Cross-layer design of an LQG controller in multihop TDMA-based wireless networked control systems

Wireless networked control systems (WNCSs) are control systems whose components are connected through wireless networks. In this paper, we consider a multihop WNCS, where controllers and controlled objects are connected through a multihop wireless network. Round-trip delays between controllers and controlled objects may cause unstable behavior of the WNCS due to inconsistency between states of the system at time when an observation packet is generated and when the corresponding control packet is received. In order to solve this problem, we propose a cross-layer design of an LQG (Linear Quadratic Gaussian) controller, which specializes in TDMA (Time Division Multiple Access)-based WNCS. In the proposed method, control packets are designed by using a property of TDMA that a sequence of round-trip delays is deterministic. When the controller receives an observation packet, it generates a control packet based on the estimated state of the controlled object at time when the control packet will reach the controlled object. Simulation results show that the proposed method achieves better performance in terms of RMSE (Root Mean Square Error) of the controlled object's state to their targets.