Design of state-aware multiple access methods for networked control systems

Abstract:

Networked Control Systems (NCSs) use a wireless network for communication between sensors and controllers, and require a Medium Access Controller (MAC) to arbitrate access to the shared medium. In our work, we advocate the use of a state-aware MAC, as opposed to an agnostic MAC, for NCSs. We use a local state-based scheduler to select a few critical data packets to send to the MAC, thus regulating the traffic in the network. We study architectural properties, performance and stability for a network of such systems. We analyze the impact of state-based schedulers on the closed-loop system, and show that there is a dual effect for the control signal, which makes determining the optimal controller difficult. We identify restrictions on the scheduling criterion that result in a separation of the scheduler, observer and controller designs. Furthermore, we analyze the performance of a network of such systems using a Carrier Sensing Multiple Access protocol. The interactions in such a network introduce correlations between the system variables of the various loops. Our analysis is based on a time-averaged Markov model, which is validated through simulations. We also use this Markov model to identify sufficient conditions for Lyapunov Mean Square Stability of a network of first-order systems.

Presentation Slides

Biography:Chithrupa Ramesh is a PhD student at the School of Electrical Engineering, KTH Royal Institute of Technology, Sweden since 2008. She obtained a Licentiate degree and her MS in Wireless Systems from KTH as well, and her BE in Telecommunications from R.V.College of Engineering, Bangalore, India. Her research interests are in networked control systems and wireless networks.