Mixed digital and subarray-based beamformer

An apparatus, comprising:

• at least one processor;
• and
• at least one memory storing instructions which, when executed by the at least one processor, cause the apparatus at least to:
• receive at least one uplink pilot associated with a receiver, wherein the at least one uplink pilot is transmitted over at least one time-frequency unit, and wherein the receiver comprises at least one digital beamforming, DBF, -panel and at least one subarray-based beamforming, SABBF, -panel, the at least one DBF-panel having an associated DBF-channel and the at least one SABBF-panel having an associated SABBF-channel;
• based on channel distributions of the DBF-channel and the SABFF-channel and further based on the at least one uplink pilot, determine at least one estimated strongest direction of a common covariance matrix associated with the at least one DBF-panel and the at least one SABBF-panel;
• and
• determine a beamforming vector for at least one transmission phase or at least one reception phase based on the at least one estimated strongest direction of the common covariance matrix.