A low earth orbit satellite space-time reference protection method, system and computer program product

Abstract

The application provides a low-orbit satellite space-time reference protection method, which comprises the following steps: step 1, acquiring time information of navigation satellites of each channel, performing time information checking on the time information of the navigation satellites of each channel, and determining each navigation satellite that is not eliminated as a first available navigation satellite; step 2, acquiring position information of the first available navigation satellite, performing position information checking on the position information of the first available navigation satellite, and determining each first available navigation satellite that is not eliminated as a second available navigation satellite; and step 3, making the second available navigation satellite participate in PVT solving to obtain a positioning result.

Description

Technical Field

[0001] This application mainly relates to the field of spacecraft communication and navigation technology, specifically to a method, system, and computer-readable medium for protecting the spatiotemporal reference of low-Earth orbit satellites. Background Technology

[0002] During the operation of low-Earth orbit (LEO) satellites, when L-band interference or spoofing signals are present in the external environment, the GNSS (Global Navigation Satellite System) receiver may fail to receive valid GNSS signals or receive valid signals containing spoofing signals with a high signal-to-noise ratio. If an erroneous signal participates in the LEO satellite's PVT (Position, Velocity, Time) calculation, the calculated position will immediately deviate significantly from the receiver's clock bias, leading to substantial discrepancies between the GNSS receiver's output position and PPS (pulses per second) information. After spoofing / interference signals skew the GNSS receiver's spatiotemporal reference, they will maintain a smooth and stable state for a period. During this stable period, the receiver will not detect any anomalies and will continue to deviate from the correct baseline until the spoofing / interference signal completely disappears. Therefore, any abnormal signals must be eliminated immediately upon detection.

[0003] In existing technologies, conventional techniques for excluding abnormal signals include:

[0004] 1) Improve anti-interference capability through antenna design: including adopting multi-antenna design, using adaptive nulling technology to dynamically suppress signals in the direction of interference sources, using beamforming antennas to directionally enhance satellite signal reception, and reducing lateral interference;

[0005] 2) Install the antenna in an ideal position on the low-orbit satellite, relying on the satellite to shield it from interference signals entering the GNSS unit from the back lobe of the antenna;

[0006] 3) By designing a multi-frequency, multi-mode GNSS receiver, the impact of deception interference on a single system or a single frequency band can be reduced.

[0007] In practical applications, GNSS units in low-orbit satellite integrated electronic subsystems often do not employ dedicated anti-jamming measures. Antenna anti-jamming technology is commonly used in missile-borne terminals. Antenna installation locations are limited by factors such as satellite body size, solar panel size, and satellite structure. The design of multi-antenna / multi-frequency multi-mode receivers is often limited by factors such as unit design size, cost, and power consumption.

[0008] Therefore, it is necessary to design a method to protect the spatiotemporal reference of low-orbit satellites in environments where GNSS signals are deceived or interfered with. By improving the GNSS standalone software, when encountering deceived / interference signals, the signals involved in the PVT calculation can be identified to avoid introducing erroneous information into the PVT calculation and causing the system's spatiotemporal reference to become skewed. Summary of the Invention

[0009] To address the aforementioned problems, this invention provides a method, system, and computer program product for protecting the spatiotemporal reference of low-Earth orbit satellites. In environments where GNSS signals may be subject to deception / interference, the invention uses GNSS standalone software to identify signals containing abnormal time information and / or abnormal location information, thereby effectively countering GNSS deception / interference signals.

[0010] The technical solution adopted in this application to solve the above-mentioned technical problems is a method for protecting the spatiotemporal reference of low-orbit satellites, the method comprising:

[0011] Step 1): Obtain the time information of navigation satellites in each channel, verify the time information of the navigation satellites, and determine the navigation satellites that have not been eliminated as the first available navigation satellites;

[0012] Step 2): Obtain the position information of the first available navigation satellite, verify the position information of the first available navigation satellite, and determine each of the first available navigation satellites that has not been eliminated as the second available navigation satellite;

[0013] Step 3): Involve the second available navigation satellite in the PVT calculation to obtain the positioning result.

[0014] Furthermore, it also includes:

[0015] Step 4): After each of the second available navigation satellites participates in the PVT solution, the post-verification residual of the PVT solution equation is obtained. The post-verification residual is compared with the preset convergence threshold. If the post-verification residual is not less than the preset convergence threshold, the positioning result is set as abnormal.

[0016] If the positioning results are all abnormal within the preset time range, then all the navigation satellites are removed, new navigation satellites are searched again, and step 1 is re-executed.

[0017] Furthermore, the method for verifying the time information in step 1) includes:

[0018] Step 1.1): Perform at least one of the following checks: week number information verification, skip second information verification, intra-week second information verification, and code phase information verification, wherein:

[0019] The week number information verification includes: comparing the week number information of navigation satellites in each channel, counting the frequency of each value in all week numbers, and selecting the value with the highest frequency as the first week number; when there is only one first week number, it is determined to be a valid week number; when there are multiple first week numbers, the last first week number to participate in the week number information verification is determined to be the valid week number; navigation satellites in channels whose week number information is not a valid week number are deemed to contain abnormal time information and are removed.

[0020] The second jump information verification includes: comparing the second jump information of the navigation satellites in each channel with the current actual second jump information in the world, taking the current actual number of second jumps as the valid number of second jumps, and determining that the navigation satellites in the channel whose second jump information is not the valid number of second jumps contain abnormal time information and removing them;

[0021] The verification of intra-week second information and code phase information includes: calculating the signal transmission time of the corresponding channel at a certain moment based on the intra-week second information and code phase information of each navigation satellite; comparing the signal transmission times of each channel; selecting a group of navigation satellites whose signal transmission time differences are all within a first preset tolerance based on the comparison results; and determining that the navigation satellites not selected contain abnormal time information and removing them.

[0022] Furthermore, the method of comparing the signal transmission times of each channel and selecting a group of navigation satellites whose signal transmission time differences are all within a first preset tolerance based on the comparison results includes:

[0023] The signal transmission times of each channel are compared pairwise. Based on the comparison results, multiple navigation satellites whose signal transmission time differences are all within a first preset tolerance are identified and grouped into a channel group. The navigation satellite corresponding to the channel group containing the most channels is selected.

[0024] Furthermore, the method for verifying time information in step 1) further includes:

[0025] Step 1.21): Calculate the number of navigation satellites that have not yet been eliminated, and compare the number with a preset number threshold. If the number is above the preset number threshold, generate a timing reference based on the time information of each of the navigation satellites that have not yet been eliminated; otherwise, continue searching for navigation satellites and return to step 1).

[0026] Step 1.22): Calculate the time difference between the time reference and the full satellite time of the low-orbit satellite. Compare the time difference with a preset time difference threshold. If the time difference is less than the preset time difference threshold, perform the time synchronization operation; otherwise, do not synchronize the time, remove the navigation satellites from all channels, re-search for navigation satellites, and return to repeat Step 1).

[0027] Furthermore, the method for verifying time information in step 1) further includes:

[0028] Step 1.23): After completing the time synchronization, the GNSS unit enters the self-time synchronization phase, compares the received time generated by the self-time synchronization with the signal transmission time of each corresponding channel, and if the deviation between the signal transmission time and the received time of the channel exceeds the second preset tolerance, it is determined that the navigation satellite of the channel contains abnormal time information and is removed.

[0029] Furthermore, the method for verifying the location information in step 2) includes:

[0030] Step 2.11): Based on the position information of each of the first available navigation satellites and the full-satellite injection orbit information of the low-Earth orbit satellites, calculate the first distance between the low-Earth orbit satellites and each of the first available navigation satellites; and calculate the first real-time pseudorange information between the low-Earth orbit satellites and each of the first available navigation satellites.

[0031] Step 2.12): Calculate the first distance difference between each of the first distances and the corresponding first real-time pseudorange information. Compare each of the first distance differences with a first preset distance difference threshold. If the first distance difference is less than the preset distance difference threshold, no processing is performed. Otherwise, the first available navigation satellite corresponding to the first distance difference is determined to contain abnormal location information and is removed.

[0032] Furthermore, if a single GNSS unit is in t k-1 The time has been successfully determined and the orbit has been set. k-1 For any given time, the method for verifying the location information in step 2) includes:

[0033] Step 2.21): Obtain t k-1 The real-time orbital position X of the low-Earth orbit satellite at the specified time. k-1 t is predicted k The predicted orbital position X of the low-Earth orbit satellite at the specified time. k , where t k For the t k-1 The next moment, X k-1 For the low-orbit satellite in t k-1 Real-time orbital position at any given moment, Xk For the low-orbit satellite in t k Predicted orbital position at any given time;

[0034] Step 2.22): Based on the predicted orbital position X of the low-Earth orbit satellite k And the position information of each of the first available navigation satellites, predicting the position at t k The second distance between the low-Earth orbit satellite and each of the first available navigation satellites is calculated at a given time. The second real-time pseudorange information between the low-Earth orbit satellite and each of the first available navigation satellites is calculated. The second distance difference between each second distance and the corresponding second real-time pseudorange information is calculated. Each second distance difference is compared with a second preset distance difference threshold. If the second distance difference is less than the preset distance difference threshold, no processing is performed. Otherwise, the first available navigation satellite corresponding to the second distance difference is determined to contain abnormal position information and is removed.

[0035] The present invention also provides a low-orbit satellite spatiotemporal reference protection system, characterized in that it comprises:

[0036] Memory is used to store instructions that can be executed by the processor;

[0037] A processor for executing the instructions to implement the low-Earth orbit satellite spatiotemporal reference protection method as described in any of the preceding claims.

[0038] The present invention also provides a computer program product stored on a computer-readable medium, characterized in that:

[0039] The computer program product includes instructions that, when executed by a computer system, cause the computer system to perform the low-orbit satellite spatiotemporal reference protection method as described in any of the preceding claims.

[0040] The beneficial effects of this invention are:

[0041] 1. The technical solution of this application realizes the anomaly detection and elimination of signals participating in PVT calculation. Without involving hardware design, it can realize the identification of abnormal time information, abnormal location information, and judgment of PVT calculation post-verification residuals through GNSS standalone software, thereby effectively improving the anti-spoofing interference performance of GNSS standalone devices, avoiding the introduction of erroneous signals into PVT calculation, and effectively preventing the system's spatiotemporal reference from being skewed.

[0042] 2. The technical solution of this application can effectively combat deception / interference signals when hardware design is limited, and ensure the real-time performance and accuracy of GNSS positioning, orbit determination and timing. It can effectively maintain the high stability spatiotemporal reference requirements of low-orbit satellites. The method has strong universality and can reduce the cost, power consumption and size of low-orbit satellite GNSS units. Attached Figure Description

[0043] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings, wherein:

[0044] Figure 1 This is a flowchart illustrating a low-orbit satellite spatiotemporal reference protection method according to an embodiment of this application;

[0045] Figure 2 This is a flowchart illustrating the process of verifying time information for low-orbit satellites before time synchronization in one embodiment of this application;

[0046] Figure 3 This is a flowchart illustrating the process of timing a low-orbit satellite and verifying the time information after timing in one embodiment of this application.

[0047] Figure 4 This is a schematic diagram of the process for verifying the position information of a low-orbit satellite in one embodiment of this application;

[0048] Figure 5 This is a flowchart illustrating the process of verifying the position information of a low-orbit satellite in another embodiment of this application;

[0049] Figure 6 This is a flowchart illustrating the process of verifying the position information of a low-orbit satellite in another embodiment of this application;

[0050] Figure 7 This is a schematic diagram of the post-verification residual verification process for PVT calculation in one embodiment of this application. Detailed Implementation

[0051] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0052] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein, and therefore this application is not limited to the specific embodiments disclosed below.

[0053] As indicated in this application and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" are not specifically singular and may include plural forms. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0054] Flowcharts are used in this application to illustrate the operations performed by the system according to embodiments of this application. It should be understood that the preceding or following operations are not necessarily performed in exact order. Instead, various steps can be processed in reverse order or simultaneously. Furthermore, other operations may be added to these processes, or one or more steps may be removed from these processes.

[0055] Figure 1 This is a flowchart illustrating a low-Earth orbit satellite spatiotemporal reference protection method according to an embodiment of this application. (Reference) Figure 1 As shown, the low-Earth orbit satellite spatiotemporal reference protection method of this embodiment includes the following steps:

[0056] Step S100: Obtain the time information of navigation satellites in each channel, verify the time information of navigation satellites in each channel, and determine the navigation satellites that have not been eliminated as the first available navigation satellites.

[0057] In one embodiment, for a low-Earth orbit satellite-borne GNSS receiver, multiple receiving channels can be configured, and each channel can process information from one navigation satellite at a time.

[0058] Understandably, the method for obtaining time information from navigation satellites in each channel can be as follows: In the GNSS receiver of a low-Earth orbit satellite, the received navigation signal undergoes AD sampling and down-conversion, followed by baseband signal processing steps such as acquisition, tracking, bit synchronization, and frame synchronization to stably output the navigation message to the backend. Subsequently, the backend performs integrity verification on the multiple subframes that make up the message and the characters they contain. Message reception and verification are highly coupled and continuous actions. After successful verification, the receiver extracts and applies key parameters for calculating system time from the authenticated message data, completing the acquisition of time information. It should be noted that any suitable method for obtaining time information from navigation satellites in each channel can be used.

[0059] Step S200: Obtain the position information of the first available navigation satellite, verify the position information of the first available navigation satellite, and determine each of the first available navigation satellites that has not been eliminated as the second available navigation satellite.

[0060] Step S300: Involve the second available navigation satellite in the PVT calculation to obtain the positioning result.

[0061] Understandably, PVT (Programmatical Virtualization) calculation is the process of calculating core information about low-Earth orbit (LEO) satellites using the core parameters of navigation satellites and observations such as pseudorange and carrier phase measured by the receiver. The objectives are typically position, velocity, and time. It is the most crucial function of a satellite navigation receiver, directly determining the accuracy and reliability of the time and space information of LEO satellites. After protection in the time and position dimensions, abnormal signals can be effectively blocked from entering the final PVT calculation, allowing navigation satellites that can participate in the PVT calculation to provide usable navigation information.

[0062] In one embodiment, the low-orbit satellite spatiotemporal reference protection method further includes step S400: verifying the post-verification residuals of the equations solved by PVT.

[0063] Figure 2 This is a schematic flowchart illustrating the time information verification process for low-Earth orbit satellites before timing synchronization, in step S100 of an embodiment of this application. (See reference) Figure 2 As shown, it includes the following steps:

[0064] Step S110: Perform at least one of the following: week number information verification, jump second information verification, week-in-week second information verification, and code phase information verification.

[0065] Understandably, depending on the actual situation, one or more of the following methods may be used: week number information verification, skip second information verification, week-in-week second information verification, and code phase information verification.

[0066] The week number verification includes: comparing the week number information of navigation satellites in each channel, counting the frequency of each value in all week numbers, selecting the value with the highest frequency as the first week number, and determining that the first week number is valid when there is only one first week number; if there are multiple first week numbers, the last first week number to participate in the week number verification is determined to be the valid week number; navigation satellites in channels whose week number information is not valid are deemed to contain abnormal time information and are removed.

[0067] Understandably, for example, when a GNSS system simultaneously acquires and tracks satellite signals from n channels, during week number verification, the week number information of all n channels is compared between channels. If the week number of the satellite signals from n-2 channels (where n is an integer greater than 4) is 'a', and the week number of the satellite signals from the other two channels is 'b', then 'a' is selected as the valid week number, and navigation satellites from the channels with week number 'b' are discarded. Conversely, if the week number of the satellite signals from the n channels is 'a', and the week numbers of the satellite signals from one or more other channels are all different from 'a', then 'a' is selected as the valid week number, and navigation satellites from the channels with week number 'b' are discarded. Excluding navigation satellites in one or more channels whose week number is not 'a'; if the satellite signals of n channels include x navigation satellites with week number 'a', x navigation satellites with week number 'b', and the number of other navigation satellites whose week number is not 'a' or 'b' is all different, or the number of navigation satellites containing any of the same week number other than 'a' and 'b' is less than x, then the week number of the last group of satellite signals from the group of navigation satellites with week number 'a' or 'b' is selected as the valid week number, and navigation satellites from other channels are eliminated; if the satellite signals of n channels all have different week numbers, then the week number of the last satellite signal from the group of navigation satellites selected as the valid week number is selected, and navigation satellites from other channels are eliminated.

[0068] The second jump information verification includes: comparing the second jump information of navigation satellites in each channel with the current actual second jump information in the world, taking the current actual number of second jumps as the valid number of second jumps, and determining that the navigation satellites in channels whose second jump information is not a valid number of second jumps are containing abnormal time information and removing them.

[0069] It should be noted that, in one embodiment, the current world actual second jump information is stored in MRAM, and the GNSS unit can obtain it from MRAM, or obtain the current world actual second jump information from any suitable source and method.

[0070] The verification of intra-week second information and code phase information includes: calculating the signal transmission time of the corresponding channel at a certain moment based on the intra-week second information and code phase information of each navigation satellite, comparing the signal transmission times of each channel, selecting a group of navigation satellites whose signal transmission time differences are all within the first preset tolerance based on the comparison results, and determining that the navigation satellites not selected contain abnormal time information and removing them.

[0071] In one embodiment, the signal transmission time of the corresponding channel at a certain moment is calculated based on the intra-week second information and code phase information of each navigation satellite. The signal transmission times of each channel are compared pairwise. Based on the comparison results, multiple navigation satellites with signal transmission time differences within a first preset tolerance are identified and grouped into a channel group. The navigation satellite corresponding to the channel group with the largest number of channels is selected. Navigation satellites that are not selected are determined to contain abnormal time information and are removed.

[0072] It should be noted that in one embodiment, the first preset tolerance is 1 second, but other suitable first preset tolerances may also be used.

[0073] Figure 3 This is a schematic diagram of the process of timing synchronization for low-orbit satellites and the subsequent timing information verification in step S100 of an embodiment of this application.

[0074] refer to Figure 3 As shown, the specific process of time synchronization and subsequent time information verification is as follows:

[0075] Step S121: Calculate the number of navigation satellites that have not been eliminated and compare the number with a preset number threshold. If the number is above the preset number threshold, generate a timing reference based on the time information of each navigation satellite that has not been eliminated. Otherwise, continue searching for navigation satellites and return to step S100.

[0076] Understandably, if the number of navigation satellites that have not yet been removed has not reached the preset threshold, the search for navigation satellites continues and step S100 is repeated until the number of navigation satellites that have not yet been removed reaches the preset threshold.

[0077] It should be noted that in one embodiment, the preset quantity threshold is 4, but other suitable effective quantity thresholds may also be used.

[0078] The timing reference is generated based on the week number, hop count, and latest launch time of the navigation satellites that have not been removed.

[0079] For example, if week number information verification is performed, the week number of the navigation satellite on which the timing reference is based is a valid week number; if week number information verification is not performed, the week number of the navigation satellite on which the timing reference is based is the week number in the time information of the last navigation satellite obtained from the unremoved navigation satellites. If jump second information verification is performed, the number of jump seconds of the navigation satellite on which the timing reference is based is a valid number of jump seconds; if jump second information verification is not performed, the number of jump seconds of the navigation satellite on which the timing reference is based is the number of jump seconds in the time information of the last navigation satellite obtained from the unremoved navigation satellites. Regardless of whether week-inclusive second information and code phase information verification are performed or not, the launch time of the navigation satellite on which the timing reference is based is the latest launch time of the unremoved navigation satellites.

[0080] Step S122: Calculate the time difference between the timing reference and the full satellite time of the low-orbit satellite, compare the time difference with the preset timing time difference threshold, if the time difference is less than the preset timing time difference threshold, perform the timing operation, otherwise do not perform timing, remove all navigation satellites in the current channel, search for navigation satellites again, and repeat step S100.

[0081] Understandably, the satellite computer periodically broadcasts the complete satellite time of the low-Earth orbit (LEO) satellite to the GNSS unit. Using this LEO satellite complete satellite time, the time difference between the time reference and the LEO satellite complete satellite time can be calculated.

[0082] Step S123: After completing the time synchronization, the GNSS unit enters the self-time synchronization stage, compares the received time generated by the self-time synchronization with the signal transmission time of each corresponding channel. If the deviation between the signal transmission time and the received time of a certain channel exceeds the second preset tolerance, the navigation satellite of that channel is determined to contain abnormal time information and is removed.

[0083] Figure 4 This is a schematic flowchart illustrating the position information verification of a low-Earth orbit satellite in step S200 of an embodiment of this application. (See reference...) Figure 4 As shown, it includes the following steps:

[0084] Step S211: Based on the position information of each first available navigation satellite and the injection orbit information of the entire low-Earth orbit satellite, calculate the first distance between the low-Earth orbit satellite and each first available navigation satellite; and calculate the first real-time pseudorange information between the low-Earth orbit satellite and each first available navigation satellite.

[0085] It is understandable that the real-time pseudorange information of the low-Earth orbit satellites and each of the first available navigation satellites is generated based on the reception time and the signal transmission time of the corresponding channel of each of the first available navigation satellites.

[0086] Step S212: Calculate the first distance difference between each first distance and the corresponding real-time pseudorange information, and compare each first distance difference with a first preset distance difference threshold. If the first distance difference is less than the preset distance difference threshold, no processing is performed; otherwise, the first available navigation satellite corresponding to the first distance difference is determined to contain abnormal location information and is removed.

[0087] Understandably, in a GNSS system, if the position coordinates of a low-Earth orbit satellite are (x, y, z), a single GNSS unit can obtain the position coordinates of each navigation satellite based on the navigation message information. Through signal tracking and demodulation, the distance ρ between each navigation satellite and the low-Earth orbit satellite (i.e., real-time pseudorange information) can be obtained in real time. Based on the above data, multiple equations can be established to calculate the time, position, and velocity information of the low-Earth orbit satellite.

[0088] Prior information includes the position and / or velocity information of low-Earth orbit (LEO) satellites at the previous moment or several consecutive moments prior. When a GNSS unit first starts operating, it has no prior information. If erroneous information is involved in the PVT (Programmable Variable Transmission) calculation, the GNSS system may acquire incorrect navigation satellite position information or incorrect distance information between navigation satellites and LEO satellites. This can cause a large immediate deviation between the position obtained from the solution equation and the receiver clock error, resulting in a significant discrepancy between the position and PPS (pulses per second) information output by the GNSS unit. This deviation will remain smooth and stable for a period of time. During this smooth and stable period, the receiver will not detect any anomalies and will continue to err on top of the errors until the deception / interference signal completely disappears and the system returns to normal.

[0089] To prevent the above situations, when the GNSS unit for a low-Earth orbit (LEO) satellite has no prior information, the initial satellite selection can be performed using a high-precision injected orbit for the entire satellite. The ground system periodically injects high-precision orbits, taking into account atmospheric conditions, light pressure, relativity, three-body dynamics, and thrust, into the LEO satellite. To fully utilize this orbital information, the satellite's computer periodically broadcasts the current injected orbit to the GNSS unit. The GNSS unit can then obtain a rough position of the LEO satellite with an accuracy of approximately ten meters based on this injected orbit information. Using the injected orbit information and the calculated positions of each navigation satellite, the distance ρ' (i.e., the first distance) between the LEO satellite and each navigation satellite can be calculated. If ρ' deviates significantly from the distance ρ calculated in real-time through signal tracking and demodulation, the navigation satellite's position information is deemed abnormal and it is discarded.

[0090] When the GNSS unit has successfully determined its position and orbit, step S200 includes the following steps:

[0091] Step S221: Obtain t k-1Real-time orbit position X of low-Earth orbit satellite k-1 Based on the orbital dynamics filtering model of low-Earth orbit satellites, t is predicted. k Predicted orbital position X of low-Earth orbit satellite k , where t k-1 Let t be any time. k For t k-1 The next moment, X k-1 For low-orbit satellites in t k-1 Real-time orbital position at any given moment, X k For low-orbit satellites in t k Predicted orbital position at any given time.

[0092] It should be noted that, in one embodiment, t is predicted based on the orbital dynamics filtering model of the low-Earth orbit satellite. k Predicted orbital position X of low-Earth orbit satellite k Alternatively, other suitable methods can be used for prediction.

[0093] Step S222: Determine the orbit position X based on the predicted orbit position of the low-Earth orbit satellite. k Based on the position information of each of the first available navigation satellites, the prediction at t k The second distance between the low-Earth orbit satellite and each of the first available navigation satellites that have not been removed is calculated; the second real-time pseudorange information between the low-Earth orbit satellite and each of the first available navigation satellites is calculated; the second distance difference between each second distance and the corresponding second real-time pseudorange information is calculated; each second distance difference is compared with a second preset distance difference threshold; if the second distance difference is less than the preset distance difference threshold, no processing is performed; otherwise, the first available navigation satellite corresponding to the second distance difference is determined to contain abnormal time information and is removed.

[0094] Understandably, once a low-Earth orbit (LEO) satellite GNSS unit has successfully completed its positioning and orbit determination, the results can serve as prior information for the next moment, allowing for secondary satellite selection. When encountering spoofing / interference signals in a certain area, suppressive interference will first cause a decrease in the signal-to-noise ratio of the normal navigation signal, leading to positioning failure. After this failure, the receiver will receive spoofing signals. At this point, the LEO satellite orbit determination module is still functioning normally. k-1 Time and real-time orbital position X k-1 Predict t k Predicting orbital position X at all times k Perform location verification.

[0095] It is understandable that the real-time pseudorange information between low-Earth orbit satellites and corresponding navigation satellites in the channel can be calculated from the reception and transmission times of the navigation satellite information for that channel. It should be noted that any suitable method for obtaining real-time pseudorange information can be used.

[0096] Figure 5 This is a flowchart illustrating the position information verification process for low-Earth orbit satellites in step S200 of another embodiment of this application. (See reference) Figure 5 As shown, it includes the following steps:

[0097] Step S211: Based on the position information of each first available navigation satellite and the injection orbit information of the entire low-Earth orbit satellite, calculate the first distance between the low-Earth orbit satellite and each first available navigation satellite; and calculate the first real-time pseudorange information between the low-Earth orbit satellite and each first available navigation satellite.

[0098] Step S212: Calculate the first distance difference between each first distance and the corresponding first real-time pseudorange information, and compare each first distance difference with a first preset distance difference threshold. If the first distance difference is less than the preset distance difference threshold, no processing is performed; otherwise, the first available navigation satellite corresponding to the first distance difference is determined to contain abnormal location information and is removed.

[0099] Figure 6 This is a flowchart illustrating the position information verification process for low-Earth orbit satellites in step S200 of another embodiment of this application. (See reference...) Figure 6 As shown, if a low-Earth orbit satellite has been successfully positioned and determined, the following steps are included:

[0100] Step S221: Obtain t k-1 Real-time orbit position X of low-Earth orbit satellite k-1 And based on the orbital dynamics filtering model of low-Earth orbit satellites, predict t k Predicted orbital position X of low-Earth orbit satellite k , where t k-1 Let t be any time. k For t k-1 The next moment, X k-1 For low-orbit satellites in t k-1 Real-time orbital position at any given moment, X k For low-orbit satellites in t k Predicted orbital position at any given time;

[0101] Step S222: Determine the orbit position X based on the predicted orbit position of the low-Earth orbit satellite. k And the position information of each of the first available navigation satellites, calculate at t kThe second distance between the low-Earth orbit satellite and each of the first available navigation satellites that have not been removed is calculated; the second real-time pseudorange information between the low-Earth orbit satellite and each of the first available navigation satellites is calculated; the second distance difference between each second distance and the corresponding second real-time pseudorange information is calculated; each second distance difference is compared with a second preset distance difference threshold; if the second distance difference is less than the preset distance difference threshold, no processing is performed; otherwise, the first available navigation satellite corresponding to the second distance difference is determined to contain abnormal time information and is removed.

[0102] Figure 7 This is a schematic flowchart illustrating the post-verification residual check of PVT calculation in one embodiment of this application. (Reference) Figure 7 As shown, step S400: After each of the second available navigation satellites participates in the PVT solution, the post-test residual of the PVT solution equation is obtained, and the post-test residual is compared with the preset convergence threshold. If the post-test residual is not less than the preset convergence threshold, the positioning result is set as abnormal.

[0103] If the positioning results are all abnormal within the preset time range, then all navigation satellites are removed, new navigation satellites are searched again, and the process is returned and step S100 is re-executed.

[0104] Understandably, after performing PVT calculations, the post-verification residuals of the equations are checked to effectively prevent the adoption of abnormal results from real-time position and clock differences. The generation frequency of PVT calculation results can be preset, for example, once per second, ten times per second, or five times per second. If discrete PVT calculation results continuously show anomalies within a preset continuous time range, it is considered that abnormal signals still exist. All navigation satellites are then removed, new navigation satellites are searched again, and a new round of verification begins, thereby effectively improving the anti-spoofing and interference performance of a single GNSS unit.

[0105] On the other hand, a low-Earth orbit satellite spatiotemporal reference protection system is provided, comprising: a memory for storing instructions executable by a processor; and a processor for executing the instructions to implement the aforementioned low-Earth orbit satellite spatiotemporal reference protection method.

[0106] On the other hand, a computer program product stored on a computer-readable medium is also provided, wherein the instructions included in the computer program product, when executed by a computer system, cause the computer system to perform the aforementioned low-orbit satellite spatiotemporal reference protection method.

[0107] The basic concepts have been described above. Obviously, for those skilled in the art, the above disclosure is merely illustrative and does not constitute a limitation of this application. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to this application. Such modifications, improvements, and corrections are suggested in this application, and therefore remain within the spirit and scope of the exemplary embodiments of this application.

[0108] Furthermore, this application uses specific terms to describe embodiments of the application. For example, "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic related to at least one embodiment of the application. Therefore, it should be emphasized and noted that "an embodiment," "one embodiment," or "an alternative embodiment" mentioned twice or more in different locations in this specification do not necessarily refer to the same embodiment. In addition, certain features, structures, or characteristics in one or more embodiments of the application can be appropriately combined.

[0109] In some embodiments, numbers describing the quantity of components and attributes are used. It should be understood that such numbers used in the description of embodiments are modified in some examples with the terms "approximately," "approximately," or "generally." Unless otherwise stated, "approximately," "approximately," or "generally" indicates that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, which may be changed depending on the characteristics required by individual embodiments. In some embodiments, numerical parameters should take into account specified significant digits and employ a general method of digit reservation. Although the numerical ranges and parameters used to confirm their breadth of scope in some embodiments of this application are approximate values, in specific embodiments, such values ​​are set as precisely as feasible.

Claims

1. A method for protecting the spatiotemporal reference of a low-Earth orbit satellite, the method comprising: Step 1): Obtain the time information of navigation satellites in each channel, verify the time information of the navigation satellites, and determine the navigation satellites that have not been eliminated as the first available navigation satellites; Step 2): Obtain the position information of the first available navigation satellite, verify the position information of the first available navigation satellite, and determine each of the first available navigation satellites that has not been eliminated as the second available navigation satellite; The location information verification includes: Step 2.11): Based on the position information of each of the first available navigation satellites and the full-satellite injection orbit information of the low-Earth orbit satellite, calculate the first distance between the low-Earth orbit satellite and each of the first available navigation satellites, and calculate the first real-time pseudorange information between the low-Earth orbit satellite and each of the first available navigation satellites; Step 2.12): Calculate the first distance difference between each first distance and the corresponding first real-time pseudorange information, and compare each first distance difference with a first preset distance difference threshold. If the first distance difference is less than the preset distance difference threshold, no processing is performed; otherwise, the first available navigation satellite corresponding to the first distance difference is determined to contain abnormal location information and is removed. Step 3): Involve the second available navigation satellite in the PVT calculation to obtain the positioning result.

2. The method for protecting the spatiotemporal reference of low-orbit satellites as described in claim 1, characterized in that, Also includes: Step 4): After each of the second available navigation satellites participates in the PVT solution, the post-verification residual of the PVT solution equation is obtained. The post-verification residual is compared with the preset convergence threshold. If the post-verification residual is not less than the preset convergence threshold, the positioning result is set as abnormal. If the positioning results are all abnormal within the preset time range, then all the navigation satellites are removed, new navigation satellites are searched again, and step 1 is re-executed.

3. The method for protecting the spatiotemporal reference of low-orbit satellites as described in claim 1, characterized in that, The method for verifying time information in step 1) includes: Step 1.1): Perform at least one of the following checks: week number information verification, skip second information verification, intra-week second information verification, and code phase information verification, wherein: The week number information verification includes: comparing the week number information of navigation satellites in each channel, counting the frequency of each value in all week numbers, and selecting the value with the highest frequency as the first week number; when there is only one first week number, it is determined to be a valid week number; when there are multiple first week numbers, the last first week number to participate in the week number information verification is determined to be the valid week number; navigation satellites in channels whose week number information is not a valid week number are deemed to contain abnormal time information and are removed. The second jump information verification includes: comparing the second jump information of the navigation satellites in each channel with the current actual second jump information in the world, taking the current actual number of second jumps as the valid number of second jumps, and determining that the navigation satellites in the channel whose second jump information is not the valid number of second jumps contain abnormal time information and removing them; The verification of intra-week second information and code phase information includes: calculating the signal transmission time of the corresponding channel at a certain moment based on the intra-week second information and code phase information of each navigation satellite; comparing the signal transmission times of each channel; selecting a group of navigation satellites whose signal transmission time differences are all within a first preset tolerance based on the comparison results; and determining that the navigation satellites not selected contain abnormal time information and removing them.

4. The method for protecting the spatiotemporal reference of low-orbit satellites as described in claim 3, characterized in that, The method of comparing the signal transmission times of each channel and selecting a group of navigation satellites whose signal transmission time differences are all within a first preset tolerance based on the comparison results includes: The signal transmission times of each channel are compared pairwise. Based on the comparison results, multiple navigation satellites whose signal transmission time differences are all within a first preset tolerance are identified and grouped into a channel group. The navigation satellite corresponding to the channel group containing the most channels is selected.

5. The method for protecting the spatiotemporal reference of low-orbit satellites as described in claim 3, characterized in that, The time information verification method in step 1) further includes: Step 1.21): Calculate the number of navigation satellites that have not yet been eliminated, and compare the number with a preset number threshold. If the number is above the preset number threshold, generate a timing reference based on the time information of each of the navigation satellites that have not yet been eliminated; otherwise, continue searching for navigation satellites and return to step 1). Step 1.22): Calculate the time difference between the time reference and the full satellite time of the low-orbit satellite. Compare the time difference with a preset time difference threshold. If the time difference is less than the preset time difference threshold, perform the time synchronization operation; otherwise, do not synchronize the time, remove the navigation satellites from all channels, re-search for navigation satellites, and return to repeat Step 1).

6. The method for protecting the spatiotemporal reference of low-orbit satellites as described in claim 5, characterized in that, The time information verification method in step 1) further includes: Step 1.23): After completing the time synchronization, the GNSS unit enters the self-time synchronization phase, compares the received time generated by the self-time synchronization with the signal transmission time of each corresponding channel, and if the deviation between the signal transmission time and the received time of the channel exceeds the second preset tolerance, it is determined that the navigation satellite of the channel contains abnormal time information and is removed.

7. The method for protecting the spatiotemporal reference of low-orbit satellites as described in claim 1, characterized in that, If a single GNSS unit is at t k-1 The time has been successfully determined and the orbit has been set. k-1 For any given time, the method for verifying the location information in step 2) includes: Step 2.21): Obtain t k-1 The real-time orbital position X of the low-Earth orbit satellite at the specified time. k-1 t is predicted k The predicted orbital position X of the low-Earth orbit satellite at the specified time. k , where t k For the t k-1 The next moment, X k-1 For the low-orbit satellite in t k-1 Real-time orbital position at any given moment, X k For the low-orbit satellite in t k Predicted orbital position at any given time; Step 2.22): Based on the predicted orbital position X of the low-Earth orbit satellite k And the position information of each of the first available navigation satellites, predicting the position at t k The second distance between the low-Earth orbit satellite and each of the first available navigation satellites is calculated at a given time. The second real-time pseudorange information between the low-Earth orbit satellite and each of the first available navigation satellites is calculated. The second distance difference between each second distance and the corresponding second real-time pseudorange information is calculated. Each second distance difference is compared with a second preset distance difference threshold. If the second distance difference is less than the preset distance difference threshold, no processing is performed. Otherwise, the first available navigation satellite corresponding to the second distance difference is determined to contain abnormal position information and is removed.

8. A low-orbit satellite spatiotemporal reference protection system, characterized in that, include: Memory is used to store instructions that can be executed by the processor; A processor for executing the instructions to implement the low-orbit satellite spatiotemporal reference protection method as described in any one of claims 1-7.

9. A computer program product stored on a computer-readable medium, characterized in that: The computer program product includes instructions that, when executed by a computer system, cause the computer system to perform the low-orbit satellite spatiotemporal reference protection method as described in any one of claims 1-7.

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