A wireless transmit receive unit (WTRU) and a method performed by the WTRU for receiving radio resource control (RRC) signaling including information indicating a primary cell and at least one non-primary cell, receiving a single message with scheduling information indicating an allocation of uplink resources and a hybrid automatic repeat request (HARQ) process ID, wherein the WTRU has one or more HARQ processes and uplink transmissions by the WTRU utilize asynchronous HARQ, and transmitting to at least the non-primary cell an uplink transmission using a HARQ process indicated by the HARQ process ID and the allocation of uplink resources.