Beam refinement in two-step random access channel (RACH) procedure

1. A method of communications, comprising:

receiving, by a user equipment (UE), a plurality of synchronization signal blocks (SSBs), a plurality of channel state information-reference signals (CSI-RSs) associated with each of the plurality of synchronization signal blocks (SSBs), and random access channel (RACH) configuration data from a gNB, the random access channel (RACH) configuration data associated with a two-step random access channel (RACH) procedure; and

transmitting, by the user equipment (UE), a first message of the two-step random access channel (RACH) procedure to the gNB, the first message including a first portion and a second portion, wherein:

the first portion includes a preamble associated with a selected channel state information-reference signal (CSI-RS) of the plurality of channel state information- reference signals (CSI-RSs), the selected channel state information-reference signal (CSI-RS) further associated with a selected synchronization signal block (SSB) of the plurality of synchronization signal blocks (SSBs), the second portion includes data associated with the preamble, the data transmitted using pre-configured or pre- allocated resources, and

a resource or resource set associated with the selected channel state information- reference signal (CSI-RS) and/or the selected synchronization signal block (SSB) is selected, the first portion transmitted using the selected resource or resource set, and the selected resource or resource set indicating, to the gNB, the selected channel state information-reference signal (CSI-RS) used for determining a transmit beam for transmitting the second portion of the first message.

2. The method of claim 1 , further comprising:

measuring reference signal receive power (RSRP) values of the plurality of synchronization signal blocks (SSBs);

selecting a synchronization signal block (SSB) of the plurality of synchronization signal blocks (SSBs) based on the measured reference signal receive power (RSRP) values of the plurality of synchronization signal blocks (SSBs);

measuring reference signal receive power (RSRP) values of a plurality of channel state information-reference signals (CSI-RSs) associated with the selected synchronization signal block (SSB); and

selecting the channel state information-reference signal (CSI-RS) of the plurality of channel state information-reference signals (CSI-RSs) based on the measured reference signal receive power (RSRP) values of the plurality of channel state information-reference signals (CSI-RSs).

3. The method of claim 1 , further comprising:

measuring reference signal receive power (RSRP) values of the plurality of channel state information-reference signals (CSI-RSs);

selecting the channel state information-reference signal (CSI-RS) of the plurality of channel state information-reference signals (CSI-RSs) based on the measured reference signal receive power (RSRP) values of the plurality of channel state information-reference signals (CSI-RSs); and

selecting the synchronization signal block (SSB) associated with the selected channel state information-reference signal (CSI-RS).

4. The method of claim 1 , wherein a time offset is present between the first and the second portions of the first message being transmitted to the gNB.

5. The method of claim 1 , wherein the random access channel (RACH) configuration data includes information on:

resources for random access channel (RACH) occasions (ROs);

mapping preambles to the random access channel (RACH) occasions (ROs);

mapping the plurality of synchronization signal blocks (SSBs) to the random access channel (RACH) occasions (ROs);

resources for transmitting the second portion of the first message; and

transmission parameters for the second portion of the first message.

6. The method of claim 5 , wherein the transmission parameters include modulation coding scheme (MCS) parameters.

7. The method of claim 1 , wherein the random access channel (RACH) configuration data includes information on:

configuration of the resources or resource sets associated with the plurality of channel state information-reference signals (CSI-RSs) and/or the plurality of the synchronization signal blocks (SSBs).

8. The method of claim 1 , wherein the transmitting of the first message further comprises:

time-division multiplexing (TDM) of the first and second portions of the first message.

9. A non-transitory computer-readable storage medium having stored thereon computer executable program code which, when executed on a computer system, causes the computer system to perform the method of claim 1 .

10. An apparatus comprising at least one processor, and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to:

receive, a plurality of synchronization signal blocks (SSBs), a plurality of channel state information-reference signals (CSI-RSs) associated with each of the plurality of synchronization signal blocks (SSBs), and random access channel (RACH) configuration data from a gNB, the random access channel (RACH) configuration data associated with a two-step random access channel (RACH) procedure; and

transmit, a first message of the two-step random access channel (RACH) procedure to the gNB, the first message including a first portion and a second portion, wherein:

the first portion includes a preamble associated with a selected channel state information-reference signal (CSI-RS) of the plurality of channel state information- reference signals (CSI-RSs), the selected channel state information-reference signal (CSI-RS) further associated with a selected synchronization signal block (SSB) of the plurality of synchronization signal blocks (SSBs), and the second portion includes data associated with the preamble, the data transmitted using pre-configured or pre- allocated resources, and

a resource or resource set associated with the selected channel state information- reference signal (CSI-RS) and/or the selected synchronization signal block (SSB) is selected, the first portion transmitted using the selected resource or resource set, and the selected resource or resource set indicating, to the gNB, the selected channel state information-reference signal (CSI-RS) used for determining a transmit beam for transmitting the second portion of the first message.

11. A method of communications, comprising:

transmitting, by a gNB, a plurality of synchronization signal blocks (SSBs), a plurality of channel state information-reference signals (CSI-RSs) associated with each of the plurality of synchronization signal blocks (SSBs), and random access channel (RACH) configuration data to a user equipment (UE), the random access channel (RACH) configuration data associated with a two-step random access channel (RACH) procedure; and

receiving, by the gNB, a first message of the two-step random access channel (RACH) procedure to the gNB, the first message including a first portion and a second portion, wherein:

the first portion includes a preamble associated with a selected channel state information-reference signal (CSI-RS) of the plurality of channel state information- reference signals (CSI-RSs), the selected channel state information-reference signal (CSI-RS) further associated with a selected synchronization signal block (SSB) of the plurality of synchronization signal blocks (SSBs), the selections performed by the user equipment (UE), the second portion includes data associated with the two-step random access channel (RACH) procedure, the data transmitted, by the user equipment (UE), using pre-configured or pre-allocated resources, and

a resource or resource set associated with the selected channel state information- reference signal (CSI-RS) and/or the selected synchronization signal block (SSB) is selected by the user equipment (UE), the first portion received using the selected resource or resource set, and the selected resource or resource set indicating, to the gNB, the selected channel state information-reference signal (CSI-RS) used for determining a transmit beam for transmitting the second portion of the first message.

12. A non-transitory computer-readable storage medium having stored thereon computer executable program code which, when executed on a computer system, causes the computer system to perform the method of claim 11 .

13. An apparatus comprising at least one processor, and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to:

transmit, a plurality of synchronization signal blocks (SSBs), a plurality of channel state information-reference signals (CSI-RSs) associated with each of the plurality of synchronization signal blocks (SSBs), and random access channel (RACH) configuration data to a user equipment (UE), the random access channel (RACH) configuration data associated with a two-step random access channel (RACH) procedure; and

receive, a first message of the two-step random access channel (RACH) procedure to the gNB, the first message including a first portion and a second portion, wherein:

the first portion includes a preamble associated with a selected channel state information-reference signal (CSI-RS) of the plurality of channel state information-reference signals (CSI-RSs), the selected channel state information-reference signal (CSI-RS) further associated with a selected synchronization signal block (SSB) of the plurality of synchronization signal blocks (SSBs), the selections performed by the user equipment (UE), the second portion includes data associated with the two-step random access channel (RACH) procedure, the data transmitted, by the user equipment (UE), using pre-configured or pre-allocated resources, and

a resource or resource set associated with the selected channel state information-reference signal (CSI-RS) and/or the selected synchronization signal block (SSB) is selected by the user equipment (UE), the first portion received using the selected resource or resource set, and the selected resource or resource set indicating, to the gNB, the selected channel state information-reference signal (CSI-RS) used for determining a transmit beam for transmitting the second portion of the first message.