CN115408652A - EKF (extended Kalman Filter) integrated navigation protection level determination method based on truncation error estimation - Google Patents
EKF (extended Kalman Filter) integrated navigation protection level determination method based on truncation error estimation Download PDFInfo
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Abstract
The invention relates to an EKF (extended Kalman filter) combined navigation protection level determination method based on truncation error estimation; establishing a GNSS/INS tight combination navigation system state space model considering truncation errors, and estimating truncation error values and covariance thereof; modifying the model with the estimated truncation error and its covariance; calculating the statistical characteristic of the corrected positioning error by considering the residual amount of the truncation error to obtain a protection level expression comprising the truncation error; acquiring actual pseudo-range, pseudo-range rate observed quantity samples and corresponding residual truncation error sample data; respectively enveloping pseudo range, pseudo range rate observation error and residual truncation error sample data based on an extreme value theory to obtain corresponding amplification factors; and substituting the amplification factor into the protection level expression to obtain the protection level of the GNSS/INS tight combination navigation system. The invention combines more accurate protection level and more accurate error tail probability distribution, and ensures the reliability of the protection level.
Description
Technical Field
The invention belongs to the technical field of integrated navigation, and particularly relates to an EKF integrated navigation protection level determination method based on truncation error estimation.
Background
The single navigation system can not meet the requirement of accurate, credible and reliable flight of the unmanned aerial vehicle in the complex environment, and the GNSS/INS combined navigation has the advantages of all-weather long-term stable GNSS navigation and high INS short-time precision, and can be used as a navigation means for the unmanned aerial vehicle to fly in the complex environment. In order to ensure flight safety, the GNSS/INS integrated navigation has to meet given integrity requirements, the confidence upper limit of the positioning error under the designated risk probability, namely the protection level, can be calculated in real time, and when the protection level exceeds the alarm limit, the navigation system is unavailable at the moment, and the user needs to be alarmed in time.
When an EKF (extended kalman filter) is used to solve the nonlinear problem, taylor series is needed to linearize the nonlinear system, but the linearization needs to discard the high-order component in the taylor expansion. The core of the integrity monitoring of the GNSS/INS integrated navigation system is to estimate the statistical characteristics of positioning errors caused by various factors so as to calculate the protection level. When the EKF method is applied to GNSS/INS combined navigation, the calculation error of truncating the middle and high order terms of Taylor expansion is artificially generated and is called truncation error.
When the system nonlinearity is strong, the calculated positioning error covariance is inaccurate due to truncation error, so that the protection level calculation is not accurate enough and the integrity requirement cannot be met. The truncation error has to be taken into account during the filtering.
In addition, in the current correlation research of the combined navigation protection level, errors are assumed to follow a zero-mean gaussian distribution, but in practice, errors such as pseudorange and pseudorange rate are non-gaussian and non-zero-mean distribution, so that the calculated protection level cannot envelop the tail of the actual error, and a potential integrity risk may be caused.
Disclosure of Invention
In view of the above analysis, the present invention aims to disclose a method for determining an EKF integrated navigation protection level based on truncation error estimation, which is used to solve the problem that the truncation error generated in the EKF linearization process makes the protection level calculation not accurate enough.
The invention discloses an EKF (extended Kalman filter) combined navigation protection level calculation method based on truncation error estimation, which comprises the following steps of:
establishing a GNSS/INS tight combination navigation system state space model considering truncation errors, and estimating truncation error values and covariance thereof;
modifying the model with the estimated truncation error and its covariance; calculating the statistical characteristic of the corrected positioning error by considering the residual amount of the truncation error to obtain a protection level expression comprising the truncation error;
obtaining actual pseudo range, pseudo range rate observed quantity samples and corresponding residual truncation error sample data;
respectively enveloping pseudo range, pseudo range rate observation error and residual truncation error sample data based on an extreme value theory to obtain corresponding amplification factors;
and substituting the amplification factor into the protection level expression to obtain the protection level of the GNSS/INS tight combination navigation system.
Further, the GNSS/INS tightly combined navigation system state space model considering truncation errors is:
wherein,kis the time of day or the like,is thatnA state vector of dimensions;is thatmA measurement vector of dimensions;is composed ofnThe state of the stages is transferred to the matrix in one step,is composed ofm×nA measurement matrix of orders;to truncate the error vector;is composed ofnThe system noise vector of the dimension(s),is composed ofmThe measurement noise vector of the dimension.
Further, the state vector of the GNSS/INS tightly combined navigation system state space model is an error state vector of 17 dimensions:
wherein,is the three-dimensional velocity error;is the three-dimensional attitude angle error;is the three-dimensional position error;is the three-dimensional accelerometer error;is the three-dimensional gyroscope error;is a one-dimensional receiver constant offset;is a one-dimensional receiver clock drift.
Further, the measurement of the GNSS/INS tightly combined navigation system state space model is the GNSS observation pseudo rangePseudorange ratePseudoranges predicted from INSPseudorange ratesThe difference between the two;
Further, estimating the truncation error value and the covariance thereof by using an NPF method specifically includes:
1) Obtaining the estimated residual error of the current-time observed quantity and the last-time observed quantity;
Wherein,is composed ofkAt the first momentiThe pseudorange observations of the satellites,is composed ofkAt the first momentiPseudo range rate observations of the particles;andis composed ofk-1 time of dayiAn estimate of the observed quantity of particles, equal to a functionIn thatk-values of the high order terms omitted after taylor expansion at the estimated localization solution at time 1;i=1,…,p,pthe number of visible stars;
Further, the GNSS/INS tightly combined navigation system state space model corrected by the estimated value of the truncation error and the covariance thereof is as follows:
in the formula,in order to estimate the truncation error by the NPF method and truncate the residual error amount,。
further, the determination of the protection stage expression including the truncation error includes:
1) Determining a positioning error according to error propagation of Kalman filtering;
2) Performing integrity hypothesis distribution to obtain a vertical positioning error expression of the GNSS/INS tight combination navigation system under the H0 hypothesis;
3) Determining the distribution characteristic of the vertical positioning error according to the vertical positioning error expression;
4) And obtaining a protection level expression comprising the truncation error under the assumption of H0 according to the error distribution characteristics.
Further, H0 assumes that the vertical positioning error expression:
wherein,;is the Kalman gain;vas error state vectorsXThe line number corresponding to the height information is obtained;
is composed ofThe elements in the row of the matrix corresponding to the height information,is composed ofThe elements in the row of the matrix corresponding to the height information,is composed ofElements in a row of the matrix corresponding to the height information;
under the assumption of H0, a guard level expression including truncation errors:
Further, the method for obtaining the corresponding amplification factor based on the extreme value theory envelope pseudo range sample data comprises the following steps:
1) Arranging the obtained actual pseudo-range samples from small to large after taking absolute values, and calculating the standard deviation of the samples;
2) Selecting a pseudo range sample as a threshold value by using an average excess function graph method;
3) Re-sampling the pseudo-range samples for B times in a Bootstrap method to obtain a group B of samples;
3) According to an extreme value theory, performing parameter estimation on each group of samples to determine a parameter confidence limit value;
4) And substituting the parameter confidence limit value into the sample distribution, and determining a pseudo-range error amplification factor according to the integrity of the probability distribution of the combined navigation pseudo-range error.
Further, substituting the amplification factor into the protection level expression to obtain the protection level of the GNSS/INS tight combination navigation system(ii) a It is composed ofIn (1),
wherein,is a firstiThe pseudorange error amplification factor for the visible satellites,is as followsiThe pseudo-range rate error magnification factor for the visible satellites,is as followsiThe pseudorange residue of the visible satellites truncates the error amplification factor,is a firstiThe pseudorange rate residual truncation error magnification factor for the visible satellites.
The invention can realize one of the following beneficial effects:
aiming at the problem that the truncation error generated in the EKF linearization process causes the calculation of the protection level to be inaccurate, the EKF integrated navigation protection level determining method based on the truncation error estimation reduces the uncertainty of the truncation error and corrects the positioning error and the distribution thereof through the estimated size of the truncation error and the covariance thereof, thereby obtaining a more accurate protection level and ensuring that the protection level meets the given integrity risk; and positioning more accurate error tail probability distribution by adopting the extreme value theory to envelop errors such as actually sampled pseudo range, pseudo range rate and the like and truncating residual error distribution. And the more accurate protection level and the more accurate error tail probability distribution are combined, so that the reliability of the protection level is ensured.
Drawings
The drawings are for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout the figures;
fig. 1 is a flowchart of a method for determining an EKF integrated navigation protection level based on truncation error estimation according to an embodiment of the present invention.
Detailed Description
The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form a part hereof, and which together with the embodiments of the invention serve to explain the principles of the invention.
An embodiment of the present invention discloses an EKF integrated navigation protection level determination method based on truncation error estimation, as shown in fig. 1, including the following steps:
s1, establishing a GNSS/INS tight integrated navigation system state space model considering truncation errors, and estimating truncation error values and covariance thereof;
s2, correcting the model by using the estimated truncation error and the covariance thereof; calculating the statistical characteristic of the corrected positioning error by considering the residual amount of the truncation error to obtain a protection level expression comprising the truncation error;
s3, obtaining actual pseudo range, pseudo range rate observed quantity samples and corresponding residual truncation error sample data;
the residual truncation error sample data comprises pseudo-range residual truncation error sample data and pseudo-range rate residual truncation error sample data;
s4, respectively enveloping pseudo range, pseudo range rate observation error and residual truncation error data based on an extreme value theory to obtain corresponding amplification factors;
and S5, substituting the amplification factor into the protection level expression to obtain the protection level of the GNSS/INS tight combination navigation system.
In step S1, the state space model of the GNSS/INS tightly combined navigation system considering the truncation error is established as follows:
wherein,kis the time of day or the like,is thatnA state vector of dimensions;is thatmA measurement vector of dimensions;andare known system configuration parameters, respectively callednA state one-step transition matrix of the order,m×nA measurement matrix of orders;to truncate the error vector;is thatnThe system noise vector of the dimension(s),is thatmThe dimensional measurement noise vectors are both zero-mean gaussian white noise vector sequences (following a normal distribution) and are uncorrelated with each other.
Namely:
Preferably, in this embodiment, the state vector of the GNSS/INS tightly combined navigation system state space model is an error state vector with 17 dimensions:
wherein,
is the three-dimensional velocity error (east, north, high) in the ENU navigation coordinate system;
is the three-dimensional position error (latitude, longitude, altitude) in the geodetic coordinate system;
Preferably, in this embodiment, the measurement of the GNSS/INS tight combination navigation system state space model is a GNSS observation pseudorangePseudorange ratePseudoranges to INS predictionsPseudorange ratesThe difference between them;
In step S1, the NPF (non-linear predictive filtering) method is sampled, and the magnitude of the truncation error and its covariance are estimated.
The method specifically comprises the following steps:
1) Obtaining a residual error of the current-time observed quantity and the estimation of the last-time observed quantity;
Wherein,is composed ofkAt the first momentiThe pseudorange observations of the satellites,is composed ofkAt the first momentiPseudo range rate observations of the particles;andis composed ofk-1 time of dayiAn estimate of the observed quantity of particles, equal to a functionIn thatk-values of the high order terms omitted after taylor expansion at the positioning solution estimated at time 1;i=1,…,p,pto be at leastSee the number of stars.
Wherein,for a weight matrix of positive semidefinite, the superscript "-1" represents the inverse of the matrix, the superscript "T"represents the transpose of the matrix.
In step S2, the process of correcting the original model with the estimated value of the truncation error and the covariance thereof includes:
1) Estimating the residual error of the current time to estimate the estimated quantity of the truncation errorSubstituting the value, and correcting a one-step prediction equation of the EKF;
2) Obtaining a corrected one-step predicted covariance matrix;
3) After the model is corrected, a certain residue still remains in the truncation error, and the residual truncation error is consideredSuppose thatObeying a zero mean gaussian distribution,(ii) a The state space model of the GNSS/INS tightly combined navigation system which is obtained by rewriting the state equation and is corrected by the estimated value of the truncation error and the covariance thereof is as follows:
in step S2, after the statistical characteristics of the positioning error are corrected in consideration of the residual truncation error amount, the process of determining the protection level expression including the truncation error includes:
1) Determining a positioning error according to error propagation of Kalman filtering;
wherein, the error propagation process of Kalman filtering comprises:
according to the Kalman filtering formula, there is a state posterior estimation value:
substituting the measurement equation into the above equation:
order toSubtracting from both sides simultaneouslyAnd substituting into the prediction equationDerivation is carried out:
to obtainkError of state at momentWhere the positioning error is the position component in the state error, the positioning error is simply written as。
Expressed by positioning errorIn a clear view of the above, it is known that,kthe time positioning error is expressed askState error at time-1, process noise at time-k-1, truncation error estimator at time-k,kThe truncation error residue at the time,kThe GNSS measurement at that time is a recursive function of five parts of noise.
2) Performing integrity hypothesis distribution to obtain a vertical positioning error expression of the GNSS/INS tightly-combined navigation system under the H0 hypothesis;
specifically, in two classes of assumptions:
h0 assumes that: no satellite fault occurs;
h1 hypothesis: a satellite failure condition.
Integrity is distributed among two classes of assumptions:
h0 assumes that system integrity is guaranteed by protection level integrity. And detecting the satellite fault by using a integrity fault monitoring algorithm under the assumption of H1, so as to realize the integrity of fault monitoring.
Wherein the protection level is an upper confidence limit of the positioning error,is the probability of no fault missing detection.
Specifically, under the assumption of H0, the vertical positioning error expression may be expressed as:
wherein,,is the Kalman gain;is composed ofThe elements in the matrix in the rows corresponding to the height information in the geodetic coordinate system,is composed ofThe elements in the row corresponding to the height information in the geodetic coordinate system,is composed ofElements in a row corresponding to height information in a geodetic coordinate system;
since, in the present embodiment, the high-level error in the 17-dimensional error state vector is established to be the 9 th dimension; therefore, the temperature of the molten metal is controlled,is composed ofRow 9 elements in the matrix;is composed ofLine 9 elements;is composed ofLine 9 elements.
3) Determining the distribution characteristic of the vertical positioning error according to the vertical positioning error expression;
、、、、in which the components are independent of each other, vertical positioning errorObeying the gaussian distribution property:
4) According to the error distribution characteristics, obtaining a protection level expression including a truncation error under the assumption of H0:
the protection level considers the influence of truncation errors generated in the linearization process of the nonlinear system on positioning errors, so that the protection level is more rigorous and accurate.
In step S3, the pseudorange, pseudorange rate observation samples, and residual truncation error sample data are obtained from the observation data of the actual receiver.
In order to ensure the independence of sample data, the time span of data acquisition is as large as possible, and the receiver positions are scattered, for example, the same constellation is observed in Beijing, shanghai and Lhasa 3 for 1 month, all the pseudo-range and pseudo-range rate error samples are sampled at time intervals of 30s, and about 40000 pseudo-range and pseudo-range rate error samples of each satellite are collected.
And calculating and obtaining the residual truncation error sample according to an actual positioning result. And substituting the combined positioning solution and the inertial navigation positioning solution of the GNSS/INS combined navigation at each moment into an EKF observation equation, and subtracting a first-order term reserved by Taylor expansion from the original observed quantity to obtain the residual truncation error at the moment. At least 40000 samples were collected.
In step S4, a pseudorange error amplification factor, a pseudorange rate error amplification factor, and a residual truncation error amplification factor are obtained by respectively enveloping the pseudorange error, the pseudorange rate error, and the residual truncation error based on an extremum theory by using the same process.
Wherein the residual truncation error amplification factor comprises a pseudorange residual truncation error amplification factor and a pseudorange rate residual truncation error amplification factor.
Specifically, the process of obtaining the pseudorange error amplification factor based on the extreme value theory envelope pseudorange error includes:
1) Arranging the obtained actual pseudo-range samples from small to large after taking absolute values, and calculating the standard deviation of the samples;
Arranging the obtained actual pseudo-range samples from small to large after taking absolute values to form a sample sequence;NThe total number of samples taken. And calculating the standard deviation of the sample。
2) Selecting a pseudo-range sample as a threshold value by using an average excess function graph method;
specifically, the average excess function is:i.e. for more than a threshold value in a sampleTAveraging the excess of (A) to obtain a threshold valueTPoint of timeContinuously taking the data from small to large with small steps at equal intervalsTThe threshold value can be selected as one of the parts of the curve which is close to linearity and has positive slopeTThe value is obtained.
3) Re-sampling the pseudo range samples B times by using a Bootstrap method in a returning way to obtain a group B of samples;,;
3) According to an extreme value theory, performing parameter estimation on each group of samples to determine a parameter confidence limit value;
the excess is greater than the threshold value in each group of samplesTOf a sample andTa difference of (i) that,,,Greater than a threshold for each set of samplesTThe number of the samples of (a) is,distribution of (2)Distribution of available samplesRepresents:
The theory of the extreme values states that,the maximum value distribution of the maximum value follows Gumbel distribution, the excess amountObeying a type I generalized Pareto distribution:
probability of a sample in each resample sample exceeding a thresholdSimilarly, the probability of the sample in the population exceeding the threshold may be obtained. Statistics of memory aid。
the log-likelihood function of a type I generalized Pareto distribution is:
i.e. of the b-th group of resampled samplesThe maximum likelihood estimate is. The parameter estimation of the overall sample can be obtained by the same method. Statistics of memory aid。
using Bootstrap method, according to the defined confidenceDetermining a parameter confidence limitAnd。
4) And substituting the parameter confidence limit value into the sample distribution, and determining a pseudo-range error amplification factor according to the integrity of the probability distribution of the combined navigation pseudo-range error.
obtaining the probability distribution of the GNSS/INS combined navigation pseudo range error:
Respectively carrying out error envelope on the pseudo-range error, the pseudo-range rate error and the residual truncation error to obtain a pseudo-range error amplification factorPseudorange rate amplification factorPseudorange residual truncation error amplification factorPseudorange rate residual truncation error amplification factor。
In step S5, in calculating the protection level,
measuring noise by Kalman filtering, measuring noise vectorThe variance of each component in the set ofkTime of day measurement noise matrixDiagonal values, whereiniPseudorange measurement noise variance of visible satellites equal tokTime of day measurement noise matrix2 nd (2)iLine 1, line 2iA column value of-1, i.eThe false of the ith visible starRange rate measurement noise variance equal tokTime of day measurement noise matrix 2 ndiLine 2iColumn values, i.e.. First, theiResidual truncation error variance of visible star pseudoranges equal tokTruncation error matrix for time of dayNo. 2iLine 1, line 2iA column value of-1, i.e(ii) a First, theiResidual truncation error variance of visible star pseudorange rate equal tokTruncation error matrix for time of day2 nd (2)iLine 2iColumn values, i.e.。
According to the pseudo range error amplification factor, the pseudo range rate amplification factor and the residual truncation error amplification factor; after the pseudo-range error variance, the pseudo-range rate error variance and the residual truncation error variance are amplified, the distribution of pseudo-range measurement noise, the pseudo-range rate measurement noise and the residual truncation error is as follows:
is as followsiThe pseudorange error amplification factors for the visible satellites,is as followsiThe pseudo-range rate error magnification factor for the visible satellites,is a firstiThe pseudorange residue of the visible satellites truncates the error amplification factor,is as followsiThe pseudo-range rate residue of the visible satellites truncates the error amplification factor.
Substituting the difference into the calculation to obtain the final protection level:
wherein,
in the embodiment, the high-degree error in the established 17-dimensional error state vector is 9 th dimension; corresponding final protection level(ii) a Namely thatv=9。
In summary, according to the method for determining the EKF integrated navigation protection level based on the truncation error estimation in the embodiment, aiming at the problem that the truncation error generated in the EKF linearization process makes the protection level calculation inaccurate, the uncertainty of the truncation error is reduced through the estimated size of the truncation error and the covariance thereof, and the positioning error and the distribution thereof are corrected, so that a more accurate protection level is obtained and meets the given integrity risk; and the error such as pseudo range, pseudo range rate and the like of actual sampling is enveloped by adopting an extreme value theory, and residual error distribution is truncated, so that more accurate error tail probability distribution is positioned. And the more accurate protection level and the more accurate error tail probability distribution are combined, so that the reliability of the protection level is ensured. And the integrity of the nonlinear GNSS/INS integrated navigation system is further guaranteed.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (10)
1. An EKF integrated navigation protection level calculation method based on truncation error estimation is characterized by comprising the following steps:
establishing a GNSS/INS tight combination navigation system state space model considering truncation errors, and estimating truncation error values and covariance thereof;
modifying the model with the estimated truncation error and its covariance; calculating the statistical characteristic of the corrected positioning error by considering the residual amount of the truncation error to obtain a protection level expression comprising the truncation error;
acquiring actual pseudo-range, pseudo-range rate observed quantity samples and corresponding residual truncation error sample data;
respectively enveloping pseudo range, pseudo range rate observation error and residual truncation error sample data based on an extreme value theory to obtain corresponding amplification factors;
and substituting the amplification factor into the protection level expression to obtain the protection level of the GNSS/INS tight combination navigation system.
2. The EKF integrated navigation protection level calculation method based on truncation error estimation according to claim 1,
the GNSS/INS tightly combined navigation system state space model considering truncation errors comprises the following steps:
wherein,kis the time of day or the like,is thatnA state vector of dimensions;is thatmA measurement vector of dimensions;is composed ofnThe state of the stage is transferred to the matrix in one step,is composed ofm×nA measurement matrix of orders;to truncate the error vector;is composed ofnThe system noise vector of the dimension(s),is composed ofmThe measurement noise vector of the dimension.
3. The method of claim 2, wherein the state vector of the GNSS/INS tightly-integrated navigation system state space model is a 17-dimensional error state vector:
wherein,is the three-dimensional velocity error;is the three-dimensional attitude angle error;is the three-dimensional position error;is the three-dimensional accelerometer error;is the three-dimensional gyroscope error;is a one-dimensional receiver constant offset;is a one-dimensional receiver clock drift.
4. The EKF combined navigation protection level calculation method based on truncation error estimation as claimed in claim 3, wherein,
measurement of GNSS/INS tightly combined navigation system state space model quantity as GNSS observation pseudo rangePseudorange ratesPseudoranges to INS predictionsPseudorange rateThe difference between them;
5. The EKF integrated navigation protection level calculation method based on truncation error estimation according to claim 4,
estimating a truncation error value and a covariance thereof by using an NPF method, specifically comprising:
1) Obtaining a residual error of the current-time observed quantity and the estimation of the last-time observed quantity;
Wherein,is composed ofkAt the first momentiThe pseudorange observations of the satellites,is composed ofkAt the first momentiPseudo range rate observed quantity of the particle;andis composed ofk-1 time of dayiEstimated value of observed quantity of particles, equal to functionIn thatk-values of the high order terms omitted after taylor expansion at the estimated localization solution at time 1;i=1,…,p,pnumber of visible stars;
6. The EKF integrated navigation protection level calculation method based on truncation error estimation according to claim 5,
the GNSS/INS tightly combined navigation system state space model corrected by the estimated value of the truncation error and the covariance thereof is as follows:
7. the EKF integrated navigation protection level calculation method based on truncation error estimation according to claim 6, wherein,
the determination of the protection level expression including the truncation error comprises:
1) Determining a positioning error according to error propagation of Kalman filtering;
2) Performing integrity hypothesis distribution to obtain a vertical positioning error expression of the GNSS/INS tight combination navigation system under the H0 hypothesis;
3) Determining the distribution characteristic of the vertical positioning error according to the vertical positioning error expression;
4) And obtaining a protection level expression comprising the truncation error under the assumption of H0 according to the error distribution characteristics.
8. The EKF integrated navigation protection level calculation method based on truncation error estimation according to claim 7,
under the assumption of H0, the vertical positioning error expression is as follows:
wherein,;is the Kalman gain;vas error state vectorsXThe line number corresponding to the height information is obtained;
is composed ofCorresponding to height information in a matrixThe elements in the row of (a) and (b),is composed ofThe elements in the row of the matrix corresponding to the height information,is composed ofElements in rows of the matrix corresponding to the height information;
h0 assumes that the guard level expression including truncation error:
9. The EKF combined navigation protection level calculation method based on truncation error estimation as claimed in claim 8,
the method for obtaining the corresponding amplification factor based on the extreme value theory envelope pseudo range sample data comprises the following steps:
1) Arranging the obtained actual pseudo-range samples from small to large after taking absolute values, and calculating the standard deviation of the samples;
2) Selecting a pseudo range sample as a threshold value by using an average excess function graph method;
3) Re-sampling the pseudo-range samples for B times in a Bootstrap method to obtain a group B of samples;
3) According to an extreme value theory, performing parameter estimation on each group of samples to determine a parameter confidence limit value;
4) And substituting the parameter confidence limit value into the sample distribution, and determining a pseudo-range error amplification factor according to the integrity of the probability distribution of the combined navigation pseudo-range error.
10. The EKF combined navigation protection level calculation method based on truncation error estimation as claimed in claim 9, wherein,
substituting the amplification factor into the protection level expression to obtain the protection level of the GNSS/INS tightly combined navigation system(ii) a Wherein,
wherein,is as followsiThe pseudorange error amplification factor for the visible satellites,is as followsiThe pseudo-range rate error magnification factor for the visible satellites,is as followsiThe pseudorange residue of the visible satellites truncates the error amplification factor,is as followsiThe pseudorange rate residual truncation error magnification factor for the visible satellites.
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