High-mobility platform random access method and system for low-orbit satellite data chain

Abstract

The invention provides a high-mobility platform random access method and system for a low-orbit satellite data chain, and the method comprises the steps: taking a satellite ephemeris and platform navigation information as initial guidance, receiving and analyzing a satellite downlink signal, and carrying out the joint estimation to obtain a space-time frequency parameter; based on the estimated timestamp as a time reference of a frequency hopping pattern, driving a local frequency hopping sequence generator, predicting and verifying the current frequency hopping pattern, and performing frequency offset correction according to the estimated Doppler frequency offset; and in response to successful verification of the frequency hopping pattern, constructing a pre-compensated uplink and starting a frequency hopping pattern tracking loop for fine tuning of the time-space-frequency parameter and the frequency hopping pattern phase, so that the user accesses the low-orbit satellite data link at random and enters steady-state communication. The time-space-frequency alignment problem and the time-varying frequency hopping pattern capturing and tracking problem are synchronously solved, and rapid, reliable and anti-interference random access of the high-mobility platform is achieved.

Description

Technical Field

[0001] This application belongs to the field of satellite communication technology, and in particular relates to a highly mobile platform access method and system for low-Earth orbit satellite data links. Background Technology

[0002] Low Earth Orbit Datalink (LEO Datalink) systems are located high above the ground and form a network that can effectively overcome geographical and terrain constraints, providing wireless access and relay transmission services comparable to terrestrial datalinks for use in the air, at sea, in high mountains, in wastelands, and in remote areas.

[0003] A typical Low Earth Orbit (LEO) satellite datalink system consists of a constellation of LEO satellites carrying datalink payloads, a network management station, a gateway station, and user terminals. LEO satellite constellations are primarily deployed in low Earth orbit (LEO) at altitudes of 500–2000 kilometers, offering advantages such as lower communication latency, greater available bandwidth, lower on-orbit satellite power consumption, and higher overall network capacity. The satellite datalink payloads provide satellite relay services to user terminals via satellite-to-ground and inter-satellite links. The network management station provides wireless resource management and user access services to user terminals via feeder links. The gateway station, acting as a gateway node, can interconnect with other terrestrial communication systems and expand services through wired connections. With the increasing communication and computing capabilities of LEO datalink payloads, the application scope of LEO satellite datalinks is continuously expanding.

[0004] With the large-scale deployment of low-Earth orbit (LEO) satellite constellations, their global coverage and low-latency communication capabilities have provided revolutionary solutions for fields such as aviation, emergency response, and tactical communications. The need for highly mobile platforms such as drones and high-speed aircraft to utilize LEO satellite constellations to build beyond-line-of-sight (BLOS) data link communications is becoming increasingly urgent. However, such satellite-based communication systems face two major technological bottlenecks: 1) The challenge of three-dimensional high dynamic alignment in time-space-frequency: Low-orbit satellites move at high speed relative to the ground (about 7km / s), while the high-mobility platform itself is also in a high-speed and high-mobility state. This results in huge, time-varying beam pointing deviations, Doppler frequency shifts and propagation delays in the satellite-to-ground communication link, rendering traditional synchronization and tracking technologies based on static or quasi-static models completely ineffective.

[0005] 2) The challenge of rapid acquisition and tracking of time-varying frequency hopping patterns: To meet the communication requirements of anti-interference and anti-interception, data links generally adopt time-varying frequency hopping technology, in which the frequency hopping pattern is strictly bound to the system time and changes dynamically. When the platform initially connects, it must complete the blind acquisition of the current frequency hopping in a very short time and maintain strict pattern synchronization in a highly dynamic environment, which is a great technical challenge.

[0006] Existing technologies typically treat physical layer synchronization and frequency hopping pattern acquisition as two sequential and independent steps. First, coarse synchronization of time, frequency, and beam is achieved, followed by frequency hopping pattern search and synchronization on the already synchronized link. This approach is lengthy, inefficient, and unsuitable for the short visibility windows of low-Earth orbit satellites. Furthermore, most solutions heavily rely on precise prior information (real-time precise ephemeris) or ground station assistance, making them impractical in highly mobile, information-constrained tactical scenarios. Summary of the Invention

[0007] In view of this, this application aims to propose a highly mobile platform-based on-the-go access method and system for low-Earth orbit satellite data links to solve at least one of the above-mentioned problems.

[0008] To achieve the above objectives, the technical solution of this application is implemented as follows: In a first aspect, this application provides a highly mobile platform-based on-the-fly access method for low-Earth orbit satellite data links, comprising: Using satellite ephemeris and platform navigation information as initial guidance, spatiotemporal frequency parameters are obtained by receiving and parsing satellite downlink signals and jointly estimating them. Based on the estimated timestamp as the time reference for the frequency hopping pattern, the local frequency hopping sequence generator is driven to predict and verify the current frequency hopping pattern, and frequency offset correction is performed based on the estimated Doppler frequency offset. In response to the successful verification of the frequency hopping pattern, a pre-compensated uplink is constructed and a frequency hopping pattern tracking loop is initiated to fine-tune the time-space-frequency parameters and the phase of the frequency hopping pattern, so that users can access the low-Earth orbit satellite data link at any time and enter steady-state communication.

[0009] Secondly, based on the same inventive concept, this application also provides a highly mobile platform on-demand access system for low-Earth orbit satellite data links, used to implement a highly mobile platform on-demand access method for low-Earth orbit satellite data links as described in the first aspect, including a physical layer processing channel, a signal layer processing channel and a central coordination and control unit, wherein the physical layer processing channel and the signal layer processing channel form a two-layer collaborative processing architecture of physical layer and signal layer. The physical layer processing channel includes a spatiotemporal frequency joint sensing and estimation module, an adaptive beam control module, and a frequency offset / delay pre-compensation module. The signal layer processing channel includes a frequency hopping pattern synchronization and tracking module, a security synchronization verification module, and a signal demodulation and decoding module; The central coordination and control unit consists of a coordination and synchronization controller, which coordinates the operation of the physical layer processing channel and the signal layer processing channel to achieve a globally optimal access strategy.

[0010] Compared with existing technologies, the highly mobile platform-based on-the-go access method and system for low-Earth orbit satellite data links described in this application has the following advantages: 1) Fast access speed: Through joint processing and prediction mechanisms, the typical time for highly mobile platforms to access low-Earth orbit satellite data links is shortened from minutes to seconds or even sub-seconds, fully adapting to the short communication windows of low-Earth orbit satellites.

[0011] 2) System resource efficiency optimization: The guided search mechanism avoids blind scanning across the entire airspace and frequency band, and the joint processing avoids repetitive signal processing procedures, reducing the demand for processing computing resources and power consumption, making it more suitable for resource-constrained airborne platforms.

[0012] 3) High synchronization accuracy and robustness: The microsecond-level time synchronization modeling provided by the physical layer ensures strict synchronization of the frequency hopping pattern. The closed-loop tracking mechanism can effectively suppress the synchronization error drift caused by the high dynamic environment, and the link stability is significantly improved.

[0013] 4) Enhanced anti-interference and security: The ability to quickly enter frequency hopping communication mode itself improves anti-interference capability; the timestamp-based synchronization mechanism avoids complex synchronization header interactions and reduces the risk of interception and interference; the entire process supports seamless integration with encryption and authentication modules.

[0014] 5) High autonomy and practicality: It has a low dependence on prior information and can still work under conditions with only rough ephemeris or even no ephemeris. It meets the autonomous communication needs of highly dynamic users in complex and unfamiliar battlefield environments and has strong practicality. Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a flowchart of a highly mobile platform for on-the-go access to a low-Earth orbit satellite data link, as described in an embodiment of this application. Figure 2 This is a schematic diagram of the structure of a highly mobile platform for on-demand access to a low-Earth orbit satellite data link, as described in an embodiment of this application. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0017] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in the embodiments of this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are only used to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0018] The design concept of the high-mobility platform on-demand access method described in this embodiment is to use satellite ephemeris and the platform's own navigation information as initial guidance. By receiving and parsing satellite downlink signals, it jointly estimates high-precision spatiotemporal parameters such as direction of arrival, Doppler shift, and propagation delay. The calculated precise timestamps are then used to directly drive the local frequency hopping sequence generator, enabling unambiguous and rapid prediction and synchronization of time-varying frequency hopping sequences. Finally, an uplink is established through adaptive beamforming and pre-compensation techniques, forming an integrated synchronous access process of "guided acquisition - joint estimation - prediction synchronization - closed-loop tracking". This solves the two major problems of spatiotemporal alignment and frequency hopping pattern acquisition simultaneously without complete prior information, enabling high-dynamic users to quickly, reliably, and securely access low-Earth orbit satellite data links.

[0019] The embodiments of this application are described in detail below with reference to the accompanying drawings.

[0020] Example 1 Please see Figure 1 As shown, this embodiment provides a highly mobile platform-based on-demand access method for low-Earth orbit satellite data links, specifically including the following steps: Step S101: Using satellite ephemeris and platform navigation information as initial guidance, the spatiotemporal frequency parameters are obtained by receiving and parsing satellite downlink signals.

[0021] Specifically, in this embodiment, step S101 includes the following steps: (1) Bootstrap initialization The guided initialization process utilizes satellite ephemeris and the high-mobility platform's own navigation information as coarse prior information to narrow the initial search space and avoid time-consuming and inefficient global blind search. The guided initialization process includes the following steps: a) Based on the loaded satellite ephemeris and the high-mobility platform's own navigation data, obtain the satellite's position vector in the geocentric inertial frame (ECI). and the position vector of the high mobility platform This allows for the determination of the satellite's inertial position vector relative to the platform. And convert it into a position vector in the station center coordinate system. : ; ; In the formula, This is the transformation matrix from the Earth-Fixed Coordinate System (ECEF) to the Station-Centered Coordinate System (ENU). This is the transformation matrix from the geocentric inertial coordinate system (ECI) to the Earth-fixed coordinate system.

[0022] Transformation matrix Depends on the platform's latitude and longitude. Given the current time (used to calculate the vernal equinox angle), let the platform's longitude be λ and its latitude be... The transformation matrix is ​​then: ; b) Calculate the satellite azimuth angle in the ENU coordinate system. Pitch angle : set up If the vector elements are the eastward component, the northward component, and the celestial component, then the pitch angle is... The calculation formula is: ; Azimuth The angle of clockwise rotation from due north to the satellite projection point is calculated using the following formula: ; In the formula, Let be the arctangent function, and its range is... In practical applications, the radians are often converted to a clockwise calculation from true north. Angle system: ; In the formula, This is a modulo operation.

[0023] c) Calculate the theoretical Doppler frequency offset: Relative radial velocity of the satellite relative to a high-dynamic user for: ; In the formula, and These are the position vectors of the satellite and the user in a common coordinate system (ECI or ECEF), respectively. and These are the velocity vectors of the satellite and the user in the common coordinate system, respectively. This indicates that the satellite and the platform are far apart, while the opposite indicates that the satellite and the platform are close together.

[0024] Theoretical Doppler frequency shift for: ; In the formula, The relative radial velocity, For carrier frequency, It is the speed of light.

[0025] d) Estimating a rough satellite system time : ; In the formula, Provides the user's local high-precision time at the instant the signal is received; The one-way propagation delay of a signal from a satellite to a user can be obtained from the relative distance between the satellite and the user; The system time difference between the satellite system time and the user's local time is usually obtained through time parameters in the ephemeris or through a rough alignment.

[0026] (2) Joint capture and estimation Joint acquisition and estimation obtains beam pointing, frequency, and time information in a single step through joint signal processing. The processing steps include: a) Perform rapid beam scanning and frequency search within the guidance range to capture downlink synchronization signals or specific preambles; b) Using the MUSIC algorithm for angle of arrival estimation: ; In the formula, For spatial spectrum estimation, the peak value corresponds to the direction of incoming wave; The direction of arrival angle to be scanned; For array guiding vector; The noise subspace matrix is ​​obtained through eigenvalue decomposition of the sampling covariance matrix; It is the conjugate transpose operator; c) Frequency offset estimation via phase difference : ; In the formula, For receiving signal samples; The sampling period is L; L is the number of lag points in the difference operation, usually L=1 for fast estimation, or a larger value to improve accuracy and noise resistance. To represent the conjugate of the complex field, Indicates the received signal sample Its delayed signal sample Conjugate multiplication; To obtain the phase angle function.

[0027] d) Delay estimation via cross-correlation peak detection : ; In the formula, It is a cross-correlation function; This is a peak detection function, which finds the position with the largest absolute value. Precise frame start time. = + ; Step S102: Based on the estimated timestamp as the time reference for the frequency hopping pattern, drive the local frequency hopping sequence generator to predict and verify the current frequency hopping pattern, and perform frequency offset correction according to the estimated Doppler frequency offset.

[0028] Specifically, in this embodiment, frequency hopping pattern prediction and verification involves directly using the high-precision time of the physical layer as the time reference for generating a frequency hopping sequence, and achieving zero-phase-difference synchronization of the frequency hopping pattern through feedback verification. The processing steps include: a) The precise frame start time estimated in step S101 ( (This is used as a time base and input to the local frequency hopping sequence generator;) b) The frequency hopping generator generates the frequency hopping sequence for the current moment based on the pre-shared frequency hopping algorithm seed. }; c) Tune the receiver to the frequency hopping sequence to receive data. If the signal quality (SNR) exceeds the threshold, the verification is successful.

[0029] This step utilizes the high-precision absolute timestamp calculated from the downlink frame synchronization header, combined with the pre-shared frequency hopping algorithm seed, to directly and unambiguously predict the current frequency hopping pattern state, skipping the time-consuming pattern phase search process and reducing the frequency hopping synchronization time by an order of magnitude.

[0030] Step S103: In response to successful frequency hopping pattern verification, a pre-compensated uplink is constructed and a frequency hopping pattern tracking loop is started to fine-tune the time-space-frequency parameters and the phase of the frequency hopping pattern, so that the user can access the low-Earth orbit satellite data link at any time and enter steady-state communication.

[0031] Specifically, in this embodiment, a pre-compensated uplink is constructed using all estimation and prediction results, and a frequency hopping pattern tracking loop is initiated to achieve alignment upon transmission, significantly improving the access success rate. Closed-loop tracking ensures that the link remains uninterrupted under severe maneuvers, and the processing steps include: a) Uplink pre-compensation, including three parts: transmission frequency, transmission time, and transmission beam pre-compensation: The transmit frequency pre-compensated downlink Doppler is: ; In the formula, This is the final uplink transmission frequency; The nominal uplink frequency; For the estimated downlink Doppler frequency offset; Launch time pre-compensation for propagation delay: ; In the formula, This refers to the actual launch time; For the target launch time slot specified in the agreement; This is the estimated one-way propagation delay; The transmitted beam points to the estimated beam azimuth angle. and pitch angle .

[0032] b) Send an access request; c) Activate the joint tracking loop: simultaneously fine-tune the beam, frequency, time, and frequency hopping phase to counteract dynamic changes in the satellite-to-ground link.

[0033] This embodiment designs a complete technology chain from ephemeris guidance and joint parameter estimation to adaptive pre-compensation and closed-loop tracking. It is specifically optimized for scenarios where both the satellite and the platform are moving at high speeds. The coupling effect between parameters is overcome by joint estimation, and the dynamics of the satellite-ground link are effectively countered by the prediction-compensation-tracking closed loop.

[0034] It should be noted that the above description describes some embodiments of this application. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in a different order than that shown in the above embodiments and still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0035] Example 2 Based on the same inventive concept, and corresponding to the methods of any of the above embodiments, to solve the time-space-frequency alignment problem and time-varying frequency hopping pattern acquisition and tracking problem faced by highly mobile platforms in accessing low-Earth orbit satellite data links, the highly mobile platform access system described in this embodiment adopts a physical layer and signal layer dual-layer collaborative processing architecture. Through a unified control closed loop, it achieves collaborative interlocking of information between the two layers, ensuring fast, reliable, and interference-resistant access in dynamic environments. The functional components of the highly mobile platform access system include a physical layer processing channel, a signal layer processing channel, and a central coordination and control unit, such as... Figure 2 As shown, the specific functions of each functional module are described below.

[0036] (1) Physical layer processing channel To address the time-space-frequency three-dimensional alignment problem in highly dynamic environments, the physical layer processing channel is designed with the following objectives: rapid beam acquisition and accurate tracking, real-time estimation and compensation of large dynamic Doppler frequency offset, and establishment of accurate time reference synchronization. Its main functional components include: a time-space-frequency joint sensing and estimation module, an adaptive beam control module, and a frequency offset / delay pre-compensation module.

[0037] 1) Spatiotemporal-frequency joint sensing and estimation module The spatiotemporal-frequency joint sensing and estimation module is responsible for solving the problem of rapid spatiotemporal-frequency alignment. It uses coarse ephemeris guidance and extracts high-precision parameters directly from the downlink signal through a joint estimation algorithm, providing accurate input for beam control and frequency / delay compensation. Its functional components include a broadband scanning unit and a multi-parameter joint estimation unit.

[0038] a) Wideband scanning unit The input to the broadband spectrum sensing unit is the intermediate frequency signal after down-conversion from the RF front-end, and the output is a list of detected signal frequencies, signal strength, and bandwidth estimation. Specific functions include: Fast scanning and capture: Supports real-time spectrum scanning with bandwidth of 100MHz-2GHz and ≤10ms; the energy detection threshold can be dynamically and adaptively adjusted according to the noise floor. Scanning strategy management: Supports priority scanning of high-probability frequency bands based on ephemeris and historical records, and can identify the hopping patterns of frequency hopping signals. b) Multi-parameter joint estimation unit The multi-parameter joint estimation unit takes the captured signal sample as input and outputs a joint estimate of the direction of arrival, Doppler frequency offset, and propagation delay. Its specific functions include: Direction of Arrival (DOA) Estimation: Supports phased array antenna signal processing, and can use MUSIC algorithm, ESPRIT algorithm and deep learning-based DOA estimation algorithm to accurately estimate the direction of arrival; Doppler frequency offset estimation: Differential phase and Kalman filtering methods can be used to achieve phase-based frequency offset estimation; Propagation delay estimation: coarse delay estimation is achieved based on cross-correlation peak detection, and fine delay estimation is achieved based on sub-sampling delay estimation of phase difference; Joint optimization process: Based on the above univariate estimation, parameter coupling modeling is performed to establish the mathematical coupling relationship between the spatiotemporal frequency parameters. The optimal joint estimate of the spatiotemporal frequency parameters is then obtained through maximum likelihood joint estimation and EM algorithm iterative optimization.

[0039] 2) Adaptive Beam Control Module The adaptive beam control module is responsible for solving the dynamic beam tracking problem. Based on the estimation results of the direction of arrival, it realizes closed-loop servo control of the beam. Its functional components include: digital beamforming, beam tracking algorithm, and phased array interface control.

[0040] a) Digital beamforming The input to digital beamforming is the received signal of each array element and the desired beam direction. The output is the beamforming weighting coefficient and the synthesized beam signal. Specific functions include: Weight calculation and optimization are performed based on algorithms such as Minimum Variance Distortionless Response (MVDR) and Linear Constrained Minimum Variance (LCMV). Beam characteristics are controlled based on constraints such as beamwidth, sidelobe suppression, and multi-beam generation, while ensuring the real-time requirement of beam switching time.

[0041] b) Beam tracking algorithm The beam tracking algorithm takes the current beam pointing, signal strength, and estimated angle of arrival (Angle of Arrival) as input and outputs the beam pointing command for the next moment. Its specific functions include: An adaptive switching tracking strategy is implemented based on gradient tracking, prediction correction, and other methods. Self-disturbance rejection design is implemented based on platform attitude change compensation, multipath effect suppression, and tracking loss detection to meet the requirements of tracking accuracy and tracking speed.

[0042] c) Phased array interface control The phased array interface control unit takes beam control commands as input and outputs amplitude and phase control signals for each element of the phased array. Its specific functions include: Amplitude and phase calibration: Online calibration is performed using beacon signals, with temperature compensation applied; Control interface: Supports multiple interface protocols such as SPI and LVDS, and supports real-time monitoring of amplitude, phase and temperature of each channel; Fault handling: Supports array element fault detection and isolation, and automatically adjusts the beam when some array elements fail.

[0043] 3) Frequency / Delay Pre-compensation Module The frequency / delay pre-compensation module pre-compensates the transmitted signal based on the estimated Doppler frequency offset and propagation delay to ensure the signal quality at the satellite receiver. Its functional components include: frequency synthesis and compensation, precise timing and synchronization, and uplink and downlink coordination.

[0044] a) Frequency Synthesis and Compensation The frequency synthesis and compensation function takes a baseband signal and a frequency control word as inputs and outputs a frequency-compensated RF signal. Its specific functions include: Frequency synthesis is performed using direct digital frequency synthesis (DDS) to meet the requirements for frequency hopping rate and frequency resolution. Doppler pre-compensation and frequency deviation rate compensation are performed based on the Doppler frequency offset estimate to meet the compensation accuracy requirements; b) Precise timing and synchronization The inputs for precise timing and synchronization are satellite downlink timing information and the local clock. The outputs are precise system time and transmission timing control signals. Specific functions include: Clock management: includes clock discipline, clock drift monitoring and compensation functions; Time synchronization protocol: Supports PTP precise time protocol, one-way delay measurement and compensation; Transmission timing control: includes frame timing generation, propagation delay compensation and jitter control functions.

[0045] c) Uplink and downlink coordination The inputs to uplink and downlink coordination are link status information and power control commands, and the output is the coordinated transmit parameters. Specific functions include: Delay difference compensation: Supports uplink and downlink asymmetric delay measurement, adaptive compensation and fast feedback adjustment; Power control: Supports open-loop power control based on link budget and closed-loop power control based on satellite feedback; Link quality assessment: Provides bit error rate estimation, signal-to-noise ratio measurement, and link budget calculation.

[0046] (2) Signal layer processing channel To address the challenge of rapidly acquiring and tracking time-varying frequency hopping patterns, the signal layer processing channel is designed with the following goals: fast frequency hopping pattern acquisition, accurate frequency hopping synchronization maintenance, support for multiple frequency hopping patterns, and anti-interference and anti-spoofing capabilities. Its main functional components include: a frequency hopping pattern synchronization and tracking module, a secure synchronization verification module, and a signal demodulation and decoding module.

[0047] 1) Frequency hopping pattern synchronization and tracking module The frequency hopping pattern synchronization and tracking module enables rapid acquisition, synchronization maintenance, and recovery from out-of-synchronization of frequency hopping patterns, ensuring reliable frequency hopping communication in dynamic environments. Its functional components include: rapid pattern acquisition, synchronization status tracking, pattern management, and switching.

[0048] a) Pattern Quick Capture The input for fast pattern acquisition is a precise time base and a pre-shared frequency hopping seed provided by the physical layer. The output is the current frequency hopping pattern state and a synchronization indicator. Specific functions include: By employing multiple hypothesis testing and parallel correlation processing, frequency domain correlation and rapid acquisition based on FFT are achieved. Frequency hopping patterns are generated in real time using precise time base input and frequency hopping seed provided by the physical layer. The search range is dynamically adjusted based on the time base accuracy to optimize the acquisition strategy.

[0049] b) Synchronization status tracking The inputs to the synchronization status tracking are the received signal and the local frequency hopping pattern, and the outputs are the synchronization status, out-of-synchronization alarm, and tracking error. Specific functions include: Phase-locked tracking: Phase error detection is performed using a digital phase-locked loop; Sequence successive verification: By verifying the matching of the received frequency with the local frequency hop by hop, false hop events are detected and counted to achieve confidence assessment; Loss of synchronization handling: By configuring a loss of synchronization detection threshold, re-acquisition is triggered when the phase error exceeds the threshold.

[0050] c) Pattern Management and Switching The inputs for pattern management and switching are network commands and environmental awareness information, and the outputs are the currently used pattern and switching commands. Specific functions include: Pattern library management: Supports storing multiple frequency hopping patterns and over-the-air pattern updates; Dynamic switching logic: Supports time-triggered and event-triggered switching logic. The former switches patterns according to a predetermined time, while the latter supports pattern switching based on interference detection, security alarms, etc. Emergency communication support includes fixed frequency modes and simplified patterns, which serve as a backup solution when frequency hopping fails, simplifying access complexity.

[0051] 2) Security Synchronization Verification Module The function of the secure synchronization verification module is to provide a secure synchronization mechanism to prevent deception and interference, and to ensure the legitimacy and security of access. Its main functional components include: encrypted synchronization, identity authentication and authorization, and anti-interference detection.

[0052] a) Encrypted synchronization The input for encrypted synchronization is a plaintext synchronization message and an encryption key. The output is an encrypted / decrypted synchronization message. Specific functions include: Encryption algorithm engine: Supports SM4 symmetric encryption and SM2 asymmetric encryption, and supports hardware acceleration; Key management: Supports key storage, key update, and key distribution functions; Synchronous message protection: Supports timestamp encryption protection, message integrity verification, and anti-replay protection.

[0053] b) Identity authentication and authorization The inputs for identity authentication and authorization are identity credentials and authentication requests, and the outputs are authentication results and authorization information. Specific functions include: Two-way authentication: Supports multiple authentication protocols such as platform authentication, satellite authentication, and TLS 1.3; Access control: Supports identity-based access control, role-based access management, and temporary user access; Security audit: Includes access log recording, abnormal behavior detection, and security incident reporting.

[0054] c) Anti-interference detection The inputs to the anti-interference detection system are the received signal and spectrum sensing data, and the outputs are the interference type, interference intensity, and avoidance suggestions. Specific functions include: Interference signal analysis: Supports interference type identification, interference parameter estimation, and interference source localization; Interference assessment: Supports interference impact assessment and threat level classification; Anti-interference strategies include frequency avoidance, pattern adaptation, and power countermeasures.

[0055] 3) Signal demodulation and decoding module The function of the signal demodulation and decoding module is to perform baseband signal processing such as demodulation and decoding on the received signal to recover the original information. Its main functional components include: adaptive demodulation, channel encoding and decoding, and protocol processing.

[0056] a) Adaptive demodulation The input to adaptive demodulation is the baseband sampled signal and channel estimation information, and the output is either demodulated soft bits or hard decision bits. Specific functions include: Modulation recognition: Modulation mode recognition is performed based on classifiers such as Support Vector Machine (SVM) and Convolutional Neural Network (CNN); Adaptive demodulation: Supports demodulation of multiple standards such as BPSK, QPSK, 8PSK, and 16QAM, and supports channel estimation and equalization; Soft decision generation: Based on the maximum likelihood criterion, iteratively optimize the quality of soft information, output soft bit information, and provide a standardized soft information format.

[0057] b) Channel encoding and decoding The inputs to the channel encoding / decoding are demodulation soft bits and encoding parameters, and the outputs are decoded information bits and decoding status. Specific functions include: Forward error correction coding: Supports LDPC coding, Turbo coding, and Polar coding at various bit rates. High-performance decoding: Supports high-performance decoding algorithms such as minimum sum and Log-MAP, and supports joint iterative decoding of inner and outer codes; Interleaving and Deinterleaving: Supports common interleaving methods such as block interleaving, convolutional interleaving, and random interleaving, and supports adaptive interleaving depth and deinterleaving delay control.

[0058] c) Protocol Processing The protocol processing takes decoded bitstreams and protocol configuration as inputs, and outputs higher-level protocol data units and control information. Specific functions include: Frame processing: Features frame synchronization, frame parsing, and frame verification functions; Protocol stack adaptation: Supports physical layer and link layer interfaces, multi-protocol support, and protocol conversion functions; Service quality assurance: Supports priority queue management, traffic shaping, and error control functions.

[0059] (3) Central Coordination and Control Unit The function of the central coordination and control unit is to coordinate the operation of the physical layer processing channel and the signal layer processing channel to achieve the globally optimal access strategy. It is mainly composed of a coordination and synchronization controller, which includes state fusion and joint decision-making functions to achieve intelligent optimization of the access process and improve the success rate and robustness in complex environments.

[0060] Through the aforementioned layered decoupling architecture, joint optimization, and dynamic adaptive design, the highly mobile platform's on-demand access system has the following advantages: 1) Layered decoupled architecture: The physical layer processing channel and the signal layer processing channel are both independent and collaborative, which facilitates technology upgrades and algorithm iterations; 2) Joint optimization design: Global optimal decision-making is achieved by combining spatiotemporal frequency alignment and frequency hopping pattern signal acquisition and tracking through a central controller; 3) Dynamic adaptive capability: It can automatically adjust its working strategy according to changes in the environment, including four working modes: fast access, high-reliability access, covert access, and anti-interference access. 4) Highly robust design: It has multiple backup and fast recovery mechanisms, providing a reliable low-Earth orbit satellite data link access solution for highly mobile platforms.

[0061] Taking the application of UAVs transmitting reconnaissance data back via low-Earth orbit satellite data links as an example, a specific embodiment of this example is illustrated below: Step 1: System Startup When the drone is powered on, the system loads stored outdated ephemeris data and its own GNSS / INS data.

[0062] Step 2: Guide Synchronization The system calculates that the target satellite's azimuth is approximately 40° ± 5° east of north, its elevation angle is 25° ± 3°, and its Doppler frequency offset is approximately +35kHz ± 20kHz.

[0063] Step 3, Joint Capture The phased array antenna scans within the guidance range and captures the downlink synchronization signal at an azimuth angle of 42° and an elevation angle of 23.5° within 38.5ms. The joint estimation module calculates the accurate Doppler frequency offset as +38.2kHz and the propagation delay as 8.7ms, and demodulates the accurate frame start time T0.

[0064] Step 4: Frequency Hopping Synchronization The central controller sends T0 to the frequency hopping sequence generator, which immediately calculates the current frequency hopping channel as f1. The receiver hops to f1, successfully demodulates the pilot, and confirms pattern synchronization.

[0065] Step 5: Uplink Access and Tracking The system sends an access request with compensated parameters, including the transmitter radio frequency, 8.7ms advance transmission time, and beam pointing towards the satellite. It receives confirmation from the satellite 150ms later. After the link is established, the system enters closed-loop tracking mode and continuously fine-tunes the parameters.

[0066] Step 6: From system startup to bidirectional link establishment, the total time was approximately 650ms, achieving on-demand access, followed by high-speed data backhaul. The link remained stable throughout the entire maneuver.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

[0068] The embodiments of this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this application should be included within the protection scope of this application.

Claims

1. A method for on-the-spot access to low-Earth orbit satellite data links on a highly mobile platform, characterized in that, include: Using satellite ephemeris and platform navigation information as initial guidance, spatiotemporal frequency parameters are obtained by receiving and parsing satellite downlink signals and jointly estimating them. Based on the estimated timestamp as the time reference for the frequency hopping pattern, the local frequency hopping sequence generator is driven to predict and verify the current frequency hopping pattern, and frequency offset correction is performed based on the estimated Doppler frequency offset. In response to the successful verification of the frequency hopping pattern, a pre-compensated uplink is constructed and a frequency hopping pattern tracking loop is initiated to fine-tune the time-space-frequency parameters and the phase of the frequency hopping pattern, so that users can access the low-Earth orbit satellite data link at any time and enter steady-state communication.

2. The method for on-demand access to a low-Earth orbit satellite data link on a highly mobile platform according to claim 1, characterized in that: Based on the loaded satellite ephemeris and platform navigation information, the position vector of the satellite in the geocentric inertial coordinate system and the position vector of the platform are obtained respectively. Based on the position vector of the satellite in the geocentric inertial coordinate system and the position vector of the platform, the inertial position vector of the satellite relative to the platform is obtained and converted into the position vector in the geocentric coordinate system. The theoretical azimuth and theoretical elevation angles of the satellite are determined based on the position vector in the station-centered coordinate system, and the relative radial velocity of the satellite relative to the platform is determined based on the position vectors and velocity vectors of the satellite and the platform in the common coordinate system. The theoretical Doppler frequency offset is obtained based on the relative radial velocity, carrier frequency, and speed of light. The satellite system time is then calculated based on the platform's local time at the moment of receiving the signal, the one-way propagation delay of the signal from the satellite to the platform, and the system time difference between the satellite system time and the platform's local time.

3. The method for highly mobile platform-based on-demand access to low-Earth orbit satellite data links according to claim 2, characterized in that: By performing beam scanning and frequency search within the pilot range, the downlink synchronization signal or a specific preamble can be captured; Multi-dimensional estimation is performed using a joint signal processing algorithm to obtain accurate beam pointing, frequency, and time information.

4. The method for highly mobile platform-based on-demand access to low-Earth orbit satellite data links according to claim 1, characterized in that: The estimated precise frame start time is used as the time reference for the frequency hopping pattern and input into the local frequency hopping sequence generator to generate the frequency hopping sequence at the current moment. Tune the receiver to the frequency hopping sequence to receive data. If the signal quality exceeds the threshold, the verification is successful.

5. The method for highly mobile platform-based on-demand access to low-Earth orbit satellite data links according to claim 1, characterized in that: The pre-compensation includes pre-compensation for transmission frequency, transmission time, and transmission beam. Among them, the transmission frequency pre-compensation downlink Doppler frequency offset, the transmission time pre-compensation propagation delay, and the transmitted beam pointing estimate obtained beam azimuth and elevation angles.

6. A highly mobile platform on-demand access system for low-Earth orbit (LEO) satellite data links, used to implement the highly mobile platform on-demand access method for LEO satellite data links as described in any one of claims 1 to 5, characterized in that: It includes a physical layer processing channel, a signal layer processing channel, and a central coordination and control unit. The physical layer processing channel and the signal layer processing channel form a two-layer collaborative processing architecture of physical layer and signal layer. The physical layer processing channel includes a spatiotemporal frequency joint sensing and estimation module, an adaptive beam control module, and a frequency offset / delay pre-compensation module. The signal layer processing channel includes a frequency hopping pattern synchronization and tracking module, a security synchronization verification module, and a signal demodulation and decoding module; The central coordination and control unit consists of a coordination and synchronization controller, which coordinates the operation of the physical layer processing channel and the signal layer processing channel to achieve a globally optimal access strategy.

7. A highly mobile platform for on-demand access to low-Earth orbit satellite data links according to claim 6, characterized in that, The spatiotemporal frequency joint sensing and estimation module includes: The broadband scanning unit takes the intermediate frequency signal after downconversion from the radio frequency front end as input to the broadband spectrum sensing unit and outputs a list of detected signal frequencies, signal strength, and bandwidth estimation. A multi-parameter joint estimation unit, wherein the input of the multi-parameter joint estimation unit is the captured signal sample, and the output is a joint estimate of the direction of arrival, Doppler frequency offset, and propagation delay; A frequency offset / delay estimation unit is used for Doppler frequency offset estimation and propagation delay estimation.

8. A highly mobile platform for on-demand access to low-Earth orbit satellite data links according to claim 6, characterized in that, The adaptive beam control module includes: The digital beamforming unit takes the received signals of each array element and the desired beam direction as inputs, and outputs the beamforming weighting coefficients and the synthesized beam signal. The beam tracking algorithm unit takes the current beam pointing, signal strength, and estimated angle of arrival as inputs and outputs the beam pointing command for the next moment. The phased array interface control unit takes beam control commands as input and outputs amplitude and phase control signals for each element of the phased array.

9. A highly mobile platform for on-demand access to low-Earth orbit satellite data links according to claim 6, characterized in that, The frequency / delay pre-compensation module includes: The frequency synthesis and compensation unit takes a baseband signal and a frequency control word as inputs and outputs a frequency-compensated radio frequency signal. The precision timing and synchronization unit takes satellite downlink timing information and local clock as inputs and outputs precise system time and transmission timing control signal. The uplink and downlink coordination unit takes link status information and power control commands as inputs and outputs coordinated transmission parameters as outputs.

10. A highly mobile platform for on-demand access to low-Earth orbit satellite data links according to claim 6, characterized in that, The frequency hopping pattern synchronization and tracking module includes: The pattern fast acquisition unit takes as input the precise time base and pre-shared frequency hopping seed provided by the physical layer, and outputs the current frequency hopping pattern state and synchronization indication. A synchronization status tracking unit, wherein the input of the synchronization status tracking unit is the received signal and the local frequency hopping pattern, and the output is the synchronization status, the out-of-synchronization alarm, and the tracking error; The pattern management and switching unit takes network commands and environmental awareness information as inputs and outputs the currently used pattern and switching commands.

Images