TY  - JOUR
A1  - Sîrbu, Alina
A1  - Becker, Martin
A1  - Caminiti, Saverio
A1  - De Baets, Bernard
A1  - Elen, Bart
A1  - Francis, Louise
A1  - Gravino, Pietro
A1  - Hotho, Andreas
A1  - Ingarra, Stefano
A1  - Loreto, Vittorio
A1  - Molino, Andrea
A1  - Mueller, Juergen
A1  - Peters, Jan
A1  - Ricchiuti, Ferdinando
A1  - Saracino, Fabio
A1  - Servedio, Vito D.P.
A1  - Stumme, Gerd
A1  - Theunis, Jan
A1  - Tria, Francesca
A1  - Van den Bossche, Joris
T1  - Participatory Patterns in an International Air Quality Monitoring Initiative
JF  - PLoS ONE
N2  - The issue of sustainability is at the top of the political and societal agenda, being considered of extreme importance and urgency. Human individual action impacts the environment both locally (e.g., local air/water quality, noise disturbance) and globally (e.g., climate change, resource use). Urban environments represent a crucial example, with an increasing realization that the most effective way of producing a change is involving the citizens themselves in monitoring campaigns (a citizen science bottom-up approach). This is possible by developing novel technologies and IT infrastructures enabling large citizen participation. Here, in the wider framework of one of the first such projects, we show results from an international competition where citizens were involved in mobile air pollution monitoring using low cost sensing devices, combined with a web-based game to monitor perceived levels of pollution. Measures of shift in perceptions over the course of the campaign are provided, together with insights into participatory patterns emerging from this study. Interesting effects related to inertia and to direct involvement in measurement activities rather than indirect information exposure are also highlighted, indicating that direct involvement can enhance learning and environmental awareness. In the future, this could result in better adoption of policies towards decreasing pollution.
KW  - transport microenvironments
KW  - exposure
KW  - pollution
KW  - carbon
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-151379
VL  - 10
IS  - 8
ER  - 
TY  - THES
A1  - Sun, Kaipeng
T1  - Six Degrees of Freedom Object Pose Estimation with Fusion Data from a Time-of-flight Camera and a Color Camera
T1  - 6DOF Posenschätzung durch Datenfusion einer Time-of-Flight-Kamera und einer Farbkamera
N2  - 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.
N2  - Die 6DOF Posenschätzung von Objekten ist ein fundamentales Problem in vielen praktischen Robotikanwendungen, bei denen sich ein Ziel- oder Hindernisobjekt, einfacher oder komplexer Form, schnell in einer unstrukturierten schwierigen Umgebung bewegt. In dieser Forschungsarbeit wird zur Lösung des Problem ein 6DOF Posenschätzer entwickelt, der auf der Fusion von Daten einer Time-of-Flight-Kamera und einer Farbkamera beruht. Der Algorithmus ist in zwei Phasen unterteilt, ein Annealed Partikel-Filter bestimmt eine grobe Posenschätzung, welche mittels eines Gradientenverfahrens in einer zweiten Phase optimiert wird. In der ersten Phase wird jeder Partikel mittels sparse represenation ausgewertet, auf diese Weise kann eine große Inter-Frame-Bewegung des Zielobjektes gut behandelt werden. In der zweiten Phase wird die genaue Pose des Zielobjektes mittels des konventionellen, auf Entfernungsdaten beruhenden, Iterative Closest Point-Algorithmus aus der groben Schätzung der ersten Stufe berechnet. Der Algorithmus wurde dabei erweitert, so dass auch Informationen über das äußere Erscheinungsbild des Zielobjektes verwendet werden. Zur Kompensation von signifikanten Beleuchtungsschwankungen während des Trackings, wurde eine Modellierung der Ausleuchtung mittels Kugelflächenfunktionen erforscht und in beide Stufen der Posenschätzung integriert. Die Leistungsfähigkeit, Robustheit und Genauigkeit des entwickelten Algorithmus wurde in Experimenten im Innen- und Außenbereich mit verschiedenen Zielobjekten gezeigt. Zudem konnte gezeigt werden, dass die Schätzung mit Hilfe von Grafikprozessoren in Echtzeit möglich ist.
T3  - Forschungsberichte in der Robotik = Research Notes in Robotics - 10 
KW  - Mustererkennung
KW  - Maschinelles Sehen
KW  - Sensor
KW  - 3D Vision
KW  - 6DOF Pose Estimation
KW  - Visual Tracking
KW  - Pattern Recognition
KW  - Computer Vision
KW  - 3D Sensor
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-105089
SN  - 978-3-923959-97-6
ER  - 
TY  - JOUR
A1  - Steininger, Michael
A1  - Kobs, Konstantin
A1  - Davidson, Padraig
A1  - Krause, Anna
A1  - Hotho, Andreas
T1  - Density-based weighting for imbalanced regression
JF  - Machine Learning
N2  - In many real world settings, imbalanced data impedes model performance of learning algorithms, like neural networks, mostly for rare cases. This is especially problematic for tasks focusing on these rare occurrences. For example, when estimating precipitation, extreme rainfall events are scarce but important considering their potential consequences. While there are numerous well studied solutions for classification settings, most of them cannot be applied to regression easily. Of the few solutions for regression tasks, barely any have explored cost-sensitive learning which is known to have advantages compared to sampling-based methods in classification tasks. In this work, we propose a sample weighting approach for imbalanced regression datasets called DenseWeight and a cost-sensitive learning approach for neural network regression with imbalanced data called DenseLoss based on our weighting scheme. DenseWeight weights data points according to their target value rarities through kernel density estimation (KDE). DenseLoss adjusts each data point’s influence on the loss according to DenseWeight, giving rare data points more influence on model training compared to common data points. We show on multiple differently distributed datasets that DenseLoss significantly improves model performance for rare data points through its density-based weighting scheme. Additionally, we compare DenseLoss to the state-of-the-art method SMOGN, finding that our method mostly yields better performance. Our approach provides more control over model training as it enables us to actively decide on the trade-off between focusing on common or rare cases through a single hyperparameter, allowing the training of better models for rare data points.
KW  - supervised learning
KW  - imbalanced regression
KW  - cost-sensitive learning
KW  - sample weighting
KW  - Kerneldensity estimation
Y1  - 2021
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-269177
SN  - 1573-0565
VL  - 110
IS  - 8
ER  - 
TY  - JOUR
A1  - Steininger, Michael
A1  - Abel, Daniel
A1  - Ziegler, Katrin
A1  - Krause, Anna
A1  - Paeth, Heiko
A1  - Hotho, Andreas
T1  - ConvMOS: climate model output statistics with deep learning
JF  - Data Mining and Knowledge Discovery
N2  - Climate models are the tool of choice for scientists researching climate change. Like all models they suffer from errors, particularly systematic and location-specific representation errors. One way to reduce these errors is model output statistics (MOS) where the model output is fitted to observational data with machine learning. In this work, we assess the use of convolutional Deep Learning climate MOS approaches and present the ConvMOS architecture which is specifically designed based on the observation that there are systematic and location-specific errors in the precipitation estimates of climate models. We apply ConvMOS models to the simulated precipitation of the regional climate model REMO, showing that a combination of per-location model parameters for reducing location-specific errors and global model parameters for reducing systematic errors is indeed beneficial for MOS performance. We find that ConvMOS models can reduce errors considerably and perform significantly better than three commonly used MOS approaches and plain ResNet and U-Net models in most cases. Our results show that non-linear MOS models underestimate the number of extreme precipitation events, which we alleviate by training models specialized towards extreme precipitation events with the imbalanced regression method DenseLoss. While we consider climate MOS, we argue that aspects of ConvMOS may also be beneficial in other domains with geospatial data, such as air pollution modeling or weather forecasts.
KW  - Klima
KW  - Modell
KW  - Deep learning
KW  - Neuronales Netz
KW  - climate
KW  - neural networks
KW  - model output statistics
Y1  - 2023
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-324213
SN  - 1384-5810
VL  - 37
IS  - 1
ER  - 
TY  - JOUR
A1  - Steinhaeusser, Sophia C.
A1  - Oberdörfer, Sebastian
A1  - von Mammen, Sebastian
A1  - Latoschik, Marc Erich
A1  - Lugrin, Birgit
T1  - Joyful adventures and frightening places – designing emotion-inducing virtual environments
JF  - Frontiers in Virtual Reality
N2  - Virtual environments (VEs) can evoke and support emotions, as experienced when playing emotionally arousing games. We theoretically approach the design of fear and joy evoking VEs based on a literature review of empirical studies on virtual and real environments as well as video games’ reviews and content analyses. We define the design space and identify central design elements that evoke specific positive and negative emotions. Based on that, we derive and present guidelines for emotion-inducing VE design with respect to design themes, colors and textures, and lighting configurations. To validate our guidelines in two user studies, we 1) expose participants to 360° videos of VEs designed following the individual guidelines and 2) immerse them in a neutral, positive and negative emotion-inducing VEs combining all respective guidelines in Virtual Reality. The results support our theoretically derived guidelines by revealing significant differences in terms of fear and joy induction.
KW  - virtual reality
KW  - virtual environments
KW  - immersion
KW  - emotions
KW  - design
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-284831
SN  - 2673-4192
VL  - 3
ER  - 
TY  - THES
A1  - Staehle, Barbara
T1  - Modeling and Optimization Methods for Wireless Sensor and Mesh Networks
T1  - Modellierungs- und Optimierungs-Methoden für drahtlose Sensor- und Mesh-Netze
N2  - Im Internet der Zukunft werden Menschen nicht nur mit Menschen, sondern auch mit „Dingen“, und sogar „Dinge“ mit „Dingen“ kommunizieren. Zusätzlich wird das Bedürfnis steigen, immer und überall Zugang zum Internet zu haben. Folglich gewinnen drahtlose Sensornetze (WSNs) und drahtlose Mesh-Netze (WMNs) an Bedeutung, da sie Daten über die Umwelt ins Internet liefern, beziehungsweise einfache Internet-Zugangsmöglichkeiten schaffen. In den vier Teilen dieser Arbeit werden unterschiedliche Modellierungs- und Optimierungsmethoden für WSNs und WMNs vorgestellt. Der Energieverbrauch ist die wichtigste Metrik, wenn es darum geht die Kommunikation in einem WSN zu optimieren. Da sich in der Literatur sehr viele unterschiedliche Energiemodelle finden, untersucht der erste Teil der Arbeit welchen Einfluss unterschiedliche Energiemodelle auf die Optimierung von WSNs haben. Aufbauend auf diesen Überlegungen beschäftigt sich der zweite Teil der Arbeit mit drei Problemen, die überwunden werden müssen um eine standardisierte energieeffiziente Kommunikations-Lösung für WSNs basierend auf IEEE 802.15.4 und ZigBee zu realisieren. Für WMNs sind beide Probleme von geringem Interesse, die Leistung des Netzes jedoch umso mehr. Der dritte Teil der Arbeit führt daher Algorithmen für die Berechnung des Max-Min fairen (MMF) Netzwerk-Durchsatzes in WMNs mit mehreren Linkraten und Internet-Gateways ein. Der letzte Teil der Arbeit untersucht die Auswirkungen des LRA-Konzeptes. Dessen grundlegende Idee ist die folgende. Falls für einen Link eine niedrigere Datenrate als theoretisch möglich verwendet wird, sinkt zwar der Link-Durchsatz, jedoch ist unter Umständen eine größere Anzahl von gleichzeitigen Übertragungen möglich und der Gesamt-Durchsatz des Netzes kann sich erhöhen. Mithilfe einer analytischen LRA Formulierung und einer systematischen Studie kann gezeigt werden, dass eine netzwerkweite Zuordnung robusterer Datenraten als nötig zu einer Erhöhung des MMF Netzwerk-Durchsatzes führt. Desweitern kann gezeigt werden, dass sich LRA positiv auf die Leistungsfähigkeit eines IEEE 802.11 WMNs auswirkt und für die Optimierung des Netzes genutzt werden kann.
N2  - In the future Internet, the people-centric communication paradigm will be complemented by a ubiquitous communication among people and devices, or even a communication between devices. This comes along with the need for a more flexible, cheap, widely available Internet access. Two types of wireless networks are considered most appropriate for attaining those goals. While wireless sensor networks (WSNs) enhance the Internet’s reach by providing data about the properties of the environment, wireless mesh networks (WMNs) extend the Internet access possibilities beyond the wired backbone. This monograph contains four chapters which present modeling and optimization methods for WSNs and WMNs. Minimizing energy consumptions is the most important goal of WSN optimization and the literature consequently provides countless energy consumption models. The first part of the monograph studies to what extent the used energy consumption model influences the outcome of analytical WSN optimizations. These considerations enable the second contribution, namely overcoming the problems on the way to a standardized energy-efficient WSN communication stack based on IEEE 802.15.4 and ZigBee. For WMNs both problems are of minor interest whereas the network performance has a higher weight. The third part of the work, therefore, presents algorithms for calculating the max-min fair network throughput in WMNs with multiple link rates and Internet gateway. The last contribution of the monograph investigates the impact of the LRA concept which proposes to systematically assign more robust link rates than actually necessary, thereby allowing to exploit the trade-off between spatial reuse and per-link throughput. A systematical study shows that a network-wide slightly more conservative LRA than necessary increases the throughput of a WMN where max-min fairness is guaranteed. It moreover turns out that LRA is suitable for increasing the performance of a contention-based WMN and is a valuable optimization tool.
T3  - Würzburger Beiträge zur Leistungsbewertung Verteilter Systeme - 01/11 
KW  - Drahtloses Sensorsystem
KW  - Drahtloses vermaschtes Netz
KW  - Modellierung
KW  - Optimierung
KW  - IEEE 802.11
KW  - IEEE 802.15.4
KW  - Energieeffizienz
KW  - Fairness
KW  - Linkratenanpassung
KW  - Energy efficiency
KW  - Fairness
KW  - Link rate adaptation
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-64884
ER  - 
TY  - THES
A1  - Spoerhase, Joachim
T1  - Competitive and Voting Location
T1  - Kompetitive und präferenzbasierte Standortprobleme
N2  - We consider competitive location problems where two competing providers place their facilities sequentially and users can decide between the competitors. We assume that both competitors act non-cooperatively and aim at maximizing their own benefits. We investigate the complexity and approximability of such problems on graphs, in particular on simple graph classes such as trees and paths. We also develop fast algorithms for single competitive location problems where each provider places a single facilty. Voting location, in contrast, aims at identifying locations that meet social criteria. The provider wants to satisfy the users (customers) of the facility to be opened. In general, there is no location that is favored by all users. Therefore, a satisfactory compromise has to be found. To this end, criteria arising from voting theory are considered. The solution of the location problem is understood as the winner of a virtual election among the users of the facilities, in which the potential locations play the role of the candidates and the users represent the voters. Competitive and voting location problems turn out to be closely related.
N2  - Wir betrachten kompetitive Standortprobleme, bei denen zwei konkurrierende Anbieter ihre Versorger sequenziell platzieren und die Kunden sich zwischen den Konkurrenten entscheiden können. Wir nehmen an, dass beide Konkurrenten nicht-kooperativ agieren und auf die Maximierung ihres eigenen Vorteils abzielen. Wir untersuchen die Komplexität und Approximierbarkeit solcher Probleme auf Graphen, insbesondere auf einfachen Graphklassen wie Bäumen und Pfaden. Ferner entwickeln wir schnelle Algorithmen für kompetitive Einzelstandortprobleme, bei denen jeder Anbieter genau einen Versorger errichtet. Im Gegensatz dazu geht es bei Voting-Standortproblemen um die Bestimmung eines Standorts, der die Benutzer oder Kunden soweit wie möglich zufrieden stellt. Solche Fragestellungen sind beispielsweise bei der Planung öffentlicher Einrichtungen relevant. In den meisten Fällen gibt es keinen Standort, der von allen Benutzern favorisiert wird. Daher muss ein Kompromiss gefunden werden. Hierzu werden Kriterien betrachtet, die auch in Wahlsystemen eingesetzt werden: Ein geeigneter Standort wird als Sieger einer gedachten Wahl verstanden, bei der die möglichen Standorte die zur Wahl stehenden Kandidaten und die Kunden die Wähler darstellen. Kompetitive Standortprobleme und Voting-Standortprobleme erweisen sich als eng miteinander verwandt.
KW  - Standortproblem
KW  - NP-hartes Problem
KW  - Approximationsalgorithmus
KW  - Graph
KW  - Effizienter Algorithmus
KW  - competitive location
KW  - voting location
KW  - NP-hardness
KW  - approximation algorithm
KW  - efficient algorithm
KW  - graph
KW  - tree
KW  - graph decomposition
Y1  - 2009
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-52978
ER  - 
TY  - RPRT
A1  - Simon, Manuel
A1  - Gallenmüller, Sebastian
A1  - Carle, Georg
T1  - Never Miss Twice - Add-On-Miss Table Updates in Software Data Planes
T2  - KuVS Fachgespräch - Würzburg Workshop on Modeling, Analysis and Simulation of Next-Generation Communication Networks 2023 (WueWoWAS’23)
N2  - State Management at line rate is crucial for critical applications in next-generation networks. P4 is a language used in software-defined networking to program the data plane. The data plane can profit in many circumstances when it is allowed to manage its state without any detour over a controller. This work is based on a previous study by investigating the potential and performance of add-on-miss insertions of state by the data plane. The state keeping capabilities of P4 are limited regarding the amount of data and the update frequency. We follow the tentative specification of an upcoming portable-NIC-architecture and implement these changes into the software P4 target T4P4S. We show that insertions are possible with only a slight overhead compared to lookups and evaluate the influence of the rate of insertions on their latency.
KW  - SDN
KW  - state management
KW  - P4
KW  - Add-on-Miss
Y1  - 2023
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-322071
ER  - 
TY  - JOUR
A1  - Seufert, Anika
A1  - Schröder, Svenja
A1  - Seufert, Michael
T1  - Delivering User Experience over Networks: Towards a Quality of Experience Centered Design Cycle for Improved Design of Networked Applications
JF  - SN Computer Science
N2  - To deliver the best user experience (UX), the human-centered design cycle (HCDC) serves as a well-established guideline to application developers. However, it does not yet cover network-specific requirements, which become increasingly crucial, as most applications deliver experience over the Internet. The missing network-centric view is provided by Quality of Experience (QoE), which could team up with UX towards an improved overall experience. By considering QoE aspects during the development process, it can be achieved that applications become network-aware by design. In this paper, the Quality of Experience Centered Design Cycle (QoE-CDC) is proposed, which provides guidelines on how to design applications with respect to network-specific requirements and QoE. Its practical value is showcased for popular application types and validated by outlining the design of a new smartphone application. We show that combining HCDC and QoE-CDC will result in an application design, which reaches a high UX and avoids QoE degradation.
KW  - user experience
KW  - human-centered design
KW  - design cycle
KW  - application design
KW  - quality of experience
Y1  - 2021
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-271762
SN  - 2661-8907
VL  - 2
IS  - 6
ER  - 
TY  - JOUR
A1  - Seufert, Anika
A1  - Poignée, Fabian
A1  - Seufert, Michael
A1  - Hoßfeld, Tobias
T1  - Share and multiply: modeling communication and generated traffic in private WhatsApp groups
JF  - IEEE Access
N2  - Group-based communication is a highly popular communication paradigm, which is especially prominent in mobile instant messaging (MIM) applications, such as WhatsApp. Chat groups in MIM applications facilitate the sharing of various types of messages (e.g., text, voice, image, video) among a large number of participants. As each message has to be transmitted to every other member of the group, which multiplies the traffic, this has a massive impact on the underlying communication networks. However, most chat groups are private and network operators cannot obtain deep insights into MIM communication via network measurements due to end-to-end encryption. Thus, the generation of traffic is not well understood, given that it depends on sizes of communication groups, speed of communication, and exchanged message types. In this work, we provide a huge data set of 5,956 private WhatsApp chat histories, which contains over 76 million messages from more than 117,000 users. We describe and model the properties of chat groups and users, and the communication within these chat groups, which gives unprecedented insights into private MIM communication. In addition, we conduct exemplary measurements for the most popular message types, which empower the provided models to estimate the traffic over time in a chat group.
KW  - communication models
KW  - group-based communication
KW  - mobile instant messaging
KW  - mobile messaging application
KW  - private chat groups
KW  - WhatsApp
Y1  - 2023
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-349430
VL  - 11
ER  - 
TY  - JOUR
A1  - Seufert, Anika
A1  - Poignée, Fabian
A1  - Hoßfeld, Tobias
A1  - Seufert, Michael
T1  - Pandemic in the digital age: analyzing WhatsApp communication behavior before, during, and after the COVID-19 lockdown
JF  - Humanities and Social Sciences Communications
N2  - The strict restrictions introduced by the COVID-19 lockdowns, which started from March 2020, changed people’s daily lives and habits on many different levels. In this work, we investigate the impact of the lockdown on the communication behavior in the mobile instant messaging application WhatsApp. Our evaluations are based on a large dataset of 2577 private chat histories with 25,378,093 messages from 51,973 users. The analysis of the one-to-one and group conversations confirms that the lockdown severely altered the communication in WhatsApp chats compared to pre-pandemic time ranges. In particular, we observe short-term effects, which caused an increased message frequency in the first lockdown months and a shifted communication activity during the day in March and April 2020. Moreover, we also see long-term effects of the ongoing pandemic situation until February 2021, which indicate a change of communication behavior towards more regular messaging, as well as a persisting change in activity during the day. The results of our work show that even anonymized chat histories can tell us a lot about people’s behavior and especially behavioral changes during the COVID-19 pandemic and thus are of great relevance for behavioral researchers. Furthermore, looking at the pandemic from an Internet provider perspective, these insights can be used during the next pandemic, or if the current COVID-19 situation worsens, to adapt communication networks to the changed usage behavior early on and thus avoid network congestion.
KW  - cultural and media studies
KW  - information systems and information technology
KW  - science, technology and society
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-300261
VL  - 9
ER  - 
TY  - RPRT
A1  - Sertbas Bülbül, Nurefsan
A1  - Ergenc, Doganalp
A1  - Fischer, Mathias
T1  - Evaluating Dynamic Path Reconfiguration for Time Sensitive Networks
T2  - Würzburg Workshop on Next-Generation Communication Networks (WueWoWas'22)
N2  - In time-sensitive networks (TSN) based on 802.1Qbv, i.e., the time-aware Shaper (TAS) protocol, precise transmission schedules and, paths are used to ensure end-to-end deterministic communication. Such resource reservations for data flows are usually established at the startup time of an application and remain untouched until the flow ends. There is no way to migrate existing flows easily to alternative paths without inducing additional delay or wasting resources. Therefore, some of the new flows cannot be embedded due to capacity limitations on certain links which leads to sub-optimal flow assignment. As future networks will need to support a large number of lowlatency flows, accommodating new flows at runtime and adapting existing flows accordingly becomes a challenging problem. In this extended abstract we summarize a previously published paper of us [1]. We combine software-defined networking (SDN), which provides better control of network flows, with TSN to be able to seamlessly migrate time-sensitive flows. For that, we formulate an optimization problem and propose different dynamic path configuration strategies under deterministic communication requirements. Our simulation results indicate that regularly reconfiguring the flow assignments can improve the latency of time-sensitive flows and can increase the number of flows embedded in the network around 4% in worst-case scenarios while still satisfying individual flow deadlines.
KW  - Datennetz
KW  - SDN
KW  - dynamic flow migration
KW  - reconfiguration
KW  - TSN
KW  - path computation
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-280743
ER  - 
TY  - THES
A1  - Selbach, Stefan
T1  - Hybride bitparallele Volltextsuche
T1  - Hybrid Bit-parallel Full-text Search
N2  - Der große Vorteil eines q-Gramm Indexes liegt darin, dass es möglich ist beliebige Zeichenketten in einer Dokumentensammlung zu suchen. Ein Nachteil jedoch liegt darin, dass bei größer werdenden Datenmengen dieser Index dazu neigt, sehr groß zu werden, was mit einem deutlichem Leistungsabfall verbunden ist. In dieser Arbeit wird eine neuartige Technik vorgestellt, die die Leistung eines q-Gramm Indexes mithilfe zusätzlicher M-Matrizen für jedes q-Gramm und durch die Kombination mit einem invertierten Index erhöht. Eine M-Matrix ist eine Bit-Matrix, die Informationen über die Positionen eines q-Gramms enthält. Auch bei der Kombination von zwei oder mehreren Q-Grammen bieten diese M-Matrizen Informationen über die Positionen der Kombination. Dies kann verwendet werden, um die Komplexität der Zusammenführung der q-Gramm Trefferlisten für eine gegebene Suchanfrage zu reduzieren und verbessert die Leistung des n-Gramm-invertierten Index. Die Kombination mit einem termbasierten invertierten Index beschleunigt die durchschnittliche Suchzeit zusätzlich und vereint die Vorteile beider Index-Formate. Redundante Informationen werden in dem q-Gramm Index reduziert und weitere Funktionalität hinzugefügt, wie z.B. die Bewertung von Treffern nach Relevanz, die Möglichkeit, nach Konzepten zu suchen oder Indexpartitionierungen nach Wichtigkeit der enthaltenen Terme zu erstellen.
N2  - The major advantage of the n-gram inverted index is the possibility to locate any given substring in a document collection. Nevertheless, the n-gram inverted index also has its drawbacks: If the collections are getting bigger, this index tends to be very large and the performance drops significantly. A novel technique is proposed to enhance the performance of an n-gram inverted index by using additional m-matrixes for each n-gram and by combining it with an inverted index. An m-matrix is a bit matrix containing information about the positions of an n-gram. When combining two or more n-grams, these m-matrixes provide information about the positions of the combination. This can be used to reduce the complexity of merging the n-gram postings lists for a given search and improves the performance of the n-gram inverted index. The combination with a term based inverted index speeds up the average search time even more and combines the benefits of both index formats. Redundant information is reduced in the n-gram index and further functionality is added like the ranking of hits, the possibility to search for concepts and to create index partitions according to the relevance of the contained terms.
KW  - Information Retrieval
KW  - Information-Retrieval-System
KW  - Suchverfahren
KW  - Invertierte Liste
KW  - n-Gramm
KW  - q-Gramm
KW  - Volltextsuche
KW  - Bit Parallelität
KW  - Konzeptsuche
KW  - q-gram
KW  - n-gram
KW  - bit-parallel
KW  - full-text search
KW  - concept search
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-66476
ER  - 
TY  - THES
A1  - Schäfer, Dirk
T1  - Globale Selbstlokalisation autonomer mobiler Roboter - Ein Schlüsselproblem der Service-Robotik
T1  - The global self-localisation problem - a key problem in the field of service robotics
N2  - Die Dissertation behandelt die Problemstellung der globalen Selbstlokalisation autonomer mobiler Roboter, welche folgendermaßen beschrieben werden kann: Ein mobiler Roboter, eingesetzt in einem Gebäude, kann unter Umständen das Wissen über seinen Standort verlieren. Man geht nun davon aus, dass dem Roboter eine Gebäudekarte als Modell zur Verfügung steht. Mit Hilfe eines Laser-Entfernungsmessers kann das mobile Gerät neue Informationen aufnehmen und damit bei korrekter Zuordnung zur Modellkarte geeignete hypothetische Standorte ermitteln. In der Regel werden diese Positionen aber mehrdeutig sein. Indem sich der Roboter intelligent in seiner Einsatzumgebung bewegt, kann er die ursprünglichen Sensordaten verifizieren und ermittelt im besten Fall seine tatsächliche Position.Für diese Problemstellung wird ein neuer Lösungsansatz in Theorie und Praxis präsentiert, welcher die jeweils aktuelle lokale Karte und damit alle Sensordaten mittels feature-basierter Matchingverfahren auf das Modell der Umgebung abbildet. Ein Explorationsalgorithmus bewegt den Roboter während der Bewegungsphase autonom zu Sensorpunkten, welche neue Informationen bereitstellen. Während der Bewegungsphase werden dabei die bisherigen hypothetischen Positionen bestärkt oder geschwächt, sodaß nach kurzer Zeit eine dominante Position, die tatsächliche Roboterposition,übrigbleibt.
N2  - This thesis is dealing with the global self-localisation problem, which is known to be one of the hardest problems among autonomous mobile systems. The problem can be described as follows: A mobile robot agent has a map of the environment but does not know its position. It is equipped with ultransonic sensors and a laser range finder as main sensor. The goal of the robot agent is to recognize its true position within the environment.The level of complexity of this task increases with the size and also with the level of symmetry of the indoor environment. To cope with the problem a new approach will be presented in this thesis using state of the art map building and exploration algorithms as well as feature based localisation methods. Decomposition of the global map into a number of submaps, informative feature selection and multiple submap localisation queries ensure the road of success. The capability of the approach to global self-localising the robot is pointed out by several practical studies.
KW  - Mobiler Roboter
KW  - Autonomer Roboter
KW  - Lokalisation
KW  - Globale Selbstlokalisation
KW  - Mobile Roboter
KW  - Kartierung
KW  - Feature-Matching
KW  - Gllobal self-localisation
KW  - mobile robots
KW  - slam
KW  - feature-matching
Y1  - 2003
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-7601
ER  - 
TY  - THES
A1  - Schmitz, Heinz
T1  - The Forbidden Pattern Approach to Concatenation Hierarchies
T1  - Verbotsmuster und Hierarchien regulärer sternfreier Sprachen
N2  - 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.
N2  - Die Arbeit beschaeftigt sich mit der Frage nach der Berechenbarkeit der Punkttiefe sternfreier regulaerer Sprachen. Dabei handelt es sich um die Aufgabe, zu einer gegebenen sternfreien regulaeren Sprache die minimal moegliche Anzahl von Wechseln zwischen den Operationen Konkatenation einerseits und Durchschnitt, Vereinigung, Komplement andererseits in einem sternfreien regulaeren Ausdruck fuer die gegebene Sprache zu bestimmen. Diese Frage wurde 1971 erstmals aufgeworfen (Brzozowski/Cohen) und gilt neben dem Problem der erweiterten Sternhoehe als eine der schwierigsten offenen Fragen der Theorie der regulaeren Sprachen. Formal fassen laesst sich das Problem der Punkttiefe durch Hierarchien von Klassen sternfreier regulaerer Sprachen B(0), B(1/2), B(1), B(3/2),...sowie L(0), L(1/2), L(1), L(3/2),.... die - ausgehend von einzelnen Buchstaben - mittels Alternierung zwischen Konkatenation und Booleschen Operationen definiert sind. Die Frage nach der Punkttiefe wird hier zur Frage nach der Entscheidbarkeit der Hierarchieklassen. In der Arbeit werden neue Fortschritte mittels sogenannter Verbotsmuster erzielt. Bei diesem Ansatz werden Klassen regulaerer Sprachen dadurch charakterisiert, dass in den zugehoerigen endlichen Automaten bestimmte Muster (Teilgraphen des Ueberfuehrungsgraphen) verboten werden. Gelingt eine solche Charakterisierung, folgt unmittelbar die Entscheidbarkeit der Klasse, da das Nichtvorhandensein eines Musters in einem gegebenen endlichen Automaten effektiv geprueft werden kann. Bisher war die Entscheidbarkeit von B(0), B(1/2), B(1) und L(0), L(1/2), L(1), L(3/2) bekannt. Mit Hilfe von Verbotsmustern erfolgt eine genaue Untersuchung dieser Klassen, die zu neuen Erkenntnissen ueber ihre innere Struktur fuehrt. Darueberhinaus gelingt der Nachweis der Entscheidbarkeit von B(3/2). Basierend auf diesen Ergebnissen wird eine Theorie der Verbotsmusteriteration entwickelt, die zur Einfuehrung von zwei neuen Hierarchien sternfreier regulaerer Sprachen fuehrt. Diese neuen Hierarchien sind zum einen entscheidbar, zum anderen stehen sie in enger Beziehung zu den Klassen B(n) und L(n). Es bleibt an dieser Stelle eine offene Frage, ob sie eventuell sogar mit ihnen uebereinstimmen. Fuer diese Vermutung werden einige Indizien gesammelt und somit ein neuer Weg fuer eine moegliche Loesung des Problems der Punkttiefe aufgezeigt. In diesem Zusammenhang erfolgt auch erstmals der Nachweis der Entscheidbarkeit der Klasse L(5/2) im eingeschraenkten Fall eines zweielementigen Alphabets.
KW  - Sternfreie Sprache
KW  - Dot-Depth-Hierarchie
KW  - Straubing-Th´erien-Hierarchie
KW  - Verbotenes Muster
KW  - Theoretische Informatik
KW  - reguläre Sprachen
KW  - endliche Automaten
KW  - Dot-Depth Problem
KW  - Entscheidbarkeit
KW  - Verbotsmuster
KW  - Theoretical Computer Science
KW  - regular languages
KW  - finite automata
KW  - dot-depth problem
KW  - decidability
KW  - forbidden patterns
Y1  - 2000
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-2832
ER  - 
TY  - THES
A1  - Schmidt, Marco
T1  - Ground Station Networks for Efficient Operation of Distributed Small Satellite Systems
T1  - Effizienter Betrieb von Verteilten Kleinsatelliten-Systemen mit Bodenstationsnetzwerken
N2  - The field of small satellite formations and constellations attracted growing attention, based on recent advances in small satellite engineering. The utilization of distributed space systems allows the realization of innovative applications and will enable improved temporal and spatial resolution in observation scenarios. On the other side, this new paradigm imposes a variety of research challenges. In this monograph new networking concepts for space missions are presented, using networks of ground stations. The developed approaches combine ground station resources in a coordinated way to achieve more robust and efficient communication links. Within this thesis, the following topics were elaborated to improve the performance in distributed space missions: Appropriate scheduling of contact windows in a distributed ground system is a necessary process to avoid low utilization of ground stations. The theoretical basis for the novel concept of redundant scheduling was elaborated in detail. Additionally to the presented algorithm was a scheduling system implemented, its performance was tested extensively with real world scheduling problems. In the scope of data management, a system was developed which autonomously synchronizes data frames in ground station networks and uses this information to detect and correct transmission errors. The system was validated with hardware in the loop experiments, demonstrating the benefits of the developed approach.
N2  - Satellitenformationen und Konstellationen rücken immer mehr in den Fokus aktueller Forschung, ausgelöst durch die jüngsten Fortschritte in der Kleinsatelliten-Entwicklung. Der Einsatz von verteilten Weltraumsystemen ermöglicht die Realisierung von innovativen Anwendungen auf Basis von hoher zeitlicher und räumlicher Auflösung in Observationsszenarien. Allerdings bringt dieses neue Paradigma der Raumfahrttechnik auch Herausforderungen in verschiedenen Forschungsfeldern mit sich. In dieser Dissertation werden neue Netzwerk-Konzepte für Raumfahrtmissionen unter Einsatz von Bodenstationnetzwerken vorgestellt. Die präsentierten Verfahren koordinieren verfügbare Bodenstationsressourcen um einen robusten und effizienten Kommunikationslink zu ermöglichen. In dieser Arbeit werden dabei folgende Themenfelder behandelt um die Performance in verteilten Raumfahrtmissionen zu steigern: Das Verteilen von Kontaktfenster (sogenanntes Scheduling) in verteilten Bodenstationssystem ist ein notwendiger Prozess um eine niedrige Auslastung der Stationen zu vermeiden. Die theoretische Grundlage für das Konzept des redundanten Scheduling wurde erarbeitet. Zusätztlich wurde das Verfahren in Form eines Scheduling Systems implementiert und dessen Performance ausführlich an real-world Szenarien getestet. Im Rahmen des Themenfeldes Data Management wurde ein System entwickelt, welches autonom Datenframes in Bodenstationsnetzwerken synchronisieren kann. Die in den Datenframes enthaltene Information wird genutzt um Übertragungsfehler zu erkennen und zu korrigieren. Das System wurde mit Hardware-in-the-loop Experimenten validiert und die Vorteile des entwickelten Verfahrens wurden gezeigt.
T3  - Forschungsberichte in der Robotik = Research Notes in Robotics - 6 
KW  - Kleinsatellit
KW  - Bodenstation
KW  - Verteiltes System
KW  - Scheduling
KW  - Ground Station Networks
KW  - Small Satellites
KW  - Distributed Space Systems
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-64999
SN  - 978-3-923959-77-8
ER  - 
TY  - JOUR
A1  - Schlör, Daniel
A1  - Ring, Markus
A1  - Hotho, Andreas
T1  - iNALU: Improved Neural Arithmetic Logic Unit
JF  - Frontiers in Artificial Intelligence
N2  - Neural networks have to capture mathematical relationships in order to learn various tasks. They approximate these relations implicitly and therefore often do not generalize well. The recently proposed Neural Arithmetic Logic Unit (NALU) is a novel neural architecture which is able to explicitly represent the mathematical relationships by the units of the network to learn operations such as summation, subtraction or multiplication. Although NALUs have been shown to perform well on various downstream tasks, an in-depth analysis reveals practical shortcomings by design, such as the inability to multiply or divide negative input values or training stability issues for deeper networks. We address these issues and propose an improved model architecture. We evaluate our model empirically in various settings from learning basic arithmetic operations to more complex functions. Our experiments indicate that our model solves stability issues and outperforms the original NALU model in means of arithmetic precision and convergence.
KW  - neural networks
KW  - machine learning
KW  - arithmetic calculations
KW  - neural architecture
KW  - experimental evaluation
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-212301
SN  - 2624-8212
VL  - 3
ER  - 
TY  - CHAP
A1  - Schlosser, Daniel
A1  - Jarschel, Michael
A1  - Duelli, Michael
A1  - Hoßfeld, Tobias
A1  - Hoffmann, Klaus
A1  - Hoffmann, Marco
A1  - Morper, Hans Jochen
A1  - Jurca, Dan
A1  - Khan, Ashiq
T1  - A Use Case Driven Approach to Network Virtualization
N2  - In today's Internet, services are very different in their requirements on the underlying transport network. In the future, this diversity will increase and it will be more difficult to accommodate all services in a single network. A possible approach to cope with this diversity within future networks is the introduction of support for running isolated networks for different services on top of a single shared physical substrate. This would also enable easy network management and ensure an economically sound operation. End-customers will readily adopt this approach as it enables new and innovative services without being expensive. In order to arrive at a concept that enables this kind of network, it needs to be designed around and constantly checked against realistic use cases. In this contribution, we present three use cases for future networks. We describe functional blocks of a virtual network architecture, which are necessary to support these use cases within the network. Furthermore, we discuss the interfaces needed between the functional blocks and consider standardization issues that arise in order to achieve a global consistent control and management structure of virtual networks.
KW  - Virtualisierung
KW  - Datenkommunikationsnetz
KW  - Internet
KW  - Rechnernetz
KW  - Anwendungsfall
KW  - Netzvirtualisierung
KW  - Standardisierung
KW  - Use case
KW  - network virtualization
KW  - future Internet architecture
KW  - standardization
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-55611
N1  - Accepted at IEEE Kaleidoscope 2010
ER  - 
TY  - THES
A1  - Schlosser, Daniel
T1  - Quality of Experience Management in Virtual Future Networks
T1  - Netzwerkmanagement unter Berücksichtigung der vom Benutzer erfahrenen Dienstgüte in virtuellen zukünftigen Netzen
N2  - Aktuell beobachten wir eine drastische Vervielfältigung der Dienste und Anwendungen, die das Internet für den Datentransport nutzen. Dabei unterscheiden sich die Anforderungen dieser Dienste an das Netzwerk deutlich. Das Netzwerkmanagement wird durch diese Diversität der nutzenden Dienste aber deutlich erschwert, da es einem Datentransportdienstleister kaum möglich ist, die unterschiedlichen Verbindungen zu unterscheiden, ohne den Inhalt der transportierten Daten zu analysieren. Netzwerkvirtualisierung ist eine vielversprechende Lösung für dieses Problem, da sie es ermöglicht für verschiedene Dienste unterschiedliche virtuelle Netze auf dem gleichen physikalischen Substrat zu betreiben. Diese Diensttrennung ermöglicht es, jedes einzelne Netz anwendungsspezifisch zu steuern. Ziel einer solchen Netzsteuerung ist es, sowohl die vom Nutzer erfahrene Dienstgüte als auch die Kosteneffizienz des Datentransports zu optimieren. Darüber hinaus wird es mit Netzwerkvirtualisierung möglich das physikalische Netz so weit zu abstrahieren, dass die aktuell fest verzahnten Rollen von Netzwerkbesitzer und Netzwerkbetreiber entkoppelt werden können. Darüber hinaus stellt Netzwerkvirtualisierung sicher, dass unterschiedliche Datennetze, die gleichzeitig auf dem gleichen physikalischen Netz betrieben werden, sich gegenseitig weder beeinflussen noch stören können. Diese Arbeit  beschäftigt sich mit ausgewählten Aspekten dieses Themenkomplexes und fokussiert sich darauf, ein virtuelles Netzwerk mit bestmöglicher Dienstqualität für den Nutzer zu betreiben und zu steuern. Dafür wird ein Top-down-Ansatz gewählt, der von den Anwendungsfällen, einer möglichen Netzwerkvirtualisierungs-Architektur und aktuellen Möglichkeiten der Hardwarevirtualisierung ausgeht. Im Weiteren fokussiert sich die Arbeit dann in Richtung Bestimmung und Optimierung der vom Nutzer erfahrenen Dienstqualität (QoE) auf Applikationsschicht und diskutiert Möglichkeiten zur Messung und Überwachung von wesentlichen Netzparametern in virtualisierten Netzen.
N2  - Currently, we observe a strong growth of services and applications, which use the Internet for data transport. However, the network requirements of these applications differ significantly. This makes network management difficult, since it complicated to separate network flows into application classes without inspecting application layer data. Network virtualization is a promising solution to this problem. It enables running different virtual network on the same physical substrate. Separating networks based on the service supported within allows controlling each network according to the specific needs of the application. The aim of such a network control is to optimize the user perceived quality as well as the cost efficiency of the data transport. Furthermore, network virtualization abstracts the network functionality from the underlying implementation and facilitates the split of the currently tightly integrated roles of Internet Service Provider and network owner. Additionally, network virtualization guarantees that different virtual networks run on the same physical substrate do not interfere with each other. This thesis discusses different aspects of the network virtualization topic. It is focused on how to manage and control a virtual network to guarantee the best Quality of Experience for the user. Therefore, a top-down approach is chosen. Starting with use cases of virtual networks, a possible architecture is derived and current implementation options based on hardware virtualization are explored. In the following, this thesis focuses on assessing the Quality of Experience perceived by the user and how it can be optimized on application layer. Furthermore, options for measuring and monitoring significant network parameters of virtual networks are considered.
T3  - Würzburger Beiträge zur Leistungsbewertung Verteilter Systeme - 01/12 
KW  - Netzwerkmanagement
KW  - Dienstgüte
KW  - Netzwerkvirtualisierung
KW  - QoS
KW  - QoE
KW  - Network Virtualization
KW  - Quality of Experience
KW  - Network Management
KW  - Quality of Service
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-69986
ER  - 
TY  - RPRT
A1  - Savvidis, Dimitrios
A1  - Roth, Robert
A1  - Tutsch, Dietmar
T1  - Static Evaluation of a Wheel-Topology for an SDN-based Network Usecase
T2  - Würzburg Workshop on Next-Generation Communication Networks (WueWoWas'22)
N2  - The increased occurrence of Software-Defined-Networking (SDN) not only improves the dynamics and maintenance of network architectures, but also opens up new use cases and application possibilities. Based on these observations, we propose a new network topology consisting of a star and a ring topology. This hybrid topology will be called wheel topology in this paper. We have considered the static characteristics of the wheel topology and compare them with known other topologies.
KW  - Datennetz
KW  - SDN
KW  - topology
KW  - wheel
Y1  - 2022
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-280715
ER  -