TRS for multicast and broadcast

1. A method of wireless communication at a base station, comprising:

determining a multicast/broadcast service to be provided to a user equipment (UE) in a multicast broadcast single frequency network (MBSFN) area; and

transmitting, to the UE, a tracking reference signal (TRS) indicating information to maintain continuity of the multicast/broadcast service between different MBSFN areas during mobility of the UE, wherein the information is based on a radio resource control (RRC) state of the UE.

2. The method of claim 1 , wherein the information indicates one or more of:

a bandwidth part (BWP) on which the multicast/broadcast service is to be received by the UE when the UE is operating in an RRC Idle state or an RRC Inactive state, or

at least one of a BWP or a serving cell on which the multicast/broadcast service is to be received by the UE when the UE is operating in an RRC Connected state.

3. The method of claim 2 , wherein the information indicates which of the at least one of the BWP or the serving cell is used in the different MBSFN areas to maintain the continuity of the multicast/broadcast service between the different MBSFN areas when the UE is operating in the RRC Connected state.

4. The method of claim 1 , wherein the TRS is a periodic TRS, the method further comprising:

transmitting periodic TRS parameters in system information or a multicast control channel (MCCH).

5. The method of claim 4 , wherein the TRS is transmitted using a periodicity that is an integer multiple of an MCCH periodicity.

6. The method of claim 1 , wherein the TRS is a semi-persistent TRS, the method further comprising:

transmitting, to the UE on a multicast control channel (MCCH), a set of parameters associated with the semi-persistent TRS; and

transmitting, to the UE in a medium access control-control element (MAC-CE), information activating transmission of the semi-persistent TRS for the UE according to the set of parameters.

7. The method of claim 6 , wherein the TRS is transmitted based on a periodicity that is an integer multiple of an MCCH periodicity.

8. The method of claim 1 , wherein the TRS is an aperiodic TRS, the method further comprising:

transmitting, to the UE, a set of parameters associated with the aperiodic TRS on a multicast control channel (MCCH) or via unicast RRC signaling; and

transmitting, to the UE in downlink control information (DCI), information triggering the aperiodic TRS.

9. The method of claim 8 , wherein the DCI includes a multicast control channel radio network temporary identifier (MCCH-RNTI), and the MCCH-RNTI indicates a schedule of the MCCH carried on a physical downlink shared channel (PDSCH).

10. The method of claim 8 , wherein the DCI includes a group radio network temporary identifier (G-RNTI) to indicate a schedule for a multicast traffic channel (MTCH).

11. The method of claim 8 , further comprising:

transmitting, to the UE, the aperiodic TRS based on DCI including the information triggering the aperiodic TRS, wherein the aperiodic TRS indicates information configuring data communication associated with the multicast/broadcast service; and

transmitting, after the aperiodic TRS, the data communication associated with the multicast/broadcast service.

12. The method of claim 8 , wherein the DCI indicates a slot offset for the aperiodic TRS relative to a slot carrying the DCI.

13. The method of claim 8 , wherein the DCI schedules a data communication associated with the multicast/broadcast service on a different BWP than a first BWP on which the data communication is currently scheduled.

14. The method of claim 1 , further comprising:

configuring a second synchronization signal block (SSB) for the multicast/broadcast service; and

transmitting the second SSB on a raster that is different than a synchronization raster.

15. The method of claim 14 , wherein the second SSB is at least one of a semi-persistent SSB, a periodic burst SSB, or quasi-located with the TRS using a same cell identifier.

16. The method of claim 1 , further comprising:

establishing a connection with a UE; and

transmitting information about a TRS for a second base station to the UE.

17. The method of claim 16 , wherein the base station comprises a source base station serving the UE and the second base station comprises a target base station in a different multicast area.

18. A method of wireless communication at a user equipment (UE), comprising:

receiving a tracking reference signal (TRS) from a base station associated with an multicast broadcast single frequency network (MBSFN) area providing a multicast/broadcast service for the UE, the TRS indicating information to maintain continuity of the multicast/broadcast service between different MBSFN areas during mobility of the UE, wherein the information is based on a radio resource control (RRC) state of the UE; and

receiving the multicast/broadcast service based on the TRS.

19. The method of claim 18 , wherein the TRS comprises at least one of an activation of a bandwidth part (BWP) for receiving the multicast/broadcast service by the UE, a switch of a BWP for receiving the multicast/broadcast service by the UE, an identifier (ID) of a cell in which to receive the multicast/broadcast service by the UE, or an ID of a beam via which to receive the multicast/broadcast service by the UE.

20. The method of claim 18 , wherein the TRS is a periodic TRS, the method further comprising:

receiving a configuration for periodic TRS parameters in system information or a multicast control channel (MCCH).

21. The method of claim 18 , wherein the TRS is a semi-persistent TRS, the method further comprising:

receiving a set of parameters associated with the semi-persistent TRS on a multicast control channel (MCCH) associated with the MBSFN area; and

receiving, in the MBSFN area, a medium access control-control element (MAC-CE) indicating information activating transmission of the semi-persistent TRS for the UE according to the set of parameters.

22. The method of claim 18 , wherein the TRS is an aperiodic TRS, the method further comprising:

receiving, in the MBSFN area, a set of parameters associated with the aperiodic TRS on a multicast control channel (MCCH) or via unicast RRC signaling; and

receiving, in downlink (DL) downlink control information (DCI), information indicating transmission of the aperiodic TRS is triggered in the MBSFN area.

23. The method of claim 18 , further comprising:

receiving a configuration for a second synchronization signal block (SSB) for the multicast/broadcast service; and

receiving the second SSB on a raster that is different than a synchronization raster.

24. The method of claim 18 , further comprising:

establishing a connection with the base station; and

receiving information from the base station about a TRS for a second base station.

25. An apparatus for wireless communication at a base station, comprising:

a memory; and

at least one processor coupled to the memory and configured to:

determine a multicast/broadcast service to be provided to a user equipment (UE) in a multicast broadcast single frequency network (MBSFN) area; and

transmit, to the UE, a tracking reference signal (TRS) indicating a bandwidth part (BWP) associated with the multicast/broadcast service to be provided to the UE, the TRS further indicating information to maintain continuity of the multicast/broadcast service between different MBSFN areas during mobility of the UE, wherein the information is based on a radio resource control (RRC) state of the UE.

26. The apparatus of claim 25 , wherein the TRS is a semi-persistent TRS, and wherein the at least one processor is further configured to:

transmit, to the UE on a multicast control channel (MCCH), a set of parameters associated with the semi-persistent TRS; and

transmit, to the UE in a medium access control-control element (MAC-CE), information activating transmission of the semi-persistent TRS for the UE according to the set of parameters.

27. The apparatus of claim 25 , wherein the TRS is an aperiodic TRS, and wherein the at least one processor is further configured to:

transmit a set of parameters associated with the aperiodic TRS on a multicast control channel (MCCH) or via unicast RRC signaling; and

transmit in downlink control information (DCI), information triggering the aperiodic TRS.

28. The apparatus of claim 25 , wherein the at least one processor is further configured to:

establish a connection with a UE; and

transmit information about a TRS for a second base station to the UE.

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

a memory; and

at least one processor coupled to the memory and configured to:

receive a tracking reference signal (TRS) indicating a bandwidth part (BWP) associated with a multicast/broadcast service, the TRS further indicating information to maintain continuity of the multicast/broadcast service between different multicast broadcast single frequency network (MBSFN) areas during mobility of the UE, wherein the information is based on a radio resource control (RRC) state of the UE, and

receive the multicast/broadcast service in a (MBSFN) area.