Make-before-break (MBB) handover operations

1. A method of wireless communication performed by a user equipment (UE), comprising:

indicating, to a source network entity, a make-before-break (MBB) handover capability of the UE, the MBB handover capability supporting MBB handovers for one or more data radio bearers (DRBs) identified by the source network entity;

receiving, via a radio resource control (RRC) message transmitted by the source network entity, configuration information for a handover from the source network entity to a target network entity, wherein:

the configuration information is conveyed in a DRB configuration information element (IE) in the RRC message and identifies the one or more DRBs to be supported for the MBB handover, and

the DRB configuration IE comprises:

a field indicating whether the MBB handover is supported for a corresponding DRB, and

an indication to not reestablish packet

data convergence protocol (PDCP) for the corresponding DRB;

determining to support the MBB handover if the configuration information identifies at least one MBB DRB; and

participating in the MBB handover according to the configuration information by continuing to maintain a connection with the source network entity and continuing to communicate data with the source network entity via the at least one MBB DRB while establishing a connection with the target network entity until a connection with the source network entity is released.

2. The method of claim 1 , wherein indicating the MBB handover capability of the UE further comprises providing signaling to the source network entity indicating at least one of:

a maximum number of MBB DRBs supported by the UE; or

specific DRBs to consider for MBB handover support.

3. The method of claim 1 , further comprising indicating a set of DRBs to consider for the MBB handover based on one or more DRB conditions, wherein the one or more DRB conditions comprise at least one of:

whether the one or more DRBs provide a communication path having the least amount of interference based on reference signal received power (RSRP);

whether the one or more DRBs provide a communication path having the least amount of interference based on reference signal received quality (RSRQ);

whether the one or more DRBs provide a communication path having the least amount of interference based on signal to noise interference (SINR) measurements; or whether quality of service (QoS) requirements of the one or more DRBs support ultra-reliable low latency communication (URLLC) services.

4. The method of claim 1 , further comprising receiving a handover command from the source network entity, wherein:

participating in the MBB handover is based on the handover command; and

participating in the MBB handover further comprises:

suspending data communication via a non-MBB DRB with the source network after receiving the handover command; and

resuming data communication via the non-MBB DRB with the target network entity after a successful handover to the target network entity, wherein the non-MBB DRB is not identified by the configuration information.

5. The method of claim 1 , further comprising maintaining a source network entity connection configuration for one or more non-MBB DRBs if the MBB handover is for at least one MBB DRB.

6. The method of claim 5 , wherein upon detecting a failure of the MBB handover or a radio link failure (RLF) on the target network entity while a connection with at least one MBB DRB is still active, the method further comprises:

declaring an RLF on the target network entity without triggering a radio resource control (RRC) reestablishment;

performing a fallback to the source network entity and operating both non-MBB DRBs and MBB DRBs using the source network entity connection configuration; and

sending RLF information to the source network entity, the RLF information comprising a cause of failure and any available target cell measurement results.

7. The method of claim 1 , further comprising triggering an RRC reestablishment during the MBB handover only when both a source network entity connection fails and a target network entity connection fails.

8. A method of wireless communication performed by a source network entity, comprising:

receiving, from a user equipment (UE), a make-before-break (MBB) handover capability of the UE, the MBB handover capability supporting MBB handovers for one or more data radio bearers (DRBs) identified by the source network entity;

transmitting, via a radio resource control (RRC) message, configuration information for the MBB handover to the UE, wherein:

the configuration information is conveyed in a DRB configuration information element (IE) in the RRC message and identified the one or more DRBs supported for the MBB handover, and

the DRB configuration IE comprises:

a field indicating whether the MBB handover is supported for a corresponding DRB, and

an indication to not reestablish packet data convergence protocol (PDCP) for the corresponding DRB; and

participating in the MBB handover according to the configuration information by continuing to maintain a connection with the UE and continuing to communicate data with the UE via the one or more DRBs supported for the MBB handover while the UE establishes a connection with a target network entity until a connection with the UE is released.

9. The method of claim 8 , further comprising:

transmitting the target network entity a set of one or more DRBs to be supported for the MBB handover of a user equipment (UE) from the source network entity to the target network entity;

receiving, from the target network entity, an indication of one or more of the set of DRBs the target network entity accepts to support for the MBB handover; and

including the indication of one or more of the set of DRBs in the configuration information sent to the UE.

10. The method of claim 8 , further comprising:

receiving signaling from the UE or another network entity indicating at least one of: a maximum number of MBB DRBs supported by the UE, or specific DRBs to consider for MBB handover support; and

determining which DRBs are to be supported for the MBB handover based, at least in part, on the received signaling.

11. An apparatus for wireless communication at a user equipment (UE), comprising:

one or more processors configured to execute instructions stored on one or more memories and to cause the UE to:

indicate a make-before-break (MBB) handover capability of the UE, the MBB handover capability supporting MBB handovers for one or more data radio bearers (DRBs) identified by a source network entity;

receive, via a radio resource control (RRC) message transmitted by the source network entity, configuration information for a handover from the source network entity to a target network entity, wherein:

the configuration information is conveyed in a DRB configuration information element (IE) in the RRC message and identifies the one or more DRBs to be supported for the MBB handover, and

the DRB configuration IE comprises:

a field indicating whether the MBB handover is supported for a corresponding DRB, and

an indication to not reestablish packet data convergence protocol (PDCP) for the corresponding DRB;

determine to support the MBB handover if the configuration information identifies at least one MBB DRB; and

participate in the MBB handover according to the configuration information by continuing to maintain a connection with the source network entity and continuing to communicate data with the source network entity via the at least one MBB DRB while establishing a connection with the target network entity until a connection with the source network entity is released.

12. The apparatus of claim 11 , wherein, in order to indicate indicate the MBB handover capability, the one or more processors are further configured to cause the UE to provide signaling to the source network entity indicating a maximum number of MBB DRBs supported by the UE.

13. The apparatus of claim 12 , wherein the one or more processors are further configured to cause the UE to indicate a set of DRBs to consider for the MBB handover based on one or more DRB conditions, wherein the one or more DRB conditions comprise at least one of:

whether the one or more DRBs provide a communication path having the least amount of interference based on reference signal received power (RSRP);

whether the one or more DRBs provide a communication path having the least amount of interference based on reference signal received quality (RSRQ);

whether the one or more DRBs provide a communication path having the least amount of interference based on signal to noise interference (SINR) measurements; or

whether quality of service (QOS) requirements of the one or more DRBs support ultra-reliable low latency communication (URLLC) services.

14. The apparatus of claim 11 , wherein:

the one or more processors are further configured to cause the UE to receive a handover command from the source network entity;

the one or more processors are further configured to cause the UE to participate in the MBB handover based on the handover command; and

in order to participate in the MBB handover, the one or more processors are further configured to cause the UE to:

suspend data communication via a non-MBB DRB with the source network entity after receiving the handover command; and

resume data communication via the non-MBB DRB with the target network entity after a successful handover to the target network entity, wherein the non-MBB DRB is not identified by the configuration information.

15. The apparatus of claim 11 , wherein the one or more processors are further configured to cause the UE to maintain a source network entity connection configuration for one or more non-MBB DRBs if the MBB handover is for at least one MBB DRB.

16. The apparatus of claim 15 , wherein upon detecting a failure of the MBB handover or a radio link failure (RLF) on the target network entity while a connection with at least one MBB DRB is still active, the one or more processors are further configured to cause the UE to:

declare RLF on the target network entity without triggering a radio resource control (RRC) reestablishment;

perform a fallback to the source network entity and operate both non-MBB DRBs and MBB DRBs using the source network entity connection configuration; and

send RLF information to the source network entity, the RLF information comprising a cause of failure and any available target cell measurement results.

17. The apparatus of claim 11 , wherein the one or more processors are further configured to cause the UE to trigger an RRC reestablishment during the MBB handover only when both a source network entity connection fails and a target network entity connection fails.

18. The apparatus of claim 11 , wherein the one or more processors are further configured to cause the UE to maintain a connection with the source network entity and continue to communicate data with the source network entity via the at least one MBB DRB after receiving a handover command from the source network entity and before connection with the source network entity is released.