Fault-tolerant controllers in Wireless Networked Control System using 802.11g

In this paper, the 802.11g standard is used without modification in a fault-tolerant networked control system with two or three cascaded workcells. Samples are sent by sensors to an 802.11g access point, which forwards this data, via Switched Ethernet, to the controller. The controller generates a control word, which is then delivered to the access point, via Switched Ethernet, and is forwarded to the corresponding wireless actuator. The effects of noise are also studied. OPNET simulations show that a two-cell system can tolerate the failure of one of its two controllers even in the presence of noise. For a three-cell system, up to two controllers can fail (in the presence of noise) and the remaining operational controller will be able to handle the load of all three cells. A performability model is then developed to simultaneously take into account controller failure data with the risk of not adhering to the required delay constraints. All OPNET delays are subjected to a 95% confidence analysis.