CN114235007B - Positioning and integrity monitoring method and system for APNT service - Google Patents

Abstract

The invention discloses a method and a system for positioning and monitoring the integrity of APNT service, wherein the method comprises the following steps: determining the positioning precision requirement under a target scene; when the positioning precision requirement is high-precision positioning, determining the position of the aircraft by adopting a combined positioning algorithm, and performing integrity monitoring on combined positioning by adopting a multi-solution separation mode; when the positioning precision requirement is low-precision positioning, judging whether the aircraft is a high-altitude user or not; if not, determining the position of the aircraft by adopting an air-to-air positioning algorithm of the high-altitude user and the low-altitude user based on LDACS, and performing integrity monitoring on the air-to-air positioning by adopting a least square residual error method. According to different requirements of users on positioning accuracy and actual application conditions, the invention can provide various APNT alternative schemes for the aircraft, and perform fault detection algorithm research aiming at each alternative scheme, so as to realize the integrity monitoring of APNT service.

Description

A method and system for positioning and integrity monitoring of APNT services

Technical field

The invention relates to the technical field of aviation navigation, and in particular to a method and system for positioning and integrity monitoring of APNT services.

Background technique

The modernization of the air transportation system has put forward higher requirements for the performance of aviation navigation systems. Global Navigation Satellite System (GNSS) mainly includes the United States' Global Positioning System (GPS), Russia's Global Navigation Satellite System (GLONASS), and Europe's Galileo Satellite Navigation System (Galileo Satellite Navigation). System) and China's BeiDou Navigation Satellite System (BDS). With its high accuracy and high availability, GNSS has become the premier system for providing positioning, navigation and timing (PNT) services worldwide.

However, GNSS signals have low power and long propagation distance, so GNSS signals are easily interrupted by radio frequency interference during the propagation process. If you only rely on the global satellite navigation system during flight, the aircraft may lose navigation information after being interrupted by interference. , which may cause flight accidents in severe cases. As a commonly used navigation system after GNSS, the errors of Inertial Navigation Systems (INS) will accumulate over time, and its use is subject to certain time restrictions. Therefore, the existing navigation assistance system must be used as a backup system to provide alternative positioning, navigation and timing (APNT) services for aircraft when GNSS is unavailable, thereby building an aviation navigation network and ensuring the continuity of flights. sex and integrity.

Navigation assistance systems mainly include Distance Measuring Equipment (DME), VHF Omnidirectional Radio Range (VOR), Instrument Landing System (ILS), barometric altimeter and other navigation-capable devices. New systems, such as L-band Digital Aeronautical Communication System (LDACS), etc.

Currently, the United States' Next Generation Air Transportation System (NextGen) and Europe's Single European Sky ATM Research (SESAR) are conducting research on APNT services and have proposed some alternatives ( such as DME enhanced systems, LDACS, SSR-based Mode N, and eLoran, etc.), but further research is still needed to determine how to choose among these options in a sustainable manner without compromising dual-frequency multi-constellation (Dual-Frequency Multi-Constellation, DFMC) GNSS implementation brings risks. SESAR conducts research on the maturity level of APNT services from three levels: short-term, medium-term and long-term. Among them, the short-term research is mainly based on DME/DME solutions to implement APNT services; the mid-term research is mainly based on the Multi-DME positioning algorithm with Receiver Autonomous Integrity Monitoring (RAIM) to implement APNT services; the long-term goal is to use LDACS Implementing APNT services with eLORAN's advanced architecture can provide better performance and use alternative technologies to support Performance Based Navigation (PBN)/Required Navigation Performance (RNP) operations. Future APNT services will utilize existing navigation equipment and new navigation technologies for modular combination to achieve the goal of RNP0.3 in the terminal mobile area.

The development of APNT services faces many problems, among which the improvement of positioning accuracy and integrity monitoring are the most urgent ones to be solved.

Contents of the invention

The purpose of the present invention is to provide a method and system for positioning and integrity monitoring of APNT services, so as to realize integrity monitoring of APNT services on the premise of ensuring positioning accuracy.

In order to achieve the above objects, the present invention provides the following solutions:

A method for positioning and integrity monitoring of APNT services, including:

Determine the positioning accuracy requirements in the target scenario;

When the positioning accuracy requirement is high-precision positioning, a combined positioning algorithm is used to determine the position of the aircraft, and a multi-solution separation method is used to monitor the integrity of the combined positioning;

When the positioning accuracy requirement is low-precision positioning, determine whether the aircraft is a high-altitude user;

If not, the air-to-air positioning algorithm of high-altitude users and low-altitude users based on LDACS is used to determine the position of the aircraft, and the least squares residual method is used to monitor the integrity of the air-to-air positioning.

Optionally, it also includes: when the aircraft is a high-altitude user, using a DME/DME-based positioning algorithm to determine the position of the aircraft, and performing integrity monitoring of the DME/DME-based positioning algorithm.

Optionally, the integrity monitoring of the DME/DME-based positioning algorithm includes:

Calculate the aircraft position before the introduction of the new measurement station and the aircraft position after the introduction of the new measurement station;

Calculate the protection level of the DME/DME-based positioning algorithm based on the aircraft position before the introduction of the new measurement station and the aircraft position after the introduction of the new measurement station;

The protection level is compared with the horizontal alarm limit required by the route to complete the integrity monitoring of the DME/DME-based positioning algorithm.

Optionally, the air-to-air positioning algorithm based on LDACS for high-altitude users and low-altitude users is used to determine the position of the aircraft, specifically including:

Use Multi-DME positioning algorithm to determine the location information of high-altitude users;

Based on the two-way ranging function of LDACS, determine the measurement distance between the high-altitude user and the low-altitude user;

The position of the aircraft is determined based on the measured distance and the location information of the high-altitude user.

Optionally, the integrity monitoring of air-to-air positioning based on the least squares residual method is used, specifically including:

Calculate the fault detection threshold through the system’s false detection probability;

Calculate the minimum detectable fault according to the detection threshold and the probability of missed detection;

Calculate the horizontal accuracy factor of the system;

Calculate the horizontal protection level of the system from the minimum detectable fault and the horizontal accuracy factor;

Based on the horizontal protection level, the integrity monitoring of air-to-air positioning is completed.

Optionally, the use of a combined positioning algorithm to determine the position of the aircraft specifically includes:

Calculate the ranging error obtained by two-way ranging by m DME stations and the pseudo-range error obtained by one-way measurement by n LDACS stations;

Based on the ranging error and the pseudorange error, construct an observation equation of the ranging system;

Taking the barometric height as the observation quantity, introducing the barometric altimeter into the system, the height observation equation is obtained;

Based on the observation equation and the height observation equation, construct an observation model of the system;

The least squares method is used to solve the observation model and determine the position of the aircraft.

Optionally, the multi-solution separation method is used to monitor the integrity of the combined positioning, specifically including:

Based on the observation model of the system, calculate the state main estimate and the state sub-estimate;

Based on the state main estimate and the state sub-estimate, calculate a difference covariance matrix;

Based on the difference covariance matrix, construct a horizontal position test statistic;

Calculate the detection threshold of the fault according to the false detection probability;

Determine whether there is a fault based on the test statistic and the detection threshold;

If there is a fault, isolate the fault and calculate the protection level of the system;

If there is no fault, the protection level of the system is calculated directly;

According to the protection level, the integrity monitoring of the combined positioning is completed.

A positioning and integrity monitoring system for APNT services, including:

The demand determination module is used to determine the positioning accuracy requirements in the target scenario;

The first positioning and integrity monitoring module is used to determine the position of the aircraft using a combined positioning algorithm when the positioning accuracy requirement is high-precision positioning, and to perform integrity monitoring of the combined positioning using a multi-solution separation method;

A judgment module used to judge whether the aircraft is a high-altitude user when the positioning accuracy requirement is low-precision positioning;

The second positioning and integrity monitoring module is used when the aircraft is a low-altitude user, using the air-to-air positioning algorithm of high-altitude users and low-altitude users based on LDACS to determine the position of the aircraft, and using the least squares residual method to determine the position of the aircraft. Empty positioning for integrity monitoring.

Optionally, it also includes: a third positioning and integrity monitoring module, used to determine the position of the aircraft using a DME/DME-based positioning algorithm when the aircraft is a high-altitude user, and perform the DME/DME-based positioning algorithm. Integrity monitoring.

Optionally, in determining the position of the aircraft using the air-to-air positioning algorithm of high-altitude users and low-altitude users based on LDACS, the second positioning and integrity monitoring module specifically includes:

The high-altitude user location information unit is used to determine the location information of high-altitude users using the Multi-DME positioning algorithm;

A measurement distance determination unit, configured to determine the measurement distance between the high-altitude user and the low-altitude user based on the two-way ranging function of LDACS;

A position determination unit is used to determine the position of the aircraft based on the measured distance and the position information of the high-altitude user.

According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

The present invention provides a method and system for positioning and integrity monitoring of APNT services. When GNSS-based aviation navigation is interfered with and causes accuracy degradation or even unavailability, it can be used according to users' different needs for positioning accuracy and actual application conditions. , providing multiple APNT alternatives for aircraft, and conducting research on fault detection algorithms for each alternative to achieve integrity monitoring of APNT services.

Description of the drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the drawings needed to be used in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some of the drawings of the present invention. Embodiments, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without exerting creative efforts.

Figure 1 is a schematic flow chart of a method for positioning and integrity monitoring of APNT services according to the present invention;

Figure 2 is an overall flow chart of an APNT service positioning and integrity monitoring method according to the present invention;

Figure 3 is a hierarchical structure diagram of the multi-solution separation method of the present invention;

Figure 4 is a flow chart of the APNT integrity monitoring algorithm for multi-solution separation according to the present invention;

Figure 5 is a schematic structural diagram of an APNT service positioning and integrity monitoring system according to the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

The most basic APNT method is based on DME/DME to achieve positioning, but this method requires the user to continuously transmit information to a certain number of DME stations during the flight. However, for aircraft flying at lower altitudes, some ground DME ranging sources may be blocked due to the influence of terrain and urban environment. This causes the positioning accuracy calculated by the user to decrease. When the number of ranging sources decreases, To a certain extent, it may even cause APNT to become unavailable. To address this problem, the present invention uses the two-way ranging function of LDACS to use high-altitude users who obtain higher positioning accuracy through Multi-DME as airborne ranging sources to provide position information for low-altitude users, similar to pseudo-range measurement in GNSS. Positioning is achieved, and air-to-air collaborative positioning integrity monitoring is implemented based on the least squares residual algorithm, and the minimum detectable fault is used to further calculate the system's protection level. However, for users with higher positioning accuracy requirements, the positioning accuracy that this method can provide is limited. In response to this problem, the present invention proposes a positioning method that combines DME, LDACS and barometric altimeter. By combining the three observations of ranging, pseudo-range and altimetry, the residual minimization algorithm is used to achieve positioning. This method can provide users with higher positioning accuracy.

Another important issue facing APNT is integrity monitoring. RNP requires that airborne equipment must have on-board performance monitoring and alerting (OPMA) capabilities, and DME/DME positioning may not support this RNP navigation specification. Therefore, the concept of On-Ground Performance Monitoring and Alerting (GPMA) based on supporting RNP is proposed, which is similar to the RAIM algorithm commonly used in GNSS to monitor the integrity of DME/DME systems. For the positioning method that combines DME, LDACS and barometric altimeter, integrity monitoring is mainly carried out through redundant measurement. The present invention builds a systematic observation model and uses a multi-solution separation method to realize the monitoring and isolation of APNT faults.

In view of this, the present invention provides a method and system for positioning and integrity monitoring of APNT services, which realizes integrity monitoring of APNT services on the premise of improving positioning accuracy.

In order to make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

The purpose of the present invention is mainly achieved through the following technical solutions:

1. Achieve accurate positioning and precision estimation of high-altitude users through DME/DME.

2. Determine the fault mode introduced in DME/DME positioning, calculate its corresponding position deviation, implement fault detection by introducing new measuring stations, calculate the system protection level, and compare the protection level with the alarm limit to determine the availability of the system.

3. The positioning of high-altitude users is realized through Multi-DME, and the two-way ranging function based on LDACS realizes air-to-air collaborative positioning between high-altitude users and low-altitude users.

4. Determine the fault modes introduced in LDACS-based air-to-air cooperative positioning, design a fault detection algorithm based on its characteristics, model the residual of the positioning error, and calculate the system protection level.

5. Combine DME/LDACS/barometric altimeter and use the least squares method to achieve high-precision positioning for users.

6. Use multi-solution separation algorithm to realize the integrity monitoring of combined positioning, calculate the positioning error of the complete set and each corresponding subset, realize the detection and elimination of APNT faults, calculate the system protection level, and judge the system availability.

Embodiment 1

As shown in Figures 1 and 2, this embodiment provides a method for positioning and integrity monitoring of APNT services, including the following steps.

Step 101: Determine the positioning accuracy requirements in the target scenario; the target scenario is a scenario when GNSS is unavailable.

Step 102: When the positioning accuracy requirement is high-precision positioning, use a combined positioning algorithm to determine the position of the aircraft, and use a multi-solution separation method to monitor the integrity of the combined positioning.

Step 103: When the positioning accuracy requirement is low-precision positioning, determine whether the aircraft is a high-altitude user; if not, perform step 104; if yes, perform step 105.

Step 104: Use the air-to-air positioning algorithm of high-altitude users and low-altitude users based on LDACS to determine the position of the aircraft, and use the least squares residual method to monitor the integrity of the air-to-air positioning.

Step 105: When the aircraft is a high-altitude user, the DME/DME-based positioning algorithm is used to determine the position of the aircraft, and the integrity of the DME/DME-based positioning algorithm is monitored.

Among them, step 105 specifically includes:

1. Positioning principle based on DME/DME

DME refers to distance meter, which is a ranging equipment widely used in aviation navigation. It consists of an airborne interrogator and a ground transponder. When working, the interrogator sends an interrogation signal, and the responder transmits responses in sequence that are synchronized with the interrogation signal. In this way, the DME system can measure the slant distance between the aircraft and the ground station. A single DME station cannot position the aircraft. The position of the aircraft can only be determined when signals from two or more DME stations are received at the same time.

When positioning based on the DME/DME positioning principle, the aircraft must be within the coverage of the DME station and be able to receive input signals from at least two DME stations simultaneously. If input from only two DME stations can be received, the angle between the aircraft and the two DME stations must be between 30 degrees and 150 degrees. DME/DME is one of the main ways to support Regional Area Navigation (RNAV), and its positioning accuracy is inferior to GNSS.

2. DME/DME integrity monitoring algorithm, specifically including: calculating the aircraft position before the introduction of the new measurement station and the aircraft position after the introduction of the new measurement station; based on the aircraft position before the introduction of the new measurement station and the introduction Based on the aircraft position after the new measurement station, calculate the protection level of the DME/DME-based positioning algorithm; compare the protection level with the horizontal alarm limit required by the route to complete the integrity of the DME/DME-based positioning algorithm Sexual monitoring; the detailed process is as follows:

DME signals may be subject to two threats during the propagation process. On the one hand, the multipath effect may be affected by the terrain, causing errors in ranging information. On the other hand, the signal may be interfered by other signals on the same channel, causing signal reception. mistake. The former can be improved through changes in signal waveforms and echo suppression mechanisms, while the latter requires frequency allocation and compatibility studies on the signal. Here, the present invention unifies it as a transponder failure, which will be reflected in the position deviation of the DME station, causing the average value of the DME error distribution to be non-zero.

Assuming that the DME errors follow a normal distribution, the average error of a non-faulty transponder is zero, and the average error of a faulty transponder is equal to the station deviation:

in, Refers to the standard deviation of the ranging deviation of the DME station,/> σ _SiS =0.05NM, σ _air =max{0.085NM,0.00125D _i }, D _i refers to the tilt distance.

Calculate the position based on two DME stations i and j, and get the horizontal position error:

Among them, α _ij is the angle between the aircraft and the two stations, Should obey normal distribution:

in:

Design a single fault scenario: Assume that the aircraft obtains the initial effective position through two fault-free DME stations. As the aircraft position changes, the initial two stations no longer meet the geometric conditions, and a new station DME3 needs to be introduced to the initial one. The measuring station is replaced, and the Flight Management System (FMS) compares the aircraft position before the new measuring station is introduced with the position after the introduction, determines the potential ranging deviation, and then calculates the protection level of the position solution solution.

Let the ranging error R ₁₂ obtained based on two fault-free initial stations obey The ranging error R ₃ based on fault DME3 obeys N(μ,σ _D ), and the fault judgment form is:

|R ₁₂ -R ₃ |>T→failure (6);

Define the test statistic R=R ₁₂ -R ₃ , where If DME3 has no fault, the test statistic R obeys N(0,σ _R ), and the fault detection threshold T can be calculated from the false detection probability P _fd :

If DME3 is faulty, the test statistic R obeys N(μ,σ _R ), and the minimum detectable deviation μ _m is obtained from the missed detection probability P _md and the detection threshold T:

It is assumed here that the aircraft uses DME3 and DME1 for ranging, and the system horizontal protection level (Horizontal Protection Level, HPL) is calculated through deviation detection:

Compare the HPL with the horizontal alarm limit required by the route. If the protection level is greater than the alarm limit, the system is unavailable.

The air-to-air positioning algorithm based on LDACS for high-altitude users and low-altitude users is used to determine the position of the aircraft, specifically including:

Multi-DME positioning algorithm is used to determine the location information of high-altitude users; based on the two-way ranging function of LDACS, the measurement distance between the high-altitude users and low-altitude users is determined; based on the measurement distance and the location information of high-altitude users, the low-altitude user is determined Aircraft position. The detailed process is as follows:

(1) Air-to-air positioning algorithm for high-altitude users and low-altitude users based on LDACS

Due to terrain obstruction, the performance of low-altitude users in sending and receiving navigation signals is limited, making it difficult to achieve positioning. In contrast, high-altitude users can obtain ranging information and ranging error information from more ground ranging sources, such as achieving accurate positioning through the Multi-DME method, and broadcasting their position to low-altitude users as an airborne ranging source. Information and covariance matrices, combined with the air-to-air communication capabilities of LDACS, can realize distance measurement between high-altitude users and low-altitude users, and low-altitude users can obtain their own positions. Considering that the number of high-altitude ranging sources is limited, only two-dimensional positioning is performed here, and a barometric altimeter is used to assist in height measurement.

Air-to-air measurement is performed based on the position measurement y _A of the high-altitude user ranging source A, and its position error ε _A obeys the distribution N(0,∑ _A ). The distance between the low-altitude user and the airborne ranging source n is:

r ⁽ⁿ⁾ = (x _u -x ⁽ⁿ⁾ )·1 ⁽ⁿ⁾ +T ⁽ⁿ⁾ +M ⁽ⁿ⁾ +c·(dt ⁽ⁿ⁾ -dt _u )+ε ⁽ⁿ⁾ (10); where x _u and x ⁽ⁿ⁾ are the positions of the aircraft and the ranging source respectively, ε ⁽ⁿ⁾ is the ranging error, T ⁽ⁿ⁾ is the tropospheric delay, M ⁽ⁿ⁾ is the multipath effect, and dt ⁽ⁿ⁾ represents the aircraft carries the clock offset of the ranging source, dt _u represents the clock offset of the user receiver, 1 ⁽ⁿ⁾ is a set of unit vectors along the direction of the connection between the user receiver and the ranging source, here it is called line of sight ( Light of Sight, LoS) vector.

In the context of RNP operation, the effects of tropospheric delay T ⁽ⁿ⁾ and multipath M ⁽ⁿ⁾ are negligible because they typically only cause random errors that are orders of magnitude smaller than σ _r . The pseudo-range measurement between the airborne ranging source and low-altitude users is achieved through the two-way ranging function of LDACS:

Among them, t _t and _tr represent the time when the low-altitude user transmits and receives the signal respectively, τ represents the known inherent delay between the high-altitude ranging source from receiving the signal to transmitting the response signal, and c represents the speed of light.

In the air-to-space positioning algorithm, the airborne ranging source is different from the satellite or ground ranging source. There is a non-negligible uncertainty in its position itself. This can be considered as the ephemeris error in the satellite, which is caused by the noise σ in the distance measurement. By adding _r to the uncertainty of the airborne ranging source along LoS, the ranging error ε ⁽ⁿ⁾ at low-altitude user j can be approximated by a zero-mean Gaussian distribution N(0,σ _n,j ), where:

∑ _n represents the error covariance matrix for positioning based on the position of the ranging source, which is related to the position uncertainty of the ranging source itself and reflects the accuracy of the distance measurement value obtained from the ranging source signal. Since the airborne ranging source is positioned through Multi-DME, its positioning accuracy can be expressed as:

Among them, H represents the directional cosine matrix between the ranging source and its multiple DME stations, then,

Then, the variance of the ranging error is expressed as:

Using the two equations (10) (11), the position is solved through the weighted minimization residual method:

δx _i =(G ^T WG) ^-1 G ^T Wδr _i (16);

Among them, G is a geometric matrix composed of line-of-sight unit vectors, which is related to the geometric position of the ranging source relative to the user. W is a weighted matrix that reflects the ranging error caused by each ranging source. Its diagonal elements δr _i is the ranging correction obtained during the iteration process. When ||x _i+1 -x _i ||≤ε,ε>0, the user position converges to/> The positioning error obeys the multivariate Gaussian distribution N(0,∑), and the covariance matrix ∑=(G ^T WG) ^-1 .

(2) Air-to-air cooperative positioning integrity monitoring based on the least squares residual method, specifically including:

Calculate the detection threshold of the fault through the false detection probability of the system; calculate the minimum detectable fault according to the detection threshold and the probability of missed detection; calculate the horizontal accuracy factor of the system; calculate the system's fault detection threshold based on the minimum detectable fault and the horizontal accuracy factor Horizontal protection level; based on the horizontal protection level, the integrity monitoring of air-to-air positioning is completed. The detailed process is:

Air-to-air co-positioning can achieve integrity monitoring through the least squares residual method.

The linearized pseudorange observation equation is as follows:

Y=GX+ε (17);

The position estimate that minimizes the sum of squares of ranging errors is obtained by the least squares method:

The ranging residual vector is expressed as:

Among them, Q _ν is the cofactor matrix of the pseudorange residual vector. Under fault-free conditions, the weighted norm of the residual vector obeys a central ^χ distribution with N-2 degrees of freedom:

Air-to-air co-location introduces a new failure mode that may result in new potential integrity risks. Similar to the ephemeris failure in satellite navigation, in air-to-air cooperative positioning, the position broadcast of the airborne ranging source may have a failure Δx. This failure will be reflected in the ranging error through the line-of-sight vector:

r ⁽ⁿ⁾ = (x _u -(x ⁽ⁿ⁾ +Δx))·1 ⁽ⁿ⁾ +c·(dt ⁽ⁿ⁾ -dt _u )+ε ⁽ⁿ⁾ (21);

Let Δr=Δx·1 ⁽ⁿ⁾ , then the ranging expression under this fault is:

r ⁽ⁿ⁾ = (x _u -x ⁽ⁿ⁾ )·1 ⁽ⁿ⁾ +Δr ⁽ⁿ⁾ +c·(dt ⁽ⁿ⁾ -dt _u )+ε ⁽ⁿ⁾ (22);

When a fault occurs, the error Δr caused by the ranging fault causes the pseudorange residual vector to change. The mean value of the ranging error corresponding to the position of the fault ranging source in the vector is no longer zero, which makes the norm of the pseudorange residual vector It obeys the non-central χ ² distribution, and the non-central parameter is Δr ² :

To evaluate the minimum detectable failure of a system, that is, the maximum possible failure where the probability of missed detection is equal to the specified integrity risk. First, calculate the fault detection threshold _TD through the system's false detection probability P _fd :

Calculate the minimum detectable fault E _r according to the detection threshold and missed detection probability:

In the actual navigation process, even if no fault occurs, the integrity monitoring algorithm may still be unavailable due to the less than ideal geometric configuration of the visible ranging source. In order to judge the usability of an algorithm, the horizontal protection level needs to be calculated. The change amount of horizontal precision factor δHDOP _i is obtained from the horizontal precision factor HDOP of the geometric configuration of the airborne ranging source and the horizontal precision factor HDOP _i after removing the i-th ranging source:

Finally, the horizontal protection level of the system is calculated from the minimum detectable fault _Er and the HDOP (horizontal precision factor) of the system:

HPL = δHDOP _max ×σ _A ×E _r (27).

The use of a combined positioning algorithm to determine the position of the aircraft specifically includes:

Calculate the ranging error obtained by two-way ranging by m DME stations and the pseudo-range error obtained by one-way measurement by n LDACS stations; based on the ranging error and the pseudo-range error, construct the observation equation of the ranging system ; Take the pressure altitude as the observation quantity, introduce the barometric altimeter into the system, and obtain the altitude observation equation; build an observation model of the system based on the observation equation and the altitude observation equation; use the least squares method to perform the observation model Solve to determine the aircraft's position.

(1) Combined positioning algorithm

When GNSS is unavailable, the APNT algorithm based on DME/DME or LDACS can provide basic PNT functions for users in different airspaces. Combined with the above integrity monitoring algorithm, it can provide users with the required navigation performance.

In order to further meet the higher requirements of some users for positioning accuracy and integrity, multiple positioning methods can be combined to improve redundant measurements, such as combining measurements from DME, LDACS and barometric altimeters, based on the residual minimization algorithm For positioning, the algorithm block diagram is shown in Figure 3. DME provides two-way distance measurement, LDACS provides one-way pseudo-range measurement, and the barometric altimeter provides altitude information by measuring air pressure. Higher-precision positioning is achieved by combining measurement information from each system.

First, calculate the ranging error under DME and LDACS positioning.

The ranging error obtained by two-way ranging from m DME stations is:

Among them, ρ _i represents the distance measured by the i-th DME station, s _i is the location of the i-th DME station, is the user's location.

The pseudorange error obtained by one-way measurement of n LDACS stations is:

Among them, ρ _Lj represents the pseudorange measured by the j-th LDACS station, s _Lj is the position of the j-th LDACS station, is the user position, and dt is the clock deviation.

Combining the two, we get the observation equation of the ranging system:

In the formula, y is the observation quantity, that is, the difference between the distance measurement and the approximate calculation distance; G is the observation matrix, a _{i, j} are the coefficients of the observation matrix; x is the three position errors (Δx , Δy, Δz) and the receiver clock deviation dt constitute the state quantity to be estimated; ε _D is an m×1-order vector, and ε _L is an n×1-order vector, which respectively represent the propagation uncertainty due to the propagation uncertainty in the DME and LDACS ranging processes. The ranging bias vector caused by the influence of characteristics and receiver noise, the standard deviations are σ _D and σ _L respectively.

In order to facilitate the introduction of the observation information of the barometric altimeter into the observation equation, the state quantity needs to be projected into the geographical coordinate system. The coordinate conversion formula is as follows:

in, a is the long radius of the reference ellipsoid, and e is the oblateness of the ellipsoid.

From this iteration, the ranging error in the geographical coordinate system can be obtained, which is expressed as:

In the formula, φ, λ and h represent latitude, longitude and height respectively, and A represents the coordinate transformation matrix.

Taking the barometric height as the observation quantity, introducing the barometric altimeter into the system, the height observation equation is obtained:

Among them, H _B is the pressure height, is the estimated user altitude, ε _B represents the measurement error of the barometric altimeter, and obeys a zero-mean Gaussian distribution with a standard deviation of σ _B .

Combining the above observations, a new observation equation is obtained:

In the formula, Z represents observation information, including DME, LDACS and barometric altimeter observations; H represents the observation matrix; distance error; V is the measurement noise matrix, its mean value is 0, and the variance matrix is AG is an n×4 order matrix, which represents the navigation system observation matrix obtained after coordinate transformation of the observation matrix G.

According to the system model, its positioning solution can be obtained through the least squares method. When the number of DME and LDACS sites exceeds 3, equation (32) has a unique solution: Δφ ₁ , Δλ ₁ , Δh ₁ , which are superimposed on the initial position φ ₀ , λ ₀ , h ₀ to obtain the next approximate position. , substitute the initial position into equation (32) and iterate until Δφ _i , Δλ _i , and Δh _i reach the required magnitude, then the least squares solution of the user's position in the geographical coordinate system can be obtained.

(2) APNT integrity monitoring based on multi-solution separation, including:

Based on the observation model of the system, calculate the state main estimate and the state sub-estimate; based on the state main estimate and the state sub-estimate, calculate the difference covariance matrix; based on the difference covariance matrix, construct a horizontal position test statistics; calculate the detection threshold of the fault based on the misdetection probability; determine whether there is a fault based on the test statistics and the detection threshold; if there is a fault, isolate the fault and calculate the protection level of the system ; If there is no fault, directly calculate the protection level of the system; based on the protection level, complete the integrity monitoring of the combined positioning.

Fault detection

On the basis of establishing the observation model of the combined system, the multi-solution separation method is used to realize the integrity monitoring of APNT. Define the estimate obtained by using all observations as the main estimate, and the estimate obtained by excluding one observation as the sub-estimate. Set the fault threshold, and realize the monitoring and isolation of APNT faults by comparing the difference between different estimates with the set threshold.

According to the observation equation, the state master estimate can be obtained under the full observation quantity:

X ₀ =Q ₀ Z = (H ^T WH) ^-1 H ^T WZ (35);

Among them, W = R ^-1 is a positive definite weighting matrix, Q ₀ is the least squares solution matrix under complete observation conditions, and the dimension is 4×(m+n+1). Remove the i-th distance observation, use the remaining observation information to solve the state, and obtain the state subestimate:

In the formula, _Q'i represents the 4×(m+n) order least squares solution matrix under incomplete observation conditions after excluding the i-th distance observation. In order to facilitate subsequent calculations, Q' is added to the i-th column by zeroing. _i is expanded to a 4×(m+n+1) order matrix Q _i to obtain a sub-estimation:

X _i =Q _i Z(i=1,2,Λ,m+n) (37);

Then the covariance matrix of the difference between the main estimate and the sub-estimate is:

Use this to construct the horizontal position test statistic Calculate the fault detection threshold _Ti according to the false detection probability P _fd :

in, Represents the maximum eigenvalue corresponding to the horizontal position direction in dP _i , erf ^-1 is the inverse function of.

Fault judgment is made based on m+n sets of test statistics and fault detection thresholds. The basis is:

(1) Failure-free H ₀ : all test statistics satisfy d _i ≤ T _i ;

(2) Faulty H ₁ : There is at least one set of test statistics satisfying d _i >T _i .

fault isolation

After a fault is detected, the fault needs to be located and identified to achieve fault isolation. _Through the _{sub - estimation} The basis for the source to be faulty is: if there is and is only one sub-estimate X _n and the test statistics X _n,j of all its sub-estimates are less than the fault detection threshold, then the nth ranging source needs to be isolated.

If all sub-estimates and all corresponding estimates are greater than the fault detection threshold, it means that a multi-ranging source fault has occurred, and further analysis needs to be done analogously to this method.

The hierarchical structure of the multi-solution separation method is shown in Figure 4.

Protection level calculation

After integrity monitoring is performed, the availability under integrity requirements should be judged and the horizontal protection level and vertical protection level (VPL) of the aircraft should be calculated.

The _{HPL i corresponding} to each sub-estimate Xi consists _of two parts: one is the threshold for solution separation of the sub _- estimate _Xi and the main _estimate The sub-estimator's own horizontal position error threshold a _i is:

HPL _i =T _i +a _i (40);

Define the error covariance matrix of the sub-estimate _Xi as:

remember is the maximum eigenvalue corresponding to the horizontal position direction in _Pi , then for a given missed detection probability P _md , we can get:

Then the horizontal protection level of the multi-solution separation method is calculated:

HPL=max(HPL _i )=max(T _i +a _i ) (43);

Similarly, the vertical protection level of the multi-solution separation method can be calculated:

VPL=max(VPL _i )=max(D _i +a _i ) (44);

in,

Embodiment 2

As shown in Figure 5, this embodiment provides an APNT service positioning and integrity monitoring system, including:

The requirement determination module 501 is used to determine the positioning accuracy requirement in the target scenario.

The first positioning and integrity monitoring module 502 is used to determine the position of the aircraft using a combined positioning algorithm when the positioning accuracy requirement is high-precision positioning, and to perform integrity monitoring of the combined positioning using a multi-solution separation method.

The determination module 503 is used to determine whether the aircraft is a high-altitude user when the positioning accuracy requirement is low-precision positioning.

The second positioning and integrity monitoring module 504 is used to determine the position of the aircraft using the air-to-air positioning algorithm of high-altitude users and low-altitude users based on LDACS when the aircraft is a low-altitude user, and use the least squares residual method to determine the position of the aircraft. Perform integrity monitoring of empty positioning.

The third positioning and integrity monitoring module 505 is used to determine the position of the aircraft using a DME/DME-based positioning algorithm when the aircraft is a high-altitude user, and perform integrity monitoring of the DME/DME-based positioning algorithm.

In terms of determining the position of the aircraft using the air-to-air positioning algorithm for high-altitude users and low-altitude users based on LDACS, the second positioning and integrity monitoring module specifically includes:

The high-altitude user location information unit is used to determine the location information of high-altitude users using the Multi-DME positioning algorithm.

A measurement distance determination unit is used to determine the measurement distance between the high-altitude user and the low-altitude user based on the two-way ranging function of LDACS.

A position determination unit is used to determine the position of the aircraft based on the measured distance and the position information of the high-altitude user.

Compared with the prior art, the innovative parts of the present invention are as follows:

The present invention proposes a classification method based on user requirements for positioning accuracy and actual application conditions. Taking into account the characteristics of various situations, three different APNT algorithms are provided;

1. An algorithm flow is proposed to realize air-to-air relative cooperative positioning using the two-way ranging function of LDACS, and the position error of the airborne ranging source achieved through Multi-DME is given. Ranging error of positioning achieved by low-altitude users through LDACS

2. Analyzed the unique fault mode in air-to-air cooperative positioning, that is, the position information fault of the airborne ranging source itself, and compared it to the ephemeris fault in satellite navigation, and gave the ranging expression under this fault mode. Formula r ⁽ⁿ⁾ = (x _u -x ⁽ⁿ⁾ )·1 ⁽ⁿ⁾ +Δr ⁽ⁿ⁾ +c·(dt ⁽ⁿ⁾ -dt _u )+ε ⁽ⁿ⁾ , an exploit is proposed for this specific fault Chi-square test is used to detect faults and how to solve the detection threshold;

3. Proposed a horizontal protection level calculation method HPL=δHDOP _max ×σ _A ×E _r suitable for the air-to-air co-positioning algorithm based on LDACS, which is used to judge the availability of the APNT system;

4. The ranging error expressions using DME and LDACS for positioning are given respectively, and the observation equation of the ranging system composed of m DME bidirectional ranging quantities and n LDACS pseudo-range measurements is given.

5. Proposed a new combined positioning method that uses the measurement information combination of DME/LDACS/barometric altimeter to realize APNT service;

6. It is proposed that the observation equation obtained by the combination of DME/LDACS is transformed into a geographical coordinate system and combined with the altitude observation provided by the barometric altimeter to obtain the combined observation equation. The method uses the least squares method to solve the positioning problem;

7. According to the characteristics of the DME/LDACS/barometric altimeter combined positioning system, the process of using the multi-solution separation algorithm for integrity monitoring is given: Calculate the state master estimate X ₀ =Q ₀ Z = (H ^T WH ) ^-1 H ^T WZ and state subestimate X _i = Q _i Z, a new horizontal position test statistic is constructed according to the system characteristics Calculate detection threshold/> Make system fault judgments based on test statistics and fault detection thresholds;

8. The process of implementing APNT ranging source fault isolation by calculating the state sub-estimate Xi and the sub-estimate X _{i ,j} after a fault is detected is given;

9. A method is proposed to calculate APNT horizontal and vertical protection levels based on the covariance matrix of the difference between the main estimate and the sub-estimate obtained from the DME/LDACS/barometric altimeter combined state equation and the system's false detection probability and missed alarm probability.

It can be seen from the solutions provided by the present invention that the beneficial effects of the present invention are:

First, the present invention provides multiple APNT alternatives to aircraft, providing a solution to the problem of aircraft positioning when GNSS is unavailable;

Second, the present invention provides a relative positioning method for low-altitude users who are blocked by terrain or buildings based on the two-way ranging function of LDACS;

Third, the present invention proposes a combined positioning method using DME/LDACS/barometric altimeter to further improve the positioning accuracy of APNT;

Fourth, in order to realize the integrity monitoring of APNT, the present invention provides a fault detection algorithm suitable for each positioning algorithm, and proves the availability of the algorithm by calculating the protection level;

Fifth, the present invention helps to increase the attention paid to APNT in China and promote the promotion and application of its algorithm.

Each embodiment in this specification is described in a progressive manner. Each embodiment focuses on its differences from other embodiments. The same and similar parts between the various embodiments can be referred to each other. As for the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple. For relevant details, please refer to the description in the method section.

This article uses specific examples to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and the core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the present invention There will be changes in the specific implementation methods and application scope of the ideas. In summary, the contents of this description should not be construed as limitations of the present invention.

Claims (8)

1. A method for positioning and integrity monitoring of an APNT service, comprising:

determining the positioning precision requirement under a target scene;

when the positioning precision requirement is high-precision positioning, determining the position of the aircraft by adopting a combined positioning algorithm, and performing integrity monitoring on combined positioning by adopting a multi-solution separation mode;

when the positioning precision requirement is low-precision positioning, judging whether the aircraft is a high-altitude user or not;

if not, determining the position of the aircraft by adopting an air-to-air positioning algorithm of a high-altitude user and a low-altitude user based on LDACS, and performing integrity monitoring on air-to-air positioning by adopting a least square residual error method;

the method for determining the position of the aircraft by adopting the air-to-air positioning algorithm of the high-altitude user and the low-altitude user based on the LDACS specifically comprises the following steps: determining the position information of the high-altitude user by adopting a Multi-DME positioning algorithm; determining a measurement distance between the high-altitude user and the low-altitude user based on the two-way ranging function of the LDACS; and determining the position of the aircraft according to the measured distance and the position information of the high-altitude user.

2. The method for locating and monitoring the integrity of an apt service of claim 1, further comprising: and when the aircraft is a high-altitude user, determining the position of the aircraft by adopting a DME/DME-based positioning algorithm, and carrying out integrity monitoring on the DME/DME-based positioning algorithm.

3. The method for positioning and integrity monitoring of an apt service according to claim 2, wherein said integrity monitoring of a DME/DME based positioning algorithm comprises:

calculating the position of the aircraft before the new station is introduced and the position of the aircraft after the new station is introduced;

calculating a protection level of the DME/DME based localization algorithm based on the aircraft position before the introduction of the new docking station and the aircraft position after the introduction of the new docking station;

the protection level is compared to the level warning limits required for the way to complete integrity monitoring of the DME/DME based positioning algorithm.

4. The method for positioning and integrity monitoring of an apt service according to claim 1, wherein said adopting a least squares residual method for integrity monitoring of an empty-space positioning specifically comprises:

calculating a fault detection threshold value through the false detection probability of the system;

calculating a minimum detectable fault according to the detection threshold and the missing detection probability;

calculating a horizontal precision factor of the system;

calculating a horizontal protection level of the system from the minimum detectable fault and the horizontal precision factor;

based on the level protection level, integrity monitoring of the air-to-air positioning is completed.

5. The method for positioning and integrity monitoring of an apt service of claim 4, wherein said determining the position of an aircraft using a combined positioning algorithm comprises:

calculating a ranging error obtained by two-way ranging of m DME stations and a pseudo range error obtained by one-way measurement of n LDACS stations;

constructing an observation equation of a ranging system based on the ranging error and the pseudo-range error;

taking the air pressure height as an observed quantity, and introducing the air pressure type height meter into a system to obtain a height observation equation;

constructing an observation model of the system based on the observation equation and the altitude observation equation;

and solving the observation model by adopting a least square method to determine the position of the aircraft.

6. The method for positioning and integrity monitoring of an apt service according to claim 5, wherein said performing integrity monitoring on a combined positioning by using a multi-resolution method specifically comprises:

calculating a state main estimate and a state sub-estimate based on an observation model of the system;

calculating a difference covariance matrix based on the state main estimate and the state sub-estimates;

constructing a horizontal position test statistic based on the difference covariance matrix;

calculating a fault detection threshold according to the false detection probability;

determining whether a fault exists according to the test statistic and the detection threshold;

if the fault exists, isolating the fault and calculating the protection level of the system;

if no fault exists, directly calculating the protection level of the system;

and completing integrity monitoring of combined positioning according to the protection level.

7. A positioning and integrity monitoring system for an APNT service, comprising:

the demand determining module is used for determining the positioning accuracy demand in the target scene;

the first positioning and integrity monitoring module is used for determining the position of the aircraft by adopting a combined positioning algorithm when the positioning precision requirement is high-precision positioning, and carrying out integrity monitoring on the combined positioning by adopting a multi-solution separation mode;

the judging module is used for judging whether the aircraft is a high-altitude user or not when the positioning precision requirement is low-precision positioning;

the second positioning and integrity monitoring module is used for determining the position of the aircraft by adopting an air-to-air positioning algorithm based on the LDACS high-altitude user and the low-altitude user when the aircraft is a low-altitude user, and carrying out integrity monitoring on the air-to-air positioning by adopting a least square residual error method;

in the aspect of determining the position of the aircraft by adopting an air-to-air positioning algorithm of a high-altitude user and a low-altitude user based on LDACS, the second positioning and integrity monitoring module specifically comprises: the high-altitude user position information unit is used for determining the position information of the high-altitude user by adopting a Multi-DME positioning algorithm; a measurement distance determining unit, configured to determine a measurement distance between the high-altitude user and the low-altitude user based on a two-way ranging function of the LDACS; and the position determining unit is used for determining the position of the aircraft according to the measured distance and the position information of the high-altitude user.

8. The system for locating and monitoring the integrity of an apt service of claim 7, further comprising: and the third positioning and integrity monitoring module is used for determining the position of the aircraft by adopting a DME/DME-based positioning algorithm when the aircraft is a high-altitude user and carrying out integrity monitoring on the DME/DME-based positioning algorithm.