Handover method and apparatus

Abstract

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

Description

[0001] This application is a divisional application. The original application has the application number 202111446655.8 and the original application date is November 30, 2021. The entire contents of the original application are incorporated herein by reference. Technical Field

[0002] This application relates to the field of wireless communication, and more particularly to switching methods and apparatus. Background Technology

[0003] To enhance communication quality and reliability, in addition to access network equipment such as base stations, terminals can also communicate with other network devices such as satellites or drones. For example, these network devices can act as base stations to provide communication services to terminals, or they can act as relay devices to assist terminals in communicating with base stations. This allows communication services to be provided in areas that access network equipment cannot cover, such as oceans and forests.

[0004] Typically, an access network device can have multiple cells, and generally, the cell identifiers of these cells remain unchanged for a long period. However, in communication between terminals and network devices such as satellites or drones, the mobility of these network devices causes the physical area covered by the network device to change. In this case, associating cell identifiers with network devices would require the terminal to frequently switch cells even if it does not move, resulting in high signaling overhead on the Uu interface. To reduce the frequency of cell switching, cell identifiers can be associated with geographical locations. However, in this case, even if the network device the terminal is communicating with changes, the terminal will not be aware of it, preventing the terminal device from performing cell synchronization. Summary of the Invention

[0005] This application provides a handover method and apparatus for completing cell synchronization between a terminal and the target cell during handover.

[0006] Firstly, a handover method is provided, wherein the communication device executing the handover method can be a terminal; or it can be a module applied in the terminal, such as a chip or chip system. The following description uses a terminal as the executing entity. This method can be applied to a terminal handover 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 above, the terminal can perform downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device, even when the first network device switches to the second network device, but the cell identifier of the cell providing services to the terminal remains unchanged. This allows the terminal to continue communicating normally after the network device switch. For example, before the network device switch, the first network device can provide services to the terminal, and the terminal can communicate with 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 network device can provide services to the terminal, and the terminal can communicate with the second network device. Alternatively, before the network device switch, the first access network device can provide services to the terminal, and the terminal can communicate with the first access network device through 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 can provide services to the terminal, and the terminal can communicate with the second access network device through the second network device.

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

[0009] Based on the above method, the cell accessed by the terminal remains unchanged after switching from the first network device to the second network device.

[0010] In one possible implementation, the method further includes: receiving first indication information, the first indication information being used to instruct the terminal to perform downlink synchronization, or the first indication information being used to instruct the terminal to stop using the downlink timing of the first cell.

[0011] Based on the above method, the terminal can be triggered to perform downlink synchronization through the first indication information, thereby enabling subsequent communication to proceed normally.

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

[0013] Based on the above method, the terminal can be triggered to perform downlink synchronization by carrying the first indication information in the same cell handover command based on time conditions.

[0014] In one possible implementation, the first indication information is carried in a dedicated Radio Resource Control (RRC) message, a dedicated Media Access Control-Control Element (MAC-CE) message, or a dedicated physical channel; or, the first indication information is carried in a public RRC message, a public MAC-CE message, or a public physical channel.

[0015] Based on the above method, the first instruction information can be carried in various types of messages, which improves the flexibility and diversity of sending the first instruction information.

[0016] In one possible implementation, the method further includes receiving configuration information that indicates the configuration of the downlink synchronization signal.

[0017] Based on the above method, the terminal can determine the time domain location of the measurement window of the downlink synchronization signal of the second cell, so that the terminal can monitor the downlink synchronization signal of the second cell at that time domain location.

[0018] In one possible implementation, the configuration information includes at least one of the following: the length of the measurement window of the downlink synchronization signal, the period information of the measurement window of the downlink synchronization signal, or a first offset, wherein at least one of the period information or the first offset is used to determine the starting position of the measurement window.

[0019] Based on the above method, the terminal can determine the starting position of the measurement window of the downlink synchronization signal of the second cell according to at least one of periodic information or the first offset, and determine the time domain position of the measurement window according to the starting position and the length of the measurement window of the downlink synchronization signal of the second cell.

[0020] In one possible implementation, the method further includes: determining that the connected network device will be switched; performing downlink synchronization with a downlink synchronization signal of a second cell sent by the second network device, including: performing downlink synchronization with the downlink synchronization signal if the absolute value of the difference between a first distance and a second distance is greater than or equal to a first threshold, wherein 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.

[0021] Based on the above method, the terminal performs downlink synchronization when it determines that it will switch the connected network device, and the absolute value of the difference between the first distance and the second distance is greater than or equal to a first threshold. That is, the terminal performs downlink synchronization when the first network device is getting farther away from the terminal, the second network device is getting 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 greater than or equal to the first threshold. It can be understood that when the distance between the terminal and the first network device is the same as or less than the difference between the distance between the terminal and the second network device, the estimated arrival time of the downlink synchronization signal from the first cell sent by the first network device is less than or equal to the estimated arrival time of the downlink synchronization signal from the second cell sent by the second network device. Therefore, to minimize unnecessary downlink synchronization, the terminal can still use the downlink synchronization used for communication with the first network device as the downlink synchronization used for communication with the second network device.

[0022] In one possible implementation, determining that the connected network device will be switched includes: determining that the connected network device will be switched when it is determined that the remaining service time of the first network device is 0.

[0023] In the above method, the remaining service time can represent the remaining time that the first network device can connect to the terminal. Therefore, based on the above method, the terminal can determine to switch to a different network device if the first network device cannot connect to the terminal.

[0024] In one possible implementation, downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device includes: searching for the downlink synchronization signal; and obtaining downlink timing based on the downlink synchronization signal.

[0025] Based on the above method, the terminal can perform downlink synchronization by searching for the downlink synchronization signal of the second cell, so as to obtain the boundaries of the system frame, subframe, time slot and symbol corresponding to the second cell.

[0026] In one possible implementation, downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device includes: obtaining the time domain location 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 terminal.

[0027] Based on the above method, the terminal can estimate the time-domain location of the downlink synchronization signal of the second cell according to the location information of the first network device, the location information of the second network device, and the terminal's location information. In this way, the terminal can obtain downlink timing, that is, obtain the boundaries of the system frame, subframe, time slot, and symbol corresponding to the second cell.

[0028] In one 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 above method, the terminal can perform a two-step random access procedure or a four-step random access procedure to access the second cell.

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

[0031] Based on the above method, before the terminal and the second network device perform downlink synchronization of the downlink synchronization signal of the second cell, the first satellite can connect with the terminal, which can provide communication services for areas that are difficult for access network devices to cover, such as oceans and forests, so as to enhance the reliability of communication.

[0032] In one possible implementation, the first satellite has the function of the first access network device; or, the first satellite has the function of the distribution unit of the first access network device; wherein the first access network device is used to provide services to the terminal before the terminal performs downlink synchronization.

[0033] Based on the above method, before the terminal and the second network device perform downlink synchronization of the downlink synchronization signal of the second cell, the first satellite can act as a first access network device to provide services to the terminal, or the first satellite can act as a distribution unit of the first access network device to provide services to the terminal. If the first satellite acts as a distribution unit of the first access network device, then the first access network device has the function of a centralized unit, or in other words, the first access network device can act as a centralized unit.

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

[0035] Based on the above method, after the terminal and the second network device perform downlink synchronization of the downlink synchronization signal of the second cell, the second satellite can connect with the terminal and provide communication services for areas that are difficult for access network devices to cover, such as oceans and forests, so as to enhance the reliability of communication.

[0036] In one possible implementation, the second satellite functions as a second access network device; or, the second satellite functions as a distribution unit of the second access network device; wherein the second access network device is used to provide services to the terminal after the terminal has performed downlink synchronization.

[0037] Based on the above method, after the terminal and the second network device perform downlink synchronization of the downlink synchronization signal of the second cell, the second satellite can serve as a second access network device to provide services to the terminal, or the second satellite can serve as a distribution unit of the second access network device to provide services to the terminal. If the second satellite serves as a distribution unit of the second access network device, then the second access network device has the function of a centralized unit, or in other words, the second access network device can serve as a centralized unit.

[0038] Secondly, a handover method is provided, wherein the communication device executing the handover method can be a first access network device; or it can be a module applied in the first access network device, such as a chip or chip system. The following description uses the first access network device as the executing entity as an example. The method includes: connecting to a terminal via a first cell, wherein the first cell is the cell to which the terminal connects via a first network device; sending first indication information to the terminal, wherein the first indication information is used to instruct the terminal to perform downlink synchronization, or, the first indication information is used to instruct the terminal to stop using the downlink timing of the first cell; connecting to the terminal via a second cell, wherein the second cell has the same cell identifier as the first cell, the second cell is the cell to which the terminal connects via 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 above, the first access network device can connect to the terminal through the first cell and instruct the terminal to perform downlink synchronization or instruct it to stop using the downlink timing of the first cell, so that the terminal can perform downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device. Subsequently, the first access network device can connect to the terminal through the second cell to continue providing services to the terminal, enabling the terminal to communicate normally.

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

[0041] Based on the above method, the cell accessed by the terminal remains unchanged after switching from the first network device to the second network device.

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

[0043] Based on the above method, the first access network device can instruct the terminal to perform downlink synchronization through a time-based intra-cell handover command, or instruct the terminal to stop using the downlink timing of the first cell.

[0044] In one possible implementation, the first indication information is carried in a dedicated Radio Resource Control (RRC) message, a dedicated Media Access Control-Control Element (MAC-CE) message, or a dedicated physical channel; or, the first indication information is carried in a public RRC message, a public MAC-CE message, or a public physical channel.

[0045] Based on the above method, the first instruction information can be carried in various types of messages, which improves the flexibility and diversity of sending the first instruction information.

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

[0047] Based on the above method, the first access network device can send a first indication message 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, to instruct the terminal to perform downlink synchronization or to instruct the terminal to stop using the downlink timing of the first cell. That is, when the first network device is moving further away from the terminal, the second network device is moving 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 greater than or equal to the first threshold, the first access network device instructs the terminal to perform downlink synchronization. It can be understood that when the distance between the terminal and the first network device is the same as or less than the difference between the distance between the terminal and the second network device, the estimated arrival time of the downlink synchronization signal of the first cell sent by the first network device to the terminal is less than or equal to the estimated arrival time of the downlink synchronization signal of the second cell sent by the second network device to the terminal. Therefore, to avoid unnecessary downlink synchronization, the terminal can still use the downlink synchronization used for communication with the first network device as the downlink synchronization used for communication with the second network device, and the first access network device may not need to send the first indication message.

[0048] In one possible implementation, the method further includes sending configuration information to the terminal, the configuration information being used to indicate the configuration of the downlink synchronization signal of the second cell.

[0049] Based on the above method, the first access network device can 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, so that the terminal can monitor the downlink synchronization signal of the second cell at that time domain position.

[0050] In one possible implementation, the configuration information includes at least one of the following: the length of the measurement window of the downlink synchronization signal, the period information of the measurement window of the downlink synchronization signal, or a first offset, wherein at least one of the period information or the first offset is used to determine the starting position of the measurement window.

[0051] Based on the above method, the terminal can determine the starting position of the measurement window of the downlink synchronization signal of the second cell according to at least one of periodic information or a first offset, and determine the time domain position of the measurement window according to the starting position and the length of the measurement window of the downlink synchronization signal of the second cell.

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

[0053] Based on the above method, the first access network device can perform a two-step random access process or a four-step random access process to enable the terminal to access the second cell.

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

[0055] Based on the above method, before the terminal and the second network device perform downlink synchronization of the downlink synchronization signal of the second cell, the first satellite can connect with the terminal, which can provide communication services for areas that are difficult for access network devices to cover, such as oceans and forests, to enhance the reliability of communication.

[0056] In one possible implementation, the first satellite has the function of the first access network device; or, the first satellite has the function of the distribution unit of the first access network device; wherein the first access network device is used to provide services to the terminal.

[0057] Based on the above method, before the terminal and the second network device perform downlink synchronization of the downlink synchronization signal of the second cell, the first satellite can act as a first access network device to provide services to the terminal, or the first satellite can act as a distribution unit of the first access network device to provide services to the terminal. If the first satellite acts as a distribution unit of the first access network device, then the first access network device has the function of a centralized unit, or in other words, the first access network device can act as a centralized unit.

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

[0059] Based on the above method, after the terminal and the second network device perform downlink synchronization of the downlink synchronization signal of the second cell, the second satellite can connect with the terminal and provide communication services for areas that are difficult for access network devices to cover, such as oceans and forests, so as to enhance the reliability of communication.

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

[0061] Based on the above method, after the terminal and the second network device perform downlink synchronization of the downlink synchronization signal of the second cell, the second satellite can serve as the first access network device to provide services to the terminal, or the second satellite can serve as a distribution unit of the first access network device to provide services to the terminal. If the second satellite serves as a distribution unit of the first access network device, then the first access network device has the function of a centralized unit, or in other words, the first access network device can serve as a centralized unit.

[0062] Thirdly, a communication device is provided for implementing the above-described method. This communication device can be the terminal described in the first aspect, or a device including the terminal. The communication device includes modules, units, or means corresponding to implementing the method provided in the first aspect. These modules, units, or means can be implemented in hardware, software, or by hardware executing corresponding software. The hardware or software includes one or more modules or units corresponding to the above-described functions.

[0063] In conjunction with the third aspect described above, in one possible implementation, the communication device may include a communication module and a processing module. The processing module can be used to implement the processing functions described in the first aspect and any of its possible implementations. The processing module may be, for example, a processor. The communication module, also referred to as a transceiver unit or transceiver module, is used to implement the sending and / or receiving functions described in the first aspect and any of its possible implementations. The communication module may consist of a transceiver circuit, a transceiver, a transceiver unit, or a communication interface.

[0064] In conjunction with the third aspect above, in one possible implementation, the communication module includes a sending module and a receiving module, which are used to implement the sending and receiving functions in the first aspect above and any possible implementation thereof.

[0065] Fourthly, a communication apparatus is provided for implementing the above-described method. This communication apparatus may be the first access network device described in the second aspect, or an apparatus comprising the first access network device. The communication apparatus includes modules, units, or means corresponding to implementing the method provided in the second aspect. These modules, units, or means may be implemented in hardware, software, or by hardware executing corresponding software. The hardware or software includes one or more modules or units corresponding to the above-described functions.

[0066] In conjunction with the fourth aspect above, in one possible implementation, the communication device may include a communication module. This communication module, also referred to as a transceiver unit or transceiver module, is used to implement the sending and / or receiving functions in the second aspect above and any of its possible implementations. The communication module may consist of a transceiver circuit, a transceiver, a transceiver unit, or a communication interface.

[0067] In conjunction with the fourth aspect above, in one possible implementation, the communication module includes a sending module and a receiving module, which are used to implement the sending and receiving functions in the second aspect above and any possible implementation thereof.

[0068] Fifthly, a communication device is provided, comprising: a processor; the processor being coupled to a memory, and after reading instructions from the memory, executing the method described in the first aspect according to the instructions. The communication device may be a terminal as described in the first aspect, or a device including the terminal.

[0069] A sixth aspect provides a communication apparatus, comprising: a processor; the processor being coupled to a memory, and after reading instructions from the memory, executing the method as described in the second aspect above according to the instructions. The communication apparatus may be the first access network device described in the second aspect, or an apparatus including the first access network device.

[0070] In conjunction with the fifth or sixth aspect above, in one possible implementation, the communication device further includes a memory for storing necessary program instructions and data.

[0071] In conjunction with the fifth or sixth aspect above, in one possible implementation, the communication device is a chip or a chip system. Optionally, when the communication device is a chip system, it can be composed of chips or may include chips and other discrete components.

[0072] A seventh aspect provides a communication device, comprising: a processor and an interface circuit; the interface circuit being configured to receive a computer program or instructions and transmit them to the processor; the processor being configured to execute the computer program or instructions to cause the communication device to perform the method described in the first aspect above.

[0073] Eighthly, a communication device is provided, comprising: a processor and an interface circuit; the interface circuit being configured to receive a computer program or instructions and transmit them to the processor; the processor being configured to execute the computer program or instructions to cause the communication device to perform the method described in the second aspect above.

[0074] In conjunction with the seventh or eighth aspect above, in one possible implementation, the communication device is a chip or a chip system. Optionally, when the communication device is a chip system, it can be composed of chips or may include chips and other discrete components.

[0075] Ninthly, a computer-readable storage medium is provided that stores instructions which, when executed on a computer, enable the computer to perform the methods described in the first or second aspect above.

[0076] In a tenth aspect, a computer program product containing instructions is provided, which, when run on a computer, enables the computer to perform the methods described in the first or second aspect above.

[0077] The technical effects of any possible implementation of the third to tenth aspects can be found in the technical effects of any one of the first to second aspects or different possible implementations of any one aspect, and will not be repeated here.

[0078] Eleventhly, a communication system is provided, comprising a terminal for performing the method described in the first aspect and a first access network device for performing the method described in the second aspect. Attached Figure Description

[0079] Figure 1A A schematic diagram of the communication system architecture provided in this application embodiment; Figure 1B A schematic diagram of CU nodes and DU nodes provided in the embodiments of this application; Figure 1C Schematic diagram of the communication system architecture provided in the embodiments of this application Figure 2 ; Figure 1D A schematic diagram of satellite motion provided for embodiments of this application; Figure 2 This is a schematic diagram of the hardware structure of the communication device provided in the embodiments of this application; Figure 3 A flowchart illustrating the switching method provided in this application embodiment; Figure 4 Flowchart of the switching method provided in the embodiments of this application Figure 2 ; Figure 5 Flowchart of the switching method provided in the embodiments of this application Figure 3 ; Figure 6 Flowchart of the switching method provided in the embodiments of this application Figure 4 ; Figure 7 Flowchart of the switching method provided in the embodiments of this application Figure 5 ; Figure 8 Flowchart of the switching method provided in the embodiments of this application Figure 6 ; Figure 9 A schematic diagram of the communication device provided in the embodiments of this application is shown below; Figure 10 Schematic diagram of the communication device provided in the embodiments of this application Figure 2 . Detailed Implementation

[0080] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0081] The method provided in this application can be used in various communication systems. For example, the communication system can be a long-term evolution (LTE) system, a 5th generation (5G) communication system, a 3GPP-related communication system, a future evolution communication system, or a system integrating multiple systems, etc., without limitation. 5G can also be referred to as new radio (NR). The following uses... Figure 1A The communication system 10 shown and Figure 1C Taking the communication system 11 shown as an example, the method provided in the embodiments of this application will be described.

[0082] like Figure 1A The diagram shown is a schematic diagram of the architecture of the communication system 10 provided in an embodiment of this application. Figure 1A In this system, 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 may also include a network device 103. Figure 1A This is merely an illustrative diagram and does not constitute a limitation on the applicable scenarios of the technical solutions provided in this application.

[0083] Figure 1A Network devices, such as network device 101 and / or network device 103, can have the functions of access network devices to provide wireless access services to terminals. Specifically, each network device corresponds to a service coverage area, and terminals entering this area can communicate with the network device to receive the wireless access services provided by the network device. Optionally, the service coverage area may include one or more cells.

[0084] In this application embodiment, the access network device can be any device with wireless transceiver capabilities. For example, the access network device refers to a radio access network (RAN) node (or device) that connects a terminal to a wireless network, and can also be called a base station. Currently, some examples of RAN nodes include: evolved Node B (gNB), transmission reception point (TRP), evolved Node B (eNB), radio network controller (RNC), Node B (NB), base station controller (BSC), base transceiver station (BTS), home base station (e.g., home-evolved Node B, or home Node B, HNB), base band unit (BBU), or wireless fidelity (Wi-Fi) access point (AP), etc.

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

[0086] As an example, such as Figure 1BAs shown, RAN equipment including CU nodes and DU nodes can decompose the protocol layer of the gNB in ​​the NR system. Some protocol layer functions are centrally controlled by the CU nodes, while the remaining partial or complete protocol layer functions are distributed in the DU nodes, which are then centrally controlled by the CU nodes. Furthermore, the CU nodes can 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, mainly including radio resource control (RRC) and the corresponding packet data convergence protocol (PDCP) layer, i.e., PDCP-C. PDCP-C is mainly responsible for control plane data encryption / decryption, integrity protection, and data transmission. The CU-UP is responsible for user plane functions, mainly including the service data adaptation protocol (SDAP) and the corresponding PDCP layer, i.e., PDCP-U. SDAP is mainly responsible for processing core network data and mapping flows to bearers. PDCP-U is mainly responsible for data plane encryption / decryption, integrity protection, header compression, sequence number maintenance, and data transmission. CU-CP and CU-UP are connected via the E1 interface. CU-CP represents the gNB connected to the core network via the NG interface. It connects to the DU via the F1 interface control plane (F1-C). CU-UP connects to the DU via the F1 interface user plane (F1-U). Alternatively, PDCP-C may also be included in CU-UP. The DU node primarily comprises the radio link control (RLC) layer, media access control (MAC) layer, and physical (PHY) layer.

[0087] As an example, network devices in communication system 10, such as network device 101 and / or network device 103, may possess all the functions of an access network device. In this case, the network device can be considered an access network device, or in other words, the network device can function as an access network device, or the network device can be replaced as an access network device.

[0088] The network devices in communication system 10, such as network device 101 and / or network device 103, can be any mobile device with wireless transceiver capabilities. These include, but are not limited to, satellites or unmanned aerial systems (UAS).

[0089] The satellite can be a regenerated satellite without an inter-satellite link (ISL) or a regenerated satellite with an ISL. A regenerated satellite can be understood as a satellite with the processing capabilities of an access network device. The UAS includes at least one of tethered UAS (TUA), lighter-than-air UAS (LTA), heavier-than-air UAS (HTA), or high-altitude platform station (HAPS). The UAS can be a regenerated UAS without an inter-UAS link or a regenerated UAS with an inter-UAS link. In this application embodiment, the device for implementing the function of the network device can be a network device; it can also be a device capable of supporting the network device in implementing this function, such as a chip system, which can be installed in the network device or used in conjunction with the network device. In this application embodiment, the chip system can be composed of chips or can include chips and other discrete devices. The method provided in this application embodiment uses a network device as an example to describe the method provided in this application embodiment.

[0090] The terminals in the communication system 10, such as terminal 102, have wireless transceiver capabilities and can be various devices that provide voice and / or data connectivity to users. They can also be called terminal equipment, user equipment (UE), mobile station, mobile terminal, etc. Terminal 102 can be deployed on land, including indoors or outdoors, handheld or vehicle-mounted; it can also be deployed on water (such as ships); and it can be deployed in the air (such as airplanes, balloons, and satellites). It is widely used in various scenarios for applications such as device-to-device (D2D), vehicle-to-everything (V2X) communication, machine-type communication (MTC), Internet of Things (IoT), virtual reality, augmented reality, industrial control, autonomous driving, telemedicine, smart grids, smart furniture, smart offices, smart wearables, smart transportation, and smart cities. Terminal 102 can be a mobile phone, tablet computer, computer with wireless transceiver capabilities, wearable device, vehicle, drone, helicopter, airplane, ship, robot, robotic arm, smart home device, etc. The terminal in this application can also be a relay node. The embodiments of this application do not limit the specific technology or device form used in the terminal. In the embodiments of this application, the chip used in the aforementioned device can also be called a terminal.

[0091] Figure 1AThe communication system 10 shown is for illustrative purposes only and is not intended to limit the technical solutions of this application. Those skilled in the art should understand that in specific implementations, the communication system 10 may also include other devices, and the number of network devices and terminals can be determined according to specific needs without limitation.

[0092] like Figure 1C The diagram shown is an architectural schematic of the communication system 11 provided in an embodiment of this application. Figure 1C In the communication system 11, the communication system 11 may include a network device 111, a terminal 112 that can communicate with the network device 111, and an access network device 113 that can communicate with the network device 111. Optionally, the communication system 11 may also include a network device 114, or the communication system 11 may further include a network device 114 and an access network device 115 that can communicate with the network device 114. Figure 1C This is merely an illustrative diagram and does not constitute a limitation on the applicable scenarios of the technical solutions provided in this application.

[0093] Figure 1C The network devices, such as network device 111 and / or network device 114, can be any mobile device with wireless transceiver capabilities. These include, but are not limited to, satellites or UAS devices.

[0094] The satellite can be a transparent satellite, or a regenerated satellite without an ISL (Inter-Service Link), or a regenerated satellite with an ISL. The UAS (User Access System) can be a transparent UAS, or a regenerated UAS without an inter-UAS link, or a regenerated UAS with an inter-UAS link. For a description of the access network equipment and terminals, please refer to the above. Figure 1A The descriptions of access network devices and terminals in the text are provided above. Other descriptions of UAS can be found in the above text. Figure 1A The description of UAS in the text will not be repeated here.

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

[0096] Similarly, network device 114 can be used to forward or transparently transmit information between terminal 112 and access network device 113, or network device 114 can be used to forward or transparently transmit information between terminal 112 and access network device 115, or network device 114 can implement a transparent payload. Understandably, in this example, network device 111 or network device 114 can be a transparent satellite.

[0097] As another example, network device 111 can possess some of the functions of an access network device, meaning network device 111 can implement a regenerative payload. For instance, network device 111 can function as a DU node in the access network device, or in other words, network device 111 can act as a DU node. In this case, access network device 113 can function as a CU node, or in other words, access network device 113 can act as a CU node. In this situation, network device 111 can be replaced as a DU node, and access network device 113 can be replaced as a CU node. As another example, network device 111 can possess integrated access and backhaul (IAB) functionality, or both network device 111 and access network device 113 can implement IAB functionality. In this case, network device 111 acts as a DU node, or in other words, network device 111 can act as a DU node within an IAB. Access network device 113 acts as a CU node, or in other words, access network device 113 can act as a CU node within an IAB.

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

[0099] Figure 1C The communication system 11 shown is for illustrative purposes only and is not intended to limit the technical solutions of this application. Those skilled in the art should understand that in specific implementations, the communication system 11 may also include other devices, and the number of network devices, access network devices, and terminals can be determined according to specific needs without limitation.

[0100] Understandably, the aforementioned network devices, such as network device 101 or network device 111, are mobile, so the physical area covered by these devices changes. This physical area may include one or more cells. If the cell identifier (e.g., cell global identifier (CGI) or physical cell identifier (PCI)) is associated with the network device, then for a given physical area, the cell identifiers of the cells included in that physical area change as the network device moves. Therefore, even if the terminal does not move, it will perceive a change in the cell identifier. In this case, the network side (such as the network device or access network device) needs to trigger a cell handover procedure for the terminal; that is, the terminal needs to frequently switch cells, resulting in significant signaling overhead on the Uu interface.

[0101] To avoid frequent cell switching by terminals, cell identifiers can be associated with geographical locations. That is, for a given geographical location, the cell identifier corresponding to that location remains unchanged as network devices move. When a network device (such as network device 101) leaves that geographical location, other network devices (such as network device 103) can provide services to terminals located in that geographical location. It should be understood that when network device 103 provides services to terminals located in that geographical location, the cell identifier of the cell in that geographical location is the same as the cell identifier of the cell in that geographical location when network device 101 provides services to terminals located in that geographical location.

[0102] For example, taking network device 101 as satellite 1 and network device 103 as satellite 2, in Figure 1D In the diagram, the cell identifier for geographic location 1 is cell #1, for geographic location 2 it is cell #2, and for geographic location 3 it is cell #3. At 10:00 AM, satellite 1 covers geographic location 1 and can provide service to terminals located in geographic location 1. At this time, the cell identifier for satellite 1 is cell #1. At 10:15 AM, the geographic location covered by satellite 1 changes to geographic location 2, and satellite 1 can provide service to terminals located in geographic location 2. The cell identifier for satellite 1 is cell #2. If satellite 2 covers geographic location 1 at this time, the satellite providing service to terminals located in geographic location 1 switches from satellite 1 to satellite 2, and the cell identifier for satellite 2 is cell #1. At 10:30 AM, the geographic location covered by satellite 1 changes to geographic location 3, and satellite 1 can provide service to terminals located in geographic location 3. The cell identifier for satellite 1 is cell #3. If satellite 2 covers geographic location 2 at this time, the satellite providing service to terminals located in geographic location 2 switches from satellite 1 to satellite 2, and the cell identifier for satellite 2 is cell #2.

[0103] As described above, when the network equipment communicating with the terminal changes, the cell identifier of the cell providing services to the terminal remains unchanged, or in other words, the cell identifier perceived by the terminal is unchanged. For example, in the example above, at 10:15, the satellite communicating with the terminal located at geographical location 1 changes from satellite 1 to satellite 2, but the cell identifier perceived by the terminal is still cell #1. In this situation, the network side (such as network equipment or access network equipment) will not trigger a cell handover procedure for the terminal, even though the network equipment or access network equipment communicating with the terminal has actually changed. Therefore, how the terminal performs cell synchronization at this time is a problem that urgently needs to be solved.

[0104] To address this issue, this application provides a handover method applicable to a terminal switching from a first network device to a second network device. The method includes: connecting to a first cell via 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 via the second network device. The first cell and the second cell share the same cell identifier. The specific process of this method will be described below. Figure 3 The embodiments shown are illustrated. It should be noted that in the embodiments of this application, the first cell and the second cell having the same cell identifier may include having the same PCI but different CGI, or having the same PCI and CGI, etc.

[0105] It is understood that the embodiments of this application can be applied to scenarios where cell identifiers and geographical locations are associated, in which the cell can also be referred to as a quasi-earth fixed cell.

[0106] Optionally, embodiments of this application Figure 1A or Figure 1C Each network element or device (such as network equipment, terminal or access network equipment, etc.) in the application can also be referred to as a communication device. It can be a general-purpose device or a special-purpose device. The embodiments of this application do not specifically limit it.

[0107] Optionally, embodiments of this application Figure 1A or Figure 1C The functions of each network element or device (such as network equipment, terminals, or access network equipment) can be implemented by one device, multiple devices working together, or one or more functional modules within a single device. This application does not specifically limit these functions. It is understood that the aforementioned functions can be network elements within hardware devices, software functions running on dedicated hardware, a combination of hardware and software, or virtualization functions instantiated on a platform (e.g., a cloud platform).

[0108] In specific implementation, the embodiments of this application Figure 1A or Figure 1C Each network element or device (such as network equipment, terminals, or access network equipment) can adopt Figure 2 The shown composition structure, or including Figure 2 The components shown. Figure 2 The diagram shows a hardware structure of a communication device applicable to embodiments of this application. The communication device 20 includes at least one processor 201 and at least one communication interface 204, used to implement the methods provided in embodiments of this application. The communication device 20 may also 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 used to control the execution of the program of the present application.

[0110] Communication line 202 may include a path for transmitting information between the aforementioned components, such as a bus.

[0111] Communication interface 204 is used for communicating with other devices or communication networks. Communication interface 204 can be any transceiver-like device, such as an Ethernet interface, a radio access network (RAN) interface, a wireless local area network (WLAN) interface, a transceiver, pins, a bus, or transceiver circuits, etc.

[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, random access memory (RAM) or other type of dynamic storage device capable of storing information and instructions, or it may be an electrically erasable programmable read-only memory (EEPROM), a compact disc read-only memory (CD-ROM) or other optical disc storage, optical disc storage (including compressed optical discs, laser discs, optical discs, digital universal optical discs, Blu-ray discs, etc.), magnetic disk storage media or other magnetic storage devices, or any other medium capable of carrying or storing desired program code in the form of instructions or data structures and accessible by a computer, but is not limited thereto. The memory may exist independently and be coupled to the processor 201 via communication line 202. The memory 203 may also be integrated with the processor 201. The memory provided in the embodiments of this application may generally be non-volatile.

[0113] The memory 203 stores computer execution instructions involved in the implementation of the scheme provided in the embodiments of this application, and the processor 201 controls the execution. The processor 201 executes the computer execution instructions stored in the memory 203 to implement the method provided in the embodiments of this application. Alternatively, in the embodiments of this application, the processor 201 may execute the processing-related functions in the method provided in the following embodiments of this application, and the communication interface 204 may be responsible for communicating with other devices or communication networks. The embodiments of this application do not specifically limit this aspect.

[0114] Optionally, the computer execution instructions in the embodiments of this application may also be referred to as application code, and the embodiments of this application do not specifically limit this.

[0115] The coupling in the embodiments of this application is an indirect coupling or communication connection between devices, units, or modules, which can be electrical, mechanical, or other forms, and is used for information interaction between devices, units, or modules.

[0116] As one embodiment, processor 201 may include one or more CPUs, for example Figure 2 CPU0 and CPU1 in the CPU.

[0117] As one embodiment, the communication device 20 may include multiple processors, such as Figure 2Processors 201 and 207 are described in the text. Each of these processors may be a single-core (single-CPU) processor or a multi-core (multi-CPU) processor. A processor here may refer to one or more devices, circuits, and / or processing cores used to process data (such as computer program instructions).

[0118] As one embodiment, the communication device 20 may further include an output device 205 and / or an input device 206. The output device 205 is coupled to the processor 201 and can display information in various 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, etc. The input device 206 is coupled to the processor 201 and can receive user input in various ways. For example, the input device 206 may be a mouse, keyboard, touchscreen device, or sensing device, etc.

[0119] Understandable. Figure 2 The structural composition shown does not constitute a limitation on the communication device, except... Figure 2 In addition to the components shown, the communication device may include more or fewer components than illustrated, or combine certain components, or have different component arrangements.

[0120] The switching method provided in the embodiments of this application will now be described with reference to the accompanying drawings. Each network element in the following embodiments may possess... Figure 2 The components shown are not described in detail.

[0121] It should be noted that the message names between network elements or the names of parameters in the messages in the following embodiments of this application are just examples. Other names may be used in the specific implementation. This application does not limit them in this respect.

[0122] It should be noted that in the embodiments of this application, " / " can indicate that the objects before and after it are in an "or" relationship. For example, A / B can mean A or B. "And / or" can be used to describe three relationships between the related objects. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. Here, A and B can be singular or plural. In addition, expressions such as "at least one of A, B, and C" or "at least one of A, B, or C" are generally used to indicate any of the following: A exists alone; B exists alone; C exists alone; A and B exist simultaneously; A and C exist simultaneously; B and C exist simultaneously; A, B, and C exist simultaneously. The above examples use three elements, A, B, and C, to illustrate the optional items of this project. When there are more elements in the expression, the meaning of the expression can be obtained according to the aforementioned rules.

[0123] To facilitate the description of the technical solutions of the embodiments of this application, the objects can be distinguished by "first", "second", "third", "A", "B", "C" and "D". The technical features described by "first", "second", "third", "A", "B", "C" and "D" have no order of precedence or size, and do not constitute a limitation on the number of objects described. Furthermore, the words "first" and "second" do not necessarily mean that the objects described are different.

[0124] In the embodiments of this application, the words "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" should not be construed as being more preferred or advantageous than other embodiments or designs. The use of the words "exemplary" or "for example" is intended to present the relevant concepts in a specific manner to facilitate understanding.

[0125] It is understood that the same step or step with the same function or technical feature in the embodiments of this application can be referenced and learned from each other in different embodiments.

[0126] It is understood that in the embodiments of this application, the terminal, and / or, network device, and / or access network device may perform some or all of the steps in the embodiments of this application. These steps are merely examples, and the embodiments of this application may also perform other steps or variations thereof. Furthermore, the steps may be performed in different orders as presented in the embodiments of this application, and it is not necessary to perform all the steps in the embodiments of this application.

[0127] like Figure 3 The diagram illustrates a handover method provided in this application, which can be applied to a terminal switching from a first network device to a second network device. The handover method includes steps S301-S303.

[0128] S301: The terminal connects to the first cell through the first network device.

[0129] Understandable. Figure 3 The switching method shown can be applied to Figure 1A The communication system 10 shown, or applied to Figure 1C The communication system 11 shown. For applying this method... Figure 1A The situation regarding the communication system 10 shown can be referred to the following description of method 1. For applying this method... Figure 1C The situation of the communication system 11 shown can be referred to the following description of mode 2. A detailed explanation follows.

[0130] Method 1: In method 1, the terminal can be the terminal in the communication system 10 described above. For example, the terminal is... Figure 1A The terminal 102 shown. The first network device can be a network device in the communication system 10 described above. For example, the first network device can be... Figure 1A The network device 101 shown.

[0131] As an example, the first network device is a first satellite. Optionally, the first satellite has the functions of a first access network device, that is, the first satellite can be regarded as a first access network device, or in other words, the first satellite can serve as a first access network device, or the first satellite can be replaced by a first access network device. In this case, the downlink synchronization signal of the first cell transmitted by the first network device is generated and transmitted by the first network device. A description of the first access network device can be found above. Figure 1A Description of access network equipment.

[0132] Understandably, the terminal connects to the first cell through the first network device. This can be understood as the first network device providing the terminal with the service of connecting to the first cell, or in other words, the first network device providing services to the terminal before downlink synchronization occurs between the terminal and the second network device via downlink synchronization signals from the second cell. The first cell is managed by the first network device. Accordingly, the first network device connects to the terminal through the first cell.

[0133] Method 2: In method 2, the terminal can be the terminal in the communication system 11 described above. For example, the terminal is... Figure 1C The terminal 112 shown. The first network device can be a network device in the aforementioned communication system 11. For example, the first network device can be... Figure 1C The network device 111 shown.

[0134] As an example, the first network device is a first satellite. Optionally, the first satellite or the first network device can be used to forward or transparently transmit information between the first access network device and the terminal, or the first satellite or the first network device can have some of the functions of the access network device (such as the functions of the DU node of the access network device, or the functions of the DU node in the IAB function). The first access network device can be the access network device in the aforementioned communication system 11. For example, the first access network device is... Figure 1C The access network device 113 shown is a first access network device that can function as a CU node.

[0135] Understandably, for method 2, if the first satellite or the first network device is used to forward or transparently transmit information between the first access network device and the terminal, then the downlink synchronization signal of the first cell transmitted by the first network device (or the first satellite) is generated and sent to the first network device (or the first satellite) by the first access network device. After receiving the downlink synchronization signal, the first network device (or the first satellite) transmits the downlink synchronization signal to the terminal. If the first satellite or the first network device has some of the functions of the access network device, then the downlink synchronization signal of the first cell transmitted by the first network device (or the first satellite) is generated and sent to the terminal by the first network device.

[0136] Understandably, for method 2, the terminal connects to the first cell through the first network device. This can be understood as the first access network device providing the terminal with the service of connecting to the first cell through the first network device. In other words, the first access network device provides services to the terminal before downlink synchronization of the downlink synchronization signal of the second cell sent by the second network device.

[0137] In this configuration, when the first network device is used to forward or transparently transmit information between the first access network device and the terminal (i.e., the first network device implements transparent payload transmission), the first cell is managed by the first access network device. When the first network device possesses some of the functions of an access network device, the first cell can be managed by either the first access network device or the first network device itself. The first cell is the cell that the terminal connects to through the first network device. Correspondingly, the first access network device connects to the terminal through the first cell. It is understandable that in method 2, information sent by the terminal can be sent to the first access network device via the first network device, and similarly, information sent by the first access network device can be sent to the terminal via the first network device. It is also understandable that when the first network device possesses some of the functions of an access network device, the first network device can also directly send some information to the terminal.

[0138] Optionally, for methods 1 and 2 above, the terminal is in a connected state, such as a radio resource control connected (RRC-connected) state.

[0139] S302: The terminal performs downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device.

[0140] For method 1: The second network device can be a network device in the aforementioned communication system 10. For example, the second network device is... Figure 1A The network device 103 is shown. The second network device is used to provide services to 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 has the same cell identifier as the first cell.

[0141] As an example, the second network device is a second satellite. The second satellite differs from the first satellite. Optionally, the second satellite possesses the functions of a second access network device; that is, the second satellite can be considered a second access network device, or in other words, the second satellite can function as a second access network device, or the second satellite can be replaced by a second access network device. Here, the second access network device differs from the first access network device. A description of the second access network device can be found above. Figure 1A Description of access network equipment.

[0142] One possible implementation is that the downlink synchronization signal of the second cell sent by the second network device is generated and sent by the second network device.

[0143] Optionally, prior to S302, the first network device sends configuration information to the terminal. Correspondingly, the terminal receives the configuration information from the first network device. This configuration information can be used to indicate the configuration of the downlink synchronization signal of the second cell. Thus, the terminal can determine the time-domain location of the measurement window for the downlink synchronization signal of the second cell. The measurement window is a duration used to detect the downlink synchronization signal.

[0144] As an example, the configuration information may include at least one of the following: the length of the measurement window for the downlink synchronization signal of the second cell, the period information of the measurement window for the downlink synchronization signal of the second cell, or a first offset. The period information of the measurement window can be used to indicate the period of the measurement window. At least one of the period information of the measurement window or the first offset can be used to determine the time-domain start position of the measurement window. Thus, the time-domain position of the measurement window can be determined based on the time-domain start position and the length of the measurement window.

[0145] For example, the terminal monitors the downlink synchronization signal of the second cell as follows: The terminal monitors the downlink synchronization signal of the second cell in system frames and subframes that meet the following conditions. The system frame number in which the measurement window is located satisfies the formula: .

[0146] Where SFN is the system frame number of the measurement window, mod is the modulo operator, FLOOR is the floor function, and Offset is the first offset. T satisfies the formula: CEIL is the floor function, and Periodicity is the period of the measurement window. If the period of the measurement window is greater than 5 subframes, then the subframe number of the measurement window satisfies the formula: If the period of the measurement window is less than or equal to 5 subframes, then the subframe number of the measurement window satisfies the formula: or .

[0147] For method 2: The second network device can be a network device in the aforementioned communication system 11. For example, the second network device is... Figure 1C The network device 114 shown.

[0148] As 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 can be used to forward or transparently transmit information between the second access network device and the terminal, or the second satellite or the second network device can have some of the functions of the second access network device (such as having the function of the DU node of the access network device, or the function of the DU node in the IAB function).

[0149] The second access network device can be the access network device in the communication system 11 described above. For example, the second access network device is... Figure 1C The access network device 113 or access network device 115 is shown. When the second network device is used to forward or transparently transmit information between the second access network device and the terminal (i.e., the second network device implements transparent transmission of the payload), the second cell is managed by the second access network device. When the second network device has some of the functions of the access network device, the second cell can be managed by the second access network device or by the second network device itself. The second cell is the cell that the terminal connects to through the second network device. The second cell has the same cell identifier as the first cell.

[0150] One possible implementation, for method 2, is that the second access network device and the first access network device may be the same or different. If the second access network device is the same as the first access network device, it means that before the terminal performs downlink synchronization (i.e., before S302), the terminal can communicate with the first access network device through the first network device; after the terminal performs downlink synchronization (i.e., after S302), the terminal can communicate with the first access network device through the second network device. In this case, the first cell and the second cell are the same, and both are managed by the first access network device; alternatively, the first cell and the second cell may be different, with the first cell managed by the first network device and the second cell managed by the second network device. If the second access network device is different from the first access network device, it means that before the terminal performs downlink synchronization (i.e., before S302), the terminal can communicate with the first access network device through the first network device; after the terminal performs downlink synchronization (i.e., after S302), the terminal can communicate with the second access network device through the second network device. In this case, the first cell and the second cell may be the same or different; the first cell is managed by the first access network device, and the second cell is managed by the second access network device; or the first cell is managed by the first network device, and the second cell is managed by the second network device.

[0151] In one possible implementation, for method 2, if the second network device (e.g., the second satellite) is used to forward or transmit information between the second access network device and the terminal, then the downlink synchronization signal of the second cell sent by the second network device is generated and sent to the second network device by the second access 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 of the functions of the second access network device, then the downlink synchronization signal of the second cell sent by the second network device is generated and sent to the terminal by the second network device.

[0152] Optionally, for 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 configuration information to the first network device, and after receiving the configuration information, the first network device sends configuration information to the terminal. The description of this configuration information can be found in the description of method 1 above. In this way, the terminal can determine the time-domain location of the measurement window for the downlink synchronization signal of the second cell.

[0153] For methods 1 and 2 above, the first cell and the second cell may be the same or different.

[0154] In this embodiment, "two cells being the same" can be understood as: the two cells have the same configuration, such as the same physical cell identifier and the same radio resource configuration for the terminal. The radio resource configuration may include at least one of the following: configurations related to the RRC layer, SDAP layer, PDCP layer, RLC layer, MAC layer, or PHY layer, etc. Therefore, "the first cell and the second cell being the same" can be understood as either the first cell and the second cell not being the same cell, but the configurations of the first cell and the second cell being the same, or the first cell and the second cell being the same cell.

[0155] The difference between the first cell and the second cell can be understood as the different configurations of the first cell and the second cell. For example, the radio resource configurations for the terminal in the first cell and the second cell are different, but the cell identifiers of the first cell and the second cell are the same. In this embodiment, the first cell can also be called the source serving cell or source cell, and the second cell can also be called the target serving cell or target cell.

[0156] Optionally, for methods 1 and 2 above, the following two possible implementations are used for downlink synchronization between the terminal and the downlink synchronization signal of the second cell sent by the second network device. In this embodiment, downlink synchronization can also be referred to as cell search.

[0157] In one possible implementation, the terminal searches for the downlink synchronization signal of the second cell and obtains the downlink timing based on the downlink synchronization signal. Understandably, since the terminal has switched connected network devices, and the downlink timing of the downlink synchronization signals of the two cells may differ, the terminal needs to search for the downlink synchronization signal of the second cell again.

[0158] As an example, the terminal determines the time domain position of the measurement window of the downlink synchronization signal of the second cell based on the above configuration information, searches for the downlink synchronization signal of the second cell at the time domain position, and obtains the downlink timing based on the downlink synchronization signal, including: obtaining the boundaries of the system frame, subframe, time slot and symbol corresponding to the second cell.

[0159] Understandably, for method 1, the boundaries of the system frame, subframe, time slot, and symbol corresponding to the second cell can be understood as the boundaries of the system frame, subframe, time slot, and symbol within the network provided by the second network device. Similarly, for method 2, the boundaries of the system frame, subframe, time slot, and symbol corresponding to the second cell can be understood as the boundaries of the system frame, subframe, time slot, and symbol within the network provided by the second network device and the second access network device.

[0160] Understandably, in this embodiment of the application, the terminal can calculate the maximum delay of the handover interruption by treating the second cell as an unknown cell.

[0161] The maximum handover interruption delay can be the maximum delay for a terminal to switch from one access network device to another, or the maximum delay for a terminal to switch from one network device to another. The maximum handover interruption delay includes the time required for the terminal to search for the target cell (i.e., the second cell). The target cell can be a known cell or an unknown cell, and the time required for the terminal to search for the target cell differs depending on whether the target cell is known or unknown. For example, when the target cell is a known cell, the time required for the terminal to search for the target cell is 0 ms. When the target cell is an unknown cell, the time required for the terminal to search for the target cell is related to the signal quality of the target cell and / or whether the target cell and the source cell (i.e., the first cell) are co-frequency or inter-frequency cells. In this embodiment, even if the cell identifiers of the source cell and the target cell are the same, the source cell and the target cell are not necessarily the same cell. Therefore, in this embodiment, the time required for the terminal to search for the target cell is not set to 0 ms. That is, the terminal does not calculate the maximum handover interruption delay based on the second cell being a known cell, but rather calculates the maximum handover interruption delay based on the second cell being an unknown cell. Whether the target cell is a known cell or an unknown cell can be determined based on some preset conditions. For example, for a source cell switching from frequency range 1 (FR1) to a target cell in frequency range 1 (FR1), and for a source cell switching from frequency range 2 (FR2) to a target cell in frequency range 1 (FR1), if the target cell meets the corresponding cell identification requirements within the first 5 seconds before the handover, the target cell is considered a known cell; otherwise, the target cell is considered an unknown cell.

[0162] In another possible implementation, where the first and second network devices in method 1 or method 2 have some of the functions of access network devices, the terminal obtains the time-domain location 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 terminal's location information. In this way, the terminal can obtain the downlink timing.

[0163] As an example, in mode 1 or mode 2, if the first network device and the second network device have some of the functions of the access network device, and the starting time of the terminal in the downlink subframe 0 of the first cell is t1, the distance between the terminal and the first network device is D1 (which can be obtained from 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 from the location information of the second network device and the location information of the terminal), then the starting time of the terminal in the downlink subframe 0 of the second cell is (t1-(D1-D2) / c1).

[0164] Where c1 is the speed of light, the start time of downlink subframe 0 of the second cell can be understood as the start time of the second network device sending the downlink synchronization signal of the second cell.

[0165] In another possible implementation, for other scenarios in Method 2 (such as the first network device being used to forward or transmit information between the first access network device and the terminal, and the second network device being used to forward or transmit information between the second access network device and the terminal), the terminal obtains the time-domain location of the downlink synchronization signal of the second cell based on the propagation delay between the terminal and the first access network device, and the delay difference between the propagation delay between the terminal and the second access network device. In this way, the terminal can obtain the downlink timing.

[0166] As an example, for other scenarios in Method 2, if the start time of downlink subframe 0 in the first cell 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), then the terminal calculates the distance D3 between itself and the first network device based on its location information and the location information of the first network device, and calculates the distance D4 between itself and the second network device based on its location information and the location information of the second network device. The start time of downlink subframe 0 in the second cell is (t1-(D3+t2*c1-D4-t3*c1) / c1). Here, the start time of downlink subframe 0 in the second cell can be understood as the start time when the second network device sends the downlink synchronization signal for the second cell.

[0167] As another example, for other scenarios in Method 2, if the start time of downlink subframe 0 in the first cell is t1, the terminal obtains the propagation delay t2 between itself and the first network device based on its location information and the location information of the first network device. Based on t2 and a delay value t3 broadcast by the first access network device (t3 may include the propagation delay between the first access network device and the first network device), the terminal obtains a delay value t4, for example, t4 = t2 + t3. Similarly, the terminal obtains the propagation delay t5 between itself and the second network device based on its location information and the location information of the second network device. Based on t5 and a delay value t6 broadcast by the second access network device (t6 may include the propagation delay between the second access network device and the second network device), the terminal obtains a delay value t7, for example, t7 = t5 + t6. Subsequently, the terminal can determine that the start time of downlink subframe 0 in the second cell is (t1 - (t4 - t7)). Here, the start time of downlink subframe 0 in the second cell can be understood as the start time when the second network device sends the downlink synchronization signal for the second cell.

[0168] Optionally, for methods 1 and 2 above, the following two possible implementation methods are used to trigger the terminal to perform downlink synchronization.

[0169] In one possible implementation, the terminal receives first indication information and, based on the first indication information, performs downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device. This process will be described below. Figure 4 The method shown will be introduced in the text.

[0170] In another possible implementation, the terminal determines that it will 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 will be described below. Figure 5 The method shown will be introduced in the text.

[0171] S303: The terminal connects to the second cell through the second network device.

[0172] Understandably, if the first cell and the second cell are the same cell, then after S302, the terminal can change the network device used to connect to the first cell from the first network device to the second network device.

[0173] As an example, with Figure 1CTaking the communication system 11 shown as an example, if 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 being access network device 113, and the second network device is network device 114, then terminal 112 first connects to the first cell of access network device 113 through network device 111, and after downlink synchronization with the downlink synchronization signal of the second cell sent by network device 114, it connects to the first cell of access network device 113 through network device 114.

[0174] Understandably, if the first cell and the second cell are not the same cell, but the configuration of the first cell and the configuration of the second cell are the same, or if the first cell and the second cell are different cells, then after S302, the terminal disconnects from the first cell and connects to the second cell through the second network device.

[0175] As an example, with Figure 1A Taking the communication system 10 shown 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, then terminal 102 first connects to the first cell of network device 101, and after performing downlink synchronization with the downlink synchronization signal of the second cell sent by network device 102, it connects to the second cell of network device 102. Here, the first cell and the second cell are different, or 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.

[0176] As another example, Figure 1C Taking the communication system 11 shown as an example, if 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 being access network device 113, and the second network device is network device 114, then terminal 112 first connects to the first cell of access network device 113 through network device 111. After performing downlink synchronization with the downlink synchronization signal of the second cell sent by network device 114, it connects to the second cell of access network device 113 through network device 114. The first cell and the second cell are not the same cell, but the configurations of the first cell and the second cell are the same.

[0177] As another example, Figure 1CTaking the communication system 11 shown as an example, if 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, then terminal 112 first connects to the first cell of access network device 113 through network device 111. After downlink synchronization with the downlink synchronization signal of the second cell sent by network device 114, it connects to the second cell of access network device 115 through network device 114. Here, the first cell and the second cell are different, or 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.

[0178] One possible implementation involves the terminal connecting to a second cell via a second network device, including: the terminal sending a random access signal to the second network device to perform a two-step random access procedure or a four-step random access procedure.

[0179] Understandably, in Mode 1 or Mode 2 where the second network device possesses some of the functions of an access network device, after receiving the random access signal, the second network device can perform subsequent procedures in either a two-step or four-step random access process. In Mode 2, where the second network device is used to forward or transparently transmit information between the second access network device and the terminal, after receiving the random access signal, the second network device sends a random access signal to the second access network device, which, upon receiving the random access signal, can then perform subsequent procedures in either a two-step or four-step random access process.

[0180] Optionally, if the first indication information is not included in the intra-cell handover command, and the terminal's uplink time adjustment timer expires, it indicates that the terminal has no uplink data to send, so the terminal may not send a random access signal to the second network device. Subsequently, if there are other requirements, such as uplink services, the terminal will then send a random access signal to the second network device.

[0181] Optionally, if the first indication information is not carried in the same-cell handover command and the terminal's uplink time adjustment timer has not timed out, it means that the terminal may have uplink data to send, so the terminal can send a random access signal to the second network device.

[0182] Understandably, during the process of a terminal initiating random access (i.e., after the terminal sends the random access signal and before the terminal accesses the second network device or the second access network device), if the terminal receives an uplink time adjustment command, the terminal can restart the uplink time adjustment timer.

[0183] based on Figure 3The method shown allows the terminal to perform downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device, even when the first network device switches to the second network device, but the cell identifier of the cell providing services to the terminal remains unchanged. This ensures that the terminal can still communicate normally after the network device switch. For example, in method 1 above, before S302, the first network device can provide services to the terminal, and the terminal can communicate with the first network device. After S302, the second network device can provide services to the terminal, and the terminal can communicate with the second network device. In method 2 above, before S302, the first access network device can provide services to the terminal, and the terminal can communicate with the first access network device through the first network device. After S302, the second access network device can provide services to the terminal, and the terminal can communicate with the second access network device through the second network device.

[0184] Optional, in Figure 3 In one possible implementation of the method shown, downlink synchronization can be triggered by the first indication information. Specifically, as... Figure 4 As shown, Figure 3 The method shown may also include S304.

[0185] S304: The terminal receives the first instruction information.

[0186] The first indication information can be used to instruct the terminal to perform downlink synchronization. For example, the first indication information can instruct the terminal to perform downlink synchronization. Alternatively, the first indication information can instruct the terminal to perform downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device. Or, the first indication information can be used to instruct the terminal to stop using the downlink timing of the first cell.

[0187] Understandably, in the case where the first network device in method 1 or method 2 has some of the functions of the access network device, the first network device sends a first instruction message to the terminal, and the terminal receives the first instruction message from the first network device.

[0188] In one possible implementation, if the absolute value of the difference between the first distance and the second distance is greater than or equal to a first threshold, the first network device sends a first indication message to the terminal.

[0189] The first distance is the distance between the terminal and the first network device, which can be obtained based on the location information of the first network device and the location information of the terminal. The second distance is the distance between the terminal and the second network device, which can be obtained based on the location information of the second network device and the location information of the terminal. The first threshold is a positive number.

[0190] In other words, when the first network device moves further away from the terminal and the second network device 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 greater than or equal to a first threshold, the first network device can instruct the terminal to perform downlink synchronization. It is understandable that when the distance between the terminal and the first network device is the same as or less than the difference between the distance between the terminal and the second network device, and the estimated arrival time of the downlink synchronization signal of the first cell sent by the first network device to the terminal differs from the estimated arrival time of the downlink synchronization signal of the second cell sent by the second network device to the terminal by the first network device by less than or equal to a first time difference, in order to avoid unnecessary downlink synchronization, the terminal can still use the downlink synchronization used for communication with the first network device as the downlink synchronization used for communication with the second network device.

[0191] In another possible implementation, if 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 a first indication message to the terminal.

[0192] Wherein, the first propagation delay is the propagation delay of information sent from the first network device to the terminal. The first propagation delay is equal to the ratio of the first distance to the speed of light. The second propagation delay is the propagation delay of information sent from the second network device to the terminal. The second propagation delay is equal to the ratio of the second distance to the speed of light. The second threshold is a positive number.

[0193] In other words, if the propagation delay of the information sent by the first network device to the terminal differs from the propagation delay of the information sent by the second network device to the terminal by a factor greater than or equal to a second threshold, the first network device can instruct the terminal to perform downlink synchronization. It is understandable that if the propagation delay of the information sent by the first network device to the terminal is the same as or differs from the propagation delay of the information sent by the second network device to the terminal by a factor less than or equal to the second threshold, and the estimated arrival time of the downlink synchronization signal of the first cell sent by the first network device to the terminal differs from the estimated arrival time of the downlink synchronization signal of the second cell sent by the second network device to the terminal by a factor less than or equal to a first time difference, then, in order to avoid unnecessary downlink synchronization, the terminal can still use the downlink synchronization used for communication with the first network device as the downlink synchronization used for communication with the second network device.

[0194] Understandably, in the case of the second network device being used to forward or transparently transmit information between the second access network device and the terminal in the above method 2, the first access network device sends a first instruction message to the terminal, and correspondingly, the terminal receives the first instruction message from the first access network device.

[0195] In one possible implementation, if the absolute value of the difference between the third distance and the fourth distance is greater than or equal to the third threshold, the first access network device sends a first indication message to the terminal.

[0196] 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, which can be obtained based on the location information of the first access network device, the first network device, and 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, which can also be obtained based on the location information of the second access network device, the second network device, and the terminal. The third threshold is a positive number. The third threshold can be the same as or different from the first threshold.

[0197] In other words, when the first network device is moving further away from the terminal, the second network device is moving closer to the terminal, and the difference between the third and fourth distances is greater than or equal to a third threshold, the first access network device can instruct the terminal to perform downlink synchronization. It is understandable that when the third and fourth distances are the same or differ less than the third threshold, the estimated arrival time of the downlink synchronization signal for the first cell sent by the first access network device to the terminal differs from the estimated arrival time of the downlink synchronization signal for the second cell sent by the second access network device to the terminal by less than or equal to a second time difference. Therefore, to minimize unnecessary downlink synchronization, the terminal can still use the downlink synchronization used for communication with the first network device as the downlink synchronization used for communication with the second network device.

[0198] In another possible implementation, if the absolute value of the difference between the third propagation delay and the fourth propagation delay is greater than or equal to the fourth threshold, the first access network device sends a first indication message to the terminal.

[0199] The third propagation delay is the propagation delay of information sent from the first access network device to the terminal via 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 from the second access network device to the terminal via 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.

[0200] In other words, if the propagation delay of information sent from the first access network device to the terminal via the first network device differs from the propagation delay of information sent from the second access network device to the terminal via the second network device by a difference greater than or equal to the fourth threshold, the first access network device can instruct the terminal to perform downlink synchronization. It is understandable that if the propagation delay of information sent from the first access network device to the terminal via the first network device is the same as or differs from the propagation delay of information sent from the second access network device to the terminal by the second network device by a difference less than the fourth threshold, and the estimated arrival time of the downlink synchronization signal of the first cell sent by the first access network device to the terminal differs from the estimated arrival time of the downlink synchronization signal of the second cell sent by the second access network device to the terminal by a difference less than or equal to the second time difference, then, in order to avoid unnecessary downlink synchronization, the terminal can still use the downlink synchronization used for communication with the first network device as the downlink synchronization used for communication with the second network device.

[0201] One possible implementation is that the first indication information is carried in a dedicated RRC message, a dedicated medium access control-control element (MAC-CE), or a dedicated physical channel; alternatively, the first indication information is carried in a public RRC message, a public MAC-CE, or a public physical channel. It is understood that the first indication information can also be carried in other messages, without limitation.

[0202] Optionally, the dedicated RRC message is a handover command within the same cell. This handover command is a time-based handover command. That is, the first indication information can be carried in the time-based handover command. The time-based handover command can also be called a time-triggered handover command.

[0203] In this context, a time-based intra-cell handover command can be understood as a command issued according to a pre-indicated time. For example, a first network device instructs a terminal to switch network devices at time T. Subsequently, at time T, the first network device sends an intra-cell handover command to the terminal; this intra-cell handover command can be called a time-based intra-cell handover command. In this embodiment, the intra-cell handover command can also be called an intra-cell handover command.

[0204] Understandably, in addition to instructing the terminal to perform downlink synchronization or to stop using the downlink timing of the first cell through the first instruction information, the first network device or the first access network device may also instruct the terminal to perform downlink synchronization or to stop using the downlink timing of the first cell through implicit instructions.

[0205] For example, a first network device or a first access network device sends a cell handover command to a terminal. This cell handover command is a time-based cell handover command and does not carry handover conditions based on location or signal quality. In this case, after receiving the cell handover command, the terminal can determine to perform downlink synchronization or determine to stop using the downlink timing of the first cell. Subsequently, the terminal can perform downlink synchronization.

[0206] Understandably, 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, the second indication information indicating that downlink synchronization is not required, or the second indication information indicating that the downlink timing of the first cell can continue to be used, then the terminal does not need to perform downlink synchronization.

[0207] For example, if 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.

[0208] Optional, in Figure 3 In one possible implementation of the method shown, the terminal performs downlink synchronization when it determines that it will switch the connected network device. Specifically, as... Figure 5 As shown, Figure 3 The method shown may also include S305.

[0209] S305: The terminal has determined that it will switch the connected network device.

[0210] One possible implementation is that the terminal determines to switch the connected network device if it determines that the remaining service time of the first network device is less than or equal to a fifth threshold. For example, the terminal determines to switch the connected network device if it determines that the remaining service time of the first network device is 0.

[0211] The remaining service time refers to the remaining time that the first network device can connect to the terminal. For example, in Mode 1 or Mode 2, if the first network device has some of the functions of an access network device, the remaining service time is the remaining time that the first network device can provide services to the terminal. In Mode 2, if the second network device is used to forward or transparently transmit information between the second access network device and the terminal, the remaining service time is the remaining time that the first network device can forward or transparently transmit information between the terminal and the first access network device.

[0212] One possible implementation, prior to S305, is that the terminal can receive an indication of the remaining service time, set a timer based on the remaining service time indicated by the indication, and determine to switch the connected network device when the timer expires.

[0213] As an example, in mode 1 or mode 2 where the first network device possesses some of the functions of an access network device, prior to S305, the first network device sends an indication of the remaining service time to the terminal via a dedicated RRC message or a broadcast message. Upon receiving the indication of the remaining service time, the terminal starts a first timer, the initial time of which is the time indicated by the indication message. Subsequently, when the first timer expires, the terminal determines that it will switch the connected network device.

[0214] As another example, in Method 2, where the second network device is used to forward or transparently transmit information between the second access network device and the terminal, before S305, the first access network device sends a dedicated RRC message or broadcast message to the terminal through the first network device. This dedicated RRC message or broadcast message carries an indication of the remaining service time. After receiving the dedicated RRC message or broadcast message, the terminal starts a second timer, the initial time of which is the time indicated by the indication message. Subsequently, when the second timer expires, the terminal determines that it will switch the connected network device.

[0215] One possible implementation is that, prior to S305, the terminal can receive an indication of the time when the first cell stops serving the terminal (e.g., indicating an absolute time). Based on this indication, when the time is reached, it is determined that the connected network device will be switched.

[0216] One possible implementation is that after the terminal determines that it will switch the connected network device, the terminal can also 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 terminal's location information. Alternatively, the terminal can also 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.

[0217] For example, in mode 1 or mode 2 where the first network device has some of the functions of an access network device, the terminal performs downlink synchronization when the absolute value of the difference between the first distance and the second distance is greater than or equal to a first threshold. The descriptions of the first distance, the second distance, and the first threshold can be found in the corresponding description in S304 above, and will not be repeated here. That is, the terminal performs downlink synchronization when the first network device is getting farther away from the terminal, the second network device is getting 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 greater than or equal to the first threshold. It can be understood that when the distance between the terminal and the first network device is the same as or less than the difference between the distance between the terminal and the second network device, the estimated arrival time of the downlink synchronization signal of the first cell sent by the first network device is less than or equal to the estimated arrival time of the downlink synchronization signal of the second cell sent by the second network device. Therefore, to minimize unnecessary downlink synchronization, the terminal can still use the downlink synchronization used for communication with the first network device as the downlink synchronization used for communication with the second network device.

[0218] For example, in mode 1 or mode 2 where the first network device has some of the functions of an access network device, the terminal performs downlink synchronization 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 descriptions of the first propagation delay, the second propagation delay, and the second threshold can be found in the corresponding description in S304 above, and will not be repeated here. That is, 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 greater than or equal to the second threshold. It can be understood that when the propagation delay of the information sent by the first network device to the terminal is the same as or differs from the propagation delay of the information sent by the second network device to the terminal by less than or equal to the second threshold, the estimated arrival time of the downlink synchronization signal of the first cell sent by the first network device to the terminal differs from the estimated arrival time of the downlink synchronization signal of the second cell sent by the second network device to the terminal by less than or equal to a first time difference. Therefore, to avoid unnecessary downlink synchronization, the terminal can still use the downlink synchronization used for communication with the first network device as the downlink synchronization used for communication with the second network device.

[0219] For example, in Method 2, where the second network device is used to forward or transparently transmit information between the second access network device and the terminal, the terminal performs downlink synchronization if the absolute value of the difference between the third and fourth propagation delays is greater than or equal to the 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; that is, the propagation delay of the information sent by the first access network device to the terminal through 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; that is, the propagation delay of the information sent by the second access network device to the terminal through the second network device. In other words, the terminal can determine the propagation delay between the first network device and the terminal based on the location information of the first network device and the terminal, and add the propagation delay between the first network device and the terminal to the propagation delay between the first network device and the first access network device (which may be notified to the terminal by the first access network device) to obtain the third propagation delay. Similarly, the terminal can determine the propagation delay between the second network device and the terminal based on the location information of the second network device and the terminal itself. The fourth propagation delay is obtained 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 (which may be notified to the terminal by the second access network device). In other words, the terminal performs downlink synchronization if the difference between the propagation delay of the information sent from the first access network device to the terminal through the first network device and the propagation delay of the information sent from the second access network device to the terminal through the second network device is greater than or equal to the fourth threshold.

[0220] Understandably, if the propagation delay of the information sent by the first access network device to the terminal through the first network device is the same as or differs from the propagation delay of the information sent by the second access network device to the terminal through the second network device by the same ...

[0221] For example, in the case where the second network device in method 2 is used to forward or transparently transmit information between the second access network device and the terminal, the terminal performs downlink synchronization when the absolute value of the difference between the third distance and the fourth distance is greater than or equal to the third threshold. The third distance can be equal to the product of the third propagation delay and the speed of light, and the fourth distance can be equal to the product of the fourth propagation delay and the speed of light. That is, the terminal performs downlink synchronization when the first network device is moving further away from the terminal, the second network device is moving closer to the terminal, and the difference between the third distance and the fourth distance is greater than or equal to the third threshold. It is understandable that when the third distance and the fourth distance are the same or differ less than the third threshold, the estimated arrival time of the downlink synchronization signal from the first cell sent by the first access network device is less than or equal to the second time difference compared to the estimated arrival time of the downlink synchronization signal from the second cell sent by the second access network device. Therefore, to minimize unnecessary downlink synchronization, the terminal can still use the downlink synchronization used for communication with the first network device as the downlink synchronization used for communication with the second network device.

[0222] It is understandable that the actions of the terminal, the first network device, the second network device, the first access network device, or the second access network device in S301-S305 above can be performed by... Figure 2 The processor 201 in the communication device 20 shown calls the application code stored in the memory 203 to execute it, and this application embodiment does not impose any limitations on this.

[0223] In the above Figures 3-5 In the method shown, the terminal is in a connected state. In specific applications, the terminal can also be in a radio resource control idle (RRC-idle) state or a radio resource control inactive (RRC-inactive) state. The following describes the switching method when the terminal is in an RRC-idle or RRC-inactive state.

[0224] like Figure 6 As shown, this is another switching method provided in the embodiment of this application, which includes S601-S603.

[0225] S601: The terminal camps on the first cell through the first network device.

[0226] Understandable. Figure 6 The switching method shown is the same as Figure 3 The switching method shown is similar and can be applied to... Figure 1A The communication system 10 shown, or applied to Figure 1CThe communication system 11 shown. For the communication system 11 shown. Figure 6 The method shown is applied to Figure 1A The situation regarding the communication system 10 shown can be referred to the following description of mode 3. For the case of... Figure 6 The method shown is applied to Figure 1C The situation of the communication system 11 shown can be referred to the following description of mode 4. A detailed explanation follows.

[0227] Method 3: In method 3, the terminal can be the terminal in the aforementioned communication system 10. For example, the terminal is... Figure 1A The terminal 102 shown. The first network device can be a network device in the communication system 10 described above. For example, the first network device can be... Figure 1A The network device 101 shown.

[0228] As an example, the first network device is a first satellite. Optionally, the first satellite has the functions of a first access network device, that is, the first satellite can be regarded as a first access network device, or in other words, the first satellite can serve as a first access network device, or the first satellite can be replaced by a first access network device. In this case, the downlink synchronization signal of the first cell transmitted by the first network device is generated and transmitted by the first network device. A description of the first access network device can be found above. Figure 1A Description of access network equipment.

[0229] It is understandable that the terminal camps on the first cell through the first network device, which can be understood as the terminal camping on the first cell of the first network device. The first cell is managed by the first network device.

[0230] Method 4: In method 4, the terminal can be the terminal in the communication system 11 described above. For example, the terminal is... Figure 1C The terminal 112 shown. The first network device can be a network device in the aforementioned communication system 11. For example, the first network device can be... Figure 1C The network device 111 shown.

[0231] As an example, the first network device is a first satellite. Optionally, the first satellite or the first network device can be used to forward or transparently transmit information between the first access network device and the terminal, or the first satellite or the first network device can have some of the functions of the access network device (such as the functions of the DU node of the access network device, or the functions of the DU node in the IAB function). The first access network device can be the access network device in the aforementioned communication system 11. For example, the first access network device is... Figure 1C The access network device 113 shown is a first access network device that can function as a CU node.

[0232] Understandably, for method 4, if the first satellite or the first network device is used to forward or transparently transmit information between the first access network device and the terminal, then the downlink synchronization signal of the first cell transmitted by the first network device (or the first satellite) is generated and sent to the first network device (or the first satellite) by the first access network device. After receiving the downlink synchronization signal, the first network device (or the first satellite) transmits the downlink synchronization signal to the terminal. If the first satellite or the first network device has some of the functions of the access network device, then the downlink synchronization signal of the first cell transmitted by the first network device (or the first satellite) is generated and sent to the terminal by the first network device.

[0233] Understandably, in method 4, the terminal camps on the first cell via the first network device, which can be understood as the terminal camping on the first cell of the first access network device via the first network device. Specifically, when the first network device is used to forward or transparently transmit information between the first access network device and the terminal (i.e., the first network device implements transparent payload transmission), the first cell is managed by the first access network device. When the first network device possesses some of the functions of an access network device, the first cell can be managed by the first access network device or by the first network device itself. Understandably, in method 2, information sent by the terminal can be sent to the first access network device via the first network device; similarly, information sent by the first access network device can be sent to the terminal via the first network device. Understandably, when the first network device possesses some of the functions of an access network device, the first network device can also directly send some information to the terminal.

[0234] Optionally, for methods 3 and 4 above, the terminal is in RRC-idle or RRC-inactive state.

[0235] S602: The terminal performs downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device.

[0236] The specific process of S602 is similar to that of S302 above, so you can refer to the description in S302 above, and will not repeat it here.

[0237] S603: The terminal camps in the second cell via the second network device.

[0238] Understandably, if the first cell and the second cell are the same cell, then after S602, the terminal can change the network device used in the first cell from the first network device to the second network device.

[0239] As an example, with Figure 1CTaking the communication system 11 shown as an example, if 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 being access network device 113, and the second network device is network device 114, then terminal 112 first camps in the first cell of access network device 113 through network device 111, and after performing downlink synchronization with the downlink synchronization signal of the second cell sent by network device 114, it camps in the first cell of access network device 113 through network device 114.

[0240] Understandably, if the first cell and the second cell are not the same cell, but the configuration of the first cell and the configuration of the second cell are the same, or if the first cell and the second cell are different cells, then after S602, the terminal will not camp on the first cell, but will camp on the second cell through the second network device.

[0241] As an example, with Figure 1A Taking the communication system 10 shown 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, then terminal 102 first camps in the first cell of network device 101. After performing downlink synchronization with the downlink synchronization signal of the second cell sent by network device 102, it camps in the second cell of network device 102. The first cell and the second cell may be different, or they may not be the same cell, but the configuration of the first cell and the configuration of the second cell may be the same.

[0242] As another example, Figure 1C Taking the communication system 11 shown as an example, if 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 being access network device 113, and the second network device is network device 114, then terminal 112 first camps on the first cell of access network device 113 through network device 111. After performing downlink synchronization with the downlink synchronization signal of the second cell sent by network device 114, terminal 112 camps on the second cell of access network device 113 through network device 114. The first cell and the second cell are not the same cell, but the configurations of the first cell and the second cell are the same.

[0243] As another example, Figure 1CTaking the communication system 11 shown as an example, if 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, then terminal 112 first camps on the first cell of access network device 113 through network device 111. After downlink synchronization with the downlink synchronization signal of the second cell sent by network device 114, terminal 112 camps on the second cell of access network device 115 through network device 114. The first cell and the second cell are different, or 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.

[0244] based on Figure 6 The method shown allows a terminal to camp on a first cell via a first network device. After downlink synchronization with a second cell's downlink synchronization signal sent by a second network device, the terminal can then camp on a second cell via the second network device. The second cell shares the same cell identifier as the first cell. This allows the terminal to perform downlink synchronization with the second cell's downlink synchronization signal sent by the second network device, even when switching from the first network device to the second network device, provided the cell identifier of the cell the terminal is camped on remains unchanged. This ensures normal subsequent communication. For example, in method 3 above, after S602, the terminal can communicate with the second network device; in method 4 above, after S602, the terminal can communicate with the second access network device via the second network device.

[0245] Optional, in Figure 6 In one possible implementation of the method shown, downlink synchronization can be triggered by the first indication information. Specifically, as... Figure 7 As shown, Figure 6 The method shown may also include S604.

[0246] S604: The terminal receives the first instruction information.

[0247] The specific process of S604 is similar to that of S304 described above, so the corresponding description in S304 can be referred to. The difference is that in S604, the first indication information cannot be carried in a dedicated RRC message, dedicated MAC-CE, or dedicated physical channel. In S604, the first indication information can be carried in a public RRC message, public MAC-CE, or public physical channel.

[0248] Optional, in Figure 6 In one possible implementation of the method shown, the terminal performs downlink synchronization when it determines that it will switch the connected network device. Specifically, as... Figure 8 As shown, Figure 6 The method shown may also include S605.

[0249] S605: The terminal determines that it will switch the connected network device.

[0250] The specific process of S605 is similar to that of S305 above, so the corresponding description in S305 can be referred to. The difference is that the remaining service time indication information cannot be carried in a dedicated RRC message, but is carried in a broadcast message.

[0251] It is understandable that the actions of the terminal, the first network device, the second network device, the first access network device, or the second access network device in S601-S605 above can be performed by... Figure 2 The processor 201 in the communication device 20 shown calls the application code stored in the memory 203 to execute it, and this application embodiment does not impose any limitations on this.

[0252] It is understood that in the above embodiments, the methods and / or steps implemented by the terminal can also be implemented by components (e.g., chips or circuits) that can be used in the terminal; the methods and / or steps implemented by the first access network device can also be implemented by components (e.g., chips or circuits) that can be used in the first access network device, without limitation.

[0253] The above mainly describes the solution provided by the embodiments of this application from the perspective of interaction between various network elements. Correspondingly, the embodiments of this application also provide a communication device, which can be the terminal in the above method embodiments, or a device including the terminal, or a component usable in the terminal; or, the communication device can be the first access network device in the above method embodiments, or a device including the first access network device, or a component usable in the first access network device. It is understood that the terminal or first access network device, etc., includes hardware structures and / or software modules corresponding to the execution of each function in order to achieve the above functions. Those skilled in the art should readily recognize that, in conjunction with the unit and algorithm operations of the various examples described in the embodiments disclosed herein, this application can be implemented in hardware or a combination of hardware and computer software. Whether a function is executed by hardware or by computer software driving hardware depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0254] This application embodiment can divide the terminal or first access network device into functional modules according to the above method example. For example, each function can be divided into a separate functional module, or two or more functions can be integrated into one processing module. The integrated module can be implemented in hardware or as a software functional module. It should be noted that the module division in this application embodiment is illustrative and only represents one logical functional division. In actual implementation, there may be other division methods.

[0255] For example, when dividing the functional modules using an integrated approach. Figure 9 A schematic diagram of a communication device 90 is shown. The communication device 90 includes a communication module 901 and a processing module 902. The communication module 901, also known as a transceiver unit or transceiver module, is used to implement transceiver functions, and can be, for example, a transceiver circuit, transceiver, transceiver device, or communication interface.

[0256] For example, the communication device 90 is used to implement the functions of a terminal. The communication device 90 is, for example, a... Figure 3 The embodiment shown, Figure 4 The illustrated embodiments Figure 5 The illustrated embodiments Figure 6 The illustrated embodiments Figure 7 The illustrated embodiments or Figure 8 The terminal described in the illustrated embodiment.

[0257] The communication module 901 is used to connect to the first cell via the first network device.

[0258] The processing module 902 is used to perform downlink synchronization with the downlink synchronization signal of the second cell sent by the second network device.

[0259] The communication module 901 is also used to connect to the second cell via a second network device. The first cell and the second cell have the same cell identifier.

[0260] In one possible implementation, the communication module 901 is also used to receive the first instruction information.

[0261] The first indication information is used to instruct the communication device 90 to perform downlink synchronization, or the first indication information is used to instruct the communication device 90 to stop using the downlink timing of the first cell.

[0262] In one possible implementation, the first indication information is carried in a time-based intra-cell handover command.

[0263] In one possible implementation, the communication module 901 is also used to receive configuration information.

[0264] The configuration information is used to indicate the configuration of the downlink synchronization signal.

[0265] In one possible implementation, the configuration information includes at least one of the following: the length of the measurement window of the downlink synchronization signal, the period information of the measurement window of the downlink synchronization signal, or a first offset, wherein at least one of the period information or the first offset is used to determine the starting position of the measurement window.

[0266] In one possible implementation, the processing module 902 is further configured to determine that the connected network device will be switched; specifically, the processing module 902 is 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.

[0267] Wherein, the first distance is the distance between the communication device 90 and the first network device, and the second distance is the distance between the communication device 90 and the second network device.

[0268] In one possible implementation, the processing module 902 is specifically configured to determine, when it is determined that the remaining service time of the first network device is 0, to switch the connected network device.

[0269] In one possible implementation, the processing module 902 is specifically used to search for the downlink synchronization signal; the processing module 902 is also specifically used to obtain the downlink timing based on the downlink synchronization signal.

[0270] In one possible implementation, the processing module 902 is specifically used to obtain the time domain location 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.

[0271] In one possible implementation, the first network device is the first satellite.

[0272] In one possible implementation, the first satellite functions as a first access network device; or, the first satellite functions as a distribution unit of the first access network device.

[0273] The first access network device is used to provide services to the communication device 90 before the communication device 90 performs downlink synchronization.

[0274] In one possible implementation, the second network device is a second satellite.

[0275] In one possible implementation, the second satellite functions as a second access network device; or, the second satellite functions as a distribution unit of the second access network device.

[0276] The second access network device is used to provide services to the communication device 90 after the communication device 90 performs downlink synchronization.

[0277] When used to implement the functions of a terminal, other functions that the communication device 90 can perform can be found in [reference needed]. Figure 3 The embodiment shown, Figure 4 The illustrated embodiments Figure 5 The illustrated embodiments Figure 6 The illustrated embodiments Figure 7 The illustrated embodiments or Figure 8 The relevant descriptions of the embodiments shown will not be elaborated upon further.

[0278] In a simplified embodiment, those skilled in the art will recognize that the communication device 90 can employ... Figure 2 The form shown. For example, Figure 2 The processor 201 can call computer execution instructions stored in the memory 203 to cause the communication device 90 to execute the method described in the above method embodiment.

[0279] For example, Figure 9 The functions / implementation process of the communication module 901 and the processing module 902 can be obtained through Figure 2 The processor 201 in the memory calls computer execution instructions stored in the memory 203 to implement the function. Alternatively, Figure 9 The function / implementation process of the processing module 902 can be achieved through... Figure 2 The processor 201 in the memory calls computer execution instructions stored in the memory 203 to implement this. Figure 9 The function / implementation process of the communication module 901 can be obtained through Figure 2 It is implemented using the communication interface 204.

[0280] For example, when dividing the functional modules using an integrated approach. Figure 10 A schematic diagram of a communication device 100 is shown. The communication device 100 includes a communication module 1001. The communication module 1001, also known as a transceiver unit or transceiver module, can be used to implement transceiver functions, and can be, for example, a transceiver circuit, a transceiver, a transceiver device, or a communication interface.

[0281] For example, the communication device 100 is used to implement the functions of the first access network device. The communication device 100 is, for example, a... Figure 3 The embodiment shown, Figure 4 The illustrated embodiments Figure 5 The illustrated embodiments Figure 6 The embodiment shown, Figure 7 The illustrated embodiments or Figure 8 The first access network device described in the illustrated embodiment.

[0282] The communication module 1001 is used to connect to the terminal via a first cell. The first cell is the cell that the terminal connects to via a first network device.

[0283] The communication module 1001 is also used to send first indication information to the terminal. The first indication information is used to instruct the terminal to perform downlink synchronization, or to instruct the terminal to stop using the downlink timing of the first cell.

[0284] The communication module 1001 is also used to connect to the terminal via a second cell. The second cell has the same cell identifier as the first cell, and the second cell is the cell that the terminal connects to via a second network device. The first cell and the second cell are managed by the communication device 100.

[0285] In one possible implementation, the first indication information is carried in a time-based intra-cell handover command.

[0286] In one possible implementation, the communication module 1001 is specifically used 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.

[0287] Wherein, 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.

[0288] In one possible implementation, the communication module 1001 is also used to send configuration information to the terminal, the configuration information being used to indicate the configuration of the downlink synchronization signal of the second cell.

[0289] In one possible implementation, the configuration information includes at least one of the following: the length of the measurement window of the downlink synchronization signal, the period information of the measurement window of the downlink synchronization signal, or a first offset, wherein at least one of the period information or the first offset is used to determine the starting position of the measurement window.

[0290] In one possible implementation, the first network device is the first satellite.

[0291] In one possible implementation, the first satellite functions as a communication device 100; or, the first satellite functions as a distribution unit of the communication device 100.

[0292] The communication device 100 is used to provide services to the terminal.

[0293] In one possible implementation, the second network device is a second satellite.

[0294] In one possible implementation, the second satellite functions as the communication device 100; or, the second satellite functions as a distribution unit of the communication device 100.

[0295] When used to implement the functions of the first access network device, other functions that the communication device 100 can perform can be referred to. Figure 3 The embodiment shown, Figure 4 The illustrated embodiments Figure 5 The illustrated embodiments Figure 6 The embodiment shown, Figure 7 The illustrated embodiments or Figure 8 The relevant descriptions of the embodiments shown will not be elaborated upon further.

[0296] In a simplified embodiment, those skilled in the art will recognize that the communication device 100 can employ... Figure 2 The form shown. For example, Figure 2 The processor 201 can call computer execution instructions stored in the memory 203 to cause the communication device 100 to execute the method described in the above method embodiment.

[0297] For example, Figure 10 The function / implementation process of the communication module 1001 can be obtained through Figure 2 The processor 201 in the memory calls computer execution instructions stored in the memory 203 to implement the function. Alternatively, Figure 10 The function / implementation process of the communication module 1001 can be obtained through Figure 2 It is implemented using the communication interface 204.

[0298] It should be noted that one or more of the above modules or units can be implemented by software, hardware, or a combination of both. When any of the above modules or units are implemented by software, the software exists as computer program instructions and is stored in memory. The processor can be used to execute the program instructions and implement the above method flow. The processor can be built into a SoC (System-on-a-Chip) or ASIC, or it can be a separate semiconductor chip. In addition to the core that executes the software instructions for computation or processing, the processor may further include necessary hardware accelerators, such as field-programmable gate arrays (FPGAs), PLDs (Programmable Logic Devices), or logic circuits that implement dedicated logic operations.

[0299] When the above modules or units are implemented in hardware, the hardware can 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, application-specific digital circuit, hardware accelerator, or non-integrated discrete device, which can run the necessary software or perform the above method flow independently of software.

[0300] Optionally, embodiments of this application also provide 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 in any of the above method embodiments is executed. In one possible implementation, the chip system further includes a memory. Optionally, the chip system may be composed of chips, or may include chips and other discrete devices; embodiments of this application do not specifically limit this.

[0301] Optionally, embodiments of this application also provide a computer-readable storage medium. All or part of the processes in the above method embodiments can be implemented by a computer program instructing related hardware. This program can be stored in the aforementioned computer-readable storage medium. When executed, the program can include the processes of the above method embodiments. The computer-readable storage medium can be an internal storage unit of the communication device in any of the foregoing embodiments, such as the hard disk or memory of the communication device. The aforementioned computer-readable storage medium can also be an external storage device of the communication device, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc., equipped on the communication device. Further, the aforementioned computer-readable storage medium can include both internal storage units and external storage devices of the communication device. The aforementioned computer-readable storage medium is used to store the aforementioned computer program and other programs and data required by the aforementioned communication device. The aforementioned computer-readable storage medium can also be used to temporarily store data that has been output or will be output.

[0302] Optionally, this application also provides a computer program product. All or part of the processes in the above method embodiments can be executed by a computer program instructing related hardware. This program can be stored in the computer program product, and when executed, it can include the processes described in the above method embodiments.

[0303] Optionally, embodiments of this application also provide computer instructions. All or part of the processes in the above method embodiments can be executed by computer instructions instructing related hardware (such as a computer, processor, access network equipment, mobility management network element, or session management network element). This program can be stored in the aforementioned computer-readable storage medium or the aforementioned computer program product.

[0304] Through the above description of the embodiments, those skilled in the art can clearly understand that, for the sake of convenience and brevity, only the division of the above functional modules is used as an example. In actual applications, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the device can be divided into different functional modules to complete all or part of the functions described above.

[0305] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another device, or some features may be ignored or not executed. Furthermore, the mutual coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0306] The units described as separate components may or may not be physically separate. A component shown as a unit can be one or more physical units; that is, it can be located in one place or distributed in multiple different locations. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0307] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

Claims

1. A handover method applied to a terminal, characterized in that, The method includes: Connect to the first cell via the first network device; Receive indication information from the first network device, the indication information indicating the time when the first cell stops providing service to the terminal; When the specified time is reached, it is determined to switch the first network device; When determining to switch the first network device, downlink synchronization is performed based on the downlink synchronization signal of the second cell sent by the second network device; The first network device connects to the second cell, and the first cell and the second cell have the same cell identifier, which corresponds to a geographical location. The first network device is a first satellite, and the second network device is a second satellite.

2. The method according to claim 1, characterized in that, The connection to the second cell via the second network device includes: Send a random access signal to the second network device.

3. The method according to claim 1, characterized in that, The method further includes: Receive configuration information, which is used to indicate the configuration of the downlink synchronization signal.

4. The method according to claim 3, characterized in that, The configuration information includes at least one of the following: the length of the measurement window of the downlink synchronization signal, the period information of the measurement window of the downlink synchronization signal, or a first offset, wherein at least one of the period information or the first offset is used to determine the starting position of the measurement window.

5. The method according to any one of claims 1-4, characterized in that, The downlink synchronization based on the downlink synchronization signal of the second cell sent by the second network device includes: The time domain location of the downlink synchronization signal is obtained 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.

6. A handover method applied to a first access network device, characterized in that, The method includes: The terminal is connected to a first cell, which is the cell that the terminal connects to through a first network device. Send indication information to the terminal, the indication information indicating the time when the first cell stops serving the terminal, wherein the indication information is used by the terminal to determine when the time arrives to switch the first network device and perform downlink synchronization based on the downlink synchronization signal of the second cell sent by the second network device; The terminal is connected to the second cell, which has the same cell identifier as the first cell. The cell identifier corresponds to a geographical location. The second cell is the cell that the terminal connects to through the second network device. The first cell and the second cell are managed by the first access network device, which is a first satellite and the second network device is a second satellite.

7. The method according to claim 6, characterized in that, The connection with the terminal via the second cell includes: Receive the random access signal sent by the terminal.

8. The method according to claim 6, characterized in that, The method further includes: Configuration information is sent to the terminal, the configuration information being used to indicate the configuration of the downlink synchronization signal of the second cell.

9. The method according to claim 8, characterized in that, The configuration information includes at least one of the following: the length of the measurement window of the downlink synchronization signal, the period information of the measurement window of the downlink synchronization signal, or a first offset, wherein at least one of the period information or the first offset is used to determine the starting position of the measurement window.

10. A communication device, characterized in that, Includes units or modules for performing the method as described in any one of claims 1-5.

11. A communication device, characterized in that, Includes units or modules for performing the method as described in any of claims 6-9.

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