Communication method and apparatus

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]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to Chinese Patent Application No. 202210188271.9, entitled "COMMUNICATION METHOD AND APPARATUS", filed with the State Intellectual Property Office of the People's Republic of China on February 28, 2022, which is hereby incorporated by reference in its entirety.

[0002] The present application relates to the field of communications technology, and in particular to communications methods and devices. [Background technology]

[0003] With the continuous development of science and technology, new Internet services such as autonomous driving and virtual reality are constantly emerging, which places higher and higher requirements on wireless communication technologies.

[0004] In wireless communication systems, the wireless link quality directly determines the data transmission capacity, so how to recover the wireless link after a terminal device detects that a problem occurs in the wireless link needs further research. Summary of the Invention

[0005] The present application provides a communication method and apparatus for quickly restoring a wireless link after a terminal device detects that a problem occurs in the wireless link. [Means for solving the problem]

[0006] According to a first aspect, an embodiment of the present application provides a communication method. The method can be applied to a terminal device or a module in the terminal device. For example, the method is applied to a terminal device. In the method, the terminal device receives, in a first cell, configuration information of at least one candidate cell from an access network device, and selects a second cell 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); 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 received in the first cell; or 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.

[0007] According to the above method, the terminal device does not need to release the configuration information of at least one candidate cell after detecting that a problem occurs in the radio link of the current serving cell. Therefore, after the terminal device selects one of the candidate cells as a 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 resend the configuration information of the new serving cell to the terminal device. This can effectively save transmission resources and quickly restore the radio link.

[0008] In one possible design, the radio link quality of the first cell satisfying the first condition includes at least one of: the radio link quality of the first cell being less than a first threshold; the radio link quality of the first cell always being less than the first threshold in a first time window; a number of out-of-sync indications continuously detected by the terminal device being greater than or equal to a second threshold; after the number of out-of-sync indications continuously detected by the terminal device is greater than or equal to the second threshold, the terminal device starts a timer and does not detect a synchronization indication within a timing window of the timer; and a radio link failure RLF occurs in the first cell.

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

[0010] In one possible design, the radio link quality of the second cell satisfies a second condition, and the radio link quality of the second cell satisfying the second condition includes: the radio link quality of the second cell being greater than or equal to a third threshold; the radio link quality of the second cell always being greater than or equal to the third threshold in a second time window; the radio link quality of the second cell being greater than or equal to a radio link quality of a candidate cell other than the second cell among the at least one candidate cell; and the radio link quality of the second cell always being greater than or equal to a radio link quality of a candidate cell other than the second cell among the at least one candidate cell in the second time window. the radio link quality of the second cell is greater than or equal to the radio link quality of the first cell; the radio link quality of the second cell is greater than the radio link quality of the first cell at all times in the second time window; the radio link quality of the second cell is greater than the sum of the radio link quality of the first cell and an offset; and the radio link quality of the second cell is greater than the sum of the radio link quality of the first cell and an offset at all times in the second time window.

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

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

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

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

[0015] In one possible design, the method further includes a step of transmitting fourth information to an access network device in the second cell, where 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.

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

[0017] In this way, the access network device can control whether the terminal device triggers a cell handover after a problem occurs in the radio link of the serving cell of the terminal device based on the enabling information, which helps the access network device to flexibly control the behavior of the terminal device.

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

[0019] According to a second aspect, an embodiment of the present application provides a communication method. The method may be applied to a second DU or a module in the second DU. For example, the method is applied to the second DU. In the method, the second DU determines that a terminal device is handed over from a first cell to a second cell, and the handover is a cell handover triggered by the terminal device. If the first cell and the second cell belong to different DUs, first indication information is sent to the CU, and the first indication information indicates that the terminal device is handed over from the first cell to the second cell, so that the CU knows that the terminal device is handed over from the first cell to the second cell. Alternatively, when both the first cell and the second cell belong to the second DU, the first instruction information and the fourth instruction information are sent to the CU, and the fourth instruction information indicates a data packet that was not successfully transmitted by the second DU to the terminal device, so that after the terminal device performs handover, the CU can transmit a data packet to the terminal device based on the data packet that was not successfully transmitted by the second DU to the terminal device, and loss or retransmission of the data packet is avoided.

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

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

[0022] In this way, the data amount information already cached by the second DU is sent to the CU, which helps the CU to control the traffic of downlink data sent to the terminal device through the second DU.

[0023] In one possible design, the third indication information includes at least one of sequence numbers of unsuccessfully transmitted PDCP PDUs and the highest sequence number of successfully transmitted PDCP PDUs.

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

[0025] According to a third aspect, an embodiment of the present application provides a communication method. The method can be applied to a CU or a module in a CU. For example, the method is applied to a CU. In the method, the CU sends second indication information to a first DU, the second indication information indicates that a terminal device is handed over from a first cell to a second cell, the handover is a cell handover triggered by the terminal device, the first cell belongs to the first DU, and the second cell belongs to the second DU, the CU receives third indication information from the first DU, the third indication information indicates a data packet that is not successfully transmitted by the first DU to the terminal device, and the CU transmits the data packet to the terminal device through the second DU based on the third indication information.

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

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

[0028] In one possible design, the third indication information includes at least one of sequence numbers of unsuccessfully transmitted PDCP PDUs and the highest sequence number of successfully transmitted PDCP PDUs.

[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 in the first DU. For example, the method is applied to a first DU. In the method, the first DU receives second indication information from a CU, the second indication information indicates that a terminal device is handed over from a first cell to a second cell, the handover is a cell handover triggered by the terminal device, the first cell belongs to the first DU, the second cell belongs to the second DU, the first DU sends third indication information to the CU based on the second indication information, and the third indication information indicates a data packet that is not successfully sent by the first DU to the terminal device.

[0030] In this way, the first DU can send the third instruction information to the CU, so that after the terminal device performs handover, the CU can send a data packet to the terminal device based on the data packet that was not successfully sent to the terminal device by the first DU, and loss or retransmission of the data packet is avoided.

[0031] In one possible design, the third indication information includes at least one of sequence numbers of unsuccessfully transmitted PDCP PDUs and the highest sequence number of successfully transmitted PDCP PDUs.

[0032] According to a fifth aspect, an embodiment of the present application provides a communication method. The method can be applied to a first DU or a module in the first DU. For example, the method is applied to the first DU. In the method, the first DU sends a handover command to a terminal device, the handover command commands a handover of the terminal device from a first cell to a second cell, the first cell belongs to the first DU, the second cell belongs to the second DU, the first DU sends third indication information to a CU, and the third indication information indicates a data packet that is not successfully transmitted by the first DU to the terminal device.

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

[0034] According to a sixth aspect, an embodiment of the present application provides a communication method. The method can be applied to a CU or a module in a CU. For example, the method is applied to a CU. In the method, the CU receives notification information and third indication information from a first DU, the notification information is used to notify the CU that a terminal device is handed over from a first cell to a second cell, the third indication information indicates a data packet that is not successfully transmitted by the first DU to the terminal device, 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 receiving information about the amount of data already cached by the second DU.

[0036] According to a seventh aspect, an embodiment of the present application provides a communication method. The method can be applied to a second DU or a module in the second DU. For example, the method is applied to the 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 is handed over from a first cell to a second cell, the first cell belongs to the first DU, the second cell belongs to the second DU, and the second DU sends 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 the second DU to transmit downlink data to the terminal device.

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

[0040] In one possible design, the communication device may include a processor, the processor being coupled to a memory. The memory may store computer programs or instructions necessary to perform functions in the first aspect. The processor may execute the computer programs or instructions stored in the memory. When the computer programs or instructions are executed, the communication device is enabled to perform a method according to any one of the possible designs or implementations of the first aspect.

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

[0042] In one possible design, the communications device includes a processor and an interface circuit, the processor 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 aspect.

[0043] According to a 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 for implementing 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 may be implemented using hardware, or may be implemented using hardware running 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 to implement communication between the communication device and another device. For example, the communication unit is configured to transmit system information to a terminal 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 any one of the operations of the second to seventh aspects.

[0045] In one possible design, the communication device may include a processor, the processor may be coupled to a memory. The memory may store computer programs or instructions necessary to perform functions in any one of the second to seventh aspects. The processor may execute the computer programs or instructions stored in the memory. When the computer programs or instructions are executed, the communication device may perform a method according to any one of the possible designs or implementations of the second to seventh aspects.

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

[0047] In one possible design, the communications device includes a processor and an interface circuit, the processor 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 to seventh aspects.

[0048] It should be understood that in the eighth and ninth aspects, the processor may be implemented by hardware or software. When the processor is implemented by hardware, the processor may be a logic circuit, an integrated circuit, etc. When the processor is implemented by software, the processor may be a general-purpose processor, and is implemented by reading software code stored in a 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 the processor may be separately located. In a specific implementation process, the memory and the processor may be integrated on the same chip, or separately located on separate chips. The type of memory and the manner of arranging the memory and the processor are not limited in the embodiments of the present application.

[0049] According to a 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 an eleventh aspect, the present application provides a computer-readable storage medium storing computer-readable instructions that, when read and executed by a computer, enable the computer to perform a method according to any one of the possible designs of the first to seventh aspects.

[0051] According to a twelfth aspect, the present application provides a computer program product, which, when read and executed by a computer, enables the computer to execute a method according to any one of the possible designs of the first to seventh aspects.

[0052] According to a thirteenth aspect, the present application provides a chip, the chip including a processor, coupled to a memory, configured to read and execute a software program stored in the memory to perform a method according to any one of the possible designs of the first to seventh aspects.

[0053] These and other aspects of the present application will become clearer and more easily understood in the following description of the embodiments. [Brief description of the drawings]

[0054] [Figure 1] 1 is a diagram of a communication system to which an embodiment of the present application can be applied; [Figure 2A] FIG. 2 is a diagram of a CU-DU split architecture according to an embodiment of the present application. [Figure 2B] FIG. 13 is a diagram of another CU-DU split architecture according to an embodiment of the present application. [Diagram 3] 1 is a schematic flowchart corresponding to a communication method according to an embodiment of the present application. [Figure 4] 1 is a schematic flowchart corresponding to a communication method according to an embodiment of the present application. [Diagram 5] 1 is a schematic flowchart corresponding to a communication method according to an embodiment of the present application. [Figure 6] 1 is a schematic flowchart corresponding to a communication method according to an embodiment of the present application. [Figure 7] 1 is a schematic flowchart corresponding to a communication method according to an embodiment of the present application. [Figure 8] FIG. 2 is a block diagram of one possible example of an apparatus according to an embodiment of the present application. [Figure 9] FIG. 2 is a diagram of the structure of an access network device according to an embodiment of the present application. [Figure 10] FIG. 2 is a diagram of the structure of a terminal device according to an embodiment of the present application; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0056] FIG. 1 is a diagram of a communication system to which an embodiment of the present application can be applied. As shown in FIG. 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 devices and the terminal devices may be a Uu interface (also called an air interface), and data may be transmitted between the access network devices 20 and the terminal devices 30 through air interface resources. For example, the 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. When 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 A terminal device, which may also be called a user equipment (UE), mobile station (MS), mobile terminal (MT), etc., is a device that provides voice and / or data connection to a user, such as a handheld device or an in-vehicle device with wireless connection capabilities. Currently, some examples of terminal devices are mobile phones, tablet computers, notebook computers, palmtop computers, mobile internet devices (MIDs), 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 An access network device is a radio access network (RAN) node (or device) that connects terminals to a wireless network, and may also be called a base station. Currently, some examples of RAN nodes are 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 (Wifi) access point (AP).

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

[0060] (4) CU-DU split 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 one CU. This architecture may be referred to as a CU-DU split architecture. For example, the interface between a CU and a DU may be referred to as 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 the processing functions of the DU may be divided based on the protocol layers of the wireless network. For example, as shown in FIG. 2A, the functions of the PDCP layer and the protocol layers above the PDCP layer are configured on the CU, and the functions of the protocol layers below the PDCP layer (e.g., the RLC layer and the MAC layer) are configured on the DU. It should be understood that the division into the processing functions of the CU and the DU based on the protocol layers is only an example, and the processing functions may be divided in another manner instead. For example, the functions of the protocol layers above the RLC layer are configured on the CU, and the functions of the RLC layer and the protocol layers below the RLC layer are configured on the DU. As another example, the CU or the DU may have more functions of the protocol layers by division. As another example, the CU or the DU may further have some processing functions of the protocol layers by division. This is not limited in the embodiment of the present application.

[0062] Furthermore, the function of the CU may be implemented by using one entity or by using separate entities. For example, the function of the CU may be further divided, i.e., the control plane and the user plane are divided and implemented by using separate entities, i.e., by using a control plane CU entity (i.e., a CU-CP entity) and a user plane CU entity (i.e., a CU-UP entity). In order to jointly accomplish the functions of the RAN device, the CU-CP entity and the CU-UP entity may be combined with the 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 DU and one CU-UP may be connected to one CU-CP. 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 coordination of multiple CU-CPs, one CU-UP may instead be connected to multiple coordinated CU-CPs, which improves the flexibility of the CU-CP. Figure 2B is a diagram of an 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 be such that the RLC layer, the MAC layer, and the PHY layer are on the DU, and the PDCP layer and the protocol layers above the PDCP layer are on the CU.

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

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

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

[0066] The following first describes the relevant technical features in the embodiments of the present application. Please note that these descriptions are intended to facilitate understanding of the embodiments of the present application, and should not be considered as limitations on the scope of protection claimed in the present application.

[0067] 1. Cell Handover The cell handover may include a cell handover performed based on layer 1 / layer 2 (shortly called a layer 1 / layer 2 handover) and a cell handover performed based on layer 3 (shortly called a layer 3 handover). The cell handover performed based on layer 1 / layer 2 may be a cell handover performed based on layer 1 or layer 2, or may be a cell handover performed based on layer 1 and layer 2. Layer 1 may be the physical layer, layer 2 may be the MAC layer, and layer 3 may be the RRC layer.

[0068] Furthermore, the Layer 1 / Layer 2 handover may include the following two types:

[0069] (1) Layer 1 / Layer 2 handover triggered by an access network device: For example, the access network device selects a target cell that satisfies a Layer 1 / Layer 2 handover criterion from the candidate cells corresponding to the Layer 1 / Layer 2 handover based on the beam level measurement result reported by the terminal device, and sends a Layer 1 / Layer 2 handover command to the terminal device to command the terminal device to hand over to the target cell. The beam level measurement result may also be called a Layer 1 measurement result.

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

[0071] Layer 3 handovers can include two types:

[0072] (1) Layer 3 handover triggered by an access network device: For example, the access network device selects a target cell that satisfies a layer 3 handover criterion from the candidate cells corresponding to the layer 3 handover based on the cell-level measurement result reported by the terminal device, and sends a layer 3 handover command to the terminal device to instruct the terminal device to handover to the target cell. The cell-level measurement result may also be referred to as a layer 3 measurement result.

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

[0074] 2. Beam level and cell level measurement results In one possible implementation, the process of the terminal device obtaining a beam level measurement result may be as follows: the access network device transmits a reference signal to multiple beam directions of a cell. The reference signal 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. Correspondingly, the terminal device performs measurements on a time-frequency resource indicated by the access network device based on the reference signal. For example, the terminal device may obtain multiple temporary signal strengths of beams corresponding to the reference signal within a certain period by sampling, and weight or combine the obtained multiple signal strengths to obtain a measurement result of the beam. The measurement result of the beam may also be referred to as beam quality. Furthermore, the measurement result of the beam may be filtered by layer 1 filtering to obtain a filtered measurement result of the beam. For example, layer 1 filtering parameters may be configured by the access network device for the terminal device. Alternatively, the terminal device may filter the multiple obtained signal strengths to further obtain a filtered measurement result of the beam. The cell level measurement result may be obtained by the terminal device combining or weighting the measurement results of multiple beams in the cell. For example, the measurement result of the cell may be obtained by combining at least one beam in the cell through the configuration of the access network device. The measurement result of the cell may also be referred to as cell quality. Furthermore, the measurement result of the cell may be filtered by layer 3 filtering to obtain a filtered measurement result of the cell. For example, layer 3 filtering parameters may be configured by the access network device for the terminal device.

[0075] 3. Radio link failure In order to maintain the reliability of communication between the terminal device and the access network device, the terminal device needs to perform radio link monitoring (RLM) in the serving cell and determine whether a radio link failure (RLF) has occurred based on the radio link monitoring result.

[0076] For example, when detecting that the radio link quality of the serving cell is less than the asynchronous threshold within a time window (for ease of explanation, the time window is hereinafter referred to as the third time window), the physical layer of the terminal device can report an "in-sync indication" to the RRC layer once, or when detecting that the radio link quality of the serving cell is equal to or greater than the synchronous threshold within the third time window, the physical layer of the terminal device can report an "in-sync indication" to the RRC layer once. Furthermore, if the number of "in-sync indications" continuously detected by the terminal device at the RRC layer is higher than a threshold (e.g., the threshold is N310), the terminal device starts a timer 1 (e.g., timer 1 is T310). If the terminal device does not detect an "in-sync indication" in the timing window of timer 1, the terminal device can determine that an RLF has occurred. If timer 1 is started and running, and the number of "in-sync indications" continuously detected by the terminal device at the RRC layer is equal to or greater than a threshold (e.g., the threshold is N311), the terminal device can stop timer 1 and consider that the radio link is restored and that an RLF has not 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 an example of a case where RLF occurs. In another possible case, the terminal device can further determine that RLF occurs. For example, the terminal device can further determine that RLF occurs when at least one of the following conditions is met: (1) a problem occurs in random access, e.g., the number of failures to initiate random access by the terminal device is equal to or greater than a predefined threshold; (2) the number of retransmissions in the RLC layer exceeds the maximum number of retransmissions; and (3) consecutive uplink listen before talk (LBT) failures occur, i.e., the terminal device fails to preempt the channel multiple times in succession.

[0078] 4. Wireless Link Quality The radio link quality may be a physical layer channel quality, for example a physical downlink control channel (PDCCH) quality or a physical downlink shared channel (PDSCH) quality.

[0079] For example, the radio link quality may be obtained based on beam level measurement results. For example, when a terminal device performs beam level measurement in cell 1 to obtain measurement results of N1 beams in cell 1, the terminal device may use an average value of the measurement results of at least one of the N1 beams as the radio link quality of cell 1, or the terminal device may use an average value of the measurement results of N2 beams having relatively good measurement results among the N1 beams as the radio link quality of cell 1. N1 and N2 are positive integers, and N2 is less than N1.

[0080] In the embodiment of the present application, based on the above description of related technical features, the implementation of restoring a wireless link by a terminal device is considered.

[0081] A possible communication method provided in this embodiment of the present application is as follows: after a terminal device detects that a problem occurs in the radio link of a serving cell, the terminal device can select a target cell that meets a cell selection criterion through a cell selection procedure to restore the radio link, and perform RRC re-establishment to access the target cell.

[0082] In the following, a possible implementation procedure is described with reference to FIG.

[0083] 3 is a schematic flowchart corresponding to a communication method according to an embodiment of the present application. As shown in FIG. 3, the method includes the following steps:

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

[0085] For example, the access network device can send the configuration information 1 to the terminal device in multiple manners: For example, the access network device can send an RRC message to the terminal device in the first cell, where the RRC message includes the configuration information 1;

[0086] The configuration information 1 may include configuration information of the first cell and configuration information of at least one candidate cell of the 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] Using one of the candidate cells as an example, the configuration information of the candidate cell may include the configuration information of the terminal device in the candidate cell, and may further include other possible information, for example, the 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. Details will not be described again.

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

[0089] It should be understood that the first cell and the candidate cell may belong to the same access network device, or the first cell and the candidate cell 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 configuration information of the candidate cell from the access network device to which the candidate cell belongs through the Xn interface.

[0090] S302: The terminal device performs radio link monitoring in the first cell, and determines that RLF occurs according to the radio link monitoring result. For a specific implementation of the terminal device determining that RLF occurs, please refer to the above description.

[0091] Here, after determining that an RLF has occurred, the terminal device releases the configuration information of the first cell (e.g., suspends transmission of all radio bearers, i.e., no control plane signaling and user plane service data can be transmitted on the radio bearers), and further releases the configuration information of at least one candidate cell that is transmitted by the access network device to the terminal device in the first cell.

[0092] S303: After the terminal device executes a cell selection procedure and selects a cell (e.g., a second cell) that meets a cell selection criterion through the cell selection procedure, the terminal device actively initiates an 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 a random access procedure.

[0093] For the specific implementation of the cell selection procedure, please refer to the prior art.

[0094] S304: After receiving an RRC connection re-establishment request message from the terminal device in the second cell, the access network device can send an RRC connection re-establishment message to the terminal device, where the RRC connection re-establishment message indicates that the second cell currently accessed by the terminal device is a new serving cell of the terminal device.

[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 completes the RRC re-establishment procedure, the access network device can send a configuration message of the second cell to the terminal device in the second cell, and correspondingly, the terminal device can receive the configuration information of the second cell.

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

[0098] From the procedure shown in Fig. 3, it can be seen that the terminal device can perform RRC re-establishment to recover the radio link. However, in the RRC re-establishment procedure, the terminal device releases the configuration information of at least one candidate cell. Therefore, even if the terminal device selects one of the candidate cells as a new serving cell, the access network device needs to resend the configuration information of the new serving cell to the terminal device. This causes a large consumption of transmission resources. In addition, the terminal device needs to release the configuration information of the first cell (e.g., suspend the transmission of all radio bearers), and can only recover the transmission of the radio bearers after the RRC re-establishment is completed. This causes a large communication interruption delay.

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

[0100] Please note that the implementation of "terminal device selects target cell" here may be different from the implementation of selecting a target cell by a terminal device in the above-mentioned Layer 1 / Layer 2 CHO and the implementation of selecting a target cell by a terminal device in the above-mentioned Layer 3 CHO. If the target cell is a candidate cell corresponding to Layer 1 / Layer 2 handover, the implementation of "handing over a terminal device to a target cell" here may be the same as the implementation of handing over a terminal device to a target cell in the above-mentioned Layer 1 / Layer 2 CHO. If the target cell is a candidate cell corresponding to Layer 3 handover, the implementation of "handing over a terminal device to a target cell" here may be the same as the implementation of handing over a terminal device to a target cell in the above-mentioned Layer 3 CHO.

[0101] In the following, with reference to embodiment 1, several possible implementations of the aforementioned communication method are described.

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

[0103] S401: An access network device sends configuration information of at least one candidate cell to a terminal device in a first cell, and the terminal device can receive the configuration information of at least one candidate cell in the first cell accordingly. For details, see S301.

[0104] For example, the access network device can further send enabling information to the terminal device in the first cell, and the enabling information is used to enable the terminal device to trigger a cell handover after a problem occurs in the radio link of the serving cell. Correspondingly, the terminal device can receive the enabling information and further execute the subsequent method steps shown in Figure 4. Otherwise (i.e., the access network device does not send the enabling information to the terminal device, and correspondingly, the terminal device does not receive the enabling information), please refer to Figure 3.

[0105] S402: If the terminal device determines that the radio link of the first cell satisfies a first condition, it selects a second cell, where the second cell may also be referred to as a target cell.

[0106] For example, the radio link quality of the first cell satisfying the first condition may include at least one of: (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 the first threshold in a first time window; (3) the number of out-of-sync indications continuously detected by the terminal device is equal to or greater than a second threshold; (4) after the number of out-of-sync indications continuously detected by the terminal device is equal to or greater than the second threshold, the terminal device starts a timer 2 and does not detect a synchronization indication within the timing window of the timer 2; and (5) an RLF occurs in the first cell. "Less than" may be replaced with "lower" and "greater than" may be replaced with "higher". The first condition may be configured by the access network device for the terminal device. For example, the access network device transmits first information to the terminal device in the first cell, and the first information is used to configure the first condition (e.g., the first information includes a first threshold, a second threshold, a duration of a timing window of timer 2, and a duration of a first time window). The first threshold may be different from the asynchronous threshold, the second threshold may be different from N310, and the first time window and the third time window may be the same or different. This is not specifically limited.

[0107] There may be multiple specific implementations for the terminal device to select the second cell. In the following, with reference to Implementation 1 and Implementation 2, two possible implementations are described using an example in which "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 is understood that the at least one candidate cell may include only candidate cells corresponding to Layer 1 / Layer 2 handover, i.e., {cell a, cell b}, or the at least one candidate cell may include only candidate cells corresponding to Layer 3 handover, i.e., {cell b, cell c}. For example, the access network device may configure at least one candidate cell for the terminal device, which includes only candidate cells corresponding to Layer 1 / Layer 2, or includes only candidate cells corresponding to Layer 3 handover, or includes candidate cells corresponding to Layer 1 / Layer 2 and candidate cells corresponding to Layer 3, or may be agreed upon in a protocol.

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

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

[0110] It should be understood that only one cell among the at least one candidate cell may satisfy the second condition, or multiple cells may satisfy the second condition. If multiple cells among the at least one candidate cell satisfy the second condition, for example, if both cell a and cell b among {cell a, cell b, cell c} satisfy the second condition, there may be three schemes: Scheme 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 of cell b, the terminal device can select cell a as the second cell. Scheme 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. Scheme 3: This depends on the internal implementation of the terminal device, i.e., the terminal device itself decides to select cell a or cell b as the second cell. For example, a specific scheme among schemes 1, 2, and 3 may be agreed upon in the protocol, or the access network device may indicate the specific scheme to be used by the terminal device.

[0111] In addition, if there is no cell whose radio link quality satisfies the second condition in {cell a, cell b, cell c}, 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 criterion through the cell selection procedure, and the cell becomes the second cell. In this case, the second cell does not belong to at least one candidate cell, i.e., the second cell is a cell other than {cell a, cell b, cell c}.

[0112] When the terminal device selects the second cell from the at least one candidate cell based on the cell-level measurement result of the 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 cell-level measurement result satisfies a third condition based on the cell-level measurement result of {cell a, cell b, cell c}. If there is a cell in {cell a, cell b, cell c} whose cell-level measurement result satisfies the third condition, the 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: (1) the cell-level measurement result of the second cell is equal to or greater than a fourth threshold; (2) the cell-level measurement result of the second cell is equal to or greater than the cell-level measurement result of a candidate cell other than the second cell among the at least one candidate cell; and (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 there is no cell in {cell a, cell b, cell c} whose cell-level measurement result satisfies the third 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 criterion through the cell selection procedure, and the cell becomes the second cell. In this case, the second cell does not belong to at least one candidate cell. It should be noted that the terminal device usually performs the cell selection procedure in an idle state. In this case, the terminal device can perform the cell selection procedure in a 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 in a 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, the access network device can send second information to the terminal device, where the second information instructs the terminal device to select the second cell based on the radio link quality. Optionally, a second condition can be further configured for the second information. For example, the second information can include a third threshold, an offset, and a duration of the second time window. Correspondingly, the terminal device can select the second cell based on the radio link quality of the at least one candidate cell after receiving the second information. Otherwise (i.e., the access network device does not send the second information to the terminal device, and correspondingly, the terminal device does not receive the second information), the terminal device can select the second cell based on the cell-level measurement result of the at least one candidate cell.

[0115] Implementation 2 The 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 result of the cells included in the second candidate cell list. The second candidate cell list can be different from the first candidate cell list, and the first candidate cell list includes at least one candidate cell, that is, the first candidate cell list can be {cell a, cell b, cell c}. In one example, in addition to all the cells included in the first candidate cell list, the second candidate cell list can further include another cell. For example, the second candidate cell list is {cell a, cell b, cell c, cell d}. In this case, please refer to implementation 1 for the 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 may not belong to at least one candidate cell.

[0116] For example, the second candidate cell list may be configured by the access network device for the terminal device. For example, the access network device can send cell list configuration information to the terminal device, where the 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 (e.g., the second cell is cell a, cell b, or cell c), the terminal device can suspend the transmission of all radio bearers but not release the configuration information of the at least one candidate cell, and later execute S403A to restore the radio link. If the terminal device determines that the selected second cell does not belong to at least one candidate cell (e.g., the second cell is cell d), the terminal device can suspend the transmission of all radio bearers, release the configuration information of the at least one candidate cell, and later execute S403B to restore the radio link.

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

[0119] Here, if the second cell is cell a, the terminal device can perform Layer 1 / Layer 2 handover for handover from the first cell to the second cell. If the second cell is cell c, the terminal device can perform Layer 3 handover for handover from the first cell to the third 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), there may be three schemes: Scheme 1: The terminal device performs Layer 1 / Layer 2 handover for handover from the first cell to the second cell. Scheme 2: The terminal device performs Layer 3 handover for handover from the first cell to the second cell. Scheme 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 handover from the first cell to the second cell, or to perform a Layer 3 handover for handover from the first cell to the second cell. For example, a particular scheme among Scheme 1, Scheme 2, and Scheme 3 may be agreed upon in a protocol, or the access network device may indicate the particular scheme to be used by the terminal device.

[0120] For example, after performing handover from a first cell to a second cell, the terminal device can notify an 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 above-mentioned scheme (e.g., implementation 1 or implementation 2). There may be multiple specific notification schemes, for example, there may be notification scheme 1 and notification scheme 2.

[0121] Notification method 1: The terminal device can send third information to an access network device in a second cell, where the third information indicates that the terminal device has been handed over from the first cell to the second cell, and the 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 an identifier of the terminal device, an identifier of the first cell (i.e., an identifier of the source cell), and an indication information a, where the indication 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 a 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 a message A of the two-step random access procedure. Further, optionally, the third information may be carried in a MAC control element (CE) of message 3 or message A. Alternatively, the third information may be carried in a message other than a message of the random access procedure.

[0122] Notification scheme 2: The terminal device can send fourth information to the access network device in the second cell, where the fourth information is carried on the first resource, where the first resource is a resource corresponding to a cell handover triggered by the terminal device. In other words, the terminal device can notify the access network device in an implicit manner. The fourth 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 may be carried in a message other than the message of the random access procedure. For example, the first resource may be a physical uplink control channel (PUCCH) resource, where the first resource may be configured by the access network device for the terminal device. For example, the access network device can send fifth information to the terminal device in the first cell, where the fifth information is used to configure the first resource.

[0123] For example, after performing handover from the first cell to the second cell, the terminal device can further transmit downlink beam information to the access network device in the second cell. The downlink beam information indicates a 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 a beam corresponding to a target SSB, and the target SSB may be an SSB associated with a 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 the third information or the fourth information, or may be additionally transmitted by the terminal device to the access network device. This is not specifically limited.

[0124] The downlink beam information may indicate a beam (e.g., a first beam), where the first beam may be a beam having an optimal measurement result among multiple beams of the second cell determined by the terminal device. Correspondingly, the access network device may transmit downlink data to the terminal device in the second cell through the first beam based on the downlink beam information. Alternatively, the downlink beam information may indicate multiple candidate beams determined by the terminal device. Correspondingly, the access network device may select one downlink beam (e.g., a second beam) from the multiple candidate beams based on the downlink beam information, and transmit downlink data to the 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 may release the configuration information of at least one candidate cell and initiate an RRC connection re-establishment procedure in the second cell. For specific implementation, see FIG. 3.

[0127] It should be understood that in the procedure shown in Figure 4, the configuration information, the first information, the second information, the fifth information, the enable information, etc. of at least one candidate cell may be carried in the same message or in separate messages, which 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 that a problem occurs in the radio link. After the terminal device selects one of the candidate cells as a 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 resend the configuration information of the new serving cell to the terminal device. This can effectively save transmission resources. In addition, the terminal device can trigger a cell handover for handover from the source cell to the new serving cell. Therefore, compared with the RRC re-establishment procedure, this method can quickly restore communication and effectively reduce communication interruption delay.

[0129] The above embodiment 1 describes the implementation procedure of this embodiment of the present application from the perspective of communication between an access network device and a terminal device. Because the access network device may include a CU and one or more DUs, the following describes some possible implementation procedures from the perspective of communication between a CU, a DU, and a terminal device with reference to embodiment 2.

[0130] EMBODIMENT 2 When the access network device includes a CU and one or more DUs, the first cell and the second cell in embodiment 1 may belong to different DUs managed by the CU. For example, the first cell belongs to the first DU, and the second cell belongs to the second DU. Alternatively, the first cell and the second cell may belong to the same DU. For example, both the first cell and the second cell belong to the second DU. In the following, possible procedures for these two cases are described separately.

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

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

[0133] S501: A CU sends configuration information of at least one candidate cell to a terminal device through a first DU to which a first cell belongs, where the first cell is a serving cell of the terminal device.

[0134] For example, the CU may send an RRC message to the first DU, which then forwards the RRC message to the terminal device, where the RRC message includes configuration information of at least one candidate cell.

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

[0136] Here, an example in which the second cell belongs to at least one candidate cell is used for explanation.

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

[0138] For the specific implementation of S501 to S503, please refer to the first embodiment.

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

[0140] Here, there may be multiple implementations of the second DU determining that the terminal device has been handed over from the first cell to the second cell. For example, the terminal device can send third information to the second DU. Correspondingly, 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 information from the terminal device. As another example, the terminal device can send fourth information to the second DU. Correspondingly, the second DU can determine that the terminal device has been handed over from the first cell to the second cell after receiving fourth information from the terminal device (the fourth information is carried on the first resource). For specific implementations, please refer to embodiment 1.

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

[0142] Optionally, the second DU can further send first downlink data delivery status (DDDS) information to the CU, where the first DDDS information is used by the CU to control the traffic of downlink data sent to the terminal device through the second DU. For example, the first DDDS information may include an amount of data already cached by the second DU.

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

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

[0145] S506: The CU sends second indication information to the first DU, where the second indication information indicates that the terminal device has been handed over from the first cell to the second cell. Correspondingly, the first DU receives the second indication information and stops communication with the terminal device (e.g., stops sending downlink data to the terminal device).

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

[0147] S507: The first DU sends third indication information to the CU, where the third indication information indicates a data packet that has not been successfully transmitted by the first DU to the terminal device. Further, the first DU can stop downlink data transmission to the terminal device.

[0148] For example, the third indication information may include at least one of a sequence number (SN) of a PDCP PDU that was not successfully transmitted by the first DU and the highest sequence number of a PDCP PDU that was successfully transmitted by the first DU.

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

[0150] S508: The CU sends a data packet to the terminal device through the second DU based on the third indication information.

[0151] For example, if the third indication information includes a sequence number of a PDCP PDU that is 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 indication information includes a highest sequence number of a PDCP PDU that is successfully transmitted by the first DU, the CU can transmit 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 send downlink beam information to the second DU (for the downlink beam information, see embodiment 1). Thus, in S505, the second DU can send a data packet to the terminal device through a 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] 6 is a schematic flowchart corresponding to a communication method according to Embodiment 2 of the present application. As shown in FIG. 6, the method includes the following steps:

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

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

[0157] Here, an example in which the second cell belongs to at least one candidate cell is used for explanation.

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

[0159] For the specific implementation of S601 to S603, please refer to the first embodiment.

[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 first indication information and fourth indication information to the CU, where the first indication information indicates that the terminal device has been handed over from the first cell to the second cell, and the fourth indication information indicates a data packet that was not successfully transmitted by the second DU to the terminal device.

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

[0163] S606: The CU sends a data packet to the terminal device through the second DU based on the data packet that was not successfully sent by the second DU to the terminal device.

[0164] For a specific implementation of the aforementioned steps shown in FIG. 6, please refer to FIG.

[0165] According to the method of embodiment 2, after detecting that a problem occurs 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 resend the configuration information of the second cell to the terminal device. This can effectively save transmission resources and reduce communication interruption delay. In addition, the source DU (i.e., the DU to which the first cell belongs) can send indication information to the CU to indicate the data packets that have not been successfully transmitted by the source DU to the terminal device, so that the CU can transmit the data packets that have not been successfully transmitted to the terminal device through the target DU, and the risk of data packet loss is effectively avoided.

[0166] It should be understood that in embodiment 2, the solution described in "S501-S504" or "S601-S604" is as follows: the terminal device selects a second cell based on the scheme 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 the third information or the fourth information sent by the terminal device. In another possible embodiment, "S501-S504" or "S601-S604" can be replaced with: the terminal device is handed over from the first cell to the second cell by 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 the handover completion information sent 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 send downlink beam information to the second DU.

[0167] EMBODIMENT 3 In embodiment 3, a possible implementation procedure of Layer 1 / Layer 2 handover triggered by an access network device is described from the perspective of communication between a CU, a DU, and a terminal device (Layer 3 handover triggered by an access network device may be implemented with reference to this).

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

[0169] S701: A CU sends configuration information of at least one candidate cell to a terminal device through a first DU to which the first cell belongs.

[0170] Here, the at least one candidate cell may include a candidate cell that supports Layer 1 / Layer 2 handover.

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

[0172] S703: The first DU selects a target cell from the at least one candidate cell based on the beam level measurement result, for example, the target cell is a second cell, and sends a Layer 1 / Layer 2 handover command to the terminal device, the handover command instructing to handover the terminal device from the first cell to the second cell. Correspondingly, the terminal device receives the handover command and is handed over from the first cell to the second cell according to the handover command.

[0173] Here, for the implementation of selecting a target cell by the first DU based on the beam level measurement result, please refer to the prior art.

[0174] For example, the Layer 1 handover command may be downlink control information (DCI), and the Layer 2 handover command may be MAC CE. The handover command may include an identity of the second cell and downlink beam information, where the downlink beam information indicates a downlink beam to be used by the second DU to which the second cell belongs to transmit downlink data to the terminal device.

[0175] S704: The first DU sends third indication information to the CU, where the third indication information indicates a data packet that is not successfully transmitted by the first DU to the terminal device. Furthermore, the first DU can stop downlink data transmission to the terminal device.

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

[0177] Optionally, the terminal device may further send downlink beam information to the second DU. In one possible implementation, the downlink beam information sent by the terminal device to the second DU may be the downlink beam information carried in the Layer 1 / Layer 2 handover command at S703. Then, the second DU can send 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 send downlink beam information to the second DU.

[0179] S706: The second DU sends notification information to the CU, where the notification information 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, the notification information may include first DDDS information, and the first DDDS information may include an amount of data already cached by the second DU.

[0181] S707: The CU sends a data packet to the terminal device through the second DU based on the third indication information.

[0182] According to the method of embodiment 3, after the first DU sends a handover command to the terminal device, the first DU can send third instruction information to the CU, so that the CU can send data packets that were not successfully sent to the terminal device through the target DU (i.e., the second DU), and effectively avoid 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 a corresponding beam according to the downlink beam information.

[0183] Regarding the first to third embodiments, it will be understood that:

[0184] (1) The first to third embodiments are described using an example in which the serving cell of the terminal device is one cell. In another possible case, for example, when the terminal device operates in a dual connectivity mode, the solutions of the first to third embodiments may be applicable to a primary base station handover of dual connectivity, or may be applicable to a secondary node (SN) / secondary cell group (SCG) addition or secondary base station / secondary cell group change. For example, after determining that the radio link of the cell of the secondary base station / secondary cell group meets the first condition, the terminal device may also use the method of the first embodiment to restore the radio link of the cell.

[0185] (2) The step numbers of the flowcharts described in the first to third embodiments are merely examples of execution procedures and do not limit the execution order of the steps. In the embodiments of the present 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 executed steps. Some steps may be deleted based on each flowchart according to actual requirements, or other possible steps may be added based on each flowchart according to actual requirements.

[0186] (3) The above focuses on the differences between different embodiments from embodiment 1 to embodiment 3, and embodiment 1 to embodiment 3 can refer to each other, except for the contents of other differences. In addition, different implementations or different examples in the same embodiment can also refer to each other.

[0187] The above mainly describes the solutions provided in the embodiments of the present application from the perspective of the interaction between communication devices. It is understood that, to implement the aforementioned functions, the terminal device and the access network device may include corresponding hardware structures and / or software modules for performing the functions. Those skilled in the art should easily notice that the example units and algorithm steps described in the embodiments of the present application 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 depends on the specific application and design constraints of the technical solution. Those skilled in the art may implement the described functions using various methods for each specific application, but it should not be considered that such implementation goes beyond the scope of the present application.

[0188] In the embodiment of the present application, functional unit division may be performed in the terminal device and the access network device according to the above method example. For example, each functional unit may be obtained by division based on each corresponding function, or two or more functions may be integrated into one unit. The integrated unit may be implemented in the form of hardware or in the form of a software functional unit.

[0189] When an integrated unit is used, FIG. 8 is a block diagram of a possible example of an apparatus according to an embodiment of the present application. As shown in FIG. 8, the apparatus 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 apparatus 800. The communication unit 803 is configured to support communication between the apparatus 800 and another device. Optionally, the communication unit 803 may be referred to as a transceiver unit and may include a receiving unit and / or a transmitting unit configured to perform receiving and transmitting operations, respectively. The apparatus 800 may further include a storage unit 801 configured to store program codes and / or data of the apparatus 800.

[0190] The apparatus 800 may be the terminal device in the above embodiment. The processing unit 802 can support the apparatus 800 in performing the operations of the terminal device in the above method examples. Alternatively, the processing unit 802 can mainly perform the internal operations of the terminal device in the method examples, and the communication unit 803 can support the communication between the apparatus 800 and another device.

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

[0192] The apparatus 800 may be the access network device in the above embodiment. The processing unit 802 can support the apparatus 800 in performing the operation of the access network device in the above method example. Alternatively, the processing unit 802 can mainly perform the internal operation of the access network device in the method example, and the communication unit 803 can support the communication between the apparatus 800 and another device.

[0193] It should be understood that the division of the units in the above-mentioned device is merely a logical division of functions. In actual implementation, all or some of the units may be integrated into one physical entity or may be physically separated. In addition, all the units in the device may be implemented in the form of software called by a processing element, or may be implemented in the form of hardware, or some units may be implemented in the form of software called by a processing element, and some units may be implemented in the form of hardware. For example, each unit may be a separately arranged processing element, or may be integrated into a chip of the device for implementation. In addition, each unit may instead be stored in a memory in the form of a program called by a processing element of the device to perform the function of the unit. In addition, all or some of the units may be integrated or implemented independently. The processing element in this document may be called a processor, and may be an integrated circuit having signal processing capabilities. In the course of implementation, the operations in the above-mentioned method or the above-mentioned units may be implemented by using a hardware integrated logic circuit in the processor element, or may be implemented in the form of the processing element calling the software.

[0194] In one example, a unit in any one of the aforementioned devices may be one or more integrated circuits configured to perform the aforementioned method, such as one or more application specific integrated circuits (ASICs), one or more microprocessors (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. As another example, if a unit in an apparatus may be implemented in a form in which the processing element schedules a program, the processing element may be a processor, such as a general-purpose central processing unit (CPU) or another processor that can call a program. As yet another example, the unit may be integrated and implemented in the form of a system-on-a-chip (SOC).

[0195] The aforementioned unit for receiving is an interface circuit of the device and is configured to receive a signal 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 a signal from another chip or device. The aforementioned unit for transmitting is an interface circuit of the device and is configured to transmit a signal 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 a signal to another chip or device.

[0196] Figure 9 is a diagram of the structure of an access network device according to an embodiment of the present application. This access network device (or base station) can be used in the communication system shown in Figure 1 to perform the functions of the access network device in the embodiment of the above-mentioned method. 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] The CU 902 is mainly configured to perform baseband processing, control the access network device, etc. The DU 901 and the CU 902 may be physically co-located or physically separated, i.e., the base station may be a distributed base station. The CU 902 is the control center of the access network device, which may also be called a processing unit, and is mainly configured to complete baseband processing functions. For example, the CU 902 may be configured to control the access network device to perform work procedures related to the access network device in the above-mentioned method embodiment.

[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. The DU may include at least one processor 9013 and at least one memory 9014, the radio frequency unit may include at least one antenna 9011 and at least one radio frequency unit 9012, and the CU may include at least one processor 9022 and at least one memory 9021.

[0199] In one example, the CU 902 may include one or more boards. The boards may jointly support one radio access network (e.g., a 5G network) with a single access instruction, or may separately support multiple radio access networks (e.g., an LTE network, a 5G network, or another network) with different access standards. The memory 9021 and the processor 9022 may be served by one or more boards. That is, the memory and the processor may be disposed on each board. Alternatively, the boards may share the same memory and the same processor. In addition, the necessary circuitry may be disposed on each board. The DU 901 may include one or more boards. The boards may jointly support one radio access network (e.g., a 5G network) with a single access instruction, or may separately support multiple radio access networks (e.g., an LTE network, a 5G network, or another network) with different access standards. The memory 9014 and the processor 9013 may be served by one or more boards. That is, the memory and the processor may be disposed on each board. Alternatively, the boards may share the same memory and the same processor. Additionally, each board may have further required circuitry disposed thereon.

[0200] The access network device shown in Fig. 9 can implement all the processes related to the access network device in the above-mentioned method embodiment. The operations and / or functions of the modules in the access network device shown in Fig. 9 are respectively used to implement the corresponding procedures in the above-mentioned method embodiment. For details, please refer to the description of the above-mentioned method embodiment. In order to avoid repetition, detailed descriptions are appropriately omitted here.

[0201] Figure 10 is a diagram of the structure of a terminal device according to an embodiment of the present application. This terminal device can be applied to the communication system shown in Figure 1 and is configured to perform the work of the terminal device in the aforementioned embodiment. 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 the respective communication protocol layers. 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 programs used to execute the methods performed by the terminal device in the above-mentioned manner may not be stored in the memory element 1032, but may be stored in a memory external to the modem subsystem and loaded and used by the modem subsystem when used. The interface circuit 1033 is configured to communicate with another subsystem.

[0204] The modem subsystem may be implemented using a chip. The chip includes at least one processing element and an interface circuit. The processing element is configured to execute the steps of any of the methods executed by the terminal device. The interface circuit is configured to communicate with other devices. In one implementation, the units of the terminal device that perform the steps of the aforementioned methods may be implemented by a program scheduled by the processing element. For example, an apparatus used in a terminal device includes a processing element and a storage element. The processing element calls a program stored in the storage element to execute the method executed by the terminal device in the aforementioned method embodiments. The storage element may be a storage element located on the same chip as the processing element, i.e. an on-chip storage element.

[0205] In another implementation, the programs used to execute the methods performed by the terminal device in the above-described methods may be in a storage element located on a different chip than the processing element, i.e. in an off-chip storage element, in which case the processing element calls or loads the programs from the off-chip storage element to the on-chip storage element in order to call and execute the methods performed by the terminal device in the above-described method embodiments.

[0206] In yet another implementation, the unit of the terminal device performing the steps of the above method may be configured as one or more processing elements. These processing elements are located in the modem subsystem. A processing element herein may be an integrated circuit, for example one or more ASICs, one or more DSPs, one or more FPGAs, or a combination of various integrated circuits. These integrated circuits may be integrated together to form a chip.

[0207] The units of the terminal device performing the steps of the aforementioned method may be integrated together and implemented in the form of a SOC. The SOC chip is configured to perform the aforementioned method. At least one processing element and a storage element may be integrated into a chip, and the processing element calls a program stored in the storage element to perform the aforementioned method executed by the terminal device. Alternatively, at least one integrated circuit may be integrated into a chip to perform the aforementioned method executed by the terminal device. Alternatively, referring to the aforementioned implementation, the functions of some units may be implemented by a program called by the processing element, and the functions of some units are implemented by an integrated circuit.

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

[0209] The processing element here may be the same as that described above and implemented using a processor. The function of the processing element may be the same as that of the processing unit described in FIG. 8. For example, the processing element may be a general-purpose processor, e.g., a CPU, or one or more integrated circuits configured to perform the above-mentioned method, e.g., one or more ASICs, one or more microprocessors DSPs, or one or more FPGAs, or a combination of at least two of these integrated circuit forms. The storage element may be implemented using a memory. The function of the storage element may be the same as that of the storage unit described in FIG. 8. The storage element may be a memory, or may be a collective term for multiple memories.

[0210] The terminal device shown in Fig. 10 can implement all the processes related to the terminal device in the above-mentioned method embodiment. The operations and / or functions of the modules in the terminal device shown in Fig. 10 are intended to implement the corresponding procedures in the above-mentioned method embodiment. For details, please refer to the description of the above-mentioned method embodiment. In order to avoid repetition, detailed descriptions are appropriately omitted here.

[0211] In the embodiments of the present 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 a relationship between related objects and indicates that three relationships may exist. For example, A and / or B may indicate three cases: when only A is present, when both A and B are present, and when only B is present, 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 combination of single items or 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 the embodiments of the present application are used to distinguish between multiple objects and are not used to limit the order, chronology, priority, or importance of the multiple objects.

[0212] Those skilled in the art should understand that the embodiments of the present application may be provided as a method, a system, or a computer program product. Thus, the present application may use the form of an embodiment that includes a hardware-only embodiment, a software-only embodiment, or a combination of software and hardware. In addition, the present application may use the form of a computer program product embodied on one or more computer usable storage media (including, but not limited to, disk memory, CD-ROM, optical memory, etc.) that includes computer usable program code.

[0213] The present application is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the present application. It should be understood that each process and / or each block of the flowcharts and / or block diagrams, and combinations of the processes and / or blocks of the flowcharts and / or block diagrams, can be implemented using computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, a special purpose computer, an embedded processor, or any other programmable data processing device to generate a machine, such that the instructions executed by the processor of the computer or any other programmable data processing device generate an apparatus that performs a particular function in one or more processes of the flowcharts and / or one or more blocks of the block diagrams.

[0214] These computer program instructions may be stored in a computer readable memory that can instruct a computer or some other programmable data processing device to act in a particular manner, such that the instructions stored in the computer readable memory create an artifact that includes an instruction apparatus that performs a particular function in one or more processes of the flowcharts and / or one or more blocks of the block diagrams.

[0215] These computer program instructions may be loaded into a computer or another programmable data processing device, causing a sequence of operations and steps to be performed on the computer or another programmable device, thereby generating a computer-implemented process. Thus, the instructions executed on the computer or another programmable device provide steps for implementing a particular function in one or more processes of the flowcharts and / or one or more blocks of the block diagrams.

[0216] It is obvious that those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. This application intends to cover these modifications and variations of this application as long as they fall within the scope of protection defined by the following claims and their equivalent technologies. [Explanation of symbols]

[0217] 10. Communication Systems 20 Access Network Devices 30 Terminal Devices 800 equipment 802 Processing Unit 803 Communication Unit 801 Storage Unit 90 Access Network Devices 901DU 902 CU 1010 Antenna 1020 Radio Frequency Unit 1030 Signal processing section 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. 1. A method of communication, comprising: receiving, in a first cell, configuration information of at least one candidate cell from an access network device; selecting a second cell if a radio link of the first cell satisfies a first condition; performing a handover from the first cell to the second cell if the second cell belongs to the at least one candidate cell, and communicating with the access network device in the second cell based on configuration information of the second cell, or performing a radio resource control (RRC) re-establishment to access the second cell if the second cell does not belong to the at least one candidate cell. A communication method comprising:

2. The radio link quality of the first cell satisfies the first condition, the radio link quality of the first cell is less than a first threshold; the radio link quality of the first cell is always less than the first threshold during a first time window; a number of out-of-sync indications successively detected by the terminal device is greater than or equal to a second threshold; after a number of out-of-sync indications successively detected by the terminal device is equal to or greater than the second threshold, the terminal device starts a timer and does not detect a sync indication within a timing window of the timer; or a radio link failure (RLF) occurs in the first cell; The method of claim 1 , comprising at least one of:

3. The method comprises: receiving, in the first cell, first information from the access network device, the first information being used to configure the first condition; The method of claim 2, further comprising:

4. the radio link quality of the second cell satisfies a second condition; The radio link quality of the second cell satisfies the second condition, the radio link quality of the second cell is greater than or equal to a third threshold; the radio link quality of the second cell is always greater than or equal to the third threshold during a second time window; the radio link quality of the second cell is equal to or greater than a radio link quality of a candidate cell other than the second cell among the at least one candidate cell; the radio link quality of the second cell is always equal to or greater than the radio link quality of a candidate cell other than the second cell among the at least one candidate cell during the second time window; the radio link quality of the second cell being greater than the radio link quality of the first cell; the radio link quality of the second cell is always greater than the radio link quality of the first cell during the second time window; the radio link quality of the second cell is greater than the sum of the radio link quality of the first cell and an offset; and the radio link quality of the second cell always exceeds the sum of the radio link quality of the first cell and the offset during the second time window; The method according to any one of claims 1 to 3, comprising at least one of:

5. The method comprises: receiving, in the first cell, second information from the access network device, the second information being used to configure the second condition; 5. The method of claim 4, further comprising:

6. The method comprises: sending third information to the access network device in the second cell, the third information indicating that the terminal device has been handed over from the first cell to the second cell, the handover being a cell handover triggered by the terminal device; 6. The method of claim 1, further comprising:

7. The third information is An identifier of the terminal device; an identifier of the first cell; downlink beam information used by the access network device to transmit downlink data to the terminal device in the second cell; and Instruction information At least one of The instruction information indicates the cell handover triggered by the terminal device. The method of claim 6.

8. The method according to claim 6 or 7, wherein the third information is carried in a message of a random access procedure initiated by the terminal device in the second cell.

9. The method comprises: transmitting fourth information to the access network device in the second cell, the fourth information being carried on first resources, the first resources being resources corresponding to a cell handover triggered by the terminal device; 6. The method of claim 1, further comprising:

10. The method comprises: receiving enabling information from the access network device in the first cell, the enabling information being used to enable the terminal device to trigger the cell handover after a problem occurs in a radio link of a serving cell of the terminal device; 10. The method of claim 1, further comprising:

11. The method according to any one of claims 1 to 10, wherein the at least one candidate cell comprises a candidate cell supporting a Layer 1 / Layer 2 handover and / or a candidate cell supporting a Layer 3 handover.

12. A communication device comprising modules configured to carry out the method according to any one of claims 1 to 11.

13. A communications device comprising a processor, the processor coupled to a memory, the memory storing a computer program, the processor configured to invoke the computer program in the memory to enable the communications device to perform a method according to any one of claims 1 to 11.

14. A communication device comprising a processor and an interface circuit, the interface circuit configured to receive signals from a communication device other than the communication device, transmit the signals to the processor, or transmit signals from the processor to a communication device other than the communication device, the processor configured to perform a method according to any one of claims 1 to 11 through logic circuits or by executing code instructions.

15. 12. A computer readable storage medium, the storage medium storing a computer program or instructions which, when executed by a computer, performs the method of any one of claims 1 to 11.

16. A computer program product, which when read and executed by a computer enables the computer to carry out the method according to any one of claims 1 to 11.

Images