Method and user equipment for switching to dual connectivity in carrier aggregation

A user equipment comprising:

• a transceiver;
• and
• a processor configured to:
• apply configuration information to a second cell which is configured by a first cell for a carrier aggregation,
• control the transceiver to receive, from a base station, a message including a request for switching the second cell from the carrier aggregation to dual connectivity,
• perform a procedure for the switching of the second cell from the carrier aggregation to the dual connectivity,
• maintain the configuration information, which has been applied for the carrier aggregation, thereby being applied to the second cell for the dual connectivity after the switching to the dual connectivity,
• wherein after the switching of the second cell from the carrier aggregation to the dual connectivity, the second cell becomes a primary secondary cell or a secondary cell of a secondary cell group (SCG), and
• wherein after the switching of the second cell from the carrier aggregation to the dual connectivity, the second cell becomes a primary secondary cell or a secondary cell of a secondary cell group (SCG), and
• control the transceiver to transmit a physical uplink control channel (PUCCH) to the primary secondary cell or the secondary cell of the SCG after the switching of the second cell from the carrier aggregation to the dual connectivity.