METHOD AND APPARATUS FOR APPLYING TRANSMISSION CONFIGURATION INDICATOR (TCI) STATE

1 . A method performed by a User Equipment (UE) for applying a Transmission Configuration Indicator (TCI) state, the method comprising:

receiving a Radio Resource Control (RRC) configuration;

receiving a first Medium Access Control (MAC) Control Element (CE) for activating at least one TCI state configured by the RRC configuration;

receiving Downlink Control Information (DCI) for indicating a first TCI state among the at least one TCI state activated by the first MAC CE;

receiving a second MAC CE for indicating a second TCI state after receiving the DCI; and

applying the first TCI state or the second TCI state for a target cell.

2 . The method of claim 1 , wherein the first TCI state and the second TCI state are the same.

3 . The method of claim 1 , further comprising:

switching from a source cell to the target cell based on the second MAC CE, wherein:

the second MAC CE comprises a Layer1/Layer2 Triggered Mobility (LTM) cell switch command MAC CE, and

the first TCI state or the second TCI state is applied after switching to the target cell.

4 . The method of claim 1 , wherein the second MAC CE comprises a TCI state identifier (ID) for indicating the second TCI state.

5 . The method of claim 1 , wherein the second MAC CE comprises an identifier associated with the target cell and timing advance information for indicating whether a time advance is valid for the target cell.

6 . The method of claim 1 , further comprising:

transmitting a Hybrid Automatic Repeat reQuest Acknowledgement (HARQ-ACK) corresponding to the DCI after receiving the second MAC CE.

7 . The method of claim 6 , wherein the first TCI state or the second TCI state is applied starting from a slot that is at least a specific duration after the transmission of the HARQ-ACK.

8 . A User Equipment (UE) for applying a Transmission Configuration Indicator (TCI) state, the UE comprising:

at least one processor; and

at least one non-transitory computer-readable medium storing one or more computer-executable instructions that, when executed by the at least one processor, cause the UE to:

receive a Radio Resource Control (RRC) configuration;

receive a first Medium Access Control (MAC) Control Element (CE) for activating at least one TCI state configured by the RRC configuration;

receive Downlink Control Information (DCI) for indicating a first TCI state among the at least one TCI state activated by the first MAC CE;

receive a second MAC CE for indicating a second TCI state after receiving the DCI; and

apply the first TCI state or the second TCI state for a target cell.

9 . The UE of claim 8 , wherein the first TCI state and the second TCI state are the same.

10 . The UE of claim 8 , wherein the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to:

switch from a source cell to the target cell based on the second MAC CE, wherein:

the second MAC CE comprises a Layer1/Layer2 Triggered Mobility (LTM) cell switch command MAC CE, and

the first TCI state or the second TCI state is applied after switching to the target cell.

11 . The UE of claim 8 , wherein the second MAC CE comprises a TCI state identifier (ID) for indicating the second TCI state.

12 . The UE of claim 8 , wherein the second MAC CE comprises an identifier associated with the target cell and timing advance information for indicating whether a time advance is valid for the target cell.

13 . The UE of claim 8 , wherein the one or more computer-executable instructions, when executed by the at least one processor, further cause the UE to transmit a Hybrid Automatic Repeat reQuest Acknowledgement (HARQ-ACK) corresponding to the DCI after receiving the second MAC CE.

14 . The UE of claim 13 , wherein the first TCI state or the second TCI state is applied starting from a slot that is at least a specific duration after the transmission of the HARQ-ACK.

15 . A Base Station (BS) for indicating a Transmission Configuration Indicator (TCI) state, the BS comprising:

at least one processor; and

at least one non-transitory computer-readable medium storing one or more computer-executable instructions that, when executed by the at least one processor, cause the BS to:

transmit, to a UE, a Radio Resource Control (RRC) configuration;

transmit, to the UE, a first Medium Access Control (MAC) Control Element (CE) for activating at least one TCI state configured by the RRC configuration;

transmit, to the UE, Downlink Control Information (DCI) for indicating a first TCI state among the at least one TCI state activated by the first MAC CE; and

transmit, to the UE, a second MAC CE for indicating a second TCI state after transmitting the DCI,

wherein the second MAC CE enables the UE to apply the first TCI state or the second TCI state for a target cell.

16 . The BS of claim 15 , wherein the first TCI state and the second TCI state are the same.

17 . The BS of claim 15 , wherein:

the second MAC CE comprises a Layer1/Layer2 Triggered Mobility (LTM) cell switch command MAC CE that enables the UE to switch from a source cell to the target cell, and

the LTM cell switch command MAC CE enables the UE to apply the first TCI state or the second TCI state after switching to the target cell.

18 . The BS of claim 15 , wherein the second MAC CE comprises a TCI state identifier (ID) for indicating the second TCI state, an identifier associated with the target cell, and timing advance information for indicating whether a time advance is valid for the target cell.

19 . The BS of claim 15 , wherein the DCI further enables the UE to transmit a Hybrid Automatic Repeat reQuest Acknowledgement (HARQ-ACK) corresponding to the DCI after the UE receives the second MAC CE.

20 . The BS of claim 19 , wherein the second MAC CE enables the UE to apply the first TCI state or the second TCI state starting from a slot that is at least a specific duration after the transmission of the HARQ-ACK.