Markus Völker

Karlsruhe Institute of Technology, Carlsruhe, Baden-Württemberg, Germany

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Publications (9)0.94 Total impact

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    ABSTRACT: This paper addresses a large-scale power plant maintenance scheduling and production planning problem, which has been proposed by the ROADEF/EURO Challenge 2010. We develop two lower bounds for the problem: a greedy heuristic and a flow network for which a minimum cost flow problem has to be solved.Furthermore, we present a solution approach that combines a constraint programming formulation of the problem with several heuristics. The problem is decomposed into an outage scheduling and a production planning phase. The first phase is solved by a constraint program, which additionally ensures the feasibility of the remaining problem. In the second phase we utilize a greedy heuristic—developed from our greedy lower bound—to assign production levels and refueling amounts for a given outage schedule. All proposed strategies are shown to be competitive in an experimental evaluation.
    Journal of Scheduling 01/2013; 16(6). · 0.94 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper addresses a large-scale power plant maintenance scheduling and production planning problem, which has been proposed by the ROADEF/EURO Challenge 2010. We develop two lower bounds for the problem: a greedy heuristic and a flow network for which a minimum cost flow problem has to be solved. Furthermore, we present a solution approach that combines a constraint programming formulation of the problem with several heuristics. The problem is decomposed into an outage scheduling and a production planning phase. The first phase is solved by a constraint program, which additionally ensures the feasibility of the remaining problem. In the second phase we utilize a greedy heuristic – developed from our greedy lower bound – to assign production levels and refueling amounts for a given outage schedule. All proposed strategies are shown to be competitive in an experimental evaluation.
    Journal of Scheduling 01/2013; 16(6). · 0.94 Impact Factor
  • Fabian Fuchs, Markus Völker, Dorothea Wagner
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    ABSTRACT: Topology control aims at optimizing throughput and energy consumption of wireless networks by adjusting transmission powers or by restricting the communication to a well-chosen subset of communication links. Over the years, a variety of topology control algorithms have been proposed. However, many of these algorithms have been mainly studied from a theoretical point of view. On the other hand, existing simulation-based studies often only compare few approaches based on rather simple simulations, e.g., abstracting from communication protocols. In this paper, we present a thorough study of a variety of topology control algorithms based on the methodology of algorithm engineering. To analyze achievable performance improvements for communication according to the IEEE 802.11g standard we use the ns-3 network simulator. In addition to analyzing the communication throughput, we also study the effects of topology control on the energy demand in the network. Based on our simulation results, we then identify properties of the computed topologies that are essential for the achieved improvements. The gained insights are finally used to motivate an extension of the well-known XTC algorithm, which enables significant performance improvements in the considered application scenario.
    Proceedings of the First Mediterranean conference on Design and Analysis of Algorithms; 12/2012
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    ABSTRACT: We propose two novel algorithms for distributed and location-free boundary recognition in wireless sensor networks. Both approaches enable a node to decide autonomously whether it is a boundary node, based solely on connectivity information of a small neighborhood. This makes our algorithms highly applicable for dynamic networks where nodes can move or become inoperative. We compare our algorithms qualitatively and quantitatively with several previous approaches. In extensive simulations, we consider various models and scenarios. Although our algorithms use less information than most other approaches, they produce significantly better results. They are very robust against variations in node degree and do not rely on simplified assumptions of the communication model. Moreover, they are much easier to implement on real sensor nodes than most existing approaches.
    Computing Research Repository - CORR. 03/2011;
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    Bastian Katz, Markus Völker, Dorothea Wagner
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    ABSTRACT: Scheduling of transmissions is one of the most fundamental problems in the context of wireless networks. In this article, we consider the problem of computing power efficient schedules with high throughput. We answer the open question concerning the complexity of scheduling with power control in the SINRG model of interference. Based on a novel scheme for dynamic computation of optimum transmission powers in feasible schedules, we introduce a new and efficient heuristic for finding good schedules along the tradeoff between throughput and energy efficiency in the physical SINR model. Since our algorithms do not rely on simplistic assumptions about path loss, they are suited for realistic scenarios with attenuation and shadowing effects. We compare our approach to a broad selection of state-of-the-art approaches in indoor and outdoor scenarios. In all situations, our approach outperforms the existing approaches with respect to schedule length and power consumption, i. e., yields paretosuperior schedules including schedules that significantly improve the throughput.
    WiOpt'10: Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks. 01/2010;
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    ABSTRACT: A binary tanglegram is a pair <S,T> of binary trees whose leaf sets are in one-to-one correspondence; matching leaves are connected by inter-tree edges. For applications, for example in phylogenetics or software engineering, it is required that the individual trees are drawn crossing-free. A natural optimization problem, denoted tanglegram layout problem, is thus to minimize the number of crossings between inter-tree edges. The tanglegram layout problem is NP-hard and is currently considered both in application domains and theory. In this paper we present an experimental comparison of a recursive algorithm of Buchin et al., our variant of their algorithm, the algorithm hierarchy sort of Holten and van Wijk, and an integer quadratic program that yields optimal solutions. Comment: see http://www.siam.org/proceedings/alenex/2009/alx09_011_nollenburgm.pdf
    06/2008;
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    Bastian Katz, Markus Völker, Dorothea Wagner
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    ABSTRACT: Choosing an appropriate interference model is crucial for link scheduling problems in sensor networks. While graph-based interference models allow for distributed and purely local coloring approaches which lead to many interesting results, a more realistic and widely agreed on model such as the signal-to-noise-plus-interference ratio (SINR) inherently makes scheduling radio transmission a non-local task, and thus impractical for the development of distributed and scalable scheduling protocols in sensor networks. In this work, we focus on interference models that are local in the sense that admissibility of transmissions only depends on local concurrent transmissions, and correct with respect to the geometric SINR model. In our analysis, we show lower bounds on the limitations that these restrictions impose an any such model as well as approximation results for greedy scheduling algorithms in a class of these models.
    Algorithmic Aspects of Wireless Sensor Networks, Fourth International Workshop, ALGOSENSORS 2008, Reykjavik, Iceland, July 2008. Revised Selected Papers; 01/2008
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    ABSTRACT: In this paper we deal with making drawings of clustered hierarchical graphs nicer. Given a planar graph G = (V,E) with an assignment of the vertices to horizontal layers, a plane drawing of G (with y-monotone edges) can be specified by stating for each layer the order of the vertices lying on and the edges intersecting that layer. Given these orders and a recursive partition of the vertices into clusters, we want to draw G such that (i) edges are straight-line segments, (ii) clusters lie in disjoint convex regions, (iii) no edge intersects a cluster boundary twice. First we investigate fast algorithms that produce drawings of the above type if the clustering fulfills certain conditions. We give two fast algo- rithms with different preconditions. Second we give a linear programming (LP) formulation that always yields a drawing that fulfills the above three requirements—if such a drawing exists. The size of our LP formulation is linear in the size of the graph.
    Proc. 33rd Internat. Conf. Current Trends Theory & Practice Comput. Sci. (SOFSEM'07); 01/2007
  • Sergey Bereg, Markus Völker, Alexander Wolff
    01/2006;
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    Markus Völker, Bastian Katz, Dorothea Wagner
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    ABSTRACT: Although being a very fundamental problem in the field of wireless networks, the complexity of transmission scheduling with power control in the Geometric SINR model is still unknown. In this article, we show that the joint problem of finding transmission powers and scheduling the transmissions is NP-hard if the available powers are bounded, independent of the actual bounds. This also implies that scheduling with a finite number of power levels is NP-hard.