Handover method and communication apparatus

Abstract

The present application provides a handover method and a communication apparatus. The method comprises: a source access network device sends first information to a candidate control plane network element, wherein the first information is used for indicating that the candidate control plane network element is a conditional handover preparation resource of a terminal device; the source access network device sends second information to the terminal device, wherein the second information is used for indicating a handover condition and at least one candidate access network device; at least one candidate control plane network element serves the at least one candidate access network device, wherein the source control plane network element serving the source access network device is different from any one candidate control plane network element. The embodiment simultaneously supports conditional handover and control plane network element handover. In addition, the embodiment does not limit the sequence of sending the first information and the second information, and the conditional handover preparation of the terminal device and the conditional handover preparation of a core network can be performed simultaneously, thereby reducing the delay of conditional handover.

Description

Switching method and communication device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of the People's Republic of China on January 29, 2024, with application number 202410121987.6 and application name "A switching method and communication device", the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the field of communication technology, and in particular to a switching method and a communication device. Background Art

[0004] Conditional handover (CHO) involves the source base station configuring handover conditions and at least one candidate base station for a terminal device. When the handover conditions are met, the terminal device selects a target base station from the at least one candidate base station based on the measurement results of the at least one candidate base station and then switches from the source base station to the target base station. Compared to traditional handover (i.e., unconditional handover), conditional handover allows the terminal device to select the target base station based on measurement results and initiate the handover. This not only avoids signaling exchanges between the terminal device and the source base station, but also prevents handover failures caused by changes in the radio link status during signaling exchanges between the source and target base stations.

[0005] In the conditional switching scenario, if the source base station and the target base station are managed by different core network elements, the switching of the core network elements will be involved. How to support both conditional switching and core network element switching needs to be considered. Summary of the Invention

[0006] The embodiments of the present application provide a switching method and a communication device for simultaneously supporting conditional switching and core network element switching.

[0007] In the first aspect, the present application provides a switching method, which can be executed by a source access network device, or by other devices including the functions of the source access network device, or by a chip system (which can also be replaced by a chip) or other functional modules, and the chip system or functional module can realize the functions of the source access network device, and the chip system or functional module is, for example, set in the source access network device. Take the method being executed by the source access network device as an example for introduction: the source access network device sends first information to at least one candidate control plane network element, and sends second information to the terminal device; the first information is used to indicate the preparation of resources for conditional switching of the terminal device; the second information is used to indicate the switching condition and at least one candidate access network device, the at least one candidate control plane network element serves the at least one candidate access network device, and the source control plane network element serving the source access network device is different from any of the at least one candidate control plane network elements.

[0008] In this embodiment, the source access network device configures conditional switching for the terminal device, and instructs the candidate control plane network element to prepare resources for conditional switching of the terminal device, thereby supporting both conditional switching and control plane network element switching. In addition, this embodiment does not limit the order of sending the first information and the second information, that is, the source access network device can configure conditional switching for the terminal device before the core network is fully prepared, or even before instructing the candidate control plane network element to prepare resources for conditional switching of the terminal device. The terminal device and the core network can perform conditional switching preparations simultaneously, which can reduce the delay of conditional switching.

[0009] In a possible implementation, the source access network device may further receive downlink data from the at least one candidate access network device; and send the downlink data to the terminal device.

[0010] This implementation is applicable to scenarios where the core network has completed resource preparation for conditional handover of a terminal device, but the terminal device has not yet completed conditional handover (i.e., has not yet switched to the target access network device). Downlink data is transmitted from the candidate user plane network element to at least one candidate access network device. The at least one candidate access network device sends the downlink data to the source access network device, which then sends the downlink data to the terminal device, thereby improving downlink data transmission efficiency.

[0011] In a possible implementation, the source access network device may also receive downlink data from the source user plane network element; the source access network device sends the downlink data to the terminal device through a target access network device among the at least one candidate access network device.

[0012] This implementation method can be applied to scenarios where the terminal device has not completed conditional switching (i.e., has not switched to the target access network device). Downlink data is transmitted from the source user plane network element to the source access network device. The source access network device sends the downlink data to the candidate access network device. After the terminal device switches to the target access network device, the target access network device sends the downlink data to the terminal device, which can avoid data loss during the process of the terminal device switching the access network device.

[0013] In one possible implementation, the source access network device may also send third information to the terminal device, where the third information is used to indicate a time window, where the time window is the time window for the terminal device to switch from the source access network device to the target access network device based on the switching condition.

[0014] In one possible implementation, the source access network device sends the downlink data to the at least one candidate access network device within a time window, and sends the downlink data to the terminal device through the target access network device among the at least one candidate access network device. The time window is the time window in which the terminal device switches from the source access network device to the target access network device based on the switching condition.

[0015] In this implementation, a time window is pre-set for conditional handover by the terminal device. Theoretically, before the time window, the terminal device has not yet switched to the target access network device, and after the time window, the terminal device has already switched to the target access network device. Downlink data is transmitted from the source user plane network element to the source access network device. The source access network device sends the downlink data to the candidate access network device within this time window. Before this time window, the source access network device can send the downlink data directly to the terminal device instead of to the candidate access network device. This time window can reduce the buffer pressure on the candidate access network device.

[0016] In one possible implementation, the source access network device may also receive fourth information, where the fourth information is used to indicate that resource preparation for conditional switching of the terminal device is completed; the source access network device sends fifth information to the terminal device, where the fifth information is used to indicate that switching of the access network device is allowed.

[0017] In this implementation, after the core network completes resource preparation, it notifies the terminal device through the source access network device. The terminal device will switch the access network device only after receiving the notification. This can avoid the situation where the core network side is not ready for resources. After the terminal device switches to the target access network device, it sends uplink data to the target access network device. The target access network device sends the uplink data to the target user plane network element. In this case, the target user plane network element may not receive the uplink data, that is, the uplink data is lost. In addition, if the target user plane network element does not receive the uplink data, it will think that the terminal device has not yet switched to the target access network device, which will also affect the transmission path of the downlink data.

[0018] In a possible implementation manner, the source access network device determines the at least one candidate access network device based on ephemeris.

[0019] On the second aspect, the present application provides a switching method, which can be executed by a terminal device, or by other devices including the functions of a terminal device, or by a chip system (which can also be replaced by a chip) or other functional modules, which can realize the functions of the terminal device, and the chip system or functional module is, for example, set in the terminal device. Take the execution of this method by a terminal device as an example for introduction: the terminal device receives second information from a source access network device, the second information is used to indicate a switching condition and at least one candidate access network device, and the control plane network elements serving the source access network device and the at least one candidate access network device are different; after determining that the switching condition is met, the terminal device switches from accessing the source access network device to accessing the target access network device, and the target access network device belongs to the at least one candidate access network device.

[0020] In one possible implementation, the terminal device may also receive third information from the source access network device, where the third information is used to indicate a time window; within the time window, the terminal device switches from accessing the source access network device to accessing the target access network device.

[0021] In a possible implementation, the terminal device may further receive fifth information from the source access network device, the fifth information being used to indicate that access network device switching is permitted.

[0022] On the third aspect, the present application provides a switching method, which can be executed by the target access network device, or by other devices including the functions of the target access network device, or by a chip system (which can also be replaced by a chip) or other functional modules, which can realize the functions of the target access network device, and the chip system or functional module is, for example, set in the target access network device. Take the method being executed by the target access network device as an example for introduction: during the conditional switching of the terminal device, the target access network device receives downlink data from the source access network device and saves it; after determining that the terminal device switches to the target access network device (i.e., receives the uplink data of the terminal device), the saved downlink data is sent to the terminal device; wherein, the target control plane network element serving the target access network device is different from the source control plane network element serving the source access network device.

[0023] In one possible implementation, the target access network device receives uplink data from the terminal device and saves it; the target access network device receives indication information from the target control plane network element, and the indication information is used to indicate that the core network side has completed resource preparation for conditional switching of the terminal device; the target access network device sends the saved uplink data to the target core network device.

[0024] In this implementation, after the terminal device conditional switching is completed (i.e., switching to the target access network device), the uplink data reaches the target access network device. The target access network first caches the uplink data, and then sends the uplink data to the core network side after the core network side is ready. This can avoid data loss caused by the target access network device sending the uplink data to the core network side before the core network is ready.

[0025] In a fourth aspect, a communication device is provided, which may be the source access network device described in the first aspect. The communication device has the functions of the source access network device. The communication device is, for example, a functional module in the source access network device, such as a baseband device or a chip system. Alternatively, the communication device may be the terminal device described in the second aspect. The communication device has the functions of the terminal device. The communication device is, for example, a functional module in the terminal device, such as a baseband device or a chip system. Alternatively, the communication device may be the target access network device described in the third aspect. The communication device has the functions of the target access network device. The communication device is, for example, a functional module in the target access network device, such as a baseband device or a chip system.

[0026] In an optional implementation, the communication device includes a baseband device and a radio frequency device. In another optional implementation, the communication device includes a processing unit (sometimes also referred to as a processing module) and a transceiver unit (sometimes also referred to as a transceiver module). The transceiver unit can implement a sending function and a receiving function. When the transceiver unit implements the sending function, it can be called a sending unit (sometimes also referred to as a sending module). When the transceiver unit implements the receiving function, it can be called a receiving unit (sometimes also referred to as a receiving module). The sending unit and the receiving unit can be the same functional module, which is called a transceiver unit, and the functional module can implement a sending function and a receiving function; or, the sending unit and the receiving unit can be different functional modules, and the transceiver unit is a general term for these functional modules.

[0027] In one possible implementation, the communication device also includes a storage unit (sometimes also referred to as a storage module), and the processing unit is used to couple with the storage unit and execute the program or instructions in the storage unit, enabling the communication device to perform the function of the source access network device described in the first aspect above, or perform the function of the terminal device described in the second aspect above, or perform the function of the target access network device described in the third aspect above.

[0028] When the communication device is the source access network device described in the first aspect, at least one of the following possible implementations is included:

[0029] In one possible implementation, the transceiver unit is used to send first information to at least one candidate control plane network element, and to send second information to the terminal device; wherein, the first information is used to indicate the preparation of resources for conditional switching of the terminal device; wherein, the second information is used to indicate the switching condition and at least one candidate access network device, the at least one candidate control plane network element serves the at least one candidate access network device, and the source control plane network element serving the communication device is different from the at least one candidate control plane network element.

[0030] In a possible implementation, the transceiver unit is further configured to receive downlink data from the at least one candidate access network device; and send the downlink data to the terminal device.

[0031] In a possible implementation, the transceiver unit is further configured to receive downlink data from the source user plane network element; and send the downlink data to the terminal device through a target access network device among the at least one candidate access network device.

[0032] In one possible implementation, the transceiver unit is further used to send third information to the terminal device, where the third information is used to indicate a time window, which is the time window for the terminal device to switch from the communication device to the target access network device based on the switching condition.

[0033] In one possible implementation, the transceiver unit, when used to send the downlink data to the terminal device through the target access network device among the at least one candidate access network device, is specifically used to: send the downlink data to the at least one candidate access network device within a time window, and send the downlink data to the terminal device through the target access network device among the at least one candidate access network device, wherein the time window is the time window in which the terminal device switches from the source access network device to the target access network device based on the switching condition.

[0034] In one possible implementation, the transceiver unit is further used to receive fourth information, where the fourth information is used to indicate that resource preparation for conditional switching of the terminal device is completed; and to send fifth information to the terminal device, where the fifth information is used to indicate that switching of the access network device is allowed.

[0035] In a possible implementation manner, the processing unit is configured to determine the at least one candidate access network device based on ephemeris.

[0036] When the communication device is the terminal device described in the second aspect, at least one of the following possible implementations is included:

[0037] In one possible implementation, the transceiver unit is used to receive second information from a source access network device, where the second information is used to indicate a switching condition and at least one candidate access network device, and the control plane network elements serving the source access network device and the at least one candidate access network device are different; the processing unit is used to switch from accessing the source access network device to accessing a target access network device after determining that the switching condition is met, and the target access network device belongs to the at least one candidate access network device.

[0038] In one possible implementation, the transceiver unit is further used to receive third information from the source access network device, where the third information is used to indicate a time window; and the processing unit is specifically used to switch from accessing the source access network device to accessing the target access network device within the time window.

[0039] In a possible implementation, the transceiver unit is further configured to receive fifth information from the source access network device, where the fifth information is used to indicate that switching of the access network device is allowed.

[0040] In a fifth aspect, a communication device is provided, comprising an interface circuit and a processor, and optionally, a memory. The memory is used to store a computer program, and the processor is coupled to the memory and the interface circuit. When the processor reads the computer program or instruction, the communication device executes the method executed by the source access network device in the first aspect, or executes the method executed by the terminal device in the second aspect, or executes the method executed by the target access network device in the third aspect. Exemplarily, the interface circuit is used to receive a signal from another communication device other than the communication device and transmit it to the processor or send a signal from the processor to another communication device other than the communication device. The processor is used to implement the method executed by the source access network device in the first aspect, or to implement the method executed by the terminal device in the second aspect, or to implement the method executed by the target access network device in the third aspect through a logic circuit or executing code instructions.

[0041] In the sixth aspect, a communication device is provided, comprising a processor and, optionally, a memory; the processor and the memory are coupled; the memory is used to store computer programs or instructions; the processor is used to execute part or all of the computer programs or instructions in the memory, and when the part or all of the computer programs or instructions are executed, it is used to implement the function of the source access network device in the first aspect above, or to implement the function of the terminal device in the second aspect above, or to implement the function of the target access network device in the third aspect above.

[0042] In one possible implementation, the apparatus may further include a transceiver configured to transmit a signal processed by the processor or receive a signal input to the processor. The transceiver may perform the transmitting action or receiving action performed by the source access network device in the first aspect, the terminal device in the second aspect, or the target access network device in the third aspect.

[0043] In one possible implementation, the processing unit in the fourth, fifth and sixth aspects can be implemented by the processor, the storage unit in the fourth, fifth and sixth aspects can be implemented by the memory, and the transceiver unit in the fourth, fifth and sixth aspects can be implemented by the transceiver.

[0044] In a seventh aspect, a communication system is provided, comprising at least two of a source access network device, a terminal device, and a target access network device, wherein the source access network device is configured to execute the method performed by the source access network device as described in the first aspect above, the terminal device is configured to execute the method performed by the terminal device as described in the second aspect above, and the target access network device is configured to execute the method performed by the target access network device as described in the third aspect above. For example, the source access network device, the terminal device, and the target access network device may be implemented using the communication apparatus described in the fourth aspect.

[0045] In an eighth aspect, a computer-readable storage medium is provided, wherein the computer-readable storage medium is used to store computer programs or instructions, which, when executed, enables the method in the above-mentioned first aspect, second aspect, or third aspect to be implemented.

[0046] In a ninth aspect, a computer program product comprising instructions is provided, which, when executed on a computer, enables the method in the first aspect, or the second aspect, or the third aspect to be implemented. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] FIG1a is a schematic diagram of the architecture of a 5G communication system provided by this application;

[0048] FIG1b is a schematic diagram of the architecture of another 5G communication system provided by this application;

[0049] FIG1c is a schematic diagram of a satellite network communication system architecture provided by this application;

[0050] FIG2 is a flow chart of a conditional switching method provided by the present application;

[0051] FIG3 is a flow chart of a communication method provided by the present application;

[0052] FIG4 is a flow chart of a communication method provided by the present application;

[0053] FIG5 is a structural diagram of a communication device provided by the present application;

[0054] FIG6 is a structural diagram of a communication device provided in this application. DETAILED DESCRIPTION

[0055] The technical solution of the present application can be applied to a terrestrial network (TN) or a non-terrestrial network (NTN), such as a satellite network. The technical solution of the present application can be applied to various wireless communication systems, including but not limited to the fourth generation (4G) mobile communication technology system (also known as the long term evolution (LTE) system), the fifth generation (5G) mobile communication technology system (also known as the new radio (NR) system), or future mobile communication systems, etc., without specific limitation.

[0056] In addition, the technical solution of the present application can be applied to device-to-device (D2D) scenarios, such as NR-D2D scenarios, or can be applied to V2X scenarios, such as NR-V2X scenarios. The technical solution of the present application can also be applied to fields such as intelligent driving, assisted driving, or intelligent connected vehicles, or factory manufacturing scenarios.

[0057] For example, Figure 1a is a schematic diagram of a 5G communication system architecture to which this application may be applied. Specifically, Figure 1a is a schematic diagram of a 5G network architecture based on a service-oriented architecture.

[0058] For example, Figure 1b is a schematic diagram of another 5G communication system architecture to which this application may be applied. Specifically, Figure 1b is a schematic diagram of a 5G architecture based on point-to-point communication. The main difference between Figure 1a and Figure 1b is that the interfaces between the network elements in Figure 1a are service-oriented interfaces, while the interfaces between the network elements in Figure 1b are point-to-point interfaces.

[0059] The 5G network architecture shown in Figures 1a and 1b includes terminal equipment, an access network, and a core network. Optionally, it also includes data network (DN) and application function (AF) network elements. Terminals access the core network through the access network, and the core network communicates with the DN or AF. The following briefly describes the functions of some of these network elements.

[0060] A terminal device (UE), also known as user equipment (UE), is a device with wireless transceiver capabilities that can be deployed on land, including indoors or outdoors, handheld or vehicle-mounted; on water (such as ships); or in the air (such as airplanes, balloons, and satellites). The terminal device can be a mobile phone, tablet computer, computer with wireless transceiver capabilities, virtual reality (VR) terminal, augmented reality (AR) terminal, wireless terminal in industrial control, wireless terminal in self-driving, wireless terminal in remote medical, wireless terminal in smart grid, wireless terminal in transportation safety, wireless terminal in smart city, wireless terminal in smart home, etc.

[0061] The (R)AN device in this application is a device that provides wireless communication functions for terminal devices. The (R)AN device is also called an access network device. The RAN equipment in this application includes but is not limited to: the next generation base station (g nodeB, gNB) in 5G, evolved node B (evolved node B, eNB), radio network controller (radio network controller, RNC), node B (node ​​B, NB), base station controller (base station controller, BSC), base transceiver station (base transceiver station, BTS), home base station (for example, home evolved nodeB, or home node B, HNB), baseband unit (baseBand unit, BBU), transmission point (transmitting and receiving point, TRP), transmission point (transmitting point, TP), mobile switching center, etc. In systems using different wireless access technologies, the names of devices with base station functions may vary. For example, in the fifth generation (5G) system, it is called RAN or gNB (5G NodeB); in the LTE system, it is called evolved NodeB (eNB or eNodeB); in the third generation (3G) system, it is called Node B, etc.

[0062] A data network (DN) can deploy a variety of services, providing data and / or voice services to terminal devices. For example, a DN is the private network of a smart factory. Sensors installed in the workshop can be terminal devices. The DN contains sensors and a control server, which provides services to the sensors. Sensors can communicate with the control server, receive instructions from the control server, and transmit collected sensor data to the control server according to the instructions. Another example is a DN that is a company's internal office network. Employees' mobile phones or computers can be terminal devices, allowing them to access information and data resources on the company's internal office network.

[0063] The application network element mainly supports interaction with the 3rd Generation Partnership Project (3GPP) core network to provide services, such as influencing data routing decisions, policy control functions, or providing some third-party services to the network side. In the 5G communication system, the application network element can be an application function (AF) network element. In future communication systems, the application network element can still be an AF network element, or it can have other names, which are not limited in this application.

[0064] The core network may include one or more of the following network elements:

[0065] The access management network element (also known as the mobility management network element) is a control plane network element provided by the operator network, responsible for access control and mobility management of terminal devices accessing the operator network, such as mobile state management, allocation of user temporary identity, authentication and user functions. In the 5G communication system, the access management network element can be an access and mobility management function (AMF) network element. In future communication systems, the access management network element can still be an AMF network element, or it can have other names, which are not limited in this application.

[0066] The session management network element is primarily responsible for session management in mobile networks, such as session establishment, modification, and release. Specific functions include allocating IP addresses to users and selecting user plane network elements that provide message forwarding functions. In 5G communication systems, this session management network element may be a session management function (SMF) network element. In future communication systems, the session management network element may still be an SMF network element, or it may have other names, which are not limited in this application.

[0067] The user plane network element is responsible for forwarding and receiving user data in the terminal device. It can receive user data from the data network and transmit it to the terminal device through the access network device; the user plane network element can also receive user data from the terminal device through the access network device and forward it to the data network. The transmission resources and scheduling functions that provide services to the terminal device in the user plane network element are managed and controlled by the SMF network element. In the 5G communication system, the user plane network element can be a user plane function (UPF) network element. In future communication systems, the user plane network element can still be a UPF network element, or it can have other names, which are not limited in this application.

[0068] The data management network element is used for generating authentication credentials, user identification processing (such as storing and managing user permanent identities), access control, and contract data management. In a 5G communication system, this data management network element can be a unified data management (UDM) network element. In future communication systems, the unified data management can still be a UDM network element, or it can have other names, which are not limited in this application.

[0069] The policy control network element mainly supports providing a unified policy framework to control network behavior, provides policy rules to the control layer network function, and is responsible for obtaining user subscription information related to policy decisions. In the 4G communication system, the policy control network element can be a policy and charging rules function (PCRF) network element. In the 5G communication system, the policy control network element can be a policy control function (PCF) network element. In future communication systems, the policy control network element can still be a PCF network element, or it can have other names, which are not limited in this application.

[0070] The data storage network element is responsible for storing structured data information, including contract information, policy information, and network data or service data defined in a standard format. In a 5G communication system, the data storage network element can be a unified data repository (UDR). In future communication systems, the network open function network element can still be a UDR network element, or it can have other names, which are not limited in this application.

[0071] The network storage network element can be used to provide network element discovery function and provide network element information corresponding to the network element type based on the request of other network elements. NRF also provides network element management services, such as network element registration, update, deregistration, and network element status subscription and push. In the 5G communication system, the network storage network element can be a network repository function (NRF) network element. In future communication systems, the network storage network element can still be an NRF network element, or it can have other names, which are not limited in this application.

[0072] A network exposure function element can be used to securely expose services and capabilities provided by 3GPP network function devices to the outside world. In a 5G communication system, the network exposure function element can be a network exposure function (NEF) element. In future communication systems, the network exposure function element can still be an NEF element, or it can have other names, which are not limited in this application.

[0073] The network slice selection network element can be used to select the appropriate network slice for the terminal's service. In a 5G communication system, the network slice selection network element can be a network slice selection function (NSSF) network element. In future communication systems, the network open function network element can still be an NSSF network element, or it can have other names, which are not limited in this application.

[0074] The network data analysis network element can collect data from various network functions (NFs), such as policy control network elements, session management network elements, user plane network elements, access management network elements, and application function network elements (through network capability exposure function network elements), and perform analysis and prediction. In a 5G communication system, the network data analysis network element can be a network data analysis function (NWDAF). In future communication systems, the network exposure function network element can still be an NWDAF network element, or it can have other names, which are not limited in this application.

[0075] It is understood that the above-mentioned network element or function can be a network element in a hardware device, a software function running on dedicated hardware, or a virtualized function instantiated on a platform (e.g., a cloud platform). In one possible implementation, the above-mentioned network element or function can be implemented by a single device, or can be implemented by multiple devices together, or can be a functional module within a single device, which is not specifically limited in the embodiments of the present application.

[0076] Figure 1c is a schematic diagram of a possible satellite network communication system architecture. Terminal equipment on the ground accesses the base station through the air interface. The base station is deployed on the satellite. The base station is connected to the core network deployed on the ground through the ground station, and the core network communicates with the DN. The ground station is responsible for forwarding signaling and service data between the satellite base station and the core network. The base station and the ground station communicate through the NG interface. The base stations communicate with each other through the Xn interface. For example, there is a wireless link between satellites to complete the signaling interaction and user data transmission between base stations. The core network includes at least one or more of the following network elements: access management network element (such as AMF), session management network element (such as SMF), and user plane network element (such as UPF). The functions of these network elements can be referred to the above introduction and will not be repeated here.

[0077] Conditional handover (CHO) means that the source base station configures candidate base stations and handover conditions for the terminal device. When the handover conditions are met, the terminal device selects a target base station from the candidate base stations based on the measurement results of the candidate base stations and switches from the source base station to the target base station.

[0078] As shown in FIG2 , a flow chart of a conditional switching method is provided, including the following steps:

[0079] Step 201: The source base station performs configuration measurement on the terminal device, and the terminal device measures surrounding cells and reports a measurement report to the source base station.

[0080] Step 202: The source base station determines the use condition switching according to the measurement report.

[0081] Step 203: The source base station sends a conditional handover request signaling to a candidate base station (ie, a neighboring base station) that meets the conditional handover requirements according to the measurement report.

[0082] Step 204: The candidate base station performs access control and reserves resources for the terminal device.

[0083] Step 205: The candidate base station feeds back a confirmation signaling to the source base station, indicating that the candidate base station agrees to the conditional handover.

[0084] Step 206: The source base station sends handover configuration information to the terminal device through RRC reconfiguration signaling. The handover configuration information includes handover conditions and configuration parameters of candidate base stations.

[0085] Step 207: The terminal device sends an RRC reconfiguration completion signaling to the source base station.

[0086] Step 208: The terminal device evaluates the switching conditions. After the switching conditions are met, the terminal device measures the candidate base stations, selects a target base station from the candidate base stations, leaves the source base station, and accesses the target base station.

[0087] Step 208a: The target base station sends a handover success message to the source base station, informing the source base station that the terminal device has successfully accessed the target base station.

[0088] Step 208b: The source base station sends serial number (SN) status information to the target base station. Subsequently, downlink user data is forwarded to the target base station.

[0089] Step 208c: The source base station sends a handover cancellation message to other candidate base stations except the target base station, informing the other candidate base stations to release the resources reserved for the terminal device.

[0090] Compared with traditional switching (i.e., non-conditional switching), conditional switching allows the terminal device to select the target base station and initiate switching based on the measurement results. On the one hand, it can avoid signaling interaction between the terminal device and the source base station. On the other hand, it can avoid changes in the wireless link status during the signaling interaction between the source base station and the target base station, resulting in terminal device switching failure.

[0091] In the conditional handover process shown in Figure 2, the source and target base stations are managed by the same AMF, and there is no AMF handover. If the source and target base stations are managed by different AMFs, a handover from the source AMF to the target AMF is required, where the source AMF serves the source base station and the target AMF serves the target base station.

[0092] In a traditional handover (non-conditional handover) scenario, if AMF handover is involved, the following process is included:

[0093] The source base station sends a handover request to the source AMF. After receiving the handover request, the source AMF selects a target AMF. The target AMF determines the target base station for the terminal device, and the target AMF and core network elements such as UPF and SMF prepare resources for the handover of the terminal device, for example, establishing a user plane tunnel for the terminal device and creating a context for the terminal device. After the preparation on the core network side is completed, the target AMF notifies the source AMF and informs the source AMF of the relevant information of the target base station.

[0094] The source AMF sends a handover command to the source base station, which then sends a handover command to the terminal device. The source AMF informs the terminal device of the relevant information of the target base station through the source base station. After receiving the handover command, the terminal device switches from the source base station to the target base station based on the relevant information of the target base station.

[0095] In the current solution, the AMF handover is not involved in the conditional handover scenario; in the AMF handover scenario, the conditional handover is not involved. This application provides a communication method that supports both conditional handover and core network element handover.

[0096] Below, some terms or concepts in the embodiments of the present application are explained to facilitate understanding by those skilled in the art.

[0097] Source access network device: The access network device currently connected to the terminal device. Candidate access network device (candidate access network device can also be called candidate target access network device): The access network device that the terminal device may connect to after performing an access network device handover. There can be one or more candidate access network devices. Target access network device: The access network device that the terminal device connects to after performing an access network device handover. The target access network device is one of the candidate access network devices.

[0098] The core network element serving the source access network device is called the source core network element. The source core network element includes the source control plane element and the source user plane element. For example, the source control plane element includes the source AMF element, and the source user plane element includes the source UPF element. The core network element serving the candidate access network is called the candidate core network element (or candidate target core network element). The candidate core network element includes the candidate control plane element and the candidate user plane element. For example, the candidate control plane element includes the candidate AMF element, and the candidate user plane element includes the candidate UPF element. The core network element serving the target access network device is called the target core network element. The target core network element includes the target control plane element and the target user plane element. For example, the target control plane element includes the target AMF element, and the target user plane element includes the target UPF element.

[0099] In addition, the source control plane network element in the present application is different from any candidate control plane network element, that is, the source access network device and any candidate access network device are served by different control plane network elements. If there are multiple candidate access network devices, then the multiple candidate access network devices can be served by the same control plane network element or by different control plane network elements. Take three candidate access network devices, namely access network device 1, access network device 2 and access network device 3 as an example: for example, these three access network devices can all be served by control plane network element 1; for another example, access network device 1 and access network device 2 are served by control plane network element 1, and access network device 3 is served by control plane network element 2; for another example, access network device 1 is served by control plane network element 1, access network device 2 is served by control plane network element 2, and access network device 3 is served by control plane network element 3.

[0100] Similarly, the source user plane network element in this application is different from any candidate user plane network element, that is, the source access network device and any candidate access network device are served by different user plane network elements. If there are multiple candidate access network devices, then the multiple candidate access network devices can be served by the same user plane network element or by different user plane network elements.

[0101] The control plane network element / user plane network element in this application serves the access network device, which means that a communication connection is established between the control plane network element / user plane network element and the access network device for transmitting control signaling or data.

[0102] The control plane network element and the user plane network element can be network elements in hardware devices, software functions running on dedicated hardware, or virtualized functions instantiated on a platform (e.g., a cloud platform). In one possible implementation, the control plane network element and the user plane network element can be implemented by a single device, or by multiple devices, or as a functional module within a single device. This is not specifically limited in the embodiments of the present application.

[0103] In order to better describe the embodiments of the present application, the following describes the methods provided by the embodiments of the present application in conjunction with the accompanying drawings. Unless otherwise specified, the steps indicated by dotted lines in the accompanying drawings corresponding to the various embodiments of the present application are all optional steps.

[0104] FIG3 is a schematic diagram of a communication process provided in an embodiment of the present application, including the following steps:

[0105] It should be noted that: in the example of Figure 3, there are two candidate access network devices, but in actual applications, there is at least one candidate access network device; in the example of Figure 3, the two candidate access network devices are served by the same candidate control plane network element, but in actual applications, the two candidate access network devices can be served by different candidate control plane network elements.

[0106] Step 300: The source access network device determines a switching condition and candidate access network devices.

[0107] In one example, the source access network device performs configuration measurements on the terminal device, and the terminal device measures surrounding cells and reports a measurement report to the source access network device. The source access network device determines, based on the measurement report, that the terminal device can use conditional handover and identifies one or more candidate access network devices.

[0108] In another example, the source access network device determines one or more candidate access network devices based on the ephemeris.

[0109] Step 301: The source access network device sends first information to the candidate control plane network element; accordingly, the candidate control plane network element receives the first information; the first information is used to indicate the preparation of resources for the conditional switching of the terminal device.

[0110] In one example, the source access network device sends first information to the candidate access network device, and the candidate access network device sends the first information to the candidate control plane network element. The first information may be carried in the conditional handover request signaling.

[0111] In another example, the source access network device sends first information to the source control plane network element, where the first information includes the candidate access network devices determined in step 300. The source control plane network element determines a candidate control plane network element corresponding to each candidate access network device, and the source control plane network element sends the first information to the candidate control plane network element.

[0112] Preparing resources for conditional handover of terminal devices is controlled and implemented through candidate control plane network elements. Preparing resources for conditional handover of terminal devices includes, but is not limited to, one or more of the following: establishing a path between the target user plane network element and the protocol data unit session anchor (PDU session anchor, PSA) user plane network element, establishing a forwarding path between the target user plane network element and the target access network device, and updating the context of the terminal device.

[0113] Step 302: The source access network device sends second information to the terminal device. Correspondingly, the terminal device receives the second information, where the second information is used to indicate the switching condition and candidate access network device determined in step 300.

[0114] The order of step 301 and step 302 is not limited.

[0115] In this embodiment, the source access network device configures conditional handover for the terminal device and instructs the candidate control plane network element to prepare resources for the conditional handover of the terminal device, thereby simultaneously supporting conditional handover and control plane network element handover. Furthermore, this embodiment does not limit the order in which the first and second information are sent; the terminal device and the core network can prepare for conditional handover simultaneously, thereby reducing the latency of conditional handover.

[0116] Step 303: After determining that the switching condition is met, the terminal device switches from accessing the source access network device to accessing the target access network device, and the target access network device belongs to the candidate access network device determined in step 300.

[0117] The switching conditions corresponding to different candidate access network devices can be different or the same. The switching conditions include but are not limited to one or more of the following: signal quality is greater than a set threshold, a preset time is reached, and the terminal device is in a set area location.

[0118] A specific example of the terminal device switching from accessing the source access network device to accessing the target access network device in step 303 is that the terminal device sends uplink data to the target access network device. After receiving the uplink data from the terminal device, the target access network device can determine that the terminal device has completed the conditional switching, left the source access network device, and accessed the target access network device.

[0119] Next, a specific example will be introduced in conjunction with FIG3 . As shown in FIG4 , in this example, a specific process of preparing resources for conditional switching of a terminal device on the core network side is introduced.

[0120] It should be noted that: in Figure 4, other candidate access network devices except the target access network device are not shown. In actual applications, there are one or more candidate access network devices. The network elements involved on the core network side include but are not limited to: candidate user plane network elements, target user plane network elements, candidate control plane network elements, target control plane network elements, and PSA user plane network elements. In Figure 4, other candidate control plane network elements except the target control plane network element are not shown, and other candidate user plane network elements except the target user plane network element are not shown. In actual applications, there are one or more candidate control plane network elements, and there are one or more candidate user plane network elements. In addition, in Figure 4, the target control plane network elements include the target AMF and SMF, and the target user plane network elements include the target UPF as an example for introduction.

[0121] Step 400: The source access network device determines the target access network device and the switching condition.

[0122] The process of step 400 can refer to the description of step 300 and will not be repeated here.

[0123] After step 400, step 401 is executed: the source access network device sends first information to the target AMF serving the target access network device, where the first information is used to indicate preparation of resources for conditional switching of the terminal device.

[0124] The process of step 401 may refer to the description of step 301 .

[0125] In one example, the source access network device sends the first information to the target access network device, and the target access network device sends the first information to the target AMF.

[0126] In another example, the source access network device sends a first message to the source AMF, where the first message includes the target access network device. The source AMF determines the target AMF serving the target access network device, and the source AMF sends the first message to the target AMF.

[0127] Step 402: The target AMF sends an indication message to the SMF connected to the target AMF, instructing to prepare resources for conditional switching of the terminal device.

[0128] Step 403: After receiving the instruction information in step 402, the SMF establishes a path between the target UPF and the PSA UPF.

[0129] Step 404: After receiving the indication information of step 402, the SMF establishes a forwarding path between the target UPF and the target access network device.

[0130] The order of step 403 and step 404 is not limited.

[0131] After step 403 and step 404, step 405 is executed: SMF sends an indication message to the target AMF, indicating that the preparation of resources for conditional switching of the terminal device is completed.

[0132] Step 406: The target AMF sends an indication message to the source access network device, indicating that the preparation of resources for conditional switching of the terminal device is completed.

[0133] In one example, the target AMF sends an indication message to the target access network device, indicating that the preparation of resources for conditional switching of the terminal device is completed; the target access network device sends an indication message to the source access network device, indicating that the preparation of resources for conditional switching of the terminal device is completed.

[0134] In another example, the target AMF sends an indication message to the source AMF, indicating that the preparation of resources for conditional switching of the terminal device is completed; the source AMF sends an indication message to the source access network device, indicating that the preparation of resources for conditional switching of the terminal device is completed.

[0135] Step 405 and step 406 are optional steps.

[0136] After step 400 , step 407 is executed: the source access network device sends the switching condition and the target access network device determined in step 400 to the terminal device.

[0137] Step 408: After determining that the switching condition is met, the terminal device sends uplink data to the target access network device. After receiving the uplink data from the terminal device, the target access network device can determine that the terminal device has completed the conditional switching, left the source access network device, and accessed the target access network device.

[0138] The processes of step 407 and step 408 may refer to the descriptions of step 302 and step 303 and will not be repeated here.

[0139] Step 408a: The target access network device sends the uplink data to the target UPF based on the forwarding path established with the target UPF in step 404.

[0140] After receiving the uplink data from the target access network device, the target UPF can determine that the terminal device has completed the conditional switching, left the source access network device, and accessed the target access network device.

[0141] Step 408b: The target UPF sends the uplink data to the PSA UPF.

[0142] After receiving the uplink data from the target UPF, the PSA UPF can determine that the terminal device has completed the conditional switching, leaving the source access network device and accessing the target access network device.

[0143] Step 409: The target access network device sends a handover success message to the source access network device, informing the source access network device that the terminal device has successfully accessed the target access network device.

[0144] Step 410: The session connection for the terminal device is released between the source AMF and SMF, and the forwarding path between the source access network device and the source UPF is deleted.

[0145] Optionally, if there are other candidate access network devices other than the target access network device, the source access network device sends a switching cancellation message to the other candidate access network devices other than the target access network device, informing the other candidate access network devices to release the resources reserved for the terminal device; the other candidate access network devices can notify the corresponding other candidate control plane network elements to release the resources reserved for the terminal device, and the other candidate control plane network elements can control the release of the resources reserved for the terminal device.

[0146] There is no restriction on the order in which the terminal device performs conditional switching and the core network side prepares resources for the conditional switching of the terminal device. This may lead to several possible situations: Situation 1: The terminal device has not yet switched to the target access network device, and the core network side has completed preparing resources for the conditional switching of the terminal device. Situation 2: The terminal device has not yet switched to the target access network device, and the core network side has not completed preparing resources for the conditional switching of the terminal device. Situation 3: The terminal device completes the conditional switching, leaves the source access network device, and switches to the target access network device, but the core network side has not completed preparing resources for the conditional switching of the terminal device. Situation 4: The terminal device completes the conditional switching, leaves the source access network device, and switches to the target access network device, and the core network side has also completed preparing resources for the conditional switching of the terminal device.

[0147] The following describes the transmission paths of uplink and downlink data for these four situations.

[0148] For situation 1 (the terminal device has not yet switched to the target access network device, and some or all candidate control plane network elements have completed resource preparation for the conditional switching of the terminal device), the following describes possible transmission paths for downlink data:

[0149] Path 1.1: Candidate user plane network element → candidate access network device (including target access network device) → terminal device.

[0150] Downlink data can be transmitted to candidate access network devices via candidate user plane network elements. After receiving downlink data from the candidate user plane network element, the candidate access network device stores the downlink data. When the terminal device switches to the target access network device, the target access network device sends the stored downlink data to the terminal device. For example, the target access network device transparently transmits the downlink data to the terminal device. Other unselected candidate access network devices can delete the downlink data. Saving downlink data on the candidate access network device prevents data loss during the terminal device's access network device handover.

[0151] Path 1.2: Candidate user plane network element → candidate access network device (including target access network device) → source access network device → terminal device.

[0152] Downlink data can be transmitted to a candidate access network device via a candidate user plane network element. After receiving downlink data from the candidate user plane network element, the candidate access network device sends the downlink data to the source access network device. After receiving the downlink data from the candidate access network device, the source access network device promptly sends the downlink data to the terminal device. For example, the source access network device transparently transmits the downlink data to the terminal device. The candidate access network device sends the downlink data to the source access network device, which can then promptly send the downlink data to the terminal device, improving downlink data transmission efficiency.

[0153] Path 1.3: Source user plane network element → source access network device → terminal device.

[0154] Downlink data can be transmitted to the source access network device through the source user plane network element. The source access network device sends the downlink data directly to the terminal device, which can improve the transmission efficiency of the downlink data.

[0155] Path 1.4: Source user plane network element → source access network device → candidate access network device (including target access network device) → terminal device.

[0156] The downlink data can be transmitted to the source access network device through the source user plane network element. The source access network device forwards the downlink data to the terminal device through the target access network device in at least one candidate access network device. Here is a possible example: the source access network device sends the downlink data to the at least one candidate access network device respectively, and the at least one candidate access network device saves the downlink data after receiving the downlink data from the source access network device. When the terminal device switches to the target access network device in the at least one candidate access network device, the target access network device sends the saved downlink data to the terminal device. For example, the source access network device transparently transmits the downlink data to the terminal device. Other unselected candidate access network devices can delete these downlink data. The candidate access network device saves the downlink data to avoid data loss during the process of the terminal device switching the access network device.

[0157] For scenario 1, the following describes possible transmission paths for uplink data:

[0158] Path 1.5: Terminal device → Source access network device → Source user plane network element.

[0159] Uplink data is sent directly to the source user plane network element through the source access network device, which can improve the transmission efficiency of uplink data.

[0160] Path 1.6: Terminal device → Source access network device → Candidate access network device (including target access network device) → Target user plane network element.

[0161] The terminal device sends uplink data to the source access network device, which then sends the uplink data to at least one candidate access network device. For example, the source access network device transparently transmits the uplink data to the at least one candidate access network device. Each candidate access network device stores the uplink data. When the terminal device switches to a target access network device among the at least one candidate access network device, the target access network device sends the stored uplink data to the target user plane network element. Other unselected candidate access network devices may delete the uplink data.

[0162] For situation 2 (the terminal device has not yet switched to the target access network device, and all candidate control plane network elements have not completed resource preparation for the conditional switching of the terminal device), the possible transmission paths of downlink data are introduced:

[0163] Path 2.1: Source user plane network element → Source access network device → Terminal device. For details on Path 2.1, refer to the introduction to Path 1.3 and will not be repeated here.

[0164] Path 2.2: Source user plane network element → source access network device → candidate access network device (including target access network device) → terminal device. The details of path 2.2 can be referred to the introduction of path 1.4 and will not be repeated here.

[0165] For situation 2, the following describes possible transmission paths for uplink data:

[0166] Path 2.3: Terminal device → Source access network device → Source user plane network element. For details on Path 2.3, refer to the introduction to Path 1.5 and will not be repeated here.

[0167] Path 2.4: Terminal device → Source access network device → Candidate access network device (including target access network device) → Target user plane network element. The details of Path 2.4 can be found in the introduction of Path 1.6 and will not be repeated here.

[0168] For situation 3 (the terminal device completes conditional handover, leaves the source access network device, and switches to the target access network device, but the core network has not yet completed resource preparation for the conditional handover of the terminal device), the following describes possible transmission paths for downlink data:

[0169] Path 3.1: Source user plane network element → source access network device → target access network device → terminal device.

[0170] For situation 3, the following describes possible transmission paths for uplink data:

[0171] Path 3.2: Terminal device → Target access network device → Target user plane network element.

[0172] Path 3.3: Terminal device → Target access network device → Source access network device → Source user plane network element.

[0173] For scenario 4 (the terminal device completes conditional handover, leaves the source access network device, and switches to the target access network device, and the core network also prepares resources for the conditional handover of the terminal device), the following describes possible transmission paths for downlink data:

[0174] Path 4.1: Target user plane network element → target access network device → terminal device.

[0175] For situation 4, the following describes possible transmission paths for uplink data:

[0176] Path 4.2: Terminal device → Target access network device → Target user plane network element.

[0177] In the above-mentioned steps 303 and 408, it is introduced that: after the terminal device determines that the switching condition is met, the terminal device switches from accessing the source access network device to accessing the target access network device. In a possible implementation, the source access network device can indicate a time window for executing conditional switching to the terminal device, and the terminal device executes conditional switching within the time window after determining that the switching condition is met. Exemplarily, the source access network device sends a third information to the terminal device, and accordingly, the terminal device receives the third information, and the third information is used to indicate a time window, and the time window is the time window for the terminal device to switch from the source access network device to the candidate access network device based on the switching condition. Accordingly, steps 303 and 408 are specifically as follows: after the terminal device determines that the switching condition is met, the terminal device switches from accessing the source access network device to accessing the target access network device within the time window. If, within the time window, the terminal device determines that the switching condition is not met, the switching of the access network device may not be executed.

[0178] When indicating a time window, the third information may indicate an absolute time window, such as from 10:00 to 10:01, or from the nth subframe / time slot to the mth subframe / time slot, where m is greater than n and m and n are positive integers. For example, the third information indicates at least two of the start time, end time, and length of the time window of the third time port.

[0179] When indicating a time window, the third information may indicate a relative time window. For example, the third information indicates a first time length and a second time length; wherein the first time length represents the time length between the reference time point and the starting point of the time window, and the second time length is the time length of the time window. Adding the first time length to the reference time point is the starting point of the time window, and adding the second time length from the starting point is the end point of the time window. The reference time point may be specified by the protocol without the need for an indication from the source access network device; alternatively, the third information may also indicate a reference time point. The reference time point may be determined based on the time point at which the terminal device receives the third information, or based on the time point at which the terminal device receives the first information, or based on the time point at which the terminal device determines that the switching condition is met. This is not limited.

[0180] In the scenario where the source access network device indicates a time window to the terminal device, theoretically, before the time window, the terminal device has not yet switched to the target access network device, and after the time window, the terminal device has switched to the target access network device. Regarding the transmission path of downlink data: source access network device → candidate access network device (including the target access network device) → terminal device (refer to path 1.4, path 2.2), that is, the source access network device sends the downlink data to the terminal device through the target access network device in the at least one candidate access network device. A possible example is: the source access network device sends the downlink data to the at least one candidate access network device within the time window, and sends the downlink data to the terminal device through the target access network device in the candidate access network device. Downlink data will only be forwarded from the source access network device to the target access network device within the execution time window of the conditional switching. Before this time window, the source access network device can send the downlink data directly to the terminal device instead of sending it to the candidate access network device. This time window reduces the data cache pressure of the target access network device before the terminal device completes the switching of the access network device.

[0181] The foregoing (e.g., step 303 and step 408) describes that after the terminal device determines that the switching condition is met, it switches from accessing the source access network device to accessing the target access network device. The terminal device can decide by itself when to switch without considering whether the core network has completed the preparation of resources for the conditional switching of the terminal device. In a possible implementation, after the terminal device determines that at least one candidate control plane network element has completed the preparation of resources for the conditional switching of the terminal device, the terminal device switches the access network device. If the candidate control plane network element has not yet completed the preparation of resources for the conditional switching of the terminal device, the terminal device does not perform the switching of the access network device even if it determines that the switching condition is met. Exemplarily, the source access network device receives fourth information, and the fourth information is used to indicate that the preparation of resources for the conditional switching of the terminal device is completed; the source access network device sends fifth information to the terminal device, and accordingly, the terminal device receives fifth information, and the fifth information is used to indicate that the switching of the access network device is allowed. Exemplarily, the source access network device sends the fifth information to the terminal device only after determining that all candidate control plane network elements have completed the preparation of resources for the conditional switching of the terminal device. The terminal device will switch the access network device only after it determines that the fifth information has been received and the switching conditions are met.

[0182] One example of the source access network device receiving the fourth information is: the candidate control plane network element sends the fourth information to the source control plane network element, the source control plane network element sends the fourth information to the source access network device, and the source access network device then receives the fourth information from the source control plane network element. Another example of the source access network device receiving the fourth information is: the candidate control plane network element sends the fourth information to the candidate access network device, the candidate access network device sends the fourth information to the source access network device, and the source access network device then receives the fourth information from the candidate access network device.

[0183] Applying this example to the example in Figure 4, the process of the access network device receiving the fourth information can be referred to in the description of step 406. After step 406, the source access network device sends the fifth information to the terminal device. In response, the terminal device receives the fifth information, which indicates that the access network device is allowed to switch. In step 408, the terminal device determines that the fifth information has been received and the switching conditions have been met before switching the access network device.

[0184] The terminal device can perform condition evaluation in advance and select the target access network device from the candidate access network devices. However, when to switch to the target access network device requires instructions from the network side. This ensures that the terminal device performs the access network device switching behavior only after the core network is ready. If the core network is not ready yet, the terminal device switches to the target access network device and sends the uplink data to the target access network device. The target access network device sends the uplink data to the target user plane network element. In this case, the target user plane network element may not receive the uplink data, which means that the uplink data is lost. In addition, if the target user plane network element does not receive the uplink data, it will think that the terminal device has not yet switched to the target access network device, which will also affect the transmission path of the downlink data.

[0185] After a terminal device switches to a target access network device, it sends its uplink data to the target access network device. Upon receiving the uplink data, the target access network can promptly send the uplink data to the target user plane network element, regardless of whether the core network has completed resource preparation for conditional handover. As previously mentioned, if the core network is not ready, the target user plane network element will not receive the uplink data, resulting in uplink data loss. Furthermore, if the target user plane network element does not receive the uplink data, it will assume that the terminal device has not yet switched to the target access network device, which will also affect the downlink data transmission path. In one possible implementation, the target access network device can first buffer the uplink data and wait until the core network is ready before sending the uplink data to the target user plane network element. For example, in the example of Figure 4, after step 405, the target AMF can send an indication to the target access network device indicating that resource preparation for conditional handover is complete. In step 408a, the target access network device will send the uplink data to the target UPF only after confirming receipt of the indication, based on the forwarding path established with the target UPF in step 404. For another example, in path 3.2, the target access network device sends the uplink data to the target user plane network element only after confirming that the indication information has been received.

[0186] In one possible implementation, after the terminal device's uplink data reaches the target user-plane network element via the target access network device (i.e., a data path is established between the terminal device and the target user-plane network element), the target user-plane network element can send a downlink data end marker to the source access network device via the target control-plane network element. This prevents the disarray and loss of downlink data forwarded to the target access network and downlink data sent directly to the target access network device.

[0187] It is understood that in order to implement the functions in the above embodiments, the terminal equipment and access network equipment include hardware structures and / or software modules corresponding to the execution of each function. Those skilled in the art should readily appreciate that, in combination with the units and method steps of the various examples described in the embodiments disclosed in this application, this application can be implemented in the form of hardware or a combination of hardware and computer software. Whether a function is executed in hardware or in a manner driven by computer software depends on the specific application scenario and design constraints of the technical solution.

[0188] Figures 5 and 6 are schematic diagrams of possible communication devices provided in embodiments of the present application. These communication devices can be used to implement the functions of the terminal device and network device in the above-mentioned method embodiments, thereby also achieving the beneficial effects of the above-mentioned method embodiments. As shown in Figure 5, communication device 500 includes a processing unit 510 and a transceiver unit 520.

[0189] For example, the communication device 500 is used to implement the functions of the target access network device, source access network device, or terminal device in the method embodiments shown in Figures 3 and 4 above. The transceiver unit 520 can perform the receiving and sending actions performed by the target access network device, source access network device, or terminal device in the method embodiments above. The processing unit 510 can perform other actions, except for the sending and receiving actions, among the actions performed by the target access network device, source access network device, or terminal device in the method embodiments above.

[0190] Exemplarily, when the communication device 500 is used to implement the functions of the source access network device in the method embodiment shown in FIG3 , the transceiver unit 520 is used to send the first information and the second information. The processing unit 510 is used to determine the switching conditions and the candidate access network devices, generate the first information, and generate the second information.

[0191] Exemplarily, when the communication device 500 is used to implement the functions of the terminal device in the method embodiment shown in FIG3 , the transceiver unit 520 is used to receive the second information. The processing unit 510 is used to parse the second information and, upon determining that a switching condition is met, switch from the source access network device to the target access network device.

[0192] Exemplarily, when the communication device 500 is used to implement the functions of the target access network device in the method embodiment shown in FIG4 , the transceiver unit 520 is used to receive uplink data from the terminal device and send a handover success indication to the source access network device. The processing unit 510 is used to establish a forwarding path between the target access network device and the target UPF.

[0193] A more detailed description of the processing unit 510 and the transceiver unit 520 can be directly obtained by referring to the relevant description of the method embodiments shown in Figures 3 and 4, and is not repeated here. The processing unit 510 can be implemented by a processor, and the transceiver unit 520 can be implemented by a transceiver.

[0194] As shown in Figure 6, communication device 600 includes a processor 610 and an interface circuit 620. Processor 610 and interface circuit 620 are coupled to each other. It is understood that interface circuit 620 can be a transceiver or an input / output interface. Optionally, communication device 600 may also include a memory 630 for storing instructions executed by processor 610, input data required by processor 610 to execute instructions, or data generated after processor 610 executes instructions. Sometimes, interface circuit 620 can also be understood as part of processor 610, in which case communication device 600 includes processor 610.

[0195] When the communication device 600 is used to implement the method shown in FIG. 3 and FIG. 4 , the processor 610 is used to implement the function of the processing unit 510 , and the interface circuit 620 is used to implement the function of the transceiver unit 520 .

[0196] When the above-mentioned communication device is a chip applied to a terminal device, the terminal device chip implements the functions of the terminal device in the above-mentioned method embodiment. When the terminal device chip receives information from the network device, it can be understood that the information is first received by other modules in the terminal device (such as a radio frequency module or antenna) and then sent to the terminal device chip by these modules. When the terminal device chip sends information to the network device, it can be understood that the information is first sent to other modules in the terminal device (such as a radio frequency module or antenna) and then sent to the network device by these modules.

[0197] When the above-mentioned communication device is a chip applied to a network device, the network device chip implements the functions of the network device in the above-mentioned method embodiment. The network device chip receives information from the terminal device, which can be understood as the information being first received by other modules in the network device (such as a radio frequency module or antenna) and then sent to the network device chip by these modules. The network device chip sends information to the terminal device, which can be understood as the information being sent to other modules in the network device (such as a radio frequency module or antenna) and then sent to the terminal device by these modules. The network device module here can be a baseband chip of the network device, or it can be a DU or other module. The DU here can be a DU under the open radio access network O-RAN architecture.

[0198] In the present application, when entity A sends information to entity B, it can be that A sends it directly to B, or that A sends it to B indirectly through other entities. Similarly, when entity B receives information from entity A, it can be that entity B directly receives the information sent by entity A, or that entity B indirectly receives the information sent by entity A through other entities. Entities A and B here can be network devices or terminal devices, or modules within a network device or modules within a terminal device. The sending and receiving of information can be information interaction between a network device and a terminal device, or information interaction between two network devices, such as information interaction between a CU and a DU; the sending and receiving of information can also be information interaction between different modules within a device, such as information interaction between a terminal device chip and other modules of the terminal device, or information interaction between a network device chip and other modules in the network device.

[0199] It is understood that the processor in the embodiments of the present application may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field programmable gate arrays (FPGA), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. The general-purpose processor may be a microprocessor or any conventional processor.

[0200] The present application also provides a computer-readable storage medium storing a computer program, which, when executed by a computer, enables the computer to perform the above-mentioned communication method. In other words, the computer program includes instructions for implementing the above-mentioned communication.

[0201] An embodiment of the present application further provides a computer program product, including: computer program code, which, when executed on a computer, enables the computer to execute the communication method provided above.

[0202] An embodiment of the present application also provides a communication system, which includes: at least two of a source access network device, a target access network device, and a terminal device that execute the above-mentioned communication method.

[0203] The method steps in the embodiments of the present application can be implemented by hardware or by a processor executing software instructions. The software instructions can be composed of corresponding software modules, and the software modules can be stored in a random access memory, a flash memory, a read-only memory, a programmable read-only memory, an erasable programmable read-only memory, an electrically erasable programmable read-only memory, a register, a hard disk, a mobile hard disk, a compact disc read-only memory (CD-ROM) (also known as a read-only optical disc) or any other form of storage medium well known in the art. An exemplary storage medium is coupled to the processor so that the processor can read information from the storage medium and write information to the storage medium. Of course, the storage medium can also be an integral part of the processor. The processor and the storage medium can be located in an ASIC. In addition, the ASIC can be located in a base station or a terminal. Of course, the processor and the storage medium can also be present in a base station or a terminal as discrete components.

[0204] The above embodiments can be implemented in whole or in part using software, hardware, firmware, or any combination thereof. When implemented using software, they can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer programs or instructions. When the computer programs or instructions are loaded and executed on a computer, the processes or functions described in the embodiments of this application are performed in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, a network device, a first control plane network element, a user equipment, or other programmable device. The computer program or instructions can be stored in a computer-readable storage medium or transferred from one computer-readable storage medium to another. For example, the computer program or instructions can be transferred from one website, computer, server, or data center to another website, computer, server, or data center via wired or wireless means. The computer-readable storage medium can be any available medium accessible by a computer or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium, such as a floppy disk, hard disk, or magnetic tape; an optical medium, such as a digital video disk; or a semiconductor medium, such as a solid-state drive. The computer-readable storage medium may be a volatile or nonvolatile storage medium, or may include both volatile and nonvolatile types of storage media.

[0205] In the various embodiments of the present application, unless otherwise specified or there is a logical conflict, the terms and / or descriptions between different embodiments are consistent and can be referenced by each other. The technical features in different embodiments can be combined to form new embodiments according to their inherent logical relationships.

[0206] In the embodiments of the present application, the number of nouns, unless otherwise specified, means "singular noun or plural noun", that is, "one or more". "At least one" means one or more, and "plural" means two or more. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone, where A or B can be singular or plural. The character " / " generally indicates that the previous and next associated objects are in an "or" relationship. For example, A / B means: A or B. "At least one of the following items" or "one or more of them" and other similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b, or c, or one or more of a, b, or c, means: a, b, c, a and b, a and c, b and c, or a and b and c. Each of a, b, and c can be single or multiple.

[0207] The ordinal numbers "first" and "second" mentioned in the embodiments of this application are used to distinguish multiple objects and are not used to limit the size, content, order, timing, priority, or importance of multiple objects. Moreover, such names do not indicate differences in the content, sender / receiver, transmission order, size, application scenario, priority, or importance of the two pieces of information. In addition, the numbering of the steps in the various embodiments introduced in this application is only for distinguishing different steps and is not used to define the order of the steps.

Claims

1. A switching method, characterized in that: Applied to the source access network side, including: Sending first information to at least one candidate control plane network element, and sending second information to the terminal device; The first information is used to indicate the preparation of resources for conditional switching of the terminal device; The second information is used to indicate a switching condition and at least one candidate access network device, the at least one candidate control plane network element serves the at least one candidate access network device, and the source control plane network element serving the source access network device is different from any of the at least one candidate control plane network elements.

2. The method according to claim 1, wherein Also includes: receiving downlink data from the at least one candidate access network device; Send the downlink data to the terminal device.

3. The method according to claim 1, wherein Also includes: Receiving downlink data from the source user plane network element; The downlink data is sent to the terminal device through a target access network device among the at least one candidate access network device.

4. The method according to claim 3, wherein Also includes: Send third information to the terminal device, where the third information is used to indicate a time window, where the time window is the time window for the terminal device to switch from the source access network device to the target access network device based on the switching condition.

5. The method according to claim 3, wherein The sending the downlink data to the terminal device through a target access network device among the at least one candidate access network device includes: Within the time window, the downlink data is sent to the at least one candidate access network device, and the downlink data is sent to the terminal device through the target access network device among the at least one candidate access network device; wherein, the time window is the time window for the terminal device to switch from the source access network device to the target access network device based on the switching condition.

6. The method according to any one of claims 1 to 3, wherein: Also includes: receiving fourth information, where the fourth information is used to indicate that preparation of resources for conditional switching of the terminal device is complete; Send fifth information to the terminal device, where the fifth information is used to indicate that switching of the access network device is allowed.

7. The method according to any one of claims 1 to 6, wherein: Also includes: The at least one candidate access network device is determined based on the ephemeris.

8. A switching method, characterized in that: include: receiving second information from a source access network device, where the second information is used to indicate a handover condition and at least one candidate access network device, where control plane network elements serving the source access network device and the at least one candidate access network device are different; After determining that the switching condition is met, the access to the source access network device is switched to the access to the target access network device, where the target access network device belongs to the at least one candidate access network device.

9. The method according to claim 8, wherein Also includes: receiving third information from the source access network device, where the third information is used to indicate a time window; The switching from accessing the source access network device to accessing the target access network device includes: Within the time window, access to the source access network device is switched to access to the target access network device.

10. The method according to claim 8, wherein Before switching from accessing the source access network device to accessing the target access network device, the method further includes: Receive fifth information from the source access network device, where the fifth information is used to indicate that switching of the access network device is allowed.

11. A switching method, characterized in that: include: During the conditional handover of the terminal device, the target access network device receives downlink data from the source access network device; After determining that the terminal device switches to the target access network device, the downlink data is sent to the terminal device; wherein the target control plane network element serving the target access network device is different from the source control plane network element serving the source access network device.

12. A switching method, characterized in that: include: The target access network device receives uplink data from the terminal device; The target access network device receives the indication information from the target control plane network element, where the indication information is used to indicate that the core network side has completed the preparation of resources for the conditional handover of the terminal device; The target access network device sends the uplink data to the target core network device.

13. A communication device, characterized in that: The method comprises a module for executing the method according to any one of claims 1 to 12.

14. A communication device, characterized in that: comprising a processor coupled to a memory; The memory is used to store computer programs or instructions; The processor is configured to execute part or all of the computer programs or instructions in the memory, and when the part or all of the computer programs or instructions are executed, is configured to implement the method according to any one of claims 1 to 12.

15. A communication device, characterized in that: including processor and memory; The memory is used to store computer programs or instructions; The processor is configured to execute part or all of the computer programs or instructions in the memory, and when the part or all of the computer programs or instructions are executed, is configured to implement the method according to any one of claims 1 to 12.

16. A communication device, characterized in that: The method comprises a processor and an interface circuit, wherein the interface circuit is used to receive signals from other communication devices outside the communication device and transmit them to the processor or send signals from the processor to other communication devices outside the communication device, and the processor is used to implement the method according to any one of claims 1 to 12 through a logic circuit or executing code instructions.

17. A computer-readable storage medium, characterized in that The storage medium stores a computer program or instruction. When the computer program or instruction is executed by the communication device, the method according to any one of claims 1 to 12 is implemented.

18. A computer program product, characterized in that The computer program product comprises: computer instructions, and when the computer instructions are executed on a computer, the method according to any one of claims 1 to 12 is implemented.

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