Interference suppression method of adaptive weighted subarray level hybrid MIMO-phased array system
Technical Field
The invention belongs to the field of subarray level mixed MIMO-phased array systems.
Background
The subarray-level hybrid MIMO-phased array system is a new system which combines a MIMO (Multiple-Input Multiple-Output) system and a phased array system, and can overcome some limitations of the existing MIMO system and phased array system.
MIMO is a new system and is a very active research hotspot at home and abroad at present. Its advantages are generally compared to conventional phased array systems. Compared with a phased array system, the MIMO system has great advantages, such as better detection performance, higher directional resolution and estimation precision, stronger robustness under electronic countermeasure and multipath environment, and the like.
However, MIMO systems also have some limitations compared to phased array systems, including: 1. each antenna array element transmits orthogonal signals without coherent processing gain of a phased array system, thereby generating beam shape loss and reducing the performance when the scattering sectional area of a target is faded. 2. Signal-to-noise ratio (SNR) loss is generated, which affects target detection and parameter estimation accuracy, etc., and although such SNR loss of the MIMO system can be compensated by increasing the accumulation time, this method has a great limitation due to the limited coherent processing time and propagation path loss, etc. in the application. 3. A modern electronic system often comprises hundreds to thousands of antenna array elements, and if a MIMO system is directly applied, many independent transmitting signals are needed and thousands of digital channels are adopted at a receiving end, which cannot bear the hardware cost and the arithmetic operation cost; and in order to obtain a proper transmitting signal, an optimization problem with huge dimensions needs to be solved.
The subarray level mixed MIMO-phased array system overcomes the limitation of the MIMO system, and can effectively reduce hardware cost and operation cost. It also has the capability of coherent processing gain of a phased array system while maintaining all the advantages of a MIMO system. However, the subarray level hybrid MIMO-phased array system has just started to be researched, and many problems need to be solved, such as the problem of adaptive interference suppression.
Disclosure of Invention
The invention provides an interference suppression method of a sub-array level mixed MIMO-phased array system with self-adaptive weighting, aiming at solving the problem of self-adaptive interference suppression of the sub-array level mixed MIMO-phased array system.
The interference suppression method of the adaptive weighted subarray level mixed MIMO-phased array system comprises the following steps:
establishing a subarray-level hybrid MIMO-phased array system, wherein the system comprises a transmitting array and a receiving array, the transmitting array and the receiving array are completely identical in structure, the receiving array comprises N array elements, the N array elements are divided into L subarrays, the distance between every two adjacent array elements is half-working wavelength, interference and noise signals output by each subarray are subjected to matched filtering through L matched filters, and both N and L are positive integers;
setting array element level steering vector of receiving array asConverting the sub-array of the array into T, and utilizing the sub-array conversion matrix T of the array and the array element level guide vector of the receiving arrayObtaining steering vectors for a receive arraySteering vectors from a receiving arrayObtaining steering vectors for virtual arraysWhere theta represents the pitch angle,representing an azimuth;
sampling the interference and noise signals output by the virtual array for K times, and setting the interference and noise vector output by the virtual array obtained by sampling for the K time as yV(k) Using the interference-plus-noise vector y output by the virtual arrayV(k) Estimating the interference-plus-noise covariance matrix of the virtual array output to obtain an estimate of the interference-plus-noise covariance matrix of the virtual array outputWherein K is more than or equal to 1 and less than or equal to K;
steering vectors using virtual arraysEstimation of interference-plus-noise covariance matrix from virtual array outputObtaining a self-adaptive weight w of a subarray level mixed MIMO-phased array system;
and weighting the interference and noise signals output by the virtual array of the subarray level hybrid MIMO-phased array by using the self-adaptive weight w, thereby realizing the self-adaptive interference suppression of the subarray level hybrid MIMO-phased array system.
The interference suppression method of the adaptive weighted subarray level mixed MIMO-phased array system can adaptively suppress interference at the receiving end of the subarray level mixed MIMO-phased array and enable the signal-to-interference-and-noise ratio output by the system to be maximum.
Drawings
FIG. 1 is a diagram of a subarray division of an array in a subarray level hybrid MIMO-phased array system;
fig. 2 is a schematic structural diagram of a receiving end in a sub-array level hybrid MIMO-phased array system;
fig. 3 is a flowchart of a method for obtaining adaptive weights for a sub-array level hybrid MIMO-phased array system.
Detailed Description
The first embodiment is as follows: the interference suppression method of the adaptive weighted sub-array level hybrid MIMO-phased array system according to the present embodiment will be described in detail with reference to fig. 1, 2 and 3, and the method includes:
establishing a subarray-level hybrid MIMO-phased array system, wherein the system comprises a transmitting array and a receiving array, the transmitting array and the receiving array are completely identical in structure, the receiving array comprises N array elements, the N array elements are divided into L subarrays, the distance between every two adjacent array elements is half-working wavelength, interference and noise signals output by each subarray are subjected to matched filtering through L matched filters, and both N and L are positive integers;
setting array element level steering vector of receiving array asConverting the sub-array of the array into T, and utilizing the sub-array conversion matrix T of the array and the array element level guide vector of the receiving arrayObtaining steering vectors for a receive arraySteering vectors from a receiving arrayObtaining steering vectors for virtual arraysWhere theta represents the pitch angle,representing an azimuth;
sampling the interference and noise signals output by the virtual array for K times, and setting the interference and noise vector output by the virtual array obtained by sampling for the K time as yV(k) Using the interference-plus-noise vector y output by the virtual arrayV(k) Estimating the interference-plus-noise covariance matrix of the virtual array output to obtain an estimate of the interference-plus-noise covariance matrix of the virtual array outputWherein K is more than or equal to 1 and less than or equal to K;
steering vectors using virtual arraysEstimation of interference-plus-noise covariance matrix from virtual array outputObtaining a self-adaptive weight w of a subarray level mixed MIMO-phased array system;
and weighting the interference and noise signals output by the virtual array of the subarray level hybrid MIMO-phased array by using the self-adaptive weight w, thereby realizing the self-adaptive interference suppression of the subarray level hybrid MIMO-phased array system.
In the sub-array level hybrid MIMO-phased array system in the present embodiment, a planar phased array is used for the array, and transmission/reception is shared. The array comprises N array elements, the spacing between the array elements is half-wavelength lambda/2, the array adopts a subarray structure, the array is divided into L subarrays, the transmitting array and the receiving array have the same subarray structure, and a subarray division structure of the array in a subarray-level hybrid MIMO-phased array system is shown in figure 1. In the present embodiment, the array and the sub-array are arbitrary, and fig. 1 illustrates an example in which both the array and the sub-array are rectangular arrays.
In the transmitting array of the subarray level mixed MIMO-phased array, coherent signals are transmitted in each subarray and work in a phased array mode; and orthogonal signals are transmitted among different sub-arrays, and the MIMO mode is operated.
At a receiving end of the subarray level mixed MIMO-phased array, a space-domain self-adaptive interference suppression technology is applied, so that a directional diagram forms null in an interference direction, and interference is suppressed in a self-adaptive mode. The receiving array comprises a phase shifter for controlling the beam direction. The output signals of the elements are weighted (e.g., Taylor weighted) for suppressing the sidelobe levels of the receive pattern. In the receiving array, adjacent array elements form a plurality of sub-arrays (the total number of the sub-arrays is L) through a sub-array synthesis network. The output of each subarray is passed through a matched filter bank for matched filtering. Since there are L transmit signals (the system transmit end has L sub-arrays, each transmitting an orthogonal signal), each matched filter bank has L matched filters. Due to the function of the matched filter bank, a virtual array is formed at the receiving end of the system.
To adaptively suppress the interference, the interference plus noise signals output by the matched filters are weighted, i.e., the interference plus noise signals output by the virtual array, so that L is needed in total2And (4) self-adaptive weight. In this embodiment modeThe adaptive weight value adopts an LCMV (Linear Constrained Minimum Variance) criterion, namely, the signal-to-interference-and-noise ratio (the ratio of signal to interference plus noise power) output by the system is maximized, namely, the optimal adaptive interference suppression performance is achieved.
The second embodiment is as follows: in this embodiment, the interference suppression method of the adaptive weighted sub-array level hybrid MIMO-phased array system described in the first embodiment is further described, in this embodiment, the array element level steering vector of the receiving array isThe obtaining method comprises the following steps:
let 1 st array element in the receiving array be located at the origin of coordinates, i.e. the reference array element, and the coordinates of the nth array element be (xn, yn), where N is 1, …, N, letProjection of unit vector of direction in x direction Projection of unit vector of direction in y directionSetting the phase shift value of the nth array elementComprises the following steps:
in the formula, λ is the working wavelength, the array element-level steering vector of the receiving array is:
the range of N is more than or equal to 1 and less than or equal to N.
In this embodiment, the array element-level steering vector of the receiving arrayIs an N-dimensional column vector in whichTIndicating transposition.
The third concrete implementation mode: in this embodiment, the interference suppression method of the adaptive weighted sub-array level hybrid MIMO-phased array system according to the first embodiment is further explained, and in this embodiment, the steering vector of the receiving array is obtained according to the following formula
In the present embodiment, the subarray transformation matrix T of the array is an N × L-dimensional matrix, which reflects the characteristics of the subarray and is determined by the subarray structure and the phase shift and amplitude weighting values of each array elementIs an L-dimensional column vector.
The fourth concrete implementation mode: in this embodiment, the interference suppression method of the adaptive weighted sub-array level hybrid MIMO-phased array system according to the first embodiment is further explained, and in this embodiment, the steering vector of the virtual array is obtained according to the following formula
Wherein q is [1,1, …,1 ]]T L×1Is an L-dimensional column vector, each element value is 1,representing the Kronecker product.
In the present embodiment, q is [1,1, …,1 ]]T L×1Is an L-dimensional column vector, andrepresents the Kronecker product (tensor product), and thusIs a L2A column vector of dimensions.
The fifth concrete implementation mode: in this embodiment, the interference suppression method of the adaptive weighted sub-array level hybrid MIMO-phased array system described in the first embodiment is further described, and in this embodiment, the obtained interference plus noise vector output by the virtual array is yV(k) The method comprises the following steps:
setting the interference plus noise vector formed by the interference plus noise output by all array elements as yele(k) Using the interference plus noise vector yele(k) The interference-plus-noise vector of the obtained subarray output is y (k) ═ THyele(k) Wherein (K is more than or equal to 1 and less than or equal to K);
let the unit function response of each matched filter be h1(k),h2(k),...,hL(k) Where the unit function response of the ith matched filter is hl(k):
Wherein L is more than or equal to 1 and less than or equal to L, fl(k) For the transmit signal of the first sub-array of the transmit array, k0Is a constant and is a positive integer,*representing taking conjugation;
let the output signal of the first sub-array in the receiving array be yl(k) The output y after passing the first matched filterV_ll(k) Comprises the following steps:
yV_ll(k)=hl(k)οyl(k)
using y as interference and noise vector output by virtual array obtained by sampling at kth timeV(k) Denotes o denotes convolution operation.
Signal y of matched filter output (i.e. virtual array output) obtained from the k-th samplingV_ll(k) Has a total of L2L is more than or equal to 1 and less than or equal to L, and L is more than or equal to 1 and less than or equal to L, so that an interference and noise vector y output by the virtual array is formedV(k)。
In this embodiment, the output signal of each sub-array passes through one matched filter bank, as shown in fig. 2, the output signal of the matched filter is the output of the virtual array, and the output of each sub-array passes through L matched filters.
Since there are N array elements in total, yele(k) Is an N-dimensional column vector and y (k) is an L-dimensional column vector.
The above interference plus noise vector is yele(k) And interference and noise vectors formed by interference and noise values output by the array elements corresponding to the k-th sampling.
The sixth specific implementation mode: this embodiment is a further description of the interference suppression method of the adaptive weighted sub-array level hybrid MIMO-phased array system described in the first embodiment, and this embodiment is described belowIn the method, an estimate of an interference-plus-noise covariance matrix of the virtual array output is obtained using the following equation
In this embodiment, received data is sampled K times, and y obtained by each sampling is usedV(k) Estimating the interference and noise covariance matrix output by the virtual array to obtainK is the number of samples taken,Hrepresents a conjugate transpose, and thusIs a L2×L2A square matrix of dimensions.
The seventh embodiment: in this embodiment, the interference suppression method for a sub-array level hybrid MIMO-phased array system with adaptive weighting according to the first embodiment is further described, and in this embodiment, the adaptive weight w of the sub-array level hybrid MIMO-phased array system is obtained by using the following formula:
where μ is a constant, let the beam of the array be directed asThenSteering vectors for the virtual array at the beam pointing direction.
The optimal adaptive weight of the subarray level is L2A column vector of dimensions, obtained based on LCMV criteria; steering vectors of virtual arrays at beam pointingIs also L2A column vector of dimensions.