WO2017002364A1

WO2017002364A1 - Ground-type satellite navigation reinforcement system and availability prediction method

Info

Publication number: WO2017002364A1
Application number: PCT/JP2016/003122
Authority: WO
Inventors: 和史鈴木
Original assignee: 日本電気株式会社
Priority date: 2015-07-01
Filing date: 2016-06-29
Publication date: 2017-01-05
Also published as: JP6741005B2; JPWO2017002364A1

Abstract

In order to improve the availability of a ground type satellite navigation reinforcement system, the present invention is provided with: a worst case ionospheric delay amount difference calculation unit which calculates a worst case ionospheric delay amount difference table for a ground system and an onboard system; a differential correction value calculation unit which creates usable satellite information; a geometric screening unit which guarantees that an error experienced by the onboard system will not exceed a protection level, regardless of which satellite set of positioning satellites is used by the onboard system; an availability prediction unit which creates availability loss information if the protection level when all usable satellites are used exceeds an alert limit; and an eliminated satellite determination unit which eliminates a prescribed number of positioning satellites from the positioning satellites included in the usable satellite information to calculate an eliminated satellite indicator, excludes from the positioning satellites included in the usable satellite information the positioning satellite which was eliminated when the eliminated satellite indicator was minimized, and using the result therefrom as usable satellite update information, causes the geometric screening unit to calculate an integrity parameter.

Description

Terrestrial satellite navigation reinforcement system and availability prediction method

The present invention relates to a terrestrial satellite navigation reinforcement system and an availability prediction method.

A technique for knowing the position of the receiving unit based on a GPS signal (positioning signal) from a GPS satellite (positioning satellite) received by the receiving unit is used in, for example, a car navigation system. However, the position obtained by such a method cannot be used for guidance or the like when the aircraft is landing because there is no guarantee of accuracy and safety necessary for navigation of the aircraft. Therefore, a ground-based satellite navigation reinforcement system (GBAS: Ground Based Augmentation System) that applies the principle of differential GPS has been developed to ensure the position accuracy and safety required for aircraft approach and landing. Has been started.

In this terrestrial satellite navigation reinforcement system, a positioning signal from a positioning satellite is received by a ground system installed on the ground or an on-board system mounted on a flying object such as an airplane. Then, the ground system or the onboard system calculates the distance between the own system and the positioning satellite from the received positioning signal. The distance at this time is called a pseudo distance, and is calculated by multiplying the time (propagation time) from when the positioning signal is transmitted until it is received by the propagation speed of the positioning signal (assuming that it is a predetermined speed). Is done. The propagation time is the difference between the transmission time of the positioning signal from the positioning satellite and the reception time of the positioning signal in the ground system or on-board system.
However, when the positioning signal transmitted from the positioning satellite passes through the ionosphere and is received by the ground system or the onboard system, it is no longer assumed that the propagation speed of the positioning signal is a predetermined speed.
That is, when the positioning signal passes through the ionosphere, the propagation speed is slowed by the influence of the ionosphere, and a delay occurs in the reception time. For this reason, an error is included in the pseudo distance calculated from the propagation time.
The ground system and the on-board system calculate the position of the own aircraft using pseudoranges between a plurality of positioning satellites. Therefore, if the pseudo distance includes an error, this error causes a decrease in the positioning position accuracy of the own device.

In order to correct such an error, a technique called differential GPS has been proposed. In the differential GPS, the ground system calculates the above-described pseudo distance and a geometric distance described later. The geometric distance is a distance between the own aircraft and the positioning satellite calculated using the position information of the ground system and the position information of the positioning satellite. Here, the position information of the ground system is strictly investigated and stored in advance. The position information of the positioning satellite is included in the satellite orbit information broadcast from the positioning satellite.

And the ground system calculates the difference between the pseudo distance and the geometric distance. If there is no error in the measurement of the pseudo distance, the pseudo distance and the geometric distance should match. However, for example, when the propagation speed of the positioning signal is slow due to the influence of the ionosphere, a difference occurs.

The errors included in the pseudorange include errors due to the ionosphere, clock errors mounted on positioning satellites, satellite orbit information broadcasts from positioning satellites, and the like. Since it is not related to this, it will be omitted in the following discussion. The ground system calculates the difference for each positioning satellite and sends it to the on-board system as a correction value. The onboard system corrects the uniquely calculated pseudorange with the correction value provided by the ground system, thereby reducing the influence of the ionosphere contained in the pseudorange and calculating the positioning position of the aircraft with high accuracy. It can be so.

Such correction by differential GPS is effective when ionospheric activity is calm and the ionospheric delay is common between the ground system and the onboard system.

However, when the ionospheric density is greatly changing in space (hereinafter, this case is referred to as an ionosphere abnormality), the ionospheric delay is not common between the ground system and the onboard system.

When such an ionospheric anomaly has occurred, if the pseudorange calculated by the onboard system is corrected using the correction value provided by the ground system, the error increases and exceeds the guaranteed protection level. Sometimes. Therefore, Non-Patent Documents 1 and 2 propose a geometry screening process that prevents the onboard system from using geometries (satellite sets) that may increase the error to an extent that exceeds the allowable limit. ing.

In the geometry screening process, the worst case positioning error is estimated for each satellite set (positioning satellite set) that the onboard system may use. If this worst case positioning error exceeds an allowable maximum error value, the ground system increases the integrity parameter provided to the onboard system. The onboard system uses this integrity parameter to calculate the protection level. The ground system increases the integrity parameter to a level where this protection level exceeds a threshold that generates an alert called an alert limit.

That is, the ground system provides the integrity parameter that the onboard system uses to calculate the protection level, but if the worst case positioning error exceeds the allowable maximum error value, the protection level will exceed the alert limit. Provide integrity parameters.

∙ This prevents the onboard system from continuing to approach and land in a state where the maximum allowable error is exceeded, thus ensuring safety.

The integrity parameter is a parameter defined in the international standard of Non-Patent Document 3, and is used when the onboard system calculates a reliability range of positioning error called a protection level.

Also, the protection level is a value calculated by the onboard system using the integrity parameter provided by the ground system, and is a reliability limit value of positioning error when positioning is performed by applying differential correction.

Furthermore, the alert limit is an alarm limit value that is determined according to the distance from the onboard system to the airport where the onboard system is about to land, and the protection level calculated by the onboard system exceeds this alert limit. The on-board system is a threshold value that determines that continuation of navigation using GBAS is impossible.

However, the geometry screening process is performed for all the satellite sets that may be used by the onboard system and increases the integrity parameter so that safety can be guaranteed for all satellite sets. As a result, there is a problem that the protection level calculated using the satellite set that can continue the approach and landing safely without the worst case positioning error exceeding the allowable maximum value is increased.

And in such a case, the increased integrity parameter is also used in an on-board system using a satellite set in which the worst case positioning error does not exceed the maximum allowable value. Therefore, the protection level calculated using this integrity parameter may exceed the alert limit, thereby impairing availability. In other words, as a result of the ground system increasing the integrity parameter corresponding to the satellite set whose worst case positioning error exceeds the allowable maximum error value, the position of the aircraft is calculated based on the satellite set that can continue to approach and land safely Even so, the protection level calculated from the integrity parameter may exceed the alert limit, resulting in loss of availability.

Accordingly, a main object of the present invention is to provide a terrestrial satellite navigation reinforcement system and an availability prediction method that can predict the availability of each positioning satellite set and eliminate positioning satellites whose availability has been reduced according to the prediction. It is.

In order to solve the above problems, the invention relating to the terrestrial satellite navigation reinforcement system in which the ground system guides the on-board system using the positioning signal from the positioning satellite, the ionospheric delay amount of the positioning signal by the ionosphere experienced by the ground system, and The difference between the ionosphere and the ionosphere delay at the predetermined calculation target position when the ionosphere state parameters are comprehensively changed while taking into account the time variation of the relative position between the ionosphere and the onboard system is maximized The worst case ionosphere delay amount difference calculation unit that calculates the worst case ionosphere delay amount difference table and the satellite position, pseudorange, and carrier phase distance of the positioning satellite are used to monitor the positioning satellite for abnormalities and are determined to be normal. A differential correction value that creates usable satellite information including the satellite position of the positioning satellite as a usable positioning satellite Set the satellite set of the positioning satellite based on the output section and usable satellite information, calculate the worst case positioning error at the calculation target position using the worst case ionosphere delay difference table, and allow using the current integrity parameter If the maximum error is calculated and the worst-case positioning error exceeds the allowable maximum error, the satellite system used by the onboard system is repeated by repeating the process of increasing the integrity parameter until the protection level exceeds the protection level judgment threshold. However, the geometry screening unit that ensures that the error experienced by the onboard system does not exceed the protection level, and whether the protection level when using all available satellites exceeds a preset alert limit. Make an availability decision and the protection level exceeds the alert limit In this case, it is determined that the availability is lost, and the availability prediction unit that creates the availability loss information, and when the availability loss information is received, the positioning included in the usable satellite information using the worst case ionosphere delay amount difference table An excluded satellite index is calculated by excluding a predetermined number of positioning satellites from the satellite, and the positioning satellite to be excluded according to the excluded satellite index is excluded from the positioning satellites included in the usable satellite information, and this is used satellite update information And an excluded satellite determination unit that causes the geometry screening unit to calculate an integrity parameter.

In addition, the invention relating to the availability prediction method used for a terrestrial satellite navigation augmentation system in which positioning is performed using a positioning signal from a positioning satellite and the ground system guides the onboard system, the positioning signal of the ionosphere experienced by the ground system is obtained. The difference between the ionospheric delay amount and the ionospheric delay amount at a predetermined calculation target position by the ionosphere when exhaustively changing the ionospheric state parameters while taking into account the temporal change in the relative position between the ionosphere and the onboard system Calculate the worst case ionosphere delay amount difference table with the largest error, monitor the positioning satellite for abnormality using the satellite position, pseudorange, and carrier phase distance of the positioning satellite, and use the positioning satellite determined to be normal As possible satellites, usable satellite information including the satellite position of the positioning satellite is created, and a satellite set of positioning satellites is created based on the usable satellite information. The worst case ionosphere delay difference table is used to calculate the worst case positioning error at the calculation target position, the allowable maximum error is calculated using the current integrity parameter, and the worst case positioning error indicates the allowable maximum error. If so, by repeating the process of increasing the integrity parameter until the protection level exceeds the protection level threshold, the error experienced by the onboard system will exceed the protection level no matter what satellite set the onboard system uses. The availability is determined whether the protection level when using all available satellites exceeds the preset alert limit. If the protection level exceeds the alert limit, the availability is lost. The loss of availability information and receive the loss of availability information Then, using the worst case ionosphere delay amount difference table, a predetermined number of positioning satellites are excluded from the positioning satellites included in the usable satellite information, an excluded satellite index is calculated, and the positioning satellites to be excluded according to the excluded satellite index are calculated. The integrity parameter is calculated as usable satellite update information, excluding the positioning satellite included in the usable satellite information.

According to the present invention, the availability when all the positioning satellites are used is predicted, and when it is determined that the availability is lost by the prediction, it is possible to eliminate the satellites that can avoid the loss of availability. This improves system availability.

It is a conceptual diagram of a ground type satellite navigation reinforcement system. It is a functional block diagram of a ground system. It is a figure explaining an ionosphere abnormality model etc. It is a flowchart which shows the worst case ionosphere delay amount difference calculation process. It is a flowchart which shows an integrity parameter calculation process. It is a flowchart which determines the satellite n to exclude. It is the figure which showed the protection level calculated using the integrity parameter. It is the table | surface which compared the frequency | count that the protection level became 10 m or more, and availability by the system of the conventional system and the system of this invention.

Embodiments of the present invention will be described. FIG. 1 is a conceptual diagram of a terrestrial satellite navigation reinforcement system 2 according to the present embodiment, and FIG. 2 is a functional block diagram of the terrestrial system 3. Moreover, FIG. 3 is a figure explaining the ionosphere abnormality model etc. which are mentioned later.

The terrestrial satellite navigation reinforcement system 2 includes a ground system 3 whose position is known, a plurality of positioning satellites 4 that output positioning signals, and an on-board system 5 that is mounted on a flying object such as an aircraft to be guided.

As shown in FIG. 2, the ground system 3 includes a worst case ionosphere delay amount difference calculation unit 11, a reception unit 12, a differential correction value calculation unit 13, an integrity parameter calculation unit 14, a transmission unit 15, and a storage unit 16.

The integrity parameter calculation unit 14 includes a geometry screening unit 14a, an availability prediction unit 14b, and an excluded satellite determination unit 14c.

The storage unit 16 stores the ionosphere abnormality model M and the calculation target position Q that are determined in advance, and also stores the worst case ionosphere delay amount difference table created by the worst case ionosphere delay amount difference calculation unit 11.

The worst case ionosphere delay amount difference calculation unit 11 performs worst case ionosphere delay amount difference calculation processing. FIG. 4 is a flowchart showing the worst case ionosphere delay amount difference calculation process.

Step SA1: The worst case ionosphere delay amount difference calculation unit 11 reads the ionosphere abnormality model from the storage unit 16. This ionospheric abnormality model is obtained by modeling the range of the ionospheric abnormality state with some state parameters. FIG. 3 shows an example in which the ionospheric anomaly is modeled by three state parameters: the ionospheric delay amount slope (S), the ionospheric anomaly moving speed (V), and the ionospheric anomaly width (W). The ionospheric abnormality model is not limited to the model shown in FIG. 3, and any model that can represent the ionospheric abnormality by some state parameters may be used.

Steps SA2 and SA3: Next, the worst case ionosphere delay amount difference calculation unit 11 reads the calculation target position from the storage unit 16. This calculation target position is a position set in advance as a point through which the onboard system 5 should pass. For example, the point Q in FIG. 3 corresponds to this. Then, the worst case ionosphere delay amount difference calculation unit 11 calculates the worst case ionosphere delay amount difference at the calculation target position Q on the assumption that there is an ionosphere abnormality within the range represented by the ionosphere abnormality model.

The ionospheric delay amount is a propagation delay amount that occurs until the positioning signal from the positioning satellite passes through the ionosphere and reaches the receiving unit 12 and the calculation target position Q. The positioning satellite and the receiving unit 12 and the calculation target This is an error factor of the measured value of the distance from the position Q.

Further, the ionospheric delay amount difference is a difference between the ionospheric delay amount at the position where the receiving unit 12 is installed and the ionospheric delay amount at the calculation target position Q. Therefore, the worst case ionosphere delay amount difference simulates the ionosphere delay amount difference by comprehensively changing the ionospheric state parameters while taking into account the temporal change of the relative position between the ionosphere and the onboard system 5. This is the maximum value of the ionospheric delay amount difference that can be experienced when the onboard system 5 reaches the calculation target position Q.

For example, the method described in Non-Patent Document 1 can be used to calculate the worst-case ionospheric delay amount difference. That is, the ionosphere delay time difference is simulated by comprehensively changing the ionospheric state parameters while taking into account the temporal change in the relative position between the ionosphere and the onboard system 5. Then, when the onboard system 5 reaches the calculation target position Q, the worst case ionosphere delay amount difference that the onboard system 5 can experience is set as the worst case ionosphere delay amount difference.

Step SA4: Next, the worst case ionosphere delay amount difference calculation unit 11 creates a worst case ionosphere delay amount difference table and stores it in the storage unit 16. This worst case ionosphere delay amount difference table is a table of the worst case ionosphere delay amount difference at the calculation target position Q as a function of the state parameter of the ionosphere abnormality model. It is not a requirement to make a table, but a requirement is to summarize the worst case ionospheric delay amount difference at the calculation target position Q as a function of the state parameter of the ionosphere abnormality model.

The receiving unit 12 receives the positioning signal received from the positioning satellite, and calculates the satellite position of the positioning satellite from the satellite orbit information included in the positioning signal. The calculated satellite position is output to the differential correction value calculation unit 13.

Also, the receiving unit 12 calculates the pseudo distance from the positioning signal and the carrier phase distance from the carrier phase, and outputs it to the differential correction value calculating unit 13.

The pseudo distance is a distance calculated by multiplying the positioning signal propagation time between the positioning satellite 4 and the receiving unit 12 measured by the positioning signal by the speed of light. The carrier phase distance is a distance calculated by continuously measuring the carrier phase angle of the positioning signal demodulated by the receiving unit 12.

The differential correction value calculation unit 13 monitors the positioning satellite for abnormality using the satellite position, pseudorange, carrier phase distance, etc. from the reception unit 12. Then, the positioning satellite determined to be normal is transmitted to the integrity parameter calculation unit 14 as usable satellite information together with the satellite position as a usable satellite.

Examples of satellite abnormality monitoring items include satellite clock anomalies, satellite orbit information anomalies sent from satellites, and modulation circuit anomalies that generate ranging signals. There are no particular limitations on the monitoring method for such satellite clock anomalies, satellite orbit information anomalies, and modulation circuit anomalies.

For example, as in Non-Patent Document 4, a method of monitoring satellite clock anomalies from the rate of change of carrier phase distance, and from the validity of satellite orbit information using multiple generations of orbit information as in Non-Patent Document 5. A method for monitoring abnormalities in satellite orbit information can be applied. In addition, as in Non-Patent Document 6, it is possible to apply a method in which a plurality of correlators is provided in the receiving unit and abnormality of the modulation circuit is monitored from the validity of the correlation waveform.

(Non-Patent Document 4) Gang Xie, "OPTIMAL ON-AIRPORT MONITORING OF THE INTEGRITY OF GPS-BASED LANDING SYSTEMS", Ph.D.Dissertation, Stanford University, March 2004.
(Non-Patent Document 5) Boris Pervan, Livio Graton, "Orbit Ephemeris Monitor for Local Area Differential GPS", IEEE Transactions on AerosPuce and Electronic Systems, Vol. 41, No. 2, April 2005.
(Non-Patent Document 6) Eric Phelts, "Multicorrelator Techniques for Robust Mitigation of Threats to GPS Signal Quality", Ph. D. Dissertation, Stanford University, June 2001.

Further, the differential correction value calculation unit 13 instructs the integrity parameter calculation unit 14 to execute the integrity parameter calculation process (parameter calculation command) at regular time intervals.

The integrity parameter calculation unit 14 uses the worst case ionosphere delay amount difference calculation unit 11 created by the worst case ionosphere delay amount difference calculation unit 11 and stored in the storage unit 16 and the usable satellite information received from the differential correction value calculation unit 13. The integrity parameter is calculated using the satellite position and the integrity parameter initial value included, and the calculated integrity parameter is transmitted to the transmission unit 15.

Here, the integrity parameter is a parameter used when the onboard system 5 calculates a reliability range of the positioning error called a protection level, and is a GBAS message type in the GBAS message format defined in the international standard of Non-Patent Document 3. 1 σpr_gnd, Ephemeris Decoration Parameter, and GBAS message type 2 σvertical_iono_gradient.

FIG. 5 is a flowchart showing the integrity parameter calculation process. In the procedure shown in FIG. 5, steps SB3 to SB7 are performed after step SB2, and the process proceeds to step SB8. Then, Steps SB8 to SB10 are performed, the process proceeds to Step SB3, and Steps SB3 to SB7 are performed. Thereafter, step SB11 is performed.

Steps SB1, SB2: Upon receiving an instruction to execute an integrity parameter calculation process from the differential correction value calculation unit 13, the integrity parameter calculation unit 14 starts an integrity parameter calculation process. The geometry screening unit 14a reads the worst case ionosphere delay amount difference table, the calculation target position Q, and the integrity parameter initial value from the storage unit 16.

Steps SB3 and SB4: The geometry screening unit 14a sets the satellites obtained by combining the positioning satellites to be screened from the positioning satellites included in the usable satellite information, the worst case ionosphere delay amount difference table, and the calculation target The worst case positioning error at the calculation target position Q is calculated using the position Q, the integrity parameter initial value, and the satellite position included in the usable satellite information.

Further, the geometry screening unit 14a calculates the allowable maximum error at the calculation target position Q using the current integrity parameter (the integrity parameter initial value or the integrity parameter changed thereafter).

The worst case positioning error is the worst case error that the onboard system 5 can experience. The allowable maximum error is a protection level calculated by the onboard system using the integrity parameter. Note that this allowable maximum error can be set to another value such as an alert limit.

Steps SB5 and SB6: Then, it is determined whether or not the worst case positioning error exceeds the allowable maximum error. If the worst case positioning error exceeds the allowable maximum error, the integrity parameter is increased until the protection level exceeds the protection level determination threshold. Note that the protection level determination threshold can be the worst case positioning error and alert limit. In the following description, the worst case positioning error will be described.

Step SB7: Such a geometry screening process is performed for all the satellite sets of positioning satellites included in the usable satellite information. Therefore, the integrity parameter after step SB7 is the maximum value. Therefore, no matter which satellite set the onboard system 5 uses, the worst case positioning error will not exceed the protection level.

The integrity parameter calculated in this way is output to the availability prediction unit 14b.

For the calculation method of the worst case positioning error at the calculation target position Q and the method of increasing the integrity parameter, the methods of Non-Patent Documents 1 and 2 can be used. Further, a method for calculating the protection level from the integrity parameter is defined in the international standard of Non-Patent Document 3.

Steps SB8 and SB9: The availability prediction unit 14b uses the integrity parameters from the geometry screening unit 14a to calculate the calculation target positions when all the positioning satellites included in the usable satellite information from the differential correction value calculation unit 13 are used. The protection level at Q is calculated. Thus, the protection level when all positioning satellites are used is described as the protection level when all usable satellites are used.

Then, the availability predicting unit 14b determines whether the protection level when using all the usable satellites exceeds the alert limit, and the protection level when using all the usable satellites exceeds the alert limit. Determines that the availability is lost, and outputs the availability loss information to the excluded satellite determination unit 14c.

On the other hand, if the protection level when using all usable satellites does not exceed the alert limit, the availability predicting unit 14b outputs the integrity parameter from the geometry screening unit 14a as it is.

Step SB10: Excluded satellite determination processing is performed when the protection level when using all usable satellites exceeds the alert limit. Generally, the protection level decreases as the number of positioning satellites used for positioning increases. Therefore, if the protection level when using all available satellites exceeds the alert limit, the protection level calculated for a smaller number of positioning satellites is also more likely to exceed the alert limit ( Likely to be lost).

If there is a high possibility that the availability will be lost, the positioning satellite which is likely to avoid the loss of availability by performing the exclusion satellite determination process to exclude the satellite is excluded from the usable satellites, and the integrity parameter is set. Calculate again. As a result, the integrity parameter can be increased moderately, and loss of availability can be suppressed.

Therefore, when the excluded satellite determining unit 14c receives the availability loss information from the availability predicting unit 14b, the excluded satellite determining unit 14c calculates an index for determining a positioning satellite to be excluded (hereinafter referred to as an excluded satellite index). Then, the satellite to be excluded is determined based on the excluded satellite index, and the positioning satellite excluding the excluded satellite is set as a new usable satellite (hereinafter, usable satellite update information). The usable satellite update information is sent to the geometry screening unit 14a, and the integrity parameter is calculated.

Now, various indicators can be considered as exclusion satellite indicators. Therefore, in the present embodiment, the worst case vertical position error (MIEV) that can occur at the calculation target position Q when it is assumed that the worst case ionosphere delay amount difference occurs simultaneously in two positioning satellites among the usable satellites. Is used.

Step SB11: The integrity parameter calculated by the above processing is transmitted from the transmission unit 15 to the onboard system 5.

FIG. 6 is a flowchart for determining the satellite n to be excluded.

Steps SC1 and SC2: First, the excluded satellite determination unit 14c reads the worst case ionosphere delay amount difference table from the storage unit 16. Next, a satellite set A (n) formed by excluding one positioning satellite (shown by the symbol n) from the usable satellites is defined.

Steps SC3 and SC4: Then, for all combinations of the satellite pairs (p1, p2) included in the satellite set A (n), the position error IEV (p1, p2) is set to IEV (p1, p2) = | Svert ( p1) · IER (p1) | + | Svert (p2) · IER (p2) | ... (1)
Svert (p) = Sv (p) + Sx (p) · tan (θGPA)
This is calculated according to Equation 1 below.

Here, IER (p1) and IER (p2) are the worst case ionospheric delay amount differences for the positioning satellites p1 and p2, respectively. The worst case ionosphere delay amount difference is calculated by, for example, the method disclosed in Non-Patent Document 1, and includes the worst case ionosphere delay amount difference table read from the storage unit 16 and the positioning satellite p1 received from the differential correction value calculation unit 13. It is determined from the position of p2.

Sv (p) and Sx (p) are contribution terms defined in the international standard of Non-Patent Document 3, and Sv (p) is a contribution to the vertical positioning error of the delay amount difference due to the ionosphere with respect to the positioning satellite p. The term Sx (p) is a contribution term to the runway direction positioning error of the delay amount difference due to the ionosphere with respect to the positioning satellite p. Furthermore, θGPA is the angle of entry into the runway.

Steps SC5 to SC7: Next, the worst case which is the maximum value of IEV (p1, p2 | p1, p2εA (n)) calculated for the satellite pair (p1, p2) of each satellite set A (n) Vertical position error MIEV (n) is
MIEV (n) = max (IEV (p1, p2 | p1, p2∈A (n))) ... (2)
It calculates | requires by Formula 2 of.

Then, among the worst case vertical position error MIEV (n), the satellite set A (nminMIEV) that has the worst value of the worst case vertical position error MIEV (n) is set as a new usable satellite, and this is updated. Output as information. Here, nminMIEV indicates one positioning satellite excluded from all usable satellites when MIEV (n) is minimized.

When the excluded satellite is determined in this way, a new usable satellite (usable satellite update information) is determined. Therefore, the geometry screening unit 14a repeats the processing described in steps SB3 to SB7 using this usable satellite update information, and calculates a new integrity parameter.

The new integrity parameter is molded into a predetermined format by the transmission unit 15 to construct a GBAS message, which is included in the reinforcement information and sent to the onboard system 5.

When the onboard system 5 receives the reinforcement information including the integrity parameter sent from the ground system 3, the onboard system 5 calculates the protection level using the integrity parameter. If the protection level is smaller than the alert limit, the position of the aircraft is corrected using information from the transmission unit 15 and the approach and landing at the airport is continued. On the other hand, when the protection level is higher than the alert limit, the approach / landing is canceled or the approach / landing using other means is switched.

Therefore, according to the present embodiment, even when the protection level exceeds the alert limit and the availability is lost in the conventional method of ensuring the safety of aviation by performing the geometry screening process and increasing the integrity parameter, according to this embodiment. Since the positioning satellite is calculated by eliminating positioning satellites that significantly increase the integrity parameter, loss of availability can be suppressed.

FIG. 7 shows the use of GPS satellite orbit information of January 1, 2014, and operates the integrity parameter calculation unit 14 every 60 seconds to create usable satellite update information, which is included in this usable satellite update information. It is the figure which showed the protection level calculated using the integrity parameter to be obtained. In FIG. 7, the ▪ marks indicate the vertical protection levels calculated using the integrity parameters according to the present embodiment. As a comparative example, the vertical protection level calculated using the integrity parameter according to the conventional method is indicated by ▲.

It should be noted that all available positioning satellites 4 are used for calculating the protection level. Further, the alert limit is set to 10 m defined by the international standard of Non-Patent Document 3 (straight line in FIG. 7).

As can be seen from FIG. 7, when the protection level calculated using all of the usable positioning satellites 4 exceeds the alert limit, a satellite to be excluded is determined by the exclusion satellite determination process, and a new usable positioning satellite is determined. Since the protection level is set to 4, the two protection levels coincide in a time zone in which the protection level does not exceed the alert limit. Even if the protection level (marked with ▲) calculated by the conventional method exceeds the alert limit and there is a time zone when the system availability is lost, the method according to this embodiment often has the protection level (marked with ■). Availability is guaranteed because it is below the alert limit.

FIG. 8 is a table comparing the number of times that the protection level exceeds the alert limit and the availability in the conventional method and the method of the present invention. The figure shows that according to the present invention, the number of times that the protection level exceeds the alert limit can be reduced from 70 times to 11 times, and the availability can be improved from 95.14% to 99.24%. .

In the above description, the calculation target position Q is described as one. However, the calculation target position Q is not limited to this and may be plural.

Further, although the maximum position error allowable in the geometry screening unit 14a is set as the protection level, this may be used as the alert limit.

Further, although the protection level determination threshold when increasing the integrity parameter in the geometry screening unit 14a is the worst case positioning error, this may be used as the alert limit at the calculation target position Q.

Further, in the exclusion satellite determination process performed by the integrity parameter calculation unit 14, MIEV (n) shown in Formula 2 is used as the exclusion satellite index when determining the exclusion satellite, but this is used as another exclusion satellite index. Is also possible.
For example,
IEV1 (p | A (n)) = | Svert (p) ・ IER (p) |… (3)
It is also possible to use a satellite that maximizes IEV1 shown in Equation 3 below.

In addition, in the availability prediction process performed by the availability prediction unit 14b, the case where the protection level at the calculation target position Q exceeds the alert limit when all the usable positioning satellites 4 are used is used as a criterion for determining the loss of availability. However, this can be used as another standard. For example, it is possible to add a case where the protection level calculated by removing one satellite from all the usable positioning satellites 4 exceeds the alert limit.

Moreover, although the availability prediction process performed by the availability prediction unit 14b and the excluded satellite determination process performed by the excluded satellite determination unit 14c have been described only once (when satellite exclusion is performed only once), this is performed multiple times. It is also possible to do. That is, the availability is lost even if the availability prediction process is performed using the integrity parameter determined by performing the geometry screening process again except the excluded satellite determined by the excluded satellite determination unit 14c by the excluded satellite determination process. In addition, it is possible to exclude positioning satellites that are likely to be able to avoid loss of availability by performing exclusion satellite determination processing to exclude the satellites.

Furthermore, the storage unit 16 is provided, and the worst case ionosphere delay amount difference calculation unit 11 calculated by the worst case ionosphere delay amount difference calculation unit 11, the calculation target position Q, and the ionosphere abnormality model M are stored therein. It is also possible to hard code this information in the worst case ionosphere delay amount difference calculation unit 11 and the integrity parameter calculation unit 14 without providing them.

Although the present invention has been described with reference to the embodiments (and examples), the present invention is not limited to the above embodiments (and examples). Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

This application claims priority based on Japanese Patent Application No. 2015-132792 filed on July 1, 2015, the entire disclosure of which is incorporated herein.

2 Ground-based satellite navigation augmentation system 3 Ground system 4 Positioning satellite 5 Onboard system 11 Worst case ionosphere delay amount difference calculation unit 12 Reception unit 13 Differential correction value calculation unit 14 Integrity parameter calculation unit 14a Geometry screening unit 14b Availability prediction unit 14c Exclusion Satellite determination unit 15 transmission unit 16 storage unit

Claims

A terrestrial satellite navigation reinforcement system in which the ground system guides the onboard system using positioning signals from positioning satellites,
When the ionospheric state parameters are comprehensively changed while considering the ionospheric delay amount of the positioning signal due to the ionosphere experienced by the ground system and the temporal change of the relative position of the ionosphere and the onboard system. A worst case ionosphere delay amount difference calculating means for calculating a worst case ionosphere delay amount difference table in which the difference between the ionosphere and the ionosphere delay amount at a predetermined calculation target position is maximized;
Abnormality monitoring of the positioning satellite is performed using the positioning satellite's satellite position, pseudorange, and carrier phase distance, and the positioning satellite determined to be normal can be used as a usable satellite, including the satellite position of the positioning satellite. Differential correction value calculating means for creating satellite information;
A satellite set of the positioning satellite is set based on the usable satellite information, the worst case positioning error at the calculation target position is calculated using the worst case ionosphere delay amount difference table, and allowed using the current integrity parameter. When the maximum error is calculated and the worst-case positioning error exceeds the allowable maximum error, the on-board system repeats the process of increasing the integrity parameter until the protection level exceeds the protection level determination threshold, so that the onboard system determines which satellite set Geometry screening means to ensure that the error experienced by the on-board system does not exceed the protection level, even if
An availability determination is made as to whether or not the protection level when using all available satellites exceeds a preset alert limit. If the protection level exceeds the alert limit, it is determined that the availability is lost. An availability prediction means for creating loss of availability information,
When the loss of availability information is received, an excluded satellite index is calculated by eliminating a predetermined number of positioning satellites from the positioning satellites included in the usable satellite information using the worst case ionosphere delay amount difference table, Excluded satellite determination means that excludes the positioning satellites excluded according to the index from the positioning satellites included in the usable satellite information, and causes the geometry screening means to calculate the integrity parameter as usable satellite update information;
A terrestrial satellite navigation reinforcement system characterized by comprising:
A terrestrial satellite navigation reinforcement system according to claim 1,
The excluded satellite determining means includes
A first means for determining a satellite set formed by combining any of the positioning satellites from a plurality of the positioning satellites in which one positioning satellite is excluded from all usable positioning satellites;
A second means for calculating a worst-case vertical position error in the satellite set;
Means for searching the satellite set according to the worst case vertical position error obtained for each satellite set by repeating the processing by the first means and the second means;
Means for eliminating the satellite excluded when determining the satellite set according to the worst case positioning error;
A terrestrial satellite navigation reinforcement system characterized by comprising:
An availability prediction method used for a terrestrial satellite navigation augmentation system in which positioning is performed using a positioning signal from a positioning satellite and the ground system guides the onboard system,
When the ionospheric state parameters are comprehensively changed while considering the ionospheric delay amount of the positioning signal due to the ionosphere experienced by the ground system and the temporal change of the relative position of the ionosphere and the onboard system. Calculate the worst case ionosphere delay amount difference table that maximizes the difference with the ionosphere delay amount at a predetermined calculation target position by the ionosphere,
Abnormality monitoring of the positioning satellite is performed using the positioning satellite's satellite position, pseudorange, and carrier phase distance, and the positioning satellite determined to be normal can be used as a usable satellite, including the satellite position of the positioning satellite. Create satellite information
A satellite set of the positioning satellite is set based on the usable satellite information, the worst case positioning error at the calculation target position is calculated using the worst case ionosphere delay amount difference table, and allowed using the current integrity parameter. When the maximum error is calculated and the worst-case positioning error exceeds the allowable maximum error, the on-board system repeats the process of increasing the integrity parameter until the protection level exceeds the protection level determination threshold, so that the onboard system determines which satellite set To ensure that the error experienced by the onboard system does not exceed the protection level,
An availability determination is made as to whether or not the protection level when using all available satellites exceeds a preset alert limit. If the protection level exceeds the alert limit, it is determined that the availability is lost. Create loss of availability information,
When the loss of availability information is received, an excluded satellite index is calculated by eliminating a predetermined number of positioning satellites from the positioning satellites included in the usable satellite information using the worst case ionosphere delay amount difference table, Removing the positioning satellites excluded according to the index from the positioning satellites included in the usable satellite information, and calculating the integrity parameter as usable satellite update information;
An availability prediction method used for a terrestrial satellite navigation augmentation system.
An availability prediction method used for the terrestrial satellite navigation reinforcement system according to claim 3,
A first procedure for determining a satellite set formed by combining arbitrary positioning satellites from a plurality of the positioning satellites in which one positioning satellite is excluded from all available positioning satellites;
A second procedure for calculating a worst-case vertical position error in the satellite set;
Repeat the process according to the first procedure and the second procedure to search for the satellite set according to the worst case vertical error obtained for each satellite set;
An availability prediction method used for a terrestrial satellite navigation reinforcement system, wherein a satellite excluded when the satellite set according to the worst-case positioning error is determined is an excluded satellite.