  A measure of quality of a control system is a quantitative extension of the
classical binary notion of controllability. In this article we study the
quality of linear control systems from a frame-theoretic perspective. We
demonstrate that all LTI systems naturally generate a frame on their state
space, and that three standard measures of quality involving the trace, minimum
eigenvalue, and the determinant of the controllability Gramian achieve their
optimum values when this generated frame is tight. Motivated by this, and in
view of some recent developments in frame-theoretic signal processing, we
propose a natural measure of quality for continuous time LTI systems based on a
measure of tightness of the frame generated by it and then discuss some
properties of this frame-theoretic measure of quality.
