Communication method and device

Abstract

The present application relates to the communication technology field and discloses a communication method and an apparatus. The method includes: a terminal device receives, in a first cell, configuration information of at least one candidate cell from an access network device; and when the radio link of the first cell meets a first condition (i.e., a problem occurs in the radio link of the first cell), selects a second cell. If the second cell belongs to the at least one candidate cell, the terminal device is handed over from the first cell to the second cell, and communicates with the access network device in the second cell based on the configuration information of the second cell. In this way, the terminal device can be handed over to the second cell after a problem occurs in the radio link of the first cell, and communicates with the access network device based on the configuration information of the second cell received in the first cell. This can effectively save transmission resources and quickly restore the radio link. Alternatively, if the second cell does not belong to the at least one candidate cell, the terminal device performs RRC re-establishment to access the second cell to restore the radio link.

Description

Technical Field

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[0001] Cross - reference to related applications This application claims priority to Chinese Patent Application No. 202210188271.9, titled "Communication Method and Apparatus", filed with the China National Intellectual Property Administration on February 28, 2022, and the entire content of the Chinese patent application is incorporated herein by reference.

[0002] This application relates to the field of communication technology, and particularly to communication methods and apparatuses.

Background Art

[0003] With the continuous development of science and technology, new Internet services such as autonomous driving and virtual reality are constantly emerging. Therefore, increasingly high requirements are imposed on wireless communication technology.

[0004] In a wireless communication system, the wireless link quality directly determines the data transmission capacity. Therefore, after the terminal device detects that a problem has occurred in the wireless link, further research is needed on how to recover the wireless link.

Summary of the Invention

[0005] This application provides a communication method and apparatus to quickly recover a wireless link after a terminal device detects that a problem has occurred in the wireless link.

Means for Solving the Problems

[0006] According to a first aspect, one embodiment of the present application provides a communication method. The method may be applied to a terminal device or a module within a terminal device. For example, the method is applied to a terminal device. In the method, the terminal device receives configuration information for at least one candidate cell from an access network device in a first cell, and if the radio link of the first cell satisfies a first condition (i.e., a problem occurs in the radio link of the first cell), it selects a second cell, and if the second cell belongs to at least one candidate cell, the terminal device is handed over from the first cell to the second cell and communicates with the access network device in the second cell based on the configuration information for the second cell received in the first cell, or if the second cell does not belong to at least one candidate cell, the terminal device performs RRC re-establishment to access the second cell.

[0007] According to the method described above, after detecting a problem with the current serving cell's wireless link, the terminal device does not need to release the configuration information of at least one candidate cell. Therefore, after the terminal device selects one of the candidate cells as the new serving cell, it can communicate with the access network device based on the configuration information of the new serving cell, and the access network device does not need to retransmit the configuration information of the new serving cell to the terminal device. This effectively saves transmission resources and allows for a rapid recovery of the wireless link.

[0008] In one possible design, the radio link quality of a first cell satisfies a first condition which includes at least one of the following: the radio link quality of the first cell is below a first threshold; the radio link quality of the first cell is always below a first threshold in a first time window; the number of asynchronous instructions continuously detected by the terminal device is greater than or equal to a second threshold; after the number of asynchronous instructions continuously detected by the terminal device becomes greater than or equal to the second threshold, the terminal device starts a timer and does not detect a synchronous instruction within the timer's timing window; and a radio link failure (RLF) occurs in the first cell.

[0009] In one possible design, the method further includes the step of receiving first information from an access network device in a first cell, wherein the first information is used to constitute a first condition.

[0010] In one possible design, the wireless link quality of the second cell satisfies the second condition, which means that the wireless link quality of the second cell is greater than or equal to the third threshold, that the wireless link quality of the second cell is always greater than or equal to the third threshold in the second time window, that the wireless link quality of the second cell is greater than or equal to the wireless link quality of at least one candidate cell other than the second cell, and that the wireless link quality of the second cell is always greater than or equal to the wireless link quality of at least one candidate cell in the second time window The wireless link quality of the second cell is greater than or equal to that of the other candidate cells; the wireless link quality of the second cell is greater than that of the first cell; the wireless link quality of the second cell is always greater than that of the first cell in the second time window; the wireless link quality of the second cell is greater than the sum of the wireless link quality of the first cell and the offset; and the wireless link quality of the second cell is always greater than the sum of the wireless link quality of the first cell and the offset in the second time window.

[0011] In one possible design, the method further includes the step of receiving second information from an access network device in a first cell, wherein the second information is used to constitute a second condition.

[0012] In one possible design, the method further includes the step of transmitting third information to an access network device in a second cell, the third information indicating that a terminal device has been handed over from a first cell to a second cell, and that this handover is a cell handover triggered by the terminal device.

[0013] In one possible design, the third information includes at least one of the following: an identifier for a terminal device, an identifier for a first cell, downlink beam information used by an access network device to transmit downlink data to a terminal device in a second cell, and instruction information, the instruction information indicating a cell handover triggered by the terminal device.

[0014] In one possible design, the third piece of information is carried by messages in a random access procedure initiated by a terminal device in the second cell.

[0015] In one possible design, the method further includes the step of transmitting fourth information to an access network device in a second cell, wherein the fourth information is carried over a first resource, and the first resource is a resource corresponding to a cell handover triggered by a terminal device.

[0016] In one possible design, the method further includes the step of receiving enable information from an access network device in a first cell, the enable information being used to enable the terminal device to trigger a cell handover after a problem occurs in the wireless link of the serving cell of the terminal device.

[0017] In this way, access network devices can control, based on enable information, whether a terminal device triggers a cell handover after a problem occurs with the serving cell's wireless link. This helps access network devices have flexible control over the behavior of terminal devices.

[0018] In one possible design, at least one candidate cell includes a candidate cell corresponding to a Layer 1 / Layer 2 handover and / or a candidate cell corresponding to a Layer 3 handover.

[0019] According to a second aspect, one embodiment of the present application provides a communication method. The method may be applied to a second DU or a module within the second DU. For example, the method is applied to a second DU. In the method, the second DU determines that a terminal device has been handed over from a first cell to a second cell, and this handover is a cell handover triggered by the terminal device. If the first and second cells belong to separate DUs, first instruction information is sent to the CU, which indicates that the terminal device has been handed over from the first cell to the second cell, so that the CU knows that the terminal device has been handed over from the first cell to the second cell. Alternatively, if both the first and second cells belong to the second DU, the first and fourth instruction information are sent to the CU, and the fourth instruction information indicates the data packets that were not successfully sent to the terminal device by the second DU. After the terminal device performs a handover, the CU can send data packets to the terminal device based on the data packets that were not successfully sent to the terminal device by the second DU, thus avoiding data packet loss or retransmission.

[0020] In one possible design, the step of determining that a terminal device has been handed over from a first cell to a second cell includes the step of receiving third information from the terminal device, wherein the third information indicates that the terminal device has been handed over from a first cell to a second cell, or the step of receiving fourth information from the terminal device, wherein the fourth information is carried on a first resource, and the first resource is a resource corresponding to a cell handover triggered by the terminal device.

[0021] In one possible design, the first instruction information includes data quantity information already cached by the second DU, or the method further includes the step of sending data quantity information already cached by the second DU to the CU.

[0022] In this way, the second DU sends data volume information already cached to the CU. This helps the CU control the downlink data traffic sent to terminal devices through the second DU.

[0023] In one possible design, the third instruction information includes at least one of the sequence numbers of PDCP PDUs that were not successfully transmitted and the highest sequence number of PDCP PDUs that were successfully transmitted.

[0024] In one possible design, the third instruction information is carried in a user plane data frame or a control plane message.

[0025] According to a third aspect, one embodiment of the present application provides a communication method. The method may be applied to a CU or a module within a CU. For example, the method is applied to a CU. In the method, the CU transmits second instruction information to a first DU, the second instruction information indicating that a terminal device has been handed over from a first cell to a second cell, the handover being a cell handover triggered by the terminal device, the first cell belonging to a first DU, and the second cell belonging to a second DU; the CU receives third instruction information from the first DU, the third instruction information indicating a data packet that was not successfully transmitted to the terminal device by the first DU; and the CU transmits the data packet to the terminal device through the second DU based on the third instruction information.

[0026] In this way, the CU can receive the third instruction information, so that after the terminal device performs a handover, the CU can send data packets to the terminal device based on the data packets that were not successfully sent to the terminal device by the first DU, thus avoiding data packet loss or retransmission.

[0027] In one possible design, the method further includes the step of receiving first instruction information from a second DU, wherein the first instruction information indicates that a terminal device has been handed over from a first cell to a second cell.

[0028] In one possible design, the third indication information includes at least one of the sequence number of the PDCP PDUs not transmitted successfully and the highest sequence number of the PDCP PDUs transmitted successfully.

[0029] According to a fourth aspect, an embodiment of the present application provides a communication method. The method can be applied to a first DU or a module within the first DU. For example, the method is applied to the first DU. In the method, the first DU receives second indication information from a CU, where the second indication information indicates that a terminal device has been handed over from a first cell to a second cell, and this handover is a cell handover triggered by the terminal device, the first cell belongs to the first DU, the second cell belongs to a second DU, and the first DU transmits third indication information to the CU based on the second indication information, where the third indication information indicates data packets not transmitted successfully to the terminal device by the first DU.

[0030] In this way, since the first DU can transmit the third indication information to the CU, after the terminal device performs the handover, the CU can transmit data packets to the terminal device based on the data packets not transmitted successfully to the terminal device by the first DU, and loss or retransmission of the data packets is avoided.

[0031] In one possible design, the third indication information includes at least one of the sequence number of the PDCP PDUs not transmitted successfully and the highest sequence number of the PDCP PDUs transmitted successfully.

[0032] According to a fifth aspect, one embodiment of the present application provides a communication method. The method may be applied to a first DU or a module within the first DU. For example, the method is applied to a first DU. In the method, the first DU sends a handover command to a terminal device, the handover command instructs the handover of the terminal device from a first cell to a second cell, the first cell belonging to a first DU, the second cell belonging to a second DU, and the first DU sends third instruction information to a CU, the third instruction information instructing data packets that were not successfully transmitted to the terminal device by the first DU.

[0033] In one possible design, the handover instruction includes downlink beam information used by a second DU to transmit downlink data to a terminal device.

[0034] According to a sixth aspect, one embodiment of the present application provides a communication method. The method may be applied to a CU or a module within a CU. For example, the method is applied to a CU. In the method, the CU receives notification information and third instruction information from a first DU, the notification information is used to notify the CU that a terminal device has been handed over from a first cell to a second cell, the third instruction information indicates a data packet that was not successfully transmitted to the terminal device by the first DU, the first cell belongs to the first DU, the second cell belongs to the second DU, and the CU transmits the data packet to the terminal device through the second DU.

[0035] In one possible design, the method further includes the step of receiving data volume information already cached by a second DU.

[0036] According to a seventh aspect, one embodiment of the present application provides a communication method. The method may be applied to a second DU or a module within the second DU. For example, the method is applied to a second DU. In the method, the second DU receives handover completion information from a terminal device, the handover completion information indicates that the terminal device has been handed over from a first cell to a second cell, the first cell belongs to a first DU, the second cell belongs to a second DU, and the second DU transmits data amount information already cached by the second DU to a CU based on the handover completion information.

[0037] In one possible design, the handover completion information includes downlink beam information used by a second DU to transmit downlink data to a terminal device.

[0038] According to the eighth aspect, the present application provides a communication device, which is, for example, a terminal device. The communication device has the function of implementing the first aspect. For example, the communication device includes a corresponding module, unit, or means for performing the work of the first aspect. The module, unit, or means may be implemented using software, or using hardware, or using hardware that runs the corresponding software.

[0039] In one possible design, the communication device includes a processing unit and a communication unit. The communication unit may be configured to receive / transmit signals in order to communicate between the communication device and another device. The processing unit may be configured to perform some internal operations of the communication device. The functions performed by the processing unit and the communication unit may correspond to the operations of the first embodiment.

[0040] In one possible design, the communication device includes a processor, which may be coupled to memory. The memory can store computer programs or instructions necessary to perform the function in the first embodiment. The processor can execute the computer programs or instructions stored in memory. Once the computer programs or instructions are executed, the communication device becomes capable of performing any one of the possible designs or implementations of the first embodiment.

[0041] In one possible design, the communication device includes a processor and memory. The memory can store computer programs or instructions necessary to perform a function in the first embodiment. The processor can execute the computer programs or instructions stored in memory. Once the computer programs or instructions are executed, the communication device becomes capable of performing a method according to any one of the possible designs or implementations of the first embodiment.

[0042] In one possible design, the communication device includes a processor and an interface circuit, the processor being configured to communicate with another device through the interface circuit and to perform a method according to any one of the possible designs or implementations of the first embodiment.

[0043] According to the ninth aspect, the present application provides a communication device. The communication device is, for example, an access network device, which may include a CU and one or more DUs. The communication device has a function that implements any one of the second to seventh aspects. For example, the communication device includes a corresponding module, unit, or means for performing the work of any one of the second to seventh aspects. The function, unit, or means may be implemented using software, or using hardware, or using hardware that runs the corresponding software.

[0044] In one possible design, the communication device includes a processing unit and a communication unit. The communication unit may be configured to receive / transmit signals in order to communicate between the communication device and another device. For example, the communication unit may be configured to send system information to a terminal device. The processing unit may be configured to perform some internal tasks of the communication device. The functions performed by the processing unit and the communication unit may correspond to any one of the tasks in the second through seventh embodiments.

[0045] In one possible design, the communication device includes a processor, which may be coupled to memory. The memory can store computer programs or instructions necessary to perform a function in any one of the second through seventh embodiments. The processor can execute the computer programs or instructions stored in memory. Once the computer programs or instructions are executed, the communication device becomes capable of performing a method in any one of the possible designs or implementations of the second through seventh embodiments.

[0046] In one possible design, the communication device includes a processor and memory, the memory being capable of storing computer programs or instructions necessary to perform a function in any one of the second through seventh embodiments. The processor is capable of executing the computer programs or instructions stored in memory. Once the computer programs or instructions are executed, the communication device becomes capable of performing a method in any one of the possible designs or implementations of the second through seventh embodiments.

[0047] In one possible design, the communication device includes a processor and an interface circuit, the processor being configured to communicate with another device through the interface circuit and to perform a method according to any one of the possible designs or implementations of the second through seventh embodiments.

[0048] In the eighth and ninth embodiments, it will be understood that the processor may be implemented in hardware or software. When the processor is implemented in hardware, it may be a logic circuit or an integrated circuit, etc. When the processor is implemented in software, it may be a general-purpose processor and is implemented by reading software code stored in memory. In addition, there may be one or more processors and one or more memories. The memory may be integrated with the processor, or the memory and processor may be located separately. In the specific implementation process, the memory and processor may be integrated on the same chip, or they may be located separately on different chips. The type of memory and the arrangement of the memory and processor are not limited in the embodiments of this application.

[0049] According to the tenth aspect, the present application provides a communication system. The communication system may include a communication device according to the eighth aspect, and may further include a communication device according to the ninth aspect.

[0050] According to the eleventh aspect, the present application provides a computer-readable storage medium. The computer storage medium stores computer-readable instructions, and when a computer reads and executes the computer-readable instructions, the computer is able to perform a method according to any one of the possible designs of the first to seventh aspects.

[0051] According to the twelfth aspect, the present application provides a computer program product. When a computer reads and executes the computer program product, the computer is able to perform a method according to any one of the possible designs of the first to seventh aspects.

[0052] According to the 13th aspect, the present application provides a chip comprising a processor, which is coupled to memory and configured to read and execute a software program stored in memory in order to carry out a method according to any one of the possible designs of the first to seventh aspects.

[0053] These or other aspects of this application are more clearly and easily understood in the following description of embodiments. [Brief explanation of the drawing]

[0054] [Figure 1] This is a diagram of a communication system to which one embodiment of this application can be applied. [Figure 2A] This is a diagram of a CU-DU partitioning architecture according to one embodiment of the present application. [Figure 2B] This is a diagram of another CU-DU partitioning architecture according to one embodiment of the present application. [Figure 3] This is a schematic flowchart corresponding to a communication method according to one embodiment of this application. [Figure 4] This is a schematic flowchart corresponding to a communication method according to one embodiment of this application. [Figure 5] This is a schematic flowchart corresponding to a communication method according to one embodiment of this application. [Figure 6] This is a schematic flowchart corresponding to a communication method according to one embodiment of this application. [Figure 7] This is a schematic flowchart corresponding to a communication method according to one embodiment of this application. [Figure 8] This is a block diagram of a possible example of a device according to one embodiment of this application. [Figure 9] This is a diagram showing the structure of an access network device according to one embodiment of this application. [Figure 10] This is a diagram showing the structure of a terminal device according to one embodiment of this application. [Modes for carrying out the invention]

[0055] The following describes the technical solutions of the embodiments of this application with reference to the accompanying drawings of the embodiments of this application.

[0056] Figure 1 is a diagram of a communication system to which one embodiment of the present application can be applied. As shown in Figure 1, the communication system 10 includes one or more access network devices 20 and one or more terminal devices 30. The interface between the access network device and the terminal device may be a Uu interface (or referred to as an air interface), and data may be transmitted between the access network device 20 and the terminal device 30 through the air interface resource. For example, a terminal device may be located within the communication coverage of one or more cells of the access network device, and there may be one or more cells serving the terminal device. If there are multiple cells serving the terminal device, the terminal device may operate using one or more transmission techniques such as carrier aggregation (CA), dual connectivity (DC), coordinated multipoint (CoMP) transmission, and multiple transmission and reception point (mTRP).

[0057] (1) Terminal device Terminal devices, also sometimes called user equipment (UE), mobile station (MS), or mobile terminal (MT), are devices that provide voice and / or data connectivity to users, such as handheld devices and in-vehicle devices with wireless connectivity. Currently, some examples of terminal devices include mobile phones, tablet computers, notebook computers, palmtop computers, mobile internet devices (MID), wearable devices, virtual reality (VR) devices, augmented reality (AR) devices, wireless terminals for industrial control, wireless terminals for self-driving, wireless terminals for remote medical surgery, wireless terminals for smart grids, wireless terminals for transportation safety, wireless terminals for smart cities, and wireless terminals for smart homes.

[0058] (2) Access network devices Access network devices are radio access network (RAN) nodes (or devices) that connect terminals to a wireless network, and are sometimes called base stations. Currently, some examples of RAN nodes include Node B (NB), continuously evolved Node B (gNB), transmission reception point (TRP), evolved Node B (eNB), radio network controller (RNC), base station controller (BSC), base transceiver station (BTS), home base station (e.g., home evolved Node B or home Node B, HNB), base band unit (BBU), and wireless fidelity (Wi-Fi) access point (AP).

[0059] (3) Communication between terminal devices and access network devices Communication between terminal devices and access network devices follows a specific protocol layer structure. For example, the control plane protocol layer structure may include the radio resource control (RRC) layer, the packet data convergence protocol (PDCP) layer, the radio link control (RLC) layer, the media access control (MAC) layer, and the physical layer (PHY). The user plane protocol layer structure may include the PDCP layer, the RLC layer, the MAC layer, and the physical layer. In one possible implementation, a service data adaptation protocol (SDAP) layer may be further included above the PDCP layer. The SDAP layer, PDCP layer, RLC layer, MAC layer, and physical layer are sometimes collectively referred to as the access layer. For a detailed explanation of the aforementioned protocol layers, please refer to the relevant technical specifications of the 3rd generation partnership project (3GPP).

[0060] (4) CU-DU partitioned architecture For example, in some possible network structures, an access network device may include one or more centralized units (CUs) and one or more distributed units (DUs), and multiple DUs may be centrally controlled by a single CU. This architecture is sometimes called a CU-DU partitioned architecture. For example, the interface between a CU and a DU may be called an F1 interface. The control plane (CP) interface may be an F1-C interface, and the user plane (UP) interface may be an F1-U interface.

[0061] The processing functions of the CU and DU may be partitioned based on the protocol layer of the wireless network. For example, as shown in Figure 2A, the functions of the PDCP layer and higher protocol layers are configured on the CU, and the functions of lower protocol layers (e.g., the RLC layer and MAC layer) are configured on the DU. It will be understood that partitioning the processing functions of the CU and DU based on the protocol layer is just one example, and the processing functions may be partitioned in a different manner instead. For example, the functions of higher protocol layers are configured on the CU, and the functions of the RLC layer and lower protocol layers are configured on the DU. As another example, the CU or DU may have more of the functions of the protocol layer through partitioning. As yet another example, the CU or DU may have several more of the processing functions of the protocol layer through partitioning. This is not limited to the embodiments of this application.

[0062] Furthermore, the functions of a CU can be implemented by using a single entity or by using separate entities. For example, the functions of a CU can be further divided, namely the control plane and the user plane, and implemented by using separate entities, namely the control plane CU entity (i.e., the CU-CP entity) and the user plane CU entity (i.e., the CU-UP entity). To jointly complete the functions of a RAN device, the CU-CP entity and the CU-UP entity can be coupled to a DU. The interface between the CU-CP entity and the CU-UP entity may be an E1 interface, the interface between the CU-CP entity and the DU may be an F1-C interface, and the interface between the CU-UP entity and the DU may be an F1-U interface. One CU-CP may be connected to one DU and one CU-UP. Under the control of the same CU-CP, one DU may be connected to multiple CU-UPs, and one CU-UP may be connected to multiple DUs. Under the cooperation of multiple CU-CPs, one CU-UP may instead be connected to multiple coordinating CU-CPs, thereby increasing the flexibility of the CU-CPs. Figure 2B is a diagram of the air interface protocol stack distribution. As shown in Figure 2B, for both the user plane and the control plane, the air interface protocol stack can have the RLC layer, MAC layer, and PHY layer on the DU, and the PDCP layer and the protocol layers above the PDCP layer on the CU.

[0063] In the architectures shown in Figures 2A and 2B, it should be noted that signaling generated by the CU may be transmitted to a terminal device through the DU, or signaling generated by a terminal device may be transmitted to the CU through the DU. The DU can transmit signaling transparently to a terminal device or CU by directly encapsulating the signaling at the protocol layer without parsing it. In the following embodiments, when such transmission of signaling between the DU and a terminal device is involved, the transmission or reception of signaling by the DU includes this scenario. For example, signaling at the RRC or PDCP layer is ultimately processed as data at the physical layer and transmitted to the terminal device, or converted from received data at the physical layer. In this architecture, it can also be considered that when signaling at the RRC or PDCP layer is transmitted by the DU, or transmitted by the DU and the radio frequency device.

[0064] It will be understood that in this embodiment of the present application, the number of access network devices and terminal devices included in the communication system is not limited. Furthermore, in addition to access network devices and terminal devices, the communication system may further include other devices and network elements such as core network devices and relay devices. This is not limited in this embodiment of the present application.

[0065] The communication system shown in Figure 1 may support various radio access technologies (RATs). For example, the communication system shown in Figure 1 may be a 4th generation (4G) communication system (sometimes called a long-term evolution (LTE) communication system), a 5th generation (5G) communication system (sometimes called a new radio (NR) communication system), a wireless fidelity (Wi-Fi) system, or a future-oriented evolutionary system. The communication systems and service scenarios described in the embodiments of this application are intended to more clearly illustrate the technical solutions of the embodiments of this application and do not constitute a limitation on the technical solutions provided in the embodiments of this application. Those skilled in the art will know that, with the evolution of communication systems and the emergence of new service scenarios, the technical solutions provided in the embodiments of this application may also be applicable to similar technical problems.

[0066] The following sections will first describe the relevant technical features of the embodiments of this application. It should be noted that these explanations are intended to facilitate understanding of the embodiments of this application and should not be considered limitations on the scope of protection claimed herein.

[0067] 1. Cell handover Cell handovers can include cell handovers performed based on Layer 1 / Layer 2 (abbreviated as Layer 1 / Layer 2 handovers) and cell handovers performed based on Layer 3 (abbreviated as Layer 3 handovers). A cell handover performed based on Layer 1 / Layer 2 can be a cell handover performed based on Layer 1 or Layer 2, or a cell handover performed based on both Layer 1 and Layer 2. Layer 1 can be the physical layer, Layer 2 can be the MAC layer, and Layer 3 can be the RRC layer.

[0068] Furthermore, Layer 1 / Layer 2 handovers can include the following two types:

[0069] (1) Layer 1 / Layer 2 handover triggered by an access network device: For example, an access network device, based on beam level measurement results reported by a terminal device, selects a target cell that meets the Layer 1 / Layer 2 handover criteria from among candidate cells corresponding to a Layer 1 / Layer 2 handover, and sends a Layer 1 / Layer 2 handover command to the terminal device to instruct it to hand over the terminal device to that target cell. The beam level measurement results are sometimes called Layer 1 measurement results.

[0070] (2) Layer 1 / Layer 2 handover triggered by a terminal device, also known as a Layer 1 / Layer 2 conditional handover (CHO): For example, a terminal device selects a target cell that meets the Layer 1 / Layer 2 handover criteria from a list of candidate cells corresponding to a Layer 1 / Layer 2 handover based on beam level measurement results, triggers an autonomous handover to that target cell, and the access network device does not deliver a handover command.

[0071] Layer 3 handovers can include the following two types:

[0072] (1) Layer 3 handover triggered by an access network device: For example, an access network device, based on cell-level measurement results reported by a terminal device, selects a target cell that meets the Layer 3 handover criteria from among candidate cells that correspond to a Layer 3 handover, and sends a Layer 3 handover command to the terminal device to instruct it to hand over the terminal device to that target cell. Cell-level measurement results are sometimes called Layer 3 measurement results.

[0073] (2) Layer 3 handover triggered by a terminal device, also known as Layer 3 CHO: For example, a terminal device selects a target cell that meets the Layer 3 handover criteria from among candidate cells that support Layer 3 handover based on cell-level measurement results, and triggers an autonomous handover to that target cell, and the access network device does not deliver a handover command.

[0074] 2. Beam-level measurement results and cell-level measurement results In one possible implementation, the process by which a terminal device obtains beam level measurement results may be as follows: The access network device transmits reference signals in multiple beam directions of the cell. The reference signals may be a synchronization signal / physical broadcast channel block (SSB), a channel state information reference signal (CSI-RS), a channel sounding reference signal (SRS), or another possible reference signal. This is not specifically limited. Accordingly, the terminal device performs measurements on the time-frequency resources indicated by the access network device based on the reference signals. For example, the terminal device may obtain multiple transient signal intensities of the beam corresponding to the reference signal within a period of time by sampling, and obtain beam measurement results by weighting or combining the obtained signal intensities. The beam measurement results are sometimes called beam quality. Furthermore, the beam measurement results can be filtered by Layer 1 filtering to obtain filtered beam measurement results. For example, Layer 1 filtering parameters may be configured by the access network device for the terminal device. Alternatively, the terminal device can filter multiple obtained signal intensities to obtain filtered beam measurements. Cell-level measurements can be obtained by the terminal device combining or weighting the measurement results of multiple beams within a cell. For example, cell measurements can be obtained by combining at least one beam within a cell through the configuration of an access network device. Cell measurements are sometimes referred to as cell quality. Furthermore, filtered cell measurements can be obtained by filtering the cell measurements using Layer 3 filtering. For example, Layer 3 filtering parameters may be configured by the access network device for the terminal device.

[0075] 3. Wireless link failure To maintain the reliability of communication between terminal devices and access network devices, terminal devices must perform radio link monitoring (RLM) at the serving cell and determine whether a radio link failure (RLF) has occurred based on the RLM results.

[0076] For example, if the serving cell's wireless link quality is detected to be below the asynchronous threshold within a time window (for simplicity, this time window will be referred to as the third time window below), the terminal device's physical layer can report an "asynchronous indication" to the RRC layer once. Alternatively, if the serving cell's wireless link quality is detected to be above the synchronous threshold within the third time window, the terminal device's physical layer can report an "in-sync indication" to the RRC layer once. Furthermore, if the number of "asynchronous indications" continuously detected by the terminal device at the RRC layer is higher than the threshold (e.g., the threshold is N310), the terminal device starts Timer 1 (e.g., Timer 1 is T310). If no "in-sync indication" is detected within the timing window of Timer 1, the terminal device can determine that an RLF has occurred. If Timer 1 is started and operating, and the number of "in-sync indications" continuously detected by the terminal device at the RRC layer is above the threshold (e.g., the threshold is N311), the terminal device can stop Timer 1, the wireless link can be restored, and it can be considered that no RLF has occurred. N310, N311, the duration of the timing window of Timer 1, and the duration of the third time window may be configured by the access network device for the terminal device.

[0077] It should be understood that the above describes one example of a case in which an RLF occurs. In other possible cases, the terminal device may further determine that an RLF has occurred. For example, the terminal device may further determine that an RLF has occurred if at least one of the following conditions is met: (1) a problem occurs with random access, e.g., the number of failures initiating random access by the terminal device exceeds a predetermined threshold; (2) the number of retransmissions in the RLC layer exceeds the maximum number of retransmissions; (3) consecutive uplink listen before talk (LBT) failures occur, i.e., the terminal device fails to preempt the channel multiple times in a row.

[0078] 4. Wireless link quality Wireless link quality can be physical layer channel quality, such as physical downlink control channel (PDCCH) quality or physical downlink shared channel (PDSCH) quality.

[0079] For example, wireless link quality can be determined based on beam level measurement results. For instance, if a terminal device performs beam level measurements in cell 1 to obtain measurement results for N1 beams within cell 1, the terminal device may use the average of at least one measurement result from the N1 beams as the wireless link quality of cell 1, or the terminal device may use the average of the measurement results of N2 beams that have relatively good measurement results from the N1 beams as the wireless link quality of cell 1. N1 and N2 are positive integers, and N2 is less than N1.

[0080] In embodiments of this application, we consider an implementation in which a terminal device restores a wireless link based on the description of the relevant technical features described above.

[0081] A possible communication method provided in this embodiment of the present application is as follows: After a terminal device detects that a problem has occurred in the radio link of a serving cell, the terminal device may, in order to restore the radio link, select a target cell that meets the cell selection criteria by a cell selection procedure and perform RRC re-establishment to access the target cell.

[0082] The following describes possible implementation procedures with reference to Figure 3.

[0083] Figure 3 is a schematic flowchart corresponding to a communication method according to one embodiment of this application. As shown in Figure 3, the method includes the following steps.

[0084] S301: After determining that the first cell managed by the access network device is the serving cell for a terminal device, the access network device can send configuration information 1 to the terminal device in the first cell.

[0085] For example, an access network device can send configuration information 1 to terminal devices in multiple ways. For instance, an access network device can send an RRC message to terminal devices in a first cell, and this RRC message contains configuration information 1.

[0086] Configuration information 1 may include configuration information for a first cell and configuration information for at least one candidate cell of a terminal device. For example, the at least one candidate cell may include a candidate cell corresponding to a Layer 1 / Layer 2 handover and / or a candidate cell corresponding to a Layer 3 handover.

[0087] Taking one of the candidate cells as an example, the configuration information of the candidate cell may include the configuration information of the terminal device within the candidate cell, and may further include other possible information, such as related information of the candidate cell. This is not specifically limited. In addition, for the configuration information of the first cell, please refer to the configuration information of the candidate cell. Further details will not be explained again.

[0088] (1) Configuration information for terminal devices within a candidate cell may include at least one of the following: radio resource configuration information for terminal devices within a candidate cell, radio bearer (RB) configuration information for terminal devices within a candidate cell, multi-connectivity (MC) configuration information for terminal devices within a candidate cell, and a cell-radio network temporary identifier (C-RNTI) assigned to the terminal device by the candidate cell, where multi-connectivity may be one of DC, CA, CoMP, and mTRP, or a combination thereof. (2) Relevant information for a candidate cell may include at least one of the following: reference signal configuration information for the candidate cell (e.g., SSB configuration information, CSI-RS configuration information, and SRS configuration information), beam measurement configuration information for the candidate cell (e.g., transmission configuration indicator (TCI) state configuration information), and physical cell identity (PCI) for the candidate cell.

[0089] It will be understood that the first cell and the candidate cell may belong to the same access network device, or they may belong to different access network devices. If the first cell and the candidate cell belong to different access network devices, the access network device to which the first cell belongs can obtain the candidate cell's configuration information from the access network device to which the candidate cell belongs via the Xn interface.

[0090] S302: The terminal device performs wireless link monitoring in the first cell and determines that an RLF has occurred based on the wireless link monitoring results. For specific implementations of how the terminal device determines that an RLF has occurred, please refer to the explanation above.

[0091] Here, after determining that an RLF has occurred, the terminal device releases the configuration information of the first cell (for example, by interrupting transmissions from all radio bearers, i.e., preventing the radio bearers from transmitting control plane signaling and user plane service data), and further releases the configuration information of at least one candidate cell that is transmitted to the terminal device in the first cell by the access network device.

[0092] S303: After the terminal device executes the cell selection procedure and selects a cell that meets the cell selection criteria (e.g., the second cell) through the cell selection procedure, the terminal device actively initiates the RRC connection re-establishment procedure in the second cell. For example, the terminal device sends an RRC connection re-establishment request message to an access network device in the second cell through the random access procedure.

[0093] For specific implementation details of the cell selection procedure, please refer to conventional techniques.

[0094] S304: In the second cell, after receiving an RRC connection re-establishment request message from the terminal device, the access network device may send an RRC connection re-establishment message to the terminal device, which indicates that the second cell currently being accessed by the terminal device is the terminal device's new serving cell.

[0095] S305: After receiving the RRC connection re-establishment message, the terminal device sends an RRC connection re-establishment complete message to the access network device.

[0096] S306: After the terminal device has completed the RRC re-establishment procedure, the access network device may send a configuration message for the second cell to the terminal device in the second cell, and the terminal device may receive the configuration information for the second cell accordingly.

[0097] S307: The terminal device communicates with the access network device based on the configuration information of the second cell (i.e., restores the wireless link) and, for example, restores wireless bearer transmission.

[0098] As shown in Figure 3, the procedure allows a terminal device to restore the wireless link by performing RRC re-establishment. However, the RRC re-establishment procedure requires the terminal device to release the configuration information of at least one candidate cell. Therefore, even if the terminal device selects one of the candidate cells as the new serving cell, the access network device must retransmit the configuration information of the new serving cell to the terminal device. This results in a significant consumption of transmission resources. In addition, the terminal device must release the configuration information of the first cell (for example, by suspending transmissions from all wireless bearers), and wireless bearer transmissions can only be restored after the RRC re-establishment is complete. This results in a large communication interruption delay.

[0099] Another possible communication method provided in this embodiment of the present application is as follows: After a terminal device detects that a problem has occurred in the radio link of a serving cell, the terminal device can select a target cell. If the target cell is a candidate cell for cell handover, the terminal device can perform a cell handover for handover to the target cell in order to restore the radio link; if the target cell is not a candidate cell for cell handover, the terminal device can perform an RRC re-establishment to access the target cell in order to restore the radio link.

[0100] It should be noted that the implementation of "the terminal device selects the target cell" here may differ from the implementation of the terminal device selecting the target cell in the Layer 1 / Layer 2 CHO described above, and the implementation of the terminal device selecting the target cell in the Layer 3 CHO described above. If the target cell is a candidate cell corresponding to a Layer 1 / Layer 2 handover, the implementation of "handing over the terminal device to the target cell" here may be the same as the implementation of handing over the terminal device to the target cell in the Layer 1 / Layer 2 CHO described above. If the target cell is a candidate cell corresponding to a Layer 3 handover, the implementation of "handing over the terminal device to the target cell" here may be the same as the implementation of handing over the terminal device to the target cell in the Layer 3 CHO described above.

[0101] Below, several possible implementations of the aforementioned communication method will be described with reference to Embodiment 1.

[0102] Embodiment 1 Figure 4 is a schematic flowchart corresponding to the communication method according to Embodiment 1 of this application. As shown in Figure 4, the method includes the following steps.

[0103] S401: The access network device transmits configuration information for at least one candidate cell to a terminal device in the first cell, and accordingly, the terminal device can receive configuration information for at least one candidate cell in the first cell. See S301 for details.

[0104] For example, the access network device may further send enable information to a terminal device in the first cell, which is used to enable the terminal device to trigger a cell handover after a problem occurs with the serving cell's radio link. Accordingly, the terminal device can receive the enable information and further perform the subsequent method steps shown in Figure 4. Otherwise (i.e., the access network device does not send enable information to the terminal device, and accordingly, the terminal device does not receive the enable information), see Figure 3.

[0105] S402: The terminal device selects a second cell when it determines that the wireless link of the first cell meets the first condition, and the second cell is sometimes called the target cell.

[0106] For example, the radio link quality of a first cell satisfying the first condition may include at least one of the following: (1) the radio link quality of the first cell is less than a first threshold; (2) the radio link quality of the first cell is always less than a first threshold in a first time window; (3) the number of asynchronous instructions continuously detected by the terminal device is greater than or equal to a second threshold; (4) after the number of asynchronous instructions continuously detected by the terminal device becomes greater than or equal to the second threshold, the terminal device starts Timer 2 and does not detect any synchronous instructions within the timing window of Timer 2; and (5) an RLF occurs in the first cell. "Less than" can be replaced with "lower," and "greater than" can be replaced with "higher." The first condition may be configured by an access network device for a terminal device. For example, an access network device transmits first information to a terminal device in a first cell, and the first information is used to constitute a first condition (for example, the first information includes a first threshold, a second threshold, the duration of the timing window of Timer 2, and the duration of the first time window). The first threshold may be different from the asynchronous threshold, the second threshold may be different from N310, and the first and third time windows may be the same or different. This is not specifically limited.

[0107] There are several possible specific implementations for a terminal device to select a second cell. Below, referring to Implementation 1 and Implementation 2, we will explain two possible implementations using the example that "at least one candidate cell includes a candidate cell corresponding to Layer 1 / Layer 2 handover and a candidate cell corresponding to Layer 3 handover, the candidate cell corresponding to Layer 1 / Layer 2 handover includes cell a and cell b, and the candidate cell corresponding to Layer 3 handover includes cell b and cell c." It will be understood that at least one candidate cell may include only the candidate cell corresponding to Layer 1 / Layer 2 handover, i.e., {cell a, cell b}, or at least one candidate cell may include only the candidate cell corresponding to Layer 3 handover, i.e., {cell b, cell c}. For example, an access network device can configure at least one candidate cell for a terminal device that includes only the candidate cell corresponding to Layer 1 / Layer 2, or only the candidate cell corresponding to Layer 3 handover, or a candidate cell corresponding to Layer 1 / Layer 2 and a candidate cell corresponding to Layer 3, or which can be agreed upon in the protocol.

[0108] Implementation 1 The terminal device can select a second cell from {cell a, cell b, cell c} based on the wireless link quality or cell-level measurement results of at least one candidate cell (i.e., {cell a, cell b, cell c}).

[0109] If a terminal device selects a second cell from at least one candidate cell based on the radio link quality of at least one candidate cell, one possible implementation is as follows: The terminal device determines whether there is a cell in {cell a, cell b, cell c} whose radio link quality satisfies the second condition, based on the radio link quality of {cell a, cell b, cell c}. If there is a cell in {cell a, cell b, cell c} whose radio link quality satisfies the second condition, that cell is used as the second cell. In this case, the second cell belongs to at least one candidate cell, i.e., the second cell is one of {cell a, cell b, cell c}. The second condition is that the wireless link quality of the second cell satisfies: (1) the wireless link quality of the second cell is equal to or greater than the third threshold; (2) the wireless link quality of the second cell is always equal to or greater than the third threshold in the second time window; (3) the wireless link quality of the second cell is equal to or greater than the wireless link quality of at least one candidate cell other than the second cell; (4) the wireless link quality of the second cell is always equal to or greater than the wireless link quality of at least one candidate cell other than the second cell in the second time window. (5) The wireless link quality of the second cell is greater than or equal to the link quality of the first cell; (6) The wireless link quality of the second cell is always greater than the wireless link quality of the first cell in the second time window; (7) The wireless link quality of the second cell is greater than the sum of the wireless link quality of the first cell and the offset; (8) The wireless link quality of the second cell is always greater than the sum of the wireless link quality of the first cell and the offset in the second time window. The offset may be a positive or negative value.

[0110] It will be understood that at least one of the candidate cells may satisfy the second condition, or that multiple cells may satisfy the second condition. If multiple cells among at least one candidate cell satisfy the second condition, for example, if both cell a and cell b of {cell a, cell b, cell c} satisfy the second condition, then there are three possible methods: Method 1: The terminal device can select one of cell a and cell b as the second cell based on the beam level measurement results of cell a and cell b. For example, if cell a has one beam (called beam 1) and the measurement result of beam 1 is better than the measurement results of all beams in cell b, the terminal device can select cell a as the second cell. Method 2: The terminal device can select one of cell a and cell b as the second cell based on the cell level measurement results of cell a and cell b. For example, if the measurement result of cell a is better than the measurement result of cell b, the terminal device can select cell a as the second cell. Method 3: This depends on the internal implementation of the terminal device, i.e., the terminal device itself decides whether to select cell a or cell b as the second cell. For example, a specific method from Methods 1, 2, and 3 may be agreed upon in the protocol, or the access network device may instruct the terminal device to use a specific method.

[0111] In addition, if there are no cells in {cell a, cell b, cell c} whose wireless link quality satisfies the second condition, that is, if the terminal device does not select a suitable cell from {cell a, cell b, cell c}, the terminal device can perform a cell selection procedure and select a cell that satisfies the cell selection criteria through the procedure, and that cell becomes the second cell. In this case, the second cell does not belong to at least one of the candidate cells, that is, the second cell is a cell other than {cell a, cell b, cell c}.

[0112] When a terminal device selects a second cell from at least one candidate cell based on the cell-level measurement result of at least one candidate cell, one possible implementation is as follows: The terminal device determines, based on the cell-level measurement results of {cell a, cell b, cell c}, whether there is a cell in {cell a, cell b, cell c} whose cell-level measurement result satisfies the third condition. If there is a cell in {cell a, cell b, cell c} whose cell-level measurement result satisfies the third condition, that cell is used as the second cell. In this case, the second cell is one of {cell a, cell b, cell c}. The cell-level measurement result of the second cell satisfying the third condition may include at least one of the following: (1) the cell-level measurement result of the second cell is greater than or equal to the fourth threshold; (2) the cell-level measurement result of the second cell is greater than or equal to the cell-level measurement result of at least one candidate cell other than the second cell; or (3) the cell-level measurement result of the second cell is greater than the cell-level measurement result of the first cell.

[0113] In addition, if the cell-level measurement results show that there are no cells in {cell a, cell b, cell c} that satisfy the third condition, i.e., if the terminal device does not select a suitable cell from {cell a, cell b, cell c}, the terminal device can perform a cell selection procedure and select a cell that satisfies the cell selection criteria through the procedure, and that cell becomes the second cell. In this case, the second cell does not belong to at least one of the candidate cells. Note that typically the terminal device performs the cell selection procedure in an idle state. In this case, the terminal device can perform the cell selection procedure during the first measurement period. However, in this embodiment of the present application, the terminal device performs the cell selection procedure in a connected state to select a suitable target cell. In this case, the terminal device can perform the cell selection procedure during the second measurement period. The second measurement period may be shorter than the first measurement period. For example, in this embodiment of the present application, the terminal device can perform the cell selection procedure based on the real-time radio link quality of the cell.

[0114] In one possible implementation, an access network device may transmit second information to a terminal device, instructing the terminal device to select a second cell based on radio link quality. Optionally, a second condition may be further configured for the second information. For example, the second information may include a third threshold, an offset, and the duration of a second time window. Accordingly, after receiving the second information, the terminal device may select a second cell based on the radio link quality of at least one candidate cell. Otherwise (i.e., the access network device does not transmit the second information to the terminal device, and accordingly, the terminal device does not receive the second information), the terminal device may select a second cell based on cell-level measurements of at least one candidate cell.

[0115] Implementation 2 A terminal device can select a second cell from the cells included in the second candidate cell list based on the radio link quality or cell level measurement results of the cells included in the second candidate cell list. The second candidate cell list may differ from the first candidate cell list, and the first candidate cell list may include at least one candidate cell, i.e., the first candidate cell list may be {cell a, cell b, cell c}. In one example, the second candidate cell list may include another cell in addition to all the cells included in the first candidate cell list. For example, the second candidate cell list may be {cell a, cell b, cell c, cell d}. In this case, see Implementation 1 for an implementation of the second cell selected by the terminal device. The second cell selected by the terminal device may belong to at least one candidate cell, or it may not belong to at least one candidate cell.

[0116] For example, a second candidate cell list may be configured by an access network device for a terminal device. For instance, the access network device may send cell list configuration information to the terminal device, and this cell list configuration information is used to configure the second candidate cell list.

[0117] Furthermore, if the terminal device determines that the selected second cell belongs to at least one candidate cell (for example, the second cell is cell a, cell b, or cell c), the terminal device may interrupt all wireless bearer transmissions but not release the configuration information of at least one candidate cell, and can later restore the wireless link by executing S403A. If the terminal device determines that the selected second cell does not belong to at least one candidate cell (for example, the second cell is cell d), the terminal device may interrupt all wireless bearer transmissions, release the configuration information of at least one candidate cell, and later restore the wireless link by executing S403B.

[0118] S403A: The terminal device is handed over from the first cell to the second cell and communicates with the access network device in the second cell based on the configuration information of the second cell.

[0119] Here, if the second cell is cell a, the terminal device can perform a Layer 1 / Layer 2 handover for a handover from the first cell to the second cell. If the second cell is cell c, the terminal device can perform a handover from the first cell to the second 2A Layer 3 handover can be performed for a handover to the cell. If the second cell is cell b (i.e., the second cell is both a candidate cell for Layer 1 / Layer 2 handover and a candidate cell for Layer 3 handover), then there are three possible methods: Method 1: The terminal device performs a Layer 1 / Layer 2 handover for the handover from the first cell to the second cell. Method 2: The terminal device performs a Layer 3 handover for the handover from the first cell to the second cell. Method 3: This depends on the internal implementation of the terminal device, i.e., the terminal device itself decides to perform a Layer 1 / Layer 2 handover for the handover from the first cell to the second cell, or to perform a Layer 3 handover for the handover from the first cell to the second cell. For example, a particular method among Method 1, Method 2, and Method 3 may be agreed upon in the protocol, or the access network device may instruct the terminal device to use a particular method.

[0120] For example, after performing a handover from the first cell to the second cell, the terminal device may notify the access network device in the second cell that the terminal device has been handed over from the first cell to the second cell, and this handover is a cell handover triggered by the terminal device. For example, the handover is a cell handover triggered by the terminal device to select the second cell based on the aforementioned method (e.g., implementation 1 or implementation 2). There may be multiple specific notification methods, for example, notification method 1 and notification method 2.

[0121] Notification method 1: A terminal device can send third information to an access network device in a second cell, indicating that the terminal device has been handed over from a first cell to a second cell, and this handover is a cell handover triggered by the terminal device. In other words, the terminal device can notify the access network device in an explicit manner. The third information may include at least one of the following: the identifier of the terminal device, the identifier of the first cell (i.e., the identifier of the source cell), and instruction information a, where instruction information a indicates a cell handover triggered by the terminal device. For example, the third information may be carried in a message of a random access procedure initiated by the terminal device in the second cell. For example, if the random access procedure is a four-step random access procedure, the third information may be carried in message 3 of the four-step random access procedure, or if the random access procedure is a two-step random access procedure, the third information may be carried in message A of the two-step random access procedure. Furthermore, optionally, the third piece of information may be carried in the MAC control element (CE) of message 3 or message A. Alternatively, the third piece of information may be carried in a message other than a message in the random access procedure.

[0122] Notification method 2: A terminal device can send a fourth piece of information to an access network device in a second cell, the fourth piece of information being carried on a first resource, the first resource being a resource corresponding to a cell handover triggered by the terminal device. In other words, the terminal device can implicitly notify the access network device. The fourth piece of information may be carried in a message of a random access procedure initiated by the terminal device in the second cell (e.g., message 3 or message A), or in a message other than a random access procedure message. For example, the first resource may be a physical uplink control channel (PUCCH) resource, the first resource may be configured by the access network device for the terminal device. For example, the access network device can send a fifth piece of information to the terminal device in the first cell, the fifth piece of information being used to configure the first resource.

[0123] For example, after performing a handover from the first cell to the second cell, the terminal device may further transmit downlink beam information to the access network device in the second cell. The downlink beam information indicates the downlink beam used by the access network device to transmit downlink data to the terminal device in the second cell. The downlink beam may be a narrower beam than the beam corresponding to the target SSB, which may be the SSB associated with the random access resource used by the terminal device to initiate random access in the second cell. For example, the downlink beam information may be included in a third or fourth piece of information, or may be transmitted additionally by the terminal device to the access network device. This is not specifically limited.

[0124] Downlink beam information can indicate a beam (e.g., a first beam), which may be the beam with the best measurement result among several beams in a second cell determined by the terminal device. Accordingly, the access network device can transmit downlink data to a terminal device in the second cell through the first beam based on the downlink beam information. Alternatively, the downlink beam information can indicate several candidate beams determined by the terminal device. Accordingly, the access network device can select one downlink beam (e.g., a second beam) from the several candidate beams based on the downlink beam information and transmit downlink data to a terminal device in the second cell through the second beam.

[0125] S403B: The terminal device performs RRC re-establishment to access the second cell.

[0126] Here, the terminal device can release the configuration information of at least one candidate cell and initiate the RRC connection re-establishment procedure in the second cell. For specific implementation details, please refer to Figure 3.

[0127] In the procedure shown in Figure 4, it will be understood that the configuration information of at least one candidate cell, the first information, the second information, the fifth information, the enable information, etc., may be carried in the same message or in separate messages. This is not specifically limited.

[0128] According to the method of Embodiment 1, the terminal device does not need to release the configuration information of at least one candidate cell after detecting a problem in the wireless link. After the terminal device selects one of the candidate cells as the new serving cell, it can communicate with the access network device based on the configuration information of the new serving cell, and the access network device does not need to retransmit the configuration information of the new serving cell to the terminal device. This effectively saves transmission resources. In addition, the terminal device can trigger a cell handover for the handover from the source cell to the new serving cell. Therefore, compared to the RRC re-establishment procedure, this method allows for rapid recovery of communication and effectively reduces communication interruption delays.

[0129] Embodiment 1 described above illustrates the implementation procedure of this embodiment of the present application from the perspective of communication between an access network device and a terminal device. Since the access network device may include a CU and one or more DUs, several possible implementation procedures will be described below with reference to Embodiment 2 from the perspective of communication between the CU, DU, and terminal device.

[0130] Embodiment 2 If the access network device includes a CU and one or more DUs, the first and second cells of Embodiment 1 may belong to separate DUs managed by the CU. For example, the first cell may belong to the first DU and the second cell may belong to the second DU. Alternatively, the first and second cells may belong to the same DU. For example, both the first and second cells may belong to the second DU. The possible procedures for these two cases will be described separately below.

[0131] Case 1: The first cell belongs to the first DU, and the second cell belongs to the second DU.

[0132] Figure 5 is a schematic flowchart corresponding to the communication method according to Embodiment 2 of this application. As shown in Figure 5, the method includes the following steps.

[0133] S501:CU transmits configuration information for at least one candidate cell to the terminal device through the first DU to which the first cell belongs, and the first cell is the serving cell of the terminal device.

[0134] For example, a CU can send an RRC message to a first DU, which then forwards the RRC message to a terminal device. This RRC message contains configuration information for at least one candidate cell.

[0135] S502: The terminal device selects the second cell when it determines that the wireless link of the first cell meets the first condition.

[0136] Here, we will use an example where the second cell belongs to at least one candidate cell for explanation.

[0137] S503: The terminal device is handed over from the first cell to the second cell.

[0138] For specific implementations of S501 to S503, please refer to Embodiment 1.

[0139] S504: The second DU determines that the terminal device has been handed over from the first cell to the second cell.

[0140] Here, there are several possible implementations for the second DU to determine that a terminal device has been handed over from the first cell to the second cell. For example, the terminal device can send a third piece of information to the second DU. Accordingly, the second DU can determine that the terminal device has been handed over from the first cell to the second cell after receiving the third piece of information from the terminal device. As another example, the terminal device can send a fourth piece of information to the second DU. Accordingly, the second DU can determine that the terminal device has been handed over from the first cell to the second cell after receiving the fourth piece of information (the fourth piece of information is carried over the first resource) from the terminal device. For specific implementations, please refer to Embodiment 1.

[0141] S505: The second DU transmits the first instruction information to the CU, which indicates that the terminal device has been handed over from the first cell to the second cell.

[0142] Optionally, the second DU may also transmit downlink data delivery status (DDDS) information from the first CU to the CU, which then uses the first DDDS information to control the traffic of downlink data sent to terminal devices through the second DU. For example, the first DDDS information may include the amount of data already cached by the second DU.

[0143] For example, the first instruction information may include an identifier for a terminal device, an identifier for a second cell (i.e., an identifier for a target cell), and at least one of instruction information b, where instruction information b indicates a cell handover triggered by the terminal device.

[0144] In one possible implementation, instruction information b may be first DDDS information (i.e., a cell handover triggered by a terminal device is implicitly indicated using the first DDDS information). In this case, instruction information b in the first instruction information may be transmitted using a user plane data frame on the F1 interface, and other information (e.g., the identifier of the terminal device and / or the identifier of the second cell) may be transmitted using a user plane data frame or using a control plane message on the F1 interface. This is not specifically limited. Alternatively, in another possible implementation, instruction information b may be other possible information. In this case, the first instruction information may be transmitted using a control plane message of an F1 interface message.

[0145] S506:CU transmits second instruction information to the first DU, which indicates that the terminal device has been handed over from the first cell to the second cell. Accordingly, the first DU receives the second instruction information and stops communicating with the terminal device (for example, by stopping the transmission of downlink data to the terminal device).

[0146] For example, the second instruction information may include at least one of the following: an identifier for a terminal device, an identifier for a second cell, and instruction information c, where instruction information c indicates a cell handover triggered by the terminal device. The second instruction information may be carried as a control plane message over the F1 interface.

[0147] S507: The first DU sends third instruction information to the CU, which instructs the first DU to stop sending data packets to the terminal device. Furthermore, the first DU can stop sending downlink data to the terminal device.

[0148] For example, the third instruction information may include at least one of the sequence numbers (SN) of PDCP PDUs that were not successfully transmitted by the first DU, and the highest sequence number of PDCP PDUs that were successfully transmitted by the first DU.

[0149] For example, the third instruction information may be included in the second DDDS information and transmitted using a user plane data frame on the F1 interface, or the third instruction information may be transmitted using a control plane message on the F1 interface. This is not specifically limited.

[0150] S508:CU transmits a data packet to the terminal device via the second DU based on the third instruction information.

[0151] For example, if the third instruction information includes a sequence number of a PDCP PDU that was not successfully transmitted by the first DU, the CU can retransmit the PDCP PDU corresponding to the sequence number through the second DU. If the third instruction information includes the highest sequence number of a PDCP PDU that was successfully transmitted by the first DU, the CU can send the PDCP PDU after the highest sequence number to the terminal device through the second DU.

[0152] In addition, from the perspective of the second DU, the terminal device can further transmit downlink beam information to the second DU (see Embodiment 1 for details on downlink beam information). Therefore, in S505, the second DU can transmit data packets to the terminal device through the corresponding downlink beam based on the downlink beam information.

[0153] Case 2: Both the first cell and the second cell belong to the second DU.

[0154] Figure 6 is a schematic flowchart corresponding to the communication method according to Embodiment 2 of this application. As shown in Figure 6, the method includes the following steps.

[0155] S601:CU transmits configuration information for at least one candidate cell to the terminal device through the second DU to which the first cell belongs, and the first cell is the serving cell of the terminal device.

[0156] S602: The terminal device selects the second cell when it determines that the wireless link of the first cell meets the first condition.

[0157] Here, we will use an example where the second cell belongs to at least one candidate cell for explanation.

[0158] S603: The terminal device is handed over from the first cell to the second cell.

[0159] For specific implementations of S601 to S603, please refer to Embodiment 1.

[0160] S604: The second DU determines that the terminal device has been handed over from the first cell to the second cell.

[0161] S605: The second DU sends the first instruction information and the fourth instruction information to the CU, the first instruction information indicating that the terminal device has been handed over from the first cell to the second cell, and the fourth instruction information indicating data packets that were not successfully sent to the terminal device by the second DU.

[0162] For information regarding the fourth instruction, please refer to the explanation of the third instruction.

[0163] S606:CU transmits data packets to the terminal device via the second DU based on data packets that were not successfully sent to the terminal device by the second DU.

[0164] For a detailed implementation of the aforementioned steps shown in Figure 6, please refer to Figure 5.

[0165] According to the method of Embodiment 2, after detecting a problem in the radio link of the first cell, the terminal device is handed over from the first cell to the second cell (the second cell belongs to at least one candidate cell), and can communicate with the target DU (i.e., the DU to which the second cell belongs) based on the configuration information of the second cell received by the first cell, and the CU does not need to retransmit the configuration information of the second cell to the terminal device. This effectively saves transmission resources and reduces communication interruption delays. Furthermore, the source DU (i.e., the DU to which the first cell belongs) can send instruction information to the CU to instruct data packets that were not successfully transmitted to the terminal device by the source DU, so that the CU can transmit the data packets that were not successfully transmitted to the terminal device through the target DU, effectively avoiding the risk of data packet loss.

[0166] In Embodiment 2, it will be understood that the solution described in "S501-S504" or "S601-S604" is as follows: The terminal device selects a second cell based on the method of Embodiment 1 and performs a Layer 1 / Layer 2 handover for handover from the first cell to the second cell. Furthermore, the second DU can determine that the terminal device has been handed over from the first cell to the second cell based on third or fourth information transmitted by the terminal device. In another possible embodiment, "S501-S504" or "S601-S604" may be replaced with: The terminal device is handed over from the first cell to the second cell by a Layer 1 / Layer 2 CHO. Furthermore, the second DU can determine that the terminal device has been handed over from the first cell to the second cell based on handover completion information transmitted by the terminal device. For example, the handover completion information may be a Layer 1 / Layer 2 message, and the handover completion information may include downlink beam information. Alternatively, the terminal device may additionally transmit downlink beam information to the second DU.

[0167] Embodiment 3 Embodiment 3 describes possible implementation procedures for Layer 1 / Layer 2 handovers triggered by access network devices, from the perspective of communication between CUs, DUs, and terminal devices (Layer 3 handovers triggered by access network devices may be implemented with reference thereto).

[0168] Figure 7 is a schematic flowchart corresponding to the communication method according to Embodiment 3 of this application. As shown in Figure 7, the method includes the following steps.

[0169] S701:CU transmits configuration information for at least one candidate cell to the terminal device through the first DU to which the first cell belongs.

[0170] Here, at least one candidate cell may contain a candidate cell corresponding to a Layer 1 / Layer 2 handover.

[0171] S702: The terminal device performs beam level measurements on the first cell and at least one candidate cell, and reports the beam level measurement results to the first DU.

[0172] S703: The first DU selects one target cell from at least one candidate cell based on the beam level measurement results, for example, the target cell being the second cell, and sends a Layer 1 / Layer 2 handover command to the terminal device, which commands the terminal device to be handed over from the first cell to the second cell. Accordingly, the terminal device receives the handover command and is handed over from the first cell to the second cell in accordance with the handover command.

[0173] For an implementation of selecting a target cell using the first DU based on beam level measurement results, please refer to the prior art.

[0174] For example, a Layer 1 handover instruction may be downlink control information (DCI), and a Layer 2 handover instruction may be a MAC CE. The handover instruction may include identification information for a second cell and downlink beam information, the downlink beam information indicating the downlink beam used by the second DU to which the second cell belongs in order to transmit downlink data to a terminal device.

[0175] S704: The first DU sends third instruction information to the CU, which instructs the first DU to stop sending data packets to the terminal device. Furthermore, the first DU can stop sending downlink data to the terminal device.

[0176] S705: The terminal device sends handover completion information to the second DU, which indicates that the terminal device has been handed over from the first cell to the second cell.

[0177] Optionally, the terminal device may further transmit downlink beam information to the second DU. In one possible implementation, the downlink beam information transmitted by the terminal device to the second DU may be the downlink beam information carried by the Layer 1 / Layer 2 handover instruction in S703. The second DU can then transmit data packets to the terminal device through the corresponding downlink beam based on the downlink beam information.

[0178] In one possible implementation, the handover completion information may be a Layer 1 / Layer 2 message. In this case, the handover completion information may include downlink beam information. Alternatively, the terminal device may additionally transmit downlink beam information to the second DU.

[0179] S706: The second DU sends notification information to the CU, which is used to notify the CU that the terminal device has been handed over from the first cell to the second cell.

[0180] For example, notification information may include first DDDS information, and first DDDS information may include the amount of data already cached by the second DU.

[0181] S707:CU transmits a data packet to the terminal device via the second DU based on the third instruction information.

[0182] According to the method of Embodiment 3, the first DU can send third instruction information to the CU after sending a handover command to the terminal device, so that the CU can send data packets that were not successfully transmitted to the terminal device through the target DU (i.e., the second DU), effectively avoiding the risk of data packet loss. In addition, the terminal device can send downlink beam information to the second DU, so that the second DU can send downlink data to the terminal device through the corresponding beam based on the downlink beam information.

[0183] The following will be understood from Embodiments 1 to 3.

[0184] (1) Embodiments 1 to 3 are described using an example in which the serving cell of the terminal device is a single cell. In another possible case, for example, when the terminal device operates in dual connectivity mode, the solutions of Embodiments 1 to 3 may be applicable to dual connectivity primary base station handover, or to the addition of secondary base stations (SNs) / secondary cell groups (SCGs) or the modification of secondary base stations / secondary cell groups. For example, after determining that the radio link of a cell in a secondary base station / secondary cell group satisfies the first condition, the terminal device may also restore the radio link of the cell using the method of Embodiment 1.

[0185] (2) The step numbers in the flowcharts described in Embodiments 1 to 3 are merely examples of execution procedures and do not limit the order in which the steps are executed. In the embodiments of this application, there is no strict execution order between steps that do not have a chronological dependency on each other. Not all steps shown in each flowchart are necessarily steps that are executed. Some steps may be deleted from each flowchart according to the actual requirements, or other possible steps may be added from each flowchart according to the actual requirements.

[0186] (3) The above focuses on the differences between the different embodiments of Embodiments 1 to 3, and Embodiments 1 to 3 can refer to one another, apart from the content of other differences. In addition, different implementations or different examples within the same embodiment can also refer to one another.

[0187] The above primarily describes the solutions provided in the embodiments of this application from the perspective of interaction between communication devices. It will be understood that, in order to implement the functions described above, terminal devices and access network devices may include corresponding hardware structures and / or software modules for performing the functions. Those skilled in the art will readily realize that, in the embodiments of this application, the example units and algorithmic steps described with reference to the embodiments disclosed herein may be implemented by hardware or by a combination of hardware and computer software. Whether the functions are performed by hardware or by hardware driven by computer software will depend on the specific application and design constraints of the technical solution. Those skilled in the art may implement the functions described using various methods for each specific application, but should not consider that such implementations exceed the scope of this application.

[0188] In embodiments of this application, functional unit partitioning may be performed in terminal devices and access network devices based on the examples of the methods described above. For example, each functional unit may be obtained by partitioning based on corresponding functions, or two or more functions may be integrated into a single unit. The integrated unit may be implemented in hardware form or in the form of a software functional unit.

[0189] When an integrated unit is used, Figure 8 is a block diagram of a possible example of a device according to one embodiment of the present application. As shown in Figure 8, the device 800 may include a processing unit 802 and a communication unit 803. The processing unit 802 is configured to control and manage the operation of the device 800. The communication unit 803 is configured to support communication between the device 800 and another device. Optionally, the communication unit 803 may also be called a transceiver unit and may include a receiving unit and / or a transmitting unit configured to perform receiving and transmitting operations, respectively. The device 800 may further include a storage unit 801 configured to store program code and / or data of the device 800.

[0190] The device 800 may be a terminal device in the embodiment described above. The processing unit 802 can support the device 800 when performing operations on the terminal device in the example of the method described above. Alternatively, the processing unit 802 may primarily perform internal operations on the terminal device in the example of the method, and the communication unit 803 may support communication between the device 800 and another device.

[0191] For example, in one embodiment, a communication unit 803 is configured to receive configuration information for at least one candidate cell from an access network device in a first cell, and a processing unit 802 is configured to select a second cell if the radio link of the first cell satisfies a first condition, and if the second cell belongs to at least one candidate cell, to perform a handover from the first cell to the second cell and communicate with an access network device in the second cell via the communication unit 803 based on the configuration information for the second cell received in the first cell, or to perform RRC re-establishment to access the second cell if the second cell does not belong to at least one candidate cell.

[0192] The device 800 may be an access network device in the embodiments described above. The processing unit 802 can support the device 800 when performing the operations of the access network device in the example of the method described above. Alternatively, the processing unit 802 may primarily perform the internal operations of the access network device in the example of the method, and the communication unit 803 may support communication between the device 800 and another device.

[0193] It should be understood that the division of units in the aforementioned device is merely a logical functional division. In actual implementation, all or part of the units may be integrated into a single physical entity, or they may be physically separated. In addition, all units in the device may be implemented in the form of software invoked by processing elements, or in the form of hardware, or some units may be implemented in the form of software invoked by processing elements, and some units may be implemented in the form of hardware. For example, each unit may be an individually located processing element, or it may be integrated into the device's chip for implementation. In addition, each unit may instead be stored in memory in the form of a program invoked by the device's processing elements to perform the unit's function. In addition, all or part of the units may be integrated, or they may be implemented independently. Processing elements in this document may also be called processors, and may be integrated circuits with signal processing capabilities. In the implementation process, the methods described above or the work in the aforementioned units may be implemented by using hardware integrated logic circuits in the processor element, or in a form in which the processing element invokes software.

[0194] In one example, a unit in any one of the aforementioned devices may be one or more integrated circuits configured to carry out the method described above, for example, one or more application-specific integrated circuits (ASICs), one or more digital signal processors (DSPs), one or more field programmable gate arrays (FPGAs), or a combination of at least two of these forms of integrated circuits. In another example, if a unit in the device may be implemented in a manner in which a processing element schedules a program, that processing element may be a processor, for example, a central processing unit (CPU), or another processor capable of calling a program. In yet another example, the unit may be integrated and implemented in the form of a system-on-a-chip (SOC).

[0195] The aforementioned receiving unit is an interface circuit of the device and is configured to receive signals from another device. For example, if the device is implemented in a chip manner, the receiving unit is an interface circuit of the chip configured to receive signals from another chip or device. The aforementioned transmitting unit is an interface circuit of the device and is configured to transmit signals to another device. For example, if the device is implemented in a chip manner, the transmitting unit is an interface circuit of the chip configured to transmit signals to another chip or device.

[0196] Figure 9 is a diagram of the structure of an access network device according to one embodiment of the present application. This access network device (or base station) may be used in the communication system shown in Figure 1 to perform the functions of the access network device in the embodiments of the method described above. As shown in Figure 9, the access network device 90 may include one or more DUs 901 and one or more CUs 902. The DU 901 may include at least one antenna 9011, at least one radio frequency unit 9012, at least one processor 9013, and at least one memory 9014. The DU 901 is mainly configured to receive / transmit radio frequency signals, perform conversion between radio frequency signals and baseband signals, and perform partial baseband processing. The CU 902 may include at least one processor 9022 and at least one memory 9021.

[0197] CU 902 is primarily configured to perform baseband processing and control access network devices. DU 901 and CU 902 may be physically located together or physically separated; that is, the base station may be a distributed base station. CU 902 is the control center for access network devices, sometimes referred to as a processing unit, and is primarily configured to complete baseband processing functions. For example, CU 902 may be configured to control access network devices to perform the work procedures associated with access network devices in the embodiments of the method described above.

[0198] In addition, optionally, the access network device 90 may include one or more radio frequency units, one or more DUs, and one or more CUs. A DU may include at least one processor 9013 and at least one memory 9014, a radio frequency unit may include at least one antenna 9011 and at least one radio frequency unit 9012, and a CU may include at least one processor 9022 and at least one memory 9021.

[0199] In one example, CU 902 may include one or more boards. Multiple boards may jointly support one radio access network (e.g., a 5G network) with a single access instruction, or they may separately support multiple radio access networks (e.g., an LTE network, a 5G network, or another network) with different access standards. Memory 9021 and processor 9022 can be served on one or more boards; that is, each board may have memory and a processor. Alternatively, multiple boards may share the same memory and the same processor. In addition, each board may have further necessary circuitry. DU 901 may include one or more boards. Multiple boards may jointly support one radio access network (e.g., a 5G network) with a single access instruction, or they may separately support multiple radio access networks (e.g., an LTE network, a 5G network, or another network) with different access standards. Memory 9014 and processor 9013 can be served on one or more boards; that is, each board may have memory and a processor. Alternatively, multiple boards may share the same memory and the same processor. In addition, each circuit board may have other necessary circuits placed on it.

[0200] The access network device shown in Figure 9 can perform all processes related to the access network device in the embodiments of the method described above. The work and / or functions of the modules within the access network device shown in Figure 9 are used, respectively, to perform the corresponding procedures in the embodiments of the method described above. For details, please refer to the description of the embodiments of the method described above. To avoid repetition, detailed explanations are appropriately omitted here.

[0201] Figure 10 is a diagram of the structure of a terminal device according to one embodiment of the present application. This terminal device may be applied to the communication system shown in Figure 1 and is configured to perform the work of the terminal device in the embodiment described above. As shown in Figure 10, the terminal device includes an antenna 1010, a radio frequency unit 1020, and a signal processing unit 1030. The antenna 1010 is connected to the radio frequency unit 1020. In the downlink direction, the radio frequency unit 1020 receives information transmitted by the network device through the antenna 1010 and transmits the information transmitted by the network device to the signal processing unit 1030 for processing. In the uplink direction, the signal processing unit 1030 processes the information of the terminal device and transmits the processed information to the radio frequency unit 1020, which processes the information of the terminal device and then transmits the processed information to the network device through the antenna 1010.

[0202] The signal processing unit 1030 may include a modem subsystem configured to process data at each communication protocol layer. The signal processing unit 1030 may further include a central processing subsystem configured to process the operating system and application layers of the terminal device. In addition, the signal processing unit 1030 may further include other subsystems, such as a multimedia subsystem and a peripheral subsystem. The multimedia subsystem is configured to control the camera or screen display of the terminal device. The peripheral subsystem is configured to connect to another device. The modem subsystem may be a separately located chip.

[0203] The modem subsystem may include one or more processing elements 1031, for example, a main control CPU and another integrated circuit. In addition, the modem subsystem may further include a memory element 1032 and an interface circuit 1033. The memory element 1032 is configured to store data and programs. However, the program used to perform the method executed by the terminal device in the manner described above does not have to be stored in the memory element 1032, but is stored in memory outside the modem subsystem and loaded and used by the modem subsystem when needed. The interface circuit 1033 is configured to communicate with another subsystem.

[0204] The modem subsystem may be implemented using a chip. This chip includes at least one processing element and an interface circuit. The processing element is configured to perform steps of any method performed by a terminal device. The interface circuit is configured to communicate with other devices. In one implementation, the unit of the terminal device that performs the steps of the aforementioned method may be implemented by a program scheduled by the processing element. For example, the device used as a terminal device includes a processing element and a memory element. The processing element invokes a program stored in the memory element to perform the method performed by the terminal device in the embodiment of the aforementioned method. The memory element may be a memory element located on the same chip as the processing element, i.e., an on-chip memory element.

[0205] In another implementation, the program used to execute the method performed by the terminal device in the manner described above may reside in a memory element located on a different chip from the processing element, i.e., in an off-chip memory element. In this case, the processing element calls or loads the program from the off-chip memory element to the on-chip memory element in order to call and execute the method performed by the terminal device in the embodiment of the method described above.

[0206] In yet another implementation, the terminal device unit that performs the steps of the method described above may be configured as one or more processing elements. These processing elements are located within the modem subsystem. The processing elements in this document may be integrated circuits, for example, one or more ASICs, one or more DSPs, one or more FPGAs, or a combination of various integrated circuits. These integrated circuits can be integrated together to form a chip.

[0207] The units of a terminal device that perform the steps of the method described above may be integrated together and implemented in the form of a System-on-a-Chip (SOC). The SOC chip is configured to perform the method described above. At least one processing element and a memory element may be integrated into the chip, and the processing element invokes a program stored in the memory element to perform the method described above, which is performed by the terminal device. Alternatively, at least one integrated circuit may be integrated into the chip to perform the method described above, which is performed by the terminal device. Alternatively, referring to the implementation described above, the functions of some units may be performed by a program invoked by the processing element, and the functions of some units may be performed by an integrated circuit.

[0208] It can be seen that the aforementioned device used in a terminal device may include at least one processing element and an interface circuit. The at least one processing element is configured to perform one of the methods performed by the terminal device provided in the embodiments of the aforementioned method. The processing element may perform some or all of the steps performed by the terminal device in a first manner, specifically by calling a program stored in a memory element; or in a second manner, specifically by using hardware integrated logic circuits in a processor element in combination with instructions; or of course, by combining the first and second manners, it may perform some or all of the steps performed by the terminal device.

[0209] The processing elements here are the same as those described above and may be implemented using a processor. The function of the processing elements may be the same as the function of the processing unit described in Figure 8. For example, the processing elements may be a general-purpose processor, such as a CPU, or one or more integrated circuits configured to carry out the methods described above, such as one or more ASICs, one or more microprocessor DSPs, or one or more FPGAs, or a combination of at least two of these integrated circuit forms. The memory elements may be implemented using memory. The function of the memory elements may be the same as the function of the memory unit described in Figure 8. The memory elements may be memory, or a collective term for multiple memories.

[0210] The terminal device shown in Figure 10 can perform all processes related to the terminal device in the embodiments of the method described above. The work and / or functions of the modules within the terminal device shown in Figure 10 are intended to perform the corresponding procedures in the embodiments of the method described above. For details, please refer to the description of the embodiments of the method described above. To avoid repetition, detailed explanations are appropriately omitted here.

[0211] In embodiments of this application, the terms “system” and “network” may be used interchangeably. “At least one” means one or more, and “multiple” means two or more. The term “and / or” describes the relationship between related objects and indicates that three relationships may exist. For example, A and / or B can indicate the following three cases: that only A exists, that both A and B exist, and that only B exists, where A and B may be singular or plural. “At least one of the following items” or similar expressions indicate any combination of these items, including any single item or any combination of multiple items. For example, “at least one of A, B, and C” includes A, B, C, AB, AC, BC, or ABC. In addition, unless otherwise specified, ordinal numbers such as “first” and “second” in embodiments of this application are used to distinguish multiple objects and are not used to limit the order, chronological order, priority, or importance of multiple objects.

[0212] Those skilled in the art will understand that embodiments of this application may be provided as methods, systems, or computer program products. Accordingly, this application may be provided in the form of hardware-only embodiments, software-only embodiments, or embodiments including a combination of software and hardware. In addition, this application may be provided in the form of computer program products implemented on one or more computer-usable storage media (including, but not limited to, disk memory, CD-ROM, optical memory, etc.) containing computer-usable program code.

[0213] This application is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products relating to this application. It should be understood that each process and / or block in a flowchart and / or block diagram can be performed using computer program instructions, as well as combinations of processes and / or blocks in a flowchart and / or block diagram. These computer program instructions may be provided to a processor of a general-purpose computer, a dedicated computer, an embedded processor, or any other programmable data processing device to generate a machine, the instructions executed by the processor of the computer or any other programmable data processing device, which generates a machine that performs a particular function in one or more processes of a flowchart and / or one or more blocks of a block diagram.

[0214] These computer program instructions may be stored in computer-readable memory, which can instruct the computer or any other programmable data processing device to operate in a specific manner, and as a result, the instructions stored in computer-readable memory generate an artifact that includes an instruction unit. The instruction unit performs a specific function in one or more processes in a flowchart and / or one or more blocks in a block diagram.

[0215] These computer program instructions may be loaded into a computer or another programmable data processing device, resulting in a series of tasks and steps being performed on the computer or other programmable device, thereby generating computer execution processes. Therefore, instructions executed on the computer or other programmable device provide steps for performing specific functions in one or more processes of a flowchart and / or one or more blocks of a block diagram.

[0216] It is clear that a person skilled in the art can make various modifications and changes to this application without departing from the spirit and scope of this application. This application is intended to encompass these modifications and changes to this application, insofar as they fall within the scope of protection defined by the following claims and their equivalents in art. [Explanation of Symbols]

[0217] 10 Communication Systems 20 Access Network Devices 30 terminal devices 800 equipment 802 Processing Unit 803 Communication Unit 801 Memory Unit 90 Access Network Devices 901 DU 902 CU 1010 Antenna 1020 Radio frequency section 1030 Signal Processing Unit 1031 Processing element 1032 memory element 1033 Interface Circuit 9011 Antenna 9012 Radio frequency unit 9013 Processor 9014 memory 9021 memory 9022 Processor

Claims

1. A communication method performed by a terminal device, wherein the method is: The first cell receives configuration information for at least one candidate cell from an access network device, The steps include selecting a second cell if the wireless link quality of the first cell satisfies a first condition, If the second cell belongs to the at least one candidate cell, the steps include performing a handover from the first cell to the second cell and communicating with the access network device in the second cell based on the configuration information of the second cell, or if the second cell does not belong to the at least one candidate cell, the steps include performing a radio resource control RRC re-establishment to access the second cell. A step of transmitting third information to the access network device in the second cell, wherein the third information indicates that the terminal device has been handed over from the first cell to the second cell, and the third information includes downlink beam information used by the access network device to transmit downlink data to the terminal device in the second cell. A communication method that includes this.

2. The wireless link quality of the first cell satisfies the first condition. The wireless link quality of the first cell is below a first threshold. The wireless link quality of the first cell is always below the first threshold in the first time window. The number of asynchronous instructions continuously detected by the terminal device is equal to or greater than the second threshold. After the number of asynchronous instructions continuously detected by the terminal device exceeds the second threshold, the terminal device starts a timer and does not detect a synchronous instruction within the timer's timing window, or A wireless link failure (RLF) occurs in the first cell described above. The method according to claim 1, comprising at least one of the following.

3. The aforementioned method, A step in which the first cell receives first information from the access network device, wherein the first information is used to constitute the first condition. The method according to claim 2, further comprising:

4. The wireless link quality of the second cell satisfies the second condition. The wireless link quality of the second cell satisfies the second condition. The wireless link quality of the second cell is equal to or greater than the third threshold. The wireless link quality of the second cell is always greater than or equal to the third threshold in the second time window. The wireless link quality of the second cell is equal to or better than the wireless link quality of the candidate cell other than the second cell among the at least one candidate cell. The wireless link quality of the second cell is always equal to or greater than the wireless link quality of the candidate cell other than the second cell among the at least one candidate cell in the second time window. The wireless link quality of the second cell is greater than the wireless link quality of the first cell. The wireless link quality of the second cell is always higher than that of the first cell in the second time window. The wireless link quality of the second cell exceeds the sum of the wireless link quality of the first cell and the offset, and The wireless link quality of the second cell always exceeds the sum of the wireless link quality of the first cell and the offset in the second time window. The method according to any one of claims 1 to 3, comprising at least one of the following.

5. The aforementioned method, A step in which the first cell receives second information from the access network device, wherein the second information is used to constitute the second condition. The method according to claim 4, further comprising:

6. The method according to claim 1, wherein the third information is carried in a message of a random access procedure initiated by the terminal device in the second cell.

7. The aforementioned method, A step of transmitting fourth information to the access network device in the second cell, wherein the fourth information is transported on a first resource, and the first resource is a resource corresponding to a cell handover. The method according to any one of claims 1 to 3, further comprising:

8. The aforementioned method, Steps include: receiving enable information from the access network device in the first cell, wherein the enable information is used to enable the terminal device to trigger a cell handover after a problem occurs in the wireless link of the serving cell of the terminal device; The method according to any one of claims 1 to 3, further comprising:

9. The method according to any one of claims 1 to 3, wherein the at least one candidate cell includes a candidate cell corresponding to a layer 1 / layer 2 handover and / or a candidate cell corresponding to a layer 3 handover.

10. A communication device comprising a module configured to perform the method described in any one of claims 1 to 3.

11. A communication device comprising a processor, wherein the processor is coupled to a memory, the memory stores a computer program, and the processor is configured to call the computer program in the memory to enable the communication device to perform the method according to any one of claims 1 to 3.

12. A communication device comprising a processor and an interface circuit, wherein the interface circuit is configured to receive a signal from a communication device other than the communication device, transmit the signal to the processor, or transmit a signal from the processor to a communication device other than the communication device, and the processor is configured to carry out the method according to any one of claims 1 to 3, either through a logic circuit or by executing code instructions.

13. A computer-readable storage medium, wherein the storage medium stores a computer program or instruction, and when the computer program or instruction is executed by a computer, the method according to any one of claims 1 to 3 is performed.

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