A wireless transmit/receive unit (WTRU) receives control information over a physical downlink control channel in a shared radio resource space monitored by the WTRU. The control information includes radio resource assignment information and an indication of whether the control information includes radio resource assignment information for an uplink shared channel or whether the control information includes radio resource assignment information for a downlink shared channel. The WTRU determines whether the control information is intended for the WTRU based on WTRU identity-masked (ID-masked) cyclic redundancy check (CRC) bits. The WTRU determines, based on the indication, whether the control information is for the uplink shared channel or whether the control information is for the downlink shared channel. The WTRU transmits data over the uplink shared channel based on the radio resource assignment information on a condition that the control information is determined to be for the uplink shared channel.