Communication method and communication apparatus

Abstract

A communication method and a communication apparatus, which can avoid a service interruption or an increase in a delay during the execution of USU communication. The method comprises: a first network element determining that a first terminal executes communication (i.e., USU communication) in a first communication mode, and sending first indication information to a first access network device, such that the first access network device senses that the first terminal executes communication in the first communication mode, and thus, when selecting a target access network device to which the first terminal is to be handed over, the first access network device can take into consideration the connection condition between a satellite where the target access network device is located and a peer serving satellite executing the USU communication, so as to select, as often as possible, a satellite that has an ISL with the peer serving satellite and has a relatively low ISL delay, thereby avoiding a service interruption (e.g., there being no ISL between a serving satellite after handover and a peer serving satellite) or an increase in a delay.

Description

Communication methods and communication devices

[0001] This application claims priority to Chinese Patent Application No. 202410710718.3, filed with the State Intellectual Property Office of China on May 31, 2024, entitled "Communication Method and Communication Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of communications, and more particularly to communication methods and communication devices. Background Technology

[0003] For scenarios where both the calling and called terminals access the network via satellite, the 3rd generation partnership project (3GPP) proposes terminal-satellite-terminal (or user equipment (UE)-satellite-UE (USU)) communication, which allows call data to be exchanged directly on satellite without passing through the terrestrial network. This can shorten transmission latency and improve user experience.

[0004] However, when satellites change (e.g., when a terminal switches to a different service satellite), it may cause interruptions or increased latency in USU communications' voice services. Summary of the Invention

[0005] The communication method and communication device provided in this application embodiment can avoid service interruption or increased latency during USU communication.

[0006] In a first aspect, a communication method is provided, comprising: a first network element determining that a first terminal performs communication in a first communication mode, and a first access network device sending first indication information. The first communication mode refers to data exchange between terminals via satellite, without terrestrial equipment. The first indication information instructs the first terminal to perform communication in the first communication mode, and the first access network device is deployed on a first satellite serving the first terminal.

[0007] In this embodiment of the application, the first network element sends a first indication information to the first access network device, which enables the first access network device to perceive that the first terminal is performing communication in the first communication mode (i.e., USU communication). As a result, when selecting the target access network device to be switched to by the first terminal, the first access network device can consider the connection between the satellite where the target access network device is located and the peer service satellite performing USU communication, so as to select the satellite with ISL and low ISL latency as much as possible. This can avoid service interruption (e.g., no ISL between the service satellite after switching and the peer service satellite) or increased latency.

[0008] In one possible implementation, the method provided in the first aspect further includes: a first network element sending first information to a first access network device, the first information including information about a second terminal, or information about a second satellite serving the second terminal, wherein the second terminal is a terminal that communicates with the first terminal using a first communication method. That is, the first network element can also send the first information to the first access network device, enabling the first access network device to obtain information about the second satellite serving the second terminal, and subsequently obtain ISL information (e.g., whether there is an ISL, or ISL latency) between each of the multiple candidate satellites corresponding to the first terminal and the second satellite. This allows the first access network device to determine a first target access network device based on the ISL information, thereby avoiding service interruption or increased latency.

[0009] In one possible implementation, the method provided by the first aspect further includes: a first network element receiving an identifier of a first target access network device from a first access network device, wherein the first target access network device is the target access network device to be handed over by the first terminal. That is, by sending first indication information and first information to the first access network device, the first network element can enable the first access network device to perceive that the first terminal is performing communication in a first communication mode based on the first indication information, and, based on the information of the second satellite, to select a satellite with a low ISL and / or low ISL latency as the target satellite to be handed over, thereby obtaining the identifier of the first target access network device deployed on the target satellite from the first access network device.

[0010] In one possible implementation, the method provided by the first aspect further includes: a first network element receiving second information from a first access network device, the second information including identification information of at least one target access network device for which the first terminal is to be handed over; the first network element determining a second target access network device from the at least one target access network device; and the first network element sending the identification of the second target access network device to the first access network device. That is, by sending at least one target access network device for which the first terminal is to be handed over to the first network element, the first access network device can, as a result, select, from the at least one target access network device, a target access network device deployed on a satellite with an ISL (Inter-Service Level) or low latency with the serving satellite of the peer as the second target access network device, and send the identification of the second target access network device to the first access network device. Thus, the first access network device can execute the handover procedure for the first terminal based on the second target access network device to avoid service interruption or increased latency.

[0011] In one possible implementation, the first network element determines a second target access network device from at least one target access network device based on information from a third satellite serving a third terminal. The third terminal is a terminal that communicates with the first terminal using a first communication method. In other words, the first network element can select, from the at least one target access network device, a target access network device deployed on a satellite that has an ISL (Independent Service Link) with the third satellite, as the second target access network device, based on information from the serving satellite (i.e., the third satellite) of the third terminal that has established a connection with the first terminal.

[0012] In one possible implementation, the first network element determines the second target access network device from at least one target access network device based on at least one of the following: inter-satellite link (ISL) information between the satellite where each target access network device is located and the third satellite; and latency information between the satellite where each target access network device is located and the third satellite. In other words, the first network element can, based on the ISL information and / or latency information between the satellite where each access network device is located and the third satellite, prioritize selecting target access network devices corresponding to satellites with low ISL and / or low latency with the third satellite as the second target access network device, thereby avoiding service interruption or increased latency after handover.

[0013] In one possible implementation, the method provided by the first aspect further includes: a first network element determining whether the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device or the second target access network device; if the first terminal cannot continue to perform communication in the first communication mode after switching to the first target access network device or the second access network device, the first network element triggers a switch from the first communication mode to the second communication mode, whereby data between terminals is exchanged through ground equipment. In other words, if the first network element determines that the first terminal cannot continue to perform communication in the first communication mode after switching to the first target access network device, the first network element can continue to enable service transmission for the first terminal by triggering a switch from the first communication mode to the second communication mode, thus avoiding service interruption.

[0014] In one possible implementation, the first network element determines, based on information from the second satellite, whether the first terminal can continue communication in the first communication mode after switching to the first target access network device; or, the first network element determines, based on information from the third satellite serving the third terminal, whether the first terminal can continue communication in the first communication mode after switching to the second target access network device, where the third terminal is the terminal communicating with the first terminal in the first communication mode. In other words, when the first network element determines that the first terminal is communicating in the first communication mode and determines that the target access network device to which the first terminal is to be switched is either the first target access network device or the second target access network device, the first network element can determine, based on information from the serving satellite of the peer, the connection status between the satellite where the first target access network device or the second target access network device is located and the serving satellite of the peer after the first terminal switches to the first target access network device or the second target access network device. This allows the first network element to determine whether the first terminal can continue communication in the first communication mode after switching to the first target access network device or the second target access network device, and whether a subsequent change in communication mode is necessary. This enables the first network element to complete the corresponding network function (NF) configuration in a timely manner, avoiding any impact on service transmission.

[0015] In one possible implementation, the method provided by the first aspect further includes: a first network element receiving second indication information from a first access network device, the second indication information indicating whether the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device; and the first network element determining, based on the second indication information, whether the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device. In other words, by sending the second indication information to the first network element, the first access network device enables the first network element to determine whether the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device, thereby determining whether a subsequent change in communication mode is necessary. This allows the first network element to complete the corresponding NF configuration in a timely manner, avoiding any impact on service transmission.

[0016] In one possible implementation, after the first terminal switches to the first target access network device, it can continue to perform communication in the first communication mode, specifically including at least one of the following: the satellite where the first target access network device is located maintains an ISL with the second satellite; the time for maintaining an ISL between the satellite where the first target access network device is located and the second satellite is greater than or equal to a first threshold; or, the time for maintaining an ISL between the satellite where the first target access network device is located and the second satellite is less than or equal to the second threshold is greater than or equal to a third threshold.

[0017] Alternatively, after the first terminal switches to the second target access network device, it can continue to perform communication in the first communication mode, specifically including at least one of the following: the satellite where the second target access network device is located maintains an ISL (Independent Service Level) with the third satellite serving the third terminal; the duration of maintaining the ISL between the satellite where the second target access network device is located and the third satellite is greater than or equal to a first threshold; or, the duration of maintaining the ISL between the satellite where the second target access network device is located and the third satellite is less than or equal to the second threshold and greater than or equal to the third threshold; wherein, the third terminal is the terminal that performs communication with the first terminal in the first communication mode. In other words, based on whether the satellite where the first target access network device is located maintains an ISL with the serving satellite (i.e., the second or third satellite), the duration of maintaining the ISL, and the duration of maintaining the ISL, the possibility of subsequent ISL interruption due to satellite and / or terminal movement can be considered in advance, further determining whether the first terminal can perform communication in the first communication mode after switching to the first target access network device, thereby avoiding service interruption or increased latency that may be caused by subsequent satellite switching.

[0018] In one possible implementation, the first network element triggers the conversion of the first communication mode to the second communication mode. Specifically, the first network element sends a third indication message to the Internet Protocol Multimedia Subsystem (IMS) network element serving the first terminal. The third indication message indicates that the first communication mode should be converted to the second communication mode. In other words, the first network element can trigger the IMS network element to convert the first communication mode to the second communication mode by sending the third indication message to the IMS network element serving the first terminal.

[0019] In one possible implementation, before the first network element determines that the first terminal is performing communication in the first communication mode, the method provided by the first aspect further includes: the first network element obtaining indication information from the IMS network element serving the first terminal, indicating that the first terminal is performing communication in the first communication mode. That is, the first network element can obtain the indication information from the IMS network element, and then determine that the first terminal is performing communication in the first communication mode based on the indication information.

[0020] In one possible implementation, the first network element determines that the first terminal performs communication using a first communication mode. Specifically, the first network element determines that the first terminal and the second terminal perform communication using the first communication mode based on the ISL (Inter-Satellite Link) duration maintained between the first satellite and the second satellite serving the second terminal. In other words, the first network element can consider the possibility of subsequent ISL interruptions due to satellite and / or terminal movement based on the ISL duration maintained between the first and second satellites, further determining whether the first terminal can perform communication using the first communication mode. This can help avoid service interruptions or increased latency that may result from subsequent satellite handover.

[0021] In a second aspect, a communication method is provided, comprising: a first access network device receiving first indication information from a first network element, the first indication information being used to instruct a first terminal to perform communication in a first communication mode, the first communication mode referring to data between terminals being exchanged via satellite and not through ground equipment, the first access network device being deployed on a first satellite serving the first terminal; the first access network device determining, based on the first indication information, a first target access network device to be switched to by the first terminal, or sending identification information of at least one target access network device to be switched to by the first terminal to the first network element.

[0022] It is understandable that the beneficial effects of the second aspect can be found in the first aspect, and will not be repeated here.

[0023] In one possible implementation, the method provided by the second aspect further includes: a first access network device receiving an identifier of a second target access network device from a first network element, wherein the second target access network device is a target access network device among at least one target access network devices. That is, by sending at least one target access network device to be handed over to the first network element, the first access network device can, as far as possible, select a target access network device deployed on a satellite with an ISL (Inter-Service Level) or low latency with the serving satellite of the other end as the second target access network device, and send the identifier of the second target access network device to the first access network device. Thus, the first access network device can execute the handover procedure for the first terminal based on the second target access network device to avoid service interruption or increased latency.

[0024] In one possible implementation, the method provided in the second aspect further includes: a first access network device receiving first information from a first network element, the first information including information about a second terminal, or information about a second satellite serving the second terminal, the information about the second terminal being used to obtain information about the second satellite, the second terminal being a terminal that communicates with the first terminal using a first communication method; the first access network device determining a first target access network device based on the first indication information and the information about the second satellite. That is, the first access network device can obtain information about the second satellite serving the second terminal by receiving the first information from the first network element, and then obtain ISL information (e.g., whether there is an ISL, or ISL latency, etc.) between each of the multiple candidate satellites corresponding to the first terminal and the second satellite, thereby determining the first target access network device based on the ISL information to avoid service interruption or increased latency.

[0025] In one possible implementation, the method provided in the second aspect further includes: a first access network device determining measurement configuration information based on information from the second satellite; and the first access network device sending the measurement configuration information to a first terminal. That is, the first access network device can determine the measurement configuration information based on information from the second satellite, and by sending the measurement configuration information to the first terminal device, the first terminal can then measure the signal of the access network device on the satellite with an ISL (Independent Signal Link) connection to the second satellite.

[0026] In one possible implementation, the method provided by the second aspect further includes: a first access network device receiving a measurement report from a first terminal; the first access network device specifically determining a first target access network device based on first indication information, information from the second satellite, and the measurement report. That is, the first access network device obtains multiple candidate access network devices from the measurement report of the first terminal, including access network devices on satellites with ISL (Independent Service Level) with the second satellite. Furthermore, it can determine the first target access network device based on the measurement results of each candidate access network device and the ISL between the satellite containing each candidate access network device and the second satellite, thereby avoiding service interruption or increased latency between the first terminal and the second terminal.

[0027] In one possible implementation, the priority among multiple measurement targets corresponding to the measurement configuration information is determined based on at least one of the following: ISL information between the satellite corresponding to each of the multiple measurement targets and the second satellite; and latency information between the satellite corresponding to each of the multiple measurement targets and the second satellite. That is, the first access network device can determine the priority among the multiple measurement targets corresponding to the measurement configuration information based on the ISL information and / or latency information between the satellite where the measurement target is located and the second satellite. This allows the first terminal to prioritize measuring the frequency points corresponding to satellites with ISL and / or low latency with the second satellite, thereby ensuring that the multiple candidate access network devices corresponding to the measurement report reported by the first terminal include access network devices on satellites with ISL with the second satellite.

[0028] In one possible implementation, the first target access network device is determined based on at least one of the following: inter-satellite link (ISL) information between the satellite where each candidate access network device is located and the second satellite; and latency information between the satellite where each candidate access network device is located and the second satellite. In other words, the first access network device can, based on the ISL information and / or latency information between the satellite where each candidate access network device is located and the second satellite, select, as far as possible, candidate access network devices corresponding to satellites with lower ISL and / or lower latency with the second satellite, thereby avoiding service interruption or increased latency after handover.

[0029] In one possible implementation, the method provided in the second aspect further includes: the first access network device sending second indication information to the first network element. The second indication information is used to indicate whether the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device. In other words, by sending the second indication information to the first network element, the first access network device enables the first network element to determine whether the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device, and thus determine whether a subsequent change in communication mode is necessary. This allows the first network element to complete the corresponding NF configuration in a timely manner, avoiding any impact on service transmission.

[0030] In one possible implementation, when the second indication information indicates that the first terminal cannot continue communication in the first communication mode after switching to the first target access network device, the second indication information is used to trigger a switch from the first communication mode to the second communication mode. The second communication mode refers to data exchange between terminals via ground equipment. In other words, when the second indication information indicates that the first terminal cannot continue communication in the first communication mode after switching to the first target access network device, the second indication information can trigger the first network element to switch from the first communication mode to the second communication mode, thereby continuing the service transmission of the first terminal and avoiding service interruption.

[0031] In one possible implementation, after the first terminal switches to the first target access network device, it can continue to perform communication in the first communication mode, specifically including at least one of the following: the satellite where the first target access network device is located maintains an ISL (Independent State Link) with the second satellite; the duration of maintaining the ISL between the satellite where the first target access network device is located and the second satellite is greater than or equal to a first threshold; or, the duration of maintaining the ISL between the satellite where the first target access network device is located and the second satellite is less than or equal to the second threshold is greater than or equal to a third threshold. In other words, based on whether the satellite where the first target access network device is located maintains an ISL with the second satellite, the duration of maintaining the ISL, and the duration of maintaining the ISL, the possibility of subsequent ISL interruptions due to satellite and / or terminal movement can be considered in advance. This further determines whether the first terminal can perform communication in the first communication mode after switching to the first target access network device, thereby avoiding service interruptions or increased latency that may result from subsequent satellite switching.

[0032] Thirdly, a communication method is provided, comprising: during a call establishment process between a first terminal and a second terminal, a first network element serving the first terminal obtains information about the service satellite of the second terminal; the first network element determines whether the first terminal performs communication in a first communication mode based on the time the service satellite of the first terminal and the service satellite of the second terminal maintain an inter-satellite link (ISL), wherein the first communication mode refers to data between terminals being exchanged via satellite without the use of ground equipment.

[0033] In this embodiment of the application, during the call setup process between the first terminal and the second terminal, the first network element can consider in advance the possibility of subsequent ISL interruption due to satellite and / or terminal movement based on the time the ISL connection is maintained between the two serving satellites. This allows for further determination of whether the first terminal can perform communication in the first communication mode (i.e., perform USU communication), thereby avoiding service interruption or increased latency that may result from subsequent satellite switching.

[0034] Fourthly, a communication method is provided, comprising: when a first terminal is to be switched to a target access network device and the first terminal is performing communication in a first communication mode, a first network element determines whether the first terminal can continue to perform communication in the first communication mode after switching to the target access network device, wherein the first communication mode refers to data between terminals being exchanged via satellite and not through ground equipment; and when the first terminal cannot continue to perform communication in the first communication mode after switching to the target access network device, the first network element triggers a switch from the first communication mode to a second communication mode, wherein the second communication mode refers to data between terminals being exchanged through ground equipment.

[0035] In the handover process of the first terminal in this application embodiment, when the first terminal performs communication in the first communication mode (i.e., USU communication), the first network element determines whether the first terminal can continue to perform USU communication after switching to the target access network device. If USU communication cannot continue, the USU communication is converted to the second communication (i.e., ground routing), thereby avoiding service interruption or increased latency after the handover.

[0036] Fifthly, a communication device is provided for implementing the various methods described above. This communication device can be a first network element or a first access network device in any of the above aspects or implementations thereof, or a device containing the first network element or the first access network device, or a device included in the first network element or the first access network device, such as a chip. The communication device includes modules, units, or means corresponding to the above methods, which can be implemented in hardware, software, or by hardware executing corresponding software. The hardware or software includes one or more modules or units corresponding to the above functions.

[0037] In some possible designs, the communication device may include a processing module and a transceiver module. The transceiver module, also referred to as a transceiver unit, is used to implement the transmission and / or reception functions in any of the above aspects and their possible implementations. The transceiver module may consist of transceiver circuits, transceivers, transceivers, or communication interfaces. The processing module can be used to implement the processing functions in any of the above aspects and their possible implementations.

[0038] In some possible designs, the transceiver module includes a sending module and a receiving module, which are used to implement the sending and receiving functions in any of the above aspects and any possible implementation methods.

[0039] A sixth aspect provides a communication device, comprising: at least one processor; said processor being configured to execute a computer program or instructions to cause the communication device to perform the method described in any of the preceding aspects.

[0040] In one possible implementation, the communication device further includes the memory. Optionally, the memory is coupled to the processor; the memory may be integrated with the processor, or the memory may be independent of the processor. Optionally, the processor is used to execute computer programs or instructions stored in the memory.

[0041] In one possible implementation, the memory is independent of the communication device.

[0042] In one possible implementation, the communication device further includes a communication interface for communicating with modules outside the communication device.

[0043] The communication device can be the first network element or the first access network device in any of the above aspects or any implementation thereof, or a device containing the first network element or the first access network device, or a device contained in the first network element or the first access network device, such as a chip.

[0044] In a seventh aspect, a computer-readable storage medium is provided, which stores a computer program or instructions that, when executed on a communication device, enable the communication device to perform the methods described in any of the above aspects or any implementation thereof.

[0045] Eighthly, a computer program product containing instructions is provided, which, when run on a communication device, enables the communication device to perform the methods described in any of the foregoing aspects or any implementation thereof.

[0046] Ninthly, a communication device (e.g., a chip or chip system) is provided, the communication device including a processor for implementing the functions involved in any of the above aspects or any implementation thereof.

[0047] In some possible designs, the communication device includes a memory for storing necessary program instructions and data.

[0048] In some possible designs, when the device is a chip system, it can be composed of chips or contain chips and other discrete components.

[0049] It is understood that when the communication device provided by any of the fifth to ninth aspects is a chip, the aforementioned sending action / function can be understood as an output, and the aforementioned receiving action / function can be understood as an input.

[0050] The technical effects of any of the design methods in aspects five through nine can be found in the technical effects of the different design methods in aspects one through four above, and will not be repeated here.

[0051] In a tenth aspect, a communication method is provided, which includes the method described in any of the foregoing aspects or any implementation thereof.

[0052] Eleventhly, a communication system is provided, comprising: the first network element described above and the first access network device described above. Attached Figure Description

[0053] Figure 1 is a schematic diagram of a non-terrestrial network (NTN) provided in an embodiment of this application;

[0054] Figure 2 is a schematic diagram of a centralized unit (CU) and distributed unit (DU) separation architecture provided in an embodiment of this application;

[0055] Figure 3 is a schematic diagram of an NG-RAN architecture based on NTN provided in an embodiment of this application;

[0056] Figure 4 is a schematic diagram of a 5GS architecture provided in an embodiment of this application;

[0057] Figure 5 is a schematic diagram of an EPS architecture provided in an embodiment of this application;

[0058] Figure 6 is a schematic diagram of an architecture for a terminal to access the IMS network via EPS or 5GS in a roaming scenario, as provided in an embodiment of this application.

[0059] Figures 7 and 8 are schematic diagrams of an architecture for USU communication provided in an embodiment of this application;

[0060] Figure 9 is a schematic diagram of a possible, non-limiting system architecture provided in an embodiment of this application;

[0061] Figures 10-18 are schematic flowcharts of a communication method provided in an embodiment of this application;

[0062] Figures 19 and 20 are schematic diagrams of the structure of a communication device provided in an embodiment of this application. Detailed Implementation

[0063] First, non-terrestrial networks (NTN):

[0064] Because traditional terrestrial networks (TN), such as new radio (NR) systems (also known as 5th generation (5G) systems) or the Internet of Things (IoT), cannot provide seamless coverage for terminals (e.g., in scenarios where communication is possible in physical areas where base stations cannot be deployed, such as the ocean, desert, or air), NR systems, IoT systems, and future communication systems can incorporate NTN to provide seamless coverage services for terminals.

[0065] NTN can deploy some or all of the functions of the radio access network (RAN) equipment in the TN on non-terrestrial network equipment (such as ships, high-altitude platforms, drones, or satellites) to provide communication coverage for terminals and improve the reliability of the communication system. It should be noted that, for ease of understanding, the following description uses the deployment of RAN equipment on a satellite as an example. This should not be construed as limiting the RAN equipment in this application to deployment on satellites. Satellites can also be replaced by other non-terrestrial network equipment, such as ships, high-altitude platforms, or drones. This application does not specifically limit this, and it will be uniformly described here and will not be elaborated further below.

[0066] Figure 1 is a schematic diagram of an NTN network architecture provided in an embodiment of this application. The network architecture may include: terminals, RAN, and core network (CN), which will be described below.

[0067] 1.1 Terminal:

[0068] In one possible implementation, the terminal can be a device for implementing wireless communication functions, such as a terminal or a chip that can be used in the terminal. Specifically, the terminal can be user equipment (UE), access terminal, terminal unit, terminal station, mobile station, mobile station, remote station, remote terminal, mobile device, terminal agent, or terminal device in a 5G network or a future evolved public land mobile network (PLMN). Access terminals can be cellular phones, cordless phones, Session Initiation Protocol (SIP) phones, Wireless Local Loop (WLL) stations, personal digital assistants (PDAs), handheld devices with wireless communication capabilities, computing devices or other processing devices connected to a wireless modem, in-vehicle devices, wearable devices, VR terminals, AR terminals, wireless terminals in industrial control, wireless terminals in self-driving, wireless terminals in remote medical care, wireless terminals in smart grids, wireless terminals in transportation safety, wireless terminals in smart cities, wireless terminals in smart homes, etc. In one possible implementation, the terminal can be mobile or fixed.

[0069] 1.2, RAN:

[0070] The RAN exists between the terminal and the CN, providing a communication connection between the two. The RAN is an entity used to transmit signals, or receive signals, or both transmit and receive signals.

[0071] In one possible implementation, the RAN equipment can also be referred to as an access node, RAN entity, RAN node, or equipment with base station processing capabilities. For example, RAN equipment can include non-terrestrial network equipment (or RAN devices) and TN-RAN equipment. RAN equipment can provide coverage for terminals by deploying base stations or partial base station functions on non-terrestrial equipment (such as satellites, high-altitude platforms, or drones). TN-RAN equipment can include base stations in NR systems (such as next-generation node B (gNodeB, gNB)), or one or a group of antenna panels (including multiple antenna panels) of a base station in 5G, or it can be a network node constituting a gNB, transmission and reception point (TRP or transmission point, TP), or transmission measurement function (TMF), such as a building base band unit (BBU), or a centralized unit (CU) or distributed unit (DU), an RSU with base station capabilities, or a wired access gateway, or a 5G CN network element. Alternatively, TN-RAN equipment may also include access points (APs) in wireless fidelity (Wi-Fi) systems, wireless relay nodes, wireless backhaul nodes, various forms of macro base stations, micro base stations (also known as small stations), relay stations, access points, wearable devices, vehicle-mounted equipment, etc. Alternatively, RAN equipment may also include: the RAN of future communication systems, or in future communication systems, the network equipment may have other naming conventions, all of which are covered within the protection scope of the embodiments of this application, and this application does not impose any limitations on them.

[0072] In one possible implementation, the RAN device may include a CU, DU, CU (control plane, CP), CU (user plane, UP), or radio unit (RU). The RAN device may also include an active antenna unit (AAU). The CU implements some of the network device's functions, and the DU implements some of the network device's functions. For example, the CU is responsible for handling non-real-time protocols and services, implementing the functions of the radio resource control (RRC) and / or packet data convergence protocol (PDCP) layers. The DU is responsible for handling physical layer protocols and real-time services, implementing the functions of the radio link control (RLC), media access control (MAC), and physical (PHY) layers. The AAU implements some physical layer processing functions, radio frequency processing, and related functions of the active antenna. Since RRC layer information ultimately becomes PHY layer information, or is derived from PHY layer information, in this architecture, higher-layer signaling, such as RRC signaling, can also be considered as being sent by the DU, or by the DU and AAU. It is understood that RAN devices can be one or more of the following: CU nodes, DU nodes, and AAU nodes. Furthermore, a CU can be classified as a network device within the RAN, or it can be classified as a network device within the CN; this application does not limit this classification.

[0073] In addition, the CU can be divided into a control plane (CU-CP) and a user plane (CU-UP), as illustrated below.

[0074] Figure 2 is a schematic diagram of a CU and DU separation architecture provided in an embodiment of this application. As shown in Figure 2, CU-CP is responsible for control plane functions, mainly including RRC and the corresponding PDCP (i.e., PDCP-C). PDCP-C is mainly responsible for encryption and decryption of control plane data, integrity protection, and data transmission. CU-UP is responsible for user plane functions, mainly including the Service Data Adaptation Protocol (SDAP) layer and the corresponding PDCP (i.e., PDCP-U). SDAP is mainly responsible for processing core network data and mapping flows to bearers. PDCP-U is mainly responsible for data plane encryption and decryption, integrity protection, header compression, sequence number maintenance, and data transmission. CU-CP and CU-UP are connected through the E1 interface. CU-CP represents the RAN device connected to the core network through the NG interface. The control plane (F1-C) and DU are connected through the F1 interface. CU-UP is connected to the user plane (F1-U) and DU through the F1 interface. Alternatively, PDCP-C may also be located within CU-UP.

[0075] It should be understood that CU (or CU-CP and CU-UP), DU, or RU may have different names in different systems, but those skilled in the art will understand their meaning. For example, in an open radio access network (O-RAN or ORAN) system, CU can also be called open CU (open CU, O-CU), DU can also be called open DU (open DU, O-DU), CU-CP can also be called open CU-CP (open CU-CP, O-CU-CP), CU-UP can also be called open CU-UP (open CU-UP, O-CU-UP), and RU can also be called open RU (open RU, O-RU). For ease of description, the embodiments of this application use 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 the embodiments of this application can be implemented by a software module, a hardware module, or a combination of a software module and a hardware module.

[0076] It should be understood that NTNs can be classified according to the satellite's operating mode, such as transparent mode architecture and regenerative mode architecture. In transparent mode architecture, the satellite's role is to perform radio frequency filtering, frequency conversion, and amplification. That is, in transparent mode, the satellite primarily acts as a layer 1 (L1) relay device, used to regenerate PHY signals (e.g., through radio frequency filtering, frequency conversion, or amplification), without involving other higher protocol layers (e.g., MAC, RLC, PDCP, SDAP, or RRC layers). Regenerative mode can refer to the satellite acting as a base station, possessing some or all of the base station's data processing capabilities.

[0077] The following examples, using the satellite's operating mode as regeneration mode and CN as 5G CN, illustrate several RAN architectures based on NTN, along with accompanying diagrams.

[0078] Figure 3 is a schematic diagram of an NTN-based NG-RAN architecture provided in an embodiment of this application. As shown in Figure 3, satellites #1 and #2 operate in regeneration mode. This NG-RAN architecture includes satellites (including satellites #1 and #2) and NTN gateways (including NTN gateway #1 and NTN gateway #2). The satellites have base station capabilities and can thus act as RAN devices to provide services to terminals. For example, satellite #1 provides access services to terminal #1, and satellite #2 provides access services to terminal #2. The satellites can access the 5G CN through the NTN gateways and then connect to the data network (DN) for communication (the interface between the 5G CN and DN is N6). The transmission link between the satellites and the NTN gateways can be called a feeder link (FL), and the interface between the satellites and the NTN gateways can be a satellite radio interface (SRI). Furthermore, the interface between the terminal and the satellite is NR-Uu, and the interface between the satellite and the 5G-CN is NG.

[0079] As shown in Figure 3, satellite #1 and satellite #2 have an inter-satellite link (ISL), which is a transmission link between satellites. It can be understood that satellite #1 can be directly or indirectly (e.g., via relay from other satellites) connected to satellite #2. An ISL refers to a direct or indirect connection between two satellites (e.g., via relay from other satellites). This will be explained uniformly here and will not be elaborated further below.

[0080] In addition, the ISL can be a wireless interface or an optical interface. The specific ISL can be defined by the 3rd generation partnership project (3GPP), for example, using the Xn interface, without specific limitations.

[0081] 1.3, CN:

[0082] CN is primarily responsible for maintaining the subscription data of the mobile network and providing terminals with functions such as session management, mobility management, policy management, and security authentication.

[0083] The following explanation will use the 5G system (5GS) as an example.

[0084] For 5GS, CN mainly includes all or some of the following functions: user plane function (UPF), authentication server function (AUSF), access and mobility management function (AMF), session management function (SMF), network slice selection function (NSSF), network exposure function (NEF), network repository function (NRF), policy control function (PCF), unified data management (UDM), unified data repository (UDR), and application function (AF).

[0085] Figure 4 is a schematic diagram of a 5GS architecture provided in an embodiment of this application. As shown in Figure 4, the UE accesses the 5G network through the RAN device. The UE communicates with the AMF through the N1 interface (N1 for short); the RAN communicates with the AMF through the N2 interface (N2 for short); the RAN communicates with the UPF through the N3 interface (N3 for short); the SMF communicates with the UPF through the N4 interface (N4 for short); and the UPF accesses the DN through the N6 interface (N6 for short). In addition, the control plane functions such as AUSF, AMF, SMF, NSSF, NEF, NRF, PCF, UDM, UDR, or AF shown in Figure 1 interact using service-oriented interfaces. For example, AUSF provides the service interface Nausf; AMF provides the service interface Namf; SMF provides the service interface Nsmf; NSSF provides the service interface Nnssf; NEF provides the service interface Nnef; NRF provides the service interface Nnrf; PCF provides the service interface Npcf; UDM provides the service interface Nudm; UDR provides the service interface Nudr; and AF provides the service interface Naf.

[0086] The User-Defined Processing (UPP) is primarily responsible for user data processing (forwarding, receiving, billing, etc.). For example, a UPF can receive user data from a Data Network (DN) and forward it to the terminal via the RAN. Alternatively, a UPF can receive user data from the terminal via the RAN and forward it to the DN. A DN refers to the operator's network that provides data transmission services to users. Examples include Internet Protocol (IP) Multimedia Service (IMS) networks and the Internet. A DN can be an external network of the operator or a network controlled by the operator, used to provide services to terminals. In a Protocol Data Unit (PDU) session, the UPF directly connected to the DN via N6 is also called the Protocol Data Unit Session Anchor (PSA).

[0087] AUSF is primarily used to perform security authentication for terminals.

[0088] AMF is primarily used for mobility management in mobile networks. Examples include user location updates, user network registration, and user handover.

[0089] SMF is primarily used for session management in mobile networks. This includes session establishment, modification, and release. Specific functions include assigning Internet Protocol (IP) addresses to users and selecting a UPF (User-Defined Provider) to handle packet forwarding.

[0090] The PCF primarily supports providing a unified policy framework to control network behavior, delivering policy rules to control-layer network functions, and acquiring user subscription information related to policy decisions. The PCF can provide policies to the AMF and SMF, such as Quality of Service (QoS) policies and slice selection policies.

[0091] NSSF is primarily used to select network slices for terminals.

[0092] NEF is primarily used to support the opening of capabilities and events.

[0093] UDM is primarily used to store user data, such as contract data and authentication / authorization data.

[0094] UDR is primarily used to store structured data, including contract data, policy data, externally exposed structured data, and application-related data.

[0095] AF primarily supports interaction with CN to provide services, such as influencing data routing decisions, policy control functions, or providing third-party services to the network side.

[0096] As can be understood, as described in the preamble of the detailed implementation, the evolved packet system (EPS) (or 4G system) can also be integrated into NTN. EPS will be introduced below.

[0097] Figure 5 is a schematic diagram of an EPS architecture provided in an embodiment of this application. As shown in Figure 5, the EPS includes: evolved UMTS territorial radio access network (E-UTRAN) equipment, mobility management entity (MME), serving gateway (SGW), packet data network (PDN) gateway (PGW), policy and charging rules function (PCRF) network element, and home subscriber server (HSS) and other network elements or equipment.

[0098] The terminal accesses the E-UTRAN device via LTE-Uu. The E-UTRAN device communicates with the MME via S1-MME, and with the SGW via S1-U. Different MMEs communicate with each other via S10 (Figure 1 only shows one MME as an example). The MME communicates with the HSS via S6a, and with the SGW via S11. The SGW communicates with the PGW via S5, the PGW accesses the server via SGi, the PGW communicates with the PCRF via Gx, and the PCRF communicates with the server via Rx.

[0099] Optionally, for backward compatibility with the general packet radio service (GPRS) data services provided by second-generation (2G) or third-generation (3G) systems, and to better achieve interoperability between EPS and 2G / 3G systems, as shown in Figure 5, the EPS may also include UTRAN or Global System for Mobile Communication (GSM) or GSM / EDGE radio access network (GERAN) equipment of 2G or 3G systems, as well as serving GPRS support node (SGSN). These participate in the inter-system mobility of the terminal between the EPS system and the 2G / 3G system, including idle-state mobility and connected-state handover. This will be explained uniformly here and will not be repeated below. When a terminal accesses a 2G / 3G system, the terminal communicates with the SGSN through the UTRAN / GERAN equipment, the UTRAN / GERAN equipment communicates with the SGW through S12, the SGSN communicates with the MME through S3, and the SGSN communicates with the SGW through S4.

[0100] It is understood that the functions mentioned in the embodiments of this application can also refer to functional network elements or functional entities. For example, UPF can be referred to as UPF network element, AMF can be referred to as AMF network element, SMF can be referred to as SMF network element, PCF can be referred to as PCF network element, and so on, without limitation.

[0101] In addition, the terms "function" and "functional network element" are used interchangeably in the following text. For example, "PCF" and "PCF network element" have the same meaning. This will be explained uniformly here and will not be repeated below.

[0102] Second, IMS:

[0103] As mentioned above regarding DN, DN can include the IMS network, thereby providing voice services (such as calls or voice and video) to the terminal. The following section describes in detail how to access the IMS network via EPS or 5GS.

[0104] Figure 6 is a schematic diagram of the architecture of a terminal accessing the IMS network via EPS or 5GS in a roaming scenario according to an embodiment of this application. As shown in Figure 6, the architecture includes: accessing the visited public land mobile network (VPLMN), the home public land mobile network (HPLMN), and the IMS network.

[0105] In roaming scenarios, the terminal (i.e., UE) can access the VPLMN using the 3GPP access type, or access the HPLMN using a non-3GPP access type.

[0106] The IMS network includes: Proxy Call Session Control Function (P-CSCF), Serving CSCF (S-CSCF), IMS Access Gateway (IMS-AGW), and Media Resource Function Processor (MRFP).

[0107] The P-CSCF is the first access point in the IMS network. The P-CSCF behaves like a proxy, accepting requests and serving them internally or forwarding them upwards. For example, as shown in Figure 6, the visiting PCRF in the VPLMN corresponding to EPS, or the visiting PCF in the VPLMN corresponding to 5GS (referred to as V-PCF), can communicate with the home PCRF in the HPLMN (referred to as H-PCRF) via S9. The H-PCRF accesses the P-CSCF via Rx.

[0108] The S-CSCF is used to perform session control services for the UE. The S-CSCF maintains session state as needed by the network operator to support services. For example, as shown in Figure 6, the P-CSCF can access the S-CSCF via Mx.

[0109] MRFP is used to provide media plane resources for voice services.

[0110] IMS-AGW is used to provide access services on the media plane. Specifically, IMS-AGW can access P-CSCF via Iq or MRFP.

[0111] It is understandable that the difference between non-roaming and roaming scenarios is that EPS or 5GS is located within HPLMN and has no V-PCRF or V-PCF.

[0112] Third, terminal-satellite-terminal (or UE-satellite-UE, USU) communication:

[0113] USU communication refers to the exchange of data between terminals using satellites within the coverage area of ​​one or more serving satellites, without passing through a ground segment.

[0114] It is understandable that if data between terminals (such as IMS call-related data) is not exchanged through terrestrial network elements (such as the UPF in Figure 4, or the IMS-AGW in the IMS system in Figure 6) (or referred to as terrestrial routing), but is exchanged directly on the satellite, transmission latency can be shortened. For example, assuming that terminals #1 and #2 serve the same satellite, the data route between terminals #1 and #2 is from terminal #1 through the serving satellite directly to terminal #2. Alternatively, if terminals #1 and #2 serve different satellites, the data route between terminals #1 and #2 is from terminal #1 through its serving satellite #1, and then through the ISL between serving satellite #1 and terminal #2's serving satellite #2, reaching serving satellite #2, and finally reaching terminal #2 through serving satellite #2.

[0115] It is understandable that in USU communication, if voice data needs to be exchanged on the satellite, the satellite's working mode needs to be regenerable mode, and the satellite needs to have the relevant functions of CN network elements deployed (e.g., at least UPF deployed on the satellite), or the relevant functions of CN network elements and IMS network elements (e.g., at least UPF and IMS-AGW deployed on the satellite). The following explanation is based on Figures 7 and 8.

[0116] Figure 7 is a schematic diagram of a USU communication architecture provided in an embodiment of this application. As shown in Figure 7(a), a UPF is also deployed on the satellite. For data between terminal #1 and terminal #2, the communication route includes, in sequence: UE#1, UPF on the satellite, and UE#2. For IMS signaling, the communication route includes, in sequence: UE#1, satellite, NTN gateway, UPF on the ground, IMS on the ground, UPF on the ground, NTN gateway, satellite, and UE#2.

[0117] It is understandable that in Figure 7(a), UE#1 and UE#2 have the same serving satellite. When the serving satellite of UE#1 and UE#2 are different, they can transmit data through ISL, such as data related to IMS calls.

[0118] For example, as shown in Figure 7(b), the serving satellite of UE#1 is satellite #1, and the serving satellite of UE#2 is satellite #2. The main difference between Figure 7(b) and Figure 7(a) is that satellite #1 and satellite #2 have an ISL, and the communication link (or communication route) between UE#1 and UE#2 also includes the ISL between satellite #1 and satellite #2.

[0119] Figure 8 is a schematic diagram of a USU communication architecture provided in an embodiment of this application. As shown in Figure 8, the main difference between Figure 7 and Figure 8 is that, in addition to the UPF, an IMS-AGW is also deployed on the satellite. In other words, in Figure 7, the network elements in the IMS network (such as P-CSCF, S-CSCF, and IMS-AGW in Figure 6) are deployed on the ground, while in Figure 8, the IMS-AGW is deployed on the satellite.

[0120] It is understandable that during the call setup process, the network (e.g., CN and / or IMS network) determines whether (or is able to) perform USU communication between the two communicating parties (i.e., UE#1 and UE#2). If so, the network can configure UPF on the satellite (e.g., the satellite in Figure 7) or UPF and IMS-AGW on the satellite (e.g., the satellite in Figure 8) for UE#1 and UE#2, thereby enabling USU communication.

[0121] It should be understood that during USU communication, as the satellite and / or terminal move, the terminal's serving satellite may change (e.g., the terminal switches serving satellites), which may cause voice service interruptions or increased latency, thereby affecting the user experience.

[0122] Specifically, in scenarios where satellite and / or terminal movement leads to satellite switching, the UPF and IMS-AGW will change (i.e., redirection), which may result in the UPF or IMS-AGW deployed on the two service satellites being unable to communicate due to the lack of ISL between the switched service satellites.

[0123] In addition, even if there is an ISL between the two serving satellites after the switch, the two serving satellites may not be directly connected, but may be relayed through one or more other satellites. This may lead to complex communication link configuration or large latency (e.g., greater than the latency of ground routing), which may result in increased latency for voice services.

[0124] To address the aforementioned technical problems, this application provides the following technical solutions, which will be described below with reference to the accompanying drawings.

[0125] In the embodiments 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 is called the information to be instructed. In the specific implementation process, there are many ways to instruct the information to be instructed, such as, but not limited to, directly instructing the information to be instructed, such as the information to be instructed itself or its index. It can also indirectly instruct the information to be instructed by instructing other information, where there is a relationship between the other information and the information to be instructed. It can also instruct only a part of the information to be instructed, while the other parts are known or pre-agreed upon. For example, 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. At the same time, common parts of various pieces of information can be identified and uniformly indicated to reduce the instruction overhead caused by individually indicating the same information.

[0126] Furthermore, the specific indication method can also be any existing indication method, such as, but not limited to, the above-mentioned indication methods and their various combinations. Specific details of various indication methods can be found in existing technologies, and will not be repeated here. As described above, for example, when multiple pieces of information of the same type need to be indicated, the indication methods for different pieces of information may differ. In the specific implementation process, the required indication method can be selected according to specific needs. This application embodiment does not limit the selected indication method; therefore, the indication methods involved in this application embodiment should be understood to cover various methods that enable the party to be indicated to obtain the information to be indicated.

[0127] It should be understood that the information to be indicated can be sent as a whole or divided into multiple sub-information messages sent separately, and the sending period and / or timing of these sub-information messages can be the same or different. The specific sending method is not limited in this application embodiment. The sending period and / or timing of these sub-information messages can be predefined, for example, according to a protocol, or configured by the sending device by sending configuration information to the receiving device.

[0128] In this application, "sending information" can be understood as one device (or communication entity) sending information to another device (or communication entity), or it can be understood as one logic module within a device sending information to another logic module. For example, "SMF sending information" can be understood as the SMF sending information to another device (such as the AMF), or it can be understood as logic module 1 in the SMF sending information to logic module 2 in another device.

[0129] In this application, "receiving information" can be understood as one device (or communication entity) receiving information from another device (or communication entity), or it can be understood as a logical module within a device receiving information from another logical module. For example, "access network device (or access network element) receiving information" can be understood as the access network device receiving information from another device (such as an AMF), or it can be understood as logical module 1 in the access network device receiving information from logical module 2 in another device.

[0130] In this application, the phrase "sending information to... (e.g., access network equipment)" or the related illustrations in the accompanying drawings can be understood as the destination of the information being the orchestration function. This can include sending information directly or indirectly to the orchestration function. Similarly, the phrases "receiving information from... (e.g., access network equipment)," "receiving information from... (e.g., access network equipment)," or "receiving information sent (e.g., by access network equipment)," or the related illustrations in the accompanying drawings, can be understood as the source of the information being the access network equipment. This can include receiving information directly or indirectly from the access network equipment. Information may undergo necessary processing between the source and destination, such as format changes, but the destination can understand the valid information from the source. Similar expressions in this application can be interpreted similarly, and will not be elaborated further here.

[0131] "Predefined" or "pre-configured" can be achieved by pre-saving corresponding codes, tables, or other means that can be used to indicate relevant information in the device. This application does not limit the specific implementation method. "Saving" can refer to saving in one or more memories. These memories can be separate installations or integrated into the encoder, decoder, processor, or communication device. Alternatively, some memories can be separately installed, while others are integrated into the decoder, processor, or communication device. The type of memory can be any form of storage medium, and this application does not limit this.

[0132] The “protocol” mentioned in the embodiments of this application may refer to a protocol family in the field of communication, a standard protocol with a similar protocol family frame structure, or a related protocol applied to future communication systems. The embodiments of this application do not specifically limit this.

[0133] In the embodiments of this application, descriptions such as "when," "under the circumstances," "if," and "if" all refer to the device making corresponding processing under certain objective circumstances, and are not limited to a specific time. They do not require the device to make a judgment action during implementation, nor do they imply any other limitations.

[0134] In the description of the embodiments of this application, unless otherwise stated, " / " indicates that the objects before and after are in an "or" relationship. For example, A / B can represent A or B. "And / or" in the embodiments of this application 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, where A and B can be singular or plural. Furthermore, in the description of the embodiments of this application, unless otherwise stated, "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 plural items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple. Additionally, to facilitate a clear description of the technical solutions of the embodiments of this application, the terms "first" and "second" are used in the embodiments of this application to distinguish identical or similar items with essentially the same function and effect. Those skilled in the art will understand that the terms "first," "second," etc., do not limit the quantity or order of execution, and that "first," "second," etc., are not necessarily different. Furthermore, in the embodiments of this application, words such as "exemplary" or "for example" are used to indicate that something is being used as an example, illustration, or description. Any embodiment or design scheme described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design schemes. Specifically, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner for ease of understanding.

[0135] The network architecture and business scenarios described in the embodiments of this application are for the purpose of more clearly illustrating the technical solutions of the embodiments of this application, and do not constitute a limitation on the technical solutions provided in the embodiments of this application. As those skilled in the art will know, with the evolution of network architecture and the emergence of new business scenarios, the technical solutions provided in the embodiments of this application are also applicable to similar technical problems.

[0136] To facilitate understanding of the embodiments of this application, a communication system will be used as an example to describe in detail the communication system applicable to the embodiments of this application.

[0137] Figure 9 is a schematic diagram of a possible, non-limiting system architecture provided by an embodiment of this application. As shown in Figure 9, the system includes a first network element and a first access network device. The first network element is a network element that provides services to a first terminal. For example, the first network element can be a network element in the IMS network that provides services to the first terminal, such as a P-CSCF or S-CSCF. Alternatively, the first network element can be a network element in the CN that provides services to the first terminal, such as an SMF in a 5GS CN that provides IMS PDU session services to the first terminal, or a PGW in an EPS that provides IMS PDN session services to the first terminal. This embodiment of the application does not specifically limit this. Furthermore, the voice session can be, for example, an IMS PDU session, that is, the DN name (DNN) corresponding to the PDU session is an IMS PDU session.

[0138] The first access network device can refer to the access network device that provides access services to the first terminal. For details regarding the first access network device, please refer to the relevant explanations in "1.2, RAN" and "Third, USU Communication" in the preamble of the specific implementation method; these will not be repeated here.

[0139] To address the issue that changes in the serving satellite of the terminal during USU communication may lead to voice service interruptions or increased latency, the system shown in Figure 9 provides the following three solutions:

[0140] Option 1: The first network element determines that the first terminal is communicating using a first communication mode and sends first indication information to the first access network device. The first communication mode refers to data exchange between terminals via satellite, without terrestrial equipment. The first indication information instructs the first terminal to communicate using the first communication mode. The first access network device is deployed on a first satellite serving the first terminal.

[0141] In other words, by sending a first instruction to the first access network device, the first network element can enable the first access network device to perceive that the first terminal is performing communication in the first communication mode (i.e., USU communication). This allows the first access network device to consider the connection between the satellite where the first terminal is located and the peer service satellite performing USU communication when selecting the target access network device to be switched to. In order to select a satellite with an ISL and a low ISL latency as much as possible, the first access network device can avoid service interruption (e.g., no ISL between the service satellite after the switch and the peer service satellite) or increased latency.

[0142] Option 2: During the call setup process between the first terminal and the second terminal, the first network element serving the first terminal obtains information about the serving satellite of the second terminal and determines whether the first terminal should perform communication using the first communication mode based on the time the inter-satellite link (ISL) is maintained between the serving satellites of the first and second terminals. The first communication mode refers to data exchange between terminals via satellite, without relying on ground equipment.

[0143] In other words, during the call setup process between the first terminal and the second terminal, the first network element can consider the possibility of subsequent ISL interruption due to satellite and / or terminal movement based on the time the ISL connection between the two serving satellites is maintained. This allows it to further determine whether the first terminal can perform communication in the first communication mode (i.e., perform USU communication), thereby avoiding service interruption or increased latency that may result from subsequent satellite switching.

[0144] Option 3: When the first terminal is about to switch to the target access network device and is communicating using the first communication mode, the first network element determines whether the first terminal can continue communicating using the first communication mode after switching to the target access network device. If the first terminal cannot continue communicating using the first communication mode after switching to the target access network device, the first network element triggers a switch from the first communication mode to the second communication mode. The first communication mode refers to data exchange between terminals via satellite without using ground equipment. The second communication mode refers to data exchange between terminals via ground equipment.

[0145] In other words, during the handover process of the first terminal, when the first terminal performs communication in the first communication mode (i.e., USU communication), the first network element determines whether the first terminal can continue to perform USU communication after handover to the target access network device. If USU communication cannot continue, the USU communication is switched to the second communication mode (i.e., ground routing), thereby avoiding service interruption or increased latency after handover.

[0146] For ease of understanding, the technical terms used in the embodiments of this application will be introduced below:

[0147] 1) First communication method. This first communication method has the same meaning as the USU communication in "Third, USU communication" in the preamble of the specific implementation method. The two can be used interchangeably. This is explained in a unified manner here and will not be repeated below.

[0148] 2) Second communication method. This second communication method has the same meaning as the ground routing in "Third, USU communication" in the preamble of the specific implementation method. The two can be used interchangeably. This is explained in a unified manner here and will not be repeated below.

[0149] 3) The first access network device, which may refer to a RAN network element or device that provides access services to the first terminal, is deployed on the first satellite. Furthermore, during the handover process of the first terminal, the first access network device serves as the source access network device for the first terminal.

[0150] Similarly, the access network equipment involved in the embodiments of this application can refer to a RAN network element or equipment that provides access services to a terminal. Additionally, the second satellite can refer to a satellite on which access network equipment serving a second terminal is deployed.

[0151] 4) The first target access network device, which may refer to the target access network device to which the first terminal is to be switched, as determined by the first access network device.

[0152] 5) At least one target access network device, wherein the at least one target access network device may refer to a candidate target access network device that the first access network device sends to the first network element for the first network element to determine.

[0153] 6) A second target access network device, wherein the second target access network device is the target access network device for the first terminal handover determined by the first network element from the above-mentioned at least one target access network device.

[0154] It should be understood that as the network evolves, the system shown in Figure 9 may also support or include other network functions, such as AI or sensing-related functions, and the embodiments of this application do not specifically limit this.

[0155] The interaction process between network elements / devices in the system shown in Figure 9 above will be specifically described below with reference to Figures 10 to 18 through a method embodiment. The communication method provided in this application embodiment can be applied to the above system and specifically applied to the various scenarios / processes mentioned in the above system.

[0156] The following section will first introduce Option 1.

[0157] Figure 10 is a flowchart illustrating a communication method provided in an embodiment of this application. This communication method is applicable to Scheme 1 provided by the system shown in Figure 9 above, and mainly involves the interaction between a first network element and a first access network device. As shown in Figure 10, the communication method includes:

[0158] S1001, The first network element determines that the first terminal performs communication in a first communication mode, wherein the first communication mode refers to the data between terminals being exchanged via satellite and without the use of ground equipment.

[0159] S1002, the first network element sends a first instruction message to the first access network device. Correspondingly, the first access network device receives the first instruction message from the first network element. The first instruction message instructs the first terminal to perform communication using a first communication method. The first access network device is deployed on a first satellite serving the first terminal.

[0160] It is understood that the first access network device, based on the first instruction information, senses that the first terminal is performing communication in the first communication mode. Therefore, during the handover, the first access network device can consider the connection between the satellite where the target access network device is located and the peer service satellite connected to the first terminal, so as to select the satellite with an ISL and a low ISL latency as the target satellite to be handed over, thereby avoiding service interruption (e.g., no ISL between the service satellite after handover and the peer service satellite) or increased latency.

[0161] In addition, considering that the first access network device may not be able to obtain the service satellites of the other end, the first access network device can select multiple target access network devices to report to the CN, and then the CN can determine the target access network device for final handover.

[0162] It is understood that the above steps S1001 and S1002 can occur during the call connection establishment process. For example, the first indication information can be sent to the first access network device during the process of the first network element configuring a call-dedicated bearer for the first terminal (e.g., a bearer or QoS flow in which the quality of service (QoS) class identifier (QCI) or 5G quality identity (5QI) is equal to 1 in an IMS PDN connection or PDU session).

[0163] In one possible implementation, the method shown in Figure 10 includes:

[0164] S1003. The first access network device determines the first target access network device to be switched to by the first terminal according to the first instruction information.

[0165] In another possible implementation, the method shown in Figure 10 includes:

[0166] S1004. The first access network device sends the identification information of at least one target access network device to be switched by the first terminal to the first network element according to the first instruction information.

[0167] Steps S1001 to S1004 are described below.

[0168] For step S1001:

[0169] It is understood that the first network element in Figure 10 can be a CN network element serving the first terminal, such as PCF or SMF in 5GS, or MME or PGW in EPS, etc. For details, please refer to the relevant description of the first network element in the communication system shown in Figure 9, which will not be repeated here.

[0170] In addition, the first network element can use various methods to determine that the first terminal performs communication in the first communication mode, which will be described in detail below.

[0171] In one possible implementation, before the first network element determines that the first terminal is performing communication in the first communication mode, the method provided in Figure 10 further includes:

[0172] S1005. The first network element obtains instruction information from the IMS network element serving the first terminal, which is used to instruct the first terminal to perform communication in the first communication mode.

[0173] It can be understood that the IMS network element can be the P-CSCF in Figure 6. The IMS network element can obtain relevant information about the second terminal that has established a connection (e.g., a call connection) with the first terminal (e.g., the access network information of the second terminal), and then determine whether the two can perform communication in the first communication mode under the first condition. The first condition can be, for example, that the first terminal and the second terminal are served by the same satellite (i.e., the first satellite also provides access service to the second terminal), or that the first satellite and the second satellite serving the second terminal have an ISL (Independent Communication Link). It should be understood that ISL can refer to a direct communication link between two satellites, or it can refer to an indirect communication link between two satellites (e.g., relayed by other satellites). This will be explained uniformly here and will not be elaborated further below.

[0174] In addition, the second satellite serving the second terminal can specifically refer to the second access network equipment serving the second terminal being deployed on the second satellite.

[0175] It can be understood that the above-mentioned communication between the first terminal and the second terminal using the first communication method can also refer to: the UPF corresponding to the data transmission session between the first terminal and the second terminal being deployed on the first satellite and the second satellite respectively; or, the UPF and IMS-AWG corresponding to the data transmission session between the first terminal and the second terminal being deployed on the first satellite and the second satellite respectively.

[0176] Furthermore, the first network element can obtain the aforementioned indication information directly or indirectly from the IMS network element. For example, assuming the first network element is an SMF, the SMF can directly interact with the P-CSCF to obtain the indication information in step S1005. Alternatively, the SMF can indirectly obtain the aforementioned indication information from the P-CSCF through the PCF serving the first terminal; this embodiment of the application does not specifically limit this.

[0177] It should be understood that the first network element obtaining the above-mentioned indication information from the IMS network element may mean that: the first network element sends a request to the IMS network element, and then the IMS network element can send the above-mentioned indication information to the first network element; or, the first network element directly receives the indication information from the IMS network element. This application embodiment does not specifically limit this.

[0178] In other words, the first network element can obtain instruction information from the IMS network element to instruct the first terminal to perform communication in the first communication mode, and then determine the first terminal to perform communication in the first communication mode based on the instruction information.

[0179] In another possible implementation, the first network element determines that the first terminal performs communication in a first communication mode, including:

[0180] The first network element determines that the first terminal and the second terminal communicate using a first communication method based on the existence of an ISL between the first satellite and the second satellite serving the second terminal.

[0181] It is understandable that the second terminal can be a terminal that establishes a connection with the first terminal, which will not be elaborated here.

[0182] Additionally, the first network element can obtain information about the second terminal (e.g., the identifier of the second terminal) or information about the second satellite from the IMS network element. Specifically, the first network element can obtain information about the second satellite from other network elements based on the information about the second terminal. For example, the first network element can obtain information about the second satellite from the CN network element serving the second terminal based on the identifier of the second terminal. It is understood that the information about the second terminal also includes other information about the second terminal, such as the session identifier of the second terminal, etc., which is not specifically limited in this embodiment. Furthermore, the information about the second satellite may include, for example, the identifier, constellation, ephemeris, or orbit of the second satellite, etc., which is not specifically limited in this embodiment.

[0183] It should be understood that for the first network element to obtain the second satellite information from the IMS network element, for example in the process of establishing a call connection between the first terminal and the second terminal, the CN network element serving the second terminal can send the second satellite information to the IMS network element serving the first terminal through the IMS network element serving the second terminal, and thus the first network element can obtain the second satellite information from the IMS network element serving the first terminal.

[0184] It is understood that the above-mentioned information about the first network element obtaining information about the second terminal or the second satellite is only an example. Other methods can also be used to obtain information about the second terminal or the second satellite. This application embodiment does not specifically limit this.

[0185] In other words, the first network element can obtain information from the second satellite, and then determine that the first terminal and the second terminal communicate using the first communication method based on the existence of an ISL between the first satellite and the second satellite.

[0186] It is understandable that the two implementation methods for determining that the first terminal performs communication in the first communication mode can be combined. For example, after the first network element obtains the indication information in step S1005 from the IMS network element, it can further determine whether the first terminal and the second terminal can perform communication in the first communication mode based on whether there is an ISL between the first satellite and the second satellite, or the connection status of the ISL. This will be described in detail below.

[0187] In one possible implementation, the first network element determines that the first terminal performs communication in a first communication mode, specifically including:

[0188] The first network element determines that the first terminal and the second terminal communicate using the first communication method based on the ISL (Inter-Service Level) maintenance time between the first satellite and the second satellite serving the second terminal.

[0189] It is understandable that if the ISL (Inter-Satellite Link) maintenance time between the first and second satellites is short, satellite handover may occur before the first and second terminals have completed service transmission, thereby increasing the risk of service interruption or increased latency. Furthermore, the first network element can determine the ISL maintenance time between the first and second satellites based on the terminal's location, satellite constellation, satellite ephemeris, satellite orbit, or ISL, etc., depending on the actual implementation of the first network element; this application embodiment does not impose specific limitations on this.

[0190] In other words, the first network element can consider the possibility of subsequent ISL interruption due to satellite and / or terminal movement based on the time the ISL connection is maintained between the first satellite and the second satellite. This allows it to further determine whether the first terminal can perform communication in the first communication mode, thereby avoiding service interruption or increased latency that may result from subsequent satellite handover.

[0191] For example, the first network element can determine that the first terminal and the second terminal will communicate using a first communication method based on the fact that the ISL (Independent State Link) time between the first satellite and the second satellite is greater than or equal to a first threshold. The first threshold can be predefined by the protocol, or negotiated in advance between the first network element and the second network element serving the second terminal (e.g., an IMS network element, SMF, or PCF serving the second terminal), or indicated by the network. This application embodiment does not specifically limit this.

[0192] For example, the first threshold can be defined by the operator's policy. For instance, the first threshold can be determined based on the average call duration based on big data statistics, or it can be determined based on the average call duration of satellite calls, or it can be determined based on the average call duration of user personalization based on statistics.

[0193] In one possible implementation, the time during which the first satellite and the second satellite maintain an ISL can refer to the time during which the ISL delay between the first satellite and the second satellite is less than or equal to a second threshold.

[0194] It is understood that, considering the impact of latency on services, the time during which the first satellite and the second satellite maintain an ISL specifically refers to the time during which the latency of the ISL meets the service communication latency requirements, that is, the time during which the ISL latency is less than or equal to the second threshold. The second threshold can be predefined by the protocol, or negotiated in advance between the first network element and the second network element serving the second terminal (e.g., an IMS network element, SMF, or PCF serving the second terminal), or indicated by the network. This application embodiment does not specifically limit this.

[0195] For example, the second threshold may be defined by the operator's policy. For instance, the second threshold may be determined based on the average communication latency based on big data statistics, or it may be determined based on the average communication latency of satellite calls. This application embodiment does not specifically limit this.

[0196] In other words, considering the impact of latency on services, the first network element can further determine whether the first terminal can perform communication in the first communication mode based on the time when the ISL between the first satellite and the second satellite is less than or equal to the second threshold, so as to avoid the increase in service latency that may be caused by subsequent satellite and / or terminal movement.

[0197] It can be understood that the ISL delay between the first and second satellites mentioned above can also be replaced by the delay of communication between the first and second terminals using the first communication method (i.e., USU communication), and the second threshold can also be replaced by the delay of communication between the first and second terminals using the second communication method. Here, the delay of communication using the first communication method is the USU communication delay. The second communication method refers to the data exchange between terminals through ground equipment, i.e., ground routing.

[0198] In other words, the time during which the first satellite and the second satellite maintain ISL can refer to the time during which the USU communication delay is less than or equal to the ground routing delay.

[0199] For example, if the delay of USU communication is less than or equal to the delay of ground routing, and the time is greater than or equal to the first threshold, then the first network element can determine that the first terminal can use the first communication method to perform communication.

[0200] For step S1002:

[0201] It is understandable that, as explained in step S1002 regarding the first network element and the interaction between the first network element and the IMS network element, the first network element can be an SMF or PCF in 5GS. Furthermore, the first network element sending the first indication information to the first access network device can mean that the SMF sends the first indication information to the first access network device (i.e., gNB in ​​5G) through the AMF, or the PCF sends the first indication information to the first access network device through the SMF and AMF.

[0202] In addition, for the first network element being a network element in EPS (such as MME), the first network element sending the first indication information to the first access network device can mean that the MME sends the first indication information to that device in the first access network (i.e., the eNodeB in 4G). For details, please refer to the relevant explanation of EPS in Figure 5, which will not be repeated here.

[0203] For step S1003:

[0204] It is understood that in step S1003, the first access network device can sense that the first terminal is communicating with other terminals in the first communication mode according to the first instruction information, and then try to select a satellite with an ISL with the peer service satellite as the target satellite for handover during the handover.

[0205] It should be understood that, as described in step S1001 above regarding the determination that the first terminal and the second terminal can communicate using the first communication method, the serving satellite between the first terminal and the second terminal can be the same (the first satellite and the second satellite are the same satellite). Therefore, when the first satellite and the second satellite are the same satellite, the first access network device can detect the second satellite (i.e., the first satellite) serving the second terminal, and thus, during handover, it can try to select a satellite with an ISL (Inter-Service Level) with the first satellite as the target satellite for handover.

[0206] It is understandable that the first access network device can obtain information about the second satellite from the first network element or other network elements, and then select, based on the information about the second satellite, a satellite with an ISL (Independent Switching Link) with the second satellite as the target satellite for handover. This will be explained in detail below.

[0207] In one possible implementation, the method provided in Figure 10 further includes:

[0208] S1006. The first network element sends first information to the first access network device. Correspondingly, the first access network device receives the first information from the first network element. The first information includes information about the second terminal, or information about a second satellite serving the second terminal. The information of the second terminal is used to obtain information from the second satellite. The second terminal is a terminal that communicates with the first terminal using a first communication method.

[0209] Accordingly, the first access network device determines the first target access network device to be switched to by the first terminal according to the first indication information (i.e., step S1003), including: the first access network device determines the first target access network device according to the first indication information and the information of the second satellite.

[0210] It is understood that the information about the second terminal is obtained based on the information about the second satellite, and the information about the second satellite is also obtained based on the information about the second terminal. For details, please refer to the relevant explanations about the information about the second terminal and the second satellite in step S1001, which will not be repeated here.

[0211] In other words, the first access network device can obtain information about the second satellite serving the second terminal by receiving the first information from the first network element, and then obtain the ISL information between each of the multiple candidate satellites corresponding to the first terminal and the second satellite (such as whether there is an ISL, or the ISL delay, etc.). Based on the ISL information, the first target access network device can be determined to avoid service interruption or increased latency.

[0212] For example, assuming that among multiple candidate satellites there is an ISL with the second satellite, the first access network device can select the access network device deployed on that candidate satellite as the first target access network device.

[0213] For example, assuming that there are at least two candidate satellites among multiple candidate satellites that have an ISL with the second satellite, the first access network device can select the access network device deployed on the candidate satellite with the smallest ISL delay or the best communication connection quality with the first terminal (e.g., the satellite where the candidate access network device is located with the highest signal power or strength in the measurement report reported by the first terminal) from the at least two candidate satellites, as the first target access network device.

[0214] For example, assuming that there is no candidate satellite with an ISL (Inter-Signal Link) with the second satellite among multiple candidate satellites, the first access network device can determine the first access network device based on the measurement report reported by the first terminal.

[0215] It is understood that the above-mentioned determination of the first access network device based on the first indication information and the information of the second satellite is only exemplary. Other methods can also be used to determine the first access network device, depending on the actual implementation of the first access network device. This application embodiment does not specifically limit this.

[0216] It can also be understood that, for the measurement report reported by the first terminal, the first access network device can send measurement configuration information to the first terminal, and then the first terminal can perform measurements based on the measurement information to obtain a measurement report, and report the measurement report to the first access network device.

[0217] In addition, the first access network device can determine the measurement configuration information based on the information from the second satellite, so as to identify the first target access network device based on the measurement report. This will be described in detail below.

[0218] In one possible implementation, the method shown in Figure 10 further includes:

[0219] S1007. The first access network device determines the measurement configuration information based on the information from the second satellite.

[0220] It is understandable that the first access network device can determine the measurement target corresponding to the measurement configuration information based on the information from the second satellite. For example, the first access network device can determine which adjacent access network devices' satellites have an ISL (Independent Frequency Link) with the second satellite based on information from neighboring cells and the second satellite, and thus these adjacent access network devices can be used as measurement targets. For example, the measurement targets corresponding to the measurement configuration information may include the frequency points of access network devices on satellites that have an ISL with the second satellite.

[0221] In addition, the measurement targets may also include: the subcarrier spacing of the access network equipment on the satellite with an ISL between it and the second satellite, or the timing configuration of the signal to be measured, the measurement priority, etc., which are not specifically limited in this application embodiment.

[0222] S1008, the first access network device sends measurement configuration information to the first terminal. Correspondingly, the first terminal receives the measurement configuration information from the first access network device.

[0223] In other words, the first access network device can determine the measurement configuration information based on the information from the second satellite, and by sending the measurement configuration information to the first terminal device, the first terminal can measure the signal of the access network device on the satellite with an ISL (Information Service Link) with the second satellite.

[0224] In one possible implementation, the method shown in Figure 10 further includes:

[0225] S1009, the first terminal sends a measurement report to the first access network device. Correspondingly, the first access network device receives the measurement report from the first terminal.

[0226] Accordingly, in step S1006 above, the first access network device determines the first target access network device based on the first indication information and the information of the second satellite, specifically including: the first access network device determines the first target access network device based on the first indication information, the information of the second satellite, and the measurement report.

[0227] It is understood that, according to the relevant description of step S1008, the first terminal performs measurement based on the measurement configuration information sent by the first access network device, and can obtain the measurement results corresponding to the access network devices on the satellite with ISL between the adjacent access network devices and the second satellite, that is, the measurement report includes the measurement results corresponding to multiple candidate access network devices, and the multiple candidate access network devices include the access network devices on the satellite with ISL between the second satellite.

[0228] It can also be understood that the first access network device can determine whether to select access network devices on satellites with an ISL (Independent Support Level) with the second satellite as the first target access network device based on the measurement results. For example, suppose the measurement report includes: the measurement results of candidate access network device #1 and candidate access network device #2 (e.g., reference signal receiving power (RSRP) #1), the measurement results of candidate access network device #2 and candidate access network device #3 (e.g., RSRP #3), and the measurement results of candidate access network device #4 and candidate access network device #5 (e.g., RSRP #3). Here, candidate access network devices #1 and #2 are access network devices on satellites with an ISL with the second satellite, while the satellite containing candidate access network device #3 does not have an ISL with the second satellite, and RSRP #3 < RSRP #1 < RSRP #2. Based on the above example, the first access network device can select candidate access network device #2 as the first target access network device.

[0229] Continuing the example above, assuming RSRP#3 < RSRP#1 < RSRP#2 is changed to RSRP#1 < RSRP#2 < RSRP#3, the first access network device can determine the first target access network device as either candidate access network device #2 or candidate access network device #3 based on the difference between RSRP#2 and RSRP#3. For example, if the difference between RSRP#2 and RSRP#3 is large, and RSRP#2 is low (e.g., less than or equal to 95 dBm), then the first access network device can determine candidate access network device #3 as the first target access network device. This avoids service interruption or increased latency compared to selecting candidate access network device #2 as the first target access network device. If RSRP#2 is large but does not affect communication, considering the larger latency of terrestrial routing, the first access network device can choose candidate access network device #2 as the first target access network device, thus avoiding increased latency.

[0230] It is understood that the above description of the first access network device determining the first target access network device based on the measurement report is only an example. The first access network device may also use other methods to determine the first target access network device, depending on the actual implementation of the first access network device. This application embodiment does not make specific limitations on this.

[0231] In other words, the first access network device obtains multiple candidate access network devices through the measurement report of the first terminal, including access network devices on satellites with ISL between the first and second satellites. Then, based on the measurement results of each candidate access network device and the ISL between the satellite where each candidate access network device is located and the second satellite, the first target access network device can be determined to avoid service interruption or increased latency between the first and second terminals.

[0232] It is understood that priorities can be set among the multiple measurement targets corresponding to the above measurement configuration information, so that the first terminal can prioritize measuring the signals of access network devices on satellites that have an ISL with the second satellite, which will be described in detail below.

[0233] In one possible implementation, the priority among multiple measurement targets corresponding to the measurement configuration information is determined based on at least one of the following:

[0234] ISL information between the satellite and the second satellite for each of the multiple measurement targets;

[0235] The time delay information between the satellite corresponding to each of the multiple measurement targets and the second satellite.

[0236] It is understood that the measurement target in the embodiments of this application may specifically refer to the frequency point of an adjacent access network device, and the satellite corresponding to each measurement target specifically refers to the satellite where the access network device corresponding to that frequency point is located.

[0237] Additionally, the ISL (Independent State Link) information between the satellite and the second satellite corresponding to each measurement target may include at least one of the following: whether an ISL exists, the type of ISL (e.g., including direct ISL and indirect ISL), or the duration of ISL retention. If there is no ISL between the satellite and the second satellite corresponding to the measurement target, then that measurement target has the lowest priority. For direct and indirect ISLs, direct ISLs have a higher priority than indirect ISLs. Regarding the duration of ISL retention, measurement targets with longer ISL retention times have a higher priority than those with shorter ISL retention times.

[0238] For example, the satellites corresponding to multiple measurement targets include satellites #1 to #4. Satellite #1 and the second satellite do not have an ISL (Indirect ISL). The ISL between satellite #2 and the second satellite is an indirect ISL. Satellites #3 and #4 each have a direct ISL with the second satellite. The duration of the ISL between satellite #3 and the second satellite is duration #1, and the duration of the ISL between satellite #4 and the second satellite is duration #2. Duration #1 is shorter than duration #2. Based on the above conditions, the measurement target corresponding to satellite #1 has the lowest priority, the measurement target corresponding to satellite #2 has a lower priority than the measurement target corresponding to satellite #3, and the measurement target corresponding to satellite #3 has a lower priority than the measurement target corresponding to satellite #4.

[0239] It can be understood that the latency information between the satellite corresponding to each measurement target and the second satellite can include: the ISL latency between the satellite corresponding to each measurement target and the second satellite, and / or the non-ISL latency between the satellite corresponding to each measurement target and the second satellite. The non-ISL latency between the satellite corresponding to each measurement target and the second satellite can refer to the latency of communication between the satellite corresponding to each measurement target and the second satellite via ground routing. The first access network device can prioritize measurement targets with lower latency than those with higher latency based on the latency between the satellite corresponding to the measurement target and the second satellite. The ISL latency can be used to determine the priority of multiple measurement targets that have ISL with the second satellite, and the non-ISL latency can be used to determine the priority of multiple measurement targets that do not have ISL with the second satellite.

[0240] Furthermore, the first access network device can combine ISL information and latency information to further determine the priority of the measurement target. For example, taking satellites #1 to #4 as examples, assuming that both duration #1 and duration #2 are greater than the first threshold in step S1001, and the ISL latency between satellite #3 and the second satellite is latency #1, and the ISL latency between satellite #4 and the second satellite is latency #2, and latency #1 is less than latency #2, then the priority of the measurement target corresponding to satellite #3 is greater than the priority of the measurement target corresponding to satellite #4.

[0241] It should be understood that the above is merely an exemplary description of determining the priority of a measurement target based on the ISL information and / or delay information between the satellite corresponding to each measurement target and the second satellite. Other methods may also be used to determine the priority of each measurement target, and this application embodiment does not specifically limit this.

[0242] In other words, the first access network device can determine the priority among multiple measurement targets corresponding to the measurement configuration information based on the ISL information and / or latency information between the satellite where the measurement target is located and the second satellite. This allows the first terminal to prioritize measuring the frequency points corresponding to satellites with ISL and / or low latency with the second satellite. This ensures that the multiple candidate access network devices corresponding to the measurement report reported by the first terminal include access network devices on satellites with ISL with the second satellite.

[0243] In one possible implementation, the first target access network device is determined based on at least one of the following:

[0244] ISL information between the satellite where each candidate access network device is located and the second satellite in a pool of candidate access network devices;

[0245] The time delay information between the satellite where each candidate access network device is located and the second satellite in a plurality of candidate access network devices.

[0246] It is understood that the aforementioned ISL information may include: whether an ISL exists, the type of ISL (e.g., including direct ISL and indirect ISL), or the duration of ISL maintenance. The aforementioned delay information may include ISL delay and non-ISL delay; for details, please refer to the relevant explanations in the priority section among the multiple measurement targets mentioned above, which will not be repeated here.

[0247] For example, multiple candidate access network devices are candidate access network devices #1 to #4, and the satellites where candidate access network devices #1 to #4 are located are satellites #1 to #4 respectively. There is no ISL between satellite #1 and the second satellite, there is an indirect ISL between satellite #2 and the second satellite, and satellites #3 and #4 have direct ISLs with the second satellite respectively. Then the first target access network device can be a candidate access network device on satellite #3 or satellite #4.

[0248] Continuing with the example above, if the time for which satellite #3 maintains an ISL with the second satellite is duration #1, and the time for which satellite #4 maintains an ISL with the second satellite is duration #2, and duration #1 is less than duration #2, then the first target access network device can be candidate access network device #4 on satellite #4.

[0249] Continuing with the example above, if the ISL delay between satellite #3 and the second satellite is delay #1, and the ISL delay between satellite #4 and the second satellite is delay #2, and delay #1 is less than delay #2, then the first target access network device can be candidate access network device #3 on satellite #3.

[0250] It should be understood that the satellite where the first target access network device, as determined by the first access network device, is located may not have an ISL (Inter-Satellite Link) with the second satellite. For example, referring to the description of the measurement results of the candidate access network device in step S1009, assuming that the measurement results corresponding to the above satellites #1 to #4 are RSRP#1 to RSRP#4 respectively, and only the measurement result RSRP#1 corresponding to satellite #1 meets the handover requirements, then candidate access network device #1 is the first target access network device, and the satellite #1 where candidate access network device #1 is located has an ISL with the second satellite.

[0251] In addition, the calculation of ISL information and / or latency information mentioned above can be performed by the first access network device or by other network devices and fed back to the first access network device. This application embodiment does not specifically limit this.

[0252] It should be understood that the above description of determining the first target access network device based on ISL information and / or latency information is only an example. Other methods can also be used to determine the first target access network device, depending on the actual implementation of the first access network device. This application embodiment does not specifically limit this.

[0253] In other words, the first access network device can select, as far as possible, the candidate access network devices corresponding to satellites with smaller ISL and / or smaller latency with the second satellite based on the ISL information and / or latency information between the satellite where each candidate access network device is located and the second satellite, thereby avoiding service interruption or increased latency after handover.

[0254] It is understandable that after the first access network device determines the first target access network device to be handed over to by the first terminal, the first access network device can send the identifier of the first target access network device to the first network element (e.g., based on the N2 handover procedure) in order to complete the relevant handover procedures.

[0255] In one possible implementation, the method shown in Figure 10 further includes:

[0256] S1010, the first access network device sends the identifier of the first target access network device to the first network element. Correspondingly, the first network element receives the identifier of the first target access network device from the first access network device. The first target access network device is the target access network device to which the first terminal is to be handed over.

[0257] It is understood that the first access network device sending the identifier of the first target access network device to the first network element may include: the first access network device sending the identifier of the first target access network device to the first network element, and / or the identifier of the first target satellite where the first target access network device is located.

[0258] It should be understood that the identifier of the target access network device involved in the embodiments of this application may refer to: the identifier of the target access network device, and / or the identifier of the target satellite where the target access network device is located. This will be explained uniformly here and will not be repeated below.

[0259] In other words, when the first access network device senses that the first terminal is performing communication in the first communication mode according to the first instruction information, and when the first terminal is switching, the first access network device can select a satellite with ISL and / or low ISL latency between the second terminal that has established a connection with the first terminal as the target satellite to be switched, based on the information of the service satellite (i.e., the second satellite) of the second terminal that has established a connection with the first terminal, and send the identifier of the first target access network device deployed on the target satellite to the first network element.

[0260] In one possible implementation, the method provided in Figure 10 further includes:

[0261] S1011. The first network element determines whether the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device.

[0262] It is understood that the first network element can determine this based on the ISL (Inter-Saving Level) between the satellite where the first target access network device is located and the second satellite, or the first network element can also use other network elements to determine this. Specifically, if the first network element determines this using other network elements, for example, other network elements could determine whether there is an ISL and / or latency information between the satellite where the first target access network device is located and the second satellite, and then feed back this ISL and / or latency information to the first network element, thereby determining whether the first terminal can continue to perform communication in the first signaling mode after switching to the first target access network device.

[0263] S1012. If the first terminal cannot continue to perform communication in the first communication mode after switching to the first target access network device, the first network element triggers the conversion of the first communication mode to the second communication mode. The second communication mode refers to the interaction of data between terminals through ground equipment.

[0264] In other words, if the first network element determines that the first terminal cannot continue to perform communication in the first communication mode after switching to the first target access network device, the first network element can trigger the conversion of the first communication mode to the second communication mode to continue the service transmission of the first terminal and avoid service interruption.

[0265] There are two ways to implement step S1011, which will be described in detail below.

[0266] In one possible implementation, the first network element determines whether the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device (i.e., step S1011), including: the first network element determines whether the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device based on the information of the second satellite.

[0267] In other words, when the first network element determines that the first terminal is performing communication in the first communication mode and receives the identifier of the first target access network device to be switched to by the first terminal, the first network element can determine whether the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device based on the connection status between the satellite where the first target access network device is located and the second satellite after the first terminal switches to the first target access network device. This allows the first network element to complete the corresponding NF configuration in a timely manner and avoid affecting service transmission.

[0268] In another possible implementation, the method shown in Figure 10 further includes:

[0269] S1013. The first access network device sends second indication information to the first network element. Correspondingly, the first network element receives the second indication information from the first access network device. The second indication information is used to indicate whether the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device.

[0270] S1014. The first network element determines, according to the second instruction information, whether the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device.

[0271] It is understandable that, based on the aforementioned description of the first target access network device, the satellite where the first target access network device is located may not have an ISL (Independent Service Level) with the second satellite. This means that after the first terminal switches to the first target access network device, it cannot continue to perform communication using the first communication method. Furthermore, according to the description in the preamble section "Third, USU Communication" of the specific implementation method, performing communication using the first communication method (i.e., USU communication) requires the CN to configure an on-board UPF for the relevant NF (e.g., UPF) serving the first terminal. If the first terminal cannot continue to perform communication using the first communication method after switching to the first target access network device, then the CN needs to reconfigure the relevant NF (e.g., ground-based IMS-AGW) to switch to another communication method for the first terminal to perform communication.

[0272] In other words, by sending the second indication information to the first network element, the first access network device can determine whether the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device, and then determine whether it is necessary to switch the communication mode in the future. This allows the first network element to complete the corresponding NF configuration in a timely manner and avoid affecting the service transmission.

[0273] In one possible implementation, if the first terminal cannot continue to perform communication in the first communication mode after the second indication information indicates that the first terminal has switched to the first target access network device, the second indication information is used to trigger the conversion of the first communication mode to the second communication mode, whereby the data between the terminals is exchanged through ground equipment.

[0274] In other words, if the first terminal cannot continue to perform communication in the first communication mode after the second instruction information instructs the first terminal to switch to the first target access network device, the second instruction information can trigger the first network element to switch the first communication mode to the second communication mode in order to continue the service transmission of the first terminal and avoid service interruption.

[0275] In one possible implementation, the first network element triggers the conversion of the first communication mode to the second communication mode (i.e., step S1104), which specifically includes: the first network element sending third indication information to the IMS network element serving the first terminal, the third indication information being used to indicate the conversion of the first communication mode to the second communication mode.

[0276] It is understandable that the third instruction information can instruct the first terminal to terminate communication in the first communication mode, or terminate USU communication, etc. Subsequently, the IMS network element can convert the first communication mode to the second communication mode based on the third instruction information, that is, convert USU communication to terrestrial routing. Furthermore, by converting the first communication mode to the second communication mode through the aforementioned IMS network element, the relevant conversion work on the IMS side can be completed. The first network element can complete the relevant configuration on the core network side for converting the first communication mode to the second communication mode, such as reconfiguring the UPF for the first terminal, that is, converting the UPF from an on-board UPF to a terrestrial UPF.

[0277] It is understood that the first network element can be an SMF, and the IMS network element can be a P-CSCF. The SMF can send the third indication information to the P-CSCF through the PCF, or the SMF can also send the third indication information directly to the P-CSCF. This application embodiment does not specifically limit this.

[0278] In other words, the first network element can send a third instruction message to the IMS network element serving the first terminal, thereby triggering the IMS network element to switch from the first communication mode to the second communication mode.

[0279] In one possible implementation, after the first terminal switches to the first target access network device, it can continue to perform communication using the first communication method, specifically including at least one of the following:

[0280] The satellite containing the first target access network equipment maintains ISL with the second satellite;

[0281] The time that the satellite where the first target access network device is located maintains ISL with the second satellite is greater than or equal to the first threshold.

[0282] Alternatively, the time during which the ISL between the satellite where the first target access network device is located and the second satellite is less than or equal to the second threshold is greater than or equal to the third threshold.

[0283] It is understandable that the implementation of determining that the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device is similar to the step S1001, in which "the first network element determines that the first terminal and the second terminal perform communication in the first communication mode based on the ISL maintained between the first satellite and the second satellite serving the second terminal". The difference is that the time for maintaining the ISL is less than or equal to the second threshold is greater than or equal to the third threshold. The third threshold may be the same as or different from the first threshold, depending on the actual implementation of the first access network device. This application embodiment does not specifically limit this.

[0284] In other words, based on whether the satellite where the first target access network device is located maintains an ISL (Inter-Service Level) with the second satellite, the duration of the ISL maintenance, and the delay in maintaining the ISL, the possibility of subsequent ISL interruption due to satellite and / or terminal movement can be considered in advance. This further determines whether the first terminal can perform communication in the first communication mode after switching to the first target access network device, thereby avoiding service interruption or increased latency that may be caused by subsequent satellite switching.

[0285] It is understood that in the Xn-based handover process, the first target access network device can send its identifier and second indication information to the first network element. The first target access network device can obtain the second indication information from other access network devices, or it can determine the second indication information itself; this embodiment does not specifically limit this.

[0286] For step S1004:

[0287] As explained above regarding step S1004, if the first access network device does not obtain information about the serving satellite of the peer communicating with the first terminal, the first access network device can send identification information of at least one target access network device (e.g., a list of at least one target access network device identifiers) to the first network element according to the first indication information, so that the first network element can select a second target access network device for handover of the first terminal from among the at least one target access network device. The first access network device can determine at least one target access network device based on the measurement results (e.g., RSRP) corresponding to multiple candidate access network devices included in the measurement report. For example, it can select at least one candidate access network device with an RSRP greater than a selection threshold as at least one target access network device, depending on the actual implementation of the first access network device. This application embodiment does not specifically limit this.

[0288] Furthermore, in this embodiment, "at least one target access network device" can specifically refer to one or at least two target access network devices. Wherein, "at least one target access network device" means only one target access network device, possibly because the measurement report indicates that only one candidate access network device's measurement result (e.g., RSRP) meets the handover requirements, while the RSRPs of other candidate access network devices do not. In other words, the number of target access network devices included in "at least one target access network device" depends specifically on the actual implementation of the first access network device, and this embodiment does not specifically limit this.

[0289] The following describes the specific implementation of the first access network device sending the above-mentioned at least one target access network device to the first network element.

[0290] In one possible implementation, the method shown in Figure 10 further includes:

[0291] S1004a, the first access network device sends second information to the first network element. Correspondingly, the first network element receives the second information from the first access network device. The second information includes identification information of at least one target access network device to which the first terminal is to be handed over.

[0292] It is understood that the information of at least one target access network device may include the identifier of each of the at least one target access network device. Additionally, the second information may also include other information, such as the identifier of the first terminal, the identifier of the session used by the first terminal to perform communication in the first communication mode, or the measurement results of each target access network device, etc. This application embodiment does not specifically limit this.

[0293] S1015. The first network element determines the second target access network device from at least one target access network device.

[0294] In one possible implementation, the first network element determines a second target access network device from at least one target access network device based on information from a third satellite serving the third terminal, wherein the third terminal is a terminal that communicates with the first terminal using a first communication method.

[0295] It should be understood that the third terminal here may be the same as or different from the second terminal. Similarly, the second satellite and the third satellite may be the same as or different from each other. This will be explained uniformly here and will not be repeated below.

[0296] In addition, the specific implementation of determining the second target access network device in step S1015 is similar to that of determining the first target access network device in step S1003. For details, please refer to the relevant description of determining the first target access network device in step S1003, which will not be repeated here.

[0297] In other words, the first network element can select, from the at least one target access network device, a target access network device deployed on a satellite that has an ISL (Independent Service Level) with the third satellite, as the second target access network device based on the information of the service satellite (i.e., the third satellite) of the third terminal that has established a connection with the first terminal.

[0298] In one possible implementation, the first network element determines the second target access network device from at least one target access network device based on at least one of the following:

[0299] ISL information between the satellite where each target access network device in at least one target access network device is located and the third satellite;

[0300] The time delay information between the satellite where each target access network device is located and the third satellite in at least one target access network device.

[0301] In other words, the first network element can select target access network devices corresponding to satellites with low ISL and / or low latency between the satellite where each access network device is located and the third satellite, based on the ISL information and / or latency information between the satellite and the third satellite, as the second target access network devices, thereby avoiding service interruption or increased latency after handover.

[0302] S1016, the first network element sends the identifier of the second target access network device to the first access network device. Correspondingly, the first access network device receives the identifier of the second target access network device from the first network element. The second target access network device is a target access network device among at least one target access network device.

[0303] In other words, by sending at least one target access network device to the first network element, the first access network device can select, as far as possible, a target access network device deployed on a satellite with ISL or low latency to the serving satellite of the other end as the second target access network device, and send the identifier of the second target access network device to the first access network device. Thus, the first access network device can perform the handover process of the first terminal according to the second target access network device to avoid service interruption or increased latency.

[0304] In one possible implementation, the method shown in Figure 10 further includes:

[0305] S1017. The first network element determines whether the first terminal can continue to perform communication in the first communication mode after switching to the second target access network device.

[0306] In one possible implementation, the first network element determines whether the first terminal can continue to perform communication in the first communication mode after switching to the second target access network device (i.e., step S1017), including: the first network element determines whether the first terminal can continue to perform communication in the first communication mode after switching to the second target access network device based on information from the third satellite serving the third terminal. The third terminal is the terminal that performs communication with the first terminal in the first communication mode.

[0307] In other words, when the first network element determines that the first terminal is performing communication in the first communication mode and determines that the target access network device to be switched to by the first terminal is the second target access network device, the first network element can determine the connection status between the satellite where the second target access network device is located and the third satellite after the first terminal switches to the second target access network device based on the information of the third satellite. This allows the first network element to determine whether the first terminal can continue to perform communication in the first communication mode after switching to the second target access network device, and whether a change in communication mode is needed subsequently. This enables the first network element to complete the corresponding NF configuration in a timely manner and avoids affecting service transmission.

[0308] It is understandable that step S1017 is specifically implemented as step S1011, which will not be elaborated here.

[0309] S1018. If the first terminal cannot continue to perform communication in the first communication mode after switching to the second target access network device, the first network element triggers the conversion of the first communication mode to the second communication mode. The second communication mode refers to the interaction of data between terminals through ground equipment.

[0310] It is understood that the first network element trigger in step S1018 will switch the first communication mode to the second communication mode. For details, please refer to the relevant explanation of step S1012, which will not be repeated here.

[0311] In other words, if the first network element determines that the first terminal cannot continue to perform communication in the first communication mode after switching to the first target access network device, the first network element can trigger the conversion of the first communication mode to the second communication mode to continue the service transmission of the first terminal and avoid service interruption.

[0312] In one possible implementation, after the first terminal switches to the second target access network device, it can continue to perform communication using the first communication method, specifically including at least one of the following:

[0313] The satellite where the second target access network equipment is located maintains an ISL (Independent State Link) with the third satellite serving the third terminal;

[0314] The time that the satellite where the second target access network device is located maintains ISL with the third satellite is greater than or equal to the first threshold.

[0315] Alternatively, the time that the ISL between the satellite where the second target access network device is located and the third satellite is less than or equal to the second threshold is greater than or equal to the third threshold.

[0316] The third terminal is a terminal that communicates with the first terminal using the first communication method.

[0317] It is understood that after the first terminal switches to the second target access network device, it can continue to perform communication in the first communication mode, which is similar to the previous step S1003 regarding "after the first terminal switches to the first target access network device, it can continue to perform communication in the first communication mode", so it will not be repeated here.

[0318] In other words, the first access network device can consider in advance whether the satellite and / or terminal movement will cause subsequent ISL interruption based on whether the satellite where the second target access network device is located maintains ISL with the third satellite, the duration of maintaining ISL, and the delay of maintaining ISL. This allows it to further determine whether the first terminal can perform communication in the first communication mode after switching to the second target access network device, thereby avoiding service interruption or increased latency that may be caused by subsequent satellite switching.

[0319] In this embodiment of the application, the first network element sends a first indication information to the first access network device, which enables the first access network device to perceive that the first terminal is performing communication in the first communication mode (i.e., USU communication). As a result, when selecting the target access network device to be switched to by the first terminal, the first access network device can consider the connection between the satellite where the target access network device is located and the peer service satellite performing USU communication, so as to select the satellite with ISL and low ISL latency as much as possible. This can avoid service interruption (e.g., no ISL between the service satellite after switching and the peer service satellite) or increased latency.

[0320] The above describes the overall method flow corresponding to Scheme 1. The following section will take the UE accessing the IMS network through the 5GS CN as an example to introduce the communication method shown in Figure 10.

[0321] Figure 11 is a schematic flowchart of a communication method provided in an embodiment of this application. As shown in Figure 11, the method flowchart involves a call setup process and a handover process. UE#1 is the calling UE (i.e., the second terminal), UE#2 is the called UE (i.e., the first terminal), the network element with the suffix #1 is the network element serving UE#1 (including CN network elements and IMS network elements), and the network element with the suffix #2 is the network element serving UE#2. The following example illustrates the method using SMF#2 serving UE#2 as the first network element, P-CSCF#2 as the IMS network element serving the first terminal, satellite #2 as the first satellite, gNB#2 as the first access network device, and satellite #1 as the second satellite.

[0322] In addition, for ease of explanation, in the method flow shown in Figure 11, the communication method of the first communication method is replaced with USU communication, and the second communication method is replaced with ground routing. This will be explained uniformly here and will not be repeated below.

[0323] It should be understood that the network elements serving UE#1 and the network elements serving UE#2 (including CN network elements and / or IMS network elements) may be the same or different, and the embodiments of this application do not specifically limit this.

[0324] As shown in Figure 11, the method includes: S1101 to S1121, S1101 to S1114 is the call setup procedure, and S11114 to S1121 is the handover procedure, which will be explained in detail below.

[0325] S1101, UE#1 initiates a call to UE#2.

[0326] In this process, UE#1 initiates a call to UE#2, which includes UE#1 sending a Session Initiation Protocol (SIP) invite message to UE#2. Correspondingly, UE#2 receives the SIP invite message from UE#1. The SIP invite message includes: an identifier indicating UE#2, a Session Description Protocol (SDP) request, or information for negotiating media type and format (or encoding / decoding method) with the called party.

[0327] It is understood that information used to negotiate media type and media format with the called party may include, for example, the media type requested by the calling party, and / or, the media formats supported by the calling party.

[0328] In addition, the SIP invite message may also include: access network information of UE#1. This access network information may include, for example, the access network type of UE#1 (e.g., UE#1 accesses via satellite, meaning the access network equipment providing services to UE#1 is deployed on a satellite (i.e., a second satellite)), the identifier of the access network equipment indicating UE#1's access, the identifier of satellite #1, or constellation information, etc. This application embodiment does not specifically limit this information.

[0329] It is understood that in the method flow shown in Figure 11, satellite #1 is the serving satellite for UE #1. Furthermore, according to the aforementioned description in "Third, USU Communication," satellite #1 can deploy an access network element gNB #1 for providing access services to UE #1, and a UPF #1 for providing data (e.g., IMS call-related data) exchange processing. This UPF #1 may include: an uplink classifier (ULCL) UPF supporting traffic offloading, and / or a local PDU session anchor (LPSA) UPF supporting user data forwarding as an anchor point for PDU sessions. For example, satellite #1 can deploy gNB #1, ULCL UPF #1, and / or LPSA UPF #1.

[0330] Optionally, satellite #1 may also deploy IMS-AGW #1 to provide IMS access gateway services for UE #1.

[0331] It is understood that before executing step S1101, UE#1 and UE#2 can respectively execute the process of establishing an IMS PDU session (i.e., a PDU session with DNN as IMS, which is used to carry IMS signaling and IMS call-related data) and the process of IMS registration. UE#1 sends the SIP invite message through the established IMS PDU session. For example, the above SIP invite message can be sent through the PDU session anchor (PSA) #1 of UE#1's IMS PDU session #1.

[0332] For example, step S1101 may specifically include steps S1101a, S1101b, and S1101c.

[0333] S1101a, UE#1 sends a SIP invite message to P-CSCF#1. Correspondingly, P-CSCF#1 receives the SIP invite message from UE#1.

[0334] It is understandable that UE#1 can send a SIP invite message to PSA#1 via gNB#1 on satellite#1, and PSA#1 can send a SIP invite message to P-CSCF#1.

[0335] S1101b, P-CSCF#1 sends a SIP invite message to P-CSCF#2. Correspondingly, P-CSCF#2 receives the SIP invite message from P-CSCF#1.

[0336] It can be understood that P-CSCF#2 is the P-CSCF providing services to UE#2. Additionally, P-CSCF#1 sending a SIP invite message to P-CSCF#2 can specifically include: P-CSCF#1 sending a SIP invite message to S-CSCF#1, which provides services to UE#1; S-CSCF#1 sending a SIP invite message to S-CSCF#2, which provides services to UE#2; and S-CSCF#2 sending the same SIP invite message to P-CSCF#2.

[0337] S1101c, P-CSCF#2 sends a SIP invite message to UE#2. Correspondingly, UE#2 receives the SIP invite message from P-CSCF#2.

[0338] It is understood that, similar to UE#1 communicating with P-CSCF#1 via PSA#1, P-CSCF#2 sends a SIP invite message to UE#2 via PSA#2, which provides services to UE#2. Additionally, PSA#2 can send the SIP invite message to UE#2 via gNB#2, which provides access services to UE#2 and is deployed on satellite#2. Satellite#2 is similar to satellite#1; it can deploy gNB#2, ULCL UPF#2, and / or LPSA UPF#2. Optionally, satellite#2 can also deploy IMS-AGW#2 to provide IMS access gateway services to UE#2.

[0339] It should be understood that in the above steps S1101a to S1101c, the SIP invite message will undergo certain processing when passing through each service network element, such as adding, deleting, or modifying some or all of the information in the message header. This application embodiment does not specifically limit this.

[0340] S1102, UE#2 sends a first response message to P-CSCF#2. Correspondingly, P-CSCF#2 receives the first response message from UE#2. This first response message may include a SIP 183 message, which instructs UE#2 to accept the call with UE#1, or confirms that UE#2 has received the SIP invite message. The SIP 183 message may include, for example, an SDP answer.

[0341] It is understandable that UE#2 sends a response message to P-CSCF#2, which may specifically include: UE#2 sending a SIP 183 message to gNB#2 on satellite#2, gNB#2 sending the SIP 183 message to PSA#2, and PSA#2 sending the SIP 183 message to P-CSCF#2.

[0342] S1103, P-CSCF#2 or S-CSCF#2 determines that IMS PDU session #2 can (or is able to) perform USU communication.

[0343] As can be understood, as described in the previous step S1101 regarding IMS PDU session #1, IMS PDU session #2 is an IMS PDU session established by UE#2 with the CN network element and IMS network element serving UE#2 to provide a service data transmission channel for UE#2.

[0344] Furthermore, IMS PDU session #2 can perform USU communication. Specifically, this means that the UPF corresponding to IMS PDU session #2 can be deployed on the serving satellite of UE #2 (i.e., satellite #2); or, the UPF and IMS-AWG corresponding to IMS PDU session #2 can be deployed on satellite #2. In other words, the data transmitted by IMS PDU session #2 is processed via the UPF deployed on the satellite, or by the UPF and IMS-AWG exchanging data, thus the data transmitted by IMS PDU session #2 can bypass the terrestrial IMS network (i.e., no transcoding operation is required from the IMS network).

[0345] It can be understood that IMS PDU session #2 being able to perform USU communication can also mean that UE#2 is able to perform USU communication, or that UE#2 is able to activate USU communication, or that UE#2 and UE#1 are able to perform USU communication. This will be explained uniformly here and will not be repeated below.

[0346] The following section details how P-CSCF#2 or S-CSCF#2 determines whether IMS PDU session #2 can perform USU communication.

[0347] For example, when P-CSCF#2 or S-CSCF#2 determines that the serving satellite between UE#1 and UE#2 meets the first condition, it determines that IMS PDU session #2 can perform USU communication. The first condition includes: UE#1 and UE#2 are served by the same satellite, or there is an ISL between the serving satellite of UE#1 and the serving satellite of UE#2. For details, please refer to step S1005, which will not be repeated here.

[0348] S1104, P-CSCF#2 sends a first request message to PCF#2. Correspondingly, PCF#2 receives the first request message from P-CSCF#2. The first request message includes the identifier of UE#2, the USU indication, and the access network information of UE#1.

[0349] It is understood that the first request message can be used to request authorization for the policy of IMS PDU session #2 corresponding to UE#2, which includes performing USU communication. Here, the identifier of UE#2 can be used to represent IMS PDU session #2 corresponding to UE#2, and the USU indication is used to indicate that IMS PDU session #2 can perform USU communication. The access network information of UE#1 can be used to determine whether IMS PDU session #2 performs USU communication; specifically, the access network information of UE#1 may include information about satellite #1.

[0350] It is understandable that the USU indication can also be replaced by a USU request, which is used to request IMS PDU session #2 to perform USU communication.

[0351] In addition, PCF#2 can also obtain the access network information of UE#1 through UE#1 or the CN that provides services to UE#1. For example, the access network information of UE#1 may be included in the SIP invite message in step S1101, or sent to P-CSCF#2 through other messages or methods. This application embodiment does not make specific limitations on this.

[0352] It should be understood that PCF#2 can determine the corresponding policy and charging control (PCC) rules based on the first request message and send them to SMF#2.

[0353] S1105, PCF#2 sends PCC rules to SMF#2. Correspondingly, SMF#2 receives the PCC rules from PCF#2. The PCC rules include an identifier for UE#2 and a USU indication.

[0354] It is understandable that if PCF#2 agrees to IMS PDU session #2 performing USU communication, the PCC rule includes a USU instruction.

[0355] Optionally, the PCC rule may also include information from satellite #1. This information can be used to determine whether IMS PDU session #2 can perform USU communication. For example, SMF #2 can determine whether IMS PDU session #2 can perform USU communication based on the information from satellite #1.

[0356] It is understood that SMF#2 can also obtain information about satellite #1 through UEE#1 or the CN that provides services to UE#1, and this application embodiment does not specifically limit this.

[0357] It should be understood that when SMF#2 determines that IMS PDU session #2 will perform USU communication according to USU instructions, SMF#2 will configure on-board UPF for UE#2's IMS PDU session #2 according to USU instructions, such as deploying ULCL UPF#2, LPSA UPF#2, and the transmission channel between ULCL UPF#2 and LPSA UPF#2 on satellite #2, etc. For details, please refer to step S1106 below.

[0358] S1106, SMF#2 configures (or deploys) the on-board UPF#2 and data forwarding rules for UE#2's IMS PDU session#2. The data forwarding rules include: ULCL UPF#2 receives uplink data from UE#2 and sends it to LPSA UPF#2; LPSA UPF#2 then sends the uplink data to the LPSA UPF#1 serving UE#1. Furthermore, up to step S1106, LPSA UPF#2 has not yet obtained the address information of UE#1's LPSA UPF#1; this address information can be obtained through subsequent process interactions.

[0359] It is understandable that SMF#2 can allocate address information for LPSA UPF#2. This address information for LPSA UPF#2 is used to receive voice data sent by UE#1 to UE#2. Specifically, the voice data is sent from LPSA UPF#1 serving UE#1 to LPSA UPF#2.

[0360] It should be understood that the serving satellite of UE#2 is satellite #2, and the specific implementation of step S1106 can be that SMF#2 configures ULCL UPF#2 and LPSA UPF#2 on satellite #2 through AMF#2.

[0361] S1107, SMF#2 sends an N2 message to gNB#2 on satellite #2 via AMF#2. Correspondingly, gNB#2 on satellite #2 receives the N2 message from SMF#2 via AMF#2. The N2 message is used by gNB#2 to establish a bearer for transmitting voice data (e.g., 5G quality identity (5QI) or quality of service (QoS) class identifier (QCI) = 1). This N2 message includes first indication information, which instructs the first terminal to perform USU communication. It can be understood that, based on the first indication information, gNB#2 can determine that the data transmitted on the aforementioned bearer is data for performing USU communication.

[0362] Optionally, the first indication information, the N2 message, may also include information about satellite #1. Based on the information about satellite #1, gNB#2 can determine which of the multiple candidate satellites corresponding to UE#2 can establish an ISL with the satellite accessed by UE#1 (i.e., satellite #1), and which satellites have lower latency with satellite #1.

[0363] It is understood that the aforementioned low latency can specifically mean less than or equal to the second threshold. For details on the second threshold, please refer to the relevant explanation of the second threshold in step S1005 of the method flow shown in Figure 10, which will not be repeated here.

[0364] In other words, by including satellite #1 information in the N2 message, gNB#2 can determine which candidate satellites corresponding to UE#2 have ISL or low latency with satellite #1 accessed by UE#1. Then, the measurement information corresponding to these candidate satellites with ISL or low latency can be configured as high priority so that UE#2 can measure these candidate satellites first.

[0365] S1108, gNB#2 sends measurement configuration information (including idle state and connected state measurement configuration information) to UE#2 based on the information from the first indication information satellite #1. Correspondingly, UE#2 receives the measurement configuration information from gNB#2. The specific details of the measurement configuration information can be found in step S1007 of Figure 10, and will not be repeated here.

[0366] It can also be understood that step S1108 may specifically include: gNB#2 sending an RRC message to UE#2, the RRC message including the aforementioned measurement configuration information.

[0367] S1109, gNB#2 sends an N2 response message to SMF#2 via AMF#2. Correspondingly, SMF#2 receives the N2 response message from gNB#2 via AMF#2. The N2 response message indicates that gNB#2 has received the N2 message.

[0368] S1110, SMF#2 sends a second response message to P-CSCF#2. Correspondingly, P-CSCF#2 receives the second response message from SMF#2. The second response message may include the address information of LPSA UPF#2, which is used to receive data sent from UE#1 to UE#2.

[0369] It can be understood that SMF#2 sends a second response message to P-CSCF#2. Specifically, SMF#2 sends a second response message to PCF#2, and then PCF#2 can send a second response message to P-CSCF#2.

[0370] S1111, P-CSCF#2, and P-CSCF#1 exchange SIP 183 messages. Specifically, P-CSCF#2 can send a SIP 183 message to S-CSCF#1, and S-CSCF#1 can then send a SIP 183 message to P-CSCF#1.

[0371] Optionally, this step may also include P / S-CSCF#2 sending the address information of LPSA UPF#2 and the access network information of UE#2 to P / S-CSCF#1.

[0372] S1112, the service network element on the UE#1 side executes the process of configuring USU communication.

[0373] It is understandable that the specific implementation of step S1112 is similar to steps S1103 to S1108 above. The network element of UE#1 performs the process of configuring USU communication, which specifically includes the IMS network element P-CSCF#1 or S-CSCF#1 determining that the IMS PDU session #1 can perform USU communication, sending a second request message to PCF#1 (similar to the first request message, except that UE#2 is replaced by UE#1), and then PCF#1 sends PCC rules to SMF#1 to trigger SMF#1 to configure on-board UPF (ULCL UPF#1, LPSA UPF#1, and the transmission channel between them) and data forwarding rules for the serving satellite of UE#1 (i.e., satellite #1). In addition, SMF#1 allocates the address information of LPSA UPF#1, which can be used to receive data sent by UE#2 to UE#1 (sent by LPSA UPF#2 serving UE#2 to LPSA UPF#1).

[0374] It is understood that the specific implementation of S1112 can be found in the aforementioned steps S1103 to S1108, and will not be repeated here.

[0375] S1113, P-CSCF#1 sends a SIP 183 message to UE#1. Correspondingly, UE#1 receives the SIP 183 message from P-CSCF#1.

[0376] For example, P-CSCF#1 sends a SIP 183 message to PSA#1, and then PSA#1 sends a SIP 183 message to UE#1 through gNB#1.

[0377] S1114, Other procedures for IMS call setup.

[0378] It is understandable that the specific implementation of step S1114 can be found in the 3GPP protocol, and will not be elaborated here.

[0379] It should be understood that the above steps S1101 to S1114 are the call setup process. After the call setup process is completed, UE#1, Satellite #1, Satellite #2, and UE#2 can communicate with each other via USU.

[0380] Additionally, as the satellite or UE moves, the serving satellite of UE#1 or UE#2 may be switched (which may be asynchronous). Figure 11 illustrates the switching process using the serving satellite switch of UE#2 as an example. It should be understood that in actual implementation, both UE#1 and UE#2 will perform measurements according to the gNB's measurement configuration and report measurement results based on event triggers or periodically.

[0381] In step S1109, UE#2 can perform measurements according to the measurement configuration information and report them to gNB#2. Then, gNB#2 can determine the target access network device for handover based on the measurement results, as follows.

[0382] S1115, UE#2 sends a measurement report to gNB#2. Correspondingly, gNB#2 receives the measurement report from UE#2. The measurement report is the result reported by UE#2 after performing measurements based on the measurement configuration information sent by gNB#2 (see step S1108 for details). Specifically, it may include the measurement target ID (e.g., frequency point, cell) and the corresponding measurement results (signal strength, signal quality, etc.). gNB#2 determines whether to perform cell handover based on the measurement results sent by UE#2.

[0383] S1116, gNB#2 determines the target gNB (i.e., the first target access network device) based on the first indication information, the access network information of UE#1, and the measurement report.

[0384] It is understandable that when selecting a target gNB, the source gNB currently serving UE#2 (i.e., gNB#2 on satellite #2) should consider that UE#2 is performing USU communication. Therefore, when selecting a target gNB, it should choose a gNB on a satellite that has better latency with the serving satellite of UE#1 (i.e., satellite #1) as the target gNB. For example, there is a direct ISL or an indirect ISL (through relay of an intermediate satellite), or the latency requirement can be met through direct or indirect ISL communication, or the latency of direct or indirect ISL is better than that of terrestrial routing. For details, please refer to the relevant explanation of step S1009 in Figure 10, which will not be repeated here.

[0385] Optionally, gNB#2 determines whether UE#2 can continue to perform USU communication after switching to the target gNB.

[0386] It is understood that the specific implementation of this step can be found in the relevant description of step S1013 in Figure 10, and will not be repeated here.

[0387] S1117, gNB#2 sends a handover request message to AMF#2. Correspondingly, AMF#2 receives the handover request message from gNB#2. The handover request message includes the identifier of the target gNB and / or the identifier of the target satellite. The target satellite is the satellite on which the target gNB resides.

[0388] Optionally, the handover request message includes a second indication information, which is used to indicate whether UE#2 can perform USU communication after handover to the target gNB.

[0389] S1118, AMF#2 sends a PDU session update session management context message to SMF#2. Correspondingly, SMF#2 receives the PDU session update session management context message from AMF#2. The PDU session update session management context message includes the identifier of the target gNB and / or the identifier of the target satellite. Optionally, the PDU session update session management context message also includes indication information indicating whether USU communication can be performed after the handover.

[0390] S1119, SMF#2 determines whether UE#2 can continue to perform USU communication after switching to the target gNB.

[0391] For example, SMF#2 can be determined based on the second instruction information in step S1118.

[0392] For example, SMF#2 determines the ISL (Inter-Service Level) time between the target satellite indicated in step S1118 and the serving satellite of UE#1 (i.e., satellite #1). In this mode, it can be determined directly by SMF#2, or it can be determined by SMF#2 with the help of other network elements. For details, please refer to step S1116, which will not be elaborated here.

[0393] S1120. If SMF#2 determines that UE#2 cannot continue to perform USU communication after switching to the target gNB, SMF#2 triggers the method of falling back USU communication to the ground route.

[0394] For example, SMF#2 modifies the data forwarding rules of UE#2's IMS PDU session #2 to configure the data transmission channel between ULCL UPF#2 and the ground PSA UPF. Another example is that SMF#2 directly configures the data transmission channel between the onboard gNB and the ground PSA UPF.

[0395] In addition, the specific implementation of step S1120 also includes SMF#2 triggering the IMS network element (SMF#2 triggering P-CSCF#2 via PCF#2) to configure ground IMS-AGW resources for IMS PDU session #2.

[0396] S1121, Perform other steps in the switching process.

[0397] It is understandable that if SMF#2 determines that UE#2 cannot continue to perform USU communication after switching to the target gNB, other steps in the handover process should continue to be performed, such as updating the PDU session management context and feeding back the address information of PSA#1 to the target satellite. This will enable UE#1 to complete voice data interaction with UE#2 after switching to the target gNB, based on the target gNB, the CN on the ground, and the IMS network on the ground. For details, please refer to the relevant description in Scheme 3, which will not be repeated here.

[0398] It should be understood that the handover process shown in Figure 11 above is a handover process based on N2. For a handover process based on Xn, the target base station (not the source base station) indicates to the CN in the path switch message whether USU communication can be performed after the handover (corresponding to step S1117). The target gNB can receive this indication information from the source base station (i.e., gNB#2), or it can be determined by the target gNB itself. This application embodiment does not specifically limit this.

[0399] In this embodiment of the application, by sending the first indication information to gNB#2, SMF#2 can enable gNB#2 to sense that UE#2 is performing USU communication. As a result, when gNB#2 selects the target gNB to be handed over to by UE#2, it can consider the connection between the satellite where the target gNB is located and satellite #1, so as to select the gNB deployed on the satellite with ISL and low ISL latency as much as possible. This can avoid service interruption (e.g., no ISL between the serving satellite after handover and the serving satellite of the other end) or increased latency.

[0400] Option 2 will be introduced below.

[0401] Figure 12 is a schematic flowchart of a communication method according to an embodiment of this application. This communication method is applicable to scheme 2 provided by the system shown in Figure 9 above, and mainly involves the first network element. As shown in Figure 12, the communication method includes:

[0402] S1201. In the call establishment process between the first terminal and the second terminal, the first network element serving the first terminal obtains information about the service satellite of the second terminal.

[0403] It is understandable that the first network element can be determined based on the SIP invite message or other messages. For details, please refer to the relevant explanation of step S1005 in Figure 10, which will not be repeated here.

[0404] S1202, the first network element determines whether the first terminal should perform communication using the first communication mode based on the ISL (In-Service Level) maintenance time between the service satellite of the first terminal and the service satellite of the second terminal. The first communication mode refers to data exchange between terminals via satellite without using ground equipment.

[0405] It is understood that the specific implementation of step S1202 can be found in the relevant description of step S1001 in Figure 10, and will not be repeated here.

[0406] In addition, in the method flow shown in Figure 12, the first network element can be the first network element in Figures 9 and 10, or it can be an IMS network element, such as P-CSCF or S-CSF. This application embodiment does not specifically limit this.

[0407] In this embodiment of the application, during the call setup process between the first terminal and the second terminal, the first network element can consider in advance the possibility of subsequent ISL interruption due to satellite and / or terminal movement based on the time the ISL connection is maintained between the two serving satellites. This allows for further determination of whether the first terminal can perform communication in the first communication mode (i.e., perform USU communication), thereby avoiding service interruption or increased latency that may result from subsequent satellite switching.

[0408] The above describes the overall method flow corresponding to Scheme 2. The following section uses the call setup process shown in Figure 11 as an example to introduce the above communication method in detail.

[0409] Figure 13 is a schematic flowchart of a communication method provided in an embodiment of this application. As shown in Figure 13, the key difference between Figure 13 and Figure 11 is that in step S1103, gNB#2 determines the USU communication connection maintenance time based on the satellite currently connected to UE#1 (i.e., satellite #1) and the satellite connected to UE#2 (i.e., satellite #2), as well as ephemeris information, and then determines whether to activate USU communication based on this time.

[0410] As shown in Figure 13, the communication method includes: S1301 to S1311, steps S1301 to S1302 are the same as steps S1101 to S1102, steps S1304 to S1306 are the same as steps S1104 to S1106, and steps S1307 to S1311 are the same as steps S1110 to S114.

[0411] S1303, P-CSCF#2 or S-CSCF#2 determines that IMS PDU session #2 can perform USU communication, specifically including: the time that UE#2 and UE#1 maintain USU communication (or the time that satellite #1 and satellite #2 maintain ISL) is greater than or equal to the second threshold.

[0412] It is understood that the specific implementation of step S1303 can be found in the relevant description of step S1001 in Figure 10, and will not be repeated here.

[0413] In the call setup process between UE#1 and UE#2 in this application embodiment, the IMS network element (e.g., P-CSCF or S-CSCF) can consider the possibility of subsequent ISL interruption or increased latency due to satellite and / or terminal movement based on the time and latency of maintaining the ISL connection between the two serving satellites, and further determine whether USU communication can be performed to avoid service interruption or increased latency due to subsequent satellite handover.

[0414] Option 3 will be introduced below.

[0415] Figure 14 is a schematic flowchart of a communication method provided in an embodiment of this application. This communication method is applicable to scheme 3 provided by the system shown in Figure 9 above, and mainly involves the first network element. As shown in Figure 14, the communication method includes:

[0416] S1401, when the first terminal is about to be switched to the target access network device and the first terminal is performing communication in the first communication mode, the first network element determines whether the first terminal can continue to perform communication in the first communication mode after switching to the target access network device. Here, the first communication mode refers to data exchange between terminals via satellite, without using ground equipment.

[0417] It is understood that the specific implementation of step S1401 can be found in step S1011 in Figure 10, and will not be repeated here.

[0418] S1402, if the first terminal cannot continue communication in the first communication mode after switching to the target access network device, the first network element triggers a switch from the first communication mode to the second communication mode. The second communication mode refers to data exchange between terminals via ground equipment.

[0419] It is understood that the specific implementation of step S1402 can be found in step S1012, and will not be repeated here.

[0420] In addition, the first network element in the embodiments of this application can be the first network element in Figure 9, such as SMF or PCF, etc., or the first network element can be an IMS network element, such as P-CSCF.

[0421] In the handover process of the first terminal in this application embodiment, when the first terminal performs communication in the first communication mode (i.e., USU communication), the first network element determines whether the first terminal can continue to perform USU communication after switching to the target access network device. If USU communication cannot continue, the USU communication is converted to the second communication (i.e., ground routing), thereby avoiding service interruption or increased latency after the handover.

[0422] The above describes the overall method flow corresponding to Scheme 3. The following section will introduce the communication method in detail with reference to Figures 15 to 18.

[0423] It is understood that handover can include N2-based handover and Xn-based handover, and during the handover process, the CN network element or IMS network element can determine whether USU communication can continue after the handover, for a total of four combinations, which will be introduced below.

[0424] It should be understood that the following method flow continues to use the architecture shown in Figure 11, that is, the first communication method is replaced by USU communication, and the second communication method is replaced by terrestrial routing. This will be explained uniformly here and will not be repeated below. In addition, the difference from the method flow shown in Figure 11 is as follows: taking SMF#1 serving UE#1 as the first network element, P-CSCF#1 as the IMS network element serving the first terminal, satellite#1 as the first satellite, gNB#1 as the first access network device, and satellite#2 as the second satellite as an example for explanation.

[0425] Method 1: Based on Xn handover, the IMS network element (e.g., P-CSCF or S-CSCF) is responsible for making the decision:

[0426] Figure 15 is a schematic flowchart of a communication method provided in an embodiment of this application. As shown in Figure 15, the communication method includes: S1501 to S1513.

[0427] S1501, determine to execute USU communication and IMS to subscribe to satellite changes from CN.

[0428] It is understood that the specific details of determining the execution of USU communication can be found in the call setup process S1101 to S1114 in Figure 11 above. Furthermore, after the call setup process is completed between UE#1 and UE#2, the IMS network element corresponding to UE#1 (e.g., P-CSCF#1 and / or S-CSCF#1) can subscribe to the target satellite change notification for UE#1 used for handover from the CN network element corresponding to UE#1 (e.g., SMF#1), so as to determine whether USU communication can continue after handover to the target satellite during the handover process.

[0429] S1502, Handover preparation.

[0430] It is understandable that in the Xn-based handover process, UE#1 sends a measurement report to gNB#1 on the serving satellite (i.e., satellite #1). Then, gNB#1 can determine that gNB#3 deployed on satellite #3 is the target access network device based on the measurement report, and thus satellite #3 is the target satellite.

[0431] S1503, Handover execution.

[0432] S1504, gNB#3 sends an N2 path switch request to AMF#1. Correspondingly, AMF#1 receives the N2 path switch request from gNB#3. The N2 path switch request is used to notify UE#1 that it has moved to the target cell, i.e., the cell covered by satellite #3.

[0433] S1505, AMF#1 sends a PDU session update session management context request to SMF#1. Correspondingly, SMF#1 receives the PDU session update session management context request from AMF#1. The PDU session update session management context request may include: an indication that the PDU session will be switched (along with information about the N3 addressing to be used and information about the transmitted QoS flow).

[0434] S1506 and SMF#1 indicate that USU communication is in progress.

[0435] It is understandable that SMF#1, upon receiving the indication that the PDU session will be switched, can first determine whether the current IMS PDU session #1 is performing USU communication. If USU communication is being performed, the information of the target satellite (i.e., satellite #3) can be notified to the IMS network element so that the IMS network element can further determine whether USU communication can be performed.

[0436] S1507, SMF#1 sends a notification message to P-CSCF#1. Correspondingly, P-CSCF#1 receives a notification message from SMF#1. The notification message includes the identification information of the target access network device, which may include the identifier of the target gNB (i.e., gNB#3) and / or the identifier of the target satellite (i.e., satellite#3).

[0437] It can be understood that SMF#1 sends a notification message to P-CSCF#1, which may specifically include: SMF#1 sending a notification message to PCF#1, and then PCF#1 sending the notification message to P-CSCF#1.

[0438] S1508, P-CSCF#1, or S-CSCF#1 determines whether UE#1 can continue to perform USU communication after switching to the target access network device based on the information from the target satellite (i.e., satellite #3) and satellite #2.

[0439] It is understood that the specific implementation of step S1508 can be found in step S1116 in Figure 11, and will not be repeated here.

[0440] S1509. If USU communication cannot continue after UE#1 switches to the target access network device, P-CSCF#1 triggers the method of falling back USU communication to the ground route.

[0441] It is understood that P-CSCF#1 can configure ground IMS-AGW#1 resources for IMS PDU session #1, and P-CSCF#2 can configure ground IMS-AGW#2 resources for IMS PDU session #2, so that voice data between UE#1 and UE#2 can be transmitted through ground IMS-AGW#1 and IMS-AGW#2. The specific implementation of step S1509 can be found in the relevant description of step S1120 in Figure 11, and will not be repeated here.

[0442] S1510, P-CSCF#1 sends a response message to SMF#1. Correspondingly, SMF#1 receives the response message from P-CSCF#1. The response message includes third indication information, which is used to indicate the termination of USU communication.

[0443] It is understandable that SMF#1 can update the session management context based on the indication information used to indicate the termination of USU communication, in order to update the data forwarding rules of UE#1's IMS PDU session #1, and configure the ground UPF, etc.

[0444] S1511, SMF#1 sends a PDU session update session management context response to AMF#1. Correspondingly, AMF#1 receives the PDU session update session management context response from SMF#1.

[0445] S1512, AMF#1 sends an N2 path switch acknowledgment (N2 path switch Ack) to gNB#3. Correspondingly, gNB#3 receives the N2 path switch acknowledgment from AMF#1. The N2 path switch acknowledgment may include the address information of PSA#1.

[0446] S1513. If UE#1 can continue to perform USU communication after switching to the target access network, update the N6 address information.

[0447] It is understandable that, if it is determined that UE3#1 can continue to perform USU communication after handover to the target access network device (i.e., gNB#3), the current IMS PDU session configuration can be maintained, and ULCL UPF and PSA UPF can be deployed on satellite #3 to complete other handover procedures, such as S1511 to S1513 mentioned above. After the handover procedure is completed, UE#1, the serving network element corresponding to UE#1, UE#2, and the serving network element of UE#2 update the N6 address information between the IMS network and the UPF.

[0448] In the Xn-based handover process of this application embodiment, the IMS network element can subscribe to satellite changes from SMF#1, thereby obtaining the target satellite during the handover process. Before the handover is completed, it can determine in advance whether USU communication can continue after the handover to the target satellite. In the event that USU communication cannot continue, USU communication can be returned to the ground route, thereby avoiding service interruption or increased latency.

[0449] Method 2: Based on N2 handover, the IMS network element is responsible for making the decision:

[0450] Figure 16 is a schematic flowchart of a communication method provided in an embodiment of this application. As shown in Figure 16, the communication method includes: S1601 to S1612, where step S1601 is the same as step S1501, steps S1604 to S1610 are the same as steps S1505 to S1511, and step S1612 is the same as step S1513.

[0451] S1602, gNB#1 confirms the trigger switch.

[0452] S1603 and gNB#1 send a handover request to AMF#1.

[0453] It is understandable that the handover request is used to notify AMF#1 that UE#1 wants to hand over to the target gNB (i.e., gNB#3) on the target satellite (i.e., satellite #3), and that the resources of IMS PDU session #1 need to be handed over.

[0454] S1611, AMF#1 sends a handover request to gNB#3. Correspondingly, gNB#3 receives the handover request from AMF#1. The handover request is used to request a switch of the serving gNB of UE#1 from gNB#1 to gNB#3.

[0455] In this embodiment of the application, during the handover process based on N2, the IMS network element can subscribe to satellite changes from SMF#1, thereby obtaining the target satellite during the handover process. Before the handover is completed, it can determine in advance whether USU communication can continue after the handover to the target satellite. In the event that USU communication cannot continue, USU communication can be returned to the ground route, thereby avoiding service interruption or increased latency.

[0456] Method 3: Based on Xn handover, the CN network element (e.g., SMF) is responsible for making the determination:

[0457] Figure 17 is a schematic flowchart of a communication method provided in an embodiment of this application. As shown in Figure 17, the communication method includes: S1701 to S1712, steps S1702 to S1705 are the same as steps S1502 to S1505, and steps S1708 to S1712 are the same as steps S1509 to S1513.

[0458] S1701, Confirm execution of USU communication.

[0459] It is understood that the specific implementation of step S1701 can be found in step S1501, and will not be repeated here.

[0460] S1706 and SMF#1 determine whether UE#1 can continue to perform USU communication after switching to the target access network equipment based on the information from the target satellite (i.e., satellite #3) and satellite #2.

[0461] It is understood that the specific implementation of step S1706 can be found in step S1116 in Figure 11, and will not be repeated here.

[0462] S1707. If USU communication cannot continue after UE#1 switches to the target access network device, SMF#1 sends a notification message to P-CSCF#1. Correspondingly, P-CSCF#1 receives the notification message from SMF#1. The notification message includes third indication information, which is used to trigger the fallback of USU communication to ground routing.

[0463] It is understandable that the third instruction message can indicate the termination of USU communication.

[0464] In the present application embodiment, in the handover process based on Xn, the CN network element SMF can obtain the target satellite during the handover process and determine in advance whether USU communication can continue after the handover to the target satellite before the handover is completed. In the case that USU communication cannot continue, the USU communication will fall back to the ground route, thereby avoiding service interruption or increased latency.

[0465] Method 4: Based on N2 handover, the CN network element is responsible for making the decision:

[0466] Figure 18 is a schematic flowchart of a communication method provided in an embodiment of this application. As shown in Figure 18, the communication method includes: S1801 to S1811, where step S1801 is the same as step S1701, steps S1802 to S1804 are the same as steps S1602 to S1604, steps S1805 to S1809 are the same as steps S1706 to S1710, and steps S1810 to S1811 are the same as steps S1611 to S1612.

[0467] It is understandable that the difference between Figure 18 and Figure 16 is that SMF#1 in the CN network element determines whether UE#1 can continue to perform USU communication after switching to the target access network device.

[0468] In this embodiment of the application, during the handover process based on N2, the CN network element SMF can obtain information about the target satellite where the target access network device is located during the handover process, and determine in advance whether UE#1 can continue to perform USU communication after handover to the target access network before the handover is completed. In the event that USU communication cannot continue to be performed, the USU communication will be returned to the ground route, thereby avoiding service interruption or increased latency.

[0469] It should be understood that, in the above-mentioned N2-based handover process, in step S1603 or SS1803, since gNB#1 may not have access network information of the peer UE#2, the handover request may not carry the identifier of the target satellite and / or the target gNB, but carries the identifier of at least two satellites and / or gNBs. Thus, the AMF and / or SMF can determine the target satellite (i.e., determine the target gNB) from the at least two satellites based on the access network information of UE#2. The target gNB can be the target satellite in S1116. For example, the target satellite has a direct ISL or indirect ISL (through relay of intermediate satellites) with the serving satellite of UE#2, or the communication through direct or indirect ISL can meet certain latency requirements, or the latency of direct or indirect ISL is better than the latency of terrestrial routing.

[0470] The above mainly describes the solutions provided by the embodiments of this application from the perspective of interaction between various network elements. Correspondingly, the embodiments of this application also provide a communication device for implementing the various methods described above. This communication device can be the first network element or the first access network device in the above method embodiments, or a device containing the first network element or the first access network device, or a component usable in the first network element or the first access network device. It is understood that, in order to achieve the above functions, the communication device includes hardware structures and / or software modules corresponding to the execution of each function. Those skilled in the art should readily recognize that, in conjunction with the units and algorithm steps of the various examples described in the embodiments disclosed herein, 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 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.

[0471] This application embodiment can divide the communication device into functional modules according to the above method embodiment. For example, each function can be divided into a separate functional module, or two or more functions can be integrated into one processing module. The integrated module can be implemented in hardware or as a software functional module. It should be noted that the module division in this application embodiment is illustrative and only represents one logical functional division. In actual implementation, there may be other division methods.

[0472] Taking the communication device as an example, specifically the first network element or the first access network device in the above method embodiments, Figure 19 is a schematic diagram of the structure of a communication device provided in an embodiment of this application. As shown in Figure 19, the communication device 1900 includes a processing module 1901 and a transceiver module 1902. The processing module 1901 is used to execute the processing functions of the first network element or the first access network device in the above method embodiments. The transceiver module 1902 is used to execute the transceiver functions of the first network element or the first access network device in the above method embodiments.

[0473] All relevant content of each step involved in the above method embodiments can be referenced from the functional description of the corresponding functional module, and will not be repeated here.

[0474] Since the communication device 1900 provided in this embodiment can execute the above-described communication method, the technical effects it can achieve can be referred to the above-described method embodiments, and will not be repeated here.

[0475] In one possible design, the transceiver module 1902 may include a receiving module and a transmitting module (not shown in Figure 19). The transceiver module is used to implement the transmitting and receiving functions of the communication device 1900.

[0476] In one possible design, the communication device 1900 may further include a storage module (not shown in FIG. 19) that stores programs or instructions. When the processing module 1901 executes the program or instructions, the communication device 1900 can perform the functions of the first network element or the first access network device in any of the methods shown in FIG. 5 to FIG. 11.

[0477] It should be understood that the processing module 1901 involved in the communication device 1900 can be implemented by a processor or processor-related circuit components, and can be a processor or processing unit; the transceiver module 1902 can be implemented by a transceiver or transceiver-related circuit components, and can be a transceiver or transceiver unit.

[0478] For example, FIG20 is a schematic diagram of another communication device provided in an embodiment of this application. The communication device may be a first network element or a first access network device, or it may be a chip (system) or other component or assembly that can be disposed in the first network element or the first access network device. As shown in FIG20, the communication device 2000 may include a processor 2001. In one possible design, the communication device 2000 may further include a memory 2002 and / or a transceiver 2003. The processor 2001 is coupled to the memory 2002 and the transceiver 2003, for example, they can be connected via a communication bus.

[0479] The following section, with reference to Figure 20, provides a detailed description of each component of the communication device 2000:

[0480] The processor 2001 is the control center of the communication device 2000. It can be a single processor or a collective term for multiple processing elements. For example, the processor 2001 can be one or more central processing units (CPUs), application-specific integrated circuits (ASICs), or one or more integrated circuits configured to implement the embodiments of this application, such as one or more digital signal processors (DSPs), or one or more field-programmable gate arrays (FPGAs).

[0481] In one possible design, the processor 2001 can perform various functions of the communication device 2000 by running or executing software programs stored in the memory 2002 and calling data stored in the memory 2002.

[0482] In a specific implementation, as one example, processor 2001 may include one or more CPUs, such as CPU0 and CPU1 shown in FIG20.

[0483] In a specific implementation, as one embodiment, the communication device 2000 may also include multiple processors, such as processors 2001 and 2004 shown in FIG. 20. Each of these processors may be a single-core processor (single-CPU) or a multi-core processor (multi-CPU). Here, a processor may refer to one or more devices, circuits, and / or processing cores for processing data (e.g., computer program instructions).

[0484] The memory 2002 is used to store the software program that executes the solution of this application, and is controlled by the processor 2001 to execute it. The specific implementation method can be referred to the above method embodiment, and will not be repeated here.

[0485] In one possible design, the memory 2002 can be a read-only memory (ROM) or other type of static storage device capable of storing static information and instructions, random access memory (RAM) or other type of dynamic storage device capable of storing information and instructions, or it can be an electrically erasable programmable read-only memory (EEPROM), a compact disc read-only memory (CD-ROM) or other optical disc storage, optical disc storage (including compressed optical discs, laser discs, optical discs, digital universal optical discs, Blu-ray discs, etc.), magnetic disk storage media or other magnetic storage devices, or any other medium capable of carrying or storing desired program code in the form of instructions or data structures and accessible by a computer, but is not limited thereto. The memory 2002 can be integrated with the processor 2001 or exist independently and coupled to the processor 2001; this application embodiment does not specifically limit this.

[0486] Transceiver 2003 is used for communication with other communication devices. For example, if communication device 2000 is a first network element, transceiver 2003 can be used to communicate with a first access network device. As another example, if communication device 2000 is a first access network device, transceiver 2003 can be used to communicate with the first network element.

[0487] In one possible design, transceiver 2003 may include a receiver and a transmitter (not shown separately in Figure 20). The receiver is used to implement the receiving function, and the transmitter is used to implement the transmitting function.

[0488] In one possible design, the transceiver 2003 can be an input / output interface or interface circuit for inputting and / or outputting signals.

[0489] In one possible design, the transceiver 2003 can be integrated with the processor 2001, or it can exist independently and be coupled to the processor 2001. This application embodiment does not specifically limit this.

[0490] It should be noted that the structure of the communication device 2000 shown in Figure 20 does not constitute a limitation on the communication device. The actual communication device may include more or fewer components than shown, or combine certain components, or have different component arrangements.

[0491] Furthermore, the communication device 2000 can execute the above-described communication method, and therefore the technical effects it can achieve can be referred to the above-described method embodiments, which will not be repeated here.

[0492] In one possible implementation, this application also provides a computer-readable storage medium storing a computer program or instructions that, when executed by a computer, implement the functions of the above-described method embodiments.

[0493] In one possible implementation, this application also provides a computer program product that, when executed by a computer, implements the functions of the above-described method embodiments.

[0494] In one possible implementation, this application embodiment also provides a communication system, which includes the first network element and the first access network device described in the above method embodiments.

[0495] In one possible implementation, this application embodiment also provides a communication method, which includes the method described in any of the above method embodiments or any implementation thereof.

[0496] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented using software programs, implementation can be, in whole or in part, in the form of a computer program product. This computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the flow or function according to the embodiments of this application is generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium accessible to a computer or a data storage device including one or more servers, data centers, etc., that can be integrated with the medium. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium, or a semiconductor medium (e.g., a solid-state drive (SSD)).

[0497] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented 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.

[0498] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0499] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0500] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0501] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0502] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0503] Although this application has been described herein in conjunction with various embodiments, those skilled in the art, by reviewing the accompanying drawings, the disclosure, and the appended claims, will understand and implement other variations of the disclosed embodiments in carrying out the claimed application. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude multiple instances. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce good results.

[0504] Although this application has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made thereto without departing from the scope of this application. Accordingly, this specification and drawings are merely exemplary illustrations of the application as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from its scope. Thus, if such modifications and modifications fall within the scope of the claims and their equivalents, this application is also intended to include such modifications and modifications.

Claims

1. A communication method characterized by comprising: The method includes: The first network element determines that the first terminal performs communication in a first communication mode, wherein the first communication mode refers to the data between terminals being exchanged via satellite and without the use of ground equipment; The first network element sends a first indication message to the first access network device. The first indication message is used to instruct the first terminal to perform communication in the first communication mode. The first access network device is deployed on the first satellite serving the first terminal.

2. The method of claim 1, wherein, The method further includes: The first network element sends first information to the first access network device. The first information includes information about the second terminal or information about the second satellite serving the second terminal. The second terminal is a terminal that communicates with the first terminal using the first communication method.

3. The method of claim 2, wherein, The method further includes: The first network element receives the identifier of the first target access network device from the first access network device, where the first target access network device is the target access network device to be switched to by the first terminal.

4. The method according to claim 1, characterized in that, The method further includes: The first network element receives second information from the first access network device, the second information including identification information of at least one target access network device to be switched by the first terminal; The first network element determines the second target access network device from the at least one target access network device; The first network element sends the identifier of the second target access network device to the first access network device.

5. The method according to claim 4, characterized in that, The first network element determines the second target access network device from the at least one target access network device based on the information of the third satellite serving the third terminal, wherein the third terminal is a terminal that communicates with the first terminal using the first communication method.

6. The method according to claim 5, characterized in that, The first network element determines the second target access network device from the at least one target access network device based on at least one of the following: Inter-satellite link (ISL) information between the satellite containing each of the at least one target access network devices and the third satellite; The time delay information between the satellite where each of the at least one target access network devices is located and the third satellite.

7. The method according to any one of claims 3-6, characterized in that, The method further includes: The first network element determines whether the first terminal can continue to perform communication using the first communication method after switching to the first target access network device or the second target access network device; If the first terminal cannot continue to perform communication in the first communication mode after switching to the first target access network device or the second target access network device, the first network element triggers the conversion of the first communication mode to the second communication mode, whereby the data between terminals is exchanged through ground equipment.

8. The method according to claim 7, characterized in that, The first network element determines, based on the information from the second satellite, whether the first terminal can continue to perform communication using the first communication method after switching to the first target access network device; Alternatively, the first network element determines, based on information from the third satellite serving the third terminal, whether the first terminal can continue to perform communication using the first communication method after switching to the second target access network device, wherein the third terminal is a terminal that performs communication with the first terminal using the first communication method.

9. The method according to claim 7, characterized in that, The method further includes: The first network element receives second indication information from the first access network device. The second indication information is used to indicate whether the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device. The first network element determines, based on the second instruction information, whether the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device.

10. The method according to any one of claims 7-9, characterized in that, After the first terminal switches to the first target access network device, it can continue to perform communication using the first communication method, specifically including at least one of the following: The satellite containing the first target access network device maintains an ISL (Independent State Link) with the second satellite; The time that the satellite where the first target access network device is located maintains ISL with the second satellite is greater than or equal to the first threshold. Alternatively, the time during which the ISL between the satellite where the first target access network device is located and the second satellite is less than or equal to the second threshold is greater than or equal to the third threshold. Alternatively, after the first terminal switches to the second target access network device, it can continue to perform communication using the first communication method, specifically including at least one of the following: The satellite where the second target access network device is located maintains an ISL (Independent State Link) with the third satellite serving the third terminal; The time that the satellite containing the second target access network device maintains an ISL with the third satellite is greater than or equal to the first threshold. Alternatively, the time during which the ISL between the satellite where the second target access network device is located and the third satellite is less than or equal to the second threshold is greater than or equal to the third threshold. The third terminal is a terminal that communicates with the first terminal using the first communication method.

11. The method according to any one of claims 7-10, characterized in that, The first network element triggers a switch from the first communication mode to the second communication mode, specifically including: The first network element sends a third instruction message to the Internet Protocol Multimedia Subsystem (IMS) network element serving the first terminal, the third instruction message being used to instruct the first communication mode to be converted to the second communication mode.

12. The method according to any one of claims 1-11, characterized in that, Before the first network element determines that the first terminal is performing communication in the first communication mode, the method further includes: The first network element obtains instruction information from the IMS network element serving the first terminal, which instructs the first terminal to perform communication in the first communication mode.

13. The method according to any one of claims 1-12, characterized in that, The first network element determines that the first terminal performs communication in a first communication mode, specifically including: The first network element determines that the first terminal and the second terminal communicate using the first communication method based on the ISL (Independent State Link) time maintained between the first satellite and the second satellite serving the second terminal.

14. A communication method, characterized in that, The method includes: The first access network device receives first indication information from the first network element. The first indication information is used to instruct the first terminal to perform communication in a first communication mode. The first communication mode refers to the data between terminals being exchanged via satellite and not through ground equipment. The first access network device is deployed on a first satellite serving the first terminal. The first access network device determines the first target access network device to be switched to by the first terminal based on the first indication information, or sends the identification information of at least one target access network device to be switched to by the first terminal to the first network element.

15. The method according to claim 14, characterized in that, The method further includes: The first access network device receives an identifier of a second target access network device from the first network element, wherein the second target access network device is a target access network device among the at least one target access network devices.

16. The method according to claim 14, characterized in that, The method further includes: The first access network device receives first information from the first network element. The first information includes information about the second terminal or information about the second satellite serving the second terminal. The information about the second terminal is used to obtain information about the second satellite. The second terminal is a terminal that communicates with the first terminal using the first communication method. The first access network device determines the first target access network device based on the first indication information and the information of the second satellite.

17. The method according to claim 16, characterized in that, The method further includes: The first access network device determines the measurement configuration information based on the information from the second satellite; The first access network device sends the measurement configuration information to the first terminal.

18. The method according to claim 17, characterized in that, The method further includes: The first access network device receives a measurement report from the first terminal; The first access network device specifically determines the first target access network device based on the first indication information, the information of the second satellite, and the measurement report.

19. The method according to claim 17 or 18, characterized in that, The priority among the multiple measurement targets corresponding to the measurement configuration information is determined based on at least one of the following: ISL information between the satellite corresponding to each of the multiple measurement targets and the second satellite; The time delay information between the satellite corresponding to each of the multiple measurement targets and the second satellite.

20. The method according to any one of claims 16-19, characterized in that, The first target access network device is determined based on at least one of the following: Inter-satellite link (ISL) information between the satellite where each candidate access network device is located and the second satellite; The time delay information between the satellite where each candidate access network device is located and the second satellite in the multiple candidate access network devices.

21. The method according to any one of claims 16-20, characterized in that, The method further includes: The first access network device sends a second indication message to the first network element. The second indication message is used to indicate whether the first terminal can continue to perform communication in the first communication mode after switching to the first target access network device.

22. The method according to claim 21, characterized in that, If the first terminal cannot continue to perform communication in the first communication mode after the second indication information indicates that the first terminal has switched to the first target access network device, the second indication information is used to trigger the conversion of the first communication mode to the second communication mode, whereby the data between the terminals is exchanged through ground equipment.

23. The method according to claim 21 or 22, characterized in that, After the first terminal switches to the first target access network device, it can continue to perform communication using the first communication method, specifically including at least one of the following: The satellite containing the first target access network device maintains an ISL (Independent State Link) with the second satellite; The time that the satellite where the first target access network device is located maintains ISL with the second satellite is greater than or equal to the first threshold. Alternatively, the time during which the ISL between the satellite where the first target access network device is located and the second satellite is less than or equal to the second threshold is greater than or equal to the third threshold.

24. A communication method, characterized in that, The method includes: In the call setup process between the first terminal and the second terminal, the first network element serving the first terminal obtains information about the service satellite of the second terminal; The first network element determines whether the first terminal performs communication in the first communication mode based on the time the service satellite of the first terminal maintains the inter-satellite link (ISL) between the service satellite of the first terminal and the service satellite of the second terminal. The first communication mode refers to the data between the terminals being exchanged through satellites without the use of ground equipment.

25. A communication method, characterized in that, The method includes: When a first terminal is to be switched to a target access network device and the first terminal is performing communication in a first communication mode, the first network element determines whether the first terminal can continue to perform communication in the first communication mode after switching to the target access network device. The first communication mode refers to the data between terminals being exchanged via satellite and not through ground equipment. If the first terminal cannot continue to perform communication in the first communication mode after switching to the target access network device, the first network element triggers the conversion of the first communication mode to the second communication mode, whereby data between terminals is exchanged through ground equipment.

26. A communication device, characterized in that, The communication device includes a module or unit for performing the method according to any one of claims 1-25.

27. A communication device, characterized in that, The communication device includes at least one processor, the at least one processor being configured to cause the communication device to perform the method as described in any one of claims 1-25 via logic circuitry and / or execution instructions.

28. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes instructions that, when executed, cause the method of any one of claims 1-25 to be implemented.

29. A computer program product, characterized in that, The computer program product includes instructions that, when executed, cause the method of any one of claims 1-25 to be implemented.

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