Variable random access channel (RACH) signature mapping

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

selecting a random access channel (RACH) signature from among one or more RACH signatures associated with a synchronization signal block (SSB),

wherein a number of the one or more RACH signatures is variable based at least in part on a beam type, of a plurality of beam types, associated with the SSB; and

transmitting, to a base station (BS), a RACH communication using the selected RACH signature.

2. The method of claim 1 , wherein each of the plurality of beam types is associated with a beam width different from a beam width associated with any other beam type of the plurality of beam types.

3. The method of claim 2 , wherein the plurality of beam types includes a narrow beam having a beam width in a given dimension, a wider beam having a beam width in the given dimension larger than the beam width of the narrow beam in the given dimension, and a widest beam having a beam width in the given dimension larger than the beam width of the wider beam in the given dimension.

4. The method of claim 2 , wherein the plurality of beam types includes at least one vertical beam having a relatively large elevation beam width and having a relatively small azimuth beam width, at least one horizontal beam having a relatively small elevation beam width and having a relatively large azimuth beam width, and/or at least one symmetric beam having equal elevation beam width and azimuth beam width.

5. The method of claim 1 , wherein the number of the one or more RACH signatures is based at least in part on a hierarchy associated with the plurality of beam types.

6. The method of claim 1 , wherein, if the beam type associated with the SSB comprises a wide beam, the number of the one or more RACH signatures comprises a first number of RACH signatures;

wherein, if the beam type associated with the SSB comprises a narrow beam, the number of the one or more RACH signatures comprises a second number of RACH signatures; and

wherein the first number of RACH signatures is different from the second number of RACH signatures.

7. The method of claim 6 , wherein the first number of RACH signatures is greater than the second number of RACH signatures.

8. The method of claim 1 , wherein the selected RACH signature comprises:

a RACH occasion and a RACH preamble; and

wherein selecting the selected RACH signature comprises:

identifying an SSB index associated with the SSB;

selecting the RACH occasion based at least in part on the SSB index; and

selecting the RACH preamble from one or more RACH preambles for the RACH occasion.

9. The method of claim 8 , wherein identifying the SSB index comprises:

identifying the SSB index based at least in part on a bitmap included in a signaling communication transmitted from the BS.

10. The method of claim 9 , wherein the signaling communication comprises at least one of:

a radio resource control (RRC) communication,

a master information block (MIB),

a system information block (SIB),

a remaining minimum system information (RMSI) communication, or

an other system information (OSI) communication.

11. The method of claim 9 , wherein a number of RACH occasions associated with the SSB is indicated by a bit position, in the bitmap, associated with the SSB index.

12. The method of claim 9 , wherein the beam type associated with the SSB is indicated by a bit position, in the bitmap, associated with the SSB index.

13. A method of wireless communication performed by a base station (BS), comprising:

transmitting a plurality of synchronization signal blocks (SSBs); and

transmitting a signaling communication that indicates respective sets of one or more random access channel (RACH) signatures associated with the plurality of SSBs,

wherein a number of a set of one or more RACH signatures associated with an SSB of the plurality of SSBs is variable based at least in part on a beam type, of a plurality of beam types, associated with the SSB.

14. The method of claim 13 , wherein the signaling communication comprises at least one of:

a radio resource control (RRC) communication,

a master information block (MIB),

a system information block (SIB),

a remaining minimum system information (RMSI) communication, or

an other system information (OSI) communication.

15. The method of claim 13 , wherein each of the plurality of beam types is associated with a beam width different from a beam width associated with any other beam type of the plurality of beam types.

16. The method of claim 15 , wherein the plurality of beam types includes a narrow beam having a beam width in a given dimension, a wider beam having a beam width in the given dimension larger than the beam width of the narrow beam in the given dimension, and a widest beam having a beam width in the given dimension larger than the beam width of the wider beam in the given dimension.

17. The method of claim 15 , wherein the plurality of beam types includes at least one vertical beam having a relatively large elevation beam width and having a relatively small azimuth beam width and/or at least one horizontal beam having a relatively small elevation beam width and having a relatively large azimuth beam width.

18. The method of claim 13 , wherein the number of the one or more RACH signatures is based at least in part on a hierarchy associated with the plurality of beam types.

19. The method of claim 13 , wherein, if the beam type associated with the SSB comprises a wide beam, the number of the one or more RACH signatures associated with the SSB comprises a first number of RACH signatures;

wherein, if the beam type associated with the SSB comprises a narrow beam, the number of the one or more RACH signatures associated with the SSB comprises a second number of RACH signatures; and

wherein the first number of RACH signatures is different from the second number of RACH signatures.

20. The method of claim 19 , wherein the first number of RACH signatures is greater than the second number of RACH signatures.

21. The method of claim 13 , wherein the one or more RACH signatures associated with the SSB comprise:

respective RACH occasions and respective RACH preambles,

wherein the respective RACH occasions are indicated by a bitmap in the signaling communication.

22. The method of claim 21 , wherein the respective RACH occasions are based at least in part on a bit position, in the bitmap, associated with an SSB index that is associated with the SSB.

23. The method of claim 21 , wherein a number of RACH occasions, included in the respective RACH occasions, is based at least in part on a bit position, in the bitmap, associated with an SSB index that is associated with the SSB.

24. The method of claim 21 , wherein the beam type associated with the SSB is indicated by a bit position, in the bitmap, associated with an SSB index that is associated with the SSB.

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

a memory; and

one or more processors operatively coupled to the memory, the memory and the one or more processors configured to:

select a random access channel (RACH) signature from among one or more RACH signatures associated with a synchronization signal block (SSB),

wherein a number of the one or more RACH signatures is variable based at least in part on a beam type, of a plurality of beam types, associated with the SSB; and

transmit, to a base station (BS), a RACH communication using the selected RACH signature.

26. The UE of claim 25 , wherein, if the beam type associated with the SSB comprises a wide beam, the number of the one or more RACH signatures comprises a first number of RACH signatures;

wherein, if the beam type associated with the SSB comprises a narrow beam, the number of the one or more RACH signatures comprises a second number of RACH signatures; and

wherein the first number of RACH signatures is different from the second number of RACH signatures.

27. The UE of claim 26 , wherein the first number of RACH signatures is greater than the second number of RACH signatures.

28. A base station (BS) for wireless communication, comprising:

a memory; and

one or more processors operatively coupled to the memory, the memory and the one or more processors configured to:

transmit a plurality of synchronization signal blocks (SSBs); and

transmit a signaling communication that indicates respective sets of one or more random access channel (RACH) signatures associated with the plurality of SSBs,

wherein a number of a set of one or more RACH signatures associated with an SSB of the plurality of SSBs is variable based at least in part on a beam type, of a plurality of beam types, associated with the SSB.

29. The BS of claim 28 , wherein, if the beam type associated with the SSB comprises a wide beam, the number of the one or more RACH signatures associated with the SSB comprises a first number of RACH signatures;

wherein, if the beam type associated with the SSB comprises a narrow beam, the number of the one or more RACH signatures associated with the SSB comprises a second number of RACH signatures; and

wherein the first number of RACH signatures is different from the second number of RACH signatures.

30. The BS of claim 29 , wherein the first number of RACH signatures is greater than the second number of RACH signatures.