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EP-4238353-B1 - HANDOVER COMMAND IN NON-TERRESTRIAL NETWORKS

EP4238353B1EP 4238353 B1EP4238353 B1EP 4238353B1EP-4238353-B1

Inventors

  • YAVUZ, Emre
  • RUNE, JOHAN
  • MÄÄTTANEN, HELKA-LIINA
  • LIBERG, OLOF
  • HE, CHAO
  • KHAN, Talha
  • PERSSON, Claes-Göran

Dates

Publication Date
20260506
Application Date
20211029

Claims (15)

  1. A method (1200) performed by a wireless device (110), the method comprising: receiving (1202), from a network node (160), handover information associated with an execution of a handover of the wireless device to a target cell, wherein at least one of the network node or the target cell is associated with a non-terrestrial network, NTN, network node and the handover information comprises at least one of: a randomised time offset; information for generating a randomised time offset; information associated with ephemeris data of a satellite serving the target cell; a time associated with an upcoming service or feeder link switch; an indication of whether an upcoming link switch is a service link switch or a feeder link switch; information associated with a timing advance; an indication to execute a previously received preconfigured handover command; an identifier associated with a previously received preconfigured handover command; an indication for disabling fallback to a source cell; and at least one parameter for determining a quality of the source cell for fallback to the source cell; and performing at least one operation of the handover based on the handover information.
  2. The method of Claim 1, wherein the handover information further comprises at least one of: an absolute time for executing the handover or for accessing the target cell; a condition to be fulfilled before execution of the handover; and at least one physical random access channel resource.
  3. The method of any one of Claims 1 to 2, wherein at least a portion of the handover information is received in a handover command
  4. The method of Claim 3, wherein at least a portion of the handover command is received one of: in a broadcast, and wherein the broadcast indicates a group of wireless devices to which the handover command applies, and via dedicated signaling.
  5. The method of any one of Claims 1 to 4, wherein the handover information indicates to trigger a random access to a target cell according to the time offset.
  6. The method of any one of Claims 1 to 5, wherein the handover : comprises: a dual active protocol stack, DAPS, handover; a conditional handover, CHO; or a Random Access Channel-less, RACH-less, handover.
  7. A method (1300) performed by a network node (160), the method comprising: transmitting (1302), to a wireless device (110), handover information to facilitate an execution of a handover of the wireless device from a source cell to a target cell, wherein at least one of the network node or the target cell is associated with a non-terrestrial network, NTN, network node and the handover information comprises at least one of: a randomised time offset; information for generating a randomised time offset; information associated with ephemeris data of a satellite serving the target cell; a time associated with an upcoming service or feeder link switch; an indication of whether an upcoming link switch is a service link switch or a feeder link switch; information associated with a timing advance; an indication to execute a previously received preconfigured handover command; an identifier associated with a previously received preconfigured handover command; an indication for disabling fallback to a source cell; and at least one parameter for determining a quality of the source cell for fallback to the source cell.
  8. The method of claim 7, wherein the handover information further comprises at least one of: an absolute time for executing the handover or for accessing the target cell; a condition to be fulfilled before execution of the handover; and at least one physical random access channel resource.
  9. The method of any one of Claims 7 to 8, wherein at least a portion of the handover information is transmitted in a handover command.
  10. The method of Claim 9, wherein at least a portion of the handover command is one of: transmitted in a broadcast, wherein the broadcast indicates a group of wireless devices to which the handover command applies, and sent via dedicated signaling.
  11. The method of any one of Claims 7 to 10, wherein the handover information indicates to trigger a random access to the target cell according to the time offset.
  12. The method of any one of Claims 7 to 11, wherein the handover comprises: a dual active protocol stack, DAPS, handover; a conditional handover, CHO; or a Random Access Channel-less, RACH-less, handover.
  13. The method of any one of Claims 7 to 12, wherein the network node is associated with a non-terrestrial network.
  14. A wireless device (110) adapted to perform the method according to any of claims 1 to 6.
  15. A network node (160) adapted to perform the method according to any of claims 7 to 13.

Description

TECHNICAL FIELD The present disclosure relates, in general, to wireless communications and, more particularly, systems and methods for enhancing handover command and the execution thereof in Non-Terrestrial Networks (NTNs). BACKGROUND Third Generation Partnership Project (3GPP) Release 8 specifies the Evolved Packet System (EPS). EPS is based on the Long-Term Evolution (LTE) radio network and the Evolved Packet Core (EPC). It was originally intended to provide voice and mobile broadband (MBB) services, but it has continuously evolved to broaden its functionality. Since Release 13, Narrowband Internet-of-Things (NB-IoT) and LTE for machines (LTE-M) are part of the LTE specifications and provide connectivity to massive machine type communications (mMTC) services. 3GPP Release 15 specifies the first release of the 5G system (5GS). This new generation radio access technology intended to serve use cases such as enhanced mobile broadband (eMBB), ultra-reliable and low latency communication (URLLC), and mMTC. The 5G specification includes the New Radio (NR) access stratum interface and the 5G Core Network (5GC). The NR physical and higher layers reuse parts of the LTE specification and add components as needed for the new use cases. In Release 15, 3GPP began the work to prepare NR for operation in a Non-Terrestrial Network (NTN). The work was performed within the study item "NR to support Non-Terrestrial Networks" and resulted in 3GPP Technical Report (TR) 38.811. See, TR 38.811, Study on New Radio (NR) to support non-terrestrial networks. In Release 16, the work to prepare NR for operation in an NTN network continued with the study item "Solutions for NR to support Non-Terrestrial Network." In parallel, the interest to adapt LTE for operation in NTN is growing. As a consequence, 3GPP is considering introducing support for NTN in both LTE and NR in Release 17. A satellite radio access network usually includes the following components: Satellite: a space-borne platform.Earth-based gateway: connects the satellite to a base station or a core network, depending on the choice of architecture.Feeder link: the link between a gateway and a satellite.Access link: the link between a satellite and a user equipment (UE). Depending on the orbit altitude, a satellite may be categorized as low earth orbit (LEO), medium earth orbit (MEO), or geostationary earth orbit (GEO) satellite: LEO: typical heights ranging from 250 - 1,500 km, with orbital periods ranging from 90 - 120 minutes.MEO: typical heights ranging from 5,000 - 25,000 km, with orbital periods ranging from 3 - 15 hours.GEO: height at about 35,786 km, with an orbital period of 24 hours. Satellite systems tend to have significantly higher path loss than terrestrial networks due to their significant orbit height. Overcoming the path loss often requires the access and feeder links to be operated in line-of-sight conditions and the UE to be equipped with an antenna offering high beam directivity. A communication satellite typically generates several beams over a given area. The "footprint" or "spotbeam" of a beam is usually in an elliptic shape, which has been traditionally considered as a cell. The spotbeam may move over the earth surface with the satellite movement (often referred to as the moving beam or moving cell case). Or, the spotbeam may be earth-fixed with some beam pointing mechanism used by the satellite to compensate for its motion (often referred to as the earth-fixed beam or earth-fixed cell case). The size of a spotbeam depends on the system design and may range from tens of kilometers to a few thousands of kilometers. FIGURE 1 illustrates an example architecture of a satellite network with bent pipe transponders. In comparison to the beams observed in a terrestrial network, the NTN beam may be very wide and may cover an area outside of the area defined by the served cell. A beam covering adjacent cells will overlap and cause significant levels of intercell interference. A typical approach for overcoming the large levels of interference in the NTN involves configuring different cells with different carrier frequencies and polarization modes. In a LEO NTN, the satellites are moving with a very high velocity. This leads to a Doppler shift of the carrier frequency on the service link of up to 24 ppm for a LEO satellite at 600 km altitude. See, TR 38.821, Solutions for NR to support non-terrestrial networks. The Doppler shift is also time variant due to the satellite motion over the sky. The Doppler shift may vary with up to 0.27 ppm/s for a LEO 600 km satellite. The Doppler shift will impact, i.e., increase or decrease, the frequency received on the service link compared to the transmitted frequency. For GEO NTN, the satellites may move in an orbit inclined relative to the plane of the equator. The inclination introduces a periodic movement of the satellite relative earth which introduces a predictable, and daily periodically repeating Doppler shift of the car