Triggering reference signals in wireless networks

1. A method for a user equipment (UE) to communicate in a wireless communication network comprising a primary serving cell (PCell) and a secondary serving cell (SCell), the method comprising:

receiving a reference signal trigger from the PCell triggering communication and processing of one or more reference signals between the UE and the SCell;

synchronizing with the SCell based on the one or more reference signals to activate the SCell for multi-cell communication; and

transmitting acknowledgement information acknowledging receipt of the reference signal trigger for activation of the SCell, the acknowledgement information being transmitted to the SCell on at least one beam associated with at least one of the one or more reference signals.

2. The method of claim 1 , wherein the reference signal trigger identifies the one or more reference signals of a plurality of reference signals configured in the SCell.

3. The method of claim 2 , wherein the receiving the reference signal trigger further comprises:

receiving a medium access control-control element (MAC-CE) comprising the reference signal trigger.

4. The method of claim 3 ,

wherein the acknowledgement information acknowledges receipt of the MAC-CE.

5. The method of claim 4 , further comprising:

selecting a serving beam pair link for communication between the SCell and the UE based on the at least one beam associated with the acknowledgement information.

6. The method of claim 1 , wherein the one or more reference signals comprise at least one of a channel state information-reference signal (CSI-RS), a synchronization signal block (SSB), or a sounding reference signal (SRS).

7. The method of claim 1 , further comprising:

transmitting an uplink reference signal of the one or more reference signals to the SCell in response to receiving the reference signal trigger.

8. The method of claim 1 , wherein the PCell comprises a first radio access technology (RAT) and the SCell comprises a second RAT.

9. The method of claim 1 , further comprising:

transmitting an activation message to the PCell to activate communication with the SCell for the multi-cell communication with the PCell and the SCell.

10. A scheduled entity in a wireless communication network comprising a primary serving cell (PCell) and a secondary serving cell (SCell), the scheduled entity comprising:

a transceiver;

a memory; and

a processor communicatively coupled to the transceiver and the memory, wherein the processor and the memory are configured to:

receive a reference signal trigger from the PCell triggering communication and processing of one or more reference signals between the UE and the SCell via the transceiver;

synchronize with the SCell based on the one or more reference signals to activate the SCell for multi-cell communication; and

transmit acknowledgement information acknowledging receipt of the reference signal trigger for activation of the SCell, the acknowledgement information being transmitted to the SCell on at least one beam associated with at least one of the one or more reference signals for selection of a serving beam pair link for communication between the SCell and the UE.

11. The scheduled entity of claim 10 , wherein the reference signal trigger identifies the one or more reference signals of a plurality of reference signals configured in the SCell.

12. The scheduled entity of claim 11 , wherein the processor and the memory are further configured to:

receive a medium access control-control element (MAC-CE) comprising the reference signal trigger,

wherein the acknowledgement information acknowledges receipt of the MAC-CE.

13. The scheduled entity of claim 12 , wherein the processor and the memory are further configured to:

select a serving beam pair link for communication between the SCell and the UE based on the at least one beam associated with the acknowledgement information.

14. The scheduled entity of claim 10 , wherein the processor and the memory are further configured to:

transmit an uplink reference signal of the one or more reference signals to the SCell in response to receiving the reference signal trigger.

15. The scheduled entity of claim 10 , wherein the processor and the memory are further configured to:

transmit an activation message to the PCell to activate communication with the SCell for the multi-cell communication with the PCell and the SCell.

16. A method for a primary serving cell (PCell) to facilitate multi-cell communication in a wireless communication network comprising the PCell and a secondary serving cell (SCell), the method comprising:

communicating with a user equipment (UE) in the PCell;

activating communication between the UE and the SCell for the multi-cell communication; and

transmitting a reference signal trigger to the UE that triggers communication and processing of one or more reference signals between the UE and the SCell, the reference signal trigger further includes a respective beam identifier of each beam associated with the one or more reference signals to configure the UE to synchronize with the SCell using the one or more reference signals and to transmit acknowledgement information acknowledging receipt of the reference signal trigger on at least one beam associated with at least one of the one or more reference signals for activation of the SCell.

17. The method of claim 16 , wherein the activating communication between the UE and the SCell further comprises:

receiving an activation message from the UE to activate the SCell for the multi-cell communication.

18. The method of claim 16 , wherein the reference signal trigger identifies the one or more reference signals of a plurality of reference signals configured in the SCell.

19. The method of claim 18 , further comprising:

selecting the one or more reference signals from the plurality of reference signals, wherein the one or more reference signals comprise a subset of the plurality of reference signals.

20. The method of claim 16 , further comprising:

transmitting an indication of the one or more reference signals identified in the reference signal trigger to the SCell.

21. The method of claim 16 , wherein the transmitting the reference signal trigger further comprises:

transmitting a medium access control-control element (MAC-CE) comprising the reference signal trigger.

22. The method of claim 21 , further comprising:

receiving the acknowledgement information from the SCell acknowledging receipt of the MAC-CE by the UE, wherein the acknowledgement information is communicated from the UE to the SCell.

23. The method of claim 16 , wherein the PCell comprises a first radio access technology (RAT) and the SCell comprises a second RAT.