CN112924926B - DOA estimation method under multi-path channel - Google Patents
DOA estimation method under multi-path channel Download PDFInfo
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- 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
- G01S3/00—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received
- G01S3/80—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using ultrasonic, sonic or infrasonic waves
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Abstract
The invention discloses a DOA estimation method under a multi-path channel, which comprises the following steps of 1: acquiring a multi-path array receiving signal of an underwater target; step 2, calculating the frequency spectrum and the power spectrum of each array element signal; step 3, adding the calculated power spectrums of the array element signals, and synthesizing a sound field time-frequency interference spectrum; step 4, obtaining destructive interference frequency in the sound field time-frequency interference spectrum; step 5, calculating an array signal covariance matrix at the destructive interference frequency point; and 6, calculating a space spectrum at the destructive interference frequency point, and performing DOA estimation. The method can improve the DOA estimation precision under the multi-path coherent channel, has no loss of array aperture and spatial resolution, is not limited by application conditions such as array type and the like, and has better solution coherence and DOA estimation performance under low signal-to-noise ratio.
Description
Technical Field
The invention relates to the technical field of underwater acoustic signal processing, in particular to a DOA estimation method under a multi-path channel.
Background
When sound waves are transmitted in water, due to refraction of a water medium and reflection of the sound waves on the sea surface and the sea bottom, a plurality of transmission paths exist from a transmitting point to a receiving point, so that a plurality of channels exist in underwater transmission, and the phenomenon is one of main reasons for reducing the underwater sound navigation positioning accuracy.
For underwater multi-path channels, signals received by the array sensor are coherent, and due to the existence of coherent sources, the covariance matrix of the source signals is not full rank, so-called rank deficiency occurs, and the mutual penetration of signal subspace and noise subspace causes the performance of the basic high-resolution DOA estimation method MVDR algorithm and MUSIC algorithm to be degraded sharply. The order of the covariance matrix of the source signal is recovered, and the realization of decoherence of the coherent source is the key of DOA estimation under a multi-path channel. The common de-coherence algorithms at the present stage are mainly classified into two types: one is a dimensionality reduction algorithm, including a space smoothing algorithm, a vector singular value algorithm, a matrix decomposition method and the like, which realizes decoherence at the cost of sacrificing array aperture and spatial resolution; and the other type of non-dimensionality reduction algorithm comprises a frequency domain smoothing algorithm, a virtual array change algorithm and a Toeplitz matrix reconstruction algorithm, and compared with the dimensionality reduction algorithm, the non-dimensionality reduction processing algorithm has the advantages that the effective aperture of the array is not lost, but the application scene is relatively limited, and the performance of some methods is reduced under the condition of low signal to noise ratio.
Disclosure of Invention
The purpose of the invention is as follows: in order to overcome the defects in the prior art, the invention provides the DOA estimation method under the multi-path channel, which can effectively solve the coherence, does not lose the array aperture, is not limited by the application conditions such as array type and the like, and still has better DOA estimation performance under the condition of low signal-to-noise ratio.
The technical scheme is as follows: in order to achieve the above object, the present invention provides a DOA estimation method under a multipath channel, comprising the steps of,
step 1: acquiring a multi-path array receiving signal of an underwater target;
step 3, adding the calculated power spectrums of the array element signals, and synthesizing a sound field time-frequency interference spectrum;
step 5, calculating an array signal covariance matrix at the destructive interference frequency point;
and 6, calculating a space spectrum at the destructive interference frequency point, and performing DOA estimation.
Further, in the present invention: in the step 3, when the observation distance is far greater than the aperture of the array, the signals of the array elements have the same interference characteristic; for the conditions of only direct waves, primary sea surface reflected waves and primary seabed reflected waves, the power spectrums of the array element signals are added to obtain a power spectrum p of the kth frame of received signalsk(f) Comprises the following steps:
wherein p isxx(f) Is the power spectrum of the source signal, H1、H2And H3Uniform gain factors, tau, for the direct wave, the sea surface and the sea bottom reflected wave paths, respectivelyd、τrAnd τ'rRespectively direct wave, sea surface and sea bottom reflected waveTime delay, and:
τd＝Rd/c
τr＝Rr/c
τ'r＝R'r/c
wherein R isd、RrAnd R'rThe distance between the direct wave propagation path and the sea surface propagation path and the distance between the sea surface propagation path and the sea bottom reflection path are respectively, c is the sound velocity, the power spectrum of the multi-path received signal is the sum of the power spectrums of the direct wave propagation path, the sea surface propagation path and the sea bottom reflection path, interference terms of three frequency components are superposed, and when the interference terms exist, interference spectrum peaks are generated by the interference spectra when the signals of the two paths are completely coherent.
Further, in the present invention: the step of obtaining the destructive interference frequency in the sound field time-frequency interference spectrum comprises the step of realizing automatic tracking of a spectrum peak, real-time online extraction of the interference frequency and destructive interference frequency estimation through accumulation of the spectrum peak of the low-frequency sound field time-frequency interference spectrum along the target motion direction.
Further, in the present invention: the covariance matrix of the array signals of the destructive interference frequency points is
R(fi)＝X(fi)XH(fi)
Wherein R (f)i) Covariance matrix of array signal as destructive interference frequency point, X (f)i) For discrete Fourier transform of array received signal at destructive interference frequency point fiValue of (c) (. 1)HRepresenting a conjugate transpose.
Further, in the present invention: the destructive interference frequency point space spectrum comprises MVDR and MUSIC space spectrums which are respectively as follows:
wherein, PMVDR(theta) and PMUSIC(theta) MVDR and MUSIC spatial spectra, respectively, theta being the scan orientation, (. alpha.)-1Representing the inverse operation, a (θ) is the array steering vector, (. cndot.)HWhich represents the transpose of the conjugate,
the position corresponding to the spatial spectrum peak is the target position.
Compared with the prior art, the invention has the beneficial effects that: the method provided by the invention aims at the problems that the existing dimension reduction type coherent solution algorithm has array aperture and spatial resolution loss, the application of the non-dimension reduction type coherent solution algorithm is limited, the interference characteristics of multi-path channels and the inherent signal interference elimination of destructive interference frequency points are utilized, the interference spectrum and the destructive interference frequency are estimated by receiving signals through the array, the space spectrum estimation and the target direction DOA estimation are carried out on the destructive interference frequency points, all array elements participate in the operation for estimating the space spectrum and the target direction, the array aperture and the spatial resolution loss are avoided, the estimation of the interference spectrum and the destructive interference frequency is suitable for any array type, the method is not limited by application conditions such as the array type in the practical application, and the better coherent solution and DOA estimation performances are still obtained under the condition of low signal to noise ratio.
Drawings
FIG. 1 is a schematic overall flow chart of a DOA estimation method under a multi-pass channel according to the present invention;
FIG. 2 is a schematic diagram of a spatial spectrum calculated from a broadband multi-pass array received signal;
FIG. 3 is a schematic diagram of a spatial spectrum calculated from destructive interference frequency points.
Detailed Description
The technical scheme of the invention is further explained in detail by combining the attached drawings:
the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
As shown in fig. 1, which is an overall flow chart of the DOA estimation method under multi-pass channel proposed by the present invention, the method includes the following steps,
step 1: acquiring a multi-path array receiving signal of an underwater target;
specifically, the linear array is used for receiving noise signals radiated by an underwater motion sound source, the parameters to be acquired comprise frequency band, sampling frequency, sound source motion speed, course, sound velocity, seabed medium sound velocity, density, sea depth, sound source depth, initial direction, receiving linear array depth, array element number and spacing, signal to noise ratio and observation data duration, for example, the known parameters are collected by technical personnel according to actual conditions and input into a bellhop sound field model to obtain multi-path array receiving signals.
For example, the frequency band of the acquired parameters is 200Hz-2000Hz, the sampling frequency is 8kHz, the sound source moves at a constant speed, the speed is 5m/s, and the course is 180 degrees; the sound velocity is 1500m/s, the sound velocity of the seabed medium is 1800m/s, the density is 1.6g/cm3, and the sea depth is 200 meters; the depth of a sound source is 25 meters, the initial direction is 60.5 degrees, the depth of a receiving linear array is 25 meters, 16 array elements are arranged, and the spacing between the array elements is 0.5 m. The signal-to-noise ratio is 0 dB. And observing data for 40s, inputting the data into a bellhop sound field model, wherein the array signals continuously change along with the movement, propagation delay and signal amplitude attenuation of an underwater target, and the bellhop sound field model can generate multi-path array receiving signals.
step 3, adding the calculated power spectrums of the array element signals, and synthesizing a sound field time-frequency interference spectrum;
specifically, when the observation distance is far greater than the aperture of the array, the signals of the array elements have the same interference characteristic; for the conditions of only direct waves, primary sea surface reflected waves and primary seabed reflected waves, the power spectrums of the array element signals are added to obtain a power spectrum p of the kth frame of received signalsk(f) Comprises the following steps:
wherein p isxx(f) Is the power spectrum of the source signal, H1、H2And H3Uniform gain factors, tau, for the direct wave, the sea surface and the sea bottom reflected wave paths, respectivelyd、τrAnd τ'rRespectively delay direct wave, sea surface and seabed reflected wave, and:
τd＝Rd/c
τr＝Rr/c
τ'r＝R'r/c
wherein R isd、RrAnd R'rThe distance between the direct wave propagation path and the sea surface propagation path and the distance between the sea surface propagation path and the sea bottom reflection path are respectively, c is the sound velocity, the power spectrum of the multi-path received signal is the sum of the power spectrums of the direct wave propagation path, the sea surface propagation path and the sea bottom reflection path, interference terms of three frequency components are superposed, and when the interference terms exist, interference spectrum peaks are generated by the interference spectra when the signals of the two paths are completely coherent.
Step 5, calculating an array signal covariance matrix at the destructive interference frequency point;
specifically, the covariance matrix of the array signal of the destructive interference frequency points is
R(fi)＝X(fi)XH(fi)
Wherein R (f)i) Covariance matrix of array signal as destructive interference frequency point, X (f)i) For discrete Fourier transform of array received signal at destructive interference frequency point fiValue of (c) (. 1)HRepresenting a conjugate transpose.
And 6, calculating a space spectrum at the destructive interference frequency point, and performing DOA estimation.
Specifically, the destructive interference frequency point spatial spectrum includes an MVDR and a MUSIC spatial spectrum, which are respectively:
wherein, PMVDR(theta) and PMUSIC(theta) MVDR and MUSIC spatial spectra, respectively, theta being the scan orientation, (. alpha.)-1Representing the inverse operation, a (θ) is the array steering vector, (. cndot.)HWhich represents the transpose of the conjugate,
the position corresponding to the spatial spectrum peak is the target position.
Referring to the illustration of fig. 2, the MVDR and MUSIC spatial spectrums calculated for the wideband multi-pass array received signal show that due to the influence of the coherence of the multi-pass signal, the side lobes of the spatial spectrum are increased, and the spectrum peak deviates from the true target azimuth. Referring to the schematic diagram of fig. 3, the spectral peaks of the MVDR and MUSIC spatial spectrums of the destructive interference frequency points calculated by the method are located at the true target position, and it can be seen that the method of the present invention effectively reduces the influence of the multipath coherent channel under the low signal-to-noise ratio of 0dB, improves the position estimation precision, reduces the spatial spectrum side lobe, and is beneficial to the weak target detection.
It should be noted that the above-mentioned examples only represent some embodiments of the present invention, and the description thereof should not be construed as limiting the scope of the present invention. It should be noted that, for those skilled in the art, various modifications can be made without departing from the spirit of the present invention, and these modifications should fall within the scope of the present invention.
Claims (1)
1. A DOA estimation method under a multi-path channel is characterized in that: comprises the following steps of (a) carrying out,
step 1: acquiring a multi-path array receiving signal of an underwater target;
step 2, calculating the frequency spectrum and the power spectrum of each array element signal;
step 3, adding the calculated power spectrums of the array element signals, and synthesizing a sound field time-frequency interference spectrum;
step 4, obtaining destructive interference frequency in the sound field time-frequency interference spectrum;
step 5, calculating an array signal covariance matrix at the destructive interference frequency point;
step 6, calculating a space spectrum at the destructive interference frequency point, and performing DOA estimation to obtain a target azimuth;
in the step 3, when the observation distance is far greater than the aperture of the array, the signals of the array elements have the same interference characteristic; for the conditions of only direct waves, primary sea surface reflected waves and primary seabed reflected waves, the power spectrums of the array element signals are added to obtain a power spectrum p of the kth frame of received signalsk(f) Comprises the following steps:
wherein p isxx(f) Is the power spectrum of the source signal, H1、H2And H3Uniform gain factors, tau, for the direct wave, the sea surface and the sea bottom reflected wave paths, respectivelyd、τrAnd τ'rRespectively delay direct wave, sea surface and seabed reflected wave, and:
τd＝Rd/c
τr＝Rr/c
τ'r＝R'r/c
wherein R isd、RrAnd R'rThe distances among propagation paths of the direct wave, the sea surface and the seabed reflected wave are respectively, c is the sound velocity, the power spectrum of the received signal of the multi-path array is the sum of the power spectrums of the signals of the three propagation paths of the direct wave, the sea surface and the seabed reflected wave, interference terms of three frequency components are superposed, and the interference terms can enable the interference spectra to generate interference spectrum peaks when the signals of the two paths are completely coherent;
the step of obtaining the destructive interference frequency in the sound field time-frequency interference spectrum comprises the steps of realizing automatic tracking of a spectrum peak, real-time online extraction of interference frequency and destructive interference frequency estimation through accumulation of the spectrum peak of the low-frequency sound field time-frequency interference spectrum along the target motion direction;
the covariance matrix of the array signal of the destructive interference frequency points is R (f)i)＝X(fi)XH(fi)
Wherein R (f)i) Covariance matrix of array signal as destructive interference frequency point, X (f)i) For discrete Fourier transform of array received signal at destructive interference frequency point fiValue of (c) (. 1)HRepresents a conjugate transpose;
the destructive interference frequency point space spectrum comprises MVDR and MUSIC space spectrums which are respectively as follows:
wherein, PMVDR(theta) and PMUSIC(theta) MVDR and MUSIC spatial spectra, respectively, theta being the scan orientation, (. alpha.)-1Representing the inverse operation, a (θ) is the array steering vector, (. cndot.)HWhich represents the transpose of the conjugate,
the position corresponding to the spatial spectrum peak is the target position.
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