WO2024159557A1 - 一种机载定位完好性监测方法及装置 - Google Patents

一种机载定位完好性监测方法及装置 Download PDF

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Publication number
WO2024159557A1
WO2024159557A1 PCT/CN2023/075788 CN2023075788W WO2024159557A1 WO 2024159557 A1 WO2024159557 A1 WO 2024159557A1 CN 2023075788 W CN2023075788 W CN 2023075788W WO 2024159557 A1 WO2024159557 A1 WO 2024159557A1
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Prior art keywords
signal
positioning
observation value
pseudorange observation
positioning signal
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PCT/CN2023/075788
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English (en)
French (fr)
Inventor
王志鹏
郭凯
方堃
常晓佳
王洪文
周嘉旗
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北京航空航天大学
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Publication of WO2024159557A1 publication Critical patent/WO2024159557A1/zh

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/20—Integrity monitoring, fault detection or fault isolation of space segment
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/03—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers
    • G01S19/10—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers providing dedicated supplementary positioning signals
    • G01S19/11—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers providing dedicated supplementary positioning signals wherein the cooperating elements are pseudolites or satellite radio beacon positioning system signal repeaters
    • G01S19/115—Airborne or satellite based pseudolites or repeaters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G01S19/25—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS
    • G01S19/254—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS relating to Doppler shift of satellite signals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/13—Receivers
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G01S19/25—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS
    • G01S19/258—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS relating to the satellite constellation, e.g. almanac, ephemeris data, lists of satellites in view
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/38—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system
    • G01S19/39—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system the satellite radio beacon positioning system transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/42—Determining position
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

Definitions

  • the present invention relates to the field of aviation navigation technology, and in particular to an airborne positioning integrity monitoring method and device.
  • GNSS Global Navigation Satellite System
  • GNSS Global System for Mobile Communications
  • 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.
  • the present invention provides the following solutions:
  • An airborne positioning integrity monitoring method comprising:
  • the positioning signal includes a GNSS signal and a LDACS signal
  • the LDACS signal includes a LDACS forward link signal and a LDACS reverse link signal
  • 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 Pseudorange observations between the user and the ground station determined based on the original LDACS signal
  • a positioning solution is performed based on the first pseudorange observation value after the abnormal elimination processing and the second pseudorange observation value after the abnormal elimination processing to determine the positioning result of the user.
  • the acquiring of the positioning signal includes:
  • 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.
  • code phase offset and Doppler frequency generated during the transmission of positioning signals are eliminated, including:
  • 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:
  • the first branch positioning signal is multiplied by the local spread spectrum code, and the product is subjected to data accumulation processing within a period, and the position of the data modulus value within the period is determined as the first position;
  • 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".
  • performing abnormal elimination processing on the first pseudorange observation value and the second pseudorange observation value includes:
  • the second pseudorange observation value corresponding to when the receiving interval is greater than the second receiving interval is deleted.
  • performing positioning solution according to 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:
  • the GNSS positioning condition is that there are at least four first pseudo-range observations after elimination processing; and the satellites corresponding to the first pseudo-range observations after elimination processing are all different;
  • the user position is determined using a first-order Taylor series expansion method and a least squares method according to the first pseudo-range observation value after the elimination process;
  • the user position is determined by using the pseudorange positioning method according to the second pseudorange observation amount after the elimination process;
  • 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;
  • the signal receiving unit is used to obtain a positioning signal;
  • the positioning signal includes a GNSS signal and a LDACS signal;
  • the LDACS signal includes a LDACS forward link signal and a LDACS reverse link signal;
  • the baseband signal processing unit is used to eliminate the code phase offset and Doppler frequency generated during the transmission of the positioning signal, and determine the original 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 according to the first pseudo-range observation value after the abnormal elimination process and the second pseudo-range observation value after the abnormal elimination process, so as to determine the positioning result of the user.
  • 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.
  • the present invention discloses the following technical effects:
  • the present invention provides an airborne positioning integrity monitoring method and device, the method comprising: 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 a satellite and a user determined according to the original GNSS signal; the second pseudorange observation value is a pseudorange observation value between a user and a ground station determined according to the original LDACS signal; performing an abnormal elimination process on the first pseudorange observation value and the second pseudorange observation value; performing positioning solution based on the first pseudorange observation value after the abnormal elimination process and the second pseudorange observation value after the abnormal elimination process to determine the positioning result of the user.
  • the present invention can improve the accuracy of airborne positioning by eliminating the abnormal elimination process and eliminating the code phase offset and Doppler frequency generated during the transmission of the positioning signal.
  • FIG1 is a flow chart of an airborne positioning integrity monitoring method according to Embodiment 1 of the present invention.
  • FIG2 is a schematic diagram of an airborne positioning integrity monitoring device according to Embodiment 2 of the present invention.
  • FIG3 is a flowchart of a baseband signal processing unit in Embodiment 2 of the present invention.
  • FIG4 is a flowchart of a capture algorithm in Embodiment 2 of the present invention.
  • FIG5 is a flowchart of a tracking algorithm in Embodiment 2 of the present invention.
  • FIG6 is a schematic diagram of the positioning principle of the LDACS ground station in Embodiment 2 of the present invention.
  • Figure 7 is a schematic diagram of the LDACS A2A assisted positioning principle in Example 2 of the present invention.
  • 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.
  • GNSS Due to the vulnerability of GNSS to spoofing attacks and intentional interference, as well as performance degradation in certain operating environments, scholars and institutions are now seeking an alternative positioning, navigation and timing (APNT) solution to ensure efficient and safe services when GNSS cannot meet high-quality requirements.
  • APNT Next Generation Air Transportation System
  • SESAR Single European Sky ATM Research
  • LDACS L-band Digital Aeronautical Communications System
  • LDACS is a future cellular-based aviation communication system designed to replace the current air-to-ground communication technology with limited capacity and available safety measures. It provides a digital broadband radio link for air-to-ground (A2G) communication, enabling connections between aircraft and ground infrastructure, and supporting data and voice communications between ground stations and airborne terminals.
  • A2G air-to-ground
  • LDACS operates in the 960MHz-1164MHz frequency band and has a cellular structure with point-to-multipoint connections.
  • the ground part contains multiple ground stations, each of which controls up to 512 airborne devices within an airspace of up to 200 nautical miles.
  • LDACS When aircraft with their own radio communication units fly over the area, they can be connected to the same ground station through a full-duplex radio link using Time Division Multiple Access (TDMA) and Orthogonal Frequency Division Multiple Access (OFDMA).
  • TDMA Time Division Multiple Access
  • OFDMA Orthogonal Frequency Division Multiple Access
  • the airborne terminal receives navigation information transmitted by the ground station through the forward link and transmits navigation information to the ground station through the reverse link.
  • LDACS also supports air-to-air (A2A) communication and receives navigation information from other airborne terminals.
  • A2A air-to-air
  • 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:
  • this embodiment provides an airborne positioning integrity monitoring method, including:
  • Step 101 Acquire a positioning signal;
  • the positioning signal includes a GNSS signal and a LDACS signal;
  • the LDACS signal includes a LDACS forward link signal and a LDACS reverse link signal;
  • Step 102 Eliminate the code phase offset and Doppler frequency generated during the transmission of the positioning signal to determine the original positioning signal;
  • Step 103 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 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;
  • Step 104 performing abnormal elimination processing on the first pseudorange observation value and the second pseudorange observation value
  • Step 105 Perform positioning calculation based on the first pseudorange observation value after the abnormal elimination process and the second pseudorange observation value after the abnormal elimination process to determine the positioning result of the user.
  • the method of acquiring a positioning signal comprises: acquiring a positioning signal; performing down-conversion processing on the positioning signal to obtain a positioning signal after the down-conversion processing; and performing analog-to-digital conversion processing on the positioning signal after the down-conversion processing to obtain a positioning signal in the form of a digital signal.
  • the code phase offset and Doppler frequency generated during the transmission of the positioning signal are measured and eliminated abnormally, including: 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 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, and obtaining 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 step of "determining the positioning signal as the first branch positioning signal" is returned.
  • 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.
  • the method of performing positioning solution according to the first pseudorange observation value after the abnormal elimination process and the second pseudorange observation value after the abnormal elimination process to determine the positioning result of the user includes: judging whether the GNSS positioning condition is met to obtain a second judgment result; the GNSS positioning condition is that there are at least 4 first pseudorange observation values after the elimination process; and the satellites corresponding to the first pseudorange observation values after the elimination process are all different; if the second judgment result is yes, determining the user position according to the first pseudorange observation value after the elimination process by 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 according to the second pseudorange observation value after the elimination process by using a pseudorange positioning method; if the third judgment result is no, returning to the step of "obtaining a positioning signal".
  • the present 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 connected in sequence; the signal receiving unit is used to obtain 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 used to eliminate the code phase offset and Doppler frequency generated during the transmission of the positioning signal to determine the original 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 the original GNSS signal; the second pseudorange observation value is a pseudorange observation value between a user and a ground station determined according to the 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
  • 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.
  • the signal receiving unit consists of a radio frequency front end and a measurement satellite antenna.
  • the receiver receives the signal transmitted by the ground end or the airborne end through the radio frequency front end, and down-converts the received signal to an intermediate frequency to generate The I and Q intermediate frequency analog signals are then converted to digital and down-converted through the A/D converter to output I and Q intermediate frequency digital signals.
  • the measurement satellite antenna includes modules such as antenna array and power board.
  • the antenna array combines a monopole antenna with a patch antenna, including 1 B1 zero-phase array element and 1 B3 zero-phase array element.
  • the RF/RDSS baseband board includes B1/B3 filter amplifier circuits. The B1/B3 filter amplifier circuit is partially powered by the 5V feed of the receiver board to achieve high-precision measurement control.
  • Baseband signal processing unit
  • 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, it is necessary to perform some related processing on the received signal 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.
  • 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 should also be observed. If the tracking module loses lock, it will jump from the tracking module to the capture module to re-capture, and work in this way.
  • the present invention appropriately increases the cumulative data length of the captured signal, and uses a method combining related accumulation and non-related accumulation to track the GPS signal.
  • the Doppler frequency on the carrier frequency and CA code caused by the relative motion between the satellite and the receiver is crucial for the capture and tracking of satellite navigation signals.
  • the Doppler frequency range generated by the relative motion between the receiver and the satellite is 5KHz, so during the capture process, it is only necessary to search the frequency of the received navigation signal within the 5KHz frequency range centered on the carrier frequency, and the search range for the code phase is one code period of the navigation signal pseudo code sequence, that is, 2046 chips.
  • the capture module will generate a peak at the correct code phase and carrier frequency.
  • a threshold value 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 calculation and consumes a lot of hardware resources. Therefore, the present invention captures signals through an improved parallel search algorithm, reduces the number of searches and the amount of calculation, and improves the capture accuracy.
  • FFT Fast Fourier Transform
  • the present invention divides the received navigation signal into 0 branch (the original received signal) and 0.5 branch (the received signal is offset by 0.5 code chips), multiplies the two branch signals with the local spread spectrum code (CA code) respectively and accumulates the data, and then delays it for one cycle, i.e., 2046 points, and counts whether the positions of the data module values of the two cycles 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.
  • CA code local spread spectrum code
  • i' represents the time delay
  • C(i) represents the i-th code chip
  • fd represents the Doppler frequency
  • Tc represents the code element width
  • ⁇ represents the initial phase.
  • n is a positive integer.
  • N is the number of data
  • R is the FFT transform of point R
  • r is the cumulative output result of the correlator.
  • ⁇ D is the angular frequency
  • f d is the frequency
  • 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, reducing IFFT calculations, greatly shortening the capture time and improving capture efficiency and accuracy.
  • the signal After determining the roughly estimated frequency and code phase value of the received signal, the signal is tracked. Signal tracking is to find the phase conversion of the navigation data and obtain more accurate Doppler frequency and code phase values. Tracking is divided into carrier tracking and code tracking: carrier tracking is to ensure that the local carrier frequency can be consistent with the frequency of the GNSS signal with Doppler frequency shift, so that the carrier can be separated and the accurate spread spectrum code can be obtained, and at the same time, the received signal can be down-converted to the baseband signal; the purpose of code tracking is to separate the pseudo code in the spread spectrum code to obtain the navigation message.
  • the frequency discriminator 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 be able to work. Therefore, after the code chips are aligned, the present invention can obtain partial gain within one code period and a larger range of frequency deviation without obtaining the complete spread spectrum gain.
  • x(n) is the captured signal and c(n) is the local carrier signal.
  • the distance between d(n) and the subsequent data related thereto should be reduced, that is, truncated correlation is performed.
  • the present invention reduces the cumulative length to 1/4 of the code period, thereby expanding the tracking range by 4 times. After a complete spread spectrum code is segmented, multiple frequencies can be obtained, and then these frequencies are averaged to obtain a frequency point as the compensation frequency for the next frame of data.
  • the extended frequency tracking range can be expressed as:
  • M is the base number of the selected multiple phase shift keying (MPSK).
  • each channel tracks the satellite signal independently.
  • Different tracking channels copy the spread spectrum pseudo code and modulated carrier signal of the corresponding satellite respectively, and use the observation vector output by the loop and the demodulated ephemeris parameters for navigation calculation.
  • the geometric position relationship between different satellites to the same user determines that the receiver reference oscillation frequency drift will introduce the same frequency interference in different signal channels, and the dynamic stress effect is also common between different channels.
  • the tracking and navigation solutions of signals from different channels are linked together through a Kalman filter, so that the filter uses the signal parameter results output by each channel to directly estimate the state parameters of the receiver, and then uses the corrected state results to directly control the NCO of each channel to generate the local replica signal of the next cycle, thereby realizing the joint tracking of satellite signals from multiple channels, reducing the noise bandwidth of the loop, improving the loop's tolerance to higher user dynamic stress, and obtaining better signal tracking performance. At the same time, it reduces the number of related integral operations in each tracking loop, greatly shortening the tracking time.
  • 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:
  • ts,k is the signal transmission time
  • t u,k is the time the receiver tracks the current signal
  • c is the speed of light
  • Xr is the true value of the receiver's position at time k
  • Xs is the position where the signal is transmitted.
  • the real Doppler frequency shift of the received signal at time k can be expressed as:
  • V r,k is the signal transmission speed
  • V s,k is the speed at which the receiver tracks the current signal
  • f 1 is the signal frequency
  • T represents transposition
  • the data processing unit is used to calculate the pseudo-range observation between the satellite and the user obtained by the GNSS signal or the pseudo-range observation between the user and the ground station obtained by the LDACS signal.
  • the GNSS signal pseudo code or LDACS signal pseudo code output by the processing unit.
  • bit synchronization is to find the phase edge of the navigation data bit so that the received signal can be divided bit by bit.
  • frame synchronization is to find the subframe edge of the navigation message so that every 30 data bits can be divided into meaningful words, so as to interpret the required navigation message parameters from the words.
  • the baseband processing unit 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, so as to obtain the pseudorange observation value between the satellite and the user and input it into the abnormal signal monitoring unit;
  • 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 distance value actually measured between the satellite and the receiver (or between receivers) is not the true distance, so it is called pseudorange.
  • ⁇ is the pseudorange
  • r is the actual distance between the receiver and the satellite
  • c is the speed of light
  • ⁇ t is the clock error, which includes the conventional clock error term of the receiver, clock delay, signal propagation delay of the phase center of the receiver antenna at the coordinate point, and the clock error noise term of the unmodeled error
  • I is the ionospheric delay
  • T is the tropospheric delay
  • ⁇ p is the noise.
  • 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 calculating the ionospheric delay by performing linear combination.
  • ⁇ GNSS is the pseudorange observation between the satellite and the user obtained from the corrected GNSS signal
  • ⁇ 1 is the pseudorange observation on the carrier L1 signal
  • ⁇ 2 is the pseudorange observation on the carrier L2 signal
  • f 1 is the frequency of the carrier L1
  • f 1 1575.42 MHz
  • f 2 is the frequency of the carrier L2.
  • the noise term is not considered.
  • the orbital ephemeris based on the data of the LDACS airborne terminal is constant, and the delay caused by the troposphere to the signal does not need to be considered.
  • the pseudorange measurements on the forward and reverse links of the ground station ranging source are linearly combined to calculate the ionospheric delay to correct the pseudorange.
  • ⁇ LDACS is the pseudorange observation between the user and the ground station obtained by the corrected LDACS signal
  • ⁇ F is the pseudorange observation transmitted from the ground station ranging source to the airborne end through the forward link
  • ⁇ R is the pseudorange observation 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.
  • 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 certain 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 during this time interval is averaged as a reference value for judging rationality.
  • ⁇ (i) is the pseudorange at time i
  • ⁇ (i-1) is the pseudorange at time i-1.
  • the present invention sets the maximum difference of the pseudorange difference between the previous and next epochs as the threshold value t of the pseudorange rationality, that is:
  • N is a positive integer.
  • ⁇ (m) is the pseudorange at epoch m
  • ⁇ (m-1) is the pseudorange at epoch m-1.
  • the positioning solution unit receives the correct pseudorange value input by the abnormal signal monitoring unit for 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.
  • the LDACS communication system is inspired by modern ground mobile communication networks, and many aspects of its functions can be achieved by similar methods. If the LDACS airborne receiver mobile receiver can receive a sufficient number of ground station signal sources, its position can be determined by trilateration or multilateration. At cruising altitude, the aircraft usually receives data transmitted synchronously by multiple ground stations on different frequencies through the forward link within its wireless television field, so the aircraft can perform independent distance measurements on all visible ground stations.
  • the LDACS airborne terminal can be positioned using principles similar to satellite positioning, and ranging positioning is performed based on the arrival time ranging principle. Therefore, the positioning algorithm can be positioned using the pseudo-range positioning method like GNSS signals.
  • the user position is solved by the pseudo-range positioning method.
  • the LDACS A2A information is used to assist positioning, otherwise it cannot be positioned.
  • the positioning solution is performed using the pseudorange positioning method.
  • the actual distance measured by the nth satellite can be expressed as
  • ⁇ n is the pseudorange of the nth satellite
  • xn is the x-coordinate of the nth satellite
  • z n is the z coordinate of the nth satellite
  • ⁇ t is the satellite receiver clock difference
  • ⁇ p is the total delay in the troposphere and ionosphere.
  • the pseudorange observation equation is a nonlinear equation. Before using the least squares method for position solution, the pseudorange equation needs to be linearized. Therefore, the present invention chooses to use the first-order Taylor series expansion method for positioning solution.
  • ⁇ t is a high-order term.
  • the solution obtained by Taylor's first-order expansion is an approximate solution with a certain linear range, and a certain number of iterative calculations are required to continuously approach the true value.
  • the geometric dilution of precision is often used to evaluate positioning accuracy. It represents the distance vector amplification factor between the receiver and the space satellite caused by the ranging error. The smaller the GDOP, the higher the positioning accuracy.
  • GDOP is calculated based on the satellite state matrix by the direction cosine method. Assuming that ⁇ , ⁇ , and ⁇ 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:
  • the subscript of each element in the matrix represents the position in the matrix.
  • W is the weight matrix, which reflects the uncertainty of the ranging source error.
  • the positioning error can be modeled as:
  • the position estimate that minimizes the sum of squared errors is obtained by the least squares method.
  • X represents the x-coordinate obtained by the least squares method.
  • the weighted norm of the residual vector obeys a central ⁇ 2 distribution with N-2 degrees of freedom (N is the total number of visible satellites).
  • the model with high ranging accuracy and accurate position estimation value and its covariance matrix can be modeled as:
  • the LDACS A2A assisted positioning method is used to solve the user position.
  • the ranging range can be modeled as having a standard deviation of An unbiased estimate of :
  • the position estimation based on the high-altitude ranging source in low-altitude flight can be modeled as:
  • ⁇ is the covariance matrix of the user location estimation model.
  • the present invention proposes a hybrid positioning algorithm to obtain the best positioning accuracy.
  • the present invention uses Bancroft's direct position calculation method to calculate the rough position, and then uses the Gauss-Newton iterative algorithm to iteratively converge to the precise position solution.
  • the specific process of this algorithm is as follows:
  • Sn is the three-dimensional coordinate of the nth ranging source
  • ⁇ n is the pseudorange of the nth ranging source
  • a parameter Qi ,k is defined to describe the positioning confidence of aircraft i in the kth positioning estimation, and its value range is (0,1].
  • each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments.
  • the same or similar parts between the embodiments can be referred to each other.
  • the description is relatively simple, and the relevant parts can be referred to the method part.

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Abstract

一种机载定位完好性监测方法及装置，方法包括：获取定位信号；消除定位信号传输过程中产生的码相位偏移和多普勒频率，确定原始定位信号；确定第一伪距观测量和第二伪距观测量；第一伪距观测量为根据原始GNSS信号确定的卫星和用户之间的伪距观测量；第二伪距观测量为根据原始LDACS信号确定的用户和地面站之间的伪距观测量；对第一伪距观测量和第二伪距观测量进行异常剔除处理；根据异常剔除处理后的第一伪距观测量和异常剔除处理后的第二伪距观测量进行定位解算，确定用户的定位结果；通过异常剔除处理和消除定位信号传输过程中产生的码相位偏移和多普勒频率，能够提高机载定位的精度。

Description

一种机载定位完好性监测方法及装置 技术领域
本发明涉及航空导航技术领域，特别是涉及一种机载定位完好性监测方法及装置。
背景技术
近年来，中国航天事业进入了新阶段，大量现代化通信产品不断涌入人类的生活，无线定位系统所提供的位置服务在人类日常生活工作中扮演的角色越来越重要。全球卫星导航系统(Global Navigation Satellite System，GNSS)凭借极佳的泛用性以及高效率、高精度和实时不间断监测等特性被市场深度接纳。现有GNSS方案在大型商场、山区峡谷或城市隧道等复杂环境下会受到干扰：用户可见星数目减少，卫星几何构型变差，导致定位精度下降、完好性风险增大，定位结果的可用性和连续性无法保证。
GNSS的发展面临诸多挑战，其中定位精度和完好性监测是最亟待解决的问题，由于地面的遮挡容易造成低海拔地区的用户能见度差异较大，几何多样性较差，以及长距离信号传输的误差和延迟，GNSS信号的可用性受到很大的限制，制约着GNSS的导航性能。
发明内容
本发明的目的是提供一种机载定位完好性监测方法及装置，能够提高机载定位的精度。
为实现上述目的，本发明提供了如下方案：
一种机载定位完好性监测方法，包括：
获取定位信号；所述定位信号包括GNSS信号和LDACS信号；所述LDACS信号包括LDACS前向链路信号和LDACS反向链路信号；
消除定位信号传输过程中产生的码相位偏移和多普勒频率，确定原始定位信号；
确定第一伪距观测量和第二伪距观测量；所述第一伪距观测量为根据原始GNSS信号确定的卫星和用户之间的伪距观测量；所述第二伪距观测量为 根据原始LDACS信号确定的用户和地面站之间的伪距观测量；
对所述第一伪距观测量和所述第二伪距观测量进行异常剔除处理；
根据异常剔除处理后的第一伪距观测量和异常剔除处理后的第二伪距观测量进行定位解算，确定用户的定位结果。
可选的，所述获取定位信号，包括：
获取定位信号；
对所述定位信号进行下变频处理，得到下变频处理后的定位信号；
将所述下变频处理后的定位信号进行模数转换处理，得到数字信号形式的定位信号。
可选的，消除定位信号传输过程中产生的码相位偏移和多普勒频率，包括：
利用改进并行搜索算法对所述定位信号进行捕获处理；
在捕获成功后对捕获的定位信号进行跟踪处理，，以消除定位信号传输过程中产生的码相位偏移和多普勒频率。
可选的，所述改进并行搜索算法包括：
将定位信号确定为第一支路定位信号；
将第一支路定位信号与本地扩频码相乘，将乘积在一个周期内进行数据累加处理，确定周期内数据模值的位置为第一位置；
将定位信号进行码片偏移，得到第二支路定位信号；
将第二支路定位信号与本地扩频码相乘，将乘积在一个周期内进行数据累加处理，确定周期内数据模值的位置为第二位置；
判断第一位置和第二位置是否相同，得到第一判断结果：
若第一判断结果为是，则判定定位信号捕获成功；
若第一判断结果为否，则判定定位信号捕获不成功，更新定位信号，并返回步骤“将定位信号确定为第一支路定位信号”。
可选的，对所述第一伪距观测量和所述第二伪距观测量进行异常剔除处理，包括：
删除接收间隔大于第一接收间隔时对应的第一伪距观测量；
删除接收间隔大于第二接收间隔时对应的第二伪距观测量。
可选的，所述根据异常剔除处理后的第一伪距观测量和异常剔除处理后的第二伪距观测量进行定位解算，确定用户的定位结果，包括：
判断是否满足GNSS定位条件，得到第二判断结果；所述GNSS定位条件为存在至少4个剔除处理后的第一伪距观测量；且剔除处理后的第一伪距观测量对应的卫星均不同；
若第二判断结果为是，则根据剔除处理后的第一伪距观测量，利用一阶泰勒级数展开法和最小二乘法确定用户位置；
若第二判断结果为否，则判断是否满足LDACS定位条件，得到第三判断结果；
若第三判断结果为是，则根据剔除处理后的第二伪距观测量，利用伪距定位法确定用户位置；
若第三判断结果为否，返回步骤“获取定位信号”。
一种机载定位完好性监测装置，包括：依次连接的信号接收单元、基带信号处理单元、数据处理单元、异常信号监测单元和定位解算单元；
所述信号接收单元用于获取定位信号；所述定位信号包括GNSS信号和LDACS信号；所述LDACS信号包括LDACS前向链路信号和LDACS反向链路信号；
所述基带信号处理单元用于消除定位信号传输过程中产生的码相位偏移和多普勒频率，确定原始定位信号；
所述数据处理单元用于确定第一伪距观测量和第二伪距观测量；所述第一伪距观测量为根据原始GNSS信号确定的卫星和用户之间的伪距观测量；所述第二伪距观测量为根据原始LDACS信号确定的用户和地面站之间的伪距观测量；
所述异常信号监测单元用于对所述第一伪距观测量和所述第二伪距观测量进行异常剔除处理；
所述定位解算单元用于根据异常剔除处理后的第一伪距观测量和异常剔除处理后的第二伪距观测量进行定位解算，确定用户的定位结果。
可选的，所述信号接收单元包括：射频前端和卫星天线；
所述射频前端与所述卫星天线和所述基带信号处理单元连接；
所述卫星天线用于接收所述定位信号；
所述射频前端用于对所述定位信号进行变频处理和模数转换处理。
根据本发明提供的具体实施例，本发明公开了以下技术效果：
本发明提供的机载定位完好性监测方法及装置，方法包括：获取定位信号；消除定位信号传输过程中产生的码相位偏移和多普勒频率，确定原始定位信号；确定第一伪距观测量和第二伪距观测量；所述第一伪距观测量为根据原始GNSS信号确定的卫星和用户之间的伪距观测量；所述第二伪距观测量为根据原始LDACS信号确定的用户和地面站之间的伪距观测量；对所述第一伪距观测量和所述第二伪距观测量进行异常剔除处理；根据异常剔除处理后的第一伪距观测量和异常剔除处理后的第二伪距观测量进行定位解算，确定用户的定位结果。本发明通过异常剔除处理和消除定位信号传输过程中产生的码相位偏移和多普勒频率，能够提高机载定位的精度。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动性的前提下，还可以根据这些附图获得其他的附图。
图1为本发明实施例1机载定位完好性监测方法流程图；
图2为本发明实施例2机载定位完好性监测装置原理图；
图3为本发明实施例2中基带信号处理单元工作流程图；
图4为本发明实施例2中捕获算法工作流程图；
图5为本发明实施例2中跟踪算法工作流程图；
图6为本发明实施例2中LDACS地面站定位原理图；
图7为本发明实施例2中LDACS A2A辅助定位定位原理图。
具体实施方式
下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做 出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
本发明的目的是提供一种机载定位完好性监测方法及装置，能够提高机载定位的精度。
为使本发明的上述目的、特征和优点能够更加明显易懂，下面结合附图和具体实施方式对本发明作进一步详细的说明。
由于GNSS对欺骗攻击和故意干扰的脆弱性，以及在某些操作环境中性能下降等原因，现在的学者和机构正在寻求一种替代定位导航授时(Alternative Positioning Navigation and Timing，APNT)的解决方案，以在GNSS无法满足高质量需求的情况下保证高效安全的服务。目前，美国的下一代航空运输系统(Next Generation Air Transportation System，NextGen)以及欧洲的单一天空空中交通管理研究项目(Single European Sky ATM Research，SESAR)都针对APNT开展研究并提出了一些备选方案，L波段数字航空通信系统(L-band Digital Aeronautical Communications System，LDACS)正是其中一种。
LDACS是一种基于蜂窝的未来航空通信系统，旨在取代目前容量和可用安全措施有限的空地通信技术，其为空对地(Air to Ground，A2G)通信提供了一种数字宽带无线电链路，可实现飞机和地面基础设施之间的连接，支持地面站和机载端之间的数据和语音通信。LDACS工作在960MHz-1164MHz频段，具有点对多点连接的蜂窝结构，地面部分包含多个地面站，每个地面站控制着高达200海里的空域范围内的最多512个机载设备。当带有各自无线电通信单元的飞机飞越该区域时可通过时分多址(Time Division Multiple Access，TDMA)和正交频分多址(Orthogonal Frequency Division Multiple Access，OFDMA)的全双工无线电链路连接到同一个地面站，机载端通过前向链路接收地面站发射的导航信息，同时通过反向链路向地面站传输导航信息。同时LDACS还支持空空(Air-to-air，A2A)通信，接受其他机载端的导航信息。本发明结合LDACS技术，提供了一种一种机载定位完好性监测方法及装置，能够提高机载定位的精度，具体如下：
实施例1
如图1所示，本实施例提供了一种机载定位完好性监测方法，包括：
步骤101：获取定位信号；所述定位信号包括GNSS信号和LDACS信号；所述LDACS信号包括LDACS前向链路信号和LDACS反向链路信号；
步骤102：消除定位信号传输过程中产生的码相位偏移和多普勒频率，确定原始定位信号；
步骤103：确定第一伪距观测量和第二伪距观测量；所述第一伪距观测量为根据原始GNSS信号确定的卫星和用户之间的伪距观测量；所述第二伪距观测量为根据原始LDACS信号确定的用户和地面站之间的伪距观测量；
步骤104：对所述第一伪距观测量和所述第二伪距观测量进行异常剔除处理；
步骤105：根据异常剔除处理后的第一伪距观测量和异常剔除处理后的第二伪距观测量进行定位解算，确定用户的定位结果。
所述获取定位信号，包括：获取定位信号；对所述定位信号进行下变频处理，得到下变频处理后的定位信号；将所述下变频处理后的定位信号进行模数转换处理，得到数字信号形式的定位信号。
具体的，测量和异常消除定位信号传输过程中产生的码相位偏移和多普勒频率，包括：利用改进并行搜索算法对所述定位信号进行捕获处理；在捕获成功后对捕获的定位信号进行跟踪处理，，以消除定位信号传输过程中产生的码相位偏移和多普勒频率。
其中，所述改进并行搜索算法包括：将定位信号确定为第一支路定位信号；将第一支路定位信号与本地扩频码相乘，将乘积在一个周期内进行数据累加处理，确定周期内数据模值的位置为第一位置；将定位信号进行码片偏移，得到第二支路定位信号；将第二支路定位信号与本地扩频码相乘，将乘积在一个周期内进行数据累加处理，确定周期内数据模值的位置为第二位置判断第一位置和第二位置是否相同，得到第一判断结果：若第一判断结果为是，则判定定位信号捕获成功；若第一判断结果为否，则判定定位信号捕获不成功，更新定位信号，并返回步骤“将定位信号确定为第一支路定位信号”。
所述对所述第一伪距观测量和所述第二伪距观测量进行异常剔除处理，包括：删除接收间隔大于第一接收间隔时对应的第一伪距观测量；删除接收间隔大于第二接收间隔时对应的第二伪距观测量。
所述根据异常剔除处理后的第一伪距观测量和异常剔除处理后的第二伪距观测量进行定位解算，确定用户的定位结果，包括：判断是否满足GNSS定位条件，得到第二判断结果；所述GNSS定位条件为存在至少4个剔除处理后的第一伪距观测量；且剔除处理后的第一伪距观测量对应的卫星均不同；若第二判断结果为是，则根据剔除处理后的第一伪距观测量，利用一阶泰勒级数展开法和最小二乘法确定用户位置；若第二判断结果为否，则判断是否满足LDACS定位条件，得到第三判断结果；若第三判断结果为是，则根据剔除处理后的第二伪距观测量，利用伪距定位法确定用户位置；若第三判断结果为否，返回步骤“获取定位信号”。
实施例2
本实施例提供了一种机载定位完好性监测装置，包括：依次连接的信号接收单元、基带信号处理单元、数据处理单元、异常信号监测单元和定位解算单元；所述信号接收单元用于获取定位信号；所述定位信号包括GNSS信号和LDACS信号；所述LDACS信号包括LDACS前向链路信号和LDACS反向链路信号；所述基带信号处理单元用于消除定位信号传输过程中产生的码相位偏移和多普勒频率，确定原始定位信号；所述数据处理单元用于确定第一伪距观测量和第二伪距观测量；所述第一伪距观测量为根据原始GNSS信号确定的卫星和用户之间的伪距观测量；所述第二伪距观测量为根据原始LDACS信号确定的用户和地面站之间的伪距观测量；所述异常信号监测单元用于对所述第一伪距观测量和所述第二伪距观测量进行异常剔除处理；所述定位解算单元用于根据异常剔除处理后的第一伪距观测量和异常剔除处理后的第二伪距观测量进行定位解算，确定用户的定位结果。其中，所述信号接收单元包括：射频前端和卫星天线；所述射频前端与所述卫星天线和所述基带信号处理单元连接；所述卫星天线用于接收所述定位信号；所述射频前端用于对所述定位信号进行变频处理和模数转换处理。下面，对本实施例作具体说明：
1.信号接收单元：
信号接收单元由射频前端和测量型卫星天线组成。接收机通过射频前端接收地面端或者机载端传输的信号，并将接收到的信号下变频至中频，产生 I、Q两路中频模拟信号，然后通过A/D转化器完成数模转换和数字下变频输出I、Q中频数字信号。
测量型卫星天线包括天线阵列和电源板等模块。其中，天线阵列将单极天线与贴片天线相结合，包括1个B1零相位阵元、1个B3零相位阵元，射频/RDSS基带板包括B1/B3滤波放大电路。B1/B3滤波放大电路部分由接收机板5V馈电供电，以实现高精度测量控制。
2.基带信号处理单元：
基带信号处理单元是导航接收机的核心部分，该模块主要是为了尽量消除在传输过程中产生的码相位偏移和多普勒频率，使得在接收端能够准确的恢复出原始信号。由于导航接收机与卫星之间存在相对运动，从而产生多普勒频移和码相位偏移，接收到的信号的载波频率和码相位与所发射的信号不一致，导致无法精确定位，因此需要对接收到的信号进行一些相关处理来消除由于运动而造成的影响，即载波频率与码相位的捕获和跟踪。捕获与跟踪相辅相成，通过不断调整本地伪码序列的初始相位，使其与接收到的号航信号的码相位误差在0.5个码片范围内，则捕获成功，捕获模块停止工作跳转至跟踪模块，否则继续捕获。同时还要观察跟踪模块，若跟踪模块失锁则从跟踪模块再跳转至捕获模块重新进行捕获，如此周而复始的进行工作。基于高精度定位需求，本发明适当的增加捕获信号的累加数据长度，采用相关累积和非相关累积相结合的方法对GPS信号进行跟踪。
2.1搜索
在实际生活当中，由于卫星与接收机之间的相对运动而引起载频和CA码上的多普勒频率对于卫星导航信号的捕获和跟踪来说是至关重要的。通常由接收机和卫星之间的相对运动而产生的多普勒频率的范围为5KHz，因此在捕获过程中只需以载波频率为中心的5KHz频率范围内对接收到的导航信号进行频率搜索，而对于码相位的搜索范围则是导航信号伪码序列的一个码周期即2046个码片。
2.2捕获
一旦搜索到信号，则捕获模块就会在正确的码相位和载波频率处产生一个波峰，为了判断该峰值是否代表真实的信号，必须设置一个门限值。如果 波峰大于该门限值，则就是所需要的信号，否则就不是。现有的时域串行搜索捕获算法实现相对简单，但其捕获时间比较长，基于快速傅里叶变换((Fast Fourier Transform，FFT)的频域并行搜索捕获算法计算量大，硬件资源消耗大，因而本发明通过改进的并行搜索算法捕获信号，减少搜索次数和计算量的同时提高捕获精度。
本发明将接收到的导航信号分为0支路(接收到的原始信号)和0.5支路(将接收到的信号进行0.5码片的偏移)，两个支路信号分别与本地扩频码(CA码)相乘并累加数据，再将其延时一个周期即2046个点，统计两周期数据模值所在位置是否相同，若相同则捕获成功转接跟踪环节；若不相同则重新捕获直到捕获成功。
为方便讨论，只考虑接收到的信号，不考虑噪声及其他干扰，假设进入捕获模块进行捕获的输入信号：
其中i'表示时延，C(i)表示第i个码片，fd表示多普勒频率，Tc表示码元宽度；Φ表示初始相位。
相关器累加输出的结果：
其中p表示匹配滤波器的长度；n为正整数。
对其进行R点的FFT：
N为数据个数，R为R点的FFT变换，r为相关器累加输出结果。
最后对其进行N点的延时相乘取均值：
其中，这是一个参数，ωD为角频率，fd为频率。
改进型的并行搜索捕获算法对接收信号进行存储偏移，而本地C/A码保持不动，且不需要设置阈值门限，只需要记录每帧所在的位置，减少IFFT计算大大缩短捕获时间，提高捕获效率和精度。
2.3跟踪
在确定了接收信号粗略估计的频率和码相位值后，对该信号进行跟踪处理。信号跟踪是为了找出导航数据的相位转换，得到较为准确的多普勒频率和码相位值。跟踪分为载波跟踪和码跟踪：载波跟踪是为了保证本地载波频率能够和有多普勒频移的GNSS信号的频率保持一致，以便能够分离载波，得到精确的扩频码，同时也是为了让接收信号能够下变频到基带信号；码跟踪的目的是为了分离扩频码中的伪码，从而得到导航电文。
由于鉴频器存在跟踪上限，若残留的频偏太大，超过了锁频环跟踪的极限，那么锁频环将无法工作，因此本发明在码片对齐以后，可以在不获取完整扩频增益的情况下，在一个码周期内部分增益，并获得较大范围的频偏。
假设接收到的信号去除本地码以后的信号为：
d(n)＝x(n)*c(n)(5)
其中，x(n)为捕获信号，c(n)为本地载波信号。
要想扩大频偏估计范围，要降低d(n)以及与之相关的后续数据的距离，即进行截断相关。本发明将累加长度缩减为1/4个码周期，因而跟踪范围扩大4倍，将一个完整的扩频码进行分段处理后可以得到多个频率，再将这些频率进行均值处理得到一个频点，作为对下一帧数据的补偿频率。
扩展的频率跟踪范围可以表示为：
其中M为选用的多进制数字相位调制(Multiple Phase Shift Keying，MPSK)的进制数。
多普勒频率经过锁频环进行跟踪补偿后仍残留有较小的频偏，使得解调时无法得到正确的导航信号，因而需要进一步的锁定补偿，即通过锁相环(PLL)进行跟踪补偿。
传统的软件接收机跟踪环路中，各个通道对卫星信号的跟踪是相互独立的，不同跟踪通道分别复制相应卫星的扩频伪码与调制载波信号，利用环路输出的观测向量及解调出的星历参数进行导航解算，但不同卫星到同一用户的几何位置关系决定了接收机基准振荡频率漂移在各个不同信号通道中会引入相同的频率干扰，动态应力作用在不同通道之间也是共同的。因此，将 不同通道信号的跟踪与导航解算通过一个卡尔曼滤波器联系在一起，使得滤波器利用各个通道输出的信号参量结果直接对接收机的状态参量进行估计，再利用校正后的状态结果直接控制各通道NCO生成下一周期本地复制信号，实现对多个通道卫星信号的联合跟踪，降低环路的噪声带宽，提高环路对更高用户动态应力的容忍能力，获得更好的信号跟踪性能，同时减少各个跟踪环路中的相关积分运算次数，大大缩短跟踪时间。
在接收机信号处理过程中，k时刻信号发射时刻估计值与跟踪环路中本地复制伪码信号相位关系可以表示为:
其中ts，k为信号发射时间，tu，k为接收机对当前信号跟踪的时间，c为光速，Xr为接收机k时刻所在位置的真实值，而Xs为信号发射所在位置，
根据多普勒信号的生成原理，可得k时刻接收信号的真实多普勒频移表示形式为：
其中Vr，k是为信号发射速度，Vs，k为接收机对当前信号跟踪的速度，f1为信号频率，T表示转置。
本地复制信号的估计多普勒频移表示形式为：
其中，为估计的信号发射速度，为估计的接收机位置，δfu,k为k时刻接收机频率。
矢量跟踪环路复制信号具体控制方式为：
其中，为多普勒频移导致的速度的真实值与估计值之差，为信号发射速度的真实值与估计值之差。
3.数据处理单元
数据处理单元用于计算GNSS信号所得卫星和用户之间的伪距观测量或者LDACS信号所得用户和地面站之间的伪距观测量，输入为基带信号处 理单元输出的GNSS信号伪码或者LDACS信号伪码。
接收到的信号通过捕获和跟踪后还需经过位同步和帧同步才能获得导航信息，位同步的目的是找到导航数据比特的相位边沿以实现将接收信号按照一比特接着一比特划分开来。而帧同步的目的则是找到导航电文的子帧边沿以实现每30个数据比特被划分成一个个有意义的字，从而从字中解译出所需的导航电文参数。
对于GNSS信号，基带处理单元输出GNSS观测值的伪码，通过数据处理单元的位同步解算导航电文，通过帧同步得到星历信息解算卫星三维位置，从而得到卫星和用户之间的伪距观测量并输入异常信号监测单元；对于LDACS信号，基带信号处理单元输出LDACS观测值的伪码，通过数据处理单元的位同步解算导航电文，通过帧同步得到伪距观测量、其他用户位置等A2A信息，并将得到的用户和地面站之间的伪距观测量输入异常信号监测单元；由于接收机和卫星时钟不同步，加上测量时会有电离层误差、对流层误差及其它测距误差，实际测量的卫星和接收机之间(或接收机与接收机之间)的距离值并不是真正的距离，因而叫做伪距。伪距的观测方程如下：
ρ＝r+cδt+cI+cT+εp(11)
其中，ρ是伪距，r是接收机和卫星的实际距离，c是光速，δt是钟差，其中包含了接收机常规钟差项、时钟延迟、坐标点接收机天线相位中心的信号传播延迟以及未建模误差的钟差噪声项，I是电离层延时，T是对流层延时，εp是噪声。
对于GNSS信号，不考虑噪声项，等式(11)中等号右边对流层延迟、实际距离和钟差项均为常数，可通过接收同一时刻同一颗卫星的L1和L2信号上的伪距测量值并进行线性组合计算电离层延时来矫正伪距。
其中，ρGNSS为校正后的GNSS信号所得卫星和用户之间的伪距观测量，ρ1为载波L1信号上的伪距观测量，ρ2为载波L2信号上的伪距观测量，f1为载波L1的频率，f1＝1575.42MHz，f2为载波L2的频率。
对于LDACS信号，不考虑噪声项，基于LDACS机载端的数据的轨道星历为常数，不需要考虑对流层对信号造成的延时，可通过接收同一机载端 和地面站测距源正向链路和反向链路上的伪距测量值进行线性组合计算电离层延时来矫正伪距。
其中，ρLDACS为校正后的LDACS信号所得用户和地面站之间的伪距观测量，ρF为地面站测距源通过正向链路传输给机载端的伪距观测量，ρR为机载端通过反向链路传输给地面站的伪距观测量，fF为正向链路的频率，fR为反向链路的频率。
4.异常信号监测单元
异常信号监测单元根据数据处理单元输出的GNSS信号所得卫星和用户之间的伪距观测量或者LDACS信号所得用户和地面站之间的伪距观测量判断信号接收是否正常、伪距值是否合理。如果超过10分钟无法接收到某一卫星数据，则该卫星数据接收异常，发出异常警告信号并对异常卫星采取剔除处理。之后对数据接收正常的卫星信号，进行合理性判断，设定一定时间间隔，将这段时间间隔内所有历元的伪距或机载端相对位置的差值平均处理作为判断合理性的参考值。若某一历元的差值与参考值的差异超出预定门限值，则判断为异常，发出异常警告信号并对异常卫星采取剔除处理，停止使用该卫星进行定位。合理性判断计算公式如下：
其中，为伪距的均值，ρ(i)为i时刻的伪距，ρ(i-1)为i-1时刻的伪距。
对于理想信号，先后两个历元的差值和载波相位差值应相等，但由于受到多径等因素的影响，会造成其结果不一致，故本发明将前后历元中伪距差值的最大差值设置为伪距合理性的门限值t，即：
其中，N为正整数。
则某一时刻m的合理性监测公式如下：
其中，ρ(m)为m历元的伪距，ρ(m-1)为m-1历元的伪距。
判断当前历元m是否满足上述公式，如满足则该历元符合合理性，可利 用该历元进行定位解算，否则该历元不符合伪距合理性，不可利用该历元进行定位解算，剔除不合理的值。
5.定位解算单元
定位解算单元接收异常信号监测单元输入的正确的伪距值进行定位解算，并根据正常的伪距值数量将定位解算分为伪距定位法和LDACS信号辅助定位法输入为软件接收机异常信号监测单元输出的正确的观测量数据，输出为精确的定位结果。
LDACS通信系统受到现代地面移动通信网络的启发，许多方面的功能可通过类似的方法实现。如果LDACS机载端接收机移动接收器能够接收到足够数量的地面站信号源，利用三边测量或多边测量则能够确定其位置。在巡航高度，飞机通常会在其无线电视界内接收到多个地面站通过前向链路在不同频率上同步传输的数据，因此飞机可以对所有可见的地面站进行独立的距离测量。可以利用类似卫星定位的原理对LDACS机载端进行定位，基于到达时间测距原理进行测距定位，因此在定位算法上可与GNSS信号一样利用伪距定位法定位。当存在4个不同的GNSS信号所得卫星和用户之间的伪距观测量或者LDACS信号所得用户和地面站之间的伪距观测量时，利用伪距定位法解算用户位置，当存在3个LDACS信号，利用LDACS A2A信息辅助定位，否则不可定位。
5.1伪距定位法
当存在4个不同的正确卫星伪距值时，通过伪距定位法进行定位解算，根据式(11)可将第n颗卫星测量得的实际距离可以表示成
其中，r为真实距离，ρn为第n颗卫星的伪距，xn为第n颗卫星的x坐标，为地面站x坐标；为第n颗卫星的y坐标；为地面站y坐标；zn为第n颗卫星的z坐标；为地面站z坐标，δt为卫星接收机时钟差；εp为对流层和电离层总延迟。
此方程中有四个未知数，至少需四个地面站数据。从上式可以看出，伪距观测方程为非线性方程，使用最小二乘法进行位置解算之前需要将伪距方程线性化，因此本发明选择运用一阶泰勒级数展开的方法进行定位解算。
伪距方程进行一阶泰勒级数展开为：




δt为高阶项。通过泰勒一阶展开计算得到的解是一种近似解，具有一定的线性范围，需通过一定次数的迭代计算来不断逼近真实值。
常采用几何精度因子(GDOP)来评定定位精度，其代表测距误差造成的接收机与空间卫星间的距离矢量放大因子，GDOP越小表明定位精度越高。GDOP基于卫星状态矩阵通过方向余弦法来计算，假设α、β、γ分别为飞机与X、Y、Z轴间的夹角，则第一状态矩阵Q、第二状态矩阵DOP和第三状态矩阵GDOP为：

矩阵中每个元素下标代表矩阵中的位置。
计算测距源位置的协方差矩阵Σ为：
Σ＝(QTWQ)-1(26)
其中，W是权重矩阵，反映了测距源误差的不确定度。
定位误差可建模为：
其中为测距误差相关模型，表示接收机处信号跟踪所导致的测量 噪声。
由最小二乘法得到使得测距误差平方和最小的位置估计
其中，X表示由最小二乘法得到的x坐标。
测距残差矢量表示为：
其在无故障条件下，残差向量的加权范数服从自由度为N-2的中心χ2分布(N为可视卫星总数)。
此时测距精度高具有准确的位置估计值及其协方差矩阵的模型，其位置估计可以建模为：
其中为用户的位置估计值，由协方差矩阵Σ通过公式(26)建模而得；为用户位置估计模型误差。y表示真实的位置；表示估计的位置。
5.2 LDACS A2A辅助定位法
当地面站测距源被遮挡的情况较为严重时，机载端接收到的地面站测距源数量少于4个，无法利用伪距定位法解算用户位置，则利用LDACS A2A辅助定位法解算用户位置。
假设已知的范围误差分布建模为零均值高斯，测距范围可建模为标准偏差为的无偏估计：
基于此，低空飞行情况下根据高空测距源进行测距的位置估计可以建模为：
其中为用户的位置估计值，由协方差矩阵Σ通过公式(1)建模而得；Σ为用户位置估计模型的协方差矩阵。
由于地面站测距源被遮挡的情况较为严重，其几何形状使定位难以实现，故本发明提出混合定位算法来获得最佳定位精度。本发明使用Bancroft的直接位置计算方法计算粗略位置，然后运用高斯-牛顿迭代算法迭代收敛至精确位置解，本算法的具体流程如下：
首先，创建测距源位置和伪距的初始矩阵X和Yn：

其中Sn为第n个测距源的三维坐标，ρn为第n个测距源的伪距。
接下来，定义矩阵A、B和C创建一元二次方程方程组：



Aλ2+2Bλ+C＝0  (38)
通过迭代方程(38)，所得的两个解λ1和λ2即为最终的定位解。
本实施例定义参数Qi,k来描述第k次定位估计时i号飞机的定位置信度，其取值范围是(0,1]。当接收到地面端信号时，修正当前的定位估计，并令Qi,k＝1表示当前定位可信；当地面端信号时，令Qi,k＝0.95，表示定位置信度随所处环境变化而逐渐缩小。
其中，表示第k次定位时由(38)解算出的结果，||*||为运算符。
本说明书中各个实施例采用递进的方式描述，每个实施例重点说明的都是与其他实施例的不同之处，各个实施例之间相同相似部分互相参见即可。对于实施例公开的系统而言，由于其与实施例公开的方法相对应，所以描述的比较简单，相关之处参见方法部分说明即可。
本文中应用了具体个例对本发明的原理及实施方式进行了阐述，以上实施例的说明只是用于帮助理解本发明的方法及其核心思想；同时，对于本领域的一般技术人员，依据本发明的思想，在具体实施方式及应用范围上均会有改变之处。综上所述，本说明书内容不应理解为对本发明的限制。

Claims (8)

  1. 一种机载定位完好性监测方法，其特征在于，包括：
    获取定位信号；所述定位信号包括GNSS信号和LDACS信号；所述LDACS信号包括LDACS前向链路信号和LDACS反向链路信号；
    消除定位信号传输过程中产生的码相位偏移和多普勒频率，确定原始定位信号；
    确定第一伪距观测量和第二伪距观测量；所述第一伪距观测量为根据原始GNSS信号确定的卫星和用户之间的伪距观测量；所述第二伪距观测量为根据原始LDACS信号确定的用户和地面站之间的伪距观测量；
    对所述第一伪距观测量和所述第二伪距观测量进行异常剔除处理；
    根据异常剔除处理后的第一伪距观测量和异常剔除处理后的第二伪距观测量进行定位解算，确定用户的定位结果。
  2. 根据权利要求1所述的一种机载定位完好性监测方法，其特征在于，所述获取定位信号，包括：
    获取定位信号；
    对所述定位信号进行下变频处理，得到下变频处理后的定位信号；
    将所述下变频处理后的定位信号进行模数转换处理，得到数字信号形式的定位信号。
  3. 根据权利要求1所述的一种机载定位完好性监测方法，其特征在于，消除定位信号传输过程中产生的码相位偏移和多普勒频率，包括：
    利用改进并行搜索算法对所述定位信号进行捕获处理；
    在捕获成功后对捕获的定位信号进行跟踪处理，，以消除定位信号传输过程中产生的码相位偏移和多普勒频率。
  4. 根据权利要求1所述的一种机载定位完好性监测方法，其特征在于，所述改进并行搜索算法包括：
    将定位信号确定为第一支路定位信号；
    将第一支路定位信号与本地扩频码相乘，将乘积在一个周期内进行数据累加处理，确定周期内数据模值的位置为第一位置；
    将定位信号进行码片偏移，得到第二支路定位信号；
    将第二支路定位信号与本地扩频码相乘，将乘积在一个周期内进行数据 累加处理，确定周期内数据模值的位置为第二位置；
    判断第一位置和第二位置是否相同，得到第一判断结果：
    若第一判断结果为是，则判定定位信号捕获成功；
    若第一判断结果为否，则判定定位信号捕获不成功，更新定位信号，并返回步骤“将定位信号确定为第一支路定位信号”。
  5. 根据权利要求1所述的一种机载定位完好性监测方法，其特征在于，对所述第一伪距观测量和所述第二伪距观测量进行异常剔除处理，包括：
    删除接收间隔大于第一接收间隔时对应的第一伪距观测量；
    删除接收间隔大于第二接收间隔时对应的第二伪距观测量。
  6. 根据权利要求1所述的一种机载定位完好性监测方法，其特征在于，所述根据异常剔除处理后的第一伪距观测量和异常剔除处理后的第二伪距观测量进行定位解算，确定用户的定位结果，包括：
    判断是否满足GNSS定位条件，得到第二判断结果；所述GNSS定位条件为存在至少4个剔除处理后的第一伪距观测量；且剔除处理后的第一伪距观测量对应的卫星均不同；
    若第二判断结果为是，则根据剔除处理后的第一伪距观测量，利用一阶泰勒级数展开法和最小二乘法确定用户位置；
    若第二判断结果为否，则判断是否满足LDACS定位条件，得到第三判断结果；
    若第三判断结果为是，则根据剔除处理后的第二伪距观测量，利用伪距定位法确定用户位置；
    若第三判断结果为否，返回步骤“获取定位信号”。
  7. 一种机载定位完好性监测装置，其特征在于，包括：依次连接的信号接收单元、基带信号处理单元、数据处理单元、异常信号监测单元和定位解算单元；
    所述信号接收单元用于获取定位信号；所述定位信号包括GNSS信号和LDACS信号；所述LDACS信号包括LDACS前向链路信号和LDACS反向链路信号；
    所述基带信号处理单元用于消除定位信号传输过程中产生的码相位偏 移和多普勒频率，确定原始定位信号；
    所述数据处理单元用于确定第一伪距观测量和第二伪距观测量；所述第一伪距观测量为根据原始GNSS信号确定的卫星和用户之间的伪距观测量；所述第二伪距观测量为根据原始LDACS信号确定的用户和地面站之间的伪距观测量；
    所述异常信号监测单元用于对所述第一伪距观测量和所述第二伪距观测量进行异常剔除处理；
    所述定位解算单元用于根据异常剔除处理后的第一伪距观测量和异常剔除处理后的第二伪距观测量进行定位解算，确定用户的定位结果。
  8. 根据权利要求7所述的一种机载定位完好性监测装置，其特征在于，所述信号接收单元包括：射频前端和卫星天线；
    所述射频前端与所述卫星天线和所述基带信号处理单元连接；
    所述卫星天线用于接收所述定位信号；
    所述射频前端用于对所述定位信号进行变频处理和模数转换处理。
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