CN101598780B - Local airport monitoring method, device and system therefor - Google Patents

Abstract

The invention provides a local airport monitoring method, a device and a system therefor. The method comprises: receiving satellite data transmitted by each receiver and calculating pseudorange corrected value corresponding to each receiver; selecting any receiver at will as a pseudo onboard user and calculating pseudorange corrected value positioning error of the pseudo onboard user; calculating monitor system positioning error of the pseudo onboard user and calculating to obtain ground monitor protection level of the pseudo onboard user according to the monitor system positioning error and wide area augmentation system (WAAS) information promulgation error; comparing ground monitor protection level of all the satellite combination of the pseudo onboard user and preset alarm limit value of the pseudo onboard user, and outputting the optimal satellite combination according to the comparison result. The invention performs calculation of pseudorange corrected value error and monitor system error on the onboard user by a ground monitor end, finishes selection of the onboard user optimal visible satellite combination by detection of ground monitor protection level, reduces calculation load of onboard user and improves instantaneity.

Description

Local airport monitoring method, device and system

Technical Field

The embodiment of the invention belongs to the technical field of satellite navigation, and particularly relates to a local airport monitoring method, device and system.

Background

When the satellite navigation system is applied to civil aviation, four performance indexes of precision, integrity, continuity and usability must be usually satisfied. Wherein, the precision refers to the difference between the measured position and the real position of the navigation system at any time; integrity refers to the ability of the system to alert or shut down in time when it is unable to provide navigation services; continuity refers to the ability of the system to provide service throughout the flight; usability refers to the ability of the system to potentially be used for navigation when desired by a user. However, the current Satellite Navigation System is generally affected by the number of available satellites, the atmosphere, the ionosphere, thundercloud, and other factors, and by the dynamic behavior of the aircraft, and therefore, the Global Positioning System (GPS) in the united states or the Global Navigation Satellite System (GLONASS) in russia cannot fully satisfy the Navigation performance requirements in the above aspects. Therefore, in order to improve the integrity, accuracy, availability and continuous service of the satellite navigation system, a satellite navigation enhancement system is formed, which can improve the performance of the satellite navigation system through some ground and satellite facilities on the basis of selecting the technology such as a differential technology and a pseudo satellite technology.

Current satellite navigation augmentation systems can be divided into three categories: a ground-based Augmentation System, a satellite-based Augmentation System and an air-based Augmentation System, wherein the ground-based Augmentation System is represented by a Local Area Augmentation System (LAAS) in the United states. The differencing technique used by LAAS is based on generating a correction to all expected commonality errors between a local reference station and subscriber stations, so LAAS can only broadcast navigation corrections within a "local" range of about 20 nautical miles, with a service space including only airports within the area. Furthermore, due to the influence of ionospheric storms, the integrity of LAAS is not guaranteed, making authentication of LAAS very difficult.

The satellite-based Augmentation System is typically a Wide Area Augmentation System (WAAS) in the united states and an European Global Navigation Overlay Service (EGNOS) in the European union. Both systems broadcast correction information to users through Geostationary Orbit (GEO), but because local monitoring is not performed, the integrity of the GEO cannot meet the performance requirement of precision approach of civil aviation.

The space-based augmentation system is typically a Receiver Autonomous Integrity Monitoring system (RAIM). Although RAIM is a simple and effective integrity monitoring method, RAIM still has usability problems. The RAIM availability means that RAIM monitoring cannot be performed at some time-space points or the RAIM monitoring result cannot guarantee that the false alarm rate and the missed detection rate can be met at the same time. There are two main factors that contribute to RAIM availability issues: firstly, the number of observation satellites is insufficient, the RAIM needs at least 5 satellites at the same time to perform redundant information consistency check to detect faults, and at least 6 satellites can perform fault identification operation. That is, at some time-space points, the condition that the RAIM monitoring cannot be performed due to the insufficient number of satellites occurs, and the condition is also called RAIM hole. The second is the geometric distribution factor. Although the number of satellites at some space-time points meets the basic requirements of RAIM, the geometric layout of the satellites may result in that faults appearing on some satellites cannot be detected during integrity monitoring, and as a result, the requirement of missed detection rate cannot be guaranteed. Thus, RAIM methods are not suitable for integrity monitoring in general.

In order to enable the LAAS system of satellite navigation to achieve the I-type precision approach performance, the United states Federal Aviation Administration (FAA) combines the LAAS system with the WAAS system, and then a Local Airport monitoring system (LAM) is provided, which improves the positioning precision and various performances of satellite navigation and eliminates the influence of ionospheric storms on the system. However, most integrity algorithms of the LAM system in the prior art need to be completed by the airborne user, which increases the burden of the user and reduces the real-time performance.

Disclosure of Invention

The embodiment of the invention provides a local airport monitoring method, a local airport monitoring device and a local airport monitoring system, which are used for solving the defects that most integrity algorithms of an LAM system in the prior art need to be completed by an airborne user, the burden of the user is increased, the practicability is reduced, and the performance of the local airport monitoring method and the local airport monitoring system is improved.

The embodiment of the invention provides a local airport monitoring method, which comprises the following steps:

acquiring receiver information of each receiver and satellite data received by the receiver from a navigation satellite, and correcting pseudo-range information in the satellite data by using enhancement information, a carrier phase observation value and a troposphere error model broadcasted by a wide area enhancement system to obtain a pseudo-range correction value of each satellite corresponding to each receiver, wherein the receiver information comprises a satellite elevation value of a visible satellite corresponding to the receiver, a real distance between the receiver and the visible satellite thereof and the number of visible satellites of each receiver;

optionally selecting one receiver as a pseudo-airborne user, calculating a pseudo-range correction value positioning error of the pseudo-airborne user by using a conversion matrix from a pseudo-range domain to a positioning domain according to the receiver information of the pseudo-airborne user and a continuity requirement value preset by the airborne user, and extracting wide area enhancement system information of the pseudo-airborne user from the pseudo-range correction value positioning error to broadcast the positioning error;

according to the receiver information of the pseudo airborne user and a preset integrity risk value of a system, calculating to obtain a monitoring system positioning error of the pseudo airborne user by using a conversion matrix from a pseudo-range domain to a positioning domain, and calculating an ideal envelope value of the sum of the monitoring system positioning error and the wide area enhancement system information broadcast positioning error to obtain a ground monitoring protection level of the pseudo airborne user, wherein the monitoring system positioning error comprises a positioning error caused by thermal noise of the airborne user and fuselage multipath, a positioning error caused by an ionized layer above a monitoring center and a positioning error caused by a troposphere above the monitoring center;

and sequentially comparing the ground monitoring protection levels of all visible satellite combinations of the pseudo airborne user with an alarm limit value preset by the airborne user, and if the ground monitoring protection levels of the visible satellite combinations are smaller than the alarm limit value, sending the visible satellite combination with the largest number of satellites and the pseudo-range correction value of each visible satellite in the visible satellite combination to the airborne user.

The embodiment of the invention provides a local airport monitoring device, which comprises:

the first calculation module is used for acquiring receiver information of each receiver and satellite data received by the receiver from a navigation satellite, and correcting pseudo-range information in the satellite data by using enhancement information broadcast by a wide area enhancement system, a carrier phase observation value and a troposphere error model to obtain a pseudo-range correction value of each satellite corresponding to each receiver, wherein the receiver information comprises a satellite elevation value of a visible satellite corresponding to the receiver, a real distance between the receiver and the visible satellite thereof and the number of the visible satellites of each receiver;

the second calculation module is connected with the first calculation module and is used for selecting one receiver as a pseudo airborne user, calculating a pseudo-range correction value positioning error of the pseudo airborne user by using a conversion matrix from a pseudo-range domain to a positioning domain according to the receiver information of the pseudo airborne user and a continuity requirement value preset by the airborne user, and extracting wide area augmentation system information broadcasting positioning error of the pseudo airborne user from the pseudo-range correction value positioning error;

a third calculation module, connected to the second calculation module, configured to calculate, according to the receiver information of the pseudo airborne user and a preset integrity risk value of the system, a positioning error of a monitoring system of the pseudo airborne user by using a conversion matrix from the pseudo-range domain to a positioning domain, and calculate an ideal envelope value of a sum of the positioning error of the monitoring system and a positioning error broadcast by the wide-area augmentation system information, so as to obtain a ground monitoring protection level of the pseudo airborne user, where the positioning error of the monitoring system includes a positioning error caused by thermal noise of the airborne user and fuselage multipath, a positioning error caused by an ionosphere above a monitoring center, and a positioning error caused by a troposphere above the monitoring center;

and the judgment module is connected with the third calculation module and is used for sequentially comparing the ground monitoring protection levels of all visible satellite combinations of the pseudo airborne user with an alarm limit value preset by the airborne user, and if the ground monitoring protection levels of the visible satellite combinations are smaller than the alarm limit value, sending the visible satellite combination with the largest number of satellites and the pseudo-range correction value of each visible satellite in the visible satellite combination to the airborne user.

The embodiment of the invention provides a local airport monitoring system, which comprises:

the system comprises a plurality of receivers, a monitoring center and a navigation satellite, wherein the receivers are used for receiving satellite data sent by the navigation satellite, carrying out analog-to-digital conversion on the satellite data and sending the satellite data after analog-to-digital conversion and receiver information of the receivers to the monitoring center, and the receiver information comprises satellite elevation values of visible satellites corresponding to the receivers, real distances between the receivers and the visible satellites and the number of the visible satellites of each receiver;

the monitoring center is connected with the receiver and used for calculating a pseudo-range correction value of each satellite corresponding to the receiver according to the received satellite data, detecting an error caused by the pseudo-range correction value of the airborne user and an error caused by a monitoring system according to the information of the receiver, calculating a ground monitoring protection level of the monitoring center, obtaining an available satellite combination by comparing the ground monitoring protection level with an alarm limit value preset by the user, and sending the available satellite combination and the pseudo-range correction value of each visible satellite in the satellite combination to the airborne user,

the monitoring center includes: the first calculation module is used for acquiring receiver information of each receiver and satellite data received by the receiver from a navigation satellite, and correcting pseudo-range information in the satellite data by using enhancement information broadcast by a wide area enhancement system, a carrier phase observation value and a troposphere error model to obtain a pseudo-range correction value of each satellite corresponding to each receiver, wherein the receiver information comprises a satellite elevation value of a visible satellite corresponding to the receiver, a real distance between the receiver and the visible satellite thereof and the number of the visible satellites of each receiver;

the second calculation module is connected with the first calculation module and is used for selecting one receiver as a pseudo airborne user, calculating a pseudo-range correction value positioning error of the pseudo airborne user by using a conversion matrix from a pseudo-range domain to a positioning domain according to the receiver information of the pseudo airborne user and a continuity requirement value preset by the airborne user, and extracting wide area augmentation system information broadcasting positioning error of the pseudo airborne user from the pseudo-range correction value positioning error;

a third calculation module, connected to the second calculation module, configured to calculate, according to the receiver information of the pseudo airborne user and a preset integrity risk value of the system, a monitoring system positioning error of the pseudo airborne user by using a conversion matrix from the pseudo-range domain to a positioning domain, and calculate an ideal envelope value of a sum of the monitoring system positioning error and a positioning error broadcast by the wide-area augmentation system information, so as to obtain a ground monitoring protection level of the pseudo airborne user, where the monitoring system positioning error includes a positioning error caused by thermal noise of the airborne user and fuselage multipath, a positioning error caused by an ionosphere above a monitoring center, and a positioning error caused by a troposphere above the monitoring center;

the judgment module is connected with the third calculation module and is used for sequentially comparing the ground monitoring protection levels of all visible satellite combinations of the pseudo airborne user with an alarm limit value preset by the airborne user, and if the ground monitoring protection levels of the visible satellite combinations are smaller than the alarm limit value, sending the visible satellite combination with the largest number of satellites and the pseudo-range correction value of each visible satellite in the visible satellite combination to the airborne user;

and the airborne user is connected with the monitoring center and used for calculating the position of the airborne user according to the visible satellite combination and the pseudo-range correction value of the visible satellite combination sent by the monitoring center.

According to the local airport monitoring method, device and system, errors caused by pseudo-range correction values and errors caused by a monitoring system are detected on the airborne user at the ground monitoring end, the concept of ground monitoring protection level is obtained according to the definition, the self protection level calculation of the airborne user is converted into the calculation of the ground monitoring protection level by the ground monitoring center, and therefore the selection of the optimal visible satellite combination of the airborne user is completed through the detection of the protection level of the ground detection center.

Drawings

FIG. 1 is a flowchart of a first embodiment of a local airport monitoring method of the present invention;

FIG. 2 is a flowchart of a second embodiment of a local airport monitoring method of the present invention;

FIG. 3 is a schematic structural diagram of an embodiment of a local airport monitoring system of the present invention;

fig. 4 is a schematic structural diagram of an embodiment of the local airport monitoring system of the present invention.

Detailed Description

The technical solutions of the embodiments of the present invention are further described below with reference to the accompanying drawings and specific embodiments.

With the vigorous development of satellite navigation business, countries around the world are building their own satellite navigation systems, such as the GPS system in the united states, the GLONASS system in russia, and the Galileo (Galileo) system in europe under construction. However, due to the influence of the ionosphere, the troposphere, the multipath effect and the thermal noise, and the problems of the satellite navigation system itself, such as ephemeris error, clock error, etc., the satellite navigation system cannot meet the performance index required by the system in many applications. For example, in the application of a precision approach system of a civil aircraft, not only is a high requirement on the precision of satellite navigation, but also the requirements on the integrity, continuity and usability are severe.

In order to solve the above problems, researchers in the navigation field invented many aiding systems to enhance the satellite navigation system. Currently, typical Satellite navigation enhancements include WAAS and LAAS in the United states, EGNOS in the European Union, and the Multi-Functional Satellite Augmentation System (MSAS) in Japan. However, because the integrity of the application of the precision approach system of the civil aircraft cannot meet the performance requirement of the precision approach of the civil aircraft, related researchers have proposed the LAM system based on the integrity requirement. However, the LAM system in the prior art lacks data verification, and is poor in robustness, and meanwhile, most integrity algorithms need to be completed by the airborne user, so that the burden of the user is increased, and the real-time performance is reduced.

Therefore, on the basis of an LAM system, the embodiment of the invention provides a local airport monitoring method, a device and a system, wherein the local airport monitoring method is realized in a ground monitoring center, the local airport monitoring method is realized by detecting and estimating satellite positioning errors of an airborne user caused by a receiver, the monitoring center and the airborne user at the ground monitoring center, calculating at the ground monitoring center to obtain a ground monitoring protection level, and converting the calculation of the protection level of the airborne user into the calculation of the ground monitoring protection level, so that the calculation burden of the airborne user is reduced, and the real-time performance is improved.

Fig. 1 is a flowchart of a first embodiment of the local airport monitoring method of the present invention, and as shown in fig. 1, the local airport monitoring method of the present invention includes:

step 100, acquiring receiver information of each receiver and satellite data received by the receiver from a navigation satellite, and correcting pseudo-range information in the satellite data by using enhancement information broadcast by a wide area enhancement system, a carrier phase observation value and a troposphere error model to obtain a pseudo-range correction value of each satellite corresponding to each receiver;

the method for monitoring the local airport in this embodiment is directed to a monitoring center in a local airport monitoring system based on multiple receivers, and since each receiver receives satellite data from a respective visible satellite, does not calculate the satellite data, but only performs analog-to-digital conversion on the satellite data, and directly transmits the satellite data after the analog-to-digital conversion to the monitoring center along with receiver information, the calculation of a pseudorange correction value of the receiver is completed in the monitoring center. Wherein the satellite data received by the monitoring center comprises stationary orbitWAAS information broadcast by a satellite (Geo-stationary Orbit; hereinafter referred to as GEO) and navigation information broadcast by a GPS satellite, and receiver information sent by a receiver comprises a satellite elevation value of a visible satellite j corresponding to the receiver i

True distance between receiver i and its visible satellite j

And the number N of visible satellites of each receiver, and the like, and the monitoring center calculates the pseudo-range correction value of each satellite corresponding to each receiver according to the received satellite data.

It should be noted that the distances between the receivers on the ground are quite negligible compared to each other, since the distances between the satellites and the earth are very close and the distances between the satellites and the earth are much greater. Thus, in the embodiment of the present invention, the number of visible satellites of each receiver can be approximately considered to be the same, and since the distances between the receivers are close, the satellite elevation angles of each visible satellite of each receiver can also be approximately consideredAre all equal and are all theta^j。

Specifically, the pseudorange correction of the receiver includes three parts: the pseudorange correction after the Hatch filtering smoothing, the wide area augmentation system pseudorange correction, and the tropospheric pseudorange correction. The pseudorange correction value smoothed by the Hatch filtering is the pseudorange observation value and the carrier phase observation value of the positioning satellite extracted from the received satellite data by the monitoring center, and then the pseudorange observation value is smoothed by the carrier phase observation value by using the Hatch filtering method to obtain the smoothed pseudorange correction value; the pseudorange correction value of the wide area augmentation system is obtained from WAAS broadcast information broadcasted by a GEO satellite, and comprises a quick correction value, a long-term correction value and an ionosphere correction value; the troposphere pseudo-range correction value is a correction value for troposphere errors, specifically, the troposphere pseudo-range correction value is calculated by using a troposphere error model, and the troposphere error model is a sagittonin model.

Step 101, selecting one of the optional receiving products as a pseudo airborne user, calculating pseudo-range correction value positioning errors of the pseudo airborne user, and extracting wide area augmentation system information broadcasting positioning errors of the pseudo airborne user from the pseudo-range correction value positioning errors;

in this embodiment, it is assumed that there are M receivers on the ground, and one receiver is arbitrarily selected from the M receivers and assumed to be a "pseudo airborne user", which is assumed to be an airborne user in a monitoring station on the ground as the name suggests. In the civil aviation system, the distance between the ground receiver and the actual airborne user is almost negligible compared with the distance between the ground receiver and the actual airborne user and the distance between the ground receiver and the satellite are almost negligible, so that the protection level calculation aiming at the actual airborne user can be embodied in the protection level calculation of the 'pseudo airborne user' arbitrarily selected from the receiver. In the calculation process of the ground monitoring protection level of the pseudo airborne user, not only is the error caused by the pseudo-range correction value considered, but also the errors caused by the monitoring center to the ionosphere and the troposphere of the actual airborne user are considered, so that the difference between the ground monitoring protection level and the actual airborne user protection level can be maximally drawn, and the monitoring result is more accurate.

In this step, the error caused by the pseudo-range correction value of the pseudo-airborne user is mainly calculated and estimated. For the error of the pseudo-range correction value of the selected pseudo-airborne user, if the measurement error of the real position is ignored, the error mainly comes from two parts: firstly, the monitoring error of the receiver is mainly caused by thermal noise and multipath on the ground and is called as the monitoring error of the receiver; the other is the error caused by the information broadcast by the WAAS, which is called the wide area enhanced system information broadcast error, namely the WAAS information broadcast error. The monitoring center will therefore first be based on the standard deviation σ of these two part errors_monAnd σ_MWAASCalculating standard deviation sigma of pseudo range correction value error by using variance transfer principle_dPRThen, according to the continuity requirement value preset by the airborne user, the continuity error amplification factor K is calculated and obtained through a statistical algorithm of Gaussian distribution_mtThe continuous error amplification factor fully considers the influence on the system continuity caused by false detection on the system, and finally the pseudo-range correction value error standard deviation sigma is obtained according to calculation_dPRAnd a continuity error amplification factor K_mtAnd calculating to obtain pseudo-range correction value positioning error of the pseudo-airborne user by using the conversion matrix from the pseudo-range domain to the positioning domain. The WAAS information broadcast positioning error of the pseudo-airborne user extracted from the pseudo-range correction value positioning error is part of the ground monitoring protection level of the pseudo-airborne user.

102, calculating to obtain a monitoring system positioning error of the pseudo airborne user according to a conversion matrix from a pseudo-range domain to a positioning domain, and calculating an ideal envelope value of the sum of the monitoring system positioning error and the wide area augmentation system information broadcasting positioning error to obtain a ground monitoring protection level of the pseudo airborne user;

in the embodiment, the core idea of the calculation of the ground monitoring protection level is as follows: the calculation of the protection level of the actual onboard user is converted into the calculation of the protection level of the ground monitoring center, that is, the calculation of the protection level of the pseudo onboard user, so that the influence of various errors on the ground monitoring protection level has to be considered in the calculation of the value of the protection level, and specifically, the following four parts are included: errors caused by WAAS broadcast information, errors caused by airborne receiver thermal noise and fuselage multipath, ionospheric errors caused by lateral components above the ground monitoring center, and tropospheric errors caused by vertical components from ground monitoring stations. In the embodiment of the present invention, since the three errors are all caused by various factors of the monitoring system, such as the factors of the onboard user or the factors of the monitoring center, the positioning errors of the three parts are collectively referred to as the monitoring system positioning errors.

For the calculation of the positioning error value of the monitoring system, firstly, the monitoring center calculates to obtain the pseudo-range domain standard deviation of each part of errors in the monitoring system errors according to the information of the receiver, then converts the pseudo-range domain standard deviation into the positioning domain standard deviation in the vertical direction respectively by using the conversion matrix from the pseudo-range domain to the positioning domain, and calculates to obtain the positioning standard deviation of the monitoring system errors by using the variance transfer principle; then, the monitoring center calculates and obtains an integrity error amplification factor K through a statistical algorithm of Gaussian distribution according to an integrity risk value preset by the system_bndCompared with the integrity risk value preset by the existing system, in the embodiment, the integrity error amplification factor also considers the influence of the WAAS fault on the whole LAM system; finally, the monitoring center obtains the positioning standard deviation of the error of the monitoring system and the integrity error amplification factor K according to calculation_bndAnd calculating by using a conversion matrix from the pseudo-range domain to the positioning domain to obtain a positioning error of a monitoring system of the pseudo-airborne user, wherein the positioning error of the monitoring system is another part of a ground monitoring protection level of the airborne user.

In this embodiment, after the monitoring center obtains the WAAS information broadcast positioning error and the monitoring system positioning error respectively through calculation, the sum of the two obtained through calculation by the end user is the actual total positioning error of the pseudo airborne user, on the basis, the actual total positioning error is further calculated by an ideal envelope value, the ground monitoring protection level of the pseudo airborne user is finally obtained, and the optimal available satellite combination can be judged in the ground monitoring center through detection of the ground monitoring protection level.

And 103, comparing the ground monitoring protection levels of all visible satellite combinations of the pseudo airborne user with a preset alarm limit value of the airborne user, acquiring the optimal available satellite combination according to the comparison result, and sending the optimal available satellite combination and the pseudo-range correction value of each visible satellite in the available satellite combination to the airborne user.

Specifically, the monitoring center divides all visible satellites of the pseudo airborne user into a plurality of satellite subsets by a round robin removal method, firstly, all visible satellites of the pseudo airborne user form a set, which is called as a first-stage satellite subset, judges whether the number of the visible satellites in the first-stage satellite subset is equal to 4, if the number of the visible satellites in the first-stage satellite subset is equal to 4, the subset division is stopped, otherwise, one satellite is removed from the set respectively according to a preset sequence to generate a second-stage satellite subset, the preset sequence referred to herein can be data of the satellites arranged according to an ascending order of elevation angles of the satellites, the removal means that only one satellite is removed each time, but not removed sequentially, namely, the number of all visible satellites is assumed to be N, when the first satellite is removed, N-1 satellites in the satellite combination are remained, when the second satellite is removed, the removed first satellite is added to the satellite combination again, n-1 satellites still remain in the satellite combination, whether the number of visible satellites in the second-level satellite subset is equal to 4 or not is judged at this time, if the number of visible satellites contained in the second-level satellite subset is equal to 4, the subset is also stopped to be divided, and if the number of visible satellites contained in the second-level satellite subset is larger than 4, the satellite subset is continuously divided according to the method to generate a new Nth-level satellite subset until the number of visible satellites in the Nth-level satellite subset is equal to 4. Assuming that the number of the last satellite subsets divided by the round robin removal method is B, B may be represented by the formula: $B=C_N^N+C_N^{N-1}+...+C_N^5+C_N^4$ and calculating, wherein N is the number of all visible satellites of the pseudo airborne user.

After the subsets of the visible satellites are divided, the monitoring center calculates the ground monitoring protection levels of all the satellite subsets of the pseudo airborne user, compares the ground monitoring protection levels of the satellite subsets with an alarm limit value preset by the user in sequence, and sends the subset containing the most visible satellites and the pseudo-range correction value of each visible satellite in the subset to the airborne user if the ground monitoring protection levels of the subsets are smaller than the alarm limit value, wherein the subset containing the most visible satellites is the optimal visible satellite combination.

The embodiment provides a local airport monitoring method, which comprises the steps of detecting errors caused by a pseudo-range correction value and errors caused by a monitoring system on a ground monitoring end for an airborne user, obtaining a concept of a ground monitoring protection level according to the definition, and converting the calculation of the protection level of the airborne user into the calculation of the ground monitoring protection level by a ground monitoring center, so that the selection of the optimal visible satellite combination of the airborne user is completed through the detection of the protection level of the ground detection center.

Fig. 2 is a flowchart of a second embodiment of the local airport monitoring method of the present invention, and as shown in fig. 2, the local airport monitoring method of the present invention includes:

step 200, obtaining the receiver information of each receiver and the satellite data received by the receiver from the navigation satellite, and calculating the pseudo-range corrected value PR of each visible satellite corresponding to each receiver according to the satellite data_i ^j；

Step 200 is the same operation as step 100 in the first embodiment, and receives satellite data transmitted by each receiver to obtain pseudorange corrections for the receiver. Specifically, for the jth satellite in view of the ith receiver, the pseudorange correction value may be expressed by the following expression:

${\mathrm{PR}}_i^j=P_{\mathrm{Si}}^j+{\mathrm{PRC}}_i^j+{\mathrm{TC}}_i^j---\left(1\right)$

wherein, P_Si ^jFor pseudorange corrections after Hatch filter smoothing, PRC_i ^jFor pseudorange corrections, TC, derived from WAAS broadcast information_i ^jTropospheric pseudorange corrections. Specifically, the monitoring center firstly extracts a pseudo-range observation value P and a carrier phase observation value phi of a positioning satellite from received satellite data, and then smoothes the pseudo-range observation value P by using the carrier phase observation value phi by using a method of Hatch filtering to obtain a pseudo-range correction value smoothed by the Hatch filtering, wherein a calculation formula of the Hatch filtering is shown as a formula (2):

<math><mrow> <msubsup> <mi>P</mi> <mi>Si</mi> <mi>j</mi> </msubsup> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfrac> <mn>1</mn> <msub> <mi>N</mi> <mi>S</mi> </msub> </mfrac> <msubsup> <mi>P</mi> <mi>i</mi> <mi>j</mi> </msubsup> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <mrow> <msub> <mi>N</mi> <mi>s</mi> </msub> <mo>-</mo> <mn>1</mn> </mrow> <msub> <mi>N</mi> <mi>s</mi> </msub> </mfrac> <mrow> <mo>(</mo> <msubsup> <mi>P</mi> <mi>Si</mi> <mi>j</mi> </msubsup> <mrow> <mo>(</mo> <mi>l</mi> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>+</mo> <mi>&phi;</mi> <mrow> <mo>(</mo> <mi>l</mi> <mo>)</mo> </mrow> <mo>-</mo> <mi>&phi;</mi> <mrow> <mo>(</mo> <mi>l</mi> <mo>-</mo> <mn>1</mn> <mo>)</mo> </mrow> <mo>)</mo> </mrow> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow></math>

wherein l represents an epoch, τ_sAs filter time constant, T_SFor measuring the interval, N_sFor the filter length: <math><mrow> <msub> <mi>N</mi> <mi>s</mi> </msub> <mo>=</mo> <mfrac> <msub> <mi>&tau;</mi> <mi>s</mi> </msub> <msub> <mi>T</mi> <mi>s</mi> </msub> </mfrac> <mo>,</mo> </mrow></math> p (l) is the pseudorange measurement for the l epoch, phi (l) is the carrier phase measurement for the l epoch, P_SAnd (l-1) is a pseudo range correction value of the l-1 th epoch after the smoothing of the Hatch filtering.

The pseudo-range observation value P achieves the purpose of removing noise after being subjected to Hatch filtering smoothing, and at the moment, the pseudo-range value obtained from the WAAS broadcast information is corrected to obtain the WAAS pseudo-range correction value PRC_i ^jThe WAAS pseudorange correction also includes three components: WAAS quick correction value FC_i ^jWAAS long-term correction LTC_i ^jAnd WAAS ionospheric correction IC_i ^jThe value of each part can be calculated according to the specific information given in the WAAS message type. PRC_i ^jThe calculation expression of (a) is as follows:

${\mathrm{PRC}}_i^j={\mathrm{FC}}_i^j+{\mathrm{LTC}}_i^j+{\mathrm{IC}}_i^j---\left(3\right)$

finally, tropospheric pseudo-range correction TC is calculated_i ^jIn this embodiment, in the process of correcting the pseudorange for the satellite data, the monitoring center processes the code pseudorange by using the hash filter in addition to the information broadcast by the WAAS, and corrects the troposphere error by using the troposphere error model, specifically, corrects the pseudorange information by using the sas temonine model, and performs TC_i ^jThe calculation formula of (2) is as follows:

<math><mrow> <msubsup> <mi>TC</mi> <mi>i</mi> <mi>j</mi> </msubsup> <mo>=</mo> <msub> <mi>N</mi> <mi>r</mi> </msub> <msub> <mi>h</mi> <mn>0</mn> </msub> <mfrac> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>6</mn> </mrow> </msup> <msqrt> <mn>0.002</mn> <mo>+</mo> <mi>sin</mi> <mrow> <mo>(</mo> <msubsup> <mi>&theta;</mi> <mi>i</mi> <mi>j</mi> </msubsup> <mo>)</mo> </mrow> </msqrt> </mfrac> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <msup> <mi>e</mi> <mrow> <mo>-</mo> <mi>&Delta;h</mi> <mo>/</mo> <msub> <mi>h</mi> <mn>0</mn> </msub> </mrow> </msup> <mo>)</mo> </mrow> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>4</mn> <mo>)</mo> </mrow> </mrow></math>

wherein N is_rIs the tropospheric refractive index, h₀For the purpose of the current layer height, it can be extracted from navigation information included in the satellite data, θ_i ^jFor satellite elevation, the data contained in the receiver information sent by the receiver, Δ h is the height of the aircraft (i.e. the onboard user) from the ground monitoring center, which can be obtained from actual measurements.

Step 201, correcting the pseudo range correction value PR_i ^jThe receiver-to-satellite range error is corrected to obtain new pseudorange corrections dPR_i ^j；

Since the position of each receiver is known, the true distance R between each receiver and the satellite_i ⁱCan be obtained by calculation in the receiver, the receiver sends the real distance R to the monitoring center_i ⁱAnd the pseudo-range correction value PR of the receiver calculated in step 200_i ^jThe receiver pseudorange correction may be further corrected for receiver-to-satellite range error to obtain a new pseudorange correction dPR_i ^j，dPR_i ^jThe calculation formula of (2) is as follows:

${\mathrm{dPR}}_i^j={\mathrm{PR}}_i^j-R_i^j---\left(4\right)$

step 202, selecting one of the receivers as a pseudo airborne user, and calculating a pseudo-range correction value positioning error of the pseudo airborne user, wherein the specific calculation process comprises the following steps:

step 2021, selecting one of the receivers as a pseudo airborne user, calculating pseudo-range correction value error standard deviation σ of the pseudo-airborne user_dPR；

In this embodiment, the pseudo-range correction error of the pseudo-airborne user mainly comes from two parts: the monitoring error of the receiver and the error caused by the information broadcast by the WAAS are respectively called the monitoring error of the receiver and the broadcast error of the WAAS information, and the errors of the two parts are assumed to follow a gaussian distribution with a mean value of 0, so the standard deviation of the errors of the two parts needs to be calculated first.

Standard deviation of monitor error sigma for receiver_monIt can be calculated by the following formula:

<math><mrow> <msub> <mi>&sigma;</mi> <mi>mon</mi> </msub> <mrow> <mo>(</mo> <msup> <mi>&theta;</mi> <mi>j</mi> </msup> <mo>)</mo> </mrow> <mo>=</mo> <msqrt> <mfrac> <msup> <mrow> <mo>(</mo> <msub> <mi>a</mi> <mn>0</mn> </msub> <mo>+</mo> <msub> <mi>a</mi> <mn>1</mn> </msub> <msup> <mi>e</mi> <mrow> <mo>-</mo> <msup> <mi>&theta;</mi> <mi>j</mi> </msup> <mo>/</mo> <msub> <mi>&theta;</mi> <mn>0</mn> </msub> </mrow> </msup> <mo>)</mo> </mrow> <mn>2</mn> </msup> <mi>M</mi> </mfrac> </msqrt> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>5</mn> <mo>)</mo> </mrow> </mrow></math>

wherein, a₀、a₁、θ₀The performance level of the receiver is determined by reference to the standard RTCA DO-245A, theta of the aviation radio technical Committee^jM is the number of receivers for the satellite elevation value.

The standard deviation of the error of the WAAS broadcast information can be calculated by the following calculation formula:

<math><mrow> <msub> <mi>&sigma;</mi> <mi>MWAAS</mi> </msub> <mrow> <mo>(</mo> <msubsup> <mi>&theta;</mi> <mi>i</mi> <mi>j</mi> </msubsup> <mo>)</mo> </mrow> <mo>=</mo> <mn>0.26</mn> <mo>&CenterDot;</mo> <mi>OF</mi> <mrow> <mo>(</mo> <msubsup> <mi>&theta;</mi> <mi>i</mi> <mi>j</mi> </msubsup> <mo>)</mo> </mrow> <mo>=</mo> <mn>0.26</mn> <mo>&CenterDot;</mo> <msup> <mrow> <mo>[</mo> <mn>1</mn> <mo>-</mo> <msup> <mrow> <mo>(</mo> <mfrac> <mrow> <msub> <mi>R</mi> <mi>e</mi> </msub> <mi>cos</mi> <msubsup> <mi>&theta;</mi> <mi>i</mi> <mi>j</mi> </msubsup> </mrow> <mrow> <msub> <mi>R</mi> <mi>e</mi> </msub> <mo>+</mo> <msub> <mi>h</mi> <mi>I</mi> </msub> </mrow> </mfrac> <mo>)</mo> </mrow> <mn>2</mn> </msup> <mo>]</mo> </mrow> <mrow> <mo>-</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> </mrow> </msup> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>6</mn> <mo>)</mo> </mrow> </mrow></math>

wherein OF is the ionospheric tilt factor, R_eIs the radius of the earth, h_IIs the ionosphere height.

While the pseudorange correction error standard deviation sigma_dPRThen it can be derived from the variance transfer principle:

<math><mrow> <msub> <mi>&sigma;</mi> <mi>dPR</mi> </msub> <mrow> <mo>(</mo> <msubsup> <mi>&theta;</mi> <mi>i</mi> <mi>j</mi> </msubsup> <mo>)</mo> </mrow> <mo>=</mo> <msqrt> <msubsup> <mi>&sigma;</mi> <mi>mon</mi> <mn>2</mn> </msubsup> <mrow> <mo>(</mo> <msubsup> <mi>&theta;</mi> <mi>i</mi> <mi>j</mi> </msubsup> <mo>)</mo> </mrow> <mo>+</mo> <msubsup> <mi>&sigma;</mi> <mi>MWAAS</mi> <mn>2</mn> </msubsup> <mrow> <mo>(</mo> <msubsup> <mi>&theta;</mi> <mi>i</mi> <mi>j</mi> </msubsup> <mo>)</mo> </mrow> </msqrt> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>7</mn> <mo>)</mo> </mrow> </mrow></math>

step 2022, calculating continuity error amplification factor K according to continuity requirement value preset by airborne user_mt；

In order to ensure the continuity of the system, a continuity error amplification factor in the pseudo-range correction value error is related to the continuity of the system. And the loss of continuity due to the resulting system generally includes two aspects: or because of a real system failure, such as a satellite failure or a ground station failure; or because of false detection of the fault, under simple processing, the two reasons can be allocated according to half of the continuity requirement preset by the user, and the continuity requirement preset by the user is assumed to be P_r(continuity):

P_{false detection}Pr (continuous)/2 (8)

For M receivers, the single receiver fault protection stage corresponding to any receiver fault may cause continuity loss, and therefore, under conservative consideration, all the single receiver fault protection stages are independent, and therefore, the probability of no fault false detection can be determined by dividing the total continuity requirement by M, that is, the probability of no fault false detection is determined by dividing the total continuity requirement by M, that is, the M receivers are all independent receivers

P_FD/M＝P_{False detection}/M (9)

The probability is for one receiver, and assuming that the number of visible satellites of the receiver is N, the false detection probability for the measured value corresponding to each satellite is:

P_FFD＝P_FFD/M/N (10)

the resulting continuity error amplification factor is therefore:

K_mt＝Q^-1(P_FFD/2) (11)

wherein, <math><mrow> <mi>Q</mi> <mrow> <mo>(</mo> <mi>x</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfrac> <mn>1</mn> <msqrt> <mn>2</mn> <mi>&pi;</mi> </msqrt> </mfrac> <msubsup> <mo>&Integral;</mo> <mi>x</mi> <mo>&infin;</mo> </msubsup> <msup> <mi>e</mi> <mrow> <mo>-</mo> <mfrac> <msup> <mi>t</mi> <mn>2</mn> </msup> <mn>2</mn> </mfrac> </mrow> </msup> <mi>dt</mi> <mo>.</mo> </mrow></math>

step 2023, calculating to obtain the pseudo-range correction value positioning error E according to the pseudo-range correction value error standard deviation and the continuity error amplification factor_k；

In order to achieve higher monitoring efficiency, the monitoring center usually converts the pseudorange errors into positioning errors by using a conversion matrix S from a pseudorange domain to a positioning domain of a positioning satellite, where the specific calculation method of the conversion matrix S is as follows:

S＝(H^TW^-1H)^-1H^TW^-1 (12)

wherein, H represents the geometric matrix of the positioning satellite, which is determined by the satellite position and the receiver position, W is a weight value, which is a diagonal matrix composed of the receiver standard deviation of the positioning satellite, and the detailed calculation formula about these two parameters can refer to the standard RTCA DO-245 of the aviation radio technical committee.

Furthermore, the transformation matrix S is divided into four rows (each representing x, y, z, t) N_kColumn, N_kNumber of visible satellites corresponding to a pseudo airborne user, S_j，vertRepresenting the z-th row of the matrix. Since the vertical direction is much more demanding than the horizontal direction in civil aviation applications, the error is converted from the pseudorange domain to the fixIn the bit domain, in this embodiment, only the vertical direction is considered, and the threshold of the pseudorange correction positioning error may be calculated according to the following formula:

<math><mrow> <msub> <mi>TE</mi> <mrow> <mi>vert</mi> <mo>,</mo> <mi>k</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>K</mi> <mi>mt</mi> </msub> <msqrt> <munderover> <mi>&Sigma;</mi> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <msub> <mi>N</mi> <mi>k</mi> </msub> </munderover> <msubsup> <mi>S</mi> <mrow> <mi>j</mi> <mo>,</mo> <mi>vert</mi> </mrow> <mn>2</mn> </msubsup> <msubsup> <mi>&sigma;</mi> <mi>dPR</mi> <mn>2</mn> </msubsup> <mrow> <mo>(</mo> <msup> <mi>&theta;</mi> <mi>j</mi> </msup> <mo>)</mo> </mrow> </msqrt> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>13</mn> <mo>)</mo> </mrow> </mrow></math>

through the steps, the monitoring center detects and calculates the error caused by the pseudo-range correction value at the receiver end of the pseudo-airborne user, and obtains the threshold value of the pseudo-range correction value positioning error of the pseudo-airborne user, namely the maximum value of the error.

Step 2024, extracting the wide area augmentation system information broadcasting positioning error E of the pseudo airborne user from the pseudo-range corrected value positioning error_WAAS，k；

Since the pseudorange correction is a positioning error monitored by the receiver_mon，kAnd positioning error E of information broadcast of WAAS_WAAS，kTwo-part, in correcting values from pseudorangesPositioning error E_kExtracting wide area enhanced system information broadcasting error E of pseudo airborne user_WAAS，kFrom pseudorange corrections, errors E need to be located_kSubtracting receiver monitor positioning error E_mon，k。

Step 203, calculating the positioning error of the monitoring system of the pseudo airborne user, wherein the specific calculation process comprises the following steps:

step 2031, calculating the standard deviation of each monitoring system error of the pseudo airborne user;

for an actual on-board user, the total error that usually needs to be considered mainly includes four parts: errors caused by WAAS broadcast information, errors caused by airborne receiver thermal noise and fuselage multipath, ionospheric errors caused by lateral components from ground monitoring centers, and tropospheric errors caused by vertical components from ground monitoring centers. Therefore, in the present embodiment, the calculation of the ground monitoring positioning error of the pseudo airborne user is mainly considered from the positioning errors caused by these four aspects. In this embodiment, because the above-mentioned specificity of civil aviation application is that the requirement in the vertical direction is much more severe than the requirement in the horizontal direction, only the case in the vertical direction is considered here, and the total error expression of the pseudo airborne user obtained by this is:

E_{total，vert，k}＝E_{MWAAS，vert，k}+E_{air，vert，k}+E_{iono，vert，k}+E_{trop，vert，k} (14)

wherein, it is assumed that:

E_{other，vert，k}＝E_{air，vert，k}+E_{iono，vert，k}+E_{trop，vert，k} (15)

and errors E caused by information broadcast by WAAS_{MWAAS，vert，k}Can be calculated by step 204, thus yielding:

E_{total，vert，k}＝E_vert，k-E_{mon，vert，k}+E_{other，vert，k} (16)

to this end, the calculation of the total error of the pseudo-airborne user becomes a calculation of the three parts mentioned above, wherein the first part is a pseudo-range corrected value positioning error E_vert，kHas been calculated in step 203 and the monitoring of the second partial receiver is determined as error E_{mon，vert，k}Obedience mean 0, standard deviation σ_monAnd the standard deviation sigma_monHas been calculated in equation (5), therefore, in this step, E should be dealt with first_{other，vert，k}The standard deviation of the included three-part error in (a) is calculated.

In particular, the standard deviation σ of the thermal noise and the fuselage multipath error for the thermal noise of the airborne user itself and the fuselage multipath induced error_{air，vert，j}Ionospheric error standard deviation σ of ionospheric error caused by lateral component of ground monitoring station_{iono，vert，j}The detailed calculation formula can refer to the standard RTCA DO-245 of the aviation radio technical Committee, which is as follows:

<math><mrow> <msub> <mi>&sigma;</mi> <mrow> <mi>air</mi> <mo>,</mo> <mi>vert</mi> <mo>,</mo> <mi>j</mi> </mrow> </msub> <mo>=</mo> <msqrt> <msubsup> <mi>&sigma;</mi> <mrow> <mi>air</mi> <mo>_</mo> <mi>noise</mi> </mrow> <mn>2</mn> </msubsup> <mo>+</mo> <msubsup> <mi>&sigma;</mi> <mrow> <mi>air</mi> <mo>_</mo> <mi>multipath</mi> </mrow> <mn>2</mn> </msubsup> </msqrt> <mo>=</mo> <msqrt> <msup> <mrow> <mo>(</mo> <mn>0.11</mn> <mo>+</mo> <mn>0.13</mn> <mo>&times;</mo> <msup> <mi>e</mi> <mfrac> <msup> <mi>&theta;</mi> <mi>j</mi> </msup> <mn>4</mn> </mfrac> </msup> <mo>)</mo> </mrow> <mn>2</mn> </msup> <mo>+</mo> <msup> <mrow> <mo>(</mo> <mn>0.13</mn> <mo>+</mo> <mn>0.53</mn> <mo>&times;</mo> <msup> <mi>e</mi> <mrow> <mo>-</mo> <mfrac> <msup> <mi>&theta;</mi> <mi>j</mi> </msup> <mn>10</mn> </mfrac> </mrow> </msup> <mo>)</mo> </mrow> <mn>2</mn> </msup> </msqrt> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>17</mn> <mo>)</mo> </mrow> </mrow></math>

σ_{iono，vert，j}＝0.106×OF(θ^j) (18)

wherein OF is the ionospheric tilt factor, θ^jIs the satellite elevation value.

And tropospheric error standard deviation sigma due to vertical component to ground monitoring station_{tropo，vert，j}In terms of the relative σ_{air，vert，j}And σ_{iono，vert，j}In terms of σ_{tropo，vert，j}Is small, so approximately:

σ_{tropo，vert，j}＝0 (19)

step 2032, calculating an integrity error amplification factor K according to the preset integrity risk value of the system_bnd；

When the monitoring system positioning error of a pseudo-airborne user is calculated, the error is approximately considered to be an ideal value, namely, the error E caused by the information broadcast by the WAAS is considered_{MWAAS，vert，k}Thermal noise of airborne receiver and errors caused by fuselage multipath_{air，vert，k}Ionospheric error E due to lateral component from ground monitoring station_{iono，vert，k}And tropospheric error E due to vertical component from ground monitoring station_{trop，vert，k}Are calculated under the assumption of Gaussian distribution, therefore, in the calculation process of the positioning error of the monitoring system, the integrity risk value assigned to the vertical protection level by the LAM system must be considered, and the risk value is specifically determined by the integrity error factor K_bndIs reflected in, in particular, K_bndThe calculation formula of (2) is as follows:

K_bnd＝Q^-1(P_{integrity of}) (20)

Wherein, <math><mrow> <mi>Q</mi> <mrow> <mo>(</mo> <mi>x</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfrac> <mn>1</mn> <msqrt> <mn>2</mn> <mi>&pi;</mi> </msqrt> </mfrac> <msubsup> <mo>&Integral;</mo> <mi>x</mi> <mo>&infin;</mo> </msubsup> <msup> <mi>e</mi> <mrow> <mo>-</mo> <mfrac> <msup> <mi>t</mi> <mn>2</mn> </msup> <mn>2</mn> </mfrac> </mrow> </msup> <mi>dt</mi> <mo>,</mo> </mrow></math> P_{integrity of}Indicating the integrity risk value assigned to the vertical protection level by the multi-receiver LAM system, specifically 8.5e-8, and P in the existing algorithm_{Integrity of}This value of this embodiment further considers the impact of WAAS failure on the LAM system compared to 2.5 e-8.

Step 2033, calculating the positioning error of the monitoring system according to the integrity error amplification factor and the standard deviation of the error of each monitoring system;

in this embodiment, in order to obtain higher monitoring efficiency, the standard deviation of the monitoring system error can be obtained by converting the standard deviation of the pseudorange domain by a conversion matrix S from the pseudorange domain to the positioning domain:

<math><mrow> <msub> <mi>&sigma;</mi> <mrow> <mi>air</mi> <mo>,</mo> <mi>vert</mi> <mo>,</mo> <mi>k</mi> </mrow> </msub> <mo>=</mo> <msqrt> <munderover> <mi>&Sigma;</mi> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <msub> <mi>N</mi> <mi>k</mi> </msub> </munderover> <msubsup> <mi>S</mi> <mrow> <mi>j</mi> <mo>,</mo> <mi>vert</mi> </mrow> <mn>2</mn> </msubsup> <msubsup> <mi>&sigma;</mi> <mrow> <mi>air</mi> <mo>,</mo> <mi>vert</mi> <mo>,</mo> <mi>j</mi> </mrow> <mn>2</mn> </msubsup> </msqrt> </mrow></math>

<math><mrow> <msub> <mi>&sigma;</mi> <mrow> <mi>iono</mi> <mo>,</mo> <mi>vert</mi> <mo>,</mo> <mi>k</mi> </mrow> </msub> <mo>=</mo> <msqrt> <munderover> <mi>&Sigma;</mi> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <msub> <mi>N</mi> <mi>k</mi> </msub> </munderover> <msubsup> <mi>S</mi> <mrow> <mi>j</mi> <mo>,</mo> <mi>vert</mi> </mrow> <mn>2</mn> </msubsup> <msubsup> <mi>&sigma;</mi> <mrow> <mi>iono</mi> <mo>,</mo> <mi>vert</mi> <mo>,</mo> <mi>j</mi> </mrow> <mn>2</mn> </msubsup> </msqrt> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>21</mn> <mo>)</mo> </mrow> </mrow></math>

<math><mrow> <msub> <mi>&sigma;</mi> <mrow> <mi>tropo</mi> <mo>,</mo> <mi>vert</mi> <mo>,</mo> <mi>k</mi> </mrow> </msub> <mo>=</mo> <msqrt> <munderover> <mi>&Sigma;</mi> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <msub> <mi>N</mi> <mi>k</mi> </msub> </munderover> <msubsup> <mi>S</mi> <mrow> <mi>j</mi> <mo>,</mo> <mi>vert</mi> </mrow> <mn>2</mn> </msubsup> <msubsup> <mi>&sigma;</mi> <mrow> <mi>tropo</mi> <mo>,</mo> <mi>vert</mi> <mo>,</mo> <mi>j</mi> </mrow> <mn>2</mn> </msubsup> </msqrt> </mrow></math>

definition of σ_{other，vert，k}The sum of the above three standard deviations can be obtained by the variance transfer principle:

<math><mrow> <msub> <mi>&sigma;</mi> <mrow> <mi>other</mi> <mo>,</mo> <mi>vert</mi> <mo>,</mo> <mi>k</mi> </mrow> </msub> <mo>=</mo> <msqrt> <msubsup> <mi>&sigma;</mi> <mrow> <mi>air</mi> <mo>,</mo> <mi>vert</mi> <mo>,</mo> <mi>k</mi> </mrow> <mn>2</mn> </msubsup> <mo>+</mo> <msubsup> <mi>&sigma;</mi> <mrow> <mi>iono</mi> <mo>,</mo> <mi>vert</mi> <mo>,</mo> <mi>k</mi> </mrow> <mn>2</mn> </msubsup> <mo>+</mo> <msubsup> <mi>&sigma;</mi> <mrow> <mi>tropo</mi> <mo>,</mo> <mi>vert</mi> <mo>,</mo> <mi>k</mi> </mrow> <mn>2</mn> </msubsup> </msqrt> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>22</mn> <mo>)</mo> </mrow> </mrow></math>

in addition, the method also comprises the step that a receiver monitors the positioning error E in the calculation of the total positioning error of the pseudo airborne user_{mon，vert，k}And the receiver monitors the positioning error E_{mon，vert，k}And monitoring system positioning error E_{other，vert，k}The same obeys a gaussian distribution with a mean value of 0, so ideally, both can be used for the calculation of the envelope value, and in particular, the above equation (16) can be converted into:

VPL_ideal，k＝|E_vert，k|+K_bndσ_{mon+other，vert，k} (23)

wherein the pseudorange correction is used to locate the error E_vert，kThe absolute value is also taken to obtain the maximum value in an ideal case, and σ is derived from the variance transfer principle_{mon+other，vert，k}Can be calculated by the following formula:

<math><mrow> <msub> <mi>&sigma;</mi> <mrow> <mi>mon</mi> <mo>+</mo> <mi>other</mi> <mo>,</mo> <mi>vert</mi> <mo>,</mo> <mi>k</mi> </mrow> </msub> <mo>=</mo> <msqrt> <msubsup> <mi>&sigma;</mi> <mrow> <mi>mon</mi> <mo>,</mo> <mi>vert</mi> <mo>,</mo> <mi>k</mi> </mrow> <mn>2</mn> </msubsup> <mo>+</mo> <msubsup> <mi>&sigma;</mi> <mrow> <mi>other</mi> <mo>,</mo> <mi>vert</mi> <mo>,</mo> <mi>k</mi> </mrow> <mn>2</mn> </msubsup> </msqrt> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>24</mn> <mo>)</mo> </mrow> </mrow></math>

step 2034, calculating to obtain the ground monitoring protection level VPL of the pseudo airborne user_mon，k；

Positioning error E due to correction of pseudo-range in equation (23)_vert，kTaking an absolute value, namely a threshold value TE of pseudo-range corrected value positioning error of the pseudo-airborne user obtained by formula (13)_vert，kFinally, the ground monitoring protection level of the pseudo airborne user is obtained as follows:

<math><mrow> <msub> <mi>VPL</mi> <mrow> <mi>mon</mi> <mo>,</mo> <mi>k</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>K</mi> <mi>mt</mi> </msub> <msqrt> <munderover> <mi>&Sigma;</mi> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <msub> <mi>N</mi> <mi>k</mi> </msub> </munderover> <msubsup> <mi>S</mi> <mrow> <mi>j</mi> <mo>,</mo> <mi>vert</mi> </mrow> <mn>2</mn> </msubsup> <msubsup> <mi>&sigma;</mi> <mi>dPR</mi> <mn>2</mn> </msubsup> <mrow> <mo>(</mo> <msup> <mi>&theta;</mi> <mi>j</mi> </msup> <mo>)</mo> </mrow> </msqrt> <mo>+</mo> <msub> <mi>K</mi> <mi>bnd</mi> </msub> <msub> <mi>&sigma;</mi> <mrow> <mi>mon</mi> <mo>+</mo> <mi>other</mi> <mo>,</mo> <mi>vert</mi> <mo>,</mo> <mi>k</mi> </mrow> </msub> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>25</mn> <mo>)</mo> </mrow> </mrow></math>

step 204, comparing the ground monitoring protection levels of all visible satellite combinations of the pseudo airborne user with an alarm limit value preset by the airborne user in sequence, if the ground monitoring protection levels of the visible satellite combinations are smaller than the alarm limit value, executing step 205, and if the ground monitoring protection levels of all the visible satellite combinations are larger than the alarm limit value, executing step 206;

specifically, in this step, the visible satellite subsets are first divided for all visible satellites of the pseudo airborne user by a round-robin removal method, and then the ground monitoring protection level of each subset is calculated for each visible satellite subset, and the specific process of dividing the visible satellite subsets is described in detail in the first embodiment, and is not described herein again. For each subset of visible satellites of the pseudo airborne user, the value of the ground monitoring protection level may be greater than or less than the warning limit preset by the airborne user, and when the value is less than the warning limit preset by the user, the visible satellite combination representing the subset is available to the airborne user, and when the value of the ground monitoring protection level is greater than the warning limit preset by the airborne user, the visible satellite combination representing the subset is not available to the airborne user, and the subset should be discarded.

Step 205, sending the visible satellite combination containing the largest number of satellites and the pseudo-range correction value of each visible satellite in the visible satellite combination to an airborne user;

if the value of the ground monitoring protection level of the pseudo airborne user is greater than the warning limit value of the airborne user, the visible satellite combination representing the subset is available for the airborne user, and the visible satellite combination is sent to the airborne user, but generally, the monitoring protection level of the combination with the larger number of satellites is smaller, the error of the user representing the airborne user is smaller for the airborne user, and therefore, the airborne user should select the visible satellite combination with the largest number of satellites. In the embodiment, the monitoring center selects the visible satellite combination, and directly sends the visible satellite combination containing the largest number of satellites and the pseudo-range correction value of each visible satellite in the visible satellite combination to the airborne user according to the comparison result of the ground monitoring protection level and the alarm limit value, so that the calculation burden of the airborne user is reduced.

And step 206, sending alarm information to the onboard user, wherein the alarm information indicates that the satellite navigation system is unavailable to the onboard user.

If the ground monitoring protection level calculated by all visible satellite combinations of the pseudo airborne user is larger than the alarm limit value, the situation that all the satellite combinations of the airborne user are unavailable is represented, the monitoring center sends alarm information to the airborne user, and the alarm information indicates that the current satellite navigation system of the airborne user is in an unavailable state.

The embodiment provides a local airport monitoring method, on the basis of a plurality of receivers, by detecting errors caused by a pseudo-range correction value and errors caused by a monitoring system on a ground monitoring end, defining the concept of obtaining a ground monitoring protection level according to the errors, converting the self protection level calculation of an airborne user into the calculation of the ground monitoring protection level by a ground monitoring center, thereby completing the selection of the optimal visible satellite combination of the airborne user by detecting the protection level of a ground detection station, compared with the method for selecting the satellite subset by the airborne user in the existing system, the method ensures the accuracy of the system, improves the robustness of the system, reduces the calculation burden of the airborne user, improves the real-time performance, further fully considers the influence of troposphere errors on the ground monitoring protection level in the calculation process of the ground monitoring protection level in the embodiment, and continuity loss caused by faults of integrity monitoring and influence of WAAS faults on the LAM system, so that the calculation of the protection level is more accurate.

Those of ordinary skill in the art will understand that: all or part of the steps for implementing the method embodiments may be implemented by hardware related to program instructions, and the program may be stored in a computer readable storage medium, and when executed, the program performs the steps including the method embodiments; and the aforementioned storage medium includes: various media that can store program codes, such as ROM, RAM, magnetic or optical disks.

Fig. 3 is a schematic structural diagram of an embodiment of the local airport monitoring device of the present invention, and as shown in fig. 3, the local airport monitoring device of the present invention includes:

the first calculation module 11 is configured to obtain receiver information of each receiver and satellite data received by the receiver from a navigation satellite, and correct pseudo-range information in the satellite data by using enhancement information broadcast by a wide area enhancement system, a carrier phase observation value, and a troposphere error model to obtain a pseudo-range correction value of each satellite corresponding to each receiver, where the receiver information includes a satellite elevation value of a visible satellite corresponding to the receiver, a true distance between the receiver and the visible satellite thereof, and a number of visible satellites of each receiver;

a second calculation module 12, connected to the first calculation module 11, configured to select one receiver as a pseudo airborne user, calculate, according to the receiver information of the pseudo airborne user and a continuity requirement value preset by the airborne user, a pseudo-range correction value positioning error of the pseudo airborne user by using a conversion matrix from a pseudo-range domain to a positioning domain, and extract, from the pseudo-range correction value positioning error, wide-area augmentation system information of the pseudo airborne user to broadcast the positioning error;

a third calculating module 13, connected to the second calculating module 12, configured to calculate, according to the receiver information of the pseudo airborne user and a preset integrity risk value of the system, a monitoring system positioning error of the pseudo airborne user by using a conversion matrix from the pseudo-range domain to the positioning domain, and calculate an ideal envelope value of a sum of the monitoring system positioning error and a wide-area enhancement system information broadcast error to obtain a ground monitoring protection level of the pseudo airborne user, where the monitoring system positioning error includes a positioning error caused by thermal noise of the airborne user and fuselage multipath, a positioning error caused by an ionosphere above a monitoring center, and a positioning error caused by a troposphere above the monitoring center;

and the decision module 14 is connected to the third calculation module 13, and configured to sequentially compare the ground monitoring protection levels of all visible satellite combinations of the pseudo airborne user with an alarm limit preset by an airborne user, and send a pseudo-range correction value of each visible satellite in the visible satellite combination and a visible satellite combination including the largest number of satellites to the airborne user if the ground monitoring protection level of the visible satellite combination is smaller than the alarm limit.

Specifically, the local airport monitoring device is disposed at a monitoring center of the local airport monitoring system, and the specific monitoring process of the local airport monitoring device is described in detail in the above embodiment of the local airport monitoring method, which is not described herein again.

The embodiment of the invention provides a local airport monitoring device, which detects errors caused by a pseudo-range correction value and errors caused by a monitoring system at a ground monitoring end, obtains a concept of ground monitoring protection level according to the definition, and converts the self protection level calculation of an airborne user into the calculation of the ground monitoring protection level by a ground monitoring center, thereby completing the selection of the optimal visible satellite combination of the airborne user by detecting the protection level of a ground detection station.

Fig. 4 is a schematic structural diagram of an embodiment of the local airport monitoring system of the present invention, and as shown in fig. 4, the local airport monitoring system of the present invention includes:

the system comprises a plurality of receivers 1, a monitoring center and a navigation satellite, wherein the receivers 1 are used for receiving satellite data sent by the navigation satellite, carrying out analog-to-digital conversion on the satellite data and sending the satellite data subjected to the digital-to-analog conversion and receiver information of the receivers to the monitoring center, and the receiver information comprises satellite elevation values of visible satellites corresponding to the receivers, real distances between the receivers and the visible satellites and the number of the visible satellites of each receiver;

the monitoring center 2 is connected with the receiver 1 and used for calculating a pseudo-range correction value of each satellite corresponding to the receiver according to received satellite data, detecting an error caused by the pseudo-range correction value of an airborne user and an error caused by a monitoring system according to the information of the receiver, calculating a ground monitoring protection level of the monitoring center, obtaining an available satellite combination according to a comparison result of the ground monitoring protection level and an alarm limit value preset by the user, and sending the available satellite combination and the pseudo-range correction value of each visible satellite in the satellite combination to the airborne user;

specifically, the monitoring center may be provided with the local airport monitoring device in the above embodiments, and all the specific calculation processes and monitoring operations of the monitoring center on the satellite data may be implemented by the local airport monitoring device, and the specific components and functions of the local airport monitoring device are described in detail in the above embodiments and will not be further described herein.

And the airborne user 3 is connected with the monitoring center 2 and used for calculating the position of the airborne user according to the visible satellite combination and the pseudo range correction value of the visible satellite combination sent by the monitoring center.

Specifically, during the approach process, the visible satellites of the airborne user and the ground monitoring station are approximately considered to be the same, and the number of the visible satellites of the airborne user is possibly more than that of the ground monitoring station due to the higher position of the airborne user, and redundant satellites are 'discarded'. And the airborne user performs protection level calculation by utilizing the subset of the optimal satellite combination transmitted by the ground monitoring station and the pseudo-range correction value of each satellite, and obtains the position of the airborne user according to the calculation result. For the calculation of the protection level of the airborne user, the protection level can be calculated according to the pseudo-range correction value of the visible satellite provided by the monitoring center, and the pseudo-range correction value is represented by a Gaussian distribution with zero mean value, so that the obtained vertical positioning error protection level is calculated by the following formula:

<math><mrow> <msub> <mi>VPL</mi> <mrow> <mi>H</mi> <mn>0</mn> <mo>,</mo> <mi>k</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>K</mi> <mi>ffmd</mi> </msub> <msqrt> <munderover> <mi>&Sigma;</mi> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <msub> <mi>N</mi> <mi>k</mi> </msub> </munderover> <msubsup> <mi>S</mi> <mrow> <mi>j</mi> <mo>,</mo> <mi>vert</mi> </mrow> <mn>2</mn> </msubsup> <msubsup> <mi>&sigma;</mi> <mi>dPR</mi> <mn>2</mn> </msubsup> <mrow> <mo>(</mo> <msup> <mi>&theta;</mi> <mi>j</mi> </msup> <mo>)</mo> </mrow> <mo>+</mo> <msubsup> <mi>&sigma;</mi> <mrow> <mi>other</mi> <mo>,</mo> <mi>vert</mi> <mo>,</mo> <mi>k</mi> </mrow> <mn>2</mn> </msubsup> </msqrt> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>26</mn> <mo>)</mo> </mrow> </mrow></math>

wherein, K_ffmdFor a no fault miss factor, a fixed value 5.847 is taken.

The embodiment of the invention provides a local airport monitoring system, which detects errors caused by a pseudo-range correction value and errors caused by a monitoring system by a ground monitoring center, obtains a concept of ground monitoring protection level according to the definition, and converts the self protection level calculation of an airborne user into the calculation of the ground monitoring protection level by the ground monitoring center, thereby completing the selection of the optimal visible satellite combination of the airborne user by detecting the protection level of a ground detection station.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (9)

1. A local airport monitoring method, comprising:

acquiring receiver information of each receiver and satellite data received by the receiver from a navigation satellite, and correcting pseudo-range information in the satellite data by using enhancement information, a carrier phase observation value and a troposphere error model broadcasted by a wide-area enhancement system to obtain a pseudo-range correction value of each satellite corresponding to each receiver, wherein the receiver information comprises a satellite elevation value of a visible satellite corresponding to the receiver, a real distance between the receiver and the visible satellite thereof and the number of visible satellites of each receiver;

optionally selecting one receiver as a pseudo-airborne user, calculating a pseudo-range correction value positioning error of the pseudo-airborne user by using a conversion matrix from a pseudo-range domain to a positioning domain according to the receiver information of the pseudo-airborne user and a continuity requirement value preset by the airborne user, and extracting wide area enhancement system information of the pseudo-airborne user from the pseudo-range correction value positioning error to broadcast the positioning error;

according to the receiver information of the pseudo airborne user and a preset integrity risk value of a system, calculating to obtain a monitoring system positioning error of the pseudo airborne user by using a conversion matrix from a pseudo-range domain to a positioning domain, and calculating an ideal envelope value of the sum of the monitoring system positioning error and the wide area enhancement system information broadcast positioning error to obtain a ground monitoring protection level of the pseudo airborne user, wherein the monitoring system positioning error comprises a positioning error caused by thermal noise of the airborne user and fuselage multipath, a positioning error caused by an ionized layer above a monitoring center and a positioning error caused by a troposphere above the monitoring center;

and sequentially comparing the ground monitoring protection levels of all visible satellite combinations of the pseudo airborne user with an alarm limit value preset by the airborne user, and if the ground monitoring protection levels of the visible satellite combinations are smaller than the alarm limit value, sending the visible satellite combination with the largest number of satellites and the pseudo-range correction value of each visible satellite in the visible satellite combination to the airborne user.

2. The local area airport monitoring method of claim 1, wherein said calculating a pseudorange corrected position error for said pseudo-airborne user using a pseudorange domain to position domain transformation matrix based on said receiver information of said pseudo-airborne user and an airborne user preset continuity requirement value comprises:

obtaining a monitoring error standard deviation of the pseudo airborne user and a wide area augmentation system broadcast information error standard deviation according to the receiver information, and calculating by using a variance transfer principle to obtain a pseudo-range correction value error standard deviation, wherein the pseudo-range correction value error standard deviation is a standard deviation when an error of a pseudo-range correction value of the pseudo airborne user obeys Gaussian distribution;

calculating to obtain a continuity error amplification factor through a Gaussian distribution statistical algorithm according to a continuity requirement value preset by an airborne user;

and calculating to obtain the pseudo-range correction value positioning error by utilizing a conversion matrix from the pseudo-range domain to the positioning domain according to the pseudo-range correction value error standard deviation and the continuity error amplification factor.

3. The local area airport monitoring method of claim 2, wherein said extracting the wide area augmentation system information dissemination positioning error of the pseudo airborne user from the pseudorange corrected value positioning error is specifically:

subtracting the pseudo-onboard user's receiver monitored positioning error from the pseudo-range corrected positioning error.

4. The local area airport monitoring method of claim 3, wherein said calculating a monitoring system position error of said pseudo-airborne user using said pseudorange domain to positioning domain transformation matrix based on said receiver information of said pseudo-airborne user and a system pre-set integrity risk value comprises:

obtaining thermal noise and a fuselage multipath error standard deviation, an ionosphere error standard deviation and a troposphere error standard deviation of the pseudo airborne user according to the receiver information, and calculating by utilizing a variance transfer principle to obtain a monitoring system error standard deviation, wherein the thermal noise and the fuselage multipath error standard deviation, the ionosphere error standard deviation and the troposphere error standard deviation are standard deviations when the thermal noise and the fuselage multipath error, the ionosphere error and the troposphere error of the pseudo airborne user obey Gaussian distribution respectively;

calculating to obtain an integrity error amplification factor through a Gaussian distribution statistical algorithm according to an integrity risk value preset by a system;

and calculating to obtain the positioning error of the monitoring system by utilizing a conversion matrix from the pseudo-range domain to the positioning domain according to the standard deviation of the error of the monitoring system and the integrity error amplification factor.

5. The local area airport monitoring method of claim 1 or 4, wherein said comparing the ground monitoring protection level of all visible satellite combinations of said pseudo airborne user with the preset alarm limit of the airborne user in turn comprises:

dividing all visible satellites of the pseudo airborne user into a plurality of satellite subsets by a round robin removal method, wherein the number of the visible satellites contained in the satellite subsets is greater than or equal to 4;

and calculating the ground monitoring protection level of each satellite subset of the pseudo airborne user, and sequentially comparing the ground monitoring protection level of the satellite subset with the alarm limit value.

6. The local area airport monitoring method of claim 5, wherein said dividing all visible satellites of said pseudo-airborne user into a plurality of satellite subsets by a round-robin removal method comprises:

forming all visible satellites of the pseudo airborne user into a first-stage satellite subset, judging whether the number of the visible satellites in the first-stage satellite subset is equal to 4, if the number of the visible satellites in the first-stage satellite subset is equal to 4, stopping dividing the satellite subset, and otherwise, respectively removing one satellite from the first satellite subset according to a preset sequence to generate a second-stage satellite subset;

judging whether the number of visible satellites in the second-stage satellite subsets is equal to 4 or not, if the number of visible satellites in the second-stage satellite subsets is equal to 4, stopping dividing the satellite subsets, and if not, continuously removing one satellite in each second-stage satellite subset according to a preset sequence to generate a third-stage satellite subset;

and the like until the number of satellites contained in the N-th level satellite subset generated by the division is equal to 4.

7. The local airport monitoring method of claim 6, further comprising:

and if the ground monitoring protection levels of all visible satellite combinations of the pseudo airborne user are greater than the alarm limit value, sending alarm information indicating that the satellite navigation system of the airborne user is unavailable to the airborne user.

8. A local airport monitoring apparatus, comprising:

the first calculation module is used for acquiring receiver information of each receiver and satellite data received by the receiver from a navigation satellite, and correcting pseudo-range information in the satellite data by using enhancement information broadcast by a wide area enhancement system, a carrier phase observation value and a troposphere error model to obtain a pseudo-range correction value of each satellite corresponding to each receiver, wherein the receiver information comprises a satellite elevation value of a visible satellite corresponding to the receiver, a real distance between the receiver and the visible satellite thereof and the number of the visible satellites of each receiver;

the second calculation module is connected with the first calculation module and is used for selecting one receiver as a pseudo airborne user, calculating a pseudo-range correction value positioning error of the pseudo airborne user by using a conversion matrix from a pseudo-range domain to a positioning domain according to the receiver information of the pseudo airborne user and a continuity requirement value preset by the airborne user, and extracting wide area augmentation system information broadcasting positioning error of the pseudo airborne user from the pseudo-range correction value positioning error;

a third calculation module, connected to the second calculation module, configured to calculate, according to the receiver information of the pseudo-airborne user and a preset integrity risk value of the system, a monitoring system positioning error of the pseudo-airborne user by using a conversion matrix from the pseudo-range domain to the positioning domain, and calculate an ideal envelope value of a sum of the monitoring system positioning error and a positioning error broadcast by the wide-area enhancement system information, so as to obtain a ground monitoring protection level of the pseudo-airborne user, where the monitoring system positioning error includes a positioning error caused by thermal noise of the airborne user and fuselage multipath, a positioning error caused by an ionosphere above a monitoring center, and a positioning error caused by a troposphere above the monitoring center;

and the judgment module is connected with the third calculation module and is used for sequentially comparing the ground monitoring protection levels of all visible satellite combinations of the pseudo airborne user with an alarm limit value preset by the airborne user, and if the ground monitoring protection levels of the visible satellite combinations are smaller than the alarm limit value, sending the visible satellite combination with the largest number of satellites and the pseudo-range correction value of each visible satellite in the visible satellite combination to the airborne user.

9. A local airport monitoring system, comprising:

the system comprises a plurality of receivers, a monitoring center and a navigation satellite, wherein the receivers are used for receiving satellite data sent by the navigation satellite, carrying out analog-to-digital conversion on the satellite data and sending the satellite data after analog-to-digital conversion and receiver information of the receivers to the monitoring center, and the receiver information comprises satellite elevation values of visible satellites corresponding to the receivers, real distances between the receivers and the visible satellites and the number of the visible satellites of each receiver;

the monitoring center is connected with the receiver and used for calculating a pseudo-range correction value of each satellite corresponding to the receiver according to the received satellite data, detecting an error caused by the pseudo-range correction value of an airborne user and an error caused by a monitoring system according to the information of the receiver, calculating a ground monitoring protection level of the monitoring center, obtaining an optimal visible satellite combination by comparing the ground monitoring protection level with a warning limit value preset by the user, and sending the optimal visible satellite combination and the pseudo-range correction value of each visible satellite in the satellite combination to the airborne user,

the monitoring center includes: the first calculation module is used for acquiring receiver information of each receiver and satellite data received by the receiver from a navigation satellite, and correcting pseudo-range information in the satellite data by using enhancement information broadcast by a wide area enhancement system, a carrier phase observation value and a troposphere error model to obtain a pseudo-range correction value of each satellite corresponding to each receiver, wherein the receiver information comprises a satellite elevation value of a visible satellite corresponding to the receiver, a real distance between the receiver and the visible satellite thereof and the number of the visible satellites of each receiver;

the second calculation module is connected with the first calculation module and is used for selecting one receiver as a pseudo airborne user, calculating a pseudo-range correction value positioning error of the pseudo airborne user by using a conversion matrix from a pseudo-range domain to a positioning domain according to the receiver information of the pseudo airborne user and a continuity requirement value preset by the airborne user, and extracting wide area augmentation system information broadcasting positioning error of the pseudo airborne user from the pseudo-range correction value positioning error;

a third calculation module, connected to the second calculation module, configured to calculate, according to the receiver information of the pseudo-airborne user and a preset integrity risk value of the system, a monitoring system positioning error of the pseudo-airborne user by using a conversion matrix from the pseudo-range domain to the positioning domain, and calculate an ideal envelope value of a sum of the monitoring system positioning error and a positioning error broadcast by the wide-area enhancement system information, so as to obtain a ground monitoring protection level of the pseudo-airborne user, where the monitoring system positioning error includes a positioning error caused by thermal noise of the airborne user and fuselage multipath, a positioning error caused by an ionosphere above a monitoring center, and a positioning error caused by a troposphere above the monitoring center;

the judgment module is connected with the third calculation module and is used for sequentially comparing the ground monitoring protection levels of all visible satellite combinations of the pseudo airborne user with an alarm limit value preset by the airborne user, and if the ground monitoring protection levels of the visible satellite combinations are smaller than the alarm limit value, sending the visible satellite combination with the largest number of satellites and the pseudo-range correction value of each visible satellite in the visible satellite combination to the airborne user;

and the airborne user is connected with the monitoring center and used for calculating the position of the airborne user according to the optimal visible satellite combination and the pseudo-range correction value of the visible satellite combination sent by the monitoring center.

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