Methods and user equipment are provided for activation of downlink component carriers. Even though configured to monitor multiple component carriers, a user equipment unit does not start to monitor them immediately, but instead monitors only one or a few carriers initially. Once a downlink scheduling assignment is received, the user equipment unit will then monitor additional component carriers. After one or more subframes where the user equipment unit is not scheduled, the user equipment unit returns to its original state where it monitors one or a few carriers.