A less-conservative stability criterion for networked control systems with time-varying packet delays

A networked output feedback loop subject to packetized transmissions of the output signal is considered. Based on the small gain theorem, an easy-to-use stability criterion covering two important cases is presented. In the first case a packet numbering mechanism is employed whereas in the second case neither packet numbering nor synchronization between sender and receiver is assumed. The analysis makes use of acausal subsystems and deduces the optimal constant time delay with respect to the minimization of the l(2) gain due to uncertain packet delays. This additional delay is then used in a nominal controller design such that additional admissible packet delay variations introduced by the network are maximized. A simulation example of a networked control system with a filtered Smith predictor illustrates the application of the proposed criterion. It is shown that the proposed novel technique is less-conservative than existing stability criteria based on the small gain theorem.