Communication method, apparatus and system

Abstract

The present application provides a communication method, apparatus and system. The method comprises: a terminal receiving a first message of a first cell, the first message comprising a handover command, and the handover command being configured for indicating handover to a second cell. The terminal maintaining a communication connection with the first cell in a first time period. The terminal sending a second message, the second message being configured for indicating that the terminal has successfully completed handover to a second cell, and the first time period being a period of time between the terminal receiving the first message and sending the second message. This reduces handover interruption time while a terminal hands over from a first cell to a second cell. The described solution improves communication reliability.

Description

Communication methods, devices and systems

[0001] This application claims priority to Chinese Patent Application No. 202411742155.2, filed on November 28, 2024, entitled "Communication Method, Apparatus and System", the entire contents of which are incorporated herein by reference. Technical Field

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

[0003] In a communication network, access network nodes can make handover decisions based on measurement reports submitted by terminals. If a handover is decided upon, a target cell is determined for the terminal. The access network node notifies the terminal to handover to the target cell and ceases data transmission with the terminal. Upon receiving the notification, the terminal executes the handover procedure. After handover to the target cell, the target cell provides data transmission services to the terminal.

[0004] In some scenarios, the data transmission service of the terminal may be interrupted for a long time before the terminal completes the handover to the target cell, resulting in terminal service interruption or dropped calls. Summary of the Invention

[0005] This application provides a communication method, apparatus, and system to reduce the interruption time of data transmission services during terminal handover processes.

[0006] Firstly, a communication method is provided, which can be executed by a terminal or by a unit / module / component (such as a chip, chip system, logic circuit, or software) configurable in (or usable in) the terminal. The following explanation uses the execution of this method by a terminal as an example.

[0007] The method includes: a terminal receiving a first message from a first cell, the first message including a handover command instructing the terminal to handover from the first cell to a second cell. The terminal maintains a communication connection with the first cell for a first time period. The terminal sends a second message indicating that the terminal has successfully handed over to the second cell, wherein the first time period is the period between receiving the first message and sending the second message.

[0008] According to the above scheme, after the source base station and the terminal transmit the handover command, they can maintain the communication connection of the serving cell for a period of time. During this period, the serving cell continues to provide data transmission services to the terminal. This reduces the handover interruption time during the terminal's handover from the source cell to the target cell, helping to reduce the probability of terminal service interruptions or dropped calls, and improving communication reliability.

[0009] Optionally, the terminal maintains a communication connection with the first cell during the first time period, including: the terminal continues to receive data transmission services from the first cell during the first time period.

[0010] Optionally, the terminal performs one or more of the following during the first time period:

[0011] The terminal does not release the configuration information of the first cell;

[0012] The terminal detects the downlink control information of the first cell;

[0013] The terminal receives data and / or information from the first cell;

[0014] The terminal sends data and / or information to the first cell.

[0015] In one implementation, the handover command includes first information, which instructs the execution of a handover to a second cell without a random access procedure.

[0016] In this way, based on the handover command, the terminal can switch to the second cell after the first time period by performing a non-random access procedure.

[0017] According to the above scheme, the terminal can maintain a communication connection with the first cell during the first time period, and the terminal can switch to the second cell after the first time period through a random access procedure-free method. This can further reduce the communication interruption time during the process of the terminal switching from the first cell to the second cell and improve the reliability of communication.

[0018] In another implementation, the terminal determines, based on the first message, to switch to the second cell by performing a random access procedure.

[0019] However, regardless of whether the terminal hands over to the second cell via a random access procedure, the terminal still needs to obtain downlink synchronization with the second cell. Therefore, the terminal needs to detect the downlink synchronization signal of the second cell in order to obtain downlink synchronization with the second cell based on the downlink synchronization signal of the second cell.

[0020] Optionally, the first time period is specifically before the arrival time of the first time resource at the terminal, and the first time resource is used to carry the synchronization signal of the second cell.

[0021] The terminal receives a synchronization signal on the first time resource and obtains downlink synchronization with the second cell based on the synchronization signal.

[0022] According to the above scheme, the first time period precedes the first time resource. For example, the end time of the first time period can be the arrival time of the first time resource at the terminal, or the time interval between the end time of the first time period and the first time resource is the first time interval. This first time interval can include the preparation time required for the terminal to detect the synchronization signal of the second cell. This can reduce the communication interruption time caused by the terminal waiting for the synchronization signal to arrive at the terminal in order to achieve downlink synchronization with the second cell, and improve the reliability of communication.

[0023] In conjunction with the first aspect, in some implementations of the first aspect, the method further includes: the terminal receiving at least one indication message, the at least one indication message being used to determine a first time period.

[0024] The terminal can determine the first time period through the following implementation method:

[0025] In one embodiment, one of the at least one indication information is used to indicate a first time period. For example, the indication information may include at least one of the start time, end time, or duration of the first time period. The terminal can determine the first time period based on the at least one indication information. Communication with the first cell is maintained during the first time period.

[0026] In another embodiment, the at least one indication information includes indication information for indicating one or more of the following:

[0027] The arrival time of resources at the terminal;

[0028] The first time resource is sent in the second cell;

[0029] The time-domain resource information of the synchronization signal is used to indicate the resources available at the first moment.

[0030] Timing offset between the first cell and the second cell.

[0031] Based on the at least one indication information, the terminal can determine a first time period. For example, the at least one indication information indicates the arrival time of the first time resource to the terminal, such as when the arrival time is an absolute time. That is, the at least one indication information can directly indicate the arrival time of the first time resource to the terminal, so that the terminal can determine the first time period based on the arrival time.

[0032] For example, if the at least one indication information indicates the transmission time of the first time resource in the second cell, the terminal can determine the arrival time of the first time resource to the terminal based on the transmission time and the second signal transmission delay (i.e., the transmission time plus the second signal transmission delay is the arrival time of the first time resource to the terminal), wherein the second signal transmission delay is the signal transmission delay between the second cell and the terminal.

[0033] For example, if the at least one indication information indicates time-domain resource information and timing offset, the terminal can determine the time when the first time resource arrives at the terminal based on the time-domain resource information, the first signal transmission delay, the second signal transmission delay, and the timing offset, wherein the first signal transmission delay is the transmission delay between the first cell and the terminal, and the second signal transmission delay is the signal transmission delay between the second cell and the terminal.

[0034] Specifically, time-domain resource information can include periodic and offset information of the synchronization signal occurrence. Based on this periodic and offset information, the terminal can determine the first time resource. A terminal that has already synchronized downlink with the first cell can know the frame boundary (taking a frame as the time unit) or frame start time of the first cell. Based on the frame boundary or frame start time of the first cell, the timing offset difference, the first signal transmission delay, the second signal transmission delay, and the frame (or subframe, time slot, etc.) in which the second cell sends the synchronization signal, the terminal can determine the time when the synchronization signal arrives at the terminal.

[0035] According to the above scheme, the terminal can determine the arrival time of the first time resource to the terminal, and determine the first time period based on the arrival time. After receiving the handover command and before the arrival of the first time resource, the terminal maintains the communication connection with the first cell, and the first cell provides data transmission services to the terminal. This can reduce the communication interruption time, help reduce the probability of problems such as terminal service interruption or dropped calls, and improve the reliability of communication.

[0036] In conjunction with the first aspect, in some implementations of the first aspect, the method further includes: after the first time period, the terminal releases the configuration information of the first cell.

[0037] Secondly, a communication method is provided, which can be executed by a network device (such as a source base station) or by a unit / module / component (such as a chip, chip system, logic circuit, or software) configurable in (or usable in) a network device. The following explanation uses a network device as the source base station as an example.

[0038] The method includes: a source base station sending a first message of a first cell to a terminal, the first message including a handover command, the handover command being used to instruct the terminal to hand over from the first cell to a second cell; maintaining a communication connection with the terminal during a second time period; and receiving a third message, the third message being used to indicate that the terminal has completed the handover to the second cell, wherein the second time period is the time period after sending the first message and before receiving the third message.

[0039] According to the above implementation method, the source base station can maintain the communication connection between the first cell and the terminal during the second time period, and continue to provide data transmission services to the terminal during the second time period, which can reduce the communication interruption time of the terminal. This reduces the probability of problems such as terminal service interruption or dropped calls, and improves the reliability of communication.

[0040] Optionally, the source base station maintains a communication connection with the terminal during the second time period, including the source base station performing one or more of the following during the second time period:

[0041] The source base station does not release the terminal's context information;

[0042] The source base station sends downlink control information (DCI) to the terminal;

[0043] The source base station sends data and / or information to the terminal;

[0044] Receive data and / or information from the terminal.

[0045] In one implementation, the second time period specifically includes a period between the time the source base station sends the first message and the time it receives the third message. The third message is used to indicate that the terminal has completed the handover to the second cell.

[0046] For example, the third message may be a UE context release message from the target base station for the terminal.

[0047] In another implementation, the source base station can determine the arrival time of the first time resource to the terminal, and determine the second time period based on the arrival time.

[0048] In this embodiment, the second time period can be the same as the first time period, meaning that the source base station and the terminal determine the time period for maintaining the communication connection using the same method. Alternatively, the source base station can determine the time period for maintaining the communication connection and then notify the terminal.

[0049] In conjunction with the second aspect, in some implementations of the second aspect, the method further includes: the source base station sending at least one indication message, the at least one indication message being used to determine a first time period, the first time period being the period during which the terminal maintains a communication connection with the first cell after receiving the first message. Accordingly, the terminal can receive at least one indication message from the source base station, and the terminal can determine the first time period based on the at least one indication message, and maintain a communication connection with the first cell (source base station) during the first time period.

[0050] To enable the terminal to determine the first time period based on the at least one indication information, the following implementation method may also be included:

[0051] In one implementation, at least one indication information is used to indicate a first time period.

[0052] In another implementation, at least one indication information includes one or more of the following: the arrival time of the first time resource at the terminal; the transmission time of the first time resource in the second cell; time-domain resource information of the synchronization signal, which is used to indicate the first time resource; and the timing offset between the first cell and the second cell.

[0053] In conjunction with the second aspect, in some implementations of the second aspect, at least one indication information includes an arrival time. In order for the source base station to determine a first time period and notify the terminal of the first time period via the indication information, the source base station may first determine the arrival time of the first time resource at the terminal, thereby determining the first time period based on the arrival time, so as to notify the terminal of the first time period via the indication information. Implementations by which the source base station determines the arrival time may include, but are not limited to, the following:

[0054] In one implementation, the source base station receives fourth information from the target base station, the fourth information being used to indicate the arrival time of the first time resource to the terminal.

[0055] In another implementation, the source base station can determine the arrival time based on the transmission time of the first time resource and the second signal transmission delay. Specifically, the arrival time can be the transmission time of the first time resource plus the second signal transmission delay. It should be understood that the transmission time of the first time resource can be sent by the target base station to the source base station, and the second signal transmission delay can be determined by the terminal and sent to the source base station, or it can be determined by the target base station and sent to the source base station.

[0056] Based on the above scheme, the source base station can determine the arrival time of the first resource to the terminal.

[0057] In conjunction with the second aspect, in some implementations of the second aspect, the method further includes: the source base station determining a first time period based on the arrival time of the first time resource reaching the terminal. That is, the end time of the first time period can be the arrival time of the first time resource reaching the terminal or a time prior to that arrival time, as described above, and will not be repeated here. Optionally, after determining the first time period, the source base station can maintain a communication connection with the terminal in the first cell during the first time period, that is, the first time period is the same as the second time period.

[0058] According to the above scheme, the source base station can determine the first time period and notify the terminal so that the terminal can maintain the communication connection with the first cell within the first time period after receiving the handover command, thereby reducing the communication interruption time of the terminal and improving communication reliability.

[0059] It should be understood that this application is not limited to this. The first time period may not be determined and notified to the terminal by the source base station. As described in the first aspect, the first time period may be determined by the terminal itself.

[0060] It should be noted that the second time period can also differ from the first time period. As described above, the end time of the second time period can be at or after the moment the third message is received. In this case, the end time of the second time period is after the end time of the first time period. That is, after the first time period, the terminal stops transmitting data in the first cell, while the source base station continues to transmit terminal data in the first cell. Data that was not successfully transmitted can be sent to the terminal by the target base station after the terminal successfully switches to the second cell.

[0061] In conjunction with the second aspect, in some implementations of the second aspect, the method further includes: after the second time period, the source base station performs one or more of the following: the source base station releases the terminal's context information; the source base station sends a fourth message indicating the sequence number status of the terminal's downlink data.

[0062] According to the above scheme, after the second time period, specifically after receiving the third message and confirming that the terminal has successfully switched to the second cell, the source base station can release the terminal's context information to reduce unnecessary overhead. The source base station can also send a fourth message to the target base station. In this way, the target base station can understand the data packets that the terminal has transmitted and those that have not yet been transmitted, enabling the target base station to continue transmitting terminal data without data loss, thus improving communication reliability.

[0063] Thirdly, a communication method is provided, which can be executed by a network device (such as a target base station) or by a unit / module / component (such as a chip, chip system, logic circuit, or software) configurable in (or usable in) a network device. The following explanation uses a network device as an example.

[0064] The method includes: a target base station determining a first time based on a first time resource, the first time resource being used to carry the synchronization signal of the second cell, the first time being the time to send a first message (i.e., the fifth message in the specific implementation), the first message being used to instruct the terminal to switch to the second cell or containing configuration information for the terminal to switch to the second cell. The target base station then sends the first message.

[0065] According to the above scheme, the target base station can select an appropriate time to send a message instructing the terminal to hand over to the target cell, i.e., the first message, based on the first time resource. This ensures that the control terminal receives the handover command shortly before the first time resource, allowing the terminal to quickly search for the synchronization signal of the target cell and complete the handover process after receiving the handover command. This reduces the communication interruption time of the terminal when handing over from the first cell (i.e., the source cell) to the second cell (i.e., the target cell). The following description, in conjunction with Figure 10, further illustrates this.

[0066] In conjunction with the third aspect, in certain implementations of the third aspect, the target base station determines the first moment based on the first time resources, including: the target base station determines the first moment based on the first time resources and one or more of the following information:

[0067] Terminal location information;

[0068] The first signal transmission delay is the signal transmission delay between the first cell and the terminal;

[0069] The second signal transmission delay is the signal transmission delay between the second cell and the terminal;

[0070] The third signal transmission delay is the signal transmission delay between the source base station and the target base station. The source base station is the access network node that manages the first cell, and the target base station is the access network node that manages the second cell.

[0071] Message processing latency of the source base station;

[0072] Terminal message processing latency;

[0073] Timing offset between the first cell and the second cell.

[0074] To enable the target base station to determine the first moment, the following implementation methods may also be included:

[0075] In one implementation, the target base station can determine the transmission delay (i.e., the second signal transmission delay) between the terminal and the second cell based on the terminal's location information, or obtain the second signal transmission delay from the source base station (such as one determined by the source base station or determined by the terminal and sent to the source base station). The target base station can then determine the arrival time of the first time resource to the terminal based on the first time resource and the second signal transmission delay. The target base station then determines the first time based on the arrival time, the first signal transmission delay, the third signal transmission delay, and the message processing delays of the terminal and the source base station.

[0076] According to the above scheme, after the target base station determines the first time using the above method, it can send the first message at that first time. This ensures a short interval between the arrival of the handover command at the terminal and the first time resource, allowing the terminal to quickly detect the synchronization signal of the second cell after receiving the handover command. Even if the terminal stops data transmission in the serving cell (i.e., the first cell) or disconnects its communication connection with the serving cell after receiving the handover command, it can avoid excessively long communication interruptions. This helps reduce the probability of terminal service interruptions or dropped calls, improving communication reliability.

[0077] In conjunction with the third aspect, in some implementations of the third aspect, the method further includes: the target base station receiving a second message from the source base station (i.e., the sixth message in the specific implementation), the second message being used to request the terminal to be switched to the second cell, the second message including the location information of the terminal.

[0078] Accordingly, after receiving the second message from the source base station, the target base station can determine that the source base station requested to switch the terminal to the second cell, and the target base station can obtain the terminal location information based on the second message, so as to determine the first moment based on the terminal location information.

[0079] Fourthly, a communication method is provided, which can be executed by a terminal or by a unit / module / component (such as a chip, chip system, logic circuit, or software) configurable in (or usable in) the terminal. The following explanation uses the execution of this method by a terminal as an example.

[0080] The method includes: before receiving a first message from a first cell, the terminal receives a synchronization signal from a second cell based on a timing offset and first time resources. The first cell is the terminal's serving cell, and the second cell is a neighboring cell of the first cell. The timing offset is the timing offset between the first and second cells, and the first time resources are the time resources of the second cell used to carry the synchronization signal. The terminal obtains downlink synchronization with the second cell based on the synchronization signal, and the first message is used to instruct the terminal to switch to the second cell.

[0081] According to the above scheme, before receiving the handover command, the terminal achieves downlink synchronization with the second cell by receiving a synchronization signal and maintains downlink synchronization with the second cell. This allows the terminal to perform cell handover immediately after receiving the handover command, reducing the communication interruption time during the handover process from the source cell to the target cell caused by the terminal waiting for the downlink synchronization signal from the target cell, thus avoiding excessively long communication interruptions. This helps reduce the probability of terminal service interruptions or dropped calls, improving communication reliability.

[0082] In conjunction with the fourth aspect, in some implementations of the fourth aspect, before receiving the first message from the first cell, the terminal receives the synchronization signal from the second cell based on the timing offset and the first time resources, including: the terminal determining that it is located within the coverage area of ​​the second cell. The terminal receives the synchronization signal from the second cell based on the timing offset and the first time resources before receiving the first message from the first cell.

[0083] According to the above scheme, specifically, after determining that the terminal is located within the coverage area of ​​the second cell (i.e., within the overlapping area of ​​the first and second cells), the terminal can assume that a cell handover may occur. Based on the timing offset and first time resources, the terminal then receives the synchronization signal from the second cell. This can reduce the communication interruption time during the handover process from the source cell to the target cell caused by the terminal waiting for the downlink synchronization signal from the target cell.

[0084] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the terminal receives first information, which is used to indicate the coverage area of ​​a target base station, which is an access network node that manages the second cell.

[0085] The first information can directly indicate the coverage area of ​​the target base station, or the first information can include the ephemeris information (or NTN parameter information) of the target base station, and the terminal can determine the coverage area of ​​the target base station based on the ephemeris information.

[0086] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the terminal determines the coverage area of ​​the second cell based on the cell distribution pattern of the target base station and the terminal's location information. The cell distribution pattern is the distribution pattern of multiple cells of the target base station within the coverage area of ​​the target base station.

[0087] By comparing the terminal's location information with the distribution pattern of multiple cells of the target base station indicated by the cell distribution pattern, the terminal can determine whether its location is within the coverage area of ​​the second cell.

[0088] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the first information includes the ephemeris information of the second access network node, and the method further includes:

[0089] The terminal determines the coverage area of ​​the second access network node based on the ephemeris information.

[0090] According to the above scheme, the first information may include the ephemeris information of the target base station, such as the base station's orbital altitude and satellite scan angle. The terminal can determine the coverage area of ​​the target base station based on the ephemeris information. This first information may be sent to the terminal by the first access network node, or it may be sent to the terminal by the target base station via broadcast.

[0091] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the terminal receives the second information, which is used to indicate the cell distribution method.

[0092] For example, the second information may be sent to the terminal by the first access network node, or it may be sent to the terminal by the network, without limitation.

[0093] According to the above scheme, the terminal can receive the synchronization signal of the second cell when the terminal is within the coverage area of ​​the second cell. This allows the terminal to immediately switch to the second cell after receiving the handover command from the first cell, reducing the service interruption time during the handover process and helping to improve the reliability of communication.

[0094] To enable the terminal to determine the timing offset, the following implementation methods may also be included:

[0095] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the terminal determines the timing offset based on the identifier of the first cell, the identifier of the second cell, and the first correspondence.

[0096] This timing offset is the timing offset of time resources between the first cell and the second cell on the network side. The first correspondence is the correspondence between the cell identifier deviation and the timing offset.

[0097] Specifically, the cell identifier deviation can be predefined as either the source cell identifier minus the target cell identifier, or the target cell identifier minus the source cell identifier. Similarly, the time offset can be predefined as the number of time units that the time unit of the source cell with the same identifier deviates from the time unit of the target cell, or the number of time units that the time unit of the target cell with the same identifier deviates from the time unit of the source cell.

[0098] For example, the first correspondence can be an offset that is n times the timing offset, where n is an integer. For instance, if the offset of the cell identifier is P, the timing offset is n*P time units. Taking a frame as an example, if the offset of the cell identifier is P, then the timing offset is n*P frames, that is, the frame of the target cell with the same frame number is offset by n*P frames compared to the frame of the source cell.

[0099] For example, taking n=1 as an example, if the identifier of the first cell is 7 and the identifier of the second cell is 3, then the deviation of the cell identifiers between the first cell and the second cell can be 3-7=-4. This can be understood as the start time of frame #0 of the second cell being 4 frames earlier than the start time of frame #0 of the first cell (i.e., the timing offset is -4). If the deviation is positive, it can be understood as the start time of subframe #0 of frame #0 of the second cell being later than the start time of subframe #0 of frame #0 of the first cell being.

[0100] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the terminal determines the arrival time of the first time resource to the terminal based on the first time resource, the timing offset, the first signal transmission delay, and the second signal transmission delay. The first signal transmission delay is the signal transmission delay between the first cell and the terminal, and the second signal transmission delay is the signal transmission delay between the second cell and the terminal.

[0101] In conjunction with the fourth aspect, in some implementations of the fourth aspect, the method further includes: the terminal acquiring the ephemeris information of the target base station. The terminal determines a second signal transmission delay based on the ephemeris information and the terminal's location information; this second signal transmission delay is the signal transmission delay between the second cell and the terminal.

[0102] The ephemeris information of the target base station (e.g., the target base station) can indicate the location of the target base station. The terminal can then confirm (estimate) the transmission delay (second signal transmission delay) from the terminal to the second cell based on the ephemeris information and the terminal's location information.

[0103] According to the above scheme, the terminal can confirm the second signal transmission delay, which helps the terminal determine the time when the first time resource arrives at the terminal. Then, the terminal can receive the synchronization signal of the second cell based on the arrival time of the first time resource to obtain downlink synchronization of the second cell.

[0104] Fifthly, a communication device is provided. In one design, the device may include modules corresponding to the methods / operations / steps / actions described in the first aspect or any embodiment of the first aspect. These modules may be hardware circuits, software, or a combination of hardware circuits and software. In one design, the device includes: a transceiver unit that receives a first message from a first cell, the first message including a handover command instructing a terminal to handover from the first cell to a second cell; a processing unit that determines a first time period and maintains a communication connection with the first cell during the first time period; and the transceiver unit that sends a second message indicating a successful handover to the second cell, wherein the first time period is the period between the transceiver unit receiving the first message and sending the second message.

[0105] In a sixth aspect, a communication device is provided. In one design, the device may include modules corresponding to the methods / operations / steps / actions described in the second aspect or any of the embodiments of the second aspect. These modules may be hardware circuits, software, or a combination of hardware circuits and software. In one design, the device includes: a transceiver unit configured to send a first message from a first cell to a terminal, the first message including a handover command indicating a handover from the first cell to a second cell; and a processing unit configured to maintain a communication connection with the terminal in the first cell during a second time period, the second time period being the period between sending the first message and receiving a third message. The transceiver unit is further configured to receive a third message indicating that the terminal has completed the handover to the second cell.

[0106] A seventh aspect provides a communication device. In one design, the device may include modules corresponding to the methods / operations / steps / actions described in the third aspect or any of the embodiments of the third aspect. These modules may be hardware circuits, software, or a combination of hardware circuits and software. In one design, the device includes: a processing unit configured to determine a first moment based on first time resources, the first time resources being used to carry a synchronization signal of the second cell, the first moment being the time to send a first message, the first message being used to instruct a terminal to switch from the first cell to the second cell; and a transceiver unit configured to send the first message.

[0107] Eighthly, a communication apparatus is provided. In one design, the apparatus may include modules corresponding to the methods / operations / steps / actions described in the fourth aspect or any of the embodiments of the fourth aspect. These modules may be hardware circuits, software, or a combination of hardware circuits and software. In one design, the apparatus includes: a transceiver unit, configured to receive a synchronization signal from a second cell based on a timing offset and a first time resource before receiving a first message from a first cell. The first cell is the serving cell of the terminal, and the second cell is a neighboring cell of the first cell. The timing offset is the timing offset between the first cell and the second cell, and the first time resource is the time resource of the second cell used to carry the synchronization signal of the second cell. A processing unit is configured to obtain downlink synchronization with the second cell based on the synchronization signal. The first message is used to instruct the terminal to switch to the second cell.

[0108] A ninth aspect provides a processor, comprising: an input circuit, an output circuit, and a processing circuit. The processing circuit is configured to receive signals through the input circuit and transmit signals through the output circuit, causing the processor to execute the methods described in the first to fourth aspects and any possible implementation thereof.

[0109] In specific implementation, the processor can be one or more chips, the input circuit can be input pins, the output circuit can be output pins, and the processing circuit can be transistors, gate circuits, flip-flops, and various logic circuits. The input signal received by the input circuit can be received and input by, for example, but not limited to, a receiver, and the signal output by the output circuit can be, for example, but not limited to, output to and transmitted by a transmitter. Furthermore, the input circuit and the output circuit can be the same circuit, which is used as both the input circuit and the output circuit at different times. This application does not limit the specific implementation of the processor and various circuits.

[0110] In a tenth aspect, a computer program product is provided, comprising: a computer program (also referred to as code or instructions) that, when run, causes a computer to perform the methods described in the first to fourth aspects and any possible implementation thereof.

[0111] Eleventhly, a computer-readable storage medium is provided that stores a computer program (also referred to as code or instructions) that, when executed on a computer, causes the computer to perform the methods of the first to fourth aspects and any possible implementation thereof.

[0112] In a twelfth aspect, a communication system is provided, including a first communication device and a second communication device, the first communication device being used to perform the first aspect or any possible implementation of the first aspect, and the second communication device being used to perform the second aspect or any possible implementation of the second aspect.

[0113] It should be understood that the beneficial effects of the features corresponding to the first aspect in the second to twelfth aspects can be referred to the relevant description of the first aspect above, and will not be repeated here. Attached Figure Description

[0114] Figure 1 is a first schematic diagram of a communication system architecture applicable to an embodiment of this application;

[0115] Figure 2 is a second schematic diagram of a communication system architecture applicable to embodiments of this application;

[0116] Figure 3 is a third schematic diagram of the communication system architecture applicable to embodiments of this application;

[0117] Figure 3a is a fourth schematic diagram of a communication system architecture applicable to an embodiment of this application;

[0118] Figure 4 is a fifth schematic diagram of a communication system architecture applicable to embodiments of this application;

[0119] Figure 5 shows a schematic flowchart of a communication method;

[0120] Figure 6 is a first schematic flowchart of the communication method provided in an embodiment of this application;

[0121] Figure 7 is a schematic diagram of the interruption duration of the terminal during the handover process provided in the embodiment of this application;

[0122] Figure 7A is a second schematic flowchart of the communication method provided in an embodiment of this application;

[0123] Figure 8 is a third schematic flowchart of the communication method provided in the embodiments of this application;

[0124] Figure 9 is a fourth schematic flowchart of the communication method provided in an embodiment of this application;

[0125] Figure 9A is the fifth schematic flowchart of the communication method provided in the embodiments of this application;

[0126] Figure 10 is a sixth schematic flowchart of the communication method provided in the embodiments of this application;

[0127] Figure 11 is a schematic diagram of the interruption duration of another terminal in the handover process provided in an embodiment of this application;

[0128] Figure 12 is a schematic diagram of a scenario to which an embodiment of this application is applicable;

[0129] Figure 13 is the seventh schematic flowchart of the communication method provided in the embodiments of this application;

[0130] Figure 14 is a schematic diagram of the interruption duration of another terminal in the handover process provided in the embodiment of this application;

[0131] Figure 15 is a schematic block diagram of an example of a communication device provided in an embodiment of this application;

[0132] Figure 16 is a schematic structural diagram of another example of the communication device provided in the embodiments of this application. Detailed Implementation

[0133] To facilitate understanding of the embodiments of this application, the following points will be explained first:

[0134] In this application, "instruction" can include direct instruction, indirect instruction, explicit instruction, and implicit instruction. When describing a certain instruction information for the purpose of instructing A, it can be understood that the instruction information carries A, directly instructs A, or indirectly instructs A.

[0135] In this application, " / " can indicate that the objects before and after are in an "or" relationship. For example, A / B can mean A or B. "And / or" can be used to describe three relationships between the related objects. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural.

[0136] In this application, "at least one" means one or more, and "more than one" means two or more, such as three, four, or more. Similar expressions (such as at least one, at least one, etc.) are used in the same way. "At least one of the following," "one or more of the following," or similar expressions refer to any combination of these items, which may include only a single item or a combination of multiple items. For example, at least one of a, b, or c can mean: a, or b, or c; a and b; or a and c; or b and c; or a, b, and c. Where a, b, and c can be single or multiple.

[0137] In this application, for the convenience of describing the technical solutions of the embodiments of this application, the terms "first" and "second" may be used to distinguish them. The terms "first" and "second" do not limit the quantity or execution order, and the terms "first" and "second" are not necessarily different.

[0138] In this application, the words "exemplary," "example," or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary," "example," or "for example" should not be construed as being more preferred or advantageous than other embodiments or designs. The use of the words "exemplary," "example," or "for example" is intended to present the relevant concepts in a specific manner to facilitate understanding.

[0139] In this application, "sending information / data" only indicates the direction of information / data transmission, including direct transmission via the device's communication interface (such as an air interface, or simply air interface). "Sending" can also be understood as the "output" of a module interface. "Sending" can include indirect transmission by the processing unit through the communication interface, meaning that after the processing unit outputs information / data through the module interface, it is transmitted to the device's communication interface and then sent out. "Receiving information / data" only indicates the direction of information / data transmission, including direct reception via the communication interface. "Receiving" can also be understood as the "input" of a module interface. "Receiving information / data" can include indirect reception by the processing unit through the communication interface, meaning that after the communication interface receives information / data, it is transmitted to the processing unit's module interface and then input to the processing unit. "Sending information / data to… (such as a terminal)" can be understood as the destination of the information being the terminal. It can include sending information / data directly or indirectly to the terminal. "Receiving information / data from… (such as a terminal)" can be understood as the source of the information being the terminal, and can include receiving information / data directly or indirectly from the terminal. Information / data may undergo necessary processing, such as format changes, between the source and destination, but the destination can understand the valid information / data from the source. Similar statements in this application can be understood in a similar way, and will not be repeated here.

[0140] The technical solutions of this application can be applied to various communication systems, such as Long Term Evolution (LTE) systems, 5th Generation (5G) communication systems, satellite communication systems, Wireless Fidelity (WiFi) systems, and the solutions provided in this application can also be applied to future communication systems or other communication systems. This application does not limit these applications.

[0141] Figure 1 illustrates a possible, non-limiting system diagram. As shown in Figure 1, the communication system 10 includes a radio access network (RAN) 100, a core network (CN) 200, and a data network (DN) 300. RAN 100 includes at least one RAN node (110a and 110b in Figure 1, collectively referred to as 110) and at least one terminal (120a-120j in Figure 1, collectively referred to as 120). RAN 100 may also include other RAN nodes, such as wireless relay devices and / or wireless backhaul devices (not shown in Figure 1). Terminal 120 is wirelessly connected to RAN node 110. Access network node (or RAN node) 110 is wirelessly or wired connected to core network 200. The core network equipment in core network 200 and access network node 110 in RAN 100 can be different physical devices, or they can be the same physical device integrating core network logical functions and radio access network logical functions.

[0142] RAN 100 can be a cellular system related to the 3rd Generation Partnership Project (3GPP), such as 4G, 5G mobile communication systems, future evolution systems, or future communication systems. RAN 100 can also be an open access network (O-RAN or ORAN), a cloud radio access network (CRAN), or a wireless fidelity (WiFi) system. RAN 100 can also be a communication system that integrates two or more of the above systems.

[0143] Access network node 110, sometimes also referred to as access network equipment, network equipment, RAN entity, or access node, constitutes part of the communication system and is used to help terminals achieve wireless access. Multiple access network nodes 110 in communication system 10 can be of the same type or different types. In some scenarios, the roles of access network node 110 and terminal 120 are relative. For example, network element 120i in Figure 1 can be a helicopter or drone, which can be configured as a mobile base station. For terminals 120j accessing RAN 100 through network element 120i, network element 120i is a base station; but for base station 110a, network element 120i is a terminal. Access network node 110 and terminal 120 are sometimes both referred to as communication devices. For example, network elements 110a and 110b in Figure 1 can be understood as communication devices with base station functions, and network elements 120a-120j can be understood as communication devices with terminal functions.

[0144] In one possible scenario, the access network node can be a base station, such as an evolved NodeB (eNodeB), a next-generation NodeB (gNB), or a base station in a future mobile communication system. The access network node can be a macro base station (as shown in Figure 1, 110a), a micro base station or indoor station (as shown in Figure 1, 110b), a relay node or donor node, or a radio controller in a CRAN scenario. Alternatively, the access network node can be an access point (AP), a transmission reception point (TRP), or an access node in a WiFi system. Optionally, the access network node can also be a server, a wearable device, a vehicle, or in-vehicle equipment. For example, the access network device in vehicle-to-everything (V2X) technology can be a roadside unit (RSU). All or part of the functions of the access network node in this application can also be implemented through software functions running on hardware, or through virtualization functions instantiated on a platform (e.g., a cloud platform). The access network node in this application may also be a logical node, logical module, or software that can implement all or part of the functions of the access network node.

[0145] In another possible scenario, multiple access network nodes collaborate to assist the terminal in achieving wireless access, with each access network node performing a portion of the base station's functions. For example, access network nodes can be central units (CUs), distributed units (DUs), CU-control plane (CPs), CU-user plane (UPs), or radio units (RUs), etc. CUs and DUs can be set up separately or included in the same network element, such as a baseband unit (BBU). RUs can be included in radio frequency equipment or radio frequency units, such as remote radio units (RRUs), active antenna units (AAUs), or remote radio heads (RRHs).

[0146] A terminal can also be called a terminal device, user equipment (UE), mobile station, mobile terminal, etc. Terminals can be widely used for communication in various scenarios. These scenarios include, but are not limited to, at least one of the following: enhanced mobile broadband (eMBB), ultra-reliable low-latency communication (URLLC), massive machine-type communications (mMTC), D2D, V2X, machine-type communication (MTC), Internet of Things (IoT), virtual reality, augmented reality, industrial control, autonomous driving, telemedicine, smart grid, smart furniture, smart office, smart wearables, intelligent transportation, sensing terminals, terminals integrating communication and sensing, or smart cities, etc. Terminals can be mobile phones (as shown in Figure 1, 120a, 120j, and 120e), tablets, computers with wireless transceiver capabilities (as shown in Figure 1, 120g), customer-premises equipment (CPE), point-of-sale (POS) machines, wearable devices, vehicles (as shown in Figure 1, 120b), drones, helicopters, airplanes (as shown in Figure 1, 120i), ships, robots, robotic arms, sensors, detectors, or smart home devices (as shown in Figure 1, 120h), etc.

[0147] Figure 2 illustrates a possible, non-limiting system diagram. The system architecture shown in Figure 2 is one possible architecture for an NTN network. As shown in Figure 2, the terminal communicates with the ground base station through the User-Universal Terrestrial Radio Access Network (Uu) interface. The satellite enables transparent payload transmission between the terminal and the ground base station. The satellite and the NTN gateway can be considered as remote radio units (RRUs) of the ground base station, achieving transparent signal forwarding. That is, the satellite only supports functions such as radio frequency filtering, frequency conversion, and amplification, while the signal waveform remains unchanged. The satellite forwarding is transparent to the terminal. The ground base station and the core network (CN) can communicate through the Next Generation (NG) interface, exchanging non-access stratum (NAS) signaling of the core network and the terminal's service data via the NG interface. The core network can also transmit service data with the data network (DN).

[0148] Figure 3 illustrates another possible, non-limiting system diagram. As shown in Figure 3, the satellite possesses some or all of the functions of an access network device and can be referred to as a satellite base station. It can provide wireless access services and schedule wireless resources for terminals accessing the network through the satellite base station. The satellite base station and the terminal communicate via the Uu interface. Specifically, the satellite base station and the CN can communicate via the NG interface, and the satellite base station and the core network can exchange NAS signaling and terminal service data via the NG interface. The satellite radio interface (SRI) is the feeder link between the NTN gateway and the satellite. In Figure 3, the SRI interface can be used as part of the NG interface to realize communication interaction between the satellite and the core network.

[0149] Figure 3a shows another possible, non-limiting system diagram. As shown in Figure 3a, there are inter-satellite links (ISLs) between satellite base stations. The satellite base stations can establish an Xn interface based on the ISL, which is used for signaling interaction between satellites.

[0150] Figure 4 illustrates another possible, non-limiting system diagram. This system architecture includes user equipment (UE), RAN nodes, and core network nodes. For example, core network nodes may include, as shown in Figure 4, policy control function (PCF) nodes, access and mobility management function (AMF) nodes, session management function (SMF) nodes, UPF nodes, and application function (AF) nodes, etc.

[0151] The functions of each core network node are described below. The AUSF node is primarily responsible for authenticating users to determine whether to allow or allow devices to access the network. The AMF node mainly performs mobility management, access authentication / authorization, and also relays user policies between the UE and PCF node. The SMF node is primarily responsible for UE network protocol (IP) address allocation. The UPF node is primarily responsible for session management functions such as selection, charging, and quality of service (QoS) policy control. The UPF node, as the interface with the data network (DN), is mainly responsible for user plane data forwarding, session / flow-level charging statistics, and bandwidth limiting. The AF node mainly relays application layer requirements to the network side. The PCF node is primarily responsible for managing charging and QoS policies.

[0152] As shown in Figure 4, the functional units can communicate with each other through the next generation (NG) network interface. For example, the UE can transmit control plane messages with the AMF node through NG interface 1 (N1), the RAN node can establish a user plane data transmission channel with the UPF through NG interface 3 (N3), the RAN node can establish a control plane signaling connection with the AMF node through NG interface 2 (N2), the UPF can interact with the SMF node through NG interface 4 (N4), the UPF can interact with the data network DN through NG interface 6 (N6), the AMF node can interact with the SMF node through NG interface 11 (N11), and the SMF node can interact with the PCF node through NG interface 7 (N7). It should be noted that Figure 4 is only an exemplary architecture diagram. In addition to the functional nodes shown in Figure 4, this network architecture may also include other functional nodes.

[0153] The system architecture may also include servers (such as cloud servers), which can be devices that provide computing or application services for services that require complete transmission integrity, including various devices such as control servers and application servers.

[0154] In the embodiments of this application, the terminal and network device can be hardware devices, or software functions running on dedicated hardware, or software functions running on general-purpose hardware, such as virtualization functions instantiated on a platform (e.g., cloud platform), or entities that include dedicated or general-purpose hardware devices and software functions. This application does not limit the specific form of the terminal and network device.

[0155] To better understand the methods provided in the embodiments of this application, the relevant technologies and terms involved in this application will be explained below.

[0156] I. Synchronization signal and physical broadcast channel block (SSB)

[0157] Network devices broadcast the SSB of each cell. The SSB enables terminals to synchronize with the network devices, and terminals can perform processes such as cell search, measurement, cell selection, or cell handover based on the SSB.

[0158] The System Message Block (SSB) includes a synchronization signal and a Physical Broadcast Channel (PBCH). The PBCH carries a Master Information Block (MIB), which includes, but is not limited to, information used to determine the system frame number, system bandwidth, and subcarrier spacing. The terminal detects the SSB broadcast by the network device through cell search and can establish a communication connection with that network device through the detected SSB. Specifically, the terminal detects the SSB and reads the MIB carried on the PBCH within it. Based on the MIB, in addition to determining the system frame number, system bandwidth, and subcarrier spacing, the terminal can also obtain the System Information Block (SIB) 1. SIB1 includes the configuration information of the Physical Random Access Channel (PRACH). The PRACH configuration information in SIB1 configures the PRACH occasion (RO) and preamble configuration information. RO represents the time-frequency resources used to carry the preamble. The terminal can initiate a random access procedure based on this configuration information.

[0159] Network devices can transmit SSBs with periods of 5ms, 10ms, 20ms, 40ms, 80ms, or 160ms. Longer SSB periods result in better network energy efficiency, while shorter periods allow for faster cell search by the terminal. Within each SSB period, the network device transmits an SSB group, which includes one or more SSBs. This SSB group is called an SSB burst set. The network device transmits the SSBs in this SSB group using beams from different directions, achieving SSB beam scanning across the cell coverage area, ensuring that all terminals within the cell's coverage area can receive the cell's SSBs. The protocol specifies that an SSB burst set must be transmitted within 5ms.

[0160] II. NTN Cell

[0161] Non-terrestrial networks (NTNs) refer to networks or portions of networks that use radio frequency (RF) signals on satellite (or unmanned aircraft systems, UAS, or high-altitude platforms). A typical NTN network provides communication services via satellite. Cells within an NTN network can be called NTN cells.

[0162] When a terminal accesses a network (such as NR, LTE, or other networks) via an NTN cell, it needs to obtain NTN parameter information (also known as NTN-Config or satellite-aided information). This NTN parameter information may include, but is not limited to, at least one of the following:

[0163] Satellite ephemeris information

[0164] The terminal can obtain satellite ephemeris information, determine the satellite's position, and predict the satellite's future position.

[0165] • Common timing advance (TA) parameter information

[0166] Common timing advance (TA) parameter information is the common timing advance value of network control. The terminal can obtain the common timing advance TA value through this parameter information. This parameter information may also include the common timing advance value, the common timing advance value drift rate, and the drift rate variation rate. The terminal can predict and estimate the future and past common timing advance values ​​through this parameter information.

[0167] • Start time parameter information (epoch time parameter information)

[0168] The epoch time parameter information is used to indicate the start time of the NTN parameter information.

[0169] • Synchronization validity period parameter information (ntn-UlSyncValidityDuration parameter information)

[0170] The synchronization validity time parameter information indicates the validity duration of the NTN parameter information. During this validity duration, which begins from the start time, the terminal can apply the NTN parameter information without needing to obtain updated NTN parameter information.

[0171] kmac parameter information

[0172] The kmac parameter information refers to the scheduling offset provided by the network when the downlink and uplink frame timings are misaligned with the gNB. This value can be 0.

[0173] Downlink (DL) polarization indication information

[0174] DL polarization indication information is used to indicate the polarization mode of the downlink of the service link. The polarization mode can be right-handed circular polarization, left-handed circular polarization, linear polarization, etc.

[0175] • Uplink (UL) polarization indication information

[0176] UL polarization indication information is used to indicate the polarization mode of the uplink service link. The polarization mode can be right-handed circular polarization, left-handed circular polarization, linear polarization, etc.

[0177] ·TA Report Enabling Information

[0178] If the NTN parameter information includes TA report enable information, the terminal will report a TA during or after the random access process.

[0179] III. Beam Jumping

[0180] In NTN scenarios, satellite communication networks suffer from limited satellite power and high propagation loss. To improve link budget, satellites use massive MIMO (Massively Multi-Span Antennas) with narrower beams to concentrate signal energy and overcome propagation loss. Narrower beams reduce the coverage area of ​​a single beam, increasing the number of beams within that area. For NTN cells with coverage areas much larger than terrestrial cells, thousands of beams may be needed to cover the entire cell area.

[0181] However, satellite hardware resources are limited, restricting the number of beams that can be simultaneously transmitted. For example, under the minimum link budget required for link coverage, the maximum number of beams that can be activated simultaneously for downlink transmission is 24. As satellite power increases, the maximum number of beams may also change. In this case, the number of beams the satellite can transmit simultaneously is far less than the number of positions in the NTN cell it can cover, making it impossible for the SSB to cover all positions in the NTN cell at the same time. For example, with a maximum beam count of 24, only the SSB transmitted through these 24 beams can simultaneously cover 24 positions. The satellite needs to achieve SSB coverage of the entire cell area by using time-division multiplexing of beams, such as covering different areas within the cell with the 24 beams at different times, achieving SSB coverage of the entire cell area over multiple time intervals. This method is also known as beam hopping.

[0182] V. Cell Switching Procedure

[0183] Figure 5 shows a schematic flowchart of a method 500 for a terminal to hand over from a source cell to a target cell. Before the terminal initiates the handover process, the terminal can transmit terminal data based on the path established between the source base station and the UPF. In Figure 5, the source base station is the network device managing the source cell, and the target base station is the network device managing the target cell.

[0184] As shown in Figure 5, the cell handover process may include, but is not limited to, the following steps:

[0185] S501, the source base station sends measurement configuration information to the terminal.

[0186] The source base station can send measurement configuration information to the terminal to instruct the terminal to measure the signal quality of other cells. The measurement configuration information may include the measurement object and measurement report configuration. The measurement object may include reference signals from at least one neighboring cell, such as the SSB and / or channel state information reference signal (CSI-RS) of the neighboring cell. At least one neighboring cell may include a cell using the same frequency as the source cell (also called a co-frequency cell), and / or a cell using a different frequency than the source cell (also called a hetero-frequency cell). The measurement report configuration can be used to instruct the terminal to report measurement results to the source base station, such as including the report format of the measurement report. The measurement configuration information may also include a measurement interval (gap) configuration, allowing the terminal to perform signal measurements of neighboring cells (such as hetero-frequency cells) within the time period configured for the measurement interval.

[0187] S502, the terminal sends a measurement report to the source base station.

[0188] After receiving the measurement configuration information, the terminal can execute the measurement process according to the configuration information to obtain the measurement results of the measurement object (such as co-frequency cells and inter-frequency cells). The measurement results can indicate the signal quality between the terminal and the measurement object. When the measurement results meet the measurement reporting conditions, the terminal can send a measurement report to the source base station.

[0189] Accordingly, the source base station receives the measurement report from the terminal, makes a handover decision based on the measurement results in the measurement report, and determines the target cell for the terminal if it decides to perform the handover.

[0190] S503, the source base station sends a handover request message to the target base station.

[0191] The source base station can send a handover request message to the target base station. The handover request message may include the target cell identifier, the terminal's identifier at the source base station, and terminal capability information. Among these, the terminal capability information can be used to indicate the terminal's hardware and / or software capabilities, such as including but not limited to the frequency bands and wireless technologies (e.g., LTE, 5G NR) that the terminal can support.

[0192] S504, the target base station sends a handover request confirmation message to the source base station.

[0193] After receiving a handover request message from the source base station, the target base station can send a handover request confirmation message to the source base station. This handover request confirmation message can be used to indicate the information required for the terminal to access the target base station.

[0194] S505: The source base station sends a radio resource control (RRC) reconfiguration message containing a handover command to the terminal.

[0195] After receiving a handover request confirmation message from the target base station, the source base station can generate an RRC reconfiguration message based on the handover request confirmation message and send the RRC reconfiguration message to the terminal so that the terminal can access the target cell based on the RRC reconfiguration message.

[0196] The RRC reconfiguration message is used to instruct the terminal to hand over from the source cell to the target cell. The handover command in the RRC reconfiguration message may include information required for the terminal to access the target cell, such as the target cell identifier, the cell radio network temporary identifier (C-RNTI) in the target cell, the target base station security algorithm identifier, the dedicated random access channel (RACH) resource, the association between the RACH resource and the SSB, the association between the RACH resource and the terminal's specific channel state information reference signal (CSI-RS) configuration, public RACH resources, and system information of the target cell.

[0197] After sending the RRC reconfiguration message, the source base station stops providing data transmission services to the terminal. Upon receiving the RRC reconfiguration message, the terminal stops data transmission within the source cell.

[0198] S506, the source base station sends a sequence number (SN) state transition message to the target base station.

[0199] SN Status Transition (SN STATUS TRANSFER) messages are used to indicate the current status of terminal data transmission, including which data packets have been successfully transmitted and which need to be retransmitted. For example, the SN STATUS TRANSFER message may specifically include the Packet Data Convergence Protocol (PDCP) SN number. The target base station uses the SN STATUS TRANSFER message to determine the data packets that have been transmitted and those that have not yet been transmitted, enabling the target base station to continue transmitting terminal data and avoid data loss.

[0200] For example, an SN state transition message can transmit the uplink PDCP SN receiver state and / or downlink PDCP SN transmitter state of data radio bearers (DRBs) with PDCP state retention. The uplink PDCP SN receiver state includes at least the PDCP SN of the first lost UL PDCP service data unit (SDU) and may include a bitmap (if any) of the receive state of out-of-order UL PDCP SDUs that the terminal needs to retransmit in the target cell. The downlink PDCP SN transmitter state indicates that the target gNB should assign the next PDCP SN to the new PDCP SDU, but no PDCP SN has yet been assigned.

[0201] After the source base station sends an SN state transition message to the target base station, the source base station can forward the terminal data packets from the UPF to the target base station. The target base station can then transmit these data packets to the terminal after the terminal successfully hands over to the target cell. This ensures that data packets arriving at the source base station from the UPF are not lost during the handover process.

[0202] After receiving an RRC reconfiguration message from the source base station, the terminal can execute a random access procedure for the target cell based on the RRC reconfiguration message to access the target cell. The following steps describe the terminal's access to the target cell using a non-contention-based 4-step random access method as an example.

[0203] S507, the terminal sends a random access preamble (MSG1) to the target base station.

[0204] Specifically, after receiving the RRC reconfiguration message, the terminal can detect the SSB of the target cell based on the information carried in the handover command, and achieve downlink synchronization with the target cell based on the target cell's SSB. Then, it sends a random access preamble to the target base station. This random access preamble is also called message 1 (MSG1) of the random access procedure. This random access preamble can be a dedicated preamble for the random access procedure configured for the terminal in the RRC reconfiguration message. The terminal can request access to the target cell by sending this dedicated preamble to the target base station.

[0205] S508, the target base station sends a random access response message (MSG2) to the terminal.

[0206] After receiving MSG1 from the terminal, the target base station responds to the terminal's access request by sending a random access response message to the terminal. The random access response message is also called message 2 (MSG2) of the random access procedure.

[0207] S509, the terminal sends an RRC reconfiguration complete message to the target base station.

[0208] The RRC reconfiguration completion message indicates that the handover process is complete and the terminal has completed the handover to the target cell.

[0209] S510, the target base station sends a path switching request message to the AMF.

[0210] After receiving the RRC reconfiguration complete message from the terminal, the target base station can send a path handover request message to the AMF to change the serving cell notified to the core network to the target cell. This path handover request message may include the target cell identifier and a list of protocol data unit (PDU) sessions to be switched.

[0211] After receiving the path switching request message, AMF triggers the core network to switch to the downlink data path of the target base station and establishes an interface instance to the target base station so that terminal data can be correctly routed to the target base station.

[0212] S511, AMF replies to the target base station with a path handover request confirmation message.

[0213] After receiving the path handover request confirmation message from the AMF, the target base station confirms that the path handover of the terminal on the network side has been completed.

[0214] S512, the target base station sends a UE context release message to the source base station.

[0215] A base station maintains a set of information for each connected terminal, which can be called the UE context (or terminal context). The UE context is used to manage and support the terminal's communication sessions, ensuring that the network can effectively provide services to the terminal. For example, the UE context may include, but is not limited to, one or more of the following: a globally unique user identifier (UUID) corresponding to the terminal, a globally unique device identifier (UUID), the terminal's security information (such as encryption keys, authentication status), session management information (such as quality of service (QoS) parameters), or connection management information (such as RRC status, time advance (TA)).

[0216] After receiving the path handover request confirmation message from the AMF, the target base station can send a UE context release message to the source base station, notifying it that the handover was successful and releasing the UE context of the terminal. The source base station then releases the radio and control plane resources associated with the terminal context based on the UE context release message.

[0217] The following analysis, using Figure 5 as an example, examines the service interruption time caused by the handover process, illustrating the terminal's transition from the source cell to the target cell. In this cell handover process, the service interruption time begins when the terminal receives the RRC reconfiguration message (S505) and ends when the terminal successfully completes the handover (S509). For example, the interruption time caused by the handover can be further subdivided as follows:

[0218] 1) The processing time of the RRC message after the terminal receives the RRC reconfiguration message (handover command), such as decoding the RRC message, which takes about 10ms.

[0219] 2) It takes about 20ms for the terminal to retune the radio frequency / baseband and update the security key and algorithm.

[0220] 3) Downlink synchronization time between the terminal and the target cell. The terminal first completes downlink synchronization using the downlink reference signal (such as SSB) of the target cell. The period of the downlink reference signal (such as the SSB period) will affect the downlink synchronization time of the terminal.

[0221] 4) The time it takes for the terminal to wait for RACH resources to arrive, including the time it takes for the terminal to execute the RACH process and synchronize uplink with the target cell, is approximately 20ms. In some scenarios, such as beam hopping scenarios or when the SSB period is large, the satellite beam scanning period may be long, and it may take a long time for the satellite beam to re-cover the original coverage area. This may cause the terminal to wait a long time after receiving the RRC reconfiguration message before it can detect the SSB of the target cell, preventing the terminal from accessing the target cell in a timely manner. Therefore, after the terminal stops data transmission with the source cell upon receiving the RRC reconfiguration message, it may take a long time to complete the handover to the target cell, potentially resulting in a prolonged service interruption, leading to terminal service interruption or dropped calls.

[0222] To address the aforementioned issues, this application proposes that after the source base station and the terminal transmit the handover command, the terminal and the source base station can maintain a communication connection with the serving cell for a period of time. During this period, the serving cell continues to provide data transmission services to the terminal. This reduces handover interruption time during the terminal's handover from the source cell to the target cell, helping to reduce issues such as terminal service interruptions or dropped calls, and improving communication reliability.

[0223] It should be understood that the embodiments of this application can be applied to satellite communication scenarios, such as when both the source cell and the target cell are NTN cells, and the source cell and the target cell belong to the same satellite, meaning that the terminal performs cell handover between different cells of the same satellite. Alternatively, the source cell and the target cell may belong to different satellites, meaning that the terminal performs cell handover between cells of different satellites. An NTN cell can correspond to one or more beams (such as satellite beams), so the terminal handover from the source cell to the target cell can be understood as the terminal handover from one beam to another.

[0224] The methods provided in the embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0225] It should be understood that, in the embodiments of this application, the communication method provided by this application is shown from the perspective of the interaction between functional nodes in the terminal, base station, and core network, but this application does not limit the executing entity of the method. In each embodiment, the function of the terminal can also be implemented by a module (such as a chip, chip system, processor, logic circuit, or software) configurable in (or used in) the terminal. In each embodiment, the function of the base station (source base station / target base station) can be implemented by the access network nodes described above. Alternatively, it can be implemented by a module (such as a chip, chip system, processor, logic circuit, or software) configurable in the base station. When the executing entity is a module in the terminal or base station, receiving / transmitting can be understood as input / output, that is, the module communicates with other modules or components of the terminal or base station. Furthermore, the operation performed by a single executing entity can also be divided into operations performed by multiple executing entities, which can be logically and / or physically separated. For example, the operation performed by the base station can be divided into operations performed by at least one of CU, DU, RU, etc.

[0226] Figure 6 is a schematic flowchart of the communication method provided in this application. This communication method may include, but is not limited to, steps S601, S602, and S603 below. Each step is described in detail below.

[0227] S601, the source base station sends a first message of the first cell to the terminal. The first message includes a handover command, which is used to indicate handover to the second cell.

[0228] Accordingly, the terminal receives the first message from the first cell, and based on the handover command in the first message, the terminal determines to hand over from the first cell to the second cell.

[0229] In this context, the first cell is the terminal's current serving cell, i.e., the source cell in the cell handover process; the second cell is the target cell in the cell handover process, which will not be elaborated further below. For example, the first message can be an RRC reconfiguration message, meaning that the RRC reconfiguration message may include a handover command. However, this application is not limited to this; the first message can also be a medium access control (MAC) control element (CE) or a physical layer (also known as a layer 1, L1) message.

[0230] The handover command in the first message may include information required for the terminal to access the second cell, such as the identification information of the second cell. Based on this handover command and the information required to access the second cell, the terminal can determine which cell to hand over to.

[0231] Optionally, the handover command in the first message includes first information, which is used to instruct the handover to the second cell to be performed without a random access procedure.

[0232] It should be understood that after receiving the first message, the terminal can determine to perform a cell handover without a random access procedure based on the first information in the handover command. This first information may include the configuration for the cell handover without a random access procedure and the terminal's TA adjustment indication information in the second cell. Cell handover without a random access procedure includes the terminal not sending a random access preamble and not receiving a random access response message during the cell handover process. The terminal can achieve a handover without a random access procedure by sending a second message to the target base station, indicating successful handover to the second cell, and receiving a message from the target base station indicating successful handover.

[0233] Optionally, the first information may also include an uplink grant (UL grant), which pre-configures periodic UL resources of the second cell. The terminal can send a second message to the target base station on this UL resource.

[0234] If the first message does not include a UL grant, the terminal can monitor the PDCCH of the second cell to obtain the UL schedule of the second cell. This UL schedule allocates UL resources to the terminal. The terminal can then send a second message to the second cell on this UL resource to indicate that the terminal has successfully switched to the second cell.

[0235] If the handover command does not include the first information, or if the handover command includes instructions to perform a cell handover based on a random access procedure, then the terminal can determine to perform a cell handover based on a random access procedure, that is, the terminal determines to hand over to the second cell through a random access procedure.

[0236] S602, the terminal maintains a communication connection with the first cell during the first time period, and the source base station maintains a communication connection with the terminal during the second time period.

[0237] The first time period is the period determined by the terminal after receiving the first message. The second time period is the period determined by the source base station after sending the first message. In other words, after transmitting the first message, the source base station and the terminal maintain the communication connection between the terminal and the first cell.

[0238] It should be noted that the first time period is the time period determined by the terminal to need to maintain a communication connection with the first cell, and the second time period is the time period determined by the source base station to need to maintain a communication connection with the terminal in the first cell. The first and second time periods may overlap completely or partially, that is, the first and second time periods may be the same or overlap within a certain duration. At least one of the first and second time periods can be determined by the terminal or the source base station and then notified to the other, or it can be determined by the terminal and the source base station respectively based on relevant parameters. This application does not limit this. The specific implementation methods of the terminal and the source base station are described below. First, the specific implementation method of the terminal maintaining a communication connection with the first cell during the first time period is introduced.

[0239] Optionally, the terminal maintains a communication connection with the first cell during the first time period, including: the terminal continues to receive data transmission services from the first cell during the first time period. Wherein, the terminal continuing to receive data transmission services from the first cell during the first time period includes the terminal performing one or more of the following:

[0240] 1) The terminal does not release the configuration information of the first cell.

[0241] The configuration information of the first cell may include information required for the terminal to transmit data in the first cell, such as the identifier of the first cell, the security algorithm identifier of the first cell, and the identifier of the terminal in the first cell. The terminal does not release the configuration information of the first cell so as to maintain the communication connection with the first cell during the first time period.

[0242] 2) The terminal detects the downlink control information (DCI) of the first cell.

[0243] The Data Interpretation (DCI) is transmitted via the Physical Downlink Control Channel (PDCCH). The terminal can monitor and parse the DCI on the PDCCH of the first cell to confirm whether the source base station has scheduled data transmission for the terminal, such as downlink data and / or uplink data transmission. Upon detecting the DCI, the terminal transmits data in the first cell based on that DCI.

[0244] 3) The terminal receives data and / or information from the first cell.

[0245] If the terminal receives one or more of the following from the first cell: downlink data, downlink control information, or downlink reference signals (such as demodulation reference signal (DMRS), CSI-RS, phase tracking reference signal (PTRS)).

[0246] 4) The terminal sends data and / or information to the first cell.

[0247] The terminal sends one or more of the following: uplink data, uplink control information, or uplink reference signals (such as demodulation reference signal (DMRS), sounding reference signal (SRS), phase tracking reference signal (PTRS), etc.).

[0248] The first time period will be described in detail below, and may include, but is not limited to, the following implementation methods one and two.

[0249] In the first implementation method, the first time period is specifically before the arrival time of the first time resource at the terminal, and the first time resource is used to carry the synchronization signal of the second cell.

[0250] Based on the first message, the terminal can determine whether to perform a cell handover without a random access procedure or a cell handover based on a random access procedure. Regardless of the handover method, in order to obtain downlink synchronization from the second cell, the terminal needs to determine the time when the synchronization signal from the second cell arrives at the terminal.

[0251] The downlink synchronization of the second cell obtained by the terminal based on the downlink synchronization signal of the second cell can be fine synchronization. Before cell handover, the terminal may have performed measurements on the second cell. To complete these measurements, the terminal obtained a certain degree of synchronization with the second cell, which can be called coarse synchronization. However, the accuracy of the coarse synchronization obtained by the terminal with the second cell is insufficient to meet the transmission requirements of data / signaling during handover. Alternatively, even if the terminal obtained synchronization with the second cell before handover (e.g., for measurement), by the time of handover, some time has passed, and the synchronization accuracy cannot guarantee the data / signaling transmission requirements of the handover process. Or, the terminal may not have maintained this synchronization at all. Therefore, the terminal needs to receive the synchronization signal of the second cell to obtain fine synchronization with it.

[0252] For example, the synchronization signal of the second cell may be an SSB, or the synchronization signal of the second cell may be other synchronization signals or channels that enable the terminal to obtain downlink synchronization of the second cell. This application does not limit this.

[0253] The first time resource is used to carry the synchronization signal of the second cell. The first time resource includes at least one time unit of the second cell. The time unit can be an orthogonal frequency division multiplexing (OFDM) symbol, OFDM symbol group, time slot, subframe or frame.

[0254] The terminal can first determine the time when the first time resource arrives at the terminal, and based on the arrival time of the first time resource, determine the end time of the first time period, maintaining communication with the first cell during the first time period. That is, the first time period is located before the arrival time of the first time resource. For example, the end time of the first time period can be the arrival time of the first time resource at the terminal. Alternatively, the time interval between the end time of the first time period and the first time resource can be called the first time interval, which may include the preparation time required for the terminal to detect the synchronization signal of the second cell.

[0255] For example, the first time interval may be determined by the terminal based on the terminal's capabilities, or predefined by the protocol, or preconfigured by the network for the terminal through signaling; this application does not limit this.

[0256] It should be noted that when a terminal receives the synchronization signal from the second cell, it needs to obtain both the time-domain resources and the frequency-domain resources of the synchronization signal, i.e., the frequency point and subcarrier spacing of the synchronization signal. However, the embodiments of this application mainly involve the time-domain resources of the synchronization signal. The first time resources include at least the time-domain resources of the synchronization signal, and the first time resources may also include the frequency-domain resources of the synchronization signal.

[0257] The specific implementation methods for determining the arrival time of resources at the terminal may include, but are not limited to, the following:

[0258] Method 1: The terminal determines the arrival time of the first time resource to the terminal based on the transmission time of the first time resource in the second cell and the second signal transmission delay. The second signal transmission delay is the signal transmission delay between the second cell and the terminal.

[0259] The second signal transmission delay is the signal transmission delay between the second cell and the terminal. Specifically, it refers to the time delay between the target base station transmitting the signal from the second cell and the signal arriving at the terminal, or the transmission time or delay of the signal transmitted from the target base station to the terminal in the wireless channel. The second signal transmission delay is the one-way delay from the target base station to the terminal, that is, half of the round trip time (RTT) between the target base station and the terminal.

[0260] For example, the arrival time t of the first time resource to the terminal R-arrival The first time resource can be used to send data in the second cell at the time of transmission (denoted as t). R-Tx Add the second signal transmission delay (denoted as t) T-delay We obtain Δt T-delay t R-Tx , Δt T-delay Satisfy: t R-arrival =t R-Tx +Δt T-delay .

[0261] The terminal can obtain the transmission time of the first time resource in the second cell and the second signal transmission delay. The following section first describes how the terminal obtains the transmission time of the first time resource in the second cell.

[0262] The terminal can receive first indication information, which indicates the transmission time of the first time resource in the second cell. The terminal obtains the transmission time of the first time resource in the second cell based on the first indication information. The first indication information can come from the source base station.

[0263] In one example, the first indication information includes a first absolute time, which is used to characterize the transmission time of the first time resource in the second cell. Specifically, it can be used to characterize the start transmission time of the first time resource in the second cell. Since the accuracy of the time indicated by the first indication information is limited, the first absolute time can be an approximation of the actual transmission time of the first time resource in the second cell, which may be before or after the actual transmission time. This application does not limit this.

[0264] In another example, the first indication information can notify the terminal of the transmission time of the first time resource in the second cell by instructing the time unit of the first cell.

[0265] Since the terminal has already obtained downlink synchronization from the first cell, the terminal knows the absolute time corresponding to the time unit of the first cell. Therefore, the source base station can, based on the first signal transmission delay, indicate the time unit of the first cell through the first indication information, thus determining the transmission time of the terminal's first time resource in the second cell. For example, if the transmission start time of the first time resource in the second cell is absolute time 1, the source base station can determine, based on the first signal transmission delay and the timing sequence of the time unit of the first cell, that absolute time 1 belongs to the time of the first time unit of the first cell on the terminal side. If the start time of the first time unit of the first cell on the terminal side is absolute time 2 and the end time is absolute time 3, then absolute time 1 lies between absolute time 2 and absolute time 3. Therefore, the source base station can notify the transmission time of the first time resource by indicating the first time unit through the first indication information.

[0266] The first signal transmission delay is the signal transmission delay between the first cell and the terminal. Specifically, it refers to the time delay between the source base station transmitting the signal from the first cell and the signal arriving at the terminal, or the transmission time or delay of the signal transmitted from the source base station to the terminal in the wireless channel. For example, the first signal transmission delay can be half of the terminal's TA (Transmission Time).

[0267] Taking a time unit as a time slot as an example, if the first time unit is time slot #s in frame #f, the first indication information may include the frame number f of frame #f and the time slot number s of time slot #s. The terminal can determine, based on the frame number and the time slot number, that the transmission time of the first time resource in the second cell belongs to time slot #s in frame #f.

[0268] For example, the first indication information includes a time slot offset, which is the time slot offset between time slot #s in frame #f and the time slot where the first indication information is located. The terminal can determine time slot #s in frame #f based on the time slot where the first indication information is located and the time slot offset. Since the start time of time slot #s in frame #f is absolute time 2 and the end time is absolute time 3 on the terminal side, the terminal can determine that the transmission time of the first time resource in the second cell is between absolute time 2 and absolute time 3. The terminal can use the start absolute time 2 of time slot #s in frame #f as (approximately) the transmission time t of the first time resource in the second cell. R-Tx .

[0269] The above example uses time units as time slots, but this application is not limited to this. The granularity indicated by the first indication information can be a frame, a subframe, or an OFDM symbol.

[0270] In the embodiments of this application, the above two examples can be used to indicate a moment by means of information. The information can indicate the absolute time corresponding to the moment or indirectly indicate the moment by means of indicating the time unit of the first cell to which the absolute time of the moment belongs. This will not be elaborated further.

[0271] Optionally, the first message includes first indication information. That is, the first message not only instructs the terminal to switch from the first cell to the second cell, but also includes first indication information so that the terminal can determine the transmission time of the first time resource in the second cell based on the first indication information. However, this application is not limited to this, and the first indication information may not be included in the first message. For example, the terminal may receive the first indication information before or after the first message.

[0272] The above describes how the terminal obtains the transmission time of the first time resource in the second cell. The following describes how the terminal obtains the transmission delay of the second signal.

[0273] The terminal can obtain the ephemeris information (or NTN parameter information) of the second cell, and determine the second signal transmission delay based on the ephemeris information (or NTN parameter information) and the terminal's location information. Specifically, the location of the target base station can be determined based on the ephemeris information (or NTN parameter information), the distance between the target base station and the terminal can be determined based on the location of the target base station and the terminal's location, and the second signal transmission delay can be determined based on the distance and the signal transmission speed.

[0274] In one example, the source base station can transmit the ephemeris information (or NTN parameter information) of the second cell via broadcast or multicast in the first cell.

[0275] In another example, the terminal can obtain the ephemeris information or NTN parameter information of the target cell from the server. This allows the terminal to obtain the ephemeris information of the target cell.

[0276] Method 2: The terminal determines the arrival time of the first time resource to the terminal based on the time-domain resource information of the synchronization signal of the second cell, the transmission delay of the first signal, the transmission delay of the second signal, and the timing offset. The time-domain resource information indicates the first time resource, and the timing offset is the timing offset between the first cell and the second cell.

[0277] For example, the time-domain resource information may include period information and offset information. The period information indicates the period duration of the synchronization signal, and the offset information indicates the offset between the time unit carrying the synchronization signal and the reference time unit. For example, the period duration and offset can be identified by the number of time units. Taking a frame as the time unit and the frame number 0 as the reference time unit (denoted as frame #0, and other frames are represented in the same way) as an example, if the time-domain resource information indicates a period duration of 50 frames and an offset of 5 frames, based on the reference frame being frame #0 and the offset being 5 frames, the frame used to carry the synchronization signal in one period can be determined to be frame #5. Based on the period duration of 50 frames, the frames carrying the synchronization signal in other periods can be determined, such as frame #55, frame #105, and so on. Here, the first time resource can be a time unit used to carry the synchronization signal within one period.

[0278] The timing of time units in different cells may differ, meaning the absolute time corresponding to the same time unit number may be different. For example, the absolute time corresponding to frame #0 in the first cell may be different from that in the second cell. The first cell serves as the terminal's serving cell, and the terminal has already obtained the timing information of the first cell. The terminal knows the frame boundaries of the first cell, or in other words, the terminal knows the frame start time of the first cell, or the correspondence between the frame boundaries and absolute time. However, the terminal has not yet received the synchronization signal from the second cell, and has not yet obtained the timing information of the target cell; therefore, the frame boundaries of the second cell are unknown. Thus, even if the terminal obtains the frame number corresponding to the first time resource through the time-domain resource information of the second cell's synchronization signal, it cannot determine the absolute time corresponding to the first time resource because the frame boundaries of the target cell are unknown. The terminal can determine the absolute time when the first time resource arrives at the terminal based on the first signal transmission delay, the second signal transmission delay, and the timing offset. This will be explained in detail below.

[0279] First, the first signal transmission delay can be half of the terminal's TA (Transmission Time) in the first cell, obtained from the source base station, or half of the terminal's RTT (Round-Trip Time) with the first cell. Alternatively, the terminal can determine the first signal transmission delay based on the ephemeris information of the first cell. For details, please refer to the previously described method of determining the second signal transmission delay based on the ephemeris information of the second cell; it will not be elaborated upon here.

[0280] The terminal can receive second indication information, which indicates the timing offset between the first cell and the second cell. This timing offset is the minimum time offset between the time units of the first cell and the second cell with the same time unit number. Taking a frame as an example, this timing offset is the minimum time offset between the frames of the first cell and the second cell with the same frame number.

[0281] Optionally, the first message includes second indication information. That is, the first message not only instructs the terminal to switch from the first cell to the second cell, but also includes second indication information so that the terminal can determine the timing offset between the first cell and the second cell based on the second indication information. However, this application is not limited to this; the second indication information may not be included in the first message. For example, the terminal may receive the second indication information before or after the first message.

[0282] After the terminal obtains the time-domain resource information of the synchronization signal of the second cell, the transmission delay of the first signal, the transmission delay of the second signal, and the timing offset, the terminal can determine the arrival time of the first time resource to the terminal.

[0283] For example, the terminal can arrive at its arrival time (denoted as t) based on frame #0 of the first cell. S-arrival ) and the first signal transmission delay (denoted as Δt) S-delay Determine the transmission time of frame #0 of the first cell (denoted as t). S-Tx ), that is, the transmission time when the source base station sends the first cell frame #0. For example, t S-arrival , Δt S-delay t S-Tx Satisfy: t S-Tx =t S-arrival -Δt S-delay .

[0284] The terminal determines the timing of frame #0 transmission from the first cell and the timing offset between the first and second cells (denoted as Δt). offset The transmission time of frame #0 of the second cell can be determined, that is, the transmission time of frame #0 of the second cell sent by the target base station (denoted as t). T-Tx For example, t S-Tx , Δt offset t T-Tx Satisfy: t T-Tx =t S-Tx -Δt offset ,

[0285] In the above formula, taking the timing offset specifically as the minimum time offset between the transmission time of a frame in the first cell with the same frame number and the transmission time of a frame in the second cell as an example, if the timing offset is specifically the minimum time offset between the transmission time of a frame in the second cell with the same frame number and the transmission time of a frame in the first cell, then t S-Tx , Δt offset t T-Tx Satisfy: t T-Tx =t S-Tx +Δt offset ,

[0286] The specific timing offset can be predefined by the protocol or preconfigured by the network for the terminal via signaling. This application does not impose any limitations on this.

[0287] The terminal determines the arrival time (denoted as t) of frame #0 from the second cell to the terminal based on the transmission time of frame #0 from the second cell and the second signal transmission delay. T-arrival For example, t T-arrival , Δt T-delay t T-Tx Satisfy: t T-arrival =t T-Tx +Δt T-delay .

[0288] In summary, the arrival time of frame #0 from the second cell to the terminal can be obtained based on the following formula: t T-arrival =t S-arrival -Δt S-delay -Δt offset +Δt T-delay .

[0289] It should be understood that the arrival time of any frame of the second cell can be determined by the above formula based on the arrival time of the frame of the first cell with the same frame number, as well as the first signal transmission delay, the second signal transmission delay, and the timing offset.

[0290] Based on the time-domain resource information of the synchronization signal of the second cell and the arrival time of frame #0 of the second cell, the terminal can obtain the arrival time of the first time resource, which is frame #5 of the second cell. The arrival time and frame length of frame #0 of the second cell are used to determine the arrival time of frame #5.

[0291] It should be understood that the above is merely a specific example provided by the embodiments of this application, and this application is not limited thereto. For example, the terminal can first determine the frame number of the second cell where the time domain resources of the synchronization signal in one cycle are located, such as frame #5, based on the time domain resource information of the synchronization signal of the second cell. The terminal can determine the arrival time of frame #5 of the second cell to the terminal based on the arrival time of frame #5 of the first cell to the terminal, as well as the first signal transmission delay, the second signal transmission delay, and the timing offset, thereby determining the arrival time of the time resources in each cycle of the synchronization signal, wherein the time resources in the most recent cycle can be the first time resources.

[0292] It should be noted that the above examples are based on frames as the unit of time. In reality, time-domain resource information can be applied to finer time units, such as subframes, time slots, and symbols, to meet the needs of different application scenarios. This will not be elaborated on here.

[0293] Method 3: The terminal can receive third indication information from the source base station, which is used to indicate the arrival time of the first time resource to the terminal.

[0294] The source base station can determine the arrival time of the first time resource to the terminal based on the transmission time of the first time resource in the second cell and the second signal transmission delay, and then notify the terminal through the third indication information.

[0295] In one example, the source base station can obtain the ephemeris information (or NTN parameter information) and terminal location information of the second cell to determine the second signal transmission delay, thereby determining the arrival time of the first time resource to the terminal. Specifically, the source base station can obtain the ephemeris information (or NTN parameter information) of the second cell from the target base station, core network, or server.

[0296] In another example, the source base station can obtain the second signal transmission delay from the terminal. Once the terminal determines the second signal transmission delay, it notifies the source base station of this delay, enabling the source base station to determine the arrival time of the first time resource at the terminal. The method by which the terminal determines the second signal transmission delay can be found in the preceding description and will not be repeated here.

[0297] In another example, the source base station can obtain the transmission delay deviation from the terminal. This transmission delay deviation is the difference between the transmission delay of the first signal and the transmission delay of the second signal. The source base station knows the transmission delay of the first signal and can determine the transmission delay of the second signal based on the transmission delay deviation, thereby determining the arrival time of the first time resource to the terminal.

[0298] In this method 3, the terminal can determine the arrival time of the first time resource based on the third indication information, and thus determine the first time period based on the arrival time.

[0299] Optionally, the first message includes third indication information. That is, the first message not only instructs the terminal to switch from the first cell to the second cell, but also includes third indication information so that the terminal can determine the arrival time of the first time resource based on the third indication information. However, this application is not limited to this, and the third indication information may not be included in the first message. For example, the terminal may receive the third indication information before or after the first message.

[0300] The above examples illustrate three methods for a terminal to determine the arrival time of a first time resource. It should be understood that this application is not limited to these methods, and the terminal may also use other methods to determine the arrival time of the first time resource. Based on the arrival time of the first time resource, the terminal determines the end time of a first time period, maintaining communication with the first cell during this first time period after receiving the first message and before receiving the synchronization signal from the second cell.

[0301] According to this second embodiment, the terminal maintains a communication connection with the first cell during a first time period after receiving the first message and before receiving the synchronization signal from the second cell. This reduces the terminal's communication interruption time, decreases the probability of terminal service interruptions or dropped calls, and improves communication reliability.

[0302] In the third implementation method, the terminal receives a fourth indication information from the source base station, which is used to indicate the first time period.

[0303] Referring to the introduction of Method 3 above, the source base station can determine the arrival time of the first resource to the terminal, and the source base station can also determine the arrival time of the first message to the terminal based on the first signal transmission delay. Therefore, the source base station can determine the first time period and notify the terminal through the fourth indication information.

[0304] For example, the fourth indication information may include the duration of the first time period (or the end time of the first time period). The terminal receives the first message as the start time of the first time period, and the first time period can be determined based on the duration of the first time period (or the end time of the first time period). However, this application is not limited to this. The fourth indication information may include at least two of the start time, duration, and end time of the first time period, so that the terminal can determine the start time and end time of the first time period based on the fourth indication information without using the arrival time of the first message as a reference.

[0305] Optionally, the first message includes fourth indication information. That is, the first message not only instructs the terminal to switch from the first cell to the second cell, but also includes fourth indication information so that the terminal can determine the first time period based on the fourth indication information. However, this application is not limited to this; the fourth indication information may not be included in the first message. For example, the terminal may receive the fourth indication information before or after the first message.

[0306] According to this third implementation method, the terminal can directly obtain the first time period through the fourth indication information and maintain a communication connection with the first cell during the first time period. This can reduce the terminal's communication interruption time, reduce the probability of terminal service interruption or dropped calls, and improve communication reliability.

[0307] The above describes the specific implementation method for the terminal to maintain a communication connection with the first cell during the first time period. The following describes the specific implementation method for the source base station to maintain a communication connection with the terminal through the first cell during the second time period.

[0308] Optionally, the source base station maintains communication connectivity with the first cell during the second time period, including: the source base station continues to provide data transmission services to the terminal through the first cell during the second time period. Wherein, the source base station continuing to provide data transmission services to the terminal through the first cell during the second time period includes the source base station performing one or more of the following:

[0309] 1) The source base station does not release the UE context of the terminal.

[0310] 2) The source base station sends downlink control information (DCI) to the terminal.

[0311] 3) The source base station sends data and / or information to the terminal.

[0312] 4) The source base station receives data and / or information from the terminal.

[0313] The above items can be referred to in the previous introduction, and will not be repeated here.

[0314] In implementation method A, the second time period specifically includes the period between the source base station sending the first message and receiving the third message. The third message is used to indicate that the terminal has completed the handover to the second cell.

[0315] For example, the third message may be a UE context release message from the target base station for the terminal.

[0316] In other words, the source base station can determine the end time of the second time period based on the third message. The source base station can maintain the communication connection between the first cell and the terminal before receiving the third message. For example, the end time of the second time period can be the moment the source base station successfully receives the third message or a moment after that. However, this application is not limited to this; the end time of the second time period can also be before the third message.

[0317] It should be understood that this implementation method A can be applied to cell handover without a random access procedure, or to cell handover based on a random access procedure. This application does not limit it in this regard.

[0318] In implementation method B, the source base station can determine the arrival time of the first time resource to the terminal, and determine the second time period based on the arrival time.

[0319] In this implementation method B, the second time period can be the same as the first time period, that is, the source base station and the terminal determine the time period for maintaining the communication connection in the same way. Alternatively, the source base station determines the time period for maintaining the communication connection and then notifies the terminal, such as when the terminal uses the implementation method three described above. Specifically, the source base station determines the arrival time of the first time resource to the terminal, which can be referred to in the previous description. The method by which the source base station determines the second time period based on the arrival time of the first time resource to the terminal can be referred to the method for determining the first time period described in implementation method three above, and will not be repeated here.

[0320] According to the above implementation method, the source base station can maintain the communication connection between the first cell and the terminal during the second time period, and continue to provide data transmission services to the terminal during the second time period, which can reduce the communication interruption time of the terminal. This reduces the probability of problems such as terminal service interruption or dropped calls, and improves the reliability of communication.

[0321] S603, the terminal sends a second message to the target base station, which indicates that the handover to the second cell has been successful.

[0322] After the first time period, the terminal detects the downlink synchronization signal of the second cell to obtain downlink synchronization with the second cell. Then, according to the network's instructions, it performs a handover to the second cell using either a no-random access procedure or a random access procedure. The terminal sends a second message to the target base station, and the target base station receives the second message to confirm that the terminal has successfully handed over to the second cell.

[0323] For example, the second message could be an RRC reconfiguration complete message.

[0324] S604, the target base station sends a third message to the source base station, which is used to indicate that the terminal has completed the handover to the second cell.

[0325] Accordingly, the source base station receives a third message from the target base station, and determines that the terminal has completed the handover to the second cell based on the third message. Optionally, the source base station can release the terminal's UE context based on the third message.

[0326] Optionally, the third message may be a UE context release message from the target base station to the terminal. However, this application is not limited to this; the third message may be sent to the terminal by the target base station before the UE context release message.

[0327] According to the above scheme, after the source base station and the terminal transmit the handover command, they can maintain the communication connection of the serving cell for a period of time. During this period, the serving cell continues to provide data transmission services to the terminal. This reduces the handover interruption time during the terminal's handover from the source cell to the target cell, helping to reduce the probability of terminal service interruptions or dropped calls, and improving communication reliability.

[0328] Figure 7 illustrates the interruption duration of the terminal during the handover process in the communication method provided in this application embodiment. The first time period is the time during which the terminal maintains a communication connection with the first cell. The current interruption duration is the duration of service interruption during the terminal's handover process, from the time the terminal disconnects its communication connection with the first cell before the arrival time of the first time resource until the handover is complete. In other words, it is the duration from the time the terminal disconnects its communication connection with the first cell until the handover is complete (as shown in Figure 7, the current interruption duration). Compared to the service interruption duration after the terminal immediately disconnects its communication connection with the first cell upon receiving the handover command until the handover is complete (as shown in Figure 7, the original interruption duration), the solution provided in this application shortens the service interruption time caused by cell handover, helping to reduce the probability of terminal service interruptions or dropped calls, and improving communication reliability.

[0329] Figure 7A is a specific example of the embodiment shown in Figure 6. The following description uses the example of the first message being an RRC reconfiguration message and the second message being an RRC reconfiguration completion message, combined with the terminal handover process shown in Figure 7A. The steps before S701 in Figure 7A can be referred to the previous description of the corresponding steps in Figure 5, and the parts in Figure 7A that are the same as those in the embodiment shown in Figure 6 can be referred to the description in the embodiment shown in Figure 6, and will not be repeated here.

[0330] S701, the source base station sends an RRC reconfiguration message to the terminal (i.e., the RRC reconfiguration message is an example of the first message). Accordingly, the terminal receives the RRC reconfiguration message from the source base station.

[0331] S702, the terminal determines to maintain a communication connection with the first cell during the first time period. The source base station determines to maintain a communication connection with the terminal in the first cell during the second time period.

[0332] For example, the first time period and the second time period can be located between S702 and S705. Regarding the above-described Embodiment 2 and Embodiment B, where the terminal performs cell handover based on a random access procedure, the first time period can specifically be between S702 and S704, and the second time period can specifically be between S702 and S706, or between S702 and S710. However, this application is not limited to these.

[0333] Optionally, in S703, the source base station sends an SN state transition message to the target base station.

[0334] After the source base station sends the RRC reconfiguration message, it can notify the target base station of the terminal's current SN status through the SN state transition message.

[0335] However, the source base station and the terminal maintain a communication connection during the second time period. During this second time period, the source base station receives terminal data from the terminal via the UPF and continues to send this terminal data to the terminal. Optionally, the source base station may also send the terminal data to the target base station. It should be understood that the source base station may also choose not to execute S703.

[0336] Optionally, in S704, the terminal receives the synchronization signal of the second cell in the first time, sends a random access preamble to the second cell, and receives the random access response message from the second cell.

[0337] If the terminal performs a cell handover based on a random access procedure, the terminal executes S704; if the terminal performs a cell handover without a random access procedure, the terminal does not execute S704.

[0338] S705, the terminal sends an RRC reconfiguration complete message to the target base station. Correspondingly, the target base station receives the RRC reconfiguration complete message from the terminal.

[0339] In one optional implementation, in S706, the target base station sends a handover success message to the source base station (i.e., the handover success message is an example of a third message). The source base station receives the handover success message from the target base station and determines that the terminal has successfully handed over to the second cell.

[0340] Optionally, the source base station releases the UE context of the terminal. For example, if S710 is not included in the handover procedure, the source base station releases the UE context of the terminal after S706. If S710 is included in the handover procedure, the source base station does not release the UE context of the terminal after S706.

[0341] Optionally, after executing S706, the source base station can execute S707, in which the source base station sends an SN state transition message to the target base station to notify the target base station of the current SN state of the terminal.

[0342] S708, the target base station sends a path switching request to the AMF.

[0343] S709, AMF sends a path switching request confirmation to the target base station.

[0344] After receiving the path handover request confirmation message from the AMF, the target base station confirms that the path handover of the terminal on the network side has been completed.

[0345] In another optional implementation, in S710, the target base station sends a UE context release message to the source base station (i.e., the UE context release message is another example of a third message). After receiving the UE context release message from the target base station, the source base station releases the UE context of the terminal.

[0346] Optionally, after executing S710, the source base station can execute S711, in which the source base station sends an SN state transition message to the target base station to notify the target base station of the current SN state of the terminal.

[0347] In another alternative implementation, the target base station may execute both S706 and S710, and this application does not limit this.

[0348] According to the above scheme, after the source base station and the terminal transmit the handover command, they can maintain the communication connection of the serving cell for a period of time. During this period, the serving cell continues to provide data transmission services to the terminal. This reduces the handover interruption time during the terminal's handover from the source cell to the target cell, helping to reduce the probability of terminal service interruptions or dropped calls, and improving communication reliability.

[0349] The following describes how, in the embodiment shown in Figure 7A, the source base station and the target base station transmit the downlink data of the terminal after the network side determines that the terminal has switched from the first cell to the second cell.

[0350] As described above, after the source base station sends a handover command, if the source base station receives downlink data from the terminal from the UPF, the source base station continues to send the terminal data to the terminal. After S701, whether the source base station sends the downlink data received from the UPF to the target base station can be implemented in two ways, including but not limited to the following, which will be described in detail below.

[0351] In one implementation, after S701, the source base station continuously forwards downlink data to the target base station. After the source base station learns that the terminal handover is successful (such as in S706 or S710), it stops sending downlink data to the terminal (or stops downlink scheduling of the terminal) and stops forwarding the terminal's downlink data to the target base station.

[0352] In this implementation, the source base station can send SN state transition messages to the target base station multiple times. For example, the source base station can execute at least two of steps S703, S707, and S711 to send SN state transition messages to the target base station two or three times.

[0353] The first SN state transition message sent by the source base station to the target base station includes a COUNT, which consists of the PDCP SN number and the superframe number. This COUNT is used by the target base station to determine which SDU the source base station is forwarding to the target base station from. In other words, the first SN state transmission message contains the COUNT of the first downlink SDU forwarded by the source base station to the target base station.

[0354] Following the initial SN status transmission message, the source base station sends a SN status transmission message to the target base station containing a COUNT. This COUNT is used by the target base station to discard / clear downlink SDUs that the source base station has successfully transmitted to the terminal, allowing the target base station to free up memory. This is because the source base station and the terminal still maintain a communication connection within the first cell and are still providing data transmission services to the terminal through the first cell. Therefore, which data has been transmitted and which has not been transmitted by the source base station is dynamically changing.

[0355] The PDCP SN number included in the last SN state transition message sent by the source base station to the target base station is the PDCP SN corresponding to the first SDU in the SDUs to be transmitted by the target base station to the terminal. Since the source base station will no longer forward data to the target base station after sending the last SN state transition message, it transfers the right to allocate SNs to the target base station. Therefore, which data was transmitted and which was not transmitted by the source base station is fixed and will not change.

[0356] The first and last SN state transition messages sent by the source base station can be determined based on which steps in S703, S707, and S711 were executed by the source base station in the specific implementation.

[0357] In another implementation, after S701, the source base station does not forward downlink data to the target base station. Optionally, the source base station does not execute S703, that is, it does not send the SN state transition message in S703 to the source base station. After the source base station learns that the terminal handover is successful (e.g., in S706 or S710), it stops sending downlink data to the terminal (or stops downlink scheduling for the terminal), and forwards downlink data that was not successfully transmitted to the terminal to the target base station, and sends the SN state transition message to the target base station (e.g., in S707 or S711).

[0358] In some scenarios, a communication interface (such as the Xn interface) may be established between a source base station and a target base station. Without this interface, the source and target base stations cannot directly exchange information. The handover process requires data and signaling forwarding through the core network between the source base station (the network equipment managing the first cell) and the target base station (the network equipment managing the second cell).

[0359] Figure 8 is a flowchart illustrating the communication method 800 provided in an embodiment of this application. It should be understood that this method 800 shows message transmission between the source base station and the target base station via AMF. The contents of each message, and other parts identical to those shown in the embodiments of Figures 5, 6, and 7A, can be implemented with reference to the preceding description and will not be repeated here. The method 800 includes the following steps:

[0360] S801, the source base station sends measurement configuration information to the terminal.

[0361] S802, the terminal sends a measurement report to the source base station.

[0362] It is understandable that the relevant descriptions of S801-S802 can be found in the relevant descriptions of S501-S502, and will not be repeated here.

[0363] It should be understood that if the source base station and the target base station may not be able to communicate directly, the source base station can execute S803.

[0364] S803, the source base station sends a handover request message to the AMF, and the AMF forwards the handover request message from the source base station to the target base station.

[0365] S804, the target base station sends a handover request confirmation message to the AMF, and the AMF forwards the handover request confirmation message from the target base station to the source base station.

[0366] S805, the source base station sends an RRC reconfiguration message containing a handover command to the terminal (i.e., the RRC reconfiguration message is an example of the first message).

[0367] S806, the terminal determines to maintain a communication connection with the first cell during the first time period. The source base station determines to maintain a communication connection with the terminal in the first cell during the second time period.

[0368] S807, the source base station sends an SN state transition message to the AMF, and the AMF forwards the SN state transition message from the source base station to the target base station.

[0369] Optionally, in S808, the terminal sends a random access preamble (MSG1) to the target base station.

[0370] Optionally, in S809, the target base station sends a random access response message (MSG2) to the terminal.

[0371] S810, the terminal sends an RRC reconfiguration complete message to the target base station (i.e., the RRC reconfiguration complete message is an example of the second message).

[0372] S811, the target base station sends a handover success message to the AMF.

[0373] After receiving a handover success message from the target base station, the AMF can notify the terminal that it has now connected to the target base station.

[0374] S812, AMF sends a UE context release message to the source base station.

[0375] After receiving the UE context release message from the AMF, the source base station releases the UE context of the terminal.

[0376] Alternatively, S812 can be replaced with: AMF sends a third UE message to the source base station (i.e., the UE context release message is an example of a third message).

[0377] Correspondingly, after receiving the UE context release message from the AMF, the source base station releases the UE context of the terminal.

[0378] S813, the source base station sends an SN state transition message to the AMF, and the AMF forwards the SN state transition message to the target base station.

[0379] S814, the source base station sends a UE context release complete message to the AMF.

[0380] The following describes the method by which the source base station and the target base station transmit the downlink data of the terminal after the network side determines that the terminal has switched from the first cell to the second cell in the embodiment shown in Figure 8. The relevant description in the embodiment shown in Figure 7A above can be referred to. The difference between the embodiment shown in Figure 8 and the embodiment shown in Figure 7 is that the source base station sends the downlink data of the terminal to the target base station through the UPF, and the source base station sends the SN state transition message to the target base station through the AMF.

[0381] The above describes a scenario where a terminal performs handover between cells managed by different base stations (referred to as inter-station handover). A terminal can also perform handover between different cells managed by the same base station (referred to as intra-station handover). For example, a base station (gNB) may include a gNB control unit (CU) and multiple gNB distributed units (DUs). gNB-CUs and gNB-DUs can communicate through an interface, which can be referred to as F1.

[0382] The CU can be used to process the higher layers of the protocol stack, which include: the Service Data Adaptation Protocol (SDAP), used for mapping and managing Quality of Service (QoS) streams; the Packet Data Convergence Protocol (PDCP), which provides functions such as data compression, encryption, integrity protection, and retransmission; and the Relay Rate Control (RRC), which is responsible for signaling, connection management, mobility management, etc.

[0383] DU can be used to process the lower layers of the protocol stack, which include: radio link control (RLC): responsible for data segmentation, reassembly, error detection and correction; medium access control (MAC): responsible for scheduling, priority management and resource allocation; and physical layer: responsible for the actual transmission and reception of data.

[0384] Therefore, during the handover process, the source cell and the target cell may be different cells managed by the same base station. This can be understood as the target cell mentioned earlier also being a cell managed by the source base station, which is the same as the source base station. Different cells of the same base station may correspond to the same DU or different DUs. For ease of distinction, the DU corresponding to the source cell will be referred to as the source DU, and the DU corresponding to the target cell will be referred to as the target DU.

[0385] It should be noted that in the embodiments of this application, the function of the source base station can be implemented by the source DU, and the function of the target base station can be implemented by the target DU. The source DU and the target DU can be different DUs of the same base station or the same DU. In specific implementations, the corresponding data / signaling transmission method can be through the CU or direct transmission between the source DU and the target DU.

[0386] In intra-station handover scenarios, the terminal and the source DU can maintain a communication connection for a period of time after exchanging RRC reconfiguration messages.

[0387] To facilitate understanding, the following section, with reference to Figure 9, describes the process of a terminal switching between different DUs within the same base station.

[0388] Figure 9 is a flowchart illustrating the communication method 900 provided in an embodiment of this application. It should be understood that, unless otherwise specified, the content of each message in this method 900 that is the same as or similar to the embodiments shown in Figures 5, 6, 7A, and 8 can be implemented with reference to the preceding description, and will not be repeated here. As shown in Figure 9, method 900 includes the following steps:

[0389] Prior to S901, the CU transmitted uplink and downlink data to the terminal via the source DU.

[0390] S901, CU sends measurement configuration to the terminal via source DU.

[0391] S902, the terminal sends a measurement report to the CU.

[0392] Upon receiving the measurement report, the CU makes a handover decision based on the measurement results. If a handover terminal is determined, the CU identifies the target cell. If the target cell and the serving cell belong to different DUs within the same base station, the CU determines to initiate the intra-base station cross-DU cell handover procedure, and the CU executes S903.

[0393] S903, the CU sends a UE context establishment request message to the target DU.

[0394] The CU sends a UE context establishment request message to the target DU to request resources for the terminal from the target DU. This UE context establishment request message may include the target cell identifier, the terminal's identifier at the source base station, terminal capability information, etc.

[0395] S904, the target DU sends a UE context establishment response message to the CU, which includes the information required for the terminal to access the target DU.

[0396] If the target DU successfully allocates resources to the terminal, the target DU sends a UE context establishment response message to the CU, which contains the information required for the terminal to access the target cell.

[0397] S905, the CU sends a UE context modification request message to the source DU.

[0398] After receiving the UE context establishment response message from the target DU, the CU generates a UE context modification request message based on the UE context establishment response message. This UE context modification request message can be used to instruct the terminal to hand over from the source DU to the target DU. For example, the UE context modification request message includes an RRC reconfiguration message, which includes a handover command to instruct the terminal to hand over from the source cell to the target cell.

[0399] In the current intra-cell handover process, the RRC reconfiguration message includes an indication that the source DU should stop L2 scheduling (i.e., indicate that the terminal's data transmission should be stopped). However, in method 900, the RRC reconfiguration message does not include an indication that the source DU should stop the terminal's data transmission. Optionally, the RRC reconfiguration message includes another indication that instructs the source DU to continue data transmission or not to stop transmitting terminal data.

[0400] S906, the source DU sends an RRC reconfiguration message containing a handover command to the terminal (i.e., the RRC reconfiguration message is an example of the first message).

[0401] After receiving a UE context modification request message from the CU, the source DU can send an RRC reconfiguration message to the terminal based on the UE context modification request message.

[0402] S907, the terminal determines to maintain a communication connection with the first cell during the first time period. The source base station determines to maintain a communication connection with the terminal in the first cell during the second time period.

[0403] S908, the source DU sends a UE context modification response message to the CU.

[0404] After receiving a UE context modification request message from the CU, the source DU can send downlink data status and UE context modification response messages to the CU.

[0405] Optionally, in S909, the terminal sends a random access preamble (MSG1) to the target DU.

[0406] Optionally, in S910, the target DU base station sends a random access response message (MSG2) to the terminal.

[0407] S911, the terminal sends an RRC reconfiguration complete message to the target DU (i.e., the RRC reconfiguration complete message is an example of the second message).

[0408] S912, the target DU sends an uplink RRC message transmission message (RRC reconfiguration complete message) to the CU.

[0409] S913, the CU sends a UE context release message to the source DU.

[0410] After receiving the UE context release message, the source DU releases the UE context.

[0411] S914, the source DU sends downlink data status to the CU.

[0412] It should be understood that in the embodiments shown in Figures 6 to 9, after the terminal transmits the first message to the source base station, the terminal and the source base station maintain a communication connection between the first cell and the terminal for a period of time. This method reduces handover interruption time during the terminal's handover from the source cell to the target cell, helping to reduce the probability of terminal service interruptions or dropped calls, and improving communication reliability.

[0413] In the embodiment shown in Figure 9, after receiving the UE context modification request message from the CU (i.e., S905 or S906), the source DU continues to send the downlink data received from the CU to the terminal. After the source DU learns that the terminal handover was successful (i.e., S913), the source DU stops sending downlink data to the terminal (or stops downlink scheduling for the terminal). Between S905 and S913, the source DU can send downlink data status messages (or downlink data transmission status messages) to the CU at any time.

[0414] For the target DU, if the terminal performs a cell handover based on a random access procedure, during the random access procedure (S909 to S910), as shown in Figure 9, the target DU can send a downlink data status message to the CU. Correspondingly, the terminal sends a data transmission status message to the target DU during the random access procedure; for example, this data transmission status is included in at least one of the msgA, msg3, or other messages sent by the terminal. This data transmission status message indicates which data has not yet been successfully transmitted. After determining that the terminal handover is successful (i.e., S913), if the target DU has downlink data to be sent to the terminal, the target DU will send this downlink data to the terminal.

[0415] After sending a UE context modification request message to the source DU (S905), the CU continues to send downlink data of the terminal to the source DU. The CU can also send the downlink data of the terminal sent to the source DU to the target DU; the specific timing and amount of data sent depend on the CU's implementation. All downlink data status messages received by the CU from the source DU can be forwarded to the target DU, or it can be understood that the source DU forwards downlink data status messages to the target DU through the CU. After the CU learns that the terminal handover was successful (S912), or after the CU receives a downlink data status message from the target DU, the CU stops sending downlink data of the terminal to the source DU. However, if the CU had not previously sent downlink data of the terminal to the target DU, the CU begins sending downlink data that the terminal has not received to the target DU, so that the target DU can then send it to the terminal.

[0416] The above describes the method by which the source DU and target DU transmit downlink data of the terminal after the CU determines that the terminal is performing an intra-station handover in the embodiment shown in Figure 9.

[0417] The terminal receives a first message in the source cell. This first message includes a handover command. For intra-site handover scenarios, this first message comes from the source DU; for inter-site handover scenarios, this first message comes from the source base station. As described above, the handover command can include information required for the terminal to access the target cell. Specifically, the handover command mainly includes measurement configuration (i.e., the neighboring cell measurement configuration of the target cell after the terminal hands over to the target cell), mobility control information (including configurations related to cell handover, such as T304 timing and whether to execute random access indication information), common radio resource configuration information of the target cell (mainly used for the terminal to perform RRC connection reconstruction or re-access the target cell in the event of handover failure), and dedicated radio resource configuration of the target cell (used to configure resources or channels, on which the terminal can perform data / signaling transmission when accessing the target cell).

[0418] In certain satellite communication scenarios, poor link quality can limit air interface signaling transmission capacity, meaning the data / signaling payload transmitted per unit of time resources is limited. This can cause a single message to require multiple time resources for transmission. In such cases, the first message sent from the source base station to the terminal may take a long time. This can also result in prolonged service interruptions for the terminal during the handover process.

[0419] In one possible implementation, the handover command can be simplified (or streamlined). The simplified handover command may contain only necessary configurations, such as mobility control information and the target cell's dedicated radio resource configuration. Alternatively, the handover command may not include measurement configuration and common radio resource configuration information for the target cell. After the terminal accesses the target cell, it can obtain the measurement configuration and common radio resource configuration information for the target cell through the RRC connection reconfiguration message received in the target cell. For intra-site handover scenarios, this RRC connection reconfiguration message comes from the CU, meaning the CU sends this RRC reconnection configuration message to the terminal through the DU corresponding to the target cell. For inter-site handover scenarios, this RRC connection reconfiguration message comes from the target base station.

[0420] When the link quality of the communication network is poor, simplifying the handover command can reduce the time spent transmitting the handover command. In this way, when the terminal hands over from the source cell to the target cell, the duration of terminal service interruption can be reduced.

[0421] It should be understood that due to differences in the hardware / software capabilities of terminals, or the different protocols or standards supported by the terminals, different terminals may support simplified handover commands differently. Some terminals may support simplified handover commands, while others may not. Therefore, the terminal can report capability information to the source base station, which indicates whether the terminal supports simplified handover commands. For example, this capability information can indicate whether the terminal supports simplified handover commands explicitly or implicitly. For instance, if the capability information indicates a first preset value using at least one bit, it means the terminal supports simplified handover commands; if the at least one bit indicates a second preset value, it means the terminal does not support simplified handover commands. For implicit indication, for example, the capability information can specifically indicate the terminal type. By understanding the correspondence between terminal type and whether simplified handover commands are supported, it can be determined whether the terminal supports simplified handover commands, such as consumer terminals or dedicated terminals supporting simplified handover commands. As another example, the capability information can indicate the service rate capability supported by the terminal. Based on the correspondence between service rate capability and whether simplified handover commands are supported, it can be determined whether the terminal supports simplified handover commands, such as terminals supporting low service rates supporting simplified handover commands. This application does not limit this.

[0422] For intra-site handover scenarios, the CU can determine whether a simplified handover command needs to be sent to the terminal based on the capability information and / or link quality reported by the terminal.

[0423] For inter-site handover scenarios, the target base station or the source base station can determine whether to send a simplified handover command to the terminal based on the capability information and / or link quality reported by the terminal.

[0424] For example, the target base station can determine whether the source base station needs to send a simplified handover command to the terminal based on the capability information and / or link quality reported by the terminal. In this case, the handover request confirmation message sent by the target base station to the source base station may include mobility control information and the target cell's dedicated radio resource configuration, but not measurement configuration and the target cell's public radio resource configuration information. The capability information and / or link quality reported by the terminal can be obtained by the target base station from the source base station.

[0425] For example, the source base station can determine to send a simplified handover command to the terminal based on the capability information and / or link quality reported by the terminal. Upon receiving a handover request confirmation message from the target base station, the source base station can generate either a non-simplified handover command or a simplified handover command based on this message. For instance, it can obtain mobility control information and the target cell's dedicated radio resource configuration from the handover request confirmation message to generate a simplified handover command, while omitting the measurement configuration and common radio resource configuration information of the target cell from the handover request confirmation message. After determining to send a simplified handover command to the terminal based on the capability information and / or link quality reported by the terminal, the source base station generates a simplified handover command based on the handover request confirmation message and sends it to the terminal.

[0426] For example, the simplified switching command can be carried in an RRC message or in a MAC CE.

[0427] Figure 9A is a schematic flowchart of a communication method 900A provided in an embodiment of this application. Method 900A describes a scenario where a terminal performs intra-site cell handover, i.e., the terminal hands over from a cell corresponding to one DU (Distributed Cell Unit) of a base station to a cell corresponding to another DU. The source DU sends a handover command to the terminal via the MAC CE. Method 900A includes, but is not limited to, the following steps:

[0428] S921, CU performs switching judgment.

[0429] The CU performs a handover determination to determine whether the terminal will perform an intra-station cross-DU cell handover. The implementation method of S921 can be referred to the relevant description of method 900, and will not be repeated here.

[0430] S922, the CU sends a handover notification message to the source DU.

[0431] Accordingly, the source DU receives the handover notification message from the CU. This handover notification message is used to instruct the terminal to hand over from the first cell to the second cell.

[0432] The handover notification message may be called a beam handover notification message or a cell handover notification message. Alternatively, the handover notification message may be a UE context modification request message. This application does not limit the type of message.

[0433] S923, the source DU generates a MAC CE containing the handover command based on the handover notification message.

[0434] The handover command in the MAC CE can include the target cell's frequency information, channel information, and the terminal's identification information in the target cell.

[0435] The handover command can be either the simplified handover command described above or a non-simplified handover command. The source base station can determine whether to simplify the handover command based on the capability information and link quality reported by the terminal.

[0436] S924, the source DU sends the MAC CE to the terminal. Accordingly, the terminal receives the MAC CE from the source DU.

[0437] Optionally, in S925, the terminal determines to maintain a communication connection with the first cell during a first time period. The base station determines to maintain a communication connection with the terminal in the first cell during a second time period.

[0438] S926, the terminal sends a handover completion message to the target DU.

[0439] This handover completion message indicates that the terminal has successfully handed over to the second cell. This handover completion message can be carried in the MAC CE sent by the terminal to the target DU.

[0440] S927, the target DU generates an uplink RRC message based on the handover completion message.

[0441] The UL RRC transfer message is used to indicate that the terminal has successfully switched to the second cell.

[0442] Since the handover completion message is carried in the MAC CE, and the CU is not responsible for processing MAC layer signaling, it cannot interpret the MAC CE. Therefore, the target DU needs to generate a UL RRC transfer message that the CU can interpret based on the MAC CE, so as to notify the terminal to complete the cell handover by using the UL RRC transfer message.

[0443] S928, the target DU sends a UL RRC transmission message to the CU. Accordingly, the CU receives the UL RRC transmission message from the target DU.

[0444] S929, the CU sends an RRC connection reconfiguration message containing measurement configuration to the terminal. Correspondingly, the terminal receives this RRC connection reconfiguration message from the CU and obtains the measurement configuration for the second cell.

[0445] This application also provides another solution to reduce terminal communication interruption time caused by handover. Specifically, the embodiments of this application propose that the target base station can determine the arrival time of the first time resource to the terminal, and the target base station can select an appropriate time to send a message instructing the terminal to handover to the target cell based on the determined arrival time of the first time resource. This allows the terminal to receive the handover command shortly before the first time resource, enabling the terminal to quickly search for the synchronization signal of the target cell and complete the handover process after receiving the handover command. This reduces the communication interruption time of the terminal when handing over from the first cell (i.e., the source cell) to the second cell (i.e., the target cell). The following description is in conjunction with Figure 10.

[0446] Figure 10 is a schematic flowchart of a communication method 1000 provided in an embodiment of this application. It should be understood that the parts of method 1000 that are the same as those in method 600 and method 800 are only briefly described or not described further; for details, please refer to the descriptions of method 600 and method 800 above. Method 1000 includes, but is not limited to, the following steps:

[0447] S1001, the target base station determines the first time based on the first time resource. The first time resource is used to carry the synchronization signal of the second cell. The first time is the time to send the fifth message. The fifth message is used to instruct the terminal to switch to the second cell or contains the configuration information of the terminal switching to the second cell.

[0448] The target base station can determine the first time to send the fifth message based on the first time resource for sending the synchronization signal of the second cell. This aims to shorten the interval between the arrival of the handover command at the terminal and the first time resource, allowing the terminal to quickly detect the synchronization signal of the second cell after receiving the handover command. This ensures that even if the terminal stops data transmission in the serving cell (i.e., the first cell) or disconnects its communication connection with the serving cell after receiving the handover command, it can avoid excessively long communication interruptions.

[0449] Optionally, the target base station determines the first moment based on the first time resources, including: the target base station determines the first duration based on the first time resources and one or more of the following information:

[0450] Terminal location information;

[0451] First signal transmission delay;

[0452] Second signal transmission delay;

[0453] The third signal transmission delay is the signal transmission delay between the source base station and the target base station;

[0454] Message processing latency of the source base station;

[0455] Terminal message processing latency;

[0456] Timing offset between the first cell and the second cell.

[0457] For example, the target base station transmits at time t in the second cell based on the first time resource. T-Tx Second signal transmission delay Δt T-delay It is possible to determine the arrival time t of the first resource to the terminal. T-arrival For example, t T-arrival , Δt T-delay t T-Tx Satisfy: t T-arrival =t T-Tx +Δt T-delay .

[0458] The terminal needs resources to arrive at the terminal at the arrival time t as soon as possible. T-arrival Previously, upon receiving an RRC reconfiguration message containing a handover command, the target base station determined the arrival time t. T-arrival Message processing latency Δt at the terminal UE-proc To determine if the RRC reconfiguration message needs to be sent at least t S-arrival Previously, upon arrival at the terminal, t, for example S-arrival , Δt UE-proc and t T-arrival Satisfy: t S-arrival =t T-arrival -Δt UE-proc .

[0459] Considering the transmission delay of the RRC reconfiguration message, i.e., the first signal transmission delay Δt S-delay The latest time t that the source base station sent the RRC reconfiguration message can be determined. T-Tx For example, t S-Tx , Δt S-delay t S-arrival Satisfy: t S-Tx =t S-arrival -Δt S-delay .

[0460] After the target base station sends the fifth message to the source base station, the fifth message needs to undergo a signal transmission delay Δt between the source base station and the target base station. T-S-delay That is, the third signal arrives at the source base station after a transmission delay. After receiving the fifth message, the source base station obtains the RRC reconfiguration message based on the fifth message. Therefore, the source base station still needs a message processing delay Δt between receiving the fifth message and sending the RRC reconfiguration message. S-proc Therefore, the latest transmission time t1 of the target base station to send the fifth message can be determined. For example, t1 and ΔtT-S-delay , Δt S-proc and t S-Tx Satisfy: t1 = t S-Tx -Δt S-proc -Δt T-S-delay .

[0461] In summary, the latest transmission time t1 of the target base station to send the fifth message can be determined based on the following formula: t1 = t T-Tx +Δt T-delay -Δt UE-proc -Δt S-delay -Δt S-proc -Δt T-S-delay .

[0462] The target base station can determine the transmission time of the fifth message, i.e., the first moment, based on the latest transmission time t1 of the fifth message. For example, the first moment can be t1-Δt. res , where Δt res ≥0, Δt res A relatively short margin of time is reserved for the target base station.

[0463] It should be understood that the above is only a specific example provided by the embodiments of this application, and this application is not limited thereto. The target base station may also use other methods to determine the sending time of the fifth message, that is, the first moment.

[0464] The following is an exemplary description of how the target base station obtains the parameters used to determine the first moment. It should be understood that this application is not limited thereto.

[0465] The target base station may obtain the first signal transmission delay in the following ways, including but not limited to:

[0466] In one implementation, the target base station can obtain a first signal transmission delay from the source base station. For example, the sixth message sent by the source base station to the target base station may include indication information for indicating the first signal transmission delay.

[0467] In another implementation, the first signal transmission delay can be determined by the target base station.

[0468] For example, the source base station can send terminal location information to the target base station, and the target base station can determine the first signal transmission delay based on the ephemeris information (or NTN parameter information) of the source base station and the terminal location information. The target base station can obtain the ephemeris information (or NTN parameter information) of the source base station from the source base station, or the target base station can obtain the ephemeris information (or NTN parameter information) of the source base station from other network nodes (such as core network nodes or servers, etc.), and this application does not limit this.

[0469] Optionally, the target base station receives a sixth message from the source base station. This sixth message requests that the terminal be switched to the second cell. The sixth message includes the terminal's location information. For example, the sixth message may be a handover request message.

[0470] For example, the target base station can obtain a transmission delay deviation from the source base station. This transmission delay deviation is the difference between the first signal transmission delay and the second signal transmission delay. The target base station can determine the first signal transmission delay based on this delay deviation and the second signal transmission delay. This transmission delay deviation can be provided to the source base station by the terminal. For instance, the measurement report sent by the terminal to the source base station may include indication information for the delay deviation. However, this application is not limited to this; the source base station can also obtain indication information for indicating the delay deviation from other information sent by the terminal to the source base station.

[0471] The target base station can obtain the second signal transmission delay from the source base station, or the second signal transmission delay can be determined by the target base station.

[0472] For example, the second signal transmission delay can be determined by the source base station based on the ephemeris information (or NTN parameter information) of the target base station and the terminal location information. Alternatively, the second signal transmission delay can be obtained by the source base station from the terminal. For instance, the measurement report sent by the terminal to the source base station may include indication information of the second signal transmission delay. However, this application is not limited to this; the source base station may also obtain indication information for indicating the second signal transmission delay from other information sent by the terminal to the source base station.

[0473] For example, the target base station can determine the second signal transmission delay based on its location and the terminal's location. Alternatively, the target base station can obtain the transmission delay deviation from the source base station and determine the second signal transmission delay based on the first signal transmission delay and the transmission delay deviation.

[0474] For example, the sixth message sent by the source base station to the target base station may include an indication of the second signal transmission delay.

[0475] The third signal transmission delay can be the maximum signal transmission delay between base stations predefined in the protocol, or the third signal transmission delay can be determined by the target base station or obtained from the source base station.

[0476] For example, the third signal transmission delay can be calculated by the source base station. The source base station can send a signal to the target base station and record a timestamp 1 when sending the signal, indicating the time when the signal was sent from the source base station. After receiving the signal, the target base station immediately sends a response signal. The source base station records a timestamp 2 when receiving the response signal. The source base station can calculate the round-trip delay between the source base station and the target base station by calculating the difference between timestamp 1 and timestamp 2, and obtain the third signal transmission delay based on the round-trip delay. That is, the third signal transmission delay is half of the round-trip delay. The source base station can send indication information to the target base station to indicate the third signal transmission delay. However, this application is not limited to this; the target base station can determine the third signal transmission delay using the above method.

[0477] The message processing latency of the source base station and the message processing latency of the terminal can be their respective maximum message processing latency predefined by the protocol, or the target base station can obtain these two processing latency values ​​from the source base station. For example, the sixth message may include indication information for indicating the message processing latency of the source base station and / or the message processing latency of the terminal. However, this application is not limited to this; the source base station may also indicate the message processing latency and / or the message processing latency of the terminal through other messages.

[0478] S1002, the target base station sends the fifth message to the source base station.

[0479] Specifically, the target base station sends the fifth message to the source base station at the first moment.

[0480] S1003, the source base station sends an RRC reconfiguration message, including a handover command, to the terminal.

[0481] This handover command instructs the terminal to switch from the first cell to the second cell. After receiving the fifth message from the target base station, the source base station sends the RRC reconfiguration message to the terminal based on the fifth message. After sending the RRC reconfiguration message, the source base station stops providing data transmission services to the terminal in the first cell. Correspondingly, the terminal receives the RRC reconfiguration message from the source base station and, upon receiving it, stops data transmission in the first cell. Alternatively, after the terminal and source base station transmit the RRC reconfiguration message, the terminal disconnects its communication connection with the first cell.

[0482] S1004, the terminal performs cell handover based on the RRC reconfiguration message.

[0483] The terminal performs a cell handover to switch to a second cell. Specifically, the terminal detects the synchronization signal of the second cell and performs a random access procedure in the second cell based on the synchronization signal. Other procedures can be referred to the description above, and will not be repeated here.

[0484] In one embodiment, the scheme of the example shown in Figure 10 can also be applied to scenarios where there is no communication interface between the source base station and the target base station. In this scenario, the signal between the target base station and the source base station needs to be transmitted through the core network. Therefore, the third signal transmission delay also includes the transmission delay and processing delay of the fifth message in the core network. For example, when the target base station calculates the first moment, it should also consider the transmission delay from the target base station to the AMF, the message processing delay of the AMF, and the transmission delay from the AMF to the source base station.

[0485] In another implementation, the scheme of the embodiment shown in Figure 10 can also be applied to intra-cell handover scenarios. In this scenario, the CU can determine the first moment based on at least one of the following: first time resource, signal transmission delay between the source DU and the terminal (i.e., first signal transmission delay), signal transmission delay between the target DU and the terminal (i.e., second signal transmission delay), signal propagation delay from the source DU to the CU (i.e., third signal transmission delay), message processing delay of the source DU, and message processing delay of the terminal. That is, in this scenario, the source base station can be replaced by the source DU, the target base station can be replaced by the target DU, the source DU and the target DU can be different DUs, or the source DU and the target DU can be the same DU, i.e., the terminal hands over between different cells corresponding to the same DU. Alternatively, the above steps can be implemented by all or part of the functions of the source base station / target base station. When the above steps require data / signaling interaction between the source base station and the target base station, the data / information interaction can be achieved by the source DU and the target DU through the CU. For intra-cell handover scenarios, the CU determines to hand over the terminal from the source cell to the target cell, so there is no need to transmit the sixth message mentioned above between the source DU and the target DU. The specific steps can be adapted and implemented according to the specific scenario architecture.

[0486] According to the above scheme, by sending a fifth message, the interval between the arrival of the handover command at the terminal and the first time resource is shortened, allowing the terminal to quickly detect the synchronization signal of the second cell after receiving the handover command. This ensures that even if the terminal stops data transmission in the serving cell (i.e., the first cell) or disconnects its communication connection with the serving cell after receiving the handover command, excessively long communication interruptions can be avoided. This helps reduce the probability of terminal service interruptions or dropped calls, improving communication reliability.

[0487] Figure 11 is a schematic diagram of the interruption duration of another terminal during the handover process provided in an embodiment of this application. It can be understood that the target base station, CU, or DU can send a first message (handover command) to the terminal at the first moment. In this way, the terminal can immediately obtain the synchronization signal after receiving the handover command and stopping data transmission with the first cell, so that the current interruption time is less than the original interruption time, which helps to improve the reliability of communication.

[0488] The above embodiments describe how the target base station, CU, or DU determines the arrival time of the first time resource at the terminal, and selects an appropriate time to send a handover command based on the determined arrival time of the first time resource. This application also provides another solution to reduce terminal communication interruption time caused by handover. Specifically, this application proposes that the terminal can perform downlink synchronization with the target cell in advance; that is, the terminal can receive a synchronization signal from the target cell before receiving the handover command. This reduces the communication interruption time during the handover process from the source cell to the target cell caused by the terminal waiting for the downlink synchronization signal from the target cell. This process is described below.

[0489] To facilitate understanding, the following section first describes the scenario where the terminal can receive synchronization signals from the target cell in advance. It should be understood that a satellite's coverage area can include one or more beam coverage areas, and one satellite coverage area can correspond to one or more cells; a cell and a satellite beam can have a one-to-many relationship or a many-to-one relationship. For ease of understanding, Figure 12 illustrates this scenario using one cell corresponding to one satellite beam as an example. As shown in Figure 12, the target base station has 7 cells (cells labeled 1 to 7), and the source base station also has 7 cells (cells labeled 1 to 7). It can be understood that as the source and target base stations move in their respective directions, causing the terminal to be located in the overlapping area of ​​cell 7 of the source base station and cell 3 of the target base station, the terminal needs to switch from cell 7 of the source base station to cell 3 of the target base station. That is, the first cell is cell 7 of the source base station, and the second cell is cell 3 of the target base station.

[0490] The following explanation, with reference to Figure 13, illustrates a method by which a terminal can receive synchronization signals from a target cell in advance.

[0491] Figure 13 is a schematic flowchart of the communication method 1300 provided in an embodiment of this application. It should be understood that, unless otherwise specified, the parts of method 1300 that are the same as those in the embodiments described above will only be briefly described or will not be described again; specific implementation can be found by referring to the preceding description. Method 1300 includes, but is not limited to, the following steps:

[0492] S1301, the terminal receives the synchronization signal of the second cell according to the timing offset and the first time resource. The first cell is the serving cell of the terminal, the second cell is the neighboring cell of the first cell, the timing offset is the timing offset between the first cell and the second cell, and the first time resource is the time resource of the second cell used to carry the synchronization signal of the second cell.

[0493] Specifically, if the terminal determines that it is within the coverage area of ​​the second cell, it can receive the synchronization signal of the second cell based on the timing offset and the first time resources. For example, if the terminal determines that it is within the coverage area of ​​the second cell, i.e., within the overlapping area of ​​the first and second cells, the terminal can assume that a cell handover may occur. Therefore, after determining that it is within the coverage area of ​​the second cell, the terminal can receive the synchronization signal of the second cell based on the timing offset and the first time resources.

[0494] Optionally, the terminal receives first information from the source base station, the first information being used to indicate the coverage area of ​​the target base station.

[0495] The first information can directly indicate the coverage area of ​​the target base station, or the first information can include the ephemeris information (or NTN parameter information) of the target base station, and the terminal can determine the coverage area of ​​the target base station based on the ephemeris information.

[0496] It should be understood that this application is not limited to this. The terminal can also determine the coverage area of ​​the target base station based on historical measurement data, or the terminal can calculate the coverage area of ​​the target base station based on satellite constellation parameter information, such as orbital altitude and satellite scan angle. Generally speaking, satellite constellation system parameter information is publicly available.

[0497] Furthermore, the terminal can determine the coverage area of ​​the second cell based on the cell distribution pattern of the target base station and the terminal's location information. The cell distribution pattern refers to the distribution of multiple cells of the target base station within its coverage area.

[0498] For example, as shown in Figure 12, the target base station is deployed on a satellite. The cell distribution of the target base station can be such that a central cell within the satellite coverage area is designated as Cell 1, and six cells are distributed around Cell 1, with the cell identifiers increasing sequentially in a clockwise direction, starting from the cell directly north of Cell 1. It should be understood that the cell distribution rule in Figure 12 is merely an example provided to better understand the scheme of this application, and this application is not limited to it. In specific implementations, it is sufficient for the base station and the terminal to reach a consensus on the cell distribution method.

[0499] Optionally, the terminal can determine the cell distribution mode by receiving second information, wherein the second information is used to indicate the cell distribution mode. Optionally, the second information can be received by the terminal in the first cell, or it can be sent to the terminal by other nodes in the network, such as core network nodes or servers. However, this application is not limited to this, and the cell distribution mode can also be predefined by a protocol.

[0500] The specific implementation methods for determining the terminal timing offset may include, but are not limited to, the following:

[0501] Optionally, the terminal determines the timing offset based on the identifier of the first cell, the identifier of the second cell, and a first correspondence relationship, wherein the first correspondence relationship is the correspondence between the deviation of the cell identifier and the timing offset.

[0502] Specifically, the cell identifier deviation can be predefined as the source cell identifier minus the target cell identifier, or the target cell identifier minus the source cell identifier. Similarly, the time offset can be predefined as the number of time units that the time unit of the source cell with the same identifier deviates from the time unit of the target cell, or the number of time units that the time unit of the target cell with the same identifier deviates from the time unit of the source cell. The following uses the deviation being the source cell identifier minus the target cell identifier, and the time offset being the number of time units that the time unit of the target cell with the same identifier deviates from the time unit of the source cell.

[0503] For example, the first correspondence can be an offset that is n times the timing offset, where n is an integer. For instance, if the offset of the cell identifier is P, the timing offset is n*P time units. Taking a frame as an example, if the offset of the cell identifier is P, then the timing offset is n*P frames, that is, the frame of the target cell with the same frame number is offset by n*P frames compared to the frame of the source cell.

[0504] Taking Figure 12 as an example, the identifier of the first cell is 7, and the identifier of the second cell is 3. The deviation of the cell identifiers between the first cell and the second cell can be 3-7=-4. This can be understood as the start time of frame #0 of the second cell being 4 frames earlier than the start time of frame #0 of the first cell (i.e., the timing offset is -4). If the deviation is positive, it can be understood as the start time of subframe #0 of frame #0 of the second cell being later than the start time of subframe #0 of frame #0 of the first cell being.

[0505] It should be understood that this application is not limited to this. The timing offset between cells can also be a predefined time length, which can be represented by the number of time units, such as 0, 1, 2, etc., or by the absolute duration.

[0506] The terminal can obtain the time-domain resource information of the synchronization signal of the second cell from the first cell, and determine the first time resource based on this time-domain resource information. For specific implementation details, please refer to the previous description; they will not be repeated here.

[0507] The terminal can determine the arrival time of the first time resource based on the timing offset, the first signal transmission delay, and the second signal transmission delay. For details, please refer to the description of Method 2 in the embodiment shown in Figure 6. Taking frame #n of the second cell as the first time resource as an example, the terminal can determine the arrival time of frame #n of the first cell and the first signal transmission delay Δt based on these parameters.S-delay Second signal transmission delay Δt T-delay and timing offset Δt offset Determine the arrival time of frame #n from the second cell to the terminal. The terminal can determine the arrival time of frame #n from the second cell based on the following relationship provided above. T-arrival =t S-arrival -Δt S-delay -Δt offset +Δt T-delay

[0508] At this point, t in the above formula S-arrival Let t be the arrival time of frame #n from the first cell to the terminal. T-arrival Let #n be the arrival time of frame #n from the second cell to the terminal. This is merely an example, and this application is not limited to it.

[0509] In another implementation, the terminal can determine the arrival time of frame #m of the second cell based on the arrival time of the synchronization signal of the first cell at frame #m, using the above formula. Then, based on the time difference between frame #n and frame #m of the second cell, the arrival time of frame #n of the second cell is determined. This time difference between frame #n and frame #m of the second cell is the time difference between the synchronization signal resources of the first and second cells. If the period of the synchronization signal of the second cell is T, then the arrival time of frame #n of the second cell at the terminal is the second cell's synchronization signal plus any multiple of T.

[0510] The terminal can receive the synchronization signal of the second cell on the first time resource, based on the arrival time of the first time resource to the terminal, after determining that it is located within the coverage area of ​​the second cell and before receiving the first message.

[0511] Optionally, the terminal may search for downlink synchronization signals in the second cell during time gaps when the first cell does not schedule terminal data (i.e., during time periods when the terminal is not scheduled to transmit data with the first cell and the terminal's radio resources are idle).

[0512] S1302, the terminal obtains downlink synchronization with the second cell based on the synchronization signal.

[0513] The terminal achieves downlink synchronization with and maintains downlink synchronization with the second cell by receiving a synchronization signal. This allows the terminal to immediately perform a cell handover upon receiving a handover command, reducing communication interruption time during the handover process from the source cell to the target cell caused by the terminal waiting for the target cell's downlink synchronization signal. This avoids excessively long communication interruptions and helps reduce the probability of service interruptions or dropped calls, thus improving communication reliability.

[0514] For example, as shown in Figure 14, based on method 1300, the terminal can obtain the synchronization signal of the second cell (target cell) in advance, obtain the downlink synchronization of the second cell, and immediately complete the handover process when the handover command arrives at the terminal. In this way, the current interruption time of the terminal in the disconnection process can be less than the original interruption time, which helps to reduce the occurrence of service interruptions.

[0515] It should be understood that the embodiment shown in Figure 13 can be applied to intra-site handover scenarios as well as inter-site handover scenarios. In the above steps, the source base station can be replaced by the source DU, and the target base station can be replaced by the target DU. The source DU and the target DU can be different DUs, or they can be the same DU, that is, the terminal hands over between different cells corresponding to the same DU. Alternatively, the above steps can be implemented by all or part of the functions of the source base station / target base station.

[0516] It is understood that, in order to achieve the functions in the above embodiments, the network devices and terminals include hardware structures and / or software modules corresponding to perform each function. Those skilled in the art should readily recognize that, based on the units and method steps described in conjunction with the embodiments disclosed in this application, this application can be implemented in hardware or a combination of hardware and computer software. Whether a function is executed by hardware or by computer software driving hardware depends on the specific application scenario and design constraints of the technical solution.

[0517] Figures 15 and 16 are schematic diagrams of possible communication devices provided in the embodiments of this application. These communication devices can be used to implement the functions of network devices (such as source base stations and target base stations) or terminals in the above-described method embodiments, and thus can also achieve the beneficial effects of the above-described method embodiments. In the embodiments of this application, the communication device can be an access network node as shown in Figures 1 to 4, one of terminals 120a-120j as shown in Figure 1, or access network node 110a or 110b as shown in Figure 1, a satellite or base station as an RRU as shown in Figure 2, a satellite base station as shown in Figure 3 or Figure 3a, a RAN node as shown in Figure 4, or a unit / module / component (such as a chip, chip system, logic circuit, or software) applied to a terminal or access network node.

[0518] The communication device 1500 includes a transceiver unit 1520, which can be used to receive or send information. The communication device 1500 may also include a processing unit 1510, which can be used to process instructions or data to achieve corresponding operations.

[0519] It should be understood that when the communication device 1500 is a chip configured in (or used in) a communication device, the transceiver unit 1520 in the communication device 1500 can be the input / output interface or circuit of the chip, and the processing unit 1510 in the communication device 1500 can be the processor in the chip.

[0520] Optionally, the communication device 1500 may further include a storage unit 1530, which can be used to store instructions or data. The processing unit 1510 can execute the instructions or data stored in the storage unit to enable the communication device to perform corresponding operations.

[0521] The communication device 1500 can be used to implement the functions of network devices (such as source base stations) or terminals in the method embodiments shown in Figures 6 to 13 above.

[0522] When the communication device 1500 is used to implement the functions of the terminal in the method embodiment shown in FIG6: the transceiver unit 1520 is used to receive a first message from a first cell, the first message including a handover command, the handover command being used to instruct the terminal to hand over from the first cell to a second cell. The processing unit 1510 is used to determine a first time period and maintain a communication connection with the first cell during the first time period. The transceiver unit 1520 is also used to send a second message, the second message being used to indicate that the handover to the second cell has been successful, wherein the first time period is the time period after the transceiver unit 1520 receives the first message and before sending the second message.

[0523] Optionally, the processing unit 1510 is further configured to perform one or more of the following during the first time period: not releasing the configuration information of the first cell; detecting the downlink control information of the first cell; and / or, the transceiver unit 1520 is further configured to perform one or more of the following during the first time period: receiving data and / or information from the first cell; sending data and / or information to the first cell.

[0524] Optionally, the first time period is specifically before the arrival time of the first time resource to the transceiver unit 1520, and the first time resource is used to carry the synchronization signal of the second cell.

[0525] Optionally, the processing unit 1510 is further configured to determine the arrival time of the first time resource to the terminal based on the transmission time of the first time resource in the second cell and the second signal transmission delay, wherein the second signal transmission delay is the signal transmission delay between the second cell and the terminal.

[0526] Optionally, the processing unit 1510 is further configured to determine the arrival time of the first time resource to the terminal based on the time-domain resource information of the synchronization signal, the first signal transmission delay, the second signal transmission delay, and the timing offset, wherein the time-domain resource information is used to indicate the first time resource, the first signal transmission delay is the transmission delay between the first cell and the terminal, and the second signal transmission delay is the signal transmission delay between the second cell and the terminal.

[0527] Optionally, the transceiver unit 1520 is further configured to receive at least one indication message, the at least one indication message being used to determine the first time period.

[0528] Optionally, the at least one indication information includes an indication information used to indicate the first time period; or, the at least one indication information includes indication information used to indicate one or more of the following: the arrival time of the first time resource to the terminal; the transmission time of the first time resource in the second cell; the time domain resource information of the synchronization signal, which is used to indicate the first time resource; and the timing offset between the first cell and the second cell.

[0529] Optionally, the handover command includes first information, which is used to instruct the handover to the second cell to be performed without a random access procedure.

[0530] When the communication device 1500 is used to implement the functions of the network device (such as a source base station) in the method embodiment shown in FIG6: the transceiver unit 1520 is used to send a first message of a first cell to the terminal, the first message including a handover command, the handover command being used to indicate a handover from the first cell to a second cell. The processing unit 1510 is used to maintain a communication connection with the terminal in the first cell for a second time period, the second time period being the time period after the transceiver unit 1520 sends the first message and before receiving a third message. The transceiver unit 1520 is also used to receive a third message, the third message being used to indicate that the terminal has completed the handover to the second cell.

[0531] Optionally, the processing unit 1510 is further configured not to release the terminal's context information. The transceiver unit 1520 is further configured to perform one or more of the following in the first cell during a second time period: sending downlink control information (DCI) to the terminal; sending data and / or information to the terminal; and receiving data and / or information from the terminal. Optionally, the second time period specifically occurs before the arrival of the first time resource at the terminal, and the first time resource is used to carry the synchronization signal of the second cell.

[0532] Optionally, the transceiver unit 1520 is further configured to transmit at least one indication message, the at least one indication message being used to determine a first time period, the first time period being the period during which the terminal maintains a communication connection with the first cell after receiving the first message. Optionally, the at least one indication message includes one indication message used to indicate the first time period; or, the at least one indication message includes indication information for indicating one or more of the following: the arrival time of the first time resource to the terminal; the transmission time of the first time resource in the second cell; the time-domain resource information of the synchronization signal, the time-domain resource information being used to indicate the first time resource; and the timing offset between the first cell and the second cell.

[0533] Optionally, the at least one indication information includes indication information for indicating the arrival time. The transceiver unit 1520 is further configured to receive fourth information, which indicates the arrival time. The processing unit 1510 is further configured to determine the arrival time based on the transmission time of the first time resource and the second signal transmission delay.

[0534] Optionally, the processing unit 1510 is further configured to determine the second time period based on the arrival time of the first time resource at the terminal.

[0535] When the communication device 1500 is used to implement the functions of the network device (such as the source base station) in the method embodiment shown in FIG10: the processing unit 1510 is used to determine a first time based on a first time resource, the first time resource being used to carry the synchronization signal of the second cell, the first time being the time to send a first message, the first message being used to instruct the terminal to switch from the first cell to the second cell. The transceiver unit 1520 is used to send the first message.

[0536] Optionally, the processing unit 1510 is further configured to determine the first moment based on the first time resource and one or more of the following information: the location information of the terminal; a first signal transmission delay, which is the signal transmission delay between the first cell and the terminal; a second signal transmission delay, which is the signal transmission delay between the second cell and the terminal; a third signal transmission delay, which is the signal transmission delay between a first access network node and a second access network node, wherein the first access network node is the access network node managing the first cell and the second access network node is the access network node managing the second cell; the message processing delay of the first access network node; the message processing delay of the terminal; and the timing offset between the first cell and the second cell.

[0537] Optionally, the transceiver unit 1520 is further configured to receive a second message from the first access network node, the second message being used to request the terminal to be switched to the second cell, the second message including the location information of the terminal.

[0538] For a more detailed description of the processing unit 1510 and the transceiver unit 1520, please refer to the relevant description in the method embodiment shown in FIG10.

[0539] When the communication device 1500 is used to implement the functions of the network device (such as a terminal) in the method embodiment shown in FIG13: the transceiver unit 1520 is used to receive the synchronization signal of the second cell according to the timing offset and the first time resource before receiving the first message of the first cell. The first message is used to instruct the terminal to switch from the first cell to the second cell. The first cell is the serving cell of the terminal, the second cell is the neighboring cell of the first cell, the timing offset is the timing offset between the first cell and the second cell, and the first time resource is the time resource of the second cell used to carry the synchronization signal of the second cell. The processing unit 1510 is used to obtain downlink synchronization with the second cell according to the synchronization signal.

[0540] Optionally, the processing unit 1510 is further configured to determine the coverage area of ​​the second cell where the terminal is located. Optionally, the transceiver unit 1520 is further configured to receive the synchronization signal of the second cell based on the timing offset and the first time resource before receiving the first message from the first cell.

[0541] Optionally, the transceiver unit 1520 is further configured to receive first information, which indicates the coverage area of ​​the second access network node, the second access network node being the access network node that manages the second cell. Optionally, the processing unit 1510 is further configured to determine the coverage area of ​​the second cell where the terminal is located based on the cell distribution pattern of the second access network node and the location information of the terminal, wherein the cell distribution pattern is the distribution pattern of multiple cells of the second access network node within the coverage area of ​​the second access network node.

[0542] Optionally, the processing unit 1510 is further configured to determine the coverage area of ​​the second access network node based on the ephemeris information.

[0543] Optionally, the transceiver unit 1520 receives second information, which is used to indicate the cell distribution method.

[0544] Optionally, the processing unit 1510 is further configured to determine the timing offset based on the identifier of the first cell, the identifier of the second cell, and a first correspondence, wherein the first correspondence is the correspondence between the deviation of the cell identifier and the timing offset.

[0545] Optionally, the processing unit 1510 is further configured to determine the arrival time of the first time resource to the terminal based on the first time resource, the timing offset, the first signal transmission delay, and the second signal transmission delay, wherein the first signal transmission delay is the signal transmission delay between the first cell and the terminal, and the second signal transmission delay is the signal transmission delay between the second cell and the terminal.

[0546] Optionally, the processing unit 1510 is further configured to acquire the ephemeris information of the second access network node; and determine the second signal transmission delay based on the ephemeris information and the location information of the terminal, wherein the second signal transmission delay is the signal transmission delay between the second cell and the terminal.

[0547] For a more detailed description of the processing unit 1510 and the transceiver unit 1520, please refer to the relevant description in the method embodiment shown in FIG13.

[0548] As shown in Figure 16, the communication device 1600 includes a processor 1610 and an interface circuit 1620. The processor 1610 and the interface circuit 1620 are coupled to each other. It is understood that the interface circuit 1620 can be a transceiver or an input / output interface. Optionally, the communication device 1600 may also include a memory 1630 for storing instructions executed by the processor 1610, or storing input data required by the processor 1610 to execute instructions, or storing data generated after the processor 1610 executes instructions.

[0549] In one implementation, the memory 1630 may be integrated into the processor 1610 or independent of the processor 1610.

[0550] When the communication device 1600 is used to implement the method shown in Figures 6 to 13, the processor 1610 is used to implement the function of the processing unit 1210, and the interface circuit 1620 is used to implement the function of the transceiver unit 1220.

[0551] When the aforementioned communication device is a chip applied to a terminal device, the terminal device chip can implement the functions of the terminal in the above method embodiments. The terminal device chip receives information from other modules (such as an RF module or antenna) in the terminal device, the information being sent to the terminal device by the network device; or, the terminal device chip sends information to other modules (such as an RF module or antenna) in the terminal device, the information being sent to the network device by the terminal device.

[0552] When the aforementioned communication device is a module applied to a network device, the network device module can implement the functions of the network device in the above method embodiments. The network device module receives information from other modules (such as radio frequency modules or antennas) in the network device, which is information sent from the terminal device to the network device; or, the network device module sends information to other modules (such as radio frequency modules or antennas) in the network device, which is information sent from the network device to the terminal device. Here, the network device module can be the baseband chip of the network device, or it can be a DU or other modules. The DU here can be a DU under an open radio access network (O-RAN) architecture.

[0553] It is understood that the processor in the embodiments of this application can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. A general-purpose processor can be a microprocessor or any conventional processor.

[0554] The method steps in the embodiments of this application can be implemented in hardware or in software instructions executable by a processor. The software instructions can consist of corresponding software modules, which can be stored in random access memory, flash memory, read-only memory, programmable read-only memory, erasable programmable read-only memory, electrically erasable programmable read-only memory, registers, hard disks, portable hard disks, CD-ROMs, or any other form of storage medium known in the art. An exemplary storage medium is coupled to a processor, enabling the processor to read information from and write information to the storage medium. The storage medium can also be a component of the processor. The processor and storage medium can reside in an ASIC. Alternatively, the ASIC can reside in an access network device or a terminal device. The processor and storage medium can also exist as discrete components in the access network device or terminal device.

[0555] According to the method provided in the application embodiments, this application embodiment also provides a computer program product, which includes: computer program code, which, when executed by one or more processors, causes a device including the processor to perform the method shown in Figures 6 to 13.

[0556] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially in the form of a computer program product. This computer program product includes one or more computer programs or instructions. When the computer program or instructions are loaded and executed on a computer, the processes or functions described in the embodiments of this application are performed, in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, network equipment, user equipment, or other programmable device.

[0557] According to the method provided in the embodiments of this application, the embodiments of this application also provide a computer-readable storage medium that stores the above-mentioned computer program or instructions. When the computer program or instructions are run by one or more processors, the apparatus including the processor performs the method shown in Figures 6 to 13.

[0558] As described above, computer programs or instructions can be stored in or transferred from one computer-readable storage medium to another. For example, the computer programs or instructions can be transferred from one website, computer, server, or data center to another website, computer, server, or data center via wired or wireless means. The computer-readable storage medium can be any available medium accessible to a computer or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium, such as a floppy disk, hard disk, or magnetic tape; it can also be an optical medium, such as a digital video optical disc; or it can be a semiconductor medium, such as a solid-state drive. The computer-readable storage medium can be a volatile or non-volatile storage medium, or it can include both volatile and non-volatile types of storage media.

[0559] According to the method provided in the embodiments of this application, the embodiments of this application also provide a communication system, including one or more of the aforementioned network devices. The system may further include one or more of the aforementioned first terminals.

[0560] In the various embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatuses described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the couplings or direct couplings or communication connections shown or discussed may be through some interfaces; indirect couplings or communication connections between apparatuses or units may be electrical, mechanical, or other forms.

[0561] The units described as separate components may or may not be physically separate. 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 the units can be selected to achieve the purpose of this solution according to actual needs.

[0562] In the various embodiments of this application, unless otherwise specified or in case of logical conflict, the terminology and / or descriptions of different embodiments are consistent and can be referenced by each other. The technical features of different embodiments can be combined to form new embodiments according to their inherent logical relationship.

[0563] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A communication method characterized by comprising: The method comprises: receiving a first message of a first cell, the first message comprising a handover command, the handover command being used to instruct a terminal to hand over from the first cell to a second cell; maintaining a communication connection with the first cell for a first time period; sending a second message, the second message being used to indicate that the terminal has successfully handed over to the second cell, wherein the first time period is a time period between receiving the first message and sending the second message.

2. The method of claim 1, wherein, The maintaining the communication connection with the first cell for the first time period comprises performing one or more of the following for the first time period: not releasing configuration information of the first cell; detecting a downlink control information of the first cell; receiving data and / or information from the first cell; sending data and / or information to the first cell.

3. The method according to claim 1 or 2, characterized in that, The first time period is specifically before a time of arrival of the first time resource at the terminal, the first time resource being used to carry a synchronization signal of the second cell.

4. The method of claim 3, wherein, The method further comprises: determining the time of arrival of the first time resource at the terminal according to a time of transmission of the second cell and a second signal transmission delay, the second signal transmission delay being a signal transmission delay between the second cell and the terminal.

5. The method of claim 3, wherein, The method further comprises: determining the time of arrival of the first time resource at the terminal according to time domain resource information of the synchronization signal, a first signal transmission delay, a second signal transmission delay, and a timing offset between the first cell and the second cell, wherein the time domain resource information is used to indicate the first time resource, the first signal transmission delay is a transmission delay between the first cell and the terminal, and the second signal transmission delay is a signal transmission delay between the second cell and the terminal.

6. The method according to any one of claims 3 to 5, characterized in that, The method further comprises: receiving at least one indication information, the at least one indication information being used to determine the first time period.

7. The method of claim 6, wherein, The at least one indication information comprises one indication information, the one indication information being used to indicate the first time period; or The at least one indication information comprises indication information used to indicate one or more of the following: the time of arrival of the first time resource at the terminal; the time of transmission of the first time resource at the second cell; time domain resource information of the synchronization signal, the time domain resource information being used to indicate the first time resource; a timing offset between the first cell and the second cell.

8. The method according to any one of claims 1 to 7, characterized in that, The handover command comprises first information, the first information being used to instruct to perform a random access procedure free handover to the second cell.

9. A communication method characterized by comprising: The method comprises: sending a first message of a first cell to a terminal, the first message comprising a handover command, the handover command being used to instruct to hand over from the first cell to a second cell; maintaining a communication connection with the terminal at the first cell for a second time period; receiving a third message, the third message being used to indicate that the terminal has completed handover to the second cell, wherein the second time period is a time period between sending the first message and receiving the third message.

10. The method of claim 9, wherein, The maintaining the communication connection with the terminal in the first cell in the second time period comprises performing one or more of the following in the second time period: not releasing context information of the terminal; sending downlink control information (DCI) to the terminal; sending data and / or information to the terminal; receiving data and / or information from the terminal.

11. The method according to claim 9 or 10, characterized in that, The second time period is specifically before a first time resource reaches the terminal, the first time resource being used to carry a synchronization signal of the second cell.

12. The method of claim 11, wherein, The method further comprises: sending at least one indication information, the at least one indication information being used to determine a first time period in which the terminal maintains the communication connection with the first cell after receiving the first message.

13. The method of claim 12, wherein, The at least one indication information comprises one indication information used to indicate the first time period; or the at least one indication information comprises indication information used to indicate one or more of the following: an arrival time at which the first time resource reaches the terminal; a sending time of the first time resource in the second cell; time domain resource information of the synchronization signal, the time domain resource information being used to indicate the first time resource; a timing offset between the first cell and the second cell.

14. The method of claim 13, wherein, The at least one indication information comprises indication information used to indicate the arrival time, and the method further comprises: receiving fourth information used to indicate the arrival time; or determining the arrival time according to a sending time of the first time resource and a second signal transmission delay.

15. The method according to any one of claims 11 to 14, characterized in that, The method further comprises: determining the second time period according to an arrival time at which the first time resource reaches the terminal.

16. A communications device, characterized by A communication apparatus comprising a processor coupled with a memory, the memory being used to store a computer program, and the processor being used to execute the computer program stored in the memory, so that the communication apparatus performs the method according to any one of claims 1 to 8; or so that the communication apparatus performs the method according to any one of claims 9 to 15.

17. A communications device, characterized by A communication apparatus comprising a processor and a communication interface, the processor being used to control the communication interface to implement the method according to any one of claims 1 to 8, or to implement the method according to any one of claims 9 to 15.

18. A computer-readable storage medium, characterized in that, A computer program product having instructions stored thereon, the instructions, when executed on a computer, causing the computer to perform the method according to any one of claims 1 to 15.

19. A computer program product, characterised in that, A computer program product comprising a computer program, the computer program, when executed, causing a computer to perform the method according to any one of claims 1 to 15.

20. A communication system, characterized by A communication apparatus comprising a first communication apparatus and a second communication apparatus, the first communication apparatus being used to perform the method according to any one of claims 1 to 8, and the second communication apparatus being used to perform the method according to any one of claims 9 to 15.

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