EP-4742763-A1 - COMMUNICATION METHOD AND RELATED DEVICE

EP4742763A1EP 4742763 A1EP4742763 A1EP 4742763A1EP-4742763-A1

Abstract

This application discloses a communication method and a related device. According to the method, the terminal device may store, after fallback succeeds, related information such as an LTE frequency point indicated by a network side for redirection for the fallback, a frequency point corresponding to an NR cell camped on before fallback, and a frequency point and a cell ID that are of an LTE cell camped on after fallback; and the terminal device may measure, before fallback, an LTE frequency point corresponding to an LTE neighboring cell of a currently camped NR cell and store related information of the LTE frequency point. The terminal device may search for an appropriate LTE cell based on the stored related information of a previous successful fallback process and/or the measured LTE frequency point. If the terminal device finds an appropriate LTE cell, the terminal device accesses the LTE cell. Otherwise, the terminal device attempts to perform searching on another LTE frequency point in another manner. According to the method, it is easier for the terminal device to quickly find an LTE cell with a good signal and access the LTE cell.

Inventors

LI, HAIBO
XUE, Chao

Assignees

Honor Device Co., Ltd.

Dates

Publication Date: 20260513
Application Date: 20240727

Claims (20)

A communication method, applied to a terminal device, wherein the method comprises: camping, by the terminal device, on a first cell, wherein the first cell is a new radio NR cell; starting, by the terminal device, a first timer and a second timer in response to receiving a first message, wherein the first message carries an indication to redirect to a target long term evolution LTE frequency point; the target LTE frequency point is an LTE frequency point indicated by a network side for redirection; duration of the first timer is less than duration of the second timer; and interval duration between a start moment of the first timer and a start moment of the second timer is short; searching, by the terminal device based on the target LTE frequency point, for an LTE cell meeting a first preset condition; if the LTE cell meeting the first preset condition is still not found until the first timer times out, searching, by the terminal device based on a first LTE frequency point set, for an LTE cell meeting a second preset condition, wherein the first LTE frequency point set comprises at least one LTE frequency point different from the target LTE frequency point; and if the LTE cell meeting the second preset condition is found when the second timer does not time out, camping, by the terminal device, on the found LTE cell meeting the second preset condition.
The method according to claim 1, wherein the first message is a radio resource control release RRC release message; and the method further comprises: if the LTE cell meeting the second preset condition is still not found until the second timer times out, selecting, by the terminal device, a second cell to camp on, wherein the second cell is an NR cell.
The method according to claim 1 or 2, wherein the first preset condition is the same as or different from the second preset condition.
The method according to claim 3, wherein that the first preset condition is different from the second preset condition specifically comprises: a preset access threshold corresponding to the second preset condition is less than a preset access threshold corresponding to the first preset condition, wherein the preset access threshold is a signal quality threshold at which access to an LTE cell is allowed.
The method according to any one of claims 1 to 4, wherein the duration of the first timer is less than duration of a third timer started on the network side; and the third timer is used by the network side to control duration of fallback.
The method according to any one of claims 1 to 5, wherein the duration of the second timer is not less than the duration of the third timer started on the network side, and is not greater than x times the duration of the third timer; the third timer is used by the network side to control the duration of fallback; and x is not less than 1, and is not greater than 2.
The method according to claim 5 or 6, wherein the duration of the third timer is 5 seconds.
The method according to any one of claims 1 to 7, wherein the first LTE frequency point set comprises first LTE frequency point information and a historical LTE frequency point; the first LTE frequency point information comprises an LTE frequency point corresponding to an LTE neighboring cell of the first cell; the historical LTE frequency point comprises an LTE frequency point corresponding to an LTE cell on which the terminal device has camped; and the searching, by the terminal device based on a first LTE frequency point set, for an LTE cell meeting a second preset condition specifically comprises: determining, by the terminal device, whether LTE cells corresponding to the LTE frequency point in the first LTE frequency point information and the historical LTE frequency point meet the second preset condition.
The method according to claim 8, wherein the determining, by the terminal device, whether LTE cells corresponding to the LTE frequency point in the first LTE frequency point information and the historical LTE frequency point meet the second preset condition specifically comprises: selecting, by the terminal device, a group of LTE frequency points from the LTE frequency point in the first LTE frequency point information and the historical LTE frequency point, and sequentially determining, in descending order of energy, whether LTE cells corresponding to the group of LTE frequency points meet the second preset condition; and if all LTE cells corresponding to the group of LTE frequency points do not meet the second preset condition, performing, by the terminal device, the step of selecting a group of LTE frequency points from the LTE frequency point in the first LTE frequency point information and the historical LTE frequency point, and sequentially determining, in descending order of energy, whether LTE cells corresponding to the group of LTE frequency points meet the second preset condition again, until all frequency points in the LTE frequency point in the first LTE frequency point information and the historical LTE frequency point are selected, wherein LTE frequency points selected by the terminal device from the LTE frequency point in the first LTE frequency point information and the historical LTE frequency point again are different from the LTE frequency points previously selected by the terminal device from the LTE frequency point in the first LTE frequency point information and the historical LTE frequency point.
The method according to claim 9, wherein the first LTE frequency point set further comprises second LTE frequency point information; and the searching, by the terminal device based on a first LTE frequency point set, for an LTE cell meeting a second preset condition specifically comprises: if all LTE cells corresponding to the LTE frequency point in the first LTE frequency point information and the historical LTE frequency point do not meet the second preset condition, searching, by the terminal device based on the second LTE frequency point information, for the LTE cell meeting the second preset condition.
The method according to claim 10, wherein the second LTE frequency point information specifically comprises at least one of the following: an LTE frequency point in a full frequency band, and an LTE frequency point in a prefer frequency band.
The method according to any one of claims 9 to 11, wherein the selecting, by the terminal device, a group of LTE frequency points from the LTE frequency point in the first LTE frequency point information and the historical LTE frequency point specifically comprises: sorting, by the terminal device, the LTE frequency point in the first LTE frequency point information and the historical LTE frequency point based on one or more of signal strengths and bandwidths of the LTE cells corresponding to the LTE frequency point in the first LTE frequency point information and the historical LTE frequency point, whether the LTE cells are anchor cells, and whether the LTE cells are high-speed rail cells, and selecting top s1 LTE frequency points as the group of LTE frequency points, wherein s1 is a positive integer.
The method according to any one of claims 1 to 7, wherein the first LTE frequency point set comprises first LTE frequency point information; the first LTE frequency point information comprises an LTE frequency point corresponding to an LTE neighboring cell of the first cell; the searching, by the terminal device based on a first LTE frequency point set, for an LTE cell meeting a second preset condition specifically comprises: determining, by the terminal device, whether an LTE cell corresponding to the LTE frequency point in the first LTE frequency point information meets the second preset condition.
The method according to claim 13, wherein the first LTE frequency point set further comprises third LTE frequency point information; and the searching, by the terminal device based on a first LTE frequency point set, for an LTE cell meeting a second preset condition specifically further comprises: if all LTE cells corresponding to the LTE frequency point in the first LTE frequency point information do not meet the second preset condition, searching, by the terminal device based on the third LTE frequency point information, for the LTE cell meeting the second preset condition.
The method according to claim 14, wherein the third LTE frequency point information specifically comprises at least one of the following: a historical LTE frequency point, an LTE frequency point in a full frequency band, and an LTE frequency point in a prefer frequency band.
The method according to any one of claims 1 to 7, wherein the first LTE frequency point set comprises first LTE frequency point information and historical fallback information; the first LTE frequency point information comprises an LTE frequency point corresponding to an LTE neighboring cell of the first cell; the historical fallback information comprises at least one historical fallback record; each historical fallback record comprises the following information in a historical fallback process in which the terminal device successfully falls back from NR to LTE: an LTE frequency point indicated by the network side for redirection, a frequency point corresponding to an NR cell camped on by the terminal device before fallback, and a frequency point corresponding to an LTE cell camped on by the terminal device after fallback; and the searching, by the terminal device based on a first LTE frequency point set, for an LTE cell meeting a second preset condition specifically comprises: determining, by the terminal device, whether an LTE cell corresponding to the LTE frequency point in the first LTE frequency point information meets the second preset condition, and determining whether the historical fallback information comprises a first historical fallback record, wherein a frequency point that corresponds to an NR cell camped on by the terminal device before fallback and that is comprised in the first historical fallback record is a frequency point corresponding to the first cell; and an LTE frequency point that is indicated by the network side for redirection and that is comprised in the first historical fallback record is the target LTE frequency point; and if the historical fallback information comprises the first historical fallback record, searching, by the terminal device based on a frequency point that corresponds to an LTE cell camped on by the terminal device after fallback and that is comprised in the first historical fallback record, for the LTE cell meeting the second preset condition.
The method according to claim 16, wherein the method further comprises: if the LTE cell corresponding to the LTE frequency point in the first LTE frequency point information meets the second preset condition, and/or the LTE cell meeting the second preset condition is found by the terminal device based on the frequency point that corresponds to the LTE cell camped on by the terminal device after fallback and that is comprised in the first historical fallback record, camping, by the terminal device, on the LTE cell meeting the second preset condition.
The method according to claim 16 or 17, wherein the method further comprises: if the LTE cell corresponding to the LTE frequency point in the first LTE frequency point information does not meet the second preset condition, and the LTE cell meeting the second preset condition is not found by the terminal device based on the frequency point that corresponds to the LTE cell camped on by the terminal device after fallback and that is comprised in the first historical fallback record, searching, by the terminal device based on fourth LTE frequency point information, for the LTE cell meeting the second preset condition.
The method according to claim 18, wherein the fourth LTE frequency point information specifically comprises at least one of the following: a historical LTE frequency point, an LTE frequency point in a full frequency band, and an LTE frequency point in a prefer frequency band.
The method according to any one of claims 13 to 19, wherein the first LTE frequency point information comprises a plurality of LTE frequency points, and the plurality of LTE frequency points comprise LTE frequency points separately corresponding to a plurality of LTE neighboring cells of the first cell; and the determining, by the terminal device, whether an LTE cell corresponding to the LTE frequency point in the first LTE frequency point information meets the second preset condition specifically comprises: sequentially determining, by the terminal device in descending order of signal strengths, whether the LTE cells corresponding to the plurality of LTE frequency points meet the second preset condition.

Description

This application claims priority to Chinese Patent Application No. 202310963466.0, filed with the China National Intellectual Property Administration on July 31, 2023 and entitled "COMMUNICATION METHOD AND RELATED DEVICE", which is incorporated herein by reference in its entirety. TECHNICAL FIELD This application relates to the field of communication technologies, and in particular, to a communication method and a related device. BACKGROUND In a mobile communication system, to ensure continuity of a service (for example, a voice service) performed by a terminal device, when a currently registered network cannot provide the corresponding service (for example, the voice service), the corresponding service needs to be provided by falling back to another appropriate network. For example, when the terminal device or a network side cannot use VoNR (for example, the terminal device/the network side does not support VoNR, or the terminal device does not turn on a VoNR switch) or a signal of an NR cell is poor (that is, 5G network signal coverage is weak, for example, a signal of an NR cell on which the terminal device camps and a signal of an NR neighboring cell of the NR cell are weak), the terminal device may fall back from a 5G (5th Generation) network to a 4G (4th Generation) network. In other words, when NR (New Radio, new radio) cannot carry a corresponding service, the corresponding service is handed over to LTE (Long Term Evolution, long term evolution) through fallback. The foregoing fallback procedure used when the terminal device or the network side cannot use VoNR includes a relatively typical voice fallback procedure, which is referred to as evolved packet system (Evolved Packet System, EPS) voice fallback (Fallback), that is, EPS fallback, and may also be referred to as EPS FB for short. EPS fallback means that when a 5G network does not have a VoNR condition, a voice service falls back from the 5G network to a 4G network, and continuity of the voice service is ensured over VoLTE. In other words, when the terminal device or the network side does not support VoNR or does not turn on the VoNR switch, the terminal device operating in a standalone (Standalone, SA) mode needs to perform EPS fallback, that is, fall back to the 4G network to perform the voice service. One of the most common manners of falling back from the 5G network to the 4G network is that the network side gives a frequency point through redirection, and the terminal device searches for an LTE cell corresponding to the frequency point. Once a signal of the LTE cell corresponding to the frequency point given by the network side is weak, the terminal device may not find an appropriate LTE cell in a long time, or may have difficulty in accessing after finding an appropriate LTE cell, leading to problems such as long access time and poor experience after access. Generally, both the terminal device and the network side are configured with timers related to fallback. Because time for searching for and accessing the LTE cell is long, the timer related to fallback may time out before a dedicated bearer is established. Once the timer times out, the corresponding service on the terminal device fails, that is, fallback fails. It can be learned from the foregoing content that the current fallback process may have problems such as unsuccessful fallback or a high fallback delay. SUMMARY Embodiments of this application provide a communication method and a related device, to optimize a fallback process of a terminal. According to a first aspect, an embodiment of this application provides a communication method. The method may be applied to a terminal device. The method may include: The terminal device camps on a first cell, where the first cell is a new radio NR cell. The terminal device starts a first timer and a second timer in response to receiving a first message, where the first message carries an indication to redirect to a target long term evolution LTE frequency point; the target LTE frequency point is an LTE frequency point indicated by a network side for redirection; duration of the first timer is less than duration of the second timer; and interval duration between a start moment of the first timer and a start moment of the second timer is short. The terminal device searches, based on the target LTE frequency point, for an LTE cell meeting a first preset condition. If the LTE cell meeting the first preset condition is still not found until the first timer times out, the terminal device searches, based on a first LTE frequency point set, for an LTE cell meeting a second preset condition, where the first LTE frequency point set includes at least one LTE frequency point different from the target LTE frequency point. If the LTE cell meeting the second preset condition is found when the second timer does not time out, the terminal device camps on the found LTE cell meeting the second preset condition. In the solution provided in this embodiment, th