A method of simulating visibility for low earth orbit satellite communication systems

Abstract

The application provides a method for simulating the visibility of a low-orbit satellite communication system, and belongs to the technical field of satellite mobile communication simulation systems.The method comprises the following steps: calculating the visibility of satellites and terminals at different time according to ephemeris, and pushing the visibility relationship between random and business beam ground TAC and terminals to each satellite-based station in a period T; determining a broadcast message according to the obtained random visibility start time T0 and terminals covered by each wave position, and generating a plurality of SFAPI messages; sending a msg1 on the random beam uplink message by a terminal, and calculating the terminal position information by a satellite-based station to determine the visibility relationship between the business beam and the terminal; filling the number k of terminals by the satellite-based station, generating an SFAPI message for each terminal, and sending the SFAPI message to the terminal. The application simulates the beam and terminal coverage of the real satellite-based station in the simulation system, and solves the problem that the ground simulation system cannot simulate the space coverage.

Description

Technical Field

[0001] This invention relates to the field of satellite mobile communication simulation system technology, and in particular to a method for simulating the visibility of low-Earth orbit satellite communication systems. Background Technology

[0002] With the rapid development of satellite internet, the number of satellite communication systems and satellites in orbit is also increasing. Satellite on-orbit maintenance requires verification and validation through ground-based simulation systems. Previously, this was often achieved by constructing a semi-physical simulation system on the ground to confirm the impact of upgrades or software patches on the original system's functionalities and to verify system functionality and individual modules. However, current satellite internet systems are evolving from on-board transparency to on-board processing, requiring ground-based simulation models to realistically simulate the satellite-to-ground communication timing and link status of on-orbit satellite communication systems. By performing 1:1 simulations of network elements such as satellites, stations, and terminals, the simulations can reproduce, synchronize, and extrapolate network status, enabling functions such as satellite communication payload status interpretation and prediction, decision support optimization, and mission extrapolation. Furthermore, these simulations must possess protocol consistency verification capabilities and the ability to verify complex business scenarios.

[0003] Because it is difficult to completely replicate the on-orbit state in terms of hardware and environment, the testing and verification using a semi-physical simulation system has shown significant limitations in terms of operating orbit, satellite attitude, and system operating modes. Specifically, the semi-physical environment cannot fully reproduce the state of thousands of real satellites in orbit on a system scale, nor can it reproduce the dynamic link states such as link delays and bit errors caused by satellite-to-ground motion.

[0004] Furthermore, in scenarios involving rapid movement of low-Earth orbit (LEO) satellites, to address the challenge of efficient dynamic resource scheduling when available communication resources are limited while service demands dynamically change, a beam-hopping access scheme combining wide-beamwidth LEO satellites and dynamic point beams is required. Each satellite transmits both a random beam and a service beam, with the random beam assisting the service beam in providing on-demand beam-hopping services to users. However, a semi-physical environment cannot simulate the timing relationship of coverage between the random beam and the service beam for satellite terminals, hindering the coordinated troubleshooting and location of on-orbit issues. Summary of the Invention

[0005] In view of this, the present invention proposes a method for simulating the visibility of low-Earth orbit satellite communication systems, which can simulate the beam and terminal coverage of on-orbit satellite base stations.

[0006] The technical solution adopted in this invention is as follows:

[0007] A method for simulating the visibility of low-Earth orbit satellite communication systems, simulating the beam and terminal coverage of on-orbit satellite base stations.

[0008] A method for simulating the visibility of low-Earth orbit satellite communication systems includes the following steps:

[0009] Step 1: Divide the service beam positions according to the fixed ground grid; divide the random beam positions according to the satellite coverage area. The random beam position scanning order is to scan in ascending order along the opposite direction of satellite movement. The random beam position index arrangement and scanning order are consistent.

[0010] Step 2: Calculate the visibility between the satellite and the terminal at different times based on the ephemeris, and provide the terminal location, satellite-to-ground delay, and visibility timing relationship to all satellite-based base stations; where visibility includes overall satellite visibility, on-the-go visibility, and service visibility.

[0011] Step 3: The satellite base station schedules the random beam to cover beam position 0 at time T0, and sends an IP packet containing a synchronization block to the first terminal UE0 and the last terminal UE500 in the coverage area. The synchronization block is filled with the timestamp T0.

[0012] Step 4: Add the signal quality of the synchronization block to the link simulator and calculate the air interface transmission delay Tdelay based on the satellite-to-ground distance; determine the link simulator delay duration based on the timestamp T0, Tdelay, and the current system time Tcur: Td = Tdelay - (Tcur - T0);

[0013] Step 5: Terminals UE0 and UE500 receive synchronization blocks at time T0+Tdelay, sort the signal quality of the received synchronization blocks from multiple adjacent satellite base stations, and select the satellite with the strongest signal quality, SatID1, for access according to the cell selection criteria; calculate the uplink transmission time T1, and terminals UE0 and UE500 transmit the preamble signal Msg1 at time T1, and transmit the preamble signal Msg2 at time T2 when the random beam scans back to wave position 0;

[0014] Step 6: Terminals UE0 and UE500 receive a random access response, including the time offset information of the synchronization block and the SFN offset information Ty.

[0015] Step 7: At time Ty0=T2+Ty, the satellite base station schedules the service beam to cover the 0 position again, and sends an IP packet containing a system information block to the first terminal UE0 and the last terminal UE500 in the coverage area. The link simulator adds channel physical parameters and time delay parameters, and forwards the IP packets to terminal UE0 and terminal UE500.

[0016] Step 8: Terminals UE0 and UE500 receive the service beam broadcast at time T4 = Ty0 + Tdelay, and send uplink Msg1 at time T5, where T5 = T4 + uplink / downlink offset - uplink advance transmission time. The satellite base station receives Msg1 at time T5_N = T5 + Tdelay. After the service beam is rescanned to beam position 0, terminals UE0 and UE500 receive the random access response of the service beam, and then send a random access request message msg3 uplink in the service beam.

[0017] Step 9: The satellite-borne base station sends a connection establishment acceptance message Msg4;

[0018] Step 10: Terminals UE0 and UE500 receive msg4 in the downlink of the service beam, and terminals UE0 and UE500 successfully join the network.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] This invention simulates the random access coverage of on-orbit satellite base stations and service beams at terminals in a simulation system. During service operations, data communication is implemented according to the beam coverage pattern caused by real-time beam hopping and satellite motion, thus solving the problem that ground simulation systems cannot simulate on-orbit space coverage. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of an application scenario of a simulated satellite mobile communication system in an embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram of the principle of the present invention based on service beam hopping.

[0023] Figure 3 This is a service flow diagram based on service beam hopping of the present invention. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to the accompanying drawings.

[0025] A method for simulating the visibility of low-Earth orbit satellite communication systems, such as Figure 1 As shown, it is based on a satellite mobile communication simulation system consisting of 1200 satellite terminals, 5 onboard base stations, 1 link simulator, 1 operation and control system, and 1 visibility computing module.

[0026] The method includes: the operation and control system configuring information such as satellite ephemeris orbital parameters, satellite beam service TAC grid, and satellite terminal UEID (UEIP+PORT) to the visibility calculation module; the visibility calculation module calculates the visibility of the satellite and the terminal at different times based on the ephemeris, and pushes the visibility relationship between the ground TAC of the random and service beams and the terminal to each satellite-based base station at a period T; the satellite-based base station determines the SSB, SIB1, and other information of the broadcast message based on the start time T0 of obtaining random visibility and the terminals covered by each beam position, generates multiple SFAPI messages, and fills the received UEID in the header of each SFAPI message packet and sends it to the target terminal IP; the terminal sends msg1 in the uplink message of the random beam, the satellite-based base station calculates the terminal location information, and determines the visibility relationship between the service beam and the terminal by combining it with the beam position information of the service beam coverage area; when the satellite-based base station sends scheduling data, it fills in the number k of terminals scheduled in that time slot, generates an SFAPI message for each terminal, generates k IP packets and sends them to the terminal.

[0027] Here are more specific examples:

[0028] Example 1:

[0029] A method for simulating the visibility of low-Earth orbit satellite communication systems includes the following steps:

[0030] (1) The visibility calculation module calculates the satellite and terminal visibility at different times based on the ephemeris and provides relevant information such as terminal location, satellite-to-ground delay, and visibility timing relationship to all satellite-borne base stations.

[0031] Overall satellite visibility: All terminals covered by this satellite within a certain period T.

[0032] Visibility in Anywhere: The allocation of positions for the Anywhere Beam differs from that of the Service Beam. While Service Beams use a fixed ground grid for position allocation, Anywhere Beam positions are allocated based on satellite coverage. The positions maintain a fixed relationship with the satellite coverage area and coordinate system, and are divided into 500 positions based on satellite orbital altitude. Position scanning proceeds in ascending order in the opposite direction of satellite motion. The position index arrangement and scanning order remain consistent, i.e., from position 1 to 500, scanning sequentially within a period T. The Anywhere Beam covers the terminals corresponding to each position. Terminals are numbered from 0 based on the total number of users (1200), and are configured with corresponding IP addresses and ports for identification. The first terminal is identified as UE0, the 501st terminal as UE500.

[0033] (SatID, Tstart, T, beamtype1, wave 0, UE0, wave 3, UE1, UE2...)

[0034] Service visibility: With a service beamwidth of 3.5° and a nadir beamwidth of 3.5°, the coverage area radius is 35.9 km. Dividing the ground into grids based on this, the grid side length is 50.7 km, thus defining TAC (Traffic Access Control) areas on the Earth's surface. The area covered by one service beam at one time for one TAC grid is one-quarter of the coverage area of ​​any random beam. Within a certain period T, the terminals corresponding to all service beam positions and TACs covered by each service beam are defined.

[0035] (SatID, Tstart, T, beamtype2, TAC0, UE0, TAC5, UE1, UE2...);

[0036] (2) The satellite base station starts scanning from position 0 at time T0, sends SSB (Synchronization Signal Block), fills in the timestamp T0, schedules the satellite base station to cover position 0 where UE0 and UE500 are located, and sends two IP packets containing broadcast information SSB to UE0 and UE500.

[0037] The link simulator module adds SSB signal quality. Based on the satellite-to-ground distance (assuming 900 km), the air interface transmission delay Tdelay = 3ms is calculated. Based on the timestamp T0, Tdelay, and the current system time Tcur, the link simulator delay duration is determined as: Td = Tdelay - (Tcur - T0).

[0038] (3) At time T0+Tdelay, UE0 receives SSB and selects SatID1 with strong signal quality based on the quality ranking of multiple adjacent satellite base station SSB signals and the cell selection criteria. Considering the 40ms delay difference between the uplink and downlink beams, the uplink transmission time T1 is calculated as T0+40ms(uplink / downlink offset)-Tdelay. UE0 transmits the preamble signal, msg1, within the time period of uplink random beam position 0. The random beam stays for 5ms per position, scans 500 positions, and calculates T2=T0+2.5s. The random beam then rescans to position 0 and transmits Msg2.

[0039] At time T3 = T2 + Tdelay = T0 + 2.5s + 3ms, UE0 receives a random access response (Msg2 RAR). This response contains time-frequency information about the service beam, primarily including the SSB time offset and SFN offset information Ty (assuming Ty = 10 and SFN = 0.1s).

[0040] (4) At the time Ty0=T2+Ty=T0+2.5s+Ty=T0+2.6s, the base station schedules the service beam to cover UE0, and UE500 is located at position 0. Two IP packets containing broadcast information SIB1 are sent to UE0 and UE500. The link simulator module adds channel physical parameters and time delay parameters and forwards them to UE0 and UE500;

[0041] (5) At time T4 = Ty0 + Tdelay = T0 + 2.5s + Ty + Tdelay = T0 + 2.603s, UE0 receives the service beam broadcast. According to the service beam time-frequency information and SatID1 provided by Msg2, at time T5, UE0 sends uplink Msg1 in the service beam. T5 = T4 + 10ms (uplink / downlink offset) - T_TA (uplink advance transmission time) = T0 + 2.607s. At time T5_N = T5 + Tdelay = T0 + 2.610s, the base station receives Msg1. At time T6 = Ty0 + x1 * 20ms = T0 + 2.6s + 20ms (SFN = 262, slot0), the service beam is rescanned to position 0. At time T6u = T6 + Tdelay = 2.623s, UE0 receives the service beam Msg2RAR. At time T7=T6u+K2=T0+2.624s (SFN=262, slot32), UE0 sends a random access request message msg3 in the uplink of the service beam;

[0042] (6) At the time T8=T6+X2*20ms=T6+20ms=T0+2.64s, the base station sends the connection establishment acceptance message Msg4;

[0043] (7) At time T9=T8+Tdelay=T0+2.643s, UE0 receives msg4 in the downlink of the service beam, and the terminal successfully joins the network.

[0044] Example 2:

[0045] A method for simulating the visibility of a low-Earth orbit (LEO) satellite communication system is presented. This method uses multiple servers to simulate a digital satellite mobile communication system comprising five onboard base stations and 1200 satellite terminals. By adding a visibility calculation module to the communication system, the beam and terminal coverage of real onboard base stations in orbit are simulated, solving the problem that ground-based simulation systems cannot simulate on-orbit space coverage. The method includes the following steps:

[0046] (1) The visibility calculation module calculates the satellite and terminal visibility at different times based on the ephemeris and provides relevant information such as terminal location, satellite-to-ground delay, and visibility timing relationship to all satellite-borne base stations.

[0047] Overall satellite visibility: All terminals covered by this satellite within a certain period T=2.5s / 5s / 10s.

[0048] Visibility in any situation: Within a certain period T=2.5s / 5s / 10s, the in any situation beam covers the terminal corresponding to each wave position.

[0049] (SatID, Tstart, T, beamtype1, wave position 0, UE0, wave position 3, UE1, UE2...)

[0050] Service visibility: Within a certain period T=2.5s / 5s / 10s, the terminals corresponding to all service beam positions (TACs) covered by each service beam.

[0051] (SatID, Tstart, T, beamtype2 TAC 0, UE0, TAC 5, UE1, UE2...);

[0052] (2) When the satellite-borne base station detects position 0 in the random beam at time T0, it sends an SSB, fills in the timestamp T0, and schedules the random beam to cover position 0 where UE0 and UE500 are located. It sends two IP packets containing broadcast information SIB1 to UE0 and UE500.

[0053] The link simulator module adds SSB1 signal quality. Based on the satellite-to-ground distance (assuming 900 km), the air interface transmission delay Tdelay = 3ms is calculated. Based on the timestamp T0, Tdelay, and the current system time Tcur, the channel simulator delay duration is determined: Td = Tdelay - (Tcur - T0).

[0054] (3) At time T0+Tdelay, UE0 receives SSB1 and selects Sat1ID for access based on the quality ranking of the received SSB signals and the cell selection criteria. At time T1=T0+40ms-Tdelay, UE0 sends a Preamble, i.e., msg1, during the uplink random beam position 0 time period. At time T2=T0+2.5s, the random beam is rescanned to position 0 and Msg2 is sent. At time T3=T2+Tdelay=T0+2.5s+3ms, UE0 receives Msg2 RAR. It contains the time and frequency information of the service beam, mainly including the SSB time offset information and SFN offset information Ty (assuming Ty=10SFN=0.1s);

[0055] (4) At the time Ty0=T2+Ty=T0+2.5s+Ty=T0+2.6s, the base station schedules the service beam to cover UE0, and UE500 is located at position 0. Two IP packets containing broadcast information SIB1 are sent to UE0 and UE500. The link simulator module adds channel physical parameters and delay, and forwards them to UE0 and UE500;

[0056] (5) At time T4 = Ty0 + Tdelay = T0 + 2.5s + Ty + Tdelay = T0 + 2.603s, UE0 receives the service beam broadcast. Based on the service beam time-frequency information and SatID provided by Msg2, at time T5 = T4 + 10ms (uplink / downlink offset) - T_TA = T0 + 2.607s, UE0 sends uplink Msg1 in the service beam. At time T5_N = T5 + Tdelay = T0 + 2.610s, the base station receives Msg1. At time T6 = Ty0 + x1 * 20ms = T0 + 2.6s + 20ms (SFN = 262, slot 0), the service beam is rescanned to position 0. At time T6u = T6 + Tdelay = 2.623s, UE0 receives the service beam Msg2 RAR.

[0057] At time T7=T6u+K2=T0+2.624s (SFN=262, slot32), UE0 sends msg3 in the uplink of the service beam;

[0058] (6) At time T8=T6+X2*20ms=T6+20ms=T0+2.64s, the base station sends Msg4;

[0059] (7) At time T9=T8+Tdelay=T0+2.643s, UE0 receives msg4 in the downlink of the service beam, and the terminal successfully joins the network.

[0060] Example 3:

[0061] A method for simulating the visibility of low-Earth orbit satellite communication systems includes the following steps:

[0062] (1) The visibility calculation module calculates the satellite and terminal visibility at different times based on the ephemeris and provides relevant information such as terminal location, satellite-to-ground delay, and visibility timing relationship to all satellite-borne base stations.

[0063] Overall satellite visibility: All terminals covered by this satellite within a certain period T=2.5s / 5s / 10s.

[0064] Visibility in any situation: Within a certain period T=2.5s / 5s / 10s, the in any situation beam covers the terminal corresponding to each wave position.

[0065] (SatID, Tstart, T, beamtype1, wave position 0, UE0, wave position 3, UE1, UE2...)

[0066] Service visibility: Within a certain period T=2.5s / 5s / 10s, the terminals corresponding to all service beam positions (TACs) covered by each service beam.

[0067] (SatID, Tstart, T, beamtype2 TAC 0, UE0, TAC 5, UE1, UE2...);

[0068] (2) When the satellite-borne base station detects position 0 in the random beam at time T0, it sends an SSB, fills in the timestamp T0, and schedules the random beam to cover UE0, where UE500 is located in position 0. UE500 sends two IP packets containing broadcast information SIB1.

[0069] The link simulator module adds SSB1 signal quality. Based on the satellite-to-ground distance (assuming 900 km), the air interface transmission delay Tdelay = 3ms is calculated. Based on the timestamp T0, Tdelay, and the current system time Tcur, the channel simulator delay duration is determined: Td = Tdelay - (Tcur - T0).

[0070] (3) At time T0+Tdelay, UE0 receives SSB1 and selects Sat1ID for access based on the quality ranking of the received SSB signals and the cell selection criteria. At time T1=T0+40ms-Tdelay, UE0 sends a Preamble, i.e., msg1, during the uplink random beam position 0 time period. At time T2=T0+2.5s, the random beam rescans to position 0 and sends Msg2. At time T3=T2+Tdelay=T0+2.5s+3ms, UE0 receives Msg2 RAR. It contains the time and frequency information of the service beam, mainly including the SSB time offset information and SFN offset information Ty (assuming Ty=10SFN=0.1s);

[0071] (4) At the time Ty0=T2+Ty=T0+2.5s++Ty=T0+2.6s, the base station schedules the service beam to cover UE0, and the wave position of UE500 is 0. Two IP packets containing broadcast information SIB1 are sent to UE0 and UE500. The link simulator module adds channel physical parameters and delay, and forwards them to UE0 and UE500;

[0072] (5) At time T4 = Ty0 + Tdelay = T0 + 2.5s + Ty + Tdelay = T0 + 2.603s, UE0 receives the service beam broadcast. Based on the service beam time-frequency information and SatID provided by Msg2, at time T5 = T4 + 10ms (uplink / downlink offset) - T_TA = T0 + 2.607s, UE0 sends uplink Msg1 in the service beam. At time T5_N = T5 + Tdelay = T0 + 2.610s, the base station receives Msg1. At time T6 = Ty0 + x1 * 20ms = T0 + 2.6s + 20ms (SFN = 262, slot 0), the service beam is rescanned to position 0. At time T6u = T6 + Tdelay = 2.623s, UE0 receives the service beam Msg2 RAR.

[0073] At time T7=T6u+K2=T0+2.624s (SFN=262, slot32), UE0 sends msg3 in the uplink of the service beam;

[0074] (6) At time T8=T6+X2*20ms=T6+20ms=T0+2.64s, the base station sends Msg4;

[0075] (7) At time T9=T8+Tdelay=T0+2.643s, UE0 receives msg4 in the downlink of the service beam, and the terminal successfully joins the network.

[0076] To implement the above method, a simulated satellite mobile communication system is provided. Figure 1 This is a schematic diagram of an application scenario simulating a satellite mobile communication system. The satellite mobile communication system includes a satellite terminal, a link simulator, an onboard base station, an operation and control system, and a visibility computing module.

[0077] Figure 2 This is a system configuration flowchart, including the following steps:

[0078] (1) The operation control system sends the terminal location information to the terminal model;

[0079] (2) The operation control system sends all terminal information (location, UEID, UEIP) to the visibility module.

[0080] (3) The operation control system sends the beam position configuration information of the random beam to the satellite base station through the SC1 interface;

[0081] (4) The satellite base station sends the beam position configuration information of the satellite's random beam to the visibility module;

[0082] (5) The onboard base station sends the scanning start time of the random beam to the visibility module;

[0083] (6) The visibility module calculates the beam position visibility information based on the terminal information and the beam position information of the random beam;

[0084] (7) The visibility module sends visibility information through the wireless link module, including beam type, beam ID or TAC grid number ID, and the corresponding UEID list;

[0085] (8) The operation control system sends all terminal information (UEID, latitude and longitude) and satellite information (satID, beamIndex0-7 and satIP0, SatIP7) to the wireless link module control module through the interface; beamIndex 0: random beam, beamIndex1-7: service beams 1-7. SatIP0: random beam IP, SatIP1-SatIP7: IP corresponding to service beams 1-7;

[0086] (9) The operation control system sends the attitude and orbit control information of each satellite to the wireless link module master control module through the interface;

[0087] (10) The link simulator sends satellite information visible to the terminal to the terminal through the interface.

[0088] Figure 3 This is a flowchart of the random access process for satellite terminals in both random and service beams, including the following steps:

[0089] (1) The operation and control system distributes the ephemeris information, satellite terminal ID, and IP information of all satellites in the constellation to each satellite terminal and the visibility calculation module. The satellite terminal will calculate the satellite coverage based on this information and receive the SSB signal of the corresponding satellite base station at the corresponding time according to the coverage relationship, thereby initiating the service.

[0090] (2) The visibility calculation module calculates the visibility time of the satellite terminal to the satellite base station based on the encounter beam and service beam of the satellite base station, and forms a constellation coverage table for a period of time, which is then distributed to the satellite base station and the link simulator.

[0091] (3) At time T0 (SFN=0, slot 0), the random beam scans to position 0 and sends SSB. The base station fills in the timestamp T0. The base station schedules the random beam to cover position 0 where UE0 and UE500 are located and sends two IP packets (containing the broadcast SFAPI-N message) to UE0 and UE500.

[0092] (4) The link simulator determines the forwarding time based on the ephemeris and wave number to cover UE0, and forwards the IP packet to UE0 and UE500 according to the destination address;

[0093] (5) The UE selects a satellite for access based on the quality of the SSB signal received and sends PRACH at uplink bit 0;

[0094] (6) The link simulator receives PRACH information, buffers uplink data, and transmits it to the satellite base station at the corresponding time of beam 0;

[0095] (7) The satellite terminal receives the RAR message cached by the link simulator at time T3, and switches to the SSB search and access of the service beam according to the message instruction;

[0096] (8) The satellite base station schedules the service beam to provide SSB signal coverage for the satellite terminal at position 0. The base station fills in the timestamp T0 and sends two IP packets containing broadcast information SIB1 to UE0 and UE500. The link simulator module adds SSB signal quality. Based on the satellite-to-ground distance (assuming 900 km), the air interface transmission delay Tdelay = 3ms is calculated, and based on the timestamp T0, Tdelay, and the current system time Tcur, the channel simulator delay duration is determined: Td = Tdelay - (Tcur - T0);

[0097] (9) At time T4=Ty0+Tdelay=T0+2.5s+Ty+Tdelay=T0+2.603s, UE0 and UE500 receive service beam broadcasts. Based on the service beam time-frequency information and SatID provided by Msg2, they determine whether it is a message that this terminal should receive and complete downlink synchronization. The broadcast is received according to the SSB signal quality sorting and content selection of SatId for access.

[0098] (10) The UE sends MSG1 during the uplink beam coverage time and accesses the service beam; T5=T4+10ms(uplink / downlink offset)-T_TA=T0+2.607s, UE0 sends uplink Msg1 in the service beam according to the service beam time and frequency information and SatID provided by the random Msg2.

[0099] (11) At time T6=T5+Tdelay=T0+2.610s, the base station receives Msg1.

[0100] (12) At time T6u=T6+Tdelay=2.623s, UE0 receives the service beam Msg2 RAR.

[0101] (13) At time T7=T6u+K2=T0+2.624s (SFN=262, slot32), UE0 sends msg3 uplink in the service beam;

[0102] (14) At time T8=T6+X2*20ms=T6+20ms=T0+2.64s, the base station sends Msg4;

[0103] (15) UE0 receives msg4 downlink and sends MSG5 uplink in the service beam, and the terminal successfully joins the network.

[0104] In summary, this invention simulates the beam and terminal coverage of a real on-orbit satellite base station in a simulation system, making it particularly suitable for satellite mobile communication systems. It verifies the system protocol process, completes the construction of a general model for broadband satellite base stations, and possesses high-level protocol stack functions, physical layer adaptation functions, and simulation functions for random beams and service beams. It enables end-to-end simulation verification under different service scenarios and evaluates and verifies process strategies in complex scenarios to support the construction of satellite internet systems.

Claims

1. A method for simulating the visibility of low-Earth orbit satellite communication systems, characterized in that, Simulate the beam and terminal coverage of an on-orbit satellite-borne base station.

2. A method for simulating the visibility of low-Earth orbit satellite communication systems, characterized in that, Includes the following steps: Step 1: Divide the service beam positions according to the fixed ground grid; divide the random beam positions according to the satellite coverage area. The random beam position scanning order is to scan in ascending order along the opposite direction of satellite movement. The random beam position index arrangement and scanning order are consistent. Step 2: Calculate the visibility between the satellite and the terminal at different times based on the ephemeris, and provide the terminal location, satellite-to-ground delay, and visibility timing relationship to all satellite-based base stations; where visibility includes overall satellite visibility, on-the-go visibility, and service visibility. Step 3: The satellite base station schedules the random beam to cover beam position 0 at time T0, and sends an IP packet containing a synchronization block to the first terminal UE0 and the last terminal UE500 in the coverage area. The synchronization block is filled with the timestamp T0. Step 4: Add the signal quality of the synchronization block to the link simulator, and calculate the air interface transmission delay Tdelay based on the satellite-to-ground distance; determine the link simulator delay duration based on the timestamp T0, Tdelay, and the current system time Tcur: Td = Tdelay - (Tcur - T0); Step 5: Terminals UE0 and UE500 receive synchronization blocks at time T0+Tdelay, sort the signal quality of the received synchronization blocks from multiple adjacent satellite base stations, and select the satellite with the strongest signal quality, SatID1, for access according to the cell selection criteria; calculate the uplink transmission time T1, and terminals UE0 and UE500 transmit the preamble signal Msg1 at time T1, and transmit the preamble signal Msg2 at time T2 when the random beam scans back to wave position 0; Step 6: Terminals UE0 and UE500 receive a random access response, including the time offset information of the synchronization block and the SFN offset information Ty. Step 7: At time Ty0=T2+Ty, the satellite base station schedules the service beam to cover the 0 position again, and sends an IP packet containing a system information block to the first terminal UE0 and the last terminal UE500 in the coverage area. The link simulator adds channel physical parameters and time delay parameters, and forwards the IP packets to terminal UE0 and terminal UE500. Step 8: Terminals UE0 and UE500 receive the service beam broadcast at time T4 = Ty0 + Tdelay, and send uplink Msg1 at time T5, where T5 = T4 + uplink / downlink offset - uplink advance transmission time. The satellite base station receives Msg1 at time T5_N = T5 + Tdelay. After the service beam is rescanned to beam position 0, terminals UE0 and UE500 receive the random access response of the service beam, and then send a random access request message msg3 uplink in the service beam. Step 9: The satellite-borne base station sends a connection establishment acceptance message Msg4; Step 10: Terminals UE0 and UE500 receive msg4 in the downlink of the service beam, and terminals UE0 and UE500 successfully join the network.

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