A wireless transmit/receive unit (WTRU) may transmit via a primary uplink carrier data, pilot and control channels for uplink transmissions on both uplink carriers, and transmit a data channel and a pilot channel via a secondary uplink carrier. Alternatively, the WTRU may transmit via a primary uplink carrier data, pilot, and control channels for uplink transmission on the primary uplink carrier, and transmit via a secondary uplink carrier data, pilot, and control channels for uplink transmissions on the secondary uplink carrier. Each uplink carrier may be associated with at least one specific downlink carrier such that the WTRU applies control information received on a downlink carrier to uplink transmissions on an uplink carrier associated with the downlink carrier on which the WTRU receives the control information.