阅读说明：本技术 一种gbas电离层延迟梯度的双平滑伪距域检测方法 (Double-smooth pseudo range domain detection method for GBAS ionosphere delay gradient ) 是由 薛瑞 胡柱 于 2021-08-24 设计创作，主要内容包括：本发明涉及一种GBAS电离层延迟梯度的双平滑伪距域检测方法,属于卫星导航技术领域,解决电离层梯度检测的问题；方法包括采用两组不同的时间常数,分别对地面和飞机上观测的载波进行相位平滑滤波,得到两组差分校正值和两组平滑伪距；采用差分校正值校正平滑伪距得到两组时间常数下的差分校正伪距；将两组差分校正伪距作差后除以两倍的时间常数之差,构建出随时间变化逐渐收敛至电离层延迟梯度的检验统计量；根据检验统计量的误差分布和III类精密进近的误警率构建检验统计量的阈值；通过比较检验统计量与阈值,检测伪距观测量中是否含有电离层梯度。本发明可以实现更快速和更精确的电离层延迟梯度检测。(The invention relates to a double smooth pseudo range domain detection method of GBAS ionosphere delay gradient, which belongs to the technical field of satellite navigation and solves the problem of ionosphere gradient detection; the method comprises the steps of respectively carrying out phase smoothing filtering on carriers observed on the ground and the airplane by adopting two groups of different time constants to obtain two groups of differential correction values and two groups of smooth pseudo-ranges; correcting the smoothed pseudoranges by adopting the differential correction values to obtain differential corrected pseudoranges under two groups of time constants; dividing the difference of the two groups of differential correction pseudo ranges by the difference of two times of time constants to construct test statistics which gradually converge to the ionospheric delay gradient along with the change of time; constructing a threshold value of the test statistic according to the error distribution of the test statistic and the class III precision approach false alarm rate; and detecting whether the pseudo-range observed quantity contains an ionospheric gradient or not by comparing the test statistic with a threshold value. The invention can realize faster and more accurate ionospheric delay gradient detection.)

1. A method for detecting a double smoothed pseudorange domain of a GBAS ionosphere delay gradient is characterized by comprising the following steps:

the method comprises the steps that two groups of different time constants are adopted, phase smoothing filtering is respectively carried out on carriers observed on the ground and the airplane, two groups of differential correction values are obtained after the phase smoothing filtering is carried out on the carriers observed on the ground, and two groups of smooth pseudo ranges are obtained after the phase smoothing filtering is carried out on the carriers observed on the airplane; correcting the smoothed pseudoranges by adopting the differential correction values to obtain differential corrected pseudoranges under two groups of time constants; dividing the difference of the two groups of differential correction pseudo ranges by the difference of two times of time constants to construct test statistics which gradually converge to the ionospheric delay gradient along with the change of time;

constructing a threshold value of the test statistic according to the error distribution of the test statistic and the class III precision approach false alarm rate;

and detecting whether the pseudo-range observed quantity contains an ionospheric gradient or not by comparing the test statistic with a threshold value.

2. The double smoothed pseudorange domain detection method of claim 1,

the method for detecting whether the pseudo-range observed quantity contains the ionospheric gradient or not by comparing the test statistic with the threshold value comprises the following steps:

judging whether the test statistic calculated within the threshold value of the detection time exceeds the threshold value; if yes, the pseudo-range observed quantity contains ionosphere gradient; if not, changing the flight speed of the airplane, and recalculating the test statistic; if the pseudo-range observation does not exceed the threshold value, determining that the pseudo-range observation does not contain ionosphere gradients; if the ionospheric gradient is exceeded, the pseudorange observations contain ionospheric gradients.

3. The method of dual smoothed pseudorange domain detection according to claim 2, wherein the range of change in airspeed is 20m/s to 40 m/s.

4. The method of double smoothed pseudorange domain detection according to claim 2, wherein the detection time threshold is 1-2 min.

5. The method of claim 1, wherein the step of calculating the differential corrections by phase smoothing filtering the carrier observed on the ground comprises:

1) carrying out phase smoothing on M carrier observed quantities arranged at k time of a receiver on the ground to obtain smoothed code pseudo range rho of the receiver M to a satellite n_s，m，n(k)；

2) Calculating the true distance R from the satellite n to the receiver m, and calculating the pseudo range rho according to the smooth code_s，m，n(k) Obtaining a pseudo range correction value rho of k time according to the real distance R_sc，m，n(k)；；

3) For pseudorange correction value rho_sc，m，n(k) The receiver clock difference contained in the code is adjusted to obtain rho_sca，m，n(k)；

4) The pseudorange correction value rho of the satellite n is obtained by averaging the pseudorange correction values of the satellite n calculated by all M ground reference receivers_corr，n(k)。

6. The method of claim 5The method for detecting the double smooth pseudo range domain is characterized in that phase smoothing is carried out on M carrier observed quantities arranged at k time of a ground receiver to obtain smooth code pseudo range rho of a satellite n by the receiver M_s，m，n(k) The method specifically comprises the following steps:

where N is τ/T, τ is the smoothing filter time constant, and T is the sampling interval of the original observed quantity; rho_m，n(k)、The code pseudoranges and carrier phase observations, respectively, for receiver m for satellite n at time k.

7. The method of double smoothed pseudorange domain detection according to claim 5, wherein the receiver clock difference isWhere ρ is_sc，m，j(k) A pseudorange correction value for receiver m to satellite j at time k; s_m(k) Set of all satellites observed by receiver m for time k, N_m(k) Is S_m(k) The number of satellites involved.

8. The dual smoothed pseudorange domain detection method according to any one of claims 1-7, wherein the two sets of smoothing filter time constants are 100s and 30s, respectively.

9. The method of double smoothed pseudorange domain detection according to claim 1, wherein the determination of the threshold of the test statistic comprises the steps of:

grouping test statistic error samples under different elevation angles by taking a preset angle as a step length to obtain error sample distribution of test statistic;

enveloping the tail part of the error sample distribution by adopting generalized extreme value distribution;

the generalized extreme value distribution satisfies the tail probability as P_FAThe quantile of (a) is a threshold value of the test statistic;

the P is_FAAnd allocating false alarm rate for CATIII precision approaching integrity requirement.

10. The method of double smoothed pseudorange domain detection according to claim 9, wherein said generalized extremum distribution:

where μ is a position parameter, σ is a scale parameter, and ξ is a shape parameter; the optimal extreme value distribution is obtained by adjusting three parameters of mu, sigma and xi, so that the optimal extreme value distribution envelops the tail of the reorganization error sample distribution.

Technical Field

The invention relates to the technical field of satellite navigation, in particular to a double smooth pseudo range domain detection method of GBAS ionized layer delay gradient.

Background

Global Navigation Satellite Systems (GNSS) gradually enter the modernized development process, and civil aviation navigation becomes one of the important development and application directions thereof. However, applying satellite navigation systems to civil aviation, it is necessary to first make them meet the civil aviation's performance requirements for navigation systems, including 4 aspects of accuracy, integrity, continuity and availability. For civil aviation class III precision, Ground Based Augmentation Systems (GBAS) are the most promising local augmentation systems to meet their higher demands and are the most studied.

The GBAS broadcasts the differential correction information of each satellite by a ground subsystem through very high frequency, and the airplane performs differential positioning after receiving corresponding information, thereby improving the positioning precision. Meanwhile, GBAS carries out integrity monitoring on the basis of differential correction, different monitoring algorithms are designed for different fault sources by a monitoring model, wherein for ionospheric anomaly, code-carrier separation (CCD) monitoring is adopted, ionospheric storm is monitored by monitoring the difference between a code pseudo-range and a carrier phase pseudo-range, code-carrier separation can be estimated mainly by adopting a Geometric Moving Average (GMA) method, a code-carrier separation value calculated by real-time monitoring is compared with a threshold value, and an alarm signal is given if the code-carrier separation value exceeds the threshold value. However, CCD monitoring cannot simultaneously shorten detection time and improve detection accuracy, and under the requirement of class III precision approach, higher positioning accuracy and integrity index require GBAS to be able to detect ionospheric anomalies more timely and accurately, so a more sensitive ionospheric gradient detection method needs to be proposed.

Disclosure of Invention

In view of the above analysis, the present invention aims to provide a method for detecting a double smoothed pseudorange domain of a GBAS ionospheric delay gradient, which solves the problem of detecting an ionospheric gradient in the pseudorange domain.

The technical scheme provided by the invention is as follows:

the invention discloses a double smooth pseudo range domain detection method of GBAS ionized layer delay gradient, which comprises the following steps:

the method comprises the steps that two groups of different time constants are adopted, phase smoothing filtering is respectively carried out on carriers observed on the ground and the airplane, two groups of differential correction values are obtained after the phase smoothing filtering is carried out on the carriers observed on the ground, and two groups of smooth pseudo ranges are obtained after the phase smoothing filtering is carried out on the carriers observed on the airplane; correcting the smoothed pseudoranges by adopting the differential correction values to obtain differential corrected pseudoranges under two groups of time constants; dividing the difference of the two groups of differential correction pseudo ranges by the difference of two times of time constants to construct test statistics which gradually converge to the ionospheric delay gradient along with the change of time;

constructing a threshold value of the test statistic according to the error distribution of the test statistic and the class III precision approach false alarm rate;

and detecting whether the pseudo-range observed quantity contains an ionospheric gradient or not by comparing the test statistic with a threshold value.

Further, the method for detecting whether the pseudorange observations contain ionospheric gradients by comparing the test statistic with a threshold comprises the following steps:

judging whether the test statistic calculated within the threshold value of the detection time exceeds the threshold value; if yes, the pseudo-range observed quantity contains ionosphere gradient; if not, changing the flight speed of the airplane, and recalculating the test statistic; if the pseudo-range observation does not exceed the threshold value, determining that the pseudo-range observation does not contain ionosphere gradients; if the ionospheric gradient is exceeded, the pseudorange observations contain ionospheric gradients.

Further, the variation range of the flying speed is 20 m/s-40 m/s.

Further, the threshold value of the detection time is 1-2 min.

Further, the calculation process of obtaining the differential correction value by performing phase smoothing filtering on the carrier wave observed on the ground includes:

1) carrying out phase smoothing on M carrier observed quantities arranged at k time of a receiver on the ground to obtain smoothed code pseudo range rho of the receiver M to a satellite n_s,m,n(k)；

2) Calculating the true distance R from the satellite n to the receiver m, and calculating the pseudo range rho according to the smooth code_s,m,n(k) Obtaining a pseudo range correction value rho of k time according to the real distance R_sc,m,n(k)；；

3) For pseudorange correction value rho_sc,m,n(k) The receiver clock difference contained in the code is adjusted to obtain rho_sca,m,n(k)；

4) Satellite calculated for all M ground reference receiversThe pseudo range correction value rho of the satellite n is obtained by averaging the pseudo range correction values of the satellite n_corr,n(k)。

Further, the phase smoothing is performed on M carrier observations set at the time k of the terrestrial receiver to obtain smoothed code pseudoranges ρ of the receiver M to the satellite n_s,m,n(k) The method specifically comprises the following steps:where N is τ/T, τ is the smoothing filter time constant, and T is the sampling interval of the original observed quantity; rho_m,n(k)、The code pseudoranges and carrier phase observations, respectively, for receiver m for satellite n at time k.

Further, the receiver clock difference isWhere ρ is_sc,m,j(k) A pseudorange correction value for receiver m to satellite j at time k; s_m(k) Set of all satellites observed by receiver m for time k, N_m(k) Is S_m(k) The number of satellites involved.

Further, the two sets of smoothing filter time constants are 100s and 30s, respectively.

Further, the determination of the threshold value of the test statistic comprises the steps of:

grouping test statistic error samples under different elevation angles by taking a preset angle as a step length to obtain error sample distribution of test statistic;

enveloping the tail part of the error sample distribution by adopting generalized extreme value distribution;

the generalized extreme value distribution satisfies the tail probability as P_FAThe quantile of (a) is a threshold value of the test statistic;

the P is_FAAnd allocating false alarm rate for CAT III precision approach integrity requirement.

Further, the generalized extremum distribution:

where μ is a position parameter, σ is a scale parameter, and ξ is a shape parameter; the optimal extreme value distribution is obtained by adjusting three parameters of mu, sigma and xi, so that the optimal extreme value distribution envelops the tail of the reorganization error sample distribution.

The invention can realize at least one of the following beneficial effects:

the method for detecting the double smooth pseudo range domain of the GBAS ionosphere delay gradient has shorter response time and convergence time of ionosphere anomaly, and can realize faster ionosphere delay gradient detection; and the detection precision is higher, and whether the pseudo-range observed quantity contains ionospheric gradient delay or not can be more accurately detected compared with CCD and double-smooth positioning domain detection.

Drawings

The drawings are only 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.

FIG. 1 is a flow chart of a method for dual smoothed pseudorange domain detection according to an embodiment of the invention;

FIG. 2 is a flow chart of a method of test statistic construction in an embodiment of the present invention;

FIG. 3 is a diagram illustrating the convergence effect of the simulation data test statistic S in the 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.

In this embodiment, as shown in fig. 1, a method for detecting a double smoothed pseudorange domain of a GBAS ionosphere delay gradient includes the following steps:

step S1, constructing test statistics which gradually converge to the ionospheric delay gradient along with the change of time;

the method comprises the steps that two groups of different time constants are adopted, phase smoothing filtering is respectively carried out on carriers observed on the ground and the airplane, two groups of differential correction values are obtained after the phase smoothing filtering is carried out on the carriers observed on the ground, and two groups of smooth pseudo ranges are obtained after the phase smoothing filtering is carried out on the carriers observed on the airplane; correcting the smoothed pseudoranges by adopting the differential correction values to obtain differential corrected pseudoranges under two groups of time constants; dividing the difference of the two groups of differential corrected pseudo ranges by the difference of two times of time constants to construct test statistics;

s2, constructing a threshold value of the test statistic according to the error distribution of the test statistic and the class III precision approach false alarm rate;

step S3 is to compare the test statistic with a threshold value to detect whether or not the pseudo-range observation includes an ionospheric gradient.

Specifically, as shown in fig. 2, step S1 includes the following sub-steps:

s101, performing phase smoothing filtering on a carrier wave observed on the ground by adopting two groups of different time constants to obtain two groups of differential correction values;

the GBAS ground subsystem is provided with M reference receivers with known positions, and two groups of carrier phase smoothing filters are respectively carried out on the reference receivers of the ground subsystem;

preferably, the two sets of smoothing filter time constants are set to 100s and 30s, respectively.

The L1 pseudoranges and carrier phase observations for GPS obtained by the receiver may be expressed as follows:

where R is the true distance of the receiver antenna to the satellite, C is the sum of the satellite clock, ephemeris and tropospheric errors, and is ρ₁Andof a common error component, i₁Is the ionospheric error at the frequency L1, N₁Is the integer ambiguity, n, of the L1 carrier_ρ1Andthe sum of the receiver noise and multipath error of the code pseudorange and carrier phase, respectively.

A process for calculating a differential correction value obtained by a reference receiver of a ground subsystem, comprising:

1) carrying out phase smoothing on M carrier observed quantities arranged at k time of a receiver on the ground to obtain smoothed code pseudo range rho of the receiver M to a satellite n_s,m,n(k) (ii) a Most of the effects of receiver thermal noise and multipath are removed by smoothing filtering.

The observed quantity is subjected to carrier phase smoothing to obtain a smoothed code pseudo range formula of the receiver m to the satellite n at the moment k, wherein the formula is as follows

Where N is τ/T, τ is the smoothing filter time constant, and T is the sampling interval of the original observed quantity; rho_m,n(k)、The code pseudoranges and carrier phase observations, respectively, for receiver m for satellite n at time k.

2) Calculating the true distance R from the satellite n to the receiver m, and calculating the pseudo range rho according to the smooth code_s,m,n(k) Obtaining a pseudo range correction value rho of k time according to the real distance R_sc,m,n(k)；

For M receivers of the ground subsystem, calculating the position of each satellite according to the navigation message, thereby calculating the real distance R from the satellite n to the receiver M;

pseudorange rho of smooth code_s,m,n(k) Subtracting R to obtain pseudo range corrected value rho at k moment_sc,m,n(k) Specifically, the following are shown:

ρ_sc,m,n(k)＝ρ_s,m,n(k)-R_m,n(k)+τ_m,n(k) (3)

wherein, tau_m,n(k) Is the star clock correction at time k.

3) For pseudorange correction value rho_sc,m,n(k) The receiver clock difference contained in the code is adjusted to obtain rho_sca,m,n(k)；

Since all the observations of the satellites received by a reference receiver contain the same receiver clock offset, the reference receiver averages all the satellite differential corrections as an estimate of its clock offset and subtracts the estimate from the correction to obtain a correction without the receiver clock offset. The correction value for the adjusted receiver clock difference is:

where ρ is_sc,m,j(k) A pseudorange correction value for receiver m to satellite j at time k; s_m(k) Set of all satellites observed by receiver m for time k, N_m(k) Is S_m(k) The number of satellites involved.

4) The pseudorange correction value rho of the satellite n is obtained by averaging the pseudorange correction values of the satellite n calculated by all M ground reference receivers_corr,n(k)。

The specific calculation formula is as follows:

wherein S is_n(k) Is a set of reference receivers, M, observing a satellite n at time k_n(k) Is S_n(k) The number of reference receivers contained in (1).

Step S102, two groups of time constants which are the same as those in step S101 are adopted, phase smoothing filtering is carried out on the carrier wave observed on the airplane to obtain two groups of smooth pseudo ranges;

respectively carrying out two groups of carrier phase smoothing filtering on a receiver on the airplane; the two sets of smoothing filter time constants are the same as the reference receiver on the ground, set to 100s and 30s, respectively.

After smoothing, a smoothed code pseudo range rho can be obtained_s,air,n(k)。

S103, correcting the smoothed pseudoranges by adopting the differential correction values to obtain differential corrected pseudoranges under two groups of time constants;

differentially corrected pseudorange ρ_sc,air,n(k) The formula of (1) is as follows:

ρ_sc,air,n(k)＝ρ_s,air,n(k)-ρ_corr,n(k) (6)

for the two sets of smooth filtering with different time constants, two sets of pseudo-range values after differential correction can be finally obtained, wherein the pseudo-range values are respectively rho_sc1,air,n(k)、ρ_sc2,air,n(k)。

And step S104, constructing a test statistic S according to the differential corrected pseudo range under the two groups of time constants.

Specifically, the test statistic S is constructed by dividing the difference between two sets of differentially corrected pseudoranges by twice the time constant.

The constructed test statistic S converges gradually to the ionospheric delay gradient over time. For rho_sc1,air,n(k) And ρ_sc2,air,n(k) Taking the difference, the steady state response can be expressed as follows:

in the formula, d Ψ_aIs a test statistic, i.e. p_sc1,air,nAnd rho_sc2,air,nMaking a frequency domain expression of the difference;

is its steady state response, d_ρAndthe divergence values of the pseudorange and carrier phase measurements, respectively;

since ionospheric gradients are a delay contribution to pseudorange, there is an advance contribution to carrier phase,Δ I is the gradient of ionospheric delay.

From this, ρ is_sc1,air,n(k) And ρ_sc2,air,n(k) The k time test statistic s (k) obtained by dividing the difference by twice the time constant is known to gradually converge to Δ I with time change.

Specifically, step S2 constructs a threshold value of the test statistic based on the error distribution of the test statistic and the class III precision approach false alarm rate;

the false alarm rate of the distribution of CAT III precision approaching integrity requirement is determined by the actual system requirement, and when the false alarm rate is P_FAThen, the threshold value of the test statistic S needs to envelop the actual distribution function of the test statistic S, and the probability of meeting the tail part of the distribution is smaller than P_FAIt is decided here to use an extremum distribution for the envelope. The specific implementation steps are as follows:

1) grouping test statistic error samples under different elevation angles by taking a preset angle as a step length to obtain error sample distribution of test statistic;

s is theoretically distributed with a thin tail, meaning that an extremum distribution envelope with a standard deviation smaller than the original error distribution standard deviation can be obtained. Because the multipath and the receiver thermal noise under different satellite elevation angles are different, the test statistic error samples under different satellite elevation angles are grouped, and the test statistic error distribution samples under different elevation angles are obtained by taking 10 degrees as step length; i.e., 10 deg. apart, the test statistic error samples are grouped. Satellite observations at different elevation angles require a large amount of historical data to ensure the accuracy of the error distribution.

2) Enveloping the tail part of the error sample distribution by adopting generalized extreme value distribution;

currently, the commonly used extremum distributions are the Gumbel distribution, the Frechet distribution and the Weibull distribution. In this embodiment, the generalized extremum distribution is preferably uniformly expressed after being appropriately transformed:

where μ is a position parameter, σ is a scale parameter, which is equivalent to a standard deviation of gaussian distribution, and ξ is a shape parameter.

And (3) obtaining the optimal extreme value distribution by adjusting three parameters of mu, sigma and xi, and enveloping the tail part of the error sample distribution in the step 1).

3) The generalized extreme value distribution satisfies the tail probability as P_FAThe quantile of (a) is a threshold value of the test statistic.

Step S3 is a monitoring procedure for detecting whether an ionospheric gradient is included in the pseudo-range observation by comparing the test statistic with the threshold, including:

judging whether the test statistic calculated within the threshold value of the detection time exceeds the threshold value; if yes, the pseudo-range observed quantity contains ionosphere gradient; if not, changing the flight speed of the airplane, and recalculating the test statistic; if the pseudo-range observation does not exceed the threshold value, determining that the pseudo-range observation does not contain ionosphere gradients; if the ionospheric gradient is exceeded, the pseudorange observations contain ionospheric gradients.

As can be seen from step 104, the test statistic S gradually converges to the ionospheric delay gradient over time, and the longer the iteration time, the more the test statistic S converges to the ionospheric delay gradient.

Preferably, as shown in the simulation result shown in fig. 3, the threshold of the detection time is selected to be 1-2min, and the test statistic S has a good convergence effect. The test statistic S calculated within the threshold may suffice to detect whether the test statistic S converges to an ionospheric delay gradient.

By detecting the test statistic S of different airplanes at different speeds, the detection precision can be improved, and whether the pseudo-range observed quantity contains ionospheric gradient delay or not can be detected more accurately.

Preferably, the flying speed of the airplane is changed in a range of 20m/s to 40 m/s.

In summary, in the method for detecting a dual-smooth pseudorange domain of a GBAS ionosphere delay gradient according to this embodiment, an ionosphere gradient is detected in a pseudorange domain, two sets of carrier phase smoothing filters are respectively disposed on the ground and an aircraft, so that the aircraft calculates to obtain two sets of differential corrected pseudorange values, a difference of the two sets of differential corrected pseudorange values is divided by a difference of two times of a smoothing time constant to obtain a test statistic, and the test statistic is compared with a set threshold to identify and exclude a pseudorange amount exceeding the threshold, and monitor a gradient value of the ionosphere delay.

The method has faster ionospheric anomaly detection speed. Compared with the traditional CCD monitoring method, the method has shorter response time and convergence time, which means that the ionospheric delay gradient can be detected more quickly.

The method has higher detection precision. Compared with a CCD and double-smooth positioning domain detection method, the method can more accurately detect whether the pseudo-range observed quantity contains ionospheric gradient delay.

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.