A method for monitoring the integrity of a satellite navigation system

Abstract

This invention relates to the field of satellite navigation system technology and proposes a method for monitoring the integrity of a satellite navigation system. The method involves the satellite navigation system performing the following actions: receiving bidirectional measurement data from an inter-satellite link and correcting errors; using predicted orbit and predicted clock bias parameters to reduce the bidirectional observation data of the inter-satellite link to determine a first inter-satellite geometric distance and a first relative clock bias; calculating a second inter-satellite geometric distance and a second relative clock bias based on satellite navigation messages; subtracting the second inter-satellite geometric distance and the second relative clock bias from the first inter-satellite geometric distance and the first relative clock bias, respectively, to determine geometric distance residuals and relative clock bias residuals; receiving pseudorange data and phase data of the satellite downlink navigation signal from a ground monitoring station and correcting errors; using satellite navigation messages to calculate the equivalent distance error of the navigation satellite; and determining the integrity status of the satellite payload based on the geometric distance residuals, relative clock bias residuals, and the equivalent distance error of the navigation satellite.

Description

Technical Field

[0001] This invention generally relates to the field of satellite navigation system technology. Specifically, this invention relates to a method for monitoring the integrity of a satellite navigation system. Background Technology

[0002] The integrity of a satellite navigation system is one of its crucial service attributes. This integrity requires the system to monitor the real-time operational status of satellites in orbit and to immediately notify users of any malfunctions affecting navigation services. Currently, both GPS and Galileo systems have logically rigorous integrity parameter systems and service mechanisms. Benefiting from the ability to deploy ground monitoring stations and data transmission links globally, GPS and Galileo systems can monitor the integrity status of satellites across the entire globe in real time and notify users of any anomalies.

[0003] The BeiDou Navigation Satellite System is a satellite navigation system independently developed by my country. Its construction followed a three-step development strategy. In 2003, the BeiDou-1 system, capable of independent positioning with constrained elevation, was completed, fulfilling the first step of the development plan. In 2012, BeiDou-2 completed its system construction, providing navigation, positioning, and timing services to the Asia-Pacific region. In 2020, the BeiDou-3 system completed its network deployment, officially providing services globally.

[0004] However, the satellite integrity monitoring methods used by GPS and Galileo systems, which rely on globally distributed monitoring stations, are not applicable to the BeiDou Navigation Satellite System. This is because the BeiDou Navigation Satellite System has not achieved a globally distributed ground station network, and the design of BeiDou satellites differs significantly from that of GPS and Galileo satellites. BeiDou satellites have more complex onboard payloads and face a greater number of integrity monitoring targets.

[0005] The BeiDou-2 system designed a complete method for real-time monitoring and anomaly alarm of satellite status, which was continued in the BeiDou-3 system. This method determines the satellite payload status in real time by monitoring the satellite clock difference measured in real-time through two-way time synchronization between the satellite and ground, and by using the satellite user equivalent distance error calculated by the monitoring receiver. If the satellite clock difference is abnormal but the user equivalent distance error is normal, the problem can be identified as an anomaly in the satellite uplink spread spectrum receiver; if both the satellite clock difference and the user equivalent distance error are abnormal, the problem can be identified as a fault in the satellite's onboard atomic clock; if the satellite clock difference is normal but the user equivalent distance error is abnormal, the problem can be identified as an anomaly in the satellite's downlink navigation signal transmission.

[0006] However, since the BeiDou Navigation Satellite System can only deploy stations regionally, when a BeiDou satellite is operating outside of China, and there are no two-way time synchronization results between the satellite and the ground, nor are there monitoring results for the equivalent distance error of the monitoring receiver user, the aforementioned monitoring methods will no longer be effective. Furthermore, unlike BeiDou-2 satellites, BeiDou-3 satellites also carry inter-satellite link payloads, and the existing methods cannot meet the integrity monitoring requirements of these payloads.

[0007] Therefore, based on the engineering practice of the BeiDou-3 satellite navigation system, it is necessary to propose a method for monitoring the integrity of the BeiDou-3 satellite's outer arc segment and issuing anomaly alarms.

[0008] Scientists at the German Aerospace Center (DLR) proposed using inter-satellite link measurements to monitor satellite integrity and issue anomaly alerts. However, this method can only identify satellite malfunctions, relying on the reliability of inter-satellite link payloads and ignoring potential failure scenarios. It cannot identify faulty satellite payloads and is prone to false alarms and missed alarms.

[0009] Currently, the BeiDou-3 satellite has designed and implemented an on-board autonomous integrity monitoring method. However, this method can only monitor small-scale satellite faults and cannot identify all satellite faults. Furthermore, the current on-orbit operation of the BeiDou-3 satellite indicates that the on-board autonomous integrity monitoring payload still suffers from problems such as poor reliability and numerous false alarms. Summary of the Invention

[0010] To at least partially address the aforementioned problems in the prior art, the present invention proposes a method for monitoring the integrity of a satellite navigation system, wherein the satellite navigation system performs the following actions:

[0011] Receive bidirectional measurement data from the inter-satellite link and correct errors, and use predicted orbit and predicted clock error parameters to reduce the bidirectional observation data of the inter-satellite link to determine the first inter-satellite geometric distance and the first relative clock error;

[0012] Calculate the second inter-satellite geometric distance and the second relative clock difference based on the satellite navigation message;

[0013] The second inter-satellite geometric distance and the second relative clock error are respectively subtracted from the first inter-satellite geometric distance and the first relative clock error to determine the geometric distance residual and the relative clock error residual;

[0014] It receives pseudorange and phase data of satellite downlink navigation signals from ground monitoring stations, corrects errors, and calculates the equivalent range error of the navigation satellite using satellite navigation messages; and

[0015] The integrity status of the satellite payload is determined based on the geometric distance residual, the relative clock error residual, and the equivalent distance error of the navigation satellite.

[0016] In one embodiment of the present invention, determining the first inter-satellite geometric distance and the first relative clock error includes the following steps:

[0017] At time t1 and time t2, bidirectional measurement data from the inter-satellite link are received and errors are subtracted to construct the observation equation, expressed as follows:

[0018]

[0019]

[0020] Where, ρ AB (t1) indicates that the second satellite receives a pseudorange measurement from the first satellite at time t1, ρ BA (t2) indicates that the first satellite receives a pseudorange measurement from the second satellite at time t2. clk represents the three-dimensional positions of the first and second satellites, respectively. A ,clk B Let Δt1 and Δt2 represent the satellite clock differences of the first and second satellites, respectively, where c represents the speed of light, and Δt1 and Δt2 represent the travel time of light. and These represent the transmission delay and reception delay of the first satellite, respectively. and These represent the launch delay and reception delay of the second satellite, respectively. and These represent the first error correction term;

[0021] The bidirectional inter-satellite link measurement data from the first time t1 and the second time t2 are reduced to the target time t0, as expressed by the following formula:

[0022]

[0023]

[0024] Where dρ AB and dρ BA Let $\mathbf{a}$ represent the satellite distance difference and satellite clock error difference between the observed epoch and the target epoch, respectively. These are calculated using the predicted orbit and predicted clock error parameters and are expressed as follows:

[0025]

[0026]

[0027] Determine the first inter-satellite geometric distance, where ρ AB (t0) and ρ BA (t0) is added together to eliminate satellite clock error information, expressed as follows:

[0028]

[0029] as well as

[0030] Determine the first relative clock difference, where ρ AB (t0) and ρ BA The difference (t0) is used to eliminate satellite orbit information, expressed as follows:

[0031]

[0032] In one embodiment of the present invention, the first error correction term includes satellite antenna phase center error, relativistic effect error, tropospheric delay error, station eccentricity error, and tidal effect error.

[0033] In one embodiment of the present invention, the geometric distance residual is expressed as follows:

[0034]

[0035] in, This represents the geometric distance residual between the first and second satellites. and These respectively represent the positions of the second and first satellites calculated using satellite navigation messages; and

[0036] The relative clock error residual is calculated as follows:

[0037]

[0038] in, clk represents the calculated residual of the relative clock bias between the first and second satellites. B (t0) and clk A (t0) represents the clock difference of the second satellite and the first satellite calculated using satellite navigation messages, respectively.

[0039] In one embodiment of the present invention, the pseudorange data P and phase data of the satellite downlink navigation signal from the ground monitoring station are specified. It can be expressed as the following formula:

[0040]

[0041] Where λ represents the wavelength corresponding to the phase data. and Let Δt represent the position vectors of the satellite and receiver, respectively, and c represent the speed of light. rcvclk and Δt satclk ΔD represents the receiver clock bias and the satellite clock bias, respectively. phs ΔD represents the phase center deviation of the satellite antenna. rel ΔD represents the delay caused by relativistic effects.trop Indicates tropospheric delay, ΔD Ion Indicates ionospheric delay, ΔD ecc Indicates station eccentricity correction, ΔD gtide Indicates the tidal correction at the observatory, ΔD plm The distance measurement deviation caused by the station displacement is represented by N, which represents the ambiguity of the phase data, and ε is the distance measurement error caused by the station displacement. c and ε P Multipath propagation and noise, respectively, representing pseudorange and phase; and

[0042] The equivalent distance error (UERE) of navigation satellites is expressed as follows:

[0043]

[0044] Where PC represents the ionosphere-free combination of pseudorange data.

[0045] In one embodiment of the present invention, a geometric distance residual threshold, a relative clock error residual threshold, and a navigation satellite equivalent distance error threshold are provided, and the geometric distance residual, relative clock error residual, and navigation satellite equivalent distance error of the first satellite relative to all other satellites in the satellite navigation system are calculated.

[0046] In one embodiment of the present invention, it is specified that when the geometric distance residual of the first satellite relative to all other satellites in the satellite navigation system exceeds the geometric distance residual threshold, and the navigation satellite equivalent distance error of all ground monitoring stations relative to the first satellite exceeds the navigation satellite equivalent distance error threshold, it is determined that the accuracy of the broadcast ephemeris of the first satellite in describing the satellite's orbital motion has decreased; and / or

[0047] When the geometric distance residual or relative clock error residual of the first satellite relative to all other satellites in the satellite navigation system exceeds the geometric distance residual threshold or the relative clock error residual threshold, and the equivalent navigation satellite distance error of all ground monitoring stations relative to the first satellite does not exceed the equivalent navigation satellite distance error threshold, the inter-satellite link measurement of the first satellite is determined to be abnormal; and / or

[0048] When the relative clock error residual of the first satellite relative to all other satellites in the satellite navigation system exceeds the relative clock error residual threshold, and the equivalent distance error of all ground monitoring stations to the first satellite exceeds the equivalent distance error threshold, the onboard atomic clock of the first satellite is determined to be abnormal; and / or

[0049] When the relative clock error residual and geometric distance residual of the first satellite relative to all other satellites in the satellite navigation system do not exceed the relative clock error residual threshold and the geometric distance residual threshold, and the navigation satellite equivalent distance error of all ground monitoring stations to the first satellite exceeds the navigation satellite equivalent distance error threshold, the downlink navigation load of the first satellite is determined to be abnormal.

[0050] In one embodiment of the present invention, an alarm is issued when it is determined that the satellite payload is abnormal.

[0051] This invention has at least the following beneficial effects: It utilizes inter-satellite link measurement as one of the means of monitoring the integrity of satellites, and comprehensively utilizes inter-satellite link measurement and pseudorange phase measurement of monitoring receivers to achieve real-time judgment of satellite payload faults, enabling precise location of faulty satellite payloads. This invention can be applied to the overseas arc segment of the BeiDou Navigation Satellite System and fully considers the integrity monitoring requirements of BeiDou-3 navigation satellite payloads, enabling the monitoring of various onboard payloads, including downlink navigation signal generators, inter-satellite link payloads, and onboard atomic clocks. Attached Figure Description

[0052] To further illustrate the advantages and other features of the various embodiments of the present invention, a more specific description of the embodiments of the present invention will be presented with reference to the accompanying drawings. It is understood that these drawings depict only typical embodiments of the invention and are therefore not intended to limit its scope. In the drawings, identical or corresponding parts will be indicated by the same or similar reference numerals for clarity.

[0053] Figure 1 A flowchart illustrating an integrity monitoring method for a satellite navigation system according to one embodiment of the present invention is shown. Detailed Implementation

[0054] It should be noted that the components in the various figures may be shown exaggeratedly for illustrative purposes and are not necessarily to scale. In each figure, the same reference numerals are used for components that are identical or have the same function.

[0055] In this invention, unless otherwise specified, "arranged on," "arranged above," and "arranged on" do not exclude the possibility of an intermediate element between them. Furthermore, "arranged on or above" merely indicates the relative positional relationship between two components, and in certain cases, such as when the product orientation is reversed, it can also be converted to "arranged below or under," and vice versa.

[0056] In this invention, the various embodiments are merely intended to illustrate the solutions of the invention and should not be construed as limiting.

[0057] In this invention, unless otherwise specified, the quantifiers “a” and “one” do not exclude scenarios involving multiple elements.

[0058] It should also be noted that, in the embodiments of the present invention, only a portion of the components or parts may be shown for clarity and simplicity. However, those skilled in the art will understand that, under the teachings of the present invention, necessary components or parts can be added as needed for specific scenarios. Furthermore, unless otherwise stated, features in different embodiments of the present invention can be combined with each other. For example, a feature in the second embodiment can replace a corresponding or functionally identical or similar feature in the first embodiment, and the resulting embodiment will also fall within the scope of disclosure or description of this application.

[0059] It should also be noted that, within the scope of this invention, the terms "same," "equal," and "equal to" do not imply that the two values ​​are absolutely equal, but rather allow for a certain reasonable margin of error. In other words, the terms also encompass "substantially the same," "substantially equal," and "substantially equal to." Similarly, in this invention, the directional terms "perpendicular to," "parallel to," etc., also encompass the meanings of "substantially perpendicular to" and "substantially parallel to."

[0060] Furthermore, the numbering of the steps in the methods of the present invention does not limit the execution order of the method steps. Unless otherwise specified, the method steps may be executed in different orders.

[0061] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0062] To address the current lack of effective integrity monitoring methods for BeiDou navigation satellites in overseas arc segments, one embodiment of this invention proposes a method that integrates inter-satellite link measurements and ground monitoring station observation data for integrity monitoring of BeiDou satellites in overseas arc segments.

[0063] Figure 1 A flowchart illustrating an integrity monitoring method for a satellite navigation system according to one embodiment of the present invention is shown. Figure 1As shown, the method may include receiving bidirectional measurement data from the inter-satellite link and correcting errors, and using predicted orbit and predicted clock error parameters to reduce the bidirectional observation data of the inter-satellite link to determine a first inter-satellite geometric distance and a first relative clock error; calculating a second inter-satellite geometric distance and a second relative clock error based on the satellite navigation message; subtracting the second inter-satellite geometric distance and the second relative clock error from the first inter-satellite geometric distance and the first relative clock error, respectively, to determine the geometric distance residual and the relative clock error residual; receiving pseudorange data and phase data of the satellite downlink navigation signal from the ground monitoring station and correcting errors, and using the satellite navigation message to calculate the equivalent distance error of the navigation satellite; and determining the integrity status of the satellite payload based on the geometric distance residual, the relative clock error residual, and the equivalent distance error of the navigation satellite.

[0064] Specifically, one embodiment of the present invention may include the following steps:

[0065] Step 100: The satellite navigation system receives the inter-satellite link bidirectional measurement data of the entire constellation in real time, deducts errors such as satellite antenna phase center, equipment delay and relativistic delay, and uses the predicted orbit and clock bias parameters to reduce the inter-satellite link bidirectional observation data to obtain the inter-satellite geometric distance and relative clock bias.

[0066] Step 200: The satellite navigation system calculates the theoretical values ​​of inter-satellite geometric distance and relative clock bias based on the satellite broadcast ephemeris and clock bias parameters included in the navigation message broadcast by the satellite. The theoretical values ​​of inter-satellite geometric distance and relative clock bias are then subtracted from the inter-satellite geometric distance and relative clock bias calculated in Step 1 to obtain the geometric distance residual and relative clock bias residual.

[0067] Step 300: The satellite navigation system receives pseudorange phase data of the satellite downlink navigation signal from the ground monitoring station in real time, which is publicly available or obtained in other forms. It deducts the relativistic delay, tropospheric delay, ionospheric delay, and receiver antenna phase center error, and calculates the navigation satellite equivalent range error (UERE) using the broadcast ephemeris, clock error, and group delay parameters contained in the BeiDou satellite navigation message.

[0068] Step 400: The satellite navigation system determines the real-time integrity status of the satellite payload based on the UERE, the relative geometric distance residual, and the relative clock error residual from the ground monitoring receiver, and immediately issues an alarm when the satellite payload is abnormal.

[0069] Step 100 may include the following steps:

[0070] Step 101: Assume that the second satellite receives the pseudorange measurement ρ from the first satellite at time t1. AB(t1), the first satellite receives the pseudorange measurement ρ from the second satellite at time t2. BA (t2) can be expressed by the following equation:

[0071]

[0072]

[0073] in, clk represents the three-dimensional positions of the first and second satellites, respectively. A ,clk B Let Δt1 and Δt2 represent the satellite clock differences of the first and second satellites, respectively, where c represents the speed of light, and Δt1 and Δt2 represent the travel time of light. and These represent the transmission delay and reception delay of the first satellite, respectively. and These represent the launch delay and reception delay of the second satellite, respectively. and These represent error correction terms that can be accurately modeled in one-way ranging. These error correction terms may include satellite antenna phase centering and relativistic effects, etc. For Earth observation, the error correction terms may also include errors such as tropospheric delay, station eccentricity, and tidal effects, all of which can be accurately modeled.

[0074] Step 102: Let t1 and t2 represent different times that differ by no more than 3 seconds.

[0075] Since the addition of two-way pseudoranges at the same instant can eliminate satellite clock bias and include only satellite distance for satellite orbit determination; and the subtraction of two-way pseudoranges at the same instant can eliminate satellite orbit bias and include only satellite clock bias for clock bias determination, two-way observations at different times can be reduced to the same instant. Assuming that the distance values ​​measured at t1 and t2 need to be reduced to the target time t0, the reduction formula can be expressed as follows:

[0076]

[0077]

[0078] Where dρ AB and dρ BA Let dρ represent the satellite distance difference and satellite clock difference between the observation epoch and the target epoch, respectively, and dρ AB and dρ BA It can be expressed as the following formula:

[0079]

[0080]

[0081] Where dρ AB and dρ BA Calculations can be performed based on the satellite's predicted orbit and predicted clock error parameters.

[0082] Step 103: ρ in Step 102 AB (t0) and ρ BA (t0) cannot be directly used for satellite orbit and clock error determination; further calculations are required.

[0083] ρ AB (t0) and ρ BA Adding (t0) eliminates satellite clock error information, leaving only constraints on satellite orbit parameters. This can be directly used for precise orbit determination, expressed as the following formula:

[0084]

[0085]

[0086] ρ AB (t0) and ρ BA The difference (t0) can eliminate satellite orbit information, leaving only satellite clock bias, which can be directly used for clock bias determination, expressed as the following formula:

[0087]

[0088] Step 200 may include the following steps:

[0089] Step 201: Calculate the satellite position using the broadcast ephemeris transmitted by the satellite navigation signal, and subtract it from the geometric distance calculated by the inter-satellite link to obtain the inter-satellite link geometric distance residual between the two satellites, expressed as the following formula:

[0090]

[0091] in, The calculated residual represents the geometric distance between the first and second satellites. and These represent the satellite positions calculated using broadcast ephemeris data.

[0092] Step 202: Calculate the satellite position using the broadcast clock error parameters transmitted by the satellite navigation signal, and subtract the relative clock error calculated from the inter-satellite link to obtain the inter-satellite link relative clock error residual between the two satellites, expressed as the following formula:

[0093]

[0094] in, clk represents the calculated residual of the relative clock bias between the first and second satellites. B(t0) and clk A (t0) represent the satellite clock bias calculated using broadcast ephemeris.

[0095] Step 300 may include the following steps:

[0096] Step 301: Pseudorange and phase data are important data sources for calculating the equivalent range error (UERE) of navigation satellites. The measurement model for pseudorange data P and phase data can be expressed as follows:

[0097]

[0098] Where λ represents the wavelength corresponding to the phase data. and Let Δt represent the position vectors of the satellite and receiver, respectively, and c represent the speed of light. rcvclk and Δt satclk ΔD represents the receiver clock bias and the satellite clock bias, respectively. phs ΔD represents the phase center deviation of the satellite antenna. rel ΔD represents the delay caused by relativistic effects. trop Indicates tropospheric delay, ΔD Ion Indicates ionospheric delay, ΔD ecc Indicates station eccentricity correction, ΔD gtide Indicates the tidal correction at the observatory, ΔD plm The distance measurement deviation caused by the station displacement is represented by N, which represents the ambiguity of the phase data, and ε is the distance measurement error caused by the station displacement. c and ε P These represent the pseudorange and phase multipath and noise, respectively.

[0099] Step 302: The equivalent distance error (UERE) of navigation satellites is affected by a combination of factors, including satellite orbital errors, clock errors, space segment medium delay correction errors, and receiver multipath and thermal noise on pseudorange measurements. For a specific navigation satellite constellation, a smaller UERE results in higher user positioning and timing accuracy. The formula for calculating UERE can be expressed as follows:

[0100]

[0101] PC represents the ionosphere-free combination of pseudorange data.

[0102] If Δt satclk Satellite clock bias measured in real time using two-way time-frequency transfer between satellite and ground can achieve an accuracy better than 0.5 ns, where ε represents receiver-end noise and multipath effects. To avoid the influence of pseudorange multipath, UERE assessment can use pseudorange observations that have been unidirectionally smoothed from phase data.

[0103] Step 400 may include the following steps:

[0104] Step 401: Determine if the accuracy of the satellite's broadcast ephemeris description of its orbital motion decreases under the following conditions:

[0105] The inter-satellite link geometric distance residual between a certain satellite and all other satellites calculated according to step 201 at a certain moment. The UERE of the satellite exceeds the set threshold, and the UERE of all monitoring stations calculated according to step 302 exceeds the set threshold.

[0106] Step 402: Determine if the inter-satellite link measurement of the satellite is abnormal when one of the following conditions occurs:

[0107] The inter-satellite link geometric distance residual between a certain satellite and all other satellites calculated according to step 201 at a certain moment. The threshold is exceeded, but the UERE of the satellite calculated by all monitoring stations according to step 302 does not exceed the threshold; or

[0108] The relative clock error residual of the inter-satellite link between a certain satellite and all other satellites, calculated according to step 201 at a certain moment. The threshold is exceeded, but the UERE of the satellite calculated by all monitoring stations according to step 302 does not exceed the threshold.

[0109] Step 403: Determine if the satellite's onboard atomic clock is malfunctioning under the following circumstances:

[0110] The relative clock error residual of the inter-satellite link between a certain satellite and all other satellites, calculated according to step 201 at a certain moment. The UERE of the satellite exceeds the set threshold, and the UERE of all monitoring stations calculated according to step 302 exceeds the set threshold.

[0111] Step 404: Determine if the downlink navigation payload of the satellite is abnormal under the following circumstances:

[0112] The relative clock error residual of the inter-satellite link between a certain satellite and all other satellites, calculated according to step 201 at a certain moment. The inter-satellite link geometric distance residual between a certain satellite and all other satellites is calculated according to step 201, provided that the set threshold is not exceeded. The set threshold was not exceeded, and the UERE of the satellite for all monitoring stations calculated according to step 302 exceeded the set threshold.

[0113] Although various embodiments of the invention have been described above, it should be understood that they are presented by way of example only and not as limitations. It will be apparent to those skilled in the art that various combinations, modifications, and alterations can be made without departing from the spirit and scope of the invention. Therefore, the breadth and scope of the invention disclosed herein should not be limited by the exemplary embodiments disclosed above, but should be defined solely by the appended claims and their equivalents.

Claims

1. A method for monitoring the integrity of a satellite navigation system, characterized in that, This includes the following actions performed by the satellite navigation system: Receive bidirectional measurement data from the inter-satellite link and correct errors, and use predicted orbit and predicted clock error parameters to reduce the bidirectional observation data of the inter-satellite link to determine the first inter-satellite geometric distance and the first relative clock error; Calculate the second inter-satellite geometric distance and the second relative clock difference based on the satellite navigation message; The second inter-satellite geometric distance and the second relative clock error are respectively subtracted from the first inter-satellite geometric distance and the first relative clock error to determine the geometric distance residual and the relative clock error residual; It receives pseudorange and phase data of satellite downlink navigation signals from ground monitoring stations and corrects errors, and uses satellite navigation messages to calculate the equivalent distance error of navigation satellites; as well as The integrity status of the satellite payload is determined based on the geometric distance residual, the relative clock error residual, and the equivalent distance error of the navigation satellite.

2. The method for monitoring the integrity of a satellite navigation system according to claim 1, characterized in that, Determining the first inter-satellite geometric distance and the first relative clock error includes the following steps: At time t1 and time t2, bidirectional measurement data from the inter-satellite link are received and errors are subtracted to construct the observation equation, expressed as follows: Where, ρ AB (t1) indicates that the second satellite receives a pseudorange measurement from the first satellite at time t1, ρ BA (t2) indicates that the first satellite receives a pseudorange measurement from the second satellite at time t2. clk represents the three-dimensional positions of the first and second satellites, respectively. A ,clk B Let Δt1 and Δt2 represent the satellite clock differences of the first and second satellites, respectively, where c represents the speed of light, and Δt1 and Δt2 represent the travel time of light. and These represent the transmission delay and reception delay of the first satellite, respectively. and These represent the launch delay and reception delay of the second satellite, respectively. and These represent the first error correction term and the second error correction term, respectively. The bidirectional inter-satellite link measurement data from the first time t1 and the second time t2 are reduced to the target time t0, as expressed by the following formula: in, and These represent the positions of the second and first satellites, calculated using satellite navigation messages, respectively. clk B (t0) and clk A (t0) represent the clock differences of the second and first satellites calculated using satellite navigation messages, respectively; dρ AB and dρ BA Let $\mathbf{a}$ represent the satellite distance difference and satellite clock error difference between the observed epoch and the target epoch, respectively. These are calculated using the predicted orbit and predicted clock error parameters and are expressed as follows: Determine the first inter-satellite geometric distance, where ρ AB (t0) and ρ BA (t0) is added together to eliminate satellite clock error information, expressed as follows: as well as Determine the first relative clock difference, where ρ AB (t0) and ρ BA The difference (t0) is used to eliminate satellite orbit information, expressed as follows:

3. The method for monitoring the integrity of a satellite navigation system according to claim 2, characterized in that, The first error correction term includes satellite antenna phase center error, relativistic effect error, tropospheric delay error, station eccentricity error, and tidal effect error.

4. The integrity monitoring method for a satellite navigation system according to claim 2, characterized in that, The geometric distance residual is expressed as follows: in, This represents the geometric distance residual between the first and second satellites. and These respectively represent the positions of the second and first satellites calculated using satellite navigation messages; and The relative clock error residual is calculated as follows: in, clk represents the calculated residual of the relative clock bias between the first and second satellites. B (t0) and clk A (t0) represents the clock difference of the second satellite and the first satellite calculated using satellite navigation messages, respectively.

5. The integrity monitoring method for a satellite navigation system according to claim 4, characterized in that, The pseudorange data P and phase data of the satellite downlink navigation signal from the ground monitoring station It can be expressed as the following formula: Where λ represents the wavelength corresponding to the phase data. and Let Δt represent the position vectors of the satellite and receiver, respectively, and c represent the speed of light. rcvclk and Δt satclk ΔD represents the receiver clock bias and the satellite clock bias, respectively. phs ΔD represents the phase center deviation of the satellite antenna. rel ΔD represents the delay caused by relativistic effects. trop Indicates tropospheric delay, ΔD Ion Indicates ionospheric delay, ΔD ecc Indicates station eccentricity correction, ΔD gtide Indicates the tidal correction at the observatory, ΔD plm The distance measurement deviation caused by the station displacement is represented by N, which represents the ambiguity of the phase data, and ε is the distance measurement error caused by the station displacement. c and ε P Multipath propagation and noise, respectively, representing pseudorange and phase; and The equivalent distance error (UERE) of navigation satellites is expressed as follows: Where PC represents the ionosphere-free combination of pseudorange data.

6. The method for monitoring the integrity of a satellite navigation system according to claim 5, characterized in that, It provides a geometric distance residual threshold, a relative clock error residual threshold, and a navigation satellite equivalent distance error threshold, and calculates the geometric distance residual, relative clock error residual, and navigation satellite equivalent distance error of the first satellite relative to all other satellites in the satellite navigation system, as well as the navigation satellite equivalent distance error of all ground monitoring stations relative to the first satellite.

7. The method for monitoring the integrity of a satellite navigation system according to claim 6, characterized in that, When the geometric distance residual of the first satellite relative to all other satellites in the satellite navigation system exceeds the geometric distance residual threshold, and the navigation satellite equivalent distance error of all ground monitoring stations to the first satellite exceeds the navigation satellite equivalent distance error threshold, it is determined that the accuracy of the broadcast ephemeris of the first satellite in describing the satellite orbital motion has decreased. and / or When the geometric distance residual or relative clock error residual of the first satellite relative to all other satellites in the satellite navigation system exceeds the geometric distance residual threshold or the relative clock error residual threshold, and the equivalent distance error of the navigation satellite for all ground monitoring stations to the first satellite does not exceed the equivalent distance error threshold, the inter-satellite link measurement of the first satellite is determined to be abnormal. and / or When the relative clock error residual of the first satellite relative to all other satellites in the satellite navigation system exceeds the relative clock error residual threshold, and the equivalent distance error of all ground monitoring stations to the first satellite exceeds the equivalent distance error threshold, the onboard atomic clock of the first satellite is determined to be abnormal. and / or When the relative clock error residual and geometric distance residual of the first satellite relative to all other satellites in the satellite navigation system do not exceed the relative clock error residual threshold and the geometric distance residual threshold, and the navigation satellite equivalent distance error of all ground monitoring stations to the first satellite exceeds the navigation satellite equivalent distance error threshold, the downlink navigation load of the first satellite is determined to be abnormal.

8. The method for monitoring the integrity of a satellite navigation system according to claim 1, characterized in that, An alarm is issued when the satellite payload is detected to be abnormal.

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