Physical downlink control channel (PDCCH) aggregation level (AL) design for new radio (NR) ultra-reliable low latency communication (URLLC)

1. A method for wireless communications by a user equipment (UE), comprising:

receiving a single physical downlink control channel (PDCCH) message at an aggregation level (AL), wherein the AL comprises a union of control channel elements (CCEs) in a plurality of search spaces within a control resource set (CORESET) in which the single PDCCH message can be carried;

receiving radio resource control (RRC) signaling of a parameter indicating a value of the AL;

determining, based on the indicated value of the AL and a predetermined rule, which of the plurality of search spaces within the CORESET to combine to determine the union of CCEs; and

decoding the single PDCCH message at the AL.

2. The method of claim 1 , wherein:

the union of CCEs comprises a union of all CCEs in search spaces having a same PDCCH scrambling identification, and

decoding the PDCCH at the AL comprises decoding using the scrambling identification.

3. The method of claim 2 , wherein the plurality of search spaces comprise UE-specific search spaces (USSs) and a common search space (CSS).

4. The method of claim 1 , wherein the union of CCEs comprises:

a union of all CCEs in UE-specific search spaces (USSs) associated with the UE;

a union of all CCEs in a common search space (CSS); or

all CCEs in a first UE-specific search spaces (USS) having a same AL.

5. The method of claim 4 , wherein the union of all CCEs in the USSs associated with the UE excludes all CCEs in the common search space associated with the UE.

6. The method of claim 4 , wherein the union of CCEs excludes CCEs in a common search space (CSS) associated with the UE which are part of the first USS having the same AL.

7. The method of claim 4 , wherein the union of CCEs further comprises a union of all CCEs in the first USS and all CCEs in a second USS, wherein the AL of the first USS is different than an AL associated with the second USS.

8. The method of claim 1 , wherein the union of CCEs comprises all CCEs within the CORESET on which the UE performs channel estimation.

9. The method of claim 8 , wherein the union of CCEs comprises all CCEs within the CORESET on which the UE performs channel estimation and all CCEs on which the demodulation reference signal (DMRS) for the PDCCH are scrambled by a same scrambling ID.

10. The method of claim 1 , further comprising:

receiving a demodulation reference signal (DMRS) for the PDCCH, wherein the DMRS spans an entire bandwidth associated with the CORESET and is transmitted to the UE using a same precoder; and

performing channel estimation on the DMRS.

11. The method of claim 1 , wherein decoding the PDCCH message at the AL comprises decoding a single decoding candidate associated with the AL.

12. A method for wireless communications by a network entity, comprising:

generating a single physical downlink control channel (PDCCH) message for transmission at an aggregation level (AL), wherein the AL comprises a union of control channel elements (CCEs) in a plurality of search spaces within a control resource set (CORESET) in which the single PDCCH message can be carried;

transmitting to a user equipment (UE), via radio resource control (RRC) signaling, a parameter indicating a value of the AL;

determining, based on the indicated value and a predetermined rule, which of the one or more search spaces within the CORESET to combine to determine the union of CCEs; and

transmitting the single PDCCH message to the UE at the AL.

13. The method of claim 12 , wherein:

the union of CCEs comprises a union of all CCEs in search spaces having a same PDCCH scrambling identification, and

transmitting the PDCCH at the AL comprises transmitting using the scrambling identification.

14. The method of claim 13 , wherein the plurality of search spaces comprise UE-specific search spaces (USSs) and a common search space (CSS).

15. The method of claim 12 , wherein the union of CCEs comprises:

a union of all CCEs in all UE-specific search spaces (USSs) associated with the UE;

a union of all CCEs in a common search space (CSS); or

all CCEs in a first UE-specific search spaces (USS) having a same AL.

16. The method of claim 15 , wherein the union of all CCEs in all USSs associated with the UE excludes all CCEs in the common search space associated with the UE.

17. The method of claim 15 , wherein the union of CCEs excludes CCEs in a common search space (CSS) associated with the UE which are part of the first USS having the same AL.

18. The method of claim 15 , wherein the union of CCEs further comprises a union of all CCEs in the first USS and all CCEs in a second USS, wherein the AL of the first USS is different than an AL associated with the second USS.

19. The method of claim 12 , wherein the union of CCEs comprises all CCEs within the CORESET on which the UE performs channel estimation.

20. The method of claim 12 , wherein the union of CCEs comprises all CCEs within the CORESET on which the UE performs channel estimation and all CCEs on which the demodulation reference signal (DMRS) for the PDCCH are scrambled by a same scrambling ID.

21. The method of claim 12 , further comprising:

transmitting a demodulation reference signal (DMRS) for the PDCCH using a same precoder, wherein the DMRS spans an entire bandwidth associated with the CORESET.

22. The method of claim 12 , further comprising:

configuring the UE to refrain from decoding the PDCCH at the AL when decoding the PDCCH at the AL would exceed a threshold number of decodes.

23. The method of claim 12 , the PDCCH at the AL is generated based, at least in part, on a size or format of a downlink control information (DCI) format of the PDCCH.

24. The method of claim 12 , wherein decoding the PDCCH message at the AL comprises decoding a single decoding candidate associated with the AL.

25. An apparatus for wireless communications by a user equipment (UE), comprising:

means for receiving a single physical downlink control channel (PDCCH) message at an aggregation level (AL), wherein the AL comprises a union of control channel elements (CCEs) in a plurality of search spaces within a control resource set (CORESET) in which the single PDCCH message can be carried;

means for receiving radio resource control (RRC) signaling of a parameter indicating a value of the AL;

means for determining, based on the indicated value of the AL and a predetermined rule, which of the plurality of search spaces within the CORESET to combine to determine the union of CCEs; and

means for decoding the single PDCCH message at the AL.

26. An apparatus for wireless communications by a network entity, comprising:

means for generating a single physical downlink control channel (PDCCH) message for transmission at an aggregation level (AL), wherein the AL comprises a union of control channel elements (CCEs) in a plurality of search spaces within a control resource set (CORESET) in which the single PDCCH message can be carried;

means for transmitting to a user equipment (UE), via radio resource control (RRC) signaling, a parameter indicating a value of the AL;

means for determining, based on the indicated value and a predetermined rule, which of the one or more search spaces within the CORESET to combine to determine the union of CCEs; and

means for transmitting the single PDCCH message to the UE at the AL.