  Reconfigurable intelligent surface (RIS) has recently drawn significant
attention in wireless communication technologies. However, identifying,
modeling, and estimating the RIS channel in multiple-input multiple-output
(MIMO) systems are considered challenging in recent studies. In this paper, a
disassembled channel estimation framework for the RIS-MIMO system is proposed
based on the eigenvalue decomposition (EVD) concept to separate the cascaded
channel links and estimate each link separately. This estimation is based on
modeling the RIS-MIMO channel as a keyhole MIMO system model. Numerical results
show that the proposed estimation method has a low estimation time overhead
while providing less estimation error.
