| Summary: | This paper proposes an adaptive switching method of feedback information for a wireless networked control system (WNCS) with unreliable communication links, which is based on a cross-layered design approach between communication and control layers. In the focused WNCS where communication errors can occur, the uncertainty in the estimation of control-state at the controller side consists of the following two factors. The one is the uncertainty as to whether the control-input has been correctly input (received). The other is the disturbance added to the controlled object (plant). This work considers the following two modes which determine the feedback information: (1)the mode in which the plant side transmits the communication result of feedforward channel (from the controller to the plant), which will be referred to as to ACK mode, (2)the mode in which the plant transmits the information of control-state observed by the sensor, which is referred to as STA mode. From a communication perspective, in the case with ACK mode, the use of ACK/NACK signaling allows a small number of bits (communication rate) to be used, and thus enables reliable feedback communication. As a result, the controller can reliably know the uncertainty of whether the control-input has been successfully received, but the uncertainty due to the disturbance still remains. On the other hand, in the case with STA mode, all the uncertainties can be eliminated only if the feedback communication is successful. However, the increase of information (rate) makes the feedback communication unreliable compared to the case with ACK mode. Furthermore, the control-input should be calculated considering the reliability of feedforward and feedback channels as well as the accuracy of the estimated control-state. As a result, the selection of feedback information deeply affects the quality of WNCS. This paper provides an adaptive switching method of feedback information and corresponding control-input, and shows that the proposed method can efficiently improve the quality of control in the WNCS with unreliable communication links.
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