A multi-user multiple-input multiple-output, MU-MIMO, transmitter for operating a radio antenna array to establish signal paths between antennas of the radio antenna array and a plurality of receivers, the MU-MIMO transmitter comprising: a mapper configured to dynamically group, for a time interval, the plurality of receivers to MU-MIMO groups, based on information indicating correlations between signal paths from antennas of the radio antenna array to receivers of the plurality of receivers and a transmission priority of each receiver of the plurality of receivers; and a selector configured to select, for the time interval, a set of receivers of the plurality of receivers from which channel state information, CSI, is to be received, and to identify one or more of the MU-MIMO groups based on the selected set of receivers, wherein the selector is configured to: examine a receiver that, among receivers that have not been selected, has a biggest product of the transmission priority multiplied with an estimated rate that the examined receiver is estimated to get; when the examined receiver belongs to a MU-MIMO group that is already identified or has a subspace having a distance from subspaces of all other already identified MU-MIMO groups that is more than a specified distance, and an estimated weighted sum rate increases by adding the examined receiver to the set of receivers selected for the time interval, add the examined receiver to the set of receivers selected for the time interval, otherwise discard the examined receiver; and iteratively perform the steps of examining and adding or discarding until all receivers have been examined, wherein the MU-MIMO transmitter is further configured to re-calculate the transmission priority of each receiver of the plurality of receivers dynamically when in operation, and wherein the mapper is further configured to form new MU-MIMO groups of receivers from the plurality of receivers based on the re-calculated transmission priority of each receiver of the plurality of receivers. a mapper configured to dynamically group, for a time interval, the plurality of receivers to MU-MIMO groups, based on information indicating correlations between signal paths from antennas of the radio antenna array to receivers of the plurality of receivers and a transmission priority of each receiver of the plurality of receivers; and a selector configured to select, for the time interval, a set of receivers of the plurality of receivers from which channel state information, CSI, is to be received, and to identify one or more of the MU-MIMO groups based on the selected set of receivers, wherein the selector is configured to: examine a receiver that, among receivers that have not been selected, has a biggest product of the transmission priority multiplied with an estimated rate that the examined receiver is estimated to get; when the examined receiver belongs to a MU-MIMO group that is already identified or has a subspace having a distance from subspaces of all other already identified MU-MIMO groups that is more than a specified distance, and an estimated weighted sum rate increases by adding the examined receiver to the set of receivers selected for the time interval, add the examined receiver to the set of receivers selected for the time interval, otherwise discard the examined receiver; and iteratively perform the steps of examining and adding or discarding until all receivers have been examined, wherein the MU-MIMO transmitter is further configured to re-calculate the transmission priority of each receiver of the plurality of receivers dynamically when in operation, and wherein the mapper is further configured to form new MU-MIMO groups of receivers from the plurality of receivers based on the re-calculated transmission priority of each receiver of the plurality of receivers. examine a receiver that, among receivers that have not been selected, has a biggest product of the transmission priority multiplied with an estimated rate that the examined receiver is estimated to get; when the examined receiver belongs to a MU-MIMO group that is already identified or has a subspace having a distance from subspaces of all other already identified MU-MIMO groups that is more than a specified distance, and an estimated weighted sum rate increases by adding the examined receiver to the set of receivers selected for the time interval, add the examined receiver to the set of receivers selected for the time interval, otherwise discard the examined receiver; and iteratively perform the steps of examining and adding or discarding until all receivers have been examined, wherein the MU-MIMO transmitter is further configured to re-calculate the transmission priority of each receiver of the plurality of receivers dynamically when in operation, and wherein the mapper is further configured to form new MU-MIMO groups of receivers from the plurality of receivers based on the re-calculated transmission priority of each receiver of the plurality of receivers.