Performing a two-step random access channel procedure

1. A method comprising:

receiving enable information from a network device indicating whether a two-step random access channel procedure is enabled and whether a four-step random access channel procedure is enabled;

determining whether to perform the two-step random access channel procedure or the four-step random access channel procedure based on a reference signal received power of a downlink pathloss reference and the enable information, wherein the two-step random access channel procedure is determined to be performed in response to the reference signal received power being greater than a predetermined threshold and the enable information indicating that the two-step random access channel procedure is enabled; and

in response to determining to perform the two-step random access channel procedure:

in a first step:

transmitting a preamble in a first time instance; and

transmitting an uplink data transmission via a physical uplink shared channel in a second time instance different from the first time instance; and

in a second step, receiving a response message corresponding to the first step,

wherein the response message comprises a radio network temporary identifier.

2. The method of claim 1 , wherein the radio network temporary identifier for the two-step random access channel procedure is calculated using a first formula, and a radio network temporary identifier for the four-step random access channel procedure is calculated using a second formula different from the first formula.

3. The method of claim 1 , wherein the uplink data transmission comprises a medium access control protocol data unit.

4. The method of claim 3 , further comprising storing the medium access control protocol data unit in a buffer.

5. The method of claim 4 , wherein the medium access control protocol data unit is stored in the buffer in response to switching from the two-step random access channel procedure to the four-step random access channel procedure.

6. The method of claim 1 , further comprising delaying for an offset time between transmission of the preamble and transmission of the uplink data transmission.

7. The method of claim 6 , wherein the offset time corresponds to a subcarrier spacing.

8. An apparatus comprising a user equipment, the apparatus further comprising:

a receiver that receives enable information from a network device indicating whether a two-step random access channel procedure is enabled and whether a four-step random access channel procedure is enabled;

a processor that determines whether to perform the two-step random access channel procedure or the four-step random access channel procedure based on a reference signal received power of a downlink pathloss reference and the enable information, wherein the two-step random access channel procedure is determined to be performed in response to the reference signal received power being greater than a predetermined threshold and the enable information indicating that the two-step random access channel procedure is enabled; and

a transmitter;

wherein in response to determining to perform the two-step random access channel procedure:

in a first step, the transmitter:

transmits a preamble in a first time instance; and

transmits an uplink data transmission via a physical uplink shared channel in a second time instance different from the first time instance; and

in a second step, the receiver receives a response message corresponding to the first step, wherein the response message comprises a radio network temporary identifier.

9. The apparatus of claim 8 , wherein the processor monitors during a response window for the response message.

10. The apparatus of claim 8 , wherein the receiver receives information configuring a requirement for performing the two-step random access channel procedure.

11. The apparatus of claim 10 , wherein the information indicates that the two-step random access channel procedure is allowed.

12. The apparatus of claim 10 , wherein the information indicates that the two-step random access channel procedure is required.

13. A method comprising:

transmitting enable information from a network device indicating whether a two-step random access channel procedure is enabled and whether a four-step random access channel procedure is enabled;

receiving a preamble in a first time instance and receiving an uplink data transmission via a physical uplink shared channel in a second time instance different from the first time instance in response to a determination by a remote unit to perform the two-step random access channel procedure, wherein the determination by the remote unit to perform the two-step random access channel procedure is based on a reference signal received power of a downlink pathloss reference and the enable information, and the two-step random access channel procedure is determined to be performed in response to the reference signal received power being greater than a predetermined threshold and the enable information indicating that the two-step random access channel procedure is enabled; and

transmitting a response message corresponding to the preamble, wherein the response message comprises a radio network temporary identifier.

14. The method of claim 13 , wherein an offset time delay is between receiving the preamble and receiving the uplink data transmission.

15. The method of claim 14 , wherein the offset time corresponds to a subcarrier spacing.

16. An apparatus comprising:

a transmitter that transmits enable information indicating whether a two-step random access channel procedure is enabled and whether a four-step random access channel procedure is enabled; and

a receiver that receives a preamble in a first time instance and receiving an uplink data transmission via a physical uplink shared channel in a second time instance different from the first time instance in response to a determination by a remote unit to perform a two-step random access channel procedure, wherein the determination by the remote unit to perform the two-step random access channel procedure is based on a reference signal received power of a downlink pathloss reference and the enable information, and the two-step random access channel procedure is determined to be performed in response to the reference signal received power being greater than a predetermined threshold and the enable information indicating that the two-step random access channel procedure is enabled;

wherein the transmitter transmits a response message corresponding to the preamble, and the response message comprises a radio network temporary identifier.

17. The apparatus of claim 16 , wherein the transmitter transmits information configuring a requirement for performing the two-step random access channel procedure.

18. The apparatus of claim 17 , wherein the information indicates that the two-step random access channel procedure is allowed.

19. The apparatus of claim 17 , wherein the information indicates that the two-step random access channel procedure is required.