  This paper gives a new solution to the output feedback H2 problem for
quadratically invariant communication delay patterns. A characterization of all
stabilizing controllers satisfying the delay constraints is given and the
decentralized H2 problem is cast as a convex model matching problem. The main
result shows that the model matching problem can be reduced to a
finite-dimensional quadratic program. A recursive state-space method for
computing the optimal controller based on vectorization is given.
