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Publications of Wolfgang Effelsberg

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Konferenz Beitrag

Forschungs Papier

  • Marcel Busse, Thomas Haenselmann und Wolfgang Effelsberg. , . 2005 An Energy-Efficient Forwarding Scheme for Wireless Sensor Networks , .
    Energy-efficient forwarding becomes important if resources and battery lifetime are limited such as in Wireless Sensor Networks. Although widely used, simple hop-based forwarding along a path from one node towards a sink can be very inefficient in terms of delivery rate as well as energy efficiency, especially in lossy environments. We will show that just minimizing the expected number of transmissions within the network is not always the most efficient forwarding strategy. Using a realistic link loss model, we derive two new forwarding schemes named Single-Link and Multi-Link Energy-Efficient Forwarding that trade off delivery rate and energy costs best by maximizing energy efficiency. Multi-Link Forwarding further benefits from addressing multiple receivers during packet forwarding, instead of a single one. By mathematical analyses, extensive simulations, and experimental experiments we contrast the performance of our approaches against a comprehensive framework of different forwarding strategies.
  • Marcel Busse, Thomas Haenselmann und Wolfgang Effelsberg. , . 2005 TECA : A Topology and Energy Control Algorithm for Sensor Networks , .
    A main challenge in the field of sensor networks is energy efficiency to prolong the sensor's operational lifetime. Due to low-cost hardware, nodes' placement or hardware design, recharging might be impossible. Since most energy is spent for radio communication, many approaches exist that put sensor nodes into sleep mode with the communication radio turned off. In this paper, we propose a new Topology and Energy Control Algorithm called TECA. We will show the performance of TECA by means of extensive simulations compared to two other approaches. In terms of operational lifetime, packet delivery and network connectivity, TECA shows promising results. Unlike many other simulations, we use an appropriate link loss model that was verified in reality. By measuring packet delivery rates, TECA is able to adapt to different environments while still maintaining network connectivity.
  • Holger Füßler, Marc Torrent-Moreno, Roland Krüger, Matthias Transier, Hannes Hartenstein und Wolfgang Effelsberg. , . 2005 Studying Vehicle Movements on Highways and their Impact on Ad-Hoc Connectivity , .
    While Mobile Ad-Hoc Networks are generally studied using a randomized node movement model such as the Random Way-Point model [8], Vehicular Ad-Hoc Networks deal with street-bound vehicles following a completely different movement pattern. This results - among other things - in a completely different connectivity situation and new challenges for data dissemination or routing/forwarding algorithms. Thus, researchers need a) suitable movement patterns for simulation, and b) a solid statistical understanding of the connectivity situation independent of the protocols utilized. In this work, we present a set of movement traces derived from typical situations on German Autobahns and an elaborate statistical analysis with respect to movement and connectivity relevant parameters. In addition, we present HWGui, a visualization, transformation, and evaluation package developed to study these scenarios. Beside the analysis capabilities HWGui is able, among other things, to generate movement files suitable for simulation with ns-2 [10].
  • Thomas King, Thomas Haenselmann, Stephan Kopf und Wolfgang Effelsberg. , . 2005 Positionierung mit Wireless-LAN und Bluetooth , .
    In diesem Artikel wird ein Überblick über bestehende Wireless-LAN- und Bluetooth-basierte Positionierungssysteme gegeben. Eine detaillierte identifikation der Merkmale und Eigenschaften der unterschiedlichen Systeme soll helfen, Positionierungsverfahren anhand ihrer Eigenschaften einzuordnen.
  • Stephan Kopf, Thomas Haenselmann und Wolfgang Effelsberg. , . 2005 Robust Character Recognition in Low-Resolution Images and Videos , .
    Although OCR techniques work very reliably for high-resolution documents, the recognition of superimposed text in low-resolution images or videos with a complex background is still a challenge. Three major parts characterize our system for recognition of superimposed text in images and videos: localization of text regions, segmentation (binarization) of characters, and recognition. We use standard approaches to locate text regions and focus in this paper on the last two steps. Many approaches (e.g., projection profiles, k-mean clustering) do not work very well for separating characters with very small font sizes. We apply in a vertical direction a shortest-path algorithm to separate the characters in a text line. The recognition of characters is based on the curvature scale space (CSS) approach which smoothes the contour of a character with a Gaussian kernel and tracks its inflection points. A major drawback of the CSS method is its poor representation of convex segments: Convex objects cannot be represented at all due to missing inflection points. We have extended the CSS approach to generate feature points for concave and convex segments of a contour. This generic approach is not only applicable to text characters but to arbitrary objects as well. In the experimental results, we compare our approach against a pattern matching algorithm, two classification algorithms based on contour analysis, and a commercial OCR system. The overall recognition results are good enough even for the indexing of low resolution images and videos.
  • Stephan Kopf, Nicolai Scheele und Wolfgang Effelsberg. , . 2005 The Interactive Lecture: Teaching and Learning Technologies for Large Classrooms , .
    Conventional lectures in large classrooms are connected to fundamental didactic problems due to a lack of interactivity and feedback opportunities. In an interactive lecture each student is equipped with a light-weight, mobile device that can be used to interact with the lecturer during the lesson, thus creating an additional channel of communication. These devices support new teaching and learning paradigms such as participatory simulations. In this paper, we present our experiences with the usage of mobile devices in lectures. After discussing the didactic benefits of interactive lectures, we introduce the software toolkits used in our scenarios, we highlight selected tools like a quiz tool or a support tool for participatory simulation, and present major results from six studies we have conducted.
  • Roland Krüger, Holger Füßler, Marc Torrent-Moreno, Matthias Transier, Hannes Hartenstein und Wolfgang Effelsberg. , . 2005 Statistical Analysis of the FleetNet Highway Movement Patterns , .
    The major objective of the FleetNet project [5, 2] was to develop a platform for inter-vehicle communication based on the principles of ad-hoc communication. In its process, unicast datagram routing served as one of the research focuses to identify and conquer the challenges of data forwarding in vehicular scenarios. Among others, car movement on highways was a scenario we paid attention to. To serve as a basis for network simulation, DaimlerChrysler provided realistic highway movement traces resulting from their own vehicular movement research [3]. This document is the complement to the Technical Report [4] where we describe the work done on the DaimlerChrysler traces in order to: a) model bidirectional scenarios, b) obtain Tcl scenarios compatible with the ns-2 simulator, and c) understand the vehicle distribution and movement of the resulting scenarios from a connectivity point of view. This report consists of the whole statistical evaluation of the basic set of scenarios listed in [4] and available to the VANET (Vehicular Ad-Hoc Network) community at [1]. We highly recommend the reading of [4], which describes the structure of this document and all parameters being analyzed.
  • Björn Scheuermann, Holger Füßler, Matthias Transier, Marcel Busse, Martin Mauve und Wolfgang Effelsberg. , . 2005 Huginn: A 3D Visualizer for Wireless ns-2 Traces , .
    Discrete-event network simulation is a major tool for the research and development of mobile ad-hoc networks (MANETs). These simulations are used for debugging, teaching, understanding, and performance-evaluating MANET protocols. For the first three tasks, visualization of the processes occurring in the simulated network is crucial for verification and credibility of the generated results. Working with the popular network simulator ns-2, we have not yet found a visualization toolkit capable of reading native ns-2 trace files and providing means to change the evaluated parameters without changing the visualization software. Thus, we developed Huginn, a software providing an intuitive way to visualize simulation properties and to determine how they should be displayed without the need of programming. In addition, Huginn has a 3D interface allowing a high exploitation of the (human) user’s perceptive system. It helps to handle the significant cognitive load associated with the mental reconstruction of simulated network processes. Besides presenting the software interface and architecture, we describe algorithmic solutions that might be of a more general interest for similar problems.
[2018] [2017] [2016] [2015] [2014] [2013] [2012] [2011] [2010] [2009] [2008] [2007] [2006] 2005 [2004] [2003] [2002] [2001] [2000] [1999] [1998] [1997] [1996] [1995] [1994] [1993] [1992] [1991] [1990] [1988] [1987] [1986] [1985] [1984] [1983] [1981] [1980] [1979]