Forschung » Abgeschlossene Projekte
Abgeschlossene Projekte
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funded by the DFG (July 2006 - May 2015)
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funded by the DFG, Research Cluster in the Excellence Initiative (November 2006 - October 2014)
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funded by the German-Israeli Foundation for Scientific Research and Development (GIF)
(January 1, 2007 - December 31, 2010)
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funded by the DFG, Schwerpunkt 1126 (since July 2001)
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funded by the European Union, Integrated Project (since Jan 2004)
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funded by the European Science Foundation, Cost Action 293 (since Jan 2005)
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funded by the DFG (since Jan 2003)
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funded by the DFG (since Oct 2005)
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Algorithmic synthesis of reactive and discrete-continuous systems
funded by the DFG (July 2006 - May 2015)
AlgoSyn is an interdisciplinary research project at the RWTH Aachen University
led by a group of ten professors representing five different disciplines.
Integrating approaches from computer and engineering sciences, the project aims
at developing methods for the automatised design of soft- and hardware.
While methods of software validation and verification are by now well
established, based on adequate formal models and tested in practical
applications, the approach of automatic synthesis of software (and hardware) is
as yet only developed in quite rudimentary form. On the other hand, in
theoretical computer science as well as in engineering disciplines a rapidly
increasing stock of techniques for the development of algorithmic synthesis
procedures is emerging, triggered by the demand to decrease development costs
by invoking algorithmics in formal modelling frameworks. However, the approach
of program synthesis is only applicable in restricted scenarios, in particular
in reactive (multi-agent) systems with low data complexity and in control
systems. Central issues in the area are the establishment of system models
which allow an algorithmic solution of the synthesis problem, the combination
of discrete and continuous pararameters in hybrid systems (as this is also
familiar from verification), and the exploration of the potential of
applications. The aim of the Graduate School is to unify the expertise from
Computer science, mathematics, and four engineering disciplines (processor
architectures, automatic control, process control engineering, train traffic
systems) and to push forward the desired integration of methods. The research
will be carried out in four subject areas: Algorithmics for agent-based
probabilistic and hybrid systems, formal methods of reactive systems and
game-theoretic methods, software development and modelling languages, and
finally applications and demonstrators.
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UMIC - Ultra High-Speed Mobile Information and Communication
funded by the DFG, Research Cluster in the Excellence Initiative (November 2006 - October 2014)
The initial goal of the UMIC cluster was to enable future Ultra High-Speed
Mobile Information and Communication, with the main vision of broadband
wireless internet access at reasonable access costs triggering the next wave of
economic and innovation growth. Today it is indeed the low cost access,
predominantly in the form of flat data rates, which drives the exponentially
increasing mobile Internet access. This has led to a strong cost pressure on
operators and equipment providers. Researching technologies that address these
problems has thus been the right approach. Over time mobile internet access
grew rapidly. UMIC reacted to this with a shift in the focus to Universal
Mobile Access to Information and Communication, thus putting more emphasis on
the user perspective with technologies supporting universal mobile access.
A major differentiator of the research centre to competitors and the usual
chair based systems in faculties is its ability to closely collaborate,
addressing particular problem domains on a broader scale. In UMIC three
interdisciplinary flagship projects emerged over the course of the
collaboration: LocalizeMe, addressing application topics, Cognitive Radios and
Networks, addressing flexible and efficient use of the wireless communication
resources, and Nucleus, addressing platforms and design methodology for
flexible (mobile) terminals. Research in the UMIC centre produced substantial
scientific results documented by, e.g. more than 1,000 peer-reviewed journal
and conference papers, by extensive technology transfer to industry partners
and via start-up companies and by one Leibniz Prize and three ERC Grants
received during the UMIC funding period.
Further, the UMIC research cluster has led to cultural and structural changes
in the involved departments of RWTH Aachen University. Most notably, it has
successfully introduced a structured career path for junior researchers based
on Junior Professor positions (assistant professorship). Out of 6 established
junior professorships 3 have got tenure in Aachen, 2 in other international top
universities, and one more is still in the tenure track. This shows the high
quality of the candidates the UMIC was able to attract. UMIC gender equality
promotion activities contributed significantly to a development where both
Computer Science and Electrical Engineering departments increased the
percentage of female researchers in post study career stages (i.e. Doctoral
degrees and Professors) to a balance with the percentage of female students.
Last but not least UMIC has been intellectual home for 176 doctoral researcher
of which 97 have already successfully defended their doctoral thesis work.
The UMIC research centre building, the new research groups and the five labs
with state-of-the-art equipment teams established through UMIC funding are the
basis of sustained UMIC research. Moreover, UMIC research is a key component of
the strategy of the Information and Communication Technology (ICT) profile area
of RWTH Aachen University.
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Generalized Congestion Games: Analysis, Computation, and Evolution
funded by the German-Israeli Foundation for Scientific Research and Development (GIF)
(January 1, 2007 - December 31, 2010)
The project proposes to bring together two disciplines - computer science and
game theory - and by doing so to address some fundamental problems of
computing in the Internet era. Combining our expertise we propose to handle
several complementary issues in non-cooperative multi-agent systems. Since we
can show that congestion and network games with player-specific payoff
functions give us the set of all strategic games, while congestion games with
player-symmetric payoff functions are the most popular type of games discussed
in the computer science literature, the study of generalized congestion games
is a most effective way to bridge the gap between computer science and game
theory.
When referring to generalized congestion games we refer both to congestion
games where agents may have different payoffs functions, as well as to
congestion games with uncertainty (e.g. about the number of participants or
other agents' costs). The nice graph-theoretic representation of general
strategic games as player-specific congestion games enables to tackle the
fundamental problem of existence of solution concepts (e.g. pure strategy
equilibrium or strong equilibrium) as a function of the graph structure, as
well as determine the complexity of computation and the speed of convergence to
solutions as a function of the graph structure. In order to deal with
congestion games with incomplete information, our aim is to tackle reasoning
about uncertainty in multi-agent systems when exact probabilistic information
is not available. For doing so, new equilibrium concepts are to be defined and
applied to congestion settings.
This is a joint project with Dov Monderer and Moshe Tennenholtz from the Technion.
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Management variabler Datenströme in Netzwerken
funded by the DFG, Schwerpunkt 1126 (since July 2001)
This project deals with dynamic routing algorithms in large networks like the
Internet. The goal is to improve our understanding of communication patterns as
well as to design algorithms routing the data in such a way that the
communication load is as evenly distributed over the available resources as
possible. This gives us the opportunity to avoid congestion on the one hand and
to guarantee a fair treatment of all participating users on the other hand. In
particular, we aim at the design of algorithms for allocating streams of data
on web servers as well as for performing intra-domain routing in networks. The
resulting research problems will be tackled theoretically, practically, and
experimentally. The project is part of the DFG research program
"Algorithmik großer und komplexer Netzwerke". We closely
cooperate with the networking group of the TU München headed by Anja
Feldmann. Our particular focus in this cooperation is mainly on the theoretical
part.
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DELIS - Dynamically Evolving Large Scale Information Systems
funded by the European Union, Integrated Project (since Jan 2004)
Most of the existing and foreseen complex networks are built, operated and used
by a multitude of diverse economic interests. A prime example is the Internet,
perhaps the most complex computational artifact of our times. The (possibly)
selfish nature of the participating entities calls for a deeper understanding
of the network dynamics in order to efficiently achieve their cooperation, by
possibly considering bounded rationality aspects. In the past few years, there
has been a flourishing amount of work in the border of Computer Science,
Economics, Game Theory and Biology that has started to address the above
issues. For example, (a) selfish network routing (and flows) were addressed in
a number of recent research papers, (b) mechanism design for algorithmic
cooperation of selfish users was proposed by many authors, (c) evolutionary
economics addresses the dynamics of self-organization in large networks, and
(d) the issues of bounded rationality of machines versus their ability for game
playing were examined by several research groups, among them the Nobel-prized
Economists work of 2001 and 2002.
Activities within the project can be grouped into two main classes:
Basic Research:
basic research to understand the dynamics of the network and the effect of
concepts like self-organization, selfishness and bounded rationalism as well as
the structure of equilibria (and the form of dynamics) in such systems.
Efficient Algorithms:
design of mechanisms and algorithms that efficiently achieve the cooperation
between the involved selfish entities, possibly applying results from
evolutionary models.
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Graphs and Algorithms in Communication Networks
funded by the European Science Foundation, Cost Action 293 (since Jan 2005)
The main objective of this Action is to create a discussion space
between applied communities and theorists in the context of communication
networks in which models and assumptions can be reviewed and formalized into
the appropriate language.
Inside the context of communication networks, the Action focusses on, but is
not restricted to the following specific fields:
- QoS networks: Quality of Service (QoS) refers to a broad
collection of networking technologies and techniques.
The goal of QoS is to provide guarantees on traffic transmission. Elements
of network performance within the scope of
QoS include availability (uptime), bandwidth (throughput), latency (delay),
delay jitter, and error rate.
- Optimization in optical networks: Optical networks using light
paths in optical fibers as communication media induce a number of problems
that cannot be directly resolved by using standard solutions from electronic
networks, but require new approaches and techniques, instead. These problems
include routing techniques, wavelength assignment on switches and cross
connects, signalling, topologies design, and path recovery (backup) for
protection and restoration.
- Optimization in wireless networks: Wireless networks were
traditionally related with voice and telephony. Nowadays, packet networks
are also supported in mobile, such as in GPRS and UMTS technologies. Trends on
wireless networks include QoS for multimedia transmission and backup paths.
Therefore, problems for static networks are moving to wireless, such as delay
minimization, traffic engineering, frequency assignment and localization. But
there are several additional challenges for wireless networks, one is for
instance the coordination of the single uncontrolled agents participation in
the network.
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Flexible Online-Algorithmen
funded by the DFG, Emmy-Noether-Programm (since Jan 2003)
Online algorithms studied in theory are characterized by the fact that they do
not have knowledge about the whole input sequence of jobs in advance. Instead,
the input sequence is generated job by job, and a new job is not issued until
the previous one is handled by the online algorithm. In real applications, jobs
can usually be delayed for a short amount of time, and hence the input sequence
of jobs can be rearranged in a limited fashion to optimize the performance.
This flexible online scenario occurs in many applications in computer science
and economics, e.g., in computer graphics: A rendering system displays a
sequence of primitives. The number of state changes of such a system are a
significant factor for the performance. State changes occur when two
consecutively rendered primitives differ in their attribute values, e.g., in
their texture or shader program. With the help of a reordering buffer in which
primitives can be buffered the sequence of primitives can be reordered online
in such a way that the number of the state changes is reduced.
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Probabilistische Analyse diskreter Optimierungsprobleme
funded by the DFG (since Oct 2005)
Many algorithmic problems are hard from a worst-case point of view but can be
solved quite well on typical inputs by heuristic approaches. Hence, worst-case
complexity does not seem to be an appropriate measure for the complexity of
these problems. This research project deals with the probabilistic analysis of
such problems and heuristics in order to narrow the gap between the
observations made in practice and the theoretical understanding of these
problems.
For many problems, average-case analyses do not provide much insight either
since inputs which occur in practice usually possess certain properties and a
certain structure which cannot be reflected by an average-case analysis alone
as it is not clear how to choose the underlying probability distribution over
the set of possible inputs. In this project, we turn our attention to more
general probabilistic input models like, e.g., the model of smoothed analysis.
The semi-random input model used in a smoothed analysis consists of two stages.
First an adversary chooses an input, then this input is randomly perturbed in
the second step. In particular, the adversary can specify a worst-case input
with certain properties which is only slightly perturbed in the second
stage.
The focus of our research are problems which can be expressed in the form of
integer linear programs. In our previous analyses we have characterized the
class of integer optimization problems with polynomial smoothed complexity. The
algorithms with polynomial smoothed complexity we designed, however, are
clearly outperformed by common heuristics used in practice, like, e.g., Branch
and Bound and Branch and Cut approaches. One of the main goals of this research
project is the probabilistic analysis of these heuristics in order to
understand why they perform so extraordinary well in practice. Our approach
consists of two steps: First structural parameters like, e.g., the number of
Pareto optimal solutions or the integrality gap, are analyzed. Then the running
time of the heuristics is analyzed in terms of these parameters.