Optimal Dynamic Transmission Scheduling for Wireless Networked Control Systems

Wireless networked control systems (WNCSs) have the potential to revolutionize industrial automation in smart factories. Optimizing closed-loop performance while maintaining stability is a fundamental challenge in WNCS due to limited bandwidth and nondeterministic link quality of wireless networks. In order to bridge the gap between network design and control system performance, we propose an optimal dynamic transmission scheduling strategy that optimizes the performance of multiloop control systems by allocating network resources based on predictions of both link quality and control performance at run time. We formulate the optimal dynamic scheduling problem as a nonlinear integer programming problem, which is relaxed to a linear programming problem. We further extend the optimization problem to balance control performance and communication cost. The proposed optimal dynamic scheduling strategy renders the closed-loop system mean-square stable under mild assumptions. Its efficacy is demonstrated by simulating a four-loop control system over an IEEE 802.15.4 wireless network simulator—TOSSIM. The run-time network reconfiguration protocol tailored for optimal scheduling is designed and implemented on a real wireless network consisting of IEEE 802.15.4 devices. Hybrid simulations integrating a real wireless network and simulated physical plant control are performed. Simulation and experimental results show that the optimal dynamic scheduling can enhance control system performance and adapt to both constant and variable wireless interference and physical disturbance to the plant.

I. Introduction

Wireless sensor–actuator networks (WSANs) are gaining rapid adoption in industrial automation for lowering deployment and maintenance costs in harsh industrial environments. Industrial standard organizations, such as ISA100 [2], WirelessHART [3], and ZigBee [4], have been actively pushing a wide range of applications of IEEE 802.15.4-based [5] wireless technologies in industrial automation, which emphasizes very low-cost communication [6], [7]. However, in wireless networked control systems (WNCSs), while advances have been made in sensing and monitoring, there are multiple challenges in closing the loop over wireless networks for control and actuation.