The present disclosure relates to a mobile station (UE) for receiving Physical Downlink Control CHannel, PDCCH, assignments in a mobile communication system including serving cells. In case the mobile station is configured with at least two serving cells having different serving cell indices, the UE monitors, for the two serving cells, a same set of candidates for PDCCH assignments defining a same UE-specific search space and which is determined independently of the indices of the serving cells with which the UE is configured, and the UE receives, for the serving cells, PDCCH assignments from among the monitored same set of candidates using carrier indicator field, CIF, values in the received PDCCH assignments for identifying the serving cells with which the UE is configured. The CIF values, included in the received PDCCH assignments, correspond to the respective indices of the serving cells with which the UE is configured.