WO2023178558A1

WO2023178558A1 - Schemes for solving sfn wrapping issues in ntn

Info

Publication number: WO2023178558A1
Application number: PCT/CN2022/082524
Authority: WO
Inventors: Wen Tang; Gilles Charbit; Xuan Wang; Mingwei Jie; Xuancheng Zhu; Abdelkader Medles
Original assignee: Mediatek Singapore Pte. Ltd.
Priority date: 2022-03-23
Filing date: 2022-03-23
Publication date: 2023-09-28

Abstract

In the NTN scenario, in order to make UE and gNB have the same understanding of epoch time SFN, it is necessary to design specific schemes. An innovative scheme is proposed to address SFN wrapping issues in NTN, which can flexibly schedule epoch time in the past or in the future and configure epoch time in range of 0-1023. The innovative method performed by a UE comprises: receiving epoch time SFN indication information in System Information Block SIBx at SIBx SFN; calculating (epoch time SFN-SIBx SFN); determining epoch time SFN is in the past, or epoch time SFN is current SFN; or epoch time SFN is in the future.

Description

SCHEMES FOR SOLVING SFN WRAPPING ISSUES IN NTN

FIELD

This disclosure relates generally to wireless communications, and, more particularly, to methods and apparatus about SFN wrapping issues in NTN.

BACKGROUND

In scenarios with large transmission delay, such as the NTN, in order to make epoch time indication without ambiguity, an effective solution for SFN wrapping is needed.

SUMMARY

In NTN (Non-Terrestrial Network) system, due to large time delay and Doppler frequency shift, gNB needs to indicate ephemeris related parameters to facilitate UE to do pre-compensation of time delay and frequency offset. Moreover, ephemeris information has a validity timer and gNB indicates epoch time to indicate the starting position of the validity timer. When gNB explicitly indicates epoch time or indicates epoch time by dedicated signaling, where gNB directly sends specific SFN (System Frame Number) and sub frame number, there will be system failure caused by gNB and UE have inconsistent understanding of SFN (in the past or in the future) . Based on this, considering the NTN scenario, the invention designs a scheme to make gNB and UE have same understanding of epoch time SFN, to ensure the normal operation of NTN system.

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a UE. The UE receives indication of epoch time at SIBx SFN. The indication contains an epoch time SFN. UE determines the indicated epoch time SFN (in the past or in the future) based on the the value of (epoch time SFN-SIBx SFN) .

To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of scenarios for NR NTN.

FIG. 2 is a diagram illustrating an example of scenarios for IoT NTN.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc. (collectively referred to as “elements” ) . These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

In scenarios with large transmission delay, such as NTN system, indication of ephemeris related information and epoch time is necessary for time and frequency synchronization. At present, the method proposed in 3GPP to indicate epoch time explicitly or by dedicated signaling utilized SFN and a sub frame number has ambiguity issues that UE and gNB have inconsistent understanding of the indicated epoch time SFN (in the past or in the future) .

This invention is motivated by, but not limited to, an NTN scenario. In such a scenario, it is necessary to indicate epoch time, and needs to design the scheme of indicating epoch time explicitly or by dedicated signaling to make gNB and UE have same understanding of epoch time SFN, then ensure the NTN system to work.

NTN refers to a network that uses radio frequency and information processing resources carried on high, medium and low orbit satellites or other high-altitude communication platforms to provide communication services for UEs. According to the load capacity on the satellite, there are two typical scenarios: transparent payload and regenerative payload. The transparent payload mode means that the satellite will not process the signal and waveform in the communication service, but only forward the data as an RF amplifier. Regenerative payload mode refers to the satellite, besides RF amplification, also has the processing capabilities of modulation/demodulation, coding/decoding, switching, routing and so on.

In order to ensure the normal operation of NTN system, gNB needs to indicate ephemeris related information, validity timer for ephemeris related information, and epoch time is the starting time of a DL sub-frame as starting point of validity timer. In 3GPP, the indication mode of epoch time has been discussed and relevant agreements have been obtained. For the indication of epoch time, there are three modes:

Mode 1: When explicitly provided through SIB, Epoch time of assistance information (i.e. Serving satellite ephemeris and Common TA parameters) is the starting time of a DL sub-frame, indicated by a SFN and a sub-frame number signaled together with the assistance information.

Mode 2: When Epoch time is not explicitly indicated in SIB, epoch time of assistance information (i.e. Serving satellite ephemeris and Common TA parameters) is implicitly known as the end of the SI window during which the NTN-specific SIB is transmitted.

Mode 3: When provided through dedicated signaling, epoch time of assistance information (i.e. Serving satellite ephemeris and Common TA parameters) is the starting time of a DL sub-frame, indicated by a SFN and a sub-frame number.

SFN is used for paging groups and system information scheduling etc. In legacy LTE/NR, the time unit of synchronization between UE and GNB is SFN. One SFN is 10ms and the SFN value range is 0-1023. When the SFN reaches 1023, it restarts from 0. The maximum period of SFN is 1024 SFN = 10240ms = 10.24s.

The present mode in 3GPP to indicate epoch time explicitly or by dedicated signaling has SFN wrapping issues. For instance, the gNB indicates an SFN=x that is in the future, while UE assumes epoch time x is in the past. When UE reads SIBx with ephemeris and common TA parameters at time t and does prediction to obtain ephemeris and related time and frequency parameters from epoch time in the past to time t, then this assumption is wrong. Because SFN=x is in the future and UE should do UE prediction backwards from epoch time to time t.

Hence, further scheme design needs to be carried out for the scenarios in which the NTN system uses SFN and a sub frame number to indicate epoch time. The scheme to address SFN wrapping in NR NTN and IoT NTN is different considering repetitions in SI window and cross SI windows in IoT NTN.

When gNB indicates epoch time with a SFN and a sub-frame number, there is SFN wrapping issue needs to be solved. The invention innovatively proposes schemes to address SFN wrapping issues when gNB indicates epoch time with a SFN and a sub-frame number.

More specifically, we propose to consider the following alternatives for NR NTN and IoT NTN:

Alternative#1: NR NTN

Indicated SFN for epoch time is,

if (epoch time SFN-SIBx SFN) is positive, choose next epoch time after SIBx SFN (i.e. SFN for epoch time is in the future) ;

else if (epoch time SFN-SIBx SFN) is negative, choose previous epoch time before SIBx SFN (i.e. SFN for epoch time is in the past) ;

else if (epoch time SFN-SIBx SFN) is zero, choose current epoch time SFN (SIBx SFN) .

Note 1: SIBx SFN is the last frame where the message indicating the Epoch time is received.

Alternative#2: IoT NTN

Indicated SFN for epoch time is,

Note 2: The UE shall not assume that the NTN-specific SIB is constant across SI windows

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more. ” The word “exemplary” is used herein to mean “serving as an example, instance, or illustration. ” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words “module, ” “mechanism, ” “element, ” “device, ” and the like may not be a substitute for the word “means. ” As such, no claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for. ”

Claims

A method performed by a UE, comprising:

receiving epoch time SFN indication information in System Information Block SIBx at SIBx SFN;

calculating (epoch time SFN-SIBx SFN) ; and

determining epoch time SFN is in the past, or epoch time SFN is current SFN; or epoch time SFN is in the future.
The method of Claim 1, wherein subframe number is additionally indicated in epoch time SFN indication.
The method of claim 1, wherein if (epoch time SFN-SIBx SFN) is positive, the epoch time SFN is the next epoch time after SIBx SFN.
The method of claim 1, wherein if (epoch time SFN-SIBx SFN) is zero, the epoch time SFN is SIBx SFN.
The method of claim 1, wherein if (epoch time SFN-SIBx SFN) is negative, the epoch time SFN is the previous epoch time after SIBx SFN.
The method of claim 1, wherein SIBx SFN is the last frame where the message indicating the Epoch time is received.
The method of claim 1, wherein The UE shall not assume that the NTN-specific SIB is constant across SI windows.