A method for direction finding of incoherent weak signals by heterodyne coupling

Abstract

This invention belongs to the field of radio direction finding, specifically relating to a method for coherent weak signal direction finding using anisotropic coupling. The invention determines the parameters of the strong signal based on the relevant parameters of the direction finding equipment, obtains the cross-correlation vector between the array snapshot signal and the strong signal waveform, and then determines the Wiener filter vector and the MVDR filter vector; next, it determines the coherent vector; then, corresponding to the search directions in the search direction set, it determines the anisotropic coupling coefficient between the direction vector and the coherent vector for each search direction in the direction vector set; finally, it determines the set of anisotropic coupling coefficients corresponding to the search direction set, and determines the anisotropically coupled coherent weak signal direction finding result from the direction corresponding to the maximum value in the anisotropic coupling coefficient set. This invention combines the advantages of Wiener filtering using waveform information and MVDR filtering using direction information, and can be used in weak signal direction finding situations where there is coherent strong signal suppression, providing higher accuracy direction finding information for radio coherent interference source direction finding.

Description

Technical Field

[0001] This invention belongs to the field of radio direction finding, specifically relating to a method for finding direction of coherent weak signals with anisotropic coupling, or more specifically, a method for finding direction of coherent weak signals under strong signal suppression. Background Technology

[0002] There is a high demand for direction finding of coherent weak signals under strong signal suppression. For example, in the field of radar jamming source detection, when the array aperture and number of array elements of the direction finding station detecting the jamming source are much smaller than those of the nearby radar, the signal receiving gain is also much smaller. Even if the target echo received by the radar already shows obvious long-range jamming source signals and the radar's detection performance deteriorates, it is still difficult to detect weak jamming signals coherent with the target echo of the nearby radar in the received signal of the direction finding station detecting the jamming source. In the field of anti-multipath radio communication, the multipath propagation effect causes communication signals from the same source to arrive at the communication signal receiving station through different paths. Compared with the signal arriving through the direct wave path, the communication signal arriving through the non-direct wave path is not only relatively weak, but also coherent with the signal arriving through the direct wave path, making it difficult to distinguish and separate, resulting in serious inter-symbol interference and deteriorating the communication bit error rate performance.

[0003] In the field of radio direction finding, there are already many methods for direction finding of coherent signals. The direction finding method based on the maximum likelihood criterion is an optimized method, insensitive to the coherence between signals, and its direction finding accuracy is close to the Cramerau limit. However, its computational complexity is high, making it difficult to meet the real-time requirements of direction finding. Utilizing the translation invariance of a uniform linear array, spatial smoothing and phase deintervention processing can be performed on the array snapshot signal first. Then, modern spatial spectrum estimation direction finding methods such as Minimum Variance Distortionless Response (MVDR) and Multi-Signal Classification (MUSIC) can be used to perform high-resolution direction finding of coherent signals. However, these methods are limited by the array configuration, sacrifice array aperture and direction finding resolution, and are difficult to use for weak coherent signals.

[0004] In the field of signal detection, since the waveform of a signal is unknown beforehand, direction finding mainly relies on spatial signal processing techniques such as spatial matched filtering, spatial adaptive filtering, and spatial signal separation. However, in the field of active target detection, the signal waveform is known. Through time-domain or frequency-domain matched filtering, not only can signal-to-noise ratio gain be obtained, improving the detection and parameter estimation performance of weak signals, but coherent signals from the same source can also be distinguished based on arrival time and frequency. Therefore, it is necessary to introduce signal waveform information into the field of signal detection to improve the direction finding capability of coherent weak signals under strong signal suppression. Summary of the Invention

[0005] This invention addresses the problem of direction finding for coherent weak signals under strong signal suppression. When the direction of arrival of the strong signal, the corresponding direction vector and amplitude, and the initial phase are unknown but the signal waveform is known, the invention enhances the direction finding capability of coherent weak signals from different unknown directions by utilizing the waveform information of the direction of arrival of the strong signal. By determining the set of phase vectors and anisotropic coupling coefficients, the invention achieves the goal of both decoherent direction finding and improving the accuracy of weak signal direction finding.

[0006] The technical solution of this invention is as follows:

[0007] A method for coherent weak signal direction finding with anisotropic coupling is proposed. First, the number of antennas, the number of search directions, the set of search directions, and the set of direction vectors corresponding to the search direction set are set, along with the number of array signal snapshots received by the direction finding device. Second, the direction of arrival of the strong signal, its corresponding direction vector and waveform, and the array snapshot signal received by the direction finding device are determined. Next, the autocorrelation matrix of the array snapshot signal and the cross-correlation vector between the array snapshot signal and the strong signal waveform are determined, leading to the determination of the Wiener filter vector and the MVDR filter vector. Then, the coherent vector is determined from the direction of arrival of the strong signal, its corresponding direction vector, the Wiener filter vector, and the MVDR filter vector. Next, corresponding to the search directions in the search direction set, the anisotropic coupling coefficient between the direction vector and the coherent vector corresponding to each search direction in the direction vector set is determined. Finally, the set of anisotropic coupling coefficients corresponding to the search direction set is determined, and the direction corresponding to the maximum value in the set of anisotropic coupling coefficients is used to determine the coherent weak signal direction finding result with anisotropic coupling.

[0008] The present invention specifically includes the following steps:

[0009] S1. Set the number of antennas of the direction finding device to M, the number of search directions to N, and the search direction to θ. n The set of search directions is {θ1, θ2, ..., θ N}, and the search direction θ n The corresponding direction vector is a(θ) n Let n = 1, 2, ..., N, and the set of all direction vectors be {a(θ1), a(θ2), ..., a(θ...}}. N The number of array signal snapshots received by the direction finding equipment is L;

[0010] S2. Determine the direction of arrival of the strong signal. The corresponding direction vector is The waveform is a 1×L order vector s, and the array snapshot signal received by the direction finding equipment is an M×L order matrix X;

[0011] S3. Determine the autocorrelation matrix of the array snapshot signal as R = XX H The cross-correlation vector between the array snapshot signal and the strong signal waveform is r = Xs. HTherefore, the Wiener filter (WF) vector is determined as follows:

[0012] w WF =R -1 r

[0013] The minimum variance distortionless response (MVDR) filter vector is

[0014]

[0015] in, H Represents the conjugate transpose of a vector or matrix. -1 Represents the inverse of a matrix;

[0016] S4. Based on the direction of arrival of the strong signal, the corresponding direction vector, the Wiener filter vector, and the MVDR filter vector, determine the phase coherence vector as follows:

[0017]

[0018] S5, the search direction θ in the corresponding search direction set n Determine the direction vector a(θ) corresponding to each search direction in the set of direction vectors. n The heterogeneous coupling coefficient between the ) and the coherent vector is

[0019]

[0020] Where || represents absolute value, and n = 1, 2, ..., N;

[0021] S6. Determine the set of opposite coupling coefficients {g(θ1), g(θ2), ..., g(θ)} corresponding to the search direction set. N )}, and determine the maximum value in the set of anisotropic coupling coefficients as the m-th anisotropic coupling coefficient g(θ) m ), corresponding to the direction θ m This is the direction finding result of coherent weak signals with opposite coupling.

[0022] The beneficial effects of this invention are as follows: Using the anisotropically coupled coherent weak signal direction finding method proposed in this invention, it can overcome the difficulties in direction finding caused by weak signals, suppression by strong signals in nearby directions, and coherence with strong signals, when modern spatial spectrum estimation direction finding methods such as Minimum Variance Distortionless Response (MVDR) and Multiple Signal Classification (MUSIC) are ineffective. This invention utilizes Wiener filtering vectors and MVDR filtering vectors determined by waveform information from the direction of arrival of the strong signal, and combines them to form a coherent vector and anisotropic coupling coefficient set. This achieves both decoherent direction finding and improved accuracy in weak signal direction finding. Therefore, this invention combines the advantages of Wiener filtering using waveform information and MVDR filtering using direction information, and can be used in weak signal direction finding situations where strong coherent signals suppress the signal, providing higher accuracy direction finding information for radio coherent interference sources. Detailed Implementation

[0023] The practicality of the present invention will be analyzed below with reference to the embodiments.

[0024] Example: In this example, the direction finding device has M = 8 antennas, N = 451 search directions, and a search direction set of {-45.0, -44.8, -44.6, ..., 44.6, 44.8, 45} degrees. The set of direction vectors corresponding one-to-one with the search direction set is {a(-45.0), a(-44.8), a(-44.6), ..., a(44.6), a(44.8), a(45)}. The number of snapshots for the acquisition array is L = 500. Relative to the direction finding device, the direction of arrival of the strong signal near the location is -19.41 degrees, with a signal-to-noise ratio of 48.16 dB; the direction of arrival of the weak signal is 20.25 degrees, with a signal-to-noise ratio of -18.06 dB. The waveform is coherent with the waveform of the strong signal near the location. It can be seen that in the array received signals of the direction finding equipment, the power of the nearby strong signal is 66.22 dB stronger than that of the coherent weak signal.

[0025] The Minimum Variance Distortionless Response (MVDR) and Multi-Signal Classification (MUSIC) direction finding methods can only accurately determine the direction of arrival of strong signals. Since the power of weak signals is 66.22 dB lower than that of strong signals in the array received signals of the direction finding equipment, if the direction of arrival of weak signals is estimated based on the peak positions of the MVDR and MUSIC spatial spectra detected near the direction of arrival of weak signals, the direction finding results for coherent weak signals are 0.80 degrees and 1.20 degrees, respectively, with direction finding errors of -19.45 degrees and -19.05 degrees, respectively. However, using the method of this invention, the direction finding result for coherent weak signals is 21.20 degrees, with a direction finding error of 0.95 degrees. By using coherent weak signal direction finding with anisotropic coupling, the goal of both decoherent direction finding and improving the accuracy of weak signal direction finding is achieved.

Claims

1. A method of heterodyne coherent weak signal direction finding, characterized in that, The method comprises the following steps: S1. Set the number of antennas of the direction finding device to M, the number of search directions to N, and the search direction to θ. n The set of search directions is {θ1, θ2, ..., θ N }, and the search direction θ n The corresponding direction vector is a(θ) n Let n = 1, 2, ..., N, and the set of all direction vectors be {a(θ1), a(θ2), ..., a(θ...}}. N The number of array signal snapshots received by the direction finding equipment is L; S2, determine the direction of arrival of strong signals is The corresponding direction vector is The waveform is a 1 × L order vector s, and the array snapshot signal received by the direction finding device is a M × L order matrix X; S3, determine the autocorrelation matrix of the array snapshot signal as R = XX H , the cross-correlation vector between the array snapshot signal and the strong signal waveform as r = Xs H , and further determine the Wiener filter vector as: w WF = R -1 r And the minimum variance distortionless response filtering vector is: where H denotes the conjugate transpose of a vector or matrix, -1 denotes the inverse of a matrix; S4, determining the coherent vector from the direction of arrival of the strong signal, the corresponding direction vector, the Wiener filtering vector and the MVDR filtering vector; S5, determining a search direction θ in the search direction set n , respectively determining a direction vector a(θ n ) corresponding to each search direction in the direction vector set and the anti-phase coupling coefficient of the phase reference vector Wherein, || represents absolute value, n=1, 2, …, N; S6, determine the set of anisotropic coupling coefficients {g(θ1), g(θ2), …, g(θ N )} corresponding to the set of search directions, and determine the maximum value in the set of anisotropic coupling coefficients as the mth anisotropic coupling coefficient g(θ m ), and the corresponding direction θ m is the anisotropic coherent weak signal direction finding result.

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