Trading Infinite Memory for Uniform Randomness in Timed Games
Krishnendu Chatterjee1
, Thomas A. Henzinger1, 2
and Vinayak S. Prabhu1 
Abstract
We consider concurrent two-player timed automaton games with ω-regular objectives specified as parity conditions. These games offer an appropriate model for the synthesis of real-time
controllers. Earlier works on timed games focused on pure strategies for each player. We study, for the first time, the use
of randomized strategies in such games. While pure (i.e., nonrandomized) strategies in timed games require infinite memory for winning
even with respect to reachability objectives, we show that randomized strategies can win with finite memory with respect to
all parity objectives. Also, the synthesized randomized real-time controllers are much simpler in structure than the corresponding
pure controllers, and therefore easier to implement. For safety objectives we prove the existence of pure finite-memory winning
strategies. Finally, while randomization helps in simplifying the strategies required for winning timed parity games, we prove
that randomization does not help in winning at more states.
This research was supported in part by the NSF grants CCR-0208875, CCR-0225610, CCR-0234690, by the Swiss National Science
Foundation, and by the Artist2 European Network of Excellence.
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