One or more nodes transmit CSI-RS symbols in a set of N CSI-RS elements, each CSI-RS element in the set corresponding to at least one resource element in a time-frequency grid of resource elements. The nodes select, from the N CSI-RS elements, a first set of CSI-RS elements to be measured by a first wireless device, the first set comprising one or several of the N CSI-RS elements. The nodes also transmit, to the first wireless device, a message comprising a first K-bit indicator identifying the first set of CSI-RS elements, wherein K