Attack-free Protocol Design with Distributed Noncontinuous Appointed-time Unknown Input Observer

This paper considers the output-feedback consensus problem of linear multi-agent systems under directed communication topologies. To avoid the network attack from potential malicious attacker, the concept of attack-free protocol is proposed, wherein the information transmission via communication channel is forbidden. Under this circumstance, only relative output measurement can be utilized to generate the observer and the protocol. In this paper, by viewing the relative input of neighboring agents as the unknown input, novel distributed unknown input observer is presented for each agent to achieve appointed-time estimation of the consensus error, where only measured relative output information is used. The fully distributed adaptive protocol is then designed based on the proposed observer. The distributed observer takes a pulsative form at some time instants, which is noncontinuous; while such form takes the advantage of reducing computational cost, compared with the pairwise observer design structure. Simulation results are also conducted to illustrate the effectiveness of the proposed attack-free protocol.