Disclosed apparatuses obtain real-time performance measurements and adaptively select multiple-input, multiple-output (MIMO) antennas to improve MIMO antenna performance. A correlation estimator determines an approximation of instantaneous antenna correlation values. One method includes obtaining a channel quality indicator (CQI) measurement for first and second antennas of a mobile device. The method determines a composite CQI for the two antennas and estimates the antenna correlation for the first and second antennas based on the composite CQI. The method can include performing a lookup operation in a CQI table mapping composite CQI to coding rates. The method can include obtaining a signal-to-noise ratio (SNR) measurement for the first and second antennas of the mobile device, and estimating the antenna correlation for the first and second antennas based on the composite CQI and the SNR measurement.