Communication method and device

Abstract

A communication method and device, relating to the technical field of communications. The method provides a handover solution in which conditional handover (CHO) and dual active protocol stack handover are combined to shorten the handover interruption time, thereby improving the user experience. Specifically, a source access network device can trigger, by means of first information, a terminal to perform CHO and dual active protocol stack handover. That is, after receiving the first information, the terminal can determine a target cell from among candidate cells on the basis of an execution condition for CHO comprised in the first information, and continues maintaining a connection with the source access network device after determining the target cell. Compared with an existing solution in which when CHO is used, a source access network device is disconnected after a target cell is determined, the manner in embodiments of the present application of continuing maintaining a connection with a source access network device after a target cell is determined can shorten the handover interruption time, thereby improving the user experience.

Description

Communication methods and devices

[0001] This application claims priority to Chinese Patent Application No. 202510069818.7, filed on January 15, 2025, entitled "Communication Method and Apparatus", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of communication technology, and in particular to a communication method and apparatus. Background Technology

[0003] Currently, the interruption latency of conditional handover (CHO) handover is approximately tens to hundreds of milliseconds, which can impact user experience. In some communication scenarios, such as non-terrestrial network (NTN) communication scenarios (taking satellite communication as an example), the current standard only supports CHO handover based on the Xn interface, thus failing to meet the requirements of satellite communication. Summary of the Invention

[0004] This application provides a communication method and apparatus that can reduce handover interruption time and improve user experience.

[0005] The present application is described below from different aspects. It should be understood that the different implementation methods and beneficial effects described below can be referenced from each other.

[0006] Firstly, this application provides a communication method that can be applied to a terminal-side communication device, such as a terminal or a communication module / processing module within a terminal, or a circuit or chip in the terminal responsible for communication functions (such as a modem chip, also known as a baseband chip, or a system-on-chip (SoC) chip or system-in-package (SIP) chip containing a modem core), or a circuit or chip in the terminal responsible for processing functions (such as a graphics processing unit (GPU), an artificial intelligence (AI) processor, or an application-specific integrated circuit (ASIC)). Taking the application of this method to a terminal as an example, in this method, the terminal receives first information from a source access network device. This first information includes execution conditions for conditional handover, configuration information of candidate cells, and configuration information for dual-activation protocol stack handover. The configuration information for dual-activation protocol stack handover indicates that when it is determined that a target cell meets the execution conditions, the connection with the source access network device should be maintained. The target cell is included in the candidate cells. When it is determined that the target cell meets the execution conditions, the terminal maintains the connection with the source access network device. The terminal synchronizes with the target cell and sends a handover completion message to the target access network device where the target cell is located, wherein the handover completion message indicates that the terminal has successfully handed over from the source access network device to the target access network device.

[0007] Understandably, the aforementioned terminal maintaining a connection with the source access network device can be understood as one or more of the following: ① The terminal does not release the configuration information of the source cell under the source access network device; ② The terminal detects the downlink control information (DCI) of the source cell; ③ The terminal receives data and / or information from the source cell; ④ The terminal sends data and / or information to the source cell.

[0008] This application proposes a handover scheme that combines CHO handover with dual active protocol stack (DAPS) handover to reduce handover interruption time, thereby improving user experience. Specifically, the source access network device can trigger the terminal to perform CHO handover and DAPS handover through first information. That is, after receiving the first information, the terminal can determine the target cell according to the execution conditions of CHO handover and continue to maintain the connection with the source access network device after determining the target cell. Compared with the existing schemes that disconnect from the source access network device after determining the target cell when using CHO handover, this application embodiment can reduce handover interruption time and improve user experience by continuing to maintain the connection with the source access network device after determining the target cell.

[0009] In one possible implementation, when it is determined that the target cell meets the execution conditions, or after it is determined that the target cell meets the execution conditions, or before sending handover completion information to the target access network device where the target cell is located, the method further includes:

[0010] Send a second message to the source access network device, the second message indicating the target cell that meets the execution conditions.

[0011] In this implementation, the terminal notifies the source access network device of its determined target cell, so that when the source access network device forwards data in the future, it only needs to forward downlink data to the target access network device where the target cell is located, instead of forwarding downlink data to the candidate target access network devices where all candidate cells are located as in existing technologies. This can reduce the waste of resources and caching overhead of the source access network device and the candidate target access network devices.

[0012] In one possible implementation, before determining that the target cell meets the execution conditions, or after receiving the first information from the source access network device, the method further includes:

[0013] Maintain the connection with the source access network device and evaluate whether the candidate cell meets the execution conditions.

[0014] In this implementation, maintaining the connection between the terminal and the source access network device before determining the target cell is beneficial for compatibility with existing protocols.

[0015] In one possible implementation, maintaining the connection with the source access network device and evaluating whether the candidate cell meets the execution conditions includes:

[0016] Maintain connectivity with all active data radio bearers (DRBs) of the source access network device and evaluate whether the candidate cell meets the execution conditions.

[0017] In this implementation, maintaining all active DRB connections between the terminal and the source access network device before determining the target cell is beneficial for compatibility with existing protocols.

[0018] In one possible implementation, the configuration information for the dual-activation protocol stack switching further indicates a first DRB or a first quality of service (QoS) flow; maintaining the connection with the source access network device when it is determined that the target cell meets the execution conditions includes:

[0019] If the target cell is determined to meet the execution conditions, the connection between the first DRB or the first QoS flow and the source access network device is maintained.

[0020] In this implementation, the configuration information for DAPS handover may specifically include information about the DRB or QoS flow that the target access network device agrees to / accepts for DAPS handover. For ease of description, this application uses the example of the target access network device agreeing to / accepting the first DRB or the first QoS flow for DAPS handover. Therefore, when the terminal determines that the target cell meets the execution conditions, the terminal can maintain the connection with the first DRB or the first QoS flow of the source access network device, which is beneficial for protocol compatibility. It should be understood that the number of first DRBs involved in the embodiments of this application can be one or more, that is, the first DRB is a collective term for the DRBs that the target access network device agrees to / accepts for DAPS handover. Similarly, the number of first QoS flows can also be one or more, that is, the first QoS flow is a collective term for the QoS flows that the target access network device agrees to / accepts for DAPS handover.

[0021] Secondly, this application provides a communication method that can be applied to network-side communication devices, such as network-side access network devices, modules (e.g., circuits, chips, or chip systems) within the access network device, or logical nodes, logical modules, or software capable of implementing all or part of the functions of the access network device. Taking the application of this method to a source access network device as an example, in this method, the source access network device sends first information to the terminal. This first information includes execution conditions for conditional handover, configuration information of candidate cells, and configuration information for dual-activation protocol stack handover. The configuration information for dual-activation protocol stack handover indicates that when a target cell is determined to meet the execution conditions, the connection with the source access network device is maintained, and the target cell is included in the candidate cells. The source access network device receives second information from the terminal and maintains the connection with the terminal. The second information indicates the target cell that meets the execution conditions. The source access network device receives handover completion information from a mobility management network element and disconnects the connection with the terminal. The handover completion information indicates that the terminal has successfully handed over from the source access network device to the target access network device where the target cell is located.

[0022] This application proposes a handover scheme that combines CHO handover and DAPS handover to reduce handover interruption time, thereby improving user experience. Specifically, the source access network device can trigger the terminal to perform CHO handover and DAPS handover through first information. That is, after receiving the first information, the terminal can determine the target cell according to the execution conditions of CHO handover, and send second information to the source access network device after determining the target cell. Correspondingly, the source access network device can continue to maintain the connection with the terminal after receiving the second information. Compared with the existing schemes that disconnect the connection with the source access network device after determining the target cell when using CHO handover, this application embodiment can reduce handover interruption time and improve user experience by continuing to maintain the connection with the source access network device after determining the target cell.

[0023] In one possible implementation, the configuration information for the dual-activation protocol stack switching also indicates a first DRB or a first Quality of Service (QoS) flow; receiving the second information from the terminal and maintaining the connection with the terminal includes:

[0024] Receive second information from the terminal and maintain the connection with the first DRB or the first QoS stream of the terminal.

[0025] In one possible implementation, before receiving the handover completion information from the mobility management network element, and / or after receiving the second information from the terminal, the method further includes:

[0026] The mobility management network element sends third information to the target access network device, the third information indicating a first count (COUNT) value; wherein, the first COUNT value is the COUNT value corresponding to the downlink data packet forwarded by the source access network device to the target access network device (e.g., the COUNT value corresponding to the first forwarded data packet), or, the first COUNT value is the COUNT value corresponding to the downlink data packet that the target access network device should release.

[0027] Receive data packets of downlink data from user plane network elements;

[0028] The data packets containing the downlink data are sent to the target access network device through the user plane network element.

[0029] In this implementation, after receiving the second information from the terminal, the source access network device sends the third information to the target access network device through the mobility management network element, instead of sending the third information to the candidate target access network device where the candidate cell is located to trigger data forwarding when or after sending the handover command of CHO or DAPS, as in the prior art. This application allows the source access network device to forward data only to the target access network device where the final selected target cell is located, without having to forward data to the candidate target access network devices where all candidate cells are located, thus reducing the resource waste and buffering overhead of the candidate target access network devices.

[0030] Optionally, the aforementioned third information can be carried in an Early State Transition (EARLY STATUS TRANSFER) message. Typically, this EARLY STATUS TRANSFER message can be sent once or multiple times. The first message serves to inform the target access network device which data packet the source access network device started forwarding to the target access network device (i.e., the first COUNT value corresponds to the COUNT value of the downlink data packet (e.g., the first data packet) forwarded by the source access network device to the target access network device). Subsequent messages instruct the target access network device to discard / clear / release the COUNT values ​​of the buffered downlink data packets successfully transmitted by the source access network device to the terminal, in order to free up memory (i.e., the first COUNT value corresponds to the COUNT value of the downlink data packets that the target access network device should release). It should be understood that after or simultaneously with the source access network device sending the third information, the source access network device can begin forwarding downlink data packets to the target access network device. Specifically, the source access network device can receive downlink data packets from user plane network elements, assign a sequence number (SN) to the received downlink data packets, and then send / forward the downlink data packets with the SN assigned by the source access network device to the target access network device through the user plane network elements.

[0031] In one possible implementation, before receiving the handover completion information from the mobility management network element, and / or after receiving the second information from the terminal, the method further includes:

[0032] The mobility management network element sends fourth information to the target access network device, the fourth information indicating a second COUNT value; wherein, the second COUNT value is the COUNT value corresponding to the SN that the target access network device should allocate for the downlink data packets received from the user plane network element (e.g., the COUNT value corresponding to the SN that should be allocated for the first data packet), or, the second COUNT value is the COUNT value corresponding to the downlink data packets that the target access network device should release;

[0033] The fifth information is sent to the mobility management network element, and the fifth information is used to trigger the user plane network element to send downlink data packets to the target access network device.

[0034] In this implementation, it is proposed that user plane network elements can send downlink data through the data transmission channel between the user plane network element and the target access network device, instead of first sending downlink data to the source access network device through the user plane network element and then having the source access network device forward the downlink data to the target access network device through the user plane network element. This can further reduce the link overhead between the user plane network element and the access network device (mainly the source access network device) caused by data forwarding. Specifically, to adapt to the implementation scheme of user plane network elements sending downlink data through the data transmission channel between the user plane network element and the target access network device, it is proposed that after receiving the second information from the terminal, the source access network device can send the fourth information to the target access network device through the mobility management network element. The second COUNT value indicated by the fourth information can be the COUNT value corresponding to the SN that the target access network device should allocate for the downlink data packet (e.g., the first data packet) received from the user plane network element, or the second COUNT value can be the COUNT value corresponding to the downlink data packet that the target access network device should release.

[0035] Thirdly, this application provides a communication method that can be applied to network-side communication devices, such as network-side access network devices, modules (e.g., circuits, chips, or chip systems) within the access network device, or logical nodes, logical modules, or software capable of implementing all or part of the functions of the access network device. Taking the application of this method to a target access network device as an example, in this method, the target access network device receives fourth information indicating a second COUNT value. The second COUNT value is the COUNT value corresponding to the SN that the target access network device, where the target cell is located, should allocate for downlink data packets received from user plane network elements (e.g., the COUNT value corresponding to the SN allocated for the first data packet), or the second COUNT value is the COUNT value corresponding to downlink data packets that the target access network device should release. The target access network device receives downlink data packets from the user plane network elements and allocates SNs for these data packets. The corresponding SNs for these data packets are allocated by the target access network device according to the second COUNT value. Furthermore, the target access network device sends the downlink data packets to a terminal, and the SNs corresponding to the downlink data packets are allocated by the target access network device according to the second COUNT value. It should be noted that after the target access network device receives the downlink data packets from the user plane network element, the target access network device can first buffer the data and then send the downlink data packets to the terminal after the terminal handover is completed.

[0036] In this embodiment of the application, it is proposed that when a user plane network element sends downlink data through the data transmission channel between the user plane network element and the target access network device, the target access network device can allocate a SN to the downlink data packet directly received from the user plane network element according to the second COUNT value indicated by the received fourth information, and cache the data. After the terminal handover is completed, the downlink data packet with the allocated SN will be sent to the terminal.

[0037] Fourthly, this application provides a communication device comprising units, modules, or means for implementing any of the methods described in the first to third aspects, or any possible implementations of any of the aspects. These modules, units, or means may be implemented in software, hardware, or a combination of software and hardware.

[0038] Fifthly, this application provides a communication device including a processor. The processor is configured to cause the communication device to implement the methods shown in any of the first to third aspects, or any possible implementation thereof.

[0039] Optionally, the communication device further includes a transceiver for sending and receiving information.

[0040] Optionally, the communication device further includes a memory storing a computer program; the processor and transceiver are used to invoke the computer program in the memory, causing the communication device to implement the method shown in any of the first to third aspects, or any possible implementation of any of the aspects.

[0041] In one possible design, the communication device can be a chip that implements the above method or a device containing a chip.

[0042] In a sixth aspect, this application provides a communication device comprising one or more processors, which implement, via logic circuits or executable code instructions, any of the methods described in the first to third aspects, or any possible implementation thereof.

[0043] Optionally, the communication device further includes an interface circuit for receiving signals from other communication devices outside the communication device and transmitting them to the processor, or sending signals from the processor to other communication devices outside the communication device.

[0044] Optionally, the communication device may further include a memory for storing part or all of the computer programs or instructions necessary to implement the functions involved in the first aspect above.

[0045] The aforementioned communication device may be a terminal, a communication module in a terminal, or a chip in a terminal that is responsible for communication functions, such as a modem chip (also known as a baseband chip) or a SoC or SIP chip that contains a modem module.

[0046] The aforementioned communication device may be an access network device, a module (e.g., a circuit, chip, or chip system) within the access network device, or a logic node, logic module, or software capable of implementing all or part of the functions of the access network device.

[0047] In a seventh aspect, this application provides a computer-readable storage medium storing a computer program or instructions that, when executed by a computer, implement the method shown in any of the first to third aspects, or any possible implementation thereof.

[0048] Eighthly, this application provides a computer program product that, when read and executed by a computer, causes the computer to perform any of the methods of the first to third aspects, or any possible implementation thereof.

[0049] Ninthly, this application provides a chip system including at least one processor and an interface, the processor being configured to read and execute a computer program or instructions in a memory, wherein when the computer program or instructions are executed, the chip performs the method as described in any one of the first or third aspects, or the method shown in any possible implementation of any of the aspects.

[0050] In a tenth aspect, this application provides a communication system that may include a terminal, a source access network device, and a target access network device. The terminal is configured to perform the method shown in the first aspect or any possible implementation thereof. The source access network device is configured to perform the method shown in any possible implementation thereof. The target access network device is configured to perform the method shown in the third aspect or any possible implementation thereof. Attached Figure Description

[0051] Figure 1 is a schematic diagram of the architecture of the communication system used in the embodiments of this application;

[0052] Figure 2 is a schematic diagram of the architecture of the O-RAN system provided in this application;

[0053] Figure 3 is a schematic diagram of the network element function division and protocol layer structure of an O-RAN device provided in this application;

[0054] Figure 4 is a schematic diagram of the NTN-based RAN architecture applicable to this application;

[0055] Figure 5 is a schematic diagram of the cell deployment scheme involved in satellite communication;

[0056] Figure 6 is a flowchart illustrating the DAPS switching process based on the NG port;

[0057] Figure 7 is a flowchart illustrating the CHO switching process based on the Xn port;

[0058] Figure 8 is a flowchart illustrating a communication method provided in an embodiment of this application;

[0059] Figure 9 is another flowchart illustrating the communication method provided in an embodiment of this application;

[0060] Figure 10 is another flowchart illustrating the communication method provided in an embodiment of this application;

[0061] Figure 11 is another flowchart illustrating the communication method provided in an embodiment of this application;

[0062] Figure 12 is another flowchart illustrating the communication method provided in an embodiment of this application;

[0063] Figure 13 is a schematic diagram of the structure of a possible communication device provided in an embodiment of this application;

[0064] Figure 14 is a schematic diagram of the structure of a possible communication device provided in an embodiment of this application;

[0065] Figure 15 is a schematic diagram of the structure of a possible communication device provided in an embodiment of this application. Detailed Implementation

[0066] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0067] In the description of this application, terms such as "first" and "second" are used only to distinguish different objects, not to describe a specific order. Furthermore, unless otherwise stated, " / " means "or," for example, A / B can mean A or B. "And / or" in this document is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, and B alone. Additionally, "at least one" refers to one or more, and "multiple" refers to two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, at least one of a, b, or c can represent: a, b, c; a and b; a and c; b and c; or a and b and c. Where a, b, and c can be single or multiple.

[0068] The terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0069] In this application, the words "exemplary" or "for example" are used to indicate that something is an example, illustration, or illustration. Any embodiment or design described as "exemplary," "for example," or "for example" in this application should not be construed as being more preferred or advantageous than other embodiments or designs. Rather, the use of the words "exemplary," "for example," or "for example" is intended to present the relevant concepts in a specific manner.

[0070] It is understood that in this application, "when," "if," and "if" all refer to the device making a corresponding action under certain objective circumstances, and are not time-limited, nor do they require the device to make a judgment when it is implemented, nor do they imply any other limitations.

[0071] In this application, the use of singular pronouns for elements is intended to indicate "one or more," rather than "one and only one," unless otherwise specified. The terms "system" and "network" in the embodiments of this application are used interchangeably.

[0072] It is understood that in the embodiments of this application, "B corresponding to A" means that there is a correspondence between A and B, and B can be determined based on A. Determining B based on A does not mean that B can be determined solely based on A; B can also be determined based on A and / or other information.

[0073] To better understand the embodiments of this application, the system architecture involved in the embodiments of this application will be described first below:

[0074] The technical solutions of this application can be applied to various communication systems, such as: terrestrial network (TN) systems, non-terrestrial network (NTN) systems, NTN and TN converged systems, long term evolution (LTE) systems, LTE frequency division duplex (FDD) systems, and LTE time division duplex (TDD) systems. The technical solutions of this application can also be applied to other communication systems, such as public land mobile network (PLMN) systems, LTE-A advanced systems, the 5th generation (5G) systems, new radio (NR) systems, machine-to-machine (M2M) systems, or other future communication systems, or various other wireless communication systems employing wireless access technologies. All of these can adopt the technical solutions of this application.

[0075] Please refer to Figure 1, which is a schematic diagram of the architecture of the communication system applied in the embodiments of this application. It should be noted that Figure 1 is a possible, non-limiting system schematic diagram. As shown in Figure 1, the communication system 10 includes a radio access network (RAN) 100 and a core network (CN) 200. Optionally, the communication system 10 may also include an Internet 300. RAN 100 includes at least one RAN node (110a and 110b in Figure 1, collectively referred to as 110) and at least one terminal (120a-120j in Figure 1, collectively referred to as 120). RAN 100 may also include other RAN nodes, such as wireless relay devices and / or wireless backhaul devices (not shown in Figure 1). Terminal 120 is wirelessly connected to RAN node 110. RAN node 110 is connected to core network 200 wirelessly or via a wired connection. The core network elements in core network 200 and RAN nodes 110 in RAN 100 can be different physical devices, or they can be the same physical device integrating core network logical functions and radio access network logical functions, or they can be a single physical device integrating some core network element functions and some RAN node 110 functions. Terminals can be interconnected with each other, and RAN nodes 110 can be interconnected with each other via wired or wireless means. Figure 1 is only a schematic diagram. This communication system may also include other network devices, such as wireless relay devices and wireless backhaul devices. Each device may also include different functional units, which are not shown in Figure 1.

[0076] The core network 200 may include network elements for implementing control plane functions, such as access and mobility function (AMF) network elements (or mobility management) network elements, primarily responsible for mobility management in the mobile network, such as terminal location updates, terminal registration with the network, and terminal handover. For example, in a 5G system, the mobility management network element may specifically be an access and mobility management (AMF) network element. The core network 200 may also include network elements for implementing user plane functions, such as user plane network elements, primarily responsible for forwarding and receiving data in the terminal. For example, in a 5G system, the user plane network element may specifically be a user plane function (UPF) network element. The core network 200 may also include network elements for implementing session management, such as session management network elements, primarily responsible for session establishment, modification, and release. For example, in a 5G system, the session management network element may specifically be a session management function (SMF) network element. It should be noted that in this application, network elements can also be referred to as entities or functional entities. For example, an AMF network element can also be referred to as an AMF entity or an AMF functional entity. Similarly, a UPF network element can also be referred to as a UPF entity or a UPF functional entity. Furthermore, an SMF entity can also be referred to as an SMF network element or an SMF functional entity, etc.

[0077] RAN 100 can be a cellular system related to the 3rd Generation Partnership Project (3GPP), such as 4G, 5G mobile communication systems, or future-oriented evolution systems. RAN 100 can also be an open RAN (O-RAN or ORAN), a cloud radio access network (CRAN), or a wireless fidelity (WiFi) system. RAN 100 can also be a communication system that integrates two or more of the above systems.

[0078] RAN node 110, sometimes also referred to as a radio access network device, access network apparatus, RAN entity, or access node, constitutes part of the communication system and is used to help terminals achieve wireless access. Multiple RAN nodes 110 in communication system 10 can be of the same type or different types. In some scenarios, the roles of RAN node 110 and terminal 120 are relative. For example, network element 120i in Figure 1 can be a helicopter or drone, which can be configured as a mobile base station. For terminals 120j accessing RAN 100 through network element 120i, network element 120i is a base station; but for base station 110a, network element 120i is a terminal. RAN node 110 and terminal 120 are sometimes both referred to as communication devices. For example, network elements 110a and 110b in Figure 1 can be understood as communication devices with base station functions, and network elements 120a-120j can be understood as communication devices with terminal functions.

[0079] In one possible scenario, RAN node 110 can be a base station, an evolved NodeB (eNodeB), an access point (AP), a transmission reception point (TRP), a next-generation NodeB (gNB), a base station in a future mobile communication system, or an access node in a WiFi system. RAN node 110 can be a macro base station (as shown in Figure 1, 110a), a micro base station or indoor station (as shown in Figure 1, 110b), a relay node or donor node, or a radio controller in a CRAN scenario. Optionally, RAN node 110 can also be a server, a wearable device, a vehicle, or an in-vehicle device. For example, the access network device in vehicle-to-everything (V2X) technology can be a roadside unit (RSU). All or part of the functions of RAN node 110 in this application can also be implemented through software functions running on hardware, or through virtualization functions instantiated on a platform (e.g., a cloud platform). In this application, RAN node 110 can also be a logical node, logical module, or software that can implement all or part of the functions of RAN node 110.

[0080] In another possible scenario, multiple RAN nodes 110 collaborate to assist the terminal in achieving wireless access, with each RAN node 110 implementing a portion of the base station's functions. For example, a RAN node 110 can be a centralized unit (CU), a distributed unit (DU), a CU-control plane (CP), a CU-user plane (UP), or a radio unit (RU), etc. CUs and DUs can be set up separately or included in the same network element, such as a baseband unit (BBU). RUs can be included in radio equipment or radio units, such as remote radio units (RRUs), active antenna units (AAUs), or remote radio heads (RRHs).

[0081] In different systems, CU (or CU-CP and CU-UP), DU, or RU may have different names, but those skilled in the art will understand their meaning. For example, in an ORAN system, CU can also be called O-CU (open CU), DU can also be called O-DU, CU-CP can also be called O-CU-CP, CU-UP can also be called O-CU-UP, and RU can also be called O-RU. For ease of description, this application uses CU, CU-CP, CU-UP, DU, and RU as examples. Any of the units among CU (or CU-CP, CU-UP), DU, and RU in this application can be implemented through software modules, hardware modules, or a combination of software and hardware modules.

[0082] For example, please refer to Figure 2, which is a schematic diagram of the architecture of the O-RAN system provided in this application. Figure 2 is only a schematic diagram, and the O-RAN system may also include other components besides those shown in Figure 2. As shown in Figure 2, the access network device (e.g., it may be an eNB, gNB, or next-generation access network device) communicates with the core network elements in the CN through a backhaul link and communicates with the terminal through the air interface.

[0083] Specifically, the BBU in the access network device communicates with the core network elements in the CN via a backhaul link, and the RU in the access network device communicates with at least one terminal via an air interface. The BBU communicates with at least one RU via a fronthaul link. The BBU and RU may or may not be co-located. The BBU includes at least one CU and at least one DU, which can communicate via at least one midhaul link.

[0084] Figure 3 illustrates a schematic diagram of the network element function division and protocol layer structure of an O-RAN device. In some examples, the CU is a logical node carrying the radio resource control (RRC) layer, service data adaptation protocol (SDAP) layer, packet data convergence protocol (PDCP) layer, and other control functions of the access network device. The CU connects to network nodes such as the core network through interfaces, which can be interfaces such as E2 interfaces. Optionally, the CU can have some of the functions of the core network. The CU (e.g., the PDCP layer and higher layers) connects to the DU (e.g., the radio link control (RLC) layer and lower layers) through interfaces, which can be interfaces such as F1 interfaces. In some examples, these interfaces (e.g., the F1 interface) can provide control plane (C-Plane) and user plane (U-Plane) functions (e.g., interface management, system information management, UE context management, RRC message transmission, etc.). F1AP is the application protocol of the F1 interface, and in some examples, it defines the signaling procedures of F1. The F1 interface supports the control plane F1-C and the user plane F1-U.

[0085] In some examples, the CU can be split into CU-CP (control unit-control plane) and CU-UP (control unit-user plane). CU-CP is a logical node carrying the RRC layer and PDCP-C (control plane part of PDCP) layer, used to implement the CU's control plane functions. CU-CP can interact with network elements in the core network used to implement control plane functions. These network elements in the core network can be access and mobility function network elements (or mobility management network elements), such as the AMF in a 5G system. The AMF network element is responsible for mobility management in the mobile network, such as terminal location updates, terminal registration with the network, and terminal handover. CU-UP is a logical node carrying the SDAP layer and PDCP-U (user plane part of PDCP) layer, used to implement the CU's user plane functions. CU-UP can interact with network elements in the core network used to implement user plane functions (referred to as user plane network elements). These network elements in the core network, such as the user plane function (UPF) in a 5G system, are responsible for forwarding and receiving data in the terminal. The above CU and DU configurations are merely examples; the functions of the CU and DU can be configured as needed. For instance, the CU or DU can be configured to have more protocol layer functions, or only some protocol layer processing functions. For example, some RLC layer functions and protocol layer functions above the RLC layer can be placed in the CU, while the remaining RLC layer functions and protocol layer functions below the RLC layer can be placed in the DU. Furthermore, the functions of the CU or DU can be divided according to service type or other system requirements, such as by latency. Functions that require low latency can be placed in the DU, while functions that do not require low latency can be placed in the CU.

[0086] In some examples, a DU is a logical node carrying the RLC layer, medium access control (MAC) layer, higher physical layer (Higher PHY) layer, and other functions. In some examples, a DU can control at least one RU. The DU connects to the RU through interfaces, which can be fronthaul interfaces. In some examples, the Higher PHY layer includes the physical (PHY) layer processing, such as forward error correction (FEC) encoding and decoding, scrambling, modulation, and demodulation.

[0087] In some examples, the RU is a logical node that carries both lower physical layer (PHY) and radio frequency (RF) processing. In some examples, the RU can be a 3GPP transmission reception point (TRP), a remote radio head (RRH), or other similar entities. In some examples, the Low-PHY includes PHY processing functions such as Fast Fourier Transform (FFT), Inverse Fast Fourier Transform (IFFT), digital beamforming, and filtering. The RU communicates with one or more terminals via a wireless link.

[0088] The DU and RU can be co-located or not. The DU and RU exchange control plane and user plane information via a fronthaul link through the Lower-Layer Split CUS-Plane (LLS-CUS) interface. LLS-CUS may include LLS-C and LLS-U interfaces providing the control plane (C-Plane) and user plane (U-Plane), respectively. In some examples, the control plane (C-Plane) refers to real-time control between the DU and RU. The DU and RU exchange management information via an LLS-M interface on the fronthaul link; the management plane (M-Plane) refers to non-real-time management operations between the DU and RU.

[0089] DU and RU can cooperate to implement the functions of the PHY layer. A DU can be connected to one or more RUs. The functions of DU and RU can be configured in various ways depending on the design. For example, a DU can be configured to implement baseband functions, and an RU can be configured to implement mid-RF functions. Another example is that a DU can be configured to implement higher-level functions in the PHY layer, and an RU can be configured to implement lower-level functions in the PHY layer, or to implement both lower-level and RF functions. Higher-level functions in the physical layer can include a portion of the physical layer's functions that are closer to the MAC layer, while lower-level functions in the physical layer can include another portion of the physical layer's functions that are closer to the mid-RF side.

[0090] A terminal is a device or module that connects to the aforementioned communication system and possesses corresponding communication functions. Terminals can also be referred to as terminal equipment, user equipment (UE), user devices, access terminals, user units, user stations, mobile stations, mobile stations (MS), remote stations, remote terminals, mobile devices, user terminals, terminal units, terminal stations, terminal devices, wireless communication equipment, user agents, or user devices, etc. Terminals typically contain communication modules, circuits, or chips that perform the corresponding communication functions. They can also be configured with program instructions for performing these functions. Terminals can be widely used in various scenarios, such as device-to-device (D2D), vehicle-to-everything (V2X) communication, machine-type communication (MTC), the Internet of Things (IoT), virtual reality, augmented reality, industrial control, autonomous driving, telemedicine, smart grids, smart furniture, smart offices, smart wearables, smart transportation, and smart cities. The terminal can be a mobile phone, tablet computer, computer with wireless transceiver function, wearable device, vehicle, drone, helicopter, airplane, ship, robot, robotic arm, smart home device, transportation vehicle with wireless communication function, communication module, roadside unit (RSU) with terminal function, etc. The embodiments of this application do not limit the device form of the terminal.

[0091] For ease of description, the following description uses a base station as an example of RAN node 110. Base stations and terminals can be fixed or mobile. Base stations and terminals can be deployed on land, including indoors or outdoors, handheld or vehicle-mounted; they can also be deployed on water; and they can be deployed on aircraft, balloons, and satellites. The embodiments of this application do not limit the application scenarios of the base stations and terminals.

[0092] The roles of base stations and terminals can be relative. For example, the helicopter or drone 120i in Figure 1 can be configured as a mobile base station. For terminals 120j that access the wireless access network 100 through 120i, terminal 120i is a base station; however, for base station 110a, 120i is a terminal, meaning that 110a and 120i communicate via a wireless air interface protocol. Of course, 110a and 120i can also communicate via a base station-to-base station interface protocol. In this case, relative to 110a, 120i is also a base station. Therefore, both base stations and terminals can be collectively referred to as communication devices. 110a and 110b in Figure 1 can be called communication devices with base station functions, and 120a-120j in Figure 1 can be called communication devices with terminal functions.

[0093] Communication between base stations and terminals, between base stations, and between terminals can be conducted using licensed spectrum, unlicensed spectrum, or both simultaneously. Communication can be conducted using spectrum below 6 GHz, spectrum above 6 GHz, or both simultaneously. The embodiments of this application do not limit the spectrum resources used for wireless communication.

[0094] In the embodiments of this application, the functions of the base station can be executed by modules (such as chips) within the base station, or by a control subsystem that includes base station functions. This control subsystem, including base station functions, can be a control center in the aforementioned application scenarios such as smart grids, industrial control, intelligent transportation, and smart cities. Similarly, the functions of the terminal can be executed by modules (such as chips or modems) within the terminal, or by a device that includes terminal functions.

[0095] In this application, the base station sends downlink signals or downlink information to the terminal, with the downlink information carried on the downlink channel; the terminal sends uplink signals or uplink information to the base station, with the uplink information carried on the uplink channel. To communicate with the base station, the terminal needs to establish a radio connection on a cell controlled by the base station. The cell with which the terminal has established a radio connection is called the terminal's serving cell. When the terminal communicates with this serving cell, it is also susceptible to interference from signals from neighboring cells.

[0096] In this application, "sending information" can be understood as one device sending information to another device, or it can also be understood as one logical module within a device sending information to another logical module. For example, "base station sending information" can be understood as the base station sending information to another device (such as a terminal), or it can be understood as logical module 1 in the base station sending information to logical module 2 in the base station.

[0097] In this application, "receiving information" can be understood as one device receiving information from another device, or it can also be understood as a logical module within a device receiving information from another logical module. For example, "base station receiving information" can be understood as the base station receiving information from another device (such as a terminal), or it can be understood as logical module 1 in the base station receiving information from logical module 2 in the base station.

[0098] The communication between different devices involved in this application can refer to direct communication between different devices (i.e., without the need for relaying or forwarding by other devices), or communication between different devices through other devices (i.e., requiring relaying or forwarding by other devices), or communication between a functional unit within a device and other devices through another functional unit. In other words, "sending information to… (e.g., a terminal)" or the relevant illustrations in the accompanying drawings can be understood as the destination of the information being the terminal. This can include sending information directly or indirectly to the terminal. "Receiving information from… (e.g., a terminal)" or "receiving information from… (e.g., a terminal)" or "receiving information sent (e.g., by a terminal)" or the relevant illustrations in the accompanying drawings can be understood as the source of the information being the terminal. This can include receiving information directly or indirectly from the terminal. Information may undergo necessary processing between the source and destination, such as format changes, analog-to-digital conversion, amplification, filtering, etc., but the destination can understand the valid information from the source. Similar expressions in this application can be understood in a similar way, and will not be elaborated further here.

[0099] To facilitate understanding of the embodiments of this application, some knowledge / terms used in the solutions of this application are introduced below. It should be noted that these explanations are for the purpose of making the embodiments of this application easier to understand, and should not be regarded as limiting the scope of protection claimed by this application.

[0100] 1. NTN

[0101] NTN (Network Telecommunications) provides communication coverage to terminals by deploying base stations or part of their functions on non-terrestrial network equipment (such as ships, high-altitude platforms, drones, or satellites), thereby improving the reliability of the communication system. It should be noted that, for ease of understanding, the following description uses satellites as an example of non-terrestrial network equipment in NTN and should not be considered a specific limitation of this application.

[0102] When the non-terrestrial network equipment is a satellite, its role can vary depending on the RAN architecture of the NTN. For example, in a transparent satellite architecture shown in Figure 4-1, the satellite's role is to perform radio frequency filtering, frequency conversion, and amplification; that is, in a transparent satellite architecture, the satellite mainly acts as a Layer 1 (L1) relay device, used to regenerate physical layer signals (i.e., radio frequency filtering, frequency conversion, and amplification), without other higher protocol layers. In a regenerative satellite architecture without inter-satellite links shown in Figure 4-2, the satellite acts as a base station, possessing base station processing functions. In a regenerative satellite architecture with inter-satellite links shown in Figure 4-3, the satellite acts as a base station, possessing base station processing functions. In a regenerative satellite architecture with DU (Distributed Unit) processing functions shown in Figure 4-4, the satellite acts as a DU, possessing DU processing functions. In a satellite architecture with integrated access and backhaul (IAB) capabilities, the satellite acts as the IAB.

[0103] 2. Residential area

[0104] The cells involved in this application may refer to TN cells or NTN cells. NTN cells can be further divided into the following three categories:

[0105] (1) Earth-fixed: The coverage area of ​​this type of NTN cell is fixed to a specific area on the ground, i.e., continuous fixed-point coverage. NTN cells provided by geostationary earth orbit (GEO) satellites are of this type. Earth-fixed NTN cells can also be called fixed cells or stationary cells.

[0106] (2) Quasi-earth-fixed: The coverage area of ​​this type of NTN cell is fixed to a certain area on the ground for a period of time, and then it will be replaced by another area on the ground after a period of time. That is, it provides fixed-point coverage for a certain period of time, as shown in Figure 5(a). Low Earth Orbit (LEO) satellites and Medium Earth Orbit (MEO) satellites can provide this type of NTN cell. Quasi-earth-fixed NTN cells can also be called quasi-fixed cells or quasi-Earth-fixed cells.

[0107] (3) Earth-moving: The coverage area of ​​this type of NTN cell slides on the ground, as shown in Figure 5(b). LEO and MEO satellites can provide this type of NTN cell. Earth-moving NTN cells can also be called earth-moving cells or moving cells.

[0108] 3. Cell handover (or handover)

[0109] In wireless communication systems, when a terminal moves / approaches another cell, a handover is required to ensure uninterrupted communication. In this embodiment, the source cell refers to the cell that provides service to the terminal before the handover, and the target cell refers to the cell that provides service to the terminal after the handover. Information about the target cell (such as its physical cell identifier (PCI), frequency information, and random access resource information required for handover to the target cell) can be indicated via an RRC reconfiguration message, which is sent from the source cell's access network device (i.e., the source access network device) to the terminal.

[0110] The handover can be intra-site handover or inter-site handover. Intra-site handover refers to the source cell and the target cell belonging to the same access network device (such as a base station), where the source cell and the target cell can be the same cell or different cells; inter-site handover refers to the source cell and the target cell belonging to different access network devices (such as base stations). This application does not limit this.

[0111] It should be understood that a cell is the coverage area of ​​an access network device, a source cell corresponds to a source access network device (e.g., a source base station), and a target cell corresponds to a target access network device (e.g., a target base station).

[0112] 4. Uplink (UL) and downlink (DL) links

[0113] The uplink is the link used to transmit signals / information / data from the terminal to the access network device, and the downlink is the link used to transmit signals / information / data from the access network device to the terminal.

[0114] 5. DAPS Switching

[0115] To ensure zero interruption during terminal handover, DAPS handover has been introduced into the communications industry standard.

[0116] In traditional handover (or basic handover), upon receiving the handover command from the source access network device, the terminal immediately disconnects its user plane (UP) from the source cell (this is because data is transmitted through the user plane). This prevents the terminal from transmitting data with any base station until a connection is established with the target cell, resulting in handover interruption delay. Unlike traditional handover, in DAPS handover, after receiving the DAPS handover command from the source access network device, the terminal accesses the target cell. Simultaneously, the terminal maintains communication with the source cell link until the target access network device notifies the terminal to completely release the source cell configuration. Only then does the terminal cease communication with the source cell and release the communication link. The handover command or DAPS handover command is carried in the RRC Reconfiguration message sent by the source access network device to the terminal.

[0117] The DAPS handover process is similar to the traditional handover process. The source access network device decides to perform the handover and then sends a handover request message to the target access network device. Further, the target access network device replies with a handover confirmation message to the source access network device, instructing the terminal to hand over to the target cell. Further, the source access network device sends a DAPS handover command to the terminal, instructing the terminal to hand over to the target cell. Then, the terminal maintains connections to both the source and target cells simultaneously. Once the terminal successfully accesses the target cell and establishes a new connection with the core network, the core network will switch the downlink data stream to the target access network device and simultaneously send an end marker packet to the source access network device. Then, the source access network device forwards the data to the target access network device. When the target access network device receives the end marker packet, it can notify the terminal to release the source cell connection, thus completing the DAPS handover process. Specifically, Figure 6 shows a schematic diagram of the DAPS handover process based on the NG interface, where:

[0118] S601. The source access network device sends a handover request message to the target access network device through the AMF.

[0119] The source access network device executes a handover decision and, when it determines that a handover is necessary, sends a handover request message to the target access network device via the AMF. This handover request message is used to request a DAPS handover. Optionally, the handover request message may include the target cell identifier, the terminal's identifier in the source access network device, and the terminal's capability information, etc.

[0120] Optionally, the source access network device may specifically request DAPS handover for one or more DRBs; that is, the handover request message may also include DRB information (e.g., DRB identifier). Optionally, the handover request message may also include information about the QoS flows for which the source access network device proposes to perform downlink data forwarding (e.g., QoS flow identifier). It should be understood that if the source access network device requests DAPS handover for a DRB, then all QoS flows mapped to the DRB should perform downlink data forwarding.

[0121] Understandably, before or during the handover decision, all active DRB connections are maintained between the terminal and the source access network device.

[0122] S602. The target access network device sends a handover request confirmation message to the source access network device through the AMF.

[0123] The handover request confirmation message includes DAPS acceptance information and information required for the terminal to access the target access network device, such as the configuration information of the candidate cells of the target access network device. Optionally, the handover request confirmation message may also include information about the DRB or QoS flow that the target access network device agrees to / accepts for DAPS handover. Optionally, the DRB or QoS flow information included in the handover request confirmation message is usually a subset of the DRB or QoS flow information included in the handover request message.

[0124] S603. The source access network device sends an RRC reconfiguration message to the terminal, which includes a DAPS handover command.

[0125] This DAPS handover command is used to trigger the terminal to perform a DAPS handover. Optionally, the DAPS handover command can also be understood as DAPS configuration information. Optionally, the RRC reconfiguration message may also include information required for accessing the target cell, such as the target cell identifier, the new cell radio network temporary identifier (C-RNTI), the target access network device security algorithm identifier, the dedicated random access channel (RACH) resource, the association between the RACH resource and the synchronization signal block (SSB), the association between the RACH resource and the terminal-specific channel state information reference signal (CSI-RS) configuration, the public RACH resource, and the system information of the target cell, etc.

[0126] It should be noted that in the case of a traditional handover, after step S603, the source access network device will stop uploading and downloading data with the terminal (or disconnect the connection between the terminal and the source access network device). However, in this DAPS handover scenario, the RRC reconfiguration message may also contain information about the DRB or QoS flow that allows the terminal to perform DAPS handover. For example, the following illustration will use the example of the RRC reconfiguration message containing the first DRB or the first QoS flow.

[0127] It should be understood that the number of first DRBs involved in the embodiments of this application can be one or more, that is, the first DRB is a collective term for DRBs that the target access network device agrees to / accepts for DAPS handover. Similarly, the number of first QoS flows can also be one or more, that is, the first QoS flows is a collective term for QoS flows that the target access network device agrees to / accepts for DAPS handover.

[0128] Optionally, after receiving the RRC reconfiguration message, the terminal may also send an RRC reconfiguration completion message to the source access network device, indicating that the terminal has successfully received the RRC reconfiguration message.

[0129] S604a, The source access network device sends an uplink radio access network early state transition message (UL RAN Early STATUS TRANSFER message) to the AMF.

[0130] S604b, AMF sends a downlink radio access network early state transition message (DL RAN Early STATUS TRANSFER message) to the target access network device.

[0131] The uplink / downlink early state transition message includes the COUNT value corresponding to the downlink data packet (e.g., the first data packet) forwarded by the source access network device to the target access network device (or the COUNT value of the (first) downlink service data unit (SDU) forwarded by the source access network device to the target access network device). Alternatively, the uplink / downlink early state transition message includes the COUNT value corresponding to the downlink data packet that the target access network device should release (or the COUNT value of the already forwarded downlink SDU discarded for the corresponding DRB during DAPS handover). The COUNT value consists of the high-order hyperframe number (HFN) and the low-order SN.

[0132] Before step S609a, the uplink / downlink early state transition message can be sent once or multiple times. The first uplink / downlink early state transition message is used by the target access network device to know which data packet (e.g., SDU) the source access network device started forwarding to the target access network device (i.e., the COUNT value corresponding to the data packet (e.g., the first data packet) containing downlink data forwarded by the source access network device to the target access network device). The subsequent uplink / downlink early state transition messages are used by the target access network device to discard / clear the buffered data packets that the source access network device has successfully transmitted to the terminal, in order to release memory (i.e., the COUNT value corresponding to the data packet containing downlink data that the target access network device should release).

[0133] Understandably, the source access network device can receive downlink data packets from the UPF and assign a SN to the downlink data packets received from the UPF. The source access network device then forwards the downlink data packets with the SN assigned by the source access network device to the target access network device via the UPF (e.g., PDCP SDU), i.e., data forwarding. Simultaneously, the source access network device can also send the downlink data packets received from the UPF to the terminal. Specifically, the source access network device can send downlink data packets with the SN assigned by the source access network device to the terminal, i.e., the terminal and the source access network device maintain the connection of the first DRB / first QoS flow.

[0134] S605. The terminal synchronizes with the target cell and executes the random access procedure.

[0135] Specifically, if the terminal is not synchronized with the target cell, it needs to first perform downlink synchronization with the target cell and then perform a random access procedure to hand over to the target access network device where the target cell is located. If the terminal has already synchronized with the target cell, it can directly perform a random access procedure to hand over to the target access network device where the target cell is located.

[0136] S606. The terminal sends an RRC reconfiguration completion message to the target access network device, which includes handover completion information.

[0137] The handover completion information indicates that the handover process is complete, or that the terminal has successfully handed over, or that the terminal has successfully accessed the target cell, or that the terminal has successfully handed over from the source access network device to the target access network device.

[0138] It should be understood that after step S606 is completed, i.e., after the terminal switches to the target cell, the target access network device can begin uplink scheduling for the terminal. For example, the terminal sends new uplink data packets (e.g., UL PDCP PDUs) to the target access network device, or the terminal switches its uplink data transmission to the target access network device. It should be noted that after the terminal switches its uplink data transmission to the target access network device, the terminal will still continue to send Layer 1 CSI feedback, Hybrid Automatic Repeat Request (HARQ) feedback, Layer 2 RLC feedback, Robust Header Compression (ROHC) feedback, HARQ data (re)transmission, and RLC data (re)transmission to the source access network device for uplink transmission.

[0139] S607. The target access network device sends a handover notification message to the AMF, which includes handover completion information.

[0140] S608 and AMF send a handover success message to the source access network device, which includes handover completion information.

[0141] Typically, after receiving a handover success message, the source access network device will cease uplink and downlink data transmission with the terminal. However, before receiving the handover success message, the source access network device will continue to send data packets containing incomplete uplink data to the UPF, and data packets containing downlink data from the UPF to the terminal.

[0142] S609a, The source access network device sends an uplink radio access network state transition message (UL RAN STATUS TRANSFER message) to the AMF.

[0143] S609b, AMF sends a downlink radio access network state transition message (DL RAN STATUS TRANSFER message) to the target access network device.

[0144] The uplink / downlink radio access network state transition message contains the COUNT value that the target access network device should assign to the next downlink data packet (e.g., DL SDU) without a SN.

[0145] S610, The target access network device sends a source cell release message to the terminal.

[0146] It should be understood that after receiving the source cell release message, the terminal can release the source cell configuration and stop receiving downlink data from the source access network device.

[0147] As shown in Figure 6, during DAPS handover, after the terminal successfully connects to the target access network device, it stops sending new uplink data to the source access network device. After the terminal successfully releases its connection with the source cell, it ceases all communication with the source access network device. Upon successful connection to the target access network device, the source access network device receives a handover success indication message from the target access network device, and thus stops sending new downlink data to the terminal. Before the terminal successfully releases its connection with the source cell, the source access network device will not send new downlink data to the terminal, but it will send retransmitted downlink data.

[0148] As described above, DAPS handover refers to the process where a terminal maintains simultaneous connections with both the source cell and the target cell during the handover process from the source cell to the target cell (or in other words, the terminal transmits data with both the source access network device (or source cell) and the target access network device (or target cell)) until the link with the target cell is successfully established, at which point the link with the source cell is released. DAPS handover can reduce the downtime caused by the terminal handover process and improve the reliability of the handover.

[0149] 6. Switching between CHO and other protocols

[0150] In the CHO mechanism, when the source cell has good communication link quality, it sends CHO configuration information to the terminal. The CHO configuration information may include CHO triggering conditions (also called CHO execution conditions, or simply execution conditions) and information about one or more candidate cells. The candidate cell information may include the candidate cell's cell global identifier (CGI) or physical cell identifier (PCI) and the corresponding frequency information. After receiving the CHO configuration information, the terminal determines whether the candidate cell meets the CHO triggering conditions and selects the candidate cell that meets the CHO triggering conditions as the target cell. Then, the terminal performs a random access procedure with the determined target cell. When the random access is successfully completed, the terminal sends an RRC message (such as an RRC reconfiguration completion message) to the target cell to notify that the condition handover is complete. Specifically, Figure 7 shows a schematic diagram of the CHO handover process based on the Xn interface, where:

[0151] S701, The source access network device sends measurement configuration to the terminal.

[0152] This measurement configuration includes the measurement object, measurement report configuration, etc.

[0153] S702, The terminal sends a measurement report to the source access network device.

[0154] The terminal can perform measurements according to the measurement configuration, and when it determines that the measurement reporting conditions are met, it reports the measurement report to the source access network device.

[0155] S703, The source access network device sends a handover request message.

[0156] After receiving a measurement report, the source access network device can make a handover decision based on the measurement results in the report to determine one or more candidate cells (typically, the cell the terminal ultimately hands over to is called the target cell, the access network device to which the target cell belongs is called the target access network device, and the access network device to which the candidate cells belong is called the candidate target access network device). The source access network device can send a handover request message to the candidate target access network device where one or more of the determined candidate cells are located. This handover request message is used to request a CHO handover. Optionally, the handover request message includes the target cell identifier, the terminal's identifier in the source access network device, terminal capability information, etc.

[0157] It should be noted that before the terminal handover is completed, the target access network devices in the flowchart shown in Figure 7 above can all be understood as candidate target access network devices. For example, the source access network device can send handover request messages to multiple candidate target access network devices, but only one target access network device is shown in the flowchart above for simplicity.

[0158] S704. The target access network device sends a handover request confirmation message to the source access network device.

[0159] The handover request confirmation message contains the configuration information of the candidate cells of the target access network device that sent the message.

[0160] S705: The source access network device sends an RRC reconfiguration message to the terminal, which includes a CHO handover command.

[0161] This CHO handover command is used to trigger the terminal to perform a CHO handover. Optionally, the CHO handover command can also be understood as CHO configuration information. Generally speaking, CHO configuration information includes CHO execution conditions (hereinafter referred to as execution conditions), candidate cell configuration information, etc.

[0162] The configuration information of the aforementioned candidate cells may include: cell identifier, new cell radio network temporary identifier (C-RNTI), target access network device security algorithm identifier, dedicated RACH resources, association between RACH resources and SSB, association between RACH resources and terminal-specific CSI-RS configuration, public RACH resources, and system information of the target cell.

[0163] Optionally, after receiving the RRC reconfiguration message, the terminal may also send an RRC reconfiguration completion message to the source access network device, indicating that the terminal has successfully received the RRC reconfiguration message.

[0164] S706. The source access network device sends an Early State Transition (EAST) message to one or more candidate target access network devices. This message contains the COUNT value corresponding to the downlink data packet (e.g., the first data packet) forwarded by the source access network device to the target access network device (or the COUNT value of the (first) downlink SDU forwarded by the source access network device to the target access network device), or the message contains the COUNT value corresponding to the downlink data packet that the target access network device should release (or the COUNT value of the already forwarded downlink SDU discarded for the corresponding DRB during CHO handover). Here, the COUNT value consists of the high-order HFN and the low-order SN.

[0165] Before step S711, the early state transition message can be sent once or multiple times. The first early state transition message is used by the target access network device to know which data packet (e.g., SDU) the source access network device started forwarding to the target access network device (i.e., the COUNT value corresponding to the data packet (e.g., the first data packet) containing downlink data forwarded by the source access network device to the target access network device). The subsequent early state transition messages are used by the target access network device to discard / clear the cached data packets that the source access network device has successfully transmitted to the terminal, in order to release memory (i.e., the COUNT value corresponding to the data packet containing downlink data that the target access network device should release).

[0166] S707. The terminal evaluates whether the candidate cell meets the execution conditions.

[0167] After receiving the CHO handover command (or CHO configuration information), the terminal maintains its connection with the source access network device and begins to evaluate the execution conditions of the candidate cell.

[0168] S708: The terminal synchronizes with the target cell and executes the random access procedure.

[0169] Generally speaking, if the terminal evaluates that at least one candidate cell meets the corresponding execution conditions, the terminal disconnects its connection with the source access network device, applies the corresponding configuration of the selected candidate cell, synchronizes to the candidate cell (at this time, the selected candidate cell is the target cell), and performs a random access procedure to switch to the target access network device where the target cell is located.

[0170] S709. The terminal sends an RRC reconfiguration completion message to the target access network device, which includes handover completion information.

[0171] The handover completion information indicates that the handover process is complete, or that the terminal has successfully handed over, or that the terminal has successfully accessed the target cell, or that the terminal has successfully handed over from the source access network device to the target access network device.

[0172] After the terminal successfully completes the handover process, it releases the stored CHO configuration information.

[0173] S710. The target access network device sends a handover success message to the source access network device, which includes handover completion information.

[0174] S711. The source access network device sends a sequence number state transition message (SN STATUS TRANSFER message) to the target access network device. This message contains the COUNT value that the target access network device should assign to the next downlink data packet (e.g., DL SDU) without a SN.

[0175] Optionally, the source access network device can also send a handover cancellation message to the candidate target access network device to which other candidate cells belong, instructing the candidate target access network device to release the access / CHO handover resources reserved for the terminal.

[0176] S712a, The target access network device sends a path switching request message to the AMF.

[0177] The path switching request message is used to notify the terminal that the serving cell has been changed. The message may carry the target cell identifier and the list of protocol data unit (PDU) sessions to be switched.

[0178] S712b, AMF, and UPF perform path switching.

[0179] Generally speaking, when the AMF receives a path switching request message, the AMF can trigger the UPF to switch to the downlink data path of the target access network device and establish an interface instance to the target access network device.

[0180] The S712c and AMF send a path switching request confirmation message to the target access network device.

[0181] S713, The target access network device sends a UE context release message to the source access network device.

[0182] Generally, after the target access network device receives a path handover request confirmation message from the AMF, the target access network device can send a UE context release message to the source access network device to notify the source access network device that the terminal handover was successful. Therefore, the source access network device can release radio and control plane related resources associated with the terminal context.

[0183] It should be noted that in some scenarios, such as satellite communication, the current standard only supports CHO handover based on the Xn interface. However, the interruption latency of CHO handover is currently around tens to hundreds of milliseconds, which greatly affects the user experience and does not meet the zero-interruption requirement of satellite communication. Furthermore, in satellite communication systems, base stations may not have direct interfaces (i.e., Xn interfaces) with each other, thus requiring NG-based handover. For example, in one scenario, the base stations are on the ground, and there are no Xn interfaces between them (as shown in the system architecture of Figure 4-1); in another scenario, the base stations may be mounted on satellites, and there may be no inter-satellite links between satellites, resulting in no Xn interfaces between them (as shown in the system architecture of Figure 4-2). Therefore, NG-based CHO handover is common in NTN scenarios, but the current standard does not support NG-based CHO handover.

[0184] Based on this, this application proposes a communication method that can reduce handover interruption time and improve user experience.

[0185] In the description of this application, "instruction" can include direct and indirect instructions, as well as explicit and implicit instructions. The information indicated by a certain piece of information (such as the configuration information, second information, and sixth information in the dual-activation protocol stack switching described below) is called the information to be instructed. In the specific implementation process, there are many ways to instruct the information to be instructed. For example, the information to be instructed can be directly indicated, including the information itself or its index. Alternatively, the information to be instructed can be indirectly indicated by indicating other information, where there is a correlation between the other information and the information to be instructed. Furthermore, only a part of the information to be instructed can be indicated, while the other parts are known, pre-agreed, or deducible. Additionally, the instruction of specific information can be achieved by using a pre-agreed (e.g., protocol-defined) arrangement of various pieces of information, thereby reducing instruction overhead to some extent.

[0186] The communication method and apparatus provided in this application will be further described below with reference to the accompanying drawings. It is understood that this application uses an access network device and a terminal as examples to illustrate the execution of the interaction, but this application does not limit the execution subject of the interaction. For example, the method executed by the access network device in this application can also be implemented by a module (e.g., a circuit, chip, or chip system) in the access network device, or a logical node, logical module, or software that can implement all or part of the functions of the access network device; the method executed by the terminal in this application can also be implemented by a communication / processing module in the terminal, or a circuit or chip (such as a modem chip (also known as a baseband chip), or a SoC chip / SIP chip containing a modem core, or a GPU / AI processor / ASIC) in the terminal responsible for communication / processing functions.

[0187] Please refer to Figure 8, which is a flowchart illustrating the communication method provided in an embodiment of this application. As shown in Figure 8, the communication method may include the following steps:

[0188] S801. The source access network device sends first information to the terminal. Correspondingly, the terminal receives the first information from the source access network device.

[0189] The first information includes the execution conditions for conditional handover (or CHO execution conditions, or CHO trigger conditions), the configuration information of the candidate cell, and the configuration information for dual-activation protocol stack handover. Alternatively, it can be described as the first information including configuration information for conditional handover (or CHO configuration information) and configuration information for dual-activation protocol stack handover (or DAPS configuration information), wherein the configuration information for conditional handover includes the execution conditions for conditional handover and the configuration information of the candidate cell, and the configuration information for dual-activation protocol stack handover indicates that when the target cell meets the execution conditions, the connection with the source access network device should be maintained. The target cell is included in the candidate cells, or the candidate cells include the target cell. It should be understood that the target cell in this application is the cell to which the terminal ultimately hands over, or the cell that provides services to the terminal after the handover.

[0190] S802. When the terminal determines that the target cell meets the execution conditions, it maintains the connection with the source access network device.

[0191] In some feasible implementations, after receiving the first information, the terminal can evaluate whether the candidate cells meet the execution conditions. If at least one candidate cell meets the execution conditions, the terminal can select one cell from the at least one candidate cell that meets the execution conditions as the target cell, for example, selecting the earliest candidate cell that meets the execution conditions as the target cell.

[0192] The terminal maintaining the connection with the source access network device can be understood as one or more of the following: ① The terminal does not release the configuration information of the source cell under the source access network device; ② The terminal detects the downlink control information of the source cell; ③ The terminal receives data and / or information from the source cell; ④ The terminal sends data and / or information to the source cell.

[0193] Optionally, before the terminal determines that the target cell meets the execution conditions, or after the terminal receives the first information from the source access network device, the terminal can also maintain the connection with the source access network device and evaluate whether the candidate cell meets the execution conditions. Here, the terminal maintaining the connection with the source access network device can be understood in the aforementioned four interpretations. The difference is that before the terminal determines that the target cell meets the execution conditions, maintaining the connection with the source access network device means that the terminal maintains the connection between all active DRBs of the source access network device (e.g., receiving downlink data / information in all active DRBs, or sending uplink data / information through active DRBs). However, when or after determining that the target cell meets the execution conditions, maintaining the connection with the source access network device means that the terminal maintains the connection between the terminal and the first DRB or the first QoS stream of the source access network device (e.g., receiving downlink data / information carried in the first DRB, or sending uplink data / information through the first DRB, or receiving the first QoS stream, or sending the first QoS stream). The first DRB or the first QoS stream can be the DRB or QoS stream that the target access network device agrees to / accepts for DAPS handover, configured / indicated in the dual-activation protocol stack handover configuration information. For example, suppose all active DRBs include DRB1, DRB2, and DRB3, where the configuration information for dual-activation protocol stack switching indicates that the first DRB is DRB1, or the first QoS flow is QoS flow 1 in DRB1. Before the terminal determines that the target cell meets the execution conditions, the terminal can maintain connections with all active DRBs (i.e., DRB1, DRB2, and DRB3) of the source access network device. Upon or after determining that the target cell meets the execution conditions, the terminal can maintain connections with DRB1 or QoS flow 1 in DRB1 of the source access network device.

[0194] S803. The terminal synchronizes with the target cell and sends a handover completion message to the target access network device where the target cell is located. Correspondingly, the target access network device receives the handover completion message from the terminal.

[0195] The handover completion information indicates that the terminal has successfully switched from the source access network device to the target access network device.

[0196] Optionally, when the terminal determines that the target cell meets the execution conditions, or after the terminal determines that the target cell meets the execution conditions, or before the terminal sends handover completion information to the target access network device where the target cell is located, the terminal may also send second information to the source access network device. Accordingly, the source access network device receives the second information from the terminal. This second information indicates the target cell that meets the execution conditions, such as the identifier of the target cell, the identifier of the execution conditions, or the identifier of the CHO configuration information, etc., where one of the identifiers of the execution conditions or one of the CHO configuration information corresponds to one target cell.

[0197] In one possible implementation (i), as shown in Figure 9, the terminal receives first information from the source access network device (step S901 in Figure 9) and evaluates whether the candidate cell meets the execution conditions (step S902 in Figure 9). If it is determined that the target cell meets the execution conditions, the terminal maintains the connection with the source access network device's first DRB or first QoS flow, where the first DRB or first QoS flow is the DRB or QoS flow configured in the dual-activation protocol stack handover configuration information. Further, before the source access network device receives handover completion information from the mobility management network element (step S905 in Figure 9), and / or after the source access network device receives second information from the terminal (step S903 in Figure 9), the source access network device can send third information to the target access network device through the mobility management network element (step S904 in Figure 9), which indicates the first COUNT value. Exemplarily, the third information can be carried in an Early State Transition (EARLY STATUS TRANSFER) message. Typically, the EARLY STATUS TRANSFER message can be sent once or multiple times. The first message is used by the target access network device to know from which data packet the source access network device started forwarding to the target access network device (i.e., the first COUNT value is the COUNT value corresponding to the data packet (e.g., the first data packet) of downlink data forwarded by the source access network device to the target access network device). Subsequent messages are used to instruct the target access network device to discard / clear / release the COUNT values ​​of the data packets of downlink data that the source access network device has successfully transmitted to the terminal, in order to free up memory (i.e., the first COUNT value is the COUNT value corresponding to the data packets of downlink data that the target access network device should release). It should be understood that after or simultaneously with the source access network device sending the third information, the source access network device can begin forwarding downlink data packets to the target access network device (as shown in data forwarding in Figure 9). Specifically, the source access network device can receive downlink data packets from user plane network elements, assign a serial number (SN) to the received downlink data packets, and then send / forward the downlink data packets with the SN assigned by the source access network device to the target access network device through the user plane network elements. At the same time, the source access network device can also send downlink data received from user plane network elements to the terminal. It should be understood that the SN contained in the downlink data packets received by the terminal here is assigned by the source access network device.

[0198] In one possible implementation (ii), as shown in Figure 10, the terminal receives first information from the source access network device (step S1001 in Figure 10) and evaluates whether the candidate cell meets the execution conditions (step S1002 in Figure 10). If it is determined that the target cell meets the execution conditions, the terminal maintains the connection with the first DRB or first QoS flow of the source access network device, where the first DRB or first QoS flow is the DRB or QoS flow configured in the dual-activation protocol stack handover configuration information. Further, before the source access network device receives the handover completion information from the mobility management network element (step S1008 in Figure 10), and / or after the source access network device receives the second information from the terminal (step S1003 in Figure 10), the source access network device can send fourth information to the target access network device through the mobility management network element (steps S1004a and S1004b in Figure 10), which indicates the second COUNT value. For example, the fourth information can be carried in an EARLY STATUS TRANSFER message, or it can be in other messages, without limitation. Generally speaking, the EARLY STATUS TRANSFER message can be sent once or multiple times, wherein the first message is used to notify the target access network device of the COUNT value corresponding to the SN that should be assigned to the downlink data packet (e.g., the first data packet) received from the user plane network element (i.e., the second COUNT value is the COUNT value corresponding to the SN that the target access network device should assign to the downlink data packet (e.g., the first data packet) received from the user plane network element; the subsequent messages are used to instruct the target access network device to discard / clear / release the COUNT value of the downlink data packets that the source access network device has successfully transmitted to the terminal, in order to release memory (i.e., the second COUNT value is the COUNT value corresponding to the downlink data packets that the target access network device should release). Understandably, the source access network device can also send a fifth message to the mobility management network element (as shown in step S1005 of Figure 10). This fifth message is used to trigger the user plane network element to send downlink data packets to the target access network device. Correspondingly, after the mobility management network element receives the fifth message from the source access network device, it can further send a PDU session modification request to the session management network element (as shown in step S1006 of Figure 10). This PDU session modification request contains information needed to trigger the user plane network element to send downlink data packets to the target access network device, such as the PDU session ID, the transfer / transmission mode (copy), and the channel ID (e.g., Tunnel ID).After the session management network element receives the PDU session modification request, the session management network element and the user plane network element can perform session modification (as shown in step S1007 of Figure 10). Specifically, the user plane network element can copy the QoS flow or DRB corresponding to the PDU session based on the PDU session ID, and then send it to the source access network device through the source path (the source path refers to the data transmission channel from the user plane network element to the source access network device) and to the target access network device through the target path (the target path refers to the data transmission channel from the user plane network element to the target access network device) (as shown in the copying in Figure 10, dual data transmission channels). At the same time, the source access network device can also send the downlink data received from the user plane network element to the terminal. It should be understood that the SN contained in the downlink data packets received by the terminal is assigned by the source access network device. It should be noted that after the target access network device receives the fourth information, it can allocate a serial number (SN) to the downlink data packet directly received from the user plane network element based on the second COUNT value indicated by the received fourth information, and buffer the data. After the terminal handover is completed, the target access network device will send the downlink data packet with the allocated SN to the terminal.

[0199] Optionally, the aforementioned fourth and fifth information may be carried in the same message, or the aforementioned fourth and fifth information may be carried in different messages, without limitation.

[0200] To make the solutions described in the embodiments of this application clearer, the above implementation method (I) and implementation method (II) will be further described in detail below with reference to Figures 11 and 12.

[0201] For implementation method (one), please refer to Figure 11, which is another flowchart illustrating the communication method provided in this application embodiment. As shown in Figure 11, the communication method may include the following steps:

[0202] S1101, The source access network device sends a measurement configuration to the terminal. Correspondingly, the terminal receives the measurement configuration from the source access network device.

[0203] This measurement configuration includes the measurement object, measurement report configuration, etc.

[0204] S1102. The terminal sends a measurement report to the source access network device. Correspondingly, the source access network device receives the measurement report from the terminal.

[0205] The terminal can perform measurements according to the measurement configuration, and when it determines that the measurement reporting conditions are met, it reports the measurement report to the source access network device.

[0206] S1103. The source access network device sends a handover request message to the target access network device through the mobility management network element. Correspondingly, the target access network device receives the handover request message.

[0207] After receiving the measurement report, the source access network device can make a handover decision based on the measurement results in the report to determine one or more candidate cells (typically, the cell the terminal ultimately hands over to is called the target cell, the access network device to which the target cell belongs is called the target access network device, and the access network device to which the candidate cells belong is called the candidate target access network device). The source access network device can send a handover request message to the candidate target access network devices containing one or more of the determined candidate cells through the mobility management network element. This handover request message is used to request CHO handover and DAPS handover. Optionally, the handover request message includes the target cell identifier, the terminal's identifier in the source access network device, terminal capability information, etc.

[0208] Optionally, the source access network device may specifically request DAPS handover for one or more DRBs; that is, the handover request message may also include DRB information (e.g., DRB identifier). Optionally, the handover request message may also include information about the QoS flows for which the source access network device proposes to perform downlink data forwarding (e.g., QoS flow identifier). It should be understood that if the source access network device requests DAPS handover for a DRB, then all QoS flows mapped to the DRB should perform downlink data forwarding.

[0209] It should be noted that before the terminal handover is completed, the target access network device in the flowchart shown in Figure 11 above can be understood as a candidate target access network device. For example, the source access network device can send handover request messages to multiple candidate target access network devices, but only one target access network device is shown in the flowchart above for simplicity.

[0210] S1104. The target access network device sends a handover request confirmation message to the source access network device through the mobility management network element. Correspondingly, the source access network device receives the handover request confirmation message.

[0211] The handover request confirmation message includes configuration information of the candidate cell of the target access network device sending the message. Optionally, the handover request confirmation message may also include DAPS acceptance information. Optionally, the handover request confirmation message may also include information about the DRB or QoS flow that the target access network device agrees to / accepts for DAPS handover. Optionally, the DRB or QoS flow information included in the handover request confirmation message is typically a subset of the DRB or QoS flow information included in the handover request message.

[0212] It should be noted that when multiple candidate target access network devices that receive handover request messages accept the handover, each of these candidate target access network devices will send a handover request confirmation message to the source access network device through the mobility management network element.

[0213] S1105. The source access network device sends first information to the terminal. Correspondingly, the terminal receives the first information from the source access network device.

[0214] For example, the first information can be carried in the RRC reconfiguration message. This first information includes a CHO handover command and a DAPS handover command. The CHO handover command triggers the terminal to perform a CHO handover, and the DAPS handover command triggers the terminal to perform a DAPS handover. Optionally, the CHO handover command can also be understood as CHO configuration information, and the DAPS handover command can also be understood as DAPS configuration information. That is, the first information includes CHO configuration information and DAPS configuration information, where the CHO configuration information includes the execution conditions for conditional handover and the configuration information of candidate cells, etc., and the DAPS configuration information indicates that when it is determined that the target cell meets the execution conditions, the connection with the source access network device should be maintained. Optionally, the DAPS configuration information may also include information about the DRB or QoS flow that the target access network device agrees to / accepts for DAPS handover. For ease of description, the first DRB / first QoS flow will be used in the following illustrative description to represent the DRB / QoS flow that the target access network device agrees to / accepts for DAPS handover. It should be understood that the number of first DRBs involved in the embodiments of this application can be one or more. That is, the first DRB is a collective term for DRBs that the target access network device agrees to / accepts for DAPS handover, and the description of "first" does not limit its number to one. Similarly, the number of first QoS flows can also be one or more. That is, the first QoS flow is a collective term for QoS flows that the target access network device agrees to / accepts for DAPS handover, and the description of "first" does not limit its number to one.

[0215] The configuration information of the aforementioned candidate cells may include: cell identifier, new C-RNTI, target access network device security algorithm identifier, dedicated RACH resources, association between RACH resources and SSB, association between RACH resources and terminal-specific CSI-RS configuration, public RACH resources, and system information of the target cell.

[0216] The above execution conditions may include: (1) Time-based CHO triggering conditions. The time is defined by T1 and T2, where T1 is an absolute time value and T2 is the duration starting from T1. The terminal obtains its current time, and if it is within the time range of T1 and T1+T2, it is considered to meet the time-based triggering conditions. (2) Location-based triggering conditions. The location is defined as the distance between the terminal and the reference point. The network configures location-based CHO triggering conditions for the terminal, including parameters such as referenceLocation1, referenceLocation2, distanceThresFromReference1, distanceThresFromReference2, and hysteresis. ReferenceLocation1 is associated with the serving cell, and referenceLocation2 is associated with the candidate target cell. When the difference between the distance between the terminal and the serving cell and the hysteresis is greater than distanceThresFromReference1 and the sum of the distance between the UE and the candidate target cell and the hysteresis is less than distanceThresFromReference2, the UE considers that the distance-based triggering conditions are met. Or, (3) Measurement-based triggering conditions, such as CondEvent A3 / A4 / A5. Conditional event A3: The measurement result of the candidate target cell for conditional reconfiguration is better than the measurement result of the serving cell by one offset value; Conditional event A4: The measurement result of the candidate target cell for conditional reconfiguration is better than a threshold; Conditional event A5: The measurement result of the serving cell is worse than threshold 1; and the measurement result of the candidate target cell for conditional reconfiguration is better than threshold 2. It should be understood that the above execution conditions can be combined. For example, two execution conditions can be combined: a time-based CHO trigger condition and a measurement-based trigger condition CondEvent A3 / A4 / A5 can be configured together for the terminal. When both execution conditions are met simultaneously, the terminal performs a handover to the target cell. Another example is a location-based CHO trigger condition and a measurement-based trigger condition CondEvent A3 / A4 / A5 configured together for the terminal. When both execution conditions are met simultaneously, the terminal performs a handover to the target cell.

[0217] Optionally, after the terminal receives the RRC reconfiguration message carrying the first information, the terminal may also send an RRC reconfiguration completion message to the source access network device, indicating that the terminal has successfully received the RRC reconfiguration message.

[0218] S1106. The terminal evaluates whether the candidate cell meets the execution conditions.

[0219] After receiving the first information, the terminal maintains the connection with all active data radio bearers (DRBs) of the source access network device and begins to evaluate the execution conditions of candidate cells. If at least one candidate cell meets the execution conditions, the terminal can select one cell from the at least one candidate cell that meets the execution conditions as the target cell, for example, selecting the earliest candidate cell that meets the execution conditions as the target cell.

[0220] S1107. The terminal sends second information to the source access network device. Correspondingly, the source access network device receives the second information from the terminal.

[0221] For example, the aforementioned second information may be carried in an RRC message, or it may be carried in other types of messages, without limitation. This second information is used to indicate the target cell that meets the execution conditions, such as the identifier of the target cell, the identifier of the execution conditions, or the identifier of the CHO configuration information, etc. One of the identifiers of the execution conditions or one of the identifiers of the CHO configuration information corresponds to one target cell.

[0222] It should be noted that, if the target cell meets the execution conditions, or after the terminal sends the second information, or after the source access network device receives the second information, the connection between the terminal and the source access network device continues to be maintained between the first DRB / first QoS flow.

[0223] S1108. The source access network device sends third information to the target access network device through the mobility management network element. Accordingly, the target access network device receives the third information.

[0224] For example, the third information can be carried in the EARLY STATUS TRANSFER message. This third information indicates a first COUNT value, which is either the COUNT value corresponding to the downlink data packet (e.g., the first data packet) forwarded by the source access network device to the target access network device, or the COUNT value corresponding to the downlink data packet that the target access network device should release. It is understood that before step S1113, the EARLY STATUS TRANSFER message can be sent once or multiple times. The function of the first message and subsequent messages can be referred to the description of the EARLY STATUS TRANSFER message in Figure 9 above, and will not be repeated here.

[0225] Following or simultaneously with step S1108, the source access network device can begin forwarding downlink data packets to the target access network device (as shown in data forwarding in Figure 11). Specifically, the source access network device can receive downlink data packets from user plane network elements, assign a serial number (SN) to the received downlink data packets, and then send / forward the downlink data packets with the SN assigned by the source access network device to the target access network device through the user plane network elements. Simultaneously, the source access network device can also send downlink data received from user plane network elements to the terminal.

[0226] S1109. The terminal synchronizes with the target cell and executes the random access procedure.

[0227] As described in step S1106, after the terminal evaluates that at least one candidate cell meets the corresponding execution conditions, the terminal continues to maintain the connection of the first DRB / first QoS flow with the source access network device. Furthermore, the terminal can also apply the corresponding configuration of the selected candidate cell, synchronize to that candidate cell (at this time, the selected candidate cell is the target cell), and perform a random access procedure to hand over to the target access network device where the target cell is located.

[0228] Optionally, in some implementations, the terminal may also complete the handover via Random Access Channel less (RACH-less). This application's embodiments primarily illustrate the example of handover to the target access network device where the target cell is located by executing a random access procedure.

[0229] S1110, The terminal sends an RRC reconfiguration complete message to the target access network device, including handover completion information. Correspondingly, the target access network device receives the RRC reconfiguration complete message from the terminal.

[0230] The handover completion message indicates that the handover process is complete, or that the terminal has successfully handed over, or that the terminal has successfully accessed the target cell, or that the terminal has successfully handed over from the source access network device to the target access network device. Typically, after successfully completing the handover process, the terminal releases the stored CHO configuration information.

[0231] It should be understood that after step S1110 is completed, i.e., after the terminal switches to the target cell, the target access network device can begin uplink scheduling for the terminal. For example, the terminal sends new uplink data packets (e.g., UL PDCP PDU) to the target access network device, or the terminal switches its uplink data transmission to the target access network device. It should be noted that after the terminal switches its uplink data transmission to the target access network device, the terminal will still continue to send Layer 1 CSI feedback, HARQ feedback, Layer 2 RLC feedback, ROHC feedback, HARQ data (re)transmission, and RLC data (re)transmission to the source access network device for uplink transmission.

[0232] S1111 The target access network device sends a handover notification message to the mobility management network element, including handover completion information. Correspondingly, the mobility management network element receives the handover notification message.

[0233] S1112. The mobility management network element sends a handover success message to the source access network device, including handover completion information. Correspondingly, the source access network device receives the handover success message.

[0234] Generally, after the source access network device receives the handover success message, or simultaneously with it, it will cease uplink and downlink data transmission with the terminal. However, before receiving the handover success message, the source access network device will continue to send data packets containing incomplete uplink data to the user plane network elements, and data packets containing downlink data from the user plane network elements to the terminal. Simultaneously, the terminal maintains a connection with the target access network device. This connection maintenance can be understood as one or more of the following: ① The terminal does not release the configuration information of the target cell under the target access network device; ② The terminal detects the downlink control information of the target cell; ③ The terminal receives data and / or information from the target cell; ④ The terminal sends data and / or information to the target cell.

[0235] Optionally, at the same time or after the source access network device receives the handover success message, or at the same time or after the source access network device receives the second information, the source access network device may send a handover cancellation message to the candidate target access network device to which other candidate cells that meet the execution conditions (or candidate cells that are not selected as target cells but meet the execution conditions) belong. The handover cancellation message is used to trigger the candidate target access network device to release the access / handover resources reserved for the terminal.

[0236] S1113. The source access network device sends the fifth information to the target access network device through the mobility management network element. Accordingly, the target access network device receives the fifth information.

[0237] For example, the fifth information may be carried in the state transition message. This fifth information indicates a third COUNT value, which is the COUNT value that the target access network device should assign to the next downlink data packet (e.g., DL SDU) without a SN.

[0238] Generally, after or simultaneously with step S1110, the terminal maintains a connection with the target access network device. Maintaining a connection between the terminal and the target access network device can be understood as one or more of the following: ① The terminal does not release the configuration information of the target cell under the target access network device; ② The terminal detects the downlink control information of the target cell; ③ The terminal receives data and / or information from the target cell; ④ The terminal sends data and / or information to the target cell.

[0239] S1114. The target access network device sends a source cell release message to the terminal. Correspondingly, the terminal receives the source cell release message from the target access network device.

[0240] It should be understood that after receiving the source cell release message, the terminal can release the source cell configuration and stop receiving downlink data from the source access network device.

[0241] For implementation method (ii), please refer to Figure 12, which is another flowchart illustrating the communication method provided in this application embodiment. As shown in Figure 12, the communication method may include the following steps:

[0242] S1201, The source access network device sends a measurement configuration to the terminal. Correspondingly, the terminal receives the measurement configuration from the source access network device.

[0243] This measurement configuration includes the measurement object, measurement report configuration, etc.

[0244] S1202, The terminal sends a measurement report to the source access network device. Correspondingly, the source access network device receives the measurement report from the terminal.

[0245] The terminal can perform measurements according to the measurement configuration, and when it determines that the measurement reporting conditions are met, it reports the measurement report to the source access network device.

[0246] S1203. The source access network device sends a handover request message to the target access network device through the mobility management network element. Correspondingly, the target access network device receives the handover request message.

[0247] After receiving the measurement report, the source access network device can make a handover decision based on the measurement results in the report to determine one or more candidate cells (usually, the cell to which the terminal ultimately hands over is called the target cell, the access network device to which the target cell belongs is called the target access network device, and the access network device to which the candidate cells belong is called the candidate target access network device). The source access network device can send a handover request message to the candidate target access network device where one or more of the determined candidate cells are located through the mobility management network element. This handover request message is used to request CHO handover and DAPS handover.

[0248] The handover request message includes a sixth piece of information. This sixth piece of information is used to request data transmission between the user plane network element and the target access network device. Alternatively, it can be described as instructing the user plane network element and the target access network device to directly transmit data, rather than the source access network device indirectly forwarding data to the target access network device through the user plane network element. Optionally, the sixth piece of information can also be specifically used to request data transmission between the user plane network element and the target access network device for a specific DRB or a specific QoS flow. Optionally, the function of the sixth piece of information can also be achieved by omitting the data forwarding indication information in the handover request message. That is, the handover request message can also omit the sixth piece of information and determine the request for direct data transmission between the user plane network element and the target access network device by not carrying data forwarding indication information. Here, the data forwarding indication information includes both direct data forwarding indication information and indirect data forwarding indication information. Direct data forwarding refers to a scenario where the source access network device and the target access network device have an Xn interface. The user plane network element sends data to the source access network device, and the source access network device sends the data to the target access network device through the Xn interface. This scenario is used for Xn-based handover. Indirect data forwarding refers to a situation where the source access network device and the target access network device do not have an Xn interface. The user plane network element sends data to the source access network device, and the source access network device then sends the data to the target access network device through the user plane network element.

[0249] Optionally, the handover request message may also include one or more of the following information: target cell identifier, terminal identifier in the source access network device, terminal capability information, target access network device identifier, PDU session ID, DAPS handover related information, etc. Among these, the DAPS handover related information includes information about the DRB for which the source access network device requests DAPS handover (e.g., the DRB identifier), and / or may also include information about the QoS flows for which the source access network device proposes to perform downlink data forwarding (e.g., the QoS flow identifier). It should be understood that if the source access network device requests DAPS handover for a DRB, then all QoS flows mapped to the DRB should perform downlink data forwarding.

[0250] Understandably, before or during the handover decision, all active DRB connections are maintained between the terminal and the source access network device.

[0251] It should be noted that before the terminal handover is completed, the target access network device in the flowchart shown in Figure 12 above can be understood as a candidate target access network device. For example, the source access network device can send handover request messages to multiple candidate target access network devices, but only one target access network device is shown in the flowchart above for simplicity.

[0252] S1204a. The target access network device sends a handover request confirmation message to the mobility management network element. Correspondingly, the mobility management network element receives the handover request confirmation message.

[0253] The handover request confirmation message contains seventh and eighth information. The seventh information indicates acceptance / agreement / allowance for data transmission between the user plane network element and the target access network device, or it can be interpreted as the seventh information indicating that the target access network device accepts data transmission from the user plane network element to the target access network device, or it can be interpreted as the seventh information indicating that the target access network device accepts direct data transmission from the user plane network element to the target access network device, rather than data forwarding from the user plane network element to the target access network device, or it can be interpreted as the seventh information indicating that the target access network device accepts / agrees / requests to establish a data transmission channel between the user plane network element and the target access network device. The eighth information indicates the N3 UP address of the target access network device, or it can be interpreted as the eighth information indicating the data transmission channel address information on the access network device side corresponding to the data transmission (such as the N3 UP address on the target access network device side). Optionally, the eighth information may also indicate the channel identification information of the data transmission channel (such as the Tunnel ID). It should be understood that the interface between the access network device and the user plane network element is called the N3 interface. UP stands for user plane, and data is transmitted through the user plane.

[0254] Optionally, the handover request confirmation message includes DAPS acceptance information and information required for the terminal to access the target access network device, such as the configuration information of the candidate cells of the target access network device. The content of the candidate cell configuration information can be found in the aforementioned description of the candidate cell configuration information, and will not be repeated here.

[0255] S1205a, the mobility management network element sends an update session management context request message (e.g., an Nsmf_PDUSession_UpdateSMContext Request message) to the session management network element. Correspondingly, the session management network element receives the update session management context request message from the mobility management network element.

[0256] The Update Session Management Context Request message includes the eighth piece of information. Optionally, the Update Session Management Context Request message may also include the sixth piece of information. For a more detailed understanding of the sixth piece of information, please refer to the previous description of the sixth piece of information, which will not be repeated here.

[0257] S1205b: The session management network element sends an N4 Session Modification Request message to the user plane network element. Correspondingly, the user plane network element receives the N4 Session Modification Request message.

[0258] It should be understood that N4 refers to the N4 interface between the session management network element and the user plane network element. This N4 session modification request message contains the eighth piece of information. Optionally, the N4 session modification request message may also include indication information requesting the establishment of a data transmission channel between the user plane network element and the target access network device, or it may implicitly indicate the request to establish a data transmission channel by not including indication information requesting the establishment of a data forwarding channel in the N4 session modification request message.

[0259] S1205c: The user plane network element sends an N4 Session Modification Response message to the session management network element. Correspondingly, the session management network element receives the N4 Session Modification Response message from the user plane network element.

[0260] The N4 session modification response message includes a ninth piece of information, which indicates the N3 UP address of the user plane network element, or, as the ninth piece of information indicates, the data transmission channel address information (such as the N3 UP address of the user plane network element) on the user plane network element side corresponding to the data transmission. Optionally, the ninth piece of information may also indicate the channel identification information of the data transmission channel (such as the user plane network element N3 Tunnel ID).

[0261] S1205d, the session management network element sends an update session management context response message (e.g., an Nsmf_PDUSession_UpdateSMContext Response message) to the mobility management network element. Correspondingly, the mobility management network element receives the update session management context response message from the session management network element.

[0262] The update session management context response message indicates that the data transmission channel between the user plane network element and the target access network device has been established.

[0263] S1204b: The mobility management network element sends a handover request confirmation message to the source access network device. Correspondingly, the source access network device receives the handover request confirmation message.

[0264] The handover request confirmation message contains a seventh piece of information, which indicates acceptance / agreement / allowance for data transmission between the user plane network element and the target access network device. Alternatively, the seventh piece of information may be interpreted as the target access network device accepting data transmission from the user plane network element to the target access network device, or as the seventh piece of information may be interpreted as the target access network device accepting direct data transmission from the user plane network element to the target access network device, rather than data forwarding from the user plane network element to the target access network device.

[0265] Optionally, the handover request confirmation message may also include configuration information of the candidate cell of the target access network device sending the message. Optionally, the handover request confirmation message may also include DAPS acceptance information.

[0266] It should be noted that when multiple candidate target access network devices that receive handover request messages accept the handover, each of these candidate target access network devices will send a handover request confirmation message to the source access network device through the mobility management network element.

[0267] S1206. The source access network device sends first information to the terminal. Correspondingly, the terminal receives the first information from the source access network device.

[0268] S1207. The terminal evaluates whether the candidate cell meets the execution conditions.

[0269] S1208. The terminal sends second information to the source access network device. Correspondingly, the source access network device receives the second information from the terminal.

[0270] For an understanding of steps S1206 to S1208, please refer to the description of steps S1105 to S1107 in Figure 11 above, which will not be repeated here.

[0271] S1209a, The source access network device sends fourth information to the mobility management network element. Correspondingly, the mobility management network element receives the fourth information from the source access network device.

[0272] S1209b: The mobility management network element sends fourth information to the target access network device. Accordingly, the target access network device receives the fourth information.

[0273] For example, the fourth information can be carried in the EARLY STATUS TRANSFER message or other messages. This fourth information indicates a second COUNT value, which is the COUNT value corresponding to the SN that the target access network device should allocate for the downlink data packet (e.g., the first data packet) received from the user plane network element, or the second COUNT value is the COUNT value corresponding to the downlink data packet that the target access network device should release. It is understood that before step S1217, the EARLY STATUS TRANSFER message can be sent once or multiple times. The function of the first message and subsequent messages can be referred to the relevant description of the EARLY STATUS TRANSFER message in Figure 10 above, and will not be repeated here.

[0274] S1210, the source access network device sends the fifth information to the mobility management network element. Correspondingly, the mobility management network element receives the fifth information from the source access network device.

[0275] The fifth information is used to trigger the user plane network element to send downlink data packets to the target access network device, or it is referred to as the fifth information being used to trigger the user plane network element to start sending downlink data packets to the target access network device, or the fifth information being used to trigger the user plane network element to send downlink data packets to the target access network device through the data transmission channel between the user plane network element and the target access network device.

[0276] S1211. The mobility management network element sends a PDU session modification request to the session management network element. Correspondingly, the session management network element receives the PDU session modification request from the mobility management network element.

[0277] Typically, after the mobility management network element receives the fifth information from the source access network device, it can further send a PDU session modification request to the session management network element. This PDU session modification request contains information needed to trigger the user plane network element to send downlink data packets to the target access network device, such as the PDU session ID, the transfer / transmission mode (replication), and the channel ID (e.g., Tunnel ID).

[0278] S1212, Session modification is performed between the session management network element and the user plane network element.

[0279] Generally, after the session management network element receives the PDU session modification request, session modification can be performed between the session management network element and the user plane network element. Specifically, the user plane network element can copy the QoS flow or DRB corresponding to the PDU session based on the PDU session ID, and then send it to the source access network device through the source path (the source path refers to the data transmission channel from the user plane network element to the source access network device) and to the target access network device through the destination path (the destination path refers to the data transmission channel from the user plane network element to the target access network device). At the same time, the source access network device can also send the downlink data received from the user plane network element to the terminal.

[0280] S1213. The terminal synchronizes with the target cell and executes the random access procedure.

[0281] S1214. The terminal sends an RRC reconfiguration complete message to the target access network device, including handover completion information. Correspondingly, the target access network device receives the RRC reconfiguration complete message from the terminal.

[0282] S1215. The target access network device sends a handover notification message to the mobility management network element, including handover completion information. Correspondingly, the mobility management network element receives the handover notification message.

[0283] S1216. The mobility management network element sends a handover success message to the source access network device, including handover completion information. Correspondingly, the source access network device receives the handover success message.

[0284] S1217. The source access network device sends the fifth information to the target access network device through the mobility management network element. Accordingly, the target access network device receives the fifth information.

[0285] S1218. The target access network device sends a source cell release message to the terminal. Correspondingly, the terminal receives the source cell release message from the target access network device.

[0286] For an understanding of steps S1213 to S1218, please refer to the description of steps S1109 to S1114 in Figure 11 above, which will not be repeated here.

[0287] This application proposes a handover scheme that combines CHO handover and DAPS handover to reduce handover interruption time, thereby improving user experience. Specifically, the above-mentioned embodiments of this application mainly disclose the design details of the combined CHO handover and DAPS handover scheme based on the NG interface (for example, the implementation scheme applicable to the system architecture shown in Figure 4-1 or Figure 4-2). It can be applied to NTN scenarios (e.g., satellite communication scenarios), or TN scenarios, or scenarios where NTN and TN are integrated. For ease of understanding, the satellite communication scenario is mainly used as an example. For example, the access network device (e.g., source access network device or target access network device) in the embodiments of this application can be understood as a satellite, that is, the access network device is deployed on a satellite. In addition to reducing handover interruption time, this application further optimizes the combined CHO handover and DAPS handover scheme. For example, in the embodiment shown in Figure 11, the source access network device does not start data forwarding immediately after executing step S1105, but performs data forwarding after step S1107 (or in the embodiment shown in Figure 9, the source access network device does not start data forwarding immediately after executing step S901, but performs data forwarding after step S903). This can save the on-board buffering overhead occupied by the target access network device when buffering and forwarding data (for scenarios where the access network device is deployed on a satellite), and save the overhead of link (or air interface) resources between the access network device and the mobility management network element that data forwarding would occupy. In addition, the source access network device only needs to forward data to the target access network device where the final selected target cell is located, and does not need to forward data to the candidate target access network devices where all candidate cells are located, which can reduce the resource waste and buffering overhead of the candidate target access network devices. In the embodiment shown in Figure 12 (or Figure 10), based on the beneficial effects of Figure 9 / Figure 11, the embodiment shown in Figure 12 proposes that the user plane network element can send downlink data through the data transmission channel between the user plane network element and the source access network device, and also through the data transmission channel between the user plane network element and the target access network device (i.e., replication, dual data transmission channel in Figure 10 / Figure 12), instead of first sending the downlink data to the source access network device through the user plane network element, and then having the source access network device forward the downlink data to the target access network device through the user plane network element. This can further reduce the link overhead between the user plane network element and the access network device (mainly the source access network device) caused by data forwarding.

[0288] Optionally, Figures 9 to 12 above show the design details of a combined CHO handover and DAPS handover scheme based on the NG interface. In some possible system architectures, there may also be a direct interface (i.e., Xn interface) between the source access network device and the target access network device. For example, in the architecture shown in Figure 4-3, there is an inter-satellite link (i.e., there is an Xn interface). Therefore, the information that needs to be forwarded by the mobility management network element between the source access network device and the target access network device in Figures 9 to 12 can also be sent directly from the source access network device to the target access network device, or directly from the target access network device to the source access network device. Examples include handover request messages, handover request confirmation messages, third information, fourth information, fifth information, handover completion information, or downlink data in data forwarding.

[0289] Optionally, the embodiments shown in Figures 8 to 12 can also be applied to the O-RAN scenario. It should be understood that in the O-RAN scenario, the access network devices (e.g., source access network devices, target access network devices) involved in Figures 8 to 12 can be replaced by CU (e.g., CU-CP or CU-UP) or DU or RU, etc.

[0290] The communication device provided in this application will now be described in detail with reference to Figures 13 to 15.

[0291] It is understood that, in order to achieve the functions in the above embodiments, the communication device includes hardware structures and / or software modules corresponding to each function. Those skilled in the art should readily recognize that, based on the units and method steps described in conjunction with the embodiments disclosed in this application, this application can be implemented in hardware or a combination of hardware and computer software. Whether a function is executed by hardware or by computer software driving hardware depends on the specific application scenario and design constraints of the technical solution.

[0292] Figures 13 to 15 are schematic diagrams illustrating the possible communication devices provided in the embodiments of this application. These communication devices can be used to implement the functions of the terminal or access network device (e.g., base station) in the above method embodiments, and thus can also achieve the beneficial effects of the above method embodiments. In the embodiments of this application, the communication device can be one of the terminals 120a-120j shown in Figure 1, or it can be RAN node 110a or 110b shown in Figure 1. Optionally, it can also be a module (e.g., a chip) applied to the terminal or access network device.

[0293] As shown in Figure 13, the communication device 1300 includes a processing unit 1310 and a transceiver unit 1320. The transceiver unit 1320 and the processing unit 1310 can be software, hardware, or a combination of both. Optionally, the communication device 1300 may further include a storage unit 1330 for storing device program code and / or data, not shown in Figure 13.

[0294] The transceiver unit 1320 can implement sending and / or receiving functions. Optionally, the transceiver unit 1320 can also be referred to as a communication unit. The transceiver unit 1320 may further include a receiving unit and / or a sending unit, wherein the receiving unit is used to implement the receiving function, and the sending unit is used to implement the sending function. Optionally, the transceiver unit 1320 can be used to receive information sent by other devices, and can also be used to send information to other devices.

[0295] The communication device 1300 is used to implement the functions of the terminal-side communication device in the method embodiments shown in Figures 8 to 12 above, such as a terminal or a communication module in a terminal, or a circuit or chip in a terminal responsible for communication functions, or to implement the functions of the network-side communication device in the method embodiments shown in Figures 8 to 12 above, such as an access network device, a module (e.g., a circuit, a chip, or a chip system) in an access network device, or a logic node, logic module, or software that can implement all or part of the functions of the access network device.

[0296] When the communication device 1300 is used to implement the functions of the terminal in the method embodiments shown in Figures 8 to 12:

[0297] The transceiver unit 1320 is configured to receive first information from the source access network device. The first information includes the execution conditions for conditional handover, the configuration information of the candidate cell, and the configuration information for dual-activation protocol stack handover. The configuration information for dual-activation protocol stack handover indicates that when it is determined that the target cell meets the execution conditions, the connection with the source access network device should be maintained. The target cell is included in the candidate cell.

[0298] Processing unit 1310 is configured to maintain the connection with the source access network device when it is determined that the target cell meets the execution conditions;

[0299] The processing unit 1310 is used to synchronize with the target cell and send handover completion information to the target access network device where the target cell is located through the transceiver unit 1320, wherein the handover completion information indicates that the terminal has successfully switched from the source access network device to the target access network device.

[0300] In one possible implementation, when it is determined that the target cell meets the execution conditions, or after it is determined that the target cell meets the execution conditions, or before sending handover completion information to the target access network device where the target cell is located, the transceiver unit 1320 is further configured to:

[0301] Send a second message to the source access network device, the second message indicating the target cell that meets the execution conditions.

[0302] In one possible implementation, before determining that the target cell meets the execution conditions, or after receiving the first information from the source access network device, the processing unit 1310 is further configured to:

[0303] Maintain the connection with the source access network device and evaluate whether the candidate cell meets the execution conditions.

[0304] In one possible implementation, when maintaining the connection with the source access network device and evaluating whether the candidate cell meets the execution conditions, the processing unit 1310 is specifically used for:

[0305] Maintain connections with all active data radio bearers (DRBs) of the source access network device and evaluate whether the candidate cell meets the execution conditions.

[0306] In one possible implementation, the configuration information for the dual-activation protocol stack switching also indicates a first DRB or a first Quality of Service (QoS) flow; when maintaining the connection with the source access network device after determining that the target cell meets the execution conditions, the processing unit 1310 is specifically used for:

[0307] If the target cell is determined to meet the execution conditions, the connection between the first DRB or the first QoS flow and the source access network device is maintained.

[0308] In one possible design, when the communication device 1300 is a terminal or a communication module within a terminal, the functionality of the processing unit 1310 can be implemented by one or more processors. Specifically, the processor may include a modem chip, or a system-on-a-chip (SoC) or SIP chip containing a modem core. The functionality of the transceiver unit 1320 can be implemented by transceiver circuitry.

[0309] In one possible design, when the communication device 1300 is a circuit or chip in a terminal responsible for communication functions, such as a modem chip or a system-on-a-chip (SoC) or SIP chip containing a modem core, the function of the processing unit 1310 can be implemented by a circuit system in the aforementioned chip that includes one or more processors or processor cores. The function of the transceiver unit 1320 can be implemented by the interface circuitry or data transceiver circuitry on the aforementioned chip.

[0310] When the communication device 1300 is used to implement the function of the source access network device in the method embodiments shown in Figures 8 to 12:

[0311] The transceiver unit 1320 is used to send first information to the terminal. The first information includes the execution conditions for conditional handover, the configuration information of the candidate cell, and the configuration information for dual-activation protocol stack handover. The configuration information for dual-activation protocol stack handover indicates that when it is determined that the target cell meets the execution conditions, the connection with the source access network device is maintained. The target cell is included in the candidate cell.

[0312] The transceiver unit 1320 is configured to receive second information from the terminal and maintain a connection with the terminal, wherein the second information indicates the target cell that satisfies the execution conditions.

[0313] The processing unit 1310 is configured to receive handover completion information from a mobility management network element and disconnect the connection with the terminal, wherein the handover completion information indicates that the terminal has successfully switched from the source access network device to the target access network device where the target cell is located.

[0314] In one possible implementation, the configuration information for the dual-activation protocol stack switching also indicates a first DRB or a first QoS flow; when receiving the second information from the terminal and maintaining the connection with the terminal, the processing unit 1310 is specifically used for:

[0315] The transceiver unit 1320 receives second information from the terminal to maintain the connection with the first DRB or the first QoS stream of the terminal.

[0316] In one possible implementation, before receiving the handover completion information from the mobility management network element, and / or after receiving the second information from the terminal, the transceiver unit 1320 is further configured to:

[0317] The mobility management network element sends third information to the target access network device, the third information indicating a first count COUNT value; wherein, the first COUNT value is the COUNT value corresponding to the downlink data packet (e.g., the first data packet) forwarded by the source access network device to the target access network device, or the first COUNT value is the COUNT value corresponding to the downlink data packet that the target access network device should release.

[0318] Receive data packets of downlink data from user plane network elements;

[0319] The data packets containing the downlink data are sent to the target access network device through the user plane network element.

[0320] In one possible implementation, before receiving the handover completion information from the mobility management network element, and / or after receiving the second information from the terminal, the transceiver unit 1320 is further configured to:

[0321] The mobility management network element sends a fourth message to the target access network device, the fourth message indicating a second count COUNT value; wherein, the second COUNT value is the COUNT value corresponding to the SN that the target access network device should allocate for the downlink data packet (e.g., the first data packet) received from the user plane network element, or the second COUNT value is the COUNT value corresponding to the downlink data packet that the target access network device should release;

[0322] The fifth information is sent to the mobility management network element, and the fifth information is used to trigger the user plane network element to send downlink data packets to the target access network device.

[0323] When the communication device 1300 is used to implement the function of the target access network device in the method embodiments shown in Figures 8 to 12:

[0324] The transceiver unit 1320 is used to receive fourth information, the fourth information indicating a second count COUNT value, the second COUNT value being the COUNT value corresponding to the SN that the target access network device where the target cell is located should allocate for the downlink data packet (e.g., the first data packet) received from the user plane network element, or the second COUNT value being the COUNT value corresponding to the downlink data packet that the target access network device should release;

[0325] The transceiver unit 1320 is used to receive data packets of downlink data from the user plane network element;

[0326] The transceiver unit 1320 is used to send the downlink data packets to the terminal, and the SN corresponding to the downlink data packets is assigned by the target base station according to the second COUNT value.

[0327] For a more detailed description of the processing unit 1310 and the transceiver unit 1320, please refer to the relevant descriptions in the method embodiments shown in Figures 8 to 12.

[0328] It is understood that the division of units in the above-described device is merely a logical functional division. Each function can correspond to a functional unit, or two or more functions can be integrated into one functional unit. In actual implementation, all or some units can be integrated into a single physical entity, or they can be distributed across different physical entities. Furthermore, the aforementioned functional units can be implemented in hardware, software, or a combination of both. Whether a function is executed in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0329] In one example, the functional unit in any of the above devices may be one or more integrated circuits configured to implement the above methods, such as: one or more application-specific integrated circuits (ASICs), or one or more central processing units (CPUs), one or more microcontroller units (MCUs), one or more digital signal processors (DSPs), or one or more field-programmable gate arrays (FPGAs), or a combination of at least two of these integrated circuit forms.

[0330] In one example, storage unit 1330 may include random access memory, flash memory, read-only memory, programmable read-only memory or electrically erasable programmable memory and / or registers, etc.

[0331] As shown in Figure 14, the communication device 1400 includes a processor 1410, and optionally an interface circuit 1420. The processor 1410 and the interface circuit 1420 are coupled to each other. It is understood that the interface circuit 1420 can be a transceiver or an input / output interface. Optionally, the communication device 1400 may also include a memory 1430 for storing computer programs or instructions executed by the processor 1410, or storing input data required by the processor 1410 to execute instructions, or storing data generated by the processor 1410 after executing computer programs or instructions.

[0332] When the communication device 1400 is used to implement the method shown in Figures 8 to 12, the processor 1410 is used to implement the function of the processing unit 1310, and the interface circuit 1420 is used to implement the function of the transceiver unit 1320.

[0333] When the aforementioned communication device is a chip applied to a terminal, the terminal chip implements the functions of the terminal in the above method embodiments. The terminal chip receives information sent to the terminal by the access network device through other modules (such as an RF module or antenna) in the terminal; or, the terminal chip sends information to other modules (such as an RF module or antenna) in the terminal, which is information sent by the terminal to the access network device.

[0334] When the aforementioned communication device is a module applied to an access network device, the access network device module implements the functions of the access network device in the above method embodiments. The access network device module receives information from other modules (such as radio frequency modules or antennas) in the access network device, which is information sent by the terminal to the access network device; or, the access network device module sends information to other modules (such as radio frequency modules or antennas) in the access network device, which is information sent by the access network device to the terminal. Here, the access network device module can be the baseband chip of the access network device, or a CU, DU, or other module, or a device under an open radio access network (O-RAN) architecture, such as an open CU, open DU, etc.

[0335] As shown in Figure 15, the communication device 1500 includes a processor 1510, a memory 1520, and a transceiver 1530. The processor 1510 is mainly used for processing communication protocols and communication data; controlling terminal / access network devices; executing software programs; and processing data from software programs. The memory 1520 can store computer program code, software programs, and data. The transceiver 1530 includes a transmitter 1531, a receiver 1532, radio frequency circuitry (not shown in the figure), and an antenna 1533.

[0336] The processor 1510 can also be called a processing unit, processing board, processing module, or processing device. The transceiver 1530 can also be called a transceiver unit, transceiver, or transceiver device.

[0337] Optionally, the device in transceiver 1530 used to implement the receiving function can be considered a receiving module, and the device in transceiver 1530 used to implement the transmitting function can be considered a transmitting module. That is, transceiver 1530 includes a receiver and / or a transmitter. A transceiver may sometimes be called a transceiver unit, transceiver module, or transceiver circuit, etc. A receiver may sometimes be called a receiver unit, receiving module, or receiving circuit, etc. A transmitter may sometimes be called a transmitter, transmitting module, or transmitting circuit, etc.

[0338] Processor 1510 is used to execute terminal-side processing operations in the embodiments shown in Figures 8-12. Transceiver 1530 is used to execute terminal-side transmission and reception operations in the embodiments shown in Figures 8-12. Alternatively, processor 1510 is used to execute network-side processing operations in the embodiments shown in Figures 8-12. Transceiver 1530 is used to execute network-side transmission and reception operations in the embodiments shown in Figures 8-12.

[0339] When the communication device is a chip, the chip includes a processor and a transceiver. The transceiver can be an input / output circuit or a communication interface. The processor can be a processing module integrated on the chip, a microprocessor, or an integrated circuit. In the above method embodiments, the terminal's transmitting operation can be understood as the chip's output, and the terminal's receiving operation can be understood as the chip's input. Similarly, in the above method embodiments, the access network device's transmitting operation can be understood as the chip's output, and the access network device's receiving operation can be understood as the chip's input.

[0340] This application also provides a computer-readable storage medium storing a computer program or instructions for implementing the methods executed by a terminal or access network device in the above-described method embodiments.

[0341] For example, when the computer program is executed by a computer, it enables the computer to implement the method performed by the terminal or access network device in the above method embodiments.

[0342] This application also provides a computer program product containing a program or instructions, which, when executed by a computer, causes the computer to implement the method executed by the terminal or access network device in the above method embodiments.

[0343] This application also provides a communication system, which includes the terminal and the access network device described in the above embodiments. The terminal is used to perform some or all of the operations performed by the terminal in the above method embodiments, and the access network device is used to perform some or all of the operations performed by the access network device in the above method embodiments.

[0344] This application also provides a chip device, including a processor, for calling a computer program or computer instructions stored in the memory, so that the processor executes the method provided in the embodiments shown in Figures 8 to 12 above.

[0345] In one possible implementation, the input of the chip device corresponds to the receiving operation in the embodiments shown in Figures 8 to 12, and the output of the chip device corresponds to the transmitting operation in the embodiments shown in Figures 8 to 12.

[0346] Optionally, the processor is coupled to the memory via an interface.

[0347] Optionally, the chip device may also include a memory in which computer programs or computer instructions are stored.

[0348] It is understood that the processor in the embodiments of this application can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. A general-purpose processor can be a microprocessor or any conventional processor.

[0349] The method steps in the embodiments of this application can be implemented in hardware or in software instructions executable by a processor. The software instructions can consist of corresponding software modules, which can be stored in random access memory, flash memory, read-only memory, programmable read-only memory, erasable programmable read-only memory, electrically erasable programmable read-only memory, registers, hard disks, portable hard disks, CD-ROMs, or any other form of storage medium known in the art. An exemplary storage medium is coupled to a processor, enabling the processor to read information from and write information to the storage medium. The storage medium can also be a component of the processor. The processor and storage medium can reside in an ASIC. Alternatively, the ASIC can reside in an access network device or terminal. The processor and storage medium can also exist as discrete components in the access network device or terminal.

[0350] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially in the form of a computer program product. The computer program product includes one or more computer programs or instructions. When the computer program or instructions are loaded and executed on a computer, the processes or functions described in the embodiments of this application are performed entirely or partially. The computer can be a general-purpose computer, a special-purpose computer, a computer network, a network device, 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 that a computer can access 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; it can also be an optical medium, such as a digital video optical disc; or it can be a semiconductor medium, such as a solid-state drive. The computer-readable storage medium may be a volatile or non-volatile storage medium, or may include both types of storage media.

[0351] In the various embodiments of this application, unless otherwise specified or in case of logical conflict, the terminology and / or descriptions between different embodiments are consistent and can be referenced by each other. Technical features in different embodiments can be combined to form new embodiments based on their inherent logical relationships.

[0352] It is understood that the various numerical designations used in the embodiments of this application are merely for descriptive convenience and are not intended to limit the scope of the embodiments of this application. The order of the process numbers described above does not imply the order of execution; the execution order of each process should be determined by its function and internal logic.

Claims

1. A communication method, characterized in that, include: The system receives first information from a source access network device. The first information includes execution conditions for conditional handover, configuration information for candidate cells, and configuration information for dual-activation protocol stack handover. The configuration information for dual-activation protocol stack handover indicates that when it is determined that a target cell meets the execution conditions, the connection with the source access network device should be maintained. The target cell is included in the candidate cells. If the target cell meets the execution conditions, the connection with the source access network device is maintained; The terminal is synchronized to the target cell and a handover completion message is sent to the target access network device where the target cell is located, wherein the handover completion message indicates that the terminal has successfully switched from the source access network device to the target access network device.

2. The method according to claim 1, characterized in that, When it is determined that the target cell meets the execution conditions, or after it is determined that the target cell meets the execution conditions, or before sending handover completion information to the target access network device where the target cell is located, the method further includes: Send a second message to the source access network device, the second message indicating the target cell that meets the execution conditions.

3. The method according to claim 1 or 2, characterized in that, Before determining that the target cell meets the execution conditions, or after receiving the first information from the source access network device, the method further includes: Maintain the connection with the source access network device and evaluate whether the candidate cell meets the execution conditions.

4. The method according to claim 3, characterized in that, Maintaining the connection with the source access network device and evaluating whether the candidate cell meets the execution conditions includes: Maintain connections with all active data radio bearers (DRBs) of the source access network device and evaluate whether the candidate cell meets the execution conditions.

5. The method according to any one of claims 1-4, characterized in that, The configuration information for the dual-activation protocol stack switching also indicates a first DRB or a first Quality of Service (QoS) flow; maintaining the connection with the source access network device when it is determined that the target cell meets the execution conditions includes: If the target cell is determined to meet the execution conditions, the connection between the first DRB or the first QoS flow and the source access network device is maintained.

6. A communication method, characterized in that, include: Send first information to the terminal. The first information includes the execution conditions for conditional handover, the configuration information of the candidate cell, and the configuration information for dual-activation protocol stack handover. The configuration information for dual-activation protocol stack handover indicates that when it is determined that the target cell meets the execution conditions, the connection with the source access network device should be maintained. The target cell is included in the candidate cell. Receive second information from the terminal, maintain the connection with the terminal, the second information indicating the target cell that meets the execution conditions; The system receives a handover completion message from a mobility management network element and disconnects from the terminal, wherein the handover completion message indicates that the terminal has successfully handed over from the source access network device to the target access network device where the target cell is located.

7. The method according to claim 6, characterized in that, The configuration information for the dual-activation protocol stack switching also indicates a first DRB or a first Quality of Service (QoS) flow; receiving the second information from the terminal and maintaining the connection with the terminal includes: Receive second information from the terminal and maintain the connection with the first DRB or the first QoS stream of the terminal.

8. The method according to claim 6 or 7, characterized in that, Before receiving the handover completion information from the mobility management network element, and / or after receiving the second information from the terminal, the method further includes: The mobility management network element sends third information to the target access network device, the third information indicating a first count COUNT value; wherein, the first COUNT value is the COUNT value corresponding to the downlink data packet forwarded by the source access network device to the target access network device, or the first COUNT value is the COUNT value corresponding to the downlink data packet that the target access network device should release. Receive data packets of downlink data from user plane network elements; The data packets containing the downlink data are sent to the target access network device through the user plane network element.

9. The method according to claim 6 or 7, characterized in that, Before receiving the handover completion information from the mobility management network element, and / or after receiving the second information from the terminal, the method further includes: The mobility management network element sends a fourth message to the target access network device, the fourth message indicating a second count COUNT value; wherein, the second COUNT value is the COUNT value corresponding to the sequence number SN that the target access network device should allocate to the downlink data packets received from the user plane network element, or, the second COUNT value is the COUNT value corresponding to the downlink data packets that the target access network device should release. The fifth information is sent to the mobility management network element, and the fifth information is used to trigger the user plane network element to send downlink data packets to the target access network device.

10. A communication device, characterized in that, It includes units or modules for implementing the method as described in any one of claims 1-5, or includes units or modules for implementing the method as described in any one of claims 6-9.

11. A communication device, characterized in that, Includes a processor for executing computer programs or instructions to cause the communication device to implement the method as described in any one of claims 1-5, or to cause the communication device to implement the method as described in any one of claims 6-9.

12. A communication device, characterized in that, The device includes a processor and a transceiver, the transceiver being used to send and receive information, and the processor being used to execute a computer program or instructions to cause the communication device to implement the method as described in any one of claims 1-5, or to cause the communication device to implement the method as described in any one of claims 6-9.

13. A communication device, characterized in that, The device includes a processor and an interface circuit. The interface circuit is used to receive signals from other communication devices besides the communication device and transmit them to the processor, or to send signals from the processor to other communication devices besides the communication device. The processor is used to execute computer programs or instructions to cause the communication device to implement the method as described in any one of claims 1-5, or to cause the communication device to implement the method as described in any one of claims 6-9.

14. A computer-readable storage medium, characterized in that, The storage medium stores a computer program or instructions, which, when executed by a communication device, implement the method as described in any one of claims 1-5, or the method as described in any one of claims 6-9.

15. A computer program product, characterized in that, Includes computer program code, which, when run on a computer, implements the method of any one of claims 1-5, or implements the method of any one of claims 6-9.

Images