An enhanced LDACS ranging method based on improved super-resolution delay estimation

Abstract

The present invention discloses an enhanced LDACS ranging method based on improved super-resolution time delay estimation, which belongs to the field of aviation navigation technology. First, the FL signal transmitted by the LDACS ground station to the airborne station is monitored and recorded in real time, and then the FL signal is coarsely synchronized, and the improved S&C algorithm is used to determine the synchronization sequence position and compensate for the frequency offset to obtain a rough arrival time TOA. Then, the weighted TLS algorithm is used to perform fine synchronization estimation on the signal transmission delay to obtain a more accurate TOA. Finally, the distance between the ground station and the airborne station is calculated based on the TOA multiplied by the speed of light. The present invention adopts an improved super-resolution time delay estimation method, combined with coarse synchronization and fine synchronization strategies, which can achieve more accurate signal transmission delay estimation in a noisy environment, improve the ranging accuracy, adaptability and robustness. Experimental results show that this method significantly improves the accuracy and stability of LDACS ranging.

Description

Technical Field

[0001] The present 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 limited availability of spectrum resources, countries have developed strategies for the Next Generation Air Transport System (NGATS) to ensure the efficient and sustainable development of the global air transport industry. Against this backdrop, the L-band Digital Aeronautical Communications System (LDACS) was proposed. This system is a new type of aeronautical communications system and a key component of the ground-to-air data link of the Future Communications Infrastructure (FCI).

[0003] LDACS uses Orthogonal Frequency Division Multiplexing (OFDM) as its modulation technology and an adaptive coding algorithm. Its data transmission rate is 50 to 200 times higher than that of traditional Very High Frequency (VHF) Data Link Mode 2 (VDL M2), thus meeting the large bandwidth, high speed, and low latency requirements of aviation communication systems. LDACS uses Frequency Division Duplexing (FDD) as its 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 capabilities.

[0005] Compared to the more mature LDACS communication function, the LDACS navigation function is still under development. Three proposed LDACS navigation modes are available: one-way pseudoranging (PR), two-way timing and ranging (TWTR), and a hybrid mode. The PR mode is a time-of-arrival (TOA)-based ranging method that estimates the TOA of the FL signal and multiplies the signal propagation time by the speed of light to calculate the distance between the GS and AS. The TWTR mode, based on two-way communication, utilizes both the FL and RL for ranging. The hybrid mode is a combination of the PR and TWTR modes. For the PR mode, Schneckenburger proposed a ranging algorithm in 2012 that uses the least squares (LS) algorithm to fit the signal phase in the frequency domain for accurate TOA estimation. This algorithm minimizes the sum of squared residuals between the sampling points and the fitted line, resulting in good performance. However, the LS algorithm only considers phase uncertainty in its residual calculation and does not account for subcarrier frequency errors. Summary of the Invention

[0006] The present invention aims to provide an enhanced LDACS ranging method based on improved super-resolution delay estimation, using a weighted total least squares (TLS) algorithm instead of the traditional LS algorithm. The weighted TLS algorithm accounts for phase and subcarrier frequency uncertainties, resulting in improved performance and contributing to the advancement of LDACS positioning and navigation capabilities.

[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 from 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 location of the synchronization sequence in the received signal, 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 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, the specific process of calculating the rough arrival time using the improved S&C algorithm in step S2 is as follows:

[0013] S21, calculating a correlation metric P between the received signal and the 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 determine 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 complex sampling point, d represents the sampling point index, N len Indicates the length of the related calculation, N diff Indicates the delay length;

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

[0022]

[0023] The specific method of 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] Where 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. Convert the long synchronization sequence to 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.

[0043] 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;

[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] Where, Indicates the frequency domain phase difference of the nth subcarrier;

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

[0050]

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

[0052] Accumulate the unwrapped phase:

[0053]

[0054] Where, Indicates the frequency domain phase difference of the nth subcarrier after dewarping.

[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 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 coefficient, 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 the Fourier transform, s(t) represents the time domain signal, S(jω) represents the frequency domain signal, and τ represents the signal transmission delay. LDACS has multiple subcarriers of different frequencies, and the phases of different subcarriers rotate by different amounts. Therefore, the signal transmission delay is obtained by calculating the slope of the line, as shown below:

[0071]

[0072] Where 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) This paper uses an improved super-resolution delay estimation method that 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 ranging accuracy.

[0075] (2) The present invention combines coarse synchronization with 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 in the face of complex channel environments or fluctuating signal quality.

[0076] (3) During the fine synchronization phase, the present invention applies a weighted TLS algorithm to effectively suppress the influence of noise on the fitting results, especially under low signal-to-noise ratio conditions. This stability ensures the consistency and reliability of the ranging results in 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 chart of an enhanced LDACS ranging method based on improved super-resolution delay estimation according to the present invention;

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

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

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

[0082] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" 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 object being described 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, the signal transmitted from the LDACS ground station to the airborne station, known as the FL signal, is monitored and recorded in real time. The FL signal is coarsely synchronized, using an improved S&C algorithm to determine the position of the synchronization sequence and perform frequency offset compensation to obtain a rough time of arrival (TOA). A weighted TLS algorithm is used to perform fine synchronization estimation of the signal transmission delay, resulting in a more accurate TOA. The distance between the GS and AS is calculated by multiplying the obtained TOA by the speed of light. The specific steps are as follows:

[0085] S1, real-time monitoring and recording of the signal transmitted from 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 location of the synchronization sequence in the received signal, 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 the received signal and the 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 complex sampling point, d represents the sampling point index, N len Indicates the length of the related 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 determine 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 offset 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] Where 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 more accurate TOA;

[0114] The specific process is as follows:

[0115] S31. Convert the long synchronization sequence to the frequency domain through Fourier transform, subtract the frequency domain phase of the received signal from the frequency domain phase information of the local sequence, and perform deconvolution. Specifically:

[0116] ①Calculate the difference between adjacent phases:

[0117]

[0118] Where, Indicates the frequency domain phase difference of the nth subcarrier;

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

[0120]

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

[0122] ③ Accumulated unwrapping phase

[0123]

[0124] Where, Indicates the frequency domain phase difference of the nth subcarrier after dewarping.

[0125] S32. Using the subcarrier frequency as the horizontal axis, 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 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 coefficient, 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 fitting 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 the 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 of different frequencies, and the phases of different subcarriers rotate by different amounts. Therefore, the signal transmission delay can be obtained by calculating the slope of the line:

[0141]

[0142] Where 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 achieves high-precision ranging in noisy environments by combining coarse synchronization and fine synchronization algorithms, which helps to promote the further development of LDACS systems.

[0145] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. 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 solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions 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, real-time monitoring and recording of the FL signal transmitted by the LDACS ground station GS to the airborne station AS; S2. Perform coarse synchronization processing on the FL signal. Use the improved S&C algorithm to determine the location of the synchronization sequence in the received signal, perform frequency offset compensation, and finally perform cross-correlation calculation with the local long synchronization sequence to obtain a rough arrival time (TOA). The specific process of calculating the rough arrival time using the improved S&C algorithm in step S2 is as follows: S21, calculating a correlation metric P between the received signal and the 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; S3, using the weighted TLS algorithm to perform precise synchronization estimation of signal transmission delay and derive a more accurate TOA; In step S3, the specific process of using the weighted TLS algorithm to perform precise synchronization estimation of the signal transmission delay is as follows: S31. Convert the long synchronization sequence to 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. 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; S33. According to the time-shift property of Fourier transform, the slope obtained by fitting is converted into the transmission delay of the signal; 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 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: ； Where, represents the complex sampling points, Indicates the sampling point index, Indicates the length of the related calculation, Indicates the delay length; The specific way to calculate the energy metric R is: ； The specific method of calculating the normalized metric M is: 。 3. The enhanced LDACS ranging method based on improved super-resolution delay estimation according to claim 1, 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: Frequency deviation is The received signal is expressed as: ； Where, is a signal with no frequency offset, is the sampling interval; According to the periodicity of the synchronization sequence, we can conclude that: ； Then the metric P is expressed as: ； Therefore, the phase of the metric P is , the estimated frequency offset of the received signal is: ； The specific method of frequency offset compensation is: 。 4. The enhanced LDACS ranging method based on improved super-resolution delay estimation according to claim 1, characterized in that: The specific method of cross-correlation calculation in step S24 is: ； Where, Represents a local synchronization sequence.

5. The enhanced LDACS ranging method based on improved super-resolution delay estimation according to claim 1, 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 : ； Where, Indicates 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 ; Accumulate the unwrapped phase: ； Where, Indicates the frequency domain phase difference of the nth subcarrier after dewarping.

6. The enhanced LDACS ranging method based on improved super-resolution delay estimation according to claim 1, 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: ； To reduce bias, the line must pass through the data The center point of the 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: ； in, Represents the weighting coefficient, which is set to the inverse of the subcarrier power; By adding The fitted variance can be rewritten as ； in, ， ， ； Using the Lagrange multiplier method, we can get the fitting variance The minimum value of is the smallest eigenvalue of the matrix, is the eigenvector corresponding to the smallest eigenvalue.

7. The enhanced LDACS ranging method based on improved super-resolution delay estimation according to claim 1, 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, ； in represents the Fourier transform, represents the time domain signal, represents the frequency domain signal, Represents the signal transmission delay, which is obtained by calculating the slope of the straight line. The expression is as follows: ； Where, represents the fitting slope, is the sampling interval.

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