Method and apparatus for secondary base station change in mobile wireless communication system

1. A method performed by a Master Node (MN), the method comprising;

transmitting, by the MN, to a target Secondary Node (SN) a first base station control message requesting resource allocation;

receiving, by the MN, from the target SN a second base station control message accepting request,

determining, by the MN, to perform a 1st reconfiguration procedure or a 2nd reconfiguration procedure;

performing, by the MN, the 1st reconfiguration procedure in response to MN receiving a 2nd information;

performing, by the MN, the 2nd reconfiguration procedure in response to MN not receiving the 2nd information;

transmitting, by the MN in response to MN determining to perform the 1st reconfiguration procedure, to a terminal a first Downlink (DL) message, wherein the first DL message includes a first identifier and one or more CondReconfigToAddMod, wherein each of the one or more CondReconfigToAddMod includes an execution condition, a second identifier, and a reconfiguration message, wherein the first identifier is a transaction identifier and the second identifier is a conditional reconfiguration identifier;

receiving, by the MN, from the terminal a first Uplink (UL) message, wherein the first UL message includes the first identifier; and

transmitting, by the MN, to a source SN a third base station control message after a second UL message is received from the terminal, wherein the second UL message includes the second identifier, wherein the second identifier corresponds to the reconfiguration message in the CondReconfigToAddMod, wherein the second UL message is received after the first UL message is received, and wherein the third base station control message requests release of the source SN,

wherein 1st information is comprised in the first base station control message in case that the 1st reconfiguration procedure is requested,

wherein the 2nd information comprises a specific cell's global identity.

2. The method of claim 1 ,

wherein the first base station control message further includes measurement results for the second base station.

3. The method of claim 1 ,

wherein the first base station control message includes first information indicating that a first reconfiguration procedure is requested.

4. The method of claim 3 ,

wherein the first reconfiguration is conditional PSCell addition.

5. The method of claim 3 ,

wherein the first information includes assistance information for the second base station to determine resource for the terminal.

6. The method of claim 1 ,

wherein the first base station control message further includes Data Radio Bearer (DRB) configuration of a one or more DRBs.

7. The method of claim 1 , further comprising:

receiving from the target SN a second base station control message in response to the first base station control message.

8. The method of claim 7 ,

wherein the second base station control message includes second information in response that first information was included in the first base station control message.

9. The method of claim 8 ,

wherein the second information includes a cell global identifier of a specific cell for a first reconfiguration procedure.

10. The method of claim 8 ,

wherein the second information includes information related to a plurality of PSCells.

11. The method of claim 7 ,

wherein the second base station control message includes Cell Group configuration.

12. The method of claim 11 ,

wherein the Cell Group configuration includes the reconfiguration message.

13. The method of claim 11 ,

wherein the Cell Group configuration further includes:

information related to Secondary Cell Group bearer; and

Discontinuous Reception configuration of Secondary Cell Group.

14. The method of claim 1 ,

wherein the first DL message includes a parameter for execution condition.

15. The method of claim 1 ,

wherein the first DL message further includes a parameter indicate the execution condition is related to measurement configuration of Secondary Cell Group.

16. The method of claim 15 ,

wherein the parameter for execution condition is determined by the source SN.

17. The method of claim 1 , further comprising:

transmitting to the target SN a third base station control message, wherein the third base station control message includes the second UL message.

18. The method of claim 1 , wherein:

the first UL message is not forwarded to the first SN; and

the second UL message is forwarded to the first SN.

19. The method of claim 1 , further comprising:

transmitting to the target SN a fourth base station control message, wherein the fourth base station control message includes Packet Data Convergence Protocol (PDCP) sequence number, and wherein data forwarding is performed based on the PDCP sequence number.

20. A Master Node (MN) in a wireless communication system, the MN comprising:

a transceiver configured to transmit and receive a signal; and

a controller configured to control the transceiver to:

transmit to a target Secondary Node (SN) a first base station control message requesting resource allocation;

receive from the target SN a second base station control message accepting request,

determine to perform a 1st reconfiguration procedure or a 2nd reconfiguration procedure;

perform the 1st reconfiguration procedure in response to MN receiving a 2nd information;

perform the 2nd reconfiguration procedure in response to MN not receiving the 2nd information;

transmit, in response to MN determining to perform the 1st reconfiguration procedure, to a terminal a first Downlink (DL) message, wherein the first DL message includes a first identifier and one or more CondReconfigToAddMod, wherein each of the one or more CondReconfigToAddMod includes an execution condition, a second identifier, and a reconfiguration message, wherein the first identifier is a transaction identifier and the second identifier is a conditional reconfiguration identifier;

receive from the terminal a first Uplink (UL) message, wherein the first UL message includes the first identifier; and

transmit to a source SN a third base station control message after a second UL message is received from the terminal, wherein the second UL message includes the second identifier, wherein the second identifier corresponds to the reconfiguration message in the CondReconfigToAddMod, wherein the second UL message is received after the first UL message is received, and wherein the third base station control message requests release of the source SN,

wherein 1st information is comprised in the first base station control message in case that the 1 st reconfiguration procedure is requested,

wherein the 2nd information comprises a specific cell's global identity.