KR101803652B1 - Method and Apparatus for improving Satellite Based Augmentation System availability through geometric measuring metric development for undersampled irregularity threat model in SBAS - Google Patents

Abstract

The purpose of the present invention is to provide a method and a device for improving availability of a satellite based augmentation system (SBAS), capable of reducing conservativeness of the threat-model of the ionized layer and improving availability performance of the SBAS. According to an embodiment of the present invention, the method for improving availability of the SBAS includes: (a) a step of obtaining a measurement value of the ionized layer; (b) a step of defining an additional metric to classify distribution of the measurement value of the ionized layer; (c) a step of adding a constraint condition generating geometric measurement about the distribution of an azimuth direction in the measurement value of the ionized layer to the additional metric; (d) a step of deriving a Lagrangian condition by suing a Lagrangian function to release the constraint condition; (e) a step of calculating a local lowest value and a whole-area lowest value of the additional metric by using the Lagrangian condition; and (f) a step of indicating the availability of the SBAS by classifying the geometric distribution of the measurement value of the ionized layer in accordance with the calculation of the local lowest value and the whole-area lowest value.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method and apparatus for enhancing SBAS availability by developing a geometric metric for an ionospheric threat model of a global reinforcement system,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a global navigation system (GNSS), and more particularly, to a global navigation system (GNSS) and a method and apparatus for improving the availability of SBAS (Satellite Based Augmentation System) availability through metrics.

In general, the availability of the satellite based augmentation system (SBAS) is determined by the errors of the ionosphere, and the error of the Global Navigation System (GNSS) is the largest and most difficult to predict.

Therefore, the SBAS broadcasts the ionospheric error correction information at the ionospheric grid point (IGP) and the grid ionospheric vertical error (GIVE), which is the uncertainty level of the residual error after using the correction information.

These correction information and the GIVE value are calculated based on the vertical ionospheric delay value near the IGP measured at the SBAS reference station. However, since the correction information and the GIVE value are calculated based only on the measurement values of the SBAS reference station, an undersampling problem occurs in which the ionosphere of the reference station does not exist or the ionosphere of a very small region is not sufficiently considered.

In particular, if there is an ionospheric heterogeneity in the region where the measurement is insufficient (that is, it causes a sudden change in the vertical ionospheric delay due to a different state of the surrounding ionosphere), and the signal from the navigation satellite to the user passes through the region, The safety of the user is threatened.

Therefore, the augmentation of the GIVE value is required, and the degree to which the GIVE value is to be reinforced is determined through an undersampled irregularity threat model (see FIG. 2).

The ionosphere threat model is constructed through simulations based on ionospheric data and undersampling scenarios acquired through post-processing of GNSS data collected during periods of severe ionospheric heterogeneity. Statistic (denoted by σ _undersampled ).

The GIVE value calculation includes σ _undersampled Values are reflected differently depending on the geometric distribution shape of the measurements used for the fitting around each IGP. The uncertainty due to undersampling is greater when the number of measurements is small or when the geometric arrangement of the baseline station measurements is uneven and biased, so the key parameters of the currently developed ionosphere threat model are the metric that reflects the density of the measurements and the geometric arrangement of the measurements And a metric that reflects the metric. A diagram showing this is shown in Fig.

Referring to FIG. 1, in the case of RCM (Relative Centroid Metric), which reflects the geometrical arrangement of measured values, E (East) axis of regional coordinates (ENU, East-North-Up) centered on IGP of each ionospheric measurement value Is defined as the ratio of R _cent , which is the weighted average of the coordinates defined along the N (North) axis, and R _fit (ionospheric measurement search radius to be used for estimation).

Here, when the number of measured values is n, x is an n-row and one-column vector having the East coordinate of the END coordinate (with the origin at the IGP position) of the measured value as a component, W is a weight matrix (n rows and n columns ), y is a vector of n rows and 1 column of the measurement, with the North coordinate of the END coordinates (with the origin at the origin), 1 is a vector of n rows and 1 column with all 1s, T is a transpose operation .

Therefore, when the measured value is uniformly distributed, the value approaches 0, and when the distributed value is distributed, the value approaches 1. However, in the case of the RCM 210, when the distribution of the measured values is symmetric, there is a limit to be recognized as a good geometry even if the distribution is uneven. FIG. 2 is a view showing this.

In this case, the uncertainty statistic (σ _undersampled ) of the situation where severe under-sampling (220) occurs occurs even though the surrounding ionosphere is evenly reflected in the estimation. This has the problem of degrading the SBAS availability performance by excessively increasing the level of protection of the user.

In addition, RCM, which is a metric for the existing SBAS ionosphere threat model, shows that if the ionosphere passing point is distributed symmetrically with respect to the IGP, then the uncertainty of the undersampling inherent in the uneven distribution of the ionospheric passing point is not uniformly distributed And the same applies to one case, which limits the conservatism of the ionosphere threat model excessively.

1. Korean Patent No. 1014339080000

1. Jung Sung-wook et al., "Algorithm Design for CAT-I GBAS Penetration of Ionospheric Threat Model," Korean Society for Aeronautical & Space Sciences Spring 2011

The present invention introduces an additional metric to reinforce the limitations of the existing RCM metric according to the above background, thereby reducing the conservatism of the ionospheric threat model by further classifying the geometric distribution of the ionospheric measurement values, thereby improving the SBAS availability performance And more particularly, to a method and an apparatus for improving the SBAS availability.

In order to achieve the above-mentioned problems, the present invention introduces additional metrics to reinforce the limitations of the existing RCM metric, thereby reducing the conservatism of the ionospheric threat model by classifying the geometric distribution of the ionospheric measurements more sub- Provides a way to improve SBAS availability to improve performance.

The SBAS availability enhancement method includes:

(a) obtaining an ionospheric measurement;

(b) defining additional metrics for classifying the distribution of the ionospheric measurements;

(c) defining an optimization problem having a constraint to uncover the mathematical nature of the additional metric so as to use the additional metric as a geometric measure of the azimuthal directional distribution of the ionospheric measurements due to mathematical properties that the metric may have ;

(d) calculating a global minimum value satisfying the constraint by using the defined Lagrangian function; And

(f) indicating the SBAS (Satellite Based Augmentation System) availability using a geometric measure of an azimuthal direction distribution of the ionospheric measurements calculated according to the calculation of the global minimum value.

At this time, the geometric distribution of the ionospheric measurement is a distribution of ionospheric measurements observed near the ionospheric grid point (IGP).

The additional metric may be defined based on an euclidean norm of a vector defined in an Euclidean space having a value of an angle between the ionospheric measurement values as an element.

In addition, the SBAS availability is a ratio of the time when the user protection level, which is a boundary value for the position error generated after the correction information is applied by combining the integrity information generated by the central processing unit, does not exceed the alarm limit given as the navigation requirement .

(여기서, θ는 전리층 측정치간 사이각을 나타낸다)로 정의되는 것을 특징으로 할 수 있다.Further,

(Where, &thetas; represents an angle between the ionospheric measurement values).

The additional metric may also be a geometric metric.

On the other hand, another embodiment of the present invention is a system, comprising: a Global Navigation System (GNSS) satellite; A global reference station receiving GPS (Global Positioning System) signals from the GNSS satellites and generating respective SBAS (Satellite Based Augmentation System) reference station data; A central processing station for generating ionospheric measurements from each generated SBAS reference station data; And defining the optimization problem with a constraint to uncover the mathematical nature of the additional metric to use the additional metric as a geometric measure for the azimuthal directional distribution of the ionospheric measurements due to mathematical properties that the metric may have, A global minimum value satisfying the constraint condition is calculated using a Lagrangian function and a satellite based augmentation system (SBAS) availability is calculated using a geometric measure of an azimuthal direction distribution of the ionospheric measurement value calculated according to the calculation of the global minimum value And a user terminal for acquiring the SBAS availability.

According to the present invention, it is possible to more accurately reflect the geometric distribution of the ionosphere passing point by adding a metric that can effectively measure the symmetry in the azimuthal direction of the ionosphere passing point distribution.

As another effect of the present invention, it is possible to segment the ionospheric threat model that has been conservatively constructed based on the existing RCM metric, and finally to improve the availability performance of the SBAS by reducing the GIVE value, which is an error level of the ionospheric correction information Can be expected.

FIG. 1 is a conceptual diagram showing a general undersampled problem. FIG.
Figure 2 is an example of a general SBAS (Undersampled Irregularity Threat Model).
3 is a network configuration diagram of a general SBAS (Satellite Based Augmentation System).
4 is a block diagram of the configuration of the central processing unit 330 shown in FIG.
5 is a diagram showing that a small uncertainty statistic (σ _undersampled ) according to the geometric distribution of the ionospheric measurements of the broad-area reference station 320 is reflected in the SBAS ionospheric threat model in general, where the distribution of the ionospheric measurements is relatively uniform .
FIG. 6 is a diagram showing a large uncertainty statistic (sigma _undersampled ) according to the geometric distribution of ionospheric measurements of wide area reference station 320 reflected in the SBAS Ionospheric Threat Model, where the distribution of ionospheric measurements is biased .
FIG. 7 is a flowchart illustrating a process for improving SBAS availability through development of a geometric measurement metric for an ionospheric heterogeneous threat model of a wide area enhancement system according to an exemplary embodiment of the present invention.
FIGS. 8 and 9 are conceptual diagrams showing the problems of the conventional RCM (Relative Centroid Metric) metric.
10 is a conceptual diagram of a metric according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Like reference numerals are used for similar elements in describing each drawing.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. The term "and / or" includes any combination of a plurality of related listed items or any of a plurality of related listed items.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Should not.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method and an apparatus for improving SBAS availability through development of a geometric measurement metric for an ionospheric heterogeneous threat model of a wide area reinforcing system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

3 is a network configuration diagram of a general SBAS (Satellite Based Augmentation System). Referring to FIG. 3, the network configuration diagram of the SBAS includes a GNSS (Global Navigation System) satellite 310, a Global Positioning System (GPS) signal from the GNSS satellite 310, A central processing unit 330 for performing a smoothing process on each generated SBAS reference station data and correcting the ionospheric layer, a satellite orbit, a time error, etc. to generate a correction message, A ground uplink station (GUS) 340, a geostationary earth orbit (GEO) 360 for receiving the broadcast correction message and transmitting the broadcasted correction message to the user terminal 350, and the like .

Global Navigation System (GNSS) is used in various fields ranging from vehicle navigation, positioning of marine vessels, geodetic surveying, and personal navigation devices for leisure. GNSS alone, however, does not meet the requirements of those who are required to be highly accurate and stable, such as aerospace and defense. To overcome these problems, a GNSS enhanced navigation system is being developed.

The satellite based augmentation system (SBAS) is a satellite based augmentation navigation system, and it is based on the measurements collected from wide area reference stations (320) distributed over a wide area. The satellite based augmentation system , Ionospheric delay error, etc., integrity information, distance information, and the like to the wide-area user terminal 350 through the GEO (geostationary-satellite) 360, thereby improving the accuracy and stability of the user navigation solution Increase. In addition, the user's SBAS receiver also improves the accuracy and stability of the navigation solution by applying smoothing of measured values and a convective layer delay correction model.

The wide area reference station 320 generates the first to Nth SBAS reference station data 320-1 to 320-N from the first to Nth reference stations (not shown) and transmits them to the central processing unit 330 .

To understand the present invention, the SBAS integrity and availability concept will be described as follows. The central processing unit 330 described above generates the correction information based on the pseudo distance information, which is a distance converted by the difference of propagation time between the GNSS satellite 310 and the receiver antenna of the reference station.

Also, integrity information (i.e., statistics) indicating the remaining error level is calculated after applying the correction information for each error element, and the integrity information is provided to the user terminal 350 as a correction message.

The user terminal 350 combines the broadcasted integrity information and calculates a protection level, which is a bound value for a position error generated after applying the correction information, thereby assuring the safety of the user. The ratio of the time that the calculated user protection level does not exceed the alert limit given as the navigation requirement is expressed as availability.

4 is a block diagram of the configuration of the central processing unit 330 shown in FIG. Referring to FIG. 4, the apparatus includes a correction information generation unit 410, an integrity information generation unit 420, and the like. The correction information generation unit 410 performs receiver-satellite inter-frequency deviation estimation based on the pseudo range information 411, generates satellite orbit error correction information 412, clock error correction information 413, and the like.

The integrity corrector 420 generates the ionospheric integrity information 421, the satellite orbit and the clock error integrity information 422, the receiver multipath integrity information 423, and the like.

FIG. 5 shows a SBAS Ionosphere Threat Model that reflects a small uncertainty statistic (sigma _undersampled ) generally according to the geometric distribution of the ionospheric measurements of the broadband reference station 320, illustrating the case where the distribution of ionospheric measurements is relatively uniform.

FIG. 6 shows a SBAS ionosphere threat model, generally reflecting the large uncertainty statistics (? _Undersampled ) according to the geometric distribution of the ionospheric measurements of the broadband reference station 320, showing the case where the distribution of ionospheric measurements is biased.

In an embodiment of the present invention, an additional metric for effectively classifying the distribution of the IGP near-ionospheric measurements used for estimating the vertical ionospheric delay value of Ionospheric Grid Point (IGP) Improves availability performance.

To do this, we first define an additional metric and use the mathematical properties of the metric to proceed in the order that the proposed metric can be a measure of the geometric distribution of the azimuthal direction of the observations. A diagram showing this sequence is shown in Fig.

의 노름(Eucledian norm)을 기반으로 정의된다(단계 S710). 이를 수학식으로 나타내면 다음과 같다.FIG. 7 is a flowchart illustrating a process for improving SBAS availability through development of a geometric measurement metric for an ionospheric heterogeneous threat model of a wide area enhancement system according to an exemplary embodiment of the present invention. Referring to FIG. 7, the additional metric presented here is a geometric metric. This geometric measurement metric is a vector defined in the Euclidean space having a value of the angle between the ionospheric measurement values ( ? , See Fig. 10) as a component.

Based on the Euclidean norm (step S710). This can be expressed by the following equation.

는 유클리드 노름(Eucledian norm)이고,

은

의 최댓값으로 2π값을 갖는다. 또한

은

의 최솟값으로

값을 갖고, n은 전리층 측정치 간 사이각(θ, 도 5 참조)의 개수를 나타낸다.here,

Is an Euclidean norm,

silver

And has a value of 2?. Also

silver

At a minimum of

And n represents the number of angles between the ionospheric measurements ( θ , see FIG. 5).

에 대해 볼록함수의 정의에 의해서 아래 수학식은 항상 성립한다.Let's look at the mathematical properties that make this metric a geometric measure of the azimuthal distribution of ionospheric measurements. First, the norm function is a downward convex function, which can be proved as follows. Arbitrary convex function

The following equation is always established by the definition of the convex function.

는 함수의 정의역을 나타내고 x, y는 정의역 내 변수를 나타낸다. 또한 모든 노름(norm)은 정의에 의해 삼각부등식(triangular inequality)을 만족하므로, 다음 수학식과 같은 관계를 만족시킨다.here,

Represents the domain of the function, and x and y represent variables in the domain. In addition, all norms satisfy the triangular inequality by definition, and thus satisfy the following equation.

Also, the right side of Equation (4) satisfies the following Equation (4) due to the homogeneity of the gambling function.

Therefore, the Euclidean norm of the vector according to Equation (5) is a convex function since it satisfies the property of the convex function corresponding to Equation (3). Therefore, in one embodiment of the present invention, the metric defined based on Euclidean normality has the property of convex function.

의 경우,

의 성분인

가 모두 동일한 값을 가질 때 최솟값을 가지게 됨이 증명가능하며, 이를 위해 아래와 같은 선형 제약조건을 가지는 최적화 문제를 고려해 볼 수 있다. 이를 수학식으로 표현하면 다음과 같다.Also,

In the case of,

Of

Can be proved to have the smallest value when all of them have the same value. For this, we can consider the optimization problem with the following linear constraints. This can be expressed as follows.

The above equation can be summarized as the following equation.

Therefore, in an embodiment of the present invention, a method based on the KKT condition (Karush-Kuhn-Tucker condition) is used to solve the optimization problem having the constraint condition expressed by Equation (7).

First, the Lagrangian function for the problem can be defined as the following equation (step S730).

와

는 라그랑지 승수(Lagrangian multiplier) 벡터이고, 최적성(optimality)을 위한 필요조건(necessary condition)인 KKT 조건은 다음 수학식 과 같다.From here

Wow

Is a Lagrangian multiplier vector and the KKT condition, which is a necessary condition for optimality, is expressed by the following equation.

와

은 각각 원 최적해(primal optimal point) 및 쌍대 최적해(dual optimal point)이다. 수학식 9로부터 모든 부등식(inequality) 제약조건이 비활성화(inactive) 되는 경우를 고려하여(즉,

) 정리하면 다음 수학식과 같다.Under this condition

Wow

Are the primal optimal point and the dual optimal point, respectively. Considering that all inequality constraints are inactive from Equation (9) (i.e.,

) In summary, the following equation is obtained.

는 볼록함수이므로, θ ₁=θ ₂=…=θ _n 일 때 주어진 제약조건 하에서

는 전역 최저치(global minimum)를 가지게 된다(단계 S730).Since the solution obtained from the above equation satisfies all of the constraints given in equation (7), there is no need to consider additional Lagrange multipliers. Also as mentioned above, the objective function < RTI ID = 0.0 >

Is a convex function, θ ₁ = θ ₂ = ... = ? _n Under given constraints

Has a global minimum (step S730).

가 최소값인

가 됨을 의미한다(수학식 2를 참고). 따라서

을 기반으로 한 제시된 metric은 전리층 통과점이 균등한 방위각 분포를 가질 때 0의 값을 가지게 되며, 방위각 방향의 전리층 통과점 분포가 가장 좋은 경우에 해당한다.This is because when the angle ( θ ) between each ionosphere passing point is uniformly formed

Is the minimum value

(See Equation 2). therefore

Presented metric has a value of 0 when the ionospheric passage has uniform azimuthal distribution and corresponds to the case where the ionospheric passage point distribution in the azimuthal direction is the best.

의 볼록성(convexity)으로 인하여 제시된 metric 또한 볼록함수가 되고, 이로 인해 θ 의 분포가 편중될수록 metric 의 값은 증가하게 된다. 특히 모든 측정치가 동일한 방향에 놓이게 되면,

는 최대값인

을 가지며 해당 metric은 1의 값을 가지게 된다(수학식 2를 참고). 따라서 본 발명의 일실시예에서 제안하는 metric이 갖는 이러한 성질에 의해, 제안 metric은 IGP(Ionospheric Grid Point) 근방에서 관측되는 전리층 측정치 분포의 와도(skewness)를 방위각 방향의 관점에서 측정할 수 있는 측도가 될 수 있다(단계 S750).Also,

Because of the convexity of the convexity, the metric also becomes a convex function. As a result, the value of the metric increases as the distribution of θ is biased. In particular, if all measurements are in the same direction,

Is the maximum value

And the metric has a value of 1 (see Equation 2). Therefore, according to the property of the metric proposed in the embodiment of the present invention, the proposed metric is a measure capable of measuring the skewness of the ionospheric measurement distribution observed near the Ionospheric Grid Point (IGP) (Step S750).

0인 경우이고, 도 9는 전리층 측정치가 고르게 분포하지 못하고,

0인 경우이다. 그러나, 도 8 및 도 9 모두 좋은 기하학적 분포로 판단된다는 문제점이 있다.FIGS. 8 and 9 are conceptual diagrams showing the problems of the conventional RCM (Relative Centroid Metric) metric. That is, Figure 8 shows that the ionospheric measurements are evenly distributed,

0, and Figure 9 shows that the ionospheric measurements are not evenly distributed,

0 < / RTI > However, both FIGS. 8 and 9 have a problem that it is judged as a good geometric distribution.

10 is a conceptual diagram of a metric according to an embodiment of the present invention. Referring to Fig. 10, the angle ? Between the ionosphere measurement points (i.e., ionospheric passage points ) is shown.

Meanwhile, the method for improving the SBAS availability through the development of the geometric measurement metric for the ionospheric heterogeneous threat model of the global enhancement system according to an embodiment of the present invention can be implemented by hardware, software, or a combination thereof.

(DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, and the like, which are designed to perform the above- , Other electronic units, or a combination thereof.

In software implementation, it may be implemented as a module that performs the above-described functions. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

310: Global Navigation System (GNSS) satellite
320: Regional Reference Bureau
330: Central processing station
340: ground uplink station
360: geostationary satellite
350: User terminal

Claims (7)

(a) obtaining an ionospheric measurement;
(b) defining additional metrics for classifying the distribution of the ionospheric measurements;
(c) defining an optimization problem having a constraint to uncover the mathematical nature of the additional metric so as to use the additional metric as a geometric measure of the azimuthal directional distribution of the ionospheric measurements due to mathematical properties that the metric may have ;
(d) calculating a global minimum value satisfying the constraint by using the defined Lagrangian function; And
(f) indicating SBAS (Satellite Based Augmentation System) availability using a geometric measure of the azimuthal direction distribution of the ionospheric measurements computed according to the calculation of the global minimum;
Wherein the SBAS availability enhancement method comprises:
The method according to claim 1,
Wherein the geometric distribution of the ionospheric measurements is a distribution of ionospheric measurements observed near an ionospheric grid point (IGP).
The method according to claim 1,
Wherein the additional metric is defined based on an Euclidean norm of a vector defined in an Euclidean space having a value of an angle between the ionospheric measurement values as an element.
The method according to claim 1,
Wherein the SBAS availability is a ratio of a time when the user protection level, which is a boundary value for a position error generated after applying the correction information by combining the integrity information generated in the central processing station, does not exceed an alarm limit given as a navigation requirement How to improve SBAS availability.
The method of claim 3,
The constraint condition may be expressed by Equation

(Where, &thetas; represents an angle between the ionospheric measurement values).
The method according to claim 1,
RTI ID = 0.0 > 1, < / RTI > wherein the additional metric is a geometric metric.
GNSS (Global Navigation System) satellite;
A global reference station receiving GPS (Global Positioning System) signals from the GNSS satellites and generating respective SBAS (Satellite Based Augmentation System) reference station data;
A central processing station for generating ionospheric measurements from each generated SBAS reference station data; And
Defining an optimization problem having a constraint to uncover the mathematical nature of the additional metric so as to use the additional metric as a geometric measure of the azimuthal directional distribution of the ionospheric measurements due to mathematical properties that the metric may have, (SBAS) using a geometric measure of an azimuthal direction distribution of the ionospheric measurements obtained according to the calculation of the global minimum value, ;
The SBAS solubility enhancement device comprising:

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