Methods, apparatus, systems and procedures for distance dependent random access channel (RACH) preamble selection in non-terrestrial networks (NTNS)

1. A method implemented by Wireless Transmit/Receive Unit (WTRU), the method comprising:

receiving, by the WTRU from a Network Access Point (NAP), configuration information indicating a set of preambles and corresponding propagation-delay thresholds;

determining propagation-delay information associated with a distance between the WTRU and the NAP or a location in a coverage area of the NAP;

selecting a subset of preambles from the set of preambles based on the determined propagation-delay information;

randomly selecting a preamble from the selected subset of preambles; and

sending the randomly selected preamble to the NAP.

2. The method of claim 1 , comprising selecting a root sequence using the determined propagation-delay information.

3. The method of claim 1 , further comprising:

receiving, by the WTRU from the NAP, network access information;

initiating, by the WTRU, network access using the network access information;

determining, by the WTRU, a Random Access Radio Network Temporary Identifier (RA-RNTI) that is a function of, derived from, or includes, at least the determined propagation-delay information; and

decoding, by the WTRU, the network access information included in a Random Access Response (RAR) using the determined RA-RNTI.

4. The method of claim 1 , wherein the NAP is included in a satellite and is a part of a non-terrestrial network, the method further comprising:

receiving, by the WTRU from the NAP, via system information, any of: (1) global navigation satellite system GNSS coordinates periodically or (2) a serviceable elevation angle of the NAP; and

determining an altitude of the WTRU,

wherein the determining of the propagation-delay information is further based on the determined altitude and the received system information.

5. The method of claim 1 , wherein the propagation-delay information includes any of: (1) a distance from the WTRU to the NAP; (2) a distance from the WTRU to a nadir of the NAP; (3) an angle between a line extending between the WTRU and the NAP and a line extending between the nadir of the NAP and the NAP; or (4) the propagation delay or a differential propagation delay of a signal sent between the WTRU and the NAP.

6. The method of claim 1 , further comprising receiving, by the WTRU, via broadcast information or dedicated signaling, Random Access configuration information indicating the set of propagation-delay thresholds and any of: (1) location information indicating a location of the NAP; or (2) path information indicating a path to be traversed by the NAP.

7. The method of claim 1 , wherein:

the selecting of the subset of preambles from the set of preambles includes selecting one orthogonal subset of the set of preambles that corresponds to a particular portion of the coverage area of the NAP;

each portion of the coverage area of the NAP corresponds to a different subset of the set of preambles; and

each orthogonal subset of the set of preambles are any of: (1) preconfigured with corresponding propagation-delay thresholds; or (2) signaled explicitly by the NAP.

8. The method of claim 1 , wherein the selecting of the subset of preambles from a set of preambles includes:

determining a subregion of the coverage area of the NAP; and

selecting the subset of preambles associated with the subregion of the coverage area of the NAP by any of: (1) comparing a determined value of the propagation-delay information to one or more propagation-delay thresholds; or (2) via a lookup table associated with the determined value of the propagation-delay information.

9. The method of claim 1 , further comprising:

receiving, by the WTRU from the NAP, restriction information; and

restricting in accordance with the restriction information any of: (1) one or more Random Access Channel (RACH) occasions to send the randomly selected preamble to the NAP; or (2) a number of cyclic shifts associated of a RACH root sequence used by the WTRU.

10. The method of claim 1 , wherein:

the sending of the randomly selected preamble is restricted to a first Random Access Channel (RACH) occasion or a first set of RACH occasions, on condition that the WTRU is in any of: (1) a first coverage area of the NAP; (2) a first range of distances to a nadir of the NAP; (3) a first range of distances to the NAP, or (4) a first range of propagation delays to the NAP; and

the sending of the randomly selected preamble is restricted to a second RACH occasion or a second set of RACH occasions, on condition that the WTRU is in any of: (1) a second coverage area of the NAP; (2) a second range of distances to a nadir of the NAP; (3) a second range of distances to the NAP, or (4) a second range of propagation delays to the NAP.

11. A Wireless Transmit/Receive Unit (WTRU), comprising:

a transceiver configured to receive from a Network Access Point (NAP), configuration information indicating a set of preambles and corresponding propagation-delay thresholds; and

a processor configured to:

determine propagation-delay information associated with a distance between the WTRU and the NAP or a location in a coverage area of the NAP,

select a subset of preambles from the set of preambles based on the determined propagation-delay information, and

randomly select a preamble from the selected subset of preambles,

wherein the transceiver is configured to send the randomly selected preamble to the NAP.

12. The WTRU of claim 11 , wherein the processor is configured to:

select a root sequence using the determined propagation-delay information.

13. The WTRU of claim 11 , wherein:

the transceiver is configured to receive from the NAP, network access information; and the processor is configured to:

initiate network access using the network access information;

determine a Random Access Radio Network Temporary Identifier (RA-RNTI) that is a function of, derived from, or includes, at least the propagation-delay information; and

decode the network access information included in a Random Access Response (RAR) using the determined RA-RNTI.

14. The WTRU of claim 11 , wherein the propagation-delay information includes any of: (1) a distance from the WTRU to the NAP; (2) a distance from the WTRU to a nadir of the NAP; (3) an angle between a line extending between the WTRU and the NAP and a line extending between the nadir of the NAP and the NAP; or (4) the propagation delay or a differential propagation delay of a signal sent between the WTRU and the NAP.

15. The WTRU of claim 11 , wherein the transceiver is configured to receive, via broadcast information or dedicated signaling, a Random Access configuration including the set of propagation-delay thresholds and any of: (1) location information indicating a location of the NAP; or (2) path information indicating a path to be traversed by the NAP.

16. The WTRU of claim 11 , wherein:

the processor is configured to select one orthogonal subset of the set of preambles that corresponds to a particular portion of the coverage area of the NAP;

each portion of the coverage area of the NAP corresponds to a different subset of the set of preambles; and

each orthogonal subset of the set of preambles are any of: (1) preconfigured with corresponding propagation-delay thresholds; or (2) signaled explicitly by the NAP.

17. The WTRU of claim 11 , wherein the processor is configured to:

determine a subregion of the coverage area of the NAP; and

select the subset of preambles associated with the subregion of the coverage area by any of: (1) comparing a determined value of the propagation-delay information to one or more propagation-delay thresholds; or (2) via a lookup table associated with the determined value of the propagation-delay information.

18. The WTRU of claim 11 , wherein the processor is configured to determine the propagation-delay information in accordance with location information indicating a location of the NAP; or (2) path information indicating a path to be traversed by the NAP.

19. The WTRU of claim 11 , further comprising:

the transceiver is configured to receive from the NAP, restriction information; and

the processor is configured to restrict in accordance with the restriction information any of: (1) one or more RACH occasions to send the randomly selected preamble to the NAP; or (2) a number of cyclic shifts associated of a RACH root sequence used by the WTRU.

20. The WTRU of claim 11 , wherein the processor is configured to:

restrict the randomly selected preamble to a first RACH occasion or a first set of RACH occasions, on condition that the WTRU is in any of: (1) a first coverage area of the NAP; (2) a first range of distances to a nadir of the NAP; (3) a first range of distances to the NAP, or (4) a first range of propagation delays to the NAP; and

restrict the randomly selected preamble to a second RACH occasion or a second set of RACH occasions, on condition that the WTRU is in any of: (1) a second coverage area of the NAP; (2) a second range of distances to a nadir of the NAP; (3) a second range of distances to the NAP, or (4) a second range of propagation delays to the NAP.