Two-Phase Parameter-Based Separate Channel Estimation in RIS-Aided MIMO OFDM Systems

We propose a novel two-phase separate channel estimation scheme in reconfigurable intelligent surface (RIS)-assisted multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. Based on the sparsity of the channel, the parameters in the user equipment (UE)-RIS channel and RIS-base station (BS) channel can be estimated in two phases and then utilized for channel reconstruction. Different from the cascaded estimation, the proposed method can achieve separate channel estimation and, thus, has higher practicability and creates room for more ingenious transceiver design. Moreover, a new pilot protocol for the RIS phase shift matrix configuration is proposed, such that new users will need only limited pilot resources. Through simulations, we prove that the proposed scheme can achieve precise channel reconstruction with low pilot overhead.