Beam sweep based random access msg 3 and msg 4

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

transmitting a first random access message to a serving cell;

receiving a second random access message from the serving cell, in response to the first random access message; and

transmitting a third random access message to one or more transmission reception points (TRPs) of the serving cell in a beam sweep pattern for reception on multiple beams and using resources for the beam sweep pattern of the third random access message based on at least one of a beam pool index or a TRP index.

2. The method of claim 1 , wherein the serving cell comprises a primary cell (PCell), a secondary cell (SCell), or a primary secondary cell (PSCell).

3. The method of claim 1 , wherein the UE transmits the first random access message using a first beam pattern of multiple beams and transmits the third random access message using a second, different beam pattern of multiple beams.

4. The method of claim 1 , further comprising:

using at least one of time division multiplexing (TDM), frequency division multiplexing (FDM), or space division multiplexing (SDM) to transmit the third random access message on the multiple beams.

5. The method of claim 4 , wherein the second random access message comprises a grant for the third random access message and indicates to the UE to use the at least one of TDM, FDM, or SDM to transmit the third random access message on the multiple beams.

6. The method of claim 5 , wherein the grant for the third random access message further indicates a number of repetitions for the third random access message.

7. The method of claim 1 , further comprising:

using a same pattern of the multiple beams to transmit the first random access message and the third random access message.

8. The method of claim 1 , further comprising:

receiving an indication of a set of beams for receiving a fourth random access message; and

receiving the fourth random access message from the one or more TRPs of the serving cell on the set of beams.

9. The method of claim 8 , further comprising:

performing one or more of time division multiplexing (TDM), frequency division multiplexing (FDM), or space division multiplexing (SDM) to transmit the fourth random access message on the set of beams.

10. The method of claim 8 , wherein resources for the fourth random access message are based on at least one of the beam pool index or the TRP index.

11. The method of claim 8 , further comprising:

using a same set of beams to receive the second random access message and the fourth random access message.

12. The method of claim 8 , wherein the indication is received in the second random access message, wherein the set of beams for receiving the fourth random access message comprise a different beam configuration than beams used to receive the second random access message.

13. The method of claim 8 , wherein the UE receives the indication in a physical downlink control channel (PDCCH) of the second random access message, and wherein the UE receives the PDCCH or a physical downlink shared channel (PDSCH) of the fourth random access message using the set of beams indicated by the indication.

14. The method of claim 8 , wherein the UE receives the indication in a physical downlink control channel (PDCCH) of the fourth random access message, and the UE receives a physical downlink shared channel (PDSCH) of the fourth random access message using the set of beams indicated in the PDCCH.

15. The method of claim 8 , further comprising:

transmitting hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback in a physical uplink control channel (PUCCH) using time division multiplexing (TDM), frequency division multiplexing (FDM), or spatial division multiplexing (SDM) beam sweeping.

16. The method of claim 15 , further comprising:

receiving information for the TDM, FDM, or SDM beam sweeping in at least one of a control part of the second random access message or the fourth random access message.

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

means for transmitting a first random access message to one or more transmission reception points (TRPs) of a serving cell;

means for receiving a second random access message from the serving cell, in response to the first random access message; and

means for transmitting a third random access message to the serving cell in a beam sweep pattern for reception on multiple beams and using resources for the beam sweep pattern of the third random access message based on at least one of a beam pool index or a TRP index.

18. A method of wireless communication at a base station, comprising:

receiving a first random access message from a user equipment (UE);

transmitting a second random access message to the UE, in response to the first random access message; and

receiving a third random access message at one or more transmission reception points (TRPs) on at least one of multiple beams that are monitored in a beam sweep pattern using resources for the beam sweep pattern of the third random access message based on at least one of a beam pool index or a TRP index.

19. The method of claim 18 , further comprising:

serving the UE as a primary cell (PCell), a secondary cell (SCell), or a primary secondary cell (PSCell).

20. The method of claim 18 , wherein the base station receives the first random access message using a first beam pattern of multiple beams, and the base station monitors for the third random access message using a second, different beam pattern of multiple beams.

21. The method of claim 20 , further comprising:

indicating the second, different beam pattern to the UE in the second random access message in response to determining a signal strength for one or more beams of the first random access message is below a threshold amount or receiving a report from the UE indicating a better beam than used for the first random access message.

22. The method of claim 18 , wherein the third random access message is one or more of time division multiplexed (TDM), frequency division multiplexed (FDM), or space division multiplexed (SDM) on the multiple beams, wherein the second random access message comprises a grant for the third random access message and indicates to the UE to use the at least one of TDM, FDM, or SDM to transmit the third random access message on the multiple beams.

23. The method of claim 18 , further comprising:

transmitting an indication of a set of beams for a fourth random access message; and

transmitting the fourth random access message from the one or more TRPs on the set of beams.

24. The method of claim 23 , further comprising:

using one or more of time division multiplexing (TDM), frequency division multiplexing (FDM), or space division multiplexing (SDM) to transmit the fourth random access message on the set of beams.

25. The method of claim 23 , wherein resources for the fourth random access message are based on at least one of the beam pool index or the TRP index.

26. The method of claim 23 , further comprising:

using a same set of beams to transmit the second random access message and the fourth random access message.

27. The method of claim 23 , wherein the base station transmits the indication in the second random access message, wherein the set of beams for transmitting the fourth random access message comprise a different beam configuration than beams used to transmit the second random access message.

28. The method of claim 23 , wherein the base station transmits the indication in a physical downlink control channel (PDCCH) of the second random access message and transmits the PDCCH or a physical downlink shared channel (PDSCH) of the fourth random access message using the set of beams indicated by the indication, or wherein the base station transmits the indication in the PDCCH of the fourth random access message and transmits the PDSCH of the fourth random access message using the set of beams indicated in the PDCCH.

29. The method of claim 23 , further comprising:

receiving hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback in a physical uplink control channel (PUCCH) from the UE using time division multiplexing (TDM), frequency division multiplexing (FDM), or spatial division multiplexing (SDM) beam sweeping; and

transmitting information for the TDM, FDM, or SDM beam sweeping in at least one of a control part of the second random access message or the fourth random access message.

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

means for receiving a first random access message from a user equipment (UE);

means for transmitting a second random access message to the UE, in response to the first random access message; and

means for receiving a third random access message at one or more transmission reception points (TRPs) on at least one of multiple beams that are monitored in a beam sweep pattern using resources for the beam sweep pattern of the third random access message based on at least one of a beam pool index or a TRP index.