Two step random-access channel (RACH) procedure in millimeter wave (MMW)
Certain aspects of the present disclosure provide techniques for random-access channel (RACH) communication. For example, certain aspects provide a method for wireless communication. The method generally includes transmitting a plurality of reference signals using one or more beams, and receiving at least one of a RACH preamble and or a RACH payload corresponding to one or more of the reference signals transmitted via at least one of the one or more beams.
1. A method for wireless communications, comprising:
transmitting, to a wireless node, a plurality of reference signals using a plurality of beams;
transmitting an indication of sub-carrier resources for transmission of a random-access channel (RACH) preamble and a RACH payload; and
receiving, from the wireless node, a RACH message comprising a RACH preamble and a RACH payload, the RACH message being transmitted via at least one of the plurality of beams, wherein the RACH message indicates that a receive signal quality parameter associated with the at least one of the plurality of beams corresponding to the one or more of the plurality of reference signals exceeds a threshold, wherein the RACH preamble and the RACH payload are received using the same beam, wherein the RACH preamble and the RACH payload are received in different time or frequency resources, and wherein the RACH preamble and the RACH payload are received based on the indicated sub-carrier resources.
2. The method of claim 1 , wherein the reference signals comprise at least one of synchronization signals, channel state information reference signals, or mobility reference signals.
3. The method of claim 1 , wherein each of the plurality of beams is transmitted towards a different direction.
4. The method of claim 1 , further comprising:
transmitting a random access response, wherein the RACH payload is received before transmitting the random access response.
5. The method of claim 1 , wherein the RACH payload comprises a UE identifier (ID).
6. The method of claim 1 , wherein the RACH payload comprises at least one of a scheduling request, buffer status request, or a beam tracking request.
7. The method of claim 1 , wherein the RACH payload is scrambled based on an identifier of the RACH preamble.
8. A method for wireless communications, comprising:
receiving, from a wireless node, a plurality of reference signals that are transmitted using a plurality of beams;
receiving an indication of sub-carrier resources for transmission of a random-access channel (RACH) preamble and a RACH payload;
determining at least one beam of the plurality of beams for transmitting a RACH message comprising a RACH preamble and a RACH payload, wherein the determination of the at least one beam is based on a receive signal quality parameter associated with one or more of the plurality of reference signals received using the at least one beam of the plurality of beams exceeding a threshold; and
transmitting, to the wireless node, the RACH message comprising the RACH preamble and the RACH payload via the at least one beam, wherein the RACH preamble and the RACH payload are transmitted using the same beam, wherein the RACH preamble and the RACH payload are transmitted in different time or frequency resources, and wherein the RACH preamble and the RACH payload are transmitted based on the indicated sub-carrier resources.
9. The method of claim 8 , further comprising:
receiving a random access response, wherein the RACH payload is transmitted before receiving the random access response.
10. The method of claim 8 , wherein the RACH payload is scrambled based on an identifier of the RACH preamble.
11. The method of claim 8 , wherein the RACH payload comprises a UE identifier (ID).
12. The method of claim 8 , further comprising:
determining a number of steps for a RACH procedure based on the receive signal quality parameter corresponding to the at least one of the plurality of beams, wherein the RACH preamble and the RACH payload are transmitted based on the determined number of steps.
13. The method of claim 12 , wherein:
the RACH procedure comprises a two-step RACH procedure if the receive signal quality parameter of at least two of the plurality of beams is determined to be acceptable by comparing the receive signal quality parameter to the threshold; and
the RACH preamble is transmitted via a first beam of the at least two beams and the RACH payload is transmitted via a second beam of the at least two beams.
14. The method of claim 12 , wherein:
the RACH procedure comprises a two-step RACH procedure if the receive signal quality parameter of a single beam of the plurality of beams is determined to be acceptable by comparing the receive signal quality parameter to the threshold; and
the RACH preamble and RACH payload are transmitted via the single beam having the acceptable signal quality and using different frequency resources.
15. The method of claim 8 , wherein total resources for receiving the RACH preamble and the RACH payload is fixed.
16. The method of claim 15 , wherein the indication comprises an indication of a resource split between the RACH preamble and the RACH payload.
17. The method of claim 8 , wherein the indication received as part of at least one of a master information block (MIB), system information block (SIB), or minimum SIB message.
18. The method of claim 17 , wherein the minimum SIB comprises minimum SIB information for conveying a RACH configuration.
19. An apparatus for wireless communications, comprising:
a memory; and
one or more processors coupled to the memory, the one or more processors being configured to:
receive, from a wireless node, a plurality of reference signals that are transmitted using a plurality of beams;
receive an indication of sub-carrier resources for transmission of a random-access channel (RACH) preamble and a RACH payload;
determine at least one beam of the plurality of beams for transmitting a RACH message comprising a RACH preamble and a RACH payload, wherein the determination of the at least one beam is based on a receive signal quality parameter associated with one or more of the plurality of reference signals received using the at least one beam of the plurality of beams exceeding a threshold; and
transmit, to the wireless node, the RACH message comprising the RACH preamble and the RACH payload via the at least one beam, wherein the RACH preamble and the RACH payload are transmitted using the same beam, wherein the RACH preamble and the RACH payload are transmitted in different time or frequency resources, and wherein the RACH preamble and the RACH payload are transmitted based on the indicated sub-carrier resources.
20. The apparatus of claim 19 , wherein the one or more processors are further configured to:
receive a random access response, wherein the RACH payload is transmitted before receiving the random access response.
21. The apparatus of claim 19 , wherein the RACH payload is scrambled based on an identifier of the RACH preamble.
22. The apparatus of claim 19 , wherein the RACH payload comprises a UE identifier (ID).
23. The apparatus of claim 19 , wherein the one or more processors are further configured to:
determine a number of steps for a RACH procedure based on the receive signal quality parameter corresponding to the at least one of the plurality of beams, wherein the RACH preamble and the RACH payload are transmitted based on the determined number of steps.
24. The apparatus of claim 23 , wherein:
the RACH procedure comprises a two-step RACH procedure if the receive signal quality parameter of at least two of the plurality of beams is determined to be acceptable by comparing the receive signal quality parameter to the threshold; and
the RACH preamble is transmitted via a first beam of the at least two beams and the RACH payload is transmitted via a second beam of the at least two beams.
25. The apparatus of claim 23 , wherein:
the RACH procedure comprises a two-step RACH procedure if the receive signal quality parameter of a single beam of the plurality of beams is determined to be acceptable by comparing the receive signal quality parameter to the threshold; and
the RACH preamble and RACH payload are transmitted via the single beam having the acceptable signal quality and using different frequency resources.
26. The apparatus of claim 19 , wherein total resources for receiving the RACH preamble and the RACH payload is fixed.
27. The apparatus of claim 26 , wherein the indication comprises an indication of a resource split between the RACH preamble and the RACH payload.
28. The apparatus of claim 19 , wherein the indication received as part of at least one of a master information block (MIB), system information block (SIB), or minimum SIB message.
29. The apparatus of claim 28 , wherein the minimum SIB comprises minimum SIB information for conveying a RACH configuration.