Performance Analysis of TDD Reciprocity Calibration for Massive MU-MIMO Systems With ZF Beamforming

This study analyzes a two-way signaling method for time division duplex reciprocity calibration (RC) in multiuser beamforming systems. The system model of RC is established, and the estimation error of the RC coefficient is derived. The effect of this error is examined in terms of the user signal-to-interference-plus-noise ratio (SINR) and capacity. Results reveal the relationship between the user SINR and RC errors as well as the number of antennas and users. Moreover, the findings show that the colocated antenna array is less sensitive to calibration errors than the case of distributed antennas even if the calibration signal-to-noise ratio (SNR) is identical. The interference resulting from imperfect calibration becomes the determinant that constrains the performance, particularly when a high user SNR is required.