N-order omnidirectional adjustable differential beam former with controllable zero point and design method

Abstract

The invention discloses an N-order omnidirectional adjustable differential beam former with a controllable zero point and a design method, and belongs to the field of signal processing, and the method comprises the steps: constructing a signal steering vector according to the physical parameters of an AVS array; selecting an ideal N-order direction-adjustable beam pattern form, and setting target and non-target direction response constraints; a controllable zero point is introduced to design an N-order omni-directional adjustable differential beam pattern, and a constraint equation set is constructed to solve an N-order omni-directional adjustable differential beam pattern coefficient; and based on Maclaurin series expansion optimization weight vectors, designing all-order omnidirectional adjustable differential beam formers. According to the method, Maclaurin series expansion is taken as a theoretical basis, a target beam pattern meeting any steering angle and zero point direction constraint is constructed, a linear mapping relation is established between the target beam pattern and a signal steering vector, a minimum norm solution of a weight vector of each channel is deduced, and unified optimization of main lobe direction flexible adjustment and interference suppression is realized; and the omnidirectional adjustable function of the beam pattern from 0 degree to 360 degrees is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of signal processing, and particularly relates to an N-order omnidirectional adjustable differential beamformer with controllable zero points and a design method. BACKGROUND

[0002] As a technology for realizing spatial filtering by using spatial differentiation of adjacent array elements, the differential beamformer is widely used in the fields of speech enhancement, underwater target detection and the like. In recent years, the differential beamformer has attracted wide attention because it is suitable for wideband signal processing and small-sized system deployment. The conventional differential beamformer is usually designed based on a linear array with a fixed structure, and the main lobe direction of the beam pattern is usually fixed in the end-on direction, which is difficult to flexibly adjust. When the target direction changes or there are multiple interference sources, the misalignment between the beam main lobe and the target direction can easily lead to signal energy loss, and the fixed zero point structure cannot effectively suppress dynamic interference.

[0003] In order to improve the adaptability of the differential beamformer, researchers have tried to introduce an adjustable beam pattern design scheme, and to realize a certain degree of steering control by means of series expansion approximation target. However, these methods usually rely on preset beam pattern functions or prior coefficients, which limits their practicability. At the same time, the number of zero points of the conventional differential beamformer usually increases linearly with the array order, and the zero point position cannot be flexibly controlled, which lacks adaptability to complex interference environments. When the zero point is too deep, it can also lead to the deterioration of white noise gain, affecting the robustness of the system.

[0004] Especially in the design of N-order differential beam pattern, how to improve the steering ability of the main lobe while realizing the flexible control of the number and position of the zero points has become a key challenge in the design of differential arrays. The existing design methods for linear acoustic vector arrays still have problems such as lack of general adjustable order structure, inflexible zero point design mechanism, lack of explicit weight expression, and the like, which makes it difficult to achieve an effective balance between the steering ability, interference suppression ability and beam pattern control precision. Therefore, there is an urgent need for a differential beamformer design method applicable to linear arrays, which has N-order omnidirectional adjustable ability and flexible zero point control ability, and can explicitly establish an analytical mapping between the beam pattern structure and the weight, so as to cope with complex interference scenarios in a variable target environment. SUMMARY

[0005] In order to solve the problems that the existing differential beamformer and its design method cannot realize omnidirectional adjustment, the zero point setting is not flexible, and the anti-interference ability is insufficient in the beam pattern design process, the application provides an N-order omnidirectional adjustable differential beamformer with controllable zero points and a design method, which has omnidirectional adjustability, flexible zero point control, strong anti-interference ability and the like.

[0006] The application provides an N-order omnidirectional adjustable differential beamformer with controllable zero points and a design method thereof.

[0007] The technical scheme adopted by the application to solve the technical problems is as follows:

[0008] The design method of the N-order omnidirectional adjustable differential beamformer with controllable zero points comprises the following steps:

[0009] (1) constructing a signal steering vector according to physical parameters of an AVS array;

[0010] (2) selecting an ideal N-order adjustable directional beam pattern form, setting target and non-target directional response constraints;

[0011] (3) introducing controllable zero point design N-order omnidirectional adjustable differential beam patterns, constructing a constraint equation group to solve N-order omnidirectional adjustable differential beam pattern coefficients;

[0012] (4) optimizing a weight value vector based on a Maclaurin series expansion, and designing each-order omnidirectional adjustable differential beamformers.

[0013] Preferably, the mathematical expression of the signal steering vector is:

[0014]

[0015] wherein, represents a corresponding phase vector, ω represents a signal angular frequency, and the superscript represents a transposition operation, , represents a Kronecker product, , represents a time delay of adjacent AVSs, , represents a far-field plane wave sound speed; represents a far-field plane wave incident angle, represents a distance between two adjacent AVSs, and M represents the number of AVSs.

[0016] Preferably, the ideal N-order adjustable directional beam pattern form is:

[0017]

[0018] wherein, represents a real coefficient, , represents a steering angle, This represents the incident angle of a far-field plane wave.

[0019] Preferably, in step (3), zero-point constraints are first set, and 2N-1 interference directions to be suppressed are selected as beam pattern zero points, requiring the beamformer to respond to plane waves to be 0 in these directions.

[0020] Preferably, in step (3), the beam pattern expression is modeled as a polynomial expansion with respect to the incident angle θ of the far-field plane wave, then the Nth-order omnidirectional adjustable differential beam pattern is expressed as:

[0021]

[0022] in, , representing the angle of alignment of 2N-1 zeros; beam pattern coefficient and Determined by the azimuth angle and the zero point, and satisfying:

[0023]

[0024]

[0025] in, The unit step function is defined as follows:

[0026] .

[0027] Preferably, in step (3), the mathematical expression of the constraint equation system is:

[0028]

[0029] in, for A column vector of dimension 1, where the first element is 1 and the rest are 0;

[0030]

[0031] in, ;

[0032] The coefficients of the Nth-order omnidirectional adjustable differential beammap are calculated using the following formula:

[0033] .

[0034] The present invention provides an Nth-order omnidirectional adjustable differential beamformer with controllable zeros, designed using the design method provided in the first aspect.

[0035] The beneficial effects of this invention are:

[0036] The application realizes the unified optimization of flexible adjustment of main lobe direction and interference suppression, effectively realizes the omnidirectional adjustable function of beam pattern from 0° to 360°, and solves the technical contradiction that the existing differential beamformer cannot consider the adjustable direction and interference suppression ability by adjusting the zero angle to control the interference direction response.

[0037] The application is suitable for a multi-channel signal structure based on a small-aperture linear acoustic vector sensor array, supports asymmetric beam pattern construction and high-resolution spatial filtering, is particularly suitable for deployment in a small platform with limited space, and has significant advantages in improving directivity gain, enhancing target detection capability and flexibly controlling interference. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 It is a design method flow chart of an N-order omnidirectional adjustable differential beamformer with controllable zero points provided by the application.

[0039] Figure 2 It is an implementation effect diagram of a first-order omnidirectional adjustable differential beamformer when the steering angle is 30°.

[0040] Figure 3 It is an implementation effect diagram of a first-order omnidirectional adjustable differential beamformer when the steering angle is 90°.

[0041] Figure 4 It is an implementation effect diagram of a first-order omnidirectional adjustable differential beamformer when the steering angle is 150°.

[0042] Figure 5 It is an implementation effect diagram of a first-order omnidirectional adjustable differential beamformer when the steering angle is 300°.

[0043] Figure 6 It is an implementation effect diagram of a second-order omnidirectional adjustable differential beamformer when the steering angle is 30°.

[0044] Figure 7 It is an implementation effect diagram of a second-order omnidirectional adjustable differential beamformer when the steering angle is 90°.

[0045] Figure 8 It is an implementation effect diagram of a second-order omnidirectional adjustable differential beamformer when the steering angle is 150°.

[0046] Figure 9 It is an implementation effect diagram of a second-order omnidirectional adjustable differential beamformer when the steering angle is 300°.

[0047] Figure 10 This is a diagram illustrating the implementation effect of the third-order omnidirectional adjustable differential beamformer of the present invention at a steering angle of 30°.

[0048] Figure 11 This is a diagram illustrating the implementation effect of the third-order omnidirectional adjustable differential beamformer of the present invention at a steering angle of 90°.

[0049] Figure 12 This is a diagram illustrating the implementation effect of the third-order omnidirectional adjustable differential beamformer of the present invention at a steering angle of 150°.

[0050] Figure 13 This is a diagram illustrating the implementation effect of the third-order omnidirectional adjustable differential beamformer of the present invention at a steering angle of 300°. Detailed Implementation

[0051] The present invention will be further described in detail below with reference to the accompanying drawings.

[0052] In a first aspect, the present invention provides a design method for an Nth-order omnidirectional adjustable differential beamformer with controllable zeros.

[0053] like Figure 1 As shown, the present invention provides a design method for an Nth-order omnidirectional adjustable differential beamformer with controllable zeros, the specific implementation process of which is as follows:

[0054] Step S1: Set the operating parameters;

[0055] Determine and initialize the operating parameters. These parameters include: the angular frequency of the detected signal, the number of array elements in the Acoustics Vector Sensor (AVS) array, and the element spacing.

[0056] Specifically, the physical parameters (number of array elements, spacing between array elements) of the AVS array can be set according to the requirements of the detection scenario (such as detection distance, anti-interference strength, etc.) to provide basic parameters for the subsequent construction of the guide vector.

[0057] Step S2: Generate and transmit detection signals;

[0058] First, a probe signal that meets specific frequency range and waveform requirements is generated using a signal generator to ensure that the probe signal bandwidth meets the narrowband assumption, which facilitates the application of the far-field plane wave model.

[0059] Then, the detection signal strength is enhanced by a power amplifier, and the detection signal is radiated directionally to the target area by a transmitting transducer array, establishing a detection signal propagation link. Furthermore, the transmission process can be repeated periodically until a valid sound source target is detected.

[0060] Step S3: Determine whether there is a sound source target. If no sound source target is detected, return to step S2 to continue detection. If a sound source target is detected, proceed to step S4.

[0061] Step S4: Signal reception and preprocessing;

[0062] S4.1: Echo signal reception;

[0063] Each element in the AVS array synchronously receives spatial echo signals. Each AVS includes: a sound pressure channel, a particle velocity channel in the x-axis direction, and a particle velocity channel in the y-axis direction.

[0064] S4.2: Signal preprocessing;

[0065] The echo signal of each channel is bandpass filtered, amplified, and normalized to eliminate DC bias and high-frequency noise.

[0066] Step S5: Core beamline design phase, the specific implementation process of which is as follows:

[0067] S5.1: Construct the signal steering vector based on the determined physical parameters of the AVS array;

[0068] Assuming the far-field plane wave travels at the speed of sound Incident on M AVSs placed along the x-axis, the distance between any two adjacent AVSs is... The angle of incidence is Then the signal steering vector can be expressed as:

[0069]

[0070] in, The superscript indicates the corresponding phase vector, ω represents the signal angular frequency, and the superscript indicates the phase vector. This indicates the transpose operation. , Represents the Kronecker product. , Indicates the delay between adjacent AVSs. .

[0071] Assuming the distance between two adjacent AVS is significantly less than half the signal wavelength, i.e. ,in denoted by wavelength, f is the signal frequency.

[0072] If the target orientation angle is The received signal can then be expressed as:

[0073]

[0074] in, S1.1: The received signal of the first AVS pressure channel is denoted as and denote the received signal vector and noise vector of the AVS, respectively.

[0075] The received signal is filtered by a conventional filter, and the output of the filter can be denoted as

[0076]

[0077] where the superscript denotes the conjugate transpose operator, denotes the received signal vector of the m-th AVS, denotes the weight vector corresponding to the N-order omnidirectional adjustable differential beamformer; denotes the weight of each channel of the m-th AVS, , and denote the weight of the m-th AVS pressure channel, x-axis direction particle velocity channel and y-axis direction particle velocity channel, respectively.

[0078] S5.2: Select an ideal N-order adjustable directional beam pattern form, set target and non-target direction response constraints;

[0079] The beam pattern represents the response of the N-order omnidirectional adjustable differential beamformer to a plane wave with different incident angles, and is defined as follows:

[0080]

[0081] To ensure that the signal is not distorted in the target direction, it is necessary to ensure that the beamformer has the maximum response (value 1) in the target direction and the response in other directions is less than 1, i.e.:

[0082]

[0083] According to the current task accuracy requirement and interference complexity, the order N is selected, the higher the order, the narrower the main lobe and the more zero points are controlled. Then according to the above definition, the ideal N-order adjustable directional beam pattern can be denoted as:

[0084]

[0085] where denotes a real coefficient, , denotes the steering angle.

[0086] The steering angle is defined as the position where the maximum response occurs, and only when reaches the maximum value, i.e.:

[0087]

[0088] The above beam pattern can be used to the incident angle of the far field plane wave Derivation, verification The position of the maximum value indicates that the design realizes the beam pattern steering technology from to That is:

[0089]

[0090] Step S6: introducing the controllable zero point design N-order omnidirectional adjustable differential beam pattern, solving the N-order omnidirectional adjustable differential beam pattern coefficient by constructing the constraint equation group;

[0091] S6.1: setting zero point constraint;

[0092] The zero point constraint is set, and 2N-1 interference directions to be suppressed can be selected according to the requirements, which are used as the beam pattern zero point, that is, the beamformer requires that the response to the plane wave in these directions is 0.

[0093] S6.2: design N-order omnidirectional adjustable differential beam pattern;

[0094] In order to realize the omnidirectional adjustment of the beam pattern from to , and arbitrarily control the zero point position of the beam pattern, the beam pattern expression is modeled as a polynomial expansion about the far field plane wave incident angle θ, then the basic form of the N-order omnidirectional adjustable differential beam pattern designed by the application can be expressed as:

[0095]

[0096] Wherein, , indicates the angle of 2N-1 zero points. The beam pattern coefficient and are determined by the steering angle and the zero point, and satisfy:

[0097]

[0098]

[0099] Wherein, indicates the unit step function, which is defined as:

[0100]

[0101] The N-order omnidirectional adjustable differential beam pattern designed above is expanded using the binomial theorem, and the following can be obtained:

[0102]

[0103] wherein, , denotes a factorial operation.

[0104] When k is odd, we have:

[0105]

[0106] wherein, is an integer and satisfies .

[0107] When k is even, we have:

[0108]

[0109] wherein, is an integer and satisfies . Therefore, we can deduce that:

[0110]

[0111] and

[0112]

[0113] wherein,

[0114]

[0115]

[0116] When , for a certain steering angle , the zero points can be flexibly controlled according to requirements, and by adjusting the zero point positions, the N-order omnidirectional adjustable differential beam pattern designed above satisfies the following equation:

[0117]

[0118] According to the above equation, it can be deduced that the N-order omnidirectional adjustable differential beam pattern designed above is an extension of the ideal N-order adjustable directional beam pattern, that is:

[0119]

[0120] The N-order omnidirectional adjustable differential beam pattern designed above not only exhibits a single peak from to , but also contains a set of 2N-1 controllable zero points to flexibly control interference and noise.

[0121] S6.3: Construct a constraint equation set to solve the N-order omnidirectional adjustable differential beam pattern coefficients;

[0122] The constructed constraint equation set is as follows:

[0123]

[0124] Controllable zero point set , satisfy the above constraint equation set. Wherein, is a column vector of dimension N, the first element is 1 and the remaining elements are 0.

[0125]

[0126] Wherein, .

[0127] The coefficients of the N-order omnidirectional adjustable differential beam pattern designed above can be calculated by the following formula:

[0128]

[0129] The coefficients that make the target direction gain 1 and the interference direction 0 can be solved by the above calculation formula.

[0130] Step S7: Optimize the weight vector based on the Maclaurin series expansion, and realize the design of each order omnidirectional adjustable differential beamformer;

[0131] In order to obtain an omnidirectional adjustable differential beamformer, when , the N-order omnidirectional adjustable differential beam pattern has a maximum value, that is, it needs to satisfy:

[0132]

[0133] And

[0134]

[0135] When designing a first-order omnidirectional adjustable differential beamformer, that is, when N=1, the ideal first-order omnidirectional adjustable differential beam pattern can be represented as:

[0136]

[0137] In order to obtain a first-order omnidirectional adjustable differential beam pattern consistent with the form of the above ideal first-order omnidirectional adjustable differential beam pattern, the weight vector is applied to each channel of the AVS, and the ideal first-order omnidirectional adjustable differential beam pattern form is approximated by using Maclaurin series expansion. It can be obtained:

[0138]

[0139] Wherein, indicates the truncation factor, , , denotes a column vector of dimension, which is specifically given by

[0140]

[0141] where the specific forms of other parameters are

[0142]

[0143]

[0144]

[0145]

[0146] In summary, the form of the first-order omnidirectional steerable differential beam pattern can be simplified as

[0147]

[0148] Comparing the above first-order omnidirectional steerable differential beam pattern with the ideal first-order omnidirectional steerable differential beam pattern, we have

[0149]

[0150] When , the minimum norm solution of the above equation is

[0151]

[0152] where , , , , denotes a zero matrix of dimension.

[0153] Similarly, when designing a second-order omnidirectional steerable differential beamformer, the ideal second-order omnidirectional steerable differential beam pattern can be expressed as

[0154]

[0155] where is determined by the difference between the sound pressure and the x-axis velocity, which can be obtained by the sound pressure differential approximation, and the x-axis velocity is determined by the sound pressure channel. By introducing a constant to represent the beam pattern weight obtained from the first-order differentiation of the sound pressure sensor. Since the constant amplitude does not change the beam pattern shape, the ideal second-order omnidirectional steerable differential beam pattern can be simplified as

[0156]

[0157] The simplified form of the second-order omnidirectional steerable differential beam pattern is:

[0158]

[0159] Comparing the above second-order omnidirectional steerable differential beam pattern with the ideal second-order omnidirectional steerable differential beam pattern, we have:

[0160]

[0161] Similarly, when , the minimum norm solution of the above formula is:

[0162]

[0163] In the case of N>1, we have:

[0164]

[0165]

[0166]

[0167] The design method of the third-order omnidirectional steerable differential beamformer is similar to that of the second-order omnidirectional steerable differential beamformer. Referring to the design method of the second-order omnidirectional steerable differential beamformer, by introducing a constant , the ideal third-order omnidirectional steerable differential beam pattern can be simplified as:

[0168]

[0169] Similarly, comparing the above ideal third-order omnidirectional steerable differential beam pattern with the third-order omnidirectional steerable differential beam pattern, we have:

[0170]

[0171] When , the minimum norm solution is:

[0172]

[0173] In summary, by introducing a constant , the expression of the ideal N-order omnidirectional steerable differential beam pattern can be simplified as:

[0174]

[0175] Using the Maclaurin series expansion to approximate the ideal N-order omnidirectional steerable differential beam pattern, we have:

[0176]

[0177] By comparing with the above-mentioned form of the expansion of the Maclaurin series, the relationship between the beam pattern coefficient and the weight vector can be obtained:

[0178]

[0179] When the minimum norm solution of the above formula is:

[0180]

[0181] Step S8; beam forming;

[0182] The above-solved weight vector is applied to the received signal to synthesize the beam pattern, and at the target direction the maximum response is realized, and according to the requirement, the zero point is set at the interference direction, and the complete beam pattern has high main lobe gain and strong side lobe suppression capability.

[0183] In the present application, Figures 2-5 the beam pattern of the first-order omnidirectional adjustable differential beam former at the steering angles of 30°, 90°, 150° and 300°, Figures 6-9 the beam pattern of the second-order omnidirectional adjustable differential beam former at the steering angles of 30°, 90°, 150° and 300°, Figures 10-13 the beam pattern of the third-order omnidirectional adjustable differential beam former at the steering angles of 30°, 90°, 150° and 300°. Wherein, the dotted line represents the beam pattern designed in the present application, and the solid line is the ideal beam pattern. The two are highly consistent at different steering angles and orders, proving the feasibility of the present application.

[0184] The above-mentioned is only the preferred embodiment of the present application, and it should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should be considered as the protection scope of the present application.

Claims

1. A design method of an Nth-order omnidirectional adjustable differential beamformer with a controllable zero point, characterized in that, The method comprises the following steps: (1) constructing a signal steering vector according to physical parameters of an AVS array; (2) selecting an ideal N-order adjustable directional beam pattern form, setting target and non-target direction response constraints; (3) introducing a controllable zero point to design an N-order omnidirectional adjustable differential beam pattern, constructing a constraint equation set to solve coefficients of the N-order omnidirectional adjustable differential beam pattern; (4) optimizing a weight vector based on a Maclaurin series expansion, and designing each-order omnidirectional adjustable differential beamformer.

2. The design method of an Nth-order omnidirectional adjustable differential beamformer with a controllable zero point according to claim 1, wherein, A mathematical expression of the signal steering vector is: ； wherein, denotes the corresponding phase vector, ω denotes the signal angular frequency, the superscript denotes the transpose operation, , denotes the Kronecker product, , denotes the time delay of adjacent AVSs, , denotes the sound speed of far-field plane wave; denotes the incident angle of far-field plane wave, denotes the distance between adjacent two AVSs, M denotes the number of AVSs.

3. The method of designing an Nth-order omnidirectional adjustable differential beamformer with a controllable zero point according to claim 1, wherein, The ideal N-order adjustable directional beam pattern form is: ； wherein denotes a real coefficient, , denotes a steering angle, denotes a far-field plane wave incidence angle.

4. The method of designing an Nth-order omnidirectional adjustable differential beamformer with a controllable zero point according to claim 1, wherein, In step (3), zero point constraints are first set, 2N-1 interference directions to be suppressed are selected as beam pattern zeros, and the beamformer is required to have a response of 0 to a plane wave in these directions.

5. The method of designing an Nth-order omnidirectional adjustable differential beamformer with a controllable zero point according to claim 1, wherein, In step (3), a beam pattern expression is modeled as a polynomial expansion about an incident angle θ of a far-field plane wave, and the N-order omnidirectional adjustable differential beam pattern is expressed as: ； wherein , denotes the angle of 2N - 1 nulls alignment; beam pattern coefficients and are determined by the steering angle and the nulls and satisfy: ； ； wherein denotes the unit step function, which is defined as: 。 6. The method of designing an Nth-order omnidirectional adjustable differential beamformer with a controllable zero point of claim 1, wherein, In step (3), a mathematical expression of the constraint equation set is: ； wherein is a column vector of ones, with the first element being 1 and the remaining elements being 0; ； wherein ; Coefficients of the N-order omnidirectional adjustable differential beam pattern are calculated by the following formula: 。 7. The N-order omnidirectional adjustable differential beamformer with controllable zeros designed by the method according to any one of claims 1-6.

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