Method for generating correction information in a satellite navigation system and program for generating correction information

Abstract

Reduce the number of reference stations in the Wide Area Differential Correction System (WADGPS). [Solution] In satellite navigation systems, including the US GPS and Japan's Quasi-Zenith Satellite System, when configuring a Wide Area Differential Correction System (WADGPS) by setting up multiple reference stations, the noise is reduced by calculating correction information regarding the clock error, position error, and ionospheric propagation delay of the navigation satellites without using distance differences or linear combinations of positioning signals of multiple frequencies measured at the reference stations, thereby reducing the number of reference stations required to configure WADGPS.

Description

Technical Field

[0001] This invention relates to the generation of correction information in a satellite navigation system.

Background Art

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

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

[0004] The timing of navigation satellites transmitting positioning signals is predetermined, and these signals are transmitted based on the time on their own clocks. High-precision atomic clocks are used for this purpose, but very slight time discrepancies are unavoidable, so satellite navigation receivers require information on the time indicated by the navigation satellite's clock. This clock information is transmitted by the navigation satellite itself, superimposed on the positioning signal. Since the clock information is created by prediction, the timing of the positioning signal transmission calculated using this information contains an error equivalent to several meters in distance, and this becomes a factor in positioning errors when calculating the receiver's position as a clock error of the navigation satellite.

[0005] During the journey of a positioning signal to the ground, it passes through the ionosphere and troposphere, and delays occur as the radio signal passes through each region. These delays are called ionospheric propagation delay and tropospheric propagation delay, respectively. Therefore, when this radio signal is used as a positioning signal, these ionospheric and tropospheric propagation delays become factors in positioning errors. The magnitudes of the ionospheric and tropospheric propagation delays, converted to distance, are called the ionospheric propagation delay amount and tropospheric delay amount, respectively.

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

[0007] Navigation messages are the orbital information and clock information that navigation satellites transmit superimposed on their positioning signals. Navigation messages may also include information about ionospheric propagation delay, but generally, their accuracy is not sufficient.

[0008] A receiver is installed at a fixed ground-based reference station, and the distance measured by this receiver is used to create correction information for distance measurement errors. This information is then provided to the user, thereby correcting the distance measured at the user station based on the correction information and improving the accuracy of the user station's position measurement (referred to as "positioning accuracy"). This method is called Differential GPS (DGPS). To distinguish it from DGPS, the method of calculating the user station's position without applying correction information is called standalone positioning.

[0009] There are several specific DGPS methods, but the most common method involves a single base station measuring the distance and using that distance to generate distance correction values ​​for each navigation satellite, which are then provided to the user station. In this method, sometimes called Local Area DGPS (LADGPS), correction information is not created separately for each factor of positioning error. Therefore, as the distance between the user station and the base station increases, the common component of the positioning error decreases, and positioning accuracy tends to deteriorate. It is generally understood by those skilled in the art that it can be used within a range of approximately several hundred kilometers from the base station, or up to several tens of kilometers depending on the ionosphere conditions.

[0010] Another type of DGPS is called Wide Area Differential GPS (WADGPS). In this method, multiple reference stations (called a group of reference stations) measure distances and use that distance to generate correction information for each factor of positioning error, such as the clock error of the navigation satellites, the position error of the navigation satellites, the ionospheric propagation delay, and the tropospheric propagation delay, and provide this information to the user station. Since the way each of these error factors manifests as distance measurement errors differs depending on the user station's location, the user station calculates the correction value it should use from the correction information based on its approximate location and uses it for correction.

[0011] The clock error of the navigation satellite manifests as a uniform distance measurement error regardless of the user station's position. The position error of the navigation satellite manifests as a distance measurement error as the dot product component of the line of sight direction when the navigation satellite is viewed from the user station. The ionospheric propagation delay manifests as a distance measurement error as the integral of the free electron density distribution (total number of electrons) in the ionospheric atmosphere along the path from the navigation satellite's transmitted ranging signal to the user station. The tropospheric propagation delay manifests as a distance measurement error as the integral of the refractive index of the neutral atmosphere along the path from the navigation satellite's transmitted ranging signal to the user station. In other words, with the exception of the navigation satellite's clock error, the distance measurement error manifests differently depending on the user station's position.

[0012] It is known that the ionospheric propagation delay is proportional to the total number of electrons in the ionospheric atmosphere through which the positioning signal passes, and inversely proportional to the square of the frequency of the positioning signal. Therefore, at a base station, if distance measurements are performed using positioning signals of multiple frequencies, the ionospheric propagation delay can be calculated from the difference between those distances. Alternatively, at a base station or user station, if distance measurements are performed using positioning signals of multiple frequencies, the distance with the ionospheric propagation delay removed can be obtained as a linear combination of those measurement results.

[0013] Furthermore, tropospheric propagation delay can be estimated with sufficient accuracy using a simple tropospheric propagation delay model, and corrections can be made at both the base station and the user station. Therefore, in WADGPS, tropospheric propagation delay does not need to be included in the correction information.

[0014] In WADGPS systems where user stations are equipped with receivers corresponding to a single-frequency positioning signal (referred to as "single-frequency WADGPS"), it is necessary to transmit the ionospheric propagation delay amount as part of the correction information. Therefore, the master station needs to determine the ionospheric propagation delay amount across the service area.

[0015] In WADGPS systems where the user station is equipped with a receiver that supports positioning signals of two frequencies (referred to as "dual-frequency WADGPS"), the correction information does not include ionospheric propagation delay. Both the base station and the user station measure distance using positioning signals of multiple frequencies, and the distance with the ionospheric propagation delay removed is obtained as a linear combination of these measurement results.

[0016] WADGPS requires defining the transmission format for correction information, and correction information is accommodated according to the factors of positioning error, such as the clock error and position error of the navigation satellite, and in the case of single-frequency WADGPS, also the ionospheric propagation delay. Although the tropospheric propagation delay can be corrected with sufficient accuracy using a tropospheric propagation delay model and does not need to be included in the WADGPS transmission format, both the master station and user stations must use a predetermined common tropospheric propagation delay model for correction.

[0017] In WADGPS, it is necessary to define not only the physical meaning of the correction information, but also how to use it, that is, the procedure for applying the correction information at the user station. Without knowing the processing details of the user station, it is impossible to generate appropriate correction information. Therefore, when the master station generates correction information, the procedure for applying the generated correction information at the user station is already known. On the other hand, there is no need to specifically define the method of generating the correction information.

[0018] One practical application of WADGPS is the SBAS (Satellite-Based Augmentation System) standardized for aircraft. The SBAS standard for single-frequency WADGPS is named "L1 SBAS," and the SBAS standard for dual-frequency WADGPS is named "L5 SBAS."

[0019] One example of an L1 SBAS is the MSAS (Michibiki-Based Satellite Augmentation System) operated by the Japan Civil Aviation Bureau, which is currently in practical use. More recently, South Korea has begun operating the KASS (Korea Augmentation Satellite System). As for L5 SBAS, there are currently no examples of it being used in practice.

[0020] In the L1 SBAS standard, correction information for the clock error and position error of navigation satellites is expressed as correction values ​​for the X-axis, Y-axis, and Z-axis directions of the navigation satellite's position error, and a correction value for the navigation satellite's clock error.

[0021] In the L1 SBAS standard, correction information regarding ionospheric propagation delay is expressed as the vertical delay amount of ionospheric propagation delay at multiple grid points. Grid points are set every 5 degrees of latitude and longitude to sufficiently cover the entire service area. User stations are required to obtain the required ionospheric propagation delay amount by linear interpolation of the vertical delay amount at grid points around the location where the positioning signal passes through the ionosphere. The standard defines the procedure for selecting grid points, the bilinear interpolation formula used for linear interpolation, and a conversion formula for converting the vertical delay amount to the line-of-sight direction.

[0022] Currently available satellite navigation systems include the US GPS, as well as Russia's GLONASS, Europe's Galileo, China's BDS, India's NavIc, and Japan's QZSS. [Prior art documents] [Non-patent literature]

[0023] [Non-Patent Document 1] Takeyasu Sakai, Shonosuke Fukushima, Naoki Arai, Ken Ito, "Prototype Evaluation of a GPS Wide-Area Augmentation System," IEICE Transactions on Electronics, Information and Communication Engineers, Vol. J89-B, No. 7, pp. 1297-1306, July 2006. [Non-Patent Document 2] T. Walter, "Robust Detection of Ionospheric Irregularities", NAVIGATION: Journal of the Institute of Navigation, Vol. 48, No. 2, pp. 89 - 199, 2001 [Non - Patent Document 3] Takeyasu Sakai, "Bias Error Estimation Method for Total Electron Content Observation of the Ionosphere by GPS", Transactions of the Institute of Electronics, Information and Communication Engineers, Vol. J88 - B, No. 12, pp. 2382 - 2389, December 2005 [Non - Patent Document 4] C. Kee, B. Parkinson, "Wide Area Differential GPS (WADGPS): Future Navigation System", IEEE Transactions on Aerospace and Electronic Systems, Vol. 32, No. 2, pp. 795 - 808, April 1996 [Summary of the Invention] [Problems to be Solved by the Invention]

[0024] In single - frequency WADGPS, correction information is generated for each factor of positioning error such as the clock error of the navigation satellite, the position error of the navigation satellite, the ionospheric propagation delay, and the tropospheric propagation delay using the distances measured by the reference station. Among these, for the tropospheric propagation delay, it can be corrected with sufficient accuracy by the tropospheric propagation delay model.

[0025] For the clock error and position error of the navigation satellite, by using the distance from which the ionospheric propagation delay obtained as a linear combination of distances from positioning signals of multiple frequencies measured at the reference station is removed, predicting the time indicated by the clock and the satellite orbit, these can be calculated as the difference from the information in the navigation message. Reversing the signs of the clock error and position error of the navigation satellite results in correction information regarding the clock error and position error.

[0026] Alternatively, regarding the clock error and position error of navigation satellites, instead of predicting the time indicated by the clock or the satellite orbit, one could remove the ionospheric propagation delay from the distance measured at the reference station, construct an equation that expresses the relationship between this and the clock error and position error of the navigation satellite, and obtain the result as the solution to that equation.

[0027] The ionospheric propagation delay can be calculated from the difference in distances between positioning signals of multiple frequencies measured at the base station, utilizing the fact that the ionospheric propagation delay is inversely proportional to the square of the positioning signal frequency. Reversing the sign of the ionospheric propagation delay results in correction information regarding the ionospheric propagation delay. The correction information provided to user stations must be capable of calculating the ionospheric propagation delay at any given location. Therefore, it is necessary to define a transmission format that enables this and to apply appropriate processing to the ionospheric propagation delay measured by the base station before incorporating it into that transmission format.

[0028] The processing method for the single-frequency WADGPS described above is explained in Non-Patent Document 1.

[0029] To obtain the distance PSR (Position Speed ​​Range), which is the distance measured by positioning signals of multiple frequencies with the ionospheric propagation delay removed, as a linear combination of these distances, the following equation is used. Hereafter, the symbol "^" indicates exponentiation.

[0030] (Math 1) PSR=(γ×PSR(f1)-PSR(f2)) / (γ-1)

[0031] Here, let the coefficient γ = f1^2 / f2^2. If the standard deviations of PSR(f1) and PSR(f2) are both σ, then when these probability distributions are independent, the standard deviation of PSR σ(PSR) is given by the following equation.

[0032] (Math 2) σ(PSR)^2=((γ^2+1) / (γ-1)^2)×σ^2

[0033] For example, if f1 is the GPS L1 frequency and f2 is the GPS L2 frequency, then σ(PSR) will be approximately three times σ. In addition, bias errors when using positioning signals of multiple frequencies, which is a major issue in Non-Patent Document 3, will also be added.

[0034] Thus, the distance obtained as a linear combination of distances measured by positioning signals of multiple frequencies, from which the ionospheric propagation delay has been removed, will have more noise than the original measured distance. Consequently, the clock and position errors of the navigation satellites obtained in this way will also have more noise, and therefore, in order to generate correction information regarding the clock and position errors of the navigation satellites with sufficient accuracy, it is necessary to use a large amount of distance measurement data. Increasing the amount of distance measurement data is only possible by increasing the number of reference stations, given that the number of navigation satellites remains the same, so in order to secure a sufficient amount of measurement data, it is necessary to set up a large number of reference stations.

[0035] Non-patent document 2 describes a method for generating correction information regarding ionospheric propagation delay that conforms to the transmission format of the SBAS standard, using the results of calculating the amount of ionospheric propagation delay from the distances obtained by positioning signals of multiple frequencies measured at a reference station.

[0036] In the SBAS standard, correction information regarding ionospheric propagation delay is expressed as the vertical ionospheric propagation delay amount at multiple grid points. Therefore, in actual SBAS systems, the ionospheric propagation delay amount at each grid point is estimated using the ionospheric propagation delay amount measured around each grid point.

[0037] Non-patent document 3 provides a detailed explanation of a method for calculating ionospheric propagation delay from distances measured at multiple frequency positioning signals at a reference station. When using positioning signals of multiple frequencies, bias errors between them become a problem, and a method for eliminating these bias errors is the main issue addressed in Non-patent document 3.

[0038] In all of Non-Patent Documents 1 to 3, the amount of ionospheric propagation delay required to generate correction information regarding ionospheric propagation delay is calculated using the distances obtained from positioning signals of multiple frequencies measured at the base station. In this process, since the difference between the distances measured at multiple frequencies is used, the calculated amount of ionospheric propagation delay is noisy.

[0039] To calculate the ionospheric propagation delay using the difference in distance measured by positioning signals of multiple frequencies, specifically, the distance PSR(f1) measured at frequency f1 and the distance PSR(f2) measured at frequency f2 are used in the following calculation.

[0040] (Math 3) I(f1)=(PSR(f1)-PSR(f2)) / (1-γ)

[0041] I(f1) is the ionospheric propagation delay at frequency f1, and the coefficient γ is the same as in (Equation 1). If the standard deviations of PSR(f1) and PSR(f2) are both σ, then when their probability distributions are independent, the standard deviation of I(f1), σ(I), is given by the following equation.

[0042] (Math 4) σ(I)^2 = (2 / (1-γ)^2) × σ^2

[0043] For example, if f1 is the GPS L1 frequency and f2 is the GPS L2 frequency, then σ(I) will be approximately 2.2 times σ. In addition, bias errors when using positioning signals of multiple frequencies, which is a major issue in Non-Patent Document 3, will also be added.

[0044] Thus, because the noise in the ionospheric propagation delay amount obtained by calculation is large, a large amount of measured ionospheric propagation delay data is required to generate correction information regarding ionospheric propagation delay with sufficient accuracy. For example, the method described in Non-Patent Document 2 requires approximately 20 to 30 measured ionospheric propagation delay data points. To increase the amount of measured ionospheric propagation delay data, if the number of navigation satellites remains the same, there is no other way than to increase the number of reference stations. Therefore, to secure a sufficient amount of measured data, it is necessary to set up a large number of reference stations.

[0045] As described above, single-frequency WADGPS systems have the problem of requiring a large number of reference stations due to the significant noise from distance information needed to generate correction information regarding the clock and position errors of navigation satellites, and the noise from ionospheric propagation delay needed to generate correction information regarding ionospheric propagation delay. Furthermore, since reference stations need to measure distance using positioning signals of multiple frequencies, if a positioning signal of any frequency becomes unavailable for any reason, it becomes impossible to generate correction information. This invention solves these problems by changing the method of generating correction information in single-frequency WADGPS systems. [Means for solving the problem]

[0046] In WADGPS, while the method for generating correction information is not specifically defined, the method for using the correction information, i.e., the procedure for applying the correction information at user stations, is defined. Therefore, when the master station generates correction information, the procedure for applying the generated correction information at user stations is already known.

[0047] Let ΔP(i,u,f) be the measurement error, excluding tropospheric propagation delay, included in the distance measured for the positioning signal of navigation satellite i at frequency f received by user station u. That is, if the measured distance is PSR(i,u,f), the distance between the position of user station u and the position of navigation satellite i determined by the navigation message is R(i,u), the clock error of navigation satellite i determined by the navigation message is B(i), and the tropospheric propagation delay is T(i,u), then ΔP(i,u,f) can be written as follows.

[0048] (Math 5) ΔP(i,u,f)=PSR(i,u,f) -R(i,u)+B(i)-T(i,u)

[0049] If this residual is zero, then no positioning error will occur. If the relationship between this residual and the correction information and the receiver clock error of the user station u is linear, then when the correction information and the receiver clock error of the user station u are represented by vector C, the relationship between them can be expressed as follows via a coefficient vector W(i,u,f). Hereafter, the symbol "·" represents the dot product of vectors, and the symbol "'" represents the transpose of a vector.

[0050] (Math 6) ΔP(i,u,f)+W(i,u,f)·C=0

[0051] The coefficient vector W(i,u,f) represents the procedure for applying correction information at the user station and is determined by the positional relationship between the navigation satellite i and the user station u. The coefficients related to correction information concerning ionospheric propagation delay are further functions of frequency f.

[0052] By the way, the position of user station u is arbitrary within the WADGPS service area. Therefore, this relationship also holds for base station k. The residual of (Equation 5) for base station k is given by the following equation.

[0053] (Number 7) ΔP(i,k,f)=PSR(i,k,f) -R(i,k)+B(i)-T(i,k)

[0054] Furthermore, the relationship in (Equation 6) becomes as follows for base station k.

[0055] (Math 8) ΔP(i,k,f)+W(i,k,f)·C=0

[0056] Assuming that all of the M reference stations receive positioning signals from N navigation satellites, we can construct at least N × M equations (Equation 8). Solving this system of equations with vector C as the unknown will yield correction information. That is, if ΔP is the vector obtained by arranging ΔP(i,k,f) vertically for all i,k,f, and W is the observation matrix obtained by arranging W(i,k,f)' vertically to match ΔP, then we can solve the following equation for vector C using an appropriate method such as the least squares method or a Kalman filter.

[0057] (Math 9) W·C=-ΔP

[0058] This equation is constructed for the position of the reference station k of station M, and does not include the position of the user station u. However, generally, due to the nature of correction information in satellite navigation systems, it can be expected that the relationship (Equation 6) holds for the position of the user station u within the geographical area enclosed by the reference station of station M and its surrounding areas.

[0059] Furthermore, ΔP(i,k,f) is determined from the distance measured for the positioning signal at frequency f, and it is acceptable for there to be multiple relationship formulas for different frequencies for the same navigation satellite i and reference station k. Also, the frequency f may be the same or different for different navigation satellites or reference stations.

[0060] Correction information for the clock and position errors of navigation satellites is represented as an N×4-dimensional vector CS, correction information for ionospheric propagation delay is represented as a K-dimensional vector CI, and the receiver clock error of the reference station is represented as an M-dimensional vector CR. N is the number of navigation satellites to be processed, M is the number of reference stations, and K is the number of correction information for ionospheric propagation delay.

[0061] As the first configuration, in order to calculate any of these, we can define vector C as follows. Hereafter, the symbol "|" means vector concatenation.

[0062] (Number 10) C=[CS'|CI'|CR']'

[0063] In this case, W(i,k,f) is given by the following equation, where WS(i,k) is the coefficient vector for the clock error and position error of the navigation satellite, WI(i,k,f) is the coefficient vector for the ionospheric propagation delay, and WR(k) is the coefficient vector for the receiver clock error of the reference station.

[0064] (Math 11) W(i,k,f)=[WS(i,k)'|WI(i,k,f)' |WR(k)']'

[0065] For example, in the L1 SBAS standard, correction information regarding the clock error and position error of navigation satellites is expressed as correction values ​​for the X-axis, Y-axis, and Z-axis directions of the navigation satellite's position error, and a correction value for the navigation satellite's clock error.

[0066] Let P(i,k) be the ranging error caused by the clock error and position error of the navigation satellite in the positioning signal received by base station k from satellite i. Since this is equal to the line-of-sight component of the clock error and position error of the navigation satellite that the user station at base station k should use for correction processing, if LOS(i,k) is the line-of-sight vector from base station k to navigation satellite i, CS(nx) is the correction value in the X-axis direction of the position error of navigation satellite i, CS(ny) is the correction value in the Y-axis direction, CS(nz) is the correction value in the Z-axis direction, and CS(ns) is the correction value of the clock error of navigation satellite i, then their relationship can be written as follows. Note that the clock error is considered in the dimension of distance by multiplying it by the speed of light. E(X), E(Y), and E(Z) are unit vectors in the X-axis, Y-axis, and Z-axis directions, respectively.

[0067] (Math 12) P(i,k)= E(X)·LOS(i,k)×CS(nx) +E(Y)·LOS(i,k)×CS(ny) +E(Z)·LOS(i,k)×CS(nz) -CS(ns)

[0068] Thus, the vector WS(i,k) can be written as follows: WS(i,k)〈n〉 represents the nth element of the vector WS(i,k), and all other elements are zero.

[0069] (Math 13) WS(i,k)〈nx〉=E(X)·LOS(i,k) WS(i,k)〈ny〉=E(Y)·LOS(i,k) WS(i,k)〈nz〉=E(Z)·LOS(i,k) WS(i,k)〈ns〉=-1

[0070] In other words, the correction information regarding the clock error and position error of navigation satellites is linearly related to the residual in (Equation 7), so the correction information can be obtained by solving the system of equations in (Equation 9).

[0071] For example, in the L1 SBAS standard, correction information regarding ionospheric propagation delay is expressed as the vertical delay amount of ionospheric propagation delay at grid points. Grid points are set every 5 degrees of latitude and longitude. User stations are required to obtain the required ionospheric propagation delay amount by linear interpolation of the vertical delay amount at grid points around the location where the positioning signal passes through the ionosphere. Along with the bilinear interpolation formula used for linear interpolation, a conversion formula for converting the vertical delay amount to the line-of-sight direction is also defined.

[0072] Let I(i,k,f) be the ionospheric propagation delay in the positioning signal of satellite i at frequency f received by base station k. Since this is equal to the ionospheric propagation delay that the user station at base station k should use for correction processing, if we take the position through which the positioning signal passes through the ionosphere as the reference point, and express the vertical ionospheric propagation delays at the nearest grid points n1 to n4 in the directions 1: southwest, 2: southeast, 3: northwest, 4: northeast as CI(n1) to CI(n4), and the coefficients in the corresponding bilinear interpolation as w1 to w4, and let S(i,k) be the conversion formula that converts the vertical delay to the line-of-sight direction, then their relationship can be written as follows.

[0073] (Number 14) I(i,k,f)=F(f)×S(i,k) ×(w1×CI(n1)+w2×CI(n2) +w3×CI(n3)+w4×CI(n4))

[0074] F(f) is a coefficient that reflects the fact that the ionospheric propagation delay is inversely proportional to the square of the positioning signal frequency, and since L1 SBAS is based on the GPS L1 frequency, if we let the GPS L1 frequency be fL1, it can be written as follows.

[0075] (Math 15) F(f) = fL1^2 / f^2

[0076] Thus, the vector WI(i,k,f) can be written as follows: WI(i,k,f)〈n〉 represents the nth element of the vector WI(i,k,f), and all other elements are zero.

[0077] (Math 16) WI(i,k,f)〈n1〉=-F(f)×S(i,k)×w1 WI(i,k,f)〈n2〉=-F(f)×S(i,k)×w2 WI(i,k,f)〈n3〉=-F(f)×S(i,k)×w3 WI(i,k,f)〈n4〉=-F(f)×S(i,k)×w4

[0078] In other words, the correction information regarding ionospheric propagation delay is linearly related to the residual in (Equation 7), so the correction information can be obtained by solving the system of equations in (Equation 9). Since CI(n1) to CI(n4) represent the amount of ionospheric propagation delay, their signs must be reversed to use them as correction values.

[0079] Furthermore, in cases where there are multiple relationships for different frequencies with respect to the same navigation satellite i and reference station k, the ionospheric propagation delay is not calculated from the difference in their distances, nor is it obtained by linearly combining those distances to remove the ionospheric propagation delay. Rather, the multiple relationships can simply be placed in parallel, and in this case, for certain frequencies f1 and f2, WI(i,k,f1) and WI(i,k,f2) have the following relationship.

[0080] (Number 17) WI(i,k,f1)×f2^2=WI(i,k,f2)×f1^2

[0081] The receiver clock error of the reference station has the effect of stretching the distance measurement made by the reference station receiver. Therefore, if the receiver clock error of the reference station k is denoted as CR(n), the vector WR(k) can be written as follows: WR(k)〈n〉 represents the nth element of the vector WR(k), and all other elements are zero.

[0082] (Number 18) WR(k)〈n〉=-1

[0083] As a second configuration, assuming that correction information CS regarding the clock error and position error of the navigation satellite is given, in order to generate only the correction information CI regarding the ionospheric propagation delay, the vector C can be defined as follows.

[0084] (Number 19) C=[CI'|CR']'

[0085] In this case, W(i,k,f) is given by the following equation. WI(i,k,f) and WR(k) are the same as in the first configuration.

[0086] (Number 20) W(i,k,f)=[WI(i,k,f)'|WR(k)']'

[0087] In all of Non-Patent Documents 1 to 3, the amount of ionospheric propagation delay required to generate correction information regarding ionospheric propagation delay is calculated using the difference in distances from positioning signals of multiple frequencies measured at the base station, and not by the residual (Equation 7) which does not use the difference.

[0088] Regarding WADGPS, there is a study example of its configuration in Non-Patent Document 4, which describes a configuration in which both the base station and the user station use a single-frequency positioning signal. In this configuration, the difference in distance measured at multiple frequencies is not used at the base station to obtain the ionospheric propagation delay amount.

[0089] However, this configuration requires a larger number of base stations compared to a configuration that uses positioning signals of multiple frequencies at a base station. Furthermore, since the method of using the difference in distance measured by multiple frequencies is considered the most reliable way to obtain the ionospheric propagation delay, the quality of correction information regarding ionospheric propagation delay is considered inferior to that of a configuration that uses positioning signals of multiple frequencies at a base station.

[0090] Non-patent document 4 states that, in principle, it is possible to measure ionospheric propagation delay using a single-frequency positioning signal, but because it uses carrier phase, further research is needed to obtain stable measurements. Furthermore, the correction information regarding ionospheric propagation delay provided by WADGPS is not described in detail, nor is its generation method mentioned.

[0091] Similar to the example described in Non-Patent Document 4, the present invention employs a configuration in which both the base station and the user station use a single-frequency positioning signal. However, the ionospheric propagation delay is incorporated into (Equation 9) and calculated integrally with the correction information CS relating to the clock error and position error of the navigation satellite and the receiver clock error CR of the base station. It is not measured using the difference in distance measured by multiple frequencies, nor is it measured using the carrier phase. In particular, by using the vertical delay amount at the grid point as the correction information relating to the ionospheric propagation delay, the relationship with the residual in (Equation 7) becomes linear, and the system of equations in (Equation 9) can be constructed.

[0092] We will examine the quality of correction information regarding ionospheric propagation delay. In cases not according to the present invention, as described in

[0039] to

[0043] , when the amount of ionospheric propagation delay is calculated using the difference in distance measured by positioning signals of GPS L1 frequency and GPS L2 frequency, noise approximately 2.2 times greater than the noise in the original distance measurement is generated. If this noise is to be compensated for by increasing the amount of measurement data, then 2.2^2 ≈ 5 times the amount of measurement data will be required. In order to increase the amount of ionospheric propagation delay measurement data, if the number of navigation satellites remains the same, there is no other way than to increase the number of reference stations, so it is necessary to set up 5 times the number of reference stations compared to the case where the difference is not used.

[0093] According to the methods described in

[0052] to

[0059] and

[0071] to

[0080] of the present invention, the correction information regarding ionospheric propagation delay is calculated from the distance measured at the reference station without using the difference. Therefore, the noise is equal to the noise in the original distance measurement and is about 1 / 2.2 of that when the difference in distance measured by the positioning signals of GPS L1 frequency and GPS L2 frequency is used. Consequently, as far as the generation of correction information regarding ionospheric propagation delay is concerned, only one-fifth the number of reference stations are required compared to the method using the difference.

[0094] Therefore, regarding correction information for ionospheric propagation delay, a single-frequency configuration does not require more reference stations than a configuration using the difference between multiple frequencies; in fact, it can significantly reduce the number of reference stations. Furthermore, when determining the amount of ionospheric propagation delay from the difference in distances using positioning signals of multiple frequencies, it is necessary to remove bias errors using methods such as those described in Non-Patent Document 3. However, since it is difficult to do this completely, a single-frequency configuration actually suppresses measurement noise when obtaining the amount of ionospheric propagation delay compared to a configuration using the difference between multiple frequencies, and the quality of the correction information for ionospheric propagation delay is not inferior.

[0095] This section examines the quality of correction information regarding the clock and position errors of navigation satellites. In cases not according to the present invention, as described in

[0029] to

[0033] , when the distance with the ionospheric propagation delay removed is calculated as a linear combination of the distances measured by the positioning signals of GPS L1 frequency and GPS L2 frequency, approximately three times the noise in the original distance measurement is generated. If this noise is to be compensated for by increasing the amount of measurement data, 3^2 ≈ 9 times the amount of measurement data is required. To increase the amount of distance measurement data, if the number of navigation satellites remains the same, there is no other way than to increase the number of reference stations, so it is necessary to install 9 times the number of reference stations compared to the case without using linear combination.

[0096] According to the methods described in

[0052] to

[0070] of the present invention, correction information regarding the clock error and position error of navigation satellites is calculated from the distance measured at the reference station without using the difference. Therefore, the noise is equal to the noise in the original distance measurement and is about one-third of that when a linear combination of the distance measured by the positioning signals of GPS L1 frequency and GPS L2 frequency is used. Consequently, as far as the generation of correction information regarding the clock error and position error of navigation satellites is concerned, only one-ninth the number of reference stations are required compared to the method using a linear combination.

[0097] Therefore, regarding correction information for the clock and position errors of navigation satellites, a single-frequency configuration does not require more reference stations than a configuration using a linear combination of multiple frequencies; in fact, it can significantly reduce the number of reference stations.

[0098] As described above, in a single-frequency WADGPS, by using measurement data of a single frequency and configuring the method for generating specific correction information as described in

[0052] to

[0082] , correction information regarding the clock error and position error of navigation satellites, as well as ionospheric propagation delay, can be calculated without using distance differences or linear combinations of positioning signals of multiple frequencies measured at the base station. As a result, noise can be kept low, and consequently, the number of base stations constituting the WADGPS can be reduced. Furthermore, if the base station receives positioning signals of multiple frequencies, the generation of correction information can continue even if a positioning signal of one of the frequencies becomes unusable for any reason.

[0099] Furthermore, in a single-frequency WADGPS, by using measurement data of a single frequency and configuring the method for generating specific correction information as described in

[0052] to

[0060] and

[0083] to

[0086] , correction information related to ionospheric propagation delay can be calculated without using the difference in distance from positioning signals of multiple frequencies measured at the base station. As a result, noise can be kept low, and consequently, the number of base stations constituting the WADGPS can be reduced. In addition, if the base station receives positioning signals of multiple frequencies, the generation of correction information can continue even if a positioning signal of one of the frequencies becomes unusable for any reason.

[0100] The invention according to claim 1 comprises a plurality of navigation satellites that transmit positioning signals, a user station that receives positioning signals transmitted by the plurality of navigation satellites and measures the distance between them, a plurality of reference stations that receive positioning signals of one or more frequencies transmitted by the plurality of navigation satellites using a receiver fixed on the ground and measure the distance between them, and a master station that uses the distances measured by the plurality of reference stations to generate correction information regarding the clock error, position error, and ionospheric propagation delay of the navigation satellites according to the factors of positioning error, and provides this correction information to the user station, wherein the correction information regarding the clock error and position error of the navigation satellites is expressed as correction values ​​for the clock error and position error of the plurality of navigation satellites in each coordinate axis direction, and the correction information regarding ionospheric propagation delay is expressed as a vertical ionospheric propagation delay amount for positioning signals of a specific frequency at a plurality of grid points arranged to sufficiently cover the geographical area of ​​the service target, thereby wide-area differential In a satellite navigation system that performs initial correction, the master station generates correction information relating to the clock error, position error, and ionospheric propagation delay of the navigation satellites. The master station generates correction information relating to the clock error, position error, and ionospheric propagation delay of the navigation satellites. The master station then collects the residuals obtained by subtracting the clock error, the distance between the navigation satellite and the reference station, and the tropospheric propagation delay amount, which are determined by the navigation message, from the distance measured by each of the multiple reference stations using the positioning signals of one or more frequencies, for each of the multiple navigation satellites, for effective combinations of the multiple navigation satellites, the multiple reference stations, and the multiple frequencies. The master station then constructs an equation representing the relationship between the clock error and position error of the multiple navigation satellites, the vertical ionospheric propagation delay amount relating to the positioning signals of specific frequencies at the multiple grid points, and the receiver clock error of the multiple reference stations. The solution to this equation is obtained as correction information relating to the clock error, position error, and ionospheric propagation delay of the navigation satellites.

[0101] The invention according to claim 2 comprises a plurality of navigation satellites that transmit positioning signals, a user station that receives positioning signals transmitted by the plurality of navigation satellites and measures the distance between them, a plurality of reference stations that receive positioning signals of one or more frequencies transmitted by the plurality of navigation satellites using a receiver fixed on the ground and measure the distance between them, and a master station that uses the distances measured by the plurality of reference stations to generate correction information regarding the clock error, position error, and ionospheric propagation delay of the navigation satellites according to the factors of positioning error, and provides this correction information to the user station, wherein the correction information regarding the clock error and position error of the navigation satellites is expressed as correction values ​​for the clock error and position error of the plurality of navigation satellites in each coordinate axis direction, and the correction information regarding ionospheric propagation delay is expressed as a vertical ionospheric propagation delay amount for positioning signals of a specific frequency at a plurality of grid points arranged to sufficiently cover the geographical area of ​​the service target, thereby wide area In a satellite navigation system that performs differential correction, the master station, when generating correction information regarding the ionospheric propagation delay, calculates the residual for each of the multiple navigation satellites, obtained by subtracting the clock error determined by the navigation message, the distance to the reference station, and the tropospheric propagation delay from the distance measured by each of the multiple reference stations using positioning signals of one or more frequencies. The master station then applies separately calculated correction information regarding the clock error and position error of the navigation satellite to this residual, and accumulates the results for effective combinations of the multiple navigation satellites, the multiple reference stations, and the multiple frequencies. The master station then constructs an equation representing the relationship between the vertical ionospheric propagation delay for positioning signals of specific frequencies at the multiple grid points and the receiver clock error of the multiple reference stations, and obtains the correction information regarding the ionospheric propagation delay as the solution to this equation. This is a method for generating correction information in a satellite navigation system.

[0102] The invention according to claim 3 comprises a plurality of navigation satellites that transmit positioning signals, a user station that receives positioning signals transmitted by the plurality of navigation satellites and measures the distance between them, a plurality of reference stations that receive positioning signals of one or more frequencies transmitted by the plurality of navigation satellites using a receiver fixed on the ground and measure the distance between them, and a master station that uses the distances measured by the plurality of reference stations to generate correction information regarding the clock error, position error, and ionospheric propagation delay of the navigation satellites according to the factors of positioning error, and provides this correction information to the user station, wherein the correction information regarding the clock error and position error of the navigation satellites is expressed as correction values ​​for the clock error and position error of the plurality of navigation satellites in each coordinate axis direction, and the correction information regarding ionospheric propagation delay is expressed as a vertical ionospheric propagation delay amount for positioning signals of a specific frequency at a plurality of grid points arranged to sufficiently cover the geographical area of ​​the service target, thereby wide-area differential correction In a satellite navigation system that performs correction, when generating correction information for the clock error, position error, and ionospheric propagation delay of the navigation satellites, which is operated at the master station, the program for generating correction information for the satellite navigation system is characterized in that, for each of the multiple navigation satellites, each of the multiple reference stations collects the residual obtained by subtracting the clock error and distance between the reference station and the navigation message, which are determined by the navigation message, and the tropospheric propagation delay from the distance measured by each of the multiple reference stations using each of the positioning signals of one or more frequencies, for effective combinations of the multiple navigation satellites, the multiple reference stations, and the multiple frequencies, and constructs an equation that represents the relationship between the clock error and position error of the multiple navigation satellites, the vertical ionospheric propagation delay for positioning signals of specific frequencies at the multiple grid points, and the receiver clock error of the multiple reference stations, and obtains correction information for the clock error and position error and ionospheric propagation delay of the navigation satellites as the solution to this equation.

[0103] The invention according to claim 4 comprises a plurality of navigation satellites that transmit positioning signals, a user station that receives positioning signals transmitted by the plurality of navigation satellites and measures the distance between them, a plurality of reference stations that receive positioning signals of one or more frequencies transmitted by the plurality of navigation satellites using a receiver fixed on the ground and measure the distance between them, and a master station that uses the distances measured by the plurality of reference stations to generate correction information relating to the clock error, position error, and ionospheric propagation delay of the navigation satellites according to the factors of positioning error, and provides this correction information to the user station, wherein the correction information relating to the clock error and position error of the navigation satellites is expressed as correction values ​​for the clock error and position error of the plurality of navigation satellites in each coordinate axis direction, and the correction information relating to ionospheric propagation delay is expressed as a vertical ionospheric propagation delay amount relating to positioning signals of a specific frequency at a plurality of grid points arranged to sufficiently cover the geographical area of ​​the service target, thereby wide-area differential In a satellite navigation system that performs initial correction, when generating correction information regarding the ionospheric propagation delay operated at the master station, the program for generating correction information in a satellite navigation system is characterized by: for each of the multiple navigation satellites, each of the multiple reference stations calculates the residual obtained by subtracting the clock error obtained from the navigation message, the distance to the reference station, and the tropospheric propagation delay from the distance measured by each of the one or more frequency positioning signals of each of the multiple reference stations for each of the multiple navigation satellites; applying separately calculated correction information regarding the clock error and position error of the navigation satellite to this residual; accumulating the results for effective combinations of the multiple navigation satellites, the multiple reference stations, and the multiple frequencies; constructing an equation that represents the relationship between the vertical ionospheric propagation delay for positioning signals of a specific frequency at the multiple grid points and the receiver clock error of the multiple reference stations; and obtaining the correction information regarding the ionospheric propagation delay as the solution to this equation. [Effects of the Invention]

[0104] As described above, the inventions according to claims 1 and 3 are configured such that, in a single-frequency WADGPS, correction information regarding the clock error, position error, and ionospheric propagation delay of navigation satellites can be calculated without using distance differences or linear combinations of positioning signals of multiple frequencies measured at the base station. This reduces noise, and as a result, the number of base stations constituting the WADGPS can be reduced. Furthermore, if the base station receives positioning signals of multiple frequencies, the generation of correction information can continue even if a positioning signal of one of the frequencies becomes unusable for any reason.

[0105] The inventions according to claims 2 and 4 are configured as described above, so in a single-frequency WADGPS, correction information regarding ionospheric propagation delay can be calculated without using the difference in distance from positioning signals of multiple frequencies measured at the base station. As a result, noise can be kept low, and the number of base stations constituting the WADGPS can be reduced. Furthermore, if the base station receives positioning signals of multiple frequencies, the generation of correction information can continue even if a positioning signal of one of the frequencies becomes unusable for any reason. [Brief explanation of the drawing]

[0106] [Figure 1] This is a schematic diagram illustrating Embodiment 1 of the present invention. [Figure 2] This is a schematic diagram illustrating Embodiment 2 of the present invention. [Figure 3] For comparison, this is a schematic diagram illustrating WADGPS using conventional technology. [Modes for carrying out the invention]

[0107] Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. [Examples]

[0108] A first embodiment of this invention will be described in detail with reference to Figure 1. This embodiment corresponds to claims 1 and 3 of this invention.

[0109] In Figure 1, navigation satellites 1 (1a, 1b...) each transmit positioning signals.

[0110] Reference station 2 (2a, 2b...) receives positioning signals transmitted by navigation satellite 1 (1a, 1b...) and measures the distance from each navigation satellite. The measured results are transmitted to master station 3.

[0111] Master station 3 calculates the residual from the distance measured by reference station 2 (2a, 2b...) by subtracting the clock error of the navigation satellite calculated from the navigation message of navigation satellite 1 (1a, 1b...), the distance between the navigation satellite and the reference station, and the tropospheric propagation delay. This corresponds to the process in (Equation 7).

[0112] Master station 3 uses the distance 31 measured by the GPS L1 frequency positioning signal at reference station 2 (2a, 2b...) for calculations. By applying (equation 7) to this, a correction calculation process 41 is performed by solving the system of equations (equation 9) on the resulting residual to obtain WADGPS correction information 51, which includes correction information regarding the clock error and position error of the navigation satellites as well as ionospheric propagation delay.

[0113] The master station 3 transmits the generated WADGPS correction information 51 to the user station 6 via the communication line 7. The user station 6 uses the transmitted WADGPS correction information to perform WADGPS correction processing.

[0114] Figure 3 is a schematic diagram illustrating the WADGPS processing method in the previous technology for comparison. The meaning of symbols common to Figure 1 is the same as in Figure 1.

[0115] Master station 3 uses the distance 31 measured by the GPS L1 frequency positioning signal and the distance 32 measured by the GPS L2 frequency positioning signal at reference station 2 (2a, 2b...) to obtain a distance with the ionospheric propagation delay removed, obtained as a linear combination of these using (Equation 1), and performs a prediction process 43 for the time indicated by the navigation satellite's clock and the satellite orbit to obtain correction information 53 regarding the clock error and position error of the navigation satellite. The prediction process 43 is performed individually for each of the multiple navigation satellites.

[0116] Master station 3 uses the distance 31 measured by the GPS L1 frequency positioning signal and the distance 32 measured by the GPS L2 frequency positioning signal at reference station 2 (2a, 2b...) to obtain the ionospheric propagation delay amount as the difference between them using (Equation 3), and performs an estimation process 44 for the vertical ionospheric propagation delay amount at multiple grid points to obtain correction information 54 regarding the ionospheric propagation delay. The estimation process 44 is performed individually for each of the multiple grid points.

[0117] In applying the method of the present invention, Figure 1 illustrates the case where a GPS L1 frequency positioning signal is used, but the satellite navigation system used may be other than GPS, and the positioning signal may also be arbitrary. For example, when using a three-frequency receiver, a relational equation (Equation 8) can be constructed for the positioning signals of each frequency, and the following three relational equations may be included in the system of equations (Equation 9).

[0118] (Math 21) ΔP(i,k,f1)+W(i,k,f1)·C=0 ΔP(i,k,f2)+W(i,k,f2)·C=0 ΔP(i,k,f3)+W(i,k,f3)·C=0

[0119] Here, when using multiple satellite navigation systems, it is necessary to incorporate a clock error for the reference station receiver for each satellite navigation system. In this case, the dimensionality of the vector CR is the number of reference stations M multiplied by the number of satellite navigation systems used.

[0120] Next, we will explain the operation.

[0121] In this embodiment, the correction information for the clock error and position error of the navigation satellite is expressed as correction values ​​for the clock error and correction values ​​for the position error in each coordinate axis direction, and the correction information for ionospheric propagation delay is expressed as vertical ionospheric propagation delay amounts at multiple grid points arranged to sufficiently cover the geographical area of ​​the service target. Therefore, all of the correction information for the clock error and position error of the navigation satellite, as well as the correction information for ionospheric propagation delay, have a linear relationship with the residual in (Equation 7).

[0122] Therefore, the master station 3 can obtain WADGPS correction information 51 by performing a correction calculation process 41 that solves the system of equations (Equation 9) on the residual obtained by applying (Equation 7) to the distance 31 measured by the GPS L1 frequency positioning signal at the reference station 2 (2a, 2b...), using the distance 31, which is measured by the GPS L1 frequency positioning signal at the reference station 2, and applying (Equation 7) to it.

[0123] Since the correction information for the clock error, position error, and ionospheric propagation delay of navigation satellites is calculated without using distance differences or linear combinations of positioning signals of multiple frequencies measured at the base station, the noise is kept to a minimum. If low-noise measurement data can be obtained, fewer base stations are needed to constitute WADGPS. Furthermore, if the base station receives positioning signals of multiple frequencies, the generation of correction information for the clock error, position error, and ionospheric propagation delay of navigation satellites can continue even if a positioning signal of one of the frequencies becomes unusable for some reason.

[0124] In contrast, in the previous technology, the master station 3 uses the distance 31 measured by the GPS L1 frequency positioning signal and the distance 32 measured by the GPS L2 frequency positioning signal at the reference station 2 (2a, 2b...) to obtain a distance from which the ionospheric propagation delay has been removed, obtained as a linear combination of these distances by (Equation 1), and performs a prediction process 43 for the time indicated by the clock and the satellite orbit to obtain correction information 53 regarding the clock error and position error of the navigation satellite. Furthermore, the master station 3 uses the distance 31 measured by the GPS L1 frequency positioning signal and the distance 32 measured by the GPS L2 frequency positioning signal at the reference station 2 (2a, 2b...) to obtain the ionospheric propagation delay as the difference between these distances by (Equation 3), and performs an estimation process 44 for the vertical ionospheric propagation delay at the grid point to obtain correction information 54 regarding the ionospheric propagation delay.

[0125] Therefore, since the correction information for the clock error, position error, and ionospheric propagation delay of navigation satellites is calculated using the difference in distance or a linear combination of positioning signals of multiple frequencies measured at the base station, the noise is high. Because only measurement data with high noise can be used, it is not possible to limit the number of base stations that make up WADGPS. Furthermore, if the positioning signal of any frequency is unavailable for any reason, it is not possible to continue generating the correction information for the clock error, position error, and ionospheric propagation delay of navigation satellites. [Examples]

[0126] A second embodiment of this invention will be described in detail with reference to Figure 2. This embodiment corresponds to claims 2 and 4 of this invention.

[0127] In Figure 2, navigation satellites 1 (1a, 1b...) each transmit positioning signals.

[0128] Reference station 2 (2a, 2b...) receives positioning signals transmitted by navigation satellite 1 (1a, 1b...) and measures the distance from each navigation satellite. The measured results are transmitted to the master station.

[0129] Master station 3 calculates the residual from the distance measured by reference station 2 (2a, 2b...) by subtracting the clock error of the navigation satellite calculated from the navigation message of navigation satellite 1 (1a, 1b...), the distance between the navigation satellite and the reference station, and the tropospheric propagation delay. This corresponds to the process in (Equation 7).

[0130] Master station 3 generates correction information 53 regarding the clock error and position error of navigation satellites by a method 43 outside the scope of the present invention, using distance 31 measured by GPS L1 frequency positioning signals at reference stations 2 (2a, 2b...), and depending on the configuration, also using distance 32 measured by GPS L2 frequency positioning signals.

[0131] Master station 3 applies correction information 53 regarding the clock error and position error of navigation satellites to the residual obtained by applying (Equation 7) to the distance 31 measured by the GPS L1 frequency positioning signal at reference station 2 (2a, 2b...). Furthermore, correction calculation processing 42 solves the simultaneous equations (Equation 9) to obtain correction information 52 regarding ionospheric propagation delay.

[0132] Master station 3 transmits WADGPS correction information 51, obtained by integrating correction information 53 regarding the clock error and position error of navigation satellites and correction information 52 regarding ionospheric propagation delay, to user station 6 via communication line 7. User station 6 uses the transmitted WADGPS correction information to perform WADGPS correction processing.

[0133] The prior art is the same as in Example 1.

[0134] Furthermore, the explanations in

[0117] to

[0119] also apply to this embodiment.

[0135] Next, we will explain the operation.

[0136] In this embodiment, the correction information regarding ionospheric propagation delay is expressed as the amount of vertical ionospheric propagation delay at grid points arranged to sufficiently cover the geographical area of ​​the service target. Therefore, the correction information regarding ionospheric propagation delay has a linear relationship with the residual in (Equation 7).

[0137] Therefore, the master station 3 uses the distance 31 measured by the GPS L1 frequency positioning signal at the reference station 2 (2a, 2b...) to apply (equation 7) to obtain the residual, then applies correction information 34 regarding the clock error and position error of the navigation satellite, and further performs a correction calculation process 42 by solving the simultaneous equations (equation 9) to obtain correction information 52 regarding ionospheric propagation delay.

[0138] Master station 3 can obtain WADGPS correction information 51 by integrating correction information 53 regarding the clock error and position error of the navigation satellite and correction information 52 regarding ionospheric propagation delay.

[0139] The correction information 52 regarding ionospheric propagation delay is calculated without using the difference in distance from positioning signals of multiple frequencies measured at the base station, thus keeping the noise low. If low-noise measurement data can be obtained, fewer base stations are needed to constitute WADGPS. Furthermore, if the base station receives positioning signals of multiple frequencies, the generation of correction information regarding ionospheric propagation delay can continue even if a positioning signal of one of the frequencies becomes unusable for some reason.

[0140] The operation of the conventional technology is the same as in Example 1. [Industrial applicability]

[0141] WADGPS has been put into practical use as SBAS and is already widespread. This invention reduces the number of base stations that make up WADGPS, thereby reducing the cost required to develop WADGPS and enabling its introduction even in areas where the placement of base stations is restricted. Furthermore, if a base station receives positioning signals on multiple frequencies, the ability to continue generating correction information even if a positioning signal on one of the frequencies becomes unusable for any reason leads to more robust navigation. [Explanation of symbols]

[0142] 1 (1a, 1b...) Navigation satellite 2(2a,2b...) Reference station 3 Master Station 31 Distance measured by GPS L1 frequency positioning signal 32 Distance measured by GPS L2 frequency positioning signal 41. Correction calculation process for clock errors, position errors, and ionospheric propagation delays of navigation satellites. 42 Correction calculation process for ionospheric propagation delay 43. Prediction processing of the time indicated by the clock of navigation satellites and the satellite orbit. Estimation process for vertical ionospheric propagation delay at 44 grid points 51 WADGPS Correction Information 52 Correction information regarding ionospheric propagation delay 53 Correction information regarding clock errors and positional errors of navigation satellites 54 Correction information regarding ionospheric propagation delay 6 User Stations 7. Communication lines

Claims

1. Multiple navigation satellites that transmit positioning signals, A user station that receives positioning signals transmitted by the aforementioned multiple navigation satellites and measures the distance between them, Multiple reference stations, each receiving positioning signals of one or more frequencies transmitted by the multiple navigation satellites via a receiver fixed on the ground, and measuring the distance between them, The system includes a master station that uses the distances measured by the aforementioned multiple reference stations to generate correction information for each factor of positioning error, including the clock error and position error of navigation satellites and ionospheric propagation delay, and provides this correction information to the user stations. The correction information regarding the clock error and position error of the navigation satellite is expressed as correction values ​​for the clock error and position error of the plurality of navigation satellites in each coordinate axis direction. The correction information regarding the ionospheric propagation delay is expressed as the vertical ionospheric propagation delay amount for positioning signals of a specific frequency at multiple grid points arranged to sufficiently cover the geographical area of ​​the service area. In a satellite navigation system that performs wide-area differential correction, The aforementioned master station, When generating correction information regarding the clock error, position error, and ionospheric propagation delay of the aforementioned navigation satellite, For each of the aforementioned multiple navigation satellites, the residual obtained by subtracting the clock error determined by the navigation message, the distance to the said reference station, and the tropospheric propagation delay from the distance measured by each of the aforementioned multiple reference stations using the positioning signals of one or more frequencies is accumulated for effective combinations of the aforementioned multiple navigation satellites, the aforementioned multiple reference stations, and the aforementioned multiple frequencies, and this is then used. An equation is constructed that expresses the relationship between the clock error and position error of the plurality of navigation satellites, the vertical ionospheric propagation delay amount for positioning signals of a specific frequency at the plurality of grid points, and the receiver clock error of the plurality of reference stations. As a solution, correction information regarding the clock error and position error of the aforementioned navigation satellite, as well as ionospheric propagation delay, is obtained. A method for generating correction information in a satellite navigation system, characterized by the above.

2. Multiple navigation satellites that transmit positioning signals, A user station that receives positioning signals transmitted by the aforementioned multiple navigation satellites and measures the distance between them, Multiple reference stations, each receiving positioning signals of one or more frequencies transmitted by the multiple navigation satellites via a receiver fixed on the ground, and measuring the distance between them, The system includes a master station that uses the distances measured by the aforementioned multiple reference stations to generate correction information for each factor of positioning error, including the clock error and position error of navigation satellites and ionospheric propagation delay, and provides this correction information to the user stations. The correction information regarding the clock error and position error of the navigation satellite is expressed as correction values ​​for the clock error and position error of the plurality of navigation satellites in each coordinate axis direction. The correction information regarding the ionospheric propagation delay is expressed as the vertical ionospheric propagation delay amount for positioning signals of a specific frequency at multiple grid points arranged to sufficiently cover the geographical area of ​​the service area. In a satellite navigation system that performs wide-area differential correction, The aforementioned master station, When generating the correction information regarding the ionospheric propagation delay, For each of the multiple navigation satellites, each of the multiple reference stations calculates the residual obtained by subtracting the clock error determined by the navigation message, the distance to the reference station, and the tropospheric propagation delay from the distance measured by each of the positioning signals of the one or more frequencies, and applies correction information regarding the clock error and position error of the navigation satellite, which has been calculated separately, to the effective combination of the multiple navigation satellites, the multiple reference stations, and the multiple frequencies, and then, An equation is constructed that expresses the relationship between the vertical ionospheric propagation delay amount for positioning signals of a specific frequency at the plurality of grid points and the receiver clock error of the plurality of reference stations. As a solution, we obtain correction information regarding the ionospheric propagation delay. A method for generating correction information in a satellite navigation system, characterized by the above.

3. Multiple navigation satellites that transmit positioning signals, A user station that receives positioning signals transmitted by the aforementioned multiple navigation satellites and measures the distance between them, Multiple reference stations, each receiving positioning signals of one or more frequencies transmitted by the multiple navigation satellites via a receiver fixed on the ground, and measuring the distance between them, The system includes a master station that uses the distances measured by the aforementioned multiple reference stations to generate correction information for each factor of positioning error, including the clock error and position error of navigation satellites and ionospheric propagation delay, and provides this correction information to the user stations. The correction information regarding the clock error and position error of the navigation satellite is expressed as correction values ​​for the clock error and position error of the plurality of navigation satellites in each coordinate axis direction. The correction information regarding the ionospheric propagation delay is expressed as the vertical ionospheric propagation delay amount for positioning signals of a specific frequency at multiple grid points arranged to sufficiently cover the geographical area of ​​the service area. In a satellite navigation system that performs wide-area differential correction, Operated at the aforementioned master station, When generating correction information regarding the clock error, position error, and ionospheric propagation delay of the aforementioned navigation satellite, For each of the aforementioned multiple navigation satellites, the residual obtained by subtracting the clock error determined by the navigation message, the distance to the said reference station, and the tropospheric propagation delay from the distance measured by each of the aforementioned multiple reference stations using the positioning signals of one or more frequencies is accumulated for effective combinations of the aforementioned multiple navigation satellites, the aforementioned multiple reference stations, and the aforementioned multiple frequencies, and this is then used. An equation is constructed that expresses the relationship between the clock error and position error of the plurality of navigation satellites, the vertical ionospheric propagation delay amount for positioning signals of a specific frequency at the plurality of grid points, and the receiver clock error of the plurality of reference stations. As a solution, correction information regarding the clock error and position error of the aforementioned navigation satellite, as well as ionospheric propagation delay, is obtained. A program that generates correction information for a satellite navigation system, characterized by the following:

4. Multiple navigation satellites that transmit positioning signals, A user station that receives positioning signals transmitted by the aforementioned multiple navigation satellites and measures the distance between them, Multiple reference stations, each receiving positioning signals of one or more frequencies transmitted by the multiple navigation satellites via a receiver fixed on the ground, and measuring the distance between them, The system includes a master station that uses the distances measured by the aforementioned multiple reference stations to generate correction information for each factor of positioning error, including the clock error and position error of navigation satellites and ionospheric propagation delay, and provides this correction information to the user stations. The correction information regarding the clock error and position error of the navigation satellite is expressed as correction values ​​for the clock error and position error of the plurality of navigation satellites in each coordinate axis direction. The correction information regarding the ionospheric propagation delay is expressed as the vertical ionospheric propagation delay amount for positioning signals of a specific frequency at multiple grid points arranged to sufficiently cover the geographical area of ​​the service area. In a satellite navigation system that performs wide-area differential correction, Operated at the aforementioned master station, When generating the correction information regarding the ionospheric propagation delay, For each of the multiple navigation satellites, each of the multiple reference stations calculates the residual obtained by subtracting the clock error determined by the navigation message, the distance to the reference station, and the tropospheric propagation delay from the distance measured by each of the positioning signals of the one or more frequencies, and applies correction information regarding the clock error and position error of the navigation satellite, which has been calculated separately, to the effective combination of the multiple navigation satellites, the multiple reference stations, and the multiple frequencies, and then, An equation is constructed that expresses the relationship between the vertical ionospheric propagation delay amount for positioning signals of a specific frequency at the plurality of grid points and the receiver clock error of the plurality of reference stations. As a solution, we obtain correction information regarding the ionospheric propagation delay. A program that generates correction information for a satellite navigation system, characterized by the following:

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