Handover method and apparatus

Abstract

Provided in the embodiments of the present application are a handover method and apparatus. The method is executed by a terminal device or a chip applied to a terminal device. The method comprises: receiving CHO configuration information from a first network device, wherein the CHO configuration information is used for a terminal device to access a first target cell when a first condition is met; determining in a first time unit whether the first condition is met, wherein the first time unit is any time unit in a communication gap that exists during the handover of a network device to which a source cell belongs; and when the first condition is met, accessing the first target cell. In the embodiments of the present application, it is clarified that a terminal device can evaluate a first condition in a communication gap that exists during the handover of a network device to which a source cell belongs, and since the terminal device may need to access a first target cell after the network device to which the source cell belongs is switched, by means of pre-evaluating the first condition in the communication gap, the handover efficiency of the terminal device can be improved.

Description

Switching method and device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of the People's Republic of China on September 28, 2023, with application number 202311285124.4 and invention name "A Switching Method and Device", the entire contents of which are incorporated by reference into this application. Technical Field

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

[0004] Non-terrestrial network (NTN) communications refer to communications achieved with the help of non-terrestrial network equipment. NTN systems can include satellite systems, among others. Introducing NTN communications into mobile network communications, such as fifth-generation (5G) communications, can improve user experience. On the one hand, NTN can provide communication services to areas difficult to reach by terrestrial networks, such as oceans, forests, deserts, and remote areas. On the other hand, NTN can enhance the reliability of mobile communications, such as providing more stable communication services for users in high-speed mobile scenarios such as trains and airplanes. Furthermore, NTN can provide more data transmission resources and support the connection of a larger number of terminal devices.

[0005] In mobile communication networks, the movement of terminal devices can cause the signal quality of the current serving cell to deteriorate, necessitating a handoff to a neighboring cell with better signal quality. In NTN systems, however, the high-speed movement of non-terrestrial network equipment relative to terrestrial coverage shortens the duration of non-terrestrial network equipment's coverage in a given area, leading to frequent changes in serving cells. Therefore, in NTN systems, the mobility of non-terrestrial network equipment is the primary cause of cell handoffs for terminal devices.

[0006] Because NTN cells cover very large areas (ranging from tens to hundreds of kilometers in radius), and a single cell contains a large number of devices, the mobility of non-terrestrial network equipment can cause numerous devices to switch cells simultaneously or frequently. This cell switching process generates a significant amount of signaling interaction, so processing a large number of cell switching requests from devices in a short period of time can burden the network and even cause signaling congestion and increased signaling overhead.

[0007] Summary of the Invention

[0008] The embodiments of the present application provide a switching method and apparatus for improving the switching efficiency of terminal devices.

[0009] In a first aspect, an embodiment of the present application provides a handover method, which can be executed by a terminal device or by a chip system that can implement the functions of the terminal device. The method includes: receiving conditional handover (CHO) configuration information from a first network device, where the first network device is a network device to which a source cell of the terminal device belongs, and the CHO configuration information is used for the terminal device to access a first target cell if a first condition is met; determining whether the first condition is met in a first time unit, where the first time unit is any time unit in a communication gap that exists during the handover of the network device to which the source cell belongs; and accessing the first target cell if the first condition is met.

[0010] In an embodiment of the present application, it is clear that when there is a communication gap during the switching of the network equipment to which the source cell belongs, the terminal device can evaluate the CHO execution condition (i.e., the first condition) in the communication gap. For example, the satellite of the source cell is switched from the first satellite to the second satellite, and there is no overlap in service time when the first satellite and the second satellite provide services to the source cell. There will be a communication gap during the switching of the first satellite and the second satellite, and the terminal device can evaluate the CHO execution condition in the communication gap. Since the terminal device may move out of the coverage of the source cell or the coverage of the first satellite and the second satellite may be inconsistent after the switching of the first satellite and the second satellite, the terminal device needs to execute CHO (i.e., access the first target cell). By evaluating the CHO execution condition in advance in the communication gap, the switching efficiency of the terminal device can be improved.

[0011] In an optional embodiment, the first condition includes one or more of the following: a time-based execution condition; a distance-based execution condition; or a signal quality-based execution condition. In this embodiment, because the terminal device cannot obtain the signal quality of the source cell during the communication gap during the handover of the network device to which the source cell belongs, and thus cannot evaluate the signal quality-based execution condition, the CHO execution condition may only include execution conditions based on time and / or distance, thereby reducing the impact of the communication gap on the evaluation of the CHO execution condition, allowing the terminal device to evaluate the CHO execution condition during the communication gap.

[0012] In an optional embodiment, the time-based execution condition includes a time window. For example, the first network device sets a time window (T1, T2) for the terminal to configure CHO execution (i.e., access the first target cell), and the terminal device can perform CHO within the time window (T1, T2).

[0013] In an optional embodiment, the distance-based execution condition includes a distance threshold. For example, the first network device configures a distance threshold D1 and a distance threshold D2 for the terminal device to execute CHO (i.e., access the first target cell). If the distance between the terminal device and the first target cell is less than the distance threshold D1, and the distance between the terminal device and the source cell is greater than the distance threshold D2, the terminal device can execute CHO.

[0014] In an optional embodiment, the execution condition based on signal quality includes one or more of an A3 event, an A4 event, or an A5 event. In this embodiment, because the terminal device cannot obtain the signal quality of the source cell during the communication gap during the handover of the network device to which the source cell belongs, and thus cannot evaluate the A3 event or the A5 event, the execution condition based on signal quality may only include the A4 event, thereby reducing the impact of the communication gap on the evaluation of the execution condition based on signal quality, so that the terminal device can evaluate the execution condition based on signal quality during the communication gap.

[0015] In an optional embodiment, the method further includes: determining whether the A3 event or the A5 event is satisfied based on the first signal quality of the source cell, the first signal quality being the signal quality of the source cell before the time when the first network device stops covering the area where the terminal device is located, or when the first network device stops covering the area where the terminal device is located; or, determining whether the A3 event or the A5 event is satisfied based on the second signal quality of the source cell, the second signal quality being a default value. In this embodiment, the terminal device can evaluate the A3 event or the A5 event based on the signal quality or the default value of the source cell before or when the terminal device is disconnected from the source cell, thereby reducing the impact of the communication gap on the evaluation of the A3 event or the A5 event, so that the terminal device can evaluate the A3 event or the A5 event during the communication gap.

[0016] In an optional embodiment, the method further includes: if the first condition is not met, accessing a second target cell, wherein the second target cell configures dedicated random access resources for the terminal device. In this embodiment, if the first condition is not met, the terminal device may choose not to access the first target cell, but instead select to access the second target cell configured with dedicated random access resources for the terminal device, thereby improving handover efficiency of the terminal device.

[0017] In an optional embodiment, the method further includes: receiving a physical cell identifier (PCI) unchanged switching indication information from the first network device, the PCI unchanged switching indication information being used to instruct the terminal device to access the second network device when a second condition is met; and access the second network device when the first condition is not met and the second condition is met. In this embodiment, if the first condition is not met and the terminal device has configured PCI unchanged switching, the terminal device may choose not to access the first target cell but to access the second network device, that is, to choose to perform PCI unchanged switching, thereby improving the switching efficiency of the terminal device.

[0018] In an optional embodiment, the second condition includes one or more of the following: the time when the first network device ceases to cover the area where the terminal device is located; the time when PCI unchanged switching takes effect; the time when the second network device and the terminal device perform downlink synchronization; or the time when the second network device begins to cover the area where the terminal device is located. In this embodiment, the terminal device can perform PCI unchanged switching at multiple times, providing a more flexible switching method.

[0019] In an optional embodiment, the method further includes: determining whether the first condition is satisfied during the first time unit when the communication gap is greater than a first threshold. In this embodiment, since the signal quality of the source cell cannot be obtained during a communication gap existing during a handover of a network device to which the terminal device cell belongs, the terminal device may determine whether to evaluate the first condition during the communication gap based on the size of the communication gap. If the communication gap is large, the terminal device may evaluate the first condition during the communication gap. If the communication gap is small, the terminal device may evaluate the first condition after the communication gap, thereby reducing the impact of the communication gap on the evaluation of the first condition.

[0020] In a second aspect, embodiments of the present application further provide a handover method, which can be executed by a first network device or a chip system capable of implementing the functions of the first network device. The method includes: sending CHO configuration information to a terminal device, where the CHO configuration information is used for the terminal device to access a first target cell when a first condition is met, where the first condition includes one or more of the following: a time-based execution condition; a distance-based execution condition; or a signal quality-based execution condition.

[0021] In an optional implementation, the time-based execution condition includes a time window.

[0022] In an optional implementation, the distance-based execution condition includes a distance threshold.

[0023] In an optional implementation, the execution condition based on signal quality includes one or more of an A3 event, an A4 event, or an A5 event.

[0024] In an optional embodiment, the method further includes: determining whether the A3 event or the A5 event is met based on the first signal quality of the source cell of the terminal device, the first signal quality being the signal quality of the source cell before the time when the first network device stops covering the area where the terminal device is located, or when the first network device stops covering the area where the terminal device is located; or, determining whether the A3 event or the A5 event is met based on the second signal quality of the source cell of the terminal device, the second signal quality being a default value.

[0025] Regarding the technical effects brought about by the second aspect or some optional implementation methods, reference may be made to the introduction to the technical effects of the first aspect or corresponding implementation methods.

[0026] In a third aspect, an embodiment of the present application further provides a switching method, which can be executed by a terminal device or by a chip system that can implement the functions of the terminal device. The method includes: receiving CHO configuration information and PCI unchanged switching indication information from a first network device, where the first network device is a network device to which a source cell of the terminal device belongs, the CHO configuration information is used by the terminal device to access a first target cell when a first condition is met, and the PCI unchanged switching indication information is used to instruct the terminal device to access a second network device when a second condition is met; and when the first condition and the second condition are met, accessing the first target cell or accessing the second network device.

[0027] In the embodiment of the present application, it is clearly stated that when the terminal device is configured with CHO and PCI unchanged switching, the terminal device can choose to execute CHO (i.e., access the first target cell) or PCI unchanged switching (i.e., access the second network device) when both the CHO execution condition (i.e., the first condition) and the PCI unchanged switching execution condition (i.e., the second condition) are met, thereby clarifying the switching strategy of the terminal device and improving the switching efficiency of the terminal device.

[0028] In an optional embodiment, the first condition includes one or more of the following: a time-based execution condition; a distance-based execution condition; or a signal quality-based execution condition. In this embodiment, because the terminal device cannot obtain the signal quality of the source cell during the communication gap during the handover of the network device to which the source cell belongs, and thus cannot evaluate the signal quality-based execution condition, the CHO execution condition may only include execution conditions based on time and / or distance, thereby reducing the impact of the communication gap on the evaluation of the CHO execution condition, allowing the terminal device to evaluate the CHO execution condition during the communication gap.

[0029] In an optional embodiment, the time-based execution condition includes a time window. For example, the first network device sets a time window (T1, T2) for the terminal to configure CHO execution (i.e., access the first target cell), and the terminal device can perform CHO within the time window (T1, T2).

[0030] In an optional embodiment, the distance-based execution condition includes a distance threshold. For example, the first network device configures a distance threshold D1 and a distance threshold D2 for the terminal device to execute CHO (i.e., access the first target cell). If the distance between the terminal device and the first target cell is less than the distance threshold D1, and the distance between the terminal device and the source cell is greater than the distance threshold D2, the terminal device can execute CHO.

[0031] In an optional embodiment, the execution condition based on signal quality includes one or more of an A3 event, an A4 event, or an A5 event. In this embodiment, because the terminal device cannot obtain the signal quality of the source cell during the communication gap during the handover of the network device to which the source cell belongs, and thus cannot evaluate the A3 event or the A5 event, the execution condition based on signal quality may only include the A4 event, thereby reducing the impact of the communication gap on the evaluation of the execution condition based on signal quality, so that the terminal device can evaluate the execution condition based on signal quality during the communication gap.

[0032] In an optional embodiment, the method further includes: determining whether the A3 event or the A5 event is satisfied based on the first signal quality of the source cell, the first signal quality being the signal quality of the source cell before the time when the first network device stops covering the area where the terminal device is located, or when the first network device stops covering the area where the terminal device is located; or, determining whether the A3 event or the A5 event is satisfied based on the second signal quality of the source cell, the second signal quality being a default value. In this embodiment, the terminal device can evaluate the A3 event or the A5 event based on the signal quality or the default value of the source cell before or when the terminal device is disconnected from the source cell, thereby reducing the impact of the communication gap on the evaluation of the A3 event or the A5 event, so that the terminal device can evaluate the A3 event or the A5 event during the communication gap.

[0033] In an optional embodiment, the second condition includes one or more of the following: the time when the first network device ceases to cover the area where the terminal device is located; the time when PCI unchanged switching takes effect; the time when the second network device and the terminal device perform downlink synchronization; or the time when the second network device begins to cover the area where the terminal device is located. In this embodiment, the terminal device can perform PCI unchanged switching at multiple times, providing a more flexible switching method.

[0034] In an optional embodiment, the method also includes: accessing the first target cell when the first condition, the second condition and the third condition are met; wherein the third condition includes one or more of the following: the time when the third network device stops covering the area where the terminal device is located is later than the time when the second network device stops covering the area where the terminal device is located, and the third network device is the network device to which the first target cell belongs; the first target cell configures dedicated random access resources for the terminal device; or the distance between the first target cell reference point and the terminal device is less than the distance between the source cell reference point and the terminal device.

[0035] In this embodiment, if both the CHO execution condition (i.e., the first condition) and the PCI unchanged switching execution condition (i.e., the second condition) are met, the switching strategy of the terminal device is clarified, thereby improving the switching efficiency of the terminal device.

[0036] In an optional embodiment, the method also includes: accessing the second network device when the first condition, the second condition and the fourth condition are met; wherein the fourth condition includes one or more of the following: the time when the second network device stops covering the area where the terminal device is located is later than the time when the third network device stops covering the area where the terminal device is located, and the third network device is the network device to which the first target cell belongs; the source cell configures dedicated random access resources for the terminal device; or the distance between the source cell reference point and the terminal device is less than the distance between the first target cell reference point and the terminal device.

[0037] In this embodiment, if both the CHO execution condition (i.e., the first condition) and the PCI unchanged switching execution condition (i.e., the second condition) are met, the switching strategy of the terminal device is clarified, and the switching efficiency of the terminal device is improved.

[0038] In a fourth aspect, embodiments of the present application further provide a handover method, which can be executed by a first network device or a chip system capable of implementing the functions of the first network device. The method includes: sending CHO configuration information and PCI unchanged handover indication information to a terminal device, wherein the CHO configuration information is used for the terminal device to access a first target cell when a first condition is met, and the PCI unchanged handover indication information is used to instruct the terminal device to access a second network device when a second condition is met, wherein the first condition includes one or more of the following: a time-based execution condition; a distance-based execution condition; or a signal quality-based execution condition.

[0039] In an optional implementation, the time-based execution condition includes a time window.

[0040] In an optional implementation, the distance-based execution condition includes a distance threshold.

[0041] In an optional implementation, the execution condition based on signal quality includes one or more of an A3 event, an A4 event, or an A5 event.

[0042] In an optional embodiment, the method further includes: determining whether the A3 event or the A5 event is met based on the first signal quality of the source cell of the terminal device, the first signal quality being the signal quality of the source cell before the time when the first network device stops covering the area where the terminal device is located, or when the first network device stops covering the area where the terminal device is located; or, determining whether the A3 event or the A5 event is met based on the second signal quality of the source cell of the terminal device, the second signal quality being a default value.

[0043] In an optional embodiment, the second condition includes one or more of the following: the time when the first network device stops covering the area where the terminal device is located; the time when the PCI unchanged switching takes effect; the time when the second network device performs downlink synchronization with the terminal device; or the time when the second network device starts to cover the area where the terminal device is located.

[0044] Regarding the technical effects brought about by the fourth aspect or some optional implementation methods, reference may be made to the introduction to the technical effects of the third aspect or corresponding implementation methods.

[0045] In a fifth aspect, embodiments of the present application provide a communication device comprising a processor and a memory; the memory is configured to store computer instructions, and when the device is running, the processor executes the computer instructions stored in the memory to cause the device to perform any of the implementation methods described in aspects 1 to 4 above. The memory can be volatile or non-volatile memory, such as a cache memory in a semiconductor chip.

[0046] In a sixth aspect, an embodiment of the present application provides a communication device, which may be a terminal device or a first network device, or a chip for the terminal device or the first network device. The device has the function of implementing any of the implementation methods of aspects 1 to 4 above. The function may be implemented by hardware or by hardware executing corresponding software. The hardware or software includes one or more modules corresponding to the above functions.

[0047] In a seventh aspect, an embodiment of the present application provides a communication device, comprising a unit or means for executing each step of any implementation method in the above-mentioned first to fourth aspects.

[0048] In an eighth aspect, an embodiment of the present application provides a communication device, comprising a processor and an interface circuit, wherein the processor is configured to communicate with another device via the interface circuit and execute any of the implementation methods described in aspects 1 to 4 above. The processor may be one or more processors.

[0049] In a ninth aspect, an embodiment of the present application provides a communication device, comprising a processor coupled to a memory, the processor configured to call a program stored in the memory to execute any of the implementation methods described in aspects 1 to 4 above. The memory may be located within or outside the device. The processor may also be one or more processors.

[0050] In the tenth aspect, an embodiment of the present application further provides a computer-readable storage medium, wherein the computer-readable storage medium stores instructions, which, when run on a communication device, enables any implementation method in the above-mentioned first to fourth aspects to be executed.

[0051] In the eleventh aspect, an embodiment of the present application further provides a computer program product, which includes a computer program or instructions. When the computer program or instructions are run by a communication device, any implementation method in the above-mentioned first to fourth aspects is executed.

[0052] In the twelfth aspect, an embodiment of the present application further provides a chip system, comprising: a processor for executing any implementation method in the above-mentioned first to fourth aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] FIG1 is a schematic diagram of an NTN system provided in an embodiment of the present application;

[0054] FIG2 is a schematic diagram of another NTN system provided in an embodiment of the present application;

[0055] FIG3 is a schematic diagram of the structure of an access network device provided in an embodiment of the present application;

[0056] FIG4 is a schematic diagram of a cell switching process provided in an embodiment of the present application;

[0057] FIG5 is a schematic diagram of a conditional switching process provided by an embodiment of the present application;

[0058] FIG6 is a schematic diagram of a geostationary cell provided in an embodiment of the present application;

[0059] FIG7 is a schematic diagram of a ground mobile cell provided in an embodiment of the present application;

[0060] FIG8 is a schematic diagram of a switching scenario provided in an embodiment of the present application;

[0061] FIG9 is a schematic diagram of a switching method flow chart provided in an embodiment of the present application;

[0062] FIG10 is a schematic diagram of the structure of a communication device provided in an embodiment of the present application;

[0063] FIG11 is a schematic diagram of the structure of a communication device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0064] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0065] The switching method provided in the embodiments of the present application can be applied to an NTN system. The NTN system can utilize non-terrestrial network devices such as drones, high altitude platform stations (HAPS), and satellites to form a network and provide services such as data transmission and voice communication to terminal devices. Furthermore, the NTN system may also include other non-terrestrial network devices, which are not limited in this application.

[0066] The NTN system can also support various mobile communication systems, such as: new radio (NR) system, long term evolution (LTE) system or other communication systems such as future communication systems, and the specific ones are not limited here.

[0067] Taking satellites as an example of non-terrestrial network equipment in the NTN system, satellites can be categorized by their altitude, i.e., the height of their orbit, into geostationary Earth orbit (GEO), medium Earth orbit (MEO), and low-Earth orbit (LEO). GEO is a geostationary Earth orbit, in which satellites remain stationary relative to Earth. The GEO orbital altitude is typically 35,786 kilometers (km). LEO and MEO are collectively referred to as non-geostationary orbits (NGSO). Satellites in these orbits move at high speeds relative to Earth. LEO's orbital altitude is typically 160 to 2000 km, while MEO's is 2000 to 35,786 km. NGSOs can be further categorized into earth moving cells and geostationary cells (quasi-Earth fixed cells), depending on whether the satellite's beam moves with it. For earth moving cells, the cell moves relative to the ground, and the satellite's beam pointing follows the satellite's movement. For earth fixed cells or quasi-Earth fixed cells, the cell remains fixed relative to the ground for a certain period of time, and the satellite antenna can use its beamforming capability to point the beam to a fixed area on the ground for a certain period of time.

[0068] In an NTN system, NTN equipment can operate in two modes: transparent and regenerative. Based on the operating mode of the NTN equipment, the NTN system architecture can be categorized into two types: a transparent forwarding architecture, in which NTN equipment can act as relays or amplifiers, performing RF filtering and amplification, and regenerating physical layer signals. NTN equipment can be responsible for Layer 1 (L1) relaying, performing physical layer forwarding, and is invisible to higher layers. A regenerative architecture, in which NTN equipment performs the processing functions of access network equipment. For example, satellites operating in regenerative mode can be categorized as regenerative satellites without inter-satellite links (ISLs) between satellites; regenerative satellites with ISLs, in which satellites have interfaces for direct data exchange, where the ISLs are Xn ports; or regenerative satellites with the processing functions of distributed units (DUs) of access network equipment, in which case the satellites act as DUs.

[0069] For example, Figure 1 shows a schematic diagram of an NTN system applicable to embodiments of the present application. This NTN system can be a transparent forwarding architecture. In the system shown in Figure 1, a terminal device can communicate with the 5G core network (CN) through the access network, and then connect to the data network (DN) through the 5G CN. Satellites and NTN gateways can serve as relay devices between terminal devices and base stations or as remote radio units (RRUs) of base stations.

[0070] For example, Figure 2 shows a schematic diagram of another NTN system applicable to embodiments of the present application. This NTN system can be a regenerative architecture. In the system shown in Figure 2, satellites can serve as base stations, forming an access network with NTN gateways. These base stations communicate with 5G CNs through the NTN gateways, and can then connect to DNs through the 5G CNs. Furthermore, satellites can provide wireless access services to terminal devices. Figure 2 exemplifies a regenerative satellite architecture without intersatellite links.

[0071] It should be noted that Figures 1 and 2 only illustrate one satellite and one NTN gateway. In actual use, an architecture with multiple satellites and / or multiple NTN gateways may be adopted as needed. Each satellite may provide services to one or more terminal devices, each NTN gateway may correspond to one or more satellites, and each satellite may correspond to one or more NTN gateways, although this embodiment of the present application does not specifically limit this.

[0072] It should be noted that FIG. 1 and FIG. 2 are merely examples of the NTN system. The NTN system may also include other specific systems, which is not limited in this application.

[0073] The devices involved in the embodiments of the present application include terminal devices and network devices, and the network devices include, for example, terrestrial network (TN) devices (such as access network devices) and non-terrestrial network devices (such as satellites).

[0074] A terminal device, also known as user equipment (UE), mobile station (MS), or mobile terminal (MT), refers to a device that provides voice and / or data connectivity to users. For example, a terminal device can be a handheld device or vehicle-mounted device with wireless connectivity. Currently, some examples of terminal devices include: mobile phones, tablets, laptops, PDAs, mobile internet devices (MIDs), wearable devices, virtual reality (VR) devices, augmented reality (AR) devices, wireless terminals in industrial control, wireless terminals in self-driving cars, wireless terminals in remote medical surgery, wireless terminals in smart grids, wireless terminals in transportation safety, wireless terminals in smart cities, and wireless terminals in smart homes.

[0075] Access network equipment may refer to a radio access network (RAN) node (or device), such as a base station, that connects a terminal device to a wireless network. 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 evolved Node B (HNB), base band unit (BBU), or wireless fidelity (Wi-Fi) access point (AP).

[0076] In one network architecture, access network equipment may include centralized unit (CU) nodes, distributed unit (DU) nodes, or both CU and DU nodes. RAN equipment including CU and DU nodes splits the protocol layers of the gNB in ​​the NR system, centrally controlling some protocol layer functions within the CU and distributing some or all of the remaining protocol layer functions within the DU, which is then centrally controlled by the CU, as shown in Figure 3. Furthermore, the CU can be divided into a control plane (CU-CP) and a user plane (CU-UP). The CU-CP is responsible for control plane functions, primarily including radio resource control (RRC) and the control plane's corresponding packet data convergence protocol (PDCP) (i.e., PDCP-C). PDCP-C is primarily responsible for encryption, decryption, integrity protection, and data transmission of control plane data. The CU-UP is responsible for user plane functions, primarily including the service data adaptation protocol (SDAP) and the user plane's corresponding PDCP (i.e., PDCP-U). SDAP is primarily responsible for processing core network data and mapping flows to bearers. The PDCP-U is primarily responsible for data plane encryption and decryption, integrity protection, header compression, sequence number maintenance, and data transmission. The CU-CP and CU-UP are connected via the E1 interface. The CU-CP represents the gNB's connection to the core network via the NG interface and to the DU via the F1 interface control plane (i.e., F1-C). The CU-UP connects to the DU via the F1 interface user plane (i.e., F1-U). Alternatively, the PDCP-C may also reside in the CU-UP.

[0077] It is understandable that in different systems, CU (including CU-CP or CU-UP) or DU may have different names, but those skilled in the art can understand their meanings. For example, in an open radio access network (O-RAN) system, CU may also be referred to as O-CU (open CU), DU may also be referred to as O-DU, CU-CP may also be referred to as O-CU-CP, and CU-UP may also be referred to as O-CU-UP. For the convenience of description, this application uses CU, CU-CP, CU-UP and DU as examples for description.

[0078] In the embodiments of the present application, the communication device for implementing the functions of a network device or a terminal device may be the network device or the terminal device itself, or may be a device capable of supporting the network device or the terminal device to implement the functions, such as a chip system, which may be installed in the network device or the terminal device. In the technical solutions provided in the embodiments of the present application, the technical solutions provided in the embodiments of the present application are described by taking the case where the device for implementing the functions of a network device is a network device, and the case where the device for implementing the functions of a terminal device is a terminal device as an example.

[0079] In the embodiments of the present application, the number of nouns, unless otherwise specified, means "singular noun or plural noun", that is, "one or more". "At least one" means one or more, and "plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. The character " / " generally indicates that the previous and next associated objects are in an "or" relationship. For example, A / B means: A or B. "At least one of the following items" or similar expressions refers to any combination of these items, including any combination of single items or plural items.

[0080] In the embodiments of this application, ordinal numbers such as "first" and "second" are used to distinguish multiple objects and are not used to limit the size, content, order, timing, priority, or importance of the multiple objects. For example, the first network device and the second network device can be the same network device or different network devices, and such names do not indicate a difference in priority or importance between the two network devices.

[0081] The above briefly introduces the communication system applicable to the embodiments of the present application. The following introduces the relevant technical solutions involved in the embodiments of the present application.

[0082] 1) Cell switching

[0083] In a TN system, the movement of a terminal device can cause the signal quality of the current serving cell to deteriorate, necessitating a handover to a neighboring cell with better signal quality. This means that due to the movement of the terminal device, the terminal device currently using network services may move from one cell (the source cell) provided by the base station to another cell (the target cell). To ensure communication continuity and service quality, the communication link between the terminal device and the source cell needs to be transferred to the target cell. The process of transferring the communication link between the terminal device and the source cell and the target cell is also called the cell handover process.

[0084] Please refer to Figure 4 for a schematic diagram of the cell handover process. Figure 4 takes the source cell as the cell of the source base station and the target cell as the cell of the target base station as an example. The cell handover includes the following steps:

[0085] Step 1: The source base station sends a measurement configuration message to the terminal device, so that the terminal device receives the measurement configuration message.

[0086] The measurement configuration message may include a measurement object, a cell list, a reporting method, etc. After receiving the measurement configuration message, the terminal device may measure neighboring cells according to the measurement configuration message and obtain a measurement reporting.

[0087] Step 2: The terminal device sends a measurement report to the source base station.

[0088] The measurement report may include the reference signal receiving power of the serving cell, the signal receiving power or signal quality of the neighboring cell, etc., so that the source base station can determine whether the terminal device performs cell switching based on the measurement report.

[0089] Among them, step 1 and step 2 are optional steps.

[0090] Step 3: The source base station determines a handover decision for the terminal device based on the measurement report.

[0091] The handover decision refers to deciding whether the terminal device should perform a cell handover. If the terminal device needs to perform a cell handover, the source base station may send a handover request message to the target base station.

[0092] Optionally, the source base station may also determine the switching decision of the terminal device based on other content.

[0093] Step 4: The source base station sends a handover request message to the target base station.

[0094] The base station determines that the terminal device needs to switch cells based on the measurement report and sends a handover request message to the target base station. The handover request message is used to request the handover of cells.

[0095] Step 5: The target base station sends a handover request response message to the source base station. The handover response message may include configuration information of the target base station.

[0096] The configuration information of the target base station can be used for the terminal device to access the target base station.

[0097] Step 6: The source base station sends a switching command to the terminal device.

[0098] The handover command is used to instruct the terminal device to perform a cell handover. The terminal device receives the handover command in the source cell and parses the handover command to obtain the configuration information of the target cell, that is, the configuration of the terminal device in the target cell is obtained, so that the terminal device can switch to the target cell according to the configuration.

[0099] Step 7: The terminal device requests random access to the target base station.

[0100] 2) Conditional handover (CHO)

[0101] In order to avoid further deterioration of the communication link quality between the terminal device and the source base station, resulting in the inability to normally interact with the signaling between the terminal device and the source base station, thereby causing the cell switching to fail to be successfully executed, the prior art proposes a CHO mechanism. Specifically, when the communication link quality with the terminal device is good, the source base station sends CHO configuration information to the terminal device. The CHO configuration information includes CHO execution conditions and information about the candidate cell (such as the global cell identification code (cell global identifier, CGI) of the candidate cell, or the physical cell identifier (physical cell identifier, PCI) of the candidate cell and the frequency information corresponding to the candidate cell). After receiving the configuration information, the terminal device determines whether the candidate cell meets the CHO execution conditions based on the configuration information, and uses a candidate cell that meets the CHO execution conditions as the target cell. Then, the terminal device initiates access to the target cell, such as initiating random access. After the random access is successful, the terminal device sends an RRC reconfiguration completion (RRCReconfigurationComplete) message to the base station to which the target cell belongs (i.e., the target base station) to notify the target base station that the CHO is completed.

[0102] Please refer to Figure 5 for a flow chart of conditional handover. Figure 5 takes the source cell as the cell of the source base station and the target cell as the cell of the target base station as an example. Conditional handover includes the following steps:

[0103] Step 1: The source base station sends an RRC reconfiguration (RRCRecofigureration) message to the terminal device.

[0104] The RRC reconfiguration message may include measurement configuration information. The measurement configuration information may include the measurement object, cell list, and reporting method. After receiving the RRC reconfiguration message, the terminal device may measure the neighboring cell according to the measurement configuration information and obtain a measurement report.

[0105] Step 2: The terminal device sends a measurement report to the source base station.

[0106] The measurement report may include the reference signal receiving power of the serving cell, the signal receiving power or signal quality of the neighboring cell, etc., so that the source base station can determine whether the terminal device performs cell switching based on the measurement report.

[0107] Among them, step 1 and step 2 are optional steps.

[0108] Step 3: The source base station determines a candidate cell according to the measurement report and sends a CHO request message to the candidate base station.

[0109] Optionally, the source base station may also determine the candidate cells according to other content.

[0110] Step 4: The candidate base station sends a CHO request response message to the source base station.

[0111] The CHO request response message may include information of candidate cells.

[0112] Step 5: The source base station sends CHO configuration information to the terminal device.

[0113] The CHO configuration information may include CHO execution conditions and information of candidate cells.

[0114] Step 6: The terminal device determines whether the CHO execution condition is met while maintaining the connection with the source base station. If a candidate cell meets the corresponding CHO execution condition, the candidate cell is determined to be the target cell.

[0115] Step 7: The terminal device accesses the target base station.

[0116] For example, the terminal device requests random access to the target base station.

[0117] Step 8: The terminal device sends an RRC reconfiguration completion message to the target base station.

[0118] 3) PCI unchanged handover (satellite handover while cell PCI remains unchanged, also known as satellite handover resynchronization)

[0119] Unlike TN systems, in NTN systems, the movement of non-terrestrial network devices can cause a large number of terminal devices to simultaneously switch cells. For example, as shown in Figure 6, for the aforementioned geostationary cell, within a certain period of time, the satellite moves from position 1 to position 2, and the cell does not move with the satellite. When the satellite moves outside the cell's coverage area (or moves to a point where it can no longer provide coverage), all terminal devices in the cell must switch to the next satellite. In this scenario, the simultaneous cell switching of a large number of terminal devices can lead to a signaling storm and cause signaling congestion. As shown in Figure 7, for the aforementioned geostationary cell, the cell moves with the non-terrestrial network devices, and terminal devices are constantly switching in and out during the movement of the non-terrestrial network devices. For example, the dotted cell represents the cell location when the satellite is in position 1, and the solid cell represents the cell location when the satellite is in position 2. The two cells partially overlap, and terminal devices outside the overlapping area within the dotted cell need to switch. Therefore, in this scenario, the frequent cell switching of a large number of terminal devices also results in significant signaling overhead.

[0120] Since for geostationary cells, the base station remains unchanged before and after satellite switching, and the satellite only performs the function of signal amplification, the PCI and frequency of the cell do not need to be changed before and after the satellite switching. For example, the frequency of the synchronization signal and physical broadcast channel block (SSB) corresponding to the cell does not need to be changed, nor does it need to introduce Layer 3 (L3) signaling. This L3 signaling is used to notify the terminal device to switch. The terminal device only needs to re-synchronize the downlink and uplink with the new satellite after the new satellite arrives. For example, uplink synchronization with the new satellite can be completed through random access, or uplink synchronization with the new satellite can be completed through a random access channel-less (random access channel-less) method. That is, the terminal device's configuration in the cell remains unchanged before and after the satellite switching. Since there is no need to introduce L3 signaling for switching, the above-mentioned signaling congestion problem is solved.

[0121] Currently, satellite handovers include two types: hard switch, where there is no overlap between the new and old satellite coverage periods, and soft switch, where there is overlap between the new and old satellite coverage periods. In hard switch scenarios, the cell's PCI does not need to be changed before and after the satellite switch, eliminating the need for a handover command. In soft switch scenarios, signal interference may occur due to the overlap between the new and old satellite coverage periods. Two solutions have been proposed: one maintains the same approach as for hard switch, with RAN1 resolving the signal interference. The other allows the cell's PCI to be changed before and after the satellite switch, while maintaining or slightly modifying the terminal device's configuration (for example, modifying a configuration strongly related to the cell's PCI, or modifying only the cell's PCI). The terminal then searches for the changed cell's PCI and performs downlink or uplink synchronization, eliminating the need for a handover command. For ease of understanding, these handovers in which the PCI changes or remains unchanged but does not require a handover command are collectively referred to as L3 signaling-free handovers.

[0122] However, as shown in Figure 8, it is a schematic diagram of a switching scenario. In this scenario, the current serving cell of the terminal device is the cell corresponding to PCI#1, and the satellite covering the cell corresponding to PCI#1 is switched from satellite 1 to satellite 2. When configuring the switching strategy of PCI unchanged switching (also known as switching without L3 signaling) for the terminal device, due to the mobility of the terminal device, the terminal device at the edge of the cell coverage corresponding to PCI#1 may move out of the coverage range of the cell corresponding to PCI#1, or because the coverage ranges of satellite 1 and satellite 2 are inconsistent, the coverage range of satellite 2 is smaller than the coverage range of satellite 1, and the terminal device at the edge of the cell coverage corresponding to PCI#1 may not be within the coverage range of satellite 2. Therefore, after adopting the switching strategy of satellite change but PCI unchanged, the terminal device at the edge of the cell coverage corresponding to PCI#1 still needs to switch to the neighboring cell. In the scenario where the terminal device at the edge of the cell coverage still needs to switch to the neighboring cell due to the mobility of the terminal device or the inconsistent coverage ranges of the new and old satellites, the network side can simultaneously configure CHO for the terminal device at the edge of the cell coverage. For example, when the signal quality of the cell corresponding to PCI#1 deteriorates, the terminal device can switch to the cell corresponding to PCI#2 according to CHO, thereby improving the robustness of the switching.

[0123] However, in a hard handover scenario, there is a coverage gap (GAP) between the old and new satellites in the cell corresponding to PCI #1. Since the terminal device is disconnected from the current serving cell during the GAP, it may not be possible for the terminal device to evaluate the CHO execution conditions. Furthermore, if both PCI unchanged handover and CHO meet their corresponding execution conditions, the terminal device cannot determine whether to execute CHO or PCI unchanged handover.

[0124] Based on this, an embodiment of the present application proposes a switching method to improve the switching efficiency of a terminal device.

[0125] This method can be applied to the scenario of handover between satellites (or base stations). In the inter-satellite handover scenario, take the case where a terminal device switches from a first network device to a second network device as an example. The first network device can be a first satellite, and the second network device can be a second satellite. For the system in Figure 1, the first satellite and the second satellite can be satellites connected to a base station. The base station connected to the first satellite and the base station connected to the second satellite can be the same base station, that is, the base station connected to the first satellite and the base station connected to the second satellite is the source base station; or the base station connected to the first satellite and the base station connected to the second satellite can be different base stations, that is, the base station connected to the first satellite is the source base station, and the base station connected to the second satellite is the target base station. For the NTN system in Figure 2, the first satellite and the second satellite can be satellites with base station functions, that is, the first satellite is the source base station, and the second satellite is the target base station.

[0126] In an inter-base station handover scenario, consider a terminal device switching from a first network device to a third network device. The first network device is the source base station, and the third network device is the target base station. For the system in Figure 1, the first and third network devices can be satellite-connected base stations. For the NTN system in Figure 2, the first and third network devices can be satellites with base station functionality.

[0127] For ease of explanation, the following takes the first network device as a source base station or a first satellite connected to the source base station, the second network device as a second satellite connected to the source base station, and the third network device as a target base station as an example.

[0128] As shown in Figure 9, a flowchart of a switching method provided in an embodiment of the present application is provided. In the following description, the method is performed by a first network device (or a chip applied to the first network device) and a terminal device (or a chip applied to the terminal device) as an example. The method includes:

[0129] S901: The first network device sends CHO configuration information to the terminal device. Correspondingly, the terminal device receives the CHO configuration information from the first network device.

[0130] The first network device may be a network device to which the source cell of the terminal device belongs. For example, the first network device may be a source base station or a first satellite connected to the source base station. Optionally, the terminal device may be located at the coverage edge of the source cell.

[0131] The CHO configuration information can be used for the terminal device to access the first target cell when the first condition is met. Specifically, the CHO configuration information may include the first condition (also known as the CHO execution condition) and information about the first target cell. The information about the first target cell includes configuration information required to access the first target cell, such as the CGI of the first target cell, or the PCI of the first target cell and frequency information corresponding to the first target cell. Optionally, the first condition may be generated by the first network device, and the information about the first target cell may be generated by the network device corresponding to the first target cell and sent to the first network device.

[0132] In one possible implementation, the first condition may include, but is not limited to, one or more of the following: a time-based execution condition; a distance-based execution condition; or a signal quality-based execution condition. For example, the first condition may include only a time-based execution condition. Alternatively, the first condition may include only a distance-based execution condition. Alternatively, the first condition may include only a signal quality-based execution condition. Alternatively, the first condition may include both a time-based execution condition and a signal quality-based execution condition. Alternatively, the first condition may include both a distance-based execution condition and a signal quality-based execution condition. Alternatively, the first condition may include both a distance-based execution condition and a time-based execution condition.

[0133] The time-based execution condition may include a time window. For example, the first network device configures a time window (T1, T2) for the terminal to execute CHO (i.e., access the first target cell). If the current time is within the time window (T1, T2), the terminal device may determine that the time-based execution condition is satisfied, and thus the terminal device may execute CHO within the time window (T1, T2).

[0134] The execution condition based on distance may include a distance threshold. For example, the first network device configures the distance threshold D1 and the distance threshold D2 for the terminal device to execute CHO (i.e., access the first target cell). If the distance from the terminal device to the first target cell is less than the distance threshold D1, and the distance from the terminal device to the source cell is greater than the distance threshold D2, the terminal device may determine that the execution condition based on distance is met, so that the terminal device may execute CHO. Optionally, the distance from the terminal device to the cell may be the distance to the cell reference point. The cell reference point may be understood as a reference point where the relative position between the network devices corresponding to the cell remains unchanged. For example, the position of the cell reference point may be the center position of the cell.

[0135] The execution condition based on signal quality may include one or more of the A1 event (event A1), the A2 event (event A2), the A3 event (event A3), the A4 event (event A4), or the A5 event (event A5). For example, the execution condition based on signal quality may include only the A1 event. Alternatively, the execution condition based on signal quality may include only the A2 event. Alternatively, the execution condition based on signal quality may include only the A3 event. Alternatively, the execution condition based on signal quality may include only the A4 event. Alternatively, the execution condition based on signal quality may include only the A5 event. Alternatively, the execution condition based on signal quality may include the A3, A4, and A5 events. Alternatively, the execution condition based on signal quality may include the A3 and A5 events. Alternatively, the execution condition based on signal quality may include the A4 and A5 events. Alternatively, the execution condition based on signal quality may include the A3 and A4 events. When the execution condition based on signal quality includes each of the above events, if the terminal device determines that each of the events is satisfied, the terminal device may determine that the execution condition based on signal quality is satisfied.

[0136] Among them, the A1 event means that the signal quality of the source cell is higher than the first absolute threshold, the A2 event means that the signal quality of the source cell is lower than the second absolute threshold, and the A3 event means that the signal quality of the first target cell is higher than the signal quality of the source cell by a bias value. The A4 event means that the signal quality of the first target cell is higher than the third absolute threshold. The A5 event means that the signal quality of the source cell is lower than the fourth absolute threshold and the signal quality of the first target cell is higher than the fifth absolute threshold. Among them, the signal quality of the first target cell or the source cell can be the reference signal received power (RSRP) of the first target cell or the source cell, the reference signal received quality (RSRQ) of the first target cell or the source cell, or a value determined based on the RSRP of the first target cell or the source cell and the RSRQ of the first target cell or the source cell. Optionally, the execution conditions based on signal quality may also include other events, which are not specifically limited in this application.

[0137] Optionally, before the first network device sends the CHO configuration information to the terminal device, the first network device and the terminal device may further perform the following steps:

[0138] Step A1: The first network device sends measurement configuration information to the terminal device, and the terminal device receives the measurement configuration information from the first network device. The measurement configuration information may include one or more of the following: measurement object; report configuration; measurement identity document (ID); measurement quantity configuration; or measurement GAP configuration.

[0139] Step A2: The terminal device sends a measurement report to the first network device, and correspondingly, the first network device receives the measurement report from the terminal device.

[0140] Step A3: The network device selects at least one candidate cell (e.g., a first target cell) for the UE based on the measurement report, and sends a CHO request message to a network device (e.g., a third network device) to which the at least one candidate cell belongs. The first target cell may be one of the at least one candidate cell, and the third network device may be a network device to which the first target cell belongs. For example, the third network device may be a target base station.

[0141] Step A4: The third network device sends a CHO request response message to the first network device, wherein the CHO request response message may include information about the first target cell.

[0142] Optionally, the first network device and the terminal device may further perform the following steps: the first network device sends PCI unchanged switching indication information to the terminal device, and correspondingly, the terminal device receives the PCI unchanged switching indication information from the first network device.

[0143] Among them, the PCI unchanged switching indication information can be carried in the system message. The PCI unchanged switching indication information is used to instruct the terminal device to switch to or access the second network device when the second condition is met. The second network device can be a network device belonging to the source cell. For example, the first network device can be a second satellite connected to the source base station. The second condition may include one or more of the following: the time when the first network device stops covering the area where the terminal device is located; the time when the PCI unchanged switching takes effect; the time when the second network device performs downlink synchronization with the terminal device; or the time when the second network device starts to cover the area where the terminal device is located. The time when the first network device stops covering the area where the terminal device is located refers to the service stop time of the first network device (for example, t-service-), wherein the first network device stops service means that the first network device stops or interrupts the service of the terminal device in the corresponding cell, or the first network device stops service means that the first network device stops covering the location of the terminal device or the cell where the terminal device is located; or the time when the first network device stops covering the area where the terminal device is located refers to the time when the source cell stops providing service for the currently served area.

[0144] Specifically, the PCI unchanged switching indication information can be a Boolean value, that is, true or false is used to instruct the terminal device to perform PCI unchanged switching. Or the PCI unchanged switching indication information can also be the information of the cell, such as the PCI of the cell, etc., which implicitly instructs the terminal device to perform PCI unchanged switching and switch to the cell corresponding to the PCI carried in the system message through the cell information. Or the PCI unchanged switching indication information can also be the time parameter t-service, which implicitly instructs the terminal device to perform PCI unchanged switching through the time parameter t-service, wherein the time parameter t-service can be the time when the first network device stops covering the area where the terminal device is located, that is, the time when the first network device stops service (for example, t-service1). Or, the PCI unchanged switching indication information can also be the time parameter t-start, which implicitly instructs the terminal device to perform PCI unchanged switching through the time parameter t-start, wherein the time parameter t-start can be the time when the second network device starts to cover the area where the terminal device is located (or also called the time when the second network device starts to provide services for the area covered by the source cell), or it can be the time when the PCI unchanged switching takes effect, or it can be the time when the second network device and the terminal device perform downlink synchronization.

[0145] S902: The terminal device determines whether a first condition is met in a first time unit.

[0146] The first time unit is any time unit in a communication gap existing during a handover of a network device to which the source cell belongs.

[0147] Exemplarily, the network device to which the source cell belongs can be switched from a first network device to a second network device, the first network device can be a first satellite connected to the source base station, and the second network device can be a second satellite connected to the source base station, that is, the satellite of the source cell can be switched from the first satellite to the second satellite. If the first satellite and the second satellite provide services for the source cell, and the first satellite and the second satellite have no overlap in service time, there will be a communication gap during the satellite switching of the source cell (for example, there is a gap between t-service and t-start). At this time, since the base station of the source cell remains unchanged before and after the satellite switching of the source cell, the terminal device can still be in the RRC connection state (RRC_CONNECTED) in the communication gap. After the terminal device receives the CHO configuration information from the first network device, it can determine whether the first condition is met in any time unit in the communication gap.

[0148] Since the terminal device has been disconnected from the source cell or the first satellite during the communication gap, the terminal device cannot obtain the signal quality of the source cell. As a result, when the first condition includes an A3 event or an A5 event, the terminal device cannot evaluate the first condition during the communication gap. Therefore, the terminal device can use the signal quality of the source cell obtained before disconnecting from the source cell or the first satellite or the default value to evaluate the A3 event or the A5 event.

[0149] Specifically, the terminal device may determine whether the A3 event or the A5 event is satisfied based on the first signal quality of the source cell. This can be understood as the terminal device determining that the signal quality of the source cell is the first signal quality.

[0150] Among them, the first signal quality is the signal quality of the source cell obtained by the terminal device before the time when the first network device stops covering the area where the terminal device is located, or when the time when the first network device stops covering the area where the terminal device is located. The time when the first network device stops covering the area where the terminal device is located refers to the expiration or arrival of the service stop time (for example, t-service1) of the first network device. The first network device stops service means that the first network device stops or interrupts the service of the terminal device in the corresponding cell, or the first network device stops service means that the first network device stops covering the location of the terminal device or the cell where the terminal device is located.

[0151] Alternatively, the terminal device may determine whether the A3 event or the A5 event is satisfied based on the second signal quality of the source cell. The second signal quality is a default value. For example, the second signal quality may be -100 decibel milliwatts (dBm). This default value may be configured by the network device or agreed upon by the protocol, and is not specifically limited in this embodiment of the present application.

[0152] Alternatively, when the first condition includes one of the A3 event or the A5 event, and includes at least one of the time-based execution condition, the distance-based execution condition, and the A4 event, the terminal device may only determine whether at least one of the time-based execution condition, the distance-based execution condition, and the A4 event in the first condition is satisfied (it can be understood that the terminal device can ignore the A3 event or the A5 event). If at least one of the time-based execution condition, the distance-based execution condition, and the A4 event in the first condition is satisfied, the terminal device may consider that the first condition is satisfied; otherwise, the first condition is considered not satisfied.

[0153] Alternatively, when the first condition includes one of the A3 event or the A5 event, the terminal device may determine whether to access the first target cell based on whether the signal quality of the first target cell exceeds threshold #1, wherein the threshold #1 may be a default value or may be sent to the terminal device by the first network device. If the signal quality of the first target cell exceeds the threshold #1, the execution condition of the first target cell is met or the terminal device accesses the first target cell; otherwise, the execution condition of the first target cell is not met or the terminal device does not access the first target cell. Furthermore, if the first condition also includes a time-based execution condition and / or a distance-based execution condition, the terminal device considers that the execution condition of the first target cell is met or the terminal device accesses the first target cell only when the time-based execution condition and / or the distance-based execution condition are met.

[0154] Alternatively, when the first condition includes one of the A3 events or the A5 events, the terminal device can determine whether to access the first target cell based on whether the terminal device has uplink or downlink data to be transmitted. If the terminal device has uplink or downlink data to be transmitted (or the amount of uplink or downlink data to be transmitted exceeds threshold #2), the execution condition of the first target cell is met or the terminal device accesses the first target cell; otherwise, the execution condition of the first target cell is not met or the terminal device does not access the first target cell. Furthermore, if the first condition also includes a time-based execution condition and / or a distance-based execution condition, the terminal device considers that the execution condition of the first target cell is met or the terminal device accesses the first target cell only when the time-based execution condition and / or the distance-based execution condition are met.

[0155] In one possible implementation, the terminal device may determine whether the first condition is satisfied in the first time unit based on a communication gap existing during a handover of the network device to which the source cell belongs. Specifically, the terminal device may determine whether the communication gap existing during a handover of the network device to which the source cell belongs is greater than a first threshold. If the communication gap is greater than the first threshold, the terminal device may determine that the first condition is satisfied in the first time unit; otherwise, the terminal device may determine that the first condition is not satisfied in the first time unit. The first threshold may be configured by the network device, may be agreed upon by a protocol, or may be determined by the terminal device, and this embodiment of the present application does not specifically limit this.

[0156] In one possible implementation, the terminal device may determine whether the first condition is satisfied in the first time unit based on a communication gap existing during a handover of a network device to which the source cell belongs. Specifically, when the communication gap existing during a handover of a network device to which the source cell belongs is greater than a first threshold, the terminal device may determine whether the first condition is satisfied in the first time unit using the rule for determining whether an A3 event or an A5 event is satisfied based on the first signal quality of the source cell described above.

[0157] In one possible implementation, after receiving the CHO configuration information from the first network device, the terminal device may not determine whether the first condition is satisfied within the first time unit. In this case, if the terminal device has received the PCI unchanged handover indication information from the first network device, the terminal device may maintain the configuration of the source cell and access the second network device when the second network device begins to cover the location or cell of the terminal device. That is, the terminal device may perform PCI unchanged handover.

[0158] If the terminal device does not determine whether the first condition is met during the first time unit, the first network device and the terminal device may retain the CHO configuration during the communication gap. The terminal device may determine whether the first condition is met during the second time unit. Optionally, the terminal device may access the first target cell if the first condition is met. The second time unit is any time unit after the communication gap that exists during the handover of the network device to which the source cell belongs.

[0159] Alternatively, the first network device and the terminal device may retain the CHO configuration during the communication gap. If the terminal device has received PCI unchanged handover indication information from the first network device, the terminal device may access the first target cell based on the information of the first target cell in the CHO configuration information when performing RRC re-establishment due to PCI unchanged handover failure.

[0160] Alternatively, the first network device and the terminal device may not retain the CHO configuration during the communication gap. The first network device may instruct the third network device to release the resources reserved by the first target cell for the terminal device during the communication gap. Alternatively, if the first condition includes a time window (T1, T2), the third network device may release the resources reserved by the first target cell for the terminal device after T2.

[0161] S903: When the first condition is met, the terminal device accesses the first target cell.

[0162] Specifically, the terminal device accesses the first target cell when the first condition is met, that is, it switches from the source cell to the first target cell. Optionally, after the handover is completed, the third network device may send a handover success message to the first network device, and the first network device instructs the network devices of other candidate cells other than the first target cell to release the resources reserved for the terminal device in the other candidate cells. If the first condition includes the time window (T1, T2), the network devices of the other candidate cells may release the resources reserved for the terminal device in the other candidate cells after T2.

[0163] In one possible implementation, if the terminal device also meets the first condition corresponding to other candidate cells other than the first target cell, the terminal device can select from the first target cell and the other candidate cells to access a cell configured with dedicated random access resources for the terminal device. For example, if the first target cell configures contention free random access (CFRA) resources for the terminal device, or configures the terminal device to access the first target cell through rach-less, the terminal device can select from the first target cell and the other candidate cells to access the first target cell. Optionally, the other candidate cells do not have CFRA resources configured for the terminal device, or do not configure the terminal device to access the first target cell through rach-less. Alternatively, the terminal device can also select from the first target cell and the other candidate cells to access the cell with the latest service stop time of the network device to which it belongs. For example, if the service stop time of the third network device (e.g., t-service3) is the latest, the terminal device can select from the first target cell and the other candidate cells to access the first target cell.

[0164] In one possible implementation, the terminal device may also access the second target cell when the first condition is not met. The second target cell configures dedicated random access resources for the terminal device. For example, the second target cell configures CFRA resources for the terminal device, or configures the terminal device to access the second target cell via random-less access.

[0165] In one possible implementation, the terminal device accesses the second network device when the first condition described above is not met but the second condition described above is met. For example, the current terminal device uses the configuration of the cell corresponding to PCI#1 to access the cell corresponding to PCI#1, i.e., the source cell is the cell corresponding to PCI#1, and the first satellite is now providing services for the source cell. As the satellite moves, the satellite covering the cell corresponding to PCI#1 switches from the first satellite to the second satellite. If the terminal device has configured a switching strategy for switching with unchanged PCI, the terminal device can maintain the configuration of the cell corresponding to PCI#1 and access the second satellite after the second satellite's coverage is established. The second satellite is now providing services for the source cell.

[0166] In a possible implementation, the terminal device accesses the first target cell or accesses the second network device when the above-mentioned first condition and the above-mentioned second condition are met.

[0167] Specifically, the terminal device can access the first target cell if the first condition, the second condition, and the third condition are met. Optionally, the first condition may be an execution condition that includes the A4 or A5 event, or an execution condition that does not include the A4 or A5 event. The third condition includes one or more of the following:

[0168] The time when the third network device (also known as the CHO target network device) stops covering the area where the terminal device is located is later than the time when the second network device (also known as the PCI unchanged switching target network device) stops covering the area where the terminal device is located. The time when the third network device stops covering the area where the terminal device is located refers to the service stop time of the third network device (for example, t-service3) (or also known as the time when the first target cell provides services to the coverage area of ​​the first target cell through the third network device), and the third network device stops service when the third network device stops or interrupts the service of the terminal device in the corresponding cell, or refers to the third network device stops covering the location of the terminal device or the cell where the terminal device is located. The time when the second network device stops covering the area where the terminal device is located refers to the service stop time of the second network device (for example, t-service2) (or also known as the time when the source cell provides services to the coverage area of ​​the source cell through the second network device), and the second network device stops service when the second network device stops or interrupts the service of the terminal device in the corresponding cell, or refers to the first network device stops covering the location of the terminal device or the cell where the terminal device is located. That is, t-service3 is later than t-service2;

[0169] The first target cell configures dedicated random access resources for the terminal device, for example, the first target cell configures CFRA resources or rach-less resources for the terminal device, or the source cell does not configure CFRA resources or rach-less resources for the terminal device; or,

[0170] The distance between the first target cell reference point and the terminal device (for example, D1) is smaller than the distance between the source cell reference point and the terminal device (for example, D2), that is, D1 is smaller than D2.

[0171] Alternatively, the terminal device may access the second network device if the first condition, the second condition, and the fourth condition are met. The fourth condition includes one or more of the following:

[0172] The time when the second network device stops covering the area where the terminal device is located is later than the time when the third network device stops covering the area where the terminal device is located. That is, t-service3 is later than t-service2;

[0173] The source cell configures dedicated random access resources for the terminal device, for example, the source cell configures CFRA resources or rach-less resources for the terminal device, or the first target cell does not configure CFRA resources or rach-less resources for the terminal device; or,

[0174] The distance between the source cell reference point and the terminal device (eg, D2) is smaller than the distance between the first target cell reference point and the terminal device (eg, D1), that is, D2 is smaller than D1.

[0175] The above solution clarifies that when a communication gap exists during a handover of a network device to which the source cell belongs, the terminal device can evaluate the CHO execution condition (i.e., the first condition) during this communication gap. For example, when the satellite of the source cell switches from a first satellite to a second satellite, and there is no overlap in the service time when the first and second satellites provide services to the source cell, a communication gap will exist during the handover of the first and second satellites. The terminal device can evaluate the CHO execution condition during this communication gap. Since the terminal device may move out of the coverage of the source cell or the coverage of the first and second satellites may be inconsistent after the handover of the first and second satellites, the terminal device needs to perform CHO (i.e., access the first target cell). By evaluating the CHO execution condition in advance during this communication gap, the handover efficiency of the terminal device can be improved. It also clarifies that when the terminal device is configured with CHO and PCI unchanged handover, the terminal device can choose to perform CHO (i.e., access the first target cell) or PCI unchanged handover (i.e., access the second network device) when both the CHO execution condition (i.e., the first condition) and the PCI unchanged handover execution condition (i.e., the second condition) are met. This clarifies the handover strategy of the terminal device and improves the handover efficiency of the terminal device.

[0176] In the embodiments of the present application, the first network device or the terminal device may perform some or all of the steps in the embodiments of the present application. These steps or operations are merely examples, and the embodiments of the present application may also perform other operations or variations of various operations. In addition, the various steps may be performed in a different order than those presented in the embodiments of the present application, and it is possible that not all of the operations in the embodiments of the present application need to be performed.

[0177] To implement the functions in the above embodiments, the first network device or terminal device includes hardware structures and / or software modules corresponding to the execution of each function. Those skilled in the art should readily appreciate that, in conjunction with the units and method steps of the various examples described in the embodiments disclosed herein, the present application can be implemented in the form of hardware or a combination of hardware and computer software. Whether a function is executed in hardware or in a manner driven by computer software depends on the specific application scenario and design constraints of the technical solution.

[0178] Figures 10 and 11 are schematic diagrams of the structures of possible communication devices provided in embodiments of the present application. These communication devices can be used to implement the functions of the first network device or terminal device in the above method embodiments, thereby also achieving the beneficial effects of the above method embodiments. In the embodiments of the present application, the communication device can be the first network device or terminal device, or it can be a module (such as a chip) applied to the first network device or terminal device.

[0179] The communication device 1000 shown in Figure 10 includes a processing unit 1010 and a communication unit 1020. The communication device 1000 is used to implement the functions of the first network device or terminal device in the above method embodiment.

[0180] When the communication device 1000 is used to implement the functions of the terminal device in the above embodiment:

[0181] a communication unit, configured to receive conditional handover (CHO) configuration information from a first network device, where the first network device is a network device to which a source cell of the terminal device belongs, and the CHO configuration information is used by the terminal device to access a first target cell when a first condition is met;

[0182] A processing unit, configured to determine whether the first condition is met in a first time unit, where the first time unit is any time unit in a communication gap existing during a handover of a network device to which the source cell belongs;

[0183] The processing unit is configured to access the first target cell when the first condition is met.

[0184] When the communication device 1000 is used to implement the function of the first network device in the above embodiment:

[0185] A communication unit is used to send CHO configuration information to a terminal device, where the CHO configuration information is used for the terminal device to access a first target cell when a first condition is met, where the first condition includes one or more of the following: a time-based execution condition; a distance-based execution condition; or a signal quality-based execution condition.

[0186] When the communication device 1000 is used to implement the functions of the terminal device in the above embodiment:

[0187] a communication unit, configured to receive CHO configuration information and PCI unchanged handover indication information from a first network device, the first network device being the network device to which a source cell of the terminal device belongs, the CHO configuration information being used for the terminal device to access a first target cell if a first condition is met, and the PCI unchanged handover indication information being used to instruct the terminal device to access a second network device if a second condition is met;

[0188] A processing unit is configured to access the first target cell or access the second network device when the first condition and the second condition are met.

[0189] When the communication device 1000 is used to implement the function of the first network device in the above embodiment:

[0190] A communication unit, used to send CHO configuration information and PCI unchanged switching indication information to a terminal device, wherein the CHO configuration information is used for the terminal device to access a first target cell when a first condition is met, and the PCI unchanged switching indication information is used to instruct the terminal device to access a second network device when a second condition is met, wherein the first condition includes one or more of the following: a time-based execution condition; a distance-based execution condition; or a signal quality-based execution condition.

[0191] For a more detailed description of the processing unit 1010 and the communication unit 1020, reference can be made to the relevant description in the above method embodiment, which will not be repeated here.

[0192] The communication device 1100 shown in FIG11 includes a processor 1110 and an interface circuit 1120. The processor 1110 and the interface circuit 1120 are coupled to each other. The interface circuit 1120 may be a transceiver or an input / output interface. For example, the communication device 1100 may further include a memory 1130 for storing instructions executed by the processor 1110, or for storing input data required by the processor 1110 to execute instructions, or for storing data generated after the processor 1110 executes instructions.

[0193] When the communication device 1100 is used to implement the above method embodiment, the processor 1110 is used to implement the functions of the above processing unit 1010 , and the interface circuit 1120 is used to implement the functions of the above communication unit 1020 .

[0194] When the communication device is a chip used in a terminal device, the chip of the terminal device implements the functions of the terminal device in the above method embodiments. The chip of the terminal device receives information from other modules in the terminal device (such as a radio frequency module or antenna), and the information is sent to the terminal device by the first network device; or the chip of the terminal device sends information to other modules in the terminal device (such as a radio frequency module or antenna), and the information is sent to the first network device by the terminal device.

[0195] When the above-mentioned communication device is a module applied to the first network device, the module of the first network device implements the functions of the first network device in the above-mentioned method embodiment. The module of the first network device receives information from other modules in the first network device (such as a radio frequency module or an antenna), and the information is sent by the terminal device to the first network device; or, the module of the first network device sends information to other modules in the first network device (such as a radio frequency module or an antenna), and the information is sent by the first network device to the terminal device. The module of the first network device here can be a chip of the first network device, or it can be a DU or other module. The DU here can be a DU under the open radio access network (O-RAN) architecture.

[0196] The processor in the embodiments of the present application may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field programmable gate arrays (FPGA), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. The general-purpose processor may be a microprocessor or any conventional processor.

[0197] The method steps in the embodiments of the present application can be implemented by hardware or by a processor executing software instructions. The software instructions can be composed of corresponding software modules, and the software modules can be stored in a random access memory, a flash memory, a read-only memory, a programmable read-only memory, an erasable programmable read-only memory, an electrically erasable programmable read-only memory, a register, a hard disk, a mobile hard disk, a compact disc read-only memory (CD-ROM) or any other form of storage medium well known in the art. An exemplary storage medium is coupled to the processor so that the processor can read information from the storage medium and can write information to the storage medium. Of course, the storage medium can also be an integral part of the processor. The processor and the storage medium can be located in an ASIC. In addition, the ASIC can be located in a first network device or a terminal device. Of course, the processor and the storage medium can also be present in the first network device or the terminal device as discrete components.

[0198] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0199] Those skilled in the art will appreciate that the various illustrative logical blocks and steps described in conjunction with the embodiments disclosed herein can be implemented using electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may 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.

[0200] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0201] In the several embodiments provided in this application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0202] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0203] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the part that essentially contributes to the technical solution of the present application or the part of the technical solution can be embodied in the form of a software product, which is stored in a storage medium and includes a number of instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a RAM, a magnetic disk or an optical disk.

[0204] Obviously, those skilled in the art may make various changes and modifications to the present application without departing from the scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is intended to include these modifications and variations.

Claims

1. A switching method, characterized in that: The method is performed by a terminal device or a chip applied to the terminal device, and includes: receiving conditional handover CHO configuration information from a first network device, where the first network device is a network device to which a source cell of the terminal device belongs, and the CHO configuration information is used for the terminal device to access a first target cell when a first condition is met; Determine whether the first condition is met in a first time unit, where the first time unit is any time unit in a communication gap existing during a switching period of a network device to which the source cell belongs; When the first condition is met, access the first target cell.

2. The method according to claim 1, characterized in that The first condition includes one or more of the following: Time-based execution conditions; Enforcement conditions based on distance; or Execution conditions based on signal quality.

3. The method according to claim 2, characterized in that The time-based execution condition includes a time window.

4. The method according to claim 2, characterized in that The distance-based execution condition includes a distance threshold.

5. The method according to claim 2, characterized in that The execution condition based on signal quality includes one or more of an A3 event, an A4 event, or an A5 event.

6. The method according to claim 5, characterized in that The method further comprises: determining whether the A3 event or the A5 event is satisfied based on a first signal quality of the source cell, wherein the first signal quality is a signal quality of the source cell before the time when the first network device stops covering the area where the terminal device is located, or when the time when the first network device stops covering the area where the terminal device is located; or Whether the A3 event or the A5 event is satisfied is determined based on a second signal quality of the source cell, where the second signal quality is a default value.

7. The method according to any one of claims 1 to 6, characterized in that: The method further comprises: When the first condition is not met, access is made to a second target cell, and the second target cell configures dedicated random access resources for the terminal device.

8. The method according to any one of claims 1 to 6, characterized in that: The method further comprises: Receiving physical cell identifier PCI unchanged switching indication information from the first network device, where the PCI unchanged switching indication information is used to instruct the terminal device to access the second network device if a second condition is met; When the first condition is not met but the second condition is met, access the second network device.

9. The method according to claim 8, characterized in that The second condition includes one or more of the following: The time when the first network device stops covering the area where the terminal device is located is reached; The time when the PCI unchanged switch takes effect; The time for the second network device to perform downlink synchronization with the terminal device; or The time when the second network device starts to cover the area where the terminal device is located.

10. The method according to any one of claims 1 to 9, characterized in that: The method further comprises: In a case where the communication gap is greater than a first threshold, it is determined whether the first condition is satisfied in the first time unit.

11. A switching method, characterized in that: The method is performed by a first network device or a chip applied to the first network device, and includes: Send CHO configuration information to a terminal device, where the CHO configuration information is used for the terminal device to access a first target cell when a first condition is met, where the first condition includes one or more of the following: Time-based execution conditions; Enforcement conditions based on distance; or Execution conditions based on signal quality.

12. The method according to claim 11, characterized in that The time-based execution condition includes a time window.

13. The method according to claim 11, characterized in that The distance-based execution condition includes a distance threshold.

14. The method according to claim 11, characterized in that The execution condition based on signal quality includes one or more of an A3 event, an A4 event, or an A5 event.

15. The method according to claim 14, characterized in that The method further comprises: Determine whether the A3 event or the A5 event is satisfied based on a first signal quality of a source cell of the terminal device, wherein the first signal quality is a signal quality of the source cell before the time when the first network device stops covering the area where the terminal device is located, or when the first network device stops covering the area where the terminal device is located; or Whether the A3 event or the A5 event is satisfied is determined based on a second signal quality of a source cell of the terminal device, where the second signal quality is a default value.

16. A communication device, characterized in that: The method comprises a module for executing the method according to any one of claims 1 to 10, or a module for executing the method according to any one of claims 11 to 15.

17. A communication device, characterized in that: It includes a processor and an interface circuit, wherein the interface circuit is used to receive signals from other communication devices outside the communication device and transmit them to the processor or send signals from the processor to other communication devices outside the communication device, and the processor implements the method as described in any one of claims 1 to 10 or the method as described in any one of claims 11 to 15 through a logic circuit or by executing code instructions.

18. A communication device, characterized in that: include: Memory for storing computer programs; A processor, configured to call and run the computer program from the memory to implement the method according to any one of claims 1 to 10, or to implement the method according to any one of claims 11 to 15.

19. A chip system, characterized in that: include: Memory for storing computer programs; A processor, configured to call and run the computer program from the memory, so that a device equipped with the chip system executes the method as claimed in any one of claims 1 to 10, or executes the method as claimed in any one of claims 11 to 15.

20. A computer program product, characterized in that The invention comprises a computer program, which, when executed by a communication device, implements the method according to any one of claims 1 to 15.

21. A computer-readable storage medium, characterized in that: The storage medium stores a computer program or an instruction. When the computer program or the instruction is executed by the communication device, the method according to any one of claims 1 to 15 is implemented.

22. A communication system, characterized in that: include: A terminal device, configured to execute the method according to any one of claims 1 to 10; The first network device is configured to execute the method according to any one of claims 11 to 15.

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