Comparison test method for causes of positioning errors in satellite navigation systems

Abstract

To conduct a comparison test on the causes of positioning errors in satellite navigation systems.SOLUTION: A program that performs comparative testing of the causes of positioning errors for satellite navigation systems including the GPS system of the United States and the Quasi-Zenith Satellite System of Japan includes the steps for calculating the position of a user station after adding a known error that assumes a specific error factor for the distance between the user station or a reference station and a plurality of navigation satellites that should be obtained by measurement, comparing this result with the position of the user station calculated without the known error being added, and evaluating the effect of the specific error factor on the calculation of the position of the user station from this difference to perform a comparative test of the causes of positioning errors.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a comparative test method for the causes of positioning errors in a satellite navigation system. [Background technology]

[0002] Satellite navigation systems that use artificial satellites to measure position are collectively known as GNSS (Global Navigation Satellite System), and a representative example is the United States' Global Positioning System (GPS). GNSS generally uses a receiver to receive positioning signals transmitted by artificial satellites called navigation satellites, and measures the distance between the navigation satellite and the receiver to calculate the position of the receiver. The receiver that determines the position is called the user receiver or user station. The error between the determined position and the true position is called the positioning error.

[0003] To calculate the receiver's position, it is necessary to know the position of the navigation satellite that is transmitting the positioning signal, and the orbital information required for this is transmitted by the navigation satellite itself by superimposing it on the positioning signal. Since the orbital information is created by prediction, it contains an error of about several meters, which becomes a factor in positioning errors when calculating the receiver's position.

[0004] Before reaching the ground, a positioning signal passes through the ionosphere and troposphere in the sky, and delays occur when the radio signal passes through each of these regions. These delays are called the ionospheric propagation delay and the troposphere propagation delay, respectively. Therefore, when this radio signal is used as a positioning signal, these ionospheric propagation delay and troposphere propagation delay become a cause of positioning errors. The magnitude of the ionospheric propagation delay and the troposphere propagation delay converted into distance are called the ionospheric propagation delay and the troposphere delay, respectively.

[0005] On the other hand, by installing a receiver at a fixed reference station on the ground and using the distance measured by this to create correction information for distance measurement errors caused by ionospheric propagation delays, tropospheric propagation delays, etc., and providing this information to users, the distance measured at the user station is corrected based on the correction information, improving the position measurement accuracy (called "positioning accuracy") at the user station. This method is called Differential GPS (hereinafter referred to as "DGPS").

[0006] Examples of practical use of DGPS include medium-frequency beacons for ships and FM multiplex digital broadcasting, but both have now been discontinued. Meanwhile, Japan's Quasi-Zenith Satellite System, which began operation in 2018, transmits DGPS correction information from satellites as SLAS (Submeter-Level Augmentation Service), CLAS (Centimeter-Level Augmentation Service), and SBAS (Satellite-Based Augmentation System). [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Takeyasu Sakai, "Bias Error Estimation Method for GPS Ionospheric Total Electron Content Observation," IEICE Transactions on Information and Communications Technology, Vol. J88-B, No. 12, pp. 2382-2389, December 2005 [Non-Patent Document 2] Geospatial Information Authority of Japan, "Development of Satellite Positioning Simulator (Software)", 7th Committee Material on Development of High-Precision Positioning Technology Using Multi-GNSS, June 2013 Summary of the Invention [Problem to be solved by the invention]

[0008] In GNSS, in addition to the errors contained in the orbit information, there are other error factors such as ionospheric propagation delay and tropospheric propagation delay, and the effects of these appear as positioning errors when calculating the position of a user station.

[0009] In general, the ionospheric propagation delay has the greatest effect on the positioning error at user stations. The error in the orbit information is usually within a few meters, and the tropospheric propagation delay can be removed with sufficient accuracy by calculation using a model formula.

[0010] The amount of ionospheric propagation delay can reach several tens of meters, especially for navigation satellites with low elevation angles, and since it is a natural phenomenon, it is difficult to eliminate it through predictive calculations. Ionospheric activity is affected by solar activity, which repeats in an 11-year cycle, and the effects of ionospheric propagation delay have become apparent during the recent solar maximum.

[0011] When a GNSS positioning signal passes through the ionosphere, the magnitude of the effect changes depending on the elevation angle of the navigation satellite, even if the position through the ionosphere is the same. In other words, the length of time that a navigation satellite with a high elevation angle passes through the ionosphere is short, while that of a navigation satellite with a low elevation angle is long. In order to incorporate this effect into position calculations, the amount of ionospheric propagation delay is generally expressed as the amount of vertical delay, and the effect of the elevation angle is expressed by the tilt coefficient. The amount of ionospheric propagation delay in the vertical direction is multiplied by the tilt coefficient corresponding to the elevation angle of the navigation satellite to obtain the amount of ionospheric propagation delay that is actually observed. The specific value of the tilt coefficient is 1 in the zenith direction (elevation angle of 90 degrees) and about 3 at an elevation angle of 5 degrees.

[0012] However, since the distance to the navigation satellite measured by the user station is the sum of the effects of all error factors, it is difficult to extract and evaluate the effect of a specific error factor or the amount of ionospheric propagation delay. As shown in Non-Patent Document 1, there is a known technology for estimating the amount of ionospheric propagation delay, but it is necessary to install many reference stations on the ground and aggregate the measurement data to perform calculations, which requires a large cost.

[0013] In order to estimate the effect of the ionospheric propagation delay contained in the positioning error under such conditions, it is considered effective to add a known error assuming the ionospheric propagation delay to the distance to the navigation satellite measured by the user station and to conduct a comparison test with the case where the known error is not added. Note that such a comparison test can be applied not only to the ionospheric propagation delay but also to other error factors.

[0014] The above comparison test may be performed by calculating the distance between the user station and the navigation satellite that the user station should measure using the previously known position of the user station and the orbital information of the navigation satellite, without using the distance actually measured by the user station. In this way, it becomes possible to perform the above comparison test without actually installing a user station.

[0015] Non-Patent Document 2 describes software that calculates the distance between a user station and a navigation satellite by using the previously known position of the user station and the orbital information of the navigation satellite. However, this software calculates the distance that the user station should measure and obtain, and adds noise according to a statistical error model, but does not attempt to perform a comparison test by adding a known error that assumes a specific error factor.

[0016] Devices that generate signals simulating the positioning signals transmitted by GPS are commercially available, and these devices calculate the distance between the user station using the known position of the user station and the orbital information of the navigation satellite, and then generate an appropriate signal. However, these devices calculate the distance that the user station should obtain by measuring it, and add noise according to a statistical error model, but they do not attempt to perform comparative tests by adding known errors that assume specific error factors.

[0017] In the field of satellite navigation, various programs that calculate position are known, but there are no programs that have the function to add known errors that assume specific error factors to the distance data given as input. Therefore, there is no way to actually carry out the above comparison test. [Means for solving the problem]

[0018] Claim 1 The present invention assumes a satellite navigation system that includes multiple navigation satellites that transmit positioning signals and a user station that receives the positioning signals transmitted by the multiple navigation satellites and measures the distances between them, In a program to compare causes of positioning errors in satellite navigation systems, This is a comparative test method for the causes of positioning errors in a satellite navigation system, characterized in that the distance between a user station and multiple navigation satellites to be measured is calculated using the user station's previously known position and the orbital information of multiple navigation satellites, a known error assuming a specific error factor is added to this calculated distance, and the position of the user station is calculated after that, this result is compared with the position of the user station calculated without adding the known error, and the effect of the specific error factor on the calculation of the user station position is evaluated from the difference.

[0019] Claim 2 The invention relates to a satellite navigation system that includes 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 between them, and a reference station that receives the positioning signals transmitted by the plurality of navigation satellites using a receiver fixed on the ground and measures the distances between them, and provides the results of subtracting the distances between the corresponding navigation satellites from the actual distances calculated from the orbital information of each of the plurality of navigation satellites as correction information to the user station, In a program to compare causes of positioning errors in satellite navigation systems,This is a comparative test method for the causes of positioning errors in a satellite navigation system, which is characterized by calculating the distance between multiple navigation satellites to be measured by the reference station using the previously known position of the receiving station and the orbital information of multiple navigation satellites, adding a known error assuming a specific error factor to the calculated distance, obtaining correction information, applying this correction information and calculating the position of the user station, comparing this result with the position of the user station calculated by applying the correction information obtained without adding the known error, and evaluating the impact of the specific error factor on the calculation of the user station position from the difference.

[0020] Claim 3 The invention relates to: Claim 1 or claim 2 In the invention described above, a known error that assumes a specific error factor is added to the distance between a user station or reference station and a navigation satellite, and in this case, the known error specifically assumes the amount of ionospheric propagation delay. Effect of the Invention

[0021] Claim 1 Since the invention is configured as described above, a comparison is made between the distance between the navigation satellite that the user station should measure and the distance when a known error assuming a specific error factor is added and when it is not added, thereby making it possible to directly evaluate the impact of the error factor.

[0022] Claim 2 Since the invention is configured as described above, a comparison is made between the distance between the navigation satellite to be measured by the reference station and the reference station when a known error assuming a specific error factor is added and when it is not added, thereby making it possible to directly evaluate the impact of the error factor.

[0023] Claim 3 The invention is configured as described above, Claim 1 or claim 2 The present invention has the same effect as the invention described in 2. Furthermore, since the amount of ionospheric propagation delay is estimated for a known error assuming a specific error factor, the influence of the amount of ionospheric propagation delay can be directly evaluated. [Brief description of the drawings]

[0024] [Figure 1] 1 is a schematic diagram illustrating an embodiment of the present invention, for explaining a comparative test method for determining causes of positioning errors in a satellite navigation system according to the present invention. [Diagram 2] This figure is for explaining the effect of the invention in an embodiment of the invention, and shows the positioning error when a known error assuming a specific error factor is added and when it is not added to the calculated distance that the receiving station should measure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings. EXAMPLES

[0026] This invention Working Example of, Figure 1 This will be explained in detail based on the above.

[0027] Figure 1 1 is a schematic diagram for explaining a comparative test method for the causes of positioning errors in the satellite navigation system of this embodiment.

[0028] Figure 1 In Navigation satellite 1 (1a, 1b...) It is assumed that each transmits a positioning signal.

[0029] Figure 1 In User station 2 teeth, Navigation satellite 1 (1a, 1b...) It is assumed that the system receives positioning signals transmitted by a navigation satellite and measures the distance from each reference station to the navigation satellite.

[0030] Figure 1 In 3 shows a schematic representation of the distribution of ionospheric propagation delay. Figure 1In the figure, the ionospheric propagation delay is small on the left side and large on the right side, but this is an example and does not necessarily indicate that the ionospheric propagation delay will necessarily show this type of distribution.

[0031] Figure 1 of 4 teeth, User station 2 The length of the arrow indicates the distance to the navigation satellite that should be measured. 4 In the case where there is no ionospheric propagation delay, the positioning error is small because the only cause of the positioning error is the error in the orbit information. In other words, the distance to the navigation satellite that the user station should measure can be calculated from the orbit information of the user station and the navigation satellite, which are known in advance, so it can be the distance that should be measured in the absence of ionospheric propagation delay.

[0032] on the other hand, 5 is an example in which a known error is added assuming ionospheric propagation delay, resulting in a large positioning error. User station 2 The distance to the navigation satellite that should be measured is calculated as a known (positive) error due to the assumed ionospheric propagation delay. 6 By adding the length shown in (a), the ionospheric propagation delay exists. By actually trying this, it is possible to understand the nature of the positioning error components caused by the ionospheric propagation delay.

[0033] Next, regarding the action Figures 1 and 2 The explanation will be based on the above.

[0034] User station 2 receives the positioning signal transmitted by the navigation satellite, Navigation satellite 1 (1a, 1b...) It is assumed that the distance from the satellite to the user station is measured. The distance to be measured can be made to exclude all of the errors contained in the orbit information, the tropospheric propagation delay, and the ionospheric propagation delay. Therefore, if the position of the user station is calculated using the distance to be measured, there will be no positioning error.

[0035] Figure 2The symbol ■ is based on the assumption that the Geospatial Information Authority of Japan's electronic reference point "Ishigaki 2" station is located, and the distance that the station should obtain by measuring is calculated. User station 2 The results show that no positioning errors occurred. The date and time for calculating the distance was 13:30-14:30 on January 17, 2021 (Japan time), during the daytime when ionospheric propagation delay is generally large.

[0036] In contrast, for a GPS satellite (PRN10 satellite) located in a southern direction, 10 meters are added as a known error to the Z-axis (northern direction parallel to the Earth's rotation axis) component of the satellite position calculated from the orbital information, and the result of similarly calculating the position is shown as the symbol + in the figure. Since a positioning error of about 0.7 to 1.8 meters occurs in the northward direction, and no other error factors are added, it can be confirmed that this is definitely the effect of errors contained in the orbital information of the navigation satellite.

[0037] On the other hand, for the same GPS satellite (PRN10 satellite), the position was calculated in the same way after adding 8 meters to the distance to the user station, assuming ionospheric propagation delay as a known error, and the result is shown by the symbol × in the figure (no error was added to the satellite position). Since a large positioning error of more than 1.8 meters occurs in the north direction, this can be said to be the effect of ionospheric propagation delay under the conditions in question. Note that 8 meters here means the vertical ionospheric propagation delay, and in order to make the ionospheric propagation delay a known error assuming a known error, it is necessary to multiply it by a tilt coefficient of

[0011] according to the elevation angle of the satellite. In addition, the reason why a GPS satellite located in the south was selected is because a phenomenon called equatorial anomaly, which occurs in the area south of Ishigaki Island, is known to cause a large ionospheric propagation delay. [Industrial Applicability]

[0038] The comparative test method for the causes of positioning errors in a satellite navigation system of this invention can be used to analyze the causes of positioning errors. The distance to a navigation satellite measured by a user station is the sum of the effects of all error factors, making it difficult to isolate and evaluate a specific error factor, but the test method of the present invention makes it possible to evaluate the influence of a specific error factor, which is useful for analyzing the causes of positioning errors. Furthermore, the test method of the present invention makes it possible to test for a phenomenon that rarely occurs, even if the phenomenon does not occur, and this can be used to evaluate the influence of the phenomenon on positioning errors. [Explanation of symbols]

[0039] 1(1a,1b...) Navigation satellite 2 User Station 3 Distribution of ionospheric propagation delay 4 Distance that the user station should measure (not including ionospheric propagation delay) 5 The distance obtained by adding a known error to the distance that the user station should measure. 6 Ionospheric propagation delay to be added as a known error

Claims

1. A plurality of navigation satellites transmitting positioning signals; In a satellite navigation system including a user station that receives positioning signals transmitted from the plurality of navigation satellites and measures the distances therebetween, calculating a position of the user station after adding a known error to the distances between the user station and the navigation satellites measured by the user station, and comparing the result with the position of the user station calculated without adding the known error or with a previously known position of the user station; A method for testing a positioning error in a satellite navigation system, comprising:

2. A plurality of navigation satellites transmitting positioning signals; a user station that receives positioning signals transmitted from the plurality of navigation satellites and measures the distances therebetween; In a satellite navigation system having a reference station, a receiver fixed on the ground receives positioning signals transmitted from the plurality of navigation satellites, measures the distances between them, subtracts the measured distances for each of the navigation satellites from the actual distances calculated from the orbital information of each of the plurality of navigation satellites, and provides the results to the user station as correction information, A known error is added to the distance between the reference station and the navigation satellites measured by the reference station, and the correction information is obtained. applying the correction information to calculate the position of the user station and comparing the result with the position of the user station calculated without adding the known error or with a previously known position of the user station. A method for testing a positioning error in a satellite navigation system, comprising:

3. Regarding the known errors, the components that are assumed to be ionospheric propagation delays in particular shall be considered.

3. A method for testing a positioning error in a satellite navigation system according to claim 1 or 2.

4. A plurality of navigation satellites transmitting positioning signals; Assuming a satellite navigation system including a user station that receives positioning signals transmitted from the plurality of navigation satellites and measures the distances therebetween, calculating distances between the user station and the plurality of navigation satellites to be measured by the user station using a previously known position of the user station and orbital information of the plurality of navigation satellites; adding a known error to the calculated distance and then calculating the position of the user station, and comparing the result with the position of the user station calculated without adding the known error or with a previously known position of the user station. A method for testing a positioning error in a satellite navigation system, comprising:

5. A plurality of navigation satellites transmitting positioning signals; a user station that receives positioning signals transmitted from the plurality of navigation satellites and measures the distances therebetween; Assuming a satellite navigation system having a reference station that receives positioning signals transmitted by the plurality of navigation satellites using a receiver fixed on the ground, measures the distances between them, subtracts the distances from the corresponding distances calculated from the orbital information of each of the plurality of navigation satellites, and provides the result to the user station as correction information, The distance between the reference station and the plurality of navigation satellites is calculated using the previously known position of the receiving station and orbital information of the plurality of navigation satellites; A known error is added to the distance calculated by this calculation, and the correction information is obtained. applying the correction information to calculate the position of the user station and comparing the result with the position of the user station calculated without adding the known error or with a previously known position of the user station. A method for testing a positioning error in a satellite navigation system, comprising:

6. Regarding the known errors, the components that are assumed to be ionospheric propagation delays in particular shall be considered.

6. A method for testing a positioning error in a satellite navigation system according to claim 4 or 5.

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