  This paper studies delayed synchronization of continuous-time multi-agent
systems (MAS) in the presence of unknown nonuniform communication delays. A
delay-free transformation is developed based on a communication network which
is a directed spanning tree, which can transform the original MAS to a new one
without delays. By using this transformation, we design a static protocol for
full-state coupling and a dynamic protocol for delayed state synchronization
for homogeneous MAS via full- and partial-state coupling. Meanwhile, the
delayed output synchronization is also studied for heterogeneous MAS, which is
achieved by using a low-gain and output regulation based dynamic protocol
design via the delay-free transformation.
