Methods and nodes for transmission of downlink control channel signals in a downlink frequency carrier of a wireless communication system, wherein at least two PRB pairs, configurable for the transmission of a downlink control channel have different numbers of time-frequency resource elements available for the transmission of said downlink control channel. The method comprises allocating at least one set S of PRB pairs; arranging time-frequency resource elements from said set S into an aggregation comprising at least one level; determining a set LS of aggregation levels supported for the transmission of a downlink control channel within the allocated set of PRB pairs, based on the number of time-frequency resource elements available for the transmission of a downlink control channel in PRB pairs of the set S; and transmitting the downlink control channel within said set S of PRB pairs.