DE102011103875A1 - Method for determining current position of airplane located in region of reference location on earth in e.g. start flight phase, involves correcting satellite navigation position data during failure of transmission of current data - Google Patents

Abstract

The method involves determining deviation of satellite navigation position data for a reference location from known position data of the reference location. The deviation is transmitted as position determination correction data to an aircraft. The satellite navigation position data received from the aircraft is corrected on the basis of the position data from an inertial navigation system in the aircraft during failure of transmission of the current position determination correction data.

Description

The invention relates to a method for determining the current position of an aircraft in the area around a reference location on earth with known position data using a satellite navigation system, an augmentation system and an inertial navigation system installed in the aircraft. This method can find particular application in a takeoff phase and / or a landing phase, but also during a flight.

The positioning of aircraft can be done relatively easily by means of satellite navigation. Possible errors in the position determination by satellite navigation systems can be largely compensated by so-called SBAS systems (Space Based Augmentation System) or GBAS systems (Ground Based Augmentation System). An example of a SBAS system is, for example, WAAS (Wide Area Augmentation System).

A disadvantage of all of the aforementioned systems including satellite navigation is that interference on the way the signal from the satellite to the user, z. As disturbances of the ionosphere, can lead to false position determinations. Such disruptions may affect the recipient in the aircraft and the recipients of the SBAS or GBAS systems differently. This is especially true when these receivers and the aircraft are relatively far apart.

All efforts to achieve a highly accurate position determination of an aircraft by means of satellite navigation systems are ultimately aimed at replacing the ILS (Instrument Landing System) systems in use today, which are relatively expensive and labor-intensive in terms of their acquisition and maintenance. However, particularly near the airport and in the final phase of a landing approach, a particularly high accuracy of the position determination of the aircraft is required.

For example, in aviation, other safety-critical applications besides the accuracy of navigation and their reliability are essential.

Task of an aircraft navigation system is therefore to meet the requirements defined for the respective flight phases and maneuvers requirements in terms of position accuracy and integrity with the existing technical and algorithmic conditions to allow safe and accurate guidance of the aircraft.

Currently, one method of ensuring the required performance parameters is the use of a satellite navigation system (GNSS), such as the US Navstar GPS, in conjunction with a GBAS system. Here, the measured distances between reference receivers at the airport and the navigation satellites are compared with the actual, calculated distances. This is possible because the receivers are at precisely measured and thus known positions and the satellite position can be calculated with sufficient accuracy from the transmitted orbital parameters at any time. From the difference of the measurement and calculation, correction signals are generated and sent to aircraft in the vicinity of the airport. Furthermore, the quality of the navigation signals can be estimated from the known method of GBAS navigation and an upper limit for a resulting position error on the aircraft can be determined for a given probability, the so-called protection level.

Another navigation system, which is very widespread in commercial aviation, is the inertial navigation system INS (Inertial Navigation System). Here, starting from a known start position (eg parking position at the airport or determined GNSS position), accelerations and rotation rates of at least three non-collinear sensors are measured and integrated over time. Current devices thus allow an accurate and reliable autonomous navigation (if a starting position was known), which due to the integrating character, however, deteriorates over time.

Due to the deteriorating position of the INS, it is state of the art to provide GNSS support. In this case, the drifts are corrected by satellite navigation signals in order to achieve an improved positional accuracy. This can be done in different ways, but they are not relevant to the invention and therefore will not be further described here.

For a GBAS-based navigation, a continuous transmission and a very timely reception of the correction data on the aircraft are necessary. Depending on the approach phase, the correction data must not be older than about 2 seconds. If there is a short-term failure in data transmission, safe navigation may no longer be guaranteed and planned maneuvers can not be carried out.

Possible approaches currently discussed include a switch to inertial navigation in order to bridge failures for a short time. However, this has the consequence that the navigation must be completely converted to another system, which u. U. can lead to difficulties in critical phases of flight, especially when starting or landing. Due to the loss of the correction data, however, conventional GNSS navigation is generally not affected. Only the parameters for estimating the position error and the corrections for improving the accuracy are not available in this case.

The object of the invention is to improve the determination of the current position of an aircraft, which is located in a region of a reference location on the ground, whose position data are known, using a satellite navigation system and a built-in inertial navigation system.

• – Empfangen von Satellitennavigationssignalen am Referenzort und durch das Luftfahrzeug,
• – Ermitteln von sich aus den Satellitennavigationssignalen ergebenden Satellitennavigationspositionsdaten des Referenzorts an diesem sowie von Satellitennavigationspositionsdaten des Luftfahrzeugs in diesem,
• – Vergleich der Satellitennavigationspositionsdaten des Referenzorts mit dessen bekannten Positionsdaten,
• – Ermitteln der Abweichung der Satellitennavigationspositionsdaten für den Referenzort von den bekannten Positionsdaten des Referenzorts,
• – Übermitteln der Abweichung an das Luftfahrzeug als Positionsbestimmungskorrekturdaten für dieses,
• – Korrigieren der im Luftfahrzeug ermittelten Satellitennavigationspositionsdaten entsprechend der übermittelten Positionsbestimmungskorrekturdaten und
• – bei Ausfall einer Übermittlung der aktuellen Positionsbestimmungskorrekturdaten, im Luftfahrzeug erfolgendes Korrigieren der vom Luftfahrzeug empfangenen Satellitennavigationspositionsdaten anhand der im Luftfahrzeug aus dem Trägheitsnavigationssystem verfügbaren Positionsdaten.

In order to achieve this object, the invention proposes a method for determining the current position of an aircraft in the area around a reference location on earth with known position data using a satellite navigation system and an inertial navigation system installed in the aircraft, the method comprising the following steps :

• Receiving satellite navigation signals at the reference location and by the aircraft,
• Determining satellite navigation position data of the reference location on the satellite as well as of satellite navigation position data of the aircraft resulting therefrom from the satellite navigation signals,
• Comparison of the satellite navigation position data of the reference location with its known position data,
• Determining the deviation of the satellite navigation position data for the reference location from the known position data of the reference location,
• Transmitting the deviation to the aircraft as position correction data for this,
• Correcting the satellite navigation position data determined in the aircraft in accordance with the transmitted position correction data and
• In the event of a failure to transmit the current positioning correction data, in the aircraft correcting the satellite navigation position data received by the aircraft from the position data available in the aircraft from the inertial navigation system.

According to the invention, therefore, in the case of a short-term failure of the data transmission by the GBAS system or with no longer current GBAS correction data, the last received data is still to be used, but with the difference that corrections and transmitted integrity parameters are no longer dependent on the GBAS system. System, but even, d. H. be generated on the aircraft side. This is possible because the aircraft knows its position with a well-defined uncertainty until the last data transfer from the GBAS system. If the aircraft does not receive new information from the GBAS system, the corrections that are normally transmitted by the GBAS are generated with a defined (steadily increasing) uncertainty even from the aircraft-side INS. Of course, the characteristic and integrity of the INS must be considered. Nevertheless, the aircraft position can still be regarded as known, which is why it is possible to generate correction data analogous to the procedure in the GBAS ground station, as well as parameters about the uncertainty.

The advantage of the invention over the prior art can be seen in the continued use of the same navigation system without switching to alternative systems. Short-term failures such as the transmission of correction data do not pose a significant risk to the continuity of the service compared to the sole use of a GBAS system because failures of a few seconds are no longer critical.

Furthermore, it is possible in an advantageous embodiment of the invention that the aircraft radiates the self-generated corrections, so that z. In addition, for example, in an airport vicinity (eg, at increased traffic density), the information of other aircraft using the same method for generating the correction data can be used to achieve greater reliability of the aircraft-side position determination by a weighted application of a plurality of corrections ,

• 1. Bei der Erfindung werden im Bedarfsfall zur Generierung von Korrekturdaten für die Satellitennavigation keine Bodenstation bzw. kein GBAS-System sondern bordeigene Systeme wie Trägheitsnavigation verwendet.
• 2. Es wird zur Generierung keine statische Referenz verwendet sondern eine bewegte, deren Position genau (bzw. unter Kenntnis der Unsicherheit) bekannt ist:
• 3. Möglichkeit der Verwendung einer Vielzahl von Korrekturen aus unterschiedlichen Quellen.

The advantages and features of the invention can be briefly summarized as follows:

• 1. In the invention, if necessary, to generate correction data for satellite navigation no ground station or no GBAS system but on-board systems such as inertial navigation are used.
• 2. No static reference is used for the generation but a moving whose position is known exactly (or with knowledge of the uncertainty):
• 3. Possibility of using a variety of corrections from different sources.

As already mentioned above, according to the invention, a comparison of the satellite navigation position data of the reference location with its known position data takes place. This adjustment and any correction data resulting therefrom are performed and generated, for example, in the GBAS system. Alternatively, it is also possible that the adjustment of the position data of the satellite navigation position data of the reference location with its known position data in the aircraft takes place and then the correction data are generated in the aircraft.

Known GBAS systems transmit in addition to the positioning correction data also (Fehlerabschätz-) data that allow the aircraft to estimate the maximum error of the aircraft side determined position to a given probability, with these data can thus be said that with a probability of, for example 1-10 ^-7 the error in the airborne position determination not greater than z. B. a few meters (for example, 3 m). Thus, an upper limit for the position error can be determined for a given error probability. This is necessary to make a decision as to whether a particular operation (eg a landing operation) is feasible under the given navigational conditions. In order to be able to utilize these advantages in the invention, it is provided in an expedient development of the invention that error estimation data are transmitted to the aircraft in addition to the positioning correction data that can be estimated in the aircraft for estimating a maximum position error possibly resulting from the determination of the position of the aircraft are used to a given probability, and that in case of failure of the transmission of the positioning correction data and / or the error estimation data to the aircraft carried out in this estimation of the maximum position error to the predetermined probability based on the last still transmitted position determination correction data and / or error estimation data and based on from Time of failure occurs from the inertial navigation system resulting data.

The invention will be described below with reference to an embodiment shown schematically in the drawing. In this case, the figure shows, for example, an approaching aircraft receiving position data via a satellite navigation system and correction data from a GBAS system.

In the exemplary embodiment, the aircraft is therefore in the operating area of a GBAS station and uses it for navigation. Onboard the aircraft is a high quality INS, which is currently standard on a variety of aircraft installed.

Positioning is analogous to standard GBAS positioning by weighted minimization of pseudorange residuals for all satellites that are in the aircraft's view. This happens by default according to the following model: P _corrected = P _n + PRC + RRC * (t - t _zcount ) + TC + c * (Δt _SV ) _L1

Where P _{n is} the calculated smoothed _{pseudo orange} generated on board, PRC is the _{pseudo orange} correction which is normally transmitted by the ground system, as well as the range rate correction RRC, t is the current time, t _{zcount is} the time of generation of the Range rate correction. (Δt _SV ) _L1 is a correction clock for the satellite clock and is calculated from parameters from the GPS navigation message, so it is also known and available after contact loss to the GBAS ground station.

PRC can now be generated from the known aircraft position by positioning using INS itself, such as: PRC _n = -∥POS _aircraft - POS _{sat_n} ∥ - P _n .

RRC is usually relatively constant and very small over short periods of time and therefore can be reused from the last available GBAS message, as well as the associated t _zcount .

The troposphere correction TC is defined as

Here, the parameters N _R and h ₀ come from the navigation message. However, these values are also usually fixed and can therefore be reused. All other components of the formula can be easily obtained and used from a standalone GNSS positioning.

The positioning as well as the determination of the protection levels takes place until the corrections fail according to the standardized procedure. If the corrections are generated from the INS, time-dependent upper limits of the INS uncertainties must be added to the last known lateral and vertical protection levels (LPL or VPL) in order to be able to further specify an integrity for the system. These uncertainties are based on the maximum tolerable error probability and the quality of the sensors.

The additive uncertainties and PRCs generated in this way can be transmitted by aircraft, so that other aircraft in close range can receive and also utilize them. In this case, for example, a distance-dependent averaging of the corrections can take place.

Claims (5)

Method for determining the current position of an aircraft in the area around a reference location on the Earth with known position data using a satellite navigation system and an inertial navigation system installed in the aircraft, comprising the following steps: Receiving satellite navigation signals at the reference location and by the aircraft, Determining satellite navigation position data of the reference location on the satellite as well as of satellite navigation position data of the aircraft resulting therefrom from the satellite navigation signals, Comparison of the satellite navigation position data of the reference location with its known position data, Determining the deviation of the satellite navigation position data for the reference location from the known position data of the reference location, Transmitting the deviation to the aircraft as position correction data for this, Correcting the satellite navigation position data determined in the aircraft in accordance with the transmitted position correction data and In the event of a failure to transmit the current positioning correction data, in the aircraft correcting the satellite navigation position data received by the aircraft from the position data available in the aircraft from the inertial navigation system. Method according to Claim 1, characterized in that the position data corrected in the aircraft are transmitted directly or indirectly to other aircraft, which likewise approach the reference location or are located in the region of the reference location, for correcting position data determined from satellite navigation signals. Method according to Claim 1 or 2, characterized in that, to correct its position data, the aircraft receives correction data which has been determined by other aircraft also approaching the reference location or located in the region of the reference location. A method according to any one of claims 1 to 3, characterized in that error estimation data is transmitted to the aircraft in addition to the positioning correction data used in the aircraft for estimating a maximum position error possibly resulting from the determination of the position of the aircraft at a predetermined probability, and in the event of the failure of the transmission of the positioning correction data and / or the error estimation data to the aircraft, the maximum position error estimate made therefrom based on the last still transmitted position determination correction data and / or error estimation data and from the inertial navigation system as of the time of failure Data takes place. Use of the method according to one of claims 1 to 4 for a take-off flight phase and / or a landing approach phase.

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