Multi-user access method applied to satellite-ground communication

Abstract

The present invention discloses a multi-user access method applied to satellite-ground communication. The method includes: a user terminal generates orthogonal transmission parameters used in the beam scanning stage and the network access stage, and uses the parameters for signal transmission; in the beam scanning stage, the satellite terminal performs beam scanning transmission. After the user terminal captures the satellite signal, it sends a synchronization signal and enters a listening state. After the satellite performs scanning transmission, it performs beam scanning reception, and uses a narrow beam to send a broadcast message at the searched beam position for time and beam position synchronization of the user terminal; in the network access stage, the user terminal sends a network access request, and the satellite makes a network access response and allocates transmission parameters for the user terminal in this stage; in the service stage, the user terminal uses the allocated parameters for service communication. The present invention can not only achieve long-distance access of multiple user terminals by using narrow beam communication, but also realize the network access operation of multiple users in a short time, and is particularly suitable for the fast access scenario of multiple users.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless communication networks, and particularly to a multi-user access method applied to satellite-ground communication. Background Art

[0002] Satellite communication is an important means for long-distance communication in modern communication. With the development of the times, satellite communication has gradually developed satellite radio and television networks, satellite broadband communication networks, satellite mobile communication networks, and military communication networks, etc. The types of users served by satellite communication have also gradually expanded from a fixed user group to a random user group.

[0003] In traditional satellite communication, broadcasting and fixed allocation methods are often used to serve multiple users. Due to the one-way communication characteristic of the broadcasting method, the usage scenarios of ground random users are greatly restricted; the fixed allocation method also has insufficient flexibility, resulting in it being difficult for random users to access satellite services in real time.

[0004] Aiming at the deficiencies of traditional satellite communication technology in serving random users, it is necessary to solve the problem of multi-user random access in satellite-ground communication. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems in the related technologies to some extent. For this reason, an object of the present invention is to provide a multi-user access method applied to satellite-ground communication. Through a series of wave position scanning processes and information broadcast distribution of the satellite in the beam scanning stage, this method realizes the narrow beam alignment of the satellite during the user access process and the time synchronization between the user terminal and the satellite. In addition, this method adopts multi-dimensional orthogonal multiple access means in the wave position scanning stage and the network access stage, which can effectively alleviate the interference problem of multi-user transmission in different stages.

[0006] To achieve the above object, the present invention is realized through the following technical solutions:

[0007] A multi-user access method applied to satellite-ground communication, the method is applied to a satellite terminal and a user terminal set on the ground. When the satellite terminal executes the method, the processes experienced include a wave position scanning stage, a network access stage, and a service stage. When the user terminal executes the method, the processes experienced include an initialization transmission parameter stage, the wave position scanning stage, the network access stage, and the service stage. The method includes:

[0008] Step S1: The user terminal determines and generates the transmission waveform parameters used by itself in the wave position scanning stage and the network access stage during the initialization transmission parameter stage;

[0009] Step S2: The satellite terminal and the user terminal perform satellite narrow beam alignment and two-terminal time synchronization operations in the wave position scanning stage, and enter the network access stage after the execution is completed;

[0010] Step S3: The satellite terminal and the user terminal perform the network access operation of the current user terminal and the operation of allocating transmission parameters for the user terminal in the service phase during the network access phase, and enter the service phase after completion.

[0011] Step S4: The satellite terminal and the user terminal complete normal service communication for multiple networked users in the service phase.

[0012] Optionally, step S1 includes:

[0013] Step S11: Each user terminal to be networked extracts its own typical information features.

[0014] Step S12: Each user terminal to be networked generates a random number seed according to the extracted information features.

[0015] Step S13: Each user terminal to be networked generates its own transmission waveform parameters used in the beam scanning phase and the network access phase according to the random number seed.

[0016] Optionally, the transmission waveform parameters include: the frequency and chips used by the user terminal in the beam scanning phase and the network access phase.

[0017] Optionally, after the satellite terminal is powered on, it enters the beam scanning phase. The steps for the satellite terminal to perform satellite narrow beam alignment and two-terminal time synchronization operations in step S2 include:

[0018] Step S210: The satellite terminal enters the beam scanning time slot, and according to the number of beam positions S in the coverage area, sequentially uses narrow beams to point to different beam position directions to send beam synchronization signals for 1 beam scanning time slot, where the total number of beam scanning time slots is S.

[0019] Step S211: The satellite terminal repeats the beam pointing in step S210, sequentially receives beam synchronization signals for 1 beam scanning time slot, and records the current beam position and capture energy when a signal is captured in the i-th beam scanning time slot, where the total number of beam scanning time slots is S.

[0020] Step S212: The satellite terminal enters the broadcast time slot, sorts the signal capture results during the search process in step S211 in descending order according to the capture energy magnitude, and when the number of signal captures N during the search process in step S211 is greater than the maximum number of broadcast time slots M, sequentially uses narrow beams to point to the corresponding first M wave positions to send the broadcast message of one broadcast time slot; when the number of signal captures N during the search process in step S211 is less than or equal to the maximum number of broadcast time slots M, sequentially uses narrow beams to point to the corresponding first N wave positions to send the broadcast message of one broadcast time slot and then silences for M - N broadcast time slots, where the total number of the broadcast time slots is M, and the broadcast message includes the time synchronization information of the satellite terminal;

[0021] Step S213: After the Mth broadcast time slot in step S212 ends, the satellite terminal enters the network access phase.

[0022] Optionally, after the user terminal is powered on, it enters the wave position scanning phase. The steps for the user terminal to perform satellite narrow beam alignment and two-terminal time synchronization operations in step S2 include:

[0023] Step S220: The user terminal enters the wave position scanning time slot and is in the synchronous signal capture listening state to continuously listen for the wave position synchronization signal sent by the satellite terminal. Wherein, when the user terminal never listens to the wave position synchronization signal sent by the satellite terminal, it always remains in the wave position synchronization signal capture listening state;

[0024] Step S221: When the user terminal captures the wave position synchronization signal sent by the satellite terminal, it enters the wave position sending state after listening to the first wave position synchronization signal sent by the satellite terminal, and performs signal transmission according to the wave position scanning phase transmission waveform parameters generated in the initialization transmission parameter phase, and lasts for S wave position scanning time slots;

[0025] Step S222: The user terminal enters the broadcast time slot and enters the broadcast message listening state to continuously listen for the broadcast message sent by the satellite terminal. When the broadcast message sent by the satellite terminal is not received within the timeout period, it goes to step S220, and when the broadcast message sent by the satellite terminal is received within the timeout period, it synchronizes time with the satellite terminal according to the time synchronization information in the broadcast message, records the satellite broadcast time slot number Q when the broadcast message is received, and enters the network access phase simultaneously with the satellite terminal after the Mth broadcast time slot of the satellite terminal ends.

[0026] Optionally, the execution steps of the satellite terminal in the network access phase specifically include:

[0027] Step S310: The satellite terminal enters the network access request time slot and is in the network access request listening state to continuously listen for the network access request information sent by the user terminal. There are a total of M network access request time slots. Among them, in the network access request listening state, the beam pointing order and direction of the satellite terminal are the same as those of the broadcast time slot in the wave position scanning stage. The satellite terminal calculates the wave position for communicating with the user terminal when receiving the network access request message of the user terminal;

[0028] Step S311: The satellite terminal enters the network access response time slot and, according to the network access request of the user terminal received in Step S310, allocates network numbers and corresponding service stage transmission parameters to at most Z user terminals allowed to access the network. When the number X of network access request messages received during the listening process in Step S310 is greater than Z, the satellite terminal sequentially uses the narrow beam to point to the corresponding first Z user wave position directions to send a network access response message for 1 network access response time slot; when the number X of network access request messages received during the listening process in Step S310 is less than or equal to Z, after sequentially using the narrow beam to point to the corresponding first X user wave position directions to send a network access response message for 1 network access response time slot, it silences Z - X network access response time slots. Among them, the total number of network access response time slots is Z;

[0029] Step S312: The satellite terminal enters the service stage after the end of the Zth network access response time slot in Step S311.

[0030] Optionally, the steps executed by the user terminal in the network access stage specifically include:

[0031] Step S320: The user terminal enters the network access request time slot, performs signal transmission according to the network access stage transmission waveform parameters generated based on the initialization transmission parameters, and after sending a network access request message for 1 time slot in the Qth network access request time slot of the satellite terminal, switches to the listening state;

[0032] Step S321: The user terminal enters the network access response time slot after the end of the Mth network access request time slot of the satellite terminal, continuously listens for the network access response message from the satellite terminal, and when no network access response message sent by the satellite terminal is received within Z network access response time slots, switches to Step S220; when a network access response message sent by the satellite terminal is received within Z network access response time slots, changes the corresponding network state according to the information in the network access response message, configures the subsequent service transmission parameters at the same time, and enters the service stage simultaneously with the satellite terminal after the end of the Zth network access response time slot of the satellite terminal.

[0033] Optionally, the execution steps of the satellite terminal in the service stage specifically include:

[0034] Step S410: The satellite terminal enters the service time slot and conducts two-way communication with the user terminal according to the divided time slots, where the total number of service time slots is C;

[0035] Step S411: After the Cth service time slot in Step S410 ends, the satellite terminal transfers to Step S210.

[0036] Optionally, the execution steps of the user terminal in the service phase specifically include:

[0037] Step S420: The user terminal enters the service time slot and conducts two-way communication with the satellite terminal according to the divided time slots and transmission parameters, where the total number of service time slots is C;

[0038] Step S421: After the Cth service time slot in Step S420 ends, the user terminal switches to the listening state and waits for the next round. After the satellite terminal ends the network access phase, it transfers to Step S420.

[0039] The present invention has at least the following technical effects:

[0040] The present invention provides a multi-user access method applied to satellite-ground communication. Its scope of use is not only applicable to satellite-ground multi-user communication scenarios, but also applicable to other multi-user communication scenarios with a central service node. In addition, the multi-user access method disclosed in the present invention does not rely on the time synchronization between the satellite and the user terminal. This method not only realizes the narrow beam alignment of the satellite when the user accesses the network, increases the user access distance, but also improves the efficiency of multi-user network access, and is particularly suitable for multi-user fast access scenarios.

[0041] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present invention. Description of the Drawings

[0042] Figure 1 It is a schematic diagram of the network architecture in the embodiment of the present invention.

[0043] Figure 2 It is a schematic diagram of the satellite time slot structure in the embodiment of the present invention.

[0044] Figure 3 It is a schematic overview flowchart of the satellite terminal side during the user access process in the embodiment of the present invention.

[0045] Figure 4 It is a schematic overview flowchart of the user terminal side during the user access process in the embodiment of the present invention.

[0046] Figure 5Flow chart of a multi - user access method for satellite - to - ground communication provided by an embodiment of the present invention. Detailed implementation manners

[0047] The following details this embodiment. Examples of the embodiment are shown in the accompanying drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0048] The following describes the multi - user access method for satellite - to - ground communication of this embodiment with reference to the accompanying drawings.

[0049] The specific implementation manner of this multi - user access method for satellite - to - ground communication can be illustrated by Figure 1 the scenarios shown. Figure 1 A specific network architecture of an embodiment of the present invention is given. In the figure, there are 4 wave positions in the satellite coverage area, and three user terminals waiting to access the satellite. Among them, user terminal 1 and user terminal 2 are in the direction of wave position 1 of the satellite, and user terminal 3 is in the direction of wave position 4 of the satellite. In the embodiment of the present invention, the satellite adopts Figure 2 the time - slot structure shown, Figure 2 in which, there are a total of 8 wave - position scanning time slots and 4 broadcast time slots in the wave - position scanning stage, a total of 4 access - request time slots and 4 access - response time slots in the access stage, and a total of 8 service time slots in the service stage. Based on Figure 2 the time - slot structure design, the satellite can serve two - way transmission services for up to 4 random users within the coverage range. The process overview on the satellite - terminal side during the user - terminal access process is as shown in Figure 3 and the process overview on the user - terminal side is as shown in Figure 4 .

[0050] Specifically, the method is applied to a satellite terminal and user terminals set on the ground. When the satellite terminal executes the method, the processes experienced include a wave - position scanning stage, an access stage, and a service stage. When the user terminal executes the method, the processes experienced include an initialization of transmission parameter stage, a wave - position scanning stage, an access stage, and a service stage. Figure 5 Flow chart of a multi - user access method for satellite - to - ground communication provided by an embodiment of the present invention. As shown in Figure 5 , the method specifically includes the following steps:

[0051] Step S1: The user terminal determines and generates the transmission waveform parameters for its own use in the wave - position scanning stage and the access stage during the initialization of transmission parameter stage.

[0052] The specific content of step S1 includes:

[0053] In the first step, user terminals 1, 2, and 3 respectively extract their own typical information features as physical addresses mac_address1, mac_address2, and mac_address3.

[0054] In the second step, user terminals 1, 2, and 3 respectively generate their own random number seeds according to mac_address1, mac_address2, and mac_address3.

[0055] In the third step, user terminals 1, 2, and 3 respectively generate frequencies f1, f2, f3 and chips c1, c2, c3 used in the wave position scanning stage and the network access stage according to the random number seeds generated in the second step.

[0056] Step S2: The satellite terminal and the user terminal perform satellite narrow beam alignment and two-terminal time synchronization operations in the wave position scanning stage, and enter the network access stage after completion.

[0057] Specifically, for the satellite terminal side process, it enters the wave position scanning stage after power-on, and the process is as follows:

[0058] In the first step, the satellite terminal enters the wave position scanning time slot, and sequentially uses narrow beams to point to wave position directions 1, 2, 3, and 4 to send wave position synchronization signals for 1 wave position scanning time slot, a total of 4 wave position scanning time slots.

[0059] In the second step, the satellite terminal repeats the beam pointing in the first step, and sequentially receives wave position synchronization signals for 1 wave position scanning time slot, a total of 4 wave position scanning time slots. If a signal is captured in the i-th wave position scanning time slot, record the current wave position and the captured energy. In this embodiment, the satellite captures the synchronization signal of user terminal 1 at the f1 frequency point and c1 chip in the first wave position scanning time slot, captures the synchronization signal of user terminal 2 at the f2 frequency point and c2 chip in the first wave position scanning time slot, captures the synchronization signal of user terminal 3 at the f3 frequency point and c3 chip in the fourth wave position scanning time slot, and record the captured wave position i, where i = 1, 4 and the energy e_ij of the j-th capture at this wave position, where j = 1, 2, a total of 3 groups of captured signals are recorded, namely {{1, e_11}, {1, e_12}, {4, e_41}}.

[0060] In the third step, the satellite terminal enters the broadcast time slot and sorts the signal capture results {e_ij} during the search process in the second step in descending order according to the capture energy. If the number of signal captures N during the search process in the second step is greater than the maximum number of broadcast time slots, which is 4, the satellite terminal sequentially uses the narrow beam to point to the corresponding first 4 wave positions to send the broadcast message of 1 broadcast time slot, totaling 4 broadcast time slots. If the number of signal captures N during the search process in the second step is less than or equal to the maximum number of broadcast time slots, which is 4, the satellite terminal sequentially uses the narrow beam to point to the corresponding first N wave positions to send the broadcast message of 1 broadcast time slot and then silences for 4 - N broadcast time slots, totaling 4 broadcast time slots. The broadcast message contains the time synchronization information of the satellite. In this embodiment, it is assumed that the capture energy of user terminal 1 is the strongest, that of user terminal 2 is the second strongest, and that of user terminal 3 is the weakest, i.e., e_11 > e_12 > e_41. The satellite terminal sequentially uses the narrow beam to point to the 1st, 1st, and 4th wave positions to send the broadcast message of 1 broadcast time slot and then silences for 1 broadcast time slot, totaling 4 broadcast time slots.

[0061] In the fourth step, the satellite terminal enters the network access stage after the end of the 4th broadcast time slot in the third step.

[0062] For the process on the user terminal side, each ground user terminal to be networked enters the wave position scanning stage after power-on. The process is as follows:

[0063] In the first step, the user terminal enters the wave position scanning time slot and is in the state of synchronizing signal capture and listening, continuously listening for the synchronizing signal sent by the satellite terminal. If the synchronizing signal sent by the satellite terminal is never heard, the user terminal remains in the state of synchronizing signal capture and listening.

[0064] In the second step, if the user terminal captures the wave position synchronizing signal sent by the satellite terminal, it transfers to the wave position sending state after hearing the first wave position synchronizing signal sent by the satellite terminal and performs signal transmission according to the frequency and chip in the wave position scanning stage generated based on the initialization transmission parameters, which lasts for a total of 4 wave position scanning time slots. In this embodiment, user terminal 1 transfers to the sending state after hearing the synchronizing signal at the end of the 1st wave position scanning time slot of the satellite terminal and sends the synchronizing signal for 4 consecutive wave position scanning time slots using frequency f1 and chip c1. User terminal 2 transfers to the sending state after hearing the synchronizing signal at the end of the 1st wave position scanning time slot of the satellite terminal and sends the synchronizing signal for 4 consecutive wave position scanning time slots using frequency f2 and chip c2. User terminal 3 transfers to the sending state after hearing the synchronizing signal at the end of the 4th wave position scanning time slot of the satellite terminal and sends the synchronizing signal for 4 consecutive wave position scanning time slots using frequency f3 and chip c3.

[0065] In the third step, the user terminal enters the broadcast time slot and switches to the broadcast message listening state, continuously listening for the broadcast messages sent by the satellite terminal. If no broadcast message sent by the satellite terminal is received within the timeout period, it goes back to the first step; if a broadcast message sent by the satellite terminal is received within the timeout period, it synchronizes time with the satellite terminal according to the time synchronization information in the broadcast message and records the satellite broadcast time slot number Q of the received broadcast message. After the end of the 4th broadcast time slot of the satellite, it enters the network access phase simultaneously with the satellite terminal. In this embodiment, the user terminal 1 records the satellite broadcast time slot number of the received broadcast message as 1, the user terminal 2 records it as 2, and the user terminal 3 records it as 3.

[0066] Step S3: The satellite terminal and the user terminal perform the network access operation of the current round of user terminals and the operation of allocating user terminal transmission parameters in the service phase during the network access phase, and enter the service phase after completion.

[0067] Specifically, for the process on the satellite terminal side, the specific process of the satellite terminal in the network access phase is as follows:

[0068] In the first step, the satellite terminal enters the network access request time slot and is in the network access request listening state, continuously listening for the network access request information sent by the user terminal, a total of 4 network access request time slots. In the network access request listening state, the beam pointing order and direction of the satellite are the same as those in the broadcast time slot during the wave position scanning phase, and it calculates the wave position for communicating with the user when receiving the network access request message of the user terminal.

[0069] In the second step, the satellite terminal enters the network access response time slot and allocates network numbers and corresponding transmission parameters in the service phase to up to 4 user terminals allowed to access the network according to the network access request of the user terminal received in the first step. If the number X of network access request messages received during the listening process in the first step is greater than 4, it sequentially uses the narrow beam to point to the first 4 corresponding user wave position directions to send 1 network access response message in the network access response time slot, a total of 4 network access responses; if the number X of network access request messages received during the listening process in the first step is less than or equal to 4, it sequentially uses the narrow beam to point to the first X corresponding user wave position directions to send 1 network access response message in the network access response time slot and then silences 4 - X network access response time slots, a total of 4 network access response time slots. In this embodiment, according to the order of the network access requests of the user terminals received in the first step, the satellite terminal allocates network number 1 and sending service time slot 1 and receiving service time slot 2 to the user terminal 1, allocates network number 2 and sending service time slot 3 and receiving service time slot 4 to the user terminal 2, allocates network number 3 and sending service time slot 5 and receiving service time slot 6 to the user terminal 3, and sequentially uses the narrow beam to point to the 1st, 1st, and 4th wave position directions to send 1 network access response message in the network access response time slot and then silences 1 network access response time slot, a total of 4 network access response time slots.

[0070] In the third step, the satellite terminal enters the service phase after the end of the 4th access response time slot in the second step.

[0071] Regarding the user terminal side process, the specific process of the user terminal access phase is as follows:

[0072] In the first step, the user terminal enters the access request time slot and transmits signals according to the access phase frequency and chips generated by the initialization transmission parameters. After sending an access request message for 1 time slot in the Qth access request time slot of the satellite terminal, it switches to the listening state. In this embodiment, user terminal 1 switches to the listening state after sending an access request message for 1 time slot in the 1st access request time slot of the satellite terminal, user terminal 2 switches to the listening state after sending an access request message for 1 time slot in the 2nd access request time slot of the satellite terminal, and user terminal 3 switches to the listening state after sending an access request message for 1 time slot in the 3rd access request time slot of the satellite terminal.

[0073] In the second step, the user terminal enters the access response time slot after the end of the 4th access request time slot of the satellite terminal and continuously listens for the access response message from the satellite. If the access response message sent by the satellite terminal is not received within 4 access response time slots, it proceeds to the first step of the user terminal beam scanning phase; if the access response message sent by the satellite terminal is received within 4 access response time slots, it changes the corresponding network number according to the information in the access response message and configures the subsequent service transmission time slots at the same time as the satellite terminal enters the service phase after the end of the 4th access response time slot of the satellite. In this embodiment, user terminal 1 sets its own network number to 1, the service sending time slot to 1, and the service receiving time slot to 2 according to the information in the access response message, user terminal 2 sets its own network number to 2, the service sending time slot to 3, and the service receiving time slot to 4 according to the information in the access response message, and user terminal 3 sets its own network number to 3, the service sending time slot to 5, and the service receiving time slot to 6 according to the information in the access response message.

[0074] Step S4: The satellite terminal and the user terminal complete normal service communication for multiple access users in the service phase.

[0075] Specifically, regarding the satellite terminal side process, the specific process of the satellite terminal service phase is as follows:

[0076] In the first step, the satellite terminal enters the service time slot and conducts two-way communication with the user terminal according to the divided time slots, a total of 8 service time slots. In this embodiment, the satellite terminal sends service data in the 2nd, 4th, and 6th time slots and receives service data from user terminals 1, 2, and 3 in the 1st, 3rd, and 5th time slots respectively.

[0077] In the second step, the satellite terminal switches to the first step of the satellite beam scanning phase after the end of the 8th service time slot in the first step.

[0078] For the user terminal side process, the specific process in the user terminal service stage is as follows:

[0079] In the first step, the user terminal enters the service time slot and conducts two-way communication with the satellite terminal according to the divided time slots and transmission parameters. There are a total of 8 service time slots. In this embodiment, user terminal 1 sends service data in the 1st time slot and receives service data from the satellite terminal in the 2nd time slot. User terminal 2 sends service data in the 3rd time slot and receives service data from the satellite terminal in the 4th time slot. User terminal 3 sends service data in the 5th time slot and receives service data from the satellite terminal in the 6th time slot.

[0080] In the second step, after the end of the 8th service time slot in the first step, the user terminal switches to the listening state and waits until the end of the next satellite terminal network access stage, then switches back to the first step.

[0081] In summary, the present invention provides a multi-user access method applied to satellite-ground communication. Its scope of use is not only applicable to satellite-ground multi-user communication scenarios, but also applicable to other multi-user communication scenarios with a central service node. In addition, the multi-user access method disclosed in the present invention does not rely on the time synchronization between the satellite and the user terminal. This method not only realizes the narrow beam alignment of the satellite when the user accesses the network, increases the access distance of the user, but also improves the efficiency of multi-user network access, and is particularly suitable for multi-user fast access scenarios.

[0082] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0083] Although the content of the present invention has been introduced in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the present invention. After those skilled in the art have read the above content, various modifications and substitutions to the present invention will be obvious. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims

1. A multi-user access method applied to satellite-ground communication, characterized in that, The method is applied to a satellite terminal and a user terminal set on the ground. When the satellite terminal executes the method, the process includes a wave position scanning stage, an access network stage, and a service stage. When the user terminal executes the method, the process includes an initialization transmission parameter stage, the wave position scanning stage, the access network stage, and the service stage. The method includes: Step S1: The user terminal determines and generates transmission waveform parameters for its own use in the wave position scanning stage and the access network stage during the initialization transmission parameter stage. Step S2: The satellite terminal and the user terminal perform satellite narrow beam alignment and two-terminal time synchronization operations in the wave position scanning stage, and enter the access network stage after the operations are completed. Step S3: The satellite terminal and the user terminal perform the access network access operation of the current user terminal and the transmission parameter allocation operation of the user terminal in the service stage in the access network stage, and enter the service stage after the operations are completed. Step S4: The satellite terminal and the user terminal complete normal service communication for multiple access network users in the service stage. Among them, after the satellite terminal is powered on, it enters the wave position scanning stage. The steps for the satellite terminal to perform satellite narrow beam alignment and two-terminal time synchronization operations in step S2 include: Step S210: The satellite terminal enters a wave position scanning time slot, and according to the number of wave positions S in the coverage area, sequentially uses a narrow beam to point to different wave position directions to send a wave position synchronization signal for 1 wave position scanning time slot. Among them, the total number of wave position scanning time slots is S. Step S211: The satellite terminal repeats the beam pointing in step S210, sequentially receives a wave position synchronization signal for 1 wave position scanning time slot, and when a signal is captured in the i-th wave position scanning time slot, records the current wave position and the capture energy. Among them, the total number of wave position scanning time slots is S. Step S212: The satellite terminal enters a broadcast time slot, and according to the signal capture results in the search process of step S211, sorts them in descending order according to the capture energy. When the number of signal captures N in the search process of step S211 is greater than the maximum broadcast time slot number M, sequentially uses a narrow beam to point to the corresponding first M wave position directions to send a broadcast message for 1 broadcast time slot; when the number of signal captures N in the search process of step S211 is less than or equal to the maximum broadcast time slot number M, sequentially uses a narrow beam to point to the corresponding first N wave position directions to send a broadcast message for 1 broadcast time slot and then silences M - N broadcast time slots. Among them, the total number of broadcast time slots is M, and the broadcast message includes the time synchronization information of the satellite terminal. Step S213: After the M-th broadcast time slot in step S212 ends, the satellite terminal enters the access network stage.

2. The multi-user access method applied to satellite-ground communication according to claim 1, characterized in that, Step S1 includes: Step S11: Each user terminal to be accessed extracts its own typical information features. Step S12: Each user terminal to be accessed generates a random number seed according to the extracted information features. Step S13: Each user terminal to be networked generates the transmission waveform parameters used by itself in the wave position scanning stage and the network access stage according to the random number seed.

3. The multi-user access method applied to satellite-ground communication according to claim 2, wherein The transmission waveform parameters include: the frequency and chips used by the user terminal in the wave position scanning stage and the network access stage.

4. The multi-user access method applied to satellite-ground communication according to claim 3, characterized in that, After the user terminal is powered on, it enters the wave position scanning stage. The steps for the user terminal to perform satellite narrow beam alignment and two-terminal time synchronization operations in step S2 include: Step S220: The user terminal enters the wave position scanning time slot and is in the synchronization signal capture and listening state to continuously listen for the wave position synchronization signal sent by the satellite terminal. If the user terminal never hears the wave position synchronization signal sent by the satellite terminal, it remains in the wave position synchronization signal capture and listening state. Step S221: When the user terminal captures the wave position synchronization signal sent by the satellite terminal, it enters the wave position transmission state after hearing the first wave position synchronization signal sent by the satellite terminal, and performs signal transmission according to the transmission waveform parameters in the wave position scanning stage generated in the initialization transmission parameter stage, and continues for S wave position scanning time slots. Step S222: The user terminal enters the broadcast time slot and switches to the broadcast message listening state to continuously listen for the broadcast message sent by the satellite terminal. If it does not receive the broadcast message sent by the satellite terminal within the timeout period, it goes back to step S220. If it receives the broadcast message sent by the satellite terminal within the timeout period, it synchronizes time with the satellite terminal according to the time synchronization information in the broadcast message, records the satellite broadcast time slot number Q when the broadcast message is received, and enters the network access stage simultaneously with the satellite terminal after the Mth broadcast time slot of the satellite terminal ends.

5. The multi-user access method applied to satellite-ground communication according to claim 4, characterized in that, The execution steps of the satellite terminal in the network access stage specifically include: Step S310: The satellite terminal enters the network access request time slot and is in the network access request listening state to continuously listen for the network access request information sent by the user terminal. There are a total of M network access request time slots. In the network access request listening state, the beam pointing order and direction of the satellite terminal are the same as those in the broadcast time slot in the wave position scanning stage. When the satellite terminal receives the network access request message from the user terminal, it calculates the wave position for communicating with the user terminal. Step S311: The satellite terminal enters the access response time slot, and according to the user terminal access request received in step S310, allocates network numbers and corresponding service phase transmission parameters to at most Z user terminals allowed to access. When the number X of access request messages received during the listening process in step S310 is greater than Z, the satellite terminal sequentially uses narrow beams to point to the corresponding first Z user wave position directions and sends an access response message for 1 access response time slot. When the number X of access request messages received during the listening process in step S310 is less than or equal to Z, the satellite terminal sequentially uses narrow beams to point to the corresponding first X user wave position directions and sends an access response message for 1 access response time slot, and then silences Z - X access response time slots, where the total number of access response time slots is Z. Step S312: After the Zth access response time slot in step S311 ends, the satellite terminal enters the service phase.

6. The multi-user access method applied to satellite-ground communication according to claim 5, characterized in that, The steps executed by the user terminal during the access phase specifically include: Step S320: The user terminal enters the access request time slot, transmits a signal according to the access phase transmission waveform parameters generated based on the initialized transmission parameters, and after sending an access request message for 1 time slot in the Qth access request time slot of the satellite terminal, switches to the listening state. Step S321: After the Mth access request time slot of the satellite terminal ends, the user terminal enters the access response time slot and continuously listens for the access response message from the satellite terminal. When no access response message sent by the satellite terminal is received within Z access response time slots, the user terminal switches to step S220. When an access response message sent by the satellite terminal is received within Z access response time slots, the user terminal changes the corresponding network state according to the information in the access response message, configures subsequent service transmission parameters, and enters the service phase simultaneously with the satellite terminal after the Zth access response time slot of the satellite terminal ends.

7. The multi-user access method for satellite-ground communication according to claim 6, wherein The steps executed by the satellite terminal during the service phase specifically include: Step S410: The satellite terminal enters the service time slot and conducts two-way communication with the user terminal according to the divided time slots, where the total number of service time slots is C. Step S411: After the Cth service time slot in step S410 ends, the satellite terminal switches to step S210.

8. The multi-user access method applied to satellite-ground communication according to claim 7, characterized in that, The steps executed by the user terminal during the service phase specifically include: Step S420: The user terminal enters the service time slot and conducts two-way communication with the satellite terminal according to the divided time slots and transmission parameters, where the total number of service time slots is C. Step S421: After the Cth service time slot in step S420 ends, the user terminal switches to the listening state and waits for the next round. After the satellite terminal ends the access phase, the user terminal switches to step S420.

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