Channel Estimation for Reconfigurable Intelligent Surface Aided Massive MIMO System

The uplink channel estimation for the reconfigurable intelligent surface (RIS) aided massive multiple-input multiple-output (MIMO) system is investigated. By changing the phase matrix of the RIS, multiple channel measurements for the channel estimation are obtained. During the initial
channel estimation that represents the initial state of the system, an iterative algorithm is proposed to estimate the channel matrix between the base station (BS) and the RIS, where the initial value of the iterative algorithm is well selected. After that, then the channel matrix between the RIS and the user equipment (UE) is estimated. During the regular channel estimation where the channel matrix between the BS and the RIS is supposed to be known, the channel matrix between the RIS and the UE and that between the BS and the UE are sequentially estimated with the consideration on the pilot overhead. Simulation results verify the effectiveness of the proposed channel estimation methods.