A method and base station supporting uplink transmissions. The method being used in a base station and comprising receiving a data block from a wireless transmit/receive unit (WTRU) using a hybrid automatic repeat request (H-ARQ) process, transmitting uplink scheduling information to the WTRU to indicate whether the data block should be retransmitted by the WTRU, wherein the uplink scheduling information includes a H-ARQ process identification for the H-ARQ process, and receiving a retransmission of the data block from the WTRU. The uplink scheduling information includes physical channel resources. The uplink scheduling information is received from a primary cell and the WTRU transmits to the primary cell and at least one secondary cell. The scheduling information indicates a modulation and coding scheme.