Over-the-Air Phase Calibration of Reconfigurable Intelligent Surfaces

Abstract

The reconfigurable intelligent surface (RIS) has emerged as a promising technology to enhance the capacity of wireless systems, as it can configure the wireless channel using low-cost passive devices, i.e., printed dipoles and phase shifters. But the real phases of the RIS elements usually deviate from the nominal values in practice, and the phase deviations need to be precisely estimated and calibrated for some applications. This letter proposes a novel over-the-air (OTA) approach that can estimate the real phases of the RIS elements at each gear. We also derive the Cramér Rao Bounds (CRBs) for the RIS calibration as a performance benchmark. The simulation results verify the effectiveness of the proposed algorithm as the root mean square errors (RMSEs) of the phase estimates are close to the CRBs.