  In the context of state estimation under communication constraints, several
notions of dynamical entropy play a fundamental role, among them: topological
entropy and restoration entropy. In this paper, we present a theorem which
demonstrates that for most dynamical systems restoration entropy strictly
exceeds topological entropy. This implies that robust estimation policies in
general require a higher rate of data transmission than non-robust ones. The
proof of our theorem is quite short, but uses sophisticated tools from the
theory of smooth dynamical systems.
