Rach conveyance of DL synchronization beam information for various DL-UL correspondence states

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

receiving a downlink (DL) signal from a base station on one or more DL beams;

selecting a DL beam of the one or more DL beams for communications from the base station to the UE;

transmitting an indication of a nature of beam correspondence between the one or more DL beams at the UE and one or more uplink (UL) beams at the UE, wherein the nature of beam correspondence corresponds to one of: full beam correspondence, partial beam correspondence, or no beam correspondence;

selecting a resource or a waveform for uplink transmission, the resource or the waveform corresponding to the selected DL beam of the one or more DL beams and selected based at least in part on the nature of beam correspondence between the selected DL beam and one or more uplink beams at the UE; and

transmitting a scheduling request message to the base station using at least one of the resource or the waveform selected based at least in part on the selected DL beam.

2. The method of claim 1 , wherein the resource or the waveform are selected based at least in part on the indication of the nature of beam correspondence.

3. The method of claim 1 , further comprising:

determining that beam correspondence is present based on the indication; and

selecting a transmission time for transmitting the scheduling request message to the base station based on the present beam correspondence, wherein the transmission time comprises a symbol of a corresponding random access subframe.

4. The method of claim 1 , further comprising:

determining that there is partial beam correspondence based on the indication; and

selecting a transmission time for transmitting the scheduling request message to the base station based on the partial beam correspondence, wherein the transmission time comprises multiple symbols of a corresponding random access subframe.

5. The method of claim 1 , further comprising:

selecting the resource or the waveform based at least in part on a symbol associated with the DL signal and the indication.

6. The method of claim 1 , wherein the waveform comprises one of a scheduling request or a random access channel (RACH) waveform.

7. The method of claim 1 , wherein the DL signal comprises a synchronization signal or a reference signal.

8. The method of claim 1 , wherein selecting the resource or the waveform comprises: selecting the resource or the waveform based at least in part on an index of the selected DL beam or a symbol of a subframe of the DL signal of the selected DL beam.

9. The method of claim 1 , wherein transmitting the scheduling request message comprises:

transmitting the scheduling request message during an entire duration of a corresponding random access subframe.

10. The method of claim 1 , wherein selecting the DL beam comprises:

identifying a preferred DL beam based at least in part on a signal strength of the DL signal on the one or more DL beams, a signal quality of the DL signal on the one or more DL beams, or combinations thereof.

11. The method of claim 1 , wherein selecting the DL beam comprises:

identifying the DL beam based at least in part on the DL signal on the one or more DL beams meeting a transmit power condition.

12. The method of claim 1 , further comprising:

selecting at least one of the resource or the waveform for transmission of the scheduling request message to the base station, the resource or the waveform being selected based at least in part on the selected DL beam.

13. The method of claim 1 , wherein a beam correspondence is absent between the one or more DL beams and one or more uplink (UL) beams at the UE.

14. The method of claim 13 , wherein the absent beam correspondence is associated with the one or more DL beams having different beam directions than the one or more UL beams.

15. The method of claim 1 , further comprising:

identifying that beam correspondence is absent by receiving information from the base station in a master information block (MIB) or a system information block (SIB).

16. The method of claim 15 , further comprising:

selecting the resource or the waveform based at least in part on the identification of the absent correspondence; and

transmitting the scheduling request message to the base station during an entire duration of a RACH subframe based at least in part on the indication of the absent correspondence.

17. The method of claim 1 , further comprising:

transmitting an indication that correspondence is absent between the one or more DL beams at the UE and one or more uplink (UL) beams at the UE.

18. The method of claim 1 , wherein the selected DL beam from the base station is different from a selected uplink (UL) beam from the UE.

19. The method of claim 1 , wherein the one or more DL beams are within a single symbol of a synchronization subframe, wherein selecting the resource or the waveform for transmission of the scheduling request message comprises:

selecting the resource or the waveform based at least in part on the single symbol of the selected DL beam.

20. A method for wireless communication at a base station, comprising:

transmitting a downlink (DL) signal on one or more DL beams;

receiving an indication of a nature of beam correspondence between the one or more DL beams at a user equipment (UE) and one or more uplink (UL) beams at the UE, wherein the nature of beam correspondence corresponds to one of: full beam correspondence, partial beam correspondence, or no beam correspondence;

receiving, on at least one of a resource or a waveform, a scheduling request message from the UE;

identifying, based at least in part on the resource or the waveform and further based at least in part on the nature of beam correspondence, a selected DL beam of the one or more DL beams for communications from the base station to the UE, the selected DL beam associated with one or more uplink beams at the base station by beam correspondence; and

transmitting one or more subsequent messages to the UE using the selected DL beam.

21. The method of claim 20 , wherein identifying the selected DL beam comprises:

associating the resource or the waveform with an index of the selected DL beam or a symbol of a subframe of the DL signal of the selected DL beam.

22. The method of claim 20 , wherein receiving the scheduling request message comprises:

receiving the scheduling request message during an entire duration of a corresponding random access subframe.

23. The method of claim 20 , wherein receiving the scheduling request message comprises:

receiving the scheduling request message on a plurality of uplink (UL) beams.

24. The method of claim 20 , wherein the nature of beam correspondence corresponds to no beam correspondence, wherein the absent correspondence is associated with the one or more DL beams having different beam directions than the one or more UL beams.

25. The method of claim 20 , further comprising:

identifying that correspondence is absent between the one or more DL beams at the UE and one or more uplink (UL) beams at the UE.

26. An apparatus for wireless communication at a user equipment (UE), comprising: a processor, memory coupled with the processor; and instructions stored in the memory and executable by the processor to cause the apparatus to:

receive a downlink (DL) signal from a base station on one or more DL beams;

select a DL beam of the one or more DL beams for communications from the base station to the UE;

transmit an indication of a nature of beam correspondence between the one or more DL beams at the UE and one or more uplink (UL) beams at the UE, wherein the nature of beam correspondence corresponds to one of: full beam correspondence, partial beam correspondence, or no beam correspondence;

select a resource or a waveform for uplink transmission, the resource or the waveform corresponding to the selected DL beam of the one or more DL beams and selected based at least in part on the beam correspondence between the selected DL beam and one or more uplink beams at the UE; and

transmit a scheduling request message to the base station using at least one of the resource or the waveform selected based at least in part on the selected DL beam.

27. An apparatus for wireless communication at a base station, comprising: a processor, memory coupled with the processor; and instructions stored in the memory and executable by the processor to cause the apparatus to:

transmit a downlink (DL) signal on one or more DL beams;

receive an indication of a nature of beam correspondence between the one or more DL beams at a user equipment (UE) and one or more uplink (UL) beams at the UE, wherein the nature of beam correspondence corresponds to one of: full beam correspondence, partial beam correspondence, or no beam correspondence;

receive, on at least one of a resource or a waveform, a scheduling request message from the UE;

identify, based at least in part on the resource or the waveform and further based at least in part on the nature of beam correspondence, a selected DL beam of the one or more DL beams for communications from the base station to the UE, the selected DL beam associated with one or more uplink beams at the base station by beam correspondence; and

transmit one or more subsequent messages to the UE using the selected DL beam.