Communication methods and communication devices

Abstract

This application provides a communication method and communication apparatus applicable to the field of L1 / L2 trigger mobility. The method includes the following: A first network device receives a contention-free random access preamble for a first candidate cell, and the first network device transmits an identifier of a target cell for switching and timing advance (TA) information of the target cell to a terminal device, where the target cell is a second candidate cell, and the TA information of the target cell is determined based on the contention-free random access preamble of the first candidate cell. In detail, the candidate cell for which the terminal device initiates a random access procedure and the candidate cell to which the terminal device switches and accesses may be two different candidate cells, and the TA information of the candidate cell to which the terminal device switches and accesses may be determined based on the candidate cell for which the terminal device initiates a random access procedure. In this way, the number of random access procedures that need to be initiated by the terminal device can be reduced in this application.

Description

Technical Field

[0001] This application relates to the field of communication technologies, and more particularly, to a communication method and a communication device.

Background Art

[0002] This application claims the priority of Chinese Patent Application No. 202310396692.5, titled "COMMUNICATION METHOD AND COMMUNICATION APPARATUS", filed with the China National Intellectual Property Administration on April 6, 2023, the entire content of which is incorporated herein by reference.

[0003] In the field of communication, the movement of a terminal device triggers cell switching in a plurality of pre-set candidate cells. Specifically, the serving cell of the terminal device switches to any one of the plurality of candidate cells. The cell switching determination is performed by a distributed unit (DU). In short, the terminal device reports the measurement reports of the candidate cells to the DU, and the DU determines a candidate cell as the target cell for switching based on the measurement reports of the candidate cells, and indicates in the cell switching command that the serving cell of the terminal device switches to the target cell.

[0004] Currently, before receiving a cell switching command, the terminal device starts a random access procedure in each of the plurality of candidate cells to obtain the timing advance (TA) of the plurality of candidate cells. The TA of the candidate cell is used by the terminal device to determine the timing advance for uplink transmission in the candidate cell. However, in the above method, the terminal device needs to start many random access procedures in the plurality of candidate cells, which causes high power consumption and high random access interference of the terminal device. Therefore, how to reduce the number of random access procedures initiated by the terminal device is an urgent technical problem to be solved.

Summary of the Invention

[0005] This application provides a communication method and a communication device for reducing the number of random access procedures initiated by a terminal device.

[0006] According to the first embodiment, a communication method is provided which includes the following: A terminal device receives the TA of a first candidate cell, and the terminal device receives the identifier of the target cell for switching and identification information of the first candidate cell, where the target cell is a second candidate cell, and the identification information of the first candidate cell indicates that the TA of the target cell is determined based on the TA of the first candidate cell.

[0007] In detail, the target cell's TA is determined based on the TA of the first candidate cell.

[0008] In detail, the terminal device can determine the TA of the second candidate cell based on the acquired TA of the first candidate cell, the identifier of the target cell, and the identification information of the first candidate cell, and the terminal device does not need to acquire the TA of the second candidate cell by initiating a random access procedure for the second candidate cell. In this way, the number of random access procedures that need to be initiated by the terminal device can be effectively reduced.

[0009] In possible implementations, this method further includes: The terminal device sends a measurement report for the second candidate cell.

[0010] In detail, the terminal device reports a measurement report for a second candidate cell, and this measurement report can be used by the network device to determine the second candidate cell as the target cell for switching.

[0011] In possible implementations, the method further includes: A terminal device receives indication information, which indicates that a contention-free random access preamble should be sent in a first candidate cell, the contention-free random access preamble being used to determine the TA of the first candidate cell, and the terminal device sends the contention-free random access preamble in the first candidate cell based on the indication information.

[0012] In this way, the terminal device can transmit a contention-free random access preamble in the first candidate cell based on the indication information. This can improve the efficiency of communication between the terminal device and the network device.

[0013] In possible implementations, the first candidate cell and the second candidate cell belong to the first network device, and the first candidate cell is distinct from the second candidate cell.

[0014] In detail, when the first candidate cell and the second candidate cell are two different candidate cells, the terminal device may initiate a random access procedure for one of the candidate cells to determine the TA of that candidate cell, and then determine the TA of the other candidate cell based on the TA of that candidate cell. This can effectively reduce the number of random access procedures that need to be initiated by the terminal device, thereby reducing the power consumption of the terminal device and random access interference.

[0015] In possible implementations, the TA of the first candidate cell and the TA of the target cell are the same.

[0016] In this way, the number of random access procedures that need to be initiated by the terminal device can be effectively reduced, and power consumption and random access interference of the terminal device can be reduced.

[0017] In possible implementations, the first candidate cell and the second candidate cell belong to the set of candidate target cells for switching.

[0018] According to a second embodiment, a communication method is provided which includes the following: A first network device receives a contention-free random access preamble for a first candidate cell; the first network device transmits an identifier for the target cell to be switched and TA information for the target cell to a terminal device, where the target cell is a second candidate cell, and the TA information for the target cell is determined based on the contention-free random access preamble for the first candidate cell.

[0019] In detail, the first network device may determine the TA of the first candidate cell based on the received contention-free random access preamble of the first candidate cell, and may further determine the TA of the second candidate cell based on the TA of the first candidate cell. In this way, when the first network device determines the second candidate cell as the target cell for switching, the first network device does not need to trigger terminal devices to initiate random access procedures for the second candidate cell. This can effectively reduce the number of random access procedures that need to be initiated by terminal devices, and can effectively reduce power consumption of terminal devices and random access interference.

[0020] In a possible implementation, the target cell's TA information includes at least one of the target cell's TA or the identification information of a first candidate cell, where the identification information of the first candidate cell determines the target cell's TA based on the first candidate cell.

[0021] In detail, the terminal device may determine the TA of the second candidate cell based on any one of the above pieces of information. In this way, the first network device does not need to trigger the terminal device to initiate a random access procedure for the second candidate cell. Furthermore, the number of random access procedures that need to be initiated by the terminal device can be effectively reduced, and the power consumption of the terminal device and random access interference can be effectively reduced.

[0022] In possible implementations, the method further includes: A first network device transmits indication information to a terminal device, where the indication information indicates that a contention-free random access preamble should be transmitted in a first candidate cell, the indication information includes contention-free random access resource information for the first candidate cell, and the contention-free random access resource information is used for transmitting the contention-free random access preamble.

[0023] In this way, the first network device can indicate that the terminal device will send a contention-free random access preamble in the first candidate cell. This helps to improve the efficiency of communication between the terminal device and the network device.

[0024] In possible implementations, this method further includes the following: The first network device sends the configuration information for the first candidate cell and the configuration information for the second candidate cell to the terminal device.

[0025] In this way, based on the configuration information of these candidate cells, the terminal device can perform cell switching and data transmission after the cell switching is complete.

[0026] In possible implementations, the first candidate cell and the second candidate cell belong to the first network device, and the first candidate cell is distinct from the second candidate cell.

[0027] Specifically, when the first candidate cell and the second candidate cell are two different candidate cells, the terminal device may start a random access procedure for one of the candidate cells to determine the TA of the candidate cell, and may determine the TA of the other candidate cell based on the TA of that candidate cell. This can effectively reduce the number of random access procedures that need to be initiated by the terminal device, and can reduce the power consumption of the terminal device and random access interference.

[0028] In a possible implementation, the TA of the first candidate cell is the same as the TA of the target cell.

[0029] In this way, the number of random access procedures that need to be initiated by the terminal device can be effectively reduced, and the power consumption of the terminal device and random access interference can be reduced.

[0030] In a possible implementation, the first candidate cell and the second candidate cell belong to a set of candidate target cells for switching.

[0031] According to a third aspect, a communication method is provided that includes the following. A first network device receives first indication information from a second network device, where the first indication information indicates determining the TA of a second candidate cell based on a first candidate cell, the first candidate cell and the second candidate cell belong to a third network device, the first network device receives TA information of the first candidate cell, and the first network device transmits an identifier of a target cell for switching and TA information of the target cell to a terminal device based on the TA information of the first candidate cell and the first indication information, where the target cell is the second candidate cell.

[0032] In detail, the first network device can determine the relationship between the TA of a first candidate cell and the TA of a second candidate cell based on first indication information, and the first network device can determine the TA of the second candidate cell based on the first indication information and the acquired TA information of the first candidate cell. In this way, the first network device does not need to trigger terminal devices to initiate random access procedures for the second candidate cell. Therefore, the number of random access procedures that need to be initiated by terminal devices can be effectively reduced, and power consumption of terminal devices and random access interference can be reduced.

[0033] In a possible implementation, the target cell's TA information includes at least one of the target cell's TA or the identification information of a first candidate cell, where the identification information of the first candidate cell determines the target cell's TA based on the first candidate cell.

[0034] In detail, the terminal device may determine the TA of the second candidate cell based on any one of the above pieces of information. In this way, the first network device does not need to trigger the terminal device to initiate a random access procedure for the second candidate cell. Furthermore, the number of random access procedures that need to be initiated by the terminal device can be effectively reduced, and the power consumption of the terminal device and random access interference can be effectively reduced.

[0035] In a possible implementation, the acquisition of TA information for a first candidate cell by a first network device includes: the first network device receiving TA information for a first candidate cell from a second network device, or the first network device receiving TA information for a first candidate cell from a terminal device.

[0036] In this way, the present application supports the acquisition of TA information of the first candidate cell in multiple ways.

[0037] In a possible implementation, the TA information of the first candidate cell includes at least one of the TA of the first candidate cell or the second indication information, where the second indication information indicates that at least one of the third network device and terminal device has the TA of the first candidate cell, and the first candidate cell belongs to the third network device.

[0038] More specifically, based on any one of the above pieces of information, the first network device can decide not to trigger the terminal device to initiate a random access procedure for the second candidate cell. Furthermore, the number of random access procedures that need to be initiated by the terminal device can be effectively reduced, and the power consumption of the terminal device and random access interference can be effectively reduced.

[0039] In possible implementations, the first indication information indicates that the TA of the second candidate cell is determined based on the TA of the first candidate cell, or the first indication information indicates that the TA of the second candidate cell is determined based on the contention-free random access setting information of the first candidate cell.

[0040] In detail, the first network device may determine the TA of a second candidate cell based on either the contention-free random access preamble or the TA of the first candidate cell. In this way, the first network device may decide not to trigger terminal devices to initiate random access procedures for the second candidate cell. Furthermore, the number of random access procedures that need to be initiated by terminal devices can be effectively reduced, and power consumption of terminal devices and random access interference can be effectively reduced.

[0041] In possible implementations, the method further includes: A first network device transmits a third indication to a terminal device, where the third indication indicates that a contention-free random access preamble should be transmitted in a first candidate cell, and the contention-free random access preamble is used to determine the TA of the first candidate cell.

[0042] In this way, the first network device can indicate that the terminal device will transmit a contention-free random access preamble in the first candidate cell. This helps to improve the efficiency of communication between the terminal device and the first network device.

[0043] In possible implementations, the method further includes: a first network device receives frequency information for a first candidate cell and frequency information for a second candidate cell from a second network device, and the first network device determines third indication information based on the frequencies of the first candidate cell, the second candidate cell, and the serving cell.

[0044] In detail, the first network device may determine third indication information based on the frequencies of the first candidate cell, the second candidate cell, and the serving cell. This helps the terminal device transmit a contention-free random access preamble in candidate cells whose frequencies are closer to the serving cell's frequency. Thus, communication interruptions caused by frequency switching performed by the terminal device can be effectively avoided.

[0045] In possible implementations, the method further includes: A first network device receives subcarrier spacing (SCS) information for a first candidate cell and SCS information for a second candidate cell from a second network device, and the first network device determines third indication information based on the SCS of the first candidate cell, the SCS of the second candidate cell, and the SCS of the serving cell.

[0046] In detail, the first network device may determine third indication information based on the SCS of the first candidate cell, the SCS of the second candidate cell, and the SCS of the serving cell. This helps the terminal device to send a contention-free random access preamble in candidate cells whose SCS is closer to the serving cell's SCS. Thus, communication interruptions caused by SCS switching performed by the terminal device can be effectively avoided.

[0047] In possible implementations, the method further includes: A first network device transmits first request information to a second network device based on the frequencies of a first candidate cell, a second candidate cell, and a serving cell, wherein the first request information is used to request contention-free random access configuration information for the first candidate cell, and the contention-free random access configuration information for the first candidate cell is used to transmit a contention-free random access preamble.

[0048] In detail, the first network device may decide to obtain contention-free random access resource information for a particular candidate cell based on the frequencies of the first candidate cell, the second candidate cell, and the serving cell. This helps the terminal device transmit a contention-free random access preamble in candidate cells whose frequencies are closer to the serving cell's frequency. Thus, communication interruptions caused by frequency switching performed by the terminal device can be effectively avoided.

[0049] In possible implementations, the method further includes the following: The first network device sends second request information to the second network device based on the SCS of the first candidate cell, the SCS of the second candidate cell, and the SCS of the serving cell, wherein the second request information is used to request contention-free random access configuration information for the first candidate cell, and the contention-free random access configuration information for the first candidate cell is used to send a contention-free random access preamble.

[0050] In detail, the first network device may decide to obtain contention-free random access configuration information for a particular candidate cell based on the SCS of the first candidate cell, the SCS of the second candidate cell, and the SCS of the serving cell. This helps the terminal device to send a contention-free random access preamble in candidate cells whose SCS is closer to the serving cell's SCS. Thus, communication interruptions caused by SCS switching performed by the terminal device can be effectively avoided.

[0051] In possible implementations, the method further includes: The first network device receives contention-free random access resource information for the first candidate cell and contention-free random access configuration information for the second candidate cell, which are from the second network device.

[0052] Thus, in this application, the first network device is supported when randomly selecting one contention-free random access configuration information. It can be understood that the first network device may determine which contention-free random access configuration information to select based on the SCS of a first candidate cell, the SCS of a second candidate cell, and the SCS of the serving cell. This helps the terminal device to transmit a contention-free random access preamble in candidate cells whose SCS is closer to the serving cell's SCS. Therefore, communication interruptions caused by SCS switching performed by the terminal device can be effectively avoided. Alternatively, the first network device may determine which contention-free random access configuration information to select based on the frequency of a first candidate cell, the frequency of a second candidate cell, and the frequency of the serving cell. This helps the terminal device to transmit a contention-free random access preamble in candidate cells whose frequency is closer to the serving cell's frequency. Therefore, communication interruptions caused by frequency switching performed by the terminal device can be effectively avoided.

[0053] In possible implementations, the TA of the first candidate cell and the TA of the target cell are the same.

[0054] In this way, the number of random access procedures that need to be initiated by the terminal device can be effectively reduced, and power consumption and random access interference of the terminal device can be reduced.

[0055] In possible implementations, the first candidate cell and the second candidate cell belong to the set of candidate target cells for switching.

[0056] According to a fourth aspect, a communication method is provided which includes the following: A first network device determines first indication information, where the first indication information indicates that TA information for a second candidate cell is determined based on a first candidate cell; and the first network device transmits the first indication information to a third network device.

[0057] In detail, the first network device can determine the relationship between the TA of a first candidate cell and the TA of a second candidate cell based on first indication information, and the first network device can determine the TA of the second candidate cell based on the first indication information and the acquired TA information of the first candidate cell. In this way, the first network device does not need to trigger terminal devices to initiate random access procedures for the second candidate cell. Therefore, the number of random access procedures that need to be initiated by terminal devices can be effectively reduced, and power consumption of terminal devices and random access interference can be reduced.

[0058] In a possible implementation, the determination of the first indication information by the first network device includes the following: The first network device receives the first indication information from the second network device.

[0059] In possible implementations, the method further includes: a first network device receives frequency information for a first candidate cell and frequency information for a second candidate cell from a second network device, and the first network device transmits the frequency information for the first candidate cell and frequency information for the second candidate cell to a third network device.

[0060] In possible implementations, the method further includes: a first network device receives SCS information for a first candidate cell and SCS information for a second candidate cell from a second network device, and the first network device transmits SCS information for the first candidate cell and SCS information for the second candidate cell to a third network device.

[0061] In possible implementations, this method further includes: a first network device receives TA information for a first candidate cell from a second network device, and the first network device transmits TA information for the first candidate cell to a third network device.

[0062] In a possible implementation, the TA information of the first candidate cell includes at least one of the TA of the first candidate cell or the second indication information, where the second indication information indicates that the second network device has the TA of the first candidate cell.

[0063] In possible implementations, the method further includes: a first network device transmits a third indication to a second network device, where the third indication constitutes contention-free random access configuration information for a first candidate cell.

[0064] In possible implementations, the method further includes: a first network device receives request information from a third network device, which is used to request contention-free random access configuration information for a first candidate cell; and the first network device sends the contention-free random access configuration information for the first candidate cell to the third network device.

[0065] In possible implementations, the TA of the first candidate cell and the TA of the target cell are the same.

[0066] In possible implementations, the first candidate cell and the second candidate cell belong to the set of candidate target cells for switching.

[0067] According to a fifth aspect, a communication method is provided which includes: a first network device determines first indication information, where the first indication information indicates that TA information for a second candidate cell is determined based on a first candidate cell; and the first network device transmits the first indication information to the second network device. In possible implementations, the method further includes: the first network device transmits frequency information for the first candidate cell and frequency information for the second candidate cell to the second network device.

[0068] In possible implementations, this method further includes: The first network device transmits the SCS of the first candidate cell and the SCS of the second candidate cell to the second network device.

[0069] In possible implementations, the method further includes: a first network device receives second indication information from a second network device, where the second indication information constitutes contention-free random access configuration information for a first candidate cell, and the first network device transmits the contention-free random access configuration information for the first candidate cell to the second network device.

[0070] Optionally, the second indication information may further indicate that contention-free random access settings are not set for candidate cell 2, and that contention-free random access settings are set only for candidate cell 1.

[0071] In possible implementations, this method further includes: A first network device receives request information from a second network device, which is used to request contention-free random access configuration information for a first candidate cell.

[0072] In possible implementations, this method further includes: The first network device sends the TA of the first candidate cell to the second network device.

[0073] In possible implementations, the TA of the first candidate cell and the TA of the target cell are the same.

[0074] In a possible implementation, the first candidate cell and the second candidate cell belong to a set of candidate target cells for switching.

[0075] According to a sixth aspect, a communication device is provided, including a transceiver unit configured to receive the TA of a first candidate cell. The transceiver unit is configured to receive an identifier of a target cell to be switched and identification information of the first candidate cell. The target cell is a second candidate cell, and the identification information of the first candidate cell indicates that the TA of the target cell is determined based on the TA of the first candidate cell.

[0076] In possible implementations, the transceiver unit is further configured to transmit measurement reports for a second candidate cell.

[0077] In a possible implementation, the transceiver unit is further configured to receive indication information, where the indication information indicates that a contention-free random access preamble should be transmitted in a first candidate cell, and the contention-free random access preamble is used to determine the TA of the first candidate cell. Based on the indication information, the transceiver unit is configured to transmit a contention-free random access preamble in the first candidate cell.

[0078] In possible implementations, the first candidate cell and the second candidate cell belong to the communication device, and the first candidate cell is different from the second candidate cell.

[0079] In possible implementations, the TA of the first candidate cell and the TA of the target cell are the same.

[0080] In possible implementations, the first candidate cell and the second candidate cell belong to the set of candidate target cells for switching.

[0081] According to a seventh aspect, a communication device is provided, including a transceiver unit configured to receive a contention-free random access preamble of a first candidate cell. The transceiver unit is configured to transmit an identifier of a target cell to be switched and TA information of the target cell to a terminal device. The target cell is a second candidate cell, and the TA information of the target cell is determined based on the contention-free random access preamble of the first candidate cell.

[0082] In a possible implementation, the target cell's TA information includes at least one of the target cell's TA or the identification information of a first candidate cell, where the identification information of the first candidate cell determines the target cell's TA based on the first candidate cell.

[0083] In a possible implementation, the transceiver unit is further configured to transmit indication information to a terminal device, where the indication information indicates that a contention-free random access preamble should be transmitted in a first candidate cell, and the indication information includes contention-free random access resource information for the first candidate cell, which is used for transmitting the contention-free random access preamble.

[0084] In possible implementations, the transceiver unit is further configured to transmit configuration information for a first candidate cell and configuration information for a second candidate cell to a terminal device.

[0085] In possible implementations, the first candidate cell and the second candidate cell belong to the communication device, and the first candidate cell is different from the second candidate cell.

[0086] In possible implementations, the TA of the first candidate cell and the TA of the target cell are the same.

[0087] In possible implementations, the first candidate cell and the second candidate cell belong to the set of candidate target cells for switching.

[0088] According to the eighth aspect, a communication device is provided, including a transceiver unit configured to receive first indication information from a second network device, wherein the first indication information indicates determining the TA of a second candidate cell based on a first candidate cell, and the first and second candidate cells belong to a third network device. The transceiver unit is further configured to acquire the TA information of the first candidate cell. The transceiver unit is further configured to transmit an identifier of a target cell for switching and the TA information of the target cell to a terminal device based on the TA information of the first candidate cell and the first indication information, wherein the target cell is a second candidate cell.

[0089] In a possible implementation, the target cell's TA information includes at least one of the target cell's TA or the identification information of a first candidate cell, where the identification information of the first candidate cell determines the target cell's TA based on the first candidate cell.

[0090] In possible implementations, the transceiver unit may be further configured to receive TA information for the first candidate cell from a second network device, or the transceiver unit may be further configured to receive TA information for the first candidate cell from a terminal device.

[0091] In a possible implementation, the TA information of the first candidate cell includes at least one of the TA of the first candidate cell or the second indication information, where the second indication information indicates that at least one of the third network device and terminal device has the TA of the first candidate cell, and the first candidate cell belongs to the third network device.

[0092] In possible implementations, the first indication information indicates that the TA of the second candidate cell is determined based on the TA of the first candidate cell, or the first indication information indicates that the TA of the second candidate cell is determined based on the contention-free random access setting information of the first candidate cell.

[0093] In a possible implementation, the transceiver unit is further configured to transmit a third indication to a terminal device, where the third indication indicates that a contention-free random access preamble should be transmitted in a first candidate cell, and the contention-free random access preamble is used to determine the TA of the first candidate cell.

[0094] In a possible implementation, the transceiver unit is further configured to receive frequency information for a first candidate cell and frequency information for a second candidate cell, which are from a second network device. The communication device further includes a processing unit configured to determine third indication information based on the frequencies of the first candidate cell, the second candidate cell, and the serving cell.

[0095] In a possible implementation, the transceiver unit is further configured to receive subcarrier interval SCS information of a first candidate cell and SCS information of a second candidate cell, which are from a second network device. The communication device further includes a processing unit configured to determine a third indication information based on the SCS of the first candidate cell, the SCS of the second candidate cell, and the SCS of the serving cell.

[0096] In a possible implementation, the transceiver unit is further configured to transmit first request information to a second network device based on the frequencies of a first candidate cell, a second candidate cell, and a serving cell, where the first request information is used to request contention-free random access configuration information for the first candidate cell, and the contention-free random access configuration information for the first candidate cell is used to transmit a contention-free random access preamble.

[0097] In a possible implementation, the transceiver unit is further configured to send second request information to a second network device based on the SCS of a first candidate cell, the SCS of a second candidate cell, and the SCS of a serving cell, where the second request information is used to request contention-free random access configuration information for the first candidate cell, and the contention-free random access configuration information for the first candidate cell is used to send a contention-free random access preamble.

[0098] In a possible implementation, the transceiver unit is further configured to receive contention-free random access configuration information for a first candidate cell and contention-free random access configuration information for a second candidate cell, which are from a second network device.

[0099] In possible implementations, the TA of the first candidate cell and the TA of the target cell are the same.

[0100] In possible implementations, the first candidate cell and the second candidate cell belong to the set of candidate target cells for switching.

[0101] According to the ninth aspect, a communication device is provided, which includes a processing unit configured to determine first indication information, wherein the first indication information indicates that TA information for a second candidate cell is determined based on a first candidate cell, and a transceiver unit configured to transmit the first indication information to a third network device.

[0102] In a possible implementation, the transceiver unit is further configured to receive the first indication information from a second network device.

[0103] In a possible implementation, the transceiver unit is further configured to receive frequency information for a first candidate cell and frequency information for a second candidate cell, which are from a second network device. The transceiver unit is further configured to transmit the frequency information for the first candidate cell and frequency information for the second candidate cell to a third network device.

[0104] In a possible implementation, the transceiver unit is further configured to receive SCS information for a first candidate cell and SCS information for a second candidate cell, which are from a second network device. The transceiver unit is further configured to transmit SCS information for a first candidate cell and SCS information for a second candidate cell to a third network device.

[0105] In a possible implementation, the transceiver unit is further configured to receive TA information for the first candidate cell from a second network device. The transceiver unit is further configured to transmit TA information for the first candidate cell to a third network device.

[0106] In a possible implementation, the TA information of the first candidate cell includes at least one of the TA of the first candidate cell or the second indication information, where the second indication information indicates that the second network device has the TA of the first candidate cell.

[0107] In a possible implementation, the transceiver unit is further configured to transmit a third indication information to a second network device, where the third indication information constitutes contention-free random access configuration information for the first candidate cell.

[0108] In a possible implementation, the transceiver unit is further configured to receive request information from a third network device, which is used to request contention-free random access configuration information for a first candidate cell. The transceiver unit is further configured to transmit the contention-free random access configuration information for the first candidate cell to the third network device.

[0109] In possible implementations, the TA of the first candidate cell and the TA of the target cell are the same.

[0110] In a possible implementation, the first candidate cell and the second candidate cell belong to a set of candidate target cells for switching.

[0111] A communication device is provided, comprising: a processing unit configured to determine first indication information, wherein the first indication information indicates that TA information for a second candidate cell is determined based on a first candidate cell; and a transceiver unit configured to transmit the first indication information to a second network device.

[0112] In a possible implementation, the transceiver unit is further configured to transmit frequency information for a first candidate cell and frequency information for a second candidate cell to a second network device.

[0113] In a possible implementation, the transceiver unit is further configured to transmit SCS information for a first candidate cell and SCS information for a second candidate cell to a second network device.

[0114] In a possible implementation, the transceiver unit is further configured to receive second indication information from a second network device, where the second indication information constitutes contention-free random access configuration information for a first candidate cell. The first network device transmits the contention-free random access configuration information for the first candidate cell to the second network device.

[0115] In a possible implementation, the transceiver unit is further configured to receive request information from a second network device, where the request is used to request contention-free random access configuration information for a first candidate cell.

[0116] In a possible implementation, the transceiver unit is further configured to transmit the TA of the first candidate cell to a second network device.

[0117] In possible implementations, the TA of the first candidate cell and the TA of the target cell are the same.

[0118] In a possible implementation, the first candidate cell and the second candidate cell belong to a set of candidate target cells for switching.

[0119] According to the eleventh aspect, a communication device including a processor is provided. The processor is configured to enable the communication device to implement a method according to any one of the first aspect and possible implementations of the first aspect, to implement a method according to any one of the second aspect and possible implementations of the second aspect, to implement a method according to any one of the third aspect and possible implementations of the third aspect, to implement a method according to any one of the fourth aspect and possible implementations of the fourth aspect, or to implement a method according to any one of the fifth aspect and possible implementations of the fifth aspect, by executing a computer program or instructions or through logic circuits.

[0120] In possible implementations, the communication device further includes memory configured to store computer programs or instructions.

[0121] In possible implementations, the communication device further includes a communication interface configured to input and / or output signals.

[0122] According to a twelfth aspect, a communication device is provided, including a logic circuit and an input / output interface. The input / output interface is configured to input and / or output signals. The logic circuit is configured to implement a method according to any one of the first aspect and any possible implementations of the first aspect. Alternatively, the logic circuit is configured to implement a method according to any one of the second aspect and any possible implementations of the second aspect. Alternatively, the logic circuit is configured to implement a method according to any one of the third aspect and any possible implementations of the third aspect. Alternatively, the logic circuit is configured to implement a method according to any one of the fourth aspect and any possible implementations of the fourth aspect. Alternatively, the logic circuit is configured to implement a method according to any one of the fifth aspect and any possible implementations of the fifth aspect.

[0123] According to the thirteenth aspect, a computer-readable storage medium is provided. The computer-readable storage medium stores a computer program or instruction. When the computer program or instruction is executed on a computer, a method according to any one of the first aspect and possible implementations of the first aspect is performed, or a method according to any one of the second aspect and possible implementations of the second aspect is performed, or a method according to any one of the third aspect and possible implementations of the third aspect is performed, or a method according to any one of the fourth aspect and possible implementations of the fourth aspect is performed, or a method according to any one of the fifth aspect and possible implementations of the fifth aspect is performed.

[0124] According to the 14th aspect, a computer program product including instructions is provided. When the instructions are executed on a computer, a method according to any one of the first aspect and possible implementations of the first aspect is performed, or a method according to any one of the second aspect and possible implementations of the second aspect is performed, or a method according to any one of the third aspect and possible implementations of the third aspect is performed, or a method according to any one of the fourth aspect and possible implementations of the fourth aspect is performed, or a method according to any one of the fifth aspect and possible implementations of the fifth aspect is performed.

[0125] According to the 15th aspect, a chip including a logic circuit is provided. The logic circuit is configured to implement a method according to any one of the first aspect and possible implementations of the first aspect. Alternatively, the logic circuit is configured to implement a method according to any one of the second aspect and possible implementations of the second aspect. Alternatively, the logic circuit is configured to implement a method according to any one of the third aspect and possible implementations of the third aspect. Alternatively, the logic circuit is configured to implement a method according to any one of the fourth aspect and possible implementations of the fourth aspect. Alternatively, the logic circuit is configured to implement a method according to any one of the fifth aspect and possible implementations of the fifth aspect.

[0126] For a description of the beneficial effects of the fourth through fifteenth aspects, please refer to the description of the beneficial effects of the first through third aspects. Further details will not be explained here. [Brief explanation of the drawing]

[0127] [Figure 1] This is a diagram of a communication system 100 to which one embodiment of this application can be applied. [Figure 2] This is a diagram of application scenario 200 according to one embodiment of this application. [Figure 3] This is a diagram illustrating the cell switching procedure. [Figure 4]This is a schematic dialogue flowchart of a communication method 400 according to one embodiment of this application. [Figure 5] This is a schematic dialogue flowchart of a communication method 500 according to one embodiment of this application. [Figure 6] This is a schematic dialogue flowchart of a communication method 600 according to one embodiment of this application. [Figure 7] This is a schematic dialogue flowchart of a communication method 700 according to one embodiment of this application. [Figure 8] This is a schematic dialogue flowchart of a communication method 800 according to one embodiment of this application. [Figure 9] This is a schematic dialogue flowchart of a communication method 900 according to one embodiment of this application. [Figure 10] This is a schematic dialogue flowchart of a communication method 1000 according to one embodiment of this application. [Figure 11] This is a schematic dialogue flowchart of a communication method 1100 according to one embodiment of this application. [Figure 12] This is a schematic dialogue flowchart of a communication method 1200 according to one embodiment of this application. [Figure 13] This is a schematic dialogue flowchart of a communication method 1300 according to one embodiment of this application. [Figure 14] This is a schematic dialogue flowchart of a communication method 1400 according to one embodiment of this application. [Figure 15] This is a schematic dialogue flowchart of a communication method 1500 according to one embodiment of this application. [Figure 16] This is a schematic dialogue flowchart of a communication method 1600 according to one embodiment of this application. [Figure 17] This is a diagram showing the structure of a communication device 1700 according to one embodiment of this application. [Figure 18] This is a diagram showing the structure of a communication device 1800 according to one embodiment of this application. [Figure 19] This is a diagram showing the structure of a communication device 1900 according to one embodiment of this application. [Figure 20] This is a diagram showing the structure of a communication device 2000 according to one embodiment of this application. [Figure 21] This is a diagram showing the structure of a communication device 2100 according to one embodiment of this application. [Modes for carrying out the invention]

[0128] The technical solution of this application will be described below with reference to the attached drawings.

[0129] The technical solutions in the embodiments of this application can be applied to various communication systems, such as long-term evolution (LTE) systems, LTE frequency division duplex (FDD) systems, LTE time division duplex (TDD) systems, universal mobile telecommunications systems (UMTS), 5th generation (5G) or new radio (NR) systems, 6th generation (6G) systems and other post-5G development systems, as well as non-terrestrial network (NTN) systems such as inter-satellite communication systems and satellite communication systems. A satellite communication system includes a satellite base station and terminal devices. The satellite base station provides communication services to the terminal devices. The satellite base station can also communicate with ground base stations. A satellite can function as a base station or as a terminal device. Satellites can be non-ground base stations, non-ground devices, etc., such as unmanned aerial vehicles, hot air balloons, low Earth orbit satellites, mid-Earth orbit satellites, or high Earth orbit satellites.

[0130] The technical solutions in the embodiments of this application are applicable to both homogeneous and heterogeneous network scenarios. Furthermore, the transmission points are not limited. Cooperative multipoint transmission can be performed between macro base stations, between micro base stations, and between macro base stations and micro base stations. The technical solutions are applicable to FDD / TDD systems. The technical solutions in the embodiments of this application are applicable not only to low-frequency scenarios (sub-6G) but also to high-frequency scenarios (above 6GHz), terahertz, optical communications, etc. The technical solutions in the embodiments of this application are applicable not only to communication between network devices and terminals but also to communication between network devices, communication between terminals, and communication in the Internet of Vehicles, the Internet of Things, the Industrial Internet, etc.

[0131] The technical solution in the embodiments of this application can also be applied to scenarios in which a terminal is connected to a single base station. The base station connected to the terminal and the core network (CN) connected to the base station are of the same standard. For example, if the CN is a 5G core, the base station is correspondingly a 5G base station, and the 5G base station is directly connected to the 5G core. Alternatively, if the CN is a 6G core, the base station is a 6G base station, and the 6G base station is directly connected to the 6G core. The technical solution in the embodiments of this application can also be applied to dual connectivity (DC) scenarios in which a terminal is connected to at least two base stations.

[0132] The technical solutions in the embodiments of this application may also use macro-micro scenarios involving different forms of base stations in a communication network. For example, the base stations may be satellites, balloon stations, or unmanned aerial vehicle stations. The technical solutions in the embodiments of this application are also applicable to scenarios in which both wide-coverage and low-coverage base stations exist.

[0133] The technical solutions in the embodiments of this application can be applied to scenarios with high reliability service requirements, such as ports, industrial manufacturing, transportation, and coal mines.

[0134] It will be further understood that the technical solutions in the embodiments of this application may be further applied to 5.5G wireless communication systems, 6G wireless communication systems, and wireless communication systems beyond 6G. Application scenarios include, but are not limited to, terrestrial cellular communication scenarios, NTN scenarios, satellite communication scenarios, high altitude platform station (HAPS) communication scenarios, vehicle-to-everything (V2X) scenarios, integrated access and backhaul (IAB) scenarios, and reconfigurable intelligent surface (RIS) communication scenarios.

[0135] In the embodiments of this application, the terminal may be a device having wireless transceiver functionality, and more specifically, it may be user equipment (UE), access terminal, subscriber unit, subscriber station, mobile station, remote station, remote terminal, mobile device, user terminal, wireless communication device, user agent, or user equipment. Terminal devices may, as alternatives, be satellite phones, cellular phones, smartphones, wireless data cards, wireless modems, or machine-type communication devices, or cordless phones, session initiation protocol (SIP) phones, wireless local loop (WLL) stations, personal digital assistants (PDAs), customer-premises equipment (CPE), smart point of sale (POS) machines, handheld devices with wireless communication capabilities, computing devices or other processing devices connected to wireless modems, in-vehicle devices, communication devices carried by high-altitude aircraft, wearable devices, unmanned aerial vehicles, robots, terminals in device-to-device (D2D) communication, terminals in V2X, virtual reality (VR) terminal devices, augmented reality (AR) terminal devices, wireless terminals in industrial control, wireless terminals in self-driving, wireless terminals in telemedicine, and smart grids. These could be wireless terminals in a grid, wireless terminals in transportation safety, wireless terminals in a smart city, wireless terminals in a smart home, or terminal devices in advanced communication networks after 5G. This is not limited to the embodiments of this application.

[0136] In embodiments of this application, a communication device configured to implement the functions of a terminal device may be a terminal device, or a device capable of supporting a terminal device in implementing those functions, such as a chip system. The device may be installed in or used in combination with a terminal device. In embodiments of this application, the chip system may include a chip, or include a chip and other discrete components.

[0137] The network device in the embodiments of this application is a device having wireless transceiver functionality and is configured to communicate with terminal devices. The access network device may be a node in a radio access network (RAN), and may also be called a base station or RAN node. The access network device may be an evolved Node B (eNB or eNode B) in LTE, a base station in a 5G network, such as a gNode B (gNB), a base station in a post-5G evolved public land mobile network (PLMN), a broadband network gateway (BNG), an aggregation switch, or a 3rd generation partnership project (3GPP) access device. For example, a RAN may be configured as a RAN as defined in the 3GPP protocol, an open radio access network (O-RAN), or a cloud radio access network (C-RAN).

[0138] The network devices in the embodiments of this application may further include various forms of base stations, such as macro base stations, micro base stations (also called small cells), relay stations, transmission reception points (TRPs), transmission points (TPs), mobile switching centers, devices that perform base station functions in device-to-device (D2D), vehicle-to-everything (V2X), and machine-to-machine (M2M) communications, and network devices in NTN communication systems. This is not particularly limited to the embodiments of this application.

[0139] The network device in the embodiments of this application may, alternatively, include network elements or modules that implement several functions of a base station, for example, one or more of a central unit (CU), a distributed unit (DU), or a radio unit (RU). Optionally, the CU may be further separated into a CU control plane (CP) and a CU user plane (UP). The functions of the CU and DU may be implemented by different network elements, or both may be implemented by the base band unit (BBU) of the base station. The functions of the RU may be implemented by the radio frequency device of the base station. For example, the radio frequency device of the base station may be a remote radio unit (RRU), a pico remote radio unit (pRRU), an active antenna unit (AAU), or another unit, module, or device with radio frequency processing capabilities. The communication interface protocol between the BBU and the radio frequency device may be, but is not limited to, the Common Public Radio Interface (CPRI) interface protocol, the Enhanced Common Public Radio Interface (eCPRI) interface protocol, or the Fronthaul Interface protocol between the DU and RU in an O-RAN system.

[0140] In embodiments of this application, a device configured to implement the functions of a network device may be a network device, or a device capable of supporting a network device in implementing its functions, such as a chip system. The device may be installed in a network device or used in combination with a network device. In embodiments of this application, the chip system may include a chip, or include a chip and other discrete components.

[0141] Figure 1 is a diagram of a communication system 100 to which one embodiment of this application may be applied. As shown in Figure 1, the communication system 100 includes a network device 110 and terminal devices 120. The number of terminal devices 120 and network devices 110 in the communication system 100 is not limited in this application. It should be understood that Figure 1 is merely an example for illustrative purposes and does not limit the scope of protection claimed in this application.

[0142] It can be understood that terminal device 120 may be any one of the terminal devices listed above, and network device 110 may be any one of the network devices listed above. This is not limited to this.

[0143] More specifically, the network device 110 may or may not use a central unit (CU)-distributed unit (DU) architecture, or it may not use a CU-DU architecture. This is not limited to this. For ease of explanation, this application will be described by using an example in which the network device 110 uses a CU-DU architecture. The network device 110 may include one CU and at least one DU, the at least one DU communicating with each other via the CU.

[0144] In the communication system 100, the DU of the network device 110 can perform cell switching determination. For details, please refer to Figure 3.

[0145] Figure 2 is a diagram of application scenario 200 according to one embodiment of the present application. As shown in Figure 2, application scenario 200 includes cells #1 to #3. Terminal device 120 is located in cell #1, which is the serving cell of terminal device 120. The terminal device receives an RRC reset message from cell #1, which includes candidate cell setting for L1 / L2 triggered mobility (LTM) of cells #2 and #3. Cells #2 and #3 are candidate cells, which are potential target cells for switching. Based on the same RRC reset message, the terminal device performs the following first LTM switching and second LTM switching.

[0146] In short, before the first LTM switchover, cell #1 is the serving cell (i.e., the source serving cell), and cells #2 and #3 are candidate cells. After the first LTM switchover, the serving cell of terminal device 120 switches from cell #1 to cell #2. After the first LTM switchover, cell #2 becomes the serving cell of terminal device 120 and remains the serving cell before the second LTM switchover. Cell #1 becomes a candidate cell for the second LTM switchover, and cell #3 remains a candidate cell. After the second LTM switchover, terminal device 120 switches from cell #2 to cell #3. After the second LTM switchover, cell #3 becomes the serving cell of terminal device 120. Cell #2 becomes a candidate cell for the third LTM switchover, and cell #1 remains a candidate cell. In other words, each of cells #1 through #3 can become a serving cell after the switchover is complete. For ease of distinction and explanation, in this application, cell #1 is defined as the source serving cell (further explanation is provided below), cell #2 is defined as the target cell for the first LTM switchover (terminal device 120 switches from cell #1 to cell #2), and cell #3 is simply a candidate cell.

[0147] In application scenario 200, the network device 110 interacting with the terminal device 120 is a base station. If the network device 110 uses a CU-DU split architecture, the network device 110 includes one CU and at least one DU. Cells #1 to #3 may belong to different DUs of the same CU, and all DUs may belong to the network device 110. Alternatively, cells #1 to #3 may all belong to the same DU, and the DU may belong to the network device 110. In this way, application scenario 200 can be applied to interactions within a base station. In application scenario 200, cells #1 to #3 may, alternatively, belong to different DUs of different CUs. For example, cell #1 may belong to DU1 of CU1, and cells #2 and #3 may belong to DU2 of CU2, which are different from CU1 and CU2. In this way, application scenario 200 can be applied to interactions between base stations.

[0148] In conclusion, application scenario 200 can be applied to communication between base stations and communication within base stations. For ease of explanation, this application defines that one cell corresponds to one device (hereinafter referred to as "network device"), and the device can be a DU or CU. For ease of distinction, network devices 100 through 400 are defined in this application. Network device 100 (corresponding to cell #1), network device 300 (corresponding to cell #2), and network device 400 (corresponding to cell #3) can all be DUs, while network device 200 is a CU. This will be further explained below.

[0149] It should be noted that the technical solutions disclosed in this application may be applied to communication between base stations (e.g., between gNBs) or to communication within a base station (e.g., within a gNB). For the sake of clarity, communication within a base station is primarily used as an example for the purposes of this application. However, the relevant explanations may be applied to scenarios of communication between base stations. For example, network device 100 and network device 200 belong to base station 1, and network device 300 belongs to base station 2. A unified explanation is provided herein. Further details are not described below.

[0150] Figure 3 is a diagram of the cell switching procedure. As shown in Figure 3, the cell switching procedure includes the following steps.

[0151] S310: Terminal device 120 transmits measurement report information to DU1.

[0152] In response, DU1 receives measurement report information. This measurement report information includes measurement results from multiple neighboring cells.

[0153] Optionally, the measurement report information is Layer 3 (L3) measurement results. The L3 measurement results include measurement results for multiple neighboring cells where terminal device 120 performed L3 smoothing processing.

[0154] S320:DU1 sends an uplink radio resource control message transfer (UL RRC message transfer) message to the CU.

[0155] In response, the CU receives a UL RRC message forwarding message. The UL RRC message forwarding message contains measurement report information in S310.

[0156] S330:CU decides to initiate the LTM configuration procedure.

[0157] In detail, the CU determines, based on the measurement report information, that the LTM setup procedure needs to be initiated for some or all of the neighboring cells in S310. In other words, the CU determines the LTM candidate cells (which may include cells #1 to #3 in Figure 2) based on the measurement report information, and as a result, the terminal device 120 performs LTM switching in the LTM candidate cells.

[0158] S340:CU sends a UE CONTEXT SETUP REQUEST MESSAGE to DU2.

[0159] In detail, the UE context setup request message includes the identifier of at least one candidate cell. At least one candidate cell includes candidate cell 1, as described below. For example, at least one candidate cell includes cells #1 through #3 in Figure 2. Candidate cell 1 could be cell #2 or cell #3.

[0160] Optionally, at least one candidate cell belongs to multiple neighboring cells. The UE context setup request message is used to request LTM configuration information for at least one candidate cell, and as a result, the terminal device 120 can perform LTM switching based on the LTM configuration information.

[0161] S350:DU sends a UE Context Setup Response Message.

[0162] In detail, if DU2 accepts the LTM configuration request, DU2 decides to respond to a UE context setup request message. The UE context setup response message includes lower layer configuration information for at least one candidate cell (e.g., radio link control (RLC) configuration information, media access control (MAC) configuration information, and physical layer (PHY) configuration information). This information may be used by the terminal device 120 to perform LTM switching and data transmission after the LTM switching is complete.

[0163] S360:CU sends a downlink (DL) RRC message transfer message to DU1.

[0164] In response, DU1 receives a DL RRC message forwarding message. The DL RRC message forwarding message includes an RRC reconfiguration message, which includes lower layer configuration information for at least one candidate cell.

[0165] S370:DU1 sends an RRC reset message to terminal device 120.

[0166] In response, terminal device 120 receives an RRC reset message.

[0167] It can be understood that the cell receiving the RRC reset message is the source serving cell, i.e., cell #1.

[0168] In detail, the RRC reconfiguration message includes LTM configuration information provided by DU2 for at least one candidate cell. In other words, terminal device 120 can perform LTM switching based on the RRC reconfiguration message.

[0169] Optionally, the RRC reconfiguration message may further include random access common configuration information for each of at least one candidate cell. The random access common configuration information is used by the terminal device 120 to send a contention-free random access preamble in the corresponding candidate cell, and the contention-free random access preamble is used to determine the TA of the candidate cell. The TA is used to control the timing of uplink transmissions from terminal devices (e.g., through a physical uplink shared channel (PUSCH) or a physical uplink control channel (PUCCH)) to ensure that the reception of uplink transmissions (e.g., through PUSCH or PUCCH) from multiple terminal devices at the base station is synchronized.

[0170] Note that the RRC reset message may be used for the initial LTM switchover (first LTM switchover) and may also be used for multiple subsequent switchovers (e.g., second LTM switchover), and no additional RRC reset messages are required. A unified explanation is provided herein. Further details are not provided below.

[0171] S380: Terminal device 120 sends an RRC reset completion message to DU1.

[0172] In response, DU1 receives a message indicating that the RRC reconfiguration is complete.

[0173] S390:DU1 sends an RRC reconfiguration complete message to the CU.

[0174] In response, the CU receives a message indicating that the RRC reconfiguration is complete.

[0175] S3100: Terminal device 120 sends the measurement report for candidate cell 1 to DU1.

[0176] In response, DU1 receives the measurement report for candidate cell 1.

[0177] More specifically, before or after S3100, DU1 may send multiple physical downlink control channel (PDCCH) orders to terminal device 120. Multiple PDCCH orders are used to indicate or trigger terminal device 120 to send contention-free random access preambles in all of at least one candidate cells in order to obtain the TA of the candidate cells. The PDCCH orders include contention-free random access configuration information for the candidate cells, which is used to send the contention-free random access preambles. Terminal device 120 sends contention-free access preambles in all of at least one candidate cells to obtain the TA of the candidate cells. For details on the function of the TA, see the description in S370. Further details are not provided here.

[0178] It can be understood that one PDCCH order corresponds to one candidate cell. DU1 sends multiple PDCCH orders to terminal device 120 to trigger terminal device 120 to initiate a random access procedure for multiple candidate cells.

[0179] Optionally, terminal device 120 receives a random access response (RAR) message, where the random access response message includes the TA of the candidate cell.

[0180] S3110:DU1 determines candidate cell 1 as the target cell for LTM switching.

[0181] In detail, DU1 determines, based on the measurement report of candidate cell 1, that the channel quality of candidate cell 1 is better than the channel quality of the serving cell, and further determines that the serving cell of terminal device 120 will be switched to candidate cell 1.

[0182] S3120:DU1 sends an LTM command to terminal device 120.

[0183] Correspondingly, terminal device 120 receives an LTM command generated by DU1, where the LTM command includes an identifier for the target cell to be switched. Terminal device 120 switches to the target cell based on the LTM command. The target cell is candidate cell 1 (for example, cell #2).

[0184] In detail, after receiving the LTM command, the terminal device 120 may access the target cell using a random access method, for example, through a random access channel (RACH), or it may access the target cell using a random access channel-less (RACH-less) or random access channel-skip (RACH-skip) method, for example, by directly accessing the target cell via PUSCH or PUCCH without having to send a random access preamble. PUSCH or PUCCH must carry indication information a, which indicates to DU2 that the terminal device 120 has successfully accessed candidate cell 1. For example, indication information a includes the cell-radio network temporary identifier (C-RNTI) of the terminal device 120.

[0185] S3130:DU1 sends an LTM notification to the CU.

[0186] In detail, the CU determines the target cell for LTM switching based on the LTM notification. The LTM notification includes the identifier of the target cell, for example, the identifier of candidate cell 1.

[0187] Furthermore, the CU sends downlink data to the DU2 corresponding to the target cell.

[0188] S3140:DU2 sends an access success message to CU.

[0189] In response, the CU receives an access success message, which includes the identifier of the target cell, indicating to the CU that terminal device 120 has successfully accessed the target cell.

[0190] It can be understood that after DU2 determines, based on the access procedure in S3120, that terminal device 120 has successfully accessed the target cell, DU2 sends an access success message to CU. Furthermore, CU determines, based on the target cell identifier in the access success message, that terminal device 120 has successfully switched to the target cell.

[0191] Generally, before an LTM cell switchover is performed, DU1 indicates that the terminal device 120 will separately initiate a random access procedure for at least one pre-configured candidate cell, and as a result, DU1 or DU2 will obtain the TA of at least one candidate cell. After receiving the LTM command, the terminal device 120 switches to the target cell based on the LTM command. In order to obtain the TA of the candidate cells before performing an LTM cell switchover, the terminal device 120 must initiate a random access procedure for each of at least one candidate cells before receiving the LTM command. If a large number of LTM candidate cells are configured for the terminal device 120, the terminal device 120 will need to initiate many unnecessary random access procedures, which results in high power consumption and high random access interference for the terminal device 120. Furthermore, communication of the terminal device 120 in the serving cell may be interrupted.

[0192] In this regard, the present application provides a communication method and a communication device for reducing the number of random access procedures initiated by a terminal device.

[0193] The following describes the communication method and communication device in the embodiments of this application with reference to the attached drawings.

[0194] Please note that Method 400 is primarily described from the DU side, Method 500 is primarily described from the source DU side, Method 600 is primarily described from the terminal device side, and Method 700 is also primarily described from the terminal device side. Methods 400, 600, and 700 are related at a technical level or are primarily described from different device sides based on the same technical problem. Relevant terms and explanations may be mutually referenced. Methods 500, 600, and 700 are related at a technical level or are primarily described from different device sides based on the same technical problem. Relevant terms and explanations may be mutually referenced. Therefore, Methods 400, 600, and 700 are related embodiments, and Methods 500, 600, and 700 are related embodiments.

[0195] Figure 4 is a schematic dialogue flowchart of a communication method 400 according to one embodiment of the present application. Method 400 may be implemented by a terminal device 120 and a network device 100, or by modules and / or components (e.g., chips or integrated circuits) installed within the terminal device 120 and the network device 100 and having corresponding functions. This is not limited to the embodiments of the present application. For illustrative purposes, the following example uses a case in which Method 400 is implemented by a terminal device 120 and a network device 100. For a description of the network device 100, see the description in Figure 2. The network device 100 manages a plurality of cells. The plurality of cells include candidate cell 1 (e.g., cell #2 in Figure 2) and candidate cell 2 (e.g., cell #3 in Figure 2). Candidate cell 1 and candidate cell 2 are the same antenna cell. As shown in Figure 4, Method 400 includes the following steps.

[0196] Optionally, in S410a, the network device 100 sends configuration information 1 for candidate cell 1 and configuration information 2 for candidate cell 2 to the terminal device 120.

[0197] Accordingly, terminal device 120 receives configuration information 1 for candidate cell 1 and configuration information 2 for candidate cell 2. For a detailed explanation of configuration information 1 and configuration information 2, please refer to the explanations of S360 and S370 in Figure 3. Further details will not be explained here. Configuration information 1 for candidate cell 1 further includes random access common configuration information, which includes the route sequence, etc.

[0198] In this way, based on the configuration information of these candidate cells, the terminal device 120 can perform cell switching and data transmission after the cell switching is complete.

[0199] Optionally, in S410b, the network device 100 transmits indication information 1 to the terminal device 120, where indication information 1 indicates that the terminal device 120 will transmit contention-free random access preamble 1 in candidate cell 1.

[0200] In detail, indication information 1 includes contention-free random access configuration information 1 for candidate cell 1, and contention-free random access configuration information 1 is used for transmitting contention-free random access preamble 1. Correspondingly, terminal device 120 receives indication information 1 from network device 100 and can transmit contention-free random access preamble 1 in candidate cell 1 based on indication information 1. In this way, terminal device 120 can transmit contention-free random access preamble 1 in candidate cell 1 based on indication information 1. This can improve the efficiency of communication between terminal device 120 and network device 100.

[0201] Furthermore, the terminal device 120 can transmit a contention-free random access preamble 1 in the candidate cell 1 based on the random access common configuration information and the contention-free random access configuration information 1.

[0202] In detail, contention-free random access configuration information 1 includes indication information for the time-frequency resource used to transmit contention-free random access preamble 1 in candidate cell 1, and / or an identifier for contention-free random access preamble 1. There is a correspondence between the time-frequency resource for contention-free random access preamble 1 and the synchronization signal and physical broadcast channel block (SSB) or channel state information (CSI)-reference signal (RS). Contention-free random access preamble 1, and / or the time-frequency resource for contention-free random access, are used to uniquely identify terminal device 120 in candidate cell 1.

[0203] In a possible implementation, indication information 1 may be in the PDCCH order described above. Network device 100, based on the PDCCH order, transmits contention-free random access preamble 1 in candidate cell 1 to determine the TA of candidate cell 1, and triggers terminal device 120 to perform a TA measurement on contention-free random access preamble 1. Furthermore, network device 100 determines that terminal device 120 is currently being accessed, based on contention-free random access preamble 1 and / or time-frequency resources for contention-free random access.

[0204] S410: Terminal device 120 transmits contention-free random access (CFRA) preamble 1 to network device 100 in candidate cell 1.

[0205] Correspondingly, the network device 100 receives the contention-free random access preamble 1 in candidate cell 1 and determines the TA of candidate cell 1 and the TA of candidate cell 2 based on the contention-free random access preamble 1. The contention-free random access preamble 1 can uniquely identify the terminal device 120 in candidate cell 1.

[0206] More specifically, the same network device (which may be network device 100 in method 400, or network device 300 in method 500 below, but is not limited to this) manages two different cells, namely cell A and cell B. If cell A and cell B are the same antenna cell, it is determined that there is a correlation between the TA of cell A and the TA of cell B. The correlation may be as follows: For the same terminal device, the TA of cell A and the TA of cell B are the same, or the absolute difference between the TA of cell A and the TA of cell B is less than a threshold. The threshold may be set to the cyclic prefix (CP) length of cell A or cell B, or another value. The above definition may be further applicable to the following embodiments. Candidate cell 1 may be cell A, and candidate cell 2 may be cell B. Therefore, there is a correlation between the TA of candidate cell 1 and the TA of candidate cell 2. This explanation is also applicable to all of the following embodiments. Further details are not described below.

[0207] In detail, the network device 100 can determine a candidate cell group. The candidate cell group includes the same antenna candidate cell, and the TAs of multiple candidate cells in the group satisfy the correlation described above. For example, candidate cell 1 and candidate cell 2 belong to the candidate cell group.

[0208] In possible implementations, candidate cell 1 and candidate cell 2 belong to a set of candidate target cells for LTM switching. The serving cell of terminal device 120 can switch to any candidate cell in the set of candidate target cells for switching. The set of candidate target cells for LTM switching can be the candidate cell group described above.

[0209] In a possible implementation, network device 100 is a DU (which corresponds to cells #1 through #3), and the DU is responsible for managing the serving cell, candidate cell 1, and candidate cell 2 of terminal device 120. For ease of understanding, the following example uses network device 100 as a DU for illustrative purposes.

[0210] S420: The network device 100 transmits the identifier of the target cell to be switched and the TA information of the target cell to the terminal device 120, where the target cell is candidate cell 2, and the TA information of the target cell is determined based on the contention-free random access preamble 1 of candidate cell 1.

[0211] In response, terminal device 120 receives the identifier of the target cell to be switched and the TA information of the target cell. Based on the target cell identification information, terminal device 120 determines candidate cell 2 as the target cell for the switch.

[0212] In possible implementations, the identifier of the target cell for switching and the TA information of the target cell are carried in an LTM command message, shown in S3120 in Figure 3. The LTM command message may be a media access control (MAC) control element and is generated by the DU.

[0213] Optionally, the identifier of the target cell for switching and the TA information of the target cell may be carried separately in the same or different information. This is not limited to these cases.

[0214] In a possible implementation, the TA information of the target cell may be determined based on the contention-free random access preamble 1 of candidate cell 1, as follows: Network device 100 (DU) determines that if candidate cell 1 and the target cell are the same antenna candidate cell, the TA of candidate cell 1 and the TA of the target cell satisfy the above correlation. Therefore, network device 100 (DU) determines the TA of candidate cell 1 (e.g., the first TA) based on the contention-free random access preamble 1, and further determines the TA of the target cell (e.g., the second TA) based on the correlation between the two TAs. For example, the first TA and the second TA are the same.

[0215] In another possible implementation, the target cell's TA information may be determined based on the contention-free random access preamble 1 of candidate cell 1, as follows: Network device 100 (DU) determines the target cell's TA based on the acquired contention-free random access preamble 1 of candidate cell 1 and the above correlation.

[0216] The TA of the target cell is determined by the method described above. When candidate cell 2 is determined as the target cell for LTM switching, the network device 100 (DU) does not need to trigger terminal device 120 to initiate a random access procedure for the target cell in order to obtain the TA of the target cell. In this way, the number of random access procedures initiated by terminal devices can be effectively reduced, and communication interruptions for the serving cell can be reduced.

[0217] In possible implementations, the TA information of the target cell is: It includes at least one of the following: the target cell's TA, or the identification information of candidate cell 1.

[0218] In Example P1, the target cell's TA is the target cell's absolute TA value. Terminal device 120 determines the target cell's absolute TA value as the uplink timing and accesses the target cell based on that absolute TA value (i.e., in a RACH-skip or RACH-less scheme).

[0219] In Example P2, before determining candidate cell 2 as the target cell, network device 100 (DU) receives contention-free random access preamble 1 in candidate cell 1, determines the TA of candidate cell 1, and sends a RAR message to terminal device 120, where the RAR message includes the TA (absolute TA value) of candidate cell 1. After determining candidate cell 2 as the target cell, network device 100 (DU) sends identification information for candidate cell 1 to terminal device 120, where the identification information for candidate cell 1 indicates that terminal device 120 will determine the TA of the target cell based on candidate cell 1. For example, the identification information for candidate cell 1 indicates that the TA of the target cell and the TA of candidate cell 1 are the same. In this way, terminal device 120 can access the target cell (i.e., candidate cell 2) based on the determined TA of the target cell (i.e., RACH-skip or RACH-less method).

[0220] In possible implementations, the identification information for candidate cell 1 includes either the identifier of candidate cell 1 (e.g., cell index index) or information about the identification features of candidate cell 1 (e.g., individual bits of candidate cell 1).

[0221] It should be noted that Method 400 can be applied to a scenario in which candidate cell 1, candidate cell 2, and serving cell all belong to the DU (i.e., network device 100). Method 400 primarily concerns the interaction between the DU and the terminal device 120.

[0222] The following describes a scenario in which candidate cell 1, candidate cell 2, and the serving cell belong separately to different DUs, with reference to other attached drawings. For example, candidate cell 1 and candidate cell 2 belong to network device 300, and the serving cell belongs to network device 100.

[0223] For further explanation of Method 400, please refer to Method 800 below.

[0224] Figure 5 is a schematic dialogue flowchart of a communication method 500 according to one embodiment of the present application. Method 500 may be implemented by a terminal device 120, a network device 100, and a network device 200, or by modules and / or components (e.g., chips or integrated circuits) installed within the terminal device 120, the network device 100, and the network device 200, and having corresponding functions. This is not limited to the embodiments of the present application. For illustrative purposes, the following example uses a case in which Method 500 is implemented by a terminal device 120, a network device 100, and a network device 200. For a description of network devices 100 and 200, see the description in Figure 2. Method 500 includes the following steps.

[0225] S510: Network device 200 transmits indication information 2 to network device 100, where indication information 2 indicates that the TA of candidate cell 2 is determined based on candidate cell 1.

[0226] Accordingly, the network device 100 receives indication information 2 and, based on indication information 2, determines that the TA of candidate cell 1 is associated with the TA of candidate cell 2 (see the above explanation in S410 for details).

[0227] In one implementation, network device 200 receives indication information 2 from network device 300 and then transmits indication information 2 to network device 100. Candidate cell 1 and candidate cell 2 are the same antenna cell and both belong to network device 300.

[0228] In another implementation, network device 200 determines indication information 2 and sends indication information 2 to network device 100.

[0229] In a possible implementation scenario, network device 100 is the source DU (the source DU is the DU corresponding to the serving cell), network device 200 is the CU, and network device 300 is the candidate DU (the candidate DU is the DU corresponding to cell #2 and cell #3). For ease of understanding, the following example uses network device 100 as the source DU, network device 300 as the candidate DU, and network device 200 as the CU. The above definitions or descriptions may apply to all of the following embodiments.

[0230] S520: Network device 100 receives TA information for candidate cell 1.

[0231] In example U1, network device 100 (source DU) receives TA information for candidate cell 1 from network device 200 (CU). More specifically, network device 200 (CU) transmits TA information for candidate cell 1 from network device 300 (candidate DU) to network device 100 (source DU).

[0232] In Example U2, network device 100 (source DU) receives TA information for candidate cell 1 from terminal device 120. More specifically, network device 100 (source DU) indicates that terminal device 120 will report TA information for candidate cell 1, and terminal device 120 reports the TA information for candidate cell 1 to network device 100 (source DU) based on the indication.

[0233] In a possible implementation, the TA information for candidate cell 1 is: The cell contains at least one of the following: the TA of candidate cell 1, or indication information 3, where indication information 3 indicates that the TA of candidate cell 1 has already been obtained, or that random access to the TA of candidate cell 1 has been completed.

[0234] In detail, in a possible implementation, indication message 3 includes an indication field indicating that at least one of the network device 300 (candidate DU) and terminal device 120 has a TA of candidate cell 1, or that the contention-free random access procedure used to obtain the TA of candidate cell 1 has been completed. Correspondingly, network device 100 (source DU) determines, based on indication message 3, that at least one of the network device 300 (candidate DU) and terminal device 120 has a TA of candidate cell 1, or that the contention-free random access procedure used to obtain the TA of candidate cell 1 has been completed.

[0235] S530: Based on the TA information and indication information 2 of candidate cell 1, the network device 100 transmits the identifier of the target cell for switching and the TA information of the target cell to the terminal device 120, where the target cell is candidate cell 2.

[0236] In detail, the identifier of the target cell for switching and the TA information of the target cell may be carried in the LTM command message in S3120 in Figure 3. For further details, see the explanation in S420. Further details are not explained here.

[0237] In detail, terminal device 120 receives the identifier of the target cell to be switched and the TA information of the target cell, and determines the TA of the target cell (i.e., the absolute TA value) based on the TA information of the target cell. The TA information of the target cell includes at least one of the TA of the target cell or the identification information of candidate cell 1. For a detailed explanation of the TA information of the target cell, see the relevant explanation in Method 400. Details are not explained again here. When the TA information of the target cell is the absolute TA value, terminal device 120 determines the absolute TA value of the target cell as the uplink timing and accesses the target cell based on that absolute TA value (i.e., in a RACH-skip or RACH-less manner). When the TA information of the target cell is the identification information of candidate cell 1, terminal device 120 determines the TA of the target cell based on the TA of candidate cell 1, specifically, the TA of the target cell and the TA of candidate cell 1 are the same, and then can access the target cell based on the TA of the target cell. For an explanation of obtaining the TA of candidate cell 1, see the relevant explanation in Method 400. Further details will not be explained here.

[0238] According to the above technical solution, the network device 100 (source DU) can determine, based on information such as indication information 2, TA information for candidate cell 1, and information that candidate cell 2 is the target cell for switching, that the terminal device 120 does not need to be triggered to initiate random access procedures for the target cell during LTM switching. In this way, the number of random access procedures initiated by the terminal device can be effectively reduced, and the power consumption of the terminal device can be reduced.

[0239] In a possible implementation, indicating that indication information 2 determines the TA of candidate cell 2 based on candidate cell 1 includes: indicating that indication information 2 determines the TA of candidate cell 2 based on the TA of candidate cell 1, or indicating that indication information 2 determines the TA of candidate cell 2 based on contention-free random access setting information 1 of candidate cell 1.

[0240] In Example T1, when indication information 2 indicates that the TA of candidate cell 2 is determined based on the TA of candidate cell 1, the network device 100 (source DU) determines the TA of the target cell based on information such as indication information 2, the acquired TA of candidate cell 1, and information that candidate cell 2 is the target cell for switching. For example, the TA of the target cell and the TA of candidate cell 1 are the same.

[0241] In Example T2, when indication information 2 indicates that the TA of candidate cell 2 will be determined based on the contention-free random access configuration information 1 of candidate cell 1, the network device 100 (source DU) determines the TA of the target cell based on the indication information 2, the contention-free random access configuration information 1 of candidate cell 1, and the information that candidate cell 2 is the target cell for switching. For example, the TA of the target cell and the TA of candidate cell 1 are the same.

[0242] Network device 100 (source DU) can obtain contention-free random access configuration information 1 for candidate cell 1 from network device 200 (CU). For an explanation of this process, please refer to the explanation in Figure 9. Further details will not be explained here.

[0243] In possible implementations, method 500 may further include the following steps:

[0244] S510a1: Network device 200 transmits the frequency information of candidate cell 1 and the frequency information of candidate cell 2 to network device 100.

[0245] S510b1: Network device 100 transmits indication information 4 to terminal device 120 based on the frequency of candidate cell 1, the frequency of candidate cell 2, and the frequency of the serving cell, where the indication information 4 indicates that terminal device 120 will transmit contention-free random access preamble 1 in candidate cell 1.

[0246] In response, terminal device 120 receives indication information 4 from network device 100 (source DU) and, based on the indication information 4, transmits contention-free random access preamble 1 in candidate cell 1.

[0247] In detail, the frequency of candidate cell 1 is close to or the same as the frequency of the serving cell (for example, the difference between the frequency of candidate cell 1 and the frequency of the serving cell satisfies a small frequency threshold). Alternatively, the frequency of candidate cell 2 and the frequency of the serving cell are different or have a large difference. Based on this, network device 100 (source DU) decides to trigger terminal device 120 to initiate a random access procedure for candidate cell 1 and sends indication information 4 to terminal device 120.

[0248] In detail, the network device 100 (source DU) may determine indication information 4 based on the frequencies of candidate cell 1, candidate cell 2, and the serving cell. This helps the terminal device 120 to transmit a contention-free random access preamble in candidate cells whose frequencies are closer to the serving cell's frequency. Thus, communication interruptions in the serving cell caused by frequency switching performed by the terminal device can be effectively avoided.

[0249] For a detailed explanation of how network device 100 (source DU) obtains frequency information 1 for candidate cell 1 and frequency information 2 for candidate cell 2 from network device 200 (CU), please refer to the explanation in Figure 10.

[0250] In possible implementations, method 500 may further include the following steps:

[0251] S520a2: Network device 200 transmits subcarrier spacing (SCS) information 1 for candidate cell 1 and SCS information 2 for candidate cell 2 to network device 100.

[0252] S520b2: Network device 100 transmits indication information 5 to terminal device 120 based on the SCS1 of candidate cell 1, the SCS2 of candidate cell 2, and the SCS of the serving cell, where the indication information 5 instructs terminal device 120 to transmit contention-free random access preamble 1 in candidate cell 1.

[0253] Accordingly, terminal device 120 receives indication information 5 from network device 100 (source DU) and transmits contention-free random access preamble 1 in candidate cell 1 based on indication information 5.

[0254] More specifically, the SCS of candidate cell 1 is close to or the same as the SCS of the serving cell (for example, the SCS difference between candidate cell 1's SCS and the serving cell's SCS satisfies a small SCS threshold). Alternatively, the SCS of candidate cell 2 is different from or has a large difference from the serving cell's SCS. Based on this, network device 100 (source DU) decides to initiate a random access procedure for candidate cell 1 and sends indication information 5 to terminal device 120.

[0255] In detail, the network device 100 (source DU) may determine indication information 5 based on the SCS of candidate cell 1, the SCS of candidate cell 2, and the SCS of the serving cell. This helps the terminal device 120 to send a contention-free random access preamble in a candidate cell that is appropriately closer to the serving cell's SCS. Thus, communication interruptions in the serving cell caused by SCS switching performed by the terminal device can be effectively avoided.

[0256] For a detailed explanation of how network device 100 (source DU) obtains the SCS of candidate cell 1 and candidate cell 2 from network device 200 (CU), please refer to the explanation in Figure 10.

[0257] In a possible implementation, when network device 100 (source DU) receives contention-free random access configuration information 1 for candidate cell 1 and contention-free random access configuration information 2 for candidate cell 2 from network device 200 (CU), network device 100 (source DU) sends indication information 4 to terminal device 120 based on the frequency of candidate cell 1, the frequency of candidate cell 2, and the frequency of the serving cell, and network device 100 (source DU) sends indication information 5 to terminal device 120 based on the SCS of candidate cell 1, the SCS of candidate cell 2, and the SCS of the serving cell.

[0258] In possible implementations, method 500 may further include the following steps:

[0259] S520c: Network device 100 sends request information 1 to network device 200 based on the frequency of candidate cell 1, the frequency of candidate cell 2, and the frequency of the serving cell, where request information 1 is used to request contention-free random access configuration information 1 for candidate cell 1.

[0260] In detail, when network device 100 (source DU) does not have contention-free random access configuration information for candidate cell 1, network device 100 (source DU) decides to send request information 1 to network device 300 (candidate DU) via network device 200 (CU) based on the frequencies of candidate cell 1, candidate cell 2, and the serving cell. Accordingly, network device 300 (candidate DU) determines the contention-free random access configuration information for candidate cell 1 based on request information 1 and sends the contention-free random access configuration information 1 for candidate cell 1 to network device 100 (source DU) via network device 200 (CU). For an explanation of the frequencies of candidate cell 1, candidate cell 2, and the serving cell, please refer to the explanation in S510a1. Further details are not explained here.

[0261] In possible implementations, method 500 may further include the following steps:

[0262] S520d: Network device 100 sends request information 2 to network device 200 based on the SCS of candidate cell 1, the SCS of candidate cell 2, and the SCS of the serving cell, where request information 2 is used to request contention-free random access configuration information 1.

[0263] In detail, when network device 100 (source DU) does not have contention-free random access configuration information for candidate cell 1, network device 100 (source DU) decides to send request information 2 to network device 300 (candidate DU) via network device 200 (CU) based on the SCS of candidate cell 1, the SCS of candidate cell 2, and the SCS of the serving cell. Accordingly, network device 300 (candidate DU) determines the contention-free random access configuration information 1 for candidate cell 1 based on the request information 2 and sends the contention-free random access configuration information 1 for candidate cell 1 to network device 100 (source DU) via network device 200 (CU). For a description of the SCS of candidate cell 1, the SCS of candidate cell 2, and the SCS of the serving cell, please refer to the description in S510a2. Further details will not be explained here.

[0264] It can be understood that Method 500 applies to a scenario in which both Candidate Cell 1 and Candidate Cell 2 belong to Candidate DU and the Serving Cell belongs to Source DU. Method 500 is involved in the interaction between Source DU, Terminal Device 120, Candidate DU, and CU.

[0265] It should be noted that Method 500 can be further applied to scenarios involving dialogue between base stations. For example, the source DU and CU belong to base station 1, and the candidate DU belongs to base station 2. For specific methods, please refer to the description above.

[0266] Figure 6 is a schematic dialogue flowchart of a communication method 600 according to one embodiment of the present application. Method 600 may be implemented by a terminal device 120, a network device 100, and a network device 300, or by modules and / or components (e.g., chips or integrated circuits) installed within the terminal device 120, the network device 100, and the network device 300 and having corresponding functions. This is not limited to the embodiments of the present application. For illustrative purposes, an example in which Method 600 is implemented by a terminal device 120, a network device 100, and a network device 300 will be used below. For a description of network devices 100 and 300, please refer to the description above. As shown in Figure 6, Method 600 includes the following steps.

[0267] S610: Terminal device 120 receives the TA of candidate cell 1.

[0268] In detail, when candidate cell 1 belongs to network device 100 (DU) (corresponding to method 400), network device 100 (DU) triggers terminal device 120 to send contention-free random preamble 1 in candidate cell 1 according to the PDCCH order (indication information 6). Furthermore, network device 100 (DU) performs a TA measurement on contention-free random access preamble 1 to determine the TA of candidate cell 1. Network device 100 (DU) sends a RAR message to terminal device 120, where the RAR message includes the TA (absolute TA value) of candidate cell 1.

[0269] In detail, when candidate cell 1 belongs to network device 300 (candidate DU) (corresponding to method 500), network device 100 (source DU) (corresponding to method 500) triggers terminal device 120 to send contention-free random preamble 1 in candidate cell 1 according to the PDCCH order (indication information 6). Furthermore, network device 300 (candidate DU) performs a TA measurement on contention-free random access preamble 1 to determine the TA of candidate cell 1. Network device 300 (candidate DU) sends a RAR message to terminal device, where the RAR message includes the TA (absolute TA value) of candidate cell 1.

[0270] According to the method described above, terminal device 120 can obtain the TA of candidate cell 1.

[0271] S620: The network device 100 transmits the identifier of the target cell to be switched and the TA information of the target cell to the terminal device 120, where the target cell is candidate cell 2.

[0272] Accordingly, terminal device 120 receives the identifier of the target cell to be switched over and the TA information of the target cell from network device 100. For details on the TA information of the target cell and the method for obtaining the TA information of the target cell by network device 100, please refer to the descriptions of methods 400 and 500. Further details will not be explained here.

[0273] In detail, the terminal device 120 can determine the target cell's TA based on the target cell's TA information. When the target cell's TA information is the target cell's TA (absolute TA value), the target cell's TA (absolute TA value) received by the terminal device in S620 and the candidate cell's TA (absolute TA value) shown in the RAR message received in S610 are the same.

[0274] Note that the network device 100 in S620 is the network device 100(DU) in method 400 or the network device 100(sourceDU) in method 500.

[0275] In possible implementations, method 600 may further include the following steps:

[0276] S610a: Terminal device 120 sends the measurement report for candidate cell 2 to network device 100.

[0277] In detail, terminal device 120 may send a measurement report of candidate cell 2 to network device 100. Based on the measurement report of candidate cell 2, network device 100 decides to use candidate cell 2 as the target cell for switching.

[0278] In accordance with the technical solution described above, in this application, the network device does not need to trigger the terminal device to initiate a random access procedure for the target cell. In this way, the number of random access procedures that need to be initiated by the terminal device can be reduced.

[0279] Method 600 can be applied to scenarios where both candidate cell 1 and candidate cell 2 belong to the same candidate DU and the serving cell belongs to the source DU, and it can also be applied to scenarios where the candidate cell, candidate cell 1, and the serving cell all belong to the same DU.

[0280] It should be noted that Method 600 may be further applied to scenarios involving communication between base stations. See the explanation above for further details. Further details are not provided here.

[0281] FIG. 7 is a schematic dialogue flowchart of a communication method 700 according to an embodiment of the present application. The method 700 can be implemented by the terminal device 120 and the network device 100, or can be implemented by modules and / or components (such as chips or integrated circuits) installed in the terminal device 120 and the network device 100 and having corresponding functions. This is not limited in the embodiments of the present application. The following uses an example in which the method 700 is implemented by the terminal device 120 and the network device 100 for the purpose of explanation. For the description of the network device 100, please refer to the above description. As shown in FIG. 7, the method 700 includes the following steps.

[0282] S710: The network device 100 transmits the identifier of the target cell for switching and the TA of the target cell to the terminal device 120, where the target cell is candidate cell 2.

[0283] Correspondingly, the terminal device 120 receives the identifier of the target cell for switching and the TA information of the target cell from the network device 100. For the detailed description of the TA information of the target cell and the method for obtaining the TA information of the target cell by the network device 100, please refer to the descriptions of method 400 and method 500. The details will not be described again here.

[0284] Note that the network device 100 in S710 can be the network device 100 (DU) in method 400, or can be the network device 100 (source DU) in method 500.

[0285] S720: The terminal device 120 accesses the target cell based on the TA of the target cell.

[0286] In accordance with the technical solution described above, in this application, the network device does not need to trigger the terminal device to initiate a random access procedure for the target cell. In this way, the number of random access procedures that need to be initiated by the terminal device can be reduced.

[0287] In this application, it should be noted that the terminal device does not need to obtain the TA of candidate cell 1, and the terminal device 120 can access the target cell based on the TA of the target cell in the LTM command (i.e., in a RACH-skip or RACH-less manner).

[0288] In possible implementations, method 700 may further include the following steps:

[0289] S710a: Terminal device 120 sends the measurement report for candidate cell 2 to network device 100.

[0290] In detail, terminal device 120 may send a measurement report of candidate cell 2 to network device 100. Based on the measurement report of candidate cell 2, network device 100 decides to use candidate cell 2 as the target cell for switching.

[0291] It can be understood that Method 700 may be applied to scenarios where both Candidate Cell 1 and Candidate Cell 2 belong to the same Candidate DU and the Serving Cell belongs to the Source DU, and may also be applied to scenarios where the Candidate Cell, Candidate Cell 1, and the Serving Cell all belong to the same DU.

[0292] It should be noted that Method 700 may be further applied to scenarios involving communication between base stations. See the explanation above for details. Further details are not provided here.

[0293] It should be further noted that Method 700 may correspond to or further include the same steps as Methods 400 to 600 above, for example, receiving setting information 1 of candidate cell 1.

[0294] The above method will be further explained below, with reference to the attached diagrams.

[0295] It should be noted that the methods shown in Figures 8 to 10 are further explanations of methods 400 to 700. Furthermore, the methods shown in Figures 8 to 10 can also be understood as supplementary explanations of methods 400 to 700. In Figure 8, DU1 may be the network device 100 described above. In Figures 9 and 10, DU1 may be the network device 100 described above, DU2 may be the network device 300 described above, and CU may be the network device 200 described above.

[0296] Figure 8 is a schematic dialogue flowchart of a communication method 800 according to one embodiment of the present application. Method 800 may be implemented by a terminal device 120, a DU1, and a CU, or by a module and / or component (e.g., a chip or integrated circuit) installed within the terminal device 120, the DU1, and the CU and having the corresponding functions. This is not limited to the embodiments of the present application. For illustrative purposes, an example in which Method 800 is implemented by a terminal device 120, a DU1, and a CU will be used below. As shown in Figure 8, Method 800 includes the following steps.

[0297] S801: Terminal device 120 transmits measurement report information to DU1.

[0298] S802:DU1 sends a UL RRC message forwarding message to CU.

[0299] S803:CU decides to initiate the LTM configuration procedure.

[0300] S804:CU sends a UE context correction request message to DU1.

[0301] For the description of S810 to S840, please refer to the description of S310 to S340. Details will not be described again here.

[0302] S805: DU1 sends a UE context modification response message to the CU.

[0303] When DU1 accepts the LTM setting request, DU1 decides to respond to the UE context modification request message. The UE context modification response message includes lower layer setting information of the candidate cell (for example, RLC setting information, MAC setting information, and PHY setting information). The information can be used by the terminal device 120 to perform LTM switching and data transmission after the LTM switching is completed. The UE context modification response message includes contention-free random access setting information 1.

[0304] Note that each candidate cell can correspond to one UE context modification request message and one UE context modification response message. Therefore, the UE context modification request message in S802 and the UE context modification request message in S805 are only used in a general sense and not as a quantity limit.

[0305] S806: The CU sends a DL RRC message transfer message to DU1.

[0306] For the description of S806, please refer to the description of S360. Details will not be described again here.

[0307] Optionally, the CU may send a UE context modification request message to DU1. The UE context modification request message includes an RRC reconfiguration message.

[0308] S807: DU1 sends an RRC reconfiguration message to the terminal device 120.

[0309] S808: Terminal device 120 sends an RRC reset completion message to DU1.

[0310] S809:DU1 sends an RRC reconfiguration completion message to the CU.

[0311] Optionally, DU1 may send a UE context correction response message to CU, which includes an RRC reset completion message.

[0312] For explanations of S807 to S09, please refer to the explanations of S370 to S390. Further details will not be explained here.

[0313] S8010:DU1 sends command 1 to terminal device 120.

[0314] In detail, command 1 is used to instruct terminal device 120 to send contention-free random access preamble 1 in candidate cell 1. Command 1 may be in PDCCH order.

[0315] S8011: Terminal device 120 transmits contention-free random access preamble 1.

[0316] In detail, command 1 includes contention-free random access configuration information 1. Terminal device 120 sends contention-free random access preamble 1 in candidate cell 1 based on contention-free random access configuration information 1. For a description of contention-free random access configuration information, please refer to the description in S410b.

[0317] Accordingly, DU1 receives contention-free random access preamble 1 in candidate cell 1 and determines the TA of candidate cell 1 based on the reception time of contention-free random access preamble 1.

[0318] Optionally, in S8012, DU1 sends RAR message 1 to terminal device 120.

[0319] Accordingly, terminal device 120 receives RAR message 1 from DU1. RAR message 1 includes the TA of candidate cell 1.

[0320] S8013: Terminal device 120 sends the measurement report for candidate cell 2 to DU1.

[0321] S8014:DU1 determines candidate cell 2 as the target cell for the switchover.

[0322] In more detail, if DU1 receives a measurement report from candidate cell 2 and determines, based on the measurement report from candidate cell 2, that the channel quality of candidate cell 2 is better than that of the serving cell, then DU1 may decide that candidate cell 2 is the target cell for switching.

[0323] S8015:DU1 sends LTM command 1 to terminal device 120.

[0324] Accordingly, terminal device 120 receives LTM command 1 from DU1. LTM command 1 includes the identifier of the target cell for switching and the TA information of the target cell. For a description of the TA information of the target cell, please refer to the description of method 400. Further details will not be explained here.

[0325] S8016:DU1 sends an LTM notification to the CU.

[0326] S8017:DU1 sends a message indicating successful access to the CU.

[0327] For explanations of S8016 to S8017, please refer to the explanations of S3130 to S3140. Further details will not be explained here.

[0328] In method 800, both candidate cell 1 and candidate cell 2 belong to DU1, and the serving cell also belongs to DU1. DU1 needs to be indicated to the serving cell of the terminal device 120 so as to switch to either candidate cell 1 or candidate cell 2. For the sake of clarity, in this embodiment of the present application, an example in which the serving cell of the terminal device 120 switches to candidate cell 2 is used for illustrative purposes, but the scenario in which the serving cell of the terminal device 120 switches to candidate cell 1 is not limited.

[0329] In conclusion, DU1, CU, and terminal device 120 perform the above interaction procedure, and therefore the serving cell of terminal device 120 switches to the target cell, where the target cell is candidate cell 2. Terminal device 120 determines the TA of candidate cell 2 based on the random access procedure for candidate cell 1. Therefore, the random access procedure is prevented from being initiated in candidate cell 2. In this way, the number of random access procedures that need to be initiated by terminal device 120 can be reduced.

[0330] It should be understood that the sequence of steps in the above procedure is used only as an example for understanding purposes and not as a final limitation. The above procedure may include further steps that are not mentioned. For example, the CU instructs the DU1 to release the serving cell's communication resources.

[0331] Please note that the message type used in the above procedure is merely an example and does not limit other possible types.

[0332] It should be further noted that Method 800 may be used as a further explanation of Method 400.

[0333] Figure 9 is a schematic dialogue flowchart of a communication method 900 according to one embodiment of the present application. Method 900 may be implemented by terminal device 120, DU1, DU2, and CU, or by modules and / or components (e.g., chips or integrated circuits) installed within terminal device 120, DU1, DU2, and CU and having corresponding functions. This is not limited to these. For illustrative purposes, an example in which Method 900 is implemented by terminal device 120, DU1, DU2, and CU will be used below. As shown in Figure 9, Method 900 includes the following steps.

[0334] S901: Terminal device 120 transmits measurement report information to DU1.

[0335] S902:DU1 sends a UL RRC message forwarding message to CU.

[0336] S903:CU decides to initiate the LTM configuration procedure.

[0337] For explanations of S901 to S903, please refer to the explanations of S310 to S330. Further details will not be explained here.

[0338] S904:CU sends a UE context setup request message to DU2.

[0339] In detail, a UE context setup request message includes UE context setup request message 1 and UE context setup request message 2. UE context setup request message 1 includes the identifier of candidate cell 1, and UE context setup request message 2 includes the identifier of candidate cell 2.

[0340] UE context setup request message 1 is used to request DU2 to provide LTM configuration information 1 for candidate cell 1, and UE context setup request message 2 is used to request DU2 to provide LTM configuration information 2 for candidate cell 2, so that terminal device 120 can perform LTM switching based on the LTM configuration information.

[0341] Optionally, the UE context setup request message 1 may further include indication information 7. The indication information 7 is used to indicate to or request DU2 to provide contention-free random access configuration information 1 for candidate cell 1, while contention-free random access configuration information is not requested to be provided for candidate cell 2.

[0342] Optionally, when UE context setup request message 1 excludes indication information 7, context setup request message 1 and context setup request message 2 include trigger information for the initial RACH for the LTM corresponding to each candidate cell. The trigger information for the initial RACH for the LTM is used by DU2 to provide contention-free random access configuration information for the candidate cell. See the description below for details.

[0343] Optionally, UE context setup request message 1 may further include a group identifier for candidate cell 1, and UE context setup request message 2 may further include a candidate cell group identifier corresponding to candidate cell 2. The TAs of candidate cells located within the candidate cells indicated by the group identifiers are correlated. The group identifier for candidate cell 1 and the group identifier for candidate cell 2 are the same.

[0344] Note that when CU determines that there is a correlation between the TA of candidate cell 1 and the TA of candidate cell 2, CU determines indication information 7 and indication information 2. When DU2 determines that there is a correlation between the TA of candidate cell 1 and the TA of candidate cell 2, DU2 determines indication information 2.

[0345] S905:DU2 sends a UE context setup response message to the CU.

[0346] In detail, the UE context setup response message sent by DU2 includes UE context setup response message 1 and UE context setup response message 2. UE context setup response message 1 corresponds to UE context setup request message 1, and UE context setup response message 2 corresponds to UE context setup request message 2.

[0347] In possible implementations, when UE context setup request message 1 includes indication information 7, DU2 decides to provide contention-free random access configuration information 1 for candidate cell 1 in UE context setup response message 1, based on the indication information 7. Correspondingly, when UE context setup request message 2 excludes indication information 7, DU2 does not provide contention-free random access configuration information 2 for candidate cell 2 in UE context setup response message 2. UE context setup response message 1 further includes LTM configuration information 1 for candidate cell 1, and UE context setup response message 2 includes LTM configuration information 2 for candidate cell 2.

[0348] In another possible implementation, when UE context setup request message 1 includes trigger information for the initial RACH for candidate cell 1's LTM, DU2 decides to provide contention-free random access configuration information 1 for candidate cell 1 based on the trigger information for the initial RACH for candidate cell 1's LTM. Correspondingly, UE context setup response message 1 includes the LTM configuration information 1 and contention-free random access configuration information 1 for candidate cell 1. When UE context setup request message 2 includes trigger information for the initial RACH for candidate cell 2's LTM, DU2 determines the TA determination configuration for candidate cell 2 based on the trigger information for the initial RACH for candidate cell 2's LTM and the configuration information provided by the contention-free random access configuration information for candidate cell 1. For example, the TA determination configuration indicates that the TA of candidate cell 2 is determined based on the TA of candidate cell 1, and specifically, could be the indication information 2 described above. In other words, UE context setup request message 2 includes indication information 2.

[0349] Optionally, instead of based on the initial RACH trigger information for the candidate cell's LTM, DU2 may decide to provide contention-free random access configuration information 1 for candidate cell 1 and determine the TA configuration information for candidate cell 2 based on DU2's requirements. In detail, UE context setup request message 1 includes contention-free random access configuration information 1 for candidate cell 1, and UE context setup message 2 includes indication information 2.

[0350] In another implementation, if DU2 does not receive indication information 7, DU2 decides to provide contention-free random access configuration information 1 for candidate cell 1 in the UE context setup response message 1.

[0351] Please note that for the logic or process by which DU2 determines to set contention-free random access setting information 1 for candidate cell 1 and not to set contention-free random access setting information 2 for candidate cell 2, please refer to the description of CU.

[0352] S906:CU sends a UE context correction request message to DU1.

[0353] In detail, the UE context correction request message includes indication information 2, which indicates that the TA of candidate cell 2 is determined based on candidate cell 1. Indication information 2 may be determined by CU or determined by DU2 and forwarded by CU. This is not limited to the above. The UE context correction request message includes an RRC reset message.

[0354] In detail, when UE context setup request message 1 contains indication information 7, CU determines indication information 2 and sends it to DU1. When UE context setup request message 1 and UE context setup request message 2 contain trigger information for the initial RACH for the LTM of their respective candidate cells, DU2 determines indication information 2 and sends it to CU, and CU forwards indication information 2 to DU1.

[0355] S907:DU1 sends an RRC reset message to terminal device 120.

[0356] S908: Terminal device 120 sends an RRC reset completion message to DU1.

[0357] S909:DU1 sends an RRC reset completion message to the CU.

[0358] For explanations of S907 to S909, please refer to the explanations of S807 to S809. Further details will not be explained here.

[0359] S9010:DU1 sends command 1 to terminal device 120.

[0360] In detail, command 1 is used to instruct terminal device 120 to send contention-free random access preamble 1 in candidate cell 1.

[0361] S9011: Terminal device 120 transmits contention-free random access preamble 1.

[0362] In detail, command 1 includes contention-free random access configuration information 1. Terminal device 120 transmits contention-free random access preamble 1 in candidate cell 1 based on contention-free random access configuration information 1. Accordingly, DU2 receives contention-free random access preamble 1 in candidate cell 1.

[0363] Optionally, in S9012, DU2 sends RAR message 2 to terminal device 120.

[0364] Accordingly, terminal device 120 receives RAR message 2. RAR message 2 includes the TA of candidate cell 1.

[0365] Optionally, terminal device 120 reports and sends the TA of candidate cell #1 to DU1.

[0366] Optionally, DU1 may trigger terminal device 120 to report the TA of candidate cell 1.

[0367] S9013: Terminal device 120 sends the measurement report for candidate cell 2 to DU1.

[0368] S9014:DU1 determines candidate cell 2 as the target cell for the switchover.

[0369] In more detail, if DU1 receives a measurement report for candidate cell 2 from terminal device 120 and determines, based on the measurement report for candidate cell 2, that the channel quality of candidate cell 2 is better than that of the serving cell, then DU1 may determine candidate cell 2 as the target cell for switching.

[0370] S9015:DU1 sends LTM command 1 to terminal device 120.

[0371] Accordingly, terminal device 120 receives LTM command 1. LTM command 1 includes the identifier of the target cell for switching and the TA information of the target cell. For an explanation of the TA information of the target cell, please refer to the explanation above.

[0372] S9016:DU1 sends an LTM notification to the CU.

[0373] S9017:DU2 sends a message indicating successful access to the CU.

[0374] For explanations of S9016 to S9017, please refer to the explanations of S3130 to S3140. Further details will not be explained here.

[0375] In method 900, both candidate cell 1 and candidate cell 2 belong to DU2, and the serving cell belongs to DU1. DU1 needs to be indicated to the serving cell of the terminal device 120 so as to switch to either candidate cell 1 or candidate cell 2. For the sake of clarity, in this embodiment of the present application, an example in which the serving cell of the terminal device 120 switches to candidate cell 2 is used for illustrative purposes, but the scenario in which the serving cell of the terminal device 120 switches to candidate cell 1 is not limited.

[0376] In conclusion, DU1, DU2, CU, and terminal device 120 perform the above interaction procedure, and therefore the serving cell of terminal device 120 switches to the target cell, where the target cell is candidate cell 2. Terminal device 120 determines the TA of candidate cell 2 based on the random access procedure for candidate cell 1. Therefore, the random access procedure is prevented from being initiated in candidate cell 2. In this way, the number of random access procedures that need to be initiated by terminal device 120 can be reduced.

[0377] It should be understood that the sequence of steps in the above procedure is used only as an example for understanding purposes and not as a final limitation. The above procedure may include further steps that are not mentioned. For example, the CU instructs the DU1 to release the serving cell's communication resources.

[0378] Please note that the message type used in the above procedure is merely an example and does not limit other possible types.

[0379] It should be further noted that Method 900 may be used as a further explanation of Method 500.

[0380] It should be further noted that Method 900 can be further applied to scenarios involving communication between base stations. For example, DU1 and CU belong to base station 1, and DU2 belongs to base station 2. For methods for communication between base stations, see Methods for communication within base stations. Details are not described again here. When Method 800 is applied to scenarios involving communication between base stations, the names of the above messages may be changed. For example, the UE context setup request message is changed to an HO (handover) request, and the UE context setup response message is changed to an HO response.

[0381] Figure 10 is a schematic dialogue flowchart of a communication method 1000 according to one embodiment of the present application. Method 1000 may be implemented by terminal device 120, DU1, DU2, and CU, or by modules and / or components (e.g., chips or integrated circuits) installed within terminal device 120, DU1, DU2, and CU and having corresponding functions. This is not limited to these. For illustrative purposes, an example in which Method 1000 is implemented by terminal device 120, DU1, DU2, and CU will be used below. As shown in Figure 10, Method 1000 includes the following steps.

[0382] For S1001 to S1005, please refer to the explanations for S901 to S905. Further details will not be explained here.

[0383] Note that in S1050, UE context setup response message 1 includes frequency information 1 and / or SCS1 for candidate cell 1, and UE context setup response message 2 includes frequency information 2 and / or SCS information 2 for candidate cell 2.

[0384] For a description of the candidate cell frequency and / or SCS, see the description in Method 500. The candidate cell frequency and / or SCS may be used by DU1 to determine whether to trigger terminal device 120 to initiate a random access procedure for candidate cell 1.

[0385] S1006:CU sends a UE context correction request message to DU1.

[0386] In detail, the UE context correction request message includes indication information 2, frequency information 1 and / or SCS information 1 for candidate cell 1 and frequency information 2 and / or SCS information 2 for candidate cell 2. The UE context correction request message also includes an RRC reset message.

[0387] Note that the UE context modification request message in S1060 may exclude contention-free random access configuration information 1 for candidate cell 1 and contention-free random access configuration information 2 for candidate cell 2. Accordingly, DU1 requests contention-free random access configuration information 1 for candidate cell 1 from DU2 based on frequency information and / or SCS information.

[0388] S1007:DU1 sends an RRC reset message to terminal device 120.

[0389] S1008: Terminal device 120 sends an RRC reset completion message to DU1.

[0390] S1009:DU1 sends an RRC reset completion message to the CU.

[0391] For explanations of S1006 to S1009, please refer to the explanations of S906 to S909. Further details will not be explained here.

[0392] S1010:DU1 sends command 1 to terminal device 120.

[0393] In detail, command 1 is used to instruct terminal device 120 to transmit contention-free random access preamble 1 in candidate cell 1. For details of S1010, see the description of frequency information and / or SCS information in method 500.

[0394] S1011: Terminal device 120 transmits contention-free random access preamble 1.

[0395] For an explanation of S1011, please refer to the explanation of S9011.

[0396] Optionally, in S1012, DU2 sends RAR message 3 to terminal device 120.

[0397] For an explanation of S1012, please refer to the explanation of S9012.

[0398] S1013: Terminal device 120 sends the measurement report for candidate cell 2 to DU1.

[0399] S1014:DU1 determines candidate cell 2 as the target cell for the switchover.

[0400] For an explanation of S1014, please refer to the explanation of S9014.

[0401] S1015:DU1 sends LTM command 1 to terminal device 120.

[0402] For an explanation of S1015, please refer to the explanation of S9015.

[0403] S1016:DU1 sends an LTM notification to CU.

[0404] S1017:DU2 sends a message indicating successful access to the CU.

[0405] For explanations of S1016 to S1017, please refer to the explanations of S3130 to S3140. Further details will not be explained here.

[0406] In method 1000, both candidate cell 1 and candidate cell 2 belong to DU2, and the serving cell belongs to DU1. DU1 needs to be indicated to the serving cell of the terminal device 120 so as to switch to either candidate cell 1 or candidate cell 2. For the sake of clarity, in this embodiment of the present application, an example in which the serving cell of the terminal device 120 switches to candidate cell 2 is used for illustrative purposes, but the scenario in which the serving cell of the terminal device 120 switches to candidate cell 1 is not limited.

[0407] In conclusion, DU1, DU2, CU, and terminal device 120 perform the above interaction procedure, and thus terminal device 120 switches from the serving cell to the target cell, where the target cell is candidate cell 2. Terminal device 120 determines the TA of candidate cell 2 based on the random access procedure for candidate cell 1. Therefore, the random access procedure is prevented from being initiated in candidate cell 2. In this way, the number of random access procedures that need to be initiated by terminal device 120 can be reduced.

[0408] It should be understood that the sequence of steps in the above procedure is used only as an example for understanding purposes and not as a final limitation. The above procedure may include further steps that are not mentioned. For example, the CU instructs the DU1 to release the serving cell's communication resources.

[0409] Please note that the message type used in the above procedure is merely an example and does not limit other possible types.

[0410] It should be further noted that Method 1000 may be used as a further explanation of Method 500.

[0411] It should be further noted that Method 1000 can be further applied to scenarios of dialogue between base stations. For example, DU1 and CU belong to base station 1, and DU2 belongs to base station 2. For methods for dialogue between base stations, see Method for dialogue within base stations. Details are not described again here. When Method 1000 is applied to scenarios of dialogue between base stations, the names of the above messages may be changed. For example, the UE context setup request message is changed to an HO (handover) request, and the UE context setup response message is changed to an HO response.

[0412] In embodiments of this application, methods 400 to 1000 may be applied to the switching field of a candidate cell, and may also be applied to the switching field of a physical cell identifier (PCI). In detail, one cell may be associated with multiple PCIs, and the multiple PCIs may include one serving PCI and multiple additional PCIs. See Figure 11 for details.

[0413] Figure 11 is a schematic dialogue flowchart of a communication method 1100 according to one embodiment of the present application. Method 1000 may be implemented by a terminal device 120, a DU1, and a CU, or by modules and / or components (e.g., chips or integrated circuits) installed within the terminal device 120, the DU1, and the CU and having corresponding functions. This is not limited to these. For illustrative purposes, an example in which Method 1100 is implemented by a terminal device 120, a DU1, and a CU will be used below. As shown in Figure 11, Method 1100 includes the following steps.

[0414] S1101:CU sends an RRC reset message to DU1.

[0415] Accordingly, DU1 receives an RRC reset message from CU. The RRC reset message includes configuration information for multiple additional PCIs (for example, configuration information for a first additional PCI and a second additional PCI, or reference signal (RS) configuration information). The multiple additional PCIs correspond to the same serving PCI. The configuration information for the first additional PCI includes RACH settings.

[0416] S1102:DU1 sends an RRC reset message to terminal device 120.

[0417] In detail, terminal device 120 receives the RRC reconfiguration message by using the transmission configuration indicator (TCI) state of the serving PCI or the first additional PCI.

[0418] S1103: Terminal device 120 sends an RRC reset completion message to DU1.

[0419] S1104:DU1 sends an RRC reset completion message to the CU.

[0420] S1105:DU1 sends a PDCCH order to terminal device 120.

[0421] Accordingly, terminal device 120 receives a PDCCH order from DU1. The PDCCH order is used to trigger a contention-free random access procedure. The PDCCH order contains the preamble and time-frequency resource information for the contention-free random access procedure. For further details, please refer to the above description of the PDCCH order.

[0422] S1106: Terminal device 120 initiates a contention-free random access preamble to DU1 based on the PDCCH order and RACH setting in the first additional PCI.

[0423] In detail, terminal device 12 sends a contention-free random access preamble to DU1, which is used to determine the TA of the first additional PCI, based on the PDCCH order and RACH setting in the first additional PCI. For a detailed description of the process, please refer to the above description of terminal device 120 sending the contention-free random access preamble in candidate cell 1. The two descriptions are the same; therefore, the details are not described again.

[0424] S1107: Terminal device 120 receives RAR message 4.

[0425] More specifically, DU1 determines the TA of the first additional PCI based on the contention-free random access preamble sent by terminal device 120. Accordingly, DU1 sends RAR message 4 to terminal device 120 containing the TA of the first additional PCI. RAR message 4 contains the first TA command, and the first TA command contains the first absolute TA value. More specifically, the first absolute TA value is the absolute TA value of the first additional PCI.

[0426] S1108: Terminal device 120 sends a lower layer measurement report to DU1, where the measurement report includes the measurement results of the TCI status of a second additional PCI.

[0427] S1109:DU1 decides to activate the TCI state of the second additional PCI.

[0428] In detail, DU1 determines, based on the lower-layer measurement report reported by terminal device 120, that the channel quality of the second additional PCI is better than that of the first additional PCI, and based on the lower-layer measurement report, DU1 decides to activate the TCI state of the second additional PCI and deactivate the TCI state of the first additional PCI.

[0429] In detail, the same DU manages two different PCIs, PCI#1 and PCI#2. If PCI#1 and PCI#2 are identical antenna PCIs, it is determined that there is a correlation between the TA of PCI#1 and the TA of PCI#2. The correlation may be as follows: For the same terminal device, the TA of PCI#1 and the TA of PCI#2 are either the same, or the absolute difference between the TA of PCI#1 and the TA of PCI#2 is less than a threshold. The threshold may be the CP length of PCI#1 or PCI#2 or another value. The first additional PCI may be PCI#1, and the second additional PCI may be PCI#2. Therefore, there is a correlation between the TA of the first additional PCI and the TA of the second additional PCI. Thus, DU1 determines the TA of the second additional PCI based on the above correlation and the contention-free random access preamble transmitted by terminal device 120 and used to determine the TA of the first additional PCI.

[0430] S1110:DU1 sends a second TA command and activation indication information to terminal device 120.

[0431] In detail, activation indication information (or TCI status indication for PDCCH) is used to activate the TCI status of the second additional PCI, and the second TA command is used to indicate the TA of the second additional PCI.

[0432] Note that terminal device 120 does not initiate RACH in the second additional PCI. The second TA command includes either a relative or absolute TA of the first TA. If the second TA command is an absolute TA, the absolute TA and the first TA are the same. If the second TA command is a relative TA, the relative TA is equal to 0, in other words, the TA of the second additional PCI is the same as the first TA.

[0433] S1111: Terminal device 120 accesses a second additional PCI using a random access channel skipping method.

[0434] In accordance with the technical solution described above, in this application, the network device does not need to trigger the terminal device to initiate a random access procedure for any additional PCIs that need to be accessed. In this way, the number of random access procedures that need to be initiated by the terminal device can be reduced.

[0435] Please note that for other technical solutions regarding PCI switching, please refer to the methods described above. Further details will not be provided here.

[0436] It should be noted that both Method 1100 and Methods 400 and 800 are similar technical solutions, and the difference between Method 1100 and Methods 400 and 800 is that Method 1100 is for PCI switching scenarios, while Methods 400 and 800 are for candidate cell switching scenarios. However, the two are related or similar in terms of technical solutions. Therefore, the technical solutions or procedural steps described in Method 1100 are used only as examples for understanding. Extensions to the technical solutions, etc., can be obtained by referring to the descriptions of Methods 400 and 800, this is not limited to.

[0437] The following further describes the technical solution in this application.

[0438] Switching is a crucial feature in 5G systems and is primarily triggered by the movement of terminal devices in a radio resource control (RRC) connection state. The basic purpose of switching is to provide continuous, uninterrupted communication service by switching terminal devices to an adjacent cell with good signal quality before the signal quality of the serving cell becomes unusable for communication, effectively preventing call drops caused by the degradation of the serving cell.

[0439] In the 5G RAN architecture, the base station's functions are divided into two functional units: a distributed unit (DU) responsible for handling high real-time performance, such as processing functions in the radio link control (RLC) layer, media access control (MAC) layer, and physical layer (PHY); and a central unit (CU) responsible for handling non-real-time performance, such as functions in layers like the service data convergence protocol (SDCP), SDAP, RRC layer, or packet data convergence protocol (PDCP) layer. The CU communicates with the DU through the F1 interface, with a maximum transmission delay of 3ms to 10ms.

[0440] In existing versions, Layer 3 (L3) handover means that the CU receives measurement results from the terminal device 120, where the measurement results are forwarded to the CU by the DU. Based on the measurement results, the CU decides whether to initiate a handover, for example, if the serving cell is insufficient. Furthermore, the CU sends a handover command to the DU, which then sends a handover command to the terminal device 120. There is some interaction via the F1 interface and a handover delay.

[0441] To reduce handover delay, LTM is initiated. A switching decision is sent from the CU to the DU to reduce F1 interaction. The DU decides whether to initiate switching (LTM cell switching) based on the measurement results of the terminal device 120. Switching mainly includes intra-DU switching and inter-DU switching. In addition, the DU directly sends switching commands to the terminal device 120. Inter-CU switching is still implemented using the existing L3 handover.

[0442] Currently, the InterDU LTM procedure and the IntraDU procedure, as shown in Figure 3, are in use. The difference between the IntraDU procedure and the InterDU LTM procedure shown in Figure 3 is that DU1 and DU2 belong to the same body, and there is no interaction between DU1 and DU2. For details on the interaction between CU, DU, and UE, please refer to the explanation in Figure 3.

[0443] When the target gNB-DU detects access from terminal device 120, the solution is random access. Specifically, random access is performed after LTM, and the target gNB-DU can know about the access from terminal device 120. Another solution is random access channelless (RACH-less or RACH-skip), where, for example, access is performed via PUSCH or PUCCH. Unique information may need to be carried to indicate access between the network device and the terminal. The application scenario of this application is primarily the latter solution.

[0444] In order for terminal device 120 to access the target gNB-DU using a random access channelless scheme, terminal device 120 must acquire a Timing Advance Command (TA) before receiving an LTM command. The TA is a command sent to terminal device 120 by the base station to coordinate the uplink transmission of terminal device 120. This process may include: terminal device 120 pre-transmitting uplink symbols in accordance with commands sent via PUSCH, PUCCH, and SRS, and the base station sending a Timing Advance Command (TAC) to notify terminal device 120 of the amount of time that the uplink transmission needs to precede.

[0445] Before receiving the LTM command, it can be understood that the terminal device 120 maintains communication with the source cell and performs a random access procedure for at least one candidate cell. Thus, the network device or terminal device 120 obtains TA information for at least one candidate cell. After receiving the LTM command, if the LTM command indicates a target cell and the target cell is one of the at least one candidate cell, the terminal device 120 may perform access through a dedicated PUSCH or PUCCH based on the previously obtained TA. A dedicated PUSCH or PUCCH means that the base station indicates the terminal device 120's PUSCH or PUCCH resource via dedicated signaling.

[0446] The random access procedure initiated by terminal device 120 before the LTM command is received is contention-free random access and mainly includes several types:

[0447] Type 1:

[0448] 1. Terminal device 120 sends a contention-free random access (CFRA) preamble to the candidate DU. The network device determines the TA based on the CFRA preamble.

[0449] 2. Terminal device 120 receives a RAR from candidate DU, where the RAR includes a TA command. Terminal device 120 receives the RAR and determines that random access is complete.

[0450] After random access, the source DU initiates LTM switching and sends an LTM switching command to terminal device 120, where the LTM switching command does not need to carry a TA command.

[0451] Type 2:

[0452] 1. Terminal device 120 sends a CFRA preamble to a candidate DU, and the network device determines the TA based on the CFRA preamble.

[0453] 2. Terminal device 120 receives the RAR of the candidate DU from the source DU, where the RAR includes a TA command. The candidate DU sends the RAR to the source DU, and the source DU sends the RAR to terminal device 120. Terminal device 120 receives the RAR and determines that the random access is complete.

[0454] After random access, the source DU initiates LTM switching and sends an LTM switching command to terminal device 120, where the LTM switching command does not need to carry a TA command.

[0455] Third type:

[0456] 1. Terminal device 120 sends a CFRA preamble to the candidate DU. The candidate DU determines the TA based on the CFRA preamble and sends the TA to the source DU. Terminal device 120 determines that random access is complete. In this solution, there is no RAR.

[0457] After random access, the source DU decides to initiate LTM switching and sends an LTM switching command to terminal device 120, where the LTM switching command must carry a TA command, the TA value in the TA command is obtained via CFRA.

[0458] Before receiving the LTM command, it can be understood that the terminal device 120 maintains communication with the source cell and initiates random access for at least one candidate cell. Therefore, excessive and unnecessary random access is initiated. In some scenarios (for example, in scenarios where the source cell and the candidate target cell are inter-frequency cells), a small amount of interruption occurs in the source cell.

[0459] Therefore, to reduce unnecessary random access, signaling overhead, and interruptions, this application provides a communication method. In this method, for multiple candidate cells, the UE initiates random access once. For example, multiple candidate cells transmit and receive signals through the same transmit / receive point TRP. Thus, the TAs of multiple candidate cells may be the same or shared.

[0460] For example, in a scenario where (a) a random access setting is given to a candidate cell through negotiation between base stations, and (b) multiple random access settings are given (different random access settings correspond to different candidate cells), the source DU or candidate DU determines the candidate cell from which the random access procedure will be initiated, based on frequency information or BWP information.

[0461] For example, in the procedure shown in Figure 12, in the intraDU scenario, the candidate cell managed by DU1 (which may be candidate cell #1 below) has an LTM CFRA resource, and the LTM CFRA resource is not allocated to another candidate cell (for example, candidate cell #2). When the source cell switches to candidate cell #2, the TA indicated by the LTM command is the same as the TA of candidate cell #1. Figure 12 includes the following steps.

[0462] For steps S1201 through S1209, please refer to the steps corresponding to Figures 3 and 8.

[0463] In S1205, both candidate cell #1 and candidate cell #2 are DU1 cells, and the configuration of candidate cell #1 includes a contention-free random access configuration, while candidate cell #2 may exclude a contention-free random access configuration. The LTM contention-free random access configuration includes an LTM contention-free random access preamble and / or an LTM contention-free random access time-frequency resource. Terminal device 120 can be uniquely identified by using the preamble and / or the time-frequency resource. Optionally, the LTM contention-free random access configuration includes an SSB or CSI-RS corresponding to the preamble or time-frequency resource.

[0464] S1210a:DU1 sends a PDCCH order to terminal device 120 based on the CFRA setting of candidate cell #1, where the PDCCH order instructs terminal device 120 to send contention-free random access to the first candidate cell.

[0465] The PDCCH order includes indication information for the LTM contention-free preamble and indication information for time-frequency resources.

[0466] S1210b: Terminal device 120 sends a contention-free random access preamble to DU1 in candidate cell #1 based on the PDCCH order.

[0467] DU1 determines the TA of candidate cell #1 based on the contention-free random access preamble, and further determines the TA of candidate cell #2. For example, since the transmitting antenna and receiving antenna are the same, DU1 determines that the TA of candidate cell #1 and / or the TA of candidate cell #2 are the same, in other words, that their TA values ​​are the same.

[0468] S1210c:DU1 sends a RAR to terminal device 120, where the RAR carries the TA (absolute TA value) of candidate cell #1.

[0469] Step 1210c is an optional step and may not be performed.

[0470] S1210: Terminal device 120 sends a measurement report of candidate cell #2 to DU1, where the measurement report includes the reference signal received power (RSRP) of candidate cell #2.

[0471] S1211:DU1 determines candidate cell #2 as the target cell for the switch, where candidate cell #2 is a different cell from candidate cell #1.

[0472] S1212:DU1 sends an LTM command to terminal device 120, which is used to instruct it to switch to the target cell. For example, the switch command includes the identifier of the target cell, which is the identifier of candidate cell #2 (e.g., the cell index).

[0473] In one example, the switch command further includes the TA of candidate cell #2. Alternatively, the switch command includes indication information that the TA of candidate cell #2 is determined based on the TA of candidate cell #1, and this indication information could be, for example, the identifier of candidate cell #1.

[0474] For steps S1213 to S1214, please refer to the steps corresponding to Figures 3 and 8.

[0475] For example, in the procedure shown in Figure 13, in the inter-DU scenario, the CU determines which candidate cells need to be given an LTM CFRA setting (e.g., candidate cell #1) and which do not (e.g., including candidate cell #2). The CU sends an LTM CFRA request indication to the candidate DU, and thus the candidate DU learns about the candidate cells that need to be given a CFRA setting. Figure 13 includes the following steps:

[0476] In one example, the CU determines the cell group for TA acquisition. The cell group includes candidate cells with LTM CFRA settings and also includes cells without LTM CFRA settings. The CU sends information to the source DU indicating that the candidate cells belong to the same cell group. The source DU further determines the TA of candidate cells without CFRA settings based on the TA of candidate cells with CFRA settings. Figure 13 includes the following steps.

[0477] For steps S1301 to S1303, please refer to the steps corresponding to Figures 3 and 9.

[0478] S1304:CU determines that the LTM CFRA configuration is given to candidate cell #1 and sends a first UE context setup request to candidate DU, where the request includes the identifier of candidate cell #1 and the LTM CFRA request indication.

[0479] The CU determines that the LTM CFRA configuration is not provided to candidate cell #2 and sends a second UE context setup request to candidate DU, which includes the identifier of candidate cell #2 but excludes the LTM CFRA request indication.

[0480] S1305: The candidate DU sends the configuration of candidate cell #1 to the CU in the first UE context setup response. The configuration of candidate cell #1 includes the LTM CFRA configuration (DU configuration) of terminal device 120 and may further include the LTM cell configuration (or LTM cell group configuration) (UE configuration) of terminal device 120. The LTM cell configuration may include, for example, RLC configuration information, MAC configuration information, and PHY configuration information. Based on the LTM cell configuration, terminal device 120 may perform an LTM switch to the corresponding cell and transmit data after the LTM switch. The LTM cell group configuration may include, for example, RLC configuration information, MAC configuration information, and PHY configuration information on a cell group basis. Based on the LTM cell configuration, terminal device 120 may perform an LTM switch to a cell in the cell group and transmit data after the LTM switch.

[0481] The DU setting indicates that the configuration information was last provided to the source DU, or that it may be read by the source DU. The UE setting indicates that the configuration was provided to the terminal device 120, or that it may be read by the terminal device 120.

[0482] The candidate DU may provide the CFRA settings for the corresponding candidate cell based on the CFRA request indication. In the second UE context setup response, the candidate DU sends the settings for candidate cell #2 to the CU. The settings for candidate cell #2 exclude the LTM CFRA settings (DU settings) but may include the settings for the LTM cell (or LTM cell group) (UE settings). In other words, the candidate DU does not provide the CFRA resources corresponding to the candidate cell without a CFRA request indication.

[0483] S1306:CU sends a UE context correction request to the source DU.

[0484] The request may include the settings for candidate cell #1 (UE settings), the settings for candidate cell #2 (UE settings), the LTM CFRA settings for candidate cell #1 on the terminal device (DU settings) (the settings may be included in the settings for candidate cell #1), and indication information. The indication information indicates that the TA for candidate cell #2 will be determined based on candidate cell #1.

[0485] For example, possible indication information would be that candidate cell #1 and candidate cell #2 belong to the same TA cell group (within a single cell group, the source DU may determine that candidate cell #1 and candidate cell #2 have the same TA). Alternatively, multiple candidate cell identifiers may be carried, for example, the identifier of candidate cell #1 and the identifier of the target cell. The identifier of the target cell is the identifier of candidate cell #2.

[0486] For steps S1307 through S1309, please refer to the steps corresponding to Figure 3.

[0487] S1310-a-1: The source DU decides to trigger a PDCCH order based on the LTM CFRA setting of candidate cell #1 and instructs terminal device 120 to send an LTM CFRA preamble to candidate cell #1.

[0488] The PDCCH order includes indication information for the LTM contention-free random access preamble and indication information for time-frequency resources.

[0489] S1310-a-2: Terminal device 120 transmits a contention-free random access preamble to candidate DU in candidate cell #1 based on the PDCCH order.

[0490] Candidate DU determines the TA for candidate cell #1 based on the contention-free random access preamble.

[0491] In S1310-a-3-1 and S1310-a-3-2, the candidate DU sends the TA of candidate cell #1 to the source DU, and the CU may forward the TA of candidate cell #1 to the source DU.

[0492] Source DU determines the TA of candidate cell #2 based on the indication information and the TA of candidate cell #1. The TA of candidate cell #2 and the TA of candidate cell #1 are the same; in other words, their TA values ​​are the same.

[0493] S1310-a-3: The candidate DU sends a RAR to terminal device 120, where the RAR carries the TA (e.g., absolute TA value) of candidate cell #1.

[0494] Please note that after S1310-a-2, S1310-a-3-1 and S1310-a-3-2 may be performed, or S1310-a-3 may be performed.

[0495] S1310: Terminal device 120 sends a measurement report for candidate cell #2 to source DU, where the measurement report includes the RSRP for candidate cell #2.

[0496] S1311: Source DU determines candidate cell 2 as the target cell for switching.

[0497] S1312: Source DU sends an LTM command to terminal device 120, where the command includes the identifier (cell index) of candidate cell #2 and optionally further includes TA indication information (e.g., TA information).

[0498] The TA indication information may include Solution 1 and the TA value (where the TA value is the same as that of candidate cell #1), or Solution 2 and the identifier of candidate cell #1 (for example, the identifier of candidate cell #1 indicates that the TA of candidate cell #2 is determined based on the TA of candidate cell #1, the network device considers the TA values ​​of the two cells to be the same, and furthermore, terminal device 120 also knows that the TA values ​​of the two cells are the same).

[0499] Solution 1 is applicable to scenarios where S1310-a-3-1 and S1310-a-3-2 are implemented, and Solution 2 is applicable to scenarios where S1310-a-3 is implemented. The TA of candidate cell #2 and the TA of candidate cell #1 are the same.

[0500] For steps S1313 to S1314, please refer to the steps corresponding to Figures 3 and 9.

[0501] For example, in the procedure shown in Figure 14, in the interDU scenario, the candidate DU determines the candidate cell (e.g., candidate cell #1) to which the LTM CFRA setting should be given. In the setting of another candidate cell (e.g., candidate cell #2), it is shown that the candidate cell and candidate cell #1 are associated with a TA. For example, the TA values ​​may be the same, or they may share the same TA value.

[0502] In one example, the candidate DU determines the cell group for obtaining the TA. The cell group includes candidate cells with LTM CFRA settings and cells without LTM CFRA settings. The candidate DU sends information to the source DU indicating that the candidate cells belong to the same cell group. The source DU further determines the TA of candidate cells without LTM CFRA settings based on the TA of candidate cells with CFRA settings. Figure 14 includes the following steps.

[0503] For steps S1401 to S1403, please refer to the steps corresponding to Figures 3 and 9.

[0504] S1404:CU sends a setup request for candidate cell #1 or candidate cell #2 to candidate DU.

[0505] Optionally, each cell's setup request may include trigger information for its respective initial RACH for LTM.

[0506] S1405: Candidate DU includes the settings for each candidate cell in the UE context setup response message for candidate cell #1 or candidate cell #2.

[0507] For example, the settings for candidate cell #1 include UE settings and DU settings, and the settings for candidate cell #2 include UE settings and DU settings. The UE settings for candidate cell #1 and candidate cell #2 each include LTM cell settings (or LTM cell group settings), the DU settings for candidate cell #1 include the LTM CFRA settings for candidate cell #1, and the DU settings for candidate cell #2 include the TA determination settings for candidate cell #2.

[0508] In detail, regarding the DU setting for candidate cell #1, the candidate DU may decide to give the LTM CFRA setting for candidate cell #1 based on the trigger information for the initial RACH for candidate cell #1's LTM, and may determine the TA determination setting for candidate cell #2 based on the trigger information for the initial RACH for candidate cell #2's LTM and the LTM CFRA setting for candidate cell #1. For example, the determination setting indicates that the TA of candidate cell #2 may be determined based on the TA of candidate cell #1 (the TAs of candidate cell #1 and candidate cell #2 are the same).

[0509] In another example, a candidate DU may not determine its settings based on the trigger information of each candidate cell, but rather determine its LTM CFRA settings and TA determination settings based on the requirements of the candidate DU. Specifically, the DU settings for candidate cell #2 include first indication information. The first indication information indicates that the TA of candidate cell #2 is determined based on the TA of candidate cell #1, for example, indicating that the TAs of candidate cell #1 and candidate cell #2 are the same or may belong to the same TA candidate cell group, or that the DU settings for candidate cell #2 include the same LTM CFRA setting identifier as that of candidate cell #1.

[0510] S1406:CU sends the settings for candidate cell #1 (including CFRA settings) and the settings for candidate cell #2 (excluding CFRA and optionally including first indication information) to candidate DU.

[0511] For steps S1407 to S1409, please refer to the steps corresponding to Figures 3 and 9.

[0512] S1410-a-1: The source DU decides to trigger a PDCCH order based on the LTM CFRA configuration of candidate cell #1 and instructs the terminal device to send an LTM CFRA preamble to candidate cell #1.

[0513] The PDCCH order includes indication information for the LTM contention-free random access preamble and indication information for time-frequency resources.

[0514] S1410-a-2: Terminal device 120 transmits a contention-free random access preamble to candidate DU in candidate cell #1 based on the PDCCH order.

[0515] Candidate DU determines the TA for candidate cell #1 based on the contention-free random access preamble.

[0516] In S1410-a-3-1 and S1410-a-3-2, the candidate DU sends the TA of candidate cell #1 to the source DU, and the CU may forward the TA of candidate cell #1 to the source DU.

[0517] Source DU determines the TA of candidate cell #2 based on the indication information and the TA of candidate cell #1. The TA of candidate cell #2 and the TA of candidate cell #1 are the same; in other words, their TA values ​​are the same.

[0518] S1410-a-3: The candidate DU sends a RAR to terminal device 120, where the RAR carries the TA (e.g., absolute TA value) of candidate cell 1.

[0519] After S1410-a-2, S1410-a-3-1 and S1410-a-3-2 may be performed, or S1410-a-3 may be performed.

[0520] S1410: Terminal device 120 sends a measurement report for candidate cell #2 to source DU, where the measurement report includes the RSRP for candidate cell #2.

[0521] S1411: Source DU determines candidate cell 2 as the target cell for switching.

[0522] S1412: Source DU sends an LTM command to terminal device 120, where the command includes the identifier (cell index) of candidate cell #2 and optionally further includes TA indication information (e.g., TA information).

[0523] The TA indication information may include Solution 1 and the TA value (where the TA value is the same as that of candidate cell #1), or Solution 2 and the identifier of candidate cell #1 (for example, the identifier of candidate cell #1 indicates that the TA of candidate cell #2 is determined based on the TA of candidate cell #1, the network device considers the TA values ​​of the two cells to be the same, and furthermore, terminal device 120 also knows that the TA values ​​of the two cells are the same).

[0524] Solution 1 is applicable to scenarios where S1410-a-3-1 and S1410-a-3-2 are implemented, and Solution 2 is applicable to scenarios where S1410-a-3 is implemented. The TA of candidate cell #2 and the TA of candidate cell #1 are the same.

[0525] For steps S1413 to S1414, please refer to the steps corresponding to Figures 3 and 9.

[0526] For example, in the procedure shown in Figure 15, in the inter-DU scenario, the source DU requests the CFRA resource for candidate cell #1 from the candidate DU based on indication information (indicating that the TA of candidate cell #2 is determined based on candidate cell #1) that determines the method for determining the TA of candidate cell #2. See the explanations in Figures 12 to 14 for how the source DU obtains the indication information. Figure 15 includes the following steps.

[0527] For steps S1501 to S1504, please refer to the steps corresponding to Figures 3 and 10.

[0528] S1505: Candidate DU decides not to assign a CFRA setting to candidate cell #1 and not to assign a CFRA setting to candidate cell #2.

[0529] The UE context setup response message for candidate cell #1 does not carry the LTM CFRA settings for candidate cell #1, and the UE context setup response message for candidate cell #2 does not carry the LTM CFRA settings for candidate cell #2. However, the response message for candidate cell #1 or candidate cell #2 includes first indication information, where first indication information indicates that the TAs of the terminal devices in candidate cell #1 and candidate cell #2 may be the same.

[0530] Each of the response messages for candidate cell #1 and candidate cell #2 may further include second indication information, where the second indication information is used for frequency information (e.g., BWP information) corresponding to the random access settings of candidate cell #1 and / or candidate cell #2.

[0531] It can be understood that the UE context setup response message for candidate cell #1 includes the settings for candidate cell #1, but the settings include the settings for the LTM cell and exclude the LTM CFRA settings, and the UE context setup response message for candidate cell #2 includes the settings for candidate cell #2, but the settings include the settings for the LTM cell and exclude the LTM CFRA settings.

[0532] S1506:CU sends an RRC reset to the source DU, where the RRC reset includes the settings (UE settings) for candidate cell #1 and candidate cell #2 and the first indication information.

[0533] Optionally, RRC reset may further include second indication information between candidate cell #1 and candidate cell #2.

[0534] For steps S1507 to S1509, please refer to the steps corresponding to Figures 3 and 10.

[0535] S1510-a: Source DU decides to send a request to candidate DU based on first indication information and / or second indication information, where the request is used to ask candidate DU to provide the LTM CFRA settings for candidate cell #1.

[0536] If the frequency of the UE's source cell and the frequency of candidate cell #1 are the same, the source DU may decide to request an LTM CFRA setting for candidate cell #1. It can be understood that the frequency of the source cell and the frequency of candidate cell #2 may be different.

[0537] S1510-b: Source DU sends a request to candidate DU, where the request is used to ask candidate DU to provide the LTM CFRA settings for candidate cell #1.

[0538] S1510-c: The source DU receives the LTM CFRA settings for candidate cell #1 from the candidate DU.

[0539] S1511-a-1: The source DU decides to trigger a PDCCH order based on the LTM CFRA setting of candidate cell #1 and instructs terminal device 120 to send an LTM CFRA preamble to candidate cell #1.

[0540] The PDCCH order includes indication information for the LTM contention-free random access preamble and indication information for time-frequency resources.

[0541] S1511-a-2: Terminal device 120 transmits a contention-free random access preamble to candidate DU in candidate cell #1 based on the PDCCH order.

[0542] Candidate DU determines the TA for candidate cell #1 based on the contention-free random access preamble.

[0543] In S1511-a-3-1 and S1511-a-3-2, the candidate DU sends the TA of candidate cell #1 to the source DU, and the CU may forward the TA of candidate cell #1 to the source DU.

[0544] Source DU determines the TA of candidate cell #2 based on the first indication information and the TA of candidate cell #1. The TA of candidate cell #2 and the TA of candidate cell #1 are the same; in other words, their TA values ​​are the same.

[0545] S1511-a-3: The candidate DU sends a RAR to terminal device 120, where the RAR carries the TA (e.g., absolute TA value) of candidate cell 1.

[0546] After S1511-a-2, S1511-a-3-1 and S1511-a-3-2 may be performed, or S1511-a-3 may be performed.

[0547] S1512: Terminal device 120 sends a measurement report for candidate cell #2 to source DU, where the measurement report includes the RSRP for candidate cell #2.

[0548] S1513: Source DU determines candidate cell 2 as the target cell for the switch.

[0549] S1514: Source DU sends an LTM command to terminal device 120, where the command includes the identifier (cell index) of candidate cell #2 and optionally further includes TA indication information (e.g., TA information).

[0550] TA indication information may include Solution 1 and the TA value (where the TA value is the same as that of candidate cell #1), or Solution 2 and the identifier of candidate cell #1 (for example, the identifier of candidate cell #1 indicates that the TA of candidate cell #2 is determined based on the TA of candidate cell #1, the network device considers the TA values ​​of the two cells to be the same, and furthermore, the UE also knows that the TA values ​​of the two cells are the same).

[0551] Solution 1 is applicable to scenarios where S1610-a-3-1 and S1610-a-3-1 are implemented, and Solution 2 is applicable to scenarios where S1610-a-3 is implemented. The TA of candidate cell #2 and the TA of candidate cell #1 are the same.

[0552] For steps S1515 to S1516, please refer to the steps corresponding to Figures 3 and 10.

[0553] For example, in the procedure shown in Figure 16, in the interDU scenario, the source DU selects an appropriate candidate cell based on the frequency information of the source serving cell and the candidate cell, and sends a PDCCH order to the terminal device 120.

[0554] For steps S1601 to S1604, please refer to the steps corresponding to Figures 3 and 10.

[0555] S1605: Candidate DU decides to assign the CFRA setting to candidate cell #1 and the CFRA setting to candidate cell #2.

[0556] The LTM CFRA of candidate cell #1 is carried in the UE context setup response message of candidate cell #1, and the LTM CFRA of candidate cell #2 is carried in the UE context setup response message of candidate cell #2. Furthermore, the response message of candidate cell #1 or candidate cell #2 includes first indication information, where the first indication information indicates that the TA of the terminal devices in candidate cell #1 and candidate cell #2 may be the same. Optionally, each of the response messages of candidate cell #1 and candidate cell #2 further includes second indication information, where the second indication information is used for frequency information (e.g., BWP information) corresponding to the random access settings of candidate cell #1 and / or candidate cell #2.

[0557] It can be understood that the UE context setup response message for candidate cell #1 includes the settings for candidate cell #1, which include the settings for the LTM cell and the LTM CFRA settings, and the UE context setup response message for candidate cell #2 includes the settings for candidate cell #2, which include the settings for the LTM cell and the LTM CFRA settings.

[0558] S1606:CU sends an RRC reset to the source DU, where the RRC reset includes the settings for candidate cell #1 and candidate cell #2 and the first indication information.

[0559] Optionally, RRC reset may further include second indication information between candidate cell #1 and candidate cell #2.

[0560] For steps S1607 to S1609, please refer to the steps corresponding to Figures 3 and 10.

[0561] S1610-a: The source DU decides to initiate random access to candidate cell #1 based on the source cell frequency and the candidate cell frequency. In other words, the source DU triggers the transmission of the PDCCH order corresponding to candidate cell 1.

[0562] If the frequency of the source cell in the UE is the same as the frequency of candidate cell #1, the source DU may decide to initiate random access to candidate cell #1. It can be understood that the frequency of the source cell and the frequency of candidate cell #2 may be different.

[0563] S1610-a-1: The source DU decides to trigger a PDCCH order based on the LTM CFRA setting of candidate cell #1 and instructs terminal device 120 to send an LTM CFRA preamble to candidate cell #1.

[0564] The PDCCH order includes indication information for the LTM contention-free random access preamble and indication information for time-frequency resources.

[0565] S1610-a-2: Terminal device 120 transmits a contention-free random access preamble to candidate DU in candidate cell #1 based on the PDCCH order.

[0566] Candidate DU determines the TA for candidate cell #1 based on the contention-free random access preamble.

[0567] In S1610-a-3-1 and S1610-a-3-2, the candidate DU sends the TA of candidate cell #1 to the source DU, and the CU may forward the TA of candidate cell #1 to the source DU. The source DU determines the TA of candidate cell #2 based on the indication information and the TA of candidate cell #1. The TA of candidate cell #2 and the TA of candidate cell #1 are the same; in other words, their TA values ​​are the same.

[0568] S1610-a-3: The candidate DU sends a RAR to terminal device 120, where the RAR carries the TA (absolute TA value) of candidate cell #1.

[0569] After S1610-a-2, S1610-a-3-1 and S1610-a-3-2 may be performed, or S1610-a-3 may be performed.

[0570] S1611: Terminal device 120 sends a measurement report for candidate cell #2 to source DU, where the measurement report includes the RSRP for candidate cell #2.

[0571] S1612: Source DU determines candidate cell 2 as the target cell for the switch.

[0572] S1613: Source DU sends an LTM command to terminal device 120, which includes the identifier (cell index) of candidate cell #2 and optionally further includes TA indication information (e.g., TA information).

[0573] TA indication information may include Solution 1 and the TA value (where the TA value is the same as that of candidate cell #1), or Solution 2 and the identifier of candidate cell #1 (for example, the identifier of candidate cell #1 indicates that the TA of candidate cell #2 is determined based on the TA of candidate cell #1, the network device considers the TA values ​​of the two cells to be the same, and furthermore, the UE also knows that the TA values ​​of the two cells are the same).

[0574] Solution 1 is applicable to scenarios where S1610-a-3-1 and S1610-a-3-2 are implemented, and Solution 2 is applicable to scenarios where S1610-a-3 is implemented. The TA of candidate cell #2 and the TA of candidate cell #1 are the same.

[0575] For steps S1614 to S1615, please refer to the steps corresponding to Figures 3 and 10.

[0576] Note that similar representations in Figures 8 through 16 can be referenced to one another.

[0577] The above describes a method embodiment in the present application, and the following describes a corresponding apparatus embodiment.

[0578] To implement the functions in the methods provided in embodiments of this application, terminals and network devices may each include hardware structures and / or software modules to implement the functions in the form of hardware structures, software modules, or combinations of hardware structures and software modules. Whether the functions in a function are implemented in the form of hardware structures, software modules, or combinations of hardware structures and software modules depends on the specific application and design constraints of the technical solution.

[0579] Figure 17 is a block diagram of a communication device 1700 according to one embodiment of the present application. The communication device 1700 may be a network device (e.g., an access network device) or a terminal device in the above embodiment, or a chip or module in a network device or terminal device, and is configured to implement the method in the above embodiment. The communication device 1700 includes a transceiver module 1710. The transceiver module 1710 will be described below by using an example.

[0580] The transceiver module 1710 may include a transmit module and a receive module, respectively, configured to implement the transmit function or the receive function in the method embodiment described above. The transceiver module 1710 may further include a processing module configured to implement functions other than transmit or receive.

[0581] When the communication device 1700 is configured to implement the functions of a network device, for example, the transceiver module 1710 is configured to receive a contention-free random access preamble 1 in candidate cell 1. The transceiver module 1710 is further configured to transmit the identifier of the target cell to be switched, TA information of the target cell, etc., to a terminal device.

[0582] Optionally, the communication device 1700 may further include a processing module 1720 configured to perform functions other than receiving and transmitting, for example, determining the TA of candidate cell 1 based on the contention-free random access preamble 1 of candidate cell 1.

[0583] Optionally, the communication device 1700 further includes a storage module 1730 (not shown in Figure 17) configured to store a program or code used to carry out the above method.

[0584] The content is used only as an example for illustrative purposes. When the communication device 1700 is configured to implement the functions of a network device, the communication device 1700 is responsible for performing the methods or steps related to the network device in the above method embodiment.

[0585] The communication device 1700 is a terminal device. For example, the transceiver module 1710 is configured to receive the TA of candidate cell 1. The transceiver module 1710 is further configured to receive the identifier of the target cell for switching and the identification information of candidate cell 1.

[0586] When the communication device 1700 is a terminal device, it should be understood that the transceiver module 1710 may be a module located within the control unit / subscriber unit / distributed unit of the terminal device and configured to implement receiving and transmitting functions.

[0587] The communication device 1700 may optionally further include a processing module 1720 configured to perform functions other than receiving and transmitting.

[0588] Optionally, the communication device 1700 further includes a storage module 1730 (not shown in Figure 17) configured to store a program or code used to carry out the above method.

[0589] The content is used only as an example for illustrative purposes. When the communication device 1700 is configured to implement the functions of a terminal device, the communication device 1700 is responsible for performing methods or steps related to the terminal device in the above method embodiment.

[0590] Furthermore, for the implementation of each operation in Figure 17, please refer to the corresponding description of the content shown in the above method embodiment. Further details will not be explained here.

[0591] Figure 18 is a block diagram of a communication device 1800 according to one embodiment of the present application. The communication device 1800 includes a processor 1810 and a communication interface 1820. The processor 1810 and the communication interface 1820 may be connected to each other through a bus 1840 (not shown in Figure 18). The communication device 1800 may be configured to implement the functions of a terminal device, or it may be configured to implement the functions of a network device.

[0592] Optionally, the communication device 1800 further includes a memory 1830.

[0593] Memory 1830 includes, but is not limited to, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), or compact disc read-only memory (CD-ROM). Memory may be configured to carry and store expected program code in the form of instructions or data structures, and may be, but is not limited to, any other medium accessible by the computer. For example, memory 1830 may be configured to store associated instructions and data.

[0594] In embodiments of this application, the processor may be a general-purpose processor, a digital signal processor, an application-specific integrated circuit, a field-programmable gate array or another programmable logic device, a discrete gate or transistor logic device, or a discrete hardware component that can implement or perform the methods, steps, and logic block diagrams disclosed in embodiments of this application. The general-purpose processor may be a microprocessor or any conventional processor. The steps of the methods disclosed in embodiments of this application may be completed directly by the hardware processor or by using a combination of hardware and software modules in the processor. For example, the processor 1810 may be one or more central processing units (CPUs). When the processor 1810 is a single CPU, the CPU may be a single-core CPU or a multi-core CPU.

[0595] When the communication device 1800 is configured to implement the functions of a terminal device, for example, the processor 1810 is configured to perform the operations of receiving TA information for candidate cell 1 and receiving the identifier of the switching target cell and identification information of candidate cell 1.

[0596] The content is used only as an example for illustrative purposes. When the communication device 1800 is configured to implement the functions of a terminal device, the communication device 1800 is responsible for performing methods or steps related to the terminal device in the above-described method embodiment.

[0597] When the communication device 1800 is configured to implement the functions of a network device, for example, the processor 1810 is configured to receive a contention-free random access preamble in candidate cell 1 and to transmit the identifier of the target cell for switching and the timing advance TA information of the target cell to the terminal device.

[0598] The content is used only as an example for illustrative purposes. When the communication device 1800 is configured to implement the functions of a network device, the communication device 1800 is responsible for performing the methods or steps related to the network device in the above-described method embodiment.

[0599] The above description is merely an example. For specific content, please refer to the content shown in the method embodiments. Furthermore, for the implementation of each operation in Figure 18, please refer to the corresponding descriptions in the method embodiments shown in Figures 3 to 16.

[0600] The communication device shown in Figures 17 and 18 is configured to implement the content described in the above method embodiment. Therefore, for specific execution steps and methods of the communication device shown in Figures 12 and 18, please refer to the content described in the above method embodiment.

[0601] It should be understood that the transceiver module described above may include a transmitting module and a receiving module. The transmitting module is configured to perform the transmitting action of the communication device, and the receiving module is configured to perform the receiving action of the communication device. For the sake of clarity, in the embodiments of this application, the transmitting module and the receiving module are combined into a single transceiver module. A unified explanation is provided hereby. Further details are not described below.

[0602] Figure 19 shows a communication device 1900 according to one embodiment of the present application. The communication device 1900 may be configured to implement the functions of a network device or terminal device in the method described above. The communication device 1900 may be a chip in a network device or terminal device. The communication device 1900 includes an input / output interface 1920 and a processor 1910. The input / output interface 1920 may be an input / output circuit. The processor 1910 may be a signal processor, chip, or other integrated circuit capable of implementing the method in the present application. The input / output interface 1920 is configured to input or output signals or data.

[0603] For example, when the communication device 1900 is a terminal device, the input / output interface 1920 is configured to receive configuration information from the network device. The input / output interface 1920 is further configured to receive TA information for candidate cell 1. The input / output interface 1920 receives the identifier of the target cell for switching and the identification information of candidate cell 1. The processor 1910 is further configured to perform some or all of the steps of any method provided in this application.

[0604] For example, when the communication device 1900 is a network device, the input / output interface 1920 is configured to receive a contention-free random access preamble in candidate cell 1. The input / output interface 1920 is further configured to transmit the identifier of the target cell to be switched and the timing advance TA information of the target cell to the terminal device.

[0605] In a possible implementation, the processor 1910 executes instructions stored in memory to implement the functions implemented by the first communication device or network device.

[0606] Optionally, the communication device 1900 further includes memory. Optionally, the processor and memory are integrated together. Optionally, the memory is located outside the communication device 1900.

[0607] In a possible implementation, the processor 1910 may be a logic circuit that inputs / outputs messages or signaling via the input / output interface 1920. The logic circuit may be a signal processor, chip, or other integrated circuit that can implement the method in the embodiments of this application.

[0608] The above description of the communication device 1900 in Figure 19 is merely an example for illustrative purposes. The communication device 1900 may be configured to implement the method in the above embodiment. For specific content, please refer to the description of the method embodiment above. Details are not described again here.

[0609] Figure 20 is a block diagram of a communication device 2000 according to one embodiment of the present application. The communication device 2000 may be a network device or a chip. The communication device 2000 may be configured to perform the operations described above, which are performed by the network device.

[0610] When the communication device 2000 is a network device, for example, a base station, Figure 20 shows a simplified structure of the base station. The base station includes module 2010, module 2020, and module 2030. Module 2010 is mainly configured to perform baseband processing, control the base station, etc. Module 2010 is usually the control center of the base station and is sometimes commonly called a processor, and is configured to control the base station to perform processing operations on the network device side in the above method embodiment. Module 2020 is mainly configured to store computer program code and data. Module 2030 is mainly configured to receive and transmit radio frequency signals and to perform conversion between radio frequency signals and baseband signals. Module 2030 is sometimes commonly called a transceiver module, transceiver machine, transceiver circuit, or transceiver. The transceiver module in module 2030, sometimes called a transceiver machine, transceiver, etc., includes an antenna 2033 and a radio frequency circuit (not shown in Figure 20), where the radio frequency circuit is configured primarily to perform radio frequency processing. Optionally, components in module 2030 configured to implement receiving functionality may be considered receivers, and components configured to implement transmitting functionality may be considered transmitters. In other words, module 2030 includes a receiver 2032 and a transmitter 2031. The receiver may also be called a receiving module, receiver machine, receiver circuit, etc., and the transmitter may also be called a transmitting module, transmitter machine, transmitter circuit, etc.

[0611] Modules 2010 and 2020 may include one or more boards, each board may include one or more processors and one or more memories. The processors are configured to read and execute programs in memory to implement baseband processing functions and control base stations. If there are multiple boards, the boards can be interconnected to expand processing capacity. In optional implementations, multiple boards may share one or more processors, multiple boards may share one or more memories, or multiple boards may share one or more processors simultaneously.

[0612] In one implementation, the transceiver module in module 2030 is configured to perform the receive and transmit-related processing performed by the network device in the embodiments shown in Figures 3 to 16. The processor in module 2010 is configured to perform the processing-related processing performed by the network device in the embodiments shown in Figures 3 to 16.

[0613] In another implementation, the processor in module 2010 is configured to perform processing-related processing that is carried out by the network device in the embodiments shown in Figures 3 to 16.

[0614] In another implementation, the transceiver module in module 2030 is configured to perform the receive and transmit-related processing performed by the network device in the embodiments shown in Figures 3 to 16.

[0615] Figure 20 is not an exhaustive example, and it should be understood that the network devices described above, including the processor, memory, and transceiver, may not depend on the structure shown in Figures 12 through 14.

[0616] When the communication device 2000 is a chip, the chip includes a transceiver, memory, and a processor. The transceiver may be an input / output circuit or a communication interface. The processor is a processor, a microprocessor, or an integrated circuit on the chip. The transmission operation performed by the network device in the above embodiment of the method may be understood as an output of the chip, and the reception operation performed by the network device in the above embodiment of the method may be understood as an input of the chip.

[0617] Figure 21 is a block diagram of a communication device 2100 according to one embodiment of the present application. The communication device 2100 may be a terminal device, a processor of a terminal device, or a chip. The communication device 2100 may be configured to perform the operations performed by the terminal device in the above method embodiment.

[0618] When the communication device 2100 is a terminal device, Figure 21 is a simplified diagram of the terminal device structure. As shown in Figure 21, the terminal device includes a processor, memory, and a transceiver. The memory may store computer program code. The transceiver includes a transmitter 2131, a receiver 2132, a radio frequency circuit (not shown in Figure 21), an antenna 2133, and an input / output device (not shown in Figure 21).

[0619] The processor is primarily configured to process communication protocols and data, control terminal devices, execute software programs, and process data for software programs. Memory is primarily configured to store software programs and data. Radio frequency circuits are primarily configured to perform conversions between baseband signals and radio frequency signals and to process radio frequency signals. Antennas are primarily configured to receive and transmit radio frequency signals in the form of electromagnetic waves. Input / output devices, such as touchscreens, displays, or keyboards, are primarily configured to receive data input from the user and output data to the user. Note that some types of terminal devices may not have input / output devices.

[0620] When data needs to be transmitted, the processor performs baseband processing on the data to be transmitted, then outputs a baseband signal to a radio frequency circuit, which performs radio frequency processing on the baseband signal and then transmits the radio frequency signal externally in the form of electromagnetic waves through an antenna. When data is transmitted to a terminal device, the radio frequency circuit receives the radio frequency signal through the antenna, converts the radio frequency signal to a baseband signal, and outputs the baseband signal to the processor. The processor converts the baseband signal to data and processes the data. For ease of explanation, Figure 21 simply shows one memory, one processor, and one transceiver. Actual terminal device products may include one or more processors and one or more memories. Memory is sometimes called a storage medium, storage device, etc. Memory may be disposed independently of the processor or may be integrated with the processor. This is not limited to the embodiments of this application.

[0621] In this embodiment of the present application, an antenna having transmitting and receiving functions and a radio frequency circuit may be considered as a transceiver module of a terminal device, and a processor having processing functions may be considered as a processing module of a terminal device.

[0622] As shown in Figure 21, the terminal device includes a processor 2110, a memory 2120, and a transceiver 2130. The processor 2110 may also be called a processing unit, processing board, processing module, or processing unit, and the transceiver 2130 may also be called a transceiver unit, transceiver machine, or transceiver device.

[0623] Optionally, any component in the transceiver 2130 configured to implement a receiving function may be considered a receiving module, and any component in the transceiver 2130 configured to implement a transmitting function may be considered a transmitting module. That is, the transceiver 2130 includes a receiver and a transmitter. The transceiver may also be called a transceiver machine, transceiver module, transceiver circuit, etc. The receiver may also be called a receiver machine, receiving module, receiver circuit, etc. The transmitter may also be called a transmitter machine, transmitting module, transmitter circuit, etc.

[0624] For example, in one implementation, the processor 2110 is configured to perform processing actions on the terminal device side in the embodiments shown in Figures 3 to 16, and the transceiver 2130 is configured to perform receiving and transmitting actions on the terminal device side in Figures 3 to 16.

[0625] For example, in one implementation, the processor 2110 is configured to perform processing actions on the terminal device side in the embodiments shown in Figures 3 to 16, and the transceiver 2130 is configured to perform receiving and transmitting actions on the terminal device side in Figures 3 to 16.

[0626] Please note that Figure 21 is merely an example, not an exhaustive one. Terminal devices, including transceiver modules and processing modules, may not depend on the structure shown in Figures 17 to 19.

[0627] When the communication device 2100 is a chip, the chip includes a processor, memory, and a transceiver. The transceiver may be an input / output circuit or a communication interface. The processor may be a processing module, a microprocessor, or an integrated circuit on the chip. The transmission operation performed by the terminal device in the above embodiment of the method may be understood as an output of the chip, and the reception operation performed by the terminal device in the above embodiment of the method may be understood as an input of the chip.

[0628] This application further provides a chip including a processor configured to call instructions from memory and execute instructions stored in memory, so that a communication device on which the chip is installed can implement the method in the above example.

[0629] This application further provides another chip including an input interface, an output interface, and a processor. The input interface, the output interface, and the processor are connected through an internal connection path. The processor is configured to execute code in memory, and when the code is executed, the processor is configured to carry out the method in the example above. Optionally, the chip further includes memory, which is configured to store computer programs or code.

[0630] This application further provides a processor configured to be coupled to memory and configured to implement the methods and functions of a network device or terminal device in any one of the embodiments described above.

[0631] Another embodiment of this application provides a computer program product including instructions. When the computer program product is executed on a computer, the method in the above embodiment is implemented.

[0632] This application further provides a computer program. When the computer program is executed in a computer, the method in the above embodiment is implemented.

[0633] Another embodiment of this application provides a computer-readable storage medium for storing computer programs. The method in the above embodiment is implemented when the computer program is executed by a computer.

[0634] In the description of embodiments of this application, unless otherwise specified, “multiple” means two or more. “At least one of the following items (parts)” or similar expressions mean any combination of these items, including a single item (part) or any combination of multiple items (parts). For example, at least one item (part) of a, b, or c could be a, b, c, a and b, a and c, b and c, or a, b, and c, where a, b, and c may be singular or plural.

[0635] Furthermore, in order to clearly illustrate the technical solutions in the embodiments of this application, terms such as “first” and “second” are used in the embodiments of this application to distinguish between the same or similar items that provide essentially the same function or purpose. Those skilled in the art will understand that terms such as “first” and “second” do not limit the quantity or execution sequence, and do not indicate a clear distinction. Furthermore, in the embodiments of this application, words such as “example” or “for example” are used to indicate an example or explanation.

[0636] In the description of embodiments of this application, unless otherwise specified, " / " represents an "or" relationship between related objects. For example, A / B may represent A or B. In this application, "and / or" represents only an association relationship between related objects, indicating that three relationships may exist. For example, A and / or B may represent the following three cases: only A exists, both A and B exist, and only B exists, where A and B may be singular or plural.

[0637] The sequence numbers of the processes described above do not represent the execution sequence in the embodiments of this application. The execution sequence of the processes should be determined based on the function and internal logic of the processes and should not be construed as any limitation to the implementation processes of the embodiments of this application.

[0638] Those skilled in the art will notice, in combination with the examples described in the embodiments disclosed herein, that units and algorithmic steps can be implemented by electronic hardware or a combination of computer software and electronic hardware. Whether a function is implemented by hardware or by software depends on the specific application and the design constraints of the technical solution. Those skilled in the art may use different methods to implement the functions described for each specific application, but such implementations should not be considered beyond the scope of this application.

[0639] For the sake of convenience and simplicity, it will be obvious to those skilled in the art that detailed working procedures of the above systems, apparatus, and units should be referred to in the corresponding procedures in the above method embodiments. Further details are not described here.

[0640] In some embodiments provided in this application, it should be understood that the disclosed systems, devices, and methods may be implemented in other ways. For example, the described device embodiments are merely examples. For example, the division into units is merely a logical functional division, and other divisions may be possible in actual implementations. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not implemented.

[0641] Furthermore, the mutual coupling, direct coupling, or communication connection shown or described may be implemented through several interfaces. Indirect coupling or communication connection between devices or units may be implemented in electronic, mechanical, or other forms.

[0642] Units described as separate parts may or may not be physically separate, and parts shown as units may or may not be physical units; in other words, they may be located in one place or distributed across multiple network units. Some or all of the units may be selected based on the actual requirements to achieve the objectives of the solution of the embodiment.

[0643] Furthermore, the functional units in the embodiments of this application may be integrated into a single processing unit, or each unit may exist physically independently, or two or more units may be integrated into a single unit.

[0644] When a function is implemented in the form of a software function unit and sold or used as an independent product, the function may be stored in a computer-readable storage medium. Based on such understanding, the technical solutions in the embodiments of this application, or parts of the technical solutions that contribute to the prior art, or parts of the technical solutions, may be implemented in the form of a software product. A computer software product is stored in a storage medium and includes several instructions for instructing a computer device (which may be a personal computer, server, network device, etc.) to perform all or part of the steps of the method in the embodiments of this application. The storage medium includes any medium that can store program code, for example, a USB flash drive, a removable hard disk, ROM, RAM, a magnetic disk, or an optical disk.

[0645] Cross-referencing may be made to the content of embodiments of this application. Unless otherwise specified or a logical conflict arises, terminology and / or descriptions in different embodiments are consistent and can be cross-referenced, and technical features in different embodiments can be combined into the new embodiment based on the internal logical relationships between the technical features.

[0646] In embodiments of this application, it can be understood that terminal devices and network devices may perform some or all of the steps in embodiments of this application. These steps or operations are merely examples. In embodiments of this application, other operations or various variations of operations may be performed. Furthermore, the steps may be performed in a sequence different from the sequence shown in embodiments of this application, and not all of the operations in embodiments of this application may be performed.

Claims

1. A communication method, wherein the method is applied to a terminal device or a chip in the terminal device. The steps include receiving the timing advance TA of the first candidate cell, A step of receiving an identifier for a target cell to be switched and identification information for the first candidate cell, wherein the target cell is a second candidate cell, and the identification information for the first candidate cell indicates that the TA of the target cell is determined based on the TA of the first candidate cell. A communication method that includes this.

2. The aforementioned method, Step of sending the measurement report of the second candidate cell. The method according to claim 1, further comprising:

3. The aforementioned method, A step of receiving indication information, wherein the indication information indicates that a contention-free random access preamble is to be transmitted in the first candidate cell, and the contention-free random access preamble is used to determine the TA of the first candidate cell, The steps include: transmitting the contention-free random access preamble in the first candidate cell based on the indication information; The method according to claim 1 or 2, further comprising:

4. The method according to any one of claims 1 to 3, wherein the first candidate cell and the second candidate cell belong to a first network device, and the first candidate cell is different from the second candidate cell.

5. The method according to any one of claims 1 to 4, wherein the TA of the first candidate cell and the TA of the target cell are the same.

6. The method according to any one of claims 1 to 5, wherein the first candidate cell and the second candidate cell belong to the set of candidate target cells for switching.

7. The first network device receives a contention-free random access preamble for a first candidate cell, The first network device transmits the identifier of the target cell for switching and the timing advance TA information of the target cell to the terminal device. A communication method including, A communication method wherein the target cell is a second candidate cell, and the TA information of the target cell is determined based on the contention-free random access preamble of the first candidate cell.

8. The TA information of the target cell is The TA of the target cell, or the identification information of the first candidate cell. The method according to claim 7, comprising at least one of the, wherein the identification information of the first candidate cell indicates that the TA of the target cell is determined based on the first candidate cell.

9. The aforementioned method, A step of transmitting indication information to the terminal device by the first network device, wherein the indication information indicates that the contention-free random access preamble is to be transmitted in the first candidate cell. It further includes, The method according to claim 7 or 8, wherein the indication information includes contention-free random access setting information for the first candidate cell, and the contention-free random access setting information is used for transmitting the contention-free random access preamble.

10. The aforementioned method, The first network device transmits the configuration information of the first candidate cell and the configuration information of the second candidate cell to the terminal device. The method according to claim 9, further comprising:

11. The method according to any one of claims 7 to 10, wherein the first candidate cell and the second candidate cell belong to the first network device, and the first candidate cell is different from the second candidate cell.

12. The method according to any one of claims 7 to 11, wherein the TA of the first candidate cell and the TA of the target cell are the same.

13. The method according to any one of claims 7 to 12, wherein the first candidate cell and the second candidate cell belong to the set of candidate target cells for switching.

14. A method of communication, A step of receiving first indication information from a second network device via a first network device, wherein the first indication information indicates that the timing advance TA of a second candidate cell is determined based on a first candidate cell, and the first candidate cell and the second candidate cell belong to a third network device. The first network device receives TA information of the first candidate cell, The first network device transmits to a terminal device, based on the TA information and first indication information of the first candidate cell, the identifier of the target cell for switching and the TA information of the target cell, wherein the target cell is the second candidate cell. A communication method that includes this.

15. The TA information of the target cell is The TA of the target cell, or the identification information of the first candidate cell. The method according to claim 14, comprising at least one of the, wherein the identification information of the first candidate cell indicates that the TA of the target cell is determined based on the first candidate cell.

16. The step of receiving the TA information of the first candidate cell by the first network device is: The first network device receives the TA information of the first candidate cell from the second network device, or The first network device receives the TA information of the first candidate cell from the terminal device. The method according to claim 14 or 15, including the method described in claim 14 or 15.

17. The TA information of the first candidate cell is The TA of the first candidate cell, or the second indication information The method according to any one of claims 14 to 16, comprising at least one of the following, wherein the second indication information indicates that at least one of the third network device and the terminal device has the TA of the first candidate cell.

18. The first indication information indicates that the TA of the second candidate cell is determined based on the TA of the first candidate cell, or The first indication information indicates that the TA of the second candidate cell is determined based on the contention-free random access setting information of the first candidate cell. The method according to any one of claims 14 to 17.

19. The aforementioned method, Steps include: transmitting third indication information to the terminal device by the first network device, wherein the third indication information indicates that a contention-free random access preamble is to be transmitted in the first candidate cell, and the contention-free random access preamble is used to determine the TA of the first candidate cell; The method according to any one of claims 14 to 18, further comprising:

20. The aforementioned method, The first network device receives frequency information of the first candidate cell and frequency information of the second candidate cell from the second network device, The first network device determines the third indication information based on the frequency of the first candidate cell, the frequency of the second candidate cell, and the frequency of the serving cell. The method according to claim 19, further comprising:

21. The aforementioned method, The first network device receives the subcarrier interval SCS information of the first candidate cell and the SCS information of the second candidate cell from the second network device. The first network device determines the third indication information based on the SCS of the first candidate cell, the SCS of the second candidate cell, and the SCS of the serving cell. The method according to claim 19, further comprising:

22. The aforementioned method, The first network device transmits first request information to the second network device based on the frequency of the first candidate cell, the frequency of the second candidate cell, and the frequency of the serving cell. It further includes, The method according to claim 20, wherein the first request information is used to request the contention-free random access setting information for the first candidate cell, and the contention-free random access setting information for the first candidate cell is used for transmitting the contention-free random access preamble.

23. The aforementioned method, The first network device transmits second request information to the second network device based on the SCS of the first candidate cell, the SCS of the second candidate cell, and the SCS of the serving cell. It further includes, The method according to claim 21, wherein the second request information is used to request the contention-free random access setting information of the first candidate cell, and the contention-free random access setting information of the first candidate cell is used for transmitting the contention-free random access preamble.

24. The aforementioned method, The first network device receives the contention-free random access setting information for the first candidate cell and the contention-free random access setting information for the second candidate cell from the second network device. The method according to claim 20 or 21, further comprising:

25. The method according to any one of claims 14 to 24, wherein the first candidate cell and the second candidate cell belong to the set of candidate target cells for switching.

26. A communication device equipped with a processor, The processor is configured to execute a computer program or instructions, or the processor is configured, through logic circuits, to enable the communication device to carry out the method according to any one of claims 1 to 25.

27. The communication device according to claim 26, further comprising a memory, wherein the memory is configured to store the computer program or the instruction.

28. The communication device according to claim 26 or 27, further comprising a communication interface, wherein the communication interface is configured to input and / or output signals.

29. A communication device comprising a logic circuit and an input / output interface, The input / output interface is configured to input signals and / or output signals, A communication device wherein the logic circuit is configured to carry out the method described in any one of claims 1 to 25.

30. A computer-readable storage medium, wherein the computer-readable storage medium stores computer programs or instructions. A computer-readable storage medium in which the method according to any one of claims 1 to 25 is carried out when the computer program or instruction is executed on a computer.

31. A computer program product equipped with instructions, A computer program product wherein, when the instruction is executed on a computer, the method according to any one of claims 1 to 25 is performed.

Images