Beam refinement using channel state information reference signal in random access procedure

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

a transceiver for wireless communication;

a memory; and

one or more processors coupled with the transceiver and the memory, wherein the one or more processors are configured to:

transmit, to a scheduling entity, a first message that initiates a random access channel (RACH) procedure;

receive, from the scheduling entity, a second message of the RACH procedure, the second message comprising an indication of one or more channel state information reference signal (CSI-RS) resources for receiving a plurality of CSI-RSs from the scheduling entity;

receive, from a same beam of the scheduling entity, the plurality of CSI-RSs using the one or more CSI-RS resources;

determine a respective quality of the plurality of CSI-RSs corresponding to a plurality of receive beams of the UE;

select one of the plurality of receive beams for communicating with the scheduling entity based on the determined quality of the plurality of CSI-RSs; and

transmit, using the selected one of the plurality of receive beams, a third message of the RACH procedure.

2. The UE of claim 1 , wherein to receive the second message, the one or more processors are further configured to:

receive downlink control information (DCI) on a physical download control channel (PDCCH), the DCI comprising the indication of the one or more CSI-RS resources; or

receive, on a physical downlink shared channel (PDSCH), the indication of the one or more CSI-RS resources.

3. The UE of claim 2 , wherein the indication is configured to indicate the one or more CSI-RS resources based on at least one of:

scheduling information in the DCI for scheduling the one or more CSI-RS resources;

one or more predetermined rules associated with resources used to receive the PDCCH; or

a bitfield contained in the DCI configured to indicate one or more predetermined rules associated the one or more CSI-RS resources.

4. The UE of claim 2 , wherein the indication is configured to indicate the one or more CSI-RS resources based on at least one of:

scheduling information in the PDSCH for scheduling the one or more CSI-RS resources;

first communication resources used for receiving the PDSCH;

second communication resources scheduled for transmitting the third message of the RACH procedure;

one or more predetermined rules associated with the first communication resources or the second communication resources; or

a bitfield contained in the PDSCH configured to indicate one or more predetermined rules associated the one or more CSI-RS resources.

5. The UE of claim 1 , wherein the second message comprises DCI containing a bitfield indicating that the UE provides a Layer 1 (L1) measurement report in response to the plurality of CSI-RSs, and the one or more processors are further configured to:

measure a beam quality metric for at least one beam of a plurality of beams from the scheduling entity based on the one or more CSI-RSs, and

transmit the L1 measurement report to the scheduling entity, the L1 measurement report comprising the beam quality metric of the at least one beam of the plurality of beams.

6. The UE of claim 1 , wherein the one or more processors are further configured to:

measure a beam quality metric for at least one beam of a plurality of beams from the scheduling entity based on the one or more CSI-RSs, and

determine communication resources for transmitting the third message based on the beam quality metric.

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

transmitting, to a scheduling entity, a first message that initiates a random access channel (RACH) procedure;

receiving, from the scheduling entity, a second message of the RACH procedure, the second message comprising an indication of one or more channel state information reference signal (CSI-RS) resources for receiving a plurality of CSI-RSs from the scheduling entity;

receiving, from a same beam of the scheduling entity, the plurality of CSI-RSs using the one or more CSI-RS resources;

determining a respective quality of the plurality of CSI-RSs corresponding to a plurality of receive beams of the UE;

selecting one of the plurality of receive beams for communicating with the scheduling entity based on the determined quality of the plurality of CSI-RSs; and

transmitting, using the selected one of the plurality of receive beams, a third message of the RACH procedure.

8. The method of claim 7 , wherein the receiving the second message comprises:

receiving downlink control information (DCI) on a physical download control channel (PDCCH), the DCI comprising the indication of the one or more CSI-RS resources; or

receiving, on a physical downlink shared channel (PDSCH), the indication of the one or more CSI-RS resources.

9. The method of claim 8 , wherein the indication is configured to indicate the one or more CSI-RS resources based on at least one of:

scheduling information in the DCI for scheduling the one or more CSI-RS resources;

one or more predetermined rules associated with resources used to receive the PDCCH; or

a bitfield contained in the DCI configured to indicate one or more predetermined rules associated the one or more CSI-RS resources.

10. The method of claim 8 , wherein the indication is configured to indicate the one or more CSI-RS resources based on at least one of:

scheduling information in the PDSCH for scheduling the one or more CSI-RS resources;

first communication resources used for receiving the PDSCH;

second communication resources scheduled for transmitting the third message of the RACH procedure;

one or more predetermined rules associated with the first communication resources or the second communication resources; or

a bitfield contained in the PDSCH configured to indicate one or more predetermined rules associated the one or more CSI-RS resources.

11. The method of claim 7 , wherein the second message comprises DCI containing a bitfield indicating that the UE provides a Layer 1 (L1) measurement report in response to the plurality of CSI-RSs, and further comprising:

measuring a beam quality metric for at least one beam of a plurality of beams from the scheduling entity based on the one or more CSI-RSs, and

transmitting the L1 measurement report to the scheduling entity, the L1 measurement report comprising the beam quality metric of the at least one beam of the plurality of beams.

12. The method of claim 7 , further comprising:

measuring a beam quality metric for at least one beam of a plurality of beams from the scheduling entity based on the one or more CSI-RSs, and

determining communication resources for transmitting the third message based on the beam quality metric.

13. A scheduling entity for wireless communication, comprising:

a transceiver for wireless communication;

a memory; and

one or more processors coupled with the transceiver and the memory, wherein the one or more processors are configured to:

receive, from a user equipment (UE), a first message that initiates a random access channel (RACH) procedure;

transmit, to the UE, a second message of the RACH procedure, the second message comprising an indication of one or more channel state information reference signal (CSI-RS) resources for transmitting a plurality of CSI-RSs, and a field indicating that the plurality of CSI-RSs not being associated with a feedback report;

transmit, in a same beam of the scheduling entity, the plurality of CSI-RSs using the one or more CSI-RS resources; and

receive a third message of the RACH procedure after transmitting the plurality of CSI-RS s.

14. The scheduling entity of claim 13 , wherein to transmit the second message, the one or more processors are further configured to:

transmit downlink control information (DCI) on a physical download control channel (PDCCH), the DCI comprising the indication of the one or more CSI-RS resources; or

transmit, on a physical downlink shared channel (PDSCH), the indication of the one or more CSI-RS resources.

15. The scheduling entity of claim 14 , wherein the indication is configured to indicate the one or more CSI-RS resources based on at least one of:

scheduling information in the DCI for scheduling the one or more CSI-RS resources;

one or more predetermined rules associated with resources used to transmit the PDCCH; or

a bitfield contained in the DCI configured to indicate one or more predetermined rules associated the one or more CSI-RS resources.

16. The scheduling entity of claim 14 , wherein the indication is configured to indicate the one or more CSI-RS resources based on at least one of:

scheduling information in the PDSCH for scheduling the one or more CSI-RS resources;

first communication resources used for transmitting the PDSCH;

second communication resources scheduled for receiving the third message of the RACH procedure;

one or more predetermined rules associated with the first communication resources or the second communication resources; or

a bitfield contained in the PDSCH configured to indicate one or more predetermined rules associated the one or more CSI-RS resources.

17. The scheduling entity of claim 13 , wherein the second message comprises DCI containing a bitfield indicating that the UE provides a Layer 1 (L1) measurement report in response to the plurality of CSI-RSs, and further comprising:

receiving a Layer (L1) measurement report from the UE, the L1 measurement report comprising a beam quality metric of at least one beam of a plurality of beams of the scheduling entity based on the one or more CSI-RSs.

18. The scheduling entity of claim 13 , wherein to receive the third message, the one or more processors are further configured to:

receive the third message using a time resource associated with at least one beam of a plurality of beams of the scheduling entity measured by the UE using the plurality of CSI-RSs.

19. A method of wireless communication at a scheduling entity, the method comprising:

receiving, from a user equipment (UE), a first message that initiates a random access channel (RACH) procedure;

transmitting, to the UE, a second message of the RACH procedure, the second message comprising an indication of one or more channel state information reference signal (CSI-RS) resources for transmitting a plurality of CSI-RSs, and a field indicating that the plurality of CSI-RSs not being associated with a feedback report;

transmitting, in a same beam of the scheduling entity, the plurality of CSI-RSs using the one or more CSI-RS resources; and

receiving a third message of the RACH procedure after transmitting the plurality of CSI-RSs.

20. The method of claim 19 , wherein the transmitting the second message comprises:

transmitting downlink control information (DCI) on a physical download control channel (PDCCH), the DCI comprising the indication of the one or more CSI-RS resources; or

transmitting, on a physical downlink shared channel (PDSCH), the indication of the one or more CSI-RS resources.

21. The method of claim 20 , wherein the indication is configured to indicate the one or more CSI-RS resources based on at least one of:

scheduling information in the DCI for scheduling the one or more CSI-RS resources;

one or more predetermined rules associated with resources used to transmit the PDCCH; or

a bitfield contained in the DCI configured to indicate one or more predetermined rules associated the one or more CSI-RS resources.

22. The method of claim 20 , wherein the indication is configured to indicate the one or more CSI-RS resources based on at least one of:

scheduling information in the PDSCH for scheduling the one or more CSI-RS resources;

first communication resources used for transmitting the PDSCH;

second communication resources scheduled for receiving the third message of the RACH procedure;

one or more predetermined rules associated with the first communication resources or the second communication resources; or

a bitfield contained in the PDSCH configured to indicate one or more predetermined rules associated the one or more CSI-RS resources.

23. The method of claim 19 , wherein the second message comprises DCI containing a bitfield indicating that the UE provides a Layer 1 (L1) measurement report in response to the plurality of CSI-RSs, and further comprising:

receiving a Layer (L1) measurement report from the UE, the L1 measurement report comprising a beam quality metric of at least one beam of a plurality of beams of the scheduling entity based on the one or more CSI-RSs.

24. The method of claim 19 , wherein the receiving the third message comprises:

receiving the third message using a time resource associated with at least one beam of a plurality of beams of the scheduling entity measured by the UE using the plurality of CSI-RSs.