  Since its first inception by Joseph Mitola III in 1998 cognitive radio (CR)
systems have seen an explosion of papers in the communication community.
However, the interaction of CR and control has remained vastly unexplored. In
fact, when combined with control theory CR may pave the way for new and
exciting control and communication applications. In this paper, the control and
estimation problem via the well known two switch model which represents a CR
link is considered. In particular, The optimal linear estimator subject to a CR
link between the sensor and the estimator is derived. Furthermore, it is shown
that in the Linear Quadratic Gaussian (LQG) Control law for a closed-loop
system over double CR links is not linear in the state estimate. Consequently,
the separation principle is shown to be violated. Several conditions of
stochastic stability are also discussed. Illustrative numerical examples are
provided to show the effectiveness of the results.
