A method, in a first wireless node, the method comprising: selecting a set of demodulation reference signal antenna ports for use in transmitting data to or receiving data from a plurality of User Equipments, UEs, in a given transmit time interval, from a plurality of sets of demodulation reference signal antenna ports that are available for use, wherein at least two of the sets of the plurality of sets of demodulation reference signal antenna ports have different demodulation reference signal densities in the frequency dimension; and sending a message to a UE indicating the selected set of demodulation reference signal antenna ports; wherein the message indicates the selected set from a plurality of possible sets of available ports, the possible sets of available ports comprising: a first set of demodulation reference signal antenna ports comprising each odd subcarrier of a physical resource block, wherein the first set of demodulation reference signal antenna ports comprises one port or two antenna ports being separated from one another by orthogonal cover codes; a second set of demodulation reference signal antenna ports comprising each even subcarrier of a physical resource block, wherein the second set of demodulation reference signal antenna ports comprises one port or two antenna ports being separated from one another by orthogonal cover codes, wherein the demodulation reference signal antenna ports of the first set and second set are different; and a third set of demodulation reference signal antenna ports corresponding to a merger in a physical resource block of the first set of demodulation reference signal antenna ports and the second set of demodulation reference signal antenna ports, wherein the third set of demodulation reference signal antenna ports comprises one port or two antenna ports being separated from one another by orthogonal cover codes. selecting a set of demodulation reference signal antenna ports for use in transmitting data to or receiving data from a plurality of User Equipments, UEs, in a given transmit time interval, from a plurality of sets of demodulation reference signal antenna ports that are available for use, wherein at least two of the sets of the plurality of sets of demodulation reference signal antenna ports have different demodulation reference signal densities in the frequency dimension; and sending a message to a UE indicating the selected set of demodulation reference signal antenna ports; wherein the message indicates the selected set from a plurality of possible sets of available ports, the possible sets of available ports comprising: a first set of demodulation reference signal antenna ports comprising each odd subcarrier of a physical resource block, wherein the first set of demodulation reference signal antenna ports comprises one port or two antenna ports being separated from one another by orthogonal cover codes; a second set of demodulation reference signal antenna ports comprising each even subcarrier of a physical resource block, wherein the second set of demodulation reference signal antenna ports comprises one port or two antenna ports being separated from one another by orthogonal cover codes, wherein the demodulation reference signal antenna ports of the first set and second set are different; and a third set of demodulation reference signal antenna ports corresponding to a merger in a physical resource block of the first set of demodulation reference signal antenna ports and the second set of demodulation reference signal antenna ports, wherein the third set of demodulation reference signal antenna ports comprises one port or two antenna ports being separated from one another by orthogonal cover codes.