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

Abstract

Relaxing requirements for Wide Area Differential Correction System (WADGPS) reference station placement [Solution] In satellite navigation systems, including the US GPS and Japan's Quasi-Zenith Satellite System, when multiple reference stations are installed to form a wide-area differential correction system (WADGPS), four or more geographically separated reference stations were previously required. However, by setting the correction amount for the navigation satellite's position error to zero, or by using a precise orbital ephemeris to determine the correction amount for the position error, and then calculating the correction amount for the clock error only, and using these correction amounts to generate correction information for the clock error and position error, or by generating correction information using estimated values ​​calculated to minimize the sum of the squares of each coordinate axis component of the position error and the clock error for the navigation satellite's clock error and position error, WADGPS can be formed even in cases where it is not possible to install four or more geographically separated reference stations.

Description

[Technical Field]

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

[0002] Satellite navigation systems that use satellites to measure position are collectively called GNSS (Global Navigation Satellite System), and a representative example is the US-based GPS (Global Positioning System). GNSS generally uses a receiver to receive positioning signals transmitted by radio from satellites called navigation satellites, and calculates the receiver's position by measuring the distance between the navigation satellite and the receiver. The receiver that determines the position is called a user receiver or user station. The error between the determined position and the true position is called the positioning error.

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

[0004] The timing at which a navigation satellite transmits a positioning signal is predetermined, and the navigation satellite transmits the positioning signal based on the time on its own clock. This clock uses a highly accurate atomic clock, but it contains an error equivalent to several meters in distance, which causes positioning errors when calculating the receiver's position.

[0005] Before reaching the ground, a positioning signal passes through the ionosphere and troposphere above, and delays occur as the radio signal passes through each of these regions. These delays are called the ionospheric propagation delay and the troposphere propagation delay, respectively. Therefore, when this radio signal is used as a positioning signal, these ionospheric propagation delay and troposphere propagation delay become a cause of positioning errors. The magnitude of the ionospheric propagation delay and the troposphere propagation delay converted into distance are called the ionospheric propagation delay and the troposphere delay, respectively.

[0006] In a satellite navigation system, the measured distance to a navigation satellite obtained by a receiver is the sum of all measurement errors due to these error factors compared to the true distance.

[0007] A receiver is installed at a fixed reference station on the ground, and the distance measured by this is used to create correction information for distance measurement errors. This information is then provided to the user, allowing the distance measured at the user station to be corrected based on the correction information, thereby improving the position measurement accuracy (called "positioning accuracy") at the user station. This method is called Differential GPS (DGPS). To distinguish it from DGPS, the method of calculating the position of a user station without applying correction information is called standalone positioning.

[0008] There are several specific DGPS methods, but the most common method uses distances measured by a single reference station to generate distance corrections for each navigation satellite and provide them to user stations. This method, sometimes called Local Area DGPS (LADGPS), does not create correction information for each cause of positioning error. Therefore, as the distance between the user station and the reference station increases, the common component of the positioning error decreases, and positioning accuracy tends to deteriorate. It is generally recognized by those skilled in the art that DGPS can be used within a range of approximately several hundred kilometers from the reference station, or up to several tens of kilometers depending on ionospheric conditions.

[0009] Another DGPS method is Wide Area Differential GPS (WADGPS). This method uses distance measurements from multiple reference stations (called reference station groups) to generate correction information for each positioning error factor, such as the navigation satellite's clock error, the navigation satellite's position error, ionospheric propagation delay, and tropospheric propagation delay, and provides this information to the user station. Since each of these error factors manifests itself differently as distance measurement errors depending on the user station's location, the user station calculates the correction value it should use from the correction information according to its approximate location and uses it for correction.

[0010] The clock error of a navigation satellite appears as a uniform distance measurement error regardless of the location of the user station. The position error of a navigation satellite appears as a distance measurement error due to the dot product with the line of sight when the navigation satellite is viewed from the user station. The ionospheric propagation delay appears as a distance measurement error due to the integral of the density distribution of the ionospheric atmosphere on the path from which the ranging signal transmitted by the navigation satellite reaches the user station. The tropospheric propagation delay appears as a distance measurement error due to the integral of the refractive index of the neutral atmosphere on the path from which the ranging signal transmitted by the navigation satellite reaches the user station. In other words, except for the clock error of the navigation satellite, the distance measurement errors appear differently depending on the location of the user station.

[0011] It is known that the amount of ionospheric propagation delay is inversely proportional to the square of the frequency. Therefore, if a reference station measures distances using positioning signals of multiple frequencies, the amount of ionospheric propagation delay can be calculated from those distances. Alternatively, if a reference station or user station measures distances using positioning signals of multiple frequencies, the distance from which the amount of ionospheric propagation delay has been removed can be obtained by linearly combining the results of those measurements.

[0012] Furthermore, the amount of tropospheric propagation delay can be estimated with sufficient accuracy using a simple tropospheric propagation delay model, and corrections can be made at the reference station and user station. Therefore, in WADGPS, the amount of tropospheric propagation delay does not need to be included in the correction information.

[0013] In the WADGPS system where user stations are equipped with receivers compatible with one frequency of positioning signals (called "single-frequency WADGPS"), the ionospheric propagation delay must be transmitted as part of the correction information, so the reference station measures distance using positioning signals of multiple frequencies, and the master station calculates the ionospheric propagation delay over the service area and stores it in a specified transmission format.

[0014] In the WADGPS system where user stations are equipped with receivers compatible with two frequencies of positioning signals (called "dual-frequency WADGPS"), the correction information does not include ionospheric propagation delay. Both the reference station and user station measure distance using positioning signals of multiple frequencies, and the distance excluding ionospheric propagation delay is obtained as a linear combination of these measurement results.

[0015] WADGPS requires four or more reference stations to calculate the clock error (one unknown) and position error (three unknowns) of the navigation satellite. These reference stations must be geographically separated to understand the change in distance measurement error due to the location of the user station. Generally, the distance between reference stations is set to about 500 to 1,000 kilometers.

[0016] As a practical example of WADGPS, SBAS (Satellite-Based Augmentation System) has been standardized for aircraft. The SBAS standard for single-frequency WADGPS is called "L1 SBAS," and the SBAS standard for dual-frequency WADGPS is called "L5 SBAS."

[0017] The SBAS standard specifies the transmission format of correction information, and correction information is transmitted from the satellite after being thoroughly included for each cause of positioning error, such as the clock error of the navigation satellite, the position error of the navigation satellite, and in L1 SBAS, the ionospheric propagation delay. Note that the tropospheric propagation delay can be corrected with sufficient accuracy using a tropospheric propagation delay model, so it is not included in the transmission format of the SBAS standard, and correction is made using a tropospheric propagation delay model predetermined by both the master station and the user station.

[0018] An example of a L1 SBAS is the Michibiki-Based Satellite Augmentation System (MSAS) operated by the Japan Civil Aviation Bureau. Recently, South Korea has begun operating the Korea Augmentation Satellite System (KASS).

[0019] MSAS currently has 13 reference stations, but before 2020 it had six. KASS uses seven reference stations. There are several other SBAS systems in use, all of which have more than 10 reference stations.

[0020] In the field of GNSS, precise ephemeris are created and used for each navigation satellite as information on its accurate clock and orbit. Precise ephemeris are often created at 15-minute or 5-minute intervals, and users can obtain accurate time and position information at any point in time by interpolating between them. Precise ephemeris created by an international organization, for example, the International GNSS Service (IGS), are made public and are used in precision positioning fields such as surveying and geodesy.

[0021] There are three types of precise ephemeris: the Final Product and Rapid Product, which are not based on predictions, and the Ultra Rapid Product, which is based on predictions. The Final Product is the most accurate, with both the navigation satellite's position error and clock error having an accuracy of 2 to 3 centimeters from the date of measurement, but requires approximately 2 to 3 weeks for analysis. The Rapid Product has an accuracy similar to the Final Product and is released approximately 1 to 2 days from the date of measurement. The Ultra Rapid Product includes predictions for up to several hours ahead from the time of release, and has an accuracy of approximately 5 centimeters for the navigation satellite's position error and approximately 1 meter for the navigation satellite's clock error. [Prior art documents] [Non-patent literature]

[0022] [Non-Patent Document 1] Takeyasu Sakai, Sonosuke Fukushima, Naoki Arai, Ken Ito, "Prototype Evaluation of GPS Wide-Area Augmentation System," IEICE Transactions on Information and Communication Engineers, Vol. J89-B, No. 7, pp. 1297-1306, July 2006 [Non-patent document 2] Takeyasu Sakai, Sonosuke Fukushima, Noboru Takeichi, and Ken Ito, "Positioning Performance of Quasi-Zenith Satellite L1-SAIF Augmentation Signals," 7th Electronic Navigation Research Institute Research Presentation, June 2007 Summary of the Invention [Problem to be solved by the invention]

[0023] WADGPS uses distances measured by reference stations to generate correction information for each cause of positioning error, such as the navigation satellite's clock error, navigation satellite's position error, ionospheric propagation delay, and tropospheric propagation delay. Of these, the navigation satellite's clock error does not depend on the user station's position. Furthermore, the tropospheric propagation delay can be corrected with sufficient accuracy using a tropospheric propagation delay model. In the case of dual-frequency WADGPS, ionospheric propagation delay is not corrected.

[0024] The position error of the navigation satellite and the amount of ionospheric propagation delay vary depending on the location of the user station. Because correction information needs to be generated to reflect these characteristics, WADGPS is generally configured with four or more, and typically six or more, reference stations located geographically apart within the service area.

[0025] The minimum number of reference stations, four, is due to the number of unknowns, including the clock error and position error of the navigation satellite. Although each reference station can measure the ionospheric propagation delay, to correctly separate and extract the clock error and position error of the navigation satellite from the distance measurement error, four or more reference stations are required to accommodate the four unknowns.

[0026] However, if the service area is small, it may not be possible to deploy four or more reference stations. Even if four or more reference stations are deployed, they may not be geographically distant enough to correctly estimate the navigation satellite's position error or ionospheric propagation delay, and in either case, WADGPS will not function. In other words, when constructing an equation relating to the clock error and position error of a navigation satellite, the solution is usually used as the correction amount, and the condition for a unique solution is that four or more reference stations are installed geographically distant from each other. Taking into account the possibility of interference with reference stations, it is technically common knowledge among those skilled in the art that WADGPS requires at least five or more reference stations.

[0027] As described above, WADGPS requires that at least four or more reference stations be installed geographically apart. The object of the present invention is to alleviate this restriction and enable WADGPS to function even when four or more reference stations are not installed geographically apart. [Means for solving the problem]

[0028] Non-Patent Documents 1 and 2 describe in detail the method for generating correction information within WADGPS. However, the purpose of these documents is to obtain correction information for navigation satellite position errors and ionospheric propagation delays using normal methods, and they assume that there are four or more reference stations. The reported test results are based on five or six reference stations, and there is no particular mention of reducing the number of reference stations. Therefore, these technical contents do not solve the problems of the present invention.

[0029] If four or more reference stations are not installed geographically far apart, it may be possible to consider not correcting for the position error of the navigation satellite in WADGPS. In other words, correction is made only for the clock error of the navigation satellite, which is expected to be similar in nature to the LADGPS method, which only corrects for distance. In a satellite navigation system, the distance between the navigation satellite and the receiver is measured using their respective clocks, so the clock error of the navigation satellite and the line-of-sight component of the position error of the navigation satellite cannot be distinguished. Therefore, correcting only for the clock error of the navigation satellite is equivalent to correcting for distance only. Here, the line-of-sight direction refers to the direction from the reference station to the navigation satellite. When multiple reference stations are used, it refers to the direction from the center of gravity of the reference stations toward the navigation satellite.

[0030] Specifically, by constructing an equation relating to the clock error and position error of a navigation satellite, if the solution cannot be uniquely determined, the position error of the navigation satellite can be treated as zero instead of estimating it. However, since the transmission format of correction information is predetermined in WADGPS, it is not possible to not correct the position error of the navigation satellite. For this reason, correction information with a correction amount of zero is generated for the position error of the navigation satellite, and an equation relating only to the clock error is constructed for the clock error of the navigation satellite, and correction information is generated based on the solution. This is the first method for solving the problems of the present invention.

[0031] If the solution to the equations relating to the clock error and position error of the navigation satellite cannot be uniquely determined, correction information may be generated using a solution that minimizes the sum of squares of each coordinate axis component of the position error and the clock error. This is the second method for solving the problems of the present invention.

[0032] If the solution to the equations relating to the clock error and position error of a navigation satellite cannot be uniquely determined, a precise orbital ephemeris that is publicly available as predicted information for the navigation satellite's orbit can be obtained, and correction information for the navigation satellite's position error can be generated as the difference between the position based on this precise orbital ephemeris and the position calculated from the navigation satellite's own orbit information that is superimposed on the positioning signal and transmitted by the navigation satellite. In this case, for the clock error of the navigation satellite, an equation relating only to the clock error is constructed, and correction information is generated from the solution to that equation. This is a third method for solving the problems of the present invention.

[0033] Although these methods enable WADGPS to function even when four or more reference stations are not installed geographically apart, they do not preclude application to cases where four or more reference stations are installed geographically apart. In such a configuration, when the service area is small, sufficient correction performance can be obtained, while the advantage of being able to continue operation even when a reference station is down can be expected.

[0034] The invention of claim 1 corresponds to the above-mentioned first method, and is a method for generating correction information in 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 between them; a reference station that receives the positioning signals transmitted by the plurality of navigation satellites using a receiver fixed on the ground and measures the distances between them; and a master station that uses the distances measured by the reference station to generate correction information for each cause of positioning error, such as the clock error and position error of the navigation satellite, and stores this correction information in a predetermined transmission format and provides it to the user station, thereby performing wide-area differential correction, wherein, when generating correction information for the clock error and position error of the navigation satellite, the master station constructs an equation for the clock error and position error of the navigation satellite, and if the solution is not uniquely determined, generates correction information for the position error of the navigation satellite with the correction amount set to zero, and for the clock error of the navigation satellite, constructs an equation for the clock error of the navigation satellite and generates correction information based on the solution.

[0035] The invention of claim 2 corresponds to the second method described above, and is a method for generating correction information in 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 between them; a reference station that receives the positioning signals transmitted by the plurality of navigation satellites using a receiver fixed on the ground and measures the distances between them; and a master station that uses the distances measured by the reference station to generate correction information for each cause of positioning error, such as the clock error and position error of the navigation satellite, and stores this correction information in a predetermined transmission format and provides it to the user station, thereby performing wide-area differential correction, characterized in that, when generating correction information for the clock error and position error of the navigation satellite, the master station constructs equations for the clock error and position error of the navigation satellite, and if the solution cannot be uniquely determined, generates correction information using a solution that minimizes the sum of squares of each coordinate axis component of the position error and the clock error.

[0036] The invention according to claim 3 corresponds to the third method, and is a satellite navigation system that performs wide-area differential correction, 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 between them; a reference station that receives the positioning signals transmitted by the plurality of navigation satellites with a receiver fixed on the ground and measures the distances between them; and a master station that uses the distances measured by the reference station to generate correction information for each cause of positioning error, such as clock error and position error of the navigation satellite, and stores this correction information in a predetermined transmission format and provides it to the user station, wherein the master station is This is a method for generating correction information in a satellite navigation system, characterized in that when generating correction information for the clock error and position error of a navigation satellite, an equation for the clock error and position error of the navigation satellite is constructed, and if the solution cannot be uniquely determined, a precise orbital ephemeris that is publicly available as predicted information for the orbit of the navigation satellite is obtained, and for the position error of the navigation satellite, correction information is generated as the difference between the position according to the precise orbital ephemeris and the position calculated from the navigation satellite's own orbit information that the navigation satellite transmits superimposed on the positioning signal, and for the clock error of the navigation satellite, an equation for the clock error of the navigation satellite is constructed, and correction information is generated from the solution of the equation.

[0037] The invention of claim 4 corresponds to the first method described above, and is an information processing device for generating correction information in 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 the plurality of navigation satellites using a receiver fixed on the ground and measures the distance between them; and a master station that uses the distances measured by the reference station to generate correction information for each cause of positioning error, such as the clock error and position error of the navigation satellite, and stores this correction information in a predetermined transmission format and provides it to the user station, thereby performing wide-area differential correction.The information processing device is provided in the master station, and when generating correction information for the clock error and position error of the navigation satellite, it constructs an equation for the clock error and position error of the navigation satellite, and if the solution is not uniquely determined, it generates correction information for the position error of the navigation satellite with the correction amount set to zero, and for the clock error of the navigation satellite, it constructs an equation for the clock error of the navigation satellite and generates correction information based on the solution.

[0038] The invention of claim 5 corresponds to the second method described above, and comprises a plurality of navigation satellites that transmit positioning signals, a user station that receives the positioning signals transmitted by the plurality of navigation satellites and measures the distance between them, a reference station that receives the positioning signals transmitted by the plurality of navigation satellites using a receiver fixed on the ground and measures the distance between them, and a master station that uses the distances measured by the reference station to generate correction information for each cause of positioning error, such as the clock error and position error of the navigation satellite, and stores this correction information in a predetermined transmission format and provides it to the user station, thereby performing wide-area differential correction.The invention of claim 5 corresponds to the second method described above, and comprises a plurality of navigation satellites that transmit positioning signals, a user station that receives the positioning signals transmitted by the plurality of navigation satellites using a receiver fixed on the ground and measures the distance between them, and a master station that uses the distances measured by the reference station to generate correction information for each cause of positioning error, such as the clock error and position error of the navigation satellite, and stores this correction information in a predetermined transmission format and provides it to the user station, and is an information processing device that generates correction information in a satellite navigation system, characterized in that, when generating correction information for the clock error and position error of the navigation satellite, the master station constructs equations for the clock error and position error of the navigation satellite, and if the solution is not uniquely determined, generates correction information using a solution that minimizes the sum of squares of each coordinate axis component of the position error and the clock error.

[0039] The invention of claim 6 corresponds to the third method described above, and comprises a plurality of navigation satellites that transmit positioning signals, a user station that receives the positioning signals transmitted by the plurality of navigation satellites and measures the distances between them, a reference station that receives the positioning signals transmitted by the plurality of navigation satellites with a receiver fixed on the ground and measures the distances between them, and a master station that uses the distances measured by the reference station to generate correction information for each cause of positioning error such as clock error and position error of the navigation satellite, and stores this correction information in a predetermined transmission format to provide it to the user station, thereby performing wide-area differential correction in a satellite navigation system that is provided in the master station and receives the positioning signals of the navigation satellites. This is an information processing device that generates correction information in a satellite navigation system, characterized in that when generating correction information for clock error and position error, an equation for the clock error and position error of the navigation satellite is constructed, and if the solution cannot be uniquely determined, a precise orbital ephemeris that is publicly available as predicted information for the navigation satellite's orbit is obtained, and for the position error of the navigation satellite, correction information is generated as the difference between the position based on the precise orbital ephemeris and the position calculated from the navigation satellite's own orbit information that the navigation satellite transmits superimposed on the positioning signal, and for the clock error of the navigation satellite, an equation for the clock error of the navigation satellite is constructed, and correction information is generated using the solution.

[0040] The invention of claim 7 corresponds to the above-mentioned first method, and 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 the plurality of navigation satellites using a receiver fixed on the ground and measures the distance between them, and a master station that uses the distances measured by the reference station to generate correction information for each cause of positioning error, such as the clock error and position error of the navigation satellite, and stores this correction information in a predetermined transmission format and provides it to the user station, thereby performing wide-area differential correction.The invention of claim 7 is a program for generating correction information in a satellite navigation system, which operates in the master station, and when generating correction information for the clock error and position error of the navigation satellite, constructs an equation for the clock error and position error of the navigation satellite, and if the solution is not uniquely determined, generates correction information for the position error of the navigation satellite with the correction amount set to zero, and for the clock error of the navigation satellite, constructs an equation for the clock error of the navigation satellite and generates correction information based on the solution.

[0041] The invention of claim 8 corresponds to the second method described above, and is a satellite navigation system that performs wide-area differential correction, 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 the plurality of navigation satellites using a receiver fixed on the ground and measures the distance between them, and a master station that uses the distances measured by the reference station to generate correction information for each cause of positioning error, such as the clock error and position error of the navigation satellite, and stores this correction information in a predetermined transmission format and provides it to the user station, characterized in that, in generating correction information for the clock error and position error of the navigation satellite, the master station operates and constructs equations for the clock error and position error of the navigation satellite, and if the solution is not uniquely determined, generates correction information using a solution that minimizes the sum of squares of each coordinate axis component of the position error and the clock error.

[0042] The invention according to claim 9 corresponds to the third method described above, and comprises a plurality of navigation satellites that transmit positioning signals, a user station that receives the positioning signals transmitted by the plurality of navigation satellites and measures the distances between them, a reference station that receives the positioning signals transmitted by the plurality of navigation satellites with a receiver fixed on the ground and measures the distances between them, and a master station that uses the distances measured by the reference station to generate correction information for each cause of positioning error, such as clock error and position error of the navigation satellite, and stores this correction information in a predetermined transmission format to provide it to the user station, thereby performing wide-area differential correction in a satellite navigation system that operates in the master station and transmits the positioning signals to the navigation satellites. This is a program for generating correction information in a satellite navigation system, characterized in that when generating correction information for the clock error and position error of a navigation satellite, an equation for the clock error and position error of the navigation satellite is constructed, and if the solution cannot be uniquely determined, a precise orbital ephemeris that is publicly available as predicted information for the orbit of the navigation satellite is obtained, and for the position error of the navigation satellite, correction information is generated as the difference between the position according to the precise orbital ephemeris and the position calculated from the navigation satellite's own orbit information that the navigation satellite transmits superimposed on the positioning signal, and for the clock error of the navigation satellite, an equation for the clock error of the navigation satellite is constructed, and correction information is generated from the solution of that equation. [Effects of the Invention]

[0043] The inventions of claims 1 to 9 are configured as described above, and therefore enable WADGPS to function even when four or more reference stations are not installed geographically apart. [Brief explanation of the drawings]

[0044] [Figure 1] 1 is a schematic diagram illustrating a method for generating correction information in a satellite navigation system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0045] Specific embodiments of the present invention will be described in detail below with reference to the drawings. [Example]

[0046] An embodiment of the present invention will be described in detail with reference to FIG.

[0047] In FIG. 1, navigation satellites 1 (1a, 1b, etc.) each transmit a positioning signal.

[0048] The reference station 2 (2a, 2b...) receives the positioning signals transmitted from the navigation satellites 1 (1a, 1b...) and measures the distance from each navigation satellite. If necessary, it also calculates the amount of ionospheric propagation delay included in the distance from each navigation satellite.

[0049] The master station 3 calculates the clock error and position error of the navigation satellite by using the residual obtained by subtracting the distance between the navigation satellite and the reference station, calculated from the orbit information of the navigation satellite 1 (1a, 1b, etc.), the tropospheric propagation delay, and the corresponding ionospheric propagation delay from the distance measured by the reference station 2 (2a, 2b, etc.), and generates correction information.

[0050] The master station 3 stores the obtained correction information in a predetermined transmission format and provides it to the user station 4 .

[0051] When the master station 3 generates correction information regarding the clock error and position error of the navigation satellite 1 (1a, 1b, etc.), it constructs equations regarding the clock error and position error of the navigation satellite, and normally generates the correction information using the solution.

[0052] The condition for the solution of this equation to be uniquely determined is that four or more reference stations are installed geographically apart, and correction information could not be generated in the past if the solution was not uniquely determined.

[0053] In such a case, the master station 3 applies the first method of the present invention, and generates correction information for the position error of the navigation satellite 1 (1a, 1b, etc.) with the correction amount set to zero, and for the clock error of the navigation satellite, constructs an equation related only to the clock error and generates correction information based on the solution.

[0054] Alternatively, the master station 3 applies the second method of the present invention and generates correction information by solving the equations relating to the clock error and position error of the navigation satellite 1 (1a, 1b, etc.) in such a way that the sum of squares of each coordinate axis component of the position error and the clock error is minimized.

[0055] Alternatively, the master station 3 applies the third method of the present invention, obtaining the precise orbital ephemeris that is made public as predicted information for the orbit of the navigation satellite 1 (1a, 1b, etc.), and generates correction information for the position error of the navigation satellite as the difference between the position based on this precise orbital ephemeris and the position calculated from the navigation satellite's own orbit information that is superimposed on the positioning signal and transmitted by the navigation satellite, and for the clock error of the navigation satellite, constructing an equation related only to the clock error and generating correction information from the solution of that equation.

[0056] Next, the operation will be explained.

[0057] When the master station 3 determines the clock error and position error of the navigation satellite 1 (1a, 1b, etc.), it is necessary that the solution of the equation relating to the clock error and position error of the navigation satellite be uniquely determined, and a condition for this is that four or more reference stations are installed geographically apart. If this condition is not met, the solution will not be uniquely determined, but in such a case, the master station applies the first method of the present invention, and generates correction information with a correction amount of zero for the position error of the navigation satellite, and for the clock error of the navigation satellite, constructs an equation relating only to the clock error and generates correction information using that solution, thereby making it possible for WADGPS to function even in cases where a solution could not be obtained previously.

[0058] If the number of reference stations is N and the residual at the reference station is r1···rN (units: meters), then the position errors x, y, z (units: meters) and clock error b (units: meters, which becomes units of seconds when divided by the speed of light) of the navigation satellite are expressed as the following equations for the position error and clock error of the navigation satellite, using an N × 4 matrix G that represents the relationship between these and the residual. The fourth column of matrix G is all 1. "'" means the transpose of a vector.

[0059] (Number 1) G[xyzb]'=[r1 r2 ··· rN]'

[0060] For this equation, no unique solution can be obtained if the number of reference stations N is 3 or less. In such a case, correction information is generated for the position error of the navigation satellite with the correction amount set to zero, and for the clock error of the navigation satellite, an equation is constructed that concerns only the clock error, and correction information is generated using that solution.The only unknown is the clock error b of the navigation satellite, and the equation becomes as follows:

[0061] (Number 2) G[0 0 0 b]'=[r1 r2 ··· rN]'

[0062] This equation can be solved if there is at least one reference station (if there are multiple reference stations, for example, the least squares method can be used), and the solution can be used to generate correction information for the clock error of the navigation satellite.As for correction information for the position error of the navigation satellite, no calculation is required because the correction amount is set to zero.

[0063] In such cases, the position error of the navigation satellite that should be corrected will not be corrected, but the line-of-sight component of the position error will be included in the clock error of the navigation satellite and corrected, so that sufficient correction performance can be obtained in a small service area due to the same effect as LADGPS.

[0064] That is, for example, if there is only one reference station, it is not possible to distinguish between the clock error and position error of the navigation satellite 1 (1a, 1b, etc.). In this case, the correction amount for the position error of the navigation satellite is set to zero, and then the correction amount is calculated for only the clock error of the navigation satellite. Correction information is generated using these correction amounts, and the sum of the line-of-sight component of the position error of the navigation satellite and the clock error corresponds to the correction information. When such correction information is applied to the user station 4, appropriate correction can be expected in the vicinity of the only reference station, and although correction performance deteriorates as the distance between the reference station and the user station increases, sufficient correction performance can be obtained within a small service area.

[0065] In cases where the solution to the equations relating to the clock error and position error of a navigation satellite cannot be uniquely determined, the master station can apply the second method of the present invention and generate correction information using a solution that minimizes the sum of the squares of each coordinate axis component of the position error and the clock error, making it possible to make WADGPS function even in cases where a solution could not be obtained previously.

[0066] In this case, the equations relating to the position error and clock error of the navigation satellite remain the same as

[0059] , and a unique solution cannot be obtained unless four or more reference stations are installed geographically apart. However, among the infinite number of solutions, there is only one solution that minimizes the sum of squares of each coordinate axis component of the position error and the clock error, as expressed by the following equation:

[0067] (Number 3) [xyzb][xyzb]'

[0068] This allows us to determine a unique solution to the equation, which can then be used to generate correction information for the clock error and position error of the navigation satellite.

[0069] In such cases, the position error of the navigation satellite that should be corrected will not be corrected correctly, but if correction information is generated using a solution that minimizes the sum of the squares of each coordinate axis component of the position error and the clock error, sufficient correction performance can be obtained within a small service range.

[0070] For example, if there are three or fewer reference stations, it is not possible to correctly separate and extract the clock error and position error of the navigation satellite 1 (1a, 1b, etc.). In this case, the same correction results can be obtained at the center of gravity of the reference station group regardless of which solution to the equation is used. However, adopting the solution that minimizes the sum of the squares of each coordinate axis component of the position error and the clock error is rational in that it means treating each coordinate axis component of the position error and the clock error equally without making any special assumptions about them, and it is less likely to cause problems when storing the correction information generated from the obtained correction amount in the specified WADGPS transmission format. When such correction information is applied to the user station 4, appropriate correction can be expected around the center of gravity of the reference station group. Although the correction performance deteriorates as the distance between the center of gravity of the reference station group and the user station increases, sufficient correction performance can be obtained within a small service area.

[0071] In cases where the solution to the equations relating to the clock error and position error of a navigation satellite cannot be uniquely determined, the master station applies the third method of the present invention, obtains the precise orbital ephemeris that is published as predicted information for the navigation satellite's orbit, and generates correction information for the navigation satellite's position error as the difference between the position based on this precise orbital ephemeris and the position calculated from the navigation satellite's own orbit information that is superimposed on the positioning signal and transmitted by the navigation satellite, and for the clock error of the navigation satellite, constructs an equation relating only to the clock error and generates correction information using that solution, making it possible for WADGPS to function even in cases where a solution could not be obtained previously.

[0072] In this method, correction information is generated by determining the amount of correction for the position error of the navigation satellite without using an equation, and for the clock error of the navigation satellite, an equation is constructed that relates only to the clock error, and correction information is generated from the solution of that equation, so the only unknown is the clock error b of the navigation satellite, and the equation is the same as

[0061] .

[0073] This equation can be solved if there is at least one reference station (if there are multiple reference stations, for example, the least squares method can be used), and the solution can be used to generate correction information for the clock error of the navigation satellite. Correction information for the position error of the navigation satellite is generated based on the precise ephemeris, so no calculation is required here.

[0074] In this method, the position error of the navigation satellite is appropriately corrected based on the precise ephemeris, so correction performance similar to that of conventional WADGPS is obtained. In this case, the precise ephemeris must be predicted in order for WADGPS to operate in real time, but as stated in

[0021] , a drawback of predicted precise ephemeris (very rapid ephemeris) is that the prediction accuracy of the clock information is poor. However, this method does not use the clock information in the precise ephemeris, and only uses position information that can be expected to be highly accurate even in predicted precise ephemeris, so the correction information obtained by this method is effective.

[0075] In the first and second methods, we will explain by a numerical example that sufficient correction performance can be obtained in a small service area. If the vector representing the position error of a navigation satellite is denoted by 〈e〉 and the unit vector pointing from the only reference station to this navigation satellite is denoted by 〈r〉, the line-of-sight component of the position error of the navigation satellite at the reference station is the dot product of these two, and can be written as 〈e〉 · 〈r〉.

[0076] Similarly, if the unit vector from a user station to the same navigation satellite is denoted as 〈r'〉, the line-of-sight component of the navigation satellite's position error at the user station can be written as 〈e〉·〈r'〉.

[0077] The difference between these can be written as follows, since 〈r〉 and 〈r'〉 are unit vectors: Here, ∠er represents the angle between vector 〈e〉 and vector 〈r〉.

[0078] (Number 4) 〈e〉・〈r〉-〈e〉・〈r'〉=e(cos∠er-cos∠er') =e·△cos

[0079] This is an estimate of the degree of degradation in correction performance at the user station in

[0064] and

[0070] .

[0080] For example, if the altitude of the navigation satellite is 21,000 kilometers and the distance between the reference station and the user station is 500 kilometers, and ∠er = 90 degrees, then ∠er' ≒ 88.6 degrees, so we can calculate that △cos ≒ 0.024. If the magnitude of the navigation satellite's position error, e, is 2 meters, we can estimate that the degradation in correction performance is about 5 centimeters. The degree of this degradation is a function of ∠er, and is greatest when ∠er = 90 degrees.

[0081] The positioning accuracy obtained by WADGPS is usually about 0.5 to 1 meter, so a degradation of about 5 centimeters in distance accuracy is often acceptable.

[0082] When there are multiple reference stations, the exact same argument can be made if the center of gravity of the group of reference stations is considered to be the reference station in

[0075] . [Industrial Applicability]

[0083] The method for generating correction information in a satellite navigation system of this invention relaxes the previous restriction that four or more reference stations must be installed geographically apart in WADGPS, allowing WADGPS to function even when four or more reference stations are not installed geographically apart. This makes it possible to configure WADGPS even when there are restrictions on the installation conditions of the reference stations, and also improves the operational continuity of existing WADGPS in the event of a reference station failure. [Explanation of symbols]

[0084] 1(1a,1b···) Navigation satellite 2(2a,2b...) Reference station 3 Master station 4 User Station

Claims

1. a plurality of navigation satellites that transmit positioning signals; a user station that receives positioning signals transmitted from the plurality of navigation satellites and measures the distances therebetween; a reference station that receives positioning signals transmitted from the plurality of navigation satellites using a receiver fixed on the ground and measures the distances between them; In a satellite navigation system that performs wide-area differential correction, the master station generates correction information for each cause of positioning error, such as clock error and position error, of the navigation satellite using the distance measured by the reference station, stores this correction information in a predetermined transmission format, and provides it to the user station, The master station When generating correction information regarding clock errors and position errors of the navigation satellites, Construct an equation relating to the clock error and position error of the navigation satellite, and if the solution is not uniquely determined, For the position error of the navigation satellite, correction information is generated with the correction amount set to zero, A method for generating correction information in a satellite navigation system, characterized in that, for the clock error of a navigation satellite, an equation relating to the clock error of the navigation satellite is constructed and correction information is generated from the solution.

2. a plurality of navigation satellites that transmit positioning signals; a user station that receives positioning signals transmitted from the plurality of navigation satellites and measures the distances therebetween; a reference station that receives positioning signals transmitted from the plurality of navigation satellites using a receiver fixed on the ground and measures the distances between them; In a satellite navigation system that performs wide-area differential correction, the master station generates correction information for each cause of positioning error, such as clock error and position error, of the navigation satellite using the distance measured by the reference station, stores this correction information in a predetermined transmission format, and provides it to the user station, The master station When generating correction information regarding clock errors and position errors of the navigation satellites, Construct an equation relating to the clock error and position error of the navigation satellite, and if the solution is not uniquely determined, A method for generating correction information in a satellite navigation system, characterized in that correction information is generated using a solution that minimizes the sum of squares of each coordinate axis component of the position error and the clock error.

3. a plurality of navigation satellites that transmit positioning signals; a user station that receives positioning signals transmitted from the plurality of navigation satellites and measures the distances therebetween; a reference station that receives positioning signals transmitted from the plurality of navigation satellites using a receiver fixed on the ground and measures the distances between them; In a satellite navigation system that performs wide-area differential correction, the master station generates correction information for each cause of positioning error, such as clock error and position error, of the navigation satellite using the distance measured by the reference station, stores this correction information in a predetermined transmission format, and provides it to the user station, The master station When generating correction information regarding clock errors and position errors of the navigation satellites, Construct an equation relating to the clock error and position error of the navigation satellite, and if the solution is not uniquely determined, Obtaining a precise orbital ephemeris that is publicly available as predicted information on the orbit of the navigation satellite, Regarding the position error of the navigation satellite, correction information is generated as the difference between the position based on the precise orbital ephemeris and the position calculated from the navigation satellite's own orbit information superimposed on the positioning signal and transmitted by the navigation satellite; A method for generating correction information in a satellite navigation system, characterized in that, for the clock error of a navigation satellite, an equation relating to the clock error of the navigation satellite is constructed and correction information is generated from the solution.

4. a plurality of navigation satellites that transmit positioning signals; a user station that receives positioning signals transmitted from the plurality of navigation satellites and measures the distances therebetween; a reference station that receives positioning signals transmitted from the plurality of navigation satellites using a receiver fixed on the ground and measures the distances between them; In a satellite navigation system that performs wide-area differential correction, the master station generates correction information for each cause of positioning error, such as clock error and position error, of the navigation satellite using the distance measured by the reference station, stores this correction information in a predetermined transmission format, and provides it to the user station, provided in the master station, When generating correction information regarding clock errors and position errors of the navigation satellites, Construct an equation relating to the clock error and position error of the navigation satellite, and if the solution is not uniquely determined, For the position error of the navigation satellite, correction information is generated with the correction amount set to zero, An information processing device that generates correction information in a satellite navigation system, characterized in that, for the clock error of a navigation satellite, an equation relating to the clock error of the navigation satellite is constructed and correction information is generated from the solution.

5. a plurality of navigation satellites that transmit positioning signals; a user station that receives positioning signals transmitted from the plurality of navigation satellites and measures the distances therebetween; a reference station that receives positioning signals transmitted from the plurality of navigation satellites using a receiver fixed on the ground and measures the distances between them; In a satellite navigation system that performs wide-area differential correction, the master station generates correction information for each cause of positioning error, such as clock error and position error, of the navigation satellite using the distance measured by the reference station, stores this correction information in a predetermined transmission format, and provides it to the user station, provided in the master station, When generating correction information regarding clock errors and position errors of the navigation satellites, Construct an equation relating to the clock error and position error of the navigation satellite, and if the solution is not uniquely determined, An information processing device for generating correction information in a satellite navigation system, characterized in that the correction information is generated using a solution that minimizes the sum of squares of each coordinate axis component of the position error and the clock error.

6. a plurality of navigation satellites that transmit positioning signals; a user station that receives positioning signals transmitted from the plurality of navigation satellites and measures the distances therebetween; a reference station that receives positioning signals transmitted from the plurality of navigation satellites using a receiver fixed on the ground and measures the distances between them; In a satellite navigation system that performs wide-area differential correction, the master station generates correction information for each cause of positioning error, such as clock error and position error, of the navigation satellite using the distance measured by the reference station, stores this correction information in a predetermined transmission format, and provides it to the user station, provided in the master station, When generating correction information regarding clock errors and position errors of the navigation satellites, Construct an equation relating to the clock error and position error of the navigation satellite, and if the solution is not uniquely determined, Obtaining a precise orbital ephemeris that is publicly available as predicted information on the orbit of the navigation satellite, Regarding the position error of the navigation satellite, correction information is generated as the difference between the position based on the precise orbital ephemeris and the position calculated from the navigation satellite's own orbit information superimposed on the positioning signal and transmitted by the navigation satellite; An information processing device that generates correction information in a satellite navigation system, characterized in that, for the clock error of a navigation satellite, an equation relating to the clock error of the navigation satellite is constructed and correction information is generated from the solution.

7. a plurality of navigation satellites that transmit positioning signals; a user station that receives positioning signals transmitted from the plurality of navigation satellites and measures the distances therebetween; a reference station that receives positioning signals transmitted from the plurality of navigation satellites using a receiver fixed on the ground and measures the distances between them; In a satellite navigation system that performs wide-area differential correction, the master station generates correction information for each cause of positioning error, such as clock error and position error, of the navigation satellite using the distance measured by the reference station, stores this correction information in a predetermined transmission format, and provides it to the user station, Operates on the master station, When generating correction information regarding clock errors and position errors of the navigation satellites, Construct an equation relating to the clock error and position error of the navigation satellite, and if the solution is not uniquely determined, For the position error of the navigation satellite, correction information is generated with the correction amount set to zero, A program for generating correction information in a satellite navigation system, which constructs an equation related to the clock error of a navigation satellite and generates correction information based on the solution.

8. a plurality of navigation satellites that transmit positioning signals; a user station that receives positioning signals transmitted from the plurality of navigation satellites and measures the distances therebetween; a reference station that receives positioning signals transmitted from the plurality of navigation satellites using a receiver fixed on the ground and measures the distances between them; In a satellite navigation system that performs wide-area differential correction, the master station generates correction information for each cause of positioning error, such as clock error and position error, of the navigation satellite using the distance measured by the reference station, stores this correction information in a predetermined transmission format, and provides it to the user station, Operates on the master station, When generating correction information regarding clock errors and position errors of the navigation satellites, Construct an equation relating to the clock error and position error of the navigation satellite, and if the solution is not uniquely determined, A program for generating correction information in a satellite navigation system, characterized by generating correction information using a solution that minimizes the sum of squares of each coordinate axis component of the position error and the clock error.

9. a plurality of navigation satellites that transmit positioning signals; a user station that receives positioning signals transmitted from the plurality of navigation satellites and measures the distances therebetween; a reference station that receives positioning signals transmitted from the plurality of navigation satellites using a receiver fixed on the ground and measures the distances between them; In a satellite navigation system that performs wide-area differential correction, the master station generates correction information for each cause of positioning error, such as clock error and position error, of the navigation satellite using the distance measured by the reference station, stores this correction information in a predetermined transmission format, and provides it to the user station, Operates on the master station, When generating correction information regarding clock errors and position errors of the navigation satellites, Construct an equation relating to the clock error and position error of the navigation satellite, and if the solution is not uniquely determined, Obtaining a precise orbital ephemeris that is publicly available as predicted information on the orbit of the navigation satellite, Regarding the position error of the navigation satellite, correction information is generated as the difference between the position based on the precise orbital ephemeris and the position calculated from the navigation satellite's own orbit information superimposed on the positioning signal and transmitted by the navigation satellite; A program for generating correction information in a satellite navigation system, which constructs an equation related to the clock error of a navigation satellite and generates correction information based on the solution.

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