Communication method and device

Abstract

This application discloses a communication method and apparatus relating to the field of communication technology. The method includes the following: a terminal receives first information indicating that a first reference signal of a first cell and a second reference signal of a second cell belong to the same group; the terminal receives second information indicating that the first cell is a target cell for handover; and the terminal accesses the target cell using the target cell's timing advance TA, the TA of the target cell being determined based on the TA of the second cell, the first reference signal, and the second reference signal. According to the method described above, after determining based on the first information that the first reference signal and the second reference signal belong to the same group, the terminal can determine the TA of the target cell based on the TA of the second cell, the first reference signal, and the second reference signal, without needing to obtain the TA of the target cell via random access. This reduces random access during cell handover and further reduces interruption delay.

Description

Technical Field

[0001] This application relates to the field of communication technologies, particularly to communication methods and devices.

Background Art

[0002] Cross-reference of related applications This application claims the priority of Chinese Patent Application No. 202310533185.1, titled "Communication Method and Device", filed with the China National Intellectual Property Administration on May 11, 2023, the entire content of which is incorporated herein by reference.

[0003] Cell handover is a very important function in a communication system. It is mainly triggered by the movement of a terminal when the terminal is in the RRC connected state, and before the signal quality of the serving cell becomes unable to support communication, the terminal device is handed over to an adjacent cell with good signal quality to provide continuous and uninterrupted communication services.

[0004] However, regarding cell handover, further study is needed on how to determine the timing advance (TA) of the target cell and access the target cell using the TA of the target cell.

Summary of the Invention

[0005] This application provides a communication method and device for determining the TA of a target cell based on the downlink timing difference to reduce random access during cell handover and further reduce interruption delay.

[0006] According to a first aspect, an embodiment of the present application provides a communication method. The method may be applied to a terminal or a module within a terminal (e.g., a chip or circuit). For example, the method is applied to a terminal. In the method, the terminal receives first information indicating that a first reference signal of a first cell and a second reference signal of a second cell belong to the same group. The terminal receives second information indicating that the first cell is a handover target cell, and the terminal accesses the target cell using the timing advance TA of the target cell, where the TA of the target cell is determined based on the TA of the second cell, the first reference signal, and the second reference signal.

[0007] According to the above method, after determining that the first reference signal and the second reference signal belong to the same group based on the first information, the terminal can determine the TA of the target cell based on the TA of the second cell, the first reference signal, and the second reference signal, eliminating the need to obtain the target cell's TA by random access. This reduces random access during cell handover and further reduces interrupt delay.

[0008] In a possible design, the first information includes parameters corresponding to the group, the parameters including the index of the first reference signal and the index of the second reference signal, the identifier of the first cell and the identifier of the second cell, or the configuration information of the first reference signal and the configuration information of the second reference signal.

[0009] In a possible design, the method further includes transmitting first capability information, the first capability information indicating that the terminal supports TA determination based on an in-frequency reference signal, where the first and second reference signals are in-frequency reference signals.

[0010] This allows the terminal to transmit first capability information to the network device, which can then determine the reference signal group information based on the first capability information. In this way, the reference signal group information becomes more appropriate, which helps improve the accuracy of the TA in determining the target cell.

[0011] In a possible design, the first and second reference signals being in-frequency reference signals includes the first and second reference signals corresponding to the same frequency, or the first and second reference signals corresponding to the same subcarrier interval.

[0012] In a possible design, the method further includes transmitting a second capability information, which indicates that the terminal supports TA determination based on an inter-frequency reference signal, where the first and second reference signals are inter-frequency reference signals.

[0013] In this way, the terminal transmits second capability information to the network device, which can then determine the reference signal group information based on the second capability information. This ensures that the reference signal group information is more appropriate, thereby improving the accuracy of the determined TA for the target cell.

[0014] In a possible design, the second capability information further indicates at least one combination of bands, each combination of bands containing at least one band, and the frequencies corresponding to the first reference signal and the second reference signal are within the same combination of bands.

[0015] In other words, due to terminal capability limitations, a terminal may support specific combinations of bands. If the frequencies corresponding to the first and second reference signals are within the same combination of bands supported by the terminal, the first and second reference signals can be used to determine the TA of the first cell.

[0016] In possible designs, the first and second reference signals being interfrequency reference signals includes the first and second reference signals corresponding to different frequencies, or the first and second reference signals corresponding to different subcarrier intervals.

[0017] In a possible design, the method further includes receiving third information from a network device, and indicating that the third information is accessed in a random access-less manner.

[0018] In this way, the network device uses third-party information to control whether to use the target cell's TA, which is determined based on the downlink timing difference, when a terminal accesses the target cell, and as a result the network device can flexibly manage and control the terminal.

[0019] According to a second aspect, embodiments of the present application provide a communication method. The method may be applied to a network device or a chip within a network device. For example, the method is applied to a network device. In the method, the network device transmits first information, the first information indicating that a first reference signal of a first cell and a second reference signal of a second cell belong to the same group; the network device transmits second information, the second information indicating that the first cell is a handover target cell; and the first and second reference signals are used to determine the TA of the target cell.

[0020] In a possible design, the first information includes parameters corresponding to the group, and the parameters include the index of the first reference signal and the index of the second reference signal, the identifier of the first cell and the identifier of the second cell, or the configuration information of the first reference signal and the configuration information of the second reference signal.

[0021] In a possible design, the method further comprises receiving first capability information, the first capability information indicating that the terminal supports determining the TA based on an in-frequency reference signal, and transmitting first information, which comprises transmitting first information based on the first capability information, configuration information of the first reference signal, and configuration information of the second reference signal, the configuration information of the first reference signal and the configuration information of the second reference signal indicating that the first reference signal and the second reference signal are in-frequency reference signals.

[0022] In a possible design, the first and second reference signals being in-frequency reference signals includes the first and second reference signals corresponding to the same frequency or the first and second reference signals corresponding to the same subcarrier interval.

[0023] In a possible design, the method further includes receiving second capability information, the second capability information indicating that the terminal supports determining the TA based on an inter-frequency reference signal, and transmitting first information, which includes transmitting first information based on the second capability information, configuration information of the first reference signal, and configuration information of the second reference signal, the configuration information of the first reference signal and the configuration information of the second reference signal indicating that the first reference signal and the second reference signal are inter-frequency reference signals.

[0024] In a possible design, the second capability information further indicates at least one combination of bands, each combination of bands containing at least one band, and the frequencies corresponding to the first and second reference signals are within the same combination of bands.

[0025] In possible designs, the first and second reference signals being interfrequency reference signals includes the first and second reference signals corresponding to different frequencies or to different subcarrier intervals.

[0026] In a possible design, the method further includes transmitting third information to the terminal, where the third information indicates accessing the target cell in a random access manner.

[0027] In the second aspect, the method recited in the claims can be understood to correspond to the method in the first aspect. For the beneficial effects of the related technical features in the second aspect, please refer to the description of the first aspect. Details will not be described again here.

[0028] According to a third aspect, an embodiment of the present application provides a communication method. The method can be applied to a terminal or a module within the terminal (for example, a chip or a circuit). For example, the method is applied to a terminal. In the method, the terminal receives first information, where the first information indicates determining the TA of a first cell based on a downlink timing difference, the terminal receives second information, where the second information indicates that the first cell is the target cell of a handover, and the terminal accesses the target cell using the TA of the target cell, where the TA of the target cell is determined based on the TA of a second cell and the downlink timing difference between the first cell and the second cell.

[0029] According to the foregoing method, the network device can improve the flexibility of the network device's indication by using additional information (i.e., the first information) to indicate whether to determine the TA of the first cell based on the downlink timing difference.

[0030] In a possible design, the method further includes receiving third information, where the third information indicates determining the TA of the first cell based on the downlink timing difference between the first cell and the second cell.

[0031] In this way, the network device can use the third information to indicate the specific cell for which the downlink timing difference with the first cell is used to determine the TA of the first cell.

[0032] In a possible design, the third piece of information would include the identifier of the second cell.

[0033] In a possible design, the method further includes transmitting first capability information, the first capability information indicating that the terminal supports determining the TA based on an in-frequency reference signal, where the first and second reference signals are in-frequency reference signals.

[0034] In a possible design, the first and second reference signals being in-frequency reference signals includes the first and second reference signals corresponding to the same frequency or the first and second reference signals corresponding to the same subcarrier interval.

[0035] In a possible design, the method further includes transmitting a second capability information, which indicates that the terminal supports determining the TA based on an inter-frequency reference signal, where the first and second reference signals are inter-frequency reference signals.

[0036] In a possible design, the second capability information further indicates at least one combination of bands, each combination of bands containing at least one band, and the frequencies corresponding to the first and second reference signals are within the same combination of bands.

[0037] In possible designs, the first and second reference signals being interfrequency reference signals includes the first and second reference signals corresponding to different frequencies or to different subcarrier intervals.

[0038] According to a fourth aspect, embodiments of the present application provide a communication method. The method may be applied to a network device or a chip within a network device. For example, the method is applied to a network device. In this method, the network device transmits first information indicating that the TA of a first cell is determined based on the downlink timing difference; the network device transmits second information indicating that the first cell is a target cell for a handover; and the TA of the first cell is used to access the target cell.

[0039] In a possible design, the method further includes transmitting a third piece of information, the third piece of information which determines the TA of the first cell based on the downlink timing difference between the first cell and the second cell.

[0040] In a possible design, the third piece of information would include the identifier of the second cell.

[0041] In a possible design, the method further comprises receiving first capability information, the first capability information indicating that the terminal supports determining the TA based on an in-frequency reference signal, and transmitting first information, which comprises transmitting first information based on the first capability information, configuration information of the first reference signal, and configuration information of the second reference signal, the configuration information of the first reference signal and the configuration information of the second reference signal indicating that the first reference signal and the second reference signal are in-frequency reference signals.

[0042] In a possible design, the first and second reference signals being in-frequency reference signals includes the first and second reference signals corresponding to the same frequency or the first and second reference signals corresponding to the same subcarrier interval.

[0043] In a possible design, the method further includes receiving second capability information, the second capability information indicating that the terminal supports determining the TA based on an inter-frequency reference signal, and transmitting first information, which includes transmitting first information based on the second capability information, configuration information of the first reference signal, and configuration information of the second reference signal, the configuration information of the first reference signal and the configuration information of the second reference signal indicating that the first reference signal and the second reference signal are inter-frequency reference signals.

[0044] In a possible design, the second capability information further indicates at least one combination of bands, each combination of bands containing at least one band, and the frequencies corresponding to the first and second reference signals are within the same combination of bands.

[0045] In possible designs, the first and second reference signals being interfrequency reference signals includes the first and second reference signals corresponding to different frequencies or to different subcarrier intervals.

[0046] For the beneficial effects of the relevant technical features in the third and fourth embodiments, please refer to the description of the first embodiment. Further details will not be explained again here.

[0047] According to a fifth aspect, embodiments of the present application provide a communication method, which may be applied to a communication device. The communication device may be a CU or a chip within a CU, or a DU or a chip within a DU. In the method, the communication device acquires configuration information of a first reference signal of a first cell and configuration information of a second reference signal of a second cell, the communication device transmits first information based on the configuration information of the first reference signal and the configuration information of the second reference signal, the first information indicating that the first reference signal and the second reference signal belong to the same group, and the first reference signal and the second reference signal are used to measure the TA of the first cell or the second cell.

[0048] In a possible design, the method further comprises receiving first capability information, the first capability information indicating that the terminal supports determining the TA based on an in-frequency reference signal, and transmitting first information based on the configuration information of the first reference signal and the configuration information of the second reference signal, which comprises transmitting first information based on the first capability information, the configuration information of the first reference signal and the configuration information of the second reference signal, indicating that the first reference signal and the second reference signal are in-frequency reference signals.

[0049] In a possible design, if the communication device is a CU or a chip within a CU, obtaining configuration information for a first reference signal of a first cell and configuration information for a second reference signal of a second cell includes receiving configuration information for a first reference signal and configuration information for a second reference signal.

[0050] In a possible design, if the communication device is a CU or a chip within a CU, the method further comprises transmitting first request information and second request information, the first request information comprising first frequency information and / or first subcarrier information, the first request information being used to request the configuration of a first reference signal for a first cell based on the first frequency information and / or first subcarrier information; the second request information comprising second frequency information and / or second subcarrier information, the second request information being used to request the configuration of a second reference signal for a second cell based on the second frequency information and / or second subcarrier information, the first frequency information being the same as the second frequency information, or the first subcarrier information being the same as the second subcarrier information.

[0051] In a possible design, if the communication device is a DU or a chip within a DU, the method further comprises receiving first request information and second request information, wherein the first request information comprises first frequency information and / or first subcarrier information, and the second request information comprises second frequency information and / or second subcarrier information, and obtaining configuration information for a first reference signal of a first cell and configuration information for a second reference signal of a second cell comprises configuring a first reference signal of a first cell based on the first frequency information and / or first subcarrier information, and configuring a second reference signal of a second cell based on the second frequency information and / or second subcarrier information, wherein the first frequency information is the same as the second frequency information, or the first subcarrier information is the same as the second subcarrier information.

[0052] In a possible design, the method further includes receiving second capability information, the second capability information indicating that the terminal supports determining the TA based on an inter-frequency reference signal; transmitting first information based on the configuration information of the first reference signal and the configuration information of the second reference signal, the first capability information, and the configuration information of the second reference signal indicating that the first reference signal and the second reference signal are inter-frequency reference signals.

[0053] In a possible design, the second capability information further indicates at least one combination of bands, each combination of bands containing at least one band, and the frequencies corresponding to the first and second reference signals are within the same combination of bands.

[0054] In a possible design, if the communication device is a CU or a chip within a CU, the method further comprises transmitting first request information and second request information, the first request information comprising first frequency information and / or first subcarrier information, the first request information being used to request the configuration of a first reference signal for a first cell based on the first frequency information and / or first subcarrier information; the second request information comprising second frequency information and / or second subcarrier information, the second request information being used to request the configuration of a second reference signal for a second cell based on the second frequency information and / or second subcarrier information, wherein the first frequency information is different from the second frequency information, or the first subcarrier information is different from the second subcarrier information.

[0055] In a possible design, if the communication device is a DU or a chip within a DU, the method further comprises receiving first request information and second request information, wherein the first request information comprises first frequency information and / or first subcarrier information, and the second request information comprises second frequency information and / or second subcarrier information, and obtaining configuration information for a first reference signal of a first cell and configuration information for a second reference signal of a second cell comprises configuring a first reference signal of a first cell based on the first frequency information and / or first subcarrier information, and configuring a second reference signal of a second cell based on the second frequency information and / or second subcarrier information, wherein the first frequency information is different from the second frequency information, or the first subcarrier information is different from the second subcarrier information.

[0056] According to a sixth aspect, an embodiment of the present application provides a communication device having a function to implement the methods of the first to fifth aspects. For example, the communication device includes corresponding modules, units, or means for performing the operations of the first to fifth aspects. The functions, units, or means may be implemented by software, by hardware, or by hardware by running corresponding software.

[0057] In a possible design, the communication device includes a processing unit and a communication unit. The communication unit may be configured to receive and transmit signals in order to implement communication between the communication device and another device. For example, the communication unit may be configured to transmit system information to a terminal. The processing unit may be configured to perform some internal operations of the communication device. The functions performed by the processing unit and the communication unit may correspond to the operations of the first through fifth embodiments.

[0058] In a possible design, the communication device may include a processor, which may be configured to be coupled to memory. The memory may store computer programs or instructions necessary to implement the functions of the first through fifth embodiments. The processor may execute the computer programs or instructions stored in memory. When a computer program or instruction is executed, the communication device is made to implement the method in any possible design or implementation of the first through fifth embodiments.

[0059] In a possible design, the communication device includes a processor and memory. The memory may store computer programs or instructions necessary to implement the functions of the first through fifth embodiments. The processor may execute the computer programs or instructions stored in memory. When a computer program or instruction is executed, the communication device is configured to implement the method in any possible design or implementation of the first through fifth embodiments.

[0060] In a possible design, the communication device includes a processor and interface circuitry. The processor communicates with another device via the interface circuitry and is configured to perform the method in any possible design or implementation from the first to the fifth embodiment.

[0061] In a sixth aspect, it may be understood that the processor may be implemented in hardware or in software. When the processor is implemented in hardware, it may be a logic circuit, an integrated circuit, etc. When the processor is implemented in software, it may be a general-purpose processor and be implemented by reading software code stored in memory. In addition, there may be one or more processors and one or more memories. The memory may be integrated with the processor, or the memory and processor may be located separately. In a particular implementation process, the memory and processor may be integrated on a single chip, or they may be located on different chips. The type of memory and the way in which the memory and processor are located are not limited to the embodiments of this application.

[0062] According to the seventh aspect, the present application provides a communication system. The communication system may include a terminal and a network device. The terminal is configured to perform the method according to the first aspect, and the network device is configured to perform the method according to the second aspect. Alternatively, the terminal is configured to perform the method according to the third aspect, and the network device is configured to perform the method according to the fourth aspect.

[0063] According to the eighth aspect, the present application provides a computer-readable storage medium. The computer storage medium stores computer-readable instructions. When a computer reads and executes a computer-readable instruction, the computer is configured to execute a method in any possible design from the first to the fifth aspects.

[0064] According to the ninth aspect, the present application provides a computer program product. When a computer reads and executes the computer program product, the computer is configured to perform the method in any possible design from the first to the fifth aspects.

[0065] According to the tenth aspect, the present application provides a chip, the chip including a processor, the processor being coupled to memory and configured to read and execute software programs stored in memory to implement a method in any possible design from the first to the fifth aspects.

[0066] These or other aspects of this application are more clearly and easily understood in the following description of embodiments. [Brief explanation of the drawing]

[0067] [Figure 1] This is a diagram of a communication system to which the embodiments of this application can be applied. [Figure 2A] This is a diagram of a CU-DU split architecture according to one embodiment of the present application. [Figure 2B] This is a diagram of another CU-DU split architecture according to one embodiment of the present application. [Figure 3] This is a diagram of a timing advance according to one embodiment of the present application. [Figure 4] This is a diagram showing the downlink timing according to one embodiment of this application. [Figure 5] This figure shows how to determine the timing interval (TA) based on the downlink timing difference, according to one embodiment of this application. [Figure 6] This is a schematic flowchart corresponding to the communication method according to Embodiment 1 of this application. [Figure 7] This is a schematic flowchart corresponding to the communication method according to Embodiment 2 of this application. [Figure 8] This is a schematic flowchart corresponding to the communication method according to Embodiment 3 of this application. [Figure 9] This is a schematic flowchart corresponding to the communication method according to Embodiment 4 of this application. [Figure 10] A possible exemplary block diagram of a device according to one embodiment of this application. [Figure 11] This is a diagram showing the structure of a network device according to one embodiment of this application. [Figure 12] This is a diagram showing the structure of a terminal according to one embodiment of this application. [Modes for carrying out the invention]

[0068] The technical solutions in the embodiments of this application will be described clearly and completely below with reference to the accompanying drawings of the embodiments. The technical solutions in the embodiments of this application may be applied to various communication systems, such as universal mobile telecommunications systems (UMTS), wireless local area networks (WLAN), wireless fidelity (Wi-Fi) systems, 4th generation (4G) mobile communication systems, such as long-term evolution (LTE) systems, 5th generation (5G) mobile communication systems, such as new radio (NR) systems, and future advanced communication systems, such as 6th generation (6G) mobile communication systems.

[0069] All aspects, embodiments, or features are presented in this application by describing systems that may include multiple devices, components, modules, etc. It should be appreciated and understood that each system may include other devices, components, modules, etc., and / or may not include all of the devices, components, modules, etc. described with reference to the accompanying drawings. In addition, combinations of these solutions may be used.

[0070] Furthermore, in embodiments of this application, terms such as “example” and “for example” are used to provide examples, illustrations, or explanations. Any embodiment or design scheme described as “example” in this application should not be described as being more preferable or having more advantages than another embodiment or design scheme. More precisely, the term “example” is used to present a concept in a particular way. In embodiments of this application, “of,” “corresponding, relevant,” and “corresponding” may be used interchangeably. Note that the meanings expressed by the terms are consistent unless differences are emphasized.

[0071] The network architectures and service scenarios described in the embodiments of this application are intended to more clearly illustrate the technical solutions in the embodiments of this application and do not constitute limitations on the technical solutions provided in the embodiments of this application. Those skilled in the art will know that, with the evolution of network architectures and the emergence of new service scenarios, the technical solutions provided in the embodiments of this application are also applicable to similar technical challenges.

[0072] To facilitate understanding of the embodiments of this application, the communication system shown in Figure 1 is first used as an example to illustrate in detail a communication system applicable to the embodiments of this application. As shown in Figure 1, the communication system 10 includes one or more network devices 20 and one or more terminals 30. The interface between the network device and the terminal may be a Uu interface (or referred to as an air interface), and data transmission may be performed between the network device 20 and the terminal 30 by using air interface resources. For example, the terminal may be located in the communication coverage area of ​​one or more cells of the network device, and there may be one or more cells (i.e., serving cells of the terminal) that provide services to the terminal. If there are multiple serving cells of the terminal, the terminal may operate with one or more transmission techniques such as Carrier Aggregation (CA), Dual Connectivity (DC), Coordinated Multipoint (CoMP) transmission, and Multiple Transmission and Reception Point (mTRP).

[0073] (1) Terminal

[0074] A terminal may be a terminal that accesses a communication system and has wireless transceiver functionality, or it may be a chip or chip system that can be located within the terminal. A terminal may also be referred to as user equipment (UE), terminal device, user equipment, access terminal, subscriber unit, subscriber station, mobile station (MS), remote station, remote terminal, mobile device, user terminal, terminal unit, terminal station, terminal equipment, wireless communication device, user agent, or user equipment.

[0075] For example, the terminal in the embodiments of this application may be a mobile phone, a personal digital assistant (PDA) computer, a laptop computer, a tablet computer (Pad), an unmanned aerial vehicle, a computer with wireless transceiver functionality, a machine-type communication (MTC) terminal, a virtual reality (VR) terminal, an augmented reality (AR) terminal, an Internet of Things (IOT) terminal, a wireless terminal for industrial control, a wireless terminal for self-driving, a wireless terminal for remote medical care, a wireless terminal for a smart grid, a wireless terminal for transportation safety, a wireless terminal for a smart city, a wireless terminal for a smart home (e.g., a game console, a smart TV, a smart speaker, a smart refrigerator, or fitness equipment), an in-vehicle terminal, or an RSU with terminal functionality.

[0076] (2) Network equipment

[0077] A network device is a device located on the network side of a communication system that has wireless transceiver functionality, or a chip or chip system that may be located within the device.

[0078] For example, the network device in the embodiments of this application may be an access point (AP) in a Wi-Fi system, such as a home gateway, router, server, switch, or bridge. The network device may also be a base station, evolved NodeB (eNB), radio network controller (RNC), base station controller (BSC), base transceiver station (BTS), home base station, baseband unit (BBU), radio relay node, radio backhaul node, transmission and reception point (TRP), or transmission point (TP), etc. Alternatively, the network device may be a next-generation NodeB (gNB) in a 5G system, network nodes forming a gNB, such as a central unit (CU), distributed unit (DU), or roadside unit (RSU) with base station functionality. Alternatively, the network device may be various forms of satellites or base stations in the future.

[0079] (3) Communication between terminals and network devices

[0080] Communication between a terminal and a network device is performed according to a specific protocol layer structure. For example, the control plane protocol layer structure may include the radio resource control (RRC) layer, the packet data convergence protocol (PDCP) layer, the radio link control (RLC) layer, the medium access control (MAC) layer, and the physical (PHY) layer. The user plane protocol layer structure may include the PDCP layer, the RLC layer, the MAC layer, and the physical layer. In possible implementations, the service data adaptation protocol (SDAP) layer may be included on top of the PDCP layer. The SDAP layer, PDCP layer, RLC layer, MAC layer, and physical layer may be collectively referred to as the access layer. For a detailed explanation of the protocol layers mentioned above, please refer to the relevant technical specifications of the 3rd generation partnership project (3GPP).

[0081] Using downlink data transmission as an example, downlink data can be encapsulated correspondingly at each layer of the network device. Data received by a specific layer from a higher layer is considered a service data unit (SDU) for that layer, and becomes a protocol data unit (PDU) through layer encapsulation, which is then sent to the next layer. For example, data received from the SDAP layer by a PDCP layer entity may be called a PDCP SDU. After encapsulating the PDCP SDU, the PDCP layer entity retrieves the PDCP PDU and sends it to the RLC layer. A PDCP PDU received from the PDCP layer by an RLC layer entity may be called an RLC SDU. After encapsulating the RLC SDU, the RLC layer entity retrieves the RLC PDU and sends it to the MAC layer.

[0082] From the terminal's perspective, after the terminal's physical layer receives a transport block from a network device, the transport block can be sequentially submitted from the physical layer to higher layers, where it can be decapsulated accordingly. In other words, the processes performed at each layer of the terminal may be the reverse processes of the processes performed at each layer of the network device.

[0083] (4) CU-DU Split Architecture

[0084] For example, in some possible network structures, a network device may include one or more central units (CUs) and one or more distributed units (DUs). Multiple DUs may be centrally controlled by a single CU. Such an architecture may be called a CU-DU split architecture. For example, the interface between a CU and a DU may be called an F1 interface. The control plane (CP) interface may be an F1-C interface, and the user plane (UP) interface may be an F1-U interface.

[0085] The processing functions of the CU and DU may be partitioned based on the protocol layers of the wireless network. For example, as shown in Figure 2A, the functions of the PDCP layer and the protocol layers above the PDCP layer are configured on the CU, and the functions of the protocol layers below the PDCP layer (e.g., the RLC layer and MAC layer) are configured on the DU. The partitioning of the processing functions of the CU and DU based on protocol layers is merely an example, and it should be understood that the partitioning may be performed in alternative ways. For example, the functions of the protocol layers above the RLC layer are configured on the CU, and the functions of the RLC layer and the protocol layers below the RLC layer are configured on the DU. In another example, the partitioning may be performed in a way that the CU or DU has the functions of more protocol layers. In yet another example, the partitioning may be performed in a way that the CU or DU has the processing functions of some of the protocol layers. This is not limited to the embodiments of this application.

[0086] Furthermore, the functionality of a CU may be implemented by the same entity or by different entities. For example, the functionality of a CU may be further divided. Specifically, the control plane and the user plane may be separated and implemented by different entities, namely, control plane CU entities (i.e., CU-CP entities) and user plane CU entities (i.e., CU-UP entities). The CU-CP entities and CU-UP entities may be coupled to a DU to jointly complete the functionality of the RAN device. The interface between the CU-CP entities and the CU-UP entities may be an E1 interface, the interface between the CU-CP entities and the DU may be an F1-C interface, and the interface between the CU-UP entities and the DU may be an F1-U interface. One DU and one CU-UP may be connected to one CU-CP. Under the control of the same CU-CP, one DU may be connected to multiple CU-UPs, and one CU-UP may be connected to multiple DUs. Under the coordination of multiple CU-CPs, one CU-UP may, as an alternative, be connected to multiple coordinated CU-CPs. This increases the flexibility of the CU-CP. Figure 2B is a diagram of the air interface protocol stack distribution. As shown in Figure 2B, for both the user plane and the control plane, the air interface protocol stack may be such that the RLC, MAC, and PHY are on the DU, and the PDCP and higher protocol layers are on the CU.

[0087] In the architectures shown in Figures 2A and 2B, it should be noted that signaling generated by the CU may be transmitted to the terminal via the DU, or signaling generated by the terminal may be transmitted to the CU via the DU. The DU may transmit the signaling transparently to the terminal or CU by directly encapsulating the signaling at the protocol layer without parsing the signaling. In the following embodiments, when such transmission of signaling between the DU and the terminal is performed, the transmission or reception of signaling by the DU includes such scenarios. For example, signaling at the RRC or PDCP layer is processed so that it is ultimately physical layer data and transmitted to the terminal, or converted from received physical layer data. In this architecture, signaling at the RRC or PDCP layer may also be considered to be transmitted by the DU, or transmitted by the DU and radio frequency equipment.

[0088] It should be understood that the number of network devices and terminals included in the communication system is not limited to the embodiments of this application. In addition to network devices and terminals, the communication system may further include other devices or network elements, such as core network devices or relay devices. This is not limited to the embodiments of this application.

[0089] The following sections will first describe the relevant technical features of the embodiments of this application. These descriptions are intended to make the embodiments of this application easier to understand, but should not be considered as limitations on the scope of protection described in the claims of this application.

[0090] 1. Cell handover

[0091] Cell handover is a crucial feature in communication systems and is primarily triggered by the movement of a terminal while it is in an RRC connection state. For example, suppose a terminal's serving cell is cell 1. If the terminal moves to cell 2 and the signal quality in cell 2 is higher than that of cell 1, a cell handover may be triggered, and the terminal is handed over from cell 1 to cell 2. The basic purpose of cell handover is to hand over the terminal to an adjacent cell with good signal quality before the serving cell's signal quality becomes unsustainable for communication, thereby providing continuous and uninterrupted communication service and effectively preventing call drops caused by serving cell degradation.

[0092] Cell handovers can include a first type of cell handover and a second type of cell handover. A first type of cell handover is a cell handover implemented based on Layer 1 / Layer 2 and may be referred to as a Layer 1 / Layer 2 handover or Layer 1 / Layer 2 triggered mobility (L1 / L2 triggered mobility, LTM). A second type of cell handover is a cell handover implemented based on Layer 3 and may be referred to as a Layer 3 handover (L3 handover). Layer 1 may be the physical layer, Layer 2 may be one or more of the MAC layer, RLC layer, PDCP layer, and SDAP layer, and Layer 3 may be the RRC layer. Note that a Layer 1 / Layer 2 handover may also be understood as a Layer 1 handover and / or a Layer 2 handover. When the relationship is "and", the operations related to the handover process are primarily performed by Layer 1 and Layer 2 as a whole. When the relationship is "or," the actions associated with the handover process are primarily performed by Layer 1 or Layer 2. Since Layers 1 and 2 are lower than the RRC layer (Layer 3) in the protocol stack, Layer 1 / Layer 2 handovers may also be called low-layer handovers, bottom-layer handovers, or lower-layer handovers. The names of specific handover techniques are not limited in this application.

[0093] Regarding Layer 3 handover, in a CU-DU split architecture, the CU receives the terminal's measurement results (transmitted to the CU by the DU), decides whether to initiate a handover based on the results, and if it decides to initiate a handover, sends a handover command to the DU, which then sends a handover command to the terminal. This process involves communication interaction between the CU and DU (i.e., interaction on the F1 interface), with a maximum transmission delay of approximately 3ms to 10ms on the F1 interface. As a result, a specific handover delay occurs.

[0094] However, the Layer 1 / Layer 2 handover decision is delivered from the CU to the DU. Specifically, the DU decides whether to initiate a handover (LTM cell switch) based on the terminal's measurement results and sends a handover command directly to the terminal so that F1 interaction can be effectively reduced and handover delay can be reduced.

[0095] 2. Cell Handover Scenario

[0096] As described above, a network device may include one or more CUs and one or more DUs. For example, a network device may include one CU and multiple DUs. Multiple DUs may be centrally controlled by a CU, and each of the multiple DUs may include one or more cells. It should be understood that "a DU includes one or more cells" can also be described as "a DU manages or controls one or more cells," "one or more cells of a DU," or "one or more cells belonging to a DU."

[0097] When a terminal is handed over between different cells, several specific handover scenarios may exist. For example, handover scenarios can be classified based on the spatial relationship between the source cell and the target cell. This spatial relationship may be whether the source cell and the target cell belong to the same CU and / or the same DU. Three possible handover scenarios, namely Scenario 1 to Scenario 3, are described herein.

[0098] Scenario 1: A terminal is handed over from one cell in a DU to another cell in the same DU. In other words, the source and target cells of the terminal belong to the same DU. The cell handover corresponding to Scenario 1 is an intra-DU handover.

[0099] Scenario 2: A terminal is handed over from a cell in DU1 controlled by a CU to a cell in DU2 controlled by the same CU. In this case, DU1 may be called the source DU, and DU2 may be called the target DU. In other words, the source and target cells of a terminal belong to different DUs controlled by the same CU. The cell handover corresponding to Scenario 2 is an inter-DU handover.

[0100] Scenario 3: A terminal is handed over from a cell in DU1 controlled by CU1 to a cell in DU3 controlled by CU2. In this case, CU1 may be called the source CU, and CU2 may be called the target CU. In other words, the source and target cells of the terminal belong to different DUs controlled by different CUs. The cell handover corresponding to Scenario 2 is an inter-CU handover.

[0101] For example, intra-DU handovers and inter-DU handovers may be implemented through Layer 1 / Layer 2 handovers, and inter-CU handovers may be implemented through Layer 3 handovers. In embodiments of this application, Layer 1 / Layer 2 handovers are used as examples for the following description.

[0102] 3. Timing Advance

[0103] Timing advance (i.e., TA) is used for uplink synchronization between a terminal and a network device. TA may be a cell-level parameter, with each cell having a corresponding TA. For example, a terminal may transmit an uplink signal to a network device by using the TA of cell 1.

[0104] Terminals 1 and 2 are used as examples. As shown in Figure 3(a), signal propagation between the network device (e.g., DU) and the terminal is delayed, and the interval between the start of the network device transmitting the downlink signal and the start of terminal 1 receiving the downlink signal is Tp1, and the interval between the start of the network device transmitting the downlink signal and the start of terminal 2 receiving the downlink signal is Tp2. If terminal 1 does not perform uplink timing adjustment and transmits an uplink signal to the network device using the start of terminal 1 receiving the downlink signal as the reference, the interval between the start of terminal 1 transmitting the uplink signal and the start of the network device receiving the uplink signal is also Tp1. Therefore, for terminal 1, there is a time difference of 2Tp1 between the start of the network device transmitting the downlink signal and the start of the network device receiving the uplink signal. Similarly, for terminal 2, there is a time difference of 2Tp2 between the start of the network device transmitting the downlink signal and the start of the network device receiving the uplink signal.

[0105] Because the distance between terminals and network devices may differ, uplink signals from different terminals may arrive at the network device at different times. If the offset between the arrival times of uplink signals from different terminals is greater than the cyclic prefix (CP) of the orthogonal frequency division multiplexing (OFDM) symbol, the different terminals will interfere with each other. To resolve the issue of interference between terminals, terminals need to perform timing adjustments to implement uplink synchronization. As shown in Figure 3(b), terminal 1 advances the start time when terminal 1 transmits its uplink signal by 2Tp1, i.e., the TA used by terminal 1 is 2Tp1, and terminal 2 advances the start time when terminal 2 transmits its uplink signal by 2Tp2, i.e., the TA used by terminal 2 is 2Tp2. In this case, the network device receives the uplink signals from terminal 1 and terminal 2 simultaneously so that the issue of mutual interference between terminals can be resolved.

[0106] 4. Downlink Timing

[0107] Downlink timing is used for downlink synchronization between a terminal and network devices. Downlink timing can be a cell-level parameter, and each cell has a corresponding downlink timing. Downlink timing is defined as the point in time when the first path (in terms of time) of the corresponding downlink frame used by the terminal to determine the downlink timing is received from the reference cell by the UE's antenna. For further details, please refer to existing protocols.

[0108] As an example, a 5G communication system is used. A slot may be used as the basic unit of time for uplink and downlink transmission, specifically, data transmission is performed once in each slot. The slot start time for network devices is fixed, and uplink and downlink slots are aligned. In the case of downlink transmission, a propagation delay occurs when the downlink signal transmitted by the network device reaches the terminal side via air propagation. For example, the signal propagation delay between DU1, to which cell A belongs, and the terminal is Tp1, and the signal propagation delay between DU2, to which cell B belongs, and the terminal is Tp2.

[0109] As shown in Figure 4, downlink signal 1 transmitted by DU1 at the downlink slot boundary of cell A arrives at the terminal after Tp1, and the terminal determines downlink slot boundary 1 based on the received downlink signal 1. There is a time difference of Tp1 between the downlink slot boundary of cell A and downlink slot boundary 1 determined by the terminal. Downlink signal 2 transmitted by DU2 at the downlink slot boundary of cell B arrives at the terminal after Tp2, and the terminal determines downlink slot boundary 2 based on the received downlink signal 2. There is a time difference of Tp2 between the downlink slot boundary of cell B and downlink slot boundary 2 determined by the terminal. Furthermore, the time difference between the downlink slot boundary determined by the terminal for cell A (e.g., downlink slot boundary 1) and the downlink slot boundary determined by the terminal for cell B (e.g., downlink slot boundary 2) is the downlink timing difference between cell A and cell B.

[0110] It can also be understood that downlink slot boundaries can be replaced by downlink frame boundaries.

[0111] 5. Measurement gap

[0112] Terminal measurements can be classified into intra-frequency measurements and inter-frequency measurements. Intra-frequency measurements refer to situations where the cell in which the terminal is currently located and the cell being measured are within the same frequency range, while inter-frequency measurements refer to situations where the cell in which the terminal is currently located and the cell being measured are not within the same frequency range.

[0113] If a terminal needs to perform inter-frequency measurements (including inter-RAT measurements), a simple approach is to install two radio frequency receivers in the terminal, one measuring the frequency of the current cell and the other the frequency of the cell under measurement, respectively. However, this increases costs and causes problems with mutual interference between different frequencies. Therefore, the measurement gap method has now been proposed, specifically by reserving a portion of time (called the measurement gap). During the measurement gap, the terminal can perform an inter-frequency measurement by switching the frequency of the radio frequency receiver to the frequency of the cell under measurement without transmitting or receiving data. At the end of the measurement gap, the terminal switches the frequency of the radio frequency receiver back to the frequency of the current cell.

[0114] For example, the measurement gap may be configured by a network device for a terminal. For example, the network device may configure the terminal's measurement gap parameters so that the terminal determines the measurement gap based on the measurement gap parameters and performs inter-frequency measurements within the measurement gap.

[0115] Based on the description of the relevant technical features described above, an implementation in which a terminal determines the TA of a target cell is considered in the embodiments of this application.

[0116] Generally, for cell handover, a terminal can acquire the target cell's TA by transmitting a random access preamble or an uplink reference signal. The uplink reference signal may be, for example, a sounding reference signal (SRS). Two possible methods, namely Method 1 and Method 2, are described below.

[0117] Method 1: After receiving a handover command, the terminal may send a random access preamble or uplink reference signal to the network device within the target cell, which in turn can measure the target cell's TA based on the random access preamble or uplink reference signal and send a timing advance command to the terminal using a random access response message. Correspondingly, the terminal may obtain the target cell's TA based on the timing advance command.

[0118] Method 2: Before performing a cell handover (or before receiving a handover command), the terminal may send a random access preamble or uplink reference signal to the network device for one or more candidate cells to acquire and store the TA of one or more candidate cells. For example, one or more candidate cells include cell 1, and the terminal may send a random access preamble or uplink reference signal to the network device within cell 1, based on a set periodicity, to acquire and store the TA of cell 1. The TA of cell 1 stored by the terminal may be the most recently acquired TA of cell 1. Furthermore, after the terminal receives a handover command, for example, if the handover command indicates that cell 1 is the target cell, the terminal may access the target cell based on the stored TA of cell 1, and it is not necessary to send a random access preamble or uplink reference signal to the network device to acquire the TA of cell 1.

[0119] However, in the aforementioned Method 1, when the terminal initiates random access to the target cell, the terminal's communication is interrupted and can only be restored after the terminal has completed its random access to the target cell. This results in a long interruption delay. In the aforementioned Method 2, after receiving a handover command, the terminal can access the target cell based on the previously acquired TA. However, the terminal needs to initiate a large number of random accesses within the candidate cell. This results in high overhead on communication resources.

[0120] Based on this, in embodiments of the present application, the TA of the target cell is determined based on the downlink timing difference so that random access is reduced and interruption delays are reduced during cell handover. In embodiments of the present application, "determining the TA based on the downlink timing difference" may also be called "UE-based TA measurement".

[0121] For example, the target cell is cell A. (1) If the downlink slot boundary between cell A and cell B (cell B may be the source cell of the terminal) is synchronized, determining the TA of cell A based on the downlink timing difference, as shown in Figure 5, can be implemented by using the following equation 1.

[0122] TA_targetcell=TA_sourcecell+2*(Tnew-Told) Formula 1 TA_targetcell represents the TA of cell A, TA_sourcecell represents the TA of cell B, Tnew-Told is the difference in downlink timing between cell A and cell B, Tnew is the downlink timing of cell A, and Told is the downlink timing of cell B.

[0123] As an alternative to the aforementioned Equation 1, TA_targetcell=TA_sourcecell-2*(Told-Tnew) It can be changed.

[0124] (2) If the downlink slot boundaries of cell A and cell B (where cell B may be the source cell of the terminal) are asynchronous, determining the TA of cell A based on the downlink timing difference can be implemented by using the following equation 2.

[0125] TA_targetcell=TA_sourcecell+2*(Tnew-Told)+offset Formula 2 The offset represents the offset between the downlink slot boundary between cell A and cell B.

[0126] In addition, whether the downlink slot boundaries of cell A and cell B are synchronized, and the offset between the downlink slot boundaries of cell A and cell B, may be indicated to the terminal by the network device. Specific implementations are not limited.

[0127] The communication methods provided in the embodiments of this application will be described in detail below with reference to Embodiments 1 to 4. Embodiment 1

[0128] Figure 6 is a schematic flowchart corresponding to the communication method according to Embodiment 1 of this application. As shown in Figure 6, the communication method includes the following steps.

[0129] S601: The network device transmits first information to the terminal, which indicates that the first reference signal of the first cell and the second reference signal of the second cell belong to the same group, and accordingly, the terminal receives the first information.

[0130] (1) Explain the group.

[0131] For example, a network device may determine the group to which reference signals from multiple cells belong and transmit a first piece of information to a terminal. This first piece of information may be understood as group information. There are several specific implementations in which a network device transmits this first piece of information to a terminal. For example, a network device may transmit this first piece of information to a terminal by using RRC messages or Layer 1 / Layer 2 messages.

[0132] The following examples use cases where multiple cells contain the first, second, third, and fourth cells.

[0133] For example, if a network device determines that the first reference signal of the first cell and the second reference signal of the second cell belong to the same group, and that the third reference signal of the third cell and the fourth reference signal of the fourth cell belong to the same group, then the first information may indicate that the first reference signal of the first cell and the second reference signal of the second cell belong to the same group (referred to as Group 1), and that the third reference signal of the third cell and the fourth reference signal of the fourth cell belong to the same group (referred to as Group 2). For example, the first information may include parameters corresponding to Group 1 and parameters corresponding to Group 2. Let's take the parameters corresponding to Group 1 as an example. The parameters corresponding to Group 1 may include the index of the first reference signal and the index of the second reference signal, the identifier of the first cell and the identifier of the second cell, or the configuration information of the first reference signal and the configuration information of the second reference signal.

[0134] In another example, if a network device determines that the first reference signal, the second reference signal, the third reference signal, and the fourth reference signal belong to the same group, the first information may indicate that the first reference signal, the second reference signal, the third reference signal, and the fourth reference signal belong to the same group.

[0135] The following can be understood: #1 Using a first cell among several cells as an example, the first reference signal of the first cell is used to measure the downlink timing of the first cell (or to implement UE-based TA measurement). The first reference signal may be a specific reference signal configured by the network device for the first cell, and this specific reference signal is dedicated to measuring the downlink timing of the first cell. Alternatively, the first reference signal may reuse another reference signal configured by the network device for the cell. That is, in addition to the downlink timing of the first cell, the first reference signal may be used to measure other possible information. Furthermore, the first cell and other cells may share the first reference signal. In other words, the first reference signal may be used to measure the downlink timing of the first cell, or it may be used to measure the downlink timing of another cell.

[0136] #2 A group may include reference signals from two cells, or from more cells. The number of reference signals included in a group is not limited to this embodiment of the present application.

[0137] #3 Multiple cells may include the terminal's current serving cell (if the terminal has multiple serving cells, multiple cells may include all of the terminal's current serving cells or only some of the serving cells) and candidate cells. All of the multiple cells may be cells managed by a network device, and the terminal may perform Layer 1 / Layer 2 handovers between the multiple cells. In other words, multiple cells include cells used by the terminal to perform Layer 1 / Layer 2 handovers.

[0138] #4 Network devices may also transmit other possible information to a terminal. For example, a network device may transmit configuration information of reference signals for multiple cells to a terminal so that the terminal receives a reference signal based on the configuration information of the reference signals for multiple cells in order to measure downlink timing. The configuration information of reference signals for multiple cells and the first information may be carried in the same message or in different messages. This is not particularly limited. A first reference signal is used as an example. The configuration information of the first reference signal may include frequency information and / or subcarrier information corresponding to the first reference signal, and may further include other possible information. For example, if the first reference signal is a reference signal shared by a first cell and another cell (e.g., a third cell), then, for example, the first reference signal may be scrambled by using the physical cell identifier of the third cell, and the configuration information of the first reference signal may further include the identifier of the third cell.

[0139] (2) We will describe an implementation in which network devices determine the group.

[0140] For example, there are several specific implementations in which a network device determines the group to which the reference signals of multiple cells belong. In possible implementations, a terminal may transmit terminal capability information to the network device, and as a result, the network device may determine the group to which the reference signals of multiple cells belong based on the terminal capability information and the configuration information of the reference signals of multiple cells.

[0141] Case 1: The terminal capability information is the first capability information, which indicates that the terminal supports determining the TA based on an in-frequency reference signal. In this case, the network device may determine which reference signals are in-frequency reference signals based on the configuration information of the first to fourth reference signals, classify the in-frequency reference signals into the same group, and classify the inter-frequency reference signals into different groups. For example, the first and second reference signals are in-frequency reference signals, the third and fourth reference signals are in-frequency reference signals, and the first (or second) and third (or fourth) reference signals are inter-frequency reference signals. In this case, the network device may classify the first and second reference signals into one group and the third and fourth reference signals into another group.

[0142] Let us use a first reference signal and a second reference signal as examples. For the first and second reference signals to be in-frequency reference signals, this may include the first and second reference signals corresponding to the same frequency or the first and second reference signals corresponding to the same subcarrier interval. For the first and second reference signals to be inter-frequency reference signals, this may include the first and second reference signals corresponding to different frequencies or the first and second reference signals corresponding to different subcarrier intervals. For example, if the first and second reference signals correspond to the same frequency and the first and second reference signals correspond to the same subcarrier interval, then the first and second reference signals are in-frequency reference signals; or if the first and second reference signals correspond to different frequencies or different subcarrier intervals, then the first and second reference signals are inter-frequency reference signals.

[0143] Case 2: The terminal capability information is second capability information, which indicates that the terminal supports determining the TA based on an inter-frequency reference signal. Optionally, the second capability information further indicates at least one combination of bands supported by the terminal, each combination of bands containing at least one band. For example, at least one combination of bands contains band combination 1 and band combination 2, where band combination 1 contains band 1, and band combination 2 contains bands 2 and 3. In this case, the network device may determine which reference signals correspond to frequencies in the same combination of bands based on the configuration information of the first to fourth reference signals, and classify these reference signals into the same group. For example, the frequency corresponding to the first reference signal is in band 1, the frequency corresponding to the second reference signal is in band 1, the frequency corresponding to the third reference signal is in band 2, and the frequency corresponding to the fourth reference signal is in band 3. That is, the frequencies corresponding to the first and second reference signals are in band combination 1, and the frequencies corresponding to the third and fourth reference signals are in band combination 2. In this case, the network device may classify the first and second reference signals into one group, and the third and fourth reference signals into another group.

[0144] In addition, in this example, the frequencies corresponding to the first and second reference signals are both within Band 1. Therefore, the first and second reference signals may be intra-frequency reference signals or inter-frequency reference signals. In other words, when a terminal supports determining a TA based on inter-frequency reference signals, the network device may classify intra-frequency reference signals into the same group, or inter-frequency reference signals into the same group.

[0145] (3) Describe the capabilities of the terminal.

[0146] As described above, the terminal may support determining the TA based on an in-frequency reference signal or based on an inter-frequency reference signal. For example, the terminal supports determining the TA based on an in-frequency reference signal. If the first and second reference signals are in-frequency reference signals, the terminal may obtain the downlink timing of a first cell through measurements based on the first reference signal, obtain the downlink timing of a second cell through measurements based on the second reference signal, and obtain the downlink timing difference between the first and second cells. Furthermore, the terminal may determine the TA of a second cell based on the TA of the first cell and the downlink timing difference between the first and second cells, or determine the TA of a first cell based on the TA of a second cell and the downlink timing difference between the first and second cells.

[0147] Different terminals may have different capabilities. For example, some terminals support determining the time axis (TA) based on an intra-frequency reference signal, while others support determining the TA based on an inter-frequency reference signal. There are several reasons why different terminals may have different capabilities. This is not limited to this embodiment of the present application. For example, in a 5G communication system, the length of time units (e.g., symbols or slots) corresponding to different subcarrier intervals may differ. For example, when the subcarrier interval of a frequency domain resource is 15 kHz, the corresponding symbol length is 1 / 15 kHz = 66.7 μs and the slot length is 1 ms, or when the subcarrier interval of a frequency domain resource is 30 kHz, the corresponding symbol length is 1 / 30 kHz and the slot length is 0.5 ms. When the first and second reference signals are inter-frequency reference signals, the accuracy of the downlink timing of the first cell obtained by the terminal through measurements based on the first reference signal may differ from the accuracy of the downlink timing of the second cell obtained by the terminal through measurements based on the second reference signal. Therefore, the calculated downlink timing difference between the first and second cells is not sufficiently accurate. As a result, the determined TA is inaccurate. Thus, if the terminal has sufficient processing power, it can calculate a relatively accurate downlink timing difference even if the first and second reference signals are inter-frequency reference signals, and the terminal can support determining the TA based on the inter-frequency reference signals. If the terminal's processing power is limited, when the first and second reference signals are inter-frequency reference signals, the calculated downlink timing difference may not be sufficiently accurate, and the terminal can support determining the TA based on the intra-frequency reference signal, but it does not support determining the TA based on the inter-frequency reference signal.

[0148] S602: The network device sends second information to the terminal, which indicates that the first cell is the target cell for the handover.

[0149] For example, a network device may send a Layer 1 / Layer 2 handover command (i.e., an LTM command) to a terminal, and the handover command includes second information. For example, the second information is a target cell field in the handover command, which carries the identifier of the first cell. The second and first information may be carried in the same message, for example, both may be carried in the handover command. Alternatively, the second and first information may be carried in different messages. For example, the second information may be carried in the handover command, and the first information in the RRC message.

[0150] Furthermore, the network device may optionally transmit a third piece of information to the terminal, indicating that it will access the target cell in a random access-less manner. "Random access-less" may also be referred to as "random access channel (RACH)-skip" or "not transmitting random access signals." For example, if, based on group information, it is determined that the target cell and the serving cell (e.g., source cell) to which the terminal is being handed over belong to the same group, the network device may transmit the third piece of information to the terminal; otherwise, the network device may not transmit the third piece of information. Of course, after determining that the target cell and the serving cell (e.g., source cell) to which the terminal is being handed over belong to the same group, the network device may further determine whether to transmit the third piece of information based on several other possible reasons.

[0151] For example, the third piece of information and the second piece of information may be carried in the same message, or they may both be carried in a handover command, or they may be carried in different messages.

[0152] S603: The terminal accesses the target cell using the target cell's TA (Terminal Adapter).

[0153] The target cell's Time Attention (TA) is determined by the terminal based on the TA of the second cell and the downlink timing difference between the first and second cells. The second cell may be the serving cell (e.g., the source cell) to which the terminal is handed over. After the terminal accesses the target cell using the target cell's TA, the terminal's serving cell changes from the second cell to the first cell.

[0154] For example, after determining, based on the first information, that the first reference signal and the second reference signal belong to the same group, the terminal may measure the downlink timing of the first cell based on the first reference signal and the downlink timing of the second cell based on the second reference signal, and determine the TA of the first cell based on the TA of the second cell and the downlink timing difference between the first and second cells. Subsequently, after receiving the second (and third) information, the terminal may directly access the first cell based on the determined TA of the first cell. In this way, handover efficiency can be improved. Of course, the terminal may, alternatively, measure the downlink timing of the first cell and the downlink timing of the second cell after receiving the second (and third) information (or determine the TA of the first cell based on the TA of the second cell and the downlink timing difference between the first and second cells). In other words, the time it takes for the terminal to measure the downlink timing of the first cell and the downlink timing of the second cell, and the time it takes for the terminal to determine the TA of the first cell based on the downlink timing difference, may depend on the internal implementation of the terminal. This is not limited to this embodiment of the present application.

[0155] Furthermore, optionally, if a network device configures a measurement gap for the terminal, the terminal may not use the measurement gap and may continuously monitor the target cell before receiving feedback from the target cell. After the terminal receives feedback from the target cell, the terminal may use the measurement gap to measure another cell or frequency.

[0156] In another possible embodiment, if a network device transmits first and second information to a terminal but not third information (or if the terminal receives first and second information from the network device but not third information), it can be understood that the terminal may determine the target cell's TA in a manner consistent with the prior art (e.g., method 1 or method 2 described above) and access the target cell. In other words, when a terminal accesses a target cell, whether or not to use the target cell's TA determined based on the downlink timing difference may be controlled by the network device, and as a result, the network device can flexibly manage and control the terminal.

[0157] The above is illustrated by using an example in which a terminal is handed over from a second cell to a first cell. The group information in this embodiment of the present application is also applicable to a sequential handover scenario. For example, the group information indicates that a first reference signal through a fourth reference signal belong to the same group. After the terminal is handed over from the second cell to the first cell, the network device may send a Layer 1 / Layer 2 handover command to the terminal, which includes second and third information, the second information indicating that the third cell is the target cell for the handover, and the third information indicating that the target cell will be accessed in a random access-less manner. Correspondingly, after determining that the first and third cells belong to the same group based on the group information, the terminal may determine the TA of the first cell and the TA of the third cell based on the downlink timing difference between the first and third cells, and access the third cell using the TA of the third cell.

[0158] According to the method described above, the network device indicates to the terminal that the first and second reference signals of the first cell belong to the same group by using the first information, and as a result the terminal can determine the TA of the target cell based on the TA of the second cell, the first reference signal, and the second reference signal, without needing to obtain the TA of the target cell via random access. This reduces random access during cell handover and further reduces interruption delay. Furthermore, the group information of the reference signals can be determined by the network device based on the terminal's capability information, resulting in more appropriate group information of the reference signals, which helps to improve the accuracy of the determined TA of the target cell. Embodiment 2

[0159] Figure 7 is a schematic flowchart corresponding to the communication method according to Embodiment 2 of this application. As shown in Figure 7, the communication method includes the following steps.

[0160] S701: The network device transmits a fourth piece of information to the terminal, which indicates that the TA of the first cell is determined based on the downlink timing difference.

[0161] For example, the fourth piece of information may indicate that the TA of at least one candidate cell is determined based on the downlink timing difference, and that at least one candidate cell includes the first cell. For example, the fourth piece of information may include the identifier of at least one candidate cell. For example, the fourth piece of information indicates that the TA of the first cell is determined based on the downlink timing difference. It should be understood that the fourth piece of information only indicates that the TA of the first cell can be determined based on the downlink timing difference, and does not indicate that the TA of the first cell is determined based on the downlink timing difference between a particular cell and the first cell. In this case, determining the TA of the first cell based on the downlink timing difference between a particular cell and the first cell may be determined in particular by the terminal. For example, after receiving the fourth piece of information, the terminal may determine the TA of the first cell based on the downlink timing difference between the terminal's serving cell and the first cell (if the terminal has multiple serving cells, the terminal may select one of the serving cells, for example, the second cell), and then calculate the TA of the first cell based on the TA of the second cell and the downlink timing difference between the first cell and the second cell.

[0162] Optionally, the network device may further transmit a sixth piece of information to the terminal (in other words, the network device may transmit the fourth and sixth pieces of information to the terminal, and the fourth and sixth pieces of information may be the same information as an alternative). The sixth piece of information indicates that the TA of the first cell is determined based on the downlink timing difference between the first cell and the second cell. For example, the sixth piece of information includes the identifier of the second cell. In other words, determining the TA of the first cell based on the downlink timing difference between a particular cell and the first cell can be indicated to the terminal by the network device using the sixth piece of information. In other words, the network device indicates by using the fourth piece of information that the terminal can determine the TA of the first cell based on the downlink timing difference, and by using the sixth piece of information that the terminal determines the TA of the first cell based on the downlink timing difference between a particular cell and the first cell. In this way, after receiving the fourth and sixth pieces of information, the terminal may calculate the TA of the first cell based on the TA of the second cell and the downlink timing difference between the first cell and the second cell.

[0163] The fourth and sixth pieces of information may be carried in the same message, for example, both in a Layer 1 / Layer 2 handover command, or they may be carried in different messages.

[0164] For example, a network device may determine candidate cells whose TA can be determined based on downlink timing differences, based on terminal capability information and configuration information of reference signals of multiple cells, and transmit fourth (and sixth) information to the terminal. For example, if the multiple cells include a first cell, a second cell, a third cell, and a fourth cell, the second cell is the serving cell, and the first, third, and fourth cells are all candidate cells, and the network device determines whether the TA of the first, third, and fourth cells can be determined based on downlink timing differences.

[0165] Case 1: The terminal capability information is the first capability information, which indicates that the terminal supports determining the TA based on an in-frequency reference signal. In this case, the network device may determine which reference signals and the second reference signal are in-frequency reference signals based on the configuration information of the first to fourth reference signals. For example, the first and second reference signals are in-frequency reference signals, the third and second reference signals are inter-frequency reference signals, and the fourth and second reference signals are inter-frequency reference signals. In this case, the network device may determine that the TA of the first cell can be determined based on the downlink timing difference, but the TAs of the third and fourth cells cannot be determined based on the downlink timing difference. In this case, the fourth information indicates that the TA of the first cell is determined based on the downlink timing difference.

[0166] Furthermore, this example is illustrated by using a case where the TA of only one candidate cell (i.e., the first cell) can be determined based on the downlink timing difference. In another possible example, if the TAs of multiple candidate cells can all be determined based on the downlink timing difference, the fourth piece of information may indicate that the TAs of multiple candidate cells are determined based on the downlink timing difference, or that the fourth piece of information is determined based on the downlink timing difference for some of the candidate cells. The portion of the candidate cells can be selected by the network device from among multiple candidate cells. For example, if the network device decides to hand over a terminal to the first cell, the network device may use the fourth piece of information to instruct the terminal to determine the TA of the first cell based on the downlink timing difference.

[0167] Case 2: The terminal capability information is second capability information, which indicates that the terminal supports determining the TA based on an inter-frequency reference signal. Optionally, the second capability information further indicates at least one combination of bands supported by the terminal, each combination of bands containing at least one band. In this case, the network device may determine, based on the configuration information of the first to fourth reference signals, which reference signal corresponds to a frequency in the same combination of bands as the frequency corresponding to the second reference signal. For example, if the frequencies corresponding to the first and second reference signals are in the same combination of bands, the network device may determine that the TA of the first cell can be determined based on the downlink timing difference, and the fourth information may indicate that the TA of the first cell is determined based on the downlink timing difference.

[0168] In another possible implementation, it can be understood that the network device may first determine the group to which the reference signals of multiple cells belong, based on the capability information of the terminal and the configuration information of the reference signals of multiple cells; then, based on the group to which the multiple cells belong, determine candidate cells to which the TA can be determined based on the downlink timing difference; and transmit the fourth (and sixth) information to the terminal. For a specific implementation of determining the group to which multiple cells belong, please refer to Embodiment 1. Details will not be explained again here.

[0169] S702: The network device transmits a fifth piece of information to the terminal, which indicates that the first cell is the target cell for the handover.

[0170] For example, a network device may send a Layer 1 / Layer 2 handover command to a terminal, and the handover command may include a fifth piece of information. For example, the fifth piece of information may be the target cell field of the handover command, which carries the identifier of the first cell. Furthermore, if the fourth piece of information indicates multiple candidate cells, the target cell indicated by the fifth piece of information may be one of those candidate cells.

[0171] The fifth and fourth pieces of information (and the sixth piece of information) may be carried in the same message, for example, both in a handover command, or they may be carried in different messages. When the fifth and fourth pieces of information (and the sixth piece of information) are carried in different messages, the fourth piece of information (and the sixth piece of information) may be carried in a UE-based TA measurement command, the fifth piece of information may be carried in a handover command, and the UE-based TA measurement command may be sent before the handover command. In this way, after receiving the UE-based TA measurement command, the terminal may determine the TA of the first cell based on the downlink timing difference, and as a result, after receiving the handover command, the terminal may directly access the first cell based on the determined TA of the first cell (i.e., perform S703). This reduces the handover delay and improves the efficiency of the handover.

[0172] For example, a network device may send UE-based TA measurement commands to a terminal by using the serving cell's physical downlink control channel (PDCCH) or MAC control element (CE).

[0173] S703: The terminal accesses the target cell using the target cell's TA.

[0174] For example, the TA of the target cell may be determined by the terminal based on the TA of the second cell and the downlink timing difference between the first and second cells after the terminal receives the fourth (and sixth) piece of information.

[0175] The difference between Embodiment 2 and Embodiment 1 is that in Embodiment 1, the network device transmits group information to the terminal, so the terminal can pre-determine the TA of candidate cells based on the group information and downlink timing difference. In this way, the terminal accesses the target cell in a timely manner after receiving the handover command. In Embodiment 2, the network device does not need to transmit group information to the terminal. Instead, the network device may use additional information to determine the TA of target cells based on downlink timing difference before (i.e., slightly before) transmitting the handover command to the terminal, or at the time of transmitting the handover command to the terminal, thereby improving the flexibility of the network device's instructions.

[0176] In Embodiments 1 and 2, the implementation process of the embodiments of this application will be described in terms of communication between a network device and a terminal. The network device may include a CU and one or more DUs. Accordingly, with reference to Embodiment 3, the implementation process of the embodiments of this application will be described below in terms of communication between the CU, DU, and terminal. Embodiment 3

[0177] Embodiment 3 describes possible interaction procedures between the CU, DU, and terminals based on Embodiment 1.

[0178] Figure 8 is a schematic flowchart corresponding to the communication method according to Embodiment 3 of this application. As shown in Figure 8, the method includes the following steps.

[0179] S801:CU sends request information to the DU to which multiple cells belong, and the request information is used to request configuration information of the reference signals of the multiple cells.

[0180] S802: A DU to which multiple cells belong transmits configuration information of the reference signals of the multiple cells to the CU.

[0181] For example, multiple cells may belong to the same DU, or they may belong to different DUs.

[0182] For example, the multiple cells include a first cell, a second cell, a third cell, and a fourth cell. The second cell is the terminal's current serving cell, the first and second cells belong to DU1, and the third and fourth cells belong to DU2. In this case, the CU may send first request information and second request information to DU1, the first request information being used to request configuration information for the first reference signal of the first cell, and the second request information being used to request configuration information for the second reference signal of the second cell. For example, the CU may send a UEcontext modification request message 1 to DU1, which includes first request information and second request information. The first request information is used as an example. The first request information may include the identifier of the first cell and a UE-based TA measurement request. A UE-based TA measurement request indicates that the first request information is a request for configuring a UE-based TA measurement of a first cell (i.e., a request for configuration information of a first reference signal). Correspondingly, DU1 may send the configuration information of the first reference signal for the first cell and the configuration information of the second reference signal for the second cell to the CU. For example, DU1 may send the configuration information of the first reference signal and the configuration information of the second reference signal to the CU using a UE context modification response message.

[0183] Furthermore, the CU may send third and fourth request information to the DU2, the third request information being used to request configuration information for the third reference signal of the third cell, and the fourth request information being used to request configuration information for the fourth reference signal of the fourth cell. For example, the CU may send a UEcontext setup request message to the DU2, which includes the third and fourth request information. Correspondingly, the DU2 may send configuration information for the third reference signal of the third cell and the fourth reference signal of the fourth cell to the CU. For example, the DU2 may send configuration information for the third and fourth reference signals to the CU using a context setup response message.

[0184] Below, we will describe two possible implementations by referring to Implementation 1 and Implementation 2.

[0185] (1) Implementation 1 The CU transmits first request information and second request information to the DU1, the first request information including first frequency information used to request the configuration of a first reference signal for a first cell based on the first frequency information, and the second request information including second frequency information used to request the configuration of a second reference signal for a second cell based on the second frequency information. Correspondingly, after receiving the first request information and second request information, the DU1 may configure a first reference signal for a first cell based on the first frequency information (for example, by configuring frequency information corresponding to the first reference signal as the first frequency information), and may configure a second reference signal for a second cell based on the second frequency information (for example, by configuring frequency information corresponding to the second reference signal as the second frequency information).

[0186] In other words, CU may propose to DU1 that frequency information corresponding to a first reference signal be configured as first frequency information, and DU1 may or may not accept the proposal. In this embodiment of the present application, an example in which DU1 accepts the proposal is used for illustrative purposes. In another implementation, DU1 may, alternatively, reject the proposal. In this case, DU1 may configure the frequency information corresponding to the first reference signal as other frequency information, or may not return the configuration information of the first reference signal to CU.

[0187] In addition, the CU further transmits third and fourth request information to the DU2, the third request information including third frequency information used to request the configuration of a third reference signal for the third cell based on the third frequency information, and the fourth request information including fourth frequency information used to request the configuration of a fourth reference signal for the fourth cell based on the fourth frequency information. For further details, please refer to the descriptions of the first and second request information.

[0188] The first through fourth frequency information can be determined by the CU based on the terminal capability information. The following provides an explanation with reference to Case 1a and Case 2a. For example, a terminal may report its capability information to the CU (e.g., using an RRC message), and the CU then transmits the terminal capability information to the DU to which multiple cells belong.

[0189] Case 1a: The terminal capability information is first capability information, which indicates that the terminal supports determining the TA based on an in-frequency reference signal. In this case, the CU may configure the first to fourth frequency information to be as similar as possible based on the first capability information, that is, the frequency information corresponding to the first to fourth reference signals may be as similar as possible (or the first to fourth reference signals may be as in-frequency reference signals as possible), and as a result the terminal can then determine the TA based on the downlink timing difference.

[0190] Case 2a: The terminal capability information is second capability information, which indicates that the terminal supports determining the TA based on an inter-frequency reference signal. Optionally, the second capability information further indicates at least one combination of bands, each combination of bands containing at least one band. In this case, the CU may be configured, based on the second capability information, such that the first through fourth frequency information are in the same band combination as much as possible, i.e., the frequencies corresponding to the first through fourth reference signals are in the same band combination as much as possible, so that the terminal can then determine the TA based on the downlink timing difference.

[0191] For the first through fourth request information, the first request information is used as an example, and it can be understood that the above explanation is provided by using an example in which the first request information includes first frequency information. In another possible implementation, the first request information may include first subcarrier information (in other words, the first request information is used to request that the first reference signal of the first cell be constructed based on the first subcarrier information), or the first request information may include first frequency information and first subcarrier information (in other words, the first request information is used to request that the first reference signal of the first cell be constructed based on the first frequency information and first subcarrier information). If the first through fourth request information includes first through fourth subcarrier information, the first through fourth subcarrier information may be determined by the CU based on terminal capability information. For further details, see the explanation, “The CU determines the first through fourth frequency information based on terminal capability information.”

[0192] (2) Implementation 2 The difference between Implementation 2 and Implementation 1 is that in Implementation 2, the requested information may not carry frequency information (or may not carry subcarrier information, or may not carry either frequency information or subcarrier information). In this case, DU1 and DU2 each determine the frequency information corresponding to the reference signal.

[0193] For example, after receiving the first request information and the second request information, DU1 may configure the frequencies corresponding to the first reference signal and the second reference signal based on the terminal capability information, and after receiving the third request information and the fourth request information, DU2 may configure the frequency corresponding to the third reference signal and the third reference signal based on the terminal capability information.

[0194] Case 1b: The terminal capability information is first capability information, which indicates that the terminal supports determining the TA based on an in-frequency reference signal. In this case, DU1 may be configured, based on the first capability information, such that the first and second reference signals correspond to the same frequency as much as possible (e.g., both correspond to frequency 1), and as a result, the terminal can then determine the TA based on the downlink timing difference. Similarly, DU2 may be configured, based on the first capability information, such that the third and fourth reference signals correspond to the same frequency as much as possible (e.g., both correspond to frequency 2).

[0195] It can be understood that frequency 1 configured by DU1 may differ from frequency 2 configured by DU2, since DU1 may not learn that the frequency configured by DU2 for the third and fourth reference signals is frequency 2, and DU2 may not learn that the frequency configured by DU1 for the first and second reference signals is frequency 1. If the second cell is the serving cell of the terminal and the third cell is the target cell for the handover, the TA of the third cell cannot be determined based on the downlink timing difference because the third cell and the second cell are inter-frequency reference signals (in other words, the TA of the third cell cannot be determined based on the TA of the second cell and the downlink timing difference between the second and third cells). Therefore, if multiple cells belong to the same DU, the CU may not need to provide a proposal, but the DU configures the reference signals of the multiple cells based on the terminal capability information. If multiple cells belong to multiple DUs, the CU may provide suggestions for the multiple DUs, and as a result, the multiple DUs can configure the reference signals of the multiple cells as in-frequency reference signals as much as possible.

[0196] Case 2b: The terminal capability information is second capability information, which indicates that the terminal supports determining the TA based on an inter-frequency reference signal. Optionally, the second capability information further indicates at least one combination of bands, each combination of bands containing at least one other band. In this case, DU1 may be configured, based on the second capability information, such that the frequencies corresponding to the first and second reference signals fall within the same combination of bands as much as possible. Similarly, DU2 may be configured, based on the first capability information, such that the frequencies corresponding to the third and fourth reference signals fall within the same combination of bands as much as possible. See Case 1b for details. Further details will not be explained again here.

[0197] S803:CU determines the group to which the reference signals of multiple cells belong, based on the configuration information of the reference signals of multiple cells.

[0198] For example, the CU may determine the group to which the reference signals of multiple cells belong, based on the terminal capability information and the configuration information of the reference signals of the multiple cells. See Embodiment 1 for details.

[0199] S804:CU transmits configuration information and group information of reference signals for multiple cells to the terminal. The group information indicates the group status of the reference signals for multiple cells, and the terminal receives the group information accordingly.

[0200] For example, the configuration and group information of the reference signals of multiple cells may be carried in the same message (e.g., the same RRC message) or in different messages. For example, CU may send UE context correction request message 2 to DU1, which includes an RRC reconfiguration message, and the RRC reconfiguration message includes the configuration and group information of the reference signals of multiple cells. Correspondingly, after receiving UE context correction request message 2, DU1 may send the RRC reconfiguration message contained therein to the terminal.

[0201] It may be understood that the UE context modification request message in this embodiment of the present application may also be replaced by another possible message, such as a downlink RRC transmission message (DL RRC message).

[0202] For example, after receiving group information, the terminal may determine the TA of a candidate cell based on the downlink timing difference. For example, the candidate cell includes a first cell. If the group information indicates that the first cell and a second cell (the second cell being the terminal's current serving cell) belong to the same group, the terminal may determine the TA of the first cell based on the TA of the second cell and the downlink timing difference between the first and second cells.

[0203] S805:CU sends group information to DU1 (i.e., the DU to which the terminal's serving cell belongs).

[0204] Here, the CU can send group information to the DU1 via the F1 interface.

[0205] S806:DU1 transmits second and third pieces of information to the terminal based on the group information. The second piece of information indicates that the first cell is the target cell for the handover, and the third piece of information indicates that the target cell will be accessed using a random access-less method.

[0206] For example, the terminal may report measurement reports for multiple candidate cells (e.g., bottom layer measurement reports) to DU1 so that DU1 can select one cell from the multiple candidate cells as a target cell based on the measurement reports of the multiple candidate cells and send second information to the terminal. In addition, if, based on group information, it is determined that the target cell and the serving cell (e.g., source cell) form to which the terminal is handed over belongs to the same group, DU1 may send third information to the terminal.

[0207] S807: The terminal accesses the target cell using the target cell's TA.

[0208] In this specification, after receiving the second and third information, the terminal is a first cell determined based on the downlink timing difference, and can access the first cell by using a TA.

[0209] The following can be understood: (1) The aforementioned group information is applicable to sequential handover scenarios. For example, when a terminal is handed over from a second cell to a first cell, the CU or source DU (i.e., the DU to which the second cell belongs) may send group information to the target DU (i.e., the DU to which the first cell belongs). In this way, when a terminal is handed over from a first cell to another cell, the DU to which the first cell belongs may, based on the group information, decide whether to indicate access to the target cell in a random access-less manner. It should be understood that if the source DU and target DU are the same DU (i.e., an intra-DU handover is performed), it is not necessary to send group information to the target DU.

[0210] (2) The above is illustrated using an example in which the CU determines the group information. In another embodiment, the DU may, as an alternative, determine the group information. For example, if multiple cells belong to the same DU (i.e., DU1), DU1 may, as an alternative, determine the group information. For specific implementations, please refer to the description of Embodiment 3. Embodiment 4

[0211] Embodiment 4 describes possible interaction procedures between the CU, DU, and terminals based on Embodiment 2.

[0212] Figure 9 is a schematic flowchart corresponding to the communication method according to Embodiment 4 of this application. As shown in Figure 9, the method includes the following steps.

[0213] S901:CU sends request information to the DU to which multiple cells belong, and the request information is used to request configuration information of the reference signals of the multiple cells.

[0214] S902: A DU (Dependency Unit) to which multiple cells belong transmits configuration information of the reference signals of the multiple cells to the CU (Control Unit).

[0215] For example, for specific implementations of S901 and S902, please refer to S801 and S802.

[0216] S903:CU determines the group to which the reference signals of multiple cells belong, based on the configuration information of the reference signals of multiple cells.

[0217] For example, the CU may determine the group to which the reference signals of multiple cells belong, based on the terminal capability information and the configuration information of the reference signals of the multiple cells. See Embodiment 1 for details.

[0218] S904:CU transmits configuration information of reference signals for multiple cells to the terminal.

[0219] S905:CU sends group information to DU1 (i.e., the DU to which the terminal's serving cell belongs).

[0220] S906:DU1 transmits a fourth piece of information to the terminal based on the group information, indicating that the TA of the first cell is determined based on the downlink timing difference.

[0221] S907:DU1 sends a fifth piece of information to the terminal, which indicates that the first cell is the target cell for the handover.

[0222] S908: The terminal accesses the target cell using the target cell's TA.

[0223] For example, steps S903 to S905 are optional. In other words, the CU may not determine group information and may transmit group information to the DU1. For example, when multiple cells belong to the same DU (i.e., DU1), the CU does not need to determine group information and transmit group information to the DU1. In this case, the DU1 may transmit fourth information to the terminal based on the terminal capability information and the configuration information of the reference signals of the multiple cells, or the DU1 may determine group information based on the terminal capability information and the configuration information of the reference signals of the multiple cells and transmit fourth information to the terminal based on the group information.

[0224] The difference between Embodiment 4 and Embodiment 3 is that in Embodiment 3, the network side transmits group information to the terminal, whereas in Embodiment 4, the network side does not need to transmit group information to the terminal. For details other than the differences, Embodiment 3 and Embodiment 4 can be cross-referenced.

[0225] In addition, with respect to Embodiments 3 and 4, it is used as an example that the CU determines group information. After determining the group information, the CU may further modify the group information based on actual requirements, or add a new cell to an existing group. For example, if it is determined that the first reference signal of a first cell and the second reference signal of a second cell belong to the same group (e.g., Group 1), and it is necessary to add the reference signal of a new cell (e.g., a fifth cell) to the group, the CU may send fifth request information to the DU to which the fifth cell belongs to request configuration information for the reference signal of the fifth cell, and the fifth request information may include first frequency information and / or first subcarrier information. Correspondingly, if the DU accepts the CU's proposal, the DU may configure the reference signal of the fifth cell based on the first frequency information and / or first subcarrier information and send the configuration information for the reference signal of the fifth cell to the CU so that the CU can add the reference signal of the fifth cell to Group 1.

[0226] The following can be understood regarding the embodiments described above.

[0227] (1) The step numbers in each flowchart described in the embodiments above are merely examples of procedure execution and do not constitute a restriction on the step execution sequence. In the embodiments of this application, there is no strict execution order between steps that do not have a chronological order dependency on each other. Not all steps shown in the flowchart are mandatory steps. Some steps may be removed from the flowchart based on actual requirements, or other possible steps may be added to the flowchart based on actual requirements.

[0228] (2) The message names used in the embodiments described above are merely examples, and message names are not limited to the embodiments of this application. The above is illustrated by using Layer 1 / Layer 2 handovers (e.g., intra-DU handovers and inter-DU handovers) as examples. The solutions in the embodiments of this application may also be extended to other scenarios. For example, the solution may be extended to Layer 3 handovers (e.g., inter-CUs). In this case, the multiple cells may belong to different network devices, or the DUs to which the multiple cells belong (e.g., source DU and target DU) may be controlled by different CUs. In another example, the solution may be extended to an mTRP, where one cell in the mTRP may correspond to multiple physical cell identifiers (PCIs). Thus, candidate cells may be replaced by PCIs, and LTM commands may be replaced by transmission configuration indication state (TCI state) activation commands.

[0229] The above describes the solutions provided in the embodiments of this application, primarily from the perspective of device interaction. It can be understood that, in order to implement the aforementioned functions, each device may include a corresponding hardware structure and / or software module for performing each function. Those skilled in the art will readily recognize, in combination with the example units and algorithmic steps described in the embodiments disclosed herein, that the embodiments of this application may be implemented in hardware, or in combination of hardware and computer software. Whether a function is performed by hardware or by hardware driven by computer software depends on the design constraints of the particular application and the technical solution. Those skilled in the art may use different methods to implement the functions described for each specific application, but such implementations should not be considered to exceed the scope of this application.

[0230] In embodiments of this application, the division into functional units may be performed on terminals and network devices based on the examples of the methods described above. For example, the division into each functional unit may be based on each corresponding function, or two or more functions may be integrated into one unit. The integrated unit may be implemented in hardware form or in the form of a software functional unit.

[0231] When an integrated unit is used, Figure 10 is a block diagram of a possible example of the apparatus according to one embodiment of the present application. As shown in Figure 10, the apparatus 1000 may include a processing unit 1002 and a communication unit 1003. The processing unit 1002 is configured to control and manage the actions of the apparatus 1000. The communication unit 1003 is configured to support communication between the apparatus 1000 and another device. Optionally, the communication unit 1003, also called a transceiver unit, may include a receiving unit and / or a transmitting unit configured to perform receiving and transmitting operations, respectively. The apparatus 1000 may further include a storage unit 1001 configured to store the program code and / or data of the apparatus 1000.

[0232] (1) The device 1000 may be a terminal as described in the embodiments above. The processing unit 1002 may support the device 1000 when performing actions of the terminal in the example of the method described above. Alternatively, the processing unit 1002 may mainly perform internal actions of the terminal in the example of the method, and the communication unit 1003 may support communication between the device 1000 and another device.

[0233] For example, in one embodiment, the communication unit 1003 is configured to receive first information indicating that the first reference signal of the first cell and the second reference signal of the second cell belong to the same group, receive second information indicating that the first cell is the target cell for handover, access the target cell using the timing advance TA of the target cell, and determine the TA of the target cell based on the TA of the second cell, the first reference signal, and the second reference signal.

[0234] In a possible design, the first information includes parameters corresponding to the group, and the parameters include the index of the first reference signal and the index of the second reference signal, the identifier of the first cell and the identifier of the second cell, or the configuration information of the first reference signal and the configuration information of the second reference signal.

[0235] In a possible design, the communication unit 1003 is further configured to transmit first capability information, which indicates that the terminal supports determining the TA based on an in-frequency reference signal, where the first and second reference signals are in-frequency reference signals.

[0236] In a possible design, the first and second reference signals being in-frequency reference signals includes the first and second reference signals corresponding to the same frequency or the first and second reference signals corresponding to the same subcarrier interval.

[0237] In a possible design, the communication unit 1003 is further configured to transmit a second capability information, which indicates that the terminal supports determining the TA based on an inter-frequency reference signal, where the first and second reference signals are inter-frequency reference signals.

[0238] In a possible design, the second capability information further indicates at least one combination of bands, each combination of bands containing at least one band, and the frequencies corresponding to the first and second reference signals are within the same combination of bands.

[0239] In possible designs, the first and second reference signals being interfrequency reference signals includes the first and second reference signals corresponding to different frequencies or to different subcarrier intervals.

[0240] In a possible design, the communication unit 1003 is further configured to receive third information from a network device, indicating that the third information is to access the target cell in a random access-less manner.

[0241] (2) The device 1000 may be a network device as described in the embodiments above. The processing unit 1002 may support the device 1000 when performing actions of the network device in the example of the method described above. Alternatively, the processing unit 1002 may mainly perform internal actions of the network device in the example of the method, and the communication unit 1003 may support communication between the device 1000 and another device.

[0242] For example, in one embodiment, the communication unit 1003 is configured to transmit first information indicating that the first reference signal of the first cell and the second reference signal of the second cell belong to the same group, and to transmit second information indicating that the first cell is the target cell for handover, and the first and second reference signals are used to determine the TA of the target cell.

[0243] In a possible design, the first information includes parameters corresponding to the group, and the parameters include the index of the first reference signal and the index of the second reference signal, the identifier of the first cell and the identifier of the second cell, or the configuration information of the first reference signal and the configuration information of the second reference signal.

[0244] In a possible design, the communication unit 1003 is further configured to receive first capability information, the first capability information indicating that the terminal supports determining the TA based on an in-frequency reference signal, transmit first information based on the first capability information, configuration information of the first reference signal, and configuration information of the second reference signal, the configuration information of the first reference signal and the configuration information of the second reference signal indicating that the first reference signal and the second reference signal are in-frequency reference signals.

[0245] In a possible design, the first and second reference signals being in-frequency reference signals includes the first and second reference signals corresponding to the same frequency or the first and second reference signals corresponding to the same subcarrier interval.

[0246] In a possible design, the communication unit 1003 is further configured to receive second capability information, the second capability information indicating that the terminal supports determining the TA based on an inter-frequency reference signal, transmit first information based on the second capability information, configuration information of the first reference signal, and configuration information of the second reference signal, the configuration information of the first reference signal and the configuration information of the second reference signal indicating that the first reference signal and the second reference signal are inter-frequency reference signals.

[0247] In a possible design, the second capability information further indicates at least one combination of bands, each combination of bands containing at least one band, and the frequencies corresponding to the first and second reference signals are within the same combination of bands.

[0248] In possible designs, the first and second reference signals being interfrequency reference signals includes the first and second reference signals corresponding to different frequencies or to different subcarrier intervals.

[0249] In a possible design, the communication unit 1003 is further configured to transmit third information to the terminal, which indicates access to the target cell in a random access-less manner.

[0250] It should be understood that the division of units in the aforementioned device is merely a logical functional division. In actual implementation, all or some of the units may be integrated into a single physical entity or physically separated. In addition, all units within the device may be implemented in the form of software invoked by a processing element, or in the form of hardware, or some units may be implemented in the form of software invoked by a processing element, and some units may be implemented in the form of hardware. For example, each unit may be a separately located processing element, or it may be integrated into the device's chip for implementation. In addition, each unit may, alternatively, be stored in memory in the form of a program invoked by the device's processing element to perform the unit's function. In addition, all or some of the units may be integrated as a whole or implemented independently. The processing element in this specification may also be referred to as a processor, and may be an integrated circuit having signal processing capabilities. In the implementation process, the aforementioned methods or the operation of the aforementioned units may be implemented by using hardware integrated logic circuits within a processor element, or in the form of a processing element invoking software.

[0251] In the example, any one unit of the aforementioned device may be one or more integrated circuits configured to implement, for example, one or more application-specific integrated circuits (ASICs), one or more digital signal processors (DSPs), one or more field programmable gate arrays (FPGAs), or a combination of at least two of these types of integrated circuits. In another example, if a unit in the device may be implemented in a way that the processing element schedules a program, the processing element may be a processor, for example, a general-purpose central processing unit (CPU), or another processor that can invoke a program. In yet another example, the module may be integrated as a whole and implemented in the form of a system-on-a-chip (SoC).

[0252] The aforementioned unit configured to receive is an interface circuit of the device and is configured to receive signals from another device. For example, if the device is implemented in the form of a chip, the receiving unit is an interface circuit of the chip and is configured to receive signals from another chip or device. The aforementioned unit configured to transmit is an interface circuit of the device and is configured to transmit signals to another device. For example, if the device is implemented in the form of a chip, the transmitting unit is an interface circuit of the chip and is configured to transmit signals to another chip or device.

[0253] Figure 11 is a diagram of the structure of a network device according to one embodiment of the present application. The network device (or base station) may be used in the communication system shown in Figure 1 to perform the functions of the network device in the embodiments of the method described above. As shown in Figure 11, the network device 110 may include one or more DU1101 and one or more CU1102. The DU1101 may include at least one antenna 11011, at least one radio frequency unit 11012, at least one processor 11013, and at least one memory 11014. The DU1101 portion is mainly configured to receive and transmit radio frequency signals, perform conversion between radio frequency signals and baseband signals, and perform partial baseband processing. The CU1102 may include at least one processor 11022 and at least one memory 11021.

[0254] The CU1102 portion is primarily configured to perform baseband processing, control network devices, and so on. The DU1101 and CU1102 may be physically located together or physically located separately, i.e., a distributed base station. The CU1102 is the control center for network devices, and may also be called a processing unit, and is primarily configured to complete baseband processing functions. For example, in embodiments of the method described above, the CU1102 may be configured to control network devices to perform operational procedures related to network devices.

[0255] Furthermore, the network device 110 may optionally include one or more radio frequency units, one or more DUs, and one or more CUs. The DU may include at least one processor 11013 and at least one memory 11014, the radio frequency unit may include at least one antenna 11011 and at least one radio frequency unit 11012, and the CU may include at least one processor 11022 and at least one memory 11021.

[0256] For example, CU1102 may include one or more boards. Multiple boards may jointly support a radio access network with a single access indication (e.g., a 5G network), or each may support a radio access network with a different access standard (e.g., an LTE network, a 5G network, or another network). Memory 11021 and processor 11022 may serve one or more boards. In other words, the memory and processor may be located on each board. Alternatively, multiple boards may share the same memory and the same processor. In addition, necessary circuitry may be further located on each board. DU1101 may include one or more boards. Multiple boards may jointly support a radio access network with a single access indication (e.g., a 5G network), or each may support a radio access network with a different access standard (e.g., an LTE network, a 5G network, or another network). Memory 11014 and processor 11013 may serve one or more boards. In other words, the memory and processor may be located on each board. Alternatively, multiple boards may share the same memory and the same processor. In addition, any necessary circuitry may be further located on each board.

[0257] The network device shown in Figure 11 can implement all the processes related to the network device in the embodiments of the method described above. The operation and / or function of each module within the network device shown in Figure 11 is intended to implement the corresponding procedure in the embodiments of the method described above. For further details, please refer to the description of the embodiments of the method described above. To avoid repetition, detailed descriptions are appropriately omitted in this specification.

[0258] Figure 12 is a diagram of the structure of a terminal according to one embodiment of the present application. The terminal may be used in the communication system shown in Figure 1 to implement the operation of the terminal in the above-described embodiment. As shown in Figure 12, the terminal includes an antenna 1210, a radio frequency unit 1220, and a signal processing unit 1230. The antenna 1210 is connected to the radio frequency unit 1220. In the downlink direction, the radio frequency unit 1220 receives information transmitted by a network device via the antenna 1210 and transmits the information transmitted by the network device to the signal processing unit 1230 for processing. In the uplink direction, the signal processing unit 1230 processes the terminal information and transmits the processed information to the radio frequency unit 1220, which then processes the terminal information and transmits the processed information to the network device via the antenna 1210.

[0259] The signal processing unit 1230 may include a modem subsystem configured to process data at each communication protocol layer. The signal processing unit 1230 may further include a central processing subsystem configured to implement the operating system's processing and the terminal's application layer. Furthermore, the signal processing unit 1230 may further include other subsystems, such as a multimedia subsystem or a peripheral subsystem. The multimedia subsystem may be configured to control the terminal's camera, screen display, etc., and the peripheral subsystem may be configured to implement connections to other devices. The modem subsystem may be a separately located chip.

[0260] The modem subsystem may include one or more processing elements 1231, for example, a main control CPU and another integrated circuit. In addition, the modem subsystem may further include a storage element 1232 and an interface circuit 1233. The storage element 1232 is configured to store data and programs. However, the program used to perform the method executed by the terminal in the manner described above may not be stored in the storage element 1232 but may be stored in memory outside the modem subsystem and loaded and used by the modem subsystem when needed. The interface circuit 1233 is configured to communicate with another subsystem.

[0261] A modem subsystem can be implemented using a chip. The chip includes at least one processing element and an interface circuit. The processing element is configured to perform steps of any method performed by the terminal. The interface circuit is configured to communicate with another device. In an implementation, a unit in the terminal for implementing the steps of the aforementioned method may be implemented in such a way that the processing element schedules a program. For example, a device used by a terminal includes a processing element and a storage element. The processing element invokes a program stored in the storage element to perform the method performed by the terminal in an embodiment of the aforementioned method. The storage element may be a storage element located on the same chip as the processing element, i.e., an on-chip storage element.

[0262] In another implementation, the program used to execute the method performed by the terminal in the aforementioned method may reside in a storage element located on a different chip from the processing element, i.e., an off-chip storage element. In this case, the processing element calls or loads the program from the off-chip storage element to the on-chip storage element in order to call and execute the method performed by the terminal in the embodiment of the aforementioned method.

[0263] In yet another implementation, the unit within the terminal for implementing the steps of the method described above may be configured as one or more processing elements. These processing elements are located on the modem subsystem. The processing elements herein may be integrated circuits, for example, one or more ASICs, one or more DSPs, one or more FPGAs, or a combination of these types of integrated circuits. These integrated circuits may be integrated as a whole to form a chip.

[0264] The units within the terminal for implementing the steps of the aforementioned method may be integrated as a whole and implemented in the form of an SoC, the SoC chip being configured to implement the aforementioned method. At least one processing element and a storage element may be integrated into the chip, the processing element implementing the aforementioned method executed by the terminal by calling a program stored in the storage element. Alternatively, at least one integrated circuit may be integrated into the chip to implement the aforementioned method executed by the terminal. Alternatively, referring to the aforementioned implementation, the functionality of some units may be implemented in the form of a processing element calling a program, and the functionality of some units may be implemented in the form of an integrated circuit.

[0265] It can be understood that the aforementioned device used in a terminal may include at least one processing element and interface circuitry. The at least one processing element is configured to perform any method performed by the terminal in embodiments of the aforementioned method. The processing element may perform some or all of the steps performed by the terminal in a first manner, i.e., by calling a program stored in a memory element, or in a second manner, i.e., by combining instructions within the processing element with hardware integrated logic circuits. Of course, some or all of the steps performed by the terminal may, alternatively, be performed by combining the first and second manners.

[0266] The processing elements here are the same as those described above and can be implemented using a processor. The function of the processing elements may be the same as the function of the processing unit described in Figure 10. For example, the processing elements may be a general-purpose processor, such as a CPU, or one or more integrated circuits configured to implement the aforementioned methods, such as one or more ASICs, one or more microprocessor DSPs, one or more FPGAs, or a combination of at least two of these types of integrated circuits. The storage elements may be implemented using memory, and the function of the storage elements may be the same as the function of the storage unit described in Figure 10. The storage elements may be a single memory or a collective term for multiple memories.

[0267] The terminal shown in Figure 12 can implement the terminal-related processing in the embodiments of the method described above. The operation and / or functions of the modules within the terminal shown in Figure 12 are intended to implement the corresponding procedures in the embodiments of the method described above. For further details, please refer to the description of the embodiments of the method described above. To avoid repetition, detailed descriptions are appropriately omitted in this specification.

[0268] The terms “system” and “network” may be used interchangeably in embodiments of this application. “At least one” means one or more, and “plural” means two or more. The term “and / or” describes a relationship between related objects and indicates that three relationships may exist. For example, A and / or B means that only A exists, both A and B exist, and only B exists, and A and B may be singular or plural. The letter “ / ” usually indicates an “or” relationship between related objects. “At least one of the following items (parts)” or similar expressions indicate any combination of these items, including any single item (part) or any combination of multiple items (parts). For example, “at least one of A, B, or C” may also be understood to include A, B, C, AB, AC, BC, or ABC, and “at least one of A, B, and C” may be understood to include A, B, C, AB, AC, BC, or ABC. Furthermore, unless otherwise specified, the ordinal numbers such as "first" and "second" in the embodiments of this application are used to distinguish between multiple objects and are not used to limit the sequence, time sequence, priority, or importance of multiple objects.

[0269] Those skilled in the art should understand that embodiments of this application may be provided as methods, systems, or computer program products. Accordingly, this application may take the form of hardware-only embodiments, software-only embodiments, or embodiments of a combination of software and hardware. Furthermore, this application may take the form of a computer program product implemented on one or more computer-available storage media (including, but not limited to, disk memory, optical memory, etc.) containing computer-available program code.

[0270] This application will be described with reference to flowcharts and / or block diagrams of the methods, devices (systems), and computer program products described herein. It should be understood that computer program instructions may be used to implement each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams. These computer program instructions may be provided for a general-purpose computer, a dedicated computer, an embedded processor, or a processor of any other programmable data processing device, so that instructions executed by the processor of the computer or any other programmable data processing device may generate a machine, generating a device for implementing one or more processes in the flowchart and / or one or more blocks in the block diagram.

[0271] These computer program instructions can be stored in computer-readable memory, which can instruct the computer or any other programmable data processing device to operate in a specific manner. As a result, the instructions stored in computer-readable memory generate artifacts, including instruction units. Instruction units implement specific functions in one or more processes in a flowchart and / or in one or more blocks in a block diagram.

[0272] These computer program instructions may, alternatively, be loaded onto a computer or another programmable data processing device, resulting in a series of operations and steps being executed on the computer or another programmable device to produce the processing implemented by the computer. Thus, instructions executed on the computer or another programmable device provide steps for implementing a particular function in one or more processes in a flowchart and / or one or more blocks in a block diagram.

[0273] Clearly, a person skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. This application is intended to cover such modifications and variations to this application, provided that such modifications and variations fall within the scope of the claims of this application and the equivalent art of the claims.

Claims

1. A method of communication, A step of receiving first information, wherein the first information indicates that a first cell and a second cell belong to the same group, and the second cell is the current serving cell of the terminal, A step of receiving second information, wherein the second information indicates that the first cell is a handover target cell. A step of accessing the target cell using the timing advance (TA) of the target cell, wherein the TA of the target cell is determined based on the TA of the second cell and the downlink timing difference between the first cell and the second cell. Methods that include...

2. The first information includes parameters corresponding to the group, The aforementioned parameters are, The index of the first reference signal of the first cell and the index of the second reference signal of the second cell, wherein the first reference signal and the second reference signal are used to determine the downlink timing difference, The identifier of the first cell and the identifier of the second cell, or Configuration information of the first reference signal and configuration information of the second reference signal The method according to claim 1, including the method described in claim 1.

3. The aforementioned method, A step of transmitting first capability information, the first capability information further includes indicating that the terminal supports determining TA based on an in-frequency reference signal, The method according to claim 2, wherein the first reference signal and the second reference signal are in-frequency reference signals.

4. The fact that the first reference signal and the second reference signal are in-frequency reference signals is that The method according to claim 3, wherein the first reference signal and the second reference signal correspond to the same frequency, or the first reference signal and the second reference signal correspond to the same subcarrier interval.

5. The aforementioned method, A step of transmitting second capability information, the second capability information further includes indicating that the terminal supports determining TA based on an inter-frequency reference signal, The method according to claim 2, wherein the first reference signal and the second reference signal are interfrequency reference signals.

6. The second capability information further indicates at least one combination of bands, each combination of bands includes at least one band. The method according to claim 5, wherein the frequencies corresponding to the first reference signal and the second reference signal are within the same band combination.

7. The fact that the first reference signal and the second reference signal are interfrequency reference signals is that The method according to claim 5 or 6, wherein the first reference signal and the second reference signal correspond to different frequencies, or the first reference signal and the second reference signal correspond to different subcarrier intervals.

8. The aforementioned method, The method according to any one of claims 1 to 7, further comprising the step of receiving a third information from the network device, wherein the third information indicates access to the target cell in a random access-less manner.

9. A method of communication, A step of transmitting first information, wherein the first information indicates that a first cell and a second cell belong to the same group, and the second cell is the current serving cell of the terminal, A step of transmitting second information, wherein the second information indicates that the first cell is a handover target cell, and the TA of the second cell and the downlink timing difference between the first cell and the second cell are used to determine the TA of the target cell. Methods that include...

10. The first information includes parameters corresponding to the group, The aforementioned parameters are, The index of the first reference signal of the first cell and the index of the second reference signal of the second cell, wherein the first reference signal and the second reference signal are used to determine the downlink timing difference, The identifier of the first cell and the identifier of the second cell, or Configuration information of the first reference signal and configuration information of the second reference signal The method according to claim 9, including the method described in claim 9.

11. The method further includes the step of receiving first capability information, wherein the first capability information indicates that the terminal supports determining TA based on an in-frequency reference signal. The method according to claim 10, wherein the step of transmitting the first information includes the step of transmitting the first information based on the first capability information, the configuration information of the first reference signal, and the configuration information of the second reference signal, wherein the configuration information of the first reference signal and the configuration information of the second reference signal indicate that the first reference signal and the second reference signal are in-frequency reference signals.

12. The fact that the first reference signal and the second reference signal are in-frequency reference signals is that The method according to claim 11, wherein the first reference signal and the second reference signal correspond to the same frequency, or the first reference signal and the second reference signal correspond to the same subcarrier interval.

13. The method further includes the step of receiving second capability information, wherein the second capability information indicates that the terminal supports determining TA based on an interfrequency reference signal. The method according to claim 10, wherein the step of transmitting the first information includes the step of transmitting the first information based on the second capability information, the configuration information of the first reference signal, and the configuration information of the second reference signal, wherein the configuration information of the first reference signal and the configuration information of the second reference signal indicate that the first reference signal and the second reference signal are interfrequency reference signals.

14. The second capability information further indicates at least one combination of bands, each combination of bands includes at least one band. The method according to claim 13, wherein the frequencies corresponding to the first reference signal and the second reference signal are within the same band combination.

15. The fact that the first reference signal and the second reference signal are interfrequency reference signals is that The method according to claim 13 or 14, wherein the first reference signal and the second reference signal correspond to different frequencies, or the first reference signal and the second reference signal correspond to different subcarrier intervals.

16. The aforementioned method, The method according to any one of claims 9 to 15, further comprising the step of transmitting a third piece of information to the terminal, wherein the third piece of information indicates that access to the target cell is performed in a random access-less manner.

17. A communication device comprising a module configured to perform the method described in any one of claims 1 to 16.

18. A communication device comprising a processor, wherein the processor is coupled to a memory, the memory stores a computer program, and the processor is configured to call the computer program in the memory to cause the communication device to execute the method according to any one of claims 1 to 16.

19. A communication system comprising a network device and a terminal, wherein the terminal is configured to perform the method described in any one of claims 1 to 8, and the network device is configured to perform the method described in any one of claims 9 to 16.

20. A computer-readable storage medium, wherein the storage medium stores a computer program or instruction, and when the computer program or instruction is executed by a computer, the method according to any one of claims 1 to 16 is implemented.

21. A computer program product wherein, when a computer reads and executes the computer program product, the computer is prompted to perform the method according to any one of claims 1 to 16.

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