Wi-Fi-based Hierarchical Wireless Networked Control Systems

This paper proposes a novel architecture for a hierarchical Wireless Networked Control System (WNCS). It consists of three cascaded workcells each containing 30 sensors, 30 actuators and one controller. The wireless communication protocol used is IEEE 802.11g with multicasting. The hierarchy of the system is such that the lowest level is that of the sensors and actuators, the intermediate level is the controllers, and the highest level is a supervisory node. This supervisor can be either active or passive. System performance is measured using OPNET simulations and the results are confirmed analytically. The system is shown to tolerate all possible controller failure scenarios. The supervisor can handle the entire control load of all three controllers, should the need arise. The system exhibits zero packet drops and delay constraints are met in all scenarios. The effect of interference is then investigated and the maximum interference that can be tolerated by the system is quantified.