A new method for proving the separation principle for the infinite-dimensional LQG regulator problem

This paper gives an alternative perspective on the standard linear quadratic Gaussian regulator problem for infinite-dimensional state-space systems. We will show that when considered on an extended Hilbert state-space, the originally stochastic control problem can be phrased as a deterministic one. In this setting we obtain a new method of proof for the well-known separation principle which does not involve probabilistic considerations.