Annual Report 2010 - Fachgruppe Informatik an der RWTH Aachen ...

Dynamic Coordination in Large Networks
M. Hoefer, A. Skopalik
funded by DFG
In this project we develop distributed protocols and analyze the resulting dynamics for
coordination problems in large networks. The goal is to derive a general understanding of
distributed algorithms and dynamics in problems with rational agents and locality of
computation and information.
In the previous year we most prominently analyzed aspects of cooperation of rational agents
and the resulting stability and convergence properties. For the prominent class of congestion
games, which are frequently used to model routing and load balancing scenarios, we showed
hardness of strong equilibria - states resilient to deviations of arbitrary coalitions of agents -
and other less stringent coalitional equilibrium concepts. Our hardness results concern
deciding existence of equilibrium in a given game, recognizing a state as equilibrium, and
computing an equilibrium if it exists. Many of these results hold even in seemingly special
classes of games with simple network structure. For classes of load balancing games,
however, computation and recognition are easy, and even fast convergence of iterative
coalitional improvement can be shown. In addition, we considered a variant of congestion
games, in which players care about bottleneck resources. For such games existence of strong
equilibria is known. We characterized the computational complexity in terms of a general
strategy packing problem, for which we can provide efficient algorithms in special cases. In
the general case, however, we were able to provide a number of complementary hardness
results. Finally, we treated adjusted variants of the concept of strong equilibrium in several
ways, e.g., pairwise equilibria in social network contribution games, or a novel concept of
considerate equilibrium in load balancing games.
For the coming year, we presently plan to treat rationality aspects in models related to
frequency assignment and power control in wireless networks. The main challenge here is the
design of simple and reliable distributed algorithms, which cope with local information,
asymmetric interference relations and dynamically changing request structure.
Lifetime Problems in Networks with Uncertain Battery Capacities
M. Ochel, K. Radke, B. Vöcking
Network lifetime problems address an inherent restriction of most modern wireless networks:
the limited energy capacity of the mobile participants. If we assume each network node
having a battery as an energy source, we can define the lifetime of the network as the time
until the first node runs out of energy.
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