Method for PDCP control PDU transmission by user equipment (UE)

A user equipment (UE) to transmit data, the UE comprising:

• a memory unit configured to buffer a packet data convergence protocol (PDCP) control protocol data unit (PDU) to transmit through an uplink (UL) split bearer;
• a controller configured to control to trigger the PDCP control PDU, and determine whether a UL grant is available for a master evolved node B (eNB);
• and
• a transceiver configured to:
• in response to the UL grant being available for the master eNB, transmit the PDCP control PDU on a link associated with the master eNB;
• and
• in response to the UL grant being unavailable for the master eNB, transmit the PDCP control PDU on a link associated with a secondary eNB,
• wherein the PDCP control PDU is triggered when PDCP UL data buffered for the UL split bearer exceeds a threshold level, and
• wherein the controller is further configured to detect whether a state of a discontinuous reception (DRX) cycle of the link associated with the master eNB is in one of an active state and a DRX state, and control the transceiver to transmit the PDCP control PDU, based on the detected state of the DRX cycle.