2-step random access

1. An apparatus, comprising:

a processor configured to cause a user equipment device (UE) to:

receive, from a base station, random access (RA) configuration information, including, first configuration information for a 2-step RA procedure, second configuration information for a 4-step RA procedure, and a criterion for power ramping, the criterion for power ramping specifying that power ramping should not be applied to an RA retransmission if a different RA type is selected relative to a previous RA attempt;

determine a condition, wherein the condition is that a measured reference signal received power (RSRP) is greater than a threshold;

determine, based on the condition that the measured RSRP is greater than the threshold, to perform the 2-step RA procedure;

perform one or more transmissions, to the base station, of respective first messages of the 2-step RA procedure, wherein a first message of the 2-step RA procedure includes a preamble and content on a physical uplink shared channel;

within a 2-step random access response window and as part of the 2-step RA procedure:

monitor a physical downlink control channel (PDCCH) masked by a msgB radio network temporary identifier (msgB-RNTI);

based on the monitoring, receive a msgB indicating a backoff indicator for a backoff mechanism to be applied on a next preamble transmission; and

when the 4-step RA procedure is selected for a next preamble transmission in response to reaching a configured number of transmission attempts of first messages of the 2-step RA procedure before falling back to the 4-step RA procedure, the backoff mechanism is not applied.

2. The apparatus of claim 1 ,

wherein the processor is further configured to cause the UE to:

start a timer associated with the 2-step random access response window when the first message of the 2-step RA procedure is transmitted.

3. The apparatus of claim 1 , wherein, to fallback to the 4-step RA procedure, the processor is further configured to cause the UE to:

transmit, to the base station, a first message of the 4-step RA procedure.

4. The apparatus of claim 1 ,

wherein at least one fallback criterion specifies a message for indicating a fallback,

wherein, to determine that the at least one fallback criterion is satisfied, the processor is further configured to cause the UE to:

receive, from the base station, the message for indicating a fallback.

5. The apparatus of claim 4 , wherein the message for indicating a fallback includes a second message of the 4-step RA procedure.

6. The apparatus of claim 1 , wherein the RA configuration information further specifies a criterion for backoff.

7. A user equipment device (UE), comprising:

a radio; and

a processor operably connected to the radio and configured to cause the UE to:

receive, from a base station, random access (RA) configuration information, including, first configuration information for a 2-step RA procedure, second configuration information for a 4-step RA procedure, and a criterion for power ramping, the criterion for power ramping specifying that power ramping should not be applied to an RA retransmission if a different RA type is selected relative to a previous RA attempt;

determine a condition, wherein the condition is that a measured reference signal received power (RSRP) is greater than a threshold;

determine, based on the condition that the measured RSRP is greater than the threshold, to perform the 2-step RA procedure;

perform one or more transmissions, to the base station, of respective first messages of the 2-step RA procedure, wherein a first message of the 2-step RA procedure includes a preamble and content on a physical uplink shared channel;

within a 2-step random access response window and as part of the 2-step RA procedure:

monitor a physical downlink control channel (PDCCH) masked by a msgB radio network temporary identifier (msgB-RNTI);

based on the monitoring, receive a msgB indicating a backoff indicator for a backoff mechanism to be applied on a next preamble transmission; and

when the 4-step RA procedure is selected for a next preamble transmission in response to reaching a configured number of transmission attempts of first messages of the 2-step RA procedure before falling back to the 4-step RA procedure, the backoff mechanism is not applied.

8. The UE of claim 7 ,

wherein the processor is further configured to cause the UE to:

start a timer associated with the 2-step random access response window when the first message of the 2-step RA procedure is transmitted.

9. The UE of claim 7 , wherein, to fallback to the 4-step RA procedure, the processor is further configured to cause the UE to:

transmit, to the base station, a first message of the 4-step RA procedure.

10. The UE of claim 7 ,

wherein at least one fallback criterion specifies a message for indicating a fallback,

wherein, to determine that the at least one fallback criterion is satisfied, the processor is further configured to cause the UE to:

receive, from the base station, the message for indicating a fallback.

11. The UE of claim 10 , wherein the message for indicating a fallback includes a second message of the 4-step RA procedure.

12. The UE of claim 7 , wherein the RA configuration information further specifies a criterion for backoff.

13. A method, comprising:

at a user equipment device (UE):

receiving, from a base station, random access (RA) configuration information, including, first configuration information for a 2-step RA procedure, second configuration information for a 4-step RA procedure, and a criterion for power ramping, the criterion for power ramping specifying that power ramping should not be applied to an RA retransmission if a different RA type is selected relative to a previous RA attempt;

determining a condition, wherein the condition is that a measured reference signal received power (RSRP) is greater than a threshold;

determining, based on the condition that the measured RSRP is greater than the threshold, to perform the 2-step RA procedure;

performing one or more transmissions, to the base station, of respective first messages of the 2-step RA procedure, wherein a first message of the 2-step RA procedure includes a preamble and content on a physical uplink shared channel;

within a 2-step random access response window and as part of the 2-step RA procedure:

monitoring a physical downlink control channel (PDCCH) masked by a msgB radio network temporary identifier (msgB-RNTI);

based on the monitoring, receiving a msgB indicating a backoff indicator for a backoff mechanism to be applied on a next preamble transmission; and

when the 4-step RA procedure is selected for a next preamble transmission in response to reaching a configured number of transmission attempts of first messages of the 2-step RA procedure before falling back to the 4-step RA procedure, the backoff mechanism is not applied.

14. The method of claim 13 ,

wherein the method further comprises:

starting a timer associated with the 2-step random access response window when the first message of the 2-step RA procedure is transmitted.

15. The method of claim 13 , wherein, to fallback to the 4-step RA procedure, comprises:

transmitting, to the base station, a first message of the 4-step RA procedure.

16. The method of claim 13 ,

wherein at least one fallback criterion specifies a message for indicating a fallback,

wherein, to determine that the at least one fallback criterion is satisfied, the method comprises:

receiving, from the base station, the message for indicating a fallback.

17. The method of claim 16 , wherein the message for indicating a fallback includes a second message of the 4-step RA procedure.

18. The method of claim 16 , wherein, to fallback to the 4-step RA procedure, the method comprises:

transmitting, to the base station, a third message of the 4-step RA procedure.

19. The method of claim 13 , wherein the RA configuration information further specifies a criterion for backoff.

20. The method of claim 19 , wherein the criterion for backoff specifies that backoff should not be applied to an RA retransmission if a different RA type is selected relative to a previous RA attempt.