Fast SCell activation

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

at least one memory; and

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

receive, from a serving cell, an activation indication for a secondary cell (SCell);

receive a first reference signal from the SCell, the first reference signal including at least one temporary reference signal;

identify whether a second reference signal is received after processing the activation indication and before an expiration of an SCell activation time; and

activate, upon identifying that the second reference signal is received, the SCell based on one or more reference signals including at least one of the first reference signal or the second reference signal.

2. The apparatus of claim 1 , wherein the at least one processor is further configured to:

transmit, to the serving cell, an acknowledgment (ACK) for the activation indication; and process the activation indication within a first time duration after the ACK is transmitted to the serving cell.

3. The apparatus of claim 1 , wherein the at least one processor is further configured to:

transmit, a channel state information (CSI) report of one of the first reference signal or the second reference signal on which the UE based the activation of the SCell.

4. The apparatus of claim 1 , wherein the at least one temporary reference signal includes an aperiodic tracking reference signal, and the activation indication indicates the aperiodic tracking reference signal transmitted by the SCell, and

wherein the activation indication is included in one of a medium access control (MAC) control element (CE) (MAC-CE) or downlink control information (DCI).

5. The apparatus of claim 4 , wherein the at least one processor is configured to:

activate the SCell no later than in slot n+K, where slot n represents a slot in which the activation indication is received, and K is based on at least one of a time period between receiving the activation indication from the serving cell and transmitting an acknowledgment (ACK) of the activation indication to the serving cell, the SCell activation time between transmission of the ACK of the activation indication and a second time duration after receiving the at least one temporary reference signal, and a delay uncertainty in acquiring one or more first available CSI reporting resources.

6. The apparatus of claim 1 , wherein the at least one temporary reference signal includes a periodic tracking reference signal, and the activation indication indicates the periodic tracking reference signal transmitted by the SCell.

7. The apparatus of claim 6 , wherein the at least one processor is configured to:

activate the SCell no later than in slot n+K, where slot n represents a slot in which the activation indication is received, and K is based on at least one of a time period between receiving the activation indication from the serving cell and transmitting an acknowledgment (ACK) of the activation indication to the serving cell, the SCell activation time between transmission of the ACK of the activation indication and a second time duration after receiving a last of the one or more reference signals on which the UE based the activation of the SCell, and a delay uncertainty in acquiring one or more first available CSI reporting resources.

8. The apparatus of claim 6 , wherein the activation indication is included in radio resource control (RRC) signaling.

9. The apparatus of claim 1 , wherein the first reference signal is received from an active serving cell, and

wherein the at least one processor is further configured to identify whether the second reference signal is received from the active serving cell.

10. The apparatus of claim 1 , wherein the first reference signal and the second reference signal are assumed to be quasi-co-located with each other.

11. The apparatus of claim 1 , wherein the activation indication indicates activating multiple SCells simultaneously, the multiple SCells including a first SCell and a second SCell.

12. The apparatus of claim 11 , wherein the first SCell and the second SCell are in a same frequency band, in contiguous carriers in the same frequency band, or in a frequency range.

13. The apparatus of claim 11 , wherein the at least one processor is configured to activate the multiple SCells based on the one or more reference signals including the at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received earliest from the multiple SCells.

14. The apparatus of claim 11 , wherein the at least one processor is configured to activate the multiple SCells based on the one or more reference signals including the at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received within an earliest activation time for the multiple SCells.

15. The apparatus of claim 11 , wherein the at least one processor is configured to activate the multiple SCells based on the one or more reference signals including the at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received latest from the multiple SCells.

16. The apparatus of claim 11 , wherein at least one processor is configured to activate the SCell no later than in slot n+K, where slot n represents a slotin which the activation indication is received, and K is based on at least one of a time period between receiving the activation indication from the serving cell and transmitting an acknowledgment (ACK) of the activation indication to the serving cell, the SCell activation time between transmission of the ACK of the activation indication and a second time duration after receiving two or four reference signals including one of the first reference signal or the second reference signal, and a delay uncertainty in acquiring one or more first available CSI reporting resources.

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

at least one memory; and

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

receive, from a serving cell, an activation indication for a secondary cell (SCell) based on a first reference signal, the activation indication indicating a transmission of the first reference signal for activating the SCell;

identify whether the first reference signal is transmitted as indicated; and

activate, upon identifying that the first reference signal is transmitted as indicated, the SCell based on one or more reference signals including the first reference signal or a second reference signal.

18. The apparatus of claim 17 , wherein the at least one processor is further configured to:

transmit, to the serving cell, an acknowledgment (ACK) of receiving the activation indication, wherein the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell.

19. The apparatus of claim 17 , wherein the first reference signal includes at least one of a periodic tracking reference signal or an aperiodic tracking reference signal.

20. The apparatus of claim 17 , wherein, to identify whether the first reference signal is transmitted as indicated, the at least one processor is configured to:

perform a clear channel assessment to determine whether a channel measurement is greater than a threshold value; and

identify that the first reference signal is not transmitted as indicated by the activation indication in response to determining that the channel measurement is greater than the threshold value.

21. The apparatus of claim 17 , wherein the at least one processor is configured to:

receive, from the serving cell, an instruction to cancel the transmission of the first reference signal wherein the UE identifies that the first reference signal is not transmitted in response to receiving the instruction to cancel the first reference signal,

wherein the instruction to cancel the activation indication for the SCell based on the first reference signal is indicated by one of a medium access control (MAC) control element (CE) (MAC-CE) or downlink control information (DCI).

22. The apparatus of claim 17 , wherein the at least one processor is configured to:

activate, based on the first reference signal is not transmitted as indicated, the SCell based on the second reference signal received from the SCell.

23. The apparatus of claim 22 , wherein the SCell is activated no later than in slot n+K, where the activation indication is received in slot n, and K is determined based on at least one of a time period between receiving the activation indication from the serving cell transmitting an acknowledgment (ACK) of the activation indication to the serving cell, an SCell activation time between the transmission of the ACK of the activation indication and a second time duration after receiving the second reference signal, and a delay uncertainty in acquiring one or more first available CSI reporting resources.

24. The apparatus of claim 17 , wherein the at least one processor is further configured to:

receive a new activation indication indicating a transmission of the second reference signal for activating the SCell,

wherein, upon receiving the new activation indication, the UE identifies that the first reference signal is not transmitted as indicated.

25. The apparatus of claim 24 , wherein the at least one processor is configured to:

activate the SCell no later than in slot n+K, where slot n represents a slot in which the activation indication is received, and K is based on at least one of a time period between receiving the activation indication from the serving cell and transmitting an acknowledgment (ACK) of the activation indication to the serving cell, an SCell activation time between the transmission of the ACK of the activation indication and a second time duration after receiving the second reference signal, and a delay uncertainty in acquiring one or more first available CSI reporting resources.

26. The apparatus of claim 17 , wherein the SCell comprises multiple sub-bands, and

wherein, to identify whether the first reference signal is transmitted as indicated, the at least one processor is configured to:

perform a clear channel assessment to determine whether channel measurements are greater than a threshold value for at least one of the multiple sub-bands; and

identify that the first reference signal is not transmitted as indicated upon determining that the channel measurements of at least one of the multiple sub-bands are greater than the threshold value.

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

receiving, from a serving cell, an activation indication for a secondary cell (SCell);

receiving a first reference signal from the SCell, the first reference signal including at least one temporary reference signal;

identifying whether a second reference signal is received after processing the activation indication and before an expiration of an SCell activation time; and

activating, upon identifying that the second reference signal is received, the SCell based on one or more reference signals including at least one of the first reference signal or the second reference signal.

28. The method of claim 27 , wherein the SCell is activated no later than in slot n+K, where the activation indication is received in slot n, and K is determined based on at least one of a time period between receiving the activation indication from the serving cell and transmitting an acknowledgment (ACK) of the activation indication to the serving cell, the SCell activation time between transmission of the ACK of the activation indication and a second time duration after receiving the at least one temporary reference signal, and a delay uncertainty in acquiring one or more first available CSI reporting resources.

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

receiving, from a serving cell, an activation indication for a secondary cell (SCell) based on a first reference signal, the activation indication indicating a transmission of the first reference signal for activating the SCell;

identifying whether the first reference signal is transmitted as indicated; and

activating, upon identifying that the first reference signal is transmitted as indicated, the SCell based on one or more reference signals including the first reference signal or a second reference signal.

30. The method of claim 29 , wherein the SCell is activated no later than in slot n+K, where the activation indication is received in slot n, and K is determined based on at least one of a time period between receiving the activation indication from the serving cell transmitting an acknowledgment (ACK) of the activation indication to the serving cell, an SCell activation time between the transmission of the ACK of the activation indication and a second time duration after receiving the second reference signal, and a delay uncertainty in acquiring one or more first available CSI reporting resources.

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

at least one memory; and

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

receive, from a serving cell, an activation indication for a secondary cell (SCell);

receive a first reference signal from the SCell, the first reference signal including at least one channel state information (CSI) reference signal (CSI RS);

receive a second reference signal prior to an expiration of an SCell activation time; and

activate, based on the second reference signal being received after the activation indication and prior to the expiration of the SCell activation time, the SCell based on the second reference signal.

32. 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, from a serving cell, an activation indication for a secondary cell (SCell) based on a first reference signal, the activation indication indicating a transmission of the first reference signal for activating the SCell;

receive, from the serving cell, a second reference signal; and

activate the SCell based on one or more reference signals including the first reference signal or the second reference signal.

33. A method for wireless communication at a user equipment (UE), comprising:

receiving, from a serving cell, an activation indication for a secondary cell (SCell);

receiving a first reference signal from the SCell, the first reference signal including at least one channel state information (CSI) reference signal (CSI RS);

receiving a second reference signal prior to an expiration of an SCell activation time; and

activating, based on the second reference signal being received after the activation indication and prior to the expiration of the SCell activation time, the SCell based on the second reference signal.

34. A method for wireless communication at a user equipment (UE), comprising:

receiving, from a serving cell, an activation indication for a secondary cell (SCell) based on a first reference signal, the activation indication indicating a transmission of the first reference signal for activating the SCell;

receiving, from the serving cell, a second reference signal; and

activating the SCell based on one or more reference signals including the first reference signal or the second reference signal.