Airborne positioning integrity monitoring method and device

Abstract

The present invention provides an airborne positioning integrity monitoring method and device, the method comprising: acquiring a positioning signal; eliminating the code phase offset and Doppler frequency generated during the transmission of the positioning signal to determine the original positioning signal; determining a first pseudorange observation value and a second pseudorange observation value; the first pseudorange observation value being a pseudorange observation value between a satellite and a user determined based on the original GNSS signal; the second pseudorange observation value being a pseudorange observation value between a user and a ground station determined based on the original LDACS signal; performing anomaly elimination processing on the first pseudorange observation value and the second pseudorange observation value; performing positioning solution based on the first pseudorange observation value after the anomaly elimination processing and the second pseudorange observation value after the anomaly elimination processing to determine the user's positioning result. The present invention can improve the accuracy of airborne positioning by eliminating anomalies and eliminating the code phase offset and Doppler frequency generated during the transmission of the positioning signal.

Description

Technical Field

[0001] The present invention relates to the field of aviation navigation technology, and in particular to an airborne positioning integrity monitoring method and device. Background Art

[0002] In recent years, China's space industry has entered a new phase, with a surge of modern communications products making their way into people's lives. The location-based services provided by wireless positioning systems are playing an increasingly important role in our daily lives and work. The Global Navigation Satellite System (GNSS) has gained widespread market acceptance due to its exceptional versatility, high efficiency, high precision, and real-time, uninterrupted monitoring. However, existing GNSS solutions are susceptible to interference in complex environments such as large shopping malls, mountainous canyons, and urban tunnels. This reduces the number of visible satellites and degrades the satellite geometry, leading to reduced positioning accuracy, increased integrity risks, and unreliable availability and continuity of positioning results.

[0003] The development of GNSS faces many challenges, among which positioning accuracy and integrity monitoring are the most urgent issues to be addressed. Due to ground obstruction, which easily causes large differences in user visibility in low-altitude areas, poor geometric diversity, and errors and delays in long-distance signal transmission, the availability of GNSS signals is greatly limited, restricting GNSS navigation performance. Summary of the Invention

[0004] The purpose of the present invention is to provide an airborne positioning integrity monitoring method and device, which can improve the accuracy of airborne positioning.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] An airborne positioning integrity monitoring method, comprising:

[0007] Acquire a positioning signal; the positioning signal includes a GNSS signal and an LDACS signal; the LDACS signal includes an LDACS forward link signal and an LDACS reverse link signal;

[0008] Eliminate the code phase offset and Doppler frequency generated during the positioning signal transmission process to determine the original positioning signal;

[0009] Determine a first pseudorange observation value and a second pseudorange observation value; the first pseudorange observation value is a pseudorange observation value between a satellite and a user determined based on an original GNSS signal; the second pseudorange observation value is a pseudorange observation value between a user and a ground station determined based on an original LDACS signal;

[0010] performing abnormality elimination processing on the first pseudorange observation value and the second pseudorange observation value;

[0011] A positioning solution is performed based on the first pseudorange observation value after the abnormality elimination process and the second pseudorange observation value after the abnormality elimination process to determine the user's positioning result.

[0012] Optionally, obtaining a positioning signal includes:

[0013] Obtain positioning signals;

[0014] Performing down-conversion processing on the positioning signal to obtain a positioning signal after down-conversion processing;

[0015] The positioning signal after the down-conversion processing is subjected to analog-to-digital conversion processing to obtain the positioning signal in the form of a digital signal.

[0016] Optionally, eliminate the code phase offset and Doppler frequency generated during the positioning signal transmission process, including:

[0017] Using an improved parallel search algorithm to capture and process the positioning signal;

[0018] After successful capture, the captured positioning signal is tracked and processed to eliminate the code phase offset and Doppler frequency generated during the transmission of the positioning signal.

[0019] Optionally, the improved parallel search algorithm includes:

[0020] determining the positioning signal as a first branch positioning signal;

[0021] Multiplying the first branch positioning signal by the local spread spectrum code, performing data accumulation processing on the product within a period, and determining the position of the data modulus value within the period as the first position;

[0022] Perform chip shift on the positioning signal to obtain a second branch positioning signal;

[0023] multiplying the second branch positioning signal by the local spread spectrum code, performing data accumulation processing on the product within a period, and determining the position of the data modulus value within the period as the second position;

[0024] Determine whether the first position and the second position are the same, and obtain a first judgment result:

[0025] If the first judgment result is yes, it is determined that the positioning signal is captured successfully;

[0026] If the first judgment result is no, it is determined that the positioning signal capture is unsuccessful, the positioning signal is updated, and the process returns to the step of "determining the positioning signal as the first branch positioning signal".

[0027] Optionally, performing abnormality elimination processing on the first pseudorange observation value and the second pseudorange observation value includes:

[0028] Deleting the first pseudorange observation corresponding to when the receiving interval is greater than the first receiving interval;

[0029] The second pseudorange observation value corresponding to when the receiving interval is greater than the second receiving interval is deleted.

[0030] Optionally, performing positioning solution based on the first pseudorange observation value after anomaly elimination processing and the second pseudorange observation value after anomaly elimination processing to determine the positioning result of the user includes:

[0031] Determining whether a GNSS positioning condition is satisfied to obtain a second determination result; wherein the GNSS positioning condition is that there are at least four first pseudorange observations after elimination processing; and the satellites corresponding to the first pseudorange observations after elimination processing are all different;

[0032] If the second judgment result is yes, the user position is determined using a first-order Taylor series expansion method and a least squares method based on the first pseudo-range observation after the elimination process;

[0033] If the second judgment result is no, then determine whether the LDACS positioning condition is met to obtain a third judgment result;

[0034] If the third judgment result is yes, the user position is determined using the pseudorange positioning method based on the second pseudorange observation value after the elimination process;

[0035] If the third judgment result is no, return to step "obtaining positioning signal".

[0036] An airborne positioning integrity monitoring device comprises: a signal receiving unit, a baseband signal processing unit, a data processing unit, an abnormal signal monitoring unit and a positioning solution unit connected in sequence;

[0037] The signal receiving unit is used to obtain a positioning signal; the positioning signal includes a GNSS signal and an LDACS signal; the LDACS signal includes an LDACS forward link signal and an LDACS reverse link signal;

[0038] The baseband signal processing unit is used to eliminate the code phase offset and Doppler frequency generated during the positioning signal transmission process to determine the original positioning signal;

[0039] The data processing unit is used to determine a first pseudorange observation value and a second pseudorange observation value; the first pseudorange observation value is a pseudorange observation value between a satellite and a user determined according to an original GNSS signal; the second pseudorange observation value is a pseudorange observation value between a user and a ground station determined according to an original LDACS signal;

[0040] The abnormal signal monitoring unit is used to perform abnormal elimination processing on the first pseudorange observation value and the second pseudorange observation value;

[0041] The positioning solution unit is used to perform positioning solution based on the first pseudo-range observation value after the abnormality elimination process and the second pseudo-range observation value after the abnormality elimination process to determine the user's positioning result.

[0042] Optionally, the signal receiving unit includes: a radio frequency front end and a satellite antenna;

[0043] The radio frequency front end is connected to the satellite antenna and the baseband signal processing unit;

[0044] The satellite antenna is used to receive the positioning signal;

[0045] The radio frequency front end is used to perform frequency conversion processing and analog-to-digital conversion processing on the positioning signal.

[0046] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0047] The present invention provides an airborne positioning integrity monitoring method and device, which includes: obtaining a positioning signal; eliminating the code phase offset and Doppler frequency generated during the transmission of the positioning signal to determine the original positioning signal; determining a first pseudorange observation value and a second pseudorange observation value; the first pseudorange observation value is a pseudorange observation value between the satellite and the user determined based on the original GNSS signal; the second pseudorange observation value is a pseudorange observation value between the user and the ground station determined based on the original LDACS signal; performing anomaly elimination processing on the first pseudorange observation value and the second pseudorange observation value; performing positioning solution based on the first pseudorange observation value after the anomaly elimination processing and the second pseudorange observation value after the anomaly elimination processing to determine the user's positioning result. The present invention can improve the accuracy of airborne positioning by eliminating anomalies and eliminating the code phase offset and Doppler frequency generated during the transmission of the positioning signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0049] Figure 1 This is a flow chart of the airborne positioning integrity monitoring method according to embodiment 1 of the present invention;

[0050] Figure 2 This is a schematic diagram of an airborne positioning integrity monitoring device according to embodiment 2 of the present invention;

[0051] Figure 3This is a flowchart of the baseband signal processing unit in Example 2 of the present invention;

[0052] Figure 4 This is a workflow diagram of the capture algorithm in Example 2 of the present invention;

[0053] Figure 5 This is a workflow diagram of the tracking algorithm in Example 2 of the present invention;

[0054] Figure 6 This is a schematic diagram of the positioning principle of the LDACS ground station in Example 2 of the present invention;

[0055] Figure 7 This is a schematic diagram of the LDACS A2A assisted positioning principle in Example 2 of the present invention. DETAILED DESCRIPTION

[0056] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0057] The purpose of the present invention is to provide an airborne positioning integrity monitoring method and device, which can improve the accuracy of airborne positioning.

[0058] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0059] Due to GNSS's vulnerability to spoofing attacks and intentional jamming, as well as performance degradation in certain operating environments, scholars and institutions are currently seeking an alternative positioning, navigation, and timing (APNT) solution to ensure efficient and secure services when GNSS cannot meet high-quality requirements. Currently, the Next Generation Air Transportation System (NextGen) in the United States and the Single European Sky ATM Research (SESAR) project in Europe are conducting research on APNT and have proposed several alternative solutions, including the L-band Digital Aeronautical Communications System (LDACS).

[0060] LDACS is a future cellular-based aviation communications system designed to replace current air-to-ground communications technologies, which have limited capacity and available safety measures. It provides a digital broadband radio link for air-to-ground (A2G) communications, connecting aircraft to ground infrastructure and supporting data and voice communications between ground stations and airborne devices. LDACS operates in the 960MHz-1164MHz frequency band and features a point-to-multipoint cellular architecture. The ground segment consists of multiple ground stations, each controlling up to 512 airborne devices within an airspace of up to 200 nautical miles. Aircraft flying over this area with their own radio communication units can connect to the same ground station via a full-duplex radio link using time division multiple access (TDMA) and orthogonal frequency division multiple access (OFDMA). Airborne devices receive navigation information transmitted by the ground station via a forward link and transmit it back to the ground station via a reverse link. LDACS also supports air-to-air (A2A) communications, receiving navigation information from other airborne devices. The present invention combines LDACS technology to provide an airborne positioning integrity monitoring method and device, which can improve the accuracy of airborne positioning, as follows:

[0061] Example 1

[0062] like Figure 1 As shown, this embodiment provides an airborne positioning integrity monitoring method, including:

[0063] Step 101: Acquire positioning signals; the positioning signals include GNSS signals and LDACS signals; the LDACS signals include LDACS forward link signals and LDACS reverse link signals;

[0064] Step 102: Eliminate the code phase offset and Doppler frequency generated during the transmission of the positioning signal to determine the original positioning signal;

[0065] Step 103: Determine a first pseudorange observation value and a second pseudorange observation value; the first pseudorange observation value is a pseudorange observation value between the satellite and the user determined based on the original GNSS signal; the second pseudorange observation value is a pseudorange observation value between the user and the ground station determined based on the original LDACS signal;

[0066] Step 104: performing abnormality elimination processing on the first pseudorange observation value and the second pseudorange observation value;

[0067] Step 105: Perform positioning calculation based on the first pseudorange observation value after the anomaly elimination process and the second pseudorange observation value after the anomaly elimination process to determine the user's positioning result.

[0068] The method of obtaining a positioning signal includes: obtaining a positioning signal; performing down-conversion processing on the positioning signal to obtain a positioning signal after down-conversion processing; and performing analog-to-digital conversion processing on the positioning signal after down-conversion processing to obtain a positioning signal in the form of a digital signal.

[0069] Specifically, the code phase offset and Doppler frequency generated during the transmission of the positioning signal are measured and abnormally eliminated, including: using an improved parallel search algorithm to capture and process the positioning signal; and tracking and processing the captured positioning signal after successful capture, so as to eliminate the code phase offset and Doppler frequency generated during the transmission of the positioning signal.

[0070] The improved parallel search algorithm includes: determining the positioning signal as the first branch positioning signal; multiplying the first branch positioning signal by the local spread spectrum code, performing data accumulation processing on the product within a cycle, and determining that the position of the data modulus value within the cycle is the first position; performing code chip shift on the positioning signal to obtain the second branch positioning signal; multiplying the second branch positioning signal by the local spread spectrum code, performing data accumulation processing on the product within a cycle, and determining that the position of the data modulus value within the cycle is the second position; determining whether the first position and the second position are the same to obtain a first judgment result: if the first judgment result is yes, it is determined that the positioning signal is captured successfully; if the first judgment result is no, it is determined that the positioning signal is captured unsuccessfully, the positioning signal is updated, and the process returns to the step of "determining the positioning signal as the first branch positioning signal".

[0071] The abnormal elimination processing of the first pseudorange observation value and the second pseudorange observation value includes: deleting the first pseudorange observation value corresponding to when the receiving interval is greater than the first receiving interval; deleting the second pseudorange observation value corresponding to when the receiving interval is greater than the second receiving interval.

[0072] The method of performing positioning solution based on the first pseudorange observation value after anomaly elimination and the second pseudorange observation value after anomaly elimination to determine the user's positioning result includes: judging whether a GNSS positioning condition is met to obtain a second judgment result; the GNSS positioning condition is that there are at least four first pseudorange observation values ​​after anomaly elimination; and the satellites corresponding to the first pseudorange observation values ​​after anomaly elimination are all different; if the second judgment result is yes, determining the user position based on the first pseudorange observation value after anomaly elimination using a first-order Taylor series expansion method and a least squares method; if the second judgment result is no, judging whether the LDACS positioning condition is met to obtain a third judgment result; if the third judgment result is yes, determining the user position based on the second pseudorange observation value after anomaly elimination using a pseudorange positioning method; if the third judgment result is no, returning to the step of "obtaining a positioning signal".

[0073] Example 2

[0074] This embodiment provides an airborne positioning integrity monitoring device, comprising: a signal receiving unit, a baseband signal processing unit, a data processing unit, an abnormal signal monitoring unit, and a positioning solution unit, which are connected in sequence. The signal receiving unit is configured to acquire a positioning signal. The positioning signal includes a GNSS signal and a LDACS signal. The LDACS signal includes an LDACS forward link signal and an LDACS reverse link signal. The baseband signal processing unit is configured to eliminate the code phase offset and Doppler frequency generated during the transmission of the positioning signal to determine an original positioning signal. The data processing unit is configured to determine a first pseudorange observation value and a second pseudorange observation value. The first pseudorange observation value is a pseudorange observation value between a satellite and a user determined based on the original GNSS signal. The second pseudorange observation value is a pseudorange observation value between a user and a ground station determined based on the original LDACS signal. The abnormal signal monitoring unit is configured to perform abnormality elimination processing on the first pseudorange observation value and the second pseudorange observation value. The positioning solution unit is configured to perform positioning solution based on the first pseudorange observation value and the second pseudorange observation value after the abnormality elimination processing to determine the user's positioning result. The signal receiving unit includes: a radio frequency front end and a satellite antenna; the radio frequency front end is connected to the satellite antenna and the baseband signal processing unit; the satellite antenna is used to receive the positioning signal; and the radio frequency front end is used to perform frequency conversion and analog-to-digital conversion on the positioning signal. This embodiment is described in detail below:

[0075] 1. Signal receiving unit:

[0076] The signal receiving unit consists of an RF front-end and a measurement satellite antenna. The receiver receives signals transmitted from the ground or airborne end through the RF front-end and down-converts the received signals to an intermediate frequency (IF), generating two IF analog signals (I and Q). These signals are then converted digitally to analog and digitally down-converted through an A / D converter to output the I and Q IF digital signals.

[0077] The measurement satellite antenna includes modules such as the antenna array and power board. The antenna array combines a monopole antenna with a patch antenna, including one B1 zero-phase array element and one B3 zero-phase array element. The RF / RDSS baseband board includes the B1 / B3 filter and amplifier circuits. These circuits are powered by the 5V feed from the receiver board, enabling high-precision measurement control.

[0078] 2. Baseband signal processing unit:

[0079] The baseband signal processing unit is the core part of the navigation receiver. This module is mainly used to eliminate the code phase offset and Doppler frequency generated during the transmission process as much as possible, so that the original signal can be accurately restored at the receiving end. Due to the relative motion between the navigation receiver and the satellite, Doppler frequency shift and code phase offset are generated. The carrier frequency and code phase of the received signal are inconsistent with the transmitted signal, resulting in the inability to accurately locate. Therefore, some related processing is required to eliminate the influence caused by the motion, that is, the capture and tracking of the carrier frequency and code phase. Capture and tracking complement each other. By continuously adjusting the initial phase of the local pseudo-code sequence so that the code phase error with the received navigation signal is within 0.5 code chips, the capture is successful, and the capture module stops working and jumps to the tracking module, otherwise it continues to capture. At the same time, the tracking module must be observed. If the tracking module loses lock, it jumps from the tracking module to the capture module to re-capture, and the work is repeated in this way. Based on the requirements of high-precision positioning, the present invention appropriately increases the cumulative data length of the captured signal and adopts a method combining related accumulation and non-related accumulation to track the GPS signal.

[0080] 2.1 Search

[0081] In real-world applications, the Doppler frequency of the carrier frequency and CA code caused by the relative motion between the satellite and the receiver is crucial for acquiring and tracking satellite navigation signals. Typically, the Doppler frequency generated by the relative motion between the receiver and the satellite is within a range of 5 kHz. Therefore, during acquisition, the frequency search for the received navigation signal only needs to be performed within a 5 kHz frequency range centered on the carrier frequency. The code phase search range is one code period of the navigation signal's pseudo-code sequence, or 2046 chips.

[0082] 2.2 Capture

[0083] Once a signal is found, the capture module generates a peak at the correct code phase and carrier frequency. In order to determine whether the peak represents a real signal, a threshold value must be set. If the peak is greater than the threshold value, it is the desired signal, otherwise it is not. The existing time-domain serial search capture algorithm is relatively simple to implement, but its capture time is relatively long. The frequency-domain parallel search capture algorithm based on Fast Fourier Transform (FFT) has a large amount of computation and consumes a lot of hardware resources. Therefore, the present invention captures signals through an improved parallel search algorithm, reducing the number of searches and the amount of computation while improving capture accuracy.

[0084] The present invention divides the received navigation signal into a 0 branch (the original received signal) and a 0.5 branch (the received signal is offset by 0.5 code chips). The two branch signals are respectively multiplied by the local spread spectrum code (CA code) and the data are accumulated. Then, the data is delayed for one cycle, that is, 2046 points. The positions of the module values ​​of the two cycle data are counted to see whether they are the same. If they are the same, the capture is successful and the tracking link is transferred; if they are not the same, the capture is repeated until the capture is successful.

[0085] For the convenience of discussion, only the received signal is considered, without considering noise and other interference. Assume that the input signal entering the capture module for capture is:

[0086]

[0087] Where i' represents the delay, C(i) represents the i-th chip, and f d represents the Doppler frequency, T c represents the symbol width; Φ represents the initial phase.

[0088] The result of the correlator cumulative output is:

[0089]

[0090] Where p represents the length of the matched filter; n is a positive integer.

[0091] Perform FFT of point R:

[0092]

[0093] N is the number of data, R is the FFT transform of point R, and r is the correlator cumulative output result.

[0094] Finally, multiply the delay of N points and take the average:

[0095]

[0096] Here, this is a parameter, ω D is the angular frequency, fd is the frequency.

[0097] The improved parallel search and capture algorithm performs storage offset on the received signal, while the local C / A code remains unchanged. There is no need to set a threshold, only the position of each frame needs to be recorded, which reduces IFFT calculations and greatly shortens the capture time, improving capture efficiency and accuracy.

[0098] 2.3 Tracking

[0099] After roughly determining the received signal's frequency and code phase, the signal is tracked. Signal tracking is performed to identify the phase shift of the navigation data and obtain relatively accurate Doppler frequency and code phase values. Tracking is divided into carrier tracking and code tracking. Carrier tracking ensures that the local carrier frequency is consistent with the frequency of the Doppler-shifted GNSS signal, allowing carrier separation and accurate spread spectrum code generation. This also allows the received signal to be down-converted to baseband. Code tracking aims to separate the pseudo-code within the spread spectrum code to obtain the navigation message.

[0100] Since the frequency discriminator has a tracking upper limit, if the residual frequency deviation is too large and exceeds the tracking limit of the frequency locked loop, the frequency locked loop will not work. Therefore, after the code chips are aligned, the present invention can obtain partial gain within one code period without obtaining the complete spread spectrum gain, and obtain a larger range of frequency deviation.

[0101] Assume that the received signal after removing the local code is:

[0102] d(n)=x(n)*c(n) (5)

[0103] Among them, x(n) is the captured signal and c(n) is the local carrier signal.

[0104] To expand the frequency offset estimation range, the distance between d(n) and subsequent data related to it must be reduced, i.e., truncated correlation is performed. This invention reduces the cumulative length to 1 / 4 of a code period, thereby expanding the tracking range by a factor of four. A complete spread spectrum code is segmented to obtain multiple frequencies, which are then averaged to obtain a single frequency point, which serves as the compensation frequency for the next frame of data.

[0105] The extended frequency tracking range can be expressed as:

[0106]

[0107] Wherein, M is the base number of the selected multiple phase shift keying (MPSK).

[0108] After the Doppler frequency is tracked and compensated by the frequency-locked loop, a small frequency offset still remains, making it impossible to obtain the correct navigation signal during demodulation. Therefore, further locking compensation is required, that is, tracking compensation through a phase-locked loop (PLL).

[0109] In traditional software receiver tracking loops, each channel tracks satellite signals independently. Different tracking channels replicate the corresponding satellite's spread spectrum pseudo-code and modulated carrier signal, and use the loop's output observation vector and demodulated ephemeris parameters for navigation calculation. However, the geometric relationship between different satellites and the same user determines that the receiver's reference oscillator frequency drift introduces the same frequency interference in each signal channel, and dynamic stress acts on all channels in common. Therefore, the tracking and navigation calculation of different channel signals are linked through a Kalman filter. The filter uses the signal parameter results output by each channel to directly estimate the receiver's state parameters. The corrected state results are then used to directly control each channel's NCO to generate a local replica signal for the next cycle. This achieves joint tracking of satellite signals from multiple channels, reduces the loop's noise bandwidth, improves the loop's tolerance to higher user dynamic stress, and achieves better signal tracking performance. It also reduces the number of correlation integral operations in each tracking loop, significantly shortening tracking time.

[0110] During the receiver signal processing, the phase relationship between the estimated value of the signal transmission time at time k and the local replica pseudo-code signal in the tracking loop can be expressed as:

[0111]

[0112] where t s，k is the signal transmission time, t u，k is the time it takes for the receiver to track the current signal, c is the speed of light, X r is the true value of the receiver's position at time k, and X s is the location where the signal is transmitted,

[0113] According to the generation principle of Doppler signal, the real Doppler frequency shift of the received signal at time k can be expressed as:

[0114]

[0115] Where V r，k is the signal transmission speed, V s，k is the speed at which the receiver tracks the current signal, f1 is the signal frequency, and T represents the transpose.

[0116] Estimated Doppler shift representation of the local replica signal for:

[0117]

[0118] in, is the estimated signal transmission speed, is the estimated receiver position, δf u，k is the receiver frequency at time k.

[0119] Vector tracking loop copy signal specific control method f k for:

[0120]

[0121] in, is the difference between the true value and the estimated value of the velocity caused by the Doppler shift, is the difference between the true value and the estimated value of the signal transmission speed.

[0122] 3. Data processing unit

[0123] The data processing unit is used to calculate the pseudo-range observation between the satellite and the user obtained from the GNSS signal or the pseudo-range observation between the user and the ground station obtained from the LDACS signal. The input is the GNSS signal pseudo-code or LDACS signal pseudo-code output by the baseband signal processing unit.

[0124] After being captured and tracked, the received signal must undergo bit synchronization and frame synchronization to obtain navigation information. Bit synchronization aims to identify the phase edges of the navigation data bits, allowing the received signal to be segmented bit by bit. Frame synchronization, on the other hand, aims to identify the subframe edges of the navigation message, dividing every 30 data bits into meaningful words, thereby deciphering the required navigation message parameters from these words.

[0125] For GNSS signals, the baseband processing unit outputs the pseudocode of the GNSS observation value, and the navigation message is solved by the bit synchronization of the data processing unit. The three-dimensional position of the satellite is solved by the ephemeris information through frame synchronization, thereby obtaining the pseudorange observation value between the satellite and the user and inputting it into the abnormal signal monitoring unit; for LDACS signals, the baseband signal processing unit outputs the pseudocode of the LDACS observation value, and the navigation message is solved by the bit synchronization of the data processing unit. The pseudorange observation value, other user positions and other A2A information are obtained through frame synchronization, and the obtained pseudorange observation value between the user and the ground station is input into the abnormal signal monitoring unit; because the receiver and satellite clocks are not synchronized, and there will be ionospheric errors, tropospheric errors and other ranging errors during measurement, the actual measured distance value between the satellite and the receiver (or between receivers) is not the true distance, so it is called pseudorange. The observation equation of pseudorange is as follows:

[0126] ρ=r+cδ t +cI+cT+ε p (11)

[0127] Where ρ is the pseudorange, r is the actual distance between the receiver and the satellite, c is the speed of light, and δ t is the clock error, which includes the receiver's conventional clock error, clock delay, signal propagation delay of the coordinate point receiver antenna phase center, and clock error noise of the unmodeled error. I is the ionospheric delay, T is the tropospheric delay, and ε p It's noise.

[0128] For GNSS signals, the noise term is not considered. The tropospheric delay, actual distance and clock error terms on the right side of the equal sign in equation (11) are all constants. The pseudorange can be corrected by receiving the pseudorange measurements on the L1 and L2 signals of the same satellite at the same time and performing linear combination to calculate the ionospheric delay.

[0129]

[0130] Among them, ρ GNSS is the pseudorange observation between the satellite and the user obtained from the corrected GNSS signal, ρ1 is the pseudorange observation on the carrier L1 signal, ρ2 is the pseudorange observation on the carrier L2 signal, f1 is the frequency of the carrier L1, f1 = 1575.42 MHz, and f2 is the frequency of the carrier L2.

[0131] For LDACS signals, the noise term is not considered. The orbital ephemeris based on the data from the LDACS airborne terminal is constant, and the signal delay caused by the troposphere does not need to be considered. The pseudorange can be corrected by linearly combining the pseudorange measurements on the forward and reverse links received from the same airborne terminal and ground station ranging source to calculate the ionospheric delay.

[0132]

[0133] Among them, ρ LDACS is the pseudorange observation between the user and the ground station obtained from the corrected LDACS signal, ρ F is the pseudo-range observation value transmitted from the ground station ranging source to the airborne terminal through the forward link, ρ R is the pseudo-range observation value transmitted from the airborne end to the ground station through the reverse link, f F is the frequency of the forward link, f R is the frequency of the reverse link.

[0134] 4. Abnormal signal monitoring unit

[0135] The abnormal signal monitoring unit determines whether the signal reception is normal and whether the pseudorange value is reasonable based on the pseudorange observation between the satellite and the user obtained from the GNSS signal output by the data processing unit, or the pseudorange observation between the user and the ground station obtained from the LDACS signal. If a satellite data cannot be received for more than 10 minutes, the satellite data reception is abnormal, an abnormal warning signal is issued, and the abnormal satellite is removed. After that, the rationality of the satellite signal with normal data reception is judged, a certain time interval is set, and the difference between the pseudorange of all epochs or the relative position of the airborne end within this time interval is averaged as a reference value for judging rationality. If the difference between the difference of a certain epoch and the reference value exceeds the predetermined threshold value, it is judged as abnormal, an abnormal warning signal is issued, the abnormal satellite is removed, and the use of the satellite for positioning is stopped. The rationality judgment calculation formula is as follows:

[0136]

[0137] in, is the mean of the pseudorange, ρ(i) is the pseudorange at time i, and ρ(i-1) is the pseudorange at time i-1.

[0138] For an ideal signal, the difference between two consecutive epochs and the carrier phase difference should be equal. However, due to the influence of factors such as multipath, the results may be inconsistent. Therefore, the present invention sets the maximum difference between the pseudorange differences in the previous and next epochs as the threshold value t of pseudorange rationality, that is:

[0139]

[0140] Wherein, N is a positive integer.

[0141] The rationality monitoring formula of m at a certain moment is as follows:

[0142]

[0143] Where ρ(m) is the pseudorange at epoch m, and ρ(m-1) is the pseudorange at epoch m-1.

[0144] Determine whether the current epoch m satisfies the above formula. If so, the epoch is reasonable and can be used for positioning solution. Otherwise, the epoch does not meet the rationality of pseudorange and cannot be used for positioning solution. Unreasonable values ​​are eliminated.

[0145] 5. Positioning solution unit

[0146] The positioning solution unit receives the correct pseudorange value input by the abnormal signal monitoring unit to perform positioning solution, and divides the positioning solution into pseudorange positioning method and LDACS signal assisted positioning method according to the number of normal pseudorange values. The input is the correct observation data output by the abnormal signal monitoring unit of the software receiver, and the output is an accurate positioning result.

[0147] The LDACS communication system is inspired by modern terrestrial mobile communication networks, and many aspects of its functionality can be implemented using similar methods. If the LDACS airborne receiver can receive a sufficient number of ground station signals, its position can be determined using trilateration or multilateration. At cruising altitude, an aircraft typically receives data from multiple ground stations simultaneously transmitted via forward links on different frequencies within its radio range, enabling independent distance measurements to all visible ground stations. The LDACS airborne terminal can be positioned using principles similar to satellite positioning, using time-of-arrival ranging (T2A) as the basis for ranging. Therefore, the positioning algorithm can utilize pseudorange positioning, similar to GNSS signals. When pseudorange observations between the satellite and the user are obtained from four different GNSS signals, or between the user and the ground station are obtained from LDACS signals, the user's position is determined using pseudorange positioning. When three LDACS signals are present, LDACS A2A information is used to assist in positioning; otherwise, no position determination is possible.

[0148] 5.1 Pseudorange Positioning Method

[0149] When there are four different correct satellite pseudorange values, the positioning solution is performed using the pseudorange positioning method. According to formula (11), the actual distance measured by the nth satellite can be expressed as

[0150]

[0151] Among them, r is the true distance, ρ n is the pseudorange of the nth satellite, x n is the x-coordinate of the n-th satellite, is the x coordinate of the ground station; is the y coordinate of the nth satellite; is the y coordinate of the ground station; a n is the z coordinate of the nth satellite; is the z coordinate of the ground station, δ t is the satellite receiver clock difference; ε p is the total delay of the troposphere and ionosphere.

[0152] This equation has four unknowns, requiring data from at least four ground stations. As can be seen from the above equation, the pseudorange observation equation is nonlinear and needs to be linearized before using the least squares method for position calculation. Therefore, this paper uses a first-order Taylor series expansion method for positioning calculation.

[0153] The pseudorange equation is expanded into a first-order Taylor series as follows:

[0154]

[0155]

[0156]

[0157]

[0158]

[0159] δ t The solution obtained by Taylor's first-order expansion is an approximate solution with a certain linear range. It requires a certain number of iterative calculations to continuously approach the true value.

[0160] The geometric dilution of precision (GDOP) is often used to assess positioning accuracy. It represents the distance vector magnification factor between the receiver and the space satellite caused by ranging errors. The smaller the GDOP, the higher the positioning accuracy. GDOP is calculated based on the satellite state matrix using the direction cosine method. Assuming that α, β, and γ are the angles between the aircraft and the X, Y, and Z axes, respectively, the first state matrix Q, the second state matrix DOP, and the third state matrix GDOP are:

[0161]

[0162]

[0163] The subscript of each element in the matrix represents the position in the matrix.

[0164]

[0165] The covariance matrix Σ of the ranging source position is calculated as:

[0166] Σ=(Q T WQ) -1 (26)

[0167] Where W is the weight matrix, which reflects the uncertainty of the ranging source error.

[0168] The positioning error can be modeled as:

[0169]

[0170] in is the ranging error correlation model, Represents the measurement noise caused by signal tracking at the receiver.

[0171] The position estimate that minimizes the sum of squared ranging errors is obtained by the least squares method.

[0172]

[0173] Here, X represents the x-coordinate obtained by the least squares method.

[0174] Ranging residual vector Expressed as:

[0175]

[0176] Under the fault-free condition, the weighted norm of the residual vector obeys the central χ with N-2 degrees of freedom. 2 Distribution (N is the total number of visible satellites).

[0177] At this time, the ranging accuracy is high and the model with accurate position estimation value and its covariance matrix can be modeled as:

[0178]

[0179] in is the estimated value of the user's position, which is modeled by the covariance matrix Σ through formula (26); Estimation model error for user location. y represents the true location; Indicates the estimated position.

[0180] 5.2LDACS A2A assisted positioning method

[0181] When the ground station ranging source is severely blocked, the number of ground station ranging sources received by the airborne terminal is less than 4, and the user position cannot be solved using the pseudorange positioning method. In this case, the LDACS A2A assisted positioning method is used to solve the user position.

[0182] Assuming the known range error distribution is modeled as a zero-mean Gaussian, the ranging range can be modeled as a standard deviation of An unbiased estimate of :

[0183]

[0184] Based on this, the position estimation based on the high-altitude ranging source in the case of low-altitude flight can be modeled as:

[0185]

[0186] in is the estimated value of the user's position, which is obtained by modeling the covariance matrix Σ through formula (1); Σ is the covariance matrix of the user position estimation model.

[0187] Because the ground station's ranging source is severely obscured, its geometry makes positioning difficult. Therefore, this paper proposes a hybrid positioning algorithm to achieve optimal positioning accuracy. This paper uses Bancroft's direct position calculation method to calculate a rough position, and then uses the Gauss-Newton iterative algorithm to iteratively converge to a precise position solution. The specific process of this algorithm is as follows:

[0188] First, create the initial matrices X and Y of the ranging source position and pseudorange n :

[0189]

[0190]

[0191] Among them S n is the three-dimensional coordinate of the nth ranging source, ρ n is the pseudorange of the nth ranging source.

[0192] Next, define matrices A, B, and C to create a quadratic system:

[0193]

[0194]

[0195]

[0196] Aλ 2 +2Bλ+C=0 (38)

[0197] By iterating equation (38), the two solutions λ1 and λ2 obtained are the final positioning solutions.

[0198] In this embodiment, the parameter Q is defined i,k To describe the positioning confidence of aircraft i at the kth positioning estimation, its value range is (0,1). When the ground terminal signal is received, the current positioning estimate is corrected and Q i,k =1 means the current positioning is reliable; when the ground terminal signal is i,k =0.95, indicating that the reliability of location determination gradually decreases as the environment changes.

[0199]

[0200] in, represents the result calculated by (38) at the kth positioning, and ||*|| is an operator.

[0201] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0202] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A method for monitoring airborne positioning integrity, characterized in that: include: Acquire positioning signals; the positioning signals include GNSS signals and LDACS signals; The LDACS signal includes an LDACS forward link signal and an LDACS reverse link signal; Eliminate the code phase offset and Doppler frequency generated during the positioning signal transmission process to determine the original positioning signal; Determining a first pseudorange observation value and a second pseudorange observation value; the first pseudorange observation value is a pseudorange observation value between a satellite and a user determined based on an original GNSS signal; The second pseudorange observation is a pseudorange observation between the user and the ground station determined according to the original LDACS signal; performing abnormality elimination processing on the first pseudorange observation value and the second pseudorange observation value; Perform positioning calculation based on the first pseudo-range observation value after anomaly elimination processing and the second pseudo-range observation value after anomaly elimination processing to determine the user's positioning result; Eliminating the code phase offset and Doppler frequency generated during the transmission of the positioning signal includes: Using an improved parallel search algorithm to capture and process the positioning signal; After successful capture, the captured positioning signal is tracked and processed to eliminate the code phase offset and Doppler frequency generated during the transmission of the positioning signal; The improved parallel search algorithm includes: determining the positioning signal as a first branch positioning signal; Multiplying the first branch positioning signal by the local spread spectrum code, performing data accumulation processing on the product within a period, and determining the position of the data modulus value within the period as the first position; Perform chip shift on the positioning signal to obtain a second branch positioning signal; multiplying the second branch positioning signal by the local spread spectrum code, performing data accumulation processing on the product within a period, and determining the position of the data modulus value within the period as the second position; Determine whether the first position and the second position are the same, and obtain a first judgment result: If the first judgment result is yes, it is determined that the positioning signal is captured successfully; If the first judgment result is no, it is determined that the positioning signal capture is unsuccessful, the positioning signal is updated, and the process returns to step "determining the positioning signal as the first branch positioning signal".

2. The airborne positioning integrity monitoring method according to claim 1, characterized in that: The obtaining of the positioning signal includes: Obtain positioning signals; Performing down-conversion processing on the positioning signal to obtain a positioning signal after down-conversion processing; The positioning signal after the down-conversion processing is subjected to analog-to-digital conversion processing to obtain the positioning signal in the form of a digital signal.

3. The airborne positioning integrity monitoring method according to claim 1, characterized in that: Performing abnormality elimination processing on the first pseudorange observation value and the second pseudorange observation value, including: Deleting the first pseudorange observation corresponding to when the receiving interval is greater than the first receiving interval; The second pseudorange observation value corresponding to when the receiving interval is greater than the second receiving interval is deleted.

4. The airborne positioning integrity monitoring method according to claim 1, characterized in that: The performing positioning calculation based on the first pseudorange observation value after the abnormality elimination process and the second pseudorange observation value after the abnormality elimination process to determine the positioning result of the user includes: Determining whether a GNSS positioning condition is satisfied to obtain a second determination result; wherein the GNSS positioning condition is that there are at least four first pseudorange observations after elimination processing; and the satellites corresponding to the first pseudorange observations after elimination processing are all different; If the second judgment result is yes, the user position is determined using a first-order Taylor series expansion method and a least squares method based on the first pseudo-range observation after the elimination process; If the second judgment result is no, then determine whether the LDACS positioning condition is met to obtain a third judgment result; If the third judgment result is yes, the user position is determined using the pseudorange positioning method based on the second pseudorange observation value after the elimination process; If the third judgment result is no, return to step "obtaining positioning signal".

5. An airborne positioning integrity monitoring device, characterized in that: include: A signal receiving unit, a baseband signal processing unit, a data processing unit, an abnormal signal monitoring unit and a positioning solution unit connected in sequence; The signal receiving unit is used to obtain a positioning signal; the positioning signal includes a GNSS signal and an LDACS signal; the LDACS signal includes an LDACS forward link signal and an LDACS reverse link signal; The baseband signal processing unit is used to eliminate the code phase offset and Doppler frequency generated during the positioning signal transmission process to determine the original positioning signal; Eliminating a code phase offset and Doppler frequency generated during the transmission of a positioning signal, comprising: capturing the positioning signal using an improved parallel search algorithm; and tracking the captured positioning signal after successful capture to eliminate the code phase offset and Doppler frequency generated during the transmission of the positioning signal. The improved parallel search algorithm comprises: determining the positioning signal as a first-branch positioning signal; multiplying the first-branch positioning signal by a local spreading code, accumulating data on the product within a cycle, and determining a position of a data modulus value within the cycle as a first position; performing a chip shift on the positioning signal to obtain a second-branch positioning signal; multiplying the second-branch positioning signal by the local spreading code, accumulating data on the product within a cycle, and determining a position of a data modulus value within the cycle as a second position; and determining whether the first position and the second position are the same to obtain a first determination result: if the first determination result is yes, determining that the positioning signal is captured successfully; if the first determination result is no, determining that the positioning signal is captured unsuccessfully, updating the positioning signal, and returning to the step of "determining the positioning signal as the first-branch positioning signal." The data processing unit is used to determine a first pseudorange observation value and a second pseudorange observation value; the first pseudorange observation value is a pseudorange observation value between a satellite and a user determined according to an original GNSS signal; the second pseudorange observation value is a pseudorange observation value between a user and a ground station determined according to an original LDACS signal; The abnormal signal monitoring unit is used to perform abnormal elimination processing on the first pseudorange observation value and the second pseudorange observation value; The positioning solution unit is used to perform positioning solution based on the first pseudo-range observation value after the abnormality elimination process and the second pseudo-range observation value after the abnormality elimination process to determine the user's positioning result.

6. The airborne positioning integrity monitoring device according to claim 5, characterized in that: The signal receiving unit includes: a radio frequency front end and a satellite antenna; The radio frequency front end is connected to the satellite antenna and the baseband signal processing unit; The satellite antenna is used to receive the positioning signal; The radio frequency front end is used to perform frequency conversion processing and analog-to-digital conversion processing on the positioning signal.

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