Method for generating correction information in satellite navigation system, information processing device for generating correction information, and program

Abstract

To construct a wide-area differential GPS without using reference stations.SOLUTION: In a satellite navigation system including GPS of the United States and the quasi-zenith satellite system of Japan, correction information for a wide-area differential GPS that corrects clock errors and position errors of navigation satellites is generated by acquiring precise ephemerides, which are publicly available as accurate information independent of predictions of clocks and orbits of navigation satellites as a difference between times and positions calculated from the precise ephemerides and times and positions calculated from broadcast ephemerides which are information on the clock and orbit of the navigation satellites transmitted by the navigation satellites superimposed on positioning signals. A user station applies this correction information to perform calculation processing, thereby constructing a wide-area differential GPS without using the reference stations.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for generating correction information in a satellite navigation system, an information processing apparatus for generating correction information, and a program.

Background Art

[0002] A satellite navigation system that measures positions using artificial satellites is generally referred to as GNSS (Global Navigation Satellite System), and a representative example thereof is GPS (Global Positioning System) by the United States. GNSS generally measures the distance between a navigation satellite and a receiver by receiving a positioning signal transmitted by an artificial satellite called a navigation satellite with the receiver, and calculates the position of the receiver through calculation. The receiver for which the position is to be determined is called a user receiver or a user station, etc. The error with respect to the true position of the obtained position is called a positioning error, and the statistical state of the positioning error is called positioning accuracy. Measuring the position is called positioning, and the calculation process therefor is called positioning calculation.

[0003] In order to calculate the position of a user receiver, it is necessary to know the position of the navigation satellite that transmits the positioning signal. However, the orbit information of the navigation satellite required for this purpose is superimposed and transmitted by the navigation satellite itself on the positioning signal. Since the orbit information is created by prediction, the position of the navigation satellite calculated therefrom includes an error of up to about several meters, which becomes a factor of the positioning error when calculating the position of the user receiver as the position error of the navigation satellite.

[0004] The timing at which a navigation satellite transmits a positioning signal is predetermined, and the navigation satellite transmits the positioning signal based on the time of the clock it carries. Although a highly accurate atomic clock is used as this clock, since a slight time deviation is inevitable, the user receiver needs information on the time indicated by the clock of the navigation satellite. This clock information is superimposed on the positioning signal and transmitted by the navigation satellite itself. Since the clock information is created by prediction, the transmission timing of the positioning signal calculated therefrom includes an error corresponding to a distance conversion of about several meters, which becomes a factor of positioning error when calculating the position of the user receiver as the clock error of the navigation satellite.

[0005] The information on its own clock and orbit transmitted by a navigation satellite is called a broadcast ephemeris. By using the broadcast ephemeris, the user receiver can calculate the time and position of the clock of the navigation satellite at any point in time.

[0006] Before the positioning signal reaches the ground, it is affected by various factors of positioning error, such as delay due to the atmosphere in the sky and the mixing of reflected waves. To remove such effects, a receiver is installed at a reference station fixed on the ground, and correction information for the measurement error of the distance caused by various error factors is generated from the measured distance, and this is provided to the user. By correcting the distance measured at the user station with the correction information, the positioning error at the user station is suppressed. This method is called differential GPS (DGPS: Differential GPS). When distinguishing from DGPS, the method of calculating the position of the user station without applying correction information is called single-point positioning.

[0007] There are several specific methods of DGPS, one of which is called Wide Area DGPS (WADGPS). In this method, correction information is generated for each of the clock error and position error of the navigation satellites using the distances measured by the reference stations and provided to the user stations. Since the clock error and position error appear as distance measurement errors depending on the position of the user station, the idea of WADGPS is to provide effective correction information for a wide range of users by generating correction information separately for each of them.

[0008] As a practical example of WADGPS, SBAS (Satellite-Based Augmentation System) has been standardized and put into practical use for the aviation field.

[0009] By the way, in the field of GNSS, for each navigation satellite, a precise orbit ephemeris is created and used as accurate clock and orbit information. The precise orbit ephemeris is often created at 15-minute or 5-minute intervals, and users can obtain accurate time and position information at any point in time by interpolating it. The precise orbit ephemeris, for example, those created by an international organization such as IGS (International GNSS Service) are publicly available and are used in the field of precise positioning such as surveying and geodesy.

[0010] At the beginning of 2024, the available GNSSs include, in addition to GPS, Galileo by Europe, BDS by China, and QZSS (Quasi-Zenith Satellite System) by Japan.

Prior Art Documents

Non-Patent Documents

[0011]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0012] In WADGPS, reference stations are installed to generate correction information, and the clock error and position error of navigation satellites are calculated using the distances measured by the reference stations. Since these reference stations need to be distributed at intervals of approximately several hundred kilometers to 1,000 kilometers in the service area of WADGPS, there is a problem that the entire WADGPS system has to be large-scale.

Means for Solving the Problems

[0013] Non-Patent Document 1 details the method of generating correction information within WADGPS. According to this, it is possible to calculate the clock error and position error of navigation satellites using the distances measured by a large number of reference stations on the premise of the existence of these reference stations.

[0014] In Non-Patent Document 2, an experimental example of WADGPS is reported. According to this, it has been demonstrated that it is possible to construct WADGPS by actually using measurement data from a large number of reference stations. Regarding the correction values of the clock and position of the navigation satellite, as shown on Slide 13 of the said document, it takes time for the calculation process inside the master station to converge.

[0015] However, since the technical contents described in Non-Patent Document 1 and Non-Patent Document 2 both assume the use of a large number of reference stations, they do not solve the problems to be solved by the present invention.

[0016] As described in Non-Patent Document 3 and Paragraph

[0009] , a precise orbit ephemeris has been created as information on the accurate clock and orbit of the navigation satellite and is publicly available for general use. The precise orbit ephemeris is not provided in real time, although it is high-precision information, and it becomes available several days to several weeks later.

[0017] Also, the broadcast orbit ephemeris is transmitted by the navigation satellite. For example, in IGS, the broadcast orbit ephemeris received on the ground is stored and is also publicly available for general use.

[0018] Since the correction information provided by WADGPS corrects the clock error and position error of the navigation satellite, if there is information on the accurate clock and orbit of the navigation satellite, it is conceivable to use them to create correction information. That is, it is conceivable to generate correction information as the difference between the time and position calculated from the precise orbit ephemeris and the time and position calculated from the broadcast orbit ephemeris.

[0019] However, WADGPS is usually assumed to be used for the navigation of a moving object, and a configuration using a precise orbit ephemeris that is not provided in real time has never been considered. However, if it is not necessary to provide correction information in real time, it is considered that the correction information of WADGPS can be generated using a precise orbit ephemeris. Also, if a precise orbit ephemeris with sufficient accuracy can be created by prediction, the correction information of WADGPS can be generated in real time using the precise orbit ephemeris.

[0020] Note that a broadcast ephemeris is also required when generating the correction information of WADGPS. It is possible to install a small number of reference stations to receive this from navigation satellites, but if the precise orbit ephemeris is obtained from IGS, it is possible to use the broadcast ephemeris stored and published by the same IGS.

[0021] On the other hand, if a precise orbit ephemeris is available, as reported in Non-Patent Document 4, it is also conceivable to perform positioning calculation processing using the precise orbit ephemeris at the user station. Such a technique is called precise single-point positioning and is a high-precision positioning method that does not rely on DGPS. If such a configuration is adopted, the correction information by WADGPS becomes unnecessary, but instead, the calculation processing inside the user station becomes complicated, and it is necessary to change it to one corresponding to the precise orbit ephemeris. In addition, the user station itself newly needs to obtain the precise orbit ephemeris through a communication line.

[0022] The present invention solves the above problems by generating the correction information of WADGPS using a precise orbit ephemeris.

[0023] The invention according to claim 1 is a satellite navigation system comprising a plurality of navigation satellites that transmit positioning signals, a user station that receives the positioning signals transmitted by the plurality of navigation satellites and measures the distances thereto, and a master station that generates correction information regarding the clock error and position error of the navigation satellites, wherein the user station corrects the positioning error using this correction information. In the satellite navigation system, the master station generates correction information as the difference between the time and position calculated from the precise orbit ephemeris, which is accurate information on the clocks and orbits of the navigation satellites, and the time and position calculated from the broadcast orbit ephemeris, which is the information on the clocks and orbits of the navigation satellites themselves superimposed on the positioning signals, without using the measured values of the distances related to the navigation satellites. This is a method for generating correction information in a satellite navigation system.

[0024] The invention according to claim 2 is an information processing apparatus for generating correction information in a satellite navigation system, which comprises a plurality of navigation satellites that transmit positioning signals, a user station that receives the positioning signals transmitted by the plurality of navigation satellites and measures the distances thereto, and a master station that generates correction information regarding the clock error and position error of the navigation satellites, wherein the user station corrects the positioning error using this correction information. The information processing apparatus is provided in the master station and generates correction information as the difference between the time and position calculated from the precise orbit ephemeris, which is accurate information on the clocks and orbits of the navigation satellites, and the time and position calculated from the broadcast orbit ephemeris, which is the information on the clocks and orbits of the navigation satellites themselves superimposed on the positioning signals, without using the measured values of the distances related to the navigation satellites.

[0025] The invention according to claim 3 is a satellite navigation system comprising a plurality of navigation satellites that transmit positioning signals, a user station that receives the positioning signals transmitted by the plurality of navigation satellites and measures the distances thereto, and a master station that generates correction information regarding the clock error and position error of the navigation satellites. The user station corrects the positioning error using this correction information. In the satellite navigation system, it operates in an information processing device provided in the master station, and without using the measured values of the distances regarding the navigation satellites, calculates the difference between the time and position calculated from the precise orbit ephemeris, which is accurate information on the clocks and orbits of the navigation satellites, and the time and position calculated from the broadcast orbit ephemeris, which is the information on its own clock and orbit that the navigation satellite transmits superimposed on the positioning signal, and generates correction information as the difference. It is a program for generating correction information in a satellite navigation system.

Advantages of the Invention

[0026] In the present invention, since the correction information of WADGPS is generated using the precise orbit ephemeris, WADGPS can be configured without using a reference station, so the system scale of WADGPS can be reduced. In addition, WADGPS can be configured without being restricted by the geographical location of the reference station.

Brief Description of the Drawings

[0027]

Figure 1

Figure 2

Figure 3

Figure 4

Best Mode for Carrying Out the Invention

[0028] Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.

Embodiment

[0029] An embodiment of this invention will be described in detail with reference to FIG. 1. FIG. 1 is a schematic diagram for explaining the generation and application of correction information in the satellite navigation system of this embodiment.

[0030] In FIG. 1, navigation satellites 1 (1a, 1b ···) each transmit a positioning signal.

[0031] A user receiver 3 inside the user station 2 receives the positioning signal transmitted by the navigation satellites 1 (1a, 1b ···) and measures the distance between the user station and the navigation satellites. At the same time, the user receiver 3 receives the broadcast ephemeris of the navigation satellites 1 (1a, 1b ···).

[0032] For the purpose of explanation by comparison with this embodiment, first, the case without using correction information will be described. In this case, the distance RR(i) and the positions RX(i), RY(i), RZ(i) of the navigation satellite i used by the user station 2 for calculation are obtained by the following equations. Here, MR(i) is the distance between the user station and the navigation satellite i measured by the user receiver 3, BC(i) is the time indicated by the clock of the navigation satellite i according to the broadcast ephemeris (based on the timing when the positioning signal should be transmitted. The same applies hereinafter), and BX(i), BY(i), BZ(i) are the positions of the navigation satellite i according to the broadcast ephemeris.

[0033] (Equation 1) RR(i)=MR(i)+BC(i) RX(i)=BX(i) RY(i)=BY(i) RZ(i)=BZ(i)

[0034] In this embodiment, the user station utilizes correction information. For this purpose, the master station 6 obtains the precise orbit ephemeris 4 and the broadcast orbit ephemeris 5, and creates correction information 7 as the difference between them. When the time indicated by the clock of the navigation satellite i according to the precise orbit ephemeris is PC(i), and the positions are PX(i), PY(i), and PZ(i), the correction value CC(i) regarding the time indicated by the clock of the navigation satellite and the correction values CX(i), CY(i), and CZ(i) regarding the position are obtained by the following equations. Note that BC(i) is the time indicated by the clock of the navigation satellite i according to the broadcast orbit ephemeris, and BX(i), BY(i), and BZ(i) are the positions of the navigation satellite i according to the broadcast orbit ephemeris, which are the same as those received by the user station.

[0035] (Equation 2) CC(i)=PC(i)-BC(i) CX(i)=PX(i)-BX(i) CY(i)=PY(i)-BY(i) CZ(i)=PZ(i)-BZ(i)

[0036] The user station 2 applies the correction information 7 to correct the satellite position and the distance measured by the user receiver, thereby obtaining the corrected satellite position and distance 8. Since the distance measured by the user receiver is MR(i), the distance RR'(i) used by the user station in the calculation and the positions RX'(i), RY'(i), and RZ'(i) of the navigation satellite i are obtained by the following equations.

[0037] (Equation 3) RR'(i)=MR(i)+BC(i)+CC(i) RX'(i)=BX(i)+CX(i) RY'(i)=BY(i)+CY(i) RZ'(i)=BZ(i)+CZ(i)

[0038] The user station calculates its position using the corrected satellite positions and distances 8, and outputs the calculation result as position information 9. At this time, since the corrected satellite positions and distances 8 are quantities as shown in the following formula due to the application of the correction information, the user station will use the time of the clock based on the precise orbit ephemeris and the satellite positions in the calculation process. That is, when compared with the description in paragraph

[0033] where no correction information is used, since BC(i), BX(i), BY(i), and BZ(i) are respectively replaced by PC(i), PX(i), PY(i), and PZ(i), it can be seen that the precise orbit ephemeris is used instead of the broadcast orbit ephemeris.

[0039] (Equation 4) RR'(i)=MR(i)+BC(i)+CC(i)=MR(i)+PC(i) RX'(i)=BX(i)+CX(i)=PX(i) RY'(i)=BY(i)+CY(i)=PY(i) RZ'(i)=BZ(i)+CZ(i)=PZ(i)

[0040] Next, the operation will be described based on FIGS. 1 to 4.

[0041] In FIG. 1, the distances from the navigation satellites 1 (1a, 1b ···) measured by the user receiver 3 to the user station 2 include the effects of the clock error and position error of the navigation satellites. Therefore, if the position of the user station is calculated using this distance without applying the correction information, it will appear as a positioning error.

[0042] The plot in FIG. 2 is the result of calculating the position of the station assuming it as the user station 2 without using the correction information, using the distance measurement data at the electronic reference point "Watariguchi" of the Geospatial Information Authority of Japan (Watariguchi-gun, Miyagi Prefecture, identification number 950179). Since the correction information is not used, it can be seen that a positioning error of about 2.33 meters (95% value of the horizontal positioning error) has occurred. The acquisition date and time of the measurement data used here is from 09:00 on August 7, 2022 to 09:00 on August 8, 2022 (Japan time).

[0043] In order to perform corrections using WADGPS, correction information was generated by the method of the present invention, that is, as the difference between the time and position calculated from the precise orbit ephemeris and the time and position calculated from the broadcast orbit ephemeris. The IGS precise orbit ephemeris is used for the generation of this correction information, and it targets all satellites of GPS and Galileo.

[0044] The plot in Figure 3 is the result of calculating the position of the station assuming it as user station 2 using the correction information generated by the method of the present invention with the same measurement data as in the case of Figure 2. By using the correction information, it can be seen that the positioning error is suppressed to about 0.93 meters (95% value of the horizontal positioning error).

[0045] The results of executing the same processing as the processing contents of Figures 2 and 3 for the electronic reference points "Wakkanai" (Wakkanai City, Hokkaido, identification number 940001), "Takayama" station (Takayama City, Gifu Prefecture, identification number 940058), "Koga" (Koga City, Fukuoka Prefecture, identification number 940087), and "Ishigaki 1" (Ishigaki City, Okinawa Prefecture, identification number 960749) are summarized in Table 1. From Table 1, since the correction information by WADGPS is applied in this embodiment, it can be confirmed that substantially the same positioning accuracy can be obtained in various places in Japan.

[0046]

Table 1

[0047] The graph in Fig. 4 shows the specific correction values for the first 120 minutes for the GPS satellite identified as PRN01. At the top of the figure, the clock of the navigation satellite is shown, and from the second to the fourth rows, the correction values for the X, Y, and Z coordinates of the navigation satellite are shown respectively (the clock is converted to distance by multiplying by the speed of light). All the correction values show smooth changes, which conforms to the physical properties of the changes in the clock and position of the navigation satellite. The discontinuous parts of the correction values are due to the influence of the switching of the broadcast ephemeris of the navigation satellite to be corrected, indicating that the correction information is being generated normally in accordance with the broadcast ephemeris in use (such switching is necessary because the broadcast ephemeris has a validity period).

[0048] As shown in Non-Patent Document 2, it may take time for the calculation process inside the master station to converge when generating correction values. However, in this embodiment, since the distance information measured for the navigation satellite is not used for generating the correction information, the correction values are generated without requiring time for convergence.

Industrial Applicability

[0049] By using the method for generating correction information, the information processing apparatus for generating correction information, and the program in the satellite navigation system of this invention, a WADGPS can be configured without using a reference station. Further, according to the present invention, correction information that is not restricted by the geographical location of the reference station can be generated, so a WADGPS that can be used anywhere in the world can be configured.

Explanation of Reference Numerals

[0050] 1 (1a, 1b ···) Navigation satellite 2 User station 3 User receiver 4 Precise ephemeris 5 Broadcast ephemeris 6 Master station 7 Correction information 8 Information on corrected satellite position and distance 9 Position output

Claims

1. A plurality of navigation satellites that transmit positioning signals, A user station having a user receiver that receives the positioning signals transmitted by the plurality of navigation satellites and measures the distances thereto, A master station that generates correction information regarding the clock error and position error of the navigation satellites, In a satellite navigation system in which the user station corrects the positioning error using the correction information, The master station, Without using the measured values of the distances related to the navigation satellites, Generating the correction information as the difference between the time and position calculated from the precise orbit ephemeris, which is accurate information on the clocks and orbits of the navigation satellites, and the time and position calculated from the broadcast orbit ephemeris, which is the information on the clocks and orbits of the navigation satellites themselves transmitted superimposed on the positioning signals A method for generating correction information in a satellite navigation system, characterized by the above.

2. A plurality of navigation satellites that transmit positioning signals, A user station having a user receiver that receives the positioning signals transmitted by the plurality of navigation satellites and measures the distances thereto, A master station that generates correction information regarding the clock error and position error of the navigation satellites, In a satellite navigation system in which the user station corrects the positioning error using the correction information, Provided in the master station, Without using the measured values of the distances related to the navigation satellites, Generating the correction information as the difference between the time and position calculated from the precise orbit ephemeris, which is accurate information on the clocks and orbits of the navigation satellites, and the time and position calculated from the broadcast orbit ephemeris, which is the information on the clocks and orbits of the navigation satellites themselves transmitted superimposed on the positioning signals An information processing apparatus for generating correction information in a satellite navigation system, characterized by the above.

3. A plurality of navigation satellites that transmit positioning signals, A user station having a user receiver that receives the positioning signals transmitted by the plurality of navigation satellites and measures the distances thereto, A master station that generates correction information regarding the clock error and position error of the navigation satellites, In a satellite navigation system in which the user station corrects the positioning error using the correction information, Operating in the information processing apparatus provided in the master station, Without using the measured values of the distances related to the navigation satellites, Generating the correction information as the difference between the time and position calculated from the precise orbit ephemeris, which is accurate information on the clocks and orbits of the navigation satellites, and the time and position calculated from the broadcast orbit ephemeris, which is the information on the clocks and orbits of the navigation satellites themselves transmitted superimposed on the positioning signals A program for generating correction information in a satellite navigation system, characterized by

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