Plenary Talks

Rajeev Alur: Interfaces for Control Components
René Boel: Coordination of Traffic Networks
Paulo Tabuada: Supervisory Control of Differential Equations


   Rajeev Alur:

    Zisman Family Professor
    Department of Computer and Information Science
    University of Pennsylvania


Interfaces for Control Components

Modern software engineering heavily relies on clearly specified interfaces for separation of concerns among designers implementing components and programmers using those components. The need for interfaces is evident for assembling complex systems from components, but more so in control applications where the components are designed by control engineers using mathematical modeling tools and used by software executing on digital computers. However, the notion of an interface for a control component must incorporate
some information about timing, and standard programming languages do not provide a way of capturing such resource requirements.

This talk will describe how finite automata over infinite words can be used to define interfaces for control components. When the resource is allocated in a time-triggered manner, the allocation from the perspective of an individual component can be described by an infinite word over a suitably chosen alphabet. The control engineer can express the interface of the component as an omega-regular language that contains all schedules that meet performance requirement. The software must ensure, then, that the runtime allocation is in this language. The main benefit of this approach is composability: conjoining specifications of two components corresponds to a simple language-theoretic operation on interfaces. We have demonstrated how to automatically compute automata for performance requirements such as exponential stability and settling time for the LQG control designs. The framework is supported by a toolkit, RTComposer, that is implemented on top of Real Time Java. The benefits of the approach will be demonstrated using applications to wireless sensor/actuator networks based on the WirelessHART protocol and to distributed control systems based on the Control Area Network (CAN) bus.

Rajeev Alur is Zisman Family Professor of Computer and Information Science, and Director of the newly introduced Embedded Systems Masters’ Program, at University of Pennsylvania. He obtained his bachelor's degree in computer science from Indian Institute of Technology at Kanpur in 1987, and PhD in computer science from Stanford University in 1991. Before joining Penn in 1997, he was with Computing Science Research Center in Bell Laboratories. The main focus of his research is foundations and tools for automated analysis of software and embedded systems. His research spans multiple computing disciplines such as computer-aided verification, embedded control systems, logic in computer science, and programming languages. He is a Fellow of the ACM, a Fellow of the IEEE, and an Alfred P. Sloan Faculty Fellow. He received the inaugural CAV (Computer-Aided Verification) Award for fundamental contributions to analysis of real-time systems


   René Boel:

    SYSTeMS Research group
    School of Engineering
    Ghent University


Coordination of Traffic Networks

Transportation problems provide a rich class of case studies for investigating the implementability of supervisory and distributed control ideas. This talk will abstract a few problems from this area into distributed supervisory control problems. Case studies are taken from on-ramp control for freeways, coordinated traffic light control in urban traffic, and control of autonomous vehicles executing task with a deadline while avoiding collisions.

Each of these problems can be modelled as a timed automaton or a piecewise affine model, with timed Petri nets and fluid Petri nets as concise graphical representations. Reachability analysis, safety analysis, and observer design for these models can be reduced to some standard algorithms, at least conceptually. Specifications must be satisfied by designing supervisory controller limiting the actions of the different components in the network.

The problem becomes particularly challenging when local controllers in each vehicle or in each intersection in the traffic system have only limited communication channels for coordinating their actions. It will be shown for a number of interesting cases how distributed controllers can be designed achieving good coordination of the local controllers.

René K. Boel received a degree in electromechanical engineering (1969) and in nuclear engineering (1970) from Ghent University, an M.Sc. (1972) and a Ph.D. degree (1974) in Electrical Engineering and Computer Sciences from the University of California, Berkeley, U.S.A.

He is currently a professor at the SYSTeMS Research group, School of Engineering, Ghent University, Ghent (Belgium). He was a research fellow of the F.W.O.-Vlaanderen (Flemish Foundation for Scientific research) until September 2000.

He has held temporary appointments at the Department of Electrical Engineering and Computer Sciences-University of California Berkeley, the department of Technical Cybernetics NTH-Trondheim Norway, the Mathematics department of the Katholieke Universiteit Leuven, the Mathematics and Statistics department of Bell laboratories Murray Hill (N.J.), the department of Computing and Control of Imperial College London, the Department of Systems Engineering, Australian National University, Canberra, the department of Electrical and Computer Engineering, University of Newcastle, Australia, and the Electrical and Electronic Engineering department, Melbourne University.

He has been associate editor for IEEE Transactions on Automatic Control, Automatica, Journal of Applied Stochastic Models in Business and and Industry, and is currently Department Editor for the Journal on Discrete Event Dynamic Systems, Associate editor for IET Control Theory and Applications, and member of the editorial board of Systems and Control Letters. He was chairman of the Steering Committee for the Workshop on Discrete Event Systems (2000-2002 and 2006-2008), and he has been on the organising committee for a large number of conferences in control, statistics, and communication networks.

His current research interests are in the field of distributed control and estimation for stochastic, discrete event and hybrid systems, with applications to traffic networks and power systems, as well as in bio-informatics.  


   Paulo Tabuada:

    Cyber-Physical Systems Laboratory
    Department of Electrical Engineering
    University of California at Los Angeles


Supervisory Control of Differential Equations

Research in the area of hybrid systems has always been influenced by supervisory control techniques developed for discrete-event systems. One typically envisions a finite-state controller having a quantized view of the world and issuing supervisory commands implemented by continuous feedback control laws. This deceptively simple idea has resisted a mathematical formalization upon which the systematic synthesis of finite-state controllers could be built. I shall report on recent advances on this problem based on the notion of approximate bisimulation. Along the way, I will also discuss new supervisory control problems arising when controlling differential equations with finite-state supervisors.

Paulo Tabuada was born in Lisbon, Portugal, one year after the Carnation Revolution. He received his "Licenciatura" degree in Aerospace Engineering from Instituto Superior Tecnico, Lisbon, Portugal in 1998 and his Ph.D. degree in Electrical and Computer Engineering in 2002 from the Institute for Systems and Robotics, a private research institute associated with Instituto Superior Tecnico. Between January 2002 and July 2003 he was a postdoctoral researcher at the University of Pennsylvania. After spending three years at the University of Notre Dame, as an Assistant Professor, he joined the Electrical Engineering Department at the University of California, Los Angeles, where he established and directs the Cyber-Physical Systems Laboratory.

Paulo Tabuada was the recipient of the Francisco de Holanda prize in 1998, for the best research project with an artistic or aesthetic component, awarded by the Portuguese Science Foundation. He also received a NSF CAREER award in 2005 and the 2009 Donald P. Eckman award from the American Automatic Control Council. In 2009 he co-chaired the International Conference Hybrid Systems: Computation and Control (HSCC'09), and he currently serves as an associate editor for the IEEE Embedded Systems Letters. His latest book, on verification and control of hybrid systems, was published by Springer in 2009.

His research interests include modeling, analysis, and control of real-time, embedded, networked, and distributed systems; geometric control theory, and mathematical systems theory.


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