Enhanced LDACS ranging method based on improved super-resolution time delay estimation

Abstract

The invention discloses an enhanced LDACS ranging method based on improved super-resolution time delay estimation, and belongs to the technical field of aviation navigation. The method comprises the following steps: firstly, monitoring and recording an FL signal transmitted from an LDACS ground station to an airborne station in real time, then carrying out coarse synchronization processing on the FL signal, and adopting an improved Samp; and the C algorithm determines a synchronization sequence position and compensates frequency deviation to obtain rough time of arrival (TOA), then a weighted TLS algorithm is adopted to carry out fine synchronization estimation on signal transmission delay to obtain more accurate TOA, and finally, the distance between the ground station and the airborne station is calculated according to the fact that the TOA is multiplied by the light velocity. The improved super-resolution time delay estimation method is adopted, the coarse synchronization strategy and the fine synchronization strategy are combined, more accurate signal transmission delay estimation can be achieved in the noise environment, the ranging precision, adaptability and robustness are improved, and experimental results show that the LDACS ranging precision and stability are remarkably improved through the method.

Description

Technical Field

[0001] The invention relates to the technical field of aviation navigation, and in particular to an enhanced LDACS ranging method based on improved super-resolution delay estimation. Background Art

[0002] Considering the rapid growth of air traffic density and the increasingly tight spectrum resource situation, countries have formulated strategies for the next generation of air transportation systems to ensure the efficient and sustainable development of the global air transportation industry. In this context, the L-band Digital Aeronautical Communications System (LDACS) was proposed, which is a new type of aeronautical communication system and an important part of the ground-to-air data link of the Future Communications Infrastructure (FCI).

[0003] LDACS uses Orthogonal Frequency Division Multiplexing (OFDM) as the modulation technology and an adaptive coding algorithm. Its data transmission rate is 50 to 200 times higher than the traditional Very High Frequency (VHF) Data Link Mode 2 (VDL M2), so it can meet the requirements of aviation communication systems for large bandwidth, high rate and low latency. LDACS uses Frequency Division Duplexing (FDD) as the duplex mode. The forward link (FL) refers to the data link from the ground station (GS) to the airborne station (AS), while the reverse link (RL) is used for data transmission in the opposite direction.

[0004] LADCS is the first truly integrated communication, navigation and surveillance (CNS) system certified by ICAO. It can provide efficient digital communication services and precise navigation and positioning functions.

[0005] Compared with the more mature LDACS communication function, the LDACS navigation function is still under development. There are three proposed modes for the LDACS navigation function: Pseudo Ranging (PR), Two-way Timing and Ranging (TWTR), and Hybrid mode. The PR mode is a ranging method based on Time of Arrival (TOA), which estimates the TOA of the FL signal and calculates the distance between the GS and AS by multiplying the signal propagation time by the speed of light. The TWTR mode is based on two-way communication and uses FL and RL for ranging at the same time. The Hybrid mode is a combination of PR and TWTR. For the PR mode, Schneckenburger proposed a ranging algorithm in 2012, which uses the Least Squares (LS) algorithm to fit the phase of the signal in the frequency domain for accurate TOA estimation. The principle of this algorithm is to minimize the sum of squares of the residuals between the sampling points and the fitting line, and has good performance. However, the LS algorithm only considers the uncertainty of the phase in the residual calculation process, and does not consider the error of the subcarrier frequency. Summary of the invention

[0006] The purpose of the present invention is to provide an enhanced LDACS ranging method based on improved super-resolution delay estimation, using a weighted total least squares (TLS) algorithm to replace the traditional LS algorithm. The weighted TLS algorithm takes into account the uncertainty of phase and subcarrier frequency, so that the algorithm has better performance and helps to promote the development of LDACS positioning and navigation functions.

[0007] To achieve the above object, the present invention provides an enhanced LDACS ranging method based on improved super-resolution delay estimation, comprising the following steps:

[0008] S1, real-time monitoring and recording of the signal transmitted by the LDACS ground station to the airborne station, namely, the FL signal;

[0009] S2, perform coarse synchronization processing on the FL signal, use the improved S&C algorithm to determine the position of the synchronization sequence in the received signal, and perform frequency offset compensation, and finally perform cross-correlation calculation with the local long synchronization sequence to obtain a rough arrival time TOA;

[0010] S3, using the weighted TLS algorithm to perform precise synchronization estimation of signal transmission delay to obtain a more accurate TOA;

[0011] S4. Calculate the distance between GS and AS based on the obtained TOA by multiplying it by the speed of light.

[0012] Preferably, in step S2, the specific process of calculating and obtaining the rough arrival time by the improved S&C algorithm is as follows:

[0013] S21, calculating a correlation metric P between a received signal and a delayed signal and an energy metric R of the received signal, and normalizing the correlation metric P using the energy metric R to obtain a normalized metric M;

[0014] S22, preliminarily determining the position of the synchronization sequence by detecting the peak value of the normalized metric M;

[0015] S23, estimating and compensating for the frequency offset of the received signal;

[0016] S24, performing cross-correlation calculation on the received signal after frequency offset compensation and the local synchronization sequence, determining the position of the sampling point according to the peak value of the modulus value of the correlation calculation result, and obtaining a rough TOA.

[0017] Preferably, the manner of calculating the correlation metric P, the energy metric R and the normalization metric M in step S21 is as follows:

[0018] The specific method of calculating the correlation measure P between the received signal and the delayed signal is:

[0019]

[0020] In the formula, r(d) represents the sampling point in complex form, d represents the sampling point index, and N len Indicates the length of the correlation calculation, N diff Indicates the delay length;

[0021] The specific way to calculate the energy metric R is:

[0022]

[0023] The specific method for calculating the normalized metric M is:

[0024]

[0025] Preferably, the specific method of estimating and compensating the received signal frequency offset in step S23 is:

[0026] The specific method of frequency offset estimation is as follows:

[0027] The received signal with a frequency deviation of Δf is expressed as:

[0028]

[0029] Where r(d) is the signal without frequency offset, T s is the sampling interval;

[0030] According to the periodicity of the synchronization sequence, we can conclude that:

[0031] r(d)=r(d+N diff );

[0032] Then the metric P is expressed as:

[0033]

[0034] Therefore, the phase of the metric P is -j2πΔfT s N diff , the estimated frequency offset of the received signal is:

[0035]

[0036] The specific method of frequency offset compensation is:

[0037]

[0038] Preferably, the specific method of cross-correlation calculation in step S24 is:

[0039]

[0040] In the formula, r sync (n) represents the local synchronization sequence.

[0041] Preferably, in step S3, the specific process of using the weighted TLS algorithm to perform precise synchronization estimation on the signal transmission delay is as follows:

[0042] S31, converting the long synchronization sequence into the frequency domain through Fourier transform, subtracting the frequency domain phase information of the received signal from the frequency domain phase information of the local sequence, and performing deconvolution;

[0043] S32, taking the subcarrier frequency as the horizontal coordinate, analyzing the relationship between the signal phase difference and the slope of the straight line, and fitting the slope of the straight line using the weighted TLS algorithm;

[0044] S33. According to the time-shift property of Fourier transform, the slope obtained by fitting is converted into the transmission delay of the signal.

[0045] Preferably, in step S31, the specific manner of unwrapping the frequency domain phase information is as follows:

[0046] Calculate the difference between adjacent phases:

[0047]

[0048] In the formula, Represents the frequency domain phase difference of the nth subcarrier;

[0049] Determine whether the difference exceeds the threshold and make adjustments:

[0050]

[0051] In the formula, T represents the judgment threshold, which is generally set to π;

[0052] Cumulative unwrapped phase:

[0053]

[0054] In the formula, Indicates the frequency domain phase difference of the nth subcarrier after unwrapping.

[0055] Preferably, in step S32, the specific process of fitting the slope of the straight line using the weighted TLS algorithm is as follows:

[0056] Assume that the equation of the straight line to be fitted is:

[0057] ax+by+c=0;

[0058] To reduce bias, the line must pass through the data The center point of the straight line is rewritten as:

[0059]

[0060] In the weighted TLS algorithm used, the weighted sum of the vertical distances from the data points to the straight line is used as the fitting variance:

[0061]

[0062] Among them, w i represents the weighting factor, which is set to the inverse of the subcarrier power. 2 +b 2 = 1, the fitted variance is rewritten as

[0063]

[0064] in,

[0065]

[0066] Using the Lagrange multiplier method, the minimum value of the fitting variance E is the minimum eigenvalue of the matrix, and z is the eigenvector corresponding to the minimum eigenvalue.

[0067] Preferably, in step S33, the specific method of converting the slope obtained by fitting into the transmission delay of the signal is as follows:

[0068] According to the time-shift characteristic of Fourier transform,

[0069] F(s(t+τ))=S(jω)e jωτ ;

[0070] Where F(·) represents Fourier transform, s(t) represents time domain signal, S(jω) represents frequency domain signal, τ represents signal transmission delay, LDACS has multiple subcarriers with different frequencies, and the phases of different subcarriers will rotate with different amplitudes. Therefore, the signal transmission delay is obtained by calculating the slope of the straight line, and the expression is as follows:

[0071]

[0072] In the formula, α represents the fitting slope.

[0073] Therefore, the present invention adopts an enhanced LDACS ranging method based on improved super-resolution delay estimation using the above structure, which has the following beneficial effects:

[0074] (1) The present invention adopts an improved super-resolution delay estimation method, which can achieve more accurate signal transmission delay estimation in the presence of noise. Compared with the traditional LS algorithm, the proposed weighted TLS algorithm comprehensively considers the uncertainty of phase and subcarrier frequency, thereby significantly improving the ranging accuracy.

[0075] (2) The present invention combines the two strategies of coarse synchronization and fine synchronization. Coarse synchronization is used to quickly lock the approximate position of the signal, while fine synchronization further accurately estimates the signal transmission delay. This combination makes the system more adaptable and robust when facing complex channel environments or signal quality fluctuations.

[0076] (3) In the fine synchronization stage, the present invention can effectively suppress the influence of noise on the fitting results by applying the weighted TLS algorithm, especially under low signal-to-noise ratio conditions. This stability ensures the consistency and reliability of the ranging results under different environments and conditions.

[0077] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 A schematic diagram of a weighted TLS algorithm flow of an enhanced LDACS ranging method based on improved super-resolution delay estimation according to the present invention;

[0079] Figure 2 A schematic diagram of the layout of an experimental device for an enhanced LDACS ranging method based on improved super-resolution delay estimation according to the present invention;

[0080] Figure 3 The diagram is a schematic diagram of an outdoor experimental layout of an enhanced LDACS ranging method based on improved super-resolution delay estimation of the present invention. DETAILED DESCRIPTION

[0081] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0082] Unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0083] Example

[0084] The present invention provides an enhanced LDACS ranging method based on improved super-resolution delay estimation, see Figure 1-3 First, monitor and record the signal transmitted by the LDACS ground station to the airborne station, namely the FL signal, in real time. Perform coarse synchronization processing on the FL signal, use the improved S&C algorithm to determine the position of the synchronization sequence, and perform frequency offset compensation to obtain a rough arrival time TOA. Use the weighted TLS algorithm to perform fine synchronization estimation on the signal transmission delay to obtain a more accurate TOA. According to the obtained TOA, multiply it by the speed of light to calculate the distance between GS and AS. The specific steps are as follows:

[0085] S1, real-time monitoring and recording of the signal transmitted by the LDACS ground station to the airborne station, namely, the FL signal;

[0086] S2, perform coarse synchronization processing on the FL signal, use the improved S&C algorithm to determine the position of the synchronization sequence in the received signal, and perform frequency offset compensation, and finally perform cross-correlation calculation with the local long synchronization sequence to obtain a rough arrival time TOA;

[0087] The specific process is as follows:

[0088] S21 . Calculate a correlation metric P between a received signal and a delayed signal and an energy metric R of the received signal, and use the energy metric R to normalize the correlation metric P to obtain a normalized metric M.

[0089] ① The specific method of calculating the correlation measure P between the received signal and the delayed signal is:

[0090]

[0091] In the formula, r(d) represents the sampling point in complex form, d represents the sampling point index, and N len Indicates the length of the correlation calculation, N diff Indicates the delay length.

[0092] ②The specific method of calculating the energy metric R is:

[0093]

[0094] ③The specific method of calculating the normalized metric M is:

[0095]

[0096] S22, preliminarily determining the position of the synchronization sequence by detecting the peak value of the normalized metric M;

[0097] S23, estimating and compensating for the frequency offset of the received signal;

[0098] ① The details of frequency offset estimation are as follows:

[0099] The received signal with a frequency deviation of Δf can be expressed as:

[0100]

[0101] Where r(d) is the signal without frequency offset, T s is the sampling interval.

[0102] According to the periodicity of the synchronization sequence, it can be concluded that:

[0103] r(d)=r(d+N diff );

[0104] Then the metric P can be expressed as:

[0105]

[0106] Therefore, the phase of the metric P is -j2πΔfT s N diff , the estimated frequency offset of the received signal is:

[0107]

[0108] ②The specific method of frequency deviation compensation is:

[0109]

[0110] S24, performing cross-correlation calculation on the received signal after frequency offset compensation and the local synchronization sequence, determining the position of the sampling point according to the peak value of the modulus value of the correlation calculation result, and obtaining a rough TOA. The specific method of cross-correlation calculation is:

[0111]

[0112] In the formula, r sync (n) represents the local synchronization sequence.

[0113] S3, using the weighted TLS algorithm to perform precise synchronization estimation of signal transmission delay to obtain a more accurate TOA;

[0114] The specific process is as follows:

[0115] S31, convert the long synchronization sequence into the frequency domain through Fourier transform, subtract the frequency domain phase information of the received signal from the frequency domain phase information of the local sequence, and perform deconvolution, specifically:

[0116] ① Calculate the difference between adjacent phases:

[0117]

[0118] In the formula, Represents the frequency domain phase difference of the nth subcarrier;

[0119] ② Determine whether the difference exceeds the threshold and make adjustments:

[0120]

[0121] In the formula, T represents the judgment threshold, which is generally set to π;

[0122] ③Accumulated unwrapping phase

[0123]

[0124] In the formula, Indicates the frequency domain phase difference of the nth subcarrier after unwrapping.

[0125] S32. Using the subcarrier frequency as the horizontal coordinate, analyze the relationship between the signal phase difference and the slope of the straight line, and use the weighted TLS algorithm to fit the slope of the straight line. Specifically:

[0126] Assume that the equation of the straight line to be fitted is:

[0127] ax+by+c=0;

[0128] To minimize bias, the line must pass through the data The center point of the straight line is rewritten as:

[0129]

[0130] In the weighted TLS algorithm used in this paper, the weighted sum of the vertical distances from the data points to the straight line is used as the fitting variance:

[0131]

[0132] Among them, w i represents the weighting factor, which is set to the inverse of the subcarrier power. 2 +b 2 = 1, the fitted variance can be rewritten as

[0133]

[0134] in,

[0135]

[0136] Using the Lagrange multiplier method, we can find that the minimum value of the fitted variance E is the minimum eigenvalue of the matrix. z is the eigenvector corresponding to the minimum eigenvalue.

[0137] S33. According to the time-shift property of Fourier transform, the slope obtained by fitting is converted into the transmission delay of the signal, specifically:

[0138] According to the time-shift characteristic of Fourier transform,

[0139] F(s(t+τ))=S(jω)e jωτ ;

[0140] Where ·(·) represents Fourier transform. s(t) represents the time domain signal. S(jω) represents the frequency domain signal. τ represents the signal transmission delay. LDACS has multiple subcarriers with different frequencies, and the phases of different subcarriers will rotate with different amplitudes. Therefore, the signal transmission delay can be obtained by calculating the slope of the straight line, that is:

[0141]

[0142] In the formula, α represents the fitting slope.

[0143] S4. Calculate the distance between GS and AS based on the obtained TOA by multiplying it by the speed of light.

[0144] Therefore, the present invention adopts the above-mentioned LDACS enhanced ranging method based on improved super-resolution delay estimation, and realizes high-precision ranging in a noisy environment by combining coarse synchronization and fine synchronization algorithms, which is helpful to promote the further development of the LDACS system.

[0145] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. An enhanced LDACS ranging method based on improved super-resolution delay estimation, characterized in that: The following steps are involved: S1, monitor and record the FL signal transmitted from the LDACS ground station to the airborne station in real time; S2, perform coarse synchronization processing on the FL signal, use the improved S&C algorithm to determine the position of the synchronization sequence in the received signal, and perform frequency offset compensation, and finally perform cross-correlation calculation with the local long synchronization sequence to obtain a rough arrival time TOA; S3, using the weighted TLS algorithm to perform precise synchronization estimation of signal transmission delay to obtain a more accurate TOA; S4. Calculate the distance between GS and AS based on the obtained TOA by multiplying it by the speed of light.

2. The enhanced LDACS ranging method based on improved super-resolution delay estimation according to claim 1, characterized in that: The specific process of calculating the rough arrival time by the improved S&C algorithm in step S2 is as follows: S21, calculating a correlation metric P between a received signal and a delayed signal and an energy metric R of the received signal, and normalizing the correlation metric P using the energy metric R to obtain a normalized metric M; S22, preliminarily determining the position of the synchronization sequence by detecting or searching for a peak value of the normalized metric M; S23, estimating and compensating for the frequency offset of the received signal; S24, performing cross-correlation calculation on the received signal after frequency offset compensation and the local synchronization sequence, determining the position of the sampling point according to the peak value of the modulus value of the correlation calculation result, and obtaining a rough TOA.

3. The enhanced LDACS ranging method based on improved super-resolution delay estimation according to claim 2, characterized in that: The manner of calculating the correlation metric P, the energy metric R and the normalization metric M in step S21 is as follows: The specific method of calculating the correlation measure P between the received signal and the delayed signal is: In the formula, r(d) represents the sampling point in complex form, d represents the sampling point index, and N len Indicates the length of the correlation calculation, N diff Indicates the delay length; The specific way to calculate the energy metric R is: The specific method for calculating the normalized metric M is:

4. The enhanced LDACS ranging method based on improved super-resolution delay estimation according to claim 2, characterized in that: The specific method of estimating and compensating the received signal frequency offset in step S23 is: The specific method of frequency offset estimation is as follows: The received signal with a frequency deviation of Δf is expressed as: Where r(d) is the signal without frequency offset, T s is the sampling interval; According to the periodicity of the synchronization sequence, we can conclude that: r(d)=r(d+N diff ); Then the metric P is expressed as: Therefore, the phase of the metric P is -j2πΔfT s N diff , the estimated frequency offset of the received signal is: The specific method of frequency offset compensation is:

5. The enhanced LDACS ranging method based on improved super-resolution delay estimation according to claim 2, characterized in that: The specific method of cross-correlation calculation in step S24 is: In the formula, r sync (n) represents the local synchronization sequence.

6. The enhanced LDACS ranging method based on improved super-resolution delay estimation according to claim 1, characterized in that: In step S3, the specific process of using the weighted TLS algorithm to perform precise synchronization estimation on the signal transmission delay is as follows: S31, converting the long synchronization sequence into the frequency domain through Fourier transform, subtracting the frequency domain phase information of the received signal from the frequency domain phase information of the local sequence, and performing deconvolution; S32, taking the subcarrier frequency as the horizontal coordinate, analyzing the relationship between the signal phase difference and the slope of the straight line, and fitting the slope of the straight line using the weighted TLS algorithm; S33. According to the time-shift property of Fourier transform, the slope obtained by fitting is converted into the transmission delay of the signal.

7. The enhanced LDACS ranging method based on improved super-resolution delay estimation according to claim 6, characterized in that: In step S31, the specific method of unwrapping the frequency domain phase information is as follows: Calculate the difference between adjacent phases In the formula, Represents the frequency domain phase difference of the nth subcarrier; Determine whether the difference exceeds the threshold and make adjustments: In the formula, T represents the judgment threshold, which is generally set to π; Cumulative unwrapped phase: In the formula, Indicates the frequency domain phase difference of the nth subcarrier after unwrapping.

8. The enhanced LDACS ranging method based on improved super-resolution delay estimation according to claim 6, characterized in that: In step S32, the specific process of fitting the slope of the straight line using the weighted TLS algorithm is as follows: Assume that the equation of the straight line to be fitted is: ax+by+c=0; To reduce bias, the line must pass through the data The center point of the straight line is rewritten as: In the weighted TLS algorithm used, the weighted sum of the vertical distances from the data points to the straight line is used as the fitting variance: Among them, w i represents the weighting factor, which is set to the inverse of the subcarrier power; By adding a 2 +b 2 = 1, the fitted variance is rewritten as in, Using the Lagrange multiplier method, the minimum value of the fitting variance E is the minimum eigenvalue of the matrix, and z is the eigenvector corresponding to the minimum eigenvalue.

9. The enhanced LDACS ranging method based on improved super-resolution delay estimation according to claim 6, characterized in that: The specific method of converting the slope obtained by fitting into the transmission delay of the signal in step S33 is as follows: According to the time-shift characteristic of Fourier transform, F(s(t+τ))=S(jω)e jωτ ; Where F(·) represents Fourier transform, s(t) represents time domain signal, S(jω) represents frequency domain signal, τ represents signal transmission delay, and the signal transmission delay is obtained by calculating the slope of the straight line. The expression is as follows: In the formula, α represents the fitting slope.

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