阅读说明：本技术 双基地展开互质阵列mimo雷达dod和doa降维估计方法 (Bistatic expansion co-prime array MIMO radar DOD and DOA dimension reduction estimation method ) 是由 周围 王强 唐俊 张维 潘英杰 于 2020-03-29 设计创作，主要内容包括：本发明涉及雷达技术领域,尤其涉及双基地展开互质阵列MIMO雷达DOD和DOA降维估计方法,该方法基于双基地展开互质阵列MIMO雷达阵列结构,提出了基于降维多重信号分类算法的双基地展开互质阵列MIMO雷达离开角、到达角联合估计方法,该方法通过增加约束并构造代价函数的方式,将二维MUSIC算法中的二维谱峰搜索最大值转化为求解带约束的一维最优值,先后得到DOA、DOD,并且DOD与DOA自动配对。本发明中降维思想的引入使得算法无需二维搜索,因而复杂度显著下降；得益于展开互质阵列更大的阵列孔径与MIMO雷达形成的虚拟阵列,使得本发明提出的方法在各方面性能优异；此外,子阵数目的互质消除了阵元间距大于半波长可能导致的相位模糊问题。(The invention relates to the technical field of radars, in particular to a bistatic unfolding co-prime array MIMO radar DOD and DOA dimension reduction estimation method, which is based on a bistatic unfolding co-prime array MIMO radar array structure and provides a bistatic unfolding co-prime array MIMO radar exit angle and arrival angle joint estimation method based on a dimension reduction multiple signal classification algorithm. The introduction of the dimension reduction idea in the invention enables the algorithm to be free from two-dimensional search, thereby obviously reducing the complexity; due to the fact that a larger array aperture of a co-prime array and a virtual array formed by the MIMO radar are unfolded, the method provided by the invention has excellent performance in all aspects; in addition, the coprime of the number of the sub-arrays eliminates the phase ambiguity problem which can be caused by the array element spacing being larger than half wavelength.)

1. A bistatic unfolding mutual prime array MIMO radar DOD and DOA dimension reduction estimation method is characterized by comprising the following steps:

solving a spatial covariance matrix for received data obtained after matching and filtering receiving array elements in a bistatic expansion co-prime array MIMO radar, and performing eigenvalue decomposition on the spatial covariance matrix to obtain a noise subspace U_n；

Noise subspace U to be obtained_nParticipating in defining the detection matrix:

carrying out optimization deformation on the detection matrix, and increasing constraint conditions to define a cost function to obtain a search formula;

carrying out peak value search on a search formula, wherein the positions corresponding to the first K spectral peaks with larger power are obtained by searching and are DOA estimation;

obtaining a steering vector corresponding to DOD under the transmitting array according to the obtained DOA estimation;

solving phi using a least squares strategy_kTo obtain an estimated transmission angle

2. The bistatic extended co-prime array MIMO radar DOD and DOA dimension reduction estimation method according to claim 1, wherein the bistatic extended co-prime array MIMO radar comprises a transmitting array and a receiving array which are placed in different places, the transmitting array and the receiving array respectively comprise a sub-array 1 and a sub-array 2 of two sparse uniform linear arrays, the sub-array 1 and the sub-array 2 are completely arranged in an extended manner in opposite directions, and the last array element of the sub-array 1 is coincident with the first array element of the sub-array 2.

3. The bistatic extended co-prime array MIMO radar DOD and DOA dimension reduction estimation method according to claim 2, wherein the bistatic extended co-prime array MIMO radar has an array element number of M, N for sub-array 1 and sub-array 2, respectively, and M, N co-prime, M < N, the array element spacing of sub-array 1 is N λ/2, the array element spacing of sub-array 2 is M λ/2, λ represents the wavelength of the electromagnetic signal incident on the extended co-prime array, and the array element numbers of the transmitting array and the receiving array are both M + N-1.

4. The bistatic extended mutual-prime array MIMO radar DOD and DOA dimension reduction estimation method according to claim 3, wherein the received data obtained after the matching filtering of the receiving array elements is as follows:

x(t)＝As(t)+n(t)

where s (t) is the echo signal vector, A is the virtual array prevalence of the extended co-prime array MIMO radar, n (t) is the mean 0, and the variance σ is²An additive white gaussian noise vector.

5. The bistatic-extended co-prime array MIMO radar DOD and DOA dimension reduction estimation method according to claim 4, wherein the spatial covariance matrix is as follows:

where Σ denotes a summation operation and H denotes a conjugate transpose operation.

6. The bistatic-unfolding relatively prime array MIMO radar DOD and DOA dimension reduction estimation method according to claim 5, wherein the constraint condition is e^Ta_t(phi) 1, where e is [1,0 … 0]。

7. The bistatic-extended co-prime array MIMO radar DOD and DOA dimension reduction estimation method of claim 6, the cost function is expressed as follows:

in the formula, ω is a constant.

8. The bistatic extended mutual prime array MIMO radar DOD and DOA dimension reduction estimation method according to claim 7, wherein the search formula is as follows:

the peak value search is to search a search formula in the range of theta belonging to (-pi/2, pi/2) and search the first K spectral peaks with larger power according to the sequence from high to low.

9. The bistatic-extended mutual-prime array MIMO radar DOD and DOA dimension reduction estimation method of claim 8, wherein the estimated emission angle isIs obtained by the following formula:

Technical Field

The invention relates to the technical field of radars, in particular to a bistatic expansion co-prime array MIMO radar DOD and DOA dimension reduction estimation method.

Background

The application of the MIMO technology in communication significantly improves channel capacity and reliability under fading channels, and is one of core technologies in the field of wireless communication. The MIMO technology was initiated, and researchers began to think whether the MIMO technology could be applied to radar systems, and the first MIMO radar was proposed by Bliss and Forsythe in the lincoln laboratory in 2003. The MIMO radar technology is characterized in that a plurality of antennas are respectively configured on a transmitting array and a receiving array for orthogonal signal transmission and echo reception of far-field signals, and the MIMO radar technology is divided into two forms of a single base for transmitting and receiving and a single base for transmitting and receiving according to whether the transmitting and receiving arrays are positioned at the same position. Under the condition of not increasing transmitting power and system bandwidth, the MIMO radar technology improves the channel capacity and the spectrum utilization rate of a system by multiple times, can also improve the channel reliability, and is superior to the radar of the traditional system in the aspects of spatial resolution, freedom degree, parameter identifiability and the like, so that more attention is paid to the academic world, and the bistatic MIMO radar is greatly improved in the aspects of interference resistance, interception resistance, speed resolution, detection performance, clutter suppression, low-altitude small target detection and the like.

The bistatic MIMO radar can simultaneously estimate the target direction of a receiving station and the target direction of a transmitting station by utilizing the direction correlation of transmitting and receiving array signals, has higher target parameter estimation precision, avoids three technical problems of time, angle and frequency (phase) synchronization in the measurement of the inherent target parameters of the bistatic, and has the double advantages of the bistatic radar and the MIMO technology. Therefore, estimation Of the angle Of Arrival (DOA) and joint estimation Of the angle Of Departure (DOD) and the angle Of Arrival (DOA) Of the bistatic MIMO radar are important research contents Of the MIMO radar, and have become one Of the hot spots Of the MIMO radar research. Although the traditional subspace algorithm such as MUSIC and ESPRTT algorithm can be suitable for angle estimation of bistatic MIMO radar, the problem of low estimation accuracy under low signal-to-noise ratio exists, and the ESPRTT algorithm utilizes the characteristic of rotation invariant factor and is only suitable for equidistant linear array. The traditional method for performing two-dimensional search on the accumulated matched filtering output signals of the receiver and determining the DOD and the DOA by searching peak values has the problems of large calculation amount and low positioning precision, and the application of the traditional method in an actual radar system is severely limited.

Disclosure of Invention

In view of the above, the present invention aims to provide a bistatic unfolding mutual prime array MIMO radar DOD and DOA dimension reduction estimation method, which converts a two-dimensional spectrum peak search maximum value in a two-dimensional MUSIC algorithm into a one-dimensional optimal value with constraint by adding constraint and constructing a cost function, so as to obtain DOA and DOD in sequence, and the DOD and DOA are automatically paired, thereby avoiding two-dimensional exhaustive search, and greatly reducing complexity; a virtual array formed by the MIMO radar and the array aperture with the larger co-prime array is expanded, and the performance of the proposed algorithm is excellent in all aspects.

The invention solves the technical problems by the following technical means:

a bistatic unfolding co-prime array MIMO radar DOD and DOA dimension reduction estimation method comprises the following steps:

solving a spatial covariance matrix for received data obtained after matching and filtering receiving array elements in a bistatic expansion co-prime array MIMO radar, and performing eigenvalue decomposition on the spatial covariance matrix to obtain a noise subspace U_n；

Noise subspace U to be obtained_nParticipating in defining the detection matrix:

carrying out optimization deformation on the detection matrix, and increasing constraint conditions to define a cost function to obtain a search formula;

carrying out peak value search on a search formula, wherein the positions corresponding to the first K spectral peaks with larger power are obtained by searching and are DOA estimation;

obtaining a steering vector corresponding to DOD under the transmitting array according to the obtained DOA estimation;

solving phi using a least squares strategy_kTo thereby obtain an estimated hairAngle of incidence

Further, the bistatic expansion co-prime array MIMO radar comprises a transmitting array and a receiving array which are placed in different places, wherein the transmitting array and the receiving array respectively comprise a sub-array 1 and a sub-array 2 of two sparse uniform linear arrays, the sub-array 1 and the sub-array 2 are completely expanded and arranged in opposite directions, and the last array element of the sub-array 1 is coincided with the first array element of the sub-array 2.

Further, in the bistatic unfolding co-prime array MIMO radar, the number of array elements of a sub-array 1 and a sub-array 2 is M, N, and M, N is co-prime, M is less than N, the distance between array elements of the sub-array 1 is N lambda/2, the distance between array elements of the sub-array 2 is M lambda/2, lambda represents the wavelength of an electromagnetic signal incident to the unfolding co-prime array, and the number of the array elements of the transmitting array and the number of the array elements of the receiving array are both M + N-1.

Further, the received data obtained after the matching filtering of the receiving array elements is as follows:

x(t)＝As(t)+n(t)

where s (t) is the echo signal vector, A is the virtual array prevalence of the extended co-prime array MIMO radar, n (t) is the mean 0, and the variance σ is²An additive white gaussian noise vector.

Further, the spatial covariance matrix is as follows:

where Σ denotes a summation operation and H denotes a conjugate transpose operation.

Further, the constraint condition is e^Ta_t(phi) 1, where e is [1,0 … 0]。

Further, the cost function is represented as follows:

in the formula, ω is a constant.

Further, the search formula is as follows:

the peak value search is to search a search formula in the range of theta belonging to (-pi/2, pi/2) and search the first K spectral peaks with larger power according to the sequence from high to low.

Further, the estimated transmission angleIs obtained by the following formula:

compared with the prior art, the invention has the following advantages:

(1) the traditional co-prime array is unfolded into two opposite directions to obtain an unfolded co-prime array, and the unfolded co-prime array completely unfolds the two sub-arrays, so that a larger array aperture is obtained compared with a uniform array and the traditional co-prime array under the condition that the number of array elements is limited. And the expanded co-prime arrays are respectively used as a transmitting array and a receiving array of the MIMO radar, and the dimensionality reduction thought in the mathematical sense is introduced by utilizing the large array aperture of the expanded co-prime arrays and the excellent spatial resolution, freedom degree, parameter identifiability and other performances of the MIMO radar, so that the algorithm does not need two-dimensional search, and the complexity is greatly reduced compared with the two-dimensional MUSIC algorithm.

(2) The DOA estimation method is different from the traditional co-prime array DOA estimation algorithm that the received data of two sub-arrays are respectively processed, so that the degree of freedom is reduced by at least half, the whole receiving array is taken as a whole, and the received data of all receiving array elements are used for DOA estimation.

(3) The mutual nature of the numbers of the sub-arrays of the transmitting array and the receiving array can eliminate the phase ambiguity problem which can be caused by the array element spacing being larger than half wavelength.

Drawings

FIG. 1 is a schematic diagram of the geometry of a bistatic unfolding co-prime array MIMO radar of the present invention;

FIG. 2 is a space two-dimensional map of DOD and DOA dimension reduction estimation under bistatic unfolding co-prime array MIMO radar, bistatic traditional co-prime array MIMO radar and uniform array MIMO radar;

FIG. 3 is a two-dimensional map estimation of a bistatic extended co-prime array MIMO radar in a multi-source scene.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Firstly, establishing a system mathematical model

The method comprises the following specific steps of forming an expanded co-prime array MIMO radar by using 2M +2N-1 antenna array elements, wherein M and N represent two co-prime integers, receiving an echo signal of a transmitting array transmitting signal reflected by K targets by a receiving array of the MIMO radar, and constructing the expanded co-prime array MIMO radar:

the bistatic expansion co-prime array MIMO radar in the embodiment of the invention comprises a transmitting array and a receiving array which are placed in different places, the geometrical structures of the transmitting array and the receiving array are shown in figure 1, the transmitting array and the receiving array respectively comprise a sub-array 1 and a sub-array 2 of two sparse uniform linear arrays, the sub-array 1 and the sub-array 2 are completely expanded and arranged in opposite directions, and the last array element of the sub-array 1 is coincident with the first array element of the sub-array 2. The number of the array elements of the subarray 1 and the subarray 2 is M, N respectively, M, N are relatively prime, and M < N is set without loss of generality. The array element spacing of the subarray 1 is N lambda/2, the array element spacing of the subarray 2 is M lambda/2, wherein lambda represents the wavelength of an electromagnetic signal incident to the expanded co-prime array, and the array element numbers of the transmitting array and the receiving array are both M + N-1.

Then, the array element positions of the transmitting array and the receiving array can be expressed as

P_t＝P_r＝{Mnd0|0≤n≤(N-1)}∪{M(N-1)d0+Nmd₀|0≤m≤(M-1)} (1)

Wherein d is₀Is a half wavelength. Each transmitting array element simultaneously transmits a same-frequency orthogonal periodic phase coding signal, and the transmitting signals meet the conditional formula (2)

Wherein s is_i、s_jThe signals of the ith and jth transmit array elements, respectively, L is the number of phase codes per repetition period, and ∑ represents the summation operation.

Acquiring the guide vectors of a transmitting subarray and a receiving subarray:

assume that there are K far-field targets that are uncorrelated with each other and satisfy K<(M+N-1)²Respectively at an emission angle of phi₁,φ₂…φ_KThe echo arrival angles of the targets are respectively theta₁,θ₂…θ_KTherefore, the steering vectors of the transmitting array and the receiving array with respect to the k-th target can be expressed by equations (3) and (4), respectively

Wherein, a_t1(φ_k)、a_t2(φ_k) Respectively, the steering vectors of the sub-array 1 and the sub-array 2 in the transmitting array, a_r1(θ_k),a_r2(θ_k) Then the steering vectors for sub-array 1 and sub-array 2 in the receiving array are respectively, K is 1,2 … K. The guide vector expressions of the transmitting subarray and the receiving subarray are respectively

Thus obtaining the array manifold A of the transmitting array and the receiving array_t，A_rAs follows

A_t＝[a_t(φ₁),a_t(φ₂),…a_t(φ_K)](7)

A_r＝[a_r(θ₁),a_r(θ₂),…a_r(θ_K)](8)

Further obtaining a virtual array manifold of the extended co-prime array MIMO radar

Wherein

Represents the Khatri-Rao product,representing the Kronecker product. Thus, the received data of the receiving array element after matched filtering can be obtained

x(t)＝As(t)+n(t) (11)

Where s (t) is the echo signal vector

β_kRadar cross section coefficient (RCS), f of the k point target_dkDoppler frequency, f, of the k point target_sThe pulse repetition frequency of the transmit waveform. n (t) is a mean of 0 and a variance of σ²An additive white gaussian noise vector.

Estimating a covariance matrix:

from which a spatial covariance matrix R is calculated_xx

WhereinIs the covariance matrix of the source and,is the power of the kth source. I is a dimension of (M + N-1)²×(M+N-1)²The unit matrix of (1), in practical engineering application, the spatial covariance matrix can be estimated by L sampling snapshots, so that

In the formula, t is 1,2 … L, and H denotes a conjugate transpose operation.

Bistatic expansion co-prime array MIMO radar DOD and DOA dimension reduction estimation algorithm

Based on the system mathematical model, the bistatic unfolding co-prime array MIMO radar DOD and DOA dimension reduction estimation algorithm of the embodiment of the invention is as follows:

first, define the detection matrix

For (16) reconstruction of the deformation, expressed as

WhereinU_nFor the noise subspace obtained after the feature decomposition of the spatial covariance matrix, equation (17) can be regarded as a suboptimal problem, i.e. the optimal solution set under the expression is foundI.e., the minimum point of V (phi, theta).

First add constraint e^Ta_t(phi) 1, where e is [1,0 … 0]To exclude a_t(φ) is a meaningless solution of all 0's. To this end, the problem is transformed into a mathematical problem that solves the optimal solution under constraint conditions, as described below

A standard method for solving the optimal value according to the Lagrange multiplier method is to define the cost function firstly

Where ω is a constant, relating to a_t(phi) and making it 0

Can be solved to obtainAnd with constraint e^Ta_t(phi) is 1, and further, can be obtained

Substitution of formula (21) intoCan obtain the product

Searching (22) in the range of theta ∈ (-pi/2, pi/2), searching the first K spectral peaks with larger power according to the sequence from high to low, wherein the positions of the K peak values are DOA estimationK represents the number of target electromagnetic signals incident to the expanded co-prime array.

Then will beBy substituting formula (23), the steering vector corresponding to the exit angle under the emitting array can be obtainedThe k-th true DOD, i.e., phi_kThe corresponding transmit array steering vector is

Definition of

Where angle () is the phase angle operation. And then solve for phi using a least squares strategy_kThe least squares fitting formula is as follows

WhereinIs an unknown parameter, c_k1Is pi sin phi_k，c_k0Other parameters may be omitted.

In particular to

Is obtained by the reaction of formula (25)

The estimated transmission angleCan be obtained from the formula (27)

The simulation calculation is carried out on the algorithm, and the result is as follows:

the number of the sub-arrays 1 and 2 is respectively 4 and 3, the signal-to-noise ratio is as low as-15 dB, and the DOD and DOA of a plurality of information sources can be accurately identified when the fast beat number is 500, and the diagram of the estimation performance of the array algorithm, the traditional co-prime array MIMO radar algorithm and the uniform array MIMO radar algorithm under the simulation condition is given in figure 2. The algorithm has excellent performance under the simulation conditions that the number of array elements of the subarrays 1 and 2 is respectively set to be 7 and 5, the signal-to-noise ratio is set to be 0dB, the number of the information sources is 57, and both DOD and DOA are distributed at equal intervals of 2.5 degrees on [ -70 degrees and 70 degrees ], as shown in FIG. 3.

Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims. The techniques, shapes, and configurations not described in detail in the present invention are all known techniques.