I. Introduction
Wireless networked control systems (WNCSs) [3], [8], [9], [11], [13] are control systems whose components such as sensors, actuators, and controllers are connected through wireless networks. The WNCSs are one of the key technologies to develop M2M (Machine-to-Machine) communications. We consider a WNCS over a multihop wireless network, where one controller (CL) and several controlled objects (COs) are connected via intermediate wireless nodes. The WNCS is divided into two parts: the control system part and the networking part. The control system part is modeled as a sampled-data feedback control system, where continuous-time COs are controlled by the discrete-time controller. On the other hand, the networking part includes network/MAC (Medium Access Control) protocols in order to connect the CL and COs through a multihop wireless network. We refer to the control system part and the networking part as the control system layer and the networking layer. Note that the control system layer corresponds to the application layer in the OSI protocol suite.