EP-4740330-A1 - SAME-PCI CELL SWITCHING IN A NON-TERRESTRIAL NETWORK

Abstract

A user equipment (UE) receives, in a serving cell, (i) an indication of a time when the serving cell stops serving a geographic area of the UE and (ii) an indication related to a new cell; performs, at the indicated time, one or more actions associated with expiration of a time alignment (TA) timer for the serving cell; and starts synchronization with the new cell.

Inventors

• WU, CHIH-HSIANG
• TAO, MING-HUNG

Assignees

• Google LLC

Dates

Publication Date

20260513

Application Date

20240726

Claims (15)

1. 1. A synchronization method implemented in a user equipment (UE), the method comprising: receiving, in a serving cell, (i) an indication of a time when the serving cell stops serving a geographic area of the UE and (ii) an indication related to a new cell; performing, at the indicated time, one or more actions associated with expiration of a time alignment (TA) timer for the serving cell; and starting synchronization with the new cell.
2. 2. The method of claim 1, wherein: the indication related to the new cell is related to a timing advance (TA).
3. 3. The method of claim 1 or 2, wherein: the indication related to the new cell includes a time when the new cell starts serving the geographic area of the UE.
4. 4. The method of any of the preceding claims, further comprising: flushing a Hybrid Automatic Repeat Request (HARQ) buffer at the indicated time
5. 5. The method of any of the preceding claims, further comprising: flushing all HARQ buffers at the indicated time.
6. 6. The method of any of the preceding claims, further comprising: receiving, in the new cell and after the starting of the synchronization, ephemeris information of the new cell.
7. 7. The method of claim 6, wherein the ephemeris information is received in a system information message.
8. 8. The method of any of the preceding claims, wherein: the indication related to the new cell includes a dedicated PRACH resource.
9. 9. The method of any of the preceding claims, wherein: the indication of a time when the serving cell stops serving the geographic area and thendication related to the new cell are received in a system information block.
10. 10. The method of any of the preceding, wherein: the indication of the time when the serving cell stops serving the geographic area is a t-ervice information element (IE).
11. 11. The method of any of the preceding claims wherein: the serving cell is associated with a first non-terrestrial network (NTN) transceiver; and the new cell is associated with a second NTN transceiver.
12. 12. The method of claim 11, wherein: the first NTN transceiver is implemented in a first satellite; and the second NTN transceiver is implemented in a second satellite.
13. 13. The method of any of the preceding claims, wherein: the serving cell and the new cell are associated with a same cell identifier.
14. 14. The method of claim 13, wherein the cell identifier is a physical cell identity (PCI).
15. 15. A user equipment (UE) comprising: a transceiver; and processing hardware; the UE configured to implement a method of any of the preceding claims.

Description

SAME-PCI CELL SWITCHING IN A NON-TERRESTRIAL NETWORK CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims priority to and the benefit of the filing date of provisional U.S. Patent Application No. 63/515,834 entitled “NTN Mobility Enhancements in the Same PCI Cell Switch Scenario,” filed on July 26, 2023. The entire contents of the provisional application are hereby expressly incorporated herein by reference. FIELD OF THE DISCLOSURE [0001] This disclosure relates generally to wireless communications and, more particularly, to enabling satellite communication, i.e., non-terrestrial network (NTN) communication, for a user equipment (UE) in the connected state to perform cell switch among the cells having the same physical cell identity (PCI). BACKGROUND [0002] This background description is provided for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. [0003] The objectives behind developing the fifth generation (5G) technology include providing a unified framework for such types of communication as enhanced mobile broadband (eMBB), ultra-reliable low-latency communications (URLLC), and massive machine type communication (mMTC). [0004] The 5G technology relies primarily on legacy terrestrial networks. However, the 3rd Generation Partnership Project (3GPP) organization has proposed to extend 5G communications to non-terrestrial networks (NTNs) with 5G new radio (NR) technologies, or with the Long-Term- Evolution (LTE) technologies tailored for the Narrowband Intemet-of-Thing (NB-IoT) or the enhanced Machine Type Communication (eMTC) scenarios. In an NTN, an RF transceiver is amounted on a satellite, an unmanned aircraft systems (UAS) also called drone, balloon, plane, or another suitable apparatus. For simplicity, the discussion below refers to all such apparatus as satellites. In addition to satellites, an NTN can include the sat-gateways that connect the NonTerrestrial Network to a public data network, feeder links between sat-gateways and satellites, service links between satellites, and inter- satellite links (ISL) when satellites form constellations. [0005] A satellite can belong to one of several types based on altitude, orbit, and beam footprint size. The types include Low-Earth Orbit (LEO) satellite, Medium-Earth Orbit (LEO) satellite, Geostationary Earth Orbit (GEO) satellite, UAS platform (including High Altitude Platform Station, HAPS), and High Elliptical Orbit (HEO) satellite. GEO satellites are also known as the Geosynchronous Orbit (GSO) satellites, and LEO/MEO satellites are also known as the non-GSO (NGSO) satellites. [0006] A GSO satellite can communicate with one or several sat-gateways deployed over a satellite targeted coverage area (e.g. a region or even a continent). A non-GSO satellite at different times can communicate with one or several serving sat-gateways. An NTN is designed to ensure service and feeder link continuity between successive serving sat-gateways, with sufficient time duration to proceed with mobility anchoring and hand-over. [0007] A satellite can support a transparent or a regenerative (with on board processing) payload, and typically generates several beams for a given service area bounded by the field of view. The footprints of the beams typically have an elliptic shape and depend on the on-board antenna configuration and the elevation angle. For a transparent payload implementation, a satellite can apply RF filtering and frequency conversion and amplification, and not change the waveform signal. For a regenerative payload implementation, a satellite can apply RF filtering, frequency conversion and amplification, demodulation and decoding, routing, and coding/modulation. This approach is effectively equivalent to implementing most of the functions of a base station, e.g., a gNB. [0008] In these and other scenarios, numerous UEs may go through frequent handovers from one cell to another cell due to the rapid satellite movement. To mitigate the impact of the long service interruption time and signaling overheads caused by these kinds of handovers, different satellites can use the same PCI when serving the same geographical area, which can prevent UEs from triggering handover procedures due to the change of service-link (i.e., the link between the satellite and UE). When the current cell and an upcoming cell use the same PCI, these cells appear to be the same single cell to the UE. However, because the satellites in fact change even if these satellites use the same PCI, the UE needs to update at least the Timing Advance (TA) value before attempting to communicate with the new satellite, to make sure the base station will be able to receive the UE