“…Optimal control of time-delay systems has been an active research area since the late 1960s, first in the H 2 (LQG) and then in the H ∞ settings, see e.g. [16,85] for the discrete-time case and [7,44,60,61,83] for the continuous-time case. Time delay can appear in state and/or in input/output(I/O) of the system model.…”