Method and apparatus for uplink timing synchronization

1. A method, comprising:

determining, by a satellite base station based on beam information of a first beam and ephemeris information of the satellite base station, an uplink timing frame number of a first cell corresponding to the first beam;

determining, by the satellite base station based on the uplink timing frame number of the first cell, timing information of a first terminal device in the first cell, wherein the timing information indicates a timing advance or a timing lag; and

outputting, by the satellite base station, the timing information of the first terminal device.

2. The method according to claim 1 , wherein determining the uplink timing frame number of the first cell corresponding to the first beam comprises:

determining, based on the beam information of the first beam and the ephemeris information of the satellite base station, a second terminal device and a third terminal device in the first cell, wherein the second terminal device is a terminal device that is closest to the satellite base station in the first cell, and the third terminal device is a terminal device that is farthest away from the satellite base station in the first cell;

determining a candidate frame number set of the first cell based on a first round-trip delay for signal transmission between the second terminal device and the satellite base station and a second round-trip delay for signal transmission between the third terminal device and the satellite base station; and

selecting a first frame number from the candidate frame number set as the uplink timing frame number of the first cell.

3. The method according to claim 2 , wherein determining the candidate frame number set based on the first round-trip delay and the second round-trip delay comprises:

determining the candidate frame number set based on the first round-trip delay, the second round-trip delay, and a plurality of first constraint conditions, wherein the plurality of first constraint conditions comprises:

candidate frame numbers are integer multiples of a time unit for communication between the satellite base station and terminal devices;

a minimum value of the candidate frame numbers is an integer that is not greater than and is closest to the first round-trip delay; and

a maximum value of the candidate frame numbers is an integer that is not less than and is closest to the second round-trip delay.

4. The method according to claim 2 , wherein selecting the first frame number from the candidate frame number set as the uplink timing frame number of the first cell comprises:

selecting, from the candidate frame number set, x a candidate frame having a smallest value of |x−RTD 1 |+|x−RTD 2 | or

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1

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 as the uplink timing frame number of the first cell, wherein x is the respective candidate frame number, RTD 1 is the first round-trip delay, and RTD 2 is the second round-trip delay.

5. The method according to claim 1 , further comprising:

after the first terminal device accesses the first cell, determining that the first terminal device triggers cell handover;

determining whether an uplink timing frame number of a target cell is consistent with the uplink timing frame number of the first cell; and

in response to determining that the uplink timing frame number of the target cell is inconsistent with the uplink timing frame number of the first cell, sending timing information of the target cell to the first terminal device.

6. The method according to claim 1 , further comprising:

after the first terminal device accesses the first cell, determining that the first terminal device triggers cell handover;

determining whether an uplink timing frame number of a target cell is consistent with the uplink timing frame number of the first cell; and

in response to determining that the uplink timing frame number of the target cell is consistent with the uplink timing frame number of the first cell, handing over the first terminal device from the first cell to the target cell.

7. The method according to claim 1 , wherein the timing information comprises a timing value and an indication of whether the timing value is positive or negative, and wherein when the timing value is positive, the timing information indicates the timing advance, or when the timing value is negative, the timing information indicates the timing lag.

8. A method, comprising:

receiving, by a terminal device, timing information usable to perform uplink timing synchronization with a first cell, wherein the timing information is determined based on an uplink timing frame number of the first cell, and the uplink timing frame number is determined based on beam information of a first beam and ephemeris information of a satellite base station;

determining, by the terminal device, a timing advance or a timing lag based on the timing information; and

performing, by the terminal device, uplink timing synchronization with the first cell based on the timing advance or the timing lag.

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

before determining the timing advance or the timing lag based on the timing information, determining that the timing information is sent from the satellite base station.

10. The method according to claim 8 , wherein the timing information comprises a timing value and an indication of whether the timing value is positive or negative, and determining the timing advance or the timing lag based on the timing information comprises:

in response to determining that the timing value is positive, determining the timing advance based on the timing value; or

in response to determining that the timing value is negative, determining the timing lag based on the timing value.

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

after accessing the first cell, triggering cell handover;

receiving timing information of a target cell from the satellite base station; and

updating the timing information of the first cell to the timing information of the target cell.

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

performing uplink timing synchronization with the target cell based on the timing information of the target cell.

13. An apparatus, comprising:

a processor; and

a non-transitory memory, wherein the non-transitory memory is configured to store a computer program, and the processor is configured to invoke and execute the computer program, and the computer program includes instructions to:

determine, based on beam information of a first beam and ephemeris information of a satellite base station, an uplink timing frame number of a first cell corresponding to the first beam;

determine, based on the uplink timing frame number of the first cell, timing information of a first terminal device in the first cell, wherein the timing information indicates a timing advance or a timing lag; and

output the timing information of the first terminal device.

14. The apparatus according to claim 13 , wherein the computer program includes instructions to:

determine, based on the beam information of the first beam and the ephemeris information of the satellite base station, a second terminal device and a third terminal device in the first cell, wherein the second terminal device is a terminal device that is closest to the satellite base station in the first cell, and the third terminal device is a terminal device that is farthest away from the satellite base station in the first cell;

determine a candidate frame number set of the first cell based on a first round-trip delay for signal transmission between the second terminal device and the satellite base station and a second round-trip delay for signal transmission between the third terminal device and the satellite base station; and

select a first frame number from the candidate frame number set as the uplink timing frame number of the first cell.

15. The apparatus according to claim 14 , wherein the computer program includes instructions to:

determine the candidate frame number set based on the first round-trip delay, the second round-trip delay, and a plurality of first constraint conditions, wherein the plurality of first constraint conditions comprises:

candidate frame numbers are integer multiples of a time unit for communication between the satellite base station and terminal devices;

a minimum value of the candidate frame numbers is an integer that is not greater than and is closest to the first round-trip delay; and

a maximum value of the candidate frame numbers is an integer that is not less than and is closest to the second round-trip delay.

16. The apparatus according to claim 14 , wherein the computer program includes instructions to:

select, from the candidate frame number set, a candidate frame number having a smallest value of |x−RTD 1 |+|x−RTD 2 | or

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x

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2

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 as the uplink timing frame number of the first cell, wherein x is the respective candidate frame number, RTD 1 is the first round-trip delay, and RTD 2 is the second round-trip delay.

17. The apparatus according to claim 13 , wherein the computer program includes instructions to:

determine that the first terminal device triggers cell handover;

determine whether an uplink timing frame number of a target cell is consistent with the uplink timing frame number of the first cell; and

in response to determining that the uplink timing frame number of the target cell is inconsistent with the uplink timing frame number of the first cell, send timing information of the target cell to the first terminal device.

18. The apparatus according to claim 13 , wherein the computer program includes instructions to:

determine that the first terminal device triggers cell handover;

determine whether an uplink timing frame number of a target cell is consistent with the uplink timing frame number of the first cell; and

in response to determining that the uplink timing frame number of the target cell is consistent with the uplink timing frame number of the first cell, hand over the first terminal device from the first cell to the target cell.

19. The apparatus according to claim 13 , wherein the timing information comprises a timing value and an indication of whether the timing value is positive or negative, and wherein:

when the timing value is positive, the timing information indicates the timing advance, or

when the timing value is negative, the timing information indicates the timing lag.