As part of carrier assignment and configuration for multicarrier wireless communications, a single uplink (UL) primary carrier may provide control information for multiple concurrent downlink (DL) carriers. Optionally, control information for each DL carrier may be transmitted over paired UL carriers. Carrier switching of UL and/or DL carriers, including primary and anchor carriers, may occur during normal operation or during handover, and may occur in only the UL or only the DL direction. A unidirectional handover is performed when only an UL carrier or only a DL carrier is switched as part of a handover. Switching of UL and/or DL carriers may be from one component carrier or a subset of carriers to another component carrier, another subset of carriers, or all carriers in the same direction.