Method and device for changing serving entity

1 . A method performed by a first base station, the method comprising:

identifying that a switch of a feeder link associated with the first base station is triggered;

transmitting, to a second base station, a first message for a handover from a first cell of the first base station to a second cell of the second base station, wherein the first message includes first information on a first frequency compensation value of the first cell, and timing advance (TA) assistance information including second information on a first TA value of the first cell;

receiving, from the second base station, a second message as a response to the first message, wherein the second message includes information on a second frequency compensation value of the second cell, and information on a TA offset between the first TA value and a second TA value of the second cell; and

transmitting, to a user equipment (UE), a third message including the first information on the TA offset,

wherein the second frequency compensation value is based on the first frequency compensation value, and

wherein the TA offset for the second cell is based on the first TA value of the first cell.

2 . The method of claim 1 , wherein

the first message further includes position information of the UE associated with the handover, and

wherein an allocation of an uplink grant for the UE is based on the position information.

3 . The method of claim 2 , wherein the TA assistance information includes information on a feeder link delay associated with the first base station, geographic position information of a non-terrestrial access network (NTN) gateway connected to the first base station, and information on a time stamp corresponding to the TA assistance information, and

wherein the position information includes at least one of information on a beam identifier (ID) of the UE, or information indicating a geographic position of the UE.

4 . The method of claim 2 , wherein the first message further includes power control information,

wherein the second message further includes transmit power control (TPC) information,

wherein the TPC information is based on the power control information, and

wherein the power control information includes a power headroom report (PHR) or a received power spectral density.

5 . The method of claim 1 , wherein the first message is one of:

a satellite connection request message, a handover request message, a handover required message, a UE context modification required message, or an uplink radio resource control (RRC) message transfer message,

wherein the second message is one of: satellite connection response message, handover request acknowledgment message, or UE context modification request message, and

wherein the third message is a message including a handover command or system information.

6 . The method of claim 1 , wherein the first base station corresponds to a master node (MN) and the second base station corresponds to a secondary node (SN),

wherein the method further comprises:

receiving, from a third base station corresponding to the SN, a fourth message including the TA assistance information, and

wherein the fourth message is a changing secondary node required message, the first message is a secondary node addition request, and the second message is an acknowledgment for the secondary node addition request.

7 . A first base station comprising:

at least one transceiver;

at least one processor communicatively coupled to the at least one transceiver; and

at least one memory, communicatively coupled to the at least one processor, storing instructions executable by the at least one processor individually or in any combination to cause the first base station to:

identify that a switch of a feeder link associated with the first base station is triggered,

transmit, to a second base station, a first message for a handover from a first cell of the first base station to a second cell of the second base station, wherein the first message includes first information on a first frequency compensation value of the first cell, and timing advance (TA) assistance information including second information on a first TA value of the first cell,

receive, from the second base station, a second message as a response to the first message, wherein the second message includes information on a second frequency compensation value of the second cell, and information on a TA offset between the first TA value and a second TA value of the second cell, and

transmit, to a user equipment (UE), a third message including the information on the TA offset,

wherein the second frequency compensation value is based on the first frequency compensation value, and

wherein the TA offset for the second cell is based on the first TA value of the first cell.

8 . The first base station of claim 7 ,

wherein the first message further includes position information of the UE associated with the handover, and

wherein an allocation of an uplink grant for the UE is based on the position information.

9 . The first base station of claim 8 , wherein the TA assistance information includes information on a feeder link delay associated with the first base station, geographic position information of a non-terrestrial access network (NTN) gateway connected to the first base station, and information on a time stamp corresponding to the TA assistance information; and

wherein the position information includes at least one of information on a beam identifier (ID) of the UE, or information indicating a geographic position of the UE.

10 . The first base station of claim 8 , wherein the first message further includes power control information,

wherein the second message further includes transmit power control (TPC) information,

wherein the TPC information is based on the power control information, and

wherein the power control information includes a power headroom report (PHR) or a received power spectral density.

11 . The first base station of claim 7 , wherein the first message is one of: a satellite connection request message, a handover request message, a handover required message, a UE context modification required message, or an uplink radio resource control (RRC) message transfer message,

wherein the second message is one of: satellite connection response message, handover request acknowledgment message, or UE context modification request message, and

wherein the third message is a message including a handover command or system information.

12 . The first base station of claim 7 , wherein the first base station corresponds to a master node (MN) and the second base station corresponds to a secondary node (SN),

wherein the instructions further cause the first base station to:

receive, from a third base station corresponding to the SN, a fourth message including the TA assistance information, and

wherein the fourth message is a changing secondary node required message, the first message is a secondary node addition request, and the second message is an acknowledgment for the secondary node addition request.

13 . A method performed by a second base station, the method comprising:

receiving, from a first base station, a first message for a handover from a first cell of the first base station to a second cell of the second base station, based on a switch of a feeder link associated with the first base station being triggered, wherein the first message includes first information on a first frequency compensation value of the first cell, and timing advance (TA) assistance information including second information on a first TA value of the first cell;

identifying a second frequency compensation value of the second cell, based on the first frequency compensation value;

identifying a TA offset between the first TA value and a second TA value of the second cell, based on the first TA value; and

transmitting, to the first base station, a second message as a response to the first message, wherein the second message includes information on the second frequency compensation value of the second cell, and information on the TA offset for the second cell.

14 . The method of claim 13 ,

wherein the first message further includes position information of a user equipment (UE) associated with the handover, and

wherein an uplink grant for the UE is allocated based on the position information.

15 . The method of claim 14 , wherein the TA assistance information includes information on a feeder link delay associated with the first base station, geographic position information of a non-terrestrial access network (NTN) gateway connected to the first base station, and information on a time stamp corresponding to the TA assistance information, and

wherein the position information includes at least one of information on a beam identifier (ID) of the UE, or information indicating a geographic position of the UE.

16 . The method of claim 14 , wherein the first message further includes power control information,

wherein the second message further includes transmit power control (TPC) information,

wherein the TPC information is based on the power control information, and

wherein the power control information includes a power headroom report (PHR) or a received power spectral density.

17 . A second base station comprising:

at least one transceiver;

at least one processor communicatively coupled to the at least one transceiver; and

at least one memory, communicatively coupled to the at least one processor, storing instructions executable by the at least one processor individually or in any combination to cause the second base station to:

receive, from a first base station, a first message for a handover from a first cell of the first base station to a second cell of the second base station, based on a switch of a feeder link associated with the first base station being triggered, wherein the first message includes first information on a first frequency compensation value of the first cell, and timing advance (TA) assistance information including second information on a first TA value of the first cell,

identify a second frequency compensation value of the second cell, based on the first frequency compensation value,

identify a TA offset between the first TA value and a second TA value of the second cell, based on the first TA value, and

transmit, to the first base station, a second message as a response to the first message,

wherein the second message includes information on the second frequency compensation value of the second cell, and information on the TA offset for the second cell.

18 . The second base station of claim 17 ,

wherein the first message further includes position information of a user equipment (UE) associated with the handover, and

wherein an uplink grant for the UE is allocated based on the position information.

19 . The second base station of claim 18 , wherein the TA assistance information includes information on a feeder link delay associated with the first base station, geographic position information of a non-terrestrial access network (NTN) gateway connected to the first base station, and information on a time stamp corresponding to the TA assistance information, and

wherein the position information includes at least one of information on a beam identifier (ID) of the UE, or information indicating a geographic position of the UE.

20 . The second base station of claim 18 , wherein the first message further includes power control information,

wherein the second message further includes transmit power control (TPC) information,

wherein the TPC information is based on the power control information, and

wherein the power control information includes a power headroom report (PHR) or a received power spectral density.