Method and system for transmitting multicast traffic

Abstract

The application provides a multicast service transmission method and system, and relates to the technical field of satellite communication. A ground terminal can receive multicast service data when being in a radio resource control idle state, and obtains ephemeris information and multicast control channel scheduling parameters of a target spaceborne base station in advance before the beam coverage of the source spaceborne base station no longer includes the ground terminal, so that the pre-compensation of Doppler frequency shift and propagation delay is completed before the beam coverage of the target spaceborne base station arrives; after the ground terminal enters the beam coverage of the target spaceborne base station, the ground terminal directly receives the multicast control channel and the multicast service data according to the pre-aligned frequency and timing parameters and the pre-known scheduling parameters, the time required for re-accessing the target spaceborne base station in a non-ground network which does not support the connected state switching is reduced, and the continuous transmission of the multicast service is realized.

Description

Technical Field

[0001] This invention relates to the field of satellite communication technology, and in particular to a method and system for transmitting multicast services. Background Technology

[0002] Low-Earth orbit (LEO) satellite networks can provide multicast services to ground terminals. Multiple ground terminals in the same multicast group receive the same multicast service data. Because LEO satellites move at high speeds relative to the ground, the beam coverage time of a single LEO satellite over a fixed ground area is limited. Therefore, ground terminals need to switch from receiving multicast services from the source satellite-based base station to receiving multicast services from the target satellite-based base station during the multicast service reception process.

[0003] Non-terrestrial networks based on narrowband IoT air interfaces do not support wireless resource control connection state switching. After the source satellite-borne base station ceases coverage, the ground terminal needs to acquire the downlink signal of the target satellite-borne base station, complete the receiving frequency and receiving timing alignment, and obtain the multicast control information broadcast by the target satellite-borne base station in order to continue receiving multicast service data.

[0004] In the initial stages of low-Earth orbit satellite network deployment, there may be situations where the beam coverage of adjacent satellites is discontinuous. After the target satellite-borne base station arrives, if the ground terminal then begins searching for the target operating frequency, obtaining multicast control channel scheduling parameters, and completing Doppler frequency shift and propagation delay compensation, the time required for multicast service recovery will be relatively long, which may easily cause service interruption when the ground terminal receives multicast services across satellites. Summary of the Invention

[0005] This invention provides a method and system for transmitting multicast services, which solves the problem of service interruption when ground terminals receive multicast services across satellites in existing low-Earth orbit satellite networks.

[0006] In a first aspect, the present invention provides a method for transmitting multicast services, applied to a ground terminal in a radio resource control idle state, the method comprising: During the process of receiving multicast service data through the source satellite base station, the ephemeris information and multicast configuration information of the target satellite base station broadcast by the source satellite base station are received. The multicast configuration information includes the multicast control channel scheduling parameters of the target satellite base station. Based on the ephemeris information and the location information of the ground terminal, calculate the beam coverage arrival time of the target satellite-borne base station; Within a preset time period before the arrival time of the beam coverage, the Doppler frequency shift and propagation delay of the target satellite base station relative to the ground terminal are pre-compensated based on the ephemeris information and the location information of the ground terminal to obtain the pre-aligned frequency and timing parameters. Within the beam coverage area of ​​the target satellite base station, based on the pre-aligned frequency and timing parameters and the multicast control channel scheduling parameters, the multicast control channel broadcast by the target satellite base station is received to obtain the group scheduling identifier corresponding to the multicast service; Based on the group scheduling identifier, the multicast service data broadcast by the target satellite base station on the multicast service channel is received.

[0007] In one possible implementation, after calculating the arrival time of the beam coverage of the target satellite-borne base station, the method further includes: determining the time when the beam coverage of the source satellite-borne base station no longer includes the ground terminal as the service interruption time; determining the service recovery preparation time based on the arrival time of the beam coverage and the preset duration; determining the time period between the service interruption time and the service recovery preparation time as the service interruption period; during the service interruption period, shutting down the radio frequency and switching to a sleep state, and switching to a wake-up state at the service recovery preparation time, so as to perform the pre-compensation within the preset duration before the arrival time of the beam coverage.

[0008] In one possible implementation, the multicast control channel scheduling parameters include the operating frequency, scheduling period, and time offset information of the multicast control channel broadcast by the target satellite base station; based on the operating frequency, scheduling period, and time offset information, the time-frequency resource position of the multicast control channel in the downlink frame of the target satellite base station is determined; the multicast control channel is received at the time-frequency resource position, and the multicast control channel is parsed to obtain the group scheduling identifier corresponding to the multicast service.

[0009] In one possible implementation, pre-compensation is performed on the Doppler frequency shift and propagation delay of the target satellite-borne base station relative to the ground terminal to obtain pre-aligned frequency and timing parameters. This includes: using the global navigation satellite system positioning result of the ground terminal as the location information of the ground terminal; calculating the relative motion velocity and signal propagation distance of the target satellite-borne base station relative to the ground terminal based on the ephemeris information of the target satellite-borne base station and the location information of the ground terminal; calculating the Doppler frequency shift based on the relative motion velocity and the signal propagation delay based on the signal propagation distance; and compensating the receiving frequency and receiving timing of the ground terminal based on the Doppler frequency shift and signal propagation delay to obtain pre-aligned frequency and timing parameters.

[0010] In one possible implementation, receiving multicast service data broadcast by the target satellite-borne base station on the multicast service channel includes: receiving multiple multicast service packets broadcast by the target satellite-borne base station on the multicast service channel and a synchronization timestamp for each multicast service packet; and sorting each multicast service packet according to the synchronization timestamp so that the multicast service packets received via the target satellite-borne base station are sequentially appended to the multicast service packets received via the source satellite-borne base station in terms of playback timing.

[0011] In one possible implementation, the multicast control channel is a single-cell multicast control channel, scheduled by a single-cell radio network temporary identifier, and the group scheduling identifier is a group radio network temporary identifier; the scheduling information of the downlink control channel is demodulated by the group radio network temporary identifier, and multicast service data carried by the single-cell multicast service channel is received on the corresponding physical downlink shared channel according to the scheduling information.

[0012] Secondly, the present invention provides a method for transmitting multicast services, applied to terrestrial network-side equipment, the method comprising: The multicast service data is sent to the source satellite base station through the first interface. The multicast service data carries a synchronization timestamp for aligning the transmission sequence between different satellite base stations. When the beam coverage area of ​​the source satellite base station includes the ground terminal, the source satellite base station is instructed to broadcast the ephemeris information and multicast configuration information of the target satellite base station to the ground terminal. The multicast configuration information includes the multicast control channel scheduling parameters of the target satellite base station. The target satellite base station is instructed to join the multicast service through the control plane interface, and a group scheduling identifier corresponding to the multicast service is sent to the target satellite base station so that the target satellite base station can receive and buffer the multicast service data and broadcast the multicast control channel that indicates the group scheduling identifier. When the beam coverage of neither the source satellite base station nor the target satellite base station includes the ground terminal, continuous synchronization timestamps are continuously allocated to the multicast service data to maintain continuous timing of the synchronization timestamps, and the multicast service data is pre-sent to the cache of the target satellite base station via the first interface.

[0013] The synchronization timestamp is used to ensure that the multicast service data broadcast by the target satellite base station is sequentially appended to the multicast service data broadcast by the source satellite base station in terms of transmission timing.

[0014] In one possible implementation, the ground network-side equipment includes a multicast coordination entity and a multicast service gateway. Through the multicast service gateway, multicast service data carrying the synchronization timestamp is sent to the source satellite-borne base station via the first interface. The multicast coordination entity sends a session establishment or update message to the target satellite-borne base station via the control plane interface, and sends the multicast service identifier, the group scheduling identifier, synchronization reference information for aligning transmission timing, and radio resource configuration for the multicast service. When the beam coverage of neither the source nor the target satellite-borne base station includes the ground terminal, the multicast service gateway continuously allocates progressively increasing synchronization timestamps to subsequent multicast service data according to the multicast service data rate.

[0015] Thirdly, the present invention provides a multicast service transmission method applied to a target satellite-based base station, the method comprising: When the beam coverage of the target satellite base station does not yet include the ground terminal, the multicast service data pre-issued by the ground network side equipment is received and cached through the first interface. The multicast service data carries a synchronization timestamp for aligning the transmission sequence between different satellite base stations. The system receives session establishment or update messages sent by the ground network side device through the control plane interface. The session establishment or update messages include the multicast service identifier of the multicast service, the group scheduling identifier corresponding to the multicast service, and the radio resource configuration. When the beam coverage of the target satellite base station includes the ground terminal, a multicast control channel is broadcast, which indicates the mapping relationship between the multicast service identifier and the group scheduling identifier; On the multicast service channel, the cached multicast service data is broadcast according to the synchronization timestamp, so that the broadcast multicast service data is continuated after the multicast service data broadcast by the source satellite base station in terms of transmission timing.

[0016] Fourthly, the present invention provides a transmission system for multicast services, including a low-Earth orbit satellite network, ground network-side equipment, and ground terminals, wherein the low-Earth orbit satellite network includes a source satellite-borne base station and a target satellite-borne base station; The ground terminal is used to perform the method as described in the first aspect; The terrestrial network-side device is used to perform the method as described in the second aspect; The source satellite-borne base station is used to broadcast multicast service data, as well as ephemeris information and multicast configuration information of the target satellite-borne base station, to ground terminals within the beam coverage area. The target satellite-borne base station is used to perform the method described in the third aspect.

[0017] The multicast service transmission method and system provided by this invention enable ground terminals to obtain ephemeris information and multicast control channel scheduling parameters of the target satellite-borne base station while the source satellite-borne base station is still providing multicast services, and to complete pre-compensation for Doppler frequency shift and propagation delay before the target satellite-borne base station's beam coverage arrives. After the ground terminal enters the beam coverage range of the target satellite-borne base station, it can receive multicast control channel and multicast service data according to pre-aligned frequency and timing parameters, thereby reducing the time required to re-acquire multicast services in non-terrestrial networks that do not support connection-state switching. The ground network side equipment continuously maintains synchronization timestamps and pre-downloads multicast service data to the target satellite-borne base station's buffer, and can also ensure that the data resumed by the target satellite-borne base station is transmitted sequentially from the data transmitted by the source satellite-borne base station. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a flowchart illustrating a transmission method for multicast services applied to ground terminals, as provided in an embodiment of the present invention. Figure 2 A schematic diagram of signaling interaction for a multicast service transmission method provided in an embodiment of the present invention; Figure 3 A flowchart illustrating a multicast service transmission method applied to terrestrial network side equipment according to an embodiment of the present invention; Figure 4 This is a flowchart illustrating a transmission method for multicast services applied to a target satellite-borne base station, as provided in an embodiment of the present invention. Figure 5 A schematic diagram of the structure of a multicast service transmission system provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0021] This invention is applied to a low-Earth orbit (LEO) satellite network. The LEO satellite network comprises multiple LEO satellites, each equipped with an onboard base station. The onboard base stations of two adjacent LEO satellites are designated as the source and target onboard base stations, respectively. Ground network equipment connects to the onboard base stations via a ground feeder link and provides multicast service data to the onboard base stations. Multiple ground terminals within the same multicast group receive the multicast service data broadcast by the onboard base stations in a Single Cell Point-to-Multipoint (SC-PTM) manner. The ground terminals can receive this multicast service data even in Radio Resource Control (RRC) idle mode. One example of a multicast service is an intercom service, where voice data is transmitted in the form of multicast service packets.

[0022] The air interface of low-Earth orbit satellite networks is based on narrowband Internet of Things (NB-IoT), and handover between satellite-based base stations is not supported in a connected state. Ground terminals receive multicast service data within the beam coverage area of ​​the source satellite-based base station, and after leaving the beam coverage area of ​​the source satellite-based base station, they wait for the coverage beam of the target satellite-based base station to arrive before continuing to receive multicast service data.

[0023] The multicast service transmission method provided in this embodiment of the invention includes, in sequence, a service maintenance phase, an active preparation phase, a service interruption period, a rapid service recovery phase, and a multicast service recovery phase, according to the time order in which the ground terminal receives multicast services across satellites.

[0024] During the service maintenance phase, the ground terminal is within the beam coverage area of ​​the source satellite-borne base station and receives multicast service data broadcast by the source satellite-borne base station in the idle state of radio resource control. The ground network side equipment sends multicast service data carrying a synchronization timestamp to the source satellite-borne base station through the first interface. During the active preparation phase, the beam coverage area of ​​the source satellite-borne base station is about to leave the ground terminal. The source satellite-borne base station broadcasts the ephemeris information and multicast configuration information of the target satellite-borne base station to the ground terminal. The ground network side equipment instructs the target satellite-borne base station to join the multicast service and sends a group scheduling identifier through the control plane interface. The target satellite-borne base station receives and buffers the multicast service data accordingly.

[0025] During service interruptions, the beam coverage of neither the source satellite base station nor the target satellite base station includes the ground terminal. The ground terminal shuts down its radio frequency and enters sleep mode to reduce power consumption, while the ground network side equipment maintains continuous timing with the synchronization timestamp.

[0026] During the rapid service recovery phase, when the beam coverage of the target satellite-borne base station approaches the target coverage area, the ground network equipment sends the cached multicast services to the target satellite-borne base station through the gateway station when the satellite is at a low elevation angle. The ground terminal pre-compensates for Doppler shift and propagation delay based on the ephemeris information of the target satellite-borne base station. The target satellite-borne base station broadcasts the multicast control channel, and the ground terminal obtains the group scheduling identifier corresponding to the multicast service under the target satellite-borne base station.

[0027] During the multicast service recovery phase, the ground terminal enters the beam coverage area of ​​the target satellite base station. The target satellite base station broadcasts the cached multicast service data on the multicast service channel according to the synchronization timestamp, so that the multicast service data received by the target satellite base station is sequentially continued from the multicast service data received by the source satellite base station.

[0028] Reference Figure 1 The transmission method for multicast services applied to ground terminals provided in this embodiment of the invention includes the following steps: In step S101, during the process of receiving multicast service data through the source satellite-borne base station, the ground terminal receives the ephemeris information and multicast configuration information of the target satellite-borne base station broadcast by the source satellite-borne base station. The multicast configuration information includes the multicast control channel scheduling parameters of the target satellite-borne base station.

[0029] Specifically, ephemeris information describes the position and operational status of the low-Earth orbit satellite where the target satellite-borne base station is located at different times. Multicast configuration information describes the control channel configuration used by the target satellite-borne base station when providing multicast services. Multicast control channel scheduling parameters indicate the operating frequency and occurrence time of the multicast control channel.

[0030] During the service maintenance phase, the ground terminal remains within the beam coverage area of ​​the source satellite-borne base station. The ground terminal simultaneously receives multicast service data broadcast by the source satellite-borne base station and listens for system information broadcast by the source satellite-borne base station. The source satellite-borne base station can carry the ephemeris information of the target satellite-borne base station and multicast configuration information related to SIB20 scheduling in the SIB15 or neighbor satellite configuration message. The multicast configuration information of the target satellite-borne base station may include operating frequency, scheduling period, and time offset information.

[0031] While the source satellite-borne base station is still able to receive multicast services, it broadcasts information about the target satellite-borne base station. Ground terminals do not need to wait for the source satellite-borne base station to leave before acquiring the target satellite-borne base station parameters. Based on this, the ground terminal can calculate the coverage time of the target satellite-borne base station and receive the multicast control channel according to the known scheduling position after the target satellite-borne base station arrives, reducing the time spent on blind searches.

[0032] In step S102, the ground terminal calculates the arrival time of the beam coverage of the target satellite base station based on the ephemeris information and the location information of the ground terminal.

[0033] Specifically, the location information of the ground terminal is used to indicate its location and can be obtained from the positioning results of the Global Navigation Satellite System. The beam coverage arrival time indicates the time when the beam of the target satellite-borne base station begins to meet the reception conditions of the ground terminal. The reception conditions can be determined by the elevation angle threshold of the target satellite-borne base station relative to the ground terminal, the link budget threshold, or a combination of both thresholds.

[0034] The ground terminal calculates the changing position of the target satellite-borne base station over time based on its ephemeris information, and then calculates the change in elevation angle of the target satellite-borne base station relative to the ground terminal based on the ground terminal's position. When the elevation angle reaches a preset reception threshold, the ground terminal determines the corresponding time as the time when beam coverage arrives.

[0035] The arrival time of beam coverage provides a time reference for ground terminals to schedule sleep, wake-up, and pre-compensation. Ground terminals can start receiving preparations before the target satellite-based base station forms effective coverage, avoiding the need to start calculating the receiving parameters of the target satellite-based base station only after effective coverage has been formed.

[0036] In step S103, within a preset time period before the beam coverage arrives, the ground terminal performs pre-compensation on the Doppler frequency shift and propagation delay of the target satellite base station relative to the ground terminal based on the ephemeris information and the location information of the ground terminal, and obtains the pre-aligned frequency and timing parameters.

[0037] Specifically, the preset duration represents the reception preparation time reserved before the beam coverage arrives. Doppler shift represents the reception frequency offset caused by the relative motion between the target satellite base station and the ground terminal. Propagation delay represents the time required for the downlink signal from the target satellite base station to propagate through space to reach the ground terminal. The pre-aligned frequency and timing parameters represent the reception parameters used by the ground terminal after frequency compensation and reception timing compensation are completed.

[0038] The ground terminal calculates the radial velocity and signal propagation distance of the target satellite-borne base station relative to the ground terminal based on the target satellite-borne base station's location and the ground terminal's location. It then determines the Doppler frequency shift based on the radial velocity and the propagation delay based on the signal propagation distance. The ground terminal adjusts its local receiving frequency and receiving window according to the calculation results.

[0039] Frequency and timing pre-compensation is completed before the target satellite base station beam arrives. When the ground terminal enters the coverage area of ​​the target satellite base station beam, it can receive downlink signals at a frequency and timing close to the target value, reducing the frequency search and timing acquisition process after coverage is reached.

[0040] In step S104, within the beam coverage area of ​​the target satellite base station, the ground terminal receives the multicast control channel broadcast by the target satellite base station according to the pre-aligned frequency and timing parameters and the multicast control channel scheduling parameters, and obtains the group scheduling identifier corresponding to the multicast service.

[0041] Specifically, the multicast control channel carries the multicast service identifier, group scheduling identifier, and multicast service channel scheduling information. The group scheduling identifier is used to distinguish different multicast groups at the radio interface. When the target satellite-borne base station adopts SC-PTM, the multicast control channel can be a single-cell multicast control channel, and the group scheduling identifier can be a temporary identifier for the group radio network.

[0042] After the target satellite-borne base station establishes effective coverage, the ground terminal first receives the broadcast signal from the target satellite-borne base station according to the pre-aligned frequency and timing parameters, and then locates the multicast control channel based on the operating frequency, scheduling period, and time offset information. The target satellite-borne base station can broadcast SIB20 via BCCH, which is used to provide the scheduling location of the single-cell multicast control channel; the ground terminal then receives the single-cell multicast control channel and obtains the mapping relationship between the temporary mobile group identifier and the group radio network temporary identifier.

[0043] The location of the multicast control channel of the target satellite base station has been delivered to the ground terminal during the service period of the source satellite base station. The ground terminal can directly access the corresponding time and frequency resources to receive the multicast control channel, reducing the control channel search time during cross-satellite reception.

[0044] In step S105, the ground terminal receives multicast service data broadcast by the target satellite base station on the multicast service channel according to the group scheduling identifier.

[0045] Specifically, the multicast service channel is used to carry data destined for multicast groups. The group scheduling identifier is used to demodulate downlink scheduling information destined for multicast groups. When using SC-PTM, the multicast service channel can be a single-cell multicast service channel, and the physical bearer can be a narrowband physical downlink shared channel.

[0046] After obtaining the group radio network temporary identifier from the multicast control channel, the ground terminal uses the group radio network temporary identifier to demodulate the scheduling information in the downlink control channel, and then receives multicast service data carried by the narrowband physical downlink shared channel according to the physical resources indicated by the scheduling information. When the source satellite base station and the target satellite base station serve the same PTT group, the temporary mobile group identifier is used to maintain the service group identity, and the group radio network temporary identifier under the target satellite base station is used to complete radio-side addressing.

[0047] In the idle state of radio resource control, the ground terminal receives multicast service data by relying on the group scheduling identifier. It does not need to maintain a dedicated connection for each multicast group member, nor does it depend on the connection state switching process.

[0048] In this embodiment, step S101 enables the ground terminal to obtain the ephemeris information and multicast control channel scheduling parameters of the target satellite-based base station while the source satellite-based base station is still providing services. Step S102 determines when the target satellite-based base station will form effective coverage based on this information. Step S103 utilizes the time before coverage arrives to complete frequency and timing pre-compensation. Step S104 uses the pre-obtained scheduling parameters to directly receive the multicast control channel of the target satellite-based base station. Step S105 uses the group scheduling identifier to continue receiving the same multicast service. When the low-Earth orbit satellite IoT non-terrestrial network does not support connection state switching, the ground terminal can still reduce the reacquisition time when switching from the source satellite-based base station to the target satellite-based base station by pre-obtaining target parameters, completing reception alignment in advance, and receiving multicast channels according to known resources. This alleviates the multicast service interruption caused by cross-satellite reception.

[0049] In some embodiments, after step S102, calculating the arrival time of the beam coverage of the target satellite base station, the method further includes: The moment when the beam coverage of the source satellite base station no longer includes the ground terminal is defined as the service interruption moment.

[0050] The service recovery preparation time is determined based on the arrival time of beam coverage and the preset duration.

[0051] The time period between the time of service interruption and the time of service recovery preparation is defined as the service interruption period.

[0052] During service interruption, the radio frequency is turned off and switched to sleep mode, and then switched to wake-up mode when service is ready to resume, so as to perform pre-compensation within a preset time before the beam coverage arrives.

[0053] Specifically, the service interruption time indicates the start time at which the ground terminal can no longer receive downlink signals from the source satellite base station. The service recovery preparation time indicates the time when the ground terminal begins to perform wake-up and parameter adjustments for downlink reception from the target satellite base station. The service interruption period indicates the time period during which the source satellite base station has left and the target satellite base station has not yet entered the reception preparation interval. The sleep state indicates that the ground terminal has turned off or reduced the operating status of its radio frequency transceiver circuits.

[0054] The ground terminal can calculate the service interruption time and the beam coverage arrival time based on the ephemeris of the source satellite base station, the target satellite base station, and the ground terminal's location. It then subtracts a preset duration from the beam coverage arrival time to obtain the service recovery preparation time. In one example, there is a coverage gap of approximately 406 seconds between the source and target satellite base stations. The ground terminal can shut down its radio frequency during this gap and begin waking up during the reserved reception preparation time before the target satellite base station arrives. The 406 seconds figure is only used to describe a constellation state and is not used to define the length of the coverage gap.

[0055] The service interruption time and service recovery preparation time jointly define the hibernation boundary. During periods without available satellite coverage, the ground terminal does not continuously perform invalid satellite searches and resumes radio frequency operation before performing Doppler shift and propagation delay pre-compensation. This reduces terminal power consumption during coverage gaps while preserving reception preparation time before the target satellite base station arrives.

[0056] In some embodiments, step S103, within a preset time period before the beam coverage arrival time, pre-compensates the Doppler frequency shift and propagation delay of the target satellite base station relative to the ground terminal based on ephemeris information and the location information of the ground terminal, to obtain pre-aligned frequency and timing parameters, including: The GPS positioning results of the ground terminal are used as the location information of the ground terminal.

[0057] Based on the ephemeris information of the target satellite-borne base station and the location information of the ground terminal, the relative motion speed and signal propagation distance of the target satellite-borne base station relative to the ground terminal are calculated.

[0058] The Doppler frequency shift is calculated based on the relative motion velocity, and the signal propagation delay is calculated based on the signal propagation distance.

[0059] Based on the Doppler frequency shift and signal propagation delay, the receiving frequency and receiving timing of the ground terminal are compensated to obtain the pre-aligned frequency and timing parameters.

[0060] Specifically, the Global Navigation Satellite System (GNSS) positioning result represents the geographic coordinates of the ground terminal. Relative velocity represents the velocity component of the target satellite-borne base station relative to the ground terminal along the line connecting the target satellite-borne base station and the ground terminal. Signal propagation distance represents the spatial distance between the target satellite-borne base station and the ground terminal. Reception timing represents the time and position at which the ground terminal opens its reception and demodulation windows.

[0061] The ground terminal calculates the position and velocity of the target satellite-borne base station at a predetermined time based on ephemeris information, determines its own position based on the GPS positioning results, and then calculates the relative velocity and distance between the target satellite-borne base station and the ground terminal. The relative velocity is used to determine the frequency offset that needs to be compensated for in the received carrier, and the distance is used to determine the propagation time that needs to be compensated for in the receiving window.

[0062] Ephemeris information and the location of the ground terminal together provide the basis for calculating Doppler frequency shift and propagation delay. The ground terminal completes the receiving frequency and timing adjustment before the target satellite-borne base station arrives. After the target satellite-borne base station forms effective coverage, the ground terminal can reduce the repeated acquisition process caused by frequency deviation and timing deviation.

[0063] In some embodiments, the multicast control channel scheduling parameters of the target satellite base station include: the operating frequency, scheduling period, and time offset information of the multicast control channel broadcast by the target satellite base station.

[0064] Step S104: Receive the multicast control channel broadcast by the target satellite base station to obtain the group scheduling identifier corresponding to the multicast service, including: Based on the operating frequency, scheduling period, and time offset information, the time-frequency resource location of the multicast control channel in the downlink frame of the target satellite base station is determined.

[0065] Receive multicast control channels at time-frequency resource locations.

[0066] Parse the multicast control channel to obtain the group scheduling identifier corresponding to the multicast service.

[0067] Specifically, the operating frequency point represents the carrier frequency location of the multicast control channel. The scheduling period represents the time period during which the multicast control channel repeats in the downlink frame structure. The time offset information represents the time offset of the multicast control channel relative to the start of the system frame or the start of the scheduling period. The time-frequency resource location represents the time and frequency resources occupied by the multicast control channel.

[0068] The source satellite-borne base station can broadcast the target satellite-borne base station's operating frequency, scheduling period, and time offset information to the ground terminal in a neighboring satellite configuration message. After the target satellite-borne base station enters the receptive range, the ground terminal sets the receiving carrier according to the operating frequency, calculates the target downlink frame position according to the scheduling period and time offset information, and reads and parses the multicast control channel at the target downlink frame position.

[0069] By narrowing the frequency search range through operating frequency points, and defining the timing of control channel appearance through scheduling cycles and time offset information, ground terminals no longer need to continuously attempt multiple frequencies and downlink times. The time-frequency position of the multicast control channel can be directly determined, thereby reducing the control channel acquisition time during cross-satellite recovery.

[0070] In some embodiments, step S105, receiving multicast service data broadcast by the target satellite base station on the multicast service channel, includes: Receive multiple multicast service packets broadcast by the target satellite base station on the multicast service channel, as well as the synchronization timestamp of each multicast service packet.

[0071] Based on the synchronization timestamp, each multicast service packet is sorted so that the multicast service packets received via the target satellite base station are sequentially followed by the multicast service packets received via the source satellite base station in terms of playback timing.

[0072] Specifically, a multicast service packet represents a data unit obtained by dividing multicast service data. A synchronization timestamp represents a timestamp assigned to a multicast service packet by the ground network-side equipment; the synchronization timestamp is used to indicate the data progress and transmission sequence of the same multicast service between different satellite-based base stations. Playback sequence indicates the order in which the ground terminal converts the multicast service packet into voice or other service content.

[0073] During the service period of the source satellite-borne base station, the terrestrial network equipment assigns synchronization timestamps to multicast service packets. During coverage gaps, it maintains continuous timing of these synchronization timestamps and pre-loads subsequent multicast service packets into the target satellite-borne base station's buffer. After coverage is restored, the target satellite-borne base station sends the buffered multicast service packets according to the synchronization timestamps. The terrestrial terminal identifies the order of events based on the synchronization timestamps and places the valid multicast service packets sent by the target satellite-borne base station after the valid multicast service packets already received by the source satellite-borne base station. When buffering is continuous and transmission is complete, the first valid multicast service packet sent by the target satellite-borne base station can be time-stamped following the last valid multicast service packet sent by the source satellite-borne base station.

[0074] Synchronized timestamps ensure that the order of data packets is independent of the local transmission clocks of the source and target satellite base stations. Ground terminals restore the playback order according to a unified timestamp, which can reduce data packet out-of-order playback, repeated playback, and playback jitter across satellite rendezvous locations.

[0075] In some embodiments, the multicast control channel is a single-cell multicast control channel, scheduled using a single-cell radio network temporary identifier. The group scheduling identifier is a group radio network temporary identifier.

[0076] Step S105: Receive multicast service data broadcast by the target satellite-borne base station on the multicast service channel, including: The scheduling information of the downlink control channel is demodulated by the temporary identifier of the group radio network.

[0077] Based on the scheduling information, multicast service data carried by the single-cell multicast service channel is received on the corresponding physical downlink shared channel.

[0078] Specifically, the Single Cell Multicast Control Channel (SC-MCCH) is used to broadcast control information for single-cell multicast services. The Single Cell Multicast Traffic Channel (SC-MTCH) is used to carry multicast service data. The Group Radio Network Temporary Identifier (G-RNTI) is used for radio-side addressing of multicast groups. The Narrowband Physical Downlink Shared Channel (NPDSCH) is used to carry downlink data.

[0079] The target satellite-based base station broadcasts the mapping relationship between the temporary mobile group identifier and the G-RNTI in the SC-MCCH, and uses the G-RNTI to scramble the scheduling information or NPDSCH data for the corresponding multicast group. After the ground terminal confirms the G-RNTI corresponding to the PTT group, it uses the G-RNTI to demodulate the downlink scheduling information, and then receives the PTT voice packets carried by the SC-MTCH on the NPDSCH resource indicated by the scheduling information. The modulation and coding scheme can be determined by the radio resource configuration, denoted as MCS_x.

[0080] SC-PTM transmits a single multicast service data packet in groups. Multiple group members in the Radio Resource Control (RRC) idle state can use the same G-RNTI to receive PTT voice packets. Ground terminals do not need to continuously maintain a dedicated connection-state bearer for multicast reception, thus reducing air interface signaling and terminal power consumption.

[0081] For example, refer to Figure 2 The signaling interaction process between the ground network equipment, the source satellite-borne base station, the target satellite-borne base station, and the ground terminal is as follows: During the service maintenance phase, the multicast service gateway sends multicast service data and synchronization timestamps to the source satellite base station via the M1 interface. The source satellite base station broadcasts SC-MTCH data on the NPDSCH and uses G-RNTI to complete radio addressing for PTT groups. The ground terminal is in the radio resource control idle state and uses G-RNTI to receive PTT voice packets broadcast by the source satellite base station.

[0082] During the active preparation phase, the source satellite-borne base station broadcasts the ephemeris information and SIB20 scheduling information of the target satellite-borne base station via SIB15 or neighbor satellite configuration messages. The source satellite-borne base station can also send base station configuration update messages via M2AP, carrying the global identifier of the cell about to cease multicasting. The ground network equipment returns a configuration update confirmation. The ground network equipment determines the target satellite-borne base station based on the satellite orbit and operating time, and when the target satellite-borne base station has the necessary ground network communication conditions, it sends a multicast session establishment or update message to the target satellite-borne base station. The multicast session establishment or update message may carry a temporary mobile group identifier, G-RNTI, synchronization reference information, quality of service parameters, and radio resource configuration.

[0083] During the service interruption phase, the ground terminal shuts down its radio frequency and enters a sleep state based on the calculated service interruption period. The multicast service gateway continues to allocate continuously increasing synchronization timestamps according to the multicast service data rate, and the multicast coordination entity continues to maintain frame timing and service session status. After the target satellite base station establishes a usable connection with the ground network side equipment, the multicast coordination entity can send an M2 Setup Request to the target satellite base station via M2AP. After the target satellite base station completes the user plane resource allocation, it returns an M2 Setup Response. The multicast coordination entity then sends an MBMS session start message, and after the target satellite base station completes the session configuration, it returns a session start response.

[0084] During the rapid service recovery phase, the ground terminal calculates the Doppler frequency shift and propagation delay based on the ephemeris information of the target satellite-borne base station, and completes frequency and timing pre-compensation before the target satellite-borne base station reaches the receiving elevation threshold. The target satellite-borne base station transmits SIB20 through the broadcast control channel. The ground terminal determines the SC-MCCH scheduling position based on SIB20, and then obtains the mapping relationship between the temporary mobile group identifier and G-RNTI from the SC-MCCH.

[0085] During the multicast service recovery phase, the multicast service gateway sends multicast service data with synchronization timestamps to the target satellite-based base station via the M1 interface. The target satellite-based base station buffers the multicast service data before the beam covers the target area. After the target satellite-based base station achieves effective coverage, it broadcasts PTT voice packets on the NPDSCH using G-RNTI. The ground terminal arranges the received PTT voice packets according to the synchronization timestamps and resumes playback. The target satellite-based base station's pre-buffering of data reduces the time spent waiting for the feeder link round-trip time (RTT) after beam coverage arrives; continuous synchronization timestamp timing reduces playback jitter and pops at the recovery location.

[0086] Reference Figure 3 This invention also provides a method for transmitting multicast services, applied to terrestrial network side equipment, the method comprising: Step S201: Multicast service data of multicast service is sent to the source satellite base station through the first interface. The multicast service data carries a synchronization timestamp for aligning the transmission sequence between different satellite base stations.

[0087] Specifically, the first interface represents the user plane interface through which the terrestrial network-side equipment transmits multicast service data to the satellite-based base station; the first interface can be the M1 interface. The synchronization timestamp represents the unified time stamp associated with the multicast service packet.

[0088] During the service maintenance phase, the multicast service gateway assigns a synchronization timestamp to the data packets entering the multicast session, and then sends the data packets and synchronization timestamps to the source satellite-borne base station via the M1 interface. The source satellite-borne base station broadcasts multicast service data to the ground terminal according to the radio resource configuration. The unified time stamp is established from the transmission phase of the source satellite-borne base station, providing a time reference for subsequent relay transmissions by the target satellite-borne base station.

[0089] Step S202: If the beam coverage of the source satellite base station includes the ground terminal, instruct the source satellite base station to broadcast the ephemeris information and multicast configuration information of the target satellite base station to the ground terminal. The multicast configuration information includes the multicast control channel scheduling parameters of the target satellite base station.

[0090] Specifically, ground network equipment can determine the target satellite-borne base station to provide service after the source satellite-borne base station based on the low-Earth orbit satellite's orbit, operating time, and target ground area. The source satellite-borne base station then provides the source satellite-borne base station with the target satellite-borne base station's ephemeris information, operating frequency, scheduling cycle, and time offset information. The source satellite-borne base station then includes the target satellite-borne base station parameters in a system broadcast message.

[0091] The target satellite-borne base station parameters are delivered to the ground terminal while the source satellite-borne base station still covers the ground terminal. The ground terminal can complete the coverage time calculation and control channel reception preparation in advance, avoiding the need to start acquiring the target satellite-borne base station parameters only after the target satellite-borne base station arrives.

[0092] Step S203: Instruct the target satellite base station to join the multicast service through the control plane interface, and send the group scheduling identifier corresponding to the multicast service to the target satellite base station so that the target satellite base station can receive and buffer the multicast service data and broadcast the multicast control channel indicating the group scheduling identifier.

[0093] Specifically, the control plane interface represents the interface used for session and resource configuration between the ground network-side equipment and the satellite-based base station. The control plane interface can be an M2AP interface. Joining a multicast service means that the target satellite-based base station establishes a session context associated with the corresponding multicast service identifier.

[0094] The multicast coordination entity sends a multicast session establishment or update message to the target satellite-based base station, and distributes the temporary mobile group identifier, G-RNTI, synchronization reference information, quality of service parameters, and radio resource configuration to the target satellite-based base station. The target satellite-based base station identifies the multicast service data that needs to be buffered based on the session context and prepares the radio resources used by the SC-MCCH and SC-MTCH.

[0095] Before the target satellite-borne base station covers the target ground area, it obtains the service identifier, group scheduling identifier, and radio resource configuration. After the target satellite-borne base station enters the service phase, it can directly broadcast the multicast control channel and multicast service data, reducing the waiting caused by temporary session establishment and temporary resource allocation.

[0096] In step S204, when the beam coverage of neither the source satellite base station nor the target satellite base station includes the ground terminal, continuous synchronization timestamps are continuously allocated to the multicast service data to maintain continuous timing of the synchronization timestamps, and the multicast service data is pre-downloaded to the cache of the target satellite base station via the first interface.

[0097] Specifically, continuous timing indicates the allocation of time stamps for multicast service data that do not cease during periods when there is no satellite coverage for the ground terminal. Pre-deployment indicates that multicast service data has already reached the target satellite-borne base station via the first interface and entered the cache before the target satellite-borne base station forms coverage of the target area.

[0098] The multicast service gateway continues to allocate incremental synchronization timestamps to subsequent voice packets according to the PTT voice data rate, and sends the voice packets with synchronization timestamps to the target satellite base station buffer. The multicast coordination entity continues to maintain frame timing and multicast session state during periods of no coverage.

[0099] Continuous synchronization of timestamps enables the target satellite-borne base station to identify service data after the last data transmission location of the source satellite-borne base station, while pre-caching ensures that the target satellite-borne base station does not need to wait for the ground network equipment to retransmit the first batch of data after coverage is restored. These two processes together reduce timing breaks and power supply link delays during transmission recovery.

[0100] In this embodiment, step S201 establishes a unified cross-satellite transmission timing sequence; step S202 sends the receiving parameters of the target satellite-borne base station to the ground terminal in advance; step S203 pre-establishes a multicast session and radio mapping on the target satellite-borne base station side; and step S204 continues to maintain time stamps and prepare buffered data during coverage gaps. The ground network-side equipment does not rely on the X2 interface between the source and target satellite-borne base stations, but instead interacts with both the source and target satellite-borne base stations via data plane and control plane respectively, enabling the target satellite-borne base station to continue transmitting the same multicast service after coverage is restored.

[0101] In some embodiments, the terrestrial network-side equipment includes a multicast coordination entity and a multicast service gateway.

[0102] Step S201, sending multicast service data of multicast service to the source satellite base station through the first interface, including: sending multicast service data carrying a synchronization timestamp to the source satellite base station through the multicast service gateway via the first interface.

[0103] Step S203: Instruct the target satellite base station to join the multicast service through the control plane interface, and send the group scheduling identifier corresponding to the multicast service to the target satellite base station. This includes: the multicast coordination entity sending a session establishment or update message to the target satellite base station through the control plane interface, and sending the multicast service identifier, group scheduling identifier, synchronization reference information for aligning transmission timing, and radio resource configuration of the multicast service.

[0104] Step S204, continuously allocating continuous synchronization timestamps to multicast service data to maintain continuous timing of synchronization timestamps, includes: when the beam coverage of neither the source satellite base station nor the target satellite base station includes the ground terminal, the multicast service gateway continuously allocates continuously increasing synchronization timestamps to subsequent multicast service data according to the data rate of the multicast service.

[0105] Specifically, the Multicast Coordination Entity (MCE) is responsible for multicast session coordination and radio resource coordination. The Multicast Service Gateway (MBMS Gateway-GW) is responsible for multicast service data replication and distribution. The multicast service identifier can be a Temporary Mobile Group Identity (TMGI). Synchronization reference information is used to indicate the current frame timing, timestamp reference, or data progress of the multicast service. Quality of Service (QoS) parameters are used to indicate the data rate, latency, or priority requirements of the multicast service.

[0106] The MCE can send MBMS Session Start, MBMS Session Update, or equivalent session control messages via M2AP. The MBMS-GW can send multicast service packets with synchronization timestamps via the M1 interface. When the source satellite base station is about to cease service, it can also send a base station configuration update message to the MCE, carrying the global identifier of the cell where multicast is about to be shut down. After the target satellite base station establishes a connection with the terrestrial network, the MCE can first execute M2Setup, and then execute MBMS session start or update.

[0107] The MCE is responsible for session, group identification, and radio resource preparation, while the MBMS-GW is responsible for continuous distribution of data and synchronization timestamps. Control plane preparation and user plane preparation are respectively completed by appropriate network elements. Therefore, the target satellite-based base station can simultaneously obtain the service context and the data to be transmitted, and the cross-satellite recovery process does not require direct transfer of the terminal connection context from the source satellite-based base station.

[0108] Reference Figure 4 This invention also provides a method for transmitting multicast services, applied to a target satellite-based base station, the method comprising: Step S301: If the beam coverage of the target satellite base station does not yet include the ground terminal, the multicast service data pre-issued by the ground network side equipment is received and cached through the first interface. The multicast service data carries a synchronization timestamp for aligning the transmission sequence between different satellite base stations.

[0109] Specifically, "caching" indicates that the target satellite-borne base station temporarily stores multicast service data and synchronization timestamps in its local storage area. "Beam coverage does not yet include ground terminals" means that the target satellite-borne base station has not yet reached the reception threshold of the target ground area, but the target satellite-borne base station is already capable of receiving data from the ground network.

[0110] The target satellite-borne base station writes the data received via the M1 interface into the corresponding buffer queue according to the multicast service identifier, and retains the synchronization timestamp of each multicast service packet. The target satellite-borne base station obtains the data to be transmitted in advance, and can directly schedule the data in the buffer queue after the target satellite-borne base station beam enters the target area, reducing the time waiting for the first batch of data to arrive from the feeder link.

[0111] Step S302: Receive session establishment or update messages sent by ground network side devices through the control plane interface. The session establishment or update messages include the multicast service identifier of the multicast service, the group scheduling identifier corresponding to the multicast service, and the radio resource configuration.

[0112] Specifically, session establishment or update messages are used to establish or modify multicast service contexts at the target satellite-based base station. Multicast service identifiers are used to identify service sessions, group scheduling identifiers are used for radio-side group addressing, and radio resource configuration is used to determine the resources occupied by multicast control channels and multicast service channels.

[0113] After receiving the session establishment or update message from the MCE, the target satellite-based base station establishes a mapping between TMGI and G-RNTI, saves synchronization reference information, quality of service parameters, and radio resource configurations, and configures corresponding resources for SC-MCCH, SC-MTCH, and NPDSCH. The service context is prepared before the target satellite-based base station begins covering the target area, and the target satellite-based base station does not need to wait for a complete session configuration again after entering the service phase.

[0114] Step S303: If the beam coverage of the target satellite base station includes the ground terminal, broadcast the multicast control channel, which indicates the mapping relationship between the multicast service identifier and the group scheduling identifier.

[0115] Specifically, the mapping relationship represents the G-RNTI corresponding to the TMGI of the same PTT group within the target satellite base station cell. The target satellite base station can indicate the SC-MCCH scheduling position via SIB20, and then broadcast the mapping between TMGI and G-RNTI in the SC-MCCH. The ground terminal confirms the PTT group that needs to be received based on the TMGI, and then obtains the G-RNTI used by the target satellite base station cell.

[0116] The multicast control channel provides ground terminals with conversion information from service layer group identifier to radio side group identifier, enabling ground terminals to still address the same PTT group after changing satellite base stations.

[0117] Step S304: On the multicast service channel, the cached multicast service data is broadcast according to the synchronization timestamp, so that the broadcast multicast service data is continuated after the multicast service data broadcast by the source satellite base station in terms of transmission timing.

[0118] Specifically, the target satellite-borne base station selects multicast service packets to be sent from the buffer queue based on the synchronization timestamp, and broadcasts the multicast service packets on the SC-MTCH and NPDSCH according to the radio resource configuration. When the synchronization timestamps are consecutive and the buffer data is complete, the first valid multicast service packet sent by the target satellite-borne base station is timestamped after the last valid multicast service packet of the source satellite-borne base station.

[0119] The target satellite-borne base station sends buffered data according to the unified timestamp maintained by the ground network equipment. The difference between the local clock of the source satellite-borne base station and the local clock of the target satellite-borne base station no longer directly determines the order of multicast service packets. The ground terminal can restore the playback order according to the synchronization timestamp, thereby reducing the out-of-order and jitter of cross-satellite recovery positions.

[0120] In this embodiment, step S301 prepares user plane data, step S302 prepares service sessions and radio resources, step S303 publishes the radio mapping between TMGI and G-RNTI to the ground terminal, and step S304 sends buffered data according to a unified synchronization timestamp. The target satellite-borne base station completes data and context preparation before forming target area coverage. After forming target area coverage, the target satellite-borne base station can quickly enter multicast transmission state and ensure that the data resuming transmission maintains timing consistency with the data previously transmitted by the source satellite-borne base station.

[0121] Reference Figure 5The present invention also provides a transmission system for multicast services, including a low-Earth orbit satellite network 100, a ground network-side device 200 and a ground terminal 300. The low-Earth orbit satellite network 100 includes a source satellite-borne base station 110 and a target satellite-borne base station 120.

[0122] The ground terminal 300 is used to execute the multicast service transmission method applied to the ground terminal 300, that is, to execute steps S101 to S105 shown in FIG1, as well as the steps applied to the ground terminal 300 in the aforementioned embodiments.

[0123] The ground network side device 200 is used to send multicast service data carrying synchronization timestamps to the source satellite base station 110 through the first interface, and instruct the source satellite base station 110 to broadcast the ephemeris information and multicast configuration information of the target satellite base station 120 to the ground terminal 300; and instruct the target satellite base station 120 to join the multicast service and send group scheduling identifiers through the control plane interface. During the service interruption period when the beam coverage of the source satellite base station 110 and the target satellite base station 120 does not include the ground terminal 300, the device continuously allocates continuous synchronization timestamps for the multicast service data to maintain the continuity of timing, and pre-sends the multicast service data to the buffer of the target satellite base station 120 through the first interface.

[0124] The source satellite base station 110 is used to broadcast multicast service data to the ground terminal 300 within the beam coverage area, as well as the ephemeris information and multicast configuration information of the target satellite base station 120.

[0125] The target satellite base station 120 is used to execute the multicast service transmission method applied to the target satellite base station 120, that is, to execute steps S301 to S304 shown in FIG4, as well as the steps applied to the target satellite base station 120 in the aforementioned embodiments.

[0126] The multicast service transmission system provided in this embodiment of the invention broadcasts the ephemeris information and multicast control channel scheduling parameters of the target satellite base station 120 in advance during the beam coverage of the ground terminal 300. The ground network side equipment 200 maintains continuous timing of the synchronization timestamp during the cross-satellite coverage gap and pre-sends multicast service data to the target satellite base station 120. The ground terminal 300 completes the pre-compensation of Doppler frequency shift and propagation delay before the beam coverage of the target satellite base station 120 arrives, so that the ground terminal 300 can directly receive the multicast control channel and service data after entering the coverage area of ​​the target satellite base station 120. This reduces the time spent reconnecting to the target satellite base station 120 in a non-terrestrial network that does not support connection state switching and realizes continuous transmission of multicast services.

[0127] Figure 6 An example is a schematic diagram of the physical structure of an electronic device, such as... Figure 6As shown, the electronic device may include a processor 810, a communications interface 820, a memory 830, and a communication bus 840, wherein the processor 810, the communications interface 820, and the memory 830 communicate with each other through the communication bus 840. The processor 810 can call logical instructions in the memory 830 to execute any of the methods described above.

[0128] Furthermore, the logical instructions in the aforementioned memory 830 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or a part 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 the present invention. 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.

[0129] On the other hand, the present invention also provides a computer program product, the computer program product including a computer program, the computer program being stored on a non-transitory computer-readable storage medium, and when the computer program is executed by a processor, the computer is able to perform any of the above methods.

[0130] In another aspect, the present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, the computer program being processed by a processor to perform any of the methods described above.

[0131] The device embodiments described above are merely illustrative. 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 modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0132] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0133] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A transmission method for multicast services, characterized in that, The method, applied to a ground terminal in a radio resource control idle state, includes: During the process of receiving multicast service data through the source satellite base station, the ephemeris information and multicast configuration information of the target satellite base station broadcast by the source satellite base station are received. The multicast configuration information includes the multicast control channel scheduling parameters of the target satellite base station. Based on the ephemeris information and the location information of the ground terminal, calculate the beam coverage arrival time of the target satellite-borne base station; Within a preset time period before the arrival time of the beam coverage, the Doppler frequency shift and propagation delay of the target satellite base station relative to the ground terminal are pre-compensated based on the ephemeris information and the location information of the ground terminal to obtain the pre-aligned frequency and timing parameters. Within the beam coverage area of ​​the target satellite base station, based on the pre-aligned frequency and timing parameters and the multicast control channel scheduling parameters, the multicast control channel broadcast by the target satellite base station is received to obtain the group scheduling identifier corresponding to the multicast service; Based on the group scheduling identifier, the multicast service data broadcast by the target satellite base station on the multicast service channel is received.

2. The method as described in claim 1, characterized in that, After calculating the beam coverage arrival time of the target satellite-borne base station, the method further includes: The moment when the beam coverage of the source satellite base station no longer includes the ground terminal is determined as the service interruption moment; The service recovery preparation time is determined based on the arrival time of the beam coverage and the preset duration; The time period between the service interruption time and the service recovery preparation time is defined as the service interruption period; During the service interruption period, the radio frequency is turned off and switched to a sleep state, and then switched to a wake-up state at the service recovery preparation time to perform the pre-compensation within a preset duration before the beam coverage arrival time.

3. The method as described in claim 1, characterized in that, The multicast control channel scheduling parameters of the target satellite base station include: the operating frequency, scheduling period, and time offset information of the multicast control channel broadcast by the target satellite base station; The step of receiving the multicast control channel broadcast by the target satellite base station to obtain the group scheduling identifier corresponding to the multicast service includes: Based on the operating frequency, the scheduling period, and the time offset information, the time-frequency resource position of the multicast control channel in the downlink frame of the target satellite base station is determined; Receive the multicast control channel at the time-frequency resource location; The multicast control channel is parsed to obtain the group scheduling identifier corresponding to the multicast service.

4. The method as described in claim 1, characterized in that, Within a preset time period prior to the arrival time of the beam coverage, based on the ephemeris information and the location information of the ground terminal, pre-compensation is performed on the Doppler frequency shift and propagation delay of the target satellite-borne base station relative to the ground terminal to obtain pre-aligned frequency and timing parameters, including: The global navigation satellite system positioning result of the ground terminal is used as the location information of the ground terminal; Based on the ephemeris information of the target satellite-borne base station and the location information of the ground terminal, calculate the relative motion speed and signal propagation distance of the target satellite-borne base station relative to the ground terminal; The Doppler frequency shift is calculated based on the relative motion velocity, and the signal propagation delay is calculated based on the signal propagation distance. Based on the Doppler frequency shift and the signal propagation delay, the receiving frequency and receiving timing of the ground terminal are compensated to obtain the pre-aligned frequency and timing parameters.

5. The method as described in claim 1, characterized in that, The receiving of multicast service data broadcast by the target satellite-borne base station on the multicast service channel includes: The receiver receives multiple multicast service packets broadcast by the target satellite base station on the multicast service channel, as well as the synchronization timestamp of each multicast service packet. Based on the synchronization timestamp, each multicast service packet is sorted so that the multicast service packet received via the target satellite base station is sequentially followed by the multicast service packet received via the source satellite base station in terms of playback timing.

6. The method as described in claim 1, characterized in that, The multicast control channel is a single-cell multicast control channel, scheduled using a single-cell radio network temporary identifier; the group scheduling identifier is a group radio network temporary identifier. The receiving of multicast service data broadcast by the target satellite-borne base station on the multicast service channel includes: Demodulate the scheduling information of the downlink control channel using the aforementioned group of wireless network temporary identifiers; Based on the scheduling information, multicast service data carried by the single-cell multicast service channel is received on the corresponding physical downlink shared channel.

7. A transmission method for multicast services, characterized in that, Applied to terrestrial network side equipment, the method includes: The multicast service data is sent to the source satellite base station through the first interface. The multicast service data carries a synchronization timestamp for aligning the transmission sequence between different satellite base stations. When the beam coverage area of ​​the source satellite base station includes the ground terminal, the source satellite base station is instructed to broadcast the ephemeris information and multicast configuration information of the target satellite base station to the ground terminal. The multicast configuration information includes the multicast control channel scheduling parameters of the target satellite base station. The target satellite base station is instructed to join the multicast service through the control plane interface, and a group scheduling identifier corresponding to the multicast service is sent to the target satellite base station so that the target satellite base station can receive and buffer the multicast service data and broadcast the multicast control channel that indicates the group scheduling identifier. When the beam coverage of neither the source satellite base station nor the target satellite base station includes the ground terminal, continuous synchronization timestamps are continuously allocated to the multicast service data to maintain the continuous timing of the synchronization timestamps, and the multicast service data is pre-sent to the cache of the target satellite base station via the first interface. The synchronization timestamp is used to ensure that the multicast service data broadcast by the target satellite base station is sequentially appended to the multicast service data broadcast by the source satellite base station in terms of transmission timing.

8. The method as described in claim 7, characterized in that, The terrestrial network-side equipment includes a multicast coordination entity and a multicast service gateway; The multicast service data sent to the source satellite base station via the first interface includes: The multicast service gateway sends the multicast service data carrying the synchronization timestamp to the source satellite base station via the first interface; The step of instructing the target satellite-borne base station to join the multicast service via the control plane interface and issuing the group scheduling identifier corresponding to the multicast service to the target satellite-borne base station includes: The multicast coordination entity sends a session establishment or update message to the target satellite base station via the control plane interface, and issues the multicast service identifier of the multicast service, the group scheduling identifier, synchronization reference information for aligning transmission timing, and radio resource configuration. The step of continuously allocating consecutive synchronization timestamps to the multicast service data to maintain the continuous timing of the synchronization timestamps includes: When the beam coverage of neither the source satellite base station nor the target satellite base station includes the ground terminal, the multicast service gateway continuously allocates progressively increasing synchronization timestamps for subsequent multicast service data according to the data rate of the multicast service.

9. A transmission method for multicast services, characterized in that, Applied to a target spaceborne base station, the method includes: When the beam coverage of the target satellite base station does not yet include the ground terminal, the multicast service data pre-issued by the ground network side equipment is received and cached through the first interface. The multicast service data carries a synchronization timestamp for aligning the transmission sequence between different satellite base stations. The system receives session establishment or update messages sent by the ground network side device through the control plane interface. The session establishment or update messages include the multicast service identifier of the multicast service, the group scheduling identifier corresponding to the multicast service, and the radio resource configuration. When the beam coverage of the target satellite base station includes the ground terminal, a multicast control channel is broadcast, which indicates the mapping relationship between the multicast service identifier and the group scheduling identifier; On the multicast service channel, the cached multicast service data is broadcast according to the synchronization timestamp, so that the broadcast multicast service data is continuated after the multicast service data broadcast by the source satellite base station in terms of transmission timing.

10. A transmission system for multicast services, characterized in that, It includes a low-Earth orbit satellite network, ground network-side equipment, and ground terminals. The low-Earth orbit satellite network includes source satellite-borne base stations and target satellite-borne base stations. The ground terminal is configured to perform the method as described in any one of claims 1 to 6; The ground network-side device is used to perform the method as described in claim 7 or 8; The source satellite-borne base station is used to broadcast multicast service data, as well as ephemeris information and multicast configuration information of the target satellite-borne base station, to ground terminals within the beam coverage area. The target satellite-borne base station is used to perform the method as described in claim 9.

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