A method includes holding in a receiver a definition of a codebook including precoding matrices, and a definition of multiple sub-codebooks including different respective subsets of the precoding matrices in the codebook. A sub-codebook is selected in coordination with a transmitter, for use in a given time interval or frequency range. A Multiple-Input Multiple-Output (MIMO) signal that is transmitted from the transmitter is received. Feedback is generated in the receiver based on the received MIMO signal. The feedback is indicative of one or more preferred precoding matrices, which are chosen from the selected sub-codebook and which are to be used in precoding subsequent MIMO signals in respective partitions of the given time interval or frequency range. The feedback is transmitted from the receiver to the transmitter.