A method and base station are disclosed. The base station comprises a wireless transceiver and a processor. The base station performs wireless communications with a wireless transmit/receive unit (WTRU) via a primary cell, transmits a message via a shared channel of the primary cell, wherein the message includes information identifying a plurality of non-primary cells, and transmits, to the WTRU, data over a downlink channel of at least one of the plurality of non-primary cells identified by the message.