104,561 research outputs found
Synthesis of Covert Actuator Attackers for Free
In this paper, we shall formulate and address a problem of covert actuator
attacker synthesis for cyber-physical systems that are modelled by
discrete-event systems. We assume the actuator attacker partially observes the
execution of the closed-loop system and is able to modify each control command
issued by the supervisor on a specified attackable subset of controllable
events. We provide straightforward but in general exponential-time reductions,
due to the use of subset construction procedure, from the covert actuator
attacker synthesis problems to the Ramadge-Wonham supervisor synthesis
problems. It then follows that it is possible to use the many techniques and
tools already developed for solving the supervisor synthesis problem to solve
the covert actuator attacker synthesis problem for free. In particular, we show
that, if the attacker cannot attack unobservable events to the supervisor, then
the reductions can be carried out in polynomial time. We also provide a brief
discussion on some other conditions under which the exponential blowup in state
size can be avoided. Finally, we show how the reduction based synthesis
procedure can be extended for the synthesis of successful covert actuator
attackers that also eavesdrop the control commands issued by the supervisor.Comment: The paper has been accepted for the journal Discrete Event Dynamic
System
PSPACE-completeness of Modular Supervisory Control Problems*
In this paper we investigate computational issues associated with the supervision of concurrent processes modeled as modular discrete-event systems. Here, modular discrete-event systems are sets of deterministic finite-state automata whose interaction is modeled by the parallel composition operation. Even with such a simple model process model, we show that in general many problems related to the supervision of these systems are PSPACE-complete. This shows that although there may be space-efficient methods for avoiding the state-explosion problem inherent to concurrent processes, there are most likely no time-efficient solutions that would aid in the study of such âlarge-scaleâ systems. We show our results using a reduction from a special class of automata intersection problem introduced here where behavior is assumed to be prefix-closed. We find that deciding if there exists a supervisor for a modular system to achieve a global specification is PSPACE-complete. We also show many verification problems for system supervision are PSPACE-complete, even for prefix-closed cases. Supervisor admissibility and online supervision operations are also discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45090/1/10626_2004_Article_6210.pd
On the use of observation equivalence in synthesis abstraction
In a previous paper we introduced the notion of synthesis abstraction, which allows efficient compositional synthesis of maximally permissive supervisors for large-scale systems of composed finite-state automata. In the current paper, observation equivalence is studied in relation to synthesis abstraction. It is shown that general observation equivalence is not useful for synthesis abstraction. Instead, we introduce additional conditions strengthening observation equivalence, so that it can be used with the compositional synthesis method. The paper concludes with an example showing the suitability of these relations to achieve substantial state reduction while computing a modular supervisor
Compositional synthesis of maximally permissive supervisors using supervision equivalence
This paper presents a general framework for efficient synthesis of supervisors for discrete event systems. The approach is based on compositional minimisation, using concepts of process equivalence. In this context, a large number of ways are suggested how a finite-state automaton can be simplified such that the results of supervisor synthesis are preserved. The proposed approach yields a compact representation of a least restrictive supervisor that ensures controllability and nonblocking. The method is demonstrated on a simple manufacturing example to significantly reduce the number of states constructed for supervisor synthesis
Three variations of observation equivalence preserving synthesis abstraction
In a previous paper we introduced the notion of synthesis abstraction, which allows efficient compositional synthesis of maximally permissive supervisors for large-scale systems of composed finite-state automata. In the current paper, observation equivalence is studied in relation to synthesis abstraction. It is shown that general observation equivalence is not useful for synthesis abstraction. Instead, we introduce additional conditions strengthening observation equivalence, so that it can be used with the compositional synthesis method. The paper concludes with an example showing the suitability of these relations to achieve substantial state reduction while computing a modular supervisor
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