JP2004205525A - Satellite positioning system, ground station thereof, and ground terminal thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem wherein the constitution of a terminal gets complicated since a D-GPS requires a GPS antenna for receiving a radio wave from a satellite, and an antenna for receiving an FM radio wave therefrom. <P>SOLUTION: Orbital information of the satellite is transmitted to the terminal 103, including error information in a radio signal from the satellite 101. An orbital calculating device 104 and a positioning error estimating device 105 including a function parameter of a positioning error are provided in a ground station 102, and data from the two devices are composed and encoded to be transmitted from a transmitter 106 to the satellite 101. The data are interpreted to conduct positioning calculation including error correction calculation in the terminal 103. The positioning error is calculated area by area, based on a data of meteorological information or the like. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a satellite positioning system that performs positioning using geostationary satellites and orbiting satellites, and a ground station and a ground terminal thereof.

  A typical positioning system using a satellite is a GPS (Global Positioning System). GPS usually arranges 24 satellites so that it can be serviced anywhere on the earth, and performs positioning by obtaining signals from the satellites. A satellite used in GPS can transmit an accurate radio wave transmission time from a satellite to a ground station by mounting an atomic clock. The distance between the satellite and the ground station is calculated from the accurate time and the reception time at the ground station, and the position on the ground is calculated based on the distance.

  When a radio wave is transmitted from a satellite to a ground station, the radio wave has a delay amount represented by a delay in the ionosphere or a delay in the atmosphere. The amount of delay in the ionosphere can be removed by using two frequencies as shown below (edited by the Geodetic Society of Japan, -GPS-Global Positioning System, 1989).

  The delay of the group velocity of microwaves (the velocity at which wave energy is transmitted) in the ionosphere is expressed by equation (1).

Here, X is a critical frequency of the ionosphere and an amount determined by a distance through which radio waves pass, τ _{GD is} a delay (s) of a group velocity of microwaves, and f is a frequency of a carrier wave. The difference between the delays of the L1 and L2 bands used in the GPS is given by equation (2).

Here, f ₁ and f ₂ are frequencies (Hz) of the L1 band and the L2 band. Since f ₁ and f ₂ are known in the case of GPS, the correct distance R corrected for the ionosphere is given by equation (3).

Here, R _L1 and R _L2 are distances measured in L1 and L2 bands before ionospheric delay is corrected, and R is a true distance.

  On the other hand, there is DGPS (Differential-GPS) as another method for reducing the positioning error. In this method, a GPS signal is received at a location whose position is accurately known in advance, an error is calculated from a position obtained by GPS and a true position, and this error value is calculated as an FM radio wave different from a radio wave from a GPS satellite. And send it to the terminal. Due to the simple method, operation has been started in many places as an actual system.

  The conventional technology has the following problems. In order to correct the positioning error due to the ionospheric delay, two types of frequencies are required, which complicates the internal configuration of the terminal device. In order to solve this, there is D-GPS described above, but D-GPS requires both a GPS antenna for receiving radio waves from satellites and an antenna for receiving FM radio waves. It gets complicated. In addition, there are many areas where FM radio waves do not reach in Japan, and when a terminal attempts to perform positioning in that area, there is a disadvantage that positioning accuracy is reduced.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to provide a satellite positioning system that can obtain the same positioning accuracy anywhere, with an inexpensive and simple configuration, and a ground station and a terminal thereof.

  According to the present invention, in order to achieve the above object, a radio signal transmitted from a satellite to a terminal is transmitted to the terminal including orbit information of the satellite and error information. For this purpose, the orbit calculation device and the terminal in the ground station interpret the data and perform positioning calculation and error correction calculation. Further, in order to improve the positioning accuracy, the error information described above, not only the absolute value of the positioning error amount, based on the device location where there is a terminal performing positioning, a function for calculating the positioning error with a precise model Include parameters. A positioning error estimating device for performing this is provided in the ground station. In addition, an orbit calculation device for calculating the orbit of the satellite is provided in the ground station, and an encoding device for combining and encoding data from these two devices is provided in the ground station. Further, a positioning terminal capable of performing accurate positioning calculation from such satellite orbit data and error parameters is provided.

  By using the positioning calculation system of the present invention, an antenna for receiving an FM radio wave, which has been required for performing high-precision positioning, becomes unnecessary, so that an in-vehicle information device having a simple device configuration can be developed.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a system configuration of the present invention, which includes artificial satellites 101-a to 101-n, a ground station 102, and a terminal 103. The artificial satellites 101-a to 101-n are provided with a number of satellites from a terminal that performs positioning, so that four or more satellites can be supplemented when performing three-dimensional positioning and three or more satellites when performing two-dimensional positioning. Need to be secured. The artificial satellite is a general satellite having a receiving antenna, a transmitting antenna, and a transponder. Satellites can be geostationary or orbiting satellites. In particular, since a long elliptical orbit satellite is suitable for positioning at a terminal mounted on a mobile body, there is no problem even if a long elliptical orbit satellite is used as an artificial satellite.

  The ground station 102 includes an orbit calculator 104 for calculating a satellite orbit of each satellite at an arbitrary time, a positioning error estimator 105 for estimating a positioning error between each satellite and a reception position, output data from the orbit calculator 104, and a positioning error. The transmission device 106 multiplexes and encodes the data from the estimation device 105 so as to be carried on radio waves, and transmits the data to the satellite.

  Next, each device in FIG. 1 will be described. The orbit calculation device 104 calculates 101-a to 101 at each time from the Kepler orbital elements of the satellite performing the positioning (orbital plane inclination angle, ascending intersection RA, orbital long radius, orbital eccentricity, perigee argument, average near store off angle). The position in the orbit of the satellite up to −n is calculated in a predetermined coordinate system.

  As shown in FIG. 2, the positioning error estimating device 105 includes a weather information providing device 201, an encoding device 202, a region dividing device 203, a reference clock 204, and a parameter calculating device 205. These devices are connected as shown. Data collected by the weather information providing device 201 is sent to the region dividing device 203 and the parameter estimating device 205. FIG. 3 shows an example of division by the region dividing device 203.

  FIG. 3 is a conceptual diagram in which the whole of Japan at a certain point in time is divided using the information on the humidity distribution, which is one of the information from the weather information providing device 201, for the Japan 301. Here, the division is performed based on the atmospheric pressure distribution, the temperature distribution, and the weather distribution which influence the positioning error, and is performed based on the latitude and longitude information of the area. Further, the division may be performed based on other geographical conditions (plain area, urban area, mountain area, etc.). This area division may be updated at a constant cycle according to the situation of weather change.

  As a result of the division, for example, regions 302 and 303 in FIG. 3 have error parameters specific to the region at an arbitrary time, for example, ionospheric delay error, tropospheric delay error, Doppler generated between satellite and receiver. A delay error due to the effect will be assigned.

  The parameter estimation device 205 obtains an error parameter at a representative point for each region divided by the region division device 203. Here, the error parameter means a delay error occurring in the air before the signal from the satellite reaches the ground, or a parameter of an equation describing the delay error, or an estimated value of a positioning error generated in the terminal. . It is also possible to add a parameter describing a system error typified by a positioning error due to other atmospheric noises to the error parameter. Generally, the above error parameters are affected by weather phenomena such as elevation angle when looking up the satellite from the terminal, density of water vapor contained in the atmosphere, temperature and air pressure at the terminal point. That is, since these values differ depending on the region where the positioning is performed, an error parameter for each region is required.

  In obtaining these error parameters, an embodiment of a calculation method for the ionospheric delay error, the tropospheric delay error, and the Doppler delay error will be described below.

(A) Ionospheric delay error The input variables are the approximate latitude of the user: Φ _u , the approximate longitude of the user: λ _u , the elevation with the satellite (elevation angle): E, the azimuth with the satellite (azimuth angle): A, Constants sent from satellites: α, β.

  (1) The earth center coordinate 中心 is calculated by the equation (4).

(2) The quasi-ionospheric latitude Φ _I is obtained by the equation (5).

If Φ _I > +0.416, Φ _I = + 0.416, and if Φ _I <−0.416, Φ _I = −0.416.

(3) Calculate the quasi-ionospheric longitude λ _{I according} to equation (6).

(4) obtained from the geomagnetic latitude [Phi _m is quasi ionospheric position viewed from the respective satellites (7).

  (5) The local time t at the quasi-ionospheric point is obtained by the equation (8).

  If t> 86400, t = t−86400, otherwise 86400 is added to t. Here, SatelliteTime is satellite time.

  (6) In order to calculate the tilt time delay, the tilt factor F is calculated by the equation (9).

  (7) In order to calculate the ionospheric delay time Tion, first, x is calculated by the equation (10).

  If | x |> 1.57, then Tiono can be determined by equation (11). Otherwise, it is obtained by the equation (12).

  This Tiono is the ionospheric delay time. The ionospheric delay error is obtained by multiplying the value of Tiono by the radio wave propagation velocity.

(B) Delay error due to the troposphere (Sastamoinen's model)
The temperature is calculated by equation (13) and the atmospheric pressure is calculated by equation (14).

Here, μ = −M / Rβ (constant), r: radius from the center of the earth, r ₀ : radius of the user, T ₀ : temperature at the position of the user, range of radius r _T from the radius r _{0 of} the user to the atmosphere. Let's move. At this time, the refractive index of the dry term can be obtained from equation (15).

The pressure P decreases exponentially from the initial value _PT according to the equation (16).

  In the Zastamoinen model using this pressure model, the atmospheric delay error Δ is expressed as in equation (17).

Here, D: 0.0026 cos2Φ + 0.00028h, Φ: latitude of the terminal, and h: altitude of the terminal.

(C) the Doppler shift delay caused by the Doppler effect error satellite and user positions caused to vary every moment D _i, when the radio waves emitted by Li band, represented by the equation (18).

Here, r _i : the position of the satellite at the time of transmission from the satellite, r _u : the position of the receiver at the time of receiving the signal, and l _i can be obtained by equation (19).

  The above Doppler can be rewritten as the delay error & as shown in the equation (20).

Where: drift speed (m / s) of the receiver clock, ε _& : error in observed value.

  As shown in FIG. 5, the weather information providing apparatus 201 stores the date and time, temperature, humidity, weather, atmospheric pressure, wind direction, and the like for each point. Historical data is stored at a time point earlier than the present time, and predicted data is stored at a future time point.

  Returning to the example of dividing the area, in the example of FIG. 3, when thunderstorms occur in the Kanto area, but the effect is not seen in the southeastern part of the Tohoku region, the Kanto and southern Tohoku areas are 302, 303 depending on the water vapor density and the allowable error range. This is an example of division as shown in FIG.

  The result of division by the region dividing device 203, and the error parameter for each region estimated by the parameter estimating device and divided by the region dividing device 203, or the absolute value of the positioning error, and the reference clock at the time of data transmission Are encoded by the encoding device 202 and sent to the transmission device 106.

  The encoding device 202 encodes the data in the format shown in FIG. In FIG. 4, reference numeral 400 denotes an encoded data sequence, reference numeral 399 denotes an identification number of a region divided by the region dividing device, 401-a denotes a header for the data content of satellite number 1, and 401-b denotes a time relating to satellite number 1. It is stamped orbit data and includes error parameters. Also, 402-a and 402-b are data corresponding to satellite number 2, and 404-a and 404-b are data corresponding to satellite number n.

  As an example of the details of this data, 411 is the time, 412 is the satellite number, 413 is the orbit data of the satellite, and 414 to 415 are the correction error amount or the correction error parameter in each of the divided areas. An area for storing the error or parameter is prepared for each region.

  For example, considering the case where the parameter of the troposphere delay amount is put in the area, the troposphere delay model stores the water vapor partial pressure, the atmospheric pressure, and the temperature in the area as shown in Expression (17). Such processing is performed for each error occurrence factor and each error region. These data are calculated for each area. For example, an error parameter is transmitted from the ground station 102 in a form in which one data in FIG. 4 corresponds to the area 302 in FIG.

  Next, the terminal device 103 that receives the above data will be described. As shown in FIG. 7, at least the terminal device 103 includes a receiving device (antenna) 801, a parameter separating device 802 for separating satellite orbit data and an error parameter, a delay amount calculating device 803 for calculating a delay error amount from the error parameter, Pseudo-range calculator 805 that calculates the pseudo-range (distance including delay error) between each satellite and the terminal from the satellite position in the satellite orbit data and the approximate position of the terminal, from the pseudo-range and the delay distance in the delay amount calculator A true distance calculation device 806 for calculating a true distance between each satellite and the terminal (an accurate distance excluding a delay distance), and a positioning calculation device 807 for calculating a terminal position from the true distance obtained by the device 806 and the coordinate position of each satellite. And an output device 808 for displaying positioning results.

  Next, a positioning calculation method in the terminal will be described with reference to FIG. Data transmitted from the ground station via the satellite is taken in from the antenna 801 of the terminal 103. Next, in process 601 the terminal 103 recognizes to which region in FIG. 3 it belongs. In this recognition procedure, the position data of the end point of the grid in FIG. 3 is stored in the terminal 103 in advance, and the corresponding grid number (for example, 302 or 303) is obtained based on the result of the previous positioning. After that, from the positioning data broadcast in the format shown in FIG. 4, only the signal sequence 400 corresponding to the previously obtained lattice number is stored in the memory on the computer that performs positioning (process 602). Further, in the process 602, the satellite orbit data (the coordinate values of each satellite) and the error parameters shown in FIG. 4 are stored in the memory of the computer.

Using the stored satellite orbit data, a pseudorange between each satellite and the terminal 103 on the ground is calculated in process 603. This is performed by a normal distance calculation using coordinate values between two points (X _i , Y _i , Z _i ) and (X ₀ , Y ₀ , Z ₀ ). Here, X _i : x coordinate of satellite, Y _i : y coordinate of satellite, Z _i : z coordinate of satellite, X ₀ : x coordinate of ground terminal, Y ₀ : y coordinate of ground terminal, Z ₀ : ground terminal. Is the z coordinate of

  Next, the error parameters corresponding to 414 to 415 obtained in the process 602 are substituted into any of the equations (11), (12), (17), and (20) stored in the delay distance calculation device 803 in advance. Then, the delay distance at the time of radio wave propagation in the corresponding area is calculated (process 604). Further, based on the obtained delay distance, the true distance between the satellite and the terminal is calculated in a process 605 by the equation (21).

  Here, since the coordinates and the true distance from each satellite have been obtained, the positioning calculation is performed in the process 606. Assuming three-dimensional positioning, positioning calculation is performed by solving simultaneous equations using data from four satellites. The specific calculation method is shown below.

  Consider three-dimensional right-handed orthogonal coordinates with the origin at the center of the earth, the z-axis with the north as the positive direction along the rotation axis, and the x-axis (the positive direction) with the orbital direction of the Meridian and Equatorial planes.

The position of each satellite is (x _i , y _i , z _i ), and the coordinates of the observation point are (x ₀ , y ₀ , z ₀ ). The true distance between the measurement point and each satellite is r _0i , and the pseudo distance is r _i . The subscript i (= 1, 2, 3, 4) of each quantity indicates the number of the satellite.

Now, pseudorange r _i is the influence of the deviation of the satellite clock, when the effect of the propagation delay distance in the atmosphere have been removed is expressed by equation (22).

  s represents the influence of the deviation of the receiver clock on the distance data. That is, assuming that the clock of the receiver is advanced by t with respect to the GPS time system, s is expressed by equation (23).

  Since the Pythagorean theorem holds between the distance data, the coordinates of the observation point, and the position of the satellite, equation (24) is obtained.

  This is substituted into equation (22) to obtain equation (25).

X ₀ , y ₀ , z ₀ and s are obtained from the equation (25). (25) To solve the equation, the unknown variable is represented by the sum of its approximate value and its correction value, the equation is expanded with the correction value, and the second-order and higher-order terms can be ignored and linearized. Equation (26) is obtained.

  However, the quantity with a dash (') is the approximate value of each variable, and the quantity with Δ is its correction value. First, equation (27) is set.

This is the distance between the approximate position of the observation point (approximate value of x, y, z) and the satellite. Then calculated the r was partially differentiated by x ₀ (28) Equation.

Since the coordinate values (x ₀ , y ₀ , z ₀₎ of the observation point in the above equation are unknown, in the actual calculation, the approximation equation (29) is used. A similar relational expression is obtained for the y and z components.

  When these are arranged, it becomes Formula (30). The equation is repeatedly calculated until Δx, Δy, Δz, and s converge to find a solution.

  The use of the positioning calculation system of the present invention eliminates the need for an antenna for receiving FM radio waves, which was necessary for performing conventional high-accuracy positioning, so that in-vehicle information that is inexpensive and has a simple device configuration Equipment can be developed.

FIG. 1 is a configuration diagram illustrating a satellite positioning system of the present invention. FIG. 1 is a configuration diagram illustrating a positioning error estimation device. FIG. 4 is an explanatory diagram showing a state of dividing an area. FIG. 3 is a schematic diagram of data transmitted from a ground station. FIG. 3 is a data configuration diagram showing an example of weather information data. 9 is a flowchart illustrating positioning calculation processing on the terminal side. FIG. 2 is a configuration diagram of a positioning terminal.

Explanation of reference numerals

  101 satellite, 102 ground station, 103 terminal, 104 orbit calculation device, 105 positioning error designation device, 106 transmission device, 201 weather information providing device, 202 encoding device, 203 region dividing device , 204: Reference clock, 205: Parameter estimating device, 301: Map, 302: Divided area, 303: Divided area, 399: Regional authentication number, 400: Data, 401: Header data, 402 to 404: Satellite position and error parameters Data, 411 to 415 data, 601 data recognition processing, 602 data storage processing, 603 pseudo distance calculation processing, 604 delay time calculation processing for each error factor, 605 true distance calculation processing, 606 positioning calculation processing 607: convergence determination processing, 608 ... alarm output processing, 801 ... receiving apparatus, 802 ... parameter separation apparatus, 803 ... delay distance calculation apparatus, 805 ... pseudo distance calculation apparatus, 806 ... true distance calculation apparatus, 807 ... positioning calculation apparatus , 808 ... output device.

Claims (10)

For a plurality of satellites, the ground station of the satellite positioning system that transmits the orbit information data of the satellite used for positioning,
A ground station of a satellite positioning system, wherein a signal transmitted from the ground station includes positioning correction information data.   2. An apparatus according to claim 1, further comprising: an orbital calculation device for calculating orbital information data indicating a position of the satellite; and a positioning error estimating device for generating said positioning correction information data. A ground station of a satellite positioning system, characterized by transmitting.   3. The ground station according to claim 2, wherein the positioning correction information data estimated and calculated by the positioning error estimating device is represented by a parameter of a function representing an error or an absolute amount of the error.   3. The positioning error estimating device according to claim 2, wherein the positioning target area is divided based on a positioning error occurrence condition represented by a weather condition, and an error parameter or an absolute amount of the positioning error for all the divided regions based on the weather condition. Terrestrial station of a satellite positioning system, which estimates the data necessary for positioning together with information of a reference clock and transmits the encoded data to a satellite.   5. The ground station according to claim 4, wherein the plurality of areas update a division state of the area at a fixed period or at an arbitrary time. 5. The satellite positioning system according to claim 4, wherein the positioning error occurrence condition includes at least one of weather information, latitude / longitude information of the area, and geographical conditions (plain area, urban area, mountain area, etc.). Ground station. In the ground terminal of the satellite positioning system that receives the orbit information data and positioning error information data of the satellite used for positioning from the satellite and performs positioning calculation,
The ground terminal calculates a pseudo distance between the satellite and the terminal based on the orbit information data and a delay distance between the satellite and the terminal based on the positioning error information data, and calculates the satellite / terminal from the pseudo distance and the delay distance. A terrestrial terminal for a satellite positioning system, comprising: a positioning calculation device that calculates a true distance between terminals and positions the terminal based on the distance. In a satellite positioning system including a ground station transmitting orbit information data of a satellite used for positioning toward a satellite, a plurality of satellites receiving a signal transmitted from the ground station, and a ground terminal receiving data transmitted from the satellite,
A satellite positioning system, wherein a signal transmitted from the ground station includes at least both orbit information data and positioning correction information data.   9. The satellite positioning system according to claim 8, wherein the ground terminal separates orbit information data and positioning correction information data received from the satellite, and calculates the position of the ground terminal based on the separated data.   10. The satellite positioning system according to claim 8, wherein a long elliptical orbit satellite is used as the satellite.

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