Detectability, Observability and Lyapunov-Type Theorems of Linear Discrete Time-Varying Stochastic Systems with Multiplicative Noise

The objective of this paper is to study detectability, observability and related Lyapunov-type theorems of linear discrete-time time-varying stochastic systems with multiplicative noise. Some new concepts such as uniform detectability, ${\cal K}^{\infty}$-exact detectability (resp. ${\cal K}^{WFT}$-exact detectability, ${\cal K}^{FT}$-exact detectability, ${\cal K}^{N}$-exact detectability) and ${\cal K}^{\infty}$-exact observability (resp. ${\cal K}^{WFT}$-exact observability, ${\cal K}^{FT}$-exact observability, ${\cal K}^{N}$-exact observability) are introduced, respectively, and nice properties associated with uniform detectability, exact detectability and exact observability are also obtained. Moreover, some Lyapunov-type theorems associated with generalized Lyapunov equations and exponential stability in mean square sense are presented under uniform detectability, ${\cal K}^{N}$-exact observability and ${\cal K}^{N}$-exact detectability, respectively.