Physical random access channel repetition and receive-beam sweep and associated beam refinement
Aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for beam refinement via physical random access channel (PRACH) repetition. A method that may be performed by a network entity includes determining resources to monitor for a PRACH transmission sent from a user equipment (UE) as part of a random access channel (RACH) procedure, performing receive beam sweeping when receiving PRACH repetitions sent using the determined resources, using results of the receive beam sweeping to refine one or more beams and to select a refined beam of the refined one or more beams, and using the selected refined beam for at least one of receiving a subsequent message from the UE as part of the RACH procedure or sending a subsequent message to the UE as part of the RACH procedure.
1. A method for wireless communications by a network entity, comprising:
determining resources to monitor for a physical random access channel (PRACH) transmission sent from a user equipment (UE) as part of a random access channel (RACH) procedure;
performing receive beam sweeping when receiving PRACH repetitions sent using the determined resources;
using results of the receive beam sweeping to refine one or more beams and to select a refined beam of the refined one or more beams; and
using the selected refined beam for at least one of receiving a subsequent message from the UE as part of the RACH procedure or sending a subsequent message to the UE as part of the RACH procedure.
2. The method of claim 1 , further comprising: receiving, from the UE, PRACH repetitions using the determined resources when one or more conditions are met.
3. The method of claim 2 , wherein the one or more conditions relate to a synchronization signal block (SSB) based reference signal received power (RSRP) measurement.
4. The method of claim 3 , further comprising configuring the UE to send PRACH repetitions using the determined resources if the SSB-based RSRP measurement is less than a threshold value.
5. The method of claim 4 , wherein configuring the UE with the threshold value comprises configuring the UE with the threshold value via at least one of:
remaining minimum system information (RMSI); or
some other system information (SI).
6. The method of claim 1 , further comprising signaling the UE an indication of time resources for the PRACH repetitions.
7. The method of claim 6 , wherein the signaling comprises at least one of:
remaining minimum system information (RMSI); or
some other system information (SI).
8. The method of claim 1 , further comprising detecting the PRACH repetitions separately for each refined beam sweep.
9. The method of claim 1 , further comprising detecting the PRACH repetitions after soft combining of received signals on different refined beams of the refined one or more beams.
10. The method of claim 1 , wherein selecting the refined beam from the refined one or more beams comprises selecting the refined beam based on comparing reference signal received power (RSRP) for different PRACH repetitions.
11. The method of claim 1 , wherein the refined one or more beams is a subset of a set of synchronization signal block (SSB) beams.
12. The method of claim 1 , wherein the resources correspond to one or more RACH occasions.
13. An apparatus for wireless communications, comprising:
at least one processor; and
a memory coupled to the at least one processor, the memory comprising code executable by the at least one processor to cause the apparatus to:
determine resources to monitor for a physical random access channel (PRACH) transmission sent from a user equipment (UE) as part of a random access channel (RACH) procedure;
perform receive beam sweeping when receiving PRACH repetitions sent using the determined resources;
use results of the beam sweeping to refine one or more beams and to select a refined beam from the refined one or more beams; and
use the selected refined beam for at least one of receiving a subsequent message from the UE as part of the RACH procedure or sending a subsequent message to the UE as part of the RACH procedure.
14. The apparatus of claim 13 , wherein the memory further comprises code executable by the at least one processor to cause the apparatus to receive, from the UE, PRACH repetitions using the determined resources when one or more conditions are met.
15. The apparatus of claim 14 , wherein the one or more conditions relate to a synchronization signal block (SSB) based reference signal received power (RSRP) measurement.
16. The apparatus of claim 15 , wherein the memory further comprises code executable by the at least one processor to cause the apparatus to configure the UE to send PRACH repetitions using the determined resources if the SSB-based RSRP measurement is less than a threshold value.
17. The apparatus of claim 16 , wherein the code executable by the at least one processor to cause the apparatus to configure the UE with the threshold value comprises code executable by the at least one processor to cause the apparatus to configure the UE with the threshold value via at least one of:
remaining minimum system information (RMSI); or
some other system information (SI).
18. The apparatus of claim 13 , wherein the memory further comprises code executable by the at least one processor to cause the apparatus to signal the UE an indication of time resources for the PRACH repetitions, wherein the code executable by the at least one processor to cause the apparatus to signal involves at least one of:
remaining minimum system information (RMSI); or
some other system information (SI).
19. The apparatus of claim 13 , wherein the memory further comprises code executable by the at least one processor to cause the apparatus to detect the PRACH repetitions separately for each refined beam sweep.
20. The apparatus of claim 13 , wherein the memory further comprises code executable by the at least one processor to cause the apparatus to detect PRACH repetitions after soft combining of received signals on different refined beams of the refined one or more beams.
21. The apparatus of claim 13 , wherein the code executable by the at least one processor to cause the apparatus to select the refined beam from the refined one or more beams comprises code executable by the at least one processor to cause the apparatus to select the refined beam based on comparing reference signal received power (RSRP) for different PRACH repetitions.
22. The apparatus of claim 13 , wherein the refined one or more beams is a subset of a set of synchronization signal block (SSB) beams.
23. The apparatus of claim 13 , wherein the resources correspond to one or more RACH occasions.
24. An apparatus for wireless communications, comprising:
means for determining resources to monitor for a physical random access channel (PRACH) transmission sent from a user equipment (UE) as part of a random access channel (RACH) procedure;
means for performing receive beam sweeping when receiving PRACH repetitions sent using the determined resources;
means for using results of the beam sweeping to refine one or more beams to and to select a refined beam from the refined one or more beams; and
means for using the selected refined beam for at least one of:
receiving a subsequent message from the UE as part of the RACH procedure; or
sending a subsequent message to the UE as part of the RACH procedure.