Discrete-Time LQG Control With Input Delay and Multiplicative Noise

This paper is concerned with linear quadratic Gaussian (LQG) control problem for discrete-time systems with both multiplicative noises and input delay. The main contributions are two-fold. First, when the state variables can be obtained exactly, the optimal LQG controller is derived which consists of the feedback form of the conditional expectation of the state and one additive deterministic term based on the coupled Riccati equations. Through the completing square approach, the optimal controller is obtained based on the complete solution to the forward and backward stochastic difference equations. Second, when the state variables are partially observed, we derive a suboptimal linear state estimate feedback controller for LQG models involving multiplicative noises and input delay. Since the separation principle does not hold and the optimal estimator cannot be obtained, the suboptimal linear state estimate feedback controller is derived by linearizing the linear optimal estimator and using the obtained results of the optimal LQG control.