A user equipment (UE) is configured to receive a handover command from a source cell, wherein the UE is configured to exchange data with the source cell after the reception of the handover command, perform downlink synchronization acquisition with a target cell while the UE is configured to exchange data with the source cell and transmit an uplink signal to the target cell, wherein the UE stops exchanging data with the source cell after transmitting the uplink signal to the target cell.