A General Matched Filter Design for Reciprocity Calibration in Multiuser Massive MIMO Systems

In this paper, we propose a novel design of calibration matrix for time-division duplex multiuser multiple-input multiple-output with maximal ratio transmit beamforming, which maximizes the achievable sum rate in the presence of reciprocity mismatch induced by radio-frequency (RF) gain responses at base station side. We show that two conventional designs are equivalent to the asymptotic expressions of proposed design when signal-to-noise ratio (SNR) tends to infinity or zero, respectively, since the proposed calibration matrix behaves as a decorrelator that rejects RF gain mismatch for the former SNR region, or as a matched filter maximizing the power of useful signal for the latter. The robust version against the channel estimation error is also investigated. Simulation results illustrate the effectiveness of our proposed design.