. In this stage, the large inter-frame motion of the target can be well handled. In the second stage, the range data based conventional Iterative Closest Point is extended by incorporating the target appearance information and used for calculating the accurate pose by refining the coarse estimate from the first stage. For dealing with significant illumination variations during the tracking, spherical harmonic illumination modeling is investigated and integrated into both stages. The robustness and accuracy of the proposed algorithm are demonstrated through experiments on various objects in both indoor and outdoor environments. Moreover, real-time performance can be achieved with graphics processing unit acceleration.},
  subject      = {Mustererkennung},
  language  = {en}
}
@phdthesis{Hopfner2008,
  author    = {Hopfner, Marbod},
  title     = {Source Code Analysis, Management, and Visualization for PROLOG},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-36300},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2008},
  abstract  = {This thesis deals with the management and analysis of source code, which is represented in XML. Using the elementary methods of the XML repository, the XML source code representation is accessed, changed, updated, and saved. We reason about the source code, refactor source code and we visualize dependency graphs for call analysis. The visualized dependencies between files, modules, or packages are used to structure the source code in order to get a system, which is easily to comprehend, to modify and to complete. Sophisticated methods have been developed to slice the source code in order to obtain a working package of a large system, containing only a specific functionality. The basic methods, on which the visualizations and analyses are built on can be changed like changing a plug-in. The visualization methods can be reused in order to handle arbitrary source code representations, e.g., JAML, PHPML, PROLOGML. Dependencies of other context can be visualized, too, e.g., ER diagrams, or website references. The tool SCAV supports source code visualization and analyzing methods.},
  subject      = {Refactoring},
  language  = {en}
}
@phdthesis{Travers2007,
  author    = {Travers, Stephen},
  title     = {Structural Properties of NP-Hard Sets and Uniform Characterisations of Complexity Classes},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-27124},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2007},
  abstract  = {This thesis is devoted to the study of computational complexity theory, a branch of theoretical computer science. Computational complexity theory investigates the inherent difficulty in designing efficient algorithms for computational problems. By doing so, it analyses the scalability of computational problems and algorithms and places practical limits on what computers can actually accomplish. Computational problems are categorised into complexity classes. Among the most important complexity classes are the class NP and the subclass of NP-complete problems, which comprises many important optimisation problems in the field of operations research. Moreover, with the P-NP-problem, the class NP represents the most important unsolved question in computer science. The first part of this thesis is devoted to the study of NP-complete-, and more generally, NP-hard problems. It aims at improving our understanding of this important complexity class by systematically studying how altering NP-hard sets affects their NP-hardness. This research is related to longstanding open questions concerning the complexity of unions of disjoint NP-complete sets, and the existence of sparse NP-hard sets. The second part of the thesis is also dedicated to complexity classes but takes a different perspective: In a sense, after investigating the interior of complexity classes in the first part, the focus shifts to the description of complexity classes and thereby to the exterior in the second part. It deals with the description of complexity classes through leaf languages, a uniform framework which allows us to characterise a great variety of important complexity classes. The known concepts are complemented by a new leaf-language model. To a certain extent, this new approach combines the advantages of the known models. The presented results give evidence that the connection between the theory of formal languages and computational complexity theory might be closer than formerly known.},
  subject      = {Berechnungskomplexit{\"a}t},
  language  = {en}
}
@phdthesis{Driewer2008,
  author    = {Driewer, Frauke},
  title     = {Teleoperation Interfaces in Human-Robot Teams},
  isbn      = {978-3-923959-57-0},
  doi       = {10.25972/OPUS-2955},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-36351},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2008},
  abstract  = {Diese Arbeit besch{\"a}ftigt sich mit der Verbesserung von Mensch-Roboter Interaktion in Mensch-Roboter Teams f{\"u}r Teleoperation Szenarien, wie z.B. robotergest{\"u}tzte Feuerwehreins{\"a}tze. Hierbei wird ein Konzept und eine Architektur f{\"u}r ein System zur Unterst{\"u}tzung von Teleoperation von Mensch-Roboter Teams vorgestellt. Die Anforderungen an Informationsaustausch und -verarbeitung, insbesondere f{\"u}r die Anwendung Rettungseinsatz, werden ausgearbeitet. Weiterhin wird das Design der Benutzerschnittstellen f{\"u}r Mensch-Roboter Teams dargestellt und Prinzipien f{\"u}r Teleoperation-Systeme und Benutzerschnittstellen erarbeitet. Alle Studien und Ans{\"a}tze werden in einem Prototypen-System implementiert und in verschiedenen Benutzertests abgesichert. Erweiterungsm{\"o}glichkeiten zum Einbinden von 3D Sensordaten und die Darstellung auf Stereovisualisierungssystemen werden gezeigt.},
  subject      = {Robotik},
  language  = {en}
}
@phdthesis{Schmitz2000,
  author    = {Schmitz, Heinz},
  title     = {The Forbidden Pattern Approach to Concatenation Hierarchies},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-2832},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2000},
  abstract  = {The thesis looks at the question asking for the computability of the dot-depth of star-free regular languages. Here one has to determine for a given star-free regular language the minimal number of alternations between concatenation on one hand, and intersection, union, complement on the other hand. This question was first raised in 1971 (Brzozowski/Cohen) and besides the extended star-heights problem usually refered to as one of the most difficult open questions on regular languages. The dot-depth problem can be captured formally by hierarchies of classes of star-free regular languages B(0), B(1/2), B(1), B(3/2),... and L(0), L(1/2), L(1), L(3/2),.... which are defined via alternating the closure under concatenation and Boolean operations, beginning with single alphabet letters. Now the question of dot-depth is the question whether these hierarchy classes have decidable membership problems. The thesis makes progress on this question using the so-called forbidden pattern approach: Classes of regular languages are characterized in terms of patterns in finite automata (subgraphs in the transition graph) that are not allowed. Such a characterization immediately implies the decidability of the respective class, since the absence of a certain pattern in a given automaton can be effectively verified. Before this work, the decidability of B(0), B(1/2), B(1) and L(0), L(1/2), L(1), L(3/2) were known. Here a detailed study of these classes with help of forbidden patterns is given which leads to new insights into their inner structure. Furthermore, the decidability of B(3/2) is proven. Based on these results a theory of pattern iteration is developed which leads to the introduction of two new hierarchies of star-free regular languages. These hierarchies are decidable on one hand, on the other hand they are in close connection to the classes B(n) and L(n). It remains an open question here whether they may in fact coincide. Some evidence is given in favour of this conjecture which opens a new way to attack the dot-depth problem. Moreover, it is shown that the class L(5/2) is decidable in the restricted case of a two-letter alphabet.},
  subject      = {Sternfreie Sprache},
  language  = {en}
}
@phdthesis{Tischler2008,
  author    = {Tischler, German},
  title     = {Theory and Applications of Parametric Weighted Finite Automata},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-28145},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2008},
  abstract  = {Parametric weighted finite automata (PWFA) are a multi-dimensional generalization of weighted finite automata. The expressiveness of PWFA contains the expressiveness of weighted finite automata as well as the expressiveness of affine iterated function system. The thesis discusses theory and applications of PWFA. The properties of PWFA definable sets are studied and it is shown that some fractal generator systems can be simulated using PWFA and that various real and complex functions can be represented by PWFA. Furthermore, the decoding of PWFA and the interpretation of PWFA definable sets is discussed.},
  subject      = {Automat <Automatentheorie>},
  language  = {en}
}
@phdthesis{Saska2009,
  author    = {Saska, Martin},
  title     = {Trajectory planning and optimal control for formations of autonomous robots},
  isbn      = {978-3-923959-56-3},
  doi       = {10.25972/OPUS-4622},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-53175},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2009},
  abstract  = {In this thesis, we present novel approaches for formation driving of nonholonomic robots and optimal trajectory planning to reach a target region. The methods consider a static known map of the environment as well as unknown and dynamic obstacles detected by sensors of the formation. The algorithms are based on leader following techniques, where the formation of car-like robots is maintained in a shape determined by curvilinear coordinates. Beyond this, the general methods of formation driving are specialized and extended for an application of airport snow shoveling. Detailed descriptions of the algorithms complemented by relevant stability and convergence studies will be provided in the following chapters. Furthermore, discussions of the applicability will be verified by various simulations in existing robotic environments and also by a hardware experiment.},
  subject      = {Autonomer Roboter},
  language  = {en}
}
@phdthesis{Freiberg2015,
  author    = {Freiberg, Martina},
  title     = {UI-, User-, \& Usability-Oriented Engineering of Participative Knowledge-Based Systems},
  publisher = {W{\"u}rzburg University Press},
  isbn      = {978-3-95826-012-2 (print)},
  doi       = {10.25972/WUP-978-3-95826-013-9},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-106072},
  school      = {W{\"u}rzburg University Press},
  pages     = {232},
  year      = {2015},
  abstract  = {Knowledge-based systems (KBS) face an ever-increasing interest in various disciplines and contexts. Yet, the former aim to construct the 'perfect intelligent software' continuously shifts to user-centered, participative solutions. Such systems enable users to contribute their personal knowledge to the problem solving process for increased efficiency and an ameliorated user experience. More precisely, we define non-functional key requirements of participative KBS as: Transparency (encompassing KBS status mediation), configurability (user adaptability, degree of user control/exploration), quality of the KB and UI, and evolvability (enabling the KBS to grow mature with their users). Many of those requirements depend on the respective target users, thus calling for a more user-centered development. Often, also highly expertise domains are targeted — inducing highly complex KBs — which requires a more careful and considerate UI/interaction design. Still, current KBS engineering (KBSE) approaches mostly focus on knowledge acquisition (KA) This often leads to non-optimal, little reusable, and non/little evaluated KBS front-end solutions. In this thesis we propose a more encompassing KBSE approach. Due to the strong mutual influences between KB and UI, we suggest a novel form of intertwined UI and KB development. We base the approach on three core components for encompassing KBSE: (1) Extensible prototyping, a tailored form of evolutionary prototyping; this builds on mature UI prototypes and offers two extension steps for the anytime creation of core KBS prototypes (KB + core UI) and fully productive KBS (core KBS prototype + common framing functionality). (2) KBS UI patterns, that define reusable solutions for the core KBS UI/interaction; we provide a basic collection of such patterns in this work. (3) Suitable usability instruments for the assessment of the KBS artifacts. Therewith, we do not strive for 'yet another' self-contained KBS engineering methodology. Rather, we motivate to extend existing approaches by the proposed key components. We demonstrate this based on an agile KBSE model. For practical support, we introduce the tailored KBSE tool ProKEt. ProKEt offers a basic selection of KBS core UI patterns and corresponding configuration options out of the box; their further adaption/extension is possible on various levels of expertise. For practical usability support, ProKEt offers facilities for quantitative and qualitative data collection. ProKEt explicitly fosters the suggested, intertwined development of UI and KB. For seamlessly integrating KA activities, it provides extension points for two selected external KA tools: For KnowOF, a standard office based KA environment. And for KnowWE, a semantic wiki for collaborative KA. Therewith, ProKEt offers powerful support for encompassing, user-centered KBSE. Finally, based on the approach and the tool, we also developed a novel KBS type: Clarification KBS as a mashup of consultation and justification KBS modules. Those denote a specifically suitable realization for participative KBS in highly expertise contexts and consequently require a specific design. In this thesis, apart from more common UI solutions, we particularly also introduce KBS UI patterns especially tailored towards Clarification KBS.},
  subject      = {Wissensbasiertes System},
  language  = {en}
}