A method includes estimating an uplink channel for a terminal device, based on an amount of antennas used by an access node for transmitting signals to the terminal device, antennas used for receiving the transmitted signals at the terminal device, and sub-bands used for transmitting the signals. Based on the estimation, a channel covariance matrix is determined for a precoder comprised in a transmitter of the access node by determining a limited number of elements of a full dimensional channel covariance matrix, which is different than the channel covariance matrix. The limited number of elements are elements corresponding to i-th row and j-th column of the channel covariance. Correlation computation is performed for the limited number of elements. Elements of the full-dimensional channel covariance matrix that are excluded from the limited number of elements are determined and set to be zero. Precoding is performed using the determined channel covariance matrix.