Optimal Cross-Layer Design of Sampling Rate Adaptation and Network Scheduling for Wireless Networked Control Systems

Authors: Jia Bai, Emeka P. Eyisi, Fan Qiu, Yuan Xue and Xenofon D. Koutsoukos

ACM/IEEE Third International Conference on Cyber-Physical Systems, Beijing, China on April 17 - 19, 2012.

Abstract:

Wireless Networked Control Systems (NCS) are
increasingly deployed to monitor and control Cyber-Physical
Systems (CPS). To achieve and maintain a desirable level of
performance, NCS face significant challenges posed by the
scarce wireless resource and network dynamics. We consider
NCS consisting of multiple physical plant and digital controller
pairs communicating over a multi-hop wireless network. The
control objective is for the plants to follow the reference
trajectories provided by the controllers. This paper presents
a novel optimization formulation for minimizing the tracking
error introduced due to discretization and packet delays and
losses. The optimization problem maximizes a utility function
that characterizes the relationship between the sampling rate
and the capability of disturbance rejection of the control system.
The constraints represent the wireless network capacity and the
end-to-end delay requirements. The solution to this optimization
problem leads to a joint design of sampling rate adaptation
and network scheduling, which can be naturally deployed over
the existing layered networking systems. Based on a passivitybased
control framework, we show that the proposed cross-layer
design can achieve both stability and performance optimality.
Simulation studies conducted in an integrated simulation environment
consisting of Matlab/Simulink and ns-2 demonstrate
that our algorithm is able to provide agile and stable sampling
rate adaptation and achieve optimal NCS performance.