Method and device for operating uplink time adjustment timer during l1/l2-based handover in mobile communication system

A base station in a wireless communication system, comprising:

• a transceiver;
• and
• a controller, wherein the controller is configured to control the transceiver to:
• receive, from a gNB-DU (distributed unit), a message related to timing advance (TA) information, and
• transmit, to a user equipment (UE), a L1/L2 triggered mobility (LTM) medium access control (MAC) control element (CE), wherein the LTM MAC CE includes at least one of candidate target configuration ID for the LTM, or timing advance command indicating a TA value.

A user equipment (UE) in a wireless communication system, comprising:

• a transceiver;
• and
• a controller, wherein the controller is configured to control the transceiver to:
• receive, from a base station, a L1/L2 triggered mobility (LTM) medium access control (MAC) control element (CE), in case that a message related to timing advance (TA) information is transmitted from a gNB-DU (distributed unit) to the base station, and
• identify that the LTM MAC CE includes at least one of candidate target configuration ID for the LTM, or timing advance command indicating a TA value.