Satellite base station handover method and apparatus, and computer-readable storage medium

Abstract

The present application relates to the field of satellite communications, and provides a satellite base station handover method and apparatus, and a computer-readable storage medium, which can support SDT of a terminal device in an RRC inactive state in an NTN, thereby effectively reducing the power consumption of the terminal device and improving the transmission efficiency. When a source satellite currently serving a first cell needs to be handed over to a target satellite, the source satellite sends first information (such as security information, context information, and cell configuration information) related to the first cell to the target satellite, and once the target satellite has received the first information, related configuration is performed in the target satellite. In this way, because the context information of a terminal device in an RRC inactive state has been saved and configured in the target satellite, in the process that the target satellite serves the first cell, the terminal device in the RRC inactive state can send uplink small data and the target satellite can quickly receive the uplink small data.

Description

Methods, apparatus and computer-readable storage media for satellite base station handover

[0001] This application claims priority to Chinese Patent Application No. 202411219046.2, filed with the State Intellectual Property Office of China on August 30, 2024, entitled "Method, Apparatus and Computer-Readable Storage Medium for Satellite Base Station Switching", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of satellite communications, and more specifically, to methods, apparatus, and computer-readable storage media for satellite base station handover in the field of satellite communications. Background Technology

[0003] In terrestrial network (TN) communication, terminal devices support small data transmission (SDT) in the radio resource control (RRC) inactive state. That is, when the terminal device is in the RRC inactive state, it does not need to enter the RRC connected state to send small data to TN communication network devices (such as gNB), thereby improving the transmission efficiency of small data and effectively reducing the power consumption of the terminal device.

[0004] In non-terrestrial network (NTN) communications such as satellite communications, long transmission distances lead to higher power consumption of terminal devices. Therefore, power consumption of terminal devices is a crucial indicator for NTN communications. Based on this, related technologies propose supporting SDT (Short-Terminal Distance) in the inactive state of RRC (Remote Control Code) for terminal devices in NTN communications to effectively reduce power consumption. Currently, there is no clear technical solution to achieve these requirements. Summary of the Invention

[0005] This application provides a method, apparatus, and computer-readable storage medium for satellite base station handover, which can support SDT of terminal equipment in RRC inactive state in NTN, effectively reducing the power consumption of terminal equipment and improving transmission efficiency.

[0006] Firstly, a method for satellite base station handover is provided, applied to a target satellite in a satellite system. The satellite system includes multiple low Earth orbit (LEO) satellites, each including a source satellite and a target satellite. The source satellite is the satellite currently serving a first cell, and the target satellite is the satellite to which the handover will take place, serving the first cell. The method includes: receiving first information transmitted by the source satellite, the first information including security information, context information, and cell configuration information of the first cell, the context information including context information of terminal devices in the first cell that are in an inactive state of Radio Resource Control (RRC); configuring the target satellite according to the first information; and receiving uplink small data transmitted by terminal devices in the first cell that are in an inactive state of RRC during the process of the target satellite serving the first cell.

[0007] The satellite base station handover method provided in this application embodiment, when the source satellite currently serving the first cell needs to be switched to the target satellite, sends first information related to the first cell to the target satellite. The first information includes security information, context information, and cell configuration information of the first cell. The context information includes the context information of terminal devices in the first cell that are in an RRC inactive state. After receiving the first information, the target satellite performs configuration on itself. Thus, when a terminal device in an RRC inactive state needs to send uplink small data while the target satellite is serving the first cell, the terminal device can send uplink small data in an RRC inactive state (without needing to enter an RRC connected state). Since the target satellite has already stored and configured the context information of the terminal device in the RRC inactive state, the target satellite does not need to request context information from the source satellite. The target satellite can directly and successfully receive uplink small data based on the already stored and configured context information, thereby minimizing the problems of increased power consumption, decreased transmission efficiency, and high signaling overhead caused by the target satellite requesting context information from the source satellite. In other words, the embodiments of this application enable terminal devices in the RRC inactive state to quickly transmit small uplink data without entering the connected state. This not only reduces signaling overhead but, more importantly, effectively improves data transmission efficiency and reduces the power consumption of the terminal devices. In NTN, the advantages of low power consumption and high transmission efficiency of SDT performed by terminal devices in the RRC inactive state are fully utilized, allowing NTN communication, such as satellite communication, to support SDT of terminal devices in the RRC inactive state. Furthermore, sending security information from the source satellite to the target satellite ensures that the target satellite and the terminal devices in the first cell have a consistent understanding of data and signaling encryption and decryption. This allows for encryption and decryption of data and signaling through security information, ensuring the security of data and signaling transmission and correct decryption as much as possible. It also avoids the problem of high signaling overhead caused by the target satellite needing to renegotiate security information with the terminal devices in the first cell, further reducing signaling interaction.

[0008] In some embodiments, the security information described above includes a control plane security key and a user plane security key.

[0009] The control plane security key is used to encrypt and decrypt higher-level signaling (such as RRC signaling), while the user plane security key is used to encrypt and decrypt user data.

[0010] The security keys for the control plane include the encryption keys for the control plane and the integrity protection keys for the control plane.

[0011] In one example (such as LTE), the user plane security key includes the user plane encryption key. In another example (such as NR), the user plane security key includes both the user plane encryption key and the user plane integrity protection key.

[0012] In some embodiments, in the step of receiving the first information sent by the source satellite, wherein the first information includes security information, the security information is received after being encrypted by the source satellite using a public key encryption algorithm.

[0013] The satellite base station handover method provided in this application uses a public key encryption algorithm to encrypt security information and then sends the encrypted security information. This can prevent the security information from being stolen or tampered with during transmission, and can ensure the security of the content carried in the security information as much as possible, thereby ensuring the security of data or signaling transmission as much as possible.

[0014] In some embodiments, prior to receiving the first information sent by the source satellite, the method further includes: receiving a satellite data synchronization request sent by the source satellite, the satellite data synchronization request being used to indicate that the source satellite is about to send data; and in response to the satellite data synchronization request, sending satellite data synchronization confirmation information to the source satellite, the satellite data synchronization confirmation information being used to indicate that the target satellite confirms receipt of the data to be sent by the source satellite.

[0015] The satellite base station handover method provided in this application embodiment allows the target satellite to ascertain, based on the satellite data synchronization request sent by the source satellite, that the source satellite is about to transmit data (such as the first information). Thus, the target satellite can determine, based on the actual situation, whether it can receive the data to be transmitted by the source satellite. If the target satellite can receive the data to be transmitted by the source satellite, it sends a satellite data synchronization confirmation message to the source satellite to inform it that it can receive the data. In this way, both the source and target satellites have the same understanding of the data transmission event, avoiding unnecessary problems. For example, if the target satellite is currently unable to receive the data to be transmitted due to actual circumstances (such as lack of resources or poor signal quality), but the source satellite has sent the first information, it will result in wasted signaling.

[0016] In some embodiments, after receiving the first information sent by the source satellite and before receiving uplink small data sent by a terminal device in the RRC inactive state within the first cell during the process of the target satellite serving the first cell, the method further includes: receiving satellite data synchronization completion information sent by the source satellite.

[0017] In this way, the target satellite does not need to continue waiting for (or listening to) the data sent by the source satellite, and can thus perform subsequent steps, saving the satellite's power consumption.

[0018] In some embodiments, during the process of the target satellite serving the first cell, in the step of receiving uplink small data sent by a terminal device in the RRC inactive state within the first cell, during the process of the target satellite serving the first cell, a third message of the random access procedure sent by the terminal device in the RRC inactive state is received, the third message including uplink small data.

[0019] The satellite base station handover method provided in this application embodiment allows a terminal device in the NTN in the RRC inactive state to send uplink small data to a satellite (such as a target satellite) through the third message (i.e., message 3) of the random access procedure. This not only effectively reduces the power consumption of the terminal device and improves transmission efficiency, but also, compared with other methods such as transmitting small data by pre-configuring radio resources, avoids the problem of unreasonable resource allocation since it does not require pre-configuration of resources. It can give full play to the advantages of flexible and reasonable use of resources in the random access procedure, and has minimal modification to existing standards, making it compatible with existing standards.

[0020] In some embodiments, the method further includes: in response to the third message, sending a fourth message (i.e. message 4) of the random access procedure to the terminal device, the fourth message including RRC release information carrying a suspension indication, the suspension indication being used to indicate that the terminal device is in an RRC inactive state.

[0021] In some embodiments, the third message may also include an RRC recovery request.

[0022] In some embodiments, multiple LEO satellites cover a cell using a staring Earth cell coverage method.

[0023] Secondly, a method for satellite base station handover is provided, applied to a source satellite in a satellite system. The satellite system includes multiple low Earth orbit (LEO) satellites, each including a source satellite and a target satellite. The source satellite is the satellite currently serving a first cell, and the target satellite is the satellite to which the user will switch from the source satellite to serve the first cell. The method includes: determining that the satellite serving the first cell needs to switch from the source satellite to the target satellite; sending first information to the target satellite, the first information including security information, context information, and cell configuration information of the first cell, the context information including context information of terminal devices in the first cell that are in the Radio Resource Control (RRC) inactive state; and stopping service to the first cell.

[0024] The satellite base station handover method provided in this application involves the source satellite, currently serving a first cell, needing to switch to a target satellite. The source satellite sends first information related to the first cell to the target satellite. This first information includes security information, context information, and cell configuration information of the first cell. The context information includes the context information of terminal devices in the first cell that are in an RRC inactive state. Upon receiving the first information, the target satellite can configure itself, possessing the same security information, first cell, and context information of the terminal devices in the RRC inactive state as the source satellite. Thus, while the target satellite is serving the first cell, when a terminal device in the RRC inactive state needs to send uplink small data, it can do so in the RRC inactive state (without needing to enter the RRC connected state). Since the target satellite has already stored and configured the context information of the terminal devices in the RRC inactive state, it does not need to request context information from the source satellite. The target satellite can directly and successfully receive uplink small data based on the already stored and configured context information, thereby minimizing the problems of increased power consumption, decreased transmission efficiency, and high signaling overhead caused by the target satellite requesting context information from the source satellite. In other words, the embodiments of this application enable terminal devices in the RRC inactive state to quickly transmit small uplink data without entering the connected state. This not only reduces signaling overhead but, more importantly, effectively improves data transmission efficiency and reduces the power consumption of the terminal devices. In NTN, the advantages of low power consumption and high transmission efficiency of SDT performed by terminal devices in the RRC inactive state are fully utilized, allowing NTN communication, such as satellite communication, to support SDT of terminal devices in the RRC inactive state. Furthermore, sending security information from the source satellite to the target satellite ensures that the target satellite and the terminal devices in the first cell have a consistent understanding of data and signaling encryption and decryption. This allows for encryption and decryption of data and signaling through security information, ensuring the security of data and signaling transmission and correct decryption as much as possible. It also avoids the problem of high signaling overhead caused by the target satellite needing to renegotiate security information with the terminal devices in the first cell, further reducing signaling interaction.

[0025] In some embodiments, security information includes a control plane security key and a user plane security key.

[0026] In some embodiments, in the step of sending first information to the target satellite, the first information including security information, the security information encrypted by the source satellite using a public-key encryption algorithm is sent to the target satellite.

[0027] In some embodiments, before stopping service in the first cell, the method further includes: receiving a first message of a random access procedure sent by a terminal device in the RRC inactive state in the first cell; and in response to the first message (i.e., message 1), sending a second message of a random access procedure (i.e., message 2) to the terminal device, wherein the second message does not include uplink resource scheduling information for indicating the third message (i.e., message 3).

[0028] The satellite base station handover method provided in this application embodiment includes a timer configured within the terminal device. The duration of this timer is determined based on the duration of the satellite handover process. During satellite handover for a cell (such as the first cell), if a terminal device in the cell that is in an RRC inactive state needs to transmit uplink small data, the terminal device sends the first message of the random access procedure (i.e., message 1) to initiate random access. The source satellite sends a second message (i.e., message 2) to the terminal device that does not include (or does not carry) scheduling information for uplink resources used to indicate the third message (i.e., message 3). It can be understood that the source satellite sending message 2, which does not include (or does not carry) scheduling information, to the terminal device means that the source satellite and the target satellite are highly likely to be in the process of satellite handover, and the source satellite does not want the terminal device to interact with it during the satellite handover process to affect data transmission. Thus, after receiving message 2, which does not include (or does not carry) scheduling information, the terminal device can determine that the source satellite currently does not want or support the transmission of small data, thereby allowing the terminal device to temporarily not continue to execute the random access procedure to transmit small data. This not only reduces signaling overhead, but also further saves power consumption of terminal equipment, and enables timely transmission of uplink small data through random access procedures after satellite handover is completed (timer timeout), thus improving the overall performance of satellite communication.

[0029] In some embodiments, the first message is a random access request, including a preamble, and the second message is a random access response.

[0030] After determining that the satellite serving the first cell needs to switch from the source satellite to the target satellite, and before sending the first information to the target satellite, in some embodiments, a satellite data synchronization request is sent to the target satellite, the satellite data synchronization request being used to indicate that the source satellite is about to send data; and a satellite data synchronization confirmation message sent by the target satellite in response to the satellite data synchronization request is received, the satellite data synchronization confirmation message being used to indicate that the target satellite confirms receipt of the data that the source satellite is about to send.

[0031] In some embodiments, after sending the first information to the target satellite as described above, the method further includes sending satellite data synchronization completion information to the target satellite.

[0032] In some embodiments, the steps described above for determining that the satellite serving the first cell needs to be switched from the source satellite to the target satellite are based on ephemeris information.

[0033] In some embodiments, multiple LEO satellites cover a cell using a staring Earth cell coverage method.

[0034] Thirdly, a method for satellite base station handover is provided, applied to a terminal device in a non-active state of Radio Resource Control (RRC). The terminal device is used to communicate with satellites in a satellite system, which includes multiple LEO satellites, including a source satellite and a target satellite. The source satellite is the satellite currently serving the first cell, and the target satellite is the satellite to which the terminal device will switch from the source satellite to serve the first cell. The terminal device is located in the first cell. The method includes: sending a first message (i.e., message 1) of the nth random access procedure, where n is an integer greater than or equal to 1; receiving a second message (i.e., message 2) sent by the source satellite in response to the first message of the nth random access procedure, wherein the second message of the nth random access procedure does not include uplink resource scheduling information used to indicate a third message (i.e., message 3); starting a timer after receiving the second message of the nth random access procedure; sending a first message of the (n+1)th random access procedure after the timer expires; and receiving a second message sent by the target satellite in response to the first message of the (n+1)th random access procedure.

[0035] The satellite base station handover method provided in this application embodiment includes a timer configured within the terminal device. The duration of this timer is determined based on the duration of the satellite handover process. During the satellite handover process for a cell (such as the first cell), if a terminal device in the cell that is in an RRC inactive state needs to transmit uplink small data, the terminal device sends message 1 of the random access procedure to initiate random access. The source satellite sends message 2 to the terminal device, which does not include (or does not carry) the uplink resource scheduling information used to indicate message 3. After receiving message 2, which does not include (or does not carry) the scheduling information, the terminal device starts the timer. During the duration of this timer, the terminal device no longer executes the random access procedure to transmit uplink small data. It is understandable that the source satellite sending message 2, which does not include (or carries) scheduling information, to the terminal device implies that the source satellite and target satellite are highly likely to be in a satellite handover process. The source satellite does not want the terminal device to interact with it during this process, thus affecting data transmission. Therefore, after receiving message 2, which does not include (or carries) scheduling information, the terminal device starts a timer and does not execute the random access procedure to transmit uplink small data within the timer's duration. This not only reduces signaling overhead but also further saves the terminal device's power consumption. After the timer expires, the terminal device attempts to execute the random access procedure again to transmit uplink small data. Therefore, in the above embodiment, by using message 2, which does not include (or carries) scheduling information, and setting the timer during satellite handover, not only is signaling overhead reduced, but the terminal device's power consumption is further saved. Furthermore, by attempting the random access procedure again to transmit uplink small data after the satellite handover is completed (timer expires), the overall performance of satellite communication is improved.

[0036] In some embodiments, the second message (i.e., message 2) of the (n+1)th random access procedure includes scheduling information for indicating uplink resources for the third message (i.e., message 3); and the method further includes: sending the third message (i.e., message 3) of the (n+1)th random access procedure according to the uplink resources indicated by the scheduling information in the second message (i.e., message 2) of the (n+1)th random access procedure, wherein the third message of the (n+1)th random access procedure includes uplink small data.

[0037] The satellite base station handover method provided in this application embodiment, after the timer expires, if there are no special circumstances, the satellite handover has been completed. At this time, the terminal device in the RRC inactive state can communicate with the target satellite. Therefore, after the terminal device tries to execute the random access procedure to send message 1 again, the target satellite sends back a normal message 2, that is, message 2 including the scheduling information of message 3. In this way, the terminal device can carry uplink small data in message 3 to realize the transmission of small data.

[0038] In some embodiments, the method further includes: receiving a fourth message (i.e., message 4) sent by the target satellite in response to a third message (i.e., message 3) in the (n+1)th random access procedure, the fourth message including RRC release information carrying a suspension indication, the suspension indication being used to indicate that the terminal device is in an RRC inactive state.

[0039] In some embodiments, the first message is a random access request, including a preamble, and the second message is a random access response.

[0040] Fourthly, the method is applied to a terminal device in a non-active state of Radio Resource Control (RRC). The terminal device is used to communicate with satellites in a satellite system, which includes multiple LEO satellites, including source satellites and target satellites. The source satellite is the satellite currently serving the first cell, and the target satellite is the satellite that will switch from the source satellite to serve the first cell. The terminal device is located in the first cell. The method includes: sending a first message of the nth random access procedure (i.e., message 1); after sending the first message of the nth random access procedure, starting a timer; if no second message (i.e., message 2) is received from the source satellite in response to the first message of the nth random access procedure within the duration of the timer, after the timer expires, sending the first message of the (n+1)th random access procedure; after sending the first message of the (n+1)th random access procedure, restarting the timer; and receiving the second message from the target satellite in response to the first message of the (n+1)th random access procedure within the duration of the restarted timer. The second message of the (n+1)th random access procedure includes uplink resource scheduling information for indicating a third message (i.e., message 3).

[0041] The satellite base station handover method provided in this application embodiment includes a timer configured within the terminal device. The duration of this timer is determined based on the duration of the satellite handover process. During satellite handover for a cell (such as the first cell), if a terminal device in the cell in an RRC inactive state needs to transmit uplink small data, the terminal device sends message 1 of the random access procedure to initiate the random access procedure, and starts the timer after sending message 1. If message 2 is not received within the duration of the timer, the terminal device will not continue to execute the random access procedure to transmit uplink small data within the duration of the timer. If the timer expires, the terminal device will then attempt to execute the random access procedure to transmit uplink small data. It's understandable that the source satellite's failure to send message 2 to the terminal device within the timer's duration indicates that the source and target satellites are likely undergoing a satellite handover. The source satellite doesn't want the terminal device to interact with it during this handover, potentially affecting data transmission. Therefore, if the terminal device doesn't receive message 2 within the timer's duration, it won't execute the random access procedure to transmit uplink small data within that timer's duration. This not only reduces signaling overhead but also further conserves the terminal device's power. After the timer expires, the terminal device re-attempts the random access procedure to send uplink small data, thus improving overall satellite communication performance.

[0042] In addition, since the terminal device starts the timer after sending message 1, it does not need to listen for and receive message 2, thus saving more power consumption and reducing signaling overhead.

[0043] In some embodiments, the method further includes: sending a third message (i.e., message 3) of the (n+1)th random access procedure based on the uplink resources indicated by the scheduling information in the second message (i.e. message 2) of the (n+1)th random access procedure, wherein the third message of the (n+1)th random access procedure includes uplink small data.

[0044] The satellite base station handover method provided in this application embodiment, after the timer expires, if there are no special circumstances, the satellite handover has been completed. At this time, the terminal device in the RRC inactive state can communicate with the target satellite. Therefore, the terminal device attempts to execute the random access procedure again to send message 1 and then restarts the timer. Within the duration of the restarted timer, it will receive message 2 sent by the target satellite. In this way, the terminal device can carry uplink small data in message 3 to realize the transmission of small data.

[0045] In some embodiments, the method further includes: receiving a fourth message sent by the target satellite in response to a third message in the (n+1)th random access procedure, the fourth message including RRC release information carrying a suspension indication, the suspension indication being used to indicate that the terminal device is in an RRC inactive state.

[0046] In some embodiments, the first message is a random access request, including a preamble, and the second message is a random access response.

[0047] Fifthly, a method for satellite base station handover is provided, applied to a communication system including a terminal device in a Radio Resource Control (RRC) inactive state and a satellite system. The satellite system includes multiple low Earth orbit (LEO) satellites, each including a source satellite and a target satellite. The source satellite is the satellite currently serving a first cell, and the target satellite is the satellite to which the terminal device will switch from the source satellite to serve the first cell. The terminal device in the RRC inactive state is located in the first cell. The method includes: the source satellite determining that the satellite serving the first cell needs to switch from the source satellite to the target satellite; the source satellite sending first information to the target satellite, the first information including security information, context information, and cell configuration information of the first cell, the context information including the context information of the terminal device in the RRC inactive state within the first cell; the target satellite configuring itself according to the first information; and during the process of the target satellite serving the first cell, the target satellite receiving uplink small data sent by the terminal device in the RRC inactive state.

[0048] In some embodiments, during the process of the target satellite serving the first cell, in the step of the target satellite receiving uplink small data sent by the terminal device in the RRC inactive state, the target satellite receives a third message of the random access procedure sent by the terminal device in the RRC inactive state, the third message including uplink small data.

[0049] In some embodiments, before the source satellite stops serving the first cell, the method further includes: a terminal device in an RRC inactive state sending a first message of the nth random access procedure, where n is an integer greater than or equal to 1; in response to the first message of the nth random access procedure, the source satellite sending a second message of the nth random access procedure to the terminal device, the second message of the nth random access procedure not including uplink resource scheduling information for indicating a third message; after receiving the second message of the nth random access procedure, the terminal device starts a timer; after the timer expires, the terminal device sends a first message of the (n+1)th random access procedure; during the process of the target satellite serving the first cell, in response to the (n+1)th random access... The process includes the following steps: First, the target satellite sends a second message for the (n+1)th random access procedure to the terminal device. This second message includes scheduling information for uplink resources used to indicate the third message. Second, the terminal device sends a third message for the (n+1)th random access procedure based on the uplink resources indicated by the scheduling information of the (n+1)th random access procedure. This third message includes uplink small data. Third, during the process of the target satellite serving the first cell, the target satellite receives the third message sent by the terminal device in the RRC inactive state.

[0050] In some embodiments, before the source satellite stops serving the first cell, the method further includes: a terminal device in an RRC inactive state sending a first message for the nth random access procedure, where n is an integer greater than or equal to 1; after sending the first message for the nth random access procedure, the terminal device starts a timer; if no second message in response to the first message for the nth random access procedure is received from the source satellite within the timer's duration, after the timer expires, the terminal device sends a first message for the (n+1)th random access procedure; after sending the first message for the (n+1)th random access procedure, the terminal device restarts the timer; during the process of the target satellite serving the first cell, in response to the first message for the (n+1)th random access procedure, the target satellite sends a (n+1)th random access procedure message to the terminal device. The second message of the access procedure, the second message of the (n+1)th random access procedure includes scheduling information for uplink resources indicating the third message; if the terminal device receives the second message of the (n+1)th random access procedure sent by the target satellite within the duration of the restarted timer, the terminal device sends the third message of the (n+1)th random access procedure according to the uplink resources indicated by the scheduling information in the second message of the (n+1)th random access procedure, the third message of the (n+1)th random access procedure includes uplink small data; and, during the process of the target satellite serving the first cell, the target satellite receives the third message sent by the terminal device in the RRC inactive state, including: during the process of the target satellite serving the first cell, the target satellite receives the third message of the (n+1)th random access procedure sent by the terminal device.

[0051] Sixthly, an apparatus for satellite base station handover is provided, the apparatus being used to perform the method provided in any one of the first to fourth aspects described above. Specifically, the apparatus may include modules for performing any one of the possible implementations of the first to fourth aspects described above.

[0052] A seventh aspect provides a satellite base station handover apparatus, including a processor. The processor is coupled to a memory and can be used to execute instructions in the memory to implement the method in any possible implementation of any of the first to fourth aspects described above. Optionally, the apparatus further includes a memory. Optionally, the apparatus further includes a communication interface, and the processor is coupled to the communication interface.

[0053] Eighthly, a communication system is provided for performing the method executed by the source satellite, target satellite, and terminal equipment in the fifth aspect above.

[0054] Ninth aspect, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a device, causes the device to implement the method in any one of the possible implementations of the first to fourth aspects described above.

[0055] In a tenth aspect, a computer program product comprising instructions is provided, which, when executed by a computer, cause a device to implement the method in any one of the possible implementations of the first to fourth aspects described above.

[0056] Eleventhly, a chip is provided, comprising: an input interface, an output interface, a processor, and a memory, wherein the input interface, the output interface, the processor, and the memory are connected via an internal connection path, and the processor is used to execute code in the memory, wherein when the code is executed, the processor is used to execute a method in any possible implementation of any one of the first to fourth aspects described above. Attached Figure Description

[0057] Figure 1 is a schematic structural diagram of a communication system of a terrestrial network provided in an embodiment of this application.

[0058] Figure 2 is a schematic flowchart of the SDT process based on 4-step RA provided in the embodiments of this application.

[0059] Figure 3 is a schematic flowchart of the UE context relocation small data transmission process provided in an embodiment of this application.

[0060] Figure 4 is a schematic diagram of the satellite system provided in an embodiment of this application.

[0061] Figure 5 is a schematic diagram of a cell coverage method using the Earth staring cell provided in an embodiment of this application.

[0062] Figure 6 is a schematic flowchart of a satellite base station handover method 600 provided in an embodiment of this application.

[0063] Figure 7 is a schematic flowchart of a satellite base station handover method 700 provided in an embodiment of this application.

[0064] Figure 8 is a schematic flowchart of a satellite base station handover method 800 provided in an embodiment of this application.

[0065] Figure 9 is a schematic flowchart of a satellite base station handover method 900 provided in an embodiment of this application.

[0066] Figure 10 is a schematic block diagram of a satellite base station handover device 1000 provided in an embodiment of this application.

[0067] Figure 11 is a schematic structural diagram of the satellite base station handover device 1100 provided in an embodiment of this application. Detailed Implementation

[0068] The technical solutions in this application will now be described with reference to the accompanying drawings.

[0069] Figure 1 is a schematic structural diagram of a communication system of a terrestrial network provided in an embodiment of this application.

[0070] The terrestrial network, or TN, can be an existing or future mobile communication network. For example, the TN can be a long-term evolution (LTE) network, an advanced long-term evolution (LTE-A) network, a new radio (NR) network, or other 5th-generation (5G) networks, NR / 5G evolution networks, LTE and 5G hybrid networks, or next-generation mobile communication networks (e.g., 6th-generation (6G) mobile communication networks). In this embodiment, the TN can support uplink and downlink communication, as well as device-to-device (D2D) communication, machine-to-machine (M2M) communication, machine-type communication (MTC), vehicle-to-vehicle (V2V) communication, and vehicle-to-everything (V2X) communication.

[0071] Referring to Figure 1, the terrestrial network communication system includes network equipment 110, at least one terminal device (terminal device 121 and terminal device 122 as shown in Figure 1), and a core network 130. The terminal devices can be mobile or fixed. The terminal devices can connect to network equipment 110 wirelessly. Network equipment 110 connects to the core network 130 wirelessly or via a wired connection. The core network equipment in the core network 130 and network equipment 110 can be independent physical devices, or they can be the same physical device integrating the logical functions of both the core network equipment and the network equipment. Each network device can provide communication coverage for a specific geographical area and can communicate with terminal devices located within that coverage area (cell).

[0072] It should be understood that Figure 1 exemplarily illustrates a communication system for a terrestrial network, but this should not be construed as limiting the scope of this application. Exemplarily, the communication system may include a greater number of network devices or terminal devices, and each network device may have an additional number of terminal devices within its coverage area; this application does not limit the scope of the embodiments therein.

[0073] The terminal device in this application embodiment is a device with wireless transceiver capabilities, which can be deployed on land, including indoors or outdoors, handheld, wearable, or vehicle-mounted; it can also be deployed on water (such as ships); and it can also be deployed in the air (e.g., on airplanes, balloons, and satellites). The terminal device can be a mobile phone, tablet computer, computer with wireless transceiver capabilities, virtual reality (VR) terminal device, augmented reality (AR) terminal device, wireless terminal in industrial control, vehicle-mounted terminal device, wireless terminal in self-driving, wireless terminal in remote medical care, wireless terminal in smart grid, wireless terminal in transportation safety, wireless terminal in smart city, wireless terminal in smart home, wearable terminal device, etc. The embodiments of this application do not limit the application scenarios. A terminal may also be referred to as a terminal device, user equipment (UE), access terminal device, vehicle-mounted terminal, industrial control terminal, UE unit, UE station, mobile station, mobile station, remote station, remote terminal device, mobile device, UE terminal device, terminal device, wireless communication device, UE agent, or UE device, etc. Terminal devices can be fixed or mobile.

[0074] The network device in this application embodiment can be a device for communicating with terminal devices, and can be any device with wireless transceiver capabilities. The network device includes, but is not limited to: evolved Node Bs (NodeBs, eNBs, or e-NodeBs) in Long Term Evolution (LTE), base stations (gNodeBs or gNBs) or transmission receiving points / transmission reception points (TRPs) in 5th generation (5G), new radio (NR), or future 6th generation (6G), and access nodes, wireless relay nodes, and wireless backhaul nodes in WiFi systems. Base stations can be: macro base stations, micro base stations, pico base stations, small cells, relay stations, or balloon stations, etc. The network device can also be a radio controller, CU, and / or DU in a cloud radio access network (CRAN) scenario. The network device can also be a server, wearable device, or vehicle-mounted device, etc. In embodiments where the network device is a base station, multiple network devices can be base stations of the same type or different types; the base station can communicate with the terminal device or communicate with the terminal device through a relay station; the terminal device can communicate with multiple base stations of different technologies, for example, the terminal device can communicate with a base station that supports LTE network or a base station that supports 5G network, and can also support dual connection with both LTE network base station and 5G network base station.

[0075] Currently, the protocol defines three RRC states for terminal devices: RRC connected (RRC_CONNECTED) state, RRC idle (RRC-IDLE) state, and RRC inactive (RRC-INACTIVE) state.

[0076] RRC idle state refers to the state of a terminal device when it is camped in a cell but has not yet performed random access. The terminal device typically enters the RRC idle state after powering on or after RRC release. In the RRC idle state, there is no RRC connection between the terminal device and network devices (e.g., the camped network device), the network device does not store the terminal device's context, and no connection has been established between the network device and the core network for that terminal device. If the terminal device needs to transition from the RRC idle state to the RRC connected state, it must initiate an RRC connection establishment process.

[0077] The RRC connected state refers to the state a terminal device is in after completing a random access procedure but before releasing the RRC. An RRC connection exists between the terminal device and network devices (e.g., access network devices). In the RRC connected state, the terminal device can transmit data with the network device, such as downlink and / or uplink data transmission. Alternatively, the terminal device can also transmit terminal-specific data and / or control channels with the network device to transmit specific information or unicast information. In the RRC connected state, both the network device and the core network retain the terminal device's context information. It should be understood that the context information of terminal devices stored by network devices and the core network are different. The context information of terminal devices stored by network devices is related to the access stratum (AS), which mainly includes the RRC (Radio Resource Control) and the radio access network application part (RAN AP) layer and the protocol layers below them. The context information of terminal devices stored by the core network is related to the non-access stratum (NAS), which is deployed above the AS layer and is mainly responsible for core network layer functions such as mobility management, session management, and security control.

[0078] RRC inactive state is a newly defined state in 5G or NR, a state between connected and idle states. Introducing RRC inactive state reduces air interface signaling, quickly restores wireless connectivity, and accelerates data transmission. Previously, the terminal device entered the RRC connected state and then released its RRC connection with the network device. However, the connection established between the network device and the core network for that terminal device was not released. In the RRC inactive state, the terminal device disconnects from the network device but retains its connection with the core network. Although the terminal device disconnects from the network device in the RRC inactive state, the network device retains the terminal device's context information to reduce air interface signaling, quickly restore wireless connectivity, and accelerate data transmission. The core network continues to retain the terminal device's context information.

[0079] In terrestrial network communication, terminal devices support SDT in the RRC-INACTIVE state. That is, when the terminal device is in the RRC-INACTIVE state, it can send small data to the terrestrial network device (such as gNB) without entering the RRC connected state. This can improve the transmission efficiency of small data and effectively reduce the power consumption of the terminal device.

[0080] The 3rd generation partnership project (3GPP) defined two methods for performing SDT in Releases 15, 16, and 17: SDT based on random access (RA) procedures (RA-SDT) and SDT based on pre-configured radio resources.

[0081] In SDT based on pre-configured radio resources, radio resources are allocated periodically based on estimates of the traffic demands of terminal devices. This uplink scheduling method is called configured grant (CG). Therefore, SDT based on pre-configured radio resources can also be abbreviated as CG-SDT. Using CG-SDT will not cause message conflicts with other terminal devices because radio resources are dedicated to each terminal device. When a terminal device leaves the connected state, the network device sends a resource allocation signal to the terminal device.

[0082] In RA SDT, there are two types of SDT: one based on two-step random access (2-step RA) and the other based on four-step random access (4-step RA). It's important to note that the standard RA procedure itself does not handle small data transmissions. Adjusting or optimizing the standard RA procedure to accommodate small data transmission needs is called RA SDT. The following sections will describe the procedures for 4-step RA-based SDT and 2-step RA-based SDT, respectively.

[0083] Figure 2 is a schematic flowchart of the SDT process based on 4-step RA provided in the embodiments of this application.

[0084] The terminal device is in an RRC inactive state and has small uplink data to be sent. Therefore, the terminal device initiates random access to the network device.

[0085] In step S210, the terminal device sends message 1 (Msg1) to the network device to initiate the random access procedure. Msg1 includes a preamble.

[0086] Message 1, also known as a random access request, includes a preamble, which can also be called a random access preamble. In a non-contention-based random access process, the preamble is configured by the network device. In a contention-based random access process, the preamble is selected by the terminal device from a pool of preambles broadcast by the network device through a system information block (SIB).

[0087] In practice, the terminal device can send a preamble on the random access channel (RACH) resource.

[0088] In step S220, in response to Msg2, the network device sends message 2 (Msg2) to the terminal device. Msg2 can be carried in the physical downlink control channel (PDCCH).

[0089] Msg2 can also be called a random access response (RAR). The RAR includes scheduling information for uplink resources indicating message 3 (Msg3) and timing advance (TA) instructions required for uplink synchronization. As an example, and not a limitation, the RAR may include more information. For example, it may include a backoff indicator (BI), which indicates the backoff time for retransmitting Msg1. As another example, it may include a random access preamble identification (RAPID), indicating the index of the received preamble in the network device's response. Yet another example is the cell-radio network temporary identifier (C-RNTI), which the initial accessing terminal device can use to decode the PDCCH of Msg4.

[0090] In step S230, in response to Msg2, the terminal device sends Msg3 to the network device. Msg3 includes an RRC resume request and uplink small data.

[0091] Specifically, the terminal device can send Msg 3 using the uplink resources indicated by the scheduling information in Msg2 from the network device. The network device receives Msg 3 and also receives the uplink small data.

[0092] In step S240, the network device sends Msg4 to the terminal device. Msg4 includes RRC release information, which carries a suspend indication; that is, Msg4 includes RRC release with suspend indication information. The RRC release information indicates the release of the connection between the terminal device and the network device. The suspend indication instructs the terminal device not to fully enter the RRC idle state after releasing the RRC connection, but rather to enter the RRC inactive state.

[0093] It should be understood that after receiving Msg3, although the RRC recovery request in Msg3 is intended to request the restoration of the connection, the network device, having received the uplink small data, can assume that the purpose of Msg3 is actually for the transmission of small data and does not need to restore the terminal device to the connected state, unless other special indications or special circumstances occur. Therefore, the network device sends an RRC release message carrying a suspend indication to the terminal device via Msg4. Thus, after receiving Msg4, the terminal device remains in the RRC inactive state.

[0094] It should also be understood that during the RA process without SDT, the Msg 3 sent by the terminal device includes an RRC resume request but does not include uplink small data. After the network device processes the RRC resume request, it sends Msg 4 to the terminal device, which includes RRC resume information. The RRC resume information includes configuration information for resuming the connection. The terminal device resumes the RRC connection with the network device based on the configuration information to perform data transmission.

[0095] In the 2-step RA-based SDT process, the terminal device sends message A (Msg A) to the network device. Msg A includes Msg 1 and Msg 3 mentioned above, as well as uplink small data, thus enabling fast transmission of small data. In response to Msg A, the network device sends message B (Msg B) to the terminal device. Message B includes Msg 4 mentioned above, as well as information from Msg 2 other than the scheduling information in Msg 3.

[0096] In terrestrial networks, when a terminal device is in an RRC inactive state, the network device saves the terminal device's context to quickly restore the connection or rapidly transmit data. To quickly initiate random access for transmitting small amounts of data, it's crucial to ensure that the network device currently initiating the random access is the same one that served the terminal device. The last network device serving the terminal device refers to the last network device that communicated with the terminal device while it was in an RRC connected state. As shown in Figure 2, the last network device serving the terminal device is the same device that initiated the random access, thus enabling rapid random access for transmitting uplink small data.

[0097] However, if the network device that initiates random access for the terminal device (denoted as the current network device) is not the last network device serving the terminal device, then the current network device that initiates random access for the terminal device needs to request the context information of the terminal device from the last network device. This process can be called UE context relocation, and SDT based on this process can be called UE context relocation small data transmission (SDT with UE context relocation).

[0098] The following section uses SDT based on 4-step RA as an example to introduce the process of small data transmission for UE context relocation.

[0099] Figure 3 is a schematic flowchart of the UE context relocation small data transmission process provided in an embodiment of this application.

[0100] The terminal device is in an RRC inactive state and has small uplink data to be sent. Therefore, the terminal device initiates random access to the current network device. In the following text, the current network device is the network device in which the terminal device initiates random access, the last network device is the last network device serving this terminal device, and the access and mobility management function (AMF) network element and the user plane function (UPF) network element are core network elements.

[0101] In step S301, the terminal device sends Msg1 during the random access procedure to the current network device to initiate the random access procedure. Msg1 includes a preamble.

[0102] In step S302, in response to Msg1, the current network device sends Msg2 to the terminal device.

[0103] In step S310, in response to Msg2, the terminal device sends Msg3 to the current network device, wherein Msg3 includes an RRC recovery request and uplink small data.

[0104] In step S320, the current network device sends a RETRIEVE UE CONTEXT REQUEST to the last network device to request the context information of the terminal device.

[0105] The current network device uses the inactive network temporary identifier (I-RNTI) to identify the last network device serving the terminal device, and sends a request to obtain UE context to the last network device via Xn-AP. The last network device retrieves the UE context based on this request. This request is for the SDT and may also provide SDT auxiliary information (such as single data packets or multiple data packets).

[0106] In step S330, the last network device sends a UE context request response to the current network device. This UE context request response includes the context information of the terminal device.

[0107] In step S340, the current network device determines to continue SDT in the RRC inactive state.

[0108] In step S351, the current network device sends the uplink small data received from the terminal device to the UPF network element of the core network.

[0109] Optionally, in step S352, in order to prevent the loss of downlink user data buffered in the last network device, the current network device sends an Xn-U address indication message to the last network device to provide a forwarding address.

[0110] In step S361, the current network device sends a path switching request to the last network device.

[0111] In step S362, the last network device sends a path switching request confirmation message to the current network device.

[0112] Thus, through steps S361 and S362, the new generation access protocol (NG-AP) path switching process is completed to establish a connection for NG UE signaling related to AMF.

[0113] Optionally, in step S354, after path switching, if the current network device has an Uplink (UL) Non-access stratum (NAS) protocol data unit (PDU), the current network device sends the UL NAS PDU to the AMF.

[0114] Then, subsequent small data (uplink small data and / or downlink small data) are transmitted between the terminal device and the core network through the current network equipment.

[0115] In step S370, the current network device determines to stop performing SDT in the RRC inactive state.

[0116] In step S380, the current network device sends Msg4 to the terminal device. Msg4 includes RRC release information and carries a suspend indication, which is used to instruct the terminal device not to fully enter the RRC idle state after releasing the RRC connection, but to enter the RRC inactive state.

[0117] In step S390, the current network device sends a UE context release message to the last network device to instruct the last network device to remove the context of the terminal device.

[0118] The process of SDT based on 2-step RA is similar to that of SDT based on 4-step RA. The terminal device sends message A, which includes Msg1, Msg3 and uplink small data. After receiving message A, the current network device executes step S320 and subsequent steps. Finally, the current network device sends message B to the terminal device. Message B includes the information in Msg2 except for the scheduling information and Msg4.

[0119] As can be seen from the UE context relocation process described above, if the current network device that the terminal device initiates random access is not the last network device serving the terminal device, the UE context relocation process performed by the current network device will not only generate a large amount of signaling interaction overhead, but more importantly, the increased processing time will cause the terminal device to wait for a long time and increase the power consumption of the terminal device.

[0120] With technological advancements, non-terrestrial networks (NTNs) have been introduced. NTNs can include satellite communication networks, high-altitude platform systems, or unmanned aircraft systems (UAS), offering advantages such as long range, high mobility, wide coverage, and high reliability. However, the long transmission distance of NTN communication, such as satellite communication, leads to higher power consumption in terminal devices. Therefore, power consumption of terminal devices is a crucial indicator for NTN communication. Based on this, related technologies propose supporting SDT (Short-Terminal Device Deactivation) in the RRC (Remote Control Response) inactive state of terminal devices within NTN communication to effectively reduce power consumption. However, applying SDT in the RRC inactive state to NTN communication presents several challenges.

[0121] In NTN communication, the network equipment (such as satellite base stations in satellite communication) moves very quickly, leading to frequent changes in the network equipment serving the terminal device, or in other words, frequent changes in the serving cell of the terminal device. Therefore, frequent changes in the serving cell (or the network equipment serving the terminal device) will be the mainstream scenario for NTN communication, especially evident in low Earth orbit (LEO) satellites. Consequently, in most cases, when a terminal device in an RRC-inactive state initiates random access, the network equipment serving that terminal device has likely already changed, triggering a UE context relocation process. This process not only affects data transmission efficiency but also increases the power consumption of the terminal device. This contradicts the original intention of SDT (Simplified Data Transmission) in the RRC-inactive state (to improve the transmission efficiency of small data and effectively reduce the power consumption of the terminal device). Instead of improving data transmission efficiency and reducing power consumption, it actually reduces data transmission efficiency and increases power consumption, and the advantages of SDT in the RRC-inactive state cannot be realized.

[0122] It should be noted that the aforementioned service cells are logical cells, formed by the area covered by network devices. For the same physical location, different network devices provide different service cells.

[0123] Based on this, this application provides a satellite base station handover method applied to a satellite system including multiple LEO satellites. When the source satellite currently serving the first cell needs to be switched to the target satellite, the source satellite sends first information related to the first cell to the target satellite. The first information includes security information, context information, and cell configuration information of the first cell. The context information includes the context information of terminal devices in the first cell that are in an RRC inactive state. After receiving the first information, the target satellite performs relevant configurations based on the first information. In this way, the first information related to the first cell is stored and configured in the target satellite serving the first cell. When a terminal device in an RRC inactive state sends uplink small data while the target satellite is serving the first cell, since the target satellite has already stored and configured the context information of the terminal device in the RRC inactive state, the target satellite does not need to request context information from the source satellite. The target satellite can directly and successfully receive uplink small data based on the already stored and configured context information, thereby avoiding the problems of increased power consumption, decreased transmission efficiency, and high signaling overhead of the terminal device caused by the target satellite requesting context information from the source satellite as much as possible. In other words, the above technical solution effectively improves the efficiency of data transmission and reduces the power consumption of terminal devices, giving full play to the advantages of low power consumption and high transmission efficiency of terminal devices performing SDT in the RRC inactive state, so that NTN communication, such as satellite communication, can well support SDT of terminal devices in the RRC inactive state.

[0124] Furthermore, sending security information from the source satellite to the target satellite ensures that the target satellite and the terminal equipment in the first cell have a consistent understanding of data and signaling encryption and decryption. This allows for the encryption and decryption of data and signaling through security information, thus ensuring the security of data and signaling transmission and the correct decryption of data and signaling as much as possible. It also avoids the problem of excessive signaling overhead caused by the target satellite having to renegotiate security information with the terminal equipment in the first cell, further reducing signaling interaction.

[0125] It should be noted that the satellite described in this application embodiment integrates at least some of the functions of network equipment such as base stations in TN communication (such as control plane functions and user plane functions). Therefore, the satellite in this application embodiment can also be called a satellite base station, and the two descriptions are interchangeable.

[0126] It should be understood that the NTN in the embodiments of this application can be a 4G-based NTN, an NR-based NTN, an Internet of Things (IoT)-based NTN, a narrowband Internet of Things (NB-IoT)-based NTN, or an NTN based on other current technologies or other technologies that may emerge in the future.

[0127] Figure 4 is a schematic diagram of a satellite system provided in an embodiment of this application. Referring to Figure 4, the satellite system includes multiple satellites, which are LEO satellites. As an example, four satellites are shown in the figure: satellite 410a, satellite 410b, satellite 410c, and satellite 410d. Each satellite covers a physical cell, and the cells covered by the satellites may overlap (not shown in the figure) or not. During the process of satellite coverage of a cell, the satellite serves each terminal device within the cell, and the terminal devices within the cell covered by each satellite can communicate with the satellite. For example, satellite 410a can communicate with terminal device 420a in its served cell, satellite 410b can communicate with terminal device 420b in its served cell, satellite 410c can communicate with terminal device 420c in its served cell, and satellite 410d can communicate with terminal device 420d in its served cell.

[0128] LEO satellites orbit the Earth at altitudes of 500-2000 km, resulting in low transmission latency and power consumption. Due to their low orbits, LEO satellites experience short signal propagation delays and low link losses, reducing the requirements for both the satellites and user terminals. Furthermore, because LEO satellites move quickly, the time from sunrise to sunset is short for a single user, leading to frequent satellite handovers.

[0129] In some embodiments, the present application can be applied to satellite systems that cover cells using an earth-fixed cell coverage method. That is, all satellites (LEO satellites) in the system use this earth-fixed cell coverage method. In this method, multiple cells are distributed at fixed locations, and the coverage area of ​​each cell does not change with the movement of the satellite. A satellite provides fixed coverage to one cell for a specific time period (typically a few minutes). After the service time of the currently served cell ends, the satellite switches to the next cell at a fixed location. In practical applications, in the earth-fixed cell coverage method, a single satellite can cover tens or hundreds of kilometers, resulting in a large coverage area. For example, there can be tens of thousands of LEO satellites covering the Earth.

[0130] Figure 5 is a schematic diagram of a coverage method using Earth staring cells provided in an embodiment of this application. Figure 5(a) shows a schematic diagram of the start and end of satellite coverage of a cell, while Figures 5(b) and (c) show schematic diagrams of the same cell being covered by different satellites at different time periods.

[0131] Referring to Figure 5(a), satellite 510a begins covering cell 520 at a fixed location at time T0, thus starting service to cell 520 at time T0. During its movement, satellite 510a can adjust the angle of its antenna to continuously cover and serve cell 520 for a certain period. When satellite 510a moves along its direction of motion to position 2 at time T1, satellite 510a ceases providing service to cell 520 and will begin covering and serving the next fixed-location cell (not shown in the figure). Here, time T0 is the start time of satellite 510a's service to cell 520, and time T1 is the end time of satellite 510a's service to cell 520.

[0132] Referring to Figure 5(b), satellite 510a begins covering and serving cell 520 at a fixed location at time T0, while satellite 520a serves other cells at fixed locations (not shown in the figure). Satellites 510a and 510b move along the direction of motion, adjusting their antenna angles during the movement to continuously cover and serve cells at fixed locations for a certain period. At time T1, satellite 510a stops providing service to cell 520 and begins covering and serving the next cell at a fixed location (not shown in the figure). At this time, satellite 510b has not yet covered cell 520. Satellites 510a and 510b continue moving along the direction of motion, and at time T2, satellite 510b begins covering and serving cell 520. In this scenario, time T0 is the start time of service for satellite 510a, time T1 is the end time of service for satellite 510a, and time T2 is the start time of service for satellite 510b. In this scenario, the coverage of the same cell is discontinuous between two adjacent satellites. During the movement, area 520 cannot be covered and served for a short period of time between time T1 and time T2.

[0133] Referring to Figure 5(c), satellite 510a begins covering and serving cell 520 at a fixed location at time T0, while satellite 520a serves other cells at fixed locations (not shown in the figure). At time T1, satellite 510a ceases to provide service to cell 520, and simultaneously, satellite 510b begins to serve cell 520. In this scenario, time T0 is the start time of service for satellite 510a, and time T1 is the end time of service for satellite 510a, which is also the start time of service for satellite 510b. In this scenario, the coverage of the same cell between two adjacent satellites is continuous.

[0134] In a satellite system, satellites (such as satellite 510a and satellite 510b) can transmit data and / or signaling via an inter-satellite link (ISL).

[0135] Figure 6 is a schematic flowchart of a satellite base station handover method 600 provided in an embodiment of this application.

[0136] Method 600 is applied to a satellite system comprising multiple LEO satellites, including a source satellite and a target satellite. The source satellite and the target satellite are adjacent to each other. The source satellite is the satellite currently serving a cell (denoted as the first cell) at a fixed location, and the target satellite is the next satellite to serve the first cell. Referring to Figure 5 above, the source satellite can be satellite 510a, the target satellite can be satellite 510b, and the first cell can be cell 520.

[0137] The first cell includes at least one terminal device (one or more terminal devices) in an RRC inactive state. Each terminal device in the RRC inactive state had previously entered an RRC connected state and then released its RRC connection with the satellite before entering the RRC inactive state.

[0138] For ease of description, this paper takes a terminal device (denoted as the first terminal device) in the RRC inactive state within the first cell as an example, and describes method 600 from the perspective of the interaction between the first terminal device, the source satellite, and the target satellite. It should be understood that the executing entity of the above method 600 can also be the processor or chip in the first terminal device, the processor or chip in the source satellite, or the processor or chip in the target satellite. This application embodiment does not make any limitation.

[0139] In step S610, the source satellite determines that the satellite serving the first cell needs to be switched from the source satellite to the target satellite.

[0140] In other words, the source satellite determines the first cell that the target satellite will serve, which is the first cell served by the source satellite.

[0141] The source satellite can not only determine that the satellite serving the first cell needs to be switched over, but also determine that the satellite after the switchover is the target satellite. In other words, the source satellite can not only determine that it will cease service to the first cell, but also determine that the next satellite to serve the first cell is the target satellite.

[0142] It should be understood that when the source satellite determines that the satellite serving the first cell needs to switch from the source satellite to the target satellite, the source satellite is still serving the first cell. However, the source satellite may have moved to the edge area of ​​the first cell and will stop serving the first cell.

[0143] In some embodiments, the source satellite may determine, based on ephemeris information, that the satellite serving the first cell needs to be switched from the source satellite to the target satellite.

[0144] Ephemeris information provides precise information on the position and velocity of each satellite in its orbit. It is a function of time and can be used to calculate the position and velocity of each satellite on its trajectory at a specific point in time. Therefore, the source satellite can use ephemeris information to determine which satellite serving the first cell needs to be switched over, and can identify the target satellite after the switchover.

[0145] In one example, the source satellite can determine the end time of its service to the first cell and its position on its orbit at the end time based on ephemeris information. This position is the location where the source satellite stops serving the first cell. Therefore, the source satellite can determine the satellite serving the first cell needs to be switched based on the end time and / or the position.

[0146] In one example, the source satellite can determine that the next satellite serving the first cell is the target satellite based on ephemeris information. In other examples, the source satellite can also determine that the next satellite serving the first cell is the target satellite based on a combination of ephemeris information and other information, such as ISL measurement information between satellites.

[0147] In step S620, the source satellite sends first information to the target satellite, which includes security information, context information, and cell configuration information of the first cell. Correspondingly, the target satellite receives the first information.

[0148] In this step, the source satellite transmits the first information via the ISL between the source satellite and the target satellite.

[0149] It should be understood that the first information is information related to the first cell, used for communication between the target satellite and the terminal equipment within the first cell.

[0150] In some embodiments, the security information includes a control plane (CP) security key and a user plane (UP) security key. The control plane security key is used to encrypt and decrypt higher-level signaling (such as RRC signaling), while the user plane security key is used to encrypt and decrypt user data.

[0151] The control plane security key includes the control plane encryption key and the control plane integrity protection key. The control plane encryption key protects the security of signaling, preventing unauthorized access to or theft of sensitive information. By encrypting signaling with the control plane encryption key, even if the signaling is intercepted during transmission or storage, a third party without the corresponding decryption key cannot read the original signaling content, thus ensuring the confidentiality of the signaling. The control plane integrity protection key is a key used to protect the integrity of signaling messages. During signaling transmission, signaling messages may be subject to attacks such as tampering or forgery, causing the signaling to be unable to be correctly parsed or executed at the receiving end. The control plane integrity protection key uses specific algorithms and mechanisms to perform integrity verification on signaling messages, ensuring that the signaling has not been tampered with or forged during transmission, thereby protecting the legitimate rights and interests of both communicating parties.

[0152] Regarding user plane security keys, in one example (such as LTE), the user plane security key includes the user plane encryption key. In another example (such as NR), the user plane security key includes the user plane encryption key and the user plane integrity protection key. The user plane encryption key is used to protect the security of user data and prevent unauthorized personnel from accessing or stealing sensitive information. The user plane integrity protection key is a key used to protect the integrity of user data. For a detailed description of the user plane encryption key and integrity protection key, please refer to the relevant descriptions of the control plane encryption key and integrity protection key above, which will not be repeated here.

[0153] In other embodiments, the security information includes not only the security keys for the control plane and the user plane, as described above, but also the selection of encryption algorithms for the control plane and the user plane, as well as integrity protection algorithms.

[0154] It should be understood that, to ensure transmission security, signaling and data transmitted over the air interface need to be encrypted, and both the sending and receiving ends must have the same understanding of encryption and decryption in order to conduct subsequent signaling and data exchanges. Therefore, sending security information from the source satellite to the target satellite ensures that the target satellite and the terminal equipment in the first cell have a consistent understanding of data and signaling encryption and decryption, enabling the correct decryption of data (such as uplink small data) and signaling sent by the terminal equipment in the first cell. Furthermore, it eliminates the need for the target satellite to renegotiate the content of the security information (such as the security key) with the terminal equipment in the first cell, further reducing signaling interactions.

[0155] Because security information is related to security, it is necessary to ensure the security of the content carried in the security information as much as possible.

[0156] Therefore, in some embodiments, the security information is information encrypted by the source satellite using a public-key encryption algorithm. Thus, the source satellite sends this encrypted security information to the target satellite. Correspondingly, after receiving the encrypted security information, the target satellite can decrypt it using a private-key encryption algorithm that matches the public-key encryption algorithm.

[0157] For example, the public key encryption algorithm can be an asymmetric encryption algorithm, such as the RSA algorithm, the Chinese national standard SM2 algorithm, or any other asymmetric encryption algorithm. For a detailed description of asymmetric encryption algorithms, please refer to the description of the relevant technologies, which will not be repeated here.

[0158] The context information includes the context information of each terminal device (including the first terminal device) in the first cell that is in the RRC inactive state. The context information of the terminal devices in the RRC inactive state represents the necessary information maintained between the network and the terminal devices to facilitate rapid restoration of connection or rapid data transmission. After the target satellite obtains the context information, it can quickly transmit data or restore connection with the terminal devices in the first cell that are in the RRC inactive state without requesting context information from the source satellite.

[0159] It should be understood that the context information of terminal devices in the RRC inactive state stored in the source satellite mainly stores the relevant information of terminal devices in the AS layer, while the relevant information of terminal devices in the NAS layer is stored in the core network.

[0160] For terminal devices in an inactive RRC state, the context information of the terminal device may include, but is not limited to, the following: the terminal device's identification information, network information, and other relevant information that can be used to restore the connection or to transmit data.

[0161] The terminal device's identification information is used to identify the terminal device. For example, the terminal device's identification information can indicate at least one of the following identifiers: 1. International Mobile Subscriber Identity (MSI), used to uniquely identify a user; 2. Globally Unique Temporary Identifier (GUTI), used to protect user privacy in the inactive state; 3. Temporary Mobile Subscriber Identity (SAE) Temporary Mobile Subscriber Identity (S-TMSI), used for quick identification of the terminal device; 4. Inactive Radio Network Temporary Identifier (I-RNTI), used to uniquely identify a terminal device in the inactive state. Network information includes registration area information and serving cell information. The registration area information includes tracking area (TA) or location area (LA) information, used to locate the terminal device. Serving cell information indicates the identifier of the last serving cell for quick reconnection. Related information may include, for example, capability information, location information, etc. Capability information indicates the terminal device's capabilities, such as supported frequency bands, modulation schemes, carrier aggregation capabilities, etc. Location information may include the last known geographic location or cell information, used for location and service recovery.

[0162] Cell configuration information is used to configure the first cell, including its various parameters and resources. For example, the cell configuration information includes the physical cell identifier (PCI) of the first cell. The PCI distinguishes the first cell from other cells; different cells correspond to different PCIs. For example, the cell configuration information may also include various parameters of the first cell, such as frequency parameters (e.g., carrier frequency), antenna parameters (e.g., antenna orientation, tilt angle, gain), channel configuration parameters, power control parameters, and neighbor cell parameters.

[0163] It should be understood that the information in the first information in the above example is merely illustrative. The source satellite may also send more information to better facilitate communication between the target satellite and the terminal devices in the first cell. For example, if the first cell also includes terminal devices in RRC connected state, the context information in the first information may also include the context information of the terminal devices in RRC connected state. In this way, the target base station stores the context information of the terminal devices in RRC connected state, and the target base station can directly communicate with the terminal devices in RRC connected state when serving the first cell. Of course, the context information may also not include the context information of the terminal devices in RRC connected state. When the target satellite serves the first cell, these terminal devices can re-initiate the random access procedure to enter the RRC connected state.

[0164] It should also be understood that the various pieces of information in the first information above can be sent from the source satellite to the target satellite all at once, or they can be sent to the target satellite in installments; no limitation is made here. For example, the source satellite may first send cell configuration information and context information, and then send security information.

[0165] In step S630, the target satellite is configured according to the first information.

[0166] Specifically, the target satellite is configured with security information, such as configuring security keys for the control plane and user plane, configuring the first cell according to cell configuration information, and configuring the context of each terminal device (including the first terminal device) in the first cell that is in the RRC inactive state according to context information.

[0167] It should be understood that configuring security information (such as control plane security keys and user plane security keys) in the target satellite can also be understood as activating the security information in the target satellite. The security information can only be used after configuration is completed on the target satellite. Configuring the first cell in the target satellite can be understood as establishing or activating the first cell in the target satellite. Only after configuration is completed can the target satellite communicate within the first cell. Configuring the context of terminal devices in the first cell that are in an RRC inactive state in the target satellite can also be understood as establishing or activating the terminal device context. Only after configuration is completed can the target satellite communicate with terminal devices in an RRC inactive state.

[0168] It should be understood that since the security information is encrypted by the source satellite using a public-key encryption algorithm, the target satellite decrypts the security information using a private-key encryption algorithm that matches the source satellite's public-key encryption algorithm, obtaining the decrypted security information. After decryption, the content of the security information is configured in the target satellite.

[0169] Once the target satellite is configured, it shares the same cell (first cell), the same security key, and the same terminal device context as the source satellite. Thus, after the target satellite moves to a location covering the first cell, it can communicate with the terminal devices within that cell based on this configuration.

[0170] In step S640, the target satellite begins serving the first cell.

[0171] During satellite movement, the target satellite adjusts its antenna orientation to begin covering the first cell, thus initiating service to the first cell. While serving the first cell, the target satellite covers the cell using a staring Earth coverage method, and communicates with terminal devices within the first cell based on the configuration in step S630.

[0172] In step S650, the source satellite stops serving the first cell.

[0173] During satellite movement, the source satellite adjusts its antenna orientation so that it no longer covers the first cell, thus ceasing service to that cell. After ceasing service to the first cell, the source satellite moves to the next cell and provides coverage and service to that cell using a staring Earth coverage method.

[0174] It should be noted that the order of steps S640 and S650 in this embodiment of the application is not limited and should be determined according to the actual situation of satellite movement. In one example, step S650 can be executed before step S640, that is, the source satellite first stops serving the first cell, and then the target satellite starts serving the first cell. This example corresponds to the scenario of discontinuous coverage of the same cell between two adjacent satellites illustrated in Figure 5(b) above. The end time of service of the source satellite (e.g., time T1) is earlier than the start time of service of the target satellite (e.g., time T2). During the movement, the first cell cannot be served during the period between the source satellite stopping service of the first cell and the target satellite starting service of the first cell. In another example, steps S650 and S640 can be executed simultaneously, that is, the target satellite starts service of the first cell at the same time as the source satellite stops service of the first cell. This example corresponds to the scenario of continuous coverage of the same cell between two adjacent satellites illustrated in Figure 5(c) above. The end time of service of the source satellite (e.g., time T1) is also the start time of service of the target satellite. In another example, step S650 can be performed after step S640, that is, the target satellite starts serving the first cell first, and then the source satellite stops serving the first cell. In this example, the coverage of the same cell between two adjacent satellites is continuous, and there is overlapping coverage of the same cell between two adjacent satellites. For example, the first cell is covered and served by both the source satellite and the target satellite during the time period between the start time of the target satellite and the end time of the source satellite.

[0175] Furthermore, the order of steps S650 and S630 is not limited and should be determined based on the actual situation of satellite movement. For example, step S650 can be executed after step S630, or step S650 can be executed before step S630 and after step S620, as long as the service to the first cell is stopped after the source satellite finishes sending the first message to the target satellite.

[0176] During the above process, the terminal device does not participate in the satellite handover process. In other words, for the terminal device in the first cell, the terminal device will not be aware of the satellite handover process, which to some extent reduces the signaling overhead generated by the interaction between the terminal device and the satellite.

[0177] Subsequently, the first terminal device, which is in the RRC inactive state, generates uplink small data to be sent.

[0178] In step S660, the first terminal device in the RRC inactive state sends uplink small data.

[0179] Correspondingly, the target satellite receives this uplink data.

[0180] Since the satellite serving the first cell has switched from the source satellite to the target satellite, the first terminal device in the RRC inactive state sending uplink small data is actually initiating a Small Data Transmission (SDT) process to the target satellite. For the target satellite, since it already stores and configures the context of the first terminal device in the RRC inactive state within the first cell, it does not need to request context information from the source satellite. The target satellite can directly and successfully receive the uplink small data sent by the first terminal device in the RRC inactive state based on the already stored context information. This allows for fast small data transmission between the first terminal device in the RRC inactive state and the satellite, effectively saving power consumption for the first terminal device. Thus, NTN fully leverages the advantages of low power consumption and high transmission efficiency of small data transmission (SDT) performed by terminal devices in the RRC inactive state, enabling NTN communication, such as satellite communication, to effectively support SDT by terminal devices in the RRC inactive state.

[0181] As mentioned earlier, the signaling and data transmitted between the terminal device and the satellite are encrypted. The uplink small data is user plane data, and the uplink small data sent by the source satellite is encrypted using the user plane security key. Therefore, after receiving the uplink small data, the target satellite needs to decrypt it using the user plane security key to obtain the decrypted uplink small data. The target satellite can then send the decrypted uplink small data to the core network for further processing.

[0182] In NTN, there are several ways for the first terminal device in the RRC inactive state to send uplink small data.

[0183] In some embodiments, a first terminal device in an RRC inactive state can transmit uplink small data based on pre-configured radio resources. These radio resources are periodically allocated based on estimates of the terminal devices' traffic demands and are dedicated to each terminal device. Furthermore, after a satellite handover for the first cell, the target satellite reconfigures radio resources for each terminal device in the first cell.

[0184] In other embodiments, the first terminal device in the RRC inactive state can send uplink small data based on the random access (RA) procedure.

[0185] In one example, a first terminal device in an RRC inactive state can send uplink small data based on a 4-step RA. Specifically, the first terminal device sends the first message of the random access procedure (referred to as message 1, Msg1), which includes a preamble; in response to message 1, the target satellite sends the second message of the random access procedure (referred to as message 2, Msg2), which can also be called a random access response (RAR). The random access response includes uplink resource scheduling information to indicate the third message (referred to as message 3) and timing advance (TA) instructions required for uplink synchronization; in response to message 2, the first terminal device sends message 3 of the random access procedure (Msg3), which includes uplink small data and an RRC recovery request. If the target satellite determines that it does not need to restore the first terminal device to a connected state, in response to message 3, the target satellite sends the fourth message of the random access procedure (referred to as message 4, Msg4) to the first terminal device. Message 4 includes RRC release information carrying a suspension indication, which indicates that the first terminal device is in an RRC inactive state. After receiving message 4, the first terminal device can determine that the uplink small data has been sent and that it remains in the RRC inactive state.

[0186] It should be understood that although the RRC recovery request in message 3 is used to request the restoration of the connection, after receiving message 3 which includes uplink small data, the target satellite can assume that message 3 is actually used for small data transmission and does not need to restore the first terminal device to the connected state, unless other special instructions or special circumstances occur. Therefore, the target satellite sends an RRC release message carrying a suspension indication to the first terminal device via message 4. Thus, after receiving message 4, the first terminal device remains in the RRC inactive state.

[0187] In another example, the first terminal device can send uplink small data based on 2-step RA.

[0188] Specifically, the first terminal device sends message A of the random access procedure. Message A includes message 1 and the aforementioned message 3 (Msg3). Message 3 includes uplink small data and also includes an RRC recovery request. In response to message A, the target satellite sends message B of the random access procedure to the first terminal device. Message B includes the aforementioned message 4 (Msg4). Message 4 includes RRC release information carrying a suspension indication, which indicates that the first terminal device is in an RRC inactive state.

[0189] In the above embodiments, the terminal device in the RRC inactive state in the NTN sends uplink small data to the satellite through the random access procedure. This not only effectively reduces the power consumption of the terminal device and improves the transmission efficiency, but also, compared with other methods such as transmitting small data through pre-configured radio resources, it avoids the problem of unreasonable resource allocation because it does not require pre-configuration of resources. It can give full play to the advantages of flexible and reasonable use of resources in the random access procedure, and has minimal modification to the existing standard, making it compatible with the existing standard.

[0190] It should be noted that the embodiments of this application are applicable to scenarios where the cell (physical cell, such as the first cell) where the terminal device in the RRC inactive state is located remains unchanged. It is understood that if the cell where the terminal device is located changes, the terminal device cannot remain in the RRC inactive state and needs to revert to the RRC connected state to perform the cell handover process. In reality, because satellites move very quickly, the handover time is approximately between 2 and 10 seconds (inclusive), while the range of a cell is between tens and hundreds of kilometers. The probability of a terminal device moving from one cell to another within the satellite's handover time is relatively small. Therefore, the embodiments of this application are applicable to most NTN scenarios.

[0191] The satellite base station handover method provided in this application embodiment, when the source satellite currently serving the first cell needs to be switched to the target satellite, sends first information related to the first cell to the target satellite. The first information includes security information, context information, and cell configuration information of the first cell. The context information includes the context information of terminal devices in the first cell that are in an RRC inactive state. After receiving the first information, the target satellite performs configuration on itself. Thus, when a terminal device in an RRC inactive state (such as the first terminal device) needs to send uplink small data while the target satellite is serving the first cell, the terminal device can send uplink small data in an RRC inactive state (without needing to enter an RRC connected state). Since the target satellite has already stored and configured the context information of the terminal device in the RRC inactive state, the target satellite does not need to request context information from the source satellite. The target satellite can directly and successfully receive uplink small data based on the already stored and configured context information, thereby minimizing the problems of increased power consumption, decreased transmission efficiency, and high signaling overhead caused by the target satellite requesting context information from the source satellite. In other words, the embodiments of this application enable terminal devices in the RRC inactive state to quickly transmit small uplink data without entering the connected state. This not only reduces signaling overhead but, more importantly, effectively improves data transmission efficiency and reduces the power consumption of the terminal devices. In NTN, the advantages of low power consumption and high transmission efficiency of SDT performed by terminal devices in the RRC inactive state are fully utilized, allowing NTN communication, such as satellite communication, to support SDT of terminal devices in the RRC inactive state. Furthermore, sending security information from the source satellite to the target satellite ensures that the target satellite and the terminal devices in the first cell have a consistent understanding of data and signaling encryption and decryption. This allows for encryption and decryption of data and signaling through security information, ensuring the security of data and signaling transmission and correct decryption as much as possible. It also avoids the problem of high signaling overhead caused by the target satellite needing to renegotiate security information with the terminal devices in the first cell, further reducing signaling interaction.

[0192] In some embodiments of this application, before the source satellite sends the first information (such as step S620), the source satellite and the target satellite can also interact via signaling to determine whether the target satellite can receive the data that the source satellite will subsequently send.

[0193] In one example, when a satellite serving the first cell needs to switch from a source satellite to a target satellite, the source satellite sends a satellite data synchronization request to the target satellite. This request indicates that the source satellite is about to transmit data. Upon receiving the synchronization request, the target satellite sends a satellite data synchronization confirmation message to the source satellite, indicating that it acknowledges receiving the data to be transmitted by the source satellite.

[0194] For example, the satellite data synchronization request may include the source satellite's identifier (such as ID), the target satellite's identifier, the size of the data to be sent, and other information.

[0195] For example, the satellite data synchronization confirmation information may include the source satellite's identifier, the target satellite's identifier, and an acknowledgment (ACK).

[0196] In the above embodiments, the target satellite can be aware of the data (such as the first information) that the source satellite is about to transmit based on the satellite data synchronization request sent by the source satellite. Thus, the target satellite can determine whether it can receive the data that the source satellite is about to transmit based on the actual situation. If the target satellite can receive the data that the source satellite is about to transmit, it sends a satellite data synchronization confirmation message to the source satellite to inform it that it can receive the data that the source satellite is about to transmit. In this way, the source satellite and the target satellite have the same awareness of the event that they are about to transmit data, which can avoid some unnecessary problems. For example, if the target satellite is currently unable to receive the data that is about to be transmitted due to actual conditions (such as lack of resources, poor signal quality, etc.), but the source satellite has sent the first information, it will lead to a waste of signaling.

[0197] In some embodiments, after the source satellite transmits the first information (as in step S620), the source satellite sends a satellite data synchronization completion message to the target satellite to indicate that the data transmission has been completed. Upon receiving this satellite data synchronization completion message, the target satellite can confirm that the source satellite has finished transmitting data. Thus, the target satellite does not need to continue waiting for (or listening to) the data transmitted by the source satellite, and can therefore perform subsequent steps, saving satellite power consumption.

[0198] The following, with reference to Figure 7 and specific examples, provides a detailed illustration of the satellite base station handover method according to an embodiment of this application.

[0199] Figure 7 is a schematic flowchart of the satellite base station handover method 700 provided in an embodiment of this application. The explanations of the first terminal device, source satellite, target satellite, and first cell are the same as in method 600 and will not be repeated. The difference from method 600 is that method 700, as an example, adds a process in which the terminal device releases resources and enters an RRC inactive state after establishing an RRC connection, and adds a process of exchanging signaling between the source satellite and the target satellite, with sending uplink small data through a random access procedure as a specific scenario.

[0200] In step S710, an RRC connection is established between the first terminal device and the source satellite.

[0201] During the process of the source satellite serving the first cell, the first terminal device initiates a random access procedure to enter the RRC connected state. Specifically, the first terminal device sends message 1 (Msg1), which includes a preamble to initiate the random access procedure. After receiving the preamble in message 1, the source satellite sends message 2 to the first terminal device. Message 2 can also be called the Random Access Response (RAR). The RAR contains the TA command required for uplink synchronization by the first terminal device, scheduling information for the uplink resources (UL grant) used to indicate message 3 (Msg3), and other information. The first terminal device uses the uplink resources provided in the scheduling information of the RAR to send an RRC connection setup request to request the establishment of an RRC connection. In response to message 3, the source satellite sends message 4 (Msg4), which includes an RRC connection setup complete message, confirming that the first terminal device has successfully accessed the network. If a contention-based random access method is used, message 4 will also include a contention resolution ID to resolve possible preamble conflicts.

[0202] In step S720, the first terminal device is in RRC connection state and performs network registration, uplink data and downlink data exchange with the source satellite.

[0203] In step S730, the source satellite sends RRC release information carrying a suspension indication to the first terminal device to instruct the first terminal device to enter the RRC inactive state.

[0204] The first terminal device releases its connection with the source satellite and enters a low-power standby RRC inactive state, but the source satellite retains the context information of the first terminal device.

[0205] It should be understood that, for the source satellite, the source satellite will save the context information of all terminal devices (such as at least one terminal device) in the first cell that are in the RRC inactive state.

[0206] It should be understood that steps S710 to S730 above only schematically describe the establishment of an RRC connection between the first terminal device and the source satellite. In reality, the first terminal device does not necessarily establish an RRC connection with the source satellite; it can establish an RRC connection with any satellite serving the first cell before the source satellite. Moreover, the first terminal device's transition from the RRC connected state to the RRC inactive state does not necessarily occur during the process of the source satellite serving the first cell; it can also occur during the process of any satellite serving the first cell before the source satellite. The RRC inactive state after the state change continues until both the source satellite and the target satellite serve the first cell.

[0207] In step S740, the source satellite determines that the satellite serving the first cell needs to be switched from the source satellite to the target satellite.

[0208] For a detailed description of this step, please refer to the description of step S610 above, which will not be repeated here.

[0209] In step S751, the source satellite sends a satellite data synchronization request to the target satellite to indicate that the source satellite is about to send data.

[0210] In step S752, in response to the satellite data synchronization request, the target satellite sends a satellite data synchronization confirmation message to the source satellite to instruct the target satellite to confirm receipt of the data to be sent by the source satellite.

[0211] In step S761, the source satellite sends first information to the target satellite. The first information includes security information, context information, and cell configuration information of the first cell.

[0212] For a detailed description of this step, please refer to the description of step S620 above, which will not be repeated here.

[0213] In step S762, the source satellite sends satellite data synchronization completion information to the target satellite to indicate that the data transmission has been completed.

[0214] In step S770, the target satellite is configured according to the first information.

[0215] Once the target satellite is configured, it shares the same cell (first cell) as the source satellite, the same security information (such as security keys), and the same terminal device context. Thus, after the target satellite moves to a location covering the first cell, it can communicate with the terminal devices within that cell based on the aforementioned configuration.

[0216] For a detailed description of this step, please refer to the description of step S630 above, which will not be repeated here.

[0217] In step S781, the target satellite begins serving the first cell.

[0218] In step S782, the source satellite stops serving the first cell.

[0219] For a detailed description of steps S781 and S782, please refer to the descriptions of steps S640 and S650 above, which will not be repeated here.

[0220] Furthermore, in the above process, steps S751, S752, and S762 are optional steps.

[0221] Subsequently, the first terminal device, which is in the RRC inactive state, generates uplink small data to be sent.

[0222] In step S781, the first terminal device sends message 1 (Msg1). Correspondingly, the target satellite receives message 1. Message 1 includes a preamble to initiate the random access procedure.

[0223] Since the satellite serving the first cell has been switched from the source satellite to the target satellite, message 1 sent by the first terminal device is actually message 1 sent to the target satellite, and the target satellite receives message 1.

[0224] In step S792, in response to message 1, the target satellite sends message 2 (Msg2). Correspondingly, the first terminal device receives message 2.

[0225] Message 2 is a Random Access Response (RAR), which includes scheduling information for uplink resources used to instruct Message 3. For example, the Random Access Response also includes information such as timing advance (TA) instructions required for uplink synchronization.

[0226] In step S793, in response to message 2, the first terminal device sends message 3 (Msg3). Correspondingly, the target satellite receives message 3.

[0227] Message 3 includes uplink small data and an RRC recovery request.

[0228] After receiving the uplink data in message 3, the target satellite decrypts the uplink data using the user plane security key, obtaining the decrypted uplink data. The target satellite can then send the decrypted uplink data to the core network for further processing.

[0229] In step S794, in response to message 3, the target satellite sends message 4 (Msg4). Correspondingly, the first terminal device receives message 4.

[0230] Message 4 includes RRC release information carrying a suspend instruction, which indicates that the first terminal device is in an RRC inactive state.

[0231] After receiving message 4, the first terminal device can determine that the uplink small data has been sent and remains in the RRC inactive state.

[0232] It should be understood that the sequence number of the steps in the above method 700 does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application. For example, step S782 can be executed before or after step S781, or steps S782 and S781 can be executed simultaneously. As another example, step S782 can be executed after step S770, or it can be executed before step S770 and after step S762, as long as the service to the first cell is stopped after the source satellite finishes transmitting the first information.

[0233] In methods 600 and 700 above, the illustrations are both embodiments of a scenario in which the terminal device initiates small data after the satellite handover is completed.

[0234] During satellite handover, if a terminal device in an inactive RRC state initiates uplink small data transmission, numerous problems arise when the source and target satellites are in the process of handover, which is very rapid (e.g., handover time is approximately 2-10 seconds, inclusive). For example, the source satellite may cease serving its previously served cell (e.g., cell 1) before receiving the uplink small data carried in message 3 from the terminal device, while the target satellite may not yet be serving that cell. This not only prevents the terminal device from successfully transmitting the uplink small data but also increases signaling overhead and wastes power. Furthermore, the communication quality between the terminal device and the satellite deteriorates during handover, leading to unstable transmission and impacting the efficiency of uplink small data transmission.

[0235] Based on this, the embodiments of this application propose two methods to solve the above problems, referred to as Method 1 and Method 2. Below, with reference to Figures 8 and 9, a detailed description of embodiments of the scenario where the terminal device initiates small data during satellite handover is provided based on Method 1 and Method 2.

[0236] Figure 8 is a schematic flowchart of a satellite base station handover method 800 provided in an embodiment of this application. In method 800, during the handover process between the source satellite and the target satellite, a first terminal device in the RRC inactive state has a need to send small data, and therefore initiates a random access procedure to send small data.

[0237] In method 800, the specific descriptions of steps S810 to S852 can be found in the descriptions of steps S740 to S782 in method 700, and will not be repeated here. Steps S821, S822, and S832 are optional.

[0238] In the embodiments of this application, the satellite handover process for the first cell is interpreted differently under different circumstances.

[0239] Case 1

[0240] When the source satellite determines that the satellite serving the first cell needs to switch to the target satellite, it indicates that the source satellite is about to terminate its service to the first cell and the target satellite is about to serve the first cell, which also means that the satellite handover is about to begin. Therefore, when the source satellite determines that the satellite serving the first cell needs to switch to the target satellite (i.e., step S810), the satellite handover process can be considered to have started, and this step (i.e., step S810) is considered the starting step of the satellite handover process. When the target satellite begins to serve the first cell (i.e., step S851), it means that the satellite handover is complete. Therefore, this step (i.e., step S851) can be considered the ending step of the satellite handover process. This process is illustrated by the dashed box in Figure 8.

[0241] Case 2

[0242] In this scenario, the satellite handover process begins only when the source satellite determines that the satellite serving the first cell needs to be switched to the target satellite, and signaling interaction occurs between the source and target satellites. Therefore, the starting step of the satellite handover process can be the step of the source satellite sending information to the target satellite (such as first information, satellite data synchronization request, etc.), and the ending step of the satellite handover process is the step of the target satellite starting to serve the first cell (i.e., step S851). Specifically, in embodiments where the source satellite needs to send a satellite data synchronization request to the target satellite (i.e., step S821), the starting step of the satellite handover process can be the step of the source satellite sending the satellite data synchronization request (i.e., step S821). In embodiments where the source satellite does not need to send a satellite data synchronization request to the target satellite (i.e., step S821), the starting step of the satellite handover process can be the step of the source satellite sending first information (i.e., step S831).

[0243] It is understandable that the satellite handover process in scenario 1 (referred to as satellite handover duration) is longer than that in scenario 2.

[0244] For ease of description, the satellite handover process described in Case 1 above (the process shown in the dashed box in Figure 8) will be used as an example for further description.

[0245] During the handover process between the source satellite and the target satellite, the first terminal device, which is in the RRC inactive state, needs to send small data and therefore initiates a random access procedure to send the small data. It should be understood that the steps of interaction between the source satellite and the first terminal device during the satellite handover process described below (such as steps S861 and S862) are steps performed before the source satellite stops serving the first cell.

[0246] Method 1

[0247] In step S861, the first terminal device, which is in the RRC inactive state, sends message 1 (Msg1). Message 1 includes a preamble to initiate the random access procedure. Correspondingly, the source satellite receives message 1.

[0248] Since the source satellite has not yet stopped serving the first cell and the target satellite has not yet started serving the first cell, message 1 sent by the first terminal device is actually message 1 sent to the source satellite, and the source satellite receives message 1.

[0249] In step S862, in response to message 1, the source satellite transmits message 2 (Msg2). Correspondingly, the first terminal device receives message 2.

[0250] Message 2 does not include (or does not carry) scheduling information for the uplink resources used to indicate message 3 (Msg3).

[0251] Message 2 is a Random Access Response (RAR). In the implementation, the field configured for scheduling information in the RAR is 0, which is an empty indicator. In other words, the scheduling of message 3 in the RAR is a random scheduling.

[0252] Thus, after receiving message 2, the first terminal device determines that the source satellite will not schedule message 3, which means that during the satellite handover process, the source satellite likely does not want the first terminal device to send data or information to it. Therefore, the first terminal device executes step S863.

[0253] In step S863, the first terminal device starts a timer.

[0254] The timer duration is based on the satellite handover duration. For example, the timer duration is greater than or equal to the satellite handover duration. In one example, the timer duration is greater than or equal to 2 seconds and less than or equal to 10 seconds. In other examples, the timer duration can be any other range; no restrictions are placed here, and the specific duration depends on the actual time spent during the satellite handover process in the actual scenario.

[0255] During the timer's duration, the first terminal device will no longer perform a random access procedure to transmit uplink small data; that is, during the timer's duration, the first terminal device will not attempt to transmit small data (SDT). This not only reduces signaling overhead but also further saves the terminal device's power consumption.

[0256] If the timer expires, the first terminal device can re-attempt the random access procedure to transmit small data. It's understood that the timer duration is based on the satellite handover duration. If the timer expires, barring unforeseen circumstances, it means the satellite handover is complete. At this point, the first terminal device, in its RRC inactive state, can communicate with the target satellite to transmit uplink small data. Thus, uplink small data transmission can proceed normally.

[0257] In step S871, if the timer times out, the first terminal device sends message 1. Correspondingly, the target satellite receives message 1.

[0258] Since the satellite serving the first cell has switched from the source satellite to the target satellite, the source satellite has stopped serving the first cell, and the target satellite is now serving the first cell, therefore, message 1 sent by the first terminal device is actually message 1 sent to the target satellite.

[0259] In step S872, since the satellite handover has been completed, the target satellite sends message 2 in response to message 1. Correspondingly, the first terminal device receives message 2.

[0260] Message 2 in this step includes scheduling information for the uplink resources used to instruct message 3.

[0261] In step S873, in response to message 2, the first terminal device sends message 3, which includes an RRC recovery request and uplink small data. Correspondingly, the target satellite receives message 3.

[0262] In this step, the first terminal device receives message 2, which includes scheduling information, and sends message 3 on the uplink resources indicated by the scheduling information. After receiving the uplink small data in message 3, the target satellite decrypts the uplink small data using the user plane security key to obtain the decrypted uplink small data. The target satellite can then send the decrypted uplink small data to the core network for further processing.

[0263] In step S874, in response to message 3, the target satellite transmits message 4. Correspondingly, the first terminal device receives message 4.

[0264] Message 4 includes RRC release information carrying a suspend indication. Thus, the first terminal device remains in the RRC inactive state.

[0265] For a detailed description of steps S871 to S874, please refer to the relevant descriptions of steps S791 to S794 in method 700, which will not be repeated here.

[0266] In a specific example, the random access procedure initiated by the first terminal device in step S861 can be defined as the nth random access procedure initiated by the first terminal device, and the random access procedure initiated by the first terminal device in step S871 can be defined as the (n+1)th random access procedure. The messages (such as message 1 and message 2) exchanged between the first terminal device and the satellite (e.g., the source satellite) during the nth random access procedure can be defined as messages in the nth random access procedure, and the messages (such as message 1, message 2, message 3, and message 4) exchanged between the first terminal device and the satellite (e.g., the target satellite) during the (n+1)th random access procedure can be defined as messages in the (n+1)th random access procedure. Here, n is an integer greater than or equal to 1.

[0267] When n is greater than 1, it means that the first terminal device has initiated a random access procedure before. It should be understood that the random access procedure initiated by the first terminal device before can be a random access procedure initiated by the first terminal device in any state.

[0268] In the above embodiments, the terminal device is equipped with a timer, the duration of which is determined based on the satellite handover process duration. During the satellite handover process for a cell (such as the first cell), if a terminal device in the cell that is in an RRC inactive state (such as the first terminal device) needs to transmit uplink small data, the terminal device sends message 1 of the random access procedure to initiate random access. The source satellite sends message 2 to the terminal device, which does not include (or does not carry) the uplink resource scheduling information used to indicate message 3. After receiving message 2, which does not include (or does not carry) the scheduling information, the terminal device starts the timer. During the duration of the timer, the terminal device no longer continues to execute the random access procedure to transmit uplink small data. It is understandable that the source satellite sending message 2, which does not include (or carries) scheduling information, to the terminal device implies that the source satellite and target satellite are highly likely to be in a satellite handover process. The source satellite does not want the terminal device to interact with it during this process, thus affecting data transmission. Therefore, after receiving message 2, the terminal device starts a timer and does not execute the random access procedure to transmit uplink small data within the timer's duration. This not only reduces signaling overhead but also further saves the terminal device's power consumption. After the timer expires, barring unforeseen circumstances, the satellite handover is complete. At this point, the terminal device, in the RRC inactive state, can communicate with the target satellite. Therefore, the terminal device attempts to execute the random access procedure again to send uplink small data. Thus, barring unforeseen circumstances, uplink small data can be successfully transmitted between the terminal device and the target satellite. Therefore, in the above embodiments, by using message 2 that does not include (or does not carry) scheduling information and setting a timer during satellite handover, not only can signaling overhead be reduced, but also the power consumption of terminal equipment can be further saved. Furthermore, after satellite handover is completed (timer expires), uplink small data can be transmitted in a timely manner through a random access procedure, thereby improving the overall performance of satellite communication.

[0269] Figure 9 is a schematic flowchart of the satellite base station handover method 900 provided in an embodiment of this application. The difference between method 900 and method 800 is that the terminal device in the RRC inactive state starts a timer directly after sending message 1, instead of waiting to receive message 2 before starting the timer. If message 2 from the source satellite is not received within the timer's duration, the random access procedure is not continued within the timer's duration. After the timer expires, the random access procedure is re-initiated to transmit small data. The following focuses on describing the differences between method 900 and method 800.

[0270] In method 900, the specific descriptions of steps S910 to S952 can be found in the descriptions of steps S740 to S782 in method 700, and will not be repeated here. Steps S921, S922, and S932 are optional.

[0271] During the handover process between the source satellite and the target satellite, the first terminal device, which is in the RRC inactive state, needs to send small data and therefore initiates a random access procedure to send the small data. It should be understood that the steps of interaction between the source satellite and the first terminal device during the satellite handover process described below (such as step S961) are steps performed before the source satellite stops serving the first cell.

[0272] Method 2

[0273] In step S961, the first terminal device sends message 1 (Msg1), which includes a preamble, to initiate the random access procedure. Correspondingly, the source satellite receives message 1.

[0274] Since the source satellite has not yet stopped serving the first cell and the target satellite has not yet started serving the first cell, message 1 sent by the first terminal device is actually message 1 sent to the source satellite, and the source satellite receives message 1.

[0275] In step S962, the first terminal device starts a timer.

[0276] If the first terminal device does not receive message 2 from the source satellite within the timer's duration (denoted as Case A), the first terminal device will no longer perform a random access procedure to transmit uplink small data within the timer's duration; in other words, the first terminal device will no longer attempt to transmit small data within the timer's duration. It should be understood that in Case A, it means that during satellite handover, the source satellite likely does not want the first terminal device to send data or information to it. This not only reduces signaling overhead but also further saves power consumption for the terminal device.

[0277] In conjunction with scenario A, further, if the first terminal device does not receive message 2 from the source satellite within the timer's duration, and after the timer expires, the first terminal device can re-attempt the random access procedure to transmit small data. It can be understood that after the timer expires, barring unforeseen circumstances, the satellite handover has been completed. At this point, the first terminal device, in its RRC inactive state, is able to communicate with the target satellite to transmit uplink small data. Thus, uplink small data can be transmitted normally.

[0278] In the case where the first terminal device receives message 2 from the source satellite within the timer's duration (denoted as Case B), message 2 includes scheduling information for uplink resources used to indicate message 3. Based on this scheduling information, the first terminal device sends message 3, which includes uplink small data, thus completing the transmission of the small data. It can be understood that in Case B, the source satellite's ability to send message 2 containing scheduling information within the timer's duration means that the source satellite has not performed a satellite handover process. Therefore, the first terminal device can normally execute the random access procedure to send uplink small data.

[0279] In method 900, after the first terminal device starts the timer, if the first terminal device does not receive message 2 sent by the source satellite within the timer duration, the first terminal device will not execute the random access procedure to transmit uplink small data within the timer duration. After the timer expires, the first terminal device executes step S971 to try to execute the random access procedure again.

[0280] In step S971, if the timer times out, the first terminal device sends message 1. Correspondingly, the target satellite receives message 2.

[0281] Since the satellite serving the first cell has switched from the source satellite to the target satellite, the source satellite has stopped serving the first cell, and the target satellite is now serving the first cell, therefore, message 1 sent by the first terminal device is actually message 1 sent to the target satellite.

[0282] In step S972, the first terminal device starts a timer.

[0283] In step S973, since the satellite handover has been completed, the target satellite sends message 2 in response to message 1. Correspondingly, the first terminal device receives message 2.

[0284] Message 2 includes scheduling information for uplink resources used to instruct Message 3.

[0285] For the first terminal device, if it receives message 2 containing scheduling information within the duration of the timer, it continues to execute the random access procedure.

[0286] In step S974, in response to message 2, the first terminal device sends message 3, which includes an RRC recovery request and uplink small data. Correspondingly, the target satellite receives message 3.

[0287] In this step, the first terminal device receives message 2, which includes scheduling information, and sends message 3 on the uplink resources indicated by the scheduling information. After receiving the uplink small data in message 3, the target satellite decrypts the uplink small data using the user plane security key to obtain the decrypted uplink small data. The target satellite can then send the decrypted uplink small data to the core network for further processing.

[0288] In step S975, in response to message 3, the target satellite transmits message 4. Correspondingly, the first terminal device receives message 4.

[0289] Message 4 includes RRC release information carrying a suspend instruction, thus the first terminal device remains in the RRC inactive state.

[0290] For a detailed description of steps S971, S973 to S975, please refer to the relevant descriptions of steps S791 to S794 in method 700, which will not be repeated here.

[0291] In a specific example, the random access procedure initiated by the first terminal device in step S961 can be defined as the nth random access procedure initiated by the first terminal device, and the random access procedure initiated by the first terminal device in step S971 can be defined as the (n+1)th random access procedure. Each message (e.g., message 1) exchanged between the first terminal device and the satellite (e.g., the source satellite) during the nth random access procedure can be defined as a message during the nth random access procedure, and each message (e.g., message 1, message 2, message 3, and message 4) exchanged between the first terminal device and the satellite (e.g., the target satellite) during the (n+1)th random access procedure can be defined as a message during the (n+1)th random access procedure.

[0292] In the above embodiments, the terminal device is equipped with a timer, the duration of which is determined based on the satellite handover process duration. During the satellite handover process for a cell (such as the first cell), if a terminal device in the RRC inactive state within that cell (such as the first terminal device) needs to transmit uplink small data, the terminal device sends message 1 of the random access procedure to initiate the random access procedure, and the terminal device starts the timer after sending message 1. If message 2 is not received within the timer's duration, the terminal device will not continue to execute the random access procedure to transmit uplink small data within the timer's duration. If the timer expires, the terminal device will attempt to execute the random access procedure again to transmit uplink small data. Thus, after the timer expires, unless there are special circumstances, the satellite handover has been completed. At this time, the terminal device in the RRC inactive state can communicate with the target satellite to transmit uplink small data. It is understandable that the source satellite did not send message 2 to the terminal device within the timer's duration. This means that the source satellite and the target satellite are likely in the process of satellite handover. The source satellite does not want the terminal device to interact with it during the satellite handover process, which would affect data transmission. Therefore, if the terminal device does not receive message 2 within the timer's duration, it will not execute the random access procedure to transmit uplink small data within the timer's duration. This not only reduces signaling overhead but also further saves the power consumption of the terminal device. Furthermore, it can promptly transmit uplink small data through the random access procedure after the satellite handover is completed (timer expires), thus improving the overall performance of satellite communication.

[0293] Furthermore, if message 2 is received within the timer's duration, it means that the source satellite has most likely not performed the satellite handover process. Therefore, the first terminal device can send message 3 carrying uplink small data based on the scheduling information of message 2 to send uplink small data normally.

[0294] In addition, compared to method 800, in method 900, since the terminal device starts the timer after sending message 1, it does not need to listen for and receive message 2. Therefore, it saves more power consumption of the terminal device and reduces signaling overhead.

[0295] It should be noted again that the sequence number of the steps in the above method embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0296] The method for satellite base station handover according to an embodiment of this application has been described in detail above with reference to Figures 1 to 9. The apparatus for satellite base station handover according to an embodiment of this application will be described in detail below with reference to Figures 10 and 11.

[0297] Figure 10 illustrates a satellite base station handover apparatus 1000 provided in an embodiment of this application. The apparatus 1000 may be the target satellite, source satellite, or first terminal device mentioned above, or it may be a chip in the target satellite, source satellite, or first terminal device. The apparatus 1000 includes a transceiver unit 1010 and a processing unit 1020.

[0298] In one possible implementation, the device 1000 is used to execute the various processes and steps corresponding to the target satellite in the above method.

[0299] The transceiver unit 1010 is used to: receive first information transmitted by the source satellite, the first information including security information, context information and cell configuration information of the first cell, the context information including the context information of the terminal device in the first cell that is in the Radio Resource Control (RRC) inactive state;

[0300] Processing unit 1020 is used to: configure the target satellite according to the first information;

[0301] The transceiver unit 1010 is also used to receive uplink small data sent by terminal devices in the first cell that are in the RRC inactive state during the process of the target satellite serving the first cell.

[0302] For a detailed description of the process and steps executed by the aforementioned device 1000, please refer to the relevant description of the process and steps executed by the target satellite above, which will not be repeated here.

[0303] In another possible implementation, the device 1000 is used to execute the various processes and steps corresponding to the source satellite in the above method.

[0304] Processing unit 1020 is used to: determine whether the satellite serving the first cell needs to be switched from the source satellite to the target satellite;

[0305] The transceiver unit 1010 is used to: send first information to the target satellite. The first information includes security information, context information and cell configuration information of the first cell. The context information includes the context information of the terminal devices in the first cell that are in the Radio Resource Control (RRC) inactive state.

[0306] Processing unit 1020 is used to: stop service in the first cell.

[0307] For a detailed description of the process and steps executed by the aforementioned device 1000, please refer to the relevant description of the process and steps executed by the source satellite above, which will not be repeated here.

[0308] In another possible implementation, the device 1000 is used to execute the various processes and steps corresponding to the first terminal device in the above method.

[0309] The transceiver unit 1010 is used to: send the first message of the nth random access procedure (i.e. message 1), where n is an integer greater than or equal to 1; and receive the second message (i.e. message 2) sent by the source satellite in response to the first message of the nth random access procedure, wherein the second message of the nth random access procedure does not include the scheduling information of the uplink resources used to indicate the third message (i.e. message 3).

[0310] Processing unit 1020 is configured to: start a timer after receiving the second message of the nth random access procedure;

[0311] The transceiver unit 1010 is also used to: send the first message of the (n+1)th random access procedure after the timer expires;

[0312] The transceiver unit 1010 is also used to: receive a second message from the target satellite in response to the first message sent during the (n+1)th random access procedure.

[0313] For a detailed description of the process and steps executed by the aforementioned device 1000, please refer to the relevant description of the process and steps executed by the first terminal device in method 800 above, which will not be repeated here.

[0314] In another possible implementation, the device 1000 is used to execute the various processes and steps corresponding to the first terminal device in the above method.

[0315] The transceiver unit 1010 is used to: send the first message (i.e. message 1) of the nth random access procedure;

[0316] Processing unit 1020 is used to: start a timer after sending the first message of the nth random access procedure;

[0317] The transceiver unit 1010 is also used to: if it does not receive a second message from the source satellite in response to the first message of the nth random access procedure within the duration of the timer, send the first message of the (n+1)th random access procedure after the timer expires;

[0318] The processing unit 1020 is also configured to: restart the timer after sending the first message of the (n+1)th random access procedure;

[0319] The transceiver unit 1010 is also configured to: receive, within the duration of a timer that is restarted, a second message sent by the target satellite in response to the first message of the (n+1)th random access procedure, wherein the second message of the (n+1)th random access procedure includes uplink resource scheduling information for indicating the third message (i.e., message 3).

[0320] For a detailed description of the process and steps executed by the aforementioned device 1000, please refer to the relevant description of the process and steps executed by the first terminal device in method 900 above, which will not be repeated here.

[0321] It should be understood that the device 1000 here is embodied in the form of a functional unit. The term "unit" here can refer to an application-specific integrated circuit (ASIC), electronic circuitry, a processor (e.g., a shared processor, a proprietary processor, or a group processor, etc.) and memory for executing one or more software or firmware programs, integrated logic circuitry, and / or other suitable components supporting the described functions. In an alternative example, those skilled in the art will understand that the device 1000 can specifically be the terminal device, source satellite, or target satellite in the above embodiments. The device 1000 can be used to execute the various processes and / or steps corresponding to the terminal device, source satellite, or target satellite in the above method embodiments; to avoid repetition, these will not be described again here.

[0322] The apparatus 1000 of each of the above schemes has the function of implementing the corresponding steps performed by the terminal device, source satellite, or target satellite in the above methods; the function can be implemented by hardware or by hardware executing corresponding software. The hardware or software includes one or more modules corresponding to the above functions; for example, the transmitting unit can be replaced by a transmitter, the receiving unit can be replaced by a receiver, and other units, such as the determining unit, can be replaced by a processor, which respectively executes the transmission and reception operations and related processing operations in each method embodiment.

[0323] Figure 11 shows a schematic structural diagram of a satellite base station handover device 1100 provided in an embodiment of this application. The device 1100 includes a processor 1110, a transceiver 1120, and a memory 1130. The processor 1110, transceiver 1120, and memory 1130 communicate with each other via an internal connection path. The memory 1130 stores instructions, and the processor 1110 executes the instructions stored in the memory 1130 to control the transceiver 1120 to transmit and / or receive signals.

[0324] In one possible implementation, the device 1100 is used to execute the various processes and steps corresponding to the target satellite in the above method.

[0325] The transceiver 1120 is used to: receive first information transmitted by the source satellite, the first information including security information, context information and cell configuration information of the first cell, the context information including the context information of terminal devices in the first cell that are in the Radio Resource Control (RRC) inactive state;

[0326] Processor 1110 is used to: configure the target satellite based on the first information;

[0327] Transceiver 1120 is also used to receive uplink small data sent by terminal equipment in the first cell that is in the RRC inactive state during the process of the target satellite serving the first cell.

[0328] For a detailed description of the process and steps performed by the aforementioned device 1100, please refer to the relevant description of the process and steps performed by the target satellite above, which will not be repeated here.

[0329] In another possible implementation, the device 1100 is used to execute the various processes and steps corresponding to the source satellite in the above method.

[0330] Processor 1110 is used to: determine whether the satellite serving the first cell needs to be switched from the source satellite to the target satellite;

[0331] The transceiver 1120 is used to: send first information to the target satellite, the first information including security information, context information and cell configuration information of the first cell, the context information including the context information of terminal devices in the first cell that are in the Radio Resource Control (RRC) inactive state;

[0332] Processor 1110 is also used for: stopping service in the first cell.

[0333] For a detailed description of the process and steps performed by the aforementioned device 1100, please refer to the relevant description of the process and steps performed by the source satellite above, which will not be repeated here.

[0334] In another possible implementation, the device 1100 is used to execute the various processes and steps corresponding to the first terminal device in the above method.

[0335] Transceiver 1120 is used to: send the first message of the nth random access procedure (i.e. message 1), where n is an integer greater than or equal to 1; receive the second message (i.e. message 2) sent by the source satellite in response to the first message of the nth random access procedure, wherein the second message of the nth random access procedure does not include scheduling information for indicating the uplink resources of the third message (i.e. message 3);

[0336] Processor 1110 is configured to: start a timer after receiving the second message of the nth random access procedure;

[0337] Transceiver 1120 is also used to: send the first message of the (n+1)th random access procedure after the timer expires;

[0338] Transceiver 1120 is also used to: receive a second message from the target satellite in response to the first message sent during the (n+1)th random access procedure.

[0339] For a detailed description of the process and steps executed by the aforementioned device 1100, please refer to the relevant description of the process and steps executed by the first terminal device in method 800 above, which will not be repeated here.

[0340] In another possible implementation, the device 1100 is used to execute the various processes and steps corresponding to the first terminal device in the above method.

[0341] Transceiver 1120 is used to: send the first message (i.e. message 1) of the nth random access procedure;

[0342] Processor 1110 is configured to: start a timer after sending the first message of the nth random access procedure;

[0343] Transceiver 1120 is also used to: if no second message in response to the first message of the nth random access procedure is received from the source satellite within the duration of the timer, after the timer expires, send the first message of the (n+1)th random access procedure;

[0344] Processor 1110 is also used to: restart the timer after sending the first message of the (n+1)th random access procedure;

[0345] Transceiver 1120 is also configured to: receive, within the duration of a reactivated timer, a second message sent by the target satellite in response to the first message of the (n+1)th random access procedure, the second message of the (n+1)th random access procedure including uplink resource scheduling information for indicating a third message (i.e., message 3).

[0346] For a detailed description of the process and steps executed by the aforementioned device 1100, please refer to the relevant description of the process and steps executed by the first terminal device in the above method 900, which will not be repeated here.

[0347] It should be understood that the apparatus 1100 may specifically be the terminal device, source satellite, or target satellite in the above embodiments, and may be used to execute the various steps and / or processes corresponding to the terminal device, source satellite, or target satellite in the above method embodiments. Optionally, the memory 1130 may include read-only memory and random access memory, and provide instructions and data to the processor. A portion of the memory may also include non-volatile random access memory. For example, the memory may also store device type information. The processor 1110 may be used to execute instructions stored in the memory, and when the processor 1110 executes instructions stored in the memory, the processor 1110 is used to execute the various steps and / or processes of the above method embodiments corresponding to the satellite, source satellite, or target satellite.

[0348] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0349] In the embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the embodiments of the terminal devices described above are merely illustrative. For instance, the division of modules is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection through some interfaces, devices, or units, and may be electrical, mechanical, or other forms.

[0350] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0351] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0352] It should be understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0353] Furthermore, the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0354] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0355] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of protection of the claims. In conclusion, the above description is merely a preferred embodiment of the technical solution of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

A method for satellite base station handover, characterized in that, The method is applied to a target satellite in a satellite system, the satellite system comprising multiple low Earth orbit (LEO) satellites, the multiple LEO satellites including a source satellite and the target satellite, the source satellite being the satellite currently serving a first cell, and the target satellite being the satellite to which the target satellite will be switched from the source satellite to serve the first cell. The method includes: The system receives first information transmitted by the source satellite. The first information includes security information, context information, and cell configuration information of the first cell. The context information includes the context information of terminal devices in the first cell that are in the Radio Resource Control (RRC) inactive state. Based on the first information, configure the target satellite accordingly; During the process of the target satellite serving the first cell, uplink small data sent by the terminal device in the first cell that is in the RRC inactive state is received. The method according to claim 1, characterized in that, The security information includes security keys for the control plane and security keys for the user plane. The method according to claim 2, characterized in that, The first information received from the source satellite includes security information, including: Receive the security information from the source satellite after it has been encrypted using a public-key cryptography algorithm. The method according to any one of claims 1 to 3 is characterized in that, Before receiving the first information transmitted by the source satellite, the method further includes: Receive a satellite data synchronization request sent by the source satellite, the satellite data synchronization request being used to indicate that the source satellite is about to send data; In response to the satellite data synchronization request, a satellite data synchronization confirmation message is sent to the source satellite. The satellite data synchronization confirmation message is used to instruct the target satellite to confirm receipt of the data to be sent by the source satellite. The method according to any one of claims 1 to 4, characterized in that, After receiving the first information transmitted by the source satellite, and before receiving uplink small data transmitted by the terminal device in the first cell that is in an RRC inactive state during the process of the target satellite serving the first cell, the method further includes: Receive satellite data synchronization completion information sent by the source satellite. The method according to any one of claims 1 to 5, characterized in that, During the process of the target satellite serving the first cell, receiving uplink small data sent by the terminal device in the first cell that is in an RRC inactive state includes: During the process of the target satellite serving the first cell, a third message of the random access procedure sent by the terminal device in the RRC inactive state is received, the third message including the uplink small data. The method according to claim 6, characterized in that, The method further includes: In response to the third message, a fourth message of the random access procedure is sent to the terminal device. The fourth message includes RRC release information carrying a suspension indication, which is used to indicate that the terminal device is in an RRC inactive state. The method according to claim 6 or 7, characterized in that, The third message also includes an RRC recovery request. The method according to any one of claims 1 to 8, characterized in that, The multiple LEO satellites cover the cell using a staring Earth cell coverage method. A method for satellite base station handover, characterized in that, The method is applied to a source satellite in a satellite system, the satellite system comprising multiple low Earth orbit (LEO) satellites, the multiple LEO satellites including the source satellite and a target satellite, the source satellite being the satellite currently serving a first cell, and the target satellite being the satellite to which the source satellite will serve the first cell after switching over. The method includes: It is determined that the satellite serving the first cell needs to be switched from the source satellite to the target satellite; Send first information to the target satellite. The first information includes security information, context information, and cell configuration information of the first cell. The context information includes the context information of terminal devices in the first cell that are in the Radio Resource Control (RRC) inactive state. Service to the first cell has been suspended. The method according to claim 10, characterized in that, The security information includes security keys for the control plane and security keys for the user plane. The method according to claim 11, characterized in that, The first information, including security information, is sent to the target satellite, including: The secure information, encrypted by the source satellite using a public-key encryption algorithm, is sent to the target satellite. The method according to any one of claims 10 to 12, characterized in that, Before stopping service to the first cell, the method further includes: Receive the first message of the random access procedure sent by the terminal device in the first cell that is in the RRC inactive state; In response to the first message, a second message of the random access procedure is sent to the terminal device, the second message not including uplink resource scheduling information for indicating the third message. The method according to claim 13, characterized in that, The first message is a random access request, including a preamble, and the second message is a random access response. The method according to any one of claims 10 to 14, characterized in that, After determining that the satellite serving the first cell needs to switch from the source satellite to the target satellite, and before sending the first information to the target satellite, the method further includes: Send a satellite data synchronization request to the target satellite, the satellite data synchronization request being used to indicate that the source satellite is about to send data; The target satellite receives a satellite data synchronization confirmation message sent in response to the satellite data synchronization request. The satellite data synchronization confirmation message is used to instruct the target satellite to confirm receipt of the data to be sent by the source satellite. The method according to any one of claims 10 to 15, characterized in that, After sending the first information to the target satellite, the method further includes: Send satellite data synchronization completion information to the target satellite. The method according to any one of claims 10 to 16, characterized in that, The step of determining that the satellite serving the first cell needs to be switched from the source satellite to the target satellite includes: Based on ephemeris information, it is determined that the satellite serving the first cell needs to be switched from the source satellite to the target satellite. The method according to any one of claims 10 to 17, characterized in that, The multiple LEO satellites cover the cell using a staring Earth cell coverage method. A method for satellite base station handover, characterized in that, The method is applied to a terminal device in a Radio Resource Control (RRC) inactive state, the terminal device being used to communicate with satellites in a satellite system, the satellite system including multiple LEO satellites, the multiple LEO satellites including source satellites and target satellites, the source satellite being the satellite currently serving a first cell, the target satellite being the satellite to which the terminal device will switch from the source satellite to serve the first cell, the terminal device being located in the first cell, the method comprising: Send the first message of the nth random access procedure, where n is an integer greater than or equal to 1; The source satellite sends a second message in response to the first message of the nth random access procedure, wherein the second message of the nth random access procedure does not include uplink resource scheduling information for indicating the third message; After receiving the second message of the nth random access procedure, start the timer; After the timer expires, the first message of the (n+1)th random access procedure is sent; Receive the second message sent by the target satellite in response to the first message of the (n+1)th random access procedure. The method according to claim 19, characterized in that, The second message of the (n+1)th random access procedure includes uplink resource scheduling information used to indicate the third message; Furthermore, the method further includes: Based on the uplink resources indicated by the scheduling information in the second message of the (n+1)th random access procedure, the third message of the (n+1)th random access procedure is sent, and the third message of the (n+1)th random access procedure includes uplink small data. The method according to claim 20, characterized in that, The method further includes: The target satellite receives a fourth message in response to the third message sent during the (n+1)th random access procedure. The fourth message includes RRC release information carrying a suspension indication, which indicates that the terminal device is in an RRC inactive state. The method according to any one of claims 19 to 21 is characterized in that, The first message is a random access request, including a preamble, and the second message is a random access response. A method for satellite base station handover, characterized in that, An application is made to a terminal device in a Radio Resource Control (RRC) inactive state, the terminal device being used to communicate with satellites in a satellite system, the satellite system including multiple LEO satellites, the multiple LEO satellites including source satellites and target satellites, the source satellite being the satellite currently serving a first cell, the target satellite being the satellite to which the terminal device will switch from the source satellite to serve the first cell, the terminal device being located in the first cell, the method comprising: Send the first message of the nth random access procedure, where n is an integer greater than or equal to 1; After sending the first message of the nth random access procedure, start the timer; If no second message is received from the source satellite in response to the first message of the nth random access procedure within the duration of the timer, the first message of the (n+1)th random access procedure is sent after the timer expires. After sending the first message of the (n+1)th random access procedure, the timer is restarted. Within the duration of the timer that is restarted, the target satellite sends a second message in response to the first message of the (n+1)th random access procedure, the second message of the (n+1)th random access procedure including uplink resource scheduling information for indicative of the third message. The method according to claim 23, characterized in that, The method further includes: Based on the uplink resources indicated by the scheduling information in the second message of the (n+1)th random access procedure, the third message of the (n+1)th random access procedure is sent, and the third message of the (n+1)th random access procedure includes uplink small data. The method according to claim 24, characterized in that, The method further includes: receiving a fourth message sent by the target satellite in response to the third message of the (n+1)th random access procedure, the fourth message including RRC release information carrying a suspension indication, the suspension indication being used to indicate that the terminal device is in an RRC inactive state. The method according to any one of claims 23 to 25, characterized in that, The first message is a random access request, including a preamble, and the second message is a random access response. A method for satellite base station handover, characterized in that, A method applicable to a communication system including a terminal device in a Radio Resource Control (RRC) inactive state and a satellite system, wherein the satellite system includes multiple low Earth orbit (LEO) satellites, the multiple LEO satellites including source satellites and target satellites, the source satellites being the satellites currently serving a first cell, and the target satellites being the satellites to be switched from the source satellites to serve the first cell, the terminal device in the RRC inactive state being located in the first cell, the method comprising: The source satellite determines that the satellite serving the first cell needs to be switched from the source satellite to the target satellite; The source satellite sends first information to the target satellite. The first information includes security information, context information, and cell configuration information of the first cell. The context information includes the context information of the terminal device in the first cell that is in an RRC inactive state. The target satellite is configured according to the first information; During the process of the target satellite serving the first cell, the target satellite receives uplink small data sent by the terminal device in the RRC inactive state. The method according to claim 27, characterized in that, During the process of the target satellite serving the first cell, the target satellite receives uplink small data sent by the terminal device in the RRC inactive state, including: During the process of the target satellite serving the first cell, the target satellite receives a third message of the random access procedure sent by the terminal device in the RRC inactive state, the third message including the uplink small data. The method according to claim 28, characterized in that, Before the source satellite ceases service to the first cell, the method further includes: The terminal device in the RRC inactive state sends the first message of the nth random access procedure, where n is an integer greater than or equal to 1; In response to the first message of the nth random access procedure, the source satellite sends a second message of the nth random access procedure to the terminal device. The second message of the nth random access procedure does not include uplink resource scheduling information used to indicate the third message. After receiving the second message of the nth random access procedure, the terminal device starts a timer; After the timer expires, the terminal device sends the first message of the (n+1)th random access procedure; During the process of the target satellite serving the first cell, in response to the first message of the (n+1)th random access procedure, the target satellite sends the second message of the (n+1)th random access procedure to the terminal device. The second message of the (n+1)th random access procedure includes uplink resource scheduling information for indicating the third message. The terminal device sends a third message for the (n+1)th random access procedure based on the uplink resources indicated by the scheduling information of the (n+1)th random access procedure, the third message including the uplink small data; and, during the process of the target satellite serving the first cell, the target satellite receives the third message sent by the terminal device in the RRC inactive state, including: During the process of the target satellite serving the first cell, the target satellite receives the third message of the (n+1)th random access procedure sent by the terminal device. The method according to claim 28, characterized in that, Before the source satellite ceases service to the first cell, the method further includes: The terminal device in the RRC inactive state sends the first message of the nth random access procedure, where n is an integer greater than or equal to 1; After sending the first message of the nth random access procedure, the terminal device starts a timer; If the source satellite does not send a second message in response to the first message of the nth random access procedure within the duration of the timer, the terminal device sends the first message of the (n+1)th random access procedure after the timer expires. After sending the first message of the (n+1)th random access procedure, the terminal device restarts the timer; During the process of the target satellite serving the first cell, in response to the first message of the (n+1)th random access procedure, the target satellite sends the second message of the (n+1)th random access procedure to the terminal device. The second message of the (n+1)th random access procedure includes uplink resource scheduling information for indicating the third message. If, within the duration of the timer being restarted, the terminal device receives the second message of the (n+1)th random access procedure from the target satellite, the terminal device, based on the uplink resources indicated by the scheduling information in the second message of the (n+1)th random access procedure, sends a third message of the (n+1)th random access procedure, the third message of the (n+1)th random access procedure including the uplink small data; and, During the process of the target satellite serving the first cell, the target satellite receives a third message sent by the terminal device in an RRC inactive state, including: During the process of the target satellite serving the first cell, the target satellite receives the third message of the (n+1)th random access procedure sent by the terminal device. A device for satellite base station handover, characterized in that, include: Memory, used to store computer instructions; A processor is configured to invoke computer instructions stored in the memory to perform the method as claimed in any one of claims 1 to 9, or any one of claims 10 to 18, or any one of claims 19 to 22, or any one of claims 23 to 26. A computer-readable storage medium, characterized in that, Used to store computer instructions for implementing the method as claimed in any one of claims 1 to 9, or any one of claims 10 to 18, or any one of claims 19 to 22, or any one of claims 23 to 26.

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