A method in a network node of selecting a subset from a predetermined set of P CSI-RS ports for receiving channel information, wherein: the network node is a network node of a wireless communication network and comprises an antenna array with controllable polarization; each CSI-RS port corresponds to a combination of a set of resource elements and an antenna port of said antenna array and is associated with an identifier being a port number p given by: p = { r + N 2 k r = 15,..., 14 + N 2 r + N 2 k + K − 1 r = 15 + N 2,..., 14 + N where K is a number of CSI reference signal configurations, k is any integer in [0, K - 1], N is an even integer being the number of antenna ports or reference signals in each of the K configurations, and r is any integer in [15,14 + N]; and the predetermined set comprises a first number P 1 of CSI-RS ports with a first polarization state associated with identifiers in a first predetermined range and a second number P 2 of CSI-RS ports with a second polarization state associated with identifiers in a second predetermined range, the first and second polarization states being distinct, the method comprising: populating the subset with Q CSI-RS ports in such manner that the ratio of CSI-RS ports respectively having the first and second polarization states is equal to the ratio of the first and second numbers, wherein one of the following holds: (i) the subset is populated with Q/2 CSI-RS ports from a lower portion of the first predetermined range and Q/2 CSI-RS ports from a lower portion of the second predetermined range; (ii) the subset is populated with Q/2 CSI-RS ports from a higher portion of the first predetermined range and Q/2 CSI-RS ports from a higher portion of the second predetermined range; if periodic CSI reporting or CSI reporting supporting at most 8 antenna ports is to be enabled, transmitting reference signals on CSI-RS ports from the subset; and, if aperiodic CSI reporting or non-precoded CSI-RS CSI reporting is to be enabled, transmitting reference signals on CSI-RS ports from the predetermined set. the network node is a network node of a wireless communication network and comprises an antenna array with controllable polarization; each CSI-RS port corresponds to a combination of a set of resource elements and an antenna port of said antenna array and is associated with an identifier being a port number p given by: p = { r + N 2 k r = 15,..., 14 + N 2 r + N 2 k + K − 1 r = 15 + N 2,..., 14 + N where K is a number of CSI reference signal configurations, k is any integer in [0, K - 1], N is an even integer being the number of antenna ports or reference signals in each of the K configurations, and r is any integer in [15,14 + N]; and the predetermined set comprises a first number P 1 of CSI-RS ports with a first polarization state associated with identifiers in a first predetermined range and a second number P 2 of CSI-RS ports with a second polarization state associated with identifiers in a second predetermined range, the first and second polarization states being distinct, where K is a number of CSI reference signal configurations, k is any integer in [0, K - 1], N is an even integer being the number of antenna ports or reference signals in each of the K configurations, and r is any integer in [15,14 + N]; and the predetermined set comprises a first number P 1 of CSI-RS ports with a first polarization state associated with identifiers in a first predetermined range and a second number P 2 of CSI-RS ports with a second polarization state associated with identifiers in a second predetermined range, the first and second polarization states being distinct, the method comprising: populating the subset with Q CSI-RS ports in such manner that the ratio of CSI-RS ports respectively having the first and second polarization states is equal to the ratio of the first and second numbers, wherein one of the following holds: (i) the subset is populated with Q/2 CSI-RS ports from a lower portion of the first predetermined range and Q/2 CSI-RS ports from a lower portion of the second predetermined range; (ii) the subset is populated with Q/2 CSI-RS ports from a higher portion of the first predetermined range and Q/2 CSI-RS ports from a higher portion of the second predetermined range; if periodic CSI reporting or CSI reporting supporting at most 8 antenna ports is to be enabled, transmitting reference signals on CSI-RS ports from the subset; and, if aperiodic CSI reporting or non-precoded CSI-RS CSI reporting is to be enabled, transmitting reference signals on CSI-RS ports from the predetermined set. populating the subset with Q CSI-RS ports in such manner that the ratio of CSI-RS ports respectively having the first and second polarization states is equal to the ratio of the first and second numbers, wherein one of the following holds: (i) the subset is populated with Q/2 CSI-RS ports from a lower portion of the first predetermined range and Q/2 CSI-RS ports from a lower portion of the second predetermined range; (ii) the subset is populated with Q/2 CSI-RS ports from a higher portion of the first predetermined range and Q/2 CSI-RS ports from a higher portion of the second predetermined range; if periodic CSI reporting or CSI reporting supporting at most 8 antenna ports is to be enabled, transmitting reference signals on CSI-RS ports from the subset; and, if aperiodic CSI reporting or non-precoded CSI-RS CSI reporting is to be enabled, transmitting reference signals on CSI-RS ports from the predetermined set.