# The discrete time $H_\infty$ control problem with measurement feedback

A.A. Stoorvogel

This paper is concerned with the discrete time $H_\infty$ control problem with measurement feedback. It follows that, as in the continuous time case, the existence of an internally stabilizing controller that makes the $H_\infty$ norm strictly less than 1 is related to the existence of stabilizing solutions to two algebraic Riccati equations. However, in the discrete time case, the solutions of these algebraic Riccati equations must satisfy extra conditions.