Techniques of reducing SCell activation delay

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

receiving, on a primary cell, an activation command from a base station for activating a secondary cell between the UE and the base station;

receiving scheduling information of a set of aperiodic tracking reference signals (TRSs); receiving a trigger indicating transmission of the set of aperiodic TRSs;

initiating a RF chain of the UE configured for the secondary cell in an interruption period;

receiving, in response to receiving the trigger and in accordance with the scheduling information, the set of aperiodic TRSs on the secondary cell prior to receiving an initial periodic synchronization signal block (SSB) or an initial periodic TRS after the interruption period; and;

performing time and frequency tracking on the secondary cell based on the set of aperiodic TRSs.

2. The method of claim 1 , wherein the trigger is carried in at least one of: a Media Access Control (MAC) Control Element (CE) that also carries the activation command;

downlink control information that is received prior to receiving the activation command and that indicates resources allocated to the activation command;

downlink control information that is received subsequent the interruption period; and

downlink control information that 1s received in each slot of a plurality of slots subsequent to the interruption period.

3. The method of claim 1 , wherein the scheduling information is carried in at least one of: a Media Access Control (MAC) Control Element (CE) that also carries the activation command; downlink control information that is received prior to receiving the activation command and that indicates resources allocated to the activation command;

downlink control information that is received subsequent the interruption period;

downlink control information that 1 s received in each slot of a plurality of slots subsequent to the interruption period; and

a Radio Resource Control (RRC) message sent from the base station.

4. The method of claim 1 , wherein the scheduling information includes (a) an indication of an offset between a slot in which the trigger is transmitted and a slot starting from which the set of aperiodic TRSs is transmitted and (b) an indication of a number of slots occupied by the set of aperiodic TRSs.

5. The method of claim 1 , wherein the activation command 1 s received in a first time slot prior to the interruption period, wherein the set of aperiodic TRSs are received in one or more slots starting from a second time slot.

6. The method of claim 5 , wherein the activation command and the trigger are carried in a Media Access Control (MAC) Control Element (CE) in the first time slot, wherein the scheduling information includes an indication of an offset between the first time slot and the second time slot and an indication of the number of slots in the one or more slots.

7. The method of claim 6 , wherein the MAC CE further includes the scheduling information.

8. The method of claim 6 , wherein the MAC CE further includes the indication of the offset, wherein the indication of the number of slots in the one or more slots is received through a Radio Resource Control (RRC) message sent from the base station.

9. The method of claim 5 , further comprising: receiving downlink control information (DCI) in a third time slot prior to the first time slot on the primary cell, wherein the DCI indicates a Media Access Control (MAC) Control Element (CE) carrying the activation command in the first time slot, wherein the DCI further includes the trigger and the scheduling information, wherein the scheduling information includes an indication of an offset between the third time slot and the second time slot and an indication of the number of slots in the one or more slots.

10. The method of claim 5 , further comprising: receiving downlink control information (DCI) in a fourth time slot subsequent to the interruption period and prior to the second time slot on the primary cell, wherein the DCI includes the trigger and the scheduling information, wherein the scheduling information includes an indication of an offset between the fourth slot and the second time slot and an indication of the number of slots in the one or more slots.

11. The method of claim 5 , further comprising: receiving, on the primary cell, respective downlink control information (DCI) in each slot of a plurality of time slots subsequent to the interruption period and prior to the second time slot, wherein the respective DCI in each slot of the plurality of slots includes the trigger and respective scheduling information, wherein the respective scheduling information in the each slot includes an indication of an offset between the each slot and the second time slot and an indication of the number of slots in the one or more slots.

12. An apparatus for wireless communication, the apparatus being a user equipment (UE), comprising: a memory; and

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

receive, on a primary cell, an activation command from a base station for activating a secondary cell between the UE and the base station;

receive scheduling information of a set of aperiodic tracking reference signals (TRSs); receive a trigger indicating transmission of the set of aperiodic TRSs;

initiate a RF chain of the UE configured for the secondary cell in an interruption period;

receive, in response to receiving the trigger and in accordance with the scheduling information, the set of aperiodic TRSs on the secondary cell prior to receiving an initial periodic synchronization signal block (SSB) or an initial periodic TRS after the interruption period; and

perform time and frequency tracking on the secondary cell based on the set of aperiodic TRSs.

13. The apparatus of claim 12 , wherein the trigger is carried in at least one of: a Media Access Control (MAC) Control Element (CE) that also carries the activation command;

downlink control information that is received prior to receiving the activation command and that indicates resources allocated to the activation command;

downlink control information that is received subsequent the interruption period; and

downlink control information that 1 s received in each slot of a plurality of slots subsequent to the interruption period.

14. The apparatus of claim 12 , wherein the scheduling information is carried in at least one of: a Media Access Control (MAC) Control Element (CE) that also carries the activation command; downlink control information that is received prior to receiving the activation command and that indicates resources allocated to the activation command; downlink control information that is received subsequent the interruption period; 25 downlink control information that 1s received in each slot of a plurality of slots subsequent to the interruption period; and a Radio Resource Control (RRC) message sent from the base station.

15. The apparatus of claim 12 , wherein the scheduling information includes (a) an indication of an offset between a slot in which the trigger is transmitted and a slot starting from which the set of aperiodic TRSs is transmitted and (b) an indication of a number of slots occupied by the set of aperiodic TRSs.

16. The apparatus of claim 12 , wherein the activation command is received in a first time slot prior to the interruption period, wherein the set of aperiodic TRSs are received in one or more slots starting from a second time slot.

17. The apparatus of claim 16 , wherein the activation command and the trigger are carried in a 5 Media Access Control (MAC) Control Element (CE) in the first time slot, wherein the scheduling information includes an indication of an offset between the first time slot and the second time slot and an indication of the number of slots in the one or more slots.

18. The apparatus of claim 17 , wherein the MAC CE further includes the scheduling information.

19. The apparatus of claim 17 , wherein the MAC CE further includes the indication of the offset, 10 wherein the indication of the number of slots in the one or more slots is received through a Radio Resource Control (RRC) message sent from the base station.

20. A Non-transitory computer readable storage medium storing a computer executable code for wireless communication of a user equipment (UE), for executing to: receive, on a primary cell, an activation command from a base station for activating a secondary cell between the UE and the base station;

receive scheduling information of a set of aperiodic tracking reference signals (TRSs);

receive a trigger indicating transmission of the set of aperiodic TRSs;

initiate a RF chain of the UE configured for the secondary cell in an interruption period; receive, in response to receiving the trigger and in accordance with the scheduling information, 20 the set of aperiodic TRSs on the secondary cell prior to receiving an initial periodic synchronization signal block (SSB) or an initial periodic TRS after the interruption period; and

perform time and frequency tracking on the secondary cell based on the set of aperiodic TRSs.