Handover method and apparatus

Abstract

The present application discloses a handover method and apparatus for completing cell synchronization between a terminal and a target cell for handover, and relates to the wireless communication field. The method can be applied to handover of a terminal from a first network device to a second network device. The method includes: connecting to a first cell through the first network device, performing downlink synchronization with a downlink synchronization signal of the second cell sent by the second network device, and connecting to the second cell through the second network device. The first cell and the second cell have the same cell identifier.

Description

[Technical Field]

[0001] The present application relates to the field of wireless communications, and in particular to a handover method and apparatus. [Background technology]

[0002] This application claims priority to Patent Application No. 202111446655.8, entitled "HANDOVER METHOD AND APPARATUS," filed with the State Intellectual Property Office of China on November 30, 2021, the entire contents of which are incorporated herein by reference.

[0003] To improve communication quality and reliability, in addition to access network devices such as base stations, terminals may also communicate with other network devices such as satellites or unmanned aerial vehicles. For example, these network devices may function as base stations to provide communication services to terminals, or these network devices may function as relay devices to help terminals communicate with base stations. In this way, communication services may be provided to areas such as oceans and forests that are difficult for access network devices to cover.

[0004] Typically, one access network device may have multiple cells. Typically, the cell identifiers of the cells do not change over a long period of time. However, in communications between a terminal and a network device, such as a satellite or an unmanned aerial vehicle, the network device may be mobile, and the physical area covered by the network device may change. In this case, if the cell identifier is associated with the network device, the terminal needs to frequently perform cell handovers even if the terminal is not moving, which increases the signaling overhead on the Uu interface. To reduce the frequency of cell handovers performed by the terminal, the cell identifier may be associated with a geographical location. However, in this case, even if the network device communicating with the terminal changes, the terminal cannot detect the change. As a result, the terminal device cannot perform cell synchronization. Summary of the Invention

[0005] The embodiments of the present application provide a handover method and apparatus for completing cell synchronization between a terminal and a target cell for handover.

[0006] According to a first aspect, a handover method is provided. A communication device implementing the handover method may be a terminal, or may be a module used in the terminal, such as a chip or a chip system. In the following, an example in which the execution body is a terminal is used for explanation. The method may be applied to handover of a terminal from a first network device to a second network device. The method includes: connecting to a first cell through the first network device; performing downlink synchronization with a downlink synchronization signal of the second cell sent by the second network device; and connecting to the second cell through the second network device. The first cell and the second cell have the same cell identifier.

[0007] Based on the method provided in the first aspect, when a first network device is switched to a second network device but the cell identifier of the cell serving the terminal does not change, the terminal may perform downlink synchronization with a downlink synchronization signal of the second cell sent by the second network device, so that the terminal can still perform normal communication after the network device switch. For example, before the network device switch, the first network device may serve the terminal, and the terminal may communicate with the first network device. After performing downlink synchronization with the downlink synchronization signal of the second cell sent from the second network device, the second network device may serve the terminal, and the terminal may communicate with the second network device. Alternatively, before the network device switch, the first access network device may serve the terminal, and the terminal may communicate with the first access network device via the first network device. After performing downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device, the second access network device may provide service to the terminal, and the terminal may communicate with the second access network device via the second network device.

[0008] In a possible implementation, the first cell is the same as the second cell.

[0009] Based on the foregoing method, after the terminal is handed over from the first network device to the second network device, the cell accessed by the terminal remains unchanged.

[0010] In a possible implementation, the method further includes receiving first indication information, wherein the first indication information indicates to the terminal to perform downlink synchronization, or the first indication information indicates to the terminal to stop using the downlink timing of the first cell.

[0011] Based on the foregoing method, the terminal may be triggered to perform downlink synchronization based on the first indication information, so that subsequent communication is performed normally.

[0012] In a possible implementation, the first indication information is carried in the intra-cell handover command based on a time condition.

[0013] Based on the foregoing method, the first indication information may be carried in the intra-cell handover command based on a time condition to trigger the terminal to perform downlink synchronization.

[0014] In a possible implementation, the first indication information is carried in a dedicated radio resource control (RRC) message, a dedicated media access control (MAC-CE) or a dedicated physical channel, or the first indication information is carried in a common RRC message, a common MAC-CE or a common physical channel.

[0015] Based on the foregoing method, the first indication information is carried in multiple types of messages, which may improve the adaptability and versatility of sending the first indication information.

[0016] In a possible implementation, the method further includes receiving configuration information, the configuration information indicating a configuration of the downlink synchronization signal.

[0017] Based on the aforementioned method, the terminal may determine the time-domain position of the measurement window of the downlink synchronization signal of the second cell, so that the terminal monitors the downlink synchronization signal of the second cell at the time-domain position.

[0018] In a possible implementation, the configuration information includes at least one of a length of a measurement window of the downlink synchronization signal, periodicity information of the measurement window of the downlink synchronization signal, or a first offset, wherein at least one of the periodicity information or the first offset is for determining a start position of the measurement window.

[0019] Based on the aforementioned method, the terminal may determine a start position of a measurement window of the downlink synchronization signal of the second cell based on at least one of the periodicity information or the first offset, and may also determine a time-domain position of the measurement window based on the start position and length of the measurement window of the downlink synchronization signal of the second cell.

[0020] In a possible implementation, the method further includes determining to switch the connected network device. Performing downlink synchronization with a downlink synchronization signal of the second cell sent by the second network device includes performing downlink synchronization with the downlink synchronization signal when an absolute value of a difference between a first distance and a second distance is greater than or equal to a first threshold, where the first distance is a distance between the terminal and the first network device and the second distance is a distance between the terminal and the second network device.

[0021] Based on the above method, the terminal performs downlink synchronization when it decides to switch the connected network device and when the absolute value of the difference between the first distance and the second distance is equal to or greater than a first threshold. In other words, the terminal performs downlink synchronization when the first network device gradually moves away from the terminal, when the second network device gradually moves closer to the terminal, and when the difference between the distance between the terminal and the first network device and the distance between the terminal and the second network device is equal to or greater than a first threshold. When the distance between the terminal and the first network device is the same as the distance between the terminal and the second network device, or when the difference between the distance between the terminal and the first network device and the distance between the terminal and the second network device is less than a first threshold, it may be understood that the difference between the time estimated by the terminal when the downlink synchronization signal of the first cell sent by the first network device arrives at the terminal and the time estimated by the terminal when the downlink synchronization signal of the second cell sent by the second network device arrives at the terminal is equal to or less than a first time difference. Therefore, to avoid performing unnecessary downlink synchronization, the terminal may still use the downlink synchronization for communication with the first network device as the downlink synchronization for communication with the second network device.

[0022] In a possible implementation, determining to switch the connected network device includes determining to switch the connected network device when the remaining service time of the first network device is determined to be 0.

[0023] In the above method, the remaining service time may indicate the remaining time during which the first network device can be connected to the terminal. Therefore, based on the above method, when the first network device cannot be connected to the terminal, the terminal may decide to switch the connected network device.

[0024] In a possible implementation, performing downlink synchronization with a downlink synchronization signal of the second cell sent by the second network device includes searching for the downlink synchronization signal and acquiring downlink timing based on the downlink synchronization signal.

[0025] Based on the above method, the terminal may perform downlink synchronization by searching for a downlink synchronization signal of the second cell to obtain a system frame boundary, a subframe boundary, a slot boundary, and a symbol boundary corresponding to the second cell.

[0026] In a possible implementation, performing downlink synchronization with a downlink synchronization signal of a second cell sent by a second network device includes obtaining a time domain position of the downlink synchronization signal based on location information of the first network device, location information of the second network device, and location information of the terminal.

[0027] Based on the above method, the terminal can estimate the time domain position of the downlink synchronization signal of the second cell based on the location information of the first network device, the location information of the second network device, and the location information of the terminal. In this way, the terminal can obtain downlink timing, i.e., obtain the system frame boundary, subframe boundary, slot boundary, and symbol boundary corresponding to the second cell.

[0028] In a possible implementation, connecting to the second cell via the second network device includes sending a random access signal to the second network device.

[0029] Based on the foregoing method, the terminal may perform a two-step random access procedure or a four-step random access procedure to access the second cell.

[0030] In a possible implementation, the first network device is a first satellite.

[0031] Based on the above method, before the terminal performs downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device, the first satellite may be connected to the terminal, and may provide communication services to areas that are difficult for the access network device to cover, such as oceans and forests, to improve communication reliability.

[0032] In a possible implementation, the first satellite has the functionality of a first access network device, or the first satellite has the functionality of a distributed unit of the first access network device, and the first access network device is configured to provide service to the terminal before the terminal performs downlink synchronization.

[0033] Based on the aforementioned method, before the terminal performs downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device, the first satellite may be used as a first access network device serving the terminal, or the first satellite may be used as a distributed unit of the first access network device serving the terminal. When the first satellite is used as a distributed unit of the first access network device, the first access network device may have the function of a central unit, or the first access network device may be used as a central unit.

[0034] In a possible implementation, the second network device is a second satellite.

[0035] Based on the above method, after the terminal performs downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device, the second satellite may be connected to the terminal, and may provide communication services to areas that are difficult for the access network device to cover, such as oceans and forests, to improve communication reliability.

[0036] In a possible implementation, the second satellite has the functionality of a second access network device, or the second satellite has the functionality of a distribution unit of a second access network device, and the second access network device is configured to provide service to the terminal after the terminal performs downlink synchronization.

[0037] Based on the above method, after the terminal performs downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device, the second satellite may be used as a second access network device to provide services to the terminal, or the second satellite may be used as a distributed unit of the second access network device to provide services to the terminal. When the second satellite is used as a distributed unit of the second access network device, the second access network device may have the function of a central unit, or the second access network device may be used as a central unit.

[0038] According to a second aspect, a handover method is provided. A communication device implementing the handover method may be a first access network device, or may be a module, such as a chip or a chip system, used in the first access network device. Hereinafter, an example in which the execution body is the first access network device is used for description. The method includes: connecting to a terminal through a first cell, where the first cell is a cell connected to the terminal through the first network device; sending first indication information to the terminal, where the first indication information indicates the terminal to perform downlink synchronization or the first indication information indicates the terminal to stop using the downlink timing of the first cell; and connecting to the terminal through a second cell, where the second cell and the first cell have the same cell identifier, the second cell is a cell connected to the terminal through the second network device, and the first cell and the second cell are managed by the first access network device.

[0039] Based on the method provided in the second aspect, a first access network device is connected to a terminal via a first cell and indicates the terminal to perform downlink synchronization or indicates the terminal to stop using the downlink timing of the first cell, so that the terminal can perform downlink synchronization with a downlink synchronization signal of a second cell sent by a second network device. Then, the first access network device is connected to the terminal via the second cell and can continue to provide service to the terminal, so that the terminal can perform normal communication.

[0040] In a possible implementation, the first cell is the same as the second cell.

[0041] Based on the foregoing method, after the terminal is handed over from the first network device to the second network device, the cell accessed by the terminal remains unchanged.

[0042] In a possible implementation, the first indication information is carried in the intra-cell handover command based on a time condition.

[0043] Based on the aforementioned method, the first access network device may indicate to the terminal to perform downlink synchronization or to stop using the downlink timing of the first cell by using an intra-cell handover command based on a time condition.

[0044] In a possible implementation, the first indication information is carried in a dedicated radio resource control (RRC) message, a dedicated media access control element (MAC-CE), or a dedicated physical channel, or the first indication information is carried in a common RRC message, a common MAC-CE, or a common physical channel.

[0045] Based on the foregoing method, the first indication information is carried in multiple types of messages, which may improve the adaptability and versatility of sending the first indication information.

[0046] In a possible implementation, sending the first indication information to the terminal includes sending the first indication information to the terminal when an absolute value of a difference between a first distance and a second distance is greater than or equal to a first threshold, where the first distance is a distance between the terminal and a first network device and the second distance is a distance between the terminal and a second network device.

[0047] Based on the aforementioned method, the first access network device may send first indication information to the terminal, when the absolute value of the difference between the first distance and the second distance is equal to or greater than a first threshold, to indicate the terminal to perform downlink synchronization or to stop using the downlink timing of the first cell. In other words, when the first network device gradually moves away from the terminal, when the second network device gradually moves closer to the terminal, and when the difference between the distance between the terminal and the first network device and the distance between the terminal and the second network device is equal to or greater than a first threshold, the first access network device indicates the terminal to perform downlink synchronization. When the distance between the terminal and the first network device is the same as the distance between the terminal and the second network device, or when the difference between the distance between the terminal and the first network device and the distance between the terminal and the second network device is less than a first threshold, it may be understood that the difference between the time estimated by the first network device when the downlink synchronization signal of the first cell sent by the first network device arrives at the terminal and the time estimated by the first network device when the downlink synchronization signal of the second cell sent by the second network device arrives at the terminal is less than or equal to a first time difference. Therefore, in order to avoid performing unnecessary downlink synchronization, the terminal may still use downlink synchronization for communication with the first network device as downlink synchronization for communication with the second network device. The first access network device may not send the first indication information.

[0048] In a possible implementation, the method further comprises sending configuration information to the terminal, the configuration information indicating a configuration of a downlink synchronization signal of the second cell.

[0049] Based on the above method, the first access network device may send configuration information to the terminal to indicate the time-domain position of the measurement window of the downlink synchronization signal of the second cell to the terminal, so that the terminal can monitor the downlink synchronization signal of the second cell at that time-domain position.

[0050] In a possible implementation, the configuration information includes at least one of a length of a measurement window of the downlink synchronization signal, periodicity information of the measurement window of the downlink synchronization signal, or a first offset, wherein at least one of the periodicity information or the first offset is for determining a start position of the measurement window.

[0051] Based on the aforementioned approach, the terminal may determine a start position of a measurement window of the downlink synchronization signal of the second cell based on at least one of the periodicity information or the first offset, and may also determine a time-domain position of the measurement window based on the start position and length of the measurement window of the downlink synchronization signal of the second cell.

[0052] In a possible implementation, connecting to the terminal via the second cell includes receiving a random access signal from the terminal.

[0053] Based on the foregoing method, the first access network device may implement a two-step random access process or a four-step random access process so that the terminal accesses the second cell.

[0054] In a possible implementation, the first network device is a first satellite.

[0055] Based on the above method, before the terminal performs downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device, the first satellite may be connected to the terminal, and may provide communication services to areas that are difficult for the access network device to cover, such as oceans and forests, to improve communication reliability.

[0056] In a possible implementation, the first satellite has the functionality of a first access network device, or the first satellite has the functionality of a distribution unit of the first access network device, and the first access network device is configured to provide services to terminals.

[0057] Based on the aforementioned method, before the terminal performs downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device, the first satellite may be used as a first access network device serving the terminal, or the first satellite may be used as a distributed unit of the first access network device serving the terminal. When the first satellite is used as a distributed unit of the first access network device, the first access network device may have the function of a central unit, or the first access network device may be used as a central unit.

[0058] In a possible implementation, the second network device is a second satellite.

[0059] Based on the above method, after the terminal performs downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device, the second satellite may be connected to the terminal, and may provide communication services to areas that are difficult for the access network device to cover, such as oceans and forests, to improve communication reliability.

[0060] In a possible implementation, the second satellite has the functionality of the first access network device, or the second satellite has the functionality of the distribution unit of the first access network device.

[0061] Based on the above method, after the terminal performs downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device, the second satellite may be used as a first access network device to provide services to the terminal, or the second satellite may be used as a distributed unit of the first access network device to provide services to the terminal. When the second satellite is used as a distributed unit of the first access network device, the first access network device may have the function of a central unit or may be used as a central unit.

[0062] According to a third aspect, a communication device is provided, configured to implement the aforementioned method. The communication device may be the terminal of the first aspect or a device including the terminal. The communication device includes corresponding modules, units, or means for implementing the aforementioned method provided in the first aspect. The modules, units, or means may be implemented by hardware, software, or hardware executing corresponding software. The hardware or software includes one or more modules or units corresponding to the aforementioned functions.

[0063] Regarding the third aspect, in a possible implementation, the communication device may include a communication module and a processing module. The processing module may be configured to implement a processing function in the first aspect and any possible implementation of the first aspect. The processing module may be, for example, a processor. The communication module may also be referred to as a transceiver unit or transceiver module, and may be configured to implement a sending function and / or a receiving function in the first aspect and any possible implementation of the first aspect. The communication module may include a transceiver circuit, a transceiver device, a transceiver, or a communication interface.

[0064] With respect to the third aspect, in a possible implementation, the communication module includes a sending module and a receiving module, which are configured to implement sending and receiving functions, respectively, in the first aspect and in any possible implementation of the first aspect.

[0065] According to a fourth aspect, there is provided a communication device for implementing the aforementioned method. The communication device may be the first access network device in the second aspect or a device including the first access network device. The communication device includes corresponding modules, units, or means for implementing the aforementioned method provided in the second aspect. The modules, units, or means may be implemented by hardware, software, or hardware executing corresponding software. The hardware or software includes one or more modules or units corresponding to the aforementioned functions.

[0066] Regarding the fourth aspect, in a possible implementation, the communication device may include a communication module. The communication module may also be referred to as a transceiver unit or a transceiver module, and may be configured to implement a sending function and / or a receiving function in the second aspect and any possible implementation of the second aspect. The communication module may include a transceiver circuit, a transceiver device, a transceiver, or a communication interface.

[0067] With respect to the fourth aspect, in a possible implementation, the communication module includes a sending module and a receiving module, which are configured to implement sending and receiving functions, respectively, in the second aspect and in any possible implementation of the second aspect.

[0068] According to a fifth aspect, there is provided a communications device, the communications device including a processor coupled to a memory and configured to read instructions in the memory and then perform the method according to the first aspect in accordance with the instructions. The communications device may be the terminal of the first aspect or a device including the terminal.

[0069] According to a sixth aspect, there is provided a communications apparatus, the communications apparatus including a processor coupled to a memory and configured to read instructions in the memory and then perform the method according to the second aspect in accordance with the instructions. The communications apparatus may be the first access network device of the second aspect or an apparatus including the first access network device.

[0070] With regard to the fifth or sixth aspect, in a possible implementation, the communication device further includes a memory, which is configured to store necessary program instructions and necessary data.

[0071] Regarding the fifth or sixth aspect, in a possible implementation, the communication device is a chip or a chip system. Optionally, when the communication device is a chip system, the communication device may include a chip, or may include a chip and another individual component.

[0072] According to a seventh aspect, there is provided a communications device, the communications device including a processor and an interface circuit, the interface circuit configured to receive a computer program or instructions and transmit the computer program or instructions to the processor, the processor configured to execute the computer program or instructions to enable the communications device to perform the method according to the first aspect.

[0073] According to an eighth aspect, there is provided a communications device, the communications device including a processor and an interface circuit, the interface circuit configured to receive a computer program or instructions and transmit the computer program or instructions to the processor, the processor configured to execute the computer program or instructions to enable the communications device to perform the method according to the second aspect.

[0074] Regarding the seventh or eighth aspect, in a possible implementation, the communication device is a chip or a chip system. Optionally, when the communication device is a chip system, the communication device may include a chip, or may include a chip and another individual component.

[0075] According to a ninth aspect, there is provided a computer-readable storage medium having instructions stored thereon that, when running on a computer, can enable the computer to perform a method according to the first or second aspect.

[0076] According to a tenth aspect, there is provided a computer program product comprising instructions which, when run on a computer, may enable the computer to perform a method according to the first or second aspect.

[0077] Regarding the technical effects achieved by any one of the possible implementations of the third to tenth aspects, please refer to the technical effects achieved by the first aspect, the second aspect, or any one of the different possible implementations of the first or second aspect, and the details will not be described again in this specification.

[0078] According to an eleventh aspect, there is provided a communication system, the communication system including a terminal configured to perform the method according to the first aspect and a first access network device configured to perform the method according to the second aspect. [Brief explanation of the drawings]

[0079] [Figure 1A] 1 is a schematic diagram 1 of the architecture of a communication system according to an embodiment of the present application; [Figure 1B] FIG. 2 is a schematic diagram of a CU node and a DU node according to an embodiment of the present application; [Figure 1C] 2 is a schematic diagram of the architecture of a communication system according to an embodiment of the present application; [Figure 1D]1 is a schematic diagram of satellite movement according to an embodiment of the present application; [Figure 2] 1 is a schematic diagram of a hardware structure of a communication device according to an embodiment of the present application; [Figure 3] 1 is a schematic flowchart 1 of a handover method according to an embodiment of the present application; [Figure 4] 2 is a schematic flowchart 2 of a handover method according to an embodiment of the present application; [Figure 5] 3 is a schematic flowchart 3 of a handover method according to an embodiment of the present application; [Figure 6] 4 is a schematic flowchart 4 of a handover method according to an embodiment of the present application; [Figure 7] 5 is a schematic flowchart 5 of a handover method according to an embodiment of the present application; [Figure 8] 6 is a schematic flowchart 6 of a handover method according to an embodiment of the present application. [Figure 9] 1 is a schematic diagram 1 of the structure of a communication device according to an embodiment of the present application; [Figure 10] 2 is a schematic diagram of the structure of a communication device according to an embodiment of the present application; DETAILED DESCRIPTION OF THE INVENTION

[0080] Hereinafter, implementations of the embodiments of the present application will be described in detail with reference to the accompanying drawings.

[0081] The method provided in the embodiments of the present application may be used in various communication systems. For example, the communication system may be a communication system related to the 3rd generation partnership project (3GPP), such as a long term evolution (LTE) system or a 5th generation (5G) communication system, a future evolved communication system, or a system integrating multiple systems. This is not limited thereto. 5G may also be called new radio (NR). In the following, the communication system 10 shown in FIG. 1A and the communication system 11 shown in FIG. 1C are used as examples to describe the method provided in the embodiments of the present application.

[0082] 1A is a schematic diagram of the architecture of a communication system 10 according to an embodiment of the present application. In FIG. 1A, the communication system 10 may include a network device 101 and a terminal 102 that can communicate with the network device 101. Optionally, the communication system 10 further includes a network device 103. FIG. 1A is merely a schematic diagram and does not limit scenarios to which the technical solutions provided in the present application are applied.

[0083] 1A, for example, network device 101 and / or network device 103, may have the function of an access network device and provide wireless access services to terminals. In particular, each network device corresponds to one service coverage area, and terminals entering the area may communicate with the network device to receive the wireless access service provided by the network device. Optionally, the service coverage area may include one or more cells.

[0084] In an embodiment of the present application, the access network device may be any device having wireless transceiver functionality. For example, the access network device is a radio access network (RAN) node (or device) that connects a terminal to a wireless network, and may also be called a base station. Currently, some examples of RAN nodes are: next generation NodeB (gNB), transmission reception point (TRP), evolved NodeB (eNB), radio network controller (RNC), NodeB (NodeB, NB), base station controller (BSC), base transceiver station (BTS), home base station (e.g., home evolved NodeB or home NodeB, HNB), baseband unit (BBU), wireless fidelity (wi-fi) access point (AP), etc.

[0085] Additionally, in some embodiments, the access network device may be a central unit (CU) node or a distributed unit (DU) node, or the access network device may be a RAN device including a CU node and a DU node.

[0086] In an example, as shown in FIG. 1B, RAN devices including a CU node and a DU node may divide the protocol layers of a gNB in ​​an NR system. Some protocol layer functions are centrally controlled by the CU node, and some or all of the remaining protocol layer functions are distributed to the DU node. The CU node centrally controls the DU node. The CU node may further be divided into a control plane CU (CU-CP) and a user plane CU (CU-UP). The CU-CP is responsible for control plane functions and mainly includes radio resource control (RRC) and a packet data convergence layer protocol (PDCP) layer corresponding to the control plane, i.e., PDCP-C. The PDCP-C is mainly responsible for data encryption / decryption, integrity protection, data transmission, etc. in the control plane. The CU-UP is responsible for user plane functions and mainly includes a service data adaptation protocol (SDAP) and a PDCP corresponding to the user plane, i.e., PDCP-U. The SDAP is primarily responsible for processing data in the core network and mapping flows to bearers. The PDCP-U is responsible for data encryption / decryption, integrity protection, header compression, sequence number maintenance, data transmission, and other user-plane functions. The CU-CP and CU-UP are connected via an E1 interface. Instead of the gNB, the CU-CP is connected to the core network via an NG interface and to the DU via the F1 interface control plane, i.e., F1-C. The CU-UP is connected to the DU via the F1 interface user plane, i.e., F1-U. It is true that in another possible implementation, the PDCP-C is also located in the CU-UP. The DU node primarily includes a radio link control (RLC) layer, a media access control (MAC) layer, and a physical (PHY) layer.

[0087] In an example, a network device, such as network device 101 and / or network device 103, of communication system 10 may have all the functionality of an access network device, in which case the network device may be considered an access network device, may be used as an access network device, or may be replaced by an access network device.

[0088] A network device, such as network device 101 and / or network device 103, of communication system 10 may be any device that is mobile and has wireless transceiver capabilities, including, but not limited to, a satellite or an unmanned aerial system (UAS).

[0089] The satellites may be regenerative satellites without an inter-satellite link (ISL) or regenerative satellites with an ISL, which may be understood to be satellites that have the processing capabilities of an access network device. The UAS includes at least one of a tethered unmanned aircraft system (TUA), a lighter than air (LTA) unmanned aircraft system, a heavier than air (HTA) unmanned aircraft system, or a high altitude platform station (HAPS). The UAS may be a regenerative UAS without an inter-UAS link or a regenerative UAS with an inter-UAS link. In the embodiments of the present application, the apparatus configured to implement the function of a network device may be a network device or an apparatus, such as a chip system, that supports the network device in implementing its function. The apparatus may be installed within or used together with the network device. In the embodiments of the present application, the chip system may include a chip, or may include a chip and another individual component. In the methods provided in the embodiments of the present application, an example in which the apparatus configured to implement the function of a network device is a network device is used to describe the methods provided in the embodiments of the present application.

[0090] A terminal of communication system 10, e.g., terminal 102, may be a variety of devices that have wireless transceiver capabilities and provide voice and / or data connectivity to a user, and may also be referred to as a terminal device, user equipment (UE), mobile station, mobile terminal, etc. Terminal 102 may be deployed on land, including indoor devices, outdoor devices, handheld devices, or vehicle-mounted devices; on water (e.g., ships); or in the air (e.g., airplanes, balloons, satellites), and is widely used in various scenarios, such as device-to-device (D2D), vehicle-to-everything (V2X) communications, machine-type communications (MTC), internet of things (IoT), virtual reality, augmented reality, industrial control, autonomous driving, telemedicine, smart grid, smart furniture, smart offices, smart wearables, smart transportation, and smart cities. The terminal 102 may be a mobile phone, a tablet computer, a computer with a wireless transceiver function, a wearable device, a vehicle, an unmanned aerial vehicle, a helicopter, an airplane, a ship, a robot, a robot arm, a smart home device, etc. The terminal in this application may also be a relay node. The specific technology used by the terminal and the specific device form are not limited in the embodiments of this application. In the embodiments of this application, the chip used in the device may be referred to as a terminal.

[0091] 1A is merely used as an example and does not limit the technical solution of the present application. Those skilled in the art should understand that in a specific implementation, the communication system 10 may further include other devices, and the number of network devices and the number of terminals may alternatively be determined based on specific requirements. This is not limited.

[0092] 1C is a schematic diagram of the architecture of a communication system 11 according to an embodiment of the present application. In FIG. 1C, the communication system 11 may include a network device 111, a terminal 112 capable of communicating with the network device 111, and an access network device 113 capable of communicating with the network device 111. Optionally, the communication system 11 may further include a network device 114, or the communication system 11 may further include the network device 114 and an access network device 115 capable of communicating with the network device 114. FIG. 1C is merely a schematic diagram and does not limit scenarios to which the technical solutions provided in the present application are applied.

[0093] The network devices of FIG. 1C, such as network device 111 and / or network device 114, may be any device that is mobile and has wireless transceiver capabilities, including, but not limited to, a satellite or a UAS.

[0094] The satellite may be a transparent satellite, or the satellite may be a regenerative satellite without an ISL or a regenerative satellite with an ISL. The UAS may be a transparent UAS, or the UAS may be a regenerative UAS without an inter-UAS link or a regenerative UAS with an inter-UAS link. For a description of the access network device and terminal, please refer to the description of the access network device and terminal in Figure 1A. For another description of the UAS, please refer to the description of the UAS in Figure 1A. Details will not be described again herein.

[0095] In an example, the network device 111 may be configured to forward or transparently transmit information between the terminal 112 and the access network device 113. In other words, the network device 111 may implement a transparent payload. For example, the network device 111 may have at least one of the following functions: a radio frequency filtering function, or a frequency conversion and amplification function. In other words, the network device 111 mainly acts as a Layer 1 relay for regenerating physical layer signals and does not have another upper protocol layer.

[0096] Similarly, network device 114 may be configured to forward or transparently transmit information between terminal 112 and access network device 113, or network device 114 may be configured to forward or transparently transmit information between terminal 112 and access network device 115, or network device 114 may implement a transparent payload. It should be understood that in this example, network device 111 or network device 114 may be a transparent satellite.

[0097] In another example, the network device 111 may have some functions of an access network device. In other words, the network device 111 may implement a regenerative payload. For example, the network device 111 may have the function of a DU node of an access network device, or the network device 111 may be used as a DU node. In this case, the access network device 113 may have the function of a CU node, or the access network device 113 may be used as a CU node. In this case, the network device 111 may be replaced as a DU node, and the access network device 113 may be replaced as a CU node. In another example, the network device 111 has an integrated access and backhaul (IAB) function, or the network device 111 and the access network device 113 implement an IAB function. In this case, the network device 111 may be used as a DU node, or the network device 111 may be used as a DU node of the IAB. The access network device 113 may be used as a CU node, or the access network device 113 may be used as a CU node of the IAB.

[0098] Similarly, the network device 114 may have some functions of an access network device (e.g., the function of a DU node of an access network device, or the function of a DU node of an IAB function). It should be understood that in this example, the network device 111 or the network device 114 may be a regenerative satellite without an ISL or a regenerative satellite with an ISL. It should be understood that in this example, the network device 111 and the network device 114 are different DU nodes of the same access network device (i.e., the network device 111 and the network device 114 communicate with the same CU node), or the network device 111 and the network device 114 are different DU nodes of different access network devices (i.e., the network device 111 and the network device 114 communicate with different CU nodes).

[0099] The communication system 11 shown in Figure 1C is used merely as an example and does not limit the technical solution of the present application. Those skilled in the art should understand that in a specific implementation process, the communication system 11 may further include other devices, and the number of network devices, access network devices, and terminals may be determined based on specific requirements. This is not limited.

[0100] It should be understood that a network device, for example, network device 101 or network device 111, has mobility, and therefore the physical area covered by the network device may change. The physical area may include one or more cells. If a cell identifier (e.g., a cell global identifier (CGI) or a physical cell identifier (PCI)) of a cell is associated with the network device for the physical area, when the network device moves, the cell identifier of the cell included in the physical area changes. Therefore, even if the terminal does not move, the terminal may detect a change in the cell identifier of a cell. In this case, the network side (e.g., a network device or an access network device) needs to trigger a cell handover procedure for the terminal. In other words, the terminal needs to perform cell handover frequently, which causes high signaling overhead on the Uu interface.

[0101] To avoid frequent cell handover of a terminal, a cell identifier of a cell may be associated with a geographical location. In other words, when a network device moves relative to a geographical location, the cell identifier corresponding to that geographical location remains unchanged. After a network device (e.g., network device 101) leaves that geographical location, another network device (e.g., network device 103) may serve a terminal at that geographical location. It should be understood that when network device 103 serves a terminal at that geographical location, the cell identifier of the cell at that geographical location is the same as the cell identifier of the cell at the geographical location when network device 101 served the terminal at that geographical location.

[0102] For example, network device 101 is satellite 1, and network device 103 is satellite 2. In FIG. 1D , the cell identifier corresponding to geographic location 1 is cell #1, the cell identifier corresponding to geographic location 2 is cell #2, and the cell identifier corresponding to geographic location 3 is cell #3. At 10:00, satellite 1 may cover geographic location 1, and satellite 1 may serve a terminal at geographic location 1. In this case, the cell identifier corresponding to satellite 1 is cell #1. At 10:15, the geographic location covered by satellite 1 changes to geographic location 2, and satellite 1 may serve a terminal at geographic location 2, and the cell identifier corresponding to satellite 1 becomes cell #2. In this case, if satellite 2 covers geographic location 1, the satellite serving the terminal at geographic location 1 is switched from satellite 1 to satellite 2, and the cell identifier corresponding to satellite 2 becomes cell #1. At 10:30, the geographic location covered by satellite 1 changes to geographic location 3, and satellite 1 may serve a terminal at geographic location 3, and the cell identifier corresponding to satellite 1 becomes cell #3. In this case, if satellite 2 covers geographical location 2, the satellite serving the terminal at geographical location 2 is switched from satellite 1 to satellite 2, and the cell identifier corresponding to satellite 2 becomes cell #2.

[0103] From the above description, it can be known that when a network device communicating with a terminal changes, the cell identifier of the cell serving the terminal does not change, or the cell identifier detected by the terminal does not change. For example, in the above example, at 10:15, the satellite communicating with the terminal at geographical location 1 changes from satellite 1 to satellite 2, but the cell identifier detected by the terminal remains cell #1. In this case, the network side (e.g., network device or access network device) does not trigger a cell handover procedure for the terminal, but the network device or access network device actually communicating with the terminal has changed. In this case, how the terminal performs cell synchronization is an issue that needs to be resolved urgently.

[0104] To solve this problem, an embodiment of the present application provides a handover method. This method can be applied to handover of a terminal from a first network device to a second network device. The method includes connecting to a first cell through the first network device, performing downlink synchronization with a downlink synchronization signal of the second cell sent by the second network device, and connecting to the second cell through the second network device. The first cell and the second cell have the same cell identifier. Specific processing of this method will be described in the following embodiment shown in FIG. 3. Note that in the embodiment of the present application, having the same cell identifier may include having the same PCI but different CGI, or both the PCI and CGI being the same.

[0105] It may be understood that embodiments of the present application may be applied to scenarios in which a cell identifier is associated with a geographic location, in which case the cell may also be referred to as a quasi-earth fixed cell.

[0106] Optionally, each network element or device (e.g., a network device, a terminal, or an access network device) in Figure 1A or 1C in the embodiments of the present application may be referred to as a communication device, and may be a general-purpose device or a dedicated device, which is not particularly limited in the embodiments of the present application.

[0107] Optionally, the relevant functions of the network elements or devices (e.g., network devices, terminals, or access network devices) in FIG. 1A or 1C in the embodiments of the present application may be implemented by one device, or may be jointly implemented by multiple devices, or may be implemented by one or more functional modules in one device. This is not particularly limited in the embodiments of the present application. It may be understood that the aforementioned functions may be network elements in a hardware device, or may be software functions running on dedicated hardware, a combination of hardware and software, or virtualized functions instantiated on a platform (e.g., a cloud platform).

[0108] In a specific implementation, each network element or device (e.g., a network device, a terminal, or an access network device) in FIG. 1A or 1C of the embodiments of the present application may use the configuration structure shown in FIG. 2 or include the components shown in FIG. 2. FIG. 2 is a schematic diagram of a hardware structure of a communication device applicable to the embodiments of the present application. The communication device 20 includes at least one processor 201 and at least one communication interface 204 and is configured to implement the method provided in the embodiments of the present application. The communication device 20 may further include a communication line 202 and a memory 203.

[0109] The processor 201 may be a general-purpose central processing unit (CPU), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits configured to control program execution in the solutions of the present application.

[0110] The communication lines 202 may include channels such as buses for transmitting information between the aforementioned components.

[0111] The communication interface 204 is configured to communicate with other devices or communication networks and may be any device, such as a transceiver, such as an Ethernet interface, a radio access network (RAN) interface, a wireless local area network (WLAN) interface, a transceiver, a pin, a bus, or transceiver circuitry.

[0112] The memory 203 may be a read-only memory (ROM) or other type of static storage device capable of storing static information and instructions, or a random access memory (RAM) or other type of dynamic storage device capable of storing information and instructions, or may be, but is not limited to, an electrically erasable programmable read-only memory (EEPROM), a compact disc read-only memory (CD-ROM) or other compact disc storage medium, an optical disc storage medium (including compact discs, laser discs, optical discs, digital versatile discs, Blu-ray discs, etc.), a magnetic disc storage medium or other magnetic storage device, or any other medium that can be configured to hold or store expected program code in the form of instruction structures or data structures and that is accessible by a computer. The memory may exist independently or be coupled to the processor 201 via communication line 202. The memory 203 may alternatively be integrated with the processor 201. The memory provided in the embodiments of the present application may typically be non-volatile.

[0113] The memory 203 is configured to store computer-executable instructions for executing the solutions provided in the embodiments of the present application, and the processor 201 controls the execution. The processor 201 is configured to execute the computer-executable instructions stored in the memory 203 to implement the methods provided in the embodiments of the present application. Alternatively, optionally, in the embodiments of the present application, the processor 201 may perform processing-related functions in the methods provided in the following embodiments of the present application, and the communication interface 204 is responsible for communication with another device or a communication network, which is not particularly limited in the embodiments of the present application.

[0114] Optionally, the computer-executable instructions in the embodiments of the present application may also be referred to as application program code, which is not particularly limited in this embodiment of the present application.

[0115] A coupling in this embodiment of the present application may be an electrical, mechanical, or other type of indirect coupling or communication connection between devices, units, or modules, used for information exchange between the devices, units, or modules.

[0116] In an embodiment, processor 201 may include one or more CPUs, for example, CPU 0 and CPU 1 of FIG.

[0117] In embodiments, communications device 20 may include multiple processors, such as processor 201 and processor 207 of FIG. 2. Each of the processors may be a single-core (single-CPU) processor or a multi-core (multi-CPU) processor. A processor herein may be one or more devices, circuits, and / or processing cores configured to process data (e.g., computer program instructions).

[0118] In a possible implementation, the communication apparatus 200 may further include an output device 205 and / or an input device 206. The output device 205 is coupled to the processor 201 and may display information in a variety of ways. For example, the output device 205 may be a liquid crystal display (LCD), a light emitting diode (LED) display device, a cathode ray tube (CRT) display device, or a projector. The input device 206 is coupled to the processor 201 and may receive user input in a variety of ways. For example, the input device 206 may be a mouse, a keyboard, a touchscreen device, or a sensor device.

[0119] It should be understood that the configuration shown in Figure 2 is not limiting of the communications device. In addition to the components shown in Figure 2, the communications device may include more or fewer components than those shown, some components may be combined, or different component arrangements may be used.

[0120] The handover method provided in the embodiments of the present application will be described below with reference to the accompanying drawings. The network elements in the following embodiments may have the components shown in Figure 2. The details will not be described again.

[0121] It should be noted that the names of messages between network elements, names of parameters in messages, etc. in the following embodiments of the present application are merely examples, and there may be other names in specific implementations, which are not particularly limited in the embodiments of the present application.

[0122] It should be noted that in the embodiments of the present application, " / " can represent an "or" relationship between related objects. For example, A / B can represent A or B. "And / or" can be used to represent the case where three relationships exist between related objects. For example, A and / or B can represent the following three cases: only A exists, both A and B exist, and only B exists. A and B may be singular or plural. In addition, expressions similar to "at least one of A, B, and C" or "at least one of A, B, or C" are usually used to represent any one of the following: only A exists; only B exists; only C exists; both A and B exist; both A and C exist; both B and C exist; or all A, B, and C exist. In the above, three elements A, B, and C are used as examples to explain optional items of a project. When more elements are present in an expression, the meaning of the expression can be obtained according to the above rules.

[0123] To facilitate description of the technical solutions of the embodiments of the present application, objects may be distinguished in the embodiments of the present application using "first," "second," "third," "A," "B," "C," and "D." The technical features described using "first," "second," "third," "A," "B," "C," and "D" do not indicate an order or magnitude, and do not limit the quantity of the objects described. Additionally, terms such as "first" and "second" do not limit the described objects to being distinct.

[0124] In the embodiments of the present application, words such as "example" or "for example" are used to indicate an example, evidence, or illustration. Any embodiment or design solution described as an "example" or "for example" should not be described as being preferred or having significant advantages over another embodiment or design solution. Words such as "example" or "for example" are used to present related concepts in a particular way that makes them easier to understand.

[0125] It may be understood that the same steps or steps or technical features having the same function in the embodiments of the present application may be cross-referenced in different embodiments.

[0126] It may be understood that in the embodiments of the present application, the terminal, and / or the network device, and / or the access network device may perform some or all of the steps of the embodiments of the present application. These steps are merely examples. In the embodiments of the present application, other steps or variations of various steps may also be performed. In addition, these steps may be performed in an order different from the order presented in the embodiments of the present application, and all steps of the embodiments of the present application need not be performed.

[0127] 3 shows a handover method according to an embodiment of the present application. This method can be applied to handover of a terminal from a first network device to a second network device. The handover method includes steps S301 to S303.

[0128] S301: A terminal is connected to a first cell via a first network device.

[0129] It may be understood that the handover method shown in Figure 3 may be applied to the communication system 10 shown in Figure 1A or the communication system 11 shown in Figure 1C. When this method is applied to the communication system 10 shown in Figure 1A, please refer to the following description of Method 1. When this method is applied to the communication system 11 shown in Figure 1C, please refer to the following description of Method 2. A detailed description is provided below.

[0130] Method 1:

[0131] In Approach 1, the terminal may be a terminal of the communication system 10. For example, the terminal is the terminal 102 shown in FIG. 1A. The first network device may be a network device of the communication system 10. For example, the first network device may be the network device 101 shown in FIG. 1A.

[0132] In the example, the first network device is a first satellite. Optionally, the first satellite has the function of a first access network device. In other words, the first satellite may be considered as the first access network device, or may be used as the first access network device, or may be replaced by the first access network device. In this case, the downlink synchronization signal of the first cell sent by the first network device is generated and sent by the first network device. For a description of the first access network device, please refer to the description of the access network device in FIG. 1A.

[0133] A terminal being connected to a first cell via a first network device may be understood to mean that the first network device provides a service for the terminal to connect to the first cell, or that the first network device is configured to provide a service to the terminal before the terminal performs downlink synchronization with a downlink synchronization signal of the second cell sent by a second network device. The first cell is managed by the first network device. Correspondingly, the first network device is connected to the terminal via the first cell.

[0134] Method 2:

[0135] In Method 2, the terminal may be a terminal of the communication system 11. For example, the terminal is the terminal 112 shown in FIG. 1C. The first network device may be a network device of the communication system 11. For example, the first network device may be the network device 111 shown in FIG. 1C.

[0136] In the example, the first network device is a first satellite. Optionally, the first satellite or the first network device may be configured to forward or transparently transmit information between the first access network device and the terminal, or the first satellite or the first network device may have some functions of an access network device (e.g., the function of a DU node of an access network device, or the function of a DU node in an IAB function). The first access network device may be an access network device of the communication system 11. For example, the first access network device is the access network device 113 shown in FIG. 1C. The first access network device may have the function of a CU node.

[0137] In Method 2, if the first satellite or the first network device is configured to forward or transparently transmit information between the first access network device and the terminal, the downlink synchronization signal of the first cell sent by the first network device (or the first satellite) may be understood to be generated by the first access network device and sent to the first network device (or the first satellite). After receiving the downlink synchronization signal, the first network device (or the first satellite) sends the downlink synchronization signal to the terminal. If the first satellite or the first network device has some functions of the access network device, the downlink synchronization signal of the first cell sent by the first network device (or the first satellite) may be generated by the first network device and sent to the terminal.

[0138] In Method 2, the terminal being connected to the first cell via the first network device may be understood as the first access network device providing a service for the terminal to connect to the first cell via the first network device, or the first access network device being configured to provide a service for the terminal before the terminal performs downlink synchronization with a downlink synchronization signal of the second cell sent by the second network device.

[0139] When the first network device is configured to forward or transparently transmit information between the first access network device and the terminal (i.e., the first network device transparently transmits the payload), the first cell is managed by the first access network device. When the first network device has some of the functions of an access network device, the first cell may be managed by the first access network device or may be managed by the first network device. The first cell is a cell to which the terminal is connected via the first network device. Correspondingly, the first access network device is connected to the terminal via the first cell. In Approach 2, it may be understood that information sent by the terminal may be sent to the first access network device via the first network device. Similarly, information sent by the first access network device may be sent to the terminal via the first network device. When the first network device has some of the functions of an access network device, it may be understood that the first network device may alternatively send some information directly to the terminal.

[0140] Optionally, in Technique 1 and Technique 2, the terminal is in a connected state, for example, a radio resource control connected (RRC-connected) state.

[0141] S302: The terminal performs downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device.

[0142] Regarding Method 1:

[0143] The second network device may be a network device of the communication system 10. For example, the second network device is the network device 103 shown in FIG. 1A. The second network device is configured to serve the terminal after the terminal performs downlink synchronization (i.e., after S302). The second cell is managed by the second network device, and the second cell and the first cell have the same cell identifier.

[0144] In the example, the second network device is a second satellite. The second satellite is different from the first satellite. Optionally, the second satellite has the functionality of a second access network device. In other words, the second satellite may be considered as a second access network device, or the second satellite may be used as a second access network device, or the second satellite may be replaced by a second access network device. The second access network device is different from the first access network device. For a description of the second access network device, please refer to the description of the access network device in FIG. 1A.

[0145] In a possible implementation, the downlink synchronization signal of the second cell sent by the second network device is generated and sent by the second network device.

[0146] Optionally, before S302, the first network device sends configuration information to the terminal. In response, the terminal receives the configuration information from the first network device. The configuration information may indicate a configuration of the downlink synchronization signal of the second cell. In this way, the terminal can determine a time domain position of a measurement window of the downlink synchronization signal of the second cell. The measurement window is a period of time for detecting the downlink synchronization signal.

[0147] In an example, the configuration information may include at least one of a length of a measurement window of the second cell's downlink synchronization signal, periodicity information of the measurement window of the second cell's downlink synchronization signal, or a first offset. The measurement window periodicity information may indicate the periodicity of the measurement window. At least one of the measurement window periodicity information or the first offset may be for determining a time-domain start position of the measurement window. In this manner, the time-domain position of the measurement window may be determined based on the time-domain start position of the measurement window and the length of the measurement window.

[0148] For example, the terminal monitors the downlink synchronization signal of the second cell in the following manner: The terminal monitors the downlink synchronization signal of the second cell in system frames and subframes that satisfy the following condition: the number of system frames corresponding to the measurement window satisfies the formula: SFN modT=(FLOOR(Offset / 10)).

[0149] SFN is the system frame number corresponding to the measurement window, mod is the modulo operation symbol, FLOOR is a round-down function, and Offset is the first offset. T satisfies the formula: T = CEIL (Periodicity / 10), where CEIL is a round-up function and Periodicity is the periodicity of the measurement window. If the periodicity of the measurement window is greater than 5 subframes, the number of subframes corresponding to the measurement window satisfies the formula: subframe = Offset mod 10. If the periodicity of the measurement window is 5 subframes or less, the number of subframes corresponding to the measurement window satisfies the formula: subframe = Offset, or subframe = Offset + 5.

[0150] Regarding Method 2:

[0151] The second network device may be a network device of the communication system 11. For example, the second network device is the network device 114 shown in FIG. 1C.

[0152] In an example, the second network device is a second satellite. The second satellite is different from the first satellite. Optionally, the second satellite or the second network device may be configured to forward or transparently transmit information between the second access network device and the terminal, or the second satellite or the second network device may have some functions of the second access network device (e.g., functions of a DU node of an access network device, or functions of a DU node of an IAB function).

[0153] The second access network device may be an access network device of the communication system 11. For example, the second access network device is the access network device 113 or the access network device 115 shown in FIG. 1C. When the second network device is configured to forward or transparently transmit information between the second access network device and the terminal (i.e., the second network device transparently transmits the payload), the second cell is managed by the second access network device. When the second network device has some functions of the access network device, the second cell may be managed by the second access network device or may be managed by the second network device. The second cell is a cell to which the terminal is connected via the second network device. The second cell and the first cell have the same cell identifier.

[0154] In a possible implementation, for Approach 2, the second access network device may be the same as or different from the first access network device. If the second access network device is the same as the first access network device, it indicates that the terminal may communicate with the first access network device through the first network device before the terminal performs downlink synchronization (i.e., before S302), and may communicate with the first access network device through the second network device after the terminal performs downlink synchronization (i.e., after S302). In this case, the first cell and the second cell are the same, and the first cell and the second cell are managed by the first access network device. Alternatively, the first cell and the second cell may be different, and the first cell is managed by the first network device, and the second cell is managed by the second network device. If the second access network device is different from the first access network device, it indicates that the terminal may communicate with the first access network device via the first network device before the terminal performs downlink synchronization (i.e., before S302), and may communicate with the second access network device via the second network device after the terminal performs downlink synchronization (i.e., after S302). In this case, the first cell is the same as or different from the second cell, and the first cell is managed by the first access network device, and the second cell is managed by the second access network device. Alternatively, the first cell is managed by the first network device, and the second cell is managed by the second network device.

[0155] In a possible implementation, with regard to Method 2, if the second network device (e.g., the second satellite) is configured to forward or transparently transmit information between the second access network device and the terminal, the downlink synchronization signal of the second cell sent by the second network device is generated by the second access network device and sent to the second network device. After receiving the downlink synchronization signal, the second network device sends the downlink synchronization signal to the terminal. If the second satellite or the second network device has some functions of the second access network device, the downlink synchronization signal of the second cell sent by the second network device is generated by the second network device and sent to the terminal.

[0156] Optionally, in Method 2, before S302, the first access network device sends configuration information to the terminal. Correspondingly, the terminal receives the configuration information from the first access network device. For example, the first access network device sends the configuration information to the first network device, and the first network device sends the configuration information to the terminal after receiving the configuration information. For a description of the configuration information, see the description in Method 1 above. In this way, the terminal can determine the time domain position of the measurement window of the downlink synchronization signal of the second cell.

[0157] In the above-mentioned methods 1 and 2, the first cell and the second cell may be the same or different.

[0158] In the embodiments of the present application, two cells being the same may be understood as meaning that the configurations of the two cells are the same. For example, the physical cell identifiers of the two cells are the same, and the radio resource configurations configured for the terminal by the two cells are the same. The radio resource configuration may include at least one of the following: an associated configuration of an RRC layer, an associated configuration of an SDAP layer, an associated configuration of a PDCP layer, an associated configuration of an RLC layer, an associated configuration of a MAC layer, and an associated configuration of a PHY layer. Therefore, a first cell and a second cell being the same may be understood as meaning that the first cell and the second cell are not the same cell, but the configuration of the first cell is the same as the configuration of the second cell, or the first cell and the second cell are the same cell.

[0159] The first cell being different from the second cell may be understood to mean that the configuration of the first cell is different from the configuration of the second cell. For example, the radio resource configuration configured for the terminal by the first cell is different from the radio resource configuration configured for the terminal by the second cell, but the cell identifier of the first cell is the same as the cell identifier of the second cell. In this embodiment of the present application, the first cell may also be referred to as a source serving cell or a source cell, and the second cell may also be referred to as a target serving cell or a target cell.

[0160] Optionally, with respect to the above-mentioned Method 1 and Method 2, the following two possible implementations are used by the terminal to perform downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device. In this embodiment of the present application, downlink synchronization may also be referred to as cell search.

[0161] In a possible implementation, the terminal searches for the downlink synchronization signal of the second cell and acquires downlink timing based on the downlink synchronization signal. It may be understood that as the terminal switches between connected network devices and the downlink timing of the downlink synchronization signals of the two cells may differ, the terminal needs to re-search for the downlink synchronization signal of the second cell.

[0162] In the example, the terminal determines, based on the configuration information, a time-domain position of a measurement window for a downlink synchronization signal of the second cell, searches for the downlink synchronization signal of the second cell at the time-domain position, and obtains downlink timing based on the downlink synchronization signal, including obtaining a system frame boundary, a subframe boundary, a slot boundary, and a symbol boundary corresponding to the second cell.

[0163] With respect to Approach 1, the system frame boundaries, subframe boundaries, slot boundaries, and symbol boundaries corresponding to the second cell may be understood to be the system frame boundaries, subframe boundaries, slot boundaries, and symbol boundaries of the second cell and within the network provided by the second network device. With respect to Approach 2, the system frame boundaries, subframe boundaries, slot boundaries, and symbol boundaries corresponding to the second cell may be understood to be the system frame boundaries, subframe boundaries, slot boundaries, and symbol boundaries of the second cell and within the network provided by the second network device and the second access network device.

[0164] It may be understood that in this embodiment of the present application, the terminal may calculate the maximum delay of handover abort based on the second cell being an unknown cell.

[0165] The maximum delay of handover interruption may be the maximum delay of handover of the terminal from one access network device to another access network device, or the maximum delay of handover of the terminal from one network device to another network device. The maximum delay of handover interruption includes the time required by the terminal to search for the target cell (i.e., the second cell). The target cell may be a known cell or an unknown cell, and the time required by the terminal to search for the target cell differs depending on whether the target cell is a known cell or an unknown cell. For example, when the target cell is a known cell, the time required by the terminal to search for the target cell is 0 ms. When the target cell is an unknown cell, the time required by the terminal to search for the target cell is related to the signal quality of the target cell and / or related to whether the target cell and the source cell (i.e., the first cell) are intra-frequency cells or inter-frequency cells. However, in this embodiment of the present application, even if the source cell and the target cell have the same cell identifier, the source cell and the target cell are not necessarily the same cell. Therefore, in this embodiment of the present application, the time required by the terminal to search for a target cell is not set to 0 ms. That is, the terminal does not calculate the maximum delay of handover abort based on the second cell being a known cell, but calculates the maximum delay of handover abort based on the second cell being an unknown cell. Whether the target cell is a known cell or an unknown cell may be determined according to some preset conditions. For example, for a handover from a source cell within the frequency domain range of frequency band 1 (frequency range 1, FR1) to a target cell in the FR1 frequency band and a handover from a source cell within the frequency domain range of frequency band 2 (frequency range 2, FR2) to a target cell in the FR1 frequency band, if the target cell meets the corresponding cell identification requirement within 5 seconds before the handover, the target cell is deemed to be a known cell; otherwise, the target cell is deemed to be an unknown cell.

[0166] In another possible implementation, when the first network device and the second network device have some functions of the access network device in Scheme 1 or Scheme 2, the terminal acquires the time domain position of the downlink synchronization signal of the second cell based on the location information of the first network device, the location information of the second network device, and the location information of the terminal. In this way, the terminal can acquire downlink timing.

[0167] In an example, in a case where the first network device and the second network device have some functions of the access network devices in Method 1 or Method 2, if the start time of downlink subframe 0 in the first cell corresponding to the terminal is t1, the distance between the terminal and the first network device is D1 (which can be obtained based on the location information of the first network device and the location information of the terminal), and the distance between the terminal and the second network device is D2 (which can be obtained based on the location information of the second network device and the location information of the terminal), the start time of downlink subframe 0 in the second cell corresponding to the terminal is (t1-(D1-D2) / c1).

[0168] It may be understood that c1 is the speed of light, and the start of downlink subframe 0 of the second cell is the start time at which the second network device sends out the downlink synchronization signal of the second cell.

[0169] In another possible implementation, for another scenario of Technique 2 (e.g., the first network device is configured to forward or transparently transmit information between the first access network device and the terminal, and the second network device is configured to forward or transparently transmit information between the second access network device and the terminal), the terminal obtains the time-domain position of the downlink synchronization signal of the second cell based on the delay difference between the propagation delay between the terminal and the first access network device and the propagation delay between the terminal and the second access network device. In this way, the terminal can obtain downlink timing.

[0170] In an example, regarding another scenario of Method 2, if the start time of downlink subframe 0 in a first cell corresponding to the terminal is t1, the propagation delay between the first network device and the first access network device is t2 (t2 may be notified to the terminal by the first access network device), and the propagation delay between the second network device and the second access network device is t3 (t3 may be notified to the terminal by the second access network device), the terminal calculates a distance D3 between the terminal and the first network device based on the location information of the terminal and the location information of the first network device, and calculates a distance D4 between the terminal and the second network device based on the location information of the terminal and the location information of the second network device. The start time of downlink subframe 0 in a second cell corresponding to the terminal is (t1-(D3+t2×c1-D4-t3×c1) / c1). The start of downlink subframe 0 of the second cell may be understood to be the start of the time at which the second network device sends out the downlink synchronization signal of the second cell.

[0171] In another example, regarding another scenario of Technique 2, when the start time of downlink subframe 0 in the first cell corresponding to the terminal is t1, the terminal obtains a propagation delay t2 between the terminal and the first network device based on the terminal's location information and the first network device's location information, and obtains a delay value t4 based on t2 and a delay value t3 broadcasted by the first access network device (t3 may include the propagation delay between the first access network device and the first network device). For example, t4 = t2 + t3. Similarly, the terminal obtains a propagation delay t5 between the terminal and the second network device based on the terminal's location information and the second network device's location information, and obtains a delay value t7 based on t5 and a delay value t6 broadcasted by the second access network device (t6 may include the propagation delay between the second access network device and the second network device). For example, t7 = t5 + t6. The terminal may then determine that the start of downlink subframe 0 in the second cell corresponding to the terminal is (t1-(t4-t7)). The start of downlink subframe 0 of the second cell may be understood to be the start of when the second network device sends out a downlink synchronization signal for the second cell.

[0172] Optionally, for the above-mentioned Method 1 and Method 2, the following two possible implementations are for triggering the terminal to perform downlink synchronization.

[0173] In a possible implementation, the terminal receives the first indication information and performs downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device based on the first indication information, which is described in the following manner and shown in FIG.

[0174] In another possible implementation, the terminal decides to switch the connected network device. In this case, the terminal performs downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device. This process is described in the following manner shown in Figure 5.

[0175] S303: The terminal is connected to a second cell via a second network device.

[0176] It may be understood that if the first cell and the second cell are the same cell, after S302, the terminal may change the network device for connecting to the first cell from the first network device to the second network device.

[0177] In the example, the communication system 11 shown in Figure 1C is used as an example. When the first network device is the network device 111, the terminal is the terminal 112, the first access network device and the second access network device are the same, both are the access network device 113, and the second network device is the network device 114, the terminal 112 is first connected to the first cell of the access network device 113 through the network device 111, and then connected to the first cell of the access network device 113 through the network device 114 after performing downlink synchronization with the downlink synchronization signal of the second cell sent by the network device 114.

[0178] If the first cell and the second cell are not the same cell but the configuration of the first cell is the same as the configuration of the second cell, or if the first cell and the second cell are different cells, it may be understood that after S302, the terminal is disconnected from the first cell and connected to the second cell via the second network device.

[0179] In the example, the communication system 10 shown in Fig. 1A is used as an example. If the first network device is network device 101, the terminal is terminal 102, and the second network device is network device 103, the terminal 102 will first be connected to the first cell of network device 101, and will then be connected to the second cell of network device 102 after performing downlink synchronization with the downlink synchronization signal of the second cell sent by network device 102. The first cell and the second cell are different, i.e., the first cell and the second cell are not the same cell, but the configuration of the first cell is the same as the configuration of the second cell.

[0180] In another example, the communication system 10 shown in Fig. 1C is used as an example. When the first network device is network device 111, the terminal is terminal 112, the first access network device and the second access network device are the same, both are access network device 113, and the second network device is network device 114, the terminal 112 first connects to the first cell of the access network device 113 through the network device 111, and then connects to the second cell of the access network device 113 through the network device 114 after performing downlink synchronization with the downlink synchronization signal of the second cell sent by the network device 114. Although the first cell and the second cell are not the same cell, the configuration of the first cell is the same as the configuration of the second cell.

[0181] In another example, the communication system 10 shown in Figure 1C is used as an example. When the first network device is network device 111, the terminal is terminal 112, the first access network device is access network device 113, the second network device is network device 114, and the second access network device is access network device 115, the terminal 112 is first connected to a first cell of the access network device 113 through the network device 111, and then connected to a second cell of the access network device 115 through the network device 114 after performing downlink synchronization with the downlink synchronization signal of the second cell sent by the network device 114. The first cell is different from the second cell, i.e., the first cell and the second cell are not the same cell, but the configuration of the first cell is the same as the configuration of the second cell.

[0182] In a possible implementation, the terminal connecting to the second cell via the second network device includes: the terminal sending a random access signal to the second network device, and a two-step random access process or a four-step random access process is performed.

[0183] It may be understood that if the second network device has some functions of the access network device in Scheme 1 or Scheme 2, after receiving the random access signal, the second network device may implement the subsequent procedure in two-step random access or four-step random access. If the second network device is configured to forward or transparently transmit information between the second access network device and the terminal in Scheme 2, after receiving the random access signal, the second network device sends a random access signal to the second access network device. After receiving the random access signal, the second access network device may implement the subsequent procedure in two-step random access or four-step random access.

[0184] Optionally, if the first indication information is not carried in the intra-cell handover command and the uplink time alignment timer of the terminal expires, it indicates that the terminal does not need to send uplink data. Therefore, the terminal does not need to send a random access signal to the second network device. Then, if there is another requirement, for example, when there is an uplink service, the terminal sends a random access signal to the second network device.

[0185] Optionally, if the first indication information is not carried in the intra-cell handover command and the uplink time alignment timer of the terminal does not expire, it indicates that the terminal may need to send uplink data. Thus, the terminal may send a random access signal to the second network device.

[0186] It may be understood that if the terminal receives an uplink time adjustment command while the terminal is in the process of initiating random access (i.e., after the terminal sends out a random access signal and before the terminal accesses the second network device or the second access network device), the terminal may restart the uplink time adjustment timer.

[0187] In a possible implementation, the terminal connecting to the second cell via the second network device includes: the terminal sending uplink data (which may be an RRC message, a MAC-CE, an RLC control protocol data unit (control PDU), a PDCP control protocol data unit (control PDU), or application layer data) to the second network device, i.e., the terminal may not need to send a random access signal to the second cell.

[0188] In an implementation, the first network device or the first access network device may allocate some uplink resources to the terminal in advance (e.g., allocate the uplink resources to the terminal using a dedicated RRC message or a broadcast message), and the terminal selects at least one resource from these uplink resources to transmit uplink data.

[0189] In another implementation, the first network device or the first access network device sends a downlink control physical channel to the terminal, where the downlink control physical channel carries uplink resources for connecting the terminal to the second cell. Further, optionally, the downlink control physical channel includes indication information #1 for indicating the terminal to use the uplink resources carried in the downlink control physical channel when connecting to the second cell.

[0190] Optionally, in method 1, when the terminal sends uplink data to the second cell via the second network device, the terminal first determines a timing advance for transmitting the uplink data between the terminal and the second network device based on a propagation delay between the terminal and the second network device or / and a propagation delay between the terminal and the first network device.

[0191] Optionally, in technique 2, when the terminal sends uplink data to the second cell via the second network device, the terminal first determines a timing advance for transmitting the uplink data between the terminal and the second network device based on the distance between the terminal and the second network device and the distance between the second network device and the second time synchronization reference point. Alternatively, in technique 2, the terminal first determines a timing advance for transmitting the uplink data between the terminal and the second network device based on the distance between the terminal and the second network device, the distance between the second network device and the second time synchronization reference point, the distance between the terminal and the first network device, and the distance between the first network device and the first time synchronization reference point.

[0192] The second time synchronization reference point is a point between the second network device and the second access network device, and may also be referred to as a point where there is an offset #2 between the downlink frame timing and the uplink frame timing (the second uplink synchronization reference point is a point where the DL and UL are frame aligned with offset #2). Offset #2 is a value broadcast by the second cell. The first time synchronization reference point is a point between the first network device and the first access network device, and may also be referred to as a point where there is an offset #1 between the downlink frame timing and the uplink frame timing (the first uplink synchronization reference point is a point where the DL and UL are frame aligned with offset #1). Offset #1 is a value broadcast by the first cell.

[0193] Based on the method shown in FIG. 3, when a first network device is switched to a second network device but the cell identifier of the cell serving the terminal does not change, the terminal may perform downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device, so that the terminal can still perform normal communication after the network device switch. For example, in Method 1, before S302, the first network device may serve the terminal, and the terminal may communicate with the first network device. After S302, the second network device may serve the terminal, and the terminal may communicate with the second network device. In Method 2, before S302, the first access network device may serve the terminal, and the terminal may communicate with the first access network device through the first network device. After S302, the second access network device may serve the terminal, and the terminal may communicate with the second access network device through the second network device.

[0194] Optionally, in a possible implementation of the method shown in Fig. 3, the first indication information may be for triggering the terminal to perform downlink synchronization. In particular, as shown in Fig. 4, the method shown in Fig. 3 may further include S304.

[0195] S304: The terminal receives first indication information.

[0196] The first indication information may indicate to the terminal to perform downlink synchronization. For example, the first indication information may indicate to the terminal to perform downlink synchronization. Alternatively, the first indication information may indicate to the terminal to perform downlink synchronization with a downlink synchronization signal of a second cell sent by a second network device. Alternatively, the first indication information may indicate to the terminal to stop using the downlink timing of the first cell.

[0197] If the first network device has some functions of the access network device in Method 1 or Method 2, it may be understood that the first network device sends first indication information to the terminal, and in response, the terminal receives the first indication information from the first network device.

[0198] In a possible implementation, when the absolute value of the difference between the first distance and the second distance is equal to or greater than a first threshold, the first network device sends a first indication to the terminal.

[0199] The first distance is a distance between the terminal and the first network device and can be obtained based on location information of the first network device and location information of the terminal. The second distance is a distance between the terminal and the second network device and can be obtained based on location information of the second network device and location information of the terminal. The first threshold is a positive number.

[0200] In other words, when the first network device gradually moves away from the terminal and the second network device gradually moves closer to the terminal, and the difference between the distance between the terminal and the first network device and the distance between the terminal and the second network device is equal to or greater than a first threshold, the first network device may indicate to the terminal to perform downlink synchronization. When the distance between the terminal and the first network device is the same as the distance between the terminal and the second network device, or when the difference between the distance between the terminal and the first network device and the distance between the terminal and the second network device is less than a first threshold, it may be understood that the difference between the time estimated by the first network device when the downlink synchronization signal of the first cell sent by the first network device arrives at the terminal and the time estimated by the first network device when the downlink synchronization signal of the second cell sent by the second network device arrives at the terminal is equal to or less than a first time difference. Therefore, to avoid performing unnecessary downlink synchronization, the terminal may still use the downlink synchronization for communication with the first network device as the downlink synchronization for communication with the second network device.

[0201] In another possible implementation, when the absolute value of the difference between the first propagation delay and the second propagation delay is greater than or equal to a second threshold, the first network device sends first indication information to the terminal.

[0202] The first propagation delay is a propagation delay of information sent by a first network device to a terminal. The first propagation delay is equal to a ratio of a first distance to the speed of light. The second propagation delay is a propagation delay of information sent by a second network device to a terminal. The second propagation delay is equal to a ratio of a second distance to the speed of light. The second threshold is a positive number.

[0203] In other words, when the difference between the propagation delay of the information sent by the first network device to the terminal and the propagation delay of the information sent by the second network device to the terminal is equal to or greater than the second threshold, the first network device may indicate to the terminal to perform downlink synchronization. When the propagation delay of the information sent by the first network device to the terminal is the same as the propagation delay of the information sent by the second network device to the terminal, or when the difference between the propagation delay of the information sent by the first network device to the terminal and the propagation delay of the information sent by the second network device to the terminal is less than the second threshold, it may be understood that the difference between the time estimated by the first network device when the downlink synchronization signal of the first cell sent by the first network device arrives at the terminal and the time estimated by the first network device when the downlink synchronization signal of the second cell sent by the second network device arrives at the terminal is equal to or less than the first time difference. Therefore, to avoid performing unnecessary downlink synchronization, the terminal may still use the downlink synchronization for communication with the first network device as the downlink synchronization for communication with the second network device.

[0204] When the second network device is configured to forward or transparently transmit information between the second access network device and the terminal in Method 2, it may be understood that the first access network device sends the first indication information to the terminal, and in response, the terminal receives the first indication information from the first access network device.

[0205] In a possible implementation, when the absolute value of the difference between the third distance and the fourth distance is equal to or greater than a third threshold, the first access network device sends first indication information to the terminal.

[0206] The third distance is the sum of the distance between the first access network device and the first network device and the distance between the first network device and the terminal, and can be obtained based on the location information of the first access network device, the location information of the first network device, and the location information of the terminal. The fourth distance is the sum of the distance between the second access network device and the second network device and the distance between the second network device and the terminal, and can be obtained based on the location information of the second access network device, the location information of the second network device, and the location information of the terminal. The third threshold is a positive number. The third threshold can be the same as or different from the first threshold.

[0207] In other words, when the first network device gradually moves away from the terminal and the second network device gradually moves closer to the terminal, and the difference between the third distance and the fourth distance is equal to or greater than the third threshold, the first access network device may indicate to the terminal to perform downlink synchronization. When the third distance is the same as the fourth distance, or when the difference between the third distance and the fourth distance is less than the third threshold, it may be understood that the difference between the time estimated by the first access network device when the downlink synchronization signal of the first cell sent by the first access network device arrives at the terminal and the time estimated by the first access network device when the downlink synchronization signal of the second cell sent by the second access network device arrives at the terminal is equal to or less than the second time difference. Therefore, in order to avoid performing unnecessary downlink synchronization, the terminal may still use the downlink synchronization for communication with the first network device as the downlink synchronization for communication with the second network device.

[0208] In another possible implementation, when the absolute value of the difference between the third propagation delay and the fourth propagation delay is greater than or equal to a fourth threshold, the first access network device sends first indication information to the terminal.

[0209] The third propagation delay is the propagation delay of information sent by the first access network device to the terminal through the first network device. The third propagation delay is equal to the ratio of the third distance to the speed of light. The fourth propagation delay is the propagation delay of information sent by the second access network device to the terminal through the second network device. The fourth propagation delay is equal to the ratio of the fourth distance to the speed of light. The fourth threshold is a positive number. The fourth threshold may be the same as or different from the second threshold.

[0210] In other words, when the difference between the propagation delay of information sent by the first access network device to the terminal via the first network device and the propagation delay of information sent by the second access network device to the terminal via the second network device is greater than or equal to a fourth threshold, the first access network device may indicate to the terminal to perform downlink synchronization. When the propagation delay of information sent by the first network device to the terminal via the first network device is the same as the propagation delay of information sent by the second access network device to the terminal via the second network device, or when the difference between the propagation delay of information sent by the first access network device to the terminal via the first network device and the propagation delay of information sent by the second access network device to the terminal via the second network device is less than a fourth threshold, it may be understood that the difference between the time estimated by the first access network device when a downlink synchronization signal of a first cell sent by the first access network device arrives at the terminal and the time estimated by the first access network device when a downlink synchronization signal of a second cell sent by the second access network device arrives at the terminal is less than a second time difference. Therefore, in order to avoid performing unnecessary downlink synchronization, the terminal may still use the downlink synchronization for communication with the first network device as the downlink synchronization for communication with the second network device as well.

[0211] In a possible implementation, the first indication information is carried in a dedicated RRC message, a dedicated medium access control element (MAC-CE), or a dedicated physical channel, or the first indication information is carried in a common RRC message, a common MAC-CE, or a common physical channel. It may be understood that the first indication information may alternatively be carried in another message. This is not a limitation.

[0212] Optionally, the dedicated RRC message is an intra-cell handover command. The intra-cell handover command is a handover command based on a time condition. In other words, the first indication information may be carried in the intra-cell handover command based on a time condition. The intra-cell handover command based on a time condition may also be referred to as an intra-cell handover command triggered based on a time condition.

[0213] An intra-cell handover command based on a time condition may be understood as an intra-cell handover command being delivered based on a pre-indicated time point. For example, a first network device indicates to a terminal to switch network devices at time point T. Then, the first network device sends an intra-cell handover command to the terminal at time point T, and this intra-cell handover command may be referred to as an intra-cell handover command based on a time condition. In this embodiment of the present application, the intra-cell handover command may also be referred to as a handover command in a cell.

[0214] It may be understood that in addition to indicating the terminal to perform downlink synchronization or to stop using the downlink timing of the first cell based on the first indication information, the first network device or the first access network device may further indicate the terminal to perform downlink synchronization or to stop using the downlink timing of the first cell in an implicit indication manner.

[0215] For example, the first network device or the first access network device sends an intra-cell handover command to the terminal. The intra-cell handover command is an intra-cell handover command based on a time condition, and the intra-cell handover command does not carry a handover condition based on a location or a signal quality. In this case, after receiving the intra-cell handover command, the terminal may decide to perform downlink synchronization or may decide to stop using the downlink timing of the first cell. Then, the terminal may perform downlink synchronization.

[0216] It may be understood that if the first network device or the first access network device does not send the first indication information to the terminal, or if the first network device or the first access network device sends the second indication information to the terminal and this second indication information indicates that downlink synchronization is not required, or if the second indication information indicates that the downlink timing of the first cell can be continued, the terminal does not need to perform downlink synchronization.

[0217] For example, when the difference between the first distance and the second distance is less than a first threshold, the first network device or the first access network device does not send the first indication information to the terminal, or the first network device or the first access network device sends the second indication information to the terminal.

[0218] Optionally, in a possible implementation of the method shown in Fig. 3, the terminal performs downlink synchronization when deciding to switch the connected network device. In particular, as shown in Fig. 5, the method shown in Fig. 3 may further include S305.

[0219] S305: The terminal decides to switch the connected network device.

[0220] In a possible implementation, when determining that the remaining service time of the first network device is less than or equal to the fifth threshold, the terminal determines to switch the connected network device. For example, when determining that the remaining service time of the first network device is 0, the terminal determines to switch the connected network device.

[0221] The remaining service time refers to the remaining time during which the first network device can be connected to the terminal. For example, when the first network device has some functions of the access network device in Approach 1 or Approach 2, the remaining service time refers to the remaining time during which the first network device can provide service to the terminal. In Approach 2, when the second network device is configured to forward or transparently transmit information between the second access network device and the terminal, the remaining service time refers to the remaining time during which the first network device can forward or transparently transmit information between the terminal and the first access network device.

[0222] In a possible implementation, before S305, the terminal may receive indication information of the remaining service time, set a timer based on the remaining service time indicated by the indication information, and decide to switch the connected network device when the timer expires.

[0223] In the example, if the first network device has some functions of the access network device in Method 1 or Method 2, before S305, the first network device sends remaining service time indication information to the terminal using a dedicated RRC message or a broadcast message. After receiving the remaining service time indication information, the terminal starts a first timer, and the initial time of the first timer is the time indicated by the indication information. Then, when the first timer expires, the terminal decides to switch the connected network device.

[0224] In another example, if the second network device is configured to forward or transparently transmit information between the second access network device and the terminal by manner 2, before S305, the first access network device sends a dedicated RRC message or a broadcast message to the terminal via the first network device, where the dedicated RRC message or the broadcast message carries indication information of the remaining service time. After receiving the dedicated RRC message or the broadcast message, the terminal starts a second timer, and the initial time of the second timer is the time indicated by the indication information. Then, when the second timer expires, the terminal decides to switch the connected network device.

[0225] In a possible implementation, before S305, the terminal may receive indication information indicating the time (e.g., indicating an absolute time) when the first cell will stop serving the terminal, and may decide to switch the connected network device based on the indication information when that time is reached.

[0226] In a possible implementation, after the terminal decides to switch the connected network device, the terminal may further determine whether to perform downlink synchronization based on the location information of the first network device, the location information of the second network device, and the location information of the terminal, or the terminal may further determine whether to perform downlink synchronization based on the propagation delay between the terminal and the first access network device and the propagation delay between the terminal and the second access network device.

[0227] For example, if the first network device has some functions of the access network device in Method 1 or Method 2, the terminal performs downlink synchronization when the absolute value of the difference between the first distance and the second distance is equal to or greater than the first threshold. For descriptions of the first distance, the second distance, and the first threshold, please refer to the description of the corresponding S304. Details will not be described again in this specification. In other words, the terminal performs downlink synchronization when the first network device gradually moves away from the terminal and the second network device gradually moves closer to the terminal, and the difference between the distance between the terminal and the first network device and the distance between the terminal and the second network device is equal to or greater than the first threshold. When the distance between the terminal and the first network device is the same as the distance between the terminal and the second network device, or when the difference between the distance between the terminal and the first network device and the distance between the terminal and the second network device is less than a first threshold, it may be understood that the difference between the time estimated by the terminal when a downlink synchronization signal of a first cell sent by the first network device arrives at the terminal and the time estimated by the terminal when a downlink synchronization signal of a second cell sent by the second network device arrives at the terminal is less than a first time difference. Therefore, in order to avoid performing unnecessary downlink synchronization, the terminal may still use downlink synchronization for communication with the first network device as downlink synchronization for communication with the second network device.

[0228] For example, if the first network device has some functions of the access network device in Method 1 or Method 2, the terminal performs downlink synchronization when the absolute value of the difference between the first propagation delay and the second propagation delay is equal to or greater than the second threshold. For descriptions of the first propagation delay, the second propagation delay, and the second threshold, please refer to the description of the corresponding S304. Details will not be described again in this specification. In other words, the terminal performs downlink synchronization when the difference between the propagation delay of the information sent by the first network device to the terminal and the propagation delay of the information sent by the second network device to the terminal is equal to or greater than the second threshold. When the propagation delay of the information sent by the first network device to the terminal is the same as the propagation delay of the information sent by the second network device to the terminal, or when the difference between the propagation delay of the information sent by the first network device to the terminal and the propagation delay of the information sent by the second network device to the terminal is less than a second threshold, it may be understood that the difference between the time estimated by the terminal when the downlink synchronization signal of the first cell sent by the first network device arrives at the terminal and the time estimated by the terminal when the downlink synchronization signal of the second cell sent by the second network device arrives at the terminal is less than a first time difference. Therefore, in order to avoid performing unnecessary downlink synchronization, the terminal may still use the downlink synchronization for communication with the first network device as the downlink synchronization for communication with the second network device.

[0229] For example, when the second network device is configured to forward or transparently transmit information between the second access network device and the terminal using scheme 2, the terminal performs downlink synchronization when the absolute value of the difference between the third propagation delay and the fourth propagation delay is equal to or greater than a fourth threshold. The third propagation delay is the sum of the propagation delay between the first access network device and the first network device and the propagation delay between the first network device and the terminal, i.e., the propagation delay of information sent by the first access network device to the terminal via the first network device. The fourth propagation delay is the sum of the propagation delay between the second access network device and the second network device and the propagation delay between the second network device and the terminal, i.e., the propagation delay of information sent by the second access network device to the terminal via the second network device. Specifically, the terminal may determine a propagation delay between the first network device and the terminal based on the location information of the first network device and the terminal, and may obtain a third propagation delay by adding the propagation delay between the first network device and the terminal and the propagation delay between the first network device and the first access network device (this propagation delay may be notified to the terminal by the first access network device). Similarly, the terminal may determine a propagation delay between the second network device and the terminal based on the location information of the second network device and the terminal, and may obtain a fourth propagation delay by adding the propagation delay between the second network device and the terminal and the propagation delay between the second network device and the second access network device (this propagation delay may be notified to the terminal by the second access network device). In other words, when the difference between the propagation delay of information sent to the terminal by the first access network device via the first network device and the propagation delay of information sent to the terminal by the second access network device via the second network device is greater than or equal to a fourth threshold, the terminal performs downlink synchronization.

[0230] When the propagation delay of information sent by the first network device to the terminal via the first network device is the same as the propagation delay of information sent by the second access network device to the terminal via the second network device, or when the difference between the propagation delay of information sent by the first access network device to the terminal via the first network device and the propagation delay of information sent by the second access network device to the terminal via the second network device is less than a fourth threshold, it may be understood that the difference between the time estimated by the terminal when a downlink synchronization signal of a first cell sent by the first access network device arrives at the terminal and the time estimated by the terminal when a downlink synchronization signal of a second cell sent by the second access network device arrives at the terminal is less than a second time difference. Therefore, in order to avoid performing unnecessary downlink synchronization, the terminal may still use the downlink synchronization for communication with the first network device as the downlink synchronization for communication with the second network device as well.

[0231] For example, when the second network device is configured to forward or transparently transmit information between the second access network device and the terminal using scheme 2, the terminal performs downlink synchronization when the absolute value of the difference between the third distance and the fourth distance is equal to or greater than a third threshold. The third distance may be equal to the product of the third propagation delay and the speed of light, and the fourth distance may be equal to the product of the fourth propagation delay and the speed of light. In other words, when the first network device gradually moves away from the terminal and the second network device gradually moves closer to the terminal, and the difference between the third distance and the fourth distance is equal to or greater than the third threshold, the terminal performs downlink synchronization. When the third distance is the same as the fourth distance, or when the difference between the third distance and the fourth distance is less than a third threshold, it may be understood that the difference between the time estimated by the terminal when the downlink synchronization signal of the first cell sent by the first access network device arrives at the terminal and the time estimated by the terminal when the downlink synchronization signal of the second cell sent by the second access network device arrives at the terminal is less than or equal to the second time difference. Thus, in order to avoid performing unnecessary downlink synchronization, the terminal may still use the downlink synchronization for communication with the first network device as the downlink synchronization for communication with the second network device.

[0232] It may be understood that the operations of the terminal, the first network device, the second network device, the first access network device, or the second access network device in S301 to S305 may be implemented by the processor 201 of the communication apparatus 20 shown in Figure 2 by calling application program codes stored in the memory 203. This is not limited in this embodiment of the present application.

[0233] 3 to 5, the terminal is in a connected state. In certain applications, the terminal may alternatively be in a radio resource control idle (RRC-idle) state or a radio resource control inactive (RRC-inactive) state. The following describes a handover method when the terminal is in the RRC idle state or the RRC inactive state.

[0234] 6 shows another handover method according to an embodiment of the present application, which includes steps S601 to S603.

[0235] S601: A terminal camps on a first cell via a first network device.

[0236] It may be understood that the handover method shown in Figure 6 is similar to the handover method shown in Figure 3, and may be applied to the communication system 10 shown in Figure 1A or the communication system 11 shown in Figure 1C. For the case where the method shown in Figure 6 is applied to the communication system 10 shown in Figure 1A, please refer to the following description of Method 3. For the case where the method shown in Figure 6 is applied to the communication system 11 shown in Figure 1C, please refer to the following description of Method 4. A detailed description is provided below.

[0237] Method 3:

[0238] In Approach 3, the terminal may be a terminal of the communication system 10. For example, the terminal is the terminal 102 shown in FIG. 1A. The first network device may be a network device of the communication system 10. For example, the first network device may be the network device 101 shown in FIG. 1A.

[0239] In the example, the first network device is a first satellite. Optionally, the first satellite has the function of a first access network device. In other words, the first satellite may be considered as the first access network device, or may be used as the first access network device, or may replace the first access network device. In this case, the downlink synchronization signal of the first cell sent by the first network device is generated and sent by the first network device. For a description of the first access network device, please refer to the description of the access network device in FIG. 1A.

[0240] A terminal camping on a first cell via a first network device may be understood as the terminal camping on a first cell of the first network device, where the first cell is managed by the first network device.

[0241] Method 4:

[0242] In approach 4, the terminal may be a terminal of communication system 11. For example, the terminal is terminal 112 shown in FIG. 1C. The first network device may be a network device of communication system 11. For example, the first network device may be network device 111 shown in FIG. 1C.

[0243] In an example, the first network device is a first satellite. Optionally, the first satellite or the first network device may be configured to forward or transparently transmit information between the first access network device and a terminal, or the first satellite or the first network device may have some functions of an access network device (e.g., the function of a DU node of an access network device, or the function of a DU node of an IAB function). The first access network device may be an access network device of the communication system 11. For example, the first access network device is the access network device 113 shown in FIG. 1C. The first access network device may have the function of a CU node.

[0244] Regarding Method 4, if the first satellite or the first network device is configured to forward or transparently transmit information between the first access network device and the terminal, it may be understood that the downlink synchronization signal of the first cell sent by the first network device (or the first satellite) is generated by the first access network device and sent to the first network device (or the first satellite). After receiving the downlink synchronization signal, the first network device (or the first satellite) sends the downlink synchronization signal to the terminal. If the first satellite or the first network device has some functions of the access network device, the downlink synchronization signal of the first cell sent by the first network device (or the first satellite) is generated by the first network device and sent to the terminal.

[0245] With regard to Method 4, a terminal camping on a first cell via a first network device may be understood as the terminal camping on a first cell of a first access network device via the first network device. When the first network device is configured to forward or transparently transmit information between the first access network device and the terminal (i.e., the first network device transparently transmits payloads), the first cell is managed by the first access network device. When the first network device has some of the functionality of an access network device, the first cell may be managed by the first access network device or may be managed by the first network device. In Method 2, information sent by the terminal may be understood to be sent to the first access network device via the first network device. Similarly, information sent by the first access network device may be sent to the terminal via the first network device. When the first network device has some of the functionality of an access network device, it may be understood that the first network device may alternatively send some information directly to the terminal.

[0246] Optionally, in Methods 3 and 4, the terminal is in an RRC idle state or an RRC inactive state.

[0247] S602: The terminal performs downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device.

[0248] The specific process of S602 is similar to that of S302, so please refer to the description of S302, and the details will not be described again in this specification.

[0249] S603: The terminal camps on a second cell via a second network device.

[0250] It may be understood that if the first cell and the second cell are the same cell, after S602, the terminal may change the network device for camping on the first cell from the first network device to the second network device.

[0251] In the example, the communication system 11 shown in Figure 1C is used as an example. If the first network device is the network device 111, the terminal is the terminal 112, the first access network device and the second access network device are the same, both are the access network device 113, and the second network device is the network device 114, the terminal 112 will first camp on the first cell of the access network device 113 through the network device 111, and will then camp on the first cell of the access network device 113 through the network device 114 after performing downlink synchronization with the downlink synchronization signal of the second cell sent by the network device 114.

[0252] If the first cell and the second cell are not the same cell, but the configuration of the first cell is the same as the configuration of the second cell, or if the first cell and the second cell are different cells, it may be understood that after S602, the terminal does not camp on the first cell, but camps on the second cell via the second network device.

[0253] In the example, the communication system 10 shown in Fig. 1A is used as an example. If the first network device is network device 101, the terminal is terminal 102, and the second network device is network device 103, the terminal 102 first camps on a first cell of network device 101, and then camps on a second cell of network device 102 after performing downlink synchronization with the downlink synchronization signal of the second cell sent by network device 102. The first cell and the second cell are different, i.e., the first cell and the second cell are not the same cell, but the configuration of the first cell is the same as the configuration of the second cell.

[0254] In another example, the communication system 11 shown in Fig. 1C is used as an example. When the first network device is the network device 111, the terminal is the terminal 112, the first access network device and the second access network device are the same, both are the access network device 113, and the second network device is the network device 114, the terminal 112 first camps on the first cell of the access network device 113 through the network device 111, and after performing downlink synchronization with the downlink synchronization signal of the second cell sent by the network device 114, camps on the second cell of the network device 113 through the network device 114. Although the first cell and the second cell are not the same cell, the configuration of the first cell is the same as the configuration of the second cell.

[0255] 1C is used as an example. When the first network device is network device 111, the terminal is terminal 112, the first access network device is access network device 113, the second access network device is access network device 114, and the second network device is network device 115, the terminal 112 first camps on a first cell of access network device 113 via network device 111, and after performing downlink synchronization with the downlink synchronization signal of the second cell sent by network device 114, camps on a second cell of network device 115 via network device 114. The first cell is different from the second cell, i.e., the first cell and the second cell are not the same cell, but the configuration of the first cell is the same as the configuration of the second cell.

[0256] Based on the method shown in FIG. 6, a terminal may camp on a first cell via a first network device. After performing downlink synchronization with a downlink synchronization signal of the second cell sent by a second network device, the terminal may camp on a second cell via the second network device. The second cell and the first cell have the same cell identifier. In this way, when the first network device switches to the second network device but the cell identifier of the cell on which the terminal is camped remains unchanged, the terminal may perform downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device, thereby enabling subsequent communication to be performed successfully. For example, with regard to Method 3, after S602, the terminal may communicate with the second network device. With regard to Method 4, after S602, the terminal may communicate with the second access network device via the second network device.

[0257] Optionally, in a possible implementation of the method shown in Fig. 6, the first indication information may be for triggering the terminal to perform downlink synchronization. In particular, as shown in Fig. 7, the method shown in Fig. 6 may further include S604.

[0258] S604: The terminal receives first indication information.

[0259] The specific process of S604 is similar to that of S304. Therefore, please refer to the description of the corresponding S304. The difference is that in S604, the first indication information cannot be carried in a dedicated RRC message, a dedicated MAC-CE, or a dedicated physical channel. In S604, the first indication information can be carried in a common RRC message, a common MAC-CE, or a common physical channel.

[0260] Optionally, in a possible implementation of the method shown in Fig. 6, the terminal performs downlink synchronization when deciding to switch the connected network device. In particular, as shown in Fig. 8, the method shown in Fig. 6 may further include S605.

[0261] S605: The terminal decides to switch the connected network device.

[0262] The specific process of S605 is similar to that of S305. Therefore, please refer to the corresponding description of S305. The difference is that the remaining service time indication information can be carried in a broadcast message, not in a dedicated RRC message.

[0263] It may be understood that the operations of the terminal, the first network device, the second network device, the first access network device, or the second access network device in S601 to S605 may be implemented by the processor 201 of the communication apparatus 20 shown in Figure 2 by calling application program codes stored in the memory 203. This is not limited in this embodiment of the present application.

[0264] In the foregoing embodiments, it may be understood that the methods and / or steps implemented by the terminal may be implemented by components (e.g., chips or circuits) that can be used in the terminal, and the methods and / or steps implemented by the first access network device may be implemented by components (e.g., chips or circuits) that can be used in the first access network device, without being limited thereto.

[0265] The above describes the solutions provided in the embodiments of the present application mainly from the perspective of interactions between network elements. Correspondingly, the embodiments of the present application further provide a communication device. The communication device may be a terminal in the above method embodiments, a device including the above terminal, or a component that can be used in the terminal. Alternatively, the communication device may be a first access network device in the above method embodiments, a device including the above first access network device, or a component that can be used in the first access network device. To implement the above functions, the terminal, the first access network device, etc. may be understood to include corresponding hardware structures and / or software modules for implementing each function. Those skilled in the art will easily recognize that the present application can be implemented by hardware or a combination of hardware and computer software as a combination of the example units and algorithm operations described in the embodiments disclosed herein. Whether the functions are implemented by hardware or by hardware driven by computer software depends on the design constraints of a specific application and technical solution. Those skilled in the art may use various methods to implement the described functions for each specific application, and such implementations are not considered to go beyond the scope of the present application.

[0266] In the embodiments of the present application, the terminal or the first access network device may be divided into functional modules based on the above-mentioned exemplary method. For example, each functional module may be obtained by dividing the functional modules based on the corresponding functions, or two or more functions may be integrated into one processing module. The integrated module may be implemented in the form of hardware or a software functional module. It should be noted that the module division in the embodiments of the present application is an example and is merely a logical functional division. In actual implementation, other division methods may be used.

[0267] For example, when each functional module is obtained by division in an integrated manner, Figure 9 is a schematic diagram of the structure of a communication device 90. The communication device 90 includes a communication module 901 and a processing module 902. The communication module 901 may also be called a transceiver unit or transceiver module, and may be configured to implement transceiver functions, and may be, for example, a transceiver circuit, a transceiver device, a transceiver, or a communication interface.

[0268] For example, the communication device 90 is configured to implement the functionality of a terminal, such as the terminal in the embodiment shown in Figure 3, the embodiment shown in Figure 4, the embodiment shown in Figure 5, the embodiment shown in Figure 6, the embodiment shown in Figure 7, or the embodiment shown in Figure 8.

[0269] The communication module 901 is configured to connect to a first cell via a first network device.

[0270] The processing module 902 is configured to perform downlink synchronization with a downlink synchronization signal of a second cell sent by a second network device.

[0271] The communication module 901 is further configured to connect to a second cell via a second network device, the first cell and the second cell having the same cell identifier.

[0272] In a possible implementation, the communication module 901 is further configured to receive a first indication information.

[0273] The first indication information indicates to the communication device 90 to perform downlink synchronization, or the first indication information indicates to the communication device 90 to stop using the downlink timing of the first cell.

[0274] In a possible implementation, the first indication information is carried in the intra-cell handover command based on a time condition.

[0275] In a possible implementation, the communication module 901 is further configured to receive configuration information.

[0276] The configuration information indicates the configuration of the downlink synchronization signal.

[0277] In a possible implementation, the configuration information includes at least one of a length of a measurement window of the downlink synchronization signal, periodicity information of the measurement window of the downlink synchronization signal, or a first offset, wherein at least one of the periodicity information or the first offset is for determining a start position of the measurement window.

[0278] In a possible implementation, the processing module 902 is further configured to determine to switch the connected network device. The processing module 902 is particularly configured to perform downlink synchronization with the downlink synchronization signal when the absolute value of the difference between the first distance and the second distance is greater than or equal to a first threshold.

[0279] The first distance is the distance between the communication device 90 and a first network device, and the second distance is the distance between the communication device 90 and a second network device.

[0280] In a possible implementation, the processing module 902 is particularly configured to determine to switch the connected network device when the remaining service time of the first network device is determined to be 0.

[0281] In a possible implementation, the processing module 902 is specifically configured to search for a downlink synchronization signal, and more specifically configured to obtain downlink timing based on the downlink synchronization signal.

[0282] In a possible implementation, the processing module 902 is specifically configured to obtain a time domain position of the downlink synchronization signal based on the location information of the first network device, the location information of the second network device, and the location information of the communication device 90.

[0283] In a possible implementation, the first network device is a first satellite.

[0284] In a possible implementation, the first satellite has the functionality of the first access network device, or the first satellite has the functionality of the distribution unit of the first access network device. The first access network device is configured to provide service to the communication device 90 before the communication device 90 performs downlink synchronization.

[0285] In a possible implementation, the second network device is a second satellite.

[0286] In a possible implementation, the second satellite has the functionality of a second access network device, or the second satellite has the functionality of a distribution unit of a second access network device.

[0287] The second access network device is configured to provide service to the communication device 90 after the communication device 90 has performed downlink synchronization.

[0288] When the communication device 90 is configured to implement the functions of a terminal, for other functions that can be implemented by the communication device 90, please refer to the relevant descriptions of the embodiment shown in Figure 3, the embodiment shown in Figure 4, the embodiment shown in Figure 5, the embodiment shown in Figure 6, the embodiment shown in Figure 7, or the embodiment shown in Figure 8. The details will not be described again.

[0289] In a simple embodiment, one skilled in the art can understand that the communication device 90 may use the configuration shown in Figure 2. For example, the processor 201 of Figure 2 may invoke computer-executable instructions stored in the memory 203 to enable the communication device 90 to perform the method of the method embodiments described above.

[0290] For example, the functionality / implementation processes of communication module 901 and processing module 902 of Figure 9 may be implemented by processor 201 of Figure 2 by invoking computer-executable instructions stored in memory 203. Alternatively, the functionality / implementation processes of processing module 902 of Figure 9 may be implemented by processor 201 of Figure 2 by invoking computer-executable instructions stored in memory 203, and the functionality / implementation processes of communication module 901 of Figure 9 may be implemented by communication interface 204 of Figure 2.

[0291] 10 is a schematic diagram of the structure of a communication device 100, for example, when each functional module is obtained by division in an integrated manner. The communication device 100 includes a communication module 1001. The communication module 1001 may also be called a transceiver unit or transceiver module, and may be configured to implement a transceiver function, and may be, for example, a transceiver circuit, a transceiver device, a transceiver, or a communication interface.

[0292] For example, the communication device 100 is configured to implement the functionality of a first access network device, such as the first access network device in the embodiment shown in Figure 3, the embodiment shown in Figure 4, the embodiment shown in Figure 5, the embodiment shown in Figure 6, the embodiment shown in Figure 7, or the embodiment shown in Figure 8.

[0293] The communication module 1001 is configured to connect to a terminal through a first cell, which is a cell to which the terminal is connected through a first network device.

[0294] The communication module 1001 is further configured to send first indication information to the terminal, where the first indication information indicates the terminal to perform downlink synchronization, or the first indication information indicates the terminal to stop using the downlink timing of the first cell.

[0295] The communication module 1001 is further configured to connect to the terminal through a second cell, where the second cell and the first cell have the same cell identifier, the second cell is a cell connected to the terminal through a second network device, and the first cell and the second cell are managed by the communication apparatus 100.

[0296] In a possible implementation, the first indication information is carried in the intra-cell handover command based on a time condition.

[0297] In a possible implementation, the communication module 1001 is particularly configured to send first indication information to the terminal when the absolute value of the difference between the first distance and the second distance is greater than or equal to a first threshold.

[0298] The first distance is the distance between the terminal and the first network device, and the second distance is the distance between the terminal and the second network device.

[0299] In a possible implementation, the communication module 1001 is further configured to send configuration information to the terminal, where the configuration information indicates a configuration of the downlink synchronization signal of the second cell.

[0300] In a possible implementation, the configuration information includes at least one of a length of a measurement window of the downlink synchronization signal, periodicity information of the measurement window of the downlink synchronization signal, or a first offset, wherein at least one of the periodicity information or the first offset is for determining a start position of the measurement window.

[0301] In a possible implementation, the first network device is a first satellite.

[0302] In a possible implementation, the first satellite has the functionality of the communication device 100 or the first satellite has the functionality of a distributed unit of the communication device 100 .

[0303] The communication device 100 is configured to provide services to terminals.

[0304] In a possible implementation, the second network device is a second satellite.

[0305] In a possible implementation, the second satellite has the functionality of the communication device 100 or the second satellite has the functionality of a distributed unit of the communication device 100 .

[0306] When the communication device 100 is configured to implement the functions of the first access network device, for other functions that can be implemented by the communication device 100, please refer to the relevant descriptions of the embodiment shown in Figure 3, the embodiment shown in Figure 4, the embodiment shown in Figure 5, the embodiment shown in Figure 6, the embodiment shown in Figure 7, or the embodiment shown in Figure 8. The details will not be described again.

[0307] In a simple embodiment, one skilled in the art can understand that the communication device 100 may use the configuration shown in Figure 2. For example, the processor 201 of Figure 2 may invoke computer-executable instructions stored in the memory 203 to enable the communication device 100 to perform the methods of the method embodiments described above.

[0308] For example, the functionality / implementation processes of the communication module 1001 of Figure 10 may be implemented by the processor 201 of Figure 2 by invoking computer-executable instructions stored in the memory 203. Alternatively, the functionality / implementation processes of the communication module 1001 of Figure 10 may be implemented by the communication interface 204 of Figure 2.

[0309] It should be noted that one or more of the aforementioned modules or units may be implemented by using software, hardware, or a combination thereof. When any one of the aforementioned modules or units is implemented by software, the software exists in the form of computer program instructions and is stored in a memory. A processor may be configured to execute the program instructions and implement the aforementioned method steps. The processor may be integrated into a system-on-chip (SoC) or an application-specific integrated circuit (ASIC), or may be an independent semiconductor chip. In addition to the core configured to perform calculations or processing by executing software instructions, the processor may further include necessary hardware accelerators, such as a field programmable gate array (FPGA), a programmable logic device (PLD), or a logic circuit that implements dedicated logic operations.

[0310] When the aforementioned modules or units are implemented using hardware, the hardware may be any one or any combination of a CPU, microprocessor, digital signal processing (DSP) chip, microcontroller unit (MCU), artificial intelligence processor, ASIC, SoC, FPGA, PLD, dedicated digital circuitry, hardware accelerator, or non-integrated discrete device, and the hardware may run software necessary to perform the aforementioned method steps or may be independent of software.

[0311] Optionally, an embodiment of the present application further provides a chip system including at least one processor and an interface, wherein the at least one processor is coupled to a memory via the interface, and when the at least one processor executes a computer program or instructions in the memory, the method of any one of the above-mentioned method embodiments is implemented. In a possible implementation, the chip system further includes a memory. Optionally, the chip system may include a chip, or may include a chip and another individual component. This is not particularly limited in this embodiment of the present application.

[0312] Optionally, embodiments of the present application further provide a computer-readable storage medium. All or part of the procedures of the aforementioned method embodiments may be implemented by a computer program instructing associated hardware. The program may be stored in a computer-readable storage medium. When the program is executed, the procedures of the aforementioned method embodiments may be included. The computer-readable storage medium may be an internal storage unit of the communication device of any one of the aforementioned embodiments, such as a hard disk or memory of the communication device. Alternatively, the computer-readable storage medium may be an external storage device of the communication device, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, or a flash card configured on the communication device. Furthermore, the computer-readable storage medium may include both an internal storage unit and an external storage device of the communication device. The computer-readable storage medium is configured to store the computer program and other programs and data required by the communication device. The computer-readable storage medium may further be configured to temporarily store data that has been output or that is to be output.

[0313] Optionally, the embodiments of the present application further provide a computer program product. All or part of the procedures of the above-mentioned method embodiments may be implemented by a computer program that instructs relevant hardware. The program may be stored in the computer program product. When the program is executed, the procedures of the above-mentioned method embodiments may be included.

[0314] Optionally, the embodiments of the present application further provide computer instructions. All or part of the procedures of the above-mentioned method embodiments may be implemented by computer instructions that instruct related hardware (such as a computer, a processor, an access network device, a mobility management network element, or a session management network element). The program may be stored in a computer-readable storage medium or a computer program product.

[0315] The above description of the implementation allows those skilled in the art to understand that the division of the above functional modules is adopted as an example for the purpose of simple and concise description. In actual applications, the above functions can be allocated and implemented in separate modules according to requirements. That is, the internal structure of the device is divided into separate functional modules to implement all or part of the above functions.

[0316] In some embodiments provided in this application, it should be understood that the disclosed devices and methods may be implemented in other manners. For example, the described device embodiments are merely examples. For example, modularization or division into units is merely a logical division of function, and other divisions may be used in actual implementation. For example, multiple units or components may be combined or integrated to form another device, or some features may be omitted or not implemented. In addition, the shown or discussed mutual couplings or direct couplings or communication connections may be implemented using some interfaces. Indirect couplings or communication connections between devices or units may be implemented in electronic, mechanical, or other forms.

[0317] The units described as separate components may or may not be physically separate, and the components shown as units may be one or more physical units, located in one location, or distributed in different locations. Some or all of the units may be selected based on actual requirements for achieving the objectives of the solutions of the embodiments.

[0318] In addition, the functional units of the embodiments of the present application may be integrated into one processing unit, each of the units may exist physically alone, or two or more units may be integrated into one unit. The integrated unit may be implemented in the form of hardware or in the form of a software functional unit.

Claims

1. A handover method applied to a terminal or an apparatus of the terminal, the method comprising: connecting to a first cell via a first network device; receiving, from the first network device, indication information indicating when the first cell will cease serving the terminal; determining to switch the first network device when the time point is reached; When determining to switch the first network device, performing downlink synchronization based on a downlink synchronization signal of a second cell sent by a second network device; connecting to the second cell via the second network device, the first cell and the second cell having the same cell identifier corresponding to a geographic location, the first network device being a first satellite, and the second network device being a second satellite; A handover method comprising:

2. The step of connecting to the second cell via the second network device comprises: sending a random access signal to the second network device; or sending uplink data to the second network device without sending a random access signal to the second network device; The method of claim 1 , comprising:

3. The method comprises: The method of claim 1 , further comprising receiving configuration information, the configuration information indicating a configuration of the downlink synchronization signal.

4. 4. The method of claim 3, wherein the configuration information includes at least one of a length of a measurement window of the downlink synchronization signal, periodicity information of the measurement window of the downlink synchronization signal, or a first offset, and at least one of the periodicity information or the first offset is for determining a start position of the measurement window.

5. The step of performing downlink synchronization with a downlink synchronization signal of a second cell sent by the second network device includes: Obtaining a time domain position of the downlink synchronization signal based on location information of the first network device, location information of the second network device, and location information of the terminal.

10. The method of claim 1, comprising:

6. 1. A handover method applied to a first access network device, the method comprising: connecting to a terminal via a first cell, the first cell being a cell connected to the terminal via a first network device; sending, to the terminal, indication information indicating a time when the first cell will stop serving the terminal, the indication information being for the terminal to decide to switch the first network device when the time is reached and to perform downlink synchronization based on a downlink synchronization signal of a second cell sent by a second network device; connecting to the terminal via the second cell, wherein the second cell and the first cell have the same cell identifier corresponding to a geographical location, the second cell is a cell connected to the terminal via the second network device, the first cell and the second cell are managed by the first access network device, the first network device is a first satellite, and the second network device is a second satellite; A handover method comprising:

7. The step of connecting to the terminal via the second cell comprises: receiving a random access signal from the terminal; or receiving uplink data from the terminal without receiving a random access signal from the terminal; The method of claim 6, comprising:

8. The method comprises: sending configuration information to the terminal, the configuration information indicating a configuration of a downlink synchronization signal of the second cell; The method of claim 6 further comprising:

9. 9. The method of claim 8, wherein the configuration information includes at least one of a length of a measurement window of the downlink synchronization signal, periodicity information of the measurement window of the downlink synchronization signal, or a first offset, and at least one of the periodicity information or the first offset is for determining a start position of the measurement window.

10. A communication device comprising a unit adapted to carry out the method according to any one of claims 1 to 5.

11. A communication device comprising a unit adapted to carry out the method according to any one of claims 6 to 9.

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