RU2777692C1 - Method for processing signals in an adaptive antenna array when receiving correlated signals and interference - Google Patents

Abstract

FIELD: radio engineering.

SUBSTANCE: invention relates to the field of radio engineering and communications, and can be used in radio location, radio navigation, and radio communication systems operating in a complex interference environment. In the implementation of the proposed method for processing signals in an adaptive antenna array, when correlated signals and interference are being received, the following sequence of operations is performed: the signals received by each Nth channel of the adaptive antenna array for the set position of maximum of the antenna pattern, wherein said signals constitute a combination of a useful signal, interference, and noise, are divided by power into the passed and branched parts - 1; the signals corresponding to the passed part of power are summed in N complex signal weighting blocks with the obtained complex weighting coefficients in channels of the antenna elements - 2; based on the signals corresponding to the branched part of power, a covariance matrix is formed, reversed, and a direction-finding characteristic is formed based on super-resolution methods, such as the Capon method or the "heat noise" method - 3; based on the direction-finding characteristic, a weighting coefficient vector corresponding to the useful signal is formed and subtracted from the signals corresponding to the branched part of power by the corresponding channels - 4; a covariance interference matrix is formed from the signals wherefrom the useful signal component is excluded, said matrix is reversed, and the complex weighting coefficient vector optimal for the adaptive antenna array by the criterion of the maximum of the signal/(interference+noise) ratio is found - 5; signals from N complex signal weighting blocks are summed, forming the output signal of the adaptive antenna array - 6.

EFFECT: increase in the effectiveness of suppressing the interference correlated with a useful signal, the direction of arrival whereof is exactly unknown apriori, in an adaptive antenna array.

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Description

The invention relates to the field of radio engineering and communications and can be used in radar, radio navigation and radio communication systems operating in a difficult interference environment.

Schemes of adaptive antenna arrays are known that implement the algorithm for maximizing the output ratio of the useful signal power to the sum of the interference and noise powers [1]. To operate an adaptive antenna array of this type, a priori information about the direction of arrival of the useful signal is used. Therefore, adaptive antenna arrays of this design are not applicable in radio engineering systems where such information is not available.

In [2], a diagram of an adaptive antenna array is presented that implements an algorithm for minimizing the standard deviation of the received signal from the reference one. For the algorithm to work in the device, it is necessary to generate a reference signal. This is possible if there is a priori information about the useful signal. And since such information is never complete, the reference signal can differ significantly from the useful one, which causes a significant decrease in the noise immunity of the adaptive antenna array.

An adaptive antenna array, the design of which is described in [3], implements an output power minimization algorithm and has relatively good noise immunity characteristics. However, in the case when there is no interference or its power is less than the power of the useful signal, then due to the minimization of the total output power, the useful signal may also be suppressed.

A common disadvantage of the considered signal processing methods in adaptive antenna arrays is the inability of the system to isolate interference that strongly correlates with the signal.

The closest in technical essence to the claimed method of processing signals in an adaptive antenna array when receiving correlated signals and interference is a method of processing signals in a modular adaptive antenna array when receiving correlated signals and interference, described in [4], taken as a prototype. The method consists in the fact that for each position of the maximum of the radiation pattern, the signals received by each N-th channel are divided by power into the transmitted and branched parts, the signals corresponding to the transmitted part of the power are summed in Ma modules, a covariance matrix of interference is formed, and determined by the criterion of the maximum ratio signal/(interference + noise) vector of complex weight coefficients, with which the output signals of the modules are summed, forming the output signal of the adaptive antenna array. In accordance with the invention, the signals corresponding to the branched part of the power are converted into N signals in which the useful signal component is excluded, taking into account information about the radiation patterns of the modules, such a change in the N converted signals into Ma interference signals is performed so that the complex amplitudes of the interference components in them approach complex noise amplitudes in the output signals of the corresponding modules, and with the help of the received Ma interference signals, a covariance matrix of interference with the size Ma × Ma is formed and the optimal for the modular adaptive antenna array is found according to the criterion of the maximum signal / (interference + noise) vector of complex weight coefficients, signals, corresponding to the transmitted part of the power, sum in Ma units with given complex weighting coefficients.

This prototype method allows you to exclude the signal component from the covariance matrix and to suppress noise similar in spectrum to the signal. However, to implement it and solve the problem of synthesizing the "zero" of the radiation pattern, it is necessary to know a priori the exact direction of arrival of the useful signal, which is difficult to implement in practice.

The technical result of the invention is to increase the efficiency of interference suppression correlated with a useful signal, the direction of arrival of which is not exactly known a priori, in an adaptive antenna array.

The specified technical result is achieved by the fact that in the method of processing signals in an adaptive antenna array when receiving correlated signals and interference, including the reception for each position of the maximum of the radiation pattern by each N-th channel of signals, which are divided by power into the transmitted and branched parts. The signals corresponding to the power tap part are converted into N signals in which the wanted signal component is eliminated based on direction-finding characteristics information such as power and direction of arrival derived from super-resolution techniques. Based on this information, a vector of weight coefficients is formed corresponding to the useful signal, and the generated vector of weight coefficients is subtracted from the signals corresponding to the branched part of the power. With the help of the received signals, an N×N noise covariance matrix is formed. The optimal for the adaptive antenna array is found according to the criterion of maximum signal/(interference+noise) vector of complex weight coefficients. The signals corresponding to the transmitted part of the power are summed with the obtained complex weight coefficients, forming the output signal of the adaptive antenna array.

When implementing the proposed signal processing method in an adaptive antenna array, when receiving correlated signals and interference, the following sequence of operations is performed:

- the signals received by each N-th channel of the adaptive antenna array for a given position of the maximum of the radiation pattern, which are a mixture of the useful signal, interference and noise, are divided by power into the transmitted and branched parts - 1;

- on the basis of the signals corresponding to the branched part of the power, a covariance matrix is formed, inverted and a direction-finding characteristic is formed based on super-resolution methods, such as the Capon method or "thermal noise" - 2;

- on the basis of the direction-finding characteristic, a vector of weight coefficients is formed corresponding to the useful signal, and it is subtracted from the signals corresponding to the branched part of the power on the corresponding channels - 3;

- from the signals in which the useful signal component is excluded, a covariance matrix of interference is formed, it is inverted and the optimal for the adaptive antenna array is found according to the criterion of the maximum signal/(interference+noise) ratio vector of complex weight coefficients - 4;

- summarize the signals from N blocks of complex signal weighting, forming the output signal of the adaptive antenna array - 5;

- the signals corresponding to the transmitted part of the power are summed in N blocks of complex signal weighting with the obtained complex weight coefficients in the channels of the antenna elements - 6.

In FIG. Figure 1 shows a block diagram of an adaptive antenna array that implements the proposed signal processing method in an adaptive antenna array when receiving correlated signals and interference.

In FIG. Figure 2 shows the radiation pattern of an adaptive antenna array with an interference power 20 dB higher than the useful signal power.

In FIG. 3 shows the directivity diagram of an adaptive antenna array with equal powers of the interference and the useful signal.

In FIG. 4 shows the direction finding characteristic of the adaptive antenna array.

The composition of the adaptive antenna array (Fig. 1) includes antenna elements 1, the first block for generating the weight vector 2, the block for generating the control vector 3, the block for generating the direction finding relief 4, the second block for generating the weight vector 5, the block for inverting the covariance matrix 6, the block formation of the covariance matrix of interference 7, block of complex summation of signals 8, block of formation of the covariance matrix 9, blocks of complex weighting of signals 10, common adder 11.

N antenna elements 1 are connected to the first inputs of the complex signal summing block 8, to the inputs of the covariance matrix formation block 9 and the first inputs of the complex signal weighting blocks 10, the outputs of which are connected to the inputs of the common adder 11, the output of which is the output of the adaptive antenna array. The output of the complex signal summation block 8 is connected to the input of the noise covariance matrix formation block 7, the output of which is connected to the first input of the covariance matrix inversion block 6. The second input of the covariance matrix inversion block 6 is connected to the output of the covariance matrix formation block 9. The first output of the covariance matrix inversion block 6 is connected to the input of the direction finding relief formation block 4, the first output of which is connected to the input of the first block for the formation of the weight vector 2, the output of which is connected to the second input of the complex signal summation block 8. The second output of the direction finding relief formation block 4 is connected to the input of the control vector formation block 3, the output of which is connected to the second input of the second block for generating the vector of weight coefficients 5, the output of which is connected to the second inputs of the blocks for complex signal weighing 10. The first input of the second block for forming the vector of weight coefficients ov 5 is the second output of the covariance matrix inversion block 6.

Before considering the functioning of an adaptive antenna array that implements the proposed signal processing method, it is necessary to state the following to justify it.

Let there be an N - element adaptive antenna array, the input of which receives one useful signal from the direction θ _o , ϕ ₀ and interference signals from the directions

The criterion of maximum signal/(interference+noise) ratio (SINR) was chosen as the adaptation criterion

where R _ss - covariance matrix of the useful signal;

R _nn - covariance matrix of interference signals;

H - symbols of operations of transposition and complex conjugation.

As is known, the optimal vector of weight coefficients for a given criterion has the form

where S ₀ is a vector, the elements of which are the complex amplitudes of the currents in the emitters, which ensure the formation of the main maximum of the RP in the direction of the useful signal.

Since in the theory of antenna technology it is considered that interference signals are statistically independent and the useful signal is known a priori, the covariance matrix of interference signals can be represented as follows

where σ ² is the power of thermal noise in the channels of the antenna array;

- мощность

-го помехового сигнала;

- power

-th interference signal;

- вектор-столбец, элементами которого являются комплексные величины, учитывающие фазовые задержки при распространении плоской волны, приходящей с направления

в излучателях антенны;

- a column vector whose elements are complex quantities that take into account phase delays in the propagation of a plane wave coming from the direction

in antenna emitters;

E - identity matrix of dimension N×N.

However, if we consider the simplest case of the arrival of a useful signal, which is unknown in advance, and one interference in the form

where P _s , P ₁ - the value of the amplitude of the useful and interfering signal, respectively, then the covariance matrix, taking into account the fact that the noise in the channels of the antenna array are statistically independent of each other and with incoming signals, will have the form

where γ is the correlation coefficient.

In this case, the weight vector (2) will not be optimal, and the adaptive antenna array will not be able to adapt. To confirm this statement, modeling of the case under consideration was carried out. A linear antenna array consisting of 25 emitters is considered. The direction of arrival of the useful signal θ ₀ =0°, the direction of arrival of the interfering signal θ ₁ =-31°. The interference power is 20 dB more than the useful signal power, the correlation coefficient γ=0.5. Figure 2 shows two radiation patterns, one of which is with "zero" in the direction of the interference for the case when the useful signal is excluded from the covariance matrix (dashed curve), the other (solid curve) - without interference suppression, for the case when the covariance matrix is represented expression (5). Figure 3 also shows two radiation patterns with the same initial data, but the power of the useful signal is equal to the power of the interference. As can be seen from the presented diagrams, with an increase in the power of the useful signal, the adaptive antenna array amplifies the interference even with a slight correlation.

In this regard, to solve the formulated problem of suppressing interference correlated with a useful signal by an adaptive antenna array, we consider the following approach.

After the formation of the covariance matrix based on expression (5) for each direction and its inversion, it is necessary to form a direction-finding characteristic based on super-resolution methods, such as the Capon method or the “thermal noise” method. These methods are less affected by correlated signals and allow accurate determination of the spatial and power characteristics of the signals. The direction finding characteristics are built on the basis of the following relations

for the Capon method and

for the "thermal noise" method,

where S(θ, ϕ) is the scanning vector;

T, * - designations of operations of transposition and complex conjugation, respectively.

The scan vector can be represented as follows

where ε ₀ , μ ₀ - absolute dielectric and magnetic permeability of free space;

ω - cyclic frequency of direction finding;

x _n , y _n - coordinates of the n-th element of the antenna array;

θ, ϕ - AR scanning angles.

Further, based on information about the exact direction of arrival of the useful signal and its power, a vector of weight coefficients is formed, which is the image of the useful signal, and is subtracted from the additive mixture of signals (5). If the signals are fully correlated and the interference signal is not resolved with the useful one, since it falls into the region of the main maximum of the directivity diagram, then such a vector of weight coefficients is formed that excludes all signals falling into the region of the main maximum of the directivity diagram.

The figure 4 shows the direction finding characteristic for the same initial data that were taken to construct the radiation pattern shown in figure 3.

Then a vector of weight coefficients of the form

where θ ₀ , ϕ ₀ - angles of arrival of the useful signal.

вычитается из выражения (5) и полезный сигнал исключается из канала адаптации.Weight vector

is subtracted from expression (5) and the useful signal is excluded from the adaptation channel.

From the signals in which the useful signal component is excluded, a covariance matrix of interference is formed, it is inverted, and the optimal for the adaptive antenna array is found according to the criterion of the maximum signal/(interference+noise) ratio vector of complex weight coefficients (2).

The degree of correlation between interfering signals does not affect the quality of adaptation.

Consider the functioning of an adaptive antenna array.

For each position of the maximum of the radiation pattern, the signals received by each antenna element 1, which are a mixture of the useful signal, interference signals and own noise of the channels of the adaptive antenna array, are divided by power into the transmitted and branched parts. The signals corresponding to the transmitted part of the power are fed to the inputs of the second blocks of complex signal weighting 10. The signals corresponding to the branched part of the power are received by the first inputs of the block of complex summation of signals 8 and the inputs of the block for forming the covariance matrix 9, where the covariance matrix is formed. The signals corresponding to the covariance matrix are fed to the second input of the covariance matrix inversion block 6, where the covariance matrix is inverted. The signals from the covariance matrix inversion block 6 are fed to the input of the direction finding relief formation block 4, in which the direction finding characteristic is formed. Signals containing information about the direction of arrival of the useful signal and its power, from the direction finding relief formation unit 4, enter the input of the control vector formation unit 3, where the control vector is formed, and to the input of the first block for the formation of the weight vector 2, in which the weight vector is formed, corresponding to the desired signal. The signals from the first block for forming the vector of weight coefficients 2 are fed to the second input of the complex summation of signals 8, where the useful signal is subtracted from the mixture of signals. The signal from the output of the block of complex signal summation 8, in which the component of the useful signal is excluded, is fed to the input of the block for generating the noise covariance matrix 7. The signals from the output of the second block for generating the covariance matrix of noise 7 are fed to the first input of the block for inverting the covariance matrix 6. Signals from the second output The covariance matrix inversion block 6 is fed to the first input of the second weight vector generation block 5. The signals from the output of the control vector formation block 3 are received at the second input of the second weight vector generation block 5. In the second weight vector generation block 5, the optimal for the adaptive antenna is formed. gratings according to the criterion of maximum signal/(interference+noise) ratio vector of complex weight coefficients. The signals from the output of the second block for the formation of the vector of weight coefficients 5 are fed to the second inputs of the blocks of complex weighting of signals 10, where they are complexly summed with the signals corresponding to the transmitted part of the power. The signals from the outputs of the blocks of complex weighing of signals 10 enter the inputs of the total adder 11, the output of which is the output of the adaptive antenna array.

An adaptive antenna array that implements the patented method can be built on the basis of microwave devices widely used in development and well mastered in production: antenna elements, controlled analog or digital phase shifters, complex signal weighting units and signal adders. To create electronic computing and control units, there is a developed element base, in particular, programmable logic integrated circuits and digital signal processors that provide the implementation of control and data processing functions.

Thus, the patent-pending method for processing signals in an adaptive antenna array when receiving correlated signals and interference is practically feasible and provides the declared technical result, which consists in increasing the efficiency of suppressing interference correlated with a useful signal, the direction of arrival of which is not exactly known a priori, in an adaptive antenna array.

Literature

1. Monzingo R.A., Miller T.W. Adaptive antenna arrays. Introduction to theory. M.: Radio and communication, 1986, p. 80-86, 179-240.

2. TIIER, 1967, v. 55, No. 12, p. 78-95.

3. IEEE Trans Antennas and Propag., vol. AP-26, 1978, No. 2, p. 228-235.

4. Patent RU 2609792 dated February 3, 2017

Claims (1)

A method for processing signals in an adaptive antenna array when receiving correlated signals and interference, consisting in the fact that for each position of the maximum of the radiation pattern, the signals received by each N-th channel are divided by power into the transmitted and branched parts, the signals corresponding to the branched part of the power are converted into N signals, in which the component of the useful signal is excluded, using the received N signals, a covariance matrix of interference with a size of N × N is formed, the optimal for the adaptive antenna array is found according to the criterion of the maximum signal / (interference + noise) vector of complex weight coefficients, signals corresponding to the transmitted parts of the power are summed with the obtained complex weight coefficients, forming the output signal of the adaptive antenna array, characterized in that the conversion of signals corresponding to the branched part of the power into N signals in which the useful signal component is excluded is performed taking into account information about the bearing characteristics, such as power and direction of arrival, obtained on the basis of super-resolution methods, based on this information, a vector of weight coefficients corresponding to the useful signal is formed, and the generated vector of weight coefficients is subtracted from the signals corresponding to the branched part of the power.

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