Method for Generating Correction Information in Satellite Navigation System

Abstract

In differential GPS, correction information that conforms to the nominal position of the reference station is generated. 【Solution means】 In a satellite positioning system using the differential GPS method including a user station and a reference station, while the nominal reference station position regarding the reference station is provided to the user station, the tropospheric propagation delay amount at the accurate position of the reference station is calculated and added to the correction value generated by the reference station for each navigation satellite, and the tropospheric propagation delay amount at the nominal position of the reference station is calculated and subtracted therefrom, thereby creating a new correction value. By collecting the new correction values that conform to the nominal position of this reference station for a plurality of navigation satellites and providing them to the user station as correction information, the influence on the positioning calculation due to the difference between the accurate position and the nominal position of the reference station is removed.

Description

Technical Field

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

Background Art

[0002] A satellite navigation system that measures a position by 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 a positioning signal transmitted by an artificial satellite called a navigation satellite by a receiver, measures the distance between the navigation satellite and the receiver, and obtains the position of the receiver by calculation. A receiver whose position is to be determined is called a user receiver or a user station. An 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 positioning error. The magnitudes of the ionospheric propagation delay and the tropospheric propagation delay converted into distances are respectively called ionospheric propagation delay amount and tropospheric delay amount.

[0004] On the other hand, a receiver is installed at a reference station fixed to the ground, and correction information for measurement errors in distance caused by ionospheric propagation delay, tropospheric propagation delay, etc. is created from the distances measured thereby and provided to the user. By correcting the distances measured at the user station based on the correction information, the measurement accuracy of the position at the user station (referred to as "positioning accuracy") is improved. This method is called Differential GPS (hereinafter referred to as "DGPS"). The correction information provided to the user station in DGPS includes correction values for distances for each of a plurality of navigation satellites.

[0005] In DGPS, since the correction information is created from the measurement errors in distance at the position of the reference station, the improvement effect of the positioning accuracy by the correction information is high in the vicinity of the reference station, but it is known that the improvement effect becomes smaller as the distance from the reference station increases. For this reason, when using DGPS at the user station, it is common to use it within a limited range from the reference station, or when multiple reference stations can be used, to select and use the nearest reference station.

[0006] As practical examples of DGPS, there were those based on medium-wave beacons for ships and FM multiplex digital broadcasts, but both are now abolished. On the other hand, Japan's quasi-zenith satellite system, which started operation in 2018, transmits DGPS correction information from artificial satellites as SLAS (Submeter-Level Augmentation Service). The SLAS service has the feature that by receiving signals from a single artificial satellite, correction information at 13 reference stations arranged throughout Japan can be obtained all at once. User receivers using the SLAS service are supposed to select and use the correction information of the nearest reference station.

[0007] In the differential GPS method, in addition to the method using individual reference stations described above, there is a method called wide-area differential GPS that integrates measurement data from multiple reference stations to create wide-area correction information effective over a wide geographical area. As services of wide-area differential GPS, MSAS in Japan and WAAS in the United States have become widespread. Therefore, DGPS that provides correction information by multiple reference stations does not currently exist except for the SLAS service of the quasi-zenith satellite system.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Non-Patent Documents

[0009]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] In DGPS, generally, as the distance from the reference station increases, the effect of correction by the correction information decreases. Therefore, when using DGPS at the user station, it is common to use it within a limited range from the reference station, or when multiple reference stations can be used, to select and use the nearest reference station.

[0011] For example, in the SLAS service of the quasi-zenith satellite system, correction information from 13 reference stations deployed throughout Japan is provided, and user stations are supposed to select and use the nearest reference station. To select the nearest reference station from multiple reference stations, the position information of each of the multiple reference stations is required. Therefore, in the SLAS service, the position information of the reference stations is transmitted together with the correction information.

[0012] Furthermore, in the specification of the SLAS service, the positions of the 13 reference stations are defined in advance, and considerations are made so that the SLAS service can be used even before receiving the position information of the reference stations. The positions of the reference stations transmitted together with the correction information and the positions of the reference stations defined in the specification of the DGPS service are referred to as the nominal positions of the reference stations.

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

[0014] On the other hand, when performing construction work on the reference station facilities or in the event of a disaster or other circumstances, it is practically possible to temporarily or permanently change the position of the reference station facilities (especially the receiving antenna). In such cases, it is conceivable to change the nominal position of the reference station in accordance with the change in the exact position of the reference station.

[0015] However, for example, in the case of the SLAS service, since the position of the reference station is defined in advance in the SLAS service specification, even if the nominal position changed according to the actual position of the reference station is transmitted to the user station, there may be a significant difference beyond expectation between the exact position of the reference station used at the user station and the nominal position of the reference station until the user station receives the position information of the reference station. Also, depending on the user receiver, there may be a design in which the position of the reference station transmitted according to the correction information is not used, and only the position of the reference station defined in the SLAS service specification is used.

[0016] Consider how much change in the correction value is actually brought about by the difference between the exact position of the reference station used at the user station and the nominal position of the reference station. Generally, as described in Non-Patent Document 1 (page 46), in the positioning calculation of a DGPS user station, it is known that attention needs to be paid to the handling of tropospheric propagation delay when there is an altitude difference between the user station and the reference station. This is because the tropospheric propagation delay amount is a function of the altitude (elevation) of the receiver. When there is no altitude difference, if the tropospheric propagation delay amounts at the user station and the reference station for a certain navigation satellite are considered approximately equal, the differential correction by the reference station can act appropriately to correct the distance measurement error of the user station. However, when there is an altitude difference, the tropospheric propagation delay amounts 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 elevation of the receiving station and the tropospheric propagation delay amount. Assuming that there is a navigation satellite in the east direction of the receiver, the relationship between the elevation of the receiving station and the tropospheric propagation delay amount is plotted for each of the cases of elevation angles of 5 degrees, 7.5 degrees, and 10 degrees. The difference in the delay amount is larger as the elevation angle of the navigation satellite becomes lower. For a navigation satellite with an elevation angle of 5 degrees, the delay amount difference reaches about 7 centimeters with an altitude difference of 25 meters. That is, for example, when there is an altitude difference of 25 meters between the exact position and the nominal position of the reference station, there is a deviation of up to about 7 centimeters in the correction value generated by the reference station compared to the case where the reference station is installed at the nominal position.

[0018] The influence due to the difference in the positions of the DGPS reference station and the user station in the horizontal plane is not large compared to the difference in the tropospheric propagation delay due to the altitude difference. However, when the difference between the accurate position and the nominal position of the reference station becomes large, an ignorable influence appears as shown in Fig. 4.

[0019] Fig. 4 shows the relationship between the longitude of the receiving station and the tropospheric propagation delay. Assuming that there is a navigation satellite in the east direction of the receiver, for each of the cases of elevation angles of 5 degrees, 7.5 degrees, and 10 degrees, the relationship between the longitude of the receiving station (relative value from 140 degrees east longitude) and the tropospheric propagation delay is plotted. The difference in the delay amount becomes larger as the elevation angle of the navigation satellite becomes lower. For a navigation satellite with an elevation angle of 5 degrees, the difference in the delay amount reaches 30 centimeters or more with a longitude difference of 0.1 degree (corresponding to a distance of about 10 kilometers near Japan). That is, for example, when there is a longitude difference of 0.1 degree between the accurate position and the nominal position of the reference station, the correction value generated by the reference station has a deviation of up to 30 centimeters or more compared to the case where the reference station is installed at the nominal position.

[0020] Generally, in DGPS, for each of the navigation satellites whose positioning signals are received by the reference station, a correction value is generated by subtracting the distance between the reference station and the navigation satellite actually measured by the reference station (at its accurate position) from the distance that should be originally measured calculated from the accurate position of the reference station. By applying the correction value generated in this way at the user station, at the user station, a correction value corresponding to the accurate position of the reference station is applied, and the position of the reference station is not explicitly shown in the normal DGPS calculation process.

[0021] Therefore, in DGPS, it is not unusual that the position of the reference station is not 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 to the extent of indicating a geographical range of user stations that can be corrected with sufficient performance, and thus information regarding the position of the reference station has not been regarded as important. Also, the difference between the accurate position and the nominal position of the DGPS reference station has not been considered to affect the correction performance of DGPS. Since the position of the reference station does not explicitly appear in the normal DGPS calculation process at the user station, such a difference has not been 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 produce 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 to 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 represented by 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 is 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 reach Pn as long as the correction information C(Pt) is applied. This relationship is expressed as follows.

[0026]

Equation

[0027] An object of the present invention is to generate correction information C(Pn) that conforms to the nominal position Pn of the reference station, so as to correctly obtain the nominal position Pn as a 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]

Equation

[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 as the result of the DGPS positioning calculation instead of Pt. 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]

Equation

Means for Solving the Problem

[0031] The correction value generated by the reference station is generated based on the measured values of the distances to the respective navigation satellites at the exact position of the reference station. Since the measured distances include the tropospheric propagation delay amount, the generated correction value includes a component that cancels out the tropospheric propagation delay amount. This tropospheric propagation delay amount corresponds to the exact position of the reference station.

[0032] To achieve the object of the present invention, it suffices to be able to replace the tropospheric propagation delay amount corresponding to the exact 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. Regarding error factors other than the tropospheric propagation delay amount in the satellite navigation system, since the influence on the positioning calculation due to the difference between the exact position and the nominal position of the DGPS reference station is not significant, the object of the present invention can be solved by the handling of the tropospheric propagation delay.

[0033] Although various formulas for obtaining the tropospheric propagation delay amount are known, an example of the simplest formula is as follows. Here, when the positioning signal transmitted by satellite i is received by a receiver at position x, it is assumed that a tropospheric propagation delay amount T(i,x) is generated, 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]

Equation

[0035] Since 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 amount T(i,Pt) corresponding to the exact position Pt of the reference station, to replace this with the tropospheric propagation delay amount T(i,Pn) corresponding to the nominal position Pn of the reference station, a new correction value C(i,Pn) may be generated as follows.

[0036]

Equation

[0037] If this new correction value C(i, Pn) obtained by correcting the correction value C(i, Pt) is provided to the user station, the user station can obtain a correction value corresponding to the nominal position of the reference station, so that the influence on the positioning calculation due to the difference between the accurate position and the nominal position of the DGPS reference station can be eliminated. The tropospheric propagation delay amount can be obtained by the calculation formula of [Equation 5] as an example, but the same calculation process can be executed in the case of using a different calculation formula.

[0038] When there are a plurality of reference stations, a new correction value at the nominal position representing the group of those reference stations can be obtained from the correction values generated by each of those reference stations. That is, the tropospheric propagation delay amounts corresponding to the correction values of each of the plurality of reference stations are added, the average of the results is obtained, and the tropospheric propagation delay amount corresponding to the nominal position representing the group of reference stations is subtracted from this to generate a new correction value, and this new correction value is provided to the user station. By such a method, the influence on the positioning calculation due to the difference between the accurate position and the nominal position of the DGPS reference station group can be eliminated.

[0039] Patent Document 1 describes a method for generating correction information in differential GPS using the average of correction values generated by a plurality of reference stations. In this method, in order to generate effective correction information at the position of the user station, after treating the tropospheric propagation delay in a manner similar to

[0038] , the average of the correction values generated by a plurality of reference stations is used. Since this method is for generating effective correction information at the position of the user station, it can only be executed by the user station.

[0040] In the process of this calculation process, the position of the reference station is explicitly used. In this case, it is necessary to use the accurate position of the reference station. The reason is that when using the nominal position of the reference station, as described in

[0016] ~

[0019] , a deviation in the correction value due to the difference between the accurate position and the nominal position of the reference station will occur. However, in general DGPS calculation processing, the position of the reference station is not required, so generally the accurate position of the reference station is not given to the user station. There are cases where the nominal position of the reference station is given to the user station, such as in the SLAS service. Even in such cases, the resolution is kept rough, and it is the common understanding of those skilled in the art that the reference station position is not important.

[0041] However, when the nominal position of the reference station is given to the user station, by applying the method of the present invention to provide the user station with new correction information obtained by modifying the correction information generated by the reference station at its accurate position 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. At this time, it is not necessary to give the accurate position of each reference station to the user station.

[0042] The invention according to claim 1 is a satellite navigation system including 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 to them, a reference station that receives the positioning signals transmitted by each of the navigation satellites by a receiver fixed on the ground and measures the distances to 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. In the satellite navigation system in which the nominal reference station position of the reference station is provided to the user station, the correction station generates a correction value corresponding to the reference station by subtracting the distance measured by the reference station from the originally measured distance calculated from the exact position of the reference station for each of the navigation satellites, calculates the tropospheric propagation delay amount at the exact position of the reference station, and obtains a correction value not including the component of the tropospheric propagation delay at the reference station by adding the tropospheric propagation delay amount obtained by this calculation to the correction value, calculates the tropospheric propagation delay amount at the nominal reference station position, and generates a new correction value by subtracting the tropospheric propagation delay amount obtained by this calculation from the correction value not including the component of the tropospheric propagation delay, and provides this new correction value to the user station as the correction information for the plurality of navigation satellites. This is a method for generating correction information in a satellite navigation system.

[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 distances thereto, a plurality of reference stations that receive the positioning signals transmitted by each of the navigation satellites by a receiver fixed on the ground and measure the distances thereto, 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 in a lump. In the satellite navigation system in which a nominal reference station position representing the plurality of reference stations is provided to the user station, the correction station generates, for each of the navigation satellites, a correction value corresponding to each of the reference stations by subtracting the distance measured by each of the reference stations from the originally measured distance calculated from the exact position of each of the reference stations, calculates the tropospheric propagation delay amount at the exact position of each of the reference stations, adds the tropospheric propagation delay amount obtained by this calculation to the correction value to obtain a correction value not including the component of the tropospheric propagation delay at each of the reference stations, obtains the average of these for the plurality of reference stations, calculates the tropospheric propagation delay amount at the nominal reference station position, and generates a new correction value by subtracting the tropospheric propagation delay amount obtained by this calculation from the average, and provides this new correction value to the user station as the correction information for the plurality of navigation satellites in a lump. This is a method for generating correction information in a satellite navigation system.

[0044] The invention according to claim 3 is the method for generating correction information in the satellite navigation system according to claim 2, characterized in that the correction station obtains the average, and at this time, uses a weighted average given a weight based on the relative positional relationship with the nominal reference station position for each of the reference stations.

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

[0046] In the invention according to claim 5, the correction station calculates the weighted average. At this time, for each of the reference stations, under the assumption that the object for which the weighted average is calculated is linear with respect to the coordinate values, the weight determined by the least squares method using the coordinate values of the reference station is used. This is a method for generating correction information in the satellite navigation system according to claim 3.

Effect of the Invention

[0047] Since the invention according to claim 1 is configured as described above, correction information that conforms to the nominal position of the reference station can be generated in DGPS, and thus the influence on the positioning calculation due to the difference between the accurate position and the nominal position of the DGPS reference station can be removed.

[0048] Since the inventions according to claims 2 to 5 are configured as described above, when there are a plurality of DGPS reference stations, correction information that conforms to the nominal position representing the group of those reference stations can be generated from the correction values generated by each of those reference stations, and thus the influence on the positioning calculation due to the difference between the accurate position and the nominal position of the DGPS reference station group can be removed.

Brief Description of the Drawings

[0049]

Figure 1

Figure 2

Figure 3

Figure 4

Best Mode for Carrying Out the Invention

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

Embodiment

[0051] A first embodiment of this invention will be described in detail with reference to FIG. 1. FIG. 1 shows a first embodiment of this invention and is a schematic diagram for explaining 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 a positioning signal.

[0053] Reference stations 3 (3a, 3b,...) are fixed on the ground and have a function of receiving the positioning signals transmitted by navigation satellites 1 (1a, 1b,...) and measuring the distance from the navigation satellites to the reference stations. There is a difference 11 between the nominal position 5 of the reference station 3 and the exact position of the reference station 3.

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

[0055] Reference numeral 2 in FIG. 1 schematically represents the distribution of the tropospheric propagation delay amount. In FIG. 1, it shows that the tropospheric propagation delay amount is large on the left side and small on the right side, but this is an example and does not necessarily mean that the tropospheric propagation delay shows such a distribution.

[0056] Reference numeral 4 in FIG. 1 represents the magnitude of the tropospheric propagation delay of the positioning signal received by the reference station 3 by the length of the arrow. Similarly, reference numeral 8 represents the magnitude of the tropospheric propagation delay of the positioning signal received by the user station 7 by the length of the arrow.

[0057] The correction station 9 receives from the reference station 3 the distance 10 between the navigation satellite 1 (1a, 1b...) measured by the reference station 3 and the reference station 3. For each of the navigation satellites 1 (1a, 1b...), the correction value is generated by subtracting the distance measured by this reference station 3 from the originally measurable distance calculated from the exact position of the reference station 3. This correction value includes a component that cancels the tropospheric propagation delay amount 4 corresponding to the exact position of the reference station 3. The correction station 9 adds the tropospheric propagation delay amount 4 corresponding to the exact position of the reference station 3 to this correction value and subtracts the tropospheric propagation delay amount 6 corresponding to the nominal position 5 of the reference station 3 to generate a new correction value 12. The correction station 9 provides this new correction value 12 to the user station 9.

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

[0059] Next, the operation will be described.

[0060] FIG. 3 shows the relationship between the altitude of the receiving station and the tropospheric propagation delay amount. Assuming that there is a satellite in the east direction of the receiver, the relationship between the altitude of the receiving station and the tropospheric propagation delay amount is plotted for each of the cases of elevation angles of 5 degrees, 7.5 degrees, and 10 degrees. The difference in the delay amount is larger as the elevation angle of the navigation satellite becomes lower. For a navigation satellite with an elevation angle of 5 degrees, the delay amount difference reaches about 7 centimeters with an altitude difference of 25 meters. That is, for example, when there is an altitude difference of 25 meters between the exact position and the nominal position of the reference station, there is a deviation of up to about 7 centimeters in the correction value generated by the reference station not according to the present invention compared to the case where 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 that the satellite is to the east of the receiver, the relationship between the longitude of the receiving station (relative value from 140°E) and the tropospheric propagation delay is plotted for each of the cases of elevation angles of 5°, 7.5°, and 10°. The difference in the delay amount is larger as the elevation angle of the navigation satellite becomes lower. For a navigation satellite with an elevation angle of 5°, the difference in the delay amount reaches about 25 cm with a longitude difference of 0.1° (corresponding to a distance of about 10 km near Japan). That is, for example, when there is a longitude difference of 0.1° between the exact position and the nominal position of the reference station, the correction value generated by the reference station not according to the present invention has a deviation that reaches up to 30 cm or more compared to the case where the reference station is installed at the nominal position.

[0062] In the present invention, such a deviation is eliminated by replacing the tropospheric propagation delay amount corresponding to the exact position of the reference station, which 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] Although various mathematical formulas for obtaining the tropospheric propagation delay amount are known, an example of the simplest mathematical formula is as shown in [Equation 5] of

[0034] .

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

[0036] .

[0065] If this new correction value C(i, Pn) is provided to the user station, the user station will obtain a correction value adapted to the nominal position of the reference station, and thus the effect of removing the influence on the positioning calculation due to the difference between the exact position and the nominal position of the DGPS reference station can be obtained. Although the tropospheric propagation delay amount is obtained, for example, by the calculation formula of [Equation 5] of

[0034] , the same calculation process can be executed even when using a different calculation formula.

[0066] Note that in this embodiment, the correction station 9 generates correction values. However, it is also possible to configure the reference station 3 to generate correction values and the correction station 9 to modify them to conform to the nominal reference station position to generate new correction values. Alternatively, it is also possible to configure the system such that the processing that should be performed by the correction station 9 in the present invention is executed inside the reference station 3 without providing a physical correction station.

Embodiment

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

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

[0069] Reference stations 3 (3a, 3b,...) are fixed on the ground and have a function of receiving the positioning signals transmitted by navigation satellites 1 (1a, 1b,...) and measuring the distances from the navigation satellites to the reference stations. The nominal position 5 representing the reference stations 3 (3a, 3b,...) is different from the exact positions of the reference stations 3 (3a, 3b,...) (the differences vary for each reference station, but all of them are not shown here).

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

[0071] Reference numeral 2 in FIG. 2 schematically represents the distribution of the tropospheric propagation delay amount. In FIG. 2, it shows that the tropospheric propagation delay amount is large on the left side and small on the right side, but this is an example and does not necessarily mean that the tropospheric propagation delay always shows such a distribution.

[0072] Reference numeral 4 (4a, 4b, ···) in Fig. 2 represents the magnitude of the tropospheric propagation delay of the positioning signal received by the reference stations 3 (3a, 3b, ···) by the length of the arrow. Similarly, reference numeral 8 represents the magnitude of the tropospheric propagation delay of the positioning signal received by the user station 7 by the length of the arrow.

[0073] The correction station 9 receives from the reference stations 3 (3a, 3b, ···) the distances 10 between the dead reckoning satellites 1 (1a, 1b, ···) measured by each of the reference stations 3 (3a, 3b, ···) and the corresponding reference stations. For each of the dead reckoning satellites 1 (1a, 1b, ···), the correction station 9 generates a correction value by subtracting the distance measured by the reference station from the originally measured distance calculated from the exact positions of each of the reference stations 3 (3a, 3b, ···). This correction value includes a component that cancels out the tropospheric propagation delay amount 4 corresponding to the exact position of each of the reference stations 3 (3a, 3b, ···). The correction station 9 adds the tropospheric propagation delay amount 4 corresponding to the exact position of each of the reference stations 3 (3a, 3b, ···) to this correction value, obtains the average of the results, and generates a new correction value 12 by subtracting the tropospheric propagation delay amount 6 corresponding to the nominal position 5 representing the reference stations 3 (3a, 3b, ···) from this average. The correction station 9 provides this new correction value 12 to the user station 9.

[0074] When obtaining the average, the correction station 9 has a function of multiplying each of the plurality of reference stations by weights W1, W2, ··· and then obtaining their sum. When the number of reference stations is N, setting the weight to 1 / N for all reference stations means this sum represents the simple average. When different weights are set for each reference station, this sum represents the weighted average.

[0075] For the case where N reference stations can be used, a specific calculation method for the weights W1, W2, ··· will be described. First, when obtaining the average of the correction values at each reference station, the weight Wk of each reference station can be calculated by the following formula.

[0076]

Equation

[0077] Also, when obtaining the weighted average of the correction values at each reference station, when using weights proportional to the reciprocals of the distances between each of the reference stations 3 (3a, 3b ···) and the nominal position 5, if the distance between each of the reference stations 3 (3a, 3b ···) and the nominal position 5 is Rk, the weight Wk of each reference station can be calculated by the following formula.

[0078]

Equation

[0079] Furthermore, when obtaining the weighted average of the correction values at each reference station, when using weights determined by the least squares method using the coordinate values of each reference station, if the longitude of each reference station is Xk, the latitude is Yk, the longitude of the nominal position is Xu, and the latitude is Yu, the weight Wk of each reference station can be calculated by the following formula.

[0080]

Equation

[0081] In this formula, the superscript T represents the transpose of a matrix, and the superscript -1 represents the inverse matrix. The N×3 matrix G that holds the longitudes and latitudes of each reference station is as follows.

[0082]

Equation

[0083] Here, each reference station and the nominal position are expressed in terms of longitude and latitude, but it can be formulated in exactly the same way when using a rectangular coordinate system.

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

[0085] Next, the operation will be described.

[0086] Focusing on each of the reference stations 3 (3a, 3b...), in the present invention, replacing the tropospheric propagation delay amount corresponding to the exact position of the reference station, which 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 is the same as in the first embodiment.

[0087] By using the average of the correction values generated for a plurality of reference stations, error factors other than the tropospheric propagation delay are subject to averaging processing. As a result, error factors that linearly change particularly with respect to the position of the reference station are removed, so that the newly generated correction value has the property of being adapted by the nominal position of the reference station group. If this new correction value is provided to the user station, the user station will obtain a correction value adapted by the nominal position of the reference station, thereby obtaining the effect of more effectively removing the influence on the positioning calculation due to the difference between the exact position and the nominal position of the DGPS reference station group.

[0088] In this embodiment, the correction station 9 generates the correction value. However, it is also possible to configure each of the reference stations 3 (3a, 3b...) to generate the correction value and have the correction station 9 modify it so as to be adapted to the nominal reference station position to generate a new correction value. Alternatively, it is also possible to configure the system such that the processing to be performed by the correction station 9 in the present invention is executed inside any of the reference stations 3 (3a, 3b...) without placing a physical correction station.

Industrial Applicability

[0089] The method for generating correction information in the satellite navigation system of the present invention can be used in a positioning system, a guidance system, etc. of a moving body. In particular, in the SLAS service in the quasi-zenith satellite system in Japan, the resolution of the nominal position of the reference station is not sufficient. However, by applying the present invention, correction information adapted to the nominal position of the reference station can be generated, thereby removing the influence due to the difference between the exact position and the nominal position of the reference station. Also, even when the position of the reference station is temporarily or permanently changed due to construction work on the reference station facility, a disaster, or some other reason, by applying the present invention, it is not necessary to change the nominal position of the reference station.

Explanation of Symbols

[0090] 1(1a, 1b ···) Navigation satellite 2 Distribution of tropospheric propagation delay amount 3(3a, 3b ···) Reference station 4(4a, 4b ···) Tropospheric propagation delay amount corresponding to the exact position of the reference station 5 Nominal position of the reference station 6 Tropospheric propagation delay amount corresponding to the nominal position 7 User station 8 Tropospheric propagation delay amount corresponding to the position of the user station 9 Correction station 10(10a, 10b ···) Correction values generated by the reference station 11 Difference between the exact position and the nominal position of the reference station 12 Correction values used by the user station for positioning calculation

Claims

1. 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; a reference station for receiving the positioning signals transmitted by each of the navigation satellites using a receiver fixed on the ground and measuring the distance between them; a correction station that generates correction values ​​corresponding to each of the navigation satellites from distance information measured by the reference station, and provides the correction values ​​to the user station as correction information for the plurality of navigation satellites; In a satellite navigation system in which the user station is provided with a nominal reference station position of the reference station, The correction station, for each of the navigation satellites, A correction value corresponding to the reference station is generated by subtracting the distance measured by the reference station from the distance that should be measured, which is calculated based on the accurate position of the reference station; Calculating the amount of tropospheric propagation delay at the exact position of the reference station, and adding the calculated amount of tropospheric propagation delay to the correction value to obtain a correction value that does not include a component of the tropospheric propagation delay at the reference station; Calculating a tropospheric propagation delay at the nominal reference station position, and subtracting the calculated tropospheric propagation delay from the correction value that does not include the tropospheric propagation delay to generate a new correction value; A method for generating correction information in a satellite navigation system, comprising: providing the new correction values ​​for the plurality of navigation satellites together as the correction information to the user station.

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; a plurality of reference stations for receiving positioning signals transmitted by each of the navigation satellites by using a receiver fixed on the ground and measuring the distance between the reference stations; a correction station that generates correction values ​​corresponding to each of the navigation satellites from information on the distances measured by the plurality of reference stations, and provides the correction values ​​to the user station as correction information for the plurality of navigation satellites; In a satellite navigation system in which the user station is provided with a nominal reference station position representative of the plurality of reference stations, The correction station, for each of the navigation satellites, 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 that should have been measured, which is calculated from the accurate position of each of the reference stations; Calculating the amount of tropospheric propagation delay at the exact position of each of the reference stations, and adding the calculated amount of tropospheric propagation delay to the correction value to obtain a correction value that does not include a component of the tropospheric propagation delay at each of the reference stations; Calculating the average of these for the plurality of reference stations; Calculating the tropospheric propagation delay at the nominal reference station position and subtracting the calculated tropospheric propagation delay from the average to generate a new correction value; A method for generating correction information in a satellite navigation system, comprising: providing the new correction values ​​for the plurality of navigation satellites together as the correction information to the user station.

3. The method for generating correction information in a satellite navigation system as described in claim 2, characterized in that the correction station determines the average by using a weighted average for each of the reference stations, the weight being based on the relative positional relationship with the nominal reference station position.

4. 4. A method for generating correction information in a satellite navigation system as described in claim 3, wherein the correction station determines the weighted average using, for each of the reference stations, a weight proportional to the inverse of the distance between that reference station and the nominal reference station position.

5. The method for generating correction information in a satellite navigation system described in claim 3, wherein the correction station calculates the weighted average by using weights determined by the least squares method using the coordinate values ​​of each of the base stations, under the assumption that the object for calculating the weighted average is linear with respect to the coordinate values.

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