Over-the-Air Calibration of Phase Shifter Network for Hybrid MIMO Systems

Abstract

Phase shifter networks (PSN) are now widely used in multi-input multi-output (MIMO) systems for various purposes, from hybrid beamforming to strong interference mitigation. These applications require the phases of the PSN elements to be precisely calibrated, but the phase deviations always exist in practice. This paper proposes a novel over-the-air (OTA) approach to estimate the deviations of the phase shifters at each gear. Having some signal sources transmit pilot signals from unknown directions, we make the phases of the PSN shift across different gears and take the samples of the PSN output. Then the maximum likelihood (ML) estimation of the PSN errors which constitutes a three-way tensor, can be solved effectively by an iterative algorithm. The simulation results verify the effectiveness of the proposed algorithm and show that the root mean square errors (RMSEs) of the phase estimates can closely approach the Cramer Rao Bounds (CRBs).