Method for generating correction information in satellite navigation systems

Abstract

In differential GPS, it generates correction information that matches the nominal position of the base station. [Solution] In a satellite positioning system using a differential GPS method, which includes a user station and a reference station, the user station is provided with the nominal reference station position for the reference station. A new correction value is created by adding the tropospheric propagation delay at the reference station's precise position to the correction value generated by the reference station for each navigation satellite, and subtracting the tropospheric propagation delay at the reference station's nominal position. This new correction value, which conforms to the nominal position of the reference station, is provided to the user station as correction information for multiple navigation satellites, thereby eliminating the influence of the difference between the reference station's precise position and its nominal position on positioning calculations.

Description

Technical Field

[0001] This invention relates to a method for generating correction information in a satellite navigation system.

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. In general, GNSS receives positioning signals transmitted by artificial satellites called navigation satellites by a receiver, measures the distance between the navigation satellite and the receiver, and obtains the position of the receiver by 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.

[0003] Generally, a radio signal (including a positioning signal) transmitted by an artificial satellite passes through the ionosphere and the troposphere before reaching the ground, and a delay occurs when the radio signal passes through each region. These delays are respectively called ionospheric propagation delay and tropospheric propagation delay. Therefore, when this radio signal is used as a positioning signal, these ionospheric propagation delay and tropospheric propagation delay are factors of the positioning error. The magnitudes of the ionospheric propagation delay and tropospheric propagation delay converted into distances are respectively called ionospheric propagation delay amount and tropospheric delay amount.

[0004] In response to this, a receiver is installed at a fixed reference station on the ground. From the distance measured by this receiver, correction information is created to compensate for distance measurement errors caused by ionospheric propagation delay and tropospheric propagation delay. This information is then provided to the user, thereby correcting the distance measured at the user station based on the correction information and improving the accuracy of the user station's position measurement (referred to as "positioning accuracy"). This method is called Differential GPS (DGPS). The correction information provided to the user station in DGPS includes distance correction values ​​for each of the multiple navigation satellites.

[0005] In DGPS, correction information is created from the distance measurement error at the base station's location. Therefore, it is known that the improvement in positioning accuracy due to this correction information is high near the base station, but decreases as the distance from the base station increases. For this reason, when using DGPS at a user station, it is common to use it within a limited range from the base station, or, if multiple base stations are available, to select and use the nearest base station.

[0006] Practical applications of DGPS included medium-wave beacons for ships and FM multiplex digital broadcasting, but both have now been discontinued. On the other hand, Japan's Quasi-Zenith Satellite System, which began operation in 2018, transmits DGPS correction information from satellites as SLAS (Submeter-Level Augmentation Service). The SLAS service has the characteristic of allowing users to obtain correction information from 13 reference stations located throughout Japan all at once by receiving a signal from a single satellite. User receivers using the SLAS service are supposed to select and use the correction information from the nearest reference station.

[0007] In addition to the individual reference station method described above, there is also a method called wide-area differential GPS that integrates measurement data from numerous reference stations to create wide-area correction information that is effective over a wide geographical area. As wide-area differential GPS services such as Japan's MSAS and the US's WAAS have become widespread, currently, DGPS that provides correction information from multiple reference stations does not exist except for the SLAS service of the Quasi-Zenith Satellite System. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 7326650 [Non-patent literature]

[0009] [Non-Patent Document 1] "Measurements and Error Factors Using GPS" by Nobuaki Kubo, https: / / www.denshi.e.kaiyodai.ac.jp / wp-content / uploads / pdf / content / 201004.pdf [Overview of the project] [Problems that the invention aims to solve]

[0010] In DGPS, the effectiveness of correction information generally decreases as you move away from the base station. Therefore, when using DGPS at a user station, it is common practice to use it within a limited range from the base station, or, if multiple base stations are available, to select and use the nearest base station.

[0011] For example, the SLAS service of the Quasi-Zenith Satellite System provides correction information from 13 reference stations located throughout Japan, and user stations are expected to select and use the nearest reference station. In order to select the nearest reference station from multiple reference stations, the location information of each of those reference stations is required. For this reason, the SLAS service transmits the location information of the reference stations along with the correction information.

[0012] Furthermore, the SLAS service specifications predefine the locations of 13 reference stations, ensuring that the SLAS service can be used even before receiving location information from the reference stations. The locations of the reference stations transmitted in conjunction with this correction information, as well as the locations of the reference stations defined in the DGPS service specifications, are referred to as the nominal locations of the reference stations.

[0013] The nominal location information of a reference station, used to select the nearest reference station from multiple reference stations, does not necessarily need to be highly accurate. For example, in the SLAS service, the location information of a reference station is transmitted with a resolution of 0.005 degrees for latitude and 50 meters for altitude. Therefore, in this example, the difference between the accurate location and the nominal location of the reference station is within 0.0025 degrees for latitude and 25 meters for altitude.

[0014] On the other hand, it is practically possible to temporarily or permanently change the location of base station equipment (especially the receiving antenna) when performing construction work on the base station equipment, during disasters, or for any other reason. In such cases, it is conceivable to change the nominal location of the base station in accordance with the change in its exact location.

[0015] However, in the case of the SLAS service, for example, the location of the reference station is predetermined in the SLAS service specification. Therefore, even if the nominal location, which has been modified to match the actual location of the reference station, is transmitted to the user station, there is a possibility that a larger-than-expected difference may occur between the accurate location of the reference station used by the user station and the nominal location of that reference station until the user station receives the reference station location information. Furthermore, some user receivers may be designed to exclusively use the reference station location defined in the SLAS service specification, rather than using the reference station location transmitted in accordance with the correction information.

[0016] We consider how much the difference between the precise location of the reference station used by the user station and the nominal location of the reference station actually affects the correction value. Generally, as described in Non-Patent Document 1 (page 46), it is known that in positioning calculations for DGPS user stations, care must be taken when handling tropospheric propagation delay when there is an altitude difference between the user station and the reference station. This is because the amount of tropospheric propagation delay is a function of the receiver's altitude (elevation). If there is no altitude difference, the amount of tropospheric propagation delay at the user station and the reference station for a given navigation satellite can be considered to be approximately equal, allowing the differential correction by the reference station to work appropriately and correct the user station's distance measurement error. However, if there is an altitude difference, the amount of tropospheric propagation delay at the user station and the reference station are different, so a simple correction cannot remove the component caused by the altitude difference.

[0017] Figure 3 shows the relationship between the altitude of the receiving station and the tropospheric propagation delay. Assuming that the navigation satellite is located to the east of the receiver, the relationship between the altitude of the receiving station and the tropospheric propagation delay is plotted for elevation angles of 5 degrees, 7.5 degrees, and 10 degrees. The difference in delay increases as the elevation angle of the navigation satellite decreases, and for a navigation satellite at an elevation angle of 5 degrees, the delay difference reaches about 7 centimeters with an altitude difference of 25 meters. In other words, for example, when there is an altitude difference of 25 meters between the accurate position of the reference station and the nominal position, the correction value generated by the reference station will have a deviation of up to about 7 centimeters compared to when the reference station is located at the nominal position.

[0018] The effect of the difference in horizontal position between the DGPS reference station and the user station is not as significant as the difference in tropospheric propagation delay due to altitude differences. However, when the difference between the accurate position and the nominal position of the reference station becomes large, a significant effect emerges, as shown in Figure 4.

[0019] Figure 4 shows the relationship between the longitude of the receiving station and the tropospheric propagation delay. Assuming a navigation satellite is located east of the receiver, the relationship between the receiving station's longitude (relative to 140 degrees east longitude) and the tropospheric propagation delay is plotted for elevation angles of 5 degrees, 7.5 degrees, and 10 degrees. The difference in delay increases as the elevation angle of the navigation satellite decreases, and for a navigation satellite at an elevation angle of 5 degrees, a difference in longitude of 0.1 degrees (corresponding to a distance of about 10 kilometers near Japan) results in a delay difference of 30 centimeters or more. In other words, for example, when there is a difference of 0.1 degrees in longitude between the accurate position of the reference station and its nominal position, the correction value generated by the reference station will have a deviation of up to 30 centimeters or more compared to when the reference station is located at its nominal position.

[0020] In general, in DGPS, for each navigation satellite from which the base station receives a positioning signal, a correction value is generated by subtracting the distance that the base station actually measured (at its precise location) between itself and the navigation satellite from the distance that should have been measured, calculated from the precise location of the base station. By applying this generated correction value at the user station, the user station applies a correction value corresponding to the precise location of the base station, and the location of the base station does not explicitly appear in the normal DGPS calculation process.

[0021] Therefore, in DGPS, it is not uncommon for the position of the reference station not to be given to the user station. Even when the position of the reference station is given to the user station, as can be seen from the resolution of the nominal position of the reference station set in, for example, the SLAS service, an accurate position is not always given. That is, in DGPS, the position of the reference station is used only as a guideline indicating the geographical range of the user station that can be corrected with sufficient performance. Therefore, information regarding the position of the reference station is considered not to be important. The difference between the accurate position and the nominal position of the DGPS reference station was not considered to affect the correction performance of DGPS either. Since the position of the reference station is not explicitly shown in the normal DGPS calculation process at the user station, the existence of such a difference was not even recognized in the first place.

[0022] However, as described above, due to the difference between the accurate position and the nominal position of the DGPS reference station, the correction value actually generated by the reference station may cause a non-negligible difference compared to the case where the reference station is installed at the nominal position. The problem of the present invention is to generate correction information that conforms to the nominal position of the reference station in DGPS and remove the influence on the positioning calculation due to the difference between the accurate position and the nominal position of the DGPS reference station.

[0023] The problem of the present invention will be described using mathematical formulas. Let Pt be the accurate position of the reference station, M(Pt) be the distance information between the reference station and a plurality of navigation satellites measured at the reference station, C(Pt) be the correction information generated based on Pt and M(Pt), and the DGPS positioning calculation that applies the correction information C to the measurement data M be expressed as the function f(M|C). Ignoring the influence of noise, these relationships can be written as follows. That is, by the DGPS positioning calculation that applies the correction information C(Pt), the correct position Pt can be obtained based on the measurement data M(Pt).

[0024]

Equation

[0025] Since the nominal position Pn of the reference station is different from the accurate position Pt, the result of the positioning calculation by DGPS at the nominal position Pn is affected by the difference between Pt and Pn, and generally does not become Pn as long as the correction information C(Pt) is applied. This relationship is expressed as follows.

[0026] [Number]

[0027] The problem of the present invention is to generate correction information C(Pn) that conforms to the nominal position Pn of the reference station so that the correct nominal position Pn can be obtained as the result of the DGPS positioning calculation at the nominal position Pn. That is, it is to generate correction information C(Pn) that obtains the following relationship.

[0028] [Number]

[0029] Note that in DGPS, it is known that if Pe is set as the position of the reference station instead of Pt, Pe is obtained instead of Pt as the result of the DGPS positioning calculation. Based on the measurement data M(Pt) at the reference station, if the correction information generated with the position of the reference station as Pe is expressed as C(Pt→Pe), this relationship is as follows, and even when Pe = Pn, the relationship of [Equation 3] still cannot be obtained.

[0030] [Number] [Means for Solving the Problem]

[0031] The correction values ​​generated by the reference station are based on measurements of the distance to each navigation satellite at the reference station's precise location. Since this measured distance includes tropospheric propagation delay, the generated correction values ​​include a component that cancels out this delay. This tropospheric propagation delay corresponds to the reference station's precise location.

[0032] To achieve the objectives of the present invention, it is sufficient to replace the tropospheric propagation delay amount corresponding to the precise position of the reference station, which is included in the correction value generated by the reference station, with the tropospheric propagation delay amount corresponding to the nominal position of the reference station. As for error factors other than tropospheric propagation delay in satellite navigation systems, the impact of the difference between the precise position and the nominal position of the DGPS reference station on positioning calculations is not significant, so the objectives of the present invention can be solved by handling tropospheric propagation delay.

[0033] Various formulas are known for obtaining the tropospheric propagation delay, but one example of the simplest formula is as follows. Here, a tropospheric propagation delay T(i,x) is generated when a positioning signal transmitted by satellite i is received by a receiver at position x, EL(i,x) is the elevation angle of satellite i at that time, and H(x) is the altitude of position x. The units of T(i,x) and H(x) are meters.

[0034]

number

[0035] The correction value C(i,Pt) generated by the DGPS reference station for navigation satellite i has a component that cancels out the tropospheric propagation delay T(i,Pt) which corresponds to the reference station's precise position Pt. Therefore, to replace this with the tropospheric propagation delay T(i,Pn) which corresponds to the reference station's nominal position Pn, a new correction value C(i,Pn) can be generated as shown in the following equation.

[0036]

number

[0037] By providing the user station with this new correction value C(i,Pn), obtained by correcting the correction value C(i,Pt), the user station can obtain a correction value corresponding to the nominal position of the reference station, thus eliminating the influence of the difference between the accurate position and the nominal position of the DGPS reference station on positioning calculations. The tropospheric propagation delay can be obtained by the calculation formula in [Equation 5] as an example, but the calculation process can be performed in exactly the same way even if a different calculation formula is used.

[0038] If there are multiple reference stations, a new correction value can be obtained for the nominal position representing the group of reference stations from the correction values ​​generated by each of those reference stations. Specifically, the corresponding tropospheric propagation delay is added to the correction value of each of the multiple reference stations, the average of the results is calculated, and the tropospheric propagation delay corresponding to the nominal position representing the group of reference stations is subtracted from this to generate a new correction value, which is then provided to the user station. This method eliminates the influence on positioning calculations due to the difference between the accurate position and the nominal position of the DGPS reference station group.

[0039] Patent Document 1 describes a method for generating correction information in a differential GPS that uses the average of correction values ​​generated by multiple reference stations. In this method, in order to generate correction information that is valid at the user station's location, the tropospheric propagation delay is treated similarly to

[0038] , and the average of correction values ​​generated by multiple reference stations is used. Since this method generates correction information that is valid at the user station's location, it can only be executed by the user station.

[0040] In this calculation process, the position of the reference station is explicitly used, and it is necessary to use the precise position of the reference station. This is because, as explained in

[0016] to

[0019] , if the nominal position of the reference station is used, a discrepancy in the correction value will occur due to the difference between the precise position and the nominal position of the reference station. However, since the position of the reference station is not necessary in general DGPS calculation processing, the precise position of the reference station is generally not provided to the user station. In some cases, such as with the SLAS service, the nominal position of the reference station is provided to the user station, but even in such cases, the resolution is kept coarse, and it is a common understanding among those skilled in the art that the position of the reference station is not important.

[0041] However, if the nominal position of the reference station is provided to the user station, then by applying the method of the present invention and configuring the system to provide the user station with new correction information that has been modified to conform to the nominal position of the reference station, even when applying the method of Patent Document 1, the user station can perform appropriate correction processing by using the nominal position of each reference station. In this case, it is not necessary to provide the user station with the exact position of each reference station.

[0042] 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 distance between them; a reference station that receives the positioning signals transmitted by each of the navigation satellites using a receiver fixed on the ground and measures the distance between them; and a correction station that generates correction values ​​corresponding to each of the navigation satellites from the distance information measured by the reference station and provides these to the user station as correction information for the plurality of navigation satellites, wherein the user station is provided with the nominal reference station position of the reference station, wherein the correction station calculates for each of the navigation satellites the originally measured value calculated from the accurate position of the reference station. This is a method for generating correction information in a satellite navigation system, characterized by: generating a correction value corresponding to the reference station by subtracting the distance measured by the reference station from the distance; calculating the tropospheric propagation delay at the precise location of the reference station and adding the tropospheric propagation delay obtained by this calculation to the correction value to obtain a correction value that does not include the tropospheric propagation delay component at the reference station; calculating the tropospheric propagation delay at the nominal reference station location and subtracting the tropospheric propagation delay obtained by this calculation from the correction value that does not include the tropospheric propagation delay component to generate a new correction value; and providing this new correction value to the user station as correction information for the multiple navigation satellites.

[0043] The invention according to claim 2 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 distance between them; a plurality of reference stations that receive the positioning signals transmitted by each of the navigation satellites using a receiver fixed on the ground and measure the distance between them; and a correction station that generates correction values ​​corresponding to each of the navigation satellites from the distance information measured by the plurality of reference stations and provides these to the user station as correction information for the plurality of navigation satellites, wherein the user station is provided with a nominal reference station position representing the plurality of reference stations, wherein the correction station calculates for each of the navigation satellites the distance that should originally be measured from the precise position of each of the reference stations This is a method for generating correction information in a satellite navigation system, characterized by: generating a correction value corresponding to each of the reference stations by subtracting the distance measured by each of the reference stations from the distance; calculating the tropospheric propagation delay at the precise position of each of the reference stations; adding the tropospheric propagation delay obtained by this calculation to the correction value to obtain a correction value that does not include the tropospheric propagation delay component at each of the reference stations; calculating the average of these for the multiple reference stations; calculating the tropospheric propagation delay at the nominal reference station position; subtracting the tropospheric propagation delay obtained by this calculation from the average to generate a new correction value; and providing this new correction value to the user station as correction information for the multiple navigation satellites.

[0044] The invention according to claim 3 is a method for generating correction information in a satellite navigation system according to claim 2, characterized in that the correction station calculates the average, and in doing so, a weighted average is used in which each of the reference stations is weighted based on its relative positional relationship with the nominal reference station position.

[0045] The invention according to claim 4 is a method for generating correction information in a satellite navigation system according to claim 3, characterized in that the correction station calculates the weighted average, and in doing so, uses a weight for each of the reference stations that is proportional to the reciprocal of the distance between the reference station and the nominal reference station position.

[0046] The invention according to claim 5 is a method for generating correction information in a satellite navigation system according to claim 3, characterized in that the correction station calculates the weighted average, and in doing so, for each of the reference stations, weights determined by the least squares method using the coordinate values ​​of the reference station are used, under the assumption that the object for which the weighted average is calculated is linear with respect to the coordinate values. [Effects of the Invention]

[0047] The invention according to claim 1 is configured as described above, so that correction information that matches the nominal position of the base station can be generated in DGPS, thereby eliminating the influence on positioning calculations due to the difference between the accurate position and the nominal position of the DGPS base station.

[0048] The inventions according to claims 2 to 5 are configured as described above, so that when there are multiple DGPS reference stations, correction information that matches the nominal position representing the group of reference stations can be generated from the correction values ​​generated by each of those reference stations, thereby eliminating the influence on positioning calculations due to the difference between the accurate position and the nominal position of the group of DGPS reference stations. [Brief explanation of the drawing]

[0049] [Figure 1] This diagram illustrates an embodiment of the present invention and is a schematic diagram illustrating a method for generating correction information in a satellite navigation system according to claim 1 of the present invention. [Figure 2] This diagram illustrates an embodiment of the present invention and is a schematic diagram illustrating a method for generating correction information in a satellite navigation system according to claims 2 to 5 of the present invention. [Figure 3] This diagram illustrates the effects of the invention in an embodiment of this invention, showing the relationship between the altitude of the receiving station and the tropospheric propagation delay when a navigation satellite is located in the east direction. [Figure 4] This diagram illustrates the effects of the invention in an embodiment of this invention, showing the relationship between the longitude of the receiving station and the tropospheric propagation delay when a navigation satellite is located in the east direction. [Modes for carrying out the invention]

[0050] Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. [Examples]

[0051] A first embodiment of this invention will be described in detail with reference to Figure 1. Figure 1 shows a first embodiment of this invention and is a schematic diagram illustrating a method for generating correction information in a satellite navigation system according to claim 1 of this invention.

[0052] Navigation satellites 1 (1a, 1b...) each transmit positioning signals.

[0053] Reference station 3 (3a, 3b...) is fixed on the ground and has the function of receiving positioning signals transmitted by navigation satellite 1 (1a, 1b...) and measuring the distance from the navigation satellite to the reference station. The nominal position 5 of reference station 3 differs 11 from the accurate position of reference station 3.

[0054] User station 7 has the function of receiving positioning signals transmitted by navigation satellites 1 (1a, 1b...) and measuring the distance from the navigation satellites to the user station.

[0055] In Figure 1, label 2 schematically represents the distribution of tropospheric propagation delay. In Figure 1, the left side shows a large tropospheric propagation delay, and the right side shows a small tropospheric propagation delay; however, this is an example and does not necessarily mean that tropospheric propagation delay always exhibits such a distribution.

[0056] In Figure 1, the length of the arrow indicates the magnitude of the tropospheric propagation delay of the positioning signal received by the base station 3. Similarly, the length of the arrow indicates the magnitude of the tropospheric propagation delay of the positioning signal received by the user station 7.

[0057] Correction station 9 receives the distance 10 between the navigation satellites 1 (1a, 1b...) and reference station 3 as measured by reference station 3 from reference station 3. For each of the navigation satellites 1 (1a, 1b...), it generates a correction value by subtracting the distance measured by reference station 3 from the distance that should have been measured, which would have been calculated from the precise position of reference station 3. This correction value includes a component that cancels out the tropospheric propagation delay 4 corresponding to the precise position of reference station 3. Correction station 9 adds the tropospheric propagation delay 4 corresponding to the precise position of reference station 3 to this correction value and subtracts the tropospheric propagation delay 6 corresponding to the nominal position 5 of reference station 3 to generate a new correction value 12. Correction station 9 provides this new correction value 12 to user station 9.

[0058] User station 7 corrects the measured distance using the new correction value 12 provided by correction station 9 and calculates its own position.

[0059] Next, I will explain the operation.

[0060] Figure 3 shows the relationship between the altitude of the receiving station and the tropospheric propagation delay. Assuming the satellite is located to the east of the receiver, the relationship between the altitude of the receiving station and the tropospheric propagation delay is plotted for elevation angles of 5 degrees, 7.5 degrees, and 10 degrees. The difference in delay increases as the elevation angle of the navigation satellite decreases, and for a navigation satellite at an elevation angle of 5 degrees, a difference in altitude of 25 meters results in a delay difference of approximately 7 centimeters. In other words, for example, when there is an altitude difference of 25 meters between the accurate position of the reference station and the nominal position, the correction value generated by a reference station not according to the present invention will have a deviation of up to approximately 7 centimeters compared to when the reference station is installed at the nominal position.

[0061] Figure 4 shows the relationship between the longitude of the receiving station and the tropospheric propagation delay. Assuming the satellite is located east of the receiver, the relationship between the receiving station's longitude (relative to 140 degrees east longitude) and the tropospheric propagation delay is plotted for elevation angles of 5 degrees, 7.5 degrees, and 10 degrees. The difference in delay increases as the elevation angle of the navigation satellite decreases, and for a navigation satellite with an elevation angle of 5 degrees, a difference in longitude of 0.1 degrees (corresponding to a distance of about 10 kilometers near Japan) results in a difference in delay of about 25 centimeters. In other words, for example, when there is a difference in longitude of 0.1 degrees between the accurate position of the reference station and the nominal position, the correction value generated by a reference station not according to the present invention will have a deviation of up to 30 centimeters or more compared to when the reference station is installed at the nominal position.

[0062] In this invention, the discrepancy is eliminated by replacing the tropospheric propagation delay amount, which corresponds to the precise position of the reference station and is included in the correction value generated by the correction station, with the tropospheric propagation delay amount corresponding to the nominal position of the reference station.

[0063] Various formulas are known for obtaining the tropospheric propagation delay, but one example of the simplest formula is shown in [Equation 5] of

[0034] .

[0064] The correction value C(i,Pt) generated by correction station 9 for reference station 3 and navigation satellite i has a component that cancels out the tropospheric propagation delay T(i,Pt) corresponding to the precise position Pt of the reference station. Therefore, in order to replace this with the tropospheric propagation delay T(i,Pn) corresponding to the nominal position Pn of the reference station, a new correction value C(i,Pn) can be generated as shown in [Equation 6] of

[0036] .

[0065] By providing this new correction value C(i,Pn) to the user station, the user station will obtain a correction value that matches the nominal position of the reference station, thereby eliminating the effect of the difference between the accurate position and the nominal position of the DGPS reference station on positioning calculations. The tropospheric propagation delay can be obtained, for example, by the calculation formula in [Equation 5] of

[0034] , but the calculation process can be performed in exactly the same way even if a different calculation formula is used.

[0066] In this embodiment, the correction station 9 generates the correction value, but it is also possible to configure the system so that the reference station 3 generates the correction value, and the correction station 9 modifies it to match the nominal reference station position to generate a new correction value. Alternatively, it is also possible to configure the system so that there is no physical correction station, and the processing that the correction station 9 would perform in this invention is carried out within the reference station 3. [Examples]

[0067] A second embodiment of this invention will be described in detail with reference to Figure 2. Figure 2 shows a second embodiment of this invention and is a schematic diagram illustrating a method for generating correction information in a satellite navigation system according to claims 2 to 5 of this invention.

[0068] Navigation satellites 1 (1a, 1b...) each transmit positioning signals.

[0069] Reference stations 3 (3a, 3b...) are fixed on the ground and have the function of receiving positioning signals transmitted by navigation satellites 1 (1a, 1b...) and measuring the distance from the navigation satellites to the reference stations. The nominal position 5 that represents reference stations 3 (3a, 3b...) differs 11 from the exact position of reference stations 3 (3a, 3b...) (the difference varies for each reference station, but not all of them are illustrated here).

[0070] User station 7 has the function of receiving positioning signals transmitted by navigation satellites 1 (1a, 1b...) and measuring the distance from the navigation satellites to the user station.

[0071] In Figure 2, the symbol 2 schematically represents the distribution of tropospheric propagation delay. In Figure 2, the left side shows a large tropospheric propagation delay, and the right side shows a small tropospheric propagation delay; however, this is an example and does not necessarily mean that tropospheric propagation delay always exhibits such a distribution.

[0072] In Figure 2, the symbols 4 (4a, 4b...) represent the magnitude of the tropospheric propagation delay of the positioning signal received by base station 3 (3a, 3b...) as indicated by the length of the arrow. Similarly, the symbols 8 represent the magnitude of the tropospheric propagation delay of the positioning signal received by user station 7 as indicated by the length of the arrow.

[0073] Correction station 9 receives the distance 10 between each navigation satellite 1 (1a, 1b...) and the reference station 3 (3a, 3b...) as measured by each of the reference stations 3 (3a, 3b...), and generates a correction value for each of the navigation satellites 1 (1a, 1b...) by subtracting the distance measured by the reference station from the distance that should have been measured, which would have been calculated from the precise positions of each of the reference stations 3 (3a, 3b...). This correction value includes a component that cancels out the tropospheric propagation delay 4, corresponding to the precise positions of each of the reference stations 3 (3a, 3b...). Correction station 9 adds the tropospheric propagation delay 4 corresponding to the precise positions of each of the reference stations 3 (3a, 3b...) to this correction value, calculates the average of the results, and subtracts the tropospheric propagation delay 6 corresponding to the nominal position 5 representing the reference stations 3 (3a, 3b...) from this average to generate a new correction value 12. Correction station 9 provides this new correction value 12 to user station 9.

[0074] Correction station 9 has the function of multiplying each of the multiple reference stations by a weight W1, W2, etc., and then obtaining the sum of these weights when calculating the average. When the number of reference stations is N, if the weight for all reference stations is 1 / N, this sum represents a simple average. If different weights are set for each reference station, this sum represents a weighted average.

[0075] The specific calculation method for weights W1, W2, etc., when N reference stations are available is described below. First, when calculating the average of the correction values ​​for each reference station, the weight Wk for each reference station can be calculated using the following formula.

[0076]

number

[0077] Furthermore, when calculating the weighted average of the correction values ​​at each reference station, if we use weights proportional to the reciprocal of the distance between each of the reference stations 3(3a, 3b...) and the nominal position 5, and let Rk be the distance between each of the reference stations 3(3a, 3b...) and the nominal position 5, then the weight Wk for each reference station can be calculated by the following formula.

[0078]

number

[0079] Furthermore, when calculating the weighted average of the correction values ​​at each base station, if we use weights determined by the least squares method using the coordinate values ​​of each base station, and let Xk be the longitude and Yk be the latitude of each base station, and Xu be the longitude and Yu be the latitude of the nominal position, then the weight Wk for each base station can be calculated by the following formula.

[0080]

number

[0081] In this equation, the superscript T represents the transpose of the matrix, and the superscript -1 represents the inverse matrix. The N×3 matrix G that holds the latitude and longitude of each base station is given by the following equation.

[0082]

number

[0083] Here, the locations of each base station and nominal position are expressed in terms of longitude and latitude, but the same formulation can be used when using a Cartesian coordinate system.

[0084] User station 7 corrects the measured distance using the new correction value 12 provided by correction station 9 and calculates its own position.

[0085] Next, I will explain the operation.

[0086] Focusing on each of the reference stations 3 (3a, 3b...), in the present invention, the tropospheric propagation delay amount corresponding to the precise position of the reference station, which is included in the correction value generated by the correction station, is replaced with the tropospheric propagation delay amount corresponding to the nominal position of the reference station, as in Example 1.

[0087] By using the average of correction values ​​generated for multiple reference stations, error factors other than tropospheric propagation delay are subjected to averaging. As a result, error factors that change linearly with respect to the reference station's position are eliminated, and the newly generated correction values ​​will have the property of being more closely suited to the nominal position of the reference station group. If these new correction values ​​are provided to user stations, the user stations will obtain correction values ​​that are more closely suited to the nominal position of the reference stations, thereby more effectively eliminating the influence of the difference between the accurate position and the nominal position of the DGPS reference station group on positioning calculations.

[0088] In this embodiment, the correction station 9 generates the correction value, but it is also possible to configure the system so that each of the reference stations 3 (3a, 3b, etc.) generates a correction value, and the correction station 9 modifies it to match the nominal reference station position to generate a new correction value. Alternatively, it is also possible to configure the system so that there is no physical correction station, and the processing that the correction station 9 would perform in this invention is carried out inside one of the reference stations 3 (3a, 3b, etc.). [Industrial applicability]

[0089] The method for generating correction information in a satellite navigation system according to the present invention can be used in positioning systems, guidance systems, and the like for moving objects. In particular, in the SLAS service of Japan's Quasi-Zenith Satellite System, the resolution of the nominal position of the reference station is insufficient, but by applying the present invention, correction information that matches the nominal position of the reference station can be generated, thereby eliminating the influence of the difference between the accurate position and the nominal position of the reference station. Furthermore, even when construction is carried out on the reference station equipment, or when the position of the reference station is temporarily or permanently changed due to disaster or other circumstances, the nominal position of the reference station does not need to be changed if the present invention is applied. [Explanation of Symbols]

[0090] 1 (1a, 1b...) Navigation satellite 2. Distribution of tropospheric propagation delay 3(3a,3b...) Reference station 4(4a,4b...) Tropospheric propagation delay corresponding to the precise location of the reference station. 5. Nominal location of the reference station 6. Tropospheric propagation delay corresponding to the nominal position 7 User Station 8. Tropospheric propagation delay corresponding to the user station's location. 9 Correction Bureau 10(10a,10b...) Correction values ​​generated by the reference station 11. Difference between the precise location and the nominal location of the reference station. 12. Correction values ​​used by user stations for positioning calculations.

Claims

1. Multiple navigation satellites that transmit positioning signals, A user station that receives positioning signals transmitted by the aforementioned multiple navigation satellites and measures the distance between them, A reference station that receives positioning signals transmitted by each of the aforementioned navigation satellites using a receiver fixed on the ground and measures the distance between them, The system includes a correction station that generates correction values ​​corresponding to each of the navigation satellites from distance information measured by the reference station, and provides these correction values ​​to the user station as correction information for the multiple navigation satellites. In a satellite navigation system in which the user station is provided with the nominal base station position of the base station, The correction station shall, for each of the navigation satellites, By subtracting the distance measured by the reference station from the distance that should have been measured, calculated from the precise location of the reference station, a correction value corresponding to the reference station is generated. By calculating the tropospheric propagation delay at the precise location of the reference station and adding the tropospheric propagation delay obtained from this calculation to the correction value, a correction value that does not include the tropospheric propagation delay component at the reference station is obtained. The tropospheric propagation delay at the aforementioned nominal reference station location is calculated, and the tropospheric propagation delay obtained from this calculation is subtracted from the correction value that does not include the tropospheric propagation delay component to generate a new correction value. A method for generating correction information in a satellite navigation system, characterized in that this new correction value is provided to the user station as correction information for the multiple navigation satellites.

2. Multiple navigation satellites that transmit positioning signals, A user station that receives positioning signals transmitted by the aforementioned multiple navigation satellites and measures the distance between them, Multiple reference stations, each receiving positioning signals transmitted by the navigation satellites via a receiver fixed on the ground and measuring the distance between them, The system includes a correction station that generates correction values ​​corresponding to each of the navigation satellites from distance information measured by the multiple reference stations, and provides these correction values ​​to the user station as correction information for the multiple navigation satellites. In a satellite navigation system in which the user station is provided with nominal reference station positions representing the plurality of reference stations, The correction station shall, for each of the navigation satellites, By subtracting the distance measured by each of the aforementioned reference stations from the distance that should have been measured, calculated from the precise location of each of the aforementioned reference stations, a correction value corresponding to each of the aforementioned reference stations is generated. By calculating the tropospheric propagation delay at the precise location of each of the aforementioned reference stations and adding the tropospheric propagation delay obtained from this calculation to the correction value, a correction value that does not include the tropospheric propagation delay component at each of the aforementioned reference stations is obtained. The average of these values ​​is calculated for the aforementioned multiple reference stations. The tropospheric propagation delay at the aforementioned nominal reference station location is calculated, and this calculated tropospheric propagation delay is subtracted from the average to generate a new correction value. A method for generating correction information in a satellite navigation system, characterized in that this new correction value is provided to the user station as correction information for the multiple navigation satellites.

3. The method for generating correction information in a satellite navigation system according to claim 2, wherein the correction station calculates the average, and in doing so, a weighted average is used in which each of the reference stations is weighted based on its relative positional relationship with the nominal reference station position.

4. The correction station calculates the weighted average, and in this process, a weight is used for each of the reference stations that is proportional to the reciprocal of the distance between the reference station and the nominal reference station position, characterized in that a method for generating correction information in a satellite navigation system according to claim 3.

5. The correction station calculates the weighted average, and in this case, for each of the reference stations, the weights determined by the least squares method using the coordinate values ​​of the reference station are used, under the assumption that the target for calculating the weighted average is linear with respect to the coordinate values. This is the method for generating correction information in a satellite navigation system according to claim 3.

Images