An antenna array of a base station is calibrated using outbound traffic signals. The antenna array includes a number of sub-arrays. A combiner in the antenna array combines the outbound traffic signals in the sub-arrays into a feedback signal. The outbound traffic signals are captured simultaneously for use as reference signals before the outbound traffic signals enter transmit paths in a radio unit of the base station. Each of the reference signals is one of the outbound traffic signals that is to be transmitted via one of the sub-arrays. An impairment estimator of the base station estimates the impairment for each of the outbound traffic signals based on the feedback signal and the reference signals. An approximate inverse of the impairment estimation is applied to the outbound traffic signals by a number of equalizers before the outbound traffic signals enter the transmit paths.