Method for correcting positioning errors in satellite navigation systems, information processing device and program for correcting positioning errors

Abstract

Differential GPS uses multiple reference stations in combination. [Solution] In a satellite positioning system using a differential GPS method, which includes a user station 2 and multiple reference stations 3a, 3b, the user station 2 obtains correction values ​​from the multiple reference stations 3a, 3b, applies these correction values ​​to the distance between itself and the navigation satellites 1a, 1b, 1c, obtains corrected distances for each navigation satellite equal to the number of reference stations that provided the correction value for that satellite, and for each of these corrected distances, sets a separate unknown corresponding to the receiver clock error for each of the reference stations 3a, 3b that provided the applied correction value, and then calculates the position of the user station 2.

Description

Technical Field

[0001] This invention relates to a method for correcting positioning errors in a satellite navigation system, an information processing apparatus for correcting positioning errors, and a program.

Background Art

[0002] A satellite navigation system that measures positions using artificial satellites is generally referred to as GNSS (Global Navigation Satellite System), and a representative example thereof is GPS (Global Positioning System) by the United States. In general, GNSS receives a positioning signal transmitted by an artificial satellite called a navigation satellite by a receiver, measures the distance between the navigation satellite and the receiver, and calculates the position of the receiver. A receiver for which the position is to be determined is called a user receiver or a user station. An error with respect to the true position of the obtained position is called a positioning error.

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

[0004] On the other hand, a receiver is installed at a reference station fixed on the ground, and correction information for measurement errors of distances caused by ionospheric propagation delay, tropospheric propagation delay, etc. is created from the distances measured thereby, and this is provided to the user, so that the distances measured at the user station are corrected based on the correction information, and the measurement accuracy of the position at the user station (referred to as "positioning accuracy") is improved. This method is called Differential GPS (hereinafter referred to as "DGPS").

[0005] Practical applications of DGPS included medium-wave beacons for ships and FM multiplex digital broadcasting, but both have now been discontinued. On the other hand, Japan's Quasi-Zenith Satellite System, which began operation in 2018, transmits DGPS correction information from satellites as SLAS (Submeter-Level Augmentation Service). The SLAS service has the characteristic of being able to obtain correction information from 13 reference stations located throughout Japan all at once by receiving a signal from a single satellite. Receivers using the SLAS service are supposed to select and use the correction information from the nearest reference station.

[0006] In addition to the individual reference station method described above, there is also a method called wide-area differential GPS that integrates measurement data from numerous reference stations to create wide-area correction information that is effective over a wide geographical area. As wide-area differential GPS services such as Japan's MSAS and the US's WAAS have become widespread, currently, DGPS that provides correction information from multiple reference stations does not exist except for the SLAS service of the Quasi-Zenith Satellite System. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 7326650 [Non-patent literature]

[0008] [Non-Patent Document 1] Takeyasu Sakai and Kazunori Iimura, "DGPS positioning accuracy when using multiple reference stations," IEICE Technical Report, SANE99-44, July 1999. [Non-Patent Document 2] Takeyasu Sakai and Kazunori Iimura, "Improvement of GPS positioning accuracy through the use of multiple reference stations," Transactions of the Japan Institute of Navigation, No. 101, pp. 15-20, September 1999. [Non-Patent Document 3] Toshiyuki Tanaka and Keita Kawamura, "Improving Positioning Accuracy in DGPS Using Long Baseline Reference Stations," Transactions of the Japanese Society for Positioning and Navigation, Vol. 1, No. 1, pp. 1-8, 2010. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] A DGPS reference station creates correction values ​​from the measurement errors of the navigation satellites visible to it. When a user station uses DGPS, it must have correction values ​​for the navigation satellites to be corrected, so it will use navigation satellites that are visible to both the reference station and the user station. For this reason, if a user station can use multiple reference stations, it is common to select and use the reference station located closest to the user station in order to maximize the number of navigation satellites that are visible to both the user station and the reference station.

[0010] For example, the SLAS service of the Quasi-Zenith Satellite System provides correction information from 13 reference stations located throughout Japan, and user stations are expected to select and use the nearest reference station. The distance between a reference station and a user station can exceed 300 km, and may be even longer if some reference stations are out of service.

[0011] As the distance between the base station and the user station increases, the number of navigation satellites visible to both decreases. Generally, in satellite navigation systems, a larger number of navigation satellites leads to better positioning accuracy, so a decrease in the number of visible satellites is disadvantageous from the standpoint of positioning accuracy.

[0012] In the case of SLAS services, correction information can be obtained from multiple reference stations. Therefore, using the methods described in Patent Document 1 and Non-Patent Documents 1-3, it is possible to improve positioning accuracy by interpolating and using the correction information from multiple reference stations for navigation satellites that are visible to all multiple reference stations and user stations. However, neither Patent Document 1 nor Non-Patent Documents 1-3 describes the use of navigation satellites that are not visible to all multiple reference stations and user stations.

[0013] In other words, when a user station can use multiple reference stations in DGPS, it is only possible to select and use one of the reference stations, or, if multiple reference stations are used, to use navigation satellites that are visible to all of the reference stations and the user station. The object of the present invention is to increase the number of navigation satellites available to a user station in DGPS when a user station can use multiple reference stations, by using the correction values ​​of each reference station in conjunction with navigation satellites that are visible to one or more reference stations, in addition to navigation satellites that are visible to all of those multiple reference stations. [Means for solving the problem]

[0014] This section describes the properties of correction values ​​in DGPS. If the sign representing the first reference station is r, the pseudo-distance measured by this reference station for satellite i can be written as follows: where R is the geometric distance between satellite i and receiver r, B is the clock error of satellite i, S is the clock error of receiver r, I is the ionospheric propagation delay between satellite i and receiver r, and T is the tropospheric propagation delay between satellite i and receiver r.

[0015] (Math 1) P(i,r)=R(i,r)-B(i)+S(r)+I(i,r) +T(i,r)

[0016] At the reference station, the distance that should be measured, calculated from the orbital information of satellite i, is determined by the following equation. Here, S'(r) is an estimated value of the receiver clock error.

[0017] (Number 2) P’(i,r) = R(i,r) - B(i) + S’(r)

[0018] The correction value C(i,r) for satellite i by reference station r is obtained as follows by subtracting (Equation 1) from (Equation 2). Here, let the estimation error of the receiver clock error be ΔS(r).

[0019] (Number 3) C(i,r) = P’(i,r) - P(i,r) = -I(i,r) - T(i,r) + ΔS(r)

[0020] Let the symbol representing the user station be u. Then, the pseudorange measured by the user station can be written as follows.

[0021] (Number 4) P(i,u) = R(i,u) - B(i) + S(u) + I(i,u) + T(i,u)

[0022] At the user station, it receives the correction value C(i,r) and adds it to the pseudorange measured by the user station. At this time, if the distance between the user station and reference station r is not large, the ionospheric propagation delay I(i,u) and I(i,r) are almost the same, and the tropospheric propagation delay T(i,u) and T(i,r) can also be regarded as almost the same. Therefore, the corrected pseudorange is as follows. Comparing with (Equation 4), the ionospheric propagation delay and the tropospheric propagation delay are eliminated. This can be said to be the basic principle of DGPS.

[0023] (Number 5) P(i,u) + C(i,r) = R(i,u) - B(i) + S(u) + ΔS(r)

[0024] Here, the estimated error ΔS(r) of the receiver clock error at the reference station remains in the corrected pseudo-distance. However, if there are only one reference station, the receiver clock error S(u) is simply replaced by S(u)+ΔS(r). Therefore, if the user station treats S(u)+ΔS(r) as the receiver clock error during the position calculation process, the position can be calculated without any problems.

[0025] Consider the case where a user station can use multiple reference stations. The user station receives a correction value C(i,s) from the second reference station s and adds this to the pseudo-distance measured by the user station. In this case, if the distance between the user station and reference station s is not large, the corrected pseudo-distance will be as follows, similar to (Equation 5).

[0026] (Math 6) P(i,u)+C(i,s)=R(i,u)-B(i)+S(u)+ΔS(s)

[0027] The estimated error ΔS(s) of the clock error of the reference station receiver will remain in the corrected pseudo-distance, but if the user station uses only the reference station s, the position can be calculated without any problems, as in paragraph

[0024] .

[0028] However, when considering the use of both base station r and base station s, the difference between S(u)+ΔS(r) and S(u)+ΔS(s) becomes a problem. Specifically, the difference between ΔS(r) and ΔS(s) is the issue, but since these are estimation errors of the receiver clock error within the base station, the user station cannot know these values.

[0029] In this invention, in order to use multiple reference stations in such cases, when calculating the position at the user station, instead of one unknown variable corresponding to the receiver clock error, the number of unknown variables corresponding to the receiver clock error is set to the number of reference stations. That is, to explain using the above example, for the pseudo-distance to which the correction value from reference station r is applied, Sr(r) is defined as the clock error at the user station receiver, and for the pseudo-distance to which the correction value from reference station s is applied, Ss(s) is defined as the clock error at the user station receiver.

[0030] (Number 7) Sr(r) = S(u) + ΔS(r) Ss(s) = S(u) + ΔS(s)

[0031] Using these, the corrected pseudo-distance can be written as follows:

[0032] (Math 8) P(i,u)+C(i,r)=R(i,u)-B(i)+Sr(r) P(i,u)+C(i,s)=R(i,u)-B(i)+Ss(s)

[0033] By using these relationships to calculate the user station's position, multiple reference stations can be used in DGPS.

[0034] Specifically, for an N×4 matrix G that is typically used in satellite navigation receivers to calculate position and represents the geometric relationship between the distance to N navigation satellites and the receiver position, if the i-th row of matrix G is G(i), then when using a single reference station, it can be written as follows, using the azimuth angle AZ(i) and elevation angle EL(i) of each navigation satellite.

[0035] (Math 9) G(i) = [-sinAZ(i)·cosEL(i)] -cosAZ(i) · cosEL(i) -sinEL(i) 1]

[0036] This fourth column corresponds to the calculation process where the receiver clock error is treated as an unknown. In other words, when a user station calculates its position using a single reference station, only one unknown is set, corresponding to the receiver clock error.

[0037] If there are, for example, two reference stations, both providing correction values ​​for N navigation satellites, then the size of matrix G is 2N × 5, and the following is done.

[0038] (Number 10) G(i) =[-sinAZ(i,r)·cosEL(i,r) -cosAZ(i,r)·cosEL(i,r) -sinEL(i,r) 1 0] G(i+N)=[-sinAZ(i,s)·cosEL(i,s) -cosAZ(i,s) · cosEL(i,s) -sinEL(i,s) 0 1]

[0039] The fourth column corresponds to the calculation process using the clock error Sr(r) related to the pseudo-distance after applying the correction value from base station r, and the fifth column corresponds to the calculation process using the clock error Ss(s) related to the pseudo-distance after applying the correction value from base station s as unknowns. Note that the azimuth and elevation angles of the navigation satellite are both expressed as AZ(i,r) and EL(i,r) respectively, as these correspond to the values ​​of the base station.

[0040] Furthermore, for the fifth column, the matrix G may be constructed as follows, with the difference in clock errors Ss(s)-Sr(r) corresponding to each base station as an unknown.

[0041] (Math 11) G(i) =[-sinAZ(i,r)·cosEL(i,r) -cosAZ(i,r)·cosEL(i,r) -sinEL(i,r) 1 0] G(i+N)=[-sinAZ(i,s)·cosEL(i,s) -cosAZ(i,s) · cosEL(i,s) -sinEL(i,s) 1 1]

[0042] If the number of reference stations is K, and each reference station provides correction values ​​for a different number of navigation satellites, then the number of unknowns is 3+K, and the size of the matrix G is M×(3+K). Here, M is as follows, where N(k) is the number of navigation satellites for which reference station k measures pseudo-distance.

[0043] (Math 12) M = N(1) + N(2) + ... + N(K)

[0044] For navigation satellites to which correction values ​​are applied at a user station, it is not necessary for them to be visible to all multiple reference stations; it is sufficient if they are visible to the user station and one or more reference stations. There are no particular restrictions on the combination of navigation satellites that provide correction values ​​to each reference station, and each reference station does not need to communicate with other reference stations.

[0045] As described above, in DGPS, when a user station can use multiple reference stations, in addition to navigation satellites that are visible to all of those reference stations, the correction values ​​of each reference station can be used in conjunction with navigation satellites that are visible to one or more reference stations, thereby increasing the number of navigation satellites available to the user station.

[0046] The invention according to claim 1 is a satellite navigation system comprising a plurality of navigation satellites that transmit positioning signals, a user station that receives positioning signals transmitted by the plurality of navigation satellites and measures the distance between them, and a plurality of reference stations that receive positioning signals transmitted by the plurality of navigation satellites using a receiver fixed on the ground and measure the distance between them, and provide the user station with a correction value obtained by subtracting this from the distance that should originally be measured calculated from the orbital information of each of the plurality of navigation satellites, for each corresponding navigation satellite, the result of which the user station obtains correction values ​​from the plurality of reference stations, applies these correction values ​​to the distance between the plurality of navigation satellites, obtains a corrected distance for each navigation satellite equal to the number of reference stations that provided a correction value for that navigation satellite, and for each of the corrected distances, sets a separate unknown corresponding to the receiver clock error for each reference station that provided the applied correction value, and then calculates the position of the user station.

[0047] The invention according to claim 2 is an information processing device for correcting positioning errors in a satellite navigation system, comprising 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, and a plurality of reference stations that receive positioning signals transmitted by the plurality of navigation satellites using a receiver fixed on the ground and measure the distance between them, and provide the user station with the result of subtracting this from the distance that should originally be measured calculated from the orbital information of each of the plurality of navigation satellites as a correction value, wherein the user station is provided with an information processing device for correcting positioning errors, characterized in that it obtains correction values ​​from the plurality of reference stations, applies these correction values ​​to the distance between the plurality of navigation satellites, obtains corrected distances for each navigation satellite equal to the number of reference stations that provided a correction value for that navigation satellite, and for each of the corrected distances, sets a separate unknown corresponding to the receiver clock error for each reference station that provided the applied correction value, and then calculates the position of the user station.

[0048] The invention according to claim 3 is a satellite navigation system comprising 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, and a plurality of reference stations that receive positioning signals transmitted by the plurality of navigation satellites using a receiver fixed on the ground and measure the distance between them, and provide the user station with the result of subtracting this from the distance that should originally be measured calculated from the orbital information of each of the plurality of navigation satellites, as a correction value, wherein the user station operates, obtains correction values ​​from the plurality of reference stations, applies these correction values ​​to the distance between the plurality of navigation satellites, obtains corrected distances for each navigation satellite equal to the number of reference stations that provided a correction value for that navigation satellite, and for each of the corrected distances, sets a separate unknown corresponding to the receiver clock error for each reference station that provided the applied correction value, and then calculates the position of the user station. [Effects of the Invention]

[0049] The inventions according to claims 1 to 3 are configured as described above, so that when a user station can use multiple reference stations in DGPS, the correction values ​​from those multiple reference stations can be used in combination to increase the number of navigation satellites available to the user station. [Brief explanation of the drawing]

[0050] [Figure 1] This diagram illustrates an embodiment of the present invention and is a schematic diagram illustrating a method for correcting positioning errors in a satellite navigation system according to the present invention. [Modes for carrying out the invention]

[0051] Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. [Examples]

[0052] Embodiments of this invention will be described in detail with reference to Figure 1. Although Figure 1 shows only three navigation satellites, this is illustrative, and configurations with four or more satellites are also possible. Similarly, although Figure 1 shows only two reference stations, this is illustrative, and configurations with three or more reference stations are also possible.

[0053] Navigation satellites 1a, 1b, and 1c each transmit positioning signals.

[0054] User station 2 has the function of receiving positioning signals transmitted by navigation satellites 1a, 1b, and 1c, and measuring the distance from each navigation satellite to the user station.

[0055] Reference station 3a is fixed on the ground and has the function of receiving positioning signals transmitted by navigation satellites 1a and 1b, measuring the distance from the navigation satellites to each reference station, and generating a correction value based on the measured distance. Similarly, reference station 3b is fixed on the ground and has the function of receiving positioning signals transmitted by navigation satellites 1a, 1b, and 1c, measuring the distance from the navigation satellites to each reference station, and generating a correction value based on the measured distance.

[0056] Reference station 3a provides correction values ​​for navigation satellites 1a and 1b to user station 2 (4a). Similarly, reference station 3b provides correction values ​​for navigation satellites 1a, 1b, and 1c to user station 2 (4b).

[0057] User station 2 applies the correction value obtained from reference station 3a to the distance between itself and navigation satellites 1a and 1b to obtain the corrected distance. Since the correction value for navigation satellite 1c cannot be obtained from reference station 3a, the corrected distance for navigation satellite 1c cannot be obtained. Therefore, two corrected distances are obtained using the correction value obtained from reference station 3a.

[0058] User station 2 applies the correction values ​​obtained from reference station 3b to the distances between itself and navigation satellites 1a, 1b, and 1c to obtain the corrected distances. Since the correction value for navigation satellite 1c is obtained from reference station 3b, the corrected distance for navigation satellite 1c can also be obtained. Therefore, three corrected distances can be obtained using the correction values ​​obtained from reference station 3b.

[0059] At user station 2, five corrected distances are obtained in total using correction values ​​from reference stations 3a and 3b. Of these, the corrected distance obtained from reference station 3a includes the first receiver clock error, and the corrected distance obtained from reference station 3b includes the second receiver clock error. By performing positioning calculations based on these assumptions, the position of the user station can be determined.

[0060] Next, we will explain the operation.

[0061] Consider the case where user station 2 uses only reference station 3a. In this case, the correction value for navigation satellite 1c cannot be obtained, and therefore the corrected distance for navigation satellite 1c cannot be obtained. Consequently, two corrected distances can be obtained using the correction value obtained from reference station 3a.

[0062] In other words, even though the user station is measuring the pseudo-distances of navigation satellites 1a, 1b, and 1c, in this example only two corrected distances are obtained.

[0063] According to the present invention, the user station can use both the reference station 3a and the reference station 3b. Since correction values ​​for navigation satellites 1a, 1b, and 1c are obtained from the reference station 3b, three corrected distances can be obtained using the correction values ​​obtained from the reference station 3b. Together with the reference station 3a, five corrected distances can be obtained, and the navigation satellite 1c also becomes available.

[0064] In satellite navigation, generally, a greater number of navigation satellites leads to better positioning accuracy. Therefore, being able to use navigation satellite 1c is advantageous for user station 2. Furthermore, for navigation satellites 1a and 1b, corrected distances can be obtained by applying the correction values ​​of both base stations 3a and 3b, and both will be used in positioning calculations. As a result, the noise included in the correction values ​​of base stations 3a and 3b will be averaged out, and an improvement in positioning accuracy can be expected. [Industrial applicability]

[0065] The method for correcting positioning errors in satellite navigation systems according to this invention allows a user station to increase the number of navigation satellites available to it when it can use multiple reference stations in a DGPS system. This is achieved by using the correction values ​​of each reference station in addition to the navigation satellites that are visible to one or more reference stations. For example, the SLAS service of the Quasi-Zenith Satellite System provides correction information from 13 reference stations located throughout Japan. By using multiple reference stations in combination instead of selecting and using the nearest reference station, the number of navigation satellites available to the user station can be increased, improving positioning accuracy. [Explanation of symbols]

[0066] 1a, 1b, 1c Navigation Satellites 2 User Stations 3a,3b Reference station 4a,4b Provision of correction values ​​from the reference station to the user station

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, In a satellite navigation system comprising multiple reference stations, each having a ground-based receiver that receives positioning signals transmitted by multiple navigation satellites, measures the distance between them, and provides the user station with a correction value obtained by subtracting this distance from the distance that should have been measured, calculated from the orbital information of each of the multiple navigation satellites, for each corresponding navigation satellite, the system provides the user station with the result. The aforementioned user station is Correction values ​​are obtained from multiple reference stations, Apply these correction values ​​to the distance between the aforementioned multiple navigation satellites, and obtain a corrected distance for each navigation satellite equal to the number of reference stations for which correction values ​​were provided for that navigation satellite. For each of the corrected distances, a separate unknown corresponding to the receiver clock error is set for each reference station that provided the applied correction value, and then the position of the user station is calculated. A method for correcting positioning errors in satellite navigation systems, characterized by the following:

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, In a satellite navigation system comprising multiple reference stations, each having a ground-based receiver that receives positioning signals transmitted by multiple navigation satellites, measures the distance between them, and provides the user station with a correction value obtained by subtracting this distance from the distance that should have been measured, calculated from the orbital information of each of the multiple navigation satellites, for each corresponding navigation satellite, the system provides the user station with the result. The user station is provided with, Correction values ​​are obtained from multiple reference stations, Apply these correction values ​​to the distance between the aforementioned multiple navigation satellites, and obtain a corrected distance for each navigation satellite equal to the number of reference stations for which correction values ​​were provided for that navigation satellite. For each of the corrected distances, a separate unknown corresponding to the receiver clock error is set for each reference station that provided the applied correction value, and then the position of the user station is calculated. An information processing device that corrects positioning errors in satellite navigation systems, characterized by the following features.

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, In a satellite navigation system comprising multiple reference stations, each having a ground-based receiver that receives positioning signals transmitted by multiple navigation satellites, measures the distance between them, and provides the user station with a correction value obtained by subtracting this distance from the distance that should have been measured, calculated from the orbital information of each of the multiple navigation satellites, for each corresponding navigation satellite, the system provides the user station with the result. It operates at the aforementioned user station, Correction values ​​are obtained from multiple reference stations, Apply these correction values ​​to the distance between the aforementioned multiple navigation satellites, and obtain a corrected distance for each navigation satellite equal to the number of reference stations for which correction values ​​were provided for that navigation satellite. For each of the corrected distances, a separate unknown corresponding to the receiver clock error is set for each reference station that provided the applied correction value, and then the position of the user station is calculated. A program that corrects positioning errors in satellite navigation systems, characterized by the following features.

Images