Communication method and device

Abstract

The invention relates to a communication method and a communication device, which are used for solving the problem that in the prior art, the time required by terminal equipment for acquiring timing advance (TA) of a candidate cell is relatively long. In the application, the method comprises the following steps: a first access network device acquires random access information of a second cell; and after determining that the terminal equipment is switched to the first cell, the first access network equipment sends a first indication to the terminal equipment according to the random access information of the second cell. Wherein the first indication is used for indicating the terminal device to perform retransmission or new transmission of the random access preamble for the second cell, the first cell is managed by the first access network device, and the second cell is the same as or different from the first cell.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of wireless communications, and in particular, to a communication method and device. Background Art

[0002] Handover is a very important feature in the 5G system. Handover is mainly triggered by the movement of the terminal device when the terminal device is in the radio resource control (RRC) connection state. The basic goal of handover is to switch to a neighboring cell with better signal quality before the signal quality of the terminal device's serving cell fails to meet the communication needs of the terminal device.

[0003] Currently, the standard is discussing Layer 1 / Layer 2 triggered mobility (L1 / L2 triggered mobility, LTM), specifically, the distributed unit (DU) determines whether to initiate an LTM cell switch (LTM cell switch) based on the measurement results of the terminal equipment.

[0004] During the LTM cell switching process, the terminal device needs to obtain the timing advance (TA) of the candidate cell, but this takes a long time. Summary of the invention

[0005] The present application provides a communication method and apparatus for solving the problem that it takes a long time for a terminal device to obtain a TA of a candidate cell.

[0006] In a first aspect, the present application provides a communication method, which can be executed by a first access network device, or a module in the first access network device, such as a chip. The following takes the execution by the first access network device as an example for explanation.

[0007] The method includes: a first access network device obtains random access information of a second cell. After determining that the terminal device switches to the first cell, the first access network device sends a first indication to the terminal device according to the random access information of the second cell. The first indication is used to instruct the terminal device to retransmit or retransmit a random access preamble to the second cell, the first cell is managed by the first access network device, and the second cell is the same as or different from the first cell. In the above technical solution, the first access network device obtains the random access information of the second cell, and instructs the terminal device to retransmit or retransmit a random access preamble to the second cell according to the random access information of the second cell, and when the terminal device retransmits the random access preamble to the second cell, there is no need to gradually increase the power from the initial power, which helps to obtain the TA of the second cell more quickly.

[0008] In a possible implementation, the first access network device receives random access information of a second cell from a third access network device, where the third access network device is an access network device for managing a third cell, and the third cell is a cell accessed by the terminal device before switching. A method for the first access network device to obtain random access information of the second cell is provided above.

[0009] In a possible implementation, the random access information of the second cell includes one or more of the following: an identifier of the second cell, a retransmission indication, a new transmission indication, failure information of a random access preamble of the second cell, and success information of a random access preamble of the second cell. In this way, the first access network device can determine the first indication according to different parameters in the random access information of the second cell.

[0010] In a possible implementation, when the first cell and the second cell are the same, when the first access network device sends the first indication to the terminal device according to the random access information of the second cell, specifically, the first access network device sends N first indications to the terminal device according to the random access information of the first cell, and the first indication is used to instruct the terminal device to retransmit the random access preamble for the first cell, wherein N is greater than or equal to the number of failed random access attempts to the first cell before the terminal device switches to the first cell, and N is a positive integer. The above technical solution is applicable to the case where the TA of the first cell obtained by the terminal device fails, and helps the terminal device to quickly obtain a new TA for the first cell.

[0011] In a possible implementation, the first cell is a time division duplex (TDD) cell, and the third cell is a frequency division duplex (FDD) cell. The first access network device determines the offset of the expected data arrival time according to the frame structure and data arrival time of the first cell, and sends the offset of the expected data arrival time to the core network device.

[0012] In the above technical solution, the first access network device can determine the offset of the expected data arrival time, and the offset of the expected data arrival time can be used by the service server to adjust the sending time of the downlink data, or used by the service server to instruct the terminal device to adjust the sending time of the uplink data, thereby helping to achieve the matching of the arrival time of the downlink data with the downlink time slot (slot) of the time division multiplexing cell, or the matching of the arrival time of the uplink data with the uplink slot of the time division multiplexing cell, avoiding data caching in the 5G network, reducing the load of the 5G network, and shortening the delay in data transmission between the terminal device and the service server.

[0013] In a second aspect, the present application provides a communication method, which can be executed by a terminal device, or a module in the terminal device, such as a chip. The following is an example of execution by a terminal device.

[0014] The method includes: the terminal device sends a random access preamble of the second cell to the second access network device according to a first power, the first power is determined according to a random access variable, and the second cell is managed by the second access network device. After switching to the first cell, the terminal device sends a random access preamble of the second cell to the second access network device according to a second power, wherein the second power is greater than or equal to the first power. In the above technical solution, after the terminal device switches to the first cell, it uses a second power greater than or equal to the first power to continue to send the random access preamble of the second cell to the second access network device without gradually increasing the power from the initial power, which helps to quickly obtain the TA of the second cell.

[0015] In a possible implementation, before the terminal device sends the random access preamble of the second cell to the second access network device according to the second power, the terminal device also receives a first indication from the first access network device, the first indication is used to indicate the retransmission of the random access preamble of the second cell, and the first cell is managed by the first access network device. Subsequently, the terminal device determines the second power according to the first indication. In a possible implementation, when the terminal device determines the second power according to the first indication, it may be specifically determined according to the first indication, the random access variable and the random access preamble power ramping step. In the above technical solution, the terminal device determines to send the retransmission of the random access preamble of the second cell to the second access network device based on the first indication from the first access network device, and then determines the second power according to the random access variable and the random access preamble power ramping step, which helps to obtain the TA of the second cell more quickly.

[0016] In a possible implementation, before switching to the first cell, the terminal device also receives a random access maintenance indication, and the random access maintenance indication is used to instruct the terminal device to maintain the random access variable after switching to the first cell. In a possible implementation, the random access variable includes one or more of the following: a random access preamble power ramp-up counter, a random access preamble transmission counter, and a variable of a random access preamble new transmission indication. In the above technical solution, the terminal device maintains the random access variable after switching to the first cell, and can then determine the second power after receiving a retransmission indication from the first access network device.

[0017] In a third aspect, the present application provides a communication method, which can be executed by a third access network device, or a module in the third access network device, such as a chip. The following takes the execution by the third access network device as an example for explanation.

[0018] The method includes: a third access network device sends a second indication to a terminal device, and the second indication is used to instruct the terminal device to initiate random access to a second cell. The third access network device determines the random access information of the second cell, and sends the random access information of the second cell to the first access network device. Among them, the cells accessed by the terminal device before and after the switching are the third cell and the first cell respectively, the third cell is managed by the third access network device, the first cell is managed by the first access network device, and the second cell is the same as or different from the first cell. In the above technical solution, the third access network device sends the random access information of the second cell to the first access network device, so that the first access network device can instruct the terminal device to retransmit or retransmit the random access preamble to the second cell according to the random access information of the second cell, which helps to obtain the TA of the second cell more quickly.

[0019] In a possible implementation, the third access network device further sends a random access maintenance indication to the terminal device. Optionally, the random access maintenance indication is carried in a radio resource control reconfiguration message or a handover command sent by the third access network device to the terminal device.

[0020] In a possible implementation, the random access information of the second cell includes one or more of the following: an identifier of the second cell, a retransmission indication, a new transmission indication, failure information of the random access preamble of the second cell, and success information of the random access preamble of the second cell.

[0021] In a possible implementation, when the third access network device determines the random access information of the second cell, specifically, the third access network device determines the random access information of the second cell without receiving the TA of the second cell. In the above technical solution, a condition for the third access network device to determine the random access information of the second cell is provided.

[0022] In a possible implementation, when the third access network device sends the second indication to the terminal device, specifically, the third access network device receives the random access configuration of the second cell; and sends the second indication to the terminal device according to the random access configuration of the second cell.

[0023] In a fourth aspect, the present application provides a communication method, which can be executed by a first access network device, or a module in the first access network device, such as a chip. The following is an example of execution by the first access network device.

[0024] The method includes: a first access network device receives the transmission configuration indicator (TCI) status information of a first cell, and the first cell is managed by the first access network device. After the first access network device determines that the terminal device switches to the first cell, it performs one or more of the following: transmitting data with the terminal device according to the data transmission information of the first TCI state in the TCI state information of the first cell; deactivating the second TCI state according to the activation information of the second TCI state in the TCI state information of the first cell; activating the third TCI state according to the deactivation information of the third TCI state in the TCI state information of the first cell. In the above technical solution, the first access network device receives the TCI state information of the first cell, and the TCI state information of the first cell is the state information of the TCI state of the first cell before the terminal device switches to the first cell. In this way, the first access network device no longer needs to instruct the terminal device to activate or deactivate the TCI state of the first cell, which helps to shorten the delay of scheduling data.

[0025] In a possible implementation, the first access network device also receives TCI status information of a second cell, which is different from the first cell; deactivates the TCI status of the second cell according to activation information in the TCI status information of the second cell; or activates the TCI status of the second cell according to deactivation information in the TCI status information of the second cell. In the above technical solution, the first access network device receives the TCI status information of the second cell, which is the status information of the TCI status of the second cell before the terminal device switches to the first cell. In this way, the first access network device no longer needs to instruct the terminal device to activate or deactivate the TCI status of the second cell.

[0026] In one possible implementation, the first cell is a time division multiplexing cell, the third cell is a frequency division multiplexing cell, and the third cell is the cell accessed by the terminal device before switching. The first access network device also determines the offset of the expected data arrival time based on the frame structure and data arrival time of the first cell, and sends the offset of the expected data arrival time to the core network device. In the above technical scheme, the first access network device can determine the offset of the expected data arrival time, and the offset of the expected data arrival time can be used by the service server to adjust the sending time of the downlink data, or used by the service server to instruct the terminal device to adjust the sending time of the uplink data, thereby facilitating the matching of the arrival time of the downlink data with the downlink slot of the time division multiplexing cell, or the matching of the arrival time of the uplink data with the uplink slot of the time division multiplexing cell, avoiding data caching in the 5G network, reducing the load of the 5G network, and shortening the delay in transmitting data between the terminal device and the service server.

[0027] In a fifth aspect, the present application provides a communication method, which can be executed by a terminal device, or a module in the terminal device, such as a chip. The following is an example of execution by a terminal device.

[0028] The method includes: the terminal device receives one or more of the following indications: a data transmission indication of a first TCI state, an activation indication of a second TCI state, and a deactivation indication of a third TCI state. After the terminal device switches to the first cell, the context of the TCI state of the first cell is maintained and one or more of the following is performed: transmission data with the first access network device; measurement of the reference signal corresponding to the second TCI state to maintain timing synchronization; no measurement of the reference signal corresponding to the third TCI state; the first TCI state, the second TCI state, and the third TCI state are the TCI states of the first cell. In the above technical solution, after the terminal device switches to the first cell, the context of the TCI state of the first cell is maintained, so that the first access network device no longer needs to instruct the terminal device to activate or deactivate the TCI state of the second cell, which helps to shorten the delay of scheduling data.

[0029] In a possible implementation, before the terminal device switches to the first cell, it also receives a TCI state maintenance indication, wherein the TCI state maintenance indication is used to indicate the context of maintaining the TCI state of the first cell after the terminal device switches to the first cell.

[0030] In a sixth aspect, the present application provides a communication method, which can be executed by a third access network device, or a module in the third access network device, such as a chip. The following is an example of execution by the third access network device.

[0031] The method includes: a third access network device determines TCI state information of a first cell, and sends the TCI state information of the first cell to the first access network device. The TCI state information of the first cell includes one or more of the following: data transmission information of the first TCI state, activation information of the second TCI state, and deactivation information of the third TCI state, and the first cell is managed by the first access network device.

[0032] In a possible implementation, the third access network device also sends a TCI state maintenance indication to the terminal device.

[0033] In one possible implementation, the third access network device also sends one or more of the following indications to the terminal device: a data transmission indication of the first TCI state, an activation indication of the second TCI state, and a deactivation indication of the third TCI state.

[0034] In a seventh aspect, an embodiment of the present application provides a communication device,

[0035] The device has the function of implementing the first access network device in the above-mentioned first aspect or any possible implementation method of the first aspect. The device can be the first access network device or a chip included in the first access network device.

[0036] The apparatus may also have the function of implementing the terminal device in the above-mentioned second aspect or any possible implementation manner of the second aspect. The apparatus may be a terminal device or a chip included in the terminal device.

[0037] The device has the function of implementing the third access network device in the above-mentioned third aspect or any possible implementation method of the third aspect. The device can be a third access network device or a chip included in the third access network device.

[0038] The device has the function of implementing the first access network device in the above-mentioned fourth aspect or any possible implementation method of the fourth aspect. The device can be the first access network device or a chip included in the first access network device.

[0039] The apparatus may also have the function of implementing the terminal device in the fifth aspect or any possible implementation of the fifth aspect. The apparatus may be a terminal device or a chip included in the terminal device.

[0040] The device has the function of implementing the third access network device in the sixth aspect or any possible implementation method of the sixth aspect. The device can be a third access network device or a chip included in the third access network device.

[0041] The functions of the above communication device can be implemented by hardware, or by hardware executing corresponding software. The hardware or software includes one or more modules or units or means corresponding to the above functions.

[0042] In a possible implementation, the structure of the device includes a processing module and a transceiver module, wherein the processing module is configured to support the device to perform the function corresponding to the first access network device in the first aspect or any implementation of the first aspect, or to perform the function corresponding to the terminal device in the second aspect or any implementation of the second aspect, or to perform the function corresponding to the third access network device in the third aspect or any implementation of the third aspect, or to perform the function corresponding to the first access network device in the fourth aspect or any implementation of the fourth aspect, or to perform the function corresponding to the terminal device in the fifth aspect or any implementation of the fifth aspect, or to perform the function corresponding to the third access network device in the sixth aspect or any implementation of the sixth aspect. The transceiver module is used to support communication between the device and other communication devices. For example, when the device is the first access network device, it can send a first indication to the terminal device. The communication device may also include a storage module, which is coupled to the processing module and stores program instructions and data necessary for the device. As an example, the processing module may be a processor, the communication module may be a transceiver, and the storage module may be a memory. The memory may be integrated with the processor or may be set separately from the processor.

[0043] In another possible implementation, the structure of the device includes a processor and may also include a memory. The processor is coupled to the memory and may be used to execute computer program instructions stored in the memory so that the device performs the function corresponding to the first access network device in the first aspect or any implementation of the first aspect, or performs the function corresponding to the terminal device in the second aspect or any implementation of the second aspect, or performs the function corresponding to the third access network device in the third aspect or any implementation of the third aspect, or performs the function corresponding to the first access network device in the fourth aspect or any implementation of the fourth aspect, or performs the function corresponding to the terminal device in the fifth aspect or any implementation of the fifth aspect, or performs the function corresponding to the third access network device in the sixth aspect or any implementation of the sixth aspect. Optionally, the device further includes a communication interface, and the processor is coupled to the communication interface. When the device is an access network device or a terminal device, the communication interface may be a transceiver or an input / output interface; when the device is a chip included in the access network device or a chip included in the terminal device, the communication interface may be an input / output interface of the chip. Optionally, the transceiver may be a transceiver circuit, and the input / output interface may be an input / output circuit.

[0044] In an eighth aspect, an embodiment of the present application provides a chip system, comprising: a processor and a memory, the processor being coupled to the memory, the memory being used to store programs or instructions, and when the program or instructions are executed by the processor, the chip system executes the function corresponding to the first access network device in the first aspect or any implementation of the first aspect, or executes the function corresponding to the terminal device in the second aspect or any implementation of the second aspect, or executes the function corresponding to the third access network device in the third aspect or any implementation of the third aspect, or executes the function corresponding to the first access network device in the fourth aspect or any implementation of the fourth aspect, or executes the function corresponding to the terminal device in the fifth aspect or any implementation of the fifth aspect, or executes the function corresponding to the third access network device in the sixth aspect or any implementation of the sixth aspect.

[0045] Optionally, the chip system also includes an interface circuit, which is used to interact with code instructions to the processor.

[0046] Optionally, there may be one or more processors in the chip system, and the processor may be implemented by hardware or software. When implemented by hardware, the processor may be a logic circuit, an integrated circuit, etc. When implemented by software, the processor may be a general-purpose processor implemented by reading software code stored in a memory.

[0047] Optionally, the memory in the chip system may be one or more. The memory may be integrated with the processor or may be separately provided with the processor. Exemplarily, the memory may be a non-transient processor, such as a read-only memory ROM, which may be integrated with the processor on the same chip or may be provided on different chips.

[0048] In the ninth aspect, the present application provides a computer-readable storage medium, in which a computer program or instruction is stored. When the computer program or instruction is executed by a communication device, the communication device executes the corresponding function of the first access network device in the first aspect or any one of the implementations of the first aspect, or executes the corresponding function of the terminal device in the second aspect or any one of the implementations of the second aspect, or executes the corresponding function of the third access network device in the third aspect or any one of the implementations of the third aspect, or executes the corresponding function of the first access network device in the fourth aspect or any one of the implementations of the fourth aspect, or executes the corresponding function of the terminal device in the fifth aspect or any one of the implementations of the fifth aspect, or executes the corresponding function of the third access network device in the sixth aspect or any one of the implementations of the sixth aspect.

[0049] In the tenth aspect, the present application provides a computer program product, which includes a computer program or instructions. When the computer program or instructions are executed by a communication device, the corresponding functions of the first access network device in the first aspect or any implementation of the first aspect are executed, or the corresponding functions of the terminal device in the second aspect or any implementation of the second aspect are executed, or the corresponding functions of the third access network device in the third aspect or any implementation of the third aspect are executed, or the corresponding functions of the first access network device in the fourth aspect or any implementation of the fourth aspect are executed, or the corresponding functions of the terminal device in the fifth aspect or any implementation of the fifth aspect are executed, or the corresponding functions of the third access network device in the sixth aspect or any implementation of the sixth aspect are executed.

[0050] In the eleventh aspect, an embodiment of the present application provides a communication system, which includes the first access network device in the above-mentioned first aspect or any implementation of the first aspect, the terminal device in the above-mentioned second aspect or any implementation of the second aspect, and the third access network device in the above-mentioned third aspect or any implementation of the third aspect.

[0051] In the twelfth aspect, an embodiment of the present application provides a communication system, which includes the first access network device in the fourth aspect or any implementation of the fourth aspect, the terminal device in the fifth aspect or any implementation of the fifth aspect, and the third access network device in the sixth aspect or any implementation of the sixth aspect.

[0052] The technical effects that can be achieved by the above aspects can be referenced to each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 A schematic diagram of a communication system architecture provided for this application;

[0054] Figure 2 A schematic diagram of an inter-DU switching process provided by this application;

[0055] Figure 3 A schematic diagram of an intra-DU switching process provided by this application;

[0056] Figure 4 A schematic diagram of a process for a terminal device to obtain a TA of a candidate cell provided in this application;

[0057] Figure 5 A flowchart of the first communication method provided in this application;

[0058] Figure 6 A flow chart of the second communication method provided by this application;

[0059] Figure 7 A flowchart of a third communication method provided in this application;

[0060] Figure 8 A flowchart of the fourth communication method provided by this application;

[0061] Fig. 9 A schematic diagram of a frame structure of an FDD cell and a TDD cell provided in the present application;

[0062] Fig.10 A flowchart of a fifth communication method provided by this application;

[0063] Fig.11 A schematic diagram of a frame structure of another FDD cell and a TDD cell provided in the present application;

[0064] Fig.12 A schematic diagram of the structure of a communication device provided by the present application;

[0065] Fig.13 A schematic diagram of the structure of another communication device provided in the present application. DETAILED DESCRIPTION

[0066] The following first explains the relevant technical features involved in the embodiments of the present application. It should be noted that these explanations are intended to make the embodiments of the present application easier to understand and should not be regarded as limiting the scope of protection claimed by the present application.

[0067] Figure 1 FIG. 1 is a schematic diagram of the architecture of a communication system 1000 used in an embodiment of the present application. Figure 1 As shown, the communication system includes a wireless access network 100 and a core network 200. Optionally, the communication system 1000 may also include the Internet 300. The wireless access network 100 may include at least one access network device (such as Figure 1 110a and 110b), and may further include at least one terminal (such as Figure 1 120a-120j in the figure). The terminal is connected to the access network device by wireless means, and the access network device is connected to the core network by wireless or wired means. The core network device and the access network device can be independent and different physical devices, or the functions of the core network device and the logical functions of the access network device can be integrated on the same physical device, or the functions of some core network devices and some access network devices can be integrated on one physical device. Terminals and access network devices can be connected to each other by wired or wireless means. Figure 1 This is just a schematic diagram. The communication system may also include other network devices, such as wireless relay devices and wireless backhaul devices. Figure 1 Not drawn in.

[0068] The access network equipment can be a base station, an evolved NodeB (eNodeB), a transmission reception point (TRP), the next generation NodeB (gNB) in the fifth generation (5G) mobile communication system, the next generation base station in the sixth generation (6G) mobile communication system, a base station in a future mobile communication system, or an access node in a WiFi system, etc.; it can also be a module or unit that completes part of the functions of a base station, for example, it can be a centralized unit (CU) or a distributed unit (DU). The CU here completes the functions of the radio resource control protocol and packet data convergence protocol (PDCP) of the base station, and can also complete the function of the service data adaptation protocol (SDAP); the DU completes the functions of the radio link control (RLC) and medium access control (MAC) layers of the base station, and can also complete some or all of the physical layer (PHY) functions. For detailed descriptions of the above-mentioned protocol layers, please refer to the relevant technical specifications of the 3rd Generation Partnership Project (3GPP). The access network equipment can be a macro base station (such as Figure 1 110a), or a micro base station or an indoor station (such as Figure 1 110b), may also be a relay node or a donor node, etc. The embodiments of the present application do not limit the specific technology and specific device form adopted by the access network device.

[0069] The terminal may also be referred to as a terminal device, user equipment (UE), mobile station, mobile terminal, etc. The terminal can be widely used in various scenarios, for example, device-to-device (D2D), vehicle-to-everything (V2X) communication, machine-type communication (MTC), Internet of Things (IOT), virtual reality, augmented reality, industrial control, automatic driving, telemedicine, smart grid, smart furniture, smart office, smart wear, smart transportation, smart city, etc. The terminal may be a mobile phone, a tablet computer, a computer with wireless transceiver function, a wearable device, a vehicle, a drone, a helicopter, an airplane, a ship, a robot, a mechanical arm, a smart home device, etc. The embodiments of the present application do not limit the specific technology and specific device form adopted by the terminal.

[0070] The access network equipment and terminal equipment can be fixed or movable. The access network equipment and terminal equipment can be deployed on land, including indoors or outdoors, handheld or vehicle-mounted; they can also be deployed on the water surface; they can also be deployed on airplanes, balloons and artificial satellites in the air. The embodiments of the present application do not limit the application scenarios of the access network equipment and terminal equipment.

[0071] The roles of access network devices and terminal devices can be relative, for example, Figure 1 The helicopter or drone 120i in the figure can be configured as a mobile access network device. For the terminal devices 120j that access the wireless access network 100 through 120i, the terminal device 120i is an access network device; but for the access network device 110a, 120i is a terminal device, that is, 110a and 120i communicate through the wireless air interface protocol. Of course, 110a and 120i can also communicate through the interface protocol between access network devices. At this time, relative to 110a, 120i is also an access network device. Therefore, access network devices and terminal devices can be collectively referred to as communication devices. Figure 1 110a and 110b in the figure may be referred to as communication devices having access network device functions. Figure 1 120a-120j in the figure can be called communication devices with terminal equipment functions.

[0072] Access network devices and terminal devices, access network devices and access network devices, and terminal devices and terminal devices may communicate through authorized spectrum, unlicensed spectrum, or both; may communicate through spectrum below 6 gigahertz (GHz), spectrum above 6 GHz, or spectrum below 6 GHz and spectrum above 6 GHz. The embodiments of the present application do not limit the spectrum resources used for wireless communication.

[0073] In the embodiments of the present application, the functions of the access network device may also be performed by a module (such as a chip) in the access network device, or by a control subsystem including the functions of the access network device. The control subsystem including the functions of the access network device here may be a control center in the above-mentioned application scenarios such as smart grid, industrial control, smart transportation, and smart city. The functions of the terminal device may also be performed by a module (such as a chip or a modem) in the terminal device, or by a device including the functions of the terminal device.

[0074] In this application, the access network device sends a downlink signal or downlink information to the terminal device, and the downlink information is carried on the downlink channel; the terminal device sends an uplink signal or uplink information to the access network device, and the uplink information is carried on the uplink channel. In order to communicate with the access network device, the terminal device needs to establish a wireless connection with the cell controlled by the access network device. The cell with which the terminal device has established a wireless connection is called the service cell of the terminal device. When the terminal device communicates with the service cell, it will also be interfered by signals from neighboring cells.

[0075] Handover is a very important feature in the 5G system. Handover is mainly triggered by the movement of the terminal device when the terminal device is in the RRC connected state. The basic goal of handover is to switch the terminal device from the current service cell to a neighboring cell with better signal quality before the signal quality of the terminal device's current service cell fails to meet the communication needs of the terminal device, thereby ensuring the continuity of the terminal device's communication. That is, to avoid as much as possible the situation where the terminal device has dropped calls due to the deterioration of the signal quality of the terminal device's service cell.

[0076] In the 5G RAN architecture, access network equipment includes CU and DU. Multiple DUs can be centrally controlled by one CU, and each DU can manage one or more cells. CU and DU communicate through the F1 interface, and the transmission delay is about 3ms to 10ms.

[0077] In the existing L3 handover, the CU receives the measurement result of the terminal device, which is forwarded to the CU through the DU. The CU determines whether to initiate the handover based on the measurement result. For example, based on the measurement result, the CU determines that the service cell of the terminal device is poor, sends the handover command to the DU, and the DU sends it to the terminal device. In this way, there are many interactions in the F1 interface, resulting in a long handover delay. In order to shorten the handover delay, the standard is discussing Layer 1 / Layer 2 triggered mobility (L1 / L2 triggered mobility, LTM), and the handover decision is moved from the CU to the DU, that is, the DU determines whether to initiate an LTM cell switch (LTM cell switch) based on the measurement result of the terminal device, and the DU generates a handover instruction and sends the handover command to the terminal device, thereby reducing the interaction of the F1 interface.

[0078] Furthermore, DU triggered switching may include inter-DU switching and intra-DU switching.

[0079] like Figure 2 A schematic diagram of an inter-DU switching process provided as an example for this application:

[0080] Step 201: measurement control and reporting.

[0081] Specifically, the terminal device sends a measurement report message to the source DU. The measurement report message includes the measurement results of the neighboring cells (such as layer 3 measurement results). Correspondingly, the source DU receives the measurement report message from the terminal device and sends an uplink RRC message transfer (UL RRC message transfer) message to the CU. The CU receives the uplink RRC message transfer message from the source DU. The uplink RRC message transfer message includes a measurement report message. The neighboring cell in this application is the neighboring cell of the serving cell.

[0082] Step 202: The CU determines to initiate an LTM configuration process.

[0083] Specifically, the CU obtains a measurement report message from the uplink RRC message transmission message, and then obtains measurement results of multiple neighboring cells from the measurement report message, and selects some or all cells from the multiple neighboring cells as candidate cells (candidate DU) according to the measurement results of the multiple neighboring cells. The CU performs the following step 203 for each candidate cell.

[0084] Step 203: The CU sends a UE context setup request message to the candidate DU. Correspondingly, the candidate DU receives the UE context setup request message from the CU.

[0085] The candidate DU manages the candidate cell. The UE context establishment request message is used to request LTM configuration, and the UE context establishment request message includes the identifier of the candidate cell.

[0086] Step 204: When the candidate DU determines to accept the LTM configuration request, it sends a UE context setup response message to the CU. Correspondingly, the CU receives the UE context setup response message from the candidate DU.

[0087] The UE context establishment response message includes the LTM configuration generated by the candidate DU for the bottom layer of the accepted candidate cell, and the bottom layer of the candidate cell includes the RLC layer, the MAC layer and the PHY layer.

[0088] Step 205: The CU sends a DL RRC message transfer message to the source DU. Correspondingly, the source DU receives a DL RRC message transfer message from the CU. The DL RRC message transfer message includes an RRC reconfiguration message, and the RRC reconfiguration message includes an LTM configuration.

[0089] Step 206: The source DU sends an RRC reconfiguration message to the terminal device. Correspondingly, the terminal device receives the RRC reconfiguration message from the source DU.

[0090] Step 207: The terminal device sends an RRC reconfiguration complete message to the source DU. Correspondingly, the source DU receives the RRC reconfiguration complete message from the terminal device.

[0091] Step 208: The source DU sends an uplink RRC message transmission message to the CU. Correspondingly, the CU receives an uplink RRC message transmission from the source DU, where the uplink RRC message transmission carries an RRC reconfiguration completion message.

[0092] Step 209: The terminal device sends a lower layer measurement report to the source DU, and correspondingly, the source DU receives the lower layer measurement report from the terminal device. Here, the lower layer measurement report includes, for example, a measurement result of the physical layer.

[0093] In step 210, the source DU determines to perform LTM to a target cell. The source DU may select one of the one or more candidate cells as a target cell according to the underlying measurement reports of the one or more candidate cells, and perform step 211 for the target cell.

[0094] Step 211: The source DU sends a handover command to the terminal device. Correspondingly, the terminal device receives the handover command from the source DU, where the handover command is used to instruct the terminal device to handover to the target cell. The handover command includes an identifier of the target cell.

[0095] The switching command may specifically be an LTM command (LTM command).

[0096] Step 212: The source DU sends an LTM signaling to the CU. Accordingly, the CU receives the LTM signaling from the source DU, which includes the identifier of the target cell. Further, the CU may decide to send downlink data to the target DU based on the LTM signaling.

[0097] Here, the LTM notification may also be replaced with the LTM cell change notification.

[0098] Step 213: The target DU detects the access of the terminal device, wherein the target DU manages the target cell.

[0099] One solution is random access, that is, after the terminal device receives the LTM switching command, it initiates a random access process, for example, sending a physical random access channel (PRACH) to the target cell. The target DU learns that the terminal device requests to access the target cell through the random access process. If the target cell accepts the request of the terminal device, the target DU sends confirmation information of successful access to the terminal device, for example, random access message 4.

[0100] Another solution is random access skip (RACH-skip) or random access-free. The terminal device sends a physical uplink shared channel (PUSCH) or a physical uplink control channel (PUCCH) to the target cell. The PUSCH or PUCCH may carry indication information, which is used to request access to the target cell. If the target cell accepts the request of the terminal device, the target DU sends confirmation information of successful access to the terminal device, for example, a physical downlink control channel (PDCCH) carrying a cell radio network temporary identifier (C-RNTI) or a UE contention resolution identifier.

[0101] Step 214, the target DU sends an access success message to the CU, and correspondingly, the CU receives the access success message from the target DU. The access success message is used to indicate that the terminal device successfully accesses the target cell, and carries the identifier of the target cell.

[0102] Step 215: Release the resources of the source cell / candidate cell in the source DU.

[0103] like Figure 3 A schematic diagram of an intra-DU switching process provided as an example for this application:

[0104] Step 301: measurement control and reporting.

[0105] Specifically, the terminal device sends a measurement report message to the DU. The measurement report message includes the measurement results of the neighboring cells (such as L3 measurement results). Correspondingly, the DU receives the measurement report message from the terminal device and sends an uplink RRC message transmission message to the CU. The CU receives the uplink RRC message transmission message from the DU. The uplink RRC message transmission message includes the measurement report message.

[0106] Step 302: CU determines to initiate the LTM configuration process. For details, please refer to the description in the above step 202.

[0107] Step 303: CU sends a UE context modification request message to DU. Correspondingly, DU receives the UE context modification request message from CU. The UE context modification request message is used to request LTM configuration and includes the identifier of the candidate cell.

[0108] Step 304: When the DU determines to accept the LTM configuration request, the DU sends a UE context modification response message to the CU. Correspondingly, the CU receives the UE context modification response message from the DU.

[0109] The UE context modification response includes the RRC configuration generated by the DU for the bottom layer of the accepted candidate cell, and the bottom layer of the candidate cell includes the RLC layer, the MAC layer and the physical layer.

[0110] Step 305: CU sends a downlink RRC message transmission message to DU. Correspondingly, DU receives a downlink RRC message transmission message from CU. The downlink RRC message transmission message includes an RRC reconfiguration message, and the RRC reconfiguration message includes LTM configuration.

[0111] Step 306: The DU sends an RRC reconfiguration message to the terminal device. Correspondingly, the terminal device receives the RRC reconfiguration message from the DU.

[0112] Step 307: The terminal device sends an RRC reconfiguration completion message to the DU. Correspondingly, the DU receives the RRC reconfiguration completion message from the terminal device.

[0113] Step 308, the DU sends an uplink RRC message transmission message to the CU, and correspondingly, the CU receives an uplink RRC message transmission from the DU, where the uplink RRC message transmission carries an RRC reconfiguration completion message.

[0114] Step 309: The terminal device sends a bottom layer measurement report to the DU, and correspondingly, the DU receives the bottom layer measurement report from the terminal device. Here, the bottom layer measurement report includes, for example, a measurement result of the physical layer.

[0115] In step 310, the DU determines to perform LTM to the target cell. The DU may select one of the one or more candidate cells as the target cell according to the underlying measurement reports of the one or more candidate cells, and perform step 311 for the target cell.

[0116] Step 311, the DU sends a switching command to the terminal device, and correspondingly, the terminal device receives the switching command from the DU, where the switching command is used to instruct the terminal device to switch to the target cell.

[0117] Step 312, the DU sends an LTM notification to the CU, and correspondingly, the CU receives the LTM notification from the DU, the LTM notification including the identifier of the target cell. Here, the LTM notification may also be replaced with an LTM cell change notification.

[0118] Step 313: DU detects access of terminal equipment.

[0119] One solution is random access, that is, after the terminal device receives the LTM switching command, it initiates a random access process, for example, sending PRACH to the target cell. Correspondingly, the DU learns that the terminal device requests to access the target cell through the random access process. If the target cell accepts the request of the terminal device, the target DU sends confirmation information of successful access to the terminal device, for example, random access message 4.

[0120] Another solution is RACH-skip or random access-free. The terminal device accesses the target cell by sending a PUSCH or PUCCH to the target cell. The PUSCH or PUCCH may carry indication information, which is used to request access to the target cell. If the target cell accepts the request of the terminal device, the target DU sends confirmation information of successful access to the terminal device, such as a PDCCH carrying a C-RNTI or a UE contention resolution identifier.

[0121] Step 314, the DU sends an access success message to the CU, and correspondingly, the CU receives the access success message from the DU. The access success message is used to indicate that the terminal device successfully accesses the target cell, and carries the identifier of the target cell.

[0122] Step 315, the CU sends a UE context modification message to the DU, and correspondingly, the DU receives the UE context modification message from the CU, where the UE context modification message is used by the DU to release resources of the prepared cell.

[0123] Step 316: After releasing the resources of the prepared cell, the DU sends a UE context modification response message to the CU. Correspondingly, the CU receives the UE context modification response message from the DU.

[0124] Before the terminal device receives the handover command, the terminal device maintains the connection with the source cell and performs a random access process for the candidate cell, thereby obtaining the timing advance (TA) of the candidate cell in advance. Further, after receiving the LTM handover command, the terminal device can obtain the identity of the target cell from the handover command, and access the target cell through RACH-skip according to the identity of the target cell and the TA of the target cell, wherein the target cell is one of the candidate cells.

[0125] When the terminal device obtains the TA of the target cell, there are three specific ways:

[0126] Mode 1: The terminal device sends a random access preamble to the candidate DU. The candidate DU determines the TA based on the random access preamble and sends a random access response to the terminal device. The random access response includes the TA. After receiving the random access response, the terminal device determines that the random access is completed. For details, see Figure 4 The process in (a).

[0127] Mode 2: The terminal device sends a random access preamble to the candidate DU. The candidate DU determines the TA based on the random access preamble and sends a random access response to the source DU. The source DU then forwards the random access response to the terminal device. The random access response includes the TA. After receiving the random access response, the terminal device determines that the random access is completed. For details, see Figure 4 The process in (b).

[0128] Mode 3: The terminal device sends a random access preamble to the candidate DU, and the candidate DU determines the TA based on the random access preamble and sends the TA to the source DU. Optionally, the terminal device determines that the random access is completed. Further, the source DU sends a handover command to the terminal device, and the handover command includes the TA. For details, see Figure 4 The process in (c).

[0129] In the present application, the random access preamble takes a content free random access (CFRA) preamble as an example.

[0130] In the current LTM cell handover, when the terminal device switches to the target cell, there are three problems as follows:

[0131] Problem 1: It takes a long time for a terminal device to obtain the TA of a candidate cell.

[0132] Question 2: When the target cell schedules the terminal device to transmit user data, the required delay is relatively long.

[0133] Question 3: When the terminal device switches from a frequency division duplexing (FDD) cell to a time division duplex (TDD) cell, user data needs to be cached in the 5G network, increasing the transmission delay.

[0134] In response to question 1, the present application provides a first communication method for shortening the time required for a terminal device to obtain a TA of a second cell after the terminal device switches to a first cell.

[0135] In the present application, the second cell is a candidate cell, the third cell is a source cell for switching, the first cell is a target cell for switching, and the second cell may be the same as or different from the first cell. The first access network device manages the first cell, the second access network device manages the second cell, and the third access network device manages the third cell. When the second cell is the same as the first cell, the first access network device and the second access network device are the same device. As follows, the first access network device is the first DU, the second access network device is the second DU, and the third access network device is the third DU.

[0136] like Figure 5 A flow chart of the first communication method provided as an example for this application:

[0137] Step 501: The first DU obtains random access information of the second cell.

[0138] There are two possible implementations for the first DU to obtain the random access information of the second cell: (1) the first DU receives the random access information of the second cell from the third DU; (2) the first DU determines the random access information of the second cell by itself. Optionally, the former implementation method can be applied to scenarios where the first DU and the third DU are different, and the latter implementation method can be applied to scenarios where the first DU and the third DU are the same. The following is a specific description based on the two implementation methods:

[0139] (1) The first DU receives random access information of the second cell from the third DU:

[0140] Specifically, there are steps a and b as follows:

[0141] Step a: The third DU determines random access information of the second cell.

[0142] In one possible example, the third DU sends a random access indication (which may be recorded as a second indication) to the terminal device, and the second indication is used to instruct the terminal device to initiate random access to the second cell, wherein the second indication may include an identifier of the second cell. Accordingly, the terminal device receives the second indication from the third DU, and initiates random access to the second cell according to the second indication. The third DU may determine the random access information of the second cell according to the number of times the second indication is sent to the terminal device. Optionally, if the third DU determines that the TA of the second cell from the second DU is not received, the failure information in the random access information of the second cell is determined according to the number of times the second indication is sent to the terminal device. Optionally, if the third DU determines that the TA of the second cell from the second DU is received, the success information in the random access information of the second cell is determined according to the number of times the second indication is sent to the terminal device.

[0143] It can be understood that at this time, the service cell of the terminal device is still the third cell. When the second DU successfully receives the random access preamble sent by the terminal device to the second cell, it determines the TA of the second cell and sends the TA of the second cell to the third DU. Subsequently, in the switching phase, the third DU sends the TA of the second cell to the terminal device in the switching command.

[0144] Among them, the third DU sends the second indication to the terminal device multiple times, specifically, the third DU sends the second indication to the terminal device for the first time, and the second indication is used to instruct the terminal device to send a new transmission of the random access preamble to the second DU, that is, to instruct the terminal device to send a new transmission of the random access preamble of the second cell to the second DU according to the initial power, wherein the initial power may be the power when the terminal device has not yet performed power ramping, and exemplarily, the initial power is equal to the sum of the target power (preamble received target power) of receiving the random access preamble and the offset (delta_preamble) of the random access preamble. If the third DU does not receive the TA of the second cell from the second DU within the first preset time length after sending the second indication, the third DU sends the second indication to the terminal device for the second time, and the second indication is used to instruct the terminal device to send a retransmission of the random access preamble to the second DU, that is, to instruct the terminal device to send a retransmission of the random access preamble of the second cell to the second DU according to the sum of the initial power and the random access preamble power ramping step. Furthermore, when the third DU sends the second indication for the second time, if the TA of the second cell is not received within the first preset time after the second indication is sent, a new second indication is sent again to instruct the terminal device to send a retransmission of the random access preamble to the second DU until the TA of the second cell is received within the first preset time after the second indication is sent.

[0145] In a specific example, before the third DU sends the second indication to the terminal device, the second DU generates a random access configuration of the second cell and sends the random access configuration of the second cell to the third DU. Accordingly, the third DU receives the random access configuration of the second cell from the second DU, and sends the second indication to the terminal device according to the random access configuration of the second cell. The random access configuration of the second cell, for example, includes a root sequence of a random access preamble. When the second DU sends the random access configuration of the second cell to the third DU, specifically, the second DU first sends the random access configuration of the second cell to the CU, and then the CU forwards the random access configuration of the second cell to the third DU.

[0146] Step b: The third DU sends random access information of the second cell to the first DU. Correspondingly, the first DU receives random access information of the second cell from the third DU. Specifically, the third DU first sends random access information of the second cell to the CU, and then the CU forwards the random access information of the second cell to the first DU.

[0147] In a specific example, the random access information of the second cell may include one or more of the following: an identifier of the second cell, a retransmission indication, a new transmission indication, failure information of the random access preamble of the second cell, and success information of the random access preamble of the second cell.

[0148] The retransmission indication is determined by the third DU.

[0149] The new transmission indication is determined by the third DU. Exemplarily, the third DU determines the time difference between the sending time of the last second indication and the current time, and if the time difference exceeds the second preset time length, the third DU determines to send the new transmission indication to the second DU.

[0150] The failure information of the random access preamble of the second cell refers to the statistical information of the failure of the random access of the terminal device in the second cell before the LTM cell switching, and may include one or more of the following: the initiation of the random access process of the second cell has been indicated to the terminal device, but the random access process has not yet succeeded; the number of times the second indication is sent; the number of failures of the random access preamble of the second cell.

[0151] The success information of the random access preamble of the second cell may include one or more of the following: the number of times the second indication is sent before the LTM switch; the number of times the random access preamble of the second cell fails before the random access succeeds.

[0152] A second possible implementation manner: the first DU determines the random access information of the second cell by itself.

[0153] For the specific implementation manner in which the first DU determines the random access information of the second cell by itself, refer to the description of step a in the first possible manner above. Optionally, the random access information of the second cell may include one or more of the following: an identifier of the second cell, failure information of the random access preamble of the second cell, and success information of the random access preamble of the second cell. For a specific explanation, refer to the description in the first possible manner.

[0154] Step 502: After determining that the terminal device switches to the first cell, the first DU sends a random access indication (which may be recorded as the first indication) to the terminal device according to the random access information of the second cell. Correspondingly, the terminal device receives the first indication from the first DU.

[0155] The first indication is used to instruct the terminal device to retransmit or retransmit the random access preamble to the second cell.

[0156] The following example provides an example in which the first DU sends a first indication to a terminal device based on the random access information of the second cell. Of course, the following example does not constitute a limitation of the present application, and the present application may also include other methods.

[0157] Example 1: The random access information of the second cell carries a retransmission indication. The first DU sends a first indication to the terminal device according to the retransmission indication. The first indication is used to instruct the terminal device to retransmit the random access preamble for the second cell.

[0158] Example 2: The random access information of the second cell carries a new transmission indication. The first DU sends a first indication to the terminal device according to the new transmission indication. The first indication is used to instruct the terminal device to perform a new transmission of the random access preamble for the second cell.

[0159] Example 3: The random access information of the second cell carries the failure information of the random access preamble of the second cell. In one possible implementation, the failure information includes the number of failures. When the number of failures is less than or equal to the number threshold, the first DU sends a first indication to the terminal device, and the first indication is used to instruct the terminal device to retransmit the random access preamble for the second cell.

[0160] In addition, the first DU may also determine not to send the first indication to the terminal device based on the random access information of the second cell. Exemplarily, the random access information of the second cell carries failure information of the random access preamble of the second cell, wherein the failure information is the number of failures, and the first DU determines not to send the first indication to the terminal device when determining that the number of failures is greater than the number threshold.

[0161] Optionally, before step 502, the third DU sends a switching command to the terminal device, and the switching command includes an identifier of the first cell, and the switching command is used to instruct the terminal device to switch to the first cell. Exemplarily, the correspondence between the cell and the TA is pre-stored in the terminal device, and the terminal device can determine the TA of the first cell based on the correspondence, and access the first cell by means of RACH skip according to the TA of the first cell. Another exemplary embodiment, the switching command also includes the TA of the first cell, and the terminal device obtains the TA of the first cell from the switching command, and accesses the first cell by means of RACH skip according to the TA of the first cell. Another exemplary embodiment, the terminal device obtains the TA of the first cell by sending a random access preamble of the first cell to the first DU, and then accesses the first cell according to the TA of the first cell.

[0162] Optionally, before sending a switching command to the terminal device, the third DU receives a measurement report from the terminal device, and the measurement report may specifically be a bottom-layer measurement report. In one example, the terminal device measures reference signals of multiple candidate cells, obtains measurement results of the multiple candidate cells, carries the measurement results of the multiple candidate cells in the measurement report and sends it to the third DU. Accordingly, the third DU may select a first cell as the target cell from the multiple candidate cells based on the measurement results of the multiple candidate cells in the measurement report. In another example, the terminal device measures reference signals of multiple candidate cells, obtains measurement results of the multiple candidate cells, selects the measurement result of the first cell from the measurement results of the multiple candidate cells, carries the measurement results of the first cell in the measurement report and sends it to the third DU.

[0163] Step 503: The terminal device retransmits or newly transmits the random access preamble to the second cell.

[0164] Optionally, before the terminal device performs cell switching, that is, before step 503, the terminal device receives a random access maintenance indication from a third DU, where the random access maintenance indication is used to instruct the terminal device to maintain a random access variable after performing cell switching.

[0165] The random access variable includes one or more of the following: a random access preamble power ramping counter (preamble_power_ramping_counter), a random access preamble transmission counter (preamble_transmission_counter), and a variable of a random access preamble new transmission indication (new preamble indication). Among them, the random access preamble power ramping counter is used to count the number of power ramping times of the random access preamble; the random access preamble transmission counter is used to count the number of transmission times of the random access preamble; the variable of the random access preamble new transmission indication may indicate whether the random access preamble transmission is a retransmission or a new transmission. Exemplarily, when the variable of the random access preamble new transmission indication flips, that is, the variable of the random access preamble new transmission indication changes from "0" to "1", or the variable of the random access preamble new transmission indication changes from "1" to "0", it indicates that this transmission is a new transmission; when the variable of the random access preamble new transmission indication does not flip (such as maintaining 0 or 1 unchanged), it indicates that this transmission is a retransmission.

[0166] In one possible manner, before switching the LTM cell, the terminal device may determine a first power according to a first random access variable, and then send a random access preamble of the second cell to the second DU according to the first power.

[0167] Exemplarily, the first random access variable is the count value of the random access preamble power ramp counter before switching, and the terminal device determines the first power according to the following formula: first power = target power of receiving random access preamble + bias of random access preamble + (first random access variable - 1) × random access preamble power ramp step. Among them, the initial power refers to the power without power ramping, which is equal to the sum of the target power of receiving random access preamble and the bias of random access preamble. Exemplarily, the count value of the first random access variable is 2, then the terminal device can determine that the first power is the sum of the initial power and 1 times the random access preamble power ramp step.

[0168] After the LTM switching, the terminal device receives the first indication, determines the second power according to the first indication, and sends the random access preamble of the second cell to the second DU according to the second power. The random access preamble of the second cell sent by the terminal device before and after the cell switching may be the same or different.

[0169] When the first indication is used to instruct the terminal device to perform a new transmission of the random access preamble for the second cell, the second power is the initial power.

[0170] When the first indication is used to instruct the terminal device to retransmit the random access preamble for the second cell, the second power is greater than or equal to the first power. Exemplarily, the terminal device determines the second power based on the second random access variable and the random access preamble power ramping step. Exemplarily, the second random access variable is the count value of the random access preamble power ramping counter after switching, and the terminal device determines the second power according to the following formula: second power = target power for receiving random access preamble + bias of random access preamble + (second random access variable - 1) × random access preamble power ramping step. Exemplarily, the count value of the second random access variable is 3, then the terminal device can determine that the second power is the sum of the initial power and 2 times the random access preamble power ramping step.

[0171] Among them, the first random access variable is the random access variable of the terminal device when sending the first power. The second random access variable is the random access variable of the terminal device when sending the second power. Optionally, the terminal device maintains the first random access variable after the LTM switching according to the random access maintenance indication. After the LTM switching, the terminal device determines the second random access variable according to the first random access variable. Exemplarily, when the first random access variable and the second random access variable are respectively two count values ​​of the random access preamble power ramp counter before and after the switching, or when the first random access variable and the second random access variable are respectively two count values ​​of the random access preamble transmission counter before and after the switching, the second random access variable is equal to the first random access variable plus 1; when the first random access variable and the second random access variable are respectively two variable values ​​of the random access preamble new transmission indication before and after the switching, when the first indication is a new transmission indication, the two variable values ​​are different (flipped); when the first indication is a retransmission indication, the two variable values ​​are the same (not flipped).

[0172] It should be supplemented that, after determining that the terminal device switches to the first cell, the first DU can instruct the terminal device to perform a new transmission or retransmission of the random access preamble to the first cell according to the random access information of the first cell.

[0173] Optionally, when determining that the TAT (TA timer) of the first cell has timed out, the first DU determines that the TA of the first cell is invalid, and further instructs the terminal device to perform a new transmission or retransmission of the random access preamble for the first cell. The invalid TA of the first cell may be referred to as the first TA.

[0174] Based on whether the terminal device maintains the random access variable, there are two cases as follows:

[0175] In case 1, the terminal device maintains the random access variable.

[0176] Optionally, after the LTM switching, the terminal device maintains the first random access variable. After the LTM switching, the terminal device determines the second random access variable according to the first random access variable (for example, the second random access variable is equal to the first random access variable plus 1).

[0177] The first DU sends a first indication to the terminal device, and the first indication is used to instruct the terminal device to retransmit the random access preamble for the first cell. Correspondingly, the terminal device can determine the second power according to the first indication and the second random access variable, and send the random access preamble of the first cell to the first DU according to the second power.

[0178] Case 2: The terminal device does not maintain the random access variable.

[0179] After the LTM switching, the terminal device does not maintain the first random access variable. After the LTM switching, the terminal device determines the second random access variable (eg, the second random access variable is equal to 1).

[0180] The first DU first sends a first indication to the terminal device, and the first indication is used to instruct the terminal device to retransmit the random access preamble for the first cell; then, the terminal device sends N first indications to the terminal device according to the number of random access failures before switching to the first cell, and each first indication here is used to instruct the terminal device to retransmit the random access preamble for the first cell, N is greater than or equal to the number of failures, and N is a positive integer. Among them, the resources of the N first indications are all sent within a random access association period, or before the resources of the random access preamble. There are no random access resources between the resources of the N first indications.

[0181] For example, the random access variable is a random access preamble power ramp counter. The first DU counts that the number of random access failures before the terminal device switches to the first cell is 5, so it first sends a new transmission indication to the terminal device, and then continues to send 5 retransmission indications to the terminal device. In this way, the terminal device determines that the random access preamble power ramp counter is equal to 6, and then determines the second power according to the starting power, the value of the random access preamble power ramp counter 6, and the random access preamble power ramp step, and sends the random access preamble of the second cell to the second DU according to the second power. In this case, the terminal device can send the random access preamble of the first cell to the first DU after receiving the first indication for the last time, and only perform power ramping after receiving the first indication several times before. This helps to reduce the consumption of the terminal device.

[0182] In addition, the first DU may also obtain channel state information (CSI) reported by the terminal device, determine the number of times N to send the first indication to the terminal device according to the CSI and the number of failures, and then send the first indication to the terminal device N times. For example, the CSI includes one or more of the following: reference signal received power (RSRP), reference signal received quality (RSRQ), and signal to interference and noise ratio (SINR).

[0183] Optionally, after receiving a random access preamble from the terminal device, the first DU may determine a second TA based on the random access preamble, and further determine the difference between the second TA and the first TA (i.e., a relative TA), and send the relative TA to the terminal device. The terminal device determines the second TA based on the first TA currently maintained by it and the received relative TA.

[0184] Or it can also be understood that in the embodiment of the present application, before switching to the first cell, the terminal device first sends the random access preamble of the second cell to the second DU according to the first power; after switching to the first cell, the terminal device sends the random access preamble of the second cell to the second DU according to the second power, wherein the second power is the initial power, or the second power is greater than or equal to the first power. Further, when the second power is greater than or equal to the first power, it can help the terminal device to obtain the TA of the second cell more quickly.

[0185] It should also be added that, when the first cell and the second cell are different, the first DU can also instruct the terminal device to switch to the second cell. Exemplarily, after the first DU sends the first indication to the terminal device, it sends a switching command to the terminal device, the switching command includes the identifier of the second cell, and the switching command is used to instruct the terminal device to switch to the second cell. Accordingly, when the first DU determines that the TA of the second cell from the second DU is not received, it determines the random access information of the second cell and sends the random access information of the second cell to the second DU. Among them, when the first DU determines the random access information of the second cell, it can specifically determine the random access information of the second cell according to the number of times the first indication is sent to the terminal device. Accordingly, after receiving the random access information of the second cell, the second DU can determine to send a third indication to the terminal device according to the random access information of the second cell, and the third indication is used to instruct the terminal device to retransmit or retransmit the random access information for the second cell. The specific implementation can be referred to the description in the above 5 related embodiments.

[0186] Above Figure 5The relevant embodiments are for a terminal device. In addition, the present application also provides another possible method: the first terminal device and the second terminal device are both terminal devices switched from the third cell to the first cell. The first DU can obtain the random access information of the first terminal device for the second cell, and then when it is determined that the second terminal device switches to the first cell, according to the random access information of the first terminal device for the second cell, send a first indication to the second terminal device. Correspondingly, the second terminal device can initiate a new transmission or retransmission of the random access preamble to the second cell according to the first indication. In this way, when the first DU cannot obtain the random access information of the second terminal device for the second cell, it can still instruct the second terminal device to initiate a new transmission or retransmission of the random access preamble to the second cell, which helps to shorten the time required for the second terminal device to obtain the TA of the second cell.

[0187] Combined with the above Figure 5 The first communication method shown is Figure 6 The second communication method provided in this application is a specific implementation of the first communication method.

[0188] Step 601, LTM configuration. In addition, during the LTM configuration process, the RRC reconfiguration message sent by the third DU to the terminal device may also carry a random access maintenance indication.

[0189] Step 602: The terminal device initiates a random access process to the first cell. Optionally, the third DU sends a random access indication to the terminal device, where the random access indication is used to instruct the terminal device to initiate a random access process to the first cell.

[0190] Step 603, the terminal device initiates a random access process to the second cell. Optionally, the third DU sends a random access indication (i.e., a second indication) to the terminal device, and the random access indication is used to instruct the terminal device to initiate a random access process to the second cell. Further, the third DU may determine the random access information of the second cell without receiving the TA of the second cell from the second DU.

[0191] Step 604: The terminal device sends a measurement report to the third DU, and correspondingly, the third DU receives the measurement report from the terminal device. The measurement report includes the measurement result of the first cell. Optionally, the measurement report also includes the measurement result of the second cell.

[0192] Step 605: The third DU sends an LTM command to the terminal device. Correspondingly, the terminal device receives the LTM command from the third DU. The LTM command includes the identifier of the first cell.

[0193] Optionally, when the RRC reconfiguration message in the above step 601 does not carry the random access maintenance indication, the random access maintenance indication may also be carried in the LTM command.

[0194] Step 606: The third DU sends an LTM notification to the first DU. Correspondingly, the first DU receives the LTM notification from the third DU. The LTM notification includes random access information of the second cell. Specifically, the third DU first sends an LTM notification to the CU, and the CU then sends an LTM notification to the first DU.

[0195] Step 607: The terminal device accesses the first cell by means of RACH-skip. And based on the random access maintenance indication, the terminal device maintains the random access variable determined before switching to the first cell.

[0196] Furthermore, there are two possible implementation methods:

[0197] Implementation 1:

[0198] Step 608: The first DU sends a first indication to the terminal device according to the random access information of the second cell. Correspondingly, the terminal device receives the first indication from the first DU. The first indication is used to instruct the terminal device to retransmit the random access preamble.

[0199] Step 609: The terminal device sends a retransmission of the random access preamble of the second cell to the second DU according to the first indication.

[0200] Implementation 2:

[0201] When the first cell and the second cell are the same, and the first DU determines that the first TA of the first cell fails:

[0202] Step 610: The first DU sends a first indication to the terminal device according to the random access information of the first cell, where the first indication is used to instruct the terminal device to retransmit the random access preamble for the first cell.

[0203] Step 611: The terminal device sends a retransmission of the random access preamble of the first cell to the first DU according to the first indication.

[0204] There are two specific methods:

[0205] In mode a, the terminal device receives a first indication from the first DU, determines a second power according to the first indication and a second random access variable, and sends a random access preamble of the first cell to the first DU according to the second power. For the description of the second power and the second random access variable, refer to the description in the above step 503.

[0206] In mode b, the first DU first sends a first indication for indicating a new transmission to the terminal device, and then continuously sends N first indications for indicating retransmission to the terminal device according to the number of failures in the random access information of the first cell. Correspondingly, the terminal device climbs N times with the random access preamble power ramping step from the initial power according to the N first indications to obtain the second power, and sends the random access preamble of the first cell to the first DU according to the second power. The description of the second power can be found in the description of step 503 above.

[0207] Step 612: After receiving the random access preamble of the first cell, the first DU determines the second TA of the first cell, determines the relative TA according to the second TA of the first cell and the first TA of the first cell, and sends the relative TA to the terminal device.

[0208] It is understandable that the explanations of terms, implementation methods, etc. between the various embodiments in this application can refer to each other. For example, the specific implementation of step 601 can refer to the description of the above steps 202 to 208; the specific implementation of step 604 can refer to the description of the above steps 209 and 502; the specific implementation of step 605 can refer to the description of the above steps 210, 211, and 502; the specific implementation of step 606 can refer to the description of the above steps 212 and 501; the specific implementation of step 607 can refer to the description of the above steps 213 and 503; the specific implementation of steps 608 to 612 can refer to the description of the above steps 502 and 503.

[0209] In the above technical solution, the first DU obtains the random access information of the second cell, and sends a first indication to the terminal device according to the random access information of the second cell, and the first indication is used to instruct the terminal device to retransmit the random access preamble for the second cell. Accordingly, the terminal device can send the retransmission of the random access preamble of the second cell according to the first indication. The terminal device does not need to gradually increase the power from the initial power until it can successfully send the random access preamble of the second cell to the second DU, and the terminal device can quickly obtain the TA of the second cell.

[0210] In response to question 2, the present application provides a third communication method for shortening data scheduling delay.

[0211] For the description of the first cell, the second cell, the third cell, the first DU, the second DU and the third DU in this embodiment, please refer to the description in the relevant embodiment of Question 1.

[0212] like Figure 7 A flow chart of a communication method provided as an example for this application:

[0213] Step 701: The third DU determines the TCI status information of the first cell.

[0214] The TCI state information of the first cell includes one or more of the following: data transmission information of the first TCI state, activation information of the second TCI state, and deactivation information of the third TCI state. The first TCI state, the second TCI state, and the third TCI state are the TCI states of the first cell. For example, the TCI state information of the first cell includes: the first TCI state--1, the second TCI state--2, and the third TCI state--3, where "1" represents that it can be used to transmit data, "2" represents activation, and "3" represents deactivation.

[0215] Among them, the TCI state is used to indicate the quasi co-location (QCL) relationship between the channel parameters of the data transmission process and the downlink reference signal, so that the terminal device can demodulate the data carried by the signal based on the TCI state. The TCI state may include the serving cell index (serve cell index), the bandwidth part (band widthpart, BWP) identifier (identifier, ID) and the reference signal resource identifier.

[0216] Further, before determining the TCI status information of the first cell, the third DU may perform one or more of the following operations:

[0217] The third DU also indicates that the first TCI state can be used to transmit data. At this time, the TCI state information of the first cell includes the data transmission information of the first TCI state. Exemplarily, the third DU sends the configuration information of the first TCI state to the terminal device, and sends the data transmission indication of the first TCI state to the terminal device. The data transmission indication is used to indicate that the first TCI state can be used to transmit data. The data here can be specifically carried in one or more channels of PDCCH, physical downlink shared channel (physical downlink shared channel, PDSCH), physical uplink control channel (physical uplink control channel, PUCCH), and physical uplink shared channel (physical uplink shared channel, PUSCH). Accordingly, the terminal device transmits data with the first DU according to the data transmission indication of the first TCI state and the configuration information of the first TCI state after switching to the first cell. Optionally, the configuration information and data transmission indication of the first TCI state can be carried in the same message, or carried in different messages. Optionally, the data transmission indication of the first TCI state can be carried in the switching instruction sent by the third DU to the terminal device.

[0218] The third DU also activates the second TCI state. At this time, the TCI state information of the first cell includes the activation information of the second TCI state. Exemplarily, the third DU sends the configuration information of the second TCI state to the terminal device, and sends the activation indication of the second TCI state to the terminal device. Correspondingly, the terminal device activates the second TCI state according to the activation indication of the second TCI state and the configuration information of the second TCI state. Among them, the activation information can specifically be a control unit (medium access control element, MAC CE) for activating the media access control layer. Optionally, the configuration information and activation indication of the second TCI state can be carried in the same message, or carried in different messages.

[0219] The third DU also deactivates the third TCI state. At this time, the TCI state information of the first cell includes the deactivation information of the third TCI state. Exemplarily, the third DU sends configuration information of the third TCI state to the terminal device, and sends deactivation information of the third TCI state to the terminal device. Correspondingly, the terminal device deactivates the third TCI state according to the deactivation indication of the third TCI state and the configuration information of the third TCI state. Among them, the deactivation indication can specifically be a deactivation MAC CE. Optionally, the configuration information and deactivation indication of the third TCI state can be carried in the same message, or carried in different messages.

[0220] The configuration information of the TCI state includes the identifier or resource of the reference signal.

[0221] Optionally, before the terminal device performs a cell switching, the third DU may also send a TCI state maintenance indication to the terminal device, and accordingly, the terminal device receives the TCI state maintenance indication from the third DU. The TCI state maintenance indication is used to indicate that the context of the TCI state of the first cell is maintained after the terminal device switches to the first cell, wherein the context includes one or more of a data transmission indication of the first TCI state, an activation indication of the second TCI state, and a deactivation indication of the third TCI state. The context can be used for the terminal device to transmit data or perform timing synchronization with the first DU after the cell switching. Of course, the present application does not exclude the solution of maintaining the context of the TCI state of the first cell by default after the terminal device switches to the first cell, and specifically, the rule may be preconfigured inside the terminal device.

[0222] Step 702: The third DU sends TCI status information of the first cell to the first DU. Correspondingly, the first DU receives TCI status information of the first cell from the third DU.

[0223] Among them, when the third DU sends the TCI status information of the first cell to the first DU, specifically, the third DU first sends the TCI status information of the first cell to the CU, and then the CU forwards the TCI status information of the first cell to the first DU.

[0224] Step 703: After determining that the terminal device switches to the first cell, the first DU may perform one or more of the following examples a to c according to the TCI state information of the first cell:

[0225] Example a: The first DU sends downlink data to the terminal device according to the data transmission information of the first TCI state, and accordingly, the terminal device receives the downlink data from the first DU according to the data transmission indication of the first TCI state in the context. Alternatively, the terminal device sends uplink data to the first DU according to the data transmission indication of the first TCI state in the context, and accordingly, the first DU receives the uplink data from the terminal device according to the data transmission information of the first TCI state.

[0226] Example b: The first DU deactivates the second TCI state according to the activation information of the second TCI state. Furthermore, the context maintained by the terminal device includes an activation indication of the second TCI state, the first DU sends a deactivation indication of the second TCI state to the terminal device, and the terminal device deactivates the second TCI state in the context according to the deactivation indication of the second TCI state.

[0227] Alternatively, the first DU sends a data transmission indication of the second TCI state to the terminal device according to the activation information of the second TCI state, and the data transmission indication is used to indicate that the second TCI state can be used to transmit data. Accordingly, the context maintained by the terminal device includes the activation indication of the second TCI state, and the terminal device measures the reference signal corresponding to the second TCI state according to the activation indication of the second TCI state to maintain timing synchronization, and after receiving the data transmission indication of the second TCI state, transmits data with the first DU according to the data transmission indication of the second TCI state.

[0228] Example c, the first DU activates the third TCI state according to the deactivation information of the third TCI state. Furthermore, the context maintained by the terminal device includes a deactivation indication of the third TCI state, the first DU sends an activation indication of the third TCI state to the terminal device, and the terminal device activates the third TCI state in the context according to the activation indication of the third TCI state.

[0229] Alternatively, the first DU does not send the reference signal corresponding to the third TCI state to the terminal device based on the deactivation information of the second TCI state. Correspondingly, the terminal device also determines not to measure the reference signal corresponding to the third TCI state based on the deactivated third TCI state in the context.

[0230] It should be supplemented that the third DU can also send the configuration information of the TCI state of the second cell to the terminal device through an RRC message, and send an activation indication to the terminal device through a MAC CE, wherein the activation indication is used for the terminal device to activate the TCI state of the second cell, or send a deactivation indication to the terminal device, wherein the deactivation indication is used for the terminal device to deactivate the TCI state of the second cell. Here, the second cell is different from the first cell. Subsequently, the third DU determines the TCI state information of the second cell, and sends the TCI state information of the second cell to the first DU, and the TCI state information of the second cell includes activation information or deactivation information of the TCI state of the second cell. Optionally, when the TCI state information of the second cell includes activation information of the TCI state of the second cell, the first DU can deactivate the TCI state of the second cell; when the TCI state information of the second cell includes deactivation information of the TCI state of the second cell, the first DU can activate the TCI state of the second cell, and the specific implementation can be referred to the description in the above steps 701 to 703.

[0231] Combined with the above Figure 7 The third communication method shown is Figure 8 The fourth communication method provided in this application is a specific implementation of the third communication method. It can be understood that the contents not described in detail here can all refer to the description of the third communication method mentioned above.

[0232] Step 801, LTM configuration, for details, please refer to the description in the above steps 202 to 208.

[0233] Step 802a, the third DU sends an activation MAC CE of the second TCI state of the first cell to the terminal device. Correspondingly, the terminal device receives the activation MAC CE of the second TCI state. The activation MAC CE is used to activate the second TCI state in the terminal device.

[0234] Step 802b, the terminal device activates the second TCI state according to the activation MAC CE of the second TCI state. Optionally, after activating the second TCI state, the terminal device measures the reference signal of the second TCI state according to the activated second TCI state, thereby maintaining timing synchronization.

[0235] Step 803a, the third DU sends a deactivation MAC CE of the third TCI state of the first cell to the terminal device. Correspondingly, the terminal device receives the deactivation MAC CE of the third TCI state. The deactivation MAC CE is used to deactivate the third TCI state of the terminal device.

[0236] Step 803b: The terminal device deactivates the third TCI state according to the deactivation MAC CE of the third TCI state.

[0237] It is understandable that step 802a and step 802b may be collectively referred to as step 802, and step 803a and step 803b may be collectively referred to as step 803. In the embodiment of the present application, step 802 and step 803 may both exist, or neither of them exists, or one of them may exist. When both step 802 and step 803 exist, the order of the two may not be limited. The activation MAC CE of the second TCI state and the deactivation MAC CE of the third TCI state may be carried in the same message or in different messages.

[0238] Step 804: The terminal device sends a measurement report to the third DU, and correspondingly, the third DU receives the measurement report from the terminal device. The measurement report includes the measurement result of the first cell. Optionally, the measurement report also includes the measurement result of the second cell.

[0239] Step 805: The third DU sends an LTM command to the terminal device. Accordingly, the terminal device receives the LTM command from the third DU. The LTM command includes a data transmission indication of the first TCI state and an identifier of the first cell. The data transmission indication of the first TCI state is used to indicate that the terminal device can receive data from the first DU according to the first TCI state.

[0240] Step 806: The third DU sends an LTM notification to the first DU. Correspondingly, the first DU receives the LTM notification from the third DU. The LTM notification includes the TCI status information of the first cell.

[0241] The TCI state information of the first cell includes data transmission information of the first TCI state. Further, when step 802 is present, the TCI state information of the first cell also includes activation information of the second TCI state; when step 803 is present, the TCI state information of the first cell also includes deactivation information of the third TCI state. For an explanation of the TCI state information of the first cell, refer to the description in the above step 701.

[0242] Specifically, the third DU first sends an LTM notification to the CU, and the CU then sends an LTM notification to the first DU.

[0243] Step 807: The terminal device accesses the first cell via RACH-skip.

[0244] Here, the terminal device can obtain the TCI state maintenance indication from the third DU in advance, and determine the context of maintaining the TCI state of the first cell after switching to the first cell based on the TCI state maintenance indication.

[0245] For the description of the TCI state maintenance indication and context, please refer to the description in the above step 701.

[0246] Step 808a: The first DU sends a deactivation MAC CE of the second TCI state of the first cell to the terminal device. Correspondingly, the terminal device receives the deactivation MAC CE of the second TCI state. The deactivation MAC CE is used to deactivate the second TCI state in the terminal device.

[0247] Step 808a: The terminal device deactivates the second TCI state according to the deactivation MAC CE of the second TCI state.

[0248] Step 809a, the first DU sends an activation MAC CE of the third TCI state of the first cell to the terminal device. Correspondingly, the terminal device receives the activation MAC CE of the third TCI state. The activation MAC CE is used to activate the third TCI state in the terminal device.

[0249] Step 809b: The terminal device activates the third TCI state according to the activation MAC CE of the third TCI state.

[0250] It is understandable that step 808a and step 808b may be collectively referred to as step 808, and step 809a and step 809b may be collectively referred to as step 809. In the embodiment of the present application, when step 802 exists, step 808 may exist; when step 803 exists, step 809 may exist.

[0251] Step 810: The first DU sends downlink control information (DCI) to the terminal device, and accordingly, the terminal device receives the DCI from the first DU, wherein the TCI state of the PDSCH indicated by the DCI is the first TCI state.

[0252] Step 810: The first DU sends data to the terminal device on the PDSCH according to the first TCI state. Correspondingly, the terminal device receives data from the first DU on the PDSCH according to the first TCI state.

[0253] It is understandable that the explanations of terms, implementation methods, etc. between the various embodiments in this application can refer to each other. For example, the specific implementation of step 801 can refer to the description of steps 202 to 208 above; the specific implementation of steps 802 and 803 can refer to the description of step 701 above; the specific implementation of step 804 can refer to the description of step 209 above; the specific implementation of step 805 can refer to the description of steps 210, 211, and 701 above; the specific implementation of step 806 can refer to the description of steps 212 and 702 above; the specific implementation of steps 808 to 811 can refer to the description of step 703 above.

[0254] In the above technical solution, the first DU receives the TCI state information of the first cell from the third DU. In this way, after the terminal device switches to the first cell, the first DU can transmit data with the terminal device according to the data transmission information of the first TCI state in the TCI state information of the first cell. Alternatively, the first DU can send a reference signal corresponding to the second TCI state according to the activation information of the second TCI state in the TCI state information of the first cell, so that the terminal device can maintain timing synchronization. In this way, it helps to shorten the scheduling delay of the data. In addition, the terminal device may not measure the reference signal corresponding to the third TCI state according to the deactivation indication of the third TCI state in the context of the TCI state of the first cell, which helps to save power of the terminal device.

[0255] In response to question 3, the present application provides a fifth communication method for avoiding caching of uplink data or downlink data in the 5G network, reducing the load of the 5G network, and shortening the delay in transmitting data between the terminal device and the service server.

[0256] For the description of the first cell, the third cell, the first DU and the third DU in this embodiment, please refer to the description in the relevant embodiment of Question 1. The fifth communication method may occur after the terminal device switches to the first cell. The data is cached in the 5G network, specifically, the data is cached in the core network device of the 5G network, or in the access network device (such as DU, CU).

[0257] The frame structure of FDD cell and TDD cell is explained as follows:

[0258] The transmission of uplink data and downlink data in an FDD cell may use the same time domain resources and different frequency domain resources. The transmission of uplink data and downlink data in a TDD cell may use the same frequency domain resources and different time domain resources.

[0259] like Fig. 9This is a schematic diagram of a frame structure of an FDD cell and a TDD cell provided by the present application, wherein 0 to 10 represent time slot numbers, DL represents a slot for transmitting downlink data (referred to as a downlink slot), UL represents a slot for transmitting uplink data (referred to as an uplink slot), and S represents a slot for transmitting reference signals, control information, and other information. Fig. 9 For example, in an FDD cell, each slot can transmit uplink data or downlink data. In a TDD cell, slot 4 and slot 9 are used to transmit uplink data, and slot 0 to slot 2 and slot 5 to slot 7 are used to transmit downlink data.

[0260] Since each slot in an FDD cell can be used to transmit uplink data, when a terminal device switches from an FDD cell to a TDD cell, the slot originally used for uplink data transmission by the terminal device may no longer be able to transmit uplink data (e.g. Fig. 9 In this case, the terminal device needs to cache the uplink data and wait until the uplink slot in the TDD cell is full before it can continue to send. Alternatively, since each slot in the FDD cell can be used to transmit downlink data, when the terminal device switches from the FDD cell to the TDD cell, the slot originally used for the service server to transmit downlink data may no longer be able to transmit downlink data (e.g. Fig. 9 At this time, the service server sends downlink data to the core network device, and the core network device sends downlink data to the access network device. The access network device needs to cache the downlink data and wait until a slot in the TDD cell that can be used to transmit downlink data is available before it can continue to send it.

[0261] like Fig.10 A flowchart of the fifth communication method provided for this application:

[0262] Step 1001: The first DU determines the offset of the expected data arrival time (referred to as the first offset) according to the frame structure and data arrival time of the first cell. The frame structure of the first cell is also the frame structure of the TDD cell. The data can be downlink data or uplink data.

[0263] Exemplarily, the first offset is specifically an offset of the data arrival time expected by the first DU.

[0264] Exemplarily, before determining the first bias, the first DU receives a data arrival time from the third DU. The data arrival time may be specifically determined by the third DU after the terminal device switches to the first cell.

[0265] Optionally, when the first DU determines that the terminal device switches to the first cell, or after the first DU receives an LTM notification from the third DU, the first DU determines the first offset according to the LTM notification, wherein the LTM notification includes the data arrival time.

[0266] When the data is uplink data:

[0267] In one possible manner, the slot boundary of the first cell is aligned with the slot boundary of the second cell. The third DU determines the uplink data arrival time and sends the uplink data arrival time to the first DU. Accordingly, the first DU receives the uplink data arrival time from the third DU and determines the first offset according to the frame structure of the first cell and the uplink data arrival time.

[0268] Combination Fig. 9 For example, the third DU determines that the uplink data arrival time is slot 0, and sends slot 0 to the first DU. The first DU determines that slot 4 in the frame structure of the first cell is the slot for transmitting uplink data, that is, determines that the uplink data arrival time should be adjusted to slot 4, and thus determines that the first offset is the duration of 4 slots.

[0269] In another possible manner, the slot boundary of the first cell is not aligned with the slot boundary of the second cell. The third DU determines the uplink data arrival time and sends the uplink data arrival time to the first DU. Accordingly, the first DU receives the uplink data arrival time from the third DU, and determines the first offset according to the frame structure of the first cell, the uplink data arrival time, and the offset between the slot boundary of the first cell and the slot boundary of the second cell. Exemplarily, the first DU determines offset 1 according to the frame structure of the first cell and the uplink data arrival time, and determines offset 2 according to the slot boundary of the first cell and the slot boundary of the second cell, and then determines the first offset according to offset 1 and offset 2. Exemplarily, the first offset is determined based on the formula UL slotoffset(between TDD cell and FDD cell)+slot boundary offset, where UL slotoffset(between TDD cell and FDD cell) is offset 1 and slot boundary offset is offset 2.

[0270] like Fig.11This is a schematic diagram of another frame structure of an FDD cell and a TDD cell provided by way of example in the present application, wherein the first DU determines that the offset 2 is a duration of 4 slots based on the slot boundary of the FDD cell (i.e., the third cell) and the slot boundary of the TDD cell (i.e., the first cell). Also, the third DU determines that the uplink data arrival time is slot 0, and sends slot 0 to the first DU. The first DU determines that slot 4 in the frame structure of the first cell is a slot for transmitting uplink data, i.e., determines that the offset 1 is a duration of 4 slots. The first DU determines that the first offset is a duration of 8 slots based on offset 1 and offset 2.

[0271] When the data is downlink data:

[0272] In one possible manner, the slot boundary of the first cell is aligned with the slot boundary of the second cell. The third DU determines the downlink data arrival time and sends the downlink data arrival time to the first DU. Accordingly, the first DU receives the downlink data arrival time from the third DU and determines the first offset according to the frame structure of the first cell and the downlink data arrival time.

[0273] Combination Fig. 9 For example, the third DU determines that the downlink data arrival time is slot 3, and sends slot 3 to the first DU. The first DU determines that slot 5 in the frame structure of the first cell is the slot for transmitting downlink data, that is, determines that the downlink data arrival time should be adjusted to slot 5, and thus determines that the first offset is the duration of 2 slots.

[0274] In another possible manner, the slot boundary of the first cell is not aligned with the slot boundary of the second cell. The third DU determines the downlink data arrival time and sends the downlink data arrival time to the first DU. Accordingly, the first DU receives the downlink data arrival time from the third DU, and determines the first offset according to the frame structure of the first cell, the downlink data arrival time, and the offset between the slot boundary of the first cell and the slot boundary of the second cell. Exemplarily, the first DU determines offset 1 according to the frame structure of the first cell and the downlink data arrival time, and determines offset 2 according to the slot boundary of the first cell and the slot boundary of the second cell, and then determines the first offset according to offset 1 and offset 2. Exemplarily, the first offset is determined based on the formula UL slotoffset(between TDD cell and FDD cell)+slot boundary offset, where UL slotoffset(between TDD cell and FDD cell) is offset 1 and slot boundary offset is offset 2.

[0275] like Fig.11 This is a schematic diagram of another frame structure of an FDD cell and a TDD cell provided by way of example in the present application, wherein the first DU determines that the offset 2 is a duration of 4 slots based on the slot boundary of the FDD cell (i.e., the third cell) and the slot boundary of the TDD cell (i.e., the first cell). Also, the third DU determines that the arrival time of the downlink data is slot 3, and sends slot 3 to the first DU. The first DU determines that slot 5 in the frame structure of the first cell is the slot for transmitting downlink data, i.e., determines that the offset 1 is a duration of 2 slots. The first DU determines that the first offset is a duration of 6 slots based on offset 1 and offset 2.

[0276] In addition, after switching to the first cell, the terminal device can also determine the offset of the data arrival time expected by the terminal device based on the frame structure and data arrival time of the first cell, and then send the offset of the data arrival time expected by the terminal device to the first DU. The first DU then determines the first offset based on the offset of the data arrival time expected by the terminal device. Exemplarily, the offset of the data arrival time expected by the terminal device is the same as the first offset. Optionally, the terminal device determines the offset of the data arrival time expected by the terminal device after determining that the terminal device switches to the first cell, or after the terminal device receives a switching command from a third DU.

[0277] Step 1002: The first DU sends a first offset to a core network device. Correspondingly, the core network device receives the first offset.

[0278] Specifically, the first DU sends the first bias to the CU of the first DU, and the CU of the first DU sends the first bias to the core network device.

[0279] Optionally, the present application also includes step 1003, in which the core network device sends an offset of the expected data arrival time to the service server (referred to as the second offset). Correspondingly, the service server receives the second offset. Exemplarily, the second offset is specifically an offset of the data arrival time expected by the core network device. Exemplarily, the core network device determines the second offset based on the first offset, and then sends the second offset to the service server.

[0280] Optionally, when the data is downlink data, the application further includes:

[0281] Step 1004: The service server adjusts the sending time of the downlink data according to the second offset, and sends the downlink data to the client according to the adjusted sending time of the downlink data.

[0282] In this way, the time when the service server sends downlink data matches the position of the downlink slot of the TDD cell, which helps to avoid the downlink data being cached in the 5G network and reduce the delay of downlink data transmission.

[0283] When the data is uplink data, the application also includes:

[0284] Step 1005: The service server sends a service adjustment indication to the client according to the second offset, where the service adjustment indication is used to instruct the client to adjust the time for sending uplink data.

[0285] Step 1006: The client adjusts the sending time of the uplink data according to the service adjustment instruction, and sends the uplink data to the service server according to the adjusted sending time of the uplink data.

[0286] In this way, the time when the terminal device sends uplink data matches the position of the uplink slot of the TDD cell, which helps to avoid the uplink data being cached in the 5G network and reduce the delay of uplink data transmission.

[0287] In this embodiment, the client may belong to the terminal device or may not belong to the terminal device. The client is, for example, an end station in the industrial internet of things (which can be expressed in English as industrial internet of things endstation, referred to as IIOT end station). Exemplarily, the IIOT end station can be a robotic arm in a factory. When the client belongs to the terminal device, when the business server transmits messages (such as uplink data, downlink data, business adjustment instructions, etc.) with the client, that is, the business server transmits messages with the terminal device. When the client does not belong to the terminal device, when the business server transmits messages with the client, the message can be forwarded via the terminal device. For example, the business server sends a business adjustment instruction to the terminal device, and the terminal device forwards the business adjustment instruction to the client. For another example, the client sends uplink data to the terminal device, and the terminal device forwards the uplink data to the business server.

[0288] In the above technical solution, when the terminal device switches from an FDD cell to a TDD cell, the first DU can determine a first bias, which can be used by the service server to adjust the sending time of downlink data, or used by the service server to instruct the terminal device to adjust the sending time of uplink data, thereby helping to achieve the time matching of downlink data with the downlink slot of the TDD cell, and the time matching of uplink data with the uplink slot of the TDD cell, avoiding data caching in the 5G network, reducing the load of the 5G network, and shortening the delay in transmitting data between the terminal device and the service server.

[0289] The following points need to be added to this application:

[0290] First, for the convenience of description, this application provides different communication methods for solving the three problems respectively, but these communication methods can be used in combination with each other. For example, after executing the first communication method, continue to execute the fifth communication method; for another example, after executing the second communication method, continue to execute the fifth communication method.

[0291] Second, the fifth communication method can be applied not only to LTM cell switching, but also to L3 handover.

[0292] Third, the above focuses on describing the differences between the first communication method to the fifth communication method. Except for the differences, the first communication method to the fifth communication method can refer to each other; in addition, in the same communication method, different implementation methods or different examples can also refer to each other.

[0293] Fourth, the step numbers of each flowchart are only an example of the execution process and do not constitute a restriction on the order of execution of the steps. There is no strict execution order between the steps in this flowchart that have no temporal dependency relationship. Not all the steps shown in each flowchart are required to be executed. Some steps can be deleted based on each flowchart according to actual needs, or other possible steps can be added based on each flowchart according to actual needs.

[0294] In the above embodiments provided by the present application, the methods provided by the embodiments of the present application are introduced from the perspective of interaction between various devices. In order to realize the various functions in the methods provided by the above embodiments of the present application, the terminal device and the access network device may include a hardware structure and / or a software module, and the above functions are realized in the form of a hardware structure, a software module, or a hardware structure plus a software module. Whether a certain function of the above functions is executed in the form of a hardware structure, a software module, or a hardware structure plus a software module depends on the specific application and design constraints of the technical solution. The division of modules in the embodiments of the present application is schematic, which is only a logical function division, and there may be other division methods in actual implementation. In addition, each functional module in each embodiment of the present application can be integrated in a processor, or it can be physically present separately, or two or more modules can be integrated in one module. The above integrated modules can be implemented in the form of hardware or in the form of software functional modules.

[0295] Based on the above content and the same idea, Fig.12 and Fig.13The following is a schematic diagram of the structure of possible communication devices provided in the present application. These communication devices can be used to implement the functions of the first access network device, the third access network device or the terminal device in the above method embodiment, so as to achieve the beneficial effects of the above method embodiment. In the present application, the communication device can be as follows: Figure 1 The terminal device shown may also be Figure 1 The access network device shown may also be a module (such as a chip) applied to a terminal device or an access network device.

[0296] like Fig.12 As shown, the communication device 1200 includes a processing module 1201 and a transceiver module 1202 .

[0297] When the communication device 1200 is used to implement the above Figure 5 , Figure 6 , Fig.10 In the relevant method embodiment, the function of the first access network device is:

[0298] The processing module 1201 is used to obtain the random access information of the second cell. After determining that the terminal device switches to the first cell, the transceiver module 1202 is controlled to send a first indication to the terminal device according to the random access information of the second cell. The first indication is used to instruct the terminal device to retransmit or retransmit the random access preamble to the second cell. The first cell is managed by the communication device 1200, and the second cell is the same as or different from the first cell.

[0299] In a possible implementation, the random access information of the second cell includes one or more of the following: an identifier of the second cell, a retransmission indication, a new transmission indication, failure information of the random access preamble of the second cell, and success information of the random access preamble of the second cell.

[0300] In a possible implementation, when the first cell and the second cell are the same, when the processing module 1201 controls the transceiver module 1202 to send a first indication to the terminal device according to the random access information of the second cell, it is specifically used to: according to the random access information of the first cell, control the transceiver module 1202 to send N first indications to the terminal device, and the first indication is used to instruct the terminal device to retransmit the random access preamble for the first cell, wherein N is greater than or equal to the number of random access failures before the terminal device switches to the first cell, and N is a positive integer.

[0301] In a possible implementation, the first cell is a time division multiplexing cell, the third cell is a frequency division multiplexing cell, and the third cell is a cell accessed by the terminal device before switching. The processing module 1201 is further used to determine the offset of the expected data arrival time according to the frame structure and data arrival time of the first cell; and control the transceiver module 1202 to send the offset of the expected data arrival time to the core network device.

[0302] When the communication device 1200 is used to implement the above Figure 7 or Figure 8 In the relevant method embodiment, the function of the first access network device is:

[0303] The transceiver module 1202 is used to: receive TCI status information of the first cell, and the first cell is managed by the communication device 1200; the processing module 1201 is used to: after determining that the terminal device has switched to the first cell, execute one or more of the following: control the transceiver module 1202 to transmit data with the terminal device according to the data transmission information of the first TCI state in the TCI status information of the first cell; deactivate the second TCI state according to the activation information of the second TCI state in the TCI status information of the first cell; activate the third TCI state according to the deactivation information of the third TCI state in the TCI status information of the first cell.

[0304] In one possible implementation, the transceiver module 1202 is also used to: receive TCI status information of a second cell, which is different from the first cell; the processing module 1201 is also used to: deactivate the TCI status of the second cell according to the activation information in the TCI status information of the second cell; or, activate the TCI status of the second cell according to the deactivation information in the TCI status information of the second cell.

[0305] When the communication device 1200 is used to implement the above Figure 5 , Figure 6 , Fig.10 When the functions of the terminal device in the relevant method embodiment are:

[0306] The processing module 1201 is used to control the transceiver module 1202 to send the random access preamble of the second cell to the second access network device according to the first power, the first power is determined according to the random access variable, and the second cell is managed by the second access network device; after switching to the first cell, the processing module 1201 is also used to control the transceiver module 1202 to send the random access preamble of the second cell to the second access network device according to the second power, and the second power is greater than or equal to the first power.

[0307] In a possible implementation, the processing module 1201 is further used to: control the transceiver module 1202 to receive a first indication from the first access network device, the first indication is used to indicate the retransmission of the random access preamble of the second cell, and the first cell is managed by the first access network device, before sending the random access preamble of the second cell to the second access network device according to the second power control transceiver module 1202; determine the second power according to the first indication. In a possible implementation, when the processing module 1201 determines the second power according to the first indication, it is specifically used to: determine the second power according to the first indication, the random access variable, and the random access preamble power ramping step.

[0308] In a possible implementation, before switching to the first cell, the transceiver module 1202 is further used to: receive a random access maintenance indication, the random access maintenance indication is used to instruct the terminal device to maintain the random access variable after switching to the first cell. In a possible implementation, the random access variable includes one or more of the following: a random access preamble power ramp-up counter, a random access preamble transmission counter, and a variable of a random access preamble new transmission indication.

[0309] When the communication device 1200 is used to implement the above Figure 7 or Figure 8 When the functions of the terminal device in the relevant method embodiment are:

[0310] The transceiver module 1202 is used to receive one or more of the following indications: a data transmission indication of a first TCI state, an activation indication of a second TCI state, and a deactivation indication of a third TCI state; the processing module 1201 is used to maintain the context of the TCI state of the first cell after switching to the first cell and execute one or more of the following: control the transmission data between the transceiver module 1202 and the first access network device; measure the reference signal corresponding to the second TCI state to maintain timing synchronization; do not measure the reference signal corresponding to the third TCI state; wherein the first TCI state, the second TCI state and the third TCI state are the TCI states of the first cell.

[0311] In one possible implementation, the transceiver module 1202 is also used to: receive a TCI state maintenance indication before the communication device 1200 switches to the first cell, wherein the TCI state maintenance indication is used to indicate the context of maintaining the TCI state of the first cell after the communication device 1200 switches to the first cell.

[0312] When the communication device 1200 is used to implement the above Figure 5 , Figure 6 , Fig.10 When the function of the third access network device in the relevant method embodiment is:

[0313] The transceiver module 1202 is used to send a second indication to the terminal device, and the second indication is used to instruct the terminal device to initiate random access to the second cell; the processing module 1201 is used to determine the random access information of the second cell and control the transceiver module 1202 to send the random access information of the second cell to the first access network device; wherein the cells accessed by the terminal device before and after the switching are the third cell and the first cell respectively, the third cell is managed by the communication device 1200, the first cell is managed by the first access network device, and the second cell is the same as or different from the first cell.

[0314] In a possible implementation, the transceiver module 1202 is further configured to send a random access maintenance indication to the terminal device. In a possible implementation, the random access maintenance indication is carried in a radio resource control reconfiguration message or a handover command sent to the terminal device.

[0315] In a possible implementation, the random access information of the second cell includes one or more of the following: an identifier of the second cell, a retransmission indication, a new transmission indication, failure information of the random access preamble of the second cell, and success information of the random access preamble of the second cell.

[0316] In a possible implementation manner, when determining the random access information of the second cell, the processing module 1201 is specifically configured to: determine the random access information of the second cell when the TA of the second cell is not received.

[0317] In a possible implementation, when the processing module 1201 controls the transceiver module 1202 to send a second indication to the terminal device, it is specifically used to: control the transceiver module 1202 to receive the random access configuration of the second cell; and control the transceiver module 1202 to send a second indication to the terminal device according to the random access configuration of the second cell.

[0318] When the communication device 1200 is used to implement the above Figure 7 or Figure 8 When the function of the third access network device in the relevant method embodiment is:

[0319] The processing module 1201 is used to determine the first TCI status information; the transceiver module 1202 is used to send the TCI status information of the first cell to the first access network device, the TCI status information of the first cell includes one or more of the following: data transmission information of the first TCI state, activation information of the second TCI state, deactivation information of the third TCI state, and the first cell is managed by the first access network device.

[0320] In a possible implementation, the transceiver module 1202 is further used to send a TCI state maintenance indication to the terminal device.

[0321] In one possible implementation, the transceiver module 1202 is also used to send one or more of the following indications to the terminal device: a data transmission indication of a first TCI state, an activation indication of a second TCI state, and a deactivation indication of a third TCI state.

[0322] like Fig.13 The device 1300 provided in an embodiment of the present application is shown. Fig.13 The device shown can be Fig.12 A hardware circuit implementation of the device shown in the figure. The device can be applied to the flowchart shown above to perform the functions of the first access network device, terminal device or third access network device in the above method embodiment.

[0323] For ease of explanation, Fig.13 Only the main components of the device are shown.

[0324] Fig.13 The device 1300 shown includes a communication interface 1310, a processor 1320 and a memory 1330, wherein the memory 1330 is used to store program instructions and / or data. The processor 1320 may operate in conjunction with the memory 1330. The processor 1320 may execute program instructions stored in the memory 1330. When the instructions or programs stored in the memory 1330 are executed, the processor 1320 is used to execute the operations performed by the processing module 1201 in the above embodiment, and the communication interface 1310 is used to execute the operations performed by the transceiver module 1202 in the above embodiment.

[0325] The memory 1330 is coupled to the processor 1320. The coupling in the embodiment of the present application is an indirect coupling or communication connection between devices, units or modules, which can be electrical, mechanical or other forms, for information exchange between devices, units or modules. At least one of the memories 1330 may be included in the processor 1320.

[0326] In the embodiment of the present application, the communication interface may be a transceiver, a circuit, a bus, a module or other types of communication interfaces. In the embodiment of the present application, when the communication interface is a transceiver, the transceiver may include an independent receiver, an independent transmitter, or a transceiver with integrated transceiver functions or a communication interface.

[0327] The device 1300 may further include a communication line 1340. The communication interface 1310, the processor 1320, and the memory 1330 may be interconnected via the communication line 1340; the communication line 1340 may be a peripheral component interconnect (PCI) bus or an extended industry standard architecture (EISA) bus. The communication line 1340 may be divided into an address bus, a data bus, a control bus, etc. For ease of representation, Fig.13 Only one thick line is used in the diagram, but this does not mean that there is only one bus or only one type of bus.

[0328] It is understood that the processor in the embodiments of the present application may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), field programmable gate arrays (FPGA) or other programmable logic devices, transistor logic devices, hardware components or any combination thereof. The general-purpose processor may be a microprocessor or any conventional processor.

[0329] The method steps in the embodiments of the present application can be implemented by hardware, or by a processor executing software instructions. The software instructions can be composed of corresponding software modules, and the software modules can be stored in a random access memory, a flash memory, a read-only memory, a programmable read-only memory, an erasable programmable read-only memory, an electrically erasable programmable read-only memory, a register, a hard disk, a mobile hard disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor so that the processor can read information from the storage medium and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and the storage medium can be located in an ASIC. In addition, the ASIC can be located in an access network device or a terminal. Of course, the processor and the storage medium can also be present in an access network device or a terminal as discrete components.

[0330] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented by software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer programs or instructions. When the computer program or instruction is loaded and executed on a computer, the process or function described in the embodiment of the present application is executed in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, a network device, a user device or other programmable device. The computer program or instruction may be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium, for example, the computer program or instruction may be transmitted from one website site, computer, server or data center to another website site, computer, server or data center by wired or wireless means. The computer-readable storage medium may be any available medium that a computer can access or a data storage device such as a server, data center, etc. that integrates one or more available media. The available medium may be a magnetic medium, for example, a floppy disk, a hard disk, a tape; it may also be an optical medium, for example, a digital video disc; it may also be a semiconductor medium, for example, a solid-state hard disk. The computer-readable storage medium may be a volatile or nonvolatile storage medium, or may include both volatile and nonvolatile types of storage media.

[0331] In the various embodiments of the present application, unless otherwise specified or provided for in any logical conflict, the terms and / or descriptions between the different embodiments are consistent and may be referenced to each other, and the technical features in the different embodiments may be combined to form new embodiments according to their inherent logical relationships.

[0332] It is understood that the various numbers involved in the embodiments of the present application are only for the convenience of description and are not used to limit the scope of the embodiments of the present application. The size of the sequence number of the above-mentioned processes does not mean the order of execution, and the execution order of each process should be determined by its function and internal logic.

Claims

1. A communication method, characterized in that: Applied to a first access network device, the method includes: Obtaining random access information of the second cell; After determining that the terminal device switches to the first cell, a first indication is sent to the terminal device according to the random access information of the second cell, wherein the first indication is used to instruct the terminal device to retransmit or retransmit a random access preamble for the second cell, the first cell is managed by the first access network device, and the second cell is the same as or different from the first cell.

2. The method according to claim 1, characterized in that The random access information of the second cell includes one or more of the following: an identifier of the second cell, a retransmission indication, a new transmission indication, failure information of a random access preamble of the second cell, and success information of a random access preamble of the second cell.

3. The method according to claim 1 or 2, characterized in that When the first cell and the second cell are the same, sending a first indication to the terminal device according to the random access information of the second cell includes: According to the random access information of the first cell, the first indication is sent to the terminal device N times, and the first indication is used to instruct the terminal device to retransmit the random access preamble for the first cell, wherein N is greater than or equal to the number of failed random accesses of the terminal device before switching to the first cell, and N is a positive integer.

4. The method according to any one of claims 1 to 3, characterized in that The first cell is a time division multiplexing cell, the third cell is a frequency division multiplexing cell, and the third cell is the cell accessed by the terminal device before switching; The method further comprises: Determining an offset of an expected data arrival time according to a frame structure and a data arrival time of the first cell; The offset of the expected data arrival time is sent to the core network device.

5. A communication method, characterized in that: Applied to a terminal device, the method comprises: Sending a random access preamble of a second cell to a second access network device according to a first power, where the first power is determined according to a random access variable, and the second cell is managed by the second access network device; After switching to the first cell, a random access preamble of the second cell is sent to the second access network device according to a second power, where the second power is greater than or equal to the first power.

6. The method according to claim 5, characterized in that Before sending the random access preamble of the second cell to the second access network device according to the second power, the method further includes: receiving a first indication from a first access network device, where the first indication is used to indicate retransmission of a random access preamble of the second cell, and the first cell is managed by the first access network device; The second power is determined according to the first indication.

7. The method according to claim 6, characterized in that The determining the second power according to the first indication includes: The second power is determined according to the first indication, the random access variable, and a random access preamble power ramping step.

8. The method according to any one of claims 5 to 7, characterized in that Before switching to the first cell, the method further includes: A random access maintenance indication is received, where the random access maintenance indication is used to instruct the terminal device to maintain the random access variable after switching to the first cell.

9. The method according to any one of claims 5 to 8, characterized in that The random access variable includes one or more of the following: a random access preamble power ramp-up counter, a random access preamble transmission counter, and a variable indicating a random access preamble new transmission.

10. A communication method, characterized in that: Applied to a third access network device, the method includes: Sending a second indication to the terminal device, where the second indication is used to instruct the terminal device to initiate random access to the second cell; determining random access information of the second cell; Sending random access information of the second cell to the first access network device; Among them, the cells accessed by the terminal device before and after the switching are the third cell and the first cell respectively, the third cell is managed by the third access network device, the first cell is managed by the first access network device, and the second cell is the same as or different from the first cell.

11. The method according to claim 10, characterized in that Also includes: Sending a random access maintenance indication to the terminal device.

12. The method according to claim 11, characterized in that The random access maintenance indication is carried in a radio resource control reconfiguration message or a switching command sent to the terminal device.

13. The method according to any one of claims 10 to 12, characterized in that The random access information of the second cell includes one or more of the following: an identifier of the second cell, a retransmission indication, a new transmission indication, failure information of a random access preamble of the second cell, and success information of a random access preamble of the second cell.

14. The method according to any one of claims 10 to 13, characterized in that The determining the random access information of the second cell includes: In a case where the timing advance TA of the second cell is not received, random access information of the second cell is determined.

15. The method according to any one of claims 10 to 14, characterized in that The sending a second instruction to the terminal device includes: receiving a random access configuration of the second cell; The second indication is sent to the terminal device according to the random access configuration of the second cell.

16. A communication method, characterized in that: Applied to a first access network device, the method includes: receiving transmission configuration indication TCI state information of a first cell, where the first cell is managed by the first access network device; After determining that the terminal device switches to the first cell, perform one or more of the following: Transmitting data with the terminal device according to the data transmission information of the first TCI state in the TCI state information of the first cell; deactivating the second TCI state according to activation information of the second TCI state in the TCI state information of the first cell; Activate the third TCI state according to the deactivation information of the third TCI state in the TCI state information of the first cell.

17. The method according to claim 16, characterized in that Also includes: receiving TCI state information of a second cell, where the second cell is different from the first cell; deactivating the TCI state of the second cell according to the activation information in the TCI state information of the second cell; Or, activate the TCI state of the second cell according to the deactivation information in the TCI state information of the second cell.

18. The method according to claim 16 or 17, characterized in that The first cell is a time division multiplexing cell, the third cell is a frequency division multiplexing cell, and the third cell is the cell accessed by the terminal device before switching; The method further comprises: Determining an offset of an expected data arrival time according to a frame structure and a data arrival time of the first cell; The offset of the expected data arrival time is sent to the core network device.

19. A communication method, characterized in that: Applied to a terminal device, the method comprises: Receiving one or more of the following indications: a data transmission indication of a first transmission configuration indicating a TCI state, an activation indication of a second TCI state, and a deactivation indication of a third TCI state; After switching to the first cell, maintain the context of the TCI state of the first cell and perform one or more of the following: Transmission data with the first access network device; measuring a reference signal corresponding to the second TCI state to maintain timing synchronization; not measuring the reference signal corresponding to the third TCI state; The first TCI state, the second TCI state and the third TCI state are TCI states of the first cell.

20. The method of claim 19, wherein: Before switching to the first cell, the method further includes: Receive a TCI state maintenance indication, wherein the TCI state maintenance indication is used to instruct the terminal device to maintain the context of the TCI state of the first cell after switching to the first cell.

21. A communication method, characterized in that: Applied to a third access network device, the method includes: Determine transmission configuration indication TCI state information of the first cell; The TCI status information of the first cell is sent to the first access network device, wherein the TCI status information of the first cell includes one or more of the following: data transmission information of the first TCI state, activation information of the second TCI state, and deactivation information of the third TCI state. The first cell is managed by the first access network device.

22. The method according to claim 21, characterized in that Also includes: Send TCI status maintenance indication to the terminal device.

23. The method according to claim 21 or 22, characterized in that Also includes: Send one or more of the following indications to the terminal device: data transmission indication of the first TCI state, activation indication of the second TCI state, and deactivation indication of the third TCI state.

24. A communication device, characterized in that: Comprising means for performing the method as claimed in any one of claims 1 to 23.

25. A communication device, characterized in that: It includes a processor and an interface circuit, wherein the interface circuit is used to receive signals from other communication devices outside the communication device and transmit them to the processor or send signals from the processor to other communication devices outside the communication device, and the processor is used to implement the method as described in any one of claims 1 to 23 through a logic circuit or executing code instructions.

26. A computer-readable storage medium, characterized in that: The storage medium stores a computer program or an instruction, and when the computer program or the instruction is executed by the communication device, the method according to any one of claims 1 to 23 is implemented.

27. A computer program product, characterized in that The computer program product comprises a computer program or instructions, and when the computer program or instructions are executed by a communication device, the method according to any one of claims 1 to 23 is implemented.

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