Multivariable controller design in the face of sensor delays: A separation principle approach

This paper deals with discrete-time multivariable feedback systems that are subject to sensor time delays. Supposing a controller exists that provides good performance without sensor delays, we consider how an estimator can be used to recover closed-loop performance when sensor time delays are introduced into the feedback loop. Using separation principle arguments, we first show that stability and tracking performance can be recovered for a broad range of estimators, and then we determine how disturbance rejection and sensor noise rejection properties of the (delayed) closed-loop system are related to those of the original (undelayed) closed-loop system and those of the estimator.