KR20070038744A - Regional ionosphere modeling estimation and application method - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates to a local ionospheric error modeling method and an error correction method using the same.

2. The technical problem to be solved by the invention

According to the present invention, in order to correct the ionospheric error that is the largest source of error for a user using a single frequency, the local ionospheric error modeling is made so that the observation error correction can be performed in real time, so that precise positioning can be made. The aim is to provide a local ionospheric error modeling method and an error correction method using the same.

3. Summary of Solution to Invention

The present invention provides a method for modeling ionospheric error in a reference station at a time, comprising: collecting GPS data in real time from a local station at a dual frequency GPS receiver; Convert the latitude / longitude coordinate system into a solar-geomagnetic coordinate system, dividing the grid points according to latitude and longitude, and collect the total number of electrons collected for each time in the basis function and the slope function for each grid point on the solar-geomagnetic coordinate system. Converting according to; A total electron number determination step of determining a signal delay or total number of electrons through the ionosphere through a Kalman filter by applying a weight to the total number of converted electrons in the coordinate system; And converting the determined total number of electrons into a local total number of electrons on a geographic coordinate system to model the local total number of electrons with respect to time for latitude, longitude, and height.

4. Important uses of the invention

The present invention is used in a location based system.

GPS, single frequency, total electron count, regional ionospheric modeling, dual frequency

Description

Regional ionosphere error modeling method and error correction method using the same {Regional ionosphere modeling estimation and application method}

1 is an explanatory diagram showing a data collection process for modeling local ionospheric error according to the present invention;

2 is a flowchart schematically illustrating a method for modeling local ionospheric error according to the present invention;

3 is a detailed flowchart of an embodiment of a method for modeling local ionospheric error according to the present invention;

4 is an exemplary diagram illustrating a process of transmitting a local ionospheric error modeling value generated according to the present invention;

FIG. 5 is a flowchart illustrating an embodiment of a process for transmitting a local ionospheric error modeling value of FIG. 4;

6 is an exemplary explanatory diagram showing an error correction method according to the present invention.

* Explanation of symbols on the main parts of the drawing

11 ~ 14: GPS satellite 20: Standard station

21 ~ 29: GPS station 30: geostationary satellite

41 ~ 44: GPS receiver

The present invention relates to a local ionospheric error modeling method and an error correction method using the same. More specifically, in order to be able to correct the ionospheric error that is the largest error cause for a user using a single frequency, the local ionospheric error modeling It is related to the local ionospheric error modeling method and the error correction method using the same, so as to enable accurate correction of the observation by making the observation error correction in real time.

As the spread of terminals having a single frequency navigation system and a global positioning system (GPS) has become more common, efforts are needed to reduce errors in positioning by reducing errors in observations.

However, the factors that reduce the accuracy of GPS positioning can be divided into three parts. First, the errors caused by structural factors include satellite time error, satellite position error, deflection of ionospheric and convective layers, noise, and multipath. Secondly, there is a geometrical error due to satellite placement, and finally, SA (Selective Availability) is the biggest source of error. All of these factors potentially add up to a very large error, which is called UERE (User Equivalent Range Error). Each error varies greatly with time and place.

In particular, most of the observed error values after the termination of SA are the signal delay effects passing through the ionosphere. Expensive dual frequencies can be used to eliminate this signal delay error, but most popular GPS receivers are single frequencies. Although a precise ionospheric error value can be calculated, a method of applying it in real time has not been devised yet, and the correction of the ionospheric error is actually largely eliminated by the post-processing process.

On the other hand, GPS stations usually have dual frequency GPS receivers, and in the case of dual frequency receivers, the total number of electrons can be calculated using the difference between the two frequencies, or the "GRAPHIC method" if they do not have two frequencies. The total number of electrons can be calculated by combining pseudorange data and carrier phase data of a single frequency, such as the " DRVID method ". The calculated total number of electrons can be used mainly for correction of observational data error for precise positioning, and also for forecasting space environment.

To calculate the total number of electrons to create a global ionospheric model, data from more than 100 permanent stations, such as "JPL" or "CODE" in Europe, are collected and bi-produced in a solar-fixed or solar-geomagnetic coordinate system. The ionospheric modeling is made by precisely determining the total number of electrons using -cubic interpolation.

By the way, "JPL" uses a combination of pseudorange data and carrier phase data to apply an Kalman filter to create an ionospheric model, whereas "CODE" uses a carrier phase data to perform a Kalman filter ( Apply the Kalman Filter to create an ionosphere model.

Local ionospheric modeling can be approached in a slightly different way than models processed with global data. For example, Canada's "Gao" uses a rectangular grid to "Klobachur model" as its initial value. Kalman Filter "to create a regional ionospheric model.

The ionospheric model is made assuming a thin sphere with two-dimensional shells, with the concentration of all guns at approximately 350-600 km altitude. In this case, each grid point is defined by a grid point or other basis function that defines an ionospheric pier point (IPP) and defines the total electron value of the point where the signal transmitted to the user in the visual direction meets the IPP and the point perpendicular to the surface. For Kalman Filter, determine the total number of electrons.

In order to cope with such disturbances of electromagnetic waves and to respond to changes in the space environment, such as when the solar activity was so active that the total number of electrons in the ionosphere due to solar storms was very high, as in 2003, the accuracy of GPS single frequency users was also increased. Positioning requires precise local ionosphere modeling.

Then, the similar prior art related to the present invention will be described.

Conventional Space Based Augmentation System (SBAS) and Wide Area Augmentation System (WAAS) transmit error correction values or other information of GPS signals to the satellite by uplinking to satellites, but the present invention focuses on local error correction. The accuracy of the positioning of the GPS user receiver is increased by providing accurate estimates of the position of the GPS satellites in real time.

On the other hand, "Robust real-time wide-area differential GPS navigation (US Patent No. 5828336) modeling the global real-time ion layer (Ionized layer) using dual frequency GPS data (hereinafter referred to as 'first prior art') In the first prior art, the global real-time ion layer (ion layer) is modeled using dual frequency GPS data, whereas in the present invention, a local real-time ion layer (ion layer) modeling is made and the modeled data is used. To use.

Although the global ion layer (ionization layer) modeling and the local ion layer (ionization layer) modeling are roughly similar, the local ion layer (ionization layer) modeling differs in covariance values for areas where data is not gathered. Must be moved according to spatial resolution. For real-time ion layer (ion layer) modeling, the bias error between GPS satellites and receivers is fixed or estimated only for satellites in the visible range to create a real time local ion layer (ion layer) model. By using the ionosphere modeling data on the geostationary satellite and sprinkling the values on the geostationary satellite, users using a single frequency can accurately determine the location by correcting the observation error in real time.

On the other hand, "Space based augmentation system and methods using ionospheric bounding data to determine geographical correction source (US Patent Registration No. 681854) which improves the precision, integrity and availability of GPS services based on SBAS (hereinafter referred to as" 2) and the present invention is somewhat similar in that the present invention is somewhat similar in that the location of the user is precisely adjusted by improving the quality of the GPS service, i.e., GPS data. By calculating the ion-layer modeled values in real time directly at the reference station and uplinking the GPS satellites and the clock error to the geostationary satellite, the information is broadcast back to the user. Compensates ionospheric error and time error in the received data and provides more accurate location than the navigation solution with large error of GPS satellite. The precision can be further improved by receiving the data in real time, and in particular, in view of the second prior art, according to the present invention, the use of local data provides accurate error information in real time without worrying about the size of data. I can receive it.

That is, in view of the second prior art, the present invention focuses on error correction, so that the present invention does not occupy large enough information data to worry about the memory and storage space of the processor. Local observation error value within the grid point and the precise position of the GPS satellite, where the GPS satellite not only provides real-time information of the satellites in the visible range, but also provides the real-time information of the time error for the visible satellite. This can be said.

The present invention has been proposed to solve the above problems, and in order to correct the ionospheric error which is the largest source of error for a user using a single frequency, it is possible to correct the observation error in real time by making a local ionospheric error modeling. It is an object of the present invention to provide a local ionospheric error modeling method and an error correction method using the same so that precise positioning can be made.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

In order to achieve the above object, the present invention provides a method for modeling ionospheric error in a reference continuous station, comprising: collecting GPS data in real time from a local continuous station having a dual frequency GPS receiver; Convert the latitude / longitude coordinate system into a solar-geomagnetic coordinate system, dividing the grid points according to latitude and longitude, and collect the total number of electrons collected for each time in the basis function and the slope function for each grid point on the solar-geomagnetic coordinate system. Converting according to; A total electron number determination step of determining a signal delay or total number of electrons through the ionosphere through a Kalman filter by applying a weight to the total number of converted electrons in the coordinate system; And converting the determined total electron number into a local total electron number on a geographic coordinate system, and modeling the local total electron number with respect to time for latitude, longitude, and height.

In addition, the present invention is characterized in that it further comprises the step of uplinking the local ionospheric error modeled value generated by modeling at the reference station, and the GPS satellite position and time error information to the geostationary satellite. .

In addition, the present invention is characterized in that the geostationary satellite further comprises the step of broadcasting a local ionospheric error modeling value, the position and time error information of the GPS satellite to a single frequency user in real time.

On the other hand, the present invention, in the method for correcting the ionospheric error value using the local ionospheric error modeling value generated by the local ionospheric error modeling method, the local ionospheric error modeled value received from the geostationary satellite; Using the GPS satellite position and time error information, the total number of electrons determined for each grid point is interpolated according to the basis function and the slope function and converted into an error value in a GPS receiver using a single frequency. It is done.

The present invention precisely calculates the total number of electrons (TEC) from an IGS data center or from a station that has a dual frequency GPS receiver from a local main station, and makes ionospheric modeling with the values in real time. By precisely transmitting information to the geostationary satellite in real-time, the orbital satellite or IGS's precise orbital information and time error information are uplinked more precisely than the information of Improve the precision of the underlying system.

In particular, the present invention calculates the total number of electrons observed using dual frequency GPS data, and determines the total number of electrons using a real-time Kalman filter to minimize the difference from the calculated value. In this case, due to the lack of data covering the real-time local grid point (covariance) values are different depending on the presence or absence of each data, and must be updated over time. The GPS satellite and receiver bias values can be fixed using a pre-calculated value in a global model or calibrated to a determined value, estimated for a visible satellite over time, The bias of the receiver position can be calculated. The total number of electrons determined in this way is again used to correct the user's position by interpolation by the basis function and the slope function. At this time, the modeled values are transmitted to the geostationary satellite to scatter the iono-layer (errors) error values, which are then distributed to the GPS single frequency user.

Real-time local ion layer (Ion Layer) modeling, which can be sprayed from geostationary satellites, allows ordinary single frequency users to correct observations.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, whereby those skilled in the art may easily implement the technical idea of the present invention. There will be. In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is an explanatory diagram illustrating a data collection process for modeling local ionospheric error according to the present invention.

The GPS permanent station (local station with a dual frequency GPS receiver) 21 to 29 receives a signal from the GPS satellites 11 to 14 at each time and delivers the GPS data to the reference permanent station 20 in real time. (101).

Then, as shown in FIG. 2, the reference constant observatory 20 calculates error values generated by the signal delay effect while passing through the ionosphere from the collected data (GPS data) (201 and 202). That is, for dual frequency GPS data collected in real time, the error value due to the ionosphere is calculated by combining the two frequencies, and for the GPS data of the single frequency, the ionospheric error value is calculated using the GRAPHIC method or the DRVID method. Calculate In order to make the ionosphere model available to the general user, the calculated values are appropriately filtered using the edit of the data and the Kalman filter (202), and the total electron count values for latitude, longitude, and height over time are obtained. Modeling (203).

For reference, a process of calculating the total electron count from GPS data will be described.

The GPS receiver has a dual frequency receiver that can receive both L1 and L2 frequencies and a single frequency receiver that only receives the L1 frequency. While the dual frequency receiver is expensive, the signal delay error caused by the ion layer (ionization layer) can be largely eliminated by using the two frequency differences. On the other hand, the receiver for a single frequency is inexpensive, but has a disadvantage in that the signal delay error caused by the ion layer (ionizing layer) cannot be completely eliminated. Therefore, the receiver for a single frequency can adjust a large part of the error by using an ion layer (ionized layer) model estimated by using GPS constant station data on the ground composed of dual frequency receivers.

Among the signals transmitted from the GPS satellites, the carrier phase has no noise and accurate total number of electrons can be calculated. However, the cycle slip phenomenon must be taken into account and the integer ambiguity must be found. On the other hand, pseudorange data does not have signal dropout and does not need to find an ambiguity constant, but there is a lot of multipath error and system noise. Therefore, the total number of electrons is calculated using phase-leveled pseudorange data that complements the advantages and disadvantages of the pseudorange and the carrier phase data.

In the case of two frequencies L1 and L2, the observed values P1 and P2 of the pseudo range data are expressed by Equation 1 below.

는 GPS 위성과 수신기 사이의 거리, c는 빛의 속도,

는 gps 위성의 시계 오차,

는 수신기 시계 오차,

는 L1, L2 주파수,

는 대류층에 의한 오차,

는 다중경로 오차,

는 L1, L2 상의 수신기 잡음 을 나타낸다. In [Equation 1]

Is the distance between the GPS satellites and the receiver, c is the speed of light,

Gps satellite clock error,

Receiver clock error,

L1, L2 frequency,

Is the error due to the convective layer,

Is the multipath error,

Denotes receiver noise on L1 and L2.

The new GPS measurement value from which the ion layer (ionization layer) error is removed by the linear combination of P1 (k) and P2 (k) of Equation 1 may be expressed as Equation 2 below.

Again, subtracting Equation 2 from P1 (k) of Equation 1 calculates an error value due to the ion layer (ionizing layer) inherent in the pseudorange at the L1 frequency.

On the other hand, the ion layer (ionization layer) error of the carrier phase can also be obtained by linear combination of the same method as calculated from the pseudorange data.

The signal delay distance due to the ion layer (ionization layer) error may be converted into the total number of electrons in the ion layer (ionization layer) (1 TECU = 0.162m). Therefore, the total number of electrons using the phase-corrected pseudorange data consists of a linear combination of the total number of electrons of the pseudorange and the carrier phase as shown in Equation 3 below.

는 시각 k에 의사거리 데이터로부터 유도된 총전자수를 의미하고,

는 반송파 위상 데이터를 이용하여 구한 시각 k와 시각 k-1 사이의 총전자수 차이를 나타낸 것이다. 또한,

와

는 k-1과 k 각각의 시각에서 위상보정 의사거리 데이터를 이용하여 계산한 총전자수를 나타낸다. In [Equation 3],

Denotes the total number of electrons derived from pseudorange data at time k ,

Denotes the difference in the total number of electrons between time k and time k-1 obtained using the carrier phase data. Also,

Wow

Denotes the total number of electrons calculated using the phase-corrected pseudorange data at each of k-1 and k .

Through this process, the total number of electrons used in modeling the local ionospheric error can be calculated.

Next, referring to FIG. 3, a detailed description will be given of a method of constructing local ion layer modeling (local ionospheric error modeling) using dual frequency GPS data.

First, the BAD data and the GPS signal data from the low altitude (for example, 0 to 15 degrees) are edited (301). In other words, data that is of poor quality, such as a multipath error, a weak signal, or a low altitude angle, is removed.

Since the total number of electrons in the ionosphere moves according to the earth's geomagnetism and the sun's activity, the coordinate system for latitude and longitude is converted into a solar-geomagnetic system (302).

Next, the lattice points are divided according to longitude and latitude, and the total number of electrons collected for each time is converted according to the basis function and the gradient function for each lattice point in the "Solar-geomagnetic system" of the "302" process. (303).

The total number of electrons determined and predicted according to the latitude and longitude at the epoch of the past time is set as an initial value or updated over time (304).

Thereafter, the weight is applied to the total number of electrons according to the elevation angle or the signal strength to determine the signal delay or the total number of electrons through the ionospheric layer through the Kalman Filter (305). At this time, the bias values of the stations receiving the GPS satellites and the dual frequency GPS data should be given. Although these values may be estimated together, these bias values may be given in a predetermined global model to speed up the real-time processing. Values can be used, fixed to precalibrated values, or only GPS satellites in the field of view can be estimated. Also, since the real-time data does not cover the entire area, the covariance values of the data where each data point exists and where it does not exist are determined to determine the value. Covariance changes over time and space must also be updated in real time. That is, for the real-time Kalman filter, the covariance value for each grid point is different depending on the value to be estimated and the window to be fixed, and the covariance change over time and space is updated in real time.

The total number of electrons determined in this way is converted to the number of local total electrons on the geographic coordinate system (306). In operation 307, modeling is performed on the latitude, longitude, and height of the local total electron counts for each hour.

As described above, in the present invention, the total number of electrons is calculated using dual frequency GPS data, and the total number of electrons is determined using a real-time Kalman filter in order to minimize the difference with the calculated value. At this time, the covariance value is changed differently for the areas that cannot be covered because it is a real-time modeling of the area, and the Kalman filter is applied after updating in time. That is, due to the lack of data covering the real-time local grid points, the covariance values are different depending on the presence or absence of each data, and are updated over time. In addition, the GPS satellite and receiver bias values may be pre-calculated in the global model, calibrated to a fixed value, estimated for visible satellites over time, or the bias of the receiver position may be calculated.

The total number of electrons determined in this way is again used to correct the user's position by interpolation by the basis function and the slope function. At this time, the modeled values are transmitted to geostationary satellites to scatter the ion layer (Ion ion layer) error values, and these values are distributed to GPS single frequency users.

4 is an exemplary diagram illustrating a process of transmitting a local ionospheric error modeling value generated according to the present invention.

In the reference constant time station 20, the local ionospheric modeling data (local ionospheric error modeling values) generated through the process of FIG. 3 and each PRN (Pseudo Random Noise) belonging to a predetermined corresponding time, that is, a visible distance, are generated. The position and time error information of the GPS satellites are uplinked to the geostationary satellite 50.

Then, the geostationary satellite 30 receives the received data (that is, the local ionospheric modeled data (local ionospheric error modeling value), the position of the GPS satellites, time error information), the terminal 41, the missile 42, the aircraft ( 43) and broadcast to a GPS receiver such as a boat 44. That is, the geostationary satellite 30 broadcasts the modeled value (local ionospheric error modeling value), location information and time error information according to each GPS PRN at a visible distance to the GPS single frequency user (broadcast).

Looking at this in more detail with reference to FIG. 5, the reference permanent observation station 20 includes a local ionospheric modeling value (local ionospheric error modeling value) made in FIG. 4 and a GPS satellite according to each PRN at a visible distance in the region. The position and time error information is transmitted to the geostationary satellite 30 (uplink) (501).

Afterwards, the geostationary satellite 30 transmits the received data (ie, local ionospheric modeling data (local ionospheric error modeling values), GPS satellite position, and time error information) to the GPS receivers 41 to 44 as signals of a CDMA method. Broacast 502. Therefore, each user (terminal 41, missile 42, aircraft 43, ship 44) has a local ionospheric modeled value (local ionospheric error modeling value), GPS according to each PRN in the line of sight within the area. The position and time error information of the satellite is transmitted (503).

Next, based on these ionospheric error correction values (i.e., local ionospheric modeled data (local ionospheric error modeling values), precise position information and time error information of the GPS satellites in the field of view, each GPS receiver is a GPS single frequency user. The precise location of may be determined (504).

Then, a method of improving the precision positioning by interpolating the received value and correcting the ion layer (ionization layer) error value at the reception position will be described with reference to FIG. 6.

6 is to interpolate the total number of electrons determined for each lattice point to an error value at a user position by interpolation according to a basis function and a slope function.

의 총전자수는 사용자의 위치에서 총전자수이고, 각 격자점 위의 수직한 총전자수는 다음의 [수학식 4]에 의해 내삽된다. here,

The total electron count of is the total electron count at the user's position, and the vertical total electron count on each lattice point is interpolated by Equation 4 below.

In [Equation 4], VTEC _J (j = 1,2,3,4) represents the total number of electrons in the vertical direction to be estimated from the grid points, _i W _ij is a TEC (the observed total number of electrons to the visual direction in IPP) and VTEC _j (4 A base function representing the total number of electrons estimated in the vertical direction on the lattice points), and is expressed by Equation 5 below.

이고,

,

이다. here,

ego,

,

to be.

In Equation 4, E denotes an elevation angle, h denotes a height up to IPP, and a slope function sf (E) is represented by Equation 6 below.

(Where E is the elevation angle of the GPS satellite, h is the height to IPP, and R _E is the radius of the earth)

As described above, the method of the present invention may be implemented as a program and stored in a recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.) in a computer-readable form. Since this process can be easily implemented by those skilled in the art will not be described in more detail.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

As described above, the present invention is capable of real-time local ion layer (ion layer) modeling, and by using an ion layer (ion layer) modeling value scattered from a geostationary satellite by a single frequency user, real-time observation error correction can be performed.

In particular, while the existing local ionospheric model determines the initial value determination using another model, according to the present invention, the ionosphere is set in real time by setting or updating the total number of electrons predicted from the preceding time through the actual observed model. Models can be enabled, weighted according to altitude in determining the total number of electrons to increase the accuracy of the real model, simplifying the bias estimation of GPS satellites and receivers, and covariance updates are performed in real time for correct data coverage. have.

In addition, according to the present invention, all the single frequency users in the area can observe the observation error by uploading the ionospheric modeling data and the position information and time error of the precise GPS satellites to the geostationary satellite, and spraying the error value by the CDMA method every predetermined time. Values can be calibrated and can improve the accuracy of precision positioning or location-based systems.

Claims (7)

In the ionospheric error modeling method in the reference permanent station, Collecting GPS data in real time from a local, continuous station with a dual frequency GPS receiver; Convert the latitude / longitude coordinate system into a solar-geomagnetic coordinate system, dividing the grid points according to latitude and longitude, and collect the total number of electrons collected for each time in the basis function and the slope function for each grid point on the solar-geomagnetic coordinate system. Converting according to; A total electron number determination step of determining a signal delay or total number of electrons through the ionosphere through a Kalman filter by applying a weight to the total number of converted electrons in the coordinate system; And Modeling the total number of local electrons over time with latitude, longitude, and height by converting the determined total number of electrons into a local total electron number on a geographic coordinate system Local ionospheric error modeling method comprising a. The method of claim 1, In the total electron number determination step, The bias of GPS satellites and dual frequency reception stations is estimated only for GPS satellites that are fixed, calibrated, or at sight, and the covariance values for each grid point are A method for modeling local ionospheric errors, which varies according to a window to be fixed and updates in real time with covariance changes over time and space. The method of claim 2, In the total electron number determination step, When the Kalman filter is applied, a weighting method is applied according to an elevation angle or signal strength of the data. The method of claim 2, Uplinking the local ionospheric error modeled value generated by modeling at the reference permanent station and position and time error information of the GPS satellites to the geostationary satellite Local ionospheric error modeling method further comprising. The method of claim 4, wherein The geostationary satellite broadcasting a local ionospheric error modeling value and position and time error information of a GPS satellite to a single frequency user in real time; Local ionospheric error modeling method further comprising. In the method of correcting the ionospheric error value by using the local ionospheric error modeling value generated by the method of any one of claims 1 to 5, Using the local ionospheric error modeled value received from the geostationary satellite and the position and time error information of the GPS satellites, the total number of electrons determined for each grid point is interpolated according to the basis function and the slope function. Error correction method characterized in that the conversion to the error value in the GPS receiver using a single frequency. The method of claim 6, When the total number of electrons is interpolated according to the basis function and the slope function and converted into an error value in a GPS receiver using a single frequency, Error correction method, characterized in that to obtain the total number of electrons at the user position based on the following equation. [Equation]

Where W _ij is the basis function,

ego, but

,

,

Is, E is the elevation angle, h is the height to the IPS (Ionospheric Pierce Point), and the slope function

being)

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