Timing advance (TA) acquisition method and related apparatus

Abstract

The present application provides a timing advance (TA) acquisition method and a related apparatus. The method comprises: a terminal device receives a first message from a network side, wherein the first message may comprise at least one of: an identifier (ID) of a cell, TA, a TA validity command, and TA validity time, the TA validity command is used for indicating that the TA is still valid after the terminal device is handed over to the cell, and the TA is used for executing an access of RACH less. The technical solution provided by the present application can reduce the signaling overhead.

Description

A timing advance TA acquisition method and related device

[0001] This application claims priority to the Chinese patent applications filed with the China Patent Office on February 7, 2024, with application number 202410175813.8 and application name “A communication method, device and computer-readable storage medium” and filed with the China Patent Office on May 10, 2024, with application number 202410598084.7 and application name “A timing advance TA acquisition method and related device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of wireless communication technology, and in particular to a timing advance (TA) acquisition method and related devices. Background Art

[0003] L1 / L2 triggered mobility (LTM) involves the network pre-configuring multiple candidate cells for a terminal device. Based on the L1 measurement results reported by the terminal device, the network can trigger a mobility management mechanism using a handover command to switch the terminal device from the source cell to the candidate cell. Prior to sending the handover command, the terminal device can be triggered to perform uplink and downlink synchronization.

[0004] In R18 uplink synchronization, the network can trigger uplink synchronization via a physical downlink control channel (PDCCH) order. Specifically, the timing advance (TA) acquisition process for uplink synchronization involves the following: the terminal device sends a preamble to the 5G Node B distributed unit (gNB-DU) of the candidate cell. The gNB-DU of the candidate cell measures the terminal device's TA and sends it to the gNB-DU of the source cell via the centralized unit (CU). The gNB-DU of the source cell then sends the target cell's TA to the terminal device when issuing the LTM command, enabling random access channel (RACH)-less access.

[0005] However, in continuous LTM, the TA acquisition process needs to be retriggered each time the terminal device switches cells. Frequent re-triggering of the TA acquisition process results in high signaling overhead for the terminal device and the network. Summary of the Invention

[0006] The embodiments of the present application provide a timing advance (TA) acquisition method and related devices, which can reduce signaling overhead.

[0007] In a first aspect, the present application provides a TA acquisition method, which can be applied to a terminal device, or to a device in the terminal device (for example, a chip, or a chip system, or a circuit), or a device that can be used in combination with the terminal device. The following description is given by taking the application to the terminal device as an example. The method may include: the terminal device receives a first message from the network side, the first message including at least one of the following: an identifier (ID) of a cell, a TA, a valid command of the TA, and a valid time of the TA; wherein the valid command of the TA is used to indicate that the terminal device is still valid after switching to the cell, and the TA is used to perform RACH less access.

[0008] In an embodiment of the present application, when the TA of a cell is valid, a first message is sent to a terminal device through the network side. The terminal device can determine to continue using the valid TA to perform RACH less access based on one or more of the cell ID, TA, valid command of the TA, and valid time of the TA in the first message, thereby avoiding re-triggering the TA acquisition process of the cell, and reducing the signaling overhead between the terminal device and the network side.

[0009] In a possible implementation, after the terminal device receives the first message from the network side, the method further includes: if the timing advance timer (time alignment timer, TAT) starts the timing timeout of the corresponding TA, the change amplitude of the reference signal receiving power (RSRP) value of the cell is greater than the preset threshold, the terminal device receives a new TA of the gNB-DU of the cell, the terminal device receives a TA failure indication command, and the terminal device receives at least one of the PDCCH indication for the cell, then the terminal device determines that the TA is failed, and the PDCCH indication is used to obtain the TA of the cell. Through the embodiment of the present application, the terminal device can maintain the validity of the TA of the cell, and maintain the validity of the TA of the cell based on the real-time situation of the terminal device, which can improve the accuracy of the LTM process access of RACH less.

[0010] In one possible implementation, the RSRP value is configured for the terminal device by the network. Alternatively, the RSRP value may be configured for the terminal device by the gNB-DU of the source cell on the network side. Alternatively, the RSRP value may be configured for the terminal by the cell, which may be the cell corresponding to the TA.

[0011] In one possible implementation, after the terminal device receives the first message from the network side, the method further includes: if at least one of the following conditions is met: the timing of starting the corresponding TA by TAT has not timed out, the change in the RSRP value of the cell is less than or equal to a preset threshold, the terminal device no longer receives a new TA from the gNB-DU of the cell, the terminal device does not receive a TA failure indication command, and the terminal device does not receive a PDCCH indication for the cell, then the terminal device determines that the TA has not failed, and the PDCCH indication is used to obtain the TA of the cell.

[0012] In a possible implementation, if the TA fails, the method further includes: the terminal device sends a TA failure indication to the network side, and the TA failure indication command includes a cell ID or a timing advance group (TAG) ID.

[0013] In one possible implementation, after the terminal device sends a TA failure indication command to the network, the method further includes: the terminal device receiving a PDCCH order from the network, the PDCCH order being used to trigger an early TA acquisition process; the terminal device sending a preamble to the indicated cell, where the cell indicated by the PDCCH order is the same cell as the cell corresponding to the TA failure command; and the gNB-DU of the source cell sending a PDCCH order to the terminal device to acquire a valid TA corresponding to the cell. The cell indicated by the PDCCH order is the same cell as the cell corresponding to the TA failure command, which can be understood as the PDCCH order being used to reacquire a valid TA corresponding to the cell.

[0014] In one possible implementation, if the TA has not expired, the method further includes: the terminal device sending valid TA information to the network, where the valid TA information includes at least one of the following: an indication of a valid TA, a list of cells with valid TAs, the TA, and a remaining TAT. If the TA validity is maintained on the terminal device, after accessing a cell, the terminal device can send the existing TA to the cell's gNB-DU for subsequent RACH-less access, saving signaling overhead.

[0015] In one possible implementation, the terminal device receiving the first message from the network side includes: the terminal device receiving the first message from the source cell on the network side. Optionally, the network side may be the CU of the source cell or the DU of the source cell. If the first message is generated by the CU of the source cell, the CU of the source cell may send the first message to the terminal device via the DU of the source cell.

[0016] In a possible implementation, the method further includes: the terminal device receives a TA failure indication command from the gNB-DU of the cell, where the TA failure indication command includes the ID of the cell.

[0017] In a possible implementation manner, the first message is carried by downlink control information (DCI), radio resource control (RRC) or media access control element (MAC CE).

[0018] In a second aspect, the present application provides a method for acquiring a TA, which can be applied to a gNB-DU of a source cell, or to a device (e.g., a chip, a chip system, or a circuit) in the gNB-DU of the source cell, or a device that can be used in conjunction with the gNB-DU of the source cell. The method is described below using the gNB-DU of the source cell as an example. The method may include: the gNB-DU of the source cell sends a first message to a terminal device, the first message including at least one of the following: a cell ID, a TA, a TA validity command, and a TA validity period; wherein the TA validity command is used to indicate to the terminal device that the TA remains valid after switching to the cell, and the TA is used by the terminal device to perform RACH-less access.

[0019] In an embodiment of the present application, when the TA of the cell is valid, a first message is sent to the terminal device through the gNB-DU of the source cell. The terminal device can determine to use the valid TA to perform RACH less access based on one or more of the cell's TA, the valid command of the TA, and the valid time of the TA in the first message, thereby avoiding re-triggering the cell's TA acquisition process, and reducing the signaling overhead between the terminal device and the network side.

[0020] It should be understood that the executor of the second aspect may be the gNB-DU of the source cell. The specific content of the second aspect corresponds to the content of the first aspect. The corresponding features and beneficial effects achieved by the second aspect can refer to the description of the first aspect. To avoid repetition, the detailed description is appropriately omitted here.

[0021] In one possible implementation, the method may further include: the gNB-DU of the source cell receives the TA of the cell and the TAT of the TA from the gNB-CU.

[0022] In one possible implementation, the TA and the TAT of the TA include at least one of the following: the TA and TAT1 of the TA sent by the cell to the gNB-DU of the source cell through the gNB-CU; or the TA sent by the cell to the gNB-DU of the source cell through the gNB-CU, and the TAT2 of the TA configuration sent by the gNB-CU to the gNB-DU of the source cell.

[0023] In a possible implementation, the method further includes: the gNB-DU of the source cell receives a TA failure indication command from the terminal device, where the TA failure indication command includes the cell ID.

[0024] A possible implementation method further includes: the gNB-DU of the source cell sends a PDCCH order to the terminal device, where the PDCCH order is used to obtain a valid TA corresponding to the cell, and the cell indicated by the PDCCH is the same cell as the cell corresponding to the TA failure command.

[0025] In one possible implementation, the method further includes: the gNB-DU of the source cell receives information about a valid TA from the terminal device, where the information about the valid TA includes at least one of the following: an indication of a valid TA, a list of cells with a valid TA, a TA corresponding to the list of cells with a valid TA, and a remaining TAT time.

[0026] In one possible implementation, the method further includes: the gNB-DU of the source cell sends a cell handover notification to the gNB-DU of the cell, where the cell handover notification includes at least one of the following: a TA, and a recent measurement result of the cell corresponding to the TA.

[0027] In a third aspect, the present application provides a method for acquiring a TA, which can be applied to a gNB-DU of a cell, or to a device (e.g., a chip, a chip system, or a circuit) in a gNB-DU of a cell, or a device capable of being used in conjunction with a gNB-DU of a cell. The method is described below using the gNB-DU of a cell as an example. The method may include: if at least one or more of the following conditions are satisfied: a timeout for starting a TA corresponding to a TAT is satisfied; a change in the RSRP value of the gNB-DU of the cell is greater than a preset threshold; and a PDCCH indication of the cell corresponding to the TA is sent, the gNB-DU of the cell determines that the TA is invalid, the PDCCH indication being used to trigger a terminal device to acquire the TA of the cell, and the TAT is TAT1 configured for the cell, or TAT2 configured for the gNB-CU.

[0028] In this embodiment of the present application, the gNB-DU of the cell can maintain the validity of the TA, and the gNB-DU of the cell on the network side can maintain the validity of the TA, which not only reduces the energy consumption of the terminal device but also improves the access accuracy of RACH-less. The cell in this embodiment of the present application can be understood as a candidate cell, a target cell, or a neighboring cell.

[0029] It should be understood that the executor of the third aspect may be the gNB-DU of the cell. The specific content of the third aspect corresponds to the content of the first aspect. The corresponding features and beneficial effects achieved by the third aspect can refer to the description of the first aspect. To avoid repetition, the detailed description is appropriately omitted here.

[0030] In one possible implementation, if the TA fails, the method further includes: the gNB-DU of the cell sends a TA failure indication command to the terminal device, and the TA failure indication command includes the cell ID or TAG ID.

[0031] In one possible implementation, the method further includes: receiving, by a gNB-DU of a cell, a cell handover notification from a gNB-DU of a source cell, the cell handover notification including at least one of the following: a TA, and a recent measurement result of a cell corresponding to the TA; and updating, by the gNB-DU of the cell, an RSRP value according to the cell handover notification.

[0032] In a possible implementation, the method may further include: after the gNB-DU of the cell obtains the TA of the terminal device, it starts the timing of the corresponding TA according to the TAT.

[0033] In a fourth aspect, the present application provides a method for acquiring a TA, which can be applied to a gNB-DU of a source cell, or to a device (e.g., a chip, a chip system, or a circuit) in the gNB-DU of the source cell, or a device capable of being used in conjunction with the gNB-DU of the source cell. The method is described below using the gNB-DU of the source cell as an example. The method can include: the gNB-DU of the source cell sending a first cell handover notification to the gNB-CU, the first cell handover notification including: a cell ID, a transport configuration instructions (TCI) status ID, and TA-related information, the TA-related information including at least one of the TA of other cells, the TAT corresponding to the TA of other cells, or the remaining duration of the TAT corresponding to the TA of other cells.

[0034] In this embodiment of the present application, the gNB-DU of the source cell can send a cell handover notification to the gNB-CU, allowing the gNB-DU of the subsequent cell to continue using the TA-related information to perform RACH-less access. This avoids re-triggering the cell's TA acquisition process and reduces network-side signaling overhead. Maintaining the validity of the TA by the network (the gNB-DU of the source cell) not only reduces terminal device energy consumption but also improves the accuracy of RACH-less access.

[0035] In a possible implementation, the method may further include: the gNB-DU of the source cell sends a second cell switching notification to the terminal device, where the second cell switching notification carries the TA of the cell.

[0036] In a possible implementation, the method may further include: the gNB-DU of the source cell receives the TA of the gNB-DU of the cell; if at least one of the following conditions is satisfied: the TAT timing of the TA or the remaining duration of the TAT of the TA times out, the change in the RSRP value of the cell is greater than a preset threshold, and the terminal device receives a new TA from the gNB-DU of the cell, the gNB-DU of the source cell determines that the TA is invalid.

[0037] In one possible implementation, the TAT corresponding to the TA includes at least one of the following: TAT1 sent by the gNB-DU of the cell to the gNB-DU of the source cell; or TAT2 configured for the TA sent by the gNB-CU to the gNB-DU of the source cell; or TAT3 determined by the gNB-DU of the source cell for the TA.

[0038] In one possible implementation, the method may further include: when the gNB-DU of the source cell receives the TA of the gNB-DU of the cell, starting the TAT timing of the TA or the remaining duration of the TAT of the TA.

[0039] In one possible implementation, after the gNB-DU of the source cell sends a second cell switching notification to the terminal device, the method further includes: the gNB-DU of the source cell sends a TA to the gNB-DU of the cell.

[0040] In a fifth aspect, the present application provides a method for acquiring a TA. This method can be applied to a gNB-CU, or to a device (e.g., a chip, a chip system, or a circuit) in a gNB-CU, or a device that can be used with a gNB-CU. The following description uses the application to a gNB-CU as an example. The method can include: the gNB-CU sending a TA and TA-related information to a gNB-DU of a cell, the TA-related information including the TA of other cells, and the TAT corresponding to the TA of other cells, or the TAT corresponding to the TA of other cells.

[0041] In this embodiment of the present application, the gNB-CU can maintain the validity of the TA. The gNB-CU sends the TA and related information to the gNB-DU of the cell, so that subsequent RACH-less access can be performed based on the TA-related information. This avoids re-triggering the cell's TA acquisition process and reduces signaling overhead on the network side. Maintaining the validity of the TA by the network side (gNB-CU) not only reduces energy consumption of the terminal device but also improves the accuracy of RACH-less access.

[0042] It should be understood that the executor of the fifth aspect may be the gNB-CU, and the specific content of the fifth aspect corresponds to the content of the fourth aspect. The corresponding features and beneficial effects achieved in the fifth aspect can refer to the description of the fourth aspect. To avoid repetition, the detailed description is appropriately omitted here.

[0043] In one possible implementation, the method may further include: the gNB-CU receiving an access success message from the gNB-DU of the cell, the access success message carrying the cell ID and a TA request, the TA request being used to request the gNB-CU to deliver an available TA. With this embodiment of the present application, the terminal device requests or forwards a TA after successfully switching to the cell (e.g., by carrying the TA request in the access success message), thereby avoiding ineffective signaling overhead and target-side maintenance costs.

[0044] In a possible implementation, the method further includes: the gNB-CU receives the TA of the gNB-DU of the cell; if at least one of the following conditions is satisfied: the TAT timing of the TA or the remaining duration timing of the TAT of the TA has expired, the change in the reference signal received power RSRP value of the cell is greater than a preset threshold, and the terminal device receives a new TA from the gNB-DU of the cell, the gNB-CU determines that the TA is invalid.

[0045] In one possible implementation, the TAT corresponding to the TA includes at least one of the following: TAT1 sent by the gNB-DU of the cell to the gNB-CU; or TAT2 configured by the gNB-CU for the TA sent by the gNB-CU to the gNB-DU of the cell; or TAT3 determined by the gNB-DU of the source cell for the TA and sent to the gNB-CU.

[0046] In one possible implementation, the method further includes: the gNB-CU receiving a second message from the gNB-DU of the cell, where the second message includes at least one of the following: a cell ID, a TA request, and an index of the terminal device, where the TA request is used to request the gNB-CU to send an available TA.

[0047] In one possible implementation, the method may further include: the gNB-CU receives the TA of the gNB-DU of the cell, and starts timing the TAT of the TA or the remaining duration of the TAT of the TA.

[0048] In one possible implementation, the method further includes: the gNB-CU sending the TA and TA-related information to the gNB-DU of the cell.

[0049] In a sixth aspect, the present application provides a TA acquisition method, which can be applied to a gNB-DU of a cell, or to a device (e.g., a chip, a chip system, or a circuit) in a gNB-DU of a cell, or a device that can be used in conjunction with a gNB-DU of a cell. The method is described below using the gNB-DU of a cell as an example. The method may include: the gNB-DU of a cell determining the TA of the cell and / or related information of the TA, the related information of the TA including the TA of other cells, the timing advance timer TAT corresponding to the TA of the other cells, or the remaining duration of the TAT corresponding to the TA of the other cells, the TA being related information used to trigger access without a random access channel (RACH) less.

[0050] In this embodiment of the present application, the gNB-DU of a cell can determine the cell's TA and / or related information of the TA, and use the cell's TA and / or related information of the TA to trigger RACH-less access, thereby eliminating the need to reacquire the TA and thus saving signaling overhead.

[0051] It should be understood that the executor of the sixth aspect may be the gNB-DU of the target cell. The specific content of the sixth aspect corresponds to the content of the fourth aspect. The corresponding features and beneficial effects achieved in the sixth aspect can refer to the description of the fourth aspect. To avoid repetition, the detailed description is appropriately omitted here.

[0052] In one possible implementation, the method further includes: the gNB-DU of the cell sends a second message to the gNB-CU, where the second message includes at least one of the following: a cell ID, a TA request, and an index of the terminal device, where the TA request is used to request the gNB-CU to send an available TA.

[0053] In a seventh aspect, an embodiment of the present application provides a communication device, which may be a terminal device or a device in a terminal device (e.g., a chip, or a chip system, or a circuit). The beneficial effects can be found in the description of the first aspect and will not be repeated here. The communication device has the function of implementing the behavior in the method example of the first aspect above. The function can be implemented by hardware or by executing corresponding software implementation by hardware. The hardware or software includes one or more modules corresponding to the above functions.

[0054] In an eighth aspect, an embodiment of the present application provides a communication device, which may be a gNB-DU of a source cell, or a device (e.g., a chip, a chip system, or a circuit) in the gNB-DU of a source cell. The beneficial effects can be found in the description of the second and fourth aspects and will not be repeated here. The communication device has the function of implementing the behaviors in the method examples of the second and fourth aspects above. The functions may be implemented by hardware or by hardware executing corresponding software. The hardware or software includes one or more modules corresponding to the above functions.

[0055] In a ninth aspect, an embodiment of the present application provides a communications device, which may be a gNB-DU of a cell, or a device (e.g., a chip, a chip system, or a circuit) in a gNB-DU of a cell. The beneficial effects can be found in the description of the third and sixth aspects and will not be repeated here. The communications device has the function of implementing the behaviors in the method examples of the third and sixth aspects above. The functions may be implemented by hardware or by hardware executing corresponding software. The hardware or software includes one or more modules corresponding to the above functions.

[0056] In a tenth aspect, an embodiment of the present application provides a communications device, which may be a gNB-CU or a device (e.g., a chip, a chip system, or a circuit) within the gNB-CU. The beneficial effects can be found in the description of the fifth aspect and are not repeated here. The communications device has the function of implementing the behavior in the method example of the fifth aspect. The functions may be implemented by hardware or by hardware executing corresponding software. The hardware or software includes one or more modules corresponding to the above functions.

[0057] In an eleventh aspect, a communication device is provided, which may be a terminal device or a device in a terminal device (e.g., a chip, a chip system, or a circuit). The device may include a processor, a memory, an input interface, and an output interface, the input interface being used to receive information from other communication devices other than the communication device, the output interface being used to output information to other communication devices other than the communication device, and the processor calling a computer program stored in the memory to perform the method provided in the first aspect or any embodiment of the first aspect.

[0058] In a twelfth aspect, a communications device is provided. The communications device may be a gNB-DU of a source cell, or a device (e.g., a chip, a chip system, or a circuit) in the gNB-DU of the source cell. The device may include a processor, a memory, an input interface, and an output interface. The input interface is configured to receive information from a communications device other than the communications device, and the output interface is configured to output information to the communications device other than the communications device. The processor invokes a computer program stored in the memory to perform the method provided in the second aspect or any embodiment of the second aspect, or the fourth aspect or any embodiment of the fourth aspect.

[0059] In a thirteenth aspect, a communications device is provided. The communications device may be a gNB-DU of a cell, or a device (e.g., a chip, a chip system, or a circuit) in the gNB-DU of a cell. The device may include a processor, a memory, an input interface, and an output interface. The input interface is configured to receive information from a communications device other than the communications device, and the output interface is configured to output information to the communications device other than the communications device. The processor invokes a computer program stored in the memory to perform the method provided in the third aspect or any embodiment of the third aspect, or the sixth aspect or any embodiment of the sixth aspect.

[0060] In a thirteenth aspect, a communications device is provided. The communications device may be a gNB-CU or a device (e.g., a chip, a chip system, or a circuit) within the gNB-CU. The device may include a processor, a memory, an input interface, and an output interface. The input interface is configured to receive information from a communications device other than the communications device, and the output interface is configured to output information to the communications device other than the communications device. The processor invokes a computer program stored in the memory to perform the method provided in the fifth aspect or any embodiment of the fifth aspect.

[0061] In the fourteenth aspect, the present application provides a communication system, which includes at least one terminal device, at least one gNB-DU of a source cell, at least one gNB-DU of a cell, and at least one gNB-CU. When the at least one terminal device, at least one gNB-DU of a source cell, at least one gNB-DU of a cell, and at least one gNB-CU are operating in the communication system, it is used to perform any one of the methods described in the first to sixth aspects above.

[0062] In the fifteenth aspect, the present application provides a computer-readable storage medium having computer instructions stored thereon. When the computer program or computer instructions are executed, the method described in the above-mentioned first aspect and any possible implementation thereof, the second aspect and any possible implementation thereof, the third aspect and any possible implementation thereof, the fourth aspect and any possible implementation thereof, the fifth aspect and any possible implementation thereof, and the sixth aspect and any possible implementation thereof is executed.

[0063] In the sixteenth aspect, the present application provides a computer program product comprising executable instructions, which, when run on a communication device, enables the methods described in the above-mentioned first aspect and any possible implementation thereof, the second aspect and any possible implementation thereof, the third aspect and any possible implementation thereof, the fourth aspect and any possible implementation thereof, the fifth aspect and any possible implementation thereof, and the sixth aspect and any possible implementation thereof to be executed.

[0064] In a seventeenth aspect, the present application provides a communication device, comprising a processor and further comprising a memory, for implementing the methods of the first aspect and any possible implementation thereof, the second aspect and any possible implementation thereof, the third aspect and any possible implementation thereof, the fourth aspect and any possible implementation thereof, the fifth aspect and any possible implementation thereof, and the sixth aspect and any possible implementation thereof. The communication device may be a chip system, which may be composed of a chip or may include a chip and other discrete devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for describing the embodiments.

[0066] FIG1 is a schematic diagram of a network architecture provided in an embodiment of the present application;

[0067] FIG2 is a schematic diagram of a network architecture of an access network device provided in an embodiment of the present application;

[0068] FIG3 is a schematic diagram of a protocol layer division provided in an embodiment of the present application;

[0069] FIG4 is an interactive flow chart of a cell handover provided in an embodiment of the present application;

[0070] FIG5 is an interactive flow chart of a cell handover provided in an embodiment of the present application;

[0071] FIG6 is a schematic diagram of an LTM cell change command MAC CE provided in an embodiment of the present application;

[0072] FIG7 is an interactive diagram of a communication method provided in an embodiment of the present application;

[0073] FIG8 is an interactive diagram of another communication method provided in an embodiment of the present application;

[0074] FIG9 is an interactive diagram of another communication method provided in an embodiment of the present application;

[0075] FIG10 is an interactive diagram of another communication method provided in an embodiment of the present application;

[0076] FIG11 is an interactive diagram of another communication method provided in an embodiment of the present application;

[0077] FIG12 is a schematic structural diagram of a communication device provided in an embodiment of the present application;

[0078] FIG13 is a schematic structural diagram of another communication device provided in an embodiment of the present application;

[0079] FIG14 is a schematic structural diagram of a terminal device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0080] In the description of this application, unless otherwise specified, “ / ” means “or”. For example, A / B can mean A or B. “And / or” in this application is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, “at least one” can refer to one or more, and “a plurality” can refer to two or more. “At least one of…” means each of the listed items and any combination thereof. For example, “at least one of A, B, and C” or “at least one of A, B, or C” can mean: A exists alone, B exists alone, C exists alone, A and B exist at the same time, B and C exist at the same time, A and C exist at the same time, and A, B, and C exist at the same time. “First”, “second”, etc. do not limit the quantity and execution order, and “first”, “second”, etc. do not necessarily limit them to be different.

[0081] It should be noted that, in this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described in this application as "exemplary" or "for example" should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0082] In the description of this application, "indication" may include direct indication and indirect indication, and may also include explicit indication and implicit indication. The information indicated by a certain information (such as the indication information described below) is called information to be indicated. In the specific implementation process, there are many ways to indicate the information to be indicated. For example, the information to be indicated can be directly indicated, such as indicating the information to be indicated itself or the index of the information to be indicated. For another example, the information to be indicated can also be indirectly indicated by indicating other information, and there is an association between the other indicated information and the information to be indicated. For another example, only a part of the information to be indicated can be indicated, while the other parts of the information to be indicated are known or agreed in advance. In addition, the indication of specific information can be achieved by means of the pre-agreed (such as specified in the protocol) order of arrangement of each information, thereby reducing the indication overhead to a certain extent.

[0083] The following is an example description of the network architecture applicable to the embodiments of the present application.

[0084] Please refer to Figure 1, which is a schematic diagram of a network architecture provided by an embodiment of the present application. As shown in Figure 1, the network architecture may include a terminal device 101 and an access network device 102. Among them, the terminal device 101 can be connected to the access network device 102 in a wireless manner. It should be noted that the number and type of access network devices and terminal devices included in the network architecture shown in Figure 1 are merely examples, and the embodiments of the present application are not limited to this. For example, more or fewer terminal devices that communicate with the access network devices may also be included. For the sake of simplicity, they are not described one by one in the accompanying drawings. In addition, in the network architecture shown in Figure 1, although access network devices and terminal devices are shown, the application scenario may not be limited to including access network devices and terminal devices. For example, it may also include core network devices for carrying virtualized network functions, etc. These are obvious to those skilled in the art and will not be described one by one here.

[0085] The technical solutions of the embodiments of the present application can be applied to various communication systems, for example: cellular systems related to the Third Generation Partnership Project (3GPP) can be supported (for example, 5G communication systems, communication systems that integrate multiple wireless technologies (for example, communication systems that integrate at least two technologies among 2G, 3G, 4G, or 5G), or future-oriented evolution systems (for example, 6G access technology)), or wireless fidelity (WiFi) systems, or communication systems that integrate 3GPP-related cellular systems with other technologies, or future communication systems, etc.

[0086] The access network device in this application is sometimes also referred to as an access node. The access network device has a wireless transceiver function and is used to communicate with the terminal. The access network device includes but is not limited to the base station (base station) in the above-mentioned communication system, the evolved base station (evolved NodeB, eNodeB), the transmission reception point (TRP), the next generation base station (next generation NodeB, gNB) in the 5G mobile communication system, the next generation base station in the sixth generation (6th generation, 6G) mobile communication system, the access network device or the module of the access network device in the open access network ORAN (open RAN, ORAN) system, the base station in the future mobile communication system or the access node in the Wi-Fi system, etc. The access network device can also be a module or unit that can realize part of the functions of the base station. For example, the access network device can be a centralized unit (CU), a distributed unit (DU), a CU-control plane (CP), a CU-user plane (UP), or a radio unit (RU), etc., as described below. Among them, in the ORAN system, CU can also be called O-CU, DU can also be called open (open, O)-DU, CU-CP can also be called O-CU-CP, CU-UP can also be called O-CUP-UP, and RU can also be called O-RU. The access network device can be a macro base station, a micro base station or an indoor station, a relay node or a donor node, or a wireless controller in a cloud radio access network (CRAN) scenario. Optionally, the access network device can also be a server, a wearable device, or a vehicle-mounted device. For example, the access network device in the vehicle to everything (V2X) technology can be a road side unit (RSU). Multiple access network devices in the communication system can be base stations of the same type or different types. The base station can communicate with the terminal, or it can communicate with the terminal through a relay station. The terminal can communicate with multiple base stations in different access technologies.

[0087] A terminal may also be referred to as a terminal device, user equipment (UE), mobile station, mobile terminal, etc. The terminal can be widely used in various communication scenarios, for example, it can be applied to device-to-device (D2D) communication, vehicle-to-everything (V2X) communication, machine-type communication (MTC), Internet of Things (IOT), virtual reality, augmented reality, industrial control, autonomous driving, telemedicine, smart grid, smart furniture, smart office, smart wearable, smart transportation, or smart city scenarios. The terminal can be a mobile phone, a tablet computer, a computer with wireless transceiver function, a wearable device, a vehicle, a drone, a helicopter, an airplane, a ship, a robot, a robotic arm, or a smart home device, etc. The present disclosure does not limit the device form of the terminal.

[0088] The access network equipment and / or terminal can be fixed or movable. The access network equipment and / or terminal can be deployed on land, including indoors or outdoors, handheld or vehicle-mounted; can also be deployed on the water surface; can also be deployed on aircraft, balloons and artificial satellites in the air. The present disclosure does not limit the application scenarios of the access network equipment and terminals. The access network equipment and terminal equipment can be deployed in the same scenario or different scenarios. For example, the access network equipment and terminal equipment are deployed on land at the same time; or, the access network equipment is deployed on land and the terminal equipment is deployed on the water surface, etc., and no further examples are given.

[0089] In this application, each element in a communication system may be considered a network element in the communication system. Access network equipment and terminal equipment may be collectively referred to as communication devices. 102 in FIG1 may be referred to as a communication device having access network equipment functionality, and 101 in FIG1 may be referred to as a communication device having terminal equipment functionality.

[0090] In this application, a communication device with access network device functionality may be an access network device, a module within the access network device (such as a chip, a chip system, or a software module), or a control subsystem that includes access network device functionality. For example, a control subsystem that includes access network device functionality may be a control center in scenarios where terminals can be applied, such as smart grids, industrial control, intelligent transportation, or smart cities.

[0091] In the present application, a communication device with terminal functions may be a terminal, or a module in a terminal (such as a chip, a chip system, a modem, or a software model, etc.), or a device including terminal functions.

[0092] Further, please refer to Figure 2, which is a schematic diagram of the network architecture of an access network device provided in an embodiment of the present application. As shown in Figure 2, the access network device may include a CU and a DU. This design can be called CU and DU separation. Multiple DUs can be centrally controlled by one CU. As an example, the interface between the CU and the DU is called the F1 interface. Among them, the control plane (CP) interface can be F1-C, and the user plane (UP) interface can be F1-U. The present disclosure does not limit the specific names of each interface.

[0093] The communication between the access network device and the terminal device may follow a certain protocol layer structure. Exemplarily, the protocol layer structure may include a control plane protocol layer structure and a user plane protocol layer structure. For example, the control plane protocol layer structure may include at least one of the following: a radio resource control (RRC) layer, a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, a media access control (MAC) layer, or a physical (PHY) layer. For example, the user plane protocol layer structure may include at least one of the following: a service data adaptation protocol (SDAP) layer, a PDCP layer, an RLC layer, a MAC layer, or a physical layer.

[0094] CU and DU can be divided according to the protocol layers of the wireless network: for example, refer to Figure 3, which is a schematic diagram of the protocol layer division provided in an embodiment of the present application. As shown in Figure 3, the functions of the PDCP layer and the protocol layers above it (such as the RRC layer and the SDAP layer, etc.) are set in the CU, and the functions of the protocol layers below the PDCP layer (such as the RLC layer, the MAC layer and the PHY layer, etc.) are set in the DU; for another example, the functions of the protocol layers above the PDCP layer are set in the CU, and the functions of the protocol layers below the PDCP layer are set in the DU, without restriction.

[0095] The above division of the processing functions of CU and DU according to the protocol layer is only an example, and they can also be divided in other ways. For example, the CU or DU can be divided into functions with more protocol layers, and the CU or DU can be divided into partial processing functions with protocol layers. For example, some functions of the RLC layer and the functions of the protocol layers above the RLC layer are set in the CU, and the remaining functions of the RLC layer and the functions of the protocol layers below the RLC layer are set in the DU. For another example, the functions of the CU or DU can be divided according to the service type or other system requirements, such as division by delay, and the functions whose processing time needs to meet the delay requirements are set in the DU, and the functions that do not need to meet the delay requirements are set in the CU.

[0096] Optionally, the CU may have one or more functions of the core network.

[0097] Optionally, the functions of the CU can be further divided, and the control plane and the user plane can be separated and implemented through different entities. The separated entities are the control plane CU entity (i.e., CU-CP entity) and the user plane CU entity (i.e., CU-UP entity). The CU-CP entity and the CU-UP entity can be connected to the DU respectively. In this application, the entity can be understood as a module or unit, and its existence can be a hardware structure, a software module, or a hardware structure plus a software module, without limitation.

[0098] In an embodiment of the present application, a terminal device or a network device includes a hardware layer, an operating system layer running on the hardware layer, and an application layer running on the operating system layer. The hardware layer includes hardware such as a central processing unit (CPU), a memory management unit (MMU), and memory (also called main memory). The operating system can be any one or more computer operating systems that implement business processing through processes, such as a Linux operating system, a Unix operating system, an Android operating system, an iOS operating system, or a Windows operating system. The application layer includes applications such as browsers, address books, word processing software, and instant messaging software. In addition, the embodiment of the present application does not specifically limit the specific structure of the execution subject of the method provided in the embodiment of the present application. As long as it is possible to communicate according to the method provided in the embodiment of the present application by running a program that records the code of the method provided in the embodiment of the present application, for example, the execution subject of the method provided in the embodiment of the present application can be a terminal device or a network device, or a functional module in the terminal device or the network device that can call a program and execute the program.

[0099] In addition, various aspects or features of the present application can be implemented as methods, apparatuses, or articles of manufacture using standard programming and / or engineering techniques. The term "article of manufacture" as used in this application encompasses a computer program that can be accessed from any computer-readable device, carrier, or medium. For example, computer-readable media may include, but are not limited to: magnetic storage devices (e.g., hard disks, floppy disks, or magnetic tapes, etc.), optical disks (e.g., compact discs (CDs), digital versatile discs (DVDs), etc.), smart cards, and flash memory devices (e.g., erasable programmable read-only memories (EPROMs), cards, sticks, or key drives, etc.). In addition, the various storage media described herein may represent one or more devices and / or other machine-readable media for storing information. The term "machine-readable medium" may include, but is not limited to, wireless channels and various other media capable of storing, containing, and / or carrying instructions and / or data.

[0100] The following are definitions of technical terms that may appear in the embodiments of this application. The terms used in the implementation section of this application are only used to explain the specific embodiments of this application and are not intended to limit this application.

[0101] (1) Protocol Stack

[0102] The control plane protocol stack between the terminal device, access network device and core network device may include the non-access stratum (NAS), RRC, PDCP, RLC, MAC and PHY layers.

[0103] NAS layer: Non-access layer, located between the UE and the AMF of the core network, is mainly responsible for registration management, session management, and authentication control. The interaction between the UE and the core network is completed through NAS messages;

[0104] RRC layer: Layer 3, radio resource control layer, mainly responsible for the control plane processes related to the radio access network;

[0105] PDCP layer: Layer 2, packet data convergence layer, is mainly responsible for providing transmission services for radio bearers (RBs). Its main functions include adding sequence numbers, compression, encryption and decryption, integrity protection and verification, etc.

[0106] RLC layer: Layer 2, radio link control layer. The RLC layer communicates with the PDCP layer through the RLC channel and with the MAC layer through the logical channel. Its main functions include segmentation and reassembly of RLC service data units (SDUs), automatic repeat request (ARQ) error correction, and duplicate detection.

[0107] MAC layer: Layer 2, media access control layer, is mainly responsible for processing the mapping between logical channels and transport channels and scheduling radio resources. Its main functions include mapping between logical channels and transport channels, multiplexing and demultiplexing of logical channels, and scheduling.

[0108] PHY layer: Layer 1, the physical layer, is located at the bottom of the air interface protocol stack and is mainly responsible for coding, modulation, multi-antenna processing, and time-frequency resource mapping.

[0109] (2) L1 / L2 triggered mobility (LTM)

[0110] L1 can refer to the physical layer, and L2 can refer to the MAC / RLC / PDCP / SDAP layer. LTM means that handover-related operations are mainly performed at L1 and / or L2. For example, the terminal device sends the L1 measurement results to the access network device via physical layer control signaling (carried on the physical uplink control channel (PUCCH)). The physical layer of the access network device reads the L1 measurement results. Based on the measurement results, the access network device makes a handover decision and sends it to the terminal device via L1 / L2 signaling. The L1 / L2 signaling can be a message carried on the physical downlink control channel (PDCCH) or a MAC control element (MAC CE).

[0111] It should be noted that L1 / L2 can be understood as L1 and / or L2. When it is an "and" relationship, the operations related to the switching process can be mainly completed by L1 and L2; when it is an "or" relationship, the switching-related operations are completed by L1 or L2.

[0112] LTM switching can be used in different scenarios such as intra-DU, inter-DU, and inter-CU. Although the specific signaling interaction content is different, the basic idea is the same. The following is an example of cell switching between different DUs under the same CU. When it comes to cross-CU scenarios, signaling or steps for interaction between CUs will be added, such as a switching request message sent by the source CU to the candidate target CU, or a switching request reply message sent by the target CU to the source CU. Please refer to Figure 4, which is an interactive flow chart of a cell switching provided in an embodiment of the present application. As shown in Figure 4, its main process can be as follows:

[0113] 1. The CU sends the candidate cell configuration to the terminal device. The CU can send the candidate cell configuration information to the terminal device via the source DU. For each candidate cell, the pre-configuration information includes the candidate cell's identifier and configuration (such as AS access configuration). After receiving the pre-configuration information, the UE does not disconnect from the source cell.

[0114] 2. The terminal device reports the measurement to the source DU. The terminal device sends the measurement results to the source DU. The measurement results may include at least one of the following: the L1 measurement result of the source cell and the L1 measurement result of at least one candidate cell. The L1 measurement results of the source cell and / or candidate cell may be cell-level measurement results or beam-level measurement results.

[0115] 3. The source DU sends a handover command to the terminal device. The source DU sends a handover command to the terminal device, sending the identification information of the associated target cell to the terminal device via L1 / L2 signaling. The L1 / L2 signaling is sent via the communication resources of the source cell. The target cell is one or more candidate cells.

[0116] 4. The terminal device performs LTM switching to the target DU and switches to the target cell. The terminal device can access the target cell using the configuration information corresponding to the target cell received in step 1, and start uplink and downlink data transmission with the target cell after successful access. Among them, the terminal device can access the target cell using random access or using random access-free access. During the random access-free switching process, the terminal device uses the uplink authorization (UL grant) of the target cell to send an uplink message to the target cell. After the target cell receives the message, it can be considered that the terminal device has successfully switched to the target cell. The prerequisite for the terminal device to perform random access-free switching is to obtain the uplink synchronization information of the target cell, such as TA.

[0117] It should be noted that before a cell handover occurs, the target DU can also be referred to as a candidate DU. When a handover occurs, the candidate DU that manages the target cell can also be referred to as a target DU. Communication between a terminal device and a cell can be understood as communication between the terminal device and the access network device to which the cell belongs, or communication using the communication resources of the cell. For example, when a terminal device sends a message to a source cell, it can be understood as the terminal device sending a message to the source DU, or the terminal device sending a message to the source access network device, or the terminal device sending a message using the communication resources of the source cell.

[0118] In addition, the target cell is one of the candidate cells. When the terminal device receives a handover command to perform a cell handover, a candidate cell can be called the target cell. Similarly, the target DU is one of the candidate DUs. When the terminal device receives a handover command to perform a cell handover, a candidate DU can be called the target DU.

[0119] (3) gNB-CU: A logical unit that controls one or more DUs and manages the RRC, SDAP, and PDCP layers (gNB) or the RRC and PDCP layers (en-gNB).

[0120] (4) gNB-DU: A logical unit whose operation is partially controlled by the gNB-CU and manages the RLC, MAC, and PHY layers of the en-gNB or gNB. A gNB-DU can support one or more cells.

[0121] It should be understood that the definitions of the above technical terms are for illustrative purposes only. For example, with the continuous development of technology, the scope of the above definitions may also change, and the embodiments of this application are not intended to limit them.

[0122] First, in order to facilitate the understanding of the embodiments of the present application, the technical problems to be specifically solved by the present application are further analyzed and proposed. At present, for the scenario of cell switching, in order to reduce the switching delay and interruption time and improve the user experience of the terminal device, L1 / L2 triggered mobility is proposed. L1 / L2 triggered mobility can also be called L1 / L2 switching. L1 / L2 switching can instruct the terminal device to perform switching through L1 signaling (such as DCI) and / or L2 signaling (such as MAC CE). The implementation of LTM includes a variety of technical solutions. The following exemplifies a RACH-less access solution, in which:

[0123] Please refer to Figure 5, which is a flowchart of a cell handover interaction provided by an embodiment of the present application. As shown in Figure 5, the following steps may be included:

[0124] User data can be exchanged between the terminal device, the gNB-DU of the source cell, and the gNB-CU.

[0125] 1. L3 measurement control and reporting are performed between the terminal device, the gNB-DU of the source cell, the gNB-DU of the candidate cell, and the gNB-CU.

[0126] 2. The gNB-CU makes LTM configuration decisions.

[0127] 3. The gNB-CU sends a UE Context Setup Request to the gNB-DU of the candidate cell.

[0128] 4. The gNB-DU of the candidate cell sends a UE Context Setup Response to the gNB-CU.

[0129] 5. The gNB-CU sends a UE Context Modification Request to the gNB-DU of the source cell.

[0130] 6. The gNB-DU of the source cell sends a UE Context Modification Response to the gNB-CU.

[0131] Optionally, 7. The gNB-CU sends a UE Context Modification Request to the gNB-DU of the candidate cell.

[0132] Optionally, 8. The gNB-DU of the candidate cell sends a UE Context Modification Response to the gNB-CU.

[0133] 9. The gNB-CU sends a DL RRC message transfer (RRC reconfiguration) to the gNB-DU of the source cell.

[0134] 10. The gNB-DU of the source cell initiates RRC reconfiguration to the UE.

[0135] 11. The UE sends an RRC reconfiguration complete message to the gNB-DU of the source cell.

[0136] 12. The gNB-DU of the source cell sends an UL RRC message transfer (RRC reconfiguration complete) to the gNB-CU.

[0137] 13. Complete early TA acquisition between the terminal device and the candidate cell.

[0138] 14. The gNB-DU of the candidate cell sends DU-CU TA information to the gNB-CU.

[0139] 15. The gNB-CU sends CU-DU TA information to the gNB-DU of the source cell.

[0140] 16. The UE sends an L1 measurement report to the gNB-DU of the source cell.

[0141] 17. The gNB-DU of the source cell makes an LTM cell handover decision.

[0142] 18. The gNB-DU of the source cell sends a cell handover command to the UE.

[0143] 19. The gNB-DU of the source cell sends a DU-CU cell handover notification (target cell ID, TCI state ID) to the gNB-CU.

[0144] 20. The gNB-CU sends a CU-DU cell handover notification (target cell ID, TCI state ID) to the gNB-DU of the candidate cell.

[0145] 21. The gNB-DU detects UE access. Specifically, the gNB-DU of the source cell, the gNB-DU of the candidate cell, and the terminal device complete access.

[0146] 22. The gNB-DU of the candidate cell sends an access success (target cell ID) message to the gNB-CU.

[0147] 23. The UE sends an RRC reconfiguration complete message to the gNB-DU of the candidate cell.

[0148] 24. The gNB-DU of the candidate cell sends UL RRC information transfer (RRC reconfiguration complete) to the gNB-CU.

[0149] 25. The gNB-CU sends a UE Context Release Command (prepared cell) to the gNB-DU of the source cell.

[0150] 26. The gNB-DU of the source cell sends a UE context release complete message to the gNB-CU.

[0151] User data can be exchanged between the terminal device, the gNB-DU of the candidate cell, and the gNB-CU.

[0152] L1 / L2 triggered mobility (LTM) involves the network pre-configuring multiple candidate cells for a terminal device. Based on the L1 measurement results reported by the terminal device, the network can continuously trigger the mobility management mechanism using handover commands carried by MAC CEs to switch the terminal device from the source cell to the candidate cells. Prior to sending the handover command, the terminal device can be triggered to perform downlink and uplink synchronization.

[0153] During uplink synchronization in Release 18, the gNB-DU in the source cell triggers the UE to send a preamble to the gNB-DU in the candidate cell via a PDCCH order. The gNB-DU in the candidate cell then measures the UE's TA and sends it to the gNB-DU in the source cell via the gNB-CU, along with the TA-related preamble and candidate cell identification (ID). The gNB-DU in the source cell receives the TA and its associated contention-free random access (CFRA) resource information (e.g., preamble value), the candidate cell ID, and the candidate cell's DU ID (omitted if the DU is the same). Using this information, the gNB-DU in the source cell determines the UE corresponding to the TA and sends the TA to the corresponding UE via a cell change command. For example, the gNB-DU in the source cell sends the target cell's TA to the UE when sending the LTM command carried in the MAC CE (as shown in Figure 5) for RACHless access.

[0154] Please refer to Figure 6, which is a schematic diagram of an LTM cell change command MAC CE provided by an embodiment of the present application. As shown in Figure 6, in the handover command, if the timing advance command (TAC) indicates whether the TA of the LTM target cell (i.e., the SpCell corresponding to the target configuration indicated by the target configuration ID field) is valid, specifically if it is set to FFF, it indicates that there is no valid timing adjustment available in the LTM target cell, otherwise the field indicates the index value TA (index value TA) used to control the number of timing adjustments that the MAC entity needs to apply.

[0155] However, during continuous LTM, the gNB-DU of the candidate cell needs to re-trigger the TA acquisition process each time the terminal device switches to a new cell. This frequent re-triggering of the TA acquisition process results in high signaling overhead for both the terminal device and the network. Specific issues that need to be addressed are:

[0156] 1. How to help determine the effectiveness of TA based on the real-time status of terminal devices.

[0157] 2. TA effectiveness on the network side maintains the available solutions and the nodes that trigger, maintain, and participate.

[0158] 3. In order to reduce the signaling overhead of the terminal device and the network side, the TA obtained through the interaction on the network side needs to consider the specific interaction time and interaction content.

[0159] 4. TA processing in the LTM fast recovery scenario.

[0160] Based on the above, the present application proposes a communication method, which will be described below through the following embodiments. Some of these communication methods are applicable only to certain processes in the TA acquisition method, while others can be applied to any one or more processes in the TA acquisition method. It should be understood that these communication methods can be used in combination with each other. For example, one process in the TA acquisition method may use one method while another process uses another method, or a process in the TA acquisition method may use both one method and another method.

[0161] It should be understood that the TA acquisition method may change as the technical solution evolves. The technical solution provided in this application is not limited to LTM switching scenarios, but is also applicable to other switching technologies or other scenarios requiring uplink synchronization. The technical solution provided in this application is also not limited to the process described below. Furthermore, the description of the scenario in the embodiments of this application is only an example, and does not limit the solution of the embodiments of this application to be applicable only to the described scenario. It is also applicable to scenarios with similar problems.

[0162] The terminal device in the embodiment of the present application (such as the embodiment corresponding to Figures 7 to 11 below) can be a terminal device in the network architecture shown in Figure 1, and the function performed by the terminal device in this embodiment can also be performed by a device in the terminal device (for example, a chip, or a chip system, or a circuit). The network side device in this embodiment can be an access network device in the network architecture shown in Figure 1, and the function performed by the access network device in this embodiment can also be performed by a device in the access network device (for example, a chip, or a chip system, or a circuit). The embodiments of the present application are uniformly explained here and will not be repeated later.

[0163] In conjunction with the above-mentioned network architecture, a communication method provided by an embodiment of the present application is described below. Please refer to Figure 7, which is an interactive schematic diagram of a communication method provided by an embodiment of the present application. As shown in Figure 7, the method may include the following steps. Among them, S702 is an optional step.

[0164] S701: The network sends a first message to a terminal device, the first message including at least one of the following: a cell ID, a TA, a TA validity command, and a TA validity period. Accordingly, the terminal device receives the first message from the network.

[0165] The network side can pre-configure multiple cells for the terminal device. Based on the L1 measurement results reported by the terminal device, the network side can use the cell switching command to trigger the mobility management mechanism to enable the terminal device to switch from the source cell to the candidate cell. Among them, before the cell switching command is sent, the network side can first trigger the terminal device to perform uplink and downlink synchronization. For example, in uplink synchronization, the network side can trigger uplink synchronization through the PDCCH order. Specifically, the network side can send the PDCCH order to the terminal device, and carry the cell ID. The terminal device sends a preamble code to the network side, so that the network side can measure the TA of the cell.

[0166] If the TA of the cell is still valid, the network side may send a first message to the terminal device, and the first message may include one or more of the cell ID, TA, TA's valid command, and TA's valid time.

[0167] The cell in the embodiment of the present application can be understood as a candidate cell, a target cell, or a neighboring cell, etc. The following is an exemplary description using a candidate cell as an example. The cell ID can be a physical cell index PCI, a candidate configuration index (candidate configuration ID), or other index that can uniquely identify a cell.

[0168] The TA is a one-to-one correspondence between a terminal device and the cell to which the terminal device transmits the preamble, meaning that the TA for a terminal device and a cell is uniquely determined. The TA validity command indicates to the terminal device that the TA remains valid after switching to a candidate cell. The TA validity period may be a specific TA period. For example, after receiving the TA validity period, the terminal device may activate the TAT corresponding to the TA based on the TA validity period. If the TAT times out, the TA is determined to be valid (also considered valid). If the TAT times out, the TA is determined to be invalid. The TAT may be configured by the network along with the TA for the terminal device, or it may be preconfigured, such as by a protocol definition. It is understood that the network determines whether the cell's TA remains valid by determining whether the cell's TA remains valid based on the terminal device's location and the location of the gNB-DU in the cell. If the terminal device's location has not changed, and the distance from the candidate cell's gNB-DU has not changed, the cell's TA is determined to be valid. If the terminal device's location has changed, and the distance from the cell's gNB-DU has changed, the cell's TA is determined to be invalid, requiring the TA acquisition process to be retriggered.

[0169] It is understandable that if the network does not give the terminal device the TA of the cell until the cell switching is triggered, it is relatively unreasonable to reuse the existing TAT, because the TA was actually obtained some time ago, so the original TAT cannot be reused, and a dedicated time for the TA needs to be given.

[0170] One possible implementation method is that if the terminal device is performing RACH less access for the first time, the first message may carry the ID of the cell. If the terminal device is not performing RACH less access for the first time (the terminal device has obtained the cell's TA in the previous RACH less access process), when the network side sends the first message to the terminal device, the cell's TA is still valid, then the first message does not need to carry the cell's TA, and only the valid command of the TA is indicated in the first message. In this way, when the TA is valid, there is no need to repeatedly transmit the 12-bit TAC, and 1 or several bits are used to indicate that the TA is still valid. The TA can be used for subsequent RACH less access, or LTM process or LTM recovery (recovery), which can reduce the signaling overhead between the terminal device and the network side.

[0171] The first message can be a cell switch command, a random access response (RAR), or other message. If the first message is a cell switch command, the network-side device can be the gNB-DU of the source cell. If the first message is a RAR or other message, the network-side device can be the gNB-DU of the source cell or a candidate cell.

[0172] The first message may be carried via DCI, RRC, MAC CE or other messages / signaling.

[0173] S702: The terminal device uses the TA to perform RACH less access.

[0174] After the terminal device receives the first message from the network side, it can determine to use the TA to perform RACH less access based on one or more of the cell ID, TA, TA's valid command, and TA's valid time in the first message. For example, if the first message includes the cell's TA and the TA's valid command, the terminal device can retain the TA and use the TA to perform RACH less access after switching to the target cell. For another example, if the first message includes the cell's TA and the TA's valid time, the terminal device can use the TA to perform RACH less access within the TA's valid time.

[0175] Unlike the prior art, in the case of continuous RACH less access, each time the terminal device switches to a new cell, it is necessary to re-trigger the cell's TA acquisition process. In an embodiment of the present application, when the cell's TA is valid, a first message is sent to the terminal device through the network side. The terminal device can determine to continue using the valid TA to perform RACH less access based on one or more of the cell's ID, TA, TA's valid command, and TA's valid time in the first message, thereby avoiding re-triggering the cell's TA acquisition process and reducing the signaling overhead between the terminal device and the network side.

[0176] In the method embodiment corresponding to FIG7 , the validity of the cell's TA can be maintained by the terminal device or the network. The method embodiment of FIG8 can correspond to the terminal device maintaining the validity of the cell's TA, and the method embodiments of FIG9 - FIG11 can correspond to the network maintaining the validity of the cell's TA. For example, FIG9 corresponds to the gNB-DU of the target cell maintaining the validity of the cell's TA on the network side, FIG10 corresponds to the gNB-DU of the source cell maintaining the validity of the cell's TA on the network side, and FIG11 corresponds to the gNB-CU maintaining the validity of the cell's TA on the network side. These are described in detail below.

[0177] It should be noted that LTM switching can be used in different scenarios such as intra-DU, inter-DU, and inter-CU. Although the specific signaling interaction content varies, the basic idea is the same. The following is an example of cell switching between different DUs under the same CU. When cross-CU scenarios are involved, signaling or steps for interaction between CUs will be added. For example, the source DU sends information to the source CU that controls the source DU, and the source CU then forwards it to the target DU through the target CU that controls the target DU.

[0178] It should be noted that when a terminal device communicates with a cell, it can be understood as the terminal device communicating with the access network equipment to which the cell belongs, or the terminal device using the communication resources of the cell for communication. For example, when a terminal device sends a message to a source cell, it can be understood as the terminal device sending a message to the gNB-DU of the source cell, or the terminal device sending a message to the source access network equipment, or the terminal device sending a message using the communication resources of the source cell.

[0179] It should be noted that the target cell is one of the candidate cells. Before the cell switching occurs, the target DU can also be called a candidate DU. When the terminal device receives a switching command to perform cell switching, the candidate DU that manages the target cell can also be called a target DU. A candidate cell can be called a target cell. Similarly, the target DU is one of the candidate DUs. When the terminal device receives a switching command to perform cell switching, a candidate DU can be called a target DU. The candidate cells and target cells that appear in the following embodiments can be equivalently replaced, and are explained here uniformly and will not be explained later.

[0180] Please refer to Figure 8, which is a schematic diagram illustrating interactions in another communication method provided in an embodiment of the present application. The network side may include a gNB-DU of a source cell, a gNB-DU of a candidate cell, and a gNB-CU. As shown in Figure 8, the method may include the following steps. Steps S806-S809 are optional.

[0181] S801. The gNB-DU of the source cell sends a PDCCH order to the terminal device. Correspondingly, the terminal device receives the PDCCH order from the gNB-DU of the source cell.

[0182] Among them, the PDCCH order can be used to trigger the terminal device to obtain the TA of the cell, or it can also be understood that the PDCCH order can be used to trigger the uplink synchronization of the terminal device, and the PDCCH order carries the cell ID.

[0183] S802: The terminal device sends a preamble to the gNB-DU of the candidate cell. In response, the gNB-DU of the candidate cell receives the preamble from the terminal device.

[0184] The UE receives the PDCCH order from the gNB-DU of the source cell, triggering uplink synchronization. The UE can then send a preamble to the gNB-DU of the candidate cell to obtain the TA of the candidate cell.

[0185] S803. The gNB-DU of the candidate cell sends the candidate cell's TA to the gNB-CU. In response, the gNB-CU receives the candidate cell's TA from the gNB-DU of the candidate cell.

[0186] After receiving the preamble from the terminal device, the gNB-DU of the candidate cell can measure the TA between itself and the terminal device and send the TA to the gNB-CU.

[0187] S804: The gNB-CU sends the TA and TAT of the candidate cell to the gNB-DU of the source cell. In response, the gNB-DU of the source cell receives the TA and TAT of the candidate cell from the gNB-CU.

[0188] In one possible implementation, the gNB-DU of the candidate cell may provide a TAT related to the TA of the cell. Specifically, before the gNB-CU sends the TA and TAT of the candidate cell to the gNB-DU of the source cell, the method further includes: the gNB-DU of the candidate cell sends the TA and TAT1 of the TA to the gNB-CU, such as the gNB-DU of the candidate cell may send the TA and TAT1 of the TA to the gNB-CU via a DU-CU TA information transfer message; and the gNB-CU sends the TA and TAT of the candidate cell to the gNB-DU of the source cell, including: the gNB-CU sends the TA and TAT1 of the TA to the gNB-DU of the source cell, such as the gNB-CU may send the TA and TAT1 of the TA to the gNB-DU of the source cell via a DU-CU TA information transfer message.

[0189] In one possible implementation, the gNB-CU may provide a TAT associated with the TA of the candidate cell. Specifically, before the gNB-CU sends the TA of the candidate cell and the TAT of the TA to the gNB-DU of the source cell, the method further includes: the gNB-DU of the candidate cell sends the TA to the gNB-CU, e.g., the gNB-DU of the candidate cell may send the TA to the gNB-CU via a DU-CU TA information transfer message; the gNB-CU obtains TAT2 of the TA; and the gNB-CU sends the TA of the candidate cell and the TAT of the TA to the gNB-DU of the source cell, including: the gNB-CU sends the TA and TAT2 to the gNB-DU of the source cell, e.g., the gNB-CU may send the TA and TAT2 of the TA to the gNB-DU of the source cell via a DU-CU TA information transfer message.

[0190] S805. The gNB-DU of the source cell sends a first message to the terminal device. The first message includes at least one of the following: a cell ID, a TA, a validity command for the TA, and a validity period for the TA. In response, the terminal device receives the first message from the gNB-DU of the source cell.

[0191] If the TA of the candidate cell is still valid, the gNB-DU of the source cell may send a first message to the terminal device. The first message may include one or more of the cell ID, TA, TA validity command, and TA validity period. The first message may be a cell switch command, a RAR message, or other message. For other related details, refer to the description of S701 above and will not be repeated here to avoid redundancy.

[0192] S806: The terminal device uses the TA to perform RACH less access.

[0193] After the terminal device receives the first message from the network side, it can determine to use the TA to execute the RACH less LTM process based on one or more of the TA of the candidate cell, the valid command of the TA, and the valid time of the TA in the first message. For example, if the first message includes the TA of the candidate cell and the valid command of the TA, the terminal device can retain the TA and use the TA to execute RACH less access after switching to the target cell. For another example, if the first message includes the TA of the candidate cell and the valid time of the TA, the terminal device can use the TA to execute RACH less access within the valid time of the TA. After the terminal device switches to the target cell, the TA can be retained. When the cell switching is triggered, if the TA is valid, RACH less access is executed.

[0194] S807: The terminal device determines whether the TA is valid. If not, execute S808; if so, execute S810.

[0195] In a possible implementation, the terminal device may start the TAT timing and determine whether the TAT has timed out. If the TAT has not timed out, the TA corresponding to the TAT is determined to be valid; if the TAT has timed out, the TA corresponding to the TAT is determined to be invalid.

[0196] In one possible implementation, upon receiving the TA for a candidate cell, the terminal device may record / update the downlink path loss reference RSRP value for the candidate cell. The reference RSRP value may be pre-configured for the terminal device by the gNB-DU of the source cell.

[0197] The terminal device determines that the TA is invalid if at least one of the following conditions is met: the timer for starting the TA corresponding to the TAT times out, the RSRP value of the cell changes by more than a preset threshold, the terminal device receives a new TA from the gNB-DU of the cell, the terminal device receives a TA failure indication command, or the terminal device receives a PDCCH order for the cell. In other words, if the timer for starting the TA corresponding to the TAT times out, and / or the RSRP value of the cell changes by more than (or equal to or greater than) a preset threshold, and / or the terminal device receives a new TA from the gNB-DU of the cell, and / or the terminal device receives a TA failure indication command, and / or the terminal device receives a PDCCH order for the cell, the TA is invalid.

[0198] A possible implementation method is that if at least one of the following conditions is met: the timing of the corresponding TA started by TAT has not timed out, the change in the RSRP value of the cell is less than or equal to the preset threshold, the terminal device no longer receives a new TA from the gNB-DU of the cell, the terminal device does not receive a TA failure indication command, and the terminal device does not receive a PDCCH indication for the cell, then the terminal device determines that the TA has not failed.

[0199] S808. The terminal device sends a TA failure indication command to the gNB-DU of the source cell. In response, the gNB-DU of the source cell receives the TA failure indication command from the terminal device.

[0200] If the TA corresponding to the TAT fails, the terminal device may send a TA failure indication command to the gNB-DU of the source cell. The TA failure indication command includes the cell ID or TAG ID. Optionally, the TA failure indication command includes one or more cell IDs or one or more TAG IDs.

[0201] Further optionally, after the terminal device sends a TA failure indication command to the gNB-DU of the source cell, it can release, discard, or no longer store the failed TA.

[0202] It should be noted that steps S807-S808 can also be executed before S805 or steps S807-S808 can be executed after S805. It can be understood that the terminal device can maintain the validity of the TA by itself, and can maintain it before the cell switching command or continue to maintain it after the cell switching command. Therefore, the embodiment of the present application does not limit the execution order of S805 and S807-S808.

[0203] S809. The gNB-DU of the source cell determines that the candidate cell does not have a valid TA.

[0204] After the gNB-DU of the source cell receives the TA failure indication command from the terminal device, it can determine that the candidate cell has no valid TA.

[0205] Furthermore, the gNB-DU of the source cell may re-execute S801, i.e., the gNB-DU of the source cell sends a PDCCH order to the terminal device to obtain a valid TA corresponding to the candidate cell. The cell indicated by the PDCCH order and the cell corresponding to the TA are the same cell. It can be understood that the PDCCH order is used to re-acquire a valid TA corresponding to the candidate cell.

[0206] Alternatively, the gNB-DU of the source cell sets the TAC field to FFF when issuing a cell handover command to the terminal device. The FFF field indicates that no valid timing adjustment is available in the LTM target cell. If no valid TA value is available, the terminal device may trigger a random access-based cell change.

[0207] S810. The terminal device sends valid TA information to the gNB-DU of the source cell. In response, the gNB-DU of the source cell receives the valid TA information from the terminal device.

[0208] The valid TA information includes at least one of the following: an indication of a valid TA, a list of cells with a valid TA, the TA, and the remaining TAT. Optionally, if the TA fails, the valid TA information may be discarded. The cell list and the valid TA may correspond to each other.

[0209] The remaining TAT can be used to communicate with the terminal device and the network about how long the TA remains valid. For example, when the terminal device is given TAs corresponding to multiple candidate cells before the cell handover command, the terminal device needs to maintain the validity of the TAs on its own. After accessing the target cell, the validity basis for one or more TAs (remaining TAT) and / or the TA can be given to the gNB-DU of the target cell. For candidate cells that already have valid TAs, the network does not need to send a PDCCH order to re-acquire the TA, thereby saving signaling overhead.

[0210] It is understood that the terminal device may transmit the valid TA information to the gNB-DU of the source cell by itself or after receiving an instruction from the network. Furthermore, if the terminal device receives a reporting instruction from the network after reporting the valid TA information, it may continue to report the valid TA information. If it does not receive a reporting instruction from the network, it does not need to report the valid TA information subsequently.

[0211] Specifically, the terminal device may report the information of the valid TA after accessing the target cell. For example, the information may be reported via PUCCH / SR / BSR (indication of the existence of a valid TA), or in the RRC reconfiguration complete message (indication of the existence of a valid TA, a list of cells with valid TAs, a list of valid TAs, and corresponding cell indexes).

[0212] If the validity of the TA is maintained for a long time on the terminal device side, the terminal device can send the existing TA to the gNB-DU of the target cell after accessing the target cell for subsequent RACH-less access.

[0213] Different from the prior art, in the case of continuous RACH less access, the terminal device needs to re-trigger the TA acquisition process of the candidate cell each time it switches to a new cell. In an embodiment of the present application, when the TA of the candidate cell is valid, a first message is sent to the terminal device through the network side, and the terminal device can determine to continue to use the valid TA to perform RACH less access based on one or more of the TA of the candidate cell, the valid command of the TA, and the valid time of the TA in the first message, thereby avoiding re-triggering the TA acquisition process of the candidate cell and reducing the signaling overhead between the terminal device and the network side. In addition, the validity of the TA of the candidate cell can be maintained by the terminal device, and the validity of the TA of the candidate cell can be maintained based on the real-time situation of the terminal device, which can improve the accuracy of RACH less access.

[0214] Please refer to Figure 9, which is a schematic diagram illustrating interactions in another communication method provided in an embodiment of the present application. The network side may include a gNB-DU of a source cell, a gNB-DU of a candidate cell, and a gNB-CU. As shown in Figure 9, the method may include the following steps. Steps S906 and S908 are optional.

[0215] S901. The gNB-DU of the source cell sends a PDCCH order to the terminal device. Correspondingly, the terminal device receives the PDCCH order from the gNB-DU of the source cell.

[0216] S902: The terminal device sends a preamble to the gNB-DU of the candidate cell. In response, the gNB-DU of the candidate cell receives the preamble from the terminal device.

[0217] S903. The gNB-DU of the candidate cell sends the measured TA of the candidate cell to the gNB-CU. Correspondingly, the gNB-CU receives the TA measured by the gNB-DU of the candidate cell.

[0218] S904. The gNB-CU sends the TA of the candidate cell and the TAT of the TA to the gNB-DU of the source cell.

[0219] S905. The gNB-DU of the source cell sends a first message to the terminal device. The first message includes at least one of the following: a cell ID, a TA, a validity command for the TA, and a validity period for the TA. In response, the terminal device receives the first message from the gNB-DU of the source cell.

[0220] S906: The terminal device uses the TA to perform RACH less access.

[0221] It can be understood that S901-S906 correspond to the above-mentioned S801-S806. For specific descriptions, please refer to the above-mentioned S801-S806. To avoid repetition, they will not be repeated here.

[0222] S907. The gNB-DU of the target cell determines whether the TA is valid. If not, execute S908.

[0223] In one possible implementation, the gNB-DU of the target cell records / updates the downlink path loss reference RSRP value of the target cell.

[0224] The gNB-DU of the target cell determines that the TA has failed if at least one of the following conditions is met: the timer for starting the TA corresponding to the TAT has timed out, the RSRP value of the gNB-DU of the cell has changed by more than a preset threshold, and the PDCCH indication of the cell corresponding to the TA has been sent.

[0225] The TAT is TAT1 configured for the cell, or TAT2 configured for the gNB-CU.

[0226] On the contrary, if at least one or more of the following conditions are met: the timer for starting the TA corresponding to the TAT has not timed out, the change in the RSRP value of the gNB-DU of the cell is less than (or less than or equal to) the preset threshold, and the PDCCH order of the cell corresponding to the TA has not been sent, the gNB-DU of the target cell determines that the TA has not failed.

[0227] Further optionally, the gNB-DU of the source cell may send a cell handover notification to the gNB-DU of the target cell. The cell handover notification includes one or more recent measurement results of the TA and the cell corresponding to the TA. The measurement results may be L1 or L3 measurement results. The gNB-DU of the target cell may update the RSRP value of the target cell according to the cell handover notification.

[0228] S908. If the TA corresponding to the TAT fails, the gNB-DU of the target cell sends a TA failure indication command to the terminal device.

[0229] If the TA corresponding to the TAT fails, the gNB-DU of the target cell may send a TA failure indication command to the terminal device. The TA failure indication command includes the ID of the candidate cell. Furthermore, optionally, after sending the TA failure indication command to the terminal device, the gNB-DU of the target cell may release, discard, or no longer store the failed TA.

[0230] Optionally, if the TA corresponding to the TAT fails, the gNB-DU of the target cell can send a PDCCH order to the terminal device to re-acquire the TA of the target cell.

[0231] Different from the prior art, in the case of continuous RACH less access, the terminal device needs to re-trigger the TA acquisition process of the candidate cell each time it switches to a new cell. In an embodiment of the present application, when the TA of the candidate cell is valid, a first message is sent to the terminal device through the network side. The terminal device can determine to continue to use the valid TA to perform RACH less access based on one or more of the TA of the candidate cell, the valid command of the TA, and the valid time of the TA in the first message, thereby avoiding re-triggering the TA acquisition process of the candidate cell and reducing the signaling overhead between the terminal device and the network side. In addition, the validity of the TA can be maintained by the gNB-DU of the target cell, and the validity of the TA can be maintained by the network side, which can not only reduce the energy consumption of the terminal device, but also improve the accuracy of RACH less access.

[0232] Please refer to Figure 10, which is a schematic diagram illustrating interactions in another communication method provided in an embodiment of the present application. The network side may include a gNB-DU of a source cell, a gNB-DU of a candidate cell, and a gNB-CU. As shown in Figure 10, the method may include the following steps.

[0233] S1001. The gNB-DU of the candidate cell sends the candidate cell's TA to the gNB-DU of the source cell. In response, the gNB-DU of the source cell receives the candidate cell's TA from the gNB-DU of the candidate cell.

[0234] S1002. The gNB-DU of the source cell sends a second cell handover notification to the terminal device. The second cell handover notification carries the TA of the candidate cell. In response, the terminal device receives the first cell handover notification from the gNB-DU of the source cell.

[0235] S1003. The gNB-DU of the source cell determines whether the TA is valid. If so, proceed to step S1004.

[0236] If at least one of the following conditions is met: the TAT timing of the TA or the remaining duration of the TAT of the TA has expired; the change in the RSRP value of the cell is greater than a preset threshold; or the terminal device receives a new TA from the gNB-DU of the cell, the gNB-DU of the source cell determines that the TA has failed.

[0237] The gNB-DU of the source cell determines whether the TA is valid. In one possible implementation, when the gNB-DU of the source cell receives the TA from the gNB-DU of the candidate cell, it starts timing the TAT of the TA or the remaining duration of the TAT of the TA. If the TAT of the TA or the remaining duration has not timed out, the TA is determined to be valid; otherwise, the TA is determined to be invalid.

[0238] The gNB-DU of the source cell starts counting the TAT of the TA or the remaining TAT of the TA to determine whether the TA is valid. In one possible implementation, when the gNB-DU of the source cell receives the TA from the gNB-DU of the candidate cell, it may record / update the downlink path loss reference RSRP value of the candidate cell and compare the absolute value of the difference between the reference RSRP value and the real-time RSRP value with a preset threshold to determine whether the TA of the candidate cell is valid. Specifically, if the change (increase or decrease) in the RSRP value of the candidate cell is less than the preset threshold, the terminal device has not received a new TA from the gNB-DU of the candidate cell, and the TAT or the remaining TAT of the TA has not expired (ifconfig), the TA is valid. Conversely, if the change in the RSRP value of the candidate cell is greater than or equal to the preset threshold, and / or the terminal device has received a new TA from the gNB-DU of the candidate cell, and / or the TAT or the remaining TAT of the TA has expired, the TA is invalid.

[0239] The TAT of the TA may include at least one of the following:

[0240] TAT1 sent by the candidate cell's gNB-DU to the source cell's gNB-DU; or

[0241] TAT2 configured for the TA, sent by the gNB-CU to the gNB-DU of the source cell; or

[0242] The gNB-DU of the source cell is TAT3 determined by the TA.

[0243] Specifically, the gNB-DU of the candidate cell may provide the TAT related to the TA of the cell, i.e., the gNB-DU of the candidate cell may send the TA and the TAT1 of the TA to the gNB-CU, e.g., the gNB-DU of the candidate cell may send the TA and the TAT1 of the TA to the gNB-CU via a DU-CU TA information transfer message, and the gNB-CU may send the TA and the TAT1 of the TA to the gNB-DU of the source cell, e.g., the gNB-CU may send the TA and the TAT1 of the TA to the gNB-DU of the source cell via a DU-CU TA information transfer message.

[0244] Regarding the TAT2 configured for the TA sent by the gNB-CU to the gNB-DU of the source cell, specifically, the gNB-CU may provide the TAT related to the TA of the candidate cell, that is, the gNB-DU of the candidate cell may send the TA to the gNB-CU, for example, the gNB-DU of the candidate cell may send the TA to the gNB-CU through DU-CU TA information transfer; the gNB-CU obtains the TAT2 of the TA; and the gNB-CU sends the TA and TAT2 to the gNB-DU of the source cell, for example, the gNB-CU may send the TA and TAT2 of the TA to the gNB-DU of the source cell through DU-CU TA information transfer message.

[0245] The gNB-DU of the source cell determines the TAT3 for the TA. Specifically, after receiving the candidate cell TA from the gNB-DU of the candidate cell, the gNB-DU of the source cell can determine a TAT for the TA, that is, determine a TAT3 for the TA. At least one TAT3 corresponds to at least one cell or one CU-DU TA information transfer, or at least one TAT3 corresponds to at least one PDCCH order command. The term "corresponding to at least one cell or one CU-DU TA information transfer" can be understood as meaning that the TAs given in the same signaling share a common TAT, i.e., the TAT is initiated upon receipt of the information, and if the TAT3 times out, all TAs given in the message become invalid; or, upon receiving a cell's TA, the TAT3 corresponding to the TA is initiated, and if the TAT3 times out, the TA for the corresponding cell becomes invalid. At least one TAT3 corresponds to at least one PDCCH order command. It can be understood that the TAs related to the same PDCCH order share a TAT, that is, the TAT is started when the PDCCH order is sent. When the TAT3 times out, the TAs corresponding to all candidate cells related to the message become invalid; or, after the PDCCH order related to a candidate cell is sent, the TAT3 corresponding to the candidate cell is started. When the TAT3 times out, the TA of the corresponding cell becomes invalid.

[0246] S1004. The gNB-DU of the source cell sends a first cell handover notification to the gNB-CU. In response, the gNB-CU receives the first cell handover notification from the gNB-DU of the source cell.

[0247] Among them, the first cell switching notification includes: cell ID, TCI status ID and relevant information of the TA, and the relevant information of the TA includes the TA of other candidate cells, the timing advance timer TAT corresponding to the TA of the other candidate cells, or at least one of the remaining duration of the timing advance timer TAT corresponding to the TA of the other candidate cells.

[0248] S1005. The gNB-CU sends the TA-related information to the gNB-DU of the target cell. Correspondingly, the gNB-DU of the target cell receives the TA-related information from the gNB-CU.

[0249] After the gNB-CU receives the first cell handover notification from the gNB-DU of the source cell, the gNB-CU may send the relevant information of the TA to the gNB-DU of the target cell.

[0250] S1006. The gNB-DU of the target cell triggers RACH less access based on the relevant information of the TA.

[0251] The gNB-DU of the target cell receives the TA information from the gNB-CU and can trigger RACH-less access based on the TA information. Because the gNB-DU of the source cell sends the TA information to the gNB-DU of the target cell via the gNB-CU, the target cell can trigger RACH-less access based on the TA information. This eliminates the need to trigger a new TA acquisition process and allows RACH-less access to be triggered based on the existing TA information of the candidate cell. This reduces access latency and reduces signaling overhead.

[0252] Unlike the prior art, in the case of continuous RACH less access, each time the terminal device switches to a new cell, it is necessary to re-trigger the TA acquisition process of the candidate cell. In an embodiment of the present application, the gNB-DU of the source cell can send a cell switching notification carrying the TA of the candidate cell to the terminal device, and maintain the validity of the TA. When the TA is valid, the gNB-CU sends the relevant information of the TA to the gNB-DU of the target cell, so that the subsequent gNB-DU of the target cell can continue to use the valid TA to perform RACH less access, thereby avoiding re-triggering the TA acquisition process of the candidate cell, and reducing the signaling overhead between the terminal device and the network side. Maintaining the validity of the TA by the network side (gNB-DU of the source cell) can not only reduce the energy consumption of the terminal device, but also improve the accuracy of RACH less access.

[0253] Please refer to Figure 11, which is a schematic diagram illustrating interactions in another communication method provided in an embodiment of the present application. The network side may include a gNB-DU of a source cell, a gNB-DU of a candidate cell, and a gNB-CU. As shown in Figure 11, the method may include the following steps.

[0254] S1101. The gNB-DU of the candidate cell sends the candidate cell's TA to the gNB-DU of the source cell. In response, the gNB-DU of the source cell receives the candidate cell's TA from the gNB-DU of the candidate cell.

[0255] S1102. The gNB-DU of the source cell sends a second cell handover notification to the terminal device. The second cell handover notification carries the TA of the candidate cell. In response, the terminal device receives the second cell handover notification from the gNB-DU of the source cell.

[0256] S1103. The terminal device accesses the target cell according to the TA.

[0257] After the terminal device receives the second cell switching notification carrying the TA of the candidate cell from the gNB-DU of the source cell, it can access the target cell according to the TA.

[0258] S1104. The gNB-DU of the candidate cell sends an access success message to the gNB-CU. In response, the gNB-CU receives the access success message from the gNB-DU of the candidate cell.

[0259] After the terminal device accesses the target cell (the target cell is a candidate cell) according to the TA, the gNB-DU of the target cell may send an access success message to the gNB-CU. This message carries the target cell ID and a TA request, which requests the gNB-CU to deliver an available TA. Exemplarily, the TA request may be a 1-bit indication or an enumeration TArequestenumerate{ture} and / or a list of cells corresponding to the requested available TA. The available TAs may include one or more available TAs.

[0260] S1105. The gNB-CU determines whether the TA of the cell is valid. If so, proceed to step S1106.

[0261] If at least one of the following conditions is satisfied: the TAT of the TA or the remaining TAT of the TA has expired; the change in the RSRP value of the cell is greater than a preset threshold; or the terminal device receives a new TA from the gNB-DU of the cell, the gNB-CU determines that the TA is invalid. For details, refer to the similar description of the terminal device determining whether the TA is valid in step S807 above, which is not repeated here.

[0262] The TAT of the TA may include at least one of the following:

[0263] The cell's gNB-DU sends the gNB-CU's TAT1; or

[0264] TAT2 of the TA configuration sent by the gNB-CU for the gNB-DU of the cell; or

[0265] The gNB-DU of the source cell determines the TAT3 based on the TA and sends it to the gNB-CU.

[0266] The gNB-DU of the candidate cell sends the TAT1 of the gNB-CU. Specifically, the gNB-DU of the candidate cell may provide the TAT related to the TA of the cell, i.e., the gNB-DU of the candidate cell sends the TA and the TAT1 of the TA to the gNB-CU. For example, the gNB-DU of the candidate cell may send the TA and the TAT1 of the TA to the gNB-CU via a DU-CU TA information transfer message.

[0267] The gNB-CU may provide the TAT2 associated with the TA of the candidate cell, which is sent by the gNB-DU of the candidate cell. Specifically, the gNB-CU may provide the TAT associated with the TA of the candidate cell, i.e., the gNB-DU of the candidate cell may send the TA to the gNB-CU, e.g., the gNB-DU of the candidate cell may send the TA to the gNB-CU via DU-CU TA information transfer; and the gNB-CU may obtain the TAT2 associated with the TA.

[0268] The gNB-DU of the source cell determines a TAT3 for the TA and sends it to the gNB-CU. Specifically, after receiving the candidate cell's TA from the gNB-DU of the candidate cell, the gNB-DU of the source cell may determine a TAT for the TA, i.e., determine a TAT3 for the TA, and send the TAT3 to the gNB-CU.

[0269] S1106. The gNB-CU sends the TA and related information about the TA to the gNB-DU of the candidate cell. In response, the gNB-DU of the candidate cell receives the TA and related information about the TA from the gNB-CU.

[0270] If the gNB-CU determines that the TA is valid, it may send the TA and related information about the TA to the gNB-DU of the target cell (the target cell is a candidate cell). The related information about the TA includes the TA of other candidate cells, the timing advance timer TAT corresponding to the TA of the other candidate cells, or the remaining duration of the timing advance timer TAT corresponding to the TA of the other candidate cells.

[0271] S1107. The gNB-DU of the candidate cell triggers RACH less access based on the relevant information of the TA.

[0272] The gNB-DU of the target cell receives the TA and related information from the gNB-CU and can trigger RACH-less access based on the TA-related information. The gNB-CU sends the TA-related information to the gNB-DU of the target cell, enabling the target cell to trigger RACH-less access based on the TA-related information. This eliminates the need to trigger a new TA acquisition procedure and can trigger RACH-less access based on the existing TA information of the candidate cell. This reduces access latency and reduces signaling overhead.

[0273] S1108. The gNB-DU of the candidate cell sends a second message to the gNB-CU. The second message includes at least one of the following: the ID of the cell, the TA request, and an index of the terminal device.

[0274] Unlike the prior art, in the case of continuous RACH less access, the terminal device needs to re-trigger the TA acquisition process of the candidate cell each time it switches to a new cell. In an embodiment of the present application, after the terminal device switches to the target cell, the gNB-CU can maintain the validity of the TA. When the TA is valid, the gNB-CU sends the TA and related information of the TA to the gNB-DU of the target cell, so that the subsequent gNB-DU of the target cell can continue to use the valid TA to perform RACH less access, thereby avoiding re-triggering the TA acquisition process of the candidate cell, which can reduce the signaling overhead of the terminal device and the network side. Maintaining the validity of the TA by the network side (gNB-CU) can not only reduce the energy consumption of the terminal device, but also improve the accuracy of RACH less access. After the terminal device successfully switches to the target cell, it requests or forwards the TA (such as carrying a TA request in the access success message), which can avoid invalid signaling overhead and maintenance costs on the target side.

[0275] One possible implementation is that if cell selection is triggered by a monitoring failure and attemptLTM-switch is configured, if the selected target cell is an LTM candidate cell, the LTM cell change procedure is executed for the selected target cell, and access is performed on the target cell. Furthermore, the target cell may also send a second message to the gNB-CU, where the second message includes at least one of the following: the target cell ID, the TA request, and a terminal device index. The TA request is used to request the gNB-CU to deliver an available TA.

[0276] One possible implementation method is that the network device can pre-configure the TAT for the terminal device. After receiving the PDCCH order (such as step S801 above), the terminal device sends a preamble and starts the pre-configured TAT. Based on the TAT, it is determined whether the TA corresponding to the cell is valid. If the TAT has not timed out, the TA corresponding to the TAT is determined to be valid. If the TAT has timed out, the TA corresponding to the TAT is determined to be invalid. It is understandable that if the network does not give the TA of the candidate cell to the terminal device until the cell handover is triggered, it is relatively unreasonable to reuse the existing TAT because the TA was actually obtained some time ago. In this case, if the terminal device starts the TAT after sending the preamble, the original TAT value can be reused to achieve the effect of maintaining the validity of the TA within a relatively reasonable time period.

[0277] A unified description of the above-mentioned method embodiments:

[0278] It should be noted that the above-mentioned source cell gNB-DU / target cell gNB-DU sending information may be a gNB-DU that supports the source cell / target cell sending information, or one of the cells supported by the gNB-DU sending information is the source cell / target cell, or the source cell / target cell sends information.

[0279] It should be noted that when the above-mentioned terminal device / gNB-DU of the source cell / gNB-DU / gNB-CU of the target cell receives the TA of the candidate cell, it starts to start the TAT of the TA. If it receives a TA update from the same cell again, it restarts the corresponding TAT.

[0280] The above describes the method embodiments provided by the embodiments of the present application. The following describes the device embodiments involved in the embodiments of the present application.

[0281] Please refer to Figure 12, which is a schematic diagram of the structure of a communication device provided in an embodiment of the present application. As shown in Figure 12, the communication device 1200 includes at least: a transceiver unit 1201 and a processing unit 1202; wherein:

[0282] In one possible implementation, the communication device may be a terminal device, or a device in the terminal device (e.g., a chip, a chip system, or a circuit):

[0283] The transceiver unit 1201 is used to receive a first message from the network side, where the first message includes at least one of the following: a cell ID, a TA, a valid command for the TA, and a valid time for the TA; wherein the valid command for the TA is used to indicate that the TA is still valid after the terminal device switches to the cell, and the TA is used to perform RACH less access.

[0284] In a possible implementation, the device further includes:

[0285] The processing unit 1202 is configured to determine that the TA is invalid after the transceiver unit 1201 receives the first message from the network side, if at least one of the following conditions is met: the timing of starting the corresponding TA times out, the change in the RSRP value of the cell is greater than a preset threshold, the terminal device receives a new TA of the gNB-DU of the cell, the terminal device receives a TA invalidation indication command, and the terminal device receives a PDCCH indication for the cell. The PDCCH indication is used to obtain the TA of the cell.

[0286] In one possible implementation, the RSRP value is configured for the terminal device by the network. Alternatively, the RSRP value may be configured for the terminal device by the gNB-DU of the source cell on the network side. Alternatively, the RSRP value may be configured for the terminal by the cell, which may be the cell corresponding to the TA.

[0287] In one possible implementation, the processing unit 1202 is configured to determine that the TA is not invalid after the transceiver unit 1201 receives the first message from the network side, if at least one of the following conditions is met: the timing of starting the corresponding TA has not timed out, the change in the RSRP value of the cell is less than or equal to the preset threshold, the terminal device no longer receives a new TA from the gNB-DU of the cell, the terminal device does not receive a TA invalidation indication command, and the terminal device does not receive a PDCCH indication for the cell, and the PDCCH indication is used to obtain the TA of the cell.

[0288] In a possible implementation, if the TA fails, the transceiver unit 1201 is further configured to send a TA failure indication to the network side, where the TA failure indication command includes the cell ID or TAGID.

[0289] In one possible implementation, after the transceiver unit 1201 sends a TA failure indication command to the network side, it is also used to receive a PDCCH order from the network side. The PDCCH order is used to trigger the early TA acquisition process. The terminal device sends a preamble to the indicated cell. The cell indicated by the PDCCH order is the same cell as the cell corresponding to the TA failure command.

[0290] In one possible implementation, if the TA is not invalid, the transceiver unit 1201 is further configured to send valid TA information to the network side, where the valid TA information includes at least one of the following: an indication of a valid TA, a list of cells with a valid TA, and the TA and TAT remaining time.

[0291] In a possible implementation, the transceiver unit 1201 receives a first message from a network side, specifically configured to receive a first message from a source cell on the network side.

[0292] In one possible implementation, the transceiver unit 1201 is further configured to receive a TA failure indication command from the gNB-DU of the cell, where the TA failure indication command includes the cell ID.

[0293] In a possible implementation manner, the first message is carried by DCI, RRC or MAC CE.

[0294] In one possible implementation, the communication device may be a gNB-DU of the source cell, or a device (e.g., a chip, a chip system, or a circuit) in the gNB-DU of the source cell:

[0295] The transceiver unit 1201 is used to send a first message to the terminal device, where the first message includes at least one of the following: a cell ID, a TA, a valid command for the TA, and a valid time for the TA; wherein the valid command for the TA is used to indicate that the terminal device is still valid after switching to the cell, and the TA is used by the terminal device to perform RACH less access.

[0296] In one possible implementation, the transceiver unit 1201 is further configured to receive the TA of the cell and the TAT of the TA from the gNB-CU.

[0297] In one possible implementation, the TA and the TAT of the TA include at least one of the following: the TA and TAT1 of the TA sent by the cell to the gNB-DU of the source cell through the gNB-CU; or the TA sent by the cell to the gNB-DU of the source cell through the gNB-CU, and the TAT2 of the TA configuration sent by the gNB-CU to the gNB-DU of the source cell.

[0298] In a possible implementation, the transceiver unit 1201 is further configured to receive a TA failure indication command from the terminal device, where the TA failure indication command includes a cell ID.

[0299] In a possible implementation, the transceiver unit 1201 is further configured to send a PDCCH order to the terminal device, where the PDCCH order is used to obtain a valid TA corresponding to a cell, and the cell indicated by the PDCCH and the cell corresponding to the TA failure command are the same cell.

[0300] In one possible implementation, the transceiver unit 1201 is further used to receive information about a valid TA from the terminal device, where the information about the valid TA includes at least one of the following: an indication of a valid TA, a list of cells with a valid TA, a TA corresponding to the list of cells with a valid TA, and a remaining TAT time.

[0301] In one possible implementation, the transceiver unit 1201 is further configured to send a cell switching notification to the gNB-DU of the cell, where the cell switching notification includes at least one of the following: TA, and a recent measurement result of the cell corresponding to the TA.

[0302] In one possible implementation, the communication device may be a gNB-DU of the target cell, or a device (e.g., a chip, a chip system, or a circuit) in the gNB-DU of the target cell:

[0303] Processing unit 1202 is configured to determine that a TA is invalid if at least one or more of the following conditions are met: a timer timeout for starting the TA corresponding to the TAT is met; a change in the RSRP value of the gNB-DU of the cell is greater than a preset threshold; and a PDCCH indication of the cell corresponding to the TA is sent, where the PDCCH indication is used to trigger the terminal device to obtain the TA of the cell, and the TAT is TAT1 configured for the cell, or TAT2 configured for the gNB-CU.

[0304] In a possible implementation, if the TA fails, the transceiver unit 1201 is configured to send a TA failure indication command to the terminal device, where the TA failure indication command includes a cell ID or a TAG ID.

[0305] In one possible implementation, the transceiver unit 1201 is further configured to receive a cell handover notification from a gNB-DU of a source cell, where the cell handover notification includes at least one of the following: a TA, and a recent measurement result of a cell corresponding to the TA;

[0306] The processing unit 1202 is further configured to update the RSRP value according to the cell switching notification.

[0307] In a possible implementation, the processing unit 1202 is further configured to obtain the TA of the terminal device and start timing corresponding to the TA according to the TAT.

[0308] In one possible implementation, the communication device may be a gNB-DU of the source cell, or a device (e.g., a chip, a chip system, or a circuit) in the gNB-DU of the source cell:

[0309] The transceiver unit 1201 is used to send a first cell switching notification to the terminal device. The first cell switching notification includes: cell ID, TCI status ID and TA related information. The TA related information includes at least one of the TA of other cells, the TAT corresponding to the TA of other cells, or the remaining duration of the TAT corresponding to the TA of other cells.

[0310] In a possible implementation, the transceiver unit 1201 is further configured to send a second cell switching notification to the terminal device, where the second cell switching notification carries the TA of the cell.

[0311] In one possible implementation, the transceiver unit 1201 is further configured to receive the TA of the gNB-DU of the cell; if at least one of the following conditions is satisfied: the TAT timing of the TA or the remaining duration of the TAT of the TA times out; the change in the RSRP value of the cell is greater than a preset threshold; and the terminal device receives a new TA from the gNB-DU of the cell, the gNB-DU of the source cell determines that the TA is invalid.

[0312] In one possible implementation, the TAT corresponding to the TA includes at least one of the following: TAT1 sent by the gNB-DU of the cell to the gNB-DU of the source cell; or TAT2 configured for the TA sent by the gNB-CU to the gNB-DU of the source cell; or TAT3 determined by the gNB-DU of the source cell for the TA.

[0313] In one possible implementation, the transceiver unit 1201 is further configured to start the TAT timing of the TA or the remaining duration of the TAT of the TA when receiving the TA of the gNB-DU of the cell.

[0314] In one possible implementation, after the transceiver unit 1201 sends the second cell switching notification to the terminal device, it is also used to send a TA to the gNB-DU of the cell.

[0315] In one possible implementation, the communication device may be a gNB-CU, or a device in the gNB-CU (e.g., a chip, a chip system, or a circuit):

[0316] The transceiver unit 1201 is configured to send the TA and TA-related information to the gNB-DU of the cell. The TA-related information includes the TA of other cells and the TAT corresponding to the TA of other cells or the TAT corresponding to the TA of other cells.

[0317] In one possible implementation, the transceiver unit 1201 is further configured to receive an access success message from the gNB-DU of the cell. The access success message carries the cell ID and a TA request. The TA request is used to request the gNB-CU to deliver an available TA.

[0318] In one possible implementation, the transceiver unit 1201 is further configured to receive the TA of the gNB-DU of the cell; if at least one of the following conditions is satisfied: the TAT timing of the TA or the remaining duration of the TAT of the TA has expired; the change in the RSRP value of the cell is greater than a preset threshold; and the terminal device receives a new TA of the gNB-DU of the cell, the gNB-CU determines that the TA is invalid.

[0319] In one possible implementation, the TAT corresponding to the TA includes at least one of the following: TAT1 sent by the gNB-DU of the cell to the gNB-CU; or TAT2 configured by the gNB-CU for the TA sent by the gNB-CU to the gNB-DU of the cell; or TAT3 determined by the gNB-DU of the source cell for the TA and sent to the gNB-CU.

[0320] In one possible implementation, the transceiver unit 1201 is further configured to receive a second message from the gNB-DU of the cell, where the second message includes at least one of the following: a cell ID, a TA request, and an index of the terminal device, where the TA request is used to request the gNB-CU to send an available TA.

[0321] In one possible implementation, the transceiver unit 1201 is further used to receive the TA of the gNB-DU of the cell, and start the TAT timing of the TA or the remaining duration of the TAT of the TA.

[0322] In one possible implementation, the transceiver unit 1201 is further configured to send the TA and TA-related information to the gNB-DU of the cell.

[0323] In one possible implementation, the communication device may be a gNB-DU of the target cell, or a device (e.g., a chip, a chip system, or a circuit) in the gNB-DU of the target cell:

[0324] The processing unit 1202 is configured to determine the TA of the cell and / or related information of the TA, where the related information of the TA includes the TA of other cells, the timing advance timer TAT corresponding to the TA of the other cells, or the remaining duration of the TAT corresponding to the TA of the other cells, where the TA is related information used to trigger access without a random access channel RACH less.

[0325] In one possible implementation, the transceiver unit 1201 is configured to send a second message to the gNB-CU, where the second message includes at least one of the following: a cell ID, a TA request, and an index of a terminal device, where the TA request is used to request the gNB-CU to send an available TA.

[0326] Please refer to Figure 13, which is a schematic diagram of the structure of another communication device provided in an embodiment of the present application. The device 110 is used to implement the functions of the network element of the present application. For example, the network element can be an access network device, a terminal device, a DU or a CU. The device 110 can be the network element, or a device that can be installed in the network element, or a device that can be used in conjunction with the network element, without limitation. For example, the device can be a chip or a chip system. As shown in Figure 13, the device 110 includes an interface 111 and a processor 112. Optionally, the processor 112 is used to execute a program 114. The processor 112 can store the program 114 or obtain the program 114 from other devices or equipment (for example, from the memory 113 or downloaded from a third-party website). Optionally, the device 110 includes a memory 113. The memory 113 is used to store a program 115. The program 115 can be pre-stored or loaded later. Optionally, the memory 113 can also be used to store necessary data. These components work together to provide the various functions described in this application.

[0327] The processor 112 may include one or more processors as a combination of computing devices. The processor 112 may include one or more of the following: a microprocessor, a microcontroller, a digital signal processor (DSP), a digital signal processing device (DSPD), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), a programmable logic device (PLD), gated logic, transistor logic, discrete hardware circuits, processing circuits, or other suitable hardware, firmware, and / or a combination of hardware and software configured to perform the various functions described in this application. The processor 112 may be a general-purpose processor or a dedicated processor. For example, the processor 112 may be a baseband processor or a central processing unit. The baseband processor may be used to process communication protocols and communication data. The central processing unit may be used to execute software programs and process data in the software programs.

[0328] The interface 111 may include any suitable hardware or software for enabling communication with one or more computer devices (e.g., network elements of the present application). For example, in some embodiments, the interface 111 may include terminals and / or pins for coupling wires for a wired connection or coupling a wireless transceiver for a wireless connection. In some embodiments, the interface 111 may include a transmitter, a receiver, a transceiver, and / or an antenna. The interface may be configured to enable communication between computer devices (e.g., network elements of the present application) using any available protocol (e.g., a 3GPP standard protocol).

[0329] The term "program" in this application refers to software in a broad sense. The software may be program code, a program, a subroutine, an instruction set, a code, a code segment, a software module, an application, a software application, etc. The program can be executed in a processor and / or a computer to perform the various functions and / or processes described in this application.

[0330] The memory 113 can store the necessary data required when the processor 112 executes the software. The memory 113 can be implemented using any suitable storage technology. For example, the memory 113 can be any available storage medium that can be accessed by the processor and / or computer. Non-limiting examples of storage media include random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM), removable media, optical disc storage, magnetic disk storage media, magnetic storage devices, flash memory, registers, state memory, remotely mounted memory, local or remote memory components, or any other medium that can carry or store software, data or information and can be accessed by the processor / computer.

[0331] The memory 113 and the processor 112 may be provided separately or integrated together. The processor 112 may read information from the memory 113 and store and / or write information in the memory. The memory 113 may be integrated into the processor 112. The processor 112 and the memory 113 may be provided in an integrated circuit (e.g., an application-specific integrated circuit (ASIC)). The integrated circuit may be provided in a network element or other network node of the present disclosure.

[0332] Optionally, the device 110 in the embodiment of the present application can be used to execute the method described in Figures 7 to 11 in the embodiment of the present application.

[0333] Please refer to Figure 14, which is a structural diagram of a terminal device provided in an embodiment of the present application. For ease of explanation, Figure 14 only shows the main components of the terminal device. As shown in Figure 14, the terminal device 1400 includes a processor, a memory, a control circuit, an antenna, and input and output devices. The processor is mainly used to process communication protocols and communication data, as well as to control the entire terminal, execute software programs, and process data of software programs. The memory is mainly used to store software programs and data. The radio frequency circuit is mainly used for converting baseband signals and radio frequency signals and processing radio frequency signals. The antenna is mainly used to transmit and receive radio frequency signals in the form of electromagnetic waves. Input and output devices, such as touch screens, display screens, keyboards, etc., are mainly used to receive data input by users and output data to users.

[0334] When the terminal is powered on, the processor reads the software program from the storage unit, parses and executes the instructions of the software program, and processes the data of the software program. When data needs to be sent wirelessly, the processor performs baseband processing on the data to be sent and outputs the baseband signal to the RF circuit. The RF circuit processes the baseband signal to obtain an RF signal and transmits the RF signal to the outside in the form of electromagnetic waves via the antenna. When data is sent to the terminal, the RF circuit receives the RF signal via the antenna, which is further converted into a baseband signal and output to the processor. The processor converts the baseband signal into data and processes the data.

[0335] For ease of explanation, FIG14 shows only one memory and processor. In an actual terminal, there may be multiple processors and memories. The memory may also be referred to as a storage medium or storage device, etc., which is not limited in the present embodiment.

[0336] As an optional implementation, the processor may include a baseband processor and a central processing unit (CPU). The baseband processor is primarily responsible for processing communication protocols and communication data, while the CPU is primarily responsible for controlling the entire terminal, executing software programs, and processing software program data. The processor in Figure 14 integrates the functions of both the baseband processor and the CPU. Those skilled in the art will appreciate that the baseband processor and the CPU may also be independent processors interconnected via a bus or other technology. Those skilled in the art will appreciate that a terminal may include multiple baseband processors to accommodate different network standards, multiple CPUs to enhance its processing capabilities, and that the various components of the terminal may be connected via various buses. The baseband processor may also be referred to as a baseband processing circuit or a baseband processing chip. The CPU may also be referred to as a central processing circuit or a central processing chip. The functionality for processing communication protocols and communication data may be built into the processor or stored as a software program in a storage unit, with the processor executing the software program to implement the baseband processing functionality.

[0337] In one example, the antenna and control circuitry with transceiver functions can be considered the transceiver unit 1401 of terminal device 1400, and the processor with processing functions can be considered the processing unit 1402 of terminal device 1400. As shown in Figure 14, terminal device 1400 includes a transceiver unit 1401 and a processing unit 1402. The transceiver unit may also be referred to as a transceiver, transceiver, or transceiver device. Alternatively, the device in transceiver unit 1401 that implements the receiving function may be considered the receiving unit, and the device in transceiver unit 1401 that implements the transmitting function may be considered the transmitting unit, i.e., transceiver unit 1401 includes a receiving unit and a transmitting unit. For example, the receiving unit may also be referred to as a receiver, receiver, or receiving circuit, and the transmitting unit may be referred to as a transmitter, transmitter, or transmitting circuit. Alternatively, the receiving unit and transmitting unit may be integrated into a single unit or multiple independent units. The receiving unit and transmitting unit may be located in a single geographic location or dispersed across multiple geographic locations.

[0338] In one embodiment, transceiver unit 1401 is configured to execute the operations performed by transceiver unit 1201 in the above embodiment. Processing unit 1402 is configured to execute the operations performed by processing unit 1202 in the above embodiment. Terminal device 1400 may also be configured to execute the various methods performed by the terminal device in the method embodiments of Figures 7-11 above, which will not be described in detail.

[0339] An embodiment of the present application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, can implement the method provided in the above method embodiment.

[0340] The present application also provides a computer program product that, when executed on a computer or processor, causes the computer or processor to perform one or more steps of any of the aforementioned methods. If the various components of the aforementioned devices are implemented as software functional units and sold or used as independent products, they may be stored in the computer-readable storage medium.

[0341] The present application also provides a chip system, including at least one processor and a communication interface, wherein the communication interface and the at least one processor are interconnected via a line, and the at least one processor is configured to execute a computer program or instruction to perform some or all of the steps described in any of the method embodiments corresponding to Figures 7-11 above. The chip system can be composed of a chip or can include a chip and other discrete devices.

[0342] An embodiment of the present application also provides a communication system, which includes a terminal device, a gNB-DU of a source cell, a gNB-DU and a gNB-CU of a target cell. For a specific description, please refer to the methods shown in Figures 7 to 11.

[0343] It should be understood that the memory mentioned in the embodiments of the present application may be a volatile memory or a non-volatile memory, or may include both volatile and non-volatile memories. Among them, the non-volatile memory may be a hard disk drive (HDD), a solid-state drive (SSD), a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), or a flash memory. The volatile memory may be a random access memory (RAM), which is used as an external cache. By way of example but not limitation, many forms of RAM are available, such as static random access memory (SRAM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), double data rate synchronous dynamic random access memory (DDR SDRAM), enhanced synchronous dynamic random access memory (ESDRAM), synchronous link dynamic random access memory (SLDRAM) and direct rambus RAM (DR RAM). Memory is any other medium that can be used to carry or store a desired program code with an instruction or data structure form and can be accessed by a computer, but is not limited thereto. The memory in the embodiment of the present application can also be a circuit or other arbitrarily capable of implementing a storage function, for storing program instructions and / or data.

[0344] It should also be understood that the processor mentioned in the embodiments of the present application may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor, etc.

[0345] It should be noted that when the processor is a general-purpose processor, DSP, ASIC, FPGA or other programmable logic device, discrete gate or transistor logic device, discrete hardware component, the memory (storage module) is integrated into the processor.

[0346] It should be noted that the memory described herein is intended to include, but not be limited to, these and any other suitable types of memory.

[0347] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0348] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments provided herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0349] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0350] In the several embodiments provided in this application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0351] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0352] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0353] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application, or the part that contributes to the technology or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes various media that can store program codes, such as a USB flash drive, a mobile hard disk, a ROM, a RAM, a magnetic disk, or an optical disk.

[0354] The steps in the method of the embodiment of the present application can be adjusted in order, combined and deleted according to actual needs.

[0355] The modules / units in the device of the embodiment of the present application can be merged, divided and deleted according to actual needs.

[0356] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for acquiring a timing advance TA, characterized in that: The method comprises: The terminal device receives a first message from the network side, where the first message includes at least one of the following: a cell identification ID, a TA, a valid command of the TA, and a valid time of the TA; wherein the valid command of the TA is used to indicate that the terminal device is still valid after switching to the cell, and the TA is used to perform access without a random access channel RACHless.

2. The method according to claim 1, characterized in that After the terminal device receives the first message from the network side, the method further includes: If at least one of the following conditions is met: the timing advance timer TAT starts the timing timeout of the corresponding TA, the increase or decrease of the reference signal received power RSRP value of the cell is greater than a preset threshold, the terminal device receives a new TA from the gNB-DU of the cell, the terminal device receives a TA failure indication command, and the terminal device receives a PDCCH indication for the cell, then the terminal device determines that the TA is failed, and the PDCCH indication is used to obtain the TA of the cell.

3. The method according to claim 2, characterized in that The RSRP value is configured by the network side for the terminal device.

4. The method according to claim 2 or 3, characterized in that If the TA fails, the method further includes: The terminal device sends a TA failure indication command to the network side, where the TA failure indication command includes a cell ID or a timing advance group TAG ID.

5. The method according to any one of claims 2 to 4, characterized in that: If the TA is not invalid, the method further includes: The terminal device sends information about a valid TA to the network side, where the information about the valid TA includes at least one of the following: an indication of a valid TA, a list of cells with a valid TA, and a TA and TAT remaining time.

6. The method according to claim 1, characterized in that The method further comprises: The terminal device receives a TA failure indication command from the gNB-DU of the cell, where the TA failure indication command includes the ID of the cell.

7. A method for acquiring a timing advance TA, characterized in that: The method comprises: The gNB-DU of the source cell sends a first message to the terminal device, where the first message includes at least one of the following: a cell identification ID, a TA, a valid command for the TA, and a valid time for the TA; wherein the valid command for the TA is used to indicate that the terminal device is still valid after switching to the cell, and the TA is used by the terminal device to perform access without a random access channel RACHless.

8. The method according to claim 7, characterized in that The method further comprises: The gNB-DU of the source cell receives the TA of the cell and the timing advance timer TAT of the TA from the gNB-CU.

9. The method according to claim 8, characterized in that The TA and the TAT of the TA include at least one of the following: The TA and TAT1 of the TA sent by the cell to the gNB-DU of the source cell via the gNB-CU; or The TA sent by the cell to the gNB-DU of the source cell through the gNB-CU, and the TAT2 of the TA configuration sent by the gNB-CU to the gNB-DU of the source cell.

10. The method according to any one of claims 7 to 9, characterized in that: The method further comprises: The gNB-DU of the source cell receives a TA failure indication command from the terminal device, where the TA failure indication command includes the cell ID.

11. The method according to any one of claims 7 to 9, characterized in that: The method further comprises: The gNB-DU of the source cell receives information about a valid TA from the terminal device, where the information about the valid TA includes at least one of the following: an indication of a valid TA, a list of cells with a valid TA, a TA corresponding to the list of cells with a valid TA, and a remaining TAT time.

12. The method according to any one of claims 7 to 9, characterized in that: The method further comprises: The gNB-DU of the source cell sends a cell handover notification to the gNB-DU of the cell, where the cell handover notification includes at least one of the following: the TA, and a recent measurement result of the cell corresponding to the TA.

13. A method for acquiring a timing advance TA, characterized in that: The method comprises: If at least one or more of the following conditions are met: the timing of the TA corresponding to the start of the timing advance timer TAT times out, the change in the reference signal received power RSRP value of the gNB-DU of the cell is greater than a preset threshold, and the PDCCH indication of the cell corresponding to the TA is sent, the gNB-DU of the cell determines that the TA is invalid. The PDCCH indication is used to trigger the terminal device to obtain the TA of the cell. The TAT is TAT1 configured for the cell, or TAT2 configured for the gNB-CU.

14. The method according to claim 13, characterized in that If the TA fails, the method further includes: The gNB-DU of the cell sends a TA failure indication command to the terminal device, where the TA failure indication command includes the ID of the cell.

15. The method according to claim 13, characterized in that The method further comprises: The gNB-DU of the cell receives a cell handover notification from the gNB-DU of the source cell, where the cell handover notification includes at least one of the following: the TA, and a recent measurement result of the cell corresponding to the TA; The gNB-DU of the cell updates the RSRP value according to the cell handover notification.

16. The method according to any one of claims 13 to 15, characterized in that: The method further comprises: After the gNB-DU of the cell obtains the TA of the terminal device, it starts the timing of the corresponding TA according to the TAT.

17. A method for acquiring a timing advance TA, characterized in that: The method comprises: The gNB-DU of the source cell sends a first cell handover notification to the gNB-CU. The first cell handover notification includes: a cell identity ID, a transmission configuration indication TCI state ID, and related information of the TA. The related information of the TA includes at least one of the TA of the other cell, the timing advance timer TAT corresponding to the TA of the other cell, or the remaining duration of the timing advance timer TAT corresponding to the TA of the other cell.

18. The method according to claim 17, characterized in that The method further comprises: The gNB-DU of the source cell sends a second cell switching notification to the terminal device, and the second cell switching notification carries the TA of the cell.

19. The method according to claim 17 or 18, characterized in that The method further comprises: The TA of the gNB-DU of the source cell and the gNB-DU of the receiving cell; If at least one of the following conditions is met: the TAT timing of the TA or the remaining duration of the TAT of the TA has expired; the change in the RSRP value of the cell is greater than a preset threshold; or the terminal device receives a new TA from the gNB-DU of the cell, the gNB-DU of the source cell determines that the TA has failed.

20. The method according to claim 19, characterized in that The TAT corresponding to the TA includes at least one of the following: TAT1 sent by the gNB-DU of the cell to the gNB-DU of the source cell; or TAT2 of the TA configuration sent by the gNB-CU to the gNB-DU of the source cell; or The gNB-DU of the source cell is TAT3 determined by the TA.

21. The method according to claim 19 or 20, characterized in that The method further comprises: When the gNB-DU of the source cell receives the TA of the gNB-DU of the cell, it starts timing the TAT of the TA or the remaining duration of the TAT of the TA.

22. The method according to any one of claims 17 to 21, characterized in that After the gNB-DU of the source cell sends a second cell handover notification to the terminal device, the method further includes: The gNB-DU of the source cell sends the TA to the gNB-DU of the cell.

23. A method for acquiring a timing advance TA, characterized in that: The method comprises: The gNB-CU sends the TA and related information about the TA to the gNB-DU of the cell. The related information about the TA includes the TA of other cells and the remaining timing advance timer TAT corresponding to the TA of the other cells or the remaining duration of the TAT corresponding to the TA of the other cells.

24. The method according to claim 23, wherein The method further comprises: The gNB-CU receives an access success message from the gNB-DU. The access success message carries the target cell ID and a TA request. The TA request is used to request the gNB-CU to deliver the cell TA.

25. The method according to claim 23 or 24, characterized in that The method further comprises: The gNB-CU receives the TA of the gNB-DU of the cell; If at least one of the following conditions is met: the TAT timing of the TA or the remaining duration of the TAT of the TA times out; the change in the RSRP value of the cell is greater than a preset threshold; or the terminal device receives a new TA from the gNB-DU of the cell, the gNB-CU determines that the TA is invalid.

26. The method according to claim 25, characterized in that The TAT corresponding to the TA includes at least one of the following: TAT1 sent by the gNB-DU of the cell to the gNB-CU; or TAT2 configured by the gNB-CU for the TA sent by the gNB-DU of the cell; or The gNB-DU of the source cell is the TAT3 determined by the TA and sent to the gNB-CU.

27. The method according to claim 23 or 24, characterized in that The method further comprises: The gNB-CU receives a second message from the gNB-DU of the cell, where the second message includes at least one of the following: an ID of the cell, a TA request, and an index of a terminal device, where the TA request is used to request the gNB-CU to deliver an available TA.

28. The method according to any one of claims 23 to 27, characterized in that The method further comprises: The gNB-CU receives the TA of the gNB-DU of the cell and starts timing the TAT of the TA or the remaining duration of the TAT of the TA.

29. The method according to any one of claims 23 to 27, characterized in that: The method further comprises: The gNB-CU sends the TA and related information of the TA to the gNB-DU of the cell.

30. A method for acquiring a timing advance TA, characterized in that: The method comprises: The gNB-DU of the cell determines the TA of the cell and / or related information of the TA, where the related information of the TA includes the TA of other cells, the timing advance timer TAT corresponding to the TA of the other cells, or the remaining duration of the TAT corresponding to the TA of the other cells, where the TA is related information used to trigger access without a random access channel RACH less.

31. The method according to claim 30, wherein The method further comprises: The gNB-DU of the cell sends a second message to the gNB-CU, where the second message includes at least one of the following: the cell ID, a TA request, and an index of the terminal device. The TA request is used to request the gNB-CU to send an available TA.

32. A communication device, characterized in that: Comprising a unit for executing the method according to any one of claims 1 to 6, or a unit for executing the method according to any one of claims 7 to 12; or a unit for executing the method according to any one of claims 13 to 16; or a unit for executing the method according to any one of claims 17 to 22; or a unit for executing the method according to any one of claims 23 to 29; or a unit for executing the method according to any one of claims 30 to 31.

33. A communication device, characterized in that: The communication device includes a processor and a storage medium, wherein the storage medium stores instructions. When the instructions are executed by the processor, the method according to any one of claims 1 to 6 is implemented, or the method according to any one of claims 7 to 12 is implemented, or the method according to any one of claims 13 to 16 is implemented, or the method according to any one of claims 17 to 22 is implemented, or the method according to any one of claims 23 to 29 is implemented, or the method according to any one of claims 30 to 31 is implemented.

34. A computer-readable storage medium, characterized in that The computer-readable storage medium includes instructions, which, when executed by a processor, enable the method according to any one of claims 1 to 6 to be implemented, or enable the method according to any one of claims 7 to 12 to be implemented, or enable the method according to any one of claims 13 to 16 to be implemented, or enable the method according to any one of claims 17 to 22 to be implemented, or enable the method according to any one of claims 23 to 29 to be implemented, or enable the method according to any one of claims 30 to 31 to be implemented.

35. A computer program product, characterized in that The computer program product includes instructions, which, when executed by a processor, enable the method according to any one of claims 1 to 6 to be implemented, or the method according to any one of claims 7 to 12 to be implemented, or the method according to any one of claims 13 to 16 to be implemented, or the method according to any one of claims 17 to 22 to be implemented, or the method according to any one of claims 23 to 29 to be implemented, or the method according to any one of claims 30 to 31 to be implemented.

36. A communication system, characterized in that: comprising a communication device according to claim 32.

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