Switching between two-step and four-step random access procedures in non-terrestrial networks

1. A method comprising:

selecting, by a wireless device and in response to initiating a two-step random access (RA) procedure, a first radio resource for transmission of a first message of the two-step RA procedure;

switching, without transmitting the first message, from the two-step RA procedure to a four-step RA procedure based on:

a cell associated with the wireless device being part of a non-terrestrial network (NTN); and

the first radio resource being invalid for the transmission of the first message; and

transmitting, via a second radio resource, a preamble for the four-step RA procedure.

2. The method of claim 1 , wherein the first radio resource comprises a first physical random access channel (PRACH) occasion and a first physical uplink shared channel (PUSCH) occasion mapped to the first PRACH occasion.

3. The method of claim 2 , wherein the first radio resource is invalid based at least one of:

the first PUSCH occasion being invalid; or

failing to satisfy a time gap condition.

4. The method of claim 3 , wherein the time gap condition is satisfied based on at least one of:

a time difference between a last symbol of the first PUSCH occasion and a last symbol of the first PRACH occasion being less than a first threshold;

a time difference between a first symbol of the first PUSCH occasion and a first symbol of the first PRACH occasion being less than the first threshold;

a time difference between the last symbol of the first PUSCH occasion and a time that the first radio resource is selected being less than the first threshold; or

a time difference between the last symbol of the first PUSCH occasion and a time that the two-step RA procedure is initiated being less than the first threshold.

5. The method of claim 4 , further comprising determining the first threshold based on at least one of:

a propagation delay between the wireless device and a node of the NTN; or

a portion of a propagation delay between the wireless device and a base station, wherein the wireless device communicates with the base station via the NTN.

6. The method of claim 2 , further comprising selecting, in response to the switching to the four-step RA procedure, the second radio resource associated with the preamble for the four-step RA procedure for transmission of the first message, wherein the second radio resource comprises a second PRACH occasion and a second PUSCH occasion mapped to the second PRACH occasion.

7. The method of claim 6 , wherein the switching to the four-step RA procedure is further based on the second radio resource being invalid.

8. The method of claim 7 , wherein the second radio resource is invalid based on:

the second PRACH occasion being valid; and

the second PUSCH occasion being invalid.

9. The method of claim 7 , wherein the second radio resource is invalid based on a time difference between the second radio resource and the first radio resource being larger than a second threshold.

10. The method of claim 1 , further comprising:

receiving, by the wireless device, one or more radio resource control (RRC) messages comprising:

first configuration parameters of a two-step random access (RA) procedure; and

second configuration parameters of a four-step RA procedure; and

initializing a preamble counter value by a first value in response to the initiating the two-step RA procedure, wherein the first value is indicated by the one or more RRC messages.

11. A wireless device comprising:

one or more processors; and

memory storing instructions that, when executed by the one or more processors, cause the wireless device to:

select, in response to initiating a two-step random access (RA) procedure, a first radio resource for transmission of a first message of the two-step RA procedure;

switch, without transmitting the first message, from the two-step RA procedure to a four-step RA procedure based on:

a cell associated with the wireless device being part of a non-terrestrial network (NTN); and

the first radio resource being invalid for the transmission of the first message; and

transmit, via a second radio resource, a preamble for the four-step RA procedure.

12. The wireless device of claim 11 , wherein the first radio resource comprises a first physical random access channel (PRACH) occasion and a first physical uplink shared channel (PUSCH) occasion mapped to the first PRACH occasion.

13. The wireless device of claim 12 , wherein the first radio resource is invalid based at least on:

the first PUSCH occasion being invalid; or

failing to satisfy a time gap condition.

14. The wireless device of claim 13 , wherein the time gap condition is satisfied based on at least one of:

a time difference between a last symbol of the first PUSCH occasion and a last symbol of the first PRACH occasion being less than a first threshold;

a time difference between a first symbol of the first PUSCH occasion and a first symbol of the first PRACH occasion being less than the first threshold;

a time difference between the last symbol of the first PUSCH occasion and a time that the first radio resource is selected being less than the first threshold; or

a time difference between the last symbol of the first PUSCH occasion and a time that the two-step RA procedure is initiated being less than the first threshold.

15. The wireless device of claim 14 , wherein the instructions further cause the wireless device to determine the first threshold based on at least one of:

a propagation delay between the wireless device and a node of the NTN; or

a portion of a propagation delay between the wireless device and a base station, wherein the wireless device communicates with the base station via the NTN.

16. The wireless device of claim 12 , wherein the instructions further cause the wireless device to select, in response to the switching to the four-step RA procedure, the second radio resource associated with the preamble for the four-step RA procedure for transmission of the first message, wherein the second radio resource comprises a second PRACH occasion and a second PUSCH occasion mapped to the second PRACH occasion.

17. The wireless device of claim 16 , wherein the switching to the four-step RA procedure is further based on the second radio resource being invalid.

18. The wireless device of claim 17 , wherein the second radio resource is invalid based on:

the second PRACH occasion being valid; and

the second PUSCH occasion being invalid.

19. The wireless device of claim 17 , wherein the second radio resource is invalid based on a time difference between the second radio resource and the first radio resource being larger than a second threshold.

20. A system comprising:

a wireless device comprising one or more first processors and memory storing instructions that, when executed by the one or more first processors, cause the wireless device to:

select, in response to initiating a two-step random access (RA) procedure, a first radio resource for transmission of a first message of the two-step RA procedure;

switch, without transmitting the first message, from the two-step RA procedure to a four-step RA procedure based on:

a cell associated with the wireless device being part of a non-terrestrial network (NTN); and

the first radio resource being invalid for the transmission of the first message; and

transmit, via a second radio resource, a preamble for the four-step RA procedure; and

a base station comprising one or more second processors and memory storing instructions that, when executed by the one or more second processors, cause the base station to:

receive the preamble for the four-step RA procedure.