Random access procedure selection

1. A client device, comprising:

at least one processor; and

at least one memory including computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the client device to:

detect a need for random access in a non-terrestrial network to a target cell of the non-terrestrial network based on a need for the client device to switch from an idle or inactive mode to a connected mode;

identify a location relation between a previous cell and the target cell;

based on the location relation, identify whether the needed random access is intra-satellite or inter-satellite, wherein the identification is based on the following:

comparing at least of identifier related to a previous cell and at least one identifier related to the target cell, wherein the at least one identifier comprises gNB identifier or global gNB identifier;

comparing a reference signal receive power and quality of the previous cell and of the target cell;

comparing a time synchronization of synchronization signals and reference signals; and

comparing broadcast channels of the previous cell and of the target cell, wherein the previous cell corresponds to a cell that the client device was last active in and the target cell corresponds to a camping cell of the client device;

in response to the needed random access being intra-satellite, perform a first random access procedure, wherein, in the first random access procedure, the client device transmits a random access preamble and a payload data in a single message; and

in response to the needed random access being inter-satellite, perform a second random access procedure wherein, in the second random access procedure, the client device transmits the random access preamble and the payload data in separate messages.

2. The client device according to claim 1 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the client device to:

detect the need for random access based further on a need for a handover; and

perform the needed handover using the first or the second random access procedure.

3. The client device according to claim 2 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the client device to:

in response to the first random access procedure failing a configured number of times, perform the second random access procedure.

4. The client device according to claim 2 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the client device to:

transmit the random access preamble using physical random-access channel; and

transmit the payload data using physical uplink shared channel.

5. The client device according to claim 4 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the client device to:

receive a configuration message from the network node device triggering the first random access procedure or the second random access procedure; and

identify whether the needed random access is intra-satellite or inter-satellite based on the received configuration message.

6. The client device according to claim 5 , wherein the random access configuration message comprises dedicated bits indicating either the first random access procedure or the second random access procedure to be used by the client device.

7. The client device according to claim 6 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the client device to:

before performing the first random access procedure or the second random access procedure, perform time synchronization based on a synchronization signal source external to the non-terrestrial network.

8. A method, comprising:

detecting a need of a client device for random access in a non-terrestrial network to a target cell of the non-terrestrial network based on a need for the client device to switch from an idle or inactive mode to a connected mode;

identifying a location relation between a previous cell and the target cell;

based on the location relation, identifying whether the needed random access is intra-satellite or inter-satellite, wherein the identification is based on the following:

comparing at least of identifier related to a previous cell and at least one identifier related to the target cell, wherein the at least one identifier comprises gNB identifier or global gNB identifier;

comparing a reference signal receive power and quality of the previous cell and of the target cell;

comparing a time synchronization of synchronization signals and/or reference signals; and

comparing broadcast channels of the previous cell and of the target cell, wherein the previous cell corresponds to a cell that the client device was last active in and the target cell corresponds to a camping cell of the client device;

in response to the needed random access being intra-satellite, performing a first random access procedure, wherein, in the first random access procedure, the client device transmits a random access preamble and a payload data in a single message; and

in response to the needed random access being inter-satellite, performing a second random access procedure wherein, in the second random access procedure, the client device transmits the random access preamble and the payload data in separate messages.

9. The method according to claim 8 , further comprising:

detecting the need for random access based further on a need for a handover; and

performing the needed handover using the first or the second random access procedure.

10. The method according to claim 8 , further comprising:

in response to the first random access procedure failing a configured number of times, performing the second random access procedure.

11. The method according to claim 9 , further comprising:

transmitting the random access preamble using physical random-access channel; and

transmitting the payload data using physical up-link shared channel.

12. The method according to claim 8 , further comprising:

receiving a configuration message from the network node device triggering the first or second random access procedure; and

identifying whether the needed random access is intra-satellite or inter-satellite based on the received configuration message.

13. The method according to claim 12 , wherein the random access configuration message comprises dedicated bits indicating either the first or second random access procedure to be used by the client device.

14. The method according to claim 8 , further comprising:

before performing the first or the second random access procedure, performing time synchronization based on a synchronization signal source external to the non-terrestrial network.

15. A computer program embodied on a non-transitory computer-readable medium, said computer program comprising program code configured to cause a computer to perform the method according to claim 8 , when the computer program is executed on the computer.

16. A network node device, comprising:

at least one processor; and

at least one memory including computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the network node device to:

receive information related to a target cell of a non-terrestrial network from a client device needing random access to the target cell;

detect a need for random access in the non-terrestrial network to the target cell of the non-terrestrial network based on a need for the client device to switch from an idle or inactive mode to a connected mode;

identify a location relation between a previous cell and the target cell;

based on the location relation, identify whether the random access is intra-satellite or inter-satellite based at least on the received information and the location relatoin, wherein the identification is based the following:

comparing at least of identifier related to a previous cell and at least one identifier related to the target cell, wherein the at least one identifier comprises gNB identifier or global gNB identifier;

comparing a reference signal receive power and quality of the previous cell and of the target cell;

comparing a time synchronization of synchronization signals and/or reference signals; and

comparing broadcast channels of the previous cell and of the target cell, wherein the previous cell corresponds to a cell that the client device was last active in and the target cell corresponds to a camping cell of the client device;

in response to the needed random access being intra-satellite, transmit a configuration message to the client device instructing the client device to perform a first random access procedure, wherein, in the first random access procedure, the client device transmits a random access preamble and a payload data in a single message; and

in response to the needed random access being inter-satellite, transmit a configuration message to the client device instructing the client device to perform a second random access procedure, wherein, in the second random access procedure, the client device transmits the random access preamble and the payload data in separate messages.