Downlink pilot assignment in massive MIMO

A network node (110) and a method for downlink pilot signal assignment and transmission, and for data transmission. The network node has a plurality of antenna elements distributed over an area. The network node determines a respective Channel State Information (CSI) and/or a respective channel hardening degree for a wireless device (120) based on an uplink pilot signal. Possibly, the network node determines a mobility condition for the wireless device. Based on one or more out of: the determined respective CSI, the determined respective channel hardening degree and the determined respective mobility condition, the network node obtains a pilot utility metric for the wireless device. Further, the network node assigns a downlink pilot signal to at least one wireless device having a pilot utility metric exceeding a predetermined threshold value. Furthermore, the network node transmits, to the at least one wireless device, data and possibly an assigned downlink pilot signal.