Dual active protocol stack operation for handover and PSCell change
A central unit (CU) of a distributed base station for configuring a dual active protocol stack (DAPS) procedure at a UE communicating with the distributed base station via a source distributed unit (DU) (i) determines ( 1002 ) that the UE is to perform the DAPS procedure in order to disconnect from the source DU and connect to a target DU; and (ii) transmits ( 1008 ), to the source DU, an indication that the source DU is to continue communicating with the UE during the DAPS procedure.
1. A method in a central unit (CU) of a distributed base station for configuring a dual active protocol stack (DAPS) procedure at a UE communicating with the distributed base station via a source distributed unit (DU), the method comprising:
determining, by the CU, that the UE is to perform the DAPS procedure in order to disconnect from the source DU and connect to a target DU;
transmitting, by the CU and to the source DU, a first message indicating that the source DU is to continue communicating with the UE during the DAPS procedure; and
subsequent to obtaining an indication of the UE connecting to the target DU during the DAPS procedure, transmitting, by the CU and to the source DU, a second message indicating that the source DU is to stop communicating with the UE.
2. The method of claim 1 , wherein the first message is a DL RRC Message Transfer message.
3. The method of claim 1 , wherein the first message is included in a handover command.
4. The method of claim 3 , wherein the handover command is included in a UE Context Modification Request.
5. The method of claim 4 , wherein the UE Context Modification Request excludes a Transmission Action Indicator field, the exclusion indicating that the source DU is to continue communicating with the UE during the DAPS procedure.
6. The method of claim 4 , wherein the UE Context Modification Request includes a Transmission Action Indicator indicative of a restart of communications with the UE, thereby indicating that the source DU is to continue communicating with the UE during the DAPS procedure.
7. The method of claim 1 ,
further comprising transmitting, by the CU and to the target DU, a message to request a DAPS configuration for the UE to perform the DAPS procedure; and
wherein the UE continues communicating with the source DU using the DAPS configuration.
8. The method of claim 7 , wherein the message transmitted to the target DU is a UE Context Setup Request message.
9. The method of claim 1 , further comprising:
causing the source DU to release a context of the UE subsequent to the obtaining of the indication of the UE connecting to the target DU during the DAPS procedure.
10. The method of claim 9 , wherein causing the source DU to release the UE context includes transmitting a UE Context Release Command to the source DU.
11. The method of claim 10 , further comprising:
receiving, from the source DU and in response to the UE Context Release Command, a UE Context Release Complete message.
12. The method of claim 1 , wherein the DAPS procedure is a DAPS handover procedure.
13. The method of claim 1 , wherein the DAPS procedure is a DAPS primary secondary cell (PSCell) change procedure.
14. A central unit (CU) of a distributed base station for configuring a dual active protocol stack (DAPS) procedure at a UE communicating with the distributed base station via a source distributed unit (DU), the CU comprising processing hardware and configured to:
determine that the UE is to perform the DAPS procedure in order to disconnect from the source DU and connect to a target DU;
transmit, to the source DU, a first message indicating that the source DU is to continue communicating with the UE during the DAPS procedure; and
subsequent to obtaining an indication of the UE connecting to the target DU during the DAPS procedure, transmit, by the CU and to the source DU, a second message indicating that the source DU is to stop communicating with the UE.
15. The CU of claim 14 , wherein the first message is a DL RRC Message Transfer message or the first message is included in a UE Context Modification Request of a handover command.
16. The CU of claim 15 , wherein the UE Context Modification Request excludes a Transmission Action Indicator field, the exclusion indicating that the source DU is to continue communicating with the UE during the DAPS procedure.
17. The CU of claim 15 , wherein the UE Context Modification Request includes a Transmission Action Indicator indicative of a restart of communications with the UE, thereby indicating that the source DU is to continue communicating with the UE during the DAPS procedure.
18. The CU of claim 14 , wherein the DAPS procedure is a DAPS handover procedure or a DAPS primary secondary cell (PSCell) change procedure.
19. The CU of claim 14 , wherein:
the CU is further configured to transmit, to the target DU, a message to request a DAPS configuration for the UE to perform the DAPS procedure; and
the UE continues communicating with the source DU using the DAPS configuration.
20. The CU of claim 14 , wherein the CU is further configured to:
cause the source DU to release a context of the UE subsequent to the obtaining of the indication of the UE connecting to the target DU during the DAPS procedure.