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EP-4451757-B1 - METHODS FOR DYNAMIC UPDATE FOR DELAY AND DOPPLER VARIATIONS IN NON-TERRESTRIAL NETWORKS

EP4451757B1EP 4451757 B1EP4451757 B1EP 4451757B1EP-4451757-B1

Inventors

  • MÄÄTTÄNEN, Helka-Liina
  • KHAN, Talha
  • SEDIN, Jonas
  • LIN, Xingqin

Dates

Publication Date
20260513
Application Date
20201005

Claims (14)

  1. A method (375) implemented by a user equipment, UE, (25, 550, 700) of maintaining synchronization with a network node (50, 500, 600) in a communications network comprising a non-terrestrial network, NTN, the method (375) comprising: receiving (380), from the network node (50, 500, 600), system information, SI, including an indication to report a timing advance; transmitting (385) a random access preamble to initiate a connection with the network node (50, 500, 600); receiving (390), from the network node (50, 500, 600) responsive to the random access preamble, a random access response; and transmitting (395), to the network node (50, 500, 600), a connection request including the timing advance according to the indication.
  2. The method according to claim 1, wherein the timing advance is reported in NTN random access MSG3 indicating the timing advance applied when transmitting MSG1.
  3. The method of any of claim 2, wherein the timing advance is reported by the UE sending a MAC CE.
  4. A method (350) implemented by a network node (50, 500, 600) in a non-terrestrial network of maintaining synchronization with a user equipment, UE, (25, 550, 700), the method (350) comprising: transmitting (355) system information, SI, to the UE, the SI including an indication to report a timing advance; receiving (360) a random access preamble transmitted by the UE (25, 450, 700) on a physical random access channel, PRACH; sending (365), to the UE, a random access response responsive to receipt of the random access preamble; and receiving (370), from the UE, a connection request including a timing advance according to the indication.
  5. The method according to claim 4, wherein the timing advance is reported in NTN random access MSG3 indicating the timing advance applied when the UE transmitted MSG1.
  6. The method of any of claim 5, wherein the timing advance is reported by the UE sending a MAC CE.
  7. A user equipment, UE, (25, 550, 700) configured to: receive, from a network node (50, 500, 600), system information, SI, including an indication to report a timing advance; transmit a random access preamble to initiate a connection with the network node (50, 500, 600); receive, from the network node (50, 500, 600) responsive to the random access preamble, a random access response; and transmit, to the network node (50, 500, 600), a connection request including the timing advance according to the indication.
  8. The UE according to claim 7, wherein the timing advance is reported in a non-terrestrial network, NTN, random access MSG3 indicating the timing advance applied when transmitting MSG1.
  9. The UE according to claim 8, wherein the timing advance is reported by the UE sending a MAC CE.
  10. A computer program (750) comprising executable instructions that, when executed by a processing circuit (730) in a user equipment, UE, (25, 550, 700) causes the UE to perform any of the methods of claims 1 to 3.
  11. A network node (50, 500, 600) for a non-terrestrial network, NTN, the network node (50, 500, 600) being configured to: transmit system information, SI, to the UE, the SI including an indication to report a timing advance; receive a random access preamble transmitted by the UE (25, 550, 700) on a physical random access channel, PRACH; send, to the UE, a random access response responsive to receipt of the random access preamble; and receive, from the UE, a connection request including a timing advance according to the indication.
  12. The network node according to claim 11, wherein the timing advance is reported in NTN random access MSG3 indicating the timing advance applied when transmitting MSG1.
  13. The network node according to claim 12 wherein the timing advance is reported by the UE sending a MAC CE.
  14. A computer program (650) comprising executable instructions that, when executed by a processing circuit (630) in a network node (50, 500, 600) in a non-terrestrial network, causes the network node to perform any of the methods of claims 4 to 6.

Description

TECHNICAL FIELD The present disclosure relates to non-terrestrial networks (NTNs) and, more particularly, to frequency and timing synchronization between a network node and a user equipment (UE) in a NTN. BACKGROUND There is an ongoing resurgence of satellite communications. Several plans for satellite networks have been announced in the past few years. The target services vary, from backhaul and fixed wireless, to transportation, to outdoor mobile, to Internet of Things (IoT). Satellite networks could complement mobile networks on the ground by providing connectivity to underserved areas and multicast/broadcast services. To benefit from the strong mobile ecosystem and economy of scale, adapting the terrestrial wireless access technologies including Long Term (LTE) and New Radio (NR) for satellite networks is drawing significant interest. For example, the Third Generation Partnership Project (3GPP) completed an initial study in Release 15 on adapting NR to support non-terrestrial networks (NTN), mainly satellite networks. See, for example, 3GPP TR 38.811, V15.0.0 (2018-08-10). This initial study focused on the channel model for the non-terrestrial networks, defining deployment scenarios, and identifying the key potential impacts. The 3GPP is conducting a follow-up study item in Release 16 on solutions evaluation for NR to support non-terrestrial networks. See, for example, "Study on solutions evaluation for NR to support nonterrestrial network", 3GPP tdoc RP-181370. In satellite communications, the propagation delay as well as the Doppler shift experienced by a user equipment (UE) can change rapidly with time due to high speed satellite motion. Due to the large Doppler shifts of signals transmitted from low Earth orbit (LEO) and medium Earth orbit (MEO) satellites, the perceived receive (RX) frequency of a UE can have a substantial frequency offset. Even if the satellite applies pre-compensation on the downlink (DL) signal such that the residual frequency offset is zero at a reference point (e.g., center) in each spotbeam, a non-zero Doppler shift will remain in other parts of the spotbeam. As the satellite moves, the received frequency offset will vary with time. This variation can have a substantial rate, especially for a LEO satellite. The Round Trip Time (RTT) is constantly changing and can vary as fast as 40 µs/s in certain LEO scenarios. Timing advance (TA) maintenance in the presence of a large drift may require excessive signaling overhead in connected mode. The UE can be allowed to self-adjust its TA in between successive TA update commands. One known solution is that the network broadcasts drift information (for a reference point like the cell center) in system information which all UEs apply to maintain their timing. This simple approach has several shortcomings, e.g., the timing drift itself may vary with time and different UEs may experience different drifts at a given time. In cases where self-adjustment by a UE cannot be assumed, a more dynamic signaling method to update delay and Doppler variation is needed. 3GPP Tdoc R2-1909753 discusses the RACH procedure in NTN scenarios based on UE capability, i.e. with or without GNSS support. SUMMARY The present disclosure provides solutions for dynamic adjustment of the frequency offset and timing advance for a UE in a NTN. Details of Medium Access Control (MAC) Control Element (CE) and Downlink Control Information (DCI) based methods for indicating the timing and/or frequency adjustment commands, either separately or jointly, in the presence of delay and/or Doppler variations in NTN are provided. A terminal, also known as a user equipment (UE), can use DCI or MAC signaling to update the timing and frequency adjustment in presence of delay and Doppler variations in NTN. Further, a configurable MAC-CE design is provided for indicating commands related to timing and/or frequency adjustment. Procedures are also provided to report, during a random access procedure, the timing and frequency adjustment applied in preamble transmission. The scope of protection sought is defined by the appended claims. Other examples and embodiments in the disclosure provide further information to better understand the invention or the context in which the claims are defined. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an example non-terrestrial network (NTN).Figure 2 depicts a trajectory of a GEO satellite.Figure 3 illustrates an example of Doppler shift in a NTN.Figure 4 illustrates the differential Doppler shift for two UEs in a NTN.Figure 5 illustrates a message format for a Medium Access Control (MAC) Control element (CE).Figure 6 illustrates another message format for a MAC CE.Figure 7 illustrates a first exemplary method implement by a network node in a NTN.Figure 8 illustrates a first exemplary method implement by a UE node in a NTN.Figure 9 illustrates a second exemplary method implement by a network node in a NTN.Figure 10 illustrates a second exemplary method imp