System model construction method and system simulation method for low earth orbit constellation system

Abstract

The application provides a low-orbit constellation system-oriented system model construction method and system simulation method, and belongs to the field of low-orbit constellation system simulation and performance evaluation.The construction method performs lightweight simulation modeling on functional entities of a space section, a ground section, an application section and an environment section, the model constructed by the space section comprises a constellation configuration model, an attitude and orbit control subsystem model and a satellite payload model, the ground section comprises a main gateway station model and a secondary gateway station model, a large-scale terminal model is constructed in the application section, the environment section comprises a satellite-ground microwave channel submodel and an inter-satellite laser channel submodel, and model interaction design is performed to form an integrated model architecture of satellite-ground integration.The application guarantees the modeling accuracy of functional entities, simultaneously meets the lightweight demand of simulation modeling, reduces the complexity of system modeling, balances the relationship between model accuracy and lightweight, and simulates, verifies and evaluates the correctness, rationality and effectiveness of the architecture design of the constellation system.

Description

Technical Field

[0001] This invention belongs to the field of low-Earth orbit constellation system system simulation and performance evaluation, specifically involving a system model construction method and system simulation method for low-Earth orbit constellation systems. Background Technology

[0002] In the field of satellite communications, low-Earth orbit (LEO) constellation systems offer significantly higher communication capacity and much lower latency compared to traditional communication satellites. LEO constellation systems consist of near-polar orbit satellites, inclined orbit satellites, and ground support systems, and are integrated with terrestrial 5G systems. They are characterized by high integration, high performance, and high complexity, and are currently mostly in the planning stage. The sheer scale and technical complexity of LEO constellation systems bring numerous unforeseen challenges to planning and feasibility studies, system development, and on-orbit management. Summary of the Invention

[0003] In view of the above-mentioned defects or deficiencies in the prior art, the present invention aims to provide a system model construction method and system simulation method for low-Earth orbit constellation systems. Based on distributed simulation, lightweight model design is carried out for the space segment, ground segment, application segment and environment segment of the low-Earth orbit constellation system, respectively. The inter-satellite laser alignment, system operating efficiency and communication evaluation indicators are evaluated, and the complex interaction process of the satellite-ground interface is simulated and verified, thereby improving the accuracy and reliability of the simulation.

[0004] To achieve the above objectives, the embodiments of the present invention adopt the following technical solutions:

[0005] In a first aspect, embodiments of the present invention provide a method for constructing a system model for low-Earth orbit constellation systems, the method comprising:

[0006] The low-Earth orbit constellation system is divided into a space segment, a ground segment, an application segment, and an environmental segment.

[0007] Lightweight modeling is performed on the space segment, which includes a constellation configuration model, an attitude and orbit control subsystem model, and a satellite payload model. During simulation, the constellation configuration model generates constellation topology and initial orbital attitude values ​​based on the constellation configuration design, and sends them to the satellite payload model and the attitude and orbit control subsystem model, respectively. The attitude and orbit control subsystem model performs orbit and attitude calculations based on orbit and attitude parameters, and sends the orbit and attitude data to the satellite payload model and the constellation configuration model. The satellite payload model implements satellite-to-ground and inter-satellite beamforming functions, service and signaling link analysis functions, network access and link establishment signaling processing functions, radio resource allocation functions, and inter-satellite routing and switching functions.

[0008] Lightweight modeling is performed on the ground segment, which includes a primary gateway station model and a secondary gateway station model. During simulation, both the primary and secondary gateway station models implement access network functions, while the primary gateway station model also implements core network functions. The access network implements the signal transmission and reception functions of the power supply link, and the core network implements the terminal registration and authentication functions.

[0009] Lightweight modeling is performed on the application segment, and a large-scale terminal model is built in the application segment. During simulation, the application segment model completes beam selection, visibility analysis, service data generation, data transmission and reception, and signaling processing functions.

[0010] The environmental segment is modeled in a lightweight manner. The environmental segment model includes a satellite-to-ground microwave channel sub-model and an inter-satellite laser channel sub-model. When performing simulations, the satellite-to-ground channel sub-model considers free space loss, Doppler effect, noise, atmospheric, rain, snow, cloud and fog loss, while the inter-satellite channel sub-model considers the impact of solar interference on the laser link.

[0011] In a preferred embodiment of the present invention, when lightweight modeling the space segment, ground segment, application segment, and environment segment, the following model interaction design is performed: the constellation configuration model, large-scale terminal model, and primary / secondary gateway station model interact with the satellite-to-ground microwave channel sub-model and the inter-satellite laser channel sub-model respectively through data middleware to exchange service information and signaling information; during instantiation, only one satellite-to-ground microwave channel sub-model and one inter-satellite laser channel sub-model are instantiated, and the data of all constellation configuration models, terminal models, and primary / secondary gateway station models are concentrated in one channel model for interaction, reducing the cross-transmission of information between constellation configuration models and large-scale terminal models; service information and signaling information are forwarded through the receiving and transmitting antenna models of various entities and transmitted using unified simplified IP data packets, realizing simplified processing of complex interfaces between models and facilitating data interaction between models.

[0012] In a preferred embodiment of the present invention, the inter-satellite topology generated by the constellation configuration model is described by a two-dimensional table, where "1" represents that there is an inter-satellite connection between satellites and "0" represents that there is no inter-satellite connection between satellites. The constellation configuration model calculates the initial values ​​of the six orbital elements and the initial values ​​of the attitude parameters of each satellite in the constellation based on the constellation configuration parameters, and uploads the data.

[0013] In a preferred embodiment of the present invention, the attitude and orbit control subsystem model includes an attitude dynamics submodel, an orbit dynamics submodel, and an onboard guidance, navigation, and control (GNC) submodel; wherein...

[0014] The orbital dynamics sub-model consists of an ideal orbital model and an HPOP high-precision orbital model. The ideal orbital model does not consider the influence of other external disturbance forces. The HPOP high-precision orbital model considers the thruster control force model, the Earth's non-spherical perturbation model, the atmospheric drag perturbation model, the solar and lunar gravitational perturbation model, and the solar radiation pressure perturbation model.

[0015] The attitude dynamics sub-model consists of an internal control torque model and an external disturbance model. The internal control torque model considers a flywheel model, a magnetic torque generator model, and a thruster model, while the external disturbance model considers a gravity gradient torque model, a solar radiation torque model, an aerodynamic torque model, and a geomagnetic torque model.

[0016] The onboard GNC control sub-model calculates key parameters for satellite attitude control, pointing control, and orbit control based on orbit and attitude data input from the orbit dynamics sub-model and attitude dynamics sub-model. It then feeds back the calculated control force to the orbit dynamics sub-model for satellite orbit adjustment and the control torque to the attitude dynamics sub-model for satellite attitude adjustment.

[0017] In a preferred embodiment of the present invention, the satellite payload model includes a narrowband mobile communication payload, a broadband integrated communication payload, an airborne surveillance payload, a power supply payload, a laser inter-satellite link payload, a payload integration processor, and a beacon payload sub-model; wherein...

[0018] The narrowband mobile communication payload includes:

[0019] A multi-beam receiving antenna model is used to complete wireless signal reception, and has functions such as beam coverage, frequency division multiplexing, beam shutdown, and power and frequency resource allocation.

[0020] A multi-beam transmitting antenna model is used to transmit wireless signals and has functions such as beam coverage, frequency division multiplexing, beam shutdown, and power and frequency resource allocation.

[0021] The receiver model is used to perform link budget analysis, match information rate, frequency, bandwidth, modulation method, and coding method, and calculate the bit error rate.

[0022] The transmitter model is used to attach information rate, frequency, bandwidth, modulation method, encoding, etc. to the signaling data packet for transmission;

[0023] The resource allocation model is used to implement the functions of initial resource allocation and reallocation, including beam, power, bandwidth, frequency, and time slot allocation;

[0024] The signaling processing model is used to complete the signaling processing for network access authentication, handover, network use, and network decommissioning.

[0025] The broadband integrated communication payload includes:

[0026] A phased array receiving antenna model, used to complete wireless signal reception, with beam coverage, beam switching and beam staring functions;

[0027] A phased array transmitting antenna model, used to transmit wireless signals, with beam coverage, beam switching, and beam staring functions;

[0028] The receiver model is used to perform link budget analysis, match information rate, frequency, bandwidth, modulation method, and coding method, and calculate the bit error rate.

[0029] The transmitter model is used to attach information rate, frequency, bandwidth, modulation method, encoding, etc. to the signaling data packet for transmission;

[0030] The resource allocation model is used to implement the functions of initial resource allocation and reallocation, including beam, power, bandwidth, frequency, and time slot allocation;

[0031] The signaling processing model is used to complete the signaling processing functions of network access authentication, handover, network use, and network deactivation on the satellite.

[0032] The aerial surveillance payload includes:

[0033] A multi-beam receiving antenna model is used to complete wireless signal reception, and has functions such as beam coverage, frequency division multiplexing, beam shutdown, and power and frequency resource allocation.

[0034] The receiver model is used to perform message collision detection (based on time tags), link budget analysis, and to match information rate, frequency, bandwidth, modulation method, and coding method to calculate bit error rate.

[0035] The power supply load includes:

[0036] A mechanically movable receiving antenna model, used to complete wireless signal reception, with beam coverage and mechanical rotation functions;

[0037] A mechanically movable transmitting antenna model, used to transmit wireless signals, featuring beam coverage, mechanical rotation, and other functions;

[0038] The feeder receiver model is used to perform link budget analysis, match information rate, frequency, bandwidth, modulation method, and coding method, and realize bit error rate calculation.

[0039] A fed transmitter model is used to attach information rate, frequency, bandwidth, modulation method, encoding, etc. to signaling data packets for transmission;

[0040] The resource allocation model is used to implement the functions of initial resource allocation and reallocation, including beam, power, bandwidth, frequency, and time slot allocation;

[0041] The signaling processing model is used to complete the signaling processing functions of gateway stations for network access authentication, handover, network use, and network deactivation.

[0042] The inter-satellite laser payload laser link includes:

[0043] A laser terminal pointing model is used to calculate the laser terminal pointing based on ephemeris data.

[0044] A laser terminal receiving telescope model is used to receive light wave signals and adjust the direction of the receiving telescope according to the target pointing data;

[0045] A laser terminal transmitting telescope model is used to send light wave signals and adjust the direction of the transmitting telescope according to the target pointing data;

[0046] The laser terminal receiver model is used to perform laser link budget analysis, match information rate, bandwidth, modulation method, and coding method, and calculate bit error rate.

[0047] A laser terminal transmitter model is used to attach information rate, frequency, bandwidth, modulation method, encoding, etc. to signaling data packets for transmission;

[0048] A resource allocation model for allocating bandwidth resources to various types of business data;

[0049] The load integration processor is used to perform routing and switching functions for various load data streams, including:

[0050] The link congestion model allows setting the resource occupancy ratio of satellite nodes and informing the routing calculation model of resource load status.

[0051] The link failure model allows for the configuration of satellite node failures and informs the routing calculation model of resource load conditions.

[0052] The service priority processing model is used to sort routing priorities according to user level and place data packets into the routing data buffer according to priority.

[0053] The routing calculation model is designed for use with the shortest path algorithm and includes functions for route calculation, routing table generation, and route update.

[0054] The routing model is used to route data packets in the buffer to obtain the next-hop address;

[0055] The data distribution model is used to distribute data packets to various ports based on the routing address.

[0056] In a preferred embodiment of the present invention, the main gateway model includes an access network sub-model and a core network sub-model, wherein the access network sub-model includes:

[0057] The receiving antenna model is used to complete the wireless signal reception of the feed link and has beam coverage and mechanical rotation functions.

[0058] The transmitting antenna model is used to complete the wireless signal transmission of the feed link and has beam coverage and mechanical rotation functions.

[0059] The receiver model is used to perform link budget analysis for services and signaling, match information rate, frequency, bandwidth, modulation method, and coding method, and calculate signal-to-noise ratio and bit error rate.

[0060] Transmitter model, used to attach information rate, frequency, bandwidth, modulation method, encoding, etc. to service and signaling data packets for transmission;

[0061] The signaling processing model is used to complete simplified protocol stack processing functions, including initial network access, random access, reconstruction, reselection, registration, and handover functions;

[0062] The packet assembly model is used to assemble and sort business data according to the simplified mode of IP packets, and to dynamically allocate IP addresses to source and target entities.

[0063] The unpacking model is used to simplify the mode by IP packet, realize packet reordering, and extract business data from the packets;

[0064] The cross-constellation service data forwarding model is used to extract service data from the feeder link and forward it to the core network for exchange; it also receives service data from the core network and sends it to the feeder uplink.

[0065] The core network sub-model includes:

[0066] The network access authentication model is used to complete user identification, network access registration, and dynamically assign IP addresses to users;

[0067] A data exchange model is used to complete the exchange and forwarding of business data across constellations.

[0068] As a preferred embodiment of the present invention, the large-scale terminal model constructed by the application segment includes:

[0069] The beam selection model is used to calculate the distance from the user to the beam center based on the user's orientation of the satellite beam center, and select the beam with the shortest distance as the access beam;

[0070] User receiving antenna model, used to complete wireless signal reception;

[0071] User transmitting antenna model, used to complete wireless signal transmission;

[0072] The receiver model is used to perform link budget analysis for services and signaling, match information rate, frequency, bandwidth, modulation method, and coding method, and calculate signal-to-noise ratio and bit error rate.

[0073] Transmitter model, used to attach information rate, frequency, bandwidth, modulation method, encoding, etc. to service and signaling data packets for transmission;

[0074] The signaling processing model is used to complete simplified protocol stack processing functions, including initial network access, random access, reconstruction, reselection, registration, and handover functions;

[0075] The packet assembly model is used to assemble and sort business data according to the simplified mode of IP packets, and to dynamically allocate IP addresses to source and target entities.

[0076] The unpacking model is used to simplify the mode by IP packet, realize packet reordering, and extract business data from the packets;

[0077] Business models are used to generate business data types (voice, data, images, video), and business characteristics are identified by text tags;

[0078] The movement model is used for linear movement, circular motion, random motion, and opposite-direction motion.

[0079] Location distribution characteristic model, used for three types of distribution: global uniform distribution, random distribution, and distribution according to global population density;

[0080] The call characteristic model assumes that the arrival time of a user call statistically follows a Poisson distribution, and the service time of a user call statistically follows an exponential distribution.

[0081] In a preferred embodiment of the present invention, the satellite-to-ground microwave channel model includes:

[0082] Free-space loss sub-model, used to calculate space attenuation based on frequency and distance;

[0083] The Doppler effect sub-model is used to calculate the Doppler frequency shift and the first-order Doppler rate of change based on relative motion.

[0084] The noise model sub-model is used to calculate noise power based on noise theory formulas.

[0085] Rainfall loss sub-model, used to calculate rainfall loss based on ITU-R empirical formula for rainfall attenuation;

[0086] Atmospheric loss sub-model, used to calculate atmospheric loss based on ITU-R empirical formula for atmospheric attenuation;

[0087] A cloud and fog loss sub-model is used to calculate atmospheric loss based on the ITU-R empirical formula for cloud and fog attenuation.

[0088] Snowfall loss sub-model, used to calculate atmospheric loss based on ITU-R empirical formula for snowfall attenuation;

[0089] The inter-satellite laser channel model includes:

[0090] The solar noise model sub-model is used to calculate the included angle based on the positional relationship between the sun, satellite, and earth station, and to make a decision based on the threshold value. If the value is less than the threshold value, communication is considered interrupted.

[0091] Secondly, embodiments of the present invention also provide a system simulation method for low-Earth orbit constellation systems, based on a system model constructed using the method described above, comprising the following steps:

[0092] In step S201, the constellation configuration model inputs initial values ​​of orbital and attitude parameters into the satellite attitude control subsystem model. The attitude control subsystem model generates real-time orbital and attitude data and sends them to other models.

[0093] Step S202: After obtaining the constellation topology and orbital position information of each satellite, the satellite payload terminal payload integrated processor model uses the shortest path algorithm to calculate the shortest distance from this satellite to other satellites and generates a routing table.

[0094] In step S203, the satellite payload model transceiver antenna calculates the antenna pointing direction using orbital and attitude data, and broadcasts the satellite position and antenna pointing information via the transmitting antenna signaling beam. All information is attached to a simplified IP data packet. The destination address in the data packet is set to the broadcast address, indicating that all ground entities can receive it, and it is transmitted downlinked via the satellite-to-ground link.

[0095] Step S204: After receiving the broadcast data packet, the terminal performs visibility calculation, that is, calculates the elevation angle from the terminal to the satellite and determines whether the elevation angle constraint condition is met; if it is met, it is determined that the satellite can establish a link and proceeds to the next step; otherwise, it is determined that the satellite cannot establish a link.

[0096] Step S205: When the satellite is visible, perform beam selection. First, calculate the distance between the terminal and the center point of the satellite beam, and select the satellite beam corresponding to the shortest distance as the selection result. Simultaneously, set a beam dwell threshold; if the distance is within a certain range, the terminal will always select that beam. When the distance exceeds the threshold, reselect the access beam using the same method.

[0097] In step S206, the terminal sends a network registration request via the transmitting antenna, with the information attached to a simplified IP data packet and the destination address set to the address of the primary gateway station; the network registration request data packet is then uploaded to the satellite network via the satellite-to-ground link.

[0098] In step S207, the satellite payload integrated processor performs routing and switching processing based on the address information of the network registration request data packet, and forwards the data packet through the inter-satellite link; when the destination address matches the address of the main gateway station accessed in the satellite, the data packet is transmitted to the main gateway station through the feeder link.

[0099] In step S208, the main gateway core network receives the data packet, performs authentication, assigns an IP address to the terminal, completes the registration request, and replies with registration request confirmation information.

[0100] Step S209: After receiving the registration request confirmation information, the terminal applies for network access; it attaches information such as beam access information, service type, bandwidth rate, and called party information to the IP packet and sends it to the satellite network through the signaling beam.

[0101] In step S210, after receiving the network usage request, the satellite accessed by the calling terminal allocates resources to it and sends confirmation information to the calling terminal; at the same time, it performs paging for the called party and forwards the paging information through the inter-satellite link.

[0102] In step S211, after receiving the paging information, the called terminal initiates a network access request to the satellite it is connected to. The satellite allocates resources and sends a confirmation message.

[0103] Step S212: When both the calling and called parties successfully allocate resources, the connection is established successfully, and the two parties can perform service interactions; when one party fails to allocate resources, the satellite that has completed resource allocation is notified to release resources, and the calling / called user is informed that the connection establishment has failed.

[0104] Step S213: If the link is successfully established, the service information of the calling and called parties is transmitted using simplified IP packets, and data transmission and reception are achieved through the accessed microwave satellite-to-ground link, while routing exchange and data forwarding are achieved through the inter-satellite laser link.

[0105] In step S214, both signaling and service information transmission pass through the channel model. The channel model obtains the location, velocity, power, and frequency information of the receiver and transmitter, and performs calculations on power attenuation, Doppler frequency shift, noise power, and propagation delay before transmitting it to the receiver.

[0106] In step S215, the receiving antennas of each entity first calculate the visibility based on the position information of the transmitting and receiving ends. If visible, frequency matching is performed. If the Doppler offset is within the receiving bandwidth, the data packet is transmitted to the receiver for further processing. For inter-satellite laser communication, the laser transmitting and receiving ends are aligned by calculating whether the angle changes of the two satellites are within the constraints of the laser terminal's pitch angle, azimuth angle, angular velocity, and angular acceleration.

[0107] Step S216: The receiver extracts the power attenuation value from the information packet, completes the link calculation, obtains the signal-to-noise ratio, and obtains the bit error rate of the receiving node by querying the bit error curve table.

[0108] Step S217: For a satellite node, if the bit error rate is higher than the threshold, the data packet is discarded and not forwarded to the next node; otherwise, the data packet is input into the payload integration processor model for routing and switching, and the data forwarding is completed until it is transmitted to the target node.

[0109] In step S218, during network usage, the primary and secondary users continuously send the beam selection results to the accessed satellites for handover judgment. When a handover is required, the source satellite sends a handover request to the target satellite. After receiving the request, the target satellite checks whether the resources are available.

[0110] In step S219, if the target satellite resources are available, the target satellite allocates resources and notifies the source satellite to forward the results to the user. After receiving this information, the user switches to the target satellite. After receiving the user's switch execution result, the target satellite notifies the source satellite to release resources and notifies the gateway station to change the path, thus completing the switchover process.

[0111] Step S220: When the user communication ends, a disconnection request is initiated. After receiving the request, the connected satellite releases its resources to complete the network usage process.

[0112] Step S221: When a user leaves the network, a leave request is initiated and forwarded to the gateway station core network via the inter-satellite network. The core network model will then deregister the user information to complete the leave process.

[0113] In a preferred embodiment of the present invention, the simulation method further includes:

[0114] Step S222: The simulation effect is evaluated using index evaluation methods, including: system bit error rate evaluation, system packet loss rate evaluation, system interruption rate evaluation, and system capacity evaluation.

[0115] The system model construction method and system simulation method for low-Earth orbit constellation systems provided in this invention have the following beneficial effects:

[0116] (1) To meet the needs of communication index analysis such as bit error rate, packet loss rate, interruption rate, latency, system capacity, and number of users, the characteristics of the payload signal and signaling processing are modeled to meet the functional requirements of the model with the minimum envelope, supporting the simulation of nearly a thousand satellite constellations and hundreds of thousands of terminals.

[0117] (2) Determine the model granularity according to different simulation needs, and accurately model the orbital attitude to solve the engineering problem of inter-satellite laser alignment, so as to realize the accurate construction of laser pointing; at the same time, it supports the accurate evaluation of the laser inter-satellite link status during satellite operation by importing on-orbit data (orbit, attitude);

[0118] (3) An event-triggered information flow design was adopted to simulate and verify the complex interaction process of the satellite-ground interface;

[0119] (4) Inter-satellite routing and switching simulation can set satellite node failure and congestion modes. By setting preset parameters, the impact of satellite node failure and load imbalance on network performance can be completed without large-scale terminal stress testing.

[0120] (5) Taking into account the impact of the channel environment on satellite communication performance, channel modeling is performed for satellite-to-ground microwave links and inter-satellite laser links to improve the accuracy and reliability of simulation.

[0121] Of course, implementing any product or method of the present invention does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0122] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0123] Figure 1 This is a schematic diagram of the system model composition and interface interaction for a low-Earth orbit constellation system provided in an embodiment of the present invention;

[0124] Figure 2 This is a simplified IP data packet format diagram in the system simulation method described in this embodiment of the invention;

[0125] Figure 3 This is the routing representation intent in the system simulation method described in the embodiments of the present invention;

[0126] Figure 4 This is a schematic diagram of the spatial segment model design in an embodiment of the present invention;

[0127] Figure 5 This is a schematic diagram of constellation topology in an embodiment of the present invention;

[0128] Figure 6 This is a schematic diagram of the inter-satellite connection topology in an embodiment of the present invention;

[0129] Figure 7 This is a schematic diagram of the gateway station model design in an embodiment of the present invention;

[0130] Figure 8 This is a schematic diagram of the terminal model design in an embodiment of the present invention;

[0131] Figure 9 This is a schematic diagram of the environmental segment model design in an embodiment of the present invention. Detailed Implementation

[0132] After discovering the aforementioned problems, the inventors of this application conducted in-depth research on low-Earth orbit (LEO) constellation systems and related theoretical issues. The research revealed that to accurately predict and judge various aspects of LEO constellation systems during the planning phase, including planning and demonstration, system development, and on-orbit management, simulation verification can be performed on key issues at different stages of systems engineering, providing effective data support for system analysis.

[0133] The International Council on Systems Engineering (INCOSE) proposed Model-Based Systems Engineering (MBSE), which has become the foundation for complex system design. From the requirements analysis phase to the evaluation phase, the model becomes the core of the design process for complex systems. The system design of complex systems is achieved through the continuous evolution and iterative expansion of the model, primarily addressing the problems of traditional document-based systems engineering. Although MBSE has gained recognition from experts in multiple systems engineering fields both domestically and internationally, there is still no mature and readily available simulation modeling technology to draw upon for the simulation and performance evaluation of low-Earth orbit constellation systems with integrated space and ground capabilities.

[0134] Therefore, there are still some problems in the system simulation of low-Earth orbit constellation systems. It is necessary to develop a system simulation and performance evaluation system for low-Earth orbit constellation systems. By combining the mission requirements at each stage, the system can map the data of individual units and the entire satellite with the simulation evaluation, and realize the simulation verification and evaluation of design indicators and response strategies. This will enable the early detection of deficiencies in system design, operation management, and fault handling, and provide full life-cycle simulation support for constellation system engineering from project initiation and demonstration to decommissioning and deorbiting.

[0135] Simulation and performance evaluation of low-Earth orbit (LEO) constellation systems require simulation modeling of various functional entities in the space segment, ground segment, application segment, and environment segment. This involves simulating satellite-ground networking functions and verifying and evaluating the correctness, rationality, and effectiveness of the constellation system's architecture and protocol design. Model construction for system simulation must ensure the modeling accuracy of functional entities without losing key characteristics, while also meeting the lightweight requirements of simulation modeling and reducing system modeling complexity. A trade-off between model accuracy and lightweight design must be struck for specific simulation evaluation requirements.

[0136] Based on this, embodiments of the present invention provide a system model construction method and system simulation method for low-Earth orbit constellation systems. Based on distributed simulation technology, the model design is carried out for the space segment, ground segment, application segment and environment segment respectively. It is suitable for system simulation and performance evaluation of low-Earth orbit constellation systems and can support constellation scale of thousands of satellites and terminal scale of 100,000.

[0137] See Figure 1 The system model construction method for low-Earth orbit constellation systems provided in this embodiment of the invention includes the following steps:

[0138] Step S1: Divide the low-Earth orbit constellation system into space segment, ground segment, application segment, and environment segment.

[0139] Step S2 involves lightweight modeling of the space segment. The model constructed for the space segment includes a constellation configuration model, an attitude and orbit control subsystem model, and a satellite payload model. Its functional components are as follows: Figure 4 As shown.

[0140] During simulation, the constellation configuration model generates constellation topology and initial orbital attitude values ​​based on the constellation configuration design, and sends them to the satellite payload model and attitude control subsystem model, respectively. The attitude control subsystem model performs orbit and attitude calculations based on orbit and attitude parameters, and sends the orbit and attitude data to the satellite payload model and constellation configuration model. The satellite payload model implements satellite-to-ground and inter-satellite beamforming functions, service and signaling link analysis functions, network access and link establishment signaling processing functions, radio resource allocation functions, and inter-satellite routing and switching functions.

[0141] Preferably, such as Figure 5 As shown, the constellation configuration model is used to generate constellation topological relationships; as Figure 6 As shown, the inter-satellite topology is described using a two-dimensional table, where "1" represents the existence of inter-satellite connections and "0" represents the absence of inter-satellite connections. The constellation configuration model calculates the initial values ​​of the six orbital elements and attitude parameters of each satellite in the constellation based on the constellation configuration parameters and uploads the data.

[0142] Preferably, the attitude and orbit control subsystem model includes an attitude dynamics submodel, an orbit dynamics submodel, and an onboard guidance, navigation, control (GNC) submodel. Wherein:

[0143] 1) Orbital dynamics sub-model

[0144] The orbital dynamics sub-model consists of an ideal orbital model and a high-precision HPOP orbital model. The ideal orbital model does not consider the influence of other external perturbation forces. The high-precision HPOP orbital model considers the thrust control force model, the Earth's non-spherical perturbation model, the atmospheric drag perturbation model, the lunar and solar gravitational perturbation model, and the solar radiation pressure perturbation model.

[0145] 2) Attitude dynamics sub-model

[0146] The attitude dynamics sub-model consists of an internal control torque model and an external disturbance model. The internal control torque model considers the flywheel model, the magnetic torque generator model, and the thruster model, while the external disturbance model considers the gravity gradient torque model, the solar radiation torque model, the aerodynamic torque model, and the geomagnetic torque model.

[0147] 3) Onboard GNC control sub-model

[0148] Based on the orbital and attitude data input from the orbital dynamics sub-model and the attitude dynamics sub-model, the key parameters for satellite attitude control, pointing control, and orbit control are calculated. The calculated control forces are fed back to the orbital dynamics sub-model for satellite orbit adjustment, and the control torques are fed back to the attitude dynamics sub-model for satellite attitude adjustment.

[0149] Preferably, the satellite payload model includes a narrowband mobile communication payload, a broadband integrated communication payload, an airborne surveillance payload, a power supply payload, a laser inter-satellite link payload, a payload integration processor, and a beacon payload sub-model. Wherein:

[0150] 1) Narrowband mobile communication payloads include:

[0151] Multi-beam receiving antenna model: Completes wireless signal reception and has functions such as beam coverage, frequency division multiplexing, beam shutdown, and power and frequency resource allocation;

[0152] Multi-beam transmitting antenna model: Completes wireless signal transmission and has functions such as beam coverage, frequency division multiplexing, beam shutdown, and power and frequency resource allocation;

[0153] Receiver model: Performs link budget analysis, matches information rate, frequency, bandwidth, modulation method, and coding method, and calculates bit error rate;

[0154] Transmitter model: Information rate, frequency, bandwidth, modulation method, encoding, etc. are appended to the signaling data packet for transmission;

[0155] Resource allocation model: Implements the functions of initial resource allocation and reallocation, including beam, power, bandwidth, frequency, and time slot allocation;

[0156] Signaling processing model: Completes signaling processing for network access authentication, handover, network use, and network deactivation.

[0157] 2) Broadband integrated communication payload includes:

[0158] Phased array receiving antenna model: Completes wireless signal reception and has beam coverage, beam switching and beam staring functions;

[0159] Phased array transmitting antenna model: Completes wireless signal transmission and has beam coverage, beam switching and beam staring functions;

[0160] Receiver model: Performs link budget analysis, matches information rate, frequency, bandwidth, modulation method, and coding method, and calculates bit error rate;

[0161] Transmitter model: Information rate, frequency, bandwidth, modulation method, encoding, etc. are appended to the signaling data packet for transmission;

[0162] Resource allocation model: Implements the functions of initial resource allocation and reallocation, including beam, power, bandwidth, frequency, and time slot allocation;

[0163] Signaling processing model: Completes the signaling processing functions for network access authentication, handover, network use, and network deactivation on the satellite.

[0164] 3) Aerial surveillance payloads include:

[0165] Multi-beam receiving antenna model: Completes wireless signal reception and has functions such as beam coverage, frequency division multiplexing, beam shutdown, and power and frequency resource allocation;

[0166] Receiver model: Performs message collision detection (based on time tags), link budget analysis, matches information rate, frequency, bandwidth, modulation method, and coding method, and calculates bit error rate.

[0167] 4) Power supply loads include:

[0168] Mechanically movable receiving antenna model: It completes wireless signal reception and has beam coverage and mechanical rotation functions;

[0169] Mechanically movable transmitting antenna model: It completes wireless signal transmission and has beam coverage, mechanical rotation, and other functions;

[0170] Feeder receiver model: Complete link budget analysis, match information rate, frequency, bandwidth, modulation method, and coding method, and realize bit error rate calculation;

[0171] Feed-based transmitter model: Information rate, frequency, bandwidth, modulation method, encoding, etc. are appended to the signaling data packet for transmission;

[0172] Resource allocation model: Implements the functions of initial resource allocation and reallocation, including beam, power, bandwidth, frequency, and time slot allocation;

[0173] Signaling processing model: Completes the signaling processing functions of gateway station for network access authentication, handover, network use, and network deactivation.

[0174] 5) The inter-satellite laser payload laser link includes:

[0175] Laser terminal pointing model: Calculate the laser terminal pointing based on ephemeris data;

[0176] Laser terminal receiving telescope model: Receives light wave signals and adjusts the direction of the receiving telescope according to the target pointing data;

[0177] Laser terminal transmitting telescope model: It sends light wave signals and adjusts the pointing of the transmitting telescope according to the target pointing data;

[0178] Laser terminal receiver model: Complete laser link budget analysis, match information rate, bandwidth, modulation method, and coding method, and realize bit error rate calculation;

[0179] Laser terminal transmitter model: Information rate, frequency, bandwidth, modulation method, encoding, etc. are appended to the signaling data packet for transmission;

[0180] Resource allocation model: Allocate bandwidth resources for multiple types of service data (narrowband, broadband, aviation surveillance, power supply services).

[0181] 6) The load integration processor is used to perform routing and switching functions for various load data streams, including:

[0182] Link congestion model: The resource occupancy ratio of satellite nodes can be set, and the resource load status can be informed to the routing calculation model;

[0183] Link failure model: Satellite node failures can be configured, and resource load information can be communicated to the routing calculation model;

[0184] Service priority processing model: Sort routes according to user level and place data packets into the routing data buffer according to priority;

[0185] Routing calculation model: Based on the shortest path algorithm, it has the functions of route calculation, routing table generation, and route update;

[0186] Routing model: Routing data packets in the buffer to obtain the next-hop address;

[0187] Data distribution model: Distribute data packets to various ports based on routing addresses.

[0188] Step S3: Perform lightweight modeling on the ground segment. The model constructed for the ground segment includes the primary gateway station model and the secondary gateway station model.

[0189] During simulation, both the primary gateway station model and the secondary gateway station model implement access network functions, while the primary gateway station model also implements core network functions. Specifically, the access network implements the signal transmission and reception functions for the power supply link, and the core network implements terminal registration and authentication functions.

[0190] like Figure 7 As shown, the main gateway model includes an access network sub-model and a core network sub-model, wherein the access network model includes:

[0191] The receiving antenna model is used to complete the wireless signal reception of the feed link and has beam coverage and mechanical rotation functions.

[0192] The transmitting antenna model is used to complete the wireless signal transmission of the feed link and has beam coverage and mechanical rotation functions.

[0193] The receiver model is used to perform link budget analysis for services and signaling, match information rate, frequency, bandwidth, modulation method, and coding method, and calculate signal-to-noise ratio and bit error rate.

[0194] Transmitter model, used to attach information rate, frequency, bandwidth, modulation method, encoding, etc. to service and signaling data packets for transmission;

[0195] The signaling processing model is used to complete simplified protocol stack processing functions, including initial network access, random access, reconstruction, reselection, registration, and handover functions;

[0196] The packet assembly model is used to assemble and sort business data according to the simplified mode of IP packets, and to dynamically allocate IP addresses to source and target entities.

[0197] The unpacking model is used to simplify the mode by IP packet, realize packet reordering, and extract business data from the packets;

[0198] The cross-constellation service data forwarding model is used to extract service data from the feeder link and forward it to the core network for exchange; it also receives service data from the core network and sends it to the feeder uplink.

[0199] The core network sub-model includes:

[0200] The network access authentication model is used to complete user identification, network access registration, and dynamically assign IP addresses to users;

[0201] A data exchange model is used to complete the exchange and forwarding of business data across constellations.

[0202] Step S4: Lightweight modeling is performed on the application segment, and a large-scale terminal model is built in the application segment; during simulation, the application segment model completes beam selection, visibility analysis, service data generation, data transmission and reception, and signaling processing functions.

[0203] like Figure 8 As shown, the large-scale terminal model constructed by the application segment includes:

[0204] The beam selection model is used to calculate the distance from the user to the beam center based on the user's orientation of the satellite beam center, and select the beam with the shortest distance as the access beam;

[0205] User receiving antenna model, used to complete wireless signal reception;

[0206] User transmitting antenna model, used to complete wireless signal transmission;

[0207] The receiver model is used to perform link budget analysis for services and signaling, match information rate, frequency, bandwidth, modulation method, and coding method, and calculate signal-to-noise ratio and bit error rate.

[0208] Transmitter model, used to attach information rate, frequency, bandwidth, modulation method, encoding, etc. to service and signaling data packets for transmission;

[0209] The signaling processing model is used to complete simplified protocol stack processing functions, including initial network access, random access, reconstruction, reselection, registration, and handover functions;

[0210] The packet assembly model is used to assemble and sort business data according to the simplified mode of IP packets, and to dynamically allocate IP addresses to source and target entities.

[0211] The unpacking model is used to simplify the mode by IP packet, realize packet reordering, and extract business data from the packets;

[0212] Business models are used to generate business data types (voice, data, images, video), and business characteristics are identified by text tags;

[0213] The movement model is used for linear movement, circular motion, random motion, and opposite-direction motion.

[0214] Location distribution characteristic model, used for three types of distribution: global uniform distribution, random distribution, and distribution according to global population density;

[0215] The call characteristic model assumes that the arrival time of a user call statistically follows a Poisson distribution, and the service time of a user call statistically follows an exponential distribution.

[0216] Step S5: Perform lightweight modeling of the environment segment. The model constructed for the environment segment includes a satellite-to-ground microwave channel sub-model and an inter-satellite laser channel sub-model. When performing simulation, the satellite-to-ground channel sub-model considers free space loss, Doppler effect, noise, atmospheric, rain, snow, cloud and fog loss, while the inter-satellite channel sub-model considers the impact of solar interference on the laser link.

[0217] like Figure 9 As shown, the satellite-to-ground microwave channel model includes:

[0218] Free-space loss sub-model, used to calculate space attenuation based on frequency and distance;

[0219] The Doppler effect sub-model is used to calculate the Doppler frequency shift and the first-order Doppler rate of change based on relative motion.

[0220] The noise model sub-model is used to calculate noise power based on noise theory formulas.

[0221] Rainfall loss sub-model, used to calculate rainfall loss based on ITU-R empirical formula for rainfall attenuation;

[0222] Atmospheric loss sub-model, used to calculate atmospheric loss based on ITU-R empirical formula for atmospheric attenuation;

[0223] A cloud and fog loss sub-model is used to calculate atmospheric loss based on the ITU-R empirical formula for cloud and fog attenuation.

[0224] The snowfall loss sub-model is used to calculate atmospheric loss based on the ITU-R empirical formula for snowfall attenuation.

[0225] Inter-satellite laser channel models include:

[0226] The solar noise model sub-model is used to calculate the included angle based on the positional relationship between the sun, satellite, and earth station, and to make a decision based on the threshold value. If the value is less than the threshold value, communication is considered interrupted.

[0227] Preferably, the lightweight modeling in steps S2-5 adopts the IOCE modeling method, where I is the input, O is the output, C is the computation, and E is the event. Low-Earth orbit constellation systems have a large number of satellites and terminals, requiring minimizing data interaction between models. Therefore, satellite entities, gateway entities, terminal entities, and channel environment entities are designed as atomic models. Sub-models within each entity are implemented using functional functions, and efficient data interaction between functional modules is achieved through memory, avoiding the problem of low model information exchange efficiency caused by excessive use of middleware for data interaction between composite models.

[0228] like Figure 2As shown, during the lightweight modeling in steps S2-5, the following model interaction design is implemented: the satellite model, terminal model, and gateway model interact with the channel model for service information and signaling information respectively through data middleware; during instantiation, only one channel model is instantiated, and all data from the satellite, terminal, and gateway models are concentrated in one channel model for interaction, reducing the redundant information transmission between large-scale satellite and large-scale terminal models; service information and signaling information are forwarded through the receiving and transmitting antenna models of various entities and transmitted using unified simplified IP data packets, simplifying the complex interface between models and facilitating data interaction between models.

[0229] It should be noted that steps S2 to S5 above are modeling processes for four different segments of the low-Earth orbit constellation system, and there is no sequential relationship between them.

[0230] Based on the constructed model, this embodiment of the invention also provides a system simulation method for low-Earth orbit constellation systems, including the following steps:

[0231] In step S201, the constellation configuration model inputs initial values ​​of orbital and attitude parameters into the satellite attitude control subsystem model. The attitude control subsystem model generates real-time orbital and attitude data and sends them to other models.

[0232] Step S202: After obtaining the constellation topology and orbital position information of each satellite, the satellite payload terminal payload integrated processor model calculates the shortest distance from this satellite to other satellites using the shortest path algorithm, and generates a routing table, such as... Figure 3 As shown.

[0233] In step S203, the satellite payload model's transceiver antenna calculates the antenna pointing direction using orbital and attitude data, and broadcasts the satellite position and antenna pointing information via the transmitting antenna signaling beam. All information is attached to a simplified IP data packet. The destination address in the data packet is set to the broadcast address, indicating that all ground entities can receive it, and the data is transmitted downlink via the satellite-to-ground link.

[0234] In step S204, after receiving the broadcast data packet, the terminal performs visibility calculation, that is, calculates the elevation angle from the terminal to the satellite and determines whether the elevation angle constraint condition is met. If it is met, it is determined that the satellite can establish a link and proceeds to the next step; otherwise, it is determined that the satellite cannot establish a link.

[0235] Step S205: When the satellite is visible, beam selection is performed. First, the distance between the terminal and the center point of the satellite beam is calculated, and the satellite beam corresponding to the shortest distance is selected as the result. Simultaneously, a beam dwell threshold is set (this threshold value is determined by the half-angle and gain of the satellite antenna beam), meaning that if the distance is within a certain range, the terminal will always select that beam. When the distance exceeds the threshold, the access beam is reselected using the same method.

[0236] In step S206, the terminal sends a network registration request via its transmitting antenna. The information is attached to a simplified IP data packet, and the destination address is set to the address of the primary gateway station. This network registration request data packet is uploaded to the satellite network via the satellite-to-ground link.

[0237] In step S207, the satellite payload integrated processor performs routing and switching processing based on the address information of the network registration request data packet, and forwards the data packet through the inter-satellite link. When the destination address matches the address of the main gateway station accessed in the satellite, the data packet is transmitted to the main gateway station through the feeder link.

[0238] In step S208, the main gateway core network receives the data packet, performs authentication, assigns an IP address to the terminal, completes the registration request, and replies with registration request confirmation information. The process is similar to the steps described above.

[0239] In step S209, after receiving the registration request confirmation information, the terminal applies for network access. Information such as beam access information, service type, bandwidth rate, and called party information are attached to the IP packet and sent to the satellite network via signaling beam.

[0240] In step S210, after receiving the network usage request, the satellite connected to the calling terminal allocates resources to it and sends an acknowledgment message to the calling party. Simultaneously, it performs paging for the called party, forwarding the paging information via inter-satellite links.

[0241] In step S211, after receiving the paging information, the called terminal initiates a network access request to the satellite it is connected to. The satellite allocates resources and sends a confirmation message.

[0242] In step S212, if both the calling and called parties successfully allocate resources, the connection is successfully established, and the two parties can perform service interactions. If one party fails to allocate resources, the satellite that has already completed resource allocation is notified to release the resources, and the calling / called user is informed that the connection establishment has failed.

[0243] In step S213, if the link is successfully established, the service information of the calling and called parties is transmitted using simplified IP packets, and data transmission and reception are achieved through the accessed microwave satellite-to-ground link, while routing exchange and data forwarding are achieved through the inter-satellite laser link.

[0244] In step S214, both signaling and service information transmission pass through the channel model. The channel model obtains the location, velocity, power, and frequency information of the receiver and transmitter, and performs calculations on power attenuation, Doppler frequency shift, noise power, and propagation delay before transmitting it to the receiver.

[0245] In step S215, the receiving antennas of each entity first calculate visibility based on the position information of the transmitting and receiving ends. If visible, frequency matching is performed; if the Doppler offset is within the receiving bandwidth, the data packet is transmitted to the receiver for further processing. For inter-satellite laser communication, the alignment of the laser transmitting and receiving ends is determined by calculating whether the angular changes of the two satellites are within the constraints of the laser terminal's elevation angle, azimuth angle, angular velocity, and angular acceleration.

[0246] In step S216, the receiver extracts the power attenuation value from the information packet, completes the link calculation, obtains the signal-to-noise ratio, and obtains the bit error rate of the receiving node by querying the bit error curve table.

[0247] In step S217, for a satellite node, if the bit error rate is higher than a threshold, the data packet is discarded and not forwarded to the next node. Otherwise, the data packet is input into the payload integration processor model for routing and switching, completing data forwarding until it reaches the target node.

[0248] In step S218, during network usage, the primary and secondary users continuously send beam selection results to the accessed satellites for handover judgment. When a handover is required, the source satellite sends a handover request to the target satellite, and the target satellite checks whether the resources are available after receiving the request.

[0249] In step S219, if the target satellite resources are available, the target satellite allocates resources and notifies the source satellite to forward the results to the user. After receiving this information, the user switches to the target satellite. After receiving the user's switch execution result, the target satellite notifies the source satellite to release resources and notifies the gateway station to change the path, thus completing the switchover process.

[0250] Step S220: When the user communication ends, a disconnection request is initiated. Upon receiving the request, the connected satellite releases its resources, thus completing the network usage process.

[0251] Step S221: When a user leaves the network, a leave request is initiated and forwarded to the gateway station core network via the inter-satellite network. The core network model will then deregister the user information to complete the leave process.

[0252] The system simulation method also includes:

[0253] Step S222: Evaluate the simulation results. Specifically, use evaluation methods including: system bit error rate evaluation, system packet loss rate evaluation, system interruption rate evaluation, and system capacity evaluation.

[0254] The system's bit error rate (BER) assessment provides BER curves through physical layer simulation. A signal-level simulation method based on software-defined radio is employed, loading an environmental segment model for modeling and simulation. After a series of additive and multiplicative channel models, the amplitude, frequency, and phase of the original signal change. The resulting signal is then fed into the receiver for signal recovery, obtaining the BER performance of a specific communication system under different signal-to-noise ratio (SNR) and Doppler conditions. Then, discrete data are curve-fitted to obtain continuous performance index curves, which are stored in the simulation system database. The physical layer is abstracted, and link calculations are performed on the satellite mobile communication link using channel empirical parameters provided by ITU-R to obtain the SNR. Doppler offset is obtained through the relative motion information of the satellite and terminal. Finally, during the simulation evaluation process, physical layer performance index data can be quickly obtained using a "lookup table method."

[0255] The system packet loss rate assessment, which evaluates packet loss caused by network node failures or excessive load leading to packet drop, primarily assesses packet loss due to congestion in the inter-satellite routing and switching network. The packet loss rate assessment employs large-scale terminal stress testing, evaluating the impact on inter-satellite routing and switching by pre-setting satellite network congestion and node failure modes.

[0256] In the satellite fault node mode, the on-board routing table fails to be updated in a timely manner within a specific time slice, resulting in packet loss. The fault modes include the following:

[0257] 1) No node failure.

[0258] 2) 5% of the satellite nodes in the constellation system fail, resulting in the failure of inter-satellite links within the same orbit and between different orbits; the faulty nodes and their durations are randomly distributed.

[0259] 3) 10% of the satellite nodes in the constellation system fail, resulting in the failure of inter-satellite links within the same orbit and between different orbits; the fault nodes and their durations are randomly distributed.

[0260] 4) 20% of the satellite nodes in the constellation system malfunction, resulting in the failure of inter-satellite links within the same orbit and between different orbits; the fault nodes and their durations are randomly distributed.

[0261] In satellite network congestion mode (assuming a congestion threshold), packet loss occurs when the on-board routing table fails to update in a timely manner within a specific time slice. Congestion modes include the following:

[0262] 1) No congestion occurred, and the load of all satellite nodes was below the set threshold.

[0263] 2) 10% of satellite nodes in the constellation system become congested, the satellite node load reaches the congestion threshold, the congested nodes are randomly distributed, and the congestion time follows an exponential distribution.

[0264] 3) 30% of satellite nodes in the constellation system become congested, the satellite node load reaches the congestion threshold, the congested nodes are randomly distributed, and the congestion time follows an exponential distribution.

[0265] 4) 50% of satellite nodes in the constellation system become congested, the satellite node load reaches the congestion threshold, the congested nodes are randomly distributed, and the congestion time follows an exponential distribution.

[0266] 5) 80% of satellite nodes in the constellation system are congested, the satellite node load reaches the congestion threshold, the congested nodes are randomly distributed, and the congestion time follows an exponential distribution.

[0267] The system outage rate assessment considers communication interruptions caused by deteriorating channel conditions or excessive network node load. Stress tests are conducted using a large number of terminals to evaluate service interruptions under both full satellite network load and channel environment model loading scenarios. The interruption scenarios include:

[0268] 1) Interruptions caused by the channel environment: The channel model mainly considers the effects of air fading, rain fading, atmospheric cloud and fog attenuation, Doppler, noise, and solar interference.

[0269] 2) Interruption caused by inter-regional handover: Under the full-load mode of the satellite network, the service interruption caused by the wireless resource handover of communication users is evaluated. The full-load mode includes: ① No satellite node full load occurs; ② 10% of the satellite nodes in the constellation system are fully loaded, with the fully loaded nodes randomly distributed and the duration following an exponential distribution; ③ 30% of the satellite nodes in the constellation system are fully loaded, with the fully loaded nodes randomly distributed and the duration following an exponential distribution; ④ 50% of the satellite nodes in the constellation system are fully loaded, with the fully loaded nodes randomly distributed and the duration following an exponential distribution; ⑤ 80% of the satellite nodes in the constellation system are fully loaded, with the fully loaded nodes randomly distributed and the duration following an exponential distribution.

[0270] The system capacity assessment divides the satellite operating cycle into multiple time slices and conducts stress tests using large-scale user-generated constellation system traffic to evaluate the impact of inter-satellite link constraints on system capacity. The assessment evaluates system capacity under different time slice divisions and various service traffic modes for fixed-location terminals, including the following:

[0271] 1) Divide the satellite's operational cycle into 32 time slices and evaluate the system capacity for large-scale terminal traffic distributions based on global uniform distribution, global random distribution, and global population density distribution.

[0272] 2) Divide the satellite's operational cycle into 48 time slices and evaluate the system capacity for large-scale terminal traffic distributions based on global uniform distribution, global random distribution, and global population density distribution.

[0273] 3) Divide the satellite's operational cycle into 60 time slices and evaluate the system capacity for large-scale terminal service traffic distributed globally, randomly globally, and by global population density.

[0274] As can be seen from the above technical solutions, the system model construction method and system simulation method for low-Earth orbit constellation systems provided in the embodiments of the present invention perform simulation modeling of various functional entities in the space segment, ground segment, application segment, and environment segment, simulate the satellite-ground networking function, and form an integrated satellite-ground model architecture. This not only ensures the modeling accuracy of functional entities and does not lose key characteristics, but also meets the lightweight requirements of simulation modeling, reduces the complexity of system modeling, and balances the relationship between model accuracy and lightweighting. Based on the simulation method of the constructed model, the correctness, rationality, and effectiveness of the constellation system's architecture design, system protocol design, etc., are verified and evaluated through simulation.

[0275] The above description is merely a preferred embodiment of the present invention and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention is not limited to the specific combination of the above-described technical features, but also includes other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in this invention.

Claims

1. A method for constructing a system model for low-Earth orbit constellation systems, characterized in that, The system model construction method includes: The low-Earth orbit constellation system is divided into a space segment, a ground segment, an application segment, and an environmental segment. Lightweight modeling is performed on the space segment, which includes a constellation configuration model, an attitude and orbit control subsystem model, and a satellite payload model. During simulation, the constellation configuration model generates constellation topology and initial orbital attitude values ​​based on the constellation configuration design, and sends them to the satellite payload model and the attitude and orbit control subsystem model, respectively. The attitude and orbit control subsystem model performs orbit and attitude calculations based on orbit and attitude parameters, and sends the orbit and attitude data to the satellite payload model and the constellation configuration model. The satellite payload model implements satellite-to-ground and inter-satellite beamforming functions, service and signaling link analysis functions, network access and link establishment signaling processing functions, radio resource allocation functions, and inter-satellite routing and switching functions. Lightweight modeling is performed on the ground segment, which includes a primary gateway station model and a secondary gateway station model. During simulation, both the primary and secondary gateway station models implement access network functions, while the primary gateway station model also implements core network functions. The access network implements the signal transmission and reception functions of the power supply link, and the core network implements the terminal registration and authentication functions. Lightweight modeling is performed on the application segment, and a large-scale terminal model is built in the application segment. During simulation, the application segment model completes beam selection, visibility analysis, service data generation, data transmission and reception, and signaling processing functions. The environmental segment is modeled in a lightweight manner. The environmental segment model includes a satellite-to-ground microwave channel sub-model and an inter-satellite laser channel sub-model. When performing simulations, the satellite-to-ground channel sub-model considers free space loss, Doppler effect, noise, atmospheric, rain, snow, cloud and fog loss, while the inter-satellite channel sub-model considers the impact of solar interference on the laser link. When performing lightweight modeling for the space segment, ground segment, application segment, and environment segment, the following model interaction design is adopted: the constellation configuration model, large-scale terminal model, and primary / secondary gateway station model interact with the satellite-to-ground microwave channel sub-model and the inter-satellite laser channel sub-model respectively through data middleware to exchange service information and signaling information; during the instantiation process, only one satellite-to-ground microwave channel sub-model and one inter-satellite laser channel sub-model are instantiated, and the data of all constellation configuration models, terminal models, and primary / secondary gateway station models are concentrated in one channel model for interaction, reducing the cross-transmission of information between constellation configuration models and large-scale terminal models; service information and signaling information are forwarded through the receiving and transmitting antenna models of various entities and transmitted using unified simplified IP data packets, which simplifies the processing of complex interfaces between models and facilitates data interaction between models.

2. The system model construction method for low-Earth orbit constellation systems according to claim 1, characterized in that, The inter-satellite topology generated by the constellation configuration model is described using a two-dimensional table, where "1" represents the existence of inter-satellite connections and "0" represents the absence of inter-satellite connections. The constellation configuration model calculates the initial values ​​of the six orbital elements and attitude parameters of each satellite in the constellation based on the constellation configuration parameters and uploads the data.

3. The method for constructing a system model for low-Earth orbit constellation systems according to claim 1, characterized in that, The attitude and orbit control subsystem model includes an attitude dynamics submodel, an orbit dynamics submodel, and an onboard guidance, navigation, and control (GNC) submodel; among which... The orbital dynamics sub-model consists of an ideal orbital model and an HPOP high-precision orbital model. The ideal orbital model does not consider the influence of other external disturbance forces. The HPOP high-precision orbital model considers the thruster control force model, the Earth's non-spherical perturbation model, the atmospheric drag perturbation model, the solar and lunar gravitational perturbation model, and the solar radiation pressure perturbation model. The attitude dynamics sub-model consists of an internal control torque model and an external disturbance model. The internal control torque model considers a flywheel model, a magnetic torque generator model, and a thruster model, while the external disturbance model considers a gravity gradient torque model, a solar radiation torque model, an aerodynamic torque model, and a geomagnetic torque model. The onboard GNC control sub-model calculates key parameters for satellite attitude control, pointing control, and orbit control based on orbit and attitude data input from the orbit dynamics sub-model and attitude dynamics sub-model. It then feeds back the calculated control force to the orbit dynamics sub-model for satellite orbit adjustment and the control torque to the attitude dynamics sub-model for satellite attitude adjustment.

4. The method for constructing a system model for low-Earth orbit constellations according to claim 1, characterized in that, The satellite payload model includes sub-models for narrowband mobile communication payload, broadband integrated communication payload, airborne surveillance payload, power supply payload, laser inter-satellite link payload, payload integration processor, and beacon payload; among them, The narrowband mobile communication payload includes: A multi-beam receiving antenna model is used to complete wireless signal reception, and has functions such as beam coverage, frequency division multiplexing, beam shutdown, and power and frequency resource allocation. A multi-beam transmitting antenna model is used to transmit wireless signals and has functions such as beam coverage, frequency division multiplexing, beam shutdown, and power and frequency resource allocation. The receiver model is used to perform link budget analysis, match information rate, frequency, bandwidth, modulation method, and coding method, and calculate the bit error rate. The transmitter model is used to attach information rate, frequency, bandwidth, modulation method, and coding method to the signaling data packet for transmission; The resource allocation model is used to implement the functions of initial resource allocation and reallocation, including beam, power, bandwidth, frequency, and time slot allocation; The signaling processing model is used to complete the signaling processing for network access authentication, handover, network use, and network decommissioning. The broadband integrated communication payload includes: A phased array receiving antenna model, used to complete wireless signal reception, with beam coverage, beam switching and beam staring functions; A phased array transmitting antenna model, used to transmit wireless signals, with beam coverage, beam switching, and beam staring functions; The receiver model is used to perform link budget analysis, match information rate, frequency, bandwidth, modulation method, and coding method, and calculate the bit error rate. The transmitter model is used to attach information rate, frequency, bandwidth, modulation method, and coding method to the signaling data packet for transmission; The resource allocation model is used to implement the functions of initial resource allocation and reallocation, including beam, power, bandwidth, frequency, and time slot allocation; The signaling processing model is used to complete the signaling processing functions of network access authentication, handover, network use, and network deactivation on the satellite. The aerial surveillance payload includes: A multi-beam receiving antenna model is used to complete wireless signal reception, and has functions such as beam coverage, frequency division multiplexing, beam shutdown, and power and frequency resource allocation. The receiver model is used to perform message collision detection, link budget analysis, match information rate, frequency, bandwidth, modulation method, and coding method, and calculate bit error rate. The power supply load includes: A mechanically movable receiving antenna model, used to complete wireless signal reception, with beam coverage and mechanical rotation functions; A mechanically movable transmitting antenna model, used to transmit wireless signals, with beam coverage and mechanical rotation functions; The feeder receiver model is used to perform link budget analysis, match information rate, frequency, bandwidth, modulation method, and coding method, and realize bit error rate calculation. The fed transmitter model is used to attach information rate, frequency, bandwidth, modulation method, and coding method to the signaling data packet for transmission; The resource allocation model is used to implement the functions of initial resource allocation and reallocation, including beam, power, bandwidth, frequency, and time slot allocation; The signaling processing model is used to complete the signaling processing functions of gateway stations for network access authentication, handover, network use, and network deactivation. The laser inter-satellite link payload includes: A laser terminal pointing model is used to calculate the laser terminal pointing based on ephemeris data. A laser terminal receiving telescope model is used to receive light wave signals and adjust the direction of the receiving telescope according to the target pointing data; A laser terminal transmitting telescope model is used to send light wave signals and adjust the direction of the transmitting telescope according to the target pointing data; The laser terminal receiver model is used to perform laser link budget analysis, match information rate, bandwidth, modulation method, and coding method, and calculate bit error rate. A laser terminal transmitter model is used to attach information rate, frequency, bandwidth, modulation method, and encoding method to signaling data packets for transmission; A resource allocation model for allocating bandwidth resources to various types of business data; The load integration processor is used to perform routing and switching functions for various load data streams, including: The link congestion model allows setting the resource occupancy ratio of satellite nodes and informing the routing calculation model of resource load status. The link failure model allows for the configuration of satellite node failures and informs the routing calculation model of resource load conditions. The service priority processing model is used to sort routing priorities according to user level and place data packets into the routing data buffer according to priority. The routing calculation model is designed for use with the shortest path algorithm and includes functions for route calculation, routing table generation, and route update. The routing model is used to route data packets in the buffer to obtain the next-hop address; The data distribution model is used to distribute data packets to various ports based on the routing address.

5. The method for constructing a system model for low-Earth orbit constellation systems according to claim 1, characterized in that, The main gateway model includes an access network sub-model and a core network model, wherein the access network model includes: The receiving antenna model is used to complete the wireless signal reception of the feed link and has beam coverage and mechanical rotation functions. The transmitting antenna model is used to complete the wireless signal transmission of the feed link and has beam coverage and mechanical rotation functions. The receiver model is used to perform link budget analysis for services and signaling, match information rate, frequency, bandwidth, modulation method, and coding method, and calculate signal-to-noise ratio and bit error rate. The transmitter model is used to attach information rate, frequency, bandwidth, modulation method, and encoding method to service and signaling data packets for transmission; The signaling processing model is used to complete simplified protocol stack processing functions, including initial network access, random access, reconstruction, reselection, registration, and handover functions; The packet assembly model is used to assemble and sort business data according to the simplified IP packet mode, and to dynamically allocate IP addresses to source and target entities. The unpacking model is used to simplify the mode by IP packet, realize packet reordering, and extract business data from the packets; The cross-constellation service data forwarding model is used to extract service data from the feeder link and forward it to the core network for exchange; it also receives service data from the core network and sends it to the feeder uplink. The core network sub-model includes: The network access authentication model is used to complete user identification, network access registration, and dynamically assign IP addresses to users; A data exchange model is used to complete the exchange and forwarding of business data across constellations.

6. The method for constructing a system model for low-Earth orbit constellation systems according to claim 1, characterized in that, The large-scale terminal model built by the application segment includes: The beam selection model is used to calculate the distance from the user to the beam center based on the user's orientation to the satellite beam center, and select the beam with the shortest distance as the access beam; User receiving antenna model, used to complete wireless signal reception; User transmitting antenna model, used to complete wireless signal transmission; The receiver model is used to perform link budget analysis for services and signaling, match information rate, frequency, bandwidth, modulation method, and coding method, and calculate signal-to-noise ratio and bit error rate. The transmitter model is used to attach information rate, frequency, bandwidth, modulation method, and encoding method to service and signaling data packets for transmission; The signaling processing model is used to complete simplified protocol stack processing functions, including initial network access, random access, reconstruction, reselection, registration, and handover functions; The packet assembly model is used to assemble and sort business data according to the simplified mode of IP packets, and to dynamically allocate IP addresses to source and target entities. The unpacking model is used to simplify the mode by IP packet, realize packet reordering, and extract business data from the packets; Business models are used to generate business data types, and business characteristics are identified by text tags; The movement model is used for linear movement, circular motion, random motion, and opposite-direction motion. Location distribution characteristic model, used for three types of distribution: global uniform distribution, random distribution, and distribution according to global population density; The call characteristic model assumes that the arrival time of a user call statistically follows a Poisson distribution, and the service time of a user call statistically follows an exponential distribution.

7. The method for constructing a system model for low-Earth orbit constellation systems according to claim 1, characterized in that, The satellite-to-ground microwave channel sub-model includes: Free-space loss sub-model, used to calculate space attenuation based on frequency and distance; The Doppler effect sub-model is used to calculate the Doppler frequency shift and the first-order Doppler rate of change based on relative motion. The noise model sub-model is used to calculate noise power based on noise theory formulas. Rainfall loss sub-model, used to calculate rainfall loss based on ITU-R empirical formulas for rainfall attenuation; Atmospheric loss sub-model, used to calculate atmospheric loss based on ITU-R empirical formula for atmospheric attenuation; A cloud and fog loss sub-model is used to calculate atmospheric loss based on the ITU-R empirical formula for cloud and fog attenuation. Snowfall loss sub-model, used to calculate atmospheric loss based on ITU-R empirical formula for snowfall attenuation; The inter-satellite laser channel sub-model includes: The solar noise model sub-model is used to calculate the included angle based on the positional relationship between the sun, satellite, and earth station, and to make a decision based on a threshold value. If the value is less than the threshold value, communication is considered to be interrupted.

8. A system simulation method for low-Earth orbit constellation systems, characterized in that, The system model constructed based on the method described in any one of claims 1-7 includes the following steps: In step S201, the constellation configuration model inputs initial values ​​of orbit and attitude parameters into the satellite attitude and orbit control subsystem model. The attitude and orbit control subsystem model generates real-time orbit and attitude data and sends them to other models. In step S202, after the satellite payload terminal payload integration processor obtains the constellation topology and the orbital position information of each satellite, it uses the shortest path algorithm to calculate the shortest distance from the satellite to other satellites and generates a routing table. In step S203, the satellite payload model transceiver antenna calculates the antenna pointing using orbital and attitude data, and broadcasts the satellite position and antenna pointing information via the transmitting antenna signaling beam. All information is attached to the simplified IP data packet. The destination address in the data packet is set to the broadcast address, meaning that all ground entities can receive it and it is transmitted down via the satellite-to-ground link; Step S204: After receiving the broadcast data packet, the terminal performs visibility calculation, that is, calculates the elevation angle from the terminal to the satellite and determines whether the elevation angle constraint condition is met. If the condition is met, the satellite is determined to be able to establish a link, and the next step is processed; otherwise, the satellite is determined to be unable to establish a link. Step S205: When the satellite is visible, perform beam selection processing; first, calculate the distance between the terminal and the center of the satellite beam, and select the satellite beam corresponding to the shortest distance as the selection result; at the same time, set a beam dwell threshold, that is, if the distance is within a certain range, the terminal will always select the beam; when the distance exceeds the threshold, the access beam is reselected in the same way. In step S206, the terminal sends a network registration request via the transmitting antenna, with the information attached to a simplified IP data packet and the destination address set to the address of the primary gateway station; the network registration request data packet is then uploaded to the satellite network via the satellite-to-ground link. In step S207, the satellite payload integrated processor performs routing and switching processing based on the address information of the network registration request data packet, and forwards the data packet through the inter-satellite link; when the destination address matches the address of the main gateway station accessed in the satellite, the data packet is transmitted to the main gateway station through the feeder link. In step S208, the main gateway core network receives the data packet, performs authentication, assigns an IP address to the terminal, completes the registration request, and replies with registration request confirmation information. Step S209: After receiving the registration request confirmation information, the terminal applies for network access; it attaches the beam access information, service type, bandwidth rate, and called party information to the IP packet and sends it to the satellite network through the signaling beam. In step S210, after receiving the network usage request, the satellite accessed by the calling terminal allocates resources to it and sends confirmation information to the calling terminal; at the same time, it performs paging for the called party and forwards the paging information through the inter-satellite link. In step S211, after receiving the paging information, the called terminal initiates a network access request to the satellite it is connected to. The satellite allocates resources and sends a confirmation message. Step S212: When both the calling and called parties successfully allocate resources, the connection is established successfully, and the two parties can perform business interactions; when one party fails to allocate resources, the satellite that has completed resource allocation is notified to release resources, and the calling / called user is informed that the connection has failed. Step S213: If the link is successfully established, the service information of the calling and called parties is transmitted using simplified IP packets, and data transmission and reception are achieved through the accessed microwave satellite-to-ground link, while routing exchange and data forwarding are achieved through the inter-satellite laser link. In step S214, the transmission of signaling and service information both pass through the channel model. The channel model obtains the position, speed, power, and frequency information of the receiver and transmitter, and performs calculations on power attenuation, Doppler frequency offset, noise power, and propagation delay before transmitting it to the receiver. In step S215, the receiving antennas of each entity first calculate the visibility based on the position information of the transmitting and receiving ends. If visible, frequency matching is performed. If the Doppler offset is within the receiving bandwidth, the data packet is transmitted to the receiving antenna for further processing. For inter-satellite laser communication, the laser transmitting and receiving ends are aligned by calculating whether the angle changes of the two satellites are within the constraints of the laser terminal's pitch angle, azimuth angle, angular velocity, and angular acceleration. Step S216: The receiver extracts the power attenuation value from the information packet, completes the link calculation, obtains the signal-to-noise ratio, and obtains the bit error rate of the receiver by querying the bit error curve table. Step S217: For a satellite node, if the bit error rate is higher than the threshold, the data packet is discarded and not forwarded to the next node; otherwise, the data packet is input to the payload integration processor for routing and switching, and the data forwarding is completed until it is transmitted to the target node. In step S218, during network usage, the calling and called users continuously send beam selection results to the accessed satellites for handover judgment. When a handover is required, the source satellite sends a handover request to the target satellite. After receiving the request, the target satellite checks whether the resources are available. Step S219: If the target satellite resources are available, the target satellite allocates resources and notifies the source satellite to forward the results to the user. After receiving the information, the user switches to the target satellite. After receiving the handover execution result from the user, the target satellite notifies the source satellite to release resources and notifies the gateway station to change the path, thus completing the handover process; Step S220: When the user communication ends, a disconnection request is initiated. After receiving the request, the connected satellite releases its resources to complete the network usage process. Step S221: When a user leaves the network, a leave request is initiated and forwarded to the gateway station core network via the inter-satellite network. The core network model will then deregister the user information to complete the leave process.

9. The system simulation method according to claim 8, characterized in that, The simulation method further includes: Step S222: The simulation effect is evaluated using index evaluation methods, including: system bit error rate evaluation, system packet loss rate evaluation, system interruption rate evaluation, and system capacity evaluation.

Images