Two-step random access procedure in wireless communication

1. A method of wireless communication at a user equipment (UE), comprising:

receiving, from a scheduling entity, random access channel (RACH) information for a RACH procedure, the RACH information indicating a plurality of resource pairs available for the RACH procedure, each of the plurality of resource pairs comprising a physical random access channel (PRACH) resource and a physical uplink shared channel (PUSCH) resource;

selecting a first resource pair of the plurality of resource pairs that satisfies a predetermined PRACH-to-PUSCH time gap; and

transmitting, to the scheduling entity, a first RACH message in the RACH procedure using the selected first resource pair, the first RACH message comprising at least a PRACH transmission,

wherein the plurality of resource pairs further comprise a second resource pair and a third resource pair, wherein:

a first time gap between a first PRACH resource and a first PUSCH resource of the first resource pair is different from a second time gap between a second PRACH resource and a second PUSCH resource of the second resource pair; and

a third time gap between a third PRACH resource and a third PUSCH resource of the third resource pair is different from the first time gap and the second time gap, and

wherein the first PRACH resource, the second PRACH resource, and the third PRACH resource correspond to at least one same time domain symbol, and the first PUSCH resource, the second PUSCH resource, and the third PUSCH resource respectively correspond to different time domain symbols.

2. The method of claim 1 , wherein the selecting the first resource pair comprises:

selecting the first resource pair instead of the second resource pair or the third resource pair when the first time gap of the first resource pair is at least equal to a minimum time gap based on a capability of the UE, and the second time gap and the third time gap are smaller than the minimum time gap,

wherein the minimum time gap is at least equal to one or more time domain symbols.

3. The method of claim 2 , wherein the first RACH message further comprises:

a PUSCH transmission using the first PUSCH resource, wherein a time domain gap between the PRACH transmission and the PUSCH transmission is at least equal to the minimum time gap.

4. The method of claim 1 , further comprising:

forgoing a PUSCH transmission in the first RACH message, if a time gap between the PRACH resource and the PUSCH resource of any of the plurality of resource pairs is smaller than a minimum time gap based on a capability of the UE.

5. The method of claim 1 , wherein the receiving the RACH information comprises at least one of:

receiving system information comprising the RACH information; or

receiving a radio resource control (RRC) message comprising the RACH information.

6. The method of claim 1 , wherein the RACH information further comprises UE control information for indicating that the UE has permission to transmit the first RACH message without a PUSCH transmission, if a time gap between the PRACH resource and the PUSCH resource of any of the plurality of resource pairs is smaller than a minimum time gap based on a capability of the UE.

7. A user equipment (UE), comprising:

a communication interface configured for wireless communication;

a memory; and

a processor operatively coupled with the communication interface and the memory,

wherein the processor and the memory are configured to:

receive, from a scheduling entity via the communication interface, random access channel (RACH) information for a RACH procedure, the RACH information indicating a plurality of resource pairs available for the RACH procedure, each of the plurality of resource pairs comprising a physical random access channel (PRACH) resource and a physical uplink shared channel (PUSCH) resource;

select a first resource pair of the plurality of resource pairs that satisfies a predetermined PRACH-to-PUSCH time gap; and

transmit, to the scheduling entity, a first RACH message in the RACH procedure using the selected first resource pair, the first RACH message comprising at least a PRACH transmission,

wherein the plurality of resource pairs further comprise a second resource pair and a third resource pair, wherein:

a first time gap between a first PRACH resource and a first PUSCH resource of the first resource pair is different from a second time gap between a second PRACH resource and a second PUSCH resource of the second resource pair; and

a third time gap between a third PRACH resource and a third PUSCH resource of the third resource pair is different from the first time gap and the second time gap, and

wherein the first PRACH resource, the second PRACH resource, and the third PRACH resource correspond to at least one same time domain symbol, and the first PUSCH resource, the second PUSCH resource, and the third PUSCH resource respectively correspond to different time domain symbols.

8. The UE of claim 7 , wherein the processor and the memory are further configured to:

select the first resource pair instead of the second resource pair or the third resource pair when the first time gap of the first resource pair is at least equal to a minimum time gap based on a capability of the UE, and the second time gap and the third time gap are smaller than the minimum time gap,

wherein the minimum time gap is at least equal to one or more time domain symbols.

9. The UE of claim 8 , wherein the first RACH message further comprises:

a PUSCH transmission using the first PUSCH resource, wherein a time domain gap between the PRACH transmission and the PUSCH transmission is at least equal to the minimum time gap.

10. The UE of claim 7 , wherein the processor and the memory are further configured to:

forgo a PUSCH transmission in the first RACH message, if a time gap between the PRACH resource and the PUSCH resource of any of the plurality of resource pairs is smaller than a minimum time gap based on a capability of the UE.

11. The UE of claim 7 , wherein the processor and the memory are further configured to at least one of:

receive system information comprising the RACH information; or

receive a radio resource control (RRC) message comprising the RACH information.

12. The UE of claim 7 , wherein the RACH information further comprises UE control information for indicating that the UE has permission to transmit the first RACH message without a PUSCH transmission, if a time gap between the PRACH resource and the PUSCH resource of any of the plurality of resource pairs is smaller than a minimum time gap based on a capability of the UE.

13. A method of wireless communication at a scheduling entity, comprising:

transmitting, to a user equipment (UE), random access channel (RACH) information for a RACH procedure, the RACH information comprising:

resource information on a plurality of resources available for a physical random access channel (PRACH) and a physical uplink shared channel (PUSCH) used in the RACH procedure; and

UE permission information for configuring the UE to transmit a first RACH message comprising a PRACH transmission in the RACH procedure without a PUSCH transmission; and

receiving, from the UE, the first RACH message in the RACH procedure.

14. The method of claim 13 , wherein the UE permission information further configures the UE to transmit the first RACH message comprising the PRACH transmission without the PUSCH transmission if a time gap between a PRACH resource and a PUSCH resource available among the plurality of resources is smaller than a predetermined time gap based on a capability of the UE.

15. The method of claim 14 , wherein the transmitting the RACH information comprises, at least one of:

transmitting system information comprising the RACH information; or

transmitting a radio resource control (RRC) message comprising the RACH information.

16. The method of claim 13 , wherein the receiving the first RACH message comprises:

receiving the PRACH transmission and the PUSCH transmission with no time gap between the PRACH transmission and the PUSCH transmission.

17. The method of claim 13 , wherein the receiving the first RACH message comprises:

receiving the PRACH transmission and the PUSCH transmission with a time gap between the PRACH transmission and the PUSCH transmission, the time gap is greater than a predetermined time gap based on a capability of the UE.

18. The method of claim 13 , further comprising:

transmitting, after receiving the PRACH transmission without receiving the PUSCH transmission in the first RACH message, a random access response (RAR) message to the UE, the RAR message scrambled by an identifier determined based on PRACH resources of the plurality of resources used for the PRACH transmission.

19. The method of claim 13 , wherein the plurality of resources comprise a plurality of resource pairs, each of the plurality of resource pairs comprises a PRACH resource and a PUSCH resource, and each of the plurality of resource pairs has a different time gap between the PRACH resource and the PUSCH resource.

20. A scheduling entity comprising:

a communication interface configured to communicate with a user equipment (UE);

a memory; and

a processor operatively coupled with the communication interface and the memory,

wherein the processor and the memory are configured to:

transmit, to a user equipment (UE), random access channel (RACH) information for a RACH procedure, the RACH information comprising:

resource information on a plurality of resources available for a physical random access channel (PRACH) and a physical uplink shared channel (PUSCH) used in the RACH procedure; and

UE permission information for configuring the UE to transmit a first RACH message comprising a PRACH transmission in the RACH procedure without a PUSCH transmission; and

receive, from the UE, the first RACH message in the RACH procedure.

21. The scheduling entity of claim 20 , wherein the UE permission information further configures the UE to transmit the first RACH message comprising the PRACH transmission without the PUSCH transmission if a time gap between a PRACH resource and a PUSCH resource available among the plurality of resources is smaller than a predetermined time gap based on a capability of the UE.

22. The scheduling entity of claim 21 , wherein the processor and the memory are further configured to, at least one of:

transmit system information comprising the RACH information; or

transmit a radio resource control (RRC) message comprising the RACH information.

23. The scheduling entity of claim 20 , wherein the processor and the memory are further configured to:

receive the PRACH transmission and the PUSCH transmission with no time gap between the PRACH transmission and the PUSCH transmission.

24. The scheduling entity of claim 20 , wherein the processor and the memory are further configured to:

receive the PRACH transmission and the PUSCH transmission with a time gap between the PRACH transmission and the PUSCH transmission, the time gap is greater than a predetermined time gap based on a capability of the UE.

25. The scheduling entity of claim 20 , wherein the processor and the memory are further configured to:

transmit, after receiving the PRACH transmission without receiving the PUSCH transmission in the first RACH message, a random access response (RAR) message to the UE, the RAR message scrambled by an identifier determined based on PRACH resources of the plurality of resources used for the PRACH transmission.

26. The scheduling entity of claim 20 , wherein the plurality of resources comprise a plurality of resource pairs, each of the plurality of resource pairs comprises a PRACH resource and a PUSCH resource, and each of the plurality of resource pairs has a different time gap between the PRACH resource and the PUSCH resource.