One embodiment is directed to determining a composite precoder for transmitting to a UE using a group of one or more of the radio units by doing the following: for each of a plurality of subsets of the radio units, transmitting separate reference signals from the different antennas of only the radio units included in that subset; receiving subset-specific preferred precoder index reports from the UE for at least each individual radio unit included in the group of one or more of the radio units; determining the composite precoder for the UE using the subset-specific preferred precoder index reports from the UE for at least the one or more radio units included in the group; and using the composite precoder for transmitting to the UE using the one or more radio units included in the group. In some embodiments, each of the subsets includes less than all of the radio units.