Communication method and device

Abstract

The invention provides a communication method and device. The method comprises: a terminal device receiving first indication information, the first indication information comprising a public time advance of at least one candidate cell, the first indication information being used for informing the terminal device that the at least one candidate cell is in a handover allowed state; and the terminal device sends a random access preamble to a target candidate cell according to a first timing advance, the target candidate cell being one of the at least one candidate cell, and the first timing advance being a common timing advance of the target candidate cell. According to the method provided by the invention, the UE can more accurately send the lead code in the switching scene.

Description

[0001] This application is a divisional application. The application number of the original application is 202010273524.3, and the filing date of the original application is April 9, 2020. The entire content of the original application is incorporated herein by reference. Technical Field

[0002] This application relates to the field of communications, and more particularly, to a communication method and apparatus. Background Art

[0003] In existing communication technologies, during uplink transmission, different user equipments (UEs) access orthogonally in time-frequency domain, that is, the uplink transmissions of different UEs from the same cell do not interfere with each other. To ensure the orthogonality of uplink transmission and avoid intra-cell interference, the base station requires that the signals of different UEs from the same subframe but different frequency-domain resources arrive at the base station basically aligned in time. To ensure time synchronization on the receiving side (base station side), the long term evolution (LTE) / new radio (NR) introduced the uplink timing advance mechanism.

[0004] To adapt to non-terrestrial networks (NTN), such as satellite communications, a 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 UEs in the idle state and does not cover the handover process of UEs in the connected state. Moreover, since the satellite is in flight, the common TA will constantly change, and relying solely on the existing mechanism will result in inaccurate common TA received by the UE. Summary of the Invention

[0005] This application provides a communication method and apparatus, in which the base station sends the common timing advance of a candidate cell, enabling the terminal device to send a preamble more accurately in a handover scenario.

[0006] In a first aspect, a communication method is provided. The method includes: a terminal device receives first indication information, the first indication information includes a common timing 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 permitted handover state; the terminal device sends a random access preamble to a target candidate cell according to a first timing advance, the target candidate cell is one of the at least one candidate cells, and the first timing advance is the common timing advance of the target candidate cell.

[0007] By receiving indication information including the common timing advance of the candidate cell, the terminal device can send the preamble more accurately in a handover scenario.

[0008] In combination with the first aspect, in some implementation manners of the first aspect, the first indication information further includes: a correspondence between a plurality of common timing advances and a plurality of moments of the at least one candidate cell; the method further includes: the terminal device determines a first timing advance corresponding to a first moment according to the correspondence, the first moment is determined according to the time when the terminal device initiates random access to a target candidate cell, and the target candidate cell is one of the at least one candidate cells. By receiving indication information including the correspondence between the plurality of timing advances and the plurality of moments, the terminal device can send the preamble more accurately in a handover scenario, thereby improving the success rate of the base station in processing the preamble and increasing the success rate of random access.

[0009] In combination with the first aspect, in some implementation manners of the first aspect, the first indication information further includes information on the type of the at least one candidate cell, and the type includes satellite communication type and / or private network type.

[0010] By indicating information on the type of the candidate cell in the indication information, the terminal device can select a more suitable cell for access according to the type information of the candidate cell, thereby improving the communication quality.

[0011] In combination with the first aspect, in some implementation manners of the first aspect, the first indication information further includes a first preset condition, and the method further includes: the terminal device determines a target candidate cell that meets the preset condition.

[0012] In combination with the first aspect, in some implementation manners of the first aspect, the terminal device receives second indication information sent by the one target candidate cell, and 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.

[0013] By introducing a mechanism of positive or negative numbers in the second timing advance, the problem of improper reference point selection in the NTN scenario is adjusted, making the timing advance received by the terminal device more accurate.

[0014] In combination with the first aspect, in some implementation manners of the first aspect, the terminal device sends third indication information to the one target candidate cell according to a third timing advance, 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.

[0015] In combination with the first aspect, in some implementation manners of the first aspect, the corresponding relationships of the multiple candidate cells of the same base station are the same.

[0016] In a second aspect, a communication method is provided, the method includes: sending first indication information to a terminal device, the first indication information includes a common timing advance of a candidate base station, and the first indication information is used to inform the terminal device that the at least one candidate cell is in an allowed handover state; receiving a random access preamble sent by the terminal device according to a first timing advance.

[0017] By sending indication information including the common timing advance of the candidate cell, the terminal device can send the preamble more accurately in the handover scenario.

[0018] In combination with the second aspect, in some implementation manners of the second aspect, the first indication information further includes: the corresponding relationship between multiple common timing advances of the candidate base station and multiple moments; receiving a random access preamble sent by the terminal device according to a first timing advance.

[0019] By sending indication information including the corresponding relationship between multiple common timing advances and multiple moments, the terminal device can send the preamble more accurately in the handover scenario, thereby improving the success rate of the base station in processing the preamble and increasing the success rate of random access.

[0020] In combination with the second aspect, in some implementation manners of the second aspect, the first indication information further includes information about the type of the candidate base station, and the type includes a satellite communication type and / or a private network type.

[0021] By indicating information about the type of the candidate cell in the indication information, the terminal device can select a more suitable cell for access according to the type information of the candidate cell, thereby improving the communication quality.

[0022] In combination with the second aspect, in some implementation manners of the second aspect, the first indication information further includes a first preset condition, and the preset condition is used for the terminal device to determine a target candidate base station that meets the preset condition.

[0023] In combination with the second aspect, in some implementations of the second aspect, second indication information is sent to the terminal device, where the second indication information includes a second timing advance, and the second timing advance is determined by the candidate base station according to the random access preamble. The second timing advance is a positive number, or the second timing advance is a negative number.

[0024] By introducing a mechanism of positive or negative numbers in the second timing advance, the problem of improper selection of reference points in the NTN scenario is adjusted, so that the timing advance received by the terminal device is more accurate.

[0025] In a third aspect, a communication device is provided. The device includes: a receiving module, configured to receive first indication information, where the first indication information includes a common timing advance of at least one candidate cell, and the first indication information is used to inform the communication device that the at least one candidate cell is in an allowable handover state; a sending module, configured to send a random access preamble to a target candidate cell according to a first timing advance, where the target candidate cell is one of the at least one candidate cells, and the first timing advance is the common timing advance of the target candidate cell.

[0026] By receiving indication information including the common timing advance of the candidate cell, the terminal device can send the preamble more accurately in the handover scenario.

[0027] In combination with the third aspect, in some implementations of the third aspect, the first indication information further includes: the corresponding relationship between multiple common timing advances and multiple moments of the at least one candidate cell; the device further includes: a processing module, configured to determine a first timing 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 of initiating random access to a target candidate cell, and the target candidate cell is one of the at least one candidate cells.

[0028] By receiving indication information including the corresponding relationship between multiple timing advances and multiple moments, the terminal device can send the preamble more accurately in the handover scenario, thereby improving the success rate of the base station in processing the preamble and increasing the success rate of random access.

[0029] In combination with the third aspect, in some implementations of the third aspect, the first indication information further 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.

[0030] By indicating information about the type of candidate cell in the indication information, the terminal device can select a more suitable cell for access according to the type information of the candidate cell, thereby improving the communication quality.

[0031] In combination with the third aspect, in some implementation manners of the third aspect, the first indication information further includes a first preset condition, and the processing module is further configured to determine a target candidate cell that meets the preset condition.

[0032] In combination with the third aspect, in some implementation manners of the third aspect, the receiving module is further configured to: receive second indication information sent by the one target candidate cell, where the second indication information includes a second timing advance, and the second timing advance is a positive number or the second timing advance is a negative number.

[0033] By introducing a mechanism of positive or negative numbers in the second timing advance, the problem of improper reference point selection in the NTN scenario is adjusted, so that the timing advance received by the terminal device is more accurate.

[0034] In combination with the third aspect, in some implementation manners of the third aspect, the sending module is further configured to: send third indication information to the one target candidate cell according to a third timing advance, where the third indication information includes a reconfiguration complete message, and the third timing advance is obtained by adding the first timing advance and the second timing advance.

[0035] In combination with the third aspect, in some implementation manners of the third aspect, the corresponding relationships of the multiple candidate cells of the same base station are the same.

[0036] In a fourth aspect, a communication device is provided, where the device includes: a sending module, configured to send first indication information to a terminal device, where the first indication information includes a common timing advance of a candidate base station, and the first indication information is used to inform the terminal device that the at least one candidate cell is in an allowable handover state; a receiving module, configured to receive a random access preamble sent by the terminal device according to a first timing advance.

[0037] By sending indication information including the common timing advance of the candidate cell, the terminal device can send a preamble more accurately in a handover scenario.

[0038] In combination with the fourth aspect, in some implementation manners of the fourth aspect, the first indication information further includes: the corresponding relationship between multiple common timing advances of the communication device and multiple moments.

[0039] By sending indication information including a plurality of common timing advances and the corresponding relationship between a plurality of moments, the terminal device can send preambles more accurately in a handover scenario, thereby improving the success rate of the base station in processing preambles and increasing the success rate of random access.

[0040] Combined with the fourth aspect, in some implementation manners of the fourth aspect, the first indication information further includes information about the type of the communication device, and the type includes satellite communication type and / or private network type.

[0041] By indicating information about the type of a candidate cell in the indication information, the terminal device can select a more suitable cell for access according to the type information of the candidate cell, thereby improving the communication quality.

[0042] Combined with the fourth aspect, in some implementation manners of the fourth aspect, the first indication information further includes a first preset condition, and the preset condition is used for the terminal device to determine a target candidate base station that meets the preset condition.

[0043] Combined with the fourth aspect, in some implementation manners of the fourth aspect, the sending module is further configured to: send second indication information to the terminal device, where the second indication information includes a second timing advance, and the second timing advance is determined by the communication device according to the random access preamble, and the second timing advance is a positive number or the second timing advance is a negative number.

[0044] By introducing a mechanism of positive or negative numbers in the second timing advance, the problem of improper selection of reference points in the NTN scenario is adjusted, so that the timing advance received by the terminal device is more accurate.

[0045] In a fifth aspect, a communication device is provided, and the device includes: a receiving module, configured to receive first indication information sent by at least one candidate base station, where the first indication information includes a common timing 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 an allowed handover state; a sending module, configured to send the first indication information to the terminal device.

[0046] By receiving indication information including the common timing advance of a candidate cell, the terminal device can send preambles more accurately in a handover scenario, thereby improving the success rate of the base station in processing preambles and increasing the success rate of random access.

[0047] Combined with the fifth aspect, in some implementation manners of the fifth aspect, the first indication information further includes: the corresponding relationship between a plurality of common timing advances of the at least one candidate cell and a plurality of moments.

[0048] By receiving indication information including the correspondence between multiple timing advances and multiple moments, the terminal device can send a preamble more accurately in a handover scenario, thereby improving the success rate of the base station in processing the preamble and increasing the success rate of random access.

[0049] In combination with the fifth aspect, in some implementation manners of the fifth aspect, the apparatus further includes: a processing module, configured to integrate multiple first indication messages sent by multiple candidate base stations into one first indication message before sending the first indication message to the terminal device.

[0050] In combination with the fifth aspect, in some implementation manners of the fifth aspect, the first indication message further 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.

[0051] By indicating information about the type of a candidate cell in the indication information, the terminal device can select a more suitable cell for access according to the type information of the candidate cell, thereby improving the communication quality.

[0052] In combination with the fifth aspect, in some implementation manners of the fifth aspect, the first indication message further includes a first preset condition, and the first preset condition is used for the terminal device to determine a target candidate base station that meets the preset condition.

[0053] In a sixth aspect, a communication device is provided, including a processor and a memory. The memory is configured to store a computer program, and the processor is configured to call and run the computer program from the memory, so that the communication device executes the methods in the first aspect and its various possible implementation manners.

[0054] In a seventh aspect, a communication device is provided, including a processor and a memory. The memory is configured to store a computer program, and the processor is configured to call and run the computer program from the memory, so that the communication device executes the methods in the second aspect and its various possible implementation manners.

[0055] In an eighth aspect, a computer-readable storage medium is provided, configured to store a computer program, and the computer program includes instructions for executing the methods in the first aspect or any possible implementation manner of the first aspect.

[0056] In a ninth aspect, a computer-readable storage medium is provided, configured to store a computer program, and the computer program includes instructions for executing the methods in the second aspect or any possible implementation manner of the second aspect.

[0057] In a tenth aspect, a computer program product is provided, including a computer program, which, when running on a computer device, causes the computer device to execute the method described in the first aspect.

[0058] In the eleventh aspect, a computer program product is provided, including a computer program which, when running on a computer device, causes the computer device to execute the method described in the second aspect. Description of the Drawings

[0059] Figure 1 is a schematic diagram of a random access process in the prior art.

[0060] Figure 2 is a schematic diagram of the principle of the common TA mechanism in the NTN scenario.

[0061] Figure 3 is a schematic diagram of the communication method according to an embodiment of the present application.

[0062] Figure 4 is a schematic flowchart of a handover process according to an embodiment of the present application.

[0063] Figure 5 is a schematic flowchart of a conditional handover process according to an embodiment of the present application.

[0064] Figure 6 is a schematic flowchart of a handover process in the CU-DU architecture according to an embodiment of the present application.

[0065] Figure 7 is a schematic diagram of a communication device according to an embodiment of the present application.

[0066] Figure 8 is a schematic diagram of another communication device according to an embodiment of the present application.

[0067] Figure 9 is a schematic diagram of another communication device according to an embodiment of the present application. Detailed Embodiments

[0068] Next, the technical solutions in the present application will be described in conjunction with the drawings.

[0069] The technical solutions of the embodiments of the present application can be applied to various communication systems, such as: Code Division Multiple Access (CDMA) systems, Wideband Code Division Multiple Access (WCDMA) systems, Long Term Evolution (LTE) systems, Fifth Generation (5G) systems or New Radio (NR), as well as future evolved communication systems, etc.

[0070] In this application, the nouns "network" and "system" are often used interchangeably. The communication devices described in this application refer to network elements in a communication system, such as terminals, base stations (source base stations or target base stations), and core network devices.

[0071] The terminal device in the embodiments of this application may refer to a user equipment, an access terminal, a user unit, a user station, a mobile station, a mobile device, a remote station, a remote terminal, a mobile device, a user terminal, a terminal, a wireless communication device, a user agent, or a 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 capabilities, a computing device, or other processing devices 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 network (PLMN). The embodiments of this application are not limited thereto.

[0072] The base station, which may also be referred to as base station equipment, is a network device deployed in a radio access network to provide wireless communication functions. The name of the base station may vary in different radio access systems. For example, in a Universal Mobile Telecommunications System (UMTS) network, the base station is called Node B; in an LTE network, the base station is called an evolved Node B (eNB or eNodeB); in a 5G system, it may be called a Transmission Reception Point (TRP), a g Node B (gNB). The base station may include one or more co-located or non-co-located TRPs. The base station may also be a radio controller, a centralized unit (CU), and / or a distributed unit (DU) in a cloud radio access network (CRAN) scenario. The base station may also be a server, a wearable device, or a vehicle-mounted device, or a non-terrestrial device such as a satellite. For ease of description, the base station is used hereinafter for description. Optionally, the base station in the present invention may also be a user equipment in a Device to Device (D2D). Optionally, the base station and the user equipment in the present invention may also be relay devices, or network devices or user devices that implement relay functions.

[0073] The base station can be an architecture with a separated centralized unit (CU) and distributed unit (DU). The RAN can be connected to the core network (e.g., it can be the core network of LTE or the core network of 5G, etc.). The CU and DU can be understood as a division of the base station from the perspective of logical functions. Physically, the CU and DU can be 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 the F1 interface. The CU and DU can be divided according to the protocol layers of the wireless network. For example, one possible division method is: the CU is used to execute the functions of the radio resource control (RRC) layer, service data adaptation protocol (SDAP) layer, and packet data convergence protocol (PDCP) layer, while the DU is used to execute the functions of the radio link control (RLC) layer, media access control (MAC) layer, physical layer, etc. It can be understood that this division of the processing functions of the CU and DU according to the protocol layers is just 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 of the protocol layers. In one design, part of the functions of the RLC layer and the protocol layers above the RLC layer are set in the CU, and the remaining functions of the RLC layer and 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, in terms of latency division, the functions that need to meet the latency requirements in terms of processing time are set in the DU, and the functions that do not need to meet this latency requirement are set in the CU. One or more CUs can be centrally set or separated. For example, the CU can be set on the network side for convenient centralized management. The DU can have multiple radio frequency functions, or the radio frequency functions can be remotely set. 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 split. For example, the control plane (CP) and user plane (UP) are separated, that is, the CU control plane (CU-CP) and CU user plane (CU-UP). For example, the CU-CP and CU-UP can be implemented by different functional entities, and the CU-CP and CU-UP can be coupled with the DU to jointly complete the functions of the base station.

[0074] In the uplink transmission, different UEs perform orthogonal multiple access in time-frequency, that is, the uplink transmissions of different UEs from the same cell do not interfere with each other. To ensure the orthogonality of the uplink transmission and avoid in-cell interference, the base station requires that the signals from different UEs in the same subframe but different frequency-domain resources arrive at the base station at basically the same time. 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, the uplink synchronization requires that the signals from different UEs in the same subframe arrive at the base station within the cyclic prefix range. To maintain the orthogonality between the uplink reference signals using different cyclic shifts, it is also required that the received uplink reference signals are time-aligned. This is also the reason why uplink synchronization is needed to ensure the time alignment of the uplink transmissions of different UEs in the same cell. To ensure the time synchronization on the receiving side (base station side), LTE / NR introduces the uplink timing advance mechanism. From the UE's perspective, the 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 the 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 farther from the base station, due to a larger transmission delay, it needs to send the uplink data earlier than a UE that is closer to the base station.

[0075] The base station has two ways 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 time advance in 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 , it will calculate the latest TA adjustment value N TA,new = N TA,old + (T A - 31) * 16 (the unit is T s ).

[0076] Specifically, Figure 1Shows a schematic diagram of the process in which a base station notifies a UE of its TA during a random access procedure in the prior art. As Figure 1 shown, the random access procedure includes steps S110 to S150. S110, random access initialization, in which parameter configuration is performed. These parameters may include: a physical random access channel (PRACH) resource set available for transmitting a random access preamble (RAP); available random access preamble groups (Group A or Group B) and the set of available preambles in each group; the maximum number of preamble transmissions; the initial transmission power of the preamble; the power ramp step; the random access response window; the maximum number of hybrid automatic repeat request (HARQ) retransmissions for the third message; the contention resolution timer, etc. S120, the terminal device sends a random access preamble to the network device. The main function of the random access preamble is to notify the network device of 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 timing and inform the terminal device of the calibration information through a timing advance command. S130, the terminal device receives a random access response (RAR) sent by the network device, where the RAR includes an uplink timing advance amount, which is determined by the network device based on 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 to confirm the success of the random access procedure.

[0077] 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, and the first message may include a preamble and / or a demodulation reference signal (DMRS), and the base station sending a second message to the terminal device. The second message may include a response message, and the response message may include information on a temporary C-RNTI, information on a timing advance command (TA command), information on uplink authorization, a contention resolution identifier, etc. Since the two-step random access method belongs to the prior art, this application will not elaborate on it too much.

[0078] The embodiments of this application are not only applicable to Figure 1The four-step random access method therein is also applicable to the two-step random access method.

[0079] Satellite communication (non-terrestrial network, NTN), that is, non-ground communication. Thanks to the concept of "anytime, anywhere" communication nowadays, the status of satellite communication networks will be further enhanced in the future. Generally speaking, the higher the orbit of a satellite, the larger its coverage area, but the longer the communication delay. Generally, the operating orbit of a satellite can be divided according to altitude into: low earth orbit (LEO): the orbit altitude is 160 - 2000 km; middle earth orbit (MEO): the orbit altitude is 2000 - 35786 km; geostationary earth orbit (GEO): the orbit altitude is 35786 km, and the relative position of the satellite operating on this orbit with respect to the earth is not affected by the earth's rotation. Among them, low-earth 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 similar to those of personal mobile devices, making them more suitable for popularization in the mass market and becoming a hot spot in the current industrial development.

[0080] Due to the long communication delay of satellite communication, the timing advance mechanism designed in the current NR system is not applicable to satellite communication. In the timing advance mechanism of the prior art, the value range of TA is 0 - 3486, and the length represented by a TA value is: 39 m when the PRACH subcarrier = 30 KHZ and 78 m when it is 15 KHZ. In the random access process of the prior art, the coverage range of the timing advance amount sent to the UE carried in the random access response message sent by the base station is approximately 300 km. For low-earth orbit satellites in satellite communication, their orbit altitude is 160 - 2000 km. Obviously, the timing advance mechanism of the prior art cannot adapt to satellite communication. To adapt to satellite communication, the prior art proposes that the UE can obtain its timing advance amount by means of the satellite broadcasting common TA. Figure 2 shows a schematic diagram of the principle of a common TA mechanism in an NTN scenario. Specifically, the satellite selects a reference point on the ground, generally the point closest to the ground, with a distance of d0, and the TA representing this distance is the common TA. The TA sent by the base station to the UE is Figure 2The 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.

[0081] 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.

[0082] 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.

[0083] S310, the terminal device receives first indication information, where the first indication information includes a common timing advance of at least one candidate cell.

[0084] 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.

[0085] 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.

[0086] Optionally, the above first indication information may be sent by the base station to which at least one candidate cell belongs through a handover confirmation message. It should be understood that the above handover confirmation message is received by the source base station of the current connected cell, and the source base station forwards the handover confirmation message to the terminal device. Optionally, the source base station may convert the handover confirmation message into a handover command or an RRC reconfiguration message and send it to the terminal device. It should be understood that the above candidate cell may be the target cell in a normal handover process or one of at least one candidate cell in a conditional handover process.

[0087] Further, the first indication information may further include the correspondence between multiple common timing advances and multiple moments of at least one candidate cell. It should be understood that the above candidate cell may be the target cell in a normal handover process or one of at least one candidate cell in a conditional handover process.

[0088] Optionally, the multiple moments may be absolute moments or relative moments, such as the system frame number (SFN). The correspondence between the multiple timing advances and the multiple moments may be in the form of a list, as shown in Table 1, or the correspondence may also be a mapping relationship, for example, common TA = SFN * 100 + 6000.

[0089] Table 1 Correspondence Table of Timing Advance and Moment

[0090] Index Common TA Time (SFN) 1 6000 10 2 6500 11 3 7000 12 … … …

[0091] Optionally, the first indication information may include information about the type of at least one candidate cell, and the type may include satellite communication type and / or private network type. The type information may be NTN-related information, such as GEO cell, LEO cell (e.g., fixed cell mode and moving cell mode); it may also be private network (non-public network, NPN)-related information, such as standalone non-public network (SNPN) cell, closed access group (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.

[0092] Optionally, the first indication information may further include priority information of cell types. The priority information of cell types 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 believes that the priority arrangement among multiple candidate cells is: NTN cell is higher than NPN cell, and NPN cell is higher than PLMN cell. After receiving the first indication information including the priority information, when both the high-priority type cell and the low-priority type cell meet the handover conditions, the terminal device may preferentially select the high-priority candidate cell as its target cell.

[0093] 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 handover, thereby improving the communication quality.

[0094] Optionally, the above type information may be applied to the common TA mechanism in the NTN scenario, or may be applied to cell handover in terrestrial base stations. This application does not make any limitations in this regard.

[0095] S320, the terminal device sends a random access preamble to a target candidate cell according to the first timing advance.

[0096] It should be understood that the target candidate cell is one of the at least one candidate cell, and the first timing advance is the common timing advance of the target candidate cell.

[0097] Optionally, when the above first indication information includes a correspondence, S320 may further include: the terminal device determines the first timing advance corresponding to the first moment according to the correspondence. The first time period is determined by the terminal device 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.

[0098] It should be understood that the moments in the correspondence between the multiple common timing advances and the 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 timing advance from the correspondence according to the time of initiating random access.

[0099] Optionally, the terminal device may determine the first moment according to the time of initiating random access, so as to determine the corresponding timing advance. For example, the first moment may be 10, and its corresponding common TA is 6000.

[0100] Optionally, during the condition switching process, before the terminal device sends a preamble to a target candidate cell, the terminal device may also determine a target candidate cell that meets the preset conditions according to the preset conditions in the first indication information (such as the signal strengths of the source cell and the candidate cell, the channel qualities of the source cell and the candidate cell, the location information of the UE, the location information of the candidate base station, etc.).

[0101] Optionally, after receiving the random access preamble sent by the terminal device, the base station to which a target candidate cell belongs may send second indication information to the terminal device through the TA command in the RAR. The second indication information may include a second timing advance, and the second timing advance may be determined by the above base station according to the random access preamble.

[0102] Optionally, the second timing advance may be a positive number or a negative number. Specifically, in the prior art, the common TA has been taken into account in the second timing advance determined by the base station according to the preamble sent by the terminal device. Generally, it is the UE's TA minus the common TA, such as Figure 2 the UE specific TA in. Because 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 timing advances obtained by the base station are all positive numbers. However, 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. However, in the existing mechanism, the TA carried in the RAR is all positive numbers, so a TA value representing a negative number can be introduced.

[0103] Optionally, after receiving the second timing advance sent by a target candidate cell, the terminal device may obtain a third timing advance by adding the first timing advance and the second timing advance, and send a third message to a target candidate cell according to the third timing advance to inform that the cell handover to be accessed is completed. Optionally, the above third message may be a reconfiguration complete message, or an RRC connection request message, an RRC connection reestablishment request, a C-RNTI MAC control unit, etc. In this application, the third message may be a C-RNTI MAC control unit.

[0104] 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 shown by the formula common TA = SFN*100 + 6000 may be used.

[0105] Optionally, the corresponding relationship between multiple common timing advances and multiple moments in the embodiments of this application may be applied to the cell handover process of a connected UE, or may be applied to the random access process of an idle UE. This application does not limit this.

[0106] It should be understood that in the embodiments of the present application, the indication information sent by the base station can be sent to one terminal device or multiple terminal devices. If the base station sends the indication information to multiple terminal devices, the indication information can also include the group identifier, group index, and in-cell identifier of multiple UEs. The present application places no restrictions on the number of terminal devices.

[0107] In a mobile communication system, when a connected UE switches to another cell, the handover process is controlled by a network device, and the network device indicates to the UE to switch to the target cell by sending a handover confirmation message. Specifically, Figure 4 shows a schematic flow diagram of a handover process according to an embodiment of the present application. As Figure 4As shown, the UE performs cell measurements according to the measurement configuration sent by the previous base station. When the conditions for measurement reporting are met, the UE will send a measurement report to the base station. In S420, the base station decides on a handover based on the measurement configuration reported by the UE and determines the target cell. Optionally, this target cell can also be referred to as a candidate cell. In S430, the source base station to which the current connected cell belongs sends a handover request message to the target base station to which the target cell belongs. In S440, the target base station sends a handover confirmation message to the source base station. The target base station decides whether to allow the access of this UE based on the number of connections in the target cell, etc. If it allows, the target base station sends a handover confirmation message to the source base station. This handover confirmation message includes the common timing advance of the target cell. Further, it can include the correspondence between multiple common timing advances of the target cell and multiple moments. Optionally, this handover confirmation message can also include information about the type of the target cell. For example, this type can include satellite communication type and / or private network type. This type information can be NTN-related information, such as GEO cell, LEO cell (e.g., fixed cell mode and moving cell mode); it can also be private network (non-public network, NPN)-related information, such as standalone non-public network (SNPN) cell, Closed Access Group (CAG) cell, etc. Optionally, this type information can further include an identifier. For example, an SNPN cell can include a standalone non-public network identifier (SNPN ID), and a CAG cell can include a CAG ID. Optionally, this handover confirmation message can also include priority information about the cell type. This priority information about the cell type can indicate the priority of a certain candidate cell type. For example, this handover confirmation message can indicate that the NTN cell is the first priority, the NPN cell is the second priority, and the PLMN cell (i.e., public network cell) is the third priority. That is, the source base station believes that the priority order among multiple candidate cells is: NTN cell is higher than NPN cell, and NPN cell is higher than PLMN cell. After receiving the handover confirmation message including this priority information, when both the high-priority type cell and the low-priority type cell meet the handover conditions, the terminal device can preferentially select the high-priority candidate cell as its target cell.

[0108] In S450, the source base station sends a handover command message, i.e., an RRC reconfiguration message, to the UEs. The content included therein comes from the handover confirmation message in S440, which is equivalent to the source base station being transparent at this layer. In S460, this step is optional. If the received indication information includes the correspondence between multiple common TAs of the target cell and multiple moments, the UE selects a suitable common TA as the TA for sending the preamble according to the time when the random access is initiated. If the indication information only includes the common time advance of the target base station, this step can be omitted. In S470, the UE sends a preamble to the target base station according to the selected common TA and attempts to perform random access. In S480, the base station places the TA that needs to be adjusted by the UE in the RAR according to the received preamble. This TA may be positive or negative. In S490, the UE can obtain the TA for sending the reconfiguration complete message by adding the TA in the received RAR to the common TA used for sending the preamble.

[0109] Optionally, the above application embodiments can be applied to the NTN scenario, such as the scenario where LEO / GEO is connected to the core network as an independent base station, or can be applied to the scenario where LEO / GEO is used as a relay base station and is connected to a terrestrial base station. This application does not make any limitations in this regard.

[0110] By sending indication information including the common time advance to the terminal device, the terminal device can send the preamble more accurately in the handover scenario, improving the success rate of the base station in processing the preamble, and then increasing the success rate of random access.

[0111] Furthermore, by sending indication information including the correspondence between multiple common time advances and multiple moments to the terminal device, the terminal device can send the preamble more accurately in the handover scenario, improving the success rate of the base station in processing the preamble, and then increasing the success rate of random access.

[0112] Based on the above handover mechanism, the prior art proposes a conditional handover (CHO) mechanism to improve the handover success rate. When the source link quality is good, the source base station sends CHO configuration information to the UE. The CHO configuration information may include CHO trigger conditions and information of one or more target 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 corresponding frequency information of the candidate cell). Specifically, Figure 5 shows a schematic flow diagram of the conditional handover process of the application embodiment. As Figure 5As shown, the UE performs measurements according to the measurement configuration sent by the previous base station. When the conditions for measurement reporting are met, the UE will send a measurement report to the base station. At S520, the source base station determines to perform conditional handover for the UE based on the UE's measurement report. At S530, the source base station sends a handover request to multiple candidate base stations. At S540, the multiple candidate base stations will decide whether to allow the UE to access according to their own situations and send a handover confirmation message, the content of which is the same as that of the embodiment shown in Figure 4 and will not be elaborated here. Optionally, the handover confirmation message may further include handover conditions, which may include, for example, the signal strengths of the source cell and the candidate cells, the channel qualities of the source cell and the candidate cells, the location information of the UE, the location information of the candidate base stations, etc. At S550, the source base station sends a conditional handover command (which is also an RRC reconfiguration message). Among them, the handover command includes the handover confirmation message in S540, which is equivalent to the source base station layer being transparent. The handover command may include the common time advance of the cells of each candidate base station, or may include the correspondence between the multiple common time advances of the cells of each candidate base station and multiple moments. At the same time, it carries the conditions for the UE to perform handover. Optionally, the source base station may also place the handover confirmation messages sent by multiple candidate base stations in the same conditional handover command. At S560, when the UE determines that the current situation meets the handover conditions, it selects a suitable target candidate cell and selects a suitable common TA for sending the preamble according to the common time advance of the target candidate cell in the handover message, or according to the correspondence between the multiple common TAs of the target candidate cell and multiple moments. The remaining steps are the same as those in Figure 4 and will not be elaborated here.

[0113] Optionally, the above application embodiments may be applied to the NTN scenario, when the LEO / GEO is used as an independent base station connected to the core network, or may be applied to the scenario where the LEO / GEO is used as a relay base station connected to a terrestrial base station. This application does not make any limitations in this regard.

[0114] Each candidate base station sends indication information including the correspondence between multiple common time advances and multiple moments of the cell of this base station to the terminal device, so that the terminal device can send the preamble more accurately in the handover scenario, improve the success rate of the base station in processing the preamble, and then increase the success rate of random access.

[0115] Figure 6 shows the handover process schematic diagram of the application embodiment under the CU-DU architecture. As shown in Figure 6As shown, at S610, the UE performs measurements according to the measurement configuration sent by the previous base station. When the conditions for measurement reporting are met, the UE will send the measurement report to the source DU. At S620, the source DU sends the measurement report to the CU, optionally forwarded via an uplink RRC message. At S630, the CU sends a group handover request to the target DU, which can also be referred to as the candidate DU, optionally via a UE context establishment request message. At S640, the target DU sends a group handover confirmation message to the CU, which includes the common timing advance of the target DU's cell, or optionally, the handover confirmation message can further include the correspondence between multiple common timing advances of the target DU's cell and multiple moments. At S650, the CU sends a group handover command to the source DU, optionally via a UE context modification request message. At S660, the source DU sends a handover command message to the UEs, that is, an RRC reconfiguration message, which can include the common timing advance of the target DU's cell, or further can include the correspondence between multiple timing advances of the target DU and multiple moments. At S670, via a UE context modification response message. At S680, the UE selects an appropriate timing advance to establish a random access procedure with the target DU. At S690, the target DU sends a group handover complete message, optionally forwarded via an uplink RRC message. At S6100, the target DU sends an RRC reconfiguration complete message to the CU. At S6100, the CU sends a UE context release command to the source DU. At S6120, the source DU sends a UE context release complete message to the CU.

[0116] The above application embodiments relate to the handover process within the CU. Optionally, the cell handover can also be an inter-CU handover, and the handover process is similar to that of Figure 4 , with the difference being that there is interaction between the internal CU-DU, and the interaction information is the same as that in the intra-CU handover in Figure 6 , which will not be elaborated here.

[0117] Optionally, the above application embodiments can be applied to the NTN scenario, the scenario where LEO / GEO acts as a relay base station and is connected to the ground DU, or can also be applied to the scenario where LEO acts as a DU and is connected to the ground CU. This application does not make any limitations in this regard.

[0118] By sending the indication information including the correspondence between multiple timing advances and multiple moments of the DU to be accessed to the terminal device, the terminal device can send preambles more accurately in the handover scenario, improving the success rate of the base station in processing preambles, and then increasing the success rate of random access.

[0119] Figure 7 shows a schematic diagram of the communication device according to the embodiments of the present application. As Figure 7 shown, the device 700 includes a receiving module 710 and a transmitting module 720.

[0120] The receiving module is used to receive first indication information, where the first indication information includes the common timing 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 an allowed handover state; the sending module is used to send a random access preamble 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 the common timing advance of the target candidate cell.

[0121] Optionally, the first indication information further includes: the correspondence between multiple common timing advances and multiple moments of the at least one candidate cell; the device further includes: a processing module, configured to determine a first timing advance corresponding to a first moment according to the correspondence, where the first moment is 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.

[0122] Optionally, the first indication information further includes information about the type of the at least one candidate cell, where the type includes satellite communication type and / or private network type.

[0123] Optionally, the first indication information further includes a first preset condition, and the processing module is further configured to determine a target candidate cell that meets the preset condition.

[0124] Optionally, the receiving module is further configured to: receive second indication information sent by the one target candidate cell, where the second indication information includes a second timing advance, and the second timing advance is a positive number or the second timing advance is a negative number.

[0125] Optionally, the sending module is further configured to: send 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.

[0126] Optionally, the correspondence of multiple candidate cells of the same base station is the same.

[0127] The above communication device 700 can also be implemented in other ways, for example, by means of at least one processor, a memory, and a transceiver. The functions of the above receiving module 710 and sending module 720 can be implemented by the transceiver.

[0128] Figure 8 A schematic diagram of another communication device according to an embodiment of the present application is shown, as Figure 8 shown, the device 800 includes a sending module 810 and a receiving module 820.

[0129] The sending module is used to send first indication information to the terminal device, where the first indication information includes the common timing advance of device 800, and the first indication information is used to inform the terminal device that the at least one candidate cell is in an allowable handover state; the receiving module is used to receive the random access preamble sent by the terminal device according to the first timing advance.

[0130] Optionally, the first indication information further includes: the corresponding relationship between multiple common timing advances of device 800 and multiple moments.

[0131] Optionally, the first indication information further includes information about the type of device 800, where the type includes satellite communication type and / or private network type.

[0132] Optionally, the first indication information further includes a first preset condition, and the preset condition is used for the terminal device to determine a target candidate base station that meets the preset condition.

[0133] Optionally, the sending module is further used to: send second indication information to the terminal device, where the second indication information includes a second timing advance, and the second timing advance is determined by device 800 according to the random access preamble, and the second timing advance is a positive number or the second timing advance is a negative number.

[0134] The above communication device 800 can also be implemented in other ways, for example, by means of at least one processor, a memory, and a transceiver. The functions of the above sending module 810 and receiving module 820 can be implemented by the transceiver.

[0135] Figure 9 Shows a schematic diagram of another communication device according to an embodiment of the present application, as Figure 9 As shown, the device 900 includes a receiving module 910 and a sending module 920.

[0136] The receiving module is used to receive first indication information sent by at least one candidate base station, where the first indication information includes the common timing 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 an allowable handover state; the sending module sends the first indication information to the terminal device.

[0137] Optionally, the first indication information further includes: the corresponding relationship between multiple common timing advances of the at least one candidate cell and multiple moments.

[0138] Optionally, the apparatus further comprises: a processing module, configured to integrate a plurality of first indication messages sent by a plurality of candidate base stations into one first indication message before sending the first indication message to the terminal device.

[0139] Optionally, the first indication message further comprises 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.

[0140] Optionally, the first indication message further comprises a first preset condition, and the first preset condition is used for the terminal device to determine a target candidate base station that meets the preset condition.

[0141] The above communication apparatus 900 may also be implemented in other ways, for example, by means of at least one processor, a memory, and a transceiver. The functions of the above receiving module 910 and sending module 920 may be implemented by the transceiver.

[0142] In several embodiments provided in the present application, it should be understood that the disclosed apparatus and method may be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative. For example, the division of the modules is only a logical function division, and there may be other division methods in actual implementation.

[0143] In the above embodiments, it may be implemented in whole or in part by software, hardware, firmware, or any combination thereof. When implemented by software, it may 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 processes or functions described in the embodiments of the present invention are generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices. The computer instructions may 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 may be transmitted from a website, a computer, a server, or a data center to another website, a computer, a server, or a data center in a wired manner (such as coaxial cable, optical fiber, digital subscriber line (DSL)) or a wireless manner (such as infrared, wireless, microwave, etc.). The computer-readable storage medium may be any available medium that can be accessed by a computer or a data storage device such as a server or a data center that includes one or more available media integrated. The available medium may be a magnetic medium (for example, a floppy disk, a hard disk, a magnetic tape), an optical medium (for example, a DVD), or a semiconductor medium (for example, a solid state disk (SSD)), etc.

Claims

1. A communication method, characterized in that, it includes: receiving first indication information from a base station to which at least one candidate cell belongs, the first indication information including a common timing advance of the at least one candidate cell; sending a random access preamble to a target candidate cell according to a first timing advance, the target candidate cell being one of the at least one candidate cells, and the first timing advance being the 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 a correspondence relationship between the common timing advance and the time of each candidate cell in the at least one candidate cell; the method further includes: determining a first timing advance corresponding to a first time according to a first correspondence relationship, the first time being determined by a terminal device according to the time of initiating random access to a target candidate cell, the target candidate cell being one of the at least one candidate cells, and the first correspondence relationship being the correspondence relationship of 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: judging the target candidate cell that meets the preset condition.

5. The method according to claim 1 or 2, characterized in that, the method further includes: receiving second indication information sent by the one target candidate cell, the second indication information including a second timing advance, the second timing advance being a positive number, or the second timing advance being a negative number.

6. The method according to claim 5, characterized in that, the method further includes: sending third indication information to the one target candidate cell according to a third timing advance, the third indication information including a reconfiguration completion message, and the third timing advance being obtained by adding the first timing advance and the second timing advance.

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

8. A communication method, characterized in that, it includes: a base station to which at least one candidate cell belongs sending first indication information to a terminal device, the first indication information including a common timing advance of the at least one candidate cell; receiving a random access preamble sent by the terminal device according to a first timing advance, the first timing advance being the common timing advance of a target candidate cell, and the target candidate cell being one of the at least one candidate cells.

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 instant of the candidate cell.

11. The method according to claim 8 or 9, wherein, the first indication information further includes a first preset condition, and the preset condition is used for the terminal device to determine a target candidate cell that meets the preset condition.

12. The method according to claim 8 or 9, wherein, the method further includes: sending second indication information to the terminal device, where the second indication information includes a second timing advance, and the second timing advance is determined by the candidate cell according to the random access preamble, and the second timing advance is a positive number or the second timing advance is a negative number.

13. A communication method, wherein, includes: The source base station receives first indication information from the base stations to which at least one candidate cell belongs, and the first indication information includes the common timing advance of the at least one candidate cell; The source base station sends the first indication information to the terminal device.

14. The method according to claim 13, wherein, 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, wherein, the first indication information further includes: the correspondence between the common timing advance and the time instant of each candidate cell in the at least one candidate cell.

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

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

18. A communication device, wherein, includes: a receiving module, configured to receive first indication information from the base stations to which at least one candidate cell belongs, and the first indication information includes the common timing advance of the at least one candidate cell; a sending module, configured to send a random access preamble 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 the common timing advance of the target candidate cell.

19. The device according to claim 18, wherein, 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, wherein, the first indication information is used to determine the correspondence between the common timing advance and the time instant of each candidate cell in the at least one candidate cell; the device further includes: A processing module, configured to determine a first timing advance corresponding to a first moment according to the corresponding relationship, where the first moment is determined by a communication device according to the time when a 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 apparatus according to claim 20, wherein, the first indication information further includes a first preset condition, and the processing module is further configured to determine the target candidate cell that meets the preset condition.

22. The apparatus according to claim 18 or 19, wherein, the receiving module is further configured to: receive second indication information sent by the one target candidate cell, where the second indication information includes a second timing advance, and the second timing advance is a positive number or the second timing advance is a negative number.

23. The apparatus according to claim 22, wherein, the sending module is further configured to: send 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 apparatus according to claim 20, wherein, the corresponding relationships of the multiple candidate cells of the same base station are the same.

25. A communication device, wherein, 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, where the first indication information includes a common timing advance of the at least one candidate cell; a receiving module, configured to receive a random access preamble 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.

26. The apparatus according to claim 25, wherein, 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 apparatus according to claim 25 or 26, wherein, the first indication information is used to determine a corresponding relationship between a common timing advance and a moment of each candidate cell in the at least one candidate cell.

28. The apparatus according to claim 25 or 26, wherein, the first indication information further includes a first preset condition, and the preset condition is used for the terminal device to determine a target candidate cell that meets the preset condition.

29. The apparatus according to claim 25 or 26, wherein, the sending module is further configured to: send second indication information to the terminal device, where the second indication information includes a second timing advance, and the second timing advance is determined by the communication device according to the random access preamble, and the second timing advance is a positive number or the second timing advance is a negative number.

30. A communication device, wherein, includes: A receiving module, configured to receive first indication information sent by a base station to which at least one candidate cell belongs, where the first indication information includes a common timing advance of at least one candidate cell; A sending module, configured to send the first indication information to a terminal device.

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

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

33. The apparatus according to claim 30 or 31, characterized in that the apparatus further includes: a processing module, configured to integrate a plurality of first indication information sent by a plurality of candidate cells into one first indication information before sending the first indication information to the terminal device.

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

35. A computer program product, characterized in that it includes a computer program, and when the computer program runs on a computer device, it causes the computer device to execute the method according to any one of claims 1 to 17 above.

36. A computer-readable storage medium, characterized in that it is used to store a computer program, and the computer program includes instructions for executing the method according to any one of claims 1 to 17 above.

37. A communication system, characterized in that it includes a communication device according to any one of claims 25 - 29, and a communication device according to any one of claims 30 - 34.

38. The communication system according to claim 37, characterized in that it further includes a communication device according to any one of claims 18 - 24.

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