Enhanced random access channel (RACH) procedure

1. A method, of a random access channel (RACH) procedure at a user equipment (UE), comprising:

selecting, at the UE, between a two-step RACH procedure or a four-step RACH procedure,

wherein the selecting is based at least on RACH configuration information received, from a base station or the RACH configuration information at the UE,

wherein selecting between the two-step or the four-step RACH procedure comprises:

determining, at the UE, a reference signal received power (RSRP) value of a synchronization signal or a reference signal, received from the base station, based at least on the received RACH configuration information; and

selecting the two-step RACH procedure in response to determining that the RSRP value of the synchronization signal or the reference signal is equal to or greater than a threshold or selecting the four-step RACH procedure in response to determining that the RS RP value of the synchronization signal or the reference signal is less than a threshold; and

transmitting, from the UE, one or more messages associated with the two-step RACH procedure or the four-step RACH procedure based on the selection.

2. The method of claim 1 , wherein the selecting includes selecting the two-step RACH procedure, and wherein the transmitting includes transmitting a first message of the one or more messages, and wherein the first message includes a physical RACH (PRACH) sequence used a reference signal (RS) by the base station or a sounding reference signal (SRS).

3. The method of claim 2 , further comprising:

transmitting, from the UE, a payload to the base station during a handover of the UE, wherein the payload is transmitted as part of the first message.

4. The method of claim 3 , wherein the payload is a measurement report, a buffer status report, channel state feedback (CSF) information, or a user data.

5. The method of claim 1 , wherein the selecting includes selecting the two-step RACH procedure, and wherein the transmitting further comprises:

transmitting, from the UE, a first message of the one or more messages to the base station; and

receiving, from the base station, a second message of the one or more messages, in response to transmitting the first message to the base station.

6. The method of claim 5 , wherein the first message is transmitted over one or more beams and the second message is received over the one or more beams.

7. The method of claim 6 , wherein the second message is received over two beams of the one or more beams, and further comprising:

receiving a random access response (RAR) payload in the second message over the two beams, wherein the RAR payload is split over the two beams or repeated over the two beams.

8. The method of claim 1 , wherein the UE receives the RACH configuration information from the base station in a master information (MIB) or a system information block (SIB).

9. The method of claim 1 , wherein the selecting includes selecting the two-step RACH procedure, and further comprising:

switching from the two-step to the four-step RACH procedure based at least on a reference signal received power (RSRP) value of a synchronization signal or a reference signal received from the base station, a transmit power, or a command received from the base station.

10. The method of claim 9 , further comprising:

using a transmit power based on the two-step RACH procedure prior to the switching, applying an offset to the transmit power based on the two-step RACH procedure prior to the switching, or using a transmit power based on the four-step RACH procedure, and prior to receiving a response from the base station.

11. An apparatus for a random access channel (RACH) procedure at a user equipment (UE), comprising:

a memory configured to store data; and

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

select, at the UE, between a two-step RACH procedure or a four-step RACH procedure, wherein the selecting is based at least on RACH configuration information received from a base station or the RACH configuration information at the UE;

determine, at the UE, a reference signal received power (RSRP) value of a synchronization signal or a reference signal, received from the base station, based at least on the received RACH configuration information,

wherein the one or more processors and the memory are configured to select the two-step RACH procedure in response to determining that the RS RP value of the synchronization signal or the reference signal is equal to or greater than a threshold or select the four-siep RACH procedure in response to determining that the RSRP value of the synchronization signal or the reference signal is less than a threshold; and

transmit, from the UE, one or more messages associated with the two-step RACH procedure or the four-step RACH procedure based on the selection.

12. The apparatus of claim 11 , wherein the one or more processors and the memory are further configured to select the two-step RACH procedure, and transmit a first message of the one or more messages, and wherein the first message includes a physical RACH (PRACH) sequence used a reference signal (RS) by the base station or a sounding reference signal (SRS).

13. The apparatus of claim 12 , wherein the one or more processors and the memory are further configured to:

transmit, from the UE, a payload to the base station during a handover of the UE, wherein the payload is transmitted as part of the first message.

14. The apparatus of claim 13 , wherein the payload is a measurement report, a buffer status report, channel state, feedback (CSF) information, or a user data.

15. The apparatus of claim 11 , wherein the selection includes selecting the two-step RACH procedure, and wherein the one or more processors and the memory are further configured to:

transmit, from the UE, a first message of the one or more messages to the base station;

receive, from the base station, a second message of the one or more messages, in response to transmitting the first message to the base station.

16. The apparatus of claim 15 , wherein the first message is transmitted over one or more beams and the second message is received over the one or more beams.

17. The apparatus of claim 16 , wherein the second message is received over two beams of the one or more beams, wherein the one or more processors and the memory are further configured to:

receive a random access response (RAR) payload in the second message over the two beams, wherein the RAR payload is split over the two beams or repeated over the two beams.

18. The apparatus of claim 11 , wherein the UE receives the RACH configuration information from the base station in a master information (MIB) or a system information block (SIB).

19. The apparatus of claim 11 , wherein the selection includes selecting the two-step RACH procedure, and wherein the one or, more processors and the memory are further configured to:

switch from the two-step to the four-step RACH procedure based at least on a reference signal received power (RSRP) value of a synchronization signal or a reference signal received from the base station, a transmit power, or a command received from the base station.

20. The apparatus of claim 19 , wherein the one or more processors and the memory are further configured to:

use a transmit power based on the two-step RACH procedure prior to the switching, apply an offset to the transmit power based on the two-step RACH procedure prior to the switch, or use a transmit power based on the four-step RACH procedure, and prior to receiving a response from the base station.

21. An apparatus for a random access channel (RACH) procedure at a user equipment (UE), comprising:

means for selecting, at the UE, between a two-step RACH procedure or a four-step RACH procedure, wherein the selecting is based at least on RACH configuration information received from a base station or the RACH configuration information at the UE;

means for determining, at the UE, a reference signal received power (RSRP) value of a synchronization signal or a reference signal, received from the base station, based at least on the received RACH configuration information,

wherein the means for selecting is configured to select the two-step RACH procedure in response to determining that the RSRP value of the synchronization signal or the reference signal is equal to or greater than a threshold and select the four-step RACH procedure in response to determining that the RSRP value of the synchronization signal or the reference signal is less than a threshold; and

means for transmitting, from the UE, one or more messages associated with the two-step RACH procedure or the four-step RACH procedure based on the selection.

22. The apparatus of claim 21 , wherein the selecting includes selecting the two-step RACH procedure, and wherein the transmitting includes transmitting a first message of the one or more messages, and wherein the first message includes a physical RACH (PRACH) sequence used a reference signal (RS) by the base station or a sounding reference signal (SRS).

23. The apparatus of claim 22 , further comprising:

means for transmitting, from the UE, a payload to the base station during a handover of the UE, wherein the payload is transmitted as part of the first message.

24. The apparatus of claim 23 , wherein the payload is a measurement report, a buffer status report, channel state feedback (CSF) information, or a user data.

25. The apparatus of claim 21 , wherein the selecting includes selecting the two-step RACH procedure, and wherein the transmitting further comprises:

means for transmitting, from the UE, a first message of the one or more messages to the base station; and

means for receiving, from the base station, a second message of the one or more messages, in response to transmitting the first message to the base station.

26. The apparatus of claim 25 , wherein the first message is transmitted over one or more beams and the second message is received over the one or more beams.

27. A non-transitory computer readable medium storing computer executable code for a random access channel (RACH) procedure at a user equipment (UE), comprising:

code for selecting, at the UE, between a two-step RACH procedure or a four-step RACH procedure, wherein the selecting is based at least on RACH configuration information received from a base station or the RACH configuration information at the UE;

code for determining, at the UE, a reference signal received power (RSRP) value of a synchronization signal or a reference signal, received from the base station, based at least on the received RACH configuration information,

wherein the code for selecting is configured to select the two-step RACH procedure in response to determining that the RSRP value of the synchronization signal or the reference signal is equal to or greater than a threshold and select the four-step RACH procedure in response to determining that the RSRP value of the synchronization signal or the reference signal is less than a threshold; and

code transmitting, from the UE, one or more messages associated with the two-step RACH procedure or the four-step RACH procedure based on the selection.