Multiple-beam uplink random access channel messages

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

transmitting a first random access channel (RACH) transmission to a base station;

receiving, from the base station in response to the first RACH transmission, a second RACH transmission that includes a first indication comprising a first beam identifier corresponding to a first beam and a second indication comprising a second beam identifier corresponding to a second beam for the UE to use to transmit a third RACH transmission;

transmitting, to the base station and based at least in part on receiving the second RACH transmission that includes the first indication and the second indication, a first instance of the third RACH transmission using the first beam corresponding to the first beam identifier and a second instance of the third RACH transmission using the second beam corresponding to the second beam identifier; and

receiving, from the base station in response to the third RACH transmission, a fourth RACH transmission that includes a third indication that the UE is to transmit a determined deployment type acknowledgement to the base station using one or more transmit beams.

2. The method of claim 1 , further comprising:

identifying receive beams used by the UE to receive synchronization signals from the base station; and

determining the two or more transmit beams based at least in part on the identified receive beams.

3. The method of claim 1 , further comprising:

transmitting, with the third RACH transmission, a beam report that is based at least in part on synchronization signals received by the UE, or reference signals received by the UE, or a combination thereof.

4. The method of claim 1 , further comprising:

identifying, based at least in part on the second RACH transmission received from the base station, a monitoring pattern for the UE to use to receive the fourth RACH transmission.

5. The method of claim 4 , wherein the monitoring pattern identifies a beam for the UE to use to receive the fourth RACH transmission.

6. The method of claim 1 , wherein the third indication that the UE is to transmit the determined deployment type acknowledgement to the base station identifies the one or more transmit beams, or uplink control channel resources, or a combination thereof.

7. The method of claim 1 , further comprising:

identifying the one or more transmit beams based at least in part on the first indication comprising the first beam identifier, the second indication comprising the second beam identifier, or both for the UE to use to transmit the third RACH transmission.

8. The method of claim 1 , further comprising:

receiving the fourth RACH transmission on a plurality of beams, wherein the fourth RACH transmission includes a group acknowledgment configuration; and

transmitting a group acknowledgment using the one or more transmit beams based at least in part on the group acknowledgment configuration.

9. The method of claim 1 , further comprising:

receiving synchronization signals from the base station after transmitting the first RACH transmission;

performing a beam refinement procedure based at least in part on the received synchronization signals; and

transmitting the third RACH transmission based at least in part on the performed beam refinement procedure.

10. The method of claim 1 , wherein the first indication comprising the first beam identifier, the second indication comprising the second beam identifier, or both are based at least in part on a type of UE deployment.

11. The method of claim 1 , wherein the first indication comprising the first beam identifier further comprises time-frequency resources for the first beam and the second indication comprising the second beam identifier further comprises time-frequency resources for the second beam.

12. The method of claim 1 , wherein:

the first RACH transmission comprises a random access request; and

the second RACH transmission comprises a random access response.

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

receiving a first random access channel (RACH) transmission from a user equipment (UE);

identifying two or more transmit beams for the UE to use to transmit a third RACH transmission to the base station;

transmitting, to the UE in response to the first RACH transmission, a second RACH transmission that includes a first indication comprising a first beam identifier corresponding to a first beam of the identified two or more transmit beams and a second indication comprising a second beam identifier corresponding to a second beam of the identified two or more transmit beams;

receiving, from the UE in response to the second RACH transmission, the third RACH transmission based at least in part on the second RACH transmission including the first indication comprising the first beam identifier, the second indication comprising the second beam identifier, or both;

determining that the UE is to transmit a first acknowledgment to the base station responsive to a fourth RACH transmission; and

transmitting, to the UE in response to the third RACH transmission, the fourth RACH transmission that includes a third indication that the UE is to transmit a second acknowledgement using one or more transmit beams based on the determination.

14. The method of claim 13 , wherein the identifying the two or more transmit beams comprises:

determining a deployment type for the UE; and

selecting the two or more transmit beams based at least in part on the determined deployment type.

15. The method of claim 13 , wherein the identifying the two or more transmit beams comprises:

performing, while receiving the first RACH transmission, a beam refinement procedure for a plurality of beams used for transmitting synchronization signals; and

selecting the two or more transmit beams based at least in part on the performed beam refinement procedure.

16. The method of claim 13 , further comprising:

identifying, based at least in part on the first indication comprising the first beam identifier, the second indication comprising the second beam identifier, or both, a monitoring pattern associated with a plurality of beams for receiving the fourth RACH transmission; and

transmitting a fourth indication of the identified monitoring pattern in the second RACH transmission.

17. The method of claim 13 , further comprising:

identifying time-frequency resources for the two or more transmit beams; and

transmitting, in the second RACH transmission, a fourth indication of the time-frequency resources for the two or more transmit beams.

18. The method of claim 13 , further comprising:

transmitting synchronization signals, or reference signals, or a combination thereof; and

receiving, from the UE and with the third RACH transmission, a beam report that is based at least in part on the transmitted synchronization signals, or the transmitted reference signals, or a combination thereof.

19. The method of claim 13 , wherein the third indication that the UE is to transmit the second acknowledgement identifies the one or more transmit beams, or uplink control channel resources, or a combination thereof.

20. The method of claim 13 , further comprising:

identifying the one or more transmit beams based at least in part on the first indication comprising the first beam identifier, the second indication comprising the second beam identifier, or both for the UE to use to transmit the third RACH transmission, or a beam report received in the third RACH transmission, or a combination thereof.

21. The method of claim 13 , further comprising:

transmitting the fourth RACH transmission on a plurality of transmit beams, wherein the fourth RACH transmission includes a group acknowledgment configuration; and

receiving a group acknowledgment using the one or more transmit beams based at least in part on the group acknowledgment configuration.

22. The method of claim 13 , further comprising:

receiving the second acknowledgment from the UE based at least in part on the third indication that the UE is to transmit the second acknowledgement using the one or more transmit beams; and

configuring, during a radio resource control (RRC) connection setup process, multiple-beam communications with the UE based at least in part on the received second acknowledgment.

23. 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 operable, when executed by the processor, to cause the apparatus to:

transmit a first random access channel (RACH) transmission to a base station;

receive, from the base station in response to the first RACH transmission, a second RACH transmission that includes a first indication comprising a first beam identifier corresponding to a first beam and a second indication comprising a second beam identifier corresponding to a second beam the UE to use to transmit a third RACH transmission;

transmit, to the base station and based at least in part on receiving the second RACH transmission that includes the first indication and the second indication, a first instance of the third RACH transmission using the first beam corresponding to the first beam identifier and a second instance of the third RACH transmission using the second beam corresponding to the second beam identifier; and

receive, from the base station in response to the third RACH transmission, a fourth RACH transmission that includes a third indication that the UE is to transmit an acknowledgement to the base station using one or more transmit beams.

24. The apparatus of claim 23 , wherein the instructions are further executable by the processor to cause the apparatus to:

identify receive beams used by the UE to receive synchronization signals from the base station; and

determine the two or more transmit beams based at least in part on the identified receive beams.

25. The apparatus of claim 23 , wherein the instructions are further executable by the processor to cause the apparatus to:

transmit, with the third RACH transmission, a beam report that is based at least in part on synchronization signals received by the UE, or reference signals received by the UE, or a combination thereof.

26. An apparatus for wireless communication at a base station, comprising:

a processor;

memory coupled with the processor; and

instructions stored in the memory and operable, when executed by the processor, to cause the apparatus to:

receive a first random access channel (RACH) transmission from a user equipment (UE);

identify two or more transmit beams for the UE to use to transmit a third RACH transmission to the base station;

transmit, to the UE in response to the first RACH transmission, a second RACH transmission that includes a first indication comprising a first beam identifier corresponding to a first beam of the identified two or more transmit beams and a second indication comprising a second beam identifier corresponding to a second beam of the identified two or more transmit beams;

receive, from the UE in response to the second RACH transmission, the third RACH transmission based at least in part on the second RACH transmission including the first indication comprising the first beam identifier, the second indication comprising the second beam identifier, or both;

determine that the UE is to transmit a first acknowledgment to the base station responsive to a fourth RACH transmission; and

transmit, to the UE in response to the third RACH transmission, the fourth RACH transmission that includes a third indication that the UE is to transmit a second acknowledgement using one or more transmit beams based on the determination.

27. The apparatus of claim 26 , wherein the instructions executable by the processor to cause the apparatus to identify the two or more transmit beams comprise instructions executable by the processor to cause the apparatus to:

determine a deployment type for the UE; and

select the two or more transmit beams based at least in part on the determined deployment type.

28. The apparatus of claim 26 , wherein the instructions executable by the processor to cause the apparatus to identify the two or more transmit beams comprise instructions executable by the processor to cause the apparatus to:

perform, while receiving the first RACH transmission, a beam refinement procedure for a plurality of beams used for transmitting synchronization signals; and

select the two or more transmit beams based at least in part on the performed beam refinement procedure.