WO2025232638A1 - Communication method, and apparatus - Google Patents

Abstract

The present application relates to the technical field of communications. Provided are a communication method and an apparatus. The method comprises: a first network device sending to a second network device a first message, the first message comprising information used for identifying a third network device; and receiving a second message from the second network device, the second message being used for indicating whether a first communication interface has been successfully established or is not successfully established between the second network device and the third network device, the first communication interface being a communication interface for handover. In the present application, the first network device determines how to add a candidate cell by considering the condition of a communication interface for handover between candidate network devices. Thus, the mode can ensure service continuity during subsequent handover, thereby ensuring the service experience of users.

Description

A communication method and apparatus

Cross-reference to related applications

This application claims priority to Chinese Patent Application No. 202410578644.2, filed on May 10, 2024, entitled "A Communication Method and Apparatus", the entire contents of which are incorporated herein by reference.

Technical Field

This application relates to the field of communication technology, and in particular to a communication method and apparatus.

Background Technology

In mobile communication systems, when a user equipment (UE) moves from the coverage area of one cell to the coverage area of another, a cell handover is required. The goal of cell handover is to switch the UE to another cell before it moves out of the service cell's coverage area, so that it can continue to receive services and thus ensure service continuity.

During cell handover, if there is no communication connection between the serving base stations of the candidate cells for performing cell handover during the UE's cell handover process, the cell handover may fail, resulting in service interruption.

Summary of the Invention

This application provides a communication method and apparatus to reduce the probability of cell handover failure and ensure the continuity of UE services.

In a first aspect, this application provides a communication method that can be executed by a first network device, a chip, or a circuit. Optionally, the chip is a chip of the first network device, and the circuit is a circuit of the first network device. This application does not specifically limit this aspect.

This method can be applied to 5G communication systems or higher, and also to non-terrestrial communication systems; this application does not specifically limit its application. The execution is as follows:

Send a first message to the second network device, the first message including information for identifying the third network device; receive a second message from the second network device, the second message indicating whether a first communication interface has been successfully established or not successfully established between the second network device and the third network device, the first communication interface being a communication interface for handover.

In this application, the first network device determines how to add candidate cells by referring to the communication interfaces between candidate network devices (the second network device and the third network device) for handover. This method can ensure the continuity of services during subsequent handovers and guarantee the user's service experience.

In one alternative approach, the first message is used to request the second network device to prepare handover resources for the terminal. The first message also includes: identification information of the second network device, and/or identification information of the second cell, wherein the second cell is managed by the second network device.

In one alternative approach, the first message further includes at least one of the following: request information, an identifier of the first network device, or an identifier of the terminal, wherein the request information is used to request the second network device to provide information about the first communication interface to the first network device.

In this application, the second network device sends a second message to the first network device, indicating whether the first communication interface has been successfully established or not, only when the first message includes a request. The first and third network devices have previously prepared handover resources. The third network device can manage these handover resources using the identifier of the first network device and the identifier of the corresponding terminal. When the first message includes the identifier of the first network device and the identifier of the corresponding terminal, the second network device (which may or may not use the core network device) requests the third network device to prepare the same handover resources for the same terminal, i.e., the same as the previously prepared handover resources. The third network device then determines to prepare the same handover resources for the same terminal, thereby improving handover efficiency.

In one alternative approach, if the first communication interface between the second and third network devices has been successfully established, the second message further includes: handover resources for the first cell, which is managed by the third network device. Based on this, the first network device can add the first cell as a candidate cell.

In one alternative approach, if the second message includes handover resources for the first cell, the first network device also sends the handover resources for the first cell to the terminal so that the terminal can perform measurement operations, etc., on the first cell.

In one alternative approach, the second message is also used to indicate the type of the first communication interface, which includes a first type of interface and/or a second type of interface, wherein the first type of interface directly connects the second network device and the third network device, and the second type of interface connects the second network device and the third network device through a core network device.

In this application, when the second message includes the first communication interface type, it facilitates the first network device in determining whether to add the first cell as a candidate cell.

In one alternative approach, the failure to establish a first communication interface between the second network device and the third network device includes: there is no communication interface between the second network device and the third network device; or, the communication interface between the second network device and the third network device is not used for handover.

In one alternative approach, the second message includes a cause value indicating that the failure to prepare the switching resources for the second network device was due to the failure to successfully establish the first communication interface.

Based on this, the first network device can clearly identify why the terminal cannot switch to the cell reception service managed by the second network device.

In one alternative approach, the information used to identify the third network device is the identification information of the third network device and/or the identification information of the first cell, wherein the first cell is managed by the third network device.

In one alternative approach, the first network device is the source network device for the initial handover, the second network device is the source network device for subsequent handovers, and the third network device is a candidate network device for subsequent handovers. The first network device, the second network device, and the third network device are all different.

Secondly, this application provides a communication method that can be executed by a second network device, a chip, or a circuit. Optionally, the chip is a chip of the second network device, and the circuit is a circuit of the second network device. This application does not specifically limit this aspect.

This method can be applied to 5G communication systems or communication systems above 5G, and can also be applied to non-terrestrial communication systems; however, this application does not specifically limit its application. The execution is as follows:

Receive a first message from a first network device, the first message including information for identifying a third network device; in response to the first message, send a second message to the first network device, the second message indicating whether a first communication interface has been successfully established or not successfully established between the second network device and the third network device, the first communication interface being a communication interface for handover.

In one alternative approach, the second network device determines whether the first communication interface has been successfully established or not based on the first message; if the second network device determines that the first communication interface has been successfully established, it sends a second message to the first network device, the second message indicating that the first communication interface has been successfully established; or, if the second network device determines that the first communication interface has not been successfully established, it sends a second message to the first network device, the second message indicating that the first communication interface has not been successfully established.

In one alternative approach, the first message is used to request the second network device to prepare handover resources for the terminal. The first message also includes: identification information of the second network device, and/or identification information of the second cell, wherein the second cell is managed by the second network device.

In one alternative approach, the first message further includes at least one of the following: request information, an identifier of the first network device, or an identifier of the terminal, wherein the request information is used to request the second network device to provide information about the first communication interface to the first network device.

In one alternative approach, if the first communication interface between the second network device and the third network device has been successfully established, the second message may also include: handover resources for the first cell, which is managed by the third network device.

In one alternative approach, the second message is also used to indicate the type of the first communication interface, which includes a first type of interface and/or a second type of interface, wherein the first type of interface directly connects the second network device and the third network device, and the second type of interface connects the second network device and the third network device through a core network device.

In one alternative approach, the failure to establish a first communication interface between the second network device and the third network device includes: there is no communication interface between the second network device and the third network device; or, the communication interface between the second network device and the third network device is not used for handover.

In one alternative approach, the second message includes a cause value indicating that the failure to prepare the switching resources for the second network device was due to the failure to successfully establish the first communication interface.

In one alternative approach, the second network device further sends a third message to the third network device, the third message being used to request the establishment of the first communication interface; receives a fourth message from the third network device, the fourth message being used to indicate whether the establishment of the first communication interface was successful or failed; if the fourth message indicates that the establishment of the first communication interface was successful, it is determined that the first communication interface has been successfully established; or if the fourth message indicates that the establishment of the first communication interface failed, it is determined that the first communication interface has not been successfully established.

In one alternative approach, if the first type of interface between the second network device and the third network device fails to be established, but the second type of interface has been successfully established, the second network device sends a fifth message to the core network device, which requests preparation of handover resources and includes information for identifying the third network device; and receives a sixth message from the core network device, which includes handover resources for the first cell managed by the third network device.

In one alternative approach, the fifth message may also include: the identifier of the first network device and the identifier of the terminal.

Furthermore, if the fifth message may include the identifier of the first network device and the identifier of the terminal corresponding to the first network device, the third network device determines that it is preparing the same handover resources for the same terminal, thereby improving the handover efficiency.

In one alternative approach, the second network device also sends identification information of candidate cells that are allowed to be handed over or candidate cells that are not allowed to be handed over to the fourth network device. The second network device and the fourth network device are different logical units under the same network architecture. The candidate cells that are allowed to be handed over include the first cell, which is managed by the third network device.

It should be noted that when the second network device is a network device with separate centralized unit (CU) and distributed unit (DU), as described above, the second network device is equivalent to the CU. Different logical units within the same network architecture also include a fourth network device (equivalent to the DU). Since cell handover is initiated by the DU, the second network device also sends identification information of candidate cells that are allowed to handover or candidate cells that are not allowed to handover to the fourth network device.

In one alternative approach, the second network device also sends key information and first information to the fourth network device. The first information is used by the fourth network device to determine the handover key information for the first cell. The second network device and the fourth network device are different logical units under the same network architecture.

Based on this, the fourth network device can send the key information to the terminal, and the terminal can change the key (replacing the key of the source cell with the key of the target cell) to switch from the source cell to the target cell to receive services, ensuring service continuity.

In one alternative approach, the first network device is the source network device for the initial handover, the second network device is the source network device for subsequent handovers, and the third network device is a candidate network device for subsequent handovers. The first network device, the second network device, and the third network device are all different.

Thirdly, embodiments of this application provide a communication device, which can be a first network device or a second network device. The communication device has the functions to implement the first to second aspects described above. For example, the communication device includes modules, units, or means that perform the steps involved in the first to second aspects. These functions, units, or means can be implemented by software, hardware, or hardware executing corresponding software.

In one possible design, the communication device includes a processing unit and a transceiver unit. The transceiver unit can be used to transmit and receive signals to enable communication between the communication device and other devices; for example, the transceiver unit is used to receive information. The processing unit can be used to perform some internal operations of the communication device. The transceiver unit can be called an input/output unit, a communication unit, etc., and can be a transceiver; the processing unit can be a processor. When the communication device is a module (e.g., a chip) in a communication device, the transceiver unit can be an input/output interface, input/output circuit, or input/output pins, etc., and can also be called an interface, communication interface, or interface circuit, etc.; the processing unit can be a processor, processing circuit, or logic circuit, etc.

In another possible design, the communication device includes a processor and may further include a transceiver for transmitting and receiving signals. The processor executes program instructions to perform the methods in any of the possible designs or implementations of the first to second aspects described above. The communication device may also include one or more memories coupled to the processor, which may store necessary computer programs or instructions for implementing the functions involved in the first aspect. The processor can execute the computer programs or instructions stored in the memory, causing the communication device to implement the methods in any of the possible designs or implementations of the first to second aspects described above.

In another possible design, the communication device includes a processor that can be coupled to a memory. The memory can store computer programs or instructions necessary to implement the functions described in the first aspect above. The processor can execute the computer programs or instructions stored in the memory, causing the communication device to implement the methods in any possible design or implementation of the first to second aspects above.

In another possible design, the communication device includes a processor and an interface circuit, wherein the processor is used to communicate with other devices through the interface circuit and to perform the methods in any possible design or implementation of the first to second aspects described above.

Understandably, in the third aspect described above, the processor can be implemented in hardware or software. When implemented in hardware, the processor can be a logic circuit, integrated circuit, etc.; when implemented in software, the processor can be a general-purpose processor that reads software code stored in memory. Furthermore, there can be one or more processors, and one or more memories. The memory can be integrated with the processor or separated from it. In specific implementations, the memory can be integrated with the processor on the same chip or disposed on different chips. This application does not limit the type of memory or the arrangement of the memory and processor.

Fourthly, embodiments of this application provide a communication system, which includes a first network device, a second network device, and a third network device as described in the first aspect above. Optionally, the first network device is the source network device for the initial handover, the second network device is the source network device for subsequent handovers, and the third network device is a candidate network device for subsequent handovers. The first network device, the second network device, and the third network device are all different.

Fifthly, this application provides a chip system including a processor and potentially a memory, for implementing the methods described in the first or second aspect above. The chip system may be composed of chips or may include chips and other discrete devices.

Sixthly, this application also provides a computer-readable storage medium storing computer-readable instructions that, when executed on a computer, cause the computer to perform the methods described in the first to second aspects.

In a seventh aspect, this application provides a computer program product containing instructions that, when run on a computer, cause the computer to perform the methods of the embodiments of the first to second aspects described above.

For the technical effects that can be achieved in the second to seventh aspects mentioned above, please refer to the description of the technical effects that can be achieved by the corresponding possible design schemes in the first aspect mentioned above. This application will not repeat them here.

Attached Figure Description

Figure 1 shows a schematic diagram of a communication system provided in an embodiment of this application;

Figure 2 shows a schematic diagram of a cell handover process;

Figure 3 shows a schematic diagram of a cell handover scenario;

Figure 4 shows a flowchart of a communication method provided in an embodiment of this application;

Figure 5 shows a flowchart of a communication method provided in an embodiment of this application;

Figure 6 shows a flowchart of a communication method provided in an embodiment of this application;

Figure 7 shows a schematic diagram of the structure of a communication device provided in an embodiment of this application;

Figure 8 shows a schematic diagram of the structure of a communication device provided in an embodiment of this application;

Figure 9 shows a schematic diagram of the structure of a communication device provided in an embodiment of this application.

Detailed Implementation

To make the objectives, technical solutions, and advantages of this application clearer, a further detailed description of this application will be provided below in conjunction with the accompanying drawings. The specific operational methods in the method embodiments can also be applied to the device embodiments or system embodiments. In the description of this application, unless otherwise stated, "multiple" means two or more. Therefore, implementations of the device and method can be referred to mutually, and repeated details will not be repeated.

The technical solutions provided in this application can be applied to 5G systems, or to future communication systems (such as 6G) or other similar communication systems. Furthermore, the technical solutions provided in this application can be applied to cellular links, public land mobile networks (PLMNs), machine-to-machine (M2M) networks, Internet of Things (IoT) networks, or other networks. They can also be applied to links between devices, such as device-to-device (D2D) links. D2D links can also be called sidelinks, which are also referred to as edge links or secondary links. In this application, the above terms all refer to links established between devices of the same type, and their meanings are the same. The so-called same type of devices can be links between terminal devices, links between base stations, links between relay nodes, etc., and this application does not limit this.

Figure 1 is a schematic diagram of a wireless communication system applicable to this application. As shown in Figure 1, the wireless communication system may include at least one network device, such as network device 111, network device 112, and network device 113. The wireless communication system may also include at least one terminal device, such as terminal device 121, terminal device 122, terminal device 123, terminal device 124, terminal device 125, terminal device 126, and terminal device 127. The communication method between network devices can be backhaul, such as the communication method between network device 111 and network device 112, or the communication method between network device 111 and network device 113. The communication method between network devices and terminal devices can be enhanced mobile broadband (eMBB), such as the communication method between network device 112 and terminal device 121. The communication method between network devices and terminal devices can be multi-site transmission, such as the communication method between network device 112, network device 113, and terminal device 124. The communication method between terminal devices can be D2D. For example, the communication method between terminal device 122 and terminal device 125.

Terminal devices can be devices capable of receiving network device scheduling and instruction information, providing users with voice and/or data connectivity, or handheld devices with wireless connectivity, or other processing devices connected to a wireless modem. Terminal devices can communicate with one or more core networks or the Internet via a radio access network (RAN). For example, terminal devices can be portable, pocket-sized, handheld, computer-embedded, or vehicle-mounted mobile devices. Terminal devices can also be referred to as subscriber units (SS), subscriber stations (MS), mobile stations (MS), remote stations (AP), access points (AP), remote terminals (APs), access terminals (APs), user agents (MS), customer premises equipment (CPE), terminals (UEs), mobile terminals (MTs), etc. Terminal devices can also be wearable devices. Terminal devices can also be devices in next-generation communication systems. For example, terminal devices in 5G networks or future PLMN networks, and terminal devices in NR communication systems. Currently, terminal devices can include: mobile phones, tablets, laptops, PDAs, customer-premises equipment (CPE), mobile internet devices (MID), wearable devices (such as smartwatches, smart bracelets, pedometers, etc.), in-vehicle equipment (e.g., cars, bicycles, electric vehicles, airplanes, ships, trains, high-speed trains, etc.), virtual reality (VR) devices, augmented reality (AR) devices, and industrial control devices. Wireless terminals in intelligent control, smart home devices (e.g., refrigerators, televisions, air conditioners, electricity meters, etc.), intelligent robots, workshop equipment, wireless terminals in self-driving, remote medical surgery, smart grids, transportation safety, smart cities, or smart homes, and flying equipment (e.g., intelligent robots, hot air balloons, drones, airplanes), etc. Terminal devices can also be other devices with terminal functions; for example, a terminal device can also be a device that performs terminal functions in D2D communication.

Network equipment is an entity on the network side used to transmit or receive signals. Examples include transmission reception points (TRPs) and gNBs. Network equipment can be an access point (AP) in a wireless local area network (WLAN), a base transceiver station (BTS) in a global system for mobile communication (GSM) or code division multiple access (CDMA), a base station (nodeB, NB) in wideband code division multiple access (WCDMA), or an evolved Node B (eNB or eNodeB) in long-term evolution (LTE). Network equipment can also be a relay station or access point, or network equipment in vehicle-mounted devices, wearable devices, and 5G networks, or network equipment in future evolved PLMNs, or gNodeB/gNB devices in NR systems. In some deployments, a gNB may include a CU and a DU. The CU implements some of the gNB's functions, and the DU implements others. For example, the CU handles non-real-time protocols and services, such as radio resource control (RRC), service data adaptation protocol (SDAP), and packet data convergence protocol (PDCP). The DU handles physical layer protocols and real-time services, such as radio link control (RLC), medium access control (MAC), and physical (PHY) layers. The gNB may also include an active antenna unit (AAU). The AAU implements some physical layer processing functions, radio frequency processing, and active antenna-related functions. Since information from the RRC layer ultimately becomes information from the PHY layer, or is derived from information from the PHY layer... Therefore, under this architecture, higher-layer signaling (e.g., RRC layer signaling) can also be considered to be sent by the DU, or by the DU and AAU. It is understood that the network device can be one or more of the following: CU node, DU node, and AAU node. Furthermore, the CU can be a network device in the radio access network (RAN), or a network device in the core network (CN); this application does not limit this. Additionally, in this embodiment, the network device provides services to a cell, and the terminal device communicates with the network device through the transmission resources (e.g., frequency domain resources, or spectrum resources) used by the cell. The cell can be the cell corresponding to the network device (e.g., a base station). The cell can belong to a macro base station or to a base station corresponding to a small cell. For example, a small cell can include: a metro cell, a micro cell, a pico cell, a femto cell, etc. Because small cells have small coverage areas and low transmission power, they can provide high-speed data transmission services. Furthermore, in other possible cases, the network device can be any other device that provides wireless communication functionality to the terminal device. The embodiments of this application do not limit the specific technology or device form used in the network device. For example, in an open radio access network (ORAN) system, CU can also be called O-CU (open CU), DU can also be called O-DU, CU-CP can also be called O-CU-CP, CU-UP can also be called O-CU-UP, and RU can also be called O-RU. For ease of description, this application uses CU, CU-CP, CU-UP, DU, and RU as examples. Any of the units among CU (or CU-CP, CU-UP), DU, and RU in this application can be implemented through a software module, a hardware module, or a combination of software and hardware modules.

The following description, with reference to Figure 2, illustrates the terminal's cell handover operation. It uses the UE as the terminal and the network devices (CU and DU) as an example, with the CU managing the source DU and candidate DU (or target DU). The operation is as follows:

S201, the UE sends a measurement report to the source DU.

This measurement report includes layer 3 (L3) measurement results, specifically including measurement results of neighboring cells. Neighboring cells refer to cells that may be handed over after the UE moves.

S202, the source DU sends a measurement report to the CU.

The source DU sends an uplink (UL) RRC message to the CU. This UL RRC message includes a measurement report.

S203, based on the measurement report, the CU decides to initiate a Layer 1/L2 Triggered Mobility (LTM) configuration.

Specifically, the CU decides to initiate LTM configuration based on the measurement results of neighboring cells included in the measurement report.

S204, the CU sends a UE context establishment request message to the candidate DU.

The UE context establishment request message may include the identity (ID) of the first candidate cell. Understandably, the CU also indicates the ID of the source DU. This source DU ID is used to request the candidate DU to provide physical random access channel (PRACH) resources to the source DU.

S205, the candidate DU sends a UE context establishment response message to the CU.

When a candidate DU accepts the LTM configuration request, it sends a UE context establishment response message to the CU. The UE context establishment response message includes at least one of the following information: the lower-layer RRC configuration corresponding to the first candidate cell, the transmission configuration indicator (TCI) status configuration, the random access channel (RACH) configuration, and the reference signal (RS) configuration.

S206, the CU sends a UE context modification request message to the source DU.

The UE context modification request message includes: RS configuration of the first candidate cell, TCI status configuration of the first candidate cell, and RACH resource configuration of the first candidate cell.

S207, the source DU sends a UE context modification response message to the CU.

The UE context modification response message may include: the channel state information (CSI) resource configuration of the source cell, which is used to send the lower-layer measurement results of the first candidate cell in the source cell.

Optionally, perform the following steps S208 and S209.

S208, the CU sends a UE context modification request message to the candidate DU.

The UE context modification request message may include: the cell ID of the source cell and the RS configuration of the source cell. It should be noted that candidate cells include the source cell.

S209, the candidate DU sends a UE context modification response message to the CU.

The UE context modification response message may include: the generated CSI resource configuration. This CSI resource configuration is used to send the CSI of the candidate cell on the first candidate cell.

S210, the CU sends a downlink (DL) RRC message to the source DU.

The DL RRC message may include an RRC reconfiguration message that includes the LTM configuration (e.g., the lower-level RRC configuration corresponding to the first candidate cell).

S211, the source DU sends an RRC reconfiguration message to the UE.

S212, the UE sends an RRC reconfiguration complete message to the source DU.

S213, the source DU sends an RRC reconfiguration complete message to the CU.

Specifically, the source DU sends the RRC reconfiguration complete message to the CU via the UL RRC message.

Optionally, execute S214 to S216.

S214, the UE and the candidate DU are synchronized in advance.

Specifically, advance synchronization includes uplink synchronization and downlink synchronization. Downlink synchronization involves the source DU sending a TCI state activation or deactivation indication for the first candidate cell to the UE. This activation indication is used to activate (or deactivate) the TCI state of the first candidate cell. The UE tracks the downlink timing of the first candidate cell based on the activation indication. In subsequent processes, the UE needs to receive downlink data, send uplink data, or perform measurements based on the downlink timing. Uplink synchronization, on the other hand, involves the UE and the candidate DU performing advance synchronization of the first candidate cell based on its random access resource configuration.

S215, the candidate DU sends the timing advance (TA) and associated contention-free random access (CFRA) resource information of the first candidate cell to the CU.

S216, the CU sends the TA of the first candidate cell and the associated CFRA resource information to the source DU.

S217, the UE sends a measurement report to the source DU.

This measurement report includes the lower-layer measurement results. The UE measures the RS according to the RS configuration, and then sends the measurement results to the source DU according to the CSI resource configuration.

S218, based on the measurement report, the source DU decides to perform LTM handover on the candidate cell.

S219, the source DU sends an LTM cell handover command to the UE.

The LTM cell handover command includes the identifier of the target cell, which is used to indicate the first candidate cell as the target cell for handover. The LTM cell handover command may also include the beam information of the target cell (e.g., TCI state identifier) and the timing advance information of the target cell, which is used by the UE to receive downlink control information in a random access-free manner.

S220, the source DU sends an LTM cell change notification message to the CU.

The LTM cell change notification message is used to indicate that an LTM cell handover command has been initiated for the UE. The LTM cell change notification message may include the target cell ID and beam information. It is understood that the target cell is a candidate cell from the preceding steps.

S221, the CU sends the target cell ID and beam information to the target DU.

It is understood that the target DU is one of the candidate DUs in the aforementioned steps, that is, the DU corresponding to the target cell. The target DU in Figure 2 is illustrated here using a candidate DU as an example, and the target DUs in the following steps are all candidate DUs.

S222, Target DU detection terminal access.

For example, a UE accesses the target DU via random access or without random access. In the case of without random access, the target DU sends downlink control information to the UE based on beam information. In the without random access method, the UE accesses the target cell via PUSCH based on the timing advance information in the LTM cell handover command, instead of via PRACH.

S223, the target DU sends a successful access message to the CU.

After detecting the UE's access, the target DU sends the successful access message to the CU.

S224, the UE sends a message to the target DU indicating that the RRC reconfiguration was successful.

S225, the target DU sends a message to the CU indicating that the RRC reconfiguration was successful.

S226, the CU sends a UE context release command message to the source DU.

The UE context release command message is used to release the resources of the candidate cell of the source DU.

S227, the source DU sends a UE context release complete message to the CU.

The process described in Figure 2 above applies to handover within cells managed by the same CU, and is not applicable to handover between cells managed by different CUs. For handover between cells managed by different CUs, as shown in Figure 3, the UE can handover from the source cell managed by the source gNB to a cell managed by a candidate gNB (e.g., gNB1/CU1, gNB2/CU2, gNB3/CU3) to receive services. Here, gNB1/CU1 manages candidate cell 1, gNB2/CU2 manages candidate cell 2, and gNB3/CU3 manages candidate cell 3. However, if it is uncertain whether there is a communication interface between the candidate gNBs for performing the handover, subsequent handovers may fail, meaning the UE cannot receive continuous services. For example, the UE hands over from the source cell to candidate cell 1, and then from the candidate cell to candidate cell 2. However, if there is no communication interface between gNB1 and gNB2 for performing the handover, the cell handover fails. The UE may then handover back from candidate cell 1 to the source cell. However, as the UE moves, it may have moved out of the source cell's coverage area, resulting in a deterioration in the quality of the communication services received by the UE, affecting its service experience.

Based on this, this application provides a communication method to reduce the probability of cell handover failure and ensure the continuity of UE services. To better illustrate the solution of this application, the terminal in the following specific embodiments can be the terminal itself or a chip inside the terminal. The following description uses data interaction between a first network device and candidate network devices (in Figure 4, only the second and third network devices are used as examples; in specific applications, the number of candidate network devices is not limited) for illustration. Furthermore, it may also involve data interaction between candidate network devices and core network devices (e.g., access and mobility management function (AMF), session management function (SMF), or user plane function (UPF) devices, etc.), which can be understood with reference to Figure 4. The first (second or third) network device can be the first (second or third) network device itself or a chip or circuit inside the first (second or third) network device. The first network device, the second network device, and the third network device described below can be devices that combine CU and DU, can be CU, or can be gNB, etc. The specific form of the network device is not specifically limited here; the following is merely an example. In this system, the first network device is the source network device for the initial handover (also known as the initial LTM) (as shown in Figure 3, the source gNB), the second network device is the source network device for subsequent handovers (also known as subsequent LTMs) (as shown in Figure 3, gNB1/CU1, gNB2/CU2, gNB3/CU3), and the third network device is a candidate network device for subsequent handovers (if the second network device is gNB1/CU1 in Figure 3, the third network device is gNB2/CU2 or gNB3/CU3; or, if the second network device is gNB2/CU2 in Figure 3, the third network device is gNB1/CU1 or gNB3/CU3; or, if the second network device is gNB3/CU3 in Figure 3, the third network device is gNB2/CU2 or gNB1/CU1). The first, second, and third network devices are all different.

Refer to Figure 4 and execute the following:

S401, the first network device sends a first message to the second network device, the first message including information for identifying the third network device. Accordingly, the second network device receives the first message.

The information used to identify the third network device, in addition to identifying the third network device, also instructs the second network device to determine whether a first communication interface (or message exchange for the handover process) between the second and third network devices has been successfully established or not. This first communication interface is a communication interface for handover (LTM handover or L3 handover). For example, this first communication interface is an XN interface for XN handover or an NG interface for NG handover (the XN and NG interfaces are understood with reference to the existing Third Generation Partnership Project (3GPP) protocol and will not be elaborated here). Specifically, if the first message includes the information used to identify the third network device, in response to this information, the second network device determines whether the first communication interface with the third network device has been successfully established.

It should be noted that failure to establish the first communication interface between the second and third network devices can be understood as either the absence of a communication interface between the two network devices (i.e., no control signaling can be exchanged) or the existence of a communication interface between the two network devices, but this interface is not used for handover purposes (e.g., it can be used for control signaling exchange for network management, but not for control signaling exchange for handover). Specifically, failure to establish the first communication interface is determined based on the following two possible implementations: Implementation 1) The second network device determines not to establish the first communication interface with the third network device; or Implementation 2) The second network device requests the establishment of the first communication interface from the third network device, but the third network device refuses to establish it.

The first communication interface includes a first type of interface and/or a second type of interface. The first type of interface directly connects the second network device and the third network device, meaning it does not require connection through core network equipment. For example, the first type of interface is an XN interface (refer to existing 3GPP protocols for understanding, which will not be elaborated here). The second type of interface connects the second network device and the third network device through core network equipment. For example, the second type of interface is an NG interface (refer to existing 3GPP protocols for understanding, which will not be elaborated here).

For example, the information used to identify the third network device in the first message mentioned above is the identification information of the third network device (e.g., the global node identifier of gNB1/CU1), and/or the identification information of the first cell (e.g., the Cell Global ID of the first cell, wherein the construction of the Cell Global ID of the first cell includes the identification information of the third network device, or the Cell Global ID of the first cell can indicate the identification information of the third network device), wherein the first cell is managed by the third network device. How the information of the third network device is specifically identified is not limited here. Furthermore, in specific applications, the cells managed by the third network device may include multiple cells, and the first cell is the candidate cell determined by the first network device for handover when deciding to initiate handover configuration.

Optionally, the first message is a handover request message, which can be sent via broadcast or unicast, without specific limitation. The first message is used to request the second network device to prepare handover resources for the terminal (i.e., the terminal currently served by the first network device). The handover resources can be understood as the configuration information (LTM configuration information, or L3 configuration information, etc.) of the candidate cell (hereinafter referred to as the second cell) managed by the second network device. The LTM configuration information includes at least one of the following: TCI state configuration, advance synchronization configuration, random access configuration, CSI resource configuration, radio bearer configuration, cell group configuration, etc. In the scheme shown in Figure 4, the handover resources are the handover resources of the second cell, such as the LTM configuration information of the second cell.

The first message also includes information for identifying the second network device. For example, the information for identifying the second network device may be the identification information of the second network device (e.g., the global node identifier of gNB2/CU2), and/or the identification information of the second cell (e.g., the global identifier of the second cell), wherein the second cell is managed by the second network device.

Optionally, the first message may further include request information, which requests the second network device to provide the first network device with information 1 of the first communication interface between the second network device and the third network device. This information 1 indicates whether the first communication interface has been successfully established or not. In response to the request information, the second network device sends a second message including information 1 to the first network device.

Optionally, the first message may also include the identifier of the first network device and the identifier of the terminal served by the first network device. For example, the identifier of the first network device may be the identifier information of the first network device or the identifier information of the source cell managed by the first network device. For example, the identifier information of the terminal may be the XnAP UE ID. The first network device and the third network device have previously prepared handover resources. The third network device can manage these handover resources using the identifier of the first network device and the identifier of the terminal corresponding to the first network device. When the first message includes the identifier of the first network device and the identifier of the terminal corresponding to the first network device, the second network device (which may or may not use the core network device) requests the third network device to prepare the same handover resources for the same terminal, i.e., the same as the previously prepared handover resources. The third network device then determines to prepare the same handover resources for the same terminal, improving handover efficiency.

S402, the second network device responds to the first message and determines whether the first communication interface between the second network device and the third network device has been successfully established or not.

For example, it is assumed here that the first communication interface is an interface of the first type.

After receiving the first message, the second network device can determine whether the first communication interface has been successfully established or not (or, in other words, whether the first type of interface handover is available or unavailable) based on the first message. For example, the second network device can determine whether the first communication interface has been successfully established or not through a handover already performed by another terminal (a handover between a cell managed by the second network device and a cell managed by the third network device), or the second network device can obtain the information from the core network device. Optionally, the second network device can also determine this through the following steps S4021-S4022, as follows:

S4021, the second network device sends a third message (e.g., XN interface creation request (XN SETUP REQUEST)) to the third network device, which is used to request the establishment of the first communication interface.

Optionally, the third message includes the identification information of the second network device (or the identification information of the second cell). Optionally, the third message also includes interface handover indication information of the first type, such as XN LTM indication information, so that the third network device can determine that the third message is an establishment request for the first type of interface.

S4022, the third network device responds to the third message and sends a fourth message to the second network device.

The fourth message indicates whether the establishment of the first communication interface (e.g., the XN interface) was successful or failed. If the fourth message indicates that the first communication interface was successfully established, the second network device determines that the first communication interface has been successfully established; or if the fourth message indicates that the first communication interface failed to be established, the second network device determines that the first communication interface was not successfully established.

Optionally, the fourth message includes the identification information of the second network device, so that the second network device can determine the establishment status of the first type of interface between the second network device and the third network device.

Optionally, if the fourth message indicates that the first communication interface has not been successfully established, but the second type of interface has been successfully established (or is available for switching), the following S4023 to S4026 determination is performed, as follows:

S4023, the second network device sends a fifth message to the core network device through a second type of interface. The fifth message is used to request the core network device to prepare for resource switching.

The fifth message includes information for identifying the third network device (which can be understood by referring to the description at S401 above and will not be elaborated here) and information for identifying the second network device. For example, the fifth message can be an NG Handover Required message for LTM, which also includes NG LTM indication information 1, which is used to request the preparation of handover resources for LTM.

Optionally, the fifth message may also include the identifier of the first network device and the identifier of the terminal corresponding to the first network device. When the fifth message carries the identifier of the first network device and the identifier of the terminal corresponding to the first network device, it facilitates the third network device in determining the same handover resources to be prepared for the same terminal, thereby improving handover efficiency. Optionally, the fifth message may also include the identifier of the first cell, which is used to request handover resources for the first cell.

In S4024, the core network device responds to the fifth message by requesting resources for handover from the third network device through the second type of interface.

The request for handover resources from the third network device may also include the identifier of the first cell, which is used to request handover resources for the first cell.

For example, the core network device sends information identifying the third network device and information identifying the second network device to the third network device. Furthermore, if the fifth message may also include the identifier of the first network device and the identifier of the terminal corresponding to the first network device, the third network device determines that it is preparing the same handover resources for the same terminal, thereby improving handover efficiency.

For example, a core network device may send an NG Handover Request message for LTM to a third network device, which includes NG LTM indication information 2, which is used to request the preparation of handover resources for LTM.

S4025, the third network device replies to the core network device with the handover resources of the first cell through the second type of interface.

For example, the handover resources for the first cell include new LTM configuration information for the first cell (during the handover process, the third network device may update the LTM configuration information for the first cell; this new LTM configuration information for the first cell can be understood as the updated LTM configuration information for the first cell, or it can be information that is equivalent to the adjusted LTM configuration information for the first cell prepared previously) or an LTM configuration information retention instruction for the first cell (i.e., continuing to use the LTM configuration information for the first cell prepared previously).

S4026, the core network device sends a sixth message to the second network device through the second type of interface, the sixth message including the handover resources of the first cell.

For example, the sixth message could be a Handover Command message.

S403, the second network device sends a second message to the first network device, the second message being used to indicate whether the first communication interface between the second network device and the third network device has been successfully established or not.

Specifically, if the second network device determines that the first type of interface has been successfully established, it sends a second message to the first network device, indicating that the first type of interface has been successfully established; or, if it determines that the first type of interface has not been successfully established, it sends a second message to the first network device, indicating that the first type of interface has not been successfully established. If the second type of interface has been successfully established between the second network device and the third network device, and the second message indicates that the second type of interface has been successfully established, in this mode, the second network device obtains handover resources from the third network device through the second type of interface. If the second type of interface has not been successfully established between the second network device and the third network device, and the second message indicates that the second type of interface has not been successfully established, in this mode, the second network device does not obtain handover resources from the third network device through the second type of interface.

In an optional implementation, if the first communication interface between the second network device and the third network device has been successfully established, the second message further includes handover resources for the first cell. Additionally, the first network device sends the handover resources for the first cell to the terminal (i.e., the terminal currently served by the first network device). Optionally, the second message may also indicate the type of the first communication interface, which may include a first type interface and/or a second type interface. For example, if the fourth message in S4022 indicates that the first communication interface has been successfully established, the second message may also indicate that the first communication interface is a first type communication interface; after S4026 is executed, the second message may also indicate that the first communication interface is a second type communication interface. Including the first communication interface type in the second message facilitates the first network device's determination of whether to add the first cell as a candidate cell.

In addition, the second network device can also indicate whether to add the first cell as a candidate cell or remove the first cell from the candidate cell list via a second message, or via other messages; these are only illustrative examples and not specific limitations. Based on this, the first network device can directly determine whether to add the first cell as a candidate cell or remove it from the candidate cell list. This method can reduce the data processing operations of the first network device and improve data processing efficiency.

In another alternative implementation, if the first communication interface between the second network device and the third network device fails to be established, the second message includes a cause value indicating that the handover resource preparation failure of the second network device is due to the failure to establish the first communication interface. Based on this, the first network device can clearly understand why the terminal cannot handover from the second network device to the cell managed by the third network device.

After the first network device receives the second message, it can further determine whether to add the first cell as a candidate cell or remove it from the candidate cell pool. This can be understood by referring to Table 1 below, using the XN interface for the first type and the NG interface for the second type as an example. When the first communication interface between the second and third network devices is both an XN interface and an NG interface, the first cell is added as a candidate cell. When the first communication interface between the second and third network devices is an XN interface (and the NG interface has not been successfully established), the first cell is added as a candidate cell. When the first communication interface between the second and third network devices is an NG interface (i.e., the XN interface has not been successfully established), if the terminal latency requirement is not high, the first cell is added as a candidate cell; if the terminal latency requirement is high, the first cell is not added as a candidate cell. If the first communication interface between the second and third network devices has not been successfully established (i.e., both the XN and NG interfaces have not been successfully established), the first cell is not added as a candidate cell. Table 1 below is only an illustrative example; in specific applications, one row can be referred to for determination.

Table 1

In this application, the first network device determines how to add candidate cells by referring to the communication interfaces between candidate network devices for handover. This method can ensure the continuity of services during subsequent handovers and guarantee the user's service experience.

In Figure 4 above, in the case of multiple network devices (including a third network device), the second network device performs the same process as the third network device for the other network devices. Based on this, the second network device can obtain candidate cells for which handover is permitted or prohibited for the terminal. Alternatively, after obtaining cells managed by the second network device for handover from the first network device, the second network device determines candidate cells for which handover is permitted or prohibited in subsequent handovers. The specific method by which the second network device determines candidate cells for which handover is permitted or prohibited is not limited here. "Permitted handover" can be understood as allowing LTM handover.

In the case where the second network device is a separate CU and DU network device, as described above, the second network device is equivalent to the CU. Different logical units within the same network architecture also include a fourth network device (equivalent to the DU), which is connected to the fourth network device via an F1 interface. Since cell handover is initiated by the DU (refer to Figure 2 above), the second network device also sends identification information of candidate cells that are allowed to handover or candidate cells that are not allowed to handover to the fourth network device, adapting to the processing flow in Figure 4 above. Here, the candidate cells allowed to handover may include the first cell. Based on the identification information of the candidate cells allowed to handover, the fourth network device determines to handover to the first cell via LTM and sends a handover command to the terminal device to handover to the first cell.

The second network device obtains key information 1, such as the next-hop chaining counter (NCC), and key information 2 from the core network device. Key information 1 and key information 2 have a corresponding relationship. Specifically, key information 1 can be used to determine key information 2. Key information 1 is used by the terminal to determine the change of communication key. For example, the change of communication key is determined by vertical deduction. The value of key information 1 is different from the key information currently used by the terminal. Key information 2 is used to indicate the key, such as the next hop (NH). NH is an intermediate key, which is derived from the core network key, and is used as input to deduce the access network key. The second network device sends key information 1 and first information to the fourth network device. The first information can be associated with the first cell or other cells. The first information can be the identification information of the first cell (e.g., the Cell Global ID of the first cell, which includes the identification information of the third network device), or the identification information of the third network device (e.g., a global node identifier), or a first identifier (the value of the first identifier associated with a cell differs for different network devices; for example, the first identifier associated with a cell for the second network device is 2, and the first identifier associated with a cell for the third network device is 3). If the fourth network device determines that the first cell is the target cell, based on the first information, the fourth network device determines to initiate a key change handover for the first cell. For example, if the fourth network device determines that the first cell is not managed by the second network device, to ensure cross-base station communication security, the fourth network device determines that the handover for the first cell uses key information 1, i.e., it determines to initiate a key change handover for the first cell. The first network device sends a handover command to the terminal. This handover command includes information indicating that the first cell is the target cell and information indicating the aforementioned key information 1 (e.g., NCC). Based on the information indicating key information 1, the terminal determines to change the key for the first cell. The terminal then determines key information 2 based on key information 1 and uses key information 2 to securely communicate with the first cell. If the fourth network device determines that the cell of the second network device (i.e., cell A, which is the same cell as the second cell, or both cell A and cell A are managed by the second network device) is the target cell, based on the cell's identification information, the fourth network device determines to initiate a handover for cell A without changing the key, i.e., without using the aforementioned key information 1. For example, if the fourth network device determines that cell X is managed by the second network device, it determines to initiate a handover for cell A without changing the key. The first network device sends a handover command to the terminal. This handover command includes information indicating that cell A is the target cell but does not include information indicating key information 1. Based on the handover command that does not include information indicating key information 1, the terminal determines not to change the key for cell A. To distinguish between the two scenarios mentioned above, the switching command format includes indication information 1. Indication information 1 indicates whether the switching command includes information indicating the aforementioned key information 1. Based on indication information 1, the terminal device can correctly parse the switching command.

The following describes the solution of this application in detail with the data interaction of the UE (equivalent to the terminal currently served by the first network device), the source gNB (equivalent to the first network device in Figure 4 above), the candidate gNB1 (equivalent to the second network device in Figure 4), the candidate gNB2 (equivalent to the third network device in Figure 4), and the AMF (equivalent to the core network device, which can also be replaced by the UPF). Here, we will explain it in different cases. The following uses the XN interface as the first type of interface and the NG interface as the second type of interface as an example, and the cell handover is LTM handover as an example. In this case, cell A is equivalent to the first cell mentioned above, and cell B is equivalent to the second cell mentioned above.

It should be noted that during LTM handover, in addition to S401 to S403 mentioned above, some other processing procedures are involved. Before the first network device sends the first message to the second network device, the serving terminal of the first network device usually sends a measurement report to the first network device. The first network device will decide whether to initiate LTM configuration based on the measurement report, as shown in S501 and S502 below. S503A and S503B below are equivalent to S401, S504A and S504B are equivalent to S402, and A to F below are equivalent to S4021 to S4025. Refer to Figure 5 for the following execution:

S501, the UE sends a measurement report to the source gNB.

Specifically, it can be understood by referring to S201 in Figure 2 above, which will not be elaborated here.

Based on the measurement report, the source gNB in S502 decides to initiate LTM configuration.

Specifically, refer to S203 in Figure 2 above for understanding, which will not be elaborated here. This LTM configuration includes the LTM configuration of candidate cells for LTM handover, such as the LTM configuration of cell A (candidate gNB2 management), cell B (candidate gNB1 management), and/or cell C (candidate gNB1 management), which are only illustrated here.

S503A, the source gNB sends the first message to the candidate gNB1.

The first message can be understood by referring to the description of S401 above, and will not be repeated here.

S504A, candidate gNB1 sends a second message to source gNB.

The second message can be either HANDOVER REQUEST ACKNOWLEDGE or FAILUERE. HANDOVER REQUEST ACKNOWLEDGE indicates that the first communication interface between candidate gNB1 and candidate gNB2 has been successfully established. HANDOVER REQUEST FAILUERE indicates that the first communication interface between candidate gNB1 and candidate gNB2 has not been successfully established.

The second message can be understood by referring to the relevant description in Figure 4 above. Similarly, the method for determining whether the first communication interface has been successfully established or not can also be understood by referring to the relevant description in Figure 4 above. The third, fourth, and fifth messages mentioned below, as well as the fourth message mentioned below, are all understood by referring to the relevant description in Figure 4 above, and will not be elaborated upon here; only a brief explanation will be provided.

Optionally, candidate gNB1 can also determine whether the first communication interface has been successfully established or not through the following steps A to F. Steps A and B are executed after S503A and before S504A. Steps C to F are executed only when step B indicates that the XN interface in the first communication interface has not been successfully established, and the NG interface in the first communication interface has been successfully established and can be used for LTM handover. Specifically, as follows:

A. Candidate gNB1 sends a third message (e.g., XN SETUP REQUEST) to candidate gNB2, which requests the establishment of an XN interface for handover.

Optionally, the third message includes XN LTM indication information and the identification information of candidate gNB2 (or the identification information of cell A).

B. In response to the third message, candidate gNB2 sends a fourth message to candidate gNB1 (e.g., XN SETUP RESPONSE or XN SETUP FAILURE).

XN SETUP RESPONSE indicates successful XN interface establishment, while XN SETUP FAILURE indicates XN interface establishment failure. Specifically, the fourth message includes the identification information of candidate gNB1. Based on XN SETUP RESPONSE, it is determined that the XN interface between candidate gNB1 and candidate gNB2 is available for LTM handover. Based on XN SETUP FAILURE, it is determined that the XN interface between candidate gNB1 and candidate gNB2 is not available for LTM handover.

If it is determined that the XN interfaces of candidate gNB1 and candidate gNB2 are unavailable for LTM handover, the second message includes a message indicating that the XN interface was not successfully established. For example, this second message can be an explicit indication, such as "The XN interface of candidate gNB1 and candidate gNB2 was not successfully established." Alternatively, the second message can implicitly indicate this through NG information 1; for example, NG information 1 indicates that the NG interfaces of candidate gNB1 and candidate gNB2 are unavailable for LTM handover, and the unavailability of the NG interfaces implies that the XN interface was not successfully established. This is merely an illustrative example and not a specific limitation.

If it is determined that the XN interfaces of candidate gNB1 and candidate gNB2 are not available for LTM handover, the second message can also indicate that the handover resource preparation for candidate gNB1 has failed. The source gNB can refuse to add the cell of candidate gNB1 as a candidate cell for LTM handover based on this second message.

If it is determined that the XN interface of candidate gNB1 and candidate gNB2 is not available for LTM handover, candidate gNB1 determines whether the NG interface with candidate gNB2 is available for LTM handover. If the NG interface is not available for LTM handover, the second message includes NG information 1, which indicates that the NG interface of candidate gNB1 and candidate gNB2 is not available for LTM handover. If the NG interface is available for LTM handover, steps C to F are executed, which are only executed if the fourth message in step B indicates XN SETUP FAILURE.

C. Candidate gNB1 sends a fifth message to the AMF through the NG interface. This fifth message is used to request the AMF to prepare for resource switching.

Specifically, the fifth message can be an NG Handover Required message for LTM, which includes NG LTM indication information and cell identification information of cell A (or identification information of candidate gNB2).

D. In response to the NG Handover Required message, the AMF sends an NG Handover Request message for LTM to candidate gNB2 through the NG interface. This message includes NG LTM indication information and cell identification information of cell A (or identification information of candidate gNB2).

It should be noted that the information included in the NG Handover Request message for LTM sent by AMF to candidate gNB2 through the NG interface in step D is consistent with the information included in the fifth message in step C. For example, if the fifth message includes the identification information of the source gNB, then the message in step D also includes the identification information of the source gNB.

E. In response to the NG Handover Request message, candidate gNB2 replies to AMF via the NG interface with an NG Handover Request Acknowledge message for LTM. This message includes handover resource 1 for cell A (which is different from the handover resource for cell A that was previously requested to be prepared by the source gNB) or an LTM configuration information preservation indication for cell A (i.e., this indication is used to indicate that the previously prepared handover resource should continue to be used).

F, AMF sends a sixth message to candidate gNB1 via the NG interface. The sixth message includes handover resource 1 for cell A (which is different from the handover resource prepared for cell A previously) or LTM configuration information preservation indication for cell A (i.e., the indication is used to indicate that the handover resource prepared by the source gNB previously requested should continue to be used).

When performing steps A through F above, S504A can be replaced by step G as follows:

G. Candidate gNB1 sends a second message to the source gNB. The second message includes NG information 2 and handover resource 1 for cell A (or LTM configuration information retention indication for cell A). The NG information 2 instructs candidate gNB1 to perform LTM handover with candidate gNB2 through the NG interface.

S503B, the source gNB sends the first message to the candidate gNB2.

S504B, candidate gNB2 sends a second message to source gNB.

Specifically, S503B can be understood with reference to S503A, and S504B can be understood with reference to S504A. Simply replace the information related to gNB2 in the descriptions of S503A and S504A with the information related to gNB1, and replace the information related to gNB1 with the information related to gNB2. For example, replace the identification information of candidate gNB2 with the identification information of candidate gNB1, etc. This is only an illustrative example and is not specifically limited; it can be understood by reference.

After receiving the second message, the source gNB further determines whether to add cell A (which is replaced by cell B when executing S503B and S504B) as a candidate cell or remove cell A from the candidate cells.

Additionally, candidate gNB1 can also indicate whether to add cell A as a candidate cell or remove cell A from the candidate cell list via a second message, or via other messages. This is merely an example and not a specific limitation. Based on this, the source gNB can directly determine whether to add cell A as a candidate cell or remove cell A from the candidate cell list. This method reduces the data processing operations of the source gNB and improves data processing efficiency.

For example, when candidate gNB1 performs LTM handover with candidate gNB2 through the XN interface, cell A can be directly used as the candidate cell; or, when candidate gNB1 performs LTM handover with candidate gNB2 through the NG interface, if the UE has low requirements for service latency, cell A can be directly used as the candidate cell, and if the UE has high requirements for service latency, cell A will not be used as the candidate cell.

If the source gNB determines to add cell A as a candidate cell, it obtains the LTM configuration information of cell A and cell B from candidate gNB1 and performs the following steps:

S505, the source gNB sends an RRC reconfiguration message to the UE, which includes the LTM configuration information of cell A and the LTM configuration information of cell B.

S506, the UE sends an RRC reconfiguration complete message to the source gNB.

S507, UE and candidate gNB1 are synchronized in advance.

This can be understood by referring to S214 above, and will not be explained in detail here.

S508, Candidate gNB1 sends the TA of cell B to source gNB.

S509, the UE sends Measurement Report 1 to the source gNB, which includes the reference signal receiving power (RSRP) of cell B.

S510, the source gNB determines to execute LTM, that is, to initiate a handover to cell B.

S511, the source gNB sends a handover command 1 (media access control control element (MAC CE)) to the UE, indicating a handover to cell B. This command may include the TA information of cell B.

S512, the source gNB sends a cell handover notification to candidate gNB1, indicating that a handover command 1 has been sent to the UE.

S513, the UE accesses cell B of candidate gNB1.

Specifically, the UE can access the target cell B using RACH or RACH-less methods.

S514, the data transmission path for the UE is switched from UPF to source gNB to UPF to candidate gNB1.

S515, the UE sends an RRC reconfiguration complete message to candidate gNB1.

S516, the UE sends Measurement Report 2 to candidate gNB1, which includes the RSRP of cell A.

S517, if candidate gNB1 determines that the Xn interface or NG interface can be used for LTM handover (that is, the first communication interface shown in Figure 4 has been successfully established), it determines to perform LTM handover, that is, to initiate handover to cell A.

S518, candidate gNB1 sends handover command 2 to UE, which indicates handover to cell A.

S519, candidate gNB1 sends cell handover notification 2 to candidate gNB2 through the available Xn interface or NG interface. The cell handover notification 2 is used to indicate that a handover command 2 has been sent to the UE.

It is important to note that if a first communication interface does not exist, the second LTM handover will fail. For example, if there is no first communication interface between candidate gNB1 and candidate gNB2, after the cell managed by the source gNB hands over to the cell managed by candidate gNB1, the cell managed by candidate gNB1 cannot hands over to the cell managed by candidate gNB2 and may hands over back to the cell managed by the source gNB, resulting in an LTM handover failure.

In the open architecture, candidate gNB1 includes candidate gNB1-CU and candidate gNB1-DU. The steps executed for candidate gNB1 in Figure 5 are all performed by candidate gNB1-CU. Under the open architecture, candidate gNB1-CU will perform some additional steps. The following explanation, combining the data interaction between the UE, source gNB-CU (equivalent to the first network device in Figure 4, and the source gNB in Figure 5), candidate gNB1-CU (equivalent to the second network device in Figure 4), candidate gNB1-DU (equivalent to the fourth network device), and candidate gNB2-CU (equivalent to the third network device in Figure 4, and the source gNB2 in Figure 5), illustrates the scheme of this application. The explanation is divided into different cases, with reference to Figure 6 for execution. Figure 6 further illustrates the flow between CU and DU based on Figure 5:

It should be noted that after candidate gNB1-CU has executed step B or step F above and determined that a first communication interface has been successfully established with candidate gNB2-CU, or after candidate gNB1-CU has determined that a first communication interface has not been successfully established with candidate gNB2-CU, in specific applications, candidate gNB1-CU can also refer to the same process to determine whether a first communication interface exists between candidate gNB1-CU and other candidate gNB1-CUs. Based on this, candidate gNB1-CU can determine the identification information of the M cells to be used for subsequent handover. These M cells are all managed by other CUs, i.e., not managed by candidate gNB1-CU.

The candidate gNB1-CU determines that the first communication interface between the candidate base station (CU in the case of CU and DU separation) corresponding to N cells can be used for LTM handover, and the first communication interface between the candidate base station (CU in the case of CU and DU separation) corresponding to L cells and the candidate gNB1-CU cannot be used for LTM handover. Here, M cells = N cells + L cells, where N cells are different from L cells, and M, N, and L are integers greater than 0.

After candidate gNB1-CU has executed step B or step F, and it is determined that a first communication interface has been successfully established with candidate gNB2-CU, or after candidate gNB1-CU has determined that a first communication interface has not been successfully established with candidate gNB2-CU, steps X to Y are executed. If only step B is executed, steps X to Y can be executed after step B, and the execution order is not limited to the other steps in Figure 5. If step F is executed, steps X to Y can be executed after step F, and the execution order is not limited to the other steps in Figure 5. In Figure 6, they are executed after step B.

X, the candidate gNB1-CU sends the identification information of N cells to the candidate gNB1-DU. The identification information of N cells is used to indicate to the candidate gNB1-DU that N cells can be used as target cells for handover initiated by the candidate gNB1-DU (i.e., cells that are allowed to be handed over).

Optionally, in step X, the candidate gNB1-CU may also send identification information of L cells to the candidate gNB1-DU. The identification information of L cells is used to indicate to the candidate gNB1-DU that L cells cannot be used as target cells for handover initiated by the candidate gNB1-DU (i.e., cells that are not allowed to be handed over).

Y, the candidate gNB1-DU is based on N cells, and the target cell for the handover initiated by the candidate gNB1-DU is determined, that is, the handover triggered by the DU.

Optionally, based on N cells, determine the LTM report configuration corresponding to each of the N cells. For L cells, the LTM report configuration corresponding to each of the L cells can be either not determined or determined.

For example, if the LTM report configuration for N cells is determined and the LTM report configuration for L cells is uncertain, the UE reports the measurement results of some or all of the N cells (using beam measurement result RSRP as an example) but does not report the measurement results of the L cells. In this way, the candidate gNB1-DU will not switch to a cell among the L cells.

For example, given the LTM report configurations for N cells and L cells, the terminal device reports the measurement results for the L cells, indicating that cell 1 among the L cells has good quality. The candidate gNB1-DU can send an L3 handover request to the candidate gNB1-CU. Here, L3 handover refers to a handover triggered by the CU, and the L3 handover request includes the RSRP of cell 1. Based on the L3 handover request, the candidate gNB1-CU determines to initiate an NG-based L3 handover. L3 handover is an existing handover, which will not be elaborated here but can be understood by referring to existing protocols. The terminal device reports the measurement results (also the beam measurement results RSRP) for the N cells, indicating that cell 2 among the N cells has good quality. The candidate gNB1-DU determines to perform an LTM handover, which is a DU-triggered handover, and sends a cell handover notification to the candidate gNB1-CU.

Furthermore, after executing S613, the candidate gNB1-CU sends handover information (such as key information 1 and first information as described above) to the candidate gNB1-DU for the gNB1-DU to determine whether to initiate a key change for the target cell. The specific processing flow can be understood by referring to the relevant descriptions of key information 1 and key information 2 above, and will not be repeated here. Based on this, the candidate gNB1-DU sends the handover information to the UE. The UE then changes its key (changing the source cell's key to the target cell's key) and switches from the source cell to the target cell to receive services, ensuring service continuity.

The foregoing primarily describes the solutions provided by the embodiments of this application from the perspective of device interaction. It is understood that, in order to achieve the above functions, each device may include corresponding hardware structures and/or software modules for executing each function. Those skilled in the art should readily recognize that, in conjunction with the units and algorithm steps of the various examples described in the embodiments disclosed herein, the embodiments of this application can be implemented in hardware or a combination of hardware and computer software. Whether a function is executed in hardware or by computer software driving hardware depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

The embodiments of this application can divide the device into functional units according to the above method examples. For example, each function can be divided into a separate functional unit, or two or more functions can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

Figure 7 illustrates a possible exemplary block diagram of a communication device according to an embodiment of this application, when using integrated units. As shown in Figure 7, the communication device 700 may include a processing unit 701 and a transceiver unit 702. The processing unit 701 is used to control and manage the operation of the communication device 700. The transceiver unit 702 is used to support communication between the communication device 700 and other devices. Optionally, the transceiver unit 702 may include a receiving unit and/or a transmitting unit, respectively used to perform receiving and transmitting operations. Optionally, the communication device 700 may also include a storage unit for storing the program code and/or data of the communication device 700. The transceiver unit may be referred to as an input/output unit, a communication unit, etc., and may be a transceiver; the processing unit may be a processor. When the communication device is a module (e.g., a chip) in a communication device, the transceiver unit may be an input/output interface, an input/output circuit, or an input/output pin, etc., and may also be referred to as an interface, a communication interface, or an interface circuit, etc.; the processing unit may be a processor, a processing circuit, or a logic circuit, etc. Specifically, the device may be the first network device, the second network device, the third network device, etc., as described above. Optionally, the first network device is the source network device for the initial handover, the second network device is the source network device for subsequent handovers, and the third network device is the candidate network device for subsequent handovers. The first network device, the second network device, and the third network device are all different.

In one example, the communication device 700 is a first network device, wherein the transceiver unit 702 is used to send a first message to a second network device, the first message including information for identifying a third network device; the transceiver unit 702 is also used to receive a second message from the second network device, the second message indicating whether a first communication interface has been successfully established or not successfully established between the second network device and the third network device, the first communication interface being a communication interface for handover.

In one alternative approach, the first message is used to request the second network device to prepare handover resources for the terminal. The first message also includes: identification information of the second network device, and/or identification information of the second cell, wherein the second cell is managed by the second network device.

In one alternative approach, the first message further includes at least one of the following: request information, an identifier of the first network device, or an identifier of the terminal, wherein the request information is used to request the second network device to provide information about the first communication interface to the first network device.

In one alternative approach, if the first communication interface between the second network device and the third network device has been successfully established, the second message may also include: handover resources for the first cell, which is managed by the third network device.

In an alternative configuration, transceiver unit 702 is also used to send handover resources of the first cell to the terminal.

In one alternative approach, the second message is also used to indicate the type of the first communication interface, which includes a first type of interface and/or a second type of interface, wherein the first type of interface directly connects the second network device and the third network device, and the second type of interface connects the second network device and the third network device through a core network device.

In one alternative approach, the failure to establish a first communication interface between the second network device and the third network device includes: there is no communication interface between the second network device and the third network device; or, the communication interface between the second network device and the third network device is not used for handover.

In one alternative approach, the second message includes a cause value indicating that the failure to prepare the switching resources for the second network device was due to the failure to successfully establish the first communication interface.

In one alternative approach, the information used to identify the third network device is the identification information of the third network device and/or the identification information of the first cell, wherein the first cell is managed by the third network device.

In another example, the communication device 700 is a second network device, wherein the transceiver unit 702 is used to receive a first message from a first network device, the first message including information for identifying a third network device; and the processing unit 701 is used to respond to the first message by sending a second message to the first network device through the transceiver unit 702, the second message indicating whether a first communication interface has been successfully established or not successfully established between the second network device and the third network device, the first communication interface being a communication interface for handover.

In one alternative approach, the processing unit 701 is specifically configured to determine whether the first communication interface has been successfully established or not, based on the first message; the transceiver unit 702 is further configured to send a second message to the first network device if it is determined that the first communication interface has been successfully established, the second message indicating that the first communication interface has been successfully established; or, if it is determined that the first communication interface has not been successfully established, send a second message to the first network device, the second message indicating that the first communication interface has not been successfully established.

In one alternative approach, the first message is used to request the second network device to prepare handover resources for the terminal. The first message also includes: identification information of the second network device, and/or identification information of the second cell, wherein the second cell is managed by the second network device.

In one alternative approach, the first message further includes at least one of the following: request information, an identifier of the first network device, or an identifier of the terminal, wherein the request information is used to request the second network device to provide information about the first communication interface to the first network device.

In one alternative approach, if the first communication interface between the second network device and the third network device has been successfully established, the second message may also include: handover resources for the first cell, which is managed by the third network device.

In one alternative approach, the second message is also used to indicate the type of the first communication interface, which includes a first type of interface and/or a second type of interface, wherein the first type of interface directly connects the second network device and the third network device, and the second type of interface connects the second network device and the third network device through a core network device.

In one alternative approach, the failure to establish a first communication interface between the second network device and the third network device includes: there is no first communication interface between the second network device and the third network device; or, the communication interface between the second network device and the third network device is not used for handover.

In one alternative approach, the second message includes a cause value indicating that the failure to prepare the switching resources for the second network device was due to the failure to successfully establish the first communication interface.

In one alternative embodiment, the transceiver unit 702 is further configured to send a third message to the third network device, the third message being used to request the establishment of the first communication interface; receive a fourth message from the third network device, the fourth message being used to indicate whether the establishment of the first communication interface was successful or failed; if the fourth message indicates that the establishment of the first communication interface was successful, the processing unit 701 is further configured to determine that the first communication interface has been successfully established; or if the fourth message indicates that the establishment of the first communication interface has failed, determine that the first communication interface has not been successfully established.

In one alternative approach, if the first type of interface between the second network device and the third network device fails to be established, but the second type of interface has been successfully established, the transceiver unit 702 is further configured to send a fifth message to the core network device, the fifth message being used to request preparation of handover resources, the fifth message including information for identifying the third network device; and receive a sixth message from the core network device, the sixth message including handover resources for the first cell, the first cell being managed by the third network device.

In one alternative approach, the fifth message may also include: the identifier of the first network device and the identifier of the terminal.

In one alternative embodiment, the transceiver unit 702 is further configured to send identification information of candidate cells that are allowed to be handed over or identification information of candidate cells that are not allowed to be handed over to the fourth network device, wherein the second network device and the fourth network device are different logical units under the same network architecture, and the candidate cells that are allowed to be handed over include the first cell, which is managed by the third network device.

In one alternative embodiment, the transceiver unit 702 is further configured to send key information and first information to the fourth network device. The first information is used by the fourth network device to determine the handover key information for the first cell. The second network device and the fourth network device are different logical units under the same network architecture.

Furthermore, Figure 8 shows a simplified structural diagram of a terminal device provided in this application. For ease of understanding and illustration, a mobile phone is used as an example of the terminal in Figure 8. As shown in Figure 8, the terminal includes a processor, memory, radio frequency circuitry, antenna, and input/output devices.

The processor is mainly used to process communication protocols and communication data, control terminal devices, execute software programs, and process data from software programs.

Memory is mainly used to store software programs and data.

Radio frequency (RF) circuits are mainly used for the conversion between baseband signals and RF signals, as well as for the processing of RF signals.

Antennas are primarily used for transmitting and receiving radio frequency signals in the form of electromagnetic waves.

Input/output devices, such as touchscreens, displays, and keyboards, are primarily used to receive user input data and output data to the user.

It should be noted that some types of terminal devices may not have input/output devices.

When data needs to be sent, the processor performs baseband processing on the data to be sent and outputs the baseband signal to the radio frequency (RF) circuit. The RF circuit then processes the baseband signal and transmits it outward as electromagnetic waves through the antenna. When data is sent to the terminal device, the RF circuit receives the RF signal through the antenna, converts it into a baseband signal, and outputs the baseband signal to the processor. The processor then converts the baseband signal back into data and processes it.

For ease of explanation, Figure 8 shows only one memory and one processor. In actual terminal device products, there may be one or more processors and one or more memories. Memory can also be called storage medium or storage device, etc. Memory can be set up independently of the processor or integrated with the processor; this application embodiment does not limit this.

In the embodiments of this application, the antenna and radio frequency circuit with transceiver function can be regarded as the transceiver unit of the terminal device, and the processor with processing function can be regarded as the processing unit of the terminal device.

As shown in Figure 8, the terminal 800 includes a transceiver unit 810 and a processing unit 820. The transceiver unit 810 can also be called a transceiver, transceiver device, or transceiver unit. The processing unit 820 can also be called a processor, processing board, processing module, or processing device.

Optionally, the devices in transceiver unit 810 used for receiving functions can be considered as receiving units, and the devices in transceiver unit 810 used for transmitting functions can be considered as transmitting units. That is, transceiver unit 810 includes both receiving and transmitting units. A transceiver unit may also be called a transceiver, transceiver circuit, etc. A receiving unit may also be called a receiver, receiver, or receiving circuit, etc. A transmitting unit may also be called a transmitter, transmitter, or transmitting circuit, etc.

It should be understood that the transceiver unit 810 is used to perform the sending and receiving operations of the terminal device in the above method embodiment, and the processing unit 820 is used to perform other operations on the terminal device in the above method embodiment besides the sending and receiving operations.

When the terminal device is a chip, the chip includes a transceiver unit 810 and a processing unit 820. The transceiver unit 810 may be an input/output circuit or a communication interface; the processing unit 820 may be a processor, microprocessor, integrated circuit, or logic circuit integrated on the chip.

This application also provides a network device. Figure 9 shows a schematic diagram of the network device 900 provided in an embodiment of this application. This network device 900 can be applied to the system shown in Figure 1. For example, the network device 900 can be the network device in the system of Figure 1, used to perform the functions of the network device in the above method embodiment. It should be understood that the following are merely examples; in future communication systems, network devices may have other forms and configurations.

For example, in a 5G communication system, network equipment 900 may include CU, DU, and AAU, compared to network equipment in an LTE communication system which consists of one or more radio frequency units, such as remote radio units (RRUs), and one or more building baseband units (BBUs):

The non-real-time portion of the original BBU will be separated and redefined as CU, responsible for handling non-real-time protocols and services. Some physical layer processing functions of the BBU, along with the original RRU and passive antenna, will be merged into AAU. The remaining functions of the BBU will be redefined as DU, responsible for handling physical layer protocols and real-time services. In short, CU and DU are distinguished by the real-time nature of the processed content, and AAU is a combination of RRU and antenna.

CU, DU, and AAU can be deployed separately or jointly, resulting in various network deployment configurations. One possible configuration, as shown in Figure 9, is consistent with traditional 4G network equipment, where CU and DU are deployed together on the same hardware. It should be understood that Figure 9 is merely an example and does not limit the scope of protection of this application. For instance, other deployment configurations could include DU deployed in the BBU room, CU centrally deployed, or DU centrally deployed, with CU centrally deployed at a higher level, etc.

The AAU1000 can perform transceiver functions, corresponding to the transceiver unit 702 in Figure 7. Optionally, the AAU1000 can also be called a transceiver, transceiver circuit, or transceiver unit, etc., and it can include at least one antenna 1001 and radio frequency unit 1002. Optionally, the AAU1000 can include a receiving unit and a transmitting unit, where the receiving unit can correspond to a receiver (or receiver circuit), and the transmitting unit can correspond to a transmitter (or transmitter circuit). The CU and DU1100 can perform internal processing functions, corresponding to the processing unit 701 in Figure 7. Optionally, the CU and DU1100 can control network devices, etc., and can be called controllers. The AAU, CU, and DU can be physically arranged together or physically separated.

In addition, the network device is not limited to the form shown in Figure 9, and may also be other forms: for example, including BBU and adaptive radio unit (ARU), or including BBU and AAU; it may also be customer premises equipment (CPE), or other forms, which are not limited in this application.

In one example, the CU and DU1100 can be composed of one or more single boards. Multiple single boards can collectively support a single access standard wireless access network (such as an LTE network), or they can each support different access standards wireless access networks (such as LTE, 5G, future networks, or other networks). The CU and DU1100 also include a memory 1101 and a processor 1102. The memory 1101 is used to store necessary instructions and data. The processor 1102 is used to control the first network device to perform necessary actions, such as controlling the network device to execute the operation procedures related to the network device in the above method embodiments. The memory 1101 and processor 1102 can serve one or more single boards. That is, each single board can have its own memory and processor, or multiple single boards can share the same memory and processor. Furthermore, each single board can also have necessary circuitry.

It should be understood that the network device 900 shown in FIG. 9 can implement the network device functions involved in the method embodiment of FIG. 4. The operation and/or function of each unit in the network device 900 are respectively for implementing the corresponding processes executed by the network device in the method embodiment of this application. To avoid repetition, detailed descriptions are appropriately omitted here. The structure of the network device shown in FIG. 9 is only one possible form and should not constitute any limitation on the embodiments of this application. This application does not exclude the possibility of other forms of network device structures that may appear in the future.

The CU and DU1100 described above can be used to perform the actions implemented internally by the network device as described in the preceding method embodiments, while the AAU190 can be used to perform the actions described in the preceding method embodiments whereby the network device sends data to or receives data from the terminal device. Please refer to the descriptions in the preceding method embodiments for details, which will not be repeated here.

This application also provides a communication system, which includes a terminal device and a network device. The terminal device is used to perform all or part of the steps performed by the terminal device in the embodiments shown in Figures 4-6. The network device is used to perform all or part of the steps performed by the network device in the embodiments shown in Figures 4-6.

Based on the above embodiments, this application also provides a readable storage medium storing instructions that, when executed, cause the methods in any of the above embodiments to be implemented. The readable storage medium may include various media capable of storing program code, such as a USB flash drive, portable hard drive, read-only memory, random access memory, magnetic disk, or optical disk.

Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk storage, compact disc read-only memory (CD-ROM), optical storage, etc.) containing computer-usable program code.

This application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to this application. It should be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in one or more flowchart illustrations and/or one or more block diagrams.

These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means that implement the functions specified in one or more flowcharts and/or one or more block diagrams.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, such that the instructions, which execute on the computer or other programmable apparatus, provide steps for implementing the functions specified in one or more flowcharts and/or one or more block diagrams.

Claims (29)

A communication method, characterized in that it is applied to a first network device, comprising: Send a first message to the second network device, the first message including information for identifying the third network device; A second message is received from the second network device, the second message indicating whether a first communication interface has been successfully established or not successfully established between the second network device and the third network device, the first communication interface being a communication interface for handover. According to the method of claim 1, the first message is used to request the second network device to prepare handover resources for the terminal, and the first message further includes: identification information of the second network device, and/or identification information of the second cell, wherein the second cell is managed by the second network device. The method according to claim 2, wherein the first message further comprises at least one of the following: The request information includes the identifier of the first network device or the identifier of the terminal, wherein the request information is used to request the second network device to provide the first network device with information about the first communication interface. The method according to claim 2 or 3 is characterized in that, when the first communication interface between the second network device and the third network device has been successfully established, the second message further includes: handover resources of the first cell, wherein the first cell is managed by the third network device. The method according to claim 4, characterized in that the method further comprises: The handover resources of the first cell are sent to the terminal. According to the method of claim 4 or 5, the second message is further used to indicate the type of the first communication interface, the first communication interface including a first type of interface and/or a second type of interface, the first type of interface directly connecting the second network device and the third network device, and the second type of interface connecting the second network device and the third network device through a core network device. The method according to any one of claims 1-3, wherein the failure to successfully establish a first communication interface between the second network device and the third network device includes: There is no communication interface between the second network device and the third network device; or, The communication interface between the second network device and the third network device is not used for switching. According to the method of claim 7, the second message includes a cause value, which indicates that the reason for the failure of the switching resource preparation of the second network device is that the first communication interface was not successfully established. The method according to any one of claims 1-8 is characterized in that the information used to identify the third network device is the identification information of the third network device and/or the identification information of the first cell, wherein the first cell is managed by the third network device. The method according to any one of claims 1-9 is characterized in that the first network device is the source network device for the initial handover, the second network device is the source network device for subsequent handovers, and the third network device is a candidate network device for subsequent handovers, wherein the first network device, the second network device, and the third network device are all different. A communication method, characterized in that it is applied to a second network device, comprising: Receive a first message from a first network device, the first message including information for identifying a third network device; In response to the first message, a second message is sent to the first network device. The second message indicates whether a first communication interface has been successfully established or not successfully established between the second network device and the third network device. The first communication interface is a communication interface for handover. The method according to claim 11, wherein the response to the first message includes: Based on the first message, determine whether the first communication interface has been successfully established or not. Sending the second message to the first network device includes: If it is determined that the first communication interface has been successfully established, a second message is sent to the first network device, the second message indicating that the first communication interface has been successfully established; or... If it is determined that the first communication interface has not been successfully established, a second message is sent to the first network device, the second message being used to indicate that the first communication interface has not been successfully established. The method according to claim 11 or 12 is characterized in that the first message is used to request the second network device to prepare handover resources for the terminal, and the first message further includes: identification information of the second network device, and/or, identification information of the second cell, wherein the second cell is managed by the second network device. The method according to claim 13, wherein the first message further comprises at least one of the following: The request information includes the identifier of the first network device or the identifier of the terminal, wherein the request information is used to request the second network device to provide the first network device with information about the first communication interface. The method according to any one of claims 11-14 is characterized in that, when the first communication interface between the second network device and the third network device has been successfully established, the second message further includes: handover resources of the first cell, wherein the first cell is managed by the third network device. According to the method of claim 15, the second message is further used to indicate the type of the first communication interface, the first communication interface including a first type of interface and/or a second type of interface, the first type of interface directly connecting the second network device and the third network device, and the second type of interface connecting the second network device and the third network device through a core network device. The method according to any one of claims 11-14, wherein the failure to successfully establish a first communication interface between the second network device and the third network device includes: There is no communication interface between the second network device and the third network device; or, The communication interface between the second network device and the third network device is not used for switching. The method according to claim 17, wherein the second message includes a cause value, the cause value being used to indicate that the reason for the failure of the switching resource preparation of the second network device is that the first communication interface was not successfully established. The method according to any one of claims 11-18, characterized in that the method further comprises: Send a third message to the third network device, the third message being used to request the establishment of the first communication interface; Receive a fourth message from the third network device, the fourth message being used to indicate whether the establishment of the first communication interface was successful or failed; If the fourth message indicates that the first communication interface has been successfully established, it is determined that the first communication interface has been successfully established; or If the fourth message indicates that the first communication interface has failed to be established, it is determined that the first communication interface has not been successfully established. The method according to claim 16, characterized in that, if the first type of interface between the second network device and the third network device is not successfully established, but the second type of interface has been successfully established, the method further includes: Send a fifth message to the core network equipment, the fifth message being used to request preparation for switching resources, the fifth message including information for identifying the third network device; A sixth message is received from the core network device, the sixth message including handover resources for a first cell, which is managed by the third network device. According to the method of claim 20, the fifth message further includes: the identifier of the first network device and the identifier of the terminal. The method according to any one of claims 11-21, characterized in that the method further comprises: The system sends identification information of candidate cells that are allowed to be handed over or candidate cells that are not allowed to be handed over to the fourth network device. The second network device and the fourth network device are different logical units under the same network architecture. The candidate cells that are allowed to be handed over include the first cell, which is managed by the third network device. The method according to claim 15, 16, 20, 21 or 22, characterized in that the method further comprises: Send key information and first information to the fourth network device. The first information is used by the fourth network device to determine whether to use the key information for handover of the first cell. The second network device and the fourth network device are different logical units under the same network architecture. The method according to any one of claims 11-23 is characterized in that the first network device is the source network device for the initial handover, the second network device is the source network device for subsequent handovers, and the third network device is a candidate network device for subsequent handovers, wherein the first network device, the second network device, and the third network device are all different. A communication device, characterized in that it comprises: a functional module that implements the method as described in any one of claims 1-24. A communication device, characterized in that it comprises: at least one processor and a memory; The memory is used to store computer programs or instructions; The at least one processor is configured to execute the computer program or instructions to cause the method of any one of claims 1-24 to be performed. A chip system, characterized in that the chip system comprises: a processing circuit; the processing circuit is coupled to a storage medium; The processing circuit is configured to execute part or all of the computer program or instructions in the storage medium, and when the part or all of the computer program or instructions are executed, to implement the method as described in any one of claims 1-24. A computer-readable storage medium, characterized in that the computer-readable storage medium stores instructions that, when executed by a computer, cause the method as described in any one of claims 1-24 to be performed. A computer program product comprising a computer program or instructions, characterized in that, when the computer program or instructions are run on a computer, the method as described in any one of claims 1-24 is performed.