Introduction - If you have any usage issues, please Google them yourself
This theory is expressed in the time domain. The basic concept is: on the basis of the state space representation of linear system, the optimal estimation of system state is obtained from output and input observation data. The state of the system described here is a set of minimum parameters for all the past inputs and disturbances of the system to be summed up, knowing that the state of the system can be used to determine the whole behavior of the system with the disturbance of future input and system.