Introduction:

The compounding complexity of digital devices, the expansion of
networks in size and diversity, and the ever increasing
dependency of business and government sectors alike on networked
infrastructures has undoubtedly resulted in a pressing need for
advanced design/analysis tools and for effective monitoring and
control strategies. More critically, however, it has become
urgently necessary to obtain scalable and effective
methodologies for diagnosing faults, assessing and estimating
system properties of interest, and operating these complex
systems in uncertain environments and possibly in the presence
of communication constraints, faults or adversaries. Depending
on the underlying application, the causes for these adversarial
conditions may range from design inconsistencies, component
malfunctions and communication delays/lapses to
variability in interconnection topologies and actions by
intruders or users/operators that are misbehaving. The
implications of faults and adversarial behavior can be far
ranging, including user dissatisfaction and nuisance, large
economic costs, and even loss of life.

This research project aimed to directly address these needs by
focusing primarily on networked control systems (initially
within the context of interacting discrete event systems and
eventually expanding to switched linear systems and to more
general hybrid systems). The project concentrated on the
following two objectives:

(i) Establishment of techniques for monitoring and diagnosing
faults or, more generally, abnormal behavior and functional
changes in dynamic systems and networks, under limited and
possibly corrupted information. The aim was to explore a variety
of techniques and models, which include both deterministic and
probabilistic settings. In particular, considering probabilistic
settings, the project studied error bounds using optimal
classification rules in hidden Markov models (WP2), and
developed extensions of probabilistic model-based diagnosis
approaches to distributed settings by combining ideas from
distributed fault diagnosis (in deterministic settings)
and belief propagation techniques (WP3). Considering
deterministic models, in an effort to handle complexity issues
that arise in large-scale systems, this part of the project
developed distributed synchronization schemes for fault
diagnosis in distributed systems (WP4).

(ii) Development of resiliency- and privacy-ensuring control
strategies for networked control systems. In particular, one of
the objectives here was to study supervisory control
strategies for preserving opacity in discrete event systems
(WP1), and also develop a game-theoretic framework for
preserving opacity in settings where multiple systems interact
(WP5).

The research was completed successfully and significant progress
was made in both of the objectives mentioned above. This
progress can ultimately enable the automated operation of
detection and control mechanisms, which will naturally lead to
resilient and safe operation of these complex systems despite
the presence of malicious or non-malicious disruptions. Though
some of these challenges have been addressed using centralized
algorithms (e.g., monolithic diagnosers and controllers for
supervisory control), the scientific challenge in the case of
the large-scale networked control systems that emerge as a
result of the proliferation of networking and digital technology
is to fully extend these techniques to distributed/decentralized
settings, understand the costs and performance tradeoffs
involved, and (if necessary) develop new algorithms that can
provide suboptimal but adequate performance at reasonable costs.
Some steps towards this direction have already been taken within
the context of this project.

Publications:

Published and accepted journal publications within the context of this project are provided below. A complete list of publications by Dr. Hadjicostis can be found here.

11) Lingxi Li and C. N. Hadjicostis, ``Minimum Initial Marking
Estimation in Labeled Petri Nets,'' IEEE Transactions on
Automatic Control (to appear).

10) A. Saboori and C. N. Hadjicostis, ``Verification of
Infinite-Step Opacity and Analysis of its Complexity,'' IEEE
Transactions on Automatic Control, vol. 57, no. 5, pp.
1265-1269, May 2012.

9) A. Saboori and C. N. Hadjicostis, ``Opacity Enforcing
Supervisory Strategies via State Estimator Constructions,'' IEEE
Transactions on Automatic Control, vol. 57, no. 5, pp.
1155-1165, May 2012. Supplement with proofs for ``Opacity
Enforcing Supervisory Strategies via State Estimator
Constructions."

8) A. Saboori and C. N. Hadjicostis, ``Coverage Analysis of
Mobile Agent Trajectory via State-Based Opacity Formulations,''
Control Engineering Practice (Special Issue on ``Selected Papers
from 2nd International Workshop on Dependable Control of
Discrete Systems"), vol. 19, no. 9, pp. 967-977, September 2011
(invited).

7) A. Saboori and C. N. Hadjicostis,
``Verification of K-Step Opacity and Analysis of its
Complexity,'' IEEE Transactions on Automation Sciences and
Engineering, vol. 8, no. 3, pp. 549-559, July 2011. Supplement
with proofs for ``Verification of K-Step Opacity and Analysis of
its Complexity."

6) Lingxi Li and C. N. Hadjicostis, ``Least-Cost Transition
Firing Sequence Estimation in Labeled Petri Nets with
Unobservable Transitions," IEEE Transactions on Automation
Science and Engineering, vol. 8, no. 2, pp. 394-403, April 2011.

5) Yu Ru and C. N. Hadjicostis, ``Sensor Selection for
Structural Observability in Discrete Event Systems Modeled by
Labeled Petri Nets,'' IEEE Transactions on Automatic Control,
vol. 55, no. 8, pp. 1751-1764, August 2010.

4) Yu Ru and C. N. Hadjicostis, ``Fault Diagnosis in Discrete
Event Systems Modeled by Partially Observed Petri Nets,''
Journal of Discrete Event Dynamic Systems (Special Issue on
``Selected Papers from WODES 2008, the 9th International
Workshop on Discrete Event Systems"), vol. 19, no. 4, pp.
551-575, December 2009 (invited).

3) E. Athanasopoulou, Lingxi Li, and C. N. Hadjicostis,
``Maximum Likelihood Failure Diagnosis in Finite State machines
Under Unreliable Observations,'' IEEE Transactions on Automatic
Control, vol. 55, no. 3, pp. 579-594, March 2010.

2) Lingxi Li and C. N. Hadjicostis, ``Least-Cost Planning
Sequence Estimation in Labeled Petri Nets,'' Transactions of the
Institute of Measurement and Control, vol. 33, no. 3-4, pp.
317-331, May 2011 (Special Issue on ``Planning and Scheduling in
Complex Systems").

1) Tung Le and C. N. Hadjicostis, ``Graphical Inference for
Multiple Intrusion Detection,'' IEEE Transactions on Information
Forensics and Security (Special Issue on ``Statistical Methods
for Network Security and Forensics"), vol. 3, no. 3, pp.
370-380, September 2008.

Published and accepted conference
publications within the context of
this project are provided below. A complete list of publications
by Dr.
Hadjicostis can be found here.

24) C. N. Hadjicostis, ``Resolution of Initial State Opacity in
Security Applications of DES," Proceedings of MED 2012, the 20th
Mediterranean Conference on Control and Automation, Barcelona,
Spain, 2012 (to appear).

23) C. Keroglou and C. N. Hadjicostis, ``Bounds on the
Probability of Misclassification among Hidden Markov Models,"
Proceedings of CDC/ECC 2011, the 50th IEEE Conference on
Decision and Control and European Control Conference, pp.
385-390, Orlando, FL, December 12-15, 2011 (presented by the
researcher).

22) Tung Le and C. N. Hadjicostis, "Marginal Analysis on Binary
Pairwise Gibbs Random Fields," Proceedings of IEEE CASE 2011,
the 7th Annual IEEE Conference on Automation Science and
Engineering, pp. 316-321, Trieste, Italy, August 2011 (presented
by the researcher).

21) C. Keroglou and C. N. Hadjicostis, ``Bound on the
Probability of Misclassification between Two HMMs," Proceedings
of MED 2011, the 19th Mediterranean Conference on Control and
Automation, pp. 449-454, Corfu Island, Greece, 2011.

20) Tung Le and C. N. Hadjicostis, ``Convergence of Belief
Propagation Algorithms on Binary Pairwise Gibbs Random Fields,"
Proceedings of 2011 IFAC World Congress, Milan, Italy (presented
by the researcher).

19) Yu Ru and C. N. Hadjicostis, ``Constrained Sensor Selection
for Discrete Event Systems Modeled by Petri Nets," Proceedings
of ACC 2011, the 2011 American Control Conference, pp.
4502-4507, San Francisco, California, 2011.

18) A. Saboori and C. N. Hadjicostis, ``Opacity Verification in
Stochastic Discrete Event Systems," Proceedings of CDC 2010, the
2010 IEEE Conference on Decision and Control, pp. 6759-6764,
Atlanta, GA, 2010 (presented by the researcher).

17) Tung Le, S. Tatikonda, and C. N. Hadjicostis, ``Performance
Analysis of Belief Propagation Algorithms for Multiple Fault
Diagnosis Applications," Proceedings of CDC 2010, the 2010 IEEE
Conference on Decision and Control, pp. 1627-1632, Atlanta, GA,
2010 (presented by the researcher).

16) C. N. Hadjicostis, ``Supervisory Control Strategies for
Enhancing System Security and Privacy," Proceedings of the 48th
Annual Allerton Conference on Communication, Control, and
Computing, pp. 1622-1627, Allerton House, IL, 2010 (invited,
presented by the researcher).

15) A. Saboori and C. N. Hadjicostis, ``Reduced-Complexity
Verification for Initial-State Opacity in Modular Discrete Event
Systems," Proceedings of WODES 2010, the 10th International
Workshop on Discrete Event Systems, Berlin, Germany, 2010
(invited, presented by the researcher).

14) A. Saboori and C. N. Hadjicostis, ``Probabilistic Opacity
for Stochastic Discrete Event Systems," Proceedings of MTNS
2010, the 19th International Symposium on Mathematical Theory of
Networks and Systems, Budapest, Hungary, 2010 (presented by the
researcher).

13) Yu Ru and C. N. Hadjicostis, ``Reachability Analysis for a
Class of Petri Nets," Proceedings of CDC 2009, the 2009 IEEE
Conference on Decision and Control, pp. 1261-1266, Shanghai,
China, 2009 (invited).

12) S. Sundaram and C. N. Hadjicostis, ``Information
Dissemination in Networks via Linear Iterative Strategies Over
Finite Fields," Proceedings of CDC 2009, the 2009 IEEE
Conference on Decision and Control, pp. 3781-3786, Shanghai,
China, 2009 (invited, presented by the researcher)).

11) A. Saboori and C. N. Hadjicostis, ``Verification of K-Step
Opacity and Analysis of its Complexity," Proceedings of CDC
2009, the 2009 IEEE Conference on Decision and Control, pp.
205-210, Shanghai, China, 2009 (presented by the researcher).

10) Lingxi Li and C. N. Hadjicostis, ``Minimum Initial Marking
Estimation in Labeled Petri Nets," Proceedings of ACC 2009, the
2009 American Control Conference, pp. 5000-5005, St. Louis, MS,
2009 (invited).

9) S. Sundaram and C. N. Hadjicostis, ``Linear Iterative
Strategies for Transmitting Input Streams in Sensor Networks,"
Proceedings of MED 2009, the 17th Mediterranean Conference on
Control and Automation, pp. 106-111, Thessaloniki, Greece, 2009
(invited, presented by the researcher).

8) A. Saboori and C. N. Hadjicostis, ``Verification of
Infinite-Step Opacity and Analysis of its Complexity,"
Proceedings of DCDS 2009, the Second IFAC Workshop on Dependable
Control of Discrete Systems, pp. 51-56, Bari, Italy, 2009
(presented by the researcher). Available online at
http://www.ifac-papersonline.net/Detailed/42295.html .

7) Yu Ru, M. P. Cabasino, A. Giua, and C. N. Hadjicostis,
``Supervisor Synthesis for Discrete Event Systems with Arbitrary
Forbidden State Specifications," Proceedings of CDC 2008, the
47th IEEE Conference on Decision and Control, pp. 1048-1053,
Cancun, Mexico, 2008.

6) E. Athanasopoulou and C. N. Hadjicostis, ``Probability of
Error Bounds for Failure Diagnosis and Classification in Hidden
Markov Models," Proceedings of CDC 2008, the 47th IEEE
Conference on Decision and Control, pp. 1477-1482, Cancun,
Mexico, 2008 (presented by the researcher).

5) A. Saboori and C. N. Hadjicostis, ``Opacity-Enforcing
Supervisory Strategies for Secure Discrete Event Systems,"
Proceedings of CDC 2008, the 47th IEEE Conference on Decision
and Control, pp. 889-894, Cancun, Mexico, 2008 (presented by the
researcher).

4) Tung Le and C. N. Hadjicostis, ``Low-Complexity Max-Product
Algorithms for Problems of Multiple Fault Diagnosis,''
Proceedings of ICARCV 2008, the 10th International Conference on
Control, Automation, Robotics and Vision, pp. 470-475, Hanoi,
Vietnam, 2008.

3) A. Saboori and C. N. Hadjicostis, ``Verification of
Initial-State Opacity in Security Applications of DES,"
Proceedings of WODES 2008, the 9th International Workshop on
Discrete Event Systems, pp. 328-333, Goteborg, Sweden, 2008
(presented by the researcher).

2) Yu Ru and C. N. Hadjicostis, ``Fault Diagnosis in Discrete
Event Systems Modeled by Petri Nets with Outputs," Proceedings
of WODES 2008, the 9th International Workshop on Discrete Event
Systems, pp. 443-448, Goteborg, Sweden, 2008 (invited, presented
by the researcher).

1) M. P. Cabasino, A. Giua, C. N. Hadjicostis, and C. Seatzu,
``Fault Model Identification with Petri Nets," Proceedings WODES
2008, the 9th International Workshop on Discrete Event Systems,
pp.455-461, Goteborg, Sweden, 2008 (invited).