A communication method and device

Abstract

The present application provides a communication method and apparatus. The method includes: a terminal device receives first indication information, the first indication information includes a common time advance of at least one candidate cell, and the first indication information is used to inform the terminal device that the at least one candidate cell is in a state where switching is allowed; the terminal device sends a random access preamble to a target candidate cell according to the first time advance, the target candidate cell is one of the at least one candidate cell, and the first time advance is the common time advance of the target candidate cell. The method provided by the present application enables the UE to send a preamble more accurately in a switching scenario.

Description

Technical Field

[0001] The present application relates to the field of communications, and more specifically, to a communication method and device. Background Art

[0002] In existing communication technologies, different user equipment (UE) use orthogonal multiple access in time and frequency during uplink transmission, that is, uplink transmissions from different UEs in the same cell do not interfere with each other. In order to ensure the orthogonality of uplink transmission and avoid intra-cell interference, the base station requires that the time when signals from different UEs in the same subframe but different frequency domain resources arrive at the base station is basically aligned. In order to ensure time synchronization on the receiving side (base station side), long term evolution (LTE) / new radio (NR) introduces an uplink timing advance mechanism.

[0003] In order to adapt to non-terrestrial networks (NTN), such as satellite communications, satellite broadcast common timing advance (common TA) can be used to ensure time synchronization on the receiving side. However, the common TA mechanism in the prior art only involves idle UEs, and does not involve the switching process of connected UEs. In addition, since the common TA will continue to change during the flight of the satellite, relying solely on the existing mechanism will make the common TA received by the UE inaccurate. Summary of the invention

[0004] The present application provides a communication method and apparatus, in which a base station sends a common time advance of a candidate cell, so that a terminal device can send a preamble code more accurately in a switching scenario.

[0005] In a first aspect, a communication method is provided, the method comprising: a terminal device receives first indication information, the first indication information comprising a common time advance of at least one candidate cell, the first indication information being used to inform the terminal device that the at least one candidate cell is in a switching allowed state; the terminal device sends a random access preamble code to a target candidate cell according to the first time advance, the target candidate cell is one of the at least one candidate cell, and the first time advance is the common time advance of the target candidate cell.

[0006] By receiving indication information including the common time advance of the candidate cells, the terminal device can send the preamble code more accurately in the switching scenario.

[0007] In combination with the first aspect, in some implementations of the first aspect, the first indication information further includes: a correspondence between multiple common time advances and multiple moments of the at least one candidate cell; the method further includes: the terminal device determines a first time advance corresponding to a first moment according to the correspondence, the first moment being determined by the terminal device according to the time when random access is initiated to a target candidate cell, and the target candidate cell is one of the at least one candidate cell. By receiving indication information including the correspondence between multiple time advances and multiple moments, the terminal device can send a preamble more accurately in a switching scenario, thereby improving the success rate of the base station processing the preamble and increasing the success rate of random access.

[0008] In combination with the first aspect, in certain implementations of the first aspect, the first indication information also includes information about the type of the at least one candidate cell, and the type includes a satellite communication type and / or a private network type.

[0009] By indicating the type of candidate cells in the indication information, the terminal device can select a more suitable cell for access according to the type information of the candidate cells, thereby improving the quality of communication.

[0010] In combination with the first aspect, in certain implementations of the first aspect, the first indication information also includes a first preset condition, and the method also includes: the terminal device determines a target candidate cell that meets the preset condition.

[0011] In combination with the first aspect, in certain implementations of the first aspect, the terminal device receives second indication information sent by the target candidate cell, the second indication information includes a second time advance, the second time advance is a positive number, or the second time advance is a negative number.

[0012] By introducing a positive or negative mechanism into the second time advance, the problem of improper reference point selection in the NTN scenario is adjusted, so that the time advance received by the terminal device is more accurate.

[0013] In combination with the first aspect, in certain implementations of the first aspect, the terminal device sends third indication information to the one target candidate cell based on a third time advance, the third indication information includes a reconfiguration completion message, and the third time advance is the sum of the first time advance and the second time advance.

[0014] In combination with the first aspect, in certain implementations of the first aspect, the corresponding relationships among the multiple candidate cells of the same base station are the same.

[0015] In a second aspect, a communication method is provided, the method comprising: sending first indication information to a terminal device, the first indication information comprising a common time advance of a candidate base station, the first indication information being used to inform the terminal device that at least one candidate cell is in a state where switching is allowed; and receiving a random access preamble code sent by the terminal device according to the first time advance.

[0016] By sending indication information including the common time advance of the candidate cells, the terminal device can send the preamble code more accurately in the switching scenario.

[0017] In combination with the second aspect, in certain implementations of the second aspect, the first indication information also includes: the correspondence between multiple common time advances of the candidate base station and multiple time moments; and receiving a random access preamble code sent by the terminal device according to the first time advance.

[0018] By sending indication information including the correspondence between multiple common time advances and multiple time moments, the terminal device can send the preamble code more accurately in the switching scenario, thereby improving the success rate of the base station processing the preamble code and increasing the success rate of random access.

[0019] In combination with the second aspect, in certain implementations of the second aspect, the first indication information also includes information about the type of the candidate base station, and the type includes a satellite communication type and / or a private network type.

[0020] By indicating the type of candidate cells in the indication information, the terminal device can select a more suitable cell for access according to the type information of the candidate cells, thereby improving the quality of communication.

[0021] In combination with the second aspect, in certain implementations of the second aspect, the first indication information also includes a first preset condition, and the preset condition is used by the terminal device to determine a target candidate base station that meets the preset condition.

[0022] In combination with the second aspect, in certain implementations of the second aspect, second indication information is sent to the terminal device, the second indication information includes a second time advance, the second time advance is determined by the candidate base station based on the random access preamble code, the second time advance is a positive number, or the second time advance is a negative number.

[0023] By introducing a positive or negative mechanism into the second time advance, the problem of improper reference point selection in the NTN scenario is adjusted, so that the time advance received by the terminal device is more accurate.

[0024] According to a third aspect, a communication device is provided, comprising: a receiving module for receiving first indication information, the first indication information comprising a common time advance of at least one candidate cell, the first indication information being used to inform the communication device that the at least one candidate cell is in a switching allowed state; and a sending module for sending a random access preamble code to a target candidate cell according to the first time advance, the target candidate cell being one of the at least one candidate cell, and the first time advance being the common time advance of the target candidate cell.

[0025] By receiving indication information including the common time advance of the candidate cells, the terminal device can send the preamble code more accurately in the switching scenario.

[0026] In combination with the third aspect, in certain implementations of the third aspect, the first indication information also includes: the correspondence between multiple common time advances of the at least one candidate cell and multiple moments; the device also includes: a processing module, used to determine a first time advance corresponding to a first moment according to the correspondence, the first moment being determined by the communication device according to the time for initiating random access to a target candidate cell, and the target candidate cell is one of the at least one candidate cell.

[0027] By receiving indication information including the correspondence between multiple time advances and multiple time moments, the terminal device can send the preamble code more accurately in the switching scenario, thereby improving the success rate of the base station processing the preamble code and increasing the success rate of random access.

[0028] In combination with the third aspect, in certain implementations of the third aspect, the first indication information also includes information on the type of the at least one candidate cell, and the type includes a satellite communication type and / or a private network type.

[0029] By indicating the type of candidate cells in the indication information, the terminal device can select a more suitable cell for access according to the type information of the candidate cells, thereby improving the quality of communication.

[0030] In combination with the third aspect, in certain implementations of the third aspect, the first indication information also includes a first preset condition, and the processing module is further used to determine a target candidate cell that meets the preset condition.

[0031] In combination with the third aspect, in certain implementations of the third aspect, the receiving module is further used to: receive second indication information sent by the target candidate cell, the second indication information including a second time advance, the second time advance is a positive number, or the second time advance is a negative number.

[0032] By introducing a positive or negative mechanism into the second time advance, the problem of improper reference point selection in the NTN scenario is adjusted, so that the time advance received by the terminal device is more accurate.

[0033] In combination with the third aspect, in certain implementations of the third aspect, the sending module is also used to: send third indication information to the one target candidate cell based on a third time advance, the third indication information includes a reconfiguration completion message, and the third time advance is the sum of the first time advance and the second time advance.

[0034] In combination with the third aspect, in certain implementations of the third aspect, the corresponding relationships among the multiple candidate cells of the same base station are the same.

[0035] In a fourth aspect, a communication device is provided, comprising: a sending module for sending first indication information to a terminal device, the first indication information comprising a common time advance of a candidate base station, the first indication information being used to inform the terminal device that at least one candidate cell is in a state where switching is allowed; and a receiving module for receiving a random access preamble code sent by the terminal device according to the first time advance.

[0036] By sending indication information including the common time advance of the candidate cells, the terminal device can send the preamble code more accurately in the switching scenario.

[0037] In combination with the fourth aspect, in certain implementations of the fourth aspect, the first indication information further includes: a correspondence between multiple common time advances of the communication device and multiple time moments.

[0038] By sending indication information including the correspondence between multiple common time advances and multiple time moments, the terminal device can send the preamble code more accurately in the switching scenario, thereby improving the success rate of the base station processing the preamble code and increasing the success rate of random access.

[0039] In combination with the fourth aspect, in certain implementations of the fourth aspect, the first indication information also includes information on the type of the communication device, and the type includes a satellite communication type and / or a private network type.

[0040] By indicating the type of candidate cells in the indication information, the terminal device can select a more suitable cell for access according to the type information of the candidate cells, thereby improving the quality of communication.

[0041] In combination with the fourth aspect, in certain implementations of the fourth aspect, the first indication information also includes a first preset condition, and the preset condition is used by the terminal device to determine a target candidate base station that meets the preset condition.

[0042] In combination with the fourth aspect, in certain implementations of the fourth aspect, the sending module is also used to: send second indication information to the terminal device, the second indication information includes a second time advance, the second time advance is determined by the communication device according to the random access preamble code, the second time advance is a positive number, or the second time advance is a negative number.

[0043] By introducing a positive or negative mechanism into the second time advance, the problem of improper reference point selection in the NTN scenario is adjusted, so that the time advance received by the terminal device is more accurate.

[0044] In a fifth aspect, a communication device is provided, comprising: a receiving module for receiving first indication information sent by at least one candidate base station, the first indication information comprising a common time advance of at least one candidate cell, the first indication information being used to inform the terminal device that the at least one candidate cell is in a state where switching is allowed; and a sending module for sending the first indication information to the terminal device.

[0045] By receiving indication information including the common time advance of the candidate cells, the terminal device can send the preamble code more accurately in the switching scenario, thereby improving the success rate of the base station processing the preamble code and increasing the success rate of random access.

[0046] In combination with the fifth aspect, in certain implementations of the fifth aspect, the first indication information also includes: a correspondence between multiple common time advances and multiple time moments of the at least one candidate cell.

[0047] By receiving indication information including the correspondence between multiple time advances and multiple time moments, the terminal device can send the preamble code more accurately in the switching scenario, thereby improving the success rate of the base station processing the preamble code and increasing the success rate of random access.

[0048] In combination with the fifth aspect, in certain implementations of the fifth aspect, the apparatus further includes: a processing module, configured to integrate multiple first indication information sent by multiple candidate base stations into one first indication information before sending the first indication information to the terminal device.

[0049] In combination with the fifth aspect, in certain implementations of the fifth aspect, the first indication information also includes information on the type of the at least one candidate base station, and the type includes a satellite communication type and / or a private network type.

[0050] By indicating the type of candidate cells in the indication information, the terminal device can select a more suitable cell for access according to the type information of the candidate cells, thereby improving the quality of communication.

[0051] In combination with the fifth aspect, in certain implementations of the fifth aspect, the first indication information also includes a first preset condition, and the first preset condition is used by the terminal device to determine a target candidate base station that meets the preset condition.

[0052] In a sixth aspect, a communication device is provided, including a processor and a memory, wherein the memory is used to store a computer program, and the processor is used to call and run the computer program from the memory, so that the communication device executes the method in the first aspect and its various possible implementations.

[0053] In a seventh aspect, a communication device is provided, comprising a processor and a memory, wherein the memory is used to store a computer program, and the processor is used to call and run the computer program from the memory, so that the communication device executes the method in the second aspect and its various possible implementations.

[0054] In an eighth aspect, a computer-readable storage medium is provided for storing a computer program, wherein the computer program includes instructions for executing the method as in the first aspect or any possible implementation of the first aspect.

[0055] In a ninth aspect, a computer-readable storage medium is provided for storing a computer program, wherein the computer program includes instructions for executing the method in the second aspect or any possible implementation of the second aspect.

[0056] In a tenth aspect, a computer program product is provided, comprising a computer program, which, when executed on a computer device, enables the computer device to execute the method as described in the first aspect.

[0057] In an eleventh aspect, a computer program product is provided, comprising a computer program, which, when executed on a computer device, enables the computer device to execute the method as described in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a schematic diagram of a random access process in the prior art.

[0059] Figure 2 This is a schematic diagram of the principle of the common TA mechanism in the NTN scenario.

[0060] Figure 3 It is a schematic diagram of a communication method according to an embodiment of the present application.

[0061] Figure 4 It is a flowchart of a switching process in an embodiment of the present application.

[0062] Figure 5 It is a flowchart of the conditional switching process of an embodiment of the present application.

[0063] Figure 6 It is a schematic diagram of the switching process under the CU-DU architecture of an embodiment of the present application.

[0064] Figure 7 It is a schematic diagram of a communication device according to an embodiment of the present application.

[0065] Figure 8 It is a schematic diagram of another communication device according to an embodiment of the present application.

[0066] Fig. 9 It is a schematic diagram of another communication device according to an embodiment of the present application. DETAILED DESCRIPTION

[0067] The technical solution in this application will be described below in conjunction with the accompanying drawings.

[0068] The technical solutions of the embodiments of the present application can be applied to various communication systems, such as: code division multiple access (CDMA) system, wideband code division multiple access (WCDMA) system, long term evolution (LTE) system, fifth generation (5G) system or new radio (NR), as well as future evolved communication systems.

[0069] In this application, the terms "network" and "system" are often used interchangeably. The communication device described in this application refers to a network element in a communication system, such as a terminal, a base station (source base station, or target base station), and a core network device.

[0070] The terminal device in the embodiments of the present application may refer to user equipment, access terminal, user unit, user station, mobile station, mobile station, remote station, remote terminal, mobile device, user terminal, terminal, wireless communication device, user agent or user device. The terminal device may also be a cellular phone, a cordless phone, a session initiation protocol (SIP) phone, a wireless local loop (WLL) station, a personal digital assistant (PDA), a handheld device with wireless communication function, a computing device or other processing device connected to a wireless modem, a vehicle-mounted device, a wearable device, a terminal device in a future 5G network or a terminal device in a future evolved public land mobile communication network (PLMN), etc., and the embodiments of the present application are not limited to this.

[0071] A base station may also be referred to as a base station device, which is a network device deployed in a wireless access network to provide wireless communication functions. The names of base stations may be different in different wireless access systems. For example, in the Universal Mobile Telecommunications System (UMTS) network, the base station is called a NodeB, in the LTE network, the base station is called an evolved NodeB (evolved NodeB, eNB or eNodeB), and in the 5G system, it may be called a Transmission Reception Point (TRP), a gNodeB (gNodeB, gNB). A base station may include one or more co-sited or non-co-sited TRPs. A base station may also be a wireless controller, a centralized unit (CU), and / or a distributed unit (DU) in a cloud radio access network (CRAN) scenario. A base station may also be a server, a wearable device, or a vehicle-mounted device, a non-terrestrial device such as a satellite, etc. For ease of description, the base station is used for description below. Optionally, the base station in the present invention may also be a user device in a device-to-device D2D (Device to Device). Optionally, the base station and user equipment in the present invention may also be relay equipment, or network equipment or user equipment that implements a relay function.

[0072] The base station can be a centralized unit (CU) and a distributed unit (DU) separated architecture. The RAN can be connected to the core network (for example, it can be the core network of LTE, or it can be the core network of 5G, etc.). CU and DU can be understood as the division of the base station from the perspective of logical functions. CU and DU can be physically separated or deployed together. Multiple DUs can share one CU. One DU can also be connected to multiple CUs. The CU and DU can be connected through an interface, such as an F1 interface. CU and DU can be divided according to the protocol layer of the wireless network. For example, one possible division method is: CU is used to perform the functions of the radio resource control (RRC) layer, the service data adaptation protocol (SDAP) layer, and the packet data convergence protocol (PDCP) layer, while DU is used to perform the functions of the radio link control (RLC) layer, the media access control (MAC) layer, the physical layer, etc. It can be understood that the division of the CU and DU processing functions according to this protocol layer is only an example, and it can also be divided in other ways. For example, the CU or DU can be divided into functions with more protocol layers. For example, the CU or DU can also be divided into partial processing functions with protocol layers. In one design, some functions of the RLC layer and the functions of the protocol layers above the RLC layer are set in the CU, and the remaining functions of the RLC layer and the functions of the protocol layers below the RLC layer are set in the DU. In another design, the functions of the CU or DU can also be divided according to the service type or other system requirements. For example, according to the delay, the functions that need to meet the delay requirements for processing time are set in the DU, and the functions that do not need to meet the delay requirements are set in the CU. One or more CUs can be set centrally or separately. For example, the CU can be set on the network side for centralized management. The DU can have multiple radio frequency functions, or the radio frequency functions can be set remotely. The functions of the CU can be implemented by one entity or by different entities. For example, the functions of the CU can be further divided, for example, the control plane (CP) and the user plane (UP) are separated, that is, the control plane (CU-CP) of the CU and the user plane (CU-UP) of the CU. For example, the CU-CP and CU-UP may be implemented by different functional entities, and the CU-CP and CU-UP may be coupled with the DU to jointly complete the function of the base station.

[0073] In uplink transmission, different UEs use orthogonal multiple access in time and frequency, that is, uplink transmissions from different UEs in the same cell do not interfere with each other. In order to ensure the orthogonality of uplink transmission and avoid interference within the cell, the base station requires that the time when signals from different UEs in the same subframe but different frequency domain resources arrive at the base station is basically aligned. As long as the base station receives the uplink data sent by the UE within the cyclic prefix range, it can correctly decode the uplink data. Therefore, uplink synchronization requires that the time when signals from different UEs in the same subframe arrive at the base station falls within the cyclic prefix range. In order to maintain the orthogonality between uplink reference signals using different cyclic shifts, the received uplink reference signals are also required to be time-aligned. This is also the reason why uplink synchronization is needed to ensure that uplink transmissions from different UEs in the same cell are aligned in time. In order to ensure time synchronization on the receiving side (base station side), LTE / NR introduces an uplink timing advance mechanism. From the UE side, timing advance is essentially a negative offset between the start time of the received downlink subframe and the time of transmitting the uplink subframe. The base station can control the time when uplink signals from different UEs arrive at the base station by appropriately controlling the offset of each UE. For example, for a UE that is far away from the base station, due to the large transmission delay, it needs to send uplink data earlier than the UE that is closer to the base station.

[0074] There are two ways for the base station to inform the UE of its TA. During the random access process, the base station determines the TA value by measuring the received preamble and sends it to the UE through the timing advance of the random access response (RAR). This process is the "initial uplink synchronization process". In the connected state, the base station needs to maintain the timing advance information. In theory, any signal sent by the UE (SRS / DMRS / CQI / ACK / NACK / PUSCH, etc.) can be used to measure the timing advance. The UE side will save the most recent TA adjustment value N TA,old When the UE receives a new timing advance command and gets T A After that, the latest TA adjustment value N will be calculated. TA,new =N TA,old +(T A -31)*16(unit is T s ).

[0075] Specifically, Figure 1 FIG. 2 shows a schematic diagram of a process in which a base station informs a UE of its TA during a random access process in the prior art. Figure 1As shown, the random access process includes steps S110 to S150. S110, random access initialization, in which parameters are configured, and these parameters may include: a physical random access channel (PRACH) resource set that can be used to transmit a random access preamble (RAP); available random access preamble groups (Group A or Group B) and available preamble sets in each group; maximum number of preamble transmissions; initial preamble transmission power; power boost step; random access response window; maximum number of hybrid automatic repeat request (HARQ) retransmissions of the third message; contention resolution timer, etc. S120, the terminal device sends a random access preamble to the network device. The function of the random access preamble is mainly to notify the network device that there is a random access request and enable the network device to estimate the transmission delay between it and the terminal device, so that the access network device can calibrate the uplink advance (uplink timing) and inform the terminal device of the calibration information through the timing advance command. S130, the terminal device receives a random access response (RAR) sent by the network device, wherein the RAR includes an uplink timing advance, which is determined by the network device according to the received random access preamble. S140, the terminal device sends a message based on scheduled transmission to the network device. S150, the terminal device receives a contention resolution message sent by the network device, confirming that the random access process is successful.

[0076] In order to shorten the random access delay, the 5G NR system supports not only the current traditional four-step random access method, but also a two-step random access method. The two-step random access method includes the terminal device sending a first message to the base station, the first message may include a preamble code and / or a demodulation reference signal (DMRS), and the base station sends a second message to the terminal device, the second message may include a response message, and the response message may include temporary C-RNTI information, timing advance command (TA command) information, uplink authorization information, contention resolution identifier, etc. Since the two-step random access method belongs to the prior art, this application will not go into details about it.

[0077] The embodiments of the present application are not only applicable to Figure 1 The four-step random access method in is also applicable to the two-step random access method.

[0078] Satellite communication (non-terrestrial network, NTN), that is, non-terrestrial communication. Thanks to the current concept of "any time, any place" communication, the status of satellite communication network will be further improved in the future. Generally speaking, the higher the orbit of the satellite, the larger its coverage area, but the longer the communication delay. Generally speaking, the orbit of the satellite can be divided into: low orbit (low earth orbit, LEO): orbit altitude of 160 ~ 2000km; middle orbit (middle earth orbit, MEO): orbit altitude of 2000 ~ 35786km; geostationary earth orbit (geostationary earth orbit, GEO): orbit altitude of 35786km, the relative position of the satellite running in this orbit and the earth is not affected by the rotation of the earth. Among them, low-orbit communication satellites are close to the ground, have short communication delays, high data transmission rates, and the weight and volume of mobile terminals are almost the same as those of personal mobile devices. They are more suitable for popularization in the mass market and have become a hot spot for current industrial development.

[0079] Due to the long delay of satellite communication, the timing advance mechanism designed for the current NR system cannot be applied to satellite communication. In the timing advance mechanism in the prior art, the value range of TA is 0~3486, and the length represented by a TA value is: 39m when PRACH subcarrier = 30KHZ, 78m when 15KHZ, and in the random access process in the prior art, the timing advance sent to the UE carried in the random access response message sent by the base station can cover a range of approximately 300km, while the low-orbit satellite in satellite communication has an orbital altitude of 160-2000km. Obviously, the timing advance mechanism of the prior art cannot adapt to satellite communication. In order to adapt to satellite communication, the prior art proposes that the UE can obtain its timing advance by broadcasting common TA through satellite. Figure 2 The schematic diagram of the principle of the common TA mechanism in an NTN scenario is shown. Specifically, the satellite selects a reference point on the ground, which is generally the point closest to the satellite and the ground, with a distance of d0. The TA at this distance is the common TA, and the TA sent by the base station to the UE is Figure 2 The UE-specific TA in the TA value has become less large after the distance of the common TA is subtracted from the TA value, so it can be represented by 12 bits in the timing advance command field in the RAR. Then the UE can obtain the TA value for sending data based on the UE-specific TA and the common TA.

[0080] However, the current common TA mechanism only involves random access of idle UEs. It informs UEs by broadcasting common TA via satellite, and then UEs send random access preambles to the target cell based on the received common TA, thereby initiating random access. Figure 1 In the random access process shown in FIG. 1 , the base station informs the UE of the TA of the UE during the random access process. However, in the scenario of satellite communication, the common TA has not been applied to the random access of the handover process of the connected UE. If only the common TA information is sent to the UE as a handover confirmation message, the common TA will continue to change during the flight of the satellite, which will also cause the common TA received by the UE to be inaccurate.

[0081] The embodiment of the present application sends indication information including the common time advance of at least one candidate cell to the UE, so that the UE can send a random access preamble to the target candidate cell according to the received common time advance, thereby improving the success rate of the base station processing the preamble, and then increasing the success rate of random access during the switching process. Figure 3 As shown, the method 300 includes steps S310 to S320, which are described in detail below.

[0082] S310, the terminal device receives first indication information, where the first indication information includes a common timing advance of at least one candidate cell.

[0083] It should be understood that the first indication information is used to inform the terminal device that the at least one candidate cell is in a switching allowed state.

[0084] Optionally, the above-mentioned first indication information may be at least one first indication information sent by a base station to which at least one candidate cell belongs.

[0085] Optionally, the first indication information may be sent by a base station to which at least one candidate cell belongs through a handover confirmation message. It should be understood that the handover confirmation message is received by the source base station of the currently connected cell, and the source base station transparently transmits the handover confirmation message to the terminal device. Optionally, the source base station may convert the handover confirmation message into a handover command, or send an RRC reconfiguration message to the terminal device. It should be understood that the candidate cell may be a target cell in a normal handover process, or may be one of at least one candidate cell in a conditional handover process.

[0086] Furthermore, the first indication information may also include a correspondence between multiple common time advances and multiple time moments of at least one candidate cell. It should be understood that the candidate cell may be a target cell in a normal handover process or one of at least one candidate cell in a conditional handover process.

[0087] Optionally, the multiple moments may be absolute moments or relative moments, such as system frame number SFN. The correspondence between multiple time advances and multiple moments may be in the form of a list, as shown in Table 1, or the correspondence may be a mapping relationship, such as common TA=SFN*100+6000.

[0088] Table 1 Correspondence between time advance and time

[0089] Index Common TA Time(SFN) 1 6000 10 2 6500 11 3 7000 12 … … …

[0090] Optionally, the first indication information may include information on the type of at least one candidate cell, and the type may include a satellite communication type and / or a private network type. The type information may be information related to NTN, such as GEO cell, LEO cell (e.g., fixed cell mode and moving cell mode); or it may be information related to a private network (NPN), such as a standalone non-public network (SNPN) cell, a closed access network (CAG) cell, etc. Optionally, the type information may further include an identifier, for example, an SNPN cell may include a standalone non-public network identifier (SNPN ID), and a CAG cell may include a CAG ID.

[0091] Optionally, the first indication information may also include priority information of the cell type. The priority information of the cell type may indicate the priority of a certain candidate cell type. For example, the first indication information may indicate that the NTN cell is the first priority, the NPN cell is the second priority, and the PLMN cell (i.e., the public network cell) is the third priority, that is, the source base station considers that the priority arrangement among the multiple candidate cells is: NTN cell is higher than NPN cell, and NPN cell is higher than PLMN cell. After the terminal device receives the first indication information including the priority information, when both the high-priority type cell and the low-priority type cell meet the switching conditions, the terminal device may give priority to the high-priority candidate cell as its target cell.

[0092] By adding the type information of the candidate cell to the indication information, the terminal device can select a more suitable cell for access before switching, thereby improving the communication quality.

[0093] Optionally, the above type of information can be applied to the common TA mechanism in the NTN scenario, and can also be applied to the cell switching in the ground base station, which is not limited in this application.

[0094] S320, the terminal device sends a random access preamble code to a target candidate cell according to the first time advance.

[0095] It should be understood that the target candidate cell is one of the at least one candidate cell, and the first timing advance is a common timing advance of the target candidate cell.

[0096] Optionally, when the above-mentioned first indication information includes a corresponding relationship, S320 may also include: the terminal device determines a first time advance corresponding to the first moment according to the corresponding relationship, and the first time period is determined by the terminal device according to the time when random access is initiated to a target candidate cell, and the target candidate cell is one of at least one candidate cell.

[0097] It should be understood that the moments in the correspondence between the above-mentioned multiple common time advances and multiple moments are discretely distributed, and the time when the terminal device initiates random access can be any time. The terminal device can select a suitable moment and the corresponding time advance from the correspondence according to the time when the random access is initiated.

[0098] Optionally, the terminal device may determine the first moment according to the time of initiating random access, thereby determining the corresponding time advance. For example, the first moment may be 10, and its corresponding common TA is 6000.

[0099] Optionally, during the conditional switching process, before the terminal device sends a preamble code to a target candidate cell, the terminal device can also determine the target candidate cell that meets the preset conditions based on the preset conditions in the first indication information (such as the signal strength of the source cell and the candidate cell, the channel quality of the source cell and the candidate cell, the location information of the UE, the location information of the candidate base station, etc.).

[0100] Optionally, after a base station to which a target candidate cell belongs receives a random access preamble code sent by a terminal device, it can send second indication information to the terminal device through a TA command in the RAR. The second indication information may include a second time advance value, which can be determined by the above-mentioned base station based on the random access preamble code.

[0101] Optionally, the second timing advance may be a positive number or a negative number. Specifically, in the prior art, the second timing advance determined by the base station according to the preamble sent by the terminal device has taken the common TA into consideration, which is generally the TA of the UE minus the common TA, such as Figure 2Because in the prior art, when the satellite selects a reference point, the default reference point selected is the point closest to the ground, so the second time advance obtained by the base station is a positive number, but if the selected reference point is not the shortest distance between the satellite and the ground, the common TA is larger than the actual TA of the UE. In this case, the TA carried in the RAR may be a negative number, but in the existing mechanism, the TA carried in the RAR is a positive number, so a TA value representing a negative number can be introduced.

[0102] Optionally, after receiving the second time advance sent by a target candidate cell, the terminal device can obtain a third time advance by adding the first time advance and the second time advance, and send a third message to a target candidate cell according to the third time advance to inform that the switching of the cell to be accessed is completed. Optionally, the third message can be a reconfiguration completion message, or an RRC connection request message, an RRC connection reestablishment request, a C-RNTI MAC control unit, etc. In the present application, the third message can be a C-RNTI MAC control unit.

[0103] Optionally, the corresponding relationships of multiple candidate cells provided by the same base station are the same. For example, the corresponding relationship shown in Table 1 or the formula common TA=SFN*100+6000 may be used.

[0104] Optionally, the correspondence between multiple common time advances and multiple time moments in the embodiment of the present application can be applied to the cell switching process of the connected state UE, and can also be applied to the random access process of the idle state UE, and the present application does not impose any restrictions on this.

[0105] It should be understood that in an embodiment of the present application, the indication information sent by the base station can be sent to one terminal device or to multiple terminal devices. If the base station sends the indication information to multiple terminal devices, the indication information can also include group identifiers, group indexes and intra-cell identifiers of multiple UEs. The present application does not limit the number of terminal devices.

[0106] In a mobile communication system, a connected UE switches to another cell. The switching process is controlled by a network device, which instructs the UE to switch to the target cell by sending a switching confirmation message. Specifically, Figure 4 FIG. 1 is a flow chart showing a switching process according to an embodiment of the present application. Figure 4As shown, the UE performs cell measurement according to the measurement configuration previously sent by the base station. When the conditions for measurement reporting are met, the UE will send the measurement report to the base station. S420, the base station decides to switch according to the measurement configuration reported by the UE, and determines the target cell. Optionally, the target cell can also be referred to as a candidate cell. S430, the source base station to which the currently connected cell belongs sends a switching request message to the target base station to which the target cell belongs. S440, the target base station sends a switching confirmation message to the source base station. The target base station decides whether to allow the UE to access based on the number of connections in the target cell and other conditions. If allowed, the target base station sends a switching confirmation message to the source base station. The switching confirmation message includes the common time advance of the target cell, and further, may include the correspondence between multiple common time advances of the target cell and multiple time moments. Optionally, the switching confirmation message may also include information about the type of the target cell. For example, the type may include a satellite communication type and / or a private network type. The type information may be information related to NTN, such as GEO cell, LEO cell (for example, fixed cell mode and moving cell mode); or it may be information related to non-public network (NPN), such as standalone non-public network (SNPN) cell, closed access network (CAG) cell, etc. Optionally, the type information may further include an identifier, for example, a SNPN cell may include a standalone non-public network identifier (SNPN ID), and a CAG cell may include a CAG ID. Optionally, the handover confirmation message may also include priority information of the cell type. The priority information of the cell type may indicate the priority of a certain candidate cell type. For example, the handover confirmation message may indicate that the NTN cell is the first priority, the NPN cell is the second priority, and the PLMN cell (i.e., the public network cell) is the third priority, that is, the source base station considers that the priority arrangement among multiple candidate cells is: the NTN cell is higher than the NPN cell, and the NPN cell is higher than the PLMN cell. After receiving the handover confirmation message including the priority information, the terminal device may preferentially select the high-priority candidate cell as its target cell when both the high-priority cell and the low-priority cell meet the handover conditions.

[0107] S450, the source base station sends a switching command message to the UEs, which is an RRC reconfiguration message. The content contained therein comes from the switching confirmation message of S440, which is equivalent to that the source base station layer is transparent. S460, this step is optional. If the received indication information includes the correspondence between multiple common TAs and multiple time moments of the target cell, the UE selects a suitable common TA as the TA for sending the preamble code according to the time of initiating random access. If the indication information only includes the common time advance of the target base station, this step can be omitted. S470, the UE sends a preamble code to the target base station according to the selected common TA and attempts to make a random access. S480, the base station puts the TA that needs to be adjusted by the UE in the RAR according to the received preamble code. The TA may be a positive number or a negative number. S490, the UE can obtain the TA used to send the reconfiguration completion message based on the TA in the received RAR plus the common TA used to send the preamble code.

[0108] Optionally, the above application embodiments can be applied to NTN scenarios, when LEO / GEO is connected to the core network as an independent base station, or can be applied to scenarios where LEO / GEO is connected to a ground base station as a relay base station, and this application is not limited to this.

[0109] By sending indication information including the common time advance to the terminal device, the terminal device can send the preamble code more accurately in the switching scenario, thereby improving the success rate of the base station processing the preamble code, and then increasing the success rate of random access.

[0110] Furthermore, by sending indication information including the correspondence between multiple common time advances and multiple time moments to the terminal device, the terminal device can send the preamble code more accurately in the switching scenario, thereby improving the success rate of the base station processing the preamble code, and then increasing the success rate of random access.

[0111] On the basis of the above-mentioned switching mechanism, the prior art proposes a conditional handover (CHO) mechanism to improve the success rate of switching. When the quality of the source link is good, the source base station sends CHO configuration information to the UE. The CHO configuration information may include CHO trigger conditions, information of one or more cells to be accessed (such as the cell global identifier (CGI) of the candidate cell, or the physical cell identifier (PCI) of the candidate cell and the frequency information corresponding to the candidate cell). Specifically, Figure 5 FIG. 2 is a flow chart showing a conditional switching process according to an embodiment of the present application. Figure 5As shown in the figure, the UE performs measurements according to the measurement configuration sent by the base station. When the measurement reporting conditions are met, the UE will send the measurement report to the base station. S520, the source base station will decide to let the UE perform conditional handover according to the UE's measurement report. S530, the source base station will send a handover request to multiple candidate base stations. S540, multiple candidate base stations will decide whether to allow the UE to access according to their own conditions and send a handover confirmation message, which contains the same content as Figure 4 The switching confirmation message is the same as the embodiment shown and will not be repeated here. Optionally, the switching confirmation message may also include a switching condition, and the switching condition may include, for example, the signal strength of the source cell and the candidate cell, the channel quality of the source cell and the candidate cell, the location information of the UE, the location information of the candidate base station, etc. S550, the source base station sends a conditional switching command (also an RRC reconfiguration message), wherein the switching command includes the switching confirmation message in S540, which is equivalent to the source base station layer being transparent. The switching command may include the common time advance of the cells of each candidate base station, or may include the correspondence between multiple common time advances of the cells of each candidate base station and multiple moments. At the same time, it carries the condition for the UE to perform the switching. Optionally, the source base station may also put the switching confirmation messages sent by multiple candidate base stations in the same conditional switching command. S560, when the UE determines that the current situation meets the switching condition, it selects a suitable target candidate cell, and selects a suitable common TA for sending the preamble code according to the common time advance of the target candidate cell in the switching message, or according to the correspondence between multiple common TAs of the target candidate cell and multiple moments. The remaining steps are the same as Figure 4 The steps are the same as in , and will not be repeated here.

[0112] Optionally, the above application embodiments can be applied to NTN scenarios, when LEO / GEO is connected to the core network as an independent base station, or can be applied to scenarios where LEO / GEO is connected to a ground base station as a relay base station, and this application is not limited to this.

[0113] Each candidate base station sends indication information of the cell of the base station, including the correspondence between multiple common time advances and multiple time moments, to the terminal device, so that the terminal device can send the preamble code more accurately in the switching scenario, thereby improving the success rate of the base station processing the preamble code, and then increasing the success rate of random access.

[0114] Figure 6 A schematic diagram of the switching process of the embodiment of the present application under the CU-DU architecture is given. Figure 6As shown, S610, the UE performs measurements according to the measurement configuration previously sent by the base station. When the conditions for measurement reporting are met, the UE will send the measurement report to the source DU. S620, the source DU sends a measurement report to the CU, optionally forwarded through an uplink RRC message. S630, the CU sends a group switching request to the target DU, which may also be called a candidate DU, optionally through a UE context establishment request message. S640, the target DU sends a group switching confirmation message to the CU, which includes the common time advance of the cell of the target DU, or optionally, the switching confirmation message may also include the correspondence between multiple common time advances of the cell of the target DU and multiple moments. S650, the CU sends a group switching command to the source DU, optionally through a UE context modification request message. S660, the source DU sends a switching command message to the UEs, that is, an RRC reconfiguration message, which may include the common time advance of the cell of the target DU, or further may include the correspondence between multiple time advances of the target DU and multiple moments. S670, through the UE context modification response message. S680, the UE selects an appropriate time advance to establish a random access process with the target DU. S690, the target DU sends a group switching completion message, optionally forwarded via an uplink RRC message. S6100, the target DU sends an RRC reconfiguration completion message to the CU. S6100, the CU sends a UE context release command to the source DU. S6120, the source DU sends a UE context release completion message to the CU.

[0115] The above application embodiment relates to the switching process within the CU. Optionally, the cell switching can also be an inter-CU switching. Figure 4 The process is similar to that of Figure 6 The switching within the CU is consistent and will not be repeated here.

[0116] Optionally, the above application embodiments can be applied to NTN scenarios, where LEO / GEO acts as a relay base station and is connected to a ground DU, or can be applied to scenarios where LEO acts as a DU and is connected to a ground CU. This application is not limited to this.

[0117] By sending indication information including the correspondence between multiple time advances and multiple time moments of the DU to be accessed to the terminal device, the terminal device can send the preamble code more accurately in the switching scenario, thereby improving the success rate of the base station in processing the preamble code, and then increasing the success rate of random access.

[0118] Figure 7 A schematic diagram of a communication device according to an embodiment of the present application is shown. Figure 7 As shown, the device 700 includes a receiving module 710 and a sending module 720 .

[0119] The receiving module is used to receive first indication information, wherein the first indication information includes a common time advance of at least one candidate cell, and the first indication information is used to inform the device 700 that the at least one candidate cell is in a switching allowed state; the sending module is used to send a random access preamble code to a target candidate cell according to the first time advance, and the target candidate cell is one of the at least one candidate cell, and the first time advance is the common time advance of the target candidate cell.

[0120] Optionally, the first indication information also includes: the correspondence between multiple common time advances and multiple moments of the at least one candidate cell; the device also includes: a processing module, used to determine a first time advance corresponding to a first moment according to the correspondence, the first moment being determined by the device 700 according to the time of initiating random access to a target candidate cell, and the target candidate cell is one of the at least one candidate cell.

[0121] Optionally, the first indication information also includes information about the type of the at least one candidate cell, and the type includes a satellite communication type and / or a private network type.

[0122] Optionally, the first indication information also includes a first preset condition, and the processing module is further used to determine a target candidate cell that meets the preset condition.

[0123] Optionally, the receiving module is further used to: receive second indication information sent by the one target candidate cell, the second indication information includes a second timing advance, the second timing advance is a positive number, or the second timing advance is a negative number.

[0124] Optionally, the sending module is further used to: send third indication information to the one target candidate cell according to a third time advance, the third indication information includes a reconfiguration completion message, and the third time advance is obtained by adding the first time advance and the second time advance.

[0125] Optionally, the corresponding relationships among multiple candidate cells of the same base station are the same.

[0126] The communication device 700 may also be implemented in other ways, such as by at least one processor, a memory, and a transceiver. The functions of the receiving module 710 and the sending module 720 may be implemented by a transceiver.

[0127] Figure 8 A schematic diagram of another communication device according to an embodiment of the present application is shown. Figure 8 As shown, the device 800 includes a sending module 810 and a receiving module 820 .

[0128] The sending module is used to send a first indication message to the terminal device, wherein the first indication message includes a common time advance of the device 800, and the first indication message is used to inform the terminal device that at least one candidate cell is in a switching allowed state; the receiving module is used to receive a random access preamble code sent by the terminal device according to the first time advance.

[0129] Optionally, the first indication information further includes: a correspondence between multiple common time advances of the device 800 and multiple time moments.

[0130] Optionally, the first indication information also includes information about the type of the device 800, and the type includes a satellite communication type and / or a private network type.

[0131] Optionally, the first indication information also includes a first preset condition, and the preset condition is used by the terminal device to determine a target candidate base station that meets the preset condition.

[0132] Optionally, the sending module is also used to: send second indication information to the terminal device, the second indication information includes a second time advance, the second time advance is determined by the device 800 according to the random access preamble code, the second time advance is a positive number, or the second time advance is a negative number.

[0133] The communication device 800 may also be implemented in other ways, such as by at least one processor, a memory, and a transceiver. The functions of the sending module 810 and the receiving module 820 may be implemented by a transceiver.

[0134] Fig. 9 A schematic diagram of another communication device according to an embodiment of the present application is shown. Fig. 9 As shown, the device 900 includes a receiving module 910 and a sending module 920 .

[0135] The receiving module is used to receive first indication information sent by at least one candidate base station, the first indication information includes the common time advance of at least one candidate cell, and the first indication information is used to inform the terminal device that the at least one candidate cell is in a switching allowed state; the sending module sends the first indication information to the terminal device.

[0136] Optionally, the first indication information also includes: a correspondence between multiple common time advances and multiple time moments of the at least one candidate cell.

[0137] Optionally, the apparatus further includes: a processing module, configured to integrate multiple first indication information sent by multiple candidate base stations into one first indication information before sending the first indication information to the terminal device.

[0138] Optionally, the first indication information also includes information about the type of the at least one candidate base station, and the type includes a satellite communication type and / or a private network type.

[0139] Optionally, the first indication information also includes a first preset condition, and the first preset condition is used by the terminal device to determine a target candidate base station that meets the preset condition.

[0140] The communication device 900 may also be implemented in other ways, such as by at least one processor, a memory, and a transceiver. The functions of the receiving module 910 and the sending module 920 may be implemented by a transceiver.

[0141] In the several embodiments provided in this application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only illustrative, for example, the division of the modules is only a logical function division, and there may be other division methods in actual implementation.

[0142] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented by software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in the embodiment of the present invention is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions can be transmitted from a website site, computer, server or data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line (digital subscriber line, DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) mode to another website site, computer, server or data center. The computer-readable storage medium can be any available medium that can be accessed by a computer or a data storage device such as a server or data center that includes one or more available media integrated. The available medium may be a magnetic medium (eg, a floppy disk, a hard disk, a magnetic tape), an optical medium (eg, a DVD), or a semiconductor medium (eg, a solid state disk (SSD)).

Claims

1. A communication method, characterized in that: include: The terminal device receives first indication information from a base station to which at least one candidate cell belongs, where the first indication information includes a common timing advance of the at least one candidate cell; The terminal device sends a random access preamble code to a target candidate cell according to a first timing advance, the target candidate cell is one of the at least one candidate cell, and the first timing advance is a common timing advance of the target candidate cell.

2. The method according to claim 1, characterized in that The candidate cell is a target cell in a normal handover process, or the candidate cell is a candidate cell in a conditional handover process.

3. The method according to claim 1 or 2, characterized in that: The first indication information is used to determine the correspondence between the common time advance and the time of each candidate cell in the at least one candidate cell; The method further comprises: The terminal device determines a first time advance corresponding to a first moment based on a first corresponding relationship, where the first moment is determined by the terminal device based on the time when random access is initiated to a target candidate cell, and the target candidate cell is one of the at least one candidate cell, and the first corresponding relationship is a corresponding relationship between the target candidate cell.

4. The method according to claim 1 or 2, characterized in that: The first indication information further includes a first preset condition, and the method further includes: The terminal device determines the target candidate cell that meets the preset condition.

5. The method according to claim 1 or 2, characterized in that: The method further comprises: The terminal device receives second indication information sent by the target candidate cell, where the second indication information includes a second timing advance, where the second timing advance is a positive number, or the second timing advance is a negative number.

6. The method according to claim 5, characterized in that The method further comprises: The terminal device sends third indication information to the one target candidate cell according to a third timing advance, where the third indication information includes a reconfiguration completion message, and the third timing advance is obtained by adding the first timing advance and the second timing advance.

7. The method according to claim 3, characterized in that The corresponding relationships among the multiple candidate cells of the same base station are the same.

8. A communication method, characterized in that: include: A base station to which at least one candidate cell belongs sends first indication information to a terminal device, where the first indication information includes a common time advance of the at least one candidate cell; A random access preamble code is received which is sent by the terminal device according to a first timing advance, where the first timing advance is a common timing advance of a target candidate cell, and the target candidate cell is one of the at least one candidate cell.

9. The method according to claim 8, characterized in that The candidate cell is a target cell in a normal handover process, or the candidate cell is a candidate cell in a conditional handover process.

10. The method according to claim 8 or 9, characterized in that: The first indication information is used to determine the correspondence between the common timing advance and the time of the candidate cell.

11. The method according to claim 8 or 9, characterized in that: The first indication information also includes a first preset condition, and the preset condition is used by the terminal device to determine a target candidate cell that meets the preset condition.

12. The method according to claim 8 or 9, characterized in that: The method further comprises: Sending second indication information to the terminal device, the second indication information includes a second time advance, the second time advance is determined by the candidate cell according to the random access preamble code, the second time advance is a positive number, or the second time advance is a negative number.

13. A communication method, characterized in that: include: The source base station receives first indication information from a base station to which at least one candidate cell belongs, where the first indication information includes a common timing advance of the at least one candidate cell; The source base station sends the first indication information to the terminal device, wherein the at least one candidate cell includes a target candidate cell, the common time advance of the at least one candidate cell includes the common time advance of the target candidate cell, and the common time advance of the target candidate cell is used by the terminal device to send a random access preamble code to the target candidate cell.

14. The method according to claim 13, characterized in that The candidate cell is a target cell in a normal handover process, or the candidate cell is a candidate cell in a conditional handover process.

15. The method according to claim 13 or 14, characterized in that The first indication information further includes: The corresponding relationship between the common timing advance and the time of each candidate cell in the at least one candidate cell.

16. The method according to claim 13 or 14, characterized in that The method further comprises: Before sending the first indication information to the terminal device, the source base station integrates multiple first indication information sent by multiple candidate cells into one first indication information.

17. The method according to claim 13 or 14, characterized in that The first indication information also includes a first preset condition, and the first preset condition is used by the terminal device to determine a target candidate cell that meets the preset condition.

18. A communication device, characterized in that: include: A receiving module, configured to receive first indication information from a base station to which at least one candidate cell belongs, wherein the first indication information includes a common timing advance of the at least one candidate cell; The sending module is used to send a random access preamble code to a target candidate cell according to a first timing advance, where the target candidate cell is one of the at least one candidate cell, and the first timing advance is a common timing advance of the target candidate cell.

19. The device according to claim 18, characterized in that The candidate cell is a target cell in a normal handover process, or the candidate cell is a candidate cell in a conditional handover process.

20. The device according to claim 18 or 19, characterized in that The first indication information is used to determine the correspondence between the common time advance and the time of each candidate cell in the at least one candidate cell; The device also includes: The processing module is used to determine a first time advance corresponding to a first moment according to the corresponding relationship, where the first moment is determined by the communication device according to the time when random access is initiated to a target candidate cell, and the target candidate cell is one of the at least one candidate cell.

21. The device according to claim 20, characterized in that The first indication information also includes a first preset condition, and the processing module is further used to determine the target candidate cell that meets the preset condition.

22. The device according to claim 18 or 19, characterized in that The receiving module is also used for: Second indication information sent by the target candidate cell is received, where the second indication information includes a second timing advance, where the second timing advance is a positive number, or the second timing advance is a negative number.

23. The device according to claim 22, characterized in that The sending module is also used for: Sending third indication information to the one target candidate cell according to a third timing advance, where the third indication information includes a reconfiguration completion message, and the third timing advance is obtained by adding the first timing advance and the second timing advance.

24. The device according to claim 20, characterized in that The corresponding relationships among the multiple candidate cells of the same base station are the same.

25. A communication device, characterized in that: The communication device is applied to a base station to which at least one candidate cell belongs, and includes: A sending module, configured to send first indication information to a terminal device, wherein the first indication information includes a common time advance of the at least one candidate cell; A receiving module is used to receive a random access preamble code sent by the terminal device according to a first time advance, where the first time advance is a common time advance of a target candidate cell, and the target candidate cell is one of the at least one candidate cell.

26. The device according to claim 25, characterized in that The candidate cell is a target cell in a normal handover process, or the candidate cell is a candidate cell in a conditional handover process.

27. The device according to claim 25 or 26, characterized in that The first indication information is used to determine a correspondence between a common timing advance and a time of each candidate cell in the at least one candidate cell.

28. The device according to claim 25 or 26, characterized in that The first indication information also includes a first preset condition, and the preset condition is used by the terminal device to determine a target candidate cell that meets the preset condition.

29. The device according to claim 25 or 26, characterized in that The sending module is also used for: Sending second indication information to the terminal device, the second indication information includes a second time advance, the second time advance is determined by the communication device according to the random access preamble code, the second time advance is a positive number, or the second time advance is a negative number.

30. A communication device, characterized in that: include: A receiving module, configured to receive first indication information sent by a base station to which at least one candidate cell belongs, wherein the first indication information includes a common timing advance of at least one candidate cell; A sending module, used to send the first indication information to a terminal device, wherein the at least one candidate cell includes a target candidate cell, the common time advance of the at least one candidate cell includes the common time advance of the target candidate cell, and the common time advance of the target candidate cell is used by the terminal device to send a random access preamble code to the target candidate cell.

31. The device according to claim 30, characterized in that The candidate cell is a target cell in a normal handover process, or the candidate cell is a candidate cell in a conditional handover process.

32. The device according to claim 30 or 31, characterized in that The first indication information further includes: The corresponding relationship between the common timing advance and the time of each candidate cell in the at least one candidate cell.

33. The device according to claim 30 or 31, characterized in that The device also includes: A processing module is used to integrate multiple first indication information sent by multiple candidate cells into one first indication information before sending the first indication information to the terminal device.

34. The device according to claim 30 or 31, characterized in that The first indication information also includes a first preset condition, and the first preset condition is used by the terminal device to determine a target candidate cell that meets the preset condition.

35. A computer program product, characterized in that The invention comprises a computer program, which, when executed on a computer device, causes the computer device to execute the method as claimed in any one of claims 1 to 17.

36. A computer-readable storage medium, characterized in that: Used to store a computer program, wherein the computer program comprises instructions for executing the method according to any one of claims 1 to 17.

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