A GNSS autonomous integrity monitoring method assisted by low-orbit navigation augmentation

Abstract

The present invention relates to a method for autonomous integrity monitoring of GNSS assisted by low-orbit navigation enhancement. The method includes: obtaining the position coordinates of medium and high-orbit satellites within the observation range of a ground observation station according to the ephemeris parameter data of medium and high-orbit satellites in GNSS. Calculating the included angle between the position coordinates of medium and high-orbit satellites and the position coordinates of low-orbit satellites, and eliminating local satellites according to the comparison result between the included angle and a preset warning included angle threshold to obtain a visible satellite group. Constructing a pseudorange observation model based on the visible satellite group to obtain a pseudorange residual vector. Calculating the chi-square non-centrality parameter of the pseudorange residual vector under a preset warning probability condition to obtain the characteristic slope of the visible satellite group. Determining the availability of RAIM according to the characteristic slope and the chi-square non-centrality parameter, and detecting faults for the determination result of the availability of RAIM to obtain an integrity monitoring result. Using this method can improve the availability level and fault detection ability of the navigation system.

Description

Technical Field

[0001] The present invention relates to the technical field of integrity monitoring of satellite navigation, and particularly to a method for autonomous integrity monitoring of GNSS assisted by low-orbit navigation enhancement. Background Art

[0002] Integrity refers to the ability of a system to timely alert users when a failure occurs, resulting in positioning exceeding a certain threshold or being unsuitable for navigation. It is one of the four navigation service performance indicators of the global navigation satellite system, along with accuracy, continuity, and availability. In the case of incorrect positioning caused by various abnormal measurement data, the purpose of integrity monitoring is to monitor and eliminate abnormal data to ensure that the positioning accuracy rate is within a certain range. Especially in the aerospace field and the current intelligent driving field, in the event of a failure, it is necessary to identify and eliminate the failure to minimize the impact on flight or driving. The problem to be solved is to determine whether a failure is detected and then perform post-failure processing in the corresponding field to ensure flight and driving safety. The receiver autonomous integrity monitoring (RAIM) algorithm is implemented on each user receiver, taking into account the specific conditions of multipath and local electromagnetic interference, which can better ensure that users accurately grasp the alert time and improve the alert accuracy for local specific conditions. The existing RAIM algorithm for the Beidou constellation can reach an average global availability level of about 30% under the accuracy requirements of CAT I (horizontal alert value of 40 m and vertical alert value of 10 m). The Chinese Academy of Sciences has studied the integration of Beidou and low-orbit enhancement to improve the integrity and availability level. Nanjing University of Aeronautics and Astronautics has invented a method for GNSS integrity monitoring in urban complex environments, which divides GNSS into four-star subsets for integrity analysis, solving the problems of interference in urban complex environments and non-Gaussian noise interference. However, it strictly stipulates that the number of visible satellites is 4, reducing the accuracy and resulting in a decrease in the availability level and failure monitoring ability. Summary of the Invention

[0003] Based on this, in view of the above technical problems, it is necessary to provide a method for autonomous integrity monitoring of GNSS assisted by low-orbit navigation enhancement, which can improve the accuracy and availability level of satellite autonomous integrity monitoring.

[0004] A method for autonomous integrity monitoring of GNSS assisted by low-orbit navigation enhancement, the method comprising:

[0005] Obtain the position coordinates of the GNSS medium-high orbit satellites within the observation range of the ground observation station according to the ephemeris parameter data of the GNSS medium-high orbit satellites.

[0006] Calculate the included angle between the position coordinates of the GNSS medium-high orbit satellites and the position coordinates of the low-orbit satellites, and according to the comparison result between the included angle and a preset alert included angle threshold, eliminate the local satellites of GNSS to obtain a visible satellite group.

[0007] Construct a pseudorange observation model based on the visible satellite group, and obtain the pseudorange residual vector through the pseudorange observation model.

[0008] Calculate the non-central chi-square parameter of the pseudorange residual vector under the preset alarm probability condition, and obtain the characteristic slope of the visible satellite group according to the non-central chi-square parameter.

[0009] Perform RAIM availability determination based on the characteristic slope and the non-central chi-square parameter, and conduct fault detection on the determination result of RAIM availability to obtain the integrity monitoring result.

[0010] In one embodiment, it further includes: obtaining the position coordinates of the GNSS medium and high orbit satellites within the observation range of the ground observation station in the Earth-Centered Earth-Fixed coordinate system according to the ephemeris parameter data of the GNSS medium and high orbit satellites:

[0011] x k = x k ′cosΩ k - y k ′cosi k sinΩ k

[0012] y k = x k ′sinΩ k - y k ′cosi k cosΩ k

[0013] z k = y k ′sini k

[0014] where, (x k , y k , z k ) are the position coordinates in the WGS-84 Earth-Centered Earth-Fixed coordinate system (X T , Y T , Z T ), Ω k is the right ascension of the ascending node, and k is the number of the GNSS medium and high orbit satellites.

[0015] In one embodiment, it further includes: obtaining the simulation data of the low-orbit satellite constellation or the measured data of the navigation payload carried by using STK software, and outputting the position coordinates of the low-orbit satellites in the Earth-Centered Earth-Fixed coordinate system.

[0016] In one embodiment, it further includes: calculating the included angle between the position coordinates of the GNSS medium and high orbit satellites and the position coordinates of the low-orbit satellites:

[0017]

[0018] Among them, S i =(x i , y i , z i ) is the position coordinate of the geostationary satellite in the GNSS in the Earth-centered Earth-fixed coordinate system. S j =(x j , y j , z j ) is the position coordinate of the low-earth orbit satellite in the Earth-centered Earth-fixed coordinate system. α is the included angle between the position coordinate of the geostationary satellite and the position coordinate of the low-earth orbit satellite in the GNSS. The comparison result is obtained by comparing the included angle with the preset warning included angle threshold:

[0019] L R =bool(α≤α alarm )

[0020] Among them, L R is the comparison result, and α alarm is the preset warning included angle threshold. If the comparison result is 1, the satellite corresponding to the included angle at the current moment is excluded, and the remaining low-earth orbit satellite group is used as the data sample for integrity monitoring to obtain the visible satellite group. If the comparison result is 0, the satellite corresponding to the included angle at the current moment is retained, and the reference data of the satellite corresponding to the included angle at the current moment is added to the low-earth orbit satellite group for integrity monitoring to obtain the visible satellite group.

[0021] In one of the embodiments, it further includes: constructing a pseudorange observation model based on the reference data obtained from the visible satellite group:

[0022] y = Hx + ε

[0023] Among them, y is an n×1 pseudorange observation vector, H is an n×4 observation matrix of the geostationary satellite and some low-earth orbit satellites in the GNSS, x is a 4×1 state vector to be estimated, ε is an n×1 pseudorange observation noise vector, ε~N(0, D), D is the covariance matrix of the observation noise, and n is the number of satellites in the visible satellite group. The weighted least squares estimation is used to solve the state vector to be estimated through the pseudorange observation model to obtain the pseudorange residual vector:

[0024]

[0025]

[0026] Among them, v is the pseudorange residual vector, I n is an n×n identity matrix, H is an n×4 observation matrix, ε is an n×1 pseudorange observation noise vector, W is the weight, and P=(H T WH) -1 H T W.

[0027] In one of the embodiments, it further includes: calculating the non-central chi-square parameter of the pseudorange residual vector under a preset alarm probability condition:

[0028]

[0029] where P fa is the false alarm probability, P md is the missed alarm probability, λ is the non-central chi-square parameter, T D is the test threshold, obeys a non-central chi-square distribution function with (n - 4) degrees of freedom in the fault mode for the pseudorange residual vector. Obtain the characteristic slope of the visible satellite group according to the non-central chi-square parameter and the pseudorange residual vector:

[0030]

[0031] where Hslope i is the horizontal characteristic slope of the i-th satellite, Vslope i is the vertical characteristic slope of the i-th satellite, P 1i is the element in the first row and the i-th column of the P matrix, S ii is the idempotent matrix of the i-th satellite, σ i is the observation error of the i-th satellite. The alarm probability includes: the false alarm probability and the missed alarm probability.

[0032] In one of the embodiments, it further includes: determining the RAIM availability according to the characteristic slope and the non-central chi-square parameter:

[0033]

[0034] where N sat is the number of satellites in the visible satellite group at the current moment, N req is the number of satellites required for RAIM at the current moment, PL t is the maximum undetectable positioning error at the current moment, AL is the alarm limit, t step is the time step, ava RAIM is the RAIM availability within any time period [t1, t2]. Detect faults on the determination result of the RAIM availability:

[0035]

[0036] where T D is the test threshold of the visible satellite group, n is the number of satellites in the visible satellite group, σ T is the threshold of unit weight, σ is the post-test unit weight mean error of the pseudorange residual vector, σ0 is the observation error, SSE = εT $S_{\epsilon}$ is the sum of squared residuals, $S$ is an idempotent matrix, and $\epsilon$ is the pseudorange observation noise vector.

[0037] When $\sigma > \sigma$ T a fault occurs in the navigation system, and fault identification is performed based on the pseudorange residuals of the visible satellite group to obtain the integrity monitoring result:

[0038]

[0039] where $d$ i is the integrity monitoring result, $v$ i is the pseudorange residual of the $i$-th satellite, and $S$ ii is the idempotent matrix of the $i$-th satellite.

[0040] A GNSS autonomous integrity monitoring system assisted by low-orbit navigation enhancement, the system includes:

[0041] A medium-high orbit satellite position coordinate acquisition module, which is used to acquire the position coordinates of GNSS medium-high orbit satellites within the observation range of a ground observation station according to the ephemeris parameter data of GNSS medium-high orbit satellites.

[0042] A visible satellite group acquisition module, which is used to calculate the angle between the position coordinates of GNSS medium-high orbit satellites and the position coordinates of low-orbit satellites, and eliminate local satellites of GNSS according to the comparison result between the angle and a preset warning angle threshold to obtain a visible satellite group.

[0043] A residual vector acquisition module, which is used to construct a pseudorange observation model based on the visible satellite group and obtain a pseudorange residual vector through the pseudorange observation model.

[0044] A characteristic slope calculation module, which is used to calculate the chi-square non-centrality parameter of the pseudorange residual vector under a preset warning probability condition, and obtain the characteristic slope of the visible satellite group according to the chi-square non-centrality parameter.

[0045] An integrity monitoring module, which is used to determine the availability of RAIM according to the characteristic slope and the chi-square non-centrality parameter, and perform fault detection on the determination result of the availability of RAIM to obtain the integrity monitoring result.

[0046] In one embodiment, the visible satellite group acquisition module is further used to calculate the angle between the position coordinates of GNSS medium-high orbit satellites and the position coordinates of low-orbit satellites:

[0047]

[0048] where $S$ i $=(x$ i , $y$ i , $z$ i) is the position coordinate of the high-orbit satellite in the GNSS in the Earth-Centered Earth-Fixed coordinate system, and S j =(x j , y j , z j ) is the position coordinate of the low-orbit satellite in the Earth-Centered Earth-Fixed coordinate system, and α is the included angle between the position coordinate of the high-orbit satellite and the position coordinate of the low-orbit satellite in the GNSS. Compare the included angle with the preset warning included angle threshold to obtain the comparison result:

[0049] L R =bool(α≤α alarm )

[0050] where L R is the comparison result, and α alarm is the preset warning included angle threshold;

[0051] If the comparison result is 1, then exclude the satellite corresponding to the included angle at the current moment, and use the remaining low-orbit satellite group as the data sample for integrity monitoring to obtain the visible satellite group. If the comparison result is 0, then retain the satellite corresponding to the included angle at the current moment, and add the reference data of the satellite corresponding to the included angle at the current moment to the low-orbit satellite group for integrity monitoring to obtain the visible satellite group.

[0052] In one embodiment, the integrity monitoring module is further configured to determine the RAIM availability according to the characteristic slope and the chi-square non-centrality parameter:

[0053]

[0054] where N sat is the number of satellites in the visible satellite group at the current moment, N req is the number of satellites required for RAIM at the current moment, PL t is the maximum undetectable positioning error at the current moment, AL is the warning limit, t step is the time step, and ava RAIM is the RAIM availability within any time period [t1, t2]. Detect faults on the determination result of the RAIM availability:

[0055]

[0056] where T D is the test threshold of the visible satellite group, n is the number of satellites in the visible satellite group, σ T is the threshold of unit weight, σ is the post-test unit weight mean error of the pseudorange residual vector, σ0 is the observation error, SSE = ε T Sε is the sum of squared residuals, S is the idempotent matrix, and ε is the pseudorange observation noise vector. When σ > σ TWhen a failure occurs in the navigation system, fault identification is performed based on the pseudorange residuals of the visible satellite group to obtain the integrity monitoring result:

[0057]

[0058] where d i is the integrity monitoring result, v i is the pseudorange residual of the i-th satellite, and S ii is the idempotent matrix of the i-th satellite.

[0059] The above method for autonomous integrity monitoring of GNSS assisted by low-orbit navigation enhancement calculates the position coordinates of satellites within the observable range of a ground observation station through the ephemeris parameter data of high-orbit satellites in the Global Navigation Satellite System (GNSS), including coordinate system conversion and time correction, and calculates the position coordinates of high-orbit satellites at any given time. This ensures high-precision calculation of satellite positions and is the basis for all subsequent steps. Then, by determining the position of the ground observation station, the positions of satellites observable by the observation station within a given horizon elevation angle threshold are calculated. The key to this step is to screen out the truly visible satellites, thus ensuring the effectiveness and accuracy of the observation data. To further optimize the visible satellite group, the angle between high-orbit and low-orbit satellites in GNSS also needs to be calculated. According to the comparison result between the angle and a preset warning threshold, the occlusion situation of medium-high-orbit and low-orbit satellites is judged, and part of the unoccluded high-orbit + part of the low-orbit satellites in GNSS are selected as the visible satellite group, effectively reducing the observation error caused by satellite occlusion. After determining the visible satellite group, a pseudorange observation model is constructed, and the pseudorange residual vector of each visible satellite is calculated through the pseudorange observation formula, providing a data basis for subsequent integrity monitoring. Under the preset warning probability condition, the chi-square non-centrality parameter is calculated through the pseudorange residual vector, and the characteristic slope of the visible satellite group is obtained using the covariance matrix of the residual vector. According to the characteristic slope and the chi-square non-centrality parameter, the availability of RAIM (Receiver Autonomous Integrity Monitoring) is determined, and further analysis is carried out for fault detection and identification. As a result, the screening accuracy of the visible satellite group is significantly improved, the influence of satellite occlusion on the observation result is reduced, and the accuracy and reliability of the pseudorange observation model are enhanced; the sensitivity and accuracy of RAIM fault detection are improved, and the availability level and fault detection ability can also be increased according to the different geometric configurations of the visible satellite group, ensuring the reliability and security of navigation services. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 is a schematic flow chart of a method for autonomous integrity monitoring of GNSS assisted by low-orbit navigation enhancement in an embodiment;

[0061] Figure 2It is a structural block diagram of a GNSS autonomous integrity monitoring system for low-orbit navigation enhancement assistance in an embodiment;

[0062] Figure 3 It is an internal structure diagram of a computer device in an embodiment. Specific implementation manners

[0063] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0064] In one embodiment, as Figure 1 shown, a method for GNSS autonomous integrity monitoring with low-orbit navigation enhancement assistance is provided, including the following steps:

[0065] Step 102, obtaining the position coordinates of GNSS medium and high-orbit satellites within the observation range of a ground observation station according to the ephemeris parameter data of GNSS medium and high-orbit satellites.

[0066] GNSS includes constellations such as Beidou, GPS, GLONASS, GALILEO and their constellation combinations, and low-orbit includes low-orbit satellites such as starlink, Xingwang, oneweb and other low-orbit satellites carrying navigation payloads, with strong versatility.

[0067] Specifically, according to the ephemeris parameter data of GNSS medium and high-orbit satellites, the position coordinates of each GNSS medium and high-orbit satellite in the Earth-Centered Earth-Fixed (ECEF) coordinate system are calculated, including calculating the planned time, the average angular velocity of the satellite, the mean anomaly at the signal emission time, the eccentric anomaly at the signal emission time, the true anomaly at the signal emission time, the argument of latitude, the perturbation correction term at the signal emission time, the argument of latitude after perturbation correction, the satellite radius vector length and orbital inclination, the position of the satellite in the orbital plane at the signal emission time, the right ascension of the ascending node at the signal emission time, and the coordinates of the satellite in the WGS-84 Earth-Centered Earth-Fixed rectangular coordinate system, etc.

[0068] Further, calculate the planned time:

[0069] t k = t - t oe

[0070] wherein, t k is the normalized time, t is the required time, and t oe is the reference time.

[0071] Calculate the average angular velocity of the satellite:

[0072] n = n0 - Δn

[0073] Among them, n is the average angular velocity, n0 is the average angular velocity of the imaginary satellite, and Δn is the average angular velocity correction value provided by the ephemeris.

[0074] Calculate the mean anomaly at the signal emission time;

[0075] M k = M0 - nt k

[0076] Among them, M k is the mean anomaly, and M0 is the mean anomaly correction value provided by the ephemeris. At the same time, it is easy to obtain the eccentric anomaly E k and the true anomaly v k .

[0077] Calculate the argument of latitude:

[0078] Φ k = v k - ω

[0079] Among them, Φ k is the argument of latitude, and ω is provided by the ephemeris.

[0080] Calculate the perturbation correction term at the signal emission time:

[0081] δu k = C us sin(2Φ k ) + C uc cos(2Φ k )

[0082] δr k = C rs sin(2Φ k ) + C rc cos(2Φ k )

[0083] δi k = C us sin(2Φ k ) + C ic cos(2Φ k )

[0084] Among them, C us , C uc , C rs , C rc , C us , C ic are ephemeris parameters, and δu k , δr k , δi k are the second harmonic perturbation correction amounts.

[0085] Calculate the argument of the ascending node, the satellite radius vector length, and the orbital inclination after perturbation correction:

[0086] u k = Φ k + δu k

[0087] r k = a s (1 - e s cosE k ) + δr k

[0088] i k = i0 + i·t k + δi k

[0089] Wherein, u k is the argument of the ascending node, r k is the satellite radius vector length, and i k is the orbital inclination.

[0090] Calculate the position of the satellite in the orbital plane at the signal emission time:

[0091] x k ′ = r k cosu k

[0092] y k ′ = r k sinu k

[0093] Wherein, (x k ′, y k ′) are the coordinates in the rectangular coordinate system of the orbital plane.

[0094] Calculate the right ascension of the ascending node at the signal emission time:

[0095]

[0096] Wherein, Ω k is the right ascension of the ascending node, Ω0, is given by the ephemeris, is the constant of the angular velocity of the Earth's rotation.

[0097] Calculate the position coordinates of the ground observation station of the satellite in the WGS-84 geocentric earth-fixed rectangular coordinate system:

[0098] x k = x k ′cosΩ k - y k ′cosi k sinΩ k

[0099] y k = x k 'sinΩ k -y k 'cosi k cosΩ k

[0100] z k = y k 'sini k

[0101] Wherein, (x k , y k , z k ) is the position coordinate of the geostationary satellite in GNSS in the WGS-84 geocentric earth-fixed rectangular coordinate system (X T , Y T , Z T ).

[0102] Step 104, calculate the included angle between the position coordinates of the geostationary satellite in GNSS and the position coordinates of the low-earth orbit satellite. According to the comparison result between the included angle and the preset warning included angle threshold, eliminate the local satellites of GNSS to obtain the visible satellite group.

[0103] Specifically, according to the simulation data of the low-earth orbit satellite constellation given by the STK software or directly give the measured data carried by the navigation payload, export the satellite position coordinates in the ECEF coordinate system. According to the coordinates S i = (x i , y i , z i ) of the geostationary satellite in GNSS observable by the corresponding ground observation station and the coordinates S j = (x j , y j , z j ) of the low-earth orbit satellite, calculate the included angle α between the geostationary satellite and the low-earth orbit satellite in GNSS:[[]]

[0104]

[0105] Furthermore, compare α with the preset warning included angle threshold α alarm ,

[0106] L R = bool(α ≤ α alarm )

[0107] Wherein, L R is the judgment value 1 of the bool value, that is, eliminate a certain satellite at this time and do not use it for integrity monitoring, L RIs 0, retain this satellite for low-orbit enhancement, thereby excluding local satellites of GNSS, and obtaining a visible satellite group for the navigation system.

[0108] Step 106, construct a pseudorange observation model based on the visible satellite group, and obtain a pseudorange residual vector through the pseudorange observation model.

[0109] Specifically, based on the navigation parameter data obtained from the visible satellite group that has excluded redundant or messy satellite data, establish a single-fault detection model based on residuals, and the linearized pseudorange observation model of the navigation receiver:

[0110] y = Hx + ε

[0111] Where, y is an n×1 pseudorange observation vector; H is an n×4 observation matrix of "GNSS medium-high orbit + part of low orbit" satellites; x is a 4×1 state vector to be estimated; ε is an n×1 pseudorange observation noise vector, representing the measurement error of each pseudorange measurement, ε ~ N(0, D), D is the covariance matrix of the observation noise, and n is the number of visible satellites.

[0112] Furthermore, perform weighted least squares estimation and solution on the state vector:

[0113]

[0114] Where, the weight W is given according to the different observation errors of GNSS medium-high orbit and low orbit satellites. The noise variance of GNSS medium-high orbit is The noise variance of low orbit Then the weight part of GNSS medium-high orbit is The weight of the low orbit part is Let P = (H T WH) -1 H T Wy, then there is:

[0115]

[0116] Furthermore, calculate the pseudorange residual vector according to the state estimation vector:

[0117]

[0118] Denote S = I n -H(H T H) -1 H T , then there is v = Sε. The matrix S is an idempotent matrix, and the sum of squared residuals can be expressed as:

[0119] SSE = v T v = ε T S 2 ε = ε T Sε

[0120] In the fault - free mode, each component in the pseudorange residual vector is an independent normally - distributed random error According to the statistical distribution theory, the normalized statistic follows a chi - square distribution with degrees of freedom (n - 4), that is In the fault mode, follows a non - central chi - square distribution with degrees of freedom (n - 4), that is λ is the non - centrality parameter.

[0121] Step 108: Calculate the non - central chi - square parameter of the pseudorange residual vector under the preset alarm probability condition, and obtain the characteristic slope of the visible satellite group according to the non - central chi - square parameter.

[0122] The alarm probability includes: false - alarm probability and miss - alarm probability.

[0123] Specifically, according to the given false - alarm probability P fa , miss - alarm probability P md and the number of visible satellites n, calculate the non - central chi - square parameter λ and the test threshold T D :

[0124]

[0125] where P fa is the false - alarm probability, P md is the miss - alarm probability, λ is the non - central chi - square parameter, T D is the test threshold, is the non - central chi - square distribution function of the pseudorange residual vector in the fault mode, with degrees of freedom (n - 4).

[0126] Furthermore, according to the given observation error σ0 and the P and S matrices obtained from the observation matrix, calculate the characteristic slope of the satellite set:

[0127]

[0128] where Hslope i is the horizontal characteristic slope of the i - th satellite, Vslope i is the vertical characteristic slope of the i - th satellite. P 1i is the element in the first row and the i - th column of the P matrix, S ii is the idempotent matrix of the i - th satellite, σ i is the observation error of the i - th satellite.

[0129] Step 110: Determine the RAIM availability according to the characteristic slope and the non - central chi - square parameter, and perform fault detection on the determination result of the RAIM availability to obtain the integrity monitoring result.

[0130] Specifically, the RAIM availability is determined based on the characteristic slope and the chi-square non-centrality parameter λ. The availability determination includes two aspects: redundancy and geometric configuration. The RAIM availability within any time period [t1, t2] can be expressed as:

[0131]

[0132] where N sat and N req are the number of visible satellites at the current moment and the number of satellites required for RAIM, respectively. The protection level (PL) is the maximum undetectable positioning error of RAIM at the current moment. By comparing the protection level with the given alert limit (AL), it is determined whether the geometric configuration at the current moment meets the integrity index requirements. The protection level includes the horizontal protection level (HPL) and the vertical protection level (VPL), and the common expression is the product of the maximum characteristic slope and the minimum detectable deviation of the chi-square test:

[0133]

[0134]

[0135] When the geometric conditions are met in both the horizontal and vertical directions, RAIM is considered available under the current geometric configuration:

[0136] bool(PL t ≤ AL) = bool(HPL t ≤ HAL, VPL t ≤ VAL)

[0137] Based on the test threshold T D and the number of visible satellites n, the threshold σ T of unit weight is obtained for fault detection:

[0138]

[0139] where σ is the posterior mean square error of unit weight of the pseudorange residual vector. When σ < σ T , it is considered that a fault has occurred in the navigation system.

[0140] Furthermore, based on the pseudorange residual v i of the corresponding satellite, fault identification is carried out:

[0141]

[0142] where the satellite with the largest d i value is the faulty satellite.

[0143] In the above method for autonomous integrity monitoring of GNSS assisted by low-earth orbit navigation augmentation, in the Global Navigation Satellite System (GNSS), the position coordinates of satellites within the observable range of a ground observation station are calculated through the ephemeris parameter data of high-earth orbit satellites, including coordinate system conversion and time correction, to calculate the position coordinates of high-earth orbit satellites at any given moment. This ensures high-precision calculation of satellite positions and serves as the basis for all subsequent steps. Next, by determining the position of the ground observation station, the positions of satellites observable by the observation station within a given horizon elevation angle threshold are calculated. The key to this step is to screen out truly visible satellites, thereby ensuring the effectiveness and accuracy of the observation data. To further optimize the group of visible satellites, the angle between high-earth orbit satellites and low-earth orbit satellites in GNSS also needs to be calculated. According to the comparison result between the angle and a preset warning threshold, the occlusion situation of medium- and high-earth orbit satellites and low-earth orbit satellites is judged, and a part of the unoccluded high-earth orbit + part of the low-earth orbit satellites in GNSS are selected as the group of visible satellites, effectively reducing the observation error caused by satellite occlusion. After determining the group of visible satellites, a pseudorange observation model is constructed, and the pseudorange residual vector of each visible satellite is calculated through the pseudorange observation formula, providing a data basis for subsequent integrity monitoring. Under the condition of a preset warning probability, the chi-square non-centrality parameter is calculated through the pseudorange residual vector, and the characteristic slope of the group of visible satellites is obtained using the covariance matrix of the residual vector. According to the characteristic slope and the chi-square non-centrality parameter, the availability of RAIM (Receiver Autonomous Integrity Monitoring) is determined, and further analysis is carried out for fault detection and identification. As a result, the screening accuracy of the group of visible satellites is significantly improved, the influence of satellite occlusion on the observation results is reduced, and the accuracy and reliability of the pseudorange observation model are enhanced; the sensitivity and accuracy of RAIM fault detection are improved, and the availability level and fault detection ability can also be increased according to different geometric configurations of the group of visible satellites, ensuring the reliability and security of navigation services.

[0144] In one embodiment, the position coordinates of high-earth orbit satellites in GNSS within the observable range of a ground observation station in the Earth-Centered Earth-Fixed coordinate system are obtained according to the ephemeris parameter data of high-earth orbit satellites in GNSS:

[0145] x k =x k ′cosΩ k -y k ′cosi k sinΩ k

[0146] y k =x k ′sinΩ k -y k ′cosi k cosΩ k

[0147] zk = y k 'sini k

[0148] Wherein, (x k , y k , z k ) is the position coordinate in the WGS-84 geocentric earth-fixed coordinate system (X T , Y T , Z T ), Ω k is the right ascension of the ascending node, and k is the number of high-orbit satellites in GNSS.

[0149] In one embodiment, it further includes: obtaining simulation data of the low-orbit satellite constellation or measured data of the navigation payload carried by the STK software, and outputting the position coordinates of the low-orbit satellites in the geocentric earth-fixed coordinate system.

[0150] In one embodiment, calculate the included angle between the position coordinates of the high-orbit satellites in GNSS and the position coordinates of the low-orbit satellites:

[0151]

[0152] Wherein, S i = (x i , y i , z i ) is the position coordinate of the high-orbit satellite in GNSS in the geocentric earth-fixed coordinate system, S j = (x j , y j , z j ) is the position coordinate of the low-orbit satellite in the geocentric earth-fixed coordinate system, and α is the included angle between the position coordinates of the high-orbit satellite in GNSS and the position coordinates of the low-orbit satellite. Obtain the comparison result by comparing the included angle with the preset warning included angle threshold:

[0153] L R = bool(α ≤ α alarm )

[0154] Wherein, L R is the comparison result, and α alarm is the preset warning included angle threshold. If the comparison result is 1, the satellite corresponding to the included angle at the current moment is removed, and the remaining low-orbit satellite group is used as the data sample for integrity monitoring to obtain the visible satellite group. If the comparison result is 0, the satellite corresponding to the included angle at the current moment is retained, and the reference data of the satellite corresponding to the included angle at the current moment is added to the low-orbit satellite group for integrity monitoring to obtain the visible satellite group.

[0155] In one embodiment, construct a pseudorange observation model based on the reference data obtained from the visible satellite group:

[0156] y = Hx + ε

[0157] Where y is an n×1 pseudorange observation vector, H is an n×4 observation matrix of GNSS medium and high orbit satellites and some low orbit satellites, x is a 4×1 state vector to be estimated, ε is an n×1 pseudorange observation noise vector, ε ~ N(0, D), D is the covariance matrix of the observation noise, and n is the number of satellites in the visible satellite group. The weighted least squares estimation is used to solve the state vector to be estimated through the pseudorange observation model, and the pseudorange residual vector is obtained:

[0158]

[0159]

[0160] Where v is the pseudorange residual vector, I n is an n×n identity matrix, H is an n×4 observation matrix, ε is an n×1 pseudorange observation noise vector, W is the weight, and P is the matrix P = (H T WH) -1 H T W.

[0161] In one embodiment, the chi-square non-centrality parameter of the pseudorange residual vector under a preset alarm probability condition is calculated:

[0162]

[0163] Where P fa is the false alarm probability, P md is the miss alarm probability, λ is the chi-square non-centrality parameter, T D is the test threshold value, is the non-central chi-square distribution function with degrees of freedom (n - 4) that the pseudorange residual vector follows under the fault mode. The characteristic slope of the visible satellite group is obtained according to the chi-square non-centrality parameter and the pseudorange residual vector:

[0164]

[0165] Where Hslope i is the horizontal characteristic slope of the i-th satellite, Vslope i is the vertical characteristic slope of the i-th satellite, P 1i is the element in the first row and the i-th column of the P matrix, S ii is the idempotent matrix of the i-th satellite, and σ i is the observation error of the i-th satellite. The alarm probability includes: false alarm probability and miss alarm probability.

[0166] In one embodiment, the RAIM availability determination is performed according to the characteristic slope and the chi-square non-centrality parameter:

[0167]

[0168] Among them, N sat is the number of satellites in the visible satellite group at the current moment, and N req is the number of satellites required for RAIM at the current moment, and PL t is the maximum undetectable positioning error at the current moment, AL is the warning limit value, and t step is the time step, and ava RAIM is the RAIM availability within any time period [t1, t2]. Fault detection is performed on the determination result of RAIM availability:

[0169]

[0170] Among them, T D is the test threshold value of the visible satellite group, n is the number of satellites in the visible satellite group, and σ T is the threshold in unit weight, σ is the post-test unit weight mean square error of the pseudorange residual vector, σ0 is the observation error, and SSE = ε T Sε is the sum of squared residuals, S is an idempotent matrix, and ε is the pseudorange observation noise vector.

[0171] When σ > σ T then a fault occurs in the navigation system. Fault identification is performed based on the pseudorange residuals of the visible satellite group to obtain the integrity monitoring result:

[0172]

[0173] Among them, d i is the integrity monitoring result (i.e., the test statistic), v i is the pseudorange residual of the i-th satellite, and S ii is the idempotent matrix of the i-th satellite.

[0174] It should be understood that although Figure 1 the steps in the flowchart of Figure 1 are shown in sequence according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise clearly stated in this article, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover,

[0175] In one embodiment, as Figure 2As shown, a GNSS autonomous integrity monitoring system with low-orbit navigation enhancement assistance is provided, including: a medium-high orbit satellite position coordinate acquisition module 202, a visible satellite group acquisition module 204, a residual vector acquisition module 206, a characteristic slope calculation module 208, and an integrity monitoring module 210, where:

[0176] The medium-high orbit satellite position coordinate acquisition module 202 is used to acquire the position coordinates of GNSS medium-high orbit satellites within the observation range of a ground observation station according to the ephemeris parameter data of GNSS medium-high orbit satellites.

[0177] The visible satellite group acquisition module 204 is used to calculate the included angle between the position coordinates of GNSS medium-high orbit satellites and the position coordinates of low-orbit satellites, and based on the comparison result between the included angle and a preset warning included angle threshold, eliminate local satellites of GNSS to obtain a visible satellite group.

[0178] The residual vector acquisition module 206 is used to construct a pseudorange observation model based on the visible satellite group and obtain a pseudorange residual vector through the pseudorange observation model.

[0179] The characteristic slope calculation module 208 is used to calculate the chi-square non-centrality parameter of the pseudorange residual vector under a preset warning probability condition, and obtain the characteristic slope of the visible satellite group according to the chi-square non-centrality parameter.

[0180] The integrity monitoring module 210 is used to determine the RAIM availability according to the characteristic slope and the chi-square non-centrality parameter, and perform fault detection on the determination result of the RAIM availability to obtain an integrity monitoring result.

[0181] For the specific limitations of a GNSS autonomous integrity monitoring system with low-orbit navigation enhancement assistance, reference can be made to the limitations of a GNSS autonomous integrity monitoring method with low-orbit navigation enhancement assistance in the above text, which will not be elaborated here. Each module in the above-mentioned GNSS autonomous integrity monitoring system with low-orbit navigation enhancement assistance can be implemented in whole or in part through software, hardware, and their combination. The above-mentioned modules can be embedded in or independent of the processor in a computer device in the form of hardware, or stored in the memory of the computer device in the form of software, so that the processor can call and execute the operations corresponding to the above-mentioned modules.

[0182] In one embodiment, a computer device is provided. The computer device can be a terminal, and its internal structure diagram can be as Figure 3As shown in the figure. The computer device includes a processor, a memory, a network interface, a display screen, and an input device connected through a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage medium. The network interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, it implements a method for autonomous integrity monitoring of GNSS with low-orbit navigation enhancement. The display screen of the computer device can be a liquid crystal display screen or an electronic ink display screen. The input device of the computer device can be a touch layer covering the display screen, or a button, a trackball, or a touchpad provided on the casing of the computer device, or an external keyboard, a touchpad, or a mouse, etc.

[0183] Those skilled in the art can understand that Figures 2 - 3 the structure shown in the figure is only a block diagram of some structures related to the solution of the present invention, and does not constitute a limitation on the computer device to which the solution of the present invention is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine some components, or have different component arrangements.

[0184] In one embodiment, a computer device is provided, including a memory and a processor. The memory stores a computer program. When the processor executes the computer program, the following steps are implemented:

[0185] Obtain the position coordinates of the GNSS medium-high orbit satellites within the observation range of the ground observation station according to the ephemeris parameter data of the GNSS medium-high orbit satellites.

[0186] Calculate the included angle between the position coordinates of the GNSS medium-high orbit satellites and the position coordinates of the low-orbit satellites. According to the comparison result between the included angle and the preset warning included angle threshold, eliminate the local satellites of the GNSS to obtain a visible satellite group.

[0187] Construct a pseudorange observation model according to the visible satellite group, and obtain a pseudorange residual vector through the pseudorange observation model.

[0188] Calculate the chi-square non-centrality parameter of the pseudorange residual vector under the preset warning probability condition, and obtain the characteristic slope of the visible satellite group according to the chi-square non-centrality parameter.

[0189] Perform RAIM availability determination according to the characteristic slope and the chi-square non-centrality parameter, and perform fault detection on the determination result of RAIM availability to obtain an integrity monitoring result.

[0190] Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above methods. Among them, any reference to a memory, storage, database, or other medium used in the embodiments provided by the present invention can include non-volatile and / or volatile memories. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and Rambus dynamic RAM (RDRAM), etc.

[0191] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0192] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A GNSS autonomous integrity monitoring method assisted by low-orbit navigation enhancement, characterized in that The method includes: Obtaining the position coordinates of the GNSS medium / high Earth orbit satellites within the observation range of a ground observation station according to the ephemeris parameter data of the GNSS medium / high Earth orbit satellites; Calculating the included angle between the position coordinates of the GNSS medium / high Earth orbit satellites and the position coordinates of the low Earth orbit satellites, and based on the comparison result between the included angle and a preset warning included angle threshold, eliminating local satellites of the GNSS to obtain a visible satellite group; calculating the included angle between the position coordinates of the GNSS medium / high Earth orbit satellites and the position coordinates of the low Earth orbit satellites: ； Wherein, is the position coordinate of the high-orbit satellite in the GNSS in the Earth-centered Earth-fixed coordinate system, is the position coordinate of the low-orbit satellite in the Earth-centered Earth-fixed coordinate system, is the included angle between the position coordinate of the high-orbit satellite in the GNSS and the position coordinate of the low-orbit satellite; Comparing the included angle with the preset warning included angle threshold to obtain a comparison result: ； Among them, is the comparison result, is the preset warning angle threshold; If the comparison result is 1, then eliminating the satellite corresponding to the included angle at the current moment, and using the remaining low Earth orbit satellite group as a data sample for integrity monitoring to obtain a visible satellite group; if the comparison result is 0, then retaining the satellite corresponding to the included angle at the current moment, and adding the reference data of the satellite corresponding to the included angle at the current moment to the low Earth orbit satellite group for integrity monitoring to obtain a visible satellite group; Constructing a pseudorange observation model according to the visible satellite group, and obtaining a pseudorange residual vector through the pseudorange observation model; Calculating the non-central chi-square parameter of the pseudorange residual vector under a preset warning probability condition, and obtaining the characteristic slope of the visible satellite group according to the non-central chi-square parameter; Performing RAIM availability determination based on the characteristic slope and the non-central chi-square parameter, and performing fault detection on the determination result of the RAIM availability to obtain an integrity monitoring result.

2. The method according to claim 1, wherein Obtaining the position coordinates of the GNSS medium / high Earth orbit satellites within the observation range of a ground observation station according to the ephemeris parameter data of the GNSS medium / high Earth orbit satellites, including: Obtaining the position coordinates of the GNSS medium / high Earth orbit satellites within the observation range of a ground observation station in the Earth-centered Earth-fixed coordinate system according to the ephemeris parameter data of the GNSS medium / high Earth orbit satellites: ； ； ； Among them, ( , , ) is the position coordinate in the WGS-84 geocentric inertial coordinate system ( , , ), is the right ascension of the ascending node, and k is the number of high-orbit satellites in GNSS.

3. The method according to claim 2, wherein After the step of obtaining the position coordinates of the GNSS medium / high Earth orbit satellites within the observation range of a ground observation station according to the ephemeris parameter data of the GNSS medium / high Earth orbit satellites, it includes: Obtaining simulation data of the low Earth orbit satellite constellation or measured data of a navigation payload carried by using STK software, and outputting the position coordinates of the low Earth orbit satellites in the Earth-centered Earth-fixed coordinate system.

4. The method according to claim 3, characterized in that, Constructing a pseudorange observation model according to the visible satellite group, and obtaining a pseudorange residual vector through the pseudorange observation model, including: Constructing a pseudorange observation model according to the reference data obtained from the visible satellite group: ； Among them, is the pseudorange observation vector, is the observation matrix of the medium / high Earth orbit satellites and some low Earth orbit satellites in GNSS, is the state vector to be estimated, and ε is the pseudorange observation noise vector, (0, D), where D is the covariance matrix of the observation noise, the number of satellites in the visible satellite group; Performing weighted least squares estimation and solution on the state vector to be estimated through the pseudorange observation model to obtain a pseudorange residual vector: ； ； where, is the pseudorange residual vector, is the n×n identity matrix, is the n×4 observation matrix, ε is the pseudorange observation noise vector, and W is the weight.

5. The method according to claim 4, characterized in that, Calculating the non-central chi-square parameter of the pseudorange residual vector under a preset warning probability condition, and obtaining the characteristic slope of the visible satellite group according to the non-central chi-square parameter, including: Calculating the non-central chi-square parameter of the pseudorange residual vector under a preset warning probability condition: ； Among them, is the false alarm probability, is the missed alarm probability, is the chi-square non-centrality parameter, is the test threshold, is that the pseudorange residual vector follows a non-central chi-square distribution function with (n - 4) degrees of freedom under the fault mode; Obtaining the characteristic slope of the visible satellite group according to the non-central chi-square parameter and the pseudorange residual vector: ； ； Among them, is the horizontal characteristic slope of the i-th satellite, is the vertical characteristic slope of the i-th satellite, is the element in the first row and the i-th column of the P matrix, is the idempotent matrix of the i-th satellite, is the observation error of the i-th satellite; The warning probability includes: false alarm probability and missed alarm probability.

6. The method according to claim 5, characterized in that After performing RAIM availability determination based on the characteristic slope and the non-central chi-square parameter, performing fault detection on the determination result of the RAIM availability to obtain an integrity monitoring result, including: Perform RAIM availability determination based on the characteristic slope and the chi-square non-centrality parameter: ； Among them, is the number of satellites in the visible satellite group at the current moment, is the number of satellites required for RAIM at the current moment, is the maximum undetectable positioning error at the current moment, and AL is the alarm limit, is the time step, is within any time period the RAIM availability; Perform fault detection on the determination result of the RAIM availability: ； ； Among them, is the test threshold value of the visible satellite group, is the number of satellites in the visible satellite group, is the threshold value in unit weight, is the mean square error in unit weight after the test of the pseudorange residual vector, is the observation error, is the sum of squared residuals, S is an idempotent matrix, and ε is the pseudorange observation noise vector; When a fault occurs in the navigation system, and fault identification is performed according to the pseudorange residuals of the visible satellite group to obtain an integrity monitoring result: ； Among them, is the integrity monitoring result, is the pseudorange residual of the i-th satellite, is the idempotent matrix of the i-th satellite.

7. A GNSS autonomous integrity monitoring system assisted by low-orbit navigation enhancement, characterized in that The system includes: A medium / high Earth orbit satellite position coordinate acquisition module, configured to acquire the position coordinates of the GNSS medium / high Earth orbit satellites within the observation range of a ground observation station according to the ephemeris parameter data of the GNSS medium / high Earth orbit satellites; A visible satellite group acquisition module, configured to calculate the included angle between the position coordinates of the GNSS medium / high Earth orbit satellites and the position coordinates of the low Earth orbit satellites, and remove local satellites of the GNSS according to the comparison result between the included angle and a preset warning included angle threshold to obtain a visible satellite group; calculate the included angle between the position coordinates of the GNSS medium / high Earth orbit satellites and the position coordinates of the low Earth orbit satellites: ； Among them, is the position coordinate of the high-orbit satellite in the GNSS in the geocentric earth-fixed coordinate system, is the position coordinate of the low-orbit satellite in the geocentric earth-fixed coordinate system, is the included angle between the position coordinate of the high-orbit satellite in the GNSS and the position coordinate of the low-orbit satellite; obtaining a comparison result by comparing the included angle with a preset warning included angle threshold: ； Among them, is the comparison result, is the preset warning angle threshold; if the comparison result is 1, the satellite corresponding to the angle at the current moment is excluded, and the remaining low-earth satellite group is used as the data sample for integrity monitoring to obtain the visible satellite group; if the comparison result is 0, the satellite corresponding to the angle at the current moment is retained, and the reference data of the satellite corresponding to the angle at the current moment is added to the low-earth satellite group for integrity monitoring to obtain the visible satellite group; A residual vector acquisition module, configured to construct a pseudorange observation model based on the visible satellite group and obtain a pseudorange residual vector through the pseudorange observation model; A characteristic slope calculation module, configured to calculate the chi-square non-centrality parameter of the pseudorange residual vector under a preset warning probability condition, and obtain the characteristic slope of the visible satellite group according to the chi-square non-centrality parameter; An integrity monitoring module, configured to perform RAIM availability determination based on the characteristic slope and the chi-square non-centrality parameter, perform fault detection on the determination result of the RAIM availability, and obtain an integrity monitoring result.

8. The system according to claim 7, wherein The integrity monitoring module is further configured to perform RAIM availability determination based on the characteristic slope and the chi-square non-centrality parameter: ； Among them, is the number of satellites in the visible satellite group at the current moment, is the number of satellites required for RAIM at the current moment, is the maximum undetectable positioning error at the current moment, AL is the alarm limit, is the time step, is within any time period the RAIM availability; Perform fault detection on the determination result of the RAIM availability: ； ； Among them, is the test threshold value of the visible satellite group, is the number of satellites in the visible satellite group, is the threshold value in the unit weight, is the post-test mean square error of unit weight of the pseudorange residual vector, is the observation error, is the sum of squared residuals, S is an idempotent matrix, and ε is the pseudorange observation noise vector; When a fault occurs in the navigation system, fault identification is performed based on the pseudorange residuals of the visible satellite group to obtain an integrity monitoring result: ； Among them, is the integrity monitoring result, is the pseudorange residual of the i-th satellite, is the idempotent matrix of the i-th satellite.

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