Communication method and related device

Abstract

The present application discloses a communication method and a related device. According to the method, on one hand, a terminal device can store, after a fallback is successful, related information indicated by a network side, such as an LTE frequency point for redirection of the fallback, a frequency point corresponding to an NR cell camped before the fallback, a frequency point of an LTE cell camped after the fallback, and a cell ID; and on the other hand, before the fallback, the terminal device can measure an LTE frequency point corresponding to an LTE neighbor cell of the currently camped NR cell and store related information of the LTE frequency point. On the basis of the stored related information of a previous fallback success process, and / or the measured LTE frequency point, the terminal device can search for whether a suitable LTE cell is present or not. If the terminal device finds a suitable LTE cell, the terminal device accesses the LTE cell; otherwise, the terminal device attempts to search for other LTE frequency points on the basis of other modes. By means of the method, a terminal device can more easily and quickly find an LTE cell having high signal intensity and access the LTE cell.

Description

A communication method and related equipment

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on July 31, 2023, with application number 202310963466.0 and application name “A Communication Method and Related Equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of communication technology, and in particular to a communication method and related equipment. Background Art

[0003] In a mobile communication system, in order to ensure the continuity of the services (for example, voice services) performed by the terminal device, when the currently registered network cannot provide the corresponding services (for example, voice services), it is necessary to provide the corresponding services by falling back to other suitable networks. For example, when the terminal device or the network side cannot use VoNR (for example, the terminal device / network side does not support VoNR, or the terminal device does not turn on the VoNR switch) or the NR cell signal is not good (that is, the covered 5G network signal is weak, such as the NR cell where the terminal device resides and its NR neighboring cells are weak), the terminal device can fall back from the 5G (5th Generation) network to the 4G (4th Generation) network. That is to say, when NR (New Radio, new wireless / new air interface) cannot provide the corresponding service bearer, the corresponding service is carried to LTE (Long-Term Evolution) by falling back. The above-mentioned fallback process when VoNR cannot be used on the terminal device or network side includes a relatively typical voice fallback process, which is called Evolved Packet System (EPS) Voice Fallback, that is, EPS Fallback, which can also be referred to as EPS FB. EPS Fallback means that when the 5G network does not have VoNR conditions, the voice service falls back from the 5G network to the 4G network, relying on VoLTE to ensure the continuity of the voice service. In other words, when the terminal device or the network side does not support VoNR or the VoNR switch is not turned on, the terminal device working in the standalone (SA) mode needs to perform EPS Fallback, that is, fall back to the 4G network to carry out voice services.

[0004] One of the most common ways to fall back from the 5G network to the 4G network is for the network side to redirect a given frequency point and let the terminal device search for the LTE cell corresponding to the frequency point. Once the LTE cell signal corresponding to the frequency point given by the network side is weak, it is likely that the terminal device will not be able to search for a suitable LTE cell for a long time, or it is likely that the terminal device will have difficulty accessing a suitable LTE cell after searching for it, resulting in problems such as long access time and poor experience after access. Generally, the terminal device and the network side are equipped with timers related to fallback. Due to the long time it takes to search for and access the LTE cell, it is likely that the timer related to fallback will time out before the dedicated bearer is established. Once the timer times out, the corresponding service on the terminal device fails, that is, the fallback fails.

[0005] According to the above content, the current fallback process may have problems such as unsuccessful fallback or long fallback delay.

[0006] Summary of the Invention

[0007] The embodiments of the present application provide a communication method and related devices to optimize the fallback process of a terminal.

[0008] In a first aspect, an embodiment of the present application provides a communication method. The method can be applied to a terminal device. The method may include: the terminal device camping on a first cell; the first cell is a New Radio / New Air Interface (NR) cell; the terminal device, in response to receiving a first message, starting a first timer and a second timer; the first message carries an indication of redirection to a target Long Term Evolution (LTE) frequency; the target LTE frequency is a redirected LTE frequency indicated by the network side; the duration of the first timer is less than the duration of the second timer; the interval between the start time of the first timer and the start time of the second timer is shorter; the terminal device searches for an LTE cell that meets a first preset condition based on the target LTE frequency; if no LTE cell that meets the first preset condition is found before the first timer times out, the terminal device searches for an LTE cell that meets a second preset condition based on a first LTE frequency set; the first LTE frequency set includes at least one LTE frequency that is different from the target LTE frequency; if an LTE cell that meets the second preset condition is found before the second timer times out, the terminal device camps on the searched LTE cell that meets the second preset condition.

[0009] In the solution provided in this embodiment, the terminal device can start the first timer and the second timer when receiving a message sent by the network side that carries an instruction to redirect to the target LTE frequency point. On the one hand, the terminal device can control the duration of searching for an LTE cell that meets the first preset condition based on the target LTE frequency point through the first timer, thereby avoiding the terminal device from searching on the target LTE frequency point when the network signal covered by the target LTE frequency point is weak and it is difficult to search for an LTE cell that meets the first preset condition on the target LTE frequency point. On the other hand, the terminal device can control the duration of the entire fallback through the second timer to avoid the user being unable to communicate for a long time due to too long a fallback time. On the other hand, when the terminal device cannot search for an LTE cell that meets the first preset condition based on the target LTE frequency point, it can search for an LTE cell that meets the second preset condition based on other LTE frequencies, thereby shortening the time to find and access an LTE cell that meets the corresponding preset condition.

[0010] In some embodiments of the present application, the first cell may be the NR cell mentioned in step S1, step S101, step S201 and step S301.

[0011] In some embodiments of the present application, the first message may be an RRC Release message. The indication of redirection to the target LTE frequency point carried in the first message may be understood as a redirection indication (as shown in step S2). The target LTE frequency point carried in the first message may be understood as the LTE frequency point to which the network side redirects the fallback indication.

[0012] In some embodiments of the present application, the first timer may be timer T1, and the second timer may be timer T2.

[0013] In some embodiments of the present application, an LTE cell that satisfies a preset condition may refer to a suitable LTE cell mentioned below. It is understood that, in conjunction with Figures 6 and 7A-7B, when timer T1 has not expired, the suitable LTE cell searched by the terminal device may refer to an LTE cell that satisfies the first preset condition, and when timer T1 has expired but timer T2 has not expired, the suitable LTE cell searched by the terminal device may refer to an LTE cell that satisfies the second preset condition.

[0014] In some embodiments of the present application, the first LTE frequency set may be LTE frequency set_1.

[0015] In combination with the first aspect, in a possible implementation, the first message is a radio resource control release RRC Release message; the method also includes: if the LTE cell that meets the second preset condition is not searched until the second timer times out, the terminal device selects the second cell to reside in; the second cell is an NR cell.

[0016] In the solution provided in this application, the terminal device can control the duration of the entire fallback process through a second timer. If the terminal device still fails to search for a suitable LTE cell (an LTE cell that meets the second preset condition) when the second timer times out, the terminal device may no longer search for a suitable LTE cell, but select an NR cell to reside in. This approach can avoid the fallback time being too long, causing the user to be unable to communicate for a long time.

[0017] In some embodiments of the present application, the second cell may be the NR cell mentioned in step S5, step S111, step S211, and step S312. It is understood that the first cell and the second cell may be the same or different.

[0018] With reference to the first aspect, in a possible implementation manner, the first preset condition is the same as or different from the second preset condition.

[0019] In some embodiments of the present application, whether searching based on the redirected target LTE frequency sent by the network side or searching based on other LTE frequencies, the terminal device can use the same access threshold to determine whether the searched LTE cell is a suitable LTE cell, thereby determining whether it can be accessed.

[0020] In some embodiments of the present application, compared to the access threshold used to determine whether a searched LTE cell is a suitable LTE cell when searching based on other LTE frequencies, a terminal device may use a higher access threshold to determine whether a searched LTE cell is a suitable LTE cell when searching based on a redirected target LTE frequency sent by the network side. This approach can avoid the problem of a long subsequent access time caused by a weak signal of a suitable LTE cell found when the terminal device searches based on the redirected target LTE frequency sent by the network side.

[0021] In combination with the first aspect, in one possible implementation method, the first preset condition is different from the second preset condition, specifically including: the preset access threshold corresponding to the second preset condition is lower than the preset access threshold corresponding to the first preset condition; the preset access threshold is the signal quality threshold for allowing access to the LTE cell.

[0022] It is understood that the preset access threshold may refer to the access threshold mentioned later. For details on signal quality, please refer to the relevant description below and will not be elaborated here.

[0023] In combination with the first aspect, in a possible implementation, the duration of the first timer is less than the duration of a third timer started by the network side; the third timer is used for the duration of the network side controlling the fallback.

[0024] In the solution provided in the present application, the duration defined by the first timer is shorter than the duration defined by the timer started by the network side for controlling the fallback, thereby achieving control over the duration of the terminal device's search for the redirected target LTE frequency point based on the network side's indication.

[0025] In some embodiments of the present application, the third timer may be the Fallback timer started by the network side mentioned later.

[0026] In combination with the first aspect, in one possible implementation, the duration of the second timer is not less than the duration of the third timer started by the network side, and not greater than x times the duration of the third timer; the third timer is used to control the duration of the fallback on the network side; the x is not less than 1 and not greater than 2.

[0027] In the solution provided in the present application, the duration defined by the second timer can be greater than or equal to the duration defined by the timer started by the network side for controlling the fallback, and not greater than x times the duration defined by the timer started by the network side for controlling the fallback, thereby achieving control over the duration of the entire fallback process and leaving time for the terminal device to search based on other LTE frequency points.

[0028] With reference to the first aspect, in a possible implementation, the duration of the three timers is 5 seconds.

[0029] In combination with the first aspect, in a possible implementation method, the first LTE frequency point set includes first LTE frequency point information and historical LTE frequency points; the first LTE frequency point information includes the LTE frequency points corresponding to the LTE neighboring cell of the first cell; the historical LTE frequency points include the LTE frequency points corresponding to the LTE cell in which the terminal device has resided; the terminal device searches for an LTE cell that meets the second preset condition based on the first LTE frequency point set, specifically including: the terminal device determines whether the LTE frequency points in the first LTE frequency point information and the LTE cell corresponding to the historical LTE frequency points meet the second preset condition.

[0030] In some embodiments of the present application, the first LTE frequency point information may be DB1 mentioned later, and the historical LTE frequency point may be ACQ DB mentioned later.

[0031] In combination with the first aspect, in a possible implementation, the terminal device determines whether the LTE frequencies in the first LTE frequency information and the LTE cells corresponding to the historical LTE frequencies meet the second preset condition, specifically including: the terminal device selects a group of LTE frequencies from the LTE frequencies in the first LTE frequency information and the historical LTE frequencies, and determines in descending order of energy whether the LTE cells corresponding to the group of LTE frequencies meet the second preset condition; if none of the LTE cells corresponding to the group of LTE frequencies meet the second preset condition, the terminal device again performs the step of selecting a group of LTE frequencies from the LTE frequencies in the first LTE frequency information and the historical LTE frequencies, and determining in descending order of energy whether the LTE cells corresponding to the group of LTE frequencies meet the second preset condition, until all the LTE frequencies in the first LTE frequency information and the historical LTE frequencies are selected. The LTE frequency selected again by the terminal device from the LTE frequencies in the first LTE frequency information and the historical LTE frequencies is different from the LTE frequency previously selected by the terminal device from the LTE frequencies in the first LTE frequency information and the historical LTE frequencies.

[0032] In the solution provided by the present application, the terminal device can first select a portion of LTE frequency points in DB1 and ACQ DB, and compare the energy of this portion of LTE frequency points, and then search in order from large to small energy to see whether there are suitable LTE cells (i.e., the LTE cells that meet the second preset condition as described above). If no suitable LTE cell is found, the terminal device can continue to select another portion of LTE frequency points in DB1 and ACQ DB, and perform the above steps for the reselected portion of LTE frequency points. This method allows the terminal device to search on LTE frequency points with greater energy first, thereby making it easier for the terminal device to find a suitable LTE frequency point in a short time, that is, increasing the probability of the terminal device finding a suitable LTE frequency point in a short time.

[0033] In some embodiments of the present application, a terminal device selects a group of LTE frequencies each time, the total number of which is a target number. In one possible implementation, the total number of LTE frequencies in the first LTE frequency information and the historical LTE frequency information is not an integer multiple of the target number. In this case, the number of LTE frequencies in the group of LTE frequencies selected by the terminal device from the LTE frequencies in the first LTE frequency information and the historical LTE frequency information for the last time is less than the target number.

[0034] In some embodiments of the present application, the target number may be s1.

[0035] In combination with the first aspect, in a possible implementation method, the first LTE frequency point set also includes second LTE frequency point information; the terminal device searches for an LTE cell that meets the second preset condition based on the first LTE frequency point set, specifically including: if the LTE frequency in the first LTE frequency point information and the LTE cell corresponding to the historical LTE frequency point do not meet the second preset condition, the terminal device searches for an LTE cell that meets the second preset condition based on the second LTE frequency point information.

[0036] In some embodiments of the present application, if the terminal device fails to find a suitable LTE cell based on the first LTE frequency information and the historical LTE frequency information, the terminal device may continue to search based on other LTE frequency points in the first LTE frequency point set. In this way, the terminal device can continue to try to search other frequency points to facilitate finding a suitable LTE frequency point.

[0037] In some embodiments of the present application, if the terminal device fails to search for a suitable LTE cell based on the first LTE frequency information and the historical LTE frequency, the terminal device may no longer search for other LTE frequencies, that is, determine that the fallback has failed, and select an NR cell for access.

[0038] In combination with the first aspect, in a possible implementation manner, the second LTE frequency information specifically includes at least one of the following: an LTE frequency in the entire frequency band, and an LTE frequency in the preferred frequency band.

[0039] It can be understood that the full frequency band refers to full band and the preferred frequency band refers to prefer band.

[0040] In some embodiments of the present application, the third LTE frequency information may be LTE frequency set_3.

[0041] In combination with the first aspect, in a possible implementation method, the terminal device selects a group of LTE frequencies from the LTE frequencies in the first LTE frequency information and the historical LTE frequencies, specifically including: the terminal device sorts the LTE frequencies in the first LTE frequency information and the historical LTE frequencies based on one or more of the signal strength, bandwidth, whether it is an anchor cell, and whether it is a high-speed rail cell of the LTE cells corresponding to the LTE frequencies in the first LTE frequency information and the historical LTE frequencies, and selects the first s1 LTE frequencies as a group of LTE frequencies; s1 is a positive integer.

[0042] In the solution provided by this application, the terminal device can select each group of LTE frequencies from the first LTE frequency information and historical LTE frequency information based on one or more ranking results of signal strength, bandwidth, whether it is an anchor cell, and whether it is a high-speed rail cell, rather than arbitrarily selecting each group of LTE frequencies. This method allows the terminal device to prioritize the LTE frequency with a better corresponding LTE cell signal, making it easier for the terminal device to search for a suitable LTE cell in a short period of time.

[0043] In combination with the first aspect, in a possible implementation method, the first LTE frequency point set includes first LTE frequency point information; the first LTE frequency point information includes the LTE frequency point corresponding to the LTE neighboring cell of the first cell; the terminal device searches for the LTE cell that meets the second preset condition based on the first LTE frequency point set, specifically including: the terminal device determines whether the LTE cell corresponding to the LTE frequency point in the first LTE frequency point information meets the second preset condition.

[0044] In the solution provided in this application, the terminal device can first search based on the LTE frequency corresponding to the LTE neighboring cell of the NR cell where the terminal device is currently located. In this way, the terminal device can search based on the relevant information of the LTE neighboring cell frequency at the current location, making it easier to search for a suitable LTE cell.

[0045] In combination with the first aspect, in a possible implementation method, the first LTE frequency point set also includes third LTE frequency point information; the terminal device searches for an LTE cell that meets the second preset condition based on the first LTE frequency point set, specifically also including: if the LTE cells corresponding to the LTE frequencies in the first LTE frequency point information do not meet the second preset condition, then the terminal device searches for an LTE cell that meets the second preset condition based on the third LTE frequency point information.

[0046] In the solution provided by this application, the terminal device can first search DB1, and if no suitable LTE cell is found, then search other LTE frequency points such as ACQ DB. This approach can increase the probability of the terminal device finding a suitable LTE cell in a short time.

[0047] In combination with the first aspect, in a possible implementation manner, the third LTE frequency information specifically includes at least one of the following: historical LTE frequency, LTE frequency in the entire frequency band, and LTE frequency in the preferred frequency band.

[0048] In combination with the first aspect, in a possible implementation, the first LTE frequency point set includes first LTE frequency point information and historical fallback information; the first LTE frequency point information includes the LTE frequency point corresponding to the LTE neighboring cell of the first cell; the historical fallback information includes at least one historical fallback record; each of the historical fallback records includes the following information during a historical fallback process in which the terminal device successfully falls back from NR to LTE: the redirected LTE frequency point indicated by the network side, the frequency point corresponding to the NR cell where the terminal device resides before the fallback, and the frequency point corresponding to the LTE cell where the terminal device resides after the fallback; the terminal device searches for an LTE cell that meets the second preset condition based on the first LTE frequency point set, The body includes: the terminal device determines whether the LTE cell corresponding to the LTE frequency in the first LTE frequency information meets the second preset condition, and determines whether the historical fallback information includes a first historical fallback record; the frequency corresponding to the NR cell where the terminal device resides before the fallback included in the first historical fallback record is the frequency corresponding to the first cell; the redirected LTE frequency indicated by the network side included in the first historical fallback record is the target LTE frequency; if the historical fallback information includes the first historical fallback record, the terminal device searches for an LTE cell that meets the second preset condition based on the frequency corresponding to the LTE cell where the terminal device resides after the fallback included in the first historical fallback record.

[0049] In some embodiments of the present application, a terminal device can first search for a suitable LTE cell based on DB1 and DB2. Since DB1 contains information about the terminal device's current LTE neighboring cell frequency and DB2 contains information about the terminal device's successful fallback, the terminal device can more easily find a suitable LTE cell in a short period of time by first searching for a suitable LTE cell based on DB1 and DB2.

[0050] In some embodiments of the present application, the historical fallback information may be the DB2 mentioned below.

[0051] In some embodiments of the present application, the terminal device first searches for a suitable LTE cell based on the LTE frequency in the first LTE frequency information, and then searches for a suitable LTE cell based on the historical fallback information if no suitable LTE cell is found based on the LTE frequency in the first LTE frequency information.

[0052] In some embodiments of the present application, the terminal device first searches for a suitable LTE cell based on historical fallback information, and then searches for a suitable LTE cell based on the LTE frequency in the first LTE frequency information if no suitable LTE cell is found based on the historical fallback information.

[0053] In some embodiments of the present application, when there is a first historical fallback record in the historical fallback information, the terminal device can select a part of the LTE frequency points corresponding to the LTE cell where the terminal device resides after the fallback included in DB1 and the first historical fallback record to compare their energy sizes, and search in order from large to small energy to see whether there is a suitable LTE cell on this part of the LTE frequency points. If no suitable LTE cell is found, the terminal device can select another part of the LTE frequency points according to the above method again, and search according to the above steps.

[0054] In combination with the first aspect, in a possible implementation, the method also includes: if the LTE cell corresponding to the LTE frequency in the first LTE frequency information meets the second preset condition, and / or the terminal device searches for the LTE cell that meets the second preset condition based on the frequency corresponding to the LTE cell where the terminal device resides after the fallback included in the first historical fallback record, the terminal device resides in the LTE cell that meets the second preset condition.

[0055] In combination with the first aspect, in a possible implementation, the method also includes: if the LTE cell corresponding to the LTE frequency in the first LTE frequency information does not meet the second preset condition, and the terminal device does not search for an LTE cell that meets the second preset condition based on the frequency corresponding to the LTE cell where the terminal device resides after the fallback included in the first historical fallback record, then the terminal device searches for an LTE cell that meets the second preset condition based on the fourth LTE frequency information.

[0056] In combination with the first aspect, in a possible implementation manner, the fourth LTE frequency information specifically includes at least one of the following: historical LTE frequency, LTE frequency in the entire frequency band, and LTE frequency in the preferred frequency band.

[0057] It is understandable that the third LTE frequency information and the fourth LTE frequency information may be the same or different.

[0058] In some embodiments of the present application, the fourth LTE frequency information may be LTE frequency set_2.

[0059] In combination with the first aspect, in a possible implementation method, the first LTE frequency point information includes multiple LTE frequencies, and the multiple LTE frequencies include LTE frequencies corresponding to multiple LTE neighboring cells of the first cell; the terminal device determines whether the LTE cell corresponding to the LTE frequency in the first LTE frequency point information meets the second preset condition, specifically including: the terminal device determines whether the LTE cells corresponding to the multiple LTE frequencies meet the second preset condition in order from large to small according to signal strength.

[0060] In some embodiments of the present application, the terminal device may search for LTE frequencies in the first LTE frequency information according to signal strength from large to small. This approach makes it easier for the terminal device to search for a suitable LTE cell in a short time.

[0061] In combination with the first aspect, in a possible implementation, after the terminal device resides on the first cell, the method also includes: the terminal device receives the fifth LTE frequency point information sent by the network device corresponding to the first cell; the fifth LTE frequency point information includes the LTE frequency point corresponding to the LTE neighboring area of ​​the first cell; the terminal device measures the signal strength of the LTE cell corresponding to the LTE frequency point included in the fifth LTE frequency point information, and / or detects the bandwidth of the LTE cell corresponding to the LTE frequency point included in the fifth LTE frequency point information, and / or detects whether the LTE cell corresponding to the LTE frequency point included in the fifth LTE frequency point information is an anchor cell for the terminal device, and obtains a first result; the terminal device sorts the LTE frequencies in the fifth LTE frequency point information based on the first result to obtain the first LTE frequency point information; the terminal device determines whether the LTE cell corresponding to the LTE frequency point in the first LTE frequency point information meets the second preset condition, specifically including: the terminal device determines in sequence according to the sorted result whether the LTE cell corresponding to the LTE frequency point in the first LTE frequency point information meets the second preset condition.

[0062] In some embodiments of the present application, the fifth LTE frequency information may be the LTE frequency information mentioned in step S102, step S202, and step S302. The above detection and measurement may be described in detail later and will not be described in detail here.

[0063] It is understandable that the first result may be the measurement and detection result mentioned later (such as step S103 ).

[0064] In combination with the first aspect, in a possible implementation method, the LTE cell that meets the first preset condition specifically includes: an LTE cell whose signal strength is greater than a first preset access threshold and the network side does not prohibit the terminal device from accessing; the LTE cell that meets the second preset condition specifically includes: an LTE cell whose signal strength is greater than a second preset access threshold and the network side does not prohibit the terminal device from accessing.

[0065] In some embodiments of the present application, the first preset access threshold and the second preset access threshold may be the same.

[0066] In some embodiments of the present application, the first preset access threshold is greater than the second preset access threshold.

[0067] In a second aspect, an embodiment of the present application provides a communication method, characterized in that it is applied to a terminal device; the method includes: the terminal device resides on a first cell; the first cell is an NR cell; the terminal device determines, in response to receiving a first message, whether the historical fallback information includes a first historical fallback record; the first message carries an indication of redirection to a target LTE frequency; the target LTE frequency is a redirected LTE frequency indicated by the network side; the historical fallback information includes at least one historical fallback record; each of the historical fallback records includes a historical fallback process in which the terminal device successfully falls back from NR to LTE. The following information: the redirected LTE frequency indicated by the network side, the frequency corresponding to the NR cell where the terminal device resides before fallback, and the frequency corresponding to the LTE cell where the terminal device resides after fallback; the NR cell where the terminal device resides before fallback included in the first historical fallback record is the first cell, and the redirected LTE frequency indicated by the network side included in the first historical fallback record is the target LTE frequency; if the historical fallback information includes the first historical fallback record, the terminal device searches for an LTE cell that meets the first preset condition based on the frequency corresponding to the LTE cell where the terminal device resides after fallback included in the first historical fallback record.

[0068] In some embodiments of the present application, upon receiving a message from the network indicating redirection to a target LTE frequency, a terminal device may first search for a suitable LTE cell based on information related to a previous successful fallback. This approach makes it easier for the terminal device to search for a suitable LTE cell in a shorter time.

[0069] In combination with the second aspect, in a possible implementation, the method also includes: if the historical fallback information does not include the first historical fallback record, or the terminal device does not search for an LTE cell that meets the first preset condition based on the frequency corresponding to the LTE cell where the terminal device resides after falling back, the terminal device starts a first timer and searches for an LTE cell that meets the first preset condition based on the target LTE frequency; if the terminal device still does not search for an LTE cell that meets the first preset condition based on the target LTE frequency until the first timer times out, the terminal device searches for an LTE cell that meets the second preset condition based on a second LTE frequency set.

[0070] In the solution provided in this embodiment, if the terminal device fails to search for a suitable LTE cell based on the relevant information of the previous successful fallback, the terminal device can search based on the redirected LTE frequency sent by the network side, and start a first timer to control the duration of the search based on the redirected LTE frequency sent by the network side. This method can avoid the terminal device from continuing to search on the target LTE frequency when the network signal covered by the target LTE frequency is weak and it is difficult to search for an LTE cell that meets the first preset condition on the target LTE frequency.

[0071] In some embodiments of the present application, the second LTE frequency set may include one or more of the following: DB1, ACQ DB, some or all LTE frequencies in the full band, and some or all LTE frequencies in the prefer band.

[0072] In combination with the second aspect, in one possible implementation method, the first preset condition is the same as or different from the second preset condition; the first preset condition is different from the second preset condition, specifically including: the preset access threshold corresponding to the second preset condition is lower than the preset access threshold corresponding to the first preset condition; the preset access threshold is the signal quality threshold for allowing access to the LTE cell.

[0073] In combination with the second aspect, in a possible implementation, the duration of the first timer is less than the duration of the third timer started by the network side; the third timer is used for the duration of the network side controlling the fallback.

[0074] In combination with the second aspect, in one possible implementation method, the duration of the second timer is not less than the duration of the third timer started by the network side, and not greater than x times the duration of the third timer; the third timer is used to control the duration of the fallback on the network side; the x is not less than 1 and not greater than 2.

[0075] In combination with the second aspect, in a possible implementation, the duration of the three timers is 5 seconds.

[0076] In combination with the second aspect, in a possible implementation method, the second LTE frequency point set includes first LTE frequency point information and third LTE frequency point information; the first LTE frequency point information includes the LTE frequency point corresponding to the LTE neighboring cell of the first cell; the terminal device searches for the LTE cell that meets the second preset condition based on the second LTE frequency point set, specifically including: the terminal device determines whether the LTE cell corresponding to the LTE frequency point in the first LTE frequency point information meets the second preset condition; if the LTE cells corresponding to the LTE frequencies in the first LTE frequency point information do not meet the second preset condition, the terminal device searches for the LTE cell that meets the second preset condition based on the third LTE frequency point information.

[0077] In combination with the second aspect, in a possible implementation, the third LTE frequency information specifically includes: at least one of historical LTE frequencies, LTE frequencies in all frequency bands, and LTE frequencies in preferred frequency bands.

[0078] In some embodiments of the present application, the third LTE frequency information may be LTE frequency set_2.

[0079] In combination with the second aspect, in a possible implementation, the method also includes: the terminal device starts a second timer in response to the first message; if an LTE cell that meets the first preset condition is searched before the first timer times out, the terminal device resides in the searched LTE cell that meets the first preset condition; if an LTE cell that meets the second preset condition is searched after the first timer times out and the second timer does not time out, the terminal device resides in the searched LTE cell that meets the second preset condition; if an LTE cell that meets the first preset condition or the second preset condition is not found until the second timer times out, the terminal device selects a second cell to reside in; the second cell is an NR cell.

[0080] In some embodiments of the present application, the terminal device can start a second timer after receiving a message sent by the network side that carries an indication of redirection to the target LTE frequency, and control the duration of the entire fallback process by the second timer. In addition, the terminal device can start a first timer when a suitable LTE cell is not found based on historical fallback information, and control the duration of searching for a suitable LTE cell based on the redirected target LTE frequency sent by the network side by the first timer. Through this method, on the one hand, it can avoid the user being unable to communicate for a long time due to a long fallback time, and on the other hand, it can avoid the terminal device from continuing to search on the target LTE frequency when the network signal covered by the target LTE frequency is weak and it is difficult to search for an LTE cell that meets the first preset condition on the target LTE frequency.

[0081] In combination with the second aspect, in a possible implementation, the method also includes: if the historical fallback information does not include the first historical fallback record, or the terminal device does not search for an LTE cell that meets the second preset condition based on the frequency corresponding to the LTE cell where the terminal device resides after the fallback included in the first historical fallback record, the terminal device starts a second timer; the interval between the start time of the first timer and the start time of the second timer is short; if an LTE cell that meets the first preset condition is searched before the first timer times out, the terminal device resides in the searched LTE cell that meets the first preset condition; if an LTE cell that meets the second preset condition is searched when the first timer times out and the second timer does not time out, the terminal device resides in the searched LTE cell that meets the second preset condition; if an LTE cell that meets the first preset condition or the second preset condition is not searched until the second timer times out, the terminal device selects a second cell to reside in; the second cell is an NR cell.

[0082] In some embodiments of the present application, when a terminal device fails to search for a suitable LTE cell based on historical fallback information, it can start a first timer and a second timer, and control the duration of searching for a suitable LTE cell based on the redirected target LTE frequency sent by the network side by the first timer, and control the duration of the entire fallback process by the second timer. Through this method, on the one hand, it can avoid the user being unable to communicate for a long time due to a long fallback time, and on the other hand, it can avoid the terminal device from continuing to search on the target LTE frequency when the network signal covered by the target LTE frequency is weak and it is difficult to search for an LTE cell that meets the first preset condition on the target LTE frequency.

[0083] In a third aspect, an embodiment of the present application provides a terminal device, comprising: one or more processors, and one or more memories; the one or more memories are coupled to the one or more processors, the memory being used to store computer program code, the computer program code comprising computer instructions, the one or more processors calling the computer instructions to enable the terminal device to execute the method described in the first aspect or any one of the implementations of the first aspect.

[0084] In a fourth aspect, the present application provides a terminal device, comprising: one or more processors, and one or more memories; the one or more memories are coupled to the one or more processors, the memory being used to store computer program code, the computer program code comprising computer instructions, the one or more processors calling the computer instructions to enable the terminal device to execute the method described in the second aspect or any one of the implementations of the second aspect.

[0085] In a fifth aspect, the present application provides a computer storage medium comprising computer instructions. When the computer instructions are executed on a terminal device, the terminal device executes the method described in the first aspect or any one of the implementations of the first aspect, or the terminal device executes the method described in the second aspect or any one of the implementations of the second aspect.

[0086] In a sixth aspect, an embodiment of the present application provides a chip system for use in a terminal device, the chip system comprising at least one processor and an interface, the interface being used to receive instructions and transmit them to the at least one processor; the at least one processor executes the instructions, causing the terminal device to execute the method described in the first aspect or any one of the implementations of the first aspect, or causing the terminal device to execute the method described in the second aspect or any one of the implementations of the second aspect.

[0087] In some embodiments of the present application, the chip system can be a modem (modem processor), that is, a baseband processor, or a system on chip (System on Chip, Soc) including a modem. The method described in the above first aspect or any implementation of the first aspect can be implemented by a modem, and the method described in the above second aspect or any implementation of the second aspect can be implemented by a modem.

[0088] In some other embodiments of the present application, the chip system may include a modem and other modules, which may be an AP (Application Processor) or a GPU (Graphics Processing Unit).

[0089] In the seventh aspect, an embodiment of the present application provides a computer program product comprising instructions, which, when the computer program product is run on a terminal device, enables the terminal device to execute the method described in the first aspect or any one of the implementations of the first aspect, or enables the terminal device to execute the method described in the second aspect or any one of the implementations of the second aspect.

[0090] It is understood that the terminal device, computer storage medium, chip system, and computer program product provided above can all execute any of the methods provided above. Therefore, the beneficial effects that can be achieved can refer to the beneficial effects of the aforementioned methods and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0091] FIG1 is a schematic diagram of a network architecture exemplarily provided in an embodiment of the present application;

[0092] FIG2 is a schematic diagram of a voice call scenario provided by an embodiment of the present application;

[0093] FIG3 is a schematic diagram of a set of user interfaces provided in an embodiment of the present application;

[0094] FIG4 is a fallback flow chart provided in an embodiment of the present application;

[0095] FIG5 is a flow chart of voice fallback in a called scenario provided by an embodiment of the present application;

[0096] FIG6 is a flow chart of a communication method provided in an embodiment of the present application;

[0097] FIG7A is a flowchart of another communication method provided in an embodiment of the present application;

[0098] FIG7B is a flowchart of another communication method provided in an embodiment of the present application;

[0099] FIG8 is a flow chart of another communication method provided in an embodiment of the present application;

[0100] FIG9 is a schematic diagram of the hardware structure of a terminal device provided in an embodiment of the present application;

[0101] FIG10 is a schematic diagram of the software structure of a terminal device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0102] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. In the description of the embodiments of the present application, unless otherwise specified, " / " means or, for example, A / B can mean A or B; "and / or" in the text is only a description of the association relationship of associated objects, indicating that there can be three relationships, for example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, in the description of the embodiments of the present application, "multiple" means two or more than two.

[0103] It should be understood that the terms "first," "second," and the like in the specification, claims, and drawings of this application are used to distinguish between different objects, rather than to describe a particular order. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements, but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0104] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may be combined with other embodiments.

[0105] In order to facilitate the understanding of this application, some of the terms and related technologies involved in this application are first explained to facilitate understanding by those skilled in the art.

[0106] 1. VoNR (Voice over NR)

[0107] VoNR is the abbreviation of Voice over NR. VoNR means to implement high-definition voice and video services solely on the 5G network. In other words, VoNR is a voice service based on the 5G network. The advantages of VoNR include: (1) When the terminal device resides on the 5G cell, it is simpler and more direct for the terminal device to use VoNR, without having to fall back to the 4G network through EPS Fallback, which can reduce signaling processes and latency and improve user experience; (2) VoNR supports Enhanced Voice Services (EVS), which can effectively improve the sound quality of voice calls to achieve high fidelity (HiFi) level.

[0108] The overall process of VoNR includes: (1) The terminal device registers with the 5G gNB and 5GC. After successful registration, the IP Multimedia Subsystem (IMS) module in the terminal device triggers the establishment of a packet data unit (PDU) bearer for IMS signaling on NR, and then registers with the IMS protocol stack. After successful registration, it enters the normal business state. (2) Call-related services follow the VoLTE process. The dial request (for example, QMI request) is sent to the modem. The modem undergoes general call processing by the call management module (CM). If the current IMS is registered, it is distributed to the IMS module. The IMS module handles VoNR calls similarly to the original VoLTE. It can be understood that the IMS module is a module inside the terminal device that is used to manage IMS-related processes and signaling transmission. QMI is a communication interface. Its English full name is Qualcomm Modem Interface, and its Chinese full name is Qualcomm Modem Communication Interface.

[0109] As you can understand, gNB is the abbreviation of gNodeB, which stands for the next generation Node B in English. Its Chinese meaning is "next generation base station", referring to 5G base stations. 5GC stands for 5G Core in English, which refers to the 5G core network.

[0110] 2. VoLTE

[0111] VoLTE stands for Voice over LTE. VoLTE is an IP data transmission technology that eliminates the need for 2G / 3G networks. All services are carried on 4G networks, unifying data and voice services within the same network. Simply put, 4G networks offer not only high-speed data services but also high-quality voice and video calls. This combination of high-definition video calls is VoLTE.

[0112] 3. EPS Fallback (Evolved Packet System Voice Fallback)

[0113] EPS Fallback means that when the 5G network does not meet the conditions for VoNR, voice services will fall back from the 5G network to the 4G network, relying on VoLTE to ensure the continuity of voice services. Specifically, when the 5G network does not support voice services, when the UE initiates or receives a voice call on the 5G network, it can fall back to the 4G network through redirection or handover, and VoLTE will provide voice services. When the voice call ends, the UE will return to the 5G network.

[0114] 4. Cell

[0115] A cell is an area within the wireless coverage of a network device (e.g., a base station). Within this area, terminal devices can reliably communicate with the network device via wireless signals. It can be understood that the coverage area of ​​each network device can be divided into one or more cells, and each cell can correspond to one or more frequencies. It can also be understood that each cell is an area formed by the coverage area of ​​one or more frequencies.

[0116] Due to differences in coverage area, transmission power, and other factors, cells can be further divided into macro cells (also known as macro cellular cells), micro cells (also known as micro cellular cells), etc. Compared with micro cells, macro cells have a larger coverage area.

[0117] In some embodiments of the present application, different cells may correspond to the same network device. That is, the network device to which cell A belongs and the network device to which cell B belongs may be the same network device. For example, cell A and cell B may be managed by the same base station. In this case, cell A and cell B may be co-located.

[0118] In some embodiments of the present application, different cells may correspond to different network devices. That is, the network device to which cell A belongs and the network device to which cell B belongs may be different network devices. For example, cell A and cell B may be managed by different base stations. For another example, cell A and cell B may be managed by the same base station, but the radio frequency processing units corresponding to cell A and cell B may be different radio frequency processing units within the same base station.

[0119] A neighboring cell, or adjacent cell, is an area within the wireless coverage of network equipment that is physically adjacent to the current serving cell and transmits signals on the same or different frequencies. In other words, a neighboring cell is a cell that is adjacent to or adjacent to the current serving cell. In layman's terms, a neighboring cell can be understood as a "surrounding cell" of the current serving cell.

[0120] In order to better understand the communication method and related equipment provided in the embodiment of the present application, the network architecture involved in the embodiment of the present application is described below.

[0121] Please refer to Figure 1, which is a schematic diagram of a network architecture provided by an embodiment of the present application. As shown in Figure 1, the network architecture may include terminal devices, LTE, NR, core network, and IMS or the Internet. The following is a detailed description of it:

[0122] (1) Terminal: Also known as User Equipment (UE), User Terminal, Mobile Station (MS), Mobile Terminal (MT), etc. Terminals can be devices that include wireless transceiver functions and can cooperate with network equipment to provide communication services to users. The terminal device can be a handheld terminal, a laptop computer, a subscriber unit (SU), a cellular phone, a smart phone, a wireless data card, a personal digital assistant (PDA) computer, a tablet computer, a wireless modem (Modem), a handheld device (Handheld), a laptop computer (Laptop Computer), a cordless phone (Cordless Phone) or a wireless local loop (WLL) station, a machine type communication (MTC) terminal, a wearable device (such as a smart watch, a smart bracelet, a pedometer, etc.), an in-vehicle device (such as a car, a bicycle, an electric car, an airplane, a ship, a train, a high-speed rail, etc.), a virtual reality (VR) device, an augmented reality (AR) device, a wireless terminal in industrial control (Industrial Control), a smart home device (such as a refrigerator, a television, an air conditioner, an electric meter, etc.), an intelligent robot, a workshop device, a wireless terminal in self-driving, a remote medical device (Remote Medical Surgery), wireless terminals in smart grids, wireless terminals in transportation safety, wireless terminals in smart cities, wireless terminals in smart homes, flying equipment (for example, smart robots, drones) or wireless terminals in 5G networks or future communication networks, etc., which are not specifically limited in the embodiments of the present application.

[0123] (2) LTE: This can be understood as the wireless access network of the 4G network. In the LTE network (commonly known as the 4G network), due to the evolutionary relationship, the access network part is called the Evolved UMTS Terrestrial Radio Access Network (E-UTRAN). In this application, the meaning of LTE is the same as that of E-UTRAN, both referring to the access network part of the 4G network. Terminal devices can access LTE through 4G base stations.

[0124] (3) NR: This can be understood as the radio access network of the 5G network. In the 5G network, the access network portion is called the Next Generation Radio Access Network (NG-RAN or NG RAN). In this application, the meaning of NR is the same as that of NG-RAN (or NG RAN), both referring to the access network portion of the 5G network.

[0125] As you can understand, both LTE and NR are access networks. The access network uses wired or wireless connections and communication technologies to connect end users to the core network (also known as the backbone) layer by layer, establishing connectivity. The access network is the edge of the network, the part closest to users and often referred to as the "last mile."

[0126] (4) Core Network: Its main functions are to provide user connections, user management, and service delivery. It serves as a bearer network and provides an interface to external networks. Establishing user connections includes functions such as mobility management (MM), call management (CM), switching / routing, and recording notifications (combined with intelligent network services to complete connections to intelligent network peripheral devices).

[0127] The core network of a 4G network is the Evolved Packet Core (EPC). The EPC is the core network of a 4G mobile communications network. It encompasses traditional mobile network capabilities, such as user subscription data storage, mobility management, and data exchange, and provides users with an ultra-high-speed Internet experience. The core network of a 5G network is the 5G Core (abbreviated as 5GC). 5GC uses general-purpose network function virtualization equipment to replace the dedicated communication equipment of 4G networks.

[0128] It should be noted that the core network in the network architecture shown in Figure 1 can be obtained by integrating EPC and 5GC. That is to say, the core network in the network architecture can include both network elements in EPC and network elements in 5GC. For example, the core network in the network architecture may include access and mobility management function (AMF) network element, mobility management entity (MME) network element, serving gateway (SGW) network element, packet data network gateway (PGW) network element, session management function (SMF) network element, user plane function (UPF) network element, unified data management function (UDM) network element and home subscriber server (HSS) network element, etc.

[0129] In some embodiments of the present application, the core network in the network architecture may include converged network elements obtained from network elements in the EPC and network elements in the 5GC. For example, SMF+PGW-C, UPF+PGW-U, UDM+HSS, etc. Among them, PGW-C is the control plane node of the PGW network element, and PGW-U is the user plane node of the PGW network element.

[0130] In some embodiments of the present application, the core network in the network architecture shown in FIG1 may include a Proxy Session Border Control (PSBC) network element, which is a combined network element that integrates a Session Border Control (SBC), a Proxy-Call Session Control Function (P-CSCF), an Access Transfer Control Function (ATCF), and an Access Transfer Gateway (ATGW). As an SBC network element, it connects the IMS core network / softswitch network with the external user access area, provides service access for IMS / softswitch users, enables interoperability of user services in different network environments, ensures IMS / softswitch network security, and supports QoS management, CAC traffic control, media management, CDR media call detail records, and other functions.

[0131] Each network element in the core network can also be called a functional entity, which can be a network element implemented on dedicated hardware, a software instance running on dedicated hardware, or an instance of a virtualized function on an appropriate platform.

[0132] It should be understood that the names of all network elements in this application are only examples. In future communications, such as 6G, they may also be called other names, or, in future communications, such as 6G, the network elements involved in this application may also be replaced by other entities or devices with the same functions, etc., and this application does not limit this. A unified explanation is given here and will not be repeated later. Optionally, the various network elements in the embodiments of the present application may be communication devices, or chips or chip systems that can be used in the communication devices, etc., and this embodiment of the present application does not limit this.

[0133] It is understood that the core network in the network architecture shown in Figure 1 may also include other devices, network elements, network entities, or network subsystems, such as a Policy Control Function (PCF) network element, and this application does not limit this. It should be noted that this application does not limit the distribution method of each network element in the core network. The specific distribution method can be referred to in relevant technical documents, and this application does not elaborate on this.

[0134] (5) IMS is a network architecture that provides voice and multimedia communication services (e.g., voice, video, and text messaging) based on the Internet Protocol (IP) network. IMS enables secure and reliable multimedia communication between different devices on different networks. The architectural model provides a unified infrastructure and common mechanisms for controlling, operating, routing, and managing sessions, as well as implementing authentication, authorization, and accounting controls. The IMS specifications include widely used Internet Engineering Task Force (IETF) recommendations. For example, the Session Initialization Protocol (SIP) is used for session control signaling.

[0135] The Internet, also known as the international network, generally refers to a vast network of interconnected networks, linked by a common set of protocols to form a single, logically vast international network. From a network communications perspective, the Internet is a data communications network that connects computer networks in countries, regions, and institutions around the world using the Transmission Control Protocol (TCP) and Internet Protocol (IP).

[0136] It should be noted that the network architecture shown in Figure 1 is not limited to including only the devices and networks shown in the figure, but may also include other devices not shown in the figure, and this application will not illustrate this one by one. It should also be noted that the network architecture shown in Figure 1 does not constitute a limitation on 5G networks.

[0137] In order to better understand the embodiments of the present application, the application scenarios of the embodiments of the present application are described below.

[0138] In a mobile communication system, in order to ensure the continuity of the services (e.g., voice services) performed by the terminal device, if the currently registered network cannot provide the corresponding service (e.g., voice service), it is necessary to provide the corresponding service by falling back to other suitable networks. For example, if the terminal device or the network side cannot use VoNR (e.g., the terminal device or the network side does not support VoNR or the VoNR switch is not turned on) or the NR cell signal is poor (i.e., the covered 5G network signal is weak), the terminal device can fall back from the 5G network to the 4G network.

[0139] The following describes the application scenarios of the embodiments of the present application in detail by taking the fallback of voice services as an example.

[0140] Please refer to Figure 2, which is a schematic diagram of a voice call scenario provided in an embodiment of the present application. As shown in Figure 2, the terminal device 100 can transmit voice data with the terminal device 200 through the network device 1, the IMS, and the network device 2. Among them, the network device 1 is the network device corresponding to the cell where the terminal device 100 is currently located, and the network device 2 is the network device corresponding to the cell where the terminal device 200 is currently located. In some embodiments of the present application, the network device 1 and the network device 2 can be the same network device. In some embodiments of the present application, the terminal device 100 can be the party that initiates the voice call to request a voice call with the terminal device 200. In some other embodiments of the present application, the terminal device 200 can be the party that initiates the voice call to request a voice call with the terminal device 100.

[0141] The network device in the embodiment of the present application can be a device for communicating with a terminal device. For example, the network device can be a base station (Base Transceiver Station, BTS) in a Global System for Mobile Communications (GSM) system or Code Division Multiple Access (CDMA), or a base station (NodeB, NB) in a Wideband Code Division Multiple Access (WCDMA) system, or an evolved base station (eNB or eNodeB) in an LTE system, or a wireless controller in a Cloud Radio Access Network (CRAN) scenario, or the network device can be a relay station, an access point, a vehicle-mounted device, a wearable device, and a network device in a future 5G network or a network after 5G, or a network device in a future evolved PLMN network, etc., for example, a transmission point (TRP or TP) in an NR system, a base station (gNB) in an NR system, one or a group (including multiple antenna panels) of antenna panels of a base station in a 5G system, etc., and the embodiment of the present application is not limited to this.

[0142] Optionally, the base station in the embodiment of the present application may include various forms of base stations, such as: macro base stations, micro base stations (also called small stations), relay stations, access points, next-generation base stations (gNodeB, gNB), transmission points (Transmitting and Receiving Point, TRP), transmission points (Transmitting Point, TP), mobile switching centers, and devices that perform base station functions in device-to-device (D2D), vehicle-to-everything (V2X), and machine-to-machine (M2M) communications, etc. The embodiment of the present application does not specifically limit this.

[0143] In the voice call scenario shown in Figure 2, if the 5G network currently registered by the terminal device cannot provide voice services, it can fall back to the 4G network to provide the voice service. During the fallback process from the 5G network to the 4G network, the terminal device may be unable to make a voice call due to the fallback failure.

[0144] For example, as shown in FIG3 , the terminal device 100 may display the user interface 10a, while the terminal device 200 may display the user interface 10b. The user interface 10b may include a display area 1, which may display the number 1. The terminal device 200 may detect a user operation on the display area 1. In response to the user operation, the terminal device 200 may dial the number 1, i.e., request a voice call from the terminal device 100 equipped with the subscriber identity module (SIM) card corresponding to the number 1, and display the user interface 10c. The user interface 10c is a dialing interface. While the terminal device 200 displays the user interface 10c, the terminal device 100 still displays the user interface 10a. It is understandable that the terminal device 200 originally resides on the NR cell. Since the 5G network cannot provide voice services, the terminal device 200 may fall back to the 4G network to provide voice services. However, during the fallback process, the terminal device 200 has been unable to find a suitable LTE cell to access, resulting in a fallback failure. As shown in FIG3 , after the terminal device 200 dials for a period of time (e.g., 2 seconds), the terminal device 200 automatically hangs up. At this time, the terminal device 100 still displays the user interface 10a, and the user is unaware of the call. It is understood that after the terminal device 200 automatically hangs up, the user interface 10b may be displayed. At this time, the terminal device 100 still displays the user interface 10a.

[0145] According to the above, if the terminal device is the called party (that is, other devices request to talk to the terminal device), once the fallback fails, the user will not feel the call. However, if the terminal device is the calling party (that is, the terminal device requests to talk to other devices), the terminal device can display the corresponding dialing interface. Once the fallback fails and the called party does not respond, the terminal device will actively hang up.

[0146] The reasons for the fallback failure in the embodiment of the present application are explained in detail below in conjunction with the fallback process.

[0147] Please refer to Figure 4, which is a fallback flow chart provided in an embodiment of the present application. As shown in Figure 4, the network architecture for implementing the voice service fallback process may include: terminal equipment, NG RAN, E-UTRAN, AMF\MME, SGW, PGW / SMF / UPF and IMS. The specific steps of the fallback process may include:

[0148] Step 1: The calling (Mobile Original, MO) or called (Mobile Terminated, MT) IMS voice session is established on the 5GS (5G System), and the Quality of Service (QoS) flow for voice establishment is initiated.

[0149] Among them, 5G System is a general term for all 5G network elements, including 5G radio access network (NG-RAN) and 5G core network (5G Core, 5GC).

[0150] Step 2: The NW initiates a PDU session modification and then sets the QoS flow for IMS voice.

[0151] It can be understood that the wireless communication network can be simply referred to as a network and abbreviated as NW.

[0152] Step 3: Trigger fallback. Before fallback, the measurement and reporting process is optional.

[0153] Step 4: Reject the PDU session modification, indicating that IMS voice fallback is in progress.

[0154] Step 5. Redirect or switch to EPS.

[0155] Step 6a: Tracking Area Update (TAU) process.

[0156] Step 6b: an attach process with a request type of "handover" and carrying a Packet Data Network (PDN) connection request.

[0157] Step 7: The NW initiates a PDN connection modification and establishes a dedicated voice bearer.

[0158] Step 8: Continue to establish the IMS voice session.

[0159] It is understandable that the specific content of the above fallback process can be referred to the 3GPP TS23.502 protocol and will not be elaborated here.

[0160] According to the above voice fallback process from the 5G network to the 4G network, redirection is one of the common ways of fallback. Specifically, the network side gives an LTE frequency through redirection, and the terminal device searches for the LTE cell corresponding to the LTE frequency. In the case that the LTE cell signal corresponding to the LTE frequency given by the network side is weak, the terminal device may not be able to search for a suitable LTE cell for a long time. Generally speaking, both the network side and the terminal device are configured with timers related to fallback. Due to the long time required to search for and access the LTE cell, it is very likely that the timer related to fallback will time out before the dedicated bearer is established. Once the timer times out, it indicates that the voice service has failed.

[0161] For example, an office is covered by cell A and cell B. Cell A is an NR cell, that is, a cell covered by a 5G network, and cell B is an LTE cell, that is, a cell covered by a 4G network. Cell B is a macro cell. Due to reasons such as obstruction by objects, the signals of cell A and cell B are weak, resulting in poor call quality when making calls in the office. After receiving this feedback, the operator added a cell C to cover the office, but did not modify the LTE frequency point redirected by the network side for the fallback indication, that is, frequency point K. Cell C is an indoor cell, and the signal of cell C is stronger. In this case, once the fallback process is triggered, the network side will still let the terminal device search for the cell corresponding to frequency point K. Only when the cell corresponding to frequency point K is not found will the search be expanded to search for cell C, which results in a longer fallback time.

[0162] For example, please refer to Figure 5, which is a voice fallback flow chart in a called scenario provided by an embodiment of the present application. As shown in Figure 5, the terminal device originally resides on the NR cell. After receiving the INVITE message, the terminal device can send a 100Trying message and a 183Session Progress message to the NR, and start timer_1 to wait for the establishment of a dedicated bearer (also called a dedicated bearer). In some embodiments of the present application, timer_1 can be a QoS timer. Accordingly, the NR can continue to send the 100Trying message and the 183Session Progress message sent by the terminal device to the core network, and the core network will send it to the IMS. Because the terminal device or the network side does not support VoNR, when the network side establishes a dedicated bearer for this call, the access network (NR as shown in Figure 1) determines that the EPS Fallback process needs to be initiated, and notifies the core network that the EPS Fallback process has been initiated. After receiving the notification that the EPS Fallback process has been initiated, the core network can start timer_2. In some embodiments of the present application, the PSBC network element in the core network can start a timer_2 with a defined duration of 6 seconds (s) to wait for the re-authentication / authorization request (Re-Auth-Request, RAR) process to be completed. After the NR notifies the core network that the EPS Fallback process has been initiated, the NR sends an RRC Release (RRC Release) message to the terminal device. Among them, RRC refers to Radio Resource Control. The RRC Release message contains redirectedCarrierInfo redirected to the Evolved UMTS Terrestrial Radio Access (EUTRA), and the redirectedCarrierInfo can include relevant information such as frequency. It can be understood that the frequency included in the redirectedCarrierInfo is the target LTE frequency indicated by the network side. Subsequent terminal devices can try to reside in the corresponding cell based on the frequency included in the redirectedCarrierInfo. In other words, the terminal device can redirect from the 5G communication system to the 4G communication system based on the RRC Release message. As shown in Figure 5, the RRC Release message includes frequency 1825, which is the redirected LTE frequency given by the network. After receiving the RRC Release message from NR, the terminal device can search for cells based on frequency 1825, that is, search for LTE cells corresponding to frequency 1825.If the terminal device searches for a suitable LTE cell on the 1825 frequency point, that is, determines that there is a suitable LTE cell in the LTE cell corresponding to the 1825 frequency point, the terminal device can perform RRC access and trigger the Tracking Area Update (TAU) process. Because the LTE cell signal corresponding to the 1825 frequency point is weak (for example, the LTE cell signal corresponding to the 1825 frequency point is weak due to reasons such as the base station being far away from the terminal device or being blocked), the terminal device has not searched for an LTE cell on the 1825 frequency point for a long time, or the terminal device searches for an LTE cell with the corresponding frequency point of 1825, but because the LTE cell signal corresponding to the frequency point is weak and does not meet the access threshold, the terminal device cannot access the LTE cell, or again, the terminal device searches for an LTE cell with the corresponding frequency point of 1825, although the LTE cell signal meets the access threshold, the weak LTE cell signal makes it difficult to send / receive signaling during the access process, resulting in a long access time.

[0163] Based on the above situation, as shown in Figure 5, in a possible implementation method, it is very likely that the terminal device cannot search for a suitable LTE cell on the 1825 frequency for a long time (for example, the terminal device cannot search for an LTE cell on the 1825 frequency for a long time, or the terminal device searches for an LTE cell with the corresponding frequency of 1825, but the LTE cell signal corresponding to the frequency is weak and does not meet the access threshold, so the terminal device cannot access the LTE cell), resulting in the terminal device being unable to fall back to the LTE cell, and then resulting in the dedicated bearer being unable to be established within the time defined by timer_1, that is, timer_1 times out. In this case, the terminal device sends a 580PreconditionFailure (resource reservation failure) message to the network side, indicating that the terminal device failed to be called this time.

[0164] Based on the above situation, as shown in Figure 5, in one possible implementation, it is very likely that the terminal device searches for a suitable LTE cell signal at the 1825 frequency point, which is weak, resulting in difficulty in sending / receiving signaling during the access process, and thus a long access time, which in turn results in the inability to establish a dedicated bearer within the duration defined by timer_1, that is, timer_1 times out. In this case, the terminal device sends a 580PreconditionFailure message to the network side, indicating that the terminal device failed to be called this time.

[0165] Similarly, as shown in Figure 5, in a possible implementation, it is very likely that the signal of a suitable LTE cell searched by the terminal device on the 1825 frequency point is weak, resulting in difficulty in sending / receiving signaling during the access process, which in turn leads to a long access time, and further leads to the inability to establish a dedicated bearer within the duration defined by timer_2, that is, timer_2 times out. In this case, the core network sends a RAR timeout message to the IMS. After receiving the RAR timeout message, the IMS can send a CANCEL message with a reason value of 503 to the terminal device, indicating that the terminal device failed to be called this time. The CANCEL message may carry "RAR timeout".

[0166] In some embodiments of the present application, the time when Timer_2 times out is later than the time when Timer_1 times out. As shown in Figure 5, in one possible implementation, the time when Timer_1 times out is earlier than the time when the terminal device searches for a suitable LTE cell based on the 1825 frequency, and the time when Timer_2 times out is later than the time when the terminal device searches for a suitable LTE cell based on the 1825 frequency.

[0167] In some embodiments of the present application, Timer_2 times out earlier than Timer_1 times out. As shown in Figure 5, in one possible implementation, both Timer_1 and Timer_2 time out later than the time when the terminal device searches for a suitable LTE cell based on the 1825 frequency, but Timer_2 times out earlier than Timer_1 times out.

[0168] It is understood that the above-mentioned INVITE message, 100Trying message, 183SessionProgress message and 580PreconditionFailure message are all Session Initiation Protocol (SIP) messages. Among them, the above-mentioned INVITE message is the incoming call request received by the terminal device, the above-mentioned 100Trying message is the response message sent by the terminal device to the network side in response to the incoming call request, the above-mentioned 183SessionProgress message is used to prompt the progress information of establishing the voice call, and the above-mentioned 580PreconditionFailure message is used to indicate the failure of establishing the dedicated bearer.

[0169] It can be understood that VoLTE uses SIP to implement the voice session signaling process. SIP is a protocol used to establish, modify, and terminate multimedia sessions. These sessions can be audio, video, chat, or other multimedia forms. The basic principle of the SIP protocol is to describe the attributes and media types of the session by establishing a Session Description Protocol (SDP), and then use SIP messages to negotiate session parameters and control the establishment and termination of the session. SIP messages are divided into requests and responses. Requests include INVITE, ACK, BYE, CANCEL, OPTIONS, REGISTER, and INFO. Responses include 1xx, 2xx, 3xx, 4xx, 5xx, 6xx, etc. The SIP protocol also defines some status codes to indicate the status of the call, such as ringing, answering, and hanging up.

[0170] Based on the above content, an embodiment of the present application provides a communication method. According to the communication method, on the one hand, the terminal device can store the LTE frequency point indicated by the network side for the redirection of the fallback, the frequency point corresponding to the NR cell where the fallback is located before, and the relevant information of the LTE cell where the fallback is successfully located (for example, frequency point, cell ID and signal strength, etc.) on the other hand, the terminal device can measure the LTE frequency point before the fallback and store the relevant information of the LTE frequency point. The terminal device can search for whether there is a suitable LTE cell based on the stored relevant information of the frequency point of the NR cell where the fallback is located before and the LTE cell where the fallback is successfully located, and / or the measured LTE frequency point. If the terminal device finds a suitable LTE cell, the terminal device accesses the LTE cell. Otherwise, the terminal device tries to search for other LTE frequencies based on other methods (for example, ACQ DB, LTE frequency points in full band, LTE frequency points in prefer band, etc.). Through this method, it is easier for the terminal device to quickly find the best frequency point and access the corresponding cell in a short time.

[0171] The following describes a communication method provided in an embodiment of the present application.

[0172] Please refer to Figure 6, which is a flow chart of a communication method provided in an embodiment of the present application. The communication method may include but is not limited to the following steps:

[0173] S1: The terminal device resides in the NR cell.

[0174] It is understandable that the terminal device can reside on the NR cell. That is, the terminal device can reside on the cell covered by the 5G network. In some embodiments of the present application, the terminal device can perform voice services while residing in the NR cell.

[0175] S2: In response to receiving an RRC Release message carrying a redirection indication, the terminal device starts timer T1 and timer T2. The duration defined by timer T2 is greater than the duration defined by timer T1. The redirection indication includes the target LTE frequency point for redirection indicated by the network side. The redirection indication is used to instruct the terminal device to fall back from the resident NR cell to the cell corresponding to the target LTE frequency point.

[0176] In some embodiments of the present application, when the terminal device / network side does not support VoNR, or the terminal device does not turn on the VoNR switch, if the terminal device conducts a voice call while residing in the NR cell, when the network side establishes a dedicated bearer for the voice call, the NR will determine that the EPS Fallback process needs to be initiated and notify the core network that the EPS Fallback process has been initiated. In this case, the terminal device can receive an RRC Release message carrying a redirection indication sent by the NR. In response to receiving the RRC Release message carrying a redirection indication sent by the NR, the terminal device can start timer T1 and timer T2.

[0177] In some embodiments of the present application, when the signal of the NR cell where the terminal device resides is poor, the network side may initiate a Fallback process by redirection. In this case, similar to the above, the terminal device may receive an RRC Release message carrying a redirection indication sent by the NR. In response to receiving the RRC Release message carrying a redirection indication sent by the NR, the terminal device may start timer T1 and timer T2.

[0178] It is understood that the redirection indication includes the target LTE frequency of the redirection indicated by the network side. The redirection indication is used to instruct the terminal device to fall back from the NR cell where it is stationed to the cell corresponding to the target LTE frequency. In some embodiments of the present application, the redirection indication can be the redirectedCarrierInfo mentioned above.

[0179] In some embodiments of the present application, a terminal device may simultaneously start timer T1 and timer T2. In some embodiments of the present application, the interval between the start time of timer T1 and the start time of timer T2 is short. It is understood that the interval between the start time of timer T1 and the start time of timer T2 is short, which may include: the terminal device simultaneously starting timer T1 and timer T2. In this case, the interval between the start time of timer T1 and the start time of timer T2 is short enough to be negligible.

[0180] In one possible implementation, the interval between the start time of timer T1 and the start time of timer T2 is short. Specifically, this may include: the interval between the start time of timer T1 and the start time of timer T2 is less than a duration threshold. It is understood that the duration threshold can be set based on actual needs and is not specifically limited in this application. For example, the duration threshold can be less than 1 millisecond.

[0181] It is understandable that the duration defined by timer T2 is greater than the duration defined by timer T1. The duration defined by timer T1 and the duration defined by timer T2 can be set according to actual needs, and this application does not impose specific restrictions on this.

[0182] In some embodiments of the present application, the duration defined by timer T1 is not less than 300 milliseconds (ms) and not more than 500 ms. In some embodiments of the present application, the duration defined by timer T2 is 10 seconds.

[0183] In some embodiments of the present application, the duration defined by timer T1 is less than the duration defined by the Fallback timer started by the network side. In some embodiments of the present application, the duration defined by timer T2 is greater than the duration defined by the Fallback timer started by the network side. In one possible implementation, the duration defined by timer T2 is x times the duration defined by the Fallback timer started by the network side. Wherein, x is greater than 1. Exemplarily, x can be within a preset range. It is understandable that the preset range can be set according to actual needs. For example, the preset range can specifically be (1,2]. That is, x can be greater than 1 and not greater than 2.

[0184] Among them, the Fallback timer started by the network side can be used to control the duration of the Fallback process. If the fallback is not successfully performed within the duration defined by the Fallback timer started by the network side, it means that the fallback has failed and the Fallback process is terminated. It can be understood that this application does not impose any specific restrictions on the duration defined by the Fallback timer started by the network side. For example, the duration defined by the Fallback timer started by the network side can be 5s. In this case, illustratively, the duration defined by timer T1 can be less than 5s, and the duration defined by timer T2 can be greater than 5s and not greater than 10s. Specifically, the duration defined by timer T1 can be 300ms, and the duration defined by timer T2 can be 10s.

[0185] It is understandable that after the terminal device receives the RRC Release message carrying the redirection indication, it will disconnect the RRC connection between the network device corresponding to the NR cell where it resides. Therefore, if the fallback fails due to the failure to search for a suitable LTE cell, the terminal device can reselect the NR cell to reside in and establish an RRC connection with the network device corresponding to the reselected NR cell. It is understandable that the NR cell where the terminal device originally resided before receiving the RRC Release message carrying the redirection indication may be the same as or different from the reselected NR cell.

[0186] S3: The terminal device searches for a suitable LTE cell based on the redirected target LTE frequency indicated by the network side.

[0187] After the terminal device starts timer T1 and timer T2, it can search for a suitable LTE cell based on the redirected target LTE frequency indicated by the network. In some embodiments of the present application, a suitable LTE cell may be an LTE cell whose signal quality meets the access threshold and to which the terminal device is not prohibited from access by the network.

[0188] In some embodiments of the present application, the signal quality meets the access threshold, which may specifically include: one or more of the signal parameters such as Reference Signal Receiving Power (RSRP), Reference Signal Received Quality (RSRQ) and Signal-to-Noise Ratio (SNR) meeting the corresponding access threshold. It can be understood that RSRP is a key parameter that can represent the strength of the wireless signal in the LTE network and one of the physical layer measurement requirements. It is the average value of the signal power received on all REs (resource elements) that carry the reference signal within a certain symbol. It can be understood that RSRP can reflect the strength of the useful signal in the cell. RSRQ mainly measures the reception quality of the downlink specific cell reference signal. RSRQ is defined as N*RSRP / RSSI. Wherein, N is the number of resource blocks (RBs) in the LTE carrier received signal strength indicator (RSSI) measurement bandwidth. RSSI refers to the total power received by the mobile phone, including useful signals, interference and background noise. SNR generally refers to Signal to Interference plus Noise Ratio (SINR), which is the ratio of the strength of the received useful signal to the strength of the received interference signal (noise and interference).

[0189] It is understandable that the signal quality mentioned in this application may include signal strength, which can be specifically represented by any one or more parameters such as RSRP, SNR, RSRQ, etc.

[0190] S4: If the terminal device has not found a suitable LTE cell based on the redirected target LTE frequency indicated by the network before timer T1 expires, the terminal device searches for frequencies in LTE frequency set_1, which includes at least one LTE frequency different from the target LTE frequency.

[0191] If the terminal device still fails to find a suitable LTE cell based on the target LTE frequency point redirected by the network before timer T1 times out, the terminal device searches for LTE frequency point set 1 based on preset order 1. It is understood that LTE frequency point set 1 can include frequencies from one or more sources. The specific frequencies from different sources can be referred to as follows:

[0192] In some embodiments of the present application, LTE frequency set_1 may include some or all LTE frequencies in ACQ DB (acquaintance database, historical resident frequency list) and / or some or all LTE frequencies in full band and / or some or all LTE frequencies in prefer band. Among them, ACQ DB includes the frequencies corresponding to the LTE cells where the terminal device has previously resided (i.e., historical LTE frequencies), and according to the update mechanism of ACQ DB, the number of historical LTE frequencies stored by the terminal device is limited, and the stored historical LTE frequencies are updated using a first-in-first-out mechanism, which may result in a low probability that the terminal device can quickly search for a suitable LTE cell. In some embodiments of the present application, ACQ DB may also include other relevant information of the historical LTE frequencies. For example, ACQ DB may also include one or more of the signal strength (such as RSRP and / or SNR and / or RSRQ) of the cell corresponding to the historical LTE frequency, bandwidth, whether it is an anchor cell, and whether it is a high-speed rail cell. The full band includes many frequencies, so it takes a long time for a terminal device to search the full band. Consequently, the probability of a terminal device quickly finding a suitable LTE cell is low. The prefer band, which is the frequency band to which a terminal device prefers to access a cell, includes many frequencies, so it takes a long time for a terminal device to search the prefer band. Consequently, the probability of a terminal device quickly finding a suitable LTE cell is low.

[0193] In some embodiments of the present application, LTE frequency set_1 may include frequencies in DB1. DB1 may include frequencies corresponding to LTE neighboring cells of NR cells where the terminal device has camped (including the NR cell currently camped).

[0194] It is understandable that DB1 may also include other relevant information about the frequency points corresponding to the LTE neighboring cells of the NR cells where the terminal device has resided (including the currently residing NR cell), such as signal strength, bandwidth, whether it is an anchor cell, whether it is a high-speed rail cell, etc.

[0195] In some embodiments of the present application, when DB1 includes not only the frequency points corresponding to the LTE neighboring cells of the NR cell where the terminal device is currently residing, but also the frequency points corresponding to the LTE neighboring cells of other NR cells where the terminal device previously resided, the LTE frequency point set_1 may include the frequency points corresponding to the LTE neighboring cells of the NR cell where the terminal device is currently residing included in DB1, but does not include the frequency points corresponding to the LTE neighboring cells of other NR cells where the terminal device previously resided.

[0196] In one possible implementation, LTE frequency set_1 may include some LTE frequency points in DB1. For example, the LTE frequency points ranked in the top y positions after sorting the LTE frequency points in DB1 (such as the y LTE frequency points whose corresponding signal strengths rank in the top y positions). It can be understood that the sorting method may be related to the signal strength, bandwidth, whether it is an anchor cell, and whether it is a high-speed rail cell of the LTE cell corresponding to the LTE frequency point in DB1. For details, please refer to the following text and will not be explained in detail here. Wherein, y is a positive integer, and y is less than the number of all frequency points in DB1. In another possible implementation, LTE frequency set_1 may include all LTE frequency points in DB1.

[0197] It can be understood that DB1 includes the frequency points corresponding to the LTE neighboring cell of the NR cell where the terminal device is currently located. Compared with ACQ DB, DB1 contains updated LTE neighboring cell information. The terminal device is more likely to search the frequency points in DB1 to find a suitable LTE neighboring cell and access it.

[0198] In some embodiments of the present application, LTE frequency set_1 may include some or all LTE frequencies in DB2. DB2 includes the target LTE frequency indicated by the network side during one or more historical fallbacks to LTE, the frequency corresponding to the NR cell camped on before the fallback, and the frequency corresponding to the LTE cell camped on after a successful fallback.

[0199] It is understood that the historical fallback process mentioned in this application refers to the process in which the terminal device successfully fell back from the 5G network to the 4G network. It is understood that the terminal device can search for a suitable LTE cell for this fallback based on the relevant information of the terminal device's previous successful fallback included in DB2. The terminal device is very likely to find a suitable LTE neighbor cell by searching DB2.

[0200] It should be noted that DB2 includes the corresponding relationship between the target LTE frequency point of redirection indicated by the network side in each historical fallback process, the frequency point corresponding to the NR cell that resided before the fallback corresponding to the fallback, and the frequency point corresponding to the LTE cell that resides after the successful fallback. In some embodiments of the present application, DB2 may include several records (i.e., historical fallback records), each of which may include the target LTE frequency point indicated by the network side in a historical fallback process, the frequency point corresponding to the NR cell that resided before the fallback corresponding to the fallback, and the frequency point corresponding to the LTE cell that resides after the successful fallback. In this case, each record can represent the corresponding relationship between the target LTE frequency point indicated by the network side in a historical fallback process, the frequency point corresponding to the NR cell that resided before the fallback corresponding to the fallback, and the frequency point corresponding to the LTE cell that resides after the successful fallback.

[0201] In some embodiments of the present application, in addition to the target LTE frequency of redirection indicated by the network side during the historical fallback to LTE process, the frequency corresponding to the NR cell that resided before the fallback, and the frequency corresponding to the LTE cell that resides after the successful fallback, DB2 may also include the cell ID corresponding to the NR cell that resided before the fallback and the signal strength (e.g., RSRP value) of the LTE cell that resides after the successful fallback. In this case, DB2 includes the corresponding relationship between the target LTE frequency of redirection indicated by the network side during the historical fallback process, the frequency corresponding to the NR cell that resided before the fallback corresponding to the fallback, the cell ID corresponding to the NR cell that resided before the fallback corresponding to the fallback, and the frequency corresponding to the LTE cell that resides after the successful fallback. In some embodiments of the present application, DB2 contains several records, each of which may include the target LTE frequency of redirection indicated by the network side during a historical fallback process, the frequency corresponding to the NR cell that resided before the fallback corresponding to the fallback, the cell ID corresponding to the NR cell that resided before the fallback corresponding to the fallback, and the frequency corresponding to the LTE cell that resides after the successful fallback. In this case, each record can represent the correspondence between the target LTE frequency of redirection indicated by the network side during a historical fallback process, the frequency corresponding to the NR cell where the fallback resided before the fallback, the cell ID corresponding to the NR cell where the fallback resided before the fallback, and the frequency corresponding to the LTE cell where the fallback resided after the successful fallback.

[0202] In some embodiments of the present application, based on the content of the DB2 record mentioned above, DB2 may also include the cell ID corresponding to the LTE cell that resides after a successful fallback in the historical fallback process. Similarly, DB2 may include the correspondence between the cell ID corresponding to the LTE cell that resides after a successful fallback in each historical fallback process and other contents of the fallback (for example, the target LTE frequency of the redirection indicated by the network side mentioned above, the frequency corresponding to the NR cell that resides before the fallback, and the frequency corresponding to the LTE cell that resides after a successful fallback). In some embodiments of the present application, each record in DB2 may include the cell ID corresponding to the LTE cell that resides after a successful fallback in a historical fallback process.

[0203] In some embodiments of the present application, DB2 may further include the signal strength (e.g., RSRP value) of the LTE cell where the user resides after a successful fallback during the historical fallback process. In some other embodiments of the present application, DB2 may further include other information (e.g., bandwidth, whether it is an anchor cell, etc.) of the LTE cell where the user resides after a successful fallback during the historical fallback process. In some other embodiments of the present application, DB2 may further include the score and / or rating of the LTE cell where the user resides after a successful fallback during the historical fallback process. It is understood that the method for obtaining the score and rating can refer to the relevant description below and will not be explained here.

[0204] For example, as shown in Table 1, DB2 includes information about three historical fallback processes of the terminal device. In one of the historical fallback processes, the frequency corresponding to the NR cell where the terminal device resided before the fallback was 627264, the PCI corresponding to the NR cell where the terminal device resided before the fallback was 285, the target LTE frequency indicated by the network side for redirection was 1825, the frequency corresponding to the LTE cell where the device resided after the successful fallback was 300, the PCI corresponding to the LTE cell where the device resided after the successful fallback was 601, and the score level corresponding to the LTE cell where the device resided after the successful fallback was excellent. In another historical fallback process, the frequency corresponding to the NR cell where the terminal device resided before the fallback was 633984, the PCI corresponding to the NR cell where the terminal device resided before the fallback was 385, the target LTE frequency indicated by the network side for redirection was 1650, the frequency corresponding to the LTE cell where the device resided after the successful fallback was 100, the PCI corresponding to the LTE cell where the device resided after the successful fallback was 501, and the score level corresponding to the LTE cell where the device resided after the successful fallback was good. There is another historical fallback process. The frequency corresponding to the NR cell where the terminal device resides before the fallback is 633984, the PCI corresponding to the NR cell where the terminal device resides before the fallback is 485, the target LTE frequency indicated by the network side for redirection is 38725, the frequency corresponding to the LTE cell where the terminal device resides after the successful fallback is 1825, the PCI corresponding to the LTE cell where the terminal device resides after the successful fallback is 401, and the score level corresponding to the LTE cell where the terminal device resides after the successful fallback is poor.

[0205] Table 1

[0206] In some embodiments of the present application, DB1 and DB2 are lists. It is understood that DB1 and DB2 can also be represented in other forms besides lists, and this application does not limit this. It should be noted that DB1 and DB2 are merely exemplary names and should not be considered as limitations of this application.

[0207] In some embodiments of the present application, the terminal device searches for the LTE frequency point set_1 based on the preset order_1, which may specifically include: the terminal device selects s1 LTE frequency points in the LTE frequency point set_1, and determines in order from high to low energy whether the LTE cells corresponding to the s1 LTE frequency points are suitable LTE cells; if no suitable LTE cell is found, the terminal device may reselect s2 LTE frequency points in the LTE frequency point set_1 except the s1 LTE frequency points, and determine in order from high to low energy whether the LTE cells corresponding to the s2 LTE frequency points are suitable LTE cells; similarly, if no suitable LTE cell is still found, the terminal device may reselect s3 LTE frequency points in the LTE frequency point set_1 except the s1 and s2 LTE frequency points, and determine in order from high to low energy whether the LTE cells corresponding to the s3 LTE frequency points are suitable LTE cells. By analogy, the terminal device can search for LTE frequency point set_1 according to the above method until a suitable LTE cell is found, or it is determined that the LTE cells corresponding to all LTE frequencies in LTE frequency point set_1 are not suitable LTE cells, or timer T2 times out, or the fallback process from 5G to 4G times out (for example, the timer started by the terminal device or the network side for this fallback times out).

[0208] It should be noted that the terminal device determining whether the LTE cells corresponding to the s1 LTE frequencies are suitable LTE cells in descending order of energy may include: the terminal device sorting the s1 LTE frequencies in descending order of energy, the terminal device first determining whether there is a suitable LTE cell among one or more LTE cells corresponding to the LTE frequency ranked rth in energy among the s1 LTE frequencies; if there is a suitable LTE cell, the terminal device stops searching; if none of the one or more LTE cells corresponding to the LTE frequency ranked rth in energy among the s1 LTE frequencies are suitable LTE cells, the terminal device continues to determine whether there is a suitable LTE cell among one or more LTE cells corresponding to the LTE frequency ranked r+1th in energy among the s1 LTE frequencies. Where r=1,…,s1.

[0209] Specifically, the terminal device sorts the s1 LTE frequency points according to energy from large to small. The terminal device first determines whether there is a suitable LTE cell in one or more LTE cells corresponding to the LTE frequency point ranked first in energy among the s1 LTE frequency points. If there is a suitable LTE cell, the terminal device determines that a suitable LTE cell has been searched and stops searching. If the one or more LTE cells corresponding to the LTE frequency point ranked first in energy among the s1 LTE frequency points are not suitable LTE cells, the terminal device continues to determine whether there is a suitable LTE cell in one or more LTE cells corresponding to the LTE frequency point ranked second in energy among the s1 LTE frequency points. By analogy, if the terminal device determines that there is no suitable LTE cell in one or more LTE cells corresponding to the LTE frequency point ranked first in energy among the s1 LTE frequency points, the terminal device has not searched for a suitable LTE cell based on the s1 LTE frequency points.

[0210] It can be understood that the specific process of the terminal device searching for a suitable LTE cell on s2 LTE frequency points and s3 LTE frequency points can refer to the above-mentioned process of searching for a suitable LTE cell on s1 LTE frequency points.

[0211] It can be understood that s1, s2 and s3 are positive integers, and their specific values ​​can be set according to actual needs, and this application does not impose any restrictions on this.

[0212] It is understandable that the terminal device can select the LTE frequency in LTE frequency set_1 based on one or more of the information such as the signal strength, bandwidth, whether it is an anchor cell, whether it is a high-speed rail cell, etc. of the LTE cell corresponding to the LTE frequency in DB1 and ACQ DB.

[0213] It should be noted that the terminal device determines whether the LTE cell corresponding to the LTE frequency is a suitable LTE cell, which can also be understood as the terminal device determining whether there is a suitable LTE cell on the LTE frequency.

[0214] It is understood that the energy of the LTE frequency mentioned in this application refers to the RSSI of a certain bandwidth (for example, RSSI per 100 kHz). RSSI refers to the linear average power of all signals received by the terminal device (including useful and interfering signals on the same frequency, adjacent frequency interference, thermal noise, etc.), reflecting the load intensity on the resource.

[0215] In some embodiments of the present application, LTE frequency set_1 may include DB1 and ACQ DB. The terminal device searches for LTE frequency set_1 based on preset order_1, which may specifically include: the terminal device searches DB1 and ACQ DB based on one or more of the information of the signal strength, bandwidth, whether it is an anchor cell, whether it is a high-speed rail cell, etc. of the LTE cell corresponding to the LTE frequency in DB1 and ACQ DB. Sort the LTE frequency points in the DB, select the first s1 LTE frequency points, and determine whether the LTE cells corresponding to the s1 LTE frequency points are suitable LTE cells according to the energy from large to small. If no suitable LTE cell is found, the terminal device can reselect the first s2 LTE frequency points in the LTE frequency point set_1 except the s1 LTE frequency points, and determine whether the LTE cells corresponding to the s2 LTE frequency points are suitable LTE cells according to the energy from large to small. Similarly, if no suitable LTE cell is still found, the terminal device can reselect the first s3 LTE frequency points in the LTE frequency point set_1 except the s1 and s2 LTE frequency points, and determine whether the LTE cells corresponding to the s3 LTE frequency points are suitable LTE cells according to the energy from large to small. By analogy, the terminal device can search DB1 and ACQ DB according to the above method until a suitable LTE cell is found, or it is determined that the LTE cells corresponding to all LTE frequency points in DB1 and ACQ DB are not suitable LTE cells, or timer T2 times out, or the fallback process from 5G to 4G times out (for example, the timer started by the terminal device or the network side for this fallback times out).

[0216] In some embodiments of the present application, LTE frequency point set_1 may include DB1, ACQ DB and LTE frequency points from other sources (for example, some or all LTE frequency points in the prefer band, some or all LTE frequency points in the full band). The terminal device searches for LTE frequency point set_1 based on the preset order_1, which may specifically include: the terminal device may first search for the LTE frequency points in DB1 and ACQ DB. If the LTE cells corresponding to the LTE frequency points in DB1 and ACQ DB are not suitable LTE cells, the terminal device may continue to search for the LTE frequency points from other sources. It is understandable that the way in which the terminal device searches for the LTE frequency points in DB1 and ACQ DB can be referred to above and will not be repeated here.

[0217] In one possible implementation, the terminal device selects a fixed number of LTE frequencies from the LTE frequency set_1 each time, unless the number of unselected LTE frequencies in the LTE frequency set_1 is less than the fixed number. For example, the number of times the terminal device selects a fixed number of LTE frequencies from the LTE frequency set_1 is no less than 3 times, then s1=s2=s3. For example, the total number of times the terminal device selects LTE frequencies from the LTE frequency set_1 is 3 times, and the number of times a fixed number of LTE frequencies is selected from the LTE frequency set_1 is 2 times, then s1=s2>s3. For example, the total number of times the terminal device selects LTE frequencies from the LTE frequency set_1 is 2 times, and the number of times a fixed number of LTE frequencies is selected from the LTE frequency set_1 is also 2 times, then s1=s2. It can be understood that the fixed number can be set according to actual needs, and this application does not impose any restrictions on this. For example, the fixed number can be 10.

[0218] For any frequency source included in LTE frequency set_1, if the frequency source specifically includes multiple frequency points, preset order_1 may specifically include the order in which the terminal device searches for the multiple frequency points. It is understood that the order in which the terminal device searches for the multiple frequency points may be related to factors such as the signal strength, bandwidth, whether the corresponding cell is an anchor cell, and whether it belongs to the preferred band of the multiple frequency points. A detailed description can be found later and is not elaborated here.

[0219] For example, if LTE frequency point set_1 includes frequencies in DB1, the terminal device searches for frequencies in LTE frequency point set_1 based on preset order_1. Specifically, the terminal device may search for frequencies in DB1 in descending order of corresponding signal strength. In this case, the frequencies in DB1 are sorted in descending order of corresponding signal strength, and the resulting order is preset order_1.

[0220] It can be understood that, in the case where the LTE frequency point set_1 includes frequencies from multiple sources, the preset order_1 may specifically include the order in which the terminal device searches for frequencies from different sources included in the LTE frequency point set_1.

[0221] For example, when the LTE frequency point set_1 includes part or all of the LTE frequency points in DB1, ACQ DB, part or all of the LTE frequency points in the full band, and part or all of the LTE frequency points in the prefer band, the terminal device searches for frequencies other than the target LTE frequency point based on the preset order_1, which may specifically include: the terminal device may first search for part or all of the LTE frequency points in DB1 according to the corresponding signal strength from large to small. If no suitable LTE cell is found, the terminal device will then search the ACQ DB, part or all of the LTE frequency points in the prefer band, and part or all of the LTE frequency points in the full band in turn.

[0222] For example, in the case where LTE frequency point set_1 includes some or all of the LTE frequency points in DB1, some or all of the LTE frequency points in DB2, some or all of the LTE in ACQ DB, the LTE frequency points in the full band, and the LTE frequency points in the prefer band, the terminal device searches for the frequency points in LTE frequency point set_1 based on the preset order_1, which may specifically include: the terminal device may first search for some or all of the LTE frequency points in DB1 and some or all of the LTE frequency points in DB2. If no suitable LTE cell is found, the terminal device then searches for some or all of the LTE frequency points in ACQ DB, some or all of the LTE frequency points in the prefer band, and some or all of the LTE frequency points in the full band in sequence. In a possible implementation, the terminal device may first search for some or all of the LTE frequency points in DB1 and some or all of the LTE frequency points in DB2, which may specifically include: the terminal device may first search for some or all of the LTE frequency points in DB1, and then search for some or all of the LTE frequency points in DB2. In one possible implementation, the terminal device may first search for some or all of the LTE frequency points in DB1 and some or all of the LTE frequency points in DB2. Specifically, the terminal device may first search for some or all of the LTE frequency points in DB2, and then search for some or all of the LTE frequency points in DB1. In one possible implementation, the terminal device may first search for some or all of the LTE frequency points in DB1 and some or all of the LTE frequency points in DB2. Specifically, the terminal device may search for the LTE frequency points in DB1 and DB2 in descending order of corresponding signal strength.

[0223] It can be understood that the terminal device searches for some or all of the LTE frequency points in DB2, which can specifically include: the terminal device can search for some or all of the historical fallback records in DB2, and determine whether the NR cell where the terminal device resided before the fallback in the part or all of the historical fallback records is the NR cell where the terminal device resided before this fallback, and the target LTE frequency point of redirection indicated by the network side is the historical fallback record of the target LTE frequency point of redirection indicated by the network side for this fallback. If such a historical fallback record exists, the terminal device can search for a suitable LTE cell based on the LTE frequency point corresponding to the LTE cell where the terminal device resides after the successful fallback in the historical fallback record.

[0224] It should be noted that in some embodiments of the present application, when the terminal device searches for the frequency points in DB2, it can first search for the frequency points in the top position in DB2, and then search for other frequency points in DB2. That is, the terminal device can first determine whether the NR cell where the terminal device resides before the fallback in the historical fallback record at the top position is the NR cell where the terminal device resides before this fallback, and determine whether the redirected LTE frequency point indicated by the network side in the historical fallback record at the top position is the target LTE frequency point indicated by the network side for this fallback. When the above two items are exactly the same, the terminal device can search for a suitable LTE cell based on the LTE frequency point corresponding to the LTE cell where the terminal device resides after the successful fallback in the historical fallback record at the top position, and when the above two items are not exactly the same, the terminal device searches for other historical fallback records in DB2 according to the above method. It can be understood that the LTE frequency point at the top position in DB2 can be the LTE frequency point stored by the terminal device for a specific location. The specific location may include a home or an office. In some embodiments of the present application, the terminal device can use a modem to self-learn the LTE frequency point corresponding to a specific location based on the length of time on the network. In some other embodiments of the present application, the terminal device can configure the LTE frequency corresponding to a specific location based on the network residence time through the AP side, or the user can set the LTE frequency corresponding to the specific location by himself.

[0225] It can be understood that DB1 and DB2 adopt the first-in-first-out principle. That is, when the LTE frequency points stored in DB1 reach the upper limit, the terminal device will clear the earliest stored LTE frequency point to store the new LTE frequency point. Similarly, when the LTE frequency points stored in DB2 reach the upper limit, the terminal device will also clear the earliest stored LTE frequency point to store the new LTE frequency point. However, unlike DB1, the top LTE frequency point in DB2 and other information related to the frequency point (for example, the cell ID of the corresponding cell, the RSRP of the corresponding cell, the corresponding fallback frequency point, and the corresponding NR cell resident before fallback) will not be cleared.

[0226] In some embodiments of the present application, one or more of DB1, DB2, ACQ DB, full band and prefer band may include a target LTE frequency point.

[0227] It should be noted that in some embodiments of the present application, LTE frequency point set_1 may further include a target LTE frequency point. In one possible implementation, one or more of DB1, DB2, ACQ DB, full band, and prefer band included in LTE frequency point set_1 may include the target LTE frequency point. In another possible implementation, in addition to including one or more of DB1, DB2, ACQ DB, full band, and prefer band, LTE frequency point set_1 may further include the target LTE frequency point.

[0228] S5: If the terminal device searches for a suitable LTE cell before timer T2 times out, the terminal device resides in the suitable LTE cell. If the terminal device still does not search for a suitable LTE cell after timer T2 times out, the terminal device selects an NR cell for access.

[0229] If the terminal device searches for a suitable LTE cell before timer T2 times out, the terminal device can reside in the suitable LTE cell, establish an RRC connection with the suitable LTE cell, and trigger the TAU process. If the terminal device still fails to search for a suitable LTE cell after timer T2 times out, the terminal device can select an NR cell for access, that is, choose to reside in the NR cell and establish an RRC connection with the NR cell.

[0230] It can be understood that the NR cell where the terminal device mentioned in step S1 and step S5 resides / accesses can be the same NR cell or different NR cells.

[0231] In some embodiments of the present application, in response to receiving an RRC Release message carrying a redirection indication sent by NR, the terminal device can start timer T2, search in DB2 whether there is an LTE frequency that matches (or corresponds to) the target LTE frequency indicated by the network side for redirection and the frequency corresponding to the currently residing NR cell, and search for a suitable LTE cell on the LTE frequency, that is, determine whether the cell corresponding to the LTE frequency is a suitable LTE cell. If there is no LTE frequency in DB2 that matches the frequency corresponding to the target LTE frequency and the currently residing NR cell, or there is an LTE frequency in DB2 that matches the frequency corresponding to the target LTE frequency and the currently residing NR cell, but the cell corresponding to the LTE frequency is not a suitable LTE cell, the terminal device can start timer T1 and execute steps S3-S5. In this case, the frequencies other than the target LTE frequency searched by the terminal device when executing step S4 do not include the frequencies in DB2.

[0232] In some embodiments of the present application, in response to receiving an RRC Release message carrying a redirection indication sent by NR, the terminal device can search in DB2 whether there is an LTE frequency that matches the target LTE frequency indicated by the network side for redirection and the frequency corresponding to the currently located NR cell, and if there is no LTE frequency that matches the target LTE frequency and the frequency corresponding to the currently located NR cell in DB2, or if there is an LTE frequency that matches the target LTE frequency and the frequency corresponding to the currently located NR cell in DB2, but the cell corresponding to the LTE frequency is not a suitable LTE cell, start timer T1 and timer T2, and execute steps S3-S5.

[0233] In some embodiments of the present application, DB2 may include the cell ID corresponding to the LTE cell that resides after a successful fallback during the historical fallback process. In this case, if the terminal device finds an LTE frequency that matches the target LTE frequency indicated by the network side for redirection and the frequency corresponding to the currently residing NR cell in DB2 based on the above method, the terminal device can find the cell ID of the LTE cell corresponding to the LTE frequency, and then the terminal device can search on the LTE frequency based on the cell ID, that is, the terminal device can search on the LTE frequency for an LTE cell whose corresponding cell ID is the found cell ID, and determine whether the LTE cell is a suitable LTE cell.

[0234] According to the above, in some embodiments of the present application, DB2 may contain several records. For example, as shown in Table 1, each row of data in Table 1 is a record of a historical fallback process. Each record may include the target LTE frequency of redirection indicated by the network side in a historical fallback process, the frequency corresponding to the NR cell that resided before the fallback corresponding to the fallback, and the frequency corresponding to the LTE cell that resided after the successful fallback. After the fallback process is triggered, the terminal device can not only determine the frequency corresponding to the currently residing NR cell, but also determine the target LTE frequency of redirection indicated by the network side of this fallback after receiving the RRC Release message carrying the redirection indication sent by the NR. In some embodiments of the present application, the terminal device searches DB2 for an LTE frequency that matches the target LTE frequency for redirection indicated by the network side and the frequency corresponding to the currently residing NR cell. Specifically, the terminal device may compare the target LTE frequency determined above and the frequency corresponding to the currently residing NR cell with each record in DB2 to check whether there is a record in DB2 that represents a target LTE frequency for redirection indicated by the network side during a historical fallback process and the frequency corresponding to the NR cell that resided before the fallback corresponding to the fallback are respectively the same as the target LTE frequency determined above and the frequency corresponding to the currently residing NR cell. If there is a record in DB2 that represents a target LTE frequency for redirection indicated by the network side during a historical fallback process and the frequency corresponding to the NR cell that resided before the fallback corresponding to the fallback are respectively the same as the target LTE frequency determined above and the frequency corresponding to the currently residing NR cell, then there is an LTE frequency that matches the target LTE frequency for redirection indicated by the network side and the frequency corresponding to the currently residing NR cell in DB2.

[0235] According to the above, a suitable LTE cell may be: an LTE cell whose signal quality meets the access threshold and the network side does not prohibit the terminal device from accessing. It should be noted that in one possible implementation method, the terminal device will increase the access threshold when executing step S3, that is, the LTE cell corresponding to the redirected target LTE frequency given by the network side must meet a higher access threshold to be a suitable LTE cell, and the access threshold used by the terminal device in the process of searching for cells on the frequency after timer T1 expires will be lower than the above-mentioned increased access threshold. In other words, the specific meanings of the suitable LTE cells mentioned in step S3 and step S5 may be different. The access threshold corresponding to the suitable LTE cell mentioned in step S5 may be lower than the access threshold corresponding to the suitable LTE cell mentioned in step S3.

[0236] It should be noted that in some embodiments of the present application, if the terminal device has not searched for a suitable LTE cell based on the redirected target LTE frequency indicated by the network side until timer T1 times out, the terminal device may also re-determine whether the LTE cell corresponding to the target LTE frequency is a suitable LTE cell in the subsequent process. In one possible implementation, the terminal device may re-search for a suitable LTE cell based on the target LTE frequency. In another possible implementation, the terminal device may re-determine whether the LTE cell corresponding to the target LTE frequency is a suitable LTE cell based on the content obtained when searching for the target LTE frequency previously.

[0237] For example, when the terminal device executes the above step S4, the ACQ DB it searches may include the target LTE frequency. In this case, the terminal device can not only search for frequencies other than the target LTE frequency in the ACQ DB, but also search for the target LTE frequency.

[0238] For example, if the terminal device fails to search for a suitable LTE cell at other frequency points after timer T1 expires, but searches for a suitable LTE cell during the process of searching for the target LTE frequency point again because the access threshold is low, in this case, the terminal device can access the LTE cell.

[0239] A specific implementation of the above embodiment is described below.

[0240] Please refer to Figure 7A, which is a flow chart of another communication method provided in an embodiment of the present application. The communication method may include but is not limited to the following steps:

[0241] S101: The terminal device resides in the NR cell.

[0242] The terminal device can reside in an NR cell. That is, the terminal device can reside in a cell covered by a 5G network. In some embodiments of the present application, the terminal device can perform voice services while residing in an NR cell.

[0243] S102: NR sends LTE frequency information to the terminal device.

[0244] It is understandable that NR can send LTE frequency information to the terminal device. The LTE frequency information may include the frequency corresponding to the inter-frequency LTE cell (i.e., inter-frequency LTE neighboring cell) in the adjacent cell (hereinafter referred to as the neighboring cell) of the cell where the terminal device is currently stationed. It is understandable that the frequency corresponding to the LTE cell can also be called the LTE frequency. It is understandable that the relevant information of the inter-frequency LTE cell can also include other information such as the cell ID corresponding to the inter-frequency LTE cell. The cell ID can refer to a physical cell identifier (PCI).

[0245] In some embodiments of the present application, LTE frequency information may be configured via an RRC Connection Reconfiguration message carrying a measurement configuration, wherein the measurement configuration includes the LTE frequency that the network indicates the terminal device needs to measure.

[0246] In some embodiments of the present application, LTE frequency information can be configured via a system message (e.g., a SIB5 message). The SIB5 message is a type of system message. The SIB5 message contains frequency information for inter-frequency neighboring E-UTRA cells (i.e., the frequencies corresponding to inter-frequency neighboring LTE cells).

[0247] It is understood that the frequency points mentioned in this application may refer to frequency point numbers. There is a corresponding relationship between frequency points and frequencies.

[0248] Correspondingly, the terminal device can receive the LTE frequency information sent by NR.

[0249] S103: The terminal device performs measurement and / or detection based on the LTE frequency information to obtain measurement and detection results.

[0250] After the terminal device receives the LTE frequency information sent by NR, it can measure and / or detect the relevant information (for example, signal strength, bandwidth, whether it is an anchor cell, whether it is a high-speed rail cell, etc.) of the LTE cell corresponding to the LTE frequency included in the LTE frequency information (that is, the LTE neighboring cell of the currently stationed NR cell) to obtain the measurement and detection results.

[0251] For example, the terminal device can measure the signal strength of the LTE cell corresponding to the LTE frequency included in the LTE frequency information. For example, the terminal device can detect the bandwidth of the LTE cell corresponding to the LTE frequency included in the LTE frequency information, and can also detect whether the LTE cell corresponding to the LTE frequency included in the LTE frequency information is an anchor cell. It is understandable that the terminal device can specifically perform the above detection process by receiving a system message. For example, the bandwidth of the LTE cell corresponding to the LTE frequency included in the LTE frequency information and whether it is an anchor cell are determined by the content in the received system message.

[0252] It is understood that the measurement and detection results may include one or more of the following: the signal strength of the LTE neighboring cell, the bandwidth of the LTE neighboring cell, whether there is an anchor cell in the LTE neighboring cell, and whether there is a high-speed rail cell in the LTE neighboring cell. It is understood that the measurement and detection results may also include other information, which is not limited in this application.

[0253] It is understood that the signal strength can be specifically represented by one or more parameters such as RSRP, RSRQ, and SNR. For example, the terminal device can measure the RSRP of the LTE neighboring cells to obtain the specific RSRP value corresponding to each LTE neighboring cell. For another example, the terminal device can measure the RSRQ of the LTE neighboring cells to obtain the specific RSRQ value corresponding to each LTE neighboring cell.

[0254] S104: The terminal device sorts the measured LTE frequency points based on the measurement detection result, and stores the measured LTE frequency points into DB1 according to the sorting result.

[0255] After the terminal device measures the signal strength of the LTE neighboring cell and obtains the measurement detection result, it can sort the LTE frequency points corresponding to the LTE neighboring cell based on the measurement detection result to obtain the sorting result, and store the sorting result and the relevant information of the measured LTE frequency points in DB1. According to the above, DB1 includes the frequency points corresponding to the LTE neighboring cells of the NR cells where the terminal device has resided (including the NR cell currently residing).

[0256] In some embodiments of the present application, DB1 may be a list. It is understood that the terminal device may also store the measured LTE frequency points in other forms such as an array, and the present application does not limit this.

[0257] In some embodiments of the present application, the terminal device may also store other relevant information of the measured LTE frequency point (for example, the corresponding cell ID, the signal strength of the corresponding cell, the bandwidth of the corresponding cell, etc.) in DB1.

[0258] It should be noted that, in some embodiments of the present application, for one LTE frequency point, the terminal device can search for multiple cells. In this case, the terminal device sorts the measured LTE frequency points based on the measurement detection results, which may specifically include: the terminal device sorts the cells corresponding to the measured LTE frequency points based on the measurement detection results, and sorts the measured LTE frequency points based on the sorting results of the cells. It can be understood that since there is a correspondence between the LTE neighboring cells of the NR cell where the terminal device is currently residing and the LTE frequency points, when there are multiple LTE neighboring cells corresponding to one LTE frequency point, the terminal device can determine the sorting results of the LTE frequency points corresponding to the LTE neighboring cells based on the sorting results obtained by sorting the LTE neighboring cells, that is, determine the sorting results of the measured LTE frequency points. Specifically, for the LTE frequency point corresponding to multiple LTE neighboring cells, the terminal device can sort the LTE frequency point according to the sequence number of the cell with the highest sorting corresponding to the LTE frequency point.

[0259] In some embodiments of the present application, the terminal device sorts the LTE frequency points corresponding to the LTE neighboring cells based on the measurement detection results, which may specifically include: the terminal device sorts the LTE frequency points corresponding to the LTE neighboring cells from large to small according to the signal strength of the LTE neighboring cells.

[0260] For example, a terminal device measures three LTE frequencies: 100, 1300, and 1650. Specifically, the terminal device can search for the cell corresponding to LTE frequency 100. One cell corresponding to LTE frequency 100 is found, and its corresponding cell ID is PCI1. Similarly, the terminal device can search for cells corresponding to LTE frequency 1300 and LTE frequency 1650. One cell corresponding to LTE frequency 1300 is found, and its corresponding cell ID is PCI2. The terminal device also finds one cell corresponding to LTE frequency 1650, and its corresponding cell ID is PCI3. The terminal device can measure the signal strength of cells with cell IDs PCI1, PCI2, and PCI3, respectively. According to the measurement results, the RSRP of the cell with cell ID PCI1 is -95 decibel milliwatts (dBm), the RSRP of the cell with cell ID PCI2 is -112 dBm, and the RSRP of the cell with cell ID PCI3 is -115 dBm. The terminal device can sort the LTE frequency points corresponding to the three cells according to the RSRP of the three cells from large to small. Specifically, since -95dBm>-112dBm>-115dBm, the LTE frequency point 100 of the cell corresponding to -95dBm is ranked first, the LTE frequency point 100 of the cell corresponding to -112dBm is ranked second, and the LTE frequency point 100 of the cell corresponding to -115dBm is ranked third. In other words, the sorting results obtained by the terminal device for sorting the LTE frequencies are: 100, 1300, 1650. It can be understood that in a possible implementation method, the terminal device can store the three LTE frequency points in DB1 according to the sorting results obtained by sorting the LTE frequencies, as shown in the first two columns of Table 2. In another possible implementation, the terminal device can not only store the three LTE frequencies in DB1 according to the sorting result obtained by sorting the LTE frequencies, but also store other relevant information of the three LTE frequencies (for example, the cell ID of the corresponding cell, the RSRP of the corresponding cell) in DB1, as shown in Table 2.

[0261] Table 2

[0262] It can be understood that when there are LTE frequencies corresponding to multiple cells among the LTE frequencies measured by the terminal device, the terminal device sorts the LTE frequencies corresponding to the LTE neighboring cells based on the measurement detection results, which can specifically include: the terminal device sorts the LTE neighboring cells from large to small according to the signal strength of the LTE neighboring cells, and sorts the corresponding LTE frequencies based on the sorting results of the LTE neighboring cells.

[0263] Exemplarily, the terminal device measures the three LTE frequency points 100, 1300, and 1650. Specifically, the terminal device can search for the cell corresponding to LTE frequency point 100. There are two cells corresponding to LTE frequency point 100 found, and their corresponding cell IDs are PCI1 and PCI2, respectively. Similarly, the terminal device can search for the cell corresponding to LTE frequency point 1300 and the cell corresponding to LTE frequency point 1650. The terminal device finds one cell corresponding to LTE frequency point 1300, and its corresponding cell ID is PCI3. The terminal device finds one cell corresponding to LTE frequency point 1650, and its corresponding cell ID is PCI4. The terminal device can measure the signal strength of cells with cell IDs PCI1, PCI2, PCI3, and PCI4, respectively. According to the measurement results, the RSRP of the cell with cell ID PCI1 is -95dBm, the RSRP of the cell with cell ID PCI2 is -110dBm, the RSRP of the cell with cell ID PCI3 is -112dBm, and the RSRP of the cell with cell ID PCI4 is -115dBm. The terminal device can sort the LTE frequencies corresponding to these four cells from largest to smallest according to their RSRP. Specifically, since -95dBm > -110dBm > -112dBm > -115dBm, the cell corresponding to -95dBm is ranked first, and the LTE frequency corresponding to this cell is 100. The cell corresponding to -110dBm is ranked second, and the LTE frequency corresponding to this cell is 100. The cell corresponding to -112dBm is ranked third, and the LTE frequency corresponding to this cell is 1300. The cell corresponding to -115dBm is ranked fourth, and the LTE frequency corresponding to this cell is 1650. It is understandable that the terminal device sorts the LTE frequency points and the resulting sorting results are: 100, 1300, 1650. The terminal device sorts the cells corresponding to the LTE frequency points and the resulting sorting results are: cells with cell ID PCI1, cells with cell ID PCI2, cells with cell ID PCI3, and cells with cell ID PCI4. In other words, the cell with cell ID PCI1 corresponds to a sequence number of 1, the cell with cell ID PCI2 corresponds to a sequence number of 2, the cell with cell ID PCI3 corresponds to a sequence number of 3, and the cell with cell ID PCI4 corresponds to a sequence number of 4. It is understandable that the terminal device can sort the measured LTE frequency points according to the above sorting results.Specifically, since LTE frequency 100 corresponds to two cells, the terminal device sorts LTE frequency 100 based on the sequence number of the cell with the highest ranking corresponding to that LTE frequency. That is, the terminal device sorts LTE frequency 100 based on the sequence number of the cell with cell ID PCI1. The sequence number corresponding to LTE frequency 100 is 1. Since the cell following the two cells corresponding to LTE frequency 100 corresponds to LTE frequency 1300, the sequence number corresponding to LTE frequency 1300 is 2. Since the cell following the cell corresponding to LTE frequency 1300 corresponds to LTE frequency 1650, the sequence number corresponding to LTE frequency 1650 is 3. It can be understood that the terminal device sorts the LTE frequencies to obtain the following ranking result: 100, 1300, 1650. It can be understood that in one possible implementation, the terminal device can store the three LTE frequencies in DB1 according to the ranking result obtained by sorting the LTE frequencies. In another possible implementation, the terminal device can not only store the three LTE frequency points in DB1 according to the sorting result obtained by sorting the LTE frequency points, but also store other relevant information of the three LTE frequency points (for example, the cell ID of the corresponding cell, the RSRP of the corresponding cell) in DB1, as shown in Table 3.

[0264] Table 3

[0265] It should be noted that in some embodiments of the present application, before the terminal device stores the measured LTE frequency and its signal strength (e.g., RSRP value) in DB1, it may determine whether the signal strength corresponding to the measured LTE frequency satisfies certain conditions. For example, the terminal device may determine whether the RSRP corresponding to the measured LTE frequency satisfies a threshold value of greater than threshold value_1. It is understood that threshold value_1 can be set according to actual needs and is not limited in this application. For example, threshold value_1 may be -115dBm.

[0266] In some embodiments of the present application, the terminal device sorts the LTE frequency points corresponding to the LTE neighboring cells based on the measurement detection results, which may specifically include: the terminal device sorts the LTE frequency points corresponding to the different-frequency LTE neighboring cells from large to small according to the bandwidth of the LTE neighboring cells.

[0267] Exemplarily, the terminal device measures the three LTE frequency points 100, 1300 and 1650. Specifically, the terminal device can search for the cells corresponding to these three LTE frequency points and measure the bandwidth of the cells corresponding to these three LTE frequency points. It is understandable that the terminal device can also measure other information (for example, signal strength) of the cells corresponding to these three LTE frequency points. LTE frequency point 100 corresponds to a cell with a cell ID of PCI2, LTE frequency point 1300 corresponds to a cell with a cell ID of PCI3, and LTE frequency point 1650 corresponds to a cell with a cell ID of PCI4. According to the measurement detection results, the bandwidth of the cell with cell ID PCI2 is 20 megahertz (M or MHz), and its RSRP is -100dBm, the bandwidth of the cell with cell ID PCI3 is 10M, and its RSRP is -105dBm, and the bandwidth of the cell with cell ID PCI4 is 15M, and its RSRP is -115dBm. The terminal device can sort the LTE frequencies corresponding to the three cells according to the bandwidth of the three cells from large to small. Specifically, since 20M>15M>10M, the LTE frequency corresponding to the cell with a bandwidth of 20M is ranked first, that is, LTE frequency 100 is ranked first, the LTE frequency corresponding to the cell with a bandwidth of 15M is ranked second, that is, LTE frequency 1650 is ranked second, and the LTE frequency corresponding to the cell with a bandwidth of 10M is ranked third, that is, LTE frequency 1300 is ranked third. In other words, the sorting result obtained by the terminal device for sorting the LTE frequencies is: 100, 1650, 1300. It can be understood that in a possible implementation method, the terminal device can store the three LTE frequencies in DB1 according to the sorting result obtained by sorting the LTE frequencies, as shown in the first and third columns of Table 4. In another possible implementation, the terminal device can not only store the three LTE frequencies in DB1 according to the sorting results obtained by sorting the LTE frequencies, but also store other relevant information of the three LTE frequencies (for example, the bandwidth of the corresponding cell, the cell ID of the corresponding cell, and the RSRP of the corresponding cell) in DB1, as shown in Table 4.

[0268] Table 4

[0269] It can be understood that when there are LTE frequencies corresponding to multiple cells among the LTE frequencies measured by the terminal device, the terminal device sorts the LTE frequencies corresponding to the LTE neighboring cells based on the measurement detection results, which can specifically include: the terminal device sorts the LTE neighboring cells from large to small according to the bandwidth of the LTE neighboring cells, and sorts the corresponding LTE frequencies based on the sorting results of the LTE neighboring cells.

[0270] Exemplarily, the terminal device measures the three LTE frequencies 100, 1300, and 1650. Specifically, the terminal device can search for the cells corresponding to these three LTE frequencies and measure the bandwidths of the cells corresponding to these three LTE frequencies. It is understandable that the terminal device can also measure other information (e.g., signal strength) of the cells corresponding to the three LTE frequencies. LTE frequency 100 corresponds to two cells, whose cell IDs are PCI1 and PCI2, respectively; LTE frequency 1300 corresponds to one cell, whose cell ID is PCI3; and LTE frequency 1650 corresponds to one cell, whose cell ID is PCI4. According to the measurement results, the bandwidth of the cell with cell ID PCI1 is 5M, and its RSRP is -95dBm; the bandwidth of the cell with cell ID PCI2 is 20M, and its RSRP is -100dBm; the bandwidth of the cell with cell ID PCI3 is 10M, and its RSRP is -105dBm; the bandwidth of the cell with cell ID PCI4 is 15M, and its RSRP is -115dBm. The terminal device can sort the four cells from largest to smallest according to their bandwidth. The terminal device sorts the cells corresponding to the LTE frequency points, and the sorting result is: the cell with cell ID PCI2, the cell with cell ID PCI4, the cell with cell ID PCI3, and the cell with cell ID PCI1. In other words, the sequence number corresponding to the cell with cell ID PCI2 is 1, the sequence number corresponding to the cell with cell ID PCI4 is 2, the sequence number corresponding to the cell with cell ID PCI3 is 3, and the sequence number corresponding to the cell with cell ID PCI1 is 4. It can be understood that the terminal device can sort the measured LTE frequency points according to the above sorting result. Specifically, since LTE frequency 100 corresponds to two cells, the terminal device sorts LTE frequency 100 based on the sequence number of the cell with the highest ranking corresponding to the LTE frequency. That is, the terminal device sorts LTE frequency 100 based on the sequence number of the cell with cell ID PCI2. The sequence number corresponding to LTE frequency 100 is 1. Since the cell ranked one level after the cell with cell ID PCI2 corresponds to LTE frequency 1650, the sequence number corresponding to LTE frequency 1650 is 2. Since the cell ranked one level after the cell corresponding to LTE frequency 1650 corresponds to LTE frequency 1300, the sequence number corresponding to LTE frequency 1300 is 3. It can be understood that the terminal device sorts the LTE frequencies to obtain the following ranking result: 100, 1650, 1300. It can be understood that in one possible implementation, the terminal device can store the three LTE frequencies in DB1 according to the ranking result obtained by sorting the LTE frequencies.In another possible implementation, the terminal device can not only store the three LTE frequencies in DB1 according to the sorting result obtained by sorting the LTE frequencies, but also store other relevant information of the three LTE frequencies (for example, the cell ID of the corresponding cell, the RSRP of the corresponding cell) in DB1, as shown in Table 5.

[0271] Table 5

[0272] In some embodiments of the present application, a terminal device may sort the LTE frequencies corresponding to LTE neighboring cells based on the signal strength and bandwidth of the LTE neighboring cells. In other words, the terminal device may sort the LTE frequencies corresponding to LTE neighboring cells by comprehensively considering the signal strength and bandwidth of inter-frequency LTE neighboring cells. The sorting rule is: the LTE frequencies corresponding to cells with greater signal strength and greater bandwidth are ranked first, while the LTE frequencies corresponding to cells with less signal strength and less bandwidth are ranked last.

[0273] Exemplarily, the terminal device measures the three LTE frequency points 100, 1300, and 1650. Specifically, the terminal device can search for the cells corresponding to these three LTE frequency points and measure the bandwidth and signal strength of the cells corresponding to these three LTE frequency points. LTE frequency point 100 corresponds to two cells, whose cell IDs are PCI1 and PCI2 respectively, LTE frequency point 1300 corresponds to one cell, whose cell ID is PCI3, and LTE frequency point 1650 corresponds to one cell, whose cell ID is PCI4. According to the measurement detection results, the bandwidth of the cell with cell ID PCI1 is 5M, and its RSRP is -95dBm, the bandwidth of the cell with cell ID PCI2 is 20M, and its RSRP is -100dBm, the bandwidth of the cell with cell ID PCI3 is 10M, and its RSRP is -105dBm, and the bandwidth of the cell with cell ID PCI4 is 15M, and its RSRP is -115dBm. The terminal device can rank the four cells based on their bandwidth and signal strength. As shown in Table 6, the cell with cell ID PCI2 is numbered 1, the cell with cell ID PCI4 is numbered 2, the cell with cell ID PCI3 is numbered 3, and the cell with cell ID PCI1 is numbered 4. It is understood that the terminal device can rank the measured LTE frequencies based on the above ranking results. Specifically, since LTE frequency 100 corresponds to two cells, the terminal device sorts LTE frequency 100 based on the sequence number of the cell with the highest ranking corresponding to the LTE frequency. That is, the terminal device sorts LTE frequency 100 based on the sequence number of the cell with cell ID PCI2. The sequence number corresponding to LTE frequency 100 is 1. Since the cell ranked one level after the cell with cell ID PCI2 corresponds to LTE frequency 1300, the sequence number corresponding to LTE frequency 1300 is 2. Since the cell ranked one level after the cell corresponding to LTE frequency 1300 corresponds to LTE frequency 1650, the sequence number corresponding to LTE frequency 1300 is 3. It can be understood that the terminal device sorts the LTE frequencies to obtain the following ranking result: 100, 1650, 1300. It can be understood that in one possible implementation, the terminal device can store the three LTE frequencies in DB1 according to the ranking result obtained by sorting the LTE frequencies. In another possible implementation, the terminal device may store the relevant information of the three LTE frequency points in DB1 according to the sorting result obtained by sorting the LTE frequency points, as shown in Table 6.

[0274] Table 6

[0275] In one possible implementation, the terminal device sorts the LTE frequency points corresponding to the heterofrequency LTE neighboring cells based on the measurement detection results, which may specifically include: the terminal device sorts the LTE neighboring cells according to the signal strength of the LTE neighboring cells from large to small, and obtains sorting result_1; the terminal device sorts the LTE neighboring cells according to the bandwidth of the heterofrequency LTE neighboring cells from large to small, and obtains sorting result_2; the sorting result_1 and the sorting result_2 are weighted, and the weighted results are sorted from small to large to obtain sorting result_3. It can be understood that sorting result_3 is the final sorting result of sorting the heterofrequency LTE neighboring cells. It should be noted that the terminal device can sort the corresponding LTE frequency points based on sorting result_3. The specific implementation method can refer to the above and will not be repeated here.

[0276] For ease of description, this application records a certain LTE neighboring cell as cell N, records the sorting number of the signal strength of cell N as num1, and records the sorting number of the bandwidth of cell N as num2. It is understandable that the terminal device can perform weighted processing on the sorting number of the signal strength of cell N and the sorting number of its bandwidth, and obtain the weighted sorting number as: num1*a1+num2*a2. The terminal device can determine the weighted sorting number corresponding to each LTE neighboring cell in this way, and then sort them in order from small to large to obtain the final sorting result. Among them, a1 is the weighting coefficient corresponding to the signal strength of cell N, and a2 is the weighting coefficient corresponding to the bandwidth of cell N. It is understandable that the specific values ​​of a1 and a2 can be set according to actual needs, and this application does not limit this. For example, a1 can be 0.5, and a2 can also be 0.5.

[0277] In some embodiments of the present application, based on the above-mentioned sorting method, the terminal device may further sort the LTE frequencies corresponding to the LTE neighboring cells in combination with information about whether the LTE neighboring cell is an anchor cell. It is understood that an anchor cell refers to a cell that can access both LTE and NR simultaneously through dual connectivity.

[0278] In one possible implementation, when there is only one anchor cell in the LTE neighboring area, the terminal device may rank the LTE frequency corresponding to the anchor cell first, and for other inter-frequency LTE neighboring areas, the terminal device may rank the LTE frequencies corresponding to the other LTE neighboring areas based on the method described above. When there are multiple anchor cells in the LTE neighboring area, the terminal device may first rank the LTE frequencies corresponding to the multiple anchor cells based on the method described above, and then rank the other LTE neighboring areas based on the method described above.

[0279] Similarly, in some embodiments of the present application, based on the above-mentioned sorting method, the terminal device can also sort the LTE frequencies corresponding to the LTE neighboring cells in combination with information about whether the LTE neighboring cell is a high-speed rail cell. It can be understood that the high-speed rail cell refers to a cell marked for special scenarios such as high-speed rail.

[0280] In some embodiments of the present application, based on the above-described sorting method, the terminal device may further sort the LTE frequencies corresponding to the LTE neighboring cells based on information about whether the LTE frequency corresponding to the LTE cell belongs to a preferred band. It is understood that the preferred band is the frequency band to which the cell frequency that the terminal device prefers to access belongs.

[0281] In one possible implementation, if a frequency belonging to the preferred band exists among the LTE frequencies corresponding to the inter-frequency LTE neighboring cells, the terminal device may rank that frequency first. For the LTE frequencies corresponding to other inter-frequency LTE neighboring cells, the terminal device may rank them based on the method described above. If there are multiple LTE frequencies belonging to the preferred band, the terminal device may first rank the multiple LTE frequencies belonging to the preferred band based on the method described above, and then rank the other LTE frequencies based on the method described above.

[0282] It is understandable that the terminal device can also adopt other methods to sort the measured LTE frequency points, and this application does not limit this.

[0283] In some embodiments of the present application, the terminal device stores the measured LTE frequency points in DB1 according to the sorting result. Specifically, the terminal device may store the corresponding LTE frequency points in DB1 in ascending order according to the sequence number of each measured LTE frequency point in the sorting result. In this case, when the terminal device checks the LTE frequency points in DB1, it can determine the order in which they were stored in DB1, so that the terminal device can subsequently search for these LTE frequency points in the order in which they were stored in DB1.

[0284] In some embodiments of the present application, the terminal device stores the measured LTE frequency points in DB1 according to the sorting result, which may specifically include: the terminal device may store the sorting result and related information of the measured LTE frequency points in DB1. Specifically, the terminal device may store the measured LTE frequency points and the sequence numbers of the measured LTE frequency points in the sorting result in DB1. For details of this part, please refer to Table 2 and Table 4. For example, as shown in Table 2, the terminal device may store the LTE frequency points in Table 2 and their corresponding sequence numbers in DB1.

[0285] The terminal device may also score (or rate) the measured LTE frequency points and store the measured LTE frequency points and their corresponding scores and / or ratings in DB1, so that when subsequently searching for frequency points in DB1, the corresponding frequency points can be searched from high to low based on the corresponding scores. It is understood that the specific implementation of the scoring method can be referred to the above-mentioned sorting method and related technical documents, and will not be described in detail here.

[0286] S105: When the EPS Fallback process is triggered, the NR notifies the core network that the EPS Fallback process has been initiated.

[0287] When the EPS Fallback procedure is triggered, the NR can notify the core network that the EPS Fallback procedure has been initiated. It is understood that the EPS Fallback procedure can be triggered by either an incoming call or an unsolicited call. The specific implementation of the EPS Fallback procedure can be described in Figure 5 and related technical documentation and is not detailed here.

[0288] In some embodiments of the present application, if the signal of the NR cell where the terminal device is currently residing is poor, the network side may also trigger the Fallback process.

[0289] S106: When the EPS Fallback process is triggered, the NR sends an instruction to redirect the terminal device to frequency A.

[0290] When the EPS Fallback process is triggered, the NR can send a command to the terminal device to redirect to frequency A. The command to redirect to frequency A can be an RRC Release message, and the RRC Release message can include frequency A. It can be understood that frequency A is the target LTE frequency for redirection indicated by the network side during this fallback process.

[0291] Correspondingly, the terminal device can receive the instruction sent by NR to redirect to frequency point A.

[0292] S107: The terminal device starts timer T1 and timer T2.

[0293] After the terminal device receives the instruction sent by NR to redirect to frequency A, it can start timer T1 and timer T2.

[0294] It is understandable that the relevant descriptions of timer T1 and timer T2 can be referred to above and will not be repeated here.

[0295] S108: The terminal device searches for a cell based on frequency A.

[0296] The terminal device can perform a cell search based on frequency A, that is, search for a suitable LTE cell corresponding to frequency A. If the terminal device finds a suitable LTE cell on frequency A, the terminal device can attempt to access the LTE cell. It is understood that the description of the suitable LTE cell can be found above and will not be repeated here.

[0297] S109: If a suitable LTE cell is not found before the timer T1 times out, the terminal device searches for LTE frequency points in DB1 and / or DB2 according to the preset order_1.

[0298] If the terminal device has not searched for a suitable LTE cell on frequency point A until timer T1 times out, the terminal device may search for LTE frequency points in DB1 and / or DB2 according to the preset order_1.

[0299] According to the above, DB1 may include other relevant information of the LTE neighboring cell of the NR cell where the terminal device is currently residing (for example, bandwidth, RSRP, cell ID, etc.). DB2 includes the target LTE frequency of redirection indicated by the network side during one or more historical fallbacks to LTE, the frequency corresponding to the NR cell where the terminal device resided before the fallback, and the frequency corresponding to the LTE cell where the terminal device resided after the successful fallback. In other words, DB2 stores the frequency corresponding to the LTE cell where the terminal device previously resided after a successful fallback, the target LTE frequency of redirection given by the network side during the successful fallback, and the frequency corresponding to the NR cell where the terminal device resided before the fallback.

[0300] In some embodiments of the present application, DB2 may also include other relevant information (eg, bandwidth, RSRP, cell ID, etc.) of the LTE cell after successful fallback in the historical fallback to LTE process, and the present application does not impose any limitation on this.

[0301] In some embodiments of the present application, if there is no LTE frequency in the top position of DB2, the terminal device may sort the LTE frequencies in DB2 according to the sorting method mentioned in step S104 above. If there is an LTE frequency in the top position of DB2, the terminal device may sort the other LTE frequencies in DB2 except the top position according to the sorting method mentioned in step S104 above.

[0302] In some embodiments of the present application, if the terminal device has not searched for a suitable LTE cell on frequency point A until timer T1 times out, the terminal device may search for the LTE frequency points in DB1 according to the preset order_1. In one possible implementation, the preset order_1 may be the default order of DB1. It is understandable that the default order of DB1 refers to the order in which the terminal device sorts the measured LTE frequency points based on the measurement detection results, that is, the order represented by the sorting results obtained after the terminal device sorts the measured LTE frequency points. In another possible implementation, the terminal device may search for the frequency points in DB1 according to the preset order_1, which may specifically include: the terminal device may select the top y LTE frequency points in DB1, and search for the y LTE frequency points according to the sorting. In another possible implementation, the terminal device may search for the frequency points in DB1 according to the preset order_1, which may specifically include: the terminal device may select the top y LTE frequency points in DB1, measure the energy of the y LTE frequency points, reorder the y LTE frequency points from large to small according to energy, and search for the y LTE frequency points in the reordered order, that is, search for cells on the y LTE frequency points in the reordered order. In this case, the preset order_1 is the order obtained after reordering the y LTE frequency points. It can be understood that the reordering method can be referred to above and will not be repeated here.

[0303] In some embodiments of the present application, if the terminal device has not found a suitable LTE cell on frequency A before timer T1 expires, the terminal device may search the LTE frequencies in DB2 according to a preset order _1. Specifically, the terminal device may first search the top LTE frequency in DB2, and then search in order based on the ranking results of the LTE frequencies other than the top frequency.

[0304] In some embodiments of the present application, if the terminal device has not searched for a suitable LTE cell on frequency point A until timer T1 times out, the terminal device may search the LTE frequency points in DB1 and DB2 according to the preset order _1. In one possible implementation, the terminal device may search the LTE frequency points in DB1 and DB2 according to the preset order _1, which may specifically include: the terminal device first searches the LTE frequency points in DB1 according to the default order of DB1, and then searches the LTE frequency points at the top position in DB2, and finally searches in order based on the sorting results of the LTE frequency points in DB2 except the top position. In one possible implementation, the terminal device may search the LTE frequency points in DB1 and DB2 according to the preset order _1, which may specifically include: the terminal device first searches the LTE frequency points at the top position in DB2, and then searches in order based on the sorting results of the LTE frequency points in DB2 except the top position, and finally searches the LTE frequency points in DB1 according to the default order of DB1. In one possible implementation, the terminal device may search for LTE frequencies in DB1 and DB2 according to a preset order_1. Specifically, the terminal device may reorder the LTE frequencies in DB1 and DB2 and search for the corresponding LTE frequencies in order based on the ordering results. It is understood that the specific ordering method can be found above (e.g., step S104), and this application will not elaborate on this.

[0305] It is understood that the terminal device searches for the frequency points in DB1 and / or DB2, which may specifically include: the terminal device searches for a suitable LTE cell on the frequency points in DB1 and / or DB2. If the terminal device finds a suitable LTE cell on the frequency points in DB1 and / or DB2, the terminal device may attempt to access the LTE cell.

[0306] In some embodiments of the present application, compared to the access threshold used by the terminal device when searching for a suitable LTE cell at the frequency points in DB1 and / or DB2, the access threshold used by the terminal device when searching for a suitable LTE cell at frequency point A is higher. This approach can prevent the terminal device from camping on a cell with a weak signal, thereby avoiding the problem of subsequent access difficulties caused by the weak signal of the camped cell, thereby shortening the access time of the terminal device to a certain extent.

[0307] S110: If no suitable LTE cell is found after searching the frequencies in DB1 and / or DB2, the terminal device attempts to search the LTE frequencies in LTE frequency set_2.

[0308] If the terminal device fails to find a suitable LTE cell after searching the frequencies in DB1 and / or DB2, the terminal device may attempt to search the LTE frequencies in LTE frequency set_2 until timer T2 times out or a suitable LTE cell is found. It is understandable that LTE frequency set_2 includes at least one LTE frequency that is different from the one that has been searched for in this fallback. In some embodiments of the present application, LTE frequency set_2 may include some or all of the LTE frequencies in the ACQ DB. In some further embodiments of the present application, LTE frequency set_2 may include some or all of the LTE frequencies in the full band. In some further embodiments of the present application, LTE frequency set_2 may include some or all of the LTE frequencies in the prefer band.

[0309] It is understood that the present application does not restrict the order in which a terminal device searches for LTE frequencies in LTE frequency set_2. In some embodiments of the present application, a terminal device attempts to search for LTE frequencies in LTE frequency set_2. Specifically, the terminal device may first search some or all LTE frequencies in the ACQ DB, then search some or all LTE frequencies in the prefer band, and finally search some or all LTE frequencies in the full band.

[0310] It can be understood that in some embodiments of the present application, LTE frequency set_1 may include all LTE frequencies in LTE frequency set_2.

[0311] S111: If the terminal device still fails to search for a suitable LTE cell when timer T2 times out / the search for LTE frequencies in LTE frequency set _2 is completed / the EPS Fallback process times out, the terminal device selects the NR cell for access.

[0312] If the terminal device has not searched for a suitable cell when timer T2 times out, the terminal device will no longer attempt to search for the LTE frequency points in LTE frequency point set_2, and select the NR cell for access.

[0313] It is understandable that if timer T2 times out / completes the search for the LTE frequency in LTE frequency set_2 / finds a suitable LTE cell / EPS Fallback process times out, the terminal device will no longer attempt to search the network, that is, no longer attempt to search for a suitable LTE cell, and selects the NR cell for access. It is understandable that the EPS Fallback process timeout refers to the timeout of the timer started when the EPS Fallback process is triggered as specified in the protocol. It is understandable that the timer started when the EPS Fallback process is triggered as specified in the protocol may include a timer set by the terminal device (for example, timer_1), and may also include a timer set on the network side (for example, timer_2).

[0314] It can be understood that the NR cell selected for access by the terminal device when executing step S111 may be the same as or different from the NR cell in which it originally resides (i.e., the NR cell in which it resides when executing step S101).

[0315] S112: If a suitable LTE cell is searched before timer T2 times out, the terminal device initiates the RRC access and TAU process, resides in the searched suitable LTE cell, and stores the frequency corresponding to the NR cell where it resided before falling back, frequency A and the frequency corresponding to the currently located LTE cell in DB2.

[0316] If the terminal device searches for a suitable LTE cell during the frequency-based search (e.g., steps S108-S110), the terminal device initiates an RRC access and TAU process and resides on the searched suitable LTE cell. It is understood that the relevant description of the RRC access and TAU process can be found in the relevant technical documentation and is not further described here.

[0317] After the fallback is successful, the terminal device can also store the frequency corresponding to the NR cell where the terminal device resided before the fallback, the target LTE frequency (i.e., frequency A) indicated by the network side for the redirection of this fallback, and the frequency corresponding to the currently resident LTE cell in DB2. The currently resident LTE cell can be understood as the LTE cell where the terminal device resides after this fallback. It is understandable that the terminal device can store the correspondence between the frequency corresponding to the NR cell where the terminal device resided before the fallback, the target LTE frequency (i.e., frequency A) indicated by the network side for the redirection of this fallback, and the frequency corresponding to the currently resident LTE cell in DB2. In some embodiments of the present application, DB2 can use a record to represent the correspondence between the frequency corresponding to the NR cell where the terminal device resided before the fallback, the target LTE frequency (i.e., frequency A) indicated by the network side for the redirection of this fallback, and the frequency corresponding to the currently resident LTE cell. It is understandable that this record can occupy one number.

[0318] In some embodiments of the present application, the terminal device may also store other relevant information of the currently resident LTE cell (eg, bandwidth, RSRP, cell ID, etc.) into DB2.

[0319] It should be noted that in some embodiments of the present application, after the terminal device executes step S103, the measured LTE frequency points and related information may be stored in DB1 without sorting the measured LTE frequency points. Specifically, after the terminal device executes steps S101-S103, the measured LTE frequency points and related information of the LTE frequency points included in the measurement detection results may be stored in DB1, and then steps S105-S108 may be executed.

[0320] In some embodiments of the present application, after the terminal device executes step S108, if a suitable LTE cell is not found before timer T1 times out, the terminal device may search for LTE frequencies in DB1 according to preset order_1 and execute steps S110 to S112. Specifically, the terminal device may search for LTE frequencies in DB1 according to preset order_1, which may include: the terminal device may sort the LTE frequencies in DB1 and search for the LTE frequencies in DB1 according to the order obtained by the sorting.

[0321] In some embodiments of the present application, after the terminal device executes step S108, if a suitable LTE cell is not found until timer T1 times out, the terminal device can search for LTE frequencies in DB1 and DB2 according to the preset order _1, and execute steps S110-S112.

[0322] In one possible implementation, the terminal device may search for the LTE frequency points in DB1 and DB2 according to a preset order _1, which may specifically include: the terminal device may first sort the LTE frequency points in DB1, and search the LTE frequency points in DB1 according to the order obtained by the sorting, and then search the LTE frequency points at the top position in DB2, and finally sort the LTE frequency points in DB2 except the top position, and search according to the order obtained by the sorting.

[0323] In one possible implementation, the terminal device may search for the LTE frequency points in DB1 and DB2 according to a preset order _1, which may specifically include: the terminal device first searches for the LTE frequency point at the top position in DB2, and finally sorts the LTE frequency points in DB2 except the top position, and searches according to the order obtained by the sorting, and then sorts the LTE frequency points in DB1, and searches for the LTE frequency points in DB1 according to the order obtained by the sorting.

[0324] In one possible implementation, the terminal device may search for the LTE frequency points in DB1 and DB2 according to a preset order _1, which may specifically include: the terminal device re-sorts the LTE frequency points in DB1 and DB2, and searches for the corresponding LTE frequency points in order according to the sorting results.

[0325] It is understandable that the specific sorting method can be referred to above (such as step S104), and this application will not elaborate on it.

[0326] According to the above, a suitable LTE cell may be: an LTE cell whose signal quality meets the access threshold and to which the terminal device is not prohibited from access by the network. It should be noted that in some embodiments of the present application, the access threshold met by the suitable LTE cell searched for by the terminal device based on frequency point A when timer T1 is started and has not timed out is higher than the access threshold met by the suitable LTE cell searched based on DB1 and / or DB2 and / or the frequencies in LTE frequency point set_2 after timer T1 has timed out.

[0327] Another specific implementation of the above embodiment is described below.

[0328] Please refer to Figure 7B, which is a flow chart of another communication method provided in an embodiment of the present application. The communication method may include but is not limited to the following steps:

[0329] S201: The terminal device resides in the NR cell.

[0330] S202: NR sends LTE frequency information to the terminal device.

[0331] S203: The terminal device performs measurement and / or detection based on the LTE frequency information to obtain measurement and detection results.

[0332] S204: The terminal device sorts the measured LTE frequency points based on the measurement detection result, and stores the measured LTE frequency points into DB1 according to the sorting result.

[0333] S205: When the EPS Fallback process is triggered, the NR notifies the core network that the EPS Fallback process has been initiated.

[0334] S206: When the EPS Fallback process is triggered, the NR sends an instruction to redirect the terminal device to frequency A.

[0335] S207: The terminal device starts timer T1 and timer T2.

[0336] S208: The terminal device searches for a cell based on frequency A.

[0337] It is understandable that the specific implementation of steps S201 to S208 can refer to the relevant description of steps S101 to S108, which will not be repeated here.

[0338] S209: If a suitable LTE cell is not found before timer T1 times out, the terminal device searches for LTE frequencies in DB1 and ACQ DB.

[0339] In some embodiments of the present application, according to the above, the terminal device searches for the LTE frequency points in DB1 and ACQ DB, which may specifically include: the terminal device searches for the LTE frequency points in DB1 and ACQ DB according to one or more of the information such as the signal strength, bandwidth, whether it is an anchor cell, whether it is a high-speed rail cell, etc. of the LTE cell corresponding to the LTE frequency points in DB1 and ACQ DB. Sort the LTE frequency points in the DB, select the first s1 LTE frequency points, and determine whether the LTE cells corresponding to the s1 LTE frequency points are suitable LTE cells according to the energy from large to small. If no suitable LTE cell is found, the terminal device can reselect the first s2 LTE frequency points in the LTE frequency point set_1 except the s1 LTE frequency points, and determine whether the LTE cells corresponding to the s2 LTE frequency points are suitable LTE cells according to the energy from large to small. Similarly, if no suitable LTE cell is still found, the terminal device can reselect the first s3 LTE frequency points in the LTE frequency point set_1 except the s1 and s2 LTE frequency points, and determine whether the LTE cells corresponding to the s3 LTE frequency points are suitable LTE cells according to the energy from large to small. By analogy, the terminal device can search DB1 and ACQ DB according to the above method until a suitable LTE cell is found, or it is determined that the LTE cells corresponding to all LTE frequency points in DB1 and ACQ DB are not suitable LTE cells, or timer T2 times out, or the fallback process from 5G to 4G times out (for example, the timer started by the terminal device or the network side for this fallback times out).

[0340] In some embodiments of the present application, the terminal device may determine whether the LTE cells corresponding to the LTE frequencies in DB1 and ACQ DB are suitable LTE cells according to energy from large to small.

[0341] S210: If no suitable LTE cell is found after searching the frequencies in DB1 and ACQ DB, the terminal device attempts to search the LTE frequencies in LTE frequency set_3.

[0342] In some embodiments of the present application, LTE frequency set_3 may include at least one of the following: some or all LTE frequencies in DB2, some or all LTE frequencies in full band, and some or all LTE frequencies in prefer band.

[0343] It is understood that in some embodiments of the present application, LTE frequency set_1 may include all LTE frequencies in LTE frequency set_3. The LTE frequencies in LTE frequency set_2 and the LTE frequencies in LTE frequency set_3 may be partially the same or different.

[0344] S211: If the terminal device still fails to search for a suitable LTE cell when timer T2 times out / the search for the LTE frequency points in LTE frequency point set_3 is completed / the EPS Fallback process times out, the terminal device selects the NR cell for access.

[0345] S212: If a suitable LTE cell is searched before timer T2 times out, the terminal device initiates the RRC access and TAU process, resides in the searched suitable LTE cell, and stores the frequency corresponding to the NR cell where it resided before falling back, frequency A and the frequency corresponding to the currently located LTE cell in DB2.

[0346] It is understandable that the specific implementation of steps S211 and S212 can refer to the relevant description of steps S111 and S112, which will not be repeated here.

[0347] In some embodiments of the present application, LTE frequency point set_1 only includes DB1 and ACQ DB. In this case, the terminal device may not perform step S210.

[0348] Another communication method provided by an embodiment of the present application is introduced below.

[0349] Please refer to Figure 8, which is a flow chart of another communication method provided in an embodiment of the present application. The communication method may include but is not limited to the following steps:

[0350] S301: The terminal device resides in the NR cell.

[0351] S302: NR sends LTE frequency information to the terminal device.

[0352] S303: The terminal device performs measurement and / or detection based on the LTE frequency information to obtain measurement and detection results.

[0353] S304: The terminal device sorts the measured LTE frequency points based on the measurement detection result, and stores the measured LTE frequency points into DB1 according to the sorting result.

[0354] S305: When the EPS Fallback process is triggered, the NR notifies the core network that the EPS Fallback process has been initiated.

[0355] S306: When the EPS Fallback process is triggered, the NR sends an instruction to redirect the terminal device to frequency A.

[0356] It is understandable that the specific implementation of steps S301 to S306 can refer to the relevant description of steps S101 to S106, which will not be repeated here.

[0357] S307: The terminal device searches DB2 for an LTE frequency that matches frequency A and the frequency corresponding to the NR cell in which the terminal device is currently located.

[0358] It is understandable that DB2 may include the target LTE frequency point of redirection indicated by the network side during one or more historical fallbacks to LTE, the frequency point corresponding to the NR cell where the terminal device resides before the fallback, and the frequency point corresponding to the LTE cell where the terminal device resides after the successful fallback. The terminal device may search in DB2 whether there is a historical fallback process in which the target LTE frequency point of redirection indicated by the network side is frequency point A, and the frequency point corresponding to the NR cell where the terminal device resides before the historical fallback is the frequency point corresponding to the NR cell where the terminal device currently resides. If there is a historical fallback process in DB2 in which the target LTE frequency point of redirection indicated by the network side and the frequency point corresponding to the NR cell where the terminal device resides before the historical fallback are respectively the same as frequency point A and the frequency point corresponding to the NR cell where the terminal device currently resides, then the terminal device may determine in DB2 that the frequency point corresponding to the LTE cell where the terminal device resides after the successful fallback in the historical fallback process is the LTE frequency point that matches frequency point A and the NR cell where the terminal device currently resides. Otherwise, the terminal device determines that there is no LTE frequency point in DB2 that matches frequency point A and the frequency point corresponding to the NR cell where the terminal device currently resides.

[0359] In some embodiments of the present application, the terminal device may also search DB2 for the cell ID of the LTE cell that matches the frequency corresponding to the fallback frequency A and the currently resided NR cell.

[0360] S308: If there is an LTE frequency in DB2 that matches frequency A and the frequency corresponding to the NR cell where the terminal device is currently located, search for the matching LTE frequency and determine whether the LTE cell corresponding to the matching LTE frequency is a suitable LTE cell.

[0361] If there is an LTE frequency in DB2 that matches frequency A and the frequency corresponding to the currently located NR cell, the terminal device can search for the LTE cell corresponding to the LTE frequency and determine whether the corresponding LTE cell is a suitable LTE cell.

[0362] S309: If there is no LTE frequency in DB2 that matches frequency A and the currently resident NR cell, or there is an LTE frequency in DB2 that matches the fallback frequency A and the frequency corresponding to the currently resident NR cell but the LTE cell corresponding to the LTE frequency is not a suitable LTE cell, the terminal device starts timer T1 and timer T2, and performs a cell search based on frequency A.

[0363] If there is no LTE frequency matching the fallback frequency A and the frequency corresponding to the currently residing NR cell in DB2, the terminal device may start timer T1 and timer T2, and perform a cell search based on frequency A. If there is an LTE frequency matching the fallback frequency A and the frequency corresponding to the currently residing NR cell in DB2, but the LTE cell corresponding to the LTE frequency is not a suitable LTE cell, the terminal device may start timer T1 and timer T2, and perform a cell search based on frequency A.

[0364] It is understandable that the relevant description of the terminal device performing cell search based on frequency point A can be referred to above and will not be repeated here.

[0365] S310: If a suitable LTE cell is not found before timer T1 times out, the terminal device searches for the frequency points in DB1 according to the preset order_1.

[0366] In one possible implementation, preset order_1 may be the default order of DB1. It is understood that the default order of DB1 refers to the order in which the terminal device sorts the measured LTE frequencies based on the measurement detection results, that is, the order represented by the sorting result obtained after the terminal device sorts the measured LTE frequencies.

[0367] In another possible implementation, the terminal device searches for the frequency points in DB1 according to a preset order _1, which may specifically include: the terminal device may select the top y LTE frequency points in DB1 and search for the y LTE frequency points according to the order.

[0368] In another possible implementation, the terminal device searches for the frequencies in DB1 according to preset order_1. Specifically, the terminal device may select the top y LTE frequencies in DB1, reorder the y LTE frequencies, and search for the y LTE frequencies according to the reordered order. In this case, preset order_1 is the order obtained after reordering the y LTE frequencies. It is understood that the reordering method can be referred to above and will not be repeated here.

[0369] S311: If no suitable LTE cell is found after searching the frequency points in DB1, the terminal device attempts to search the LTE frequency point set_2.

[0370] In some embodiments of the present application, LTE frequency set_2 may include a target LTE frequency, that is, frequency A. In this case, the terminal device may search for frequency A again.

[0371] In some embodiments of the present application, the access threshold that the terminal device needs to meet when searching for a suitable LTE cell when executing step S309 is higher than the access threshold that the terminal device needs to meet when searching for a suitable LTE cell when executing step S311. In some embodiments of the present application, the access threshold that the terminal device needs to meet when searching for a suitable LTE cell when executing step S308 is higher than the access threshold that the terminal device needs to meet when searching for a suitable LTE cell when executing step S311. In some embodiments of the present application, the access threshold that the terminal device needs to meet when searching for a suitable LTE cell when executing steps S308 and S309 is the same. It can be understood that the access threshold that needs to be met for a suitable LTE cell can be specifically set according to actual needs, and this application does not impose specific restrictions on this.

[0372] S312: If the terminal device still fails to search for a suitable LTE cell when timer T2 times out, the terminal device no longer attempts to search for LTE frequency set_2 and selects the NR cell for access.

[0373] S313: If a suitable LTE cell is found, the terminal device initiates the RRC access and TAU process, resides in the found suitable LTE cell, and stores the frequency corresponding to the NR cell where it resided before falling back, frequency A, and the frequency corresponding to the currently located LTE cell in DB2.

[0374] It is understandable that the specific implementation of steps S310 to S313 can refer to the relevant description of steps S109 to S112, which will not be repeated here.

[0375] It should be noted that in some embodiments of the present application, the terminal device can start timer T2 in response to receiving an instruction sent by NR to redirect to frequency A, and start timer T1 when there is no LTE frequency matching frequency A and the currently resident NR cell in DB2, or when there is an LTE frequency matching the fallback frequency A and the frequency corresponding to the currently resident NR cell in DB2 but the LTE cell corresponding to the LTE frequency is not a suitable LTE cell.

[0376] It is worth noting that in some embodiments of the present application, after the terminal device executes step S303, the measured LTE frequency points and related information thereof may be stored in DB1 without sorting the measured LTE frequency points. Specifically, after the terminal device executes steps S301-S303, the measured LTE frequency points and related information of the LTE frequency points included in the measurement detection results may be stored in DB1, and then steps S305-S309 may be executed.

[0377] In some embodiments of the present application, after the terminal device executes step S309, if a suitable LTE cell is not found before timer T1 times out, the terminal device may search for LTE frequencies in DB1 according to preset order_1 and execute steps S311-S313. Specifically, the terminal device may search for LTE frequencies in DB1 according to preset order_1, which may include: the terminal device may sort the LTE frequencies in DB1 and search for the LTE frequencies in DB1 in the order obtained by the sorting.

[0378] It is understandable that the specific sorting method can be referred to above (such as step S104), and this application will not elaborate on it.

[0379] It is worth noting that the communication method when the NR cell signal is poor can refer to the above embodiment, and this application will not elaborate on it here.

[0380] The following describes the device involved in the embodiments of the present application.

[0381] FIG9 is a schematic diagram of the hardware structure of a terminal device provided in an embodiment of the present application.

[0382] As shown in Figure 9, the structure of the terminal device may include: a processor, an external memory interface, an internal memory, a Universal Serial Bus (USB) interface, a charging management module, a power management module, a battery, antenna 1, antenna 2, a mobile communication module, a wireless communication module, a sensor module, buttons, a motor, an indicator, a camera, a display, and a SIM card slot. The audio module may include a speaker, a receiver, a microphone, and a headphone jack, and the sensor module may include a pressure sensor, a gyroscope sensor, an air pressure sensor, a magnetic sensor, an acceleration sensor, a distance sensor, a proximity light sensor, a fingerprint sensor, a temperature sensor, a touch sensor, an ambient light sensor, and a bone conduction sensor.

[0383] It is understood that the structures illustrated in the embodiments of this application do not constitute specific limitations on the terminal device. In other embodiments, the terminal device may include more or fewer components than shown, or may combine or separate certain components, or arrange the components differently. The illustrated components may be implemented in hardware, software, or a combination of software and hardware.

[0384] The processor may include one or more processing units, for example, the processor may include an application processor (AP), a modem processor (also known as a baseband processor), a graphics processor (GPU), an image signal processor (ISP), a controller, a video codec, a digital signal processor (DSP), and / or a neural-network processing unit (NPU). Different processing units may be independent devices or integrated into one or more processors. The processor is the nerve center and command center of the terminal device. The controller can generate operation control signals based on instruction opcodes and timing signals to complete the control of instruction fetching and execution.

[0385] The wireless communication function of the terminal device can be implemented through antenna 1, antenna 2, a mobile communication module, a wireless communication module, and a modem. In some embodiments, antenna 1 of the terminal device is coupled to the mobile communication module, and antenna 2 is coupled to the wireless communication module, so that the terminal device can communicate with the network and other devices through wireless communication technology.

[0386] The operating system of the terminal device can adopt a layered architecture, an event-driven architecture, a micro-kernel architecture, a microservice architecture, or a cloud architecture. The embodiment of the present application takes the Android system with a layered architecture as an example to illustrate the software structure of the terminal device. It should be noted that although the embodiment of the present application is described using the Android system as an example, its basic principles are also applicable to terminals based on operating systems such as iOS or Windows.

[0387] FIG10 is a schematic diagram of the software structure of a terminal device provided in an embodiment of the present application.

[0388] The software structure of a terminal device adopts a layered architecture, which divides the software into several layers, each with a clear role and division of labor. Layers communicate with each other through software interfaces. Taking the Android system running on an AP as an example, in some embodiments, the Android system is divided into five layers: from top to bottom: the application layer, the application framework layer (Framework), the Android runtime (Android runtime) and system libraries, the hardware abstraction layer (HAL), and the system kernel layer (Kernel).

[0389] The application layer can include a series of application packages. These packages may include apps such as camera, gallery, calendar, call, map, WLAN, Bluetooth, music, video, and short messaging. The application layer may also include the system UI, which is used to display the terminal device interface, such as the signal icon corresponding to the SIM card and the call interface. The application framework layer provides the application programming interface (API) and programming framework for applications in the application layer. The application framework layer includes some predefined functions. For example, the application framework layer may include a window manager, content provider, view system, phone manager, resource manager, notification manager, etc. The phone manager is used to provide call functions for the terminal device, such as call status management (including answering and hanging up). The phone manager is represented by the telephony in Figure 10. The application framework layer may also include the radio interface layer (RIL), through which the modem processor (modem) can exchange information with the telephony.

[0390] The modem can include the physical (PHY) layer, the medium access control (MAC) layer, the radio link control (RLC) layer, the packet data convergence protocol (PDCP) layer, the RRC layer, and the non-access stratum (NAS). The specific meanings of the PHY, MAC, RLC, PDCP, RRC, and NAS layers can be found in relevant technical documentation and are not detailed here. Each of these layers can be a software module. The modem can interact with the base station via an antenna.

[0391] In some embodiments of the present application, the RRC layer in the modem can receive an RRC Release message sent by the network side and send the LTE frequency to the underlying layer (e.g., the MAC layer) for the underlying layer to search for a suitable LTE cell. The methods provided in some embodiments of the present application can be primarily controlled or executed by the RRC layer.

[0392] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A communication method, characterized in that: Applied to terminal equipment; the method comprises: The terminal device resides in a first cell; the first cell is a new wireless / new air interface NR cell; The terminal device starts a first timer and a second timer in response to receiving a first message; the first message carries an indication of redirection to a target Long Term Evolution LTE frequency point; the target LTE frequency point is a redirected LTE frequency point indicated by the network side; the duration of the first timer is less than the duration of the second timer; and the interval between the start time of the first timer and the start time of the second timer is shorter; The terminal device searches for an LTE cell that meets a first preset condition based on the target LTE frequency point; If an LTE cell satisfying the first preset condition is not found until the first timer times out, the terminal device searches for an LTE cell satisfying the second preset condition based on a first LTE frequency point set; the first LTE frequency point set includes at least one LTE frequency point different from the target LTE frequency point; If an LTE cell satisfying the second preset condition is searched before the second timer times out, the terminal device resides in the searched LTE cell satisfying the second preset condition.

2. The method according to claim 1, characterized in that The first message is a radio resource control release RRC Release message; the method also includes: if an LTE cell that meets the second preset condition is not searched until the second timer times out, the terminal device selects a second cell to reside in; the second cell is an NR cell.

3. The method according to claim 1 or 2, characterized in that The first preset condition is the same as or different from the second preset condition.

4. The method according to claim 3, characterized in that The first preset condition is different from the second preset condition, specifically including: a preset access threshold corresponding to the second preset condition is lower than the preset access threshold corresponding to the first preset condition; and the preset access threshold is a signal quality threshold for allowing access to an LTE cell.

5. The method according to any one of claims 1 to 4, characterized in that The duration of the first timer is less than the duration of the third timer started by the network side; the third timer is used for the duration of the network side controlling the fallback.

6. The method according to any one of claims 1 to 5, characterized in that The duration of the second timer is not less than the duration of the third timer started by the network side, and is not greater than x times the duration of the third timer; the third timer is used for the duration of the network side to control the fallback; x is not less than 1 and not greater than 2.

7. The method according to claim 5 or 6, characterized in that The duration of the three timers is 5 seconds.

8. The method according to any one of claims 1 to 7, characterized in that The first LTE frequency set includes first LTE frequency information and historical LTE frequency; the first LTE frequency information includes an LTE frequency corresponding to an LTE neighboring cell of the first cell; the historical LTE frequency includes an LTE frequency corresponding to an LTE cell where the terminal device has resided; The terminal device searches for an LTE cell that meets a second preset condition based on the first LTE frequency point set, specifically including: The terminal device determines whether the LTE frequency in the first LTE frequency information and the LTE cell corresponding to the historical LTE frequency meet the second preset condition.

9. The method according to claim 8, characterized in that The terminal device determines whether the LTE frequency in the first LTE frequency information and the LTE cell corresponding to the historical LTE frequency meet the second preset condition, specifically including: The terminal device selects a group of LTE frequencies from the LTE frequencies in the first LTE frequency information and the historical LTE frequencies, and determines, in descending order of energy, whether the LTE cells corresponding to the group of LTE frequencies meet the second preset condition; If none of the LTE cells corresponding to the group of LTE frequencies meets the second preset condition, the terminal device again performs the step of selecting a group of LTE frequencies from the LTE frequencies in the first LTE frequency information and the historical LTE frequencies, and determining in descending order of energy whether the LTE cells corresponding to the group of LTE frequencies meet the second preset condition, until all the LTE frequencies in the first LTE frequency information and the historical LTE frequencies are selected; Among them, the LTE frequency selected by the terminal device again from the LTE frequencies in the first LTE frequency information and the historical LTE frequencies is different from the LTE frequencies previously selected by the terminal device from the LTE frequencies in the first LTE frequency information and the historical LTE frequencies.

10. The method according to claim 9, characterized in that The first LTE frequency point set also includes second LTE frequency point information; The terminal device searches for an LTE cell that meets a second preset condition based on the first LTE frequency point set, specifically including: If the LTE frequency in the first LTE frequency information and the LTE cell corresponding to the historical LTE frequency do not meet the second preset condition, the terminal device searches for an LTE cell that meets the second preset condition based on the second LTE frequency information.

11. The method according to claim 10, characterized in that The second LTE frequency information specifically includes at least one of the following: an LTE frequency in the entire frequency band, and an LTE frequency in the preferred frequency band.

12. The method according to any one of claims 9 to 11, characterized in that The terminal device selects a group of LTE frequencies from the LTE frequencies in the first LTE frequency information and the historical LTE frequencies, specifically including: The terminal device sorts the LTE frequencies in the first LTE frequency information and the historical LTE frequencies based on one or more of the signal strength, bandwidth, whether it is an anchor cell, and whether it is a high-speed railway cell of the LTE cells corresponding to the LTE frequencies in the first LTE frequency information and the historical LTE frequencies, and selects the first s1 LTE frequencies as a group of LTE frequencies; s1 is a positive integer.

13. The method according to any one of claims 1 to 7, characterized in that The first LTE frequency point set includes first LTE frequency point information; the first LTE frequency point information includes an LTE frequency point corresponding to an LTE neighboring cell of the first cell; The terminal device searches for an LTE cell that meets a second preset condition based on the first LTE frequency point set, specifically including: The terminal device determines whether the LTE cell corresponding to the LTE frequency in the first LTE frequency information meets the second preset condition.

14. The method according to claim 13, characterized in that The first LTE frequency point set also includes third LTE frequency point information; The terminal device searches for an LTE cell that meets a second preset condition based on the first LTE frequency point set, specifically including: If none of the LTE cells corresponding to the LTE frequencies in the first LTE frequency information meets the second preset condition, The terminal device searches for an LTE cell that meets the second preset condition based on the third LTE frequency information.

15. The method according to claim 14, characterized in that The third LTE frequency information specifically includes at least one of the following: historical LTE frequency, LTE frequency in the full frequency band, and LTE frequency in the preferred frequency band.

16. The method according to any one of claims 1 to 7, characterized in that The first LTE frequency set includes first LTE frequency information and historical fallback information; the first LTE frequency information includes the LTE frequency corresponding to the LTE neighboring cell of the first cell; the historical fallback information includes at least one historical fallback record; each of the historical fallback records includes the following information during a historical fallback process in which the terminal device successfully falls back from NR to LTE: the redirected LTE frequency indicated by the network side, the frequency corresponding to the NR cell where the terminal device resides before the fallback, and the frequency corresponding to the LTE cell where the terminal device resides after the fallback; The terminal device searches for an LTE cell that meets a second preset condition based on the first LTE frequency point set, specifically including: The terminal device determines whether the LTE cell corresponding to the LTE frequency in the first LTE frequency information meets the second preset condition, and determines whether the historical fallback information includes a first historical fallback record; the frequency corresponding to the NR cell in which the terminal device resides before the fallback included in the first historical fallback record is the frequency corresponding to the first cell; the redirected LTE frequency indicated by the network side included in the first historical fallback record is the target LTE frequency; If the historical fallback information includes the first historical fallback record, the terminal device searches for an LTE cell that meets the second preset condition based on the frequency corresponding to the LTE cell in which the terminal device resides after the fallback included in the first historical fallback record.

17. The method according to claim 16, characterized in that The method further comprises: If the LTE cell corresponding to the LTE frequency in the first LTE frequency information meets the second preset condition, and / or the terminal device searches for an LTE cell that meets the second preset condition based on the frequency corresponding to the LTE cell where the terminal device resides after the fallback included in the first historical fallback record, the terminal device resides in the LTE cell that meets the second preset condition.

18. The method according to claim 16 or 17, characterized in that The method further comprises: If the LTE cell corresponding to the LTE frequency in the first LTE frequency information does not meet the second preset condition, and the terminal device does not search for an LTE cell that meets the second preset condition based on the frequency corresponding to the LTE cell where the terminal device resides after the fallback included in the first historical fallback record, the terminal device searches for an LTE cell that meets the second preset condition based on the fourth LTE frequency information.

19. The method according to claim 18, characterized in that The fourth LTE frequency information specifically includes at least one of the following: a historical LTE frequency, an LTE frequency in a full frequency band, and an LTE frequency in a preferred frequency band.

20. The method according to any one of claims 13 to 19, characterized in that The first LTE frequency point information includes multiple LTE frequency points, and the multiple LTE frequency points include LTE frequency points corresponding to multiple LTE neighboring cells of the first cell respectively; The terminal device determines whether the LTE cell corresponding to the LTE frequency in the first LTE frequency information meets the second preset condition, specifically including: the terminal device determines whether the LTE cells corresponding to the multiple LTE frequencies meet the second preset condition in order from large to small according to signal strength.

21. The method according to any one of claims 13 to 19, characterized in that After the terminal device resides on the first cell, the method further includes: The terminal device receives fifth LTE frequency information sent by the network device corresponding to the first cell; the fifth LTE frequency information includes an LTE frequency corresponding to an LTE neighboring cell of the first cell; The terminal device measures the signal strength of the LTE cell corresponding to the LTE frequency included in the fifth LTE frequency information, and / or detects the bandwidth of the LTE cell corresponding to the LTE frequency included in the fifth LTE frequency information, and / or detects whether the LTE cell corresponding to the LTE frequency included in the fifth LTE frequency information is an anchor cell, to obtain a first result; The terminal device sorts the LTE frequencies in the fifth LTE frequency information based on the first result to obtain the first LTE frequency information; The terminal device determines whether the LTE cell corresponding to the LTE frequency in the first LTE frequency information meets the second preset condition, specifically including: the terminal device determines whether the LTE cell corresponding to the LTE frequency in the first LTE frequency information meets the second preset condition in sequence according to the sorted result.

22. The method according to any one of claims 1 to 21, characterized in that The LTE cell that meets the first preset condition specifically includes: an LTE cell whose signal strength is greater than a first preset access threshold and the network side does not prohibit the terminal device from accessing; The LTE cell that meets the second preset condition specifically includes: an LTE cell whose signal strength is greater than the second preset access threshold and the network side does not prohibit the terminal device from accessing.

23. A communication method, characterized in that: Applied to terminal equipment; the method comprises: The terminal device resides in a first cell; the first cell is an NR cell; The terminal device determines, in response to receiving the first message, whether the historical fallback information includes a first historical fallback record; the first message carries an indication of redirection to a target LTE frequency; the target LTE frequency is a redirected LTE frequency indicated by the network side; the historical fallback information includes at least one historical fallback record; each of the historical fallback records includes the following information during a historical fallback process in which the terminal device successfully falls back from NR to LTE: the redirected LTE frequency indicated by the network side, the frequency corresponding to the NR cell where the terminal device resides before the fallback, and the frequency corresponding to the LTE cell where the terminal device resides after the fallback; the NR cell where the terminal device resides before the fallback included in the first historical fallback record is the first cell, and the redirected LTE frequency indicated by the network side included in the first historical fallback record is the target LTE frequency; If the historical fallback information includes the first historical fallback record, the terminal device searches for an LTE cell that meets a first preset condition based on a frequency corresponding to the LTE cell where the terminal device resides after the fallback, as included in the first historical fallback record.

24. The method of claim 23, wherein: The method further comprises: If the historical fallback information does not include the first historical fallback record, or the terminal device does not search for an LTE cell that meets the first preset condition based on the frequency corresponding to the LTE cell where the terminal device resides after falling back, the terminal device starts a first timer and searches for an LTE cell based on the target LTE frequency. An LTE cell that meets the first preset condition; If the terminal device has not searched for an LTE cell that meets the first preset condition based on the target LTE frequency point until the first timer times out, the terminal device searches for an LTE cell that meets the second preset condition based on a second LTE frequency point set.

25. The method according to claim 23 or 24, characterized in that The first preset condition is the same as or different from the second preset condition; the first preset condition is different from the second preset condition, specifically including: the preset access threshold corresponding to the second preset condition is lower than the preset access threshold corresponding to the first preset condition; the preset access threshold is the signal quality threshold for allowing access to the LTE cell.

26. The method according to any one of claims 23 to 25, characterized in that The duration of the first timer is less than the duration of the third timer started by the network side; the third timer is used for the duration of the network side controlling the fallback.

27. The method according to any one of claims 23 to 26, characterized in that The duration of the second timer is not less than the duration of the third timer started by the network side, and is not greater than x times the duration of the third timer; the third timer is used for the duration of the network side to control the fallback; x is not less than 1 and not greater than 2.

28. The method according to claim 26 or 27, characterized in that The duration of the three timers is 5 seconds.

29. The method of claim 24, wherein: The second LTE frequency set includes first LTE frequency information and third LTE frequency information; the first LTE frequency information includes an LTE frequency corresponding to an LTE neighboring cell of the first cell; The terminal device searches for an LTE cell that meets the second preset condition based on the second LTE frequency point set, specifically including: The terminal device determines whether the LTE cell corresponding to the LTE frequency in the first LTE frequency information meets the second preset condition; If none of the LTE cells corresponding to the LTE frequencies in the first LTE frequency information satisfy the second preset condition, the terminal device searches for an LTE cell that satisfies the second preset condition based on the third LTE frequency information.

30. The method of claim 29, wherein: The third LTE frequency point information specifically includes: at least one of a historical LTE frequency point, an LTE frequency point in a full frequency band, and an LTE frequency point in a preferred frequency band.

31. The method according to any one of claims 23 to 30, characterized in that The method further comprises: The terminal device starts a second timer in response to the first message; If an LTE cell satisfying the first preset condition is searched before the first timer times out, the terminal device resides in the searched LTE cell satisfying the first preset condition; If an LTE cell satisfying the second preset condition is searched when the first timer times out and the second timer does not time out, the terminal device resides in the searched LTE cell satisfying the second preset condition; If an LTE cell that meets the first preset condition or the second preset condition is not found until the second timer times out, the terminal device selects a second cell to reside in; the second cell is an NR cell.

32. The method according to any one of claims 23 to 30, characterized in that The method further comprises: If the historical fallback information does not include the first historical fallback record, or the terminal device fails to search for an LTE cell that meets the second preset condition based on the frequency corresponding to the LTE cell where the terminal device resides after the fallback included in the first historical fallback record, the terminal device starts a second timer; the interval between the start time of the first timer and the start time of the second timer is shorter; If an LTE cell satisfying the first preset condition is searched before the first timer times out, the terminal device resides in the searched LTE cell satisfying the first preset condition; If an LTE cell satisfying the second preset condition is searched when the first timer times out and the second timer does not time out, the terminal device resides in the searched LTE cell satisfying the second preset condition; If an LTE cell that meets the first preset condition or the second preset condition is not found until the second timer times out, the terminal device selects a second cell to reside in; the second cell is an NR cell.

33. A terminal device, characterized in that: It includes a processor and a memory, wherein the processor calls and executes a computer program stored in the memory, so that the terminal device implements the method as claimed in any one of claims 1 to 22 or any one of claims 23 to 32.

34. A chip system, applied to a terminal device, characterized in that: The chip system includes at least one processor and an interface, wherein the interface is used to receive instructions and transmit them to the at least one processor; the at least one processor executes the instructions so that the terminal device executes the method as described in any one of claims 1-22 or any one of claims 23-32.

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