Communication method and communication apparatus

Abstract

Provided in the present application are a communication method and a communication apparatus. The communication method comprises: receiving a handover command, where the handover command is used to instruct a terminal to switch from a first cell to a second cell; receiving first information, where the first information is used for the terminal to determine an arrival time at which a downlink synchronization signal of the second cell arrives at the terminal; and performing data transmission with the first cell within the time period from the time at which the handover command is received to a first time, and, at the first time, disconnecting data transmission with the first cell and accessing the second cell, where the first time is determined on the basis of the arrival time. The communication method can reduce the duration of service interruption when a terminal performs a handover, thereby improving user experience.

Description

Communication methods and communication devices

[0001] This application claims priority to Chinese patent application filed on November 28, 2024, with application number 202411731938.0 and entitled "Communication Method and Communication Apparatus", 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 and a communication device. Background Technology

[0003] In a communication system, a terminal can change its serving cell from one cell to another by performing a cell handover, also known as a cell handover.

[0004] However, analysis revealed that when a terminal switches from a cellular cell to a non-terrestrial network (NTN) cell, issues such as service interruption or dropped calls may occur, affecting the user experience. Summary of the Invention

[0005] This application provides a communication method and a communication device that can reduce the duration of service interruption when a terminal performs a handover, thereby improving the user experience.

[0006] In a first aspect, this application provides a communication method, which can be executed by a terminal, or by a component configured in the terminal (such as a chip, chip system, etc.), or by a logic module or software capable of implementing all or part of the terminal functions, and this application does not limit it.

[0007] The communication method includes: receiving a handover command, which instructs a terminal to handover from a first cell to a second cell; receiving first information, which is used by the terminal to determine the arrival time of a downlink synchronization signal from the second cell to the terminal; transmitting data with the first cell during a period between the time of receiving the handover command and a first time; and disconnecting the data transmission with the first cell and accessing the second cell at the first time, wherein the first time is determined based on the arrival time.

[0008] The term "cell" in this application can also be replaced with "cell". For example, in a satellite communication system, the aforementioned handover command, used to instruct a terminal to hand over from a first cell to a second cell, can also be replaced with "handover from a first beam to a second beam".

[0009] The downlink synchronization signal of the second cell is used by the terminal to achieve downlink synchronization with the second cell. For example, the downlink synchronization signal of the second cell is the synchronization signal block (SSB) of the second cell.

[0010] Data transmission with the first cell can also be understood as one or more of the following: not releasing the configuration information of the first cell, detecting the downlink control information of the first cell, receiving data and / or information from the first cell, and sending data and / or information to the first cell.

[0011] Understandably, accessing the second cell as described above includes: the terminal obtaining downlink synchronization with the second cell based on the downlink synchronization signal of the second cell, and accessing the second cell after obtaining downlink synchronization.

[0012] In this application, disconnecting data transmission with the first cell and accessing the second cell at the first moment can also be understood as disconnecting the connection with the first cell and switching to the second cell at the first moment.

[0013] Disconnecting data transmission with the first cell can also be understood as one or more of the following: releasing the configuration information of the first cell, not detecting the downlink control information of the first cell, not receiving data and / or information from the first cell, and not sending data and / or information to the first cell.

[0014] For example, the first time can be a time before the arrival time, or the first time can be the arrival time itself. In other words, disconnecting data transmission with the first cell and connecting to the second cell at the first time can also be understood as disconnecting data transmission with the first cell and connecting to the second cell before or at the arrival time.

[0015] By using the communication method provided in the first aspect, since the terminal can maintain data transmission with the first cell during the time between receiving the handover command and the first time, the technical solution provided in this application can reduce the interruption latency when the terminal hands over from the first cell to the second cell, thereby improving the user experience, compared to the terminal disconnecting / stopping data transmission with the first cell as soon as it receives the handover command.

[0016] In conjunction with the first aspect, in one possible implementation, the first information includes first indication information, which is used to indicate the time-domain resources occupied by the downlink synchronization signal.

[0017] The aforementioned first indication information is used to indicate the time-domain resources occupied by the downlink synchronization signal, and can also be replaced by the first indication information being used to indicate the time-frequency resources (time-domain resources and frequency-domain resources) occupied by the downlink synchronization signal.

[0018] In this implementation, by instructing the terminal on the time domain resources occupied by the downlink synchronization signal of the second cell, the terminal can determine the arrival time of the downlink synchronization signal of the second cell to the terminal.

[0019] For example, the first indication information is used to indicate the time domain resources occupied by the downlink synchronization signal, including: the first indication information is used to indicate the absolute time when the second cell transmits the downlink synchronization signal.

[0020] In this implementation, the terminal is instructed on the absolute time when the second cell sends the downlink synchronization signal. This allows the terminal to determine the arrival time of the downlink synchronization signal from the second cell based on the absolute time of the second cell's downlink synchronization signal transmission, the round-trip time (RTT) between the terminal and the second cell, or the one-way propagation delay. The one-way propagation delay between the terminal and the second cell is half the RTT between them (i.e., RTT / 2). In essence, the arrival time equals the absolute time of the second cell's downlink synchronization signal transmission plus RTT / 2.

[0021] In conjunction with the first aspect, in one possible implementation, the first information includes second indication information, which is used to indicate the start time of the first frame of the second cell.

[0022] The second indication information is used to indicate the start time of the first frame of the second cell, which can also be understood as: the second indication information is used to indicate the start time of the second cell transmitting the first frame. Alternatively, it can be understood as: the second indication information is used to indicate the absolute time corresponding to the start time of the second cell transmitting the first frame.

[0023] Understandably, the first frame can also be a frame with any frame index value.

[0024] For example, the first frame is the frame with frame index 0, meaning the second indication information is used to indicate the absolute time corresponding to the start time of the second cell transmitting frame #0. It can be understood that the second indication information indicating the absolute time corresponding to the start time of the second cell transmitting frame #0 can also be considered as: the second indication information indicating the absolute time corresponding to the start time of the second cell's frame #0 subframe #0.

[0025] After instructing the terminal on the start time of sending the first frame from the second cell, the terminal can determine the arrival time of the downlink synchronization signal from the second cell based on the start time of the first frame from the second cell and the time domain resources occupied by the downlink synchronization signal from the second cell.

[0026] For example, in one implementation, the terminal determines the arrival time of the downlink synchronization signal of the second cell to the terminal based on the start time of the first frame of the second cell and the first time offset. The first time offset is the time offset between the time domain resources occupied by the downlink synchronization signal of the second cell and the first frame.

[0027] For example, the terminal determines the time when the second cell transmits the downlink synchronization signal based on the start time and the first time offset of the first frame of the second cell. Then, it obtains the arrival time based on the time the second cell transmits the downlink synchronization signal and the RTT or one-way propagation delay (RTT / 2) between the terminal and the second cell. For instance, if the second indication information indicates the absolute time corresponding to the start time of subframe #0 of frame #0 transmitted by the second cell, and the time domain resources occupied by the downlink synchronization signal of the second cell are offset by m frames from frame #0, then the terminal first adds the duration of m frames to the absolute time corresponding to the start time of subframe #0 of frame #0 to obtain the time the second cell transmits the downlink synchronization signal. Then, it adds the aforementioned RTT / 2 to the time the second cell transmits the downlink synchronization signal to obtain the arrival time. Understandably, the arrival time is equal to the absolute time of the second cell transmitting the downlink synchronization signal plus RTT / 2.

[0028] In conjunction with the first aspect, in one possible implementation, the first information includes third indication information, which is used to indicate the timing offset between the second cell and the first cell.

[0029] After indicating the timing offset between the second cell and the first cell to the terminal, the terminal can determine the arrival time based on the timing offset between the second cell and the first cell and the time domain resources occupied by the downlink synchronization signal.

[0030] For example, the arrival time can be determined based on the start time of the second frame of the second cell and the second time offset; wherein, the start time of the second frame of the second cell is determined based on the timing offset between the second cell and the first cell, and the second time offset is the time offset between the time domain resources occupied by the downlink synchronization signal and the second frame.

[0031] In one example, the second frame could also be the frame carrying the downlink synchronization signal.

[0032] In other words, the terminal can first determine the start time of the second frame of the second cell based on the timing offset between the second cell and the first cell; then, based on the start time of the second frame of the second cell, the time offset between the time domain resources occupied by the downlink synchronization signal and the second frame, it can determine the time when the second cell sends the downlink synchronization signal. Further, the arrival time can be obtained by using the time when the second cell sends the downlink synchronization signal and the RTT or one-way propagation delay (i.e., RTT / 2) between the terminal and the second cell. Understandably, the arrival time is equal to the absolute time of the second cell sending the downlink synchronization signal plus RTT / 2.

[0033] In conjunction with the first aspect, in one possible implementation, the first information includes fourth indication information, which is used to indicate the frame number, subframe number, or time slot number of the second cell corresponding to the handover command.

[0034] After instructing the terminal on the frame number, subframe number, or timeslot number of the second cell corresponding to the handover command, the terminal can determine the arrival time based on the start or end time of the handover command, the frame number, subframe number, or timeslot number of the second cell corresponding to the frame or subframe in which the handover command is located, and the time domain resources occupied by the downlink synchronization signal.

[0035] For example, in one implementation, the arrival time is determined based on the start time of the third frame of the second cell and the third time offset; wherein, the start time of the third frame is determined based on the frame number, subframe number, or time slot number of the second cell corresponding to the handover command, and the third time offset is the time offset between the time domain resources occupied by the downlink synchronization signal and the third frame.

[0036] In one example, the third frame could also be the frame carrying the downlink synchronization signal.

[0037] For example, the terminal can first determine the timing offset between the second cell and the first cell based on the frame number, subframe number, or timeslot number of the second cell corresponding to the handover command; then, based on the absolute time corresponding to the start time of the first cell's frame #0 subframe #0 and the timing offset between the second cell and the first cell, it can determine the absolute time corresponding to the start time of the second cell's frame #0 subframe #0. If the time domain resources occupied by the downlink synchronization signal of the second cell are offset from frame #0 by m frames, then the terminal can obtain the time when the second cell sends the downlink synchronization signal by adding the duration of m frames to the absolute time corresponding to the start time of the second cell's frame #0 subframe #0. Furthermore, the arrival time can be obtained by using the time when the second cell sends the downlink synchronization signal and the RTT or one-way propagation delay (i.e., RTT / 2) between the terminal and the second cell. Understandably, the arrival time is equal to the absolute time when the second cell sends the downlink synchronization signal plus RTT / 2.

[0038] Furthermore, this example only uses frame 0 and subframe 0; frame 0 and subframe 0 can be replaced with any frame and subframe. In other words, the third frame can be any frame.

[0039] Secondly, embodiments of this application provide a communication method that can be applied to the network side, such as a first access network device on the network side, a module (e.g., circuit, chip, or chip system) in the first access network device, or a logical node, logical module, or software that can implement all or part of the functions of the first access network device. Taking the application of this method to a first access network device as an example...

[0040] The communication method includes: sending a handover command to instruct the terminal to handover from a first cell to a second cell; sending first information to determine the arrival time of the downlink synchronization signal of the second cell to the terminal; and stopping data transmission with the terminal upon receiving second information or a terminal context release message, wherein the second information indicates that the terminal has successfully handed over from the first cell to the second cell.

[0041] The term "cell" in this application can also be replaced with "cell". For example, in a satellite communication system, the aforementioned handover command, used to instruct a terminal to hand over from a first cell to a second cell, can also be replaced with "handover from a first beam to a second beam".

[0042] Stopping data transmission with the terminal can also be understood as one or more of the following: releasing the terminal's configuration information, not receiving data and / or information from the terminal, and not sending data and / or information to the terminal.

[0043] By using the communication method provided in the second aspect, since the first access network device only stops / interrupts data transmission with the terminal when it receives the second information or the terminal context release message, compared to the first access network device stopping / disconnecting data transmission with the terminal after sending a handover command, the interruption latency when the terminal switches from the first cell to the second cell can be reduced, thereby improving the user experience.

[0044] In conjunction with the second aspect, in one possible implementation, the first information includes first indication information, which is used to indicate the time-domain resources occupied by the downlink synchronization signal.

[0045] In conjunction with the second aspect, in one possible implementation, the first indication information is used to indicate the time-domain resources occupied by the downlink synchronization signal, including: the first indication information is used to indicate the absolute time when the second cell transmits the downlink synchronization signal.

[0046] In conjunction with the second aspect, in one possible implementation, the first information includes second indication information, which is used to indicate the start time of the first frame of the second cell.

[0047] In conjunction with the second aspect, in one possible implementation, the frame index of the first frame is 0.

[0048] In conjunction with the second aspect, in one possible implementation, the arrival time is determined based on the start time of the first frame and a first time offset, where the first time offset is the time offset between the time domain resources occupied by the downlink synchronization signal and the first frame.

[0049] In conjunction with the second aspect, in one possible implementation, the first information includes third indication information, which is used to indicate the timing offset between the second cell and the first cell.

[0050] In conjunction with the second aspect, in one possible implementation, the arrival time is determined based on the start time of the second frame of the second cell and a second time offset; wherein the start time of the second frame is determined based on the timing offset between the second cell and the first cell, and the second time offset is the time offset between the time domain resources occupied by the downlink synchronization signal and the second frame.

[0051] In conjunction with the second aspect, in one possible implementation, the first information includes fourth indication information, which is used to indicate the frame number, subframe number, or time slot number of the second cell corresponding to the start or end time of the handover command.

[0052] In conjunction with the second aspect, in one possible implementation, the arrival time is determined based on the start time of the third frame of the second cell and the third time offset; wherein, the start time of the third frame is determined based on the frame number, subframe number, or time slot number of the second cell corresponding to the handover command, and the third time offset is the time offset between the time domain resources occupied by the downlink synchronization signal and the third frame.

[0053] In conjunction with the second aspect, in one possible implementation, the method further includes: after stopping data transmission between the terminal and the second access network device, indicating to the second access network device that the terminal has successfully received the data, the second access network device being the access network device to which the second cell belongs.

[0054] In conjunction with the second aspect, in one possible implementation, information indicating that the terminal has successfully received data is forwarded to the second access network device via the core network device. For example, information indicating that the terminal has successfully received data is forwarded to the second access network device via the access and mobility function (AMF).

[0055] Thirdly, embodiments of this application provide a communication method that can be applied to the network side, such as a second access network device on the network side, a module (e.g., circuit, chip, or chip system) in the second access network device, or a logical node, logical module, or software that can implement all or part of the functions of the second access network device. Taking the application of this method to a second access network device as an example...

[0056] The method includes: when a terminal switches from a first cell to a second cell, instructing a first access network device or a core network device that the terminal has successfully switched from the first cell to the second cell, wherein the second cell is a cell included in the second access network device, and the core network device is the core network device managing the terminal. For example, the core network device is an AMF (Advanced Management Function).

[0057] Fourthly, this application provides a communication method, which can be executed by a terminal, or by a component configured in the terminal (such as a chip, chip system, etc.), or by a logic module or software capable of implementing all or part of the terminal functions. This application does not limit the scope of the method.

[0058] The communication method includes: receiving third information, the third information being used to instruct the terminal to perform conditional handover, the third information including at least one handover trigger condition corresponding to a cell;

[0059] When the handover triggering condition corresponding to the second cell in at least one cell is met, the handover is performed from the first cell to the second cell.

[0060] The handover triggering conditions for the second cell include a first condition, which is that the distance between the terminal and the reference point of the second cell is less than a first threshold.

[0061] In satellite communication systems, the signal strength differences between the cell or beamcenter and edge are relatively small, as are the signal strength differences between cells. Terminals' measurement-triggered handover is often inaccurate, easily leading to handover failures. After a handover failure, the terminal reselects and reconnects to a cell, resulting in longer service interruptions. Based on the communication method provided in the fourth aspect above, introducing location-based handover triggering conditions can improve handover accuracy and reduce the probability of handover failures.

[0062] In conjunction with the fourth aspect, in one possible implementation, at least one cell includes both terrestrial network (TN) cells and NTN cells;

[0063] The method further includes: if both the handover triggering conditions for the TN cell and the handover triggering conditions for the NTN cell are met simultaneously, determining to hand over from the first cell to the TN cell.

[0064] In other words, under this implementation, if both the handover triggering conditions for the TN cell and the handover triggering conditions for the NTN cell are met simultaneously, the terminal will preferentially select the TN cell as the cell after handover in order to provide the terminal with better service quality.

[0065] In conjunction with the fourth aspect, in one possible implementation, the handover triggering condition for the second cell also includes a second condition, which is that the signal strength or quality of the first cell is worse than a second threshold, and the signal strength or quality of the second cell is better than a third threshold.

[0066] In other words, under this implementation, the handover triggering conditions for the terminal to switch to the second cell include: the distance between the terminal and the reference point of the second cell is less than a first threshold, and the signal strength or quality of the first cell is worse than a second threshold and the signal strength or quality of the second cell is better than a third threshold.

[0067] In conjunction with the fourth aspect, in one possible implementation, the method further includes: when the terminal is not covered by any cell other than the first cell, and / or when the service quality of the first cell deteriorates, and / or when a wireless link failure is detected, the terminal enters an idle state.

[0068] This implementation method can save power consumption in the terminal.

[0069] Optionally, when the terminal enters the idle state, the terminal may shut down, deactivate, or suspend the processing of the access layer AS.

[0070] In this implementation, since the terminal also shuts down, deactivates, or suspends the processing of the access layer AS when it enters the idle state, the power consumption of the terminal can be further saved.

[0071] In conjunction with the fourth aspect, in one possible implementation, the method further includes: receiving fourth information, the fourth information being used by the terminal to determine the time when the second cell begins to cover the terminal; determining the time when the second cell begins to cover the terminal based on the fourth information; and detecting whether the handover triggering condition corresponding to the second cell is met starting from a second time, the second time being determined based on the time when the second cell begins to cover the terminal.

[0072] For example, the second time is the time before the second cell begins to cover the terminal, or the second time is the time after the second cell begins to cover the terminal, or the second time is the time when the second cell begins to cover the terminal.

[0073] For example, the second cell is a quasi-fixed cell, and the fourth information includes the start time of the terminal coverage in the second cell and the coverage area of ​​the second cell.

[0074] For example, if the second cell is a mobile cell, the fourth information includes the reference point and radius of the second cell, as well as the timestamp information corresponding to the reference point.

[0075] Fifthly, embodiments of this application provide a communication method that can be applied to the network side, such as a first access network device on the network side, a module (e.g., circuit, chip, or chip system) in the first access network device, or a logical node, logical module, or software that can implement all or part of the functions of the first access network device. Taking the application of this method to a first access network device as an example...

[0076] The communication method includes: sending third information, which is used to instruct the terminal to perform conditional handover, the third information including at least one cell corresponding to a handover triggering condition; wherein, the at least one cell includes a second cell, and the handover triggering condition corresponding to the second cell includes a first condition, the first condition being that the distance between the terminal and the reference point of the second cell is less than a first threshold.

[0077] In conjunction with the fifth aspect, in one possible implementation, the handover triggering condition for the second cell also includes a second condition, which is that the signal strength or quality of the first cell is worse than a second threshold, and the signal strength or quality of the second cell is better than a third threshold.

[0078] In conjunction with the fifth aspect, in one possible implementation, the method further includes: sending fourth information, which is used by the terminal to determine the time when the second cell begins to cover the terminal.

[0079] In conjunction with the fifth aspect, in one possible implementation, the method further includes: stopping data transmission with the terminal upon receiving a terminal context release message.

[0080] In conjunction with the fifth aspect, in one possible implementation, the method further includes: after stopping data transmission between the terminal and the terminal, instructing the second access network device that the terminal has successfully received the data.

[0081] Sixthly, this application provides a communication device that has the functions of the first aspect described above. For example, the communication device includes modules, units, or means that perform the operations involved in the first aspect. These modules, units, or means can be implemented by software, hardware, or a combination of software and hardware.

[0082] In a seventh aspect, this application provides a communication device that has the functions of the second aspect described above. For example, the communication device includes modules, units, or means that perform the operations involved in the second aspect described above. These modules, units, or means can be implemented by software, hardware, or a combination of software and hardware.

[0083] Eighthly, this application provides a communication device that has the functions of the third aspect above. For example, the communication device includes modules, units, or means that perform the operations involved in the first aspect above. These modules, units, or means can be implemented by software, hardware, or a combination of software and hardware.

[0084] Ninthly, this application provides a communication device that has the functions of the fourth aspect above. For example, the communication device includes modules, units, or means that perform the operations involved in the second aspect above. These modules, units, or means can be implemented by software, hardware, or a combination of software and hardware.

[0085] In a tenth aspect, this application provides a communication device that has the functions of the fifth aspect above. For example, the communication device includes modules, units, or means that perform the operations involved in the second aspect above. These modules, units, or means can be implemented by software, hardware, or a combination of software and hardware.

[0086] Eleventhly, this application provides a communication device including an interface circuit and one or more processors. The one or more processors are coupled to a memory. The memory stores part or all of the necessary computer program or instructions for implementing the functions described in the first aspect above. The one or more processors can execute the computer program or instructions, causing the communication device to implement the methods in any possible design or implementation of the first aspect above when executed. The interface circuit is used to implement the communication functions within the communication device and / or the communication functions between the communication device and other devices or components.

[0087] In one possible design, the processor is used to communicate with other devices or components through the interface circuit.

[0088] In one possible design, the communication device may also include the memory.

[0089] The aforementioned communication device may be a terminal, a communication module in a terminal, or a chip in a terminal that is responsible for communication functions, such as a modem chip (also known as a baseband chip) or a SoC or SIP chip containing a modem module.

[0090] In a twelfth aspect, this application provides a communication device including an interface circuit and one or more processors. The one or more processors are coupled to a memory. The memory stores part or all of a computer program or instructions necessary for implementing the functions described in the second aspect above. The one or more processors are executable to carry out the computer program or instructions, causing the communication device to implement the methods in any possible design or implementation of the second aspect above. The interface circuit is used to implement communication functions within the communication device and / or communication functions between the communication device and other devices or components.

[0091] In one possible design, the processor is used to communicate with other devices or components through the interface circuit.

[0092] In one possible design, the communication device may also include the memory.

[0093] The aforementioned communication device may be a first access network device, or a communication module in the first access network device, or a chip in the first access network device responsible for communication functions, such as a modem chip (also known as a baseband chip) or a SoC or SIP chip containing a modem module.

[0094] In a thirteenth aspect, this application provides a communication device including an interface circuit and one or more processors. The one or more processors are coupled to a memory. The memory stores part or all of a computer program or instructions necessary for implementing the functions described in the third aspect above. The one or more processors are executable to carry out the computer program or instructions, causing the communication device to implement the methods in any possible design or implementation of the third aspect above. The interface circuit is used to implement the communication functions within the communication device and / or the communication functions between the communication device and other devices or components.

[0095] In one possible design, the processor is used to communicate with other devices or components through the interface circuit.

[0096] In one possible design, the communication device may also include the memory.

[0097] The aforementioned communication device may be a second access network device, or a communication module in the second access network device, or a chip in the second access network device responsible for communication functions, such as a modem chip (also known as a baseband chip) or a SoC or SIP chip containing a modem module.

[0098] In a fourteenth aspect, this application provides a communication device including an interface circuit and one or more processors. The one or more processors are coupled to a memory. The memory stores part or all of a computer program or instructions necessary for implementing the functions described in the fourth aspect above. The one or more processors are executable to carry out the computer program or instructions, causing the communication device to implement the methods in any possible design or implementation of the fourth aspect above. The interface circuit is used to implement communication functions within the communication device and / or communication functions between the communication device and other devices or components.

[0099] In one possible design, the processor is used to communicate with other devices or components through the interface circuit.

[0100] In one possible design, the communication device may also include the memory.

[0101] The aforementioned communication device may be a terminal, a communication module in a terminal, or a chip in a terminal that is responsible for communication functions, such as a modem chip (also known as a baseband chip) or a SoC or SIP chip containing a modem module.

[0102] In a fifteenth aspect, this application provides a communication device including an interface circuit and one or more processors. The one or more processors are coupled to a memory. The memory stores part or all of a computer program or instructions necessary for implementing the functions described in the fifth aspect above. The one or more processors are executable to carry out the computer program or instructions, causing the communication device to implement the methods in any possible design or implementation of the fifth aspect above when executed. The interface circuit is used to implement communication functions within the communication device and / or communication functions between the communication device and other devices or components.

[0103] In one possible design, the processor is used to communicate with other devices or components through the interface circuit.

[0104] In one possible design, the communication device may also include the memory.

[0105] The aforementioned communication device may be a first access network device, or a communication module in the first access network device, or a chip in the first access network device responsible for communication functions, such as a modem chip (also known as a baseband chip) or a SoC or SIP chip containing a modem module.

[0106] In a sixteenth aspect, this application provides a communication system that includes the communication devices described in aspects eleven, twelfth, and thirteen; or, the communication system includes the communication devices described in aspects fourteen and fifteen.

[0107] In a seventeenth aspect, this application provides a computer-readable storage medium storing computer-readable instructions that, when read and executed by a computer, cause the computer to perform any of the possible designs in the first to fifth aspects described above.

[0108] In an eighteenth aspect, this application provides a computer program product that, when read and executed by a computer, causes the computer to perform any of the possible designs in the first to fourth aspects described above. Attached Figure Description

[0109] Figure 1 shows a schematic diagram of two types of NTN cells;

[0110] Figure 2 shows a schematic diagram of an SSB;

[0111] Figure 3 shows a schematic diagram of SSB transmission;

[0112] Figure 4 shows a schematic diagram of a hopping beam;

[0113] Figure 5 illustrates several procedural diagrams of a terminal performing random access;

[0114] Figure 6 shows a schematic diagram of the terminal's access-free process;

[0115] Figure 7 shows a structural schematic diagram of an access network device;

[0116] Figures 8 to 11 show schematic diagrams of several scenarios in which the technical solution of this application can be applied;

[0117] Figure 12 is a schematic diagram of a current terminal switching process;

[0118] Figure 13 is a flowchart illustrating a communication method provided in one embodiment of this application;

[0119] Figure 14 is a schematic diagram of the terminal latency reduction provided by this application;

[0120] Figure 15 is a flowchart illustrating a communication method provided in another embodiment of this application;

[0121] Figure 16 is a flowchart illustrating a communication method provided in yet another embodiment of this application;

[0122] Figure 17 is a flowchart illustrating a communication device provided in an embodiment of this application;

[0123] Figure 18 is a flowchart illustrating a communication device provided in another embodiment of this application. Detailed Implementation

[0124] First, some terms used in the embodiments of this application will be briefly explained. It should be understood that these explanations are only for the purpose of understanding the embodiments of this application and should not constitute any limitation on this application.

[0125] 1. Non-terrestrial networks (NTN)

[0126] With the development of information technology, there are more urgent demands for efficient, mobile, and diverse communication, leading to the emergence of on-terrestrial network (NTN) technology. NTN communication has unique characteristics compared to terrestrial network communication. For example, by introducing non-terrestrial network communication such as satellites and drones, it can not only provide communication services to areas such as oceans and forests that are not covered by terrestrial communication networks, but also enhance the reliability of 5G communication, ensuring higher-quality communication services for users on airplanes, trains, and other modes of transportation; it can also provide more data transmission resources for 5G communication, improving network speed. Therefore, simultaneously supporting communication between terrestrial and non-terrestrial base stations such as satellites and drones is an inevitable trend in future 5G communication, offering significant benefits in terms of wide coverage, reliability, multiple connections, and high throughput. Thanks to the current concept of "anytime, anywhere" communication, the status of non-terrestrial communication networks will be further enhanced in the future.

[0127] For example, taking satellites as an example, generally speaking, the higher the satellite's orbit, the larger its coverage area. Generally speaking, satellite orbits can be divided into low Earth orbit (LEO), medium Earth orbit (MEO), and geostationary orbit (GEO) based on altitude. Non-Geosynchronous orbit (NGSO) includes low Earth orbit with an altitude of approximately 300 km to 1500 km and medium Earth orbit with an altitude of approximately 7000 km to 25000 km.

[0128] 2. NTN cell

[0129] NTN cells can be divided into fixed cells (or stationary cells), quasi-fixed cells, and mobile cells.

[0130] A fixed cell refers to a cell that provides fixed coverage to a specific geographical area. It can also be understood as a beam, cell, or satellite that provides fixed coverage to a specific geographical area.

[0131] Quasi-fixed cells refer to cells that cover one geographic area within a limited time period and another geographic area within a different time period. This can also be understood as a beam, cell, or satellite covering one geographic area within a limited time period and a different geographic area within another time period. As shown in Figure 1(a), at time T1, the satellite is at position 1; at time T2, the satellite moves to position 2; and at time T3, the satellite moves to position 3. During the satellite's movement, the geographic area covered by the satellite's beam remains almost the same.

[0132] A moving cell refers to a cell whose coverage area has shifted. That is, the coverage area of ​​the beam, cell, or satellite has shifted. As shown in Figure 1(b), at time T1, the satellite is at position 1, and the geographical area covered by the satellite's beam is region 1. At time T2, the satellite moves to position 2, and the geographical area covered by the satellite's beam is region 2. At time T3, the satellite moves to position 3, and the geographical area covered by the satellite's beam is region 3.

[0133] 3. NTN parameter information

[0134] Terminals need NTN parameter information to access NR / LTE (or other networks) via NTN. NTN parameter information can also be called NTN configuration information. When the NTN network is a satellite network, NTN parameter information can also be called satellite auxiliary information.

[0135] Taking NTN networks as an example, which are satellite networks, NTN parameter information can include satellite ephemeris information, common timing advance (TA) parameter information, epoch time parameter information, ntn-UlSync validity duration parameter information, kmac parameter information, downlink (DL) polarization indication information, uplink (UL) polarization indication information, TA report enable information, etc.

[0136] Among them, satellite ephemeris information is used to indicate satellite ephemeris, and the terminal can obtain and / or predict the position of the satellite through satellite ephemeris.

[0137] Common TA parameter information is used to indicate the common TA value of network control. The terminal can obtain the common TA value through the common TA parameter information. This parameter information may also include the common common TA value, the common TA value drift rate, and the common TA value drift rate variation. The terminal can predict and estimate the future and past common TA values ​​through this parameter information.

[0138] The start time parameter information is used to indicate the start time of the NTN parameter information.

[0139] The ntn-UlSync validity duration parameter information indicates the valid duration of NTN parameter information, during which the terminal can apply the NTN parameter information without needing to obtain new NTN parameter information (starting from the start time).

[0140] The kmac parameter information is used to indicate the scheduling offset provided by the network when the downlink and uplink frame timings are misaligned at the base station. This value can be 0. For example, for non-terrestrial networks, the round trip time (RTT) between the terminal and the base station is the sum of the terminal's timing advance and the kmac value. The terminal can round to the nearest time slot or subframe; or the terminal can choose not to round.

[0141] 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.

[0142] 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.

[0143] If the TA report enable information exists, the terminal will report a TA during or after the random access process.

[0144] 4. Synchronization signal block

[0145] The synchronization signal block (SSB), also known as the synchronization signal or PBCH block, is specifically composed of three parts: the primary synchronization signal (PSS), the secondary synchronization signal (SSS), and the physical broadcasting channel block (PBCH). When a terminal moves within the communication system, it continuously performs cell search and measurement based on the SSB, selecting an appropriate SSB beam to achieve initial access and mobility management for the terminal device.

[0146] For example, Figure 2 illustrates the subcarrier positions occupied by the PSS, SSS, and PBCH within an SSB. As shown in Figure 2, one SSB occupies four orthogonal frequency division multiplexing (OFDM) symbols in the time domain and 20 consecutive resource blocks (RBs) in the frequency domain, i.e., 240 consecutive subcarriers. The first symbol of the SSB is the PSS, and the third symbol is the SSS, both occupying 127 subcarriers. The PBCH is distributed across the second to fourth symbols of the SSB, occupying 240 subcarriers in the second and fourth symbols. Additionally, as shown in Figure 2, there are some unused resource elements (REs) on both sides of the SSS in the third symbol.

[0147] The SSB is a crucial pilot channel or signal used in 5G NR, its role affecting many aspects of terminal access to a cell, such as cell search, measurement, cell selection and reselection, and handover. For example, the terminal obtains the master information block (MIB) information from the PBCH to acquire basic information about the cell, such as whether access is prohibited, as well as the location information of system information block (SIB) 1. After obtaining the SIB 1 location information according to the MIB information, the terminal retrieves the SIB 1 information at the corresponding location to obtain the remaining basic information needed for cell selection during initial network access and the scheduling information of other SIBs. SIB 1 can also be called remaining minimum system information (RMSI).

[0148] In NR, SSBs are transmitted in the form of beam scanning. That is, a base station can transmit one beam direction at a given moment, and transmit different beams at multiple moments to cover the directions needed for the entire cell. Let L be the number of SSBs transmitted in different directions in a single beam scan. The total number of SSBs transmitted in this scan is called an SSB Burst, representing a set of one or more SSBs. To avoid ambiguity, the following text uses SSB to refer to a single SSB occupying 4 symbols in the time domain, and SSB Burst to refer to all SSBs transmitted in a single beam scan.

[0149] SSB Burst can be sent at periods of 5 milliseconds (ms), 10ms, 20ms, 40ms, 80ms, or 160ms. This can also be understood as the SSB scan period being 5 milliseconds (ms), 10ms, 20ms, 40ms, 80ms, or 160ms. A longer period results in better network energy efficiency, while a shorter period allows for faster cell search for the terminal.

[0150] During initial cell search or terrorist attack mode mobility, the protocol specifies that terminals can assume a default SSB Burst period of 20ms, and the SSB Burst transmission window is in half-frame (5ms) units, as shown in Figure 3, located in the first half of a radio frame. That is, within this 20ms period, the SSB Burst is always limited to a 5ms (half-frame) time interval, with no SSB transmission for the remaining 15ms.

[0151] 5. Beam skipping

[0152] Generally, a single satellite has a wide coverage area, with a coverage radius of thousands or even tens of thousands of kilometers, while the coverage area of ​​a single beam can be as small as tens or even thousands of meters. Therefore, to support wide-area coverage, a single high-throughput satellite is usually equipped with hundreds or even thousands of beams, which poses a significant challenge to the payload of satellites, especially low Earth orbit (LEO) satellites. For example, under the minimum link budget required to meet link coverage, the maximum number of beams that can be activated simultaneously for downlink transmission is 24, and the maximum number of beams will change as the satellite power increases.

[0153] To alleviate the contradiction between small payload capacity and wide coverage of a single satellite, hopping beam satellite communication systems have emerged. Specifically, in a hopping beam satellite system, a single satellite is equipped with only a small number of beams (e.g., dozens of beams), which serve the entire coverage area of ​​the single satellite through time-division multiplexing. Referring to Figure 4, which is a schematic diagram of a hopping beam satellite communication system, as shown in Figure 4, the satellite can only form four beams at a time. At the four time points T1, T2, T3, and T4, each of the four beams corresponding to the diagonal lines serves the entire coverage area of ​​the single satellite (i.e., the area corresponding to 16 beams) through time-division multiplexing.

[0154] In beam-hopping scenarios, because the satellite beam scan period can be very long, it can take a considerable amount of time for the satellite beam to re-cover the previously covered area. Therefore, if the terminal still defaults to using a 20ms SSB Burst scan period, the terminal may fail to receive the SSB, resulting in the terminal being unable to access the cell in a timely manner. Therefore, it is currently proposed to extend the SSB scan period and / or default the SSB scan period.

[0155] It should be noted that, for satellites, a satellite cell can contain one or more SSBs. A cell includes one or more satellite beams. The relationship between satellite beams and SSBs is not restricted; for example, one satellite beam can correspond to one SSB, or one satellite beam can correspond to multiple SSBs.

[0156] 6. Random Access

[0157] After the user equipment (UE) achieves downlink synchronization with the cell, it also needs to achieve uplink synchronization with the cell and obtain uplink resource allocation before it can initiate uplink transmission. Random access (RA) is used to achieve uplink synchronization between the terminal and the cell. After successful random access, the UE can establish an RRC connection with the cell and send RRC messages to the cell. Below, we introduce several implementation methods of random access.

[0158] I. Competition-based four-step random access

[0159] Referring to Figure 5(a), Figure 5(a) illustrates a schematic diagram of a contention-based four-step random access procedure. As shown in Figure 5(a), the contention-based four-step random access procedure includes:

[0160] Step 1: After the UE and the base station achieve downlink synchronization, the UE determines the physical random access channel (PRACH) resource for sending the RA preamble, and then sends the random access preamble, i.e., message 1 (MSG1), on this resource.

[0161] The random access preamble is also called the random access preamble sequence or random access preamble code.

[0162] For example, the UE opens the random access response window at the time of the preamble ending subframe + 3 subframes + UE-base station RTT (UE-base station RTT). The size (or duration) of the random access response window is configured by the base station. If the UE repeatedly sends multiple preambles, the random access response window opens at the time of the last preamble ending subframe + 3 subframes + UE-base station RTT. In a 5G system, the random access response window opens at the time of the preamble ending subframe + UE-base station RTT; that is, the 3 subframes here can also be 0 subframes or other numbers of subframes.

[0163] The UE determines the random access radio network temporary identifier (RA-RNTI) and detects the physical downlink control channel (PDCCH) scrambled with the RA-RNTI, i.e., it monitors within the random access response window. It's important to note that after sending the preamble, the UE starts the RA response window, continuously detecting the PDCCH channel within the RA sliding window until it obtains the required RA response on the physical downlink shared channel (PDSCH). Based on the information in the PDCCH, the UE can determine the location (time-frequency resource location) of the PDSCH.

[0164] Step 2: The base station sends a random access response.

[0165] The message carrying the random access response is also called message 2 (MSG2).

[0166] One implementation is as follows: The base station determines the RA-RNTI and scrambles the PDCCH using the RA-RNTI; after receiving the UE's preamble, the base station obtains the terminal's TA based on the preamble. The base station sends a random access response on the PDSCH channel via MSG2 to indicate that it has received the preamble, and carries the TA value to the UE via MSG2 for adjusting the UE's transmission timing. The information carried in the random access response also includes the identifier (ID) of the random access preamble sent by the UE in step 1, the uplink grant (UL grant), and the cell radio network temporary identifier (Temporary C-RNTI).

[0167] Step 3: After receiving MSG2, the UE achieves uplink synchronization and can transmit message 3 (MSG3) on the predetermined PUSCH. MSG3 carries the UE's unique identifier (UE ID), which is used for conflict resolution in Step 4 to distinguish UEs that sent conflicting messages. If the UE has previously connected to a cell, it uses the cell's identifier C-RNTI as its ID, which is unique within that cell; otherwise, the UE uses an identifier from the core network (S-TMSI or a random number).

[0168] Specifically, after receiving the random access response, the UE stops the random access response window. In the first symbol or subframe after the end of all repetitions of all MSG3 transmissions plus the UE-base station RTT, the contention resolution timer is started or restarted. During the contention resolution timer's operation, the UE detects the PDCCH, such as a TC-RNTI or C-RNTI scrambled PDCCH.

[0169] Step 4: The base station sends a contention resolution message, also known as message 4 (MSG4), to the UE.

[0170] The base station assists the UE in contention resolution by using C-RNTI on the PDCCH or the UE contention resolution identifier on the PDSCH. Before the contention resolution timer expires, the UE continuously monitors the PDCCH channel. If any of the following conditions exist, the UE considers the contention resolution successful (i.e., the UE has successfully accessed the network) and stops the contention resolution timer; otherwise, the timer remains active:

[0171] The UE detects its C-RNTI on the PDCCH via MSG 4. At this point, the UE will stop the contention resolution timer and discard the Temporary C-RNTI.

[0172] The UE detects its Temporary C-RNTI on the PDCCH via MSG 4, and the UE contention resolution identity contained in the Media Access Control Layer (MAC) Protocol Data Unit (PDU) received by the UE from the PDSCH is the same as the UE contention resolution identity carried in MSG 3 sent by the UE (i.e., MAC PDU decoding is successful). At this point, the UE will stop the contention resolution timer and set the Temporary C-RNTI to C-RNTI.

[0173] Additionally, if the contention resolution timer times out, the UE will discard the Temporary C-RNTI and consider the contention resolution to have failed.

[0174] II. Four-step random access based on non-contention

[0175] Referring to Figure 5(b), Figure 5(b) illustrates a schematic diagram of a contention-based four-step random access procedure. As shown in Figure 5(b), the contention-based four-step random access procedure includes:

[0176] Step 1: The base station assigns a random access preamble to the UE;

[0177] Step 2: The UE sends a random access preamble, that is, the UE sends MSG1 to the base station;

[0178] Step 3: Based on the random access preamble sent by the UE, the base station sends a random access response message (i.e., MSG2) to the UE;

[0179] Step 4: After receiving MSG2, the UE sends an RRC connection establishment request message (i.e., MSG3) to the base station.

[0180] It can be seen that, compared with the contention-based four-step random access, the contention-based random access preamble is allocated by the base station, which reduces the contention resolution process.

[0181] III. Competition-based two-step random access

[0182] Referring to Figure 5(c), Figure 5(c) illustrates a schematic diagram of a contention-based two-step random access procedure. As shown in Figure 5(c), the contention-based two-step random access procedure includes:

[0183] 1. The UE sends message A (MSGA) to the base station.

[0184] MSGA transmission can be divided into two parts: RA Preamble transmission and PUSCH payload transmission, corresponding to MSG1 and MSG3 in the four-step random access process, respectively. This can be understood as follows: when the UE receives the two-step random access configuration, it receives information about transmitting the Preamble on the PRACH channel and also an authorization related to transmitting the Preamble to send the content that should have been sent on MSG3 on the PUSCH. Therefore, MSGA is not a single message sent at the same TTI, but rather two messages sent at different times: the Preamble is sent at TTI1, and the PUSCH payload is sent on the corresponding biased PUSCH resource. Specifically:

[0185] The UE opens a random access response window (corresponding to message B (MSGB) response window) at the subframe, symbol, or time slot where PUSCH or Preamble ends and the UE-base station RTT time. The size (or duration) of the random access response window is configured by the base station.

[0186] The UE determines the MSGB-RNTI and detects the PDCCH scrambled with MSGB-RNTI or / and C-RNTI, i.e., within the random access response window.

[0187] The PUSCH carries a unique identifier for the UE (UE ID), which is used for collision resolution in the MSGB to distinguish the UE that sent the conflicting message. If the UE has previously connected to a cell, it uses the cell's Radio Network Identifier (C-RNTI) as its ID, which is unique within that cell; otherwise, the UE uses an identifier from the core network (S-TMSI or a random number).

[0188] 2. After receiving the MSGA, the base station needs to parse both the Preamble sent by the UE and the associated grant content (pusch paylaod). If both are parsed, the MSGB will be sent to resolve contention conflicts. At the same time, the RRC connection establishment content can also be sent in this message.

[0189] IV. Two-Step Random Access Based on Non-Contesting

[0190] Referring to Figure 5(d), Figure 5(d) illustrates a schematic diagram of a contention-based two-step random access procedure. As shown in Figure 5(d), the contention-based two-step random access procedure includes: 0. The base station allocates RA preamble and PUSCH resources to the UE; 1. The UE uses the RA preamble and PUSCH resources to send the MSGA; 2. The base station sends the RA response, i.e., MSGB.

[0191] 7. RACH-less

[0192] Referring to Figure 6, which illustrates the process of random access-free access, the source base station refers to the base station of the source cell, and the target base station refers to the base station of the target cell. The source cell refers to the cell before the UE hands over, and the target cell refers to the cell after the UE hands over.

[0193] As shown in Figure 6, the process for eliminating random access includes:

[0194] Step 1: The UE receives the RRC reconfiguration message (handover command) sent by the source base station. This handover command includes RACH-less handover configuration, and may also include a timing advance adjustment indication and optional pre-allocated uplink grants (i.e., pre-configured resources shown in Figure 6). The UE performs the handover, and the terminal starts the timing advance timer (TAT).

[0195] Step 2: The UE sends an RRC reconfiguration complete message.

[0196] Specifically, if the handover command includes pre-configured periodic UL resources, the UE sends an RRC reconfiguration complete message using those UL resources. Otherwise, the UE detects the PDCCH of the target cell to obtain UL scheduling and sends an RRC reconfiguration complete message.

[0197] Step 3: When the terminal receives a MAC control element (CE) containing the UE contention resolution identity, it considers the handover successful and releases resources related to non-random access, such as pre-allocated uplink authorization.

[0198] The technical solution of this application can be applied to non-terrestrial networks (NTNs) or scenarios where NTNs are integrated with terrestrial networks (TNs). NTN systems can be, for example, satellite communication systems, high altitude platform station (HAPS) communication systems, global navigation satellite systems (GNSS), etc. TN systems can be, for example, 4th generation (4G) communication systems (e.g., long term evolution (LTE) systems), worldwide interoperability for microwave access (WiMAX) communication systems, 5th generation (5G) communication systems (e.g., new radio (NR) systems), and future mobile communication systems. Furthermore, NTN systems can also be NTN systems integrated with 4G, 5G, and any future generation of communication systems.

[0199] In this embodiment of the application, the radio access network (R)AN device is used to provide access services for user equipment and to forward user equipment data between the user equipment and the core network. The (R)AN can also be understood as a base station in the network, which is a device deployed in the radio access network to provide wireless communication functions for mobile stations (MS).

[0200] For example, the access network device in this application embodiment can be any communication device with wireless transceiver function for communicating with user equipment. The access network equipment includes, but is not limited to: evolved Node B (eNB), radio network controller (RNC), Node B (NB), base station controller (BSC), base transceiver station (BTS), home evolved Node B (HeNB, or home Node B (HNB), baseband unit (BBU), access point (AP), wireless relay node, wireless backhaul node, transmission point (TP), or transmission and reception point (TRP) in a wireless fidelity (WiFi) system. It can also be a gNB in ​​a 5G system, or a transmission point (TRP or TP), one or a group of antenna panels (including multiple antenna panels) of a base station in a 5G system, or a network node constituting a gNB or transmission point, such as a baseband unit (BBU) or a distributed unit (DU). It is understood that all or part of the functions of the access network device in this application can also be implemented through software functions running on hardware, or through virtualization functions instantiated on a platform (such as a cloud platform).

[0201] In some deployments, access network equipment may include centralized unit (CU) nodes, distributed unit (DU) nodes, or RAN equipment comprising both CU and DU nodes. RAN equipment including CU and DU nodes splits the gNB's protocol layers, with some protocol layer functions centrally controlled by the CU, and the remaining partial or complete protocol layer functions distributed across the DUs, which are then centrally controlled by the CU. Furthermore, referring to Figure 7, the centralized unit (CU) can be further divided into a CU-control plane (CP) and a CU-user plane (UP). The CU-CP is responsible for control plane functions, primarily including radio resource control (RRC) and the corresponding packet data convergence protocol (PDCP). The PDCP for the control plane is also called PDCP-C. PDCP-C is mainly responsible for control plane data encryption / decryption, integrity protection, and data transmission. The CU-UP is responsible for user plane functions, primarily including the service data adaptation protocol (SDAP) and the corresponding PDCP for the user plane. The PDCP for the user plane is also called PDCP-U. SDAP is primarily responsible for processing core network data and mapping flows to bearers. PDCP-U is mainly responsible for data plane encryption / decryption, integrity protection, header compression, sequence number maintenance, and data transmission. CU-CP and CU-UP are connected via the E1 interface. CU-CP represents the gNB and connects to the core network via the NG interface. It connects to the DU via the F1 interface control plane (F1-C). CU-UP connects to the DU via the F1 interface user plane (F1-U). Alternatively, PDCP-C may also be located within CU-UP.

[0202] The terminal device in this application embodiment can also be referred to as user equipment (UE), access terminal, user unit, user station, mobile station, mobile station, remote station, remote terminal, mobile device, user terminal, terminal, wireless communication device, user agent, or user device. The terminal device can be a device that provides voice / data, such as a handheld device or vehicle-mounted device with wireless connectivity. Currently, examples of terminals include: mobile phones, tablets, laptops, PDAs, mobile internet devices (MIDs), wearable devices, virtual reality (VR) devices, augmented reality (AR) devices, wireless terminals in industrial control, wireless terminals in self-driving, wireless terminals in remote medical surgery, wireless terminals in smart grids, wireless terminals in transportation safety, wireless terminals in smart cities, wireless terminals in smart homes, cellular phones, cordless phones, session initiation protocol (SIP) phones, wireless local loop (WLL) stations, personal digital assistants (PDAs), handheld devices with wireless communication capabilities, computing devices or other processing devices connected to a wireless modem, wearable devices, terminal devices in 5G networks, or future public land mobile communication networks. Terminal devices in a network (PLMN), etc., are not limited to this in the embodiments of this application.

[0203] By way of example and not limitation, in this embodiment, the terminal device can also be a wearable device. Wearable devices, also known as wearable smart devices, are a general term for devices that utilize wearable technology to intelligently design and develop everyday wearables, such as glasses, gloves, watches, clothing, and shoes. Wearable devices are portable devices that are worn directly on the body or integrated into the user's clothing or accessories. Wearable devices are not merely hardware devices, but also achieve powerful functions through software support, data interaction, and cloud interaction. Broadly speaking, wearable smart devices include those that are feature-rich, large in size, and can achieve complete or partial functions without relying on a smartphone, such as smartwatches or smart glasses, as well as those that focus on a specific type of application function and require the use of other devices such as smartphones, such as various smart bracelets and smart jewelry for vital sign monitoring.

[0204] In this embodiment, the device for implementing the functions of the terminal device can be the terminal device itself, or it can be any device capable of supporting the terminal device in implementing those functions, such as a chip system. This device can be installed in or used in conjunction with the terminal device. In this embodiment, the chip system can be composed of chips or may include chips and other discrete components. This embodiment only uses the terminal device as an example to illustrate the device for implementing the functions of the terminal device, and does not constitute a limitation on the solution of this embodiment.

[0205] The following, with reference to Figures 8 to 11, illustrates a schematic diagram of the network architecture applicable to the embodiments of this application.

[0206] Figure 8 is a schematic diagram of an architecture of a communication system applicable to embodiments of this application. The architecture shown in Figure 8 is also called a transparent satellite RAN architecture. As shown in Figure 8, in a transparent scenario, the satellite's role is radio frequency filtering, frequency conversion, and amplification. That is, the satellite primarily acts as an L1 relay, regenerating physical layer signals and does not have other higher-level protocol layers. Therefore, the satellite replicates the NR Uu radio interface signal from the feeder link to the service link, and vice versa. The feeder link refers to the link between the NTN gateway and the satellite, and the service link refers to the link between the satellite and the terminal. The satellite radio interface (SRI) on the feeder link transmits the NR Uu interface signal; that is, the satellite does not terminate the NR Uu interface signal but replicates it. The NTN gateway supports all necessary functions for forwarding the NR-Uu interface signal. Different transmission satellites can connect to the same ground gNB.

[0207] Figure 9 is a schematic diagram of another architecture of the communication system applicable to embodiments of this application. The architecture shown in Figure 9 is also called a regenerative satellite without ISL (inter-satellite link) architecture. As shown in Figure 9, in this architecture, the satellite acts as a base station to regenerate signals received from the ground. That is, NR Uu radio interface signals are transmitted on the service link between the terminal and the satellite, and SRI signals are transmitted on the feed link between the NTN gateway and the satellite. The SRI interface is a transmission link between the NTN gateway and the satellite. The NG interface signal is transmitted to the NTN gateway through the SRI interface, and then forwarded by the NTN gateway to the ground core network equipment. The process of the NG interface signal being transmitted from the ground core network equipment to the satellite base station is similar and will not be described again here.

[0208] Figure 10 is a schematic diagram of another architecture of the communication system applicable to embodiments of this application. The architecture shown in Figure 10 is called a regenerative satellite with ISL architecture. In this scenario, the satellite also acts as a base station. The difference from the scenario shown in Figure 9 is that this scenario has an ISL. An ISL is an inter-satellite transmission link. As shown in Figure 10, a terminal served by an on-board base station can access the 5G core network through the ISL. Base stations on different satellites can connect to the same terrestrial 5G core network.

[0209] Figure 11 is a schematic diagram of another architecture of the communication system applicable to embodiments of this application. The architecture shown in Figure 11 is named NG-RAN with a regenerative satellite based on gNB-DU. In this scenario, the CU and DU of the base station are separated. The satellite, as the DU of the base station, is on-board. The satellite realizes the regeneration of signals received from the ground, that is, it transmits NR Uu radio interface signals on the service link between the terminal and the satellite, and transmits SRI signals on the feed link between the NTN gateway and the satellite. The satellite radio interface is a transmission link capable of transmitting the 3GPP standard logical interface F1 signal. F1 protocol signals are transmitted on the satellite radio interface. The satellite can provide inter-satellite links (ISL). The NTN gateway is a transmission network layer node and supports all necessary transmission protocols. DUs on different satellites can be connected to the same ground CU.

[0210] It should be noted that the above architecture is merely illustrative and is not intended to limit the scope of this application. For example, in another architecture, the satellite may function as an integrated access and backhaul (IAB), or the satellite may have IAB functionality.

[0211] The network elements in Figures 8 to 11 and their interfaces are described below:

[0212] NTN gateway: responsible for forwarding signaling and service data between satellite base stations and the 5G core network.

[0213] 5G New Radio: The wireless link between a terminal and a base station.

[0214] Xn interface: The interface between 5G base stations, mainly used for signaling interactions such as handover.

[0215] NG interface: The interface between 5G base stations and 5G core networks, mainly used for the interaction of non-access-stratum (NAS) signaling of the core network and user service data.

[0216] 5G Core Network: This refers to the equipment in the core network (CN) that provides service support for terminal devices in a 5G network. It consists of multiple functional units, mainly including user equipment functions (UPF) and control plane functions. The UPF is primarily responsible for packet forwarding, quality of service (QoS) control, billing information statistics, and connecting to external networks. The control plane functions are mainly responsible for service process interaction, issuing packet forwarding policies to the user plane, and QoS control policies. For example, the network elements in the control plane functions mainly include: access and mobility function (AMF), session management function (SMF), policy control function (PCF), application function (AF), and network exposure function (NEF). Detailed concepts of each network element can be found in relevant technical descriptions and will not be elaborated upon here.

[0217] In a communication system, a terminal can change its serving cell from one cell to another by performing a cell handover, also known as a cell handover.

[0218] In this application, the cell before handover is referred to as the source cell, and the cell after handover is referred to as the target cell. The base station to which the source cell belongs is also referred to as the source base station, and the base station to which the target cell belongs is also referred to as the target base station. Understandably, in NTN communication scenarios, such as satellite communication scenarios, the cell can also be replaced by a beam.

[0219] For example, both the source cell before the handover and the target cell after the handover are cellular cells. That is, the terminal hands over from the source cellular cell to the target cellular cell.

[0220] For example, both the source cell before the handover and the target cell after the handover are NTN cells. That is, the terminal hands over from the NTN source cell to the NTN target cell.

[0221] For example, the source cell before the handover is a cellular cell, and the target cell after the handover is an NTN cell. That is, the terminal hands over from the cellular source cell to the NTN target cell.

[0222] For example, the source cell before the handover is an NTN cell, and the target cell after the handover is a cellular cell. That is, the terminal hands over from the NTN source cell to the cellular target cell.

[0223] The following, with reference to Figure 12, describes a process for a terminal to perform cell handover. As shown in Figure 12, the cell handover process includes:

[0224] 1. The source base station sends measurement configuration to the terminal, including measurement object (same frequency / different frequency), measurement report configuration, and measurement interval (GAP) configuration.

[0225] 2. The terminal performs measurements according to the measurement configuration. When it determines that the measurement reporting conditions are met, it reports the measurement report to the source base station.

[0226] 3. Upon receiving the measurement report, the source base station makes a handover decision based on the measurement results, determines that the terminal will perform the handover, and identifies the target cell. After identifying the target cell, the source base station sends a handover request message to the target base station where the selected target cell is located to initiate the handover request.

[0227] For example, the handover request message contains the identifier of the target cell, the identifier of the terminal at the source base station, and the terminal's capability information.

[0228] 4. The target base station sends a handover request confirmation message to the source base station. This message contains the information required for the terminal to access the target base station.

[0229] 5. The source base station sends a handover command to the terminal, which instructs the terminal to hand over to the target cell.

[0230] For example, the cell handover command is carried in the RRC reconfiguration message. The RRC reconfiguration message includes, for example, the following information required to access the target cell: the target cell identifier, the new cell radio network temporary identifier (C-RNTI), 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 specific channel state information reference signal (CSI-RS) configuration, the public RACH resource, and the system information of the target cell, etc.

[0231] After the source base station sends a handover command to the terminal, the source cell stops transmitting data uplink and downlink to the terminal.

[0232] 6. The source base station sends the PDCP serial number (SN) to the target base station.

[0233] For example, the uplink PDCP SN receiver status and / or downlink PDCP SN transmitter status of data radio bearers (DRBs) with PDCP state retention for transmission applications. The uplink PDCP SN receiver status 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 status of out-of-order UL PDCP SDUs that the terminal needs to retransmit in the target cell. The downlink PDCP SN transmitter status indicates the next PDCP SN that the target gNB should assign to the new PDCP SDU, but which does not yet have a PDCP SN.

[0234] 7. The terminal accesses the target cell.

[0235] For example, let's take a non-contention-based 4-step random access method as an example. After receiving the cell handover command, the terminal leaves the source cell, releases the source cell's configuration, and stops uplink and downlink data transmission with the source cell. The terminal sends a dedicated preamble for random access, i.e., message 1 (MSG1), to the target cell of the target base station; after receiving MSG1, the target base station sends MSG2 to the terminal; after receiving MSG2, the terminal sends an RRC reconfiguration complete message to the target base station, thus completing the handover process.

[0236] The aforementioned terminal sends a dedicated preamble for random access to the target cell of the target base station, for example, by carrying it in the RRC reconfiguration message in step 5.

[0237] 8. The terminal sends an RRC reconfiguration complete message to the target base station to complete the handover process.

[0238] 9. The target base station sends a path handover request message to the AMF, notifying the terminal that the serving cell has changed. The path handover request message carries the identifier of the target cell and the list of protocol data unit (PDU) sessions to be switched. After receiving this message, the core network triggers a switch to the downlink data path of the target base station and establishes an interface instance to the target base station.

[0239] 10. The AMF replies to the target base station with a path handover request confirmation message.

[0240] 11. After receiving the path handover request confirmation message from the AMF, the target base station sends a terminal context release message to the source base station, notifying it that the handover was successful. Upon receiving the terminal context release message, the source base station can release the radio and control plane resources associated with the terminal context.

[0241] As can be seen from the above handover process, the service interruption time caused by the handover (also known as the handover interruption time) begins from the time the terminal receives the handover command until the terminal successfully accesses the target cell. The service interruption time is further divided into:

[0242] When the handover command is carried in the RRC message, the processing time of the terminal after receiving the handover command and processing the RRC message, such as decoding the RRC message, is approximately 10ms.

[0243] The time it takes for the terminal to retune the RF / baseband and update the security key and algorithm is approximately 20ms.

[0244] The 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.

[0245] The time it takes for the terminal to send MSG1 resources, execute the RACH procedure, and synchronize uplink with the target cell is, for example, approximately 20ms.

[0246] In beam-hopping scenarios, which can be understood as scenarios with extended SSB scan cycles or scenarios where the terminal switches from the source cell to the target cell in the NTN, the downlink synchronization time between the terminal and the target cell will increase, resulting in longer service interruption time for the terminal. In this case, service interruption or dropped calls may occur, affecting the user experience.

[0247] In view of this, this application provides a communication method and a communication device in order to reduce the duration of service interruption when the terminal performs a handover.

[0248] The communication method and communication device provided in the embodiments of this application will now be described with reference to the accompanying drawings.

[0249] Figure 13 is a flowchart illustrating a communication method 1300 provided in an embodiment of this application. As shown in Figure 13, method 1300 includes:

[0250] S1301, the first access network device sends a handover command to the terminal, and the terminal receives the handover command accordingly; the handover command is used to instruct the terminal to hand over from the first cell to the second cell.

[0251] In this application, when the first access network device determines that the terminal needs to switch from the first cell to the second cell, it will send a first message to the terminal. The first message is used to instruct the terminal to switch from the first cell to the second cell.

[0252] Understandably, the first access network device is the access network device to which the first cell belongs. That is, the first access network device includes the access network devices of the first cell.

[0253] The first cell mentioned above can also be called the source cell, which can be considered the cell that the terminal connects to or accesses before the handover. The second cell can also be called the target cell, which can be considered the cell that the terminal connects to or accesses after the handover is successful.

[0254] For example, the first cell is a cellular cell, and the second cell is an NTN cell.

[0255] For example, the first cell is an NTN cell, and the second cell is a cellular cell.

[0256] For example, both the first and second cells are cellular cells, or both the first and second cells are NTN cells.

[0257] In this application, the access network equipment to which the second cell belongs is referred to as the second access network equipment. That is to say, the second access network equipment includes the access network equipment of the second cell.

[0258] In this application, the first access network device to which the first cell belongs is also referred to as the source access network device or the source base station, and the second access network device to which the second cell belongs is also referred to as the target access network device or the target base station, etc.

[0259] For example, in one implementation, as shown in Figure 13, the first access network device sends measurement configuration information to the terminal, including the measurement object (same frequency / different frequency), measurement report configuration, and GAP configuration, etc. After receiving the measurement configuration information, the terminal performs measurements according to the measurement configuration information, and reports a measurement report to the first access network device when it determines that the measurement reporting conditions are met. After receiving the measurement report, the first access network device decides to switch the terminal from the first cell to the second cell based on the results of the measurement report. Then, the first access network device initiates a handover request to the second access network device, which requests the terminal to access the second cell. After receiving the handover request, the second access network device sends a handover request confirmation message to the first access network device, which indicates that the terminal can access the second cell. After receiving the handover request confirmation message, the first access network device sends a handover command to the terminal to instruct the terminal to switch from the first cell to the second cell. For example, the handover command includes information required to access the second cell, such as the identification information of the second cell.

[0260] For example, the first access network device sends the handover command to the terminal in an RRC reconfiguration message. Alternatively, the first access network device sends the handover command to the terminal in a MAC CE or a Layer 1 (L1) message.

[0261] S1302, the first access network device sends first information to the terminal, and the corresponding terminal receives the first information; the first information is used by the terminal to determine the arrival time of the downlink synchronization signal of the second cell to the terminal.

[0262] For example, the first information is carried in the RRC reconfiguration message.

[0263] In this embodiment, when the first access network device determines that the terminal is switching from the first cell to the second cell, in addition to sending a handover command to the terminal, it also sends first information to the terminal. The first information is used by the terminal to determine the arrival time of the downlink synchronization signal of the second cell. In this application, the first information is also referred to as auxiliary information, that is, information used to assist the terminal in determining the arrival time of the downlink synchronization signal of the second cell.

[0264] The downlink synchronization signal of the second cell is used by the terminal to achieve downlink synchronization with the second cell. The downlink synchronization signal of the second cell can also be called the downlink synchronization reference signal of the second cell or the downlink synchronization message of the second cell, etc.

[0265] For example, the downlink synchronization signal of the second cell is the synchronization signal block (SSB) of the second cell. It should be noted that the SSB here is only an example and does not constitute a limitation of this application. Any signal or message that can be used for downlink synchronization between the terminal and the second cell can be considered as the downlink synchronization signal of the second cell.

[0266] Optionally, the first access network device can also send the NTN parameter information corresponding to the second cell to the terminal. For example, the NTN parameter information of the second cell can be sent to the terminal via broadcast or unicast. The NTN parameter information can be found in the terminology introduction above, and will not be repeated here.

[0267] It should be noted that in this application, there is no specific execution order between S1301 and S1302. In one implementation, the first information and the switching command can be carried in the same message. That is, the switching command and the first information are sent through the same message.

[0268] The implementation of the first information and the terminal determining the arrival time of the downlink synchronization signal of the second cell to the terminal based on the first information will be described in S1303, and will not be elaborated here.

[0269] S1303, the terminal transmits data with the first cell during the period between receiving the handover command and the first time, and disconnects the data transmission with the first cell and accesses the second cell during the first time.

[0270] Understandably, S1303 specifically includes S1303a to S1303b.

[0271] S1303a: The terminal transmits data with the first cell during the period between receiving the handover command and the first time, and disconnects the data transmission with the first cell at the first time and starts searching for the downlink synchronization signal of the second cell, so as to obtain downlink synchronization with the second cell based on the downlink synchronization signal of the second cell.

[0272] S1303b: After achieving downlink synchronization with the second cell based on the downlink synchronization signal of the second cell, access the second cell.

[0273] The transmission of data with the first cell can also be understood as one or more of the following: not releasing the configuration information of the first cell, detecting the downlink control information of the first cell, receiving data and / or information from the first cell, and sending data and / or information to the first cell.

[0274] Disconnecting data transmission with the first cell at the first moment can also be understood as: disconnecting the connection with the first cell at the first moment. Disconnecting data transmission with the first cell can also be understood as one or more of the following: releasing the configuration information of the first cell, not detecting the downlink control information of the first cell, not receiving data and / or information from the first cell, and not sending data and / or information to the first cell.

[0275] Specifically, the first time is determined based on the arrival time of the downlink synchronization signal from the second cell to the terminal. For example, the first time can be a time before the arrival time, or the first time can be the arrival time itself. That is, the terminal determines / estimates the arrival time of the downlink synchronization signal from the second cell to the terminal based on the first information, and then disconnects data transmission with the first cell before or at the arrival time and accesses the second cell.

[0276] In other words, in this embodiment, after the first access network device sends a handover command to the terminal, it does not immediately stop / disconnect uplink and downlink data transmission with the terminal, but continues to transmit uplink and downlink data. Correspondingly, after receiving the handover command, the terminal will not leave the first cell (source cell) or release its configuration with the first cell during the period from receiving the handover command to the first time. It will not stop uplink data transmission with the first cell and will continue to transmit data with the first cell. Then, at the first time, it will disconnect data transmission with the first cell and access the second cell.

[0277] The following describes how the first access network device sends first information to the terminal, and the terminal determines the arrival time of the downlink synchronization signal of the second cell based on the first information.

[0278] For example, the first indication information in the first information is used to indicate the time-domain resources occupied by the downlink synchronization signal of the second cell. Alternatively, the first indication information is used to indicate the time-frequency resources (including time-domain resources and frequency-domain resources) occupied by the downlink synchronization signal of the second cell. For example, the time-domain resources occupied by the downlink synchronization signal of the second cell can be the start time and duration information of the downlink synchronization signal of the second cell, or it can be periodic information, offset information, etc. The terminal can determine the time of occurrence of the downlink synchronization signal by the time-domain resources occupied by the downlink synchronization signal of the second cell, such as the frame number, subframe number (and / or time slot number), symbol information, etc.

[0279] In one implementation, the first indication information can be sent to the terminal via broadcast or unicast before S1301. Optionally, if the time-domain and / or frequency-domain resources of the downlink synchronization signal are fixed, the first indication information may not need to be sent.

[0280] For example, in one implementation, the first indication information is used to indicate the time-domain resources occupied by the downlink synchronization signal, including: the first indication information is used to indicate the absolute time when the second cell transmits the downlink synchronization signal.

[0281] The first indication information is used to indicate the absolute time when the second cell transmits the downlink synchronization signal. It can also be understood as indicating the start time of the frame / subframe in which the second cell's downlink synchronization signal is located, expressed in absolute time. Alternatively, it can be understood as indicating the start time of the frame / subframe in which the second cell begins transmitting the downlink synchronization signal, expressed in absolute time. Furthermore, it can be understood as indicating the absolute time when the second cell begins transmitting the downlink synchronization signal. Understandably, accurate absolute time is difficult to represent, and approximate values ​​are generally used. Therefore, the absolute time may be the actual start time of the second cell transmitting the downlink synchronization signal, or a time before or after the actual start time.

[0282] Optionally, when the first indication information indicates the absolute time for the second cell to transmit the downlink synchronization signal, the first indication information may also include the period information and duration information of the downlink synchronization signal of the second cell. It is understood that the absolute time for the second cell to transmit the downlink synchronization signal can be the absolute time for the downlink synchronization signal transmitted by the second cell in any given period.

[0283] Understandably, once the first indication information indicates the absolute time when the second cell transmits the downlink synchronization signal, the terminal can determine this absolute time based on the first indication information. Furthermore, the terminal can obtain the arrival time of the downlink synchronization signal from the second cell by using the absolute time of the downlink synchronization signal transmission from the second cell and the RTT or one-way propagation delay (i.e., RTT / 2) between the terminal and the second cell. Understandably, the arrival time equals the absolute time of the second cell transmitting the downlink synchronization signal plus RTT / 2.

[0284] For example, in another implementation, the first information includes second indication information, which is used to indicate the start time of the first frame of the second cell.

[0285] The second indication information is used to indicate the start time of the first frame of the second cell. It can also be understood as: the second indication information is used to indicate the absolute time corresponding to the start time of the first frame of the second cell, or the second information is used to indicate the absolute time corresponding to the start time of the second cell sending the first frame, or the second information is used to indicate the absolute time when the second cell starts sending the first frame.

[0286] Understandably, if the start time of the first frame of the second cell is indicated by the second indication information, the terminal can determine the occurrence time of the downlink synchronization signal of the second cell based on the start time of the first frame of the second cell and the time domain resources occupied by the downlink synchronization signal of the second cell, and then determine the arrival time of the downlink synchronization signal of the second cell to the terminal.

[0287] Understandably, the first frame can also be a frame with any frame index value. For example, in one instance, the first frame could be a frame carrying a downlink synchronization signal.

[0288] It should be noted that the time-frequency resources occupied by the downlink synchronization signal can be specifically subframes or symbols. Therefore, there may be scenarios where the starting position of the resources occupied by the downlink synchronization signal in the time domain may not be the start time of the first frame. Understandably, in such scenarios, the position where the downlink synchronization signal appears is offset from the start position of the first frame.

[0289] For example, in one implementation, the terminal determines the arrival time of the downlink synchronization signal of the second cell by: determining the time domain resources where the downlink synchronization signal of the second cell is located based on the time-frequency resource configuration information of the downlink synchronization signal of the second cell, such as the frame number or subframe number of the downlink synchronization signal; determining the time offset between the time domain resources where the downlink synchronization signal of the second cell is located and the first frame, which is also called the first time offset; obtaining the time when the second cell transmits the downlink synchronization signal through the start time of the first frame of the second cell and the first time offset; and obtaining the arrival time of the downlink synchronization signal of the second cell at the terminal by the time when the second cell transmits the downlink synchronization signal and the RTT or one-way propagation delay (i.e., RTT / 2) between the terminal and the second cell. Understandably, the arrival time is equal to the absolute time when the second cell transmits the downlink synchronization signal plus RTT / 2.

[0290] Optionally, when the second indication information is used to indicate the start time of the first frame of the second cell, the first frame can be the very first frame of the second cell. For example, if the frame index starts from 0, the first frame is the frame with frame index 0, for example, denoted as frame #0. That is, the second indication information is used to indicate the start time of frame #0 of the second cell. It can also be understood that the second indication information is used to indicate the absolute time corresponding to the start time of frame #0 of the second cell. It is understandable that the absolute time corresponding to the start time of frame #0 can also be considered as the absolute time corresponding to the start time of the subframe with subframe index 0 within the frame with frame index 0.

[0291] For example, let's denote the subframe with index 0 within the frame with frame index 0 as subframe #0 of frame #0. If the second indication information indicates the start time of frame #0 of the second cell, and the terminal determines that the downlink synchronization signal of the second cell is located in frame #m based on the time-domain resources of the downlink synchronization signal of the second cell, then the terminal can determine that the time when the second cell sends the downlink synchronization signal (i.e., the time when it sends frame #m) is the absolute time corresponding to the start time of subframe #0 of frame #0 plus (m-0) frame durations. Understandably, m frame durations are equal to m * the duration of one frame. Further, after determining the time when the second cell sends the downlink synchronization signal, adding the one-way propagation delay between the terminal and the second access network device will give the arrival time of the downlink synchronization signal of the second cell at the terminal.

[0292] For example, in another implementation, the first information includes third indication information, which is used to indicate the timing offset between the second cell and the first cell.

[0293] Understandably, the third indication information is used to indicate the timing offset between the second cell and the first cell; that is, the third indication information is used to indicate the offset between the start times of frames with the same frame number in the second and second cells. For example, taking frame #0 as an example, the timing offset between the second cell and the first cell is the offset between the start time of frame #0 in the second cell and the start time of frame #0 in the first cell. For example, in one implementation, the timing offset between the second cell and the first cell is the start time of frame #0 in the first cell minus the start time of frame #0 in the second cell. In another implementation, the timing offset between the second cell and the first cell is the start time of frame #0 in the first cell minus the start time of frame #0 in the second cell.

[0294] For example, when both the first access network device and the second access network device are satellites, the first information includes the offset value of the start time of frame #0 of the target satellite beam and the source satellite beam.

[0295] Understandably, if the timing offset between the second cell and the first cell is indicated by the third indication information, the terminal can determine the occurrence time of the downlink synchronization signal of the second cell based on the timing offset between the second cell and the first cell and the time domain resources occupied by the downlink synchronization signal of the second cell, and then determine the arrival time of the downlink synchronization signal of the second cell to the terminal.

[0296] For example, in one implementation, the terminal determines the arrival time of the downlink synchronization signal from the second cell. This includes: the terminal determining the start time of the second frame of the second cell based on the timing offset between the second cell and the first cell, for example, determining the absolute time of the second frame; determining the time offset between the time domain resources containing the downlink synchronization signal of the second cell and the second frame, also known as the second time offset; obtaining the time when the second cell transmits the downlink synchronization signal using the start time of the second frame and the second time offset; and obtaining the arrival time of the downlink synchronization signal from the second cell using the transmission time of the downlink synchronization signal from the second cell and the RTT or one-way propagation delay between the terminal and the second cell. Understandably, the arrival time is equal to the absolute time of the second cell transmitting the downlink synchronization signal plus RTT / 2.

[0297] For example, the first information includes the periodicity and offset information of the downlink synchronization signal of the second cell. The terminal uses this periodicity and offset information to determine the frame in which the downlink synchronization signal of the second cell is located. For instance, the NR system uses 1024 frames as a period, numbered starting from 0 (frame #0). Assuming the periodicity and offset information of the downlink synchronization signal are 50 frames and 5 frames respectively, then the frame number of the downlink synchronization signal would be frame #5, frame #55, frame #105, etc. It is understood that this example uses frame granularity; finer granularity is also possible, such as subframes, time slots, symbols, etc.

[0298] For example, the frame index of the second frame mentioned above is #i, and the second frame is denoted as frame #i. Since the terminal and the first cell have already achieved downlink synchronization, the terminal can determine the start time of the first cell transmitting frame #i. That is, the terminal determines the time of the first cell transmitting frame #i by subtracting the one-way propagation delay between the terminal and the first cell from the time it received frame #i. Further, the terminal obtains the absolute time of the second cell transmitting frame #i based on the time of the first cell transmitting frame #i and the timing offset between the second cell and the first cell. That is, the absolute time of the second cell transmitting frame #i plus the timing offset between the second cell and the first cell gives the absolute time of the second cell transmitting frame #i. Understandably, once the terminal determines the absolute time when the second cell sends frame #i, it can deduce the absolute time when the second cell sends the downlink synchronization signal based on the time offset between the time domain resources where the downlink synchronization signal of the second cell is located and frame #i. Then, based on the absolute time when the second cell sends the downlink synchronization signal and the RTT or one-way propagation delay (i.e., RTT / 2) between the terminal and the second cell, it can obtain the arrival time of the downlink synchronization signal of the second cell to the terminal. Understandably, the arrival time is equal to the absolute time when the second cell sends the downlink synchronization signal plus RTT / 2.

[0299] Understandably, frame i (i.e. the second frame) can be any frame.

[0300] For example, since the terminal and the first cell have already achieved downlink synchronization, the terminal can determine the time when the first cell transmits subframe #0 (i.e., the start time of subframe #0 in the first cell or the absolute time corresponding to the start boundary of subframe #0 in the first cell). For instance, the terminal determines the time when the first cell transmits subframe #0 by subtracting the one-way propagation delay between the terminal and the first cell from the time it receives subframe #0. Further, the terminal adds the timing offset between the second cell and the first cell to the time when the second cell transmits subframe #0 to obtain the time when the second cell transmits subframe #0 (i.e., the start time of subframe #0 in the second cell or the absolute time corresponding to the start boundary of subframe #0 in the second cell). After the terminal obtains the time of the transmission of subframe #0 of the second cell, it can deduce the absolute time of the transmission of the downlink synchronization signal of the second cell based on the time offset between the time domain resources where the downlink synchronization signal of the second cell is located and the transmission of subframe #0 of the second cell. Then, it can obtain the arrival time of the downlink synchronization signal of the second cell to the terminal by adding the one-way propagation delay of the signal between the terminal and the second cell to the absolute time of the transmission of the downlink synchronization signal of the second cell.

[0301] For example, in another implementation, the first information includes fourth indication information, which is used to indicate the frame number, subframe number, or time slot number of the second cell corresponding to the handover command.

[0302] Understandably, when the first access network device sends the fourth indication information to the terminal, the terminal can determine the occurrence time of the downlink synchronization signal of the second cell based on the start or end time of the handover command, the frame number, subframe number, or timeslot number of the second cell corresponding to the frame or subframe in which the handover command is located, and the time domain resources occupied by the downlink synchronization signal of the second cell. This allows the terminal to determine the arrival time of the downlink synchronization signal of the second cell to reach the terminal.

[0303] For example, if the frame number of the handover command corresponding to the first cell is frame #p (only frames are used as an example), that is, the terminal receives the handover command at frame #p of the first cell. The fourth indication information indicates that the frame number of the handover command corresponding to the second cell is frame #q. Then the offset between the second cell and frame #0 of the first cell (or the start time of frame #0) is qp frames.

[0304] For example, the terminal determines the arrival time by: determining the timing offset between the second cell and the first cell based on the frame number, subframe number, or timeslot number of the second cell corresponding to the handover command; determining the start time of the third frame of the second cell based on the timing offset between the second cell and the first cell, for example, determining the absolute time of the third frame of the second cell; determining the time offset between the time domain resources where the downlink synchronization signal of the second cell is located and the third frame, which is also called the third time offset; obtaining the time when the second cell sends the downlink synchronization signal through the start time of the third frame of the second cell and the third time offset; and obtaining the arrival time of the terminal of the downlink synchronization signal of the second cell by adding the RTT or one-way propagation delay (i.e., RTT / 2) between the terminal and the second cell to the time when the downlink synchronization signal of the second cell is sent.

[0305] For example, after determining the timing offset between the second cell and the first cell based on the frame number, subframe number, or timeslot number of the second cell corresponding to the handover command, the terminal adds the timing offset between the second cell and the first cell to obtain the time when the second cell sends frame #0 subframe #0 (i.e., the start time of frame #0 subframe #0 of the second cell or the absolute time corresponding to the start boundary of frame #0 subframe #0 of the second cell). Then, based on the time offset between the time domain resources where the downlink synchronization signal of the second cell is located and the time offset between the second cell sending frame #0 subframe #0, the terminal derives the absolute time when the second cell sends the downlink synchronization signal. Finally, based on the absolute time when the second cell sends the downlink synchronization signal and the RTT or one-way propagation delay (RTT / 2) between the terminal and the second cell, the arrival time of the downlink synchronization signal from the second cell to the terminal is obtained. Understandably, the arrival time is equal to the absolute time when the second cell sends the downlink synchronization signal plus RTT / 2.

[0306] It should be noted that this embodiment does not limit the specific implementation method of how the terminal accesses the second access network device in S1303b.

[0307] For example, one implementation uses a contention-based random access procedure.

[0308] For example, one implementation method is based on a non-contention-based random access procedure.

[0309] For example, the first access network device instructs the terminal to perform a no-random access procedure. Correspondingly, after the terminal achieves downlink synchronization with the second cell, it accesses the second cell by performing a no-random access procedure to further reduce handover interruption latency.

[0310] The concept of random access for terminals can be found in the terminology section above, and will not be repeated here.

[0311] Optionally, after the terminal accesses the second cell, in method 1, as shown in Figure 13, method 1300 includes S1304 to S1305:

[0312] S1304, the second access network device sends second information to the first access network device, and the first access network device receives the second information, which is used to indicate that the terminal has successfully switched from the first cell to the second cell.

[0313] S1305, after receiving the second information, the first access network device stops data transmission with the terminal.

[0314] Stopping data transmission with the terminal can also be understood as one or more of the following: releasing the terminal's configuration information, not receiving data and / or information from the terminal, and not sending data and / or information to the terminal.

[0315] Optionally, in implementation method 1, as shown in Figure 13, after executing S1305, the first access network device can also execute S1306: instructing the second access network device that the terminal has successfully received the data. For example, the first access network device sends the PDCP SN number to the second access network device through an SN STATUS TRANSFER message. Specifically, the PDCP SN number here is used by the second access network device to know which data has been successfully sent to the terminal and from which data packet should the transmission to the terminal begin. That is, the PDCP SN number is the PDCP SN corresponding to the first SDU in the SDU to be transmitted by the second access network device to the terminal. Optionally, after the terminal accesses the second cell, in implementation method 2, as shown in Figure 13, method 1300 includes S1307 to S1308.

[0316] S1307: After receiving the path switching request confirmation message from the AMF, the second access network device sends a terminal context release message to the first access network device.

[0317] S1308: After receiving the terminal context release message, the first access network device stops data transmission with the terminal.

[0318] Optionally, in implementation method 2, as shown in Figure 13, the terminal can instruct S1309 after executing S1308: The second access network device indicates that the terminal has successfully received the data. For example, the first access network device sends the PDCP SN number to the second access network device via SN STATUS TRANSFER, so that the second access network device knows which data has been successfully sent to the terminal and from which data should the transmission to the terminal begin. Specifically, the PDCP SN number here is used by the second access network device to know which data has been successfully sent to the terminal and from which data packet the transmission to the terminal should begin. That is, the PDCP SN number here is the PDCP SN corresponding to the first SDU in the SDU to be transmitted by the second access network device to the terminal.

[0319] It should be noted that if step S1307 is omitted, the first access network device can release the radio and control plane resources associated with the terminal context after receiving the second information. Understandably, if S1304 is executed, then S1307 may not need to be executed.

[0320] Understandably, if S1306 is executed, then S1309 may not need to be executed.

[0321] In other words, in this embodiment, the first access network device will stop data transmission with the terminal only when it receives second information sent by the second access network device to indicate that the terminal has successfully switched from the first cell to the second cell, or a terminal context release message sent by the second access network device.

[0322] In one possible implementation, after the first access network device sends the handover command, it continues to send downlink data received from the UPF to the terminal, and also continuously forwards downlink data to the second access network device. Upon learning that the terminal handover is successful (step S1304 or step S1307), the first access network device stops sending downlink data to the terminal (or stops downlink scheduling for the terminal) and stops forwarding data to the second access network device. In this implementation, before S1308 or S1309 in Figure 13, the first access network device can also send multiple SN status transmission messages. Among these multiple SN status messages, the COUNT (composed of PDCP SN number and PDCP superframe number) contained in the first SN status transmission message is used by the second access network device to know from which SDU the first access network device started forwarding to the second access network device (i.e., the first SN status transmission message contains the COUNT of the first downlink SDU forwarded by the first access network device to the second access network device). The COUNT contained in the SN status transmission messages after the first one (i.e., subsequent SN status messages) is used by the second access network device to discard / clear the downlink SDUs that the first access network device has successfully transmitted to the terminal in order to free up memory.

[0323] In another possible implementation, after the first access network device sends the handover command, it continues to send downlink data received from the UPF to the terminal, but it does not forward downlink data to the second access network device, nor does it send an SN status transmission message to the second access network device. After the first access network device learns that the terminal handover was successful (step S1304 or step S1307), it stops sending downlink data to the terminal (or stops downlink scheduling for the terminal), begins forwarding data that was not successfully transmitted to the terminal to the second access network device, and sends an SN status transmission message to the second access network device. Understandably, in this implementation, only step S1308 or S1309 needs to be executed.

[0324] Referring to Figure 14, which illustrates how the interruption latency of a terminal can be reduced when it switches from a first cell to a second cell based on the method provided in Figure 13.

[0325] The communication method 1300 provided in this application has been described above. It can be seen that in method 1300, since the terminal can maintain data transmission with the first cell during the period between receiving the handover command and the first time, compared to the terminal disconnecting / stopping data transmission with the first cell as soon as it receives the handover command, the technical solution provided in this application can reduce the interruption latency when the terminal hands over from the first cell to the second cell, thereby improving the user experience.

[0326] It is understood that the communication method 1300 provided in Figure 13 above is a communication method based on the XN port. It is also understood that the method provided in this application, which allows the terminal to maintain data transmission with the first cell during the period from receiving the handover command to the first time, is also applicable to the handover process based on the NG port. The following explanation is in conjunction with Figure 15.

[0327] Figure 15 is a flowchart illustrating a communication method 1500 provided in an embodiment of this application. As shown in Figure 15, method 1500 includes:

[0328] S1501, the first access network device sends a handover command to the terminal, and the terminal receives the handover command accordingly; the handover command is used to instruct the terminal to hand over from the first cell to the second cell.

[0329] A detailed description of this step can be found in the embodiment shown in Figure 13, and will not be repeated here.

[0330] As shown in Figure 15, in this embodiment, there is no direct interface between the first access network device and the second access network device, and data or signaling needs to be forwarded through the core network device.

[0331] For example, as shown in Figure 15, the first access network device sends the handover request, SN status transmission message and user data to the second access network device through the AMF.

[0332] For example, as shown in Figure 15, the second access network device sends a handover request confirmation message to the first access network device through the AMF.

[0333] S1502, the first access network device sends first information to the terminal, and the corresponding terminal receives the first information; the first information is used by the terminal to determine the arrival time of the downlink synchronization signal of the second cell to the terminal.

[0334] For a detailed description of this step, please refer to the description in S1302 of the embodiment shown in Figure 13, which will not be repeated here.

[0335] It should be noted that in this application, there is no specific order of execution between S1501 and S1502.

[0336] In one implementation, the initial information and the switching command can be carried in the same message. That is, the switching command and the initial information are sent through the same message.

[0337] S1503, the terminal transmits data with the first cell during the period between receiving the handover command and the first time, and disconnects the data transmission with the first cell and accesses the second cell during the first time.

[0338] Understandably, S1503 specifically includes:

[0339] S1503a: The terminal transmits data with the first cell during the period between receiving the handover command and the first time, and disconnects the data transmission with the first cell at the first time and begins to search for the downlink synchronization signal of the second cell, so as to obtain downlink synchronization with the second cell based on the downlink synchronization signal of the second cell.

[0340] S1503b: After achieving downlink synchronization with the second cell based on the downlink synchronization signal of the second cell, access the second cell.

[0341] The implementation of S1503 can be referred to the description in the embodiment of Figure 13, and will not be repeated here.

[0342] S1504, the second access network device indicates to the AMF that the terminal has successfully switched from the first cell to the second cell.

[0343] Understandably, after the AMF learns that the terminal has successfully switched from the first cell to the second cell, the AMF and UPF will perform a path handover (not shown in Figure 15). The process of the AMF and UPF performing the path handover can be found in the descriptions in relevant technologies, and will not be repeated here.

[0344] S1505, the AMF sends a terminal context release message to the first access network device to indicate to the first access network device that the terminal has successfully switched to the second access network device.

[0345] S1506, the first access network device stops data transmission with the terminal.

[0346] Optionally, the first access network device may release the radio and control plane resources associated with the terminal context. Optionally, after releasing the radio and control plane resources associated with the terminal context, the first access network device sends a terminal context release completion message to the AMF to indicate that the first access network device has released the radio and control plane resources associated with the terminal context.

[0347] Optionally, as shown in Figure 15, after executing 1506, the terminal executes S1507: informing the second access network device via AMF that the terminal has successfully received the data. For example, the first access network device forwards the PDCP SN number to the second access network device via AMF through the SN STATUS TRANSFER message. Specifically, the PDCP SN number here is used by the second access network device to know which data has been successfully sent to the terminal and from which data packet to start transmitting to the terminal. That is, the PDCP SN number is the PDCP SN corresponding to the first SDU in the SDU to be transmitted by the second access network device to the terminal.

[0348] In one possible implementation, after the first access network device sends the handover command, it continues to send downlink data received from the UPF to the terminal, and continuously forwards downlink data to the second access network device through the AMF. Upon learning that the terminal handover is successful (step S1505), the first access network device stops sending downlink data to the terminal (or stops downlink scheduling for the terminal) and stops forwarding data to the second access network device through the AMF. In this implementation, before S1507 in Figure 15, the first access network device can also send multiple SN status transmission messages to the second access device via AMF. Among these multiple SN status messages, the COUNT contained in the first SN status transmission message is used by the second access network device to know from which SDU the first access network device started forwarding to the second access network device (i.e., the first SN status transmission message contains the COUNT of the first downlink SDU forwarded by the first access network device to the second access network device). The COUNT contained in the SN status transmission messages after the first one (i.e., subsequent SN status messages) is used by the second access network device to discard the downlink SDUs that the first access network device has successfully transmitted to the terminal, so as to free up memory.

[0349] In another possible implementation, after the first access network device sends the handover command, it continues to send downlink data received from the UPF to the terminal. However, the first access network device does not forward downlink data to the second access network device through the AMF, nor does it send an SN status transmission message to the second access network device through the AMF. After the first access network device learns that the terminal handover is successful (step S1505), it stops sending downlink data to the terminal (or stops downlink scheduling for the terminal), begins forwarding data that was not successfully transmitted to the terminal to the second access network device with the AMF, and sends an SN status transmission message to the second access network device. Understandably, in this implementation, only step S1305 needs to be executed.

[0350] As can be seen, in method 1500, since the terminal can maintain data transmission with the first cell during the time between receiving the handover command and the first time, the technical solution provided by this application can reduce the interruption latency when the terminal hands over from the first cell to the second cell, thereby improving the user experience, compared to the terminal disconnecting / stopping data transmission with the first cell as soon as it receives the handover command.

[0351] Additionally, it should be noted that Figure 15 illustrates an example where the first access network device and the second access network device are connected to the same core network. Understandably, the first access network device and the second access network device may be connected to different core networks, such as different AMFs or UPFs. In this case, signaling between the first access network device and the second access network device can be forwarded in the following manner: first access network device - core network connected to the first access network device - core network connected to the second access network device - second access network device.

[0352] Figure 16 is a flowchart illustrating a communication method 1600 provided in an embodiment of this application. As shown in Figure 16, method 1600 includes:

[0353] S1601, the first access network device sends third information to the terminal. The third information is used to instruct the terminal to perform conditional handover (CHO). The third information includes at least one handover trigger condition corresponding to a cell. The terminal receives the third information.

[0354] For example, the first access network device carries the third information in the RRC reconfiguration message. Optionally, after receiving the third information, the terminal sends an RRC reconfiguration complete message to the first access network device.

[0355] Third information, also known as the conditional toggle CHO command.

[0356] In this embodiment, the third information includes at least one handover triggering condition corresponding to a cell. The handover triggering condition is also called the handover execution triggering condition. For example, if at least one cell includes cell 1, then the handover triggering condition corresponding to cell 1 can be understood as the condition that triggers the handover to cell 1.

[0357] The number of at least one cell can be one or more. At least one cell is also called at least one candidate cell; that is, the third information terminal indicates the radio interface configuration information of all candidate cells. In this embodiment, when there are multiple candidate cells, which candidate cell is ultimately switched to depends on which candidate cell's handover conditions are met first.

[0358] In this embodiment, after the first access network device sends the third information to the terminal, the first access network device continues to transmit data with the terminal. Optionally, after the first access network device sends the third information to the terminal, before executing S1604, the first access network device can also send multiple SN status messages to the second access network device through the core network. Among these multiple SN status messages, the COUNT contained in the first SN status transmission message is used by the second access network device to know from which SDU the first access network device started forwarding to the second access network device (i.e., the first SN status transmission message contains the COUNT of the first downlink SDU forwarded by the first access network device to the second access network device). The COUNT contained in the SN status transmission messages after the first one (i.e., subsequent SN status messages) is used by the second access network device to discard the downlink SDUs that the first access network device has successfully transmitted to the terminal, in order to free up memory.

[0359] S1602, when the terminal meets the handover triggering condition corresponding to the second cell in at least one cell, it hands over from the first cell to the second cell, wherein the second cell is included in at least one cell.

[0360] In this embodiment, the second cell to which the terminal will be handed over is also referred to as the target cell. It should be noted that since there may be multiple candidate cells, if at least one candidate cell includes both NTN and TN cells, and the handover triggering conditions corresponding to both the NTN and TN cells are met, then the terminal will preferentially hand over to the TN cell, because the TN cell can provide better service quality.

[0361] Optionally, the third information sent by the first access network device may also include ephemeris information of the second cell and / or identification information of the second cell / beam.

[0362] Understandably, S1602 specifically includes S1602a to S1602b.

[0363] S1602a: When the terminal meets the handover triggering condition corresponding to the second cell, it achieves downlink synchronization with the second cell based on the downlink synchronization signal of the second cell.

[0364] S1602b: After achieving downlink synchronization with the second cell based on the downlink synchronization signal of the second cell, access the second cell.

[0365] In other words, in this embodiment, after receiving the third information (CHO handover command), the terminal continues to transmit data with the first access network device, and the terminal will only perform the handover to the second cell if the handover triggering conditions corresponding to the second cell are met.

[0366] Specifically, in this embodiment, when the terminal evaluates whether the handover triggering condition corresponding to the second cell is met, the handover triggering condition corresponding to the second cell includes a first condition, which is that the distance between the terminal and the reference point of the second cell is less than a first threshold. This first condition can also be referred to as event D3. It is understood that the first condition or event D3 is just a name, and other names are also possible, which does not constitute a limitation of this application.

[0367] The reference point for the second cell can be any point within the range of the second cell, such as the center point of the second cell.

[0368] For example, if the second cell is a quasi-fixed cell (e.g., a low-Earth orbit satellite system), the reference point of the quasi-fixed cell is stationary for a period of time and does not move with the movement of the satellite. The terminal can calculate the distance from the terminal to the reference point of the second cell based on its own position and the position of the reference point of the second cell. If it is less than the first threshold, the first condition is considered to be met.

[0369] For example, if the second cell is a mobile cell (e.g., a low-Earth orbit satellite system), the reference point of the mobile cell changes as the satellite moves. The RRC reconfiguration message (or other preceding messages) sends the second cell reference point, the corresponding timestamp information, and ephemeris information (or NTN auxiliary information) to the terminal. Based on this information, the terminal can determine a valid second cell reference point (or a real-time second cell reference point). The terminal can calculate the distance to the second cell reference point based on its own location and the location of the second cell reference point. If the distance is less than a first distance threshold, the first condition is considered met.

[0370] Optionally, if the second cell is a fixed cell (e.g., a high-orbit satellite system), the coverage area of ​​a fixed cell is generally large. In this scenario, the first condition is less necessary and can be omitted. If the coverage area of ​​the fixed cell is relatively small, then the first condition can be configured. Understandably, the reference point of a fixed cell is also fixed, similar to a quasi-fixed cell. It should be noted that there may be minor movements in the satellite constellation, in which case the reference point of the fixed cell may also change slightly. Even in scenarios with minor changes, the reference point is considered fixed.

[0371] Optionally, the handover triggering condition for the second cell may also include a second condition, wherein the signal strength or quality of the first cell is worse than a second threshold, and the signal strength or quality of the second cell is better than a third threshold. This second condition is also called event D3.

[0372] S1603, the first access network device receives the terminal context release message and stops data transmission with the terminal.

[0373] In this embodiment, as shown in Figure 16, after the terminal accesses the second access network device, the second access network device can indicate to the AMF that the terminal has successfully switched from the first cell to the second cell. Further, after the AMF learns that the terminal has successfully switched from the first cell to the second cell, the AMF can send a terminal context release message to the first access network device.

[0374] In this embodiment, after receiving the terminal context release message, the first access network device stops data transmission with the terminal. Optionally, as shown in FIG16, after executing 1603, the terminal executes S1604: informing the second access network device of the data successfully received by the terminal via AMF. For example, the first access network device sends a PDCP SN number to the second access network device via SN STATUS TRANSFER, so that the second access network device knows which data has been successfully sent to the terminal and from which data transmission should begin.

[0375] Optionally, after the first access network device stops data transmission with the terminal, it can release the radio and control plane resources associated with the terminal context and send a terminal context release completion message to the AMF to inform the core network side that the first access network device has released the radio and control plane resources associated with the terminal context.

[0376] Understandably, it is possible that after the first access network device sends the third information (CHO handover command) to the terminal, the terminal may not be covered by any other cell besides the first cell. In this scenario, method 1600 may further include S1606: the first access network device may send a fourth information to the terminal, the fourth information being used by the terminal to determine the time when the second cell begins to cover the terminal; correspondingly, the terminal can determine / predict the time when the second cell begins to cover the terminal based on the fourth information.

[0377] For example, the fourth piece of information includes coverage information or footprint information of the second cell.

[0378] For example, if the second cell is a quasi-fixed cell, then the fourth piece of information could be the coverage start time and coverage area (such as reference point and radius) of the second cell.

[0379] For example, if the second cell is a mobile cell, the fourth information could be the left and right elevation angles and radius of the second cell's coverage area (optional), or it could be the reference point and radius of the second cell, as well as the timestamp information corresponding to the reference point of the second cell.

[0380] When the terminal is not covered by any other cell besides the first cell, in one implementation, if the terminal determines that there is no TN neighbor cell coverage, and / or no NTN neighbor cell coverage, and / or determines that the serving cell has deteriorated (e.g., T310 is running; when the terminal detects a physical layer problem in the serving cell, i.e., when it receives N310 consecutive out-of-synchronization indications from the lower layer / physical layer, the T310 timer is started), and / or detects a radio link failure, the terminal directly enters the idle state to save power consumption. Furthermore, the terminal can also disable / deactivate / suspend the access stratum (AS), refraining from cell search, measurement, cell selection, and reselection to further save power. For example, the terminal can save AS-related configuration information, and can also keep all running timers running, but the terminal does not perform any idle mode tasks, such as measurement. Then, at the second time, the terminal begins to check whether the handover trigger condition corresponding to the second cell is met, i.e., it performs idle state tasks. The second time is determined based on the time when the second cell begins to cover the terminal. For example, the second time is the time before the second cell begins to cover the terminal, or the second time is the time after the second cell begins to cover the terminal, or the second time is the time when the second cell begins to cover the terminal.

[0381] It should be noted that the communication method shown in Figure 16 is described using the NG port as an example. This method can also be applied to the handover process based on the XN port. The difference between the XN port-based method and the embodiment in Figure 16 is that the first access network device and the second access network device can directly transmit data and signaling without the need for the core network to relay.

[0382] The transmission method of the embodiments of this application has been described in detail above. The transmission device provided by the embodiments of this application will be described in detail below with reference to FIG17 and FIG18.

[0383] Figure 17 is a structural schematic diagram of the communication device provided in an embodiment of this application. Specifically, as shown in Figure 17, the device 1700 includes: a transceiver module 1701 and a processing module 1702.

[0384] For example, in one embodiment, device 1700 can be applied to a terminal.

[0385] For example, transceiver module 1701 is used to receive a handover command, which instructs the terminal to handover from the first cell to the second cell; transceiver module 1102 is also used to receive first information, which is used by the terminal to determine the arrival time of the downlink synchronization signal of the second cell to the terminal; processing module 1702 is used to transmit data with the first cell during the period between the time of receiving the handover command and the first time, and to disconnect the data transmission with the first cell and access the second cell at the first time, wherein the first time is determined based on the arrival time.

[0386] In one possible implementation, the first information includes first indication information, which is used to indicate the time-domain resources occupied by the downlink synchronization signal.

[0387] In one possible implementation, the first indication information is used to indicate the time-domain resources occupied by the downlink synchronization signal, including: the first indication information is used to indicate the absolute time when the second cell transmits the downlink synchronization signal.

[0388] In one possible implementation, the first information includes second indication information, which is used to indicate the start time of the first frame of the second cell.

[0389] In one possible implementation, the frame index of the first frame is 0.

[0390] In one possible implementation, the arrival time is determined based on the start time of the first frame and a first time offset, where the first time offset is the time offset between the time domain resources occupied by the downlink synchronization signal and the first frame.

[0391] In one possible implementation, the arrival time is determined based on the start time of the second frame of the second cell and a second time offset; wherein the start time of the second frame is determined based on the timing offset between the second cell and the first cell, and the second time offset is the time offset between the time domain resources occupied by the downlink synchronization signal and the second frame.

[0392] In one possible implementation, the first information includes fourth indication information, which is used to indicate the frame number, subframe number, or time slot number of the second cell corresponding to the handover command.

[0393] In one possible implementation, the arrival time is determined based on the start time of the third frame of the second cell and the third time offset; wherein, the start time of the third frame is determined based on the frame number, subframe number, or time slot number of the second cell corresponding to the handover command, and the third time offset is the time offset between the time domain resources occupied by the downlink synchronization signal and the third frame.

[0394] For example, in two embodiments, the device can be applied to a first access network device.

[0395] For example, transceiver module 1701 is used to send a handover command, which instructs the terminal to handover from the first cell to the second cell; transceiver module 1701 is also used to send first information, which is used by the terminal to determine the arrival time of the downlink synchronization signal of the second cell to the terminal; processing module 1702 is used to stop data transmission with the terminal when it receives the second information or the terminal context release message, which instructs the terminal to successfully handover from the first cell to the second cell.

[0396] In one possible implementation, the first information includes first indication information, which is used to indicate the time-domain resources occupied by the downlink synchronization signal.

[0397] In one possible implementation, the first indication information is used to indicate the time-domain resources occupied by the downlink synchronization signal, including: the first indication information is used to indicate the absolute time when the second cell transmits the downlink synchronization signal.

[0398] In one possible implementation, the first information includes second indication information, which is used to indicate the start time of the first frame of the second cell.

[0399] In one possible implementation, the frame index of the first frame is 0.

[0400] In one possible implementation, the arrival time is determined based on the start time of the first frame and a first time offset, where the first time offset is the time offset between the time domain resources occupied by the downlink synchronization signal and the first frame.

[0401] In one possible implementation, the first information includes third indication information, which is used to indicate the timing offset between the second cell and the first cell.

[0402] In one possible implementation, the arrival time is determined based on the start time of the second frame of the second cell and a second time offset; wherein the start time of the second frame is determined based on the timing offset between the second cell and the first cell, and the second time offset is the time offset between the time domain resources occupied by the downlink synchronization signal and the second frame.

[0403] In one possible implementation, the first information includes fourth indication information, which is used to indicate the frame number, subframe number, or time slot number of the second cell corresponding to the handover command.

[0404] In one possible implementation, the arrival time is determined based on the start time of the third frame of the second cell and the third time offset; wherein, the start time of the third frame is determined based on the frame number, subframe number, or time slot number of the second cell corresponding to the handover command, and the third time offset is the time offset between the time domain resources occupied by the downlink synchronization signal and the third frame.

[0405] In one possible implementation, the transceiver module 1701 is further configured to indicate to the second access network device that the terminal has successfully received the data after the data transmission between the terminal is stopped, wherein the second access network device is the access network device to which the second cell belongs.

[0406] In one possible implementation, information indicating that the terminal has successfully received data is forwarded to the second access network device via the core network device.

[0407] In the third embodiment, the device can be applied to a second access network device.

[0408] For example, the transceiver module 1701 is used to send second information to the first access network device or the core network device when the terminal switches from the first cell to the second cell. The second information is used to indicate that the terminal has successfully switched from the first cell to the second cell. The second cell is the cell included in the second access network device, and the core network device is the core network device that manages the terminal.

[0409] In a fourth embodiment, the device can be applied to a terminal.

[0410] For example, the transceiver module 1701 is used to: receive third information, the third information being used to instruct the terminal to perform conditional handover, the third information including at least one handover triggering condition corresponding to a cell; the processing module 1702 is used to: when the handover triggering condition corresponding to the second cell in at least one cell is met, handover from the first cell to the second cell; wherein, the handover triggering condition corresponding to the second cell includes a first condition, the first condition being that the distance between the terminal and the reference point of the second cell is less than a first threshold.

[0411] In one possible implementation, at least one cell includes a TN cell and an NTN cell; the processing module 1702 is used to: determine to switch from the first cell to the TN cell if both the handover triggering conditions corresponding to the TN cell and the handover triggering conditions corresponding to the NTN cell are met simultaneously.

[0412] In one possible implementation, the handover triggering condition for the second cell also includes a second condition, which is that the signal strength or quality of the first cell is worse than a second threshold, and the signal strength or quality of the second cell is better than a third threshold.

[0413] In one possible implementation, the processing module 1702 is further configured to: when the terminal is not covered by any cell other than the first cell, and / or when the service quality of the first cell deteriorates, and / or when a wireless link failure is detected, the terminal enters an idle state.

[0414] Optionally, when the terminal enters the idle state, the terminal may shut down, deactivate, or suspend the processing of the access layer AS.

[0415] In one possible implementation, the transceiver module 1701 is further configured to: receive fourth information, the fourth information being used by the terminal to determine the time when the second cell begins to cover the terminal; the processing module 1702 is further configured to: determine the time when the second cell begins to cover the terminal based on the fourth information; the processing module 1702 is further configured to: detect whether the handover triggering condition corresponding to the second cell is met starting from the second time, the second time being determined based on the time when the second cell begins to cover the terminal.

[0416] Figure 18 is a structural schematic diagram of another communication device provided in an embodiment of this application. The device shown in Figure 18 can be used to perform the method described in any of the foregoing embodiments.

[0417] As shown in Figure 18, the device 1800 of this embodiment includes a memory 1801 and a processor 1802. In one implementation, the device 1800 further includes a communication interface 1803 and a bus 1804. The memory 1801, processor 1802, and communication interface 1803 are interconnected via the bus 1804.

[0418] The memory 1801 may be a read-only memory (ROM), a static storage device, a dynamic storage device, or a random access memory (RAM). The memory 1801 may store a program, and when the program stored in the memory 1801 is executed by the processor 1802, the processor 1802 performs the various steps of the methods shown in Figures 13, 15, and 16.

[0419] The processor 1802 may be a general-purpose central processing unit (CPU), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits, used to execute relevant programs to implement the methods shown in Figures 13, 15 and 16 of the embodiments of this application.

[0420] The processor 1802 can also be an integrated circuit chip with signal processing capabilities. In implementation, the various steps of the methods in Figures 13, 15, and 16 of this application embodiment can be completed by the integrated logic circuitry in the processor 1802 or by software instructions.

[0421] The processor 1802 described above can also be a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components. It can implement or execute the methods, steps, and logic block diagrams disclosed in the embodiments of this application. The general-purpose processor can be a microprocessor or a conventional processor, etc.

[0422] The steps of the method disclosed in the embodiments of this application can be directly implemented by a hardware decoding processor, or implemented by a combination of hardware and software modules in the decoding processor. The software modules can reside in random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, registers, or other mature storage media in the art. This storage medium is located in memory 1801. The processor 1802 reads information from memory 1801 and, in conjunction with its hardware, performs the functions required by the units included in the device of this application. For example, it can execute the various steps / functions of the embodiments shown in Figures 13, 15, and 16.

[0423] The communication interface 1803 can use, but is not limited to, transceivers to enable communication between the device 1800 and other devices or communication networks.

[0424] Bus 1804 may include a pathway for transmitting information between various components of device 1800 (e.g., memory 1801, processor 1802, communication interface 1803).

[0425] It should be understood that the device 1800 shown in the embodiments of this application can be deployed in network devices or terminals.

[0426] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer programs are loaded or executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be a usable medium accessible to a computer or a data storage device such as a server or data center containing one or more sets of usable media. The usable medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium. A semiconductor medium can be a solid-state drive.

[0427] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. Additionally, the character " / " in this article generally indicates an "or" relationship between the preceding and following related objects, but it can also represent an "and / or" relationship. Please refer to the context for a more accurate understanding.

[0428] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, at least one of a, b, or c can mean: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple.

[0429] It should be understood that in the various embodiments of this application, the order of the above-mentioned processes does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not limit the implementation process of the embodiments of this application.

[0430] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0431] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0432] In the several 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 apparatus embodiments 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 coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0433] 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 embodiment according to actual needs.

[0434] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0435] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory, random access memory, magnetic disks, or optical disks.

Claims

1. A communication method characterized by comprising: include: Receive a handover command, the handover command being used to instruct the terminal to hand over from the first cell to the second cell; The terminal receives first information, which is used to determine the arrival time of the downlink synchronization signal of the second cell to the terminal. The system transmits data with the first cell during the period between the time the handover command is received and the first time, and disconnects the data transmission with the first cell and accesses the second cell at the first time, wherein the first time is determined based on the arrival time.

2. The method of claim 1, wherein, The first information includes first indication information, which is used to indicate the time domain resources occupied by the downlink synchronization signal.

3. The method according to claim 2, characterized in that, The first indication information is used to indicate the time-domain resources occupied by the downlink synchronization signal, including: The first indication information is used to indicate the absolute time when the second cell sends the downlink synchronization signal.

4. The method according to claim 2, characterized in that, The first information includes second indication information, which is used to indicate the start time of the first frame of the second cell.

5. The method according to claim 4, characterized in that, The frame index of the first frame is 0.

6. The method according to claim 4 or 5, characterized in that, The arrival time is determined based on the start time of the first frame and a first time offset, where the first time offset is the time offset between the time domain resources occupied by the downlink synchronization signal and the first frame.

7. The method according to claim 2, characterized in that, The first information includes third indication information, which is used to indicate the timing offset between the second cell and the first cell.

8. The method according to claim 7, characterized in that, The arrival time is determined based on the start time of the second frame of the second cell and the second time offset; The start time of the second frame is determined based on the timing offset between the second cell and the first cell, and the second timing offset is the timing offset between the time domain resources occupied by the downlink synchronization signal and the second frame.

9. The method according to claim 2, characterized in that, The first information includes fourth indication information, which is used to indicate the frame number, subframe number, or time slot number of the second cell corresponding to the handover command.

10. The method according to claim 9, characterized in that, The arrival time is determined based on the start time and third time offset of the third frame of the second cell; The start time of the third frame is determined based on the frame number, subframe number, or time slot number of the second cell corresponding to the handover command, and the third time offset is the time offset between the time domain resources occupied by the downlink synchronization signal and the third frame.

11. A communication method, characterized in that, include: Send a handover command, the handover command being used to instruct the terminal to hand over from the first cell to the second cell; Send first information, the first information being used by the terminal to determine the arrival time of the downlink synchronization signal of the second cell to the terminal; Data transmission with the terminal is stopped upon receiving a second message or a terminal context release message, wherein the second message indicates that the terminal has successfully switched from the first cell to the second cell.

12. The method according to claim 11, characterized in that, The first information includes first indication information, which is used to indicate the time domain resources occupied by the downlink synchronization signal.

13. The method according to claim 12, characterized in that, The first indication information is used to indicate the time-domain resources occupied by the downlink synchronization signal, including: The first indication information is used to indicate the absolute time when the second cell sends the downlink synchronization signal.

14. The method according to claim 12, characterized in that, The first information includes second indication information, which is used to indicate the start time of the first frame of the second cell.

15. The method according to claim 14, characterized in that, The frame index of the first frame is 0.

16. The method according to claim 14 or 15, characterized in that, The arrival time is determined based on the start time of the first frame and a first time offset, where the first time offset is the time offset between the time domain resources occupied by the downlink synchronization signal and the first frame.

17. The method according to claim 12, characterized in that, The first information includes third indication information, which is used to indicate the timing offset between the second cell and the first cell.

18. The method according to claim 17, characterized in that, The arrival time is determined based on the start time of the second frame of the second cell and the second time offset; The start time of the second frame is determined based on the timing offset between the second cell and the first cell, and the second timing offset is the timing offset between the time domain resources occupied by the downlink synchronization signal and the second frame.

19. The method according to claim 12, characterized in that, The first information includes fourth indication information, which is used to indicate the frame number, subframe number, or time slot number of the second cell corresponding to the handover command.

20. The method according to claim 19, characterized in that, The arrival time is determined based on the start time and third time offset of the third frame of the second cell; The start time of the third frame is determined based on the frame number, subframe number, or time slot number of the second cell corresponding to the handover command, and the third time offset is the time offset between the time domain resources occupied by the downlink synchronization signal and the third frame.

21. The method according to any one of claims 11 to 20, characterized in that, The method further includes: After stopping data transmission with the terminal, the system indicates to the second access network device that the terminal has successfully received the data. The second access network device is the access network device to which the second cell belongs.

22. The method according to claim 21, characterized in that, Information indicating that the terminal has successfully received data is forwarded to the second access network device through the core network device.

23. A communication device, characterized in that, It includes a module for performing the method as described in any one of claims 1 to 10; or, it includes a module for performing the method as described in any one of claims 11 to 22.

24. A computer-readable storage medium, characterized in that, The computer-readable storage medium is used to store a program or instructions that, when executed, cause the method as claimed in any one of claims 1 to 10 to be implemented; or cause the method as claimed in any one of claims 11 to 22 to be implemented.

25. A computer program product, characterized in that, The computer program product includes a computer program that, when run, causes the method as described in any one of claims 1 to 10 to be implemented; or causes the method as described in any one of claims 11 to 22 to be implemented.

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