Methods and apparatuses are described for wireless communication supporting carrier aggregation. The method includes monitoring a first search space and a second search space on a primary component carrier, to receive a scheduling assignment including information indicating a component carrier on which data is transmitted, wherein a scheduling assignment for the primary component carrier is received in the first search space, and a scheduling assignment for a secondary component carrier is received in the second search space; and receiving the data on one of the primary component carrier and the secondary component carrier. The first search space for the primary component carrier is different from the second search space for the secondary component carrier.