  In this article, we consider a cooperative control problem involving a
heterogeneous network of dynamically decoupled continuous-time linear plants.
The (output-feedback) controllers for each plant may communicate with each
other according to a fixed and known transitively closed directed graph. Each
transmission incurs a fixed and known time delay. We provide an explicit
closed-form expression for the optimal decentralized controller and its
associated cost under these communication constraints and standard linear
quadratic Gaussian (LQG) assumptions for the plants and cost function. We find
the exact solution without discretizing or otherwise approximating the delays.
We also present an implementation of each sub-controller that is efficiently
computable, and is composed of standard finite-dimensional linear
time-invariant (LTI) and finite impulse response (FIR) components, and has an
intuitive observer-regulator architecture reminiscent of the classical
separation principle.
