Passivity-based control over differentiated-services packet networks

This paper proposes a novel architecture for networked embedded systems which exploits a differentiated services approach to guarantee control performance even in case of time-varying network condition. Control commands are transmitted as high-priority packets when the plant behavior is far from the desired target or network condition does not assure the reliable and prompt reception of commands and measurements. The assignment of different priorities to packets belonging to the same flow (i.e., commands or measurements) may lead to out-of-sequence forwarding which may compromise the plant stability and the estimation of the state at the controller side. As far as we know this is the first work which solves such important issues by combining priority-based forwarding with the passivity mechanism to ensure stability. Moreover, we adopt an optimized filter for plant state estimation which takes into account the vector of the last commands used by the plant (updated through information received from the plant together with measurements) and the vector of the last measurements. Different packet marking strategies are compared: the best one leads to the same performance of random marking by using a smaller fraction of the high-priority bandwidth.