A low-inclination low-earth-orbit satellite constellation-based internet of things terminal direct connection satellite communication method and system

Abstract

The application discloses a kind of based on low inclination low-orbit satellite constellation's internet of things terminal direct connection satellite communication method and system, belong to satellite communication technical field, including: according to the orbit height of low-orbit satellite and inclination division ground coverage area, and determine terminal attribution.Satellite broadcast ephemeris, terminal receives after combining own position carries out orbit prediction, generates and corrects coverage prediction time series, according to this in window outside hibernation, window before wake up.According to service type and electric quantity after wake up, execute hierarchical wake-up timing.In wake-up period, calculate Doppler shift, and according to coverage area type selection compensation strategy to complete frequency synchronization.Meanwhile, satellite determines beam pointing angle according to subsatellite point latitude table, so that beam center points to target grid.After completing frequency synchronization and beam covers terminal, terminal executes data transmission.The application realizes low-power consumption, high reliability, low-cost low-orbit satellite internet of things terminal direct connection satellite communication.

Description

Technical Field

[0001] This invention belongs to the field of satellite communication technology, and in particular relates to a method and system for direct satellite communication between Internet of Things (IoT) terminals and satellites based on a low-inclination low-Earth orbit (LEO) satellite constellation. Background Technology

[0002] Low-Earth orbit (LEO) satellite IoT communication is an important area of ​​current development. IoT terminals typically feature low power consumption, low data rates, and massive connectivity, which places unique demands on communication protocol design.

[0003] There are already various low-Earth orbit satellite IoT communication solutions in the existing technology, but these solutions all have the following shortcomings: First, existing technologies are mainly geared towards general low-Earth orbit satellite communication scenarios and have not systematically adapted communication protocols for specific orbital parameters (such as a 45° low inclination angle and a 900km orbital altitude).

[0004] Second, existing Doppler frequency shift compensation schemes are generally designed for general low-Earth orbit satellite scenarios. Their Doppler frequency shift range decreases slightly with increasing orbital altitude. Existing compensation algorithms need to be fine-tuned for different altitude layers. They fail to optimize for the specific geometric occlusion and edge coverage characteristics generated by a 45° low-inclination orbit at an altitude of 900km, resulting in insufficient compensation accuracy of low-power terminals in the edge coverage area.

[0005] Third, the 45° low-inclination orbit constellation has discontinuous coverage and long interruption periods in mid-to-high latitude regions. Existing solutions lack a systematic approach to address this, resulting in ineffective terminal wake-ups and wasted power.

[0006] Therefore, there is an urgent need for a direct satellite communication method for IoT terminals of low-orbit satellite constellations with low inclination and specific orbital altitudes. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method for direct satellite communication between an IoT terminal and a low-inclination low-Earth orbit satellite constellation, comprising the following steps: Based on the orbital altitude and inclination of the low-Earth orbit satellite constellation, the layering type of the ground coverage area is determined, and the coverage area type to which the IoT terminal belongs is determined based on the geographical location of the deployment. Satellite broadcast ephemeris data; The IoT terminal receives the ephemeris data, generates a coverage prediction time series based on the ephemeris data and its own geographical location, and corrects the coverage prediction time series according to the coverage area type. Based on the corrected coverage prediction time series, it enters a deep sleep mode outside the predicted communication window and wakes up before the predicted communication window. After the IoT terminal is woken up, the wake-up level is determined according to the service type and power status, and the corresponding wake-up sequence is executed according to the wake-up level. During the wake-up period of the IoT terminal, the relative velocity vector between the satellite and the IoT terminal is obtained, the Doppler frequency shift is determined based on the relative velocity vector and the carrier frequency, the Doppler compensation strategy is determined based on the coverage area type to which the IoT terminal belongs, and frequency synchronization is performed. While the IoT terminal performs frequency synchronization, the satellite determines the corresponding beam pointing angle from the preset beam pointing schedule table based on the current latitude of the sub-satellite point, and controls the center of the satellite beam to point to the preset ground grid position. After frequency synchronization is completed and the satellite beam is pointed at the location of the IoT terminal, the IoT terminal performs data transmission.

[0008] Optionally, the layering type of the ground coverage area can be determined based on the orbital altitude and orbital inclination of the low-Earth orbit satellite constellation, including: The latitude range of the ground area covered by the satellite is calculated based on the orbital altitude and orbital inclination, and the Earth's surface is divided into the core coverage area, the edge coverage area, and the extended coverage area.

[0009] Optionally, the coverage prediction time series is corrected according to the coverage area type, including: For IoT terminals located in edge coverage areas, a dual prediction mechanism is adopted. The first prediction is based on the standard transit time prediction of satellite ephemeris, and the second prediction is based on the historical communication success rate stored locally on the terminal to adaptively adjust the prediction time window.

[0010] Optionally, after the IoT terminal is woken up, a tiered wake-up level is determined based on the service type and battery status, and the corresponding wake-up sequence is executed according to the tiered wake-up level, including: Configure different wake-up levels based on service type and battery status, including Level 1, Level 2 and Level 3; The first level configuration is to wake up at the first wake-up time in advance and maintain a preset standby time after the window ends; the second level configuration is to wake up at the second wake-up time in advance and immediately go to sleep after the window ends; the third level configuration is to wake up once every preset number of communication windows.

[0011] Optionally, a Doppler compensation strategy is determined based on the coverage area type to which the IoT terminal belongs, including: For IoT terminals located in the core coverage area, a combined scheme of satellite-side coarse compensation and terminal-side fine compensation is adopted. For IoT terminals located in edge coverage areas, a terminal-only fine compensation scheme is adopted.

[0012] Optionally, it also includes an interruption recovery step: When an IoT terminal fails to establish a connection within the predicted communication window, an interruption recovery process is executed according to the coverage area type; a retry counter is set, and when the number of consecutive retries exceeds a preset threshold, retries are stopped and the system switches to backup communication mode or reports an alarm signal.

[0013] Optionally, an interruption recovery procedure is performed based on the coverage area type, including: For core coverage areas, IoT terminals will re-initiate access after a short interval. For edge coverage areas, IoT terminals immediately enter temporary caching mode, storing the data to be transmitted in the local cache and waiting for the next prediction window to retransmit.

[0014] Optionally, the IoT terminal includes a track feature parameter library, which includes at least track height, track inclination, a pre-calculated visible geocentric angle mapping table, and a Doppler frequency shift mapping table.

[0015] This invention also proposes an IoT terminal direct satellite communication system based on a low-inclination low-Earth orbit satellite constellation, for implementing the method, including: A low-Earth orbit (LEO) satellite constellation consists of multiple LEO satellites with orbital altitude and orbital inclination. It is used to broadcast ephemeris data and determine the corresponding beam pointing angle from a preset beam pointing schedule table based on the current latitude of the satellite's nadir point, so as to control the on-board beam center to point to a preset ground grid position. The Internet of Things (IoT) terminal is used to receive broadcast ephemeris data, combine it with its own geographical location to make orbit predictions to autonomously determine the sleep-wake sequence, and adaptively perform hierarchical wake-up, Doppler compensation and data transmission according to the coverage area type, service type and power status. Ground gateway stations are used to receive IoT data relayed by satellites and upload ephemeris updates and beam control commands to satellites. The orbit sensing and scheduling center, deployed on the ground network side, is used to calculate and update satellite ephemeris data, and upload it to the satellite through the ground gateway station, which then broadcasts it to the entire network. The coverage area type of the IoT terminal is determined by the ground coverage area layering type based on the orbital altitude and orbital inclination of the low-Earth orbit satellite constellation, as well as the geographical location of the terminal's deployment.

[0016] Optionally, it also includes a coverage prediction optimization module, which is used to collect deviation data between the actual successful access time of the terminal and the prediction time window, train a prediction error correction model with terminal location, satellite number, and historical weather conditions as input features, and feed the correction amount back to the hibernation wake-up scheduling table to learn and correct the prediction error of the satellite transit time window.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects: This invention determines the layering of ground coverage areas based on orbital altitude and inclination, enabling terminals to predict orbits using ephemeris data and their own geographical location. This generates a corrected coverage prediction time series, allowing the terminal to enter deep sleep outside the predicted communication window and only wake up before the window opens. This avoids the ineffective blind searches and frequent scans performed in traditional solutions due to unpredictable transit times. Furthermore, it implements a tiered wake-up sequence based on service type and battery status, allowing terminals with different needs to adopt differentiated wake-up strategies, minimizing unnecessary wake-up time. Through this combination of predictive sleep / wake-up and tiered wake-up, terminal power consumption is significantly reduced, with actual tests showing a reduction from several months of battery life to over a year of maintenance-free operation.

[0018] To address the characteristics of discontinuous coverage and long interruptions in mid-to-high latitude regions exhibited by low-inclination low-Earth orbit constellations, this invention modifies the coverage prediction time series based on the coverage area type of the terminal, ensuring accurate wake-up when the satellite passes overhead. Simultaneously, during the wake-up period, a differentiated Doppler compensation strategy is determined based on the coverage area type, and the satellite, using a lookup table based on the latitude of the nadir point, determines the beam pointing angle, ensuring the onboard beam center accurately points to the ground grid location. Through these methods of adaptive coverage area correction, layered Doppler compensation, and coordinated onboard beam pointing control, the geometric obstruction and synchronous acquisition difficulties in edge coverage areas are effectively resolved, significantly improving the data transmission success rate.

[0019] In this invention, the satellite directly determines the beam pointing angle from a pre-set beam pointing schedule table based on the current sub-satellite latitude, eliminating the need for real-time offset angle calculation and reducing onboard computational overhead. Simultaneously, a terminal-side fine-compensation scheme is employed for terminals in edge coverage areas, avoiding reliance on satellite-side coarse-compensation resources and enabling reasonable offloading of Doppler compensation tasks. Through this onboard pre-set scheduling and terminal-side compensation layering approach, the resource utilization efficiency of the onboard processing unit is improved, while reducing the hardware complexity and cost of the terminals.

[0020] In summary, this invention achieves low-power, high-reliability, and low-cost direct satellite communication for low-Earth orbit satellite IoT terminals by deeply coupling the communication protocol stack with orbital geometry features and employing a series of interconnected technical means, such as orbital parameter-driven coverage area layering, predictive sleep wake-up, graded wake-up, layered Doppler compensation, and on-board beam pointing lookup table control. Attached Figure Description

[0021] 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 schematic diagram of the method flow according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the coverage area layering according to an embodiment of the present invention; Figure 3 This is a state machine diagram of the terminal hierarchical wake-up strategy according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the Doppler frequency shift layered compensation architecture according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the on-board beam pointing adaptive control principle according to an embodiment of the present invention; Figure 6 This is a block diagram of the module composition of the communication system according to an embodiment of the present invention; Figure 7 This is a flowchart illustrating the training process of the machine learning model in the coverage prediction optimization module of this invention. Detailed Implementation

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0024] Example 1 This embodiment provides a method for direct satellite communication between an IoT terminal and a low-inclination low-Earth orbit satellite constellation, including the following steps: Based on the orbital altitude and inclination of the low-Earth orbit satellite constellation, the layering type of the ground coverage area is determined, and the coverage area type to which the IoT terminal belongs is determined based on the geographical location of the deployment. Satellite broadcast ephemeris data; The IoT terminal receives the ephemeris data, generates a coverage prediction time series based on the ephemeris data and its own geographical location, and corrects the coverage prediction time series according to the coverage area type. Based on the corrected coverage prediction time series, it enters a deep sleep mode outside the predicted communication window and wakes up before the predicted communication window. After the IoT terminal is woken up, the wake-up level is determined according to the service type and power status, and the corresponding wake-up sequence is executed according to the wake-up level. During the wake-up period of the IoT terminal, the relative velocity vector between the satellite and the IoT terminal is obtained, the Doppler frequency shift is determined based on the relative velocity vector and the carrier frequency, the Doppler compensation strategy is determined based on the coverage area type to which the IoT terminal belongs, and frequency synchronization is performed. While the IoT terminal performs frequency synchronization, the satellite determines the corresponding beam pointing angle from the preset beam pointing schedule table based on the current latitude of the sub-satellite point, and controls the center of the satellite beam to point to the preset ground grid position. After frequency synchronization is completed and the satellite beam is pointed at the location of the IoT terminal, the IoT terminal performs data transmission.

[0025] As a specific implementation method, such as Figure 1 As shown, the specific steps include: Step S1: Extraction of orbital feature parameters and layering of coverage areas: like Figure 2 As shown, based on the orbital altitude of the satellite constellation and orbital inclination The system calculates the latitudinal range of the ground area covered by satellites, divides the Earth's surface into core coverage area, edge coverage area, and extended coverage area, and classifies the IoT terminals into the corresponding coverage area type based on their geographical location. The track height is feasible. The orbital inclination is 900 km. It is 45°.

[0026] Step S2: Dynamic Coverage Prediction and Sleep / Wake-up Scheduling: Satellites broadcast ephemeris data; after receiving the ephemeris, the terminal uses an orbit prediction algorithm to locally calculate the nadir trajectory and transit time window of each satellite, generates a coverage prediction time series, and corrects the prediction time window based on the coverage area type. The terminal enters deep sleep mode outside the prediction window according to the coverage prediction time series and wakes up before the prediction window. The feasible step S2, which involves correcting the prediction time window based on the coverage area type, includes: for IoT terminals located in the edge coverage area, a dual prediction mechanism is adopted. The first prediction is based on the standard transit time prediction of satellite ephemeris, and the second prediction is based on the correction factor of historical communication success rate. The prediction time window is adaptively adjusted according to the historical communication success rate of the terminal's location.

[0027] Step S3: Terminal Tiered Wake-up Strategy: Based on the service type and power status of the IoT terminal, a hierarchical wake-up control signaling is generated to drive the power management module of the IoT terminal to execute the corresponding hierarchical wake-up sequence. Different levels of terminals are configured with different wake-up advance amounts and standby durations after the window ends.

[0028] In this embodiment, different wake-up levels are configured according to the service type and power status, including a first level, a second level, and a third level. The first level is configured to wake up in advance of the first wake-up time and maintain a preset standby time after the window ends. The second level is configured to wake up in advance of the second wake-up time and immediately go into hibernation after the window ends. The third level is configured to wake up once every preset number of communication windows.

[0029] Specifically, such as Figure 3 As shown, the configuration is tiered based on service type and power status: Level A: In advance Time awakens, The time is determined based on the power-on stabilization time of the RF front-end and the Doppler acquisition time, preferably 5–10 seconds; after the window ends, maintain [the current position]. Standby, The value is determined based on the transition time of the baseband processing unit entering sleep mode, preferably 3 to 5 seconds.

[0030] Level B: Advance wake, The time is determined based on the frequency synthesizer lock-in time and the synchronization acquisition time, preferably 2 to 5 seconds; the window ends and the device immediately goes into hibernation.

[0031] Grade C: Every Each window is woken up once. The optimal value is 2 to 10, determined based on battery capacity and delay tolerance.

[0032] Step S4: Doppler frequency shift layer compensation: The relative velocity vector between the satellite and the IoT terminal is obtained, the Doppler frequency shift is calculated, and the Doppler compensation strategy is dynamically adjusted according to the coverage area type of the IoT terminal. For terminals located in the core coverage area, a joint scheme of satellite-side coarse compensation and terminal-side fine compensation is adopted, while for terminals located in the edge coverage area, a terminal-side fine compensation scheme is adopted only. Furthermore, the relative velocity vector between the satellite and the terminal is obtained, and the Doppler frequency shift is calculated: based on the relative radial velocity... carrier frequency and the speed of light Calculate the fundamental frequency offset; the calculation formula is as follows: .

[0033] Furthermore, refer to Figure 4The Doppler frequency shift hierarchical compensation architecture in this embodiment includes a coarse compensation layer, a fine compensation layer, and an adaptive adjustment layer. The coarse compensation layer is deployed on the satellite side to acquire ephemeris and terminal location grids, calculate pre-compensated Doppler values, and perform pre-compensation during signal transmission. The fine compensation layer is deployed on the terminal side to receive pilot signals, estimate residual frequency offset through correlation calculations, and perform compensation using a digital frequency control loop. The adaptive adjustment layer dynamically selects the compensation scheme based on the coverage area type of the terminal: for core coverage areas, a combined coarse and fine compensation scheme is used; for edge coverage areas, only the fine compensation scheme is used.

[0034] Step S5: On-board beam pointing adaptive control: like Figure 5 As shown, the onboard multi-beam antenna uses a pre-set beam pointing schedule. Based on the current latitude of the satellite's nadir point, the corresponding beam pointing angle is selected from the schedule to ensure that the beam center points to a preset ground grid position. This schedule is pre-calculated based on the ground service distribution density and does not calculate the offset angle in real time.

[0035] Step S6: Terminal Access and Data Transmission After the terminal is woken up, it scans the frequency band, selects the optimal satellite, sends an access request, and sends IoT data on the allocated resources.

[0036] Step S7: Interruption recovery and data retransmission mechanism: When an IoT terminal fails to establish a connection within the predicted communication window, an interruption recovery process is executed based on the coverage area type.

[0037] Feasible, for core coverage areas, terminals wait for short intervals Then re-initiate access. The value ranges from 1 to 3 seconds; for edge coverage areas, the terminal immediately enters temporary buffer mode, stores the data to be transmitted in the local buffer, and waits for the next prediction window to retransmit; a retry counter is set. When the number of consecutive retries Exceeding the preset threshold When this happens, the terminal stops retrying and switches to backup communication mode or reports an alarm signal.

[0038] Set retry counter Initially After a core coverage area interruption, a short retry interval will occur; after a perimeter coverage area interruption, a buffer mode will be entered to wait for the next window. If the number of consecutive retries exceeds a threshold... (Preferred) When the number of attempts reaches (number of times), stop retrying and switch to backup communication mode or report an alarm.

[0039] Implementable, the communication module of the IoT terminal has a built-in track feature parameter library, which includes at least track height. Track inclination Pre-computed visual geocentric angle mapping table and Doppler frequency shift mapping table.

[0040] On the other hand, such as Figure 6 As shown, this embodiment provides an IoT terminal direct satellite communication system based on a low-inclination low-Earth orbit satellite constellation, used to implement the aforementioned communication method. The system includes: Low Earth Orbit (LEO) satellite constellation: Composed of multiple LEO satellites (orbital altitude >900km, inclination >45°). Each satellite carries a multi-beam communication payload, an onboard processing unit, and an inter-satellite link module. Specifically: The multi-beam communication payload generates multiple beams based on a beam pointing adaptive control unit and determines the beam pointing offset angle corresponding to the current ground point by looking up a pre-set ground grid beam position table, thus controlling the beam center to point to the preset ground grid position; the onboard processing unit executes onboard protocol processing, including parsing terminal access requests, allocating communication resources, and forwarding received IoT data to ground gateway stations via inter-satellite links or directly; the inter-satellite link module enables data exchange and ephemeris synchronization between satellites, ensuring the continuity of the constellation's overall coverage.

[0041] The IoT terminal comprises a communication module, a power management module, and a storage module. The communication module is configured with a pre-set set of communication parameters based on orbital characteristics (e.g., orbital altitude, orbital inclination, a pre-calculated visible geocentric angle mapping table, and a Doppler frequency shift mapping table). It receives ephemeris data broadcast by satellite, performs orbital prediction based on its geographical location to autonomously determine its sleep / wake-up sequence, and adaptively performs graded wake-up, Doppler compensation, and data transmission according to its coverage area type, service type, and power status. The power management module executes the graded wake-up sequence, controlling the power-on and power-off of components such as the RF front-end and frequency synthesizer according to the terminal's wake-up level, and puts the terminal into deep sleep mode outside the predicted communication window. The storage module caches IoT data to be transmitted, especially in edge coverage areas where access failure occurs, temporarily storing data to await retransmission in the next predicted window.

[0042] Ground gateway station: Used to receive IoT data relayed by satellite and upload ephemeris updates and beam control commands to the satellite.

[0043] Orbit Sensing and Scheduling Center: Deployed on the ground network side, it calculates and updates satellite ephemeris data and uploads it to the satellite via ground gateway stations, from which the satellite broadcasts it to the entire network. This center does not generate personalized scheduling tables for each terminal.

[0044] The coverage area type of the IoT terminal is determined by the ground coverage area layering type based on the orbital altitude of the low-Earth orbit satellite constellation (900km) and the orbital inclination (45°), as well as the geographical location of the terminal's deployment.

[0045] Furthermore, such as Figure 7 As shown, the system also includes a coverage prediction optimization module: used to collect deviation data between the actual successful access time of the terminal and the prediction time window, train the prediction error correction model with terminal location, satellite number, and historical weather conditions as input features, and feed the correction amount back to the hibernation wake-up scheduling table to learn and correct the prediction error of the satellite transit time window.

[0046] Compared with the prior art, this embodiment has the following advantages: This embodiment, based on the characteristics of a satellite constellation with low inclination and specific orbital altitude, systematically adapts various aspects of the communication protocol, such as ground coverage area layering, terminal sleep / wake-up scheduling, Doppler shift compensation, and on-board beam pointing control, to orbital geometry parameters, forming an integrated collaborative working mechanism. Under this combination of orbital parameters, deep coupling between the communication protocol and orbital characteristics is achieved, thereby optimizing overall performance. By employing a mechanism combining satellite broadcast ephemeris and terminal local coverage prediction, IoT terminals can accurately calculate satellite transit time windows based on their geographical location and enter deep sleep mode outside the predicted window, only waking up before the window. This avoids the ineffective blind searches and frequent scans performed by traditional solutions due to the inability to predict transit times. Simultaneously, a tiered wake-up strategy allows terminals with different service types and power states to use differentiated wake-up sequences, significantly reducing terminal power consumption and extending battery life from the short-cycle of traditional solutions to a long-cycle maintenance-free level.

[0047] To address the issues of discontinuous coverage and long interruptions in mid-to-high latitude regions for low-inclination low-Earth orbit constellations, this embodiment corrects the coverage prediction time series based on the coverage area type of the terminal. It also employs a dual prediction mechanism that combines standard prediction based on ephemeris with adaptive correction based on historical communication success rates to ensure accurate wake-up of the terminal when the satellite passes overhead. Combined with a layered Doppler compensation strategy and lookup table control for onboard beam pointing, this effectively solves the problems of geometric obstruction and synchronous acquisition difficulties in edge coverage areas, achieving high-success-rate data transmission in discontinuous coverage scenarios.

[0048] This embodiment employs a layered Doppler compensation strategy. For terminals in the core coverage area, a combined scheme of satellite-side coarse compensation and terminal-side fine compensation is used, while for terminals in the edge coverage area, only the terminal-side fine compensation scheme is used. This avoids the problem of satellite-side coarse compensation failing due to geometric obstruction in the edge coverage area, and at the same time reduces the terminal's dependence on high-precision frequency synthesizers, thereby reducing terminal hardware costs. On the satellite side, a pre-set beam pointing schedule table is used to directly determine the beam pointing angle based on the latitude of the sub-satellite point, eliminating the need for real-time calculation of the offset angle, saving on-board computing resources, and improving the resource utilization efficiency of the on-board processing unit.

[0049] Example 2 In this embodiment, the satellite constellation consists of 36 low-Earth orbit satellites with an altitude of 900 km and an inclination of 45°. The IoT terminal is a soil moisture sensor node that reports data 12 times per day. The implementation of this invention is illustrated using examples of terminals deployed in different geographical locations.

[0050] First, the system calculates the coverage area based on orbital altitude and inclination, dividing the Earth's surface into core coverage area, edge coverage area, and extended coverage area. The system then determines the coverage area type based on the terminal's geographical location. In this embodiment, when the terminal is deployed at 35° North latitude (belonging to the edge coverage area), the satellite broadcasts ephemeris data. Upon receiving this data, the terminal, combined with its own geographical location, calculates the transit time window locally. There are eight transit opportunities within 24 hours, each window lasting approximately 4 to 6 minutes. The terminal configures a second-level wake-up sequence based on the service type (low-power sensor) and battery status, waking up 3 seconds in advance (2 seconds for frequency synthesizer locking and 1 second for synchronization acquisition). During wake-up, the terminal executes a Doppler compensation strategy with only terminal-side fine compensation, resulting in a residual frequency offset of less than 500Hz. Simultaneously, the onboard beam scheduling table instructs the satellite to appropriately offset the beam pointing center point southward relative to the nadir point within this latitude range to compensate for geometric obstruction by the low-inclination orbit in the edge coverage area, ensuring the terminal is within the effective beam coverage area when the satellite transits. After the terminal wakes up, it sends 12 bytes of humidity data, which is received by the satellite and forwarded to the ground gateway station. If the access fails due to cloud cover or other reasons, the terminal stores the data to be sent in a local cache, sets a retry counter, and waits for the next prediction window to resend. After three consecutive failures, an alarm signal is reported through a backup communication link (such as LoRa).

[0051] When the terminal is deployed near the equator (2°N), it falls within the core coverage area. The difference from the edge coverage area lies in the terminal's configuration: it is configured with a first-level wake-up timing, waking up 8 seconds in advance (3 seconds for RF front-end power-up and 5 seconds for Doppler acquisition), and employs a combined Doppler compensation scheme combining satellite-side coarse compensation and terminal-side fine compensation. The terminal has approximately 12 transit opportunities per day. A power consumption comparison is made using a core coverage area terminal as an example: In the traditional blind search scheme, the terminal lacks ephemeris information and wakes up every 15 minutes, performing a 30-second full-band scan each time, with an average receiver operating current of 40mA. In this invention, the terminal receives the broadcast ephemeris and accurately calculates the satellite transit time window locally. Each wake-up requires only 8 seconds to complete synchronization and data transmission and reception, with a peak current of 200mA for RF transmission (1 second) and 120mA for reception (7 seconds), and deep sleep (<1μA) for the remaining time. The average current per single duty cycle is (200×1+120×7) / 8=130mA, but due to the extremely low duty cycle (<0.1%), the system's daily equivalent average current is only 0.032mA (i.e., 32μA). The daily power consumption calculation is shown in Table 1. Table 1 Special note: The 130mA in the table is the instantaneous operating current during RF transmission and reception. Due to the use of a predictive wake-up mechanism, the duty cycle of this current is extremely low (<0.1%), so the system's daily equivalent average current is only 32μA, which is the key to achieving long battery life.

[0052] Considering battery self-discharge and temperature effects, this embodiment can achieve maintenance-free operation for more than one year, while the traditional solution requires battery replacement approximately every two months. It should be noted that the traditional solution's wake-up frequency of 96 times / day corresponds to the actual overflight opportunities under a constellation of 38 low-Earth orbit satellites. However, because the terminal cannot predict the precise overflight time, it has to scan frequently, resulting in higher daily energy consumption.

[0053] Reference Figure 7 This embodiment also demonstrates the specific training process of the coverage prediction optimization module. The terminal is deployed at 40°S latitude (also within the edge coverage area). The terminal locally collects the deviation data between the actual successful access time and the local prediction window over the past 30 days, using date, satellite number, and historical weather conditions as features to train the prediction error correction model. In low-computing-power scenarios, the model parameters can also be trained on the central server and then distributed to the terminal. After 30 days of learning, the average absolute error of the prediction time window is reduced from ±45 seconds to ±12 seconds, the terminal wake-up advance can be reduced from 5 seconds to 2 seconds, and power consumption is further reduced by approximately 30%.

[0054] In summary, this embodiment, based on a low-Earth orbit satellite constellation with a 45° inclination and an altitude of 900 km, utilizes interconnected technologies such as orbit parameter-driven ground coverage area layering, terminal-based local coverage prediction and sleep / wake-up based on ephemeris data, tiered wake-up strategies, layered Doppler compensation, on-board beam pointing lookup table control, and optional interruption recovery and machine learning enhancement. This enables IoT terminals to achieve low-power, high-reliability direct data communication with satellites in both edge and core coverage areas. The various steps are mutually supportive and synergistic: coverage prediction and tiered wake-up address the problem of invalid wake-up under discontinuous coverage; layered Doppler compensation and on-board beam pointing control solve the problems of geometric obstruction and synchronization acquisition difficulties in edge coverage areas; and interruption recovery and machine learning correction further enhance the system's robustness and adaptability.

[0055] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for direct satellite communication between an Internet of Things (IoT) terminal and a low-inclination low-Earth orbit (LEO) satellite constellation, characterized in that: Includes the following steps: Based on the orbital altitude and inclination of the low-Earth orbit satellite constellation, the layering type of the ground coverage area is determined, and the coverage area type to which the IoT terminal belongs is determined based on the geographical location of the deployment. Satellite broadcast ephemeris data; The IoT terminal receives the ephemeris data, generates a coverage prediction time series based on the ephemeris data and its own geographical location, and corrects the coverage prediction time series according to the coverage area type. Based on the corrected coverage prediction time series, it enters a deep sleep mode outside the predicted communication window and wakes up before the predicted communication window. After the IoT terminal is woken up, the wake-up level is determined according to the service type and power status, and the corresponding wake-up sequence is executed according to the wake-up level. During the wake-up period of the IoT terminal, the relative velocity vector between the satellite and the IoT terminal is obtained, the Doppler frequency shift is determined based on the relative velocity vector and the carrier frequency, the Doppler compensation strategy is determined based on the coverage area type to which the IoT terminal belongs, and frequency synchronization is performed. While the IoT terminal performs frequency synchronization, the satellite determines the corresponding beam pointing angle from the preset beam pointing schedule table based on the current latitude of the sub-satellite point, and controls the center of the satellite beam to point to the preset ground grid position. After frequency synchronization is completed and the satellite beam is pointed at the location of the IoT terminal, the IoT terminal performs data transmission.

2. The method according to claim 1, characterized in that, Based on the orbital altitude and inclination of the low-Earth orbit satellite constellation, the layering type of the ground coverage area is determined, including: The latitude range of the ground area covered by the satellite is calculated based on the orbital altitude and orbital inclination, and the Earth's surface is divided into the core coverage area, the edge coverage area, and the extended coverage area.

3. The method according to claim 1, characterized in that, The coverage prediction time series is corrected according to the coverage area type, including: For IoT terminals located in edge coverage areas, a dual prediction mechanism is adopted. The first prediction is based on the standard transit time prediction of satellite ephemeris, and the second prediction is based on the historical communication success rate stored locally on the terminal to adaptively adjust the prediction time window.

4. The method according to claim 1, characterized in that, After the IoT terminal is woken up, a tiered wake-up level is determined based on the service type and battery status, and the corresponding wake-up sequence is executed according to the tiered wake-up level, including: Configure different wake-up levels based on service type and battery status, including Level 1, Level 2 and Level 3; The first level configuration is to wake up at the first wake-up time in advance and maintain a preset standby time after the window ends; the second level configuration is to wake up at the second wake-up time in advance and immediately go to sleep after the window ends; the third level configuration is to wake up once every preset number of communication windows.

5. The method according to claim 1, characterized in that, The Doppler compensation strategy is determined based on the coverage area type of the IoT terminal, including: For IoT terminals located in the core coverage area, a combined scheme of satellite-side coarse compensation and terminal-side fine compensation is adopted. For IoT terminals located in edge coverage areas, a terminal-only fine compensation scheme is adopted.

6. The method according to claim 1, characterized in that, It also includes interrupt recovery steps: When an IoT terminal fails to establish a connection within the predicted communication window, an interruption recovery process is executed based on the coverage area type. Set a retry counter. When the number of consecutive retries exceeds a preset threshold, stop retries and switch to backup communication mode or report an alarm signal.

7. The method according to claim 6, characterized in that, The interruption recovery process is executed according to the coverage area type, including: For core coverage areas, IoT terminals will re-initiate access after a short interval. For edge coverage areas, IoT terminals immediately enter temporary caching mode, storing the data to be transmitted in the local cache and waiting for the next prediction window to retransmit.

8. The method according to claim 1, characterized in that, The Internet of Things (IoT) terminal includes a track feature parameter library, which includes at least track height, track inclination, a pre-calculated visible geocentric angle mapping table, and a Doppler frequency shift mapping table.

9. A direct satellite communication system for IoT terminals based on a low-inclination low-Earth orbit satellite constellation, characterized in that, For implementing the method according to any one of claims 1-8, comprising: A low-Earth orbit (LEO) satellite constellation consists of multiple LEO satellites with orbital altitude and orbital inclination. It is used to broadcast ephemeris data and determine the corresponding beam pointing angle from a preset beam pointing schedule table based on the current latitude of the satellite's nadir point, so as to control the on-board beam center to point to a preset ground grid position. The Internet of Things (IoT) terminal is used to receive broadcast ephemeris data, combine it with its own geographical location to make orbit predictions to autonomously determine the sleep-wake sequence, and adaptively perform hierarchical wake-up, Doppler compensation and data transmission according to the coverage area type, service type and power status. Ground gateway stations are used to receive IoT data relayed by satellites and upload ephemeris updates and beam control commands to satellites. The orbit sensing and scheduling center, deployed on the ground network side, is used to calculate and update satellite ephemeris data, and upload it to the satellite through the ground gateway station, which then broadcasts it to the entire network. The coverage area type of the IoT terminal is determined by the ground coverage area layering type based on the orbital altitude and orbital inclination of the low-Earth orbit satellite constellation, as well as the geographical location of the terminal's deployment.

10. The system according to claim 9, characterized in that, It also includes a coverage prediction optimization module, which is used to collect the deviation data between the actual successful access time of the terminal and the prediction time window, train the prediction error correction model with the terminal location, satellite number and historical weather conditions as input features, and feed the correction amount back to the hibernation wake-up scheduling table to learn and correct the prediction error of the satellite transit time window.

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